Cumulant functions are introduced to describe the statistical state of a radiation field. These functions are simply related
to the optical coherence functions but have some interesting features. It is shown that if the cumulant functions of all orders
greater than some numberN0 vanish then they also vanish for all orders greater than 2. Thermal field is the only field having this property. This property
holds whether the field is described by a classical stochastic process or by a quantum density operator. Further the particular
operator ordering used in defining these cumulant functions for the quantized field affects only the second order cumulant
function. To describe the statistical state of a vector field such as partially polarized or unpolarized radiation, one would
need to introduce cumulant tensors. 相似文献
This paper presents the use of least-squares support vector machine (LS-SVM) for quantitative determination of hydroxyl value (OHV) of hydroxylated soybean oils by horizontal attenuated total reflection Fourier transform infrared (HATR/FT-IR) spectroscopy. A least-squares support vector machine (LS-SVM) calibration model for the prediction of hydroxyl value (OHV) was developed using the range 1805.1-649.9 cm(-1). Validation of the method was carried out by comparing the OHV of a series of hydroxylated soybean oil predicted by the LS-SVM model to the values obtained by the AOCS standard method. A correlation coefficient equal to 0.989 and RMSEP = 4.96 mg of KOH/g was obtained. This study demonstrates a better prediction ability of the LS-SVM technique to determine OHV in hydroxylated soybean oil samples by HATR/FT-IR spectra. 相似文献
We present a novel approach for the determination of activation energy for the unimolecular dissociation of a large (>50 atoms) ion, based on measurement of the unimolecular dissociation rate constant as a function of continuous-wave CO(2) laser intensity. Following a short ( approximately 1 s) induction period, CO(2) laser irradiation produces an essentially blackbody internal energy distribution, whose 'temperature' varies inversely with laser intensity. The only currently available method for measuring such activation energies is blackbody infrared radiative dissociation (BIRD). Compared with BIRD, FRAGMENT: (a) eliminates the need to heat the surrounding ion trap and vacuum chamber to each of several temperatures (each requiring hours for temperature equilibration); (b) offers a three-fold wider range of effective blackbody temperature; and (c) extends the range of applications to include initially cold ions (e.g., gas-phase H/D exchange). Our FRAGMENT-determined activation energy for dissociation of protonated bradykinin, 1.2 +/- 0.1 eV, agrees within experimental error to the value, 1.3 +/- 0.1 eV, previously reported by Williams et al. from BIRD experiments. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
We report first results on the controlled radical polymerization of 2,3‐epithiopropyl methacrylate (ETMA) also known as thiiran‐2‐ylmethyl methacrylate. Reversible addition‐fragmentation chain transfer (RAFT) of ETMA was carried out in bulk and in solution, using AIBN as initiator and the chain transfer agents: cyanopropyl dithiobenzoate (CPDB) and cumyl dithiobenzoate (CDB). A linear increase of the number‐average molecular weight and decrease of the polydispersity with monomer conversion were observed using CPDB as transfer agent, indicating a controlled process. Atom transfer radical polymerization (ATRP) of ETMA was performed under different reaction conditions using copper bromide complexed by tertiary amine ligands and ethyl 2‐bromoisobutyrate (EBiB) or 2‐bromopropionitrile (BPN) as initiator. All experiments lead to a crosslinked polymer. Preliminary studies in the absence of initiator showed that the CuBr/ligand complex alone initiates the ring‐opening polymerization of thiirane leading to a poly(propylene sulfide) with pendant methacrylate groups.
New block copolymers with narrow molecular weight distribution based on (2,3-epithiopropylmethacrylate) (ETMA), methylmethacrylate (MMA) and n-butylmethacrylate (nBMA) have been successfully synthesized via reversible addition-fragmentation transfer (RAFT) polymerization. First, RAFT homopolymerization of ETMA and MMA was carried out using 2-(2-cyanopropyl) dithiobenzoate (CPDB) as the chain transfer agent (CTA) and 2,2-azobisisobutyronitrile (AIBN) as the initiator. PETMA-b-P(nBMA) copolymers were synthesized using PETMA homopolymers as the macro-chain transfer agent (MCTA), while PMMA-b-PETMA diblock copolymers were synthesized using PMMA as the MCTA. The evolution of the molecular weight and molecular weight distribution of the homo- and co-polymers were compatible with the RAFT polymerization features. Thin films from the block copolymers were prepared by spin coating a 1 wt% polymer solution from toluene, chloroform or THF. After the preparation, the films were annealed under 80% vapor pressure of chloroform for 1, 2 and 4 h and investigated with scanning electron microscopy (SEM). The most interesting results were found in the films prepared using PETMA-b-P(nBMA) copolymers (). The observed images suggested the formation of hybrid lamellar structures, ascribed to the combination of its higher molecular weight and solvents viscosity. 相似文献