6,834 research outputs found
On-chip high-speed sorting of micron-sized particles for high-throughput analysis
A new design of particle sorting chip is presented. The device employs a dielectrophoretic gate that deflects particles into one of two microfluidic channels at high speed. The device operates by focussing particles into the central streamline of the main flow channel using dielectrophoretic focussing. At the sorting junction (T- or Y-junction) two sets of electrodes produce a small dielectrophoretic force that pushes the particle into one or other of the outlet channels, where they are carried under the pressure-driven fluid flow to the outlet. For a 40mm wide and high channel, it is shown that 6micron diameter particles can be deflected at a rate of 300particles/s. The principle of a fully automated sorting device is demonstrated by separating fluorescent from non-fluorescent latex beads
High throughput particle analysis: combining dielectrophoretic particle focussing with confocal optical detection
A microflow cytometer has been fabricated that detects and counts fluorescent particles flowing through a microchannel at a high speed based upon their fluorescence emission intensity. Dielectrophoresis is used to continuously focus particles within the flowing fluid stream into the centre of the device, which is 40 μm high and 250 μm wide. The method ensures that all the particles pass through an interrogation region approximately 5 μm in diameter, which is created by focusing a beam of light into a spot. The functioning of the device was demonstrated by detecting and counting fluorescent latex particles at a rate of up to 250 particles/s. A mixture of three different populations of latex particle was used, each sub-population with a distinct level of fluorescent intensity. The device was evaluated by comparison with a conventional fluorescent activated cell sorter (FACS) and numerical simulation demonstrated that for 6 mico m beads, and for this design of chip the theoretical throughput is of the order of 1000 particles/s (corresponding to a particle velocty of 1 mm/s)
Fluctuating Cu-O-Cu Bond model of high temperature superconductivity in cuprates
Twenty years of extensive research has yet to produce a general consensus on
the origin of high temperature superconductivity (HTS). However, several
generic characteristics of the cuprate superconductors have emerged as the
essential ingredients of and/or constraints on any viable microscopic model of
HTS. Besides a Tc of order 100K, the most prominent on the list include a
d-wave superconducting gap with Fermi liquid nodal excitations, a d-wave
pseudogap with the characteristic temperature scale T*, an anomalous
doping-dependent oxygen isotope shift, nanometer-scale gap inhomogeneity, etc..
The key role of planar oxygen vibrations implied by the isotope shift and other
evidence, in the context of CuO2 plane symmetry and charge constraints from the
strong intra-3d Coulomb repulsion U, enforces an anharmonic mechanism in which
the oxygen vibrational amplitude modulates the strength of the in-plane Cu-Cu
bond. We show, within a Fermi liquid framework, that this mechanism can lead to
strong d-wave pairing and to a natural explanation of the salient features of
HTS
Periodic Instanton and Phase Transition in Quantum Tunneling of Spin Systems
The quantum-classical transitions of the escape rates in a uniaxial spin
model relevant to the molecular magnet MnAc and a biaxial anisotropic
ferromagnetic particle are investigated by applying the periodic instanton
method. The effective free energies are expanded around the top of the
potential barrier in analogy to Landau theory of phase transitions. We show
that the first-order transitions occur below the critical external magnetic
field for the uniaxial spin model and beyond the critical
anisotropy constant ratio for the biaxial ferromagnetic grains,
which are in good agreement with earlier works.Comment: 14 pages, revtex, 5 postscript figure
Thermal and Dynamical Properties of the Two-band Hubbard Model Compared with FeSi
We study the two-band Hubbard model introduced by Fu and Doniach as a model
for FeSi which is suggested to be a Kondo insulator. Using the self-consistent
second-order perturbation theory combined with the local approximation which
becomes exact in the limit of infinite dimensions, we calculate the specific
heat, the spin susceptibility and the dynamical conductivity and point out that
the reduction of the energy gap due to correlation is not significant in
contrast to the previous calculation. It is also demonstrated that the gap at
low temperatures in the optical conductivity is filled up at a rather low
temperature than the gap size, which is consistent with the experiment.Comment: 6 pages, LaTeX, 7 PS figures included, uses RevTe
Oxygen-covered tungsten crystal shape: time effects, equilibrium, surface energy and the edge-rounding temperature
The equilibrium crystal shape (ECS) of oxygen-covered tungsten micricrystal
is studied as a function of temperature. The specially designed ultrafast
crystal quenching setup with the cooling rate of 6000 K/s allows to draw
conclusions about ECS at high temperatures. The edge-rounding transition is
shown to occur between 1300 K and 1430 K. The ratio of surface free energies
is determined as a function of temperature.Comment: 8 pages, 10 figures, submitted for publicatio
Correlation Effects on Optical Conductivity of FeSi
Effects of electron correlation in FeSi are studied in terms of the two-band
Hubbard model with the density of states obtained from the band calculation.
Using the self-consistent second-order perturbation theory combined with the
local approximation, the correlation effects are investigated on the density of
states and the optical conductivity spectrum, which are found to reproduce the
experiments done by Damascelli et al. semiquantitatively. It is also found that
the peak at the gap edge shifts to lower energy region by correlation effects,
as is seen in the experiments.Comment: 4 pages, 3 figure
Nonequilibrium corrections in the pressure tensor due to an energy flux
The physical interpretation of the nonequilibrium corrections in the pressure
tensor for radiation submitted to an energy flux obtained in some previous
works is revisited. Such pressure tensor is shown to describe a moving
equilibrium system but not a real nonequilibrium situation.Comment: 4 pages, REVTeX, Brief Report to appear in PRE Dec 9
Stereoselective Syntheses of Deuterated Pipecolic Acids as Tools to Investigate the Stereoselectivity of the Hydroxylase GetF
Members of the GE81112 family are interesting candidates for the development of antibiotics. The configuration of the OH group on the pipecolic acid moiety plays a pivotal role in antibiotic activity. To investigate the stereoselectivity of the corresponding hydroxylase GetF, involved in the biosynthetic pathway, we synthesized the two deuterium-labeled pipecolic acid diastereomers in a highly stereoselective fashion via chelate-enolate Claisen rearrangement. The stereochemical outcome of the enzymatic hydroxylation step could easily be determined by analysis of mass differences between the products
Stereoselective Syntheses of Deuterated Pipecolic Acids as Tools to Investigate the Stereoselectivity of the Hydroxylase GetF
Members of the GE81112 family are interesting candidates for
the development of antibiotics. The configuration of the OH
group on the pipecolic acid moiety plays a pivotal role in
antibiotic activity. To investigate the stereoselectivity of the
corresponding hydroxylase GetF, involved in the biosynthetic
pathway, we synthesized the two deuterium-labeled pipecolic
acid diastereomers in a highly stereoselective fashion via
chelate-enolate Claisen rearrangement. The stereochemical outcome of the enzymatic hydroxylation step could easily be
determined by analysis of mass differences between the
products
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