1,211 research outputs found
Suspending test masses in terrestrial millihertz gravitational-wave detectors: a case study with a magnetic assisted torsion pendulum
Current terrestrial gravitational-wave detectors operate at frequencies above
10 Hz. There is strong astrophysical motivation to construct low-frequency
gravitational-wave detectors capable of observing 10 mHz - 10Hz signals. While
space-based detectors provide one means of achieving this end, one may also
consider terretrial detectors. However, there are numerous technological
challenges. In particular, it is difficult to isolate test masses so that they
are both seismically isolated and freely falling under the influence of gravity
at millihertz frequencies. We investigate the challenges of low-frequency
suspension in a hypothetical terrestrial detector. As a case study, we consider
a Magnetically Assisted Gravitational-wave Pendulum Intorsion (MAGPI)
suspension design. We construct a noise budget to estimate some of the required
specifications. In doing so, we identify what are likely to be a number of
generic limiting noise sources for terrestrial millihertz gravitational-wave
suspension systems (as well as some peculiar to the MAGPI design). We highlight
significant experimental challenges in order to argue that the development of
millihertz suspensions will be a daunting task. Any system that relies on
magnets faces even greater challenges. Entirely mechanical designs such as
Zollner pendulums may provide the best path forward.Comment: 6 pages, 4 figure
Ammonia toxicity: from head to toe?
Ammonia is diffused and transported across all plasma membranes. This entails that hyperammonemia leads to an increase in ammonia in all organs and tissues. It is known that the toxic ramifications of ammonia primarily touch the brain and cause neurological impairment. However, the deleterious effects of ammonia are not specific to the brain, as the direct effect of increased ammonia (change in pH, membrane potential, metabolism) can occur in any type of cell. Therefore, in the setting of chronic liver disease where multi-organ dysfunction is common, the role of ammonia, only as neurotoxin, is challenged. This review provides insights and evidence that increased ammonia can disturb many organ and cell types and hence lead to dysfunction
Simultaneous Triggered Collapse of the Presolar Dense Cloud Core and Injection of Short-Lived Radioisotopes by a Supernova Shock Wave
Cosmochemical evidence for the existence of short-lived radioisotopes (SLRI)
such as Al and Fe at the time of the formation of primitive
meteorites requires that these isotopes were synthesized in a massive star and
then incorporated into chondrites within yr. A supernova shock wave
has long been hypothesized to have transported the SLRI to the presolar dense
cloud core, triggered cloud collapse, and injected the isotopes. Previous
numerical calculations have shown that this scenario is plausible when the
shock wave and dense cloud core are assumed to be isothermal at K,
but not when compressional heating to K is assumed. We show here
for the first time that when calculated with the FLASH2.5 adaptive mesh
refinement (AMR) hydrodynamics code, a 20 km/sec shock wave can indeed trigger
the collapse of a 1 cloud while simultaneously injecting shock wave
isotopes into the collapsing cloud, provided that cooling by molecular species
such as HO, CO, and H is included. These calculations imply that
the supernova trigger hypothesis is the most likely mechanism for delivering
the SLRI present during the formation of the solar system.Comment: 12 pages, 4 color figures. Astrophysical Journal Letters (in press
Photoinjector-generation of a flat electron beam with transverse emittance ratio of 100
The generation of a flat electron beam directly from a photoinjector is an
attractive alternative to the electron damping ring as envisioned for linear
colliders. It also has potential applications to light sources such as the
generation of ultra-short x-ray pulses or Smith-Purcell free electron lasers.
In this Letter, we report on the experimental generation of a flat-beam with a
measured transverse emittance ratio of for a bunch charge of
nC; the smaller measured normalized root-mean-square emittance is
m and is limited by the resolution of our experimental setup.
The experimental data, obtained at the Fermilab/NICADD Photoinjector
Laboratory, are compared with numerical simulations and the expected scaling
laws.Comment: 5 pages, 3 figure
Black Hole Genealogy: Identifying Hierarchical Mergers with Gravitational Waves
In dense stellar environments, the merger products of binary black hole mergers may undergo additional mergers. These hierarchical mergers are naturally expected to have higher masses than the first generation of black holes made from stars. The components of hierarchical mergers are expected to have significant characteristic spins, imprinted by the orbital angular momentum of the previous mergers. However, since the population properties of first-generation black holes are uncertain, it is difficult to know if any given merger is first-generation or hierarchical. We use observations of gravitational waves to reconstruct the binary black hole mass and spin spectrum of a population including the possibility of hierarchical mergers. We employ a phenomenological model that captures the properties of merging binary black holes from simulations of globular clusters. Inspired by recent work on the formation of low-spin black holes, we include a zero-spin subpopulation. We analyze binary black holes from LIGO and Virgo's first two observing runs, and find that this catalog is consistent with having no hierarchical mergers. We find that the most massive system in this catalog, GW170729, is mostly likely a first-generation merger, having a 4% probability of being a hierarchical merger assuming a 5 Ă 10â” M_â globular cluster mass. Using our model, we find that 99% of first-generation black holes in coalescing binaries have masses below 44 M_â, and the fraction of binaries with near-zero component spins is less than 0.16 (90% probability). Upcoming observations will determine if hierarchical mergers are a common source of gravitational waves
Linking the rates of neutron star binaries and short gamma-ray bursts
Short gamma-ray bursts are believed to be produced by both binary neutron
star (BNS) and neutron star-black hole (NSBH) mergers. We use current estimates
for the BNS and NSBH merger rates to calculate the fraction of observable short
gamma-ray bursts produced through each channel. This allows us to constrain
merger rates of BNS to ( credible interval), a decrease in the rate
uncertainties from the second LIGO--Virgo Gravitational-Wave Transient Catalog,
GWTC-2. Assuming a top-hat emission profile with a large Lorentz factor, we
constrain the average opening angle of gamma-ray burst jets produced in BNS
mergers to . We also measure the fraction of BNS and NSBH
mergers that produce an observable short gamma-ray burst to be
and , respectively and find that of BNS mergers launch jets (90\% confidence). We forecast constraints for
future gravitational-wave detections given different modelling assumptions,
including the possibility that BNS and NSBH jets are different. With BNS
and NSBH observations, expected within six months of the LIGO-Virgo-KAGRA
network operating at design sensitivity, it will be possible to constrain the
fraction of BNS and NSBH mergers that launch jets with precision. Within
a year of observations, we can determine whether the jets launched in NSBH
mergers have a different structure than those launched in BNS mergers and rule
out whether of binary neutron star mergers launch jets. We
discuss the implications of future constraints on understanding the physics of
short gamma-ray bursts and binary evolution.Comment: Accepted in Physical Review D: 13 pages, 5 figure
Evolution of the Solar Nebula. IX. Gradients in the Spatial Heterogeneity of the Short-Lived Radioisotopes Fe and Al and the Stable Oxygen Isotopes
Short-lived radioisotopes (SLRI) such as Fe and Al were likely
injected into the solar nebula in a spatially and temporally heterogeneous
manner. Marginally gravitationally unstable (MGU) disks, of the type required
to form gas giant planets, are capable of rapid homogenization of isotopic
heterogeneity as well as of rapid radial transport of dust grains and gases
throughout a protoplanetary disk. Two different types of new models of a MGU
disk in orbit around a solar-mass protostar are presented. The first set has
variations in the number of terms in the spherical harmonic solution for the
gravitational potential, effectively studying the effect of varying the spatial
resolution of the gravitational torques responsible for MGU disk evolution. The
second set explores the effects of varying the initial minimum value of the
Toomre stability parameter, from values of 1.4 to 2.5, i.e., toward
increasingly less unstable disks. The new models show that the basic results
are largely independent of both sets of variations. MGU disk models robustly
result in rapid mixing of initially highly heterogeneous distributions of SLRIs
to levels of 10% in both the inner ( 10 AU) disk
regions, and to even lower levels ( 2%) in intermediate regions, where
gravitational torques are most effective at mixing. These gradients should have
cosmochemical implications for the distribution of SLRIs and stable oxygen
isotopes contained in planetesimals (e.g., comets) formed in the giant planet
region ( 5 to 10 AU) compared to those formed elsewhere.Comment: 37 pages, 1 table, 19 figures, ApJ accepte
Gravitational waves from Sco X-1: A comparison of search methods and prospects for detection with advanced detectors
The low-mass X-ray binary Scorpius X-1 (Sco X-1) is potentially the most
luminous source of continuous gravitational-wave radiation for interferometers
such as LIGO and Virgo. For low-mass X-ray binaries this radiation would be
sustained by active accretion of matter from its binary companion. With the
Advanced Detector Era fast approaching, work is underway to develop an array of
robust tools for maximizing the science and detection potential of Sco X-1. We
describe the plans and progress of a project designed to compare the numerous
independent search algorithms currently available. We employ a mock-data
challenge in which the search pipelines are tested for their relative
proficiencies in parameter estimation, computational efficiency, robust- ness,
and most importantly, search sensitivity. The mock-data challenge data contains
an ensemble of 50 Scorpius X-1 (Sco X-1) type signals, simulated within a
frequency band of 50-1500 Hz. Simulated detector noise was generated assuming
the expected best strain sensitivity of Advanced LIGO and Advanced VIRGO ( Hz). A distribution of signal amplitudes was then
chosen so as to allow a useful comparison of search methodologies. A factor of
2 in strain separates the quietest detected signal, at
strain, from the torque-balance limit at a spin frequency of 300 Hz, although
this limit could range from (25 Hz) to (750 Hz) depending on the unknown frequency of Sco X-1. With future
improvements to the search algorithms and using advanced detector data, our
expectations for probing below the theoretical torque-balance strain limit are
optimistic.Comment: 33 pages, 11 figure
Mixing in the Solar Nebula: Implications for Isotopic Heterogeneity and Large-Scale Transport of Refractory Grains
The discovery of refractory grains amongst the particles collected from Comet
81P/Wild 2 by the Stardust spacecraft (Brownlee et al. 2006) provides the
ground truth for large-scale transport of materials formed in high temperature
regions close to the protosun outward to the comet-forming regions of the solar
nebula. While accretion disk models driven by a generic turbulent viscosity
have been invoked as a means to explain such large-scale transport, the
detailed physics behind such an ``alpha'' viscosity remains unclear. We present
here an alternative physical mechanism for large-scale transport in the solar
nebula: gravitational torques associated with the transient spiral arms in a
marginally gravitationally unstable disk, of the type that appears to be
necessary to form gas giant planets. Three dimensional models are presented of
the time evolution of self-gravitating disks, including radiative transfer and
detailed equations of state, showing that small dust grains will be transported
upstream and downstream (with respect to the mean inward flow of gas and dust
being accreted by the central protostar) inside the disk on time scales of less
than 1000 yr inside 10 AU. These models furthermore show that any initial
spatial heterogeneities present (e.g., in short-lived isotopes such as 26Al)
will be homogenized by disk mixing down to a level of ~10%, preserving the use
of short-lived isotopes as accurate nebular chronometers, while simultaneously
allowing for the spread of stable oxygen isotope ratios. This finite level of
nebular spatial heterogeneity appears to be related to the coarse mixing
achieved by spiral arms, with radial widths of order 1 AU, over time scales of
~1000 yrs.Comment: 22 pages, 10 figures. Earth & Planetary Science Letters, accepte
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