2,666 research outputs found
Short-range Magnetic interactions in the Spin-Ice compound HoTiO
Magnetization and susceptibility studies on single crystals of the pyrochlore
HoTiO are reported for the first time. Magnetization
isotherms are shown to be qualitatively similar to that predicted by the
nearest neighbor spin-ice model. Below the lock-in temperature, K, magnetization is consistent with the locking of spins along
[111] directions in a specific two-spins-in, two-spins-out arrangement. Below
the magnetization for displays a two step behavior
signalling the breaking of the ice rules.Comment: 4 pages, 3 figure
Context-Dependent Memory under Stressful Conditions: The Case of Skydiving
Two experiments examined the effect of differing levels of emotional arousal on learning and memory for words in matching and mismatching contexts. In Experiment 1, experienced skydivers learned words either in the air or on the ground and recalled them in the same context or in the other context. Experiment 2 replicated the stimuli and design of the first experiment except that participants were shown a skydiving video in lieu of skydiving. Recall was poor in air-learning conditions with actual skydiving, but when lists were learned on land, recall was higher in the matching context than in the mismatching context. In the skydiving video experiment, recall was higher in matching learn-recall contexts regardless of the situation in which learning occurred. We propose that under extremely emotionally arousing circumstances, environmental and/or mood cues are unlikely to become encoded or linked to newly acquired information and thus cannot serve as cues to retrieval. Results can be applied to understanding variations in context-dependent memory in occupations (e.g., police, military special operations, and Special Weapons and Tactics teams) in which the worker experiences considerable emotional stress while learning or recalling new information
Compressibility of and (M = Rh, Ir and Co) Compounds
The lattice parameters of the tetragonal compounds CeIn and
CeIn(Rh, Ir and Co) have been studied as a function of
pressure up to 15 GPa using a diamond anvil cell under both hydrostatic and
quasihydrostatic conditions at room temperature. The addition of In
layers to the parent CeIn compound is found to stiffen the lattice as the
2-layer systems (average of bulk modulus values is 70.4 GPa) have a
larger than CeIn (67 GPa), while the 1-layer systems with the are
even stiffer (average of is 81.4 GPa). Estimating the hybridization
using parameters from tight binding calculations shows that the dominant
hybridization is in nature between the Ce and In atoms. The values of
at the pressure where the superconducting transition temperature
reaches a maximum is the same for all CeIn compounds. By
plotting the maximum values of the superconducting transition temperature
versus for the studied compounds and Pu-based superconductors, we
find a universal versus behavior when these quantities are
normalized appropriately. These results are consistent with magnetically
mediated superconductivity.Comment: Updated version resubmitted to Phys. Rev.
Matrix Metalloproteinases: Pro- and Anti-Angiogenic Activities
Matrix metalloproteinases (MMP) are a family of structurally related proteinases most widely recognized for their ability to degrade extracellular matrix, although recent investigations have demonstrated other biologic functions for these enzymes. MMP are typically not constitutively expressed, but are regulated by: (1) cytokines, growth factors, and cell–cell and cell–matrix interactions that control gene expression; (2) activation of their proenzyme form; and (3) the presence of MMP inhibitors [tissue inhibitors of metalloproteinases, (TIMP)]. MMP have important roles in normal processes including development, wound healing, mammary gland, and uterine involution, but are also involved in angiogenesis, tumor growth, and metastasis. Angiogenesis, characteristically defined as the establishment of new vessels from pre-existing vasculature, is required for biologic processes such as wound healing and pathologic processes such as arthritis, tumor growth, and metastasis. Blocking of MMP activity has been studied for potential therapeutic efficacy in controlling such pathologic processes. Synthetic MMP inhibitors, most notably the hydroxymates, have been engineered for this purpose and are presently in clinical trial. These inhibitors may have broad versus specific MMP inhibitory activity. As increased nonmatrix degrading capabilities of MMP are recognized, however, i.e., cytokine activation, processing of proteins to molecules of distinct biologic function, it becomes less clear whether the nonselective inhibition of MMP activity for all pathologic processes involving MMP is appropriate. This review focuses upon the contribution of MMP to the process of tumor invasion and angiogenesis, and discusses the design and use of MMP inhibitors as therapeutic agents in these processes
Yang-Mills action from minimally coupled bosons on R^4 and on the 4D Moyal plane
We consider bosons on Euclidean R^4 that are minimally coupled to an external
Yang-Mills field. We compute the logarithmically divergent part of the cut-off
regularized quantum effective action of this system. We confirm the known
result that this term is proportional to the Yang-Mills action.
We use pseudodifferential operator methods throughout to prepare the ground
for a generalization of our calculation to the noncommutative four-dimensional
Moyal plane (also known as noncommutative flat space). We also include a
detailed comparison of our cut-off regularization to heat kernel techniques.
In the case of the noncommutative space, we complement the usual technique of
asymptotic expansion in the momentum variable with operator theoretic arguments
in order to keep separated quantum from noncommutativity effects. We show that
the result from the commutative space R^4 still holds if one replaces all
pointwise products by the noncommutative Moyal product.Comment: 37 pages, v2 contains an improved treatment of the theta function in
Appendix A.
Field-induced magnetic transitions in the quasi-two-dimensional heavy-fermion antiferromagnets Ce_{n}RhIn_{3n+2} (n=1 or 2)
We have measured the field-dependent heat capacity in the tetragonal
antiferromagnets CeRhIn and CeRhIn, both of which have an
enhanced value of the electronic specific heat coefficient
mJ/mol-Ce K above . For the specific heat data at zero
applied magnetic field are consistent with the existence of an anisotropic
spin-density wave opening a gap in the Fermi surface for CeRhIn while
CeRhIn shows behavior consistent with a simple antiferromagnetic
magnon. From these results, the magnetic structure, in a manner similar to the
crystal structure, appears more two-dimensional in CeRhIn than in
CeRhIn where only about 12% of the Fermi surface remains ungapped
relative to 92% for CeRhIn. When both compounds behave in a
manner expected for heavy fermion systems as both and the electronic
heat capacity decrease as field is applied. When the field is applied in the
tetragonal basal plane (), CeRhIn and CeRhIn have very
similar phase diagrams which contain both first- and second-order field-induced
magnetic transitions .Comment: 15 pages, 4 figure
Engajamento Político Transnacional e a Incorporação Cívica de Imigrantes Mexicanos nos Estados Unidos
Many migrants to the U.S. are engaged in public affairs in their country of origin. Whether such engagement impedes or encourages engagement in American politics remains an open question. Drawing from a unique two-wave panel survey of Mexican immigrants conducted in 2006, with surveys waves fielded to correspond to national elections in Mexico and the United States, we examine the relationship between transnational political engagement and attentiveness to American politics. The findings indicate that remote political engagement in Mexican politics is not a barrier to incorporation in the U.S. context. On the contrary, engagement in Mexican campaigns can stimulate interest and participation in U.S. elections.Muchos de los migrantes a los Estados Unidos se involucran en la vida cívica de su país de origen. Es pregunta abierta si tal participación impide o promueve la participación en la política norteamericana. Utilizando datos de una encuesta de inmigrantes mexicanos en dos olas llevadas a cabo en 2006, coordinadas con las elecciones nacionales en México y los Estados Unidos, investigamos la relación entre la participación política trasnacional y la atención a la política norteamericana. Los hallazgos señalan que la participación en la política mexicana no es obstáculo a la incorporación cívica en el contexto norteamericano. Al contrario, la atención a las campañas mexicanas puede estimular el interés y la participación en las elecciones estadunidenses.Muitas pessoas que migram para os Estados Unidos continuam engajadas em assuntos públicos em seu país de origem, mas não está claro se esse engajamento impede ou incentiva o envolvimento na política americana. O presente estudo examina a relação entre o engajamento político transnacional e a atenção à política americana, com base em uma pesquisa de painel de duas ondas realizada com imigrantes mexicanos em 2006. As duas ondas da pesquisa correspondem às eleições nacionais no México e nos Estados Unidos. Os resultados indicam que o engajamento à distância na política mexicana não é uma barreira para a incorporação no contexto dos Estados Unidos. Pelo contrário, o engajamento em campanhas mexicanas pode estimular o interesse e a participação nas eleições americanas
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