Spin-resonance modes of the spin-gap magnet TlCuCl_3

Three kinds of magnetic resonance signals were detected in crystals of the spin-gap magnet TlCuCl_3. First, we have observed the microwave absorption due to the excitation of the transitions between the singlet ground state and the excited triplet states. This mode has the linear frequency-field dependence corresponding to the previously known value of the zero-field spin-gap of 156 GHz and to the closing of spin-gap at the magnetic field H_c of about 50 kOe. Second, the thermally activated resonance absorption due to the transitions between the spin sublevels of the triplet excitations was found. These sublevels are split by the crystal field and external magnetic field. Finally, we have observed antiferromagnetic resonance absorption in the field-induced antiferromagnetic phase above the critical field H_c. This resonance frequency is strongly anisotropic with respect to the direction of the magnetic field.Comment: v.2: typo correction (one of the field directions was misprinted in the v.1

q-Analog of Gelfand-Graev Basis for the Noncompact Quantum Algebra Uq(u(n,1))

For the quantum algebra Uq(gl(n+1)) in its reduction on the subalgebra Uq(gl(n)) an explicit description of a Mickelsson-Zhelobenko reduction Z-algebra Zq(gl(n+1),gl(n)) is given in terms of the generators and their defining relations. Using this Z-algebra we describe Hermitian irreducible representations of a discrete series for the noncompact quantum algebra Uq(u(n,1)) which is a real form of Uq(gl(n+1)), namely, an orthonormal Gelfand-Graev basis is constructed in an explicit form

Desenvolvimento de sistema de poupança de energia baseado em bomba de calor

This article describes the structure and the operation of energy-saving systems based on a heat pump with the use of renewable energy sources. Using the method of an experiment three-factor active planning, the response surfaces and their two-dimensional cross sections were constructed in the isolines of the transition process duration and the amount of the energy carrier heat from the the electric heater power. The developed energy-saving systems support the temperature regime of an agricultural object by using solar energy, low-potential and artificial energy sources throughout the year. The developed system (option one), installed in hard-to-reach places at agricultural facilities, is designed to generate thermal energy, electricity, and provides significant energy savings during energy supply. Due to the speed of the electric regulator with solid filler and electric heater, the efficiency of the heat pump is increased, which maintains the microclimate parameters of the agricultural object.Este artículo describe la estructura y el funcionamiento de los sistemas de ahorro de energía basados en una bomba de calor con el uso de fuentes de energía renovables. Utilizando el método de un experimento de planificación activa de tres factores, las superficies de respuesta y sus secciones transversales bidimensionales se construyeron en las isolinas de la duración del proceso de transición y la cantidad de calor del portador de energía de la potencia del calentador eléctrico. Los sistemas de ahorro de energía desarrollados apoyan el régimen de temperatura de un objeto agrícola mediante el uso de energía solar, potencial bajo y fuentes de energía artificial durante todo el año. El sistema desarrollado (opción uno), instalado en lugares de difícil acceso en las instalaciones agrícolas, está diseñado para generar energía térmica, electricidad y proporciona ahorros de energía significativos durante el suministro de energía. Debido a la velocidad del regulador eléctrico con relleno sólido y calentador eléctrico, se incrementa la eficiencia de la bomba de calor, lo que mantiene los parámetros de microclima del objeto agrícola.Este artigo descreve a estrutura e a operação de sistemas de economia de energia baseados em uma bomba de calor com o uso de fontes de energia renováveis. Utilizando o método de um planejamento ativo de três fatores experimentais, as superfícies de resposta e suas seções transversais bidimensionais foram construídas nas isolinhas da duração do processo de transição e na quantidade de calor do portador de energia a partir da potência do aquecedor elétrico. Os sistemas de economia de energia desenvolvidos suportam o regime de temperatura de um objeto agrícola usando energia solar, fontes de energia artificiais e com baixo potencial ao longo do ano. O sistema desenvolvido (opção 1), instalado em locais de difícil acesso em instalações agrícolas, é projetado para gerar energia térmica, eletricidade e proporcionar economias de energia significativas durante o fornecimento de energia. Devido à velocidade do regulador elétrico com enchimento sólido e aquecedor elétrico, a eficiência da bomba de calor é aumentada, o que mantém os parâmetros microclima do objeto agrícola

Separation of the magnetic phases at the N\'{e}el point in the diluted spin-Peierls magnet CuGeO3

The impurity induced antiferromagnetic ordering of the doped spin-Peierls magnet Cu(1-x)Mg(x)GeO(3) was studied by ESR technique. Crystals with the Mg concentration x<4% demonstrate a coexistence of paramagnetic and antiferromagnetic ESR modes. This coexistence indicates the separation of a macroscopically uniform sample in the paramagnetic and antiferromagnetic phases. In the presence of the long-range spin-Peierls order (in a sample with x=1.71%) the volume of the antiferromagnetic phase immediately below the N\'{e}el point T_N is much smaller than the volume of the paramagnetic phase. In the presence of the short-range spin-Peierls order (in samples with x=2.88%, x= 3.2%) there are comparable volumes of paramagnetic and antiferromagnetic phases at T=T_N. The fraction of the antiferromagnetic phase increases with lowering temperature. In the absence of the spin-Peierls dimerization (at x=4.57%)the whole sample exhibits the transition into the antiferromagnetic state and there is no phase separation. The phase separation is explained by the consideration of clusters of staggered magnetization located near impurity atoms. In this model the areas occupied by coherently correlated spins expand with decreasing temperature and the percolation of the ordered area through a macroscopic distance occurs.Comment: 7pages, 10 figure

Investigation of thermal and magnetic properties of defects in a spin-gap compound NaV2O5

The specific heat, magnetic susceptibility and ESR signals of a Na-deficient vanadate Na_xV_2O_5 (x=1.00 - 0.90) were studied in the temperature range 0.07 - 10 K, well below the transition point to a spin-gap state. The contribution of defects provided by sodium vacancies to the specific heat was observed. It has a low temperature part which does not tend to zero till at least 0.3 K and a high temperature power-like tail appears above 2 K. Such dependence may correspond to the existence of local modes and correlations between defects in V-O layers. The magnetic measurements and ESR data reveal S=1/2 degrees of freedom for the defects, with their effective number increasing in temperature and under magnetic field. The latter results in the nonsaturating magnetization at low temperature. No long-range magnetic ordering in the system of defects was found. A model for the defects based on electron jumps near vacancies is proposed to explain the observed effects. The concept of a frustrated two-dimensional correlated magnet induced by the defects is considered to be responsible for the absence of magnetic ordering.Comment: 6 pages, 8 figure

Search for light pseudoscalar sgoldstino in K- decays

A search for the light pseudoscalar sgoldstino production in the three body K- decay K-->pipi0P has been performed with the ISTRA+ detector exposed to the 25 GeV negative secondary beam of the U70 proton synchrotron. No signal is seen. An upper limit for the branching ratio Br(K->pipi0P), at 90% confidence level, is found to be around 9*10**-6 in the effective mass m(P) range from 0 till 200 MeV, excluding the region near m(pi0) where it degrades to 3.5*10**-5.Comment: 10 pages, LATEX, 8 EPS figures, revised version, to be published in Phys.Lett.