550 research outputs found
Increased Alpha-Band Power during the Retention of Shapes and Shape-Location Associations in Visual Short-Term Memory
Studies exploring the role of neural oscillations in cognition have revealed sustained increases in alpha-band (~8–14 Hz) power during the delay period of delayed-recognition short-term memory tasks. These increases have been proposed to reflect the inhibition, for example, of cortical areas representing task-irrelevant information, or of potentially interfering representations from previous trials. Another possibility, however, is that elevated delay-period alpha-band power (DPABP) reflects the selection and maintenance of information, rather than, or in addition to, the inhibition of task-irrelevant information. In the present study, we explored these possibilities using a delayed-recognition paradigm in which the presence and task relevance of shape information was systematically manipulated across trial blocks and electroencephalographic was used to measure alpha-band power. In the first trial block, participants remembered locations marked by identical black circles. The second block featured the same instructions, but locations were marked by unique shapes. The third block featured the same stimulus presentation as the second, but with pretrial instructions indicating, on a trial-by-trial basis, whether memory for shape or location was required, the other dimension being irrelevant. In the final block, participants remembered the unique pairing of shape and location for each stimulus. Results revealed minimal DPABP in each of the location-memory conditions, whether locations were marked with identical circles or with unique task-irrelevant shapes. In contrast, alpha-band power increases were observed in both the shape-memory condition, in which location was task irrelevant, and in the critical final condition, in which both shape and location were task relevant. These results provide support for the proposal that alpha-band oscillations reflect the retention of shape information and/or shape–location associations in short-term memory
Constraining warm dark matter with cosmic shear power spectra
We investigate potential constraints from cosmic shear on the dark matter
particle mass, assuming all dark matter is made up of light thermal relic
particles. Given the theoretical uncertainties involved in making cosmological
predictions in such warm dark matter scenarios we use analytical fits to linear
warm dark matter power spectra and compare (i) the halo model using a mass
function evaluated from these linear power spectra and (ii) an analytical fit
to the non-linear evolution of the linear power spectra. We optimistically
ignore the competing effect of baryons for this work. We find approach (ii) to
be conservative compared to approach (i). We evaluate cosmological constraints
using these methods, marginalising over four other cosmological parameters.
Using the more conservative method we find that a Euclid-like weak lensing
survey together with constraints from the Planck cosmic microwave background
mission primary anisotropies could achieve a lower limit on the particle mass
of 2.5 keV.Comment: 26 pages, 9 figures, minor changes to match the version accepted for
publication in JCA
Flowing with Time: a New Approach to Nonlinear Cosmological Perturbations
Nonlinear effects are crucial in order to compute the cosmological matter
power spectrum to the accuracy required by future generation surveys. Here, a
new approach is presented, in which the power spectrum, the bispectrum and
higher order correlations, are obtained -- at any redshift and for any momentum
scale -- by integrating a system of differential equations. The method is
similar to the familiar BBGKY hierarchy. Truncating at the level of the
trispectrum, the solution of the equations corresponds to the summation of an
infinite class of perturbative corrections. Compared to other resummation
frameworks, the scheme discussed here is particularly suited to cosmologies
other than LambdaCDM, such as those based on modifications of gravity and those
containing massive neutrinos. As a first application, we compute the Baryonic
Acoustic Oscillation feature of the power spectrum, and compare the results
with perturbation theory, the halo model, and N-body simulations. The
density-velocity and velocity-velocity power spectra are also computed, showing
that they are much less contaminated by nonlinearities than the density-density
one. The approach can be seen as a particular formulation of the
renormalization group, in which time is the flow parameter.Comment: 20 pages, 7 figures. Matches version published on JCA
Microlensing of Quasars By Stars In Their Damped Lyman alpha Absorbers
The damped Lyman alpha absorbers (DLAs) in quasar spectra are believed to be
the progenitors of present-day disk galaxies. We examine the probability for
microlensing of background quasars by stars in their DLAs. Microlensing by an
individual star should magnify the continuum but not the broad emission lines
of the quasars. Consequently, the equivalent width distribution of microlensed
quasars would be distorted. We model a representative spiral galaxy as a closed
system composed of a bulge, a disk, and a halo, and evolve the mass fraction of
stars in the disk based on the observed metallicity of DLAs at high redshifts.
The microlensing signatures are stronger if the halo of the galaxy is made of
Massive Compact Halo Objects (MACHOs). In this case, the distortion imprinted
by microlensing on the equivalent width distribution of quasar emission lines
can be detected with high significance in a sample of about 10 DLAs with HI
column densities N>10^21 cm^-2 and absorption redshifts z_abs<1. About a tenth
of all quasars with DLAs (N>10^20 cm^-2) might show excess variability on
timescales shorter than five years. A search for these signals would complement
microlensing searches in local galaxies and calibrate the MACHO mass fraction
in galactic halos at high redshifts.Comment: 25 pages, 8 figures, final version accepted for publication in Ap
Gravitational Analogues, Geometric Effects and Gravitomagnetic Charge
This essay discusses some geometric effects associated with gravitomagnetic
fields and gravitomagnetic charge as well as the gravity theory of the latter.
Gravitomagnetic charge is the duality of gravitoelectric charge (mass) and is
therefore also termed the dual mass which represents the topological property
of gravitation. The field equation of gravitomagnetic matter is suggested and a
static spherically symmetric solution of this equation is offered. A possible
explanation of the anomalous acceleration acting on Pioneer spacecrafts are
briefly proposed.Comment: 9 pages,0 figures, Late
Imagining Sounds and Images : Decoding the Contribution of Unimodal and Transmodal Brain Regions to Semantic Retrieval in the Absence of Meaningful Input
In the absence of sensory information, we can generate meaningful images and sounds from representations in memory. However, it remains unclear which neural systems underpin this process and whether tasks requiring the top-down generation of different kinds of features recruit similar or different neural networks. We asked people to internally generate the visual and auditory features of objects, either in isolation (car, dog) or in specific and complex meaning-based contexts (car/dog race). Using an fMRI decoding approach, in conjunction with functional connectivity analysis, we examined the role of auditory/visual cortex and transmodal brain regions. Conceptual retrieval in the absence of external input recruited sensory and transmodal cortex. The response in transmodal regions-including anterior middle temporal gyrus-was of equal magnitude for visual and auditory features yet nevertheless captured modality information in the pattern of response across voxels. In contrast, sensory regions showed greater activation for modality-relevant features in imagination (even when external inputs did not differ). These data are consistent with the view that transmodal regions support internally generated experiences and that they play a role in integrating perceptual features encoded in memory
Topology of non-linear structure in the 2dF Galaxy Redshift Survey
We study the evolution of non-linear structure as a function of scale in
samples from the 2dF Galaxy Redshift Survey, constituting over 221 000 galaxies
at a median redshift of z=0.11. The two flux-limited galaxy samples, located
near the southern galactic pole and the galactic equator, are smoothed with
Gaussian filters of width ranging from 5 to 8 Mpc/h to produce a continuous
galaxy density field. The topological genus statistic is used to measure the
relative abundance of overdense clusters to void regions at each scale; these
results are compared to the predictions of analytic theory, in the form of the
genus statistic for i) the linear regime case of a Gaussian random field; and
ii) a first-order perturbative expansion of the weakly non-linear evolved
field. The measurements demonstrate a statistically significant detection of an
asymmetry in the genus statistic between regions corresponding to low- and
high-density volumes of the universe. We attribute the asymmetry to the
non-linear effects of gravitational evolution and biased galaxy formation, and
demonstrate that these effects evolve as a function of scale. We find that
neither analytic prescription satisfactorily reproduces the measurements,
though the weakly non-linear theory yields substantially better results in some
cases, and we discuss the potential explanations for this result.Comment: 13 pages, matching proof to be published in MNRAS; new version adds
reference and corrects figure
Propylene glycol inactivates respiratory viruses and prevents airborne transmission
Viruses are vulnerable as they transmit between hosts, and we aimed to exploit this critical window. We found that the ubiquitous, safe, inexpensive and biodegradable small molecule propylene glycol (PG) has robust virucidal activity. Propylene glycol rapidly inactivates a broad range of viruses including influenza A, SARS-CoV-2 and rotavirus and reduces disease burden in mice when administered intranasally at concentrations commonly found in nasal sprays. Most critically, vaporised PG efficiently abolishes influenza A virus and SARS-CoV-2 infectivity within airborne droplets, potently preventing infection at levels well below those tolerated by mammals. We present PG vapour as a first-in-class non-toxic airborne virucide that can prevent transmission of existing and emergent viral pathogens, with clear and immediate implications for public health
The effects of short-term, progressive exercise training on disease activity in smouldering multiple myeloma and monoclonal gammopathy of undetermined significance:a single-arm pilot study
Background: High levels of physical activity are associated with reduced risk of the blood cancer multiple myeloma (MM). MM is preceded by the asymptomatic stages of monoclonal gammopathy of undetermined significance (MGUS) and smouldering multiple myeloma (SMM) which are clinically managed by watchful waiting. A case study (N = 1) of a former elite athlete aged 44 years previously indicated that a multi-modal exercise programme reversed SMM disease activity. To build from this prior case study, the present pilot study firstly examined if short-term exercise training was feasible and safe for a group of MGUS and SMM patients, and secondly investigated the effects on MGUS/SMM disease activity. Methods: In this single-arm pilot study, N = 20 participants diagnosed with MGUS or SMM were allocated to receive a 16-week progressive exercise programme. Primary outcome measures were feasibility and safety. Secondary outcomes were pre- to post-exercise training changes to blood biomarkers of MGUS and SMM disease activity– monoclonal (M)-protein and free light chains (FLC)– plus cardiorespiratory and functional fitness, body composition, quality of life, blood immunophenotype, and blood biomarkers of inflammation. Results: Fifteen (3 MGUS and 12 SMM) participants completed the exercise programme. Adherence was 91 ± 11%. Compliance was 75 ± 25% overall, with a notable decline in compliance at intensities > 70% V̇O2PEAK. There were no serious adverse events. There were no changes to M-protein (0.0 ± 1.0 g/L, P =.903), involved FLC (+ 1.8 ± 16.8 mg/L, P =.839), or FLC difference (+ 0.2 ± 15.6 mg/L, P =.946) from pre- to post-exercise training. There were pre- to post-exercise training improvements to diastolic blood pressure (− 3 ± 5 mmHg, P =.033), sit-to-stand test performance (+ 5 ± 5 repetitions, P =.002), and energy/fatigue scores (+ 10 ± 15%, P =.026). Other secondary outcomes were unchanged. Conclusions: A 16-week progressive exercise programme was feasible and safe, but did not reverse MGUS/SMM disease activity, contrasting a prior case study showing that five years of exercise training reversed SMM in a 44-year-old former athlete. Longer exercise interventions should be explored in a group of MGUS/SMM patients, with measurements of disease biomarkers, along with rates of disease progression (i.e., MGUS/SMM to MM). Registration: https://www.isrctn.com/ISRCTN65527208 (14/05/2018)
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