20,030 research outputs found
Characterising small solutions in delay differential equations through numerical approximations
This paper discusses how the existence of small solutions for delay differential equations can be predicted from the behaviour of the spectrum of the finite dimensional approximations.Manchester Centre for Computational Mathematic
Neutrinoless Double Beta Decay with SNO+
SNO+ will search for neutrinoless double beta decay by loading 780 tonnes of
linear alkylbenzene liquid scintillator with O(tonne) of neodymium. Using
natural Nd at 0.1% loading will provide 43.7 kg of 150Nd given its 5.6%
abundance and allow the experiment to reach a sensitivity to the effective
neutrino mass of 100-200 meV at 90% C.L in a 3 year run. The SNO+ detector has
ultra low backgrounds with 7000 tonnes of water shielding and self-shielding of
the scintillator. Distillation and several other purification techniques will
be used with the aim of achieving Borexino levels of backgrounds. The
experiment is fully funded and data taking with light-water will commence in
2012 with scintillator data following in 2013.Comment: 4 pages, 2 figures, prepared for TAUP 201
Free energy of formation of clusters of sulphuric acid and water molecules determined by guided disassembly
We evaluate the grand potential of a cluster of two molecular species,
equivalent to its free energy of formation from a binary vapour phase, using a
nonequilibrium molecular dynamics technique where guide particles, each
tethered to a molecule by a harmonic force, move apart to disassemble a cluster
into its components. The mechanical work performed in an ensemble of
trajectories is analysed using the Jarzynski equality to obtain a free energy
of disassembly, a contribution to the cluster grand potential. We study
clusters of sulphuric acid and water at 300 K, using a classical interaction
scheme, and contrast two modes of guided disassembly. In one, the cluster is
broken apart through simple pulling by the guide particles, but we find the
trajectories tend to be mechanically irreversible. In the second approach, the
guide motion and strength of tethering are modified in a way that prises the
cluster apart, a procedure that seems more reversible. We construct a surface
representing the cluster grand potential, and identify a critical cluster for
droplet nucleation under given vapour conditions. We compare the equilibrium
populations of clusters with calculations reported by Henschel et al. [J. Phys.
Chem. A 118, 2599 (2014)] based on optimised quantum chemical structures
Gravitons and Lightcone Fluctuations II: Correlation Functions
A model of a fluctuating lightcone due to a bath of gravitons is further
investigated. The flight times of photons between a source and a detector may
be either longer or shorter than the light propagation time in the background
classical spacetime, and will form a Gaussian distribution centered around the
classical flight time. However, a pair of photons emitted in rapid succession
will tend to have correlated flight times. We derive and discuss a correlation
function which describes this effect. This enables us to understand more fully
the operational significance of a fluctuating lightcone. Our results may be
combined with observational data on pulsar timing to place some constraints on
the quantum state of cosmological gravitons.Comment: 16 pages and two figures, uses eps
A quantum weak energy inequality for the Dirac field in two-dimensional flat spacetime
Fewster and Mistry have given an explicit, non-optimal quantum weak energy
inequality that constrains the smeared energy density of Dirac fields in
Minkowski spacetime. Here, their argument is adapted to the case of flat,
two-dimensional spacetime. The non-optimal bound thereby obtained has the same
order of magnitude, in the limit of zero mass, as the optimal bound of Vollick.
In contrast with Vollick's bound, the bound presented here holds for all
(non-negative) values of the field mass.Comment: Version published in Classical and Quantum Gravity. 7 pages, 1 figur
The unphysical nature of "Warp Drive"
We will apply the quantum inequality type restrictions to Alcubierre's warp
drive metric on a scale in which a local region of spacetime can be considered
``flat''. These are inequalities that restrict the magnitude and extent of the
negative energy which is needed to form the warp drive metric. From this we are
able to place limits on the parameters of the ``Warp Bubble''. It will be shown
that the bubble wall thickness is on the order of only a few hundred Planck
lengths. Then we will show that the total integrated energy density needed to
maintain the warp metric with such thin walls is physically unattainable.Comment: 11 pages, 3 figures, latex. This revision corrects a typographical
sign error in Eq. (3
Exponential Divergence and Long Time Relaxation in Chaotic Quantum Dynamics
Phase space representations of the dynamics of the quantal and classical cat
map are used to explore quantum--classical correspondence in a K-system: as
, the classical chaotic behavior is shown to emerge smoothly and
exactly. The quantum dynamics near the classical limit displays both
exponential separation of adjacent distributions and long time relaxation, two
characteristic features of classical chaotic motion.Comment: 10 pages, ReVTeX, to appear in Phys. Rev. Lett. 13 figures NOT
included. Available either as LARGE (uuencoded gzipped) postscript files or
hard-copies from [email protected]
Whole-blood thiopurine S-methyltransferase activity with genotype concordance: a new, simplified phenotyping assay.
BackgroundWe have developed a new thiopurine S-methyltransferase (TPMT) phenotyping method that measures TPMT activity in whole blood. To evaluate this assay, we compared it with conventional TPMT phenotyping, which uses a red blood cell (RBC) lysate and genotyping for analysis of common TPMT mutations.MethodsWhole-blood and RBC lysates were prepared from 402 patients' samples received for routine analysis. The TPMT activity of lysates was determined using 6-thioguanine as substrate with high-performance liquid chromatographic (HPLC) analysis and fluorimetric detection. DNA was extracted from buffy coats using phenol-chloroform extraction. A multiplex amplification refractory mutation system (ARMS) strategy was used to screen for the common TPMT mutations TPMT*2 and TPMT*3 (TPMT*3A, TPMT*3C and TPMT*3D).ResultsTPMT activities were higher in the whole-blood (mean TPMT activity 51 nmol 6-MTG/gHb/h) compared with the RBC lysate (37 nmol 6-MTG/gHb/h). Overall, concordance with TPMT genotypic analysis was 97% for both the new whole-blood and standard RBC lysate methods. Between low TPMT activity and heterozygotes, both phenotypic methods gave a concordance of 79%.ConclusionUsing multiplex ARMS testing for TPMT*2 and 3*C mutations to define the cut-off between low and normal TPMT activity, we have demonstrated that the new whole-blood TPMT phenotyping method performs as well as the conventional RBC lysate assay. This new method overcomes the need to prepare a RBC lysate, a process which is time consuming and increases analytical variation. The resulting assay is better suited to a regional or national TPMT phenotyping service
Classical Scalar Fields and the Generalized Second Law
It has been shown that classical non-minimally coupled scalar fields can
violate all of the standard energy conditions in general relativity. Violations
of the null and averaged null energy conditions obtainable with such fields
have been suggested as possible exotic matter candidates required for the
maintenance of traversable wormholes. In this paper, we explore the possibility
that if such fields exist, they might be used to produce large negative energy
fluxes and macroscopic violations of the generalized second law (GSL) of
thermodynamics. We find that it appears to be very easy to produce large
magnitude negative energy fluxes in flat spacetime. However we also find,
somewhat surprisingly, that these same types of fluxes injected into a black
hole do {\it not} produce violations of the GSL. This is true even in cases
where the flux results in a decrease in the area of the horizon. We demonstrate
that two effects are responsible for the rescue of the GSL: the acausal
behavior of the horizon and the modification of the usual black hole entropy
formula by an additional term which depends on the scalar field.Comment: 25 pages, 2 figures; paper substantially rewritten, major changes in
the conclusion
Quantum Inequalities for the Electromagnetic Field
A quantum inequality for the quantized electromagnetic field is developed for
observers in static curved spacetimes. The quantum inequality derived is a
generalized expression given by a mode function expansion of the four-vector
potential, and the sampling function used to weight the energy integrals is
left arbitrary up to the constraints that it be a positive, continuous function
of unit area and that it decays at infinity. Examples of the quantum inequality
are developed for Minkowski spacetime, Rindler spacetime and the Einstein
closed universe.Comment: 19 pages, 1 table and 1 figure. RevTex styl
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