The Effective Cross Section

The effection cross section concept for low intensity light illumination of gas discharges is shown to be analogous to high intensity breakdown of gases as interpreted by Panarella's "effective photon" concept. This mathematical result is suggested as a possible interpretation of strikingly similar nonlinearities of gas breakdown by light measured in both cases at their respectively different intensity levels.     

Simultaneous hypervirial relations for approximate wavefunctions

An approximate wavefunction can systematically be improved by requiring simultaneous satisfaction of any set of hypervirial relations. When the operators involved form a Lie algebra, the connection between the conditions for extremum and the hypervirial relations takes a particularly simple form. For this case stability conditions are also obtained.     

Novel synthetic approach in microwave-assisted solid-supported oxidations using ‘in situ’ generated molecular oxygen

Three different types of oxidation reactions were carried out under microwave (MW) conditions in dry media, with nearly quantitative yield, using ‘in situ’, yet separately generated molecular oxygen as the reactive gas. The latter is formed by a controlled decomposition of potassium chlorate (220-306 °C) adsorbed on zeolite support, and is used as a reactive oxidizing agent for the solid-supported oxidations. The MW-assisted oxidations include an oxidative decomplexation of (η⁶-arene)Cr(CO)₃ complexes to the corresponding arenes using silica as solid support (100 °C), an oxidation of fluorene to fluorenone induced by KF-alumina support (150 °C), and oxidation of benzyl alcohol to benzaldehyde using a supported ruthenium catalyst (150 °C). This synthetic approach allows to carry out in synchronized manner two different solid-supported reactions (oxygen generation and oxidation) at different temperatures and on different solid supports together in the same sealed system. It was made possible by tuning the absorption efficiency of MWs through accurate selection of the solid supports employed in the reactions. The high feasibility of this novel synthetic approach resulted from a preliminary study of the interaction between MWs and mineral oxides such as alumina, silica, clay, and zeolite particularly when mixed with additives such as water, ionic liquids or graphite (5% w/w). The use of these MW absorber additives allows the MW transparent or poorly absorbing mineral oxides to be efficiently heated to very high temperatures in few minutes.     

Reduced-order model for laminar vortex-induced vibration of a rigid circular cylinder with an internal nonlinear absorber

The nonlinear interaction of a laminar flow and a sprung rigid circular cylinder results in vortex-induced vibration (VIV) of the cylinder. Passive suppression of the VIV by attaching an internal nonlinear vibration absorber that acts, in essence, as a nonlinear energy sink (NES) to the cylinder has been observed in finite-element computations involving thousands of degrees of freedom (DOF). A single-DOF self-excited oscillator is developed to approximate the limit-cycle oscillation (LCO) of the cylinder undergoing VIV. This self-excited oscillator models the interaction of the flow and the cylinder. Then, a two-DOF reduced-order model for the system with the internal NES is constructed by coupling the single-DOF NES to the single-DOF self-excited oscillator. Hence, the complicated high-dimensional system of flow-cylinder-NES involving thousands of DOF is reduced to a two-DOF model. The two targeted energy transfer mechanisms responsible for passive VIV suppression that are observed in the finite-element computations are fully reproduced using the two-DOF reduced-order model. This reduction of the dynamics to an easily tractable low-dimensional reduced-order model facilitates the approximate analysis of the underlying dynamics. Moreover, the underlying assumptions of the order reduction, and the parameter ranges of validity of the reduced-order model are formulated and systematically studied.     

Introduction to biology and chromosomal instabilities in cancer

The recent decade has witnessed a surge of physicists to biology. Some of the activities of the participating groups focus on bona fide physics questions, posed on biological systems (such as the physics of molecular motors, for example). Another kind of research in which physicists take part alongside computer scientists and applied mathematicians, deals with questions that are of direct interest to biologists; they come under the umbrella of computational and systems biology. The topic of these lectures lies at the most biological end of this spectrum, addressing problems of clinical relevance which were posed and initiated by biologists.The objective of these lectures is to help the curious physicist to learn and to understand more about this emerging, highly interdisciplinary field of research, by providing brief introductions to molecular biology and cancer research. This is followed by a cursory review of some recent research done by the “Domany group” and its collaborations with biological and clinical labs. Furthermore, we mention (mainly in footnotes) a small subset of studies in which physicists have contributed to this field during the past years. A more detailed review of recent contributions by physicists is beyond the scope of this introductory text.The introductory nature of these lecture notes naturally induces a strong bias regarding publications cited; consequently, these lecture notes do not provide a fair, historically correct and updated review of relevant literature.     

Manufacturability of Electronic Chips

If the size of features on a microchip are of order of or smaller than the wavelength of the light used in their manufacture, manufacturability of the chip suffers due to diffraction. The degrading effect of diffraction can be handled by biasing masks used for patterning the chips and by optimizing optical system (stepper) parameters. In this paper, algorithms for biasing masks and optimizing stepper parameters are designed and implemented. The algorithms are efficient and feasible for industrial size masks. Received 16 January 1997 and accepted 23 April 1997     

Rapid and sensitive identification of ricin in environmental samples based on lactamyl agarose beads using LC‐MS/MS (MRM)

Ricin, a plant‐derived toxin extracted from the seeds of Ricinus communis (castor bean plant), is one of the most toxic proteins known. Ricin's high toxicity, widespread availability, and ease of its extraction make it a potential agent for bioterrorist attacks. Most ricin detection methods are based on immunoassays. These methods may suffer from low efficiency in matrices containing interfering substances, or from false positive results due to antibody cross reactivity, with highly homologous proteins. In this study, we have developed a simple, rapid, sensitive, and selective mass spectrometry assay, for the identification of ricin in complex environmental samples. This assay involves three main stages: (a) Ricin affinity capture by commercial lactamyl‐agarose (LA) beads. (b) Tryptic digestion. (c) LC‐MS/MS (MRM) analysis of tryptic fragments. The assay was validated using 60 diverse environmental samples such as soil, asphalt, and vegetation, taken from various geographic regions. The assay's selectivity was established in the presence of high concentrations of competing lectin interferences. Based on our findings, we have defined strict criteria for unambiguous identification of ricin. Our novel method, which combines affinity capture beads followed by MRM‐based analysis, enabled the identification of 1 ppb ricin spiked into complex environmental matrices. This methodology has the potential to be extended for the identification of ricin in body fluids from individuals exposed (deliberately or accidentally) to the toxin, contaminated food or for the detection of the entire family of RIP‐II toxins, by applying multiplex format.     

Fixing the fixed-point system—Applying Dynamic Renormalization Group to systems with long-range interactions

In this paper, a mode of using the Dynamic Renormalization Group (DRG) method is suggested in order to cope with inconsistent results obtained when applying it to a continuous family of one-dimensional nonlocal models. The key observation is that the correct fixed-point dynamical system has to be identified during the analysis in order to account for all the relevant terms that are generated under renormalization. This is well established for static problems, however poorly implemented in dynamical ones. An application of this approach to a nonlocal extension of the Kardar–Parisi–Zhang equation resolves certain problems in one-dimension. Namely, obviously problematic predictions are eliminated and the existing exact analytic results are recovered.     

A Two-Dimensional Ising Model in a Magnetic Field—A Scalar Representation of the Partition Function

The partition function of the two-dimensional Ising model in the presence of a magnetic field is expressed as a fourfold integral of a double product of elementary functions. The correlation functions and the magnetization per site are obtained as well.     

Proposed structure of hydrogen on Ni(111)

Recent observation of an order-disorder transition in H on Ni(111) is interpreted as indicating a transition to a (2 × 2) honeycomb state. Comparison with theoretical calculations leads us to infer that third neighbor attractions in addition to first and second-neighbor repulsions are present. The magnitude of the latter repulsion is estimated.