Lower Pressure Thresholds Research Articles

Optical and acoustical characterization of the subharmonic response of single UCA microbubbles

Coated microbubbles, unlike tissue, are able to scatter sound subharmonically. Therefore, the subharmonic behavior of coated microbubbles can be used to enhance the contrast in ultrasound contrast imaging. Theoretically, a threshold amplitude of the driving pressure can be calculated above which subharmonic oscillations of microbubbles are initiated. Interestingly, earlier experimental studies on coated microbubbles demonstrated that the threshold for these bubbles is much lower than predicted by the traditional linear viscoelastic shell models. Here we present an optical and acoustical study on the subharmonic response of individual microbubbles, e.g. the radial subharmonic response of the microbubbles was recorded with the Brandaris ultra high-speed camera as a function of both the amplitude and the frequency of the driving pulse. Threshold pressures for subharmonic generation as low as 5 kPa were found near a driving frequency equal to twice the resonance frequency of the bubble. An explanation for this low threshold pressure is provided by the shell buckling model proposed by Marmottant et al. It is shown that the change in the elasticity of the bubble shell as a function of bubble radius enhances the subharmonic behavior of the microbubbles.

178 MUSCLE PRECURSOR CELLS (MPCS) AND ADIPOSE-DERIVED STEM CELLS (ADSCS) FOR THE TREATMENT OF

You have accessJournal of UrologyStem Cell Research1 Apr 2011178 MUSCLE PRECURSOR CELLS (MPCS) AND ADIPOSE-DERIVED STEM CELLS (ADSCS) FOR THE TREATMENT OF Mathias Tremp, Souzan Salemi, Tamer Aboushwareb, Tullio Sulser, and Eberli Daniel Mathias TrempMathias Tremp Zürich, Switzerland More articles by this author , Souzan SalemiSouzan Salemi Zürich, Switzerland More articles by this author , Tamer AboushwarebTamer Aboushwareb Winston Salem, NC More articles by this author , Tullio SulserTullio Sulser Zürich, Switzerland More articles by this author , and Eberli DanielEberli Daniel Zürich, Switzerland More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2011.02.247AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Bladder voiding dysfunction (BVD) in the elderly is commonly due to bladder outflow obstruction (benign prostatic hyperplasia, BPH) with 30% of men at the age of 65 affected. Currently there is no treatment modality that reverses the underlying cause, the decreased bladder contractility. Muscle Precursor Cells (MPCs) and adipose-derived stem cells (ADSCs) are envisioned as promising cell sources with the capability to regenerate muscle fibers. The goal of this research was to evaluate the use of adult stem cells for the treatment of bladder voiding dysfunction due to decrease muscle contractility. METHODS Infravesical obstruction was performed in 66 male Lewis rat (6–8 weeks old); six weeks later, eight rats were evaluated as a positive control by cystometry and later by organ bath analysis. In addition, morphological (histomorphometry, Western-Blotting, RT-PCR) bladder tissue changes were analysed. MPCs from the soleus muscle and ADSC from the inguinal region of adult male Lewis rats were expanded in culture and characterized. In sixteen rats, stem cell injection with an insulin syringe (1.5 x 106 cells) into the bladder wall and deligation was performed six weeks after the obstruction. Target cells were labelled with PKH-67. 4 and 8 weeks after stem cell injection, morphological and functional changes were assessed. Healthy, age matched rats served as a control. RESULTS MPCs and ADSCs used were positively characterised by FACS. Obstructed rats had a greater bladder weight, lower threshold pressure, maximum bladder pressure and lower contractility on Electrical Field Stimulation (EFS) at 80V and 32Hz than age matched rats (1.09g±0.273g vs. 11.269g±2.9g, p=0.001). Histomorphometric analysis showed a higher connective tissue-to-smooth muscle ratio between the animals with obstruction and controls. After stem cell injection, we were able to track the cells by PKH67. Functional analysis 4 and 8 weeks after stem cell injection showed a significantly improved bladder contraction (3.37g±0.52g for ADSC, p=0.01; 4.26g±0.97g for MPC, p<0.001) and higher intermicturition pressure. The same trend was seen by RT-PCR and Western-Blotting where gene expression and protein translation of smoothelin and caldesmon after stem cell therapy was closer to normal. CONCLUSIONS In our study, we were able to establish a model of hypocontractile bladder in a small animal and demonstrated that MPCs and ADSCs can support the restoration of bladder voiding dysfunction. Our results show improved contractility, voiding pressures and molecular expression after cell therapy. © 2011 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 185Issue 4SApril 2011Page: e74 Peer Review Report Advertisement Copyright & Permissions© 2011 by American Urological Association Education and Research, Inc.MetricsAuthor Information Mathias Tremp Zürich, Switzerland More articles by this author Souzan Salemi Zürich, Switzerland More articles by this author Tamer Aboushwareb Winston Salem, NC More articles by this author Tullio Sulser Zürich, Switzerland More articles by this author Eberli Daniel Zürich, Switzerland More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Subharmonic behavior of phospholipid-coated ultrasound contrast agent microbubbles

Coated microbubbles, unlike tissue are able to scatter sound subharmonically. Therefore, the subharmonic behavior of coated microbubbles can be used to enhance the contrast in ultrasound contrast imaging. Theoretically, a threshold amplitude of the driving pressure can be calculated above which subharmonic oscillations of microbubbles are initiated. Interestingly, earlier experimental studies on coated microbubbles demonstrated that the threshold for these bubbles is much lower than predicted by the traditional linear viscoelastic shell models. This paper presents an experimental study on the subharmonic behavior of differently sized individual phospholipid coated microbubbles. The radial subharmonic response of the microbubbles was recorded with the Brandaris ultra high-speed camera as a function of both the amplitude and the frequency of the driving pulse. Threshold pressures for subharmonic generation as low as 5 kPa were found near a driving frequency equal to twice the resonance frequency of the bubble. An explanation for this low threshold pressure is provided by the shell buckling model proposed by Marmottant et al. [J. Acoust. Soc. Am. 118, 3499-3505 (2005)]. It is shown that the change in the elasticity of the bubble shell as a function of bubble radius as proposed in this model, enhances the subharmonic behavior of the microbubbles.

Vocal power and pressure–flow relationships in excised tiger larynges

Despite the functional importance of loud, low-pitched vocalizations in big cats of the genus Panthera, little is known about the physics and physiology of the mechanisms producing such calls. We investigated laryngeal sound production in the laboratory using an excised-larynx setup combined with sound-level measurements and pressure-flow instrumentation. The larynges of five tigers (three Siberian or Amur, one generic non-pedigreed tiger with Bengal ancestry and one Sumatran), which had died of natural causes, were provided by Omaha's Henry Doorly Zoo over a five-year period. Anatomical investigation indicated the presence of both a rigid cartilaginous plate in the arytenoid portion of the glottis, and a vocal fold fused with a ventricular fold. Both of these features have been confusingly termed 'vocal pads' in the previous literature. We successfully induced phonation in all of these larynges. Our results showed that aerodynamic power in the glottis was of the order of 1.0 W for all specimens, acoustic power radiated (without a vocal tract) was of the order of 0.1 mW, and fundamental frequency ranged between 20 and 100 Hz when a lung pressure in the range of 0-2.0 kPa was applied. The mean glottal airflow increased to the order of 1.0 l s(-1) per 1.0 kPa of pressure, which is predictable from scaling human and canine larynges by glottal length and vibrational amplitude. Phonation threshold pressure was remarkably low, on the order of 0.3 kPa, which is lower than for human and canine larynges phonated without a vocal tract. Our results indicate that a vocal fold length approximately three times greater than that of humans is predictive of the low fundamental frequency, and the extraordinarily flat and broad medial surface of the vocal folds is predictive of the low phonation threshold pressure.

Detonation Limit Thresholds in H2/O2 Rotating Detonation Engine

The rotating detonation engine (RDE) is a new engine system using detonation, which may provide a higher performance and smaller and simpler design in comparison with the pulse detonation engine (PDE) and other traditional engines. However the research on RDE stands just at the first step now. The authors perform a numerical analysis to understand about RDE in terms of features of rotating detonation and its propagation limit. The lower threshold pressure of detonation limit was 2.6 MPa and the upper threshold pressure of detonation limit was 7.1 MPa. The engine performance analysis shows that the maximum mixture based specific impulse (I spm ) was about 440 s, which is comparable with that of the present typical rocket engine.

Antihypertensive Treatments, Cognitive Decline, and Dementia

Chronic hypertension is associated with an increased risk of both vascular dementia and Alzheimer's disease (AD). In this context, the role of anti-hypertensive therapy for the prevention and delay of cognitive decline and dementia is of central importance. Most longitudinal studies have shown a significant inverse association between anti-hypertensive therapies and dementia incidence and for some of these, particularly in AD. Seven randomized, double blind placebo-controlled trials have evaluated the benefit of antihypertensive treatments on cognition. Three of them found positive results in term of prevention of dementia (SYST-EUR) or cognitive decline (PROGRESS, HOPE). Others disclosed non-significant results (MRC, SHEP, SCOPE, HYVET-COG). This discrepancy emphasizes the difficulty to perform such trials: the follow-up has to be long enough to disclose a benefit, a large number of patients is needed for these studies, and because of ethical reasons some anti-hypertensive treatments are often prescribed in the placebo group. Results of the two more recent meta-analyses are inconsistent, possibly due to methodological issues. Antihypertensive treatments could be beneficial to cognitive function by lowering blood pressure and/or by specific neuroprotective effect. Three main antihypertensive subclasses have been associated with a beneficial effect on cognitive function beyond blood pressure reduction (calcium channel blockers, angiotensin converting enzyme inhibitor, angiotensin-AT1-receptor-blockers). Further long-term randomized trials, designed especially to assess a link between antihypertensive therapy and cognitive decline or dementia are therefore needed with cognition as the primary outcome. A low blood pressure threshold that could be deleterious for cognitive function should also be determined.

Where do the embryos of Riftia pachyptila develop? Pressure tolerances, temperature tolerances, and buoyancy during prolonged embryonic dispersal

Abstract The giant vent tubeworm Riftia pachyptila releases slightly buoyant lipid-rich zygotes into the water column, where embryos develop and disperse for 21–25 days before they become ciliated larvae capable of controlling their position in the water column. If embryos rise too rapidly, either from their own buoyancy or by being entrained in a buoyant plume, they could encounter warmer temperatures or lower pressures than the embryos can tolerate. Likewise, if they are entrained among the tubes of the adults or in near-bottom currents, the embryos could encounter warm water and adverse chemical conditions. To determine the range of physiological tolerances for normal development of R. pachyptila, we examined survival of embryos at various combinations of pressure and temperature in the laboratory using small pressure vessels. We also used small incubation chambers deployed in and above tubeworm clusters at our study site on the East Pacific Rise. These served as an in situ comparison for the laboratory data. Temperatures were measured at each incubation site with temperature data loggers. The ambient temperature away from the vents at the study site was 2 °C, and the upper thermal limit for 50% normal development was 6 °C for embryos cultured in the pressure vessels and approximately 7 °C in situ. This limited temperature tolerance defines the embryos physiologically as “cold stenotherms”. In laboratory experiments conducted at 2 °C, embryos developed normally at the near-ambient vent pressure of 238 and also at 170 atm. Cleavage rates at 170 atm were much slower than at the higher pressure, however, suggesting that the embryos were probably near their low-pressure threshold. No development occurred at 100 or at 1 atm. During upward migration, embryos would encounter a pressure of 170 atm at a significantly greater depth (1700 m) than they would encounter a temperature of 6 °C, suggesting that embryonic survival should be pressure limited before temperature becomes a controlling factor. To determine the likelihood that these physiological stresses would be encountered during embryogenesis, we measured flotation rates of zygotes and early embryos. At ambient vent pressure (250 atm) and temperature, the zygotes rose at an average rate of 2 m day−1. As the embryos develop, they consume wax esters and therefore lose some buoyancy, but assuming a constant flotation of 2 m day−1 for 25 days, this would bring the embryos approximately 50 m off the bottom. If embryos were entrained in a buoyant plume however, they would reach a depth of slightly more than 2300 m (230 atm) before the plume becomes neutrally buoyant. In either case, the embryos would remain below the critical depth for normal development. Because development is inhibited at temperatures above 6–7 °C, it is unlikely that embryos are retained in or among the adult tubes.

Fine‐touch pressure thresholds in the adult penis

To map the fine-touch pressure thresholds of the adult penis in circumcised and uncircumcised men, and to compare the two populations. Adult male volunteers with no history of penile pathology or diabetes were evaluated with a Semmes-Weinstein monofilament touch-test to map the fine-touch pressure thresholds of the penis. Circumcised and uncircumcised men were compared using mixed models for repeated data, controlling for age, type of underwear worn, time since last ejaculation, ethnicity, country of birth, and level of education. The glans of the uncircumcised men had significantly lower mean (sem) pressure thresholds than that of the circumcised men, at 0.161 (0.078) g (P = 0.040) when controlled for age, location of measurement, type of underwear worn, and ethnicity. There were significant differences in pressure thresholds by location on the penis (P < 0.001). The most sensitive location on the circumcised penis was the circumcision scar on the ventral surface. Five locations on the uncircumcised penis that are routinely removed at circumcision had lower pressure thresholds than the ventral scar of the circumcised penis. The glans of the circumcised penis is less sensitive to fine touch than the glans of the uncircumcised penis. The transitional region from the external to the internal prepuce is the most sensitive region of the uncircumcised penis and more sensitive than the most sensitive region of the circumcised penis. Circumcision ablates the most sensitive parts of the penis.

Scaling of Tip Vortex Cavitation Inception Noise With a Bubble Dynamics Model Accounting for Nuclei Size Distribution

The acoustic pressure generated by cavitation inception in a tip vortex flow was simulated in water containing a realistic bubble nuclei size distribution using a surface-averaged pressure (SAP) spherical bubble dynamics model. The flow field was obtained by the Reynolds-averaged Navier–Stokes computations for three geometrically similar scales of a finite-span elliptic hydrofoil. An “acoustic” criterion, which defines cavitation inception as the flow condition at which the number of acoustical “peaks” above a pre-selected pressure level exceeds a reference number per unit time, was applied to the three scales. It was found that the scaling of cavitation inception depended on the reference values (pressure amplitude and number of peaks) selected. Scaling effects (i.e., deviation from the classical σi∝Re0.4) increase as the reference inception criteria become more stringent (lower threshold pressures and less number of peaks). Larger scales tend to detect more cavitation inception events per unit time than obtained by classical scaling because a relatively larger number of nuclei are excited by the tip vortex at the larger scale due to simultaneous increase of the nuclei capture area and of the size of the vortex core. The average nuclei size in the nuclei distribution was also found to have an important impact on cavitation inception number. Scaling effects (i.e., deviation from classical expressions) become more important as the average nuclei size decreases.

A Novel Approach to Derive a Compression Parameter Indicating Effective Particle Deformability

In this article, a compression parameter is derived and its physical significance discussed. Tablets were formed from two sodium chloride powders and from two sucrose powders over a wide range of compaction pressures and the tensile strength and the porosity of the tablets were determined. From these data, the novel compression parameter and the Heckel parameter were calculated. Above a lower pressure threshold, the tablet strength increased relatively linear with compaction pressure up to 300–500 MPa and thereafter, the tablet strength leveled off. From the linear region, the compression parameter was derived. The tablet porosity data obeyed reasonably the Heckel function and from the linear region, the yield strength was calculated. For all four powders, a ratio between the compression parameter and the Heckel yield strength of about 3 was obtained. It is concluded that the suggested compression parameter represents an indication of the effective deformability of particles during compression which is suggested to correlate with the hardness of the particles.

Methanogenium marinum sp. nov., a H2-using methanogen from Skan Bay, Alaska, and kinetics of H2 utilization.

A methanogen, strain AK-1, was isolated from permanently cold marine sediments, 38- to 45-cm below the sediment surface at Skan Bay, Alaska. The cells were highly irregular, nonmotile coccoids (diameter, 1 to 1.2 microm), occurring singly. Cells grew by reducing CO2 with H2 or formate as electron donor. Growth on formate was much slower than that on H2. Acetate, methanol, ethanol, 1- or 2-propanol, 1- or 2-butanol and trimethylamine were not catabolized. The cells required acetate, thiamine, riboflavin, a high concentration of vitamin B12, and peptones for growth; yeast extract stimulated growth but was not required. The cells grew fastest at 25 degrees C (range 5 degrees C to 25 degrees C), at a pH of 6.0-6.6 (growth range, pH 5.5-7.5), and at a salinity of 0.25-1.25 M Na+. Cells of this and other H2-using methanogens from saline environments metabolized H2 to a very low threshold pressure (less than 1 Pa) that was dependent on the methane partial pressure. We propose that the threshold pressure may be limited by the energetics of catabolism. The sequence of the 16S rDNA gene of strain AK-1 was most similar (98%) to the sequences of Methanogenium cariaci JR-1 and Methanogeniumfrigidum Ace-2. DNA-DNA hybridization between strain AK-1 and these two strains showed only 34.9% similarity to strain JR-1 and 56.5% similarity to strain Ace-2. These analyses indicated strain AK-1 should be classified as a new species within the genus Methanogenium. Phenotypic differences between strain AK-1 and these strains (including growth temperature, salinity range, pH range, and nutrient requirements) support this. Therefore, a new species, Methanogenium marinum, is proposed with strain AK-1 as type strain.

H. pylori Infection and Visceral Hypersensitivity in Patients with Irritable Bowel Syndrome

Background/Aim: Irritable bowel syndrome (IBS) is characterized by abdominal pain and changes in stool habits. Visceral hypersensitivity (VH) is a key factor in the pathophysiology of IBS. The role of Helicobacter pylori infection in the induction of VH in the upper gastrointestinal tract is controversially discussed. The aim of this study is to evaluate the value of rectal barostat in eliciting abdominal symptoms in patients with IBS in relation to H. pylori infection. Patients and Methods: 31 patients (19 female, 12 male, mean age 45.6 ± 10 years) with normal colonoscopy and clinical signs of IBS were examined by rectal barostat (pressure-controlled balloon distension in the rectum). Induction of typical abdominal discomfort (far from the balloon) defined the examination positive. Level of nonpainful perception (L1), feeling of defecation (L2), and pain or stool urgency (L3) were registered in comparison with a healthy control group (CG; n = 15, 9 female, 6 male). The H. pylori status was defined by ¹³C-urea breath test (n = 46). Results: Typical abdominal discomfort was induced in 9 patients (pain group, PG) by pressure-controlled rectal distension (H. pylori status: 8 positive, 1 negative). Patients not presenting with abdominal pain to rectal distension (nonpain group, NPG) were all H. pylori negative (p < 0.001). L3 as an indicator of VH was reached at a lower pressure threshold in PG than in NPG or CG (p < 0.05). The perception was not different between NPG and CG (p > 0.05). Conclusions: The induction of typical abdominal discomfort in patients with IBS by the use of rectal barostat occurred predominantly in H. pylori infected patients and suggests that H. pylori infection may be involved in triggering VH in patients with IBS. Further studies in larger patient groups and after H. pylori eradication therapy are needed to confirm and extend this observation.

Sensory fibers of the pelvic nerve innervating the Rat's urinary bladder.

Much attention has been given to the pelvic nerve afferent innervation of the urinary bladder; however, reports differ considerably in descriptions of afferent receptor types, their conduction velocities, and their potential roles in bladder reflexes and sensation. The present study was undertaken to do a relatively unbiased sampling of bladder afferent fibers of the pelvic nerve in adult female rats. The search stimulus for units to be studied was electrical stimulation of both the bladder nerves and the pelvic nerve. Single-unit activity of 100 L(6) dorsal root fibers, activated by both pelvic and bladder nerve stimulation, was analyzed. Sixty-five units had C-fiber and 35 units had Adelta-fiber conduction velocities. Receptive characteristics were established by direct mechanical stimulation, filling of the bladder with 0.9% NaCl at a physiological speed and by filling the bladder with solutions containing capsaicin, potassium, or turpentine oil. The majority (61) of these fibers were unambiguously excited by bladder filling with 0.9% NaCl and were classified as mechanoreceptors. All mechanoreceptors with receptive fields on the body of the bladder had low pressure thresholds (</=10 mmHg). Receptive fields of units with higher thresholds were near the ureterovesical junction, on the base of the bladder or could not be found. Neither thresholds nor suprathreshold responses could be related to conduction velocity. Bladder compliance and mechanoreceptor thresholds were influenced by the stage of the estrous cycle: both were lowest in proestrous rats and highest in metaestrous rats. Mechanoreceptors innervating the body of the bladder and the region near the ureterovesical junction showed two patterns of responsiveness to slow bladder filling. One group of units exhibited increasing activity with increasing pressure up to 40 mmHg, while the other group showed a peak in activity at pressures below 40 mmHg followed by a plateau or decrease in activity with increasing pressure. It is proposed that differences in stimulus transduction relate to the different response patterns. Thirty-nine units failed to respond to bladder filling. Eight of these were excited by intravesical potassium or capsaicin and were classified as chemoreceptors. The remaining 31 units were not excited by any stimulus tested. Chemoreceptors and unexcited units had both Adelta and C afferent fibers. We conclude that the pelvic nerve sensory innervation of the rat bladder is complex, may be sensitive to hormonal status, and that the properties of individual sensory receptors are not related in an obvious manner to the conduction velocity of their fibers.

EGJ opening with hiatal hernia: Lower pressure threshold, wider diameter

EGJ opening with hiatal hernia: Lower pressure threshold, wider diameter

Subharmonic backscattering from ultrasound contrast agents.

The ultrasonic contrast of blood in tissue, which is needed for ultrasonic estimation of tissue perfusion, can be increased by injecting the blood with bubbles or hollow microspheres. It has been shown that an even greater improvement in contrast can be obtained by using the subharmonic generated by irradiated microspheres. By obtaining analytical solutions to the modified RPNNP equation for a coated microbubble, the relationship between the physical parameters of the encapsulated bubble and the threshold pressure is established. The observed increase in the resonance frequency of a coated microsphere is explained by introducing the concept of "acoustic radius" of the encapsulated bubble. It is predicted that subharmonic generation in contrast agents requires a threshold insonifying pressure, and should be a minimum when microspheres are insonated at twice their resonance frequency. Experiments confirm the existence of this optimum incident frequency and of a reasonably low threshold pressure for the generation of the subharmonic. The existence of the low threshold pressures for subharmonic generation in contrast agents may prove to be very valuable in ultrasonic contrast imaging.

Effects of local compression on peroneal nerve function in humans

A new apparatus was developed to compress the anterior compartment selectively and reproducibly in humans. Thirty-five normal volunteers were studied to determine short-term thresholds of local tissue pressure that produce significant neuromuscular dysfunction. Local tissue fluid pressure adjacent to the deep peroneal nerve was elevated by the compression apparatus and continuously monitored for 2-3 h by the slit catheter technique. Elevation of tissue fluid pressure to within 35-40 mm Hg of diastolic blood pressure (approximately 40 mm Hg of in situ pressure in our subjects) elicited a consistent progression of neuromuscular deterioration including, in order, (a) gradual loss of sensation, as assessed by Semmes-Weinstein monofilaments, (b) subjective complaints, (c) reduced nerve conduction velocity, (d) decreased action potential amplitude of the extensor digitorum brevis muscle, and (e) motor weakness of muscles within the anterior compartment. Generally, higher intracompartmental pressures caused more rapid deterioration of neuromuscular function. In two subjects, when in situ compression levels were 0 and 30 mm Hg, normal neuromuscular function was maintained for 3 h. Threshold pressures for significant dysfunction were not always the same for each functional parameter studied, and the magnitudes of each functional deficit did not always correlate with compression level. This variable tolerance to elevated pressure emphasizes the need to monitor clinical signs and symptoms carefully in the diagnosis of compartment syndromes. The nature of the present studies was short term; longer term compression of myoneural tissues may result in dysfunction at lower pressure thresholds.

Adaptations to high hydrostatic pressure.

The importance of adaptation to high pressure has long been implicit in the findings of studies in which 1 atm-adapted species were subjected to elevated pressures. Recent comparative studies have shown that pressure sensitivities of enzymes, structural proteins, and membrane-based systems differ markedly between shallow- and deep-living species. These studies allow operational definition of what constitutes high pressures for different biological structures and processes. These are the habitat (adaptation) pressures at which a given type of system first exhibits reduced perturbation by pressure. These threshold pressures vary among physiological systems, but are similar for a given system among different species. Dehydrogenase enzymes and adenylyl cyclases exhibit threshold perturbation pressures of only 50-100 atm; the Na(+)-K(+)-ATPase of teleost gills appears to have a pressure perturbation threshold near 200 atm, and a similar threshold was found for actin self-assembly. Even this limited sample of physiological processes indicates that the terms deep and high pressure begin to apply at depths of only 500 m or less--and processes yet to be examined in comparative analysis may yield even lower pressure thresholds. The differences in sensitivity to pressure of homologous systems in shallow- and deep-living organisms have implications at several levels of biological organization. The vertical distribution patterns of species in aquatic habitats may be established, in part, by interspecific differences in resistance to pressure. High pressures may restrict the depths to which shallow-living species can penetrate, and the obligately barophilic systems found in deep-living organisms may limit their upper distribution limits. The similarities noted among the adaptations of deep-sea species with different shallow-water ancestors reflect a high degree of convergent evolution in pressure adaptation. It will be interesting to learn if the similarities in pressure-resistance of function among diverse deep-sea species are the result of similar or identical changes at the molecular level, e.g. in protein sequence. Acclimation to pressure may be of widespread occurrence among species that undergo large changes in depth, e.g. during ontogeny. Pressure acclimation may require pressure-regulation of gene expression. Lastly, comparisons of species from the cold deep sea with those from hydrothermal vents have shown that adaptations to both temperature and pressure play critical roles in determining the distribution patterns of deep-living species.

Similarity analysis of fracture growth and flame spread in deformable solid propellants

Fracture growth and flame spread in deformable gas-generating pyrotechnics are analyzed using a transient one-dimensional model of the fluid motion along the fracture, coupled with a quasi-steady model of the two-dimensional elastic deformation of a brittle material having negligible fracture toughness. Fracture wall recession and the associated mass generation within the fracture are described by a pressure dependent burning rate of the form ap n , and the gaseous combustion products are considered ideal and isothermal. For fully turbulent flow, the fracture speed and flame spreading rate are constant in time, and the profiles of the pressure, aperture, and fluid velocity along the fracture are self-similar. A broad range of similarity solutions is presented to illustrate the dependence of the propagation speed and internal pressure distribution on material properties, burning rate constants, confining stress and fracture inlet pressure. Additional solutions are presented for an alternate scaling appropriate to very large burning rates, and for cases in which the burning rate exhibits a low-pressure threshold.

マイカセラミックス粒子／アルミニウム複合系の臨界溶浸圧

Wettability of ceramic reinforcements with molten metals plays a vital role in the quality of metal matrix composites (MMCs) fabricated through liquid processing: the poor wettability causes non-infiltrated defects to remain in pressure cast MMCs with a low applied pressure. Threshold pressure for infiltration is one of the promising methods to evaluate wettability, since the reinforcement itself in MMCs can be utilized in this method. The mica-ceramic particles which had been classified into three sizes (L, M, S) were supplied to measure the threshold pressure for molten aluminum infiltration. Pressure infiltrations to the particle preforms were performed at 998K in vacuum or air atmosphere. The threshold pressures for molten aluminum infiltration were found to be 80.9 (L), 77.8 (M) and 159kPa (S) in vacuum, and 96.9 (L), 96.1 (M) and 162kPa (S) in air atmosphere. The lower threshold pressures in vacuum can be ascribed to the better wettability. Non-infiltrated defects with a meniscus configuration were observed in the vicinity of a contact point of two particles. However, flat defects appeared between quasi-tangential planes in MMCs using L-size particle preforms, and aggregate defects were observed in S-size preforms. Modelling the defect with a meniscus configuration to estimate the defect size, the relation between the threshold pressure and the wettability can be derived from the work done by an applied pressure balancing the interfacial energy changes. The contact angle of mica-ceramics with molten aluminum in vacuum is calculated to be approximately 2.39rad which is obtained from the threshold pressure into the M-size particle preforms with less flat or aggregate defects. Hence, the relation between the threshold pressure and the contact angle depends on a configuration of non-infiltrated defects.

The suppression by pressure of negative differential resistance in GaAs/GaAlAs double barrier structures

High-pressure measurements of thermionic emission (TE) and of resonant tunneling in Ga1−xAlxAs/GaAs double barrier structures are reported, where x=1 or 0.33. For x=1, TE in a structure with a very narrow well yields a direct measurement of ∼150 meV for the Γ-X barrier height, and a shift of ∼−11 meV/kbar. For a structure with a well width of ∼70 Å and barriers of ∼40 Å, negative differential resistance (NDR) is observed, which is suppressed at a pressure of ∼8 kbar, when the height of the Γ-X barrier is approximately equal to the confinement energy of the state in the well. For x=0.33, and in samples with spacer layers, the same criterion for suppression of the NDR applies as for x=1. When spacer layers are absent, anomalies occur in the variation of the first NDR resonance with pressure, and for sufficiently large samples, the threshold for loss of NDR is much lower than expected. The anomalous behavior is related to the higher concentration of impurities in the barriers. The low-pressure threshold of the anomaly, and the dependence of the anomaly on sample size, suggest that impurity correlation may play a significant role in the suppression of NDR. At low pressures, or in the absence of anomalies, the pressure dependence of the peak and valley currents of all resonances which are always in the range −1% to −3%/kbar, indicates that the Γ profile controls the tunneling, through the pressure dependence of the effective mass.