A spread spectrum technique for the study of outdoor noise propagation

This paper describes field measurements to assess innovative correlation techniques for the study of meteorological and topographical effects on sound propagation. To take advantage of the properties of coded signals in a time-varying system, the correlation signal is produced by the modulation of a code sequence onto an acoustic carrier. An established method of increasing signal-to-noise ratio is to use correlation techniques with maximum length sequences. However, this standard method is restricted in its use outdoors because of the time-variant nature of the atmosphere. On the other hand, the correlation properties of a directly carrier-modulated code sequence modulation signal may be exploited in a time-varying environment. An experiment is described in which the correlation properties of the spread spectrum signal are demonstrated and are used to calculate accurate times of flight that compare well with sonic anemometer measurements of speed of sound. The results illustrate that an acoustical spread spectrum system can provide significantly improved ways of measuring sound propagation outdoors.     

MeV proton generation and efficiency from an intense laser irradiated foil

The proton energy distribution generated from the interaction of an intense (Iλ² ≈ 10²⁰ W/cm² μm²) short-pulse (100 fs) laser with a thin foil is investigated using energy resolved measurements and 2D collisional PIC-hybrid simulations. The measured absolute proton spectrum is well matched by a 1.7 MeV exponential function for energies <11 MeV. The proton conversion efficiency from hot electrons ≈6%. Simulations predict a strong radial dependence on the maximum proton energy and on the radial extent of 12 Å hydrocarbon depletion region. C and O ions in the hydrocarbon layer gain significant energies, limiting the efficiency to the protons. The efficiency scaling for ion mixtures is derived using a simple model, and is shown to strongly depend on the cooling rate of the hot electrons. Simulations using hydrogen-rich, layered targets predict much higher efficiencies.     

Photochemical and assisted cleavages of halo-9-thiabicyclononanes

A new, high-yield photodehydroiodination of $\text{8}$ is contrasted with base and silver salt treatments of thiabicyclic halides, which mainly undergo replacements by substitution or elimination-addition.     

Preparations,structures and thermal decomposition of some bis(pentafluorobenzoato)dioxouranium(VI) complexes

Reaction Of UO₂(O₂CCH₃)₂ with pentafluorobenzoic acid yields UO₂(O₂CC₆F₅)₂, which has been converted into the solvated complexes UO₂(O₂CC₆F₅)₂L₂·S [L₂ = 2,2′-bipyridyl (bpy), S = 0.33 (PhH) or 0.07 (t-BuOH); L = Ph₃PO, S = t-BuOH; L = Ph₃AsO, S = 0.40 (t-BuOH)] and the solvent free UO₂(O₂CC₆F₅)₂L₂ [L₂ = bpy; L = Ph₃PO]. The crystal structure of UO₂(O₂CC₆F₅)₂bpy (orthorhombic, space group P2₁2₁2₁; a = 18.45(2), b = 18.94(2), c = 7.069(8) Å, Z = 4] reveals distorted hexagonal bipyramidal stereochemistry with a trans UO₂ group, chelating pentafluorobenzoate ligands, and chelating 2,2′-bipyridyl, which is significantly displaced from the hexagonal plane. The structure of UO₂(O₂CC₆F₅)₂(OPPh₃)₂·t-BuOH [rhombohedral, space group R3; a = 21.51(3) Å, α = 117.28(5)°, Z = 3] shows trans UO₂, pseudo trans Ph₃PO ligands, and one unidentate and one disordered chelating pentafluorobenzoate ligand, whilst t-BuOH could not be located because it is highly disordered. Relationships between ν (CO₂) frequencies and the carboxylate coordination are discussed, and UO₂(O₂CC₆F₅)₂(OAsPh₃)₂.0.40 (t-BuOH) is considered to have stereochemistry similar to that of the phosphine oxide complex. The complexes undergo decarboxylation in dimethyl sulphoxide yielding pentafluorobenzene and carbonatodioxouranium(VI) species not UO₂(C₆F₅)₂ derivatives.     

Opto-acoustic spectroscopy with a visible CW dye laser

The first use of a tunable visible laser in conjunction with an opto-acoustic cell is described. By using a longitudinal resonance of the gas cell NO₂ can be detected around 10 p.p.b., the same order of detectivity as in the infrared. The use of the technique for studying photodissociation in the visible and u.v. is discussed.     

The crystal and molecular structure of dioxo bis (2,2,6,6 - tetramethylheptane -3,5 dionato)methanol uranium (VI)

UO₂(thd)₂ CH₃OH (thd = tetramethylheptane-3,5-dione) is monoclinic, with a = 10.602(11), b = 22.883(20), c = 12.054(11) Å and β = 105.90(3)°, Z = 4 and space group P2₁/c. The structure, which is molecular, was solved by conventional Patterson and Fourier techniques with 3173 independent (hkl) reflexions collected with MoKα radiation (λ = 0.7107 Å), and refined to R = σ(|Fo|-|Fc|)/σ|Fo| = 0.093. The uranium coordination polyhedron is a pentagonal bipyramid, with UO (carbonyl) distances between 2.25 and 2.37 Å and a longer UO (methanol) distance of 2.50 Å. The uranyl group is linear (uranyl angle 179.3(8)°). The pentagon oxygen atoms and uranium do not form a planar system, as there are deviations of up to 0.17 Å from the mean plane. If the methanol oxygen atom O(7) is excluded from the plane calculation, the remaining atoms are more nearly planar. The four carbonyl oxygens are coplanar, with uranium 0.08 Å from their plane. The methanol oxygen is 0.28(4) Å from this second plane.The two (thd) molecules, excluding methyl carbons, are planar and are inclined at 43.6° to each other in a boat form and at 29.1 and 14.5° to the pentagonal plane. The methanol CO bond is inclined at 133° to the UO bond, confirming the ligand is the neutral CH₃OH molecule, and not CHO^?₃.     

Micellar hydrolysis of hydroxamic acids. Michaelis-menten kinetics

Rates of reaction for the alkaline hydrolysis of various hydroxamic acids in the presence of cetyltrimethylammonium bromide have been determined. Empirical reaction orders of zero, one-half, and one were found for the hydroxamic acids depending upon reaction conditions and substrate structure. N -methylhydroxamic acids exhibited only first-order kinetics. The results are consistent with the Michaelis-Menten rate equation.     

Ultrasonic study of spin-splitting of landau levels in bismuth

A study has been made, using ultrasonic quantum oscillations, of the spin-splitting factor of electrons and of holes in bismuth with the magnetic field direction varied in the XZ plane. The results are consistent with the general picture of spin-splitting in bismuth.