588 research outputs found
Millimeter wave transmission spectroscopy of gated two-dimensional hole systems
We developed a differential transmission to study cyclotron resonance of GaAs/AlxGa1 xAs
two-dimensional hole samples. The technique utilizes a modulated AuPd gate isolated by a Si3N4
dielectric from the sample, which is irradiated opposite the gate by millimeter waves ranging from
2 to 40GHz. This technique effectively removes the background signal and yields a hole effective
mass of 0:41me with a cyclotron scattering time of 20 ps, consistent with the previous results using
different techniques
Strongly Anisotropic Transport in Higher Two-Dimensional Landau Levels
Low-temperature, electronic transport in Landau levels N>1 of a
two-dimensional electron system is strongly anisotropic. At half-filling of
either spin level of each such Landau level the magnetoresistance either
collapses to form a deep minimum or is peaked in a sharp maximum, depending on
the in-plane current direction. Such anisotropies are absent in the N=0 and N=1
Landau level, which are dominated by the states of the fractional quantum Hall
effect. The transport anisotropies may be indicative of a new many particle
state, which forms exclusively in higher Landau levels.Comment: 12 pages, 3 Postscript figure
Ultrafast photoisomerisation of an isolated retinoid
The photoinduced excited state dynamics of gas-phase trans-retinoate (deprotonated trans-retinoic acid, trans-RA−) are studied using tandem ion mobility spectrometry coupled with laser spectroscopy, and frequency-, angle- and time-resolved photoelectron imaging. Photoexcitation of the bright S3(ππ*) ← S0 transition leads to internal conversion to the S1(ππ*) state on a ≈80 fs timescale followed by recovery of S0 and concomitant isomerisation to give the 13-cis (major) and 9-cis (minor) photoisomers on a ≈180 fs timescale. The sub-200 fs stereoselective photoisomerisation parallels that for the retinal protonated Schiff base chromophore in bacteriorhodopsin. Measurements on trans-RA− in methanol using the solution photoisomerisation action spectroscopy technique show that 13-cis-RA− is also the principal photoisomer, although the 13-cis and 9-cis photoisomers are formed with an inverted branching ratio with photon energy in methanol when compared with the gas phase, presumably due to solvent-induced modification of potential energy surfaces and inhibition of electron detachment processes. Comparison of the gas-phase time-resolved data with transient absorption spectroscopy measurements on retinoic acid in methanol suggest that photoisomerisation is roughly six times slower in solution. This work provides clear evidence that solvation significantly affects the photoisomerisation dynamics of retinoid molecules
Curvature corrections and Kac-Moody compatibility conditions
We study possible restrictions on the structure of curvature corrections to
gravitational theories in the context of their corresponding Kac--Moody
algebras, following the initial work on E10 in Class. Quant. Grav. 22 (2005)
2849. We first emphasize that the leading quantum corrections of M-theory can
be naturally interpreted in terms of (non-gravity) fundamental weights of E10.
We then heuristically explore the extent to which this remark can be
generalized to all over-extended algebras by determining which curvature
corrections are compatible with their weight structure, and by comparing these
curvature terms with known results on the quantum corrections for the
corresponding gravitational theories.Comment: 27 page
New insulating phases of two-dimensional electrons in high Landau levels: observation of sharp thresholds to conduction
The intriguing re-entrant integer quantized Hall states recently discovered
in high Landau levels of high-mobility 2D electron systems are found to exhibit
extremely non-linear transport. At small currents these states reflect
insulating behavior of the electrons in the uppermost Landau level. At larger
currents, however, a discontinuous and hysteretic transition to a conducting
state is observed. These phenomena, found only in very narrow magnetic field
ranges, are suggestive of the depinning of a charge density wave state, but
other explanations can also be constructed.Comment: 5 pages, 5 figure
Trail Over-Expression on Donor T Cells Enhances GVT and Suppresses GVHD by Inhibiting Alloreactive T Cells and Impairing Host APC Functions
On complexity of special maximum matchings constructing
For bipartite graphs the NP-completeness is proved for the problem of
existence of maximum matching which removal leads to a graph with given
lower(upper)bound for the cardinality of its maximum matching.Comment: 12 pages, 8 figures. Discrete Mathematics, to appea
AdS/CFT Equivalence Transformation
We show that any conformal field theory in d-dimensional Minkowski space, in
a phase with spontaneously broken conformal symmetry and with the dilaton among
its fields, can be rewritten in terms of the static gauge (d-1)-brane on
AdS_(d+1) by means of an invertible change of variables. This nonlinear
holographic transformation maps the Minkowski space coordinates onto the brane
worldvolume ones and the dilaton onto the transverse AdS brane coordinate. One
of the consequences of the existence of this map is that any (d-1)-brane
worldvolume action on AdS_(d+1)\times X^m (with X^m standing for the sphere S^m
or more complicated curved manifold) admits an equivalent description in
Minkowski space as a nonlinear and higher-derivative extension of some
conventional conformal field theory action, with the conformal group being
realized in a standard way. The holographic transformation explicitly relates
the standard realization of the conformal group to its field-dependent
nonlinear realization as the isometry group of the brane AdS_(d+1) background.
Some possible implications of this transformation, in particular, for the study
of the quantum effective action of N=4 super Yang-Mills theory in the context
of AdS/CFT correspondence, are briefly discussed.Comment: LaTeX, 19 pages, minor correction in Abstrac
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