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1.
2.
The facility layout problem is concerned with finding the most efficient arrangement of a given number of departments with unequal area requirements within a facility. The facility layout problem is a hard problem, and therefore, exact solution methods are only feasible for small or greatly restricted problems. In this paper, we propose a spring-embedding approach that unlike previous approaches results in a model that is convex. Numerical results demonstrating the potential of our model and the efficiency of our solution procedure are presented. 相似文献
3.
Photoinduced charge separation is a fundamental step in photochemical energy conversion. In the design of molecularly based systems for light-to-chemical energy conversion, this step is studied through the construction of two- and three-component systems (dyads and triads) having suitable electron donor and acceptor moieties placed at specific positions on a charge-transfer chromophore. The most extensively studied chromophores in this regard are ruthenium(II) tris(diimine) systems with a common 3MLCT excited state, as well as related ruthenium(II) bis(terpyridyl) systems. This Forum contribution focuses on dyads and triads of an alternative chromophore, namely, platinum(II) di- and triimine systems having acetylide ligands. These d8 chromophores all possess a 3MLCT excited state in which the lowest unoccupied molecular orbital is a pi orbital on the heterocyclic aromatic ligand. The excited-state energies of these Pt(II) chromophores are generally higher than those found for the ruthenium(II) tris(diimine) systems, and the directionality of the charge transfer is more certain. The first platinum diimine bis(arylacetylide) triad, constructed by attaching phenothiazene donors to the arylacetylide ligands and a nitrophenyl acceptor to 5-ethynylphenanthroline of the chromophore, exhibited a charge-separated state of 75-ns duration. The first Pt(tpy)(arylacetylide)+-based triad contains a trimethoxybenzamide donor and a pyridinium acceptor and has been structurally characterized. The triad has an edge-to-edge separation between donor and acceptor fragments of 27.95 Angstroms. However, while quenching of the emission is complete for this system, transient absorption (TA) studies reveal that charge transfer does not move onto the pyridinium acceptor. A new set of triads described in detail here and having the formula [Pt(NO2phtpy)(p-C triple-bond C-C6H4CH2(PTZ-R)](PF6), where NO2phtpy = 4'-{4-[2-(4-nitrophenyl)vinyl]phenyl}-2,2';6',2'-terpyridine and PTZ = phenothiazine with R = H, OMe, possess an unsaturated linkage between the chromophore and a nitrophenyl acceptor. While the parent chromophore [Pt(ttpy)(C triple-bond CC6H5)]PF6 is brightly luminescent in a fluid solution at 298 K, the triads exhibit complete quenching of the emission, as do the related donor-chromophore (D-C) dyads. Electrochemically, the triads and D-C dyads exhibit a quasi-reversible oxidation wave corresponding to the PTZ ligand, while the R = H triad and related C-A dyad display a facile quasi-reversible reduction assignable to the acceptor. TA spectroscopy shows that one of the triads possesses a long-lived charge-separated state of approximately 230 ns. 相似文献
4.
Kohtani M Jones TC Schneider JE Jarrold MF 《Journal of the American Chemical Society》2004,126(24):7420-7421
High-temperature ion mobility measurements have been performed for alpha-helical Ac-A15K+H+ and globular Ac-KA15+H+ peptides. The alpha-helical and globular conformations do not melt into random coils as the temperature is raised. Instead, both conformations survive to the point where the peptide signals vanishes due to fragmentation. This occurs at 600 K for the globular Ac-KA15+H+ peptide and at 725 K for the alpha-helical Ac-A15K+H+. For the helical Ac-A15K+H+ peptide it appears that fragmentation is triggered by disruption of the helical conformation. 相似文献
5.
The rotational spectra of the three carbon chain molecules vinyldiacetylene (hex-1-ene-3,5-diyne, C(6)H(4)), vinyltriacetylene (oct-1-ene-3,5,7-triyne, C8H4), and its cyano analog vinylcyanodiacetylene (1-cyanohex-5-ene-1,3-diyne, C7H3N) have been observed for the first time by Fourier transform microwave spectroscopy of a supersonic molecular beam. The molecules were observed as products of an electrical discharge through selected precursor mixtures: ethylene/diacetylene and vinylacetylene/diacetylene for the pure hydrocarbon molecules and vinylacetylene/cyanoacetylene for vinylcyanodiacetylene. The measurements yield precise sets of rotational constants that compare very well with theoretical constants obtained by quantum chemical calculations at the B3LYP/cc-pVTZ level of theory. Since these three carbon chains are similar in structure and composition to known astronomical molecules and because of their significant polarity, all three are candidates for radio astronomical detection. 相似文献
6.
Stanton JF Dudek J Theulé P Gupta H McCarthy MC Thaddeus P 《The Journal of chemical physics》2005,122(12):124314
The C 1B1<--X 1A1 band system of the potential interstellar species Si3C has been recorded in a silane/acetylene discharge by resonant two-color two-photon ionization spectroscopy. The origin band is located near 24,925 cm-1 (3.09 eV). Several other features in the spectrum are assigned to progressions in the Si-Si stretching modes as well as to sequence and hot band transitions. The assignment was facilitated by ab initio calculations, which also indicate that this is the strongest electronic transition of Si3C in the visible region of the spectrum. Features in the spectrum are broadened considerably (ca. 10 cm-1), and suggest an excited state lifetime of a few picoseconds. Possible reasons for the short-lived nature of the excited state are discussed. 相似文献
7.
The chromone epoxide ring system has been synthesised. Base-catalysed cyclization and dehydrobromination of α-bromo-o-acyl (aroyl) oxyacetopheones or 2-bromo-1, 3-diones yielded 3-substituted chromone epoxides. Acid-catalysed rearrangement of a 2-methylchromone epoxide in an aprotic solvent gave a 2-methylenech-romanonol, while a 3-methoxymethylchromone epoxide fragmented to chromonol under these conditions; in alchols, chromone epoxides gave 2-alkoxychromanonols. 相似文献
8.
Thaddeus Prusik Tatiana Kolubayev Michael J. Morelli Henry C. Brenner 《Photochemistry and photobiology》1980,31(4):315-321
Abstract— The luminescence of acridine dyes intercalated in DNA was studied as a function of the concurrent binding of metal ions to DNA, in an effort to deduce specific site interactions of the dyes. Two dyes, proflavine (PF) and acridine orange (AO), and two metal ions, silver and mercuric, were used. Both ions quench the fluorescence of the dyes in aqueous solution at room temperature. The metal ions have a different effect on the fluorescence of these dyes when they are intercalated between the base pairs of DNA. The fluorescence of AO is decreased when silver is bound, while the fluorescence of PF is enhanced. Since Ag+ initially binds to GC sites in DNA, which quench the PF fluorescence, it ostensibly 'turns off' the quenching by DNA at these sites, and this effect is greater than the quenching effect of the silver ion itself. Hg2+ ion initially binds to AT sites in DNA. Since both dyes fluoresce from AT sites, Hg2 + is expected to quench their fluorescence. This behavior is observed at low r (metal ion/base). At higher r values, however, where Hg2 + is expected to begin binding to GC sites, the fluorescence of PF is enhanced. These quenching turn-off effects are tentatively interpreted in terms of a change in the structure of the dye/DNA complex which occurs when a metal ion binds at the intercalation site. At 77 K. no fluorescence enhancement is observed when metal ions bind; Ag+ quenches the fluorescence and enhances the phosphorescence of both dyes. Qualitatively similar results are obtained with Hg2 + . 相似文献
9.
Thorwirth S McCarthy MC Gottlieb CA Thaddeus P Gupta H Stanton JF 《The Journal of chemical physics》2005,123(5):054326
The sulfur molecules thiozone S3 and tetrasulfur S4 have been observed in a supersonic molecular beam in the centimeter-wave band by Fourier transform microwave spectroscopy, and in the millimeter- and submillimeter-wave bands in a low-pressure glow discharge. For S3 over 150 rotational transitions between 10 and 458 GHz were measured, and for S4 a comparable number between 6 and 271 GHz. The spectrum of S3 is reproduced to within the measurement uncertainties by an asymmetric top Hamiltonian with three rotational and 12 centrifugal distortion constants; ten distortion constants, but an additional term to account for very small level shifts caused by interchange tunneling, are required to reproduce to comparable accuracy the spectrum of S4. Empirical equilibrium (r(e)(emp)) structures of S3 and S4 were derived from experimental rotational constants of the normal and sulfur-34 species and vibrational corrections from coupled-cluster theory calculations. Quantum chemical calculations show that interchange tunneling occurs because S4 automerizes through a transition state with D2h symmetry which lies about 500 cm(-1) above the two equivalent C2upsilon minima on the potential energy surface. 相似文献
10.
A Beckmann Rearrangement/Friedel-Crafts strategy was utilized to prepare 5-amidotetralones in high yield. 相似文献