High speed switching between arbitrary spatial light profiles

Complex images, inscribed into the spatial profile of a laser beam or even a single photon, offer a highly efficient method of data encoding. Here we present a prototype system which can quickly modulate between arbitrary images. We display an array of holograms, each defined by its phase and intensity profile, on a spatial light modulator. The input beam is then steered by an acousto-optic modulator to one of these holograms, where it is converted into the desired light mode. We demonstrate switching between characters within three separate alphabets at a switching rate of up to10 kHz. This rate is limited by our detection system, and we anticipate that the system is capable of far higher rates. Furthermore our system is not limited in efficiency by channel number, making it ideal for quantum communication applications

Verification of a Transactional Memory Manager under Hardware Failures and Restarts

Abstract. We present our formal verification of the persistent mem-ory manager in IBM’s 4765 secure coprocessor. Its task is to achieve a transactional semantics of memory updates in the face of restarts and hardware failures and to provide resilience against the latter. The inclu-sion of hardware failures is novel in this area and incurs a significant jump in system complexity. We tackle the resulting verification challenge by a combination of a monad-based model, an abstraction that reduces the system’s non-determinism, and stepwise refinement. We propose novel proof rules for handling repeated restarts and nested metadata transac-tions. Our entire development is formalized in Isabelle/HOL.

Discrete exterior calculus (DEC) for the surface Navier-Stokes equation

We consider a numerical approach for the incompressible surface Navier-Stokes equation. The approach is based on the covariant form and uses discrete exterior calculus (DEC) in space and a semi-implicit discretization in time. The discretization is described in detail and related to finite difference schemes on staggered grids in flat space for which we demonstrate second order convergence. We compare computational results with a vorticity-stream function approach for surfaces with genus 0 and demonstrate the interplay between topology, geometry and flow properties. Our discretization also allows to handle harmonic vector fields, which we demonstrate on a torus.Comment: 21 pages, 9 figure

Insights into the influence of solvent polarity on the crystallization of poly(ethylene oxide) spin-coated thin films via in situ grazing incidence wide-angle X-ray scattering

Controlling polymer thin-film morphology and crystallinity is crucial for a wide range of applications, particularly in thin-film organic electronic devices. In this work, the crystallization behavior of a model polymer, poly(ethylene oxide) (PEO), during spin-coating is studied. PEO films were spun-cast from solvents possessing different polarities (chloroform, THF, and methanol) and probed via in situ grazing incidence wide-angle X-ray scattering. The crystallization behavior was found to follow the solvent polarity order (where chloroform chloroform > methanol). When spun-cast from nonpolar chloroform, crystallization largely followed Avrami kinetics, resulting in the formation of morphologies comprising large spherulites. PEO solutions cast from more polar solvents (THF and methanol) do not form well-defined highly crystalline morphologies and are largely amorphous with the presence of small crystalline regions. The difference in morphological development of PEO spun-cast from polar solvents is attributed to clustering phenomena that inhibit polymer crystallization. This work highlights the importance of considering individual components of polymer solubility, rather than simple total solubility, when designing processing routes for the generation of morphologies with optimum crystallinities or morphologies

Relativistic description of electron scattering on the deuteron

Within a quasipotential framework a relativistic analysis is presented of the deuteron current. Assuming that the singularities from the nucleon propagators are important, a so-called equal time approximation of the current is constructed. This is applied to both elastic and inelastic electron scattering. As dynamical model the relativistic one boson exchange model is used. Reasonable agreement is found with a previous relativistic calculation of the elastic electromagnetic form factors of the deuteron. For the unpolarized inelastic electron scattering effects of final state interactions and relativistic corrections to the structure functions are considered in the impulse approximation. Two specific kinematic situations are studied as examples.Comment: (19 pages in revtex + 15 figures not included, available upon request.) report THU-93-10

Selective molecular annealing:in situ small angle X-ray scattering study of microwave-assisted annealing of block copolymers

Microwave annealing has emerged as an alternative to traditional thermal annealing approaches for optimising block copolymer self-assembly. A novel sample environment enabling small angle X-ray scattering to be performed in situ during microwave annealing is demonstrated, which has enabled, for the first time, the direct study of the effects of microwave annealing upon the self-assembly behavior of a model, commercial triblock copolymer system [polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene]. Results show that the block copolymer is a poor microwave absorber, resulting in no change in the block copolymer morphology upon application of microwave energy. The block copolymer species may only indirectly interact with the microwave energy when a small molecule microwave-interactive species [diethylene glycol dibenzoate (DEGDB)] is incorporated directly into the polymer matrix. Then significant morphological development is observed at DEGDB loadings ≥6 wt%. Through spatial localisation of the microwave-interactive species, we demonstrate targeted annealing of specific regions of a multi-component system, opening routes for the development of "smart" manufacturing methodologies

Guardian: Hypervisor as Security Foothold for Personal Computers

Abstract. Personal computers lack of a security foothold to allow the end-users to protect their systems or to mitigate the damage. Existing candidates either rely on a large Trusted Computing Base (TCB) or are too costly to widely deploy for commodity use. To fill this gap, we propose a hypervisor-based security foothold, named as Guardian, for commodity personal computers. We innovate a bootup and shutdown mechanism to achieve both integrity and availability of Guardian. We also propose two security utilities based on Guardian. One is a device mon-itor which detects malicious manipulation on camera and network adaptors. The other is hyper-firewall whereby Guardian expects incoming and outgoing network packets based on policies specified by the user. We have implemented Guardian ( ≈ 25K SLOC) and the two utilities ( ≈ 2.1K SLOC) on a PC with an Intel pro-cessor. Our experiments show that Guardian is practical and incurs insignificant overhead to the system.

Primordial Nucleosynthesis for the New Cosmology: Determining Uncertainties and Examining Concordance

Big bang nucleosynthesis (BBN) and the cosmic microwave background (CMB) have a long history together in the standard cosmology. The general concordance between the predicted and observed light element abundances provides a direct probe of the universal baryon density. Recent CMB anisotropy measurements, particularly the observations performed by the WMAP satellite, examine this concordance by independently measuring the cosmic baryon density. Key to this test of concordance is a quantitative understanding of the uncertainties in the BBN light element abundance predictions. These uncertainties are dominated by systematic errors in nuclear cross sections. We critically analyze the cross section data, producing representations that describe this data and its uncertainties, taking into account the correlations among data, and explicitly treating the systematic errors between data sets. Using these updated nuclear inputs, we compute the new BBN abundance predictions, and quantitatively examine their concordance with observations. Depending on what deuterium observations are adopted, one gets the following constraints on the baryon density: OmegaBh^2=0.0229\pm0.0013 or OmegaBh^2 = 0.0216^{+0.0020}_{-0.0021} at 68% confidence, fixing N_{\nu,eff}=3.0. Concerns over systematics in helium and lithium observations limit the confidence constraints based on this data provide. With new nuclear cross section data, light element abundance observations and the ever increasing resolution of the CMB anisotropy, tighter constraints can be placed on nuclear and particle astrophysics. ABRIDGEDComment: 54 pages, 20 figures, 5 tables v2: reflects PRD version minor changes to text and reference

Biomedical colonialism or local autonomy?: local healers in the fight against tuberculosis

Analiza el papel de los agentes médicos autóctonos y sus conocimientos en las campañas antituberculosas contemporáneas en el África subsahariana. Sitúa la medicina contemporánea, llevada a cabo en África en la herencia cultural de la medicina colonial, para comprender el marco histórico en el que se desarrollaron, a partir de los años setenta del siglo XX, las estrategias de la Organización Mundial de la Salud de promoción y desarrollo de las medicinas 'tradicionales'. En los proyectos sanitarios analizados, se evalúan las prácticas médicas locales y se entrenan a los agentes autóctonos para integrarlos en actividades estrictamente biomédicas: identificación de síntomas, remisión a hospitales o supervisión de tratamientos farmacológicos.The article explores the role played by indigenous medical agents, and their knowledge, within contemporary tuberculosis campaigns in sub-Saharan Africa. To understand the historical framework within which the World Health Organization devised its strategies to promote and develop traditional medicine as of the 1970s, the article contextualizes contemporary medicine as a cultural legacy of colonial medicine. Under the public healthcare projects analyzed in the article, local medical practices were assessed and indigenous agents trained so they could take part in strictly biomedical activities, like symptom identification, referrals to hospitals, or supervision of drug treatments.Trabajo realizado para la obtención del Diploma de Estudios Avanzados (DEA) en el programa de doctorado Salud: Antropología e Historia, bajo la dirección de la profesora Rosa María Medina Doménech

The upgrade of the ALICE TPC with GEMs and continuous readout

The upgrade of the ALICE TPC will allow the experiment to cope with the high interaction rates foreseen for the forthcoming Run 3 and Run 4 at the CERN LHC. In this article, we describe the design of new readout chambers and front-end electronics, which are driven by the goals of the experiment. Gas Electron Multiplier (GEM) detectors arranged in stacks containing four GEMs each, and continuous readout electronics based on the SAMPA chip, an ALICE development, are replacing the previous elements. The construction of these new elements, together with their associated quality control procedures, is explained in detail. Finally, the readout chamber and front-end electronics cards replacement, together with the commissioning of the detector prior to installation in the experimental cavern, are presented. After a nine-year period of R&D, construction, and assembly, the upgrade of the TPC was completed in 2020.publishedVersio