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Search Results: 1 - 10 of 326955 matches for " S Sarkar "
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Studies on Aluminum-Iron Ore in-Situ Particulate Composite  [PDF]
S. Sarkar, Akhilesh Singh
Open Journal of Composite Materials (OJCM) , 2012, DOI: 10.4236/ojcm.2012.21004
Abstract: Discontinuously reinforced aluminium matrix composites are fast emerging as engineering materials and competing with common metals and alloys. They are gaining significant acceptance because of higher specific strength, specific modulus and good wear resistance as compared to ordinary unreinforced alloys. Reinforcing particles or short fibers normally used are silicon carbide and alumina which are added externally. Recently it has been shown that alumina particles can be produced in-situ by reaction with metallic oxides reduced by aluminium. Alumina particles thus produced are dispersed in the aluminium matrix and the elementary metal gives solid solution strengthening of the matrix. In-situ particulate composites in comparison with conventional cast particulate composites produced by external addition promote cleaner interface, eliminates interface incompatibility of the matrices with the reinforcements, help to achieve greater thermodynamic stability of reinforcement particles in the matrix at elevated temperature and also increase the possibility of developing coherency between the matrix and particles formed in-situ. The morphology and the distribution of particles strongly influence the physical and mechanical properties of composites. In the present investigation, iron ore was added to molten aluminium, aluminium-magnesium and aluminium-silicon alloys by vortex method. The iron oxides present in the iron ore are observed to react with aluminium, magnesium resulting in production of Al2O3, MgO and metallic iron which dissolved in liquid aluminium. The composites thus produced were cast into cast iron die. The mechanical properties of the composites were evaluated. The dry sliding wear behavior of the cast composites was studied at different loads and different sliding velocities using Pin-On-Disk configuration wear testing machine. The worn surfaces and the wear debris were also analyzed using optical microscope and scanning electron microscope.
Study of isomers in neutron-rich magic $^{132}$Sn region
S. Sarkar,M. Saha Sarkar
Physics , 2005,
Abstract: Shell model calculations have been done for interpreting two representative isomeric states in neutron rich $^{132}Sn$ region using SMN and SMPN Hamiltonians. They are, (i) 2.91 min isomer in $^{138}Cs$ and (ii) the 0.57 $\mu s$ isomer in $^{136}$Sb nuclei. The results are compared with those obtained with KH5082 and CW5082 Hamiltonians. How the results clearly distinguish the most appropriate interaction has been discussed.
Pairing and shell evolution in neutron rich nuclei
M. Saha Sarkar,S. Sarkar
Physics , 2012,
Abstract: From the experimental data on odd-even staggering of masses, we have shown that variation of pairing as a function of neutron number plays an important role in many distinctive features like occurrence of new shell closures, shell erosion, anomalous reduction of the energy of the first 2+ state and slower increase in the B(E2, 2_{+}^{1} \rightarrow 0_{+}^{1}) in the neutron-rich even-even nuclei in different mass regions. New predictions have been made in a model independent way. Results of theoretical calculations support the phenomenological findings.
Structure of A=138 isobars above the 132Sn core and the N-N interaction in the neutron-rich environment
S. Sarkar,M. Saha Sarkar
Physics , 2008, DOI: 10.1103/PhysRevC.78.024308
Abstract: Large basis untruncated shell model calculations have been done for the A=138 neutron -rich nuclei in the pi(gdsh) X nu(hfpi) valence space above the 132Sn core. Two (1+2) -body nuclear Hamiltonians, viz., realistic CWG and empirical SMPN in this model space have been used. Calculated ground state binding energies, level spectra and other spectroscopic properties have been compared with the available experimental data. Importance of untruncated shell model calculations in this model space has been pointed out. Shell model results for the very neutron rich Sn isotope (138Sn, N/Z=1.76) of astrophysical interest for which no spectroscopic information except beta -decay half life is available, have been presented. Shell structure and evolution of collectivity in the even-even A=138 isobars have been studied as a function of valence neutron and /or proton numbers. Calculations done for the first time, reproduce remarkably well the collective vibrational states in 138Te and 138Xe. Comparison of some of the important two-body matrix elements of the empirical SMPN, CW5082 and the realistic CWG interactions has been done. These matrix elements are important for ground state binding energies and low-lying spectra of nuclei in this region. Consideration of the predictability of the two interactions seems to suggest that, in order to incorporate the special features of the N-N interaction in such exotic n-rich environment above the 132Sn core, the use of local spectroscopic information from the region might be essential.
Astrophysical Implication of Low E(2^+_1) in Neutron-rich Sn Isotopes
S. Sarkar,M. Saha Sarkar
Physics , 2009, DOI: 10.1063/1.3258221
Abstract: The observation and prediction of unusually depressed first excited 2^+_1 states in even-A neutron - rich isotopes of semi-magic Sn above 132Sn provide motivations for reviewing the problems related to the nuclear astrophysics in general. In the present work, the beta-decay rates of the exotic even Sn isotopes (134,136Sn) above the 132Sn core have been calculated as a function of temperature (T). In order to get the necessary ft values, B(GT) values corresponding to allowed Gamow Teller (GT-) beta-decay have been theoretically calculated using shell model. The total decay rate shows decrease with increasing temperature as the ground state population is depleted and population of excited states with slower decay rates increases. The abundance at each Z value is inversely proportional to the decay constant of the waiting point nucleus for that particular Z. So the increase in half-life of isotopes of Sn, like 136Sn, might have substantial impact on the r-process nucleosynthesis.
New magic number for neutron rich Sn isotopes
S. Sarkar,M. Saha Sarkar
Physics , 2009, DOI: 10.1103/PhysRevC.81.064328
Abstract: The variation of E(2+_1) of (134-140)Sn calculated with empirical SMPN interaction has striking similarity with that of experimental E(2+_1) of even-even (18-22)O and (42-48)Ca, showing clearly that N=84-88 spectra exhibit the effect of gradual filling up of \nu(2f_{7/2}) orbital which finally culminates in a new shell closure at N=90. Realistic two-body interaction CWG does not show this feature. Spin-tensor decomposition of SMPN and CWG interactions and variation of their components with valence neutron number reveals that the origin of the shell closure at 140Sn lies in the three body effects. Calculations with CWG3, which is obtained by including a simple three-body monopole term in the CWG interaction, predict decreasing E(2+_1) for (134-138)Sn and a shell closure at 140Sn.
136Sn and three body forces
M. Saha Sarkar,S. Sarkar
Physics , 2014,
Abstract: New experimental data on 2+ energies of 136,138Sn confirms the trend of lower 2+ excitation energies of even-even tin isotopes with N > 82 compared to those with N< 82. However, none of the theoretical predictions using both realistic and empirical interactions can reproduce experimental data on excitation energies as well as the transition probabilities (B(E2; 6+ -> 4+)) of these nuclei, simultaneously, apart from one whose matrix elements have been changed empirically to produce mixed seniority states by weakening pairing. We have shown that the experimental result also shows good agreement with the theory in which three body forces have been included in a realistic interaction. The new theoretical results on transition probabilities have been discussed to identify the experimental quantities which will clearly distinguish between different views.
Study of trace elements in mixed saliva of caries free and caries active children
Zahir S,Sarkar S
Journal of the Indian Society of Pedodontics and Preventive Dentistry , 2006,
Abstract: The present study was carried out to find out the amount of cariogenic and cariostatic trace elements in mixed saliva. It was observed that Cu, Pb, Na showed significant variation in case of one surface as compared to caries free group. Between the non-caries and multiple caries group Cu, Pb, K showed no significant variation Zn showed highly significant variation.
Infrared absorption in a quantum wire in the presence of spin-orbit coupling: a technique to measure different types of spin-orbit interaction strengths
S. Bandyopadhyay,S. Sarkar
Physics , 2005, DOI: 10.1063/1.2200391
Abstract: We show that the dominant absorption peak due to inter-subband transition in a gated quantum wire, with two occupied subbands, will split into a main peak and two satellite peaks if both Rashba and Dresselhaus spin-orbit interactions are present. One satellite peak will be red-shifted, and the other blue-shifted. From the relative intensity of either satellite peak, and the magnitude of the red- or blue-shift, we can determine both Rashba and Dresselhaus interaction strengths separately, if we also carry out a Hall measurement to determine the carrier concentration and a quantized conductance step measurement to determine the energy separation between subbands. This method may be a convenient alternative to usual magneto-transport measurements used to measure spin orbit interaction strengths. It is also more powerful because it allows us to measure the strengths of the two types of interactions separately.
An EPQ Model with Two-Component Demand under Fuzzy Environment and Weibull Distribution Deterioration with Shortages
S. Sarkar,T. Chakrabarti
Advances in Operations Research , 2012, DOI: 10.1155/2012/264182
Abstract: A single-item economic production model is developed in which inventory is depleted not only due to demand but also by deterioration. The rate of deterioration is taken to be time dependent, and the time to deterioration is assumed to follow a two-parameter Weibull distribution. The Weibull distribution, which is capable of representing constant, increasing, and decreasing rates of deterioration, is used to represent the distribution of the time to deterioration. In many real-life situations it is not possible to have a single rate of production throughout the production period. Items are produced at different rates during subperiods so as to meet various constraints that arise due to change in demand pattern, market fluctuations, and so forth. This paper models such a situation. Here it is assumed that demand rate is uncertain in fuzzy sense, that is, it is imprecise in nature and so demand rate is taken as triangular fuzzy number. Then by using -cut for defuzzification the total variable cost per unit time is derived. Therefore the problem is reduced to crisp average costs. The multiobjective model is solved by Global Criteria method with the help of GRG (Generalized Reduced Gradient) Technique. In this model shortages are permitted and fully backordered. Numerical examples are given to illustrate the solution procedure of the two models. 1. Introduction The classical EOQ (Economic Order Quantity) inventory models were developed under the assumption of constant demand. Later many researchers developed EOQ models taking linearly increasing or decreasing demand. Donaldson [1] discussed for the first time the classical no-shortage inventory policy for the case of a linear, positive trend in demand. Wagner and Whitin [2] developed a discrete version of the problem. Silver and Meal [3] formulated an approximate solution procedure as “Silver Meal heuristic” for a deterministic time-dependent demand pattern. Mitra et al. [4] extended the model to accommodate a demand pattern having increasing and decreasing linear trends. Deb and Chaudhuri [5] extended for the first time the inventory replenishment policy with linear trend to accommodate shortages. After some correction in the above model [5], Dave [6] applied Silver’s [7] heuristic to it incorporating shortages. Researchers have also worked on inventory models with time-dependent demand and deterioration. Models by Dave and Patel [8], Sachan [9], Bahari-Kashani [10], Goswami and Chaudhuri [11], and Hariga [12] all belong to this category. In addition to these demand patterns, some researchers use ramp type
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