Eye-safe compact scanning LIDAR technology

A 1.5-μm eye-safe, 3-D scanning, and compact Mie LIght Detection and Ranging (LIDAR) is presented. The transmitter of the LIDAR is based on a KTA optical parameter oscillator (OPO) resonator. For detecting return signals, an InGaAs APD is used. The all solid-state OPO laser transmitter has the feature of small volume and lightweight, which allows a 165-lb compact eye-safe scanning LIDAR to be constructed. A system simulation using our own model was conducted to direct the system development. A method to solve the problem with small active area APD detectors was developed and described. The preliminary field-test measurement results indicated that the LIDAR has the capability to detect aerosols and clouds in lower atmospheres up to three dimensions.     

Outflow refreshment angiography: A bright blood, bright static tissue technique

A new “bright blood” strategy, outflow refreshment imaging, is introduced in which a number of overlapping slices are excited in rapid succession. Flowing spins that refresh each overlapped slice portion contribute a bright signal. Additionally, static tissue in each non-overlapped slice portion also yields a bright signal. However, the flow/static contrast is comparable to that produced in inflow refreshment images, and angiograms can be generated by conventional maximum intensity projection processing. The dual ability to visualize angiograms and static tissue images is a major benefit of the strategy. Computer simulations of flow sensitivities and in vivo results are presented which compare the outflow and inflow refreshment imaging strategies.     

Inhibition of the reduction of Cr(VI) at the magnetite–water interface by calcium carbonate coatings

The effect of calcium carbonate coatings on the reduction of aqueous chromate on the magnetite(1 1 1) surface has been investigated using a combination of synchrotron based X-ray photoemission spectroscopy (PES) and X-ray absorption near edge structure (XANES) spectroscopy, along with laboratory-based powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). CaCO₃ coatings (dominantly calcite with minor quantities of aragonite and vaterite) of thicknesses ranging from 10 Å to 20 m were grown on magnetite(1 1 1) surfaces by exposure to supersaturated aqueous solutions followed by evaporation of the solution—a process that mimics pore-water evaporation in vadose zones leading to the formation of caliche and calcium carbonate coatings on mineral grains. Coating thicknesses were determined from attenuation of the Fe 2p photoemission signal by the carbonate coating. For coatings less than 15 Å thick, Cr 2p photoemission and Cr L_II, L_III-edge XANES spectra show that chromate is reduced by the underlying magnetite surface; however, as the minimum coating thickness increases beyond 15 Å, the magnetite surface becomes passivated and further chromate reduction ceases. Our findings suggest that carbonate coatings on natural magnetite grains can significantly reduce or eliminate their ability to reduce Cr(VI), which is a toxic and highly mobile environmental contaminant.     

On the evolution of islands

Letn cells be arranged in a ring, or alternatively, in a row. Initially, all cells are unmarked. Sequentially, one of the unmarked cells is chosen at random and marked until, aftern steps, each cell is marked. After thekth cell has been marked the configuration of marked cells defines some number of islands: maximal sets of adjacent marked cells. Let ξ _k denote the random number of islands afterk cells have been marked. We give explicit expressions for moments of products of ξ _k ’s and for moments of products of 1/ξ _k ’s. These are used in a companion paper to prove that if a random graph on the natural number is made by drawing an edge betweeni≧1 andj>i with probabilityλ/j, then the graph is almost surely connected ifλ>1/4 and almost surely disconnected ifλ≦1/4.     

Synthesis and structure of fluorotricyanomethane

Fluorotricyanomethane is prepared from potassium tricyanomethanide and perchlorylfluoride. The crystal structure of this compound (orthorhombic, space group P2₁2₁2₁, with a=6.270, b=6.734, c=11.776 Å) has been determined by X-ray analysis. The results are discussed in relation to those of (NC)₃C? X (X=? CH₃, ? Cl, ? Br or ? CN).     

Dirhodium(II)-catalyzed carbonyl ylide generation. Stereoelectronic control in dioxolane formation

The combination of ethyl diazoacetate with aryl aldehydes in the presence of copper(I) or rhodium(II) catalysts results in the formation of 1,3-dioxolane products in moderate to good yields. These reactions occur through a pathway that involves ylide intermediates. Catalyst-dependent diastereocontrol is observed and suggests that metal-associated ylides are involved in the product-determining step. The influence of aryl aldehyde substituents has been determined. Current address. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 961–965, May, 1998.