Magnetic Nanoparticles for Power Absorption: optimizing size, shape and magnetic properties

We present a study on the magnetic properties of naked and silica-coated Fe3O4 nanoparticles with sizes between 5 and 110 nm. Their efficiency as heating agents was assessed through specific power absorption (SPA) measurements as a function of particle size and shape. The results show a strong dependence of the SPA with the particle size, with a maximum around 30 nm, as expected for a Neel relaxation mechanism in single-domain particles. The SiO2 shell thickness was found to play an important role in the SPA mechanism by hindering the heat outflow, thus decreasing the heating efficiency. It is concluded that a compromise between good heating efficiency and surface functionality for biomedical purposes can be attained by making the SiO2 functional coating as thin as possible.Comment: 15 pages, 7 figures, 2 table

Ultrasound attenuation in gap-anisotropic systems

Transverse ultrasound attenuation provides a weakly-coupled probe of momentum current correlations in electronic systems. We develop a simple theory for the interpretation of transverse ultrasound attenuation coefficients in systems with nodal gap anisotropy. Applying this theory we show how ultrasound can delineate between extended-s and d-wave scenarios for the cuprate superconductors.Comment: Uuencode file: 4 pages (Revtex), 3 figures. Some references adde

On the low temperature properties and specific anisotropy of pure anisotropically paired superconductors

Dependences of low temperature behavior and anisotropy of various physical quantities for pure unconventional superconductors upon a particular form of momentum direction dependence for the superconducting order parameter (within the framework of the same symmetry type of superconducting pairing) are considered. A special attention is drawn to the possibility of different multiplicities of the nodes of the order parameter under their fixed positions on the Fermi surface, which are governed by symmetry. The problem of an unambiguous identification of a type of superconducting pairing on the basis of corresponding experimental results is discussed. Quasiparticle density of states at low energy for both homogeneous and mixed states, the low temperature dependences of the specific heat, penetration depth and thermal conductivity, the I-V curves of SS and NS tunnel junctions at low voltages are examined. A specific anisotropy of the boundary conditions for unconventional superconducting order parameter near $T_c$ for the case of specular reflection from the boundary is also investigated.Comment: 20 page

Distinguishing d-wave from highly anisotropic s-wave superconductors

Systematic impurity doping in the Cu-O plane of the hole-doped cuprate superconductors may allow one to decide between unconvention al ("d-wave") and anisotropic conventional ("s-wave") states as possible candidates for the order parameter in these materials. We show that potential scattering of any strength always increases the gap minima of such s-wave states, leading to activated behavior in temperature with characteristic impurity concentration dependence in observable quantities such as the penetration depth. A magnetic component to the scattering may destroy the energy gap and give rise to conventional gapless behavior, or lead to a nonmonotonic dependence of the gap on impurity concentration. We discuss how experiments constrain this analysis.Comment: 5 page

First observation of the ( 4 He, 8 B) reaction

The ( 4 He, 8 B) reaction on 27 Al and 66 Zn targets has been studied at E α =109MeV, the first observation of this reaction. Five groups appear in the first 4 MeV of excitation in the 23 Ne spectrum, with laboratory differential cross sections ranging from 35 to 384 nb/sr at θ lab =8 0 . Individual levels in 62 Co were not resolved in the exposure on the 66 Zn target. However, 8 B events were observed which are tentatively attributed to the 66 Zn(α, 8 B) 62 Co reaction, since contributions from plausible target contaminants can be eliminated on the basis of Q value. The observed yield at 8 0 indicates a laboratory cross section of 540 nb/sr summed over the first 4.6 MeV of excitation in 62 Co.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45824/1/10050_2005_Article_BF01547474.pd

Pulsar-wind nebulae and magnetar outflows: observations at radio, X-ray, and gamma-ray wavelengths

We review observations of several classes of neutron-star-powered outflows: pulsar-wind nebulae (PWNe) inside shell supernova remnants (SNRs), PWNe interacting directly with interstellar medium (ISM), and magnetar-powered outflows. We describe radio, X-ray, and gamma-ray observations of PWNe, focusing first on integrated spectral-energy distributions (SEDs) and global spectral properties. High-resolution X-ray imaging of PWNe shows a bewildering array of morphologies, with jets, trails, and other structures. Several of the 23 so far identified magnetars show evidence for continuous or sporadic emission of material, sometimes associated with giant flares, and a few possible "magnetar-wind nebulae" have been recently identified.Comment: 61 pages, 44 figures (reduced in quality for size reasons). Published in Space Science Reviews, "Jets and Winds in Pulsar Wind Nebulae, Gamma-ray Bursts and Blazars: Physics of Extreme Energy Release

Recent improvements to RC-line encoded position-sensitive proportional counters

Continuing research on the principles of position encoding with RC lines has advanced the design of position-sensitive proportional counters (PSPCs) to meet the requirements for high count rates (>10/sup 5/ counts/sec) and good spatial resolution (>10/sup 4/ spatial elements) in small-angle scattering experiments with x rays and neutrons. Low-noise preamplifiers were developed with pole-zero cancellation in the feedback circuit and modular linear amplifiers with passive RCL shaping which, compared to previous designs, reduce output saturation at high count rates approx.20 times and shorten the position signal processing time to <1 ..mu..sec. Using resistive self-heating and propylene decomposition, the conductance and film thickness of pyrolytic-carbon anodes were increased to match the RC time-constants of line PSPCs with the linear amplifiers, to reduce the effects of electron erosion of the anodes at high count rates, and to improve the PSPC linearity. A large-area PSPC (480 x 780 mm/sup 2/) for low-energy (<60 keV) photon imaging was developed. The electronic uncertainty in the position measurement of 20-keV photons is <0.5 mm (fwhm) in both dimensions. The technology developed for this PSPC is applicable to the design of large-area detectors (>800 x 800 mm/sup 2/) for the measurement of small-angle scattering with neutrons. The method of electronic thickness discrimination was applied to change the effective thickness of an area PSPC from 12 to 2 cm whenever the molybdenum target of an x-ray generator was changed to a copper target. This thickness adjustment increased the signal-to-background ratio by a factor of approx.6 for the 8-keV photons from the copper target, while maintaining a >90% detection efficiency