Gamma-Ray Burst Dust Echoes Revisited: Expectations at Early Times

Gamma-ray burst (GRB) dust echoes were first proposed as an alternative explanation for the supernova-like (SN-like) components to the afterglows of GRB 980326 and GRB 970228. However, the spectroscopic identification of Type Ic SN 2003dh associated with GRB 030329, as well as the identification of SN-like components to the afterglows of other GRBs, appears to have confirmed the GRB/SN paradigm. However, the likely progenitors of Type Ic SNe are Wolf-Rayet WC stars, and late-type WC stars have been observed to be surrounded by dust, at a distance of 10^14 -- 10^15 cm from the star. Consequently, we revisit the possibility of GRB dust echoes, not on a timescale of weeks after the burst but on a timescale of minutes to hours. We find that if the optical flash is sufficiently bright and the jet sufficiently wide, GRB afterglows may be accompanied by chromatic variations on this timescale. From these signatures, such model parameters as the inner radius of the dust distribution, the initial opening angle of the jet, etc., may be deduced. With rapid and regular localizations of GRBs by HETE-2, Integral, and now Swift, and new and improved robotic telescope systems, these early-time GRB dust echoes may soon be detected. We describe one such robotic telescope system, called PROMPT, that the University of North Carolina at Chapel Hill is building at the Cerro Tololo Inter-American Observatory in greater detail.Comment: Accepted to The Astrophysical Journal, 15 pages, 5 figures, LaTe

Preventive War and the Crisis of July, 1914; Strategic Insights, v. 1, issue 9 (November 2002)

This article appeared in Strategic Insights, v.1, issue 9 (November 2002)Approved for public release; distribution is unlimited

Book Review by Daniel Moran of The Iraq War: Strategy, Tactics, and Military Lessons by Anthony H. Cordesman, and The Iraq War: A Military History by Williamson Murray and Major General Robert H. Scales

Reviewed: The Iraq War: Strategy, Tactics, and Military Lessons, by Anthony H. Cordesman, and The Iraq War: A Military History, by Williamson Murray and Major General Robert H. ScalesThe United States and its allies went to war against Iraq in 2003, as Williamson Murray and Robert Scales reasonably propose, “to make an example out of Saddam’s regime, for better or worse” (p. 44). Exactly what the war exemplified, and whether the results are better or worse than might have been achieved by other means, are, to say the least, matters of continuing dispute. In the meantime, we might as well start getting the facts straight, at least as far as military operations are concerned. The two books above are both contributions to that necessary work. They are exercises in bridge-building, reaching forward from wartime journalism and postwar postmortems to the more mature scholarship of the future. Given the time pressure under which they were prepared, they are far better than anyone would have had reason to expect

International law of the sea in a globalized world

Sensible people have long recognized the incongruity of the claim that Christopher Columbus discovered America, already home to perhaps a million souls at the time of his arrival. It is less widely recalled that Columbus did not mean to discover anything. He thought he knew where he was going, and, famously, did not quite realize he had not gotten there. His motives, and that of his royal patrons, were more commercial than scientific. Columbus set out not to uncover new lands but to demonstrate the feasibility of transoceanic travel. It was this achievement, and not his accidental encounter with an unsuspected continent, that proved transformative. Three centuries later, Adam Smith, the evangelist of modern capitalism, would declare the voyages of Columbus and his successors to be the greatest events in the history of the world, a sentiment that has resonated among recent students of what is now called globalization. Although it is not a point of view to be accepted uncritically, the fact remains that the inhabitants of the Americas were descended from Asian migrants who arrived on foot via a since-vanished land bridge across the Bering Strait. When Columbus sailed, neither they nor any other major human population had reached its present position on the globe by transiting the high seas. Afterward, this would begin to change

Illegal Combatants and the Law of Armed Conflict; Strategic Insights: v.2, issue 6 (August 2002)

This article appeared in Strategic Insights,Volume 2, Issue 6 (August 2002)As a consequence of its operations in Afghanistan, the United States has found itself holding several hundred Taliban and al-Qaida prisoners whom it has identified as "illegal combatants." Similar status has also been ascribed to at least one American citizen, arrested by civil authorities, who is suspected of being part of the al-Qaida terrorist organization, and who is being treated, for the time being at least, as a subject of military justice. The classification of prisoners taken in Afghanistan as "illegal combatants" immediately attracted much scrutiny, in part because international law provides no precise definition of what such a categorization implies, and in part because its use in the present instance was intended to deprive Taliban and al-Qaida fighters of the protections afforded prisoners of war under the 1949 Geneva Conventions. Although United States officials have routinely referred to the struggle against terrorism as a "war," that characterization is, to all appearances, not acceptable when applied to the conduct of those on the other side

Active classification with comparison queries

We study an extension of active learning in which the learning algorithm may ask the annotator to compare the distances of two examples from the boundary of their label-class. For example, in a recommendation system application (say for restaurants), the annotator may be asked whether she liked or disliked a specific restaurant (a label query); or which one of two restaurants did she like more (a comparison query). We focus on the class of half spaces, and show that under natural assumptions, such as large margin or bounded bit-description of the input examples, it is possible to reveal all the labels of a sample of size $n$ using approximately $O(\log n)$ queries. This implies an exponential improvement over classical active learning, where only label queries are allowed. We complement these results by showing that if any of these assumptions is removed then, in the worst case, $\Omega(n)$ queries are required. Our results follow from a new general framework of active learning with additional queries. We identify a combinatorial dimension, called the \emph{inference dimension}, that captures the query complexity when each additional query is determined by $O(1)$ examples (such as comparison queries, each of which is determined by the two compared examples). Our results for half spaces follow by bounding the inference dimension in the cases discussed above.Comment: 23 pages (not including references), 1 figure. The new version contains a minor fix in the proof of Lemma 4.

La respuesta al problema de la medida de figuras planas en los antiguos griegos

El problema de la cuadratura del círculo ha sido de gran importancia a través de la historia, pues constituye un elemento movilizador de algunas ramas de la matemática como la Geometría Analítica, el Cálculo y el Análisis. Euclides de Alejandría (aprox. 300 a.C.) en su monumental obra Elementos da una respuesta parcial al problema, estableciendo un proceso para la cuadratura de figuras rectilíneas y deja implícito el proceso que posteriormente será el eje central de la medida. Estos resultados son retomados por Arquímedes para la cuadratura de figuras que no son rectilíneas. En el presente escrito se intenta abordar estos resultados de Euclides y su relación con los resultados de Arquímedes al problema de medir, uno de los ejes centrales en el desarrollo de las Matemáticas

Long-Range Temporal Correlations in Resting State Beta Oscillations are Reduced in Schizophrenia

Symptoms of schizophrenia (SCZ) are likely to be generated by genetically mediated synaptic dysfunction, which contribute to large-scale functional neural dysconnectivity. Recent electrophysiological studies suggest that this dysconnectivity is present not only at a spatial level but also at a temporal level, operationalized as long-range temporal correlations (LRTCs). Previous research suggests that alpha and beta frequency bands have weaker temporal stability in people with SCZ. This study sought to replicate these findings with high-density electroencephalography (EEG), enabling a spatially more accurate analysis of LRTC differences, and to test associations with characteristic SCZ symptoms and cognitive deficits. A 128-channel EEG was used to record eyes-open resting state brain activity of 23 people with SCZ and 24 matched healthy controls (HCs). LRTCs were derived for alpha (8–12 Hz) and beta (13–25 Hz) frequency bands. As an exploratory analysis, LRTC was source projected using sLoreta. People with SCZ showed an area of significantly reduced beta-band LRTC compared with HCs over bilateral posterior regions. There were no between-group differences in alpha-band activity. Individual symptoms of SCZ were not related to LRTC values nor were cognitive deficits. The study confirms that people with SCZ have reduced temporal stability in the beta frequency band. The absence of group differences in the alpha band may be attributed to the fact that people had, in contrast to previous studies, their eyes open in the current study. Taken together, our study confirms the utility of LRTC as a marker of network instability in people with SCZ and provides a novel empirical perspective for future examinations of network dysfunction salience in SCZ research