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Eighty years ago, it was proposed that solid hydrogen would become metallic at sufficiently high density. Despite numerous investigations, this transition has not yet been experimentally observed. More recently, there has been much interest in the analog of this predicted metallic transition in the dense liquid, due to its relevance to planetary science. Here, we show direct observation of an abrupt insulator-to-metal transition in dense liquid deuterium. Experimental determination of the location of this transition provides a much-needed benchmark for theory and may constrain the region of hydrogen-helium immiscibility and the boundary-layer pressure in standard models of the internal structure of gas-giant planets.

We have conceived a new class of prime-power sources for pulsed-power accelerators: impedance-matched Marx generators (IMGs). The fundamental building block of an IMG is a brick, which consists of two capacitors connected electrically in series with a single switch. An IMG comprises a single stage or several stages distributed axially and connected in series. Each stage is powered by a single brick or several bricks distributed azimuthally within the stage and connected in parallel. The stages of a multistage IMG drive an impedance-matched coaxial transmission line with a conical center conductor. When the stages are triggered sequentially to launch a coherent traveling wave along the coaxial line, the IMG achieves electromagnetic-power amplification by triggered emission of radiation. Hence a multistage IMG is a pulsed-power analogue of a laser. To illustrate the IMG approach to prime power, we have developed conceptual designs of two ten-stage IMGs with LC time constants on the order of 100 ns. One design includes 20 bricks per stage, and delivers a peak electrical power of 1.05 TW to a matched-impedance 1.22−Ω load. The design generates 113 kV per stage and has a maximum energy efficiency of 89%. The other design includes a single brick per stage, delivers 68 GW to a matched-impedance 19−Ω load, generates 113 kV per stage, and has a maximum energy efficiency of 90%. For a given electrical-power-output time history, an IMG is less expensive and slightly more efficient than a linear transformer driver, since an IMG does not use ferromagnetic cores.

Presented are voltage measurements taken near the load region on the Z pulsed-power accelerator using an inductive voltage monitor (IVM). Specifically, the IVM was connected to, and thus monitored the voltage at, the bottom level of the accelerator’s vacuum double post-hole convolute. Additional voltage and current measurements were taken at the accelerator’s vacuum-insulator stack (at a radius of 1.6 m) by using standard D -dot and B -dot probes, respectively. During postprocessing, the measurements taken at the stack were translated to the location of the IVM measurements by using a lossless propagation model of the Z accelerator’s magnetically insulated transmission lines (MITLs) and a lumped inductor model of the vacuum post-hole convolute. Across a wide variety of experiments conducted on the Z accelerator, the voltage histories obtained from the IVM and the lossless propagation technique agree well in overall shape and magnitude. However, large-amplitude, high-frequency oscillations are more pronounced in the IVM records. It is unclear whether these larger oscillations represent true voltage oscillations at the convolute or if they are due to noise pickup and/or transit-time effects and other resonant modes in the IVM. Results using a transit-time-correction technique and Fourier analysis support the latter. Regardless of which interpretation is correct, both true voltage oscillations and the excitement of resonant modes could be the result of transient electrical breakdowns in the post-hole convolute, though more information is required to determine definitively if such breakdowns occurred. Despite the larger oscillations in the IVM records, the general agreement found between the lossless propagation results and the results of the IVM shows that large voltages are transmitted efficiently through the MITLs on Z . These results are complementary to previous studies [R. D. McBride et al., Phys. Rev. ST Accel. Beams 13, 120401 (2010)] that showed efficient transmission of large currents through the MITLs on Z . Taken together, the two studies demonstrate the overall efficient delivery of very large electrical powers through the MITLs on Z .

We demonstrate that a wide variety of current-pulse shapes can be generated using a linear-transformer-driver (LTD) module that drives an internal water-insulated transmission line. The shapes are produced by varying the timing and initial charge voltage of each of the module’s cavities. The LTD-driven accelerator architecture outlined in [Phys. Rev. ST Accel. Beams 10, 030401 (2007)] provides additional pulse-shaping flexibility by allowing the modules that drive the accelerator to be triggered at different times. The module output pulses would be combined and symmetrized by water-insulated radial-transmission-line impedance transformers [Phys. Rev. ST Accel. Beams 11, 030401 (2008)].

Experimental data is presented that illustrates important displacement current phenomena in the magnetically insulated transmission lines (MITLs) of the refurbished Z accelerator [D. V. Rose et al., Phys. Rev. ST Accel. Beams 13, 010402 (2010)]. Specifically, we show how displacement current in the MITLs causes significant differences between the accelerator current measured at the vacuum-insulator stack (at a radial position of about 1.6 m from the Z axis of symmetry) and the accelerator current measured at the load (at a radial position of about 6 cm from the Z axis of symmetry). The importance of accounting for these differences was first emphasized by Jennings et al. [C. A. Jennings et al., IEEE Trans. Plasma Sci. 38, 529 (2010)], who calculated them using a full transmission-line-equivalent model of the four-level MITL system. However, in the data presented by Jennings et al., many of the interesting displacement current phenomena were obscured by parasitic current losses that occurred between the vacuum-insulator stack and the load (e.g., electron flow across the anode-cathode gap). By contrast, the data presented herein contain very little parasitic current loss, and thus for these low-loss experiments we are able to demonstrate that the differences between the current measured at the stack and the current measured at the load are due primarily to the displacement current that results from the shunt capacitance of the MITLs (about 8.41 nF total). Demonstrating this is important because displacement current is an energy storage mechanism, where energy is stored in the MITL electric fields and can later be used by the system. Thus, even for higher-loss experiments, the differences between the current measured at the stack and the current measured at the load are often largely due to energy storage and subsequent release, as opposed to being due solely to some combination of measurement error and current loss in the MITLs and/or double post-hole convolute. Displacement current also explains why the current measured downstream of the MITLs (i.e., the load current) often exceeds the current measured upstream of the MITLs (i.e., the stack current) at various times in the power pulse (this particular phenomenon was initially thought to be due to timing and/or calibration errors). To facilitate a better understanding of these phenomena, we also introduce and analyze a simple LC circuit model of the MITLs. This model is easily implemented as a simple drive circuit in simulation codes, which has now been done for the LASNEX code [G. B. Zimmerman and W. L. Kruer, Comments Plasma Phys. Controlled Fusion 2, 51 (1975)] at Sandia, as well as for simpler MATLAB®-based codes at Sandia. An example of this LC model used as a drive circuit will also be presented.

The effects of various postchill deboning times on functional, color, yield, and sensory attributes of broiler breast meat were determined. Broiler breast muscles were deboned at 2, 4, 6, and 24 h postmortem, and pH, color change, cooking yield, shear force values, and sensory traits of the breast meat were recorded. Data were examined by multivariate data analysis, namely principal component analysis (PCA). Averages of 13 variables (pH, delta a*, shear force, and sensory attributes of cardboardy, wet feathers, springiness, cohesiveness, hardness, moisture release, particle size, bolus size, chewiness, and metallic aftertaste-afterfeel) decreased gradually as deboning time increased from 2 to 24 h, especially for shear values after 4 h of postmortem aging. Univariate correlation coefficients among 24 variables indicated several significant correlations. Warner-Bratzler shear force had high positive correlations with 5 sensory texture attributes (cohesiveness, hardness, particle size, bolus size, and chewiness). The parameters of pH, delta L*, delta a*, delta b*, and cooking yield were not obviously correlated with shear force values or any of the 18 sensory characteristics. PCA score plot showed no clear separation of the breast muscles deboned at different postmortem times, but it was still possible to differentiate them. The loading biplot suggested that 18 variables were effective in sample differentiation, including delta L*, shear force, cooking yield, 6 sensory flavor attributes (brothy, cardboardy, wet feathers, blood/serumy, salty, and sour), all sensory texture attributes except springiness, and all afterfeel-aftertaste properties.

A 6.1-MV, 0.79-MA laser-triggered gas switch (LTGS) is used to synchronize the 36 modules of the Z machine at Sandia National Laboratories. Each module includes one switch, which serves as the last command-fired switch of the module, and hence is used to determine the time at which each module electrically closes relative to the other modules. The switch is ∼81−cm in length, ∼45−cm in diameter, and is immersed in mineral oil. The outer switch envelope consists of six corrugated monomer-cast acrylic insulators and five contoured stainless-steel rings. The trigger electrodes are fabricated from copper-infused tungsten. The switch is pressurized with several atmospheres of sulfur hexafluoride (SF6 ), which is turbulently purged within 2 seconds after every shot. Each switch is powered from a 6-MV, 0.78-MJ Marx generator which pulse charges a 24-nF intermediate-store water capacitor in 1.4−μs . Closure of the switch allows power to flow into pulse-forming transmission lines. The power pulse is subsequently compressed by water switches, which results in a total accelerator output power in excess of 70-TW. A previous version of the LTGS performed exceptionally at a 5.4-MV, 0.7-MA level on an engineering test module used for switch development. It exhibited a 1−σ jitter of ∼5ns , a prefire and flashover rate less than 0.1%, and a lifetime in excess of 150 shots. When installed on the Z accelerator, however, the switch exhibited a prefire probability of ∼3% , a flashover probability of ∼7% , and a 15-ns jitter. The difference in performance is attributed to several factors such as higher total charge transfer, exposure to more debris, and more stressful dynamic mechanical loading upon machine discharge. Under these conditions, the replacement lifetime was less than ten shots. Since refurbishment of Z in October 2007, there have been three LTGS design iterations to improve the performance at 6.1-MV. The most recent design exhibits a prefire rate of less than 0.1%, a flashover rate of ∼0.2% , a single switch jitter of ∼6−ns , and a lifetime of greater than 75 shots. Modifications to achieve the performance improvement are detailed in this article.

The feasibility of predicting pH, color, shear force, and sensory characteristics of chicken breasts deboned at 2, 4, 6, and 24 h postmortem by visible/near infrared reflectance spectroscopy (NIRS) in the 400 to 1850 nm region was determined. Prediction of physical attributes of Commission Internationale de l'Eclairage (CIE) color values (L*, a*, and b*), pH, and shear force had better accuracies than those of individual sensory attributes. Calibration and validation statistics for shear force and sensory traits indicated that visible/near infrared models were not significantly improved for cooked muscles compared with predictions based on raw muscle characteristics. On the basis of predicted shear values from the partial least squares (PLS) model, breast samples were classified into \"tender\" and \"tough\" classes with a correct classification of 74.0% if the boundary was set at 7.5 kg. The model developed from measured shears using soft independent modeling of class analogy/principal components analysis (SIMCA/PCA) showed nearly the same classification success.

To determine whether rheumatoid arthritis disease activity correlates with changing weather conditions. A longitudinal analysis of 133 patients attending the Department of Rheumatology, Musgrave Park Hospital, Belfast was performed. Participants had a diagnosis of rheumatoid arthritis and were receiving subcutaneous anti-TNF therapy (Adalimumab or Etanercept) for a period of >6 months. Data were collected at five time points. This included tender joint count, swollen joint count, patient visual analogue score (VAS), erythrocyte sedimentation rate, C-reactive protein, VAS, and DAS-28 (Disease Activity Score). Each weather factor (maximum, minimum temperature, pressure, rainfall, sunshine, humidity, and wind-speed) was analysed against each patients’ DAS-28 score at five time points, using an analysis of covariance. A significant correlation was noted between low DAS-28 and increased hours of sunshine ( p  < 0.001). Sunny conditions were associated with a DAS-28 reduction of 0.037 (95 % CI −0.059, −0.016) p  < 0.001. A significant correlation between humidity and DAS-28 was also noted ( p  = 0.016). Increased humidity was associated with an increased DAS-28 of 0.007 (95 % CI 0.001, 0.013) p  = 0.016. Higher temperatures were associated with a non-significant decrease in DAS-28 ( p  = 0.16). In this study, rheumatoid arthritis disease activity (as measured by DAS-28) was significantly lower in both more sunny and less humid conditions.

Laser triggered, megavolt, megampere gas switches are frequently utilized to synchronize multiple pulsed power driver modules for inertial-confinement fusion, isentropic compression, and radiation physics experiments. The device developed to synchronize the 36 modules of the refurbished accelerator at Sandia National Laboratories is a 5.4 MV, 700 kA, sulfur-hexafluoride () filled, laser triggered gas switch. At this operating level, switch jitter is 5 ns, the prefire rate is less than 0.1%, the average optic lifetime is greater than 200 shots, and the flashover rate is less than 1%. Over 1000 shots on a single-module test facility were conducted while iterating several potential design improvements, including utilizing low-erosion electrode material, varying pressure, and modifying internal switch geometry all while keeping the basic switch architecture and footprint constant. Results of this development effort are presented herein.