186 research outputs found
Journey Across the Nunataks of Central East Greenland, 1951
Contains an account of a trip made in Aug. 1951 by a three-man party from the Lauge Koch expedition, which met and joined for part of the journey on the icecap, a weasel-equipped party of the French polar expedition of P.E. Victor. The main results of this trip are briefly described here; for the scientific results, maps, etc., see Arctic Bibliography No. 23166. From Ella O (72 51 N, 25 02 W) a circular route within roughly 72 30-74 N, 31-24 W was covered by plane, weasel, and the northern leg of it, devoted to the study proper, on foot. Observations on temperature, winds, ice and glacier conditions were also made during the preceding, southwestern and western leg of the journey on the weasels in cooperation with the French party. Geology of the westernmost part of central East Greenland was found to be very complex, crustal movements having apparently occurred up to the most recent epochs; it was also discovered that the Caledonian belt extends westward beyond any outcrop that can be found and, that during the Late Precambrian the geosynclinal trough had its central parts west of the present fjord-region; the western foreland of the Caledonian Syncline is therefore expected to be reached in the northernmost area, somewhere between 80 degrees and 82 degrees North
D'Entrecasteaux zone, trench and western chain of the central New Hebrides island arc : their significance and tectonic relationship
Evaluating the stability of disulfide bridges in proteins: a torsional potential energy surface for diethyl disulfide
Disulfide bonds formed by the oxidation of cysteine residues in proteins are the major form of intra- and inter-molecular covalent linkages in the polypeptide chain. To better understand the conformational energetics of this linkage, we have used the MP2(full)/6-31G(d) method to generate a full potential energy surface (PES) for the torsion of the model compound diethyl disulfide (DEDS) around its three critical dihedral angles (χ2, χ3, χ2′). The use of ten degree increments for each of the parameters resulted in a continuous, fine-grained surface. This allowed us to accurately predict the relative stabilities of disulfide bonds in high resolution structures from the Protein Data Bank. The MP2(full) surface showed significant qualitative differences from the PES calculated using the Amber force field. In particular, a different ordering was seen for the relative energies of the local minima. Thus, Amber energies are not reliable for comparison of the relative stabilities of disulfide bonds. Surprisingly, the surface did not show a minimum associated with χ2 − 60°, χ390, χ2′ − 60°. This is due to steric interference between Hα atoms. Despite this, significant populations of disulfides were found to adopt this conformation. In most cases this conformation is associated with an unusual secondary structure motif, the cross-strand disulfide. The relative instability of cross-strand disulfides is of great interest, as they have the potential to act as functional switches in redox processes.<br /
The lives of FR I radio galaxies
After a brief introduction to the morphological properties of FRI radio
sources, we discuss the possibility that FRI jets are relativistic at their
bases and decelerate quickly to non-relativistic velocities. From two-frequency
data we determine spectral index distributions and consequently the ages of FRI
sources. We show that in the large majority of cases synchrotron theory
provides unambiguous and plausible answers; in a few objects re-acceleration of
electrons may be needed. The derived ages are of the order 10^7-10^8 years, 2-4
times larger than the ages inferred from dynamical arguments and a factor 5-10
larger than the ages of FRII sources. The linear sizes of FRI and FRII sources
make it unlikely that many FRII's evolve into FRI's. A brief discussion is
given of the possibility that radio sources go through different cycles of
activity.Comment: 19 pages, including 13 figures, to appear in `Life Cycles of Radio
Galaxies', ed. J. Biretta et al., New Astronomy Review
An exact solution of the moving boundary problem for the relativistic plasma expansion in a dipole magnetic field
An exact analytic solution is obtained for a uniformly expanding, neutral,
highly conducting plasma sphere in an ambient dipole magnetic field with an
arbitrary orientation of the dipole moment in the space. Based on this solution
the electrodynamical aspects related to the emission and transformation of
energy have been considered. In order to highlight the effect of the
orientation of the dipole moment in the space we compare our results obtained
for parallel orientation with those for transversal orientation. The results
obtained can be used to treat qualitatively experimental and simulation data,
and several phenomena of astrophysical and laboratory significance.Comment: 7 pages, 2 figures. arXiv admin note: substantial text overlap with
arXiv:physics/060323
Torus knots and mirror symmetry
We propose a spectral curve describing torus knots and links in the B-model.
In particular, the application of the topological recursion to this curve
generates all their colored HOMFLY invariants. The curve is obtained by
exploiting the full Sl(2, Z) symmetry of the spectral curve of the resolved
conifold, and should be regarded as the mirror of the topological D-brane
associated to torus knots in the large N Gopakumar-Vafa duality. Moreover, we
derive the curve as the large N limit of the matrix model computing torus knot
invariants.Comment: 30 pages + appendix, 3 figure
Instanton counting, Macdonald function and the moduli space of D-branes
We argue the connection of Nekrasov's partition function in the \Omega
background and the moduli space of D-branes, suggested by the idea of geometric
engineering and Gopakumar-Vafa invariants. In the instanton expansion of N=2
SU(2) Yang-Mills theory the Nakrasov's partition function with equivariant
parameters \epsilon_1, \epsilon_2 of toric action on C^2 factorizes correctly
as the character of SU(2)_L \times SU(2)_R spin representation. We show that up
to two instantons the spin contents are consistent with the Lefschetz action on
the moduli space of D2-branes on (local) F_0. We also present an attempt at
constructing a refined topological vertex in terms of the Macdonald function.
The refined topological vertex with two parameters of T^2 action allows us to
obtain the generating functions of equivariant \chi_y and elliptic genera of
the Hilbert scheme of n points on C^2 by the method of topological vertex.Comment: 33 pages, 2 figures, (v2) minor changes, references added, (v3)
Comments and more references adde
Schistosoma mansoni: preclinical studies with 9-acridanone-hydrazones in Cebus monkeys experimentally infected
Chronic neuropsychiatric sequelae of SARSâCoVâ2: Protocol and methods from the Alzheimer's Association Global Consortium
Introduction
Coronavirus disease 2019 (COVID-19) has caused >3.5 million deaths worldwide and affected >160 million people. At least twice as many have been infected but remained asymptomatic or minimally symptomatic. COVID-19 includes central nervous system manifestations mediated by inflammation and cerebrovascular, anoxic, and/or viral neurotoxicity mechanisms. More than one third of patients with COVID-19 develop neurologic problems during the acute phase of the illness, including loss of sense of smell or taste, seizures, and stroke. Damage or functional changes to the brain may result in chronic sequelae. The risk of incident cognitive and neuropsychiatric complications appears independent from the severity of the original pulmonary illness. It behooves the scientific and medical community to attempt to understand the molecular and/or systemic factors linking COVID-19 to neurologic illness, both short and long term.
Methods
This article describes what is known so far in terms of links among COVID-19, the brain, neurological symptoms, and Alzheimer's disease (AD) and related dementias. We focus on risk factors and possible molecular, inflammatory, and viral mechanisms underlying neurological injury. We also provide a comprehensive description of the Alzheimer's Association Consortium on Chronic Neuropsychiatric Sequelae of SARS-CoV-2 infection (CNS SC2) harmonized methodology to address these questions using a worldwide network of researchers and institutions.
Results
Successful harmonization of designs and methods was achieved through a consensus process initially fragmented by specific interest groups (epidemiology, clinical assessments, cognitive evaluation, biomarkers, and neuroimaging). Conclusions from subcommittees were presented to the whole group and discussed extensively. Presently data collection is ongoing at 19 sites in 12 countries representing Asia, Africa, the Americas, and Europe.
Discussion
The Alzheimer's Association Global Consortium harmonized methodology is proposed as a model to study long-term neurocognitive sequelae of SARS-CoV-2 infection
Fontes de carboidratos e porcentagem de volumosos em dietas para ovinos: balanço de nitrogĂȘnio, digestibilidade e fluxo portal de nutrientes
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