Crosstalk between nanotube devices: contact and channel effects

At reduced dimensionality, Coulomb interactions play a crucial role in determining device properties. While such interactions within the same carbon nanotube have been shown to have unexpected properties, device integration and multi-nanotube devices require the consideration of inter-nanotube interactions. We present calculations of the characteristics of planar carbon nanotube transistors including interactions between semiconducting nanotubes and between semiconducting and metallic nanotubes. The results indicate that inter-tube interactions affect both the channel behavior and the contacts. For long channel devices, a separation of the order of the gate oxide thickness is necessary to eliminate inter-nanotube effects. Because of an exponential dependence of this length scale on dielectric constant, very high device densities are possible by using high-k dielectrics and embedded contacts

Retroceso de escarpes en ambientes semiáridos a partir de facetas triangulares de ladera (depresión del Ebro)

[Resumen] La evolución de las laderas en las regiones áridas puede dar lugar a la generaciónde facetas triangulares de ladera situadas al pie de relieves estructurales. Al Surde Zaragoza (Depresión del Ebro) existe un buen ejemplo de secuencias de facetas triangulares donde se pueden identificar cinco estadios de evolución de laderas (Sl a Ss' de la más reciente a la más antigua). Los depósitos de estas laderas contienen fragmentos de cerámicas, carbón vegetal y cenizas que permiten obtener dataciones relativas y absolutas. El contenido en cerámicas de las acumulaciones indica una edad final de generación posterior al siglo XIX para Sl y posterior al Bronce Medio-Final (3.500-3.100 BP) para S2. Las dataciones por Carbono-14 obtenidas son 2.529±52 BP y 2.930±60 BP para S2' 27.862±444 BP para S3 y 35.570±490 BP' para S4. La acumulación más antigua no ha podido ser datada. La extrapolación de las ecuaciones logarítmicas ajustadas a los perfiles de las facetas permite calcular los retrocesos del escarpe. Los datos obtenidos indican velocidades de retroceso del escarpe de 0.9-1 m/l.000 años para los últimos 35.000 años.[Abstract] Slope evolution in arid regions may result in the development of talus flatiron sequences at the foot of structural reliefs. A good example exists to the South of Zaragoza (Ebro Basin), where five stages of slope evolution have been identified in the talus flatiron sequences (Sl to Ss' youngest to oldest). The deposits of these slopes contain pottery remains, charcoal and ashes which permit to carry out relative and absolute datings of the slope accumulations. Based on the pottery content, the most recent accumulation stage (Sl) is post-19th century. The pottery remains of the previous one (S2) indicate an age post-Middle-Late Bronze (3.5003.100 BP) and 14C datings obtained for this accumulation are 2.529±52 BP and 2.930±60 BP. The talus flatirons S3 have provided an age of 27.862±444 BP by 14C and for S4 the age is 35.570±490 BP. The oldest accumulation has not been dated. The extrapolation of the logaritmic equation fit from the talus flatiron profiles allows to calculate the scarp retreats. The data supplied indicate rates of scarp retreat of 0.9-1 m/1.000 years over the past 35.000 years

Phase Separation Driven by External Fluctuations

The influence of external fluctuations in phase separation processes is analysed. These fluctuations arise from random variations of an external control parameter. A linear stability analysis of the homogeneous state shows that phase separation dynamics can be induced by external noise. The spatial structure of the noise is found to have a relevant role in this phenomenon. Numerical simulations confirm these results. A comparison with order-disorder noise induced phase transitions is also made.Comment: 4 pages, 4 Postscript figures included in text. LaTeX (with Revtex macros

From subdiffusion to superdiffusion of particles on solid surfaces

We present a numerical and partially analytical study of classical particles obeying a Langevin equation that describes diffusion on a surface modeled by a two dimensional potential. The potential may be either periodic or random. Depending on the potential and the damping, we observe superdiffusion, large-step diffusion, diffusion, and subdiffusion. Superdiffusive behavior is associated with low damping and is in most cases transient, albeit often long. Subdiffusive behavior is associated with highly damped particles in random potentials. In some cases subdiffusive behavior persists over our entire simulation and may be characterized as metastable. In any case, we stress that this rich variety of behaviors emerges naturally from an ordinary Langevin equation for a system described by ordinary canonical Maxwell-Boltzmann statistics

Ab initio vibrations in nonequilibrium nanowires

We review recent results on electronic and thermal transport in two different quasi one-dimensional systems: Silicon nanowires (SiNW) and atomic gold chains. For SiNW's we compute the ballistic electronic and thermal transport properties on equal footing, allowing us to make quantitative predictions for the thermoelectric properties, while for the atomic gold chains we evaluate microscopically the damping of the vibrations, due to the coupling of the chain atoms to the modes in the bulk contacts. Both approaches are based on a combination of density-functional theory, and nonequilibrium Green's functions.Comment: 16 pages, to appear in Progress in Nonequilibrium Green's Functions IV (PNGF4), Eds. M. Bonitz and K. Baltzer, Glasgow, August 200

Pinning and switching of magnetic moments in bilayer graphene

We examine the magnetic properties of the localized states induced by lattice vacancies in bilayer graphene with an unrestricted Hartree-Fock calculation. We show that with realistic values of the parameters and for experimentally accessible gate voltages we can have a magnetic switching between an unpolarized and a fully polarized system.Comment: 9 pages, 4 figure

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

An experimental methodology to characterise post-necking behaviour and quantify ductile damage accumulation in isotropic materials

The development of ductile damage, that occurs beyond the point of necking in a tensile test, can be difficult to quantify. An experimental methodology has been developed to accurately characterise the post-necking deformation response of a material through continuous monitoring of the specimens shape up until rupture. By studying the evolution of the neck geometry, the correct values of the local stress and strain have been determined in samples of grade 304L stainless steel and C110 copper. Notched bar specimens of various notch acuities were examined enabling the effects of stress triaxiality on ductile fracture to be determined. The methodology developed has provided a robust framework for macroscopic measurements of ductile damage during the necking process. To characterise the material degradation process, the elastic modulus reduction method was employed on hourglass-shaped specimens of the same materials. Stiffness degradation was measured using a small gauge extensometer during uninterrupted tensile tests with partial elastic unloadings. A metallographic study was conducted on progressively damaged specimens in order to validate the macroscopic damage measurements. A new non-linear ductile damage accumulation law has been developed and calibrated, which provides an advanced representation of the experimental results, and a significant improvement compared to linear accumulation models frequently employed. This realistic modelling approach considers the degradation of the material when it has undergone severe plastic deformation, and provides a more accurate representation of the near failure behaviour by considering the effects of stress triaxiality. The methodology provides accurate data for damage model development and calibration, to improve the predictions of remnant life from ductile damage in engineering components