1,399 research outputs found
On the Implementation of AM/AM AM/PM Behavioral Models in System Level Simulation
The use of nonlinear device behavioral models offers an economical way of simulating the performance of complex communication systems. A concrete method for implementing the AM/AM AM/PM behavioral model in system level simulation using ADS is developed. This method seamlessly tansfers the data from the circuit level simulation to system level simulation, where the AM/AM AM/PM model is automatically built. The methodology is extendible for use in other software packages or between different software packages
On the Analysis of Quasi-Static Bandpass Nonlinearities Using Volterra Series
This paper reexamines the AM-AM and AM-PM data-based behavioral model of a narrowband quasistatic nonlinear system via Volterra series analysis. It is shown that, under narrowband input signal and flat basedband impedance assumptions, the model is in compliance with bandpass nonlinearity theory. Consequentially, there exists a relationship based on the Chebyshev-Fourier transform between the nonlinearity's one tone and two tone AM-AM transfer functions
80-Gb/s OTDM system analysis of a vertical microcavity-based saturable absorber for the enhancement of pulse pedestal suppression
In future high-speed optical time-division-multiplexed (OTDM) systems, an important factor that needs to be considered for optical pulse generation schemes is the impact of pulse pedestals on the overall system performance. The results presented in this letter are two-fold; first, the impact due to the height of pulse pedestals in an 80-Gb/s OTDM system are established. Second, a solution is provided to overcome these high pedestal levels through the use of a vertical microcavity saturable absorber, which can significantly reduce the pulse pedestal level and give enhanced system performanc
A maximum density rule for surfaces of quasicrystals
A rule due to Bravais of wide validity for crystals is that their surfaces
correspond to the densest planes of atoms in the bulk of the material.
Comparing a theoretical model of i-AlPdMn with experimental results, we find
that this correspondence breaks down and that surfaces parallel to the densest
planes in the bulk are not the most stable, i.e. they are not so-called bulk
terminations. The correspondence can be restored by recognizing that there is a
contribution to the surface not just from one geometrical plane but from a
layer of stacked atoms, possibly containing more than one plane. We find that
not only does the stability of high-symmetry surfaces match the density of the
corresponding layer-like bulk terminations but the exact spacings between
surface terraces and their degree of pittedness may be determined by a simple
analysis of the density of layers predicted by the bulk geometric model.Comment: 8 pages of ps-file, 3 Figs (jpg
Anomalous and dimensional scaling in anisotropic turbulence
We present a numerical study of anisotropic statistical fluctuations in
homogeneous turbulent flows. We give an argument to predict the dimensional
scaling exponents, (p+j)/3, for the projections of p-th order structure
function in the j-th sector of the rotational group. We show that measured
exponents are anomalous, showing a clear deviation from the dimensional
prediction. Dimensional scaling is subleading and it is recovered only after a
random reshuffling of all velocity phases, in the stationary ensemble. This
supports the idea that anomalous scaling is the result of a genuine inertial
evolution, independent of large-scale behavior.Comment: 4 pages, 3 figure
Scaling Exponents in Anisotropic Hydrodynamic Turbulence
In anisotropic turbulence the correlation functions are decomposed in the
irreducible representations of the SO(3) symmetry group (with different
"angular momenta" ). For different values of the second order
correlation function is characterized by different scaling exponents
. In this paper we compute these scaling exponents in a Direct
Interaction Approximation (DIA). By linearizing the DIA equations in small
anisotropy we set up a linear operator and find its zero-modes in the inertial
interval of scales. Thus the scaling exponents in each -sector follow
from solvability condition, and are not determined by dimensional analysis. The
main result of our calculation is that the scaling exponents
form a strictly increasing spectrum at least until , guaranteeing that
the effects of anisotropy decay as power laws when the scale of observation
diminishes. The results of our calculations are compared to available
experiments and simulations.Comment: 10 pages, 4 figures, PRE submitted. Fixed problems with figure
Genetic clustering on the hippocampal surface for genome-wide association studies
Imaging genetics aims to discover how variants in the human genome influence brain measures derived from images. Genome-wide association scans (GWAS) can screen the genome for common differences in our DNA that relate to brain measures. In small samples, GWAS has low power as individual gene effects are weak and one must also correct for multiple comparisons across the genome and the image. Here we extend recent work on genetic clustering of images, to analyze surface-based models of anatomy using GWAS. We performed spherical harmonic analysis of hippocampal surfaces, automatically extracted from brain MRI scans of 1254 subjects. We clustered hippocampal surface regions with common genetic influences by examining genetic correlations (rg) between the normalized deformation values at all pairs of surface points. Using genetic correlations to cluster surface measures, we were able to boost effect sizes for genetic associations, compared to clustering with traditional phenotypic correlations using Pearson's r
Repression of SOX6 transcriptional activity by SUMO modification
AbstractSOX6 plays key functions in several developmental processes, including neurogenesis and skeleton formation. In this report, we show that SOX6 is modified in vitro and in vivo by small ubiquitin-related modifier (SUMO) on two distinct sites. Mutation of both sites abolished SOX6 sumoylation and increased SOX6 transcriptional activity. SUMO dependent repression of SOX6 transcription was promoted by UBC9 whereas siRNA to UBC9, cotransfection of inactive UBC9 or a SUMO protease increased SOX6 transcriptional activity. Furthermore, co-expression of SOX6 with SUMO2 results in the appearance of SOX6 in a punctate nuclear pattern that colocalized with promyelocytic leukemia protein, which was partially abolished by mutations in SOX6 sumoylation sites
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