6,457 research outputs found
Mulch Types on Soil Temperature at Varying Depths in Drip Irrigated Summer and Winter Peppers
Mulch Types on Soil Temperature at Varying Depths in Drip Irrigated Summer and Winter Pepper
Non-canonical binding site for bacterial initiation factor 3 on the large ribosomal subunit.
Canonical translation initiation in bacteria entails the assembly of the 30S initiation complex (IC), which binds the 50S subunit to form a 70S IC. IF3, a key initiation factor, is recruited to the 30S subunit at an early stage and is displaced from its primary binding site upon subunit joining. We employed four different FRET pairs to monitor IF3 relocation after 50S joining. IF3 moves away from the 30S subunit, IF1 and IF2, but can remain bound to the mature 70S IC. The secondary binding site is located on the 50S subunit in the vicinity of ribosomal protein L33. The interaction between IF3 and the 50S subunit is largely electrostatic with very high rates of IF3 binding and dissociation. The existence of the non-canonical binding site may help explain how IF3 participates in alternative initiation modes performed directly by the 70S ribosomes, such as initiation on leaderless mRNAs or re-initiation
ESTIMATION OF POTENTIAL EVAPOTRANSPIRATION WITH HARGREAVES-SAMANI MODEL AT VARIOUS LOCATIONS IN PUERTO RICO
ESTIMATION OF POTENTIAL EVAPOTRANSPIRATION WITH HARGREAVES-SAMANI MODEL AT VARIOUS LOCATIONS IN PUERTO RIC
ac Losses in a Finite Z Stack Using an Anisotropic Homogeneous-Medium Approximation
A finite stack of thin superconducting tapes, all carrying a fixed current I,
can be approximated by an anisotropic superconducting bar with critical current
density Jc=Ic/2aD, where Ic is the critical current of each tape, 2a is the
tape width, and D is the tape-to-tape periodicity. The current density J must
obey the constraint \int J dx = I/D, where the tapes lie parallel to the x axis
and are stacked along the z axis. We suppose that Jc is independent of field
(Bean approximation) and look for a solution to the critical state for
arbitrary height 2b of the stack. For c<|x|<a we have J=Jc, and for |x|<c the
critical state requires that Bz=0. We show that this implies \partial
J/\partial x=0 in the central region. Setting c as a constant (independent of
z) results in field profiles remarkably close to the desired one (Bz=0 for
|x|<c) as long as the aspect ratio b/a is not too small. We evaluate various
criteria for choosing c, and we show that the calculated hysteretic losses
depend only weakly on how c is chosen. We argue that for small D/a the
anisotropic homogeneous-medium approximation gives a reasonably accurate
estimate of the ac losses in a finite Z stack. The results for a Z stack can be
used to calculate the transport losses in a pancake coil wound with
superconducting tape.Comment: 21 pages, 17 figures, accepted by Supercond. Sci. Techno
Optimizing spread dynamics on graphs by message passing
Cascade processes are responsible for many important phenomena in natural and
social sciences. Simple models of irreversible dynamics on graphs, in which
nodes activate depending on the state of their neighbors, have been
successfully applied to describe cascades in a large variety of contexts. Over
the last decades, many efforts have been devoted to understand the typical
behaviour of the cascades arising from initial conditions extracted at random
from some given ensemble. However, the problem of optimizing the trajectory of
the system, i.e. of identifying appropriate initial conditions to maximize (or
minimize) the final number of active nodes, is still considered to be
practically intractable, with the only exception of models that satisfy a sort
of diminishing returns property called submodularity. Submodular models can be
approximately solved by means of greedy strategies, but by definition they lack
cooperative characteristics which are fundamental in many real systems. Here we
introduce an efficient algorithm based on statistical physics for the
optimization of trajectories in cascade processes on graphs. We show that for a
wide class of irreversible dynamics, even in the absence of submodularity, the
spread optimization problem can be solved efficiently on large networks.
Analytic and algorithmic results on random graphs are complemented by the
solution of the spread maximization problem on a real-world network (the
Epinions consumer reviews network).Comment: Replacement for "The Spread Optimization Problem
Smoothed Analysis of Tensor Decompositions
Low rank tensor decompositions are a powerful tool for learning generative
models, and uniqueness results give them a significant advantage over matrix
decomposition methods. However, tensors pose significant algorithmic challenges
and tensors analogs of much of the matrix algebra toolkit are unlikely to exist
because of hardness results. Efficient decomposition in the overcomplete case
(where rank exceeds dimension) is particularly challenging. We introduce a
smoothed analysis model for studying these questions and develop an efficient
algorithm for tensor decomposition in the highly overcomplete case (rank
polynomial in the dimension). In this setting, we show that our algorithm is
robust to inverse polynomial error -- a crucial property for applications in
learning since we are only allowed a polynomial number of samples. While
algorithms are known for exact tensor decomposition in some overcomplete
settings, our main contribution is in analyzing their stability in the
framework of smoothed analysis.
Our main technical contribution is to show that tensor products of perturbed
vectors are linearly independent in a robust sense (i.e. the associated matrix
has singular values that are at least an inverse polynomial). This key result
paves the way for applying tensor methods to learning problems in the smoothed
setting. In particular, we use it to obtain results for learning multi-view
models and mixtures of axis-aligned Gaussians where there are many more
"components" than dimensions. The assumption here is that the model is not
adversarially chosen, formalized by a perturbation of model parameters. We
believe this an appealing way to analyze realistic instances of learning
problems, since this framework allows us to overcome many of the usual
limitations of using tensor methods.Comment: 32 pages (including appendix
Young stellar population and ongoing star formation in the HII complex Sh2-252
In this paper an extensive survey of the star forming complex Sh2-252 has
been undertaken with an aim to explore its hidden young stellar population as
well as to understand the structure and star formation history. This complex is
composed of five embedded clusters associated with the sub-regions A, C, E, NGC
2175s and Teu 136. Using 2MASS-NIR and Spitzer-IRAC, MIPS photometry we
identified 577 young stellar objects (YSOs), of which, 163 are Class I, 400 are
Class II and 14 are transition disk YSOs. Spatial distribution of the candidate
YSOs shows that they are mostly clustered around the sub-regions in the western
half of the complex, suggesting enhanced star formation activity towards its
west. Using the spectral energy distribution and optical colour-magnitude
diagram based age analyses, we derived probable evolutionary status of the
sub-regions of Sh2-252. Our analysis shows that the region A is the youngest (~
0.5 Myr), the regions B, C and E are of similar evolutionary stage (~ 1-2 Myr)
and the clusters NGC 2175s and Teu 136 are slightly evolved (~ 2-3 Myr).
Morphology of the region in the 1.1 mm map shows a semi-circular shaped
molecular shell composed of several clumps and YSOs bordering the western
ionization front of Sh2-252. Our analyses suggest that next generation star
formation is currently under way along this border and that possibly
fragmentation of the matter collected during the expansion of the HII region as
one of the major processes responsible for such stars. We observed the densest
concentration of YSOs (mostly Class I, ~ 0.5 Myr) at the western outskirts of
the complex, within a molecular clump associated with water and methanol masers
and we suggest that it is indeed a site of cluster formation at a very early
evolutionary stage, sandwiched between the two relatively evolved CHII regions
A and B.Comment: 19 pages, 13 figures, Accepted for publication in MNRA
Evolution of Coordination in Social Networks: A Numerical Study
Coordination games are important to explain efficient and desirable social
behavior. Here we study these games by extensive numerical simulation on
networked social structures using an evolutionary approach. We show that local
network effects may promote selection of efficient equilibria in both pure and
general coordination games and may explain social polarization. These results
are put into perspective with respect to known theoretical results. The main
insight we obtain is that clustering, and especially community structure in
social networks has a positive role in promoting socially efficient outcomes.Comment: preprint submitted to IJMP
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