Free Expansion Model Research Articles

Spatial mapping of low pressure cluster jets using Rayleigh scattering

In this work, we report evolution of atomic clusters in a highly under-expanded supersonic jet of Argon. A high resolution and sensitive Rayleigh scattering based experimental set-up is designed to overcome the limitations encountered in conventional set-ups. Further, the measurement range could be extended from a few nozzle diameters to 50 nozzle diameters. Simultaneously, we had been able to generate 2D profiles of the distribution of clusters inside the jet. This paves the way to track the growth of clusters along the flow direction experimentally, which until now was limited to few nozzle diameters. The results show that spatial distribution of clusters inside the supersonic core deviates considerably from the prediction of the free expansion model. We exploit this to estimate cluster growth along the expansion direction. Further, it is observed that the growth of the clusters gets saturated after a certain distance from the nozzle. At the jet boundary, we see substantial cluster strengthening immediately upstream of barrel shock while the normal shock exhibits disintegration of clusters. These observations are noticed for the first time, which, we believe will further the understanding of cluster dynamics in a supersonic jet.

Experimental investigation of rarefied flows through supersonic nozzles

In this paper, we report experimental investigation to improve the shape of a supersonic nozzle for rarefied flows for high axial density at extended distances from the nozzle. The reported work is significant for molecular jet/beam applications that require high center-line density and narrow jet profile. We investigate a parabolic nozzle whose profile is generated using the virtual source model of free expansion and compare its performance with a set of conical nozzles having different cone angles using simulations as well as experiments. Axial density and lateral spread of the jets are measured using a pitot tube assembly. The accuracy and operational limit of the pitot tube for rarefied flow is quantified by using established mathematical and empirical models for a sonic nozzle. The study demonstrates that the performance of the parabolic nozzle is comparable or slightly better as compared to conical counterparts. Moreover, the parabolic profile can be used for optimizing the opening angle for conical nozzles of various lengths.

The Center of Expansion and Age of the Oxygen-rich Supernova Remnant 1E 0102.2-7219

Abstract We present new proper-motion measurements of optically emitting oxygen-rich knots of supernova remnant 1E 0102.2-7219 (E0102), which are used to estimate the remnant’s center of expansion and age. Four epochs of high-resolution Hubble Space Telescope images spanning 19 yr were retrieved and analyzed. We found a robust center of expansion of α = 1h04m02.ˢ48 and δ = −72°01′53.″92 (J2000) with 1σ uncertainty of 1.″77 using 45 knots from images obtained with the Advanced Camera for Surveys using the F475W filter in 2003 and 2013 having the highest signal-to-noise ratio. We also estimate an upper limit explosion age of 1738 ± 175 yr by selecting the knots with the highest proper motions and these knots are assumed to be the least decelerated. We find evidence of an asymmetry in the proper motions of the knots as a function of position angle. We conclude that these asymmetries were most likely caused by interaction between E0102's original supernova blast wave and an inhomogeneous surrounding environment, as opposed to intrinsic explosion asymmetry. The observed nonhomologous expansion suggests that the use of a free expansion model inaccurately offsets the center of expansion and leads to an overestimated explosion age. We discuss our findings as they compare to previous age and center of expansion estimates of E0102, as well as their relevance to a recently identified candidate central compact object.

The Formation of Bimodal Dust Species in Nova Ejecta

The formation of bimodal dust species (namely the silicate and amorphous carbon dust grains coexistent) in a nova eruption is an open problem. According to the nova model simulated by Modules for Experiments in Stellar Astrophysics code, we calculate the formation and growth of carbon (C) and forsterite (Mg2SiO4) dust grains purely in nova ejecta for the fee-expansion model and the radiative shock model by assuming spherical geometry of the nova ejecta. In these models, the chemical properties of pre-existing circumstellar medium are not taken into account. In the free-expansion model, the nova ejecta is not an idea environment for dust nucleation. However, it can efficiently produce dust in the radiative shock model. We estimate that every nova can produce C grains with an average mass of about 10−9 and 10−8 M⊙, and Mg2SiO4 grains with an average mass of about 10−8 and 10−7 M⊙. Based on the mass of ejected gas, the ratio of dust to gas is about 1%. The C grains form first after several or tens of days of nova eruption. After that, the Mg2SiO4 grains begin to grow in tens of days, which is consistent with observations.

Flexural Forces of the Working Rollers and the Broadening of Thin Steel Strip in Hot Rolling

On the basis of the Jourdain variational principle for a rigid–plastic body and the kinematically permissible velocity field, a model of the free expansion in the hot rolling of thin sheet is developed. The functional used in the variational equation is the total power of the internal resistances, the slipping-friction forces, the shear forces, and the front and rear tension. The Ritz method is used in solving the Jourdain variational equation for rolling with tension. The Jourdain variational equation is converted to a system of uniform equations, with a derivative of a variable parameter on the left side of each. The variable parameters are the exponent of the kinematic condition; the total broadening in the plastic-deformation region; and the expansion in its neutral cross section. The mathematical model developed for the broadening of hot-rolled strip may be used to investigate the distribution of broadening along the plastic-deformation region as a function of the parameters of the rolling process and the strip. To verify the model of free expansion, experiments are conducted on a two-roller laboratory cold-rolling mill. Lead samples are rolled. Their measured broadening matches the theoretical values to within 10%. The cold rolling of lead samples simulates hot rolling. Theoretical analysis of the influence of tension on the free expansion is consistent with practical results in the literature. The nonuniform tensile stress seen in the input and output cross sections of the deformation region when tension is applied gives rise to additional powers in the balance equation, with consequent decrease in the broadening. The resulting nonuniformity of the tensile stress may be used to regulate the broadening in thin-sheet rolling. In turn, the nonuniformity of the tensile stress over the strip width may be increased or decreased by means of the flexural forces of the working rollers in the mill. A method of regulating the broadening of the strip in hot rolling by means of the flexural forces of the working rollers is outlined in the present work.

Swelling characteristics of soils derived from black shales heightened by cations in Northern Chongqing, China

Black shale is widely distributed in southern and western China. The swelling and breakdown characteristics of black shale are important physicomechanical properties in engineering activities. Aqueous solutions with different compositions exert various influences on the swelling characteristic of black shale because of the complexity of its composition. Soils derived from black shale are most commonly developed on black shales with bedded horizons that generally have cutting and weathering profiles. This paper reports an axial free swelling study for soils derived from black shales and developed in the Lower Cambrian black shales in Chengkou County, Chongqing Municipality, Southwest China. To discuss the swelling characteristics of black shale under the influence of cations, an axial free swelling test was conducted on black shale samples while considering the initial water content, weathering stage of black shale, and different cationic solutions with various concentrations. Results showed that the swelling deformation curve of black shale could be divided into three phases: acceleration, deceleration, and stability. The axial swelling ratio eventually decreased with increasing water content, and the axial free swelling rate changed with the free expansion model of the exponential relationship. Under a constant initial water content, the axial swelling rate increased with the intensity of black shale weathering in the same immersion solution. When different types of immersion solutions were used, the cationic price was high and the axial swelling rate increased with rising cation valence. The changes in the swelling ratio were significant at a valence of one or two. The results of this study provide further understanding of the engineering geological characteristics of black shale and the geological hazards caused by the swelling characteristics of black shale.

Spatial characterization of laser induced Yb plasma in argon using optical emission spectroscopy: Pressure effect

• Laser induced Yb plasma at different pressure of Argon is spatially investigated. • O-TOF profiles and excitation temperature are used to characterize the plasma. • At 100 Pa of argon background gas, shock wave begins to be formed. • Drag force expansion describes the plasma propagation at pressures bigger than 1 Pa. • Two components of velocity distribution of the Yb atoms are estimated. Spatial and temporal behavior of laser induced Ytterbium plasma plume is studied using optical emission spectroscopy technique. A third harmonic Nd:YAG nanosecond laser was used to generate Yb plasma plume at different Argon background pressures (1, 10, 10 2 , 10 3 and 10 4 Pa). The plasma dynamics was investigated based on the spatial behavior of the excitation temperature coupled with optical time of flight (O-TOF) profiles of neutral Yb emission line (555.65 nm) along the propagation axe of the plasma plume. Drag force model was appropriate to describe the propagation dynamics at all pressures except of the lowest one (1 Pa) where free expansion model is dominant. The velocity distribution of Yb I atoms were extracted using two terms of Shifted Maxwell–Boltzmann (SMB) distribution. The correlation between the spatial comportment of both excitation temperature and O-TOF profiles is discussed.

EXPANDING EJECTA IN THE OXYGEN-RICH SUPERNOVA REMNANT G292.0+1.8: DIRECT MEASUREMENT THROUGH PROPER MOTIONS

We report here the first study of proper motions of fast filaments in the young, oxygen-rich supernova remnant G292.0+1.8, carried out using a series of [O III] 5007 A emission-line images taken over a period of more than 21 years. Images taken at seven epochs from 1986 to 2008, all from telescopes at the Cerro Tololo Inter-American Observatory, show oxygen-emitting filaments, presumably ejecta fragments, throughout most of the remnant. We have measured the proper motions for 67 discrete filaments through two-dimensional correlations between images from different epochs. While the motions are small, mostly 20 to 100 milli-arcsec, they are nevertheless measurable through a robust technique of averaging measurements from many epoch pairs. The data are qualitatively consistent with a free-expansion model, and clearly show systematic motions outward from a point near the center of the radio/X-ray shell. Global fits using this model indicate an expansion center at R.A.(2000.0) = 11:24:34.4, Dec.(2000.0) = -59:15:51, and a kinematic age of 2990+-60 years. The young pulsar PSR J1124-5916 is located 46 arcsec southeast of the expansion center. Assuming that it was launched by the supernova, we expect the pulsar to be moving southeastward at 16 milli-arcsec, or a transverse velocity of 440 km/s. We find the fastest ejecta along an axis oriented roughly N-S in the plane of the sky, suggesting that a bipolar explosion produced G292.0+1.8, as appears to have been the case for Cas A.

Electromagnetic emission under uniaxial compression of ice: II. Analysis of the relationship between an electromagnetic signal and the dynamics of charged dislocation pile-ups

The nature of the electrical activity of mesoscopic defects in Ih ice and the relationship of this activity with the kinetics of plastic deformation and fracture is discussed. The theoretical time dependences of the shear caused by active dislocation pile-ups are compared with the shapes of actual electromagnetic signals generated in different stages of the plastic deformation of Ih ice. Good agreement with the model of free expansion of a conservative dislocation pile-up and the model of nucleation and propagation of a slip band is established.

Manufacturing and Testing of Active Composite Panels with Embedded Piezoelectric Sensors and Actuators

This work presents the manufacturing and testing of active composite panels (ACPs) with embedded piezoelectric sensors and actuators. The composite material employed here is a plain weave carbon/epoxy prepreg fabric with 0.30 mm ply thickness. A cross-ply type stacking sequence is employed for the ACPs. The piezoelectric flexible patches employed here are Active Fiber Composite (AFC) piezoceramics with 0.33 mm thickness. Composite layers with openings are used to fill the space around the embedded piezo patches to minimize the problems associated with ply drops in composites. The AFC piezoceramic patches were embedded inside the composite laminate. High-temperature wires were soldered to the piezo leads, insulated from the carbon substructure by high-temperature materials, and were taken out of the composite laminates employing cutout hole, molded-in hole, and embedding techniques. The laminated ACPs with their embedded piezoelectric sensors and actuators were vacuum bagged and co-cured inside an autoclave employing the cure cycle recommended by the composite material supplier. The Curie temperature of the embedded piezo patches should be well above the curing temperature of the composite materials as was the case here. The capacitance of the piezoelectric patches was measured before and after cure for quality control. The manufactured ACPs were trimmed and then tested for their functionality. A finite element analysis (FEA) model was developed to verify the free expansion of the AFC FEA. Next, the FEA model of the manufactured ACP was developed based on the AFC FEA free expansion model and was employed to test the functionality of the AFCs embedded within the ACPs. Both static and dynamic FEA results of the modeled ACPs showed very good agreements with their corresponding experimental results. Finally, vibration suppression as well as simultaneous vibration suppression and precision positioning tests, using Hybrid Adaptive Control (HAC), were successfully conducted on the manufactured ACP beams and their functionality was further demonstrated. The advantages and disadvantages of ACPs with embedded piezoelectric sensor and actuator patches manufactured employing the abovementioned three wires out techniques are also presented in terms of manufacturing and performance.

A New Optical Sample of Supernova Remnants in M33

We present a new and larger sample of supernova remnants in the nearby spiral galaxy M33. The sample is based upon CCD interference filter observations obtained with the Kitt Peak 4 m telescope and spectroscopic observations obtained with the Multiple Mirror Telescope. Using optical emission-line ratios, supplemented by a radio continuum map of M33 (Duric et al.; Gordon et al.), we have identified 98 supernova remnant (SNR) candidates, of which 53 were previously unknown. We have obtained spectra of 27 SNR candidates, bringing the total number of M33 SNRs for which spectra are available to 72. All the spectra show the characteristic signature of shock-heated gas, which leads us to believe that the rest of the candidates are also supernova remnants. The large sample provides a useful database to investigate the global properties of SNRs. In this paper, we present a new cumulative number-diameter [N(<D)] relation for SNRs. We find that the free expansion model is inconsistent with the observed N(<D) relation and that the Sedov-Taylor (ST) expansion model is a much better fit. The ST expansion model is used to derive a SN rate in M33 of one SN every 360 yr. The spectroscopic sample of SNRs is the largest of its kind in any galaxy. Our investigations show no relation between [N II]:Hα and [S II] λ6717:λ6731. We do, however, find weak trends between the SNR diameter and [N II]:Hα and [S II]:Hα. Further, we find a strong correlation between [N II]:Hα and the galactocentric distance (GCD) indicative of an abundance gradient. There is a large dispersion in the [N II]:Hα ratio at a given GCD that cannot be explained by evolutionary effects and that may be due to a larger abundance dispersion in the inner part of the galaxy.

Theory and modelling of the interaction of two parallel supersonic plasma jets

The objective of the present work is to predict the profile of the shock front formed by the interaction of two parallel diverging supersonic plasma jets. The form of the front is determined by the divergence of the plasma jets and by the distance between their sources, but the maximum angle of the front inclination at the head point of the shock wave is determined by the plasma properties only. The streamlines of the two plasma jets are diverging before the front and are parallel behind it. The diffusion of the ions flying from two different sources was calculated numerically up to a distance of 10 times the source separation in the region bounded by two symmetric shock fronts. For an ion temperature of K, a jet velocity of , and initial densities of and (corresponding to a Mach number of 10 and Knudsen numbers of 0.04 and 0.4 respectively) the partial and total density distribution in the diffusion zone was found. The ion distribution is not homogeneous in all of investigated regions. The most homogeneous distribution was obtained with an initial density of . The shock model predictions were compared with a free expansion model, and the densities are radically different.

Mechanisms affecting kinetic energies of laser-ablated materials

A dynamic source effect was found to accelerate the plume expansion velocity much higher than that from a conventional free-expansion model. A self-similar theory and a hydrodynamic model are developed to study this effect, which may help to explain experimentally observed high front expansion velocity. Background gas can also affect the kinetic energies. High background gas may cause the ablated materials to go backward. Experimentally observed plume splitting is also discussed.

Flight-out-of-view effects in time resolved investigations of excited molecules

In the process of measuring lifetimes of fluorescent molecules, distortions may develop in the exponential decay data due to the tendency of the molecules to escape the field of view during the fluorescent decay. Analytical and numerical methods are discussed in cases where the excitation of the observed molecules is achieved with a pulsed laser and the dispersion of excited molecules is caused by diffusion. The diffusion model approach is compared to the free expansion model approach and the applicability of these models is discussed.

A Pulsed Neutral Particle Source for Active Plasma Diagnosties

A z-pinch gun with a gas puffer was studied as a pulsed neutral particle source for active plasma diagnostics. Typical thermal and drift energies of the gun plasma were 120 eV and 140 eV, respectively. The peak density of fast neutral particles converted from the gun plasma was 6.2×1011cm-3 with an energy of 400 eV at a distance of 1.8 m from the gun. The pulse width was about 4 µsec. It is suggested that this kind of particle source with these values can be used for measuring the spatially-resolved ion temperature of plasmas. The experimental results are analyzed by a collisionless free-expansion model.

Strong shock propagation through decreasing density

The acceleration of a shock wave in an ideal gas of decreasing density has previously been studied. The problem is reconsidered here with empirical inclusion of real-gas effects for strong shocks in hydrogen. Experimental results suggest that previous shock acceleration models are valid only for a limited range of the Knudsen number in finite geometries and that for large final-state Knudsen numbers a free-expansion model best describes the experimental results.