52 research outputs found
How much do helioseismological inferences depend upon the assumed reference model?
We investigate systematic uncertainties in determining the profiles of the
solar sound speed, density, and adiabatic index by helioseismological
techniques. We find that rms uncertainties-averaged over the sun of ~ 0.2%-0.4%
are contributed to the sound speed profile by each of three sources: 1)the
choice of assumed reference model, 2) the width of the inversion kernel, and 3)
the measurements errors. The density profile is about an order of magnitude
less well determined by the helioseismological measurements. The profile of the
adiabatic index is determined to an accuracy of about 0.2% . We find that even
relatively crude reference models yield reasonably accurate solar parameters.Comment: Accepted for publication in ApJ . Related material at
http://www.sns.ias.edu/~jn
Limfangiektazija jajovoda kao posljedica leiomioma mezosalpinksa u kokoši (Gallus gallus domesticus)
A rare case of oviductal lymphangiectasia was described in a 73-week old Nera-black layer, brought from a farm in the western part of Nigeria with a capacity of 41,000 birds. The layer was found dead inside the cage, without premonitory signs. Necropsy examination revealed marked oedema of the oviduct, with prominent mucosal folds. The dorsal ligament showed prominent and markedly dilated lymphatic vessels, having a discrete, soft but fi rm, pouch-like appearance and a centrally located oval-shaped, solid encapsulated tumorous mass. Histologically, there was severe oedema of the lamina propria, submucosa and muscularis of the oviduct, with ballooning dilatation of their lymphatic vessels and those of the dorsal ligament, which contained deeply eosinophilic proteinaceous fl uid and moderate mononuclear cells, mostly lymphocytes and macrophages. The tumorous mass revealed interlacing bundles of elongated cells that showed eosinophilic cytoplasm and oval to cigar-shaped nuclei. The tumorous mass was positive with Van Gieson stain. This is the fi rst reported case of oviductal lymphangiectasia secondary to mesosalphinx leiomyoma in a domestic chicken.Rijedak slučaj limfangiektazije jajovoda opisan je u 73 tjedna stare nesilice podrijetlom s farme od 41000 ptica u zapadnom dijelu Nigerije. Nesilica je nađena uginula bez prethodnih znakova bolesti. Pri razudbi je ustanovljen edem jajovoda s izraženim sluzničnim naborima. Na dorzalnom ligamentu isticale su se znatno proširene limfne žile s mekanom, ali čvrstom vrećastom tvorevinom u čijem se središtu nalazila jajasta, solidna, učahurena tumorska masa. Histološki je ustanovljen jak edem lamine proprije te submukoze i mišićnice jajovoda s balonskim proširenjem njegovih limfnih žila i onih na dorzalnom ligamentu koje su sadržavale bjelančevinsku tekućinu i eozinofile te nešto mononuklearnih stanica, pretežito limfocita i makrofaga. Tumorska masa sastojala se od isprepletenih snopića izduženih stanica koje su imale eozinofilnu citoplazmu s jezgrama jajastoga do cigarastoga oblika. Tumorska masa bila je pozitivna bojenjem po Van Giesonu. To je prvi opisani slučaj limfangiektazije jajovoda kao posljedice leiomioma mezosalpinksa u domaće kokoši
Writing biology, assessing biology: The nature and effects of variation in terminology
There has been substantial research into terminology as an issue in learning science, especially against the backdrop of concerns over school literacy in science and as sometimes reflected in the poor performance of high school students in assessment tasks. Relevant research has emphasized issues such as lexical load, complexity and metaphor. Variation in the use of terminology has, however, been relatively under researched, although there is evidence that terminology use does vary within and across high school textbooks of science. Drawing on an eclectic theoretical framework comprising transitivity analysis (Halliday 1994), legitimation code theory semantics (Maton 2013a), and the context-specific term model (Gerzymisch-Arbogast 2008), this article identifies and classifies variations in the terminology employed in three high school textbooks of biology in Nigeria. It then determines what impact assessment tasks which use terms that differ from those employed in students’ study materials have on students. Examples are found of variant terminology impeding science literacy and task performance, even though there is reason to suspect such variation might in fact have been leveraged to enhance cognition
Changes in Solar Dynamics from 1995 to 2002
Data obtained by the GONG and MDI instruments over the last seven years are
used to study how solar dynamics -- both rotation and other large scale flows
-- have changed with time. In addition to the well known phenomenon of bands of
faster and slower rotation moving towards the equator and pole, we find that
the zonal flow pattern rises upwards with time. Like the zonal flows, the
meridional flows also show distinct solar activity related changes. In
particular, the anti-symmetric component of the meridional flow shows a
decrease in speed with activity. We do not see any significant temporal
variations in the dynamics of the tachocline region where the solar dynamo is
believed to be operating.Comment: To appear in ApJ, March 1 200
OPserver: interactive online-computations of opacities and radiative accelerations
Codes to compute mean opacities and radiative accelerations for arbitrary
chemical mixtures using the Opacity Project recently revised data have been
restructured in a client--server architecture and transcribed as a subroutine
library. This implementation increases efficiency in stellar modelling where
element stratification due to diffusion processes is depth dependent, and thus
requires repeated fast opacity reestimates. Three user modes are provided to
fit different computing environments, namely a web browser, a local workstation
and a distributed grid.Comment: 5 pages, 1 figur
Solar Models: current epoch and time dependences, neutrinos, and helioseismological properties
We calculate accurate solar models and report the detailed time dependences
of important solar quantities. We use helioseismology to constrain the
luminosity evolution of the sun and report the discovery of semi-convection in
evolved solar models that include diffusion. In addition, we compare the
computed sound speeds with the results of p-mode observations by BiSON, GOLF,
GONG, LOWL, and MDI instruments. We contrast the neutrino predictions from a
set of eight standard-like solar models and four deviant (or deficient) solar
models with the results of solar neutrino experiments. For solar neutrino and
for helioseismological applications, we present present-epoch numerical
tabulations of characteristics of the standard solar model as a function of
solar radius, including the principal physical and composition variables, sound
speeds, neutrino fluxes, and functions needed for calculating solar neutrino
oscillations.Comment: Accepted ApJ. Have used refined satellite value for solar luminosity.
Changes slightly best neutrino fluxes. Include new references, number density
of scatterers of sterile neutrinos, some additional helioseismological
predictions. 70 pages, 16 figures, additional material at
http://www.sns.ias.edu/~jn
Presupernova Evolution of Rotating Massive Stars I: Numerical Method and Evolution of the Internal Stellar Structure
The evolution of rotating stars with zero-age main sequence (ZAMS) masses in
the range 8 to 25 M_sun is followed through all stages of stable evolution. The
initial angular momentum is chosen such that the star's equatorial rotational
velocity on the ZAMS ranges from zero to ~ 70 % of break-up. Redistribution of
angular momentum and chemical species are then followed as a consequence of
rotationally induced circulation and instablities. The effects of the
centrifugal force on the stellar structure are included. Uncertain mixing
efficiencies are gauged by observations. We find, as noted in previous work,
that rotation increases the helium core masses and enriches the stellar
envelopes with products of hydrogen burning. We determine, for the first time,
the angular momentum distribution in typical presupernova stars along with
their detailed chemical structure. Angular momentum loss due to (non-magnetic)
stellar winds and the redistribution of angular momentum during core hydrogen
burning are of crucial importance for the specific angular momentum of the
core. Neglecting magnetic fields, we find angular momentum transport from the
core to the envelope to be unimportant after core helium burning. We obtain
specific angular momenta for the iron core and overlaying material of
1E16...1E17 erg s. These values are insensitive to the initial angular
momentum. They are small enough to avoid triaxial deformations of the iron core
before it collapses, but could lead to neutron stars which rotate close to
break-up. They are also in the range required for the collapsar model of
gamma-ray bursts. The apparent discrepancy with the measured rotation rates of
young pulsars is discussed.Comment: 62 pages, including 7 tables and 19 figures. Accepted by Ap
Can three-flavor oscillations solve the solar neutrino problem?
The most promising solution to the solar neutrino problem are neutrino
oscillations, which usually are analyzed within the reduced 2-flavor scheme,
because the solutions found therein reasonably well reproduce the recent data
of Super-Kamiokande about the recoil-electron energy spectrum, zenith-angle and
seasonal variations, and the event rate data of all the neutrino detectors. In
this work, however, a survey of the complete parameter space of 3-flavor
oscillations is performed. Basically eight new additional solutions could be
identified, where the best one with \Delta m(12)^2=2.7x10^(-10) eV^2, \Delta
m(13)^2=1.0x10^(-5) eV^2, \Theta(12)=23, and \Theta(13)=1.3 (denoted SVO) is
slightly more probable than any 2-flavor solution. However, including the
results of the atmospheric neutrino problem excludes all 3-flavour solutions
apart from the SLMA-solution (\Delta m(12)^2=7.9x10^(-6) eV^2, \Delta
m(13)^2=2.5x10^(-4) eV^2, \Theta(12)=1.4, and \Theta(13)=20). Besides, the
ability of SNO and Borexino to discriminate the various 2- and 3-flavor
solutions is investigated. Only with very good statistics in these experiments
the correct solution to the solar neutrino problem can be identified
unambiguously.Comment: 22 pages, 19 figures, REVTeX, submitted to Phys.Rev.D, article with
better resolved figures available under
http://www.mpa-garching.mpg.de/~schlattl/public.htm
Astrophysical turbulence modeling
The role of turbulence in various astrophysical settings is reviewed. Among
the differences to laboratory and atmospheric turbulence we highlight the
ubiquitous presence of magnetic fields that are generally produced and
maintained by dynamo action. The extreme temperature and density contrasts and
stratifications are emphasized in connection with turbulence in the
interstellar medium and in stars with outer convection zones, respectively. In
many cases turbulence plays an essential role in facilitating enhanced
transport of mass, momentum, energy, and magnetic fields in terms of the
corresponding coarse-grained mean fields. Those transport properties are
usually strongly modified by anisotropies and often completely new effects
emerge in such a description that have no correspondence in terms of the
original (non coarse-grained) fields.Comment: 88 pages, 26 figures, published in Reports on Progress in Physic
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