503 research outputs found
Enhancing interfacial thermal conductance of amorphous interface by optimized interfacial mass distribution
Interfacial thermal resistance arises challenges for the thermal management
as the modern semiconductors are miniatured to nanoscale. Previous studies
found that graded mass distribution in interface can maximumly enhance the
interfacial thermal conductance of crystalline interface, however, whether this
strategy is effective for amorphous interface is less explored. In this work,
graded mass distribution in the amorphous interface between crystalline Si and
crystalline Ge is optimized to increase the interfacial thermal conductance by
the extended atomistic Greens function method
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Thermoelasticity of SSP Materials: An Integrated Ultrasonic and X-radiation Study
It has been a very productive year for accomplishing the tasks outlined in the original proposal. Quite a few crystalline materials [tantalum (Ta), molybdenum (Mo), cerium (Ce) beryllium (Be)] and amorphous materials [zirconium tungstate (ZrW2O8), SiO2, and germanium diselenide (GeSe2) glasses] have been assessed at high pressures up to 12 GPa and acoustic velocities and densities have been obtained simultaneously using our unique technique. Major activities include sample preparation, high pressure cell assembly testing, and conducting ultrasonic and X-ray diffraction measurements at BNL as well as resonance ultrasonic spectroscopy (RUS) measurements at UCLA on appropriate samples. Sample preparations for Ce and Be were made at Los Alamos National Lab for which special grades and specialized machining of the sample are required. Pilot experiments for optimizing high pressure cell assemblies were conducted using the 1000-ton multi-anvil press (USCA-1000) in the High Pressure Lab at Stony Brook, and simultaneous ultrasonic and X-ray diffraction experiments were conducted using the DDIA apparatus installed at X17B2 of NSLS at BNL. New data analysis protocols have been developed for deriving density of amorphous materials at high pressure and therefore its equation of state. Following on previous years effort, attempts have been made to derive single crystal elastic constants based on the current measurements on polycrystalline samples at high pressure in conjunction with previous data as well as the current RUS measurements at ambient conditions. Single crystal elastic constants of Tantalum have been measured using RUS techniques at room pressure and high temperature. Educational and training opportunities have been provided for postdoctoral associate researchers, Drs. Wei Liu (project leader for Mo, and ZrW2O8 and SiO2 glass) and Qiong Liu (Ta project leader) and graduate students Mr. Matthew Whitaker (Project Ce and FeSi) and Sytle Antao (GeSe2 glass project). A total of 6 undergraduate students (2 summer students at Stony Brook University, and 4 undergraduates from Azusa Pacific University) participated in the experiments at various stages and benefited from the discussions about the science and research work conducted by our collaborators of the current project at DoE national labs
3D nonrigid medical image registration using a new information theoretic measure.
International audienceThis work presents a novel method for the nonrigid registration of medical images based on the Arimoto entropy, a generalization of the Shannon entropy. The proposed method employed the Jensen-Arimoto divergence measure as a similarity metric to measure the statistical dependence between medical images. Free-form deformations were adopted as the transformation model and the Parzen window estimation was applied to compute the probability distributions. A penalty term is incorporated into the objective function to smooth the nonrigid transformation. The goal of registration is to optimize an objective function consisting of a dissimilarity term and a penalty term, which would be minimal when two deformed images are perfectly aligned using the limited memory BFGS optimization method, and thus to get the optimal geometric transformation. To validate the performance of the proposed method, experiments on both simulated 3D brain MR images and real 3D thoracic CT data sets were designed and performed on the open source elastix package. For the simulated experiments, the registration errors of 3D brain MR images with various magnitudes of known deformations and different levels of noise were measured. For the real data tests, four data sets of 4D thoracic CT from four patients were selected to assess the registration performance of the method, including ten 3D CT images for each 4D CT data covering an entire respiration cycle. These results were compared with the normalized cross correlation and the mutual information methods and show a slight but true improvement in registration accuracy
ETCH: Efficient Channel Hopping for Communication Rendezvous in Dynamic Spectrum Access Networks
In a dynamic spectrum access (DSA) network, communication rendezvous is the first step for two secondary users to be able to communicate with each other. In this step, the pair of secondary users meet on the same channel, over which they negotiate on the communication parameters, to establish the communication link. This paper presents ETCH, Efficient Channel Hopping based MAC-layer protocols for communication rendezvous in DSA networks. We propose two protocols, SYNC-ETCH and ASYNC-ETCH. Both protocols achieve better time-to-rendezvous and throughput compared to previous work
Multiplexed Frequency-Selective Incoherent Holography
We propose a new incoherent optical holographic spectrum stripping reconstruction method, called incoherent multiplexing frequency-selective holography, which compresses two or more on-axis holograms into a single multiplexed on-axis hologram without loss of magnification and resolution. The technique described in this chapter effectively suppresses the background bias term and conjugate term. The acquired spectrum is obtained by stripping in the overlapping confounding correlation terms. The experimental results show the potential of the method in areas such as compressed holography and extended field of view imaging
Long-term Navigation Optimal Operation of Cascaded Reservoirs
Water Resources Planning and Managemen
Construction of a complete set of orthogonal Fourier-Mellin moment invariants for pattern recognition applications
International audienceThe completeness property of a set of invariant descriptors is of fundamental importance from the theoretical as well as the practical points of view. In this paper, we propose a general approach to construct a complete set of orthogonal Fourier-Mellin moment (OFMM) invariants. By establishing a relationship between the OFMMs of the original image and those of the image having the same shape but distinct orientation and scale, a complete set of scale and rotation invariants is derived. The efficiency and the robustness to noise of the method for recognition tasks are shown by comparing it with some existing methods on several data sets
Multicarrier communication over underwater acoustic channels with nonuniform Doppler shifts
Author Posting. © IEEE, 2008. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 33 (2008): 198-209, doi:10.1109/JOE.2008.920471.Underwater acoustic (UWA) channels are wideband in nature due to the small ratio of the carrier frequency to the signal bandwidth, which introduces frequency-dependent Doppler shifts. In this paper, we treat the channel as having a common Doppler scaling factor on all propagation paths, and propose a two-step approach to mitigating the Doppler effect: 1) nonuniform Doppler compensation via resampling that converts a "wideband" problem into a "narrowband" problem and 2) high-resolution uniform compensation of the residual Doppler. We focus on zero-padded orthogonal frequency-division multiplexing (OFDM) to minimize the transmission power. Null subcarriers are used to facilitate Doppler compensation, and pilot subcarriers are used for channel estimation. The receiver is based on block-by-block processing, and does not rely on channel dependence across OFDM blocks; thus, it is suitable for fast-varying UWA channels. The data from two shallow-water experiments near Woods Hole, MA, are used to demonstrate the receiver performance. Excellent performance results are obtained even when the transmitter and the receiver are moving at a relative speed of up to 10 kn, at which the Doppler shifts are greater than the OFDM subcarrier spacing. These results suggest that OFDM is a viable option for high-rate communications over wideband UWA channels with nonuniform Doppler shifts.B.
Li and S. Zhou are supported by the ONR YIP grant N00014-07-1-0805
and the NSF grant ECCS-0725562. M. Stojanovic is supported by the ONR
grant N00014-07-1-0202. L. Freitag is supported by the ONR grants N00014-
02-6-0201 and N00014-07-1-0229. P. Willett is supported by the ONR
grant N00014-07-1-0055
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