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21.
An experimental investigation of the gas-phase photooxidation of toluene–NOx–air mixtures at part-per-million concentrations has been carried out in a 65-m3, outdoor smog chamber to assess our understanding of the atmospheric chemistry of toluene. In addition, six CO? NOx–air irradiations were conducted to characterize the chamber with regard to any wall radical sources. Measured parameters in the toluene–NOx experiments included O3, NO, NO2, HNO3, peroxyacetyl nitrate (PAN), CO, toluene, benzaldehyde, o-cresol, m-nitrotoluene, peroxybenzoyl nitrate (PBZN), temperature, relative humidity, aerosol size distributions, and particulate organic carbon. Predictions of the reaction mechanism of Leone and Seinfeld [7] are found to be in good agreement with the data under a variety of initial conditions. Additional simulations are used to investigate various mechanistic pathways in areas where our understanding of toluene chemistry is still incomplete. 相似文献
22.
We study the low temperature properties of p-spin glass models with finite connectivity and of some optimization problems. Using a one-step functional replica symmetry breaking ansatz we can solve exactly the saddle-point equations for graphs with uniform connectivity. The resulting ground state energy is in perfect agreement with numerical simulations. For fluctuating connectivity graphs, the same ansatz can be used in a variational way: For p-spin models (known as p-XOR-SAT in computer science) it provides the exact configurational entropy together with the dynamical and static critical connectivities (for p = 3, gamma(d) = 0.818, and gamma(s) = 0.918), whereas for hard optimization problems like 3-SAT or Bicoloring it provides new upper bounds for their critical thresholds ( gamma(var)(c) = 4.396 and gamma(var)(c) = 2.149). 相似文献
23.
Comparison of the filamentation and the hollow-core fiber characteristics for pulse compression into the few-cycle regime 总被引:1,自引:0,他引:1
L. Gallmann T. Pfeifer P.M. Nagel M.J. Abel D.M. Neumark S.R. Leone 《Applied physics. B, Lasers and optics》2007,86(4):561-566
The gas-filled hollow-core fiber compression and the optical filamentation technique are compared experimentally in a parameter
regime suitable for intense few-cycle pulse generation. In particular, pointing stability, spectral properties, and spatial
chirp are investigated. It is found that in the case of filamentation, the critical parameter for pointing stability is gas
pressure inside the generation cell whereas for the hollow-core fiber it is alignment that plays this role. The hollow-core
fiber technique yields spectra that are better suited for chirped-mirror pulse compression whereas filamentation offers higher
throughput and prospects for easy-to-implement self-compression. We present spectral phase interferometry for direct electric-field
reconstruction (SPIDER) measurements that directly show the transition in the spectral phase of the output continua into the
self-compression regime as the gas pressure is increased.
PACS 42.65.Re; 42.65.Jx; 42.65.Tg 相似文献
24.
The structure of trans‐[Cr(Me2tn)2Cl2]2ZnCl4 (Me2tn = 2,2‐dimethylpropane‐1,3‐diamine) was determined by a single‐crystal X‐ray diffraction study at 173 K. The analysis reveals that there are three crystallographically independent chromium(III) complex cations in the title compound. The chromium(III) atoms are coordinated by four nitrogen atoms of Me2tn and two chlorine atoms in a trans arrangement, displaying a distorted octahedral geometry. The two six‐membered chelate rings in three complex cations are oriented in an anti chair–chair conformation with respect to each other. The Cr–N and Cr–Cl bond lengths average 2.0862(2) and 2.3112(6) Å, respectively. The ZnCl42– have slightly distorted tetrahedral arrangement with Zn–Cl lengths and the Cl–Zn–Cl angles are influenced by hydrogen bonding. The resolved absorption maxima in the electronic d–d spectrum were fitted with a secular determinant for a quartet energy state of the d3 configuration in a tetragonal field. It is confirmed that the nitrogen atoms of the Me2tn ligand are strong σ donors, but the chloro ligands have weak σ‐ and π donor properties toward the chromium(III) ion. 相似文献
25.
Complex tripodal tris(2-aminoethyl)amine (tren)-based ligands have been prepared in a single-pot reaction of tren with 3 equiv each of cyclohexenone and a benzaldehyde derivative (i.e., from seven components and three molecular types). The highest yield of product was obtained for p-nitrobenzaldehyde, the most electrophilic aldehyde used. 相似文献
26.
John M. Leone 《国际流体数值方法杂志》1990,11(7):969-984
This paper presents a detailed numerical solution to a simplified version of two-dimensional stratified flow over a backward-facing step with a Froude number of 16/9, a Reynolds number of 800 and a Prandtl number of 1—one of the Open Boundary Condition Symposium test problems. The steady state solution was derived by integrating the time-dependent Boussinesq equations forward in time using a semi-implicit finite-element-based model on a 38400-element mesh. In addition to presenting the results derived on this grid, the paper also presents the results of a Richardson extrapolation calculation for a set of ‘key’ parameters. It is hoped that this solution can be used as a baseline to compare the performance of the various techniques discussed at the Open Boundary Condition Symposium. 相似文献
27.
Zhanghua Zeng Dr. Angel A. J. Torriero Dr. Alan M. Bond Prof. Leone Spiccia Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(30):9154-9163
The [Fc? bis{ZnII(TACN)(Py)}] complex, comprising two ZnII(TACN) ligands (Fc=ferrocene; Py=pyrene; TACN=1,4,7‐triazacyclononane) bearing fluorescent pyrene chromophores linked by an electrochemically active ferrocene molecule has been synthesised in high yield through a multistep procedure. In the absence of the polyphosphate guest molecules, very weak excimer emission was observed, indicating that the two pyrene‐bearing ZnII(TACN) units are arranged in a trans‐like configuration with respect to the ferrocene bridging unit. Binding of a variety of polyphosphate anionic guests (PPi and nucleotides di‐ and triphosphate) promotes the interaction between pyrene units and results in an enhancement in excimer emission. Investigations of phosphate binding by 31P NMR spectroscopy, fluorescence and electrochemical techniques confirmed a 1:1 stoichiometry for the binding of PPi and nucleotide polyphosphate anions to the bis(ZnII(TACN)) moiety of [Fc? bis{ZnII(TACN)(Py)}] and indicated that binding induces a trans to cis configuration rearrangement of the bis(ZnII(TACN)) complexes that is responsible for the enhancement of the pyrene excimer emission. Pyrophosphate was concluded to have the strongest affinity to [Fc? bis{ZnII(TACN)(Py)}] among the anions tested based on a six‐fold fluorescence enhancement and 0.1 V negative shift in the potential of the ferrocene/ferrocenium couple. The binding constant for a variety of polyphosphate anions was determined from the change in the intensity of pyrene excimer emission with polyphosphate concentration, measured at 475 nm in CH3CN/Tris‐HCl (1:9) buffer solution (10.0 mM , pH 7.4). These measurements confirmed that pyrophosphate binds more strongly (Kb=(4.45±0.41)×106 M ?1) than the other nucleotide di‐ and triphosphates (Kb=1–50×105 M ?1) tested. 相似文献
28.
Kornilov O Bünermann O Haxton DJ Leone SR Neumark DM Gessner O 《The journal of physical chemistry. A》2011,115(27):7891-7900
Ultrafast relaxation of electronically excited pure He droplets is investigated by femtosecond time-resolved photoelectron imaging. Droplets are excited by extreme ultraviolet (EUV) pulses with photon energies below 24 eV. Excited states and relaxation products are probed by ionization with an infrared (IR) pulse with 1.6 eV photon energy. An initially excited droplet state decays on a time scale of 220 fs, leading predominantly to the emission of unaligned 1s3d Rydberg atoms. In a second relaxation channel, electronically aligned 1s4p Rydberg atoms are emitted from the droplet within less than 120 fs. The experimental results are described within a model that approximates electronically excited droplet states by localized, atomic Rydberg states perturbed by the local droplet environment in which the atom is embedded. The model suggests that, below 24 eV, EUV excitation preferentially leads to states that are localized in the surface region of the droplet. Electronically aligned 1s4p Rydberg atoms are expected to originate from excitations in the outermost surface regions, while nonaligned 1s3d Rydberg atoms emerge from a deeper surface region with higher local densities. The model is used to simulate the He droplet EUV absorption spectrum in good agreement with previously reported fluorescence excitation measurements. 相似文献
29.
In this paper we study a variable coefficient Sine-Gordon (vSG) equation given by theta(tt)-theta(xx)+F(x,t)sin theta=0 where F(x,t) is a real function. To establish if it may be integrable we have performed the standard test of Weiss, Tabor, and Carnevale (WTC). We have got that the (vSG) equation has the Painleve' property (Pp) if the function F(x,t) satisfies a well-defined nonlinear partial differential equation. We have found the general solution of this last equation and, consequently, the functions F(x,t) such that the (vSG) equation possesses the (Pp), are given by F(x,t)=F(1)(x+t)F(2)(x-t) where F(1)(x+t) and F(2)(x-t) are arbitrary functions. Using this last result we have obtained some particular solutions of the vSG equation. (c) 1995 American Institute of Physics. 相似文献
30.
Thomas Merakis Annette Murphy Leone Spiccia Alan Beguin Werner Marty 《Helvetica chimica acta》1989,72(5):993-995
Crystalline salts of the hydrolytic dimer of Cr(III), [Cr2(μ-OH)2(H2O)8]X4·n H2O (X = p-toluenesulfonate (tos) or mesitylene-2-sulfonate (dmtos)) have been prepared in good yields via a simple two-step procedure: H+ oxidation of Cr metal to give Cr2+ (T ≈? 70°) followed by O2 oxidation, of Cr2+ to give the dimer (T ≈? 25°). The mechanism of conversion of Cr2+ into the dimer is discussed. 相似文献