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Full-Text Articles in Physics

Magnetic Behavior Of Melt-Spun Gadolinium, P. M. Shand, J. G. Bohnet, Jeffrey E. Shield, D. Schmitter, G. Shelburne, Diandra Leslie-Pelecky May 2008

Magnetic Behavior Of Melt-Spun Gadolinium, P. M. Shand, J. G. Bohnet, Jeffrey E. Shield, D. Schmitter, G. Shelburne, Diandra Leslie-Pelecky

Diandra Leslie-Pelecky Publications

Melt-spun Gd is a structurally inhomogeneous system consisting of crystalline grains with an average size of 24±3 nm that are separated by an amorphous interphase. This system exhibits a depression of TC (289.70±0.01 K) relative to bulk Gd (293 K). The effective critical exponents (βeff=0.389±0.017, γeff =1.300±0.014, and δ =4.32±0.02) and critical amplitudes indicate that for the reduced-temperature range in this work, the paramagnetic-to-ferromagnetic transition is consistent with the isotropic dipolar universality class shown by bulk Gd. There is, however, evidence of enhanced ...


Examining The Cognitive Processes Used By Adolescent Girls And Women Scientists In Identifying Science Role Models: A Feminist Approach, Gayle A. Buck, Vicki L. Plano Clark, Diandra Leslie-Pelecky, Yun Lu, Patricia Cerda-Lizarraga Jan 2008

Examining The Cognitive Processes Used By Adolescent Girls And Women Scientists In Identifying Science Role Models: A Feminist Approach, Gayle A. Buck, Vicki L. Plano Clark, Diandra Leslie-Pelecky, Yun Lu, Patricia Cerda-Lizarraga

Diandra Leslie-Pelecky Publications

Women remain underrepresented in science professions. Studies have shown that students are more likely to select careers when they can identify a role model in that career path. Further research has shown that the success of this strategy is enhanced by the use of gender-matched role models. While prior work provides insights into the value of using role models, it does not explain the cognitive process involved in girls identifying role models from nontraditional careers for women. This feminist study addresses this gap by examining the cognitive process eighth-grade girls use in identifying a person as a science role model ...


Examining The Cognitive Processes Used By Adolescent Girls And Women Scientists In Identifying Science Role Models: A Feminist Approach, Gayle A. Buck, Vicki L. Plano Clark, Diandra Leslie-Pelecky, Yun Lu, Patricia R. Cerda-Lizarraga Jan 2008

Examining The Cognitive Processes Used By Adolescent Girls And Women Scientists In Identifying Science Role Models: A Feminist Approach, Gayle A. Buck, Vicki L. Plano Clark, Diandra Leslie-Pelecky, Yun Lu, Patricia R. Cerda-Lizarraga

Diandra Leslie-Pelecky Publications

Women remain underrepresented in science professions. Studies have shown that students are more likely to select careers when they can identify a role model in that career path. Further research has shown that the success of this strategy is enhanced by the use of gender-matched role models. While prior work provides insights into the value of using role models, it does not explain the cognitive process involved in girls identifying role models from nontraditional careers for women. This feminist study addresses this gap by examining the cognitive process eighth-grade girls use in identifying a person as a science role model ...


Surface Anisotropy And Magnetic Freezing Of Mno Nanoparticles, Marco Morales Torres, Ralph Skomski, Shannon Fritz, G. Shelburne, Jeffrey E. Shield, Ming Yin, Stephen O'Brien, Diandra Leslie-Pelecky Apr 2007

Surface Anisotropy And Magnetic Freezing Of Mno Nanoparticles, Marco Morales Torres, Ralph Skomski, Shannon Fritz, G. Shelburne, Jeffrey E. Shield, Ming Yin, Stephen O'Brien, Diandra Leslie-Pelecky

Diandra Leslie-Pelecky Publications

Nanoparticles of bulk antiferromagnets often exhibit ferromagnetic behavior due to uncompensated surface spins. The peak temperature in the zero-field-cooled magnetization of MnO—in contrast to other antiferromagnetic nanoparticles—has anomalous behavior, shifting to higher temperatures with decreasing nanoparticle size. We attribute this behavior to surface anisotropy enhanced by the specific occupancy of 3d levels in Mn, which produces a high-spin–low-spin transition not present in NiO nanoparticles.


Self-Definition Of Women Experiencing A Nontraditional Graduate Fellowship Program, Gayle A. Buck, Diandra Leslie-Pelecky, Yun Lu, Vicki L. Plano Clark, John W. Creswell May 2006

Self-Definition Of Women Experiencing A Nontraditional Graduate Fellowship Program, Gayle A. Buck, Diandra Leslie-Pelecky, Yun Lu, Vicki L. Plano Clark, John W. Creswell

Diandra Leslie-Pelecky Publications

Women continue to be underrepresented in the fields of science, technology, engineering, and mathematics (STEM). One factor contributing to this underrepresentation is the graduate school experience. Graduate programs in STEM fields are constructed around assumptions that ignore the reality of women’s lives; however, emerging opportunities may lead to experiences that are more compatible for women. One such opportunity is the Graduate Teaching Fellows in K–12 Education (GK–12) Program, which was introduced by the National Science Foundation in 1999. Although this nontraditional graduate program was not designed explicitly for women, it provided an unprecedented context in which to ...


Spin Glass Or Random Anisotropy?: The Origin Of Magnetically Glassy Behavior In Nanostructured Gdal2, P. M. Shand, C. C. Stark, D. Williams, Marco Morales Torres, T. M. Pekarek, Diandra Leslie-Pelecky May 2005

Spin Glass Or Random Anisotropy?: The Origin Of Magnetically Glassy Behavior In Nanostructured Gdal2, P. M. Shand, C. C. Stark, D. Williams, Marco Morales Torres, T. M. Pekarek, Diandra Leslie-Pelecky

Diandra Leslie-Pelecky Publications

Initially crystalline GdAl2 was mechanically milled for long times to produce a highly chemically disordered phase with approximately 8-nm grains. Analysis of dc magnetization measurements using an Arrott plot and the approach to saturation suggest the presence of significant random anisotropy. ac susceptibility measurements showed that the shift in the peak temperature with frequency usually seen in magnetically glassy and superparamagnetic systems was virtually undetectable in the 10–1000-Hz frequency range. Based on these results, we believe that this material represents an interacting system with random anisotropy, where the anisotropy is the result of surface and interface asymmetries. ©2005 ...


Magnetic Studies Of Iron Oxide Nanoparticles Coated With Oleic Acid And Pluronic® Block Copolymer, Marco Morales Torres, Tapan Kumar Jain, V. Labhasetwar, Diandra Leslie-Pelecky May 2005

Magnetic Studies Of Iron Oxide Nanoparticles Coated With Oleic Acid And Pluronic® Block Copolymer, Marco Morales Torres, Tapan Kumar Jain, V. Labhasetwar, Diandra Leslie-Pelecky

Diandra Leslie-Pelecky Publications

We have prepared and studied iron-oxide nanoparticles coated with oleic acid (OA) and Pluronic® polymer. The mean diameter of the iron-oxide nanoparticles was 9.3(±)0.8 nm. Saturation magnetization values measured at 10 K varied from 66.1(±0.7) emu/g to 98.7(±0.5) emu/g. At 300 K the loops showed negligible coercive field. The peaks in zero-field-cooled susceptibility decreased from 280 to 168 K with increasing OA concentration up to 10.6 wt %, and remained nearly constant for higher concentrations. This suggests that incomplete coverage of the OA allows small, interacting agglomerates to form.


Iron Oxide Nanoparticles For Sustained Delivery Of Anticancer Agents, Tapan K. Jain, Marco Morales Torres, Sanjeeb K. Sahoo, Diandra Leslie-Pelecky, Vinod Labhasetwar Apr 2005

Iron Oxide Nanoparticles For Sustained Delivery Of Anticancer Agents, Tapan K. Jain, Marco Morales Torres, Sanjeeb K. Sahoo, Diandra Leslie-Pelecky, Vinod Labhasetwar

Diandra Leslie-Pelecky Publications

We have developed a novel water-dispersible oleic acid (OA)-Pluronic-coated iron oxide magnetic nanoparticle formulation that can be loaded easily with high doses of water-insoluble anticancer agents. Drug partitions into the OA shell surrounding iron oxide nanoparticles, and the Pluronic that anchors at the OA-water interface confers aqueous dispersity to the formulation. Neither the formulation components nor the drug loading affected the magnetic properties of the core iron oxide nanoparticles. Sustained release of the incorporated drug is observed over 2 weeks under in vitro conditions. The nanoparticles further demonstrated sustained intracellular drug retention relative to drug in solution and a ...


The Stability And Oxidation Resistance Of Iron- And Cobalt-Based Magnetic Nanoparticle Fluids Fabricated By Inert-Gas Condensation, Nguyen H. Hai, Raymond Lemoine, Shaina Remboldt, Michelle A. Strand, Steve Wignall, Jeffrey E. Shield, Diandra Leslie-Pelecky Jan 2005

The Stability And Oxidation Resistance Of Iron- And Cobalt-Based Magnetic Nanoparticle Fluids Fabricated By Inert-Gas Condensation, Nguyen H. Hai, Raymond Lemoine, Shaina Remboldt, Michelle A. Strand, Steve Wignall, Jeffrey E. Shield, Diandra Leslie-Pelecky

Diandra Leslie-Pelecky Publications

Magnetic nanoparticle fluids have numerous biomedical applications, including magnetic imaging, drug delivery, and hyperthemia treatment for cancer. Ideal magnetic nanoparticle fluids have well-separated, biocompatible nanoparticles with a small size distribution that form a stable colloid. We have combined inert-gas condensation, which produces nanoparticles with low polydispersity, with deposition directly into a surfactant-laden fluid to prevent agglomeration. Iron, cobalt, and iron-nitride nanoparticle fluids fabricated using inert-gas condensation have with mean particle sizes from 5-50 nm and remain stable over long periods of time. Iron and cobalt nanoparticles oxidize on exposure to air, with oxidation rates dependent on surfactant type and concentration ...


Broadening Middle-School Students’ Images Of Science And Scientists, Diandra Leslie-Pelecky, Gayle A. Buck, Angela Zabawa Jan 2005

Broadening Middle-School Students’ Images Of Science And Scientists, Diandra Leslie-Pelecky, Gayle A. Buck, Angela Zabawa

Diandra Leslie-Pelecky Publications

The ‘mad scientist’ stereotype is alive and well – and not an image most K-12 students can (or want to) embrace. Project Fulcrum, a National Science Foundation-funded GK-12 program, partners math, science and engineering graduate students with elementary and middle-level teachers. One project goal – broadening student images of science and scientists –is addressed by projects developed by the teacher/scientist teams that are focused on the specific needs of their students. The projects developed focus on scientists, the use of science in different types of jobs, and developing scientific skills. Pre-project research, in which teachers probe the motivation behind their students ...


Disorder-Induced Depression Of The Curie Temperature In Mechanically Milled Gdal2, Marco Morales Torres, D. S. Williams, P. M. Shand, C. Stark, T. M. Pekarek, Lanping Yue, V. Petkov, Diandra Leslie-Pelecky Nov 2004

Disorder-Induced Depression Of The Curie Temperature In Mechanically Milled Gdal2, Marco Morales Torres, D. S. Williams, P. M. Shand, C. Stark, T. M. Pekarek, Lanping Yue, V. Petkov, Diandra Leslie-Pelecky

Diandra Leslie-Pelecky Publications

The effect of disorder on the ferromagnetic transition is investigated in mechanically milled GdAl2. GdAl2 is a ferromagnet when crystalline and a spin glass when amorphous. Mechanical milling progressively disorders the alloy, allowing observation of the change from ferromagnetic to a disordered magnetic state. X-ray diffraction and pair-distribution-function analysis are used to determine the grain size, lattice parameter, and mean-squared atomic displacements. The magnetization as a function of temperature is described by a Gaussian distribution of Curie temperatures. The mean Curie temperature decreases with decreasing lattice parameter, where lattice parameter serves as a measure of defect concentration. Two ...


Curie–Weiss Analysis Of Ferromagnetic And Glassy Transitions In Nanostructured Gdal2, D. Williams, P. M. Shand, C. Stark, T. Pekarek, R. Brown, Lanping Yue, Diandra Leslie-Pelecky May 2003

Curie–Weiss Analysis Of Ferromagnetic And Glassy Transitions In Nanostructured Gdal2, D. Williams, P. M. Shand, C. Stark, T. Pekarek, R. Brown, Lanping Yue, Diandra Leslie-Pelecky

Diandra Leslie-Pelecky Publications

Structural inhomogeneity on length scales comparable to magnetic interaction lengths can produce complex magnetic behavior. Crystalline GdAl2 is a ferromagnet with a Curie temperature of 170 K, while amorphous GdAl2 thin films exhibit classic spin-glass behavior with a freezing temperature of 16 K. Nanostructured GdAl2, made by mechanically milling initially crystalline GdAl2, exhibits ferromagnetic and spin-glass-like transitions; however, the spin-glass-like transition occurs at a higher temperature than the freezing temperature of amorphous GdAl2 thin films. Curie–Weiss analysis suggests that the paramagnetic-to-ferromagnetic transition is due to the ferromagnetic ordering of small GdAl2 clusters and ...


Coexistence Of Ferromagnetic And Glassy States In Mechanically Milled Gdal2, C. Stark, P. M. Shand, T. M. Pekarek, D. Williams, R. Brown, Lanping Yue, Diandra Leslie-Pelecky Dec 2002

Coexistence Of Ferromagnetic And Glassy States In Mechanically Milled Gdal2, C. Stark, P. M. Shand, T. M. Pekarek, D. Williams, R. Brown, Lanping Yue, Diandra Leslie-Pelecky

Diandra Leslie-Pelecky Publications

Measurements of DC susceptibility, AC susceptibility, and AC susceptibility with an applied DC bias field were performed on mechanically milled GdAl2. A paramagnetic phase exists above a temperature T ≈ 140 K. However, there are significant deviations from the Curie-Weiss Law in this temperature regime, suggesting multiple magnetic components. Fits to the high temperature data show that two Curie-Weiss terms represent the data quite well. Below 140 K one of these magnetic components becomes ferromagnetic as indicated by a shoulder in the AC susceptibility and DC susceptibility data. This ferromagnetic component is suppressed by the application of sufficiently strong DC ...


Cooperative Freezing In Spin Glasses And Magnetic Nanostructures, Ralph Skomski, Diandra Leslie-Pelecky Jun 2001

Cooperative Freezing In Spin Glasses And Magnetic Nanostructures, Ralph Skomski, Diandra Leslie-Pelecky

Diandra Leslie-Pelecky Publications

Relaxation processes in disordered nanostructures and spin glasses are investigated by examining the role of the magnetic anisotropy. To abstract from freezing processes associated with phase transitions, the consideration is restricted to a one-dimensional bond-disordered Ising spin glass. Using a Mattis-type gauge transformation, the spin glass is mapped onto a disordered ferromagnet. Based on the behavior of the spin chain we argue that spin-glass freezing is not necessarily related to a phase transition. The magnetic anisotropy, which is largely ignored in the Glauber approach to Ising dynamics, gives rise to cooperative deviations from the Arrhenius behavior and mimics Vogel–Fulcher ...


Magnetic Properties Of Disordered Ni3C, Lanping Yue, R. Sabiryanov, E.M. Kirkpatrick, Diandra Leslie-Pelecky Oct 2000

Magnetic Properties Of Disordered Ni3C, Lanping Yue, R. Sabiryanov, E.M. Kirkpatrick, Diandra Leslie-Pelecky

Diandra Leslie-Pelecky Publications

The metastable Ni3C phase has been produced by mechanically alloying Ni and C. Ni3C particles of diameter 10 nm are produced after 90 h of mechanical alloying with no evidence of crystalline Ni in x ray or electron diffraction. Linear muffin-tin orbital band-structure calculations show that Ni3C is not expected to be ferromagnetic due to strong Ni-C hybridization in the ordered alloy; however, the introduction of even small amounts of disorder produces locally Ni-rich regions that can sustain magnetism. Mechanically alloyed Ni3C is ferromagnetic, with a room-temperature coercivity of 70 Oe and ...


Structural And Magnetic Properties Of Mechanically Milled Smco5:C, E.M. Kirkpatrick, Diandra Leslie-Pelecky May 2000

Structural And Magnetic Properties Of Mechanically Milled Smco5:C, E.M. Kirkpatrick, Diandra Leslie-Pelecky

Diandra Leslie-Pelecky Publications

Mechanically milling SmCo5 powder significantly increases coercivity and remanence ratio by introducing defects; however, these defects can be removed by room-temperature aging, with a resultant decrease in coercivity. A series of (SmCo5) x:C1–x (0.15 ≤ x ≤1) samples has been fabricated to investigate the effect of C on oxidation protection and magnetic properties. SmCo5 was premilled for 1 h, then added to C powder and milled for times ranging from 15 min to 7 h. X-ray diffraction indicates the presence of crystalline graphite and SmCo5 for milling times ≤ 6 h and also shows the ...


Interactive Worksheets In Large Introductory Physics Courses, Diandra Leslie-Pelecky Mar 2000

Interactive Worksheets In Large Introductory Physics Courses, Diandra Leslie-Pelecky

Diandra Leslie-Pelecky Publications

Physics education research indicates that interactive instruction techniques improve student performance. 1 A variety of methods have been developed to promote interactivity, including peer instruction, 2 tutorials, 3 ranking tasks, 4 and in-class worksheets.5 These techniques are attractive because they are adaptable to classes of all sizes and rarely require the instructor to make radical changes in the course content or pedagogical approach. Our Physics 151 is a one-semester algebra-based course for which the primary audience is architecture, construction management, natural resources, and business majors. Eighty to 140 students are in each section. The course has three hours of ...


Magnetic And Structural Properties Of Mg–Co Nanostructures Fabricated, E.M. Kirkpatrick, Diandra Leslie-Pelecky, S.-H. Kim, R.D. Rieke Apr 1999

Magnetic And Structural Properties Of Mg–Co Nanostructures Fabricated, E.M. Kirkpatrick, Diandra Leslie-Pelecky, S.-H. Kim, R.D. Rieke

Diandra Leslie-Pelecky Publications

Reductive chemical synthesis is a versatile tool for fabricating elemental nanostructures; however, less work has been completed on understanding and controlling alloy formation. Magnetic Mg–Co and Mg–Co–C nanocomposites have been fabricated using a reductive chemical synthesis designed to produce highly active metals. The as-synthesized powder was annealed at temperatures from 150 to 650 °C. Samples were investigated using x-ray diffraction, alternating gradient force magnetometry, and superconducting quantum interference device magnetometry. X-ray diffraction indicates that the resulting structures are multiphase with MgCo2, MgCo3C0. 5, fcc Co, Mg, MgO, and Li2CO3 present depending ...


Scienceworks: A University-Based Science Outreach Group, Rochelle Payne Ondracek, Diandra Leslie-Pelecky Jan 1999

Scienceworks: A University-Based Science Outreach Group, Rochelle Payne Ondracek, Diandra Leslie-Pelecky

Diandra Leslie-Pelecky Publications

ScienceWorks is a science and engineering outreach group at the University of Nebraska- Lincoln, comprised of faculty, graduate students, undergraduates and community volunteers. We are brought together by one goal - to make science fun and accessible for everyone. ScienceWorks has developed over 30 modules that emphasize a range of scientific and engineering topics and guide the participants in discovery-based learning. Modules cover a wide variety of topics, including pressure, materials, electromagnetism, archaeology, DNA, optics and fracture. Most ScienceWorks modules involve hands-on activities. In Electromagnetism for example, students are asked to use a length of wire and a nail to design ...


Effect Of Disorder On The Magnetic Properties Of Smco5, Diandra Leslie-Pelecky, R.L. Schalek Jan 1999

Effect Of Disorder On The Magnetic Properties Of Smco5, Diandra Leslie-Pelecky, R.L. Schalek

Diandra Leslie-Pelecky Publications

Mechanical milling of initially ordered ferromagnetic SmCo5 produces dramatic increases in coercivity after short (15 min to 1 h) milling times, accompanied by remanence ratios on the order of 0.7 and shifted hysteresis loops. X-ray diffraction shows that milling induces both chemical and structural disorder. The hysteresis-loop shift is continuous and nonlinear with temperature over the range 5–300 K. The high coercivities are attributed to the formation of a nanostructure consisting of crystalline SmCo5 regions separated by a disordered interphase.


Chemical Synthesis Of Nanostructured Cobalt At Elevated Temperatures, Diandra Leslie-Pelecky, M. Bonder, T. Martin, E.M. Kirkpatrick, X.Q. Zhang, S.-H. Kim, Reuben D. Reike Jul 1998

Chemical Synthesis Of Nanostructured Cobalt At Elevated Temperatures, Diandra Leslie-Pelecky, M. Bonder, T. Martin, E.M. Kirkpatrick, X.Q. Zhang, S.-H. Kim, Reuben D. Reike

Diandra Leslie-Pelecky Publications

Chemical synthesis is a versatile technique for fabricating novel nanostructured materials. In the Rieke process, a metal salt is reduced by an alkali in a hydrocarbon solvent to form small, highly reactive particles. Synthesis at an elevated temperature (200°C) increases the as-synthesized particle size and produces higher coercivities and remanence ratios than observed in similar syntheses at room temperature. The ratio of synthesis temperature to solvent boiling point appears to be an important parameter in both coercivity and oxidation resistance.


Self-Stabilized Magnetic Colloids: Ultrafine Co Particles In Polymers, Diandra Leslie-Pelecky, X.Q. Zhang, Reuben D. Reike Apr 1996

Self-Stabilized Magnetic Colloids: Ultrafine Co Particles In Polymers, Diandra Leslie-Pelecky, X.Q. Zhang, Reuben D. Reike

Diandra Leslie-Pelecky Publications

Self-stabilized magnetic colloids consist of magnetic particles dispersed in an appropriate matrix. Fixing the particles in a stabilizing matrix has the advantage of preventing particle agglomeration, increasing resistance to oxidation, and allowing control over the interparticle spacing and particle size. We describe the chemical synthesis of cobalt nanoparticles in a polystyrene/triphenylphosphine polymer matrix. Depending on the synthesis parameters, magnetic properties of the as-synthesized nanocomposites range from superparamagnetic to ferromagnetic with coercivities on the order of 130 Oe. Solvent choice and polymer crosslinking significantly affect the magnetic properties. Annealing in vacuum produces coercivities of up to 600 Oe and remanence ...