4,311 research outputs found
Predictive Crime Mapping: Arbitrary Grids or Street Networks?
OBJECTIVES: Decades of empirical research demonstrate that crime is concentrated at a range of spatial scales, including street segments. Further, the degree of clustering at particular geographic units remains noticeably stable and consistent; a finding that Weisburd (Criminology 53:133–157, 2015) has recently termed the ‘law of crime concentration at places’. Such findings suggest that the future locations of crime should—to some extent at least—be predictable. To date, methods of forecasting where crime is most likely to next occur have focused either on area-level or grid-based predictions. No studies of which we are aware have developed and tested the accuracy of methods for predicting the future risk of crime at the street segment level. This is surprising given that it is at this level of place that many crimes are committed and policing resources are deployed. METHODS: Using data for property crimes for a large UK metropolitan police force area, we introduce and calibrate a network-based version of prospective crime mapping [e.g. Bowers et al. (Br J Criminol 44:641–658, 2004)], and compare its performance against grid-based alternatives. We also examine how measures of predictive accuracy can be translated to the network context, and show how differences in performance between the two cases can be quantified and tested. RESULTS: Findings demonstrate that the calibrated network-based model substantially outperforms a grid-based alternative in terms of predictive accuracy, with, for example, approximately 20 % more crime identified at a coverage level of 5 %. The improvement in accuracy is highly statistically significant at all coverage levels tested (from 1 to 10 %). CONCLUSIONS: This study suggests that, for property crime at least, network-based methods of crime forecasting are likely to outperform grid-based alternatives, and hence should be used in operational policing. More sophisticated variations of the model tested are possible and should be developed and tested in future research
Characterizing upward lightning with and without a terrestrial gamma-ray flash
We compare two observations of gamma-rays before, during, and after lightning
flashes initiated by upward leaders from a tower during low-altitude winter
thunderstorms on the western coast of Honshu, Japan. While the two leaders
appear similar, one produced a terrestrial gamma-ray flash (TGF) so bright that
it paralyzed the gamma-ray detectors while it was occurring, and could be
observed only via the weaker flux of neutrons created in its wake, while the
other produced no detectable TGF gamma-rays at all. The ratio between the
indirectly derived gamma-ray fluence for the TGF and the 95% confidence
gamma-ray upper limit for the gamma-ray quiet flash is a factor of
. With the only two observations of this type providing such
dramatically different results -- a TGF probably as bright as those seen from
space and a powerful upper limit -- we recognize that weak, sub-luminous TGFs
in this situation are probably not common, and we quantify this conclusion.
While the gamma-ray quiet flash appeared to have a faster leader and more
powerful initial continuous current pulse than the flash that produced a TGF,
the TGF-producing flash occurred during a weak gamma-ray "glow", while the
gamma-ray quiet flash did not, implying a higher electric field aloft when the
TGF was produced. We suggest that the field in the high-field region approached
by a leader may be more important for whether a TGF is produced than the
characteristics of the leader itself.Comment: 21 pages, 6 figures, accepted for publication by the Journal of
Geophysical Research - Atmosphere
Cruise: YR130612, Stations: S5127- S5138, York River Estuary and Pamunkey River, Virginia, MUDBED Longitudinal Profiler Station Survey bracketing a Flood Tide.
Dataset consists of profile and water column burst Data collected as part of a longitudinal profiler station survey at approximately 20 km, 25 km, 35 km, 45 km, 56 km and 62 km upriver from the mouth of the York River Estuary
Termination of Electron Acceleration in Thundercloud by Intra/Inter-cloud Discharge
An on-ground observation program for high energy atmospheric phenomena in
winter thunderstorms along Japan Sea has been performed via measurements of
gamma-ray radiation, atmospheric electric field and low-frequency radio band.
On February 11, 2017, the radiation detectors recorded gamma-ray emission
lasting for 75 sec. The gamma-ray spectrum extended up to 20 MeV and was
reproduced by a cutoff power-law model with a photon index of
, being consistent with a Bremsstrahlung radiation from a
thundercloud (as known as a gamma-ray glow and a thunderstorm ground
enhancement). Then the gamma-ray glow was abruptly terminated with a nearby
lightning discharge. The low-frequency radio monitors, installed 50 km
away from the gamma-ray observation site recorded leader development of an
intra/inter-cloud discharge spreading over 60 km area with a 300 ms
duration. The timing of the gamma-ray termination coincided with the moment
when the leader development of the intra/inter-cloud discharge passed 0.7 km
horizontally away from the radiation monitors. The intra/inter-cloud discharge
started 15 km away from the gamma-ray observation site. Therefore, the
glow was terminated by the leader development, while it did not trigger the
lightning discharge in the present case.Comment: 12 pages, 4 figures, accepted for publication in Geophysical Research
Letter
Raman scattering from fractals. Simulation on large structures by the method of moments
We have employed the method of spectral moments to study the density of
vibrational states and the Raman coupling coefficient of large 2- and 3-
dimensional percolators at threshold and at higher concentration. We first
discuss the over-and under-flow problems of the procedure which arise when
-like in the present case- it is necessary to calculate a few thousand moments.
Then we report on the numerical results; these show that different scattering
mechanisms, all {\it a priori} equally probable in real systems, produce
largely different coupling coefficients with different frequency dependence.
Our results are compared with existing scaling theories of Raman scattering.
The situation that emerges is complex; on the one hand, there is indication
that the existing theory is not satisfactory; on the other hand, the
simulations above threshold show that in this case the coupling coefficients
have very little resemblance, if any, with the same quantities at threshold.Comment: 26 pages, RevTex, 8 figures available on reques
P02.123. The anti-diabetic and cholesterol-lowering effects of common and cassia cinnamon (Cinnamomum verum and C. aromaticum): a randomized controlled trial
This paper accompanies a poster presentation on the anti-diabetic and cholesterol-lowering effects of common and cassia cinnamon (Cinnamomum verum and C. aromaticum)
Casimir Energy of a Spherical Shell
The Casimir energy for a conducting spherical shell of radius is computed
using a direct mode summation approach. An essential ingredient is the
implementation of a recently proposed method based on Cauchy's theorem for an
evaluation of the eigenfrequencies of the system. It is shown, however, that
this earlier calculation uses an improper set of modes to describe the waves
exterior to the sphere. Upon making the necessary corrections and taking care
to ensure that no mathematically ill-defined expressions occur, the technique
is shown to leave numerical results unaltered while avoiding a longstanding
criticism raised against earlier calculations of the Casimir energy.Comment: LaTeX, 14 pages, 1 figur
The D/H Ratio in Interstellar Gas Towards G191-B2B
We reinvestigate the question of spatial variation of the local D/H
abundance, using both archival GHRS spectra, and new echelle spectra of
G191-B2B obtained with the Space Telescope Imaging Spectrograph (STIS) aboard
HST. Our analysis uses stratified line-blanketed non-LTE model atmosphere
calculations to determine the shape of the intrinsic WD Lyman-alpha profile and
estimate the WD photospheric contamination of the interstellar lines. Although
three velocity components were reported previously towards G191-B2B, we detect
only two velocity components. The first component is at V(hel) ~ 8.6 km/s and
the second at V(hel) ~ 19.3 km/s, which we identify with the Local Interstellar
Cloud (LIC). From the STIS data we derive D/H = 1.60(+0.39,-0.27)X10^-5 for the
LIC component, and D/H > 1.26X10^-5 for the 8.6 km/s component (uncertainties
denote 2-sigma or 95% confidence limits). The STIS data provide no evidence for
local or component-to-component variation in the D/H ratio. Despite using two
velocity components for the profile fitting and using a more physically
realistic WD Lyman-alpha profile for G191-B2B, our re-analysis of the GHRS data
indicates a component-to-component variation as well as a variation of the D/H
ratio in the LISM, neither of which are supported by the newer STIS data. We
believe the most probable cause for this difference is the characterization of
the background due to scattered light in the GHRS and STIS spectrographs. The
two-dimensional MAMA detectors of STIS measure both the spatial and wavelength
dependences of scattered light, allowing more accurate scattered light
corrections than was possible with GHRS.Comment: Accepted for publication in Astrophysical Journal Letters. 10 pages +
3 figures. (Abstract is abridged.
Water masses constrain the distribution of deep-sea sponges in the North Atlantic Ocean and Nordic Seas
Water masses are bodies of water with distinctive physical and biogeochemical properties. They impart vertical structure to the deep ocean, participate in circulation, and can be traced over great distances, potentially influencing the distributions of deep-sea fauna. The classic potential temperature-salinity (theta-s) diagram was used to investigate deep-sea sponge (demosponge genus Geodia) association with water masses over the North Atlantic Ocean and Nordic Seas. A novel analysis was conducted, based on sampling the curvature of climatological mean theta-s curves at sponge locations. Sponges were particularly associated with turning points in the theta-s curves, indicative of intermediate and deep water masses. Arctic geodiid species (G. hentscheli and G. parva) were associated with Arctic intermediate and deep waters in the Nordic Seas, and with dense overflows into the northern North Atlantic. Boreal species (G. atlantica, G. barretti, G. macandrewii, and G. phlegraei) were associated with upper and intermediate water masses in the Northeast Atlantic and with upper, Atlantic-derived waters in the Nordic Seas. Taken together with distributional patterns, a link with thermohaline currents was also inferred. We conclude that water masses and major current pathways structure the distribution of a key deep-sea benthic faunal group on an ocean basin scale. This is most likely because of a combination of the physical constraints they place on the dispersal of early life-history stages, ecophysiological adaptation (evolved tolerances) to specific water masses, and the benefits to filter-feeders of certain phenomena linked to water column structure (e.g. nepheloid layers, internal waves/ tides, density-driven currents)
- …