Cavitation Scaling Experiments With Headforms: Bubble Acoustics

Recently Ceccio and Brennen [1][2][3] have examined the interaction between individual traveling cavitation bubbles and the structure of the boundary layer and flow field in which the bubble is growing and collapsing. They were able to show that individual bubbles are often fissioned by the fluid shear and that this process can significantly effect the acoustic signal produced by the collapse. Furthermore they were able to demonstrate a relationship between the number of cavitation events and the nuclei number distribution measured by holographic methods in the upstream flow. Kumar and Brennen [4][5] have further examined the statistical properties of the acoustical signals from individual cavitation bubbles on two different headforms in order to learn more about the bubble/flow interactions. All of these experiments were, however, conducted in the same facility with the same size of headform (5.08cm in diameter) and over a fairly narrow range of flow velocities (around 9m/s). Clearly this raises the issue of how the phenomena identified change with speed, scale and facility. The present paper will describe further results from experiments conducted in order to try to answer some of these important questions regarding the scaling of the cavitation phenomena. These experiments (see also Kuhn de Chizelle et al. [6][7]) were conducted in the Large Cavitation Channel of the David Taylor Research Center in Memphis Tennessee, on similar Schiebe headforms which are 5.08, 25.4 and 50.8cm in diameter for speeds ranging up to 15m/s and for a range of cavitation numbers

On numerical issues for the wave/finite element method

The waveguide finite element (WFE) method is a numerical method to investigate wave motion in a uniform waveguide. Numerical issues for the WFE method are specifically illustrated in this report. The method starts from finite element mass and stiffness matrices of only one element of the section of the waveguide. The matrices may be derived from commercial FE software such that existing element libraries can be used to model complex general structures. The transfer matrix, and hence the eigenvalue problem, is formed from the dynamic stiffness matrix in conjunction with a periodicity condition. The results of the eigenvalue problem represent the free wave characteristics in the waveguide. This reportconcerns numerical errors occurring in the WFE results and proposing approaches to improve the errors.In the WFE method, numerical errors arise because of (1) the FE discretisation error, (2) round-off errors due to the inertia term and (3) ill-conditioning. The FE discretisation error becomes large when element length becomes large enough compared to the wavelength. However, the round-off error due to the inertia term becomes large for small element lengths when the dynamic stiffness matrix is formed. This tendency is illustrated by numerical examples for one-dimensional structures.Ill-conditioning occurs when the eigenvalue problem is formed and solved and the resulting errors can become large, especially for complex structures. Zhong’s method is used to improve the conditioning of the eigenvalue problem in this report. Errors in the eigenvalue problem are first mathematically discussed and Zhong’s method validated. In addition, singular value decomposition is proposed to reduce errors in numerically determining theeigenvectors. For waveguides with a one-dimensional cross-section, the effect of the aspect ratio of the elements on the conditioning is also illustrated. For general structures, there is a crude trade-off between the conditioning, the FE discretisation error and the round-off error due to the inertia term. To alleviate the trade-off, the model with internal nodes is applied. At low frequencies, the approximate condensation formulation is derived and significant errorreduction in the force eigenvector components is observed.Three approaches to numerically calculate the group velocity are compared and the finite difference and the power and energy relationship are shown to be efficient approaches for general structures

Properties of the Nearly Free Electron Superconductor Ag5Pb2O6 Inferred from Fermi Surface Measurements

We measured the Fermi surface of the recently discovered superconductor Ag5Pb2O6 via a de Haas-van Alphen rotation study. Two frequency branches were observed and identified with the neck and belly orbits of a very simple, nearly free electron Fermi surface. We use the observed Fermi surface geometry to quantitatively deduce superconducting properties such as the in-plane and out-of-plane penetration depths, the coherence length in the clean limit, and the critical field; as well as normal state properties such as the specific heat and the resistivity anisotropy.Comment: 2 pages, 1 figure, submitted to Physica C (M2S Proceedings

Effects of pulsed electric fields (PEF) on vitamin C and its antioxidant properties

In this study, pulsed electric fields (PEF) treatments and their effects on the structure of vitamin C (VIT-C) were estimated by fluorescence and Fourier transform infrared (FT-IR) spectroscopy, the relative content of VIT-C was measured by HPLC and the antioxidant properties of treated VIT-C by DPPH radical scavenging as well as reducing power tests. The fluorescence intensity of treated VIT-C increased slightly compared to the untreated VIT-C. Moreover, the effect of PEF on the structure of VIT-C was observed using the FT-IR spectra. These phenomena indicated that the PEF affected the conformation of VIT-C, which promoted the VIT-C isomer transformed enol-form into keto-form. In addition, the PEF treatments did not suffer the damage to VIT-C and could slow down the oxidation process in involving of experimental conditions by HPLC. The antioxidant properties of the treated VIT-C were enhanced, which was proved by radical scavenging and also the reducing power tests

An Integrated Circuit for Signal Processing of the AMS RICH Photmultipliers Tubes

An analog integrated circuit has been designed, in a BiCMOS 0.8 micron technology, for the feasability study of the signal processing of the AMS RICH photomultiplier tubes. This low power, three channel gated integrator includes its own gate and no external analog delay is requiered. It processes PMT pulses over a dynamic range of more than 100. A logic output that indicates whether the analog charge has to be considered is provided. This gated integrator is used with a compact DSP based acquisition system in a 132 channels RICH prototype. The charge calibration of each channel is carried out using a LED. The pedestal measurement is performed on activation of a dedicated input. The noise contribution study of the input RC network and amplifiers is presented.Comment: IEEE symp. on Nucl. Sci. and Med. Imaging, Toront

The temporal relationship between per capita alcohol consumption and harm: A systematic review of time lag specifications in aggregate time series analyses

Background: Changes in per capita alcohol consumption are temporally linked to changes in rates of alcohol-related harm. Methodological approaches for analysing this relationship have been suggested, however, the problem of time lags is not well-addressed. This study provides a review of time lag specifications, looking at a) time to first effect on harm, b) time to full effect and c) the functional form of the effect accumulation from first to full effect to inform modelling of the relationship between changes in aggregate alcohol consumption and changes in rates of harm. Methods: Bibliographic databases were searched and citation and reference checking was used to identify studies. Included studies were time series analyses of the relationship between aggregated population alcohol consumption and rates of alcohol-related harms where time lag specifications had been derived or tested. Results: 36 studies were included with liver cirrhosis, heart disease and suicide dominating the evidence base. For a large number of alcohol-related harms, no literature was identified. There was strong evidence of an immediate first effect following a change in consumption for most harms. Recommended lag specifications are proposed for a set of alcohol-attributable harms. Conclusions: Research on time lag specifications is under-developed for most harms although we provide suggested specifications based on the findings of the review. Greater methodological attention needs to be given to the rationale for choosing or applying lag specifications and the inherent complexity of the time lag process. More consistent and transparent reporting of methodological decisions would aide progress in the field

Intentions and Attitudes Towards Parenthood and Fertility Awareness Among Chinese University Students in Hong Kong: A Comparison with Western Samples

STUDY QUESTION What are the levels of awareness regarding female fertility and the intentions and attitudes towards parenthood among Chinese university students in Hong Kong compared with their counterparts in the West? SUMMARY ANSWER Chinese university students in Hong Kong were similarly over-optimistic about the age-related fertility decline, although they were less inclined to have children and undergo fertility treatment compared with their Western counterparts. WHAT IS KNOWN ALREADY Past studies of highly educated young adults in Europe and the USA have found that they are not sufficiently aware of the age-related decline in female fertility, and falsely believe that advanced reproductive treatments such as IVF will overcome fertility problems associated with age. Little is known about the perceptions of Chinese students in Hong Kong, a modernized Chinese city where the fertility rate is among the lowest in the world. STUDY DESIGN, SIZE, DURATION An online cross-sectional survey of Chinese university students in Hong Kong was conducted in 2013. Results were compared with two similar studies in Sweden and the USA. PARTICIPANTS/MATERIALS, SETTING, METHODS A total of 367 university students in Hong Kong (275 female, 92 male; mean age 23) responded to an e-mail invitation to participate in an online survey. Intentions and attitudes towards parenthood and awareness regarding female fertility were assessed using the Swedish Fertility Awareness Questionnaire. MAIN RESULTS AND THE ROLE OF CHANCE Like their Western counterparts, a large proportion of Chinese university students underestimated the age-related fertility decline (92%) and overestimated the fertility treatment success rate (66%). However, they were less inclined to have children, were more aware of and less concerned with infertility and were less motivated to seek solutions in the event of a fertility problem. These comparisons were significant at P \u3c 0.05. LIMITATIONS, REASONS FOR CAUTION Self-selection bias was inevitable in the questionnaire survey, and the anonymous nature of the survey did not permit the collection of characteristics of non-responders. International comparisons warrant caution because the Hong Kong sample was older than the US sample (mean age 20), but not older than the Sweden sample (mean age 24). WIDER IMPLICATION OF FINDINGS While this study was consistent with past Western studies on the lack of fertility awareness among highly educated young people, the findings reveal significant cultural differences in family planning and responses to infertility between Asia and the West

Calculating the random guess scores of multiple-response and matching test items

For achievement tests, the guess score is often used as a baseline for the lowest possible grade for score to grade transformations and setting the cut scores. For test item types such as multiple-response, matching and drag-and-drop, determin-ing the guess score requires more elaborate calculations than the more straight-forward calculation of the guess score for True-False and multiple-choice test item formats. For various variants of multiple-response and matching types with respect to dichotomous and polytomous scoring, methods for determining the guess score are presented and illustrated with practical applications. The implica-tions for theory and practice are discussed

Injury Alcohol-Attributable Fractions: Methodological Issues and Developments

Background: Alcohol-attributable fractions (AAFs) are routinely used to estimate the burden of injury resulting from alcohol. Recent methodological advances allow AAFs to be estimated using national survey data. However, this requires assuming that the drinking patterns are equivalent to those used by epidemiological studies estimating the relative risk of injury. This study explores the implications of this assumption and presents an improved method of estimating injury AAFs. Methods: Diary survey is used to describe individuals’ drinking occasions and estimate AAFs. Statistical methods and numerical integration are used to combine the evidence on the risk of injury when intoxicated with the diary data. Alternative assumptions are chosen to explore the implications of using national survey data. Results:Overall, an estimated 27% of road traffic accident (RTA) and 23% of non-RTA injuries in Britain are attributable to alcohol. AAF estimates for RTAs range from 54% to 2% and for non-RTAs from 36% to 8% in men aged 16-24 and women aged 55-64 respectively. Two potentially more realistic assumptions relating to the use of national survey data resulted in substantially lower AAF estimates for RTAs. Conclusion: Current methods of estimating injury AAFs using national survey data are flawed for some harms, particularly RTAs, where the data is not consistent with the epidemiological literature. Our findings indicate that the burden of injuries from RTAs in England has been previously overestimated. Further research into the prevalence of risky behaviours when intoxicated is required to refine these methods and produce more robust burden of injury estimates

Why Do Only Some Galaxy Clusters Have Cool Cores?

Flux-limited X-ray samples indicate that about half of rich galaxy clusters have cool cores. Why do only some clusters have cool cores while others do not? In this paper, cosmological N-body + Eulerian hydrodynamic simulations, including radiative cooling and heating, are used to address this question as we examine the formation and evolution of cool core (CC) and non-cool core (NCC) clusters. These adaptive mesh refinement simulations produce both CC and NCC clusters in the same volume. They have a peak resolution of 15.6 h^{-1} kpc within a (256 h^{-1} Mpc)^3 box. Our simulations suggest that there are important evolutionary differences between CC clusters and their NCC counterparts. Many of the numerical CC clusters accreted mass more slowly over time and grew enhanced cool cores via hierarchical mergers; when late major mergers occurred, the CC's survived the collisions. By contrast, NCC clusters experienced major mergers early in their evolution that destroyed embryonic cool cores and produced conditions that prevented CC re-formation. As a result, our simulations predict observationally testable distinctions in the properties of CC and NCC beyond the core regions in clusters. In particular, we find differences between CC versus NCC clusters in the shapes of X-ray surface brightness profiles, between the temperatures and hardness ratios beyond the cores, between the distribution of masses, and between their supercluster environs. It also appears that CC clusters are no closer to hydrostatic equilibrium than NCC clusters, an issue important for precision cosmology measurements.Comment: 17 emulateapj pages, 17 figures, replaced with version accepted to Ap