534 research outputs found
Microwave Absorption of Surface-State Electrons on Liquid He
We have investigated the intersubband transitions of surface state electrons
(SSE) on liquid He induced by microwave radiation at temperatures from 1.1
K down to 0.01 K. Above 0.4 K, the transition linewidth is proportional to the
density of He vapor atoms. This proportionality is explained well by Ando's
theory, in which the linewidth is determined by the electron - vapor atom
scattering. However, the linewidth is larger than the calculation by a factor
of 2.1. This discrepancy strongly suggests that the theory underestimates the
electron - vapor atom scattering rate. At lower temperatures, the absorption
spectrum splits into several peaks. The multiple peak structure is partly
attributed to the spatial inhomogeneity of the static holding electric field
perpendicular to the electron sheet.Comment: 15 pages, 7 figures, submitted to J. Phys. Soc. Jp
Rotation-induced 3D vorticity in 4He superfluid films adsorbed on a porous glass
Detailed study of torsional oscillator experiments under steady rotation up
to 6.28 rad/sec is reported for a 4He superfluid monolayer film formed in 1
micrometer-pore diameter porous glass. We found a new dissipation peak with the
height being in proportion to the rotation speed, which is located to the lower
temperature than the vortex pair unbinding peak observed in the static state.
We propose that 3D coreless vortices ("pore vortices") appear under rotation to
explain this new peak. That is, the new peak originates from dissipation close
to the pore vortex lines, where large superfluid velocity shifts the vortex
pair unbinding dissipation to lower temperature. This explanation is confirmed
by observation of nonlinear effects at high oscillation amplitudes.Comment: 4pages, 5figure
Observation of non-classical rotational inertia in bulk solid 4He
In recent torsional oscillator experiments by Kim and Chan (KC), a decrease
of rotational inertia has been observed in solid 4He in porous materials and in
a bulk annular channel. This observation strongly suggests the existence of
"non-classical rotational inertia" (NCRI), i.e. superflow, in solid 4He. In
order to study such a possible "supersolid" phase, we perform torsional
oscillator experiments for cylindrical solid 4He samples. We have observed
decreases of rotational inertia below 200 mK for two solid samples (pressures P
= 4.1 and 3.0 MPa). The observed NCRI fraction at 70 mK is 0.14 %, which is
about 1/3 of the fraction observed in the annulus by KC. Our observation is the
first experimental confirmation of the possible supersolid finding by KC.Comment: 6 pages, 3 firures, submitted to J. Low Temp. Phys. (Proceedings of
QFS2006
Non-Classical Response from Quench-Cooled Solid Helium Confined in Porous Gold
We have investigated the non-classical response of solid 4He confined in
porous gold set to torsional oscillation. When solid helium is grown rapidly,
nearly 7% of the solid helium appears to be decoupled from the oscillation
below about 200 mK. Dissipation appears at temperatures where the decoupling
shows maximum variation. In contrast, the decoupling is substantially reduced
in slowly grown solid helium. The dynamic response of solid helium was also
studied by imposing a sudden increase in the amplitude of oscillation. Extended
relaxation in the resonant period shift, suggesting the emergence of the
pinning of low energy excitations, was observed below the onset temperature of
the non-classical response. The motion of a dislocation or a glassy solid is
restricted in the entangled narrow pores and is not likely responsible for the
period shift and long relaxation
Time-dependent approach to three-body rearrangement collisions: Application to the capture of heavy negatively charged particles by hydrogen atoms
We present a theoretical method for Coulomb three-body rearrangement collisions solving a Chew-Goldberger-type integral equation directly. The scattering boundary condition is automatically satisfied by adiabatically switching on the interaction between the projectile and hydrogen atom. Hence the outgoing wave function is obtained without the tedious procedure of adjusting the total wave function in the asymptotic region. All the dynamical information can be derived from the outgoing wave function obtained on pseudospectral grids numerically. Taking µ−+H(1s) and [overline p]+H(1s) collisions as examples, we demonstrate the usefulness and powerfulness of the method and present the state-specified capture cross sections of heavy negatively charged particles by hydrogen atoms. The convergence and accuracy of the numerical procedure are examined with sufficient care
Binding of molecules to DNA and other semiflexible polymers
A theory is presented for the binding of small molecules such as surfactants
to semiflexible polymers. The persistence length is assumed to be large
compared to the monomer size but much smaller than the total chain length. Such
polymers (e.g. DNA) represent an intermediate case between flexible polymers
and stiff, rod-like ones, whose association with small molecules was previously
studied. The chains are not flexible enough to actively participate in the
self-assembly, yet their fluctuations induce long-range attractive interactions
between bound molecules. In cases where the binding significantly affects the
local chain stiffness, those interactions lead to a very sharp, cooperative
association. This scenario is of relevance to the association of DNA with
surfactants and compact proteins such as RecA. External tension exerted on the
chain is found to significantly modify the binding by suppressing the
fluctuation-induced interaction.Comment: 15 pages, 7 figures, RevTex, the published versio
Bose-Einstein Condensate in Solid Helium
We present neutron scattering measurements of the atomic momentum
distribution, n(k), in solid helium under a pressure p = 41 bars and at
temperatures between 80 mK and 500 mK. The aim is to determine whether there is
Bose-Einstein condensation (BEC) below the critical temperature, T_c = 200 mK
where a superfluid density has been observed. Assuming BEC appears as a
macroscopic occupation of the k = 0 state below T_c, we find a condensate
fraction of n_0 = (-0.10 \pm 1.20)% at T = 80 mK and n_0 = (0.08\pm0.78)% at T
= 120 mK, consistent with zero. The shape of n(k) also does not change on
crossing T_c within measurement precision.Comment: 4 pages, 5 figures (in press
Preliminary evidence of dual-marked lymphocytes in thoracic duct lymph fluid
Thoracic duct lymphocytes from patients receiving thoracic duct drainage as a pretransplant therapy were examined for cell surface markers. Patients followed over the drainage time period showed a variable but decreasing percentage of E-rosette-positive cells in the lymph fluid. A substantial percentage of these E-rosette-positive cells also had C3 receptors on their cell surface. Reactions of the whole lymphocytes with a heteroantisera to human B-lymphocyte antigens reflected the increasing proportion of B cells in the sample, but also indicated that a fraction of the T cells have Ia-like antigens on their surface. Some cells may have all 3 surface marker characteristics. Significance of these cells with respect to graft survival is discussed
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