Dr. O. S. K. Subramanya Sastry
@hpcu.ac.in
Professor, Department of Physics and Astronomical Sciences
Central University of Himachal Pradesh
RESEARCH INTERESTS
Nuclear physics
Computational physics
Physics Education Research
Impact of Veda Chanting on Cognitive functions
Science and Spirituality
Scopus Publications
Scopus Publications
Anil Khachi, Lalit Kumar, Ayushi Awasthi, and O S K S Sastri
IOP Publishing
Abstract Reference potential approach (RPA) has been successful in obtaining inverse potentials for weakly bound diatomic molecules using the Morse function. In this work, our goal is to construct inverse potentials for all the available ℓ-channels of np-scattering using RPA. Riccati-type phase equations for various ℓ-channels are solved using 5th order Runge-Kutta method to obtain the scattering phase shifts (SPS) in tandem with an optimisation procedure to minimize mean squared error (MSE). Interaction potentials for a total of 18 states have been constructed using only a three parameter Morse interaction model. The obtained MSE is <1% for 1 S 0, 3 P 1 and 3 D 1 channels and <2% for 1 P 1 channel and <0.1% for rest of the 14 channels. Total scattering cross-sections at various lab energies obtained using RPA are found to match well with experimental ones. A complete study of the np-scattering using RPA has been undertaken using Morse function as zeroth reference for the first time.
Anil Khachi, Lalit Kumar, M. R. Ganesh Kumar, and O. S. K. S. Sastri
American Physical Society (APS)
Anil Khachi, Lalit Kumar, and O. S. K. S. Sastri
Pleiades Publishing Ltd
Swapna Gora, O S K S Sastri, and S K Soni
IOP Publishing
Abstract In this paper, both least squares minimization (LSM) and variational Monte-Carlo techniques have been implemented to determine the co-efficients of semi-empirical mass formula (SEMF). First, the experimental binding energies (BEs) are determined for all the available nuclei from atomic mass evaluation (AME2016) data. Then, LSM technique is implemented in Gnumeric worksheet to minimize relative mean squared error (RMSE) to obtain the SEMF co-efficients by considering only the first three co-efficients which are deduced from liquid drop model. The mean percentage error (MPE) value, between obtained BEs from the optimized co-efficients and the experimental BEs, has been determined. Then, to emphasize the relevance of empirical terms, they have been introduced successively one after other and the procedure has been repeated. A reduction in MPE-value has been observed after each iteration. This same procedure has also been employed using Monte-Carlo approach to obtain SEMF co-efficients by minimizing RMSE-value as in variational principle.
O.S.K.S Sastri, Anil Khachi, and Lalit Kumar
Springer Science and Business Media LLC
In this paper, we present an innovative approach to construct inverse potentials for np-interaction directly from experimental scattering phase shifts ( SPS ) by considering the Morse function as an interaction potential. The inverse potentials corresponding to SPS for $$\\ell = 0$$ ℓ = 0 -channel of np interaction is obtained using the variational Monte-Carlo ( VMC ) technique in tandem with the phase function method ( PFM ) for the first time. The S-channel SPS for $$^3S_1$$ 3 S 1 and $$^1S_0$$ 1 S 0 have been obtained, with a mean percentage error with respect to experimental multiple energy analysis data ( MEAD ) for lab energies up to 350 MeV, to less than 3 $$\\%$$ % . Similarly, the inverse potential for the $$^1S_0$$ 1 S 0 proton-proton (pp) interaction, with the Coulomb term modeled as proportional to erf(), has also been obtained to match experimental values to less than 3 $$\\%$$ % . This approach can be utilized for obtaining inverse potentials for various scattering processes modeled via different interaction potentials.
Aditi Sharma and O S K S Sastri
IOP Publishing
Abstract In this paper, the Numerov matrix method is implemented in a pedagogic manner for simulation of a CO molecule. First, the Numerov algorithm is implemented in the spreadsheet environment ‘Gnumeric’ to obtain coarse vibrational, rotational and ro-vibrational spectrum. Then, the code is written in Scilab so that simulation can be performed for smaller step-sizes so as to achieve greater accuracy for frequencies in ro-vibrational fine-structure spectrum. The simulated vibrational frequencies have been obtained to an accuracy of 0.01% with respect to the experimental ones. The values of rotational constant (B e ) and anharmonicity constant ( ω ¯ e x e ) have been obtained to accuracies of 0.6 and 1.22% respectively. This procedure can be easily integrated as a simulation activity for determination of ro-vibrational spectra of various heterogenous diatomic molecules at undergraduate level.
Aditi Sharma and Oruganti S. K. S. Sastri
Wiley
Aditi Sharma and O S K S Sastri
IOP Publishing
The Quantum Anharmonic Oscillator(QAO) has been solved numerically using matrix diagonalization technique. The interaction potential consisting of quadratic ( 12 kx 2 ) and quartic (λx 4 ) terms is embedded within an infinite square well potential of appropriate width, 'a' and its sine eigen functions are used as basis functions 'N' for the employed matrix method. The energy eigen values for the resultant hamiltonian are solved in a free open source software(FOSS), Gnumeric, a simple worksheet environment. The numerical parameters 'a' and 'N' are optimized to converge to the expected energies for the harmonic oscillator and those for the anharmonic oscillator from perturbation theory for small values of physical parameter, 'λ'. The pure quartic oscillator is studied for both small and large values of λ and validated with results obtained from other numerical techniques. The breakdown of perturbation approximation for large values of λ is also shown.
Aditi Sharma, Swapna Gora, Jithin Bhagavathi, and O. S. K. S Sastri
American Association of Physics Teachers (AAPT)
Single-particle energy states for a neutron and a proton are obtained by solving the time-independent Schrodinger equation for the mean-field Woods–Saxon potential along with the spin-orbit term. The wavefunctions are expanded as a linear combination of simple sine-wave basis states, which are eigenfunctions of the infinite spherical-well potential. The requisite algorithm based on matrix diagonalization is implemented in Free Open Source Software (FOSS) Scilab. Initial values for the simulation were taken from model parameters given in the book on Nuclear Structure by Bohr and Mottelson, which were then optimized to obtain the best convergence with the available experimental energy values of various nuclei with magic proton and neutron numbers. The level scheme, as well as the energy values for doubly magic nuclei 82 208Pb and 20 40Ca, which are obtained using our simulation, is presented in this paper. Finally, energy level diagrams for neutrons and protons with respect to mass number A were arrived at, based on those obtained for various magic nuclei. The evaluation method, which is based on the sine-wave basis, is akin to Fourier analysis. When done with the aid of FOSS Scilab, this technique becomes easily accessible to students at the under-graduate (UG) level and may be studied through small projects.
Jithin B.P. and O.S.K.S. Sastri
Elsevier BV
Abstract We present the development of a compact gamma spectrometer that is also capable of coincidence measurements, by connecting two units by a cable. The spectrometer consists of a CsI scintillator mated to a PIN photo-diode as the detector, a charge sensitive pre-amplifier, a shaping amplifier, and a 1024 bin Multi-Channel analyser. The assembly fits on a single PCB of dimensions 55mm x 105mm enclosed in a compact aluminum box. The USB powered plug and play design of the spectrometer makes it a highly portable surveying tool. While the pre-amplifier and shaping amplifier circuits are derived from schematics available in the open source domain, the MCA has been custom built. The data acquisition, analysis cum visualization software has been written in Python and is open sourced. A dual parameter list mode MCA capable of recording time stamped energy data from each of the individual gamma spectrometers including identification of coincident events was also developed for energy-gated coincidence measurements, and algorithms to visualize heat maps and surface plots of the obtained list mode data have been incorporated into the software. An FWHM of 81.2 keV was measured for the 1332 keV peak of 60 C o . Two point calibration using the 1173 keV and 1332 keV peaks was carried out. The calculated calibration factors are applied to the 661.7 keV peak of 137 C s . The measured peak is at 661.3 keV, corresponding to 0.1% accuracy. However, a full-range linearity testing with a commercial pulser showed a non-linearity with a maximum value of 0.6%. The dead time of the electronics was measured using a pulse generator, and was found to be less than 20 microseconds. Photopeak efficiency of the detector measured with the 661.7 keV peak of 137 C s was found to be around 29%. In a novel approach, the MCA firmware has been modified to demonstrate non-energy gated gamma-gamma coincidence with no additional circuitry. The coincidence filtering has been verified with a 1 μ C 22 N a source using a timing window of 400 ns.
Tapender Singh, O. S. K. S. Sastri, and Padmnabh Rai
AIP Publishing
The cylindrically gated (10,0) carbon nanotube field effect transistor having n-i-n device structure has been simulated by using the non-equilibrium Green function method and self-consistent calculations. The gate bias polarity and device temperature have been found to significantly influence the drain current obtained from energy-position resolved current spectrum under ballistic transport limit through simulations. The effect of temperature on drain current is seen to be more pronounced in thermionic emission as compared to band-to-band tunnelling.The cylindrically gated (10,0) carbon nanotube field effect transistor having n-i-n device structure has been simulated by using the non-equilibrium Green function method and self-consistent calculations. The gate bias polarity and device temperature have been found to significantly influence the drain current obtained from energy-position resolved current spectrum under ballistic transport limit through simulations. The effect of temperature on drain current is seen to be more pronounced in thermionic emission as compared to band-to-band tunnelling.
Neetu Sharma, Anita Padam, O. S. K. S Sastri, Shivani Mahajan, Rajesh Sharma, and Deepak Sharma
Medknow
Background: A high level of preoperative anxiety is common among patients undergoing medical and surgical procedures. Anxiety impacts of gastroenterological procedures on psychological and physiological responses are worth consideration. Aims and Objectives: To analyze the effect of listening to Vedic chants and Indian classical instrumental music on anxiety levels and on blood pressure (BP), heart rate (HR), and oxygen saturation in patients undergoing upper gastrointestinal (GI) endoscopy. Materials and Methods: A prospective, randomized controlled trial was done on 199 patients undergoing upper GI endoscopy. On arrival, their anxiety levels were assessed using state and trait scores and various physiological parameters such as HR, BP, and SpO2. Patients were randomly divided into three groups: Group I of 67 patients who were made to listen prerecorded Vedic chants for 10 min, Group II consisting of 66 patients who listened to Indian classical instrumental music for 10 min, and Group III of 66 controls who remained seated for same period in the same environment. Thereafter, their anxiety state scores and physiological parameters were reassessed. Results: A significant reduction in anxiety state scores was observed in the patients in Group I (from 40.4 ± 8.9 to 38.5 ± 10.7; P < 0.05) and Group II (from 41.8 ± 9.9 to 38.0 ± 8.6; P < 0.001) while Group III controls showed no significant change in the anxiety scores. A significant decrease in systolic BP (P < 0.001), diastolic BP (P < 0.05), and SpO2 (P < 0.05 was also observed in Group II. Conclusion: Listening to Vedic chants and Indian classical instrumental music has beneficial effects on alleviating anxiety levels induced by apprehension of invasive procedures and can be of therapeutic use.
Abhinav Nag, O. S. K. S. Sastri, and Jagdish Kumar
Author(s)
First principle study of electronic properties of pure and doped HgSe have been performed using all electron Full Potential Linearized Augmented Plane Wave (FP-LAPW) method using ELK code. The electronic exchange and co-relations are considered using Generalized Gradient Approach (GGA). Lattice parameter, Density of States (DOS) and Band structure calculations have been performed. The total energy curve (Energy vs Lattice parameter), DOS and band structure calculations are in good agreement with the experimental values and those obtained using other DFT codes. The doped material is studied within the Virtual Crystal Approximation (VCA) with doping levels of 10% to 25% of electrons (hole) per unit cell. Results predict zero band gap in undopedHgSe and bands meet at Fermi level near the symmetry point Г. For doped HgSe, we found that by electron (hole) doping, the point where conduction and valence bands meet can be shifted below (above) the fermi level.
Vandana Sharda, O S K S Sastri, Jyoti Bhardwaj, and Arbind K Jha
IOP Publishing
In this paper, we present a simple spreadsheet based simulation activity that can be performed by students at the undergraduate level. This simulation is implemented in free open source software (FOSS) LibreOffice Calc, which is available for both Windows and Linux platform. This activity aims at building the probability distribution for the possible macro-states of a system. This has been achieved by randomly sampling the configuration space consisting of all the possible microstates and determining the corresponding macrostate for each of the samples, which is akin to Monte-Carlo simulation. This simulation could act as a very useful tool in engaging students for learning the concepts of microstates, macrostates and steady state equilibrium, once the ideas have been introduced in the classroom. Further, the effect of the number of particles on the quality of steady state equilibrium achieved demonstrates the idea of thermodynamic limit.
Abhinav Nag, Jagdish Kumar, and O. S. K. S. Sastri
AIP Publishing LLC
The electronic structure of pure and doped two dimensional crystalline material graphene have been computed and analyzed. Density functional theory has been employed to perform calculations. The electronic exchange and correlations are considered using local density approximation (LDA). The doped material is studied within virtual crystal approximation (VCA) upto 0.15e excess as well as deficient charge per unit cell. Full Potential Linear Augmented Plane Wave basis as implemented in ELK code has been used to perform the calculations. To ensures the monolayer of graphene, distance after which energy is almost constant when interlayer seperation is varied, is taken as separating distance between the layers. The obtained density of states and band structure is analyzed. Results show that there is zero band gap in undoped graphene and conduction and valence band meets at fermi level at symmetry point K. PDOS graph shows that near the fermi level the main contribution is due to 2pz electrons. By using VCA, ca...
Tapender Singh, Jagdish Kumar, and O. S. K. S. Sastri
AIP Publishing LLC
We have studied electronic properties of double layered hexagonal structure of the Niobium Di-Sulphide (2H-NbS2) superconductor for various strains introduced along the c-axis using ab-initio calculations. The DFT calculations based on Full Potential Linearized Augmented Plane Wave (FPLAPW) method are performed using the ELK code. The total energy curve (E vs a), Density of States (DOS) and the Band structure calculations obtained in this work are matching with the earlier reports. The Pressure-Volume (P-V) diagram for 2H-NbS2 was obtained using the Equation of State(EOS) calculations, which provides the relationship between the pressure and strain applied along the c-axis. The band structures for various strains ranging from 0 percent to 10 percent along c-axis in steps of 2 percent are obtained. We note that there are increasing number of bands crossing over the Fermi energy level with increase in strain. Thus, we conclude that with increasing strain along c-axis, number of conduction bands crossing the EF increases, which gives rise to more conduction states and hence higher conductivity.
S. Sharma, O. Sastri, P. K. Ahluwalia, Boonchoat Paosawatyanyong, and Pornrat Wattanakasiwich
AIP
It is well known that most of the undergraduate study in India is conducted through the affiliate system in which affiliated colleges run the courses prescribed by a Board of Studies of the affiliating University in the form of a syllabus, which happens to be the only academic link between the students, teachers and the examiners. This document is limited only to defining the contents of the course without any hint about the instructional/learning objectives. Given these limitations of the existing course structure an attempt has been made to define the instructional/learning objectives for an undergraduate course of study in Solid State Physics prescribed in B. Sc. (Honours and Pass Course) in Physics of Himachal Pradesh University, India. It is not only the first step to enhance learning but to make teaching research based as well, as has been practiced in US and West as a foundation of Physics Education Research. The instructional objectives/learning objectives are written using Mager’s approach and cl...
P. C. Sood, O. S. K. S. Sastri, and R. K. Jain
Springer Science and Business Media LLC
The role of the band quantum number K in influencing the character of allowed $ \\beta$ transitions in heavy deformed nuclei is examined. The conditions for the occurrence of K -forbidden decays in this region are explored. Specific cases of “allowed” $ \\beta$ decays proceeding via $ \\Delta$K = 2 to $ \\Delta$K = 6 channels are presented to illustrate the phenomenon. The listed $ \\Delta$K = 2 transitions, which by themselves contribute over 10% of all the presently known allowed transitions for A$ \\geq$ 228 nuclei, are seen to have an average $\\ensuremath\\log ft \\geq 9.0$ , which is clearly outside the normal range for allowed transitions. It is concluded that, wherever the $ \\beta$ -connected states can be confidently labelled using the $\\ensuremath I^{\\pi}K$ quantum numbers, the K -forbiddenness is in general as significant as that involving the other two (spin and parity) quantum numbers.
P C Sood, O S K S Sastri, and Raj Kumar Jain
IOP Publishing
It is shown that, contrary to the normal feature witnessed all across the periodic table that even–even nuclei are more abundant/longer-lived than their odd-A neighbours, many odd-mass heavy nuclei are seen to be much longer-lived than their even–even neighbours. In the trans-plutonium domain of even-Z actinides, all the predominantly alpha-decaying odd-N nuclei are longer-lived than their even-mass neighbours. Similar behaviour is observed for heavy odd-Z actinides as well. A semi-empirical criterion is stated to determine the relative longevity of the odd-N and even-N nuclei. This feature is sought to be explained by examining the respective alpha decay rates. A detailed discussion of α-decays of the β-stable curium (Z = 96) isotopic chain is presented to illustrate this phenomenon. Correspondence with a similar occurrence in spontaneously fissioning nuclei is briefly pointed out.
O S K S Sastri, Raj Kumar Jain, and P C Sood
IOP Publishing
Intrinsic structures of nuclear levels, connected by highly hindered 'allowed' beta transitions in heavy nuclei, are examined to seek the physical basis of this unusual hindrance. A detailed analysis of the inter-relationships of relevant Nilsson wavefunctions reveals that the model-independent shape-dependent quantum number ? plays a decisive role in this context. An operative selection rule is suggested specifying that beta transitions involving ?? ? 2 are 'intrinsically forbidden', even though they may have been classified as 'allowed' by the usual spin-parity selection rules. Over 20 instances of such intrinsically forbidden 'allowed' transitions from the mass region A = 228?254 are presented to illustrate the applicability of this rule.
P. C. Sood, Raj Kumar Jain, and O. S. K. S. Sastri
American Physical Society (APS)
A detailed examination of all the available $\\mathrm{log}\\phantom{\\rule{0.3em}{0ex}}ft$ values for $\\ensuremath{\\beta}$ transitions in heavy $(Ag228)\\phantom{\\rule{0.3em}{0ex}}\\text{nuclei}$ reveals a very similar distribution of these values for the allowed and the first-forbidden decays in this region, in sharp contrast with the observed trends over the whole periodic table. Data for over 500 transitions belonging to both the allowed and forbidden categories are presented in the form of histograms. Physical basis for this unusual behavior is sought by examining the interrelationships between the Nilsson model asymptotic quantum numbers of the $\\ensuremath{\\beta}$ connected states. Explicit selection rules specific to this region, in terms of these quantum numbers, are proposed and their applicability is demonstrated by citing illustrative examples from the allowed decays of odd-$A$ actinides.
P C Sood, Raj Kumar Jain, and O S K S Sastri
IOP Publishing
Examination of the first-forbidden beta decays in very heavy (A ≥ 245) nuclei leads to the first identification of a four-quasiparticle (4qp) state in a nucleus of this 'frontier' region. The 1658.0 keV 2+ state in the N = 152 nucleus 250Cf, fed in β− decay from the 3.21 h 2− 250Bk parent and in -decay from the 2.22 h 1− 250Es parent, is assigned the 4qp configuration 2+(p1:7/2[633] ⊗ p2:3/2 [521] ⊗ n1:1/2[620] ⊗ n2:9/2 [734]) on the basis of the observed beta decay features. This assignment is supported by the observed gamma decays of this 250Cf state, excitation energies of the constituent one-, two- and three-quasiparticle bands in core nuclei and the experimental log ft values for the corresponding n:1/2 [620] p:3/2[521] and the n:9/2 [734] p:7/2[633] transformations in nuclei of this region. It is further shown that the same underlying single-particle transformation populates the 1qp, 2qp, 3qp and 4qp states with comparable log ft values in fast (log ft = 6.5 ± 0.6) first forbidden beta transitions in this 'frontier' region. An operative selection rule for such transitions is suggested.