140 research outputs found
A chloride channel in rat and human axons
Current recordings from single chloride channels were obtained from excised and cell-attached patches of rat and human axons. In rat axons the channels showed an outwardly rectifying current-voltage relationship with a slope conductance of 33 pS at negative membrane potentials and 65 pS at positive potentials (symmetrical 150 mM CsCl). They were measurably for cations (PNa/PCs/PCl=0.1/0.2/1). Channel currents were independent of cytoplasmatic calcium concentration. Inactivation was not observed and gating was weakly voltage dependent. Clâ channels in human axons showed similar gating behavior but had a lower conductance
Lensing constraints on ultradense dark matter halos
Cosmological observations precisely measure primordial variations in the
density of the Universe at megaparsec and larger scales, but much smaller
scales remain poorly constrained. However, sufficiently large initial
perturbations at small scales can lead to an abundance of ultradense dark
matter minihalos that form during the radiation epoch and survive into the
late-time Universe. Because of their early formation, these objects can be
compact enough to produce detectable microlensing signatures. We investigate
whether the EROS, OGLE, and HSC surveys can probe these halos by fully
accounting for finite source size and extended lens effects. We find that
current data may already constrain the amplitudes of primordial curvature
perturbations in a new region of parameter space, but this conclusion is
strongly sensitive to yet undetermined details about the internal structures of
these ultradense halos. Under optimistic assumptions, current and future HSC
data would constrain a power spectrum that features an enhancement at scales , and an amplitude as low as may be accessible. This is a particularly interesting regime because
it connects to primordial black hole formation in a portion of the
LIGO/Virgo/Kagra mass range and the production of scalar-induced gravitational
waves in the nanohertz frequency range reachable by pulsar timing arrays. These
prospects motivate further study of the ultradense halo formation scenario to
clarify their internal structures.Comment: 17 pages, 10 figures. v2: matching published versio
The Ineludible non-Gaussianity of the Primordial Black Hole Abundance
We study the formation of primordial black holes when they are generated by
the collapse of large overdensities in the early universe. Since the density
contrast is related to the comoving curvature perturbation by a nonlinear
relation, the overdensity statistics is unavoidably non-Gaussian. We show that
the abundance of primordial black holes at formation may not be captured by a
perturbative approach which retains the first few cumulants of the non-Gaussian
probability distribution. We provide two techniques to calculate the
non-Gaussian abundance of primordial black holes at formation, one based on
peak theory and the other on threshold statistics. Our results show that the
unavoidable non-Gaussian nature of the inhomogeneities in the energy density
makes it harder to generate PBHs. We provide simple (semi-)analytical
expressions to calculate the non-Gaussian abundances of the primordial black
holes and show that for both narrow and broad power spectra the gaussian case
from threshold statistics is reproduced by increasing the amplitude of the
power spectrum by a factor .Comment: 26 pages, 10 figures, matching published versio
Testing Primordial Black Holes as Dark Matter through LISA
The idea that primordial black holes (PBHs) can comprise most of the dark
matter of the universe has recently reacquired a lot of momentum. Observational
constraints, however, rule out this possibility for most of the PBH masses,
with a notable exception around . These light PBHs may be
originated when a sizeable comoving curvature perturbation generated during
inflation re-enters the horizon during the radiation phase. During such a
stage, it is unavoidable that gravitational waves (GWs) are generated. Since
their source is quadratic in the curvature perturbations, these GWs are
generated fully non-Gaussian. Their frequency today is about the mHz, which is
exactly the range where the LISA mission has the maximum of its sensitivity.
This is certainly an impressive coincidence. We show that this scenario of PBHs
as dark matter can be tested by LISA by measuring the GW two-point correlator.
On the other hand, we show that the short observation time (as compared to the
age of the universe) and propagation effects of the GWs across the perturbed
universe from the production point to the LISA detector suppress the bispectrum
to an unobservable level. This suppression is completely general and not
specific to our model.Comment: 22 pages, 12 figures. v3: matching published versio
The JWST High Redshift Observations and Primordial Non-Gaussianity
Several bright and massive galaxy candidates at high redshifts have been
recently observed by the James Webb Space Telescope. Such early massive
galaxies seem difficult to reconcile with standard Cold Dark Matter
model predictions. We discuss under which circumstances such observed massive
galaxy candidates can be explained by introducing primordial non-Gaussianity in
the initial conditions of the cosmological perturbations.Comment: 10 pages, 4 figure
Primordial black holes from inflation and quantum diffusion
Primordial black holes as dark matter may be generated in single-field models
of inflation thanks to the enhancement at small scales of the comoving
curvature perturbation. This mechanism requires leaving the slow-roll phase to
enter a non-attractor phase during which the inflaton travels across a plateau
and its velocity drops down exponentially. We argue that quantum diffusion has
a significant impact on the primordial black hole mass fraction making the
classical standard prediction not trustable.Comment: 25+12 pages, 12 figures. v3: Appendix added with comments in response
to arXiv:1807.0905
Searching for Primordial Black Holes with the Einstein Telescope: impact of design and systematics
Primordial Black Holes (PBHs) have recently attracted much attention as they
may explain some of the LIGO/Virgo/KAGRA observations and significantly
contribute to the dark matter in our universe. The next generation of
Gravitational Wave (GW) detectors will have the unique opportunity to set
stringent bounds on this putative population of objects. Focusing on the
Einstein Telescope (ET), in this paper we analyse in detail the impact of
systematics and different detector designs on our future capability of
observing key quantities that would allow us to discover and/or constrain a
population of PBH mergers. We also perform a population analysis, with a mass
and redshift distribution compatible with the current observational bounds. Our
results indicate that ET alone can reach an exquisite level of accuracy on the
key observables considered, as well as detect up to tens of thousands of PBH
binaries per year, but for some key signatures (in particular high--redshift
sources) the cryogenic instrument optimised for low frequencies turns out to be
crucial, both for the number of observations and the error on the parameters
reconstruction. As far as the detector geometry is concerned, we find that a
network consisting of two separated L--shaped interferometers of 15 (20)~km arm
length, oriented at with respect to each other performs better
than a single triangular shaped instrument of 10 (15)~km arm length, for all
the metrics considered.Comment: 24 pages, 13 figure
The Impact of Service Quality on Consumer Perceived Value in Medical Clinics
Service quality has been viewed as a determinant of consumer perceived value. Different dimensions of service quality have been considered by various researchers. This study identifies components of service quality of medical clinics in Jaffna. From the coeficients table it can be seen that significance P value is less than .05 therefore all hypotheses are accepted according to the highest beta value tangibility contributes more towards customer perceived value of medical clinic services in Jaffna district. Keywords: service quality, consumer perceived value, Medical clinics, Jaffn
Adaptive design of experiments for efficient and accurate estimation of aerodynamic loads
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