The cultivated tomato (Lycopersicon esculentum) has a unipinnate compound leaf. In the developing leaf primordium, major leaflet initiation is basipetal, and lobe formation and early vascular differentiation are acropetal. We show that engineered alterations in the expression of a tomato homeobox gene, LeT6, can cause dramatic changes in leaf morphology. The morphological states are variable and unstable and the phenotypes produced indicate that the tomato leaf has an inherent level of indeterminacy. This is manifested by the production of multiple orders of compounding in the leaf, by numerous shoot, inflorescence, and floral meristems on leaves, and by the conversion of rachis-petiolule junctions into "axillary" positions where floral buds can arise. Overexpression of a heterologous homeobox transgene, kn1, does not produce such phenotypic variability. This indicates that LeT6 may differ from the heterologous kn1 gene in the effects manifested on overexpression, and that 35S-LeT6 plants may be subject to alterations in expression of both the introduced and endogenous LeT6 genes. The expression patterns of LeT6 argue in favor of a fundamental role for LeT6 in morphogenesis of leaves in tomato and also suggest that variability in homeobox gene expression may account for some of the diversity in leaf form seen in nature.During vegetative growth most higher plants are indeterminate. The SAM produces a radially symmetrical, acropetally differentiating shoot axis (stem) and determinate, bilaterally symmetrical lateral organs (leaves). Leaves can be one of two types, simple or compound, and the nature of these has been a matter of debate. The ontogenetic relationship of the dicot compound leaf to the simple leaf is unclear (Merrill, 1986), with various researchers concluding that the basic leaf form is simple (Eames, 1961) or compound pinnate (Hagemann, 1984), or that compound leaves have some shoot-like features and may represent a continuum between shoots and leaves (Sattler and Rutishauser, 1992; Lacroix and Sattler, 1994).To determine morphogenetic patterns and the level of indeterminacy in compound leaves, we have used homeobox genes that were cloned from tomato (Lycopersicon esculentum) (Chen et al., 1997; Janssen et al., 1998). Homeobox genes encode transcription factors that control the regulation of cell fate (McGinnis et al., 1984;Scott et al., 1989). The first plant homeobox gene cloned was the maize knotted1 (kn1) gene (Vollbrecht et al., 1991). kn1-like homeobox (knox) genes have been placed into two classes (Kerstetter et al., 1994). Although no specific function has as yet been ascertained for class II knox genes (Serikawa et al., 1997), class I knox genes play a role in meristem maintenance and leaf and flower determination at the shoot apex. Class I knox genes are not expressed in initiating organ primordia, mature leaves, or floral organs in simpleleaved species (Smith et al., 1992; Jackson et al., 1994; Long et al., 1996).We have cloned a class I knox gene, LeT6 (L. esculentum T6), and shown tha...
OMEGA, a 60-beam, 351 nm, Nd:glass laser with an on-target energy capability of more than 40 kJ, is a flexible facility that can be used for both direct- and indirect-drive targets and is designed to ultimately achieve irradiation uniformity of 1% on direct-drive capsules with shaped laser pulses (dynamic range ≳400:1). The OMEGA program for the next five years includes plasma physics experiments to investigate laser–matter interaction physics at temperatures, densities, and scale lengths approaching those of direct-drive capsules designed for the 1.8 MJ National Ignition Facility (NIF); experiments to characterize and mitigate the deleterious effects of hydrodynamic instabilities; and implosion experiments with capsules that are hydrodynamically equivalent to high-gain, direct-drive capsules. Details are presented of the OMEGA direct-drive experimental program and initial data from direct-drive implosion experiments that have achieved the highest thermonuclear yield (1014 DT neutrons) and yield efficiency (1% of scientific breakeven) ever attained in laser-fusion experiments.
Direct drive laser fusion ignition experiments rely on detailed understanding and control of irradiation uniformity, the Rayleigh-Taylor instability and target fabrication. The Laboratory for Laser Energetics (LLE) is investigating various theoretical aspects of a direct drive National Ignition Facility (NIF) ignition target based on an 'all-DT' design: a spherical target of ∼3.4 mm diameter, with a 1-2 µm CH wall thickness and a DT ice layer of ∼340 µm near the triple point of DT (∼19 K). OMEGA experiments are designed to address the critical issues related to direct drive laser fusion and to provide the necessary data to validate the predictive capability of LLE computer codes. The cryogenic targets to be used on OMEGA are hydrodynamically equivalent to those planned for the NIF. The current experimental studies on OMEGA address the essential components of direct drive laser fusion: irradiation uniformity and laser imprinting, Rayleigh-Taylor growth and saturation, compressed core performance and shell-fuel mixing, laser-plasma interactions and their effect on target performance, and cryogenic target fabrication and handling.
Ignition target designs for inertial confinement fusion on the National Ignition Facility ͑NIF͒ ͓W. J. Hogan et al., Nucl. Fusion 41, 567 ͑2001͔͒ are based on a spherical ablator containing a solid, cryogenic-fuel layer of deuterium and tritium. The need for solid-fuel layers was recognized more than 30 years ago and considerable effort has resulted in the production of cryogenic targets that meet most of the critical fabrication tolerances for ignition on the NIF. At the University of Rochester's Laboratory for Laser Energetics ͑LLE͒, the inner-ice surface of cryogenic DT capsules formed using -layering meets the surface-smoothness requirement for ignition ͑Ͻ1-m rms in all modes͒. Prototype x-ray-drive cryogenic targets being produced at the Lawrence Livermore National Laboratory are nearing the tolerances required for ignition on the NIF. At LLE, these cryogenic DT ͑and D 2 ͒ capsules are being imploded on the direct-drive 60-beam, 30-kJ UV OMEGA laser ͓T. R. Boehly et al., Opt. Commun. 133, 495 ͑1997͔͒. The designs of these cryogenic targets for OMEGA are energy scaled from the baseline direct-drive-ignition design for the NIF. Significant progress with the formation and characterization of cryogenic targets for both direct and x-ray drive will be described. Results from recent cryogenic implosions will also be presented.
Initial results from direct-drive spherical cryogenic target implosions on the 60-beam OMEGA laser system [T. R. Boehly, D. L. Brown, R. S. Craxton et al., Opt. Commun. 133, 495 (1997)] are presented. These experiments are part of the scientific base leading to direct-drive ignition implosions planned for the National Ignition Facility (NIF) [W. J. Hogan, E. I. Moses, B. E. Warner et al., Nucl. Fusion 41, 567 (2001)]. Polymer shells (1-mm diam with walls <3 μm) are filled with up to 1000 atm of D2 to provide 100-μm-thick ice layers. The ice layers are smoothed by IR heating with 3.16-μm laser light and are characterized using shadowgraphy. The targets are imploded by a 1-ns square pulse with up to ∼24 kJ of 351-nm laser light at a beam-to-beam rms energy balance of <3% and full-beam smoothing. Results shown include neutron yield, secondary neutron and proton yields, the time of peak neutron emission, and both time-integrated and time-resolved x-ray images of the imploding core. The experimental values are compared with 1-D numerical simulations. The target with an ice-layer nonuniformity of σrms=9 μm showed 30% of the 1-D predicted neutron yield. These initial results are encouraging for future cryogenic implosions on OMEGA and the NIF.
Price codes: Printed Copy A04Microfiche A01 Semyon Papernov, a scientist in the Optical Technology Group, uses a Digital Instruments Nanoscope I11 atomic force microscope (AFM) operated in contact mode to evaluate the morphology of 3w laser-damage features on a multilayer, quarter-wave-stack OMEGA transport HR coating made from HfO, and Si02 Surface mapping of damaged and undamaged sites on production witness pieces by atomic force microscopy has shown that nodular growth defects, long considered to be the dominant laser-damage driver in dielectric thin films, can remain unaffected under 35 1-nm irradiation conditions, while other defect-driving mechanisms dominate damage crater formation in the immediate vicinity of the nodules.This report was prepared as an account of work conducted by the Laboratory for Laser Energetics and sponsored by New York State Energy Research and Development Authority, the University of Rochester, the U.S. Department of Energy, and other agencies. Neither the above named sponsors, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, mark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof or any other sponsor. Results reported in the LLE Review should not be taken as necessarily final results as they represent active research. The views and opinions of authors expressed herein do not necessarily state or reflect those of any of the above sponsoring entities.The work described in this volume includes current research at the Laboratory for Laser Energetics, which is supported by New York State Research and Development Authority, the University of Rochester, the U.S. In BriefThis volume of the LLE review, covering the period of January-March 1995, contains articles on the evaluation of the mechanism for laser damage in OMEGA UV multilayer coatings using a combination of conventional laser-damage characterization methods and atomic force microscopy; a dual-amplitude, fiber-coupled waveguide integrated-optic modulation device for generating temporally shaped optical pulses in OMEGA; a proposal for modifying the indirect-drive irradiation geometry of the National Ignition Facility (NIF) to provide the additional flexibility for performing direct-drive experiments; direct measurements of terminal-level lifetime in several different Nd:YLF laser media; an overview of the materials science issues, basic mechanisms, and potential device applications for light-emitting porous silicon; and a study of the time-dependent reflection and surface temperatures for laser-irradiated dental hard tissue at two CO2 laser wavelengths.Highlights of the research pre...
Direct-drive spherical implosions of cryogenic, D2-filled capsules are performed on the 60-beam OMEGA laser system [T. R. Boehly, D. L. Brown, R. S. Craxton, R. L. Keck, J. P. Knauer, J. H. Kelly, T. J. Kessler, S. A. Kumpan, S. J. Loucks, S. A. Letzring, F. J. Marshall, R. L. McCrory, S. F. B. Morse, W. Seka, J. M. Soures, and C. P. Verdon, Opt. Commun. 133, 495 (1997)]. The targets are energy scaled from the base line ignition design developed for the National Ignition Facility [W. J. Hogan et al., Nucl. Fusion 41, 567 (2001)]. Thin-walled (∼4μm), ∼860μm diam deuterated polymer shells are permeation filled with D2 gas and cooled to the triple point (∼18.7K). Cryogenic ice layers with a uniformity of ∼2μm rms are formed and maintained. The targets are imploded with high-contrast pulse shapes with full single-beam smoothing (1THz bandwidth, two-dimensional smoothing by spectral dispersion with polarization smoothing) to study the effects of the acceleration- and deceleration-phase Rayleigh–Taylor growth on target performance. Two-dimensional hydrocode simulations show good agreement with the experimental observations. Scattered-light and neutron-burn-history measurements are consistent with predicted absorption and hydrodynamic coupling calculations. Time-resolved and static x-ray images show the progress of the imploding shell, the shape, and temperature of the stagnating core. Particle-based instruments measure the fusion yield and rate, the ion temperature in the core, and the fuel areal density at the time of neutron production. These experiments have produced fuel areal densities of up to ∼100mg∕cm2, primary neutron yields of ∼4×1010, and secondary neutron yields of 1% to 2% of the primary yield. These results validate the hydrocode predictions for the direct-drive ignition-point design, giving increasing confidence in the direct-drive approach to inertial confinement fusion ignition.
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