13,942 research outputs found
Inadequacy of Scaling Arguments for Neutrino Cross Sections
The problem with the use of scaling arguments for simultaneous studies of
different weak interaction processes is discussed. When different neutrino
scattering cross sections involving quite different momentum transfers are
being compared it difficult to define a meaningful single scaling factor to
renormalize calculated cross sections. It has been suggested that the use of
such scaling can be used to estimate high energy neutrino cross sections from
low energy neutrino cross sections. This argument has lead to questions on the
consistency of the magnitude of the LSND muon neutrino cross sections on
C relative to other lower energy weak processes. The issue is revisited
here and from inspection of the structure of the form factors involved it is
seen that the problem arises from a poor description of the transition form
factors at high momentum transfer. When wave functions that reproduce the
transverse magnetic inelastic (e,e') scattering form factor for the 15.11 MeV
state in C are used there is no longer a need for scaling the axial
current, and the different weak interactions rates involving the T=1 1
triplet in mass 12 are consistent with one another.Comment: 3 pages, 1 figur
Engineering Electromagnetic Properties of Periodic Nanostructures Using Electrostatic Resonances
Electromagnetic properties of periodic two-dimensional sub-wavelength
structures consisting of closely-packed inclusions of materials with negative
dielectric permittivity in a dielectric host with positive
can be engineered using the concept of multiple electrostatic
resonances. Fully electromagnetic solutions of Maxwell's equations reveal
multiple wave propagation bands, with the wavelengths much longer than the
nanostructure period. It is shown that some of these bands are described using
the quasi-static theory of the effective dielectric permittivity
, and are independent of the nanostructure period. Those bands
exhibit multiple cutoffs and resonances which are found to be related to each
other through a duality condition. An additional propagation band characterized
by a negative magnetic permeability develops when a magnetic moment is induced
in a given nano-particle by its neighbors. Imaging with sub-wavelength
resolution in that band is demonstrated
Raman frequency shift in oxygen functionalized carbon nanotubes
In terms of lattice dynamics theory, we study the vibrational properties of
the oxygen-functionalized single wall carbon nanotubes (O-SWCNs). Due to the
C-O and O-O interactions, many degenerate phonon modes are split and even some
new phonon modes are obtained, different from the bare SWCNs. A distinct Raman
shift is found in both the radial breathing mode and G modes, depending not
only on the tube diameter and chirality but also on oxygen coverage and
adsorption configurations. With the oxygen coverage increasing, interesting, a
nonmonotonic up- and down-shift is observed in G modes, which is contributed to
the competition between the bond expansion and contraction, there coexisting in
the functionalized carbon nanotube.Comment: 4 pages, 3 figures, 1 tabl
Soft Spin Wave Near nu=1: Evidence for a Magnetic Instability in Skyrmion Systems
The ground state of the two dimensional electron gas near =1 is
investigated by inelastic light scattering measurements carried down to very
low temperatures. Away from =1, the ferromagnetic spin wave collapses and
a new low-energy spin wave emerges below the Zeeman gap. The emergent spin wave
shows soft behavior as its energy increases with temperature and reaches the
Zeeman energy for temperatures above 2 K. The observed softening indicates an
instability of the two dimensional electron gas towards a magnetic order that
breaks spin rotational symmetry. We discuss our findings in light of the
possible existence of a Skyrme crystal.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let
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A 3D printed drug delivery implant formed from a dynamic supramolecular polyurethane formulation
Using a novel molecular design approach, we have prepared a thermo-responsive supramolecular polyurethane as a matrix material for use in drug eluting implants. The dynamic supramolecular polyurethane (SPU) is able to self-assemble through hydrogen bonding and π-π stacking interactions, resulting in an addressable polymer network with a relatively low processing temperature. The mechanical properties of the SPU demonstrated the material was self-supporting, stiff, yet flexible thus making it suitable for hot-melt extrusion processing, inclusive of related 3D printing approaches. Cell-based toxicity assays revealed the SPU to be non-toxic and therefore a viable candidate as a biocompatible polymer for implant applications. To this end, the SPU was formulated with paracetamol (16 %w/w) and 4 wt% or 8 wt% poly(ethylene glycol) (PEG) as an excipient and hot melt extruded at 100 °C to afford a 3D printed prototype implant to explore the extended drug release required for an implant and the potential manipulation of the release profile. Furthermore, rheological, infra-red spectroscopy, powder X-ray diffraction and scanning electron microscopy studies revealed the chemical and physical properties and compatibility of the formulation components. Successful release of paracetamol was achieved from in vitro dissolution studies and it was predicted that the drug would be released over a period of up to 8.5 months with hydrophilic PEG being able to influence the release rate. This extended release time is consistent with applications of this novel dynamic polymer as a drug eluting implant matrix
Fluorescent Silicon Clusters and Nanoparticles
The fluorescence of silicon clusters is reviewed. Atomic clusters of silicon
have been at the focus of research for several decades because of the relevance
of size effects for material properties, the importance of silicon in
electronics and the potential applications in bio-medicine. To date numerous
examples of nanostructured forms of fluorescent silicon have been reported.
This article introduces the principles and underlying concepts relevant for
fluorescence of nanostructured silicon such as excitation, energy relaxation,
radiative and non-radiative decay pathways and surface passivation.
Experimental methods for the production of silicon clusters are presented. The
geometric and electronic properties are reviewed and the implications for the
ability to emit fluorescence are discussed. Free and pure silicon clusters
produced in molecular beams appear to have properties that are unfavourable for
light emission. However, when passivated or embedded in a suitable host, they
may emit fluorescence. The current available data show that both quantum
confinement and localised transitions, often at the surface, are responsible
for fluorescence. By building silicon clusters atom by atom, and by embedding
them in shells atom by atom, new insights into the microscopic origins of
fluorescence from nanoscale silicon can be expected.Comment: 5 figures, chapter in "Silicon Nanomaterials Sourcebook", editor
Klaus D. Sattler, CRC Press, August 201
Local structure and site occupancy of Cd and Hg substitutions in CeTIn5 (T=Co, Rh, Ir)
The CeTIn5 superconductors (T=Co, Rh, or Ir) have generated great interest
due to their relatively Tc's, NFL behavior, and their proximity to AF order and
quantum critical points. In contrast to small changes with the T-species,
electron doping in CeT(In{1-x}Mx)5 with M=Sn and hole doping with Cd or Hg have
a dramatic effect on the electronic properties at very low concentrations. The
present work reports EXAFS measurements that address the substituent atom
distribution as a function of T, M, and x, near the superconducting phase.
Together with previous measurements for M=Sn, the proportion of the M atom
residing on the In(1) site, f{In(1)}, increases in the order M=Cd, Sn, and Hg,
ranging from about 40% to 70%, showing a strong preference for these
substituents to occupy the In(1) site (random=20%). In addition, f{In(1)}
ranges from 70% to 100% for M=Hg in the order T=Co, Rh, and Ir. These fractions
track the changes in the atomic radii of the various species, and help explain
the sharp dependence of Tc on substituting into the In site. However, it is
difficult to reconcile the small concentrations of M with the dramatic changes
in the ground state in the hole-doped materials with only an impurity
scattering model. These results therefore indicate that while such
substitutions have interesting local atomic structures with important
electronic and magnetic consequences, other local changes in the electronic and
magnetic structure are equally important in determining the bulk properties of
these materials.Comment: 10 pages, 7 figures, to appear in PR
Tamoxifen therapy reduced platelet counts without change in platelet function
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109840/1/cptclpt2005247.pd
Optimisation problems and replica symmetry breaking in finite connectivity spin-glasses
A formalism capable of handling the first step of hierarchical replica
symmetry breaking in finite-connectivity models is introduced. The emerging
order parameter is claimed to be a probability distribution over the space of
field distributions (or, equivalently magnetisation distributions) inside the
cluster of states. The approach is shown to coincide with the previous works in
the replica symmetric case and in the two limit cases m=0,1 where m is Parisi's
break-point. As an application to the study of optimization problems, the
ground-state properties of the random 3-Satisfiability problem are investigated
and we present a first RSB solution improving replica symmetric results.Comment: 16 pages Revtex file, 1 figure; amended version with two new
appendices; to be published in J.Phys.
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