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PubMed2005

Phase-space analysis of acoustics fields and its application to waveguide.

A description of two-dimensional acoustic fields by means of a joint "space-wave number" representation is discussed. A function defined in the phase-space domain (x,y,k(x),k(y)) is associated with a signal which is a function of spatial coordinates (x,y). This paper presents two methods to realize it. The first is to associate with each point (x,y) of the wave field a two-dimensional wave number spectrum (k(x),k(y)), called local spectrum. The second is to process by other coordinates the wave field along an arbitrary direction, introduced in quantum mechanics for the study of classical billiards, and provided by the Birkhoff variables (s,cos phi). Phase-space diagrams are given by quadratic phase-space distributions. Simulations are presented for wave fields in a 2D planar waveguide for a pedagogical point of view with Gaussian beam or point-source excitation, and nonuniform waveguides as a sudden area expansion chamber and an open billiard with a single incoming mode at the entrance of each of them. In these problems, local spectrum and Birkhoff analysis are used in order to identify the structures hidden in the field. The result is the contribution of different wave vectors which contribute to the field value at the analysis point or at a certain section of the boundary, and show complicated structure of the acoustic field like whispering gallery or diffracted waves.

Journal Article↗
PubMed1985

Bacterial fouling in a model core system.

We have used a sintered glass bead core to simulate the spaces and surfaces of reservoir rock in studies of the bacterial plugging phenomenon that affects waterflood oil recovery operations. The passage of pure or mixed natural populations of bacteria through this solid matrix was initially seen to promote the formation of adherent bacterial microcolonies on available surfaces. Bacteria within these microcolonies produced huge amounts of exopolysaccharides and coalesced to form a confluent plugging biofilm that eventually caused a >99% decrease in core permeability. Aerobic bacteria developed a plugging biofilm on the inlet face of the core, facultative anaerobes plugged throughout the core, and dead bacteria did not effectively plug the narrow (33-mum) spaces of this solid matrix because they neither adhered extensively to surfaces nor produced the extensive exopolysaccharides characteristic of living cells. The presence of particles in the water used in these experiments rapidly decreased the core permeability because they became trapped in the developing biofilm and accelerated the plugging of pore spaces. Once established, cells within the bacterial biofilm could be killed by treatment with a biocide (isothiazalone), but their essentially inert carbohydrate biofilm matrix persisted and continued to plug the pore spaces, whereas treatment with 5% sodium hypochlorite killed the bacteria, dissolved the exopolysaccharide biofilm matrix, and restored permeability to these plugged glass bead cores.

Journal Article↗
PubMed2003

Myocardial oxygenation in isolated hearts predicted by an anatomically realistic microvascular transport model.

An anatomically realistic model for oxygen transport in cardiac tissue is introduced for analyzing data measured from isolated perfused guinea pig hearts. The model is constructed to match the microvascular anatomy of cardiac tissue based on available morphometric data. Transport in the three-dimensional system (divided into distinct microvascular, interstitial, and parenchymal spaces) is simulated. The model is used to interpret experimental data on mean cardiac tissue myoglobin saturation and to reveal differences in tissue oxygenation between buffer-perfused and red blood cell-perfused isolated hearts. Interpretation of measured mean myoglobin saturation is strongly dependent on the oxygen content of the perfusate (e.g., red blood cell-containing vs. cell-free perfusate). Model calculations match experimental values of mean tissue myoglobin saturation, measured mean myoglobin, and venous oxygen tension and can be used to predict distributions of intracellular oxygen tension. Calculations reveal that approximately 20% of the tissue is hypoxic with an oxygen tension of <0.5 mmHg when the buffer is equilibrated with 95% oxygen to give an arterial oxygen tension of over 600 mmHg. The addition of red blood cells to give a hematocrit of only 5% prevents tissue hypoxia. It is incorrect to assume that the usual buffer-perfused Langendorff heart preparation is adequately oxygenated for flows in the range of < or =10 ml. min-1. ml tissue-1.

Animals↗
PubMed1994

Doppler evaluation of cardiac filling and ejection properties in humans during parabolic flight.

The cardiac filling and ejection properties of seven normal human subjects were examined during microgravity created on a National Aeronautics and Space Administration aircraft during parabolic flight. Doppler echocardiography was used to measure intracardiac velocities in sitting and supine subjects during three phases of flight: hypergravity (phase I), early microgravity (phase III), and late microgravity (phase IV). Heart rate declined 6% (P < 0.001) and right ventricular inflow velocities rose (46%, early; 26%, mean; P < 0.01) between phase I and phases III or IV in the sitting position only. Peak left ventricular outflow velocities rose 12% and inflow velocities rose (13%, early; 20%, mean) between phases I and IV while subjects were in the supine position (P < 0.05). A 14% rise in early velocities alone was seen between phases I and IV while subjects were in the sitting position (P < 0.05). In subjects entering microgravity while sitting, right heart chambers can accept additional venous return. When microgravity was entered while subjects were supine, however, venous augmentation was not observed. Left heart filling was more prominently enhanced when microgravity was entered while subjects were supine, suggesting a shift of fluid within the pulmonary vasculature.

Adult↗
PubMedDate not supplied

Effect of fluoridated toothpicks and dental flosses on enamel and dentine and on plaque composition in situ.

The aim was to evaluate the effect of two toothpicks and two dental flosses on demineralized enamel and dentine and on plaque composition, using an in situ model with simulated approximal spaces within dentures. Fifteen subjects with full dentures were recruited and 14 completed the study. It consisted of two crossover periods, the first comparing a birch toothpick with AmF and a birch toothpick with NaF, and the second comparing a dental floss with AmF + NaF and a dental floss without F. Between these four periods, there was a control period without any approximal cleaning. In small, rectangular sample holders, one enamel and one dentine specimen were embedded, forming a triangular, approximal-like space. Two sample holders were mounted in the premolar-molar region of the upper or lower dentures. The subjects used the toothpicks or dental flosses 3 times/day for 4 weeks. The results showed that all toothpicks and dental flosses inhibited further demineralization compared to the control period (p < 0.001). The dental flosses were somewhat more effective in this respect than the toothpicks, especially in dentine. There were relatively small numerical differences between AmF and NaF toothpicks, but in favour of NaF regarding mineral gain (p < 0.05). The fluoridated floss gave somewhat less lesion depth in dentine than the non-fluoridated floss (p < 0.01). Toothpicks and flosses resulted in lower counts of microorganisms in plaque compared to the control period (p < 0.001); the AmF toothpick gave a more pronounced reduction than the NaF toothpick (p < 0.001).

Aged↗
PubMed2000

Antarctica natural laboratory and space analogue for psychological research.

This introduction to the special issue traces the history of psychosocial concerns related to Antarctic exploration, from the heroic age of early explorers through the International Geophysical Year (IGY) of 1957 to 1958 to recent and current systematic research projects. The introduction discusses the organization and topics of international psychological investigations in polar stations and summarizes the articles that follow. Living in Antarctica imposes some unusual restrictions as well as opportunities, and it requires psychological adaptation to extreme environmental circumstances. The thrust of previous scientific and popular literature has been to focus on the negative effects of the situation and ignore the positive ones; however, ongoing studies are bringing about a more balanced view. Having an accurate understanding is important not only intrinsically and for appropriate application in the Antarctic itself but also in analogous extreme and unusual environments. These include extended space flight and space habitation, such as the projected voyage to Mars.

Adaptation, Psychological↗
PubMed2000

How self-image and personality influence performance in an isolated environment.

The purpose of this research is to explore the relationships between self-image and personality characteristics with cognitive impairment in an isolated group during wintering. Cognitive performance is measured with the Stres Battery (SB), self-image by Abraham's Matrix of Intra- and Inter-Processes in Groups (MIPG), and interpersonal characteristics by the usual personality inventories. Results show that good cognitive performances are related to discordances between the real self and the ideal self and that bad performances are related to harmony between these two images. Moreover, the best cognitive performers have low scores in extroversion and assertiveness. The results are discussed in terms of specific adaptive reactions to wintering.

Adaptation, Psychological↗
PubMed2002

A 1-year, three-couple expedition as a crew analog for a Mars mission.

This study assessed the intrapersonal and interpersonal functioning of a three-couple expedition group that included a 2 1/2-year-old child which was ice-locked on a boat in the High Arctic during a major portion of the expedition. Personality assessment indicated that team members were generally well adjusted, scoring relatively higher on well-being and achievement and relatively lower on stress reactivity. Weekly mood ratings showed that the group exhibited significantly higher positive than negative affect. Reported negative events were relatively most frequent at the beginning of the Arctic stay and toward the end of the darkness period and were lowest during the initial darkness interval. The period of darkness had both a salutary and negative impact. A highly important means of coping with stress was seeking emotional support from one's partner. Selection of couples with strong bonds with their partner appears to be one viable approach for crew selection for long-duration missions.

Adaptation, Psychological↗
PubMed2005

The effect of purified compared with nonpurified diet on bone changes induced by hindlimb suspension of female rats.

The purpose of this study was to compare the bone changes induced by unloading in rats fed different diets, because space flight studies use a semipurified diet, whereas space flight simulation studies typically use nonpurified diets. Female Sprague-Dawley rats were fed a purified American Institute of Nutrition (AIN) 93G diet or a standard nonpurified diet and kept ambulatory or subjected to unloading by hindlimb suspension (HLS) for 38 days. Bone mineral content (BMC), mechanical strength, and factors related to the diet that affect bone (i.e., urinary calcium excretion, estradiol, and corticosterone) were measured. Average food intakes (grams per day) differed for diets, but caloric intake (kilocalories per day) and the final body masses of treatment groups were similar. The HLS-induced decrease in femoral BMC was not statistically different for rats fed a nonpurified diet (-8.6%) compared with a purified AIN-93G diet (-11.4%). The HLS-induced decrease in femoral mechanical strength was not statistically different for rats fed a nonpurified diet (-24%) compared with a purified AIN-93G diet (-31%). However, bone lengths were decreased (P < 0.05) in rats fed a nonpurified diet compared with a purified diet. Plasma estradiol levels were lower (P < 0.05) in the HLS/AIN-93G group but similar in the HLS and ambulatory rats fed a nonpurified diet. Plasma estradiol was related to femoral BMC (r = 0.85, P < 0.01). Urinary calcium excretion was higher (P < 0.05) in rats fed a nonpurified diet than those fed a purified AIN-93G diet, which is consistent with the higher level of calcium in the nonpurified diet. Urinary corticosterone levels were higher (P < 0.05) in rats fed a nonpurified diet than rats fed the AIN-93G diet. Although the osteopenia induced by unloading was similar in both diet groups, there were differences in longitudinal bone growth, calcium excretion, plasma estradiol levels, and urinary corticosterone levels. Results indicate that the type of standard diet used is an important factor to consider when measuring bone end points.

Animals↗
PubMed2005

Ultrasound guidance for facet joint injections in the lumbar spine: a computed tomography-controlled feasibility study.

UNLABELLED: We conducted this study to develop an ultrasound-guided approach for facet joint injections of the lumbar spine. Five zygapophyseal joints (L1-S1) on each side of 5 embalmed cadavers were examined by ultrasound for a total of 50 examinations. The joint space was demonstrated under ultrasound guidance. The midpoint of the joint space, defined as the middle of its cranio-caudal extension on its dorsal surface, was taken as a reference point, and its position was computed from its depth and lateral distance from the spinous process. Forty-two of 50 approaches could be clearly visualized. Subsequently, these distances were compared to those obtained by computed tomography (CT). To assess the efficacy of ultrasound in the needle placement, all lumbar facet joints were approached in one embalmed cadaver. The exact placement of the needle tips was again evaluated by CT. Ultrasound and CT measurements showed the same mean depth and lateral distance to the reference point, 3.15 +/- 0.5 cm and 1.9 +/- 0.6 cm, respectively. Pearson's coefficient of correlation was 0.86 (P < 0.0001) between ultrasound and CT. All 10 needle tips were within the joint space during simulated facet joint injections. We conclude that ultrasound guidance might be a useful adjunct for facet joint injections in the lumbar spine. IMPLICATIONS: This study was designed to develop an ultrasound-guided approach to the facet joints of the lumbar spine and to assess its feasibility and accuracy by means of a comparison to computed tomography images. The imaging study demonstrated a significant correlation between ultrasound and computed tomography measurements. During simulated facet injection, ultrasound guidance consistently resulted in accurate needle placement.

Cadaver↗
PubMed2001

Effect of geometric field of view on stereoscopic spatial judgments.

Within a stereoscopic display the field of view (FOV) was held constant at 13.86 degrees while the geometric field of view (GFOV) was varied across four levels: 0 degrees (parallel), 13.86 degrees (veridical), 50 degrees and 100 degrees. Participants performed a distance-matching task where they adjusted the distance of a standard track from the centre of the display to match the distance of a target track from the same point. The results indicated that while the least error occurred in the veridical GFOV condition, small variations of GFOV away from the veridical have little effect. Large differences between FOV and GFOV (36 degrees and 86 degrees) increased errors markedly. A trend toward better performance in the veridical GFOV condition relative to the parallel GFOV condition suggests that the use of linear perspective information in a stereoscopic display may facilitate more accurate spatial perception. Actual or potential applications of this work include stereoscopic display design in aviation and non-aviation settings.

Adult↗
PubMed2001

Pathway HUDs: are they viable?

We describe two experiments that examine 3D pathway displays in a head-up location for aircraft landing and taxi. We address both guidance performance and pilot strategies in dividing, focusing, and allocating attention between flight path information and event monitoring. In Experiment 1 the 3D pathway head-up display (HUD) was compared with a conventional 2D HUD. The former was found to produce better guidance, with few costs to event detection. Some evidence was provided that attentional tunneling of the pathway HUD inhibits the detection of unexpected traffic events. In Experiment 2, the pathway display was compared in a head-up versus a head-down location. Excellent guidance was achieved in both locations. A slight HUD cost for vertical tracking in the air was offset by a HUD benefit for event detection and for lateral tracking during taxi (i.e., on the ground). The results of both experiments are interpreted within the framework of object- and space-based theories of visual attention and point to the conclusion that pathway HUDs combine the independent advantages of pathways and HUDs, particularly during ground operations. Actual or potential applications include understanding the costs and benefits of positioning a 3D pathway display in a head-up location.

Aircraft↗
PubMed2001

Mutations in mammalian cells induced by heavy charged particles: an indicator for risk assessment in space.

Induction of mutations at the HPRT locus in V79 Chinese hamster cells by heavy charged particles is reviewed. A unique dependence of mutation induction cross sections on LET or any other physical parameter of the particles cannot be found. There is, however, a general trend showing an increase up to about 100 keV/microm and an indication of a saturation with higher LET. An empirical expression is given approximating the data which may be useful for practical purposes. On the basis of this expression, it is suggested that the formula used by the ICRP for the quality factor overestimates the risk for very heavy particles. This may have implications for the assessment of the risk of exposure to iron ions in space.

Aerospace Medicine↗
PubMed2005

The immune system in space, including Earth-based benefits of space-based research.

Exposure to space flight conditions has been shown to result in alterations in immune responses. Changes in immune responses of humans and experimental animals have been shown to be altered during and after space flight of humans and experimental animals or cell cultures of lymphoid cells. Exposure of subjects to ground-based models of space flight conditions, such as hindlimb unloading of rodents or chronic bed rest of humans, has also resulted in changes in the immune system. The relationship of these changes to compromised resistance to infection or tumors in space flight has not been fully established, but results from model systems suggest that alterations in the immune system that occur in space flight conditions may be related to decreases in resistance to infection. The establishment of such a relationship could lead to the development of countermeasures that could prevent or ameliorate any compromises in resistance to infection resulting from exposure to space flight conditions. An understanding of the mechanisms of space flight conditions effects on the immune response and development of countermeasures to prevent them could contribute to the development of treatments for compromised immunity on earth.

Aerospace Medicine↗
PubMedDate not supplied

Development of a gravity-independent wastewater bioprocessor for advanced life support in space.

Operation of aerobic biological reactors in space is controlled by a number of challenging constraints, mainly stemming from mass transfer limitations and phase separation. Immobilized-cell packed-bed bioreactors, specially designed to function in the absence of gravity, offer a viable solution for the treatment of gray water generated in space stations and spacecrafts. A novel gravity-independent wastewater biological processor, capable of carbon oxidation and nitrification of high-strength aqueous waste streams, is presented. The system, consisting of a fully saturated pressurized packed bed and a membrane oxygenation module attached to an external recirculation loop, operated continuously for over one year. The system attained high carbon oxidation efficiencies often exceeding 90% and ammonia oxidation reaching approximately 60%. The oxygen supply module relies on hydrophobic, nonporous, oxygen selective membranes, in a shell and tube configuration, for transferring oxygen to the packed bed, while keeping the gaseous and liquid phases separated. This reactor configuration and operating mode render the system gravity-independent and suitable for space applications.

Bacteria, Aerobic↗
PubMedDate not supplied

Problems of intergroup behavior in human spaceflight operations.

This paper discusses intergroup dynamics in human spaceflight operations. A definition of intergroup behavior is presented and prerequisite conditions for intergroup conflict are explored. Research and anecdotal evidence of intergroup conflict between groups and subgroups in exotic environments and space operations is presented. Concepts from the literature on intergroup conflicts are discussed in the context of possible conflict resolution interventions. Factors that may affect intergroup dynamics in human spaceflight operations and the need for intergroup research are highlighted.

Aerospace Medicine↗
PubMedDate not supplied

Psychosocial effects of adjustment in Antarctica: lessons for long-duration spaceflight.

This paper examines the utility of remote, isolated Antarctic research stations as analogs for long-duration spaceflights from the perspective of psychosocial processes of adaptation and adjustment. Certain features of the physical and man-made environments found in Antarctica are similar to those that will be encountered in outer space. In both settings, men and women are likely to experience a number of physiological and psychological changes in response to the extreme environmental conditions and the prolonged isolation and confinement. Biomedical research in Antarctica provides an opportunity to study the causes of these changes and to develop strategies for reducing the risks to health and well-being before they pose a serious threat to crew safety and mission success. A number of lessons for long-duration spaceflight are examined, including screening and selection of personnel; training programs designed to facilitate individual adjustment and group adaptation and minimize group conflict; identification of optimal leadership characteristics for small, isolated groups; an understanding of social dynamics and group "microcultures" necessary for the organization and management of small but heterogeneous groups; organization of work activities; facility design; and support infrastructure.

Adaptation, Physiological↗