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Search Results: 1 - 10 of 201766 matches for " Datta P "
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Book Review
Datta P K
Indian Journal of Dermatology , 2003,
Abstract:
The Theory of Uncertainty for Derived Results: Properties of Equations Representing Physicochemical Evaluation Systems
B. P. Datta
Physics , 2007,
Abstract: Any physiochemical variable (Ym) is always determined from certain measured variables {Xi}. The uncertainties {ui} of measuring {Xi} are generally a priori ensured as acceptable. However, there is no general method for assessing uncertainty (em) in the desired Ym, i.e. irrespective of whatever might be its system-specific-relationship (SSR) with {Xi}, and/ or be the causes of {ui}. We here therefore study the behaviors of different typical SSRs. The study shows that any SSR is characterized by a set of parameters, which govern em. That is, em is shown to represent a net SSR-driven (purely systematic) change in ui(s); and it cannot vary for whether ui(s) be caused by either or both statistical and systematic reasons. We thus present the general relationship of em with ui(s), and discuss how it can be used to predict a priori the requirements for an evaluated Ym to be representative, and hence to set the guidelines for designing experiments and also really appropriate evaluation models. Say: Y_m= f_m ({X_i}_(i=1)^N), then, although: e_m= g_m ({u_i}_(i=1)^N), "N" is not a key factor in governing em. However, simply for varying "fm", the em is demonstrated to be either equaling a ui, or >ui, or even
Geometric Phase in Vacuum Instability:APPLICATIONS in Quantum Cosmology
D. P. Datta
Physics , 1993, DOI: 10.1103/PhysRevD.48.5746
Abstract: Three different methods viz. i) a perturbative analysis of the Schr\"odinger equation ii) abstract differential geometric method and iii) a semiclassical reduction of the Wheeler-Dewitt equation, relating Pancharatnam phase to vacuum instability are discussed. An improved semiclassical reduction is also shown to yield the correct zeroth order semicalssical Einstein equations with backreaction. This constitutes an extension of our earlier discussions on the topic
Study of variations as desired-relative (DELTA), rather than absolute, differences: falsification of the purpose of achieving source-representative and closely comparable lab-results
B. P. Datta
Physics , 2014,
Abstract: Recently (arXiv:1101.0973), it has been pointed out by us that the possible variation in any source (S) specific elemental isotopic (viz. 2H/1H) abundance ratio SR can more accurately be assessed by its absolute estimate Sr [viz. as (Sr - DR), with D as a standard-source] than by either corresponding measured-relative (S/W-DELTA) estimate ([Sr/Wr] - 1) or DELTA-scale-converted-relative (S/D-DELTA) estimate ([Sr/DR] - 1). Here, we present the fundamentals behind scale-conversion, thereby enabling to understand why at all Sr should be the source- and/ or variation-characterizing key, i.e. why different lab-specific results should be more closely comparable as absolute estimates (SrLab1, SrLab2) than as desired-relative (S/D-DELTALab1, S/D-DELTALab2) estimates. Further, the study clarifies that: (i) the DELTA-scale-conversion (S/W-DELTA into S/D-DELTA, even with the aid of calibrated auxiliary-reference-standard(s) Ai(s)) cannot make the estimates (as S/D-DELTA, and thus Sr) free of the measurement-reference W; (ii) the employing of (increasing number of) Ai-standards should cause the estimates to be rather (increasingly) inaccurate and, additionally, Ai(s)-specific; and (iii) the S/D-DELTA-estimate may, specifically if S happens to be very close to D in isotopic composition (IC), even misrepresent S; but the corresponding Sr should be very accurate. However, for S and W to be increasingly closer in IC, the S/D-DELTA-estimate and also Sr are shown to be increasingly accurate, irrespective of whether the S/W-DELTA-measurement accuracy could thus be improved or not. Clearly, improvement in measurement-accuracy should ensure additional accuracy in results.
Transmission and reflection in a perfectly amplifying and absorbing medium
P. K. Datta
Physics , 1998, DOI: 10.1103/PhysRevB.59.10980
Abstract: We study transmission and reflection properties of a perfectly amplifying as well as absorbing medium analytically by using the tight binding equation. Different expressions for transmittance and reflectance are obtained for even and odd values of the sample length which is the origin of their oscillatory behavior. In a weak amplifying medium, a cross-over length scale exists below which transmittance and reflectance increase exponentially and above which transmittance decays exponentially while the reflectance gets saturated. Depending on amplification transmittance and reflectance show singular behavior at the cross-over length. In a weak absorbing medium we do not find any cross-over length scale. The transmission coefficient behaves similar to that in an amplifying medium in the asymptotic limit. In a strong amplifying/absorbing medium, the transmission coefficient decays exponentially in the large length limit. In both weak as well as strong absorbing media the logarithm of the reflection coefficient shows the same behavior as obtained in an amplifying medium but with opposite sign.
Uncertainty Factors for Stage-Specific and Cumulative Results of Indirect Measurements
B. P. Datta
Physics , 2009,
Abstract: Evaluation of a variable Yd from certain measured variable(s) Xi(s), by making use of their system-specific-relationship (SSR), is generally referred as the indirect measurement. Naturally the SSR may stand for a simple data-translation process in a given case, but a set of equations, or even a cascade of different such processes, in some other case. Further, though the measurements are a priori ensured to be accurate, there is no definite method for examining whether the result obtained at the end of an SSR, specifically a cascade of SSRs, is really representative as the measured Xi-values. Of Course, it was recently shown that the uncertainty (ed) in the estimate (yd) of a specified Yd is given by a specified linear combination of corresponding measurement-uncertainties (uis). Here, further insight into this principle is provided by its application to the cases represented by cascade-SSRs. It is exemplified how the different stage-wise uncertainties (Ied, IIed, ... ed), that is to say the requirements for the evaluation to be successful, could even a priori be predicted. The theoretical tools (SSRs) have resemblance with the real world measuring devices (MDs), and hence are referred as also the data transformation scales (DTSs). However, non-uniform behavior appears to be the feature of the DTSs rather than of the MDs.
Prospects of ratio and differential (δ) ratio based measurement-models: a case study for IRMS evaluation
B. P. Datta
Physics , 2015,
Abstract: The suitability of a mathematical-model Y = f({Xi}) in serving a purpose whatsoever (should be preset by the function f specific input-to-output variation-rates, i.e.) can be judged beforehand. We thus evaluate here the two apparently similar models: YA = fA(SRi,WRi) = (SRi/WRi) and: YD = fd(SRi,WRi) = ([SRi,WRi] - 1) = (YA - 1), with SRi and WRi representing certain measurable-variables (e.g. the sample S and the working-lab-reference W specific ith-isotopic-abundance-ratios, respectively, for a case as the isotope ratio mass spectrometry (IRMS)). The idea is to ascertain whether fD should represent a better model than fA, specifically, for the well-known IRMS evaluation. The study clarifies that fA and fD should really represent different model-families. For example, the possible variation, eA, of an absolute estimate as the yA (and/ or the risk of running a machine on the basis of the measurement-model fA) should be dictated by the possible Ri-measurement-variations (u_S and u_W) only: eA = (u_S + u_W); i.e., at worst: eA = 2ui. However, the variation, eD, of the corresponding differential (i.e. YD) estimate yd should largely be decided by SRi and WRi values: ed = 2(|m_i |x u_i) = (|m_i | x eA); with: mi = (SRi/[SRi - WRi]). Thus, any IRMS measurement (i.e. for which |SRi - WRi| is nearly zero is a requirement) should signify that |mi| tends to infinity. Clearly, yD should be less accurate than yA, and/ or even turn out to be highly erroneous (eD tends to infinity). Nevertheless, the evaluation as the absolute yA, and hence as the sample isotopic ratio Sri, is shown to be equivalent to our previously reported finding that the conversion of a D-estimate (here, yD) into Sri should help to improve the achievable output-accuracy and -comparability.
Pros and cons of the technique of processing IRMS data as desired-delta values: uncertainty and comparability in results, a case study for determining carbon and oxygen isotopic abundance ratios as CO_2^+
B. P. Datta
Physics , 2011,
Abstract: In isotope ratio mass spectrometry (IRMS), any sample (S) measurement is performed as a relative-difference ((S/W)di) from a working-lab-reference (W), but the result is evaluated relative to a recommended-standard (D): (S/D)di. It is thus assumed that different source specific results ((S1/D)di, (S2/D)di) would represent their sources (S1, S2), and be accurately intercomparable. However, the assumption has never been checked. In this manuscript we carry out this task by considering a system as CO2+-IRMS. We present a model for a priori predicting output-uncertainty. Our study shows that scale-conversion, even with the aid of auxiliary-reference-standard(s) Ai(s), cannot make (S/D)di free from W; and the ((S/W)di,(A1/W)di,(A2/W)di) To (S/D)di conversion-formula normally used in the literature is invalid. Besides, the latter-relation has been worked out, which leads to e.g., fJ([(S/W)dJCO2pmp%],[(A1/W)dJCO2pmp%],[(A2/W)dJCO2pmp%]) = ((S/D)dJCO2pm4.5p%); whereas FJ([(S/W)dJCO2pmp%],[(A1/W)dJCO2pmp%]) = ((S/D)dJCO2pm1.2p%). That is, contrary to the general belief (Nature 1978, 271, 534), the scale-conversion by employing one than two Ai-standards should ensure (S/D)di to be more accurate. However, a more valuable finding is that the transformation of any d-estimate into its absolute value helps improve accuracy, or any reverse-process enhances uncertainty. Thus, equally accurate though the absolute-estimates of isotopic-CO2 and constituent-elemental-isotopic abundance-ratios could be, in contradistinction any differential-estimate is shown to be less accurate. Further, for S and D to be similar, any absolute estimate is shown to turn out nearly absolute accurate but any (S/D)d value as really absurd. That is, estimated source specific absolute values, rather than corresponding differential results, should really represent their sources, and/ or be closely intercomparable.
Josephson Effect in Unconventional Superconductors
Supriyo Datta,Manoj P. Samanta
Physics , 1996,
Abstract: In this letter we present a simple relation, that allows one to predict the Josephson current between two unconventional superconductors with arbitrary band-structure and pairing symmetry. We illustrate this relation with examples of s-wave and d-wave junctions and show a detailed numerical comparison with the phenomenological Sigrist and Rice relation commonly used to interpret tunneling experiments between d-wave superconductors. Our relation automatically accounts for `mid-gap states' that occur in d-wave superconductors and clearly shows how these states lead to a temperature-sensitive contribution to the Josephson current for certain orientations of the junction. This relation should be useful in exploring the effects of disordered junctions, multiple atomic orbitals and complicated order parameters.
Time evolution of models described by one-dimensional discrete nonlinear Schr?dinger equation
P. K. Datta,K. Kundu
Physics , 1996, DOI: 10.1103/PhysRevB.53.14929
Abstract: The dynamics of models described by a one-dimensional discrete nonlinear Schr\"odinger equation is studied. The nonlinearity in these models appears due to the coupling of the electronic motion to optical oscillators which are treated in adiabatic approximation. First, various sizes of nonlinear cluster embedded in an infinite linear chain are considered. The initial excitation is applied either at the end-site or at the middle-site of the cluster. In both the cases we obtain two kinds of transition: (i) a cluster-trapping transition and (ii) a self-trapping transition. The dynamics of the quasiparticle with the end-site initial excitation are found to exhibit, (i) a sharp self-trapping transition, (ii) an amplitude-transition in the site-probabilities and (iii) propagating soliton-like waves in large clusters. Ballistic propagation is observed in random nonlinear systems. The effect of nonlinear impurities on the superdiffusive behavior of random-dimer model is also studied.
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