Ultra-fast magnetisation rates within the Landau-Lifshitz-Bloch model

The ultra-fast magnetisation relaxation rates during the laser-induced magnetisation process are analyzed in terms of the Landau-Lifshitz-Bloch (LLB) equation for different values of spin $S$. The LLB equation is equivalent in the limit $S \rightarrow \infty$ to the atomistic Landau-Lifshitz-Gilbert (LLG) Langevin dynamics and for $S=1/2$ to the M3TM model [B. Koopmans, {\em et al.} Nature Mat. \textbf{9} (2010) 259]. Within the LLB model the ultra-fast demagnetisation time ($\tau_{M}$) and the transverse damping ($\alpha_{\perp}$) are parameterized by the intrinsic coupling-to-the-bath parameter $\lambda$, defined by microscopic spin-flip rate. We show that for the phonon-mediated Elliott-Yafet mechanism, $\lambda$ is proportional to the ratio between the non-equilibrium phonon and electron temperatures. We investigate the influence of the finite spin number and the scattering rate parameter $\lambda$ on the magnetisation relaxation rates. The relation between the fs demagnetisation rate and the LLG damping, provided by the LLB theory, is checked basing on the available experimental data. A good agreement is obtained for Ni, Co and Gd favoring the idea that the same intrinsic scattering process is acting on the femtosecond and nanosecond timescale.Comment: 9 pages, 7 figure

Transition between radial and toroidal orders in a trimer-based magnetic metasurface

The change in the arrangement of magnetic dipole moments in a magnetic metasurface, due to the influence of an external static magnetic field, is discussed. Each meta-atom of the metasurface is composed of three identical disk-shaped resonators (trimer) made of magnetically saturated ferrite. To provide physical insight, full-wave numerical simulations of the near-fields and transmission characteristics of the metasurface are complemented by the theoretical description based on the multipole decomposition method. With these methods, the study of eigenmodes and scattering conditions of a single magnetic resonator, trimer, and their array forming the metasurface is performed. It is found that the magnetic dipole-based collective hybrid mode of the trimer can be gradually transformed from the radial (pseudomonopole) to azimuthal (toroidal) order and vice versa by varying the bias magnetic field strength. This is because the magnetic dipole moment of each individual disk constituting the trimer undergoes rotation as the bias magnetic field strength changes. This transition between two orders is accompanied by various patterns of localization of the electric field inside the meta-atoms. Due to the unique field configuration of these modes, the proposed metasurface can be considered for designing magnetic field sensors and nonreciprocal devices.Comment: 14 pages, 8 figure

Pressure effect on the in-plane magnetic penetration depth in YBa_2Cu_4O_8

We report a study of the pressure effect (PE) on the in-plane magnetic field penetration depth lambda_{ab} in YBa_2Cu_4O_8 by means of Meissner fraction measurements. A pronounced PE on lambda_{ab}^{-2}(0) was observed with a maximum relative shift of \Delta\lambda^{-2}_{ab}/\lambda^{-2}_{ab}= 44(3)% at a pressure of 10.2 kbar. It arises from the pressure dependence of the effective in-plane charge carrier mass and pressure induced charge carrier transfer from the CuO chains to the superconducting CuO_2 planes. The present results imply that the charge carriers in YBa_2Cu_4O_8 are coupled to the lattice.Comment: 4pages 3 figure

X-ray emission during the muonic cascade in hydrogen

We report our investigations of X rays emitted during the muonic cascade in hydrogen employing charge coupled devices as X-ray detectors. The density dependence of the relative X-ray yields for the muonic hydrogen lines (K_alpha, K_beta, K_gamma) has been measured at densities between 0.00115 and 0.97 of liquid hydrogen density. In this density region collisional processes dominate the cascade down to low energy levels. A comparison with recent calculations is given in order to demonstrate the influence of Coulomb deexcitation.Comment: 5 pages, Tex, 4 figures, submitted to Physical Review Letter

Моделюючий вплив Селену на організм курчат-бройлерів

In recent years, based on new scientific data, many countries worldwide have been revising the existing standards for introducing trace elements in mixed feed for highly productive broiler chicken crosses. This also applies to selenium, which is recognized as an indispensable biotic ultramicroelement with a wide range of biological action according to modern classification. However, some aspects of the selenium effects on poultry have not been elucidated yet. We have conducted comprehensive research to deepen and expand modern ideas about the biological role of selenium, its impact on the interior and productive qualities of broiler chickens in the post-embryonic period of ontogenesis. One of the tasks was to study the causal relationship between the level of selenium consumption by broiler chickens and the studied indicators. The research was conducted on broiler chickens of the Cobb 500 cross. During the rearing period, the feeding of broiler chickens of all groups was carried out with dry full-fledged mixed feeds following the existing norms. The poultry of the first control group did not receive selenium supplementation. The poultry of the second experimental group was additionally injected with Selenium at the rate of 0.2 mg/kg, the third of 0.3, and the fourth of 0.4 mg/kg. When conducting a correlation analysis of the obtained experimental data, it was found that there are different levels and directions of relationship between internal and economically valuable features included in the study, which may vary depending on the selenium content in mixed feed for broiler chickens. A scheme of modeling the effect of selenium on broiler chickens’ bodies is proposed.Останніми роками у багатьох країнах світу переглядаються, із урахуванням нових наукових даних уже існуючі норми введення мікроелементів у комбікорми для високопродуктивних кросів курчат-бройлерів. Це стосується і Селену, який, згідно з сучасною класифікацією, визнаний незамінним біотичним ультрамікроелементом з широким спектром біологічної дії. Проте деякі аспекти впливу Селену на організм птиці ще остаточно не з’ясовані. З метою поглиблення і розширення сучасних уявлень про біологічну роль Селену, його вплив на інтер’єр та продуктивні якості курчат-бройлерів у постембріональний період онтогенезу нами були проведені комплексні наукові дослідження. Одним із завдань було вивчення причинно-наслідкового взаємозв’язку між рівнем споживання курчатами-бройлерами Селену та досліджуваними показниками. Дослідження проводилися на курчатах-бройлерах кросу СОВВ 500. Годівля курчат-бройлерів усіх груп упродовж періоду вирощування здійснювалася сухими повнораціонними комбікормами відповідно до існуючих норм. Птиця першої контрольної групи добавку селену не одержували. Птиці другої дослідної групи у комбікорми додатково вводили Селен із розрахунку 0,2 мг/кг, третьої – 0,3 та четвертої – 0,4 мг/кг. При проведенні кореляційного аналізу одержаних експериментальних даних встановлено, що між інтер’єрними та господарсько корисними ознаками, що входили в аналіз, мають місце різні рівні й напрями взаємозв’язку, які можуть змінюватися залежно від вмісту Селену в комбікормах для курчат-бройлерів. Запропоновано схему моделюючого впливу селену на організм курчат-бройлерів

Neurons Controlling Aplysia Feeding Inhibit Themselves by Continuous NO Production

Neural activity can be affected by nitric oxide (NO) produced by spiking neurons. Can neural activity also be affected by NO produced in neurons in the absence of spiking?Applying an NO scavenger to quiescent Aplysia buccal ganglia initiated fictive feeding, indicating that NO production at rest inhibits feeding. The inhibition is in part via effects on neurons B31/B32, neurons initiating food consumption. Applying NO scavengers or nitric oxide synthase (NOS) blockers to B31/B32 neurons cultured in isolation caused inactive neurons to depolarize and fire, indicating that B31/B32 produce NO tonically without action potentials, and tonic NO production contributes to the B31/B32 resting potentials. Guanylyl cyclase blockers also caused depolarization and firing, indicating that the cGMP second messenger cascade, presumably activated by the tonic presence of NO, contributes to the B31/B32 resting potential. Blocking NO while voltage-clamping revealed an inward leak current, indicating that NO prevents this current from depolarizing the neuron. Blocking nitrergic transmission had no effect on a number of other cultured, isolated neurons. However, treatment with NO blockers did excite cerebral ganglion neuron C-PR, a command-like neuron initiating food-finding behavior, both in situ, and when the neuron was cultured in isolation, indicating that this neuron also inhibits itself by producing NO at rest.Self-inhibitory, tonic NO production is a novel mechanism for the modulation of neural activity. Localization of this mechanism to critical neurons in different ganglia controlling different aspects of a behavior provides a mechanism by which a humeral signal affecting background NO production, such as the NO precursor L-arginine, could control multiple aspects of the behavior