Pressure-Induced Excitations in the Out-of-Plane Optical Response of the Nodal-Line Semimetal ZrSiS

The anisotropic optical response of the layered, nodal-line semimetal ZrSiS at ambient and high pressure is investigated by frequency-dependent reflectivity measurements for the polarization along and perpendicular to the layers. The highly anisotropic optical conductivity is in very good agreement with results from density-functional theory calculations and confirms the anisotropic character of ZrSiS. Whereas the in-plane optical conductivity shows only modest pressure-induced changes, we found strong effects on the out-of-plane optical conductivity spectrum of ZrSiS, with the appearance of two prominent excitations. These pronounced pressure-induced effects can neither be attributed to a structural phase transition according to our single-crystal x-ray diffraction measurements, nor can they be explained by electronic correlation and electron-hole pairing effects, as revealed by theoretical calculations. Our findings are discussed in the context of the recently proposed excitonic insulator phase in ZrSiS

Bone Marrow Changes in Adolescent Girls With Anorexia Nervosa

Early osteoporosis is common among adolescent girls with anorexia nervosa (AN) and may result from premature conversion of red (RM) to yellow bone marrow. We performed right knee magnetic resonance imaging (MRI) on a 1.0 T extremity scanner in 20 patients and 20 healthy controls, aged 16.2 ± 1.6 years (mean ± SD). Coronal T1-weighted (T1W) images and T1 maps were generated from T1 relaxometry images. Blinded radiologists visually assessed RM in the distal femoral and proximal tibial metaphyses in T1W images using a scale of signal intensity from 0 (homogeneous hyperintensity, no RM) to 4 (all dark, complete RM). Subjects with AN exhibited nearly twofold lower metaphyseal RM scores in both the femur (0.64 versus 1.22, p = .03) and tibia (0.54 versus 0.96, p = .08). In relaxometric measurements of four selected regions (femur and tibia amd epiphysis and metaphysis), subjects with AN showed higher mean epiphyseal but lower metaphyseal T1. The net AN-control difference between epiphysis and metaphysis was 70 ms in the femur (+31 versus −35 ms, p = .02) and of smaller magnitude in the tibia. In relaxometry data from the full width of the femur adjacent to the growth plate, AN subjects showed mean T1 consistently lower than in controls by 30 to 50 ms in virtually every part of the sampling region. These findings suggest that adolescents with AN exhibit premature conversion of hematopoietic to fat cells in the marrow of the peripheral skeleton potentially owing to adipocyte over osteoblast differentiation in the mesenchymal stem cell pool. © 2010 American Society for Bone and Mineral Researc

Poly NIPAM Microgels with Different Cross Linker Densities Scaling Behavior of the Network Fluctuations in the Vicinity of the Volume Phase Transition

Thermoresponsive microgel particles made of the monomer N isopropylacrylamide NIPAM and the cross linker molecule N,N methylenebisacrylamide BIS were synthesized using three different cross linker molar ratios. The volume phase transition behavior of these colloids was investigated by means of dynamic light scattering DLS and small angle neutron scattering SANS covering the different length scales of interest. Both methods provide the temperature of the volume phase transition in good agreement. The volume change as followed by DLS is described using the Flory Rehner theory, leading to the determination of the spinodal temperature. Furthermore, the network correlation length amp; 958;, which is available from appropriate fits of the measured SANS profiles, was used to study the critical behavior in terms of scaling laws. The results from DLS and SANS show a strong cross linker density dependenc

Stroboscopic Small Angle Neutron Scattering Investigations of Microsecond Dynamics in Magnetic Nanomaterials

Time resolved Small Angle Neutron Scattering SANS techniques have recently been developed that allow ordering and relaxation processes of magnetic moments in nanoparticles to be monitored. In stroboscopic experiments, time frame data acquisition has been synchronized with a periodic external magnetic field. Slow relaxation of magnetic particle moments onto equilibrium has been studied in periods of the order of 30 s after switch off a static field. By applying a sine wave modulated magnetic field at frequencies above 50 Hz, the time resolved SANS response to a forced oscillation could be analyzed. When a continuous neutron flux was used in conventional SANS, the shortest accessible time range was limited to about 3 ms resulting from the wavelength spread. A breakthrough of time resolution into the micro second range was achieved with the pulsed frame overlap TISANE technique, which allows us to exploit a dynamical range similar to that of X ray photon correlation spectroscopy. Here we present a combination of these stroboscopic neutron techniques on surfactant stabilized ferrofluids with nearly monodisperse Cobalt and Fe3O4 nanoparticles. Results are compared to a solid CuCo alloy with superparamagnetic nanosized Cobalt precipitates. The SANS scattering response was measured stroboscopically in an oscillating applied magnetic field at frequencies up to 2800 Hz. As long as the magnetic moments followed the applied field, the 2D scattering patterns alternated between fully isotropic and strongly anisotropic. The analysis of time dependent SANS data as a function of frequency, field and temperature allowed us i to proof the validity of the Langevin statistics describing the particle moment orientation, ii to extract the effect of field induced interparticle correlations, iii to monitor the slowing down of the dynamics of moment rotation with decreasing temperature, iv to study the effect of freezing of the solvent on the dynamics of the particle moments, and v to decide between the possible relaxation mechanisms N el and Brownia

Buried target signature extraction from ground penetrating radar signal based on the equivalence principle

Ground penetrating radar is poised to be a very valuable tool in the field of humanitarian demining. Recently a monostatic stepped-frequency continuous wave (SFCW) ground penetrating radar (GPR) has been developed for the characterization of the soil electromagnetic (EM) parameters epsi (dielectric permittivity), mu (magnetic permeability) and sigma (electric conductivity). The approach is extended here for the GPR signal extraction of buried targets. The equivalence principle is used to decompose the GPR signal in its soil and target-in-soil contributions. It permits the subtraction of the soil contribution from the total GPR signal, which provides the signature of the buried target. We have extracted clean frequency and time-domain signatures of a metallic sphere and a PMIN-2 plastic mine embedded in a multilayered medium at various moisture levels. The GPR signal of the metallic sphere has been simulated using the method of moments and shows good agreement with its measured counterpart.Anglai