Gradient-echo imaging of hemorrhage at 1.5 Tesla

We report in vitro and in vivo MR studies of hemorrhage using the gradient-echo pulse sequence, FISP (steady state free precession) and FLASH (spoiling of transverse magnetization) at 1.5 Tesla. Phantoms containing methemoglobin, ferromagnetic particles, human serum and blood clot were scanned using both spin-echo and gradient-echo techniques. FLASH signal intensities were more sensitive to methemoglobin concentration than high T1-weighted spin-echo images. FISP showed little change in signal intensity with varying concentrations of methemoglobin and a contrast relationship similar to T2-weighted spin-echo techniques. FISP and FLASH showed intensity changes at lower concentrations of ferromagnetic material than T2-weighted spin-echo sequences. In vitro blood clot was less intense when observed by FISP and FLASH sequences than on the T2-weighted spin-echo sequences. Maximum contrast between clot and other blood components occurred at a flip angle of 45 degrees for FLASH and 60 degrees for FISP. FISP and FLASH scans of patients with hemorrhage demonstrated a marked decrease in signal intensity in the region of blood clot. This decrease was more pronounced with the gradient-echo sequences than with T2-weighted spin-echo images. We conclude that FLASH is useful for detecting methemoglobin and that both FISP and FLASH are useful for evaluating hemorrhage because of their sensitivity to methemoglobin.     

Energetics and structural stability of Cs3C60

Using the ab initio pseudopotential total-energy method and the density-functional theory, we study the energetics of face-centered-cubic Cs₃C₆₀ which is a material of great interest as a possible high transition-temperature superconductor. At the optimized lattice constant the volume per C₆₀ is found to be smaller than the the most-stable hexagon-coordination A15 phase, while the total energy of the fcc phase is about 0.9 eV higher than the A15 phase. These results indicate that a low-temperature and high-pressure synthesis method might be a possible way to produce the fcc Cs₃C₆₀ phase. In addition, it is also found that the A15 Cs₃C₆₀ should show a phase transformation from a hexagon-coordination phase to a pentagon-coordination phase under hydrostatic pressure.     

Orientation-dependent C60 electronic structures revealed by photoemission spectroscopy

We observe, with angle-resolved photoemission, a dramatic change in the electronic structure of two C60 monolayers, deposited, respectively, on Ag (111) and (100) substrates, and similarly doped with potassium to half filling of the C60 lowest unoccupied molecular orbital. The Fermi surface symmetry, the bandwidth, and the curvature of the dispersion at Gamma point are different. Orientations of the C60 molecules on the two substrates are known to be the main structural difference between the two monolayers, and we present new band-structure calculations for some of these orientations. We conclude that orientations play a key role in the electronic structure of fullerides.     

Shear-induced configurations of confined colloidal suspensions

We show that geometric confinement dramatically affects the shear-induced configurations of dense monodisperse colloidal suspensions; a new structure emerges, where layers of particles buckle to stack in a more efficient packing. The volume fraction in the shear zone is controlled by a balance between the viscous stresses and the osmotic pressure of a contacting reservoir of unsheared particles. We present a model that accounts for our observations and helps elucidate the complex interplay between particle packing and shear stress for confined suspensions.     

Equilibrium capillary forces with atomic force microscopy

We present measurements of equilibrium forces resulting from capillary condensation. The results give access to the ultralow interfacial tensions between the capillary bridge and the coexisting bulk phase. We demonstrate this with solutions of associative polymers and an aqueous mixture of gelatin and dextran, with interfacial tensions around 10 microN/m. The equilibrium nature of the capillary forces is attributed to the combination of a low interfacial tension and a microscopic confinement geometry, based on nucleation and growth arguments.     

Scaling of particle trajectories on a lattice

The scaling behavior of the closed trajectories of a moving particle generated by randomly placed rotators or mirrors on a square or triangular lattice is studied numerically. On both lattices, for most concentrations of the scatterers the trajectories close exponentially fast. For special critical concentrations infinitely extended trajectories can occur which exhibit a scaling behavior similar to that of the perimeters of percolation clusters.At criticality, in addition to the two critical exponents =15/7 andd _f=7/4 found before, the critical exponent =3/7 appears. This exponent determines structural scaling properties of closed trajectories of finite size when they approach infinity. New scaling behavior was found for the square lattice partially occupied by rotators, indicating a different universality class than that of percolation clusters.Near criticality, in the critical region, two scaling functions were determined numerically:f(x), related to the trajectory length (S) distributionn _s, andh(x), related to the trajectory sizeR _s (gyration radius) distribution, respectively. The scaling functionf(x) is in most cases found to be a symmetric double Gaussian with the same characteristic size exponent =0.433/7 as at criticality, leading to a stretched exponential dependence ofn _S onS, n_Sexp(–S ^6/7). However, for the rotator model on the partially occupied square lattice an alternative scaling function is found, leading to a new exponent =1.6±0.3 and a superexponential dependence ofn _S onS.h(x) is essentially a constant, which depends on the type of lattice and the concentration of the scatterers. The appearance of the same exponent =3/7 at and near a critical point is discussed.     

Acetylene on Cu(111): imaging a molecular surface arrangement with a constantly rearranging tip

Acetylene on Cu(111) is investigated by scanning tunnelling microscopy (STM); a surface pattern previously derived from diffraction measurements can be validated, if the variation of the STM image transfer function through absorption of an acetylene molecule onto the tip apex is taken into account. Density functional theory simulations point to a balance between short-range repulsive interactions of acetylene/Cu(111) associated with surface stress and longer range attractive interactions as the origin of the ordering.     

Dynamic Entanglement and Separability Criteria for Quantum Computing Bit States

A theoretical framework is demonstrated to evaluate the degree of entanglement of bit states in quantum computing. Separability of general superposition of Hilbert space unit vectors is discussed, and criteria in amplitude as well as in phase are derived. By these criteria the possibility of different quantum gates such as controlled not (CN), controlled controlled not (CCN), controlled rotation (CR), and controlled phase shift (CPS), to create the entanglement is examined. Furthermore, the selection of measurement mode external to the quantum system is incorporated in the formula using Kronecker delta (δ _kx ), introducing the concept of dynamic entanglement. With this the process of wavefunction collapse upon measurement is understood as the result of the activation of the dynamic entanglement. A firefly in a box model is used to show a pure state of ontological uncertainty, which is in a dynamically entangled state in Hilbert space.     

LWIR/SWIR switchable two color device based on InP/InGaAs integrated HBT/QWIP

A novel two color infrared (IR) device that allows fast electrical switching between the short wavelength IR (SWIR) band (0.9–1.6 μm) and the long wavelength IR (LWIR) band (8–12 μm) is presented. The integrated sensor is based on MOCVD grown, lattice matched (to InP substrate) epilayers of InGaAs/InP and consists of two, monolithically integrated sections of heterojunction bipolar transistor (HBT) and quantum well infrared photodetector (QWIP).     

The effect of the rotational angle on MR diffusion indices in nerves: is the rms displacement of the slow-diffusing component a good measure of fiber orientation?

In recent years, much effort has been made to increase our ability to infer nerve fiber direction through the use of diffusion MR. The present study examines the effect of the rotational angle (alpha), i.e. the angle between the diffusion sensitizing gradients and the main axis of the fibers in the nerves, on different NMR indices. The indices examined were the apparent diffusion coefficient (ADC), extracted from low b-values (b(max) approximately 1200 s/mm(2)), and the root mean square (rms) displacement of the fast and the slow-diffusing components extracted from high b-value q-space diffusion MR data. In addition, the effect of both the diffusion time and myelination was evaluated. We found that the most sensitive index to the rotational angle is the rms displacement of the slow-diffusing component extracted from the high b-value q-space diffusion MR experiment. For this component the rms displacement was nearly constant for alpha values ranging from -10 degrees to +80 degrees (where alpha=0 degrees is the z direction), but it changed dramatically when diffusion was measured nearly perpendicular to the nerve fiber direction, i.e., for alpha=90+/-10 degrees. The ADC and the rms displacement of the fast-diffusing component exhibited only gradual changes, with a maximal change at alpha=45+/-15 degrees. The sensitivity of the rms displacement of the slow-diffusing component to the rotational angle was found to be higher at longer diffusion times and in mature fully myelinated nerves. The relevance of these observations for determining the fiber direction is briefly discussed.