741 research outputs found
Dynamics of Circumstellar Disks II: Heating and Cooling
We present a series of 2-d () hydrodynamic simulations of marginally
self gravitating disks around protostars using an SPH code. We implement simple
dynamical heating and we cool each location as a black body, using a
photosphere temperature obtained from the local vertical structure. We
synthesize SEDs from our simulations and compare them to fiducial SEDs derived
from observed systems. These simulations produce less distinct spiral structure
than isothermally evolved systems, especially in the inner third of the disk.
Pattern are similar further from the star but do not collapse into condensed
objects. The photosphere temperature is well fit to a power law in radius with
index , which is very steep. Far from the star, internal heating
( work and shocks) are not responsible for generating a large fraction of
the thermal energy contained in the disk matter. Gravitational torques
responsible for such shocks cannot transport mass and angular momentum
efficiently in the outer disk. Within 5--10 AU of the star, rapid break
up and reformation of spiral structure causes shocks, which provide sufficient
dissipation to power a larger fraction of the near IR energy output. The
spatial and size distribution of grains can have marked consequences on the
observed near IR SED and can lead to increased emission and variability on
year time scales. When grains are vaporized they do not reform
into a size distribution similar to that from which most opacity calculations
are based. With rapid grain reformation into the original size distribution,
the disk does not emit near infrared photons. With a plausible modification to
the opacity, it contributes much more.Comment: Accepted by ApJ, 60pg incl 24 figure
Distribusi Vertikal Karang Batu (Scleractinia) Di Perairan Desa Kalasey, Kabupaten Minahasa
Penelitian ini dilaksanakan dengan tujuan untuk mengetahui struktur komunitas dan distribusi vertikal karang scleractinia di perairan Desa Kalasey.Jumlah spesies yang ditemukan pada lereng terumbu berjumlah 48 dan pada rataan terumbu 38.Jumlah koloni pada lereng terumbu berjumlah 190 dan pada rataan terumbu 133.Spesies Porites lobata memiliki kepadatan relatif tertinggi pada lereng terumbu dan Favites halicora pada rataan terumbu, masing-masing dengan nilai 20%. Nilai indeks keanekaragaman menunjukkan keanekaragaman tinggi pada lereng terumbu (3,12) dan keanekaragaman sedang pada rataan terumbu (2,95). Secara umum, kedua loaksi tersebut memiliki pola penyebaran seragam. Hasil indeks kemerataan pada lereng terumbu 0,80 dan rataan terumbu 0,81. Kedua nilai tersebut digolongkan pada komunitas yang stabil
Shining new light on mammalian diving physiology using wearable near-infrared spectroscopy
Investigation of marine mammal dive-by-dive blood distribution and oxygenation has been limited by a lack of non-invasive technology for use in freely diving animals. Here, we developed a non-invasive near-infrared spectroscopy (NIRS) device to measure relative changes in blood volume and haemoglobin oxygenation continuously in the blubber and brain of voluntarily diving harbour seals. Our results show that seals routinely exhibit preparatory peripheral vasoconstriction accompanied by increased cerebral blood volume approximately 15 s before submersion. These anticipatory adjustments confirm that blood redistribution in seals is under some degree of cognitive control that precedes the mammalian dive response. Seals also routinely increase cerebral oxygenation at a consistent time during each dive, despite a lack of access to ambient air. We suggest that this frequent and reproducible reoxygenation pattern, without access to ambient air, is underpinned by previously unrecognised changes in cerebral drainage. The ability to track blood volume and oxygenation in different tissues using NIRS will facilitate a more accurate understanding of physiological plasticity in diving animals in an increasingly disturbed and exploited environment
Characterization of oligomers from methylglyoxal under dark conditions : a pathway to produce secondary organic aerosol through cloud processing during nighttime
Aqueous-phase oligomer formation from methylglyoxal, a major atmospheric photooxidation product, has been investigated in a simulated cloud matrix under dark conditions. The aim of this study was to explore an additional pathway producing secondary organic aerosol (SOA) through cloud processes without participation of photochemistry during nighttime. Indeed, atmospheric models still underestimate SOA formation, as field measurements have revealed more SOA than predicted. Soluble oligomers (n = 1-8) formed in the course of acid-catalyzed aldol condensation and acid-catalyzed hydration followed by acetal formation have been detected and characterized by positive and negative ion electrospray ionization mass spectrometry. Aldol condensation proved to be a favorable mechanism under simulated cloud conditions, while hydration/acetal formation was found to strongly depend on the pH of the system and only occurred at a pH < 3.5. No evidence was found for formation of organosulfates. The aldol oligomer series starts with a beta-hydroxy ketone via aldol condensation, where oligomers are formed by multiple additions of C3H4O2 units (72 Da) to the parent beta-hydroxy ketone. Ion trap mass spectrometry experiments were performed to structurally characterize the major oligomer species. A mechanistic pathway for the growth of oligomers under cloud conditions and in the absence of UV-light and OH radicals, which could substantially enhance in-cloud SOA yields, is proposed here for the first time
On the Early Evolution of Forming Jovian Planets II: Analysis of Accretion and Gravitational Torques
(abridged) We find that a disk can supply a forming planet with mass at an
essentially infinite rate (\mj/25 yr) so that a gap could form very
quickly. We show that mass accretion rates faster than \mj/yr are
not physically reasonable in the limit of either a thin, circumplanetary disk
or of a spherical envelope. Planet growth and ultimately survival are therefore
limited to the planet's ability to accept additional matter, not by the disk in
which it resides. We find that common analytic torque approximations predict
values that are a factor larger than those obtained from the
simulations. Accounting for the disk's vertical structure (crudely modeled
through a gravitational softening parameter), small shifts in resonance
positions due to pressure gradients, to disk self gravity and to inclusion of
non-WKB terms in the analysis (Artymowicz 1993) reduce the difference to a
factor . Torques from the corotation resonances that are positive in
sign contribute 20-30% or more of the net torque on the planet. The assumption
of linearity underlying theoretical analyses is recovered in the simulations
with planets with masses below 0.5\mj, but the assumption that interactions
occur only at the resonances is more difficult to support. The detailed shape
of the disk's response varies from pattern to pattern, making its true position
less clear. We speculate that the finite width allows for overlap and mixing
between resonances and may be responsible for the remainder of the differences
between torques from theory and simulation, but whether accounting for such
overlap in a theory will improve the agreement with the simulations is not
clear.Comment: 52 pages including 20 figures. also available at
http://www.maths.ed.ac.uk/~andy/publications.htm
Hevein: an antifungal protein from rubber-tree ( Hevea brasiliensis ) latex
Several chitin-binding proteins were isolated from the âbottom fractionâ of Hevea brasiliensis (MĂŒll.) Arg. latex. One of these chitin-binding proteins is hevein, a small monomeric protein which strongly resembles the lectin from stinging nettle ( Urtica dioica L.). Like the latter, hevein showed strong antifungal activity against several fungi in vitro. The possible involvement of this protein in the defense against invasion by potentially pathogenic fungi is discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47477/1/425_2004_Article_BF00197797.pd
The Berwald-type linearisation of generalised connections
We study the existence of a natural `linearisation' process for generalised
connections on an affine bundle. It is shown that this leads to an affine
generalised connection over a prolonged bundle, which is the analogue of what
is called a connection of Berwald type in the standard theory of connections.
Various new insights are being obtained in the fine structure of affine bundles
over an anchored vector bundle and affineness of generalised connections on
such bundles.Comment: 25 page
Nonlinearity of Mechanochemical Motions in Motor Proteins
The assumption of linear response of protein molecules to thermal noise or
structural perturbations, such as ligand binding or detachment, is broadly used
in the studies of protein dynamics. Conformational motions in proteins are
traditionally analyzed in terms of normal modes and experimental data on
thermal fluctuations in such macromolecules is also usually interpreted in
terms of the excitation of normal modes. We have chosen two important protein
motors - myosin V and kinesin KIF1A - and performed numerical investigations of
their conformational relaxation properties within the coarse-grained elastic
network approximation. We have found that the linearity assumption is deficient
for ligand-induced conformational motions and can even be violated for
characteristic thermal fluctuations. The deficiency is particularly pronounced
in KIF1A where the normal mode description fails completely in describing
functional mechanochemical motions. These results indicate that important
assumptions of the theory of protein dynamics may need to be reconsidered.
Neither a single normal mode, nor a superposition of such modes yield an
approximation of strongly nonlinear dynamics.Comment: 10 pages, 6 figure
Recommended from our members
Neoadjuvant anti-PD-1 immunotherapy promotes a survival benefit with intratumoral and systemic immune responses in recurrent glioblastoma.
Glioblastoma is the most common primary malignant brain tumor in adults and is associated with poor survival. The Ivy Foundation Early Phase Clinical Trials Consortium conducted a randomized, multi-institution clinical trial to evaluate immune responses and survival following neoadjuvant and/or adjuvant therapy with pembrolizumab in 35 patients with recurrent, surgically resectable glioblastoma. Patients who were randomized to receive neoadjuvant pembrolizumab, with continued adjuvant therapy following surgery, had significantly extended overall survival compared to patients that were randomized to receive adjuvant, post-surgical programmed cell death protein 1 (PD-1) blockade alone. Neoadjuvant PD-1 blockade was associated with upregulation of T cell- and interferon-Îł-related gene expression, but downregulation of cell-cycle-related gene expression within the tumor, which was not seen in patients that received adjuvant therapy alone. Focal induction of programmed death-ligand 1 in the tumor microenvironment, enhanced clonal expansion of T cells, decreased PD-1 expression on peripheral blood T cells and a decreasing monocytic population was observed more frequently in the neoadjuvant group than in patients treated only in the adjuvant setting. These findings suggest that the neoadjuvant administration of PD-1 blockade enhances both the local and systemic antitumor immune response and may represent a more efficacious approach to the treatment of this uniformly lethal brain tumor
- âŠ