Sharpening of the front of the current through a cylindrical foil liner

Results are presented from experiments on the electromagnetic implosion of aluminum foil liners at the MIG generator with a current rise time of ≈80 ns. Plasma with a density of 10¹⁷ cm^–3 was preliminarily injected into the liner region by using a set of radial plasma guns. The Lorentz force J × B causes plasma acceleration in the radial direction. Since the magnetic field pressure is inversely proportional to the radius squared, the plasma displacement is maximum near the liner surface. As a result, plasma motion becomes two-dimensional, a gap appears between the plasma and the liner, and the generator current is switched over to the liner. The plasma velocity at the liner surface is close to the local Alfvén velocity, while the time during which the current is switched over to the liner is nearly equal to the ratio of the liner length to the Alfvén velocity. The proposed scheme allows one to decrease the rise time of the current through the liner to several nano-seconds and, as a result, to reduce the initial liner radius and improve the stability of liner implosion.     

Gas-puff liner implosion in the configuration with helical current return rods

Results of experiments with double-shell gas-puff liners carried out on a high-current MIG generator (2 MA, 80 ns) are presented. To stabilize the process of liner implosion and increase the efficiency of energy transfer from the generator to the liner plasma, a current return in the form of a multifilar helix was used. The effect of the configuration of the current return on the parameters of the generated pulses of argon and neon K-shell radiation (with photon energies of 3–5 and 0.9–1.5 keV, respectively) and the neutron yield from a deuterium liner were studied.     

Relation between the electric parameters of a Z-pinch discharge and plasma production in the load during the implosion of a cylindrical wire array

A study of the process of implosion of a cylindrical tungsten wire array by electrical and optical methods shows that it involves two phases. In the first phase, the plasma is produced from the dense wire cores under the action of the heat flux from the current-carrying plasma. This plasma then fills the internal space of the liner array. The measured inductance of the liner and its visible diameter vary only slightly in this phase. During the second phase, the total material of the liner is compressed toward the axis and the inductance of the discharge gap increases. The process of the implosion of wire arrays is studied by analyzing the electric parameters (current and voltage) of the load in the Angara-5-1 facility. The time behavior of the load inductance, the average current radius, and the start time of the liner compression are determined. The compression start time determined from the visible size of the liner is found to coincide with that determined from electric measurements. The compression ratio of the liner in terms of the average current radius turns out to be lower than that measured by optical and X-ray diagnostics. The reason is that, by the instant of maximum compression, only a portion of the current flows at the periphery of the initial wire array.     

Interferometric measurements of the plasma density at the Z-pinch periphery in the angara-5-1 facility

Knowledge of spatial mass distribution is important for understanding the physics of implosion of megaampere-current wire arrays. The paper presents results from studying the electron density distribution at the periphery of a tungsten wire array near the instant of maximum compression by using laser interferometry at λ=0.69 µm. It is found that, at the instant of maximum compression (～100 ns after the beginning of the discharge), the estimated maximum local electron density inside the wire array reaches ～10¹⁸ cm^?3 at a distance of 0.3–3 mm from the initial wire positions. Assuming the average tungsten ion charge to be 10, the local linear mass density in this region turns out to be 3 µg/cm, which amounts to about 10% of the total linear mass density of the liner. A fraction of the generator current flows through this plasma. The duration of the soft X-ray pulse is 5–8 ns, which indicates the achievement of a fairly high compression ratio.     

Initial stability of modular acetabular components. Comparative in-vitro study with polyethylene and ceramic liners.

Modular acetabular components with alumina ceramic liners are currently used in total hip arthroplasty, but concerns have emerged regarding their high stiffness, which could cause impairment of stability, stress-shielding phenomena, and loosening. The purpose of the present biomechanical investigation was to compare the in-vitro initial stability of a modular press-fit acetabular component using a polyethylene liner and using an alumina liner. The initial stability was investigated by measuring the micromotion between the implant and the acetabulum during the application of physiological load (2.39 kN). The micromotion of the acetabular component was investigated in 10 acetabuli using a polyethylene liner and in 10 acetabuli using an alumina liner. Micromotion was assessed at the level of the Os ilium, Os pubis, and Os ischium using 3 electromagnetic transducers. The transducers have a sensitivity of 1 micron and a range of measurement of 500 microns. All implants have been fixed on human pelves made of polyurethane. Measurement of implant micromotion showed stable conditions at the level of the three main sectors of the acetabulum during all tests. No statistically significant differences of results were observed between the group of specimens with polyethylene liner and the group of specimens with alumina liner. The mean micromotion values of the uncemented cups were similar to the mean micromotion values of 10 cemented cups investigated to achieve comparative data of stability. In conclusion, the modular acetabular components inserted using an alumina liner showed a satisfactory initial stability in-vitro. The results do not contrast with those achieved using the same cup inserted with a polyethylene liner.     

Ceramic cups for hip endoprostheses. 5: Consideration of designs]

Using the combination ceramic on ceramic for hip prostheses, the wear rate can be reduced to less than 1 micron per million cycles. More than 20 years of experience are now available for various concepts involving alumina ceramics in THR. In the early days, monolithic ceramic cups were employed. However, since alumina ceramic has an unsatisfactory potential for bone integration, soft tissue forms at the interface, with the result that the sockets migrate and penetrate. To improve bony integration, monoblock cups surfaced with ceramic beads were introduced. For the past 10 years, there has been a trend towards the use of modular acetabular components comprising a metal shell and a liner made of Biolox forte ceramic. Two concepts for the fixation of the ceramic liners are employed: locking of the ceramic in the metal shell (CeraLock) and the sandwich concept with a polyethylene layer interposed between liner and shell. The basic design and important aspects such as diameter, range of motion, and the possibility for revision, clinical experience, and trends are discussed.     

K-shell radiation from double-shell argon plasma liners

Experiments on the generation of argon K-shell radiation during the implosion of double-shell plasma liners are described. The optimum liner length with respect to the maximum K-shell radiation yield is determined. At a liner current of ～1.4 MA, the conversion efficiency of the generator electric energy into the K-shell radiation energy attains 8–9%. The spectrum of the argon K-shell radiation is measured by a set of photoeission X-ray diodes with different filters (including an argon gas filter). Based on the measurements of the emission power in different spectral intervals and calculations by the collision-radiative model, the ion density and electron temperature of the pinch plasma are estimated.     

Experiments on the implosion of heterogeneous wire arrays on the S-300 facility

Results are presented from experiments on the implosion of simple and nested wire arrays of different mass and material composition (W and/or Al). The experiments were performed on the S-300 facility (a high-current pulsed power generator with a voltage pulse amplitude of 700 kV, current amplitude of 2.5–3.5 MA, and pulse duration of 100 ns) at the Kurchatov Institute (Moscow). The imploding arrays were recorded using five-frame laser shadowgraphy, three-frame image-tube photography, an optical streak camera, X-ray pinhole cameras with different filters, X-ray polychromator, and X-ray spectrometer on the basis of a convex mica crystal. Laser probing measurements indicate that the current-carrying structure undergoes a fast (over a time shorter than 10 ns) global rearrangement, which manifests itself as the emergence of transparent regions. This effect is presumably related to the grouping of the wires, which carry currents of a few tens of kiloamperes, or to the current filamentation in their common plasma corona. The radiation of liners of different chemical composition in the final compressed state has been investigated. Electric measurements performed in experiments with nested arrays (e.g., with an aluminum outer liner and a tungsten inner liner) indicate that the inner array, which is still at rest, intercepts the electric current from the outer array when the latter penetrates through it. The effect of the “fall” of the outer liner through the inner one in the course of magnetic implosion has been revealed for the first time by analyzing X-ray emission spectra.     

Evaluation of alginate compressed matrices as prolonged drug delivery systems

This research investigated the use of sodium alginate for the preparation of hydrophylic matrix tablets intended for prolonged drug release using ketoprofen as a model drug. The matrix tablets were prepared by direct compression using sodium alginate, calcium gluconate, and hydroxypropylmethylcellulose (HPMC) in different combinations and ratios. In vitro release tests and erosion studies of the matrix tablets were carried out in USP phosphate buffer (pH 7.4). Matrices consisting of sodium alginate alone or in combination with 10% and 20% of HPMC give a prolonged drug release at a fairly constant rate. Incorporation of different ratios of calcium gluconate leads to an enhancement of the release rate from the matrices and to the loss of the constant release rate of the drug. Only the matrices containing the highest quantity of HPMC (20%) maintained their capacity to release ketoprofen for a prolonged time.     

The effects of topology and relative density of lattice liners on traumatic brain injury mitigation

This paper evaluates the effects of topology and relative density of helmet lattice liners on mitigating Traumatic Brain Injury (TBI). Finite Element (FE) models of new lattice liners with prismatic and tetrahedral topologies were developed. A typical frontal head impact in motorcycle accidents was simulated, and linear and rotational accelerations of the head were recorded. A high-fidelity FE model of TBI was loaded with the accelerations to predict the brain response during the accident. The results show that prismatic lattices have better performance in preventing TBI than tetrahedral lattices and EPS that is typically used in helmets. Moreover, varying the cell size through the thickness of the liner improves its performance, but this effect was marginal. The relative density also has a significant effect, with lattices with lower relative densities providing better protection. Across different lattices studied here, the prismatic lattice with a relative density of 6% had the best performance and reduced the peak linear and rotational accelerations, Head Injury Criterion (HIC), brain strain and strain rate by 48%, 37%, 49%, 32% and 65% respectively, compared to the EPS liner. These results can be used to guide the design of lattice helmet liners for better mitigation of TBI.     

Design factors influencing performance of constrained acetabular liners: finite element characterization

Constrained acetabular liners are utilized to deal with the infrequent but devastating problem of recurrent dislocation. While an encouraging treatment of last resort, the clinical performance of contemporary constrained liners has been somewhat mixed. There are multiple factors contributing to this variability, one of which is the limited understanding of the intrinsic mechanical characteristics of these specialty devices. To address this issue, a three-dimensional, materially nonlinear, multi-surface contact finite element model of a representative constrained liner was created. The model was physically validated, and then used for parametric testing to explore the effects of individual design features. The model was exercised for both intra-operative assembly and lever-out dislocation. It was found that the coefficient of friction between the femoral head and the liner substantially affected both the force required to seat the femoral head into the liner during assembly, and the peak moment resisting dislocation (226% increase in assembly force for friction coefficients of 0.2 versus 0.0; 49% reduction in dislocation moment for friction coefficients of 0.013 versus 0.135). As expected, the cup opening radius also had a dominant effect on both maneuvers: decreasing the opening radius from 13.9 to 13.6 mm increased assembly force by 506 N and increased the dislocation moment by over 3.5 N-m, whereas the influence of other design parameters was much more modest.     

Finite element simulation of early creep and wear in total hip arthroplasty

Polyethylene wear particulate has been implicated in osteolytic lesion development and may lead to implant loosening and revision surgery. Wear in total hip arthroplasty is frequently estimated from patient radiographs by measurement of penetration of the femoral head into the polyethylene liner. Penetration, however, is multi-factorial, and includes components of wear and deformation due to creep. From a clinical perspective, it is of great interest to separate these elements to better evaluate true wear rates in vivo. Thus, the aim of this study was to determine polyethylene creep and wear penetration and volumetric wear during simulated gait loading conditions for variables of head size, liner thickness, and head–liner clearance. A finite element model of hip replacement articulation was developed, and creep and wear simulation was performed to 1 million gait cycles. Creep of the liner occurred quickly and increased the predicted contact areas by up to 56%, subsequently reducing contact pressures by up to 41%. Greater creep penetration was found with smaller heads, thicker liners, and larger clearance. The least volumetric wear but the most linear penetration was found with the smallest head size. Although polyethylene thickness increases from 4 to 16 mm produced only slight increases in volumetric wear and modest effects on total penetration, the fraction of creep in total penetration varied with thickness from 10% to over 50%. With thicker liners and smaller heads, creep will comprise a significant fraction of early penetration. These results will aid an understanding of the complex interaction of creep and wear.     

Time-course of tomato whole-plant respiration and fruit and stem growth during prolonged darkness in relation to carbohydrate reserves

To evaluate the relevance of a simple carbon balance model (Seginer et al., 1994, Scientia Horticulturae 60: 55-80) in source-limiting conditions, the dynamics of growth, respiration and carbohydrate reserves of tomato plants were observed in prolonged darkness. Four days prior to the experiments, plants were exposed to high or low light levels and CO(2) concentrations. The concentration of carbohydrates in vegetative organs was 30-50 % lower in plants that were exposed to low carbon assimilation conditions compared with those exposed to high carbon assimilation conditions. During prolonged darkness, plants with low carbohydrate reserves exhibited a lower whole-plant respiration rate, which decreased rapidly to almost zero after 24 h, and carbohydrate pools were almost exhausted in leaves, roots and flowers. In plants with high carbohydrate reserves, the whole-plant respiration rate was maintained for a longer period and carbohydrates remained available for at least 48 h in leaves and flowers. In contrast, fruits maintained fairly stable and identical concentrations of carbohydrates and the reduction in their rate of expansion was moderate irrespective of the pre-treatment carbon assimilation conditions. The time-course of asparagine and glutamine concentrations showed the occurrence of carbon stress in leaves and flowers. Estimation of source and sink activities indicated that even after low carbon assimilation, vegetative organs contained enough carbohydrates to support fruit growth provided their own growth stopped. The time of exhaustion of these carbohydrates corresponded grossly to the maintenance stage simulated by the model proposed by Seginer et al. (1994), thus validating the use of such a model for optimizing plant growth.     

Study of micromotion in modular acetabular components during gait and subluxation: a finite element investigation

Polyethylene wear after total hip arthroplasty may occur as a result of normal gait and as a result of subluxation and relocation with impact. Relocation of a subluxed hip may impart a moment to the cup creating sliding as well as compression at the cup liner interface. The purpose of the current study is to quantify, by a validated finite element model, the forces generated in a hip arthroplasty as a result of subluxation relocation and compare them to the forces generated during normal gait. The micromotion between the liner and acetabular shell was quantified by computing the sliding track and the deformation at several points of the interface. A finite element analysis of polyethylene liner stress and liner/cup micromotion in total hip arthroplasty was performed under two dynamic profiles. The first profile was a gait loading profile simulating the force vectors developed in the hip arthroplasty during normal gait. The second profile is generated during subluxation and subsequent relocation of the femoral head. The forces generated by subluxation relocation of a total hip arthroplasty can exceed those forces generated during normal gait. The induced micromotion at the cup polyethylene interface as a result of subluxation can exceed micromotion as a result of the normal gait cycle. This may play a significant role in the generation of backsided wear. Minimizing joint subluxation by restoring balance to the hip joint after arthroplasty should be explored as a strategy to minimize backsided wear.     

Studies of penetration of the magnetic field into electrically imploded loads in the Angara-5-1 facility

Results are presented from measurements of the distributions of the azimuthal magnetic field in aluminum, copper, molybdenum, tungsten and other wire arrays electrically imploded at currents of up to 3 MA in the Angara-5-1 facility. It is shown that the time during which the magnetic field of the current pulse reaches the array axis depends on the material of the wires or wire coating. The current of the precursor formed on the array axis before the implosion of the main load mass is measured. It is shown that the penetration of the load material with the frozen-in magnetic field into a polymer (agar-agar) foam liner is drastically different from that in the case of a wire array. It is found that the rate of current transfer to the array axis is maximum for tungsten wire arrays. The rates of plasma production during implosion of loads made of different materials are compared.     

X-ray backlighting of the axial region of a multiwire liner plasma in the angara-5-1 facility

Results are presented from experiments on the X-ray backlighting of the axial region of an imploding high-current multiwire liner. Backlighting was performed with the use of an X-pinch serving as a source of soft X-ray emission, which was recorded by pin diodes. The use of several filters with different passbands in front of the pin diodes allowed the interpretation of the results of measurements in experiments with cascade composite liners. The sensitivity of the diagnostics was ≈125 µg/cm² for a plasma of high-Z elements (W) and ≈220 µg/cm² for a plasma of low-Z elements (C, O, N) at a photon energy of the probing radiation of 1.0–1.5 keV. An advantage of the method is its high time resolution (≈1 ns) and the possibility of the separation in time of the emission bursts from Z-and X-pinches on the liner axis. The method does not impose restrictions on the pulse duration of the backlighting radiation source.     

Non-biological production of ethylene in the acetylene reduction assay for nitrogenase

Summary Ethylene is formed as a result of contact between trichloroacetic acid and the rubber serum cap liners commonly used in the acetylene reduction assay for nitrogenase activity. The amount of ethylene produced varies from one rubber liner to another, but the rate is approximately linear over an eight-day experimental period. Immediate withdrawal of a sample of the gas phase from the incubation bottle at the end of the experiment, and storage in another vessel is recommended as an alternative to the addition of any substance to terminate experiments.     

Study of the current-sheath formation during the implosion of multishell gas puffs

Results are presented from experimental studies of the dynamics of large-diameter multishell gas puffs imploded by microsecond megampere current pulses. The experiments were conducted on the GIT-12 generator in the regime of microsecond implosion (t _imp = 1.1–1.2 μs, I ₀ = 3.4–3.7 MA). The influence of the load configuration on the dynamics of current losses and gas-puff radiative characteristics was studied. The correlation between the radial compression ratio (the ratio between the initial and final Z-pinch radii) and the magnitude of the current flowing at the plasma periphery was investigated. The experiments show that, in a multishell gas puff, large-scale instabilities insignificantly affect the gas-puff implosion even over microsecond time intervals and that a compact dense pinch with a relatively high average electron temperature (400–600 eV) forms at the Z-pinch axis. The diameter of the plasma column radiating in the K-shell lines of neon is about 3–4 mm, the K-shell radiation yield being 5–11 kJ/cm. In the final stage of implosion, only a small portion of the current flows through the high-temperature central region of the pinch plasma, whereas the major part of the generator current flows through the residual peripheral plasma.     

Egg shell quality in Japanese quail: characteristics,heritabilities and genetic and phenotypic relationships

The objective of the present study was to estimate heritabilities as well as genetic and phenotypic correlations for egg weight, specific gravity, shape index, shell ratio, egg shell strength, egg length, egg width and shell weight in Japanese quail eggs. External egg quality traits were measured on 5864 eggs of 934 female quails from a dam line selected for two generations. Within the Bayesian framework, using Gibbs Sampling algorithm, a multivariate animal model was applied to estimate heritabilities and genetic correlations for external egg quality traits. The heritability estimates for external egg quality traits were moderate to high and ranged from 0.29 to 0.81. The heritability estimates for egg and shell weight of 0.81 and 0.76 were fairly high. The genetic and phenotypic correlations between egg shell strength with specific gravity, shell ratio and shell weight ranging from 0.55 to 0.79 were relatively high. It can be concluded that it is possible to determine egg shell quality using the egg specific gravity values utilizing its high heritability and fairly high positive correlation with most of the egg shell quality traits. As a result, egg specific gravity may be the choice of selection criterion rather than other external egg traits for genetic improvement of egg shell quality in Japanese quails.     

Dynamics of a high-temperature pinch in the presence of dust

Results are presented from experimental studies of the formation of a pinch in a plasma focus discharge in the presence of Al₂O₃ dust grains. Considerable attention is given to an analysis of the method for creating a dust target and determining its parameters. Phase transitions in a dust medium have been analyzed. It is found that the phase state of the dust component can be substantially affected by the radiation of the imploding plasma shell even in the preimplosion phase of the discharge. It is shown that a pinch produced in the presence of dust is more stable against MHD instabilities.