3,832 research outputs found
Some taste substances are direct activators of G-proteins
Amphiphilic substances may stimulate cellular events through direct activation of G-proteins. The present experiments indicate that several amphiphilic sweeteners and the bitter tastant, quinine, activate transducin and Gi/Go-proteins. Concentrations of taste substances required to activate G-proteins in vitro correlated with those used to elicit taste. These data support the hypothesis that amphiphilic taste substances may elicit taste through direct activation of G-proteins
El análisis de datos cualitativos como proceso de clasificación
El artículo describe detalladamente el procedimiento referido a la Investiga
sobre las teorías implícitas de maestros de la escuela primaria sobre-ción
debilidad aritmética de niños y discute las consecuencias de los hallazgos
para la formación de maestros. Utiliza dos ejemplos adicionales de estudios
sobre profesores (problemas de disciplina en el aula; control por el profesor
y aprendizaje auto-regulado). También se contempla un intento de generalizar
la relevancia del enfoque descrito.___________________________________
This article describes In detail the procedure to take in relation to the research
on the implicit theories of Primary education teachers about the arithmetical
weakness of children and discusses the consequences of the findings for the
training of teachers. The paper uses two additional examples of studies about
teachers (discipline problems in the classroom, teacher control and the selfregulated
learning), as well as attempt to generalise the relevance of this
approach
Variational methods with coupled Gaussian functions for Bose-Einstein condensates with long-range interactions. II. Applications
Bose-Einstein condensates with an attractive 1/r interaction and with
dipole-dipole interaction are investigated in the framework of the Gaussian
variational ansatz introduced by S. Rau, J. Main, and G. Wunner [Phys. Rev. A,
submitted]. We demonstrate that the method of coupled Gaussian wave packets is
a full-fledged alternative to direct numerical solutions of the
Gross-Pitaevskii equation, or even superior in that coupled Gaussians are
capable of producing both, stable and unstable states of the Gross-Pitaevskii
equation, and thus of giving access to yet unexplored regions of the space of
solutions of the Gross-Pitaevskii equation. As an alternative to numerical
solutions of the Bogoliubov-de Gennes equations, the stability of the
stationary condensate wave functions is investigated by analyzing the stability
properties of the dynamical equations of motion for the Gaussian variational
parameters in the local vicinity of the stationary fixed points. For
blood-cell-shaped dipolar condensates it is shown that on the route to collapse
the condensate passes through a pitchfork bifurcation, where the ground state
itself turns unstable, before it finally vanishes in a tangent bifurcation.Comment: 14 pages, 14 figures, submitted to Phys. Rev. A, some equations
correcte
Dynamic Kosterlitz-Thouless transition in 2D Bose mixtures of ultra-cold atoms
We propose a realistic experiment to demonstrate a dynamic
Kosterlitz-Thouless transition in ultra-cold atomic gases in two dimensions.
With a numerical implementation of the Truncated Wigner Approximation we
simulate the time evolution of several correlation functions, which can be
measured via matter wave interference. We demonstrate that the relaxational
dynamics is well-described by a real-time renormalization group approach, and
argue that these experiments can guide the development of a theoretical
framework for the understanding of critical dynamics.Comment: 5 pages, 6 figure
Cavity-induced temperature control of a two-level system
We consider a two-level atom interacting with a single mode of the
electromagnetic field in a cavity within the Jaynes-Cummings model. Initially,
the atom is thermal while the cavity is in a coherent state. The atom interacts
with the cavity field for a fixed time. After removing the atom from the cavity
and applying a laser pulse the atom will be in a thermal state again. Depending
on the interaction time with the cavity field the final temperature can be
varied over a large range. We discuss how this method can be used to cool the
internal degrees of freedom of atoms and create heat baths suitable for
studying thermodynamics at the nanoscale
Bernoulli HMMs at subword level for handwritten word recognition
This paper presents a handwritten word recogniser based on HMMs at subword level (characters) in which state-emission probabilities are governed by multivariate Bernoulli probability functions. This recogniser works directly with raw binary pixels of the image, instead of conventional, real-valued local features. A detailed experimentation has been carried out by varying the number of states, and comparing the results with those from a conventional system based on continuous (Gaussian) densities. From this experimentation, it becomes clear that the proposed recogniser is much better than the conventional systemWork supported by the EC (FEDER) and the Spanish MEC under the MIPRCV “Consolider Ingenio 2010” research programme (CSD2007-00018), the iTransDoc research project (TIN2006-15694-CO2-01), and the FPU grant AP2005-1840.Giménez Pastor, A.; Juan, A. (2009). Bernoulli HMMs at subword level for handwritten word recognition. En Pattern Recognition and Image Analysis. Springer Verlag (Germany). 497-504. https://doi.org/10.1007/978-3-642-02172-5_64S497504Giménez-Pastor, A., Juan-Císcar, A.: Bernoulli HMMs for Off-line Handwriting Recognition. In: Proc. of the 8th Int. Workshop on Pattern Recognition in Information Systems (PRIS 2008), Barcelona, Spain, pp. 86–91 (June 2008)Günter, S., Bunke, H.: HMM-based handwritten word recognition: on the optimization of the number of states, training iterations and Gaussian components. Pattern Recognition 37, 2069–2079 (2004)Gadea, M.P.: Aportaciones al reconocimiento automático de texto manuscrito. PhD thesis, Dep. de Sistemes Informàtics i Computació, València, Spain. Advisors: Vidal, E., Tosselli, A.H. (October 2007)Juan, A., Vidal, E.: Bernoulli mixture models for binary images. In: Proc. of the 17th Int. Conf. on Pattern Recognition (ICPR 2004), Cambridge, UK, vol. 3 (August 2004)Marti, U.V., Bunke, H.: The IAM-database: an English sentence database for offline handwriting recognition. 5(1), 39–46 (2002)Rabiner, L., Juang, B.-H.: Fundamentals of speech recognition. Prentice-Hall, Englewood Cliffs (1993)Romero, V., Giménez, A., Juan, A.: Explicit Modelling of Invariances in Bernoulli Mixtures for Binary Images. In: Martí, J., Benedí, J.M., Mendonça, A.M., Serrat, J. (eds.) IbPRIA 2007. LNCS (LNAI), vol. 4477, pp. 539–546. Springer, Heidelberg (2007)Young, S., et al.: The HTK Book. Cambridge University Engineering Department (1995
Symmetry-breaking thermally induced collapse of dipolar Bose-Einstein condensates
We investigate a Bose-Einstein condensate with additional long-range dipolar
interaction in a cylindrically symmetric trap within a variational framework.
Compared to the ground state of this system, little attention has as yet been
payed to its unstable excited states. For thermal excitations, however, the
latter is of great interest, because it forms the "activated complex" that
mediates the collapse of the condensate. For a certain value of the s-wave
scatting length our investigations reveal a bifurcation in the transition
state, leading to the emergence of two additional and symmetry-breaking excited
states. Because these are of lower energy than their symmetric counterpart, we
predict the occurrence of a symmetry-breaking thermally induced collapse of
dipolar condensates. We show that its occurrence crucially depends on the trap
geometry and calculate the thermal decay rates of the system within leading
order transition state theory with the help of a uniform rate formula near the
rank-2 saddle which allows to smoothly pass the bifurcation.Comment: 6 pages, 3 figure
Relation between the eigenfrequencies of Bogoliubov excitations of Bose-Einstein condensates and the eigenvalues of the Jacobian in a time-dependent variational approach
We study the relation between the eigenfrequencies of the Bogoliubov
excitations of Bose-Einstein condensates, and the eigenvalues of the Jacobian
stability matrix in a variational approach which maps the Gross-Pitaevskii
equation to a system of equations of motion for the variational parameters. We
do this for Bose-Einstein condensates with attractive contact interaction in an
external trap, and for a simple model of a self-trapped Bose-Einstein
condensate with attractive 1/r interaction. The stationary solutions of the
Gross-Pitaevskii equation and Bogoliubov excitations are calculated using a
finite-difference scheme. The Bogoliubov spectra of the ground and excited
state of the self-trapped monopolar condensate exhibits a Rydberg-like
structure, which can be explained by means of a quantum defect theory. On the
variational side, we treat the problem using an ansatz of time-dependent
coupled Gaussians combined with spherical harmonics. We first apply this ansatz
to a condensate in an external trap without long-range interaction, and
calculate the excitation spectrum with the help of the time-dependent
variational principle. Comparing with the full-numerical results, we find a
good agreement for the eigenfrequencies of the lowest excitation modes with
arbitrary angular momenta. The variational method is then applied to calculate
the excitations of the self-trapped monopolar condensates, and the
eigenfrequencies of the excitation modes are compared.Comment: 15 pages, 12 figure
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