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Dental administrators, it is suggested, must examine their internal organizational operations and begin to refine their management techniques in order to adhere to current resource limits. Basic requirements of a management system allowing dental schools to increase operating efficiency are outlined. (Author/MLW)

The monomeric iron(II) amido derivatives are prepared and analyzed in order to determine the effects of geometric changes on their unusual magnetic properties. The data for the two amido complexes have shown a very large quenching of the orbital magnetic moment upon bending the linear geometry and also a strong correlation of high internal orbital field component ([H.sub.L]) with overall formal symmetry.

The synthesis and characterization of a range of Sn(II) hydrides are described and shown that modification of the terphenyl ligand has produced different structural types. Hydrides and relevant model species have shown that increased steric hindrance has favored the asymmetric form ArSnSn[(H).sub.2]Ar relative to the centrosymmetric isomer due to the widening of the interligand angles at tin.

The synthesis and structural characterization of the first homologous, molecular M-M bonded series for the group 12 metals are described. The results have shown that the decomposition of Ar'Cd[([mu-H).sub.2]CdAr' at room temperature has led to the M-M bonded Ar'CdCdAr', thus supporting the view that the reduction of the reduction of the iodide has proceeded via the hydride intermediate.

A simple donor-stabilization strategy is used to prepare a new class of stable main group species featuring P[double bond]B and As[double bond]B bonds. The attempts to generate the Sb[double bond]B analogue were not successful, but the formation of a stable B-N triple bond has occurred in preference to a donor-stabilized B[double bond]N double bond.

In this article, we consider the portfolio selection problem as a Bayesian decision problem. We compare the traditional mean-variance and mean-variance-skewness efficient portfolios. We develop bi-level programming problem to investigate the market's preference for risk by using observed (market) weights. Numerical experiments are conducted on a portfolio formed by the 30 stocks in the Dow Jones Industrial Average. Numerical results show that the market's preferences are better explained when skewness is included. [ABSTRACT FROM AUTHOR]

A theoretical model was developed in order to predict the size of agglomerates ejected from aluminized composite solid propellants. The model accounts for aspects of both mechanistic and geometric approaches. A thin mobile surface layer is assumed to dominate particle accumulation. Agglomeration number Nag expressing the ratio between ignition and accumulation times, was found to greatly affect the characteristics of agglomeration phenomena, as noted in previous works. The concept of a characteristic distance De of the mobile surface layer was introduced, depending mostly on coarse AP particle diameter and loading. It was found to have a significant effect on the resulting agglomerate diameter. An agglomeration threshold was defined as the particle diameter equal to the mobile layer thickness. Particles smaller than this threshold have shown tendency to form large agglomerates, whereas particles with a somewhat larger diameter have demonstrated faster ignition and smaller ejected agglomerates. Model predictions for a number of propellant compositions showed good agreement with other theoretical studies as well as with experimental results. [ABSTRACT FROM AUTHOR]

The complexes M(II){N(H)ArPr16}2 (M = Co, 1 or Ni, 2; ArPr16 = C6H3 -2,6(C6H2-2,4,6-Pr'3)2), which have rigorously linear, N-M-N = 180°, metal coordination, and M(II){N(H)ArMe6}2 (M = Co, 3 or Ni, 4; ArMe6 = C6H32,6(C6H2-2,4,6-Me3)2), which have bent, N-Co-N = 144.1(4)°, and N-Ni-N = 154.60(14)°, metal coordination, were synthesized and characterized to study the effects of the metal coordination geometries on their magnetic properties. The magnetometry studies show that the linear cobalt(II) species 1 has a very high ambient temperature moment of about 6.2 μB (cf. spin oniy value = 3.87 μB) whereas the bent cobalt species 3 had a lower μB value of about 4.7 μB. In contrast both the linear and the bent nickel complexes 2 and 4 have magnetic moments near 3.0 μB at ambient temperatures, whirls is dose to the spin only value of 2.83 μB. The studies suggest that in the linear cobalt spedes 1 there is a vely strong enhanced spin orbital coupling which leads to magnetic moments that broach the free ion value of 6.63 P8 probably as a result of the relatively weak ligand field and its rigorously linear coordination. For the linear nickel species 2, however, the expected strong first order orbital angular momentum contribution does not occur (cf. free ion value 5.6 μB) possibly bemuse of zr bonding effects involving the nitrogen p orbitals and the dxz and dyz orbitals (whose degeneracy is lifted in the C2h local symmetry of the Ni(N(H)C(q,so)}2 array) whirls quench the orbital angular momentum. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of the mononuclear chromium(II) terphenyl substituted primary amido-complexes Cr{N(H)ArPri6}2 (ArPri6 = C6H3-2,6-(C6H2-2,4,6-iPr3)2 (1), Cr{N(H)ArPri4}2 (ArPri4 = C6H3-2,6-(C6H3-2,6-iPr2)2 (2), Cr{N(H)ArMe6}2 (ArMe6 = C6H3-2,6-(C6H2-2,4,6-Me3)2 (4), and the Lewis base adduct Cr{N(H)ArMe6}2(THF) (3) are described. Reaction of the terphenyl primary amido lithium derivatives Li{N(H)ArPri6} and Li{N(H)ArPri4} with CrCl2(THF)2 in a 2:1 ratio afforded complexes 1 and 2, which are extremely rare examples of two coordinate chromium and the first stable chromium amides to have linear coordinated high-spin Cr2+. The reaction of the less crowded terphenyl primary amido lithium salt Li{N(H)ArMe6} with CrCl2(THF)2 gave the tetrahydrofuran (THF) complex 3, which has a distorted T-shaped metal coordination. Desolvation of 3 at about 70 °C gave 4 which has a formally two-coordinate chromous ion with a very strongly bent core geometry (N-Cr-N= 121.49(13)°) with secondary Cr--C(aryl ring) interactions of 2.338(4) Å to the ligand. Magnetometry studies showed that the two linear chromium species 1 and 2 have ambient temperature magnetic moments of about 4.20 μB and 4.33 μB which are lower than the spin-only value of 4.90 μB typically observed for six coordinate Cr2+. The bent complex 4 has a similar room temperature magnetic moment of about 4.36 μB. These studies suggest that the two-coordinate chromium complexes have significant spin-orbit coupling effects which lead to moments lower than the spin only value of 4.90 μB because λ (the spin orbit coupling parameter) is positive. The three-coordinated complex 3 had a magnetic moment of 3.79 μB. [ABSTRACT FROM AUTHOR]

Reaction of M(N(SiMe3)2)2 (M = Ge, Sn, or Pb) with the sterically encumbered primary phosphine Ar'PH2 (2), Ar1 = C6H3-2.6-(C6H3-2,6-Pr'2), at ca. 200 °C afforded the highly colored phosphinidene dimers (M(μ-PAr'))2, M = Ge(3), Sn(4), or Pb(5), with disilylamine elimination. The compounds were characterized by single-crystal X-ray crystallography and heteronuclear NMR spectroscopy. The structures of 3.4, and 5 featured similar M2P2 ring cores, of which 4 and 5 have 50/50 P atom disorder, consistent with either a planar four-membered M2P2 arrangement with anti aryl groups or with an M2P2 ring folded along the M-M axis with syn aryl groups. A syn-folded structure was resolved for the Ge2P2 ring in compound 3. The M-P distances resembled those in M( II) phosphido complexes and are consistent with single bonding. The coordination geometries at the phosphorus atoms are pyramidal. DFT calculations on the gas phase models (M(μ-PMe))2 (M = Ge, Sn. Pb) agreed with the syn (M-M folded) structural interpretation of the X-ray data. The synthesis of the bulky phosphine Ar'PH2 2 with the use of the aryl transfer agent Ar'MgBr(THF)2 is also reported. This route afforded a significantly higher yield of product than that which was obtained using LiAr', which tends to result in aryl halide elimination and the observation of insoluble red phosphorus. [ABSTRACT FROM AUTHOR]

Abstract: The complexities of the flame structure above a composite propellant containing 86% ammonium perchlorate (AP) and 14% hydroxy-terminated-polybutadiene (HTPB) have been elucidated using a two-dimensional, detailed gas-phase kinetic mechanism diffusion flame model. The model utilizes a vorticity formulation of the transport equations, which essentially eliminates the pressure field calculation and speeds convergence. Mass and energy coupling between the condensed and gas phases are achieved through iteration with one-dimensional, premixed combustion models to dynamically update the inlet boundary conditions. The model uses a detailed gas-phase kinetic mechanism consisting of 37 species and 127 reactions. Numerical studies have been performed to examine the influence of particle size on the flame structure above the AP/HTPB propellant. Three different combustion zones, based on AP particle size, were predicted: the AP monopropellant limit, the diffusion flame region, and the premixed limit. The modeled flame structure changed dramatically with particle size and was found to be qualitatively similar to the Beckstead–Derr–Price Model. Mechanistic insights are presented to explain AP’s unique ability to modify a propellant burning rate based on particle size alone. The premixed limit at which decreasing the size of the AP particles no longer influences the burning rate was also predicted. Results show promise in predicting formulistic effects using fundamental calculations. [Copyright &y& Elsevier]