On the formation of low-mass black holes in massive binary stars

Recently (Brown \& Bethe 1994) it was suggested that most stars with main sequence mass in the range of about $18 - 30 M_{\odot}$ explode, returning matter to the Galaxy, and then go into low-mass ($\geq 1.5 M_{\odot}$) black holes. Even more massive main-sequence stars would, presumably, chiefly g o into high-mass ($\sim 10 M_{\odot}$) black holes. The Brown-Bethe estimates gave approximately $5 \times {10}^{8}$ low-mass black holes in the Galaxy. A pressing question, which we attempt to answer here, is why, with the possible exception of the compact objects in SN1987A and 4U\,1700--37, none of these have been seen. We address this question in three parts. Firstly, black holes are generally ``seen'' only in binaries, by the accretion of matter from a companion star. High mass black holes are capable of accreting more matter than low-mass black holes, so there is a selection effect favoring them. This, in itself, would not be sufficient to show why low-mass black holes have not been seen, since neutron stars (of nearly the same mass) are seen in abundance. Secondly, and this is our main point, the primary star in a binary ---the first star to evolve--- loses its hydrogen envelope by transfer of matter to the secondary and loss into space, and the resulting ``naked'' helium star evolves differently than a helium core, which is at least initially covered by the hydrogen envelope in a massive main-sequence star. We show that primary stars in binaries can end up as neutron stars even if their initial mass substantially exceeds the mass limit for neutron star formation from single stars ($\sim 18 M_{\odot}$). An example is 4U\,1223--62, in which we suggest that the initial primary mass exceeded $35 M_{\odot}$, yet X-ray pulsationsComment: uuencoded compressed postscript. The preprint is also available at http://www.ast.cam.ac.uk/preprint/PrePrint.htm

Electric dipole moments and disalignment of interstellar dust grains

The degree to which interstellar grains align with respect to the interstellar magnetic field depends on disaligning as well as aligning mechanisms. For decades, it was assumed that disalignment was due primarily to the random angular impulses a grain receives when colliding with gas-phase atoms. Recently, a new disalignment mechanism has been considered, which may be very potent for a grain that has a time-varying electric dipole moment and drifts across the magnetic field. We provide quantitative estimates of the disalignment times for silicate grains with size > approximately 0.1 micron. These appear to be shorter than the time-scale for alignment by radiative torques, unless the grains contain superparamagnetic inclusions.Comment: 12 pages, 9 figures, submitted to MNRA

Eliciting Information During a Standardized Patient History

ELICITING INFORMATION DURING A STANDARDIZED PATIENT HISTORY AUTHORS Sydney Greene, BA Candidate; Emily J Noonan, PhD, MA; Laura A. Weingartner, PhD, MS BACKGROUND Learning how to take a detailed patient history is a fundamental skill that is essential for all medical students to master. Understanding the amount of information elicited in various categories of a patient history may reveal areas where many students struggle to engage the patient, gaps in medical education that could be addressed, or possible predictors of patient satisfaction. METHODS I coded videos of rising third year medical students as they took a patient history and counted each time the student elicited information, the student gave explanations, and the patient asked questions. These counts were compared across the main categories of the patient history, which included past medical history, a hormone use discussion specific to this encounter, family medical history, social history, mental health history, sexual history, and the treatment plan. RESULTS On average, students prompted for information 50 times during a new patient encounter while providing about 12 explanations. Under 4% of questions were related to the patient’s mental health on average compared to 23% of student questions about past medical history and 24% about social history. Patients asked about four questions on average, with most being asked during discussions of the treatment plan. DISCUSSION The results may indicate that students feel uncomfortable asking questions relating to mental health or that students feel mental health is less important to consider than other factors when taking a patient history. In comparison, students seem to feel confident and comfortable discussing the past medical history and social history of the patient. REFERENCES: Ha et al. Doctor-Patient Communication: A Review. Ochsner Journal. V(10):2010. Teutsch, Carol. Patient-Doctor Communication. Medical Clinics of North America. V(87):2003

13-month climatology of the aerosol hygroscopicity at the free tropospheric site Jungfraujoch (3580 m a.s.l.)

A hygroscopicity tandem differential mobility analyzer (HTDMA) was operated at the high-alpine site Jungfraujoch in order to characterize the hygroscopic diameter growth factors of the free tropospheric Aitken and accumulation mode aerosol. More than ~5000 h of valid data were collected for the dry diameters <i>D</i><sub>0</sub> = 35, 50, 75, 110, 165, and 265 nm during the 13-month measurement period from 1 May 2008 through 31 May 2009. No distinct seasonal variability of the hygroscopic properties was observed. Annual mean hygroscopic diameter growth factors (<i>D</i>/<i>D</i><sub>0</sub>) at 90% relative humidity were found to be 1.34, 1.43, and 1.46 for <i>D</i><sub>0</sub> = 50, 110, and 265 nm, respectively. This size dependence can largely be attributed to the Kelvin effect because corresponding values of the hygroscopicity parameter κ are nearly independent of size. The mean hygroscopicity of the Aitken and accumulation mode aerosol at the free tropospheric site Jungfraujoch was found to be κ≈0.24 with little variability throughout the year. <br><br> The impact of Saharan dust events, a frequent phenomenon at the Jungfraujoch, on aerosol hygroscopicity was shown to be negligible for <i>D</i><sub>0</sub><265 nm. Thermally driven injections of planetary boundary layer (PBL) air, particularly observed in the early afternoon of summer days with convective anticyclonic weather conditions, lead to a decrease of aerosol hygroscopicity. However, the effect of PBL influence is not seen in the annual mean hygroscopicity data because the effect is small and those conditions (weather class, season and time of day) with PBL influence are relatively rare. <br><br> Aerosol hygroscopicity was found to be virtually independent of synoptic wind direction during advective weather situations, i.e. when horizontal motion of the atmosphere dominates over thermally driven convection. This indicates that the hygroscopic behavior of the aerosol observed at the Jungfraujoch can be considered representative of the lower free troposphere on at least a regional if not continental scale

The impact of spatial wind variations on freshwater transport by the Alaska Coastal Current

The Alaska Coastal Current (ACC) is located in a region with prevailing downwelling-favorable winds, flows over a long stretch of coastline (over 2000 km), and is driven by multiple sources of freshwater discharge totaling 24000 m3 s–1 along its length. Using the Regional Ocean Modeling System (ROMS) we attempt to determine how spatially variable winds affect the downstream transport of freshwater along a long coastline with nearly continuous sources of freshwater. The model domain represents a fraction of the ACC region and periodic boundary conditions are applied to allow propagation of the buoyant flow from upstream. The model is forced by multiple freshwater sources in the central part of the domain and by both constant and spatially-varying, predominantly downwelling-favorable, winds. Freshwater flux gain in the coastal current (as opposed to spreading offshore) is calculated by taking a 30-day averaged difference between freshwater fluxes at the downstream and upstream edges of the buoyancy forcing region. Model runs are split into two categories: relatively high gains (50 – 60% of total discharge) were observed under moderate wind stress (∼0.05 Pa) or no wind conditions while lower gains (35– 45%) were observed under light average wind stresses (∼0.025 Pa), especially when wind varied alongshore. The offshore freshwater transport is eddy-driven and is enhanced in the areas of converging wind forcing. Eddy generation is associated with the wind-induced deepening of the buoyant layer near the coast. When the surface boundary layer is thin under light wind conditions, this deepening translates into enhanced vertical shear of the alongshore current through the thermal wind balance. Reversal of alongshore wind to upwelling-favorable wind effectively blocks the downstream freshwater transport and spreads the buoyant layer offshore

Evaluating the capabilities and uncertainties of droplet measurements for the fog droplet spectrometer (FM-100)

Droplet size spectra measurements are crucial to obtain a quantitative microphysical description of clouds and fog. However, cloud droplet size measurements are subject to various uncertainties. This work focuses on the error analysis of two key measurement uncertainties arising during cloud droplet size measurements with a conventional droplet size spectrometer (FM-100): first, we addressed the precision with which droplets can be sized with the FM-100 on the basis of the Mie theory. We deduced error assumptions and proposed a new method on how to correct measured size distributions for these errors by redistributing the measured droplet size distribution using a stochastic approach. Second, based on a literature study, we summarized corrections for particle losses during sampling with the FM-100. We applied both corrections to cloud droplet size spectra measured at the high alpine site Jungfraujoch for a temperature range from 0 °C to 11 °C. We showed that Mie scattering led to spikes in the droplet size distributions using the default sizing procedure, while the new stochastic approach reproduced the ambient size distribution adequately. A detailed analysis of the FM-100 sampling efficiency revealed that particle losses were typically below 10% for droplet diameters up to 10 μm. For larger droplets, particle losses can increase up to 90% for the largest droplets of 50 μm at ambient wind speeds below 4.4 m s<sup>−1</sup> and even to >90% for larger angles between the instrument orientation and the wind vector (sampling angle) at higher wind speeds. Comparisons of the FM-100 to other reference instruments revealed that the total liquid water content (LWC) measured by the FM-100 was more sensitive to particle losses than to re-sizing based on Mie scattering, while the total number concentration was only marginally influenced by particle losses. Consequently, for further LWC measurements with the FM-100 we strongly recommend to consider (1) the error arising due to Mie scattering, and (2) the particle losses, especially for larger droplets depending on the set-up and wind conditions

Perspectives on Interstellar Dust Inside and Outside of the Heliosphere

Measurements by dust detectors on interplanetary spacecraft appear to indicate a substantial flux of interstellar particles with masses exceeding 10^{-12}gram. The reported abundance of these massive grains cannot be typical of interstellar gas: it is incompatible with both interstellar elemental abundances and the observed extinction properties of the interstellar dust population. We discuss the likelihood that the Solar System is by chance located near an unusual concentration of massive grains and conclude that this is unlikely, unless dynamical processes in the ISM are responsible for such concentrations. Radiation pressure might conceivably drive large grains into "magnetic valleys". If the influx direction of interstellar gas and dust is varying on a ~10 yr timescale, as suggested by some observations, this would have dramatic implications for the small-scale structure of the interstellar medium.Comment: 13 pages. To appear in Space Science Review

Chemical and physical influences on aerosol activation in liquid clouds: a study based on observations from the Jungfraujoch, Switzerland

A simple statistical model to predict the number of aerosols which activate to form cloud droplets in warm clouds has been established, based on regression analysis of data from four summertime Cloud and Aerosol Characterisation Experiments (CLACE) at the high-altitude site Jungfraujoch (JFJ). It is shown that 79 % of the observed variance in droplet numbers can be represented by a model accounting only for the number of potential cloud condensation nuclei (defined as number of particles larger than 80 nm in diameter), while the mean errors in the model representation may be reduced by the addition of further explanatory variables, such as the mixing ratios of O3, CO, and the height of the measurements above cloud base. The statistical model has a similar ability to represent the observed droplet numbers in each of the individual years, as well as for the two predominant local wind directions at the JFJ (northwest and southeast). Given the central European location of the JFJ, with air masses in summer being representative of the free troposphere with regular boundary layer in-mixing via convection, we expect that this statistical model is generally applicable to warm clouds under conditions where droplet formation is aerosol limited (i.e. at relatively high updraught velocities and/or relatively low aerosol number concentrations). A comparison between the statistical model and an established microphysical parametrization shows good agreement between the two and supports the conclusion that cloud droplet formation at the JFJ is predominantly controlled by the number concentration of aerosol particles

Bowhead Whales Along the Chukotka Coast in Autumn

Bowhead whales (Balaena mysticetus) were seen in autumn 1992 and 1993 only along the northern coast of Chukotka, Russia, although an extensive area of the Chukchi Sea was searched during ship cruises. Single-day counts for 76 and 50 bowheads were made on 1 October 1992 and 3 October 1993, respectively, with only a few whales seen on other days. Whales seen between Cape Schmidt and Cape Vankarem on 1 October 1992 appeared to be feeding, but there was no means to detect or sample subsurface forage that year. On 3 October 1993, bowheads appeared to be feeding in an area where a 5 m x 8 km patch of zooplankton was identified, via acoustics, at 25-30 m in water 35 m deep. A vertical-tow sample near the patch indicated the euphausiid Thysanoessa rachii, a common bowhead prey species, was abundant in the water column. The location of the zooplankton patch corresponded with a sharp salinity (proxy density) gradient. In addition, whale distribution coincided with a surface thermal boundary, identified by satellite-borne Advanced Very High Resolution Radiometer (AVHRR) imagery. The confinement of bowhead sightings to the northern coast of Chukotka in 1992-93 corresponds to reports from autumn surveys in 1979, 1980 and 1990, while the association of whales with physical oceanographic fronts is similar to findings from a study of bowhead feeding areas in the southern Beaufort Sea. These observations suggest that the Chukotka coast may be an important feeding or staging area for the Bering Sea stock and that oceanographic patterns influencing whale occurrence may be identifiable from standard oceanographic measurements.Key words: bowhead whale, Balaena mysticetus, migration, Chukchi Sea, Bering Sea, Chukotka, Thysanoessa rachii, satellite imagery, AVHRRDurant l'automne de 1992 et celui de 1993, on n'a pu observer de baleines boréales (Balaena mysticetus) que le long de la côte nord de Chukotka (Russie), bien que des recherches aient eu lieu dans une zone étendue de la mer des Tchouktches lors de croisières en bateau. Des comptages de 76 et 50 baleines boréales ont été obtenus respectivement le 1er octobre 1992 et le 3 octobre 1993, alors qu'on n'en a observé que quelques-unes les autres jours. Les baleines observées entre Cape Schmidt et Cape Vankarem le 1er octobre 1992 semblaient être en train de s'alimenter, mais on ne disposait pas de moyens pour détecter le genre de nourriture sous la surface, ni pour en prélever un échantillon cette année-là. Le 3 octobre 1993, les baleines semblaient s'alimenter là où une plaque de zooplancton de 5 m x 8 km avait été identifiée par méthode acoustique entre 25 et 30 m de profondeur, dans une zone de 35 m de fond. Un échantillon prélevé par hâlage vertical près de la plaque a indiqué que l'euphausiacé Thysanoessa rachii, une proie courante de la baleine boréale, était abondant dans la colonne d'eau. L'emplacement de la plaque de zooplancton correspondait à un fort gradient de salinité (approximation par la densité). De plus, la distribution des baleines coïncidait avec une limite thermique de surface identifiée au moyen de l'imagerie par radiomètre perfectionné à très haute résolution, transporté par satellite. Le confinement des observations de baleines à la côte nord de Chukotka en 1992-93 correspond aux rapports des relevés d'automne de 1979, 1980 et 1990, tandis que l'association des baleines à des fronts physiques océanographiques cadre avec les résultats d'une étude des zones d'alimentation de la baleine boréale dans le sud de la mer de Beaufort. Ces observations suggèrent que la côte de Chukotka pourrait être une importante zone d'alimentation ou de rassemblement pour la population de la mer de Béring, et que les caractéristiques océanographiques qui influencent la présence des baleines pourraient être identifiables à partir des mesures océanographiques courantes.Mots clés: baleine boréale, Balaena mysticetus, migration, mer des Tchouktches, mer de Béring, Chukotka, Thysanoessa rachii, imagerie par satellite, radiomètre perfectionné à très haute résolutio