761 research outputs found
A matched-filter approach to radio variability and transients: searching for orphan afterglows in the VAST Pilot Survey
Radio transient searches using traditional variability metrics struggle to
recover sources whose evolution timescale is significantly longer than the
survey cadence. Motivated by the recent observations of slowly evolving radio
afterglows at gigahertz frequency, we present the results of a search for radio
variables and transients using an alternative matched-filter approach. We
designed our matched-filter to recover sources with radio light curves that
have a high-significance fit to power-law and smoothly broken power-law
functions; light curves following these functions are characteristic of
synchrotron transients, including "orphan" gamma-ray burst afterglows, which
were the primary targets of our search. Applying this matched-filter approach
to data from Variables and Slow Transients Pilot Survey conducted using the
Australian SKA Pathfinder, we produced five candidates in our search.
Subsequent Australia Telescope Compact Array observations and analysis revealed
that: one is likely a synchrotron transient; one is likely a flaring active
galactic nucleus, exhibiting a flat-to-steep spectral transition over
months; one is associated with a starburst galaxy, with the radio emission
originating from either star formation or an underlying slowly-evolving
transient; and the remaining two are likely extrinsic variables caused by
interstellar scintillation. The synchrotron transient, VAST J175036.1181454,
has a multi-frequency light curve, peak spectral luminosity and volumetric rate
that is consistent with both an off-axis afterglow and an off-axis tidal
disruption event; interpreted as an off-axis afterglow would imply an average
inverse beaming factor , or equivalently, an average jet opening angle of deg.Comment: 20 pages, 6 figures; accepted for publication in MNRA
A pilot ASKAP survey for radio transients towards the Galactic Centre
We present the results of a radio transient and polarisation survey towards
the Galactic Centre, conducted as part of the Australian Square Kilometre Array
Pathfinder Variables and Slow Transients pilot survey. The survey region
consisted of five fields covering (, ). Each field was observed
for 12\,minutes, with between 7 and 9 repeats on cadences of between one day
and four months. We detected eight highly variable sources and seven highly
circularly-polarised sources (14 unique sources in total). Seven of these
sources are known pulsars including the rotating radio transient
PSR~J1739--2521 and the eclipsing pulsar PSR~J1723--2837. One of them is a low
mass X-ray binary, 4U 1758--25. Three of them are coincident with optical or
infrared sources and are likely to be stars. The remaining three may be related
to the class of Galactic Centre Radio Transients (including a highly likely
one, VAST~J173608.2--321634, that has been reported previously), although this
class is not yet understood. In the coming years, we expect to detect 40
bursts from this kind of source with the proposed four-year VAST survey if the
distribution of the source is isotropic over the Galactic fields.Comment: 17 pages, 13 figures, Accepted for publication in MNRA
Realization of quantum process tomography in NMR
Quantum process tomography is a procedure by which the unknown dynamical
evolution of an open quantum system can be fully experimentally characterized.
We demonstrate explicitly how this procedure can be implemented with a nuclear
magnetic resonance quantum computer. This allows us to measure the fidelity of
a controlled-not logic gate and to experimentally investigate the error model
for our computer. Based on the latter analysis, we test an important assumption
underlying nearly all models of quantum error correction, the independence of
errors on different qubits.Comment: 8 pages, 7 EPS figures, REVTe
Recommended from our members
Simulated 50 % radiation dose reduction in coronary CT angiography using adaptive iterative dose reduction in three-dimensions (AIDR3D)
To compare the image quality of coronary CT angiography (CTA) studies between standard filtered back projection (FBP) and adaptive iterative dose reduction in three-dimensions (AIDR3D) reconstruction using CT noise additional software to simulate reduced radiation exposure. Images from 93 consecutive clinical coronary CTA studies were processed utilizing standard FBP, FBP with 50 % simulated dose reduction (FBP50 %), and AIDR3D with simulated 50 % dose reduction (AIDR50 %). Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were measured within 5 regions-of-interest, and image quality for each reconstruction strategy was assessed by two independent readers using a 4-point scale. Compared to FBP, the SNR measured from the AIDR50 % images was similar or higher (airway: 38.3 ± 12.7 vs. 38.5 ± 14.5, p = 0.81, fat: 5.5 ± 1.9 vs. 5.4 ± 2.0, p = 0.20, muscle: 3.2 ± 1.2 vs. 3.1 ± 1.3, p = 0.38, aorta: 22.6 ± 9.4 vs. 20.2 ± 9.7, p < 0.0001, liver: 2.7 ± 1.0 vs. 2.3 ± 1.1, p < 0.0001), while the SNR of the FBP50 % images were all lower (p values < 0.0001). The CNR measured from AIDR50 % images was also higher than that from the FBP images for the aorta relative to muscle (20.5 ± 9.0 vs. 18.3 ± 9.2, p < 0.0001). The interobserver agreement in the image quality score was excellent (κ = 0.82). The quality score was significantly higher for the AIDR50 % images compared to the FBP images (3.6 ± 0.6 vs. 3.3 ± 0.7, p = 0.004). Simulated radiation dose reduction applied to clinical coronary CTA images suggests that a 50 % reduction in radiation dose can be achieved with adaptive iterative dose reduction software with image quality that is at least comparable to images acquired at standard radiation exposure and reconstructed with filtered back projection
Classical Novae in the ASKAP Pilot Surveys
We present a systematic search for radio counterparts of novae using the
Australian Square Kilometer Array Pathfinder (ASKAP). Our search used the Rapid
ASKAP Continuum Survey, which covered the entire sky south of declination
( square degrees) at a central frequency of 887.5
MHz, the Variables and Slow Transients Pilot Survey, which covered
square degrees per epoch (887.5 MHz), and other ASKAP pilot surveys, which
covered square degrees with 2-12 hour integration times. We
crossmatched radio sources found in these surveys over a two-year period, from
April 2019 to August 2021, with 440 previously identified optical novae, and
found radio counterparts for four novae: V5668 Sgr, V1369 Cen, YZ Ret, and RR
Tel. Follow-up observations with the Australian Telescope Compact Array confirm
the ejecta thinning across all observed bands with spectral analysis indicative
of synchrotron emission in V1369 Cen and YZ Ret. Our light-curve fit with the
Hubble Flow model yields a value of
for the mass ejected in V1369 Cen. We also derive a peak surface brightness
temperature of K for YZ Ret. Using Hubble Flow model simulated radio
lightcurves for novae, we demonstrate that with a 5 sensitivity limit
of 1.5 mJy in 15-min survey observations, we can detect radio emission up to a
distance of 4 kpc if ejecta mass is in the range , and
upto 1 kpc if ejecta mass is in the range . Our
study highlights ASKAP's ability to contribute to future radio observations for
novae within a distance of 1 kpc hosted on white dwarfs with masses
, and within a distance of 4 kpc hosted on white dwarfs
with masses .Comment: This paper has been accepted for publication in PASA. It consists of
13 pages, 5 figures and 4 table
Lower bounds on the complexity of simulating quantum gates
We give a simple proof of a formula for the minimal time required to simulate
a two-qubit unitary operation using a fixed two-qubit Hamiltonian together with
fast local unitaries. We also note that a related lower bound holds for
arbitrary n-qubit gates.Comment: 6 page
Multimode photon blockade
Interactions are essential for the creation of correlated quantum many-body
states. While two-body interactions underlie most natural phenomena, three- and
four-body interactions are important for the physics of nuclei [1], exotic
few-body states in ultracold quantum gases [2], the fractional quantum Hall
effect [3], quantum error correction [4], and holography [5, 6]. Recently, a
number of artificial quantum systems have emerged as simulators for many-body
physics, featuring the ability to engineer strong interactions. However, the
interactions in these systems have largely been limited to the two-body
paradigm, and require building up multi-body interactions by combining two-body
forces. Here, we demonstrate a pure N-body interaction between microwave
photons stored in an arbitrary number of electromagnetic modes of a multimode
cavity. The system is dressed such that there is collectively no interaction
until a target total photon number is reached across multiple distinct modes,
at which point they interact strongly. The microwave cavity features 9 modes
with photon lifetimes of ms coupled to a superconducting transmon
circuit, forming a multimode circuit QED system with single photon
cooperativities of . We generate multimode interactions by using
cavity photon number resolved drives on the transmon circuit to blockade any
multiphoton state with a chosen total photon number distributed across the
target modes. We harness the interaction for state preparation, preparing Fock
states of increasing photon number via quantum optimal control pulses acting
only on the cavity modes. We demonstrate multimode interactions by generating
entanglement purely with uniform cavity drives and multimode photon blockade,
and characterize the resulting two- and three-mode W states using a new
protocol for multimode Wigner tomography.Comment: 5 pages of main text with 5 figures. 11 pages of supplementary
information with 10 figure
CD36 Mediates the Innate Host Response to β-Amyloid
Accumulation of inflammatory microglia in Alzheimer's senile plaques is a hallmark of the innate response to β-amyloid fibrils and can initiate and propagate neurodegeneration characteristic of Alzheimer's disease (AD). The molecular mechanism whereby fibrillar β-amyloid activates the inflammatory response has not been elucidated. CD36, a class B scavenger receptor, is expressed on microglia in normal and AD brains and binds to β-amyloid fibrils in vitro. We report here that microglia and macrophages, isolated from CD36 null mice, had marked reductions in fibrillar β-amyloid–induced secretion of cytokines, chemokines, and reactive oxygen species. Intraperitoneal and stereotaxic intracerebral injection of fibrillar β-amyloid in CD36 null mice induced significantly less macrophage and microglial recruitment into the peritoneum and brain, respectively, than in wild-type mice. Our data reveal that CD36, a major pattern recognition receptor, mediates microglial and macrophage response to β-amyloid, and imply that CD36 plays a key role in the proinflammatory events associated with AD
Decomposition, Reformulation, and Diving in University Course Timetabling
In many real-life optimisation problems, there are multiple interacting
components in a solution. For example, different components might specify
assignments to different kinds of resource. Often, each component is associated
with different sets of soft constraints, and so with different measures of soft
constraint violation. The goal is then to minimise a linear combination of such
measures. This paper studies an approach to such problems, which can be thought
of as multiphase exploitation of multiple objective-/value-restricted
submodels. In this approach, only one computationally difficult component of a
problem and the associated subset of objectives is considered at first. This
produces partial solutions, which define interesting neighbourhoods in the
search space of the complete problem. Often, it is possible to pick the initial
component so that variable aggregation can be performed at the first stage, and
the neighbourhoods to be explored next are guaranteed to contain feasible
solutions. Using integer programming, it is then easy to implement heuristics
producing solutions with bounds on their quality.
Our study is performed on a university course timetabling problem used in the
2007 International Timetabling Competition, also known as the Udine Course
Timetabling Problem. In the proposed heuristic, an objective-restricted
neighbourhood generator produces assignments of periods to events, with
decreasing numbers of violations of two period-related soft constraints. Those
are relaxed into assignments of events to days, which define neighbourhoods
that are easier to search with respect to all four soft constraints. Integer
programming formulations for all subproblems are given and evaluated using ILOG
CPLEX 11. The wider applicability of this approach is analysed and discussed.Comment: 45 pages, 7 figures. Improved typesetting of figures and table
Cytoplasmic cyclin E is an independent marker of aggressive tumor biology and breast cancer-specific mortality in women over 70 years of age
© 2020 by the authors. Licensee MDPI, Basel, Switzerland. Multi-cohort analysis demonstrated that cytoplasmic cyclin E expression in primary breast tumors predicts aggressive disease. However, compared to their younger counterparts, older patients have favorable tumor biology and are less likely to die of breast cancer. Biomarkers therefore require interpretation in this specific context. Here, we assess data on cytoplasmic cyclin E from a UK cohort of older women alongside a panel of >20 biomarkers. Between 1973 and 2010, 813 women ≥70 years of age underwent initial surgery for early breast cancer, from which a tissue microarray was constructed (n = 517). Biomarker expression was assessed by immunohistochemistry. Multivariate analysis of breast cancer-specific survival was performed using Cox’s proportional hazards. We found that cytoplasmic cyclin E was the only biological factor independently predictive of breast cancer-specific survival in this cohort of older women (hazard ratio (HR) = 6.23, 95% confidence interval (CI) = 1.93–20.14; p = 0.002). At ten years, 42% of older patients with cytoplasmic cyclin E-positive tumors had died of breast cancer versus 8% of negative cases (p < 0.0005). We conclude that cytoplasmic cyclin E is an exquisite marker of aggressive tumor biology in older women. Patients with cytoplasmic cyclin E-negative tumors are unlikely to die of breast cancer. These data have the potential to influence treatment strategy in older patients
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