Non-neoclassical up/down asymmetry of impurity emission on Alcator C-Mod

We demonstrate that existing theories are insufficient to explain up/down asymmetries of argon x-ray emission in Alcator C-Mod ohmic plasmas. Instead of the poloidal variation, ñ[subscript z]/〈n[subscript z]〉, being of order the inverse aspect ratio, ϵ, and scaling linearly with B[subscript t][superscript _ over n][subscript e]/I[2 over p], it is observed over 0.8 < r/a < 1.0 to be of order unity and exhibits a threshold behaviour between 3.5 <B[subscript t][superscript _ over n][subscript e]/I[subscript p] < 4.0 (T10[superscript 20] m[superscript −3] MA[superscript −1]). The transition from a poloidally symmetric to asymmetric impurity distribution is shown to occur at densities just below those that trigger a reversal of the core toroidal rotation direction, thought to be linked to the transition between the linear and saturated ohmic confinement regimes. A possible drive is discussed by which anomalous radial transport might sustain the impurity density asymmetry as the ratio of the perpendicular to parallel equilibration times, τ[subscript ⊥,z]/τ[subscript ∥,z], approaches unity. This explanation requires a strong up/down asymmetry in radial flux which, while not observable on C-Mod, has been measured in TEXT and Tore Supra ohmic plasmas.United States. Dept. of Energy (Contract DE-FC02-99ER54512)United States. Dept. of Energy (Fusion Research Postdoctoral Research Program

The structure phase transition in quantum wires of bismuth under elastic tension

Access full text – https://doi.org/10.1007/BF02571200It was established that at 4.2 K for thin (d<1μm)Bi wires there existed a complicated λ-form dependence of the resistanceR¯ on the strong elastic deformation ξ. The drastic fall in the oscillation amplitude of the flux-quantification type together with theR (ξ) behavior in dependence on the values of temperatureT, impurity concentrationC, wire diameterd and current densityJ indicate the presence of the structure phase transition within the subsurface region due to the shear deformation in the investigated layered structure. The intensive carrier scattering at the fluctuation oscillations of the atoms within the subsurface region brings about sharp resistance rise. Formation of a new long range order in the said region excludes the following rise inR¯(ξ) and ensures the maximum of the said quantity

Acid Corrosion Inhibitor from Tobacco Waste for Steel of Oil Pipes

AbstractA technology of an acid corrosion inhibitor production for steel of oil pipes has been developed. The inhibitor is obtained by extracting nicotine and related substances with an aqueous solution of benzoic acid from tobacco waste. Extraction, chromato-mass spectrometry, weight and electrochemical methods were applied as research methods for determining inhibitor effectiveness

Manifestare neaşteptată concomitentă a supraconductibilităţii şi feromagnetismului slab la interfeţele bicristalelor de Bi şi a izolatorilor topologici tridimensionali BiSb

Two/one superconducting phases with the onset of transition ≤ 36K are observed at CIs of bicrystals, while the rhombohedral Bi and 3D topological insulator (3DTI) BiSb are diamagnetic and do not exhibit superconductivity. In large crystallite disorientation angle Bi-Sb interfaces both superconductivity and weak ferromagnetism were revealed simultaneously

Magnetic and Electronic Transport Properties of Large Crystallite Disorientation Angle Interfaces of a Bi-Sb 3d Topological Insulator

Sursa: Conferinţa - „Masa rotundă "Multidisciplinarity in Modern Science for the Benefit of Society", 21-22 septembrie 2017.→ https://ibn.idsi.md/ro/collection_view/36We present results of a study of the magnetic and galvanomagnetic properties of Bi1-xSbx (0.07 < x < 0.2) bicrystals in a temperature range of 1.6-100 K using a Quantum Design SQUID magnetometer and a Physical Property Measuring System (PPMS) with a 140-kOe induction magnet. The quantum oscillations of galvanomagnetic effects were registered in stationary (up to 180 kOe) and pulse magnetic fields (up to 400 kOe) directed along the C3 axis of the crystallites. The studied bicrystals consisting of two single crystalline blocks (crystallites) and the perfect superconducting nano-width crystallite interfaces with a solitary central part (thickness of about 60 nm) and two similar adjacent layers (~20 nm) on both sides of it were prepared by the horizontal zone recrystallization method

Thermomagnetic transport due to the superconducting interfaces in inclination bicrystals of Bi

Only AbstractThe group- V semimetals are of major interest for solid state physics, because of easy access to the quantum limit in high magnetic fields and possibility of studying the unusual behaviour of Dirac electrons under extremal conditions of a strong phonon drag effect, electronic topological phase transitions, and proximity-induced superconducting order. Some of these materials like Bi, exhibit remarkable electron transport properties and unique thermoelectric and thermomagnetic characteristics, defining new directions in this field of science. In this report we show the high - field thermomagnetic power Sii(B) and Nernst–Ettingshausen effect Sij(B) in Bi inclination bicrystals with superconducting nano-width interfaces (~ 100 nm). We found that the thermomagnetic effects in small disorientation angle bicrystals (SDA) are considerably higher than in single crystalline Bi and large disorientation angle (LDA) samples. A weak increase of the monotonic Sii(B) in SDA bicrystals and completely saturated thermomagnetic power in LDA specimens were detected, indicating a varying contribution of thermally excited carriers and a different degrees of interface disorder. It was also revealed that the maximum of temperature dependences of Sii(B) quantum oscillation amplitude in SDA bicrystals is shifted ~ 1 K at low temperatures, compared to Bi single crystals. Two new quantum oscillation harmonics we have found in quantizing magnetic fields, characterizing different densities of electronic states and different levels of disorder both in LDA and in SDA interfaces. It should be assumed that the obtained results are important for future applications in thermoelectricity and spintronic devices

Grain boundary wetting in the Al-Mg system and synthesis of magnesium diboride in contact with melt

Access full text - https://doi.org/10.3103/S1062873809090056The interaction between a Mg-containing melt and B under conditions of partial and complete wetting of Al/Al grain boundaries by Al-Mg melt has been investigated. The study was performed on Al polycrystals with Mg contents of 5, 10, 15, 18, and 25 wt %. Correspondingly, the Mg content in the melt was determined by the liquidus line and was in the range from 5 to 30 wt %. The obtained metal-matrix composites were investigated by light and scanning electron microscopy, electron-probe microanalysis, and X-ray diffraction. The possibility of synthesizing MgB2 in the contact with a melt having a relatively low Mg content (from 15 to 30 wt %) has been demonstrated

Recent results from the electron cyclotron heated plasmas in Tokamak à Configuration Variable (TCV)

In noninductively driven discharges, 0.9 MW second harmonic (X2) off-axis co-electron cyclotron current drive deposition is combined with 0.45 MW X2 central heating to create an electron internal transport barrier (eITB) in steady plasma conditions resulting in a 1.6-fold increase of the confinement time (tau(Ee)) over ITER-98L-mode scaling. The eITB is associated with a reversed shear current profile enhanced by a large bootstrap current fraction (up to 80%) and is sustained for up to 10 current redistribution times. A linear dependence of the confinement improvement on the product of the global shear reversal factor (q(0)/q(min)) and the reversed shear volume (rho(q-min)(2)) is shown. In other discharges heated with X2 the sawteeth are destabilized (respectively stabilized) when heating just inside (respectively outside) the q=1 surface. Control of the sawteeth may allow the avoidance of neoclassical tearing modes that can be seeded by the sawtooth instability. Results on H-mode and highly elongated plasmas using the newly completed third harmonic (X3) system and achieving up to 100% absorption are also discussed, along with comparison of experimental results with the TORAY-GA ray tracing code [K. Matsuda, IEEE Trans. Plasma Sci. PS-17, 6 (1989); R. H. Cohen, Phys. Fluids 30, 2442 (1987)]. (C) 2003 American Institute of Physics