A stable Langevin model with diffusive-reflective boundary conditions

In this note, we consider the construction of a one-dimensional stable Langevin type process confined in the upper half-plane and submitted to reflective-diffusive boundary conditions whenever the particle position hits 0. We show that two main different regimes appear according to the values of the chosen parameters. We then use this study to construct the law of a (free) stable Langevin process conditioned to stay positive, thus extending earlier works on integrated Brownian motion. This construction further allows to obtain the exact asymptotics of the persistence probability of the integrated stable L{\'e}vy process. In addition, the paper is concluded by solving the associated trace problem in the symmetric case

Effectiveness of Asynchronous Reference Services for Distance Learning Students Within Florida\u27s Community College System

The impact of distance learning on higher education and the need to provide equitable library services to students in the digital environment emerged as critical areas during the 1990s. Library services available to distance learning students included digital reference and instructional services, remote access to online research tools, database and research tutorials, interlibrary loan, and document delivery. Digital reference services appeared to be one of the more significant services proffered by academic libraries although these services were developed often without forethought to goals and assessment. The purpose of this study was to examine the adequacy of asynchronous e-mail reference services offered through Florida\u27s 28 community college libraries and the contribution of these digital reference service providers to the students\u27 online learning community. The researcher analyzed data obtained through an unobtrusive study of asynchronous digital reference services and interviews conducted with digital reference service providers. Studies existed for traditional and telephone reference service; however, the literature lacked studies addressing asynchronous digital reference service. Results from the unobtrusive portion of this study showed that the researcher received 240 of a possible 392 responses from the digital reference service providers. The researcher scored 24% as accurate with source information, 4% as accurate without source information, 20% as partly accurate with source information, and 7% as partly accurate without source information. The students scored 48% as accurate with source information, 12% as accurate without source information, 17% as partly accurate with source information, and 9% as partly accurate without source information. Responses took anywhere from 6 seconds to 20 days. The communication techniques exercised by the DRSPs were substandard. The study resulted in recommendations for the areas of digital environment, unobtrusive methodology, standards, accuracy, measurements, online relationships, training of digital reference service providers, student training, institutional responsibility, and marketing

Electronic, dynamical and superconducting properties of CaBeSi

We report first-principles calculations on the normal and superconducting state of CaBe(x)Si(2-x) (x=1), in the framework of density functional theory for superconductors (SCDFT). CaBeSi is isostructural and isoelectronic to MgB2 and this makes possible a direct comparison of the electronic and vibrational properties and the electron-phonon interaction of the two materials. Despite the many similarities with MgB2 (e.g. sigma bands at the Fermi level and a larger Fermi surface nesting), according to our calculations CaBeSi has a very low critical temperature (Tc ~ 0.4 K, consistent with the experiment). CaBeSi exhibits a complex gap structure, with three gaps at Fermi level: besides the two sigma and pi gaps, present also in MgB2, the appearance of a third gap is related to the anisotropy of the Coulomb repulsion, acting in different way on the bonding and antibonding electronic pi states.Comment: 6 pages, 5 figure

Memory in a Contact Line

We study the behavior of the liquid-solid-vapor contact line of water held in a narrow gap between two plates. A syringe pump injects and withdraws a constant, small volume of the water, driving the contact line back and forth repeatedly and changing its shape. We take photos of the contact line after each cycle. Comparing subsequent images to each other, we find that after several cycles the contact line reaches one of two steady states: a reversible steady state, where the shape is not changing, or a fluctuating steady state, where the shape continues to change slightly. Experiments on acrylic plates show a fluctuating steady state at higher volumes, while experiments on glass plates become reversible even at high volumes. This behavior motivated the search for return point memory in the contact line on glass plates. On glass, we train the contact line with a certain volume to reach a steady state, which we show is erased by larger volumes but not smaller volumes. This suggests memory exists, and that the trained volume can be stored as information in the contact line

Alloyed surfaces: new substrates for graphene growth

We report a systematic ab-initio density functional theory investigation of Ni(111) surface alloyed with elements of group IV (Si, Ge and Sn), demonstrating the possibility to use it to grow high quality graphene. Ni(111) surface represents an ideal substrate for graphene, due to its catalytic properties and perfect matching with the graphene lattice constant. However, Dirac bands of graphene growth on Ni(111) are completely destroyed due to the strong hybridization between carbon pz and Ni d orbitals. Group IV atoms, namely Si, Ge and Sn, once deposited on Ni(111) surface, form an ordered alloyed surface with √ 3 × √ 3-R30◦ reconstruction. We demonstrate that, at variance with the pure Ni(111) surface, alloyed surfaces effectively decouple graphene from the substrate, resulting unstrained due to the nearly perfect lattice matching and preserves linear Dirac bands without the strong hybridization with Ni d states. The proposed surfaces can be prepared before graphene growth without resorting on post-growth processes which necessarily alter the electronic and structural properties of graphene

Static and Dynamical Susceptibility of LaO1-xFxFeAs

The mechanism of superconductivity and magnetism and their possible interplay have recently been under debate in pnictides. A likely pairing mechanism includes an important role of spin fluctuations and can be expressed in terms of the magnetic susceptibility chi. The latter is therefore a key quantity in the determination of both the magnetic properties of the system in the normal state, and of the contribution of spin fluctuations to the pairing potential. A basic ingredient to obtain chi is the independent-electron susceptibility chi0. Using LaO1-xFxFeAs as a prototype material, in this report we present a detailed ab-initio study of chi0(q,omega), as a function of doping and of the internal atomic positions. The resulting static chi0(q,0) is consistent with both the observed M-point related magnetic stripe phase in the parent compound, and with the existence of incommensurate magnetic structures predicted by ab-initio calculations upon doping.Comment: 15 pages, 8 figure

Desempenho da bananeira em diferentes manejos do solo no sistema orgânico.

A banana (Musa spp.), uma das frutas mais consumidas mundialmente, é cultivada na maioria dos países tropicais. A produção mundial de banana em 2009 foi de aproximadamente 97,3 milhões de toneladas, ocupando o Brasil a quinta posição (7,0%). Apesar da grande área cultivada com banana no Brasil (480 mil hectares) não existem dados disponíveis quanto ao montante destinado ao manejo orgânico; contudo, em todos os polos de produção de banana de Norte a Sul do País existem plantações sob esse manejo.PDF. 140_11

Reversible Motion In a Contact Line

When a body of liquid sits on a surface, an irregular border between the wet and dry regions of the surface exists, called the contact line. Driving this contact line back and forth repeatedly can change its shape.We use a syringe pump to cyclically infuse and withdraw a predetermined volume of water, and take photos of the contact line after each cycle. Comparing these images to each other determines if the contact line is returning to the same shape. We find that below a critical value of infused volume, after many cycles the contact line reaches a steady state in which it always returns to the same shape. Above that value the shape fluctuates in the steady state. This suggests a transition similar to that seen in other systems like particle suspensions and solids