142,887 research outputs found
Wavelength tunable 10-GHz 3-ps pulse source using a dispersion decreasing fiber-based nonlinear optical loop mirror
Get PDFWe experimentally demonstrate the use of a dispersion decreasing fiber (DDF)-based nonlinear optical loop mirror (NOLM) for the generation of wavelength tunable soliton-like pulses at a repetition rate of 10 GHz. We compress ~12 ps Gaussian pulses from an electro-absorption modulator (EAM) (followed by 125 m of DCF for preliminary linear dispersion compensation) into 3 ps pedestal-free pulses using both high-order soliton compression and nonlinear switching effects within an 8.5 km DDF-based loop mirror. The output pulses from the DDF-based NOLM show considerable pedestal reduction compared to those obtained by directly compressing the EAM seed pulses via a single passage through the DDF. Wavelength tuning of the compressed pulses over a ~15 nm bandwidth (from 1541 to 1556 nm) is demonstrated without a significant increase in pulse duration or degradation in pulse quality
Aggregation behavior of homo-PS/PS-b-P2VP blends at the air/water interface
No full textThe mixed Langmuir monolayers and Langmuir-Blodgett (LB) films of horno-polystyrene (h-PS) and the diblock copolymer polystyrene- block-poly(2 -vinylpyridine) (PS-b-P2VP) have been characterized by the Langmuir monolayer technique and tapping mode atomic force microscony (AFM) resnectivelv. When the content of Y h-PS is below 80 wt.-%, the mixed LB films of h-PS/PS-b-P2VP mainly exhibit isolated circular nanoaggregates. With a further increase of the h-PS content (80-95%), however, highly uniform and stable necklace -network structures are observed in the mixed LB films.X1112sciescopu
Comparing molecular photofragmentation dynamics in the gas and liquid phases
No full textThis article explores the extent to which insights gleaned from detailed studies of molecular photodissociations in the gas phase (i.e. under isolated molecule conditions) can inform our understanding of the corresponding photofragmentation processes in solution. Systems selected for comparison include a thiophenol (p-methylthiophenol), a thioanisole (p-methylthioanisole) and phenol, in vacuum and in cyclohexane solution. UV excitation in the gas phase results in RX-Y (X = O, S; Y = H, CH3) bond fission in all cases, but over timescales that vary by similar to 4 orders of magnitude - all of which behaviours can be rationalised on the basis of the relevant bound and dissociative excited state potential energy surfaces (PESs) accessed by UV photoexcitation, and of the conical intersections that facilitate radiationless transfer between these PESs. Time-resolved UV pump-broadband UV/visible probe and/or UV pump-broadband IR probe studies of the corresponding systems in cyclohexane solution reveal additional processes that are unique to the condensed phase. Thus, for example, the data clearly reveal evidence of (i) vibrational relaxation of the photoexcited molecules prior to their dissociation and of the radical fragments formed upon X-Y bond fission, and (ii) geminate recombination of the RX and Y products (leading to reformation of the ground state parent and/or isomeric adducts). Nonetheless, the data also show that, in each case, the characteristics (and the timescale) of the initial bond fission process that occurs under isolated molecule conditions are barely changed by the presence of a weakly interacting solvent like cyclohexane. These condensed phase studies are then extended to an ether analogue of phenol (allyl phenyl ether), wherein UV photo-induced RO-allyl bond fission constitutes the first step of a photo-Claisen rearrangement.</p
Player agency in interactive narrative: audience, actor & author
Get PDFThe question motivating this review paper is, how can
computer-based interactive narrative be used as a constructivist learn-
ing activity? The paper proposes that player agency can be used to
link interactive narrative to learner agency in constructivist theory,
and to classify approaches to interactive narrative. The traditional
question driving research in interactive narrative is, ‘how can an in-
teractive narrative deal with a high degree of player agency, while
maintaining a coherent and well-formed narrative?’ This question
derives from an Aristotelian approach to interactive narrative that,
as the question shows, is inherently antagonistic to player agency.
Within this approach, player agency must be restricted and manip-
ulated to maintain the narrative. Two alternative approaches based
on Brecht’s Epic Theatre and Boal’s Theatre of the Oppressed are
reviewed. If a Boalian approach to interactive narrative is taken the
conflict between narrative and player agency dissolves. The question
that emerges from this approach is quite different from the traditional
question above, and presents a more useful approach to applying in-
teractive narrative as a constructivist learning activity
The elastic collision of two H-like atoms including the exotic Ps and Mu
Get PDFThe elastic collision between two H-like atoms utilizing an ab-initio
static-exchange model (SEM) in the center of mass (CM) frame considering the
system as a four-body Coulomb problem where all the Coulomb interaction terms
in the direct and exchange channels are treated exactly, is studied thoroughly.
A coupled-channel methodology in momentum space is used to solve
Lippman-Schwinger equation following the integral approach. The new SEM code
[1-5] in which the Born-Oppenheimer (BO) scattering amplitude acts as input to
derive the SEM amplitude using partial wave analysis, is utilized to study the
s-, p-, d- wave elastic phase shifts and the corresponding partial cross
sections. An augmented-Born approximation is used to include the contribution
of higher partial waves more accurately to determine the total/integrated
elastic cross sections. The effective range theory is used to determine the
scattering lengths and effective ranges in the s-wave elastic scattering. The
systems studied are Ps-Ps, Ps-Mu, Ps-H, Ps-D, Ps-T, Mu-Mu, Mu-H, Mu-D, Mu-T,
H-H, H-D, H-T, D-D, D-T, T-T. The SEM includes the non-adiabatic short-range
effects due to exchange. The MSEM code [1] is used to study the effect of the
long-range van der Waals interaction due to induced dipole polarizabilities of
the atoms in H(1s)-H(1s) elastic collision. The dependence of scattering length
on the reduced mass of the system and the dependence of scattering length on
the strength of long-range van der Waals interaction that varies with the
minimum interatomic distance are observed [3].Comment: 15 pages, 8 figures, 9 tables. arXiv admin note: text overlap with
arXiv:1409.337
Importance of the H- channel in Ps-H scattering
No full textIt is shown that virtual H- formation has a profound effect upon low-energy Ps(1s)-H(1s) scattering, yet H- formation only accounts for about 10% of the total cross section just above threshold. Infinite series of Rydberg resonances converging on to the H- formation threshold are seen
DETECTION OF THE HPS FREE RADICAL BY LASER SPECTROSCOPY
No full textAuthor Institution: Department of Chemistry, University of Kentucky, Lexington, KY 40506-0055, USA; Dipartimento di Chimica Fisica ed Inorganica, Universita di Bologna, 40136 Bologna, ItalyThe previously unobserved HPS free radical has been detected by laser-induced fluorescence (LIF) techniques. HPS (and DPS) were produced in a pulsed discharge jet using a precursor gas mixture of ClPS vapor and hydrogen (or deuterium) in high pressure argon. Our \italic{ab} \italic{initio} predictions of the ground and excited state frequencies and excitation energy are in good agreement with the results obtained by vibrational analysis of the LIF and single vibronic level (SVL) emission spectra. High-resolution spectra of the hybrid bands of HPS and DPS were analyzed by band contour methods to obtain approximate ground and excited state rotational constants and molecular structures. The electronic transition involves promotion of an electron from the to the orbital and is assigned as AA. The results will be discussed in comparison to \italic{ab} \italic{initio} predictions and the spectra of other XPS radicals recently studied in our laboratory
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Positronium and antihydrogen formation in thee+-H and Ps-p¯ systems
Get PDFThe close coupling equations for the e+-H and Ps-p̄ systems are solved for a model calculation comprising three hydrogen H(1s, 2s, 2p) and three positronium Ps(1s, 2s, Ps(1s), Ps(2s), and Ps(2p) states for e++H→Ps+p reaction achieves a peak of 2.7πa02 and is smaller than the only existing set of experimental data. The cross section for antihydrogen formation in the Ps+p̄→e+H̄ reaction reaches a maximum of (13-14)πa02 for incident antiproton energies between 6.5 and 11 keV
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