Predicting caustic crossing high magnification events in Q2237+0305

The central regions of the gravitationally lensed quasar Q2237+0305 can be indirectly resolved on nano-arcsecond scales if viewed spectrophotometricly during a microlensing high magnification event (HME). Q2237+0305 is currently being monitored from the ground (eg. OGLE collaboration, Apache Point Observatory), with the goal, among others, of triggering ground and spacecraft based target of opportunity (TOO) observations of an HME. In this work we investigate the rate of change (trigger) in image brightness that signals an imminent HME and importantly, the separation between the trigger and the event peak. In addition, we produce colour dependent model light-curves by combining high-resolution microlensing simulations with a realistic model for a thermal accretion disc source. We make hypothetical target of opportunity spectroscopic observations using our determination of the appropriate trigger as a guide. We find that if the source spectrum varies with source radius, a 3 observation TOO program should be able to observe a microlensing change in the continuum slope following a light-curve trigger with a success rate of >80%.Comment: 17 pages, 16 figures, accepted for publication in M.N.R.A.

A measurement of the transverse velocity of Q2237+0305

Determination of microlensing parameters in the gravitationally lensed quasar Q2237+0305 from the statistics of high magnification events will require monitoring for more than 100 years (Wambsganss, Paczynski & Schneider 1990). However we show that the effective transverse velocity of the lensing galaxy can be determined on a more realistic time-scale through consideration of the distribution of light-curve derivatives. The 10 years of existing monitoring data for Q2237+0305 are analysed. These data display strong evidence for microlensing that is not associated with a high magnification event. An upper limit of v < 500 km/sec is obtained for the galactic transverse velocity which is smaller than previously assumed values. The analysis suggests that the observed microlensing variation may be predominantly due to stellar proper motions. The statistical significance of the results obtained from our method will be increased by the addition of data points from current and future monitoring campaigns. However reduced photometric errors will be more valuable than an increased sampling rate.Comment: 16 pages, including 17 figures. Accepted for publication in M.N.R.A.

Interpretation of the OGLE Q2237+0305 microlensing light-curve

The four bright images of the gravitationally lensed quasar Q2237+0305 are being monitored from the ground (eg. OGLE collaboration, Apache Point Observatory) in the hope of observing a high magnification event (HME). Over the past three seasons (1997-1999) the OGLE collaboration has produced microlensing light-curves with unprecedented coverage. These demonstrate smooth, independent (therefore microlensing) variability between the images (Wozniak et al. 2000a,b; OGLE web page). We have retrospectively compared probability functions for high-magnification event parameters with several observed light-curve features. We conclude that the 1999 image C peak was due to the source having passed outside of a cusp rather than to a caustic crossing. In addition, we find that the image C light-curve shows evidence for a caustic crossing between the 1997 and 1998 observing seasons involving the appearance of new critical images. Our models predict that the next image C event is most likely to arrive 500 days following the 1999 peak, but with a large uncertainty (100-2000 days). Finally, given the image A light-curve derivative at the end of the 1999 observing season, our modelling suggests that a caustic crossing will occur between the 1999 and 2000 observing seasons, implying a minimum for the image A light-curve ~1-1.5 magnitudes fainter than the November 1999 level.Comment: 11 pages, 15 figures. Accepted for publication in M.N.R.A.

Limits on the microlens mass function of Q2237+0305

Gravitational microlensing at cosmological distances is potentially a powerful tool for probing the mass functions of stars and compact objects in other galaxies. In the case of multiply-imaged quasars, microlensing data has been used to determine the average microlens mass. However the measurements have relied on an assumed transverse velocity for the lensing galaxy. Since the measured mass scales with the square of the transverse velocity, published mass limits are quite uncertain. In the case of Q2237+0305 we have properly constrained this uncertainty. The distribution of light curve derivatives allows quantitative treatment of the relative rates of microlensing due to proper motions of microlenses, the orbital stream motion of microlenses and the bulk galactic transverse velocity. By demanding that the microlensing rate due to the motions of microlenses is the minimum that should be observed we determine lower limits for the average mass of stars and compact objects in the bulge of Q2237+0305. If microlenses are assumed to move in an orbital stream the lower limit ranges between 0.005 and 0.023 solar masses where the the systematic dependence is due to the fraction of smooth matter and the size of photometric error assumed for published monitoring data. However, if the microlenses are assumed to move according to an isotropic velocity dispersion then a larger lower limit of 0.019-0.11 solar masses is obtained. A significant contribution of Jupiter mass compact objects to the mass distribution of the galactic bulge of Q2237+0305 is therefore unambiguously ruled out.Comment: 10 pages, 5 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Society. New version has improved presentatio

Diffraction-contrast imaging of cold atoms

We consider the inverse problem of in-line holography, applied to minimally-destructive imaging of cold atom clouds. Absorption imaging near-resonance provides a simple, but destructive measurement of atom column density. Imaging off resonance greatly reduces heating, and sequential images may be taken. Under the conditions required for off-resonant imaging, the generally-intractable inverse problem may be linearized. A minimally-destructive, quantitative and high-resolution image of the atom cloud column density is then retrieved from a single diffraction pattern.Comment: 4 pages, 3 figures v2: minor changes in response to referee reports, mostly additional experimental detail v3: revisions to figure 3: added trace and changed image. Minor text and referencing changes. Accepted by Phys Rev A (Rapid Commun

Identification of dividing, determined sensory neuron precursors in the mammalian neural crest

Sensory and autonomic neurons of the vertebrate peripheral nervous system are derived from the neural crest. Here we use the expression of lineage-specific transcription factors as a means to identify neuronal subtypes that develop in rat neural crest cultures grown in a defined medium. Sensory neurons, identified by expression of the POU-domain transcription factor Brn-3.0, develop from dividing precursors that differentiate within 2 days following emigration from the neural tube. Most of these precursors generate sensory neurons even when challenged with BMP2, a factor that induces autonomic neurogenesis in many other cells in the explants. Moreover, BMP2 fails to prevent expression of the sensory-specific basic helix-loop-helix (bHLH) transcription factors neurogenin1, neurogenin2 and neuroD, although it induces expression of the autonomic-specific bHLH factor MASH1 and the paired homeodomain factor Phox2a in other cells. These data suggest that there are mitotically active precursors in the mammalian neural crest that can generate sensory neurons even in the presence of a strong autonomic-inducing cue. Further characterization of the neurons generated from such precursors indicates that, under these culture conditions, they exhibit a proprioceptive and/or mechanosensory, but not nociceptive, phenotype. Such precursors may therefore correspond to a lineally (Frank, E. and Sanes, J. (1991) Development 111, 895-908) and genetically (Ma, Q., Fode, C., Guillemot, F. and Anderson, D. J. (1999) Genes Dev. 13, in press) distinct subset of early-differentiating precursors of large-diameter sensory neurons identified in vivo

Inlet spillage drag tests and numerical flow-field analysis at subsonic and transonic speeds of a 1/8-scale, two-dimensional, external-compression, variable-geometry, supersonic inlet configuration

Accurate spillage drag and pressure data are presented for a realistic supersonic inlet configuration. Results are compared with predictions from a finite-differencing, inviscid analysis computer procedure. The analytical technique shows good promise for the evaluation of inlet drag, but necessary refinements were identified. A detailed description of the analytical procedure is contained in the Appendix

Association of inferior vena cava filter placement for venous thromboembolic disease and a contraindication to anticoagulation with 30-day mortality

Importance: Despite the absence of data from randomized clinical trials, professional societies recommend inferior vena cava (IVC) filters for patients with venous thromboembolic disease (VTE) and a contraindication to anticoagulation therapy. Prior observational studies of IVC filters have suggested a mortality benefit associated with IVC filter insertion but have often failed to adjust for immortal time bias, which is the time before IVC filter insertion, during which death can only occur in the control group. Objective: To determine the association of IVC filter placement with 30-day mortality after adjustment for immortal time bias. Design, Setting, and Participants: This comparative effectiveness, retrospective cohort study used a population-based sample of hospitalized patients with VTE and a contraindication to anticoagulation using the State Inpatient Database and the State Emergency Department Database, part of the Healthcare Cost and Utilization Project of the Agency for Healthcare Research and Quality, from hospitals in California (January 1, 2005, to December 31, 2011), Florida (January 1, 2005, to December 31, 2013), and New York (January 1, 2005, to December 31, 2012). Data analysis was conducted from September 15, 2015, to March 14, 2018. Exposure: Inferior vena cava filter placement. Main Outcomes and Measures: Multivariable Cox proportional hazard models were constructed with IVC filters as a time-dependent variable that adjusts for immortal time bias. The Cox model was further adjusted using the propensity score as an adjustment variable. Results: Of 126 030 patients with VTE, 61 281 (48.6%) were male and the mean (SD) age was 66.9 (16.6) years. In this cohort, 45 771 (36.3%) were treated with an IVC filter, whereas 80 259 (63.7%) did not receive a filter. In the Cox model with IVC filter status analyzed as a time-dependent variable to account for immortal time bias, IVC filter placement was associated with a significantly increased hazard ratio of 30-day mortality (1.18; 95% CI, 1.13-1.22; P \u3c .001). When the propensity score was included in the Cox model, IVC filter placement remained associated with an increased hazard ratio of 30-day mortality (1.18; 95% CI, 1.13-1.22; P \u3c .001). Conclusions and Relevance: After adjustment for immortal time bias, IVC filter placement was associated with increased 30-day mortality in patients with VTE and a contraindication to anticoagulation. Randomized clinical trials are needed to determine the efficacy of IVC filter placement in patients with VTE and a contraindication to anticoagulation

Light forces in ultracold photoassociation

We study the time-resolved photoassociation of ultracold sodium in an optical dipole trap. The photoassociation laser excites pairs of atoms to molecular states of large total angular momentum at high intensities (above 20 kW/cm$^{2}$). Such transitions are generally suppressed at ultracold temperatures by the centrifugal barriers for high partial waves. Time-resolved ionization measurements reveal that the atoms are accelerated by the dipole potential of the photoassociation beam. We change the collision energy by varying the potential depth, and observe a strong variation of the photoassociation rate. These results demonstrate the important role of light forces in cw photoassociation at high intensities.Comment: 7 pages, 3 figure