Ananda Shastri

Followers

Following

Co-author

Public Views

Nilli Lavie

University College London

SAURABH GUPTA

NIT RAIPUR

Talis Bachmann

University of Tartu

Valentino Gasparini

Universidad Carlos III de Madrid

laila craighero

Università degli Studi di Ferrara

Kiril Marinow

The University of Lodz

Milan Kumar Lal

INDIAN AGRICULTURAL RESEARCH INSTITUTE, NEW DELHI, INDIA

James Antaki

Cornell University

Digital library Bohemia

Eric Sigmund

New York University

Interests

Uploads

Papers by Ananda Shastri

23Na nuclear magnetic resonance study of yNa2S + (1 − y)[xSiS2 + (1 − x)PS5/2] glassy solid electrolytes

Solid State Ionics

Abstract 23 Na NMR spin lattice relaxation times, T 1 , and central linewidths were obtained for ... more Abstract 23 Na NMR spin lattice relaxation times, T 1 , and central linewidths were obtained for yNa 2 S + (1 − y)[xSiS 2  + (1 − x)PS 5/2 ] glassy solid electrolytes for two series of glasses, y = 0.5 and 0.67, and x = 0.1, 0.3, 0.5, 0.7, and 0.9. No pronounced mixed glass former effect in the activation energy was observed within experimental uncertainty for either series of glasses. Energy barriers to sodium motion were calculated using the Anderson-Stuart model for the y = 0.67 sample, and the results suggested that the energy barriers as a function of composition are strongly influenced by the dielectric constant of these glasses. DC Na + ion conductivity values calculated using NMR-derived correlation times, an available Na + ion site coordination number in the range z = 3–4, and an energy cutoff determined from the critical percolation threshold, were in agreement with the increasing trend in the experimental values for the y = 0.67 glasses. Using the same model, the conductivity values were calculated for the y = 0.50 glasses, which have as yet to be measured, and these revealed a decreasing conductivity as x increased. Sodium NMR second moment studies showed that the cation spatial arrangement followed a homogeneous distribution for y = 0.50 and 0.67 samples over most of the composition range, but deviated significantly away from this above a sodium concentration of 1.85 × 10 28  m -3 , suggesting a tendency for sodium to cluster under these conditions.

Are There Really No Evolutionarily Stable Strategies in the Iterated Prisoner's Dilemma?

Journal of Theoretical Biology, Feb 1, 2002

The evolutionary form of the iterated prisoner&#39;s dilemma (IPD) is a repeated game where p... more The evolutionary form of the iterated prisoner&#39;s dilemma (IPD) is a repeated game where players strategically choose whether to cooperate with or exploit opponents and reproduce in proportion to game success. It has been widely used to study the evolution of cooperation among selfish agents. In the past 15 years, researchers proved over a series of papers that there is no evolutionarily stable strategy (ESS) in the IPD when players maintain long-term relationships. This makes it difficult to make predictions about what strategies can actually persist as prevalent in a population over time. Here, we show that this no ESS finding may be a mathematical technicality, relying on implausible players who are &quot;too perfect&quot; in that their probability of cooperating on any move is arbitrarily close to either 0 or 1. Specifically, in the no ESS proof, all strategies were allowed, meaning that after a strategy X experiences any history H, X cooperates with an unrestricted probability p (X, H) where 0&lt; or =p (X, H)&lt; or =1. Here, we restrict strategies to the set S in which X is a member of S [corrected] if after any H, X cooperates with a restricted probability p (X, H) where e&lt; or =p (X, H)&lt; or =1-e and 0&lt;e&lt;1/2. The variables e and 1-e may be thought of as the biological limits to how perfect (pure) a strategy can be. In S, we first prove that an ESS must be a Nash equilibrium and boundary strategy of S where a boundary strategy has allowable probabilities of cooperating of e or 1-e after any history. We then prove that X is an ESS in S if and only if X is a Nash equilibrium in the set consisting of only S&#39;s boundary strategies. Thus, in searching for ESSs in S, we only need to consider what happens when boundary strategies interact with one another. This greatly simplifies the search for ESSs. Using these results, we finally show that when e is sufficiently small, exactly three one-move memory ESSs exist in S: [1] Pavlov-e which generally cooperates (i.e. cooperates with maximum probability 1-e) after both players either simultaneously cooperated or simultaneously defected; otherwise, Pavlov-e generally defects (i.e. cooperates with minimum probability e). [2] Grudge-e which generally cooperates after both players simultaneously cooperated; otherwise, Grudge-e generally defects. [3] ALLD-e which generally defects after all histories.

1H NMR study of the hydrogen dynamics in the (NaS)xGe(OH)4−x·yH2O ceramic proton conductors

Solid State Ionics, 2012

H NMR was performed on the ceramic proton conductor (NaS) x Ge(OH) 4 −x ·yH 2 O for x = 2, 3 and ... more H NMR was performed on the ceramic proton conductor (NaS) x Ge(OH) 4 −x ·yH 2 O for x = 2, 3 and y~1-4 over the temperature range of − 100°C to 400°C. NMR spectra, nuclear spin-lattice relaxation rates (R 1 ), spin-spin relaxation rates (R 2 ), and rotating frame relaxation rates (R 1ρ ) were obtained for both hydrated and dehydrated samples. It was found that the low temperature NMR spectra were consistent with simulated H 2 O lineshapes, and the presence of H 3 O + at low temperature was not detected within the experimental uncertainty. Short-and long-range hydrogen motion occurred together, a signature of Grotthuss conduction mechanisms. The long range motion was a combination of H + and H 2 O diffusion, with H 2 O motion limiting H + dynamics as the onset temperature was approached.

Download

Systems and Methods for Detecting Deception by Measuring Brain Activity

by Mark George and Ananda Shastri

Invest. Radiol

Proton spin-lattice relaxation and spin dynamics in magnetic molecular clusters

We present data of proton spin-lattice relaxation rate (NSLR) in the temperature range 4-300K and... more We present data of proton spin-lattice relaxation rate (NSLR) in the temperature range 4-300K and as a function of external magnetic field from 0.1 to 9.1 Tesla in magnetic molecular clusters : (i) almost coplanar rings of respectively six(Fe6) and ten(Fe10) iron(III) ions with spin S=5/2 ; (ii) the dodecanuclear manganese cluster Mn12; (iii) the core of biological molecule ferritin

$Research paper thumbnail of ^{1} H NMR study of hydrogen in quasicrystalline Ti_ {0.45-x} V_ {x} Zr_ {0.38} Ni_ {0.17}$

^{1} H NMR study of hydrogen in quasicrystalline Ti_ {0.45-x} V_ {x} Zr_ {0.38} Ni_ {0.17}

Physical review. B, Condensed matter

1H nuclear-magnetic-resonance (NMR) spectra and spin-lattice relaxation rates (R1) were studied i... more 1H nuclear-magnetic-resonance (NMR) spectra and spin-lattice relaxation rates (R1) were studied in the hydrogenated Ti0.45-xVxZr0.38Ni0.17 quasicrystal for x=0.00, 0.02, and a hydrogen-to-metal-atom ratio (H/M)=1.88. NMR measurements were made from 4 to 550 K at resonance frequencies of 8, 18, 55, and 200 MHz. Theoretical 1H second-moment values (M2) were calculated based on Bergman and Mackay cluster models and compared with experimental M2 values. The R1 data reveal a distribution of activation energies for the 1H diffusion through the quasilattice; the distribution is insensitive to the vanadium concentration, x. Low-temperature R1 data reveal an additional low-temperature relaxation mechanism that is not yet well understood.

Interleaving transcranial magnetic stimulation with steady state magnetic resonance imaging of the brain

NeuroImage

Shastri A, George MS, Bohning DE. Performance of a system for interleaving transcranial magnetic stimulation with steady-state magnetic resonance imaging. Electroencephalogr Clin Neurophysiol Suppl 51: 55-64

Electroencephalography and clinical neurophysiology. Supplement

Proton NMR and μSR in Mn 12 O 12 acetate: A mesoscopic magnetic molecular cluster

Physical Review B, 1998

The spin dynamics of Mn spins in the dodecanuclear manganese cluster of formula [Mn12O12(CH3COO)1... more The spin dynamics of Mn spins in the dodecanuclear manganese cluster of formula [Mn12O12(CH3COO)16(H2O)4].2CH3-COOH.4H2O(Mn12) has been investigated by 1H NMR and muon spin-lattice relaxation rate 1/T1 as a function of temperature (10-400 K) and external magnetic field (0-9.4 T). At room temperature, the proton 1/T1 depends on the measuring frequency. The results can be interpreted in terms of a slow

NMR and NQR study of the electronic and structural properties of Al-Cu-Fe and Al-Cu-Ru quasicrystals

Physical review. B, Condensed matter, 1994

2 7~1 and 6 3 , 6 5~~ NMR measurements are reported for powder samples of stable Al-Cu-Fe and Al-... more 2 7~1 and 6 3 , 6 5~~ NMR measurements are reported for powder samples of stable Al-Cu-Fe and Al-Cu-Ru icosahedral quasicrystals and their crystalline approximants, and for an Al-Pd-Mn singlegrain quasicrystal. Furthermore, ' '~1 NQR spectra at 4.2 K have been observed in the Al-Cu-Fe and Al-Cu-Ru samples. From the quadrupole-perturbed NMR spectra at different magnetic fields, and from the zero-field NQR spectra, a wide distribution of local electric-field gradient (EFG) tensor components and principal-axis-system orientations was found at the Al site. A model EFG calculation based on a 1/1 Al-Cu-Fe approximant was successful in explaining the observed NQR spectra. The average local gradient is largely determined by the p-electron wave function at the A1 site, while the width of the distribution is due to the lattice contribution to the EFG. Comparison of "CU NMR with 27Al NMR shows the EFG distribution at the two sites is similar, but the electronic contribution to the EFG is considerably smaller at the Cu site, in agreement with a more s-type wave function of the conduction electrons. The overall spread of EFG values is well reproduced by the calculation based on the approximant. However, the experimental spectra indicate a much larger number of nonequivalent sites when compared with the simulated NQR spectra based on the 1/1 approximant. The short-range, local chemical order is well represented by the approximant, but differences in coordination must be included at intermediate range in the quasicrystal. Measurements of 27Al Knight shift, magnetic susceptibility, and nuclear spin-lattice relaxation time as a function of temperature yield results which indicate a reduction of the density of states at the Fermi level by a factor of 7 or 8 from the value in Al metal, consistent with the notion of a pseudogap for these quasicrystals. No differences in the measured parameters were detected as a function of composition of the quasicrystatline alloys, arguing against a fine structure in the density of states at the Fermi level.

Download

Distribution of nonequivalent aluminum sites revealed in Al-Cu-Ru and Al-Cu-Fe quasicrystals by 27Al NQR

Physical review. B, Condensed matter, 1994

The distribution of nonequivalent aluminum sites was studied in Al-Cu-Fe and Al-Cu-Ru stable icos... more The distribution of nonequivalent aluminum sites was studied in Al-Cu-Fe and Al-Cu-Ru stable icosahedral quasicrystalline phases using 27Al NQR spectra taken at 4.2 K. The observed spectra-which give directly the distribution of nonequivalent aluminum sites-were broad, asymmetric, and structureless. A simple electric-field-gradient model calculation accounted for the spectral width in terms of a wide distribution of local atomic environments, and an estimate for the lower limit on the number of nonequivalent aluminum sites was found.

Erratum:1H NMR study of hydrogen in quasicrystalline Ti0.45-xVxZr0.38Ni0.17 [Phys. Rev. B 57, 5148 (1998)]

Physical Review B, 1999

NMR and Nqr Study of the Thermodynamically Stable Quasicrystals

^{27}Al and ^{63,65}Cu NMR measurements are reported for powder samples of stable AlCuFe and AlCu... more ^{27}Al and ^{63,65}Cu NMR measurements are reported for powder samples of stable AlCuFe and AlCuRu icosahedral quasicrystals and their crystalline approximants, and for a AlPdMn single grain quasicrystal. Furthermore, ^{27}Al NQR spectra at 4.2 K have been observed in the AlCuFe and AlCuRu samples. From the quadrupole perturbed NMR spectra at different magnetic fields, and from the zero field NQR spectra, a wide distribution of local electric field gradient (EFG) tensor components and principal axis system orientations was found at the Al site. A model EFG calculation based on a 1/1 AlCuFe approximant was successful in explaining the observed NQR spectra. It is concluded that the average local gradient is largely determined by the p-electron wave function at the Al site, while the width of the distribution is due to the lattice contribution to the EFG. Comparison of ^{63}Cu NMR with ^{27}Al NMR shows that the EFG distribution at the two sites is similar, but that the electronic con...

Download

Studying the Effects of Nuclear Weapons Using a Slide-Rule Computer

The Physics Teacher, 2007

This paper describes the construction of a slide-rule computer that allows one to quickly determi... more This paper describes the construction of a slide-rule computer that allows one to quickly determine magnitudes of several effects that result from the detonation of a nuclear device. Suggestions for exercises are also included that allow high school and college-level physics students to explore scenarios involving these effects. It is hoped that discussing the effects objectively will inform students and allow them to make sound judgments on issues concerning nuclear weapons. The material in this paper was presented to high school students in a day-long activity session hosted by the author's university.

Magnetic susceptibility and spin dynamics of a polyoxovanadate cluster: A proton NMR study of a model spin tetramer

Physical Review B, 2004

We report susceptibility and nuclear magnetic resonance (NMR) measurements in a polyoxovanadate c... more We report susceptibility and nuclear magnetic resonance (NMR) measurements in a polyoxovanadate compound with formula (NHEt)3[VIV8VV4As8O40(H2O)]sH2O≡{V12}. The magnetic properties can be described by considering only the central square of localized V4+ ions and treated by an isotropic Heisenberg Hamiltonian of four intrinsic spins 1/2 coupled by nearest-neighbor antiferromagnetic interaction with J˜17.6 K. In this simplified description the ground state is nonmagnetic with ST=0. The 1H NMR linewidth (full width at half maximum) data depend on both the magnetic field and temperature, and are explained by the dipolar interaction between proton nuclei and V4+ ion spins. The behavior of the nuclear spin-lattice relaxation rate T-11 in the temperature range (4.2 300 K) is similar to that of chiT vs T and it does not show any peak at low temperatures contrary to previous observations in antiferromagnetic rings with larger intrinsic spins. The results are explained by using the general features of the Moriya formula and by introducing a single T-independent broadening parameter for the electronic spin system. From the exponential T dependence of T-11 at low T (2.5 K<T<4.2 K) we have obtained a field dependent gap following the linear relation DeltaNMR=Delta0-gmuBH, with the gap Delta0˜17.6 K in agreement with the susceptibility data. Below 2.5 K the proton T-11 deviates from the exponential decrease indicating the presence of a small, almost temperature independent, but strongly field dependent, nuclear relaxation contribution, which we will investigate in detail in the near future.

^1H NMR study of the quasicrystalline hydride Ti_0.45-xV_xZr_0.38Ni_0.17Hy

^1H nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation rates (R_1) were measure... more ^1H nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation rates (R_1) were measured in the Ti_0.45-xV_xZr_0.38Ni_0.17Hy system, where x = 0, 0.02 and y = 1.88, from 150 - 550 K at resonance frequencies of 8 and 18 MHz. Analysis of the NMR powder spectrum using a structural model based on the Bergman cluster yielded an estimate of the quasilattice parameter in good agreement with the value obtained by x-ray diffraction. Unlike what is typically found in crystalline hydrides, the behavior of the R1 data reveals a distribution of activation energies for hydrogen diffusion through the quasilattice. The mean activation energy and the width of the distribution are estimated. R1 data taken between 4 and 90 K at 200 MHz reveals non-Korringa like behavior which may be explained by hydrogen tunneling between asymmetric potential wells.

The train length dependence of BOLD-fMRI response to 1 Hz transcranial magnetic stimulation (TMS) compares favorably with a finite recovery hemodynamic model for short train lengths

by Mark George and Ananda Shastri

NeuroImage, 2000

Download

The TMS motor threshold depends on the distance from coil to underlying cortex: A replication in healthy adults

by Mark George and Ananda Shastri

Neuroimage, 2000

Download

Are There Really No Evolutionarily Stable Strategies in the Iterated Prisoner's Dilemma?

Journal of Theoretical Biology, 2002

23Na nuclear magnetic resonance study of yNa2S + (1 − y)[xSiS2 + (1 − x)PS5/2] glassy solid electrolytes

Solid State Ionics

Are There Really No Evolutionarily Stable Strategies in the Iterated Prisoner's Dilemma?

Journal of Theoretical Biology, Feb 1, 2002

1H NMR study of the hydrogen dynamics in the (NaS)xGe(OH)4−x·yH2O ceramic proton conductors

Solid State Ionics, 2012

Download

Systems and Methods for Detecting Deception by Measuring Brain Activity

by Mark George and Ananda Shastri

Invest. Radiol

Proton spin-lattice relaxation and spin dynamics in magnetic molecular clusters

$Research paper thumbnail of ^{1} H NMR study of hydrogen in quasicrystalline Ti_ {0.45-x} V_ {x} Zr_ {0.38} Ni_ {0.17}$

^{1} H NMR study of hydrogen in quasicrystalline Ti_ {0.45-x} V_ {x} Zr_ {0.38} Ni_ {0.17}

Physical review. B, Condensed matter

Interleaving transcranial magnetic stimulation with steady state magnetic resonance imaging of the brain

NeuroImage

Electroencephalography and clinical neurophysiology. Supplement

Proton NMR and μSR in Mn 12 O 12 acetate: A mesoscopic magnetic molecular cluster

Physical Review B, 1998

NMR and NQR study of the electronic and structural properties of Al-Cu-Fe and Al-Cu-Ru quasicrystals

Physical review. B, Condensed matter, 1994

Download

Distribution of nonequivalent aluminum sites revealed in Al-Cu-Ru and Al-Cu-Fe quasicrystals by 27Al NQR

Physical review. B, Condensed matter, 1994

Erratum:1H NMR study of hydrogen in quasicrystalline Ti0.45-xVxZr0.38Ni0.17 [Phys. Rev. B 57, 5148 (1998)]

Physical Review B, 1999

NMR and Nqr Study of the Thermodynamically Stable Quasicrystals

Download

Studying the Effects of Nuclear Weapons Using a Slide-Rule Computer

The Physics Teacher, 2007

Magnetic susceptibility and spin dynamics of a polyoxovanadate cluster: A proton NMR study of a model spin tetramer

Physical Review B, 2004

^1H NMR study of the quasicrystalline hydride Ti_0.45-xV_xZr_0.38Ni_0.17Hy

The train length dependence of BOLD-fMRI response to 1 Hz transcranial magnetic stimulation (TMS) compares favorably with a finite recovery hemodynamic model for short train lengths

by Mark George and Ananda Shastri

NeuroImage, 2000

Download

The TMS motor threshold depends on the distance from coil to underlying cortex: A replication in healthy adults

by Mark George and Ananda Shastri

Neuroimage, 2000

Download

Are There Really No Evolutionarily Stable Strategies in the Iterated Prisoner's Dilemma?

Journal of Theoretical Biology, 2002

Ananda Shastri

Related Authors

Uploads

Papers by Ananda Shastri

Log In