Success and failure of dead-time models as applied to hybrid pixel detectors in high-flux applications.

The performance of a single-photon-counting hybrid pixel detector has been investigated at the Australian Synchrotron. Results are compared with the body of accepted analytical models previously validated with other detectors. Detector functionals are valuable for empirical calibration. It is shown that the matching of the detector dead-time with the temporal synchrotron source structure leads to substantial improvements in count rate and linearity of response. Standard implementations are linear up to ∼0.36 MHz pixel(-1); the optimized linearity in this configuration has an extended range up to ∼0.71 MHz pixel(-1); these are further correctable with a transfer function to ∼1.77 MHz pixel(-1). This new approach has wide application both in high-accuracy fundamental experiments and in standard crystallographic X-ray fluorescence and other X-ray measurements. The explicit use of data variance (rather than N(1/2) noise) and direct measures of goodness-of-fit (χ(r)(2)) are introduced, raising issues not encountered in previous literature for any detector, and suggesting that these inadequacies of models may apply to most detector types. Specifically, parametrization of models with non-physical values can lead to remarkable agreement for a range of count-rate, pulse-frequency and temporal structure. However, especially when the dead-time is near resonant with the temporal structure, limitations of these classical models become apparent. Further, a lack of agreement at extreme count rates was evident.

Effect of high doses of vitamin D on arterial properties, adiponectin, leptin and glucose homeostasis in type 2 diabetic patients.

BACKGROUND & AIMS: Vitamin D supplementation has the potential to alleviate the cardiovascular damage in diabetic patients. The present study was designed to evaluate long term impact of high doses of vitamin D on arterial properties, glucose homeostasis, adiponectin and leptin in patients with type 2 diabetes mellitus. METHODS AND RESULTS: In randomized, placebo-controlled study 47 diabetic patients were assigned into two groups: Group 1 received oral daily supplementation with vitamin D at a dose of 1000 U/day for 12 months. Group 2 received matching placebo capsules. Blood sampling for metabolic parameters, including fasting glucose, lipid profile, HbA1C, insulin, hs-CRP, 25 OH Vit D, adiponectin and leptin was performed at baseline and at the end of the study. Insulin resistance was assessed by homeostasis model assessment (HOMA-IR). Central aortic augmentation index (AI) was evaluated using SphygmoCor. RESULTS: The two groups were similar at baseline in terms of hemodynamic parameters. After 12 months, AI decreased significantly during the treatment period in patients received vitamin D (p < 0.0001) and did not change in placebo group. Glucose homeostasis parameters, leptin as well as leptin adiponectin ratio did not change in both groups. 25 OH Vit D level significantly increased (p = 0.022) and circulating adiponectin marginally increased (p = 0.065) during 12 month treatment period in active treatment and did not change in placebo group. CONCLUSIONS: High doses of vitamin D supplementation in diabetic patients was associated with significant decrease in AI during one year treatment. This beneficial vascular effect was not associated with improvement in glucose homeostasis parameters.

New consistency tests for high-accuracy measurements of X-ray mass attenuation coefficients by the X-ray extended-range technique.

An extension of the X-ray extended-range technique is described for measuring X-ray mass attenuation coefficients by introducing absolute measurement of a number of foils - the multiple independent foil technique. Illustrating the technique with the results of measurements for gold in the 38-50 keV energy range, it is shown that its use enables selection of the most uniform and well defined of available foils, leading to more accurate measurements; it allows one to test the consistency of independently measured absolute values of the mass attenuation coefficient with those obtained by the thickness transfer method; and it tests the linearity of the response of the counter and counting chain throughout the range of X-ray intensities encountered in a given experiment. In light of the results for gold, the strategy to be ideally employed in measuring absolute X-ray mass attenuation coefficients, X-ray absorption fine structure and related quantities is discussed.

A critical and comparative review of the prevention of drug and alcohol abuse in Israel.

The article reviews the various programs and intervention strategies of substance abuse prevention in Israel. It concentrates mainly on the stages of primary and secondary prevention among youth. School-based prevention programs, those designated for detached youth as well as community-based programs, are presented and analyzed. The prevention efforts in Israel are also compared to those in other Western countries. The discussion includes recommendations for future developments in this domain.

Alcohol and psychoactive drug use among Israeli adolescents: an epidemiological and demographic investigation.

One thousand nine hundred Israeli adolescents--51.8% males and 48.2% females--aged 15 to 18, were questioned twice about their current and "ever" substance use. The first study was undertaken during September-October 1982 and the second about a year later. The findings clearly indicated a slight rise in the incidence and a moderate growth of the prevalence of substance use among Israeli adolescents. The relationships between substance use and several background sociodemographic variables that were studied are discussed.

Alcohol consumption among Israeli youth--1989: epidemiology and demographics.

Epidemiological and sociodemographic findings on alcohol (wine, beer, hard liquor) consumption among the Israeli youth are presented. Three samples of adolescents, aged 12-18, were studied by means of an anonymous self-report questionnaire: a nationwide representative sample of high school students; a sample of detached youth; and a sample of inmates in institutions for juvenile delinquents. Alcohol consumption was assessed by three indices: frequency of use during the last year, use during the last month and use during the last week. Since alcohol is imbibed ceremonially in the Jewish tradition, only non-ritualistic consumption of alcoholic beverages was considered. Prevalence of drinking during the last year was 58%, during the last month 42% and during the last week 25%. Thus, it appears that Israeli youth are approaching the drinking prevalence of European adolescents. The results clearly indicate that alcohol consumption is concentrated among groups of deviant adolescents. These adolescents consume all types of alcoholic beverages at rates considerably exceeding those found among high school students. As for the effect of sociodemographic variables, the results strongly support previous findings showing that the patterns and contexts of alcohol use among Israeli youth are similar to those found among youth in other cultures.

Substance use and abuse among deviant and non-deviant adolescents in Israel.

The study examined the hypothesis that the use of psychoactive substances is strongly associated with social deviance. Patterns of alcohol and drug use among two samples of deviant adolescents were investigated and compared to patterns of use among a sample of non-deviant youths. The participants were as follows: ninety-seven juvenile delinquents, inmates in institutions, aged twelve through eighteen; 184 detached youth, aged twelve through eighteen, who are in treatment programs of the Departments of Youth Advancement, Ministry of Education & Ministry of Welfare; and a nationwide representative sample of 8151 high school students, aged twelve through eighteen. Substance use was measured by three self-report indices: frequency of use during the last year, use during the last month, and use during the last week. The results clearly indicate that psychoactive substance use is concentrated among Israeli groups of deviant adolescents. These adolescents use all types of substances, licit as well as illicit, at rates considerably exceeding those found among high school students. However, a great similarity was found between the deviant groups of adolescents and the high school students in several personality correlates (sensation seeking, anxiety, depressive mood and learned resourcefulness) of substance use, and to a much lesser degree in its interpersonal correlates (perceived closeness to parents and to peers). The results' implications for prevention are discussed.

Personality, cognitive, and interpersonal factors in adolescent substance use: A longitudinal test of an integrative model.

This study tests a multidimensional model of adolescent drug use. The model incorporates sociodemographic variables, personality variables (state and trait anxiety, depressive mood, and sensation seeking), cognitive variables (knowledge, attitudes, and intentions), interpersonal factors (relationships with peers and parents), and the availability of drugs. The model was tested in a longitudinal study, comprising two phases. A total of 1446 high school students served as subjects. The role of cognitive (attitudinal) and interpersonal factors (relationships with parents and peers) was confirmed. In addition, sensation seeking proved to have significant predictive power. Anxiety, depression, and sociodemographic factors, by contrast, had virtually no influence. Availability had a minor effect. The multidimensional explanation was validated longitudinally. The factors related to drug use at the first phase predicted use at the second. This multidimensional explanation accounted for the use of various substances, suggesting that different substances-whether legal or illegal-share a common multidimensional explanation.

Personality and substance use among adolescents: a longitudinal study.

The following hypotheses have been tested: (a) sensation seeking, A-State and Trait and Depressive Mood should positively affect the initiation and continuation of adolescent substance use: and (b) Following Zuckerman's conclusion with regard to the relationships between sensation seeking and drug use, and Khantzian's 'self medication hypothesis', different patterns of relationships between personality variables and substance use should be found: Whereas sensation seeking will be associated with substance use regardless of the specific psychopharmacological properties of a given substance, anxiety and depressive mood will be primarily associated with the use of depressants. One thousand nine hundred adolescents, 14-19 years old, were tested twice, 12 months apart, for alcohol and drug use. The major findings were as follows: (a) Sensation seeking was found to affect substance use among adolescents more than State and Trait Anxiety, and Depressive Mood; (b) Sensation seeking differentiated among abstainers, beginners, and users of all substances. A different pattern of relationship between State-Trait Anxiety, and Depressive Moods and substance use was found. These personality variables appeared to differentiate only among those subjects who used depressants; (c) It is also evident that previous experimentation with drugs significantly affect current-use. The implications of these findings for interventions among adolescents are discussed.

Sensation seeking, state and trait anxiety, and depressive mood in adolescent substance users.

The following hypothesis has been tested: sensation seeking, A-state and A-trait, and depressive mood should positively affect adolescent substance use. The personality variables and alcohol and drug use were assessed among 1,900 Israel adolescents, 14 to 19 years old. The major findings were as follows: (a) Sensation seeking and availability significantly affected the "ever" and "current" substance use among adolescents. On the other hand, contrary to our hypothesis, neither A-trait nor depressive mood significantly affected substance use. (b) A-State affected the use of alcoholic beverages and nonprescribed medications. (c) The data emphasized the significant role of availability of drugs in the understanding of adolescents' substance use. The implications of these findings for interventions among adolescents are discussed.

X-ray mass attenuation coefficient of silicon: theory versus experiment.

We compare new experimental x-ray total mass attenuation coefficients of silicon obtained with the x-ray extended-range technique (XERT) from 5 to 20 keV with theoretical calculations and earlier experimental measurements over a 5 to 50 keV energy range. The accuracy of between 0.27% and 0.5% of the XERT data allows us to probe alternate atomic and solid state wave function calculations and to test dominant scattering mechanisms. Discrepancies between experimental results and theoretical computations of the order of 5% are discussed in detail. No single theoretical computation is currently able to reproduce the experimental results over the entire 5 to 50 keV energy range investigated.

Focusing of X-rays by Total External Reflection from a Paraboloidally Tapered Glass Capillary.

The first observation of a true geometrical focus of X-rays well beyond the exit of a paraboloidally tapered glass monocapillary is reported. An intensity gain of 250 +/- 20 into a 6 x 9 mum pinhole for 8 keV X-rays and transmission efficiencies of more than 90% below 20 keV were observed.

Protein Crystal Diffraction Patterns Using a Capillary-Focused Synchrotron X-ray Beam.

A paraboloidally tapered glass monocapillary was used to focus an 8 keV monochromated synchrotron bending-magnet X-ray beam into a 40 (+/-5) mum focal spot located 45 (+/-5) mm from the exit of the capillary. This focal spot had a measured intensity gain of 120 (+/-10) times the intensity present in an equivalent cross section of the unfocused beam from the monochromator. This focused beam was used to obtain oscillation diffraction patterns on image plates from a hen egg-white lysozyme protein crystal in two distinct geometries: one with the specimen crystal at the capillary exit and the other with the crystal at the beam focus. In the first geometry, focused Bragg reflections were observed at the focal plane. In the second geometry, diverging Bragg reflections of high intensity from a small crystal volume were observed. Image-plate diffraction patterns for these two geometries were compared with exposures with equivalent integrated diffracted intensities obtained using a 100 x 100 mum unfocused X-ray beam with the same crystal. The use of the focused beam resulted in a reduction in the exposure time required to produce equivalent patterns by a factor of between 70 and 100.