1,197 research outputs found
Risk of Tooth Loss After Cigarette Smoking Cessation
INTRODUCTION. Little is known about the effect of cigarette smoking cessation on risk of tooth loss. We examined how risk of tooth loss changed with longer periods of smoking abstinence in a prospective study of oral health in men. METHODS. Research subjects were 789 men who participated in the Veterans Administration Dental Longitudinal Study from 1968 to 2004. Tooth status and smoking status were determined at examinations performed every 3 years, for a maximum follow-up time of 35 years. Risk of tooth loss subsequent to smoking cessation was assessed sequentially at 1-year intervals with multivariate proportional hazards regression models. Men who never smoked cigarettes, cigars, or pipes formed the reference group. Hazard ratios were adjusted for age, education, total pack-years of cigarette exposure, frequency of brushing, and use of floss. RESULTS. The hazard ratio for tooth loss was 2.1 (95% confidence interval [CI], 1.5-3.1) among men who smoked cigarettes during all or part of follow-up. Risk of tooth loss among men who quit smoking declined as time after smoking cessation increased, from 2.0 (95% CI, 1.4-2.9) after 1 year of abstinence to 1.0 (95% CI, 0.5-2.2) after 15 years of abstinence. The risk remained significantly elevated for the first 9 years of abstinence but eventually dropped to the level of men who never smoked after 13 or more years. CONCLUSION. These results indicate that smoking cessation is beneficial for tooth retention, but long-term abstinence is required to reduce the risk to the level of people who have never smoked.U.S. Department of Veterans Affairs Epidemiology (Merit Review grant); Massachusetts Veterans Epidemiology Research and Information Center; National Institutes of Health (R01 DA10073, R03 DE016357, R15 DE12644, K24 DE00419
First air–sea gas exchange laboratory study at hurricane wind speeds
In a pilot study conducted in October and November 2011, air–sea gas transfer velocities of the two sparingly soluble trace gases hexafluorobenzene and 1,4-difluorobenzene were measured in the unique High-Speed Wind-Wave Tank at Kyoto University, Japan. This air–sea interaction facility is capable of producing hurricane strength wind speeds of up to u10=67 m s−1. This constitutes the first lab study of gas transfer at such high wind speeds. The measured transfer velocities k600 spanned two orders of magnitude, lying between 11 cm h−1 and 1180 cm h−1 with the latter being the highest ever measured wind induced gas transfer velocity. The measured gas transfer velocities are in agreement with the only available dataset at hurricane wind speeds (McNeil and D'Asaro, 2007). The disproportionately large increase of the transfer velocities found at highest wind speeds indicates a new regime of air–sea gas transfer, which is characterized by strong wave breaking, enhanced turbulence and bubble cloud entrainment. It was found that tracers spanning a wide range of solubilities and diffusivities are needed to separate the effects of enhanced surface area and turbulence due to breaking waves from the effects of bubble and spray mediated gas transfer
Comparative heat and gas exchange measurements in the Heidelberg Aeolotron, a large annular wind-wave tank
A comparative study of simultaneous heat and gas exchange measurements was performed in the large annular Heidelberg Air–Sea Interaction Facility, the Aeolotron, under homogeneous water surface conditions. The use of two gas tracers, N2O and C2HF5, resulted not only in gas transfer velocities, but also in the measurement of the Schmidt number exponent n with a precision of ± 0.025. The original controlled flux or active thermographic technique proposed by Jähne et al. (1989) was applied by heating a large patch at the water surface to measure heat transfer velocities. Heating a large patch, the active thermography technique is laterally homogeneous and problems of lateral transport effects are avoided. Using the measured Schmidt number exponents, the ratio of the scaled heat transfer velocities to the measured gas transfer velocities is 1.046 ± 0.040, a good agreement within the limits of experimental uncertainties. This indicates the possibility to scale heat transfer velocities measured by active thermography to gas transfer velocities, provided the Schmidt number exponent is known and that the heated patch is large enough to reach the thermal equilibrium
Higher Inpatient Medical Surgical Bed Occupancy Extends Admitted Patients’ Stay
Objective: Determine the effect that increased medical surgical (med/surg) bed occupancy has on the time interval from admission order to arrival in the bed for the patients admitted from the emergency department (ED).Methods: This retrospective observational study compares the total hospital bed occupancy rate and the medical surgical inpatient bed occupancy rate to daily averages for the time interval from admission order (patient posting for admission) to the patient’s arrival in the inpatient bed. Medical surgical inpatient bed occupancy of 92% was chosen because beyond that rate we observed more frequent extended daily transfer times. The data is from a single large tertiary care institute with 590 beds and an annual ED census of 80,000.Results: Group 1 includes 38 days with (med/surg) inpatient bed occupancy rate of less than 92%, with an average ED daily wait of 2.5 hrs (95% confidence interval 2.23-2.96) for transfer from the ED to the appropriate hospital bed. Group 2 includes 68 days with med/surg census greater than 92% with an average ED daily wait of 4.1 hours (95% confidence interval 3.7-4.5). Minimum daily average for the two groups was 1.2 hrs and 1.3 hrs, respectively. The maximum average was 5.6 hrs for group 1 and 8.6 hrs for group 2. Comparison of group 1 to 2 for wait time to hospital bed yielded p <0.01. Total reported hospital occupied capacity shows a correlation coefficient of 0.16 to transfer time interval, which indicates a weak relationship between total occupancy and transfer time into the hospital. Med/surg occupancy, the beds typically used by ED patients, has a 0.62 correlation coefficient for a moderately strong relationship.Conclusions: Med/surg bed occupancy has a better correlation to extended transfer times, and occupancy over 92% at 5 AM in our institution corresponds to an increased frequency of extended transfer times from the ED. The process of ED evaluation, hospital admission, and subsequent transfer into the hospital are all complex processes. This study begins to demonstrate one variable, med/surg occupancy, as one of the intervals that can be followed to evaluate the process of ED admission and hospital flow. [WestJEM. 2009;10:93-96.
High Energy Electron Confinement in a Magnetic Cusp Configuration
We report experimental results validating the concept that plasma confinement
is enhanced in a magnetic cusp configuration when beta (plasma
pressure/magnetic field pressure) is order of unity. This enhancement is
required for a fusion power reactor based on cusp confinement to be feasible.
The magnetic cusp configuration possesses a critical advantage: the plasma is
stable to large scale perturbations. However, early work indicated that plasma
loss rates in a reactor based on a cusp configuration were too large for net
power production. Grad and others theorized that at high beta a sharp boundary
would form between the plasma and the magnetic field, leading to substantially
smaller loss rates. The current experiment validates this theoretical
conjecture for the first time and represents critical progress toward the
Polywell fusion concept which combines a high beta cusp configuration with an
electrostatic fusion for a compact, economical, power-producing nuclear fusion
reactor.Comment: 12 pages, figures included. 5 movies in Ancillary file
A naked singularity stable under scalar field perturbations
We prove the stability of a spacetime with a naked singularity under scalar
field perturbations, where the perturbations are regular at the singularity.
This spacetime, found by Janis, Newman and Winicour, and independently by
Wyman, is sourced by a massless scalar field and also arises as a certain limit
of a class of charged dilatonic solutions in string theory. This stability
result opens up specific questions for investigation related to the cosmic
censorship conjecture and the mechanism by which it is implemented in nature.Comment: 19 pages, version to appear in IJMPD, references adde
Two-Stream Instability Model With Electrons Trapped in Quadrupoles
We formulate the theory of the two-stream instability (e-cloud instability)
with electrons trapped in quadrupole magnets. We show that a linear instability
theory can be sensibly formulated and analyzed. The growth rates are
considerably smaller than the linear growth rates for the two-stream
instability in drift spaces and are close to those actually observed
Space-filter techniques for quasi-neutral hybrid-kinetic models
The space-filter approach has proved a fundamental tool in studying
turbulence in neutral fluids, providing the ability to analyze scale-to-scale
energy transfer in configuration space. It is well known that turbulence in
plasma presents challenges different from neutral fluids, especially when the
scale of interests include kinetic effects. The space-filter approach is still
largely unexplored for kinetic plasma. Here we derive the space-filtered (or,
equivalently "coarse-grained") equations in configuration space for a
quasi-neutral hybrid-kinetic plasma model, in which ions are fully kinetic and
electrons are a neutralizing fluid. Different models and closures for the
electron fluid are considered, including finite electron-inertia effects and
full electrons' pressure-tensor dynamics. Implications for the cascade of
turbulent fluctuations in real space depending on different approximations are
discussed.Comment: 43 pages, 2 figure
Environments for Magnetic Field Amplification by Cosmic Rays
We consider a recently discovered class of instabilities, driven by cosmic
ray streaming, in a variety of environments. We show that although these
instabilities have been discussed primarily in the context of supernova driven
interstellar shocks, they can also operate in the intergalactic medium and in
galaxies with weak magnetic fields, where, as a strong source of helical
magnetic fluctuations, they could contribute to the overall evolution of the
magnetic field. Within the Milky Way, these instabilities are strongest in warm
ionized gas, and appear to be weak in hot, low density gas unless the injection
efficiency of cosmic rays is very high.Comment: 9 pages, 8 figures; Accepted to Ap
Nonlinear Electron Oscillations in a Viscous and Resistive Plasma
New non-linear, spatially periodic, long wavelength electrostatic modes of an
electron fluid oscillating against a motionless ion fluid (Langmuir waves) are
given, with viscous and resistive effects included. The cold plasma
approximation is adopted, which requires the wavelength to be sufficiently
large. The pertinent requirement valid for large amplitude waves is determined.
The general non-linear solution of the continuity and momentum transfer
equations for the electron fluid along with Poisson's equation is obtained in
simple parametric form. It is shown that in all typical hydrogen plasmas, the
influence of plasma resistivity on the modes in question is negligible. Within
the limitations of the solution found, the non-linear time evolution of any
(periodic) initial electron number density profile n_e(x, t=0) can be
determined (examples). For the modes in question, an idealized model of a
strictly cold and collisionless plasma is shown to be applicable to any real
plasma, provided that the wavelength lambda >> lambda_{min}(n_0,T_e), where n_0
= const and T_e are the equilibrium values of the electron number density and
electron temperature. Within this idealized model, the minimum of the initial
electron density n_e(x_{min}, t=0) must be larger than half its equilibrium
value, n_0/2. Otherwise, the corresponding maximum n_e(x_{max},t=tau_p/2),
obtained after half a period of the plasma oscillation blows up. Relaxation of
this restriction on n_e(x, t=0) as one decreases lambda, due to the increase of
the electron viscosity effects, is examined in detail. Strong plasma viscosity
is shown to change considerably the density profile during the time evolution,
e.g., by splitting the largest maximum in two.Comment: 16 one column pages, 11 figures, Abstract and Sec. I, extended, Sec.
VIII modified, Phys. Rev. E in pres
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