Lifted inequalities for 0\mathord {-}1 mixed-integer bilinear covering sets

In this paper, we study $0\mathord {-}1$ mixed-integer bilinear covering sets. We derive several families of facet-defining inequalities via sequence-independent lifting techniques. We then show that these sets have a polyhedral structure that is similar to that of a certain fixed-charge single-node flow set. As a result, we also obtain new facet-defining inequalities for the single-node flow set that generalize well-known lifted flow cover inequalities from the integer programming literature.     

Explicit convex and concave envelopes through polyhedral subdivisions

In this paper, we derive explicit characterizations of convex and concave envelopes of several nonlinear functions over various subsets of a hyper-rectangle. These envelopes are obtained by identifying polyhedral subdivisions of the hyper-rectangle over which the envelopes can be constructed easily. In particular, we use these techniques to derive, in closed-form, the concave envelopes of concave-extendable supermodular functions and the convex envelopes of disjunctive convex functions.     

Electron impact total cross section calculations for CH3SH (methanethiol) from threshold to 5 keV

We report calculated total elastic cross sections Q_el, total ionisation cross sections, Q_ion, summed total excitation cross sections ∑Q_exc and total cross sections Q_T for CH₃SH upon electron impact for energies from ionisation threshold to 5 keV. We have employed Spherical Complex Optical Potential (SCOP) formalism to calculate total elastic cross section Q_el, and total inelastic cross section Q_inel and used Complex Scattering Potential – the ionisation contribution (CSP-ic) method to extract the ionisation cross sections, Q_ion, from the calculated Q_inel. The calculated total cross sections are examined as functions of incident electron energy and are compared with available data wherever possible and overall good agreement is observed. In this work Q_el, Q_ion, and ∑Q_exc are reported for the first time for CH₃SH in this energy range.     

Characteristic-based schemes for dispersive waves I. The method of characteristics for smooth solutions

In order to embark on the development of numerical schemes for stiff problems, we have studied a model of relaxing heat flow. To isolate those errors unavoidably associated with discretization, a method of characteristics is developed, containing three free parameters depending on the stiffness ratio. It is shown that such “decoupled” schemes do not take into account the interaction between the wave families and hence result in incorrect wave speeds. We also demonstrate that schemes can differ by up to two orders of magnitude in their rms errors even while maintaining second-order accuracy. We show that no method of characteristics solution can be better than second-order accurate. Next, we develop “coupled” schemes which account for the interactions, and here we obtain two additional free parameters. We demonstrate how coupling of the two wave families can be introduced in simple ways and how the results are greatly enhanced by this coupling. Finally, numerical results for several decoupled and coupled schemes are presented, and we observe that dispersion relationships can be a very useful qualitative tool for analysis of numerical algorithms for dispersive waves. © 1993 John Wiley & Sons, Inc.     

Global optimization of mixed-integer nonlinear programs: A theoretical and computational study

This work addresses the development of an efficient solution strategy for obtaining global optima of continuous, integer, and mixed-integer nonlinear programs. Towards this end, we develop novel relaxation schemes, range reduction tests, and branching strategies which we incorporate into the prototypical branch-and-bound algorithm. In the theoretical/algorithmic part of the paper, we begin by developing novel strategies for constructing linear relaxations of mixed-integer nonlinear programs and prove that these relaxations enjoy quadratic convergence properties. We then use Lagrangian/linear programming duality to develop a unifying theory of domain reduction strategies as a consequence of which we derive many range reduction strategies currently used in nonlinear programming and integer linear programming. This theory leads to new range reduction schemes, including a learning heuristic that improves initial branching decisions by relaying data across siblings in a branch-and-bound tree. Finally, we incorporate these relaxation and reduction strategies in a branch-and-bound algorithm that incorporates branching strategies that guarantee finiteness for certain classes of continuous global optimization problems. In the computational part of the paper, we describe our implementation discussing, wherever appropriate, the use of suitable data structures and associated algorithms. We present computational experience with benchmark separable concave quadratic programs, fractional 0–1 programs, and mixed-integer nonlinear programs from applications in synthesis of chemical processes, engineering design, just-in-time manufacturing, and molecular design.The research was supported in part by ExxonMobil Upstream Research Company, National Science Foundation awards DMII 95-02722, BES 98-73586, ECS 00-98770, and CTS 01-24751, and the Computational Science and Engineering Program of the University of Illinois.     

Development of a laser-induced cell lysis system

A novel cell lysis system was developed that is based on laser-induced disruption of bacterial and yeast cells. It will find application as a rapid, efficient and clean sample preparation step in bioanalytical detection systems. Using E. coli as our model analyte, we optimized cell lysis with respect to optimal laser wavelength, lowest energy input requirements, RNA release from the cells, and potential protein damage. The optimized system was finally applied to the lysis of four additional microorganisms. All experiments were carried out with about 2000 cells per sample or less. Initially, lysis was determined by the detection of cell survival after laser treatment using standard microbiological techniques, (i.e., cells were grown on nutrient agar plates). Then, actual release of mRNA from the cells was proven. Wavelengths investigated ranged from 500 nm to 1550 nm. An average power of 100 mW for the lasers was shown to be sufficient to obtain cell lysis at wavelengths above 1000 nm, with optimal wavelengths between 1250 nm and 1550 nm. Since water absorbs energy at those wavelengths, it is assumed that laser exposure results in an instantaneous increase of the cell temperature, which causes rupture of the cell membrane. Second, damage to protein solutions treated under optimized laser-lysis conditions was also studied. Using a pure solution of horseradish peroxidase as a model protein, no loss in enzyme activity was observed. Thus, it was concluded that damage to intracellular proteins is unlikely. Third, RNA release was tested using an E. coli specific RNA biosensor. Release of RNA was not detected from untreated cells, but laser-treated E. coli cells displayed significant RNA release due to laser-induced cell lysis. Finally, lysis of M. luteus, B. subtilis, B. cereus, and S. cerevisiae were investigated under optimized conditions. In all cases, laser-induced lysis of the cells was confirmed by determination of cell survival. Hence, laser-induced cell lysis is an efficient procedure that can be used for sample preparation, without damage to macromolecules, in bioanalytical detection systems for microorganisms. Miniaturized lasers and miniaturized cell-lysis chambers will create a simple, field-usable cell lysis system and allow the application of laser-induced cell lysis in micro Total Analysis Systems.     

Preparation and characterization of γ-In2Se3 thin-film photoanodes for photoelectrochemical water splitting

Journal of Solid State Electrochemistry - Indium selenide (γ-In2Se3) films were prepared using RF magnetron sputtering. Influence of deposition time on structural, optical, morphological, and...     

Development of ADPribosyl Ubiquitin Analogues to Study Enzymes Involved in Legionella Infection

Legionnaires’ disease is caused by infection with the intracellularly replicating Gram-negative bacterium Legionella pneumophila. This pathogen uses an unconventional way of ubiquitinating host proteins by generating a phosphoribosyl linkage between substrate proteins and ubiquitin by making use of an ADPribosylated ubiquitin (Ub^ADPr) intermediate. The family of SidE effector enzymes that catalyze this reaction is counteracted by Legionella hydrolases, which are called Dups. This unusual ubiquitination process is important for Legionella proliferation and understanding these processes on a molecular level might prove invaluable in finding new treatments. Herein, a modular approach is used for the synthesis of triazole-linked Ub^ADPr, and analogues thereof, and their affinity towards the hydrolase DupA is determined and hydrolysis rates are compared to natively linked Ub^ADPr. The inhibitory effects of modified Ub on the canonical eukaryotic E1-enzyme Uba1 are investigated and rationalized in the context of a high-resolution crystal structure reported herein. Finally, it is shown that synthetic Ub^ADPr analogues can be used to effectively pull-down overexpressed DupA from cell lysate.