The Vela Pulsar and its Synchrotron Nebula

(Abridged) We present high-resolution Chandra X-ray observations of PSR B0833-45, the 89 ms pulsar associated with the Vela supernova remnant. We have acquired two observations separated by one month to search for changes in the pulsar and its environment following an extreme glitch in its rotation frequency. We find a well-resolved nebula with a toroidal morphology remarkably similar to that observed in the Crab Nebula, along with an axial Crab-like jet. Between the two observations the flux from the pulsar is found to be steady to within 0.75%; the 3 sigma limit on the fractional increase in the pulsar's X-ray flux is < ~10^-5 of the inferred glitch energy. We use this limit to constrain parameters of glitch models and neutron star structure. We do find a significant increase in the flux of the nebula's outer arc; if associated with the glitch, the inferred propagation velocity is > 0.7c, similar to that seen in the brightening of the Crab Nebula wisps. We propose an explanation for the X-ray structure of the Vela synchrotron nebula based on a model originally developed for the Crab Nebula. In a departure from the Crab model, the magnetization parameter "sigma" of the Vela pulsar wind is allowed to be of order unity; this is consistent with the simplest MHD transport of magnetic field from the pulsar to the nebula, where B < 4 X 10^-4 G. We review effects that may enhance the probability of alignment between the spin axis and space velocity of a pulsar, and speculate that short-period, slowly moving pulsars are just the ones best-suited to producing synchrotron nebulae with such aligned structures.Comment: 16 pages with 8 figures, uses LaTex, emulateapj.sty. Refereed version. To appear in The Astrophysical Journa

Empiric combination antibiotic therapy is associated with improved outcome against sepsis due to gram-negative bacteria: A retrospective analysis

The optimal approach for empirical antibiotic therapy in patients with severe sepsis and septic shock remains controversial. A retrospective cohort study was conducted in the intensive care units of a university hospital. The data from 760 patients with severe sepsis or septic shock associated with Gram-negative bacteremia was analyzed. Among this cohort, 238 (31.3%) patients received inappropriate initial antimicrobial therapy (IIAT). The hospital mortality rate was statistically greater among patients receiving IIAT compared to those initially treated with an appropriate antibiotic regimen (51.7% versus 36.4%; P < 0.001). Patients treated with an empirical combination antibiotic regimen directed against Gram-negative bacteria (i.e., β-lactam plus aminoglycoside or fluoroquinolone) were less likely to receive IIAT compared to monotherapy (22.2% versus 36.0%; P < 0.001). The addition of an aminoglycoside to a carbapenem would have increased appropriate initial therapy from 89.7 to 94.2%. Similarly, the addition of an aminoglycoside would have increased the appropriate initial therapy for cefepime (83.4 to 89.9%) and piperacillin-tazobactam (79.6 to 91.4%). Logistic regression analysis identified IIAT (adjusted odds ratio [AOR], 2.30; 95% confidence interval [CI] = 1.89 to 2.80) and increasing Apache II scores (1-point increments) (AOR, 1.11; 95% CI = 1.09 to 1.13) as independent predictors for hospital mortality. In conclusion, combination empirical antimicrobial therapy directed against Gram-negative bacteria was associated with greater initial appropriate therapy compared to monotherapy in patients with severe sepsis and septic shock. Our experience suggests that aminoglycosides offer broader coverage than fluoroquinolones as combination agents for patients with this serious infection

Modeling of the Vela complex including the Vela supernova remnant, the binary system gamma2 Velorum, and the Gum nebula

We study the geometry and dynamics of the Vela complex including the Vela supernova remnant (SNR), the binary system gamma2 Velorum and the Gum nebula. We show that the Vela SNR belongs to a subclass of non-Sedov adiabatic remnants in a cloudy interstellar medium (ISM), the dynamics of which is determined by the heating and evaporation of ISM clouds. We explain observable characteristics of the Vela SNR with a SN explosion with energy 1.4 x 10^50 ergs near the step-like boundary of the ISM with low intercloud densities (~ 10^{-3} cm^{-3}) and with a volume-averaged density of clouds evaporated by shock in the north-east (NE) part about four times higher than the one in the south-west (SW) part. The observed asymmetry between the NE and SW parts of the Vela SNR could be explained by the presence of a stellar wind bubble (SWB) blown by the nearest-to-the Earth Wolf-Rayet (WR) star in the gamma2 Velorum system. We show that the size and kinematics of gamma2 Velorum SWB agree with predictions of numerical calculations for the evolution of the SWB of M_ini = 35M* star. The low initial mass of the WR star in gamma2 Velorum implies that the luminosity of the nuclear line of 26Al, produced by gamma2 Velorum, is below the sensitivity of existing gamma-ray telescopes.Comment: 8 pages, 2 figures, accepted for publication in A&

Gravitational waves from single neutron stars: an advanced detector era survey

With the doors beginning to swing open on the new gravitational wave astronomy, this review provides an up-to-date survey of the most important physical mechanisms that could lead to emission of potentially detectable gravitational radiation from isolated and accreting neutron stars. In particular we discuss the gravitational wave-driven instability and asteroseismology formalism of the f- and r-modes, the different ways that a neutron star could form and sustain a non-axisymmetric quadrupolar "mountain" deformation, the excitation of oscillations during magnetar flares and the possible gravitational wave signature of pulsar glitches. We focus on progress made in the recent years in each topic, make a fresh assessment of the gravitational wave detectability of each mechanism and, finally, highlight key problems and desiderata for future work.Comment: 39 pages, 12 figures, 2 tables. Chapter of the book "Physics and Astrophysics of Neutron Stars", NewCompStar COST Action 1304. Minor corrections to match published versio

Effect of Fabrication Parameters on the Ferroelectricity of Hafnium Zirconium Oxide Films: A Statistical Study

Ferroelectricity in hafnium zirconium oxide (Hf1−xZrxO2) and the factors that impact it have been a popular research topic since its discovery in 2011. Although the general trends are known, the interactions between fabrication parameters and their effect on the ferroelectricity of Hf1−xZrxO2 require further investigation. In this paper, we present a statistical study and a model that relates Zr concentration (x), film thickness (tf), and annealing temperature (Ta) with the remanent polarization (Pr) in tungsten (W)-capped Hf1−xZrxO2. This work involved the fabrication and characterization of 36 samples containing multiple sets of metal-ferroelectric-metal capacitors while varying x (0.26, 0.48, and 0.57), tf (10 and 19 nm), and Ta (300, 400, 500, and 600 °C). In addition to the well-understood effects of x and Ta on the ferroelectricity of Hf1−xZrxO2, the statistical analysis showed that thicker Hf1−xZrxO2 films or films with higher x require lower Ta to crystallize and demonstrated that there is no statistical difference between samples annealed to 500 and 600 °C, thus suggesting that most films fully crystallize with Ta ∼ 500 °C for 60 s. Our model explains 95% of the variability in the Pr data for the films fabricated, presents the estimates of the phase composition of the film, and provides a starting point for selecting fabrication parameters when a specific Pr is desired

A pilot study using tactile cueing for gait rehabilitation following stroke

Recovery of walking function is a vital goal of post-stroke rehabilitation. Cueing using audio metronomes has been shown to improve gait, but can be impractical when interacting with others, particularly outdoors where awareness of vehicles and bicycles is essential. Audio is also unsuitable in environments with high background noise, or for those with a hearing impairment. If successful, lightweight portable tactile cueing has the potential to take the benefits of cueing out of the laboratory and into everyday life. The Haptic Bracelets are lightweight wireless devices containing a computer, accelerometers and low-latency vibrotactiles with a wide dynamic range. In this paper we review gait rehabilitation problems and existing solutions, and present an early pilot in which the Haptic Bracelets were applied to post-stroke gait rehabilitation. Tactile cueing during walking was well received in the pilot, and analysis of motion capture data showed immediate improvements in gait

Democracy and Religion

Relations between American democracy and religion have always been somewhat equivocal.On the one hand, moral and ethical principles derived from the Judeo-Christian tradition have been a major source of democratic values. Religion was an important motivating factor in both the colonization of North America and the American Revolution. The Founding Fathers set such high store by religion that they included its free exercise along with free speech and a free press among the liberties specifically protected by the First Amendment to the Constitution. Organized religion played a key role in such drives to perfect democracy as the abolition of slavery, the enactment of woman's suffrage, and the civil rights struggle of the 1960s. Perhaps most important, the so-called Protestant ethic provided the moral bedrock on which republican institutions were built.On the other hand, democratic theorists and much of the general public have been wary of the absolutist social outlook often associated with religion. Practically all religions claim to embody ultimate truths about the nature of the universe and the human condition. At some level, therefore, they can hardly be tolerant of rival beliefs. Religious bodies can avoid social intolerance by acknowledging that human imperfection clouds and corrupts the judgments of all institutions, including the churches, or by limiting their social pronouncement to broad moral directives. In practice, however, individuals or institutions claiming to represent transcendent moral authority are often tempted to attach certainty to their opinions on complex issues in secular politics.</jats:p