Developing a platform for Fresnel diffractive radiography with 1 µm spatial resolution at the National Ignition Facility.

An x-ray Fresnel diffractive radiography platform was designed for use at the National Ignition Facility. It will enable measurements of micron-scale changes in the density gradients across an interface between isochorically heated warm dense matter materials, the evolution of which is driven primarily through thermal conductivity and mutual diffusion. We use 4.75 keV Ti K-shell x-ray emission to heat a 1000 µm diameter plastic cylinder, with a central 30 µm diameter channel filled with liquid D2, up to 8 eV. This leads to a cylindrical implosion of the liquid D2 column, compressing it to ∼2.3 g/cm3. After pressure equilibration, the location of the D2/plastic interface remains steady for several nanoseconds, which enables us to track density gradient changes across the material interface with high precision. For radiography, we use Cu He-α x rays at 8.3 keV. Using a slit aperture of only 1 µm width increases the spatial coherence of the source, giving rise to significant diffraction features in the radiography signal, in addition to the refraction enhancement, which further increases its sensitivity to density scale length changes at the D2/plastic interface.

Foam-lined hohlraum, inertial confinement fusion experiments on the National Ignition Facility.

Experiments on the National Ignition Facility (NIF) to study hohlraums lined with a 20-mg/cc 400-µm-thick Ta_{2}O_{5} aerogel at full scale (hohlraum diameter = 6.72 mm) are reported. Driven with a 1.6-MJ, 450-TW laser pulse, the performance of the foam liner is diagnosed using implosion hot-spot symmetry measurements of the high-density carbon (HDC) capsule and measurement of inner beam propagation through a thin-wall 8-µm Au window in the hohlraum. Results show an improved capsule performance due to laser energy deposition further inside the hohlraum, leading to a modest increase in x-ray drive and reduced preheat due to changes in the x-ray spectrum when the foam liner is included. In addition, the outer cone bubble uniformity is improved, but the predicted improvement in inner beam propagation to improve symmetry control is not realized for this foam thickness and density.

First Liquid Layer Inertial Confinement Fusion Implosions at the National Ignition Facility.

The first cryogenic deuterium and deuterium-tritium liquid layer implosions at the National Ignition Facility (NIF) demonstrate D_{2} and DT layer inertial confinement fusion (ICF) implosions that can access a low-to-moderate hot-spot convergence ratio (1230) DT ice layer implosions. Although high CR is desirable in an idealized 1D sense, it amplifies the deleterious effects of asymmetries. To date, these asymmetries prevented the achievement of ignition at the NIF and are the major cause of simulation-experiment disagreement. In the initial liquid layer experiments, high neutron yields were achieved with CRs of 12-17, and the hot-spot formation is well understood, demonstrated by a good agreement between the experimental data and the radiation hydrodynamic simulations. These initial experiments open a new NIF experimental capability that provides an opportunity to explore the relationship between hot-spot convergence ratio and the robustness of hot-spot formation during ICF implosions.

Demonstration of x-ray fluorescence imaging of a high-energy-density plasma.

Experiments at the Trident Laser Facility have successfully demonstrated the use of x-ray fluorescence imaging (XRFI) to diagnose shocked carbonized resorcinol formaldehyde (CRF) foams doped with Ti. One laser beam created a shock wave in the doped foam. A second laser beam produced a flux of vanadium He-α x-rays, which in turn induced Ti K-shell fluorescence within the foam. Spectrally resolved 1D imaging of the x-ray fluorescence provided shock location and compression measurements. Additionally, experiments using a collimator demonstrated that one can probe specific regions within a target. These results show that XRFI is a capable alternative to path-integrated measurements for diagnosing hydrodynamic experiments at high energy density.

Unraveling the potential and pore-size dependent capacitance of slit-shaped graphitic carbon pores in aqueous electrolytes.

Understanding and leveraging physicochemical processes at the pore scale are believed to be essential to future performance improvements of supercapacitors and capacitive desalination (CD) cells. Here, we report on a combination of electrochemical experiments and fully atomistic simulations to study the effect of pore size and surface charge density on the capacitance of graphitic nanoporous carbon electrodes. Specifically, we used cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) to study the effect of potential and pore size on the capacitance of nanoporous carbon foams. Molecular dynamics simulations were performed to study the pore-size dependent accumulation of aqueous electrolytes in slit-shaped graphitic carbon pores of different widths (0.65 to 1.6 nm). Experimentally, we observe a pronounced increase of the capacitance of sub-nm pores as the applied potential window gets wider, from a few F g(-1) for narrow potential ranges (-0.3 to 0.3 V vs. Ag/AgCl) to ~40 F g(-1) for wider potential windows (-0.9 V to 0.9 V vs. Ag/AgCl). By contrast, the capacitance of wider pores does not depend significantly on the applied potential window. Molecular dynamics simulations confirm that the penetration of ions into pores becomes more difficult with decreasing pore width and increasing strength of the hydration shell. Consistent with our experimental results, we observe a pore- and ion-size dependent threshold-like charging behavior when the pore width becomes comparable to the size of the hydrated ion (0.65 nm pores for Na(+) and 0.79 nm pores for Cl(-) ions). The observed pore-size and potential dependent accumulation of ions in slit-shaped carbon pores can be explained by the hydration structure of the ions entering the charged pores. The results are discussed in view of their effect on energy-storage and desalination efficiency.

Prevalence, kinetic changes and possible reasons of elevated cardiac troponin T in patients with AV nodal re-entrant tachycardia.

BACKGROUND: Elevated cardiac troponin (cTn) has been reported to occur with AVNRT. Little is known about prevalence, kinetic changes, and possible reasons of increased cTn. METHODS: We evaluated 139 consecutive patients presenting with AVNRT to the emergency department between 2006 and 2010. Cardiac troponin T (cTnT) was measured serially at baseline, after three and six hours. Patients were evaluated for the presence of structural heart disease or CAD. Troponin was defined as elevated if a value exceeded the lower limit of detection (10 ng/l) using the fourth generation cTnT, or if the value > 99 th percentile (14 ng/l) using the new highly sensitive cTn assay. RESULTS: A cTnT > LLD (n = 29) or > 99 th percentile (n = 16) was found in 45 patients (32.4%) within the initial six hours after hospitalization. All patients were symptomatic with palpitations, chest discomfort or dyspnea. A complete cardiac evaluation was carried out, including coronary angiography in 32 patients demonstrating an underlying structural heart disease or CAD in 18 cases (56%). Significant CAD was detected in 16 cases. 8 cases required PCI during hospitalization. Elevated cTnT was seen in patients with and without structural heart disease. CONCLUSIONS: AVNRT is a possible reason for elevated cTnT, even in the absence of relevant structural heart disease or CAD.

Diagnostic and prognostic performance of a novel high-sensitivity cardiac troponin T assay compared to a contemporary sensitive cardiac troponin I assay in patients with acute coronary syndrome.

OBJECTIVE: The study sought to compare the clinical performance of two more sensitive cardiac troponin (cTn) assays, a novel high-sensitivity (hs) troponin T assay and a contemporary cTnI assay. METHODS: We measured hs-cTnT (Roche TnThs) and cTnI (Siemens Centaur Ultra) on presentation in 1,384 patients with suspected acute coronary syndrome (ACS) who underwent early invasive strategy within 24 h after presentation. Kaplan-Meier, Cox proportional hazards, and receiver-operating characteristic (ROC) analysis was used to compare their prognostic performance for the prediction of all-cause death and death/MI (myocardial infarction) after a median of 271 days. We also compared the diagnostic performance of these assays on presentation for early diagnosis of non-STEMI. RESULTS: Both hs-cTnT and cTnI were independently predictive of long-term death (OR 3.51 vs. 2.19) and the composite of death/MI (OR 9.24 vs. 3.61), across the spectrum of ACS and in patients without ACS. When used as a continuous variable, ROC analysis demonstrated significantly higher areas under the curve (AUC) for hs-cTnT as compared to cTnI for the prediction of death/MI (0.721 vs. 0.672, P = 0.024), a trend to better prediction of all-cause death (0.721 vs. 0.672, P = 0.093) and significantly higher AUC for early diagnosis of non-STEMI (0.965 vs. 0.901, P < 0.001). CONCLUSION: Using the 99th percentile cutoff for hs-cTnT and cTnI, both assays enable prediction of adverse long-term outcomes and earlier diagnosis of non-STEMI. Used as a continuous variable, the hs-cTnT assay showed superior performance compared to the cTnI assay, especially in regard to prognosis.

Surface-chemistry-driven actuation in nanoporous gold.

Although actuation in biological systems is exclusively powered by chemical energy, this concept has not been realized in man-made actuator technologies, as these rely on generating heat or electricity first. Here, we demonstrate that surface-chemistry-driven actuation can be realized in high-surface-area materials such as nanoporous gold. For example, we achieve reversible strain amplitudes of the order of a few tenths of a per cent by alternating exposure of nanoporous Au to ozone and carbon monoxide. The effect can be explained by adsorbate-induced changes of the surface stress, and can be used to convert chemical energy directly into a mechanical response, thus opening the door to surface-chemistry-driven actuator and sensor technologies.