51,251 research outputs found
Numerical studies on erosive burning in cylindrical solid propellant grain
No full textThis paper addresses erosive burning of a cylindrical composite propellant grain. Equations governing the steady axisymmetric, chemically reacting boundary layer are solved numerically. The turbulence is described by the two equation (k-?) model and Spalding’s eddy break up model is employed for the gas phase reaction rate. The governing equations are transformed and solved in the normalized stream function coordinate system. The results indicate that the dominant reaction zone lies within 20% of the boundary layer thickness close to the wall. The sharp gradient of the temperature profile near the wall is found responsible for bringing the maximum heat release zone near the surface and hence enhancement in the burning rate. The model reproduces the experimental observation that erosive burning commences only above a threshold value of axial velocit
Spectra-structure relationship: Synthesis, characterization of copper(II) complexes with ibuprofenate, o-methoxybenzoate, p-ethoxybenzoate and single crystal X-ray structure determinations of [trans-Cu(en)2(H2O)2](L)2 where en=ethylenediammine,L= o-methoxy benzoate/p-ethoxybenzoate
No full textTo investigate the spectra–structure relationship, three new copper(II) complex salts of composition
[trans-Cu(en)2(H2O)2](L1)2 2H2O(1), [trans-Cu(en)2(H2O)2](L2)2(2) and [trans-Cu(en)2(H2O)2](L3)2 (3)
(where L1 = ibuprofenate, L2 = o-methoxybenzoate and L3 = p-ethoxybenzoate) were obtained when ethylenediamine
was added to ‘Cu(L)2’ (L = L1/L2/L3) in methanol–water solution. The intermediate ‘Cu(L)2’ salts were prepared by reaction of copper sulphate with sodium salt of ibuprofen, o-methoxybenzoic acid or p-ethoxybenzoic acid, respectively, in aqueous medium in 1:2 molar ratio. The newly synthesized complex salts have been characterized by elemental analyses, spectroscopic techniques (UV/visible and IR), magnetic moment determinations and conductance measurements. X-ray structure determination
revealed an ionic structure consisting of one [trans-Cu(en)2(H2O)2]2+, two [C8H7O3]- ions in 2 and one [trans-Cu(en)2(H2O)2]2+, two (C9H8O3)- ions in 3. In these complex salts central metal ion copper(II) is coordinated by four nitrogen atoms, originating from two chelating ethylenediamine ligands and two oxygen atoms of two coordinated water molecules, showing distorted octahedral geometry around copper metal ion. Both of these structurally correlated octahedral [trans-Co(en)2(H2O)2]2+ species have shown absorption at kmax 540 nm in the UV/visible spectrum
On the structure and origin of pressure fluctuations in wall turbulence: predictions based on the resolvent analysis
Full text linkWe generate predictions for the fluctuating pressure field in turbulent pipe flow by re-formulating the resolvent analysis of McKeon & Sharma (2010) in terms of the so-called primitive variables. Under this analysis, the nonlinear convective terms in the Fourier-transformed Navier-Stokes equations are treated as a forcing that is mapped to a velocity and pressure response by the resolvent of the linearized Navier-Stokes operator. At each wavenumber-frequency combination, the turbulent velocity and pressure field are represented by the most-amplified (rank-1) response modes, identified via a singular value decomposition of the resolvent. We show that these rank-1 response modes reconcile many of the key relationships between the velocity field, coherent structure (i.e., hairpin vortices), and the high-amplitude wall-pressure events observed in previous experiment and DNS. A Green’s function representation shows that the pressure fields obtained under this analysis correspond primarily to the fast pressure contribution arising from the linear interaction between the mean shear and the turbulent wall-normal velocity. Recovering the slow pressure requires an explicit treatment of the nonlinear interactions between the Fourier response modes. By considering the velocity and pressure fields associated with the triadically-consistent mode combination studied by Sharma & McKeon (2013), we identify the possibility of an apparent amplitude modulation effect in the pressure field, similar to that observed for the streamwise velocity field. However, unlike the streamwise velocity, for which the large scales of the flow are in phase with the envelope of the small-scale activity close to the wall, we expect there to be a ?/2 phase difference between the large scale wall-pressure and the envelope of the small-scale activity. Finally, we generate spectral predictions based on a rank-1 model assuming broadband forcing across all wavenumber-frequency combinations. Despite the significant simplifying assumptions, this approach reproduces trends observed in previous DNS for the wavenumber spectra of velocity and pressure, and for the scale-dependence of wall-pressure propagation speed
Concomitant formation of differently coordinated copper(II) complexes in the same reaction: Structural studies of [trans-Cu(γ-picoline) 2(H 2O) 4](p-toluene sulfonate) 2·2H 2O and [trans-Cu(γ-picoline) 4](p-toluenesulfonate) 2·2H 2O
No full textTwo new copper(II) complexes comprising of coordinated and non-coordinated p-toluenesulfonate, [trans-Cu(γ-pic) 2(H 2O) 4](pts) 2·2H 2O, 1 and [trans-Cu(γ-pic) 4(pts) 2]·2H 2O, 2 (where p-toluenesulfonate = pts and γ-picoline = γ-pic) have been isolated from the same reaction mixture. These complexes have been characterized by spectroscopic techniques, molar conductance, TGA, magnetic susceptibility studies, and single crystal X-ray structure determination. Both complexes crystallize in the monoclinic crystal system with P2 1/c space group having cell dimensions of a = 8.0203(2) , b = 19.4471(4) , c = 10.3000(3) , β = 93.4420(9)°, V = 1603.61(7) 3, (Z = 2) in 1 and a = 10.1473(2) , b = 10.9948(2) , c = 18.0952(5) , β = 93.0340(9)°, V = 2015.96(8) 3, (Z = 2) in 2. Single -crystal X-ray structure determinations revealed the presence of ionic complex, viz: one complex cation [trans-Cu(γ-pic) 2(H 2O) 4], two pts anions and two water molecules of crystallization in the complex 1 and neutral [trans-Cu(γ-pic) 4(pts) 2] and two water molecules of crystallization in 2. The crystal packing in both complexes is stabilized by OH⋯O, CH⋯O hydrogen bonds and CH⋯π interactions
The Folio: F. C. C. Magazine
No full textSharma, O. P.-Editorial. pp. 1-2; Strickler, H. J.-Speech-Treasure, New and Old. pp. 2-10; Sir Maharaj Singh-Speech-Convocation Address. pp. 10-13; Pasricha, K. L.-Speech-Valedictory Address. pp. 14-16; Velte, F. M.-Article-The Place of Sport in our Colleges. pp. 16-21; Sharma, O. P.-Poetry-A Call to the Spirit. pp. 21; Letters to the Editors. pp. 22-25; Singh, V. Z.-Poetry-The First Signs. pp. 25; Thoughts on the Eve of New Year. pp. 25-27; Creighton, W.-Co-Eds'Corner. pp. 27-28; Sharma, O. P.-The Fifteen. pp. 28-31; Societies. pp. 31-35; News & Notes. pp. 35-36; Halls of Residence. pp. 36-38; Sports. pp. 38-39; Obituary. pp. 39-40; Poetry-An Elegy. pp. 40; [Hindi]. 16 p.; The Folio [Urdu]. 16 p.The Fifteen 1941-42. after page 3
Opposition control within the resolvent analysis framework
Full text linkThis paper extends the resolvent analysis of McKeon & Sharma (2010) to consider flow control techniques that employ linear control laws, focusing on opposition control (Choi et al. 1994) as an example. Under this formulation, the velocity field for turbulent pipe flow is decomposed into a series of highly amplified (rank-1) response modes, identified from a gain analysis of the Fourier-transformed Navier-Stokes equations. These rank-1 velocity responses represent propagating structures of given streamwise/spanwise wavelength and temporal frequency, whose wall-normal footprint depends on the phase speed of the mode. Opposition control, introduced via the boundary condition on wall-normal velocity, affects the amplification characteristics (and wall-normal structure) of these response modes; a decrease in gain indicates mode suppression, which leads to a decrease in the drag contribution from that mode. With basic assumptions, this rank-1 model reproduces trends observed in previous DNS and LES, without requiring high-performance computing facilities. Further, a wavenumber-frequency breakdown of control explains the deterioration of opposition control performance with increasing sensor elevation and Reynolds number. It is shown that slower-moving modes localized near the wall (i.e. attached modes) are suppressed by opposition control. Faster-moving detached modes, which are more energetic at higher Reynolds number and more likely to be detected by sensors far from the wall, are further amplified. These faster-moving modes require a phase lag between sensor and actuator velocity for suppression. Thus, the effectiveness of opposition control is determined by a trade-off between the modes detected by the sensor. However, it may be possible to develop control strategies optimized for individual modes. A brief exploration of such mode-optimized control suggests the potential for significant performance improvement
Sodium dinitritobis(pyrazine-2-carboxylato-N,O)cobaltate(II)
No full textR. P. Sharma, K. K. Bhasin, E. R. T. Tiekin
Effect of grain size and Gd-Co substitutions on multiferroic BiFeO3 thin films
No full textMultiferroics has attracted attention of researchers worldwide due to its fundamental and technological applications. Amongst multiferroics BiFeO3 (BFO) is the only known material to possess ferroelectric Curie temperature (TC=1143K) and antiferromagnetic Ne`el temperature (TN=643 K) well above room temperature. BFO crystallizes in a rhombohedrally distorted perovskite structure with R3c space group at room temperature. This is analogous to the hexagonal setting that contains six formula units of BFO in it with lattice constants ah = 5.587 Å, ch = 13.867 Å. The antiferromagnetic ordering of BFO is G-type having a spiral spin modulation with an incommensurate long-wavelength period of ~ 62 nm. Due to its antiferromagnetic nature; bulk BFO shows ineffectual magnetism that limits its device applications. On the other hand low resistivity of BFO leads to large leakage current limiting its ferroelectric applications. To overcome these limitations, attention has been diverted towards synthesis of thin films. Till date various techniques have been used to prepare and optimize conditions for preparation of BFO thin films. Considering the great potential of large magneto-electric effect in thin films, efforts have been made by researchers in the production of quality thin films of BFO. The magnetization and ferroelectric behaviour in BFO can be tailored by altering the grain size by adopting different methodology which includes varying annealing temperature and the film thickness. Besides, low level substitution of rare earth metal ions at Bi3+ site or transition metal ions at Fe3+ site also affects the magnetic and electrical properties. However, the recent approaches in the preparation of high quality polycrystalline thin films restrict the formation of grains with uniform size. It is therefore necessary to investigate the effect of grain size distribution to further reveal the intricate magnetic and electrical behaviour of BFO thin films. The present work focuses on the grain size distribution dependent magnetic and electrical properties of sol-gel driven BFO thin films. Further, the effect of substitution of Gd ion at Bi site and Co ion at Fe site has been studied. Also, the effect of simultaneous substitution of Gd and-Co has been investigated
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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