Spin Glass Phase in Spin-Density-Wave Cr–Co Alloys

A spin glass (SG) phase was observed in the spin-density wave (SDW) alloys Cr1−xCox at high Co concentrations (x≥13%). After zero-field cooling, the temperature dependence of the magnetization M(T) of Cr0.87Co0.13 and Cr0.85Co0.15, measured in an applied field H=100 Oe with a SQUID magnetometer, exhibits a low T maximum, characteristic of a SG. Cooling in the measuring field, however, gives quite a different behavior. The field dependence of the magnetization M(H) is nonlinear, with a pronounced hysteresis. A strong time relaxation M(t) is also an indication of a SG phase. SG in Cr1−xCox is formed at high impurity concentrations, possibly due to clustering of the magnetic impurities

Influence of intermartensitic transitions on transport properties of Ni2.16Mn0.84Ga alloy

Magnetic, transport, and x-ray diffraction measurements of ferromagnetic shape memory alloy Ni$_{2.16}$Mn$_{0.84}$Ga revealed that this alloy undergoes an intermartensitic transition upon cooling, whereas no such a transition is observed upon subsequent heating. The difference in the modulation of the martensite forming upon cooling from the high-temperature austenitic state [5-layered (5M) martensite], and the martensite forming upon the intermartensitic transition [7-layered (7M) martensite] strongly affects the magnetic and transport properties of the alloy and results in a large thermal hysteresis of the resistivity $\rho$ and magnetization $M$. The intermartensitic transition has an especially marked influence on the transport properties, as is evident from a large difference in the resistivity of the 5M and 7M martensite, $(\rho_{\mathrm{5M}} - \rho_{\mathrm{7M}})/\rho _{\mathrm{5M}} \approx 15$, which is larger than the jump of resistivity at the martensitic transition from the cubic austenitic phase to the monoclinic 5M martensitic phase. We assume that this significant difference in $\rho$ between the martensitic phases is accounted for by nesting features of the Fermi surface. It is also suggested that the nesting hypothesis can explain the uncommon behavior of the resistivity at the martensitic transition, observed in stoichiometric and near-stoichiometric Ni-Mn-Ga alloys.Comment: 7 pages, 6 figures, REVTEX

Uso de modelos de simulação sócio-bio-econômico integrado como ferramenta para o desenvolvimento agrário na região sudoeste do Rio Grande Sul.

Suporte tecnológico tem sido oferecido aos produtores com a finalidade de aumentar a eficiência produtiva e fornecer subsídios para as suas tomadas de decisões; entretanto, os métodos tradicionais de pesquisa e extensão estão sendo cada vez mais questionados, principalmente quanto ao custo e tempo necessário para oferecer soluções aos problemas enfrentados pelos produtores.bitstream/item/109814/1/USO-DE-MODELOS-DE-SIMULACAO.pd

Magnetic phase diagram of the Hubbard model

The competition between commensurate and incommensurate spin-density-wave phases in the infinite-dimensional single-band Hubbard model is examined with quantum Monte Carlo simulation and strong and weak coupling approximations. Quantum fluctuations modify the weak-coupling phase diagram by factors of order unity and produce remarkable agreement with the quantum Monte Carlo data, but strong-coupling theories (that map onto effective Falicov-Kimball models) display pathological behavior. The single-band model can be used to describe much of the experimental data in Cr and its dilute alloys with V and Mn.Comment: 12 pages plus 3 uuencoded postscript figures, ReVTe

Magnetic phase diagram and transport properties of FeGe_2

We have used resistivity measurements to study the magnetic phase diagram of the itinerant antiferromagnet FeGe_2 in the temperature range from 0.3->300 K in magnetic fields up to 16 T. In contrast to theoretical predictions, the incommensurate spin density wave phase is found to be stable at least up to 16 T, with an estimated critical field \mu _0H_c of ~ 30 T. We have also studied the low temperature magnetoresistance in the [100], [110], and [001] directions. The transverse magnetoresistance is well described by a power law for magnetic fields above 1 T with no saturation observed at high fields. We discuss our results in terms of the magnetic structure and the calculated electronic bandstructure of FeGe_2. We have also observed, for the first time in this compound, Shubnikov-de Haas oscillations in the transverse magnetoresistance with a frequency of 190 +- 10 T for a magnetic field along [001].Comment: 13 pages, RevTeX, 7 postscript figures, to appear in Journal of Physics: Condensed Matte

Trauma Surveillance in Cape Town, South Africa: An Analysis of 9236 Consecutive Trauma Center Admissions.

PublishedJournal ArticleResearch Support, Non-U.S. Gov'tThis is the final version of the article. Available from American Medical Association via the DOI in this record.IMPORTANCE: Trauma is a leading cause of death and disability worldwide. In many low- and middle-income countries, formal trauma surveillance strategies have not yet been widely implemented. OBJECTIVE: To formalize injury data collection at Groote Schuur Hospital, the chief academic hospital of the University of Cape Town, a level I trauma center, and one of the largest trauma referral hospitals in the world. DESIGN, SETTING, AND PARTICIPANTS: This was a prospective study of all trauma admissions from October 1, 2010, through September 30, 2011, at Groote Schuur Hospital. A standard admission form was developed with multidisciplinary input and was used for both clinical and data abstraction purposes. Analysis of data was performed in 3 parts: demographics of injury, injury risk by location, and access to and maturity of trauma services. Geographic information science was then used to create satellite imaging of injury "hot spots" and to track referral patterns. Finally, the World Health Organization trauma system maturity index was used to evaluate the current breadth of the trauma system in place. MAIN OUTCOMES AND MEASURES: The demographics of trauma patients, the distribution of injury in a large metropolitan catchment, and the patterns of injury referral and patient movement within the trauma system. RESULTS: The minimum 34-point data set captured relevant demographic, geographic, incident, and clinical data for 9236 patients. Data field completion rates were highly variable. An analysis of demographics of injury (age, sex, and mechanism of injury) was performed. Most violence occurred toward males (71.3%) who were younger than 40 years of age (74.6%). We demonstrated high rates of violent interpersonal injury (71.6% of intentional injury) and motor vehicle injury (18.8% of all injuries). There was a strong association between injury and alcohol use, with alcohol implicated in at least 30.1% of trauma admissions. From a systems standpoint, the data suggest a mature pattern of referral consistent with the presence of an inclusive trauma system. CONCLUSIONS AND RELEVANCE: The implementation of injury surveillance at Groote Schuur Hospital improved insights about injury risk based on demographics and neighborhood as well as access to service based on patterns of referral. This information will guide further development of South Africa's already advanced trauma system.This work was supported by the Canadian Institute for Health Research and the Social Sciences and Humanities Research Council

Electronic Structure and Charge Dynamics of Huesler Alloy Fe2TiSn Probed by Infrared and Optical Spectroscopy

We report on the electrodynamics of a Heusler alloy Fe2TiSn probed over four decades in energy: from the far infrared to the ultraviolet. Our results do not support the suggestion of Kondo-lattice behavior inferred from specific heat measurements. Instead, we find a conventional Drude-like response of free carriers, with two additional absorption bands centered at around 0.1 and 0.87 eV. The latter feature can be interpreted as excitations across a pseudogap, in accord with band structure calculations.Comment: 3 pages, 4 figure

Harmonic crossover exponents in O(n) models with the pseudo-epsilon expansion approach

We determine the crossover exponents associated with the traceless tensorial quadratic field, the third- and fourth-harmonic operators for O(n) vector models by re-analyzing the existing six-loop fixed dimension series with pseudo-epsilon expansion. Within this approach we obtain the most accurate theoretical estimates that are in optimum agreement with other theoretical and experimental results.Comment: 12 pages, 1 figure. Final version accepted for publicatio

Sum rules and electrodynamics of high-Tc cuprates in the pseudogap state

We explore connections between the electronic density of states (DOS) in a conducting system and the frequency dependence of the scattering rate $1/\tau(\omega)$ inferred from infrared spectroscopy. We show that changes in the DOS upon the development of energy gaps can be reliably tracked through the examination of the $1/\tau(\omega)$ spectra using the sum rules discussed in the text. Applying this analysis to the charge dynamics in high-$T_c$ cuprates we found radically different trends in the evolution of the DOS in the pseudogap state and in the superconducting state.Comment: 4 pages, 3 figure

On the injectivity of the circular Radon transform arising in thermoacoustic tomography

The circular Radon transform integrates a function over the set of all spheres with a given set of centers. The problem of injectivity of this transform (as well as inversion formulas, range descriptions, etc.) arises in many fields from approximation theory to integral geometry, to inverse problems for PDEs, and recently to newly developing types of tomography. The article discusses known and provides new results that one can obtain by methods that essentially involve only the finite speed of propagation and domain dependence for the wave equation.Comment: To appear in Inverse Problem