Photodetachment study of He^- quartet resonances below the He(n=3) thresholds

The photodetachment cross section of He^- has been measured in the photon energy range 2.9 eV to 3.3 eV in order to investigate doubly excited states. Measurements were made channel specific by selectively detecting the residual He atoms left in a particular excited state following detachment. Three Feshbach resonances were found in the He(1s2p ^3P)+e^-(epsilon p) partial cross section: a ^4S resonance below the He(1s3s ^3S) threshold and two ^4P resonances below the He(1s3p ^3P) threshold. The measured energies of these doubly excited states are 2.959260(6) eV, 3.072(7) eV and 3.26487(4) eV. The corresponding widths are found to be 0.20(2) meV, 50(5) meV and 0.61(5) meV. The measured energies agree well with recent theoretical predictions for the 1s3s4s ^4S, 1s3p^2 ^4P and 1s3p4p ^4P states, respectively, but the widths deviate noticeably from calculations for 1s3p^2 ^4P and 1s3p4p ^4P states.Comment: 10 pages, 3 figures, LaTeX2e scrartcl, amsmath. Accepted by Journal of Physics B; minor changes after referee repor

Imaginary Phases in Two-Level Model with Spontaneous Decay

We study a two-level model coupled to the electromagnetic vacuum and to an external classic electric field with fixed frequency. The amplitude of the external electric field is supposed to vary very slow in time. Garrison and Wright [{\it Phys. Lett.} {\bf A128} (1988) 177] used the non-hermitian Hamiltonian approach to study the adiabatic limit of this model and obtained that the probability of this two-level system to be in its upper level has an imaginary geometric phase. Using the master equation for describing the time evolution of the two-level system we obtain that the imaginary phase due to dissipative effects is time dependent, in opposition to Garrison and Wright result. The present results show that the non-hermitian hamiltonian method should not be used to discuss the nature of the imaginary phases in open systems.Comment: 11 pages, new version, to appear in J. Phys.

Dissolving the Dichotomies Between Online and Campus-Based Teaching: a Collective Response to The Manifesto for Teaching Online (Bayne et al. 2020)

This article is a collective response to the 2020 iteration of The Manifesto for Teaching Online. Originally published in 2011 as 20 simple but provocative statements, the aim was, and continues to be, to critically challenge the normalization of education as techno-corporate enterprise and the failure to properly account for digital methods in teaching in Higher Education. The 2020 Manifesto continues in the same critically provocative fashion, and, as the response collected here demonstrates, its publication could not be timelier. Though the Manifesto was written before the Covid-19 pandemic, many of the responses gathered here inevitably reflect on the experiences of moving to digital, distant, online teaching under unprecedented conditions. As these contributions reveal, the challenges were many and varied, ranging from the positive, breakthrough opportunities that digital learning offered to many students, including the disabled, to the problematic, such as poor digital networks and access, and simple digital poverty. Regardless of the nature of each response, taken together, what they show is that The Manifesto for Teaching Online offers welcome insights into and practical advice on how to teach online, and creatively confront the supremacy of face-to-face teaching

Utility of certain nucleophilic aromatic substitution reactions for the assay of pregabalin in capsules

<p>Abstract</p> <p>Background</p> <p>Pregabalin (PG) is an anticonvulsant, analgesic and anxiolytic drug. A survey of the literature reveals that all the reported spectrophotometric methods are either don't offer high sensitivity, need tedious extraction procedures, recommend the measurement of absorbance in the near UV region where interference most probably occurs and/or use non specific reagent that don't offer suitable linearity range.</p> <p>Results</p> <p>Two new sensitive and simple spectrophotometric methods were developed for determination of pregabalin (PG) in capsules. Method (I) is based on the reaction of PG with 1,2-naphthoquinone-4-sulphonate sodium (NQS), yielding an orange colored product that was measured at 473 nm. Method (II) is based on the reaction of the drug with 2,4-dinitrofluorobenzene (DNFB) producing a yellow product measured at 373 nm. The different experimental parameters affecting the development and stability of the reaction product in methods (I) and (II) were carefully studied and optimized. The absorbance-concentration plots were rectilinear over the concentration ranges of 2-25 and 0.5-8 μg mL^-1for methods (I) and (II) respectively. The lower detection limits (LOD) were 0.15 and 0.13 μg mL^-1and the lower quantitation limits (LOQ) were 0.46 and 0.4 μg mL^-1for methods (I) and (II) respectively.</p> <p>Conclusion</p> <p>The developed methods were successfully applied to the analysis of the drug in its commercial capsules. The mean percentage recoveries of PG in its capsule were 99.11 ± 0.98 and 100.11 ± 1.2 (n = 3). Statistical analysis of the results revealed good agreement with those given by the comparison method. Proposals of the reaction pathways were postulated.</p

Dynamic dipole polarizabilities of the ground and excited states of confined hydrogen atom computed by means of a mapped Fourier grid method

Accurate theoretical estimates of static and dynamic dipole polarizabilities are reported for the ground and excited states of hydrogen atom confined at the center of a spherical "box" with impenetrable walls using a novel theoretical algorithm that combines the variational-perturbation approach with an appropriately adapted mapped Fourier grid method and uniformly maintains the numerical accuracy. A variation of computed polarizabilities is observed as a function of the number of grid points. However, rapid convergence to their correct values, even far into the anomalous dispersion region, is achieved by an extrapolation procedure to the limit of an infinitely large number of grid points using a small number of the lowest-order Padé approximants. It is shown that dipole polarizabilities strongly depend upon the electronic state and the radius of confinement. In particular, the static polarizability of 2s state changes sign under strong confinement

Waterfall, Cradle plateau, Cradle Mountain-Lake St Clair National Park, Tasmania, 1977 [transparency] /

Title from acquisitions documentation, see file NLA06/1618.; Part of the Peter Dombrovskis archive of photographs.; Dombrovskis number: 950.; Also available online at: http://nla.gov.au/nla.pic-vn5978541

Quantum-mechanical versus semiclassical calculations of dc-field-induced tunneling rates for helium for field strengths in the range 0.067-1.0 a.u

Journal URL: http://pra.aps.org