Estimation of Expected Shortfall Using Quantile Regression: A Comparison Study

Computational Economics - Expected Shortfall ( $$\mathrm {ES}$$ ) is one of the most heavily used measures of financial risk. It is defined as a scaled integral of the quantile of the...     

Evaluation of radiation dose during pacemaker implantations

The purpose was to evaluate patient radiation doses and compare with other interventional procedures. One hundred and twenty-eight procedures were carried out with a recently installed mobile undercouch C-arm machine with a 23-cm diameter image intensifier. The radiation dose is provided by the X-ray machine, in terms of cumulative dose (CD). Kerma-Area product (KAP) was then estimated from CD and the X-ray field size. Other patient parameters recorded were patient weight, age, kilovolt, milliampere and fluoroscopy time (T). Median (range) CD, KAP and T were 15.2 mGy (3.2-110 mGy), 6.3 Gy cm(2) (1.3-45.7 Gy cm(2)) and 5.2 (1.5-27.4 min) min, respectively. Median E was 1.1 mSv (conversion factor: 0.18 mSv per Gy cm(2)), which corresponds to approximately one lumbar spine X-ray radiography. The effective dose is much lower than a coronary angiography (8 mSv) or an electrophysiology study (6 mSv). Radiation dose is low compared with other interventional cardiology procedures.     

C-SAM sounds the warning for IC packaging defects

C-mode acoustic microscopy provides unique advantages over SLAM techniques in detecting microcracks, voids, and delaminations. The reliability of integrated circuit (IC) packages depends in many respects on their mechanical integrity. The effect of structural weaknesses caused by poor bonding, voids, microcracks or delaminations may not be evident in the electrical performance characteristics, but may cause premature failure. C-mode scanning acoustic microscopy (C SAM) is an excellent tool for non-destructive failure analysis of IC packages. It provides a rapid and comprehensive imaging of critical package defects and the location of these defects in three dimensions within the package     

Magnetic Quantum Tunneling in the Single-Molecule Magnet Mn12-Acetate

The symmetry of magnetic quantum tunneling (MQT) in the single molecule magnet Mn₂-acetate has been determined by sensitive low-temperature magnetic measurements in the pure quantum tunneling regime and high frequency EPR spectroscopy in the presence of large transverse magnetic fields. The combined data set definitely establishes the transverse anisotropy terms responsible for the low temperature quantum dynamics. MQT is due to a disorder induced locally varying quadratic transverse anisotropy associated with rhombic distortions in the molecular environment (2nd order in the spin-operators). This is superimposed on a 4th order transverse magnetic anisotropy consistent with the global (average) S₄ molecule site symmetry. These forms of the transverse anisotropy are incommensurate, leading to a complex interplay between local and global symmetries, the consequences of which are analyzed in detail. The resulting model explains: (1) the observation of a twofold symmetry of MQT as a function of the angle of the transverse magnetic field when a subset of molecules in a single crystal are studied; (2) the non-monotonic dependence of the tunneling probability on the magnitude of the transverse magnetic field, which is ascribed to an interference (Berry phase)effect; and (3) the angular dependence of EPR absorption peaks, including the fine structure in the peaks, among many other phenomena. This work also establishes the magnitude of the 2nd and 4th order transverse anisotropy terms for Mn₁₂-acetate single crystals and the angle between the hard magnetic anisotropy axes of these terms. EPR as a function of the angle of the field with respect to the easy axes (close to the hard-medium plane) confirms that there are discrete tilts of the molecular magnetic easy axis from the global (average) easy axis of a crystal, also associated with solvent disorder. The latter observation provides a very plausible explanation for the lack of MQT selection rules, which has been a puzzle for many years.     

High temperature device simulation and thermal characteristics of GaAs MESFETs on CVD diamond substrates

The temperature stability and high temperature characteristics of GaAs FETs on CVD diamond heat sinks were investigated by modeling the high-temperature electrical characteristics for GaAs MESFETs and by experimentally measuring the elevated-temperature performance. The bias region for the zero temperature coefficient (ZTC) was determined. The thermal characteristics were determined by infrared microscopy and the results were correlated with a finite element analysis calculation of the GaAs FET thermal distribution. The utilization of CVD diamond as a heat spreading substrate is shown to reduce the peak channel temperature by 30 percent when the FET is biased at the 1 dB compression point.     

Deep level transient spectroscopy of n-AlGaAs/GaAs high electron mobility transistors

Deep level transient spectroscopy has been used to characterise the traps found in MBE grown n-AlGaAs/GaAs HEMTs. In addition to DX centres two further traps common to different HEMT structures are reported. The authors have identified an electron trap (E/sub a/=0.6 eV) distributed nonuniformly in the AlGaAs donor layer, and an interface state trap (E/sub a/=0.55 eV) located close to the two dimensional electron gas.<>     

Au-Mg improved ohmic contacts to p-GaAs

A novel ohmic contact alloy to p-GaAs consisting of 96 weight % Au and 4 weight % Mg, a Mo barrier metal and Au overlay is described. Contact resistivities as low as 8 × 10?5 cm2 were achieved on heavily doped substrates. Auger sputter profiles have shown these contacts to be thermally stable up to 450°C.