34,302 research outputs found
Template-based Gravitational-Wave Echoes Search Using Bayesian Model Selection
The ringdown of the gravitational-wave signal from a merger of two black
holes has been suggested as a probe of the structure of the remnant compact
object, which may be more exotic than a black hole. It has been pointed out
that there will be a train of echoes in the late-time ringdown stage for
different types of exotic compact objects. In this paper, we present a
template-based search methodology using Bayesian statistics to search for
echoes of gravitational waves. Evidence for the presence or absence of echoes
in gravitational-wave events can be established by performing Bayesian model
selection. The Occam factor in Bayesian model selection will automatically
penalize the more complicated model that echoes are present in
gravitational-wave strain data because of its higher degree of freedom to fit
the data. We find that the search methodology was able to identify
gravitational-wave echoes with Abedi et al.'s echoes waveform model about 82.3%
of the time in simulated Gaussian noise in the Advanced LIGO and Virgo network
and about 61.1% of the time in real noise in the first observing run of
Advanced LIGO with significance. Analyses using this method are
performed on the data of Advanced LIGO's first observing run, and we find no
statistical significant evidence for the detection of gravitational-wave
echoes. In particular, we find combined evidence of the three events
in Advanced LIGO's first observing run. The analysis technique developed in
this paper is independent of the waveform model used, and can be used with
different parametrized echoes waveform models to provide more realistic
evidence of the existence of echoes from exotic compact objects.Comment: 16 pages, 6 figure
Stark shift and field ionization of arsenic donors in Si-SOI structures
We develop an efficient back gate for silicon-on-insulator (SOI) devices
operating at cryogenic temperatures, and measure the quadratic hyperfine Stark
shift parameter of arsenic donors in isotopically purified Si-SOI layers
using such structures. The back gate is implemented using MeV ion implantation
through the SOI layer forming a metallic electrode in the handle wafer,
enabling large and uniform electric fields up to 2 V/m to be
applied across the SOI layer. Utilizing this structure we measure the Stark
shift parameters of arsenic donors embedded in the Si SOI layer and find
a contact hyperfine Stark parameter of m/V. We also demonstrate electric-field driven dopant ionization in
the SOI device layer, measured by electron spin resonance.Comment: 5 pages, 3 figure
Structural change of vortex patterns in anisotropic Bose-Einstein condensates
We study the changes in the spatial distribution of vortices in a rotating
Bose-Einstein condensate due to an increasing anisotropy of the trapping
potential. Once the rotational symmetry is broken, we find that the vortex
system undergoes a rich variety of structural changes, including the formation
of zig-zag and linear configurations. These spatial re-arrangements are well
signaled by the change in the behavior of the vortex-pattern eigenmodes against
the anisotropy parameter. The existence of such structural changes opens up
possibilities for the coherent exploitation of effective many-body systems
based on vortex patterns.Comment: 5 pages, 4 figure
Intrinsic tethering activity of endosomal Rab proteins.
Rab small G proteins control membrane trafficking events required for many processes including secretion, lipid metabolism, antigen presentation and growth factor signaling. Rabs recruit effectors that mediate diverse functions including vesicle tethering and fusion. However, many mechanistic questions about Rab-regulated vesicle tethering are unresolved. Using chemically defined reaction systems, we discovered that Vps21, a Saccharomyces cerevisiae ortholog of mammalian endosomal Rab5, functions in trans with itself and with at least two other endosomal Rabs to directly mediate GTP-dependent tethering. Vps21-mediated tethering was stringently and reversibly regulated by an upstream activator, Vps9, and an inhibitor, Gyp1, which were sufficient to drive dynamic cycles of tethering and detethering. These experiments reveal a previously undescribed mode of tethering by endocytic Rabs. In our working model, the intrinsic tethering capacity Vps21 operates in concert with conventional effectors and SNAREs to drive efficient docking and fusion
Distinct subpopulations of enteric neuronal progenitors defined by time of development, sympathoadrenal lineage markers and Mash-1-dependence
Enteric and sympathetic neurons have previously been proposed to be lineally related. We present independent lines of evidence that suggest that enteric neurons arise from at least two lineages, only one of which expresses markers in common with sympathoadrenal cells. In the rat, sympathoadrenal markers are expressed, in the same order as in sympathetic neurons, by a subset of enteric neuronal precursors, which also transiently express tyrosine hydroxylase. If this precursor pool is eliminated in vitro by complement-mediated lysis, enteric neurons continue to develop; however, none of these are serotonergic. In the mouse, the Mash-1−/− mutation, which eliminates sympathetic neurons, also prevents the development of enteric serotonergic neurons. Other enteric neuronal populations, however, including those that contain calcitonin gene related peptide are present. Enteric tyrosine hydroxylase-containing cells co-express Mash-1 and are eliminated by the Mash-1−/− mutation, consistent with the idea that in the mouse, as in the rat, these precursors generate serotonergic neurons. Serotonergic neurons are generated early in development, while calcitonin gene related peptide-containing enteric neurons are generated much later. These data suggest that enteric neurons are derived from at least two progenitor lineages. One transiently expresses sympathoadrenal markers, is Mash-1-dependent, and generates early-born enteric neurons, some of which are serotonergic. The other is Mash-1-independent, does not express sympathoadrenal markers, and generates late-born enteric neurons, some of which contain calcitonin gene related peptide
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