465 research outputs found
Perturbative corrections to the Gutzwiller mean-field solution of the Mott-Hubbard model
We study the Mott-insulator transition of bosonic atoms in optical lattices.
Using perturbation theory, we analyze the deviations from the mean-field
Gutzwiller ansatz, which become appreciable for intermediate values of the
ratio between hopping amplitude and interaction energy. We discuss corrections
to number fluctuations, order parameter, and compressibility. In particular, we
improve the description of the short-range correlations in the one-particle
density matrix. These corrections are important for experimentally observed
expansion patterns, both for bulk lattices and in a confining trap potential.Comment: 10 pages, 10 figue
Circulatory responses to hypoxia in experimental myocardial infarction
Hypoxia affecting circulatory responses in dogs, such as cardiac output, left ventricular dp/dt, and stroke volum
Dynamic model of a spherical robot from first principles
Department Head: Allan Thomson Kirkpatrick.2010 Summer.Includes bibliographical references (pages 77-78).A prototype of a pendulum driven spherical robot has been developed during previous research and shown to exhibit unique dynamic behavior. Starting from first principles, a mathematical model for this spherical robot rolling on flat ground was developed in order to determine if this unique behavior was inherent to spherical robots in general or simply peculiar to this prototype. The complete equations of motion were found using Lagrangian methods, and numerically integrated using computer tools. A 3D simulation program was written to animate the results of integrating the equations. The dynamics apparent in the simulations were found to closely match the observed dynamics of the physical prototype
The AdHOC study of older adults’ adherence to medication in 11 countries
BACKGROUND: Compared with the resources expended developing, evaluating
and making clinical decisions about prescribing medication, we know little about
what determines whether people take it. Older adults are prescribed more
medication than any other group. Poor adherence is a common reason for nonresponse
to medication.
OBJECTIVES: To investigate cross-nationally the impact of demographic,
psychiatric (including cognitive), physical health, behavioural and medication factors
on adherence to medication in older adults.
METHODS: Researchers interviewed 3881 people over 65 who receive home
care services using a structured interview at participants’ places of residence in
eleven countries. The main outcome measure was the percentage participants not
adherent to medication.
RESULTS: 12.5% (n= 456) of people reported they were not fully adherent to
medication. Non-adherence was predicted by problem drinking (OR=3.6), not having
a doctor review medication (OR=3.3), dementia (OR=1.4 for every one point
increase in impairment), good physical health (OR=1.2), resisting care (OR=2.1)
being married (OR=2.3) and living in the Czech Republic (OR=4.7) or Germany
(OR=1.4).
CONCLUSION: People, who screen positive for problem drinking and with
dementia, often undiagnosed are less likely to adhere to medication. Therefore
doctors should consider dementia and problem drinking when prescribing for older
adults. Interventions to improve adherence in older adults might be more effective if
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targeted at these groups. It is possible that medication review enhances adherence,
by improving the patient-doctor relationship, or by emphasising the relevance of
medications
Design of a spherical vehicle with flywheel momentum storage for high torque capabilities
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references (leaf 26).A novel method for supplementing the propulsion of a spherical ground vehicle was conceived and developed. The addition of angular momentum storage via counter-rotating control moment gyroscopes is proposed in order to overcome significant limitations in the performance of earlier designs of spherical vehicles. Analysis and design of a fully functioning spherical vehicle incorporating such a mechanism is completed and indicates significantly increased torque capabilities for ascending steep inclines and stairs. A fully functional prototype is built and testing is ongoing to verify its capabilities.by Gregory C. Schroll.S.B
Role of type 1 and type 3 fimbriae in Klebsiella pneumoniae biofilm formation
<p>Abstract</p> <p>Background</p> <p><it>Klebsiella pneumoniae </it>is an important gram-negative opportunistic pathogen causing primarily urinary tract infections, respiratory infections, and bacteraemia. The ability of bacteria to form biofilms on medical devices, e.g. catheters, has a major role in development of many nosocomial infections. Most clinical <it>K. pneumoniae </it>isolates express two types of fimbrial adhesins, type 1 fimbriae and type 3 fimbriae. In this study, we characterized the role of type 1 and type 3 fimbriae in <it>K. pneumoniae </it>biofilm formation.</p> <p>Results</p> <p>Isogenic fimbriae mutants of the clinical <it>K. pneumoniae </it>isolate C3091 were constructed, and their ability to form biofilm was investigated in a flow cell system by confocal scanning laser microscopy. The wild type strain was found to form characteristic biofilm and development of <it>K. pneumoniae </it>biofilm occurred primarily by clonal growth, not by recruitment of planktonic cells. Type 1 fimbriae did not influence biofilm formation and the expression of type 1 fimbriae was found to be down-regulated in biofilm forming cells. In contrast, expression of type 3 fimbriae was found to strongly promote biofilm formation.</p> <p>Conclusion</p> <p>By use of well defined isogenic mutants we found that type 3 fimbriae, but not type 1 fimbriae, strongly promote biofilm formation in <it>K. pneumoniae </it>C3091. As the vast majority of clinical <it>K. pneumoniae </it>isolates express type 3 fimbriae, this fimbrial adhesin may play a significant role in development of catheter associated <it>K. pneumoniae </it>infections.</p
Stable Carbon Isotope Signature of Methane Released From Phytoplankton
Unidad de excelencia MarÃa de Maeztu CEX2019-000940-MAquatic ecosystems play an important role in global methane cycling and many field studies have reported methane supersaturation in the oxic surface mixed layer (SML) of the ocean and in the epilimnion of lakes. The origin of methane formed under oxic condition is hotly debated and several pathways have recently been offered to explain the "methane paradox." In this context, stable isotope measurements have been applied to constrain methane sources in supersaturated oxygenated waters. Here we present stable carbon isotope signatures for six widespread marine phytoplankton species, three haptophyte algae and three cyanobacteria, incubated under laboratory conditions. The observed isotopic patterns implicate that methane formed by phytoplankton might be clearly distinguished from methane produced by methanogenic archaea. Comparing results from phytoplankton experiments with isotopic data from field measurements, suggests that algal and cyanobacterial populations may contribute substantially to methane formationobserved in the SML of oceans and lakes
Nanoscale atomic waveguides with suspended carbon nanotubes
We propose an experimentally viable setup for the realization of
one-dimensional ultracold atom gases in a nanoscale magnetic waveguide formed
by single doubly-clamped suspended carbon nanotubes. We show that all common
decoherence and atom loss mechanisms are small guaranteeing a stable operation
of the trap. Since the extremely large current densities in carbon nanotubes
are spatially homogeneous, our proposed architecture allows to overcome the
problem of fragmentation of the atom cloud. Adding a second nanowire allows to
create a double-well potential with a moderate tunneling barrier which is
desired for tunneling and interference experiments with the advantage of
tunneling distances being in the nanometer regime.Comment: Replaced with the published version, 7 pages, 3 figure
Impact of a Viscous Liquid Drop
We simulate the impact of a viscous liquid drop onto a smooth dry solid
surface. As in experiments, when ambient air effects are negligible, impact
flattens the falling drop without producing a splash. The no-slip boundary
condition at the wall produces a boundary layer inside the liquid. Later, the
flattening surface of the drop traces out the boundary layer. As a result, the
eventual shape of the drop is a "pancake" of uniform thickness except at the
rim, where surface tension effects are significant. The thickness of the
pancake is simply the height where the drop surface first collides with the
boundary layer.Comment: 5 pages, 3 figures, submitted to Physical Review Letter
Research techniques made simple: workflow for searching databases to reduce evidence selection bias in systematic reviews
Clinical trials and basic science studies without statistically significant results are less likely to be published than studies with statistically significant results. Systematic reviews and meta-analyses that omit unpublished data are at high risk of distorted conclusions. Here, we describe methods to search beyond bibliographical databases to reduce evidence selection bias in systematic reviews. Unpublished studies may be identified by searching conference proceedings. Moreover, clinical trial registries—databases of planned and ongoing trials—and regulatory agency websites such as the European Medicine Agency (EMA) and the United States Food and Drug Administration (FDA) may provide summaries of efficacy and safety data. Primary and secondary outcomes are prespecified in trial registries, thus allowing the assessment of outcome reporting bias by comparison with the trial report. The sources of trial data and documents are still evolving, with ongoing initiatives promoting broader access to clinical study reports and individual patient data. There is currently no established methodology to ensure that the multiple sources of information are incorporated. Nonetheless, systematic reviews must adapt to these improvements and cover the new sources in their search strategies
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