25,731 research outputs found
Coherent optical control of polarization with a critical metasurface
We describe the mechanism by which a metamaterial surface can act as an ideal
phase-controlled rotatable linear polarizer. With equal-power linearly
polarized beams incident on each side of the surface, varying the relative
phase rotates the polarization angles of the output beams, while keeping the
polarization exactly linear. The explanation is based on coupled-mode theory
and the idea of coherent perfect absorption into auxiliary polarization
channels. The polarization-rotating behavior occurs at a critical point of the
coupled-mode theory, which can be associated with the exceptional point of a
parity-time (PT) symmetric effective Hamiltonian
Modeling and Validation of Temperature and Concentration for Rapid Freeze Prototyping
Rapid Freeze Prototyping is a solid freeform fabrication process that uses water as the main build
material in a cold environment to create three-dimensional parts. A eutectic sugar-water solution
(C6H12O6 – H2O) has been used as a sacrificial material in order to create complex 3D parts with
features such as overhangs. A study of the interaction of the build and support materials is
presented in this paper. The temperature of both materials during deposition and subsequent
cooling is modeled using a semi-empirical model and a theoretical model. A concentration
model is used to predict the concentration in the fabricated parts around the interface of the two
materials with predicted temperatures as input. Experiments are conducted to validate both the
temperature and concentration models.Mechanical Engineerin
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Study on Incorporating Support Material in Rapid Freeze Prototyping
Rapid Freeze Prototyping (RFP) is a rapid prototyping method that uses water freezing
into ice to make three-dimensional parts. Each layer of a geometry is deposited and allowed to
freeze before the next layer is added. Using a support material in RFP is a relatively new
addition to the process. Validating the successful use of a support material in conjunction with
the main build material of water is presented in this paper. The support material selected for use
is a eutectic sugar solution. The selection criteria, properties, and characteristics of the support
material are discussed. Of particular interest is the diffusion between the support and main build
material, which must be minimized to an acceptable level for producing good quality,
reproducible, complex parts.Mechanical Engineerin
Coupled rotor-body vibrations with inplane degrees of freedom
In an effort to understand the vibration mechanisms of helicopters, the following basic studies are considered. A coupled rotor-fuselage vibration analysis including inplane degrees of freedom of both rotor and airframe is performed by matching of rotor and fuselage impedances at the hub. A rigid blade model including hub motion is used to set up the rotor flaplag equations. For the airframe, 9 degrees of freedom and hub offsets are used. The equations are solved by harmonic balance. For a 4-bladed rotor, the coupled responses and hub loads are calculated for various parameters in forward flight. The results show that the addition of inplane degrees of freedom does not significantly affect the vertical vibrations for the cases considered, and that inplane vibrations have similar resonance trends as do flapping vibrations
Periodic solitons for the elliptic-elliptic focussing Davey-Stewartson equations
We consider the elliptic-elliptic, focussing Davey-Stewartson equations,
which have an explicit bright line soliton solution. The existence of a family
of periodic solitons, which have the profile of the line soliton in the
longitudinal spatial direction and are periodic in the transverse spatial
direction, is established using dynamical systems arguments. We also show that
the line soliton is linearly unstable with respect to perturbations in the
transverse direction.Comment: arXiv admin note: text overlap with arXiv:1411.247
Prediction of Functional Sites in SCOP Domains using Dynamics Perturbation Analysis
Dynamics perturbation analysis (DPA) finds regions in a protein structure where proteins are "ticklish", i.e., where interactions cause a large change in protein dynamics. Previously, such regions were shown to predict the location of native binding sites in a docking test set, but the more general applicability of DPA to the prediction of functional sites in proteins was not shown. Here we describe the results of applying an accelerated algorithm, called Fast DPA, to predict functional sites in over 50,000 SCOP domains
Convex Optimization Methods for Dimension Reduction and Coefficient Estimation in Multivariate Linear Regression
In this paper, we study convex optimization methods for computing the trace
norm regularized least squares estimate in multivariate linear regression. The
so-called factor estimation and selection (FES) method, recently proposed by
Yuan et al. [22], conducts parameter estimation and factor selection
simultaneously and have been shown to enjoy nice properties in both large and
finite samples. To compute the estimates, however, can be very challenging in
practice because of the high dimensionality and the trace norm constraint. In
this paper, we explore a variant of Nesterov's smooth method [20] and interior
point methods for computing the penalized least squares estimate. The
performance of these methods is then compared using a set of randomly generated
instances. We show that the variant of Nesterov's smooth method [20] generally
outperforms the interior point method implemented in SDPT3 version 4.0 (beta)
[19] substantially . Moreover, the former method is much more memory efficient.Comment: 27 page
Optimization of miRNA-seq data preprocessing.
The past two decades of microRNA (miRNA) research has solidified the role of these small non-coding RNAs as key regulators of many biological processes and promising biomarkers for disease. The concurrent development in high-throughput profiling technology has further advanced our understanding of the impact of their dysregulation on a global scale. Currently, next-generation sequencing is the platform of choice for the discovery and quantification of miRNAs. Despite this, there is no clear consensus on how the data should be preprocessed before conducting downstream analyses. Often overlooked, data preprocessing is an essential step in data analysis: the presence of unreliable features and noise can affect the conclusions drawn from downstream analyses. Using a spike-in dilution study, we evaluated the effects of several general-purpose aligners (BWA, Bowtie, Bowtie 2 and Novoalign), and normalization methods (counts-per-million, total count scaling, upper quartile scaling, Trimmed Mean of M, DESeq, linear regression, cyclic loess and quantile) with respect to the final miRNA count data distribution, variance, bias and accuracy of differential expression analysis. We make practical recommendations on the optimal preprocessing methods for the extraction and interpretation of miRNA count data from small RNA-sequencing experiments
Using Swing Resistance and Assistance to Improve Gait Symmetry in Individuals Post-Stroke
A major characteristic of hemiplegic gait observed in individuals post-stroke is spatial and temporal asymmetry, which may increase energy expenditure and the risk of falls. The purpose of this study was to examine the effects of swing resistance/assistance applied to the affected leg on gait symmetry in individuals post-stroke. We recruited 10 subjects with chronic stroke who demonstrated a shorter step length with their affected leg in comparison to the non-affected leg during walking. They participated in two test sessions for swing resistance and swing assistance, respectively. During the adaptation period, subjects counteracted the step length deviation caused by the applied swing resistance force, resulting in an aftereffect consisting of improved step length symmetry during the post-adaptation period. In contrast, subjects did not counteract step length deviation caused by swing assistance during adaptation period and produced no aftereffect during the post-adaptation period. Locomotor training with swing resistance applied to the affected leg may improve step length symmetry through error-based learning. Swing assistance reduces errors in step length during stepping; however, it is unclear whether this approach would improve step length symmetry. Results from this study may be used to develop training paradigms for improving gait symmetry of stroke survivors
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