635 research outputs found
Recommended from our members
Single-Cell RNA-seq Reveals Profound Alterations in Mechanosensitive Dorsal Root Ganglion Neurons with Vitamin E Deficiency.
Ninety percent of Americans consume less than the estimated average requirements of dietary vitamin E (vitE). Severe vitE deficiency due to genetic mutations in the tocopherol transfer protein (TTPA) in humans results in ataxia with vitE deficiency (AVED), with proprioceptive deficits and somatosensory degeneration arising from dorsal root ganglia neurons (DRGNs). Single-cell RNA-sequencing of DRGNs was performed in Ttpa-/- mice, an established model of AVED. In stark contrast to expected changes in proprioceptive neurons, Ttpa-/- DRGNs showed marked upregulation of voltage-gated Ca2+ and K+ channels in mechanosensitive, tyrosine-hydroxylase positive (TH+) DRGNs. The ensuing significant conductance changes resulted in reduced excitability in mechanosensitive Ttpa-/- DRGNs. A highly supplemented vitE diet (600 mg dl-α-tocopheryl acetate/kg diet) prevented the cellular and molecular alterations and improved mechanosensation. VitE deficiency profoundly alters the molecular signature and functional properties of mechanosensitive TH+ DRGN, representing an intriguing shift of the prevailing paradigm from proprioception to mechanical sensation
Design and Implementation of Views: Isolated Perspectives of a File System for Regulatory Compliance
We present Views, a file system architecture designed to meet the role-based access control (RBAC) requirement of federal regulations, such as those in HIPAA. Views allows for discrete IO entities, such as users, groups or processes, to have a logically complete but isolated perspective of the file system. Entities may perform IO using the standard system call interface without affecting the views of other entities. Views is designed to be file system independent, extremely easy to use and manage, and flexible in defining isolation and sharing polices. Our implementation of Views is built on ext3cow, which additionally provides versioning capabilities to all entities. Preliminary results show the performance of Views is comparable with other traditional disk file systems.The Johns Hopkins Universit
Open-target sparse sensing of biological agents using DNA microarray
Background
Current biosensors are designed to target and react to specific nucleic acid sequences or structural epitopes. These 'target-specific' platforms require creation of new physical capture reagents when new organisms are targeted. An 'open-target' approach to DNA microarray biosensing is proposed and substantiated using laboratory generated data. The microarray consisted of 12,900 25 bp oligonucleotide capture probes derived from a statistical model trained on randomly selected genomic segments of pathogenic prokaryotic organisms. Open-target detection of organisms was accomplished using a reference library of hybridization patterns for three test organisms whose DNA sequences were not included in the design of the microarray probes.
Results
A multivariate mathematical model based on the partial least squares regression (PLSR) was developed to detect the presence of three test organisms in mixed samples. When all 12,900 probes were used, the model correctly detected the signature of three test organisms in all mixed samples (mean(R2)) = 0.76, CI = 0.95), with a 6% false positive rate. A sampling algorithm was then developed to sparsely sample the probe space for a minimal number of probes required to capture the hybridization imprints of the test organisms. The PLSR detection model was capable of correctly identifying the presence of the three test organisms in all mixed samples using only 47 probes (mean(R2)) = 0.77, CI = 0.95) with nearly 100% specificity.
Conclusions
We conceived an 'open-target' approach to biosensing, and hypothesized that a relatively small, non-specifically designed, DNA microarray is capable of identifying the presence of multiple organisms in mixed samples. Coupled with a mathematical model applied to laboratory generated data, and sparse sampling of capture probes, the prototype microarray platform was able to capture the signature of each organism in all mixed samples with high sensitivity and specificity. It was demonstrated that this new approach to biosensing closely follows the principles of sparse sensing.Mitre Corporatio
The HBI in a quasi-global model of the intracluster medium
In this paper we investigate how convective instabilities influence heat
conduction in the intracluster medium (ICM) of cool-core galaxy clusters. The
ICM is a high-beta, weakly collisional plasma in which the transport of
momentum and heat is aligned with the magnetic field. The anisotropy of heat
conduction, in particular, gives rise to instabilities that can access energy
stored in a temperature gradient of either sign. We focus on the heat-flux
buoyancy-driven instability (HBI), which feeds on the outwardly increasing
temperature profile of cluster cool cores. Our aim is to elucidate how the
global structure of a cluster impacts on the growth and morphology of the
linear HBI modes when in the presence of Braginskii viscosity, and ultimately
on the ability of the HBI to thermally insulate cores. We employ an idealised
quasi-global model, the plane-parallel atmosphere, which captures the essential
physics -- e.g. the global radial profile of the cluster -- while letting the
problem remain analytically tractable. Our main result is that the dominant HBI
modes are localised to the the innermost (~<20%) regions of cool cores. It is
then probable that, in the nonlinear regime, appreciable field-line insulation
will be similarly localised. Thus, while radio-mode feedback appears necessary
in the central few tens of kpc, heat conduction may be capable of offsetting
radiative losses throughout most of a cool core over a significant fraction of
the Hubble time. Finally, our linear solutions provide a convenient numerical
test for the nonlinear codes that tackle the saturation of such convective
instabilities in the presence of anisotropic transport.Comment: MNRAS, in press; minor modifications from v
The Lick AGN Monitoring Project: Broad-Line Region Radii and Black Hole Masses from Reverberation Mapping of Hbeta
We have recently completed a 64-night spectroscopic monitoring campaign at
the Lick Observatory 3-m Shane telescope with the aim of measuring the masses
of the black holes in 12 nearby (z < 0.05) Seyfert 1 galaxies with expected
masses in the range ~10^6-10^7 M_sun and also the well-studied nearby active
galactic nucleus (AGN) NGC 5548. Nine of the objects in the sample (including
NGC 5548) showed optical variability of sufficient strength during the
monitoring campaign to allow for a time lag to be measured between the
continuum fluctuations and the response to these fluctuations in the broad
Hbeta emission. We present here the light curves for the objects in this sample
and the subsequent Hbeta time lags for the nine objects where these
measurements were possible. The Hbeta lag time is directly related to the size
of the broad-line region, and by combining the lag time with the measured width
of the Hbeta emission line in the variable part of the spectrum, we determine
the virial mass of the central supermassive black hole in these nine AGNs. The
absolute calibration of the black hole masses is based on the normalization
derived by Onken et al. We also examine the time lag response as a function of
velocity across the Hbeta line profile for six of the AGNs. The analysis of
four leads to ambiguous results with relatively flat time lags as a function of
velocity. However, SBS 1116+583A exhibits a symmetric time lag response around
the line center reminiscent of simple models for circularly orbiting broad-line
region (BLR) clouds, and Arp 151 shows an asymmetric profile that is most
easily explained by a simple gravitational infall model. Further investigation
will be necessary to fully understand the constraints placed on physical models
of the BLR by the velocity-resolved response in these objects.Comment: 24 pages, 16 figures and 13 tables, submitted to Ap
Recommended from our members
Zebrafish behavioural profiling identifies GABA and serotonin receptor ligands related to sedation and paradoxical excitation.
Anesthetics are generally associated with sedation, but some anesthetics can also increase brain and motor activity-a phenomenon known as paradoxical excitation. Previous studies have identified GABAA receptors as the primary targets of most anesthetic drugs, but how these compounds produce paradoxical excitation is poorly understood. To identify and understand such compounds, we applied a behavior-based drug profiling approach. Here, we show that a subset of central nervous system depressants cause paradoxical excitation in zebrafish. Using this behavior as a readout, we screened thousands of compounds and identified dozens of hits that caused paradoxical excitation. Many hit compounds modulated human GABAA receptors, while others appeared to modulate different neuronal targets, including the human serotonin-6 receptor. Ligands at these receptors generally decreased neuronal activity, but paradoxically increased activity in the caudal hindbrain. Together, these studies identify ligands, targets, and neurons affecting sedation and paradoxical excitation in vivo in zebrafish
Intensive HST, RXTE and ASCA Monitoring of NGC 3516: Evidence Against Thermal Reprocessing
During 1998 April 13-16, NGC 3516 was monitored almost continuously with HST
for 10.3 hr in the UV and 2.8 d in the optical, and simultaneous RXTE and ASCA
monitoring covered the same period. The X-rays were strongly variable with the
soft (0.5-2 keV) showing stronger variations (~65% peak-to-peak) than the hard
(2-10 keV; ~50% peak-to-peak). The optical continuum showed much smaller but
highly significant variations: a slow ~2.5% rise followed by a faster ~3.5%
decline. The short UV observation did not show significant variability.
The soft and hard X-ray light curves were strongly correlated with no
significant lag. Likewise, the optical continuum bands (3590 and 5510 A) were
also strongly correlated with no measurable lag above limits of <0.15 d.
However no significant correlation or simple relationship could be found for
the optical and X-ray light curves. These results appear difficult to reconcile
with previous reports of correlations between X-ray and optical variations and
of measurable lags within the optical band for some other Seyfert 1s.
These results also present serious problems for "reprocessing" models in
which the X-ray source heats a stratified accretion disk which then reemits in
the optical/ultraviolet: the synchronous variations within the optical would
suggest that the emitting region is <0.3 lt-d across, while the lack of
correlation between X-ray and optical variations would indicate, in the context
of this model, that any reprocessing region must be >1 lt-d in size. It may be
possible to resolve this conflict by invoking anisotropic emission or special
geometry, but the most natural explanation appears to be that the bulk of the
optical luminosity is generated by some other mechanism than reprocessing.Comment: 23 pages including 6 figures, accepted for publication in Ap
The Lick AGN Monitoring Project: Reverberation Mapping of Optical Hydrogen and Helium Recombination Lines
We have recently completed a 64-night spectroscopic monitoring campaign at
the Lick Observatory 3-m Shane telescope with the aim of measuring the masses
of the black holes in 12 nearby (z < 0.05) Seyfert 1 galaxies with expected
masses in the range ~10^6-10^7M_sun and also the well-studied nearby active
galactic nucleus (AGN) NGC 5548. Nine of the objects in the sample (including
NGC 5548) showed optical variability of sufficient strength during the
monitoring campaign to allow for a time lag to be measured between the
continuum fluctuations and the response to these fluctuations in the broad
Hbeta emission, which we have previously reported. We present here the light
curves for the Halpha, Hgamma, HeII 4686, and HeI 5876 emission lines and the
time lags for the emission-line responses relative to changes in the continuum
flux. Combining each emission-line time lag with the measured width of the line
in the variable part of the spectrum, we determine a virial mass of the central
supermassive black hole from several independent emission lines. We find that
the masses are generally consistent within the uncertainties. The time-lag
response as a function of velocity across the Balmer line profiles is examined
for six of the AGNs. Finally we compare several trends seen in the dataset
against the predictions from photoionization calculations as presented by
Korista & Goad. We confirm several of their predictions, including an increase
in responsivity and a decrease in the mean time lag as the excitation and
ionization level for the species increases. Further confirmation of
photoionization predictions for broad-line gas behavior will require additional
monitoring programs for these AGNs while they are in different luminosity
states. [abridged]Comment: 37 pages, 18 figures and 15 tables, accepted for publication in the
Astrophysical Journa
The Lick AGN Monitoring Project: Recalibrating Single-Epoch Virial Black Hole Mass Estimates
We investigate the calibration and uncertainties of black hole mass estimates
based on the single-epoch (SE) method, using homogeneous and high-quality
multi-epoch spectra obtained by the Lick Active Galactic Nucleus (AGN)
Monitoring Project for 9 local Seyfert 1 galaxies with black hole masses < 10^8
M_sun. By decomposing the spectra into their AGN and stellar components, we
study the variability of the single-epoch Hbeta line width (full width at
half-maximum intensity, FWHM_Hbeta; or dispersion, sigma_Hbeta) and of the AGN
continuum luminosity at 5100A (L_5100). From the distribution of the "virial
products" (~ FWHM_Hbeta^2 L_5100^0.5 or sigma_Hbeta^2 L_5100^0.5) measured from
SE spectra, we estimate the uncertainty due to the combined variability as ~
0.05 dex (12%). This is subdominant with respect to the total uncertainty in SE
mass estimates, which is dominated by uncertainties in the size-luminosity
relation and virial coefficient, and is estimated to be ~ 0.46 dex (factor of ~
3). By comparing the Hbeta line profile of the SE, mean, and root-mean-square
(rms) spectra, we find that the Hbeta line is broader in the mean (and SE)
spectra than in the rms spectra by ~ 0.1 dex (25%) for our sample with
FWHM_Hbeta < 3000 km/s. This result is at variance with larger mass black holes
where the difference is typically found to be much less than 0.1 dex. To
correct for this systematic difference of the Hbeta line profile, we introduce
a line-width dependent virial factor, resulting in a recalibration of SE black
hole mass estimators for low-mass AGNs.Comment: Accepted for publication in ApJ. 18 pages, 17 figure
The Lick AGN Monitoring Project: Alternate Routes to a Broad-line Region Radius
It is now possible to estimate black hole masses across cosmic time, using
broad emission lines in active galaxies. This technique informs our views of
how galaxies and their central black holes coevolve. Unfortunately, there are
many outstanding uncertainties associated with these "virial" mass estimates.
One of these comes from using the accretion luminosity to infer a size for the
broad-line region. Incorporating the new sample of low-luminosity active
galaxies from our recent monitoring campaign at Lick Observatory, we
recalibrate the radius-luminosity relation with tracers of the accretion
luminosity other than the optical continuum. We find that the radius of the
broad-line region scales as the square root of the X-ray and Hbeta
luminosities, in agreement with recent optical studies. On the other hand, the
scaling appears to be marginally steeper with narrow-line luminosities. This is
consistent with a previously observed decrease in the ratio of narrow-line to
X-ray luminosity with increasing total luminosity. The radius of the broad-line
region correlates most tightly with Hbeta luminosity, while the X-ray and
narrow-line relations both have comparable scatter of a factor of two. These
correlations provide useful alternative virial BH masses in objects with no
detectable optical/UV continuum emission, such as high-redshift galaxies with
broad emission lines, radio-loud objects, or local active galaxies with
galaxy-dominated continua.Comment: 8 pages, 1 figure, accepted for publication in Ap
- …