353 research outputs found
Use Of Secondary Equilibria For The Separation Of Small Solutes By Field-Flow Fractionation
The dynamic range and selectivity of field-flow fractionation (FFF) can be Increased by using secondary chemical equilibria (SCE). SCE are established by adding a macromolecular additive or aggregate, which strongly Interacts with the field, to the carrier solution. In this study an oil-ln-water (O/W) microemulsion was used as the carrier solution in a sedimentation FFF apparatus. The microemulsion droplets (referred to as the support ) interact with the field and are retained relative to the bulk water. Small solutes that partition or bind to the microemulsion droplets are also retained relative to solutes that do not Interact with the support. In this way It Is possible to separate somewhat polar compounds, such as ascorbic acid and sodium benzoate, which prefer bulk water, from a polar solute, such as toluene, which prefers the support. In addition, the study of retention times in this system allows one to calculate the average microemulsion droplet radius. It appears that SCE-FFF could be a useful way to obtain Important Information on the physicochemical properties of a variety of colloidal supports. © 1988, American Chemical Society. All rights reserved
Heterovalent interlayers and interface states: an ab initio study of GaAs/Si/GaAs (110) and (100) heterostructures
We have investigated ab initio the existence of localized states and
resonances in abrupt GaAs/Si/GaAs (110)- and (100)-oriented heterostructures
incorporating 1 or 2 monolayers (MLs) of Si, as well as in the fully developed
Si/GaAs (110) heterojunction. In (100)-oriented structures, we find both
valence- and conduction-band related near-band edge states localized at the
Si/GaAs interface. In the (110) systems, instead, interface states occur deeper
in the valence band; the highest valence-related resonances being about 1 eV
below the GaAs valence-band maximum. Using their characteristic bonding
properties and atomic character, we are able to follow the evolution of the
localized states and resonances from the fully developed Si/GaAs binary
junction to the ternary GaAs/Si/GaAs (110) systems incorporating 2 or 1 ML of
Si. This approach also allows us to show the link between the interface states
of the (110) and (100) systems. Finally, the conditions for the existence of
localized states at the Si/GaAs (110) interface are discussed based on a
Koster-Slater model developed for the interface-state problem.Comment: REVTeX 4, 14 pages, 15 EPS figure
Hall effect in strongly correlated low dimensional systems
We investigate the Hall effect in a quasi one-dimensional system made of
weakly coupled Luttinger Liquids at half filling. Using a memory function
approach, we compute the Hall coefficient as a function of temperature and
frequency in the presence of umklapp scattering. We find a power-law correction
to the free-fermion value (band value), with an exponent depending on the
Luttinger parameter . At high enough temperature or frequency the
Hall coefficient approaches the band value.Comment: 7 pages, 3 figure
Schottky barrier heights at polar metal/semiconductor interfaces
Using a first-principle pseudopotential approach, we have investigated the
Schottky barrier heights of abrupt Al/Ge, Al/GaAs, Al/AlAs, and Al/ZnSe (100)
junctions, and their dependence on the semiconductor chemical composition and
surface termination. A model based on linear-response theory is developed,
which provides a simple, yet accurate description of the barrier-height
variations with the chemical composition of the semiconductor. The larger
barrier values found for the anion- than for the cation-terminated surfaces are
explained in terms of the screened charge of the polar semiconductor surface
and its image charge at the metal surface. Atomic scale computations show how
the classical image charge concept, valid for charges placed at large distances
from the metal, extends to distances shorter than the decay length of the
metal-induced-gap states.Comment: REVTeX 4, 11 pages, 6 EPS figure
Imaging the essential role of spin-fluctuations in high-Tc superconductivity
We have used scanning tunneling spectroscopy to investigate short-length
electronic correlations in three-layer Bi2Sr2Ca2Cu3O(10+d) (Bi-2223). We show
that the superconducting gap and the energy Omega_dip, defined as the
difference between the dip minimum and the gap, are both modulated in space
following the lattice superstructure, and are locally anti-correlated. Based on
fits of our data to a microscopic strong-coupling model we show that Omega_dip
is an accurate measure of the collective mode energy in Bi-2223. We conclude
that the collective mode responsible for the dip is a local excitation with a
doping dependent energy, and is most likely the (pi,pi) spin resonance.Comment: 4 pages, 4 figure
Soil carbon stock impacts following reversion of Miscanthus x giganteus and short rotation coppice willow commercial plantations into arable cropping
There are posited links between the establishment of perennial bioenergy, such as Short Rotation Coppice (SRC) willow and Miscanthus x giganteus, on low carbon soils and enhanced soil C sequestration. Sequestration provides additional climate mitigation, however, few studies have explored impacts on soil C stocks of bioenergy crop removal, thus the permanence of any sequestered C is unclear. This uncertainty has led some authors to question the handling of soil C stocks with carbon accounting e.g. through LCA. Here we provide additional data for this debate, reporting on the soil C impacts of the reversion (removal and return) to arable cropping of commercial SRC willow and Miscanthus across four sites in the UK, two for each bioenergy crop, with 8 reversions nested within these sites. Using a paired‐site approach, soil C stocks (0–1 m) were compared between 3 and 7 years after bioenergy crop removal. Impacts on soil C stocks varied, ranging from an increase of 70.16 ± 10.81 Mg C ha‐1 7 years after reversion of SRC willow to a decrease of 33.38 ± 5.33 Mg C ha‐1 3 years after reversion of Miscanthus compared to paired arable land. The implications for carbon accounting will depend on the method used to allocate this stock change between current and past land use. However, with, published life cycle assessment values for the lifetime C reduction provided by these crops ranging from 29.50 to 138.55 Mg C ha‐1, the magnitude of these changes in stock are significant. We discuss the potential underlying mechanisms driving variability in soil C stock change, including the age of bioenergy crop at removal, removal methods, and differences in the recalcitrant of the crop residues, and highlight the need to design management methods to limit negative outcomes
Evidence for a Fermi liquid in the pseudogap phase of high-Tc cuprates
Cuprate high-T_c superconductors on the Mott-insulating side of "optimal
doping" (with respect to the highest T_c's) exhibit enigmatic behavior in the
non-superconducting state. Near optimal doping the transport and spectroscopic
properties are unlike those of a Landau-Fermi liquid. For carrier
concentrations below optimal doping a pseudogap removes quasi-particle spectral
weight from parts of the Fermi surface, and causes a break-up of the Fermi
surface into disconnected nodal and anti-nodal sectors. Here we show that the
near-nodal excitations of underdoped cuprates obey Fermi liquid behavior. Our
optical measurements reveal that the dynamical relaxation rate 1/tau(omega,T)
collapses on a universal function proportional to (hbar omega)^2+(1.5 pi k_B
T)^2. Hints at possible Fermi liquid behavior came from the recent discovery of
quantum oscillations at low temperature and high magnetic field in underdoped
YBa2Cu3O6+d and YBa2Cu4O8, from the observed T^2-dependence of the DC
({\omega}=0) resistivity for both overdoped and underdoped cuprates, and from
the two-fluid analysis of nuclear magnetic resonance data. However, the direct
spectroscopic determination of the energy dependence of the life-time of the
excitations -provided by our measurements- has been elusive up to now. This
observation defies the standard lore of non-Fermi liquid physics in high T_c
cuprates on the underdoped side of the phase diagram.Comment: 15 pages, 11 figure
Vaccination with LAG-3Ig (IMP321) and Peptides Induces Specific CD4 and CD8 T-Cell Responses in Metastatic Melanoma Patients-Report of a Phase I/IIa Clinical Trial.
PURPOSE: Cancer vaccines aim to generate and maintain antitumor immune responses. We designed a phase I/IIa clinical trial to test a vaccine formulation composed of Montanide ISA-51 (Incomplete Freund's Adjuvant), LAG-3Ig (IMP321, a non-Toll like Receptor agonist with adjuvant properties), and five synthetic peptides derived from tumor-associated antigens (four short 9/10-mers targeting CD8 T-cells, and one longer 15-mer targeting CD4 T-cells). Primary endpoints were safety and T-cell responses.
EXPERIMENTAL DESIGN: Sixteen metastatic melanoma patients received serial vaccinations. Up to nine injections were subcutaneously administered in three cycles, each with three vaccinations every 3 weeks, with 6 to 14 weeks interval between cycles. Blood samples were collected at baseline, 1-week after the third, sixth and ninth vaccination, and 6 months after the last vaccination. Circulating T-cells were monitored by tetramer staining directly ex vivo, and by combinatorial tetramer and cytokine staining on in vitro stimulated cells.
RESULTS: Side effects were mild to moderate, comparable to vaccines with Montanide alone. Specific CD8 T-cell responses to at least one peptide formulated in the vaccine preparation were found in 13 of 16 patients. However, two of the four short peptides of the vaccine formulation did not elicit CD8 T-cell responses. Specific CD4 T-cell responses were found in all 16 patients.
CONCLUSIONS: We conclude that vaccination with IMP321 is a promising and safe strategy for inducing sustained immune responses, encouraging further development for cancer vaccines as components of combination therapies. Clin Cancer Res; 22(6); 1330-40. ©2015 AACR
Myiases d’ici et d’ailleurs : pseudo-furonculose et bactériémie à Ignatzschineria larvae [Myases from here and elsewhere : pseudo-furonculosis and Ignatzschineria larvae bacteremia]
Myiasis is an infestation by maggots. In humans, it predominates in regions with low socio-economic development. We report on two cases of myiasis acquired during a tropical travel and in Switzerland, respectively. The first one presented as a furunculous-like disease due to the invasion of subcutaneous tissues by Cordylobia sp. larvae. The second corresponded to a chronic wound infestation that resulted in a rarely reported bacteremia due to Ignatzschineria larvae, a commensal bacteria of maggots' digestive tract. Surgery was necessary in both cases, mainly for psychological reasons in the first case. Both the entomologist and molecular biology were instrumental for treatment decisions
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