2,903 research outputs found
Tracking continuous gravitational waves from a neutron star at once and twice the spin frequency with a hidden Markov model
Searches for continuous gravitational waves from rapidly spinning neutron
stars normally assume that the star rotates about one of its principal axes of
moment of inertia, and hence the gravitational radiation emits only at twice
the spin frequency of the star, . The superfluid interior of a star
pinned to the crust along an axis nonaligned with any of its principal axes
allows the star to emit gravitational waves at both and , even
without free precession, a phenomenon not clearly observed in known pulsars.
The dual-harmonic emission mechanism motivates searches combining the two
frequency components of a signal to improve signal-to-noise ratio. We describe
an economical, semicoherent, dual-harmonic search method, combined with a
maximum likelihood coherent matched filter, F-statistic, and improved from an
existing hidden Markov model (HMM) tracking scheme to track two frequency
components simultaneously. We validate the method and demonstrate its
performance through Monte Carlo simulations. We find that for sources emitting
gravitational waves at both and , the rate of correctly recovering
synthetic signals (i.e., detection efficiency), at a given false alarm
probability, can be improved by %-70% by tracking two frequencies
simultaneously compared to tracking a single component only. For sources
emitting at only, dual-harmonic tracking only leads to minor sensitivity
loss, producing lower detection efficiency than tracking a
single component. In directed continuous-wave searches where is unknown
and hence the full frequency band is searched, the computationally efficient
HMM tracking algorithm provides an option of conducting both the dual-harmonic
search and the conventional single frequency tracking to obtain optimal
sensitivity, with a typical run time of core-hr for one year's
observation
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Unsaturated Ligands Seed an Order to Disorder Transition in Mixed Ligand Shells of CdSe/CdS Quantum Dots.
A phase transition within the ligand shell of core/shell quantum dots is studied in the prototypical system of colloidal CdSe/CdS quantum dots with a ligand shell composed of bound oleate (OA) and octadecylphosphonate (ODPA). The ligand shell composition is tuned using a ligand exchange procedure and quantified through proton NMR spectroscopy. Temperature-dependent photoluminescence spectroscopy reveals a signature of a phase transition within the organic ligand shell. Surprisingly, the ligand order to disorder phase transition triggers an abrupt increase in the photoluminescence quantum yield (PLQY) and full-width at half-maximum (FWHM) with increasing temperature. The temperature and width of the phase transition show a clear dependence on ligand shell composition, such that QDs with higher ODPA fractions have sharper phase transitions that occur at higher temperatures. In order to gain a molecular understanding of the changes in ligand ordering, Fourier transform infrared and vibrational sum frequency generation spectroscopies are performed. These measurements confirm that an order/disorder transition in the ligand shell tracks with the photoluminescence changes that accompany the ligand phase transition. The phase transition is simulated through a lattice model that suggests that the ligand shell is well-mixed and does not have completely segregated domains of OA and ODPA. Furthermore, we show that the unsaturated chains of OA seed disorder within the ligand shell
The imprint of superradiance on hierarchical black hole mergers
Ultralight bosons are a proposed solution to outstanding problems in
cosmology and particle physics: they provide a dark-matter candidate while
potentially explaining the strong charge-parity problem. If they exist,
ultralight bosons can interact with black holes through the superradiant
instability. In this work we explore the consequences of this instability on
the evolution of hierarchical black holes within dense stellar clusters. By
reducing the spin of individual black holes, superradiance reduce the recoil
velocity of merging binary black holes, which, in turn, increases the retention
fraction of hierarchical merger remnants. We show that the existence of
ultralight bosons with mass would lead to an increased rate of hierarchical black
hole mergers in nuclear star clusters. An ultralight boson in this energy range
would result in up to more present-day nuclear star clusters
supporting hierarchical growth. The presence of an ultralight boson can also
double the rate of intermediate mass black hole mergers to
\,Gpc\,yr in the local Universe. These results imply
that a select range of ultralight boson mass can have far-reaching consequences
for the population of black holes in dense stellar environments. Future studies
into black hole cluster populations and the spin distribution of hierarchically
formed black holes will test this scenario.Comment: 20 pages, 7 figure
Tracking continuous gravitational waves from a neutron star at once and twice the spin frequency with a hidden Markov model
Searches for continuous gravitational waves from rapidly spinning neutron stars normally assume that the star rotates about one of its principal axes of moment of inertia, and hence the gravitational radiation emits only at twice the spin frequency of the star, 2f⋆. The superfluid interior of a star pinned to the crust along an axis nonaligned with any of its principal axes allows the star to emit gravitational waves at both f⋆ and 2f⋆, even without free precession, a phenomenon not clearly observed in known pulsars. The dual-harmonic emission mechanism motivates searches combining the two frequency components of a signal to improve signal-to-noise ratio. We describe an economical, semicoherent, dual-harmonic search method, combined with a maximum likelihood coherent matched filter, F-statistic, and improved from an existing hidden Markov model (HMM) tracking scheme to track two frequency components simultaneously. We validate the method and demonstrate its performance through Monte Carlo simulations. We find that for sources emitting gravitational waves at both f⋆ and 2f⋆, the rate of correctly recovering synthetic signals (i.e., detection efficiency), at a given false alarm probability, can be improved by ∼10%–70% by tracking two frequencies simultaneously compared to tracking a single component only. For sources emitting at 2f⋆ only, dual-harmonic tracking only leads to minor sensitivity loss, producing ≲10% lower detection efficiency than tracking a single component. In directed continuous-wave searches where f⋆ is unknown and hence the full frequency band is searched, the computationally efficient HMM tracking algorithm provides an option of conducting both the dual-harmonic search and the conventional single frequency tracking to obtain optimal sensitivity, with a typical run time of ∼10^3 core-hr for one year’s observation
Epstein-Barr Virus BART9 miRNA Modulates LMP1 Levels and Affects Growth Rate of Nasal NK T Cell Lymphomas
Nasal NK/T cell lymphomas (NKTCL) are a subset of aggressive Epstein-Barr virus (EBV)-associated non-Hodgkin's lymphomas. The role of EBV in pathogenesis of NKTCL is not clear. Intriguingly, EBV encodes more than 40 microRNAs (miRNA) that are differentially expressed and largely conserved in lymphocryptoviruses. While miRNAs play a critical role in the pathogenesis of cancer, especially lymphomas, the expression and function of EBV transcribed miRNAs in NKTCL are not known. To examine the role of EBV miRNAs in NKTCL, we used microarray profiling and qRT-PCR to identify and validate expression of viral miRNAs in SNK6 and SNT16 cells, which are two independently derived NKTCL cell lines that maintain the type II EBV latency program. All EBV BART miRNAs except BHRF-derived miRNAs were expressed and some of these miRNAs are expressed at higher levels than in nasopharyngeal carcinomas. Modulating the expression of BART9 with antisense RNAs consistently reduced SNK6 and SNT16 proliferation, while antisense RNAs to BARTs-7 and -17-5p affected proliferation only in SNK6 cells. Furthermore, the EBV LMP-1 oncoprotein and transcript levels were repressed when an inhibitor of BART9 miRNA was transfected into SNK6 cells, and overexpression of BART9 miRNA increased LMP-1 protein and mRNA expression. Our data indicate that BART9 is involved in NKTCL proliferation, and one of its mechanisms of action appears to be regulating LMP-1 levels. Our findings may have direct application for improving NKTCL diagnosis and for developing possible novel treatment approaches for this tumor, for which current chemotherapeutic drugs have limited effectiveness
Atoh1-dependent rhombic lip neurons are required for temporal delay between independent respiratory oscillators in embryonic mice
All motor behaviors require precise temporal coordination of different muscle groups. Breathing, for example, involves the sequential activation of numerous muscles hypothesized to be driven by a primary respiratory oscillator, the preBotzinger Complex, and at least one other as-yet unidentified rhythmogenic population. We tested the roles of Atoh1-, Phox2b-, and Dbx1-derived neurons (three groups that have known roles in respiration) in the generation and coordination of respiratory output in embryonic mice. We found that Dbx1-derived neurons are necessary for all respiratory behaviors, whereas independent but coupled respiratory rhythms persist from at least three different motor pools after eliminating or silencing Phox2b-or Atoh1-expressing hindbrain neurons. Without Atoh1 neurons, however, the motor pools become temporally disorganized and coupling between independent respiratory oscillators decreases. We propose Atoh1 neurons tune the sequential activation of independent oscillators essential for the fine control of different muscles during breathing
Polymorphisms in the SOCS7 gene and glucose homeostasis traits
BACKGROUND: SOCS7 is a member of the suppressor of cytokine signaling family of proteins and is expressed in skeletal muscle and islets. SOCS7 deficient mice develop islet hyperplasia in the setting of increased insulin sensitivity and normal glucose tolerance. The objective of this study was to determine if variants in SOCS7 play a role in variation of glucose and insulin levels and the development of type 2 diabetes (T2DM). RESULTS: Five SOCS7 tagging SNPs were genotyped in diabetic and nondiabetic Old Order Amish. A case–control study was performed in T2DM (n = 145) and normal glucose tolerant (n = 358) subjects. Nominal associations were observed with T2DM and the minor alleles for rs8068600 (P = 0.01) and rs8074124 (P = 0.04); however, only rs8068600 remained significant after Bonferroni adjustment for multiple comparisons (P = 0.01). Among nondiabetic Amish (n = 765), no significant associations with glucose or insulin traits including fasting or 2 hour glucose and insulin from the oral glucose tolerance test, insulin or glucose area under the curve, Matsuda Index or HOMA-IR were found for any of the SNPs. CONCLUSION: In conclusion, genetic variants in the SOCS7 gene do not impact variation in glucose homeostasis traits and only minimally impact risk of T2DM in the Old Order Amish. Our study was not able to address whether rare variants that potentially impact gene function might influence T2DM risk
Reentrant Peak Effect in an anisotropic superconductor 2H-NbSe_2 : Role of disorder
The reentrant nature of Peak Effect is established in a single crystal of
2H-NbSe_2 via electrical transport and dc magnetisation studies. The role of
disorder on the reentrant branch of PE has been examined in three single
crystals with varying levels of quenched random disorder. Increasing disorder
presumably shrinks the (H,T) parameter space over which vortex array retains
spatial order. Although, the upper branch of the PE curve is somewhat robust,
the lower reentrant branch of the same curve is strongly affected by disorder.Comment: 5 Pages of text, 4 figure
Multi-messenger astronomy with a Southern-Hemisphere gravitational-wave observatory
Joint observations of gravitational waves and electromagnetic counterparts
will answer questions about cosmology, gamma-ray bursts, and the behaviour of
matter at supranuclear densities. The addition of a Southern-Hemisphere
gravitational-wave observatory to proposed global networks creates a longer
baseline, which is beneficial for sky localisation. We analyse how an
observatory in Australia can enhance the multi-messenger astronomy capabilities
of future networks. We estimate the number of binary neutron star mergers with
joint observations of gravitational waves and kilonova counterparts detectable
by the Vera C. Rubin Observatory. First, we consider a network of upgrades to
current observatories. Adding an Australian observatory to a three-observatory
network (comprising two observatories in the USA and one in Europe) boosts the
rate of joint observations from per year to
per year (a factor of two improvement). Then, we consider a
network of next-generation observatories. Adding a km Australian
observatory to a global network of a Cosmic Explorer km in the USA and an
Einstein Telescope in Europe only marginally increases the rate from
per year to per year (a factor of 1.1
improvement). The addition of an Australian observatory, however, ensures that
at least two observatories are online far more often. When the Cosmic Explorer
km is offline for a major upgrade, the Australian observatory increases
the joint observation rate from per year to
per year (a factor of 82 improvement). When the Einstein
Telescope is offline, the joint observation rate increases from
per year to per year (a factor of 113
improvement). We sketch out the broader science case for a Southern-Hemisphere
gravitational-wave observatory.Comment: v1, 13 pages, 7 figures. Submitted to PRD on August 24 202
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