Constant Momentum Research Articles

On optical Airy beams in integrable and non-integrable systems

The interaction of an accelerating Airy beam and a solitary wave is investigated for integrable and non-integrable equations governing nonlinear optical propagation in various media. For the integrable nonlinear Schrödinger equation, by way of a Bäcklund transformation, we show that no momentum exchange takes place, as the only effect of the interaction is to modulate the amplitude of the solitary wave. The latter result also holds for propagation in anisotropic media with birefringent walkoff and nonlocality, as specifically addressed with reference to uniaxial nematic liquid crystals in the absence of beam curvature. When the wavefront curvature characteristic of accelerating Airy beams is accounted for, both asymptotic and numerical solutions show that a small amount of momentum is initially exchanged, with the solitary wave rapidly settling to a state of constant momentum.

Effect of Atmospheric Forcing on Plume Dispersion and Study of Nuclear Effluent Trajectories for the Kalpakkam Coast, India

AbstractThe air–sea interaction process and its implication at the outfall location of a nuclear power plant have been studied using the Princeton ocean model (POM) under varied environmental forcing parameters (momentum and heat fluxes). In the first set of numerical experiments, constant momentum flux is used with reversing wind speeds of 2 and 10 ms−1 respectively. It is observed that with an increase in wind speed, the plume exhibited a narrow directional spread unlike that for low winds. Incorporation of constant heat flux and momentum flux showed marginal difference in the computed sea surface temperature (SST) at the outfall location. In the second set of experiments, variable momentum and heat fluxes were introduced that led to significant variations in SST, salinity, and circulation patterns. A net variation of approximately 2–3°C in SST has been recorded at the outfall location. Finally, the POM and the particle-trajectory tracking model (PTTM) have been integrated to trace the nuclear effluent...

Spray atomization characteristics of a GDI injector equipped with a group-hole nozzle

The main purpose of this paper is to analyze the spray characteristics of a group-hole nozzle in terms of spray behavior and atomization process in comparison to the characteristics of a single-hole nozzle as reference. Spray visualization and PDPA (phase Doppler particle analyzer) experiments were performed using a GDI adjustable injector, which can adopt a different type of nozzle at free spray conditions. By analyzing the spray development behavior and distribution of droplet velocity and diameter based on a time series, and comparing these results with that of a single-hole nozzle, the effects of the group-hole nozzle on the spray characteristics in a GDI injection were elucidated.Experimental results showed that the development processes of spray behavior from a group-hole nozzle were similar to that of the single-hole nozzle. Both the sprays had similar spray tip penetration and dispersion at the same stages of development. However, owing to the constant spray momentum from a spray interaction, the spray behavior from the group-hole nozzle seemed to be more stable than that of the single-hole nozzle. In terms of the averaged droplet size, the group-hole nozzle held an advantage over the single-hole nozzle in decreasing Sauter mean diameter (SMD) by approximately 2μm. In addition, in comparison to the spatial distribution of droplet diameter and velocity between them, it can be confirmed that the group-hole nozzle has strong effects on reduction in diameter as well as rapid dispersion of droplet due to active air entrainment. These atomization characteristics are considered as an important advantages for improving mixture formation in GDI engine.

Pam Johnston Dahl Helm: Lost to our Mothers

In the time I knew Pam Johnstoni during her doctoral study at the University of Wollongong (1995-1998) the search for mothers, the need for certain and indissoluble affections underpinned her art and writing. The father was lost and absent: there was a constant matrilineal momentum in her positioning of herself. “To explore mother daughter relationships, to examine oral histories as a way back to Aboriginal connections to land”, she wrote, was pivotal to her work ( Johnston 1997, p.5). As a tribute to her, and because of my admiration for her courage and passion for justice I would like to tease out some of the complexities of her exploration by placing her in the context of her times.

PLASMA EFFECTS ON FAST PAIR BEAMS. III. OBLIQUE ELECTROSTATIC GROWTH RATES FOR PERPENDICULAR MAXWELLIAN PAIR BEAMS

The distant universe is opaque to γ radiation from blazars due to gamma-gamma attenuation with extragalactic background light. This process produces electron-positron pair beams that interact with the intergalactic medium and are unstable to linear instabilities, particularly the electrostatic and Weibel instabilities. The electrostatic instability grows faster and so determines the dissipation of the free energy of the beam. Here, we generalize the calculation of the electrostatic growth rate to a beam plasma system with a Maxwellian perpendicular momentum spread and allow for oblique propagation directions. We show that the growth rate for the oblique electrostatic mode has a maximum value that is even higher than for a cold beam or for one with a constant perpendicular momentum spread.

Experimental Investigations on Diesel Engine Forced Induction and Exhaust Gas Recirculation (EGR) Using Exhaust Gas Assisted Jet Compressor

Even though the conventional method of supercharging and turbocharging of an internal combustion engine increases the engine specific power output, part of the shaft power developed by the engine is consumed by the superchargers. The control system that is present in both the chargers further complicates the system. This study proposes a novel method of forced induction in a diesel engine by using a jet compressor run by exhaust gas recirculation (EGR). This method apart from increasing the specific power output reduces the NOx formation by the engine due to forced induction. Performance analysis of the jet compressor using exhaust gas as the motive stream and atmospheric air as the propelled stream was carried out. Using the standard available code, the governing equations were solved numerically to get the optimum operating conditions such as exhaust gas pressure, temperature, and flow rate for a three cylinder diesel engine. The dimensions of the jet compressor were determined by solving the energy balance equations obtained from the constant rate momentum change method. Using the commercial software fluent, the performance optimization of jet compressor used for forced induction in a diesel engine was made for different percentage of EGR input and estimated the power output. From the results obtained, a performance map was drawn for the three cylinder diesel engine to get the optimum boost pressure and maximum entrainment ratio for a given percentage of exhaust gas recirculation and power output. Experiments were conducted on a three cylinder diesel engine fitted with a fabricated jet compressor with EGR used for forced induction application. Results obtained from the experiments were in good agreement with the numerical results obtained from fluent analysis.

How Constant Momentum Acceleration Decouples Energy and Space Focusing in Distance–of–Flight and Time–of–Flight Mass Spectrometries

Resolution in time-of-flight mass spectrometry (TOFMS) is ordinarily limited by the initial energy and space distributions within an instrument's acceleration region and by the length of the field-free flight zone. With gaseous ion sources, these distributions lead to systematic flight-time errors that cannot be simultaneously corrected with conventional static-field ion-focusing devices (i.e., an ion mirror). It is known that initial energy and space distributions produce non-linearly correlated errors in both ion velocity and exit time from the acceleration region. Here we reinvestigate an old acceleration technique, constant-momentum acceleration (CMA), to decouple the effects of initial energy and space distributions. In CMA, only initial ion energies (and not their positions) affect the velocity ions gain. Therefore, with CMA, the spatial distribution within the acceleration region can be manipulated without creating ion-velocity error. The velocity differences caused by a spread in initial ion energy can be corrected with an ion mirror. We discuss here the use of CMA and independent focusing of energy and space distributions for both distance-of-flight mass spectrometry (DOFMS) and TOFMS. Performance characteristics of our CMA-DOFMS and CMA-TOFMS instrument, fitted with a glow-discharge ionization source, are described. In CMA-DOFMS, resolving powers (FWHM) of greater than 1000 are achieved for atomic ions with a flight length of 285 mm. In CMA-TOFMS, only ions over a narrow range of m/z values can be energy-focused; however, the technique offers improved resolution for these focused ions, with resolving powers of greater than 2000 for a separation distance of 350 mm.

Measuring Fermi velocities with ARPES in narrow band systems: The case of layered cobaltates

ARPES is a priori a technique of choice to measure the Fermi velocities vF in metals. In correlated systems, it is interesting to compare this experimental value to that obtained in band structure calculations, as deviations are usually taken as a good indicator of the presence of strong electronic correlations. Nevertheless, it is not always straightforward to extract vF from ARPES spectra. We study here the case of layered cobaltates, an interesting family of correlated metals. We compare the results obtained by standard methods, namely the fit of spectra at constant momentum k (energy distribution curve, EDC) or constant binding energy ω (momentum distribution curve, MDC). We find that the difference of vF between the two methods can be as large as a factor 2. The reliability of the 2 methods is intimately linked to the degree of k- and ω-dependence of the electronic self-energy. As the k-dependence is usually much smaller than the ω dependence for a correlated system, the MDC analysis is generally expected to give more reliable results. However, we review here several examples within cobaltates, where the MDC analysis apparently leads to unphysical results, while the EDC analysis appears coherent. We attribute the difference between the EDC and MDC analysis to a strong variation of the photoemission intensity with the momentum k. This distorts the MDC lineshapes but does not affect the EDC ones. Simulations including a k dependence of the intensity allow to reproduce the difference between MDC and EDC analysis very well. This momentum dependence could be of extrinsic or intrinsic. We argue that the latter is the most likely and actually contains valuable information on the nature of the correlations that would be interesting to extract further.

Experimental study of the structure of milled diamond-containing particles obtained by the detonation method

A diamond-containing material (DCM) produced by detonation was mechanically milled using KM-1 and AGO-2S mills. Experimental spectra for infrared (IR) absorption, Raman scattering and X-ray diffraction patterns (XRD) were obtained for the treated DCM samples. We compared the Raman and IR spectra for the KM-1 milled samples and concluded that the surface of the DCM particles was not uniform. The mechanical force that resulted from milling with the AGO-2S destroyed the non-diamond part of the particles and initiated irreversible physical and chemical changes in them. The destruction of the diamond grains was the consequence of these irreversible changes. It follows from the experiments that the dipole momentum of the DCM particle was caused by the presence of polar fragments of molecules. The constant dipole momentum of the particles facilitated the aggregation. Based on this, we proposed a model of a structurally inhomogeneous DCM particle.

Many More Hills to Climb: The Journey of Magnet™ Organizations

After climbing a great hill, one only finds that there many more hills to climb. 1 —Nelson Mandela For those on the Journey to Magnet Excellence™, the quest never really ends, although plateaus may periodically be reached. Magnet organizations must maintain constant forward momentum and consistently evolve. How does an organization that has achieved American Nurse Credentialing Center (ANCC) Magnet Recognition Program® status climb the next hill? It reaches the pinnacle by closely adhering to the 5 Model Components, which are essential to the continued development of the nursing profession and to quality outcomes in patient care, according the ANCC.

Modeling Ammonia Mass Transfer Process from a Model Pig House Based on Ventilation Characteristics

Airflow characteristics above the emission surface inside animal houses play an important role in gaseous and odor emissions. The influence of airflow characteristics, i.e., air velocities and turbulence intensities, on ammonia mass transfer processes were investigated in a model of a finishing pig house. The 1:6 scale model was 1750 1000 605 mm (L W H) and had two sidewall inlets and an exhaust opening in the middle of the ceiling. Different airflow characteristics were generated by using three ventilation control strategies: constant inlet opening area, constant inlet velocity, and constant inlet momentum. Due to the symmetrical nature of the airflow pattern in the scale model, the investigation was conducted in left half of the model. Nonlinear modeling simulated the ammonia mass transfer coefficient (AMTC) as a function of airflow characteristics and jet momentum number. Changes in ventilation control strategies, given the variation of floor air characteristics, changed the ammonia emissions and AMTC. The mean floor air velocities and the root mean square of the floor air velocity fluctuations were correlated to the jet momentum number to the power of 0.56 and 0.54, respectively. AMTC increased proportionally to floor air velocity and turbulence intensity. The AMTC values determined in this experiment were compared to a published study using a 1:12.5 scale model. The correlation of AMTC and jet momentum number for the two models was similar. The relationships obtained in this study could be helpful in understanding the airflow characteristics in the floor region and simulating emission rates from pig houses, while the dependence of AMTC on jet momentum number was confirmed for two different scale models. There is a need to validate it in full-scale houses since the presence of pigs, slatted floors, and porous partitions could alter the relationship of jet momentum number with AMTC.

Constant Momentum Exchange to Maintain Spacecraft Formations

Constant Momentum Exchange to Maintain Spacecraft Formations

Constant Momentum Exchange to Maintain Spacecraft Formations

Constant Momentum Exchange to Maintain Spacecraft Formations

Effect of Top and Bottom Boundary Conditions on Symmetric Instability under Full-Component Coriolis Force

Abstract The linear stability of a zonal flow confined in a domain within horizontal top and bottom boundaries is examined under full consideration of the Coriolis force. The basic zonal flow is assumed to be in thermal wind balance with the density field and to be sheared in both vertical and horizontal directions under statically and inertially stable conditions. By imposing top and bottom boundary conditions in this framework, the number of wave modes increases to four, instead of two in an unbounded domain, as already reported in studies on internal gravity waves. The four modes are classified into two pairs of high- and low-frequency modes: the high modes are superinertial and the low modes are subinertial. The discriminant of symmetric instability is nevertheless determined by the sign of the potential vorticity of the basic zonal flow, as in the case of an unbounded domain. The solutions satisfying the top and bottom boundary conditions are interpreted as the superposition of incident and reflected waves, revealing that the neutral solutions consist of two neutral plane waves with oppositely directed vertical group velocities. This may explain why the properties of wave behavior, such as the instability criteria, remain the same in both the bounded and unbounded domains, although the manifestation of wave activity, such as the order of dispersion relation, is quite different in the two cases. Furthermore, the slope of the constant momentum surface, the slope of the isopycnic surface including the nontraditional effect of the Coriolis force, and the ratio between the frequencies of gravity and inertial waves form an essential set of parameters for symmetric motion. The combination of these dimensionless quantities determines the fundamental nature of symmetric motions, such as stability, regardless of boundary conditions with and without the horizontal component of the planetary vorticity.

The Fokker-Planck equation and statistical characteristics of penetrative convection in the upper ocean

We consider the problem of penetrative convection in the upper ocean under the conditions of sharp surface cooling and a constant momentum flux connected with the existing system of random waves. The Langevin equation with a random right part is used to describe a convective ensemble of thermals. The kinetic Fokker-Planck equation is built for the angular probability density of an ensemble of convective elements. The stationary solution of this equation allows one to find an analogue of the Boltzman distribution for convective currents over speed and height. The Maxwell speed distribution is implemented in this case for convective thermals at a fixed depth. The results allow interpretation of certain data on turbulence in the convective near-surface ocean layer.

Numerical investigation of the grid spatial resolution and the anisotropic character of EMMS in CFB multiphase flow

During the last years, considerable efforts have been made for the optimization of numerical methods simulating the operation of the Circulating Fluidized Bed Combustors (CFBC), which imply both the accuracy increase and the computational cost decrease. A foremost goal is the efficient description of its operation under isothermal conditions and the in-depth understanding of the governing complex multiphase flow mechanisms. Grid construction and the calculation of the drag force experienced by the inert material in the two-phase flow are two important parameters for the optimization of the numerical approaches in the case of CFB simulation. The aim of the present investigation is to investigate both the effect of grid density distribution on simulation results and the validity of an anisotropic approach for the drag force calculation through an Energy Minimization Multi-Scale (EMMS) scheme. Grid density distribution is found to affect the numerical accuracy and the real time of simulations. Uniform grid density distribution is found to be the most efficient choice in terms of balance between computational cost and numerical accuracy. On the other hand, EMMS scheme improves the efficiency of detecting complex particle structures (clusters) without an explicit modeling of these spatio-temporal formations. Moreover, applying EMMS scheme only for calculation of the z-component of drag force yielded better numerical results compared to a constant interphase momentum exchange coefficient for all the three directions.

Damköhler Number Similarity for Static Flame Stability in Gaseous-Fueled Augmentor Flows

Afterburners (or augmentors) are used to increase thrust in aircraft engines. Static flame stability, or the robustness to flame blowoff, is an important metric in the performance assessment of combustion in aircraft engine afterburners, where bluff-body-type flame holders are typically used to stabilize the flame. The design of such flame holders is complicated by the operating conditions, which involve flows at high speed, high temperature, and low pressure. In this paper, experimental and computational studies of Damköhler (Da) number similarity are presented with relevance to augmentor flame stability. The Da number describes the ratio of flow and chemical time scales. Hence, as long as a reference Da number is kept constant, similar characteristics of static stability should be expected of the bluff-body stabilized flame at low and high speeds. Flame stability in high-speed vitiated flows could then be studied at low speed if the chemical time scale is reduced, for instance by lowering the oxidizer flow temperature. However, each chemical reaction has its own Da number and not all can be kept constant at the same time. Since different stabilization mechanisms are governed by different chemical reactions, it is not necessarily clear what the relevant Da number is. Here, a consistent method for defining the Da number is provided based on the analysis of the modeled governing equations. Numerical simulations are performed for three different velocities with the inflow temperature adjusted to keep the Da number constant. Results are validated by comparison with experimental PIV data and the reported flame liftoff height. For the same characteristic Da number and constant momentum ratio between the fuel jet and the vitiated cross flow, the three flames show similar mean features for the recirculation zone and the flame shape. The flow field is found to exhibit von Kármán vortex shedding with the same Strouhal number for all cases. The average nondimensional flame liftoff height is also found to be the same for all cases. These results suggest a method to properly define the Da number to test augmentor stability features in low-speed test facilities under the conditions of similarity.

ENERGY CONTENTS OF GRAVITATIONAL WAVES IN TELEPARALLEL GRAVITY

The conserved quantities, that are, gravitational energy–momentum and its relevant quantities are investigated for cylindrical and spherical gravitational waves in the framework of teleparallel equivalent of General Relativity using the Hamiltonian approach. For both cylindrical and spherical gravitational waves, we obtain definite energy and constant momentum. The constant momentum shows consistency with the results available in General Relativity and teleparallel gravity. The angular momentum for cylindrical and spherical gravitational waves also turn out to be constant. Further, we evaluate their gravitational energy–momentum fluxes and gravitational pressure.

Liquid sheet disintegration at high pressure: An experimental approach

The primary atomization was studied in a 300 μm thickness water sheet, generated by a planar airblast atomizer. The research novelty consisted in increasing the airflow absolute pressure from atmospheric conditions to 6 bar. The experimental techniques employed included Oscillometry by Laser Intensity Reflexion (ORIL), Laser Doppler Velocimetry (LDV) and flow visualization by fast video camera. The atomization mechanisms, described in the literature at atmospheric environments, were observed at high pressure conditions, for a constant momentum flux ratio. Furthermore, a new atomization mechanism was observed at high values of this ratio. Finally, dimensionless relations have been proposed for the global oscillation frequency, minimum air oscillation velocity, break-up distance and transversal wavelength. To cite this article: V.G. Fernandez et al., C. R. Mecanique 337 (2009).

Wall-Propelled, In-Tube Propulsion with Repetitive-Pulse Laser Ablation

Proof-of-principle experiments of in-tube propulsion in which the propellant was supplied from the launch tube wall were conducted. The launch tube had a 25 mm × 25 mm square inner cross-section. A pair of opposing launch tube walls were made of polyacetal (POM), which was ablated using repetitive Transeversely-Excited Atmospheric (TEA) CO2 laser pulses. The laser beam was sent through a ZnSe window at the tube bottom to the symmetric parabolic surfaces of the projectile, and focused onto the ablator surfaces. The momentum coupling coefficient was measured from a vertical launch trajectory. When the breech of the launch tube was plugged, a momentum coupling coefficient of 4 mN-s/J at least was obtained. Even when the breech was connected to a vacuum chamber at a pressure lower than 20 Pa, the projectile could be vertically launched with a constant momentum coupling coefficient of 0.14 mN-s/J, the value of which was the same order as that obtained by directly irradiating a laser pulse onto a POM ablator.