1,057 research outputs found
Baryonically Closed Galaxy Groups
Elliptical galaxies and their groups having the largest L_x/L_B lie close to
the locus in the L_x,L_B diagram expected for closed systems with baryon
fractions equal to the cosmic mean value, f_b = 0.16. The estimated baryon
fractions for several of these galaxies/groups are also close to 0.16 when the
gas density is extrapolated to the virial radius. Evidently they are the least
massive baryonically closed systems. Gas retention in these groups implies that
non-gravitational heating cannot exceed about 1 keV per particle, consistent
with the heating required to produce the deviation of groups from the L_x - T
correlation for more massive clusters. Isolated galaxies/groups with X-ray
luminosities significantly lower than baryonically closed groups may have
undermassive dark halos, overactive central AGNs, or higher star formation
efficiencies. The virial mass and hot gas temperatures of nearly or completely
closed groups correlate with the group X-ray luminosities and the optical
luminosities of the group-centered elliptical galaxy, an expected consequence
of their merging history. The ratio of halo mass to the mass of the central
galaxy for X-ray luminous galaxy/groups is about 80.Comment: 7 pages; Accepted by ApJ Letter
Disruption of the UL41 gene in the herpes simplex virus 2 dl5-29 mutant increases its immunogenicity and protective capacity in a murine model of genital herpes
AbstractThe herpes simplex virus 2 dl5-29 replication-defective mutant virus has been shown to induce protective immunity in mice and both prophylactic and therapeutic immunity in guinea pigs. In an attempt to improve the efficacy of dl5-29 we disrupted its UL41 gene, producing the triple mutant virus dl5-29-41L. dl5-29-41L has a decreased ability to inhibit host cell protein synthesis and a reduced cytopathic effect on cultured cells. When used to immunize mice, dl5-29-41L elicited significantly stronger neutralizing antibody responses and significantly stronger CD4+ and CD8+ cellular immune responses than dl5-29. The enhanced immune responses corresponded with increased protective capacity in a murine model of genital herpes. The protective immunity elicited by either virus was very durable, protecting mice for at least 7 months. Furthermore, we show that cell lysate preparations of both viruses were significantly more efficacious than the corresponding extracellular virus preparations
Evolutionary tracks for Betelgeuse
We have constructed a series of non-rotating quasi-hydrostatic evolutionary
models for the M2 Iab supergiant Betelgeuse (). Our models are
constrained by multiple observed values for the temperature, luminosity,
surface composition and mass loss for this star, along with the parallax
distance and high resolution imagery that determines its radius. We have then
applied our best-fit models to analyze the observed variations in surface
luminosity and the size of detected surface bright spots as the result of
up-flowing convective material from regions of high temperature in the surface
convective zone. We also attempt to explain the intermittently observed
periodic variability in a simple radial linear adiabatic pulsation model. Based
upon the best fit to all observed data, we suggest a best progenitor mass
estimate of and a current age from the start of the
zero-age main sequence of Myr based upon the observed ejected mass
while on the giant branch.Comment: 27 pages, 11 figures, Revised per referee suggestions, Accepted for
publication in the Astrophysical Journa
Detection of non-coding RNAs on the basis of predicted secondary structure formation free energy change
BACKGROUND: Non-coding RNAs (ncRNAs) have a multitude of roles in the cell, many of which remain to be discovered. However, it is difficult to detect novel ncRNAs in biochemical screens. To advance biological knowledge, computational methods that can accurately detect ncRNAs in sequenced genomes are therefore desirable. The increasing number of genomic sequences provides a rich dataset for computational comparative sequence analysis and detection of novel ncRNAs. RESULTS: Here, Dynalign, a program for predicting secondary structures common to two RNA sequences on the basis of minimizing folding free energy change, is utilized as a computational ncRNA detection tool. The Dynalign-computed optimal total free energy change, which scores the structural alignment and the free energy change of folding into a common structure for two RNA sequences, is shown to be an effective measure for distinguishing ncRNA from randomized sequences. To make the classification as a ncRNA, the total free energy change of an input sequence pair can either be compared with the total free energy changes of a set of control sequence pairs, or be used in combination with sequence length and nucleotide frequencies as input to a classification support vector machine. The latter method is much faster, but slightly less sensitive at a given specificity. Additionally, the classification support vector machine method is shown to be sensitive and specific on genomic ncRNA screens of two different Escherichia coli and Salmonella typhi genome alignments, in which many ncRNAs are known. The Dynalign computational experiments are also compared with two other ncRNA detection programs, RNAz and QRNA. CONCLUSION: The Dynalign-based support vector machine method is more sensitive for known ncRNAs in the test genomic screens than RNAz and QRNA. Additionally, both Dynalign-based methods are more sensitive than RNAz and QRNA at low sequence pair identities. Dynalign can be used as a comparable or more accurate tool than RNAz or QRNA in genomic screens, especially for low-identity regions. Dynalign provides a method for discovering ncRNAs in sequenced genomes that other methods may not identify. Significant improvements in Dynalign runtime have also been achieved
Fully quantum mechanical dynamic analysis of single-photon transport in a single-mode waveguide coupled to a traveling-wave resonator
We analyze the dynamics of single photon transport in a single-mode waveguide
coupled to a micro-optical resonator using a fully quantum mechanical model. We
examine the propagation of a single-photon Gaussian packet through the system
under various coupling conditions. We review the theory of single photon
transport phenomena as applied to the system and we develop a discussion on the
numerical technique we used to solve for dynamical behavior of the quantized
field. To demonstrate our method and to establish robust single photon results,
we study the process of adiabatically lowering or raising the energy of a
single photon trapped in an optical resonator under active tuning of the
resonator. We show that our fully quantum mechanical approach reproduces the
semi-classical result in the appropriate limit and that the adiabatic invariant
has the same form in each case. Finally, we explore the trapping of a single
photon in a system of dynamically tuned, coupled optical cavities.Comment: 24 pages, 10 figure
The X-Ray Concentration-Virial Mass Relation
We present the concentration (c)-virial mass (M) relation of 39 galaxy
systems ranging in mass from individual early-type galaxies up to the most
massive galaxy clusters, (0.06-20) x 10^{14} M_sun. We selected for analysis
the most relaxed systems possessing the highest quality data currently
available in the Chandra and XMM public data archives. A power-law model fitted
to the X-ray c-M relation requires at high significance (6.6 sigma) that c
decreases with increasing M, which is a general feature of CDM models. The
median and scatter of the c-M relation produced by the flat, concordance LCDM
model (Omega_m=0.3, sigma_8=0.9) agrees with the X-ray data provided the sample
is comprised of the most relaxed, early forming systems, which is consistent
with our selection criteria. Holding the rest of the cosmological parameters
fixed to those in the concordance model the c-M relation requires 0.76< sigma_8
<1.07 (99% conf.), assuming a 10% upward bias in the concentrations for early
forming systems. The tilted, low-sigma_8 model suggested by a new WMAP analysis
is rejected at 99.99% confidence, but a model with the same tilt and
normalization can be reconciled with the X-ray data by increasing the dark
energy equation of state parameter to w ~ -0.8. When imposing the additional
constraint of the tight relation between sigma_8 and Omega_m from studies of
cluster abundances, the X-ray c-M relation excludes (>99% conf.) both open CDM
models and flat CDM models with Omega_m ~1. This result provides novel evidence
for a flat, low-Omega_m universe with dark energy using observations only in
the local (z << 1) universe. Possible systematic errors in the X-ray mass
measurements of a magnitude ~10% suggested by CDM simulations do not change our
conclusions.Comment: Accepted for Publication in ApJ; 13 pages, 4 figures; minor
clarifications and updates; correlation coefficients corrected in Table 1
(correct values were used in the analysis in previous versions); conclusions
unchange
The Absence of Adiabatic Contraction of the Radial Dark Matter Profile in the Galaxy Cluster A2589
We present an X-ray analysis of the radial mass profile of the radio-quiet
galaxy cluster A2589 between 0.015-0.25 r_vir using an XMM-Newton observation.
Except for a ~16 kpc shift of the X-ray center of the R=45-60 kpc annulus,
A2589 possesses a remarkably symmetrical X-ray image and is therefore an
exceptional candidate for precision studies of its mass profile by applying
hydrostatic equilibrium. The total gravitating matter profile is well described
by the NFW model (fractional residuals <~10%) with c_vir=6.1 +/- 0.3 and M_vir
= 3.3 +/- 0.3 x 10^{14} M_sun (r_vir = 1.74 +/- 0.05 Mpc) in excellent
agreement with LCDM. When the mass of the hot ICM is subtracted from the
gravitating matter profile, the NFW model fitted to the resulting dark matter
(DM) profile produces essentially the same result. However, if a component
accounting for the stellar mass (M_*) of the cD galaxy is included, then the
NFW fit to the DM profile is substantially degraded in the central r ~50 kpc
for reasonable M_*/L_V. Modifying the NFW DM halo by adiabatic contraction
arising from the early condensation of stellar baryons in the cD galaxy further
degrades the fit. The fit is improved substantially with a Sersic-like model
recently suggested by high resolution N-body simulations but with an inverse
Sersic index, alpha ~0.5, a factor of ~3 higher than predicted. We argue that
neither random turbulent motions nor magnetic fields can provide sufficient
non-thermal pressure support to reconcile the XMM mass profile with adiabatic
contraction of a CDM halo assuming reasonable M_*/L_V. Our results support the
scenario where, at least for galaxy clusters, processes during halo formation
counteract adiabatic contraction so that the total gravitating mass in the core
approximately follows the NFW profile.Comment: 15 pages, 11 figures, accepted for publication in ApJ. Minor changes
to match published versio
Masses and Mixings in a Grand Unified Toy Model
The generation of the fermion mass hierarchy in the standard model of
particle physics is a long-standing puzzle. The recent discoveries from
neutrino physics suggests that the mixing in the lepton sector is large
compared to the quark mixings. To understand this asymmetry between the quark
and lepton mixings is an important aim for particle physics. In this regard,
two promising approaches from the theoretical side are grand unified theories
and family symmetries. In this note we try to understand certain general
features of grand unified theories with Abelian family symmetries by taking the
simplest SU(5) grand unified theory as a prototype. We construct an SU(5) toy
model with family symmetry
that, in a natural way, duplicates the observed mass hierarchy and mixing
matrices to lowest approximation. The system for generating the mass hierarchy
is through a Froggatt-Nielsen type mechanism. One idea that we use in the model
is that the quark and charged lepton sectors are hierarchical with small mixing
angles while the light neutrino sector is democratic with larger mixing angles.
We also discuss some of the difficulties in incorporating finer details into
the model without making further assumptions or adding a large scalar sector.Comment: 21 pages, 2 figures, RevTeX, v2: references updated and typos
corrected, v3: updated top quark mass, comments on MiniBooNE result, and
typos correcte
Vacuum Stability with Tachyonic Boundary Higgs Masses in No-Scale Supersymmetry or Gaugino Mediation
No-scale supersymmetry or gaugino mediation augmented with large negative
Higgs soft masses at the input scale provides a simple solution to the
supersymmetric flavor problem while giving rise to a neutralino LSP. However,
to obtain a neutralino LSP it is often necessary to have tachyonic input Higgs
soft masses that can give rise to charge-and-color-breaking (CCB) minima and
unbounded-from-below (UFB) directions in the low energy theory. We investigate
the vacuum structure in these theories to determine when such problematic
features are present. When the standard electroweak vacuum is only metastable,
we compute its lifetime under vacuum tunneling. We find that vacuum
metastability leads to severe restrictions on the parameter space for larger
, while for smaller , only minor
restrictions are found. Along the way, we derive an exact bounce solution for
tunneling through an inverted parabolic potential.Comment: 18 Pages, 5 Figure
Magnetization reversal mechanism in La0.67Sr0.33MnO3 thin films on NdGaO3 substrates
The field angle dependence of the coercive field of La0.67Sr0.33MnO3 thin films grown epitaxially on NdGaO3 substrates with different crystallographic orientations was determined. All films show uniaxial anisotropy. The angle dependence of the coercivity is best described by a two-phase model, explaining the strong increase in the coercive field for increasing field angles, away from the easy axis direction, as well as the sharp decrease for angles close to the hard direction. This implies that magnetization reversal starts with the depinning of domain walls, analogous to the Kondorsky model. With increasing field the reversal in the domains is not abrupt, but is determined by the gradual displacement of the domain walls. These results are of significance for understanding and possibly engineering of the switching behavior of magnetic tunnel junctions
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