1,610 research outputs found
Three-dimensional Models of Core-collapse Supernovae From Low-mass Progenitors With Implications for Crab
We present 3D full-sphere supernova simulations of non-rotating low-mass (~9
Msun) progenitors, covering the entire evolution from core collapse through
bounce and shock revival, through shock breakout from the stellar surface,
until fallback is completed several days later. We obtain low-energy explosions
[~(0.5-1.0)x 10^{50} erg] of iron-core progenitors at the low-mass end of the
core-collapse supernova (LMCCSN) domain and compare to a super-AGB (sAGB)
progenitor with an oxygen-neon-magnesium core that collapses and explodes as
electron-capture supernova (ECSN). The onset of the explosion in the LMCCSN
models is modelled self-consistently using the Vertex-Prometheus code, whereas
the ECSN explosion is modelled using parametric neutrino transport in the
Prometheus-HOTB code, choosing different explosion energies in the range of
previous self-consistent models. The sAGB and LMCCSN progenitors that share
structural similarities have almost spherical explosions with little metal
mixing into the hydrogen envelope. A LMCCSN with less 2nd dredge-up results in
a highly asymmetric explosion. It shows efficient mixing and dramatic shock
deceleration in the extended hydrogen envelope. Both properties allow fast
nickel plumes to catch up with the shock, leading to extreme shock deformation
and aspherical shock breakout. Fallback masses of <~5x10^{-3} Msun have no
significant effects on the neutron star (NS) masses and kicks. The anisotropic
fallback carries considerable angular momentum, however, and determines the
spin of the newly-born NS. The LMCCSNe model with less 2nd dredge-up results in
a hydrodynamic and neutrino-induced NS kick of >40 km/s and a NS spin period of
~30 ms, both not largely different from those of the Crab pulsar at birth.Comment: 47 pages, 27 figures, 6 tables; minor revisions, accepted by MNRA
Evolutionary Multi-Objective Design of SARS-CoV-2 Protease Inhibitor Candidates
Computational drug design based on artificial intelligence is an emerging
research area. At the time of writing this paper, the world suffers from an
outbreak of the coronavirus SARS-CoV-2. A promising way to stop the virus
replication is via protease inhibition. We propose an evolutionary
multi-objective algorithm (EMOA) to design potential protease inhibitors for
SARS-CoV-2's main protease. Based on the SELFIES representation the EMOA
maximizes the binding of candidate ligands to the protein using the docking
tool QuickVina 2, while at the same time taking into account further objectives
like drug-likeliness or the fulfillment of filter constraints. The experimental
part analyzes the evolutionary process and discusses the inhibitor candidates.Comment: 15 pages, 7 figures, submitted to PPSN 202
An Exact Conformal Symmetry Ansatz on Kaluza-Klein Reduced TMG
Using a Kaluza-Klein dimensional reduction, and further imposing a conformal
Killing symmetry on the reduced metric generated by the dilaton, we show an
Ansatz that yields many of the known stationary axisymmetric solutions to TMG.Comment: 20 pages, 1 figure, v3: postprint, added one re
Topologically Massive Gravity and Ricci-Cotton Flow
We consider Topologically Massive Gravity (TMG), which is three dimensional
general relativity with a cosmological constant and a gravitational
Chern-Simons term. When the cosmological constant is negative the theory has
two potential vacuum solutions: Anti-de Sitter space and Warped Anti-de Sitter
space. The theory also contains a massive graviton state which renders these
solutions unstable for certain values of the parameters and boundary
conditions. We study the decay of these solutions due to the condensation of
the massive graviton mode using Ricci-Cotton flow, which is the appropriate
generalization of Ricci flow to TMG. When the Chern-Simons coupling is small
the AdS solution flows to warped AdS by the condensation of the massive
graviton mode. When the coupling is large the situation is reversed, and warped
AdS flows to AdS. Minisuperspace models are constructed where these flows are
studied explicitly
All stationary axi-symmetric local solutions of topologically massive gravity
We classify all stationary axi-symmetric solutions of topologically massive
gravity into Einstein, Schr\"odinger, warped and generic solutions. We
construct explicitly all local solutions in the first three sectors and present
an algorithm for the numerical construction of all local solutions in the
generic sector. The only input for this algorithm is the value of one constant
of motion if the solution has an analytic centre, and three constants of motion
otherwise. We present several examples, including soliton solutions that
asymptote to warped AdS.Comment: 42 pages, 9 figures. v2: Changed potentially confusing labelling of
one sector, added references. v3: Minor changes, matches published versio
Dynamics of Electron-Induced Manipulation of Individual CO Molecules on Cu(111)
Electrons tunneling from a scanning tunneling microscope tip to individual CO molecules on Cu(111) can cause their hopping from the surface to the tip if the bias exceeds a threshold of 2.4 V. Polarization- and time-resolved two-photon photoemission identifies the underlying elementary process as intermediate population of a CO 2π* -derived level, which exhibits an ultrashort lifetime of 0.8–5 fs. From an isotope effect of 2.7 - 0.5 + 0.3 it can be calculated that ≈ 0.05 % of the tunneling current transiently occupies this level while a desorption of the excited molecule occurs only in 5 × 10 - 9 of the cases
The value of the 4-day headdown bedrest model for screening countermeasures
In order to evaluate the benefits of periodic exposure to the +G(z) vector as a countermeasure to the physiological responses to minus 6 degree head down bedrest (HDT), we considered a two-tiered approach: (a) to use 4 days HDT as a quick and inexpensive means of screening countermeasures, (b) to use a 60 day HDT to validate the most promising candidates. The approach and results of a 4 day study are described here. Methods: Nine males were admitted to our Human Research Facility for one ambulatory control day followed by 4 days HDT and were released on the next day after completion of a peak oxygen consumption test (VO(sub 2 peak)). A battery of tests was selected and standardized to evaluate the known early effects of HDT on plasma volume, early bone markers, orthostatic tolerance, physical performance, and fluid and electrolytes and their hormone regulation. Fluid sodium (Na) and potassium (K) intake and output in the urine were monitored throughout. Plasma volume was determined with a modified Evans Blue method and orthostatic tolerance with a 60 degree head-up tilt test for 30 minutes - both of which were determined on the ambulatory control day and on day 4 of HDT. Immediately after completion of the tilt test subjects were returned to the minus 6 degree position until the next morning when a VO(sub 2 peak) (horizontal ergometer) was done. This was compared to a similar control test determined on 2 separate occasions before subject admission. Results: Four hours after going HDT produced significant decreases (p less than 0.05) in the circulating concentration of fluid and electrolyte regulating hormones. Plasma volume, orthostatic tolerance and VO(sub 2 peak) changed significantly after 4 days HDT. There was also the expected natriuresis on day 1 of HDT but no significant diuresis. The consistency of the pre-bedrest VO(sub 2 peak) tilt tests and plasma volumes was remarkable. Conclusions: The 4 day HDT model seems highly promising for screening a variety of countermeasures alone and in combination before validating their benefits in extended bedrest or flight experiments
T-cell cytotoxicity in the absence of viral protein synthesis in target cells
CYTOTOXIC T cells lyse only those virus infected target cells in vitro which express, in addition to the viral antigen(s), those K or D region products of the major histocompati-bility complex (MHC) which were present during anti-viral sensitisation in vivo. This 'associative recogniton' by cytotoxic T cells could reflect the interaction of two T-cell receptors with specificity for target K or D gene products and independently for the viral antigen, or one receptor with specificity for virally altered K or D region products (see ref. 1 and refs therein). There are various ways that the MHC antigens could be altered, including 'modification from within', where the virus modifies host protein synthesis by interfering with transcription2, translation or post-translational glycosylation; or 'modification from without' where enzymic or chemical alteration of cell membrane proteins are induced by virus activity at the cell surface. In this report we show that inactivated Sendai virus or isolated Sendai virus envelopes can serve to modify a cell and make it a specific target for Sendai-immune T-cell killing, thus excluding the possibility of 'modification from within' in this system
- …