21,569 research outputs found
Geothermal Heat Flux and its Influence on the Oceanic Abyssal Circulation and Radiocarbon Distribution
Simulation of interaction Hamiltonians by quantum feedback: a comment on the dynamics of information exchange between coupled systems
Since quantum feedback is based on classically accessible measurement
results, it can provide fundamental insights into the dynamics of quantum
systems by making available classical information on the evolution of system
properties and on the conditional forces acting on the system. In this paper,
the feedback-induced interaction dynamics between a pair of quantum systems is
analyzed. It is pointed out that any interaction Hamiltonian can be simulated
by local feedback if the levels of decoherence are sufficiently high. The
boundary between genuine entanglement generating quantum interactions and
non-entangling classical interactions is identified and the nature of the
information exchange between two quantum systems during an interaction is
discussed.Comment: 14 pages, 4 figures; invited paper for the special issue of J. Opt. B
on quantum contro
Seeing is Believing: Dynamic Evolution of Gene Families
Department of Integrative Biology, Center for Computational Biology, Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, TX 78712Supported by National Science Foundation Grants IOS- 0843712 and IOS-1354942 (to H.A.H.) and DBI-0939454 for the BEACON Center for the Study of Evolution in Action.Integrative Biolog
Quantum parallelism of the controlled-NOT operation: an experimental criterion for the evaluation of device performance
It is shown that a quantum controlled-NOT gate simultaneously performs the
logical functions of three distinct conditional local operations. Each of these
local operations can be verified by measuring a corresponding truth table of
four local inputs and four local outputs. The quantum parallelism of the gate
can then be observed directly in a set of three simple experimental tests, each
of which has a clear intuitive interpretation in terms of classical logical
operations. Specifically, quantum parallelism is achieved if the average
fidelity of the three classical operations exceeds 2/3. It is thus possible to
evaluate the essential quantum parallelism of an experimental controlled-NOT
gate by testing only three characteristic classical operations performed by the
gate.Comment: 6 pages, no figures, added references and discussio
Implications of the VHE Gamma-Ray Detection of the Quasar 3C279
The MAGIC collaboration recently reported the detection of the quasar 3C279
at > 100 GeV gamma-ray energies. Here we present simultaneous optical (BVRI)
and X-ray (RXTE PCA) data from the day of the VHE detection and discuss the
implications of the snap-shot spectral energy distribution for jet models of
blazars. A one-zone synchrotron-self-Compton origin of the entire SED,
including the VHE gamma-ray emission can be ruled out. The VHE emission could,
in principle, be interpreted as Compton upscattering of external radiation
(e.g., from the broad-line regions). However, such an interpretation would
require either an unusually low magnetic field of B ~ 0.03 G or an
unrealistically high Doppler factor of Gamma ~ 140. In addition, such a model
fails to reproduce the observed X-ray flux. This as well as the lack of
correlated variability in the optical with the VHE gamma-ray emission and the
substantial gamma-gamma opacity of the BLR radiation field to VHE gamma-rays
suggests a multi-zone model. In particular, an SSC model with an emission
region far outside the BLR reproduces the simultaneous X-ray -- VHE gamma-ray
spectrum of 3C279. Alternatively, a hadronic model is capable of reproducing
the observed SED of 3C279 reasonably well. However, the hadronic model requires
a rather extreme jet power of L_j ~ 10^{49} erg s^{-1}, compared to a
requirement of L_j ~ 2 X 10^{47} erg s^{-1} for a multi-zone leptonic model.Comment: Accepted for pulication. Several clarifications and additions to the
manuscript to match the accepted versio
Computing Web-scale Topic Models using an Asynchronous Parameter Server
Topic models such as Latent Dirichlet Allocation (LDA) have been widely used
in information retrieval for tasks ranging from smoothing and feedback methods
to tools for exploratory search and discovery. However, classical methods for
inferring topic models do not scale up to the massive size of today's publicly
available Web-scale data sets. The state-of-the-art approaches rely on custom
strategies, implementations and hardware to facilitate their asynchronous,
communication-intensive workloads.
We present APS-LDA, which integrates state-of-the-art topic modeling with
cluster computing frameworks such as Spark using a novel asynchronous parameter
server. Advantages of this integration include convenient usage of existing
data processing pipelines and eliminating the need for disk writes as data can
be kept in memory from start to finish. Our goal is not to outperform highly
customized implementations, but to propose a general high-performance topic
modeling framework that can easily be used in today's data processing
pipelines. We compare APS-LDA to the existing Spark LDA implementations and
show that our system can, on a 480-core cluster, process up to 135 times more
data and 10 times more topics without sacrificing model quality.Comment: To appear in SIGIR 201
GeMSE: A new Low-Background Facility for Meteorite and Material Screening
We are currently setting up a facility for low-background gamma-ray
spectrometry based on a HPGe detector. It is dedicated to material screening
for the XENON and DARWIN dark matter projects as well as to the
characterization of meteorites. The detector will be installed in a medium
depth (620 m.w.e.) underground laboratory in Switzerland with several
layers of shielding and an active muon-veto. The GeMSE facility will be
operational by fall 2015 with an expected background rate of 250
counts/day (100-2700 keV).Comment: The following article appeared in AIP Conf. Proc. 1672, 120004 (2015)
and may be found at
http://scitation.aip.org/content/aip/proceeding/aipcp/10.1063/1.4928010. The
muon spectrum in Figure 4 (left) was corrected due to a bug in the code.
After correction the muon flux is reduced by a factor of about
Analysis of an experimental quantum logic gate by complementary classical operations
Quantum logic gates can perform calculations much more efficiently than their
classical counterparts. However, the level of control needed to obtain a
reliable quantum operation is correspondingly higher. In order to evaluate the
performance of experimental quantum gates, it is therefore necessary to
identify the essential features that indicate quantum coherent operation. In
this paper, we show that an efficient characterization of an experimental
device can be obtained by investigating the classical logic operations on a
pair of complementary basis sets. It is then possible to obtain reliable
predictions about the quantum coherent operations of the gate such as
entanglement generation and Bell state discrimination even without performing
these operations directly.Comment: 14 pages, 1 figure, 3 tables, Brief Review for Modern Physics Letters
A, includes a more detailed analysis of the experimental data in Phys. Rev.
Lett. 95, 210506 (2005) (quant-ph/0506263). v2 has minor corrections in
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