Maximum Compression Ratio Research Articles

Effect of the second-throat on the performance of supersonic-supersonic ejectors

The pressure matching and recovery performances of the second-throat supersonic-supersonic ejector have been performed experimentally and numerically in the current study. Schlieren pictures of flow structure in former part of the mixing chamber with varied stagnation pressure ratio of the primary and secondary flows have been taken, and the maximum compression ratios have been obtained. Additionally, the relevant numerical simulations have been performed. The obtained results show that the pressure matching performance of the second-throat supersonic-supersonic ejector is weaker than that of the constant area one, and the pressure recovery performance of the former is better than that of the latter. For the ejectors tested in this paper, the stagnation pressure ratios of the second-throat supersonic-supersonic ejector at the limiting condition are approximately 10% lower than those of the constant area one when the contraction angle of the mixing chamber is 4°, and the maximum compression ratio is 12%–30% higher. When the contraction angle of the mixing chamber is 6°, the pressure matching performance of the second-throat supersonic-supersonic ejector declines sharply, and the pressure recovery performance remains almost the same. When the contraction angle of the mixing chamber is 8°, the supersonic-supersonic ejection phenomenon does not take place any longer.

Effects of errors in velocity tilt on maximum longitudinal compression during neutralized drift compression of intense beam pulses: II. Analysis of experimental data of the Neutralized Drift Compression eXperiment-I (NDCX-I)

Neutralized drift compression offers an effective means for particle beam focusing and current amplification with applications to heavy ion fusion. In the Neutralized Drift Compression eXperiment-I (NDCX-I), a non-relativistic ion beam pulse is passed through an inductive bunching module that produces a longitudinal velocity modulation. Due to the applied velocity tilt, the beam pulse compresses during neutralized drift. The ion beam pulse can be compressed by a factor of more than 100; however, errors in the velocity modulation affect the compression ratio in complex ways. We have performed a study of how the longitudinal compression of a typical NDCX-I ion beam pulse is affected by the initial errors in the acquired velocity modulation. Without any voltage errors, an ideal compression is limited only by the initial energy spread of the ion beam, ΔΕb. In the presence of large voltage errors, δU⪢ΔEb, the maximum compression ratio is found to be inversely proportional to the geometric mean of the relative error in velocity modulation and the relative intrinsic energy spread of the beam ions. Although small parts of a beam pulse can achieve high local values of compression ratio, the acquired velocity errors cause these parts to compress at different times, limiting the overall compression of the ion beam pulse.

Effects of errors in velocity tilt on maximum longitudinal compression during neutralized drift compression of intense beam pulses: I. general description

Neutralized drift compression offers an effective means for particle beam pulse compression and current amplification. In neutralized drift compression, a linear longitudinal velocity tilt (head-to-tail gradient) is applied to the non-relativistic beam pulse, so that the beam pulse compresses as it drifts in the focusing section. The beam current can increase by more than a factor of 100 in the longitudinal direction. We have performed an analytical study of how errors in the velocity tilt acquired by the beam in the induction bunching module limit the maximum longitudinal compression. It is found that the compression ratio is determined by the relative errors in the velocity tilt. That is, one-percent errors may limit the compression to a factor of one hundred. However, a part of the beam pulse where the errors are small may compress to much higher values, which are determined by the initial thermal spread of the beam pulse. It is also shown that sharp jumps in the compressed current density profile can be produced due to overlaying of different parts of the pulse near the focal plane. Examples of slowly varying and rapidly varying errors compared to the beam pulse duration are studied. For beam velocity errors given by a cubic function, the compression ratio can be described analytically. In this limit, a significant portion of the beam pulse is located in the broad wings of the pulse and is poorly compressed. The central part of the compressed pulse is determined by the thermal spread. The scaling law for maximum compression ratio is derived. In addition to a smooth variation in the velocity tilt, fast-changing errors during the pulse may appear in the induction bunching module if the voltage pulse is formed by several pulsed elements. Different parts of the pulse compress nearly simultaneously at the target and the compressed profile may have many peaks. The maximum compression is a function of both thermal spread and the velocity errors. The effects of the finite gap width of the bunching module on compression are analyzed analytically.

Ultrasound Beamforming Using Compressed Data

The rapid advancements in electronics technologies have made software-based beamformers for ultrasound array imaging feasible, thus facilitating the rapid development of high-performance and potentially low-cost systems. However, one challenge to realizing a fully software-based system is transferring data from the analog front end to the software back end at rates of up to a few gigabits per second. This study investigated the use of data compression to reduce the data transfer requirements and optimize the associated trade-off with beamforming quality. JPEG and JPEG2000 compression techniques were adopted. The acoustic data of a line phantom were acquired with a 128-channel array transducer at a center frequency of 3.5 MHz, and the acoustic data of a cyst phantom were acquired with a 64-channel array transducer at a center frequency of 3.33 MHz. The receive-channel data associated with each transmit event are separated into 8 × 8 blocks and several tiles before JPEG and JPEG2000 data compression is applied, respectively. In one scheme, the compression was applied to raw RF data, while in another only the amplitude of baseband data was compressed. The maximum compression ratio of RF data compression to produce an average error of lower than 5 dB was 15 with JPEG compression and 20 with JPEG2000 compression. The image quality is higher with baseband amplitude data compression than with RF data compression; although the maximum overall compression ratio (compared with the original RF data size), which was limited by the data size of uncompressed phase data, was lower than 12, the average error in this case was lower than 1 dB when the compression ratio was lower than 8.

An Analytical Model for a Piezoelectric Axially Driven Membrane Microcompressor for Optimum Scaled Down Design

A new and comprehensive analytical model for membrane microcompressors driven axially by a single lead zirconium titanate (PZT) stack actuator that incorporates assembly variation errors is presented. The model can be used as a future design aid, to predict dynamic device performance as a function of error severity and as microcompressor dimensions are scaled down from the macro to micro scale. The major conclusion of this work is that since micro compressors can be made adjustable to achieve maximum compression ratio another factor besides assembly variation error reduces the achievable compression ratio. An analytical method to predict the maximum pressure to within ∼5% of that experimentally measured is developed. Also, a numerical method to predict the maximum pressure to within ∼0.6% of that experimentally measured is defined. Moreover, an analytical method to predict the compression ratio degradation factor as a function of assembly variation error for adjustable and fixed devices is presented. It is shown that compression ratio is a function of this single net error parameter, and that this function is scale invariant. The model also outputs membrane moments, vertical shear forces, and stresses throughout actuation cycles.

Performance increase in turbomolecular pumps with curved type blades

Mostly, flat-type blades are used in the turbomolecular pumps in both rotor and stator sections. In this study, performance characteristics of the turbomolecular pumps consist of one rotor or rotor–stator pair with flat-type blades is calculated in different flow regimes. Next, the same calculations are realized for the curved-type blades in dissimilar geometries. Following, these performance characteristics are compared to find out which combination is the most efficient in terms of maximum pumping speed and maximum compression ratio. In case of turbomolecular pump consists of only one rotor, flat blades give the best performance. However in rotor–stator pairs, the performance of the flat-type only blades is surpassed by a combination of rotor with flat-type blades and stator with curved-type blades. Consequently, it is concluded that curved-type blades should also be considered in stator sections in addition to the flat-type blades in order to increase the performance of the multi-stage turbomolecular pumps.

Simulation Research on how to Improve the Range Resolution of Pulse Compression Radar Based on Phase Coding

Phase coded radar signal is one of the pulse-pulse modulation signal in the radar system. Based on the characteristics of matched filtering, we theoretically analyze the basic principle of the phase coded compression radar system. In the Matlab platform, we set up a simulation model which is used for matching filter, when the radar transmitting signal is Barke code signal. The simulation results show that Echo signal can obtain certain pulse compression ratio. By the matched filter, the main lobe amplitude of 13 bits Barker code signal is 22 times the rate of side-lobe. 13 bits Barker codes by the matched filter have the maximum pulse compression ratio.

Converging shocks in elastic-plastic solids

We present an approximate description of the behavior of an elastic-plastic material processed by a cylindrically or spherically symmetric converging shock, following Whitham's shock dynamics theory. Originally applied with success to various gas dynamics problems, this theory is presently derived for solid media, in both elastic and plastic regimes. The exact solutions of the shock dynamics equations obtained reproduce well the results obtained by high-resolution numerical simulations. The examined constitutive laws share a compressible neo-Hookean structure for the internal energy e=e(s)(I(1))+e(h)(ρ,ς), where e(s) accounts for shear through the first invariant of the Cauchy-Green tensor, and e(h) represents the hydrostatic contribution as a function of the density ρ and entropy ς. In the strong-shock limit, reached as the shock approaches the axis or origin r=0, we show that compression effects are dominant over shear deformations. For an isothermal constitutive law, i.e., e(h)=e(h)(ρ), with a power-law dependence e(h) is proportional to ρ(α), shock dynamics predicts that for a converging shock located at r=R(t) at time t, the Mach number increases as M is proportional to [log(1/R)](α), independently of the space index s, where s=2 in cylindrical geometry and 3 in spherical geometry. An alternative isothermal constitutive law with p(ρ) of the arctanh type, which enforces a finite density in the strong-shock limit, leads to M is proportional to R(-(s-1)) for strong shocks. A nonisothermal constitutive law, whose hydrostatic part e(h) is that of an ideal gas, is also tested, recovering the strong-shock limit M is proportional to R(-(s-1)/n(γ)) originally derived by Whitham for perfect gases, where γ is inherently related to the maximum compression ratio that the material can reach, (γ+1)/(γ-1). From these strong-shock limits, we also estimate analytically the density, radial velocity, pressure, and sound speed immediately behind the shock. While the hydrostatic part of the energy essentially commands the strong-shock behavior, the shear modulus and yield stress modify the compression ratio and velocity of the shock far from the axis or origin. A characterization of the elastic-plastic transition in converging shocks, which involves an elastic precursor and a plastic compression region, is finally exposed.

Simulation Analysis of Transmission-Line Impedance Transformers With the Gaussian, Exponential, and Linear Impedance Profiles for Pulsed-Power Accelerators

Based on the transmission-line code, a 1-D circuit model for the transmission-line impedance transformer with an arbitrary impedance profile is developed, and the simulation results are compared with those of the existing literatures. By using this model, the power efficiencies and pulse compression ratios of the transformers (with Gaussian, exponential, and linear impedance profiles) were quantified as functions of Ψ (the ratio of the output impedance to the input impedance of the transformers) and Γ (the ratio of the pulsewidth to the one-way transit time of the transformers). The simulation results indicate that the exponential transformers have the maximum power efficiencies and pulse compression ratios. However, in the limit h <; 0.05 (where h is the Gaussian parameter), the Gaussian transformers almost have the same power efficiencies and pulse compression ratios as the exponential ones. Finally, the performances of a radial transformer line in smoothing the arrival time variations in the forward-going power pulses were studied. The simulation results show that, for the cases considered, the rise time (0-1.0) of the output pulse is prolonged by about half of the maximum difference in the time at which the pulses are launched, and the reduction of the peak output power is less than 2% when the maximum difference is 30 ns.

Fuel and diluent property effects during wet compression of a fuel aerosol under RCM conditions

Wet compression of fuel aerosols has been proposed as a means of creating gas-phase mixtures of involatile diesel-representative fuels and oxidizer+diluent gases for rapid compression machine (RCM) experiments. The intent of this study is to investigate the effects of fuel and diluent gas properties on the wet compression process, specifically to: (a) explore a range of fuels which could have applicability in aerosol RCM experiments, and illustrate important limitations due to fuel properties, and (b) fundamentally understand how fuel and diluent gas properties affect the wet compression process and assess which ones are most important. Insight gained from this work can be utilized to aid the design and successful operation of aerosol RCMs. A spherically-symmetric, single-droplet wet compression model is used where n-heptane, n-dodecane, 2,2,4,4,6,8,8-heptamethylnonane (isocetane), n-hexadecane (cetane) and n-eicosane are investigated as the diesel-representative fuels, while comparisons are made to water droplets. Nitrogen, neon and argon are selected as the gas-phase diluents while the oxidizer is considered to be oxygen at atmospheric concentrations. Initial droplet diameters of d0=3 and 8μm are used based on results of previous studies where the overall compression time is set to 15.3ms with the maximum volumetric compression ratio 13.4. An overall equivalence ratio of φ=1.0 is used.It is shown that under these conditions, involatile fuels up to ∼n-hexadecane appear to be candidates for aerosol RCM experiments. However, the use of small droplets (d0<5μm) will be necessary in order to ensure complete vaporization and adequate gas-phase mixing in advance of low temperature chemical reactivity. Fuels with higher boiling points might not be useable unless extremely small droplets (d0<1μm) and low pressures (e.g., P0<0.5bar) are employed along with longer compression times. In addition, the boiling curve (i.e., saturation pressure) and Lf are found to be the dominant fuel properties while the density-weighted mass diffusivity, ρgDg, which controls the rate of gas phase mass diffusion, and thus compositional stratification, generally plays a secondary role. The heat capacity and molar mass are the dominant diluent properties that affect the near-droplet and ‘far-field’ conditions. The gas-phase mixture Lewis number (Leg) contributes to either greater compositional (Leg>1) or thermal (Leg<1) stratification. For large hydrocarbons and oxygenated hydrocarbons that are representative of diesel fuels Leg∼3–5, and therefore compositional stratification could be significant; this characteristic has the potential to complicate interpretation of ignition/oxidation data acquired from these machines.

Rayleigh-Taylor instabilities in Type Ia supernova remnants undergoing cosmic ray particle acceleration - low adiabatic index solutions

This study investigates the evolution of Rayleigh–Taylor (R–T) instabilities in Type Ia supernova remnants that are associated with a low adiabatic index γ, where γ < 5/3, which reflects the expected change in the supernova shock structure as a result of cosmic ray particle acceleration. Extreme cases, such as the case with the maximum compression ratio that corresponds to γ= 1.1, are examined. As γ decreases, the shock compression ratio rises, and an increasingly narrow intershock region with a more pronounced initial mixture of R–T unstable gas is produced. Consequently, the remnant outline may be perturbed by small-amplitude, small-wavelength bumps. However, as the instability decays over time, the extent of convective mixing in terms of the ratio of the radius of the R–T fingers to the blast wave does not strongly depend on the value of γ for γ≥ 1.2. As a result of the age of the remnant, the unstable gas cannot extend sufficiently far to form metal-enriched filaments of ejecta material close to the periphery of Tycho’s supernova remnant. The consistency of the dynamic properties of Tycho’s remnant with the adiabatic model γ= 5/3 reveals that the injection of cosmic rays is too weak to alter the shock structure. Even with very efficient acceleration of cosmic rays at the shock, significantly enhanced mixing is not expected in Type Ia supernova remnants.

Resolution improvement of femtosecond laser induced two-photon polymerization based on phase filtering

Femtosecond laser induced two-photon polymerization has the advantages of high resolution and capability of true three-dimensional (3D) fabrication. In this work, a phase filter-based super-resolution tech- nique was adopted to reduce the size of focus spot in order to achieve exceeded diffraction limit fabrication resolution. The principle of phase modulation of a femtosecond laser was introduced, the parameters of the phase filter were optimized using a genetic algorithm, and then a 3D super-resolution annular phase filter was fabricated. Experimental results proved that the aspect ratio as well as the axial and radial sizes of so- lidified units was compressed by the optimized phase filter. A maximum aspect ratio compression ratio of 20.8% was achieved. The radial com- pression ratio of the modulated spot decreased with the increase of laser exposure amount, while the axial compression ratio and aspect ratio com- pression ratio increased. C 2011 Society of Photo-Optical Instrumentation Engineers

Exploring Application-Level Semantics for Data Compression

Natural phenomena show that many creatures form large social groups and move in regular patterns. However, previous works focus on finding the movement patterns of each single object or all objects. In this paper, we first propose an efficient distributed mining algorithm to jointly identify a group of moving objects and discover their movement patterns in wireless sensor networks. Afterward, we propose a compression algorithm, called 2P2D, which exploits the obtained group movement patterns to reduce the amount of delivered data. The compression algorithm includes a sequence merge and an entropy reduction phases. In the sequence merge phase, we propose a Merge algorithm to merge and compress the location data of a group of moving objects. In the entropy reduction phase, we formulate a Hit Item Replacement (HIR) problem and propose a Replace algorithm that obtains the optimal solution. Moreover, we devise three replacement rules and derive the maximum compression ratio. The experimental results show that the proposed compression algorithm leverages the group movement patterns to reduce the amount of delivered data effectively and efficiently.

Numerical simulation of turbomolecular pump over a wide range of gas rarefaction

A gas flow through a turbomolecular pump is modeled by the direct-simulation Monte Carlo method over a wide range of gas rarefaction covering the free-molecular, transitional, and hydrodynamic regimes. Several values of the rotor speed are considered. The main characteristics of the pump, such as maximum pumping speed and compression ratio, are reported. It is pointed out that in the range between the free-molecular and transitional regimes, the pump characteristics change slightly, but they vary significantly in the hydrodynamic regime. It is shown that the pumping speed increases in the hydrodynamic regime when the rotor speed is high, but it decreases for a small value of the speed. The compression ratio always decreases when approaching the hydrodynamic regime.

Hugoniot of shocked liquid deuterium up to 300 GPa: Quantum molecular dynamic simulations

Quantum molecular dynamic (QMD) simulations are introduced to study the thermophysical properties of liquid deuterium under shock compression. The principal Hugoniot is determined from the equation of states, where contributions from molecular dissociation and atomic ionization are also added onto the QMD data. At pressures below 100 GPa, our results show that the local maximum compression ratio of 4.5 can be achieved at 40 GPa, which is in good agreement with magnetically driven flyer and convergent-explosive experiments; At the pressure between 100 and 300 GPa, the compression ratio reaches a maximum of 4.95, which agrees well with recent high power laser-driven experiments. In addition, the nonmetal-metal transition and optical properties are also discussed.

New spiral molecular drag stage design for high compression ratio, compact turbomolecular-drag pumps

Currently, commercially available turbo-drag pumps for high vacuum systems are based on either Gaede- or Holweck-type molecular drag pumping stages used in series downstream of axial bladed stages to extend the maximum compression ratio up to the 10 mbar foreline pressure range. Modern Gaede-type molecular drag stages use a disk-shaped impeller, allowing a very compact design, and the maximum compression ratio is limited by the leakage effect to about 10 per stage. Holweck stages are able to supply a high pumping speed, thanks to the presence of many channels in parallel and a high compression ratio, but this is obtained with the use of a less compact drum-shaped impeller. In this article, a new spiral molecular drag stage design is presented with the advantages of both high compression ratio and pumping speed per stage and very compact design: a stage occupying the very small axial space of one Gaede can supply the same compression ratio and pumping speed of a Holweck stage of the same diameter and peripheral speed in a much smaller axial space. The new spiral drag stage allows the design of very compact, high compression ratio turbo-drag pumps. The comparison of a 700 l/s turbo-drag pump implementing the new spiral molecular drag pump design with the existing Gaede- and Holweck-based products of the same pumping speed is presented, showing the performance advantages of the new design.

Effects of Body Weight, Height, and Rib Cage Area Moment of Inertia on Blunt Chest Impact Response

Objective: The purpose of this study was to determine the effects of body weight, height, and rib cage area moment of inertia on human chest impact responses in frontal pendulum impacts. Methods: A series of parametric studies was conducted with 11 cases of finite element (FE) analysis using a commercially available three-dimensional (3-D) FE model of the whole human body, Total HUman Model for Safety (THUMS). Selected parameters in this study were body weight, height, and area moment of inertia of the rib cage and of the ribs alone. Three body sizes assumed were those of a large male (AM95), a mid-sized male (AM50), and a small female (AF05). The initial impact response, maximum chest force, maximum deflection, maximum compression ratio, and the number of rib fractures and fractured ribs were examined for statistical analysis. Results: Body weight and height of the human body do not show any correlation with any injury variable considered in this study. However, area moment of inertia of the rib cage correlated (r = −0.86 and p = 0.001) with maximum chest compression ratio, which is the best predictor of the number of rib fractures. Conclusion: The area moment of inertia of the rib cage or ribs alone would affect the response and injury variables in frontal pendulum impacts.

Experimental Demonstration of Emittance Compensation with Velocity Bunching

In this Letter we report the first experiments aimed at the simultaneous demonstration of the emittance compensation process and velocity bunching in a high brightness electron source, the SPARC photoinjector in INFN-LNF. While a maximum compression ratio up to a factor 14 has been observed, in a particular case of interest a compression factor of 3, yielding a slice current of 120 A with less than 2 microm slice emittance, has been measured. This technique may be crucial in achieving high brightness beams in photoinjectors aiming at optimized performance of short wavelength single-pass free electron lasers or other advanced applications in laser-plasma accelerators.

An Efficient Low Complexity Lossless Coding Algorithm for Medical Images

Problem statement: Nowadays a large number of various medical images are generated from hospitals and medical centers with sophisticated image acquisition devices, the movement toward digital images in radiology presents the problem of how to conveniently and economically store, retrieve and transmit the volume of digital images. Thus digital image data compression is necessary in order to solve this problem. So in a wide range of medical applications such as disease diagnostic and during the compression process, the loss of information is unacceptable; hence medical images are required to be at high resolution as possible. Instead of lossy compression with relatively high compression ratio, mathematical lossless compression methods are favored in this field. Approach: In this study, an efficient new lossless image coding algorithm using a simple technique was presented. Our coding algorithm was based on pixel redundancy reduction by formulating two matrices only, which were Gray Scale Matrix (GSM) and Binary Matrix (BM). These matrices had been used for coding and decoding processes. Results: Results showed that the maximum compression ratio achieved using the proposed method was 4:1, which was more efficient than the present lossless techniques, moreover the computational complexity is greatly simplified; therefore producing very fast coding and decoding. Conclusion: This algorithm was most suitable for those images where lossy compression was avoided such as medical images used for teleradiology and other telemedicine purposed and it can be applied to other medical modalities.

Thermodynamic conditions of shock Hugoniot curves in hot dense matter

We use a self-consistent model combining the Quotidian Equation Of State and a nonrelativistic screened-hydrogenic model with ℓ-splitting to study the thermodynamic conditions encountered along shock Hugoniot curves. We focus on the maximum compression ratio reached on shock Hugoniot curves for simple elements that are solid at normal temperature and pressure. Electron shell effect and pressure ionization can have a strong impact on the results. Numerical calculations are presented and discussed. Some of the physical points addressed in this work could be tested experimentally when the National Ignition Facility laser in the USA attains full power or when the Laser Mégajoule in France comes online.