14,007 research outputs found
Hot Routes: Developing a New Technique for the Spatial Analysis of Crime
The use of hotspot mapping techniques such as KDE to represent the geographical spread of linear events can be problematic. Network-constrained data (for example transport-related crime) require a different approach to visualize concentration. We propose a methodology called Hot Routes, which measures the risk distribution of crime along a linear network by calculating the rate of crimes per section of road. This method has been designed for everyday crime analysts, and requires only a Geographical Information System (GIS), and suitable data to calculate. A demonstration is provided using crime data collected from London bus routes
Phenomenology of the minimal B-L extension of the Standard Model
We present the Large Hadron Collider (LHC) discovery potential in the
and heavy neutrino sectors of a enlarged Standard Model also
encompassing three heavy Majorana neutrinos. This model exhibits novel
signatures at the LHC, the most interesting arising from a decay chain
involving heavy neutrinos, eventually decaying into leptons and jets. In
particular, this signature allows one to measure the and heavy neutrino
masses involved. In addition, over a large region of parameter space, the heavy
neutrinos are rather long-lived particles producing distinctive displaced
vertices that can be seen in the detectors. Lastly, the simultaneous
measurement of both the heavy neutrino mass and decay length enables an
estimate of the absolute mass of the parent light neutrino. For completeness,
we will also compare the LHC and a future Linear Collider (LC) discovery
potentials.Comment: 4 pages, no figures. LaTeX. Talk given at "The 2009 Europhysics
Conference on High Energy Physics", Krakow, Poland, July 16-22, 200
VLBA Imaging of NGC 4261: Symmetric Parsec-scale Jets and the Inner Accretion Region
We observed the nuclear region of NGC 4261 (3C270) with the VLBA at two
frequencies (1.6 and 8.4 GHz) simultaneously. We find that the position angle
of the parsec-scale radio axis agrees, within the errors, with the position
angle of the VLA-scale jet. Our observations also reveal basically symmetric
radio structures at both 1.6 and 8.4 GHz. Analysis of these images shows that
most of the central 10 pc of this source is not significantly affected by
free-free absorption, even though HST images show that the nucleus contains a
nearly edge-on disk of gas and dust on larger scales. Our highest angular
resolution image shows a very narrow gap in emission, which we interpret as an
absorption feature, just east of the radio core. This suggests that there may
be a small, dense inner accretion disk whose width is less than 0.1 pc. If the
inclination of this inner disk is close to that of the larger-scale HST disk it
becomes optically thin to 8.4 GHz radiation at a deprojected radius of about
0.8 pc. The brightness of the pc-scale jets falls off very rapidly on both
sides of the core, suggesting that the jets are rapidly expanding during the
the first several pc of their travel. It appears that there is a small dense
inner disk centered on the radio core (the base of the jets; less than 1 pc), a
low density bubble filling most of the the inner several pc of the nucleus
(within which the radio jets expand rapidly; ~10 pc), and a surrounding cool,
higher density region (of which the HST absorption disk is part; tens to
hundreds of pc) within which the transverse expansion of the radio jets, as
implied by the rate of decrease in jet brightness, is nearly halted.Comment: Accepted by the Astrophysical Journa
On the existence of dyons and dyonic black holes in Einstein-Yang-Mills theory
We study dyonic soliton and black hole solutions of the
Einstein-Yang-Mills equations in asymptotically anti-de Sitter space. We prove
the existence of non-trivial dyonic soliton and black hole solutions in a
neighbourhood of the trivial solution. For these solutions the magnetic gauge
field function has no zeros and we conjecture that at least some of these
non-trivial solutions will be stable. The global existence proof uses local
existence results and a non-linear perturbation argument based on the (Banach
space) implicit function theorem.Comment: 23 pages, 2 figures. Minor revisions; references adde
Characterization of gravity current formation for the use in detonation refraction experiments
Detonation propagation through an interface is being studied at Caltech. In these
experiments, the interface shape is determined by the gravity currents. This report
presents an experimental study of the formation and the development of these
gravity currents by an analog system in a water channel using water and salt water to
simulate the density differences in detonation experiments. The major parameters
such as the Reynolds number and the density difference were matched in both
experiments to be able to compare the gravity current in the water channel and the
gravity current in the Galcit detonation tube. In the present study, the gravity current
was generated by the removal of a plate, and was visualized by adding food dye. The
results confirm previous studies; Keulegan demonstrated in 1957 that the velocity of
the gravity current is a function of the square root of the density difference. The
interface is affect by the retracting of the plate which creates the wake effects. The
Kelvin-Helmholtz instabilities on the upstream side of the gravity current create the
visualized mixing zones. Finally, this study revealed how the gravity current interface
into the Galcit detonation tube should develop and where the mixing zones should
occur
The Starburst in the Central Kiloparsec of Markarian 231
We present VLBA observations at 0.33 and 0.61 GHz, and VLA observations
between 5 and 22 GHz, of subkiloparsec scale radio emission from Mrk 231. In
addition to jet components clearly associated with the AGN, we also find a
smooth extended component of size 100 - 1000 pc most probably related to the
purported massive star forming disk in Mrk 231. The diffuse radio emission from
the disk is found to have a steep spectrum at high frequencies, characteristic
of optically thin synchrotron emission. The required relativistic particle
density in the disk can be produced by a star formation rate of 220 Msolar/yr
in the central kiloparsec. At low frequencies the disk is absorbed, most likely
by ionized gas with an emission measure of 8 x 10^5 pc cm-6. We have also
identified 4 candidate radio supernovae that, if confirmed, represent direct
evidence for ongoing star formation in the central kiloparsec.Comment: in press at ApJ for v. 519 July 1999, 14 page LaTeX document includes
6 postscript figure
Cellular localization and trafficking of vascular adhesion protein-1 as revealed by an N-terminal GFP fusion protein
Recent studies of vascular adhesion protein-1 (VAP-1) have greatly advanced our understanding of the important role this protein plays in the establishment and progression of inflammatory disease. To facilitate more detailed studies on the function of VAP-1, we developed a GFP-fusion protein that enabled us to monitor the trafficking of the protein in three selected cell types: hepatic sinusoidal endothelial cells, liver myofibroblasts and an hepatic stellate cell line (LX-2). The fusion protein was detected as punctate cytoplasmic GFP staining, but was present only at low levels at the cell surface in all cell types studied. The subcellular distribution of the protein was not altered in a catalytically inactive mutant form of the protein (Tyr471Phe) or in the presence of exogenous VAP-1 substrate (methylamine) or inhibitor (semicarbazide). The GFP-VAP-1 protein was localized to the Golgi apparatus (GM-130), endoplasmic reticulum (GRP94) and early endosomes (EEA-1). Additional staining for VAP-1 revealed that the overexpressed protein was also present in vesicles that were negative for GFP fluorescent signal and did not express EEA-1. We propose that these vesicles are responsible for recycling the fusion protein and that the fluorescence of the GFP moiety is quenched at the low pH within these vesicles. This feature of the protein makes it well suited for live cell imaging studies where we wish to track protein that is being actively trafficked within the cell in preference to that which is being recycled. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00702-013-1003-3) contains supplementary material, which is available to authorized users
In the Shadow of the Accretion Disk: Higher Resolution Imaging of the Central Parsec in NGC 4261
The physical conditions in the inner parsec of accretion disks believed to
orbit the central black holes in active galactic nuclei can be probed by
imaging the absorption (by ionized gas in the disk) of background emission from
a radio counterjet. We report high angular resolution VLBI observations of the
nearby (about 40 Mpc) radio galaxy NGC 4261 that confirm free-free absorption
of radio emission from a counterjet by a geometrically thin, nearly edge-on
disk at 1.6, 4.8, and 8.4 GHz. The angular width and depth of the absorption
appears to increase with decreasing frequency, as expected. We derive an
average electron density of ~10E4 per cc at a disk radius of about 0.2 pc,
assuming that the inner disk inclination and opening angles are the same as at
larger radii. Pressure balance between the thermal gas and the magnetic field
in the disk implies an average field strength of 0.1 milligauss at a radius of
0.2 pc. These are the closest-in free-free absorption measurements to date of
the conditions in an extragalactic accretion disk orbiting a black hole with a
well-determined mass. If a standard advection-dominated accretion flow exists
in the disk center, then the transition between thin and thick disk regions
must occur at a radius less than 0.2 pc (4000 Schwarzschild radii).Comment: 20 pages including 12 figures. Accepted for publication in Ap
Measuring the brightness temperature distribution of extragalactic radio sources with space VLBI
We have used VSOP space very long baseline interferometry observations to
measure the brightness temperature distribution of a well-defined sub-set of
the Pearson-Readhead sample of extragalactic radio sources. VLBI which is
restricted to Earth-diameter baselines is not generally sensitive to emitting
regions with brightness temperatures greater than approximately K,
coincidentally close to theoretical estimates of brightness temperature limits,
K. We find that a significant proportion of our sample have
brightness temperatures greater than K; many have unresolved
components on the longest baselines, and some remain completely unresolved.
These observations begin to bridge the gap between the extended jets seen with
ground-based VLBI and the microarcsecond structures inferred from intraday
variability, evidenced here by the discovery of a relationship between intraday
variability and VSOP-measured brightness temperature, likely due to the effects
of relativistic beaming. Also, lower limits on jet Lorentz factors, estimated
from space VLBI observations, are starting to challenge numerical simulations
that predict low Lorentz factor jets.Comment: 4 pages + 1 figure, ApJ letters, accepte
Comparison of measured and calculated sound pressure levels around a large horizontal axis wind turbine generator
Results are reported from a large number of simultaneous acoustic measurements around a large horizontal axis downwind configuration wind turbine generator. In addition, comparisons are made between measurements and calculations of both the discrete frequency rotational harmonics and the broad band noise components. Sound pressure time histories and noise radiation patterns as well as narrow band and broadband noise spectra are presented for a range of operating conditions. The data are useful for purposes of environmental impact assessment
- …