Entropic transport: kinetics, scaling, and control mechanisms

We show that transport in the presence of entropic barriers exhibits peculiar characteristics which makes it distinctly different from that occurring through energy barriers. The constrained dynamics yields a scaling regime for the particle current and the diffusion coefficient in terms of the ratio between the work done to the particles and available thermal energy. This interesting property, genuine to the entropic nature of the barriers, can be utilized to effectively control transport through quasi-one-dimensional structures in which irregularities or tortuosity of the boundaries cause entropic effects. The accuracy of the kinetic description has been corroborated by simulations. Applications to different dynamic situations involving entropic barriers are outlined.

Entropic transport in confined media: a challenge for computational studies in biological and soft-matter systems

Transport in small-scale biological and soft-matter systems typically occurs under confinement conditions in which particles proceed through obstacles and irregularities of the boundaries that may significantly alter their trajectories. A transport model that assimilates the confinement to the presence of entropic barriers provides an efficient approach to quantify its effect on the particle current and the diffusion coefficient. We review the main peculiarities of entropic transport and treat two cases in which confinement effects play a crucial role, with the appearance of emergent properties. The presence of entropic barriers modifies the mean first-passage time distribution and therefore plays a very important role in ion transport through micro- and nano-channels. The functionality of molecular motors, modeled as Brownian ratchets, is strongly affected when the motor proceeds in a confined medium that may constitute another source of rectification. The interplay between ratchet and entropic rectification gives rise to a wide variety of dynamical behaviors, not observed when the Brownian motor proceeds in an unbounded medium. Entropic transport offers new venues of transport control and particle manipulation and new ways to engineer more efficient devices for transport at the nanoscale.

Take me away : Aplicació Android per compartir transport privat i els recursos que l'engloben

Take me away és un projecte SIG orientat a desenvolupar una aplicació mòbil per a Android que permeti cercar rutes de viatge coincidents de manera geogràfica amb l'objectiu final que els usuaris es posin en contacte per tal de compartir el transport privat i els recursos que l'engloben.

Individual differences in control of language interference in late bilinguals are mainly related to general executive abilities

Background: Recent research based on comparisons between bilinguals and monolinguals postulates that bilingualism enhances cognitive control functions, because the parallel activation of languages necessitates control of interference. In a novel approach we investigated two groups of bilinguals, distinguished by their susceptibility to cross-language interference, asking whether bilinguals with strong language control abilities ('non-switchers") have an advantage in executive functions (inhibition of irrelevant information, problem solving, planning efficiency, generative fluency and self-monitoring) compared to those bilinguals showing weaker language control abilities ('switchers"). Methods: 29 late bilinguals (21 women) were evaluated using various cognitive control neuropsychological tests [e.g., Tower of Hanoi, Ruff Figural Fluency Task, Divided Attention, Go/noGo] tapping executive functions as well as four subtests of the Wechsler Adult Intelligence Scale. The analysis involved t-tests (two independent samples). Non-switchers (n = 16) were distinguished from switchers (n = 13) by their performance observed in a bilingual picture-naming task. Results: The non-switcher group demonstrated a better performance on the Tower of Hanoi and Ruff Figural Fluency task, faster reaction time in a Go/noGo and Divided Attention task, and produced significantly fewer errors in the Tower of Hanoi, Go/noGo, and Divided Attention tasks when compared to the switchers. Non-switchers performed significantly better on two verbal subtests of the Wechsler Adult Intelligence Scale (Information and Similarity), but not on the Performance subtests (Picture Completion, Block Design). Conclusions: The present results suggest that bilinguals with stronger language control have indeed a cognitive advantage in the administered tests involving executive functions, in particular inhibition, self-monitoring, problem solving, and generative fluency, and in two of the intelligence tests. What remains unclear is the direction of the relationship between executive functions and language control abilities.

Kinesin-5/Eg5 is important for transport of CARTS from the trans-Golgi network to the cell surface

Here we report that the kinesin-5 motor Klp61F, which is known for its role in bipolar spindle formation in mitosis, is required for protein transport from the Golgi complex to the cell surface in Drosophila S2 cells. Disrupting the function of its mammalian orthologue, Eg5, in HeLa cells inhibited secretion of a protein called pancreatic adenocarcinoma up-regulated factor (PAUF) but, surprisingly, not the trafficking of vesicular stomatitis virus G protein (VSV-G) to the cell surface. We have previously reported that PAUF is transported from the trans-Golgi network (TGN) to the cell surface in specific carriers called CARTS that exclude VSV-G. Inhibition of Eg5 function did not affect the biogenesis of CARTS; however, their migration was delayed and they accumulated near the Golgi complex. Altogether, our findings reveal a surprising new role of Eg5 in nonmitotic cells in the facilitation of the transport of specific carriers, CARTS, from the TGN to the cell surface.

Entitat Metropolitana del Transport. Centre Operatiu d'Autobusos del Prat

El projecte contempla la resolució d’un Centre Operatiu d’Autobusos Metropolitans amb un programa que ha de donar cabuda a un mínim de 300 places d’aparcament de diferents mesures, tallers de manteniment, túnels de neteja, sortidors de repostatge, vestuaris, administració, oficines i serveis generals. L’emplaçament se situa en el barri de Sant Cosme del Prat de Llobregat, en un solar que esdevé la façana d’aquesta població a l’entrada a Barcelona des de l’aeroport. L’entorn el conformen els espais de protecció de les pistes que es perllonguen fins a tocar el Parc Natural del Delta del Llobregat, una zona humida protegida d’àmbit europeu. Al mateix temps, els requeriments del concurs sol•liciten mantenir un 50% de la superfície del solar com a parc urbà. Això comporta abordar la resolució d’un edifici extens, però de 3 alçades i mitja, per tal de poder encabir tot el programa. Tot i així, la proposta integra el gran volum de l’edificació en harmonia compositiva i cromàtica amb el canyissar i manté l’alçària en una cota similar a la dels edificis de l’entorn. L’àrea verda es concentra en la part de la parcel•la que té continuïtat directe amb el pati del nou Esplai del barri, per tal de optimitzar-ne l’ús. Al mateix temps, les àrees de circulació, neteja i manteniment dels autobusos se situen a la part posterior del solar, per fer-les compatibles amb la resta de requeriments funcionals i perquè la volumetria principal doni front a les vies d’entrada a l’àrea metropolitana. La cotxera està continguda en un únic volum lleugerament soterrat, per limitar l’alçària total. La construcció principal, de 120 x 55 x 14,5 metres, es troba configurada per una estructura regular que respecta les mesures i moviments dels autobusos, i per una pell consistent en una gelosia oberta en tres cares, i tancada en l’alçat nord. Aquest tancament es realitza amb prismes verticals de colors similars a la vegetació del entorn, separats harmònicament per tal de dissoldre lleument els contorns del volum. Com a contrapunt a la gran peça principal, es proposa un petit edifici vidriat que indica l’entrada a les oficines i conté les activitats administratives.Les àrees de funcionament es resumeixen en les següents:1. La circulació dels autobusos: el conjunt disposa de tres vies simultànies, una d’accés i dues de sortida, situades en línia amb dos punts de repostatge, aspiració interior i traspàs de dades i recaptacions, aptes per a ser utilitzades per tres vehicles alhora. També es disposen tres túnels de rentat previs a l’entrada a l’interior de la cotxera, amb pas per a tres carrils en by-pass. Es preveu una quarta via especial d’accés i sortida directes al taller, per situacions extraordinàries.2. La circulació dels vehicles de personal: tenen un accés i un recorregut independent al dels autobusos, amb control informatitzat. 3. La entrada peatonal de visites o personal: l’edifici disposa també d’una entrada peatonal que es produeix des de la porta principal, situada en el front del edifici administratiu.4. El edifici principal: consta de diferents nivells. El Nivell 0, a cota –1,3 m. es troba ocupat per la zona d’aparcament de vehicles privats (98 uts), l’aparcament de minibusos (20 uts), el taller d’autobusos (23 uts standard amb ITV, 2 uts articulats, 1 ut pintura articulat, 2 uts reparcions sostres), i l’àrea d’explotació i de dependències per conductors (vestidors, àrea de descans, cafeteria i espais habitables).El Nivell 1, a cota 2,4 m. està ocupat per l’aparcament de 47 autobusos de 13 m. de llarg i per 20 autobusos de 15 m.El Nivell 2, a cota 4,8 m. l’ocupen 22 places d’autobusos de 15 m., 6 places d’articulats i 37 de 13 m.El Nivell 3, a cota 7,2 m. és idèntic al Nivell 1.El Nivell 4, és idèntic al Nivell 2 i permet que la rampa continuï fins a un Nivell 5 de coberta, que excepcionalment pot convertir-se en aparcament descobert de 67 autobusos de més.La proposta contempla amb fermesa criteris de Sostenibilitat. Aquests es centren en primer lloc en la sobrietat del projecte que garanteix una organització clara en quan a circulacions i rendiment del espai i que, per tant, no malbarata més recursos dels necessaris. En segon lloc, s’aprofiten al màxim la llum i la ventilació naturals i, al mateix temps, es genera la pròpia energia per millorar la eficiència. També es resol el re-processament dels residus generats pel complex, es re-aprofiten les aigües utilitzades en els vestuaris i oficines pel rentat dels vehicles, i s’emmagatzemen les aigües pluvials per tal de complementar la generació d’energia i per escalfar amb el sol aigua calenta de neteja. En tercer lloc, es té especial cura en l’impacte ambiental del edifici, procurant adequar-lo a l’estructura urbana tant en alineacions com el alçària. També s’evita la contaminació acústica apantallant el so intern per tal de no enviar-lo a les àrees habitades, s’endrecen els accessos dels autobusos des de la rotonda de la via pública per alterar el mínim el trànsit dels veïns, i es concentra l’àrea verda en la zona on es té més contacte amb l’activitat veïnal comunitària: l’Esplai del barri.

When supply travels far beyond demand: Causes of oversupply in Spain’s transport infrastructure

Spain’s transport infrastructure policy has become a paradigmatic case of oversupply and of mismatch with demand. The massive expansion of the country’s transport infrastructure over the last decade has not been a response to demand bottlenecks or previously identified needs. For this reason, the intensity of use today on all interurban modes of transport in Spain falls well below that of other EU countries. This paper analyzes the institutional and regulatory factors that have permitted this policy, allowing us to draw lessons from the Spanish case that should help other countries avoid the pitfalls and shortcomings of Spanish policy.

When supply travels far beyond demand: Causes of oversupply in Spain’s transport infrastructure

Spain’s transport infrastructure policy has become a paradigmatic case of oversupply and of mismatch with demand. The massive expansion of the country’s transport infrastructure over the last decade has not been a response to demand bottlenecks or previously identified needs. For this reason, the intensity of use today on all interurban modes of transport in Spain falls well below that of other EU countries. This paper analyzes the institutional and regulatory factors that have permitted this policy, allowing us to draw lessons from the Spanish case that should help other countries avoid the pitfalls and shortcomings of Spanish policy.

Estudi d'un model de transport turístic en zona d'alta muntanya

El projecte consisteix en fer un estudi de viabilitat en funció de les limitacions que ofereixen unes instal·lacions de funicular i carrilet situades a la Vall Fosca i dels requeriments marcats per la seva història i la seva ubicació. Un cop finalitzat l'estudi, es procedeix al disseny d'un tren apte per les instal·lacions existents. El tren es compon bàsicament per una locomotora d'acumuladors, quatre bogis i quatre cotxes de passatgers. També es consideren els treballs de recuperació de la via malmesa pel pas dels anys.

Transport i emmagatzematge de les àmfores en l'antiguitat:l'aportació de les ciències dels materials

[spa]Las ánforas son ejemplos claros de cerámicas utilitarias que requieren de unas características técnicas necesarias para cumplir su funcionalidad: servir de envase de almacenamiento y transporte. En este trabajo se propone el estudio del comportamiento funcional de estos envases a través de la evaluación de las propiedades mecánicas de resistencia y tenacidad a la fractura. Propiedades mecánicas, ámforas ibéricas, ámforas romanas, tecnología, funcionalidad.

Investigation of defect formation and electronic transport in microcrystalline silicon deposited by hot-wire CVD

We have investigated doped and undoped layers of microcrystalline silicon prepared by hot-wire chemical vapour deposition optically, electrically and by means of transmission electron microscopy. Besides needle-like crystals grown perpendicular to the substrate's surface, all of the layers contained a noncrystalline phase with a volume fraction between 4% and 25%. A high oxygen content of several per cent in the porous phase was detected by electron energy loss spectrometry. Deep-level transient spectroscopy of the crystals suggests that the concentration of electrically active defects is less than 1% of the undoped background concentration of typically 10^17 cm -3. Frequency-dependent measurements of the conductance and capacitance perpendicular to the substrate surface showed that a hopping process takes place within the noncrystalline phase parallel to the conduction in the crystals. The parasitic contribution to the electrical circuit arising from the porous phase is believed to be an important loss mechanism in the output of a pin-structured photovoltaic solar cell deposited by hot-wire CVD.

Current transport and electroluminescence mechanisms in thin SiO2 films containing Si nanocluster-sensitized erbium ions.

We have studied the current transport and electroluminescence properties of metal oxide semiconductor MOS devices in which the oxide layer, which is codoped with silicon nanoclusters and erbium ions, is made by magnetron sputtering. Electrical measurements have allowed us to identify a Poole-Frenkel conduction mechanism. We observe an important contribution of the Si nanoclusters to the conduction in silicon oxide films, and no evidence of Fowler-Nordheim tunneling. The results suggest that the electroluminescence of the erbium ions in these layers is generated by energy transfer from the Si nanoparticles. Finally, we report an electroluminescence power efficiency above 10−3%. © 2009 American Institute of Physics. doi:10.1063/1.3213386

Electrical pump & probe and injected carrier losses quantification in Er doped Si slot waveguides

Electrically driven Er3+ doped Si slot waveguides emitting at 1530 nm are demonstrated. Two different Er3+ doped active layers were fabricated in the slot region: a pure SiO2 and a Si-rich oxide. Pulsed polarization driving of the waveguides was used to characterize the time response of the electroluminescence (EL) and of the signal probe transmission in 1 mm long waveguides. Injected carrier absorption losses modulate the EL signal and, since the carrier lifetime is much smaller than that of Er3+ ions, a sharp EL peak was observed when the polarization was switched off. A time-resolved electrical pump & probe measurement in combination with lock-in amplifier techniques allowed to quantify the injected carrier absorption losses. We found an extinction ratio of 6 dB, passive propagation losses of about 4 dB/mm, and a spectral bandwidth > 25 nm at an effective d.c. power consumption of 120 μW. All these performances suggest the usage of these devices as electro-optical modulators.

A Database of >20 keV Electron Green's Functions of Interplanetary Transport at 1 AU

We use interplanetary transport simulations to compute a database of electron Green's functions, i.e., differential intensities resulting at the spacecraft position from an impulsive injection of energetic (>20 keV) electrons close to the Sun, for a large number of values of two standard interplanetary transport parameters: the scattering mean free path and the solar wind speed. The nominal energy channels of the ACE, STEREO, and Wind spacecraft have been used in the interplanetary transport simulations to conceive a unique tool for the study of near-relativistic electron events observed at 1 AU. In this paper, we quantify the characteristic times of the Green's functions (onset and peak time, rise and decay phase duration) as a function of the interplanetary transport conditions. We use the database to calculate the FWHM of the pitch-angle distributions at different times of the event and under different scattering conditions. This allows us to provide a first quantitative result that can be compared with observations, and to assess the validity of the frequently used term beam-like pitch-angle distribution.

The embryonic blood-CSF barrier has molecular elements for specific glucose transport and for the general transport of molecules via transcellular routes.

In vertebrates, early brain development takes place at the expanded anterior end of the neural tube, which is filled with embryonic cerebrospinal fluid (E-CSF). We have recently identified a transient blood-CSF barrier that forms between embryonic days E3 and E4 in chick embryos and that is responsible for the transport of proteins and control of E-CSF homeostasis, including osmolarity. Here we examined the presence of glucose transporter GLUT-1 as well the presence of caveolae-structural protein Caveolin1 (CAV-1) in the embryonic blood-CSF barrier which may be involved in the transport of glucose and of proteins, water and ions respectively across the neuroectoderm. In this paper we demonstrate the presence of GLUT-1 and CAV-1 in endothelial cells of blood vessels as well as in adjacent neuroectodermal cells, located in the embryonic blood-CSF barrier. In blood vessels, these proteins were detected as early as E4 in chick embryos and E12.7 in rat embryos, i.e. the point at which the embryonic blood-CSF barrier acquires this function. In the neuroectoderm of the embryonic blood-CSF barrier, GLUT-1 was also detected at E4 and E12.7 respectively, and CAV-1 was detected shortly thereafter in both experimental models. These experiments contribute to delineating the extent to which the blood-CSF embryonic barrier controls E-CSF composition and homeostasis during early stages of brain development in avians and mammals. Our results suggest the regulation of glucose transport to the E-CSF by means of GLUT-1 and also suggest a mechanism by which proteins are transported via transcellular routes across the neuroectoderm, thus reinforcing the crucial role of E-CSF in brain development.