21,432 research outputs found
Continuous Data Assimilation with Stochastically Noisy Data
We analyze the performance of a data-assimilation algorithm based on a linear
feedback control when used with observational data that contains measurement
errors. Our model problem consists of dynamics governed by the two-dimension
incompressible Navier-Stokes equations, observational measurements given by
finite volume elements or nodal points of the velocity field and measurement
errors which are represented by stochastic noise. Under these assumptions, the
data-assimilation algorithm consists of a system of stochastically forced
Navier-Stokes equations. The main result of this paper provides explicit
conditions on the observation density (resolution) which guarantee explicit
asymptotic bounds, as the time tends to infinity, on the error between the
approximate solution and the actual solutions which is corresponding to these
measurements, in terms of the variance of the noise in the measurements.
Specifically, such bounds are given for the the limit supremum, as the time
tends to infinity, of the expected value of the -norm and of the
Sobolev norm of the difference between the approximating solution and the
actual solution. Moreover, results on the average time error in mean are
stated
A connection between the Camassa-Holm equations and turbulent flows in channels and pipes
In this paper we discuss recent progress in using the Camassa-Holm equations
to model turbulent flows. The Camassa-Holm equations, given their special
geometric and physical properties, appear particularly well suited for studying
turbulent flows. We identify the steady solution of the Camassa-Holm equation
with the mean flow of the Reynolds equation and compare the results with
empirical data for turbulent flows in channels and pipes. The data suggests
that the constant version of the Camassa-Holm equations, derived under
the assumptions that the fluctuation statistics are isotropic and homogeneous,
holds to order distance from the boundaries. Near a boundary, these
assumptions are no longer valid and the length scale is seen to depend
on the distance to the nearest wall. Thus, a turbulent flow is divided into two
regions: the constant region away from boundaries, and the near wall
region. In the near wall region, Reynolds number scaling conditions imply that
decreases as Reynolds number increases. Away from boundaries, these
scaling conditions imply is independent of Reynolds number. Given the
agreement with empirical and numerical data, our current work indicates that
the Camassa-Holm equations provide a promising theoretical framework from which
to understand some turbulent flows.Comment: tex file, 29 pages, 4 figures, Physics of Fluids (in press
Pulsation of EE Cam
EE Cam is a previously little studied Delta Scuti pulsator with amplitudes
between those of the HADS (High-Amplitude Delta Scuti stars) group and the
average low-amplitude pulsators. Since the size of stellar rotation determines
both which pulsation modes are selected by the star as well as their
amplitudes, the star offers a great opportunity to examine the astrophysical
connections. Extensive photometric measurements covering several months were
carried out. 15 significant pulsation frequencies were extracted. The dominant
mode at 4.934 cd was identified as a radial mode by examining the phase
shifts at different wavelengths. Medium-dispersion spectra yielded a
value of km s. This shows that EE Cam belongs to the
important transition region between the HADS and normal Delta Scuti stars.Comment: 13 pages, 3 figures, 3 table
Understanding the measurement of hunger and food insecurity in the elderly
The elderly are one of the population subgroups at greatest risk for hunger and food insecurity. To date, no accurate measures of this problem have been developed. What is needed are a thorough understanding of the phenomenon, and an assessment of how the elderly perceive and answer items commonly used to measure hunger and food insecurity in other subgroups. In-depth, open-ended interviews were conducted with forty-one low-income urban black and rural white residents of upstate New York. Results suggest a conceptual framework of food insecurity in the elderly with two significant differences from frameworks proposed for younger families: the major role of health problems and physical disabilities, and the impact of personal history on perceptions of food insecurity. In a telephone follow-up (approximately six months after the initial interviews) twenty-four respondents were asked commonly used food insecurity questionnaire items from six different sources. Results suggest that hunger and food insecurity among the elderly can be measured directly. The commonly used measures tested here will help categorize the stages of food insecurity. However, these direct measures might underestimate the prevalence of food insecurity because of a perceived reluctance to report problems with food.
Nutritional Consequences of Food Insecurity in a Rural New York State County
This study of women with children in a rural county of upstate New York examined the relationships of food insecurity and income with two nutritional consequences (adiposity and fruit and vegetables consumption), and assessed whether disordered eating patterns is a mediator for the effects of food insecurity and income on these nutritional consequences. Each of 193 respondents was interviewed twice in her home. Data were collected on household food stores, socioeconomic and demographic characteristics, methods of obtaining food, food program participation, household expenditures, food intake, the Radimer/Cornell hunger and food insecurity items, height, weight, frequency of fruit and vegetable consumption, and disordered eating patterns. Regression analysis was used to analyze the relationships of body mass index and an obesity classification with height, income, education, single parenthood, employment, food insecurity, disordered eating, and frequency of fruit and vegetable consumption. Regression analysis was also used to examine the relationships of disordered eating and frequency of fruit and vegetable consumption with the other variables. Lower income and unemployment were related to higher adiposity. The effects of income on adiposity were not mediated through disordered eating patterns or through fruit and vegetable consumption. Food insecurity was related to adiposity, and part of this effect of food insecurity was mediated through disordered eating. This mediating effect of disordered eating partially explained why those experiencing the least severe food insecurity were more likely to be overweight than those who were food secure, but those experiencing the most severe food insecurity were less likely to be overweight than those who were food secure. Food insecurity was related to lower fruit and vegetable consumption, but this did not translate into effects on adiposity.
Solicitors General Panel on the Legacy of the Rehnquist Court
All of us who are speaking probably share the same giddy feeling in front of a microphone with no red light. For years, my daughter told people that the greatest threat to Western civilization was her father at a podium without a red light. Before becoming Solicitor General, I spent my career as a trial lawyer, arguing only a few appeals. I found this red light tradition a little peculiar. More often than not, timers and lights in courts of appeals are viewed as advisory at best. I\u27ve had arguments where ten minutes were allocated per side, and yet argument extended until the afternoon. In another case that allocated ninety minutes per side and began at nine o\u27clock, we didn\u27t actually finish until four o\u27clock in the afternoon. So coming into the SG\u27s office, my view about the red light was, well, perhaps it shows your time has nominally expired, but undoubtedly the Justices will have other questions. And in any event, I might want to take a few extra minutes to address additional points. That was so wrong. The red light ended everything-absolutely everything-and not just for the advocates; it also ended the questioning of the Associate Justices. The Chief Justice was an equal opportunity cutter-offer. On many occasions, he cut off oral argument when a Justice was at the outset of a question he or she had been trying to get out in the open oral combat that was advocacy in the Supreme Court of Chief Justice Rehnquist
Is It Worth It? Examining the Educational Benefits of Synchronous Activities in an Online Theology Course
To explore the effect of adding synchronous activities to an online course, one section of a theology course was conducted in an asynchronous environment while the second section incorporated weekly Adobe Connect sessions. No significant differences were found on measures of academic achievement, student satisfaction, or classroom community
Estimating the prevalence of hunger and food insecurity: The validity of questionnaire-based measures for the identification of households
This study had three objectives: (1) to assess the validity of questionnaire-based measures in identifying households experiencing hunger and food insecurity, (2) to examine the interrelationships of different questionnaire-based measures, and (3) to examine the construction of a continuous food insecurity scale intended to differentiate three levels of food insecurity within households. A 1993 survey of 193 randomly sampled rural households with women and children living at home provided data on demographics, risk factors for food insecurity, Radimer/Cornell, CCHIP, and NHANES III hunger and food insecurity items, coping strategies, fruit and vegetable consumption, disordered eating behaviors, height, weight, dietary recall, and household food-stores inventory. This information was used to develop a definitive criterion measure for hunger and food insecurity, against which the Radimer/Cornell and CCHIP questionnaire-based measures, the NHANES III item, and the continuous food insecurity scale were tested for their specificity and sensitivity in measuring levels of food insecurity.
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