Laser Guide Star for 3.6m and 8m telescopes: Performances and astrophysical implications

We have constructed an analytical model to simulate the behavior of an adaptive optics system coupled with a sodium laser guide star. The code is applied to a 3.6-m and 8m class telescopes. The results are given in terms of Strehl ratio and full width at half maximum of the point spread function. Two atmospheric models are used, one representing good atmospheric conditions (20 per cent of the time), the other median conditions. Sky coverage is computed for natural guide star and laser guide star systems, with two different methods. The first one is a statistical approach, using stellar densities, to compute the probability to find a nearby reference. The second is a cross-correlation of a science object catalogue and the USNO catalogue. Results are given in terms of percentage of the sky that can be accessed with given performances, and in terms of number of science object that can be observed, with Strehls greater than 0.2 and 0.1 in K and J bands.Comment: 14 pages, 17 figures, accepted for publication in MNRAS. Also available at: http://www-obs.univ-lyon1.fr/~lelouarn

Charles R. Foy review of Michael J. Jarvis, “In the Eye of all Trade: Bermuda, Bermudians, and the Maritime Atlantic World,” in Common-place 10:4 (July 2010) (www.common-place.org).

In his comprehensive study of colonial Bermuda Jarvis places Bermuda in the eye of trade, i.e., the center of the Anglo-American Atlantic. He proceeds to use this new perspective to explore six key characteristics of Bermudian life: its transition from a tobacco society to a maritime society; the island’s unique system of slavery; the emphasis placed on kinship connections and communal activities; Bermudian exploitation of the Atlantic’s natural resources; the effect of Bermuda’s maritime economy on its residents; and the impact of the American Revolution on Bermudian society. With their maritime skills, unique slave system and extensive kinship connections Bermudians were, as Jarvis convincingly demonstrates, able to exploit maritime hinterlands to supplement their intercolonial trade and shipbuilding. Jarvis\u27 emphasis on Bermudians’ adaptability to their isolated location stands as a useful reminder of how many early British settlers saw areas often referred to as “frontiers” or “borderlands” as central to their lives and economic well-being

“Compelled to Row: Blacks on Royal Navy Galleys During the American Revolution”

Work on Royal Navy galleys in North America during the American Revolution was physically demanding, lacked in sufficient shelter for their crews and rarely resulted in sailors obtaining prize monies. These conditions resulted in desertion rates five times greater than on other Royal Navy vessels and the frequent employment of older men. At the same time, Blacks served British galleys at twice the rate as on other Royal Navy vessels. This was due to the hiring out of slaves onto galleys by Loyalists, the impressment of free black seamen by galley commanders and fugitive slaves seeking freedom through service on naval galleys. Thus, while whites did all they could to avoid service on naval galleys Blacks found themselves doing this unappealing work. In this, as with promotion, pay and pensions, Blacks in the Royal Navy often found themselves disadvantaged due to their race

“Many Middle Passages: Forced Migration and the Making of the Modern World”

This anthology of essay provides a persuasive basis for widening our geographic Emma Christopher et. al. (eds.), “Many Middle Passages: Forced Migration and the Making of the Modern World,” Journal of the Early Republic 28:3 (Fall 2008): 474-477. lens when considering coerced voyages across the Atlantic. It offers as a useful framing tool to consider the social and cultural transformations of a variety of people coercively transported that middle passages were ‘‘the structuring link between expropriation in one geographic setting and exploitation in another.” Additionally, the editors consider a variety of ‘‘prisons’’ central to these middle passages, and claim that the history of labor transported across oceans is a ‘‘thesis-antithesis-synthesis’’ of terror, resistance, and cultural creativit

Jane Wilson McWilliams, “Annapolis, A City on the Severn: A History” in Maryland Historical Magazine, 107, no. 2 (Summer 2012), 234-35.

McWilliams frames Annapolis’ history as one in which disparate newcomers, including white retirees and striving Hispanic immigrants, have been drawn to the port by its “location, its culture, or its economic possibilities.” A strength of the book is its inclusion of short essays by other historians. Where the book is lacking is in not connecting Annapolis’ history to larger national and global issues

Charles R. Foy review of Simon Middleton and Billy G. Smith, “Class Matters: Early North America and the Atlantic World,” Journal of the Early Republic 27:2 (Summer 2009): 168-171.

Class Matters is the culmination of an ongoing effort by Smith and Middleton to make class, often disparaged during the past two decades as of little use, once again a relevant category of historical analysis. The editors seek to encourage scores of different approaches, recognizing that the variety of early modern contexts makes a unified approach inapt. Applying a multitude of approaches, each of the collection’s authors agrees that socioeconomic inequality remains critical to understanding the lives of all those who lived in the Atlantic world during the transition from the early modern to the modern era. The essays are transnational, ranging across the Atlantic from Glasgow to West Africa, the West Indies, North American ports, and interior regions occupied by Native Americans and tenant farmers. The essays apply class analysis to the lives of diverse groups of peoples: women, Native Americans, laves, laborers, the middle class, and the elite. The wide range of these writings reinforces the editors’ point that class analysis is applicable to all geographic regions and groups

‘Unkle Sommerset\u27s’ freedom: liberty in England for black sailors

With his 1772 decree in Somerset v. Steuart that slavery was ‘so odious that nothing can be suffered to support it [in England] but positive law’, Lord Mansfield altered the legal landscape regarding black rights in England. While earlier judicial decisions had implied that slaves who came to England were free, prior to the Somerset decision there was no judicial consensus on the issue. The Somerset decision did not decree that slavery was illegal in England. Yet many blacks believed it ‘emancipated’ any slave who reached the shores of England. This understanding, combined with the British military welcoming runaways into its ranks during the American Revolution, led to several thousand former slaves reaching England, a considerable number of whom were mariners. Although the Royal Navy was not isolated from the racism or harsh legal treatment of blacks, naval personnel often assisted ex-slaves to obtain freedom in England. The freedom black mariners found in England was fairly limited; they remained subject to re-enslavement, had limited legal protections over employment conditions and were often homeless and poor. Despite such conditions, life in England was a considerable improvement over enslavement in the Americas for many former slave mariners. Slave mariners on the sloop Lawrence illustrate the means black mariners took to obtain freedom, the Royal Navy\u27s role in ex-slave mariners becoming free and the limits of freedom in England

Charles R. Foy review of Simon Middleton and Billy G. Smith, “Class Matters: Early North America and the Atlantic World,” Journal of the Early Republic 27:2 (Summer 2009): 168-171.

Class Matters is the culmination of an ongoing effort by Smith and Middleton to make class, often disparaged during the past two decades as of little use, once again a relevant category of historical analysis. The editors seek to encourage scores of different approaches, recognizing that the variety of early modern contexts makes a unified approach inapt. Applying a multitude of approaches, each of the collection’s authors agrees that socioeconomic inequality remains critical to understanding the lives of all those who lived in the Atlantic world during the transition from the early modern to the modern era. The essays are transnational, ranging across the Atlantic from Glasgow to West Africa, the West Indies, North American ports, and interior regions occupied by Native Americans and tenant farmers. The essays apply class analysis to the lives of diverse groups of peoples: women, Native Americans, laves, laborers, the middle class, and the elite. The wide range of these writings reinforces the editors’ point that class analysis is applicable to all geographic regions and groups

Quantitative Flow Field Imaging about a Hydrophobic Sphere Impacting on a Free Surface

This fluid dynamics video shows the impact of a hydrophobic sphere impacting a water surface. The sphere has a mass ratio of m* = 1.15, a wetting angle of 110 degrees, a diameter of 9.5 mm, and impacts the surface with a Froude number of Fr = 9.2. The first sequence shows an impact of a sphere on the free surface illustrating the formation of the splash crown and air cavity. The cavity grows both in the axial and radial direction until it eventually collapses at a point roughly half of the distance from the free surface to the sphere, which is known as the pinch-off point. The second set of videos shows a sphere impacting the free surface under the same conditions using Particle Image Velocimetry (PIV) to quantify the flow field. A laser sheet illuminates the mid-plane of the sphere, and the fluid is seeded with particles whose motion is captured by a high-speed video camera. Velocity fields are then calculated from the images. The video sequences from left to right depict the radial velocity, the axial velocity, and the vorticity respectively in the flow field. The color bar on the far left indicates the magnitude of the velocity and vorticity. All videos were taken at 2610 fps and the PIV data was processed using a 16 x 16 window with a 50% overlap.Comment: American Physical Society Division of Fluid Dynamics 2008 Annual Meeting Replaced previous version because abstract had LaTex markup and was too long, missing periods on middle initial of first two name