Plasma sheath effects on ion collection by a pinhole

This work presents tables to assist in the evaluation of pinhole collection effects on spacecraft. These tables summarize results of a computer model which tracks particle trajectories through a simplified electric field in the plasma sheath. A technique is proposed to account for plasma sheath effects in the application of these results and scaling rules are proposed to apply the calculations to specific situations. This model is compared to ion current measurements obtained by another worker, and the agreement is very good

Ion collection from a plasma by a pinhole

Ion focusing by a biased pinhole is studied numerically. Laplace's equation is solved in 3-D for cylindrical symmetry on a constant grid to determine the potential field produced by a biased pinhole in a dielectric material. Focusing factors are studied for ions of uniform incident velocity with a 3-D Maxwellian distribution superimposed. Ion currents to the pinhole are found by particle tracking. The focusing factor of positive ions as a function of initial velocity, temperature, injection radius, and hole size is reported. For a typical Space Station Freedom environment (oxygen ions having a 4.5 eV ram energy, 0.1 eV temperature, and a -140 V biased pinhole), a focusing factor of 13.35 is found for a 1.5 mm radius pinhole

Tapping to a slow tempo in the presence of simple and complex musical meters reveals experience-specific biases for processing music

Musical meters vary considerably across cultures, yet relatively little is known about how culture-specific experience influences metrical processing. In Experiment 1, we compared American and Indian listeners\u27 synchronous tapping to slow sequences. Inter-tone intervals contained silence or to-be-ignored rhythms that were designed to induce a simple meter (familiar to Americans and Indians) or a complex meter (familiar only to Indians). A subset of trials contained an abrupt switch from one rhythm to another to assess the disruptive effects of contradicting the initially implied meter. In the unfilled condition, both groups tapped earlier than the target and showed large tap-tone asynchronies (measured in relative phase). When inter-tone intervals were filled with simple-meter rhythms, American listeners tapped later than targets, but their asynchronies were smaller and declined more rapidly. Likewise, asynchronies rose sharply following a switch away from simple-meter but not from complex-meter rhythm. By contrast, Indian listeners performed similarly across all rhythm types, with asynchronies rapidly declining over the course of complex- and simple-meter trials. For these listeners, a switch from either simple or complex meter increased asynchronies. Experiment 2 tested American listeners but doubled the duration of the synchronization phase prior to (and after) the switch. Here, compared with simple meters, complex-meter rhythms elicited larger asynchronies that declined at a slower rate, however, asynchronies increased after the switch for all conditions. Our results provide evidence that ease of meter processing depends to a great extent on the amount of experience with specific meters

Preliminary Survey of the Terrestrial Isopods (Isopoda), Millipedes (Diplopoda), Harvestmen (Opiliones), and Spiders (Araneae) of Toft Point Natural Area, Door County, Wisconsin

Toft Point Natural Area is a National Natural Landmark owned and managed by the University of Wisconsin – Green Bay and located on the Lake Michigan shore of Wisconsin’s Door Peninsula. With twelve biotic communities on 700 acres, Toft Point contains considerable biological diversity. We conducted a preliminary survey of the arachnids (spiders and harvestmen, excluding mites and pseudoscorpions), millipedes (diplopods), and terrestrial isopods (Isopoda: Oniscoidea). Sampling occurred on three dates in 2001 using leaf litter collection with Berlese extraction and a timed collection by hand that incorporated a variety of techniques. Specimens from a 1992 survey and assorted collecting events were also used to compile a species list. The list includes five isopods, four millipedes, six harvestmen, and 113 spiders, including 16 new state records (two millipedes and 14 spiders) and 90 new Door County records. Litter collection and sampling in wetland habitats were both especially productive

Omnidirectional Sensory and Motor Volumes in Electric Fish

Active sensing organisms, such as bats, dolphins, and weakly electric fish, generate a 3-D space for active sensation by emitting self-generated energy into the environment. For a weakly electric fish, we demonstrate that the electrosensory space for prey detection has an unusual, omnidirectional shape. We compare this sensory volume with the animal's motor volume—the volume swept out by the body over selected time intervals and over the time it takes to come to a stop from typical hunting velocities. We find that the motor volume has a similar omnidirectional shape, which can be attributed to the fish's backward-swimming capabilities and body dynamics. We assessed the electrosensory space for prey detection by analyzing simulated changes in spiking activity of primary electrosensory afferents during empirically measured and synthetic prey capture trials. The animal's motor volume was reconstructed from video recordings of body motion during prey capture behavior. Our results suggest that in weakly electric fish, there is a close connection between the shape of the sensory and motor volumes. We consider three general spatial relationships between 3-D sensory and motor volumes in active and passive-sensing animals, and we examine hypotheses about these relationships in the context of the volumes we quantify for weakly electric fish. We propose that the ratio of the sensory volume to the motor volume provides insight into behavioral control strategies across all animals

Pouvoirs de l’équivoque

Fig. 1. Humbert de Molard, la fontaine Saint Furcy à Lagny, papier salé, détail d’une épreuve de 16,5 x 22 cm (voir fig. 7), 1847. Depuis les premiers temps de la photographie circule l’idée que les photographes “capturent des images”. Merveilleuse figure, qui assimile les opérateurs à des chasseurs de gros gibier ou à des zoologistes de terrain. Ainsi, les images flotteraient autour de nous comme des papillons de nuit, et les photographes les attraperaient dans leurs filets diaphanes, tels d..

Photographie, ontologie, analogie, compulsion

Notre compulsion à croire en l’identité entre les photographies et leur modèle alimente un répertoire d'analogies stéréotypées – fossile, empreinte, trace de pas, masque, relique, etc. – qui restent des ponts-aux-ânes de la réflexion théorique. L'article d'André Bazin, « Ontologie de la photographie » (1945), brillante réflexion sur l'opacité de la croyance, proposait un mythe moderne de la représentation. La répétition de ces métaphores depuis les années 1930 s'apparente en revanche à un ressassement. Le flou d'une photographie ou le dessin persistant d'un éclair fugace suffit à montrer les limites du modèle de transfert de présence. La photographie est une technologie picturale d’une remarquable plasticité, qui ne se laisse pas enfermer dans les catégories d'une pensée paresseuse.Our compulsion to believe in the identity between photographs and their model props up a range of stereotyped analogies – fossil, stamp, footprint, mask, relic, etc. - which together form the entry level of all theoretical reflection on the subject. André Bazin's article “Ontologie de la photographie” (1945), a dazzling meditation on the opacity of belief, sets out a modern myth of representation. In contrast, the repetition since the 1930s of the former metaphors constitutes a worn out yarn. Photographic blur or the traced permanence of a lightning flash, for example, are all the evidence needed to lay bare the limits of the transfer of presence model. Photography as a pictorial technology has remarkable plasticity, resistant to enclosure within the categories of cursory thinking

CROSS-CULTURAL INFORMATION TECHNOLOGY RESEARCH: THE CASE OF EASTERN EUROPE AND THE USSR

This paper discusses the specific problems and issues involved in studying information technologies in Eastern Europe and the USSR in the more general context of cross-cultural information technology (IT) research. The results reported are based on eight years of research into international information technologies by the Mosaic Group at the University of Arizona. The problems of doing this kind of work, where field and empirical studies are often impractical, are examined. Four analytical techniques, supported by a computer-based research environment, are advanced as means to solve these problems