HIGH-VOLTAGE OPTICAL-EMISSION IN BINARY GASEOUS-MIXTURES OF N-2

Cataloged from PDF version of article.Optical emission in 1:1 binary gaseous mixtures under high voltage displays a varying character depending on pressure, applied voltage polarity, and chemical nature of the mixture. Under negative polarity, in pure N-2 and 50% mixture of Ar, O-2 and CO2, emission stemming from N-2(+) is enhanced relative to emission from neutral N-2. On mixtures of N-2 with gases containing halogens (CCl4, CHCl3, CH2Cl2, CF3H, CF2Cl2 and SF6) a reversal is observed, i.e. the N-2(+) emission is suppressed. An enhancement factor is defined as the ratio of the emission under negative polarity to positive polarity to quantify this polarity dependence. This enhancement factor varies between 0.01 and 50 depending on the second component in the mixture

Dating the Sea of Marmara sediments by a uniform mixing model

The sedimentation rates and Pb-210 fluxes on sediment surfaces were measured in the north, northwestern and southwestern parts of the Sea of Marmara. Each core had varying thickness of constant Pb-210 activity regions followed by a decreasing part with sediment depth. The sedimentation rates of the samples collected from the Bosporus and the Dardanelles could not be analysed due to the homogenization of activity in the strong currents of these straits. A uniform mixing model is proposed for the simultaneous analysis of sedimentation rates, Pb-210 fluxes and mixing depths from the experimental data. In this model, the parameters were obtained by minimizing the multi-dimensional parameter space using a grid search algorithm. The Pb-210 fluxes were found to be about 0.048 Bq cm(-2) year(-1) for all sampling sites. The mass sedimentation rates were 0.19 and 0.073 g cm(-2) year(-1) at the shelves of the Bosporus and the Dardanelles and 0.055 and 0.064 g cm(-2) year(-1) in the northwestern and middle northern basins, respectively, of the Sea of Marmara. Copyright (C) 1996 Elsevier Science Limite

Observation of fractional quantum Hall effect at even-denominator 1/2 and 1/4 fillings in asymmetric wide quantum wells

We report the observation of developing fractional quantum Hall states at Landau level filling factors $\nu = 1/2$ and 1/4 in electron systems confined to wide GaAs quantum wells with significantly $asymmetric$ charge distributions. The very large electric subband separation and the highly asymmetric charge distribution at which we observe these quantum Hall states, together with the fact that they disappear when the charge distribution is made symmetric, suggest that these are one-component states, possibly described by the Moore-Read Pfaffian wavefunction.Comment: submitted for publicatio

Total Mass and Charge Distributions in the p + 27-Al Reaction at 180 MeV

This work was supported by the National Science Foundation Grants NSF PHY 78-22774 A03, NSF PHY 81-14339, and by Indiana Universit

A Global Study of the p+27-Al Reaction at 180 MeV

This work was supported by the National Science Foundation Grant NSF PHY 81-14339 and by Indiana Universit

Joinability of Particulate Reinforced Alumix 231 Based Composite Materials Produced by Powder Metallurgy Route

In the present study, weldability of Alumix 231 based composite materials reinforced with Al₂O₃ and B₄C and produced by powder metallurgy route is investigated. Various amounts of (0, 5, 10, and 15% wt.)Al₂O₃ and B₄C powders are added to the pre-alloyed Alumix 231 (Al—2.5% Cu—0.5% Mg—14% Si) powders separately and then mixed in a three-dimensional mixer for 45 min. Powders are compacted and sintered in an argon atmosphere at 640°C for 4 h. Produced blocks are welded by the Tungsten Inert Gas (TIG) welding at 25 V, 197 A and 14 l/min shielded gas flow in commercially pure argon atmosphere. Macro- and microexamination together with some mechanical properties of the welded area are studied. The results show that, although high amount of particles resulted in a decrease in the density, these composite materials can still be welded by the TIG welding method successfully.Исследуется свариваемость произведённых методом порошковой металлургии композитных материалов на основе Alumix 231, армированных Al₂O₃ и B₄C. Различные количества (0, 5, 10 и 15 масс.%) порошков Al₂O₃ и B₄C по отдельности добавлялись в предварительно сплавленные порошки Alumix 231 (Al—2,5% Cu—0,5% Mg—14% Si), а затем перемешивались в трёхмерном миксере в течение 45 минут. Затем порошки прессовались и спекались в атмосфере аргона при 640°C в течение 4 часов. Полученные блоки сваривались вольфрамовой сваркой в атмосфере инертного газа при 25 В, 197 А и потоке инертного газа в 14 л/мин в атмосфере технически чистого аргона. Были проведены макро- и микроисследования некоторых механических свойств сварной зоны. Их результаты показали, что, хотя оказалось большое количество частиц с пониженной плотностью, эти композитные материалы могут быть успешно сварены методом вольфрамовой сварки в атмосфере инертного газа.Досліджується зварюваність вироблених методою порошкової металургії композитних матеріялів на основі Alumix 231, армованих Al₂O₃ і B₄C. Різні кількості (0, 5, 10 і 15 мас.% ) порошків Al₂O₃ і B₄C окремо додавалися у попередньо стоплені порошки Alumix 231 (Al—2,5% Cu—0,5% Mg—14% Si), а потім перемішувалися в тривимірному міксері впродовж 45 хвилин. Потім порошки пресувалися та спікалися в атмосфері арґону при 640°C впродовж 4 годин. Одержані блоки зварювалися вольфрамовим зваренням в атмосфері інертного газу при 25 В, 197 А та потоці інертного газу у 14 л/хв. в атмосфері технічно чистого арґону. Було виконано макро- та мікродослідження деяких механічних властивостей зварної зони. їх результати показали, що, хоча виявилася велика кількість частинок зі зниженою густиною, ці композитні матеріяли можуть бути успішно зварені методою вольфрамового зварювання в атмосфері інертного газу

Screening of suitable cationic dopants for solar absorber material CZTS/Se: A first principles study

The earth abundant and non-toxic solar absorber material kesterite Cu2ZnSn(S/Se)(4) has been studied to achieve high power conversion efficiency beyond various limitations, such as secondary phases, antisite defects, band gap adjustment and microstructure. To alleviate these hurdles, we employed screening based approach to find suitable cationic dopant that can promote the current density and the theoretical maximum upper limit of the energy conversion efficiency (P(%)) of CZTS/Se solar devices. For this task, the hybrid functional (Heyd, Scuseria and Ernzerhof, HSE06) were used to study the electronic and optical properties of cation (Al, Sb, Ga, Ba) doped CZTS/Se. Our in-depth investigation reveals that the Sb atom is suitable dopant of CZTS/CZTSe and also it has comparable bulk modulus as of pure material. The optical absorption coefficient of Sb doped CZTS/Se is considerably larger than the pure materials because of easy formation of visible range exciton due to the presence of defect state below the Fermi level, which leads to an increase in the current density and P(%). Our results demonstrate that the lower formation energy, preferable energy gap and excellent optical absorption of the Sb doped CZTS/Se make it potential component for relatively high efficient solar cells

Spin-valley phase diagram of the two-dimensional metal-insulator transition

Using symmetry breaking strain to tune the valley occupation of a two-dimensional (2D) electron system in an AlAs quantum well, together with an applied in-plane magnetic field to tune the spin polarization, we independently control the system's valley and spin degrees of freedom and map out a spin-valley phase diagram for the 2D metal-insulator transition. The insulating phase occurs in the quadrant where the system is both spin- and valley-polarized. This observation establishes the equivalent roles of spin and valley degrees of freedom in the 2D metal-insulator transition.Comment: 4 pages, 2 figure

Large tunable valley splitting in edge-free graphene quantum dots on boron nitride

Coherent manipulation of binary degrees of freedom is at the heart of modern quantum technologies. Graphene offers two binary degrees: the electron spin and the valley. Efficient spin control has been demonstrated in many solid state systems, while exploitation of the valley has only recently been started, yet without control on the single electron level. Here, we show that van-der Waals stacking of graphene onto hexagonal boron nitride offers a natural platform for valley control. We use a graphene quantum dot induced by the tip of a scanning tunneling microscope and demonstrate valley splitting that is tunable from -5 to +10 meV (including valley inversion) by sub-10-nm displacements of the quantum dot position. This boosts the range of controlled valley splitting by about one order of magnitude. The tunable inversion of spin and valley states should enable coherent superposition of these degrees of freedom as a first step towards graphene-based qubits