354,074 research outputs found
Sparse Recovery Analysis of Preconditioned Frames via Convex Optimization
Orthogonal Matching Pursuit and Basis Pursuit are popular reconstruction
algorithms for recovery of sparse signals. The exact recovery property of both
the methods has a relation with the coherence of the underlying redundant
dictionary, i.e. a frame. A frame with low coherence provides better guarantees
for exact recovery. An equivalent formulation of the associated linear system
is obtained via premultiplication by a non-singular matrix. In view of bounds
that guarantee sparse recovery, it is very useful to generate the
preconditioner in such way that the preconditioned frame has low coherence as
compared to the original. In this paper, we discuss the impact of
preconditioning on sparse recovery. Further, we formulate a convex optimization
problem for designing the preconditioner that yields a frame with improved
coherence. In addition to reducing coherence, we focus on designing well
conditioned frames and numerically study the relationship between the condition
number of the preconditioner and the coherence of the new frame. Alongside
theoretical justifications, we demonstrate through simulations the efficacy of
the preconditioner in reducing coherence as well as recovering sparse signals.Comment: 9 pages, 5 Figure
Quantum Error Correction via Convex Optimization
We show that the problem of designing a quantum information error correcting
procedure can be cast as a bi-convex optimization problem, iterating between
encoding and recovery, each being a semidefinite program. For a given encoding
operator the problem is convex in the recovery operator. For a given method of
recovery, the problem is convex in the encoding scheme. This allows us to
derive new codes that are locally optimal. We present examples of such codes
that can handle errors which are too strong for codes derived by analogy to
classical error correction techniques.Comment: 16 page
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Carbon Monoxide Oxidation Promoted by Surface Polarization Charges in a CuO/Ag Hybrid Catalyst.
Composite structures have been widely utilized to improve material performance. Here we report a semiconductor-metal hybrid structure (CuO/Ag) for CO oxidation that possesses very promising activity. Our first-principles calculations demonstrate that the significant improvement in this system's catalytic performance mainly comes from the polarized charge injection that results from the Schottky barrier formed at the CuO/Ag interface due to the work function differential there. Moreover, we propose a synergistic mechanism underlying the recovery process of this catalyst, which could significantly promote the recovery of oxygen vacancy created via the M-vK mechanism. These findings provide a new strategy for designing high performance heterogeneous catalysts
Inlet technology for powered-lift aircraft
The concepts, analytical tools, and experimental data available for designing inlets for powered lift aircraft are discussed. It is shown that inlets can be designed to meet noise, distortion, and cruise drag requirements at the flight and engine operating conditions of a powered lift aircraft. The penalty in pressure recovery for achieving the required noise suppression was 0.3 percent
New understanding of the shape-memory response in thiol-epoxy click systems: towards controlling the recovery process
Our research group has recently found excellent shape-memory response in “thiol-epoxy” thermosets obtained with click-chemistry. In this study, we use their well-designed, homogeneous and tailorable network structures to investigate parameters for better control of the shape-recovery process. We present a new methodology to analyse the shape-recovery process, enabling easy and efficient comparison of shape-memory experiments on the programming conditions. Shape-memory experiments at different programming conditions have been carried out to that end. Additionally, the programming process has been extensively analysed in uniaxial tensile experiments at different shape-memory testing temperatures. The results showed that the shape-memory response for a specific operational design can be optimized by choosing the correct programming conditions and accurately designing the network structure. When programming at a high temperature (T » Tg), under high network mobility conditions, high shape-recovery ratios and homogeneous shape-recovery processes are obtained for the network structure and the programmed strain level (eD). However, considerably lower stress and strain levels can be achieved. Meanwhile, when programming at temperatures lower than Tg, considerably higher stress and strain levels are attained but under low network mobility conditions. The shape-recovery process heavily depends on both the network structure and eD. Network relaxation occurs during the loading stage, resulting in a noticeable decrease in the shape-recovery rate as eD increases. Moreover, at a certain level of strain, permanent and non-recoverable deformations may occur, impeding the completion and modifying the whole path of the shape-recovery process.Postprint (author's final draft
Erasure coding for distributed matrix multiplication for matrices with bounded entries
Distributed matrix multiplication is widely used in several scientific
domains. It is well recognized that computation times on distributed clusters
are often dominated by the slowest workers (called stragglers). Recent work has
demonstrated that straggler mitigation can be viewed as a problem of designing
erasure codes. For matrices and , the technique
essentially maps the computation of into the
multiplication of smaller (coded) submatrices. The stragglers are treated as
erasures in this process. The computation can be completed as long as a certain
number of workers (called the recovery threshold) complete their assigned
tasks.
We present a novel coding strategy for this problem when the absolute values
of the matrix entries are sufficiently small. We demonstrate a tradeoff between
the assumed absolute value bounds on the matrix entries and the recovery
threshold. At one extreme, we are optimal with respect to the recovery
threshold and on the other extreme, we match the threshold of prior work.
Experimental results on cloud-based clusters validate the benefits of our
method
The application of the ventilation equations to cleanrooms - Part 2: Decay of contamination
This article is the second of a three-part
series that investigates the application of
the ventilation equations to designing
and testing cleanrooms. This part is
concerned with the decay equation. The
recovery test, described in ISO 14644-3
(2005) is discussed, and improvements
recommended. The application of
the decay equation to the ‘clean up’
requirement given in the EU GGMP
(2008) is also discussed. Finally, a method
is considered that calculates the time
needed for airborne contamination in
cleanroom areas to decay to acceptable
concentrations
Low-Cost Compressive Sensing for Color Video and Depth
A simple and inexpensive (low-power and low-bandwidth) modification is made
to a conventional off-the-shelf color video camera, from which we recover
{multiple} color frames for each of the original measured frames, and each of
the recovered frames can be focused at a different depth. The recovery of
multiple frames for each measured frame is made possible via high-speed coding,
manifested via translation of a single coded aperture; the inexpensive
translation is constituted by mounting the binary code on a piezoelectric
device. To simultaneously recover depth information, a {liquid} lens is
modulated at high speed, via a variable voltage. Consequently, during the
aforementioned coding process, the liquid lens allows the camera to sweep the
focus through multiple depths. In addition to designing and implementing the
camera, fast recovery is achieved by an anytime algorithm exploiting the
group-sparsity of wavelet/DCT coefficients.Comment: 8 pages, CVPR 201
Area targeting and storage temperature selection for heat recovery loops
Inter-plant heat integration across a large site can be achieved using a Heat Recovery Loop (HRL). In this paper the relationship between HRL storage temperatures, heating and cooling utility savings (heat recovery) and total HRL exchanger area is investigated. A methodology for designing a HRL based on a ΔTmin approach is compared to three global optimisation approaches where heat exchangers are constrained to have either the same Number of Heat Transfer Units (NTU), Log-Mean Temperature Difference (LMTD) or no constraints (actual global optimum). Analysis is performed using time averaged flow rate and temperature data. Attention is given to understanding the actual temperature driving force of the HRL heat exchangers compared to the apparent driving force as indicated by the composite curves. The cold storage temperature is also varied to minimise the total heat exchanger area. Results for the same heat recovery level show that the ΔTmin approach is effective at minimising total area to within 5 % of the unconstrained global optimisation approach. The study also demonstrates the efficiency of the ΔT min approach to HRL design compared to the other methods which require considerable computational resources
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