Synthetizing hydrodynamic turbulence from noise: formalism and applications to plankton dynamics

We present an analytical scheme, easily implemented numerically, to generate synthetic Gaussian 2D turbulent flows by using linear stochastic partial differential equations, where the noise term acts as a random force of well-prescribed statistics. This methodology leads to a divergence-free, isotropic, stationary and homogeneous velocity field, whose characteristic parameters are well reproduced, in particular the kinematic viscosity and energy spectrum. This practical approach to tailor a turbulent flow is justified by its versatility when analizing different physical processes occurring in advectely mixed systems. Here, we focuss on an application to study the dynamics of Planktonic populations in the ocean

Dynamics of an inchworm nano-walker

An inchworm processive mechanism is proposed to explain the motion of dimeric molecular motors such as kinesin. We present here preliminary results for this mechanism focusing on observables like mean velocity, coupling ratio and efficiency versus ATP concentration and the external load F.Comment: 6 pages, 2 figure

Does the educational management model matter? New evidence from a quasiexperimental approach

A growing literature has appeared in the last 2 decades with the aim to explore if the way in which publicly funded private schools are managed (a very autonomous mode) is more effective, than that applied in public schools (where decisions are highly centralized), concerning the promotion of student’s educational skills. Our paper contributes to this literature providing new evidence from the Spanish experience. To this end, we use the Spanish Assessment named “Evaluación de Diagnóstico, ” a national yearly standardized test given to students in the fourth grade and administered by the Regional Educational Authorities. In particular, our data are those corresponding to the assessment conducted in the Spanish region of Aragón in 2010. Our methodological strategy is defined by the sequential application of two methods: propensity score matching and hierarchical linear models. Additionally, the sensitivity of our estimates is also tested with respect to unobserved heterogeneity. Our results underline the existence of a slight advantage of the private management model of schools in the promotion of scientific abilities of students and in the acquisition of foreign language (English) skills

Ratchet, pawl and spring Brownian motor

We present a model for a thermal Brownian motor based on Feynman's famous ratchet and pawl device. Its main feature is that the ratchet and the pawl are in different thermal baths and connected by an harmonic spring. We simulate its dynamics, explore its main features and also derive an approximate analytical solution for the mean velocity as a function of the external torque applied and the temperatures of the baths. Such theoretical predictions and the results from numerical simulations agree within the ranges of the approximations performed.Comment: Submitted to Physica

Intraoperative ultrasound in conservative surgery for non-palpable breast cancer after neoadjuvant chemotherapy

AbstractAimsA complete clinical response after neoadjuvant chemotherapy (NACT) in breast cancer patients hinders the localization of the residual lesion and the removal of a minimum amount of breast tissue. The aim of the present work is to report our single-centre experience with intraoperative ultrasound-guided (IOUS) excision performed by surgeons in these patients.Patients and methodsFrom January 2008 to December 2012, IOUS excisions were performed on 58 patients with a previous intralesional ultrasound-detectable metallic marker and non-palpable breast cancer after NACT. The specimen margins were estimated by ultrasonography and macroscopic pathologic examination. Successful lesion removal, specimen weight, and analysis of the results as regards margins were evaluated, and the need for breast-conserving re-excision and mastectomy was considered.ResultsAfter NACT the average ultrasound/mammography and MRI diameters were 11.7 mm (0–30) and 9.1 mm (0–40) respectively. In all cases, the residual lesion or tissue around the marker was removed. The average weight of the specimens was 26.4 g (6–84), being lower in cases of complete response according to ultrasound (p < 0.05). In 4 patients (6.8%), breast-conserving re-excision was carried out, and in 3 patients (5.2%) a secondary mastectomy was performed, two of which had invasive lobular carcinoma.ConclusionsThe emplacement of a readily echodetectable metal marker before NACT makes IOUS excision feasible in an increasing number of complete clinical responses, with the excision of small amounts of breast tissue and a high percentage of conservative breast surgery. This technique requires surgeons to be trained, but has the advantage of a reduced use of other hospital services, better planning of operating theatres, and less discomfort for patients, which means that it is attractive and indeed recommendable

La maravillosa historia de los números

La maravillosa historia de los números es un cuento-relato elaborado como material de divulgación por El CSIC en la Escuela [ http://www.csicenlaescuela.csic.es ] para el portal WEB Museo Virtual de la Ciencia del CSIC [ http://museovirtual.csic.es ].PDF de 12 páginas con 21 figuras a color. Se autoriza el uso de los textos y el material gráfico del Museo Virtual de la Ciencia únicamente con fines didácticos o divulgativos y citando siempre la fuente(Museo Virtual de la Ciencia / CSIC en la Escuela) y el autor/a correspondiente. Los autores de los textos y material gráfico se encuentran a pie de cada página. Los recursos contenidos en el Museo Virtual de la Ciencia del CSIC están creados para el uso de profesionales de la enseñanza, especialmente profesores de Infantil, Primaria y Secundaria; para estudiantes de Educación Secundaria y para todo público interesado en la divulgación de la ciencia.Proponemos un cuento, una historia, una maravillosa historia de los números, para que los docentes puedan trabajar en el aula conceptos como los de número, cantidad y medida. Intentamos explicar, de forma amena, como las distintas civilizaciones han contribuido al concepto de número y por lo tanto a las matemáticas en general. Pretendemos que los maestros entiendan que los números son el alfabeto universal del lenguaje de las matemáticas y que pueden explicarse de forma divertida en clase. Material de divulgación elaborado por El CSIC en la Escuela para el Museo Virtual de la Ciencia del CSIC.Consejo Superior de Investigaciones CientíficasN

Phenomenological approach to non-linear Langevin equations

In this paper we address the problem of consistently construct Langevin equations to describe fluctuations in non-linear systems. Detailed balance severely restricts the choice of the random force, but we prove that this property together with the macroscopic knowledge of the system is not enough to determine all the properties of the random force. If the cause of the fluctuations is weakly coupled to the fluctuating variable, then the statistical properties of the random force can be completely specified. For variables odd under time-reversal, microscopic reversibility and weak coupling impose symmetry relations on the variable-dependent Onsager coefficients. We then analyze the fluctuations in two cases: Brownian motion in position space and an asymmetric diode, for which the analysis based in the master equation approach is known. We find that, to the order of validity of the Langevin equation proposed here, the phenomenological theory is in agreement with the results predicted by more microscopic models.Comment: LaTex file, 2 figures available upon request, to appear in Phys.Rev.

Intrinsic noise-induced phase transitions: beyond the noise interpretation

We discuss intrinsic noise effects in stochastic multiplicative-noise partial differential equations, which are qualitatively independent of the noise interpretation (Ito vs. Stratonovich), in particular in the context of noise-induced ordering phase transitions. We study a model which, contrary to all cases known so far, exhibits such ordering transitions when the noise is interpreted not only according to Stratonovich, but also to Ito. The main feature of this model is the absence of a linear instability at the transition point. The dynamical properties of the resulting noise-induced growth processes are studied and compared in the two interpretations and with a reference Ginzburg-Landau type model. A detailed discussion of new numerical algorithms used in both interpretations is also presented.Comment: 9 pages, 8 figures, to be published in Phys. Rev.