1,503 research outputs found
Topological properties defined by nets
AbstractNets are used to generalize a result of Murtinová and to define and study a class of properties related to sequential compactness
Correlation functions quantify super-resolution images and estimate apparent clustering due to over-counting
We present an analytical method to quantify clustering in super-resolution
localization images of static surfaces in two dimensions. The method also
describes how over-counting of labeled molecules contributes to apparent
self-clustering and how the effective lateral resolution of an image can be
determined. This treatment applies to clustering of proteins and lipids in
membranes, where there is significant interest in using super-resolution
localization techniques to probe membrane heterogeneity. When images are
quantified using pair correlation functions, the magnitude of apparent
clustering due to over-counting will vary inversely with the surface density of
labeled molecules and does not depend on the number of times an average
molecule is counted. Over-counting does not yield apparent co-clustering in
double label experiments when pair cross-correlation functions are measured. We
apply our analytical method to quantify the distribution of the IgE receptor
(Fc{\epsilon}RI) on the plasma membranes of chemically fixed RBL-2H3 mast cells
from images acquired using stochastic optical reconstruction microscopy (STORM)
and scanning electron microscopy (SEM). We find that apparent clustering of
labeled IgE bound to Fc{\epsilon}RI detected with both methods arises from
over-counting of individual complexes. Thus our results indicate that these
receptors are randomly distributed within the resolution and sensitivity limits
of these experiments.Comment: 22 pages, 5 figure
DC-electric-field-induced and low-frequency electromodulation second-harmonic generation spectroscopy of Si(001)-SiO interfaces
The mechanism of DC-Electric-Field-Induced Second-Harmonic (EFISH) generation
at weakly nonlinear buried Si(001)-SiO interfaces is studied experimentally
in planar Si(001)-SiO-Cr MOS structures by optical second-harmonic
generation (SHG) spectroscopy with a tunable Ti:sapphire femtosecond laser. The
spectral dependence of the EFISH contribution near the direct two-photon
transition of silicon is extracted. A systematic phenomenological model of the
EFISH phenomenon, including a detailed description of the space charge region
(SCR) at the semiconductor-dielectric interface in accumulation, depletion, and
inversion regimes, has been developed. The influence of surface quantization
effects, interface states, charge traps in the oxide layer, doping
concentration and oxide thickness on nonlocal screening of the DC-electric
field and on breaking of inversion symmetry in the SCR is considered. The model
describes EFISH generation in the SCR using a Green function formalism which
takes into account all retardation and absorption effects of the fundamental
and second harmonic (SH) waves, optical interference between field-dependent
and field-independent contributions to the SH field and multiple reflection
interference in the SiO layer. Good agreement between the phenomenological
model and our recent and new EFISH spectroscopic results is demonstrated.
Finally, low-frequency electromodulated EFISH is demonstrated as a useful
differential spectroscopic technique for studies of the Si-SiO interface in
silicon-based MOS structures.Comment: 31 pages, 14 figures, 1 table, figures are also available at
http://kali.ilc.msu.su/articles/50/efish.ht
Biases in abundance derivations for metal-rich nebulae
Using ab-initio photoionization models of giant HII regions, we test methods
for abundance determinations based on a direct measurement of the electron
temperature, now possible even for moderate to high-metallicity objects. We
find that, for metallicities larger than solar, the computed abundances deviate
systematically from the real ones, generally by larger amounts for more
metal-rich HII regions. We discuss the reasons for this, and present diagrams
allowing the reader to better understand the various factors coming into play.
We briefly discuss less classical methods to derive abundances in metal-rich
HII regions. In particular, we comment on the interest of the oxygen and carbon
recombination lines. We also show that, contrary to the case of giant HII
regions, the physical conditions in bright extragalactic planetary nebulae are
such that their chemical composition can be accurately derived even at high
metallicities. Thus, extragalactic planetary nebulae are promising potential
probes of the metallicity of the interstellar medium in the internal parts of
spiral galaxies as well as in metal-rich elliptical galaxies.Comment: 15 pages, 13 figures, Accepted for publication in A&
Results from the Super Cryogenic Dark Matter Search (SuperCDMS) experiment at Soudan
We report the result of a blinded search for Weakly Interacting Massive
Particles (WIMPs) using the majority of the SuperCDMS Soudan dataset. With an
exposure of 1690 kg days, a single candidate event is observed, consistent with
expected backgrounds. This analysis (combined with previous Ge results) sets an
upper limit on the spin-independent WIMP--nucleon cross section of () cm at 46 GeV/. These results set the
strongest limits for WIMP--germanium-nucleus interactions for masses 12
GeV/
Long-distance endosome trafficking drives fungal effector production during plant infection
To cause plant disease, pathogenic fungi can secrete effector proteins into plant cells to suppress plant immunity and facilitate fungal infection. Most fungal pathogens infect plants using very long strand-like cells, called hyphae, that secrete effectors from their tips into host tissue. How fungi undergo long-distance cell signalling to regulate effector production during infection is not known. Here we show that long-distance retrograde motility of early endosomes (EEs) is necessary to trigger transcription of effector-encoding genes during plant infection by the pathogenic fungus Ustilago maydis. We demonstrate that motor-dependent retrograde EE motility is necessary for regulation of effector production and secretion during host cell invasion. We further show that retrograde signalling involves the mitogen-activated kinase Crk1 that travels on EEs and participates in control of effector production. Fungal pathogens therefore undergo long-range signalling to orchestrate host invasion
Double parton interactions in photon+3 jet events in ppbar collisions sqrt{s}=1.96 TeV
We have used a sample of photon+3 jets events collected by the D0 experiment
with an integrated luminosity of about 1 fb^-1 to determine the fraction of
events with double parton scattering (f_DP) in a single ppbar collision at
sqrt{s}=1.96 TeV. The DP fraction and effective cross section (sigma_eff), a
process-independent scale parameter related to the parton density inside the
nucleon, are measured in three intervals of the second (ordered in pT) jet
transverse momentum pT_jet2 within the range 15 < pT_jet2 < 30 GeV. In this
range, f_DP varies between 0.23 < f_DP < 0.47, while sigma_eff has the average
value sigma_eff_ave = 16.4 +- 0.3(stat) +- 2.3(syst) mb.Comment: 15 pages, 13 figure
Dependence of the production cross section on the transverse momentum of the top quark
We present a measurement of the differential cross section for
events produced in collisions at TeV as a function
of the transverse momentum () of the top quark. The selected events
contain a high- lepton (), four or more jets, and a large imbalance
in , and correspond to 1 fb of integrated luminosity recorded
with the D0 detector. Each event must have at least one candidate for a
jet. Objects in the event are associated through a constrained kinematic fit to
the process. Results
from next-to-leading-order perturbative QCD calculations agree with the
measured differential cross section. Comparisons are also provided to
predictions from Monte Carlo event generators using QCD calculations at
different levels of precision.Comment: 8 pages, 6 figures, 4 tables, updated to reflect the published
versio
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