In situ imaging of field emission from individual carbon nanotubes and their structural damage

©2002 American Institute of Physics. The electronic version of this article is the complete one and can be found online at: http://link.aip.org/link/?APPLAB/80/856/1DOI:10.1063/1.1446994Field emission of individual carbon nanotubes was observed by in situ transmission electron microscopy. A fluctuation in emission current was due to a variation in distance between the nanotube tip and the counter electrode owing to a "head-shaking" effect of the nanotube during field emission. Strong field-induced structural damage of a nanotube occurs in two ways: a piece-by-piece and segment-by-segment pilling process of the graphitic layers, and a concentrical layer-by-layer stripping process. The former is believed owing to a strong electrostatic force, and the latter is likely due to heating produced by emission current that flowed through the most outer graphitic layers

Longitudinal spin excitations and magnetic anisotropy in antiferromagnetically ordered BaFe2As2

We report on a spin-polarized inelastic neutron scattering study of spin waves in the antiferromagnetically ordered state of BaFe2As2. Three distinct excitation components are identified, with spins fluctuating along the c-axis, perpendicular to the ordering direction in the ab-plane, and parallel to the ordering direction. While the first two "transverse" components can be described by a linear spin-wave theory with magnetic anisotropy and inter-layer coupling, the third "longitudinal" component is generically incompatible with the local moment picture. It points towards a contribution of itinerant electrons to the magnetism already in the parent compound of this family of Fe-based superconductors.Comment: 4 pages, 4 figures, plus Supplemental Materia

Atomic spatial coherence with spontaneous emission in a strong coupling cavity

The role of spontaneous emission in the interaction between a two-level atom and a pumped micro-cavity in the strong coupling regime is discussed in this paper. Especially, using a quantum Monte-Carlo simulation, we investigate atomic spatial coherence. It is found that atomic spontaneous emission destroys the coherence between neighboring lattice sites, while the cavity decay does not. Furthermore, our computation of the spatial coherence function shows that the in-site locality is little affected by the cavity decay, but greatly depends on the cavity pump amplitude.Comment: 4 pages, 5 figures, accepted by PR

Paths to Mobility Support in the Future Internet

The efficient support of various mobility types is one of the main challenges in anticipating evolutions towards the Future Internet. The European 4WARD project applies a "clean-slate" architectural approach where the Generic Path, a new communication abstraction, organizes the necessary cooperation between nodes for realising a wide range of communication services from unicast/multicast conversational services to multi point transfer between cooperating information objects. Our work addresses the challenges of supporting different mobility types in the context of Generic Paths by elaborating innovative schemes that will be further evaluated and combined in a second step. The Dynamic Mobility Anchoring proposal considers the distribution of mobility anchors in Access Nodes realising the necessary traffic indirection when hosts connectivities change. Anchorless mobility applies a more abstract approach where so called compartment are used to realise dynamic bindings between end points. A main issue for supporting wide scale mobility is the availability of a common namespace and an efficient resolution scheme. We address this issue with a high focus. Lastly considering mobile ad hoc networking as a key environment for its high level of dynamicity, we envisage the application of end to end concurrent multi-path transfer methods in such a context. Our research opens several future perspectives such as further designing, evaluating, refining and combining the different innovations and algorithms in a coherent mobility framework for Generic Paths

Famine Early Warning Systems Network (FEWS NET) Land Data Assimilation System (LDAS) and Other Assimilated Hydrological Data at NASA GES DISC

The NASA Goddard Earth Sciences Data and Information Services Center (GES DISC) provides science support for several data sets relevant to agriculture and food security, including the Famine Early Warning Systems Network (FEWS NET) Land Data Assimilation System (LDAS), or FLDAS data set. The GES DISC is one of twelve NASA Earth Observing System (EOS) data centers that process, archive, document, and distribute data from Earth science missions and related projects. The GES DISC hosts a wide range of remote sensing and model data, and provides reliable and robust data access and other services to users worldwide. Beyond data archive and access, the GES DISC offers many services to visualize and analyze the data. This presentation provides a summary of the hydrological data available at the GES DISC, along with an overview of related data services. Specifically, the FLDAS data set has been adapted to work with domains, data streams, and monitoring and forecast requirements associated with food security assessment in data-sparse, developing country settings. The FLDAS global monthly data have a 0.1 x 0.1 degree spatial resolution covering the period from January 1982 to present. Global FLDAS monthly anomaly and monthly climatology data are also available at the GES DISC to evaluate how current conditions compare to averages over the FLDAS 35-year period. Several case studies using the FLDAS soil moisture, evapotranspiration, rainfall, runoff, and surface temperature data will be presented

First Principles Studies on 3-Dimentional Strong Topological Insulators: Bi2Te3, Bi2Se3 and Sb2Te3

Bi2Se3, Bi2Te3 and Sb2Te3 compounds are recently predicted to be 3-dimentional (3D) strong topological insulators. In this paper, based on ab-initio calculations, we study in detail the topological nature and the surface states of this family compounds. The penetration depth and the spin-resolved Fermi surfaces of the surface states will be analyzed. We will also present an procedure, from which highly accurate effective Hamiltonian can be constructed, based on projected atomic Wannier functions (which keep the symmetries of the systems). Such Hamiltonian can be used to study the semi-infinite systems or slab type supercells efficiently. Finally, we discuss the 3D topological phase transition in Sb2(Te1-xSex)3 alloy system.Comment: 8 pages,17 figure

Adsorption of carbon dioxide, methane, and nitrogen on zn(Dcpa) metal-organic framework

Norma Transitória DL 57/2016 ELAC2014/BEE0367Adsorption-based processes using metal-organic frameworks (MOFs) are a promising option for carbon dioxide (CO2 ) capture from flue gases and biogas upgrading to biomethane. Here, the adsorption of CO2, methane (CH4 ), and nitrogen (N2 ) on Zn(dcpa) MOF (dcpa (2,6-dichloro-phenylacetate)) is reported. The characterization of the MOF by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), and N2 physisorption at 77 K shows that it is stable up to 650 K, and confirms previous observations suggesting framework flexibility upon exposure to guest molecules. The adsorption equilibrium isotherms of the pure components (CO2, CH4, and N2 ), measured at 273–323 K, and up to 35 bar, are Langmuirian, except for that of CO2 at 273 K, which exhibits a stepwise shape with hysteresis. The latter is accurately interpreted in terms of the osmotic thermodynamic theory, with further refinement by assuming that the free energy difference between the two metastable structures of Zn(dcpa) is a normally distributed variable due to the existence of different crystal sizes and defects in a real sample. The ideal selectivities of the equimolar mixtures of CO2 /N2 and CO2 /CH4 at 1 bar and 303 K are 12.8 and 2.9, respectively, which are large enough for Zn(dcpa) to be usable in pressure swing adsorption.publishersversionpublishe

Identifying mobility patterns of socioeconomic classes in a transportation context case study : São Carlos -SP (Brazil)

This article presents the results of a study in São Carlos (Brazil), whose goal was the characterization of mobility patterns associated with socioeconomic classes. This study helps to understand the relations between mobility patterns and socioeconomic classes and aims to demonstrate the modal choice distribution in an urban region by analyzing the socioeconomic characteristics of households. Information from an OD Survey, made in 2007, was used as database. After a geospatial location process, elaborated with a help of Geographic Information System (GIS), the database was analyzed qualitatively, in order to obtain the mobility patterns of each socioeconomic class, considering gender, age, modal choice and distance traveled. Results showed that (i) differences between modal choices in each daily trip depend on the user class; (ii) divergences between distance traveled and modal choice considering gender and age was observed in the daily trip

Two-column relay simulated moving-bed for gas-phase separations

A new two-column, relay, simulated moving bed process (2-column R-SMB) for gas-phase separations has been designed and implemented experimentally in this work. R-SMB differs from classical SMB processes by avoiding the partial withdrawal of products, since the outlet streams are handled in a relay mode. The outlet streams are either fully collected as product/waste or completely recycled to another column. In this work, the relay concept is applied for the first time in 2-column SMB processes and gas-phase separations. The process is designed and optimized through model-based computational simulation and the results obtained are validated experimentally. For the purpose, a new experimental lab-scale unit was designed and assembled. Please click Additional Files below to see the full abstract

Boolean Chaos

We observe deterministic chaos in a simple network of electronic logic gates that are not regulated by a clocking signal. The resulting power spectrum is ultra-wide-band, extending from dc to beyond 2 GHz. The observed behavior is reproduced qualitatively using an autonomously updating Boolean model with signal propagation times that depend on the recent history of the gates and filtering of pulses of short duration, whose presence is confirmed experimentally. Electronic Boolean chaos may find application as an ultra-wide-band source of radio wavesComment: 10 pages and 4 figur