Exchange Bias driven by Dzyaloshinskii-Moriya interactions

The exchange bias effect in compensated IrMn3/Co(111) system is studied using multiscale modeling from "ab initio" to atomistic calculations. We evaluate numerically the out-of-plane hysteresis loops of the bi-layer for different thickness of the ferromagnetic layer. The results show the existence of a perpendicular exchange bias field and an enhancement of the coercivity of the system. In order to elucidate the possible origin of the exchange bias, we analyze the hysteresis loops of a selected bi-layer by tuning the different contributions to the exchange interactions across the interface. Our results indicate that the exchange bias is primarily induced by the Dzyaloshinskii-Moriya interactions, while the coercivity is increased mainly due to a spin-flop mechanism

Effective anisotropies and energy barriers of magnetic nanoparticles with Néel surface anisotropy

Magnetic nanoparticles with Néel surface anisotropy, different internal structures, surface arrangements, and elongation are modeled as many-spin systems. The results suggest that the energy of many-spin nanoparticles cut from cubic lattices can be represented by an effective one-spin potential containing uniaxial and cubic anisotropies. It is shown that the values and signs of the corresponding constants depend strongly on the particle's surface arrangement, internal structure, and shape. Particles cut from a simple cubic lattice have the opposite sign of the effective cubic term, as compared to particles cut from the face-centered cubic lattice. Furthermore, other remarkable phenomena are observed in nanoparticles with relatively strong surface effects. (i) In elongated particles surface effects can change the sign of the uniaxial anisotropy. (ii) In symmetric particles (spherical and truncated octahedral) with cubic core anisotropy surface effects can change the sing of the latter. We also show that the competition between the core and surface anisotropies leads to a new energy that contributes to both the second- and fourth-order effective anisotropies. We evaluate energy barriers ΔE as functions of the strength of the surface anisotropy and the particle size. The results are analyzed with the help of the effective one-spin potential, which allows us to assess the consistency of the widely used formula ΔE/V= K∞ +6 Ks /D, where K∞ is the core anisotropy constant, Ks is a phenomenological constant related to surface anisotropy, and D is the particle's diameter. We show that the energy barriers are consistent with this formula only for elongated particles for which the surface contribution to the effective uniaxial anisotropy scales with the surface and is linear in the constant of the Néel surface anisotropy. © 2007 The American Physical Society

Constrained Monte Carlo Method and Calculation of the Temperature Dependence of Magnetic Anisotropy

We introduce a constrained Monte Carlo method which allows us to traverse the phase space of a classical spin system while fixing the magnetization direction. Subsequently we show the method's capability to model the temperature dependence of magnetic anisotropy, and for bulk uniaxial and cubic anisotropies we recover the low-temperature Callen-Callen power laws in M. We also calculate the temperature scaling of the 2-ion anisotropy in L10 FePt, and recover the experimentally observed M^2.1 scaling. The method is newly applied to evaluate the temperature dependent effective anisotropy in the presence of the N'eel surface anisotropy in thin films with different easy axis configurations. In systems having different surface and bulk easy axes, we show the capability to model the temperature-induced reorientation transition. The intrinsic surface anisotropy is found to follow a linear temperature behavior in a large range of temperatures

Hubungan Tingkat Kecemasan Dengan Mekanisme Koping Pada Penderita Diabetes Melitus Tipe II Di Poliklinik Penyakit Dalam Rumah Sakit Umum Daerah Tobelo Kabupaten Halmahera Utara

. Diabetes mellitus is a chronic disease that has a negative impact on psychological well-being of patients, the psychological effects such as anxiety. Anxiety is a reaction to the disease as perceived as a threat, discomfort. Coping mechanism is a method to adapt to the changes that occur. The purpose of the study was to determine the level of anxiety is there a relationship with coping mechanisms in patients with type II diabetes mellitus in internal medicine clinic Tobelo hospital. The design of this study using cross-sectional approach. Sample of 32 people, with purposive sampling method. Data were collected by interview using a questionnaire. The results of the study found a 12,5% rate of mild anxiety, medium anxiety 43,8%, severe anxiety 43,8% and adaptive coping mechanism 62,5%, maladaptive coping 37,5% . The results of hypothesis testing with Chi Square test shows that the value of p = 0,002, p is less than α (0,05) . Conclusion that there is a relationship anxiety levels with coping mechanisms in patients with type II diabetes mellitus

Reducing torque pulsations in PMa-SynRM: A way for improving motor performance

This paper aims to evaluate the performance of synchronous reluctance motors assisted by a permanent magnet (PMa-SynRM) focused on efficiency and torque pulsations. PMa-SynRM shows high efficiency and power factor, compared to induction motors (IM), although they have a greater cost. These machines develop relatively high torque ripple, cogging torque, and torque imbalances. Consequently, the electromagnetic torque is reduced, the motor temperature is increased, and mechanical vibrations are induced. The optimal design of the machine structures such as flow barriers, permanent magnets, and stator slots, among others, allow reducing torque pulsations. A comparison is made between different designs of the PMa-SynRM reported in the scientific literature, and the effects on efficiency, torque pulsation, and operating costs are evaluated. A case study on the motor driving the air conditioner blower in a hotel room was made, to determine the best economic variant between IM or PMa-SynRM. A sensitive analysis was made to evaluate several uncertainties. The advantages of using one of the PMa-SynRM analyzed were demonstrated. Also, it was proved that the investment is feasible economically, although NPV and payback are not the best, due to low load factor in inverter-controlled motors in air conditioners

Adaptación transcultural de un cuestionario para medir la calidad de vida de los pacientes con anticoagulación oral

ObjetivoAdaptar a la cultura y el idioma españoles un cuestionario desarrollado para evaluar la calidad de vida de los pacientes con tratamiento anticoagulante oral (TAO) y medir su validezDiseñoEstudio observacional, descriptivo, de validación de un instrumento de medida de calidad de vida relacionada con la salud. Emplazamiento. Atención primaria y atención especializadaParticipantesUn total de 225 pacientes que incluía a todos los pacientes de nuestro centro que utilizan TAO y una muestra consecutiva de pacientes con TAO del servicio de hematología del hospital de referenciaMediciones principalesTraducción directa,traducción inversa y prueba de validez. Análisis factorial y agrupación por dimensiones de los ítems, análisis de la consistencia interna y análisis de correlación ítem-total de la versión definitiva del cuestionario en españolResultadosLa edad media de los pacientes fue de 65 ± 13 años, el 51,1% era mujer y el 45,8% era controlado en atención primaria. En el estudio de validez se realizó un análisis factorial con la extracción de 5 factores que explican el 41,62% del valor total de la varianza y la obtención de una agrupación diferente de la original, con unvalor de alfa de Cronbach global de 0,82 y de 0,56–0,74 en las diferentes dimensiones y análisis de correlación ítem-total con valores estadísticamente significativos, excepto en la pregunta número 29ConclusionesTras realizar la adaptación a la cultura y el idioma españoles de un cuestionario desarrollado para evaluar la calidad de vida de los pacientes con TAO, se ha obtenido un instrumento útil y válido para nuestro entornoObjectiveTo adapt to Spanish culture and language a questionnaire developed to evaluate the quality of life of patients taking oral anticoagulation treatment (OAT) and to measure its validityDesignA descriptive observation study to validate an instrument to measure health-related quality of lifeSettingPrimary and specialist careParticipants225 patients, all the patients at our centre who were on OAT and a consecutive sample of patients on OAT from the referral hospital's haemotology serviceMain measurementsDirect translation, back- translation, and pilot study. Factor analysis and item-dimension grouping, internal consistency analysis and analysis of the item- total correlation of the definitive version of the questionnaire in SpanishResultsMean age was 65 (SD=13 years); 51% were women; 45.8% were monitored in PC. Validity study: factor analysis extracted 5 factors that explained 41.62% of total variance value and obtained a grouping different from the original; Cronbach's alpha was .82 overall and ran from .56 to .74 in the various dimensions; and item-total correlation analysis had statistically significant values,except for question 29ConclusionsAfter adaptation to Spanish culture and language of a questionnaire developed to evaluate the quality of life of patients taking OAT, it was found to be a useful instrument, valid for use in our milie

Herramientas para la gestión energética empresarial

En este artículo se presenta una metodología para el estudio de la Tecnología de Gestión Total Eficiente de la Energía, que consiste en la aplicación de herramientas técnico-organizativas que, aplicadas de forma continua con la filosofía y procedimientos de la gestión total de la calidad, permiten identificar y utilizar todas las oportunidades de ahorro, conservación de energía y reducción de los gastos en los distintos sistemas energéticos de una empresa