Saddle Points and Stark Ladders: Exact Calculations of Exciton Spectra in Superlattices

A new, exact method for calculating excitonic absorption in superlattices is described. It is used to obtain high resolution spectra showing the saddle point exciton feature near the top of the miniband. The evolution of this feature is followed through a series of structures with increasing miniband width. The Stark ladder of peaks produced by an axial electric field is investigated, and it is shown that for weak fields the line shapes are strongly modified by coupling to continuum states, taking the form of Fano resonances. The calculated spectra, when suitably broadened, are found to be in good agreement with experimental results.Comment: 9 pages Revtex v3.0, followed by 4 uuencoded postscript figures, SISSA-CM-94-00

Speech-plans: Generating evaluative responses in spoken dialogue

Recent work on evaluation of spoken dialogue systems indicates that better algorithms are needed for the presentation of complex information in speech. Current dialogue systems often rely on presenting sets of options and their attributes sequentially. This places a large memory burden on users, who have to remember complex trade-offs between multiple options and their attributes. To address these problems we build on previous work using multiattribute decision theory to devise speech-planning algorithms that present usertailored summaries, comparisons and recommendations that allow users to focus on critical differences between options and their attributes. We discuss the differences between speech and text planning that result from the particular demands of the speech situation.

The AdS_5xS^5 superstring worldsheet S-matrix and crossing symmetry

An S-matrix satisying the Yang-Baxter equation with symmetries relevant to the AdS_5xS^5 superstring has recently been determined up to an unknown scalar factor. Such scalar factors are typically fixed using crossing relations, however due to the lack of conventional relativistic invariance, in this case its determination remained an open problem. In this paper we propose an algebraic way to implement crossing relations for the AdS_5xS^5 superstring worldsheet S-matrix. We base our construction on a Hopf-algebraic formulation of crossing in terms of the antipode and introduce generalized rapidities living on the universal cover of the parameter space which is constructed through an auxillary, coupling constant dependent, elliptic curve. We determine the crossing transformation and write functional equations for the scalar factor of the S-matrix in the generalized rapidity plane.Comment: 27 pages, no figures; v2: sign typo fixed in (24), everything else unchange

Magnetic Susceptibility, Freezing Point Diagram, Density, and Spectral Absorption of the System Vanadium Tetrachloride-Carbon Tetrachloride

On the basis of results of freezing point lowering experiments, it was reported by Simons and Powell that an equilibrium existed between VCl_4, and V_2Cl_8 in carbon tetrachloride solution. Since vanadium tetrachloride is an odd molecule, it was implied that dimerization could take place, as in nitrogen dioxide, such that the odd electrons become paired. In the present paper are reported the results of a study on the system by means of magnetic susceptibility measurements, freezing point diagram determination, and spectral absorption of the solution, as a function of concentration of vanadium tetrachloride in carbon tetrachloride

Family memories in the home: contrasting physical and digital mementos

We carried out fieldwork to characterise and compare physical and digital mementos in the home. Physical mementos are highly valued, heterogeneous and support different types of recollection. Contrary to expectations, we found physical mementos are not purely representational, and can involve appropriating common objects and more idiosyncratic forms. In contrast, digital mementos were initially perceived as less valuable, although participants later reconsidered this. Digital mementos were somewhat limited in function and expression, largely involving representational photos and videos, and infrequently accessed. We explain these digital limitations and conclude with design guidelines for digital mementos, including better techniques for accessing and integrating these into everyday life, allowing them to acquire the symbolic associations and lasting value that characterise their physical counterparts

Multisectoral approach to support use of insecticide-treated net for malaria prevention among mobile and migrant populations in Myanmar: a systematic review

BACKGROUND: Myanmar is a premalaria elimination country with artemisinin-resistant malaria. A strategy for transmission control is focused on vulnerable groups such as mobile and migrant populations (MMPs), and includes improving access to insecticide-treated bed nets in the Myanmar artemisinin resistance containment (MARC) zones using multisectoral approaches (MSA). METHODS: This narrative systematic review addressed MSAs targeted to MMPs in Myanmar for malaria prevention. We searched relevant studies in electronic databases and present the narrative findings in 4 domains: stakeholder groups, net coverage and utilization, social determinates, and facilitators/barriers. RESULTS: Nine studies were included. The review identified stakeholders involved in intersectoral collaboration. Net ownership was higher than utilization rates in the MARC zones and rates remained below the WHO recommended target of 100%. There was inadequate description of roles and responsibilities for implementation and on channels of communication within the partnerships and with the Government. CONCLUSIONS: Findings show that interventions to distribute treated bed nets were supported by the multiple stakeholders. Due to the design of the primary studies, analysis of the added value of intersectoral collaboration was limited. More attention must be paid to designing studies to document and evaluate the contributions and outcomes of intersectoral collaboration

How can we help novice child protection social workers to see situations like experienced practitioners? A randomised controlled trial evaluation of the ShadowBox™ method using pre-recorded video feedback

Background Protecting children for abuse and neglect is a complex area of decision-making but frequent staff turnover has meant that many frontline child protection social workers are often relatively inexperienced. The ShadoxBoxTM method is an educational intervention that enables novice practitioners to gain decision-making skills quickly. Aim: This study was an RCT evaluation of an educational intervention for novice social workers that used the ShadoxBoxTM method adapted to include pre-recorded video feedback from an expert panel to test whether novice decision making would become more similar to experienced practitioners. Methods: The study was an RCT in which participants completed complex scenarios in a computer lab in control and intervention groups. The training method involved participants receiving feedback from highly experienced practitioners at each decision point within the scenarios. The intervention group received pre-recorded video feedback from a panel of highly experienced practitioners while the control group received no feedback. Participants and Setting Participants (n=83) were trainee social workers from a London university randomly allocated to control and intervention groups. Data was collected on computer stations using Qualtrics. Results Undertaking the scenarios improved both groups but greater improvement was seen in participants who had received video feedback from a panel of experienced practitioners. The results were promising, with participant accuracy increasing by 44% (from 31% to 75%) in the intervention group compared to an increase of 31% (from 32% to 63%) in the control group. Considerable improvements were noted in both intervention and control groups, which suggest that scenario-based interventions can be a promising educational method as learning is rooted in real life scenarios and participants have the opportunity to reflect upon their decisions. The qualitative findings are that novice participants make predictable errors, including: • Making shallow assumptions • Focusing exclusively on the parents rather than the child. • Jumping to early conclusions with insufficient information. Conclusions • ShadoxBoxTM training appears to be a promising intervention for improving decision making. • Novices benefitted from having concentrated exposure to complex scenarios focused on assessing risk and making professional judgements. • When this was augmented by direct feedback from a panel of highly experienced practitioners, these benefits were increased considerably. • The complexity of the scenarios also exposed the novices to real life pressures rather than the simplified versions used in decision research

Quasi-point separation of variables for the Henon-Heiles system and a system with quartic potential

We examine the problem of integrability of two-dimensional Hamiltonian systems by means of separation of variables. The systematic approach to construction of the special non-pure coordinate separation of variables for certain natural two-dimensional Hamiltonians is presented. The relations with SUSY quantum mechanics are discussed.Comment: 11 pages, Late

Zero modes on cosmic strings in an external magnetic field

A classical analysis suggests that an external magnetic field can cause trajectories of charge carriers on a superconducting domain wall or cosmic string to bend, thus expelling charge carriers with energy above the mass threshold into the bulk. We study this process by solving the Dirac equation for a fermion of mass $m_f$ and charge $e$, in the background of a domain wall and a magnetic field of strength $B$. We find that the modes of the charge carriers get shifted into the bulk, in agreement with classical expectations. However the dispersion relation for the zero modes changes dramatically -- instead of the usual linear dispersion relation, $\omega_k =k$, the new dispersion relation is well fit by $\omega \approx m_f tanh(k/k_*)$ where $k_*=m_f$ for a thin wall in the weak field limit, and $k_*=eBw$ for a thick wall of width $w$. This result shows that the energy of the charge carriers on the domain wall remains below the threshold for expulsion even in the presence of an external magnetic field. If charge carriers are expelled due to an additional perturbation, they are most likely to be ejected at the threshold energy $\sim m_f$.Comment: 9 pages, 4 figure

Adiabatic-Impulse approximation for avoided level crossings: from phase transition dynamics to Landau-Zener evolutions and back again

We show that a simple approximation based on concepts underlying the Kibble-Zurek theory of second order phase transition dynamics can be used to treat avoided level crossing problems. The approach discussed in this paper provides an intuitive insight into quantum dynamics of two level systems, and may serve as a link between the theory of dynamics of classical and quantum phase transitions. To illustrate these ideas we analyze dynamics of a paramagnet-ferromagnet quantum phase transition in the Ising model. We also present exact unpublished solutions of the Landau-Zener like problems.Comment: 12 pages & 6 figures, minor corrections, version accepted in Phys. Rev.