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The structure and magnetic properties of polycrystalline GdCo9Si2 compound have been investigated. It has a BaCd11 structure and undergoes two magnetic phase transitions: an antiferromagnetic to ferrimagnetic transition occurring at rv93 K, and a ferrimagnetic to paramagnetic transition at 420 K, which results in a positive and a negative magnetic entropy change, respectively. The two peak values of magnetic entropy change are -0.6 and 1.1 J·kg-1 K-1 for DH ¼ 5 T. Furthermore, there exists a metal-semiconductor transition temperature (TP), below which the resistance increases with increasing temperature, while the semiconductor characteristic is observed above TP. The magnetic domain structures are characterized by stripe and grid structures 1 lm wide. Although the MCE is small for applications, its study is useful to clearly understand the nature of multiple magnetic phase transitions in the GdCo9Si2 compound.

Gd5Si2.05-xGe1.95-xNi2x (2x ¼ 0.08, 0.1) alloys were prepared by arc melting followed by annealing at 1273 K for 96 h. Mixed monoclinic Gd5Si2Ge2-type phase, orthorhombic Gd5Si4-type phase, and a small amount of Gd5Si3-type phase were obtained in these alloys. Gd5Si2.01Ge1.91Ni0.08 alloy undergoes a second-order transition (TC) around 300 K, whereas Gd5Si2Ge1.9Ni0.1 alloy exhibits two II I transitions including a first-order transition (TC ) at rv295 K and second-order transition (TC ) at rv301 K. Ni substitution can effectively reduce the thermal hysteresis and magnetic hysteresis while max maintaining large magnetic entropy change. The maximum magnetic entropy changes (|DSM |) of 1 -1 Gd5Si2.05-xGe1.95-xNi2x alloys with 2x ¼ 0.08 and 0.1 are 4.4 and 5.0 J kg- K, respectively, for 0–2 T, and are 8.0 and 9.1 J kg-1 K-1, respectively, for 0–5 T. Low hysteresis performance and relatively large magnetic entropy change make these alloys favorable for magnetic refrigeration applications.

In the version of the single-degenerate scenario of Type Ia supernovae (SNe Ia) studied here, a carbon–oxygen white dwarf explodes close to the Chandrasekhar limit after accreting material from a non-degenerate helium (He) companion star. In the present study, we employ the Stellar GADGET code to perform three-dimensional hydrodynamical simulations of the interaction of the SN Ia ejecta with the He companion star taking into account its orbital motion and spin. It is found that only 2%–5% of the initial companion mass is stripped off from the outer layers of He companion stars due to the supernova (SN) impact. The dependence of the unbound mass (or the kick velocity) on the orbital separation can be fitted to a good approximation by a power law for a given companion model. After the SN impact, the outer layers of a He donor star are significantly enriched with heavy elements from the low-expansion-velocity tail of SN Ia ejecta. The total mass of accumulated SN-ejecta material on the companion surface reaches about 10−3 M for different companion models. This enrichment with heavy elements provides a potential way to observationally identify the surviving companion star in SN remnants. Finally, by artificially adjusting the explosion energy of the W7 explosion model, we find that the total accumulation of SN ejecta on the companion surface is also dependent on the explosion energy with a power-law relation to a good approximation.

Context: In the single-degenerate (SD) scenario of type Ia supernovae (SNe Ia) the non-degenerate companion star survives the supernova (SN) explosion and thus should be visible near the center of the SN remnant and may show some unusual features. Therefo

The amorphous alloys Gd60Co40−xMnx (x = 0, 5, 10, 15) were prepared by melt spinning. The Curie temperature,T c, increases monotonously with Mn addition, ranging from 198 K for x = 0 to 205 K for x = 15, while the maximum values of −ΔSM under the applied field change from 0 to 5 T are 7.7, 7.1, 6.2 and 5.4 J·kg−1·K−1 for x = 0, 5, 10, and 15, respectively. All samples undergo a second order ferri-paramagnetic phase transition. The critical behavior around the transitiontemperature is investigated in detail, using both the standard Kouvel-Fisher procedure as well as the study of the field dependence of the magnetocaloric effect. Results indicate that the obtained critical exponents are reliable, and that the present alloys exhibit local magnetic interaction.

Glial cells perform critical functions that alter the metabolism and activity of neurons, and there is increasing interest in their role in appetite and energy balance. Leptin, a key regulator of appetite and metabolism, has previously been reported to influence glial structural proteins and morphology. Here, we demonstrate that metabolic status and leptin also modify astrocyte-specific glutamate and glucose transporters, indicating that metabolic signals influence synaptic efficacy and glucose uptake and, ultimately, neuronal function. We found that basal and glucose-stimulated electrical activity of hypothalamic proopiomelanocortin (POMC) neurons in mice were altered in the offspring of mothers fed a high-fat diet. In adulthood, increased body weight and fasting also altered the expression of glucose and glutamate transporters. These results demonstrate that whole-organism metabolism alters hypothalamic glial cell activity and suggest that these cells play an important role in the pathology of obesity.

Density functional calculations are performed to study the electronic structure of recently proposed graphene/graphane based core/shell quantum dots, which have a type I band alignment and exhibit quantized carrier energy levels. Strong confinement is robust with shell thickness. The bandgap, band offset, and the number of confined carrier orbitals with different size and geometry are determined. Our findings indicate that these core/shell dots are potentially well suited for the design of advanced diode lasers and room-temperature single electron devices. The proposed method to determine the number of confined orbitals is applicable for other quantum dot systems.

We report the fabrication and characterization of a cylindrically symmetric fiber structure that possesses significant and thermodynamically stable second-order nonlinearity. Such fiber structure is produced through nanoscale self-assembly of nonlinear molecules on a silica fiber taper and possesses full rotational symmetry. Despite its highly symmetric configuration, we observed significant second harmonic generation (SHG) and obtained good agreement between experimental results and theoretical predictions. (C) 2011 Optical Society of America

We report a second-order nonlinear nanoprobe for characterizing ultrafast optical near fields. The proposed nanoprobe comprises second harmonic nanocrystals attached to a carbon nanotube, which is in turn attached to a silica fiber taper. We demonstrate in situ pulse characterization directly in the air core of a photonic crystal fiber. Further, it is shown that nanoprobes containing a single nanocrystal in the tip of the nanotube can be fabricated by auxiliary focused ion beam nanomilling. These results indicate that the proposed nanoprobe can open an avenue for probing the evolution of ultrafast optical fields in complex three-dimensional micro-or nanostructures. (C) 2010 American Institute of Physics. [doi:10.1063/1.3532112]

Near-field scanning can achieve nanoscale resolution while ultrashort pulse diagnostic tools can characterize femtosecond pulses. Yet currently it is still challenging to nonperturbatively characterize the near field of an ultrashort optical pulse with nanofemtoscale spatiotemporal resolution. To address this challenge, we propose to develop a nonlinear nanoprobe composed of a silica fiber taper, a nanowire, and nonlinear fluorescent spheres. Using such a nanoprobe, we also report proof-of-principle characterization of femtosecond optical pulse through interferometric autocorrelation measurement.

The authors propose a general approach that can produce a silica fiber with large and thermodynamically stable second order nonlinearity. They estimate that it is possible to achieve second harmonic generation efficiency of more than 10% in such a nonlinear fiber with a length of a few hundred microns. By maintaining a high degree of spatial symmetry, the proposed nonlinear fiber can naturally generate polarization entangled photon pairs, a physical object of enormous significance for quantum information technology. (c) 2007 American Institute of Physics.