1,089 research outputs found
The Interplay of Methyl-Group Distribution and Hydration Pattern of Isomeric Amphiphilic Osmolytes
© 2018 American Chemical Society. The intermolecular interactions and dynamics of aqueous 1,1-dimethyurea (1,1-DMU) solutions were studied by examining the concentration dependence of the solvent and solute relaxations detected by dielectric spectroscopy. Molecular dynamics simulations were carried out to facilitate interpretation of the dielectric data and to get a deeper insight into the behavior of the system components at the microscopic level. In particular, the simulations allowed for explaining the main differences between the dielectric spectra of aqueous solutions of 1,1-DMU and of its structural isomer 1,3-DMU. Similar to the previously studied compounds urea and 1,3-DMU, 1,1-DMU forms rather stable hydrates. This is evidenced by an effective solute dipole moment that significantly exceeds the value of a neat 1,1-DMU molecule, indicating pronounced parallel alignment of the solute dipole with two to three H2O moments. The MD simulations revealed that the involved water molecules form strong hydrogen bonds with the carbonyl group. However, in contrast to 1,3-DMU, it was not possible to resolve a "slow-water" mode in the dielectric spectra, suggesting rather different hydration-shell dynamics for 1,1-DMU as confirmed by the simulations. In contrast to aqueous urea and 1,3-DMU, addition of 1,1-DMU to water leads to a weak decrease of the static permittivity. This is explained by the emergence of antiparallel dipole-dipole correlations among 1,1-DMU hydrates with rising concentration
Agricultural abandonment and re-cultivation during and after the Chechen Wars in the northern Caucasus
A MeerKAT view of the pulsars in the globular cluster NGC 6522
We present the results of observations aimed at discovering and studying
pulsars in the core-collapsed globular cluster (GC) NGC 6522 performed by the
MeerTIME and TRAPUM Large Survey Project with the MeerKAT telescope. We have
discovered two new isolated pulsars bringing the total number of known pulsars
in the cluster to six. PSR J18033002E is a mildly recycled pulsar with spin
period of 17.9 ms while pulsar PSR J18033002F is a slow pulsar with spin
period of 148.1 ms. The presence of isolated and slow pulsars is expected in
NGC 6522 and confirms the predictions of previous theories for clusters at this
stage in evolution. We further present a tentative timing solution for the
millisecond pulsar (MSP) PSR J18033002C combining older observations taken
with the Parkes 64m radio telescope, Murriyang. This solution implies a
relatively small characteristic age of the pulsar in contrast with the old age
of the GC. The presence of a slow pulsar and an apparently young MSP, both rare
in GCs, suggests that their formation might be linked to the evolutionary stage
of the cluster.Comment: 8 pages, 5 figues, 3 tables. Accepted for publication in Astronomy
and Astrophysic
Prospects for joint radio telescope and gravitational wave searches for astrophysical transients
The radio skies remain mostly unobserved when it comes to transient
phenomena. The direct detection of gravitational waves will mark a major
milestone of modern astronomy, as an entirely new window will open on the
universe. Two apparently independent phenomena can be brought together in a
coincident effort that has the potential to boost both searches. In this paper
we will outline the scientific case that stands behind these future joint
observations and will describe the methods that might be used to conduct the
searches and analyze the data. The targeted sources are binary systems of
compact objects, known to be strong candidate sources for gravitational waves.
Detection of transients coincident in these two channels would be a significant
smoking gun for first direct detection of gravitational waves, and would open
up a new field for characterization of astrophysical transients involving
massive compact objects.Comment: 12 pages, Amaldi 8 Conference (New York, 2009) proceedings pape
The MPIfR-MeerKAT Galactic Plane Survey II. The eccentric double neutron star system PSR J1208-5936 and a neutron star merger rate update
The MMGPS-L is the most sensitive pulsar survey in the Southern Hemisphere.
We present a follow-up study of one of these new discoveries, PSR J1208-5936, a
28.71-ms recycled pulsar in a double neutron star system with an orbital period
of Pb=0.632 days and an eccentricity of e=0.348. Through timing of almost one
year of observations, we detected the relativistic advance of periastron
(0.918(1) deg/yr), resulting in a total system mass of Mt=2.586(5) Mo. We also
achieved low-significance constraints on the amplitude of the Einstein delay
and Shapiro delay, in turn yielding constraints on the pulsar mass
(Mp=1.26(+0.13/-0.25) Mo), the companion mass (Mc=1.32(+0.25/-0.13) Mo, and the
inclination angle (i=57(2) degrees). This system is highly eccentric compared
to other Galactic field double neutron stars with similar periods, possibly
hinting at a larger-than-usual supernova kick during the formation of the
second-born neutron star. The binary will merge within 7.2(2) Gyr due to the
emission of gravitational waves. With the improved sensitivity of the MMGPS-L,
we updated the Milky Way neutron star merger rate to be 25(+19/-9) Myr
within 90% credible intervals, which is lower than previous studies based on
known Galactic binaries owing to the lack of further detections despite the
highly sensitive nature of the survey. This implies a local cosmic neutron star
merger rate of 293(+222/-103} Gpc/yr, consistent with LIGO and Virgo O3
observations. With this, we predict the observation of 10(+8/-4) neutron star
merger events during the LIGO-Virgo-KAGRA O4 run. We predict the uncertainties
on the component masses and the inclination angle will be reduced to
5x10 Mo and 0.4 degrees after two decades of timing, and that in at
least a decade from now the detection of the shift in Pb and the sky proper
motion will serve to make an independent constraint of the distance to the
system
Microscopic Theory of Heterogeneity and Non-Exponential Relaxations in Supercooled Liquids
Recent experiments and computer simulations show that supercooled liquids
around the glass transition temperature are "dynamically heterogeneous" [1].
Such heterogeneity is expected from the random first order transition theory of
the glass transition. Using a microscopic approach based on this theory, we
derive a relation between the departure from Debye relaxation as characterized
by the value of a stretched exponential response function , and the fragility of the liquid. The
value is also predicted to depend on temperature and to vanish as the ideal
glass transition is approached at the Kauzmann temperature.Comment: 4 pages including 3 eps figure
Giant pulses from J1823-3021A observed with the MeerKAT telescope
The millisecond pulsar J1823-3021A is a very active giant pulse emitter in
the globular cluster NGC 6624. New observations with the MeerKAT radio
telescope have revealed 14350 giant pulses over 5 hours of integration time,
with an average wait time of about 1 second between giant pulses. The giant
pulses occur in phases compatible with the ordinary radio emission, follow a
power-law distribution with an index of -2.63 0.02 and contribute 4
percent of the total integrated flux. The spectral index of the giant pulses
follows a Gaussian distribution centered around -1.9 with a standard deviation
of 0.6 and is on average flatter than the integrated emission, which has a
spectral index of -2.81 0.02. The waiting times between the GPs are
accurately described by a Poissonian distribution, suggesting that the time of
occurrence of a GP is independent from the times of occurrence of other GPs. 76
GPs show multiple peaks within the same rotation, a rate that is also
compatible with the mutual independence of the GP times of occurrence. We
studied the polarization properties of the giant pulses finding, on average,
linear polarization only at the 1 percent level and circular polarization at
the 3 percent level, similar to the polarization percentages of the total
integrated emission. In 4 cases it was possible to measure the RM of the GPs
which are highly variable and, in two cases, is inconsistent with the mean RM
of the total integrated pulsar signal.Comment: Accepted for publication in MNRAS. 8 Pages, 11 Figure
Small anisotropy of the lower critical field and -wave two-gap feature in single crystal LiFeAs
The in- and out-of-plane lower critical fields and magnetic penetration
depths for LiFeAs were examined. The anisotropy ratio is
smaller than the expected theoretical value, and increased slightly with
increasing temperature from 0.6 to . This small degree of anisotropy
was numerically confirmed by considering electron correlation effect. The
temperature dependence of the penetration depths followed a power
law() below 0.3, with 3.5 for both and
. Based on theoretical studies of iron-based superconductors, these
results suggest that the superconductivity of LiFeAs can be represented by an
extended -wave due to weak impurity scattering effect. And the
magnitudes of the two gaps were also evaluted by fitting the superfluid density
for both the in- and out-of-plane to the two-gap model. The estimated values
for the two gaps are consistent with the results of angle resolved
photoemission spectroscopy and specific heat experiments.Comment: 10 pages, 5 figure
Normal calcium-activated anion secretion in a mouse selectively lacking TMEM16A in intestinal epithelium
Calcium-activated anion secretion is expected to ameliorate cystic fibrosis, a genetic disease that carries an anion secretory defect in exocrine tissues. Human patients and animal models of the disease that present a mild intestinal phenotype have been postulated to bear a compensatory calcium-activated anion secretion in the intestine. TMEM16A is calcium-activated anion channel whose presence in the intestinal epithelium is contradictory. We aim to test the functional expression of TMEM16A using animal models with Cftr and/or Tmem16a intestinal silencing. Expression of TMEM16A was studied in a wild type and intestinal Tmem16a knockout mice by mRNA-seq, mass-spectrometry, q-PCR, Western blotting and immunolocalization. Calcium-activated anion secretion was recorded in the ileum and proximal colon of these animals including intestinal Cftr knockout and double mutants with dual Tmem16a and Cftr intestinal ablation. Mucus homeostasis was studied by immune-analysis of Mucin-2 (Muc2) and survival curves were recorded. Tmem16a transcript was found in intestine. Nevertheless, protein was barely detected in colon samples. Electrophysiological measurements demonstrated that the intestinal deletion of Tmem16a did not change calcium-activated anion secretion induced by carbachol or ATP in ileum and proximal colon. Muc2 architecture was not altered by Tmem16a silencing as was observed when Cftr was deleted from mouse intestine. Tmem16a silencing neither affected animal survival nor modified the lethality observed in the intestinal Cftr-null mouse. Our results demonstrate that TMEM16A function in the murine intestine is not related to electrogenic calcium-activated anion transport and does not affect mucus homeostasis and survival of animals
A MeerKAT look at the polarization of 47 Tucanae pulsars: magnetic field implications
We present the polarization profiles of 22 pulsars in the globular cluster 47
Tucanae using observations from the MeerKAT radio telescope at UHF-band
(544-1088 MHz) and report precise values of dispersion measure (DM) and
rotation measure (RM). We use these measurements to investigate the presence of
turbulence in electron density and magnetic fields. The structure function of
DM shows a break at arcsec ( pc at the distance of 47
Tucanae) that suggests the presence of turbulence in the gas in the cluster
driven by the motion of wind-shedding stars. On the other hand, the structure
function of RM does not show evidence of a break. This non-detection could be
explained either by the limited number of pulsars or by the effects of the
intervening gas in the Galaxy along the line of sight. Future pulsar
discoveries in the cluster could help confirm the presence and localise the
turbulence.Comment: Accepted for publication in MNRAS, 14 pages, 6 figure
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