**5. Recent developments of plant-derived active compounds in drug development**

 With the recent interest in molecular modeling, combinatorial chemistry, and other synthetic chemistry techniques by pharmaceutical companies and funding organizations, natural products, and particularly medicinal plants, remains an important source of new drugs, new drug leads, and NCEs [56]. In both 2001 and 2002, approximately one quarter of the bestselling drugs worldwide were natural products or derived from natural products. Some of the plant-derived drugs and their significance are listed in the **Table 2**. Many plant-derived compounds have been used as drugs, either in their original or semisynthetic form. Recent developments in drug discovery from plants, including information on approved drugs and

#### **Table 2.**

*Selected compounds derived from medicinal plants.*

plant extracts or compounds now in clinical trials, are available [57]. It is anticipated that in the future, plant-derived compounds will still be an essential aspect of the therapeutic array of medicines available to the physician [57].


**14. Special aspects of nanominerals**

Trace minerals such as Se is essential in minute quantities in poultry diet to reduce stress, improve immunity and overall health, but safe limit of inorganic Se is very narrow. Hu et al. [51] observed a wider range between the optimal and toxic dietary levels of nano-Se compared to inorganic sodium selenite in broiler chickens. But contradictory reports exist regarding occurrence of severe pathological changes in liver due to increase in nano-Se concentration from 0.15 to 0.3 mg/ kg diet [124]. One of the possible mechanisms of nano-Se action in poultry could be conversion of nano-Se into selenite, H2Se or Se-phosphate followed by synthesis of selenoproteins by gut microbiota, which was also reported by Surai et al. [125] in *Veiollonella*. Reports suggest lower toxicity of Se NP than selenomethionine [126]. Also, Gangadoo et al. [127] reported that nano Se did not cause any damage to epithelial cells in the digestive system and neuronal bodies in brain tissue signifying its lesser toxicity in animal models. Nano-Ag in higher concentration (8 and 12 mg/ kg diet) had detrimental effect on organs such as liver [128]. Ag-NP supplementation in drinking water (15 mg/L) of broilers had no significant growth promoting or coccidiostat action [129]. At higher concentration (50 mg/L) in drinking water, no effect on the intestinal colonization of C. jejuni was found; however, reduced body weight gain was observed in broiler chickens [130]. Dietary ZnO NP at 40 and 60 mg/kg alleviated the negative results of heat stress evident from lowering of serum corticosterone level [131]. Saki and Abbasinezhad [132] reported improved embryonic growth and development in broiler on supplementation of 25 mg/kg diet of nano-Fe and 100 mg/kg diet of Fe-nano-alimet chelate. But toxicity of nano-FeO was reported in chick embryo possibly due to its interaction with egg albumen.

*Advances in Poultry Nutrition Research*

were expressed quickly by Cu-NP [107].

delivery and diagnostics [110].

**12. Nanominerals as antimicrobial feed additives**

coarse CuSO4 [106]. A study involving Cu-NP, agglomerates of Cu-NP and Cu microparticles on the metabolism in broiler chickens after a single intramuscular injection revealed that all these forms had growth stimulating effect along with increased red cell level, hemoglobin, Cu and protein in blood serum, where effects

Pathogenic microbial load in the gut of poultry is detrimental as they reduce growth rate, feed efficiency and mortality, and are some of these contaminants may survive during food processing and storage. The in-feed antibiotics used for preventing the pathogens as well as growth promoters has been great concern due to possible emergence of drug resistance in microbes as well as appearance of the drug residue in poultry products and subsequently affecting consumer's health [108]. There is an optimism of using nano-minerals as antibiotic alternatives due to their antimicrobial properties [109]. NP use has been established in therapeutics, drug

Many research carried has explored the antimicrobial action of metal oxide-NP [109]. Nano-Ag supplementation at 4 mg/kg diet in broiler chickens reduced serum cholesterol, aspartate aminotransferase levels and reduced caecal *Escherichia coli*, but had no significant effect on Lactobacillus count [70]. Nano-Ag in water (25 mg/ kg) increased the population of lactic acid bacteria without any adverse effect on enterocytes of duodenal villi [111]. Nano-Ag lowered the number of *Escherichia coli*, *Streptococcus*, *Salmonella*, and total mesophilic bacteria in the litter [112]. ZnO-NP was found be effective against both gram positive and gram-negative bacteria [109, 113] as well as spores that are resistant to high temperature and pressure [29]. ZnO-NP are also effective in inhibiting the growth of fungi (*Aspergillus flavus*, *A. ochraceus* and *A. niger*) and their mycotoxins production [114]. Some possible mechanisms of bactericidal action of metal oxide NP was generation of reactive oxygen species inside the bacterial cells (e.g., hydroxyl, hydroperoxide, and superoxide radicals) that may damage lipid membranes of cells and organelles of bacteria [109, 115] or they alter permeability of bacteria after entering their plasma membrane resulting in cell death [116]. They may damage bacterial cell after penetration by interacting with sulfur and phosphorus containing important compounds like DNA [113]. As per Rajendran et al. [117], ZnO NP inactivates the proteins that are responsible for transport of nutrients, thus decreasing the membrane permeability and eventually causing the cellular death. Another explanation about antimicrobial action of metal oxide NP is that microorganisms carrying a negative charge are electromagnetically attracted towards metal oxides carrying a positive charge, subsequently leading to oxidization and death of microbe [113]. The antibacterial activity depends on the size, with better result obtained with smaller size [118]. But, Arabi et al. [113] observed the significance of surface area and concentration of NP,

whereas crystalline structure and shape of NP have little significance.

**13. Environment implication of nanomineral supplementation**

In high intensified production system, trace minerals are added to poultry diets in high amounts exceeding the birds' requirements, with a large safety margin, creating environmental issues particularly in areas of intensive poultry production [8]. A study reported that by using poultry manure, Zn content in soil was found in excess by 660% in comparison to plant Zn requirements, predisposing to

**72**

FeO NP caused 100% mortality at 200 mg/L and decreased body weights and crown-rump lengths of embryo at 50 and 100 mg/mL and 50–60% degeneration of neurons in brain at 10–100 mg/L dose range [133]. It seems few minerals in their nanoforms are more toxic than their coarser forms. Therefore, safety and toxicity levels of different nanominerals should be widely evaluated before recommending them at an optimum dose for their use in poultry.


**1. Introduction**

The prevalence of obesity has been rising regardless of age, sex, and race for the past few decades [1] and is a growing public healthcare concern worldwide [2–4]. Obesity has been implicated in the development of several chronic comorbidities, including type 2 diabetes mellitus, hypertension, cardiovascular disease, stroke, dyslipidemia, obstructive sleep apnea, fatty liver and biliary disease, osteoarthritis, and malignancies, leading to increased cardiovascular and all-cause mortality [5–7]. Obesity is also associated with a significantly increased risk of chronic kidney disease (CKD) progression and development of end-stage renal disease (ESRD) [8,9].

The renal e ffects of obesity include both structural and functional adaptations. Excessive body weight is related to intrarenal hemodynamic parameters, namely increased renal blood flow and hyperfiltration. Pathologically, this promotes low glomerular density with glomerulomegaly and thickening of the glomerular basement membrane (GBM) [10–12]. These glomerular changes are defined as obesity-related glomerulopathy, a secondary form of focal segmental glomerulosclerosis (FSGS) [13]. Clinically, obesity-related glomerulopathy presents with subnephrotic or nephrotic-range proteinuria without other features of nephrotic syndrome and rapid loss of kidney function [14,15]. In addition to obesity-related glomerulopathy, obesity may be a risk factor for progression of IgA nephropathy (IgAN) [16–21]. Most studies demonstrated that excessive BMI, especially a BMI greater than 25 kg/m2, was a risk factor for renal disease progression in IgAN patients [16,17]. On the other hand, BMI was not an independent predictor for IgAN progression in some reports [18,22]. Furthermore, recent research showed that underweight, rather than obesity, was an independent risk factor for progression to ESRD, which might be associated with malnutrition status [21]. Therefore, it is di fficult to conclude the overall e ffect of BMI on progression of IgAN with the existing evidence. This may be due to the complex pathophysiological association among obesity, metabolic abnormalities, and renal outcomes.

To date, there are few studies regarding the e ffect of obesity on histopathological changes in IgAN. Therefore, we conducted a multi-center cohort study using a kidney biopsy registry to elucidate the complex association between obesity and the clinicopathological characteristics of IgAN in Korea. We focused on the impact of obesity on histopathologic and clinical severity at the time of kidney biopsy in IgAN.

#### **2. Materials and Methods**

#### *2.1. Study Design and Data Source*

This was a cross-sectional study of a multi-center cohort that included patients older than 18 who underwent kidney biopsy at eight university hospitals a ffiliated with the College of Medicine Catholic University of Korea between January 2015 and November 2019. This study was conducted in accordance with the Declaration of Helsinki and was approved by the Institutional Review Board of the College of Medicine, Catholic University of Korea (XC19OEDI0025). Written informed consent was obtained from patients at the time of biopsy.

We retrospectively collected records from patients with primary IgAN. We excluded 20 out of 557 patients diagnosed with IgAN whose histologic descriptive form was not in accordance with others. A total of 537 patients were finally enrolled in the present study. Patients with Henoch-Schonlein purpura nephritis were ineligible. Patients were divided into three groups according to body mass index (BMI). BMI was calculated as (weight in kilograms)/(height in meters)2. Subjects were categorized according to the Asia-Pacific obesity classification as follows: underweight (<18.5 kg/m2), normal weight/overweight (18.5–24.9 kg/m2), and obese (≥25 kg/m2) [23]. The BMI cut-o ffs in the World Health Organization (WHO) classification have categorized BMI 25–29.9 as overweight and ≥30 kg/m2 as obese [24]. The Asia-Pacific classification of BMI has a lower cut-o ff for overweight and obese categories compared to the WHO classification. Because the Korean Society for the Study of Obesity defined obesity as BMI ≥ 25 kg/m2 according to the Asia-Pacific obesity classification [25], we used a

cut-o ff point for BMI of 25 kg/m2 in the present study. A flow diagram for patient selection is presented in Figure S1 (Supplementary Materials).

#### *2.2. Data Collection and Definitions*

Using the database from the Kidney Biopsy Registry of Catholic Medical Center, all patients were admitted for kidney biopsy and we collected the following data at the time of kidney biopsy. Baseline demographics and clinical data ([including age, sex, height, weight, BMI, co-morbidities, systolic blood pressure (SBP), diastolic blood pressure (DBP), laboratory data, and treatment characteristics) were collected. Blood chemistry data included hemoglobin, high sensitivity-C-reactive protein (hs-CRP), fasting glucose, creatinine, albumin, aspartate aminotransferase (AST), alanine aminotransferase (ALT), uric acid, total cholesterol, triglycerides, low density lipoprotein-cholesterol (LDL-C), high density lipoprotein-cholesterol (HDL-C), serum complement 3 (C3), complement 4 (C4), and serum IgA levels. Proteinuria was assessed by 24 h urine collection. The estimated glomerular filtration rate (eGFR) was calculated from the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation [26]. The degree of urinary red blood cells (RBC) sediment was scored in five phases, as follows: <3 RBCs/high power field (HPF), 0; 3–5 RBCs/HPF, 1; 5–9 RBCs/HPF, 2; 10–19 RBCs/HPF, 3; and more than 19 RBCs/HPF, 4. We also assessed treatment plans after the diagnosis of IgAN, including use of anti-hypertensive medications, diuretics, lipid-lowering drugs, and immunosuppressive medications.

## *2.3. Histopathologic Parameters*

All kidney tissue specimens were obtained by percutaneous needle biopsy. Pathologic slides were reviewed by expert renal pathologists in each center. On light microscopy, the total number of glomeruli and the percentage of glomerulosclerosis and crescents were assessed quantitatively. Renal histologic findings were scored according to the histologic grading system from our university as follows. The severity of mesangial matrix expansion (MME), mesangial cell proliferation, endocapillary proliferation, interstitial fibrosis (IF), tubular atrophy (TA), arterial intimal hyalinosis, and fibrous vessel wall thickening were semi-quantitatively graded from 0 to 4 as follows: grade 0, absent; grade 1, trace (<20%); grade 2, mild (20%–40%); grade 3, moderate (40%–70%); and grade 4, severe (≥70%). Renal biopsy findings were also assessed according to the Oxford classification (MEST score) [27] or the WHO classification (class I to VI) [28]. On immunofluorescence microscopy, the severity of mesangial deposition of IgA, C3, and C4d were graded as 0 (absent), +1 (trace), +2 (mild), +3 (moderate), and +4 (marked).

## *2.4. Statistical Analysis*

Continuous data were expressed as mean ± standard deviation and were compared using one-way ANOVA followed by Sche ffe's post-hoc comparisons (parametric) or Kruskal–Wallis test (non-parametric) as appropriate. Categorical data were expressed as numbers (percentage) and compared using the chi-squared test. Spearman correlation coe fficients were calculated for correlations between BMI and clinical/laboratory variables. Linear regression analyses were performed to evaluate the association between BMI and histopathologic parameters and the associations between eGFR and 24 h proteinuria and clinicopathological parameters. Logistic regression analyses were performed to estimate the odds ratios (ORs) and 95% confidence intervals (CIs) for high grades of MME, IF, and TA, and positive mesangial deposition of C3 and IgA according to the BMI groups. High-grade MME, IF, and TA were defined as grades 2–4, and positive mesangial C3 and IgA deposition was defined as scores ≥ +2. A *p* value of <0.05 was considered statistically significant. The statistical analyses were performed using SPSS version 20.0 software (SPSS, Inc., Chicago, IL, USA).


**1. Introduction**

Over the last few years, there have been many studies using fractional-order differential and integral operators to generalize classical differential and integral calculus with the aim of further understanding the nature of complex systems. Currently, attempts are being made to apply fractional calculus to solve various physical, mechanical, biological, or chemical problems. While classical integer-order operators are dependent only on the local behavior of the function, fractional-order operators accumulate all the information about the function. Another fundamental feature of fractional derivatives is that they are defined along a segment, not at a point, as is the case with classical derivatives. This feature ensures a more accurate and effective analysis of different phenomena. One of the shortcomings that most models have to overcome is that, mathematically, velocity is an instantaneous velocity defined at a point. Thus, it can be seen from the literature that differential calculus is used in the heat transfer theory.

It has been found, for example, that variable thermal conductivity is a key physical property of materials, especially when it is dependent on temperature. Variable thermal conductivity is of significance in a wide range of applications, including modern physics and mechanical engineering. It is taken into consideration primarily to determine the effect of temperature on the performance of machine elements. Special attention is paid to this property when rapid changes in temperature occur, as they may affect the operation of mechanical assemblies and subassemblies, and consequently the whole machine. The relationship between variable thermal conductivity and fractional differential calculus

**Citation:** Blasiak, S. Heat Transfer Analysis for Non-Contacting Mechanical Face Seals Using the Variable-Order Derivative Approach. *Energies* **2021**, *14*, 5512. https:// doi.org/10.3390/en14175512

Academic Editor: Chi-Ming Lai

Received: 20 July 2021 Accepted: 31 August 2021 Published: 3 September 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

has been investigated extensively for problems related to fluid mechanics [1,2], viscous elasticity [3], relaxation [4], thermal elasticity and conductivity [5,6], control theory [7,8], and many others [9–11]. Over the years, researchers have extended the classical theory of elasticity and introduced the theory of thermoelasticity.

The mechanical properties, especially the relaxation, of additively manufactured materials were analyzed, for example, in [4]. A mathematical model was developed using fractional differential calculus to further fit the relaxation curves with the experimental data.

Warbhe et al. [5] used the quasi-static approach to the fractional-order theory of thermoelasticity to solve a two-dimensional problem for a thin circular plate with zero temperature across the lower surface and constant and evenly distributed temperature across the insulated upper surface. The integral transform technique was employed to solve the physical problem, while the displacement potential function was applied to calculate thermal stresses. Povstenko and Kyrylych [6] studied the interface between two solids. They considered generalized boundary conditions of a non-ideal thermal contact to solve the heat conduction equation of the fractional order as a function of time using the Caputo derivative.

The extensive monograph by Kaczorek [7] presented the theoretical and practical aspects of the application of fractional calculus to fractional discrete-time linear systems.

The research by Nowacki, described for instance in [12–14], was a breakthrough in this field. His findings are still valid and thus widely cited, as they can be applied to solve a large number of theoretical and practical engineering problems.

Knowledge of all theories available in this area is crucial to understand the deformations of elastic materials. Their thermal and mechanical behavior needs to be taken into account whenever thermoelastic deformations result in leaks, as is the case with noncontacting face seals, where the gap height may range from one to several micrometers.

Fractional differential calculus has proved well-suited to predict many physical phenomena associated with elastic media, e.g., thermal conductivity, heat transfer, and viscoelasticity. The classical differential equations describing physical phenomena are modified using the variable-order derivative (VOD) time fractional approach. Recently, there has been much research focusing on extending the applications of fractional differential calculus, e.g., [15–18]. These studies provide an insight into many important aspects associated with heat conduction. In [15], for example, Povstenko presented fundamental solutions to the time-fractional advection diffusion equation for two cases: the plane and the half-plane. He also considered Cauchy problems, inverse source problems, and Dirichlet problems. The solutions were expressed in terms of Bessel integral functions combined with Mittag–Leffler functions. In his other articles [16,17], Povstenko discussed solutions for heat transfer in composite media, in which he employed the time-fractional heat conduction equation with the Caputo derivative of fractional order to describe heat transfer in both constituent materials (0 < α ≤ 2 and 0 < β ≤ 2, respectively). The problem was solved under ideal contact conditions. This suggests that the temperature of the two materials and the heat fluxes were the same.

Liu et al. [19] proposed an approach to solving the time fractional nonlinear heat conduction equation. Similar solutions were proposed by Koca and Lotfy [20,21].

Another issue is an inverse problem in heat transfer. Liu and Feng [22], for instance, solved it using the fractional differential equation for a time-dependent derivative. The solution to the 2D time-fractional inverse problem of diffusion was based on an improved kernel technique. Maximum a posteriori estimation was required. Convergence was achieved using the regularization term and deriving a priori probability.

The primary aim of this article was to show how the results obtained by solving the classical equation of heat transfer differ from those obtained for the same physical phenomenon by employing the fractional differential equation. The study involved using the derivative order as a time-dependent function. The results from the two approaches were compared graphically. The analytical solutions of the main physical quantities were developed using the Marchi–Zgrablich transform, the finite Fourier cosine transform, and, finally, the Laplace transform.


**4. Ore deposits**

Thorianite, thorite, and uranothorite are the only true thorium minerals, but they are not recently recovered. Some resources of these minerals are coupled with quartz-pebble conglomerates in Canada (Elliot Lake region) and South Africa (Witwatersrand). World thorium resources in terms of the genetic types of ore deposits are displayed in **Table 1** [9].

**Table 1.** World thorium resources in terms of the deposit types [9].

The main recently available resources of thorium are coupled with monazite-enriched placer deposits in alluvial or marine sediments occurring mainly in Australia, India, Brazil, Venezuela, the USA, and Egypt. These deposits contain variable proportions of monazite, ilmenite, rutile, xenotime, zircon, and/or cassiterite. The main minerals, which are mined on these placer deposits, are ilmenite, rutile, zircon, and cassiterite. Associated minerals, which are rarely of economic significance, can include garnet and kyanite. Monazite, when also extracted, represents only an accidental product.

beach sands containing 10 ppm Th, and limestone averages about 2 ppm. Shale contains 10–15 ppm Th, small amounts of thorium may adsorb clay particles during weathering. Twelve isotopes of thorium are known, with atomic masses from 223 to 234. However, natural thorium is present as nearly 100% 232Th isotope. The other important natural isotope of thorium 230Th

In general, thorium occurs in relative small number of Th-enriched minerals: thorite (ThSiO4

monazite and bastnaesite. Monazite is a primary source of light REE. Monazite concentrates, which are mined from beach sands in India, Brazil, the USA, Malaysia, Korea, and Sri Lanka,

Other, especially, potentially based resources of thorium are coupled with carbonate-

Kola peninsula (Russia) contain rare REE-enriched mineral loparite (Na,REE,Ca) (Ti, Nb) O2

apatite ore deposit on the Kola Peninsula in the Russia. Apatite containing higher concentrations of thorium occurs also in the alkalic magmatic rocks on the Vishnevyye Mountains of the Urals range in the Russia [1]. A large variety of other minerals contain minor amounts of

Thorianite, thorite, and uranothorite are the only true thorium minerals, but they are not recently recovered. Some resources of these minerals are coupled with quartz-pebble conglomerates in Canada (Elliot Lake region) and South Africa (Witwatersrand). World thorium

resources in terms of the genetic types of ore deposits are displayed in **Table 1** [9].

**Deposit type Metric tons of thorium**

Placers 2,182,000 Carbonatites 1,783,000 Vein-type 1,528,000 Alkaline igneous rocks 584,000 Others 135,000 Total 6,212,000

**Table 1.** World thorium resources in terms of the deposit types [9].

enriched magmatic rocks (carbonatites), containing bastnaesite (up to 2.8 wt.% ThO2

], bastnaesite [(Ce, La)CO3

and 40.7–65.0 wt.% REO (rare earths oxides). However, monazites

), and synchysite [CaREE(CO3

[8]. Some higher concentrations of thorium have also important

.

1−x(OH)4−x]. However, the main world resources of thorium are coupled with

). Highly rare alkali-rich nephelinite syenites from the Lovozero pluton on the

),

), parisite

(F, OH)] (up to

F], and thorogum-

)2

is generally presented in uranium minerals.

204 Descriptive Inorganic Chemistry Researches of Metal Compounds

), monazite [(Ce, La, Nd,Th,U)PO4

from some granitic rocks could contain up to 27 wt.% ThO2

thorium (e.g., allanite, xenotime, zircon, and uraninite).

] (up to 4.0 wt.% ThO2

thorianite (ThO2

)

contain 3.1–14.32 wt.% ThO2

(CO3 )3 (F,OH)2

**4. Ore deposits**

with up to 1.6 wt.% ThO2

mite [Th(SiO4

[CaREE2

5.0 wt.% ThO2

Placer deposits are found where water waves have concentrated heavy mineral grains on a sea beaches. These deposits may occur in both modern and ancient shorelines. Many of the heavy mineral sand deposits are concentrated by wave action in both parallel and transgressive dunes. Monazite placers are reported from Australia, Egypt, India, Liberia, Brazil, Burma, Malaysia, Sri Lanka, and the USA.

The placer deposits in Australia are mined for their ilmenite, rutile, and zircon content. The monazite content in heavy mineral concentrates varied from 0.2 to 1.5 wt.%. Present-day shoreline deposits are evolved on the east coast in the SE Queensland. The most important placer sand deposits are coupled with the Tertiary fossil shoreline deposits in the Murray Basin, in the southwest Australia. Monazite grades in this deposits are around 1–1.5 wt.%.

Although monazite occurs associated with ilmenite and other heavy minerals in beach sands, skirting the entire Peninsular India, its economic concentration is confined to only some areas with suitable physiographic conditions. The west coast placers are essentially beach or barrier deposits with development of dunes evolved on dry months. On the other hand, the east coasts deposits consist of extensive dunes fringing the coasts. The beach sands of Chavara bar (Kerala) on the West coast contain 73 vol.% heavy minerals, 60–70 vol.% ilmenite, 4–7 vol.% garnet, 5–8 vol.% zircon, and 0.5–1.0 vol.% monazite. The east coast beach placers and dunes are low grade with 8–20 vol.% of heavy minerals. The most important placer deposit on the East coast is the Chatrapur deposit (Orissa) with about 20 vol.% heavy minerals and 0.5 vol.% monazite. In the Malaysian deposits, monazite is associated with columbite, xenotime, and cassiterite. The cassiterite placers at Trengganu contain as much as 58 vol.% monazite. In Sri Lanka, the largest placer deposit near Pulmoddai contains 3 million tons of sand with 0.4 vol.% monazite, 18 vol.% rutile, and 62 vol.% ilmenite [10].

In Brazil, monazite occurs associated with ilmenite and zircon in placer deposits evolved along the eastern and south-eastern Atlantic coast. In Burma, placer deposits occur in the southern Shan states. Weathering of quartz veins and pegmatite dykes injected into the granites derives considerable quantities of cassiterite and wolframite occurring in the placers.

In the USA, alluvial deposits of monazite are known to occur in the intermountain valleys of Idaho, the Carolina Piedmont of North and South Carolina, and the beach deposits of north-eastern Florida to south-eastern Georgia. The three monazite placer districts, namely the North and South Carolina stream deposits, Idaho stream deposits, and Florida-Georgia beaches, are the largest volume known alluvial thorium deposits in the USA. The modern and raised Pleistocene and Pliocene beach deposits of north-eastern Florida and south-eastern Georgia host low-grade but persistent concentrations of thorium. Heavy minerals constitute a small part of the beach sands. The most abundant heavy mineral in this beach deposits is ilmenite, in many places forming more than 50 vol.% of the heavy-mineral fraction. Monazite forms a minor part of the heavy-mineral fraction, usually less than 1 vol.%. The beach placer deposits of this region contain total reserves of about 14,700 tons of ThO2 , which occur in 330,000 tons of monazite. These placer deposits were mined primarily for ilmenite and rutile. Mining ceased in this area in late 1978 since increasing environmental regulations made mining operations more costly [11].

The ore bodies constituting quartz-pebble conglomerates are represented in particular by the Blind River-Elliot Lake deposits in Ontario, Canada and the Witwatersrand deposits in South Africa. These ore bodies occur mainly in pyrite-bearing oligomictic conglomerates. In the Blind River-Elliot Lake deposits, thorium together with uranium occurs mainly in a brannerite-uraninite-monazite mineral assemblage. Principal ore minerals are uraninite, brannerite, and monazite, with minor coffinite, uranothorite, xenotime, and gummite. Uraninite is partly enriched in thorium with average content of 6.5 wt.% ThO2 . The Witwatersrand reefs are not only rich in gold but also represent significant uranium deposit. The principal uranium minerals are uraninite and lesser uranothorite, brannerite, and coffinite. Uraninite from this deposit is enriched in thorium (average 3.9 wt.% Th) [12].

Carbonatites, which recently represented the most important source of REE, are also considered as potential source of thorium. Carbonatites are igneous rocks containing >50% of primary carbonate minerals. The most carbonatites are actually polygenetic and show evidence of hydrothermal and metasomatic reworking. These rocks generally contain <50 ppm Th; however, some contain higher concentrations. The majority of carbonatites occur in association with broadly coeval ultramafic and alkaline silicate rocks.

From the mid-1960s to 1985, the carbonatite-hosted Mountain Pass deposit in the USA was the world's main source of REE, producing over 20 kt REO at its zenith. Recently, almost all (~97%, or 120–130 kt REO in 2006–2010) of the world's REE supply comes from China, with 40–50% of this production contributed by the giant Fe–REE–Nb deposit at Bayan Obo [8].

Carbonatite-related deposits can be subdivided into deposits where magmatic and/or hydrothermal processes are important and those where secondary processes such as supergene enrichment and laterization predominate. The most important primary carbonatite-related deposit is the Bayan Obo deposit in Inner Mongolia, China, which represents 70% of the world's REE resources. The most abundant REE minerals at Bayan Obo are monazite and bastnaesite. Carbonatites with appreciable REE and Th mineralization have been reported also at Khibiny (Kola, Russia), Ozerny and Arshan (Siberia, Russia), Fen (Norway), Sokli (Finland), Mount Weld, Cummins Range, Mud Tank (Australia), Palabora (South Africa), Khanneshin (Afghanistan), Amba Dogar (India), Barra do Itapirapuã (Brazil), Tundulu and Kangankunde (Malawi), and Wigu Hill (Tanzania) among many others [13].

Highly potential sources of REE and Th represent intrusions of alkaline and peralkaline igneous rocks. Some well-known examples of these rock series being the Ilímaussaq intrusion in southern Greenland, Lovozero and Khibiny alkaline plutons on the Kola Peninsula (Russia), the Red Wine-Letitia alkaline province in Canada, alkaline laccolith at Poços de Caldas (Brazil), and alkaline syenite body at Pilanesberg (South Africa) [14, 15]. All these magmatic complexes are zoned or layered, enriched with Na and K, and contain a variety of relatively rare minerals including thorite, monazite, loparite, zircon, and apatite. Thorium is present in thorite, monazite, zircon, loparite, and some other accessory minerals of REE. Local thorium contents in these rock complexes may range up to 1500 ppm Th, but overall they rarely contain in excess of 50 ppm Th [16].

a small part of the beach sands. The most abundant heavy mineral in this beach deposits is ilmenite, in many places forming more than 50 vol.% of the heavy-mineral fraction. Monazite forms a minor part of the heavy-mineral fraction, usually less than 1 vol.%. The beach placer

330,000 tons of monazite. These placer deposits were mined primarily for ilmenite and rutile. Mining ceased in this area in late 1978 since increasing environmental regulations made min-

The ore bodies constituting quartz-pebble conglomerates are represented in particular by the Blind River-Elliot Lake deposits in Ontario, Canada and the Witwatersrand deposits in South Africa. These ore bodies occur mainly in pyrite-bearing oligomictic conglomerates. In the Blind River-Elliot Lake deposits, thorium together with uranium occurs mainly in a brannerite-uraninite-monazite mineral assemblage. Principal ore minerals are uraninite, brannerite, and monazite, with minor coffinite, uranothorite, xenotime, and gummite. Uraninite is partly

not only rich in gold but also represent significant uranium deposit. The principal uranium minerals are uraninite and lesser uranothorite, brannerite, and coffinite. Uraninite from this

Carbonatites, which recently represented the most important source of REE, are also considered as potential source of thorium. Carbonatites are igneous rocks containing >50% of primary carbonate minerals. The most carbonatites are actually polygenetic and show evidence of hydrothermal and metasomatic reworking. These rocks generally contain <50 ppm Th; however, some contain higher concentrations. The majority of carbonatites occur in associa-

From the mid-1960s to 1985, the carbonatite-hosted Mountain Pass deposit in the USA was the world's main source of REE, producing over 20 kt REO at its zenith. Recently, almost all (~97%, or 120–130 kt REO in 2006–2010) of the world's REE supply comes from China, with 40–50% of this production contributed by the giant Fe–REE–Nb deposit at Bayan Obo [8].

Carbonatite-related deposits can be subdivided into deposits where magmatic and/or hydrothermal processes are important and those where secondary processes such as supergene enrichment and laterization predominate. The most important primary carbonatite-related deposit is the Bayan Obo deposit in Inner Mongolia, China, which represents 70% of the world's REE resources. The most abundant REE minerals at Bayan Obo are monazite and bastnaesite. Carbonatites with appreciable REE and Th mineralization have been reported also at Khibiny (Kola, Russia), Ozerny and Arshan (Siberia, Russia), Fen (Norway), Sokli (Finland), Mount Weld, Cummins Range, Mud Tank (Australia), Palabora (South Africa), Khanneshin (Afghanistan), Amba Dogar (India), Barra do Itapirapuã (Brazil), Tundulu and Kangankunde

Highly potential sources of REE and Th represent intrusions of alkaline and peralkaline igneous rocks. Some well-known examples of these rock series being the Ilímaussaq intrusion in southern Greenland, Lovozero and Khibiny alkaline plutons on the Kola Peninsula (Russia), the Red Wine-Letitia alkaline province in Canada, alkaline laccolith at Poços de Caldas

, which occur in

. The Witwatersrand reefs are

deposits of this region contain total reserves of about 14,700 tons of ThO2

enriched in thorium with average content of 6.5 wt.% ThO2

tion with broadly coeval ultramafic and alkaline silicate rocks.

(Malawi), and Wigu Hill (Tanzania) among many others [13].

deposit is enriched in thorium (average 3.9 wt.% Th) [12].

ing operations more costly [11].

206 Descriptive Inorganic Chemistry Researches of Metal Compounds

On the Ilímaussaq complex is bounded highly interested REE-Y-U-Th mneralization at Kvanefjeld (Kuannersuit) coupled on agpaitic nepheline syenites. Recently performed exploration is concentrated on potential recovery of REO, Y, together with production of U and Zn as valuable by-products. The Lovozero complex in the Kola Peninsula is represented by layered intrusion of varied varieties of nepheline syenite with loparite as main economic interested mineral. Several loparite-rich units were mined since 1951 as the major source of LREE, Nb, and Ta for Soviet industry [13].

Some other potential sources of thorium represent Th-bearing granites and pegmatites, which are known in many parts of world. The thorium-enriched pegmatites most commonly occur in near granitic or syenitic bodies or in high-grade metamorphic rock series near their contacts with granitic stocks or batholiths. The principal thorium-bearing minerals in these deposits are uraninite, thorite, brannerite, uranothorite, monazite, and some other REE-, Th-, and U-bearing accessory minerals.

Most of the Th-enriched granites and pegmatites are not of commercial importance at present but provide a large reserve of thorium and uranium for the future. Thorium-bearing granitic rocks and pegmatite-bearing rock complexes occur in the Bancroft area of Ontario (Canada), Rössing (Namibia), Crockers Well, Greenbushes, Radium Hill (Australia). The Th-bearing minerals are represented by allanite, betafite, brannerite, davidite, monazite, thorite, and some others rare REE-, Th-, and U-bearing minerals. The ore zones at the Greenbushes contain low levels of thorium with average grades in range 3–25 ppm Th [17]. The uranium deposits in the Bancroft area coupled with anatectic pegmatites produced a total of 5700 tons U between 1956 and 1982. The principal ore minerals were uraninite, with up to 10 wt.% ThO2 , and uranothorite.

Uranium mineralization associated with leucogranite dykes on the Rössing deposit in Namibia was derived by the partial melting of U-rich sedimentary rocks. Uraniferous leucogranite bodies are located in high-grade metasediments of the Damara Pan-African belt. Within mineralized leucogranites, the distribution of uranium can be extremely variable. Main uranium mineral is Th-bearing uraninite with 3.3–8.0 wt.% ThO2 . The Rössing uranium deposit is mined from 1976 and total production by the end of 2007 was slightly over 90,000 tones U [18].

Relatively rare thorium-bearing vein deposits are distributed throughout the world. They are localized in shear zones, faults, breccias zones in metasedimentary and metavolcanic rocks and are often associated with alkalic rocks complexes and carbonatites. The principal Th-bearing minerals in vein deposits are thorite, thorogummite, and monazite, which are associated with some REE-minerals (allanite, bastnaesite, and xenotime). Examples of these ore deposits include the Lemhi Pass in the USA, Steenkampskraal and Vanrhynsdorp in South Africa, Eskisehir deposit in Turkey, and Nolans Bore in Australia [16, 19].

The Lemhi Pass district on the Montana-Idaho border in the USA contains numerous thoriumrich veins in the central Beaverhead Mountains. This district is thought to represent the largest concentration of thorium resources in the USA. The district contains total reserves of 64,000 tons of ThO2 [20]. Most of mineralized veins are quartz-hematite-thorite veins, which fill fractures, shears, and brecciated zones in quartzitic rocks. Rare-earth- and Th-bearing allanite and monazite are locally abundant. The thorite veins of the Lemhi Pass district are approximately equally enriched in thorium and REE. The total REE-oxide contents range from 0.07 to 2.20 wt.%, with an average value of 0.43 wt.%. The average concentrations of Th are 0.43 wt.%. [11].

At Steenkampskraal (South Africa) from the 1950s to 1963 about 50,000 tons of monazite concentrates were extracted, which contained between 3.3 and 7.6 wt.% Th before operation of the mine was halted. New economic assessment of this deposit was completed in 2012 and currently were established resources of 86,900 wt.% of REO [9].

The Nolans Bore deposit in the Northern Territory (Australia) is coupled with mineralized shear zones evolved in variably deformed and altered granitic gneiss, pegmatite, and minor calcsilicate rocks. Massive fluorapatite dykes enriched in REE and Th form the mineralization. The thorium content of Nolans Bore fluorapatite generally ranges from 0.07 to 0.59 wt.% Th (average 0.23 wt.% Th) [21].


Progress in Carotenoid Research

*Edited by Leila Queiroz Zepka, Eduardo Jacob-Lopes and Veridiana Vera De Rosso*

**PROGRESS IN**

**CAROTENOID RESEARCH**

Edited by **Leila Queiroz Zepka, Eduardo**

**Jacob-Lopes** and **Veridiana Vera De Rosso**


*Edited by Kenneth Eloghene Okedu*

This book is intended for academics and engineers working in universities, research institutes, and industry sectors wishing to acquire new information and enhance their knowledge of the current trends in wind turbine technology. Readers will gain new ideas and special experience with in-depth information about modeling, stability control, assessment, reliability, and future prospects of wind turbines. This book contains a number of problems and solutions that can be integrated into larger research findings and projects. The book enhances studies concerning the state of the art of wind turbines, modeling and intelligent control of wind turbines, power quality of wind turbines, robust controllers for wind turbines in cold weather, etc. The book also looks at recent developments in wind turbine supporting structures, noise reduction estimation methods, reliability and prospects of wind turbines, etc. As I enjoyed preparing this book, I am sure that it will be valuable for a large sector of readers.

Published in London, UK © 2018 IntechOpen © Aria Pearlilla / iStock

Stability Control and Reliable Performance of Wind Turbines

Stability Control

and Reliable Performance of

Wind Turbines


2.4 Evaluation of air void content

The air entrainment was reduced in the SCC mix with the addition of finely divided mineral admixtures, such as fly ash and silica fume. Samples with the dimensions of 80 80 12 mm were acquired from both types of concretes at w/cm ratios of 0.30, 0.45, and 0.60 to study their air-entrained properties. Air voids larger than 200 microns only were considered for the analysis. The measurements showed that SCC samples exhibited half the amount of air voids compared to NC. Visual analyses of the "air voids" sizes and shapes revealed that SCC had smaller and more round-shaped voids than NC which presented slightly larger and irregular shaped voids (by 15–20%) (Figure 4).

#### Figure 4. Distribution of air voids (white spots) in: (a) NC and (b) SCC.

Moreover, while the air voids in the SCC appeared more clustered in certain areas of the cut specimen, the voids in NC were relatively well dispersed in the

specimens. These data indicate that the lower air void content also contributed to an increase in strength of the SCC as cracks initiate more easily in the cement paste with higher air voids. Some of these air voids represent "flaws" in the cement paste at the aggregate-paste boundary possibly forming microcracks or "bond cracks" in the ITZ which ultimately lead to the failure of the concrete due to the propagation of microcracks under localized tensile stresses.