Showing papers by "Stevens Institute of Technology published in 1972"

Water-drop response to sudden accelerations

Abstract: The deformation of initially spherical drops of radius r0 subjected to an external flow of velocity u is experimentally examined for a large range of Weber and Bond numbers. Observations of the changes in the response are compared with recent analytical predictions. The data show that beyond a critical Weber number the response ceases to be vibratory and becomes monotonic with time. Subsequently, it is found that, although the response is unstable, the deformation imposed by the external aerodynamic pressure distribution remains the dominant factor. Measurements of the drag coefficient yield a mean value ofCD = 2·5 over a large Reynolds-number range. The time at which Taylor instability occurs is shown to be inversely proportional to Bond number to the one-quarter power. There is little evidence of the instability occurring until a normalized time is the real time.

The stability of Poiseuille flow in a pipe of circular cross-section

Abstract: The stability of Poiseuille flow in a pipe of circular cross-section to azimuthally varying as well as axisymmetric disturbances has been studied. The perturbation velocity and pressure were expanded in a complete set of orthonormal functions which satisfy the boundary conditions. Truncating the expansion yielded a matrix differential equation for the time dependence of the expansion coefficients. The stability characteristics were determined from the eigenvalues of the matrix, which were calculated numerically. Calculations were carried out for the azimuthal wavenumbers n = 0,…, 5, axial wavenumbers α between 0·1 and 10·0 and αR [les ] 50000, R being the Reynolds number. Our results show that pipe flow is stable to infinitesimal disturbances for all values of α, R and n in these ranges.

On the homeotopy group of a non-orientable surface

Abstract: Let X be a closed, compact connected 2-manifold (a surface ), which we will denote by O or N if we wish to stress that X is orientable or non-orientable. Let G ( X ) denote the group of all homeomorphisms X → X , D ( X ) the normal subgroup of homeomorphisms isotopic to the identity, and H ( X ) the factor group G ( X )/ D ( X ), i.e. the homeotopy group of X . The problem of determining generators for H ( O ) was considered by Lickorish in ( 7, 8 ), and the second of these papers specifies a finite set of generators of a particularly simple type. In (10) and (11) Lickorish considered the analogous problem for non-orientable surfaces, and, using Lickorish's partial results, Chilling-worth (4) determined a finite set of generators for H ( N ). While the generators obtained for H ( O ) and H ( N ) were strikingly similar, it was noteworthy that the techniques used in the two cases were different, and in particular that little use was made in the non-orientable case of the earlier results obtained on the orientable case. The purpose of this note is to show that the results of Lickorish and Chillingworth on non-orientable surfaces follow rather easily from the work in ( 7, 8 ) by an application of some ideas from the theory of covering spaces (2). Moreover, while Lickorish and Chillingworth sought only to find generators , we are able to show (Theorem 1) how in fact the entire structure of the group H ( N ) is determined by H ( O ), where O is an orientable double cover of N. Finally, we are able to determine defining relations for H ( N ) for the case where N is the connected sum of 3 projective planes (Theorem 3).

Specific heats of solid hydrogen, solid deuterium, and solid mixtures of hydrogen and deuterium

Abstract: Measurements have been made in the temperature range 0.5–5 K of the specific heats of pure solid H2, pure solid D2, and four solid mixtures of H2 and D2 with D2 fractions between 15 and 95%, all of which systems had low concentrationc of molecules in the rotational stateJ=1. For the H2,c=0.0023, and for the D2,c=0.030. It was found that the observed specific heats could be described as the sum of three terms as follows. (1) A lattice specific heat. This was found to follow aT 3 function with θ D =122 K for solid H2 and θD=113.8 K for solid D2. For the solid mixtures the lattice specifi heats have in first approximation values given by a weighted mean of the lattice specific heats of the pure components. (2) A Schottky term with a maximum at about 1.3 K for solid H2 and 1.4 K for solid D2, which can quantitatively be described in terms of electric quadrupole-quadrupole (EQQ) interactions in nearest-neighbor pairs and triples of molecules in the rotational stateJ=1. This term led to evaluation of г, the EQQ interaction energy, giving г/k=0.9 ± 0.1 K for solid H2 and 0.93 ± 0.05 K for solid D2. It was found, moreover, that in solid H2 there was an appreciable enhancement with time of the number of clusters of molecules in the rotational stateJ=1 at the expense of the number of isolated singles of similar molecules, due to rotation diffusion. On the other hand no rotation diffusion was observed in solid D2 or in the solid mixtures of H2 and D2, except possibly in those mixtures containing 85% H2. (3) A second anomalous term occurring at temperatures below about 0.8 K and, by extrapolation, having its maximum below 0.5 K (the lowest temperature of our measurements). This anomaly was observed only in those samples containing D2 and is, as yet, unexplained in detail. A further major conclusion from our results in the temperature range 0.5–5 K is that there was no evidence in the form of a sharp anomalous jump in the specific heat of any of the mixtures which could be interpreted as indicating the occurrence of isotopic phase separation. This absence of phase separation is noted, in spite of the fact that thermodynamically it is energetically favorable in the temperature range of observation.

Adsorption of3He and4He on copper and on argon-coated copper below 20 K

Abstract: Measurements have been made of adsorption isotherms of3He and of4He on copper and on a monolayer of argon deposited on copper in the temperature range 6.18–18.55 K and in the pressure range 0.25 to 75 Torr. From these many isotherms, calculations have been made of the isosteric heat of adsorptionQst/R. In the limit of zero coverage on the argon monolayerQst/R=76±2 K for3He and 76±2 K for4He. For adsorption on the bare copper,Qst/R is difficult to extrapolate to zero coverage, but it probably lies (for both3He and4He) between 135 and 165 K. At theoretical monolayer helium coverage,Qst/R=44±2 K for3He on the argon monolayer and 47±2 K for4He. At theoretical monolayer helium coverage on the bare copper,Qst/R=61±4 K for3He and 77±5 K for4He. The results are compared with theoretical evaluations for helium adsorbed on an argon monolayer and with some previous experimental data, and the agreement is found to be fair. All the data are summarized in tables. Finally, a review is given of evaluations, including those from this work, of the monolayer capacity of3He and4He on the substrates studied.

Directional stability and control of ships in waves

Abstract: The stability and oscillatory motions of ships (automatically steered and unsteered) in the horizontal plane were examined on a digital computer for the case of regular following seas. Available hydrodynamic data for Series 60 hull forms were used. Analysis of directional stability was made for the case of zero encounter frequency (i.e., the ship runs at high speeds equal to the wave celerity.) The ship (which is hydrodynamically stable without automatic control in calm water) is directionally unstable in following seas except for the small region near the ascending node of the waves. Addition of automatic control can give the ship directional stability when it is located on the wave trough, but not when it is located on the wave crest. At relatively high frequency (i.e., at low speeds in following seas), the rudder and control system are almost incapable of reducing oscillatory motion. Violent rudder activity in following seas can be decreased by reducing the yaw-rate-gain control constant and by increasing the rudder-response-time constant.

A semi-empirical approach to the viscosities of polyelectrolyte solutions

Abstract: : The concentration dependence of a number of polyelectrolytes was found to be adequately described by an equation eta(sp)/c = eta(infinity) x (1 + k/sq root of c)) as long as the concentration is not too low. The parameter eta(infinity) represents the intrinsic viscosity of the well-shielded polyion and corresponds to values of (eta) determined in salt solutions and may possibly correspond to the theory of Harris and Rice on polyion expansion. Heuristic arguments based in part on the work of Katchalsky, et al, lead to a definite expression for the parameter k in terms of molecular properties. The result shows that the above equation is valid only for strong polyelectrolytes with the constant activity coefficients of counterion. The calculated values of k agree well with experiment except when specific intramolicular interactions (e. g., internal hydrogen bonding) occur. For highly charged polyions one finds surprisingly, that k depends only on the properties of the polymer backbone and not on electrical properties. (Author)

Morphological changes in nylon 6 and effect on mechanical properties. II. Dynamic mechanical properties

Abstract: Dynamic mechanical measurements were carried out on nylon 6 film treated with heat and swelling agents to produce changes in the crystalline morphology. The original smectic hexagonal crystal form was changed by heat treatment and phenol treatment to an unoriented and oriented α-crystalline form, respectively, and by I2/KI treatment to a preferentially oriented γ-crystalline form. The behavior of the αa mechanical loss peak located at about +70°C was investigated in most detail. This peak was independent of frequency on the low-temperature side of the peak but markedly frequency-dependent on the high-temperature side. The low-temperature side of the peak probably represents a thermodynamically controlled “melting” or bond-breaking process which frees molecular units to participate in a viscoelastic relaxation process which is the controlling factor in the high-temperature side of the peak. Frequency-temperature superposition of data from the high-temperature side of the peak gave shift factor values which showed two straight-line regions in the Arrhenius plot for the specimens containing some smectic hexagonal form, and a single straight line in the other cases. Activation energy values obtained were 30–50 kcal. The αa peak split into two components with an increase in absorbed phenol, indicating that two loss mechanisms corresponding to two noncrystalline phases (one amorphous and one more highly ordered or hindered) are involved.

The Quasi-Stationary State Approximation in Polymerization Kinetics.

Abstract: : The errors incurred in free-radical chain addition polymerizations through the use of the popular quasi-stationary state approximation (QSSA) under server, but fairly common, reaction conditions are examined in detail and simple, useful criteria for applicability of the QSSA are proposed. The conditions examined are 'dead-end' polymerization, polymerization with hindered termination and non-isothermal polymerization. It is concluded that the proposed criteria are reasonably accurate and that in most known free-radical polymerizations only hindered termination might possibly lead to appreciable errors through application of the QSSA. (Author)

Viscosity of heparin as a function of dielectric constant and of desulfation

Abstract: The effect of dielectric constant (D) of the solvent on the viscosity of heparin was examined using the relation , where [η]∞ is the shielded intrinsic viscosity obtained by extrapolating to infinite concentration, and k is an interaction parameter independent of the dielectric constant of the solvent. This equation was previously reported by the authors9 for describing the reduced viscosities of strong polyelectrolytes in salt-free polar solvents. It was found that the [η]∞ of heparin increases linearly with increasing dielectric constant of the solvent whereas the k values were, within experimental error, independent of D in the range 54.7 < D < 93.2 examined. Graded hydrolysis of heparin from its acid form (heparinic acid) at 57°C resulted in samples of varying degree of desulfation with corresponding decrease in biological activity. It was found that both [η]∞ and k decrease with increasing desulfation.

Some comments on neighborhood size for tessellation automata

Abstract: The simplest possible neighborhood interconnection patterns that can be constructed from both partition and cover blocking preserving behavioral isomorphism are established for a broad class of two-dimensional arrays.

Adsorption of nitrogen, argon, and neon on sintered copper and of neon on argon-coated sintered copper at low temperatures

Abstract: The results of measurements of adsorption isotherms are given for nitrogen, argon, and neon on bare sintered copper and on sintered copper covered with a monolayer of argon. The temperatures employed where 77.3 K for the N2 and argon, and 17.26, 20.22, 22.64, 25.71, and 27.00 K for the neon, and the pressure range was from 0.25 to 200 Torr. The sintered copper specimen was of mass 170 g, made with powder (Alcan Metal Powders, Inc., “Druid Copper,” grade MD60), which had an average particle size of 2 × 2 × 0.5 µ. The sintering was done at 650°C for 0.5 h. The bare surface area e in m2/g, of the sintered copper specimen was found from the N2 adsorption isotherms at 77.3 K. This gave e=0.41 m2/g, based on a molecular area of N2 of 13.8 A2 (solid N2). The N2 and argon isotherms on the bare sintered copper at 77.3 K yielded values of the monolayer coverage ofV m =0.11 cm3(STP)/g for N2 andV m =0.11 cm3(STP)/g for argon. The neon results showed that at any given pressure and temperature the mass of neon adsorbed was less when the adsorption was on argon-coated copper than on bare copper. Calculations were made of the isosteric heat of adsorptionQ st for neon, and the results are presented graphically as functions of the coverage. For neon adsorption on the bare copper,Q st /R had a maximum value of about 390 K at a coverage of about 0.2 cm3(STP)/m2, and it decreased to about 275 K at 0.5 cm3(STP)/m2. For neon on the argon-coated copper,Q st /R had a maximum value of about 320 K- at the lowest coverages and fell to about 245 K at 0.5 cm3(STP)/m2. The shape of theQ st /R curve vs. coverage for neon indicated that the argoncoated copper was more homogeneous from an adsorptive point of view than the bare copper. TheQ st /R vs. coverage curves allowed an assessment to be made of the monolayer coveragesV m , which were 0.38 cm3(STP)/m2 for neon on the bare sintered copper and 0.34 cm 3 (STP)/m 2 on the argon monolayer coated on the sintered copper. This indicated that the effective area for adsorption on the argon monolayer was 0.37 m 2 /g, which was 10% less than that for the bare copper. In addition, theQ st /R values at monolayer coverage were found to be 306 K on the bare copper and 275 K on the argon monolayer.

Impact ionization in bulk GaAs high field domain

Abstract: An investigation of impact ionization in the high field domains of GaAs Gunn effect devices has been carried out. A method of measuring the number of excess electrons generated per domain transit was developed, based on the measurement of the increase in the valley current from one domain transit to the next while impact ionization is occurring in the domain. This method was used to experimentally determine the carrier generation per domain transit \Delta n/n_{0} as a function of excess domain potential V D for three material carrier concentrations. These results are compared to a theoretical calculation of \Delta n/n_{0} based upon an approximate solution of the continuity equation and invariant domain calculations. The experimental and theoretical results agree to within 2 percent for n_{0} = 3 \times 10^{14} cm-3and 6 percent for n_{0} = 4 \times 10^{14} cm-3.

Production of Quiescent Plasmas in a Magnetic Field by a Beam-Plasma Discharge

Abstract: Very quiet, steady-state plasmas in axial magnetic fields with density fluctuations less than 0.1% may be produced in a beam-plasm discharge. The dependence of the density and electron temperature on the discharge parameters are in accordance with the predictions of a one-dimensional plasma model.

Single-Particle Scattering from Solid He 4

Abstract: An investigation of the high-energy, large-momentum-transfer neutron scattering from the low-density hcp and bcc phases of $^{4}\mathrm{He}$ has revealed scattered neutron groups with the same characteristics as those associated with single-particle scattering in liquid $^{4}\mathrm{He}$. The observed groups of this type are independent of the crystallographic phase and of direction within the accuracy of this investigation. Such neutron groups have been observed at energies as low as 1.5 times the maximum phonon energy in the bcc phase.