Showing papers by "Rensselaer Polytechnic Institute published in 1969"

Distant side-walls cause slow amplitude modulation of cellular convection

Abstract: The effect of vertical boundaries on convection in a shallow layer of fluid heated from below is considered. By means of a multiple-scale perturbation analysis, results for horizontally unbounded layers are modified so that they ‘fit in’ to a rectangular region. The critical Rayleigh number and critical wave-number are determined. Motion is predicted to have the form of finite ‘rolls’ whose axes are parallel to the shorter sides of the dish. Aspects of the non-linear development and stability of this motion are studied. The general question of convective pattern selection in a bounded layer is discussed in the light of available theoretical and experimental results. This paper deals with an aspect of the theory of convection in a bounded horizontal layer of fluid heated from below. Almost all previous theoretical investigations of this problem have assumed that the layer is unbounded. (When we speak of an unbounded or a bounded layer we shall be referring to whether or not the layer extends to infinity in horizontal directions.) A premise of such investigations has been that the inevitable presence of side-walls has little or no effect in a sufficiently shallow layer. What follows is a first attempt to demonstrate that the concept of slow amplitude modulation can be employed to show how shallow the layer need be if the side-walls are to have ‘essentially ’ no effect and to estimate what their effect is if that effect is not too large. Readers unfamiliar with developments in convection theory for unbounded layers might find it useful to consult one or more of the surveys by Brindley (1967), Gortler & Velte (1967), or Segel (1966). Directly relevant is the recent paper by Davis (1967), who considered rectangular dishes with length to depth ratios which varied from to 6. His linear stability analysis, using the Galerkin method, showed that convection should commence in the form of finite rolls parallel to the shorter side-wall of the dish. If co-ordinates are chosen so that the side-walls are parallel to the 5- and y-axes then the two possible types of finite rolls are calledfinite y rolls andfinite x rolls. The latter is a motion which is periodic (or nearly so) in the 2-direction and has a zero velocity component in the y-direction (v 3 0). Finite y rolls have a corresponding definition. As Davis did, we emphasize the three-dimensional nature of finite rolls, which have no velocity component in the axial direction but depend on all three spatial co-ordinates.

General theory for pinched operation of the junction-gate FET

Abstract: A device oriented model is developed to describe the operation of the junction-gate field-effect transistor (FET) beyond pinch-off. The model is derived on the basis of a generalized structure with an arbitrary channel doping profile. It provides a qualitative and quantitative description of the current conduction mechanism, and is applicable over the entire dynamic range of device operation. Current conduction mechanisms in the vicinity of the source and the drain are examined separately. It is shown that the saturation of carrier drift velocities at high electric fields results in formation of a drain space-charge region of finite length. An approximate solution of the two-dimensional Poisson's equation is developed to describe the potential distribution within this region. A significant result of the device model is the prediction of a finite drain resistance in pinched operation, which shows a strong dependence on the device operation point.

Aging in Tetragonal Ferroelectric Barium Titanate

Abstract: The aging phenomenon in tetragonal ferroelectric bairum titanate was investigated by optical microscopy and by electrical measurements. Transmission electron microscopy was used to observe in detail domain reactions which occurred during aging. Aging may be characterized as an exhaustion-type process because of the increase in the apparent activation energy with time. It is concluded that aging is the relief of the residual stresses of the ferroelectric transition by the thermally activated nucleation of 90° domains.

Corrosion and fracture of type 316 SMO orthopedic implants.

Abstract: Orthopedic appliances of type 316 (SMO) stainless steel were examined in detail after being removed from human subjects. Techniques included conventional microscopy with various lighting methods, together with electron microscope fractography. Corrosion, fatigue failure, and manufacturing defects were identified and statistically tabulated. Corrosion damage occurred on 91% of all multicomponent devices and the overall incidence of fracture failure was 9%. These results indicate an urgent ueed for stronger, more corrosion-resistant implant alloys.

Thermodynamic Properties of Solid Ar, Kr, and Xe Based Upon a Short-Range Central Force and the Conventional Perturbation Expansion of the Partition Function

Abstract: Thermodynamic properties of the rare-gas solids Ar, Kr, and Xe are calculated using phenomenological two-body central potentials. The cubic and quartic anharmonic terms in the crystal Hamiltonian have been included, using conventional perturbation theory. Although some definite discrepancies with experiment exist for $Tl\frac{1}{3}{T}_{\mathrm{melting}}$ these simple models give a fair over-all account of both the volume and temperature dependence of the Helmholtz energy. However, for $Tg\frac{1}{3}{T}_{\mathrm{melting}}$ (rms deviations greater than \ensuremath{\sim}6% of the nearest-neighbor distance), anharmonic contributions to the thermodynamic properties become unrealistically large, indicating, we believe, the breakdown of perturbation theory to the order considered in this work.

Extended‐chain crystals. I. General crystallization conditions and review of pressure crystallization of polyethylene

Abstract: This is the first paper of a series of reports concerning extended-chain crystals of flexible, linear high polymers. The general conditions for crystal growth are discussed. Polymer crystallization is described as a two-step process: nucleation of each crystallizing molecule to a folded-chain conformation, followed by an increase in fold length in a solid-state reorganization step. This reorganization step is enhanced in the case of polyethylene by crystallization at high temperature under elevated pressure. Mechanical deformation during crystallization is also able to produce extended-chain crystals. The most promising method, however, is crystallization during polymerization. Previous work on crystallization of polyethylene under elevated pressure is critically reviewed.

Heat capacities of solid polymers

Abstract: Linear high polymer heat capacities by adding contributions from chain segments, deriving table of heat capacity contributions of polymer constituents

Effects of opiates and opiate antagonists on the Straub tail reaction in mice.

Abstract: 1. Subcutaneous injections of opiates produced the Straub tail reaction in mice. The potencies of the opiates in mice were consistent with previous estimates of the analgesic potencies in animals and in man.2. The potencies of sixteen antagonists in counteracting the reaction were consistent with those previously obtained with the rat tail-flick test.3. The (-) isomers of four benzomorphan derivatives were much more potent in counteracting the reaction than their (+) isomers and about twice as potent as their racemates. The activity of the isomers seemed to follow Pfeiffer's rule: the lower the effective dose of a drug, the greater the difference in the pharmacological effects of the optical isomers. One of the trans isomers acted like an opiate, while its cis isomer acted like an antagonist.4. Naloxone and nalorphine fulfilled conventional criteria for competitive antagonism, whereas atropine and the (-) and the (+) isomers of pentazocine and of cyclazocine did not do so.5. The Straub tail test seems to be useful for studying structure-activity relations among opiates and opiate antagonists.

Photochemical reactions and the chemical evolution of purines and nicotinamide derivatives.

Abstract: The photochemical rearrangement of a tetramer of hydrogen cyanide to 4-aminoimidazole-5-carbonitrile, a critical step in the proposed prebiotic synthesis of purines, proceeds in high yield in the absence of oxygen without photodestruction of the reaction product. The mechanism of the rearrangement involves the conversion of the excited singlet of the hydrogen cyanide tetramer to 2-imino-3-cyano-4-aminoazetine, which then rearranges to the imidazole product. The photolysis of the vinylogous enaminonitrile 1,3-dicyano4-amino-1,3-butadiene yields 6-aminonicotinonitrile. The latter reaction affords an efficient route to a nicotinamide derivative from cyanoacetylene.

NEUTRON RADIATIVE CAPTURE IN Na, Al, Fe, AND Ni FROM 1 TO 200 keV.

Abstract: Neutron radiative capture in Na, Al, Fe, and Ni has been measured from 100 eV to 200 keV with a 1.25-m-diam liquid scintillator detector at the Rensselaer LINAC Laboratory. Radiation widths were determined for those resonances whose neutron widths are well known, while the resonance capture areas (${\ensuremath{\sigma}}_{0}{\ensuremath{\Gamma}}_{\ensuremath{\gamma}}$) were determined for most of the other resonances. Considerably more resonances were observed in the capture measurements upon Fe and Ni than had been observed in total cross-section measurements. It is reasonable to assign most if not all of these previously undetected resonances to $p$-wave neutrons, and from these data $p$-wave strength functions of (0.10\ifmmode\pm\else\textpm\fi{}0.04) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$ and (0.04\ifmmode\pm\else\textpm\fi{}0.03) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$ were determined, respectively, for $^{56}\mathrm{Fe}$ and $^{58}\mathrm{Ni}$. These strength functions are probably just upper limits to the true $p$-wave strength functions and are an order of magnitude smaller than optical-model predictions.

Mechanism of Action of Nalidixic Acid on Escherichia coli VI. Cell-free Studies

Abstract: The effects of nalidixic acid in vitro on deoxyribonucleic acid (DNA)- polymerase (deoxyribonucleosidetriphosphate: DNA deoxynucleotidyltransferase, EC 2.7.7.7), deoxyribonucleotide kinases (ATP: deoxymono- and diphosphate phosphotransferases), and deoxyribosyl transferase (nucleoside: purine deoxyribosyltransferase, EC 2.4.2.6) were examined employing partially purified and crude extracts of Escherichia coli ATCC 11229 and E. coli 15TAU. Nalidixic acid had no inhibitory effect on the DNA-polymerase of the wild-type strain E. coli ATCC 11229 at concentrations of 1.4 × 10−3 to 2.8 × 10−3m. No inhibition of deoxyribonucleotide kinase activity was observed at concentrations of nalidixic acid ranging from 2 × 10−3 to 8.6 × 10−3m. Nalidixic acid (0.43 × 10−4 to 0.43 × 10−3m) had no inhibitory effect on the deoxyribosyl transferase activity of crude extracts obtained from E. coli ATCC 11229 or E. coli 15TAU. Analytical CsCl density gradient centrifugation demonstrated that the DNA obtained after treatment of E. coli 15TAU with nalidixic acid was not cross-linked. These results suggest that the prevention of DNA synthesis in vivo by nalidixic acid is not attributable to inhibition of DNA polymerase, deoxyribonucleotide kinase, deoxyribosyl transferase, or to cross-linking of the DNA of treated cells.

Aspects of Group Theory in Electron Dynamics

Abstract: Publisher Summary This chapter discusses the nature of electronic states in crystals under the influence of electric and magnetic fields. The techniques of group theory are used to establish the nature of the states in a periodic lattice and a uniform magnetic field. It is found that the effective Hamiltonian method is consistent with the requirements of group theory and leads to a convenient formulation on which most of the understanding of magnetic phenomena is based. It is seen that the discrete Landau levels are associated with closed contours of Heff(k) and are very accurately given by the Roth correction term to the Onsager formula. The structure of the broadened magnetic bands depends sensitively on the precise value of the magnetic field through the rationality parameter l / N. It is not likely that the states associated with such structure are susceptible to exact analysis in a real physical situation.

Differential thermal analysis of polyethylene under high pressure

Abstract: The design of a differential thermal analysis apparatus for use at elevated pressure is described. Experiments on melting and crystallization of folded-chain crystals of polyethylene and poly(ethylene–butene-1) copolymer, and melting of extended-chain polyethylene crystals have been conducted at pressures up to 4200 bars. The precision in transition temperature measurement was ±1°C. The Clausius-Clapeyron equation predicts the melting point increase with pressure at atmospheric pressure to be 32.0°C/kb. The melting point depression due to copolymerization remained constant over the complete pressure range analyzed on the poly(ethylene–butene-1) used in this study. Crystallization of polyethylene is retarded at elevated pressures, and a 50% larger degree of supercooling is necessary at 5000 bars to give a crystallization rate equal to that observed at atmospheric pressure. The difference in melting point between folded-chain and extended-chain polyethylene increases from 8.4°C at 1 bar to 25.6°C at 3000 bars.

Effects of ganglion blocking agents on nicotine extensor convulsions and lethality in mice.

Abstract: 1. The ganglion blocking agents, chlorisondamine, pentamethonium, mecamylamine, decamethonium and hexamethonium all block nicotine extensor convulsions when administered intraventricularly in mice. Tetraethylammonium was inactive. 2. For the intraventricular route, there is a relationship between ganglionic blocking potency and blocking of nicotine extensor convulsions. Indirect evidence suggests that the site(s) of action of nicotine extensor convulsions and lethality is central in origin and associated with brain areas near the ventricles. 3. When ganglion blocking agents are given orally, subcutaneously or intravenously varying degrees of protection can be observed probably depending on factors such as whether or not the drugs cross the blood-brain barrier, absorption, etc., and the effectiveness in protecting mice from nicotine is not related to ganglionic blocking potency. 4. Atropine and morphine given intraventricularly or subcutaneously did not protect mice from the LD95 of nicotine. Chlorpromazine gave very erratic results and phenobarbitone was effective subcutaneously and to a lesser extent intraventricularly.

Extended‐chain crystals. V. Thermal analysis and electron microscopy of the melting process in polyethylene

Abstract: Polyethylene extended chain crystals melting process via electron microscopy and differential thermal analysis

Voltages induced on overhead multiconductor lines by lightning strokes

Abstract: The voltages on an untransposed multiconductor line over a perfect earth, induced by the return stroke of lightning, are analysed. The magnitude of the induced voltage on a multiconductor line is higher than that on a single-conductor line of the same height above earth. Earth wires reduce this magnitude somewhat, but not enough to consider them as an effective means of protection. Shielding against induced overvoltages caused by lightning may be accomplished by other means, such as protector tubes and automatic reclosers.