994 research outputs found
Armstrong on Probabilistic Laws of Nature
D. M. Armstrong famously claims that deterministic laws of nature are contingent relations between universals and that his account can also be straightforwardly extended to irreducibly probabilistic laws of nature. For the most part, philosophers have neglected to scrutinize Armstrong’s account of probabilistic laws. This is surprising precisely because his own claims about probabilistic laws make it unclear just what he takes them to be. We offer three interpretations of what Armstrong-style probabilistic laws are, and argue that all three interpretations are incompatible either with some feature of Armstrong’s broader metaphysics or with essential features of his account of laws (or both)
PRFdb: A database of computationally predicted eukaryotic programmed -1 ribosomal frameshift signals
The Programmed Ribosomal Frameshift Database (PRFdb) provides an interface to help researchers identify potential programmed -1 ribosomal frameshift (-1 PRF) signals in eukaryotic genes or sequences of interest. To identify putative -1 PRF signals, sequences are first imported from whole genomes or datasets, e.g. the yeast genome project and mammalian gene collection. They are then filtered through multiple algorithms to identify potential -1 PRF signals as defined by a heptameric slippery site followed by an mRNA pseudoknot. The significance of each candidate -1 PRF signal is evaluated by comparing the predicted thermodynamic stability (ΔG°) of the native mRNA sequence against a distribution of ΔG° values of a pool of randomized sequences derived from the original. The data have been compiled in a user-friendly, easily searchable relational database. The PRFdB enables members of the research community to determine whether genes that they are investigating contain potential -1 PRF signals, and can be used as a metasource of information for cross referencing with other databases. It is available on the web at http://dinmanlab.umd.edu/prfdb .https://doi.org/10.1186/1471-2164-9-33
What Next-Generation 21 cm Power Spectrum Measurements Can Teach Us About the Epoch of Reionization
A number of experiments are currently working towards a measurement of the 21
cm signal from the Epoch of Reionization. Whether or not these experiments
deliver a detection of cosmological emission, their limited sensitivity will
prevent them from providing detailed information about the astrophysics of
reionization. In this work, we consider what types of measurements will be
enabled by a next-generation of larger 21 cm EoR telescopes. To calculate the
type of constraints that will be possible with such arrays, we use simple
models for the instrument, foreground emission, and the reionization history.
We focus primarily on an instrument modeled after the
collecting area Hydrogen Epoch of Reionization Array (HERA) concept design, and
parameterize the uncertainties with regard to foreground emission by
considering different limits to the recently described "wedge" footprint in
k-space. Uncertainties in the reionization history are accounted for using a
series of simulations which vary the ionizing efficiency and minimum virial
temperature of the galaxies responsible for reionization, as well as the mean
free path of ionizing photons through the IGM. Given various combinations of
models, we consider the significance of the possible power spectrum detections,
the ability to trace the power spectrum evolution versus redshift, the
detectability of salient power spectrum features, and the achievable level of
quantitative constraints on astrophysical parameters. Ultimately, we find that
of collecting area is enough to ensure a very high significance
() detection of the reionization power spectrum in even the
most pessimistic scenarios. This sensitivity should allow for meaningful
constraints on the reionization history and astrophysical parameters,
especially if foreground subtraction techniques can be improved and
successfully implemented.Comment: 27 pages, 18 figures, updated SKA numbers in appendi
Optimal local implementation of non-local quantum gates
We investigate the minimal resources that are required in the local
implementation of non-local quantum gates in a distributed quantum computer.
Both classical communication requirements and entanglement consumption are
investigated. We present general statements on the minimal resource
requirements and present optimal procedures for a number of important gates,
including CNOT and Toffoli gates. We show that one bit of classical
communication in each direction is both necessary and sufficient for the
non-local implementation of the quantum CNOT, while in general two bits in each
direction is required for the implementation of a general two bit quantum gate.
In particular, the state-swapper requires this maximum classical communication
overhead. Extensions of these ideas to multi-party gates are presented.Comment: 7 pages, 5 figures; Replaced with published version, correcting minor
typo
From Linear Optical Quantum Computing to Heisenberg-Limited Interferometry
The working principles of linear optical quantum computing are based on
photodetection, namely, projective measurements. The use of photodetection can
provide efficient nonlinear interactions between photons at the single-photon
level, which is technically problematic otherwise. We report an application of
such a technique to prepare quantum correlations as an important resource for
Heisenberg-limited optical interferometry, where the sensitivity of phase
measurements can be improved beyond the usual shot-noise limit. Furthermore,
using such nonlinearities, optical quantum nondemolition measurements can now
be carried out at the single-photon level.Comment: 10 pages, 5 figures; Submitted to a Special Issue of J. Opt. B on
"Fluctuations and Noise in Photonics and Quantum Optics" (Herman Haus
Memorial Issue); v2: minor change
Characterizing Signal Loss in the 21 cm Reionization Power Spectrum: A Revised Study of PAPER-64
The Epoch of Reionization (EoR) is an uncharted era in our Universe's history
during which the birth of the first stars and galaxies led to the ionization of
neutral hydrogen in the intergalactic medium. There are many experiments
investigating the EoR by tracing the 21cm line of neutral hydrogen. Because
this signal is very faint and difficult to isolate, it is crucial to develop
analysis techniques that maximize sensitivity and suppress contaminants in
data. It is also imperative to understand the trade-offs between different
analysis methods and their effects on power spectrum estimates. Specifically,
with a statistical power spectrum detection in HERA's foreseeable future, it
has become increasingly important to understand how certain analysis choices
can lead to the loss of the EoR signal. In this paper, we focus on signal loss
associated with power spectrum estimation. We describe the origin of this loss
using both toy models and data taken by the 64-element configuration of the
Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER).
In particular, we highlight how detailed investigations of signal loss have led
to a revised, higher 21cm power spectrum upper limit from PAPER-64.
Additionally, we summarize errors associated with power spectrum error
estimation that were previously unaccounted for. We focus on a subset of
PAPER-64 data in this paper; revised power spectrum limits from the PAPER
experiment are presented in a forthcoming paper by Kolopanis et al. (in prep.)
and supersede results from previously published PAPER analyses.Comment: 25 pages, 18 figures, Accepted by Ap
Heat and dehydration induced oxidative damage and antioxidant defenses following incubator heat stress and a simulated heat wave in wild caught four-striped field mice Rhabdomys dilectus
Heat waves are known for their disastrous mass die-off effects due to dehydration and cell
damage, but little is known about the non-lethal consequences of surviving severe heat
exposure. Severe heat exposure can cause oxidative stress which can have negative consequences
on animal cognition, reproduction and life expectancy. We investigated the current
oxidative stress experienced by a mesic mouse species, the four striped field mouse,
Rhabdomys dilectus through a heat wave simulation with ad lib water and a more severe
temperature exposure with minimal water. Wild four striped field mice were caught between
2017 and 2019. We predicted that wild four striped field mice in the heat wave simulation
would show less susceptibility to oxidative stress as compared to a more severe heat stress
which is likely to occur in the future. Oxidative stress was determined in the liver, kidney and
brain using malondialdehyde (MDA) and protein carbonyl (PC) as markers for oxidative
damage, and superoxide dismutase (SOD) and total antioxidant capacity (TAC) as markers
of antioxidant defense. Incubator heat stress was brought about by increasing the body temperatures
of animals to 39–40.8˚C for 6 hours. A heat wave (one hot day, followed by a 3-
day heatwave) was simulated by using temperature cycle that wild four striped field mice
would experience in their local habitat (determined through weather station data using temperature
and humidity), with maximal ambient temperature of 39ËšC. The liver and kidney
demonstrated no changes in the simulated heat wave, but the liver had significantly higher
SOD activity and the kidney had significantly higher lipid peroxidation in the incubator experiment.
Dehydration significantly contributed to the increase of these markers, as is evident
from the decrease in body mass after the experiment. The brain only showed significantly higher lipid peroxidation following the simulated heat wave with no significant changes following
the incubator experiment. The significant increase in lipid peroxidation was not correlated
to body mass after the experiment. The magnitude and duration of heat stress, in
conjunction with dehydration, played a critical role in the oxidative stress experienced by each tissue, with the results demonstrating the importance of measuring multiple tissues to
determine the physiological state of an animal. Current heat waves in this species have the
potential of causing oxidative stress in the brain with future heat waves to possibly stress the
kidney and liver depending on the hydration state of animals.S1 Table. The control and stressed PIT animal body temperature recordings inside the
incubator throughout the 6 hour period.S2 Table. The body mass before, body mass after and % body mass change of each individual
across all experiments.A DSTNRF SARChI research chair for Mammal Behavioural Ecology and Physiology; a University of Pretoria doctoral research bursary and a University of Pretoria department of research and innovation international cooperation postgraduate exchange bursary.http://www.plosone.orgam2021Mammal Research InstituteZoology and Entomolog
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