11,450 research outputs found
Coupled Two-Way Clustering Analysis of Gene Microarray Data
We present a novel coupled two-way clustering approach to gene microarray
data analysis. The main idea is to identify subsets of the genes and samples,
such that when one of these is used to cluster the other, stable and
significant partitions emerge. The search for such subsets is a computationally
complex task: we present an algorithm, based on iterative clustering, which
performs such a search. This analysis is especially suitable for gene
microarray data, where the contributions of a variety of biological mechanisms
to the gene expression levels are entangled in a large body of experimental
data. The method was applied to two gene microarray data sets, on colon cancer
and leukemia. By identifying relevant subsets of the data and focusing on them
we were able to discover partitions and correlations that were masked and
hidden when the full dataset was used in the analysis. Some of these partitions
have clear biological interpretation; others can serve to identify possible
directions for future research
Noninvasive Measurement of Dissipation in Colloidal Systems
According to Harada and Sasa [Phys. Rev. Lett. 95, 130602 (2005)], heat
production generated in a non-equilibrium steady state can be inferred from
measuring response and correlation functions. In many colloidal systems,
however, it is a nontrivial task to determine response functions, whereas
details about spatial steady state trajectories are easily accessible. Using a
simple conditional averaging procedure, we show how this fact can be exploited
to reliably evaluate average heat production. We test this method using
Brownian dynamics simulations, and apply it to experimental data of an
interacting driven colloidal system
Red conceptual como estrategia de integración de contenidos disciplinares en enseñanza de las ciencias
La enseñanza de la ciencias busca la integración disciplinar como resultado de la experiencia educativa y de teorías como las de Morín (2002); Astolfi (1992,1994) entre otros. Partiendo de allí, este trabajo expone una experiencia efectuada durante el curso Cultivo in vitro de Tejidos Vegetales, con el uso de un Organizador Gráfico, Red Conceptual (Galagovsky, 1996), el cual permite la representación de las relaciones entre las disciplinas con un enfoque integrado. Se desarrolló como una investigación-acción sobre la práctica pedagógica, utilizando entrevistas, observación, y gráficos. La red elaborada mostró una alta interrelación entre los conceptos de diversas disciplinas de las Ciencias Naturales y Sociales. Hubo consenso en que la estrategia es apropiada para integrar diversos contenidos disciplinares desde el contexto de una asignatura como campo de estudio
Unexpected phase locking of magnetic fluctuations in the multi-k magnet USb
The spin waves in the multi-k antiferromagnet USb soften and become quasielastic well below the antiferromagnetic ordering temperature TN. This occurs without a magnetic or structural transition. It has been suggested that this change is in fact due to dephasing of the different multi-k components: a switch from 3-k to 1-k behavior. In this work, we use inelastic neutron scattering with tridirectional polarization analysis to probe the quasielastic magnetic excitations and reveal that the 3-k structure does not dephase. More surprisingly, the paramagnetic correlations also maintain the same clear phase correlations well above TN (up to at least 1.4TN)
Multi-k magnetic structures in USb_{0.9}Te_{0.1} and UAs_{0.8}Se_{0.2} observed via resonant x-ray scattering at the U M4 edge
Experiments with resonant photons at the U M4 edge have been performed on a
sample of USb_{0.9}Te_{0.1}, which has an incommensurate magnetic structure
with k = 0.596(2) reciprocal lattice units. The reflections of the form ,
as observed previously in a commensurate k = 1/2 system [N. Bernhoeft et al.,
Phys. Rev. B 69 174415 (2004)] are observed, removing any doubt that these
occur because of multiple scattering or high-order contamination of the
incident photon beam. They are clearly connected with the presence of a 3k
configuration. Measurements of the reflections from the sample
UAs_{0.8}Se_{0.2} in a magnetic field show that the transition at T* ~ 50 K is
between a low-temperature 2k and high-temperature 3k state and that this
transition is sensitive to an applied magnetic field. These experiments stress
the need for quantitative theory to explain the intensities of these
reflections.Comment: submitted to Phys. Rev.
Temperature-dependent Hall scattering factor and drift mobility in remotely doped Si:B/SiGe/Si heterostructures
Hall-and-Strip measurements on modulation-doped SiGe heterostructures and combined Hall and capacitance–voltage measurements on metal-oxide-semiconductor (MOS)-gated enhancement mode structures have been used to deduce Hall scattering factors, rH, in the Si1 – xGex two-dimensional hole gas. At 300 K, rH was found to be equal to 0.4 for x = 0.2 and x = 0.3. Knowing rH, it is possible to calculate the 300 K drift mobilities in the modulation-doped structures which are found to be 400 cm2 V – 1 s – 1 at a carrier density of 3.3 × 1011 cm – 2 for x = 0.2 and 300 cm2 V – 1 s – 1 at 6.3 × 1011 cm – 2 for x = 0.3, factors of between 1.5 and 2.0 greater than a Si pMOS control
Magnetic Excitations in NpCoGa5
We report the results of inelastic neutron scattering experiments on
NpCoGa, an isostructural analogue of the PuCoGa superconductor. Two
energy scales characterize the magnetic response in the antiferromagnetic
phase. One is related to a non-dispersive excitation between two crystal field
levels. The other at lower energies corresponds to dispersive fluctuations
emanating from the magnetic zone center. The fluctuations persist in the
paramagnetic phase also, although weaker in intensity. This supports the
possibility that magnetic fluctuations are present in PuCoGa, where
unconventional d-wave superconductivity is achieved in the absence of magnetic
order.Comment: 4 pages, 5 figure
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