Stirring the Embers: High Sensitivity VLBI Observations of GRB030329

We present high sensitivity Very Long Baseline Interferometry (VLBI) observations 806 days after the gamma-ray burst of 2003 March 29 (GRB030329). The angular diameter of the radio afterglow is measured to be 0.347 +- 0.09 mas, corresponding to 0.99 +- 0.26 pc at the redshift of GRB030329 (z = 0.1685). The evolution of the image size favors a uniform external density over an R^-2 wind-like density profile (at distances of R >~10^18 cm from the source), although the latter cannot be ruled out yet. The current apparent expansion velocity of the image size is only mildly relativistic, suggesting a non-relativistic transition time of t_NR ~ 1 yr. A rebrightening, or at least a significant flattening in the flux decay, is expected within the next several years as the counter-jet becomes visible (this has not yet been observed). An upper limit of <1.9c is set on the proper motion of the flux centroid.Comment: 16 pages, 5 figures, accepted for publication in Astrophysical Journa

Stick shift

Thesis (S.B. in Creative Writing)--Massachusetts Institute of Technology, Dept. of Humanities, Program in Writing and Humanistic Studies, 2004.Stick Shift is a novel that has undergone several rounds of significant revision. Scott, the book's main character, is a sarcastic American who travels to England to move in with an ex-girlfriend. He experiences all of the obstacles involved in moving to a new country, leaving his home, and settling down with a woman in a comic sequence told in seven chapters.The introduction to this piece outlines my history as a writer, primarily focusing on my development at MIT. The thesis project is discussed and followed from its initial seed all the way through to its current state.by Aaron Parness.S.B.in Creative Writin

A High Luminosity e+e- Collider to study the Higgs Boson

A strong candidate for the Standard Model Scalar boson, H(126), has been discovered by the Large Hadron Collider (LHC) experiments. In order to study this fundamental particle with unprecedented precision, and to perform precision tests of the closure of the Standard Model, we investigate the possibilities offered by An e+e- storage ring collider. We use a design inspired by the B-factories, taking into account the performance achieved at LEP2, and imposing a synchrotron radiation power limit of 100 MW. At the most relevant centre-of-mass energy of 240 GeV, near-constant luminosities of 10^34 cm^{-2}s^{-1} are possible in up to four collision points for a ring of 27km circumference. The achievable luminosity increases with the bending radius, and for 80km circumference, a luminosity of 5 10^34 cm^{-2}s^{-1} in four collision points appears feasible. Beamstrahlung becomes relevant at these high luminosities, leading to a design requirement of large momentum acceptance both in the accelerating system and in the optics. The larger machine could reach the top quark threshold, would yield luminosities per interaction point of 10^36 cm^{-2}s^{-1} at the Z pole (91 GeV) and 2 10^35 cm^{-2}s^{-1} at the W pair production threshold (80 GeV per beam). The energy spread is reduced in the larger ring with respect to what is was at LEP, giving confidence that beam polarization for energy calibration purposes should be available up to the W pair threshold. The capabilities in term of physics performance are outlined.Comment: Submitted to the European Strategy Preparatory Group 01-04-2013 new version as re-submitted to PRSTA

Mortality Reduction Associated with HIV/AIDS Care and Antiretroviral Treatment in Rural Malawi: Evidence from Registers, Coffin Sales and Funerals

BACKGROUND: To report on the trend in all-cause mortality in a rural district of Malawi that has successfully scaled-up HIV/AIDS care including antiretroviral treatment (ART) to its population, through corroborative evidence from a) registered deaths at traditional authorities (TAs), b) coffin sales and c) church funerals. METHODS AND FINDINGS: Retrospective study in 5 of 12 TAs (covering approximately 50% of the population) during the period 2000-2007. A total of 210 villages, 24 coffin workshops and 23 churches were included. There were a total of 18,473 registered deaths at TAs, 15781 coffins sold, and 2762 church funerals. Between 2000 and 2007, there was a highly significant linear downward trend in death rates, sale of coffins and church funerals (X(2) for linear trend: 338.4 P<0.0001, 989 P<0.0001 and 197, P<0.0001 respectively). Using data from TAs as the most reliable source of data on deaths, overall death rate reduction was 37% (95% CI:33-40) for the period. The mean annual incremental death rate reduction was 0.52/1000/year. Death rates decreased over time as the percentage of people living with HIV/AIDS enrolled into care and ART increased. Extrapolating these data to the entire district population, an estimated 10,156 (95% CI: 9786-10259) deaths would have been averted during the 8-year period. CONCLUSIONS: Registered deaths at traditional authorities, the sale of coffins and church funerals showed a significant downward trend over a 8-year period which we believe was associated with the scaling up HIV/AIDS care and ART

Nanofiber fabrication in a temperature and humidity controlled environment for improved fibre consistency

To fabricate nanofibers with reproducible characteristics, an important demand for many applications, the effect of controlled atmospheric conditions on resulting electrospun cellulose acetate (CA) nanofibers was evaluated for temperature ranging 17.5 - 35&#xb0;C and relative humidity ranging 20% - 70%. With the potential application of nanofibers in many industries, especially membrane and filter fabrication, their reproducible production must be established to ensure commercially viability.&#xd;&#xa;Cellulose acetate (CA) solution (0.2 g/ml) in a solvent mixture of acetone/DMF/ethanol (2:2:1) was electrospun into nonwoven fibre mesh with the fibre diameter ranging from 150nm to 1&#xb5;m.&#xd;&#xa;The resulting nanofibers were observed and analyzed by scanning electron microscopy (SEM), showing a correlation of reducing average fibre diameter with increasing atmospheric temperature. A less pronounced correlation was seen with changes in relative humidity regarding fibre diameter, though it was shown that increased humidity reduced the effect of fibre beading yielding a more consistent, and therefore better quality of fibre fabrication.&#xd;&#xa;Differential scanning calorimetry (DSC) studies observed lower melt enthalpies for finer CA nanofibers in the first heating cycle confirming the results gained from SEM analysis. From the conditions that were explored in this study the temperature and humidity that gave the most suitable fibre mats for a membrane purpose were 25.0&#xb0;C and 50%RH due to the highest level of fibre diameter uniformity, the lowest level of beading while maintaining a low fibre diameter for increased surface area and increased pore size homogeneity. This study has highlighted the requirement to control the atmospheric conditions during the electrospinning process in order to fabricate reproducible fibre mats

Multiple Interactions and the Structure of Beam Remnants

Recent experimental data have established some of the basic features of multiple interactions in hadron-hadron collisions. The emphasis is therefore now shifting, to one of exploring more detailed aspects. Starting from a brief review of the current situation, a next-generation model is developed, wherein a detailed account is given of correlated flavour, colour, longitudinal and transverse momentum distributions, encompassing both the partons initiating perturbative interactions and the partons left in the beam remnants. Some of the main features are illustrated for the Tevatron and the LHC.Comment: 69pp, 33 figure

ω(→π+π−π0) \omega (\to \pi^+\pi^-\pi^0) meson photoproduction on proton

The cross section is estimated for the $\pi^+\pi^-\pi^0$ invariant mass distribution in the $\gamma p$ reaction in the GeV region. This reaction is assumed to proceed through the formation of the $\omega$ meson in the intermediate state, since the production cross section for this meson in the $\gamma p$ reaction in GeV region is significant and it has large branching ratio (88.8%) in the $\pi^+\pi^-\pi^0$ channel. The cross sections for this reaction have been calculated using the energy dependent reaction amplitude, i.e., $f_{\gamma p \to \omega p}(0)$, extracted from the latest $\omega$ meson photoproduction data. We use established procedure to calculate other factors, like width and propagator of the $\omega$ meson, so that our calculation can provide reliable cross section. The calculated results reproduce the measured $\pi^+\pi^-\pi^0$ invariant mass distribution spectra in the $\gamma p$ reaction.Comment: 13 pages, 5 figure

Spatiotemporal Accessibility of COVID-19 Healthcare Facilities in Jakarta, Indonesia

During the first year of the COVID-19 pandemic in Jakarta, Indonesia, the government designated some hospitals as specific COVID-19 healthcare centers to meet demand and ensure accessibility. However, the policy demand evaluation was based on a purely spatial approach. Studies on accessibility to healthcare are widely available, but those that consider temporal as well as spatial dynamics are lacking. This study aims to analyze the spatiotemporal dynamics of healthcare accessibility against COVID-19 cases within the first year of the COVID-19 pandemic, and the overall pattern of spatiotemporal accessibility. A two-step floating catchment area (2SFCA) was used to analyze the accessibility of COVID-19 healthcare against the monthly data of the COVID-19 infected population, as the demand. Such a spatiotemporal approach to 2SFCA has never been used in previous studies. Furthermore, rather than the traditional buffer commonly used to define catchments, the 2SFCA in this study was improved with automated delineation based on the road network using ArcGIS Service Areas Analysis tools. The accessibility tends to follow the distance decay principle, which is relatively high in the city’s center and low in the outskirts. This contrasts with the city’s population distribution, which is higher on the outskirts and lower in the center. This research is a step toward optimizing the spatial distribution of hospital locations to correspond with the severity of the pandemic condition. One method to stop the transmission of disease during a pandemic that requires localizing the infected patient is to designate specific healthcare facilities to manage the sick individuals. ‘What-if’ scenarios may be used to experiment with the locations of these healthcare facilities, which are then assessed using the methodology described in this work to obtain the distribution that is most optimal

On the influence of the cosmological constant on gravitational lensing in small systems

The cosmological constant Lambda affects gravitational lensing phenomena. The contribution of Lambda to the observable angular positions of multiple images and to their amplification and time delay is here computed through a study in the weak deflection limit of the equations of motion in the Schwarzschild-de Sitter metric. Due to Lambda the unresolved images are slightly demagnified, the radius of the Einstein ring decreases and the time delay increases. The effect is however negligible for near lenses. In the case of null cosmological constant, we provide some updated results on lensing by a Schwarzschild black hole.Comment: 8 pages, 1 figure; v2: extended discussion on the lens equation, references added, results unchanged, in press on PR