Search

Recent developments in the fabrication and simulation of prototype silicon-on-insulator (SOI) microdosimeter arrays are presented. A new planar array design has been proposed which has a number of advantages over the previous elongated parallelepiped and cylindrical mesa array designs. This novel planar array design, which incorporates a guard ring, is based upon 2500 planar cylindrically shaped p-i-n detectors and was fabricated via dopant diffusion and ion implantation. The dopant-diffused arrays were successfully fabricated and tested using 2 [micro]m and 10-[micro]m-thick SOI substrates. Technology computer-aided design modeling of the ion-implanted structure is presented which includes the electrostatic potential profile, showing possible avalanche signal multiplication around the n+ core of the microdosimeter. The alpha particle charge transient response was simulated to determine the charge collection in the sensitive region. Index Terms--Avalanche signal multiplication, microdosimeter, p-i-n detectors, silicon-on-insulator (SOI), SOI substrates, technology computer-aided design (TCAD) modeling.

A novel silicon-on-insulator (SOI) microdosimeter has been designed and fabricated using planar processing techniques to realise a device with a micron-scale well-defined sensitive volume. Cylindrical structures were employed to allow for an improved definition of the average chord length of the sensitive volume over that of previous elongated parallelepiped solid-state detector designs. The structures were manufactured on individual silicon mesas situated on top of a buried oxide insulating layer. The mesa design eliminated lateral charge diffusion. Two kinds of test structures were designed with sensitive region widths of 2 [micro]m and 10 [micro]m. In addition, an array of 900 cylindrical diodes was fabricated to increase the charge collection statistics. TCAD (Technology Computer Aided Design) modeling of the electrostatic potential and electric field profile of the cylindrical microdosimeter was carried out to obtain 3D potential and electric field profiles. The modeling revealed a radial electric field within the cylindrical-shaped sensitive volume with a 1/r dependence. While the electric field at the core of the cylindrical microdosimeter was not sufficiently high to induce avalanche signal multiplication, the higher electric field at the core should still assist in the measurement of low linear-energy transfer (LET) events. Index Terms--Detector arrays, IBIC, microdosimeter, silicon-on-insulator, TCAD modeling.

The purpose of this investigation was to assess the effects of social support and exposure to community violence (i.e., the extent to which students perceive danger in the neighborhood, and the extent to which they personally experience neighborhood crime and violence either directly or indirectly) on high school students' school behavior, school affect, and grades. Results indicated that neighborhood danger, especially when experienced personally, had an important negative influence on high school students' attendance, trouble avoidance, and school satisfaction, and less influence on their grades. The usefulness of social support in moderating this influence varied depending on the particular school outcome of interest: it had its greatest moderating influence on school satisfaction and grades, and it was less influential on the outcomes of attendance and trouble avoidance. Results of analyses using structural equation modeling showed social support having both a direct effect on each school outcome and serving as a moderating variable through students' personally experienced neighborhood danger.

As we move into the new millennium, it is important that we improve our understanding of radiation effects on humans and nanoelectronic systems. This understanding is essential in a number of areas including radiation therapy for cancer treatment and extended human presence in outer space. Nanodosimetry in low-pressure gases enables measurement of the energy deposition of ionizing radiation on a scale equivalent to the dimensions of the DNA molecule. This is extremely important for not only biological applications but also electronic applications, as the effect of radiation on nanoelectronics needs to be determined before they are installed and deployed in complex radiation fields. However, before nanodosimetry can be widely applied, further investigation is required to link the output of gas-based nanodosimeters to the actual effect of the radiation on a biological or electronic system. The purpose of this research is to conduct nanodosimetric measurements of proton radiation fields at the proton accelerator of Loma Linda University Medical Center (LLUMC) and to develop a Monte Carlo simulation system to validate and support further developments of experimental nanodosimetry. To achieve this, measured ion cluster size distributions are compared to the output from the Monte Carlo simulation system that simulates the characteristics of the LLUMC beam line and the performance of the nanodosimeter installed on one of LLUMC's proton research beam lines. Index Terms--GEANT4, Monte Carlo, nanodosimetry, proton.

The dosimetry of X-ray microbeams using MOSFETs results in an asymmetrical beam profile due to a lack of lateral charged particle equilibrium. Monte Carlo simulations were carried out using PENELOPE and GEANT4 codes to study this effect and a MOSFET on a micropositioner was scanned in the microbeam. Based on the simulations a new method of microbeam dosimetry is proposed. The proposed edge-on face-to-face (EOFF) MOSFET detector, a die arrangement proposed here for the first time, should alleviate the asymmetry. Further improvement is possible by thinning the silicon body of the MOSFET. Index Terms--Charged-particle equilibrium (CPE), dose enhancement effects (DEEs), dosimetry, microbeam, MOSFET, radiotherapy, synchrotron.

The irradiation of various tissue-like materials by therapeutic proton beams was simulated using Monte Carlo. The contribution of inelastic reaction products to the depth-dose distribution was determined. The use of silicon microdosimeters for verifying Monte Carlo calculations was also investigated. The importance of these studies to Monte Carlo-based treatment planning systems is emphasized.

This paper reports on the development of an interactive, intraoperative dose planning system for seed implant brachytherapy in cancer treatment. This system involves in vivo dosimetry and the ability to determine implanted seed positions. The first stage of this project is the development of a urethral alarm probe to measure the dose along the urethra during a prostate brachytherapy treatment procedure. Ultimately, the system will be used to advise the physicians upon reaching a preset dose rate or dose after total seed decay in the urethra during the seed placement. The second stage is the development of a method and instrumentation for in vivo measurements of the location of implanted seeds in the same frame as for dose planning and the use of these in intraoperative treatment planning. We have developed a silicon mini-detector, miniature front-end, and shaping amplifier with discriminator, connected to the mini-silicon detector at the end of a cable placed in a urological catheter, to satisfy the spectroscopic requirements of the urethral probe. This technique will avoid complications related to overdosing the urethra and the rectum.

Silicon microdosimetry measurements in Fast Neutron Therapy were simulated using the GEANT4 Monte Carlo toolkit. The possibility of using silicon microdosimeters for verification of Monte Carlo based treatment planning systems in hadron therapy is suggested. Index Terms--Fast neutron therapy (FNT), microdosimetry, Monte Carlo.

This investigation examined the relationship of information adequacy to job satisfaction and organizational culture in a healthcare organization with both office and field personnel. Information adequacy was assessed in four areas: personal performance, organizational policies, organizational performance, and organizational objectives. Comparisons of field and office personnel indicated that they did not differ on information adequacy or job satisfaction; they did, however, differ on several dimensions of organizational culture. Also, the relationship of information inadequacy to job satisfaction and organizational culture differed for employees depending on whether they worked primarily in the field or primarily in the office. Implications of the findings are drawn for organizations with a dispersed-network structure. Keywords: Information Adequacy; Job Satisfaction; Work Environment; Dispersed Network; Organizational Culture

New nonionizing energy losses (NIEL) sensors based on silicon planar p-i-n diodes of different geometry have been investigated and their response to fast neutron field compared with bulk diodes. The possibility of obtaining a wide range of sensitivities in these NIEL sensors simultaneously with measurements of IEL has been demonstrated. Index Terms--Gamma dosimetry, neutron dosimetry, p-i-n diode.

A heavy ion microprobe was used to conduct ion beam induced charge (IBIC) collection imaging of silicon microdosimeters. The GEANT4 Monte Carlo toolkit was used to simulate these measurements to calculate ion energy loss in the device overlayer and energy deposition in the device sensitive volume. A comparison between experimental and theoretical results facilitated the calculation of charge collection efficiency profiles for several ions. Index Terms--Charge collection efficiency, microbeam, microdosimetry, Monte Carlo.

This study assesses the extent to which portrayals of father-adolescent daughter relationships in four Disney feature films (The Little Mermaid, Aladdin, Beauty and the Beast, and Pocahontas) correspond with the qualities of successful and unsuccessful father-adolescent daughter relationships as revealed in the research literature. Findings indicated that the relationships in The Little Mermaid and Aladdin correspond to father-adolescent daughter relationships in which the father denies his daughter freedom to explore her adolescence, while the relationships in Beauty and the Beast and Pocahontas are more consistent with father-adolescent daughter relationships in which the father allows the daughter freedom to negotiate her adolescence. Implications of these findings are discussed.

In a previous simulation study, we demonstrated the feasibility of using coded apertures together with pixelated detectors for small animal SPECT. In this paper, we further explore the potential of this approach with a prototype detector and simulated multipinhole apertures. We also investigated the effect of multiplexing due to overlapped projections on convergence properties, image signal-to-noise ratio (SNR) and spatial resolution. The detector comprises a 48 x 44 array of NaI(TI) crystals, each 1 mm x 1 mm x 5 mm on a 1.25-mm pitch. The crystal array is directly coupled to a Hamamatsu R3941 8 cm position sensitive photomultiplier tube. Multipinhole apertures were simulated by performing repeated SPECT acquisitions of the same object with a single tungsten pinhole translated to different positions in the aperture plane. Image reconstruction is based on a three-dimensional ray driven projector which is an extension of a method described for single pinhole SPECT with a displaced center of rotation. Image estimates are updated using the maximum likelihood expectation maximization (ML-EM) algorithm. The effect of multiplexing was to slow convergence and reduce the achievable SNR by approximately 15% compared with nonmultiplexed data (but the result may be achieved in a fraction of the time). The reconstructed resolution obtained with a resolution phantom was 1.5-mm full width at half maximum and there was no appreciable difference between the resolution of multiplexed and nonmultiplexed data. These results encourage us to develop a prototype coded aperture system for high sensitivity, high resolution small animal SPECT. Index Terms--Coded aperature, iterature reconstruction, single photon emission computed tomography (SPECT), small animal imaging.

Improvements have been made in the measurement of dose profiles in several types of X-ray beams. These include 120-kVp X-ray beams from an orthovoltage X-ray machine, 6-MV Bremsstrahlung from a medical LINAC in conformal mode and the 50-200 keV energy spectrum of microbeams produced at the medical beamline station of the European Synchrotron Radiation Facility. Using a quadruple metal-oxide--semiconductor field-effect transistor (MOSFET) sensor chip in 'edge on' mode together with a newly developed sensor readout system, the feasibility of online scanning of the profiles of quasi-static and pulsed radiation beams was demonstrated. Measurements of synchrotron pulsed microbeams showed that a micrometer-scale spatial resolution was achievable. The use of several MOSFETs on the same chip gave rise to the correction of misalignments of the oxide films of the sensor with respect to the microbeam, ensuring that the excellent spatial resolution of the MOSFET used in 'edge-on' mode was fully utilized.

The importance of social support from parents, friends and teachers on the school outcomes of students. Secondary school students who perceive high supportiveness have better attendance, spend more time studying, obtain better grades and avoid problem behavior.

This study explores the relationship between supportive communication and school outcomes for two groups of lower socioeconomic high school students: those identified as 'at-risk' of poor school performance and those not identified as 'at-risk'. Results indicate that parents are major sources of social support for both groups of students; however, at-risk students also receive support from their friends. With respect to school outcomes, different types of social support are associated with different outcomes. Also, for students not identified at-risk, grades and school satisfaction appear to be the primary functions of support; for students identified at-risk, however, hours studying and attendance appear to be the primary functions. Teachers and other school personnel can use the findings of this investigation as part of a plan to develop intervention strategies that utilize the social support process to affect specific school outcomes for at-risk students as well as for other students. Keywords: social support, at-risk students, school outcomes

The present investigation replicates Jackson and McGill's study (1996) and extends it by considering the effects of respondents' own height, weight, and body mass on perceptions of attractiveness. Results, although generally supportive of those found by Jackson and McGill's, point to the influence of respondents' own physical characteristics in the process of perceptions of attractiveness: only 1 of Jackson and McGill's 3 (of a possible 19) differences between responses of African- and Euro-American women was corroborated (the importance of silky hair for EuroAmerican women), whereas a second difference (the importance of round buttocks for African-American women) disappeared when controlling for respondents' weight, height, and body mass. Although differences between the two investigations may be attributed to regional differences in the surveyed students (Michigan and North Carolina), the small effect of one's own weight, height, and body mass in assessing an other-sex person's attractiveness may reflect adherence to norms learned very early in life that are subject to regional variations.

This study explores the relationship between supportive communication and school outcomes for lower socioeconomic middle school students identified as 'at-risk' and students not identified as 'at-risk' of poor school performance. Results indicate that parents are major sources of social support for both groups of students; however, while parents are the only source of support for at-risk middle school students, the not-identified-at-risk students also receive support.from their teachers and friends. With respect to school outcomes, different types of social support are associated with different outcomes. Also, students not identified as at-risk appear to benefit more from the social support they receive than students identified as at-risk. Teachers and other school personnel can use the findings of this investigation to develop intervention strategies that utilize the social support process to affect specific school outcomes for academically at-risk students as well as for other students. Keywords: social support, at-risk students, school outcomes

The positive relationship between social support and an individual's physical and mental well-being (Ganster & Victor, 1988; Hardy, Richman, & Rosenfeld, 1991) has provided the impetus for a great deal [...], Social support, widely studied as a variable that positively affects the adaptation of adolescents, is often less present in the lives of youths at risk of school failure. This study explores the social support of at-risk students, including who provides each of eight types of support, and the effects of particular types of social support on school performance outcomes. Results of analyses of data from students enrolled in Communities In Schools programs, indicate that parents and adult caretakers are major sources of social support for both middle and high school at-risk students. Analyses of school outcomes data indicate that particular types of social support are associated with different desirable school outcomes. The article presents implications for social work practice and the development of intervention strategies to enhance students' school performance and behavior. Key words: at-risk students; school failure; school outcomes; social support

The application of MOSFET dosimeters in complicated mixed radiation fields for measurement of absorbed dose distribution in tissue equivalent phantoms has been studied. The spectra of secondary charged particles have been measured simultaneously with average absorbed doses by the same MOSFET dosimeter. A good correlation has been observed between neutron depth dose distribution in a water phantom obtained using MOSFETs in integral mode and a tissue equivalent (T.E.) ionisation chamber. Such MOSFET dosimeters are a promising tool for micro-macro dosimetry in Boron Neutron Capture Therapy (BNCT) and Fast Neutron Therapy (FNT). Paired MOSFETs with one of the dosimeters covered by 10B have been applied for measuring of average boron dose distribution and microdosimetric spectra due to alpha particles and 7Li ions throughout a perspex phantom exposed in the epithermal neutron beam at the Brookhaven Medical Research Reactor (BMRR).

Social support in sororities and fraternities have differences based on gender. Members of the sororities feel satisfied with the emotional support from the 'sisters', while members of the fraternities are dissatisfied with the emotional support they receive from the 'brothers.' The sororities often fail to provide technical challenges and tangible support to their fellow sisters, which are considered masculine. However, sorority and fraternity members are satisfied with the technical appreciation support, reality confirmation support and personal assistance support that they receive.

The purpose of this study was to test Chesebro et al.'s (1992) conjecture - based on research with at-risk students - that students highly apprehensive in speaking in dyads and groups, and who perceive themselves as lacking competence in speaking to strangers and acquaintances, do not fare well academically. A group of academically successful students was used. It was expected that the areas identified by Chesebro et al. as associated with low academic achievement for at-risk students would be associated with high academic achievement for students identified as academically talented. Findings are mostly supportive. Specifically, whereas at-risk students were most apprehensive about speaking in groups, the academically talented students were least apprehensive; also, whereas at-risk students perceived themselves least competent in speaking to strangers, the academically talented students perceived themselves most competent. Taken together, results of the present investigation and of the Chesebro et al. study point to what might be the key communication variables affecting academic success: apprehension about speaking in groups, and self-perceived competency in speaking to strangers.

The purpose of this investigation was to compare female and male perceptions of interactants in scenes involving a 'minor' sexual violation--one in which a male denies consent for a kiss and a woman kisses him regardless, and another in which a woman denies consent and a man kisses her regardless. Undergraduate students (n = 387--approximately 82.5% White, 11% Black, 4.7% Hispanic, 1% Native American, and .8% other) completed scenarios adapted from L. Margolin [(1990) 'Gender and the Stolen Kiss: The Social Support of Males and Females to Violate a Partner's Sexual Consenting Noncoercive Situation,' Archives of Sexual Behavior, Vol. 19, pp. 281-291], and evaluated scenario interactants using two sets of semantic differential items and two open-ended questions. Results of several analyses indicated that, first and most importantly, violators' behaviors are considered less acceptable, more negatively aggressive, more complimenting, and less appropriate than deniers' behaviors. Second, violations of sex-role expectations (i.e., female aggressing and male denying consent) are seen as less predictable and more complimenting than interactions where sex role expectations are not violated. Finally, minor distinctions between female and male respondents also were found. In general, findings support Margolin's conclusion that women have more social support than men for determining their sexual behavior and extend his findings to private interactions where motivations are not explicit. Also, trust was found to be an important factor defining perceptions of 'minor' sexual violations, which raises the possibility that an initiation of a kiss and a violation of consent are viewed as different actions.

Work on Adaption-Innovation theory has downplayed the importance of the three subscales, focusing instead on the Kirton Adaption-Innovation Inventory and on its total score. Although most Kirton inventory subscale scores correlate with the over-all score, a significant number do not. For this group of 44 successful entrepreneurs, subscale scores differed from those of technology managers in one company and also from the subscale scores of Kirton's original sample. Dividing the subscale continuum into four zones was instrumental in exploring how entrepreneurs' subscale profiles might differ from population norms. The study clearly showed that for the entrepreneur sample there was a distinct mixture of subscale combinations, and rule conformity acted as a moderating variable for originality. This may prove useful in understanding the differences between groups of entrepreneurs. These findings indicate not only a need for more thorough research of the Kirton subscales but also the usefulness of zones for interpreting scores on subscales.

This investigation assessed two competing hypotheses regarding the relationship between self-disclosure in marriage and the marital satisfaction of husbands and wives: an interaction-effect hypothesis, which suggests the relationship between self-disclosure and marital satisfaction for either spouse is contingent on the level of self-disclosure of the other, and a direct-effect hypothesis, which suggests that the marital satisfaction of each spouse varies directly as a function of the level of self-disclosure of both self and other in marriage. The simpler, lower-order, direct-effect hypothesis is concluded to account adequately for the data., Marital Disclosure and Marital Satisfaction: Direct-Effect Versus Interaction-Effect [...]

The purpose of this investigation was to assess athletes' perceptions of social support provided by their head coaches, assistant coaches, and athletic trainers, pre-injury and during rehabilitation. Data were collected [...]

An ion transport code was developed for simulating ionization energy deposition by energetic ions in sensitive volumes of complex structures. The code was used to simulate recent microdosimetry measurements performed with silicon-on-insulator (SOI) microdosimeters in Fast Neutron Therapy (FNT).

I. INTRODUCTION The lending practices of the World Bank(1) have been subject to scrutiny and criticism by environmentalists and governments for nearly two decades. In particular, numerous investments in large-scale [...], This Article presents a case study of lending by the International Finance Corporation (IFC), the private-sector lending arm of the World Bank Group, in the oil and gas sector in Guatemala. The case study emphasizes the need for additional environmental reform at IFC. With two separate loans in 1994 and 1996, IFC supported the activities of a small international oil company that was operating within a national park in the northern Guatemalan Peten, an area of rich tropical forests and globally important wetlands. The company's operations had been 'grandfathered' into the park upon its creation in 1990. Funding from IFC was used to construct a pipeline from the oil field in the park to a refinery outside of the park. The crux of the authors' findings is that the pipeline should have been constructed to follow the path of an existing road, rather than along the chosen route that crosses significant stretches of primary tropical forest and that opened a new right-of-way into a park already facing continued pressure from colonization. The authors conclude that a stronger set of IFC lending policies, combined with a better environmental impact assessment and more extensive public consultation, would have led to a less environmentally damaging outcome. Although the authors acknowledge the complex questions about the role of governments, development agencies, the private sector, conservation organizations, and local communities raised by this issue, they focus on the narrow subject of IFC's role in this matter, stressing the need for a reform agenda at that institution.

We present results of simulations performed as part of the development of a gamma-ray detector module comprising a nonpixellated scintillator and pixellated photodiode detector. The simulations have been carried out to determine the effect of surface treatment and dimensions of the scintillator on the ability to determine the two-dimensional position of interaction. A set of 32 different combinations of surface treatments have been considered for each crystal size. Scintillator dimensions considered have been 25 X 25 x (3-6 [mm.sup.3]). For scintillator thicknesses at the low end of this range, an average accuracy of 0.5-0.6 mm is achievable for many different surface treatments. At the higher end of the thickness range, 6 mm, the average accuracy reduces to around 0.7 mm and is more dependent on the surface treatment. Index Terms--Light propagation, Monte Carlo simulation, positron emission tomograpby (PET), scintillators.

In this paper, we report on spectral response data and gamma ray spectroscopy measurements using two newly developed silicon photodetectors that are designed to have enhanced sensitivity in the blue spectral region. The enhanced sensitivity is a result of our newly developed ion implantation profile used to create the active area of the photodetector. The quantum efficiency of the new photodetectors (without any optimized antireflective coating) has been measured to be ~40% at a wavelength of 420 nm. Gamma ray spectroscopy experiments have been performed using a thallium doped cesium iodide, [CsI(Tl)], and a cerium doped lutetium oxy-orthosilicate, (LSO) crystal excited by a [sup.137]Cs or [sup.22]Na source and read out by the new photodetectors. We have measured an energy resolution of 7.7% and 22.7% full-width at half-maximum (FWHM) for the 662-keV gamma rays from a [sup.137]Cs for the CsI(TI) and LSO scintillator crystal respectively. We intend to use the photodetectors, in the form of a detector array optically coupled to CsI(TI) or LSO, in the development of a new scintillator detector module for use in positron emission tomography (PET). Index Terms--Detector module, positron emission tomography (PET), silicon photodetector.