Tesi sul tema "Chromium research"
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1
Shaddick, Lindsay Raymond, University of Western Sydney, of Science Technology and Environment College e of Science Food and Horticulture School. "The geochemistry of chromium in the supergene environment : chromium (VI) and related species". THESIS_CSTE_SFH_Shaddick_ L .xml, 2003. http://handle.uws.edu.au:8081/1959.7/474.
Testo completoAbstract (sommario):
A description of the role of chromium in aqueous solution with respect to its geochemistry and the formation of secondary chromium minerals in the supergene environment is developed. Secondary chromium minerals are relatively rare in Nature and apart from the lead chromate crocoite which is by far the most common and also the most keenly sought after by collectors due its great beauty, little is known of related species. In attempt to redress this situation the initial aim of this study is to present an up-to-date list and description of secondary chromium minerals. It has long been recognised that secondary chromium mineralisation, in the form of chromates and compound chromates, occurs as a minor component of total secondary mineralisation in oxidised zones of some sulphide ore bodies. A thermochemical approach is adopted and a model to describe the geochemistry of chromium in aqueous solution as applied to mineral formation in the supergene environment and its transport in near surface waters is established. The model confirms that species distribution of chromium in aqueous solution is quite pH dependent and that at concentrations appropriate to those experienced in Nature, chromate is the only important species in basic solutions under highly oxidising conditionsMaster of Science (Hons.)
2
Shaddick, Lindsay Raymond. "The geochemistry of chromium in the supergene environment : chromium (VI) and related species". Thesis, View thesis, 2003. http://handle.uws.edu.au:8081/1959.7/474.
Testo completoAbstract (sommario):
A description of the role of chromium in aqueous solution with respect to its geochemistry and the formation of secondary chromium minerals in the supergene environment is developed. Secondary chromium minerals are relatively rare in Nature and apart from the lead chromate crocoite which is by far the most common and also the most keenly sought after by collectors due its great beauty, little is known of related species. In attempt to redress this situation the initial aim of this study is to present an up-to-date list and description of secondary chromium minerals. It has long been recognised that secondary chromium mineralisation, in the form of chromates and compound chromates, occurs as a minor component of total secondary mineralisation in oxidised zones of some sulphide ore bodies. A thermochemical approach is adopted and a model to describe the geochemistry of chromium in aqueous solution as applied to mineral formation in the supergene environment and its transport in near surface waters is established. The model confirms that species distribution of chromium in aqueous solution is quite pH dependent and that at concentrations appropriate to those experienced in Nature, chromate is the only important species in basic solutions under highly oxidising conditions
3
Panaščikaitė, Erika. "Determination of manganese and chromium by electroanalytical stripping methods research". Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2012. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2012~D_20120710_120425-12220.
Testo completoAbstract (sommario):
There was proposed method for the determination of manganese in drinking water by inverse voltammetry using a mercury film electrode. The determination of manganese in drinking water does not need chemical treatment of a sample. Optimal detection conditions: accumulation potential of -1.75 V, accumulation time 5-30 s, anodic dissolution is performed using square wave voltammetry. Manganese accumulation by the detection limit of 30 seconds is about 0.4 mg l-1, and the relative standard deviations of the working range of concentrations do not exceed 0.10. Actual calcium, magnesium and iron ion concentration in samples of drinking water does not influence the manganese determination. Method comparison with a standard photometric method showed that they are equivalent, but the electrochemical method can be applied in very small concentrations of the manganese, in addition, it does not influence the iron ions in the drinking water.
Determination of chromium in cement can be performed by catalytic adsorption voltammetry method using a hanging mercury drop electrode. The medium composition for Cr (VI) determination: 0.15 mol L-1 CH3COONa, 5 mmol l-1 diethylenetriaminepentaacetic acid (DTPA), 0.7 mol l-1 NaNO3, pH = 6. Optimal voltammetry conditions: accumulation potential of -0.9 V, accumulation time 5-10 s, square wave voltammetry mode. Cr (VI) detection limit is about 0.05 mg l-1, the relative standard deviation does not exceed 3%. Chromium was extracted from the cement samples... [to full text]Pasiūlytas mangano nustatymo metodas geriamajame vandenyje inversinės voltamperometrijos metodu naudojant gyvsidabrio plėvelinį elektrodą. Manganui nustatyti vandens mėginio nereikia chemiškai apdoroti. Optimalios nustatymo sąlygos: kaupimo potencialas –1,75 V, kaupimo trukmė 5–30 s, anodinis tirpinimas atliekamas naudojant kvadratinės bangos voltamperometriją. Mangano aptikimo riba kaupiant jį 30 s yra apie 0,4 μg l–1, o santykiniai standartiniai nuokrypiai darbiniame koncentracijų intervale ne didesni kaip 0,10. Realios kalcio, magnio ir geležies jonų koncentracijos geriamojo vandens mėginiuose netrukdo nustatyti manganą. Metodo palyginimas su standartiniu fotometriniu metodu parodė, kad jie yra ekvivalentiški, tačiau elektrocheminis metodas gali būti taikomas labai mažoms mangano koncentracijoms nustatyti, be to, jam netrukdo geriamajame vandenyje esantys geležies jonai. Chromo nustatymui cemente gali būti naudojamas katalitinės adsorbcinės voltamperometrijos metodas naudojant kabančio gyvsidabrio lašo elektrodą. Terpės sudėtis Cr(VI) nustatyti: 0,15 mol l-1 CH3COONa, 5 mmol l-1 dietilentriaminpentaacto rūgšties (DTPA), 0.7 mol l-1 NaNO3, pH = 6. Optimalios votamperometrijos sąlygos: kaupimo potencialas –0.9 V, kaupimo trukmė 5-10 s, kvadratinės bangos voltamperometrijos režimas. Cr(VI) aptikimo riba yra apie 0,05 µg l 1, santykinis standartinis nuokrypis neviršija 3%. Iš cemento mėginių chromas išekstrahuojamas vandeniu arba azoto rūgštimi. Bendras chromo kiekis... [toliau žr. visą tekstą]
4
Ganguly, Rituparna. "THROMBOSPONDIN-1 AS A TARGET OF MICRONUTRIENT TRIVALENT CHROMIUM IN DIABETIC VASCULAR COMPLICATION". Kent State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=kent1461323798.
Testo completo
5
Lipps, Jody Patricia. "RESEARCH INTERNSHIP AT BATTELLE MEMORIAL INSTITUTE DEPARTMENT OF ENVIRONMENTAL RESTORATION". Miami University / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=miami1070400640.
Testo completo
6
Marin, Cordoba Roberto. "Chromium Carcinogenesis: Characterization of DNA damaging Intermediates by EPR 31P NMR, HPLC, ESI-MS and Magnetic Susceptibility". Ohio University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1261417590.
Testo completo
7
JACOB, YVAN PIERRE. "A pre-normative research on the isothermal and cyclic oxidation high temperature oxidation behaviour of chromium". Clermont-Ferrand 2, 2001. http://www.theses.fr/2001CLF22279.
Testo completoAbstract (sommario):
De nombreux parametres experimentaux intervenant lors de l'oxydation du chrome a haute temperature ont ete etudies afin de comprendre leurs effets sur la croissance et l'integrite de la couche de chromine qui se forme lors de cette oxydation. Hormis les techniques classiques utilisees pour l'etude de l'oxydation a haute temperature, nous nous sommes servis de la methode d'activation nucleaires des couches minces (tla) permettant de quantifier les pertes eventuelles d'oxyde par ecaillage lors d'oxydations isothermes ou cycliques. Le but de ce travail, par l'etude systematique de differents parametres, est de servir de reference et de permettre une comparaison et une traduction correcte des resultats provenant de differentes etudes. Nous avons montre que l'oxydation isotherme du chrome suit un regime parabolique avec une fracturation periodique de la chromine due a une nitruration du metal (diffusion d'azote dans le metal). En cyclage, a 1000\c, nous avons detecte un decollement de l'oxyde principalement dans les angles des echantillons. Nous avons egalement mis en evidence le role benefique du si et negatif du c (present sous forme d'impuretes) sur l'oxydation. En atmosphere humide, l'oxygene de la vapeur d'eau participe a la formation de la chromine. Enfin, nous avons observe que la diffusion aux joints de grains de l'oxyde augmente en presence d'azote et/ou de vapeur d'eau. Plus la frequence de cyclage est faible et plus nous avons un ecaillage important de l'oxyde du a une accumulation des contraintes de croissance. Les echantillons de petites dimensions montrent des decollements proportionnellement plus important lors d'oxydations cycliques a 1000\c. Nous avons egalement montre que la preparation de la surface n'a pas d'effet sur le mecanisme et la vitesse d'oxydation. Enfin l'yttrium implante a un effet benefique uniquement a 800 et 900\c en limitant la prise de masse, la diffusion d'azote et la fracturation de la couche.
8
Dai, Lu. "EFFECTS OF CHROMIUM ON MOUSE SPLENIC T LYMPHOCYTES AND EFFECTS OF ETHANOL EXPOSURE DURING EARLY NEURODEVELOPMENT ON BEHAVIORS IN MICE". UKnowledge, 2017. https://uknowledge.uky.edu/toxicology_etds/18.
Testo completoAbstract (sommario):
The dissertation consists of three major projects with the focus on the immunotoxicity of chromium and the behavior disorders caused by early ETOH exposure respectively.
Hexavalent chromium [Cr(VI)] is widely used in various industrial processes and has been recognized as a carcinogen. As the first line of host defense system, the immune system can be a primary target of Cr(VI). T cell population represents a major arm of the immune system that plays a critical role in host anti-tumor immunity. Dysfunction of T cells compromises host anti-tumor immunity resulting in oncogenesis. Using mouse splenic T cells as an in vitro model system, the present study assessed the effects of Cr(VI) on T cell functions, as the first step of our investigation of the mechanism underlying Cr(VI)-inhibited immunosurveillance and carcinogenesis. Our results showed that Cr(VI) decreased the viability of CD4+ and CD8+ T cells, inhibited T cell activation, functions, including cytokine release, and degranulation.
Fetal ethanol (ETOH) exposure can damage the developing central nervous system and lead to cognitive and behavioral deficits, known as fetal alcohol spectrum disorders (FASD). The use of animal models, especially mouse models is essential for investigating the neurogenetic mechanism of fetal ETOH effects and screening pharmacotherapies against it, due to the extensive knowledge of mouse genetics. However, the availability of mouse model is limited. Via adopting various dosage, timing and administration routes of ETOH exposure, we developed two mouse models to assess behavioral or cognitive changes caused by fetal ETOH exposure in pre-weaning and adolescent period. Our results show that high dosage of ETOH exposure (4 g/kg) during PD 4-10 resulted in hyperactivity, disinhibition, and deficits in learning and memory in mouse offspring, which lays the groundwork for the future FASD research.
9
Rink, Cameron L. "Nutritional Intervention And Modeling Of Acute Ischemic Stroke". The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1210957018.
Testo completo
10
Midander, Klara. "Metal Particles – Hazard or Risk? Elaboration and Implementation of a Research Strategy from a Surface and Corrosion Perspective". Doctoral thesis, Stockholm : Kungliga Tekniska högskolan, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11695.
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11
Brunner, David R. "The Composition and Distribution of Coal-Ash Deposits Under Reducing and Oxidizing Conditions From a Suite of Eight Coals". BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/2642.
Testo completoAbstract (sommario):
Eighteen elements, including: carbon, oxygen, sodium, magnesium, aluminum, silicon, phosphorus, sulfur, chlorine, potassium, calcium, titanium, chromium, manganese, iron, nickel, strontium, and barium were measured using a scanning electron microscope with energy dispersive spectroscopy from deposits. The deposits were collected by burning eight different coals in a 160 kWth, staged, down-fired, swirl-stabilized combustor. Both up-stream and down-stream deposits from an oxidizing region (equivalence ratio 0.86) and reducing region (equivalence ratio 1.15) were collected. Within the deposits, the particle size and morphology were studied. The average particle cross-sectional area from the up-stream deposits ranged from 10 - 75 µm2 and had a standard deviation of 36 - 340 µm2. These up-stream particles were of various shapes: spherical, previously molten particles; irregular particle that had not melted, hollowed spherical shells; and layered or strands of particles. These particles were a mixture of burned and unburned coal being deposited at various stages of burnout and having completed some burnout after deposition. The average particle cross-sectional area from the down-stream deposits ranged 0.9 - 7 µm2 and the standard deviation range of 2.6 - 30 µm2. The shape of the particles on the bottom sleeves are typically spherical indicating melting prior to deposition. Particles contained a distribution of elemental compositions that were not tightly grouped on ternary phase diagrams. This indicated that particles were not single compounds or phases but each particle contained a mixture of multiple compounds. Coals' deposit sulfur was strongly correlated with the calcium and iron content of the ASTM ash analysis. The low rank sub-bituminous and lignite coals that had high calcium content produced high sulfur deposits, particularly in the oxidizing region, down-stream deposits. The high iron bituminous coals, also produced high sulfur deposits, but more so in the reducing region, up-stream deposits. The low calcium and low iron coals produced low sulfur deposits. Mahoning was an exception being high in iron content but remaining low in sulfur content in the deposit. Gatling coal showed numerous deposit particles that contained only iron and sulfur consistent with the high pyrite content of Gatling coal. The average concentration of chlorine was insignificant in all of the deposits with the concentration being less than 100 ppm. Individual particles containing chlorine were found and were associated with potassium, sodium, and iron.
12
Chang, Yu-Kuan, e 張毓寬. "Fundmental research in resources recovery of chromium sludge". Thesis, 2002. http://ndltd.ncl.edu.tw/handle/uxyrmj.
Testo completoAbstract (sommario):
碩士國立成功大學
資源工程學系碩博士班
90
This study point on the real quantity of electroplating and tannery chromium sludge in Taiwan, and studied on the physical and chemical characteristics, TCLP test, acid leaching, and recycle residue of chromium sludge. Besides, ferrite process was used to transform the chromium sludge into ferrite, in order to stabilized and recycled. The basic property was showed, chromium sludge was about Cr 5~28%, pH was about 6.5~9.5, moisture 50~84%, electroplating sludge mass loss was about 26~28%, tannery sludge contain more organic matter so the mass loss was about 58~61%. The sludge roasting in 600℃, Cr3+ will oxidize to be Cr6+ and compose with Ca to become CaCrO4. The results of TCLP(Toxicity Characteristic Leaching Process)tests show that it can conform to the EPA regulations in the limit concentration of Cr、Pb and Cu. The reason was Cr(OH)3 dissolve between two kinds of leaching solution(pH=4.93 and pH=2.88)and it won’t be extract in diluted solution after aging. To consider the acid rain and wasteyard effusion water were the solution at low pH, and those diluted acid solution will had bad influence to chromium sludge.At TCLP test use extraction solution in pH=3.5, and it will be more comparatively. In acid leaching experience shows that H2SO4 was better than HCl, and in concentrtaed、long reacted time and high temperature the high extraction percent would got. EA sludge in 2N H2SO4, 100℃, 2 hour can extract Cr 98% and CaSO4 residule would be got. Leaching solution can produce many kinds of chromium technology in many kinds of pure technology. The CaSO4 can pass the TCLP tests, whatever revovery or bury are suitable. Use ferrite process transform simulate chromium sludge to stabilize and resources recycling, the result shows that was suitable. But the real sludge contain too many impurities and series bubble to be formed, only EB sludge can get better ferrites. When use TCLP test of those ferrites in pH=3.5 leaching solution shows that the concentration of heavy metal leaching from ferrites is lower than original sludge.
13
Su, Jing-Yu, e 蘇靖宇. "Research and Fabrication of Chromium Carbide Solar Heat Selective Absorbers". Thesis, 2011. http://ndltd.ncl.edu.tw/handle/12801653122376022896.
Testo completoAbstract (sommario):
碩士國立高雄第一科技大學
光電工程研究所
99
In this study, Chromium Carbide (CrC) is used as solar heat selective absorbers, and decided that the film structure is SiO2 /CrC deposited on stainless steel substrate and the silicon substrate. Using our own sputter and the closed field unbalanced magnetron sputter, we fabricated the solar selective absorbers. And this thesis uses the UV-VIS-NIR Spectrophotometer to measure the reflectance spectrum of the sample to caculate the photothemal conversion efficiency. By using the recipe of Ar/C2H2=45/15, we fabricated the CrC solar heat selective absorber film and its best photothemal conversion efficiency is 81.91％. After depositing an anti-reflection layer consisted of 100nm SiO2 on CrC film, we fabricated the SiO2/CrC solar heat selective absorber film and its best photothemal conversion efficiency is up to 95.39%. In this study, we also used the Field-Emission Scanning Electron Microscope (FESEM), X-ray thin film diffraction (XRD) and Raman Spectrometer to measure the surface morphology and crystal analysis of the solar selective absorbers.
14
Tsai, Pei-jung, e 蔡珮容. "The Research of Alkylation of Tricarbonyl Chromium Polycyclic Aromatic Compounds". Thesis, 1996. http://ndltd.ncl.edu.tw/handle/78638018559140732766.
Testo completoAbstract (sommario):
碩士靜宜大學
應用化學系
84
Abstract In the chemistry of these satu- aturated-polycyclic aromatictricar bonyl ch- romiumcomplexes., we find it includes high regio-selectivity, and th ey have an obvious sign of C-H bond activation at proton NMR analysis. Beca use of the electronic density distribution on polycyclic arenes, the reaction mostly occurred on certain parts of the polycyclic ring, and their high electr onic density and strong C-H bond strength will make the substitution reac- tio n, especially the alkylation, become very difficult. After the coordination of tricarbonyl chromium with polycyclic arene, the strong electron with drawi ng character of metal will lower the electron density of arene, and activate t he C-H bonding of arene, make the proton easier to substituted by lithium cati on. We have found that the alkylation of these complexes will have the hig h regio-selectivity, and the substitution occurred at coor-dinated ring sites. Due to the easy demetallation of polycyclic aromatic tricarbonyl chromium complexes, this type of organometallic synthesis procedures should be very use ful at the synthetic field of organic chemist. We hope its farther appl ication can be extended into the general synthesis reaction.
15
Jiao-YenDeng e 鄧教言. "Characteristic Research for Cobalt Chromium Molybdenum Alloy Powder in Selective Laser Melting". Thesis, 2017. http://ndltd.ncl.edu.tw/handle/tu85r3.
Testo completo
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Liu, Tzu-Hao, e 劉子豪. "Research of Preparing Iron-Chromium based SOFC Anode Substrate by Rotating Electrode Processing". Thesis, 2011. http://ndltd.ncl.edu.tw/handle/18119830302966732069.
Testo completoAbstract (sommario):
碩士國立臺灣大學
材料科學與工程學研究所
100
Conventional anode support of solid oxide fuel cell (SOFC) with Ni-YSZ composite materials has the drawback of high material cost. Recently research works attempt to use stainless steel instead of using Ni-base alloy as anode support materials to reduce the cost of SOFC fuel cells. The stainless steel substrate is highly competitive materials for anode materials due to the properties of good match with solid electrolyte in thermal expansion coefficient as well as better oxidation resistance than Ni-base alloy. However the porous anode substrate with conventional processing method is time spending and expansive, therefore in this report a process will be proposed to fabricate the anode support substrate with powder metallurgy method. Stainless steel420 -based spherical powder with particle size of around 150 um has been made with rotating electrode process. The experiment is carried out with tungsten cathode and anode of rod of stainless steel. It was than sintered with proper sintering condition and binders. The results of experiment indicated that alloys substrate made with this technique could contain large pore and porosity. The sintered specimens were than evaluated with TMA analysis of thermal expansion coefficient, oxidation test and SEM observation of microstructure .
17
Ivanov, Pavel G. Lind David. "Expitaxial films of chromium dioxide from a new precursor (Cr8O21) and research on their application in spin-electronic devices". 2002. http://etd.lib.fsu.edu/theses/available/etd-06192003-114213/.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Florida State University, 2002.Advisor: Dr. David Lind, Florida State University, College of Arts and Sciences, Dept. of Physics. Title and description from dissertation home page (viewed Sept. 29, 2003). Includes bibliographical references.
18
Li, Sheng Shan, e 盛珊琍. "The Research of Synthetical Mechanism and Chemical Reactions of Tricarbonyl Chromium Polycyclic Aromatic Compound". Thesis, 1994. http://ndltd.ncl.edu.tw/handle/70034276176963973203.
Testo completoAbstract (sommario):
碩士靜宜大學
應用化學系
82
We have synthesized and exhibited a series of the sub- stituted, saturated-PAHCr(CO)▋.In the process of synthesis, because the PAHCr(CO)▋are difficult to be synthesized and low in yield,it is a great disadvantage in the application of organic synthesis. We have developed a modified synthetic way:the Cr(CO)▋L▋is used instead of Cr(CO)▋,and the solvent system and reaction temperature is changed.By the new synthetic way,we get a product of higher yield on the synthesis of PAHCr(CO)▋.In a series of substituted-PAH Cr(CO)▋compounds,we find it includes high regio-selectivity.In this report,we search for the change of the Cr(CO)▋group's coordination on the PAHCr(CO)▋.Besides considering highest electronic density area,the electron factor or steric factor of the substituted-PAH complex also affects coordination of the Cr(CO)▋.The structures of these complexes could be determined by analysis of proton NMR spectral data.On the other hand,we express and judge the synthetic way and result of the PAHCr(CO)▋by MNDO theory calculation. Besides, the synthesis and reaction of PAH is an important part of toxiology chemistry. Because of the electronic density distribution on PAH,the reaction mostly happens on small parts of the aromatic ring.And because of its high electronic density, nucleophilic substitution reaction usually has the great difficulty in the synthesis.When PAHs are bonds to Cr(CO) ▋, nucleophilic substitution reaction could take place in the coordinated ring,it is because metals have the electron withdrawing characteristics.It includes Nitration,Bromination, Alkylation reactions,etc.The reaction can be done under normal conditions,it doesn't need high temperature and high pressure. It couldn't be accomplished by organic synthetic process before, but now it can be done through organometallic intermediates.And we hope to spread its practical factor to general organic synthetic reactions.
19
Penque, Brent A. "Mechanisms of hexosamine-induced cholesterol accumulation and therapeutic actions of chromium". Thesis, 2014. http://hdl.handle.net/1805/3805.
Testo completoAbstract (sommario):
Indiana University-Purdue University Indianapolis (IUPUI)Excess caloric intake and/or obesity currently remain the largest predisposing risk factors for the development of type 2 diabetes. Discerning the cellular and molecular mechanisms responsible and amendable to therapy represents a growing challenge in medicine. At a cellular level, increased activity of the hexosamine biosynthesis pathway (HBP), a sensor of excess energy status, has been suggested to promote the exacerbation of insulin resistance through increasing adipose tissue and skeletal muscle membrane cholesterol content. This in turn compromises cortical filamentous actin structure necessary for proper incorporation of the insulin-sensitive glucose transporter GLUT4 into the plasma membrane. The current studies attempted to elucidate the mechanism by which hexosamines provoke membrane cholesterol toxicity and insulin resistance. In 3T3-L1 adipocytes cultured with pathophysiologic hyperinsulinemia to induce insulin resistance, increased HBP flux was observed. This occurred concomitant with gains in the mRNA and protein levels of HMG-CoA reductase (HMGR), the rate limiting enzyme in cholesterol synthesis. Mechanistically, immunoprecipitation demonstrated increased HBP-induced N-acetylglucosamine (O-GlcNAc) modification of specificity protein 1 (Sp1), a regulator of HMGR synthesis. This was associated with increased affinity toward and activity of Hmgcr, the gene encoding HMGR. Global HBP inhibition or Sp1 binding to DNA prevented membrane cholesterol accrual, filamentous actin loss, and glucose transport dysfunction. Furthermore, hyperinsulinemia and HBP activation impaired cholesterol efflux in adipocytes, exacerbating cholesterol toxicity and potentially contributing to cardiovascular disease. In this regard, chromium picolinate (CrPic), known to have beneficial effects on glucose and lipoprotein metabolism, improved cholesterol efflux and restored membrane cholesterol content. To test the role of membrane cholesterol accumulation in vivo, studies were conducted on C57Bl/6J mice fed a low or high fat diet. High fat feeding promoted increased HBP activity, membrane cholesterol accumulation, and insulin resistance. Supplementation of mice with CrPic in their drinking water (8µg/kg/day) countered these derangements and improved insulin sensitivity. Together, these data provide mechanistic insight for the role of membrane cholesterol stress in the development of insulin resistance, as well as cardiovascular disease, and highlight a novel therapeutic action of chromium entailing inhibition of the HBP pathway.
20
Rahman, G. M. Mizanur. "Development, research and validation of environmental speciation methods evaluation by speciated isotope dilution mass spectrometry in mercury and chromium speciation analysis /". 2004. http://etd1.library.duq.edu/theses/available/etd-08112004-135836/.
Testo completo
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Yen, Chien-Lung, e 嚴建隆. "Research on the Wear-Resistance of High-Chromium White Cast Iron and Multi-component White Cast Iron". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/00719880767916922761.
Testo completoAbstract (sommario):
博士國立臺灣大學
機械工程學研究所
101
This research studied the difference of wear resistance between high chromium white cast iron and multi-component white cast iron under two optimum conditions (including optimal alloy composition and optimal heat treatment) by using Pin-On-Disk wear test and solid particle erosion test. The composition of cast iron has a close relationship with its phase change of mold status and it directly influences its wear resistance and erosion properties. The test results found that wear resistance of high chromium white cast iron has linear relationship with testing time. There were obvious scratching grooves on the surface of specimen and various sheared pits. The depth of pits is about 4.5~8.0 mm by observing its sub surface. Crack deformation path after quenching was observed clearly at the martensite crystalline grain boundaries .After tempering treatment, Toughness was increased by changing its state to tempered martensite. Tempered martensite has a better resistance toward the formation of crack. The deformation path occurs only along the martensite grain boundaries and has no any sign of spreading .On the other hand , the wear resistance of multi-component white cast iron showed non-linear relationship with testing time. There were obvious shallow scratches on the surface of specimen. The depth of pits is about 4.0 mm by observing its sub surface. After tempering (570¬oC) and erosion treatment, the hardness of alloy was lowered, however, the larger matrix, is able to resist ductile fracture. As the amount of tungsten (W) is low (2.15%), thus the amount of secondary carbide separated out is not much. It implies that the amount of hole on the surface of secondary carbide is smaller and able to resist brittle fracture. Therefore, no obvious deformation path was observed. The deformation path occurs only in crater region and has no any sign of spreading. The establishment of phase diagram is important in expand the application scope of high chromium white cast iron and multi-component white cast iron. Thus , we have conducted high temperature differential scanning calorimeter (DSC) using a sample from our designated alloy and measured the temperature point of phase change using thermal analysis .The experimental results are also consistent with the simulation results by commercial software Thermo Calc. Keywords：High chromium white cast iron, multi-component white cast iron, phase diagrams.
22
Curr, Thomas Robert. "The dissolution of a Transvaal chromite in liquid silicate slags under an inert atmosphere at 1550 celcius degrees and 1650 celsius degrees". Thesis, 1990. https://hdl.handle.net/10539/24333.
Testo completoAbstract (sommario):
A dissertation submitted to the faculty of Engineering, University of the Witwatersrand, in fulfillment of the requirements for the degree of Master of Science in Engineering.The role of chromite dissolution in the smelting of ferrochromium was investigated with the object of improving the throughput and chromium recovery of the process. The solubility of a typical Transvaal chromite in silicate slags with cao/si02 ratios from 0,03 to 0,55 at 1550·C and 1650·C was determined. Synthetic slags were melted in porous chromite crucibles and the slag underwent repeated reactions with the chromite grains as it penetrated the crucible wall. Finally the slag came into equilibrium with -''the ,original chromite towards the outer part of the crucible wall. Microprobe analysis of this slag yielded the maximum or saturated solubilities of the chromite constituents in the slag. The solubility of cr203 was found to be low (-1 per cent) while the remaining components' solubilities (A1203 -16 per cent, FeO)T 12 per cent and MgO-8 per cent) were significantly higher. CaO/Sio2 ratios greater than 0,1 lowered the solubility of Mg0 significantly (e.g. from 14,1 per cent to 5,8 per cent at 1650·C). The complete dissolution of this chromite in these slags requires the slag to contain less than the solubility limits of each of these species simultaneously. It was recommended that the best way to achieve this in practice would be a well-stirred slag bath containing suspended carbon particles, in which a cao/Sio2 ratio of less -than 0,1 was maintained. Further work to investigate the effect of slag composition (including Na20 and CaF2) on the kinetics of chromite reduction in such a system was recommended.
AC 2018
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Hoffman, Nolan John. "The Effects of Chromium on Skeletal Muscle Membrane/Cytoskeletal Parameters and Insulin Sensitivity". Thesis, 2012. http://hdl.handle.net/1805/2840.
Testo completoAbstract (sommario):
Indiana University-Purdue University Indianapolis (IUPUI)A recent review of randomized controlled trials found that trivalent chromium (Cr3+) supplementation significantly improved glycemia among patients with diabetes, consistent with a long-standing appreciation that this micronutrient optimizes carbohydrate metabolism. Nevertheless, a clear limitation in the current evidence is a lack of understanding of Cr3+ action. We tested if increased AMP-activated protein kinase (AMPK) activity, previously observed in Cr3+-treated cells or tissues from Cr3+-supplemented animals, mediates improved glucose transport regulation under insulin-resistant hyperinsulinemic conditions. In L6 myotubes stably expressing the glucose transporter GLUT4 carrying an exofacial myc-epitope tag, acute insulin stimulation increased GLUT4myc translocation by 69% and glucose uptake by 97%. In contrast, the hyperinsulinemic state impaired insulin stimulation of these processes. Consistent with Cr3+’s beneficial effect on glycemic status, chromium picolinate (CrPic) restored insulin’s ability to fully regulate GLUT4myc translocation and glucose transport. Insulin-resistant myotubes did not display impaired insulin signaling, nor did CrPic amplify insulin signaling. However, CrPic normalized elevated membrane cholesterol that impaired cortical filamentous actin (F-actin) structure. Mechanistically, data support that CrPic lowered membrane cholesterol via AMPK. Consistent with this data, siRNA-mediated AMPK silencing blocked CrPic’s beneficial effects on GLUT4 and glucose transport regulation. Furthermore, the AMPK agonist 5-aminoimidazole-4-carboxamide-1-ß-D-ribonucleoside (AICAR) protected against hyperinsulinemia-induced membrane/cytoskeletal defects and GLUT4 dysregulation. To next test Cr3+ action in vivo, we utilized obesity-prone C57Bl/6J mice fed a low fat (LF) or high fat (HF) diet for eight weeks without or with CrPic supplementation administered in the drinking water (8 µg/kg/day). HF feeding increased body weight beginning four weeks after diet intervention regardless of CrPic supplementation and was independent of changes in food consumption. Early CrPic supplementation during a five week acclimation period protected against glucose intolerance induced by the subsequent eight weeks of HF feeding. As observed in other insulin-resistant animal models, skeletal muscle from HF-fed mice displayed membrane cholesterol accrual and loss of F-actin. Skeletal muscle from CrPic-supplemented HF-fed mice showed increased AMPK activity and protection against membrane cholesterol accrual and F-actin loss. Together these data suggest a mechanism by which Cr3+ may positively impact glycemic status, thereby stressing a plausible beneficial action of Cr3+ in glucose homeostasis.
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Vest, Brian Michael. "The electronic, structural, and magnetic properties of the chromium dihalides - from the gas-phase to the solid-state : a thesis submitted in partial fulfillment of the requirements of the degree of Doctor of Philosophy in Theoretical Chemistry at Massey University, Albany, New Zealand". 2008. http://hdl.handle.net/10179/744.
Testo completoAbstract (sommario):
Unrestricted Kohn-Sham (broken symmetry) density functional calculations have been used to determine the low-energy geometries of the chromium dihalide molecules (CrX2) and their clusters, Cr2X4, Cr3X6, and Cr4X8. The monomers are also investigated at a higher level, including coupled-cluster and state-average CASSCF computations. Our calculations show that the monomers have a 5B2 ground state arising from the Renner-Teller distorted 5IIg transition state, leading to a bent geometry. The global minima of the gas-phase clusters of CrF2 and CrCl2 consist of two-dimensional, anti-ferromagnetically coupled chains of CrX2 units forming four-membered, doubly bridged Cr2X2 rings, closely resembling their solid-state structures. The global minima of the CrBr2 and CrI2 clusters consist of the same two-dimensional chain-like structures for their dimers, but their trimers and tetramers consist of three-dimensional ’triangular’ structures which contain two capping ligands bound to three chromium atoms along with a Cr-Cr bond. Each Cr atom within these clusters has spin quantum number S=2. There is approximately a constant change in energy, between 45-55 kcal/mol, with every new CrX2 unit during cluster formation. Information about the structure of the CrCl2 clusters is used in the reanalysis of high-temperature electron diffraction data. The vapor at 1170 K contains about 77% monomeric molecules, 19% dimers, and a small amount of trimers. Monomeric CrCl2 is found to be bent with a bond angle of 149(10)degrees, in good agreement with our computations. Solid-state DFT calculations are performed on alpha-CrCl2 to determine the lattice structure and spin-coupling constants for the Cr atoms within the crystals. The GGA (PW91) method produces a structure in good agreement with the literature. In the lowest energy structure, the spins of the Cr atoms within the chains along the crystallographic c-axis are anti-ferromagnetically coupled with four parallel spins situated almost exclusively in the d-bands of Cr along these chains. This anti-ferromagnetic coupling is also seen in the CrX2 clusters.