Bogos Nubar Sismanoglu

Characterization of microhollow cathode discharges

This work is devoted to the study of the electrical characteristics of microhollow cathode discharges (MHCD) at moderate to high pressure in argon and air for different geometries. High-pressure glow discharges can be operated in MHCD devices with µm electrode spacing. Experiments have been performed to determine the so-called Paschen curves, i.e. the dependence of the breakdown voltage on the product electrode gap and gas pressure. Current-voltage characteristic curves were obtained as a function of the pressure and hole diameter. MHCD enables stable direct current discharges that could be ignited for pressures ranging from 12 to 800 Torr, in a very wide range of current densities and electrodes materials. Evidence of electron field emission was observed for several ranges of gap spacing.

A utilização da filmadora digital para o estudo do movimento dos corpos

Using a digital camera and public common software VirtualDub it was possible to record the space-time evolution of a fast dynamic system, such as a body in free fall. This paper treats two classical free fall experiments: a) falling chain and b) a free falling folded chain (bungee jump). Analyzed empirically in a simple setup, these experiments showed very important concepts of mechanics. The VirtualDub program enables the selection of frames from the video record. The analysis of these frames provides elements of several dynamical variables such as velocity, force and acceleration, and is a powerful tool in the study of the movement.

Optical and electrical diagnostics of microdischarges at moderate to high pressure in argon

Microdischarges at moderate to high pressure in argon were investigated. A hole opening diameter of 500 µm direct current (dc) microhollow cathode discharges (MHCD) were characterized by electrical measurements and optical emission spectroscopy (OES) for pressures ranging between 90 and 800 Torr and current from 5 to 20 mA. Current-voltage characteristic curves were obtained as a function of the pressure for this hole diameter. MHCD enables stable dc discharges for molybdenum electrodes material at constant Ar + 2%H2 flow of 0.03 l/min. Optical emission spectroscopy and analysis of the spectral line broadening of plasma line emissions were performed in order to measure gas discharge parameters. Electron number densities were obtained from Hβ Balmer line ( ~ 1014 cm-3). For the above mentioned discharge conditions, gas temperature was estimated to be 550 - 850 K from OH rotational bands. Excitation temperature was measured based on two lines method (from atomic Mo lines) and from 4p - 4s and 5p - 4s Ar radiative transitions. Hydrogen atom temperature was measured for 800 Torr ( ~ 12000 K).

Dinâmica de massa variável: corrente suspensa na máquina de Atwood

This paper deals with the study of a variable mass dynamic where is developed the Atwood machine experiment with variable mass of a resting chain in which one end is attached to a fine string which passes over a pulley and carries a weight. The damped harmonic oscillation was observed. The Newtons second law was employed to obtaining of the upward motion of the chain. Using a digital camera and free software VirtualDub it was possible to record the evolution of the space-time and to reproduce it in a number of frames in a low cost operation. Good agreement was obtained between experimental results and the predictions of the movement dynamical variables. Comparisons between these results and those obtained using expensive photogates were done. These photogates shown bad results of the measurements done at the beginning of the movement.

Dynamics of Environmental Ionizing Radiation between May to September 2016 in the Region of São José dos Campos, SP, Brazil

Measurements of gamma radiation (200 keV to 10 MeV) were performed between May 25 to September 3

Electric field gradient in microplasmas

Linear Stark splitting of the Hβ Balmer line components and spatially resolved optical emission spectroscopy (OES) measurements were used to estimate the electric field gradient in the cathode sheath region (~70 μm long) of an atmospheric pressure direct current argon flow-stabilized microplasma jet. Also, plasma parameters in the negative glow region were investigated by both OES and electrical diagnostics. OES was used to diagnose near-cathode region (negative glow and cathode sheath) of the microplasma jet in order to measure both, the basic discharge parameters, in the plasma bulk, and electric field distribution along the cathode sheath. In addition, the main mechanisms responsible for Hβ spectral line broadenings were investigated.

Visualizando tunelamento quântico através da geração de microplasmas

The quantum tunneling is a phenomenon that provides numerous technological applications through direct application of the concepts of quantum mechanics. According to this phenomenon, electrons can be extracted from metal surfaces under which there is a huge potential gradient, ie, an intense local electric field. Through a system known as microhollow cathode two metal layers interspersed by a thin mica layer (with thickness d = 3 μm), perforated with holes of diameter D = 200 μm at a pressure of 20 Torr, led the extraction of cold electrons at a local electric microfield of approximately 15 V/nm. The voltage of about 390 V applied at these metals allowed the passage of electrons through the potential barrier at the cathode hole region. The Fowler-Nordheim curve confirmed the effectiveness of the phenomenon in the generation of microplasma inside the hole, visible to the naked eyes.

Enhancing wettability of high density polyethylenes (HDPE) through microplasma jets

This paper aims at the characterization of plasma microjets generated by open microhollow cathodes to ionize gases such as air, N2, He and O2. The electrical and optical parameters were raised. Through the optical emission spectroscopy, gas temperature (Tg) and the excitation temperature were estimated. Tg ranging from 2100K to 600K for a gas flow rate ranging from 0 to 400ml/min. From 150 to 400ml/min Tg remained close to 700K. As an application, the treatment of smooth surfaces of high density polyethylenes (HDPE) was performed with a view to improve the hydrophilic property of the surface.

Máquina de Atwood com massa variável em movimento oscilatório atípico

An Atwood machine with variable mass is presented in this work using a robust configuration that enables data acquisition from the dynamic oscillatory motion during a relatively long time interval. The system is easily implemented through the use of a pulley and a set of three bodies whose masses satisfy the relationship M>m1>m2, and M<m1 + m2. The problem can be treated in a playful way for high school students or with greater depth, using the Lagrangian formalism for undergraduate students. The oscillatory motion of the system is not similar to any of the cases of periodic or aperiodic damping reported in the literature, because the mass of the system changes with decreasing time intervals. Through the use of photogates (sensors) coupled to the pulley and Tracker Software it was obtained a set of dynamic variables to be compared with the expected results derived from the analytical description.

Properties of thin silicon carbide films prepared by rapid thermal annealing

We report experimental results related to the structural and electrical properties of thin SiC films. Thin carbon films with thicknesses 50 A and 300 A were deposited by R.F. sputtering and processed by rapid thermal annealing (RTA) for 3 min at temperatures of 800 °C and 1400 °C in a vacuum chamber at 2×10−5 Torr. The thin films properties were studied by Raman spectroscopy and electrical cross-conductance.