The combinatorial game Nofil played on Steiner triple systems

We introduce an impartial combinatorial game on Steiner triple systems called Next One to Fill Is the Loser (Nofil ). Players move alternately, choosing points of the triple system. If a player is forced to fill a block on their turn, they lose. By computing nim-values, we determine optimal strategies for Nofil on all Steiner triple systems up to order 15 and a sampling for orders 19, 21 and 25. The game Nofil can be thought of in terms of play on a corresponding hypergraph which will become a graph during play. At that point Nofil is equivalent to playing the game Node Kayles on the graph. We prove necessary conditions and sufficient conditions for a graph to reached playing Nofil. We conclude that the complexity of determining the outcome of the game Nofil on Steiner triple systems is PSPACE-complete for randomized reductions.     

Atomic force microscopy studies of chemical–mechanical processes on silicon(100) surfaces

Atomic force microscopy (AFM) is used to examine chemical–mechanical processes on Si(100) surfaces. The AFM tip serves as a single asperity contact to exert tribological forces as well as an imaging tool. By scanning in chemically aggressive solutions, material removal can be observed directly. In the silicon system, high-force scans are used to remove oxide and initiate etching in selected locations, followed by low-force scans to image the resulting surfaces. Material removal rates were measured as a function of applied load, number of scans, solution composition, and time. In basic solution, places where the underlying silicon is exposed etch rapidly, producing structures 100 nm or less in size. Although the surface roughness initially increases during etching, the final surfaces are smooth. The oxide is extremely sensitive to applied stress: even very light scanning accelerates oxide dissolution. Once the oxide is removed, chemical etching proceeds through the underlying silicon with or without AFM scanning; but the silicon etches more rapidly if AFM scanning is continued, due to true chemical–mechanical (tribochemical) effects.     

Unique charge-separated pyridinium-barbituric acid zwitterions

A synthetic procedure for the preparation of the unusual charge-separated pyridinium barbiturate zwitterion 2 from 1,3-dimethylbarbituric acid and 2-pyridinecarbaldehyde in methanol was developed. The structure of the compound was confirmed with X-ray analysis to demonstrate the strong charge separation throughout the molecule. One would expect that this charge separation would increase its reactivity; however, contrary to this expectation, the compound is very stable in acidic media, and in the presence of a base, decarbonylation occurs on one barbituric acid while the zwitterionic moiety of the molecule stays intact.     

The ϱ and A2 exchange amplitudes in meson-baryon scattering for ϱlab between 2.5 and 200 GeV/c

We present a parametrization of the ? and A₂ exchange amplitudes which fits all the available data on the reactions $\text{π}{}^{\mathrm{?}}\text{p}\text{→ π}{}^0\text{n}\text{, π}{}^{\mathrm{?}}\text{p}\text{→}\text{K}{}^0\text{n}\text{,}\text{and K}{}^{\mathrm{+}}\text{n}\text{→}\text{K}{}^0\text{p}$ in the momentum range from 2.5 to 200 GeV/c and for momentum transfers up to t = ?2.0 (GeV/c)².     

Electronic surface resonances and the thermally induced W(001) structure transition

The surface weighted effective potentials of the clean W(001) surface at temperatures T = 550 K[(1×1)] and T = 440 K[(√2×√2)R45°] are experimentally obtained from the surface resonance band structure. It is deduced that the transition W(001)-(1×1) → (√2×√2)R45° is a temperature-dependent reconstruction in which there is a contraction of the top layer atoms towards the bulk involving periodic displacements of the atoms normal to the surface.     

Reaction products from a discharge of N2 and H2S: The microwave spectrum of two conformers of sulfur diimide (HNSNH)

The rotational spectra of two conformations of sulfur diimide (HNSNH) are reported. The HNSNH species are produced in a low-pressure microwave discharge of N₂ and H₂S. The microwave spectrum of the normal isotopic form, HNSNH, and dideutro form, DNSND, of the cis,trans and cis,cis forms have been observed. The electric dipole moment components of both forms have been determined. The molecular structures were determined from the experimental rotational constants and from geometry optimized ab initio calculations with 4-31G Gaussian basis sets and CEP-31G basis sets including polarization. The experimentally and theoretically derived molecular properties are found to be in good agreement.     

Toward an understanding of the furoxan-dinitrosoethylene equilibrium

The tautomerism of furoxan (1,2,5-oxadiazole-2-oxide) has been investigated by different computational methods comprising modern density functionals as well as single-reference and multi-reference ab initio methods. The ring-opening process to 1,2-dinitrosoethylene is the most critical step of the reaction and cannot be treated reliably by low-level computations. The existence of cis-cis-trans-1,2-dinitrosoethylene as a stable intermediate is advocated by perturbational methods, but high-level coupled-cluster calculations identify this as an artifact. In contrast to the analogous reaction in benzofuroxans, cis-cis-cis-1,2-dinitrosoethylene was found to be a transition state rather than a local minimum. Model potentials were used to explain the occurrence and the disappearing of transition states and local minima relative to the reaction of benzofuroxan. Low-lying triplet states that can be accessed due to spin-orbit coupling were investigated as taking part in alternative routes to a proposed singlet pathway. Barriers for rotations of the nitroso groups on the S(0) and T(1) surfaces are reported.     

Aqueous solution speciation of Fe(III) complexes with dihydroxamate siderophores alcaligin and rhodotorulic acid and synthetic analogues using electrospray ionization mass spectrometry

Aqueous solutions of Fe3+ complexes of cyclic (alcaligin) and linear (rhodotorulic acid) dihydroxamate siderophores and synthetic linear eight-carbon-chain and two-carbon-chain dihydroxamic acids ([CH3N(OH)C=O)]2(CH2)n; H2Ln; n = 2 and 8) were investigated by electrospray ionization mass spectrometry (ESI-MS). Information was obtained relevant to the structure and the speciation of various Fe(III)-dihydroxamate complexes present in aqueous solution by (1) comparing different ionization techniques (ESI and FAB), (2) altering the experimental parameters (Fe3+/ligand ratio, pH, cone voltage), (3) using high-stability hexacoordinated Fe(III) siderophore complex mixtures (ferrioxamine B/ferrioxamine E) as a calibrant to quantify intrinsically neutral (H+ clustered or protonated) and intrinsically charged complexes, and (4) using mixed-metal complexes containing Fe3+, Ga3+, and Al3+. These results illustrate that for all dihydroxamic acid ligands investigated multiple tris- and bis-chelated mono- and di-Fe(III) species are present in relative concentrations that depend on the pH and Fe/L ratio.