431 research outputs found
Probabilistic estimation of the rank 1 cross approximation accuracy
In the construction of low-rank matrix approximation and maximum element
search it is effective to use maxvol algorithm. Nevertheless, even in the case
of rank 1 approximation the algorithm does not always converge to the maximum
matrix element, and it is unclear how often close to the maximum element can be
found. In this article it is shown that with a certain degree of randomness in
the matrix and proper selection of the starting column, the algorithm with high
probability in a few steps converges to an element, which module differs little
from the maximum. It is also shown that with more severe restrictions on the
error matrix no restrictions on the starting column need to be introduced
Close to optimal column approximations with a single SVD
The best column approximation in the Frobenius norm with columns has an
error at most times larger than the truncated singular value
decomposition. Reaching this bound in practice involves either expensive random
volume sampling or at least executions of singular value decomposition. In
this paper it will be shown that the same column approximation bound can be
reached with only a single SVD (which can also be replaced with approximate
SVD). As a corollary, it will be shown how to find a highly nondegenerate
submatrix in rows of size in just operations, which mostly
has the same properties as the maximum volume submatrix
Exact solutions of temperature-dependent Smoluchowski equations
We report a number of exact solutions for temperature-dependent Smoluchowski
equations. These equations quantify the ballistic agglomeration, where the
evolution of densities of agglomerates of different size is entangled with the
evolution of the mean kinetic energy (partial temperatures) of such clusters.
The obtained exact solutions may be used as a benchmark to assess the accuracy
and computational efficiency of the numerical approaches, developed to solve
the temperature-dependent Smoluchowski equations. Moreover, they may also
illustrate the possible evolution regimes in these systems. The exact solutions
have been obtained for a series of model rate coefficients, and we demonstrate
that there may be an infinite number of such model coefficient which allow
exact analysis. We compare our exact solutions with the numerical solutions for
various evolution regimes; an excellent agreement between numerical and exact
results proves the accuracy of the exploited numerical method
Collision fragmentation of aggregates. The role of the interaction potential between comprising particles
We investigate disruptive collisions of aggregates comprised of particles
with different interaction potentials. We study Lennard-Jones (L-J), Tersoff,
modified L-J potential and the one associated with Johnson-Kendall-Roberts
(JKR) model. These refer to short, middle and long-ranged inter-particle
potentials and describe both inter-atomic interactions and interactions of
macroscopic adhesive bodies. We perform comprehensive molecular dynamics
simulations and observe for all four potentials power-law dependencies for the
size distribution of collision fragments and for their size-velocity
correlation. We introduce a new fragmentation characteristic -- the shattering
degree , quantifying the fraction of monomers in debris and reveal its
universal behavior. Namely, we demonstrate that for all potentials, is
described by a universal function of the impact velocity. Using the above
results, we perform the impact classification and construct the respective
collision phase diagram. Finally, we present a qualitative theory that explains
the observed scaling behavior.Comment: Submitted to Physica
P60. Hypoxia-regulated proteins in gastric cancer: Correlation with disseminated tumor cells and clinical outcome
Dynamics of ligand substitution in labile cobalt complexes resolved by ultrafast T-jump
Ligand exchange of hydrated metal complexes is common in chemical and biological systems. Using the ultrafast T-jump, we examined this process, specifically the transformation of aqua cobalt (II) complexes to their fully halogenated species. The results reveal a stepwise mechanism with time scales varying from hundreds of picoseconds to nanoseconds. The dynamics are significantly faster when the structure is retained but becomes rate-limited when the octahedral-to-tetrahedral structural change bottlenecks the transformation. Evidence is presented, from bimolecular kinetics and energetics (enthalpic and entropic), for a reaction in which the ligand assists the displacement of water molecules, with the retention of the entering ligand in the activated state. The reaction time scale deviates by one to two orders of magnitude from that of ionic diffusion, suggesting the involvement of a collisional barrier between the ion and the much larger complex
Theoretical Performance Bound of Uplink Channel Estimation Accuracy in Massive MIMO
In this paper, we present a new performance bound for uplink channel
estimation (CE) accuracy in the Massive Multiple Input Multiple Output (MIMO)
system. The proposed approach is based on noise power prediction after the CE
unit. Our method outperforms the accuracy of a well-known Cramer-Rao lower
bound (CRLB) due to considering more statistics since performance strongly
depends on a number of channel taps and power ratio between them. Simulation
results are presented for the non-line of sight (NLOS) 3D-UMa model of 5G
QuaDRiGa 2.0 channel and compared with CRLB and state-of-the-art CE algorithms.Comment: accepted for presentation in a poster session at the ICASSP 2020
conferenc
Study of temperature dependence for the electron injection-induced effects in GaN
Electron-beam injection-induced increase of minority carrier diffusion length in p-type GaN was studied as a function of sample temperature ranging from 25 degreesC to 130 degreesC. It was found that the rate for diffusion length increase exponentially decays with increasing temperature. This decay was attributed to a temperature-activated release of electron-beam injected electrons trapped on Mg levels. The activation energy of these levels was found to be similar to178 meV. This is in good agreement with the previously reported position for Mg levels in the GaN band gap
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