The Electromigration Force in Metallic Bulk

The voltage induced driving force on a migrating atom in a metallic system is discussed in the perspective of the Hellmann-Feynman force concept, local screening concepts and the linear-response approach. Since the force operator is well defined in quantum mechanics it appears to be only confusing to refer to the Hellmann-Feynman theorem in the context of electromigration. Local screening concepts are shown to be mainly of historical value. The physics involved is completely represented in ab initio local density treatments of dilute alloys and the implementation does not require additional precautions about screening, being typical for jellium treatments. The linear-response approach is shown to be a reliable guide in deciding about the two contributions to the driving force, the direct force and the wind force. Results are given for the wind valence for electromigration in a number of FCC and BCC metals, calculated using an {\it ab initio} KKR-Green's function description of a dilute alloy.Comment: 14 pages, 1 Postscript figur

The Fermi LAT detection of magnetar-like pulsar PSR J1846-0258 at high-energy gamma-rays

We report the detection of the pulsed signal of the radio-quiet magnetar-like pulsar PSR J1846-0258 in the high-energy \gr-ray data of the Fermi Large Area Telescope (Fermi LAT). We produced phase-coherent timing models exploiting RXTE PCA and Swift XRT monitoring data for the post- (magnetar-like) outburst period from 2007 August 28 to 2016 September 4, with independent verification using INTEGRAL ISGRI and Fermi GBM data. Phase-folding barycentric arrival times of selected Fermi LAT events from PSR J1846-0258, resulted in a 4.2 sigma detection (30--100 MeV) of a broad pulse consistent in shape and aligned in phase with the profiles that we measured with Swift XRT (2.5--10 keV), INTEGRAL ISGRI (20--150 keV) and Fermi GBM (20--300 keV). The pulsed flux (30--100 MeV) is (3.91 +/- 0.97)E-9 photons/(cm^2 s MeV). Declining significances of the INTEGRAL ISGRI 20--150 keV pulse profiles suggest fading of the pulsed hard X-ray emission during the post-outburst epochs. We revisited with greatly improved statistics the timing and spectral characteristics of PSR B1509-58 as measured with the Fermi LAT. The broad-band pulsed emission spectra (from 2 keV up to GeV energies) of PSR J1846-0258 and PSR B1509-58 can be accurately described with similarly curved shapes, with maximum luminosities at 3.5 +/- 1.1 MeV (PSR J1846-0258) and 2.23 +/- 0.11 MeV (PSR B1509-58). We discuss possible explanations for observational differences between Fermi LAT detected pulsars that reach maximum luminosities at GeV energies, like the second magnetar-like pulsar PSR J1119-6127, and pulsars with maximum luminosities at MeV energies, which might be due to geometric differences rather than exotic physics in high-B fields.Comment: 13 pages, 8 figures, accepted by MNRAS on 2017 November 3

'Aurora'-a time domain based meta-algorithm for the rapid simulation and design of complex optical circuits

A new simulation tool called ‘Aurora’, specifically developed to efficiently simulate highly complex optical devices such as OADMs and Routers based on (higher order)microring resonators, is presented. The meta-simulation algorithm used by Aurora creates a framework in which many different simulation algorithms can be properly combined rather than providing a simulation algorithm itself. The calculations of this program use a simple scheme based in the time domain from which the frequency response can easily be derived. Simulation results of a 4-port OADM and waveguide gratings show excellent agreement when compared to experimentally obtained measurement data and conventional simulation methods

(Re)Coding the Past for the Future.

In light of increasing social unrest and wars around the globe, a growing number of not-for-profit organizations and commercial businesses are trying to fill the gaps that befall cultural heritage sites due to bomb strikes and looting. 3D scanning and printing are among the main vehicles to restore cultural heritage by generating detailed copies of an artifact, building or even site. In terms of accessibility and preservation there are undeniable benefits, but in what ways do these technologies affect cultural heritage politics? While commercial businesses profit from selling copyrighted files, or by providing restricted access, several artists’ initiatives try to counter these practices. Even though they use similar technology, their aim is to empower people by giving them control over their lost heritage. These ‘decolonial’ practices signify a desire to overcome or resist a colonial conditioning, favoring collaboration and freely sharing over individual and/or monetary gains. In the process, such examples challenge the conventional meaning of value, which is dictated by the market and based on copyrights around authorship and ownership. Instead what is valued and becomes valuable is belonging to a wider community in which control over (re)use is embedded in the network

The Art and Care of Curating Online

Following the International Conference on Art, Museums and Digital Cultures (April 2021), this e-book seeks to extend the discussion on the concept of change that is usually associated with the relationship between culture and technology. Through the contributions of 32 authors from 12 countries, the book not only questions how digital media have inspired new artistic and curatorial practices, but also how, conversely, critical and creative proposals in the fields of art and museums have opened up alternative paths to technological development. Acknowledging the different approaches to the topic, ranging from retrospective readings to the analysis of recent issues and projects, the book is divided into seven sections and a visual essay, highlighting collaborative territories and the crossovers between different areas of scientific knowledge. Available in open access, this publication is the result of a collaborative project promoted by the Institute of Art History of the School of Social Sciences and Humanities, NOVA University of Lisbon and maat – Museum of Art, Architecture and Technology.

How much of this is fiction

Exploring the radical shift in the boundary between fiction and reality in a world increasingly governed by ‘post-truth’ politic

Low energy ion bombardment on c-Ge surfaces

Amorphous germanium thin films (25–60 Å) were prepared by low energy (500, 800 eV) bombardment of noble gas ions (Ne, Ar, Kr) on c-Ge(001). The films were examined by spectroscopic ellipsometry and analysed using linear regression analysis (LRA). The most probable composition of the damaged toplayer is that of void free amorphous germanium, comparable with those obtained by dc-magnetron sputtering. The results are in excellent agreement with Monte Carlo simulations of the transport of ions in matter (TRIM86)

Atomic force microscopy shows that vaccinia topoisomerase IB generates filaments on DNA in a cooperative fashion

Type IB DNA topoisomerases cleave and rejoin one strand of the DNA duplex, allowing for the removal of supercoils generated during replication and transcription. In addition, electron microscopy of cellular and viral TopIB–DNA complexes has suggested that the enzyme promotes long-range DNA–DNA crossovers and synapses. Here, we have used the atomic force microscope to visualize and quantify the interaction between vaccinia topoisomerase IB (vTopIB) and DNA. vTopIB was found to form filaments on nicked-circular DNA by intramolecular synapsis of two segments of a single DNA molecule. Measuring the filament length as a function of protein concentration showed that synapsis is a highly cooperative process. At high protein:DNA ratios, synapses between distinct DNA molecules were observed, which led to the formation of large vTopIB-induced DNA clusters. These clusters were observed in the presence of Mg(2+), Ca(2+) or Mn(2+), suggesting that the formation of intermolecular vTopIB-mediated DNA synapsis is favored by screening of the DNA charge

Flexible Labor and Innovation Performance: Evidence from Longitudinal Firm-Level Data

Firms with high shares of workers on fixed-term contracts have significantly higher sales of imitative new products but perform significantly worse on sales of inno¬va¬tive new products (“first on the marketâ€). High functional flexibility in “insider-outsider†la¬bor markets enhances a firm’s new product sales, as do training efforts and highly edu¬ca¬¬ted personnel. We find weak evidence that larger and older firms have higher new pro¬duct sales than do younger and smaller firms. Our findings should be food for thought to eco-nomists making unqualified pleas for the deregulation of labor markets.J5;M5;O15;O31;OSA longitudinal dataset;SMEs;innovation performance;new product sales;numerical flexibility

Ultrafast all-optical wavelength conversion in silicon-insulator waveguides by means of cross phase modulation using 300 femtosecond pulses

In this paper we report the ultrafast all-optical wavelength conversion in Silicon-on-Insulator (SOI) waveguides. We used a pump-probe setup with 300 femtosecond pulses to demonstrate large temporal phase-shifts, caused by the Kerr effect and free carrier generation. Large wavelength shifts of a 1683nm probe signal have been observed. The wavelength conversion, ranging from 10nm redshifts to 15nm blueshifts, depending on the time delay between the pump and probe pulses, is caused by the pump induced Cross Phase Modulation. Furthermore, an all-optical switching scheme using SOI microring resonators is discussed. These results enable ultrafast all-optical switching using SOI microring resonators