8,949 research outputs found
Growth of Intermediate-Mass Black Holes in Globular Clusters
We present results of numerical simulations of sequences of binary-single
scattering events of black holes in dense stellar environments. The simulations
cover a wide range of mass ratios from equal mass objects to 1000:10:10 solar
masses and compare purely Newtonian simulations to simulations in which
Newtonian encounters are interspersed with gravitational wave emission from the
binary. In both cases, the sequence is terminated when the binary's merger time
due to gravitational radiation is less than the arrival time of the next
interloper. We find that black hole binaries typically merge with a very high
eccentricity (0.93 < e < 0.95 pure Newtonian; 0.85 < e < 0.90 with
gravitational wave emission) and that adding gravitational wave emission
decreases the time to harden a binary until merger by ~ 30% to 40%. We discuss
the implications of this work for the formation of intermediate-mass black
holes and gravitational wave detection.Comment: 28 pages including 9 figures, submitted to Ap
Gender Bias and Stereotypes in Medicine: A Medical Student Experience
Gender bias is a universal phenomenon that is strongly embedded in human society. Its omnipresence originates consequences that have a lasting structural impact. Despite social, scientific, and cultural changes, gender discrimination remains prevalent in the twenty-first century. In this paper, we describe a situation in which a medical student was discouraged by a professor when she expressed the professional path she intended to pursue in the future just because of her gender. In addition, we discuss possible solutions such as raising awareness, developing educational programs, increasing women representation, and addressing everyone’s needs. It is imperative that we, as a society, educate ourselves in identifying stereotypes and gender-biased situations to eliminate gender discrimination in science and in our systems
Do projects really end late? On the shortcomings of the classical scheduling techniques
Many engineering projects fail to meet their planned completion dates in real practice. This is a recurrent topic
in the project management literature, with poor planning and controlling practices frequently cited among the
most significant causes of delays. Unfortunately, hardly any attention has been paid to the fact that the classical
scheduling techniques—Gantt chart, Critical Path Method (CPM), and Program Evaluation and Review
Technique (PERT)—may not be as fit for purpose as they seem. Arguably, because of their relative simplicity,
these techniques are still almost the only ones taught nowadays in most introductory courses to scheduling in
many engineering and management degrees. However, by utterly ignoring or inappropriately dealing with activity
duration variability, these techniques provide optimistic completion dates, while suffering from other
shortcomings. Through a series of simple case studies that can be developed with a few participants and
common dice, a systematic critique of the classical scheduling techniques is offered. Discussion of the case
studies results illustrate why limiting the contents of scheduling education and teaching can be detrimental, as the
aforementioned classical scheduling techniques cannot not provide project managers with sufficient resources to
effectively plan and control real projects
Thermal Effect on TL Response of Single Doped LiF+NaF:RE Polycrystalline Phosphors
In this work, the sintering and annealing effects on the thermoluminescent (TL) behavior of undoped and rare earth (RE)-doped LiF+NaF powder samples (RE = Ce3+, Eu3+, Lu3+ or Tl+, at 0.5 mol%) was analyzed by evaluating the sensitivity to gamma radiation and TL response of the material. The polycrystalline samples were obtained by solid state reaction at 1000°C. The samples were irradiated in a Gammacell-3000 Elan irradiator loaded with 137Cs sources. The glow curves of the LiF+NaF doped with lutetium or thallium show an intense glow peak at about 175°C and 135°C, respectively. When the phosphor was doped with cerium or europium the glow curves were complex in their structure, with TL peaks observed at 155°C and 165°C, respectively. The linear dose-response was between 10 and 50 Gy for cerium, europium or lutetium doped LiF+NaF samples, while for the thallium doped and undoped samples such intervals were 10-100 Gy and 10-500 Gy, respectively. Because the shape of the glow curves were complex, the analysis was carried out in (i) samples without a sintering treatment where the TL response was found insensitive to pre-irradiation annealing treatment, and (ii) sintered samples (300, 350, 400 or 500 °C), in this last case the TL response was dependent on the annealing temperature (100-400 °C), finally (iii) the kinetics parameters of the glow curves were analyzed by assuming a general order kinetics model. The observed glow curves and TL characteristics of the LiF+NaF:RE phosphor make attractive this material to be useful in gamma dose dosimetry
The warm interstellar medium around the Cygnus Loop
Observations of the oxygen lines [OII]3729 and [OIII]5007 in the medium
immediately beyond the Cygnus Loop supernova remnant were carried out with the
scanning Fabry-P\'erot spectrophotometer ESOP. Both lines were detected in
three different directions - east, northeast and southwest - and up to a
distance of 15 pc from the shock front. The ionized medium is in the immediate
vicinity of the remnant, as evinced by the smooth brightening of both lines as
the adiabatic shock transition (defined by the X-ray perimeter) is crossed.
These lines are usually brighter around the Cygnus Loop than in the general
background in directions where the galactic latitude is above 5 degrees. There
is also marginal (but significant) evidence that the degree of ionization is
somewhat larger around the Cygnus Loop. We conclude that the energy necessary
to ionize this large bubble of gas could have been supplied by an O8 or O9 type
progenitor or the particles heated by the expanding shock front. The second
possibility, though highly atractive, would have to be assessed by extensive
modelling.Comment: 18 pages, 8 figures, ApJ 512 in pres
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