378 research outputs found
The cosmological constant and the relaxed universe
We study the role of the cosmological constant (CC) as a component of dark
energy (DE). It is argued that the cosmological term is in general unavoidable
and it should not be ignored even when dynamical DE sources are considered.
From the theoretical point of view quantum zero-point energy and phase
transitions suggest a CC of large magnitude in contrast to its tiny observed
value. Simply relieving this disaccord with a counterterm requires extreme
fine-tuning which is referred to as the old CC problem. To avoid it, we discuss
some recent approaches for neutralising a large CC dynamically without adding a
fine-tuned counterterm. This can be realised by an effective DE component which
relaxes the cosmic expansion by counteracting the effect of the large CC.
Alternatively, a CC filter is constructed by modifying gravity to make it
insensitive to vacuum energy.Comment: 6 pages, no figures, based on a talk presented at PASCOS 201
The extranasal glioma - a cause of neonatal respiratory distress
Normal brain tissue in an abnonnal configuration, occurring at a site away from the cranial cavity, is temied an Extranasal Glioma. Since its first description in 1852 by Reid2, only 140 patients with this entity have been reported. Heterotopic brain tissue when present in a confined area may cause obstmction, pressure and pain. Its occurrence in the nasopharyngeal region is relatively rare and only 19 cases have been reported so far2, the majority presenting with respiratory distress in the early neonatal period. The objective of this report is to create an awareness amongst the physicians of the presentation and management of this condition
Constraints on the origin of the first light from SN2014J
We study the very early lightcurve of supernova 2014J (SN 2014J) using the
high-cadence broad-band imaging data obtained by the Kilodegree Extremely
Little Telescope (KELT), which fortuitously observed M 82 around the time of
the explosion, starting more than two months prior to detection, with up to 20
observations per night. These observations are complemented by observations in
two narrow-band filters used in an H survey of nearby galaxies by the
intermediate Palomar Transient Factory (iPTF) that also captured the first days
of the brightening of the \sn. The evolution of the lightcurves is consistent
with the expected signal from the cooling of shock heated material of large
scale dimensions, \gsim 1 R_{\odot}. This could be due to heated material of
the progenitor, a companion star or pre-existing circumstellar environment,
e.g., in the form of an accretion disk. Structure seen in the lightcurves
during the first days after explosion could also originate from radioactive
material in the outer parts of an exploding white dwarf, as suggested from the
early detection of gamma-rays. The model degeneracy translates into a
systematic uncertainty of days on the estimate of the first light
from SN 2014J.Comment: Accepted by ApJ. Companion paper by Siverd et al, arXiv:1411.415
Level of depression and its associated factors among the frontline physicians of Bangladesh during the COVID-19 outbreak
The COVID-19 pandemic has exposed the frontline physicians to a greater risk of getting infected, tremendous workload, and drastic changes in their work environment, leading to an increased prevalence of depression among doctors from many countries, including Bangladesh. The aim of this study was to examine the association of various personal, professional and psychosocial factors with different degrees of depressive symptoms among the frontline doctors of Bangladesh working during the COVID-19 pandemic. An online, cross-sectional survey was conducted for that purpose and data were collected from 312 doctors working in Bangladeshi hospitals using a self-administered survey questionnaire inclusive of a validated tool (Patient Health Questionnaire-9). Among the participants, around half were of age 30-34 years (51.3%), 81.8% worked in public hospitals and 70.5% did not have any comorbidity. Regarding workplace conditions, 77% of the doctors reported a perceived shortage of healthcare providers at their workplace, while 95% reported a perceived shortage of equipment, most commonly N95 masks (49%), gowns (35%), eye-protective shields (35%). A total of 199 (63.8%) participants received formal training since the beginning of the pandemic. According to the response from PHQ-9 questionnaire, 17 (5%) participants reported having no depression, while 18 (6%), 18 (6%), 25 (8%), and 234 (75%) reported having mild, moderate, moderately severe, and severe depression. Findings from multiple logistic regression showed the odds of moderate-to-severe depression to be higher among physicians with comorbidities (OR:7.47, CI: 1.27-43.89, P: 0.026) and those who felt extremely worried from looking at negative news on social/mass media (aOR: 15.180, CI:1.98-116.683, P: 0.009). To preserve and promote the psychological well-being of Bangladeshi doctors, it is, therefore, crucial to take these identified sources and risk factors of depression under sincere consideration by the responsible authorities and appropriate measures should be designed to remove these sources of depression to better support the physicians of the country
The peculiar Type Ia supernova iPTF14atg: Chandrasekhar-mass explosion or violent merger?
iPTF14atg, a subluminous peculiar Type Ia supernova (SN Ia) similar to SN
2002es, is the first SN Ia for which a strong UV flash was observed in the
early-time light curves. This has been interpreted as evidence for a
single-degenerate (SD) progenitor system where such a signal is expected from
interactions between the SN ejecta and the non-degenerate companion star. Here,
we compare synthetic observables of multi-dimensional state-of-the-art
explosion models for different progenitor scenarios to the light curves and
spectra of iPTF14atg. From our models, we have difficulties explaining the
spectral evolution of iPTF14atg within the SD progenitor channel. In contrast,
we find that a violent merger of two carbon-oxygen white dwarfs with 0.9 and
0.76 solar masses, respectively, provides an excellent match to the spectral
evolution of iPTF14atg from 10d before to several weeks after maximum light.
Our merger model does not naturally explain the initial UV flash of iPTF14atg.
We discuss several possibilities like interactions of the SN ejecta with the
circum-stellar medium and surface radioactivity from a He ignited merger that
may be able to account for the early UV emission in violent merger models.Comment: 12 pages, 7 figures, accepted for publication in MNRA
Mass-varying neutrino in light of cosmic microwave background and weak lensing
We aim to constrain mass-varying neutrino models using large scale structure
observations and produce forecast for the Euclid survey. We investigate two
models with different scalar field potential and both positive and negative
coupling parameters \beta. These parameters correspond to growing or decreasing
neutrino mass, respectively. We explore couplings up to |\beta|<5. In the case
of the exponential potential, we find an upper limit on <0.004
at 2- level. In the case of the inverse power law potential the null
coupling can be excluded with more than 2-\sigma significance; the limits on
the coupling are \beta>3 for the growing neutrino mass and \beta<-1.5 for the
decreasing mass case. This is a clear sign for a preference of higher
couplings. When including a prior on the present neutrino mass the upper limit
on the coupling becomes |\beta|<3 at 2- level for the exponential
potential. Finally, we present a Fisher forecast using the tomographic weak
lensing from an Euclid-like experiment and we also consider the combination
with the cosmic microwave background (CMB) temperature and polarisation spectra
from a Planck-like mission. If considered alone, lensing data is more efficient
in constraining with respect to CMB data alone. There is, however,
a strong degeneracy in the \beta- plane. When the two data sets
are combined, the latter degeneracy remains, but the errors are reduced by a
factor ~2 for both parameters.Comment: 5 pages, 6 figures. Now published in A&A 500, 657-665 (2009
Cost-effectiveness of household contact investigation for detection of tuberculosis in Pakistan
Objectives
Despite WHO guidelines recommending household contact investigation, and studies showing the impact of active screening, most tuberculosis (TB) programmes in resource-limited settings only carry out passive contact investigation. The cost of such strategies is often cited as barriers to their implementation. However, little data are available for the additional costs required to implement this strategy. We aimed to estimate the cost and cost-effectiveness of active contact investigation as compared with passive contact investigation in urban Pakistan.
Methods
We estimated the cost-effectiveness of ‘enhanced’ (passive with follow-up) and ‘active’ (household visit) contact investigations compared with standard ‘passive’ contact investigation from providers and the programme’s perspective using a simple decision tree. Costs were collected in Pakistan from a TB clinic performing passive contact investigation and from studies of active contact tracing interventions conducted. The effectiveness was based on the number of patients with TB identified among household contacts screened.
Results
The addition of enhanced contact investigation to the existing passive mode detected 3.8 times more cases of TB per index patient compared with passive contact investigation alone. The incremental cost was US120 per incremental patient identified with TB. The active contact investigation was 1.5 times more effective than enhanced contact investigation with an incremental cost of US$238 per incremental patient with TB identified.
Conclusion
Our results show that enhanced and active approaches to contact investigation effectively identify additional patients with TB among household contacts at a relatively modest cost. These strategies can be added to the passive contact investigation in a high burden setting to find the people with TB who are missed and meet the End TB strategy goals.publishedVersio
Carnegie Hubble Program: A Mid-Infrared Calibration of the Hubble Constant
Using a mid-infrared calibration of the Cepheid distance scale based on
recent observations at 3.6 um with the Spitzer Space Telescope, we have
obtained a new, high-accuracy calibration of the Hubble constant. We have
established the mid-IR zero point of the Leavitt Law (the Cepheid
Period-Luminosity relation) using time-averaged 3.6 um data for ten
high-metallicity, Milky Way Cepheids having independently-measured
trigonometric parallaxes. We have adopted the slope of the PL relation using
time-averaged 3.6 um data for 80 long-period Large Magellanic Cloud (LMC)
Cepheids falling in the period range 0.8 < log(P) < 1.8. We find a new
reddening-corrected distance to the LMC of 18.477 +/- 0.033 (systematic) mag.
We re-examine the systematic uncertainties in H0, also taking into account new
data over the past decade. In combination with the new Spitzer calibration, the
systematic uncertainty in H0 over that obtained by the Hubble Space Telescope
(HST) Key Project has decreased by over a factor of three. Applying the Spitzer
calibration to the Key Project sample, we find a value of H0 = 74.3 with a
systematic uncertainty of +/-2.1 (systematic) km/s/Mpc, corresponding to a 2.8%
systematic uncertainty in the Hubble constant. This result, in combination with
WMAP7 measurements of the cosmic microwave background anisotropies and assuming
a flat universe, yields a value of the equation of state for dark energy, w0 =
-1.09 +/- 0.10. Alternatively, relaxing the constraints on flatness and the
numbers of relativistic species, and combining our results with those of WMAP7,
Type Ia supernovae and baryon acoustic oscillations yields w0 = -1.08 +/- 0.10
and a value of N_eff = 4.13 +/- 0.67, mildly consistent with the existence of a
fourth neutrino species.Comment: 27 pages, 8 figures, Accepted for publication in Ap
Measuring the cosmological bulk flow using the peculiar velocities of supernovae
We study large-scale coherent motion in our universe using the existing Type
IA supernovae data. If the recently observed bulk flow is real, then some
imprint must be left on supernovae motion. We run a series of Monte Carlo
Markov Chain runs in various redshift bins and find a sharp contrast between
the z 0.05 data. The$z < 0.05 data are consistent with the bulk
flow in the direction (l,b)=({290^{+39}_{-31}}^{\circ},
{20^{+32}_{-32}}^{\circ}) with a magnitude of v_bulk = 188^{+119}_{-103} km/s
at 68% confidence. The significance of detection (compared to the null
hypothesis) is 95%. In contrast, z > 0.05 data (which contains 425 of the 557
supernovae in the Union2 data set) show no evidence for bulk flow. While the
direction of the bulk flow agrees very well with previous studies, the
magnitude is significantly smaller. For example, the Kashlinsky, et al.'s
original bulk flow result of v_bulk > 600 km/s is inconsistent with our
analysis at greater than 99.7% confidence level. Furthermore, our best-fit bulk
flow velocity is consistent with the expectation for the \Lambda CDM model,
which lies inside the 68% confidence limit.Comment: Version published in JCA
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