486 research outputs found
Magnetic shape-memory effects in La2-xSrxCuO4 crystals
The magnetic field affects the motion of electrons and the orientation of
spins in solids, but it is believed to have little impact on the crystal
structure. This common perception has been challenged recently by ferromagnetic
shape-memory alloys, where the spin-lattice coupling is so strong that
crystallographic axes even in a fixed sample are forced to rotate, following
the direction of moments. One would, however, least expect any structural
change to be induced in antiferromagnets where spins are antiparallel and give
no net moment. Here we report on such unexpected magnetic shape-memory effects
that take place ironically in one of the best-studied 2D antiferromagnets,
La2-xSrxCuO4 (LSCO). We find that lightly-doped LSCO crystals tend to align
their b axis along the magnetic field, and if the crystal orientation is fixed,
this alignment occurs through the generation and motion of crystallographic
twin boundaries. Both resistivity and magnetic susceptibility exhibit curious
switching and memory effects induced by the crystal-axes rotation; moreover,
clear kinks moving over the crystal surfaces allow one to watch the crystal
rearrangement directly with a microscope or even bare eyes.Comment: 3 pages, 4 figures; shortend version of this paper has been published
in Nature as a Brief Communicatio
Gas chromatography-mass spectrometry-based metabolite profiling of Salmonella enterica serovar Typhimurium differentiates between biofilm and planktonic phenotypes
The aim of this study was to utilize gas chromatography coupled with mass spectrometry (GC-MS) to compare and identify patterns of biochemical change between Salmonella cells grown in planktonic and biofilm phases and Salmonella biofilms of different ages. Our results showed a clear separation between planktonic and biofilm modes of growth. The majority of metabolites contributing to variance between planktonic and biofilm supernatants were identified as amino acids, including alanine, glutamic acid, glycine, and ornithine. Metabolites contributing to variance in intracellular profiles were identified as succinic acid, putrescine, pyroglutamic acid, and N-acetylglutamic acid. Principal-component analysis revealed no significant differences between the various ages of intracellular profiles, which would otherwise allow differentiation of biofilm cells on the basis of age. A shifting pattern across the score plot was illustrated when analyzing extracellular metabolites sampled from different days of biofilm growth, and amino acids were again identified as the metabolites contributing most to variance. An understanding of biofilm-specific metabolic responses to perturbations, especially antibiotics, can lead to the identification of novel drug targets and potential therapies for combating biofilm-associated diseases. We concluded that under the conditions of this study, GC-MS can be successfully applied as a high-throughput technique for "bottom-up" metabolomic biofilm research
Impurity-assisted Andreev reflection at a spin-active half-metal-superconductor interface
The Andreev reflection amplitude at a clean interface between a half-metallic
ferromagnet (H) and a superconductor (S) for which the half metal's
magnetization has a gradient perpendicular to the interface is proportional to
the excitation energy and vanishes at [B\'{e}ri
{\em et al.}, Phys.\ Rev.\ B {\bf 79}, 024517 (2009)]. Here we show that the
presence of impurities at or in the immediate vicinity of the HS interface
leads to a finite Andreev reflection amplitude at . This
impurity-assisted Andreev reflection dominates the low-bias conductance of a HS
junction and the Josephson current of an SHS junction in the long-junction
limit.Comment: 12 pages, 2 figure
Green criminology and the corporate extraction of water in Canada
v, 197 leaves ; 29 cmIncludes abstract.Includes bibliographical references (leaves 168-197).Inadequate government regulation of for-profit corporate water extraction is a significant issue in Canada but lacks scholarly research, notably in the field of criminology. The thesis aims to examine and critically analyze, from a green criminological perspective, issues associated with groundwater extraction in Canada for the commercial production of bottled water. Specifically, the research examines the extent to which for-profit corporate water extraction in Canada constitutes a green crime. Focusing on an exploration of the issues surrounding the Nestlé bottled water plant in Ontario, this thesis explores how notions of green crimes and green harms regarding corporate water extraction are conceptualized by four parties involved in the case study (i.e., the state, Nestlé Waters Canada, non-governmental organizations, and the local community). Based on definitions founded on a mixture green criminological literature and the findings from this case study, it is suggested that corporate water extraction should constitute a green crime
Frequency Response of Acoustic-Assisted Ni–Mn–Ga Ferromagnetic- Shape-Memory-Alloy Actuator
A prototype of Ni–Mn–Ga based ferromagnetic-shape-memory-alloy (FSMA) actuator was designed and built; an acoustic-assist technique was applied to the actuator to enhance its performance. A piezoelectric stack actuator was attached to the Ni–Mn–Ga sample to generate acoustic energy to enhance twin-boundary mobility and, hence, reduce the magnetic threshold field required for activating twin-boundary motion. The dynamic response of the acoustic-assist FSMA actuator was measured up to 1 kHz actuation. The acoustic assistance improves the actuator performance by increasing the reversible magnetic-field-induced strain (MFIS) by up to 100% (increase from 0.017 to 0.03 at 10 Hz) for drive frequencies below 150 Hz. For frequencies above 150 Hz, the acoustic-assist effect becomes negligible and the resonant characteristic of the actuator takes over the actuator response. Even though the acoustic assist does not improve the actuation at high frequencies, the MFIS output of 5% can be obtained at the resonant frequency of 450 Hz without acoustic assistance. The FSMA actuator is shown to be ideal for applications that require large strain at a specific high frequency.United States. Office of Naval Research (Multi-University Research Initiative, Grant No. N0014-01-0758
Temperature dependent magnetic anisotropy in metallic magnets from an ab-initio electronic structure theory: L1_0-ordered FePt
On the basis of a first-principles, relativistic electronic structure theory
of finite temperature metallic magnetism, we investigate the variation of
magnetic anisotropy, K, with magnetisation, M, in metallic ferromagnets. We
apply the theory to the high magnetic anisotropy material, L1_0-ordered FePt,
and find its uniaxial K consistent with a magnetic easy axis perpendicular to
the Fe/Pt layering for all M and to be proportional to M^2 for a broad range of
values of M. For small M, near the Curie temperature, the calculations pick out
the easy axis for the onset of magnetic order. Our results are in good
agreement with recent experimental measurements on this important magnetic
material.Comment: 4 pages, 2 figure
Giardia duodenalis mouse model for the development of novel antigiardial agents
This study describes a neonatal mouse model of Giardia infection for development of novel antigiardials. Mice were infected with the axenically cultured Assemblage A BAH2c2 strain, with 105 trophozoites per animal recovered. This model proved to be robust and consistent for use in preliminary drug efficacy trials and drug development
Temperature-dependent proximity magnetism in Pt
We experimentally demonstrate the existence of magnetic coupling between two
ferromagnets separated by a thin Pt layer. The coupling remains ferromagnetic
regardless of the Pt thickness, and exhibits a significant dependence on
temperature. Therefore, it cannot be explained by the established mechanisms of
magnetic coupling across nonmagnetic spacers. We show that the experimental
results are consistent with the presence of magnetism induced in Pt in
proximity to ferromagnets, in direct analogy to the well-known proximity
effects in superconductivity.Comment: 4 pages, 3 figure
Electric field driven magnetic domain wall motion in ferromagnetic-ferroelectric heterostructures
We investigate magnetic domain wall (MDW) dynamics induced by applied electric fields in ferromagnetic-ferroelectric thin-film heterostructures. In contrast to conventional driving mechanisms where MDW motion is induced directly by magnetic fields or electric currents, MDW motion arises here as a result of strong pinning of MDWs onto ferroelectric domain walls (FDWs) via local strain coupling. By performing extensive micromagnetic simulations, we find several dynamical regimes, including instabilities such as spin wave emission and complex transformations of the MDW structure. In all cases, the time-averaged MDW velocity equals that of the FDW, indicating the absence of Walker breakdown.Peer reviewe
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