19,870 research outputs found
Supermassive Black Holes and Galaxy Formation
The formation of supermassive black holes (SMBH) is intimately related to
galaxy formation, although precisely how remains a mystery. I speculate that
formation of, and feedback from, SMBH may alleviate problems that have arisen
in our understanding of the cores of dark halos of galaxies.Comment: Talk at conference on Matter in the Universe, March 2001, ISSI Ber
Morphometric study of lingual foramina in macerated mandibles to assist in implant placement in the anterior mandibular region
The object of our study was to contribute to anatomical knowledge of this region with data on the prevalence, number and location of lingual foramina (LF) in dentate and edentate macerated mandibles from Brazilian individuals, differenÂtiating them by sex and race. In this way we hope to help dental surgeons with their planning prior to implant placement in the anterior mandibular region. 103 macerated mandibles were analysed. The prevalence, number and location of LF were analysed in the median (MLF) and lateral (LLF) regions and the median (AMLF) and lateral (ALLF) alveolar process regions. Measurements for their location were taken with a digital calliper. 99% of the mandibles presented at least 1 MLF, 82.5% at least 1 LLF, and the frequency of ALLF was 67%. In dentate mandibles, MLF were located in the region superior to the genial spine, and in edentate mandibles in the regions superior and inferior to the genial spine. LLF were located in the middle region in both dentate and edentate mandibles. The height of the symphysis was significantly greater in dentate than in edentate cases. The distance from the alveolar crest (AC) to the MLF was significantly greater in dentate than in edentate mandibles. LF are constant structures, with MLF found more frequently than LLF. Mandibles which present a smaller measured distance from the base of mandible to AC present MFL and LLF closer to AC, implying a greater risk of complication during implant placement. (Folia Morphol 2018; 77, 2: 310â322
The Arecibo 430-MHz Intermediate Galactic Latitude Survey: Discovery of Nine Radio Pulsars
We have used the Arecibo Radio Telescope to search for millisecond pulsars in
two intermediate Galactic latitude regions (7 deg < | b | < 20 deg) accessible
to this telescope. For these latitudes the useful millisecond pulsar search
volume achieved by Arecibo's 430-MHz beam is predicted to be maximal. Searching
a total of 130 square degrees, we have discovered nine new pulsars and detected
four previously known objects. We compare the results of this survey with those
of other 430-MHz surveys carried out at Arecibo and of an intermediate latitude
survey made at Parkes that included part of our search area; the latter
independently found two of the nine pulsars we have discovered.
At least six of our discoveries are isolated pulsars with ages between 5 and
300 Myr; one of these, PSR J1819+1305, exhibits very marked and periodic
nulling. We have also found a recycled pulsar, PSR J2016+1948. With a
rotational period of 65 ms, this is a member of a binary system with a 635-day
orbital period. We discuss some of the the properties of this system in detail,
and indicate its potential to provide a test of the Strong Equivalence
Principle. This pulsar and PSR J0407+16, a similar system now being timed at
Arecibo, are by far the best systems known for such a test.Comment: Accepted for publication in ApJ Referee format: 22 pages, 7 figure
Particles and energy fluxes from a CFT perspective
We analyze the creation of particles in two dimensions under the action of
conformal transformations. We focus our attention on Mobius transformations and
compare the usual approach, based on the Bogolubov coefficients, with an
alternative but equivalent viewpoint based on correlation functions. In the
latter approach the absence of particle production under full Mobius
transformations is manifest. Moreover, we give examples, using the
moving-mirror analogy, to illustrate the close relation between the production
of quanta and energy.Comment: Revised version. To appear in Phys.Rev.
Continued fraction approximation for the nuclear matter response function
We use a continued fraction approximation to calculate the RPA response
function of nuclear matter. The convergence of the approximation is assessed by
comparing with the numerically exact response function obtained with a typical
effective finite-range interaction used in nuclear physics. It is shown that
just the first order term of the expansion can give reliable results at
densities up to the saturation density value
Long-term Stellar Variability in the Galactic Centre Region
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.We report the detection of variable stars within a 11.5' x 11.5' region near the Galactic centre (GC) that includes the Arches and Quintuplet clusters, as revealed by the VISTA Variables in the Via Lactea (VVV) survey. There are 353 sources that show Ks-band variability, of which the large majority (81%) correspond to red giant stars, mostly in the asymptotic giant branch (AGB) phase. We analyze a population of 52 red giants with long-term trends that cannot be classified into the typical pulsating star categories. Distances and extinctions are calculated for 9 Mira variables, and we discuss the impact of the chosen extinction law on the derived distances. We also report the presence of 48 new identified young stellar object (YSO) candidates in the region.Peer reviewe
Dark Energy, scalar-curvature couplings and a critical acceleration scale
We study the effects of coupling a cosmologically rolling scalar field to
higher order curvature terms. We show that when the strong coupling scale of
the theory is on the 10^{-3}-10^{-1}eV range, the model passes all experimental
bounds on the existence of fifth forces even if the field has a mass of the
order of the Hubble scale in vacuum and non-suppressed couplings to SM fields.
The reason is that the coupling to certain curvature invariant acts as an
effective mass that grows in regions of large curvature. This prevents the
field from rolling down its potential near sources and makes its effects on
fifth-force search experiments performed in the laboratory to be observable
only at the sub-mm scale. We obtain the static spherically symmetric solutions
of the theory and show that a long-range force appears but it is turned on only
below a fixed Newtonian acceleration scale of the order of the Hubble constant.
We comment on the possibility of using this feature of the model to alleviate
the CDM small scale crisis and on its possible relation to MOND.Comment: 12 pages, 2 figure
Cluster Mass Estimate and a Cusp of the Mass Density Distribution in Clusters of Galaxies
We study density cusps in the center of clusters of galaxies to reconcile
X-ray mass estimates with gravitational lensing masses. For various mass
density models with cusps we compute X-ray surface brightness distribution, and
fit them to observations to measure the range of parameters in the density
models. The Einstein radii estimated from these density models are compared
with Einstein radii derived from the observed arcs for Abell 2163, Abell 2218,
and RX J1347.5-1145. The X-ray masses and lensing masses corresponding to these
Einstein radii are also compared. While steeper cusps give smaller ratios of
lensing mass to X-ray mass, the X-ray surface brightnesses estimated from
flatter cusps are better fits to the observations. For Abell 2163 and Abell
2218, although the isothermal sphere with a finite core cannot produce giant
arc images, a density model with a central cusp can produce a finite Einstein
radius, which is smaller than the observed radii. We find that a total mass
density profile which declines as produces the largest radius
in models which are consistent with the X-ray surface brightness profile. As
the result, the extremely large ratio of the lensing mass to the X-ray mass is
improved from 2.2 to 1.4 for Abell 2163, and from 3 to 2.4 for Abell 2218. For
RX J1347.5-1145, which is a cooling flow cluster, we cannot reduce the mass
discrepancy.Comment: 23 pages, 10 figures, Latex, uses aasms4.sty, accepted for
publication in ApJ, Part
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