A Constrained Object Model for Configuration Based Workflow Composition

Automatic or assisted workflow composition is a field of intense research for applications to the world wide web or to business process modeling. Workflow composition is traditionally addressed in various ways, generally via theorem proving techniques. Recent research observed that building a composite workflow bears strong relationships with finite model search, and that some workflow languages can be defined as constrained object metamodels . This lead to consider the viability of applying configuration techniques to this problem, which was proven feasible. Constrained based configuration expects a constrained object model as input. The purpose of this document is to formally specify the constrained object model involved in ongoing experiments and research using the Z specification language.Comment: This is an extended version of the article published at BPM'05, Third International Conference on Business Process Management, Nancy Franc

How CSMA/CA With Deferral Affects Performance and Dynamics in Power-Line Communications

Power-line communications (PLC) are becoming a key component in home networking, because they provide easy and high-throughput connectivity. The dominant MAC protocol for high data-rate PLC, the IEEE 1901, employs a CSMA/CA mechanism similar to the backoff process of 802.11. Existing performance evaluation studies of this protocol assume that the backoff processes of the stations are independent (the so-called decoupling assumption). However, in contrast to 802.11, 1901 stations can change their state after sensing the medium busy, which is regulated by the so-called deferral counter. This mechanism introduces strong coupling between the stations and, as a result, makes existing analyses inaccurate. In this paper, we propose a performance model for 1901, which does not rely on the decoupling assumption. We prove that our model admits a unique solution for a wide range of configurations and confirm the accuracy of the model using simulations. Our results show that we outperform current models based on the decoupling assumption. In addition to evaluating the performance in steady state, we further study the transient dynamics of 1901, which is also affected by the deferral counter.Comment: To appear, IEEE/ACM Transactions on Networking 201

Plans for the LIGO–TAMA joint search for gravitational wave bursts

We describe the plans for a joint search for unmodelled gravitational wave bursts being carried out by the LIGO and TAMA Collaborations using data collected during February–April 2003. We take a conservative approach to detection, requiring candidate gravitational wave bursts to be seen in coincidence by all four interferometers. We focus on some of the complications of performing this coincidence analysis, in particular the effects of the different alignments and noise spectra of the interferometers

Vacuum harmonic generation in slowly varying electromagnetic backgrounds

Relativistische Quantentheorie sagt die Existenz von virtuellen Elektron-Positron-Paaren vorher, die innerhalb einer typischen Zeitskala, der Compton-Zeit des Elektrons, erzeugt und wieder vernichtet werden. Diese virtuellen Dipole machen das Vakuum zu einem polarisierbaren Medium, was zu einer Abänderung der klassischen Maxwell-Gleichungen führt. Falls die Photonen eine Energie haben, welche deutlich kleiner ist als die Ruheenergie des Elektrons, werden diese Effekte durch die “Heisenberg-Euler”-Lagrange-Dichte im Rahmen der Quantenelektrodynamik beschrieben. Für Feldstärken, die klein sind im Vergleich zu dem “kritischen” Feld Ecr = 1.3 · 10^16 Vcm^−1, können diese Korrekturen zur Ausbreitung von elektromagnetischen Wellen explizit ausgewertet werden. In dieser Arbeit werden die Maxwell-Gleichungen mitsamt dieser Korrekturen für schwache Felder numerisch in einer Anregungs-Abfrage-Konfiguration von zwei zusammenstoßenden, ebenen Wellen gelöst. Die entsprechende Wellengleichung wird dann analytisch gelöst. Die Anfangsbedingungen bestehen dabei aus einem (optischen) gaußschen “Abfrage”-Puls, der sich entgegengesetzt der “Anregung” in Form eines nur schwach variierenden, starken Hintergrunds, ausbreitet. Dabei werden Vakuumpolarisations-Effekte wie Doppelbrechung und die Erzeugung von Harmonischen (ähnlich zu Prozessen in einem nichtlinearen Kerr-Medium) untersucht. Der erste Teil dieser Arbeit befasst sich mit der Analyse der zeitaufgelösten Dynamik der Kollision des Abfrage-Pulses mit einem gaußförmigen, starken Hintergrund. Dabei wird ein “Überlappungs”-Feld identifiziert, welches nur im Wechselwirkungsbereich vorhanden ist und verschwindet, wenn die Pulse weit voneinander entfernt sind. Der zweite Teil untersucht die Erzeugung von höheren Harmonischen im Vakuum, wobei der Hintergrund nun als ebene Welle mit verschwindender Frequenz gewählt wird. Falls die Weglänge des Abfrage-Pulses im externen Feld groß genug ist, können höhere Harmonische durch hintereinander stattfindende Streuprozesse erzeugt werden. Für parallele Polarisationen der beiden Pulse wird ein Multi-Skalen-Parameter identifiziert, welcher angibt, wann diese Selbstwechselwirkung relevant wird. Wenn dieser Parameter gegen eins strebt, entwickelt der Abfrage-Puls eine Unstetigkeit in der Trägerfrequenz, welche auch “Schock” genannt wird.Relativistic quantum theory predicts the existence of virtual electron-positron pairs that are generated and annihilated over a typical time scale given by the electron Compton time. These virtual dipoles render the vacuum a polarisable medium thereby modifying the classical Maxwell vacuum equations. For photons with energy much smaller than the electron rest energy, these effects are well-described by the “Heisenberg-Euler” Lagrangian within the framework of Quantum Electrodynamics. In the case of field strengths that are small compared to the “critical” field Ecr = 1.3 · 10^16 Vcm^−1, the resulting nonlinear corrections to the electromagnetic wave propagation can be evaluated explicitly. In this thesis, Maxwell equations that include these weak-field corrections are solved numerically for a “pump-probe” setup of two colliding plane waves. The corresponding wave equation is then solved analytically. The inital configuration is a weak (optical) Gaussian probe pulse that counterpropagates with a slowly-varying strong “background”. Vacuum polarisation effects such as birefringence and the generation of harmonics (similar to processes in a nonlinear Kerr-medium) are analysed. The first part of the thesis is dedicated to the study of the time-resolved dynamics when the probe collides with a Gaussian strong pulse and an “overlap” signal is identified, which is only present in the interaction region and disappears when the pulses are well separated. The second part of the thesis considers vacuum high harmonic generation in a plane wave background of vanishing frequency. If the propagation length of the probe in the external field is long enough, higher harmonics of the probe frequency can be generated due to multiple scattering events. For parallel polarisations of probe and strong pulse, a multi-scale parameter is identified which indicates when this self-interaction becomes important. If this parameter approaches unity, the probe pulse develops a discontinuity or “shock” in the carrier wave

The Jenny Interviews and Other Sightings: Needle(s) in the Proverbial Haystack(s)

Article originally published in the Pitcairn Log in July 2021On April 28, 1789, acting Lieutenant Fletcher Christian disposed “Captain” William Bligh and 18 crew from the HMAV Bounty just of Tofua, South Pacific Ocean. Bligh’s successful open-boat journey to Timor ranks amongst the greatest survival stories in naval history. Christian’s returned to Tahiti, failed settlement at Tubuai, and eventual “rediscovery” of Pitcairn Island are well known among Bounty enthusiasts. Hundreds, if not thousands, of books and articles have been written on the Bounty/Pitcairn Island Saga over the last 230 years including those written by naval officers, early visitors, descendants (Rosalind Amelia Young, Glynn Christian), journalists, and scholars from most notably history, but also those with credentials in anthropology, sociology, geography, and even psychology. Prior to Henry Evans Maude’s (1958) article published in The Journal of the Polynesian Society (volume 11, 1964) titled “In search of a home: From the mutiny to Pitcairn Island (1789-1790),” the Bounty’s post-mutiny peregrinations from its return to Matavia Bay, Tahiti, on 6 June 1789 and the "rediscovery” of Pitcairn Island on January 15, 1790, were sketchy at best. Maude, a former colonial administrator and subsequent research fellow at the Australian National University, located two “lost” newspaper articles pertaining to the Bounty and Pitcairn Island. These articles contained interviews with Teehuteatuaona (aka Jenny), the consort initially of mutineers Alexander Smith (John Adams) then Isaac Martin. In these interviews Jenny provided geographic references and clues that elucidated the Bounty’s path post mutiny. Jenny’s accounts also illuminated life on Pitcairn Island, especially the violence that occurred during its first ten years

The anomalous accretion disk of the Cataclysmic Variable RW Sextantis

Synthetic spectra covering the wavelength range 900\AA~to 3000\AA~provide an accurate fit, established by a ${\chi}_{\nu}^2$ analysis, to a combined observed spectrum of RW Sextantis. Two separately calibrated distances to the system establish the synthetic spectrum comparison on an absolute flux basis but with two alternative scaling factors, requiring alternative values of $\dot{M}$ for final models. Based on comparisons for a range of $\dot{M}$ values, the observed spectrum does not follow the standard model. Rather than the exponent 0.25 in the expression for the radial temperature profile, a value close to 0.125 produces a synthetic spectrum with an accurate fit to the combined spectrum. A study of time-series $FUSE$ spectra shows that a proposed warped or tilted disk is not supported by the data; an alternative proposal is that an observed non-axisymmetric wind results from an interaction with the mass transfer stream debris.Comment: 56 pages, 15 figures, 11 tables. Accepted for The Astrophysical Journa

Coherent network analysis technique for discriminating gravitational-wave bursts from instrumental noise

Existing coherent network analysis techniques for detecting gravitational-wave bursts simultaneously test data from multiple observatories for consistency with the expected properties of the signals. These techniques assume the output of the detector network to be the sum of a stationary Gaussian noise process and a gravitational-wave signal, and they may fail in the presence of transient non-stationarities, which are common in real detectors. In order to address this problem we introduce a consistency test that is robust against noise non-stationarities and allows one to distinguish between gravitational-wave bursts and noise transients. This technique does not require any a priori knowledge of the putative burst waveform.Comment: 18 pages, 11 figures; corrected corrupted figur

Buckets of Water into the Ocean: Non-public Revenue in Public Charter and Traditional Public Schools

The funding of K-12 education remains a contentious public policy issue. Questions of funding adequacy and equity across school sectors, school districts and individual schools are prominent in discussions of how to improve educational outcomes, especially for students from disadvantaged backgrounds (Downes & Stiefel 2008; Ladd 2008). Although scholars are divided regarding the extent to which money affects student outcomes in K-12 education (Jackson, Johnson, & Persico 2015; Hanushek, 1997; Burtless 1996), there is basic agreement that more education revenue is better so long as the increased resources are directed towards productive educational activities and programs (Murnane & Levy 1996). If you ask education practitioners, the majority will say that more resources will make their schools better

Solutions for Impact Investors: From Strategy to Implementation

In writing this monograph, our main goal is to provide impact investors with tools to tighten the link between their investment decisions and impact creation. Our intent is threefold: to attract more capital to impact investing; to assist impact investors as they move from organizational change to executing and refining their impact investment decision-making process; and to narrow the gap within foundations between program professionals and investment professionals thereby contributing to a mutual understanding and implementation of a portfolio approach to impact investing.Additionally, we intend to help break down the barriers making it difficult to identify opportunities in impact investing. To this end, we provide examples throughout the monograph and at www.rockpa.org/impactinvesting of impact investment opportunities in most major asset classes.While we understand the important role that impact investors can play in providing financial capital, we also want to acknowledge the wide range of non-financial resources needed to address the world's problems. Our intent with this monograph is not to provide a comprehensive list of investments across asset classes nor any type of investment advice with regard to the selected profiles. We strongly encourage the reader to conduct their own assessment and evaluation for risk and suitability before considering any investment