Architecture, implementation, and testing of a multiple-shell gas injection system for high current implosions on the Z accelerator.

Tests are ongoing to conduct ~20 MA z-pinch implosions on the Z accelerator at Sandia National Laboratory using Ar, Kr, and D2 gas puffs as the imploding loads. The relatively high cost of operations on a machine of this scale imposes stringent requirements on the functionality, reliability, and safety of gas puff hardware. Here we describe the development of a prototype gas puff system including the multiple-shell nozzles, electromagnetic drivers for each nozzle's valve, a UV pre-ionizer, and an inductive isolator to isolate the ~2.4 MV machine voltage pulse present at the gas load from the necessary electrical and fluid connections made to the puff system from outside the Z vacuum chamber. This paper shows how the assembly couples to the overall Z system and presents data taken to validate the functionality of the overall system.

Observations of modified three-dimensional instability structure for imploding z-pinch liners that are premagnetized with an axial field.

Novel experimental data are reported that reveal helical instability formation on imploding z-pinch liners that are premagnetized with an axial field. Such instabilities differ dramatically from the mostly azimuthally symmetric instabilities that form on unmagnetized liners. The helical structure persists at nearly constant pitch as the liner implodes. This is surprising since, at the liner surface, the azimuthal drive field presumably dwarfs the axial field for all but the earliest stages of the experiment. These fundamentally 3D results provide a unique and challenging test for 3D-magnetohydrodynamics simulations.

Measurement of temperature, density, and particle transport with localized dopants in wire-array Z pinches.

Axially localized NaF dopants are coated onto Al cylindrical wire arrays in order to act as spectroscopic tracers in the stagnated z-pinch plasma. Non-local-thermodynamic-equilibrium kinetic models fit to Na K-shell lines provide an independent measurement of the density and temperature that is consistent with spectroscopic analysis of K-shell emissions from Al and an alloyed Mg dopant. Axial transport of the Na dopant is observed, enabling quantitative study of instabilities in dense z-pinch plasmas.

Study of three-dimensional structure in wire-array z pinches by controlled seeding of axial modulations in wire radius.

Three-dimensional perturbations have been seeded in wire-array z pinches by etching 15 microm diameter aluminum wires to introduce 20% modulations in radius with a controlled axial wavelength. These perturbations seed additional three-dimensional imploding structures that are studied experimentally and with magnetohydrodynamics calculations, highlighting the role of current path nonuniformity in perturbation-induced magnetic bubble formation.

Theoretical z -pinch scaling relations for thermonuclear-fusion experiments.

We have developed wire-array z -pinch scaling relations for plasma-physics and inertial-confinement-fusion (ICF) experiments. The relations can be applied to the design of z -pinch accelerators for high-fusion-yield (approximately 0.4 GJ/shot) and inertial-fusion-energy (approximately 3 GJ/shot) research. We find that (delta(a)/delta(RT)) proportional (m/l)1/4 (Rgamma)(-1/2), where delta(a) is the imploding-sheath thickness of a wire-ablation-dominated pinch, delta(RT) is the sheath thickness of a Rayleigh-Taylor-dominated pinch, m is the total wire-array mass, l is the axial length of the array, R is the initial array radius, and gamma is a dimensionless functional of the shape of the current pulse that drives the pinch implosion. When the product Rgamma is held constant the sheath thickness is, at sufficiently large values of m/l, determined primarily by wire ablation. For an ablation-dominated pinch, we estimate that the peak radiated x-ray power P(r) proportional (I/tau(i))(3/2)Rlphigamma, where I is the peak pinch current, tau(i) is the pinch implosion time, and phi is a dimensionless functional of the current-pulse shape. This scaling relation is consistent with experiment when 13 MA < or = I < or = 20 MA, 93 ns < or = tau(i) < or = 169 ns, 10 mm < or = R < or = 20 mm, 10 mm < or = l < or = 20 mm, and 2.0 mg/cm < or = m/l < or = 7.3 mg/cm. Assuming an ablation-dominated pinch and that Rlphigamma is held constant, we find that the x-ray-power efficiency eta(x) congruent to P(r)/P(a) of a coupled pinch-accelerator system is proportional to (tau(i)P(r)(7/9 ))(-1), where P(a) is the peak accelerator power. The pinch current and accelerator power required to achieve a given value of P(r) are proportional to tau(i), and the requisite accelerator energy E(a) is proportional to tau2(i). These results suggest that the performance of an ablation-dominated pinch, and the efficiency of a coupled pinch-accelerator system, can be improved substantially by decreasing the implosion time tau(i). For an accelerator coupled to a double-pinch-driven hohlraum that drives the implosion of an ICF fuel capsule, we find that the accelerator power and energy required to achieve high-yield fusion scale as tau(i)0.36 and tau(i)1.36, respectively. Thus the accelerator requirements decrease as the implosion time is decreased. However, the x-ray-power and thermonuclear-yield efficiencies of such a coupled system increase with tau(i). We also find that increasing the anode-cathode gap of the pinch from 2 to 4 mm increases the requisite values of P(a) and E(a) by as much as a factor of 2.

X-ray emission from z pinches at 10 7 A: current scaling, gap closure, and shot-to-shot fluctuations.

We have measured the x-ray power and energy radiated by a tungsten-wire-array z pinch as a function of the peak pinch current and the width of the anode-cathode gap at the base of the pinch. The measurements were performed at 13- and 19-MA currents and 1-, 2-, 3-, and 4-mm gaps. The wire material, number of wires, wire-array diameter, wire-array length, wire-array-electrode design, normalized-pinch-current time history, implosion time, and diagnostic package were held constant for the experiments. To keep the implosion time constant, the mass of the array was increased as I2 (i.e., the diameter of each wire was increased as I), where I is the peak pinch current. At 19 MA, the mass of the 300-wire 20-mm-diam 10-mm-length array was 5.9 mg. For the configuration studied, we find that to eliminate the effects of gap closure on the radiated energy, the width of the gap must be increased approximately as I. For shots unaffected by gap closure, we find that the peak radiated x-ray power P(r) proportional to I1.24+/-0.18, the total radiated x-ray energy E(r) proportional to I1.73+/-0.18, the x-ray-power rise time tau(r) proportional to I0.39+/-0.34, and the x-ray-power pulse width tau(w) proportional to demonstrate that the internal energy and radiative opacity of the pinch are not responsible for the observed subquadratic power scaling. Heuristic wire-ablation arguments suggest that quadratic power scaling will be achieved if the implosion time tau(i) is scaled as I(-1/3). The measured 1sigma shot-to-shot fluctuations in P(r), E(r), tau(r), tau(w), and tau(i) are approximately 12%, 9%, 26%, 9%, and 2%, respectively, assuming that the fluctuations are independent of I. These variations are for one-half of the pinch. If the half observed radiates in a manner that is statistically independent of the other half, the variations are a factor of 2(1/2) less for the entire pinch. We calculate the effect that shot-to-shot fluctuations of a single pinch would have on the shot-success probability of the double-pinch inertial-confinement-fusion driver proposed by Hammer et al. [Phys. Plasmas 6, 2129 (1999)]. We find that on a given shot, the probability that two independent pinches would radiate the same peak power to within a factor of 1+/-alpha (where 0< or =alpha<<1) is equal to erf(alpha/2sigma), where sigma is the 1sigma fractional variation of the peak power radiated by a single pinch. Assuming alpha must be < or =7% to achieve adequate odd-Legendre-mode radiation symmetry for thermonuclear-fusion experiments, sigma must be <3% for the shot-success probability to be > or =90%. The observed (12/2(1/2))%=8.5% fluctuation in P(r) would provide adequate symmetry on 44% of the shots. We propose that three-dimensional radiative-magnetohydrodynamic simulations be performed to quantify the sensitivity of the x-ray emission to various initial conditions, and to determine whether an imploding z pinch is a spatiotemporal chaotic system.

Coronary heart disease surveillance: field application of an epidemiologic algorithm.

This report describes the performance of a surveillance system and computerized algorithm for the assignment of definite or probable hospitalized cardiac events for large epidemiologic studies. The algorithm, developed by the Coordinating Committee for Community Demonstration Studies (CCCDS), evolved from the Gillum criteria, and included selected ICD-9-CM codes including codes 410 through 414 for discharge record screening, plus creatine kinase. For the small percentage of cases in which enzyme analysis was inconclusive (8%), presence of pain and/or Minnesota-coded electrocardiograms were included to define the outcome. All data items were easily obtained from medical records by trained lay record abstractors and required no interpretation. From January 1980 through December 1991, 21,183 medical records were screened for ICD-9-CM codes 410 through 414. Of all 410 to 411 ICD-9-CM codes (n = 9026), 36.9% (n = 3220) were classified as definite cardiac events and 10.6% (n = 1057) as probable events. Of all 412 through 414 codes (n = 9070), only 1.8% (n = 227) were classified as definite cardiac events and 5.4% (n = 716) as probable events. The epidemiologic diagnostic algorithm presented in this article used computerized data to assign diagnoses in a standard, objective manner, and was a lower cost alternative to classification of cardiac events on the basis of clinical review and/or more complex record abstraction approaches.

The association between perceived risk and actual cardiovascular disease.

We examined the association between self-rated risk of stroke or myocardial infarction and actual morbidity and mortality by gender among participants of the Pawtucket Heart Health Program Health Survey in a nested case-control study. We defined cases (N = 191) as survey participants who later had a cardiac event registered in the Pawtucket Heart Health Program cardiovascular disease morbidity and mortality surveillance system. We matched controls (N = 573) on age, sex, date of survey, and city of residence. Women reporting a high perceived risk of stroke or myocardial infarction were four times as likely as women who indicated low perceived risk to have a future cardiovascular event [adjusted odds ratio = 4.0; 95% confidence interval (CI) = 1.5-10.3]. Men who perceived their risk as average were twice as likely as those who rated their risk as low to have a future myocardial infarction or stroke (adjusted odds ratio = 1.9; 95% CI = 1.0-3.6), whereas those who perceived their risk as high were at only slightly higher risk of morbid or mortal events (adjusted odds ratio = 1.8; 95% CI = 0.9-3.9).

Dietary differences in smokers and nonsmokers from two southeastern New England communities.

OBJECTIVE: Previous studies based on 24-hour dietary recall data have shown that smokers tend to consume less healthful diets than nonsmokers. We tested this hypothesis using data from food frequency questionnaires (FFQs) in a group of men and women. DESIGN: Characteristics of smokers and nonsmokers were compared using data collected from a cross-sectional household health survey. SUBJECTS: Adults aged 18 through 64 years from two communities in southeastern New England were randomly selected for the study and interviewed in their homes by trained personnel. The interview included questions on demographic and behavioral characteristics. Height, weight, blood pressure, and serum lipids were measured using standard protocols. The Willett FFQ was completed by 1,608 of 2,531 eligible respondents who made up our study sample. STATISTICAL ANALYSES PERFORMED: Respondents were categorized as current cigarette smokers or nonsmokers. Demographic, behavioral, physiologic, and dietary characteristics were compared between smokers and nonsmokers by analysis of covariance with age as the covariate. RESULTS: Eligible respondents who did not complete the FFQ differed from respondents with respect to age, gender, smoking prevalence, and several other demographic characteristics. Smokers consumed more energy, fat, alcohol, and caffeine than nonsmokers. Smoking status was inversely associated with intake of vitamins A and C, dietary fiber, folate, and iron among women, whereas differences were smaller and not significant among men. Women who smoked consumed fewer servings of fruits and vegetables than nonsmokers, but this trend was not noted in men. The association between diet and smoking was only slightly diminished by multivariate adjustment for age, income, regular exercise, marital status, and working status but most clinically relevant associations remained. The interaction between gender and smoking was not statistically significant for most dietary variables. CONCLUSIONS: These results suggest that health promotion messages targeted to smokers should include dietary instructions, especially for women.

Possible influence of the prospective payment system on the assignment of discharge diagnoses for coronary heart disease.

BACKGROUND: The prospective payment system, under which diagnosis-related groups (DRGs) are used to reimburse hospitals for the care of Medicare patients, replaced the fee-for-service method of payment in Rhode Island in 1983 and in Massachusetts in 1985. Changes in financial incentives resulting from the use of the DRG system may have influenced the assignment of discharge diagnostic codes away from those with lower reimbursement toward codes with higher reimbursement. METHODS: We collected data from the hospital records of patients 35 through 74 years of age who were discharged with codes 410 through 414 (representing various categories of coronary heart disease) of the International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM). The patients were discharged from seven hospitals in two New England communities (one in Rhode Island and one in Massachusetts) between 1980 and 1988. The rates of diagnosis of various forms of coronary heart disease were determined by studying ICD-9-CM hospital discharge codes (codes 410 and 411 for acute forms of coronary heart disease and codes 412, 413, and 414 for chronic forms) and by using a computerized diagnostic algorithm designed to detect definite myocardial infarction and fatal coronary heart disease. RESULTS: The rates of definite coronary events diagnosed by the algorithm and by the study of ICD-9-CM codes 410 through 414 were constant or increased slightly during the study period. However, the frequency of assignment of codes for the acute forms of coronary heart disease (which entail higher reimbursement) rose from 35.2 percent to 48.4 percent among discharged patients with cardiac disease after the institution of DRGs. The majority of this increase was associated with the code for unstable angina pectoris. The frequency of assignment of codes for the chronic forms of coronary heart disease (which entail lower reimbursement) decreased reciprocally, from 64.8 percent to 51.6 percent (P < 0.001). CONCLUSIONS: Our data are consistent with the hypothesis that the prospective reimbursement system has influenced the assignment of hospital discharge codes in a way that would increase payment to hospitals. However, the data do not permit us to distinguish whether hospitals began to assign more precise diagnoses with the advent of the DRG system, or whether they began to favor diagnoses of acute conditions solely for financial reasons.

A new approach to surveillance for acute myocardial infarction: reproducibility and cost efficiency.

A new approach to surveillance of myocardial infarction, the major cardiovascular endpoint is described using an algorithm which depends primarily on enzyme data, using evidence of chest pain and positive electrocardiogram findings as supplemental information only. This approach is evaluated with respect to reproducibility by minimally trained abstractors, cost, and robustness with respect to different hospital systems as well as changes in diagnostic techniques and/or labelling over time. Two pilot studies demonstrate that, in comparison to more traditional approaches, the new surveillance system provides at least a 50% reduction in cost, is highly reproducible over different hospital systems, and potentially, is resilient to changes in diagnostic procedures or coding. The more general applicability of such an innovative surveillance approach to other disease endpoints, in which one reliable procedure contains most of the diagnostic information, is discussed with particular reference to cancer.

The information archipelago--plotting a course.

Information systems applications in some aspects resemble those of a decade ago--they cost a lot, are technically complex, and take a long time to develop. Moreover, as the technology continues to change rapidly, managers find themselves continually squeezed by a shortage of the technical staff and financial resources they need to keep up. A company can use knowledge of its particular strengths and weaknesses in regard to IS to steer its way onto a safe course, say these authors in the second article of a series dealing with the "islands" of information: computers, telecommunications, and office automation (see "The Information Archipelago--Maps and Bridges," HBR September-October 1982). Setting a safe course requires a new planning approach, for which the guideposts are the company's familiarity with any one technology, the importance of the technology to corporate strategy, and certain business characteristics such as size, complexity of product lines, and the general approach to corporate planning.

Computer and information networks.

The most basic conclusion coming out of the EDUCOM seminars is that computer networking must be acknowledged as an important new mode for obtaining information and computation (15). It is a real alternative that needs to be given serious attention in current planning and decision-making. Yet the fact is that many institutions are not taking account of networks when they confer on whether or how to replace their main computer. Articulation of the possibilities of computer networks goes back to the early 1960's and before, and working networks have been in evidence for several years now, both commercially and in universities. What is new, however, is the unmistakable recognition-bordering on a sense of the inevitable-that networks are finally practical and here to stay. The visionary and promotional phases of computer networks are over. It is time for hard-nosed comparative analysis (16). Another conclusion of the seminars has to do with the factors that hinder the fuller development of networking. The major problems to be overcome in applying networks to research and education are political, organizational, and economic in nature rather than technological. This is not to say that the hardware and software problems of linking computers and information systems are completely solved, but they are not the big bottlenecks at present. Research and educational institutions must find ways to organize themselves as well as their computers to work together for greater resource sharing. The coming of age of networks takes on special significance as a result of widespread dissatisfactions expressed with the present computing situation. There is a feeling that the current mode of autonomous, self-sufficient operation in the provision of computing and information services is frequently wasteful, deficient, and unresponsive to users' needs because of duplication of effort from one installation to another, incompatibilities, and inadequate documentation, program support, and user assistance. Complaints about the relative lack of uniform standards and the paucity of information on what programs and data are available and how to get and use them are commonplace. The human tendency, when beset by problems such as these, is to seek a savior in the next new technology-networks in this case. But networking does not in and of itself offer a solution to current deficiencies. What it does offer is a promising vehicle with which to bring about important changes in user practices, institutional procedures, and government policy that can lead to effective solutions. Thus more critical than whether networking is developed and applied is how it is developed and applied. For example, networking emphasizes the need for standards and good documentation. Unless effective mechanisms are developed and strong measures taken in networking to ensure that suitable standards and documentation are developed, present inadequacies could get worse, not better.