7,750 research outputs found
Endoscopic Submucosal Dissection for Gastric Epithelial Tumors: A Multicenter Study in Taiwan
Background/PurposeEndoscopic submucosal dissection (ESD) is an advanced endoscopic procedure to resect early gastric cancer (EGC). The purpose of this study was to determine the effectiveness and complications of ESD for gastric epithelial tumors in Taiwan.MethodsWe retrospectively analyzed the efficacy and outcome of ESD in patients who received ESD for gastric epithelial tumors between June 2004 and August 2007.ResultsA total of 70 patients with gastric epithelial tumors were treated by ESD. The mean age was 66.5 ±12.9 years (range, 35–84 years). The mean size of the gastric epithelial tumors was 1.85 ± 0.81 cm. The mean size of resected specimens was 3.26 ± 1.39 cm. The one-piece resection rate was 91.4% (64/70). The median operation time was 92.4 minutes. The complicating bleeding and perforation rates were 5.7% (4/70) and 4.3% (3/70), respectively. Emergency surgery was performed for three patients with perforations. The local recurrence rate of gastric cancer was 2.8%. Except for one patient who died of congestive heart failure and another who died of stroke, the remaining 68 patients (97.1%) survived.ConclusionESD is a promising local curative treatment option for EGC in Taiwan but it still carries risks of perforation and bleeding. The education and learning curve of endoscopists will improve the outcome of this procedure
Magneto-electrodynamics at high frequencies in the antiferromagnetic and superconducting states of DyNi_2B_2C
We report the observation of novel behaviour in the radio frequency (rf) and
microwave response of DyNi_2B_2C over a wide range of temperature (T) and
magnetic field (H) in the antiferromagnetic (AFM) and superconducting (SC)
states. At microwave frequencies of 10 GHz, the T dependence of the surface
impedance Z_s=R_s+iX_s was measured which yields the T dependence of the
complex conductivity \sigma_1-i\sigma_2 in the SC and AFM states. At radio
frequencies (4 MHz), the H and T dependence of the penetration depth
\lambda(T,H) were measured. The establishment of antiferromagnetic order at
T_N=10.3 K results in a marked decrease in the scattering of charge carriers,
leading to sharp decreases in R_s and X_s. However, R_s and X_s differ from
each other in the AFM state. We show that the results are consistent with
conductivity relaxation whence the scattering rate becomes comparable to the
microwave frequency. The rf measurements yield a rich dependence of the
scattering on the magnetic field near and below T_N. Anomalous decrease of
scattering at moderate applied fields is observed at temperatures near and
above T_N, and arises due to a crossover from a negative magnetoresistance
state, possibly associated with a loss of spin disorder scattering at low
fields, to a positive magnetoresistance state associated with the metallic
nature. The normal state magnetoresistance is positive at all temperatures for
\mu_0H>2T and at all fields for T>15K. Several characteristic field and
temperature scales associated with metamagnetic transitions (H_M1(T), H_M2(T))
and onset of spin disorder H_D(T), in addition to T_c, T_N and H_c2(T) are
observed in the rf measurements.Comment: 9 pages, Latex, Uses REVTeX, This and related publications also
available at http://sagar.physics.neu.edu/ Submitted to Phys. Rev.
Investigation of the Spin Density Wave in NaxCoO2
Magnetic susceptibility, transport and heat capacity measurements of single
crystal NaxCoO2 (x=0.71) are reported. A transition to a spin density wave
(SDW) state at Tmag = 22 K is observable in all measurements, except chi(ac)
data in which a cusp is observed at 4 K and attributed to a low temperature
glassy phase. M(H) loops are hysteretic below 15 K. Both the SDW transition and
low temperature hysteresis are only visible along the c-axis. The system also
exhibits a substantial (~40%) positive magnetoresistance below this
temperature. Calculations of the electronic heat capacity gamma above and below
Tmag and the size of the jump in C indicate that the onset of the SDW brings
about the opening of gap and the removal of part of the Fermi surface. Reduced
in-plane electron-electron scattering counteracts the loss of carriers below
the transition and as a result we see a net reduction in resistivity below
Tmag. Sodium ordering transitions at higher temperatures are observable as
peaks in the heat capacity with a corresponding increase in resistivity.Comment: 14 pages, 6 figure
Si solid-state quantum dot-based materials for tandem solar cells
The concept of third-generation photovoltaics is to significantly increase device efficiencies whilst still using thin-film processes and abundant non-toxic materials. A strong potential approach is to fabricate tandem cells using thin-film deposition that can optimise collection of energy in a series of cells with decreasing band gap stacked on top of each other. Quantum dot materials, in which Si quantum dots (QDs) are embedded in a dielectric matrix, offer the potential to tune the effective band gap, through quantum confinement, and allow fabrication of optimised tandem solar cell devices in one growth run in a thin-film process. Such cells can be fabricated by sputtering of thin layers of silicon rich oxide sandwiched between a stoichiometric oxide that on annealing crystallise to form Si QDs of uniform and controllable size. For approximately 2-nm diameter QDs, these result in an effective band gap of 1.8 eV. Introduction of phosphorous or boron during the growth of the multilayers results in doping and a rectifying junction, which demonstrates photovoltaic behaviour with an open circuit voltage (VOC) of almost 500 mV. However, the doping behaviour of P and B in these QD materials is not well understood. A modified modulation doping model for the doping mechanisms in these materials is discussed which relies on doping of a sub-oxide region around the Si QDs
The Escherichia coli transcriptome mostly consists of independently regulated modules
Underlying cellular responses is a transcriptional regulatory network (TRN) that modulates gene expression. A useful description of the TRN would decompose the transcriptome into targeted effects of individual transcriptional regulators. Here, we apply unsupervised machine learning to a diverse compendium of over 250 high-quality Escherichia coli RNA-seq datasets to identify 92 statistically independent signals that modulate the expression of specific gene sets. We show that 61 of these transcriptomic signals represent the effects of currently characterized transcriptional regulators. Condition-specific activation of signals is validated by exposure of E. coli to new environmental conditions. The resulting decomposition of the transcriptome provides: a mechanistic, systems-level, network-based explanation of responses to environmental and genetic perturbations; a guide to gene and regulator function discovery; and a basis for characterizing transcriptomic differences in multiple strains. Taken together, our results show that signal summation describes the composition of a model prokaryotic transcriptome
Controlling crystallization and its absence: Proteins, colloids and patchy models
The ability to control the crystallization behaviour (including its absence)
of particles, be they biomolecules such as globular proteins, inorganic
colloids, nanoparticles, or metal atoms in an alloy, is of both fundamental and
technological importance. Much can be learnt from the exquisite control that
biological systems exert over the behaviour of proteins, where protein
crystallization and aggregation are generally suppressed, but where in
particular instances complex crystalline assemblies can be formed that have a
functional purpose. We also explore the insights that can be obtained from
computational modelling, focussing on the subtle interplay between the
interparticle interactions, the preferred local order and the resulting
crystallization kinetics. In particular, we highlight the role played by
``frustration'', where there is an incompatibility between the preferred local
order and the global crystalline order, using examples from atomic glass
formers and model anisotropic particles.Comment: 11 pages, 7 figure
Leading power SCET analysis of
Recently, Belle and BaBar Collaborations observed surprising suppression in
the endpoint spectrum, which stimulates us to examine the endpoint
behaviors of the production. We calculate the
momentum and angular distributions for this process within the framework of the
soft-collinear effective theory (SCET). The decreasing spectrum in the endpoint
region is obtained by summing the Sudakov logarithms. We also find a large
discrepancy between the NRQCD and SCET spectrum in the endpoint region even
before the large logarithms are summed, which is probably due to the fact that
only the scalar structure of the two-gluon system is picked out in the leading
power expansion. A comparison with the process is
made.Comment: 12 pages, 3 figures, one reference added and some minor changes,
version to appear in Phys. Lett.
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