4,550 research outputs found
Liquid-core low-refractive-index-contrast Bragg fiber sensor
We propose and experimentally demonstrate a low-refractive-index-contrast
hollow-core Bragg fiber sensor for liquid analyte refractive index detection.
The sensor operates using a resonant sensing principle- when the refractive
index of a liquid analyte in the fiber core changes, the resonant confinement
of the fiber guided mode will also change, leading to both the spectral shifts
and intensity changes in fiber transmission. As a demonstration, we
characterize the Bragg fiber sensor using a set of NaCl solutions with
different concentrations. Strong spectral shifts are obtained with the sensor
experimental sensitivity found to be ~1400nm/RIU (refractive index unit).
Besides, using theoretical modeling we show that low-refractive-index-contrast
Bragg fibers are more suitable for liquid-analyte sensing applications than
their high-refractive-index-contrast counterparts.Comment: 3 pages, 4 figure
DNA mismatch binding and antiproliferative activity of rhodium metalloinsertors
Deficiencies in mismatch repair (MMR) are associated with carcinogenesis. Rhodium metalloinsertors bind to DNA base mismatches with high specificity and inhibit cellular proliferation preferentially in MMR-deficient cells versus MMR-proficient cells. A family of chrysenequinone diimine complexes of rhodium with varying ancillary ligands that serve as DNA metalloinsertors has been synthesized, and both DNA mismatch binding affinities and antiproliferative activities against the human colorectal carcinoma cell lines HCT116N and HCT116O, an isogenic model system for MMR deficiency, have been determined. DNA photocleavage experiments reveal that all complexes bind to the mismatch sites with high specificities; DNA binding affinities to oligonucleotides containing single base CA and CC mismatches, obtained through photocleavage titration or competition, vary from 10^4 to 10^8 M^−1 for the series of complexes. Significantly, binding affinities are found to be inversely related to ancillary ligand size and directly related to differential inhibition of the HCT116 cell lines. The observed trend in binding affinity is consistent with the metalloinsertion mode where the complex binds from the minor groove with ejection of mismatched base pairs. The correlation between binding affinity and targeting of the MMR-deficient cell line suggests that rhodium metalloinsertors exert their selective biological effects on MMR-deficient cells through mismatch binding in vivo
Effective interactions and melting of a one dimensional defect lattice within a two-dimensional confined colloidal solid
We report Monte Carlo studies of a two-dimensional soft colloidal crystal
confined in a strip geometry by parallel walls. The wall-particle interaction
has corrugations along the length of the strip. Compressing the crystal by
decreasing the distance between the walls induces a structural transition
characterized by the sudden appearance of a one-dimensional array of extended
defects each of which span several lattice parameters, a "soliton staircase".
We obtain the effective interaction between these defects. A Lindemann
criterion shows that the reduction of dimensionality causes a finite periodic
chain of these defects to readily melt as the temperature is raised. We discuss
possible experimental realizations and speculate on potential applications.Comment: 4 pages 5 embedded figure
The Observation of Formation and Annihilation of Solitons and Standing Strain Wave Superstructures in a Two-Dimensional Colloidal Crystal
Confining a colloidal crystal within a long narrow channel produced by two
parallel walls can be used to impose a meso-scale superstructure of a
predominantly mechanical elastic character [Chui et al., EPL 2008, 83, 58004].
When the crystal is compressed in the direction perpendicular to the walls, we
obtain a structural transition when the number of rows of particles parallel to
the walls decreases by one. All the particles of this vanishing row are
distributed throughout the crystal. If the confining walls are structured (say
with a corrugation along the length of the walls), then these extra particles
are distributed neither uniformly nor randomly; rather, defect structures are
created along the boundaries resembling "soliton staircases", inducing a
non-uniform strain pattern within the crystal. Here we study the conditions of
stability, formation and annihilation of these solitons using a coarse grained
description of the dynamics. The processes are shown by comparing superimposed
configurations as well as molecular animations obtained from our simulations.
Also the corresponding normal and shear stresses during the transformation are
calculated. A study of these dynamical processes should be useful for
controlling strain wave superstructures in the self-assembly of various nano-
and meso scaled particles.Comment: 26 pages, 6 figure
Universality classes and crossover behaviors in non-Abelian directed sandpiles
We study universality classes and crossover behaviors in non-Abelian directed
sandpile models, in terms of the metastable pattern analysis. The non-Abelian
property induces spatially correlated metastable patterns, characterized by the
algebraic decay of the grain density along the propagation direction of an
avalanche. Crossover scaling behaviors are observed in the grain density due to
the interplay between the toppling randomness and the parity of the threshold
value. In the presence of such crossovers, we show that the broadness of the
grain distribution plays a crucial role in resolving the ambiguity of the
universality class. Finally, we claim that the metastable pattern analysis is
important as much as the conventional analysis of avalanche dynamics.Comment: 10 pages, 7 figures, 1 table; published in PRE as the full paper of
PRL v101, 218001 (2008
Backaction of a charge detector on a double quantum dot
We develop a master equation approach to study the backaction of quantum
point contact (QPC) on a double quantum dot (DQD) at zero bias voltage. We
reveal why electrons can pass through the zero-bias DQD only when the bias
voltage across the QPC exceeds a threshold value determined by the eigenstate
energy difference of the DQD. This derived excitation condition agrees well
with experiments on QPC-induced inelastic electron tunneling through a DQD [S.
Gustavsson et al., Phys. Rev. Lett. 99, 206804(2007)]. Moreover, we propose a
new scheme to generate a pure spin current by the QPC in the absence of a
charge current.Comment: 6 pages, 4 figure
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