Differential cross sections for collisions of hexapole state-selected NO with He

The first measurements of differential inelastic collision cross sections of fully state-selected NO (j=12, Omega=12, epsilon= -1) with He are presented. Full state selection is achieved by a 2 m long hexapole, which allows for a systematic study of the effect of parity conservation and breaking on the differential cross section. The collisionally excited NO molecules are detected using a resonant (1+1') REMPI ionization scheme in combination with the velocity-mapped, ion-imaging technique. The current experimental configuration minimizes the contribution of noncolliding NO molecules in other rotational states j, Omega, epsilon--that contaminates images--and allows for study of the collision process at an unprecedented level of detail. A simple method to correct ion images for collision-induced alignment is presented as well and its performance is demonstrated. The present results show a significant difference between differential cross sections for scattering into the upper and lower component of the Lambda-doublet of NO. This result cannot be due to the energy splitting between these components.     

Lens epithelial cell response to polymer stiffness and polymer chemistry

Posterior capsule opacification (PCO) is the most common complication of cataract surgery, and intraocular lens (IOL) implantation is the standard of care for cataract patients. Induction of postoperative epithelial-mesenchymal transition (EMT) in residual lens epithelial cells (LEC) is the main mechanism by which PCO forms. Previous studies have shown that IOLs made with different materials have varying incidence of PCO. The aim of this paper was to study the interactions between human (h)LEC and polymer substrates. Polymers and copolymers of 2-hydroxyethyl methacrylate (HEMA) and 3-methacryloxypropyl tris(trimethylsiloxy)silane (TRIS) were synthesized and evaluated due to the clinical use of these materials as ocular biomaterials and implants. The chemical properties of the polymer surfaces were evaluated by contact angle, and polymer stiffness and roughness were measured using atomic force microscopy. In vitro studies showed the effect of polymer mechanical properties on the behavior of hLECs. Stiffer polymers increased α-smooth muscle actin expression and induced cell elongation. Hydrophobic and rough polymer surfaces increased cell attachment. These results demonstrate that attachment of hLECs on different surfaces is affected by surface properties in vitro, and evaluating these properties may be useful for investigating prevention of PCO.     

General N-Body Theory of Nonrelativistic Quantum Scattering

 The two-Hilbert-space theory of scattering is reviewed with particular reference to its application to nonrelativistic multichannel quantum- mechanical scattering theory. In Part I the abstract assumptions of the theory are collected, transition operators (both on- and off-energy-shell) are defined, the dynamical equations that determine the off-shell transition operators are presented and their real-energy limits examined, and the convergence of sequences of approximate transition operators is established. A section on how to incorporate group symmetries into the formalism reports new work. The material of Part I is relevant to a variety of both classical and quantum scattering systems. In Part II attention is directed specifically to N-body nonrelativistic quantum scattering systems in which the particles interact via short-range pair potentials. A method of constructing approximate transition operators is presented and shown to satisfy all the abstract assumptions of Part I. The dynamical equations that determine the half-on-shell approximate transition operators are shown to be coupled one-dimensional integral equations that have compact kernels and unique solutions when considered as operators on a Hilbert space of H?lder continuous functions. Moreover, the on-shell parts of those approximate transition amplitudes are shown to converge to the exact on-shell amplitudes as the order of the approximation increases. Detailed formulas for the kernels of the integral equations are written down for systems of particles that are distinguishable and for systems containing identical particles. Finally, some important open problems are described. Received July 2, 1999; accepted in final form October 27, 1999     

Investigation of prolate-oblate shape-coexistence in 74Kr

The atomic nucleus ⁷⁴Kr has been investigated using combined conversion-electron (CE) and γ-ray spectroscopy. In order to confirm the existence of the expected low-lying isomeric 0⁺ ₂ state, the possibility of an electric-monopole (E0) decay to the ground state was examined. The observation of an E0 transition at 508 keV allowed the determination of the mixing between coexisting prolate and oblate shapes. Received: 16 November 1998     

Trench formation and lateral damage induced by gallium milling of silicon

Molecular dynamics simulations are performed to model the nanomachining of materials via focused ion beams (FIBs). The goal of this research is to investigate the fundamental dynamics which govern the interaction of FIB with materials which are vital to the semiconductor industry, namely silicon. Specifically, we focus on the formation of trenches/holes within the sample and the dynamics responsible for their characteristic v-shape, as well as the extent of lateral damage due to a gallium beam. These phenomena have been successfully modelled, with evidence that the lateral and subsurface damage created is much larger than the beam itself. The results presented here begin to elucidate the dynamics governing the spatial resolution of these experiments, and provide an idea of some of the technical issues associated with these beams.     

Ueber die Anwendung des Spectroskopes zum Probiren von Metalllegirungen

Ohne Zusammenfassung     

Time-resolved X-ray spectroscopy of hot spots in an X-pinch

The plasma parameters in hot spots of an X-pinch are determined by using time-resolved data from X-ray spectroscopy in experiments on the implosion of crossed Ti wires in the XP device with a current of 480 kA and pulse duration of 100 ns. The electron densities and temperatures calculated from these data are in the ranges (0.8–3)×10²³cm^–3 and 1–2.5 keV, respectively. An analysis performed shows that the plasma processes are highly nonequilibrium.     

Tunable solvation effects on the size-selective fractionation of metal nanoparticles in CO2 gas-expanded solvents

This paper presents an environmentally friendly, inexpensive, rapid, and efficient process for size-selective fractionation of polydisperse metal nanoparticle dispersions into multiple narrow size populations. The dispersibility of ligand-stabilized silver and gold nanoparticles is controlled by altering the ligand tails-solvent interaction (solvation) by the addition of carbon dioxide (CO2) gas as an antisolvent, thereby tailoring the bulk solvent strength. This is accomplished by adjusting the CO2 pressure over the liquid, resulting in a simple means to tune the nanoparticle precipitation by size. This study also details the influence of various factors on the size-separation process, such as the types of metal, ligand, and solvent, as well as the use of recursive fractionation and the time allowed for settling during each fractionation step. The pressure range required for the precipitation process is the same for both the silver and gold particles capped with dodecanethiol ligands. A change in ligand or solvent length has an effect on the interaction between the solvent and the ligand tails and therefore the pressure range required for precipitation. Stronger interactions between solvent and ligand tails require greater CO2 pressure to precipitate the particles. Temperature is another variable that impacts the dispersibility of the nanoparticles through changes in the density and the mole fraction of CO2 in the gas-expanded liquids. Recursive fractionation for a given system within a particular pressure range (solvent strength) further reduces the polydispersity of the fraction obtained within that pressure range. Specifically, this work utilizes the highly tunable solvent properties of organic/CO2 solvent mixtures to selectively size-separate dispersions of polydisperse nanoparticles (2 to 12 nm) into more monodisperse fractions (+/-2 nm). In addition to providing efficient separation of the particles, this process also allows all of the solvent and antisolvent to be recovered, thereby rendering it a green solvent process.     

Extending the Kantorovic̆ inequality to normal matrices

Let A be a normal, strictly accretive matrix. The value of min{(Reχ¹A)χ/|χ| |Aχ| : χ≠0} is found, in terms of the spectrum of A. The result is, in the special case of A self-adjoint, a form of the Kantorovic? inequality.