4,085 research outputs found
Constraining Perturbative Early Dark Energy with Current Observations
In this work, we study a class of early dark energy (EDE) models, in which,
unlike in standard DE models, a substantial amount of DE exists in the
matter-dominated era, self-consistently including DE perturbations. Our
analysis shows that, marginalizing over the non DE parameters such as , current CMB observations alone can constrain the scale factor of
transition from early DE to late time DE to and width of
transition to . The equation of state at present is somewhat
weakly constrained to , if we allow km/s/Mpc. Taken
together with other observations, such as supernovae, HST, and SDSS LRGs, the
constraints are tighter-- .
The evolution of the equation of state for EDE models is thus close to
CDM at low redshifts. Incorrectly assuming DE perturbations to be
negligible leads to different constraints on the equation of state parameters,
thus highlighting the necessity of self-consistently including DE perturbations
in the analysis. If we allow the spatial curvature to be a free parameter, then
the constraints are relaxed to with for CMB+other observations. For
perturbed EDE models, the lower limit on () is much lower than that in CDM (), thus
raising the interesting possibility of discriminating EDE from CDM
using future observations such as halo mass functions or the Sunyaev-Zeldovich
power spectrum.Comment: 12 pages, 5 figures, references updated, accepted for publication in
Ap
Development and validation of a risk score for chronic kidney disease in HIV infection using prospective cohort data from the D:A:D study.
Chronic kidney disease (CKD) is a major health issue for HIV-positive individuals, associated with increased morbidity and mortality. Development and implementation of a risk score model for CKD would allow comparison of the risks and benefits of adding potentially nephrotoxic antiretrovirals to a treatment regimen and would identify those at greatest risk of CKD. The aims of this study were to develop a simple, externally validated, and widely applicable long-term risk score model for CKD in HIV-positive individuals that can guide decision making in clinical practice
Prediction of the in situ coronal mass ejection rate for solar cycle 25: Implications for parker solar probe in situ observations
The Parker Solar Probe (PSP) and Solar Orbiter missions are designed to make groundbreaking observations of the
Sun and interplanetary space within this decade. We show that a particularly interesting in situ observation of an
interplanetary coronal mass ejection (ICME) by PSP may arise during close solar flybys (<0.1 au). During these
times, the same magnetic flux rope inside an ICME could be observed in situ by PSP twice, by impacting its frontal
part as well as its leg. Investigating the odds of this situation, we forecast the ICME rate in solar cycle 25 based on
two models for the sunspot number (SSN): (1) the forecast of an expert panel in 2019 (maximum SSN = 115), and
(2) a prediction by McIntosh et al. (2020, maximum SSN = 232). We link the SSN to the observed ICME rates in
solar cycles 23 and 24 with the Richardson and Cane list and our own ICME catalog, and calculate that between
one and seven ICMEs will be observed by PSP at heliocentric distances <0.1 au until 2025, including 1σ
uncertainties. We then model the potential flux rope signatures of such a double-crossing event with the
semiempirical 3DCORE flux rope model, showing a telltale elevation of the radial magnetic field component BR,
and a sign reversal in the component BN normal to the solar equator compared to field rotation in the first
encounter. This holds considerable promise to determine the structure of CMEs close to their origin in the solar
corona
Extracellular calcium reduction strongly increases the lytic capacity of pneumolysin from streptococcus pneumoniae in brain tissue
Background. Streptococcus pneumoniae causes serious diseases such as pneumonia and meningitis. Its major pathogenic factor is the cholesterol-dependent cytolysin pneumolysin, which produces lytic pores at high concentrations. At low concentrations, it has other effects, including induction of apoptosis. Many cellular effects of pneumolysin appear to be calcium dependent. Methods. Live imaging of primary mouse astroglia exposed to sublytic amounts of pneumolysin at various concentrations of extracellular calcium was used to measure changes in cellular permeability (as judged by lactate dehydrogenase release and propidium iodide chromatin staining). Individual pore properties were analyzed by conductance across artificial lipid bilayer. Tissue toxicity was studied in continuously oxygenated acute brain slices. Results. The reduction of extracellular calcium increased the lytic capacity of the toxin due to increased membrane binding. Reduction of calcium did not influence the conductance properties of individual toxin pores. In acute cortical brain slices, the reduction of extracellular calcium from 2 to 1 mM conferred lytic activity to pathophysiologically relevant nonlytic concentrations of pneumolysin. Conclusions. Reduction of extracellular calcium strongly enhanced the lytic capacity of pneumolysin due to increased membrane binding. Thus, extracellular calcium concentration should be considered as a factor of primary importance for the course of pneumococcal meningitis
Water induced sediment levitation enhances downslope transport on Mars
On Mars, locally warm surface temperatures (~293 K) occur, leading to the possibility of (transient) liquid water on the surface. However, water exposed to the martian atmosphere will boil, and the sediment transport capacity of such unstable water is not well understood. Here, we present laboratory studies of a newly recognized transport mechanism: “levitation” of saturated sediment bodies on a cushion of vapor released by boiling. Sediment transport where this mechanism is active is about nine times greater than without this effect, reducing the amount of water required to transport comparable sediment volumes by nearly an order of magnitude. Our calculations show that the effect of levitation could persist up to ~48 times longer under reduced martian gravity. Sediment levitation must therefore be considered when evaluating the formation of recent and present-day martian mass wasting features, as much less water may be required to form such features than previously thought
Limits on decaying dark energy density models from the CMB temperature-redshift relation
The nature of the dark energy is still a mystery and several models have been
proposed to explain it. Here we consider a phenomenological model for dark
energy decay into photons and particles as proposed by Lima (J. Lima, Phys.
Rev. D 54, 2571 (1996)). He studied the thermodynamic aspects of decaying dark
energy models in particular in the case of a continuous photon creation and/or
disruption. Following his approach, we derive a temperature redshift relation
for the CMB which depends on the effective equation of state and on
the "adiabatic index" . Comparing our relation with the data on the CMB
temperature as a function of the redshift obtained from Sunyaev-Zel'dovich
observations and at higher redshift from quasar absorption line spectra, we
find , adopting for the adiabatic index ,
in good agreement with current estimates and still compatible with
, implying that the dark energy content being constant in time.Comment: 8 pages, 1 figur
The 'not-so-strange' body in the mirror: : A principal components analysis of direct and mirror self-observation
This document is the Accepted Manuscript version of the following article: Paul M. Jenkinson, and Catherine Preston, ‘The “not-so-strange” body in the mirror: A principal components analysis of direct and mirror self-observation’, Consciousness and Cognition, Vol. 48, pp. 262-272, first published online 4 January 2017, doi: http://dx.doi.org/10.1016/j.concog.2016.12.007 This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/.In this study we adopted a psychometric approach to examine how the body is subjectively experienced in a mirror. One hundred and twenty-four healthy participants viewed their body for five minutes directly or via a mirror, and then completed a 20-item questionnaire designed to capture subjective experiences of the body. PCA revealed a two-component structure for both direct and mirror conditions, comprising body evaluations (and alienation) and unusual feelings and perceptions. The relationship between these components and pre-existing tendencies for appearance anxiety, body dysmorphic-type beliefs, dissociative symptomatology, self-objectification and delusion ideation further supported the similarity between direct and mirror conditions; however, the occurrence of strange experiences like those reported to occur during prolonged face viewing was not confirmed. These results suggest that, despite obvious differences in visual feedback, observing the body via a mirror (as an outside observer) is subjectively equivalent to observing the body directly (from our own viewpoint).Peer reviewedFinal Accepted Versio
Leftward Lateralization of Auditory Cortex Underlies Holistic Sound Perception in Williams Syndrome
BACKGROUND: Individuals with the rare genetic disorder Williams-Beuren syndrome (WS) are known for their characteristic auditory phenotype including strong affinity to music and sounds. In this work we attempted to pinpoint a neural substrate for the characteristic musicality in WS individuals by studying the structure-function relationship of their auditory cortex. Since WS subjects had only minor musical training due to psychomotor constraints we hypothesized that any changes compared to the control group would reflect the contribution of genetic factors to auditory processing and musicality. METHODOLOGY/PRINCIPAL FINDINGS: Using psychoacoustics, magnetoencephalography and magnetic resonance imaging, we show that WS individuals exhibit extreme and almost exclusive holistic sound perception, which stands in marked contrast to the even distribution of this trait in the general population. Functionally, this was reflected by increased amplitudes of left auditory evoked fields. On the structural level, volume of the left auditory cortex was 2.2-fold increased in WS subjects as compared to control subjects. Equivalent volumes of the auditory cortex have been previously reported for professional musicians. CONCLUSIONS/SIGNIFICANCE: There has been an ongoing debate in the neuroscience community as to whether increased gray matter of the auditory cortex in musicians is attributable to the amount of training or innate disposition. In this study musical education of WS subjects was negligible and control subjects were carefully matched for this parameter. Therefore our results not only unravel the neural substrate for this particular auditory phenotype, but in addition propose WS as a unique genetic model for training-independent auditory system properties
Small Scale Structure Formation in Chameleon Cosmology
Chameleon fields are scalar fields whose mass depends on the ambient matter
density. We investigate the effects of these fields on the growth of density
perturbations on sub-galactic scales and the formation of the first dark matter
halos. Density perturbations on comoving scales go non--linear
and collapse to form structure much earlier than in standard CDM
cosmology. The resulting mini-halos are hence more dense and resilient to
disruption. We therefore expect (provided that the density perturbations on
these scales have not been erased by damping processes) that the dark matter
distribution on small scales would be more clumpy in chameleon cosmology than
in the CDM model.Comment: 13 pages, 4 figure
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