4,985 research outputs found
UK open source crime data: accuracy and possibilities for research
In the United Kingdom, since 2011 data regarding individual police recorded crimes have been made openly available to the public via the police.uk website. To protect the location privacy of victims these data are obfuscated using geomasking techniques to reduce their spatial accuracy. This paper examines the spatial accuracy of the police.uk data to determine at what level(s) of spatial resolution â if any â it is suitable for analysis in the context of theory testing and falsification, evaluation research, or crime analysis. Police.uk data are compared to police recorded data for one large metropolitan Police Force and spatial accuracy is quantified for four different levels of geography across five crime types. Hypotheses regarding systematic errors are tested using appropriate statistical approaches, including methods of maximum likelihood. Finally, a âbest-fitâ statistical model is presented to explain the error as well as to develop a model that can correct it. The implications of the findings for researchers using the police.uk data for spatial analysis are discussed
Low Gain Avalanche Detectors (LGAD) for particle physics and synchrotron applications
A new avalanche silicon detector concept is introduced with a low gain in the region of ten, known as a Low Gain Avalanche Detector, LGAD. The detector's characteristics are simulated via a full process simulation to obtain the required doping profiles which demonstrate the desired operational characteristics of high breakdown voltage (500 V) and a gain of 10 at 200 V reverse bias for X-ray detection. The first low gain avalanche detectors fabricated by Micron Semiconductor Ltd are presented. The doping profiles of the multiplication junctions were measured with SIMS and reproduced by simulating the full fabrication process which enabled further development of the manufacturing process. The detectors are 300 ÎŒm thick p-type silicon with a resistivity of 8.5 kΩcm, which fully depletes at 116 V. The current characteristics are presented and demonstrate breakdown voltages in excess of 500 V and a current density of 40 to 100 nAcmâ2 before breakdown measured at 20oC. The gain of the LGAD has been measured with a red laser (660 nm) and shown to be between 9 and 12 for an external bias voltage range from 150 V to 300 V
Rotational Doppler Effect in Magnetic Resonance
We compute the shift in the frequency of the spin resonance in a solid that
rotates in the field of a circularly polarized electromagnetic wave. Electron
spin resonance, nuclear magnetic resonance, and ferromagnetic resonance are
considered. We show that contrary to the case of the rotating LC circuit, the
shift in the frequency of the spin resonance has strong dependence on the
symmetry of the receiver. The shift due to rotation occurs only when rotational
symmetry is broken by the anisotropy of the gyromagnetic tensor, by the shape
of the body, or by magnetocrystalline anisotropy. General expressions for the
resonance frequency and power absorption are derived and implications for
experiment are discussed.Comment: 8 pages, 4 figure
Gravitational Self-Force Correction to the Binding Energy of Compact Binary Systems
Using the first law of binary black-hole mechanics, we compute the binding
energy E and total angular momentum J of two non-spinning compact objects
moving on circular orbits with frequency Omega, at leading order beyond the
test-particle approximation. By minimizing E(Omega) we recover the exact
frequency shift of the Schwarzschild innermost stable circular orbit induced by
the conservative piece of the gravitational self-force. Comparing our results
for the coordinate invariant relation E(J) to those recently obtained from
numerical simulations of comparable-mass non-spinning black-hole binaries, we
find a remarkably good agreement, even in the strong-field regime. Our findings
confirm that the domain of validity of perturbative calculations may extend
well beyond the extreme mass-ratio limit.Comment: 5 pages, 1 figure; matches the published versio
The Diverse Infrared Properties of a Complete Sample of Star-Forming Dwarf Galaxies
We present mid-infrared Spitzer Space Telescope observations of a complete
sample of star-forming dwarf galaxies selected from the KPNO International
Spectroscopic Survey. The galaxies span a wide range in mid-infrared
properties. Contrary to expectations, some of the galaxies emit strongly at 8
micron indicating the presence of hot dust and/or PAHs. The ratio of this
mid-infrared dust emission to the stellar emission is compared with the
galaxies' luminosity, star-formation rate, metallicity, and optical reddening.
We find that the strength of the 8.0 micron dust emission to the stellar
emission ratio is more strongly correlated with the star-formation rate than it
is with the metallicity or the optical reddening in these systems. Nonetheless,
there is a correlation between the 8.0 micron luminosity and metallicity. The
slope of this luminosity-metallicity correlation is shallower than
corresponding ones in the B-band and 3.6 micron. The precise nature of the 8.0
micron emission seen in these galaxies (i.e., PAH versus hot dust or some
combination of the two) will require future study, including deep mid-IR
spectroscopy.Comment: 14 pages, accepted Ap
On the micro mechanics of one-dimensional normal compression
Discrete-element modelling has been used to investigate the micro mechanics of one-dimensional compression. One-dimensional compression is modelled in three dimensions using an oedometer and a large number of particles, and without the use of agglomerates. The fracture of a particle is governed by the octahedral shear stress within the particle due to the multiple contacts and a Weibull distribution of strengths. Different fracture mechanisms are considered, and the influence of the distribution of fragments produced for each fracture on the global particle size distribution and the slope of the normal compression line is investigated. Using the discrete-element method, compression is related to the evolution of a fractal distribution of particles. The compression index is found to be solely a function of the strengths of the particles as a function of size
New measurements of the cosmic infrared background fluctuations in deep Spitzer/IRAC survey data and their cosmological implications
We extend previous measurements of cosmic infrared background (CIB)
fluctuations to ~ 1 deg using new data from the Spitzer Extended Deep Survey.
Two fields, with depths of ~12 hr/pixel over 3 epochs, are analyzed at 3.6 and
4.5 mic. Maps of the fields were assembled using a self-calibration method
uniquely suitable for probing faint diffuse backgrounds. Resolved sources were
removed from the maps to a magnitude limit of AB mag ~ 25, as indicated by the
level of the remaining shot noise. The maps were then Fourier-transformed and
their power spectra were evaluated. Instrumental noise was estimated from the
time-differenced data, and subtracting this isolates the spatial fluctuations
of the actual sky. The power spectra of the source-subtracted fields remain
identical (within the observational uncertainties) for the three epochs
indicating that zodiacal light contributes negligibly to the fluctuations.
Comparing to 8 mic power spectra shows that Galactic cirrus cannot account for
the fluctuations. The signal appears isotropically distributed on the sky as
required for an extragalactic origin. The CIB fluctuations continue to diverge
to > 10 times those of known galaxy populations on angular scales out to < 1
deg. The low shot noise levels remaining in the diffuse maps indicate that the
large scale fluctuations arise from the spatial clustering of faint sources
well below the confusion noise. The spatial spectrum of these fluctuations is
in reasonable agreement with an origin in populations clustered according to
the standard cosmological model (LCDM) at epochs coinciding with the first
stars era.Comment: ApJ, to be publishe
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