1,902 research outputs found
Relaxation Methods for Mixed-Integer Optimal Control of Partial Differential Equations
We consider integer-restricted optimal control of systems governed by
abstract semilinear evolution equations. This includes the problem of optimal
control design for certain distributed parameter systems endowed with multiple
actuators, where the task is to minimize costs associated with the dynamics of
the system by choosing, for each instant in time, one of the actuators together
with ordinary controls. We consider relaxation techniques that are already used
successfully for mixed-integer optimal control of ordinary differential
equations. Our analysis yields sufficient conditions such that the optimal
value and the optimal state of the relaxed problem can be approximated with
arbitrary precision by a control satisfying the integer restrictions. The
results are obtained by semigroup theory methods. The approach is constructive
and gives rise to a numerical method. We supplement the analysis with numerical
experiments
Atmospheric leakage and condensate production in NASA's biomass production chamber. Effect of diurnal temperature cycles
A series of tests were conducted to monitor atmospheric leakage rate and condensate production in NASA's Biomass Production Chamber (BPC). Water was circulated through the 64 plant culture trays inside the chamber during the tests but no plants were present. Environmental conditions were set to a 12-hr photoperiod with either a matching 26 C (light)/20 C (dark) thermoperiod, or a constant 23 C temperature. Leakage, as determined by carbon dioxide decay rates, averaged about 9.8 percent for the 26 C/20 C regime and 7.3 percent for the constant 23 C regime. Increasing the temperature from 20 C to 26 C caused a temporary increase in pressure (up to 0.5 kPa) relative to ambient, while decreasing the temperature caused a temporary decrease in pressure of similar magnitude. Little pressure change was observed during transition between 23 C (light) and 23 C (dark). The lack of large pressure events under isothermal conditions may explain the lower leakage rate observed. When only the plant support inserts were placed in the culture trays, condensate production averaged about 37 liters per day. Placing acrylic germination covers over the tops of culture trays reduced condensate production to about 7 liters per day. During both tests, condensate production from the lower air handling system was 60 to 70 percent greater than from the upper system, suggesting imbalances exist in chilled and hot water flows for the two air handling systems. Results indicate that atmospheric leakage rates are sufficiently low to measure CO2 exchange rates by plants and the accumulation of certain volatile contaminants (e.g., ethylene). Control system changes are recommended in order to balance operational differences (e.g., humidity and temperature) between the two halves of the chamber
Non-Newtonian gravity or gravity anomalies?
Geophysical measurements of G differ from laboratory values, indicating that gravity may be non-Newtonian. A spherical harmonic formulation is presented for the variation of (Newtonian) gravity inside the Earth. Using the GEM-10B Earth Gravitational Field Model, it is shown that long-wavelength gravity anomalies, if not corrected, may masquerade as non-Newtonian gravity by providing significant influences on experimental observation of delta g/delta r and G. An apparent contradiction in other studies is also resolved: i.e., local densities appear in equations when average densities of layers seem to be called for
Administrative Practice Before Federal Agencies
There exist more than forty federal executive and administrative agencies before which lawyers (and in many cases, laymen) may practice and serve the interests of clients. The complexities of our society, the specializations which are a by-product of a complex industrial state, and the persistent growth of government\u27s bureaucracy, point up the continuing importance of practice before federal administrative agencies
Determination of Acaricide Resistance in Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) Field Populations of Argentina, South Africa, and Australia With the Larval Tarsal Test
Infestations with ticks have an important economic impact on the cattle industry worldwide and resistance to acaricides has become a widespread phenomenon. To optimize their treatment strategy, farmers need to know if and against which classes potential acaricide-resistance does occur. Bioassays are used to assess the resistance level and pattern of Rhipicephalus (Boophilus) microplus populations. The objective of the current study was to assess the susceptibility of field populations originating from Argentina (8), South Africa (3), and Australia (2) using the Larval Tarsal Test. Nine acaricidal compounds from five major classes were tested: organosphosphates, synthetic pyrethroids (SP), macrocyclic lactones, phenylpyrazols, and amidines. The resistance ratios at concentrations inducing 50 and 90% mortality were used to detect established and emerging resistance. This study confirmed the newly reported presence of amitraz resistance in populations from Argentina. In addition, resistance to SP appeared to be widespread (88%) in the Argentinean farms, which had been selected based on the observation of lack of treatment efficacy by farmers. In South Africa one of the three populations was found to be resistant to SP and to a phenylpyrazol compound (pyriprol). Furthermore, resistance to organosphosphates and SP was observed in Australia. Finally, the Larval Tarsal Test proved to be a suitable test to evaluate the susceptibility of R. microplus field populations to the most relevant acaricidal classe
Coprological study on intestinal helminths in Swiss dogs: temporal aspects of anthelminthic treatment
Coproscopic examination of 505 dogs originating from the western or central part of Switzerland revealed the presence (prevalence data) of the following helminthes: Toxocara canis (7.1%), hookworms (6.9%), Trichuris vulpis (5.5%), Toxascaris leonina (1.3%), Taeniidae (1.3%), Capillaria spp. (0.8%), and Diphyllobothrium latum (0.4%). Potential risk factors for infection were identified by a questionnaire: dogs from rural areas significantly more often had hookworms and taeniid eggs in their feces when compared to urban family dogs. Access to small rodents, offal, and carrion was identified as risk factor for hookworm and Taeniidae, while feeding of fresh and uncooked meat did not result in higher prevalences for these helminths. A group of 111 dogs was treated every 3months with a combined medication of pyrantel embonate, praziquantel, and febantel, and fecal samples were collected for coproscopy in monthly intervals. Despite treatment, the yearly incidence of T. canis was 32%, while hookworms, T. vulpis, Capillaria spp., and Taeniidae reached incidences ranging from 11 to 22%. Fifty-seven percent of the 111 dogs had helminth eggs in their feces at least once during the 1-year study period. This finding implicates that an infection risk with potential zoonotic pathogens cannot be ruled out for the dog owner despite regular deworming four times a yea
Strong Coupling Corrections to the Ginzburg-Landau Theory of Superfluid ^{3}He
In the Ginzburg-Landau theory of superfluid He, the free energy is
expressed as an expansion of invariants of a complex order parameter. Strong
coupling effects, which increase with increasing pressure, are embodied in the
set of coefficients of these order parameter invariants\cite{Leg75,Thu87}.
Experiments can be used to determine four independent combinations of the
coefficients of the five fourth order invariants. This leaves the
phenomenological description of the thermodynamics near incomplete.
Theoretical understanding of these coefficients is also quite limited. We
analyze our measurements of the magnetic susceptibility and the NMR frequency
shift in the -phase which refine the four experimental inputs to the
phenomenological theory. We propose a model based on existing experiments,
combined with calculations by Sauls and Serene\cite{Sau81} of the pressure
dependence of these coefficients, in order to determine all five fourth order
terms. This model leads us to a better understanding of the thermodynamics of
superfluid He in its various states. We discuss the surface tension of
bulk superfluid He and predictions for novel states of the superfluid
such as those that are stabilized by elastic scattering of quasiparticles from
a highly porous silica aerogel.Comment: 9 pages, 7 figures, 2 table
Analysis of Strong-Coupling Parameters for Superfluid 3He
Superfluid He experiments show strong deviation from the weak-coupling
limit of the Ginzburg-Landau theory, and this discrepancy grows with increasing
pressure. Strong-coupling contributions to the quasiparticle interactions are
known to account for this effect and they are manifest in the five
-coefficients of the fourth order Ginzburg-Landau free energy terms. The
Ginzburg-Landau free energy also has a coefficient to include magnetic
field coupling to the order parameter. From NMR susceptibility experiments, we
find the deviation of from its weak-coupling value to be negligible at
all pressures. New results for the pressure dependence of four different
combinations of -coefficients, _{345}, _{12},
_{245}, and _{5} are calculated and comparison is made with
theory.Comment: 6 pages, 2 figures, 1 table. Manuscript prepared for QFS200
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