986 research outputs found
Low Frequency Gravitational Waves from Black Hole MACHO Binaries
Nakamura, Sasaki, Tanaka, and Thorne have recently estimated the initial
distribution of binary MACHOs in the galactic halo assuming that the MACHOs are
primordial half solar mass black holes, and considered their coalescence as a
possible source for ground-based interferometer gravitational wave detectors
such as LIGO. Evolving their binary distribution forward in time to the
present, the low-frequency (10^{-5} < f < 10^{-1} Hz) spectrum of gravitational
waves associated with such a population of compact binaries is calculated. The
resulting gravitational waves would form a strong stochastic background in
proposed space interferometers such as LISA and OMEGA. Low frequency
gravitational waves are likely to become a key tool for determining the
properties of binaries within the dark MACHO population.Comment: 8 pages + 2 ps figures; AASTe
Low Frequency Gravitational Waves from White Dwarf MACHO Binaries
The possibility that Galactic halo MACHOs are white dwarfs has recently
attracted much attention. Using the known properties of white dwarf binaries in
the Galactic disk as a model, we estimate the possible contribution of halo
white dwarf binaries to the low-frequency (10^{-5} Hz} < f < 10^{-1}Hz)
gravitational wave background. Assuming the fraction of white dwarfs in
binaries is the same in the halo as in the disk, we find the confusion
background from halo white dwarf binaries could be five times stronger than the
expected contribution from Galactic disk binaries, dominating the response of
the proposed space based interferometer LISA. Low-frequency gravitational wave
observations will be the key to discovering the nature of the dark MACHO binary
population.Comment: 9 pages, 1 figure, AASTe
Consensus approach to discrepancies arising from independent double reading of screening mammograms
Astrophysical Bounds on Global Strings
Global topological defects produce nonzero stress-energy throughout
spacetime, and as a result can have observable gravitational influence on
surrounding matter. Gravitational effects of global strings are used to place
bounds on their cosmic abundance. The minimum separation between global strings
is estimated by considering the defects' contribution to the cosmological
energy density. More rigorous constraints on the abundance of global strings
are constructed by examining the tidal forces such defects will have on
observable astrophysical systems. The small number of observed tidally
disrupted systems indicates there can be very few of these objects in the
observable universe.Comment: 14 pages, REVTe
Smoking patterns in Great Britain: the rise of cheap cigarette brands and roll your own (RYO) tobacco
This is the final version. Available from Oxford University Press via the DOI in this record.Background
In Britain, the tobacco industry segments cigarettes into four price categories—premium, mid-price, economy and ultra-low-price (ULP). Our previous work shows that tobacco companies have kept ULP prices stable in real terms. Roll your own (RYO) tobacco remains cheaper still.
Methods
Analysis of 2001–08 General Household Survey data to examine trends in use of these cheap products and, using logistic regression, the profile of users of these products.
Results
Among smokers, the proportion using cheap products (economy, ULP and RYO combined) increased significantly in almost all age groups and geographic areas. Increases were most marked in under 24 year olds, 76% of whom smoked cheap cigarettes by 2008. All cheap products were more commonly used in lower socio-economic groups. Men and younger smokers were more likely to smoke RYO while women smoked economy brands. Smokers outside London and the South East of England were more likely to smoke some form of cheap tobacco even once socio-economic differences were accounted for.
Conclusions
This paper demonstrates that cheap tobacco use is increasing among young and disadvantaged smokers compromising declines in population smoking prevalence. Thus, tobacco industry pricing appears to play a key role in explaining smoking patterns and inequalities in smoking
Renormalization of the charged scalar field in curved space
The DeWitt-Schwinger proper time point-splitting procedure is applied to a
massive complex scalar field with arbitrary curvature coupling interacting with
a classical electromagnetic field in a general curved spacetime. The scalar
field current is found to have a linear divergence. The presence of the
external background gauge field is found to modify the stress-energy tensor
results of Christensen for the neutral scalar field by adding terms of the form
to the logarithmic counterterms. These results are shown to be
expected from an analysis of the degree of divergence of scalar quantum
electrodynamics.Comment: 24 pages REVTe
Temperature Evolution Law of Imperfect Relativistic Fluids
The first-order general relativistic theory of a generic dissipative
(heat-conducting, viscous, particle-creating) fluid is rediscussed from a
unified covariant frame-independent point of view. By generalizing some
previous works in the literature, we derive a formula for the temperature
variation rate, which is valid both in Eckart's (particle) and in the
Landau-Lifshitz (energy) frames. Particular attention is paid to the case of
gravitational particle creation and its possible cross-effect with the bulk
viscosity mechanism.Comment: 14 pages, no figure, revte
Geochemical constraints on the origin of enigmatic cemented chalks, Norfolk, UK
Very hard cemented chalk stacks and crusts found locally in the upper part of the Cretaceous Chalk of north Norfolk, UK, are related to solution features. The solution features, mainly pipes and caves, formed after deposition of the overlying Middle Pleistocene Wroxham Crag, probably by routing of sub-glacial, or glacial, melt-waters derived from late Pleistocene glaciers. New geochemical (particularly stable isotope) data shows that cementation of the chalks, although related spatially to the solution features, was not caused by glacier-derived waters. The carbon isotope composition of the chalk cements is typically around -9.5‰, indicative of biologically active soils. Moreover, the oxygen isotope compositions of the cements, around -5‰, are incompatible with water d18O values much below -9 to -10‰ (which probably precludes isotopically negative glacier-derived water), as resulting palaeo-temperatures are below zero. Taken together, the isotope data suggest chalk cementation occurred under interglacial conditions similar to the present. Dissolved calcium carbonate for cementation came from dissolution of reworked chalk in overlying MIS 12 glacial tills
High-temporal Resolution Sediment Fingerprinting in the River Wensum Demonstration Test Catchment, UK: A Bayesian Approach
A high-temporal resolution fluvial sediment source apportionment model, set within an empirical Bayesian framework, is presented for the River Wensum Demonstration Test Catchment (DTC), UK. Direct X-ray fluorescence (XRF) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis of sediment covered filter papers were used in conjunction with ISCO automatic water samplers to monitor suspended particulate matter (SPM) geochemistry at high-temporal resolution throughout the progression of five heavy precipitation events during 2012-2013. Exploiting the spatial and temporal variation in four potential sediment source areas and SPM geochemistry respectively, we are able to apportion sediment contributions from eroding stream channel banks, arable topsoils, damaged road verges and agricultural field drains at 60-120 minute resolution. For all monitored precipitation episodes, pre- and post-event conditions are dominated by elevated SPM calcium concentrations that indicate major sediment inputs from carbonate-rich subsurface sources. Conversely, precipitation events coincide with an increase in concentrations of clay-associated elements and a consequent increase in predicted contributions from surface sources. Employing a Gibbs sampling Markov Chain Monte-Carlo mixing model procedure has enabled full characterisation of both spatial geochemical variability and instrument precision to quantify uncertainty around posterior distributions. All model source apportionment estimates correspond favourably with understanding of the regional geology, analysis of hysteresis behaviour, and visual observations of catchment processes. The results presented here demonstrate how to directly analyse SPM trapped on filter papers by spectroscopy to yield the high-temporal resolution source apportionment estimates required by catchment managers to help mitigate the deleterious effects of land-to-river sediment transfer
Algebraic approach to time-delay data analysis for LISA
Cancellation of laser frequency noise in interferometers is crucial for
attaining the requisite sensitivity of the triangular 3-spacecraft LISA
configuration. Raw laser noise is several orders of magnitude above the other
noises and thus it is essential to bring it down to the level of other noises
such as shot, acceleration, etc. Since it is impossible to maintain equal
distances between spacecrafts, laser noise cancellation must be achieved by
appropriately combining the six beams with appropriate time-delays. It has been
shown in several recent papers that such combinations are possible. In this
paper, we present a rigorous and systematic formalism based on algebraic
geometrical methods involving computational commutative algebra, which
generates in principle {\it all} the data combinations cancelling the laser
frequency noise. The relevant data combinations form the first module of
syzygies, as it is called in the literature of algebraic geometry. The module
is over a polynomial ring in three variables, the three variables corresponding
to the three time-delays around the LISA triangle. Specifically, we list
several sets of generators for the module whose linear combinations with
polynomial coefficients generate the entire module. We find that this formalism
can also be extended in a straight forward way to cancel Doppler shifts due to
optical bench motions. The two modules are infact isomorphic.
We use our formalism to obtain the transfer functions for the six beams and
for the generators. We specifically investigate monochromatic gravitational
wave sources in the LISA band and carry out the maximisiation over linear
combinations of the generators of the signal-to-noise ratios with the frequency
and source direction angles as parameters.Comment: 27 Pages, 6 figure
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