**4. References**

	- [4] Doyle J.F. (2001). *Nonlinear analysis of thin-walled structures.* Springer-Verlag, Berlin, Germany

**Chapter 9**

© 2012 Kubiak, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

© 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,

distribution, and reproduction in any medium, provided the original work is properly cited.

and reproduction in any medium, provided the original work is properly cited.

The buckling and postbuckling of thin-walled structures subjected to static load have been investigated by many authors for more than one hundred years. To the group of precursors of the investigation on the stability of thin-walled structures problem should be included

**Nonlinear Plate Theory**

Additional information is available at the end of the chapter

Tomasz Kubiak

**1. Introduction**

http://dx.doi.org/10.5772/48961

subjected to static and dynamic load.

following scientists: Euler [1], Timoshenko [2] and Volmir [3].

**1.1. Static buckling**

**for Postbuckling Behaviour of Thin-Walled**

**Structures Under Static and Dynamic Load**

A thin plate or thin-walled constructions are used in the sports industry, automotive, aerospace and civil engineering. As an example of such structural elements snowboard, skis, poles may be mentioned, as well as all kinds of crane girders, structural components of automobiles (car body sheathing or all longitudinal members), aircraft fuselages and wings, supporting structures of the walls and roofs of large halls and warehouses. All the above structures, as well as many others which can be regarded as a thin, exhaust carrying capacity not by exceeding the allowable stresses but by the stability loss. Therefore, not only critical load but also the postbuckling behaviour of thin-walled structures subjected to static and dynamic load is essential knowledge for designers. The use of more accurate mathematical models allows to explore the phenomena occurring after the loss of stability and to describe more precisely their behaviour. Engineers and designers need guidelines to construct as well as quick and easy software to use for analyse the behaviour of thin-walled structures. Therefore, the author of this chapter decided to explore this issue, propose a mathematical model and the method of analysis of orthotropic thin-walled structures

Tomasz Kubiak

218 Nonlinearity, Bifurcation and Chaos – Theory and Applications

*structures.* Springer, Berlin, Germany

*systems.* Springer, Berlin, Germany

(5), 2008, 1515-1529.

Germany

1515.

Poland

[4] Doyle J.F. (2001). *Nonlinear analysis of thin-walled structures.* Springer-Verlag, Berlin,

[5] Andrianov J., Awrejcewicz J., Manewitch L.I. (2004) *Asymptotical Mechanics of thin-walled*

[6] Awrejcewicz J., Krysko V.A., Vakakis A.F. (2004) N*onlinear dynamics of continuous elastic*

[7] A.V. Krysko, J. Awrejcewicz, E.S. Kuznetsova, V.A. Krysko, *Chaotic vibrations of closed cylindrical shells in a temperature field*, International Journal of Bifurcation and Chaos, 18

[8] A.V. Krysko, J. Awrejcewicz, E.S. Kuznetsova, V.A. Krysko, *Chaotic vibrations of closed cylindrical shells in a temperature field*, Shock and Vibration, 15 (3-4), 2008, 335-343. [9] I.V. Andrianov, V.M. Verbonol, J. Awrejcewicz, *Buckling analysis of discretely stringerstiffened cylindrical shells*, International Journal of Mechanical Sciences, 48, 2006, 1505-

[10] Arborcz J. (1985). *Post-buckling behavior of structures. Numerical techniques for more*

[11] Kopecki T. (2010). *Advanced deformation states in thin-walled load-bearing structure design work.* Publishing House of Rzeszów University of Technology, Rzeszów, Poland [12] Niu M. C. (1988). *Airframe structural design.* Conmilit Press Ltd., Hong Kong10] Lynch C., Murphy A., Price M., Gibson A. (2004). *The computational post buckling analysis of fuselage stiffened panels loaded in compression.* Thin-Walled Structures, 42:1445-1464, USA [13] Mohri F., Azrar L., Potier-Ferry M. (2002). *Lateral post buckling analysis of thin-walled open*

[14] Rakowski G., Kacprzyk Z. (2005). *Finite elements method in structure mechanics.*

[15] Ramm E. (1987). *The Riks/Wempner Approach – An extension of the displacement control method in nonlinear analysis*. Pineridge Press, Swensea, UK Aben H. (1979). *Integrated*

[16] Brzoska Z. (1965). *Statics and stability of bar and thin-walled structures.* PWN, Warszawa,

Publishing House of Technical University of Warszawa, Warszawa, Poland

*complicated structures.* Lecture Notes In Physics, 228, USA

*section beams*. Thin-Walled Structures, 40:1013-1036, USA

*photoelasticity.* Mc Graw-Hill Book Co., London, UK

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/48961


**3.2.2 Schottky diode**

310 Solar Cells – Thin-Film Technologies

more stable behaviors are observed in the triode-deposited a-Si:H films in the degraded states. The trend is best seen in the film prepared at the *d*ms of 4 cm where the lowest Si-H2

Fig. 7. Change in the neutral spin density (*N*s) due to light soaking as a function of Si-H2

Fig. 8. Light-induced change in the fill-factor (*FF = FFini - FFdeg*) of the Schottky diode having the intrinsic layer produced at the each condition. Closed circle: triode-deposited film (triode), open circle: conventionally prepared film (diode). [Shimizu et al., 2005]

bond density is observed as shown in figure 3.

bond density in the film. [Shimizu et al., 2008]

Furthermore, the stabilities of the triode-deposited a-Si:H films were studied with fabricating the Schottky diodes where their fill-factor (*FF*) changes were evaluated as a measure of degradation. The intrinsic layer of the Schottky diode was fabricated either by a triode or a diode system under the various conditions. The fill-factors in the initial state (*FF*ini) are almost the same throughout the samples: 52 - 54 %. On the other hand, the fill-factors in the degraded state (*FF*deg) are different each other. In figure 8, the change in the fill-factor (*FF* = *FF*ini – *FF*deg) is plotted against Si-H2 bond density [Shimizu et al., 2005]. For comparison, those of the films prepared with the diode system under the various conditions are also shown [Nishimoto et el., 2002]. One can see that the triode-deposited a-Si:H films contain low Si-H2 bond densities, and correspondingly, the observed *FF*s are low. Note that, the scattered correlation is observed when *FF*s are plotted against the Si-H densities of the films [Shimizu et al., 2005].


**5. Outlook and some concluding remarks**

The interest in heat transfer through fins will continue unabated. This is brought about by applications of fins in engineering appliances. The solutions to the problems give insight into effectiveness and efficiency of different fins. In this chapter we provided a summary of some of the work in recent times. In particular, we reviewed the exact and approximate analytical solutions. We demonstrated that although the models describing hear transfer seem to be simple, they are in fact challenging to solve exactly. When constructed, the exact solutions are used as benchmarks for the approximate solutions. It appears that some models including contracting or expanding have attracted some attention. The analysis of these problems provide insight into heat transfer phenomena and assist in the design of fins. The challenge is the construction of exact solutions, however one may construct approximate analytical solutions. The problems discussed here are not exhaustive.

## **Conflict of interest**

The authors declare no conflict of interest.

#### **Nomenclature**

*Survey of Some Exact and Approximate Analytical Solutions for Heat Transfer in Extended… DOI: http://dx.doi.org/10.5772/intechopen.95490*


**1. Introduction**

All electronic devices starting from a small remote-controlled car to large aerospace vehicles require numerous interconnects within the circuit to complete the electrical pathways for its smooth functionality. For making these contact points, soldering plays the most important role. Until recently, Sn63-Pb37 (Sn-Pb eutectic) solders were used widely for making these contact points. The whole electronic industry was depending on the Sn-Pb alloy due to their low cost, good solder ability, low melting temperature, and satisfactory mechanical and functional properties. However, it has been observed that there arise serious environmental and health hazards caused due to the extensive use of electronic gadgets containing lead. So, there came strict restrictions imposed by the Restriction of Hazardous Substance (2002/95/EC (RoHS 1)) and Waste Electrical and Electronic (WEEE) directives and other similar bodies in use of lead in the electronic gadgets. Hence, the need for the development of lead-free solder alloy for electronics and microelectronic devices has come into the limelight.

However, the miniaturization of electronic devices aiming at high performance has made the task very complex for all the researchers to develop reliable and costeffective electronic joining materials/technologies. Scientists have developed different lead-free soldering alloys for making consumer electronic devices; however, after more than couples of decades, it is yet to conclude the best possible solder that can withstand different harsh environmental conditions and provide good reliability and improve the service life of the device/joints (compared to the Sn-Pb eutectic solder). In recent days, we have observed that the service life of any electronic gadgets have been reduced drastically. These early failures of various consumer electronic gadgets have been often linked with the absence of a good lead-free solder material, which can withstand various service-exposed conditions [1–8].

After many years of research, different lead-free solder alloys like SAC105, SAC205, SAC305, SAC405, SN100C, Sn-Zn-, Sn-Cu-, and Sn-Bi-based solders have been explored by the industry and academia [9–11]. However, SAC305 (Sn-3.0Ag-0.5Cu), a lead-free solder alloy, has been identified as a nearest substitute of the conventionally used Sn37Pb solder.

Although SAC305 alloy is widely used in electronic industry, there is still a large scope for its modification or introduction of other joining technologies/procedures in order to get the optimized reliable joints, which we lack even now. Joints produced using such alloys have been investigated extensively by different researchers. It has been found that the interfacial microstructure, orientation of IMC at the interface, and its volume fraction are the key factors for optimizations of the mechanical and functional properties of the joints [12–15].

It has been realized that focusing only on Pb-free solder alloy development would certainly reduce the environmental pollution. But while achieving this, rise in processing temperature (because of the higher melting point of the lead-free solder) would in turn enhance the energy consumption while manufacturing the solder joints, thereby causing thermal pollution again. So, we have focused on finding suitable method/s for lowering the processing temperature and controlling the interfacial intermetallics growth of lead-free soldering, thereby increasing the reliability of the gadgets.

In this regard for lowering the processing temperature, we have used the transient liquid phase (TLP)-like soldering technique to join two copper substrates along with solder alloy Sn-3.0Ag-0.5Cu (SAC305). In case of high-temperature metal joining (welding/brazing), it is observed that the TLP bonding along with some interlayers generally produces IMC layer at the interface with lesser thickness compared to that in the conventional brazing/welding. Also, it produces homogeneous interface [16]. By dint of TLP-like soldering technique, we have prepared lead-free solder joint of Cu using thin multilayer structure of tin along with SAC305 solder alloy, hereafter termed as Cu-Sn/SAC/Sn-Cu solder system. In order to compare the effect of this thin multilayered structure, conventional solder joint of copper pads using SAC305, hereafter termed as Cu-SAC-Cu, has been prepared. We have produced the solder joints at 230°C, which is about 15–30°C lower than that of the conventional reflow soldering process generally used for making the lead-free solder joints [17].

Already reported studies in the literature show that joints produced at high processing temperature consist of higher volume fraction of IMCs with inhomogeneous interfacial microstructure (mostly scallop shaped), which essentially produce internal stress and exhibit premature failure [18].

It is found that the interfacial morphology and distribution of the IMC across the interface plays the key role in determining the quality and reliability of any solder joints [4, 19, 20]. Therefore, researchers have attempted to develop homogeneous interfacial microstructure with restricted growth of intermetallics in order to produce solder joints with better mechanical and functional properties. But, it is yet to conclude the best suitable and optimized temperature or processing technique that would give us reliable lead-free solder joint with improved service life of the electronic gadgets [21–24].

For Sn-3.0Ag-0.5Cu/Cu solder joint prepared at 250°C, Tong et al. showed that after long hours of aging (˃288 h) at 150°C, the growth rate of Cu3Sn surpasses the growth rate of Cu6Sn5 phase, where the total IMC thickness increases by almost 97.56% after aging of only 500 h [25].

Compared to conventional Cu-SAC-Cu solder joints (**Figure 1**), we have been able to produce Cu-Sn/SAC/Sn-Cu solder joints at 230°C (**Figure 2**), which exhibit a reduced growth rate with respect to the total IMC thickness and show homogeneous interfacial microstructure structure across the solder joint interface. Interestingly, even after aging of 1200 h at 150°C, it has been observed that there is only 68.85% increment in the total IMC thickness for Cu-Sn/SAC/Sn-Cu solder joint (**Figure 3a**), whereas there is an increment in the total IMC thickness of about 78% for conventional Cu-SAC-Cu solder joint (**Figure 4a**). It has also been observed that the growth rate of conventional Cu-SAC-Cu solder joint is increasing rapidly from 0.005 to

**3**

**Figure 3.**

**Figure 1.**

**Figure 2.**

*Introductory Chapter: Overview of Pb-Free Solders and Effect of Multilayered Thin Film of Sn…*

around 0.01 μm/h at 1200 h of aging (**Figure 4b**). Whereas a reduced growth rate of total IMC thickness has been detected for Cu-Sn/SAC/Sn-Cu solder joint across the solder joint interface, which is gradually decreasing from 0.008 (as soldered condition) to 0.001 μm/h at 1200 h of aging, suggesting that the IMC formation has been

*Optical images of the IMC microstructure of Cu-SAC-Cu solder joint with varying aging time at 150°C. (a) As*

*Optical images of the IMC microstructure of Cu-Sn/SAC/Sn-Cu solder joint with varying aging time at 150°C. (a) As cast, (b) 100 h aging, (c) 300 h aging, (d) 500 h aging, (e) 700 h aging, and (f) 1200 h aging.*

*(a) Total IMC thickness of Cu-Sn/SAC/Sn-Cu solder joint with variation of aging time in hours. (b) First*

*derivative of total IMC thickness of Cu-Sn/SAC/Sn-Cu solder joint with aging time in hours.*

*cast, (b) 100 h aging, (c) 300 h aging, (d) 500 h aging, (e) 700 h aging, and (f) 1200 h aging.*

controlled with the help of thin multilayer of tin film as shown in **Figure 3b**.

*DOI: http://dx.doi.org/10.5772/intechopen.86713*

*Introductory Chapter: Overview of Pb-Free Solders and Effect of Multilayered Thin Film of Sn… DOI: http://dx.doi.org/10.5772/intechopen.86713*

around 0.01 μm/h at 1200 h of aging (**Figure 4b**). Whereas a reduced growth rate of total IMC thickness has been detected for Cu-Sn/SAC/Sn-Cu solder joint across the solder joint interface, which is gradually decreasing from 0.008 (as soldered condition) to 0.001 μm/h at 1200 h of aging, suggesting that the IMC formation has been controlled with the help of thin multilayer of tin film as shown in **Figure 3b**.

#### **Figure 1.**

*Lead Free Solders*

reliability of the gadgets.

electronic gadgets [21–24].

97.56% after aging of only 500 h [25].

Although SAC305 alloy is widely used in electronic industry, there is still a large scope for its modification or introduction of other joining technologies/procedures in order to get the optimized reliable joints, which we lack even now. Joints produced using such alloys have been investigated extensively by different researchers. It has been found that the interfacial microstructure, orientation of IMC at the interface, and its volume fraction are the key factors for optimizations of the

It has been realized that focusing only on Pb-free solder alloy development would certainly reduce the environmental pollution. But while achieving this, rise in processing temperature (because of the higher melting point of the lead-free solder) would in turn enhance the energy consumption while manufacturing the solder joints, thereby causing thermal pollution again. So, we have focused on finding suitable method/s for lowering the processing temperature and controlling the interfacial intermetallics growth of lead-free soldering, thereby increasing the

In this regard for lowering the processing temperature, we have used the transient liquid phase (TLP)-like soldering technique to join two copper substrates along with solder alloy Sn-3.0Ag-0.5Cu (SAC305). In case of high-temperature metal joining (welding/brazing), it is observed that the TLP bonding along with some interlayers generally produces IMC layer at the interface with lesser thickness compared to that in the conventional brazing/welding. Also, it produces homogeneous interface [16]. By dint of TLP-like soldering technique, we have prepared lead-free solder joint of Cu using thin multilayer structure of tin along with SAC305 solder alloy, hereafter termed as Cu-Sn/SAC/Sn-Cu solder system. In order to compare the effect of this thin multilayered structure, conventional solder joint of copper pads using SAC305, hereafter termed as Cu-SAC-Cu, has been prepared. We have produced the solder joints at 230°C, which is about 15–30°C lower than that of the conventional reflow soldering process generally used for making the lead-free solder joints [17].

Already reported studies in the literature show that joints produced at high processing temperature consist of higher volume fraction of IMCs with inhomogeneous interfacial microstructure (mostly scallop shaped), which essentially produce

It is found that the interfacial morphology and distribution of the IMC across the interface plays the key role in determining the quality and reliability of any solder joints [4, 19, 20]. Therefore, researchers have attempted to develop homogeneous interfacial microstructure with restricted growth of intermetallics in order to produce solder joints with better mechanical and functional properties. But, it is yet to conclude the best suitable and optimized temperature or processing technique that would give us reliable lead-free solder joint with improved service life of the

For Sn-3.0Ag-0.5Cu/Cu solder joint prepared at 250°C, Tong et al. showed that after long hours of aging (˃288 h) at 150°C, the growth rate of Cu3Sn surpasses the growth rate of Cu6Sn5 phase, where the total IMC thickness increases by almost

Compared to conventional Cu-SAC-Cu solder joints (**Figure 1**), we have been able to produce Cu-Sn/SAC/Sn-Cu solder joints at 230°C (**Figure 2**), which exhibit a reduced growth rate with respect to the total IMC thickness and show homogeneous interfacial microstructure structure across the solder joint interface. Interestingly, even after aging of 1200 h at 150°C, it has been observed that there is only 68.85% increment in the total IMC thickness for Cu-Sn/SAC/Sn-Cu solder joint (**Figure 3a**), whereas there is an increment in the total IMC thickness of about 78% for conventional Cu-SAC-Cu solder joint (**Figure 4a**). It has also been observed that the growth rate of conventional Cu-SAC-Cu solder joint is increasing rapidly from 0.005 to

internal stress and exhibit premature failure [18].

mechanical and functional properties of the joints [12–15].

**2**

*Optical images of the IMC microstructure of Cu-SAC-Cu solder joint with varying aging time at 150°C. (a) As cast, (b) 100 h aging, (c) 300 h aging, (d) 500 h aging, (e) 700 h aging, and (f) 1200 h aging.*

#### **Figure 2.**

*Optical images of the IMC microstructure of Cu-Sn/SAC/Sn-Cu solder joint with varying aging time at 150°C. (a) As cast, (b) 100 h aging, (c) 300 h aging, (d) 500 h aging, (e) 700 h aging, and (f) 1200 h aging.*

#### **Figure 3.**

*(a) Total IMC thickness of Cu-Sn/SAC/Sn-Cu solder joint with variation of aging time in hours. (b) First derivative of total IMC thickness of Cu-Sn/SAC/Sn-Cu solder joint with aging time in hours.*

**Figure 4.**

*(a) Plot of total IMC thickness of Cu-SAC-Cu solder joint with variation of aging time in hours. (b) Derivative plot of total IMC thickness of Cu-SAC-Cu solder joint with variation of aging time in hours.*

In order to control the IMC thickness across the solder joint interface, many researchers have also tried to add the fourth element, which would get mixed up with the solder alloy and would restrict the diffusion of Cu from substrate toward solder and thereby restricting tin to get diffused from solder toward substrate. But, an optimized growth rate of IMC formation has not been achieved yet. Ni-doped SAC solder alloy has been studied by Benabou et al. Ni is considered to be one of the best elements in restricting the diffusion of copper across the interface [26]. Study shows that though Ni-doped solder alloy produces joints with thinner IMC layer, it could not be able to restrict the formation of voids in Cu3Sn layer with aging time and it produces cavities in (Cu, Ni)6Sn5 phase, which would be the point of initiation of failure of solder joint. Also, it increases the electrical resistivity of the solder joint system due to the discontinuity in the electrical pathways because of the presence of the voids.

Kang et al. have reported SAC solder alloy with surface finish of Ni(P)/Au, which produces Ni3Sn4 IMC layer, which grows faster than Cu-Sn IMC (Cu6Sn5 and Cu3Sn phases) on bare Cu and remains detached from the substrate. This detachment of the Ni3Sn4 phase from the substrate decreases the shear strength as well as increases the electrical resistivity of the solder joint due to the discontinuity in the electrical pathways [27]. However, our proposed multilayer structure in the Cu-Sn/ SAC/Sn-Cu solder joint shows neither void at the Cu3Sn phase nor any cavities at Cu6Sn5 phase; moreover, a controlled rate of IMC formation has been observed. This may be attributed due to the formation of solid solution of β-Sn phase in the interface, which restricts the Cu diffusion from substrate to solder. On the other hand, a significant improvement in the electrical properties has been observed for the solder joints produced using this TLP-like soldering and multilayered structure.

### **2. Electrical conductivity**

The electrical resistivity across the solder joints has been investigated by four probe methods. For the Cu-Sn/SAC/Sn-Cu solder joint it was found 1.4\*10−5 Ω-mm for as soldered samples and 2.66\*10−5 Ω-mm after 1200 h of thermal aging, whereas the electrical resistivity of the conventional Cu-SAC-Cu solder joint has been found to be 4.9\*10−5 Ω-mm at 1200 h of thermal aging, which is almost twice that of Cu-Sn/SAC/Sn-Cu solder joint aged up to 1200 h. Thinner interfacial IMC layers cause lower associated localized Joule heating, resulting in enhanced electronic transport across the joints.

**5**

*Introductory Chapter: Overview of Pb-Free Solders and Effect of Multilayered Thin Film of Sn…*

The rate of increment of resistivity is also slow in case of Cu-Sn/SAC/Sn-Cu solder joints than that of the Cu-SAC-Cu solder joint, as revealed from the slope of the curve (**Figure 5**). This may be attributed due to controlled IMC formation at the interface achieved by using thin multilayers of Sn film for Cu-Sn/SAC/Sn-Cu solder joints. Sn has lower resistivity than SAC solder paste (resistivity value: Sn ≈ 1.15 and SAC ≈ 3.57 μΩ cm). Also, ionization enthalpy of Sn is lower than that of Cu (CuIonization Energy = 745.5 and SnIonization Energy = 708.6 kJ/mol); therefore, Sn loses its outermost electron much earlier than Cu after getting little amount of energy, so it provides more number of charge carriers to conduct electricity, thereby reducing its resistance and increasing the conductivity in comparison with the Cu-SAC-Cu

*Resistivity plot of Cu-Sn/SAC/Sn-Cu solder system and Cu-SAC-Cu solder joint system with varying aging time.*

This introductory chapter discusses the overview of the lead-free solders, its importance, and necessity in the cutting-edge research carried out across the globe for making environment friendly electronic devices. For any solder joints, the interfacial characteristics like mechanical and functional properties along with the microstructural morphology play the mostly vital role. Therefore, a systematic and detailed knowledge of the interfacial products and their structures are of fundamental interest for understanding the behavior of the solder joints. The concept of transient liquid phase-like soldering technique has been discussed, and the effect of thin multilayered film of Sn has been reported toward obtaining a more reliable

We have demonstrated that incorporation of thin multilayer of Sn film along with SAC305 paste could produce good solder joints at 230°C. Cu pads have been joined by TLP-like soldering. For Cu-Sn/SAC/Sn-Cu solder joints, homogeneous interfacial microstructures have been formed across the solder joint interface as compared to scallop like IMC in the conventional Cu-SAC-Cu solder joint. Incorporation of thin multilayers of Sn film is capable of reducing the IMC growth

solder joints where no multilayers are been used.

**3. Conclusion**

**Figure 5.**

lead-free solder joint.

*DOI: http://dx.doi.org/10.5772/intechopen.86713*

*Introductory Chapter: Overview of Pb-Free Solders and Effect of Multilayered Thin Film of Sn… DOI: http://dx.doi.org/10.5772/intechopen.86713*

**Figure 5.** *Resistivity plot of Cu-Sn/SAC/Sn-Cu solder system and Cu-SAC-Cu solder joint system with varying aging time.*

The rate of increment of resistivity is also slow in case of Cu-Sn/SAC/Sn-Cu solder joints than that of the Cu-SAC-Cu solder joint, as revealed from the slope of the curve (**Figure 5**). This may be attributed due to controlled IMC formation at the interface achieved by using thin multilayers of Sn film for Cu-Sn/SAC/Sn-Cu solder joints. Sn has lower resistivity than SAC solder paste (resistivity value: Sn ≈ 1.15 and SAC ≈ 3.57 μΩ cm). Also, ionization enthalpy of Sn is lower than that of Cu (CuIonization Energy = 745.5 and SnIonization Energy = 708.6 kJ/mol); therefore, Sn loses its outermost electron much earlier than Cu after getting little amount of energy, so it provides more number of charge carriers to conduct electricity, thereby reducing its resistance and increasing the conductivity in comparison with the Cu-SAC-Cu solder joints where no multilayers are been used.


**2.3. The group of britholite**

The structure and the crystal habit of the mineral fluorstrophite are shown in **Fig. 26**. It is a green, yellow-green or colorless mineral with vitreous-greasy luster that crystallizes in hexagonal system with the space group P63/M or P63. The crystallographic parameters of the unit cell are *a* = 9.565 and *c* = 7.115 Å, the ration *a*:*c* = 1:0.744, *V* = 563.74 Å3 and *Z* = 2. The hardness of the mineral on the Mohs scale is 5. Calculated and measured densities are 3.74

The mineral kuannersuite-(Ce) (Na2Ce2Ba6(PO4)6FCl [88]) was found and named according to the locality (Kuannersuit plateau) in the Ilímaussaq alkaline complex, South Greenland (**Fig. 27**). It occurs associated with the minerals including aegirine, analcime, beryllite

((Na,Ca)2(Si,Al)5O10·3H2O [94]), lovdarite (K2Na6Be4Si14O36·9H2O [95],[96]), nabesite (Na2BeSi4O10·4H2O [97],[98]), neptunite, pectolite, polylithionite (KLi2AlSi4O10F2 [99]), pyro‐

17 There are three minerals: gmelinite-(Ca), gmelinite-(K), and gmelinite-(Na) with the composition of

18 The member of the pyrochlore group ((Na,Ca)2Nb2O6(OH,F)). A new scheme of nomenclature for the pyrochlore supergroup, approved by the CNMNC–IMA, is based on the ions at the A, B, and Y sites. The subgroups should be changed to the groups: pyrochlore (1), microlite (2), roméite (3), betafite (4), and elsmoreite (5). The new names are composed of two prefixes and one root name (identical to the name of the group). The first prefix refers to the dominant anion (or cation) of the dominant valence [either H2O or □] at the Y site. The second prefix refers to the dominant cation of the dominant valence [either H2O or □] at the A site. The prefix "keno–" represents "vacancy." Where the first and the

Ca2(Si8Al4)O24·11H2O [90],[91], K4(Si8Al4)O24·11H2O [93], and Na4(Si8Al4)O24·11H2O [91],[93], respectively.

[90],[91],[92],[93], gonnardite

and 3.84 g·cm−3, respectively. It has imperfect cleavage to {1010}.

80 Apatites and their Synthetic Analogues - Synthesis, Structure, Properties and Applications

(Be3SiO4(OH)2·H2O [89]), chkalovite, galena, gmelinite17

[100], sphalerite (ZnS [101]) and tugtupite.

**Fig. 27** The locality for the mineral kuannersuite-(Ce).

second prefix are equal, only one prefix is applied [100].

**2.2.7. Kuannersuite-(Ce)**

chlore18

Britholites are typically phosphorus-bearing silicates with apatite structure and general formula: (REE,Ca)5[(Si,P)O4]3**Z**, where REE is usually yttrium and *Z* = OH− , F− or Cl− . The minerals from the group of britholite usually contain significant impurities of thorium and sometimes also uranium. These minerals are widespread in alkaline rocks such as pegma‐ tites and metasomites19 related to syenite15 and nepheline–syenite complexes [102]. The name of this group is derived from the Greek word *brithos* for weight in order to refer to the high density of the mineral. The following minerals are described below.

The structure and the crystallographic data of some of the minerals from the group of britholite were introduced in **Fig. 29** and **Table 1**, respectively. The structural, thermodynamic and electronic properties of britholites were investigated by NJEMA et al [103].

19 The series of metamorphic processes whereby chemical changes occur in minerals or rocks as the result of the introduction of material, often in hot aqueous solutions, from external sources.

**Fig. 29** The structure (the view according to axis *c*) of mineral: (a) britholite-(Ce), (b) britholite-(Y) and (c) fluorbritho‐ lite-(Ce). Coupled heterovalent substitution at M and T site in the series apatite–calciobritholite–britholite [1].

**Table 1** The crystallographic data of minerals from the group of britholite

#### **2.3.1. Britholite-(Ce)**

The britholite-(Ce) (Lessignite-(Ce), (Ce,Ca)5(SiO4)3OH) [104],[105],[106]) mineral (**Fig. 30**) was first recognized as the new mineral by G. FLINK (1897) in the pegmatite form of the nepheline– syenite at Naujakasik, Ilímaussaq complex, Greenland. Known localities for the mineral britholite are shown in **Fig. 31**.

The specimen was named and described by CHR. WINTHER [104] as opaque, brown crystals of the composition of 3[4SiO2,2(Ce,La,Di,Fe)2O3,3(Ca,Mg)O,H2O,NaF],2[P2O5,Ce2O3], which are apparently hexagonal prisms with pyramids, but it actually consists of biaxial orthorhombic individuals twined together as in aragonite. The Th-rich britholite-(Ce) was also known as fenghuangshite [107]. Britholite-(Ce) (first described as britholite) is the forefather of the

**Fig. 30** The crystal (13 mm) of britholite-(Ce) from Ostkogen, Tvedalen, Norway.

Ca5 Ca3.5 REE1.5

82 Apatites and their Synthetic Analogues - Synthesis, Structure, Properties and Applications

X (PO4)1.5(SiO4)1.5 (PO4)3

Ca5(PO4)3F Fluorapatite

Measured/calculated

**2.3.1. Britholite-(Ce)**

britholite are shown in **Fig. 31**.

Apatite Fluorcalciobritholite

**Fig. 29** The structure (the view according to axis *c*) of mineral: (a) britholite-(Ce), (b) britholite-(Y) and (c) fluorbritho‐ lite-(Ce). Coupled heterovalent substitution at M and T site in the series apatite–calciobritholite–britholite [1].

The britholite-(Ce) (Lessignite-(Ce), (Ce,Ca)5(SiO4)3OH) [104],[105],[106]) mineral (**Fig. 30**) was first recognized as the new mineral by G. FLINK (1897) in the pegmatite form of the nepheline– syenite at Naujakasik, Ilímaussaq complex, Greenland. Known localities for the mineral

The specimen was named and described by CHR. WINTHER [104] as opaque, brown crystals of the composition of 3[4SiO2,2(Ce,La,Di,Fe)2O3,3(Ca,Mg)O,H2O,NaF],2[P2O5,Ce2O3], which are apparently hexagonal prisms with pyramids, but it actually consists of biaxial orthorhombic individuals twined together as in aragonite. The Th-rich britholite-(Ce) was also known as fenghuangshite [107]. Britholite-(Ce) (first described as britholite) is the forefather of the

**Mineral name Crystallographic parameters Hardness (Mohs)** *a c a***:***c Z V* **SG Density\***

**[Å] — — [Å3**

Britholite-(Ce) 9.63 7.03 1:0.730 2 564.60 P63/M 4.45/4.49 5½ Britholite-(Y) 9.43 6.81 1:0.722 524.45 4.25/4.07 5.0

Fluorbritholite-(Y) 9.44 6.82 1:0.722 526.68 —/4.61 5½ Fluorcalciobritholite 9.58 6.99 1:0.729 555.17 4.20/4.25 5½ Tritomite-(Ce) 9.35 6.88 1:0.736 520.89 4.20/5.02 5.5 Tritomite-(Y) 9.32 6.84 1:0.734 514.54 3.22/4.48 3.5-6.5

Fluorbritholite-(Ce) 9.52 6.98 1:0.734 547.74 4.66/4.67

**Table 1** The crystallographic data of minerals from the group of britholite

M Ca2.5 REE2.5 Ca2 REE3

Ideal composition

Fluorcalciobritholite Fluorbritholite

Ca3Ce2 (SiO4)2(PO4)F Ce3Ca2 (SiO4)3F

**] — [g·cm−3]**

Britholite

(PO4)0.5(SiO4)2.5 (SiO4)3

**Fig. 31** The localities for the mineral britholite-(Ce).

**Fig. 32** The crystal structure (perspective view according to *c*-axis) of britholite-(Ce) and some common crystal shapes.

**Fig. 33** Depiction of Ca(1)-O(3) triangles in apatite (a) and REE(1)-O(3) triangles in hexagonal (b) and monoclinic bri‐ tholite (*c*). The dashed and solid lines in the structure of britholite indicate short and long REE-O bonds, respectively [106].

britholite group [108]. The structure of monoclinic britholite-(Ce) is shown in **Fig. 32** and the crystallographic data are listed in **Table 1**.

The crystal structure of monoclinic dimorphs **Fig. 33** of the mineral britholite-(Ce) (and also of britholite-(Y)described below) was solved in **P21** space group by NOE et al [106]. The monoclinic britholite dimorph differs from its hexagonal counterpart principally in the ligation of the REE equivalent of the apatite Ca(l) site. Whereas in **P63** britholite each Ca(l) equivalent has either three short or three long REE-O(3) bonds; in the **P21** dimorph, the Ca(1) equiva‐ lents have either one long and two short REE-O(3) bonds or one short and two long REE-O(3) bonds. Arrangement of short and long bonds leads to **P63** symmetry in hexagonal britholite due to removal of **M** from symmetry elements of apatite, and **P21** symmetry in monoclinic britholite due to removal of symmetry elements **3** and **M**. The reduction in symmetry ex‐ plains the common observation of biaxial optical characteristics of britholite samples [106].


**8. Data treatment**

Data were statistically analyzed [19] using SPSS software (statistical package for social sciences, version 8). One-way ANOVA was carried out to test the variation of different variables between different four sites. Linear correlation coefficient, *r*, was estimated to find out the relationships between age dating, height and tree cover.


Preface

Terpenes belong to the diverse class of chemical constituents isolated from materials found in nature (plants, fungi, insects, marine organisms, plant pathogens, animals and endo‐ phytes). Theses metabolites have simple to complex structures derived from Isopentyl di‐ phosphate (IPP), dimethyl allyl diphosphate (DMAPP), mevalonate and deoxyxylulose biosynthetic pathways. Terpenes play a very important role in human health and have sig‐ nificant biological activities (anticancer, antimicrobial, anti-inflammatory, antioxidant, anti‐ allergic, skin permeation enhancer, anti-diabetic, immunomodulatory, anti-insecticidal). According to new research, terpenes cineole (a spicy eucalyptus-derived flavoring oil) are ready to be directly converted to biofuel as soon as they are produced. This book provides an overview and highlights recent research in the phytochemical and biological understand‐ ing of terpenes and terpenoid and explains the most essential functions of these kinds of secondary metabolites isolated from natural sources.

#### **Dr. Shagufta Perveen (MACS-USA, MRSC-UK, MIUPAC-USA)**

Department of Pharmacognosy College of Pharmacy King Saud University Riyadh, Saudi Arabia

#### **Prof. Dr. Areej Al-Taweel**

Department of Pharmacognosy College of Pharmacy King Saud University Riyadh, Saudi Arabia

**Chapter 1**

**Provisional chapter**

**Introductory Chapter: Terpenes and Terpenoids**

**Introductory Chapter: Terpenes and Terpenoids**

DOI: 10.5772/intechopen.79683

Natural products are the compounds which isolate from different natural sources such as plants, animals, microbes, insects, plant pathogens, and endophytes and marine. These are known as secondary metabolites since they are formed due to the enzymatic resections of primary metabolites (amino acids, sugars, vitamins, etc.). Terpenes belong to the biggest

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.79683

**1. Terpenes and terpenoids**

**Figure 1.** Classification of terpenes.

Shagufta Perveen

Shagufta Perveen

#### **Introductory Chapter: Terpenes and Terpenoids Introductory Chapter: Terpenes and Terpenoids**

DOI: 10.5772/intechopen.79683


**4. Unfractionated standard heparin**

#### **4.1 Mechanism of action**

Unfractionated standard heparin enhances the rate by which antithrombin III neutralizes the activity of several coagulation factors including factor Xa and thrombin [17].

Average half-life when administered intravenously is 60 minutes in adults. Its half-life is dose dependent (higher dose has more duration in the circulation). It has a shorter half-life than normal in patients with thrombotic disease and a longer half-life than normal in cirrhosis or uremia patients.

Contraindications of unfractionated standard heparin include recent bleeding in the central nervous system, bleeding from an inaccessible site, malignant hypertension, bacterial endocarditis, and recent surgery.

Partial thromboplastin time (PTT) may not reflect the correct degree of anticoagulation, therefore specific heparin level should be determined (heparin level is 0.35–0.70 U/ml by anti-factor Xa assay or 0.2–0.4 U/ml by protamine sulfate assay).

Protamine sulfate can neutralize heparin immediately. Because of the rapid clearance rate of heparin, stopping the infusion is adequate treatment for most patients (1 mg of protamine sulfate can neutralize 90–110 units of heparin). In addition, heparin has rapid metabolic decay and therefore it needs only one-half of a total dose of protamine.

#### **4.2 Enoxaparin**

Enoxaparin is an effective and convenient alternative to standard heparin therapy [17]. Adult patients rarely need to have their heparin level monitored, but in pediatric patients there is more diversity of response. Monitoring is critical to ensure that a therapeutic level is achieved.

PTT cannot be used to monitor heparin levels; a specific assay should be used. Once therapeutic range is achieved, routine monitoring is not required or is required infrequently.

When enoxaparin is used for prophylaxis against thrombosis, the dose is 0.5 mg/ kg/12 hr subcutaneously.

#### **4.3 Warfarin**

Warfarin is an oral anticoagulant drug that acts to reduce the functional level of vitamin K-dependent factors II, IIV, IX, and X as well as proteins S and C [17]. Warfarin will reduce the level of following factors gradually depending on the half life, factor VII is firstly as the shortest its half life, followed by factor IX and X and lastly factor II, it usually needed 4-5 days to decrease all these factors. PT is a clotting test used to monitor warfarin therapy.

The most adverse effect is hemorrhage, which is related to dose or metabolism and is treated by discontinuation of the drug along with administration of vitamin K (vitamin K given is equal to the daily warfarin dose) either orally, subcutaneously, or intravenously (not intramuscularly). The parenteral route has a much longer half-life and may overshoot the correction. Sometimes, warfarin is associated with life-threatening bleeding. When severe hemorrhage develops, 15 ml/kg of fresh frozen plasma should be given in addition to vitamin K.


**4.4 Filtration**

Owing to their fine, compact structure, microfiber textiles offer excellent filtration effects for both air and fluid filtration. Ultra-fine microfiber products such as 0.05 dtex PP microfiber nonwovens, in combination with a high electrical voltage, which will provide permanent

of comfort in wearing when used as surgical gowns and for application as surgical face

The biocompatibility of microfibers offers great potential and manifold possibilities of use in the medical field. Microfiber filter produced from melt blown polyester are sold to hospitals for use in blood transfusion and blood donation. Polyester microfibers are very compatible with human organs and have proved themselves in use of vascular prothesis (Rupp &

Polypropylene and bi-component microfibers can be very important components of fiberreinforced composites, as they function not only as a reinforcing element, but also as a binder fiber between the individual layers. Polypropylene and bi-component microfibers are used in many different composite products: Microfiber reinforced concrete (to reinforce and prevent cracks), insulation material (to avoid the use of chemical binders), multifunctional liquid transport media (acquisition and distribution layers), woven fabrics (as a dimensional stability network), and laminated products (lamination between textiles and boards)

Microfilaments demand extraordinarily high quality weaving warps (Rupp & Yonenaga, 2000). In the case of warping microfiber yarns versus warping conventional fiber yarns, it must be considered that the smaller amount of force is needed to break a microfiber filament during warping. In addition, the eyelets used in the tension device in the creel of warping machine must be made of a low friction material. The surfaces must be free of cuts and

Due to their fineness the total surface area of microfiber yarn is far greater than ordinary fibers (Anonymous, 2000). The surface of microfiber yarns is 10-15% larger than conventional fiber yarns. Due to the higher surface area of microfiber smoothed yarn absorbs approximately 10% more sizing agent and textured yarns approximately 15% more sizing agent than conventional yarn. By reducing the viscosity of the sizing agent distribution of the sizing agent may be improved. The squeezing pressure must be adapted to the speed to achieve regular sizing. As a result of the larger surface and the small mass of the individual filaments the microfiber can be heated faster as drying also occurs faster. So cooling must be effected in a few seconds. The drying temperature can be lowered by 10% in the case of microfilaments (Basu, 2001). Since microfibers have very small interstices, desizing become quite difficult and costly. Desizing must always be clean to prevent problems in dyeing. Knowledge of the type of size used is very important to optimize the desizing process. Pretreatment must be done either on tensionless open width washers or in the overflow or jet dyeing machine. Control of PH is important for optimum size removal

Many machine manufacturers recommend the use of air jet and rapier looms for microfilament woven fabric production. They also recommend the use of prewinding units and yarn brakes, which are suitable for processing filament yarns for weft insertion.

snags. Also, the reed blades must be absolutely free of any snags or bars (Basu, 2001).

masks (Mukhopadhyay & Ramakrishnan, 2008).

Yonenaga, 2000).

**4.7 Construction applications**

(Purane & Panigrahi, 2007).

**5. Weaving of microfibers**

(Anonymous, 2000; Rupp & Yonenaga, 2000).

polarization to the nonwoven, attract and absorb charged dust particles. Microfiber textiles can produce excellent filtration effects in the process of filtering solid or liquid materials. Microfiber liquid filters offer; high water passage speed, high extraction performance and ease of cleaning micro-particles from the filter (Rupp & Yonenaga, 2000). The extremely fine diameter of splittable synthetic microfibers makes them suitable for filter applications by increasing the filtration performance. The splittable microfibers are more suited as flexresistant materials. In pulsing applications where the filter medium is continuously flexed but also requires stiffness, splittable synthetic fibers add a high degree of reinforcement to the filter medium. Because there are at least 16 times the numbers of fibers available for reinforcement when they are split for segmented fibers (Mukhopadhyay & Ramakrishnan, 2008).

### **4.5 Microfibers for cleaning**

The microfiber fabric can be used for producing cleaning cloths. Most of the stick dirt is caused by dust accumulating on thin layers of fat which merely spreads and barely touched by conventional wiping cloths. This is because the fiber of these wiping cloths is normally 10 mm thick and is unable to capture 1 µm thick oil layers (Basu, 2001). Unlike ordinary cleaning fabrics that move or push dirt and dust from one place to another, the microfilaments can penetrate into the thin fatty layer of dirt and trap it within the micropockets among the filaments and then store the dirt particles in the fabric until it is washed. They are perfect for asthma and allergy sufferers, as they remove dust and dust mites without chemicals. They are also excellent at removing fingerprints from any surface. Grease, tar, splattered bugs come off with the cleaning cloth (Purane & Panigrahi, 2007). The cleaning properties of the microfibers are further enhanced because they have a cationic (positive) charge due to the presence of the polyamide in the microfibers. Most dirt and dust particles, bacteria, pollen, oxidation on metals, etc., have an anionic (negative) charge. Thus, the microfibers naturally attract negatively charged particles, bacteria, etc. (Mukhopadhyay & Ramakrishnan, 2008). The dirt trapped in the micropockets can be removed by washing. These wiping cloths are used for cleaning car mirrors, computers, jewels and noble metals, fingerprints from photos and films (Basu, 2001). Microfiber cleaning towels are used for cleaning floors, windows, furnishings and interior and exterior of cars.

#### **4.6 Medical applications**

When compared to commonly textiles to microfiber nonwovens, they are lower in cost, easier to use, more versatile, safer, and features of better disposability. With this in mind, it is no wonder that microfiber nonwovens are found in hospital surgical drapes and gowns, protective face masks, gloves, surgical packs, and bedding (Purane & Panigrahi, 2007). Fabrics from microfibers have excellent breathability and have been used for wound care. Polypropylene microfiber spunbonds have application in wound-care, where they are used as hydrophobic backings. At the same time, the air permeability and breathability of these nonwovens promote healing and their softness and flexibility allow excellent adaptation to the skin. In addition, polypropylene microfiber spunbonds have potential application in disposable surgical gowns and masks where spunlaced fabrics are widely used. The barrier properties of these spunbonds are more than 25% better than the spunlaced fabrics at about half their weight. Their softness, high permeability and breathability guarantee a high level

polarization to the nonwoven, attract and absorb charged dust particles. Microfiber textiles can produce excellent filtration effects in the process of filtering solid or liquid materials. Microfiber liquid filters offer; high water passage speed, high extraction performance and ease of cleaning micro-particles from the filter (Rupp & Yonenaga, 2000). The extremely fine diameter of splittable synthetic microfibers makes them suitable for filter applications by increasing the filtration performance. The splittable microfibers are more suited as flexresistant materials. In pulsing applications where the filter medium is continuously flexed but also requires stiffness, splittable synthetic fibers add a high degree of reinforcement to the filter medium. Because there are at least 16 times the numbers of fibers available for reinforcement when they are split for segmented fibers (Mukhopadhyay & Ramakrishnan,

The microfiber fabric can be used for producing cleaning cloths. Most of the stick dirt is caused by dust accumulating on thin layers of fat which merely spreads and barely touched by conventional wiping cloths. This is because the fiber of these wiping cloths is normally 10 mm thick and is unable to capture 1 µm thick oil layers (Basu, 2001). Unlike ordinary cleaning fabrics that move or push dirt and dust from one place to another, the microfilaments can penetrate into the thin fatty layer of dirt and trap it within the micropockets among the filaments and then store the dirt particles in the fabric until it is washed. They are perfect for asthma and allergy sufferers, as they remove dust and dust mites without chemicals. They are also excellent at removing fingerprints from any surface. Grease, tar, splattered bugs come off with the cleaning cloth (Purane & Panigrahi, 2007). The cleaning properties of the microfibers are further enhanced because they have a cationic (positive) charge due to the presence of the polyamide in the microfibers. Most dirt and dust particles, bacteria, pollen, oxidation on metals, etc., have an anionic (negative) charge. Thus, the microfibers naturally attract negatively charged particles, bacteria, etc. (Mukhopadhyay & Ramakrishnan, 2008). The dirt trapped in the micropockets can be removed by washing. These wiping cloths are used for cleaning car mirrors, computers, jewels and noble metals, fingerprints from photos and films (Basu, 2001). Microfiber cleaning towels are used for

When compared to commonly textiles to microfiber nonwovens, they are lower in cost, easier to use, more versatile, safer, and features of better disposability. With this in mind, it is no wonder that microfiber nonwovens are found in hospital surgical drapes and gowns, protective face masks, gloves, surgical packs, and bedding (Purane & Panigrahi, 2007). Fabrics from microfibers have excellent breathability and have been used for wound care. Polypropylene microfiber spunbonds have application in wound-care, where they are used as hydrophobic backings. At the same time, the air permeability and breathability of these nonwovens promote healing and their softness and flexibility allow excellent adaptation to the skin. In addition, polypropylene microfiber spunbonds have potential application in disposable surgical gowns and masks where spunlaced fabrics are widely used. The barrier properties of these spunbonds are more than 25% better than the spunlaced fabrics at about half their weight. Their softness, high permeability and breathability guarantee a high level

cleaning floors, windows, furnishings and interior and exterior of cars.

2008).

**4.5 Microfibers for cleaning**

**4.6 Medical applications**

of comfort in wearing when used as surgical gowns and for application as surgical face masks (Mukhopadhyay & Ramakrishnan, 2008).

The biocompatibility of microfibers offers great potential and manifold possibilities of use in the medical field. Microfiber filter produced from melt blown polyester are sold to hospitals for use in blood transfusion and blood donation. Polyester microfibers are very compatible with human organs and have proved themselves in use of vascular prothesis (Rupp & Yonenaga, 2000).


**4. Conditions that modify the barrier function**

During hydration the greater part of the water is associated with intracellular keratin; the natural factor of hydration or natural moisturizing factor (NMF) absorbs a noticeable amount of water (10% of the weight of the corneocyte). Corneocytes swell and the barrier properties of the stratum corneum are deeply altered. In the intercellular space the small

Topical Delivery of Haptens: Methods of Modulation of the

coefficient.

preparations [**28**].

way of penetration [**30**].

**5.2 Carrier vesicular systems**

**5.3 Scratch-patch test**

Cutaneous Permeability to Increase the Diagnosis of Allergic Contact Dermatitis 65

stratum corneum. Chemical enhancers may: a) increase the diffusibility of the substance inside the barrier, b) increase the solubility in the vehicle or both, or c) improve the partition

These substances may frequently have a not specific action. Enhancers of this type, that are not widely used, are Azone, Dermac SR-38, and oleic acid [**27**]. In some cases, however, these have an irritating effect and must be carefully evaluated in the various

Excipients like ethanol, propylene-glycol, and dimethylsulfoxide (DMSO) may increase the diffusion by altering the organization of lipids of the horny layer [**29**]. The interference with the biosynthesis of some lipids may alter the structure of the barrier and increase the penetration. Methods have also been studied that interfere with secretion and organization of lipids (e.g., brefeldine, monetine, and cloroquine). In addition, enhancers that alter the supramolecolar organization of the bistratified lamellae (synthetic analogs of fats, inducing abnormalities of the organization of the membranes; complex precursors that can not be metabolized, etc.) have been studied. These methods produce an alteration of the critical molar ratio among ceramides, cholesterol, and fatty acids; if there is decrease or excess of one of these 3 key lipids, the lamellar organization cannot be maintained. There may be separation of the phases with more permeable interestitial spaces and formation of a new

The efficacy of the enhancers may be increased by inhibition of the metabolic reaction of repair once the alteration of the barrier has been obtained. This would involve inhibiting metabolic sequences that can rebuild and maintain the barrier function. Inhibitors of enzymes with relevant functions (e.g., lovastatin) or specific inhibitors of enzymes synthesizing ceramides or fatty acids induces alteration of the molar ratio of the three critical lipids and leads to discontinuity in the lamellar layer system [**31**]. Other

The number of drugs for which transdermic methods for systemic use has been possible is very small and restricted to lipophilic and low molecular weight substances (e.g. nicotinic

Liposome formulations can be very effective. However, they probably increase penetration only through the transappendigeal avenue [**34**]. Niosomes and transferosomes, formed by modified liposomes (phosphatidilcoline, sodium cholate, ethanol), are systems based on the ability of vesicles to cross the unaltered horny layer because of the osmotic gradient between external and internal layers of the barrier. These are "flexible" vesicles able to transport their

Although closed patch tests are the mainstay for the evaluation of allergic contact dermatitis, occasionally, even when appropriate concentrations of allergens are used and contact allergy is strongly suspected, positive reactions are not always obtained. As in the cases that will be described patch test with high molecular weight substances as heparin,

enhancements may be obtained by modifying the polarity [**32**].

acid, nitroglycerin, clonidine, steroid hormones, and scopolamine) [**33**].

contents through the intercellular tortuous route of the corneous layer.

amount of water linked to polar groups by hydration does not alter the organization of lipids and does not reduce of permeability [**17**]. The effect of the hydration however has a discontinuous effect; the increase in permeability may be by ten times for some substances and very limited for others [**18**]. Occlusion partially hinders the loss of humidity of the skin, increasing the content of water of the horny layer. However the NMF level in the horny layer is almost zero. It seems therefore that there is a homeostatic mechanism that prevents hyperhydration of the skin [**9**]. Occlusion may increase the absorption by several times, especially for hydrophilic compounds. However, in some conditions it may promote the formation of a reservoir effect. The acidity of the cutaneous surface, controlling homeostasis and enzymatic activities, influences permeability [**19**]; the metabolic activity of the skin (enzymatic oxidoreductive processes) may modify the substances applied, influencing permeability and effects.

Absorption is also influenced by other skin properties that vary at different cutaneous anatomical sites. For instance, the absorption diminishes greatly as one moves from the palpebral skin to the plantar surfaces [**20**].

Age influences skin absorption. Various biological activities are lower in the skin of the aged individual. Great variation is also noted for the premature infant and neonate, who have greater cutaneous permeability [**21**]. There are no experimental data confirming the validity of friction on transcutaneous absorption [**6**]. Alterations of the barrier induce modifications of TEWL [**9**]. In addition, the horny layer may be defined as a biosensor; alterations of external humidity regulate proteolysis of filaggrin, synthesis of lipids, DNA, and proteins within keratinocytes, which can lead also to inflammatory phenomena [**22**].

The cutaneous bioavailability of most commercial dermatological formulations IS about 1-5% of applied dose [**23**].

The active substances of topical formulations are generally absorbed in small quantities; only a reduced fraction passes from the vehicle into the stratum corneum. The greater part remains on the surface of the skin, subject to loss in several ways such as by sweating, chemical degradation, and removal. Future standards would therefore aim to make formulations not merely high in concentration, but pharmaceutically optimized to have an elevated (50-100%) bioavailability. On the other hand, one must consider the marked variations of the different cutaneous areas and skin conditions that make uncertain the therapeutic equivalence when compared with other ways of administration in clinical conditions [**24**].


**4. Problem statement**

In solving the smart routing problem via cross-layer design, the goal is to solve the 4-tuple defined by,

6 Wireless Sensor Networks / Book 1

194 Wireless Sensor Networks – Technology and Protocols Cross-Layer Design for Smart Routing in

be used between the application layer and the PHY layer. For example, the application layer may inform the PHY layer of transmission parameters such as transmit power and operating

The design of a cross-layer optimization algorithm for WSNs that consider both performance and energy factors requires efficient communication between protocol stack layers such as the PHY, link, network and application layers. Direct signaling between application layers reduces latency in the communication between multiple layers and is crucial in the design of cross-layer optimization algorithms [9]. The direct signaling scheme for our protocol stack

The goal of direct signaling is to exchange information between important protocol layers for smart routing. This ensures that the required information to perform cross-layer optimization is retrieved, and allocation decisions are sent, with minimal delay. For example, the cluster-head's PHY layer will inform the application layer of the sensor and mesh node state information which includes energy rating information, surrounding interference and more. State information and coordination protocols to provide feedback to the cluster-head are covered in Section 9. The link layer and network layer will also inform the application layer of the channel conditions and available path information, respectively. Furthermore, upon executing the cross-layer optimization policy, the application layer will inform the PHY layer of the necessary resource allocations and the link layer of the next-hop information. Direct signaling enables these interactions with minimal delay for optimized and timely responses

*lx*,*ly* for the direct signaling

(*n* − 1) (1)

frequency to use during transmission.

model is illustrated in Figure 4.

in our distributed network.

speed-up factor of (*n* − 1) [9].

method is calculated as,

where *TL*

**Figure 4.** Protocol Stack Model to Enable Smart Routing

For any two non-adjacent layers, *lx* and *ly*, the propagation latency *TDS*

*TDS lx*,*ly* = *TL*

*lx*,*ly*

*lx*,*ly* is the propagation latency between layers *lx* and *ly* in a traditional layered protocol

stack with (*n* − 1) layers between them. Hence, the direct signaling method provides a

to identify the most suitable path that satisfies both performance needs of an application and energy conservation considerations; this path routes data from a source sensor to a centralized controlling station. In doing so, the cross-layer optimization policy focuses on functions at three layers: path selection at the network layer; channel selection at the link layer; and, transmit power allocation at the physical (PHY) layer. Hence, the 4-tuple defines the operating point for the network in solving the resource allocation for a single transmission.

The 4-tuple forms the basis of utility functions that model the preferences of nodes in allocating various PHY layer resources to throughput; the optimization problem exists since these PHY layer resources also impact network lifetime. Utility functions quantify the performance benefits and power costs associated with the allocation prior to selecting the optimal operating point. In doing so, the criticality of the application plays a major role in determining the necessary tradeoff for the given sensor.