Necessary conditions for joining optimal singular and nonsingular subarcs

Necessary conditions for optimality of junctions between singular and nonsingular subarcs for singular optimal control problem

Measure Factors, Tension, and Correlations of Fluid Membranes

We study two geometrical factors needed for the correct construction of statistical ensembles of surfaces. Such ensembles appear in the study of fluid bilayer membranes, though our results are more generally applicable. The naive functional measure over height fluctuations must be corrected by these factors in order to give correct, self-consistent formulas for the free energy and correlation functions of the height. While one of these corrections -- the Faddeev-Popov determinant -- has been studied extensively, our derivation proceeds from very simple geometrical ideas, which we hope removes some of its mystery. The other factor is similar to the Liouville correction in string theory. Since our formulas differ from those of previous authors, we include some explicit calculations of the effective frame tension and two-point function to show that our version indeed secures coordinate-invariance and consistency to lowest nontrivial order in a temperature expansion.Comment: 24 pp; plain Te

Front Propagation in the Pearling Instability of Tubular Vesicles

Recently Bar-Ziv and Moses discovered a dynamical shape transformation induced in cylindrical lipid bilayer vesicles by the action of laser tweezers. We develop a hydrodynamic theory of fluid bilayers in interaction with the surrounding water and argue that the effect of the laser is to induce a sudden tension in the membrane. We refine our previous analysis to account for the fact that the shape transformation is not uniform but propagates outward from the laser trap. Applying the marginal stability criterion to this situation gives us an improved prediction for the selected initial wavelength and a new prediction for the propagation velocity, both in rough agreement with the experimental values. For example, a tubule of initial radius 0.7\micron\ has a predicted initial sinusoidal perturbation in its diameter with wavelength 5.5\micron, as observed. The perturbation propagates as a front with the qualitatively correct front velocity a bit less than 100\micron/sec. In particular we show why this velocity is initially constant, as observed, and so much smaller than the natural scale set by the tension. We also predict that the front velocity should increase linearly with laser power. Finally we introduce an approximate hydrodynamic model applicable to the fully nonlinear regime. This model exhibits propagating fronts as well as fully-developed ``pearled" vesicles similar to those seen in the experiments.Comment: 42 pages, 6 eps figures included with text in uuencoded file, ps file available from ftp://dept.physics.upenn.edu/pub/Nelson/pearl_propagation.ps submitted to Journal de Physiqu

Ceramic component reliability with the restructured NASA/CARES computer program

The Ceramics Analysis and Reliability Evaluation of Structures (CARES) integrated design program on statistical fast fracture reliability and monolithic ceramic components is enhanced to include the use of a neutral data base, two-dimensional modeling, and variable problem size. The data base allows for the efficient transfer of element stresses, temperatures, and volumes/areas from the finite element output to the reliability analysis program. Elements are divided to insure a direct correspondence between the subelements and the Gaussian integration points. Two-dimensional modeling is accomplished by assessing the volume flaw reliability with shell elements. To demonstrate the improvements in the algorithm, example problems are selected from a round-robin conducted by WELFEP (WEakest Link failure probability prediction by Finite Element Postprocessors)

Seasonal variability in ichthyoplankton abundance and assemblage composition in the northern Gulf of Mexico off Alabama

Multiyear ichthyoplankton surveys used to monitor larval fish seasonality, abundance, and assemblage structure can provide early indicators of regional ecosystem changes. Numerous ichthyoplankton surveys have been conducted in the northern Gulf of Mexico, but few have had high levels of temporal resolution and sample replication. In this study, ichthyoplankton samples were collected monthly (October 2004–October 2006) at a single station off the coast of Alabama as part of a long-term biological survey. Four seasonal periods were identified from observed and historic water temperatures, including a relatively long (June–October) “summer” period (water temperature >26°C). Fish egg abundance, total larval abundance, and larval taxonomic diversity were significantly related to water temperature (but not salinity), with peaks in the spring, spring–summer, and summer periods, respectively. Larvae collected during the survey represented 58 different families, of which engraulids, sciaenids, carangids, and clupeids were the most prominent. The most abundant taxa collected were unidentified engraulids (50%), sand seatrout (Cynoscion arenarius, 7.5%), Atlantic bumper (Chloroscombrus chrysurus, 5.4%), Atlantic croaker (Micropogonias undulatus, 4.4%), Gulf menhaden (Brevoortia patronus, 3.8%), and unidentified gobiids (3.6%). Larval concentrations for dominant taxa were highly variable between years, but the timing of seasonal occurrence for these taxa was relatively consistent. Documented increases in sea surface temperature on the Alabama shelf may have various implications for larval fish dynamics, as indicated by the presence of tropical larval forms (e.g., fistularids, labrids, scarids, and acanthurids) in our ichthyoplankton collections and in recent juvenile surveys of Alabama and northern Gulf of Mexico seagrass habitats

Does Disclosure Reduce Pollution? Evidence from India's Green Rating Project

Public disclosure programs that collect and disseminate information about firms’ environmental performance are increasingly popular in both developed and developing countries. Yet little is known about whether they actually improve environmental performance, particularly in the latter setting. We use detailed plant-level survey data to evaluate the impact of India’s Green Rating Project (GRP) on the environmental performance of the country’s largest pulp and paper plants. We find that the GRP drove significant reductions in pollution loadings among dirty plants but not among cleaner ones. This result comports with statistical and anecdotal evaluations of similar disclosure programs. We also find that plants located in wealthier communities were more responsive to GRP ratings, as were single-plant firms.public disclosure, pollution control, India, pulp and paper

COLD-SAT: An orbital cryogenic hydrogen technology experiment

The COLD-SAT spacecraft will perform subcritical liquid hydrogen storage and transfer experiments under low-gravity conditions to provide engineering data for future space transportation missions. Consisting of an experiment module mated to a spacecraft bus, COLD-SAT will be placed in an initial 460 km circular orbit by an Atlas I commercial launch vehicle. After deployment, the three-axis-controlled spacecraft bus will provide electric power, experiment control and data management, communications, and attitude control along with propulsive acceleration levels ranging from 10(-6) to 10(-4)g. These accelerations are an important aspect of some of the experiments, as it is desired to know the effects that low gravity levels might have on the heat and mass transfer processes involved. The experiment module will contain the three liquid hydrogen tanks, valves, pressurization equipment, and instrumentation. At launch all the hydrogen will be in the largest tank, which has helium-purged MLI and is loaded and topped off by the hydrogen tanking system used for the Centaur upper stage of the Atlas. The two smaller tanks will be utilized in orbit for performing some of the experiments. The experiments are grouped into two classes on the basis of their priority, and include six regarded as enabling technology and nine regarded as enhancing technology

Compression and Relaxation of Fishing Effort in Response to Changes in Length of Fishing Season for Red Snapper (Lutjanus campechanus) in the Northern Gulf of Mexico

A standard method used by fisheries managers to decrease catch and effort is to shorten the length of a fishery; however, data on recreational angler response to this simple approach are surprisingly lacking. We assessed the effect of variable season length on daily fishing effort, measured by using numbers of boat launches per day, anglers per boat, and anglers per day from video observations, in the recreational sector of the federal fishery for red snapper (Lutjanus campechanus) in coastal Alabama. From 2012 through 2017, season length fluctuated from 3 to 40 d. Daily effort, measured by using mean number of boat launches per day (coefficient of multiple determination [R2]=0.58) and mean number of anglers per day (R2=0.67), increased linearly with season shortening, indicating effort compression. In 2017, 2 seasons were allowed: an early season (3 d) and an unanticipated late season (39 d). Daily effort decreased during the late season, indicating that effort can also be relaxed if anglers anticipate longer seasons. Model fit for mean number of anglers per day improved with the addition of a daily wind factor (R2=0.94). The results of this study indicate that responses of anglers to changing fishing seasons are dynamic

Switching conditions and a synthesis technique for the singular Saturn guidance problem

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76180/1/AIAA-1970-965-334.pd