Computation of laminar heat transfer from gaseous plasmas in electromagnetic fields

Heat transfer analysis procedure is presented for two-temperature gaseous plasma. Analysis is based on laminar flow of singly-ionized, quasineutral plasma with variable properties. Sheath analysis is described for species in accelerating field, decelerating field, emitted from wall, and recombining at wall

Laminar flow heat transfer from a gaseous plasma at elevated electron temperature in the presence of electromagnetic fields

Electromagnetic field effects on heat transfer of two temperature gaseous plasm

Superconductivity in Boron under pressure - why are the measured Tc_c's so low?

Using the full potential linear muffin-tin orbitals (FP-LMTO) method we examine the pressure-dependence of superconductivity in the two metallic phases of Boron: bct and fcc. Linear response calculations are carried out to examine the phonon frequencies and electron-phonon coupling for various lattice parameters, and superconducting transition temperatures are obtained from the Eliashberg equation. In both bct and fcc phases the superconducting transition temperature T$_c$ is found to decrease with increasing pressure, due to stiffening of phonons with an accompanying decrease in electron-phonon coupling. This is in contrast to a recent report, where T$_c$ is found to increase with pressure. Even more drastic is the difference between the measured T$_c$, in the range 4-11 K, and the calculated values for both bct and fcc phases, in the range 60-100 K. The calculation reveals that the transition from the fcc to bct phase, as a result of increasing volume or decreasing pressure, is caused by the softening of the X-point transverse phonons. This phonon softening also causes large electron-phonon coupling for high volumes in the fcc phase, resulting in coupling constants in excess of 2.5 and T$_c$ nearing 100 K. We discuss possible causes as to why the experiment might have revealed T$_c$'s much lower than what is suggested by the present study. The main assertion of this paper is that the possibility of high T$_c$, in excess of 50 K, in high pressure pure metallic phases of boron cannot be ruled out, thus substantiating the need for further experimental investigations of the superconducting properties of high pressure pure phases of boron.Comment: 16 pages, 8 figures, 1 Tabl

Entanglement and dynamics of spin-chains in periodically-pulsed magnetic fields: accelerator modes

We study the dynamics of a single excitation in a Heisenberg spin-chain subjected to a sequence of periodic pulses from an external, parabolic, magnetic field. We show that, for experimentally reasonable parameters, a pair of counter-propagating coherent states are ejected from the centre of the chain. We find an illuminating correspondence with the quantum time evolution of the well-known paradigm of quantum chaos, the Quantum Kicked Rotor (QKR). From this we can analyse the entanglement production and interpret the ejected coherent states as a manifestation of so-called `accelerator modes' of a classically chaotic system.Comment: 5 pages, 2 figures; minor corrections, tidied presentatio

Momentum-resolved electron-phonon interaction in lead determined by neutron resonance spin-echo spectroscopy

Neutron resonance spin-echo spectroscopy was used to monitor the temperature evolution of the linewidths of transverse acoustic phonons in lead across the superconducting transition temperature, $T_c$, over an extended range of the Brillouin zone. For phonons with energies below the superconducting energy gap, a linewidth reduction of maximum amplitude $\sim 6 \mu$eV was observed below $T_c$. The electron-phonon contribution to the phonon lifetime extracted from these data is in satisfactory overall agreement with {\it ab-initio} lattice-dynamical calculations, but significant deviations are found

Single hole doped strongly correlated ladder with a static impurity

We consider a strongly correlated ladder with diagonal hopping and exchange interactions described by $t-J$ type hamiltonian. We study the dynamics of a single hole in this model in the presence of a static non-magnetic (or magnetic) impurity. In the case of a non-magnetic (NM) impurity we solve the problem analytically both in the triplet (S=1) and singlet (S=0) sectors. In the triplet sector the hole doesn't form any bound state with the impurity. However, in the singlet sector the hole forms bound states of different symmetries with increasing $J/t$ values. Binding energies of those impurity-hole bound states are compared with the binding energy of a pair of holes in absence of any impurity. In the case of magnetic impurity the analytical eigenvalue equations are solved for a large (50 X 2) lattice. In this case also, with increasing $J/t$ values, impurity-hole bound states of different symmetries are obtained. Binding of the hole with the impurity is favoured for the case of a ferromagnetic (FM) impurity than in the case of antiferromagnetic (AFM) impurity. However binding energy is found to be maximum for the NM impurity. Comparison of binding energies and various impurity-hole correlation functions indicates a pair breaking mechanism by NM impurity.Comment: 15 Pages, 6 figure

Development of various modules of environment friendly furnaces concerning melting and castings of iron, brass and bell metal products

Since over a decade there is a worldwide trend towards using fuel alternative tocoal/ coke concerning casting production due to the excessive emission undesirable level of suspended particulate material and toxic gases beyond acceptable limit with flue emitted from coal/coke based units. India is an important global player in the casting sector and the study on ferrous as well as non-ferrous casting reveals that : (i) there are above several thousand coke based foundries currently operating in different parts of India and (ii) there are numerous cottage based brass and bell metal industries in India which mainly use coal/coke/wood / wood charcoal as main fuel. Exhaust emission with flue from these coal/ coke based industries normally carries lots of Suspended Particulate Materials (SPM), Toxic gases such as SO , NO , etc. Normal emission of SPM and SO x x x from these foundries/ melting and casting unit is about 1000-3000 mg / NM3 and beyond 700 mg / NM3 respectively. Stringent specifications set by not only Pollution Control Boards of various First & Second World countries but also by CPCB (Central Pollution Control Board of India) threaten the existence of most of the coke/coal based medium and small scale casting sectors as operation of these solid fuel based furnaces is reported extremely unhealthy because of the excessive presence of SPM and toxic gases. Coke less cupola using sulfur-stripped hydrocarbon based oils (LDO, Kerosene Oil)/ Gases (LPG, LNG, NG) developed by M/s Richard Taft1, Ducker2, NML/CSIR3, in Russia4 as well as in Japan5 is presently in the process of replacing coke based cupola concerning iron casting / foundries. Therefore, an attempt had been made in this work to carry out research and development of environment-friendly furnaces of various sizes for brass and bell metal melting and casting in connection with the production of thin section of not only traditional items/ utensils such as lota/small size pitcher, ghara/ big size pitcher, tumbler, thali/saucer/plate, flower vase, but also of artifact. Number of visits to various clusters of Brass and Bell metal Industries of West Bengal, especially at places and around Bishnupur in Bankura district were made. Thorough discussion with practitioners as well as artisans and witnessing some of the present practice were carried out. State of precarious ambient condition due to excessive presence of SPM as well as toxic gas in and working places as a result of using highly ash content coke was noticed. Based on mutual agreement and self financing, an eco friendly furnace was envisaged to design and developed to deal with melting and casting of about 5 kg weighing standard Kalsi. Concept design of coke less furnaces using sulfur-stripped hydrocarbon based oils (LDO, HSD, Furnace Oil) / Gases (LPG, LNG, NG) was envisaged to be utilized as exhaust emission from these ensures SPM and toxic gases much less to the extent of about 10 ~ 25 mg/ Nm3 from the limit of 150 mg/ Nm3 set by any local Pollution Control Board [CPCB]. The developmental work of such a furnace [a module unit of melting and casting] envisaged to include a set of either oil or gas burners which are to be positioned/ placed spirally along the hearth portion of the furnace to provide necessary heat for heating and melting. Around the burners, there shall be some of refractory coated [heat insulated]grate bar to support entire load of permeable bed and mould containing desired raw materials for melting and casting of Kalsi/ pot. Desired quality permeable bed may be improvised to be made by using either by making highly insulated and unbreakable quality ball made from cast able quality refractory ball [about 50 Ø mm. ] or by breaking and shaping of granular size rejected graphite block [-55 + 50 mm] from used and rejected graphite electrode. Permeable bed is envisaged to extract and absorbed heat from flue and suitably transfer the heat to the mould. During the operation of the mentioned furnace, hot gases/flue from burners is expected to flow up through the permeable bed placed along the annulus space between furnace and the mould. Heated flue which is ejected out from the mentioned burners while passing along mould and permeable bed is expected to accomplish preheating, heating, maintaining temperature for complete melting of raw materials. Through permeable bed area, the proposed design is envisaged to control/ adjust the operating temperature of furnace, mould and raw materials. Molten metal with desired flow ability is expected to get into the cavities of investment mould to produce thin shell utensils/ Kalsi when it is tilted upside down after getting superheated in the stated furnace. The desired furnace was designed and developed in the premises of an entrepreneur at Bishnupur locality in Bankura District of West Bengal. No. of successful campaigns then carried out which reveals not only the acceptability and validity of the developed Furnace based on using Sulfur stripped domestic fuel such as mainly LPG [ Liquid Petroleum Gas] as well as Kerosene but also market acceptability of the product i.e. Kalsi/Ghara/Pot. In near future, the developed technology is expected to be utilized by the Practitioner as well as Artisan of the Brass and Bell metal product cluster with sulfur stripped either LPG from west coast or NG [Natural Gas] from Assam when these are expected to be supplied through National Piping Net Working

An insight into the properties of magnesite and magnesite-chromite refrectories for ferro-chrome industry

A few qualities of magnesite and magnesite-chromite bricks and magnesite ramming masses manufactured indi-genously are being used in making ferro-chrome alloy in India. In this paper an attempt has been made for evalu-ating different qualities of magnesite and magnesitech-romite refractories by studying the relevant physico-chemical properties. As the bricks are to withstand severe corrosion and erosion by the molten metal and slag at high temperatures, the mineralogy, microstructure and the modulus of rupture at different temperatures were studied. The hot modulus of rupture values are correlated with the mineralogical compositions of the bricks. A ramming mass based on sea water magnesia has been developed for chute area application and the detailed properties of the same are given