3,265 research outputs found
Cosmological Constraints from Moments of the Thermal Sunyaev-Zel'dovich Effect
In this paper, we explain how moments of the thermal Sunyaev-Zel'dovich (tSZ)
effect can constrain both cosmological parameters and the astrophysics of the
intracluster medium (ICM). As the tSZ signal is strongly non-Gaussian, higher
moments of tSZ maps contain useful information. We first calculate the
dependence of the tSZ moments on cosmological parameters, finding that higher
moments scale more steeply with sigma_8 and are sourced by more massive galaxy
clusters. Taking advantage of the different dependence of the variance and
skewness on cosmological and astrophysical parameters, we construct a
statistic, ||/^1.4, which cancels much of the dependence on cosmology
(i.e., sigma_8) yet remains sensitive to the astrophysics of intracluster gas
(in particular, to the gas fraction in low-mass clusters). Constraining the ICM
astrophysics using this statistic could break the well-known degeneracy between
cosmology and gas physics in tSZ measurements, allowing for tight constraints
on cosmological parameters. Although detailed simulations will be needed to
fully characterize the accuracy of this technique, we provide a first
application to data from the Atacama Cosmology Telescope and the South Pole
Telescope. We estimate that a Planck-like full-sky tSZ map could achieve a <1%
constraint on sigma_8 and a 1-sigma error on the sum of the neutrino masses
that is comparable to the existing lower bound from oscillation measurements.Comment: 11 pages, 12 figures, to be submitted to Phys. Rev. D; v2: 14 pages,
16 figures, matches PRD accepted version (changes from v1 include additional
calculations with primordial non-Gaussianity and a new appendix discussing
the tSZ kurtosis
Making graphene visible
Microfabrication of graphene devices used in many experimental studies
currently relies on the fact that graphene crystallites can be visualized using
optical microscopy if prepared on top of silicon wafers with a certain
thickness of silicon dioxide. We study graphene's visibility and show that it
depends strongly on both thickness of silicon dioxide and light wavelength. We
have found that by using monochromatic illumination, graphene can be isolated
for any silicon dioxide thickness, albeit 300 nm (the current standard) and,
especially, approx. 100 nm are most suitable for its visual detection. By using
a Fresnel-law-based model, we quantitatively describe the experimental data
without any fitting parameters.Comment: Since v1: minor changes to text and figures to improve clarity;
references added. Submitted to Applied Physics Letters, 30-Apr-07. 3 pages, 3
figure
On resonant scatterers as a factor limiting carrier mobility in graphene
We show that graphene deposited on a substrate has a non-negligible density
of atomic scale defects. This is evidenced by a previously unnoticed D peak in
the Raman spectra with intensity of about 1% with respect to the G peak. We
evaluated the effect of such impurities on electron transport by mimicking them
with hydrogen adsorbates and measuring the induced changes in both mobility and
Raman intensity. If the intervalley scatterers responsible for the D peak are
monovalent, their concentration is sufficient to account for the limited
mobilities achievable in graphene on a substrate.Comment: version 2: several comments are taken into account and refs adde
Hyperoxia Causes Mitochondrial Fragmentation in Pulmonary Endothelial Cells by Increasing Expression of Pro-Fission Proteins
Objective—We explored mechanisms that alter mitochondrial structure and function in pulmonary endothelial cells (PEC) function after hyperoxia. Approach and Results—Mitochondrial structures of PECs exposed to hyperoxia or normoxia were visualized and mitochondrial fragmentation quantified. Expression of pro-fission or fusion proteins or autophagy-related proteins were assessed by Western blot. Mitochondrial oxidative state was determined using mito-roGFP. Tetramethylrhodamine methyl ester estimated mitochondrial polarization in treatment groups. The role of mitochondrially derived reactive oxygen species in mt-fragmentation was investigated with mito-TEMPOL and mitochondrial DNA (mtDNA) damage studied by using ENDO III (mt-tat-endonuclease III), a protein that repairs mDNA damage. Drp-1 (dynamin-related protein 1) was overexpressed or silenced to test the role of this protein in cell survival or transwell resistance. Hyperoxia increased fragmentation of PEC mitochondria in a time-dependent manner through 48 hours of exposure. Hyperoxic PECs exhibited increased phosphorylation of Drp-1 (serine 616), decreases in Mfn1 (mitofusion protein 1), but increases in OPA-1 (optic atrophy 1). Pro-autophagy proteins p62 (LC3 adapter–binding protein SQSTM1/p62), PINK-1 (PTEN-induced putative kinase 1), and LC3B (microtubule-associated protein 1A/1B-light chain 3) were increased. Returning cells to normoxia for 24 hours reversed the increased mt-fragmentation and changes in expression of pro-fission proteins. Hyperoxia-induced changes in mitochondrial structure or cell survival were mitigated by antioxidants mito-TEMPOL, Drp-1 silencing, or inhibition or protection by the mitochondrial endonuclease ENDO III. Hyperoxia induced oxidation and mitochondrial depolarization and impaired transwell resistance. Decrease in resistance was mitigated by mito-TEMPOL or ENDO III and reproduced by overexpression of Drp-1. Conclusions—Because hyperoxia evoked mt-fragmentation, cell survival and transwell resistance are prevented by ENDO III and mito-TEMPOL and Drp-1 silencing, and these data link hyperoxia-induced mt-DNA damage, Drp-1 expression, mt-fragmentation, and PEC dysfunction
Radial Velocity Studies of Close Binary Stars. XI
Radial-velocity measurements and sine-curve fits to the orbital radial
velocity variations are presented for ten close binary systems: DU Boo, ET Boo,
TX Cnc, V1073 Cyg, HL Dra, AK Her, VW LMi, V566 Oph, TV UMi and AG Vir. By this
contribution, the DDO program has reached the point of 100 published radial
velocity orbits. The radial velocities have been determined using an improved
fitting technique which uses rotational profiles to approximate individual
peaks in broadening functions.
Three systems, ET Boo, VW LMi and TV UMi, were found to be quadruple while AG
Vir appears to be a spectroscopic triple. ET Boo, a member of a close visual
binary with years, was previously known to be a multiple
system, but we show that the second component is actually a close,
non-eclipsing binary. The new observations enabled us to determine the
spectroscopic orbits of the companion, non-eclipsing pairs in ET Boo and VW
LMi. The particularly interesting case is VW LMi, where the period of the
mutual revolution of the two spectroscopic binaries is only 355 days.
While most of the studied eclipsing pairs are contact binaries, ET Boo is
composed of two double-lined detached binaries and HL Dra is single-lined
detached or semi-detached system. Five systems of this group were observed
spectroscopically before: TX Cnc, V1073 Cyg, AK Her (as a single-lined binary),
V566 Oph, AG Vir, but our new data are of much higher quality than the previous
studies.Comment: Accepted by AJ, August 2006, 10 figures, 3 table
Radial Velocity Studies of Close Binary Stars. XV
Radial-velocity measurements and sine-curve fits to the orbital radial
velocity variations are presented for the last eight close binary systems
analyzed the same way as in the previous papers of this series: QX And, DY Cet,
MR Del, HI Dra, DD Mon, V868 Mon, ER Ori, and Y Sex. For another seven systems
(TT Cet, AA Cet, CW Lyn, V563 Lyr, CW Sge, LV Vir and MW Vir) phase coverage is
insufficient to provide reliable orbits but radial velocities of individual
components were measured. Observations of a few complicated systems observed
throughout the DDO close-binary program are also presented; among them an
especially interesting is the multiple system V857 Her which - in addition to
the contact binary - very probably contains one or more sub-dwarf components of
much earlier spectral type. All suspected binaries which were found to be most
probably pulsating stars are briefly discussed in terms of mean radial
velocities and projected rotation velocities (v sin i) as well as spectral type
estimates. In two of them, CU CVn and V752 Mon, the broadening functions show a
clear presence of non-radial pulsations. The previously missing spectral types
for the DDO I paper are given here in addition to such estimates for most of
the program stars of this paper.Comment: submitted to A
Physical and chemical conditions in methanol maser selected hot-cores and UCHII regions
We present the results of a targeted 3-mm spectral line survey towards the
eighty-three 6.67 GHz methanol maser selected star forming clumps observed by
Purcell et al. 2006. In addition to the previously reported measurements of
HCO+ (1 - 0), H13CO+ (1 - 0), and CH3CN (5 - 4) & (6 -5), we used the Mopra
antenna to detect emission lines of N2H+ (1 - 0), HCN (1 - 0) and HNC (1 - 0)
towards 82/83 clumps (99 per cent), and CH3OH (2 - 1) towards 78/83 clumps (94
per cent). The molecular line data have been used to derive virial and LTE
masses, rotational temperatures and chemical abundances in the clumps, and
these properties have been compared between sub-samples associated with
different indicators of evolution. The greatest differences are found between
clumps associated with 8.6 GHz radio emission, indicating the presence of an
Ultra-Compact HII region, and `isolated' masers (without associated radio
emission), and between clumps exhibiting CH3CN emission and those without. In
particular, thermal CH3OH is found to be brighter and more abundant in
Ultra-Compact HII (UCHII) regions and in sources with detected CH3CN, and may
constitute a crude molecular clock in single dish observations. Clumps
associated with 8.6 GHz radio emission tend to be more massive and more
luminous than clumps without radio emission. This is likely because the most
massive clumps evolve so rapidly that a Hyper-Compact HII or UCHII region is
the first visible tracer of star-formation. The gas-mass to sub-mm/IR
luminosity relation for the combined sample was found to be L proportional to
M**0.68, considerably shallower than expected for massive main-sequence stars
The Energetic Particle Detector (EPD) Investigation and the Energetic Ion Spectrometer (EIS) for the Magnetospheric Multiscale (MMS) Mission
Abstract The Energetic Particle Detector (EPD) Investigation is one of 5 fields-and-particles investigations on the Magnetospheric Multiscale (MMS) mission. MMS comprises 4 spacecraft flying in close formation in highly elliptical, near-Earth-equatorial orbits targeting understanding of the fundamental physics of the important physical process called magnetic reconnection using Earth’s magnetosphere as a plasma laboratory. EPD comprises two sensor types, the Energetic Ion Spectrometer (EIS) with one instrument on each of the 4 spacecraft, and the Fly’s Eye Energetic Particle Spectrometer (FEEPS) with 2 instruments on each of the 4 spacecraft. EIS measures energetic ion energy, angle and elemental compositional distributions from a required low energy limit of 20 keV for protons and 45 keV for oxygen ions, up to \u3e0.5 MeV (with capabilities to measure up to \u3e1 MeV). FEEPS measures instantaneous all sky images of energetic electrons from 25 keV to \u3e0.5 MeV, and also measures total ion energy distributions from 45 keV to \u3e0.5 MeV to be used in conjunction with EIS to measure all sky ion distributions. In this report we describe the EPD investigation and the details of the EIS sensor. Specifically we describe EPD-level science objectives, the science and measurement requirements, and the challenges that the EPD team had in meeting these requirements. Here we also describe the design and operation of the EIS instruments, their calibrated performances, and the EIS in-flight and ground operations. Blake et al. (The Flys Eye Energetic Particle Spectrometer (FEEPS) contribution to the Energetic Particle Detector (EPD) investigation of the Magnetospheric Magnetoscale (MMS) Mission, this issue) describe the design and operation of the FEEPS instruments, their calibrated performances, and the FEEPS in-flight and ground operations. The MMS spacecraft will launch in early 2015, and over its 2-year mission will provide comprehensive measurements of magnetic reconnection at Earth’s magnetopause during the 18 months that comprise orbital phase 1, and magnetic reconnection within Earth’s magnetotail during the about 6 months that comprise orbital phase 2
Bioengineering nisin to overcome the nisin resistance protein
The emergence and dissemination of antibiotic resistant bacteria is a major medical challenge. Lantibiotics are highly modified bacterially produced antimicrobial peptides that have attracted considerable interest as alternatives or adjuncts to existing antibiotics. Nisin, the most widely studied and commercially exploited lantibiotic, exhibits high efficacy against many pathogens. However, some clinically relevant bacteria express highly specific membrane‐associated nisin resistance proteins. One notable example is the nisin resistance protein (NSR) that acts by cleaving the peptide bond between ring E and the adjacent serine 29, resulting in a truncated peptide with significantly less activity. We utilised a complete bank of bioengineered nisin (nisin A) producers in which the serine 29 residue has been replaced with every alternative amino acid. The nisin A S29P derivative was found to be as active as nisin A against a variety of bacterial targets but, crucially, exhibited a 20‐fold increase in specific activity against a strain expressing the nisin resistance protein. Another derivative, nisin PV, exhibited similar properties but was much less prone to oxidation. This version of nisin with enhanced resistance to specific resistance mechanisms could prove useful in the fight against antibiotic resistant pathogens
Flowing with Time: a New Approach to Nonlinear Cosmological Perturbations
Nonlinear effects are crucial in order to compute the cosmological matter
power spectrum to the accuracy required by future generation surveys. Here, a
new approach is presented, in which the power spectrum, the bispectrum and
higher order correlations, are obtained -- at any redshift and for any momentum
scale -- by integrating a system of differential equations. The method is
similar to the familiar BBGKY hierarchy. Truncating at the level of the
trispectrum, the solution of the equations corresponds to the summation of an
infinite class of perturbative corrections. Compared to other resummation
frameworks, the scheme discussed here is particularly suited to cosmologies
other than LambdaCDM, such as those based on modifications of gravity and those
containing massive neutrinos. As a first application, we compute the Baryonic
Acoustic Oscillation feature of the power spectrum, and compare the results
with perturbation theory, the halo model, and N-body simulations. The
density-velocity and velocity-velocity power spectra are also computed, showing
that they are much less contaminated by nonlinearities than the density-density
one. The approach can be seen as a particular formulation of the
renormalization group, in which time is the flow parameter.Comment: 20 pages, 7 figures. Matches version published on JCA
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