Uniform polymer particles by dispersion polymerization in alcohol

Uniform polystyrene particles in 1–10 μm size range and up to 40% solid contents have been prepared by polymerizing styrene in ethyl alcohol with azo-type initiators and a polymeric stabilizer polyvinylpyrrolidone along with an anionic, nonionic, or comonomeric co-stabilizer. Effects of polymerization parameters, such as monomer concentration, type of co-stabilizer, initiator type and concentration, crosslinking monomer, and diluent on average particle size and size distribution have been studied. Functional groups such as hydroxyl, carboxyl, amine, amide, silane, polydimethylsiloxane, and silacrown have been successfully incorporated onto the particles by copolymerization. A mechanism for particle formation and growth in dispersion polymerization is presented.     

Effective optimization-based approach for designing active noise control systems in enclosures

An efficient constrained optimization-based prototype program OPTANC is developed to expedite the optimum design of active noise control systems in enclosures. The boundary element method is used to model the sound field of enclosures in which the walls provide complex impedance and point noise sources may exist at arbitrary locations. A sequential quadratic programming algorithm is selected as the optimizer for the deisgn because of its accuracy, efficiency, and reliability. The program is coded in C with portability on micro, mini, and mainframe computers, and is also modularized for future expansion. Simulations show that the software can effectively and efficiently produce the optimal locations and sound strengths of the control sources for active noise control problems.     

Synthesis and Biological Activities of Aryl Propargyl Sulfone

A series of molecules containing monopropargyl sulfone or 1, 2-bis-propargyl sulfone were synthesized. The cytotoxicity of these compounds against human carcinoma cells was also examined. This study indicated that the formation of a biradical intermediate is important to the potency of cytotoxicity.     

Relaxation methods for problems with strictly convex separable costs and linear constraints

We consider the minimization problem with strictly convex, possibly nondifferentiable, separable cost and linear constraints. The dual of this problem is an unconstrained minimization problem with differentiable cost which is well suited for solution by parallel methods based on Gauss-Seidel relaxation. We show that these methods yield the optimal primal solution and, under additional assumptions, an optimal dual solution. To do this it is necessary to extend the classical Gauss-Seidel convergence results because the dual cost may not be strictly convex, and may have unbounded level sets. Work supported by the National Science Foundation under grant NSF-ECS-3217668.     

Determination of traces of lithium in biological, environmental and metal samples by neutron activation analysis

Summary Lithium in environmental, biological and metal samples was determined by neutron activation analysis via the⁶Li(n,)T and¹⁶O(T,n)¹⁸F reactions. The samples were converted to aqueous solutions either by dissolution or by digestion and their aliquots were irradiated in a nuclear reactor for 2 h. The irradiated sample solution, was placed in a ZrO₂ column on which the¹⁸F nuclide was adsorbed. Most of the coexisting nuclides²⁴Na,⁸²Br,³⁸Cl,⁶⁴Cu, etc. were separated by elution with pH 1 3 solution. The column was subjected to a Ge(Li) detector for-ray spectrometry. The lithium content in the sample was estimated from the¹⁸F activity obtained. The matrix effect can be eliminated by either strong dilution of the samples in aqueous medium or by the method of standard addition. Lithium can be determined with high precision and accuracy in sub-ppm samples.

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Bestimmung von Lithiumspuren in biologischen, Umwelt- und Metallproben mit Hilfe der Neutronenaktivierungsanalyse

Zusammenfassung Lithium wird über die Reaktionen⁶Li(n,)T und¹⁶O(T,n)¹⁸F bestimmt. Die Proben werden durch Auflösung oder Aufschluß in wäßrige Lösung übergeführt und im Reaktor 2 h lang bestrahlt. Die bestrahlte Lösung wird auf eine ZrO₂-Säule gegeben, wo die¹⁸F-Nuklide adsorbiert werden. Die meisten anderen Nuklide (²⁴Na,⁸²Br,³⁸Cl,⁶⁴Cu usw.) werden durch Elution mit Säurelösung pH 1 3 abgetrennt. Die-Spektrometrie erfolgt mit einem Ge(Li)-Detektor. Der Lithiumgehalt ergibt sich aus der¹⁸F-Aktivität. Durch starke Verdünnung oder durch das Standardzugabeverfahren kann der Matrixeffekt eliminiert werden. Lithium ist so mit hoher Präzision und Genauigkeit in sub-ppm-Proben bestimmbar.

     

Instrumental neutron activation analysis of urinary calculi

Five kinds of urinary stones from 42 patients have been determined for a total of 19 elements by instrumental neutron activation analysis. Of these elements, Ca, Mg, Sr, Na, and Cl are found to be present in the core of all kinds of stones. The differences in elemental composition among the different kinds of stones as well as across the layers of stone are statistically evaluated.     

Search for a fourth-generation quark more massive than the Z0 boson in p&pmacr; collisions at radicals = 1.8 TeV

We present the results of a search for pair production of a fourth-generation charge -1 / 3 quark (b(')) in sqrt[s] = 1.8 TeV p&pmacr; collisions using 88 pb(-1) of data obtained with the Collider Detector at Fermilab. We assume that both quarks decay via the flavor-changing neutral current process b(')-->bZ(0) and that the b(') mass is greater than m(Z)+m(b). We studied the decay mode b(')b(');-->Z(0)Z(0)b&bmacr; where one Z0 decays into e(+)e(-) or &mgr;(+)&mgr;(-) and the other decays hadronically, giving a signature of two leptons plus jets. An upper limit on the sigma(p&pmacr;-->b(')b(');)x[B(b(')-->bZ(0))](2) is established as a function of the b(') mass. We exclude at 95% confidence level a b(') quark with mass between 100 and 199 GeV/c(2) for B(b(')-->bZ(0)) = 100%.     

Stochastic resonance and nonlinear response using NMR spectroscopy

We revisit the phenomenon of quantum stochastic resonance in the regime of validity of the Bloch equations. We find that a stochastic resonance behavior in the steady-state response of the system is present whenever the noise-induced relaxation dynamics can be characterized via a single relaxation time scale. The picture is validated by a simple nuclear magnetic resonance experiment on water.