3,060 research outputs found
Magnetic quantum tunnelling in Fe8 with excited nuclei
We investigate the effect of dynamic nuclear spin fluctuation on quantum
tunneling of the magnetization (QTM) in the molecular magnet Fe8 by increasing
the nuclei temperature using radio frequency (RF) pulses before the hysteresis
loop measurements. The RF pulses do not change the electrons spin temperature.
Independently we show that the nuclear spin-spin relaxation time T2 has strong
temperature dependence. Nevertheless, we found no effect of the nuclear spin
temperature on the tunneling probability. This suggests that in our
experimental conditions only the hyperfine field strength is relevant for QTM.
We demonstrate theoretically how this can occur.Comment: 4 pages, 4 figure
A new deep-water species of Myopiarolis Bruce, 2009 (Crustacea: Isopoda: Serolidae) from New Zealand waters
Myopiarolis tona sp. nov. is described from the Challenger Plateau, southern Lord Howe Rise and the west coast of the North Island, New Zealand at depths of 634–1250 m. M. tona sp. nov. can be identified by the prominent posteriorly directed dorsal nodule on fused pereonites 5–7. There are nine species in four genera of the cold-water, epibenthic family Serolidae recorded from New Zealand waters, three species of Myopiarolis Bruce, 2009, one undescribed species of Acutiserolis Brandt, 1988, four of Brucerolis Poore and Storey, 2009 and the monotypic Spinoserolis Brandt, 1988
Scaling behavior in steady-state contractile actomyosin network flow
Contractile actomyosin network flows are crucial for many cellular processes
including cell division and motility, morphogenesis and transport. How local
remodeling of actin architecture tunes stress production and dissipation and
regulates large-scale network flow remains poorly understood. Here, we generate
contractile actomyosin networks with rapid turnover in vitro, by encapsulating
cytoplasmic Xenopus egg extracts into cell-sized 'water-in-oil' droplets.
Within minutes, the networks reach a dynamic steady-state with continuous
inward flow. The networks exhibit homogenous, density-independent contraction
for a wide range of physiological conditions, indicating that the
myosin-generated stress driving contraction is proportional to the effective
network viscosity. We further find that the contraction rate approximately
scales with the network turnover rate, but this relation breaks down in the
presence of excessive crosslinking or branching. Our findings suggest that
cells use diverse biochemical mechanisms to generate robust, yet tunable, actin
flows by regulating two parameters: turnover rate and network geometry
A quest for frustration driven distortion in Y2Mo2O7
We investigated the nature of the freezing in the geometrically frustrated
Heisenberg spin-glass Y2Mo2O7 by measuring the temperature dependence of the
static internal magnetic field distribution above the spin-glass temperature,
Tg, using the muSR technique. The evolution of the field distribution cannot be
explained by changes in the spin susceptibility alone and suggests a lattice
deformation. This possibility is addressed by numerical simulations of the
Heisenberg Hamiltonian with magneto-elastic coupling at T>0.Comment: 5 pages 4 figures. Accepted for publication in PR
Experimental investigation of the origin of the cross-over temperature in the cuprates
We investigate the cross-over temperature T* as a function of doping in
(Ca_{x}La_{1-x})(Ba_{1.75-x}La_{0.25+x})Cu_3O_{y}, where the maximum Tc
(Tc^max) varies continuously by 30% between families (x) with minimal
structural changes. T* is determined by DC-susceptibility measurements. We find
that T* scales with the maximum Neel temperature TN^max of each family. This
result strongly supports a magnetic origin of T*, and indicates that three
dimensional interactions play a role in its magnitude.Comment: 4 pages, 4 figure
Ga NMR study of the local susceptibility in SrCr8Ga4O19: pseudogap and paramagnetic defects
We present the first Ga(4f) NMR study of the Cr susceptibility in the
archetype of Kagome based frustrated antiferromagnets,
SrCrGaO. Our major finding is that the susceptibility of the
frustrated lattice goes through a maximum around 50 K. Our data also supports
the existence of paramagnetic ``clusters'' of spins, responsible for the Curie
behavior observed in the macroscopic susceptibility at low T. These results set
novel features for the constantly debated physics of geometrically frustrated
magnets.Comment: 4 pages, 5 figures Submitted to Phys. Rev. Let
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