Extremely simple device for measuring 20-fs pulses

We demonstrate an extremely simple frequency-resolved optical-gating device (GRENOUILLE) capable of measuring pulses with spectra wider than 100 nm. Its nearly all-reflective geometry minimizes the material dispersion, allowing accurate measurement of pulses as short as 19 fs.     

Practical issues in ultra-short-pulse measurements with ‘GRENOUILLE’

We examine the characteristics and limitations of GRENOUILLE, a simple and compact implementation of the second-harmonic-generation (SHG) frequency-resolved-optical-gating (FROG) technique. We show that it can be made to operate effectively over a relatively wide range of pulse lengths and wavelengths. We also describe procedures for its design and calibration, and we discuss the use of arbitrary nonlinear SHG crystals. PACS 42.65.-k; 42.65.ReAn erratum to this article can be found at     

Electron-stimulated reactions at the interfaces of amorphous solid water films driven by long-range energy transfer from the bulk

The electron-stimulated production of D2 from amorphous solid D2O deposited on Pt(111) is investigated as a function of film thickness. The D2 yield has two components that have distinct reaction kinetics. Using isotopically layered films of H2O and D2O demonstrates that the D2 is produced in reactions that occur at both the Pt/amorphous solid water (ASW) interface and the ASW/vacuum interface, but not in the bulk. The energy for the reactions, however, is absorbed in the bulk of the films and electronic excitations diffuse to the interfaces where they drive the reactions.     

The Cost of the Missing Bit: Communication Complexity with Help

Dedicated to the Memory of Paul Erdős We generalize the multiparty communication model of Chandra, Furst, and Lipton (1983) to functions with b-bit output (b = 1 in the CFL model). We allow the players to receive up to b - 1 bits of information from an all-powerful benevolent Helper who can see all the input. Extending results of Babai, Nisan, and Szegedy (1992) to this model, we construct families of explicit functions for which bits of communication are required to find the "missing bit", where n is the length of each player's input and k is the number of players. As a consequence we settle the problem of separating the one-way vs. multiround communication complexities (in the CFL sense) for players, extending a result of Nisan and Wigderson (1991) who demonstrated this separation for k = 3 players. As a by-product we obtain lower bounds for the multiparty complexity (in the CFL sense) of new families of explicit boolean functions (not derivable from BNS). The proofs exploit the interplay between two concepts of multicolor discrepancy; discrete Fourier analysis is the basic tool. We also include an unpublished lower bound by A. Wigderson regarding the one-way complexity of the 3-party pointer jumping function. Received November 12, 1998 RID="*" ID="*" Supported in part by NSA grant MSPR-96G-184. RID="†" ID="†" Supported in part by an NSF Graduate Fellowship.     

Modelling,simulation, animation,and real-time control (MoSART) for a class of electromechanical systems: a system-theoretic approach

This paper describes an interactive modelling, simulation, animation, and real-time control (MoSART) environment for a class of ‘cart-pendulum’ electromechanical systems that may be used to enhance learning within differential equations and linear algebra classes. The environment is useful for conveying fundamental mathematical/systems concepts through computer-aided analysis, design, graphical visualization, and 3D animation. Referred to as Cart-Pendulum Control3D-Lab1Control3D-Lab-short for control 3D animation laboratory. The author to whom correspondence should be addressed., the environment is based on Microsoft Windows/Visual C++/Direct-3D and MATLAB/Simulink2MATLAB and Simulant are trademarks of The Masterworks, Inc.. Pull-down menus provide access to systems/models/control laws, exogenous signals, parameters, animation models and visual indicators, a suite of (easy-to-modify) Simulant diagrams containing models and control laws, MATLAB m-files for detailed analysis and design, and detailed documentation for each of the above. Three blocks enable animation, joystick inputs, and real-time animation within Simulant. Examples are presented to illustrate the utility of the environment as a valuable tool for analysing/visualizing the above class of electromechanical systems and for enhancing mathematics instruction.     

The Saffman-Taylor problem for an extremely shear-thinning fluid

We consider a steady flow driven by pushing a finger of gasinto a highly shear-thinning power-law fluid, with exponentn, in a Hele-Shaw channel. We formulate the problem in termsof the streamfunction , which satisfies the p-Laplacian equation (with ), and investigate travelling wave solutions in the large-n (extreme shear-thinning) limit.We take a Legendre transform of the free-boundary problem for, which reduces it to a linear problem on a fixed domain. The solution to this problem is foundby using matched asymptotic expansions and the resulting shapeof the finger deduced (being, to leading order, a semi-infinitestrip). The nonlinear problem for the streamfunction is alsotreated using matched asymptotic expansion in the physical plane.The finger-width selection problem is briefly discussed in termsof our results.     

HUMIC MACROMOLECULES IN NATURAL WATERS

Abstract

Humic substances are the major organic constituents of soils and sediments. They also occur in small concentrations in natural surface waters and groundwaters. They form through the breakdown of plant and animal tissues by chemical and biological processes that tend to produce complex chemical structures that are more stable than the original material from which they were derived. One of the more important characteristics of humic substances is their ability to form water-soluble and water-insoluble complexes with metal ions and hydrous oxides and to interact with clay minerals and various organic compounds such as alkanes, fatty acids, and toxic organic substances such as pesticides.     

Multianalyte Microphysiometry of Macrophage Responses to Phorbol Myristate Acetate,Lipopolysaccharide, and Lipoarabinomannan

This study examined the hypothesis that mycobacterial antigens generate different metabolic responses in macrophages as compared to gram‐negative effectors and macrophage activators. To this end, we utilized platinum electrodes and a light addressable potentiometric sensor to observe dynamic electrochemical changes in metabolic flux, as well as extracellular acidification. While phorbol myristate acetate (PMA) is commonly used to study macrophage activation, the concentration used to create this physiological response varies. The response of RAW‐264.7 macrophages is concentration‐dependent, where the metabolic response to high concentrations of PMA decreases suggesting deactivation. The gram‐negative effector, lipopolysaccharide (LPS), was seen to promote oxygen production which was used to produce a delayed onset of oxidative burst. Pre‐incubation with interferon‐γ (IFN‐γ) allowed a synergistic effect between IFN‐γ and LPS, allowing immediate initiation of oxidative burst. These studies exhibited a stark contrast with lipoarabinomannan (LAM), an antigenic glycolipid component associated with the bacterial genus Mycobacterium. The presence of LAM effectively inhibits any metabolic response preventing consumption of glucose and oxygen for the promotion of oxidative burst and to ensure pathogenic proliferation. This study demonstrates for the first time the immediate inhibitory metabolic effects LAM has on macrophages, suggesting implications for future intervention studies with Mycobacterium tuberculosis.