Comparison of Weibull strength parameters from flexure and spin tests of brittle materials

Fracture data from five series of four point bend tests of beam and spin tests of flat annular disks were reanalyzed. Silicon nitride and graphite were the test materials. The experimental fracture strengths of the disks were compared with the predicted strengths based on both volume flaw and surface flaw analyses of four point bend data. Volume flaw analysis resulted in a better correlation between disks and beams in three of the five test series than did surface flaw analysis. The Weibull (moduli) and characteristic gage strengths for the disks and beams were also compared. Differences in the experimental Weibull slopes were not statistically significant. It was shown that results from the beam tests can predict the fracture strength of rotating disks

Investigation of Weibull statistics in fracture analysis of cast aluminum

The fracture strengths of two large batches of A357-T6 cast aluminum coupon specimens were compared by using two-parameter Weibull analysis. The minimum number of these specimens necessary to find the fracture strength of the material was determined. The applicability of three-parameter Weibull analysis was also investigated. A design methodology based on the combination of elementary stress analysis and Weibull statistical analysis is advanced and applied to the design of a spherical pressure vessel shell. The results from this design methodology are compared with results from the applicable ASME pressure vessel code

Electron--phonon coupling and anharmonic effects in metal clusters

The periods of the harmonic oscillations of the ion core of charged sodium clusters around the equilibrium shapes are considered. It is found that these periods are of the order of magnitude of the experimentally measured relaxation times of the plasmons, which suggests the importance of the electron-ion coupling and stresses the role played by the electron-phonon interaction in the dissipation of the plasmon energy. The relation of the process to fission is briefly discussed.Comment: 6 pages, no figures, to appear in EPLetter

Delay-dependent amplification of a probe pulse via stimulated Rayleigh scattering

Stimulated Rayleigh scattering of pump and probe light pulses of close carrier frequencies is considered. A nonzero time delay between the two pulses is shown to give rise to amplification of the delayed (probe) pulse accompanied by attenuation of the pump, both on resonance and off resonance. In either case, phase-matching effects are shown to provide a sufficiently large gain, which can exceed significantly direct one-photon-absorption losses

Characterization of the relationship between spontaneous locomotor activity and cardiovascular parameters in conscious freely moving rats

In freely behaving rats, variations in heart rate (HR) and blood pressure (BP) are coupled closely with changes in locomotor activity (Act). We have attempted to characterize this relationship mathematically. In 10- and 16-week-old rats, HR, BP and Act were recorded telemetrically every minute for 2 days under 12h:12h light-dark cycling. After examining data for individual rats, we found that the relationship between Act and HR could be approximated by the negative exponential function HR(Act)=HRmax-(HRmax-HRmin)∗exp(-Act/Acte), where HRmax, HRmin, and Acte are constants. These constants were calculated separately for light and dark periods by non-linear curve fitting. HR corresponding to maximal locomotion was similar during the light and dark phases, while HR at rest during the dark phase was higher than during the light phase. The range of HR variability associated with Act during the dark phase was similar in young and older animals, but minimal HR was significantly lower in older rats. The relationship between Act and BP was approximated with a similar function. We have found no differences between BP at rest and at maximal locomotion between light and dark and between 10-week and 16-week-old rats. Our results indicate that in rats, cardiovascular parameters are coupled to locomotion to a high degree; however both the HR and the BP reach maximal values when locomotor activity is relatively low. We also found that the phase of daily cycle affects HR in conscious rats independent of locomotor activity

Treatment of Postcatheterisation False Aneurysms: Ultrasound-guided Compression vs Ultrasound-guided Thrombin Injection

AbstractObjectives: to compare the efficacy and cost-effectiveness of ultrasound-guided compression (UGC) with ultrasound-guided thrombin injection (UGTI) for treatment of postcatheterisation arterial false aneurysms (cFA). Design: prospective clinical study using historical controls. Materials and Methods: we prospectively collected data on 33 consecutive patients diagnosed with cFA larger than 1.5 cm in diameter. These were treated with UGTI. We performed a retrospective review of data on a former group of 33 consecutive historical control patients that were treated by UGC. Results: the groups were similar in respect of demographic and clinical variables. Thirty patients were suitable for UGC and 33 patients were suitable for UGTI. The success rate for UGC was 26/30 (87%) compared to 33/33 (100%) for UGTI (p<0.05). Thrombosis was achieved during the first treatment session in 7/26 patients treated by UGC, compared to 26/33 in the UGTI group (p<0.0001). Four patients that failed UGC and two patients that were unsuitable for UGC required surgical repair. UGTI as compared to UGC was shorter in duration (25 vs 75 min) and required no sedation. No thromboembolic or systemic complications occurred in either group. Cost analysis revealed savings of $US 517 for each patient treated by UGTI as compared with UGC. Conclusions: in our study, UGTI is superior to UGC, and we suggest that UGTI should become the procedure of choice for the treatment of cFA

Representations of (2,n)(2,n)-semigroups by multiplace functions

We describe the representations of $(2,n)$-semigroups, i.e. groupoids with $n$ binary associative operations, by partial $n$-place functions and prove that any such representation is a union of some family of representations induced by Schein's determining pairs.Comment: 17 page

Yohimbine is a 5-HT1A agonist in rats in doses exceeding 1 mg/kg.

Yohimbine is a prototypical alpha2-adrenergic receptor antagonist. Due to its relatively high selectivity, yohimbine is often used in experiments whose purpose is to examine the role of these receptors. For example, yohimbine has been employed at doses of 1–5 mg/kg to reinstate drug-seeking behavior after extinction or to antagonize general anesthesia, an effects presumably being a consequence of blocking alpha2-adrenergic receptors. In this report we characterized dose-dependent autonomic and behavioral effects of yohimbine and its interaction with an antagonist of 5-HT1A receptors, WAY 100635. In low doses (0.5 – 2 mg/kg i.p.) yohimbine induced locomotor activation which was accompanied by a tachycardia and mild hypertension. Increasing the dose to 3–4.5 mg/kg reversed the hypertension and locomotor activation and induced profound hypothermia. The hypothermia as well as the suppression of the locomotion and the hypertension could be reversed by the blockade of 5-HT1A receptors with WAY 100635. Our data confirm that yohimbine possesses 5-HT1A properties, and demonstrated that in doses above 1 mg/kg significantly activate these receptors

Admittance of CdS nanowires embedded in porous alumina template

CdSnanowires of 10nm diameter, electrodeposited in porous alumina films, had shown a conductance bistability in the past [Appl. Phys. Lett.76, 460 (2000)]. The conductance has a high (ON) and a low (OFF) state. In the ON state, different sets of nanowires display qualitatively different relation between the conductance and capacitance. We propose a model to explain this anomalous behavior. Based on this model, we predict that the inelastic mean free path of electrons in the nanowires is 3–3.5nm at room temperature. This short mean free path may be a consequence of acoustic phonon confinement

Tissue oxidative metabolism can increase the difference between local temperature and arterial blood temperature by up to 1.3oC: Implications for brain, brown adipose tissue, and muscle physiology

Tissue temperature increases, when oxidative metabolism is boosted. The source of nutrients and oxygen for this metabolism is the blood. The blood also cools down the tissue, and this is the only cooling mechanism, when direct dissipation of heat from the tissue to the environment is insignificant, e.g., in the brain. While this concept is relatively simple, it has not been described quantitatively. The purpose of the present work was to answer two questions: 1) to what extent can oxidative metabolism make the organ tissue warmer than the body core, and, 2) how quickly are changes in the local metabolism reflected in the temperature of the tissue? Our theoretical analysis demonstrates that, at equilibrium, given that heat exchange with the organ is provided by the blood, the temperature difference between the organ tissue and the arterial blood is proportional to the arteriovenous difference in oxygen content, does not depend on the blood flow, and cannot exceed 1.3oC. Unlike the equilibrium temperature difference, the rate of change of the local temperature, with respect to time, does depend on the blood flow. In organs with high perfusion rates, such as the brain and muscles, temperature changes occur on a time scale of a few minutes. In organs with low perfusion rates, such changes may have characteristic time constants of tens or hundreds of minutes. Our analysis explains, why arterial blood temperature is the main determinant of the temperature of tissues with limited heat exchange, such as the brain