873 research outputs found
Chaos assisted instanton tunneling in one dimensional perturbed periodic potential
For the system with one-dimensional spatially periodic potential we
demonstrate that small periodic in time perturbation results in appearance of
chaotic instanton solutions. We estimate parameter of local instability, width
of stochastic layer and correlator for perturbed instanton solutions.
Application of the instanton technique enables to calculate the amplitude of
the tunneling, the form of the spectrum and the lower bound for width of the
ground quasienergy zone
Momentum flux density, kinetic energy density and their fluctuations for one-dimensional confined gases of non-interacting fermions
We present a Green's function method for the evaluation of the particle
density profile and of the higher moments of the one-body density matrix in a
mesoscopic system of N Fermi particles moving independently in a linear
potential. The usefulness of the method is illustrated by applications to a
Fermi gas confined in a harmonic potential well, for which we evaluate the
momentum flux and kinetic energy densities as well as their quantal mean-square
fluctuations. We also study some properties of the kinetic energy functional
E_{kin}[n(x)] in the same system. Whereas a local approximation to the kinetic
energy density yields a multi-valued function, an exact single-valued
relationship between the density derivative of E_{kin}[n(x)] and the particle
density n(x) is demonstrated and evaluated for various values of the number of
particles in the system.Comment: 10 pages, 5 figure
Effects of old landfills on groundwater quality. Phase 2, investigation of the Thriplow landfill 1996–1997
Disused sand and gravel excavations overlying the major Chalk aquifer at Thriplow in Cambridgeshire have
been filled with domestic waste in two phases. One area (Phase 1) was filled between 1957–77 with little compaction
of the refuse and was left uncapped, while Phase 2 was deposited between 1981–87 and capped with
clay. Aerial photography and surface resistivity surveys indicate that the site geometry is complex, with several
phases of landfilling into excavations of differing depths. Drilling through the waste indicates that leachate production
and waste stabilisation proceed at different rates in capped and uncapped landfills. Analysis of leachate
obtained by centrifugation or squeezing appears to give more insight into the pollution potential than do leach
tests with distilled water. The Biological Methane Potential (BMP) of the waste appears to be related to the
quantity of decomposable material but the chemical oxygen demand (COD) values are distorted by the presence
of reduced metals. Too few boreholes have been drilled to define the leachate source in terms of its spatial distribution
and little is known of how its composition has changed with time. However, hydraulic conductivity measurements
on the landfill caps suggest that it is sufficiently permeable for all rainfall to potentially infiltrate the
waste.
Boreholes outside the landfill penetrate the Upper and Lower Chalk, and identify the Melbourn Rock and underlying
Plenus Marls at the junction of the two formations about 20 m below ground level (bgl). Surface resistivity
surveys using the BGS RESCAN system, confirm aerial photographs of the extent of the landfill and also
suggest that leachate has migrated beyond the base of the landfill. Evidence of leachate migration in pre-existing
screened boreholes completed above and below the Plenus Marls suggests that leachate is flowing above the
Plenus Marls. Hydraulic head measurements whilst drilling a borehole to the base of the lower Chalk approx. 70
m bgl revealed the potential for upward groundwater flow through the Plenus Marls. Thus, previously-drilled
boreholes penetrating the Plenus Marls are expected to recharge upwards into the shallow aquifer above the
Plenus Marls diluting any leachate in the upper aquifer and distorting the flow regime. Several of these boreholes
have subsequently been modified to stem the flow across the Plenus Marls.
One borehole down-gradient to the west of the site revealed a large thickness of drift composed of both sand and
clay rich material. This suggests the existence of a buried channel, the hydrogeological significance of which has
yet to be assessed.
Groundwater chemistry appears to be influenced by three major factors. (a) the landfill leachate (b) the composition
of shallow groundwater in the top 10 m of the Chalk, and (c) the composition of water from the Lower
Chalk. Limited groundwater monitoring data appear to display a cyclic variation in chloride concentration. The
origin for this is not clear but it may correlate with cyclic variations in groundwater levels when the water table
rises into the waste. Cyclic flushing of the landfill may release leachate into the aquifer giving rise to pulses of
chloride. Alternatively changes in chloride may arise by the changing direction of groundwater flow which as yet
has not been assessed.
A conceptual hydrogeological model in which flow is limited to above the Plenus Marls has been used to
develop a more appropriate groundwater flow and solute transport model. However, the model lacks data on
aquifer properties, on contaminant inputs concentrations, fluxes and spatial variations, and there is a paucity of
monitoring data for calibration. Nonetheless preliminary transport modelling using an equivalent porous medium
approach shows that an effective porosity of about 5% best fits the regional data. Since this is much less than the
total porosity of about 40% for the Chalk, it would appear that only part of the Chalk is available for flow but
that matrix diffusion could play an important role in leachate attenuation. Discrete fracture modelling using the
FRACTRAN code has allowed some scoping to be made of the hydraulic properties of the aquifer by comparison
with chloride hydrographs, but these again need to be better conditioned by in-situ measurement of fracture
distributions and transmissivities.
A number of additional activities are required to improve the understanding of flow and contaminant transport at
the site. These include better spatial definition of the waste distribution, improved data on the hydraulic properties
of the Chalk aquifer, and the use of automatic monitoring to record temporal changes in groundwater chemistry
and groundwater levels
Kaon-Nucleon Scattering Amplitudes and Z-Enhancements from Quark Born Diagrams
We derive closed form kaon-nucleon scattering amplitudes using the ``quark
Born diagram" formalism, which describes the scattering as a single interaction
(here the OGE spin-spin term) followed by quark line rearrangement. The low
energy I=0 and I=1 S-wave KN phase shifts are in reasonably good agreement with
experiment given conventional quark model parameters. For Gev
however the I=1 elastic phase shift is larger than predicted by Gaussian
wavefunctions, and we suggest possible reasons for this discrepancy. Equivalent
low energy KN potentials for S-wave scattering are also derived. Finally we
consider OGE forces in the related channels K, KN and K,
and determine which have attractive interactions and might therefore exhibit
strong threshold enhancements or ``Z-molecule" meson-baryon bound states.
We find that the minimum-spin, minimum-isospin channels and two additional
K channels are most conducive to the formation of bound states.
Related interesting topics for future experimental and theoretical studies of
KN interactions are also discussed.Comment: 34 pages, figures available from the authors, revte
Hamiltonian Study of Improved Lattice Gauge Theory in Three Dimensions
A comprehensive analysis of the Symanzik improved anisotropic
three-dimensional U(1) lattice gauge theory in the Hamiltonian limit is made.
Monte Carlo techniques are used to obtain numerical results for the static
potential, ratio of the renormalized and bare anisotropies, the string tension,
lowest glueball masses and the mass ratio. Evidence that rotational symmetry is
established more accurately for the Symanzik improved anisotropic action is
presented. The discretization errors in the static potential and the
renormalization of the bare anisotropy are found to be only a few percent
compared to errors of about 20-25% for the unimproved gauge action. Evidence of
scaling in the string tension, antisymmetric mass gap and the mass ratio is
observed in the weak coupling region and the behaviour is tested against
analytic and numerical results obtained in various other Hamiltonian studies of
the theory. We find that more accurate determination of the scaling
coefficients of the string tension and the antisymmetric mass gap has been
achieved, and the agreement with various other Hamiltonian studies of the
theory is excellent. The improved action is found to give faster convergence to
the continuum limit. Very clear evidence is obtained that in the continuum
limit the glueball ratio approaches exactly 2, as expected in a
theory of free, massive bosons.Comment: 13 pages, 15 figures, submitted to Phys. Rev.
Dietary intake and risk of non-severe hypoglycemia in adolescents with type 1 diabetes
Aims To determine the association between dietary intake and risk of non-severe hypoglycemia in adolescents with type 1 diabetes. Methods Type 1 adolescents from a randomized trial wore a blinded continuous glucose monitoring (CGM) system at baseline for one week in free-living conditions. Dietary intake was calculated as the average from two 24-h dietary recalls. Non-severe hypoglycemia was defined as having blood glucose < 70 mg/dL for ≥ 10 min but not requiring external assistance, categorized as daytime and nocturnal (11 PM–7AM). Data were analyzed using logistic regression models. Results Among 98 participants with 14,277 h of CGM data, 70 had daytime hypoglycemia, 66 had nocturnal hypoglycemia, 55 had both, and 17 had neither. Soluble fiber and protein intake were positively associated with both daytime and nocturnal hypoglycemia. Glycemic index, monounsaturated fat, and polyunsaturated fat were negatively associated with daytime hypoglycemia only. Adjusting for total daily insulin dose per kilogram eliminated all associations. Conclusions Dietary intake was differentially associated with daytime and nocturnal hypoglycemia. Over 80% of type 1 adolescents had hypoglycemia in a week, which may be attributed to the mismatch between optimal insulin dose needed for each meal and actually delivered insulin dose without considering quality of carbohydrate and nutrients beyond carbohydrate
Cardiac metastases
We report a case of esophageal cancer with symptomatic metastases to the heart; the patient was treated with short-course radiotherapy with good symptomatic relief. We reviewed the current literature regarding the epidemiology, clinical presentation, diagnostic tools, treatment modalities, and the prognosis of cardiac metastases. In this report we summarize the most recent autopsy studies (published between 1975 and 2007), in which we found an autopsy incidence of cardiac metastases of 2.3% among the general population, while the incidence among autopsies of cancer patients was 7.1%. Therefore, we share the opinion with others that there has been an increase in the incidence of cardiac metastases among cancer patients diagnosed after 1970, in comparison with the reported incidences in older series before 1970 (7.1% vs 3.8%; Kruskal-Wallis rank test; P = 0.039). Special attention was given to the role of radiotherapy in the management of cardiac metastases
Dissecting the enterococcal polysaccharide antigen (EPA) structure to explore innate immune evasion and phage specificity
Streptococci, Lactococci and Enterococci all produce L-rhamnose-containing cell wall polysaccharides which define Lancefield serotypes and represent promising candidates for the design of glycoconjugate vaccines. The L-rhamnose containing Enterococcal Polysaccharide Antigen (EPA), produced by the opportunistic pathogen Enterococcus faecalis, plays a critical role in normal growth, division, biofilm formation, antimicrobial resistance, phage susceptibility, and innate immune evasion. Despite the critical role of this polymer in E. faecalis physiology and host-pathogen interactions, little information is available on its structure and biosynthesis. Here, using an NMR approach, we elucidate the structure of EPA and propose a model for biosynthesis. We report the structure of the EPA-peptidoglycan linkage unit and reveal an unprecedented complexity of the EPA rhamnose backbone and decoration subunits. Finally, we explore the impact of several EPA structural modifications on innate immune evasion and recognition by bacteriophages. This work represents a first step towards the functional characterisation of EPA and the rational design of therapeutic strategies against a group of important pathogens
Measurement of the B0-anti-B0-Oscillation Frequency with Inclusive Dilepton Events
The - oscillation frequency has been measured with a sample of
23 million \B\bar B pairs collected with the BABAR detector at the PEP-II
asymmetric B Factory at SLAC. In this sample, we select events in which both B
mesons decay semileptonically and use the charge of the leptons to identify the
flavor of each B meson. A simultaneous fit to the decay time difference
distributions for opposite- and same-sign dilepton events gives ps.Comment: 7 pages, 1 figure, submitted to Physical Review Letter
A measurement of the tau mass and the first CPT test with tau leptons
We measure the mass of the tau lepton to be 1775.1+-1.6(stat)+-1.0(syst.) MeV
using tau pairs from Z0 decays. To test CPT invariance we compare the masses of
the positively and negatively charged tau leptons. The relative mass difference
is found to be smaller than 3.0 10^-3 at the 90% confidence level.Comment: 10 pages, 4 figures, Submitted to Phys. Letts.
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