Enhancing Bremsstrahlung Production From Ultraintense Laser-Solid Interactions With Front Surface Structures

We report the results of a combined study of particle-in-cell and Monte Carlo modeling that investigates the production of Bremsstrahlung radiation produced when an ultraintense laser interacts with a tower-structured target. These targets are found to significantly narrow the electron angular distribution as well as produce significantly higher energies. These features combine to create a significant enhancement in directionality and energy of the Bremstrahlung radiation produced by a high-Z converter target. These studies employ short-pulse, high intensity laser pulses, and indicate that novel target design has potential to greatly enhance the yield and narrow the directionality of high energy electrons and $\gamma$-rays. We find that the peak $\gamma$-ray brightness for this source is 6.0$\times$10$^{19}$ ${\rm s^{-1}mm^{-2}mrad^{-2}}$ at 10MeV and 1.4$\times$10$^{19}$ ${\rm s^{-1}mm^{-2}mrad^{-2}}$ at 100MeV (0.1$\%$ bandwidth).Comment: arXiv admin note: text overlap with arXiv:1310.328

Factors of Influence on the Performance of a Short-Latency Non-Invasive Brain Switch: Evidence in Healthy Individuals and Implication for Motor Function Rehabilitation.

Brain-computer interfacing (BCI) has recently been applied as a rehabilitation approach for patients with motor disorders, such as stroke. In these closed-loop applications, a brain switch detects the motor intention from brain signals, e.g., scalp EEG, and triggers a neuroprosthetic device, either to deliver sensory feedback or to mimic real movements, thus re-establishing the compromised sensory-motor control loop and promoting neural plasticity. In this context, single trial detection of motor intention with short latency is a prerequisite. The performance of the event detection from EEG recordings is mainly determined by three factors: the type of motor imagery (e.g., repetitive, ballistic), the frequency band (or signal modality) used for discrimination (e.g., alpha, beta, gamma, and MRCP, i.e., movement-related cortical potential), and the processing technique (e.g., time-series analysis, sub-band power estimation). In this study, we investigated single trial EEG traces during movement imagination on healthy individuals, and provided a comprehensive analysis of the performance of a short-latency brain switch when varying these three factors. The morphological investigation showed a cross-subject consistency of a prolonged negative phase in MRCP, and a delayed beta rebound in sensory-motor rhythms during repetitive tasks. The detection performance had the greatest accuracy when using ballistic MRCP with time-series analysis. In this case, the true positive rate (TPR) was ~70% for a detection latency of ~200 ms. The results presented here are of practical relevance for designing BCI systems for motor function rehabilitation

MHD Simulation of the Inner-Heliospheric Magnetic Field

Maps of the radial magnetic field at a heliocentric distance of ten solar radii are used as boundary conditions in the MHD code CRONOS to simulate a 3D inner-heliospheric solar wind emanating from the rotating Sun out to 1 AU. The input data for the magnetic field are the result of solar surface flux transport modelling using observational data of sunspot groups coupled with a current sheet source surface model. Amongst several advancements, this allows for higher angular resolution than that of comparable observational data from synoptic magnetograms. The required initial conditions for the other MHD quantities are obtained following an empirical approach using an inverse relation between flux tube expansion and radial solar wind speed. The computations are performed for representative solar minimum and maximum conditions, and the corresponding state of the solar wind up to the Earths orbit is obtained. After a successful comparison of the latter with observational data, they can be used to drive outer-heliospheric models.Comment: for associated wmv movie files accompanying Figure 7, see http://www.tp4.rub.de/~tow/max.wmv and http://www.tp4.rub.de/~tow/min.wm

Fabrication and characterizations of proton-exchanged LiNbO3 waveguides fabricated by inductively coupled plasma technique

This Letter reports the use of an inductively coupled plasma technique for fabrication of proton-exchanged (PE) LiNbO3 (LN) waveguides. Planar and stripe waveguides have been formed in Y-cut LN which are difficult to obtain with the conventional molten acid method due to the occurrence of surface damage. Secondary ion mass spectrometry, scanning electron microscopy, and infrared absorption spectrum characterization results revealed that a uniform vertical PE profile with a single low order crystal phase has been directly obtained as a result of this unique process. X-ray photoelectron spectroscopy characterization of the treated surface revealed the existence of NbO as the cause for a sometimes darkened surface and confirms the ability to completely restore the surface to LN by oxygen plasma treatment. Atomic force microscopy measurement confirms that good surface quality has been maintained after regeneration of the surface to LN

Characterization Of Thermal Stresses And Plasticity In Through-Silicon Via Structures For Three-Dimensional Integration

Through-silicon via (TSV) is a critical element connecting stacked dies in three-dimensional (3D) integration. The mismatch of thermal expansion coefficients between the Cu via and Si can generate significant stresses in the TSV structure to cause reliability problems. In this study, the thermal stress in the TSV structure was measured by the wafer curvature method and its unique stress characteristics were compared to that of a Cu thin film structure. The thermo-mechanical characteristics of the Cu TSV structure were correlated to microstructure evolution during thermal cycling and the local plasticity in Cu in a triaxial stress state. These findings were confirmed by microstructure analysis of the Cu vias and finite element analysis (FEA) of the stress characteristics. In addition, the local plasticity and deformation in and around individual TSVs were measured by synchrotron x-ray microdiffraction to supplement the wafer curvature measurements. The importance and implication of the local plasticity and residual stress on TSV reliabilities are discussed for TSV extrusion and device keep-out zone (KOZ).Microelectronics Research Cente