The parallel susceptibility at 0 K of the double magnetic helix

The parallel susceptibility x^∥ at 0 K of a double magnetic helix of pitch angle ? in which two species of magnetic ions are acted on by unequal molecular fields is determined. The conditions under which x^∥ is equal to the 0 K perpendicular susceptibility x^⊥ calculated in the past are determined. Comparison is made with the powder susceptibility measurements performed on the orthorhombic compound La₂Fe_1.5Mn_0.5S₅ which displays a double magnetic helix up to T_N = 85 K.     

Behaviour of ferrocholesterics under external magnetic fields

The influence of an external magnetic field on the orientational behaviour of a ferrocholesteric with a positive magnetic anisotropy is investigated. Both the phenomena arising when the field was switched on or switched off are considered. It is found that the field needed for a ferrocholesteric–ferronematic transition B_FC↑ is higher when compared to that obtained for the pure cholesteric (B_C↑). A similar result was obtained when estimating the critical field for the homeotropic ferronematic–ferrocholesteric (focal conic) transition, occurring when the magnetic field was decreased or switched off. We found that B_FC↓>B_C↓. These results are explained when considering that the magnetic moments of the magnetic powder are not oriented parallel to the liquid crystal molecular directors, therefore hindering their orientation under a magnetic field.     

Behaviour and spectroscopy of (anti) hydrogen atoms in strong magnetic fields

Since it has been demonstrated that antiprotons can be captured in sizeable amounts in ion traps, the intriguing question has been raised whether or not these antiprotons can be used for producingantihydrogen atoms. One route proposed is the merging of trapped antiprotons with a cold trapped plasma of positrons. In this case the formation of antihydrogen proceeds most likely through three-body recombination (p⁻e⁺e⁺→ e⁺) into high Rydberg states of , followed by a rapid cascade of transitions to low-lying states. To assess the influence of the trapping magnetic field (on the order of a few tesla) upon the formation process of we review the present knowledge of the behaviour and properties of hydrogen (and antihydrogen) atoms in strong magnetic fields — a subject which has been very topical in recent years because of its relation to the problem of “quantum” chaos.     

Charge transport along the lambda-DNA double helix

We have measured the conductivity sigma along the lambda phage DNA (lambda-DNA) double helix at microwave frequencies using lyophilized DNA in and also without a buffer. The conductivity is strongly temperature dependent around room temperature with a crossover to a weakly temperature dependent conductivity at low temperatures. Removal of the water mantle around the double helix leads to reduced conductivity.     

Behaviour of two‐dimensional liquid dusty plasmas under perpendicular magnetic fields

The collective behaviour of two‐dimensional (2D) liquid dusty plasmas under perpendicular magnetic fields is studied using Langevin dynamic simulations. Based on the positions and velocities of the simulated dust particles, the dynamic parameters of intermediate scattering functions and probability distribution functions are calculated. It is found that, under different 2D liquid dusty plasma conditions, the motion of individual dust particles tends to be more super‐diffusive under stronger perpendicular magnetic fields, well consistent with the previous finding using a different diagnostic technique.     

Quantum hall effect at low magnetic fields

The temperature and scale dependence of resistivities in the standard scaling theory of the integer quantum Hall effect is discussed. It is shown that recent experiments, claiming to observe a discrepancy with the global phase diagram of the quantum Hall effect, are in fact in agreement with the standard theory. The apparent low-field transition observed in the experiments is identified as a crossover due to weak localization and a strong reduction of the conductivity when Landau quantization becomes dominant.     

Thickness dependence of the perpendicular critical magnetic fields of Pb/Cu double layers

We have investigated the proximity effect of a normal metal (Cu) on the perpendicular critical magnetic fields H_c⊥ of superconducting Pb-films. Special attention was devoted to the dependence of H_c⊥ on the thickness of the superconducting layers. The experimental results are compared with calculations based on the Ginzburg-Landau theory.     

Oscillations of the magnetic polarization in a Kondo system at finite magnetic fields

The electronic properties of a Kondo impurity are investigated in a magnetic field using linear response theory. The distribution of electrical charge and magnetic polarization are calculated in real space. The (small) magnetic field does not change the charge distribution. However, it unmasks the Kondo cloud and generates a Kondo polarization. The weight of the d-electron components with their magnetic moment up and down is shifted and the compensating moments of the s-electron clouds don’t cancel any longer (a requirement for an experimental detection of the Kondo cloud). In addition to the polarization cloud (of the conduction electrons) an oscillating polarization component with a period of half the Fermi wave length is observed. This represents an internal electronic structure of the Kondo impurity.     

Breathing modes and induced resonant melting of the double helix

Breathing modes are found in double helical DNA which can induce melting by excessive stretching of H-bonds. Energy for such melting may be supplied by splitting of nucleoside triphosphate bonds.     

Perturbed soliton excitations in the DNA double helix

We study the nonlinear dynamics of the inhomogeneous DNA double-helical chain using the dynamic plane-base rotator model by considering angular rotation of bases in a plane normal to the helical axis. The DNA dynamics in this case is found to be governed by a perturbed sine-Gordon equation, while taking into account the interstrand hydrogen bonding energy, between bases, and the intrastrand inhomogeneous stacking energy and by making an analogy with the Heisenberg model of the Hamiltonian of an inhomogeneous anisotropic spin ladder with ferromagnetic legs and antiferromagnetic rung coupling. In the homogeneous limit the dynamics is governed by the kink-antikink soliton of the sine-Gordon equation which represents the formation of an open state configuration in the DNA double helix. The effect of inhomogeneity in the stacking energy in the form of localized and periodic variations on the formation of open states in DNA is studied under perturbation. The perturbed soliton is obtained using a multiple-scale soliton perturbation theory by solving the associated linear eigenvalue problem and by constructing the complete set of eigenfunctions. The inhomogeneity in stacking energy is found to modulate the width and speed of the soliton depending on the nature of the inhomogeneity. Also it introduces fluctuations in the form of a train of pulses or periodic oscillations in the open state configuration.     

双量子阱结构OLED效率和电流的磁效应

通过结构为ITO/NPB(60 nm)/ Alq₃ ∶1 wt% rubrene(20 nm)/ Alq₃(3 nm)/ Alq₃ ∶1 wt% rubrene(20 nm)/ Alq₃(20 nm)/LiF/Al的双量子阱的黄色有机电致发光器件,研究了不同磁场强度下的发光效率和电流变化特性. 研究结果表明该器件的电流是随着磁场强度的增加而单调下降的,显示了器件的电阻是随着磁场强度的增加而增加的. 同时也得到了该结构有 关键词： 量子阱 磁场 OLED 磁效应     

Electron-phonon scattering in potassium at high magnetic fields

We have measured the temperature dependence of both the zero-field resistivity and the transverse magnetoresistance of polycrystalline potassium wires (?(300 K)/?(4.2 K)=140 to 6000) in fieldsH?35 kG and at temperaturesT?4.2 K. Our principal findings are: 1) The presence of a large magnetic fieldH=35 kG does not alter the temperature dependence of ? from that observed atH=0; below 4.2 K theT-dependent part of the resistivities,_?T (H=0) and_?T (H=35 kG), fit well to the function exp (?Θ*/T) with the same Θ*=23K. 2) Deviations from Matthiessen's rule are significantly reduced in a strong field so that the magnitude of_?T (H=0) approaches that of_?T (H=35 kG) as sample purity decreases. 3) The slope of the high-field linear magnetoresistance increases slightly (?8%) from 1.5 K to 4.2 K. We attribute the exponential temperature dependence of_?T (H) to the freezing out of electron-phonon umklapp processes as has been shown for the zero-field resistivity. The reduction in deviations from Matthiessen's rule at high fields can be understood within semiclassical theory, but the latter cannot explain the failure of_?T (H) to saturate at high fields. A proposal by Young that electron-phonon umklapp scattering may contribute aT-dependent high-field linear magnetoresistance in potassium is considered.