4,320 research outputs found
Quantum Spin Hall Insulator State in HgTe Quantum Wells
Recent theory predicted that the Quantum Spin Hall Effect, a fundamentally
novel quantum state of matter that exists at zero external magnetic field, may
be realized in HgTe/(Hg,Cd)Te quantum wells. We have fabricated such sample
structures with low density and high mobility in which we can tune, through an
external gate voltage, the carrier conduction from n-type to the p-type,
passing through an insulating regime. For thin quantum wells with well width d
< 6.3 nm, the insulating regime shows the conventional behavior of vanishingly
small conductance at low temperature. However, for thicker quantum wells (d >
6.3 nm), the nominally insulating regime shows a plateau of residual
conductance close to 2e^2/h. The residual conductance is independent of the
sample width, indicating that it is caused by edge states. Furthermore, the
residual conductance is destroyed by a small external magnetic field. The
quantum phase transition at the critical thickness, d = 6.3 nm, is also
independently determined from the magnetic field induced insulator to metal
transition. These observations provide experimental evidence of the quantum
spin Hall effect.Comment: 16 pages, 5 figure
Exact entanglement renormalization for string-net models
We construct an explicit renormalization-group transformation for Levin and Wenâs string-net models on a hexagonal lattice. The transformation leaves invariant the ground-state âfixed-pointâ wave function of the string-net condensed phase. Our construction also produces an exact representation of the wave function in terms of the multiscale entanglement renormalization ansatz (MERA). This sets the stage for efficient numerical simulations of string-net models using MERA algorithms. It also provides an explicit quantum circuit to prepare the string-net ground-state wave function using a quantum computer
A large-deviations principle for all the cluster sizes of a sparse ErdĆsâRĂ©nyi graph
Let (Formula presented.) be the ErdĆsâRĂ©nyi graph with connection probability (Formula presented.) as N â â for a fixed t â (0, â). We derive a large-deviations principle for the empirical measure of the sizes of all the connected components of (Formula presented.), registered according to microscopic sizes (i.e., of finite order), macroscopic ones (i.e., of order N), and mesoscopic ones (everything in between). The rate function explicitly describes the microscopic and macroscopic components and the fraction of vertices in components of mesoscopic sizes. Moreover, it clearly captures the well known phase transition at t = 1 as part of a comprehensive picture. The proofs rely on elementary combinatorics and on known estimates and asymptotics for the probability that subgraphs are connected. We also draw conclusions for the strongly related model of the multiplicative coalescent, the MarcusâLushnikov coagulation model with monodisperse initial condition, and its gelation phase transition
Evaluation of aircraft microwave data for locating zones for well stimulation and enhanced gas recovery
Imaging radar was evaluated as an adjunct to conventional petroleum exploration techniques, especially linear mapping. Linear features were mapped from several remote sensor data sources including stereo photography, enhanced LANDSAT imagery, SLAR radar imagery, enhanced SAR radar imagery, and SAR radar/LANDSAT combinations. Linear feature maps were compared with surface joint data, subsurface and geophysical data, and gas production in the Arkansas part of the Arkoma basin. The best LANDSAT enhanced product for linear detection was found to be a winter scene, band 7, uniform distribution stretch. Of the individual SAR data products, the VH (cross polarized) SAR radar mosaic provides for detection of most linears; however, none of the SAR enhancements is significantly better than the others. Radar/LANDSAT merges may provide better linear detection than a single sensor mapping mode, but because of operator variability, the results are inconclusive. Radar/LANDSAT combinations appear promising as an optimum linear mapping technique, if the advantages and disadvantages of each remote sensor are considered
Further evidence that imbalance of WT1 isoforms may be involved in Denys-Drash syndrome
No abstract availabl
Exploring the environment, magnetic fields, and feedback effects of massive high-redshift galaxies with [CII]
Massive galaxies are expected to grow through different transformative
evolutionary phases where high-redshift starburst galaxies and quasars are
examples of such phases. The physical mechanisms driving these phases include
companion galaxy interactions, active galactic nuclei feedback, and magnetic
fields. Our aim is to characterize the physical properties and the environment
of the submillimeter galaxy AzTEC-3 at z = 5.3 and the lensed quasar BRI
0952-0115 at z = 4.4, to set a limit on the polarization properties, as well as
placing both in the broader context of galaxy evolution. We used full
polarization, sub-arcsecond-resolution, ALMA band-7 observations of both BRI
0952-0115 and AzTEC-3 and detect [CII] line emission towards both galaxies,
along with companions in each field. We present an updated gravitational
lensing model for BRI 0952-0115. We present infrared luminosities,
star-formation rates, and [CII] line to infrared luminosity ratios for each
source. The [CII] emission line profile for both BRI 0952-0115 and AzTEC-3
exhibit a broad, complex morphology, indicating the possible presence of
outflows. We present evidence of a 'gas bridge' between AzTEC-3 and a companion
source. Using a simple dynamical mass estimate for the sources, we suggest that
both systems are undergoing minor or major mergers. No polarization is detected
for the [CII], placing an upper limit below that of theoretical predictions.
Our results show that high-velocity wings are detected, indicating possible
signs of massive outflows; however, the presence of companion galaxies can
affect the final interpretation. Furthermore, the results provide additional
evidence in support of the hypothesis that massive galaxies form in overdense
regions, growing through interactions. Finally, strong, ordered magnetic fields
are unlikely to exist at the kiloparsec scale in the two studied sources
A human MAP kinase interactome.
Mitogen-activated protein kinase (MAPK) pathways form the backbone of signal transduction in the mammalian cell. Here we applied a systematic experimental and computational approach to map 2,269 interactions between human MAPK-related proteins and other cellular machinery and to assemble these data into functional modules. Multiple lines of evidence including conservation with yeast supported a core network of 641 interactions. Using small interfering RNA knockdowns, we observed that approximately one-third of MAPK-interacting proteins modulated MAPK-mediated signaling. We uncovered the Na-H exchanger NHE1 as a potential MAPK scaffold, found links between HSP90 chaperones and MAPK pathways and identified MUC12 as the human analog to the yeast signaling mucin Msb2. This study makes available a large resource of MAPK interactions and clone libraries, and it illustrates a methodology for probing signaling networks based on functional refinement of experimentally derived protein-interaction maps
Synchronized dynamics of cortical neurons with time-delay feedback
The dynamics of three mutually coupled cortical neurons with time delays in
the coupling are explored numerically and analytically. The neurons are coupled
in a line, with the middle neuron sending a somewhat stronger projection to the
outer neurons than the feedback it receives, to model for instance the relay of
a signal from primary to higher cortical areas. For a given coupling
architecture, the delays introduce correlations in the time series at the
time-scale of the delay. It was found that the middle neuron leads the outer
ones by the delay time, while the outer neurons are synchronized with zero lag
times. Synchronization is found to be highly dependent on the synaptic time
constant, with faster synapses increasing both the degree of synchronization
and the firing rate. Analysis shows that presynaptic input during the
interspike interval stabilizes the synchronous state, even for arbitrarily weak
coupling, and independent of the initial phase. The finding may be of
significance to synchronization of large groups of cells in the cortex that are
spatially distanced from each other.Comment: 21 pages, 11 figure
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