Vertical laser beam propagation through the troposphere

The characteristics of the earth's atmosphere and its effects upon laser beams was investigated in a series of balloon borne, optical propagation experiments. These experiments were designed to simulate the space to ground laser link. An experiment to determine the amplitude fluctuation, commonly called scintillation, caused by the atmosphere was described

Cp,Cp*-Dimethyltantalum Triflate

(η^5-Cyclopentadienyl)(dimethyl)(η^5-pentamethylcyclopentadienyl)tantalum trifluoromethylsulfonate, [Ta(C_5H_5)(C_(10)H_(15)CH_3)_2]CF_3S0_3, M_r = 560.41, orthorhombic, Pbca, ɑ = 14.230 (4), b = 19.283 (4), c = 14.628 (4) Å, v = 4014 (2) Å^3, z = 8, D_x = 1.855 g cm^(-3), λ(Mo Kɑ)= 0.71073 Å, μ = 55.3 cm^(-1), F(000) = 2192, room temperature, R(F) = 0.038 for 1882 reflections with F_o^2 > 3σ(F_o^2). The Ta-C(methyl)Å distances are virtually equal at 2.171 (12) Å, with a C-Ta-C angle of 95.8 (5)º. The coordination of the two η^5 ligands is normal; the Cp(centroid}-Ta-Cp^*(centroid) angle is 136.2°. Intermolecular contacts are all approximately at van der Waals distances, with indications of CH···O hydrogen bonding between methyl groups and the triflate anion

On the appearance of hyperons in neutron stars

By employing a recently constructed hyperon-nucleon potential the equation of state of \beta-equilibrated and charge neutral nucleonic matter is calculated. The hyperon-nucleon potential is a low-momentum potential which is obtained within a renormalization group framework. Based on the Hartree-Fock approximation at zero temperature the densities at which hyperons appear in neutron stars are estimated. For several different bare hyperon-nucleon potentials and a wide range of nuclear matter parameters it is found that hyperons in neutron stars are always present. These findings have profound consequences for the mass and radius of neutron stars.Comment: 12 pages, 12 figures, RevTeX4; summary and conclusions are strengthened, to appear in PR

Tip Anchor Flap in Decubital Surgery

Anchoring a flap remains a key procedure in decubital surgery because a flap needs to be stable against shearing forces. This allows an early mobilization and undisturbed primary wound healing. This study evaluated a uniform group of eight paraplegic patients with sacral decubital ulcers and covered the lesions using gluteal rotation flaps with a deepithelialized tip to anchor the flap subcutaneously on the contralateral ischial tuber. Initial wound healing and recurrence after one year were evaluated. All but one flap showed uneventful wound healing, and all the flaps presented without any signs of recurrence or instability. The authors suggest that sufficient anchoring using a deepithelialized part of the flap helps to integrate and stabilize sacral rotation flap

The monopotassium salt of the ligand of a Ziegler–Natta catalyst

The anion of dipotassium (tert-butylamino)-dimethyl(tetramethylcyclopentadienyl)silanediide can coordinate to transition metals to form precursors for single-component Ziegler-Natta polymerization catalysts. The related monoanion derivative potassium (tert-butylamino )dimethyl( tetramethyl-cyclopentadienyl) silanide tetrahydrofuran solvate has been isolated as the first crystalline salt of this important ligand family. The tetramethylcyclopentadienyl group in the crystal has a potassium ion on each face, 2.8 Å from the center of the five-membered ring; each K atom is bonded to two rings and one tetrahydrofuran solvent molecule

Structure of Hydroxo(methyl)bis(η^5-pentamethylcyclopentadienyl)tantalum(V) Hydroxotris(pentafluorophenyl)borate

[Ta(C_(10)H_(15))i(OH)(CH_3)][B(OH)(C_6F_5)_3], M_r = 1001.63, monoclinic, P2_1/n, ɑ = 12.217 (2), b = 16.848 (6), c = 18.834 (3) Å, β = 100.37 (2)°, V = 3813.l (15) Å^3, Z = 4, D_x = 1.75 g cm^(-3), λ{Mo Kɑ) = 0.71073 Å, μ = 29.52 cm^(-1), F(000) = 1972, room temperature, R = 0.031 for 3534 reflections with F_o^2 > 3σ(F_o^2). The Ta cation has the expected geometry, with Ta-C and Ta-O distances 2.211 (6) and 1.865 (5) Å, respectively. The anion has not been characterized previously; its geometry is irregular with tetrahedral angles at boron ranging from 103.6 (6) to 113.8 (6)º, and systematic angular distortions in the C_6F_5 rings

Analysis of electron-positron momentum spectra of metallic alloys as supported by first-principles calculations

Electron-positron momentum distributions measured by the coincidence Doppler broadening method can be used in the chemical analysis of the annihilation environment, typically a vacancy-impurity complex in a solid. In the present work, we study possibilities for a quantitative analysis, i.e., for distinguishing the average numbers of different atomic species around the defect. First-principles electronic structure calculations self-consistently determining electron and positron densities and ion positions are performed for vacancy-solute complexes in Al-Cu, Al-Mg-Cu, and Al-Mg-Cu-Ag alloys. The ensuing simulated coincidence Doppler broadening spectra are compared with measured ones for defect identification. A linear fitting procedure, which uses the spectra for positrons trapped at vacancies in pure constituent metals as components, has previously been employed to find the relative percentages of different atomic species around the vacancy [A. Somoza et al. Phys. Rev. B 65, 094107 (2002)]. We test the reliability of the procedure by the help of first-principles results for vacancy-solute complexes and vacancies in constituent metals.Comment: Submitted to Physical Review B on September 19 2006. Revised version submitted on November 8 2006. Published on February 14 200

Structures of chlorohydroxobis(pentamethylcyclopentadienyl)tantalum(V) trifluoromethanesulfonate (triflate) and dihydroxobis(pentamethylcyclopentadienyl)tantalum(V) triflate

[Ta(C_(10)H_(15))2(C1)(OH)][CF_3SO_3] (I), Mr = 652.94, monoclinic, P2_1/n, a = 9.965(7), b = 18.796 (5), c = 13.269 (3)Å, β = 94.02 (3)°, V = 2479-2 (19)Å^3, Z = 4, D_x = 1.75 g cm^(-3), λ(Mo Kce) = 0.71073 Å, µ = 46 cm^(-1), F(000) = 1288, room temperature, R = 0.107 for 3702 reflections with F_o^2 > 0 [R=0.053 for 2094 reflections with F_o^2 > 3σ(F_o^2)]. [Ta(C_(10)H_(15))_2(OH)_2][CF_3SO_3] (II), M_r = 634.49, triclinic, P1, a = 10⋅052 (2), b = 10⋅111 (2), c = 12⋅739(2) Å, ɑ = 71⋅38(2), β = 78⋅21 (1), y = 77⋅40 (2)°, V = 1184⋅7 (4)Å^3, Z = 2, D_x = 1⋅78 g cm^(-3), λ(Mo Kɑ) = 0⋅71073 Å, µ = 47 cm^(-1) F(000) = 628, room temperature, R = 0⋅032 for 4046 reflections with Fo g > 0 [R = 0⋅026 for 3664 reflections with F_o^2 > 3σ(F_o^2)]. Severe disorder of the triflate anion in (I) led to a less satisfactory structure, but cations in both compounds are well defined, with normal Ta─Cp^* geometry. Ta─C1 2⋅343 (4), Ta─O 1⋅853 (8)Å and C1─Ta─O 96⋅4 (3)° in (I); Ta─O 1⋅907(6)A and O─Ta─O 100⋅4(2)° in (II). Tantalum-bound OH groups are hydrogen bonded to triflate O atoms

Rule Out (R/O) Intracranial Aneurysm

When imaging patients for intracranial aneurysm, the goals are: (1) to assess the contour of the intracranial arteries, particularly in he regions of the ACOM (anterior communicating artery), PCOM (posterior communicating artery), ICA (internal carotid artery) bifurcation, MCA (middle cerebral artery) trifurcation, basilar tip, and PICA (posterior inferior cerebellar artery); (2) to assess the anatomy of the Circle of Willis and direction of flow, and; (3) to determine if there is evidence of a recent subarachnoid bleed. This unit describes a that can be used for standard imaging of aneurysm in stable patients. An is described for situations when there is concern for vasospasm and infarction.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/145398/1/cpmia0102.pd

Cerebral Infarct/Intracranial Cerebrovascular Disease

Imaging goals for intracranial cerebral vascular disease are (1) to assess the degree of parenchymal injury and identify intraparenchymal hemorrhage; (2) to determine if there are areas of altered perfusion that may be at risk for future injury; and (3) to assess the intracranial arteries (patency as well as direction of flow). This unit describes a that can be used to evaluate stable patients with acute, subacute, or chronic cerebrovascular symptoms. An is also given for cases of hyperacute strokes or cerebrovascular symptoms in an unstable patient.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/145276/1/cpmia0101.pd