Structure and dynamics of colliding plasma jets

Monoenergetic-proton radiographs of laser-generated, high-Mach-number plasma jets colliding at various angles shed light on the structures and dynamics of these collisions. The observations compare favorably with results from 2D hydrodynamic simulations of multistream plasma jets, and also with results from an analytic treatment of electron flow and magnetic field advection. In collisions of two noncollinear jets, the observed flow structure is similar to the analytic model's prediction of a characteristic feature with a narrow structure pointing in one direction and a much thicker one pointing in the opposite direction. Spontaneous magnetic fields, largely azimuthal around the colliding jets and generated by the well-known ∇T(e)×∇n(e) Biermann battery effect near the periphery of the laser spots, are demonstrated to be "frozen in" the plasma (due to high magnetic Reynolds number Re(M)∼5×10(4)) and advected along the jet streamlines of the electron flow. These studies provide novel insight into the interactions and dynamics of colliding plasma jets.

Intra-individual, randomised comparison of the MRI contrast agents gadobutrol versus gadoteridol in patients with primary and secondary brain tumours, evaluated in a blinded read

OBJECTIVE

To prove that 1.0 M gadobutrol provides superior contrast enhancement and MRI image characteristics of primary and secondary brain tumours compared with 0.5 M gadoteridol, thereby providing superior diagnostic information.

METHODS

Brain MRI was performed in two separate examinations in patients scheduled for neurosurgery. Independent injections of 1.0 M gadobutrol and 0.5 M gadoteridol at doses of 0.1 mmol Gd/kg body weight were administered per patient in randomised order. Evaluation was performed in an off-site blinded read.

RESULTS

Fifty-one patients in the full analysis set (FAS) were eligible for efficacy analysis and 44 for the per-protocol analysis. For the primary efficacy variable "preference in contrast enhancement for one contrast agent or the other", the rate of "gadobutrol preferred" was estimated at 0.73 (95 % confidence interval 0.61; 0.83), showing significant superiority of gadobutrol over gadoteridol. Calculated lesion-to-brain contrast and the results of all qualitative secondary efficacy variables were also in favour of gadobutrol. Keeping a sufficient time delay after contrast application proved to be essential to get optimal image quality.

CONCLUSION

Compared with 0.5 M gadoteridol, 1.0 M gadobutrol was proven to have significantly superior contrast enhancement characteristics in a routine MRI protocol of primary and secondary brain tumours.

Patient weighting of osteoporosis medication attributes across racial and ethnic groups: a study of osteoporosis medication preferences using conjoint analysis

We studied the ranking of osteoporosis (OP) medication attributes in a convenience sample of four different racial/ethnic groups in the United States. Our study showed that postmenopausal women differ in the ranking of OP medication attributes based on age, educational level, income, and prior fracture history.

INTRODUCTION

Decision making about OP medication-related behavior relies heavily on patient preferences about specific medication attributes. Patients may decide to initiate, change, or stop therapies based on ranking of perceived attributes of the therapy and their personal attitudes toward those attributes. We used MaxDiff, a form of conjoint analysis (Ryan and Farrar 2000), to explore patient weighting of attributes across four racial/ethnic groups at two sites in the United States and defined four critical attributes that influence such decisions (safety, efficacy, cost, and convenience) from qualitative interviews.

METHODS

We recruited a sample of 367 Postmenopausal (PM) women at risk of OP fractures from four racial/ethnic groups: Caucasian (n = 100), African American (n = 100), Asian American (n = 82), and Hispanic American (n = 85). Respondents completed a laptop-based questionnaire that included demographic items, several short scales on medical care preference and OP patient perceptions, and a MaxDiff procedure that determines comparative ranking of attributes either as least important or most important to their decisions.

RESULTS

MaxDiff analyses were done to evaluate the relative weight of specific statements for each participant and to determine whether racial/ethnic groups differed across dimensions. Overall, participants in all four groups rated efficacy > safety > cost > convenience.

CONCLUSIONS

Although there were no significant differences among the racial/ethnic groups on overall ranking of attributes, subgroup analyses revealed significant impact of age, education, income, and prior fracture on these decisions. The findings from this study suggest that postmenopausal women differ in their ranking of OP medication attributes, and healthcare providers must account for personal preferences in their communication about and selection of OP medications.

A novel mutation in the GAN gene causes an intermediate form of giant axonal neuropathy in an Arab-Israeli family

Giant axonal neuropathy is a severe autosomal recessive neurodegenerative disorder of childhood that affects both the peripheral and central nervous systems. It is caused by mutations in the GAN gene linked to chromosome 16q24.1 At least 45 distinct disease-causing mutations have been identified throughout the gene in families of various ethnic origins, with different symptomatologies and different clinical courses. To date, no characteristic mutation or phenotype-genotype correlation has been established. We describe a novel missense mutation in four siblings born to consanguineous parents of Arab original with clinical and molecular features compatible with giant axonal neuropathy. The phenotype was characterized by a predominant motor and sensory peripheral neuropathies and severe skeletal deformities.

Kelvin-Helmholtz turbulence associated with collisionless shocks in laser produced plasmas

We report the experimental results of a turbulent electric field driven by Kelvin-Helmholtz instability associated with laser produced collisionless shock waves. By irradiating an aluminum double plane target with a high-power laser, counterstreaming plasma flows are generated. As the consequence of the two plasma interactions, two shock waves and the contact surface are excited. The shock electric field and transverse modulation of the contact surface are observed by proton radiography. Performing hydrodynamic simulations, we reproduce the time evolutions of the reverse shocks and the transverse modulation driven by Kelvin-Helmholtz instability.

Experiment in planar geometry for shock ignition studies

The capacity to launch a strong shock wave in a compressed target in the presence of large preplasma has been investigated experimentally and numerically in a planar geometry. The experiment was performed on the LULI 2000 laser facility using one laser beam to compress the target and a second to launch the strong shock simulating the intensity spike in the shock ignition scheme. Thanks to a large set of diagnostics, it has been possible to compare accurately experimental results with 2D numerical simulations. A good agreement has been observed even if a more detailed study of the laser-plasma interaction for the spike is necessary in order to confirm that this scheme is a possible alternative for inertial confinement fusion.

X-ray diagnosis of the pressure induced Mott nonmetal-metal transition

The evolution of the K-edge x-ray absorption near-edge spectroscopy (XANES) spectrum is investigated for an aluminum plasma expanding from the solid density down to 0.5  g/cm{3}, with temperatures lying from 5 down to 2 eV. The dense plasma is generated by nanosecond laser-induced shock compression. These conditions correspond to the density-temperature region where a metal-nonmetal transition occurs as the density decreases. This transition is directly observed in XANES spectra measurements through the progressive formation of a preedge structure for densities around 1.6  g/cm{3}. Ab initio calculations based on density functional theory and a jellium model have been efficiently tested through direct comparison with the experimental measurements and show that this preedge corresponds to the relocalization of the 3p atomic orbital as the system evolves from a dense plasma toward a partially ionized atomic fluid.

Electronic structure investigation of highly compressed aluminum with K edge absorption spectroscopy

The electronic structure evolution of highly compressed aluminum has been investigated using time resolved K edge x-ray absorption spectroscopy. A long laser pulse (500 ps, I(L)≈8×10(13) W/cm(2)) was used to create a uniform shock. A second ps pulse (I(L)≈10(17)  W/cm(2)) generated an ultrashort broadband x-ray source near the Al K edge. The main target was designed to probe aluminum at reshocked conditions up to now unexplored (3 times the solid density and temperatures around 8 eV). The hydrodynamical conditions were obtained using rear side visible diagnostics. Data were compared to ab initio and dense plasma calculations, indicating potential improvements in either description. This comparison shows that x-ray-absorption near-edge structure measurements provide a unique capability to probe matter at these extreme conditions and severally constrains theoretical approaches currently used.

Magnetically guided fast electrons in cylindrically compressed matter

Fast electrons produced by a 10 ps, 160 J laser pulse through laser-compressed plastic cylinders are studied experimentally and numerically in the context of fast ignition. K(α)-emission images reveal a collimated or scattered electron beam depending on the initial density and the compression timing. A numerical transport model shows that implosion-driven electrical resistivity gradients induce strong magnetic fields able to guide the electrons. The good agreement with measured beam sizes provides the first experimental evidence for fast-electron magnetic collimation in laser-compressed matter.

Time evolution of collisionless shock in counterstreaming laser-produced plasmas

We investigated the time evolution of a strong collisionless shock in counterstreaming plasmas produced using a high-power laser pulse. The counterstreaming plasmas were generated by irradiating a CH double-plane target with the laser. In self-emission streaked optical pyrometry data, steepening of the self-emission profile as the two-plasma interaction evolved indicated shock formation. The shock thickness was less than the mean free path of the counterstreaming ions. Two-dimensional snapshots of the self-emission and shadowgrams also showed very thin shock structures. The Mach numbers estimated from the flow velocity and the brightness temperatures are very high.