4,046 research outputs found
Factors that influence career progression among postdoctoral clinical academics: a scoping review of the literature
Background: The future of academic medicine is uncertain. Concerns regarding the future availability of qualified and willing trainee clinical academics have been raised worldwide. Of significant concern is our failure to retain postdoctoral trainee clinical academics, who are likely to be our next generation of leaders in scientific discovery. / Objectives: To review the literature about factors that may influence postdoctoral career progression in early career clinical academics. / Design: This study employed a scoping review method. Three reviewers separately assessed whether the articles found fit the inclusion criteria. / Data sources: PubMed, Scopus, Web of Science and Google Scholar (1991â2015). / Article selection: The review encompassed a broad search of English language studies published anytime up to November 2015. All articles were eligible for inclusion, including research papers employing either quantitative or qualitative methods, as well as editorials and other summary articles. / Data extraction: Data extracted from included publications were charted according to author(s), sample population, study design, key findings, country of origin and year of publication. / Results: Our review identified 6 key influences: intrinsic motivation, workâlife balance, inclusiveness, work environment, mentorship and availability of funding. It also detected significant gaps within the literature about these influences. / Conclusions: Three key steps are proposed to help support postdoctoral trainee clinical academics. These focus on ensuring that researchers feel encouraged in their workplace, involved in collaborative dialogue with key stakeholders and able to access reliable information regarding their chosen career pathway. Finally, we highlight recommendations for future research
Dynamical effects of the neutrino gravitational clustering at Planck angular scales
We study the CMB anisotropy induced by the non-linear perturbations in the
massive neutrino density associated to the non-linear gravitational clustering
proceses. Our results show that for the neutrino fraction in agreement with
that indicated by the astroparticle and nuclear physics experiments and a
cosmological accreting mass comparable with the mass of known clusters, the
angular resolution and the sensitivity of the CMB anisotropy measurements from
the Planck surveyor will allow the detection of the dynamical effects of the
neutrino gravitational clustering.Comment: 40 pages and 12 figures, submitted to ApJ (14 March 2002
Spectrum of Sizes for Perfect Deletion-Correcting Codes
One peculiarity with deletion-correcting codes is that perfect
-deletion-correcting codes of the same length over the same alphabet can
have different numbers of codewords, because the balls of radius with
respect to the Levenshte\u{\i}n distance may be of different sizes. There is
interest, therefore, in determining all possible sizes of a perfect
-deletion-correcting code, given the length and the alphabet size~.
In this paper, we determine completely the spectrum of possible sizes for
perfect -ary 1-deletion-correcting codes of length three for all , and
perfect -ary 2-deletion-correcting codes of length four for almost all ,
leaving only a small finite number of cases in doubt.Comment: 23 page
Radio Emission and Particle Acceleration in SN 1993J
The radio light curves of SN 1993J are found to be well fit by a synchrotron
spectrum, suppressed by external free-free absorption and synchrotron
self-absorption. A standard r^-2 circumstellar medium is assumed, and found to
be adequate. The magnetic field and number density of relativistic electrons
behind the shock are determined. The strength of the magnetic field argues
strongly for turbulent amplification behind the shock. The ratio of the
magnetic and thermal energy density behind the shock is ~0.14. Synchrotron and
Coulomb cooling dominate the losses of the electrons. The injected electron
spectrum has a power law index -2.1, consistent with diffusive shock
acceleration, and the number density scales with the thermal electron energy
density. The total energy density of the relativistic electrons is, if
extrapolated to gamma ~ 1, ~ 5x10^-4 of the thermal energy density. The
free-free absorption required is consistent with previous calculations of the
circumstellar temperature of SN 1993J, T_e ~ (2-10)x10^5 K. The relative
importance of free-free absorption, Razin suppression, and the synchrotron
self-absorption effect for other supernovae are briefly discussed. Guidelines
for the modeling and interpretation of VLBI observations are given.Comment: accepted for Ap.
Jet-Induced Emission-Line Nebulosity and Star Formation in the High-Redshift Radio Galaxy 4C41.17
The high redshift radio galaxy 4C41.17 consists of a powerful radio source in
which previous work has shown that there is strong evidence for jet-induced
star formation along the radio axis. We argue that nuclear photoionization is
not responsible for the excitation of the emission line clouds and we construct
a jet-cloud interaction model to explain the major features revealed by the
data. The interaction of a high-powered jet with a dense cloud in the halo of
4C41.17 produces shock-excited emission-line nebulosity through ~1000 km/s
shocks and induces star formation. The CIII to CIV line ratio and the CIV
luminosity emanating from the shock, imply that the pre-shock density in the
line-emitting cloud is high enough (~1-10 cm^-3) that shock initiated star
formation could proceed on a timescale of order a few x 10^6 yrs, well within
the estimated dynamical age of the radio source. Broad (FWHM ~ 100 - 1400 km/s)
emission lines are attributed to the disturbance of the gas cloud by a partial
bow--shock and narrow emission lines (FWHM ~ 500 - 650 km/s) (in particular
CIV) arise in precursor emission in relatively low metallicity gas. The implied
baryonic mass ~ 8 \times 10^{10} solar masses of the cloud is high and implies
that Milky Way size condensations existed in the environments of forming radio
galaxies at a redshift of 3.8. Our interpretation of the data provides a
physical basis for the alignment of the radio, emission-line and UV continuum
images in some of the highest redshift radio galaxies and the analysis
presented here may form a basis for the calculation of densities and cloud
masses in other high redshift radio galaxies.Comment: 18 pages, 5 figures; uses astrobib.sty and aaspp4.sty. Better
versions of figures available via anonymous from
ftp://mso.anu.edu.au:pub/pub/geoff/4C41.1
5-10 GeV Neutrinos from Gamma-Ray Burst Fireballs
A gamma-ray burst fireball is likely to contain an admixture of neutrons, in
addition to protons, in essentially all progenitor scenarios. Inelastic
collisions between differentially streaming protons and neutrons in the
fireball produce muon neutrinos (antineutrinos) of ~ 10 GeV as well as electron
neutrinos (antineutrinos) of ~ 5 GeV, which could produce ~ 7 events/year in
kilometer cube detectors, if the neutron abundance is comparable to that of
protons. Photons of ~ 10 GeV from pi-zero decay and ~ 100 MeV electron
antineutrinos from neutron decay are also produced, but will be difficult to
detect. Photons with energies < 1 MeV from shocks following neutron decay
produce a characteristic signal which may be distinguishable from the
proton-related MeV photons.Comment: 4 pages, latex, 1 figure, aps style files. Final version, accepted in
Phys.Rev.Lett., 6/22/2000; some clarifications in the text, same conclusion
The Low Redshift Lyman Alpha Forest in Cold Dark Matter Cosmologies
We study the physical origin of the low-redshift Lyman alpha forest in
hydrodynamic simulations of four CDM cosmologies. Our main conclusions are
insensitive to the cosmological model but depend on our assumption that the UV
background declines at low redshift. We find that the expansion of the universe
drives rapid evolution of dN/dz (the number of absorbers per unit z) at z >
1.7, but that at lower redshift the fading of the UV background counters the
influence of expansion, leading to slow evolution. At every redshift, weaker
lines come primarily from moderate fluctuations of the diffuse, unshocked IGM,
and stronger lines originate in shocked or radiatively cooled gas of higher
overdensity. However, the neutral hydrogen column density associated with
structures of fixed overdensity drops as the universe expands, so an absorber
at z = 0 is dynamically analogous to an absorber with neutral hydrogen column
density 10 to 50 times higher at z = 2-3. We find no clear distinction between
lines arising in "galaxy halos" and lines arising in larger scale structures;
however, galaxies tend to lie near the dense regions of the IGM that produce
strong Lyman alpha lines. The simulations provide a unified physical picture
that accounts for the most distinctive observed properties of the low redshift
Lyman alpha forest: (1) a sharp transition in the evolution of dN/dz at z ~
1.7, (2) stronger evolution for absorbers of higher equivalent width, (3) a
correlation of increasing Lyman alpha equivalent width with decreasing galaxy
impact parameter, and (4) a tendency for stronger lines to arise in close
proximity to galaxies while weaker lines trace more diffuse large scale
structure. (Abridged)Comment: 57 pages, 18 figures, submitted to Ap
Efficiency of Electron-Positron Pair Productionby Neutrino Flux from Accretion Disk of a Kerr Black Hole
Dominant processes of neutrino production and neutrino-induced \ep-pair
production are examined in the model of a disk hyper-accreting onto a Kerr
black hole. The efficiency of plasma production by a neutrino flux from the
disk, obtained for the both cases of presence and absence of a magnetic field,
is found to be no more than several tenths of percent and, therefore, not
enough for the origin of cosmological gamma-ray bursts.Comment: 8 pages, 1 figur
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