Initial Expansion Stage Research Articles

Composition and gas dynamics of laser ablated AlN plumes

The formation, composition and propagation of pulsed laser produced plasma plumes from an AlN target have been studied in real time by spatially and temporally resolved optical spectroscopy. The mean front velocity has been measured and appears to be slightly slower in the presence of added gas than in vacuum. In the initial stage of expansion, this velocity is almost the same for all neutral particles in the plume in the initial stage of expansion. Velocities of neutral and ionic species have been measured by their time of arrival from the target to a quadrupole mass spectrometer and their expansion beam Maxwell-Boltzmann (MB) temperature determined. The plume electronic temperature has been determined by assuming a local thermodynamic equilibrium of the emitting species.

Exact solutions of a flat cosmological model in BSTT

We solve the cosmological equations for the bimetric scalar—tensor theory of gravitation (BSTT) for a flat model of the Friedmann type with the equation of state p = ae. In the initial stage of expansion, the energy density of the scalar field dominates over the energy density of matter. As a result, the behavior of the solution in this limit does not depend on a. For later stages of expansion of the Universe, the solution obtained goes to a special solution having the form of a power law function of time. In this case, the relative change in the gravitational scalar is proportional to the Hubble parameter. In the limit of large values for the parameter of the theory, only a simple solution with zero value of the constant of integration goes to the corresponding Friedmann solution of general relativity theory.

Structure of the tail plasma/current sheet at ∼11 RE and its changes in the course of a substorm

At the end of April 2, 1978, the ISEE 1 and 2 spacecraft moved inbound at ∼11 RE on the nightside (0130 MLT). Due to a flapping motion of the plasma sheet the spacecraft crossed the neutral sheet region (central region of the plasma sheet) more than 10 times in the hour between 2115 and 2215 UT. This provided a unique opportunity to study the structure of the plasma/current region and its evolution during substorm growth and early expansion before the final disruption of the current sheet. Using minimum variance analysis of the magnetic field variations during the crossings as well as finite ion gyroradius diagnostics, we determine the orientation of the current sheet (CS) and then estimate the CS thickness as well as the value of its normal component, Bn. Typically, the current distribution was inferred to be very inhomogeneous with a current concentrated in a very thin CS (only 0.2 to 0.8 RE as thick) embedded inside the thicker plasma sheet. Current sheet crossings could be classified as regular or turbulent. The first type prevailed during the growth phase and at the initial stage of expansion when the spacecraft were well outside (in longitude) of the active region of the substorm and no large plasma flow was detected. The normal field component Bn was typically very small (∼1 nT) in the CS center in comparison to the larger shear magnetic By component. In the course of the growth phase we inferred an increase of the lobe field Bx and a decrease of the CS half thickness h (from h∼3000 km to ∼800 km just before the expansion onset), i.e., a very large increase (up to an order of magnitude) of the current density. At the same time, in disagreement with the usual cartoon picture of magnetic reconfiguration, the magnetic field magnitude in the CS center increased (instead of decreased) at the expense of the shear component. Three turbulent crossings were found during substorm expansion within the longitude range of the substorm current wedge (SCW). The second of them was detected ∼1 min before the main dipolarization and was characterized by a rather small CS thickness (h < 600 km), by strong earthward plasma flow and by a positive normal magnetic field component. That period showed signatures of concentration of both cross‐B and field‐aligned current at the outer edge of CS and may indicate a nearby reconnection region. The main result of this study is that the region of very thin current sheet (thickness of the order of the gyroradius of thermal protons in the field just outside the current sheet), which contained a very small normal component, clearly appeared in the near tail prior to the sudden onset of current disruption as predicted by some quantitative models of quasi‐static evolution of earthward convecting plasma sheet flux tubes. Comparing these observations to theoretical results, we find that the threshold conditions for the growth of the tearing mode instability in sheared magnetic fields were apparently satisfied in this case, but the growth rate was too slow for sudden initiation of substorm expansion.

Dielectric function and electrical resistivity of liquid carbon determined by femtosecond spectroscopy

Femtosecond pump-probe reflectance of graphite and diamond targets following intense laser irradiation is used to measure the optical properties of the pressurized liquid carbon phase while it retains an optically sharp surface before expanding hydrodynamically as a hot plasma. These measurements allow the historically elusive liquid phase of carbon to be characterized optically for the first time. A Drude dielectric model of the reflectance spectrum 1 ps after excitation just above the melting threshold reveals a poorly conducting liquid metal with a dc resistivity 625±75μΩ · cm. The optically determined resistivity decreases with increasing sample excitation. The initial stages of hydrodynamic surface expansion of Al, W, and C targets are also quantitatively characterized by time-resolved reflectance, revealing the expansion speed as well as further dielectric properties of the high-temperature-pressure phase.

Effect of ovariectomy on blastocyst expansion and survival in ferrets (Mustela putorius furo).

The initial objective was to investigate whether progesterone alone can support full blastocyst expansion in ferrets ovariectomized on Day 5 post coitum (p.c.). By Day 11 p.c. blastocysts from control animals had expanded to approximately 2000 microns in diameter, whereas by Days 11 or 14 p.c. blastocysts from ovariectomized animals given progesterone had diameters of < 1000 microns. Thus, ovarian factors in addition to progesterone are apparently required for normal blastocyst expansion in this species. Subsequent experiments indicated that an initial stage of expansion (from approximately 200 microns to approximately 400 microns) occurred regardless of whether ovariectomy was performed on Day 2 or 3 p.c. A second stage of expansion resulted in blastocysts of approximately 700 microns in diameter and it occurred in ovariectomized animals if progesterone was given or if ovariectomy was delayed until Day 5 p.c. A third phase of expansion resulted in blastocysts of approximately 2000 microns in diameter and occurred only if ovariectomy was delayed until Day 8 p.c. Although blastocyst expansion appeared normal in these animals, implantation did not occur in the absence of progesterone replacement. In addition, blastocysts retained in the oviduct by ligation of the uterotubal junction failed to expand beyond approximately 400 microns in diameter. These results suggest that progesterone acts upon the uterus to promote blastocyst expansion up to a diameter of approximately 1000 microns and that additional ovarian factors are required for further blastocyst expansion.

Relationship between brisance of explosives and their molecular-atomic structures

The explosives with various molecular-atomic structures substantially differ by their detonation velocities and brisance but often are similar by the expansion of their detonation products (DP's) which mainly consist of the same molecules. Such explosives referred to as “usual” show the relationship between ϱD and brisance determined by different methods. There are linear correlation relations between the results obtained. This relationship is not observed with the “unusual” explosives which differ from the “usual” ones by the chemistry of detonation processes. These explosives include liquid explosives, explosive-oxidants. CNO- and HNO-explosives and also CHNOF-explosives. Their calculation of thc detonation parameters and brisance from the same criterions which characterize the chemical composition of the explosives and the detonation products, results in some errors. Taking these differences into account it is possible in some cases markedly to increase the accuracy of the detonation parameters. As an example is the calculation of the detonation pressure to within 3% based on the linear correlation relation between the pressure (PJ) and the relative detonation impulse (Irel) which characterizes the charge ability to do work at the initial stages of thc expansion of the detonation products: The relative impulse, in its turn, may be calculated both for “usual” and “unusual” explosives from the atomic composition of an explosive, its density and the enthalpy of the formation with the error that does not exceed the experimental (2%).

Development of Nitrate Reductase Activity in Expanding Leaves of Nicotiana tabacum in Relation to the Concentration of Nitrate and Potassium

Up to 80% of the total nitrate reductase activity (NRA) determined in vivo in different parts of vegetative tobacco plant (Nicotiana tabacum) was located in the leaves. The NRA reached a peak when a leaf had expanded to 27% of its final weight and 33% of its final area. Thereafter, with advancing expansion and age of the leaf, the activity declined. This pattern of development of NRA during the ontogenesis of leaves was not influenced by raising the supply of NO(3) (-) from 3 to 6 milliequivalent per cubic decimeter in the substrate solution. The concentration of NO(3) (-) in leaves, stem and root was inversely related to NRA at both NO(3) (-) levels. Raising the supply of K(+) from 1 to 6 milliequivalent per cubic decimeter at either concentration of NO(3) (-) slowed down the development of NRA in the initial stages of expansion, but promoted it subsequently. The peak of the activity which developed in a leaf of 62% of its final area was higher at the higher supply of K(+). The higher activity was maintained thereafter in the expanding and in matured and older leaves. It was concluded that NRA and the pattern of its development in expanding leaves is related to the availability of metabolites and their incorporation into enzyme proteins. Both these processes are influenced by: (a) the vertical profile of concentration of K(+) in the shoot and (b) the concentration of K(+) in a leaf, which depend upon its supply.

Expansion and evolution of heavy gas and particulate clouds

Physical and mathematical models have been applied to stages of two phase releases following the failure of pressurised vessels. The initial expansion stage has been modelled using an experimental apparatus involving the measurement of pressure versus time and of Freon-11 aerosol particle sizes and velocities. An analysis of the experimental data combined with an appreciation of the thermodynamics has allowed estimations of the time dependent processes. The analytical description of the critical pressure decrease on the opening of the vessel is given. The later evolution stage has been mathematically modelled by assuming that the two phases have separate velocities. The cloud motion characteristics have been shown to depend upon the degree of hydrodynamic interaction between the particles via the gaseous phase. For small particle fractional volumes, this interaction is small and each particle behaves as a single particle corresponding to a “filtration” regime. However, for larger concentrations the air between the particles becomes entrained due to the particle motion and the cloud velocity exceeds that of the single particle. In this “entrainment” regime large scale vortex motion occurs. The cloud is transformed either into two cylindrical vortices for planar symmetry or into a toroidal vortex for axial symmetry. The regime of the cloud motion defines the sedimentation characteristics of the particles.

Laser-initiated channels for ion transport: Breakdown and channel evolution

The electrical breakdown and discharge evolution in CO2 laser-heated molecular gases has been studied. With the laser tuned to a vibrational mode of NH3, C2H4, CH2CHCN, or CH3OH the breakdown potential decreases as much as 10-fold for laser pulse energies up to 35 J/cm2. The subsequent 50–142-cm discharges are straight, stable, and reproducible. Analogous tests in D2 and air yield only a small alteration of breakdown potential and do not cause a straight discharge. The expansion of the initial laser-heated gas has been modeled by the CHARTB hydrocode with the addition of the NH3 equation of state in tabular and analytic form to that code. The breakdown characteristics and initial expansion stage confirm the earlier calculation of laser heating to 1900–2100 °K. Experimental observations of the discharge evolution in NH3 have measured (1) the radial expansion velocity by streak-camera photography of the Hβ emission zone, (2) the plasma temperature by the Niv/Niii line-ratio method, and (3) the electron-density profile by holographic interferometry. The central zone of the channel is heated to 5.5 eV and expands with a radial velocity of 1.0–1.2 mm/μs for the case of a 27-kA discharge in 20 Torr of NH3. Preliminary hydrocode simulations of the discharge show qualitative agreement with observations.

High-speed multiframe interferometry in a laser beam

A description is given of high-speed multiframe interferometry for investigating the spatial distribution of the electron density in plasmas. Special attention is paid to a method for synchronizing a laser source of probe radiation pulses of approximately-less-than1 nsec duration with the beginning of the process being investigated. It is shown that the proposed method can be used for effective monitoring of the degree of symmetry of a laser plasma during the initial stage of expansion after spherical irradiation of a target.

Physical aspects of the improvement of dough by fat

Shortening containing a fraction which is solid at dough temperatures is an essential ingredient in rapid breadmaking processes, but optional in long fermentation processes. Hypotheses concerning the action of fat are reviewed, and it is concluded that physical mechanisms, rather than those involving lipid oxidation, account for the increased loaf volume on the addition of shortening to the dough. Recent work using ‘model’ fats has shown that increased loaf volume results when sufficient of the solid component remains ‘free’ in the dough, and work with stored flour confirmed the importance of the free lipid fraction. A study of carbon dioxide release from doughs during baking showed that fat increases gas retention in the initial stage of rapid expansion. It is suggested that the solid components of the fat facilitate the production of orientated structures in dough, which can persist even when the temperature exceeds the melting point of the fat, and that these structures favour gas retention in the earliest stages of baking.

Nonsteady radial expansion of a gas into a flooded space from a suddenly turned on steady source

The problem of the radial expansion of a gas into a medium of low pressure from a suddenly turned on steady source with M ≥1 is examined in the report. The examination concerns mainly the unsteady flow of gas in the initial stage of expansion. The laws of motion of the surface of a powerful explosion, which determine the structure of the region of flow, are established for the initial stage of expansion with the help of a simple approximate solution of the problem. A method is proposed and a numerical solution of the problem is obtained for a viscous thermally conducting gas in a general formulation.

Criteria for excitation of a shock wave and its intensity during an explosion in a rarefied gas

The effect of the initial pressure of the surrounding gas on the intensity of the shock wave (SW) formed during the dispersion of material vaporized by a powerful laser pulse is examined. The initial stage of expansion of the plasma generated through the focusing of powerful laser radiation on the surface of a solid material in air was studied experimentally in [1, 2]. The times of formation and the initial radii of the SW were recorded on the photo-scans of the SW front radiation presented in these reports. It is found that at an air pressure below ∼ 0.1 mm Hg the recordings of the intrinsic radiation of a flare do not differ from the corresponding recordings in a vacuum. For instance, in [2] a bright shock front was observed at a pressure of 0.18 mm Hg, while at a pressure of 0.1 mm Hg SW radiation was not detected. In [2] the hypothesis was made that at an air pressure below ∼ 0.1 mm Hg a SW is not formed and the interaction of the vaporized material with the surrounding gas has a diffusion nature. However, in [1] SW were detected by the Schlieren method at a considerably lower pressure, about 2 · 10−2 mm Hg. It will be shown below that the sharp decrease observed in the brightness of the radiation of SW fronts generated during laser heating of a solid material in a rarefied gas is explained by the rapid decrease in the maximum SW velocity at a pressure below ∼ 0.1 mm Hg. The expansion of the vaporized material at a pressure of the surrounding gas much less than 0.1 mm Hg is also examined.

Initial stages of hydrodynamic expansion of plasma heated by intense laser radiation

The hydrodynamic equations describing the average behavior of a one-dimensionally expanding plasma heated by laser radiation are solved analytically. For the small parameter approximation, the hydrodynamic expansion depends on the parameter (16P/9Ml02)1/3τL, where P is the laser power, M is the plasma mass, l0 is the initial plasma length, and τL is the laser pulse duration. With τL=τei, the electron ion relaxation time, it is possible to compute φmax (≈5.6×10−6n04l03miT−9/2, where mi is the plasma ion mass and T is the temperature), the maximum flux density below which the hydrodynamic expansion may be neglected. We find that a 5-kJ 75-ns neodymium glass laser is capable of acheiving break-even conditions for a 50% mixture of deuterium-tritium gas.

The growth and development of the storage root of sugar beet

SUMMARYA study was made of the growth of the storage root of sugar beet as a sugar accumulating organ. The storage root grew by simultaneous cell multiplication and expansion from a series of peripheral secondary meristems laid down during the early stages of development. The weight of water and of non‐sugar dry matter per cell increased in proportion to the increase in cell volume. The amount of sugar per cell was proportional to cell volume only during the initial stage of cell expansion up to volumes of about 15 times 10‐8 cm3; thereafter it was less proportional. Thus, average cell size is a major determinant of the sugar concentration of the storage root. The implications of this are discussed.

The Effect of Nitrogen on the Growth and Sugar Content of Sugar-beet

Nitrogen fertilizer applied to sugar-beet increased plant and root dry weight and leaf area, and decreased the sugar content of the roots per cent of both fresh and dry weight. Change in leaf area accounted wholly for the increase in plant dry weight produced by nitrogen, because net assimilation rate was unaffected. Nitrogen did not alter the partition of the total assimilate between roots and shoots, but increased the fraction of total assimilate entering the roots that was used in growth, at the expense of that stored as sugar. Thus, plants with more nitrogen had a smaller proportion of their root dry weight as sugar because more was metabolized in growth of the roots, and not because less entered the roots. The heavier roots of plants given more nitrogen were larger in cross-sectional area because the areas of both parenchyma and vascular zones of each peripheral ring within the root were larger; the number of rings was not increased. Nitrogen increased the areas of the tissues in these zones by enlarging cell volumes, not by increasing the number of cells within the tissues. Increase in cell volume was accompanied by proportional increases in the weights of non-sugar dry matter per cell and water per cell, but the amount of sugar per cell was proportional to cell volume only during the initial stage of cell expansion up to cell volumes of about 15 X io~8 cm3; thereafter it was less than proportional, so that sugar per cent of both fresh and dry weight decreased as cell size increased beyond 15 X io~8 cm3. The relation of sugar per cell to cell volume was the same with both amounts of nitrogen given. This implies that increase in nitrogen supply made the sugar concentration of the root less by increasing the size of the root cells and not by a specific effect on sugar storage.

Turbulence in the Hot Universe

THE development of von Weizsacker's cosmogonical hypothesis1 has led to work2 on the combined hydrodynamical motions of the photon gas and the cosmic plasma in the early hot universe, when the radiation density ρr greatly exceeds the density of matter ρ. In the case of vortex motions, the initial stage of cosmological expansion is non-Friedmannian with anisotropic and inhomogeneous geometry2. But there is some speculation in favour of the motion having a potential character, and in this case the departures from the Friedmann model are small at all epochs, from the general theory3. Here I consider hydrodynamical aspects of the evolution of the cosmic fluid at the matter-dominated stage, assuming cosmological expansion to be described by an open Friedmann model because of a number of observational and theoretical arguments4–6.

Economic Evaluations

Abstract Formulas are developed and presented graphically which permit the rapid evaluation of projects, with the minimum of data and calculation. Methods for more detailed appraisals are discussed with particular reference to the Canadian income taxes, but U.S. taxes are also treated. "Rate of return", or "profitability index", is related to payout times and "profit ratio" for 100 per cent working interest cases. Introduction Many arguments can be put forth both for and against the inclusion of a tax factor in economic analyses. No attempt is made in this paper to resolve this particular controversy, other than to suggest that the payment of income taxes is inevitable, sooner or later, and in one form or another, for any company that is to survive beyond an initial expansion stage. In the first part of this paper, the formulas and arguments are developed both for those who (for policy or other reasons) ignore income taxes, as well as for those who face the prospect of reaching a taxable position in the near future. For the latter cases, it is assumed that the project under consideration is subject to various income tax rates from zero upwards. This, of course, can lead to a conservative estimate, and further, it allows a consistent series of analyses to be made in line with any given tax policy which will be directly comparable as to profitability.