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Personal Passions and Carthusian Influences Evident in Rogier Van Der Weyden's  Crucified Christ between the Virgin and Saint John and Diptych of the Crucifixion (open access)

Personal Passions and Carthusian Influences Evident in Rogier Van Der Weyden's Crucified Christ between the Virgin and Saint John and Diptych of the Crucifixion

This thesis examines Rogier Van Der Weyden's two unique fifteenth century Crucifixions, The Crucified Christ Between the Virgin and Saint John and The Diptych of the Crucifixion, in light of Carthusian beliefs, practices and relevant devotional texts. The specific text used to support this examination is the Vita Christi by Ludolph of Saxony, which in part deals specifically with the Hours of the Passion. Ludolph's text is given visual form in Rogier's paintings and supports the assertion that Rogier and Ludolph were connected by a shared belief and worldview. Key aspects of Rogier's life, supported by original documentation- familial ties, associates, patrons, use of finances, and his close involvement with the Carthusians-- support this assertion. Other models of connections of belief, evidenced through artist's work, are corroborated in the work of Grunewald, Sluter and Durer.
Date: May 2006
Creator: Smith, Tamytha Cameron
System: The UNT Digital Library
Relationships between selected sociometric variables and academic performance for counselors in training. (open access)

Relationships between selected sociometric variables and academic performance for counselors in training.

The purpose of this research was to examine what relationships existed between selected sociometric variables and measures of academic performance for students in a counselor training program. The sociometric variables included counseling ability, counseling knowledge, and friendship. Academic performance measures included subject GPAs, group counseling participation and final grades, prepracticum grades, and practicum grades. Data was collected from sociometric questionnaires and academic records from the years 1991 to 2004, for 840 subjects who participated in a group counseling class at the University of North Texas. Counseling knowledge had the highest correlations with all academic measures except group counseling final grades, in which counseling ability had the highest strength. The strongest correlations for all three sociometric variables occurred with group counseling final grades; correlations were r = 0.42 for counseling ability, r = 0.40 for counseling knowledge, and r = 0.30 for friendship. The sociometric variable of friendship had the lowest correlations in all academic measures, but was more significant than expected. The friendship sociometric variable may account for likeability as a factor in making sociometric choices. Combined sociometric scores led to increased correlation strength and explained variances that reached the large level of 30% with group counseling final grades. A …
Date: May 2006
Creator: Smith, Michael Robert
System: The UNT Digital Library
Reported Impact of a Correctional Facility's Presence on Community Solidarity: Huntsville, Texas (open access)

Reported Impact of a Correctional Facility's Presence on Community Solidarity: Huntsville, Texas

The problem examined is community solidarity in a well-established prison town. The primary question addressed in this study is "what is the reported impact of a correctional facility's presence on community solidarity?" This study is concerned with the community's perception about the problems, as well as the benefits involved in the housing of a prison and in particular the solidarity of the community. The relevant literature dates from 1929 to 2004 and examines a wide range of concepts associated with community studies and prison studies. Based on themes found in the review of prison literature; work issues, safety, concern about children, stress, community image, benefits, community identity, and community cohesion, seven research questions were constructed. A semi-structured interview was conducted of 81 residents of Walker County in Huntsville, Texas. Huntsville houses 9 prisons. The prison system is the primary employer in the county. A qualitative data analysis using Altius/tr as a tool for content analysis was used. Throughout the data, community residents consistently indicated solidarity. Emerging from the data were seven themes associated with community solidarity:(a) unqualified community pride, (b) normalization, (c) defensiveness against the media, (d) qualified community pride, (e) denial, (f) community and myths, (g) economics.
Date: May 2006
Creator: Nation, Patricia Ann Campo
System: The UNT Digital Library
"Mad Mary Sane" and Other Stories (open access)

"Mad Mary Sane" and Other Stories

The following is a multi-genre collection, including short shorts, short fiction, non-fiction, and drama. Each piece utilizes Gothic motifs and dark comedy in an effort to explore life and loss.
Date: May 2006
Creator: Myers, Amanda Sullivan
System: The UNT Digital Library
A Dual Dielectric Approach for Performance Aware Reduction of Gate Leakage in Combinational Circuits (open access)

A Dual Dielectric Approach for Performance Aware Reduction of Gate Leakage in Combinational Circuits

Design of systems in the low-end nanometer domain has introduced new dimensions in power consumption and dissipation in CMOS devices. With continued and aggressive scaling, using low thickness SiO2 for the transistor gates, gate leakage due to gate oxide direct tunneling current has emerged as the major component of leakage in the CMOS circuits. Therefore, providing a solution to the issue of gate oxide leakage has become one of the key concerns in achieving low power and high performance CMOS VLSI circuits. In this thesis, a new approach is proposed involving dual dielectric of dual thicknesses (DKDT) for the reducing both ON and OFF state gate leakage. It is claimed that the simultaneous utilization of SiON and SiO2 each with multiple thicknesses is a better approach for gate leakage reduction than the conventional usage of a single gate dielectric (SiO2), possibly with multiple thicknesses. An algorithm is developed for DKDT assignment that minimizes the overall leakage for a circuit without compromising with the performance. Extensive experiments were carried out on ISCAS'85 benchmarks using 45nm technology which showed that the proposed approach can reduce the leakage, as much as 98% (in an average 89.5%), without degrading the performance.
Date: May 2006
Creator: Mukherjee, Valmiki
System: The UNT Digital Library
Synthesis and Characterization of 2,3-Dichloropyrrolo[1,2-a]benzimidazol-1-one and Its Methylthiol Derivatives (open access)

Synthesis and Characterization of 2,3-Dichloropyrrolo[1,2-a]benzimidazol-1-one and Its Methylthiol Derivatives

Condensation of 2,3-dichloromaleic anhydride and o-phenylenediamine in refluxing toluene affords the three compounds 2,3-dichloro-N-o-C6H4(NH2)maleimide (1), N,N¢-o-C6H4-bis(2,3-dichloromaleimide) (2), and 2,3-dichloropyrrolo[1,2-a]benzimidazol-1-one (3), with compound 1 as the major product. Repeating the same reaction in the presence of added PTSA furnishes compound 3 as the major product. Treatment of 3 with methylthiol in the presence of pyridine affords monosulfide compounds 2-chloro-3-methylthiopyrrolo[1,2-a]benzimidazol-1-one (4) and and the disulfide derivatives 2,3-di(methylthio)pyrrolo[1,2-a]benzimidazol-1-one (5). The substitution of the first chlorine group in compound 3 occurs regioselectively at C-3 to produce compound 4, followed by replacement of the remaining chlorine group to furnish the disulfide compounds 5. The new compounds 1-5 have been isolated by column chromatography and characterized by IR, NMR, XRD, CV and etc.
Date: May 2006
Creator: Wu, Guanmin
System: The UNT Digital Library
Technical Communication and the Needs of Small 501(c)(3) Organizations (open access)

Technical Communication and the Needs of Small 501(c)(3) Organizations

This exploratory study examines documentation practices and processes in ten small non-profit organizations. The objectives of this study were to answer the following two research questions: (1) What organizational needs do small non-profit organizations have that are relevant to technical communication? and (2) How are small 501(c)(3) organizations attempting to meet these needs? Which of these attempted solutions are ineffective? Semi-structured interviews were conducted with two people from each organization: the executive director and a volunteer. Interviews were transcribed and analyzed, and grounded theory was used to identify coding categories related to documentation development. Primary findings suggest that interviewees are aware that they need documentation, yet they often postpone developing such documentation until problems develop. The study findings also suggest that interviewees across different nonprofit organizations value documentation for similar reasons. Strategies are provided for technical communicators interested in working with nonprofit organizations, and additional research avenues are identified.
Date: May 2006
Creator: Walton, Rebecca W.
System: The UNT Digital Library
Mathematical Modeling of Charged Liquid Droplets: Numerical Simulation and Stability Analysis (open access)

Mathematical Modeling of Charged Liquid Droplets: Numerical Simulation and Stability Analysis

The goal of this thesis is to study of the evolution of 3D electrically charged liquid droplets of fluid evolving under the influence of surface tension and electrostatic forces. In the first part of the thesis, an appropriate mathematical model of the problem is introduced and the linear stability analysis is developed by perturbing a sphere with spherical harmonics. In the second part, the numerical solution of the problem is described with the use of the boundary elements method (BEM) on an adaptive mesh of triangular elements. The numerical method is validated by comparison with exact solutions. Finally, various numerical results are presented. These include neck formation in droplets, the evolution of surfaces with holes, singularity formation on droplets with various symmetries and numerical evidence that oblate spheroids are unstable.
Date: May 2006
Creator: Vantzos, Orestis
System: The UNT Digital Library

Generic Algebras and Kazhdan-Lusztig Theory for Monomial Groups

Access: Use of this item is restricted to the UNT Community
The Iwahori-Hecke algebras of Coxeter groups play a central role in the study of representations of semisimple Lie-type groups. An important tool is the combinatorial approach to representations of Iwahori-Hecke algebras introduced by Kazhdan and Lusztig in 1979. In this dissertation, I discuss a generalization of the Iwahori-Hecke algebra of the symmetric group that is instead based on the complex reflection group G(r,1,n). Using the analogues of Kazhdan and Lusztig's R-polynomials, I show that this algebra determines a partial order on G(r,1,n) that generalizes the Chevalley-Bruhat order on the symmetric group. I also consider possible analogues of Kazhdan-Lusztig polynomials.
Date: May 2006
Creator: Alhaddad, Shemsi I.
System: The UNT Digital Library
A Rhetorical Guide to Ebb (open access)

A Rhetorical Guide to Ebb

In the essay A Rhetorical Guide to Ebb I explore the diverse array of influences in art, and music that guided the creation of the composition Ebb, for 13 musicians and electronics. Of those influences, the boxes of the American artist Joseph Cornell played a particularly important role. Having based the conceptual framework for Ebb on ideas taken from Cornell, the essay, instead of being driven by a single thesis, involves the creation of conceptual boxes. These conceptual boxes emphasize the influence of the artist Joseph Cornell, along with the composers Iannis Xenakis and Gérard Grisey. In addition, a time line documenting the stages in Ebb's creation is included.
Date: May 2006
Creator: Zajicek, Daniel James
System: The UNT Digital Library
Improving Recall of Browsing Sets in Image Retrieval from a Semiotics Perspective (open access)

Improving Recall of Browsing Sets in Image Retrieval from a Semiotics Perspective

The purpose of dissertation is to utilize connotative messages for enhancing image retrieval and browsing. By adopting semiotics as a theoretical tool, this study explores problems of image retrieval and proposes an image retrieval model. The semiotics approach conceptually demonstrates that: 1) a fundamental reason for the dissonance between retrieved images and user needs is representation of connotative messages, and 2) the image retrieval model which makes use of denotative index terms is able to facilitate users to browse connotatively related images effectively even when the users' needs are potentially expressed in the form of denotative query. Two experiments are performed for verifying the semiotic-based image retrieval model and evaluating the effectiveness of the model. As data sources, 5,199 records are collected from Artefacts Canada: Humanities by Canadian Heritage Information Network, and the candidate terms of connotation and denotation are extracted from Art & Architecture Thesaurus. The first experiment, by applying term association measures, verifies that the connotative messages of an image can be derived from denotative messages of the image. The second experiment reveals that the association thesaurus which is constructed based on the associations between connotation and denotation facilitates assigning connotative terms to image documents. In addition, the …
Date: May 2006
Creator: Yoon, JungWon
System: The UNT Digital Library
Effects of Cautioning and Education in the Detection of Malingered Mild Traumatic Brain Injury (open access)

Effects of Cautioning and Education in the Detection of Malingered Mild Traumatic Brain Injury

This study examined the effectiveness of cautioning and education on simulating a mild traumatic brain injury on several neuropsychological measures. The measures used included the Word Memory Test (WMT), Wechsler Adult Intelligence Scales® - Third Edition (WAIS®-III), Wechsler Memory Scales®-3rd Edition instrument (WMS®-III), 16-item version of the Rey Memory Test, and a self-report symptom checklist. Five experimental groups were used including clinical and non-clinical controls, as well as three simulation groups. The design and implementation of this study also attempted to correct several methodological short comings of prior research by increasing the incentives for participants, expanding the generalizability of findings and examining research compliance and participant self-perception through debriefing. Discriminant analysis was utilized to determine if specific functions existed that would correctly classify and distinguish each experimental group. Several discriminant functions had at least moderate canonical correlations and good classification accuracy. Results also include utility estimates given projected varying base rates of malingering.
Date: May 2006
Creator: Scholtz, Brendon P.
System: The UNT Digital Library
Ion-Induced Damage In Si: A Fundamental Study of Basic Mechanisms over a Wide Range of Implantation Conditions (open access)

Ion-Induced Damage In Si: A Fundamental Study of Basic Mechanisms over a Wide Range of Implantation Conditions

A new understanding of the damage formation mechanisms in Si is developed and investigated over an extended range of ion energy, dose, and irradiation temperature. A simple model for dealing with ion-induced damage is proposed, which is shown to be applicable over the range of implantation conditions. In particular the concept of defect "excesses" will be discussed. An excess exists in the lattice when there is a local surplus of one particular type of defect, such as an interstitial, over its complimentary defect (i.e., a vacancy). Mechanisms for producing such excesses by implantation will be discussed. The basis of this model specifies that accumulation of stable lattice damage during implantation depends upon the excess defects and not the total number of defects. The excess defect model is validated by fundamental damage studies involving ion implantation over a range of conditions. Confirmation of the model is provided by comparing damage profiles after implantation with computer simulation results. It will be shown that transport of ions in matter (TRIM) can be used effectively to model the ion-induced damage profile, i.e. excess defect distributions, by a simple subtraction process in which the spatially correlated defects are removed, thereby simulating recombination. Classic defect studies …
Date: May 2006
Creator: Roth, Elaine Grannan
System: The UNT Digital Library
Effect of Biofeedback-Assisted Relaxation Therapy on the Psychophysiological Measures of Stressed-Out Working Professional Mothers (open access)

Effect of Biofeedback-Assisted Relaxation Therapy on the Psychophysiological Measures of Stressed-Out Working Professional Mothers

This study was designed to determine the effectiveness of biofeedback-assisted relaxation therapy on reducing psychophysiological stress levels of working professional mothers. Participants were 14 working professional mothers from a major daily newspaper. Reported stress levels were measured with the 123 question Stress Profile (Nowack, 1990) three times during the eight week treatment study that was held at the women's workplace. A repeated measure ANOVA design was used to analyze the data and a partial eta squared was used to calculate effect size. As hypothesized, the study found a statistically significant reduction of reported stress levels (F=8.62; p=.001) and a statistically significant (F=3.65; p=.01) reduction in measured muscle tension across subjects. Practical significance (effect size) was found for reduction in reported stress levels (n=.39) and reduction in muscle tension (n=.21).
Date: May 2006
Creator: Valdez, Diana Carol
System: The UNT Digital Library
Propagation analysis of a 900 MHz spread spectrum centralized traffic signal control system. (open access)

Propagation analysis of a 900 MHz spread spectrum centralized traffic signal control system.

The objective of this research is to investigate different propagation models to determine if specified models accurately predict received signal levels for short path 900 MHz spread spectrum radio systems. The City of Denton, Texas provided data and physical facilities used in the course of this study. The literature review indicates that propagation models have not been studied specifically for short path spread spectrum radio systems. This work should provide guidelines and be a useful example for planning and implementing such radio systems. The propagation model involves the following considerations: analysis of intervening terrain, path length, and fixed system gains and losses.
Date: May 2006
Creator: Urban, Brian L.
System: The UNT Digital Library
MBE Growth and Instrumentation (open access)

MBE Growth and Instrumentation

This thesis mainly aims at application of principles of engineering technology in the field of molecular beam epitaxy (MBE). MBE is a versatile technique for growing epitaxial thin films of semiconductors and metals by impinging molecular beams of atoms onto a heated substrate under ultra-high vacuum (UHV) conditions. Here, a LabVIEW® (laboratory virtual instrument engineering workbench) software (National Instruments Corp., http://www.ni.com/legal/termsofuse/unitedstates/usH) program is developed that would form the basis of a real-time control system that would transform MBE into a true-production technology. Growth conditions can be monitored in real-time with the help of reflection high energy electron diffraction (RHEED) technique. The period of one RHEED oscillation corresponds exactly to the growth of one monolayer of atoms of the semiconductor material. The PCI-1409 frame grabber card supplied by National Instruments is used in conjunction with the LabVIEW software to capture the RHEED images and capture the intensity of RHEED oscillations. The intensity values are written to a text file and plotted in the form of a graph. A fast Fourier transform of these oscillations gives the growth rate of the epi-wafer being grown. All the data being captured by the LabVIEW program can be saved to file forming a growth pedigree …
Date: May 2006
Creator: Tarigopula, Sriteja
System: The UNT Digital Library
An Analytical Study of Robert Muczynski's Second Piano Trio (open access)

An Analytical Study of Robert Muczynski's Second Piano Trio

The purpose of this study is to provide scholastic research on Robert Muczynski's Second Piano Trio (1975) by presenting his biographical background, discussing influences and his musical style, and analyzing the work. Robert Muczynski (b.1929), a composer-pianist of Polish descent, studied with Alexander Tcherepnin (1899-1977). From traditional forms and techniques, he fashioned his own unique and innovative compositional style. The second piano trio, in particular, was deeper and more complex in its conception and affect than previous compositions. The first movement Andante molto opening leads to an allegro section, and the somber second movement builds to a heavy climax. The third movement is highly rhythmic and dramatically driven. Chapter I outlines the purpose of the study and the composer's biography. Chapter II describes Muczynski's compositional influences and the evolution of his musical language. Emphasis in this respect will be placed on the pedagogical role of Alexander Therepnin, as well as the important connections between Prokofiev, Tcherepnin and Muczynski. An exploration of other elements that have informed Muczynski's style is offered. Chapter III details the circumstances, general characteristics, and compositional technique of the Second Piano Trio. Detailed analysis of all three movements will be provided, with particular attention paid to aspects …
Date: May 2006
Creator: Oh, Eun Jun
System: The UNT Digital Library
The Effects of an Inquiry-based American History Program on the Achievement of Middle School and High School Students. (open access)

The Effects of an Inquiry-based American History Program on the Achievement of Middle School and High School Students.

Implicit in the call for educational reform in the teaching of social studies has been the suggestion that pursuing inquiry-based principles will lead to improvement in student achievement. The purpose of this study was to compare the effectiveness of two types of pedagogy: traditional and inquiry-based upon student achievement as measured by a standards-based, state administered examination. Second, this study examined the relationship between the treatment teachers' level of implementation and student achievement. A nonequivalent control group posttest and experimental design was used in this study. Subjects involved in this study include 84 secondary American history teachers and their respective students from a large urban public school district in Texas. The sample consisted of two groups, one taught by traditional/didactic instruction (n=48) and the other taught by inquiry-based pedagogy (n=36). Data for this study were collected using a classroom observation protocol based upon the level of use rubric developed by the concerns-based adoption model. An analysis of variance (ANOVA) (p<.05) was used to measure the effects of inquiry-based instruction and traditional pedagogy on student achievement. Student achievement results were measured by the Texas Assessment of Knowledge and Skills (TAKS) for American history, grades 8 and 11. The study found that …
Date: May 2006
Creator: Harmon, Larry G.
System: The UNT Digital Library
Faith and politics: The socio-political discourses engaged by Mexican ex-voto paintings from the nineteenth-century and beyond. (open access)

Faith and politics: The socio-political discourses engaged by Mexican ex-voto paintings from the nineteenth-century and beyond.

The Universalis Ecclesiae of 1508 authorized Spanish colonization of the Americas in return for the conversion of native populations to Christianity. From its inception therefore, the Mexican nation lived an alliance between Church and State. This alliance promoted the transfer of Castilian Catholicism to American shores. Catholic practices, specifically the ex-voto tradition, visualize this intermingling of religion and politics. The ex-voto is a devotional painting that expresses gratitude to a religious figure for his/her intervention in a moment of peril. It is commissioned by the devotee as a means of direct communication to the divine. This project analyzes 40 Mexican ex-votos for their reflection of political issues in Mexico. I assert that the Mexican ex-votos engage discussions of social politics. To support this argument, visualizations of socio-political discourses such as the Virgin of Guadalupe as a national religious symbol, police action and economic disparity were examined.
Date: May 2006
Creator: Hamman, Amy
System: The UNT Digital Library

Automated Low-cost Instrument for Measuring Total Column Ozone

Access: Use of this item is restricted to the UNT Community
Networks of ground-based and satellite borne instruments to measure ultraviolet (UV) sunlight and total column ozone have greatly contributed to an understanding of increased amounts of UV reaching the surface of the Earth caused by stratospheric ozone depletion. Increased UV radiation has important potential effects on human health, and agricultural and ecological systems. Observations from these networks make it possible to monitor total ozone decreases and to predict ozone recovery trends due to global efforts to curb the use of products releasing chemicals harmful to the ozone layer. Thus, continued and expanded global monitoring of ozone and UV is needed. However, existing automatic stratospheric ozone monitors are complex and expensive instruments. The main objective of this research was the development of a low-cost fully automated total column ozone monitoring instrument which, because of its affordability, will increase the number of instruments available for ground-based observations. The new instrument is based on a high-resolution fiber optic spectrometer, coupled with fiber optics that are precisely aimed by a pan and tilt positioning mechanism and with controlling programs written in commonly available software platforms which run on a personal computer. This project makes use of novel low-cost fiber optic spectrometer technology. A cost …
Date: May 2006
Creator: Nebgen, Gilbert Bernard
System: The UNT Digital Library
In Situ Adsorption Studies at the Solid/Liquid Interface:Characterization of Biological Surfaces and Interfaces Using SumFrequency Generation Vibrational Spectroscopy, Atomic Force Microscopy,and Quartz Crystal Microbalance (open access)

In Situ Adsorption Studies at the Solid/Liquid Interface:Characterization of Biological Surfaces and Interfaces Using SumFrequency Generation Vibrational Spectroscopy, Atomic Force Microscopy,and Quartz Crystal Microbalance

Sum frequency generation (SFG) vibrational spectroscopy, atomic force microscopy (AFM), and quartz crystal microbalance (QCM) have been used to study the molecular surface structure, surface topography and mechanical properties, and quantitative adsorbed amount of biological molecules at the solid-liquid interface. The molecular-level behavior of designed peptides adsorbed on hydrophobic polystyrene and hydrophilic silica substrates has been examined as a model of protein adsorption on polymeric biomaterial surfaces. Proteins are such large and complex molecules that it is difficult to identify the features in their structure that lead to adsorption and interaction with solid surfaces. Designed peptides which possess secondary structure provide simple model systems for understanding protein adsorption. Depending on the amino acid sequence of a peptide, different secondary structures ({alpha}-helix and {beta}-sheet) can be induced at apolar (air/liquid or air/solid) interfaces. Having a well-defined secondary structure allows experiments to be carried out under controlled conditions, where it is possible to investigate the affects of peptide amino acid sequence and chain length, concentration, buffering effects, etc. on adsorbed peptide structure. The experiments presented in this dissertation demonstrate that SFG vibrational spectroscopy can be used to directly probe the interaction of adsorbing biomolecules with a surface or interface. The use of …
Date: May 16, 2006
Creator: Phillips, Diana Christine
System: The UNT Digital Library
Structure and function evolution of thiolate monolayers on gold (open access)

Structure and function evolution of thiolate monolayers on gold

None
Date: May 6, 2006
Creator: Edwards, Grant Alvin
System: The UNT Digital Library
Structure and Function Evolution of Thiolate Monolayers on Gold (open access)

Structure and Function Evolution of Thiolate Monolayers on Gold

The use of n-alkanethiolate self-assembled monolayers on gold has blossomed in the past few years. These systems have functioned as models for common interfaces. Thiolate monolayers are ideal because they are easily modified before or after deposition. The works contained within this dissertation include interfacial characterization (inbred reflection absorption spectroscopy, ellipsometry, contact angle, scanning probe microscopy, and heterogeneous electron-transfer kinetics) and various modeling scenarios. The results of these characterizations present ground-breaking insights into the structure, function, and reproducible preparation of these monolayers. Surprisingly, three interfacial properties (electron-transfer, contact angle, and ellipsometry) were discovered to depend directly on the odd-even character of the monolayer components. Molecular modeling was utilized to investigate adlayer orientation, and suggests that these effects are adlayer structure specific. Finally, the electric force microscopy and theoretical modeling investigations of monolayer samples are presented, which show that the film dielectric constant, thickness, and dipole moment directly affect image contrast. In addition, the prospects for utilization of this emerging technique are outlined.
Date: May 1, 2006
Creator: Edwards, Grant Alvin
System: The UNT Digital Library
Exploration of R2XM2 (R=Sc, Y, Ti, Zr, Hf, rare earth; X=main group element; M=transition metal, Si, Ge): Structural Motifs, the novel Compound Gd2AlGe2 and Analysis of the U3Si2 and Zr3Al2 Structure Types (open access)

Exploration of R2XM2 (R=Sc, Y, Ti, Zr, Hf, rare earth; X=main group element; M=transition metal, Si, Ge): Structural Motifs, the novel Compound Gd2AlGe2 and Analysis of the U3Si2 and Zr3Al2 Structure Types

In the process of exploring and understanding the influence of crystal structure on the system of compounds with the composition Gd{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} several new compounds were synthesized with different crystal structures, but similar structural features. In Gd{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4}, the main feature of interest is the magnetocaloric effect (MCE), which allows the material to be useful in magnetic refrigeration applications. The MCE is based on the magnetic interactions of the Gd atoms in the crystal structure, which varies with x (the amount of Si in the compound). The crystal structure of Gd{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} can be thought of as being formed from two 3{sup 2}434 nets of Gd atoms, with additional Gd atoms in the cubic voids and Si/Ge atoms in the trigonal prismatic voids. Attempts were made to substitute nonmagnetic atoms for magnetic Gd using In, Mg and Al. Gd{sub 2}MgGe{sub 2} and Gd{sub 2}InGe{sub 2} both possess the same 3{sup 2}434 nets of Gd atoms as Gd{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4}, but these nets are connected differently, forming the Mo{sub 2}FeB{sub 2} crystal structure. A search of the literature revealed that compounds with the composition R{sub 2}XM{sub 2} (R=Sc, Y, Ti, …
Date: May 1, 2006
Creator: McWhorter, Sean William
System: The UNT Digital Library