2,090 research outputs found
Tough Love In the District: Management Reform Under the District of Columbia Financial Responsibility and Management Assistance Act
Local variations in spatial synchrony of influenza epidemics
Background: Understanding the mechanism of influenza spread across multiple geographic scales is not complete. While the mechanism of dissemination across regions and states of the United States has been described, understanding the determinants of dissemination between counties has not been elucidated. The paucity of high resolution spatial-temporal influenza incidence data to evaluate disease structure is often not available. Methodology and Findings: We report on the underlying relationship between the spread of influenza and human movement between counties of one state. Significant synchrony in the timing of epidemics exists across the entire state and decay with distance (regional correlation = 62%). Synchrony as a function of population size display evidence of hierarchical spread with more synchronized epidemics occurring among the most populated counties. A gravity model describing movement between two populations is a stronger predictor of influenza spread than adult movement to and from workplaces suggesting that non-routine and leisure travel drive local epidemics. Conclusions: These findings highlight the complex nature of influenza spread across multiple geographic scales. © 2012 Stark et al
Rapid Quantitative Analysis of Toxic Norditerpenoid Alkaloids in Larkspur (Delphinium spp.) by Flow Injection - Electrospray Ionization – Mass Spectrometry
A rapid flow injection - electrospray ionization – mass spectrometry (FI-ESI-MS) method for the quantitative and qualitative analysis of norditerpenoid alkaloids in larkspur plants was developed. The FI-ESI-MS method was calibrated for alkaloid concentrations with larkspur plant samples against an existing Fourier transform infrared spectroscopy FTIR method. There was a strong correlation (r = 0.9926, r = 0.9891) between the FTIR and FI-ESI-MS methods. The relative standard deviation (RSD) for all measurements were ≤ 6.2 % except for the sample with the lowest concentration which was 19%. The sample throughput of the FI-ESI-MS method is much higher than the FTIR method due to simpler sample preparation, autosampling capabilities, and short analysis times. Finally, the FIA-ESI-MS can be used to qualitatively analyze the alkaloids in larkspur samples since the data allows the observation of all ions that comprise the alkaloid signals
Effects of Bulk and Surface Conductivity on the Performance of CdZnTe Pixel Detectors
We studied the effects of bulk and surface conductivity on the performance of
high-resistivity CdZnTe (CZT) pixel detectors with Pt contacts. We emphasize
the difference in mechanisms of the bulk and surface conductivity as indicated
by their different temperature behaviors. In addition, the existence of a thin
(10-100 A) oxide layer on the surface of CZT, formed during the fabrication
process, affects both bulk and surface leakage currents. We demonstrate that
the measured I-V dependencies of bulk current can be explained by considering
the CZT detector as a metal-semiconductor-metal system with two back-to-back
Schottky-barrier contacts. The high surface leakage current is apparently due
to the presence of a low-resistivity surface layer that has characteristics
which differ considerably from those of the bulk material. This surface layer
has a profound effect on the charge collection efficiency in detectors with
multi-contact geometry; some fraction of the electric field lines originated on
the cathode intersects the surface areas between the pixel contacts where the
charge produced by an ionizing particle gets trapped. To overcome this effect
we place a grid of thin electrodes between the pixel contacts; when the grid is
negatively biased, the strong electric field in the gaps between the pixels
forces the electrons landing on the surface to move toward the contacts,
preventing the charge loss. We have investigated these effects by using CZT
pixel detectors indium bump bonded to a custom-built VLSI readout chip
Differential Forms and Wave Equations for General Relativity
Recently, Choquet-Bruhat and York and Abrahams, Anderson, Choquet-Bruhat, and
York (AACY) have cast the 3+1 evolution equations of general relativity in
gauge-covariant and causal ``first-order symmetric hyperbolic form,'' thereby
cleanly separating physical from gauge degrees of freedom in the Cauchy problem
for general relativity. A key ingredient in their construction is a certain
wave equation which governs the light-speed propagation of the extrinsic
curvature tensor. Along a similar line, we construct a related wave equation
which, as the key equation in a system, describes vacuum general relativity.
Whereas the approach of AACY is based on tensor-index methods, the present
formulation is written solely in the language of differential forms. Our
approach starts with Sparling's tetrad-dependent differential forms, and our
wave equation governs the propagation of Sparling's 2-form, which in the
``time-gauge'' is built linearly from the ``extrinsic curvature 1-form.'' The
tensor-index version of our wave equation describes the propagation of (what is
essentially) the Arnowitt-Deser-Misner gravitational momentum.Comment: REVTeX, 26 pages, no figures, 1 macr
Clustering of solutions in the random satisfiability problem
Using elementary rigorous methods we prove the existence of a clustered phase
in the random -SAT problem, for . In this phase the solutions are
grouped into clusters which are far away from each other. The results are in
agreement with previous predictions of the cavity method and give a rigorous
confirmation to one of its main building blocks. It can be generalized to other
systems of both physical and computational interest.Comment: 4 pages, 1 figur
Implications of the problem orientated medical record (POMR) for research using electronic GP databases: a comparison of the Doctors Independent Network Database (DIN) and the General Practice Research Database (GPRD).
Background
The General Practice Research Database (GPRD) and Doctor's Independent Network Database (DIN), are large electronic primary care databases compiled in the UK during the 1990s. They provide a valuable resource for epidemiological and health services research. GPRD (based on VAMP) presents notes as a series of discrete episodes, whereas DIN is based on a system (MEDITEL) that used a Problem Orientated Medical Record (POMR) which links prescriptions to diagnostic problems. We have examined the implications for research of these different underlying philosophies.
Methods
Records of 40,183 children from 141 practices in DIN and 76,310 from 464 practices in GRPD who were followed to age 5 were used to compare the volume of recording of prescribing and diagnostic codes in the two databases. To assess the importance and additional value of the POMR within DIN, the appropriateness of diagnostic linking to skin emollient prescriptions was investigated.
Results
Variation between practices for both the number of days on which prescriptions were issued and diagnoses were recorded was marked in both databases. Mean number of "prescription days" during the first 5 years of life was similar in DIN (19.5) and in GPRD (19.8), but the average number of "diagnostic days" was lower in DIN (15.8) than in GPRD (22.9). Adjustment for linkage increased the average "diagnostic days" to 23.1 in DIN. 32.7% of emollient prescriptions in GPRD appeared with an eczema diagnosis on the same day compared to only 19.4% in DIN; however, 86.4% of prescriptions in DIN were linked to an earlier eczema diagnosis. More specifically 83% of emollient prescriptions appeared under a problem heading of eczema in the 121 practices that were using problem headings satisfactorily.
Conclusion
Prescribing records in DIN and GPRD are very similar, but the usage of diagnostic codes is more parsimonious in DIN because of its POMR structure. Period prevalence rates will be underestimated in DIN unless this structure is taken into account. The advantage of the POMR is that in 121 of 141 practices using problem headings as intended, most prescriptions can be linked to a problem heading providing a specific reason for their issue
Controllable Finite-Momenta Dynamical Quasicondensation in the Periodically Driven One-Dimensional Fermi-Hubbard Model
In the strongly interacting limit of the Hubbard model localized
double-occupancies form effective hard-core bosonic excitations, called a
doublons, which are long-lived due to energy conservation. Using time-dependent
density-matrix renormalisation group we investigate numerically the dynamics of
doublons arising from the sudden expansion of a spatially confined
band-insulating state in one spatial dimension. By analysing the occupation
scaling of the natural orbitals within the many-body state, we show that
doublons dynamically quasicondense at the band edges, consistent with the
spontaneous emergence of an eta-quasicondensate. Building on this, we study the
effect of periodically driving the system during the expansion. Floquet
analysis reveals that doublon-hopping and doublon-repulsion are strongly
renormalised by the drive, breaking the eta-SU(2) symmetry of the Hubbard
model. Numerical simulation of the driven expansion dynamics demonstrate that
the momentum in which doublons quasicondense can be controlled by the driving
amplitude. These results point to new pathways for engineering non-equilibrium
condensates in fermionic cold-atom experiments and are potentially relevant to
driven solid-state systems.Comment: 17 page
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