Secondary Plasma Research Articles

Photocatalytic performance and microstructure of thermal-sprayed nanostructured TiO 2 coatings

Titanium dioxide coatings were deposited by atmospheric plasma spraying (APS) with the use of agglomerated P25 powders and different spraying parameters (e.g. power) to determine their influence on the microstructure and photocatalytic performance of the coatings. The microstructure of as-sprayed TiO 2 coatings was characterized by scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD). The photocatalytic performance was evaluated by using methylene blue (MB) aqueous solution. The results showed that the power and flow of the secondary plasma gas have an important influence on the microstructure and on the anatase content of the TiO 2 coatings. Porosity is also a key factor in determining the photocatalytic performance of the TiO 2 coatings.

JNK Regulates DKK1 Expression in Multiple Myeloma Cells.

Multiple myeloma (MM), a tumor of terminally differentiated plasma cells, depends on the bone marrow for growth and survival. MM is characterized by extensive bone loss and osteolytic lesions located at the sites of medullary plasmacytomas, suggesting that myeloma cells alter the biology of bone remodeling. Wnt signaling in osteoblasts is essential for the maintenance of osteoblast and osteoclast homeostasis and thus coupled bone turnover. MM plasma cells, but not those from healthy donors or MGUS, secrete Wnt signaling inhibitors DKK1, sFRP-2 and sFRP-3. The production of these factors contributes to osteolytic lesions by inhibiting Wnt signaling in the bone marrow milieu. It is currently not known how DKK1 expression is activated and regulated in MM. Here we report that DKK-1 expression is significantly lower in 45 myeloma cell lines (MMCL) and 5 secondary plasma cell leukemias/ pleural effusions compared to primary myeloma cells and down-regulated in all 9 primary myeloma cells with high DKK1 expression levels (Affymetrix Signal > 1,000) following co-culture with osteoclasts. This inhibition of DKK1 is associated with the simultaneous down-regulation of JUN, FOS, and FOSB, of which JUN has been shown to regulate DKK1 (Grotewald and Ruther, 2002). Ectopic expression of c-Jun in Jun negative MMCLs did not induce DKK1 expression, indicating that DKK1 transcription in this cell type is not solely dependent on c-Jun. DKK1 transcription increased 2- to 20-fold in myeloma cells from 21 of 42 primary MM following 48 hour of in-vivo exposure to thalidomide and 19 of 24 exposed to lenolidomide. The JNK-specific inhibitor SP600125 could significantly inhibit the up-regulation of DKK1 in 7 of 9 primary MM cells following in-vitro exposure to thalidomide or lenolidomide. Finally, treatment of MMCL and primary MM with the JNK activator Anisomycin resulted in up-regulation of DKK1 2- to 5-fold, but not in the presence of SP600125. These data indicate that DKK1 expression in MM cells is, in part, dependent on JNK signaling and suggests that JNK inhibitors may be an effective means of inhibiting both DKK1 expression and MM bone disease.

TALKING ABOUT…

TALKING ABOUT…

Optical observations of the development of secondary instabilities on the eastern wall of an equatorial plasma bubble

Optical evidence is presented for the growth of a local secondary plasma instability on the eastern wall of an equatorial plasma bubble observed from the Haleakala Volcano, Hawaii (geographic: 20.71 N, 203.83 E; geomagnetic: 21.31 N, 271.45 E). Typically, only the western wall of depletions at tropical latitudes are susceptible to secondary structuring. This event occurs during a minor geomagnetic storm when the plasma bubble is observed to be drifting to the west, rather than with the typical eastward drift velocity. The data are interpreted in terms of the generalized E × B instability with an anomalous wind directed westward and toward the equator. This wind drives the eastern wall of the depletion region unstable. The anomalous wind is associated with an equatorward propagating neutral wind surge caused by an ongoing geomagnetic storm. The observations of the growth of these instabilities in the local tropical ionosphere are in stark contrast to the typical development of secondary instabilities on equatorial plasma bubbles, which grow near the equatorial plane on the western wall of the primary depletion and map along the magnetic field lines to off‐equatorial latitudes.

VAD combination chemotherapy followed by bortezomib may be an effective treatment in secondary plasma cell leukemia

VAD combination chemotherapy followed by bortezomib may be an effective treatment in secondary plasma cell leukemia

Suppression of aromatase activity in populations of bream ( Abramis brama) from the river Elbe, Germany

Aromatase activity was determined in brain and gonads of wild bream collected along the river Elbe, Germany, and correlated with other endocrine and reproductive endpoints such as plasma sex steroid concentrations, secondary sex characteristics (STI), plasma vitellogenin, gonad size (GSI), and maturation stages of germ cells (MS) that were reported for the same fish in a previous study. Furthermore, regional patterns of aromatase activity were correlated to a number of environmental factors such as exposure to environmental contaminants and parasitism. While aromatase activity was not detectable in the gonads of male and female fish with the assay used, fish of both genders revealed relatively great brain enzyme activities. As for most of the endocrine and reproductive parameters, with the exception of plasma testosterone (T), aromatase activities were significantly less in fish from a river stretch characterized by elevated exposures to organic contaminants and metals. Brain aromatase activity was positively and significantly correlated with plasma estradiol (E2) and MS in females, and showed a similar trend with plasma 11-ketotestosterone (11KT) and STI in males. No comparable trend occurred for T. This decrease of the reproductively relevant hormones 11KT and E2 may be indicative of a disruption of the last step in sex hormone synthesis, a hypothesis that was supported for E2 by the strong ( R 2 = 0.78, p < 0.05) linear regression between aromatase activity and E2 in female bream. It is also hypothesized that the effects on brain aromatase activity were likely to be related to the disruption of other reproductive parameters including sexual maturity and expression of secondary sex characteristics. Although a number of factors such as exposure to pollutants and prevalence of the tapeworm Ligula intestinalis correlated with the suppression of aromatase activity, the exact causes for the regional decrease in brain aromatase activity remain unclear due to inconsistencies of these correlations between sampling events or gender.

Investigation of the electrical discharge parameters in electrodeless inductive lamps with a re-entrant coupler and magnetic core

The inductively coupled fluorescent lamp with a cored induction coil placed in a re-entrant cavity is in fact a coaxial transformer operated in the radiofrequency range between 100 kHz and a few MHz. The magnetic coupling coefficient k between the primary coil and the plasma ring is relatively low because of the open magnetic circuit. The acting mutual inductance M enables us to quantify the interaction between the magnetic field produced by the primary coil current I1 and the opposing magnetic field produced by the powerful plasma current I2. A contra-electromotive force jωMI2 is induced in the induction coil L1, defining the primary voltage V1 = I1(R1 + jω L1) − jωMI2. The current I1 induces in the secondary conductive plasma the driving electromotive force jωMI1 supplying the secondary load consisting of the average plasma resistance R2 and the secondary inductance L2, according to the equation jωMI2 = I2(R2 + jωL2). It is the aim of this paper to find a model to determine k on the basis of the measured primary parameters V1, I1, P1, L1, R1 and finally all electrical inaccessible parameters, such as M, V2, I2, φ2, L2, R2, in order to optimize the discharge and lamp efficacy. The complex characteristic of plasma inductance for this type of lamp is analysed and clarified. Some reflexive basic relations verifying the correctness of the inferred plasma parameters are also developed. The described experiments are related to a lamp working at about 2.6 MHz.Corrections were made to this article on 7 July 2006. The corrections were made to the third line from the end of the right-hand column of page 466 and the second row of table 2 on page 472. The corrected electronic version is identical to the print version.

Development of chronic tests for endocrine active chemicals: Part 1. An extended fish early-life stage test for oestrogenic active chemicals in the fathead minnow ( Pimephales promelas)

An extended early-life stage test (based on OECD test guideline 210) was developed to allow the evaluation of a weak environmental oestrogen, 4- tert-pentyphenol (4TPP), on sexual differentiation and gonadal development. Fathead minnow ( Pimephales promelas) embryos were exposed to three concentrations of 4TPP (56, 180 and 560 μg l −1) in a flow-through system, at 25 ± 1 °C, for <107 days post-hatch (dph). In addition, some embryos were exposed to 180 μg 4TPP l −1 until 30 or 60 dph, after which they were exposed to dilution water only until 107 dph. At 30, 60 and 107 dph fish were evaluated for growth and gonadal development (via histology), and at 107 dph fish were also evaluated for secondary sexual characteristics (SSC), gonadosomatic index (GSI) and plasma vitellogenin (VTG). There were no effects of 4TPP on hatching success or survival, however, there was a delay in the time taken for embryos to hatch (560 μg 4TPP l −1). No treatment-related effects were observed on fish growth, with the exception of at 107 dph when the condition factor in female fish was reduced in all 4TPP continuous exposure treatments. Plasma VTG was only elevated in female fish exposed to 180 μg 4TPP l −1 and inhibition of gonadal growth (GSI) occurred only in females exposed to 560 μg 4TPP l −1. Histological examination of the gonads revealed delays and disruption in male sexual differentiation and development (180 μg 4TPP l −1) and no testicular tissue was observed in any fish exposed to 560 μg 4TPP l −1. Mixed gonads (predominately testes with a scattering of primary oocytes) were present in fish exposed to all doses of 180 μg 4TPP l −1 at 107 dph. Feminisation of the reproductive ducts (formation of an ovarian like cavity) occurred in the testis of all males exposed to 180 μg l −1, regardless of length of 4TPP exposure. Results indicate that the period of 30–60 dph appears to be the sensitive window for disruption of formation of the reproductive duct and this effect is not reversible when the fish are transferred to dilution water. The data also show that this integrative test is suitable for the detection of a weak environmental oestrogen and comparisons of these results with that of a fish full life-cycle, in medaka, indicate that this test could be a suitable surrogate for a fish full life-cycle.

Europa's atmosphere, gas tori, and magnetospheric implications

A two-dimensional kinetic model calculation for the water group species (H 2O, H 2, O 2, OH, O, H) in Europa's atmosphere is undertaken to determine its basic compositional structure, gas escape rates, and velocity distribution information to initialize neutral cloud model calculations for the most important gas tori. The dominant atmospheric species is O 2 at low altitudes and H 2 at higher altitudes with average day–night column densities of 4.5 × 10 14 and 7.7 × 10 13 cm −2 , respectively. H 2 forms the most important gas torus with an escape rate of ∼ 2 × 10 27 s −1 followed by O with an escape rate of ∼ 5 × 10 26 s −1 , created primarily as exothermic O products from O 2 dissociation by magnetospheric electrons. The circumplanetary distributions of H 2 and O are highly peaked about the satellite location and asymmetrically distributed near Europa's orbit about Jupiter, have substantial forward clouds extending radially inward to Io's orbit, and have spatially integrated cloud populations of 4.2 × 10 33 molecules for H 2 and 4.0 × 10 32 atoms for O that are larger than their corresponding populations in Europa's local atmosphere by a factor of ∼200 and ∼1000, respectively. The cloud population for H 2 is a factor of ∼3 times larger than that for the combined cloud population of Io's O and S neutral clouds and provides the dominant neutral population beyond the so-called ramp region at 7.4–7.8 R J in the plasma torus. The calculated brightness of Europa's O cloud on the sky plane is very dim at the sub-Rayleigh level. The H 2 and O tori provide a new source of europagenic molecular and atomic pickup ions for the thermal plasma and introduce a neutral barrier in which new plasma sinks are created for the cooler iogenic plasma as it is transported radially outward and in which new sinks are created to alter the population and pitch angle distribution of the energetic plasma as it is transported radially inward. The europagenic instantaneous pickup ion rates are peaked at Europa's orbit, dominate the iogenic pickup ion rates beyond the ramp region, and introduce new secondary plasma source peaks in the solution of the plasma transport problem. The H 2 torus is identified as the unknown Europa gas torus that creates both the observed loss of energetic H + ions at Europa's orbit and the corresponding measured ENA production rate for H.

Plasma nitriding of Al alloys by DC glow discharge

Substrates of Al alloys 1100 and 2025 were plasma nitrided using a secondary vacuum dc plasma nitriding unit. The influence of process parameters such as, working gas, gas mixture and treatment time on the nitride layer characteristic were examined by ex situ analysis using SEM, EDX, GDS and RBS in order to optimize the plasma nitriding process. Sputtering step was carried out in Ar and H 2 (50 : 50) plasma at 400 °C for 50 min. All nitriding treatments were carried at a temperature of 400 °C using 700 V dc voltage. The experimental results showed a dense and continuous AlN layer with thickness about 2.2 μm and nitrogen content about 35–40 at.% for both specimens after 20 h nitriding at pressure of 80 Pa using N 2–H 24 gas with vol.% of 80/20. The XRD analysis confirmed the presence of AlN phase with a face centered cubic lattice together with fcc metallic Al and aluminum oxide.

Quo vadis haemapheresis: Current developments in haemapheresis

The techniques of haemapheresis originated in the development of centrifugal devices separating cells from plasma and later on plasma from cells. Subsequently membrane filtration was developed allowing for plasma—cell separation. The unspecificity of therapeutic plasma exchange led to the development of secondary plasma separation technologies being specific, semi-selective or selective such as adsorption, filtration or precipitation. In contrast on-line differential separation of cells is still under development. Whereas erythrocytapheresis, granulocytapheresis, lymphocytapheresis and stem cell apheresis are technically advanced, monocytapheresis may need further improvement. Also, indications such as erythrocytapheresis for the treatment of polycythaemia vera or photopheresis though being clinically effective and of considerable importance for an appropriate disease control are to some extent under debate as being either too costly or without sufficient understanding of the mechanism. Other forms of cell therapy are under development. Rheohaemapheresis as the most advanced technology of extracorporeal haemorheotherapy is a rapidly developing approach contributing to the treatment of microcirculatory diseases and tissue repair. Whereas the control of a considerable number of (auto-) antibody mediated diseases is beyond discussion, the indication of apheresis therapy for immune complex mediated diseases is quite often still under debate. Detoxification for artificial liver support advanced considerably during the last years, whereas conclusions on the efficacy of septicaemia treatment are debatable indeed. LDL-apheresis initiated in 1981 as immune apheresis is well established since 24 years, other semi-selective or unspecific procedures, allowing for the elimination of LDL-cholesterol among other plasma components are also being used. Correspondingly Lp(a) apheresis is available as a specific, highly efficient elimination procedure superior to techniques which also eliminate Lp(a). Quality control systems, more economical technologies as for instance by increasing automation, influencing the over-interpretation of evidence based medicine especially in patients with rare diseases without treatment alternative, more insight into the need of controlled clinical trials or alternatively improved diagnostic procedures are among others tools ways to expand the application of haemapheresis so far applied in cardiology, dermatology, haematology, immunology, nephrology, neurology, ophthalmology, otology, paediatrics, rheumatology, surgery and transfusion medicine.

Residual stress control in MoCr thin films deposited by ionized magnetron sputtering

This study reports on the control of intrinsic stress in MoCr films deposited by ionized magnetron sputtering using a secondary plasma created through a radio-frequency (13.56 MHz) antenna. The efficiency of the additional antenna has been investigated by optical emission spectroscopy for a MoCr target. It appears that ionization of the sputtered species is significantly enhanced compared to a conventional magnetron sputtering. Moreover, by controlling the substrate bias, the RF power on the antenna and the discharge gas pressure (argon), the ion energy and flux can be strongly modified. Therefore, we have the ability to act on composition, growth rate, microstructure and residual stress of the deposited film. Indeed, the films exhibit residual stress varying from compressive value (− 3.4 GPa) to tensile one (1.7 GPa). In particular, only by varying the RF power on the antenna, a wide range of tensile and compressive stress can be obtained without affecting the chemical composition of the films. These results will be useful when elaborating stress-engineered micro-objects such as micro-springs.

Plasma Cells from Secondary Plasma Cell Leukemia Display Different Cytogenetics Pattern When Compared with Primary Plasma Cell Leukemia.

Background: Plasma cell leukemia (PCL) is a rare plasma cell (PC) dyscrasia which may be designated as primary (PPCL) or de novo PCL when recognized at the time of diagnosis and secondary (SPCL) when there is leukemic transformation of a previously recognized multiple myeloma (MM). PCL has been reported to exhibit distinct clinical and immunophenotypic features that distinguish it from MM, but little is known about the specific genetics of this disease. To better understand the genetic features of the clonal PC from PPCL and SCPL we assessed in these patients the molecular and cytogenetic abnormalities most commonly found in MM.Patients and Methods: In our study we analyzed 3 groups of patients; 18 with PPCL, 23 with SPCL and a control group of 345 newly diagnosed MM previously published. Diagnostic criteria for PCL followed the presence of >2 x103/L PC in PB (Kyle et al. Arch Intern Med 1974; 133–813–8). Cytogenetic abnormalities were assessed by the c-Ig FISH method; mutational analysis was performed using Conformational-sensitive gel electrophoresis (CSGE). Methylation was analyzed by methyl specific PCR (MSP) after bisulfite genomic DNA modification.Results: Translocation of immunoglobulin heavy chain with Cyclin D1 (t (11; 14)) was present in 76.9% (10 of 13) of PPCL, 71% (5 of 7) of SPCL, in contrast to 15.8% (53 of 336) of MM cases. Translocations' involving the FGFR3-MMSET genes (4p16.3 locus) and c-MAF (16q32) genes were not observed among 10 patients studied with PPCL, but were present in 12.7 % each in SPCL. The t (4;14)(p16;q32) was present in 12.7% cases of MM and the t(14;16)(q32;q23) was present in 4.6 % of MM cases. Deletion of 17p13.1 (p53 locus) was found in 10% (37 of 345) of MM cases, 53.8% (7 of 13) for PPCL and 42.8% (3 of 7) for SPCL. Deletion of 13q was present in 54.2% (176 of 325) of MM, 76.9 % (10 of 13) of PPCL and 57.1% of SPCL. Ras mutations were found in 15% (2/13) of PPCL, located in codon 1 and 2 of the K-ras gene. In addition, 23% for SPCL presented mutations in the N-ras gene. Two mutations were located in codon 2 of N-ras and 1 patients in showed a mutation in codon 1 of K-ras gene. Ras mutations were present in 27% of MM cases. Mutations for p53 gene were present in 30.7% (4/13) of PPCL, 17% (3/17) for SPCL and 5% for MM. Methylation specific PCR for p16 gene was found in 23% (3/13) of PPCL, 29% of SPCL and 33.9% (149/439) of MM. Hypermethylation of p14 was not detected in PPCL but a 23 % was found in SPCL.Conclusions: In this study we demonstrate that PCs from PPCL more frequently carry the t (11; 14). Comparing SPCL and MM, PC's from de novo PPCL do not show t (4; 14) or (16; 14). Deletion of 13q was more prevalent among patients with PPCL. Ras mutations appear to be as frequent in MM as in PPCL and SPCL. Mutations in p53 appeared to be more prevalent in PPCL than in SPCL and MM. Hypermethylation of p16 does not differ while hypermethylation of p14 is more frequent in SPCL than PPCL. These characteristics may lead to a different onset or disease evolution of PPCL compared to MM and secondary plasma cell leukemia and this may be important for diagnostic and treatment.

High power single-shot laser ablation of silicon with nanosecond 355 nm

We report on high intensity single-shot laser ablation of monocrystalline silicon with a nanosecond Nd:YAG at 355 nm. It is shown that for incident laser intensities exceeding ∼11.5 GW/cm 2 on the silicon surface, unusually high etch depths can be achieved reaching values up to 60 μm. The results support previous observations of dramatic increase in etch rates in single-shot laser ablation at 266 nm. A laser-induced explosive boiling mechanism together with secondary plasma heating is believed to be associated with this effect.

Screening and Testing for Endocrine Disruption in Fish—Biomarkers As “Signposts,” Not “Traffic Lights,” in Risk Assessment

Biomarkers are currently best used as mechanistic “signposts” rather than as “traffic lights” in the environmental risk assessment of endocrine-disrupting chemicals (EDCs). In field studies, biomarkers of exposure [e.g., vitellogenin (VTG) induction in male fish] are powerful tools for tracking single substances and mixtures of concern. Biomarkers also provide linkage between field and laboratory data, thereby playing an important role in directing the need for and design of fish chronic tests for EDCs. It is the adverse effect end points (e.g., altered development, growth, and/or reproduction) from such tests that are most valuable for calculating adverseNOEC (no observed effect oncentration) or adverseEC10 (effective concentration for a 10% response) and subsequently deriving predicted no effect concentrations (PNECs). With current uncertainties, biomarkerNOEC or biomarkerEC10 data should not be used in isolation to derive PNECs. In the future, however, there may be scope to increasingly use biomarker data in environmental decision making, if plausible linkages can be made across levels of organization such that adverse outcomes might be envisaged relative to biomarker responses. For biomarkers to fulfil their potential, they should be mechanistically relevant and reproducible (as measured by interlaboratory comparisons of the same protocol). VTG is a good example of such a biomarker in that it provides an insight to the mode of action (estrogenicity) that is vital to fish reproductive health. Interlaboratory reproducibility data for VTG are also encouraging; recent comparisons (using the same immunoassay protocol) have provided coefficients of variation (CVs) of 38–55% (comparable to published CVs of 19–58% for fish survival and growth end points used in regulatory test guidelines). While concern over environmental xenoestrogens has led to the evaluation of reproductive biomarkers in fish, it must be remembered that many substances act via diverse mechanisms of action such that the environmental risk assessment for EDCs is a broad and complex issue. Also, biomarkers such as secondary sexual characteristics, gonadosomatic indices, plasma steroids, and gonadal histology have significant potential for guiding interspecies assessments of EDCs and designing fish chronic tests. To strengthen the utility of EDC biomarkers in fish, we need to establish a historical control database (also considering natural variability) to help differentiate between statistically detectable versus biologically significant responses. In conclusion, as research continues to develop a range of useful EDC biomarkers, environmental decision-making needs to move forward, and it is proposed that the “biomarkers as signposts” approach is a pragmatic way forward in the current risk assessment of EDCs.

Spatial distribution of the vacuum arc plasma fluxes in a curvilinear magnetic duct

The spatial distribution of stationary vacuum arc plasma fluxes in a curvilinear magnetic field, with a strength that is satisfied to the condition of unmagnetized ions, is described. We report here, that along with the main beam, which moves along the curvilinear magnetic field B, there are a secondary plasma fluxes: radial, having a speed component in R-direction, and a transversal one, propagated in B/spl times/R direction (R is the radius-vector of magnetic line of force). Plasma distribution between these fluxes was monitored under a changing of positive bias voltage, applied to the duct.

On the 3-dimensional structure of the streamer belt of the solar corona

We investigate the three-dimensional structure of the streamer belt of the solar corona using a model that allows us to simulate its quasi-stationary configuration. Starting from the National Solar Observatory photospheric magnetograms, the position of the neutral line at the source surface () is determined using the potential field source surface model. A plasma sheet is centered around the current sheet represented as the radial extension of the neutral line. Comparing the synoptic maps of the streamer belt obtained with the SOHO/LASCO-C2 coronagraph and the simulated synoptic maps constructed from our model of the warped plasma sheet, we confirm earlier findings by Wang et al. (1997, ApJ, 485, 875; Wang et al. 2000, Geophys. Res. Lett., 27, 149) that the streamers are associated with folds in the plasma sheet. Although the large-scale structure of the streamer belt is described reasonably well, some features, however, cannot be explained in this framework. We propose that two types of large-scale structures take part in the formation of these additional features. The first one is an additional fold of the neutral line, which does not appear in the modeled source surface neutral line, but is well visible in photospheric magnetograms. The second one is a plasma sheet with a ramification in the form of a secondary short plasma sheet. We show that these structures better describe the observed configurations of the streamer belt. The secondary plasma sheet can be formed between two secondary current sheets connected to the main current sheet. Our results suggest that the potential field source surface model is not fully adequate for the description of the fine structure of the streamer belt, even during the time of low solar activity.

Effect of Focusing on Charge-Induced Current and Spectral Emission in a Plasma Generated by a Nd:YAG Laser at Low Pressures

The effect of laser focusing condition on the emission and charge-induced current characteristics of the copper plasma induced by a Q-switched Nd-YAG laser (37 mJ, 8ns) at reduced pressures of air has been studied to examine the excitation process of the ablated atoms in the secondary plasma. The charge-induced current measurement has been conducted by placing a partially transmitted nickel mesh in front of the sample surface at a certain distance. Also by using the rainbow interferometric technique, the density jump in the secondary plasma could be clearly observed. The relationship analysis on the secondary plasma emission intensity, the charge-induced current and the average velocity of the shock front as a function of laser irradiation focusing condition revealed clearly the role of the shock wave in the excitation mechanisms of the secondary plasma, proving the electron collision and the electronion recombination are not major processes.

Excitation Mechanism in Laser-Induced Plasma at Atmospheric Air Pressure

A special interferometric technique has been devised on the basis of rainbow refractometry without the use of an additional and delicate amplitude- splitting setup. This new technique was used for the characterization of plasma induced by a Q-switched Nd-YAG laser on zinc samples under atmospheric air pressure. An unmistakable signal of the density jump was detected simultaneously with the observation of the emission front signal. It was proved that the emission front and the front of the shock wave coincided and moved together with time at the initial stage of the secondary plasma expansion. However, at a later stage, the emission front began to separate from and left behind the shock wave front propagating in the surrounding air. With the use of zinc sample, the experimental results showed that the separation of the emission front and shock wave front took place at about 4 mm above sample surface for laser energy of 26 mJ. It was also found that the separation time increased by increasing the power density which further supported shock wave model. Analysis of the data of the shock front movement along with the emission characteristics has led us to the conclusion that models other than the shock wave model, such as the gas breakdown model, should be excluded, at least for a zinc sample, as not satisfactorily explaining the excitation process in the secondary plasma generated at atmospheric air pressure of 760 Torr.

Combined Effect of Secondary Electron Emission, Plasma Ion and Electron Number Density Variation due to Dust Charging and Ionization-Recombination Processes on Dust Ion Acoustic Wave Propagation

In a dusty plasma, in addition to influencing the dust charge state the secondary electron emission also leads to an enhancement of the electron number density. For proper accounting for secondary electron emission effect one has therefore, for the sake of consistency, also to take into account the ambient electron and ion loss due to charging collisions. The existence of a steady state for the dusty plasma is possible only through compensation of such particle losses or gain – a likely candidate for which are ionization and recombination processes in dusty plasma. Taking into account the combined effects all these processes and assuming that the frequencies of the various types of interparticle collisions associated with the above-mentioned processes are much less than the dust ion acoustic (DIA) frequency it is shown that a small perturbation of the steady state of the dusty plasma may result in DIA wave growth provided the ionization rate is sufficiently high. Threshold values of the ratio of the ionization rate to recombination rate depending on different plasma parameters are shown graphically. The analysis presented is restricted to the case when the dust charge remains negative. It is seen that instability persists even when there is no secondary emission. The threshold for instability is lower for smaller values of the dimensionless charge parameter z0 = Zd0e2/aTe when secondary emission takes place, compared to the case when it is absent. The situation tends to get reversed as z0 increases. The possibility of the existence of such instability was not noted earlier.