Characterization of the high—voltage pulsed discharge plasma of ammonia by emission spectroscopy

We have used optical emission spectroscopy to characterize the high-voltage pulsed discharge of ammonia.Ammonia was highly dissociated in the discharge at low pressures.More atomic nitrogen was generated as compared to the discharge of nitrogen gas at the same pressure of 0.8kPa.We discuss the elimination of the oxygen impurity in the ammonia discharge,and we estimate the time-dependent atomic excitation temperature and the electron density from the measured spectra.     

Effect of the plasma location on the deflagration-to-detonation transition of a hydrogen–air flame enhanced by nanosecond repetitively pulsed discharges

This work presents a method for using nanosecond repetitively pulsed (NRP) plasma discharges for accelerating a propagating flame such that the deflagration-to-detonation transition occurs. A strategy is developed for bringing the location of the plasma near the tube wall and, thus, reducing the presence of the electrodes in the combustion tube as well as presenting a configuration in which cooling of the electrodes is viable for practical applications. Time-of-flight measurements were used in combination with energy deposition measurements and high-speed OH*-chemiluminescence imagery to investigate the flame acceleration process. For stoichiometric hydrogen–air flames, successful transition to detonation was achieved by applying a burst of 110 pulses at 100 kHz, with energies as low as 10 mJ per pulse. This was also achieved when plasma discharges were applied in the vicinity of the wall. Two enhancement mechanisms for flame acceleration were identified. The essential role of shock–flame interaction was established as being the main mechanism for flame acceleration when the discharges are located near the wall. This work presents an effective alternative that allows for NRP discharges to be applied near the wall while successfully maintaining a promising success rate for detonation transition.     

Quantum effects on the Rayleigh–Taylor instability of stratified plasma in the presence of suspended particles

The effects of quantum correction on the Rayleigh–Taylor instability (RTI) in stratified plasma layer have been investigated in the presence of suspended particles. A general dispersion relation is obtained from the linearized set of quantum hydrodynamic (QHD) equations. Two particular cases of suspended particle parameters (f ^? and α ₀) with and without quantum corrections are analysed. The condition of RTI is derived while the stability of the system is discussed by applying Routh–Hurwitz (RH) criterion in the polynomial equation. The results show that, in the absence of quantum term, the relaxation frequency of the suspended particles has a destabilizing effect, while the mass concentration of the suspended particles has a stabilizing effect on the growth rates of RTI. In the presence of the quantum term, the relaxation frequency of the suspended particle yields to the stability behaviour on the growth rates of RTI.     

Optical frequency measurement of the 1S–3S two-photon transition in hydrogen

This article reports the first optical frequency measurement of the 1S–3S transition in hydrogen. The excitation of this transition occurs at a wavelength of 205 nm which is obtained with two frequency doubling stages of a titanium sapphire laser at 820 nm. Its frequency is measured with an optical frequency comb. The second-order Doppler effect is evaluated from the observation of the motional Stark effect due to a transverse magnetic field perpendicular to the atomic beam. The measured value of the 1S_1/21\mathrm{S}_{1/2}(F = 1)-3S_1/2(F = 1) frequency splitting is 2 922 742 936.729(13) MHz with a relative uncertainty of 4.5 × 10^-12. After the measurement of the 1S–2S frequency, this result is the most precise of the optical frequencies in hydrogen.     

Charmonium suppression in the presence of dissipative forces in a strongly-coupled quark–gluon plasma

We study the survival of charmonium states in a strongly-coupled quark–gluon plasma in the presence of dissipative forces. We consider first-order dissipative corrections to the plasma equation of motion in the Bjorken boost-invariant expansion with a strongly-coupled equation of state for QGP and study the survival of these states with the dissociation temperatures obtained by correcting the full Cornell potential not its Coulomb part alone with a dielectric function encoding the effects of deconfined medium. We further explore the sensitivity of prompt and sequential suppression of these states to the shear viscosity-to-entropy density ratio, η/s from perturbative QCD and AdS/CFT predictions. Our results show nice agreement with the recent experimental results at RHIC.     

Bias-dependent bandwidth of the conductance in the presence of electron–phonon interaction

We study the electronic transport in the presence of electron–phonon interaction (EPI) for a molecular electronic device. Instead of mean field approximation (MFA), the related phonon correlation function is conducted with the Langreth theorem (LT). We present formal expressions for the bandwidth of the electron’s spectral function in the central region of the devices, such as quantum dot (QD), or single molecular transistor (SMT). Our results show that the out-tunneling rate depends on the energy, bias voltage and the phonon field. Besides, the predicted conductance map, behaving as a function of bias voltage and the gate voltage, gets blurred at the high bias voltage region. These EPI effects are consistent with the experimental observations in the EPI transport experiment.     

Stoichiometric transfer by infrared pulsed laser deposition of y-doped Bi–Sr–Ca–Cu–O investigated using time-resolved optical emission spectroscopy

Pulsed laser deposition of Bi₂Sr2Ca_1–x YxCu₂O_8+δ (Bi-22Y2) with x = 0, 0.30, and 0.49 on an MgO (100) substrate was conducted using a Q-switched 1064 nm Nd:YAG laser The laser-produced plasma (LPP) emission was collected during the deposition. Time-resolved optical emission spectroscopy reveals that the plasma plume consists of neutral atoms and ions. SEM images indicate that clusters of correct stoichiometry arrive on the substrate surface. Our result confirms that IR PLD transfers material stoichiometrically.     

Pair-vibrational states in the presence of neutron–proton pairing

Pair vibrations are studied for a Hamiltonian with neutron–neutron, proton–proton and neutron–proton pairing. The spectrum is found to be rich in strongly correlated, low-lying excited states. Changing the ratio of diagonal to off-diagonal pairing matrix elements is found to have a large impact on the excited-state spectrum. The variational configuration interaction (VCI) method, used to calculate the excitation spectrum, is found to be in very good agreement with exact solutions for systems with large degeneracies having equal T=0$T=0$ and T=1$T=1$ pairing strengths.     

Laser–plasma interaction physics in the context of fusion

Of vital importance for Inertial Confinement Fusion (ICF) are the understanding and control of the nonlinear processes which can occur during the propagation of the laser pulses through the underdense plasma surrounding the fusion capsule. The control of parametric instabilities has been studied experimentally, using the LULI six-beam laser facility, and also theoretically and numerically. New results based on the direct observation of plasma waves with Thomson scattering of a short wavelength probe beam have revealed the occurence of the Langmuir decay instability. This secondary instability may play an imporant role in the saturation of stimulated Raman scattering. Another mechanism for reducing the growth of the scattering instabilities is the so-called `plasma-induced incoherence'. Namely, recent theoretical studies have shown that the propagation of laser beams through the underdense plasma can increase their spatial and temporal incoherence. This plasma-induced beam smoothing can reduce the levels of parametric instabilities. One signature of this process is a large increase of the spectral width of the laser light after propagation through the plasma. Comparison of the experimental results with numerical simulations shows an excellent agreement between the observed and calculated time-resolved spectra of the transmitted laser light at various laser intensities.     

Study of Yang–Mills–Chern–Simons theory in presence of the Gribov horizon

The two-point gauge correlation function in Yang–Mills–Chern–Simons theory in three dimensional Euclidean space is analysed by taking into account the non-perturbative effects of the Gribov horizon. In this way, we are able to describe the confinement and de-confinement regimes, which naturally depend on the topological mass and on the gauge coupling constant of the theory.     

X-ray emission and Raman spectroscopy of CN<Subscript>0 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 0.5</Subscript> nanocondensates prepared by pulsed arc sputtering of graphite in the presence of nitrogen

The nanocomposite structure of the DLC-C₂N condensate is confirmed by analyzing the x-ray emission spectra of the CN_{0 ≤ x ≤ 0.5} films prepared by pulsed arc sputtering of graphite in the presence of nitrogen.     

Determination of the population of the A 3Σu electronic state of nitrogen molecules in a glow-discharge plasma

Results on determining the population of the A ³Σ_u electronic state of N₂ molecules in a gas discharge using a relatively simple spectroscopic technique are reported. The technique proposed can be used not only in pure N₂, but also in nitrogen-containing gas mixtures. The populations of the metastable and nonequilibrium B ³Π_g states of nitrogen molecules are determined. It is shown that the electron-impact excitation is a dominant mechanism for populating the B ³Π_g state.     

Study on the effect of laser parameters on wakefield excitation in femtosecond pulsed laser–plasma interaction using PIC method

Propagation of an intense short laser pulse through under-dense plasma can produce huge amplitude plasma wake field. A 3D particle in cell (PIC) method was used to simulate the wakefield generation for different laser parameters such as intensity, pulse duration, spot size and temporal pulse shape. Our study shows that the amplitude of wakefield is increased with laser intensity, but it is decreased with spot size. The results for pulse shape and pulse duration depend on their optimum values.     

Response of hydrogen bonding to low-intensity 50 Hz electromagnetic field in typical proteins in bi-distilled water solution

Samples of hemoglobin and bovine serum albumin in different bi-distilled water solutions were exposed to a 50?Hz electromagnetic field at the intensity of 1?mT to investigate the response of hydrogen bonding to the applied field after exposure of 3?h by means of Fourier Transform Infrared spectroscopy. Spectral analysis evidenced a significant decrease in the absorbance signal of the Amide I vibration in exposed samples of hemoglobin and bovine serum albumin water solutions. In addition, Fourier self-deconvolution analysis and min-max normalization applied in the mid-infrared region to exposed and unexposed hemoglobin samples revealed a significant increase in the absorbance signal of the Amide II band and an up-shift toward the high energies of 1.5?cm^?1 after exposure. Similar findings were observed after exposure of bovine serum albumin. These results can be easily explained assuming that hydrogen bonding in the secondary structure of these proteins in bi-distilled water solutions was enhanced after exposure to 50?Hz electromagnetic field.     

Computation of emission characteristics of Ar–Fe arc plasma column during the synthesis of nano particles of Fe-oxides

The article reports the results of the computationally determined radiative emission characteristics of a transferred arc argon plasma source used in plasma-assisted nano particles synthesis of Fe-oxides. A thermodynamic code uses a spectroscopic database to compute internal partition functions and densities of various charged states in argon–iron vapor plasma system during the synthesis of Fe-oxides. The net amount of radiation emitted by the plasma at different axial positions along the column has been monitored by optical emission spectroscopy. It was also used to determine the amount of metal vapors mixing inside the plasma column during the synthesis process. The net emission coefficient estimated along a certain line of sight shows an effective increase even for a small inclusion of Fe vapors (0.11%) inside the column. It has been noticed that the radiations emitted by the plasma inside the reactor chamber might also be one of the factors, controlling the crystalline phase of Fe-oxide particles.     

Turbulent propagation of premixed flames in the presence of Darrieus–Landau instability

We investigate the role played by hydrodynamic instability in the wrinkled flamelet regime of turbulent combustion, where the intensity of turbulence is small compared to the laminar flame speed and the scale large compared to the flame thickness. To this end the Michelson–Sivashinsky (MS) equation for flame front propagation in one and two spatial dimensions is studied in the presence of uncorrelated and correlated noise representing a turbulent flow field. The combined effect of turbulence intensity, integral scale, and an instability parameter related to the Markstein length are examined and turbulent propagation speed monitored for both stable planar flames and corrugated flames for which the planar conformation is unstable. For planar flames a particularly simple scaling law emerges, involving quadratic dependence on intensity and a linear dependence on the degree of instability. For corrugated flames we find the dependence on intensity to be substantially weaker than quadratic, revealing that corrugated flames are more resilient to turbulence than planar flames. The existence of a threshold turbulence intensity is also observed, below which the corrugated flame in the presence of turbulence behaves like a laminar flame. We also analyze the conformation of the flame surface in the presence of turbulence, revealing primary, large-scale wrinkles of a size comparable to the main corrugation. When the integral scale is much smaller than the characteristic corrugation length we observe, in addition to primary wrinkles, secondary small-scale wrinkles contaminating the surface. The flame then acquires a multi-scale, self-similar conformation, with a fractal dimension, for one-dimensional flames, plateauing at 1.23 for large intensities. The existence of an intermediate integral scale is also found at which the turbulent speed is maximized. When two-dimensional flames are subject to turbulence, the primary wrinkling patterns give rise to polyhedral-cellular structures which bear a very close resemblance to those observed in experiments on hydrodynamically unstable expanding spherical flames.