Precursor state of skyrmions in MnSi: a heat capacity study

The magnetic phase diagram of MnSi based on the detailed magneto‐heat capacity study is presented. It shows the A‐phase, a precursor to the formation of stable skyrmion lattice, along with the intermediate, helical, conical, ferromagnetic and paramagnetic phases. The field isotherms of specific heat in and around the transition temperature reveal the different magnetic modulations. The local minima represent the relatively low entropy state due to the formation of A‐phase as a precursor to the stable skyrmion lattice. The field‐induced second‐order phase transition is observed by melting the intermediate phase. The region of existence of first‐order phase transition is found to be, effectively, from helical to the intermediate phase. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of solute atoms on grain boundary sliding in magnesium alloys

The effect of solid-solution alloying on grain boundary sliding (GBS) was investigated using pure magnesium and six kinds of Mg–X (X?=?Ag, Al, Li, Pb, Y and Zn) dilute binary solid solutions with an average grain size of 10?µm. A sharp increase in damping capacity caused by GBS was observed above a certain temperature. The temperature at which a sharp increase in damping capacity occurred depended on the alloying element. The addition of Y and Ag markedly increased the onset temperature (more than 100?K) for a sharp increase in damping capacity, whereas the addition of Zn, Al and Li slightly increased the onset temperature (less than 50?K) as compared with that for pure magnesium. Tensile tests at a temperature of 423?K revealed that the higher the onset temperature, the lower the strain rate sensitivity of the flow stress. It is suggested that the former elements (Y and Ag) are more effective in suppressing GBS in magnesium alloys than the latter ones (Zn, Al and Li). The suppression of GBS was associated with low grain boundary energy, and the extent to which the energy is reduced depended on the alloying element. It was suggested that the change in the lattice parameter (the so-called c/a ratio) affects the grain boundary energy, and thus, the occurrence of GBS.     

冰蓄冷空调系统设备选择的数学模型及简化求解

从工程经济学角度,引进等额年金,设计日负荷修正系数,得出冰蓄冷空调系统设备选择的目标函数,对各参数进行赋值,求得最佳的系统设备选择,并用一个工程实例验证,结果表明此数学模型是有效的。所得的结论可供设计者在设汁时参考。     

Numerical study of the directed polymer in a 1 + 3 dimensional random medium

The directed polymer in a 1+3 dimensional random medium is known to present a disorder-induced phase transition. For a polymer of length L, the high temperature phase is characterized by a diffusive behavior for the end-point displacement R² ∼L and by free-energy fluctuations of order ΔF(L) ∼O(1). The low-temperature phase is characterized by an anomalous wandering exponent R²/L ∼L^ω and by free-energy fluctuations of order ΔF(L) ∼L^ω where ω∼0.18. In this paper, we first study the scaling behavior of various properties to localize the critical temperature T_c. Our results concerning R²/L and ΔF(L) point towards 0.76 < T_c ≤T₂=0.79, so our conclusion is that T_c is equal or very close to the upper bound T₂ derived by Derrida and coworkers (T₂ corresponds to the temperature above which the ratio remains finite as L ↦ ∞). We then present histograms for the free-energy, energy and entropy over disorder samples. For T ≫T_c, the free-energy distribution is found to be Gaussian. For T ≪T_c, the free-energy distribution coincides with the ground state energy distribution, in agreement with the zero-temperature fixed point picture. Moreover the entropy fluctuations are of order ΔS ∼L^1/2 and follow a Gaussian distribution, in agreement with the droplet predictions, where the free-energy term ΔF ∼L^ω is a near cancellation of energy and entropy contributions of order L^1/2.     

Rigorous bounds on the storage capacity of the dilute Hopfield model

We study a neural network model consisting ofN neurons where a dendritic connection between each pair of neurons exists with probabilityp and is absent with probability 1-p. For the Hopfield Hamiltonian on such a network, we prove that ifp c[(lnN)/N]^1/2, the model can store at leastm= _cpN patterns, where _c 0.027 ifc 3 and decreases proportional to 1/(–lnc) forc small. This generalizes the results of Newman for the standard Hopfield model.     

不同结构毛细管网辐射板供冷性能实验研究

对两种不同结构毛细管网辐射板的性能进行了实验研究,分析了在不同供水温度下,该两种辐射板在表面温度分布、供冷能力、安装辐射板房间温度变化情况之间的差异,为今后毛细管网辐射供冷空调系统辐射末端的设计应用及运行控制提供依据。     

固体棒状热容激光器的热分析

 计算出固体棒状热容激光器在不同散热边界条件下的温度分布和随时间的演变,与实验测量的结果进行了对比。计算结果表明：激光器工作在热容模式时,不同散热边界条件下激光介质内的温度分布在激光发射期间区别不大,激光发射期间,激光介质内的温度分布主要取决于泵浦光的吸收。但是散热过程中的不同散热边界条件下温度分布演化大不相同,此时的温度分布主要取决于散热边界条件。     

Characterization of the smectic-A-hexatic-B transition in 65OBC by adiabatic scanning calorimetry

We investigated the smectic-A-hexatic-B (SmA-HexB) transition in the liquid-crystal n-hexyl-4-n-pentyloxybiphenyl-4-carboxilate (65OBC) with adiabatic scanning calorimetry. We were able to prove in a direct way that this transition is indeed very weakly first order, as was already suggested in the literature. The latent heat at the transition was determined to be H_L = 0.04±0.02 J/g. Our experiments confirm the high value for the heat capacity critical exponent earlier reported, yielding = 0.64±0.05.     

<Emphasis Type="Italic">Comment on</Emphasis>¶Low temperature specific heat of blue bronze K <Emphasis Type="Bold">0.30</Emphasis>MoO <Emphasis Type="Bold">3</Emphasis>, by J. Odin,J.C. Lasjaunias,K. Biljaković, K. Hasselbach,and P. Monceau

Eur. Phys. J. B 24, 315 (2001) Here we comment on a recently published paper on the presence of a phason contribution in the low temperature heat capacity data of the charge-density-wave compounds K_0.3MoO₃ and (TaSe₄)₂I. We have shown that the anomaly in the C _P / T ³ data reported by Odin et al. is straightforwardly interpreted in terms of low energy phonon modes resulting from the peculiar topology of these compounds. Received 21 February 2002 Published online 19 July 2002     

Probing antiferromagnetic order with heat capacity in exchange-biased structures

We explore the magnetic heat capacity in exchange-biased ferromagnet/antiferromagnet bilayers theoretically. We show that changes in the antiferromagnetic structure due to the reversal of the ferromagnet layer can be detected by distinct features in the heat capacity. This offers a method for probing antiferromagnetic domains in exchange-biased systems.