3,402 research outputs found
CoGeNT, DAMA, and Light Neutralino Dark Matter
Recent observations by the CoGeNT collaboration (as well as long standing
observations by DAMA/LIBRA) suggest the presence of a -10 GeV dark
matter particle with a somewhat large elastic scattering cross section with
nucleons ( cm).Within the context of the minimal
supersymmetric standard model (MSSM), neutralinos in this mass range are not
able to possess such large cross sections, and would be overproduced in the
early universe. Simple extensions of the MSSM, however, can easily accommodate
these observations. In particular, the extension of the MSSM by a chiral
singlet superfield allows for the possibility that the dark matter is made up
of a light singlino that interacts with nucleons largely through the exchange
of a fairly light (30-70 GeV) singlet-like scalar higgs, \hi. Such a
scenario is consistent with all current collider constraints and can generate
the signals reported by CoGeNT and DAMA/LIBRA. Furthermore, there is a generic
limit of the extended model in which there is a singlet-like pseudoscalar
higgs, \ai, with \mai\sim \mhi and in which the and b\anti
b, s\anti s coupling magnitudes of the \hi and \ai are very similar. In
this case, the thermal relic abundance is automatically consistent with the
measured density of dark matter if \mchi is sufficiently small that
\chi^0\chi^0\to b\anti b is forbidden.Comment: 6 pages, published versio
Structure of a Solvated Nickel(II) Complex of (\u3cem\u3eS\u3c/em\u3e)-2\u27-(\u3cem\u3eN\u3c/em\u3e-benzylprolyl)aminoacetophenone and (\u3cem\u3eR\u3c/em\u3e)-valine Schiff base, C\u3csub\u3e25\u3c/sub\u3eH\u3csub\u3e29\u3c/sub\u3eN\u3csub\u3e3\u3c/sub\u3eNiO\u3csub\u3e3\u3c/sub\u3e.1/2C\u3csub\u3e4\u3c/sub\u3eH\u3csub\u3e8\u3c/sub\u3eO. Conformational Calculation of Diastereomeric Complexes of (\u3cem\u3eR\u3c/em\u3e)-valine and (\u3cem\u3eS\u3c/em\u3e)-valine
How Dark Matter Reionized The Universe
Although empirical evidence indicates that that the universe's gas had become
ionized by redshift z ~ 6, the mechanism by which this transition occurred
remains unclear. In this article, we explore the possibility that dark matter
annihilations may have played the dominant role in this process. Energetic
electrons produced in these annihilations can scatter with the cosmic microwave
background to generate relatively low energy gamma rays, which ionize and heat
gas far more efficiently than higher energy prompt photons. In contrast to
previous studies, we find that viable dark matter candidates with electroweak
scale masses can naturally provide the dominant contribution to the
reionization of the universe. Intriguingly, we find that dark matter candidates
capable of producing the recent cosmic ray excesses observed by PAMELA and/or
ATIC are also predicted to lead to the full reionization of the universe by z ~
6.Comment: 10 pages, 6 figures; error in figure 2 corrected, conclusions
unchange
The Isotropic Radio Background and Annihilating Dark Matter
Observations by ARCADE-2 and other telescopes sensitive to low frequency
radiation have revealed the presence of an isotropic radio background with a
hard spectral index. The intensity of this observed background is found to
exceed the flux predicted from astrophysical sources by a factor of
approximately 5-6. In this article, we consider the possibility that
annihilating dark matter particles provide the primary contribution to the
observed isotropic radio background through the emission of synchrotron
radiation from electron and positron annihilation products. For reasonable
estimates of the magnetic fields present in clusters and galaxies, we find that
dark matter could potentially account for the observed radio excess, but only
if it annihilates mostly to electrons and/or muons, and only if it possesses a
mass in the range of approximately 5-50 GeV. For such models, the annihilation
cross section required to normalize the synchrotron signal to the observed
excess is sigma v ~ (0.4-30) x 10^-26 cm^3/s, similar to the value predicted
for a simple thermal relic (sigma v ~ 3 x 10^-26 cm^3/s). We find that in any
scenario in which dark matter annihilations are responsible for the observed
excess radio emission, a significant fraction of the isotropic gamma ray
background observed by Fermi must result from dark matter as well.Comment: 11 pages, 6 figure
Surface-dependent osteoblasts response to TiO2 nanotubes of different crystallinity
One of the major challenges of implantology is to design nanoscale modifications of titanium implant surfaces inducing osseointegration. The aim of this study was to investigate the behavior of rat osteoblasts cultured on anodized TiO2 nanotubes of different crystallinity (amorphous and anatase phase) up to 24 days. TiO2 nanotubes were fabricated on VT1–0 titanium foil via a two-step anodization at 20 V using NH4F as an electrolyte. Anatase-phase samples were prepared by heat treatment at 500 °C for 1 h. VT1–0 samples with flat surfaces were used as controls. Primary rat osteoblasts were seeded over experimental surfaces for several incubation times. Scanning electron microscopy (SEM) was used to analyze tested surfaces and cell morphology. Cell adhesion and proliferation were investigated by cell counting. Osteogenic differentiation of cells was evaluated by qPCR of runt-related transcription factor 2 (RUNX2), osteopontin (OPN), integrin binding sialoprotein (IBSP), alkaline phosphatase (ALP) and osteocalcin (OCN). Cell adhesion and proliferation, cell morphology and the expression of osteogenic markers were affected by TiO2 nanotube layered substrates of amorphous and anatase crystallinity. In comparison with flat titanium, along with increased cell adhesion and cell growth a large portion of osteoblasts grown on the both nanostructured surfaces exhibited an osteocyte-like morphology as early as 48 h of culture. Moreover, the expression of all tested osteogenic markers in cells cultured on amorphous and anatase TiO2 nanotubes was upregulated at least at one of the analyzed time points. To summarize, we demonstrated that amorphous and anodized TiO2 layered substrates are highly biocompatible with rat osteoblasts and that the surface modification with about 1500 nm length nanotubes of 35 ± 4 (amorphous phase) and 41 ± 8 nm (anatase phase) in diameter is sufficient to induce their osteogenic differentiation. Such results are significant to the engineering of coating strategies for orthopedic implants aimed to establish a more efficient bone to implant contact and enhance bone repair. © 2020 by the author. Licensee MDPI, Basel, Switzerland.Deutscher Akademischer Austauschdienst, DAADRussian Science Foundation, RSF: 18‐13‐00220Ministry of Education and Science of the Russian Federation, Minobrnauka: 57447934PPN/BEK/2018/1/00071Funding: The experimental work was funded by the Russian Science Foundation (grant no. 18‐13‐00220). This research was partially supported by DAAD together with the Ministry of Education and Science of the Russian Federation within Michael Lomonosov Program (project No. 57447934); M.W. was financially supported by the Polish National Agency for Academic Exchange (PPN/BEK/2018/1/00071)
Ab Initio Calculations of the Walls Shear Strength of Carbon Nanotubes
The dependence of the energy of interwall interaction in double-walled carbon
nanotubes (DWNT) on the relative position of walls has been calculated using
the density functional method. This dependence is used to evaluate forces that
are necessary for the relative telescopic motion of walls and to calculate the
shear strength of DWNT for the relative sliding of walls along the nanotube
axis and for their relative rotation about this axis. The possibility of
experimental verification of the obtained results is discussed.Comment: 4 pages, 1 figur
Study of the Gamma-ray Spectrum from the Galactic Center in view of Multi-TeV Dark Matter Candidates
Motivated by the complex gamma-ray spectrum of the Galactic Center source now
measured over five decades in energy, we revisit the issue of the role of dark
matter annihilations in this interesting region. We reassess whether the
emission measured by the HESS collaboration could be a signature of dark matter
annihilation, and we use the {\em Fermi} LAT spectrum to model the emission
from SgrA*, using power-law spectral fits. We find that good fits are achieved
by a power law with an index , in combination with a spectrum
similar to the one observed from pulsar population and with a spectrum from a
\gsi10 TeV DM annihilating to a mixture of and harder channels and with boost factors of the order of a hundred.
Alternatively, we also consider the combination of a log-parabola fit with the
DM contribution. Finally, as both the spectrum of gamma rays from the Galactic
Center and the spectrum of cosmic ray electrons exhibit a cutoff at TeV
energies, we study the dark matter fits to both data-sets. Constraining the
spectral shape of the purported dark matter signal provides a robust way of
comparing data. We find a marginal overlap only between the 99.999% C.L.
regions in parameter space.Comment: 16 pages, 14 figure
Adjoint of the Global Eulerian Lagrangian Coupled Atmospheric transport model (A-GELCA v1.0): development and validation
Abstract. We present the development of the Adjoint of the Global Eulerian–Lagrangian Coupled Atmospheric (A-GELCA) model that consists of the National Institute for Environmental Studies (NIES) model as an Eulerian three-dimensional transport model (TM), and FLEXPART (FLEXible PARTicle dispersion model) as the Lagrangian plume diffusion model (LPDM). The tangent and adjoint components of the Eulerian model were constructed directly from the original NIES TM code using an automatic differentiation tool known as TAF (Transformation of Algorithms in Fortran; http://www.FastOpt.com), with additional manual pre- and post-processing aimed at improving the performance of the computing, including MPI (Message Passing Interface). As results, the adjoint of Eulerian model is discrete. Construction of the adjoint of the Lagrangian component did not require any code modification, as LPDMs are able to track a significant number of particles back in time and thereby calculate the sensitivity of observations to the neighboring emissions areas. Eulerian and Lagrangian adjoint components were coupled at the time boundary in the global domain.The results are verified using a series of test experiments. The forward simulation shown the coupled model is effective in reproducing the seasonal cycle and short-term variability of CO2 even in the case of multiple limiting factors, such as high uncertainty of fluxes and the low resolution of the Eulerian model. The adjoint model demonstrates the high accuracy compared to direct forward sensitivity calculations and fast performance. The developed adjoint of the coupled model combines the flux conservation and stability of an Eulerian discrete adjoint formulation with the flexibility, accuracy, and high resolution of a Lagrangian backward trajectory formulation.
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Two-dimensional mathematical modeling of 2013 and 2020 Amur River floods
Predicting river flooding of the territory where people live and engage in economic activities is urgent. The most problematic area in the Russian Far East is the territory through which the Amur River and its tributaries flow. The article considers the calculations of two Amur River floods: 2013 – catastrophic flood and 2020 – low flood. The simulation was carried out using a system of two-dimensional Saint-Venant equations using the Stream 2D CUDA program. The solution of the system of equations by numerical methods is based on the original author’s methodology. Channel depth maps and WordDEMTM (Airbus Defense and Space, Intelligence) data at 24 m resolution were used as a digital elevation model. Calculations of river floods in 2013 and 2020 were performed on a built-in and calibrated mathematical model, which matches the observational data well
Velocity Dispersion of Dissolving OB Associations Affected by External Pressure of Formation Environment
This paper presents a possible way to understand dissolution of OB
associations (or groups). Assuming rapid escape of parental cloud gas from
associations, we show that the shadow of the formation environment for
associations can be partially imprinted on the velocity dispersion at their
dissolution. This conclusion is not surprising as long as associations are
formed in a multiphase interstellar medium, because the external pressure
should suppress expansion caused by the internal motion of the parental clouds.
Our model predicts a few km s as the internal velocity dispersion.
Observationally, the internal velocity dispersion is km s which
is smaller than our prediction. This suggests that the dissipation of internal
energy happens before the formation of OB associations.Comment: 6 pages. AJ accepte
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