Time-Resolved Fuel Density Profiles of the Stagnation Phase of Indirect-Drive Inertial Confinement Implosions.

The implosion efficiency in inertial confinement fusion depends on the degree of stagnated fuel compression, density uniformity, sphericity, and minimum residual kinetic energy achieved. Compton scattering-mediated 50-200 keV x-ray radiographs of indirect-drive cryogenic implosions at the National Ignition Facility capture the dynamic evolution of the fuel as it goes through peak compression, revealing low-mode 3D nonuniformities and thicker fuel with lower peak density than simulated. By differencing two radiographs taken at different times during the same implosion, we also measure the residual kinetic energy not transferred to the hot spot and quantify its impact on the implosion performance.

Simultaneous visualization of wall motion, beam propagation, and implosion symmetry on the National Ignition Facility (invited).

Achieving a symmetric implosion in National Ignition Facility indirect drive targets requires understanding and control of dynamic changes to the laser power transport in the hohlraum. We developed a new experimental platform to simultaneously visualize wall-plasma motion and dynamic laser power transport in the hohlraum and are using it to investigate correlations of these measurements with the imploded capsule symmetry. In a series of experiments where we made one single parameter variation, we show the value of this new platform in developing an understanding of laser transport and implosion symmetry. This platform also provides a new way to evaluate dynamic performance of advanced hohlraum designs.

Observation of hohlraum-wall motion with spectrally selective x-ray imaging at the National Ignition Facility.

The high fuel capsule compression required for indirect drive inertial confinement fusion requires careful control of the X-ray drive symmetry throughout the laser pulse. When the outer cone beams strike the hohlraum wall, the plasma ablated off the hohlraum wall expands into the hohlraum and can alter both the outer and inner cone beam propagations and hence the X-ray drive symmetry especially at the final stage of the drive pulse. To quantitatively understand the wall motion, we developed a new experimental technique which visualizes the expansion and stagnation of the hohlraum wall plasma. Details of the experiment and the technique of spectrally selective x-ray imaging are discussed.

Carbopol improves the early cellular immune responses induced by the modified-life vaccine Ingelvac PRRS® MLV.

Adjuvants enhance both the magnitude and duration of immune responses, therefore representing a central component of vaccines. The nature of the adjuvant can determine the particular type of immune response, which may be skewed toward cytotoxic T cell (CTL) responses, antibody responses, or particular classes of T helper (Th) responses and antibody isotypes. Traditionally, adjuvants have been added to intrinsically poor immunogenic vaccines, such as those using whole killed organisms or subunit vaccines. Here, we have compared cellular immune responses induced by the immunogenic modified life-attenuated vaccine Ingelvac PRRS® MLV when administered alone or in combination with carbopol, a widely used adjuvant in veterinary medicine. Using functional readouts (IFN-γ ELISpot and cell proliferation) and analyzing phenotypical hallmarks of CD4T cell differentiation, we show that carbopol improves cellular immunity by inducing early IFN-γ-producing cells and by preferentially driving T cell differentiation to effector phenotypes. Our data suggest that adjuvants may enhance and modulate life-attenuated--not only subunit/inactivated--vaccines.

Reduced instability growth with high-adiabat high-foot implosions at the National Ignition Facility.

Hydrodynamic instabilities are a major obstacle in the quest to achieve ignition as they cause preexisting capsule defects to grow and ultimately quench the fusion burn in experiments at the National Ignition Facility. Unstable growth at the ablation front has been dramatically reduced in implosions with "high-foot" drives as measured using x-ray radiography of modulations at the most dangerous wavelengths (Legendre mode numbers of 30-90). These growth reductions have helped to improve the performance of layered DT implosions reported by O. A. Hurricane et al. [Nature (London) 506, 343 (2014)], when compared to previous "low-foot" experiments, demonstrating the value of stabilizing ablation-front growth and providing directions for future ignition designs.

2D X-ray radiography of imploding capsules at the national ignition facility.

First measurements of the in-flight shape of imploding inertial confinement fusion (ICF) capsules at the National Ignition Facility (NIF) were obtained by using two-dimensional x-ray radiography. The sequence of area-backlit, time-gated pinhole images is analyzed for implosion velocity, low-mode shape and density asymmetries, and the absolute offset and center-of-mass velocity of the capsule shell. The in-flight shell is often observed to be asymmetric even when the concomitant core self-emission is round. A ∼ 15 µm shell asymmetry amplitude of the Y(40) spherical harmonic mode was observed for standard NIF ICF hohlraums at a shell radius of ∼ 200 µm (capsule at ∼ 5× radial compression). This asymmetry is mitigated by a ∼ 10% increase in the hohlraum length.

Precision shock tuning on the national ignition facility.

Ignition implosions on the National Ignition Facility [J. D. Lindl et al., Phys. Plasmas 11, 339 (2004)] are underway with the goal of compressing deuterium-tritium fuel to a sufficiently high areal density (ρR) to sustain a self-propagating burn wave required for fusion power gain greater than unity. These implosions are driven with a very carefully tailored sequence of four shock waves that must be timed to very high precision to keep the fuel entropy and adiabat low and ρR high. The first series of precision tuning experiments on the National Ignition Facility, which use optical diagnostics to directly measure the strength and timing of all four shocks inside a hohlraum-driven, cryogenic liquid-deuterium-filled capsule interior have now been performed. The results of these experiments are presented demonstrating a significant decrease in adiabat over previously untuned implosions. The impact of the improved shock timing is confirmed in related deuterium-tritium layered capsule implosions, which show the highest fuel compression (ρR~1.0 g/cm(2)) measured to date, exceeding the previous record [V. Goncharov et al., Phys. Rev. Lett. 104, 165001 (2010)] by more than a factor of 3. The experiments also clearly reveal an issue with the 4th shock velocity, which is observed to be 20% slower than predictions from numerical simulation.

Lipopolysaccharide-based enzyme-linked immunosorbent assay for experimental use in detection of antibodies to Lawsonia intracellularis in pigs.

An enzyme-linked immunosorbent assay (ELISA) for Lawsonia intracellularis was developed and compared with a whole-cell antigen-based immunofluorescence antibody test (IFAT). The antigen-containing lipopolysaccharide (LPS) was derived from Percoll gradient purified cultures of L. intracellularis by using a modification of the Westphal hot phenol procedure. The antigen was bound directly to polystyrene 96-well microtiter plates, and the assay was performed in an indirect ELISA format. Specificity and sensitivity values based on 80 known positive and 80 known negative serum samples from controlled experimental trials were 93.7% and 88.7%, respectively. Serological results from a controlled L. intracellularis challenge exposure study confirmed the high specificity and sensitivity of this assay (100% and 99.5%, respectively). Comparisons between the LPS ELISA and the IFAT in detecting anti-Lawsonia antibodies in this controlled study revealed significantly more LPS ELISA-positive pigs than IFAT-positive pigs on days 21, 28, 35, and 42 (P = 0.003, 0.030, 0.002, and 0.006, respectively). This indirect ELISA (LPS ELISA) test is an improved method of detecting antibodies in pigs soon after exposure to L. intracellularis, regardless of isolate type (vaccine or wild type) in experimental studies. The LPS ELISA may be used as a tool to support future research trials on vaccine efficacy and to further understand the immune response induced by L. intracellularis.

Selective inhibition of sequence-specific protein-DNA interactions by incorporation of 6-thioguanine: cleavage by restriction endonucleases.

Incorporation of the antileukemic agent 6-thioguanine (TG) into cellular DNA has been demonstrated to be a major determinant of its cytotoxicity. We have previously shown that complete replacement of G by TG within one DNA strand of the SV40 origin of replication can completely inhibit sequence-specific binding of the viral replication protein T antigen. The aim of the present study was to determine the effect of more selective TG substitutions on DNA-protein interactions, by utilizing the simpler base recognition sequence motifs of restriction endonucleases. In the first part of our study, we replaced G with TG in one or two of four possible sites within the duplex hexameric recognition sequence of BamHI (5'-G decreases GATCC-3'), by enzymatic extension of primed oligonucleotides. This extension was stalled, but not completely inhibited, at locations where insertion of consecutive TG moieties was required. Both strands of molecules containing a single substitution were cleaved by BamHI at reduced rates, with the substituted strand inhibited to a greater degree. In molecules containing two substitutions, neither strand was cut by BamHI. In contrast, we found that scission of these same mono- and disubstituted substrates by the less stringent isoschizomer MboI (5'-N decreases GATCN-3') was inhibited only slightly. In the second part of our study, we investigated the effect of analog substitution on scission by the type II-S enzymes AlwI and FokI, in order to separately determine the effects of restriction site modification versus scission site modification. We found that the reactivity of these enzymes was completely abolished by TG substitution within the recognition site, whereas substitution at the scission site had no effect. Our results demonstrate that infrequent TG substitutions within symmetric DNA sequences can inhibit sequence-specific interactions in an asymmetric fashion. In addition, although previous reports have shown that TG forms a relatively weak base pair with cytosine, it appears that the inhibition of restriction endonuclease-mediated cleavage resulting from TG incorporation is a function of the sequence requirements of the protein and not a general consequence of disrupted base-pairing at the recognition locus. These data support the idea that the cytotoxic consequences of TG incorporation may be due to inhibition of sequence-specific protein-DNA interactions.

Effects of incorporation of 6-thioguanine into SV40 DNA.

The antileukemic agent 6-thioguanine (TG) is thought to inhibit DNA synthesis as a result of its incorporation into DNA. In the present study we have examined the nature of this inhibition, using replication of SV40 viral DNA as a model system. Addition of TG to SV40-infected CV1P cells from 22 to 24 hr post infection causes a dose-dependent inhibition of viral DNA synthesis. This inhibition plateaus between 250 and 2500 microM TG, resulting in a maximum decrease of viral DNA synthesis of about 50%. Pulse-chase experiments showed no detectable slowing of elongation of nascent DNA chains, whereas measurement of the conversion of incorporated 3H-dThd into supercoiled viral DNA suggested that elongation might be slightly inhibited, but by no more than 20%. Since inhibition of elongation could not account for the total depression of DNA synthesis, we hypothesized that inhibition of initiation of DNA replication takes place. This hypothesis was tested by radioactively labeling newly synthesized viral DNA and then assessing the ability of these molecules to reenter the replicating pool by density labeling with bromodeoxyuridine. The fraction of TG-containing molecules able to re-initiate replication was decreased 15%, compared to control. This effect, which was dependent on the concentration of TG added to the medium, was closely correlated to the extent of TG incorporation into the viral genome. We concluded that a portion of SV40 viral DNA synthesis inhibited by TG is due to an effect on initiation, and hypothesized that this effect may be caused by the substitution of TG for guanine in critical recognition sequences at the origin of replication. We proceeded to test this hypothesis by constructing SV40 origin sequences containing TG and then measuring their ability to bind T-antigen in vitro. The necessary deoxynucleoside triphosphate, TdGTP, was obtained by chemical phosphorylation of thiodeoxyguanosine. In order to selectively place TG within the desired region, a plasmid containing the T-antigen binding sequences was linearized so as to place these sequences at one end of the molecule, and then digested briefly with exonuclease III. The excised strand was resynthesized by use of the Klenow fragment of DNA polymerase I along with various nucleotide mixtures. Although resynthesis with mixtures containing TdGTP in place of dGTP was impeded somewhat, it was possible to achieve complete resynthesis with this analog.(ABSTRACT TRUNCATED AT 400 WORDS)