Pacific Northwest National Laboratory

About: Pacific Northwest National Laboratory is a facility organization based out in Richland, Washington, United States. It is known for research contribution in the topics: Catalysis & Aerosol. The organization has 11581 authors who have published 27934 publications receiving 1120489 citations. The organization is also known as: PNL & PNNL.

Graphene/TiO2 nanocomposites: synthesis, characterization and application in hydrogen evolution from water photocatalytic splitting

Abstract: A series of titanium dioxide and graphene sheets (GSs) composites were synthesized with a sol–gel method using tetrabutyl titanate and graphite oxide (GO) as the starting materials. The obtained TiO2/GSs photocatalysts are characterized by X-ray diffraction, N2 adsorption analysis, Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy. The photocatalytic activity of the as-prepared samples was evaluated by hydrogen evolution from water photo-splitting under UV-vis illumination. The influence of GSs content and calcinations atmosphere on the photocatalytic activity was also investigated. The results show that both GSs content and the calcinations atmosphere can affect the photocatalytic activity of the obtained composites.

Economic and environmental choices in the stabilization of atmospheric CO2concentrations

Abstract: THE ultimate goal of the UN Framework Convention on Climate Change is to achieve "stabilization of greenhouse-gas concentrations at a level that would prevent dangerous anthropogenic interference with the climate system". With the concentration targets yet to be determined, Working Group I of the Intergovernmental Panel on Climate Change developed a set of illustrative pathways for stabilizing the atmospheric CO2 concentration at 350, 450, 550, 650 and 750 p.p.m.v. over the next few hundred years1,2. But no attempt was made to determine whether the implied emissions might constitute a realistic transition away from the current heavy dependence on fossil fuels. Here we devise new stabilization profiles that explicitly (albeit qualitatively) incorporate considerations of the global economic system, estimate the corresponding anthropogenic emissions requirements, and assess the significance of the profiles in terms of global-mean temperature and sea level changes. Our findings raise a number of important issues for those engaged in climate-change policy making, particularly with regard to the optimal timing of mitigation measures.

Theory of Nanometric Optical Tweezers

Abstract: We propose a scheme for optical trapping and alignment of dielectric particles in aqueous environments at the nanometer scale. The scheme is based on the highly enhanced electric field close to a laser-illuminated metal tip and the strong mechanical forces and torque associated with these fields. We obtain a rigorous solution of Maxwell’s equations for the electromagnetic fields near the tip and calculate the trapping potentials for a dielectric particle beyond the Rayleigh approximation. The results indicate the feasibility of the scheme. [S0031-9007(97)03687-9] Optical trapping by highly focused laser beams has been extensively used for the manipulation of submicronsize particles and biological structures [1]. Conventional optical tweezers rely on the field gradients near the focus of a laser beam which give rise to a trapping force towards the focus. The trapping volume of these tweezers is diffraction limited. Near-field optical microscopy enables the optical measurements at dimensions beyond the diffraction limit and makes it possible to optically monitor dynamics of single biomolecules [2]. The potential application of optical near fields to manipulate atoms or nanoparticles has been discussed in Ref. [3]. In this Letter, we present a new methodology for calculating rigorously and self-consistently the trapping forces acting on a nanometric particle in the optical near field and propose a novel high-resolution trapping scheme. The proposed nanometric optical tweezers rely on the strongly enhanced electric field at a sharply pointed metal tip under laser illumination. The near field close to the tip mainly consists of evanescent components which decay rapidly with distance from the tip. The utilization of the metal tip for optical trapping offers the following advantages: (1) The highly confined evanescent fields significantly reduce the trapping volume; (2) the large field gradients result in a larger trapping force; and (3) the field enhancement allows the reduction of illumination power and radiation damages to the sample. High resolution surface modification based on the field enhancement at laser-illuminated metal tips has been recently demonstrated [4]. It is essential to perform a rigorous electromagnetic analysis to understand the underlying mechanism for the field enhancement. Our analysis is therefore relevant not only to optical tweezers, but also to other applications, such as surface modification, nonlinear spectroscopy and near-field optical imaging. To solve Maxwell’s equations in the specific geometry of the tip and its environment, we employ the multiple multipole method (MMP) which recently has been applied to various near-field optical problems [5]. In MMP, electromagnetic fields are represented by a series expansion of known analytical solutions of Maxwell’s equations. To determine the unknown coefficients in the series expansion, boundary conditions are imposed at discrete points on the interfaces between adjacent homogeneous domains. Once the resulting system of equations is solved and the coefficients are determined, the solution is represented by a self-consistent analytical expression. Figure 1 shows our three dimensional MMP simulation of the foremost part of a gold tip (5 nm tip radius) in water for two different monochromatic plane-wave excitations. The wavelength of the illuminating light is l › 810 nm (Ti:sapphire laser), which does not match the surface plasmon resonance. The dielectric constants of tip and water were taken to be « › 224.9 1 1.57i and « › 1.77, respectively [6]. In Fig. 1(a), a plane wave is incident from the bottom with the polarization perpendicular to the tip axis, whereas in Fig. 1( b) the tip is illuminated from the side with the polarization parallel to the tip axis. A striking difference is seen for the two different polarizations: in Fig. 1( b), the intensity

Methods for Fault Detection, Diagnostics and Prognostics for Building Systems - A Review Part II

Abstract: This paper is the second of a two-part review of methods for automated fault detection and diagnostics (FDD) and prognostics whose intent is to increase awareness of the HVAC&R research and development community to the body of FDD and prognostics developments in other fields as well as advancements in the field of HVAC&R. The first part of the review focused on generic FDD and prognostics, provided a framework for categorizing methods, described them, and identified their primary strengths and weaknesses (Katipamula and Brambley 2005). In this paper we address research and applications specific to the fields of HVAC&R, provide a brief discussion on the current state of diagnostics in buildings, and discuss the future of automated diagnostics in buildings.

Automatic Keyword Extraction from Individual Documents

Abstract: Keywords, which we define as a sequence of one or more words, provide a compact representation of a document’s content. Ideally, keywords represent in condensed form the essential content of a document.