National Diagnostic Working Group (NDWG) for inertial confinement fusion (ICF)/high-energy density (HED) science: The whole exceeds the sum of its parts.

The National Diagnostic Working Group (NDWG) has led the effort to fully exploit the major inertial confinement fusion/high-energy density facilities in the US with the best available diagnostics. These diagnostics provide key data used to falsify early theories for ignition and suggest new theories, recently leading to an experiment that exceeds the Lawson condition required for ignition. The factors contributing to the success of the NDWG, collaboration and scope evolution, and the methods of accomplishment of the NDWG are discussed in this Review. Examples of collaborations in neutron and gamma spectroscopy, x-ray and neutron imaging, x-ray spectroscopy, and deep-ultraviolet Thomson scattering are given. An abbreviated history of the multi-decade collaborations and the present semiformal management framework is given together with the latest National Diagnostic Plan.

Direct drive with the argon fluoride laser as a path to high fusion gain with sub-megajoule laser energy.

Argon fluoride (ArF) is currently the shortest wavelength laser that can credibly scale to the energy and power required for high gain inertial fusion. ArF's deep ultraviolet light and capability to provide much wider bandwidth than other contemporary inertial confinement fusion (ICF) laser drivers would drastically improve the laser target coupling efficiency and enable substantially higher pressures to drive an implosion. Our radiation hydrodynamics simulations indicate gains greater than 100 are feasible with a sub-megajoule ArF driver. Our laser kinetics simulations indicate that the electron beam-pumped ArF laser can have intrinsic efficiencies of more than 16%, versus about 12% for the next most efficient krypton fluoride excimer laser. We expect at least 10% 'wall plug' efficiency for delivering ArF light to target should be achievable using solid-state pulsed power and efficient electron beam transport to the laser gas that was demonstrated with the U.S. Naval Research Laboratory's Electra facility. These advantages could enable the development of modest size and lower cost fusion power plant modules. This would drastically change the present view on inertial fusion energy as being too expensive and the power plant size too large. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 1)'.

Mitigation of cross-beam energy transfer in inertial-confinement-fusion plasmas with enhanced laser bandwidth.

Cross-beam energy transfer (CBET) is a significant energy-loss mechanism in directly driven inertial-confinement-fusion (ICF) targets. One strategy for mitigating CBET is to increase the bandwidth of the laser light, thereby disrupting the resonant three-wave interactions that underlie this nonlinear scattering process. Here, we report on numerical simulations performed with the wave-based code lpse that show a significant reduction in CBET for bandwidths of 2-5 THz (corresponding to a normalized bandwidth of 0.2%-0.6% at a laser wavelength of 351nm) under realistic plasma conditions. Such bandwidths are beyond those available with current high-energy lasers used for ICF, but could be achieved using stimulated rotation Raman scattering in diatomic gases like nitrogen.

Capsule implosions for continuum x-ray backlighting of opacity samples at the National Ignition Facility.

Direct drive implosions of plastic capsules have been performed at the National Ignition Facility to provide a broad-spectrum (500-2000 eV) X-ray continuum source for X-ray transmission spectroscopy. The source was developed for the high-temperature plasma opacity experimental platform. Initial experiments using 2.0 mm diameter polyalpha-methyl styrene capsules with ∼20 µm thickness have been performed. X-ray yields of up to ∼1 kJ/sr have been measured using the Dante multichannel diode array. The backlighter source size was measured to be ∼100 µm FWHM, with ∼350 ps pulse duration during the peak emission stage. Results are used to simulate transmission spectra for a hypothetical iron opacity sample at 150 eV, enabling the derivation of photometrics requirements for future opacity experiments.

Measurements of electron density and temperature profiles in plasma produced by Nike KrF laser for laser plasma instability research.

A grid image refractometer (GIR) has been implemented at the Nike krypton fluoride laser facility of the Naval Research Laboratory. This instrument simultaneously measures propagation angles and transmissions of UV probe rays (λ = 263 nm, Δt = 10 ps) refracted through plasma. We report results of the first Nike-GIR measurement on a CH plasma produced by the Nike laser pulse (∼1 ns FWHM) with the intensity of 1.1 × 10(15) W/cm(2). The measured angles and transmissions were processed to construct spatial profiles of electron density (ne) and temperature (Te) in the underdense coronal region of the plasma. Using an inversion algorithm developed for the strongly refracted rays, the deployed GIR system probed electron densities up to 4 × 10(21) cm(-3) with the density scale length of 120 µm along the plasma symmetry axis. The resulting n(e) and T(e) profiles are verified to be self-consistent with the measured quantities of the refracted probe light.

Suppression of laser nonuniformity imprinting using a thin high-z coating.

Imprinting of laser nonuniformity is a limiting factor in direct-drive inertial confinement fusion experiments, particularly when available laser smoothing is limited. A thin (∼400 Å) high-Z metal coating is found to substantially suppress laser imprint for planar targets driven by pulse shapes and intensities relevant to implosions on the National Ignition Facility while retaining low adiabat target acceleration. A hybrid of indirect and direct drive, this configuration results in initial ablation by x rays from the heated high-Z layer, creating a large standoff for perturbation smoothing.

Implementation of focal zooming on the Nike KrF laser.

In direct drive inertial confinement laser fusion, a pellet containing D-T fuel is imploded by ablation arising from absorption of laser energy at its outer surface. For optimal coupling, the focal spot of the laser would continuously decrease to match the reduction in the pellet's diameter, thereby minimizing wasted energy. A krypton-fluoride laser (λ = 248 nm) that incorporates beam smoothing by induced spatial incoherence has the ability to produce a high quality focal profile whose diameter varies with time, a property known as focal zooming. A two-stage focal zoom has been demonstrated on the Nike laser at the Naval Research Laboratory. In the experiment, a 4.4 ns laser pulse was created in which the on-target focal spot diameter was 1.3 mm (full width at half maximum) for the first 2.4 ns and 0.28 mm for the final 2 ns. These two diameters appear in time-integrated focal plane equivalent images taken at several locations in the amplification chain. Eight of the zoomed output beams were overlapped on a 60 µm thick planar polystyrene target. Time resolved images of self-emission from the rear of the target show the separate shocks launched by the two corresponding laser focal diameters.

Tissue distribution and histopathological effects of titanium dioxide nanoparticles after intravenous or subcutaneous injection in mice.

Nanoparticles can be formed following degradation of medical devices such as orthopedic implants. To evaluate the safety of titanium alloy orthopedic materials, data are needed on the long-term distribution and tissue effects of injected titanium nanoparticles in experimental animals. In this study, we evaluated the tissue distribution and histopathological effects of titanium dioxide (TiO(2)) nanoparticles (approximately 120 nm diameter) in mice after intravenous (i.v.; 56 or 560 mg kg(-1) per mouse) or subcutaneous (s.c.; 560 or 5600 mg kg(-1) per mouse) injection on two consecutive days. Animals were examined 1 and 3 days, and 2, 4, 12 and 26 weeks after the final injection. When examined by light microscopy, particle agglomerates identified as TiO(2) were observed mainly in the major filtration organs - liver, lung and spleen - following i.v. injection. Particles were still observed 26 weeks after injection, indicating that tissue clearance is limited. In addition, redistribution within the histological micro-compartments of organs, especially in the spleen, was noted. Following s.c. injection, the largest particle agglomerates were found mainly in the draining inguinal lymph node, and to a lesser extent, the liver, spleen and lung. With the exception of a foreign body response at the site of s.c. injection and the appearance of an increased number of macrophages in the lung and liver, there was no histopathological evidence of tissue damage observed in any tissue at any time point.

Basic hydrodynamics of Richtmyer-Meshkov-type growth and oscillations in the inertial confinement fusion-relevant conditions.

In inertial confinement fusion (ICF), the possibility of ignition or high energy gain is largely determined by our ability to control the Rayleigh-Taylor (RT) instability growth in the target. The exponentially amplified RT perturbation eigenmodes are formed from all sources of the target and radiation non-uniformity in a process called seeding. This process involves a variety of physical mechanisms that are somewhat similar to the classical Richtmyer-Meshkov (RM) instability (in particular, most of them are active in the absence of acceleration), but differ from it in many ways. In the last decade, radiographic diagnostic techniques have been developed that made direct observations of the RM-type effects in the ICF-relevant conditions possible. New experiments stimulated the advancement of the theory of the RM-type processes. The progress in the experimental and theoretical studies of such phenomena as ablative RM instability, re-shock of the RM-unstable interface, feedout and perturbation development associated with impulsive loading is reviewed.

Stability of a shock-decelerated ablation front.

Experimental study of a shock-decelerated ablation front is reported. A planar solid plastic target is accelerated by a laser across a vacuum gap and collides with a lower-density plastic foam layer. While the target is accelerated, a fast Rayleigh-Taylor (RT) growth of the seeded single-mode perturbation at the ablation front is observed. After the collision, the velocity of the ablation front is seen to remain constant. The reshock quenches the RT growth but does not trigger any Richtmyer-Meshkov growth at the ablation front, which is shown to be consistent with both theory and simulations.

Experimental benchmark for an improved simulation of absolute soft-x-ray emission from polystyrene targets irradiated with the Nike laser.

Absolutely calibrated, time-resolved spectral intensity measurements of soft-x-ray emission (hnu approximately 0.1-1.0 keV) from laser-irradiated polystyrene targets are compared to radiation-hydrodynamic simulations that include our new postprocessor, Virtual Spectro. This new capability allows a unified, detailed treatment of atomic physics and radiative transfer in nonlocal thermodynamic equilibrium conditions for simple spectra from low-Z materials as well as complex spectra from high-Z materials. The excellent agreement (within a factor of approximately 1.5) demonstrates the powerful predictive capability of the codes for the complex conditions in the ablating plasma. A comparison to data with high spectral resolution (E/deltaE approximately 1000) emphasizes the importance of including radiation coupling in the quantitative simulation of emission spectra.

Flow cytometric enumeration of micronucleated reticulocytes: high transferability among 14 laboratories.

This laboratory previously described a single-laser flow cytometric method, which effectively resolves micronucleated erythrocyte populations in rodent peripheral blood samples. Even so, the rarity and variable size of micronuclei make it difficult to configure instrument settings consistently and define analysis regions rationally to enumerate the cell populations of interest. Murine erythrocytes from animals infected with the malaria parasite Plasmodium berghei contain a high prevalence of erythrocytes with a uniform DNA content. This biological model for micronucleated erythrocytes offers a means by which the micronucleus analysis regions can be rationally defined, and a means for controlling interexperimental variation. The experiments described herein were performed to extend these studies by testing whether malaria-infected erythrocytes could also be used to enhance the transferability of the method, as well as control intra- and interlaboratory variation. For these studies, blood samples from mice infected with malaria, or treated with vehicle or the clastogen methyl methanesulfonate, were fixed and shipped to collaborating laboratories for analysis. After configuring instrumentation parameters and guiding the position of analysis regions with the malaria-infected blood samples, micronucleated reticulocyte frequencies were measured (20,000 reticulocytes per sample). To evaluate both intra- and interlaboratory variation, five replicates were analyzed per day, and these analyses were repeated on up to five separate days. The data of 14 laboratories presented herein indicate that transferability of this flow cytometric technique is high when instrumentation is guided by the biological standard Plasmodium berghei.

Evaluation of the rodent micronucleus assay by a 28-day treatment protocol: Summary of the 13th Collaborative Study by the Collaborative Study Group for the Micronucleus Test (CSGMT)/Environmental Mutagen Society of Japan (JEMS)-Mammalian Mutagenicity Study Group (MMS).

To examine whether micronucleus tests can be incorporated into general toxicology assays, we performed micronucleus tests applying the treatment protocols typically used in such assays. In this 13th Collaborative Study of the CSGMT, both rats and mice were tested, although rats were used in the majority of the studies. Fifteen mutagens were tested in rats, mainly by oral (p.o.) administration. Micronucleus induction was evaluated 2, 3, and 4 days, and 1, 2, 3, and 28 days after the beginning of the treatment in the peripheral blood, and at 28 days in the bone marrow. Of the 15 chemicals that induced micronuclei in rats in short-term assays, two chemicals (1,2-dimethylhydrazine.2HCl and mitomycin C) were negative in all our experiments, possibly because of insufficient dose levels. The remaining 13 were positive within the estimated dose range of a general toxicology assay, suggesting the possibility of integrating the micronucleus assay into general toxicology assays. Three patterns were observed in micronucleus induction during the period of repeated treatment: (1) gradual increases in micronucleus frequency with sequential doses, (2) a peak at 3-5 days followed by gradual decreases in micronucleus frequency with sequential doses, and (3) a rapid increase in micronucleus frequency followed by a plateau. We evaluated factors that might have been involved in those patterns, such as the spleen function, target organ exposure, extramedullary hematopoiesis, hypothermia, and hypoxia. Another factor we considered was dosage. Because the dosages employed in a general toxicity assay are usually lower than those used in short-term micronucleus assays, this discrepancy was considered the greatest potential problem for integrating the micronucleus assay into general toxicology assays. Our results indicate that the integration of the micronucleus assay into a 28-day toxicological assay is feasible. To serve this purpose, blood samples collected 4 days after the beginning of treatment and blood and bone marrow samples collected at autopsy should be examined. Furthermore, although it is recognized that mice may be suitable for performing independent micronucleus assays, we propose that rats can provide biologically important and relevant information regarding potential chemical mutagens that can be evaluated under conditions used in the conduct of general toxicology studies.

Vision readiness of the reserve forces of the U.S. Army.

In 1996 and 1997, the Army conducted an exercise to assess the ability to rapidly mobilize the reserve forces. In accordance with Army requirements, each soldier was evaluated to determine if he or she met vision and optical readiness standards. Of the 1,947 individuals processed through the optometry section, 40% met vision requirements without correction and 32% met vision requirements with their current spectacles. The remaining 28% required examination. A major impediment to processing reserve units for deployment is the lack of vision and optical readiness. In the mobilization for the Persian Gulf War, significant delays were incurred because of the time required to perform eye examinations and fabricate eyewear. However, as a result of this exercise, current prescriptions will be available in the event of mobilization. To ensure readiness, all units should perform such exercises periodically.

Calibration of an extreme-ultraviolet transmission grating spectrometer with synchrotron radiation.

The responsivity of an extreme-ultraviolet transmission grating spectrometer with silicon photodiode detectors was measured with synchrotron radiation. The spectrometer was designed to record the absolute radiation flux in a wavelength bandpass centered at 30 nm. The transmission grating had a period of 200 nm and relatively high efficiencies in the +1 and the -1 diffraction orders that were dispersed on either side of the zero-order beam. Three photodiodes were positioned to measure the signals in the zero order and in the +1 and -1 orders. The photodiodes had aluminum overcoatings that passed the desired wavelength bandpass centered at 30 nm and attenuated higher-order radiation and wavelengths longer than approximately 80 nm. The spectrometer's responsivity, the ratio of the photodiode current to the incident radiation power, was determined as a function of the incident wavelength and the angle of the spectrometer with respect to the incident radiation beam. The spectrometer's responsivity was consistent with the product of the photodiode responsivity and the grating efficiency, both of which were separately measured while removed from the spectrometer.

Board certification in optometry.

BACKGROUND: In keeping with current expectations in the health care community, the purpose of the American Board of Optometric Practice (ABOP) is to enhance the quality of optometric care available to the public by fostering continued competence for practitioners through administering education and examinations for certification and re-certification. The formation of ABOP makes possible for the first time a board certification process for optometrists. METHODS: The optometry model for board certification and recertification emphasizes the breadth of the profession. ABOP certification will be accomplished through a combination of examinations and high-quality, tested Board Certified Continuing Education (BCCE). Specific requirements for practitioners at various stages of their careers are presented. RESULTS: Board certification provides one important mechanism for an optometrist to demonstrate commitment to quality, professionalism, and ongoing clinical competence. The optometrist benefits from high-quality continuing education designed for timeliness, importance, and breadth. The public benefits by the enhancement of continued competence within the optometric profession. Health care agencies benefit by being able to recognize providers who have elected to demonstrate their qualifications through certification. CONCLUSIONS: Through board certification, optometrists will be able to demonstrate their commitment to maintaining clinical competence through a nationally uniform program, and they will be able to comply with standards that are generally recognized and required throughout the health care community.

Flow cytometry assay for counting micronucleated erythrocytes: development process.

Development of any new assay proceeds in several phases. When an assay is intended for regular use to support regulatory decision-making, there are significant additional stages in the development process beyond the initial description of the method. In this paper we discuss some of the studies related to the development of a flow cytometric method for counting micronuclei in rodent erythrocytes. Studies related to fixation methods and conditions, standardization of DNA staining, and antibody staining are discussed. These studies, while not part of the formal description of the method, are needed as part of the preparation for the formal validation of the method. In addition, the lessons learned in transferring the method to other laboratories are briefly discussed in relation to defining the final protocol.

Motorist vision policy.

BACKGROUND: The primary purpose of public policy requiring vision testing for driver license renewal is to identify individuals with functional vision impairments and, when necessary, to restrict their driving. This is based on the presumption that poor vision is causally related to poor driving and traffic crashes. METHODS: The AOA Environmental and Occupational Vision Committee performed a synthesis of relevant empirical literature on policy-based research and developed potential options for enhancing traffic safety. RESULTS: Presently, some states require vision testing for driver's license renewal and some do not. Regional and nationwide studies report that vision-related license renewal policies are associated with enhanced traffic safety. However, contemporary vision screening tests may be of limited value in identifying individuals with functional vision impairments. CONCLUSION: The most cost-effective and valid method for identifying, treating and counseling visually impaired drivers is to require a comprehensive eye examination as a condition for driver license renewal for those with a high prevalence or high probability of vision impairment.