The effects of closed loop tracking on a subjective tilt threshold in the roll axis

The indifference thresholds for the perception of tilt in the roll axis were experimentally determined in a moving base simulator under three tracking task difficulties. The threshold level determined in this experiment is approximately 5 to 7 degrees (.lg)

A computerized program for statistical treatment of biological data

Biologists frequently conduct experiments which measure the patterns of inactivation of bacterial populations after exposure to a lethal environment. A computer program is discussed which calculates many of the quantities that have proven to be useful in the analysis of such experimental data

Pull-in control due to Casimir forces using external magnetic fields

We present a theoretical calculation of the pull-in control in capacitive micro switches actuated by Casimir forces, using external magnetic fields. The external magnetic fields induces an optical anisotropy due to the excitation of magneto plasmons, that reduces the Casimir force. The calculations are performed in the Voigt configuration, and the results show that as the magnetic field increases the system becomes more stable. The detachment length for a cantilever is also calculated for a cantilever, showing that it increases with increasing magnetic field. At the pull-in separation, the stiffness of the system decreases with increasing magnetic field.Comment: accepted for publication in App. Phys. Let

Scaling Laws of Stress and Strain in Brittle Fracture

A numerical realization of an elastic beam lattice is used to obtain scaling exponents relevant to the extent of damage within the controlled, catastrophic and total regimes of mode-I brittle fracture. The relative fraction of damage at the onset of catastrophic rupture approaches a fixed value in the continuum limit. This enables disorder in a real material to be quantified through its relationship with random samples generated on the computer.Comment: 4 pages and 6 figure

Interstellar Grains

Observational and theoretical interpretations of interstellar grains - conference paper

Body size and symbiotic status influence gonad development in \u3cem\u3eAiptasia pallida\u3c/em\u3e anemones

Pale anemones (Aiptasia pallida) coexist with dinoflagellates (primarily Symbiodinium minutum) in a mutualistic relationship. The purpose of this study was to investigate the role of these symbionts in gonad development of anemone hosts. Symbiotic and aposymbiotic anemones were subjected to light cycles that induced gametogenesis. These anemones were then sampled weekly for nine weeks, and gonad development was analyzed histologically. Anemone size was measured as mean body column diameter, and oocytes or sperm follicles were counted for each anemone. Generalized linear models were used to evaluate the influence of body size and symbiotic status on whether gonads were present and on the number of oocytes or sperm follicles produced. Body size predicted whether gonads were present, with larger anemones being more likely than smaller anemones to develop gonads. Both body size and symbiotic status predicted gonad size, such that larger and symbiotic anemones produced more oocytes and sperm follicles than smaller and aposymbiotic anemones. Overall, only 22 % of aposymbiotic females produced oocytes, whereas 63 % of symbiotic females produced oocytes. Similarly, 6 % of aposymbiotic males produced sperm follicles, whereas 60 % of symbiotic males produced sperm follicles. Thus, while gonads were present in 62 % of symbiotic anemones, they were present in only 11 % of aposymbiotic anemones. These results indicate that dinoflagellate symbionts influence gonad development and thus sexual maturation in both female and male Aiptasia pallida anemones. This finding substantiates and expands our current understanding of the importance of symbionts in the development and physiology of cnidarian hosts

Selected Hydrologic Data for Cache Valley, Utah and Idaho, 1969-91

This report contains hydrologic data collected in Cache Valley from 1969 to 1991. The report area is in north-central Utah and southeast Idaho, within the Basin and Range physiographic province described by Fenneman (1931), and includes about 660 square miles. Most of the data in this report were collected by the U.S. Geological Survey in cooperation with the Utah Department of Natural Resources, Divisions or Water Resources and Water Rights. Some of the data collected before 1969 were previously published by McGreevy and Bjorklund (1970). The purpose of this report is to provide hydrologic data for use by the general public and by officials managing the area\u27s water resources, and to supplement interpretive reports for the area. Tables 1 to 7 contain selected well, spring, and surface-water data. The numbering systems used in this report for hydrologic-data sites are illustrated in figure 1. Hydrologic-data sites are shown on plate 1. These data could not have been collected without the cooperation of local residents and officials of irrigation companies and municipalities, that permitted access to their wells, springs, and canals to measure water levels in wells and flow in springs and canals. The Idaho Deparment of Water Resources also provided valuable assistance Ind data

Conductance of Ideally Cation Selective Channel Depends on Anion Type

poster abstractGramicidin A (gA) is a transmembrane, cation selective ion channel that has been used in many biophysical studies of lipid bilayers, in particular for investigations of lipid-protein interactions and membrane electrostatics. In addition, it was found that ionic interactions with neutral lipid membranes also affect the kinetics of gA channels. Here we report measurements of gA ion-channels for a series of sodium and potassium salts that show an anion-dependence of gA conductance. We find that gA conductance varies significantly with the anion type with ClO4 and SCN producing distinctly larger conductance values than Cl, F, and H2PO4. These results can provide new insights into ion-lipid membrane interactions and ion channel functions in general

Methodological precision of in situ and in vitro algal density measurements in the model cnidarian, Exaiptasia diaphana

In cnidarian symbiosis research, studying algal uptake, maintenance, and expulsion typically requires quantification of algal density in host tissue. Multiple methods are used to measure algal density including in vitro cell counts of holobiont homogenate and in situ cell counts of tentacle clippings. The relative precision of both types of measurement has not previously been reported for the model cnidarian Exaiptasia diaphana in the fully symbiotic state. The objective of this study was to evaluate the precision of in vitro and in situ algal density measurement protocols using light, fluorescent, and confocal microscopy and an automated cell counter. In situ algal density was quantified as algal area fraction (%) using confocal images of tentacle clippings mounted on two types of slides. In vitro algal density of holobiont homogenate was quantified as algal cells/µl of holobiont homogenate using an automated cell counter and a hemocytometer viewed using light and fluorescent microscopy. Triplicate measurements of each method for ten anemones were collected and the coefficient of variation was calculated and compared across the ten anemones within each method. The algal density measurements were equally precise when they were obtained by quantifying in vitro cell counts using a hemocytometer and when they were obtained by quantifying in situ cell counts. While both light and fluorescent microscopy yielded similar measurement precision of in vitro cell counts, use of a fluorescent microscope was more efficient and convenient than use of a light microscope, and both methods required terminal sampling. Conversely, in situ methods required more sophisticated equipment (namely a confocal microscope) but involved non-terminal sampling. An automated cell counter was ineffective for in vitro quantification of algal density, although the potential utility of this technology warrants future attempts using a more robust algal cell purification process that could include filtering homogenate prior to analysis. This study demonstrated that in vitro and in situ methods yield estimates of algal density with comparable precision, which is information that researchers can use for future studies when making decisions about methodology

Cation-selective channel is regulated by anions according to their Hofmeister ranking

Specificity of small ions, the Hofmeister ranking, is long-known and has many applications including medicine. Yet it evades consistent theoretical description. Here we study the effect of Hofmeister anions on gramicidin A channels in lipid membranes. Counterintuitively, we find that conductance of this perfectly cation-selective channel increases about two-fold in the H2PO4−<Cl−≈Br−≈NO3−<ClO4−<SCN− series. Channel dissociation kinetics show even stronger dependence, with the dwell time increasing ~20-fold. While the conductance can be quantitatively explained by the changes in membrane surface potential due to exclusion of kosmotropes from (or accumulation of chaotropes at) the surface, the kinetics proved to be more difficult to treat. We estimate the effects of changes in the energetics at the bilayer surfaces on the channel dwell time, concluding that the change would have to be greater than typically observed for the Hofmeister effect outside the context of the lipid bilayer., Ion specificity and, in particular, the distinctive effects of anions in salt-induced protein precipitation have been known since the 1880’s, when Franz Hofmeister established the ranking of anions in their ability to regulate egg yolk protein water solubility []. Experimental and theoretical studies have given a detailed empirical picture of the phenomenon, the nature of the ionic interactions with the surfaces leading to the Hofmeister effect is still under debate []. The only consensus is that it cannot be explained by standard theories of electrolytes. For example, bromide is unique in that its salts were recognized as a drug to treat epilepsy a couple of dozen years before Hofmeister’s studies [] and they are still in use to treat specific types of refractory seizures in children [], but the mechanism of their action remains elusive., , Hofmeister effect studied with a nanopore in a neutral lipid membrane. Rather unexpectedly, we find that conductance of a purely cation-selective peptide pore is regulated by anions in correlation with their position in the Hofmeister series. Moreover, the pore conformational dynamics are highly sensitive to the anion species. We relate both effects to preferential depletion of kosmotropic anions (accumulation of chaotropic anions) at the membrane-water interface