Optical control of solar sails using distributed reflectivity

The dynamics of solar sails with a variable surface reflectivity distribution are investigated. When changing the reflectivity across the sail film, which can be achieved using electro-chromic coatings, the solar radiation pressure forces and torques across the sail film can be controlled without changing the attitude of the spacecraft relative to the Sun and without using mechanical systems. The paper presents two approaches. First, a continuous reflectivity distribution is presented to control the sail attitude under the influence of, for example, gravity gradient torques in Earth orbit. The second approach assumes discrete on/o reflectivity regions across the surface. Both concepts of `optical reconfiguration' of solar sails enable a more flexible steering of the spacecraft and minimize actuation effort

History of the Introduction and Culture of Cuba Tobacco in Florida

An address delivered before the Florida Fruit Growers Association, at Jacksonville, January 20, 1875, by Ex-Chief Justice Charles H. DuPont of the Supreme Court of Florida, and taken from the Proceedings of that meeting. It is now believed that in the history of a people a record of the lives of the people themselves is of greater import than that of those in authority. The facts regarding early tobacco growing in Florida are now generally unknown, but of greater importance is the record of Judge Dupont’s observations extending over a period of forty years on “the influence of tobacco culture upon the moral and intellectual status of the population” of Gadsden County

Orbit targeting specialist function: Level C formulation requirements

A definition of the level C requirements for onboard maneuver targeting software is provided. Included are revisions of the level C software requirements delineated in JSC IN 78-FM-27, Proximity Operations Software; Level C Requirements, dated May 1978. The software supports the terminal phase midcourse (TPM) maneuver, braking and close-in operations as well as supporting computation of the rendezvous corrective combination maneuver (NCC), and the terminal phase initiation (TPI). Specific formulation is contained here for the orbit targeting specialist function including the processing logic, linkage, and data base definitions for all modules. The crew interface with the software is through the keyboard and the ORBIT-TGT display

Hydrogen production by sorption-enhanced steam reforming of glycerol

Catalytic steam reforming of glycerol for H(2) production has been evaluated experimentally in a continuous flow fixed-bed reactor. The experiments were carried out under atmospheric pressure within a temperature range of 400-700 degrees C. A commercial Ni-based catalyst and a dolomite sorbent were used for the steam reforming reactions and in situ CO(2) removal. The product gases were measured by on-line gas analysers. The results show that H(2) productivity is greatly increased with increasing temperature and the formation of methane by-product becomes negligible above 500 degrees C. The results suggest an optimal temperature of approximately 500 degrees C for the glycerol steam reforming with in situ CO(2) removal using calcined dolomite as the sorbent, at which the CO(2) breakthrough time is longest and the H(2) purity is highest. The shrinking core model and the 1D-diffusion model describe well the CO(2) removal under the conditions of this work

Thirty thousand years of vegetation development and climate change in Angola (Ocean Drilling Program Site 1078)

ODP Site 1078 situated under the coast of Angola provides the first record of the vegetation history for Angola. The upper 11 m of the core covers the past 30 thousand years, which has been analysed palynologically in decadal to centennial resolution. Alkenone sea surface temperature estimates were analysed in centennial resolution. We studied sea surface temperatures and vegetation development during full glacial, deglacial, and interglacial conditions. During the glacial the vegetation in Angola was very open consisting of grass and heath lands, deserts and semi-deserts, which suggests a cool and dry climate. A change to warmer and more humid conditions is indicated by forest expansion starting in step with the earliest temperature rise in Antarctica, 22 thousand years ago. We infer that around the period of Heinrich Event 1, a northward excursion of the Angola Benguela Front and the Congo Air Boundary resulted in cool sea surface temperatures but rain forest remained present in the northern lowlands of Angola. Rain forest and dry forest area increase 15 thousand years ago. During the Holocene, dry forests and Miombo woodlands expanded. Also in Angola globally recognised climate changes at 8 thousand and 4 thousand years ago had an impact on the vegetation. During the past 2 thousand years, savannah vegetation became dominant

Corrigendum to "Thirty thousand years of vegetation development and climate change in Angola (Ocean Drilling Program Site 1078)" published in Clim. Past, 4, 107–124, 2008

No abstract available

Cluster algebras of type A2(1)A_2^{(1)}

In this paper we study cluster algebras \myAA of type $A_2^{(1)}$. We solve the recurrence relations among the cluster variables (which form a T--system of type $A_2^{(1)}$). We solve the recurrence relations among the coefficients of \myAA (which form a Y--system of type $A_2^{(1)}$). In \myAA there is a natural notion of positivity. We find linear bases \BB of \myAA such that positive linear combinations of elements of \BB coincide with the cone of positive elements. We call these bases \emph{atomic bases} of \myAA. These are the analogue of the "canonical bases" found by Sherman and Zelevinsky in type $A_{1}^{(1)}$. Every atomic basis consists of cluster monomials together with extra elements. We provide explicit expressions for the elements of such bases in every cluster. We prove that the elements of \BB are parameterized by \ZZ^3 via their $\mathbf{g}$--vectors in every cluster. We prove that the denominator vector map in every acyclic seed of \myAA restricts to a bijection between \BB and \ZZ^3. In particular this gives an explicit algorithm to determine the "virtual" canonical decomposition of every element of the root lattice of type $A_2^{(1)}$. We find explicit recurrence relations to express every element of \myAA as linear combinations of elements of \BB.Comment: Latex, 40 pages; Published online in Algebras and Representation Theory, springer, 201