Diagnostics on an atmospheric pressure plasma jet

The atmospheric pressure plasma jet (APPJ) is a homogeneous non-equilibrium discharge at ambient pressure. It operates with a noble base gas and a percentage-volume admixture of a molecular gas. Applications of the discharge are mainly based on reactive species in the effluent. The effluent region of a discharge operated in helium with an oxygen admixture has been investigated. The optical emission from atomic oxygen decreases with distance from the discharge but can still be observed several centimetres in the effluent. Ground state atomic oxygen, measured using absolutely calibrated two-photon laser induced fluorescence spectroscopy, shows a similar behaviour. Detailed understanding of energy transport mechanisms requires investigations of the discharge volume and the effluent region. An atmospheric pressure plasma jet has been designed providing excellent diagnostics access and a simple geometry ideally suited for modelling and simulation. Laser spectroscopy and optical emission spectroscopy can be applied in the discharge volume and the effluent region.

The VLT-FLAMES survey of massive stars: atmospheric parameters and rotational velocity distributions for B-type stars in the Magellanic Clouds

Aims.We aim to provide the atmospheric parameters and rotational velocities for a large sample of O- and early B-type stars, analysed in a homogeneous and consistent manner, for use in constraining theoretical models. Methods: Atmospheric parameters, stellar masses, and rotational velocities have been estimated for approximately 250 early B-type stars in the Large (LMC) and Small (SMC) Magellanic Clouds from high-resolution VLT-FLAMES data using the non-LTE TLUSTY model atmosphere code. This data set has been supplemented with our previous analyses of some 50 O-type stars (Mokiem et al. 2006, 2007) and 100 narrow-lined early B-type stars (Hunter et al. 2006; Trundle et al. 2007) from the same survey, providing a sample of ~400 early-type objects. Results: Comparison of the rotational velocities with evolutionary tracks suggests that the end of core hydrogen burning occurs later than currently predicted and we argue for an extension of the evolutionary tracks. We also show that the large number of the luminous blue supergiants observed in the fields are unlikely to have directly evolved from main-sequence massive O-type stars as neither their low rotational velocities nor their position on the H-R diagram are predicted. We suggest that blue loops or mass-transfer binary systems may populate the blue supergiant regime. By comparing the rotational velocity distributions of the Magellanic Cloud stars to a similar Galactic sample, we find that (at 3s confidence level) massive stars (above 8 M?) in the SMC rotate faster than those in the solar neighbourhood. However there appears to be no significant difference between the rotational velocity distributions in the Galaxy and the LMC. We find that the v sin i distributions in the SMC and LMC can modelled with an intrinsic rotational velocity distribution that is a Gaussian peaking at 175 km s-1 (SMC) and 100 km s-1 (LMC) with a 1/e half width of 150 km s-1. We find that in NGC 346 in the SMC, the 10-25 M? main-sequence stars appear to rotate faster than their higher mass counterparts. It is not expected that O-type stars spin down significantly through angular momentum loss via stellar winds at SMC metallicity, hence this could be a reflection of mass dependent birth spin rates. Recently Yoon et al. (2006) have determined rates of GRBs by modelling rapidly rotating massive star progenitors. Our measured rotational velocity distribution for the 10-25 M? stars is peaked at slightly higher velocities than they assume, supporting the idea that GRBs could come from rapid rotators with initial masses as low as 14 M? at low metallicities.

Ultrasmall radio frequency driven microhollow cathode discharge

We have operated 25-100 mu m diameter radio frequency microhollow cathode discharges stably, for many hours, in neon and in argon. Electrical and spectroscopic measurements were used to explore three possible electron heating modes and obtain detail regarding the electron energy distribution. Analysis points to the possibility of pendular electron heating at low voltages.

Acoustic, volumetric, compressibility and refractivity properties and Flory’s reduction parameters of some homologous series of alkyl alkanoates from 298.15 to 333.15 K

The speeds of sound u in, densities ? and refractive indices nD of some homologous series, such as n-alkyl ethanoates, n-alkyl propionates, methyl alkanoates, ethyl alkanoates, dialkyl malonates, and alkyl haloalkanoates, were measured in the temperature range from 298.15 to 333.15 K. Molar volume V, isentropic and isothermal compressibilities ?S and ?T, molar refraction Rm, Eykman’s constant Cm, molecular radius r, Rao’s molar function R, thermal expansion coefficient a, thermal pressure coefficient ?, and Flory’s characteristic parameters image, P*, V*, and T* have been calculated from the measured experimental data. Applicability of Rao theory and Flory–Patterson–Pandey (FPP) theory have been examined and discussed for these alkanoates.

Acoustic, volumetric, compressibility and refractivity properties and reduction parameters for the ERAS and Flory models of some homologous series of amines from 298.15 to 328.15 K

The speeds of sound u, densities ? and refractive indices nD of homologous series of mono-, di-, and tri-alkylamines were measured in the temperature range from 298.15 to 328.15 K. Isentropic and isothermal compressibilities ?S and ?T, molar refraction Rm, Eykman’s constant Cm, Rao’s molar sound function R, thermal expansion coefficient a, thermal pressure coefficient ?, and reduction parameters P*, V*, and T* in frameworks of the ERAS model for associated amines and Flory model for tertiary amines have been calculated from the measured experimental data. Applicability of the Rao theory and the ERAS and Flory models have been examined and discussed for the alkyl amines.

Higher order statistics for lognormal small-scale fading in mobile radio channels

This letter reports the statistical characterization and modeling of the indoor radio channel for a mobile wireless personal area network operating at 868 MHz. Line of sight (LOS) and non-LOS conditions were considered for three environments: anechoic chamber, open office area and hallway. Overall, the Nakagami-m cdf best described fading for bodyworn operation in 60% of all measured channels in anechoic chamber and open office area environments. The Nakagami distribution was also found to provide a good description of Rician distributed channels which predominated in the hallway. Multipath played an important role in channel statistics with the mean recorded m value being reduced from 7.8 in the anechoic chamber to 1.3 in both the open office area and hallway.

Simulation or measurement: the effect of radio map creation on indoor WLAN-based localisation accuracy

Indoor wireless network based client localisation requires the use of a radio map to relate received signal strength to specific locations. However, signal strength measurements are time consuming, expensive and usually require unrestricted access to all parts of the building concerned. An obvious option for circumventing this difficulty is to estimate the radio map using a propagation model. This paper compares the effect of measured and simulated radio maps on the accuracy of two different methods of wireless network based localisation. The results presented indicate that, although the propagation model used underestimated the signal strength by up to 15 dB at certain locations, there was not a signigicant reduction in localisation performance. In general, the difference in performance between the simulated and measured radio maps was around a 30 % increase in rms error

Head-SAR dependence on spectacle frame shape for operator of 450 MHz personal radio

Power deposition in the head of a user wearing metal-framed spectacles was calculated with a 450 MHz personal radio transmitting in close proximity. Peak tissue SAR in the head depended on lens shape whether circular half-rim or rectangular with 70 and 174% increases, respectively, compared to the spectacle-free case. However, localised screening occurred with square frames, with a 40% reduction of peak SAR in the eye closest to the antenna.

Plasma Ionization in Low-Pressure Radio-Frequency Discharges. Part I: Optical Measurements

The electron dynamics in the low-pressure operation regime ($«$ 5 Pa) of a neon capacitively coupled plasma is investigated using phase-resolved optical emission spectroscopy. Plasma ionization and sustainment mechanisms are governed by the expanding and contracting sheath and complex wave–particle interactions. Electrons are energized through the advancing and retreating electric field of the RF sheath. The associated interaction of energetic sheath electrons with thermal bulk plasma electrons drives a two-stream instability also dissipating power in the plasma.

Plasma Ionization in Low-Pressure Radio-Frequency Discharges—Part II: Particle-in-Cell Simulation

Plasma ionization in the low-pressure operation regime ( $«$ 5 Pa) of RF capacitively coupled plasmas (CCPs) is governed by a complex interplay of various mechanisms, such as field reversal, sheath expansion, and wave–particle interactions. In a previous paper, it was shown that experimental observations in a hydrogen CCP operated at 13.56 MHz are qualitatively well described in a 1-D symmetrical particle-in-cell (PIC) simulation. In this paper, a spherical asymmetrical PIC simulation that is closer to the conditions of the highly asymmetrical experimental device is used to simulate a low-pressure neon CCP operated at 2 MHz. The results show a similar behavior, with pronounced ionization through field reversal, sheath expansion, and wave–particle interactions, and can be exploited for more accurate quantitative comparisons with experimental observations.

Spatially resolved diagnostics on a micro atmospheric pressure plasma jet

Despite enormous potential for technological applications, fundamentals of stable non-equilibrium micro-plasmas at ambient pressure are still only partly understood. Micro-plasma jets are one sub-group of these plasma sources. For an understanding it is particularly important to analyse transport phenomena of energy and particles within and between the core and effluent of the discharge. The complexity of the problem requires the combination and correlation of various highly sophisticated diagnostics yielding different information with an extremely high temporal and spatial resolution. A specially designed rf microscale atmospheric pressure plasma jet (µ-APPJ) provides excellent access for optical diagnostics to the discharge volume and the effluent region. This allows detailed investigations of the discharge dynamics and energy transport mechanisms from the discharge to the effluent. Here we present examples for diagnostics applicable to different regions and combine the results. The diagnostics applied are optical emission spectroscopy (OES) in the visible and ultraviolet and two-photon absorption laser-induced fluorescence spectroscopy. By the latter spatially resolved absolutely calibrated density maps of atomic oxygen have been determined for the effluent. OES yields an insight into energy transport mechanisms from the core into the effluent. The first results of spatially and phase-resolved OES measurements of the discharge dynamics of the core are presented.

Fast imaging of an atmospheric pressure glow discharge in he with a polymer film

To visualize the development of an atmospheric pressure glow discharge in He and the influence of polymer film on the discharge, short exposure time images were recorded using a gated intensified charge coupled detector. If the polymer film is stretched in the middle of the gap, a discharge region on each side of the polymer is created with the characteristic structure of a glow discharge. In this case, strongly asymmetric discharge current pulses can be generated depending on the frequency and the applied voltage.

Electrical characterization of radio frequency discharges

Two electrical techniques that are frequently used to characterize radio frequency plasmas are described: current-voltage probes for plasma power input and compensated Langmuir probes for electron energy probability functions and other parameters. The following examples of the use of these techniques, sometimes in conjunction with other diagnostic methods, are presented: plasma source standardization, plasma system comparison, power efficiency, plasma modelling and complex processing plasma mechanisms.