31,102 research outputs found
Can Dark Matter Annihilation Dominate the Extragalactic Gamma-Ray Background?
Annihilating dark matter (DM) has been discussed as a possible source of
gamma-rays from the galactic center (GC) and contributing to the extragalactic
gamma-ray background (EGB). Assuming universality of the density profile of DM
halos, we show that it is quite unlikely that DM annihilation is a main
constituent of EGB, without exceeding the observed gamma-ray flux from the GC.
This argument becomes stronger when we include enhancement of the density
profiles by supermassive black holes or baryon cooling. The presence of
substructure may loosen the constraint, but only if a very large cross section
as well as the rather flat profile are realized.Comment: 4 pages, 2 figures, accepted by PR
Detailed stratigraphic correlation of the Neogene sedimentary sequences on the Ontong Java Plateau by well logging; ODP Sites 803, 805, 806, 807, and DSDP Site 586
We used well logs, in some cases combined with shipboard physical properties measurements to make more complete profiles and to correlate between sites on the Ontong Java Plateau. By comparing sediment bulk density, velocity, and resistivity logs from adjacent holes at the same site, we showed that even subtle features of the well logs are reproducible and are caused by variations in sedimentation. With only minor amounts of biostratigraphic information, we could readily correlate these sedimentary features across the entire top of the Ontong Java Plateau, demonstrating that for most of the Neogene the top of the plateau is a single sedimentary province. We found it more difficult, but still possible, to correlate in detail sites from the top of the plateau to those drilled on the flanks. The pattern of sedimentation rate variation down the flank of the plateau cannot be interpreted as simply controlled by dissolution. Site 805, in particular, oscillates between accumulating sediment at roughly the same rate as cores on top of the Ontong Java Plateau, and accumulating sediment as slowly as Site 803, 200 m deeper in the water column. These oscillations do not match earlier reconstructions of central Pacific carbonate compensation depth variations
Distribution of carbonate in surface sediments of the Pacific Ocean
The distribution of carbonate on the floor of the Pacific has been remapped on the basis of 1313 points from 80 references stored in the World Ocean Sediment Data Bank of Scripps Institution of Oceanography. Percent distribution maps and carbonate versus depth diagrams generally agree with previously published information and reflect the major controlling factors of carbonate sedimentation (depth, hydrography, fertility, and sedimentary processes). While carbonate distributions are of limited use in attempting to construct dissolution profiles, major trends are identifiable. In particular, the degree of lowering of the equatorial calcite compensation depth (CCD) together with an estimate of the differences in supply rates between the equator and the subtropical gyre can be used to estimate dissolution rate increase below the lysocline. There is considerable variation in the sharpness of the âCCD transitionâ a concept defined here. This variation is thought to reflect both geographic differences in dissolution rate gradients and redeposition processes (carbonate, deep-sea sediments, calcite, and compensation depth)
Kinetics of silicide formation by thin films of V on Si and SiO_2 substrates
The reaction rate of vacuumâevaporated films of V of the order of 1000 Ă
thick is investigated by MeV He backscattering spectrometry. On substrates of singleâcrystal Si and for anneal times up to several hours in the temperature range 570â650°C, VSi_2 is formed at a linear rate in time. The activation energy of the process is 1.7±0.2 eV. The presence of oxygen in amounts of 10% can significantly decelerate the reaction. On substrates of SiO_2 in the temperature range 730â820°C and anneal times of several hours or less, V_3Si is formed at a squareâroot rate in time. The activation energy of this process is 2.0±0.2 eV
Chelate-modified polymers for atmospheric gas chromatography
Chromatographic materials were developed to serve as the stationary phase of columns used in the separation of atmospheric gases. These materials consist of a crosslinked porous polymer matrix, e.g., a divinylbenzene polymer, into which has been embedded an inorganic complexed ion such as N,N'-ethylene-bis-(acetylacetoniminato)-cobalt (2). Organic nitrogenous bases, such as pyridine, may be incorporated into the chelate polymer complexes to increase their chromatographic utility. With such materials, the process of gas chromatography is greatly simplified, especially in terms of time and quantity of material needed for a gas separation
Management of erectile dysfunction post-radical prostatectomy
© 2015 Saleh et al.Radical prostatectomy is a commonly performed procedure for the treatment of localized prostate cancer. One of the long-term complications is erectile dysfunction. There is little consensus on the optimal management; however, it is agreed that treatment must be prompt to prevent fibrosis and increase oxygenation of penile tissue. It is vital that patient expectations are discussed, a realistic time frame of treatment provided, and treatment started as close to the prostatectomy as possible. Current treatment regimens rely on phosphodiesterase 5 inhibitors as a first-line therapy, with vacuum erection devices and intraurethral suppositories of alprostadil as possible treatment combination options. With nonresponders to these therapies, intracavernosal injections are resorted to. As a final measure, patients undergo the highly invasive penile prosthesis implantation. There is no uniform, objective treatment program for erectile dysfunction post-radical prostatectomy. Management plans are based on poorly conducted and often underpowered studies in combination with physician and patient preferences. They involve the aforementioned drugs and treatment methods in different sequences and doses. Prospective treatments include dietary supplements and gene therapy, which have shown promise with there proposed mechanisms of improving erectile function but are yet to be applied successfully in human patients
On the spectrum of Farey and Gauss maps
In this paper we introduce Hilbert spaces of holomorphic functions given by
generalized Borel and Laplace transforms which are left invariant by the
transfer operators of the Farey map and its induced version, the Gauss map,
respectively. By means of a suitable operator-valued power series we are able
to study simultaneously the spectrum of both these operators along with the
analytic properties of the associated dynamical zeta functions.Comment: 23 page
Variations of porosity in calcareous sediments from the Ontong Java Plateau
Based on index properties measurements made on board the JOIDES Resolution, we studied porosity changes with depth in the fairly homogeneous deep-sea calcareous sediments cored during Ocean Drilling Program Leg 130 on the Ontong Java Plateau. Using Leg 130 data, we present evidence that the rate of porosity decrease with burial in calcareous oozes and chalks is related to the depth of deposition and thus probably depends on the conditioning of calcareous sediments by winnowing or dissolution processes during the time of deposition. The ooze-to-chalk transition is not clearly reflected in porosity profiles. In the ooze-chalk sections studied (the upper 600 mbsf), mechanical compaction is most likely the major process controlling the porosity decrease with depth of burial, whereas the chalk-limestone transition (at about 1100 mbsf at Site 807) is characterized by an intense chemical compaction leading to a drastic decrease in porosity values within 100 m. In oozes and chalks, porosity values were corrected to original (uncompacted) values using site-specific empirical regression equations. When plotted vs. age, corrected porosity profiles appear to correlate quite well from site to site in the sediments deposited during the last 15 m.y. This observation has considerable implications for seismic stratigraphy. Our attempt to correlate variations in porosity (or wet-bulk density) profiles with changes in carbonate content remained unsatisfactory. Index properties changes are likely caused by changes in the foraminifer content. If this is the case, we propose that large-scale porosity fluctuations that correlate from site to site are the result of changes in the surface productivity that lead to changes in the foraminifers-to-nannofossils ratio
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