Ravi Kumar

Bio: Ravi Kumar is an academic researcher from Indian Institute of Technology Roorkee. The author has contributed to research in topics: Irradiation & Magnetization. The author has an hindex of 48, co-authored 719 publications receiving 10970 citations. Previous affiliations of Ravi Kumar include Raja Ramanna Centre for Advanced Technology & Sanjay Gandhi Post Graduate Institute of Medical Sciences.

Effectiveness of anisotropic etching of silicon in aqueous alkaline solutions

Abstract: Optical effectiveness of anisotropic etching of (1 0 0) silicon in inorganic alkaline solution has been studied from the view point of its application in commercial silicon solar cells. The damage caused by ID saw or wire saw during slicing of the wafer is required to be removed for fabrication of solar cells. The etch rates for removal of the surface damages for boron doped Czochralski wafers of 1–2 Ω cm resistivity in 20% NaOH solution at 80°C was measured and was found to be ∼1.4 μm/min. After the damage removal, texturisation was obtained in 2% NaOH solution buffered with isopropyl alcohol at 80°C. An optical effectiveness parameter feff,λ was defined and its value was estimated from the study of reflectivity and topography of the wafers textured for different durations of time. The kinetics of anisotropic etching was studied which indicated that growth of pyramids begins at preferential sites which may arise due to crystalline defects or wetting. Silicon solar cells have been realized by standard process involving phosphorous diffusion and vacuum evaporated front and back contacts. The value of optical effectiveness parameter is found to have a direct correlation with the improvement in short circuit current density of the textured cells.

Performance of a double pass solar air collector

Abstract: Double pass counter flow solar air collector with porous material in the second air passage is one of the important and attractive design improvement that has been proposed to improve the thermal performance. This paper presents theoretical and experimental analysis of double pass solar air collector with and without porous material. A mathematical model has been developed based on volumetric heat transfer coefficient. Effects of various parameters on the thermal performance and pressure drop characteristics have been discussed. Comparison of results reveals that the thermal efficiency of double pass solar air collector with porous absorbing material is 20–25% and 30–35% higher than that of double pass solar air collector without porous absorbing material and single pass collector respectively.

Structural, electrical and magnetic properties of Co-Cu ferrite nanoparticles

Abstract: We report structural, electrical and magnetic properties of Cu doped Co ferrite nanoparticles prepared by sol–gel method. Analysis of structural properties has been carried out by using XRD and reveals that all samples have single phase cubic spinel structure. The permittivity ( ɛ ), dielectric loss (tan δ ) and ac conductivity ( σ ac ) were determined at room temperature as a function of frequency. The results of dielectric properties indicated the normal Maxwell–Wagner type dielectric dispersion due to interfacial polarization. Complex impedance spectroscopic studies reveal that the conduction in these samples is through the grain boundaries. Room temperature magnetic hysteresis measurements infer that the saturation magnetization decreases with Cu doping which may be due to the difference of the magnetic moment of Cu and Fe ions.

Magnetocaloric effect in Heusler alloys Ni50Mn34In16 and Ni50Mn34Sn16

Abstract: We present results of detailed ac susceptibility, magnetization and specific heat measurements in Heusler alloys Ni50Mn34In16 and Ni50Mn34Sn16 These alloys undergo a paramagnetic to ferromagnetic transition around 305 K, which is followed by a martensitic transition in the temperature regime around 220 K Inside the martensite phase both the alloys show signatures of field-induced transition from martensite to austenite phase Both field- and temperature-induced martensite–austenite transitions are relatively sharp in Ni50Mn34In16 We estimate the isothermal magnetic entropy change and adiabatic temperature change across the various phase transitions in these alloys and investigate the possible influence of these transitions on the estimated magnetocaloric effect The sharp martensitic transition in Ni50Mn34In16 gives rise to a comparatively large inverse magnetocaloric effect across this transition On the other hand the magnitudes of the conventional magnetocaloric effect associated with the paramagnetic to ferromagnetic transition are quite comparable in these alloys

AHTPDB: a comprehensive platform for analysis and presentation of antihypertensive peptides

Abstract: AHTPDB (http://crdd.osdd.net/raghava/ahtpdb/) is a manually curated database of experimentally validated antihypertensive peptides. Information pertaining to peptides with antihypertensive activity was collected from research articles and from various peptide repositories. These peptides were derived from 35 major sources that include milk, egg, fish, pork, chicken, soybean, etc. In AHTPDB, most of the peptides belong to a family of angiotensin-I converting enzyme inhibiting peptides. The current release of AHTPDB contains 5978 peptide entries among which 1694 are unique peptides. Each entry provides detailed information about a peptide like sequence, inhibitory concentration (IC50), toxicity/bitterness value, source, length, molecular mass and information related to purification of peptides. In addition, the database provides structural information of these peptides that includes predicted tertiary and secondary structures. A user-friendly web interface with various tools has been developed to retrieve and analyse the data. It is anticipated that AHTPDB will be a useful and unique resource for the researchers working in the field of antihypertensive peptides.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Bose-Einstein condensation in a gas of sodium atoms

Abstract: Bose-Einstein condensation (BEC) has been observed in a dilute gas of sodium atoms. A Bose-Einstein condensate consists of a macroscopic population of the ground state of the system, and is a coherent state of matter. In an ideal gas, this phase transition is purely quantum-statistical. The study of BEC in weakly interacting systems which can be controlled and observed with precision holds the promise of revealing new macroscopic quantum phenomena that can be understood from first principles.

Ferromagnetic materials

Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.