Absence Of Oscillations Research Articles

Monte-Carlo simulations of MBE growth of III–V semiconductors: The growth kinetics, mechanism, and consequences for the dynamics of RHEED intensity

Results of Monte Carlo simulations carried out to examine the nature of the growth mechanism in MBE of lattice matched III–V compounds are presented. The role of surface molecular reaction kinetics associated with the dissociative chemisorption of the group V molecular specie is explicitly investigated for the first time and shown to lead to a new configuration-dependent-reactive-incorporation (CDRI) growth process, quite distinct from the conventional notions of nucleation and continuous growth. For very slow dissociative reaction kinetics the CDRI growth process is shown to lead to a reaction-limited-incorporation (RLI) growth mechanism and the accompanying growth rate exhibits oscillatory behavior. For fast dissociative reaction kinetics, accompanied with a sufficiently fast surface interlayer migration kinetics of the group III atoms, the CDRI growth process gives rise to a configuration-limited-reactive-incorporation (CLRI) growth mechanism. The crystal growth rate once again exhibits oscillations. It is also shown that under conditions involving specially delicate balance between the various kinetic rates, growth can proceed without oscillations in the growth rate. An essentially layer-by-layer mode of material addition is realized in all the aforementioned cases. Consequences of the resulting growth front morphology for the time dependence of the RHEED specular beam intensity are investigated and shown to give rise to a damped oscillatory behavior, including in the absence of oscillations in the crystal growth rate.

Heat transfer by high-frequency oscillations: A new hydrodynamic technique for achieving large effective thermal conductivities

Heat transfer between two fluid reservoirs maintained at different temperatures and connected to each other via a capillary bundle is examined when the fluid within the capillaries is oscillated axially. Very large effective axial heat conduction rates, exceeding those possible with heat pipes by several orders of magnitude, are found to be achievable. A laminar hydrodynamic theory is developed to describe the phenomenon and to show that the enhanced heat conduction is one involving radial heat transfer across very thin Stokes’s boundary layers existing in these flows. Experimental measurements using water as the working fluid show effective thermal diffusivities up to 17 900 times those existing in the absence of oscillations. Since the process involves no net convective mass transport, it offers considerable promise as a means for the rapid removal of heat from radioactive fluids.

Homeostatic Characteristics of Single Species Fish Stocks in Arctic Lakes

The results of investigations on the fish stocks of seven Arctic lakes covering a period of 23 yr are described. These lakes have remained largely undisturbed since their formation in late glacial times; all but one are completely autonomous and of comparatively small size. Such lakes provide a unique opportunity for the development and testing of conceptual models. In all cases the only fish species present is Arctic charr, Salvelinus alpinus. Length frequency distributions derived from gillnet catch curves are shown to be, within reasonable limits, representative of the actual populations in the lake, and not artifacts of the sampling procedure. Length frequency curves show a unimodal or bimodal distribution and this structure, in the absence of perturbation, appears to remain constant indefinitely. Individuals are of great age but age-at-length is highly variable. Age and size structure are shown to be comparable with the age and size structure of the dominant tree species in a climax forest; it is concluded that forces of great generality fashion these configurations. It is hypothesized that all species tend to move towards a state of least energy dissipation; this can be most readily seen in the dominant species at the climax in an autonomous system. The dominant species is characterized by large individual size, a high degree of uniformity, high total biomass, great mean age, indeterminate age-at-death, and a low incidence of replacement stock. After severe perturbation it is shown that the charr stock returns to a state of least dissipation without oscillation. Absence of oscillation during the return to the initial state, combined with the long-term stability shown in control lakes, indicates the presence of an effective damping mechanism; this in turn indicates the existence of organization within the stock as a whole. Organization develops through an interactive mechanism described under the doctrine of homeokinesis, which is responsible for energy equipartitioning and the maintenance of uniformity. These concepts help to explain phenomena observed in more complex systems and help our understanding of ecosystem functioning.

The electron neutrino oscillation problem

If we accept the Moscow tritium decay results, indicating that v e is mostly made of mass 14–44 eV components, and if we exclude near degeneracies between these heavier components, we find rather tight correlations between v e → v e oscillations in different ranges of distance/energy. This argument allows a closer comparison between experiments in different ranges, and suggests that some results (or interpretations) are in conflict. For example, the absence of oscillations in accelerator experiments puts a stringent bound on reactor and solar effects, contrary to some reactor results and to the popular interpretation of the solar neutrino puzzle. Non-diagonal v e → v α ( α ≠ e) effects are also bounded. This adds further interest to checking the tritium decay result and to examining possible theoretical reasons for mass degeneracy.

The Hybrid Parametric Amplifier

This paper calculates the gain and noise performance of a new version of the parametric arnplifier in which the signal circuit is part of an artificial transmission line while the idler circuit is resonant. A particularly useful property of this type of parametric amplifier is absence of oscillation with increasing pump power.

Comments on "A new continuously tunable sinusoidal oscillator without external capacitors"

Bhattacharyya and Natarajan have established the condition for oscillation of a three operational amplifier (OA) active-R oscillator. This letter shows that the integrator model used by them is incorrect. Analysis, based on single pole model, indicates the absence of oscillations. However, conditions for oscillations exist when a two pole model of the OA's is taken.

Absence of oscillations in the magnetic field dependence of the rate of carbonylation of nickel

Measurements of the temperature, pressure, and magnetic field dependence of the rate of the reaction Ni + 4CO = Ni(CO)/sub 4/ are presented. No evidence for an oscillatory dependence of the rate on the strength of the magnetic field is found. 6 figures.

Dynamic properties of a heterogeneous catalytic reaction with several steady states

For the simplest catalytic mechanism (three-stage) permitting several steady states of the surface, a qualitative analysis of the properties of its kinetic model trajectories has been performed. Types of the steady states have been determined. Absence of oscillations (damped and undamped) has been shown.

Fusion Cross Sections of Light Heavy-Ion Systems: Resonances and Shell Effects

The total fusion cross sections for the systems $^{12}\mathrm{C}$ + $^{12}\mathrm{C}$, $^{18}\mathrm{O}$ + $^{12}\mathrm{C}$, and $^{19}\mathrm{F}$ + $^{12}\mathrm{C}$ have been measured as a function of bombarding energy and compared with results for other light heavy-ion systems. The presence or absence of oscillations in the fusion excitation function and the overall magnitude of the cross section at high energies appear to depend on the structure of the colliding nuclei.

Convective Losses in a Thermionic Plasma with Shear

Experiments on anomalous transport in a Q machine with a hard core providing magnetic shear show shear-dependent particle losses in the absence of oscillations. It is demonstrated that these Bohmlike losses are caused by steady plasma convection in asymmetric electric fields produced by small temperature gradients in the end plates and that the effect of shear is to symmetrize the convective patterns by twisting the equipotentials into tight spirals. A finite-Larmor-radius theory of transport by convection is presented which correctly predicts the observed increase of confinement with shear. Estimates of the absolute magnitude of losses by this mechanism indicate that at least half of the anomalous transport in Q machines is due to plasma convection, at least in magnetic fields below 4 kG.

Aggregation of Cat Platelets in Vitro

SummaryAggregation of cat platelets in the citrated plasma is examined by means of Born’s absorptiometer. A marked tendency of the platelets of this species to spontaneous aggregation necessitated first of all the development of an improved technique of blood collection.A hypothesis according to which 5-HT is released from the platelets, explains the absence of oscillations on the base line of the absorptiometer, the absence of platelet swelling, when ADP is added, and the effect of stirring on the aggregation curves in cat PRP. The average volume of cat platelets amounts to 10.46 μ3 when directly fixed in the blood, when fixed from PRP to 12.17 μ3, when fixed from stirred PRP to 13.51 μ3.In low concentrations (0.3-2 μM) ADP produce reversible aggregation; in narrowly restricted, individually dissimilar mean concentrations irreversible aggregation in two phases and in high concentrations, irreversible aggregation in one phase. Like ADP serotonin produces 2 phase irreversible aggregation in concentrations of 3-10 μM, but unlike ADP, the aggregation velocity decreases again with high 5-HT concentrations (>100 μM). Adrenaline does not produce aggregation and it is likely that adenosine and adenosine monophosphate inhibit the aggregation by serotonin but not by ADP. Species differences in the aggregation of human, rabbit and cat platelets are discussed.

INTERACTION MECHANISMS OF LASER TRANSITIONS IN ARGON AND KRYPTON ION LASER

A mechanism is proposed to explain anomalous interaction effects between laser lines in Ar+ and Kr+. Radiative transitions connecting the upper level of the directly modulated laser line and the lower level of the cross-modulated line are responsible for the anomalous behavior. This mechanism is supported by the presence or the absence of reciprocity in the anomalous interaction related with the presence or the absence of oscillation on the connecting transition, by the strong ``out-of-phase'' cross modulation on the connecting transition, and by the lack of upper-level pumping processes suitable for explaining the anomalous interaction.

Ultrasonic sensing of objects in gaseous media

This paper describes the method detecting objects in gaseous media when they interrupt an ultrasonic acoustic beam forming part of a closed-loop arrangement. The loop (Fig 1) consists of transmitting and receiving sensors respectively connected to the output and input terminals of an amplifier, with the acoustic beam linking the two sensors. Negatively damped oscillations occur when the open-loop gain exceeds unity and when the loop phase shift is an integral number of 2π radians. The presence or absence of oscillations in the loop determine whether the acoustic beam is clear or has been interrupted by an object. Some properties of the sensors and acoustic beam are given so that operation of the sensing system as a closed loop may be described.

CHEMICAL REACTIONS IN ELECTRICAL DISCHARGES: III. THE POSITIVE COLUMN IN D-C. GLOW DISCHARGES THROUGH OXYGEN

Discharges through fast-flowing oxygen have been investigated. It has been shown that the electrical field remains constant in the positive column of a particular mode, even in the presence of a large pressure gradient. It was found that five types of discharges could be distinguished and they can be characterized by fluctuations of the voltage at the electrodes. These oscillations are linked with the absence or presence of travelling waves in the column. The conditions of existence of the various discharges are outlined. It has also been shown that the structure of the positive column is not as homogeneous as previously thought. In particular, even at constant field, changes in the electron temperature and the number density of charged species are shown to occur. The change in electron temperature and the presence or absence of oscillations have been shown to affect the rate of production of atomic oxygen and the emission intensity of the spectrum of these discharges.

Fetal respiratory movements in response to rapid changes of CO2 in carotid artery

Recent studies have suggested that chemoreceptors may respond to the rate of change of carbon dioxide as well as its level in arterial blood. The blood which perfuses the carotid body of the fetus would be expected to have less cyclic changes in blood gases since the placenta is the organ of gas exchange. The absence of oscillations in blood gases may contribute to the lack of sustained respiratory activity in utero. Slow changes in fetal blood gases do not initiate fetal respiratory activity. Rapid infusions of blood equilibrated with high CO2 mixtures into the carotid artery of exteriorized fetal guinea pigs and a lamb were associated with gasps. It is proposed that the initiation of rhythmic breathing at birth may depend in part on the oscillations in CO2 which follow use of the lung as the organ of gas exchange. oscillations, Pco2; first breath; chemoreceptors Submitted on July 20, 1964

On the Stability of a Plane Flame Front in Oscillating Flow

Recent experimental studies revealed a close connection between spontaneous excitation of organ-pipe oscillations by flames propagating in tubes and flame front instability characterized by cellular structure. On the basis of these observations a dominant mechanism of vibratory flame movement is proposed, consisting of the following two steps: 1. As a consequence of acceleration instability, the oscillation of the gas column alternatingly distorts and flattens the flame front, thus creating the observed vibration-induced cell structure. 2. The distortions of the flame front cause in turn periodic changes of flame surface area and therefore of burning rate. Spontaneous oscillations are excited if the phase relation between burning rate variation and pressure oscillation is favorable. In this paper only the first step is analyzed. The linearized treatment yields stability limits in terms of dimensionless parameters representing amplitude and frequency of gas column oscillation and wavelength of flame front distortion. The properties of the flame front entering into the analysis are the ratio of densities of unburned and burned gases, the burning velocity of the plane flame front, and a characteristic length that determines its stability in the absence of oscillations. Results in qualitative agreement with experimental observations are derived.

A Direct Measurement of the Intensity Variations of the Helium Lines with Voltage

The intensity variations with voltage of some of the brighter lines of the low voltage helium arc spectrum were determined by means of a recently developed photoelectric spectrophotometer. The radiation was developed in a copper ball, 20 cm in diameter. The equipotential cathode and grid from a commercial three-electrode tube formed the internal structure, the sphere itself being the anode. This arrangment gave an extremely bright spectrum, even at the striking voltage, with a relatively low current density in the space. The results on $5016 (1^{1}S\ensuremath{-}2^{1}P)$ and on $6678 (1^{1}P\ensuremath{-}2^{1}D)$ were generally smooth curves. Lines $4026 (1^{3}P\ensuremath{-}4^{3}D)$, $4471 (1^{3}P\ensuremath{-}3^{3}D)$, and $5876 (1^{3}P\ensuremath{-}2^{3}D)$, show a region of constant intensity with arc voltages from 27 to 35 volts, thereafter increasing smoothly. Line $4713 (1^{3}P\ensuremath{-}3^{3}S)$ shows definite maxima near the critical exciting potentials. The accurate linear relationship between the intensity of the light admitted to the photoelectric cell and the amplified output of the photoelectric cell was established by a separate experiment. For the measurements on the spectrum lines, every intensity measurement was referred to a standard lamp operated at a constant resistance. The absence of oscillations in the arc current was shown by a vacuum tube voltmeter.