39,168 research outputs found
Why the critical temperature of high-<i>T<sub>c</sub></i> cuprate superconductors is so low: The importance of the dynamical vertex structure
No full textTo fathom the mechanism of high-temperature (T-c) superconductivity, the dynamical vertex approximation is evoked for the two-dimensional repulsive Hubbard model. After showing that our results reproduce well the cuprate phase diagram with a reasonable T-c and dome structure, we keep track of the scattering processes that primarily affect T-c. We find that local particle particle diagrams significantly screen the bare interaction at low frequencies, which in turn suppresses antiferromagnetic spin fluctuations and hence the pairing interaction. Thus we identify dynamical vertex corrections as one of the main oppressors of T-c which may provide a hint toward higher T-c's
FiFoSiM - an integrated tax benefit microsimulation and CGE model for Germany
No full textThis paper describes FiFoSiM, the integrated tax benefit microsimulation and computable general equilibrium (CGE) model of the Center of Public Economics at the University of Cologne. FiFoSiM consists of three main parts. The first part is a static tax benefit microsimulation module. The second part adds a behavioural component to the model; an econometrically estimated labour supply model. The third module is a CGE model which allows the user of FiFoSiM to assess the global economic effects of policy measures. Two specific features distinguish FiFoSiM from other tax benefit models: First, the simultaneous use of two databases for the tax benefit module and second, the linkage of the tax benefit model to a CGE model.FiFoSiM; microsimulation; CGE
Letter from Carl T. Hayden to C. H. Gensler, Havasupai Reservation
No full textLetter from Carl T. Hayden to C. H. Gensler, Havasupai Indian Reservation, regarding Hualapai and Cataract Canyons geography
1, 2-H shift in benzylchlorocarbene: isotope effect and influence of the solvent
No full textLaser flash photolysis of 3-chloro-3-benzyldiazirine and 3-chloro-3-(phenyldideuteriomethyl)diazirine in isooctane over the 60 to -80-degrees-C temperature range gives rise to curved Arrhenius plots for both 1,2-H and 1,2-D migration in benzylchlorcarbene. The k(H)/k(D) values increase smoothly from 0.87 to 2.62 when the temperature increases from -60 to +30-degrees-C. The k(H)/k(D) value is approximately 4 for most of the temperatures studied if a solvent correction is applied. Quantum mechanical tunnelling or the influence of the solvent may be a possible explanation for these observations.PT: J; CR: BONNEAU R, 1989, J AM CHEM SOC, V111, P5973 BONNEAU R, 1992, J PHOTOCH PHOTOBIO A, V68, P97 DIX EJ, 1993, J AM CHEM SOC, V115, P10424 EVANSECK JD, 1990, J PHYS CHEM-US, V94, P5518 GRAHAM WH, 1965, J AM CHEM SOC, V87, P4396 JACKSON JE, 1994, ADV CARBENE CHEM JONES M, 1980, REACTIVE INTERMEDIAT, V2 KIRMSE W, 1971, CARBENE CHEM LIU MTH, 1984, TETRAHEDRON, V40, P887 LIU MTH, 1990, J AM CHEM SOC, V112, P3915 LIU MTH, 1992, J PHOTOCH PHOTOBIO A, V63, P115 LIU MTH, 1992, J PHYS ORG CHEM, V15, P285 LIU MTH, 1994, RES CHEM INTERMEDIAT, V20, P195 MODARELLI DA, 1992, J AM CHEM SOC, V114, P7034 MOSS RA, 1992, TETRAHEDRON LETT, V33, P4287 MOSS RA, 1994, ADV CARBENE CHEM MUROV SL, 1973, HDB PHOTOCHEMISTRY NICKON A, 1993, ACCOUNTS CHEM RES, V26, P84 SALIS GA, 1968, J PHYS CHEM-US, V72, P752 SANDER W, 1994, UNPUB SCHAEFER HF, 1979, ACCOUNTS CHEM RES, V12, P288 SCHOLLER WW, 1989, HOUBEN WEYL METHODEN, P41 SHIMANOUCHI T, 1972, TABLES MOL VIBRATION, V1 SUGIYAMA MH, 1992, J AM CHEM SOC, V114, P966 WIERLACHER S, 1993, J AM CHEM SOC, V115, P8943; NR: 25; TC: 20; J9: J PHOTOCHEM PHOTOBIOL A-CHEM; PG: 5; GA: PV021Source type: Electronic(1
Is SH4, the simplest 10-S-4 sulfurane, observable?
No full textThe kinetic stability of SH4 was investigated theoretically with the coupled cluster ansatz. The two possible modes of decomposition into SH2 and H-2 through either a C-2v or a C-1 transition structure (TS) were investigated using intrinsic reaction coordinate (IRC) computations; orbital interactions along the reaction paths were analyzed. The two dissociation modes are due to differences in the electron delocalization in the TSs. While the C-2v TS is bonded rather covalently by a three center-four electron (3c-4e) interaction which is lost in a strictly synchronous way (two electrons occupy the same orbital at a time along the reaction coordinate), the bonding orbital in the C-1 TS is merely occupied by a single electron. Surprisingly, this highly polarized TS has a lower barrier. Computations at the CCSD(T)/cc-pVQZ level of theory show that the zero-point corrected enthalpy (Delta H(0)double dagger) of the C-1 TS is 16 kcal mol(-1) above the C-4v symmetric ground state; the barrier along the C-2v path is 40 kcal mol(-1). The overall exothermicity for the dissociation into SH2 and H-2 was estimated to be Delta H-0 = -76 kcal mol(-1). The fundamental IR absorptions of SH4 (obtained by scaling the computed harmonic vibrational frequencies taken from the CCSD(T)/cc-pVQZ level of theory) are 1432 and 2037 cm(-1)
Temperature and matrix effects on competitive intermolecular and intramolecular reaction of benzylchlorocarbenes in ethanol
No full textPT: J; CR: GRILLER D, 1982, J AM CHEM SOC, V104, P5549 LIN CT, 1980, TETRAHEDRON LETT, V21, P3553 LIU MTH, 1983, TETRAHEDRON LETT, P5713 MOSS RA, 1978, J AM CHEM SOC, V100, P4475 MOSS RA, 1978, J CHEM SOC CHEM COMM, P255 MOSS RA, 1981, TETRAHEDRON LETT, V22, P997 POMERANTZ M, 1973, J AM CHEM SOC, V95, P5877 SCHAEFER HF, 1979, ACCOUNTS CHEM RES, V12, P288 SENTHILNATHAN VP, 1980, J AM CHEM SOC, V102, P7637 SENTHILNATHAN VP, 1981, J AM CHEM SOC, V103, P5503 SU DTT, 1978, J AM CHEM SOC, V100, P1872 TOMIOKA H, 1977, J AM CHEM SOC, V99, P6128 TOMIOKA H, 1979, J AM CHEM SOC, V101, P256 TOMIOKA H, 1979, J AM CHEM SOC, V101, P6009 TOMIOKA H, 1980, J AM CHEM SOC, V102, P7123 TOMIOKA H, 1980, J AM CHEM SOC, V102, P7817 TOMIOKA H, 1982, CHEM LETT, P843 TOMIOKA H, 1982, J AM CHEM SOC, V104, P3156 TOMIOKA H, 1983, J AM CHEM SOC, V105, P5053 TOMIOKA H, 1984, J AM CHEM SOC, V106, P454 TOMIOKA H, 1984, J CHEM SOC CHEM COMM, P476 TROZZOLO AM, 1973, CARBENES, V2, P185 TURRO NJ, 1982, J AM CHEM SOC, V104, P1754; NR: 23; TC: 8; J9: TETRAHEDRON LETT; PG: 4; GA: TL386Source type: Electronic(1
Letter from Charles H. Burke to Carl Hayden
No full textLetter from Charles H. Burke to Carl T. Hayden about mining on Diné (formerly Navajo) national land
Letter from John H. Page to Carl Hayden
No full textLetter from John H. Page to Carl T. Hayden regarding his company's rights to build a railway if they choose to
Laser flash photolysis study of substituent effects on the rate of 1, 2-H migration in a series of benzylchlorocarbenes
No full textLaser flash photolysis of para-substituted 3-chloro-3-benzyldiazirines in isooctane produces the corresponding carbenes, which react with pyridine to form ylides or undergo 1,2-H migration to form the (Z)- and (E)-beta-chlorostyrenes. The rate for the 1,2-H migration is determined by plotting the pseudo-first-order rate constants for the growth of the ylide vs [pyridine] and extrapolating to zero pyridine concentration. In the case of (p-chlorobenzyl)chlorocarbene, the carbene decay can be monitored directly at 310 nm, whereas in [p-(trifluoromethyl)benzyl]chlorocarbene, the 285-nm trace may bc analyzed as the sum of the absorption of the carbene and of the product beta-chlorostyrenes. A Hammett plot of the logarithms of the rate constants for 1,2-H migration vs sigma(p) values gave a rho-value of -1.0, consistent with a hydride-like 1,2-H shift to the carbene center. The rate constants for the cyclopropanation of carbenes with tetramethylethylene (TME) were determined. In particular, the cyclopropanation of (p-chlorobenzyl)chlorocarbene with TME gave a negative activation energy of -4.7 kcal mol-1.PT: J; CR: BONNEAU R, 1989, J AM CHEM SOC, V111, P5973 BONNEAU R, 1989, J PHYS CHEM-US, V93, P4802 CARMICHAEL I, 1986, J PHYS CHEM REF DATA, V15, P1 DOYLE MP, 1987, J ORG CHEM, V52, P1619 EVANSECK JD, 1990, J PHYS CHEM-US, V94, P5518 GOULD IR, 1985, TETRAHEDRON, V41, P1987 GRAHAM WH, 1965, J AM CHEM SOC, V87, P4396 HO GJ, 1989, J AM CHEM SOC, V111, P6875 HOUK KN, 1984, J AM CHEM SOC, V106, P4291 JACKSON JE, 1989, J AM CHEM SOC, V111, P6874 JONES M, 1980, REACTIVE INTERMEDIAT, V2 JONES WM, 1980, REARRANGEMENTS GROUN KIRMSE W, 1971, CARBENE CHEM LAVILLA JA, 1989, J AM CHEM SOC, V111, P6877 LIU MTH, 1908, J ORG CHEM, V52, P4223 LIU MTH, 1985, J CHEM SOC CHEM COMM, P982 LIU MTH, 1987, CHEM DIAZIRINES, CH5 LIU MTH, 1989, J AM CHEM SOC, V111, P6873 LIU MTH, 1989, J CHEM SOC CHEM COMM, V12 LIU MTH, 1990, J AM CHEM SOC, V112, P3915 LIU MTH, 1992, J PHOTOCH PHOTOBIO A, V63, P115 MORGAN S, 1991, J AM CHEM SOC, V113, P2782 MOSS RA, 1986, J AM CHEM SOC, V108, P7028 MOSS RA, 1990, J AM CHEM SOC, V112, P5642 SCHAEFER HF, 1979, ACCOUNTS CHEM RES, V12, P288; NR: 25; TC: 27; J9: J AMER CHEM SOC; PG: 4; GA: HT801Source type: Electronic(1
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