Free Arc Research Articles

Macroparticles Reduction Using Filter Free Cathodic Vacuum Arc Deposition Method in ZnO Thin Films.

We report a new method to reduce macroparticles in ZnO thin films using filter free cathodic vacuum arc deposition without using any cooling arrangements operated at low arc current. The detailed mechanism has been proposed to reduce macroparticles during thin film deposition. The successful reduction of macroparticles was confirmed employing FESEM-EDX studies. FESEM images of ZnO thin films deposited with cathode spot to substrate distance from 10 to 20 cm revealed that the population of the macroparticles were reduced with the increase of cathode spot to substrate distances at low arc current. The prepared ZnO films were characterised and showed good structural and optical properties.

Measurement and Analysis of Plasma Arc Components

To better understand keyhole plasma arc (PA) and help improve the process, the authors recently observed that the electron flow may deviate from its ionized arc plasma which is electrically neutral. This phenomenon has been referred to as the arc separability which provides a better way to understand the arc fundamentally. Hence, in this study the authors designed an innovative experimental system to measure/record the heat and pressure from the separated arc components—arc plasma and electron flow. An algorithm was proposed to calculate/derive the distribution of the pressure from its bulk measurements that are easy to obtain accurately. Experiments were conducted to study the effects of welding parameters on the heat and pressure in the arc components. It is found that for the constrained PA, the heat applied into the work-piece through the arc plasma exceeds that from the electron flow and this dominance increases as the current increases. However, for the heat from the electron flow, the constraint on the arc does not change it significantly as can be seen from the comparison with that in free gas tungsten arc (GTA). For the pressure in PA, the arc plasma plays the dominant role in determining its amplitude, while the electron flow only primarily contributes to the distribution.

Formula omitted]-Homogeneous n-fold hyperspace suspensions

We study 12-homogeneity of the n-fold hyperspace suspension of continua. We prove that if X is a decomposable continuum and its n-fold hyperspace suspension is 12-homogeneous, then X must be continuum chainable. We also characterize 12-homogeneity of the hyperspace suspension for several classes of continua including: continua containing a free arc, atriodic and decomposable continua, decomposable irreducible continua about a finite set.

SU‐F‐BRD‐05: Dosimetric Comparison of Protocol‐Based SBRT Lung Treatment Modalities: Statistically Significant VMAT Advantages Over Fixed‐ Beam IMRT

Purpose:The purpose of this study is to inter‐compare and find statistically significant differences between flattened field fixed‐beam (FB) IMRT with flattening‐filter free (FFF) volumetric modulated arc therapy (VMAT) for stereotactic body radiation therapy SBRT.Methods:SBRT plans using FB IMRT and FFF VMAT were generated for fifteen SBRT lung patients using 6 MV beams. For each patient, both IMRT and VMAT plans were created for comparison. Plans were generated utilizing RTOG 0915 (peripheral, 10 patients) and RTOG 0813 (medial, 5 patients) lung protocols. Target dose, critical structure dose, and treatment time were compared and tested for statistical significance. Parameters of interest included prescription isodose surface coverage, target dose heterogeneity, high dose spillage (location and volume), low dose spillage (location and volume), lung dose spillage, and critical structure maximum‐ and volumetric‐dose limits.Results:For all criteria, we found equivalent or higher conformality with VMAT plans as well as reduced critical structure doses. Several differences passed a Student's t‐test of significance: VMAT reduced the high dose spillage, evaluated with conformality index (CI), by an average of 9.4%±15.1% (p=0.030) compared to IMRT. VMAT plans reduced the lung volume receiving 20 Gy by 16.2%±15.0% (p=0.016) compared with IMRT. For the RTOG 0915 peripheral lesions, the volumes of lung receiving 12.4 Gy and 11.6 Gy were reduced by 27.0%±13.8% and 27.5%±12.6% (for both, p<0.001) in VMAT plans. Of the 26 protocol pass/fail criteria, VMAT plans were able to achieve an average of 0.2±0.7 (p=0.026) more constraints than the IMRT plans.Conclusions:FFF VMAT has dosimetric advantages over fixed beam IMRT for lung SBRT. Significant advantages included increased dose conformity, and reduced organs‐at‐risk doses. The overall improvements in terms of protocol pass/fail criteria were more modest and will require more patient data to establish difference trends of more statistical significance.

Spectroscopy peculiarities of thermal plasma of electric arc discharge between electrodes with Zn admixtures

Plasma of the free burning electric arc between Ag–SnO2–ZnO composite electrodes as well as brass electrodes were investigated. The plasma temperature distributions were obtained by Boltzmann plot method involving Cu I, Ag I or Zn I spectral line emissions. The electron density distributions were obtained from the width and from absolute intensity of spectral lines. The laser absorption spectroscopy was used for measurement of copper atom concentration in plasma. Plasma equilibrium composition was calculated using two independent groups of experimental values (temperature and copper atom concentration, temperature and electron density). It was found that plasma of the free burning electric arc between brass electrodes is in local thermodynamical equilibrium. The experimental verification of the spectroscopic data of Zn I spectral lines was carried out.

Topological entropy of transitive dendrite maps

AbstractWe show that every dendrite$X$satisfying the condition that no subtree of$X$contains all free arcs admits a transitive, even exactly Devaney chaotic map with arbitrarily small entropy. This gives a partial answer to a question of Baldwin from 2001.

Observation of Arc Spots Initiated on Nanostructured Tungsten

When tungsten is exposed to helium plasmas, it was found that nanostructures are grown on the surface. Arcing can be easily initiated in response to a transient heat load with a pulsed laser, which demonstrates transient heat loads in fusion devices. In this paper, we show the behavior of arcing initiated on the nanostructured tungsten. From the measurement of field-emission current, it is thought that the increase in the field emission by helium irradiation may be a key process for the initiation. The behavior of the free running arc spots are observed with fast framing camera. Interesting behavior of initiated arc spots including retrograde motion, bifurcation, and random motion are shown. The spectroscopic study of the emission from the arc spot revealed that the emission contained a continuum emission in visible range in addition to many line emissions.

Improving of Energy Density in Welding Arc and its Mechanism Study

As to traditional single electrode free welding arc, changes about energy density of the ionizing region in the center of arc column is not obvious with current increases due to structural limitations. In this paper, we developed parallel multi-electrode arc discharge torch which is based on the mechanism of self-magnetic contraction effect in welding arc, the torch effectively improve energy density of ionization region in non-melting inert gas arc, which is proved by experiments, and we discussed, effect of the pulse input energy and pulse frequency to energy density of the arc with parallel multi-electrode torch. This study demonstrated the approach of improving the energy density of arc ionizing region by self-magnetic pinch effect is feasible.

Frameless high dose rate stereotactic lung radiotherapy: Intrafraction tumor position and delivery time

Intrafraction change in tumor position (Δ) was evaluated for stereotactic lung radiotherapy delivered with flattening filter free volumetric modulated arc therapy. In 140 fractions from 32 patients mean Δ (±SD) was −0.7±1.4mm (vertical), −0.7±1.3mm (longitudinal) and +0.2±1.2mm (lateral) with mean vector 2.1±1.2mm. Mean delivery time was 4.4±3.4min (mean beam-on 1.9±0.4min).

Effect of Magnetic Field on the Growth of Aligned Carbon Nanotubes Using a Metal Free Arc Discharge Method and their Purification

Multiwalled Carbon Nanotubes (MWCNTs) have been synthesized using a low cost arc discharge method without using metal catalyst and vacuum devices. Effect of magnetic field on the synthesis of MWCNTs and their purity has been scrutinized. A magnetic field of 310 gauss has been found to give better purity of carbon nanotubes as confirmed by Raman spectroscopy. However, the removal of amorphous carbon from the surface of so prepared multiwalled carbon nanotubes has been achieved by different oxidizing conditions. It has been observed that the maximum removal of amorphous carbon found by using the strong oxidizing agent HNO3/H2O2. This strong oxidizing agent HNO3/H2O2removes most of the carbonaceous impurities leading to thermal stability of carbon nanotubes suggested by thermo gravimetric analysis. X-ray diffraction show the formation of carbon nanotubes having a peak indexed at (002) as the fingerprint for multiwalled carbon nanotubes. Fourier Transform Infrared (FTIR) spectra confirmed the formation of the multiwalled carbon nanotubes showing a characteristic stretching band at 1615 cm-1corresponding to the C=C bonds of tubular carbon. Raman spectroscopy revealed invaluable insights into the purification of nanotubes. G-band (1577 cm-1) corresponds to the confirmation of MWCNTs. Defect induced D-band (1355 cm-1) has been minimized after purifying CNTs with HNO3/H2O2for 24 hrs. Transmission Electron microscopic (TEM) studies indicate the formation of CNTs with controlled alignment having diameter in the range 2-8 nm.

Possibilities of application of plasma technologies to recycle organic-containing substances: Particularities of high current free burning arcs

Studies of the free burning high current arcs fanned by weak nitrogen or argon flow, with parameters typical for plasmochemical reactors and currents of about 10 kA, are performed. The electrodes were made of carbon and metals. In this case we show that, under the arc stabilization by nitrogen or argon, a significant number of charge carriers enter the arc due to ionization of carbon and metal atoms. When the high current arc is switched by a melt the main part of the arc energy is imparted into the melt and not more than 35% of the energy is transferred into the bulk of the reactor.

Entropy and exact Devaney chaos on totally regular continua

We study topological entropy of exactly Devaney chaotic maps on totally regular continua, i.e. on (topologically) rectifiable curves. After introducing the so-called $P$-Lipschitz maps (where $P$ is a finite invariant set) we give an upper bound for their topological entropy. We prove that if a non-degenerate totally regular continuum $X$ contains a free arc which does not disconnect $X$ or if $X$ contains arbitrarily large generalized stars then $X$ admits an exactly Devaney chaotic map with arbitrarily small entropy. A possible application for further study of the best lower bounds of topological entropies of transitive/Devaney chaotic maps is indicated.

Theoretical and Experimental Analysis of Breech Fed and 40-Distributed Energy Stage Plasma Arc Railguns

The design and experimental results of a 40-stage distributed energy store (DES) plasma arc railgun are presented. The railgun drives a free running hypervelocity plasma arc, one that is not pushing a payload, to velocities in excess of 10 km/s. These high velocities are of interest as they are required to successfully launch payloads into low earth orbit (LEO). The ability to launch payloads into LEO using a hypervelocity electromagnetic launcher has many financial benefits over the more conventional chemical combustion launchers. In collaboration with an Air Force Office of Scientific Research funded Multidisciplinary University Research Initiative project, the Center for Pulsed Power and Power Electronics at Texas Tech University in Lubbock, Texas has been responsible for developing and investigating a functional scale model of a multistage DES railgun to determine its effectiveness to suppress restrike phenomenon and increase plasma armature railgun performance. The distributed energy scheme is theorized to suppress restrike arc formation because the back emf voltage is localized to active stage regions where high gas density and low temperature inhibits breakdown. B-dot sensors positioned along the length of the launcher provide data to measure the plasma arc velocity and detect restrike, arc splitting, or additional secondary arc formation phenomena.

Remelting treatment of the non-conductive oxide coatings by means of the modified GTAW method

The primary objective of the study was to adapt the GTAW (Gas Tungsten Arc Welding) technique for the purposes of the surface remelting processing of non-conductive plasma sprayed coatings. Modification concerned the surface layer of complex oxide compositions based on ZrO2 and Al2O3, which had been applied onto a steel substrate using the plasma spraying technique. In the course of research it was demonstrated that the process of surface remelting of non-conductive oxide coatings may be successfully conducted using welding sources of heat provided that the standard welding station is previously redesigned and additionally equipped. The methodological and apparatus-related work undertaken led to the development and construction of a welding set with a free independent arc, in which the active participation of the oxide coating in the creation of the electric arc and its stabilisation has been eliminated.The effects of the remelting treatment on the structure of the plasma sprayed coatings have been investigated. The microstructures of both the as-deposited and the remelted coatings were observed by optical microscope and scanning electron microscope (SEM). Observation of the remelted coating structure allowed to distinguish areas with characteristic structural and morphological effects and changes in the structure thereof. On the basis of regularities noted and observations made, a zonal model of the remelted coating structure was put forward and elaborated.

Global optimality conditions for a dynamic blocking problem

The paper is concerned with a class of optimal blocking problems in the plane. We consider a time dependent set R (t ) ⊂ ℝ2 , described as the reachable set for a differential inclusion. To restrict its growth, a barrier Γ can be constructed, in real time. This is a one-dimensional rectifiable set which blocks the trajectories of the differential inclusion. In this paper we introduce a definition of “regular strategy”, based on a careful classification of blocking arcs. Moreover, we derive local and global necessary conditions for an optimal strategy, which minimizes the total value of the burned region plus the cost of constructing the barrier. We show that a Lagrange multiplier, corresponding to the constraint on the construction speed, can be interpreted as the “instantaneous value of time”. This value, which we compute by two separate formulas, remains constant when free arcs are constructed and is monotone decreasing otherwise.

Universal space in the Cartesian product of Peano curves without free arcs

We prove that there is the universal space for the class of n-dimensional separable metric spaces in the Cartesian product K 1 × ⋯ × K n + 1 of Peano curves without free arcs. It is also shown that the set of embeddings of any n-dimensional separable metric space X into this universal space is a residual set in C ( X , K 1 × ⋯ × K n + 1 ) . Other properties of product of Peano curves without free arcs are also proved.

Structural Memory in the Contractile Ring Makes the Duration of Cytokinesis Independent of Cell Size

Cytokinesis is accomplished by constriction of a cortical contractile ring. We show that during the early embryonic divisions in C. elegans, ring constriction occurs in two phases--an initial phase at a constant rate followed by a second phase during which the constriction rate decreases in proportion to ring perimeter. Cytokinesis completes in the same amount of time, despite the reduction in cell size during successive divisions, due to a strict proportionality between initial ring size and the constant constriction rate. During closure, the myosin motor in the ring decreases in proportion to perimeter without turning over. We propose a "contractile unit" model to explain how the ring retains a structural memory of its initial size as it disassembles. The scalability of constriction may facilitate coordination of mitotic events and cytokinesis when cell size, and hence the distance traversed by the ring, varies during embryogenesis and in other contexts.

Simulation Method of Column Behavior on Long Gap Free Arc in Air

Simulation Method of Column Behavior on Long Gap Free Arc in Air

Three dimensional simulation of a DC free burning arc. Application to lightning physics

One of the mechanisms assumed to be involved in the ignition channel cut off is associated with the development of instability. Like any other electric arc, lightning channels become unstable if the provided power is insufficient. In order to study this phenomenon, ONERA in collaboration with EDF has performed 3D simulations of a part of a lightning channel in order to compute the main characteristics of the arc and understand in the future the physical conditions for the ignition of instability. The model, based on the resistive magneto hydro dynamic equations, was adapted to the lightning channel context. In a first step, the results were compared to the experiment of Tanaka et al. [Tanaka, S., Sunabe, K., and Goda, Y., 2000. Three dimensional behaviour analysis of D.C. free arc column by image processing technique, XIII Int'l Conf on Gas Discharges and their applications, Glasgow.] on long electric arcs subjected to continuing current at mean sea level. A good agreement between computations and measurements was found for times greater than tens of millisecond. Results also showed that the internal resistance continuously decreases with time. Finally, this model was adapted to investigate the effects of altitude on the characteristics of the arc column. Results showed that the effects of altitudes are negligible for altitudes lower than 4 km.

Making holes in hyperspaces

Let X be a metric continuum and C ( X ) the hyperspace of all nonempty subcontinua of X. Let A ∈ C ( X ) , A is said to make a hole in C ( X ) , if C ( X ) − { A } is not unicoherent. In this paper we study the following problem. Problem: For which A ∈ C ( X ) , A makes a hole in C ( X ) . In this paper we present some partial solutions to this problem in the following cases: (1) A is a free arc; (2) A is a one-point set; (3) A is a free simple closed curve; (4) A = X .