Ultraviolet Absorption and Luminescence Investigations

Ultraviolet photographic system for remote detection of luminescent minerals and rocks and discriminating among nonluminescent materials on basis of ultraviolet absorptio

Continuum description of finite-size particles advected by external flows. The effect of collisions

The equation of the density field of an assembly of macroscopic particles advected by a hydrodynamic flow is derived from the microscopic description of the system. This equation allows to recognize the role and the relative importance of the different microscopic processes implicit in the model: the driving of the external flow, the inertia of the particles, and the collisions among them. The validity of the density description is confirmed by comparisons of numerical studies of the continuum equation with Direct Simulation Monte Carlo (DSMC) simulations of hard disks advected by a chaotic flow. We show that the collisions have two competing roles: a dispersing-like effect and a clustering effect (even for elastic collisions). An unexpected feature is also observed in the system: the presence of collisions can reverse the effect of inertia, so that grains with lower inertia are more clusterized.Comment: Final (strongly modified) version accepted in PRE; 6 pages, 3 figure

Development and Application of Acousto-Optic Background Correction for Inductively Coupled Plasma Atomic Emission Spectrometry

In two con gurations, a solid-state acousto-optic (AO) de ector or modulator is mounted in a 0.5 m monochromator for background correction with inductively coupled plasma atomic emission spectrometry (ICP-AES). A fused silica acousto-optic modulator (AOM) is used in the ultraviolet (UV) spectral region applications while a glass AO de ector (AOD) is used for the visible (VIS) region. The system provides rapid sequential observation of adjacent on- and off-line wavelengths for background correction. Seventeen elements are examined using pneumatic nebulization (PN) and electrothermal vaporization (ETV) sample introduction. Calibration plots were obtained with each sample introduction technique. Potable water and vitamin tablets were analyzed. Flame atomic absorption (FAA) was used to verify the accuracy of the AO background correction system

Pipeline column separation flow regimes

A generalized set of pipeline column separation equations is presented describing all conventional types of low-pressure regions. These include water hammer zones, distributed vaporous cavitation, vapor cavities, and shocks (that eliminate distributed vaporous cavitation zones). Numerical methods for solving these equations are then considered, leading to a review of three numerical models of column separation. These include the discrete vapor cavity model, the discrete gas cavity model, and the generalized interface vaporous cavitation model. The generalized interface vaporous cavitation model enables direct tracking of actual column separation phenomena (e.g., discrete cavities, vaporous cavitation zones), and consequently, better insight into the transient event. Numerical results from the three column separation models are compared with results of measurements for a number of flow regimes initiated by a rapid closure of a downstream valve in a sloping pipeline laboratory apparatus. Finally, conclusions are drawn about the accuracy of the modeling approaches. A new classification of column separation (active or passive) is proposed based on whether the maximum pressure in a pipeline following column separation results in a short-duration pressure pulse that exceeds the magnitude of the Joukowsky pressure rise for rapid valve closure.Anton Bergant and Angus R. Simpso

First record of \u3ci\u3eOrsilochides scurrilis\u3c/i\u3e (Stål) (Hemiptera: Heteroptera: Scutelleridae: Pachycorinae) in the United States, with notes on the biology and distribution of U.S. species of \u3ci\u3eOrsilochides\u3c/i\u3e Kirkaldy

Orsilochides scurrilis (Stål) (Hemiptera: Heteroptera: Scutelleridae) is reported from the United States for the first time based on a specimen collected in Santa Cruz County, Arizona. A key to separate the U.S. species of Orsilochides Kirkaldy is provided. In addition, host plant records and distribution of the other two species of Orsilochides that occur in the U.S., Orsilochides guttata (Herrich-Schäffer) and Orsilochides stictica (Dallas), are analyzed through a combination of digital photo records and museum specimens

Determination of Active Pharmaceutical Ingredients by Heteroatom Selective Detection Using Inductively Coupled Plasma Mass Spectrometry with Ultrasonic Nebuilization and Membrane Desolvation Sample Introduction

The combination of ultrasonic nebulization with membrane desolvation (USN-MD) is utilized to determine active pharmaceutical ingredients (API) by heteroatom inductively coupled mass spectroscopy (ICP-MS) detection. Ultrasonic nebulization provides efficient sampling while use of the membrane desolvator acts to reduce solvent-based interferences. This approach reduces interferences sufficiently so that a standard argon ICPquadrupole MS can be utilized. Examined APIs and associated heteroatoms included: phosphomycin (P), amoxicillin (S), chlorpropamide (Cl), and ofloxacin (F). The optimum plasma r.f. powers for P, S, and Cl were in the 1000 to 1200 watts range. The high ionization energy of F required that the plasma be operated at 1500W. The 16O2 þ interference at mass 32 precluded determinations using the sulfur-32. The sulfur-34 (4.2% natural isotopic abundance), however, was relatively free of isobaric interferences. Interferences were relatively small at the mass 35 isotope of Cl, but increased with higher ICP r.f. powers. Overlaps were significant at the masses of monoisotopic species, fluorine-19 and phosphorus-31. Detection limits for P, S, Cl, and F of 2, 3, 90, and 3000 ng/mL, respectively, were generally lower than those produced with other quadrupole systems and comparable to or better than values published utilizing high-resolution instruments

Fractionation effects in phase equilibria of polydisperse hard sphere colloids

The equilibrium phase behaviour of hard spheres with size polydispersity is studied theoretically. We solve numerically the exact phase equilibrium equations that result from accurate free energy expressions for the fluid and solid phases, while accounting fully for size fractionation between coexisting phases. Fluids up to the largest polydispersities that we can study (around 14%) can phase separate by splitting off a solid with a much narrower size distribution. This shows that experimentally observed terminal polydispersities above which phase separation no longer occurs must be due to non-equilibrium effects. We find no evidence of re-entrant melting; instead, sufficiently compressed solids phase separate into two or more solid phases. Under appropriate conditions, coexistence of multiple solids with a fluid phase is also predicted. The solids have smaller polydispersities than the parent phase as expected, while the reverse is true for the fluid phase, which contains predominantly smaller particles but also residual amounts of the larger ones. The properties of the coexisting phases are studied in detail; mean diameter, polydispersity and volume fraction of the phases all reveal marked fractionation. We also propose a method for constructing quantities that optimally distinguish between the coexisting phases, using Principal Component Analysis in the space of density distributions. We conclude by comparing our predictions to perturbative theories for near-monodisperse systems and to Monte Carlo simulations at imposed chemical potential distribution, and find excellent agreement.Comment: 21 pages, 23 figures, 2 table

A recurrent neural network with ever changing synapses

A recurrent neural network with noisy input is studied analytically, on the basis of a Discrete Time Master Equation. The latter is derived from a biologically realizable learning rule for the weights of the connections. In a numerical study it is found that the fixed points of the dynamics of the net are time dependent, implying that the representation in the brain of a fixed piece of information (e.g., a word to be recognized) is not fixed in time.Comment: 17 pages, LaTeX, 4 figure

Derivation of Hebb's rule

On the basis of the general form for the energy needed to adapt the connection strengths of a network in which learning takes place, a local learning rule is found for the changes of the weights. This biologically realizable learning rule turns out to comply with Hebb's neuro-physiological postulate, but is not of the form of any of the learning rules proposed in the literature. It is shown that, if a finite set of the same patterns is presented over and over again to the network, the weights of the synapses converge to finite values. Furthermore, it is proved that the final values found in this biologically realizable limit are the same as those found via a mathematical approach to the problem of finding the weights of a partially connected neural network that can store a collection of patterns. The mathematical solution is obtained via a modified version of the so-called method of the pseudo-inverse, and has the inverse of a reduced correlation matrix, rather than the usual correlation matrix, as its basic ingredient. Thus, a biological network might realize the final results of the mathematician by the energetically economic rule for the adaption of the synapses found in this article.Comment: 29 pages, LaTeX, 3 figure