Showing papers by "Illinois Institute of Technology published in 1975"

A Deborah number for diffusion in polymer‐solvent systems

Abstract: A Deborah number is introduced as a means of characterizing diffusional transport in amorphous polymer-solvent systems. Two types of temperature-penetrant concentration diagrams are constructed, and the various regions on these figures are identified by their Deborah number values. The utility of the diffusion Deborah number is demonstrated by using this dimensionless group to anticipate conditions under which thickness anomalies can be expected in sorption experiments for the atactic polystyrenepentane system.

Exact quantum, quasiclassical, and semiclassical reaction probabilities for the collinear F+H2 → FH+H reaction

Abstract: Exact quantum, quasiclassical, and semiclassical reaction probabilities and rate constants for the collinear reaction F+D_2 → FD+D are presented. In all calculations, a high degree of population inversion is predicted with P^R_(03) and P^R(04) being the dominant reaction probabilities. In analogy with the F+H_2 reaction (preceding paper), the exact quantum 0→3 and 0→4 probabilities show markedly different energy dependence with PR03 having a much smaller effective threshold energy (E_T=0.014 eV) than P^R_(04) (0.055 eV). The corresponding quasiclassical forward probabilities P^R_(03) and P^R_(04) are in poor agreement with the exact quantum ones, while their quasiclassical reverse and semiclassical counterparts provide much better approximations to the exact results. Similar comparisons are also made in the analysis of the corresponding EQ, QCF, QCR, and USC rate constants. An information theoretic analysis of the EQ and QCF reaction probabilities indicates nonlinear surprisal behavior as well as a significant isotope dependence. Additional quantum results at higher energies are presented and discussed in terms of threshold behavior and resonances. Exact quantum reaction probabilities for the related F+HD → FH+D and F+DH → FD+H reactions are given and an attempt to explain the observed isotope effects is made.

Photodynamic sensitization by 8-methoxypsoralen via the singlet oxygen mechanism.

Abstract: There is ample evidence that biological sensitization by furocoumarins does not require oxygen [e.g. Musajo and Rhodighiero, 19723. However, it has been shown that the active sensitizers psoralen and 8-methoxy-psoralen (8-MOP) exhibit low-temperature phosphorescence and UV-induced solvent EPR signals characteristic of reactive triplet states (Pathak et al., 1961; Yeargers and Augenstein, 1965; Song et al., 1971). It is not known how furocoumarins differ from the many synthetic dyes and natural pigments that act as photodynamic sensitizers via the type I1 (dyeoxygen) mechanism. We have found that 8-MOP is a good photodynamic sensitizer in aqueous solution, and that singlet oxygen (lo2) generated by triplet energy transfer is the principal reactive intermediate in the inactivation of lysozyme and oxidation of aqueous iodide ion. Evidence is presented to indicate that the binding of 8-MOP to double stranded poly(dA-dT) inhibits its ability to sensitize via this mechanism. The triplet state of 8-MOP was identified by flash photolysis in aqueous and glycerol solutions using the apparatus described by Grossweiner and Usui (1971). Figure 1 shows the transient absorption generated by

Propagation of photons in homogeneous magnetic fields: index of refraction

Abstract: The index of refraction associated with the vacuum polarization induced by homogeneous magnetic fields is calculated for two cases: (i) high-energy photons traversing fields weak compared with the critical field, ${H}_{\mathrm{cr}}=\frac{{m}^{2}{c}^{3}}{e\ensuremath{\hbar}}\ensuremath{\cong}4.41\ifmmode\times\else\texttimes\fi{}{10}^{13}$ G; and (ii) low-energy photons in fields of arbitrary intensity. Some implications for the physical optics of intense magnetic fields are briefly discussed.

Starting vortex, separation bubbles and stall: a numerical study of laminar unsteady flow around an airfoil

Abstract: The stalling characteristics of an airfoil in a laminar viscous incompressible fluid are investigated. The governing equations in terms of the vorticity and stream function are solved using an implicit finite-difference scheme and point successive relaxation procedure. The development of the impulsively started flow, the initial generation of circulation, and the behavior of the forces at large times are studied. Following the impulsive start, the lift is at first very large and then it rapidly drops. The subsequent growth of circulation and lift is associated with the starting vortex. After incipient separation, the lift increases owing to enlargement of the separation bubble and intensification of the flow rotation in it. The extension of this bubble beyond the trailing edge causes it to rupture and brings about the stalling characteristics of the airfoil. Subsequently, new bubbles are formed near the upper surface of the airfoil and are swept away. The behavior of the lift acting on the airfoil is explained in terms of the strength and sense of these bubbles.

Indirect threaded code

Abstract: An efficient arrangement for interpretive code is described. It is related to Bell's notion of threaded code but requires less space and is more amenable to machine independent implementations.

On a classification scheme for flow fields

Abstract: There are some flows in which certain strain components grow exponentially in time, while there are other flows in which the components depend otherwise on the time. In this paper the former type are called strong flows and the latter weak. An examination of theJordan form of the matrix of the velocity gradient of a steady, homogeneous, isochoric flow is made, along with the eigenvalues of such a matrix, to discover when such a flow is strong or weak. It is shown that if the eigenvalues are all zero or if one is zero and the other two purely imaginary, then the flow is weak, with the remaining cases leading to strong flows.

Crack Growth Resistance of Random Fiber Composites

Abstract: Crack growth resistance of a random glass fiber composite has been studied by applying the concepts of Linear Elastic Fracture Mechanics. The crack growth resistance curves (R-curves) for epoxy and polyester composites have been developed to study the total fracture behavior of these composites. It is shown that the R-curve approach is suitable for these type of materials. An attempt has been made to use the information from the R-curves to predict the fracture strength of plate specimens with a hole at the center and subjected to tensile loading.

Photosensitizing properties of N-formylkynurenine.

Abstract: UV-irradiation of tryptophan (Trp) or tryptophyl residues in proteins leads to N-formylkynurenine (FK) as an oxidation product (Deschreider and Renard, 1955; Pirie, 1971; Asquith and Rivett, 1971; Pirie and Dilley, 1974). Walrant and Santus (1974a) found that FK is a photodynamic sensitizer of amino acids for wavelengths above 320 nm where Trp is not excited. The quantum yield for histidine oxidation sensitized by FK was enhanced by a factor of 5 on changing the solvent from H 2 0 to D20 while the addition of 0.01 M NaN, led to complete protection, proving that ‘Ag 02* is the major oxidizing agent (Nilsson et al., 1972). In the case of Trp, however, the same diagnostic tests indicate a competing pathway, postulated as oxidation of Trp by 0; from the dependence of the quantum yield on the Trp and O2 concentrations. Similar reactions were proposed in connection with the photoinactivation of bovine carbonic anhydrase (BCA) by UV (A > 280nm) and sensitized by external FK (1 > 320nm), where the addition of azide protected against loss of enzymic activity and histidine destruction under oxygenated conditions (Walrant and Santus, 1974b). However, Trp destruction in BCA was not altered in the presence of azide indicative of the alternate oxidation pathway. The present work was undertaken to investigate the “non-singlet oxygen” process by which FK sensitizes the photooxidation of Trp. Spectral studies on FK (Walrant and Santus, 1974a) show the longest wavelength absorption band is located at 320 nm (pH 7.6, p = 0.15 M Pi buffer). At 77K the phosphorescence lifetime is 0.5 s (1:l water-ethylene glycol) with undetectable fluorescence indicating a high intersystem crossing efficiency. Xenon lamp flash photolysis of air-free FK in the pH 7.6 buffer led to the 435 nm band in Fig. 1A attributed to the triplet state (3FK). Dhe apparatus * Present address: Laboratoire de Biophysique, Museum National Naturelle 61 rue Buffon 75005-Paris. France. t COO-2217-7. employed has been described by Grossweiner and Usui (1971)l. This transient was not observed in the presence of air and is quenched by KI according to Stern-Volmer kinetics with quenching constant 3 x lo3 M ’ . The triplet decay was first order with 2 ps lifetime as determined with a quadrupled Nd:glass laser system described by Bryant et a/. (To be submitted). A different transient product was observed by flash photolysis of FK in N,-saturated ethanol, with the absorption maximum at 465nm (Fig. 1B). The decay was second order with kJE = 8.5 x lo5 cm s l at 465 nm. This species is attributed to the FK semiquinone radical (FKH) formed by

Caisson Evaluation by Stress Wave Propagation Method

Abstract: The theoretical aspects of wave propagation were verified in the laboratory by experiments on bars of aluminum and concrete which showed that it is possible to detect discontinuities and abrupt changes in the cross-sectional areas of long members. The theory is based on stress wave propagation in elastic solids and on the Rayleigh theory of surface waves. Field tests demonstrated that the method could be used for in-situ installations of caissons and piles, resulting in very little interference with normal construction operations. Basic data and records are presented for laboratory experiments on aluminum and concrete bars, and field tests on cast-in-place caissons and piles. The results indicate that the stress wave propagation method has the potential for providing a simple, rapid, inexpensive, and reliable method for detecting irregularities in caissons and piles.

Capacitance of a Circular Disk for Applications in Microwave Integrated Circuits (Short Papers)

Abstract: The quasi-static solution for a circular disk separated from a ground plane by a dielectric substrate is studied using the dual integral equation approach. A simple expression for equivalent capacitance is determined.

Role of premeiotic replication in gene conversion.

Abstract: CURRENT molecular models of meiotic recombination have attempted to explain both classical reciprocal recombination (crossing over) and non-reciprocal intragenic recombination (gene conversion), with a single unified mechanism1,2. An important assumption inherent in such models is that both types of recombination occur during the prophase following premeiotic chromosome replication. To date, however, only crossing over (chiasma) has been convincingly shown to occur during meiotic prophase3. Gene conversion, which has been most extensively studied in the ascomycete fungi4, has, for a number of cogent reasons5, also been assumed to occur during prophase, yet direct evidence supporting this critical point is lacking. In fact, in an important paper6, concerning recombination in yeast, evidence was presented indicating that intragenic recombination and premeiotic replication coincided, a finding which argues against much current speculation. To clarify this situation we simultaneously measured premeiotic replication and gene conversion in the yeast Saccharomyces cerevisiae, and examined the genetic consequences of inhibiting DNA synthesis with hydroxyurea (HU). We show that during the premeiotic S phase cells acquire a ‘potential’ for completing gene conversion, but that the actual formation of stable intragenic recombinants occurs after replication and depends on a period of postreplicative DNA synthesis.

Cellular Snow Generation—A Doppler Radar Study

Abstract: Snow generating cells were observed by vertically pointing Doppler radar. Analysis was carried out in three distinct regions. The region exhibiting cellular structure was found to consist of convective elements with vertical velocities ±1.5 m s−1 in magnitude. A generation region was found to exist beneath the convective region with updrafts of 0.5 in s−1 sustained over a 7 km path length which originated at a generating level less than 75 m in depth associated with an inversion layer. The trail region below exhibited maximum downdrafts of 0.5 m s−1 or no net vertical motions. Maximum ice content was estimated to be no larger than 0.24 g m−2 in the convective cells. Growth appeared to take place throughout the rise and fall of the snow crystals in the updraft regions.

Reflection of electromagnetic waves from oscillating surfaces

Abstract: The problem of reflection of electromagnetic waves from oscillating surfaces is discussed. Using the induction theorem, the interface is replaced by equivalent current sources that radiate into an unbounded medium. Spatial movement is ascribed to these sources to account for oscillations of the surface. The general solution for the far-field due to any arbitrary surface motion is developed. A few deterministic and random functions for surface motion are considered. Most of the initial discussion pertains to normal reflection from planar surfaces, but the solution is also obtained for arbitrary incidence and for an oscillating cylinder.

Stimulation of the vestibular receptor by means of step temperature changes during continuous aural irrigation.

Abstract: A technique for rapid, balanced hot/cold stimu-ition of the vestibular receptor is presented. During con-inuous aural irrigation the temperature of the irrigation luid is switched between hot and cold values at times computed according to a mathematical model of heat conduction in the labyrinth area. As a result, the induced temperature difference across the lateral semicircular canal describes an approximately sinusoidal time course, reaching peak values of equal magnitude but opposite sign. Application of the test to 32 clinical subjects demonstrated that the heat conduction model and the analysis used in timing the sequence of thermal pulses was accurate. We expect that, with further refinements, the new technique will prove superior to conventional caloric test methods in the detection and measurement of subtle as well as gross abnormalities of the vestibular system.

Characteristics and stability analyses of transient one-dimensional two- phase flow equations and their finite difference approximations

Abstract: Equation systems describing one-dimensional, transient, two-phase flow with separate continuity, momentum, and energy equations for each phase are classified by use of the method of characteristics. Little attempt is made to justify the physics of these equations. Many of the equation systems possess complex-valued characteristics and hence, according to well-known mathematical theorems, are not well-posed as initial-value problems (IVPs). Real-valued characteristics are necessary but not sufficient to insure well-posedness. In the absence of lower order source or sink terms (potential type flows), which can affect the well-posedness of IVPs, the complex characteristics associated with these two-phase flow equations imply unbounded exponential growth for disturbances of all wavelengths. Analytical and numerical examples show that the ill-posedness of IVPs for the two-phase flow partial differential equations which possess complex characteristics produce unstable numerical schemes. These unstable numerical schemes can produce apparently stable and even accurate results if the growth rate resulting from the complex characteristics remains small throughout the time span of the numerical experiment or if sufficient numerical damping is present for the increment size used. Other examples show that clearly nonphysical numerical instabilities resulting from the complex characteristics can be produced. These latter types of numerical instabilities are shown to be removed by the addition of physically motivated differential terms which eliminate the complex characteristics. (auth)