Analysis of cylindrical shells of nonuniform thickness using two-dimensional photoelastic models

An experimental method is described whereby symmetrically loaded cylinders of nonuniform thickness are analyzed using two-dimensional photoelastic models mounted on elastic foundations. The technique is most conveniently applied to ring-stiffened or notched cylinders. The particular model studied simulated a notched cylindrical pressure vessel which had been previously studied with three-dimensional photoelasticity. The stress-concentration factors at the base of the notch, found using both methods, showed excellent agreement. An analysis was also performed which allows estimation of the error involved when a beam-on-elastic-foundation model does not rigorously simulate a cylinder.     

New fascaplysin-based CDK4-specific inhibitors: design, synthesis and biological activity

The first biologically active non-planar analogues of the toxic anti-cancer agent, fascaplysin, have been produced; we present the design, synthesis and biological activity of three tryptamine derivatives.     

Baryon exotics in the quark model, the skyrme model, and QCD

We derive the quantum numbers of baryon exotics in the quark model and the Skyrme model and show that they agree for arbitrary colors and flavors. We define exoticness E, which can be used to classify the states. The exotic baryons include the recently discovered qqqqq pentaquarks (E=1), as well as exotic baryons with additional qq pairs (E>/=1). The mass formula for nonexotic and exotic baryons is given as an expansion in 1/N(c) and allows one to relate the moment of inertia of the Skyrme soliton to the mass of a constituent quark.     

Driving forces for self-organized coadsorption: C6H6/2O and C6H6/2CO on Ni[111

The self-organized (2log3 x 2log3) coadsorbed phases of C(6)H(6) with O and with CO are investigated within first-principles density functional theory. The main driving force for formation of the C(6)H(6)/2O phase is found to be the reduction of O adatom repulsive interactions, while for the C(6)H(6)/2CO phase it is the interspecies attractive interactions and benzene-benzene repulsive interactions which are most important.     

Search for DeltaS = 2 nonleptonic hyperon decays

A sensitive search for the rare decays Omega(-)--> Lambdapi(-) and Xi(0)--> ppi(-) has been performed using data from the 1997 run of the HyperCP (Fermilab E871) experiment. Limits on other such processes do not exclude the possibility of observable rates for |DeltaS| = 2 nonleptonic hyperon decays, provided the decays occur through parity-odd operators. We obtain the branching-fraction limits B(Omega(-)-->Lambdapi(-)) < 2.9 x 10(-6) and B(Xi(0)--> ppi(-)) < 8.2 x 10(-6), both at 90% confidence level.     

Stabilizing CO on Au with NO2: electronegative species as promoters on coinage metals?

CO adsorption on NO(2)-predosed Au[111] reveals an unexpected attractive coadsorbate interaction, associated with an unprecedented blueshift of the CO stretch frequency, a sizeable attenuation of the infrared NO(2) symmetric stretch band, and a (sq.rt(7) x sq.rt(7))R19 degrees structure characterized by scanning tunneling microscopy and low energy electron diffraction. Density functional calculations allow us to rationalize these observations, and point towards a general pattern of behavior for electronegative coadsorbates on coinage metals, with important implications for catalytic promotion.     

Step-enhanced selectivity of NO reduction on platinum-group metals

The conversion of NO to N2 is a key issue encountered in the control of emission from vehicles. The selectivity of NO reduction on two platinum group metals, Ir and Pt, including the close-packed flat surface and the monatomic steps are extensively studied within the first-principles density functional theory framework. A stepped Ir surface is found to possess high selectivity for NO reduction, which is attributed to both the electronic and geometric structures of the Ir steps. The other surfaces considered fail to combine both attributes, activity and selectivity. In particular, a stepped Pt surface has a poor N2 selectivity with a large tendency for N2O production. The results explain the observed metal dependency and the structure sensitivity of the NO reduction under excess O2 conditions.     

Odd perfect numbers have a prime factor exceeding

It is proved that every odd perfect number is divisible by a prime greater than .