Analytical expressions for optimum alignment modes of highly segmented mirrors

The major sources causing deterioration of optical quality in extremely large optical telescopes are misadjustments of the mirrors, deformations of monolithic mirrors, and misalignments of segments in segmented mirrors. For active optics corrections, all three errors, which can partially compensate each other, are measured simultaneously. It is therefore of interest to understand the similarities and differences between the three corresponding types of modes which describe these errors. The first two types are best represented by Zernike polynomials and elastic modes respectively, both of them being continuous and smooth functions. The segment misaligment modes, which are derived by singular value decomposition, are by their nature not smooth and in general discontinuous. However, for mirrors with a large number of segments, the lowest modes become effectively both smooth and continuous. This paper derives analytical expressions for these modes, using differential operators and their adjoints, for the limit case of infinitesimally small segments. For segmented mirrors with approximately 1000 segments, it is shown that these modes agree well with the corresponding lowest singular value decomposition modes. Furthermore, the analytical expressions reveal the nature of the segment misalignment modes and allow for a detailed comparison with the elastic modes of monolithic mirrors. Some mathematical features emerge as identical in the two cases.Comment: 24 pages, 13 figures, accepted for publication in Journal of Modern Optic

Gastric pseudoaneurysm in the setting of Loey’s Dietz Syndrome

Loey’s Dietz syndrome is a disorder of connective tissue caused by a mutation in the genes that encode transforming growth factor (TGF) beta receptor 1 and 2. It is an autosomal dominant disorder similar to Marfan’s syndrome but with a more aggressive clinical course. Patients with Loey’s-Dietz syndrome have progressive dilatation of the aortic root that can lead to aortic dissection and rupture. The location of non-aortic arterial aneurysms may be wide spread but often occur in the head and neck vessels.peer-reviewe

Laboratory experiments and models of diffusive emplacement of ground ice on Mars

Experiments demonstrate for the first time the deposition of subsurface ice directly from atmospheric water vapor under Mars surface conditions. Deposition occurs at pressures below the triple point of water and therefore in the absence of a bulk liquid phase. Significant quantities of ice are observed to deposit in porous medium interstices; the maximum filling fraction observed in our experiments is ~90%, but the evidence is consistent with ice density in pore spaces asymptotically approaching 100% filling. The micromorphology of the deposited ice reveals several noteworthy characteristics including preferential early deposition at grain contact points, complete pore filling between some grains, and captured atmospheric gas bubbles. The boundary between ice-bearing and ice-free soil, the “ice table,” is a sharp interface, consistent with theoretical investigations of subsurface ice dynamics. Changes of surface radiative properties are shown to affect ice table morphology through their modulation of the local temperature profile. Accumulation of ice is shown to reduce the diffusive flux and thus reduce the rate of further ice deposition. Numerical models of the experiments based on diffusion physics are able to reproduce experimental ice contents if the parameterization of growth rate reduction has expected contributions in addition to reduced porosity. Several phenomena related to the evolution of subsurface ice are discussed in light of these results, and interpretations are given for a range of potential observations being made by the Phoenix Scout Lander

IMPORT DEMAND FOR DISAGGREGATED FRESH FRUITS IN JAPAN

Using annual Japanese fresh fruit import data from 1971 to 1997, this study analyzes the import patterns of Japan's seven most popular fresh fruits by implementing and testing a general differential dmand system that nests four alternative import demand specifications. When tested against the general system using the five-good case (bananas, grapefutis, oranges, and lemons and aggregating pineapples, berries, and grapes), the analysis rejects the Almost Ideal Demand System and National Bureau of Research specifications but does not reject Rotterdam and Central Bureau of Statistics models. When estimated using the six-good case (bananas, grapefuits, oranges, lemons, and pineapples and aggregating berries and grapes), the analysis rejects all specifications except the Rotterdam model.Almost Ideal Demand System, consumer demand, fruit, import demand, Japan, Rotterdam, Demand and Price Analysis, C3, F1, Q0,

Import Demand for Disaggregated Fresh Fruits in Japan

Using annual Japanese fresh fruit import data from 1971-1997, this study analyzes the import patterns of Japan's seven most popular fresh fruits by implementing and testing a general differential demand system that nests four alternative import demand specifications. When tested against the general system using the five-good case (bananas, grapefruits, oranges, and lemons and aggregating pineapples, berries, and grapes), the analysis rejects the AIDS and NBR specifications, but does not reject Rotterdam and CBS. When estimated using the six-good case (bananas, grapefruits, oranges, lemons, pineapples, and aggregating berries and grapes), the analysis rejects all specifications except the Rotterdam model.Almost Ideal Demand System, consumer demand, fruit, import demand, Japan, Rotterdam model, Demand and Price Analysis, International Relations/Trade,

Welfare Implications of the Byrd Amendment

International Relations/Trade,

Dynamic interaction between tectonic plates, subducting slabs, and the mantle

Mantle convection models have been formulated to investigate the relation between plate kinematics and mantle dynamics. The cylindrical geometry models incorporate mobile, faulted plate margins, a phase change at 670 km depth, non-Newtonian rheology, and tectonic plates. Models with a variety of parameters indicate that a relatively stationary trench is more likely to be associated with a subducted slab that penetrates into the lower mantle with a steep dip angle. However, a subducted slab that is deflected above the 670-km phase change with a shallow dip is more likely to be associated with a margin that has undergone rapid retrograde trench migration. This relation between slab morphology and plate kinematics is consistent with seismic tomography and plate reconstruction of western Pacific subduction zones. The efficiency of slab penetration through the 670-km phase change is controlled by both the buoyancy of the subducting plate and the mobility of the overriding plate. While older subducting plates have a greater propensity for slab penetration, trench mobility reduces the propensity for slab penetration. Smaller overriding plates have a greater mobility. When subducted slabs approach the bottom thermal boundary layer, hot fluid is pushed aside, and plumes form on the periphery of slab accumulations. There are sharp temperature contrasts between the subducted slab and the thermal boundary layer at the core mantle boundary (CMB). Old subducted slabs and a thermal boundary layer lead to large-scale lateral structure near the CMB

Multiple Glaciation in the McMurdo Sound, Antarctica.

Submitted to the U.S. National Committee for the IGY, National Academy of Sciences, in partial fulfillment of IGY Project Number 4.10 - NSF Grant No. Y/4.10/285.At least four major Quaternary glaciations, each successively less extensive than the former, are recorded in the McMurdo Sound region of Antarctica. Deposits of the earliest recognized glacial advance occur high on ridges and flat areas. The deposits are 2,000 feet above the valley floor, are badly weathered, and have little or no morainal form. Ice of this glaciation filled all the valleys and must have filled McMurdo Sound to an elevation of 2,000 feet. Deposits of the next two succeeding glaciations are distributed around the Sound as well-preserved but considerably subdued moraines of both outlet and alpine glaciers. During the earlier of these two glaciations, alpine glaciers reached the expanded Koettlitz and Ferrar outlet glaciers. Outlet glaciers filled the southern part of McMurdo Sound to an elevation of about 1,000 feet. During the latter of these two advances many alpine glaciers did not reach the outlet glaciers. The latest major glaciation is represented by well-preserved ice-cored moraines. Number and position of deltas in drained glacier-ice-blocked lakes suggest possible three stillstands or minor advances during this glaciation. Radiocarbon dating of algae in drained ponds indicates a minimum age of 6,000 years for this glaciation.National Science Foundation Grant No. Y/4.10/285