Search for massive photon pair production at the CERN intersecting storage rings

A search for massive photon pair production at \(\sqrt s = 63 GeV\) has been carried out on the data sample previously employed for the electron pair production study. Positive evidence is reported form _γγ>6GeV, with a production cross-section similar to Drell-Yan electron pairs. The ratio γγ/π⁰π⁰ was measured to be ～10^?3 for ap _T of each γ or γ or π⁰ above 3 GeV/c.     

Porphyrin Clathrates. Crystal Structures of Two Unexpected Products Obtained by Solvothermal Reactions of Pt-tetra(4-carboxyphenyl)porphyrin with Copper Acetate

The X-ray crystal structure of IX, perchlorate salt of R-(–-2-ethyl-N-benzyl-4,7,19,13-tetraoxa-8,9-benzo-1-azacyclopentadec-8-ene has been determined. In the molecule, the protonated nitrogen atom participates in two N-HO hydrogen bonds. The unusually high proton affinity of aza crown ether leads to the formation of diastreomer instead of complex formation with chiral R-(+)-1-phenyl ethyl ammonium perchlorate and S-(–)-1-phenyl ethyl ammonium perchlorate. The complex ability of host ethers was evaluated in terms of structural modification.     

Green photoluminescence from platinum(II) complexes bearing silylacetylide ligands

The synthesis, structural characterization, photoluminescence properties, and density functional theory analysis of three Pt(II) diimine complexes, Pt(dbbpy)(C triple bond CR)2 [dbbpy = 4,4'-di(tert-butyl-2,2'-bipyridine; R = -SiMe3, -CC-SiMe3, or -t-Bu], are presented. The Pt(dbbpy)(C triple bond C-tBu)2 complex serves as a carbon-based ligand structure for which the photophysical properties of the two silicon-bearing complexes are compared in dichloromethane. Pt(dbbpy)(C triple bond C-SiMe3)2 and Pt(dbbpy)(C triple bond C-C triple bond C-SiMe3)2 display visible absorptions with strong green emission (lambda(emmax) = 526 and 524 nm, respectively) while Pt(dbbpy)(C triple bond C-t-Bu)2 displays efficient, long-lived yellow emission (lambda(emmax) = 557 nm). Direct side by side comparisons of Pt(dbbpy)(C triple bond C-SiMe3)2 and Pt(dbbpy)(C triple bond C-t-Bu)2 suggest that the difference in excited state energy results from the relative sigma-donor strength of the acetylide ligands.     

Evaluation of MNDO calculated proton affinities

A large set of charged species arising mainly from protonation or deprotonation of hydrocarbons, alcohols, ethers, carboxylic acids, amines, imines, and nitriles has been studied by means of the semiempirical self-consistent-field (SCF ) molecular orbital (MO ) MNDO method. From the calculated heats of formation of such charged species and those of neutral molecules, MNDO -estimated proton affinities have been obtained and the results compared with experimental gas-phase proton affinities. If the small size anions and acetylides, for which the method predicts heats of formation too large, are ruled out, the mean absolute error in calculated proton affinities is ca. 7 kcal/mol for hydrocarbons (22 acid-base pairs) and ca. 8 kcal/mol for oxygen-containing compounds (25 acid-base pairs). For nitrogen-containing molecules it is necessary to discard, in addition, the values corresponding to the protonation of alkylamines and imines in order to achieve a reasonable mean absolute error of 7–8 kcal/mol.     

Structural, spectral and thermal studies of N-2-(4-picolyl)- and N-2-(6-picolyl)-N′-(2-chlorophenyl)thioureas and N-2-(6-picolyl)-N′-(2-bromophenyl)thiourea

N-2-(4-picolyl)-N′-2-chlorophenylthiourea, 4PicTu2Cl, monoclinic, P2₁/c, a=10.068(5), b=11.715(2), β=96.88(4)°, and Z=4; N-2-(6-picolyl)-N′-2-chlorophenylthiourea, 6PicTu2Cl, triclinic, P-1, a=7.4250(8), b=7.5690(16), c=12.664(3) Å, =105.706(17), β=103.181(13), γ=90.063(13)°, V=665.6(2) ų and Z=2 and N-2-(6-picolyl)-N′-2-bromophenylthiourea, 6PicTu2Br, triclinic, P-1, a=7.512(4), b=7.535(6), c=12.575(4) Å, a=103.14(3), β=105.67(3), γ=90.28(4)°, V=665.7(2) ų and Z=2. The intramolecular hydrogen bonding between N′H and the pyridine nitrogen and intermolecular hydrogen bonding involving the thione sulfur and the NH hydrogen, as well as the planarity of the molecules, are affected by the position of the methyl substituent on the pyridine ring. The enthalpies of fusion and melting points of these thioureas are also affected. ¹H NMR studies in CDCl₃ show the NH′ hydrogen resonance considerably downfield from other resonances in their spectra.     

Limiting behavior of asymptotically flat gravitational fields

Couch and Torrence suggest that the vacuum Einstein equations admit a larger class of asymptotically flat solutions than those exhibiting the peeling property. Starting with the assumption that , (d/dr) and (/x ^A ) , wherex ^A (A = 2, 3) are angular coordinates, they show that , where ₁ 2 and ₁<₀; , where ₂ 1 and ₁< ₁; and ₄ and ₃ peel as they would under the stronger peeling conditions. The Winicour-Tamburino energy-momentun and angular momentum integrals for these solutions, in general, diverge. In fact, since Couch and Torrence determine only the radial dependence of the solution, it is not clear that the solutions are well defined. We find that the stronger assumption , (d/dr) , and (/x ^A ) does result in well-defined solutions for which both the energy-momentum and angular momentum intergrals are not only finite but result in the same expressions as are obtained for peeling space-times. This assumption appears to be the minimal assumption that is necessary for investigating outgoing radiation at null infinity.In part based on a dissertation by Stephanie Novak and submitted to Syracuse University in partial fulfillment of the requirement for the Ph.D. degree.     

Manganese(I)-Catalyzed Regioselective C−H Allenylation: Direct Access to 2-Allenylindoles

A Mn^I-catalyzed regioselective C−H allenylation is reported that allows a broad range of 2-allenylindoles to be synthesized regioselectively on a gram scale under simple conditions. Notably, a highly efficient chirality transfer was observed (up to 93 % ee) in this transformation. This procedure was further found to allow, for the first time, the direct preparation of ketones by Mn^I-catalyzed C−H activation. Mechanistic investigations revealed that the precoordination of the oxygen atom to the manganese center as well as the congested tertiary carbon atom in the propargylic carbonates play a crucial role.     

An amphibious vibration-driven microrobot with a piezoelectric actuator

This article concerns microrobots for solid and liquid environments. A short overview of microrobotics, suitable actuators and energy systems is given. The principles of terrestrial and aquatic locomotion are discussed and illustrated with examples from the literature on robotics. The state of the art with a focus on piezo microrobots for solid and liquid environments is presented. Furthermore, we report an amphibious prototype, which can move on flat solid ground and on the free surface of water. The design, characteristic parameters and experiments on locomotion are described. The robot is characterized by a light and simple design and can perform twodimensional locomotion in different environments with a speed up to 30 mm/s. An analytical model to predict the maximum carrying capacity of the robot on water is solved numerically.     

Facile synthesis of potassium tetrathiooxalate – The “true” monomer for the preparation of electron-conductive poly(nickel-ethylenetetrathiolate)

Herein, aiming at optimization of the polymerization process leading to a family of hole- and electron-conducting 1,1,2,2-ethenetetrathiolate-based polymers, such as poly(nickel-1,1,2,2-ethenetetrathiolate), poly[K_x(Ni-ett)], we investigated transformations of the monomer precursor 1,3,4,6-tetrathiapentalene-2,5-dione (TPD) occurring under polymerization conditions. We found that only one ring of TPD opens upon its reaction with potassium methoxide under inert conditions at room temperature which leads to the formation of potassium 2-oxo-1,3-dithiol-4,5-dithiolate (K₂[3]). Heating of K₂[3] under reflux in methanol solution under inert conditions opens the second ring, however the resulting product is not potassium ethenetetrathiolate (K₄[2]), the product of an exhaustive methanolysis of TPD, but potassium tetrathiooxalate (K₂[4]), the product of the decarbonylation of K₂[3]. Preliminary experiments reveal that the involvement of K₂[4] in the polymerization process is beneficial for reproducible formation of high quality 1,1,2,2-ethenetetrathiolate-based polymers suitable for thermoelectric applications.