689 research outputs found
Fast and Slow Coherent Cascades in Anti-de Sitter Spacetime
We study the phase and amplitude dynamics of small perturbations in 3+1
dimensional Anti-de Sitter spacetime using the truncated resonant
approximation, also known as the Two Time Framework (TTF). We analyse the phase
spectrum for different classes of initial data and find that higher frequency
modes turn on with coherently aligned phases. Combining numerical and
analytical results, we conjecture that there is a class of initial conditions
that collapse in infinite slow time and to which the well-studied case of the
two-mode, equal energy initial data belongs. We additionally study
perturbations that collapse in finite time, and find that the energy spectrum
approaches a power law, with the energy per mode scaling approximately as the
inverse first power of the frequency.Comment: 19 pages, multiple figures. v2: version published in CQ
Short- and intermediate-time behavior of the linear stress relaxation in semiflexible polymers
The linear viscoelasticity of semiflexible polymers is studied through Brownian Dynamics simulations covering a broad range of chain stiffness and time scales. Our results agree with existing theoretical predictions in the flexible and stiff limits; however, we find that over a wide intermediate-time window spanning several decades, the stress relaxation is described by a single power law t^(-alpha), with the exponent alpha apparently varying continuously from 1/2 for flexible chains, to 5/4 for stiff ones. Our study identifies the limits of validity of the t^(-3/4) power law at short times predicted by recent theories. An additional regime is identified, the "ultrastiff" chains, where this behavior disappears. In the absence of Brownian motion, the purely mechanical stress relaxation produces a t^(-3/4) power law for both short and intermediate times
Real-time ECG Monitoring using Compressive sensing on a Heterogeneous Multicore Edge-Device
The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.In a typical ambulatory health monitoring systems, wearable medical sensors
are deployed on the human body to continuously collect and transmit physiological
signals to a nearby gateway that forward the measured data to the
cloud-based healthcare platform. However, this model often fails to respect the
strict requirements of healthcare systems. Wearable medical sensors are very
limited in terms of battery lifetime, in addition, the system reliance on a cloud
makes it vulnerable to connectivity and latency issues. Compressive sensing
(CS) theory has been widely deployed in electrocardiogramme ECG monitoring
application to optimize the wearable sensors power consumption. The proposed
solution in this paper aims to tackle these limitations by empowering a gatewaycentric
connected health solution, where the most power consuming tasks are
performed locally on a multicore processor. This paper explores the efficiency
of real-time CS-based recovery of ECG signals on an IoT-gateway embedded
with ARM’s big.littleTM multicore for different signal dimension and allocated
computational resources. Experimental results show that the gateway is able
to reconstruct ECG signals in real-time. Moreover, it demonstrates that using
a high number of cores speeds up the execution time and it further optimizes
energy consumption. The paper identifies the best configurations of resource
allocation that provides the optimal performance. The paper concludes that
multicore processors have the computational capacity and energy efficiency to
promote gateway-centric solution rather than cloud-centric platforms
Ambipolar charge injection and transport in a single pentacene monolayer island
Electrons and holes are locally injected in a single pentacene monolayer
island. The two-dimensional distribution and concentration of the injected
carriers are measured by electrical force microscopy. In crystalline monolayer
islands, both carriers are delocalized over the whole island. On disordered
monolayer, carriers stay localized at their injection point. These results
provide insight into the electronic properties, at the nanometer scale, of
organic monolayers governing performances of organic transistors and molecular
devices.Comment: To be published in Nano Letter
Exsolution-enhanced reverse water-gas shift chemical looping activity of Sr2FeMo0.6Ni0.4O6-δ double perovskite
This study investigates the structural evolution and redox characteristics of the double perovskite Sr2FeMo0.6Ni0.4O6-delta (SFMN) during hydrogen (H2) and carbon dioxide (CO2) redox cycles and explores the material performance in the Reverse Water-Gas Shift Chemical Looping (RWGS-CL) reaction. In-situ and ex-situ X-Ray Diffraction (XRD) and High-Resolution Transmission Electron Microscopy (HRTEM) studies reveal that H2 reduction at temperatures above 800 degrees C leads to the exsolution of bimetallic Ni-Fe alloy particles and the formation of a Ruddlesden-Popper (RP) phase. A core-shell structure with Ni-Fe core and a perovskite oxide shell is formed with subsequent redox cycles, and the resulting material exhibits better performance and high stability in the RWGS-CL process. Thermogravimetric (TGA) and Temperature Programmed Reduction (TPR) and Oxidation (TPO) analyses show that the optimal reduction and oxidation temperatures for maximizing the CO yield are around 850 degrees C and 750 degrees C respectively, and that the cycled material is able to work steadily under isothermal conditions at 850 degrees C
On the Munn-Silbey approach to polaron transport with off-diagonal coupling
Improved results using a method similar to the Munn-Silbey approach have been
obtained on the temperature dependence of transport properties of an extended
Holstein model incorporating simultaneous diagonal and off-diagonal
exciton-phonon coupling. The Hamiltonian is partially diagonalized by a
canonical transformation, and optimal transformation coefficients are
determined in a self-consistent manner. Calculated transport properties exhibit
substantial corrections on those obtained previously by Munn and Silbey for a
wide range of temperatures thanks to a numerically exact evaluation and an
added momentum-dependence of the transformation matrix. Results on the
diffusion coefficient in the moderate and weak coupling regime show distinct
band-like and hopping-like transport features as a function of temperature.Comment: 12 pages, 6 figures, accpeted in Journal of Physical Chemistry B:
Shaul Mukamel Festschrift (2011
Performance of Monolayer Graphene Nanomechanical Resonators with Electrical Readout
The enormous stiffness and low density of graphene make it an ideal material
for nanoelectromechanical (NEMS) applications. We demonstrate fabrication and
electrical readout of monolayer graphene resonators, and test their response to
changes in mass and temperature. The devices show resonances in the MHz range.
The strong dependence of the resonant frequency on applied gate voltage can be
fit to a membrane model, which yields the mass density and built-in strain.
Upon removal and addition of mass, we observe changes in both the density and
the strain, indicating that adsorbates impart tension to the graphene. Upon
cooling, the frequency increases; the shift rate can be used to measure the
unusual negative thermal expansion coefficient of graphene. The quality factor
increases with decreasing temperature, reaching ~10,000 at 5 K. By establishing
many of the basic attributes of monolayer graphene resonators, these studies
lay the groundwork for applications, including high-sensitivity mass detectors
Deregulation of methylation of transcribed-ultra conserved regions in colorectal cancer and their value for detection of adenomas and adenocarcinomas
Expression of Transcribed Ultraconserved Regions (T-UCRs) is often deregulated in cancer. The present study assesses the expression and methylation of three T-UCRs (Uc160, Uc283 and Uc346) in colorectal cancer (CRC) and explores the potential of T-UCR methylation in circulating DNA for the detection of adenomas and adenocarcinomas. Expression levels of Uc160, Uc283 and Uc346 were lower in neoplastic tissues from 64 CRC patients (statistically significant for Uc160, p<0.001), compared to non-malignant tissues, while methylation levels displayed the inverse pattern (p<0.001, p=0.001 and p=0.004 respectively). In colon cancer cell lines, overexpression of Uc160 and Uc346 led to increased proliferation and migration rates. Methylation levels of Uc160 in plasma of 50 CRC, 59 adenoma patients, 40 healthy subjects and 12 patients with colon inflammation or diverticulosis predicted the presence of CRC with 35% sensitivity and 89% specificity (p=0.016), while methylation levels of the combination of all three T-UCRs resulted in 45% sensitivity and 74.3% specificity (p=0.013). In conclusion, studied T-UCRs’ expression and methylation status are deregulated in CRC while Uc160 and Uc346 appear to have a complicated role in CRC progression. Moreover their methylation status appears a promising non-invasive screening test for CRC, provided that the sensitivity of the assay is improved
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