25,371 research outputs found
Imaging and Nulling with the Space Interferometry Mission
We present numerical simulations for a possible synthesis imaging mode of the
Space Interferometer Mission (SIM). We summarize the general techniques that
SIM offers to perform imaging of high surface brightness sources, and discuss
their strengths and weaknesses. We describe an interactive software package
that is used to provide realistic, photometrically correct estimates of SIM
performance for various classes of astronomical objects. In particular, we
simulate the cases of gaseous disks around black holes in the nuclei of
galaxies, and zodiacal dust disks around young stellar objects. Regarding the
first, we show that a Keplerian velocity gradient of the line-emitting gaseous
disk -- and thus the mass of the putative black hole -- can be determined with
SIM to unprecedented accuracy in about 5 hours of integration time for objects
with H_alpha surface brigthness comparable to the prototype M 87. Detections
and observations of exo-zodiacal dust disks depend critically on the disk
properties and the nulling capabilities of SIM. Systems with similar disk size
and at least one tenth of the dust content of beta Pic can be detected by SIM
at distances between 100 pc and a few kpc, if a nulling efficiency of 1/10000
is achieved. Possible inner clear regions indicative of the presence of massive
planets can also be detected and imaged. On the other hand, exo-zodiacal disks
with properties more similar to the solar system will not be found in
reasonable integration times with SIM.Comment: 28 pages, incl. 8 postscript figures, excl. 10 gif-figures Submitted
to Ap
R Function Related to Entanglement of Formation
By investigating the convex property of the function R, appeared in computing
the entanglement of formation for isotropic states in Phys. Rev. Lett. 85, 2625
(2000), and a tight lower bound of entanglement of formation for arbitrary
bipartite mixed states in Phys. Rev. Lett. 95, 210501 (2005), we show
analytically that the very nice results in these papers are valid not only for
dimensions 2 and 3 but any dimensions.Comment: 3 page
Accelerating Training of Deep Neural Networks via Sparse Edge Processing
We propose a reconfigurable hardware architecture for deep neural networks
(DNNs) capable of online training and inference, which uses algorithmically
pre-determined, structured sparsity to significantly lower memory and
computational requirements. This novel architecture introduces the notion of
edge-processing to provide flexibility and combines junction pipelining and
operational parallelization to speed up training. The overall effect is to
reduce network complexity by factors up to 30x and training time by up to 35x
relative to GPUs, while maintaining high fidelity of inference results. This
has the potential to enable extensive parameter searches and development of the
largely unexplored theoretical foundation of DNNs. The architecture
automatically adapts itself to different network sizes given available hardware
resources. As proof of concept, we show results obtained for different bit
widths.Comment: Presented at the 26th International Conference on Artificial Neural
Networks (ICANN) 2017 in Alghero, Ital
Computational Soundness for Dalvik Bytecode
Automatically analyzing information flow within Android applications that
rely on cryptographic operations with their computational security guarantees
imposes formidable challenges that existing approaches for understanding an
app's behavior struggle to meet. These approaches do not distinguish
cryptographic and non-cryptographic operations, and hence do not account for
cryptographic protections: f(m) is considered sensitive for a sensitive message
m irrespective of potential secrecy properties offered by a cryptographic
operation f. These approaches consequently provide a safe approximation of the
app's behavior, but they mistakenly classify a large fraction of apps as
potentially insecure and consequently yield overly pessimistic results.
In this paper, we show how cryptographic operations can be faithfully
included into existing approaches for automated app analysis. To this end, we
first show how cryptographic operations can be expressed as symbolic
abstractions within the comprehensive Dalvik bytecode language. These
abstractions are accessible to automated analysis, and they can be conveniently
added to existing app analysis tools using minor changes in their semantics.
Second, we show that our abstractions are faithful by providing the first
computational soundness result for Dalvik bytecode, i.e., the absence of
attacks against our symbolically abstracted program entails the absence of any
attacks against a suitable cryptographic program realization. We cast our
computational soundness result in the CoSP framework, which makes the result
modular and composable.Comment: Technical report for the ACM CCS 2016 conference pape
Residual Symmetries for Neutrino Mixing with a Large theta_13 and Nearly Maximal delta_D
The residual Z^s_2(k) and bar Z^s_2(k) symmetries induce a direct and unique
phenomenological relation with theta_x (= theta_13) expressed in terms of the
other two mixing angles, theta_s (= theta_12) and theta_a (= theta_23), and the
Dirac CP phase delta_D. Z^s_2(k) predicts a theta_x probability distribution
centered around 3^o ~ 6^o with an uncertainty of 2^o to 4^o while those from
bar Z^s_2(k) are approximately a factor of two larger. Either result fits the
T2K, MINOS and Double CHOOZ measurements. Alternately a prediction for the
Dirac CP phase delta_D results in a peak at +-74^o (+-106^o) for Z^s_2(k) or
+-123^o (+-57^o) for bar Z^s_2(k) which is consistent with the latest global
fit. We also give a distribution for the leptonic Jarslkog invariant J_v which
can provide further tests from measurements at T2K and NOvA.Comment: Accepted for publication in PR
A Naturally Minute Quantum Correction to the Cosmological Constant Descended from the Hierarchy
We demonstrate that an extremely small but positive quantum correction, or
the Casimir energy, to the cosmological constant can arise from a massive bulk
fermion field in the Randall-Sundrum model. Specifically, a cosmological
constant doubly descended from the Planck-electroweak hierarchy and as minute
as the observed dark energy scale can be naturally achieved without fine-tuning
of the bulk fermion mass. To ensure the stabilization of the system, we discuss
two stabilization mechanisms under this setup. It is found that the
Goldberger-Wise mechanism can be successfully introduced in the presence of a
massive bulk fermion, without spoiling the smallness of the quantum correction.Comment: 5 page
Low-noise top-gate graphene transistors
We report results of experimental investigation of the low-frequency noise in
the top-gate graphene transistors. The back-gate graphene devices were modified
via addition of the top gate separated by 20 nm of HfO2 from the single-layer
graphene channels. The measurements revealed low flicker noise levels with the
normalized noise spectral density close to 1/f (f is the frequency) and Hooge
parameter below 2 x 10^-3. The analysis of the noise spectral density
dependence on the top and bottom gate biases helped us to elucidate the noise
sources in these devices and develop a strategy for the electronic noise
reduction. The obtained results are important for all proposed graphene
applications in electronics and sensors.Comment: 9 pages, 4 figure
Tele-autonomous control involving contacts: The applications of a high precision laser line range sensor
The object localization algorithm based on line-segment matching is presented. The method is very simple and computationally fast. In most cases, closed-form formulas are used to derive the solution. The method is also quite flexible, because only few surfaces (one or two) need to be accessed (sensed) to gather necessary range data. For example, if the line-segments are extracted from boundaries of a planar surface, only parameters of one surface and two of its boundaries need to be extracted, as compared with traditional point-surface matching or line-surface matching algorithms which need to access at least three surfaces in order to locate a planar object. Therefore, this method is especially suitable for applications when an object is surrounded by many other work pieces and most of the object is very difficult, is not impossible, to be measured; or when not all parts of the object can be reached. The theoretical ground on how to use line range sensor to located an object was laid. Much work has to be done in order to be really useful
Concurrence of arbitrary dimensional bipartite quantum states
We derive an analytical lower bound for the concurrence of a bipartite
quantum state in arbitrary dimension. A functional relation is established
relating concurrence, the Peres-Horodecki criterion and the realignment
criterion. We demonstrate that our bound is exact for some mixed quantum
states. The significance of our method is illustrated by giving a quantitative
evaluation of entanglement for many bound entangled states, some of which fail
to be identified by the usual concurrence estimation method.Comment: 4 pages, published versio
Entanglement of Formation of Bipartite Quantum States
We give an explicit tight lower bound for the entanglement of formation for
arbitrary bipartite mixed states by using the convex hull construction of a
certain function. This is achieved by revealing a novel connection among the
entanglement of formation, the well-known Peres-Horodecki and realignment
criteria. The bound gives a quite simple and efficiently computable way to
evaluate quantitatively the degree of entanglement for any bipartite quantum
state.Comment: 4 page
- …