Gas-phase hydrogen abstraction from asymmetrically halogenated ethanes by chlorine atoms

The hydrogen abstraction from asymmetrically fluorinated and chlorofluorinated ethanes by chlorine atoms has been investigated in the gas phase between 264 and 333°K using the competition method. Arrhenius parameters for the reaction on both sites of the molecules are discussed.     

Traffic noise reduction by means of surface wave exclusion above parallel grooves in the roadside

A new method to reduce traffic noise by means of an ‘invisible’ wall has been investigated both theoretically and experimentally. A formula was derived for the frequency dependent impedance of an infinite structure of parallel ribs on an impedance boundary. From the definition of surface waves it followed that these waves can only exist for certain combinations of frequencies, heights of ribs and phases of the complex reflection coefficient of the underlying surface. Upon making this surface softer, more low frequency sound is absorbed. Outdoor experiments above an array of 16 or 21 low brick walls showed a considerable absorption of sound. Attenuations occurred up to 20 dB in the one-third octave bands from 125 to 400 Hz and amplifications up to 12 dB in the range of 400–1000 Hz. It was possible to explain these measurements qualitatively by the theory of surface waves. The wall structure caused an insertion loss of approximately 4 dB(A) in the total sound pressure level of the A-weighted one-third octave bands from 100 to 12,500 Hz.     

Analysis of a hollow-cathode reflex discharge in a hydrocarbon flow

Variation of parameters of a reflex discharge with a hollow cathode operating continuously in propane with a flow rate of 1.3–5.6 (m³ mPa)/s and a discharge current of 0.1–0.4 A is analyzed. It is shown that for a hydrocarbon flow rate of 2.4 (m³ mPa)/s and higher, an increase in the discharge voltage takes place after a time interval depending on the discharge current and gas pressure; this is explained by the formation of coating of the dissociation products of hydrocarbon molecules on the electrodes of the discharge chamber. An increase in the thickness of the carbon coating of the cathodes with time and their charging with ions lead to electric breakdown of coatings and the formation of cathode spots. The oscillograms of the discharge current and voltage indicate a short-term transformation of the glow discharge into the arc discharge. The energy spectra of ions emerging from the discharge are measured, and the effect of the discharge current and the gas flow rate on the energy spread of ions is analyzed. The operation time of the discharge in hydrocarbon after which the cleaning of the discharge chamber is required is determined. The possibility of using an ion source based on the reflex discharge with a hollow cathode for technological purposes is established.     

A Raman and infrared spectroscopic study of the uranyl silicates--weeksite, soddyite and haiweeite

Raman spectroscopy has been used to study the molecular structure of a series of selected uranyl silicate minerals, including weeksite K2[(UO2)2(Si5O13)].H2O, soddyite [(UO2)2SiO4.2H2O] and haiweeite Ca[(UO2)2(Si5O12(OH)2](H2O)3 with UO2(2+)/SiO2 molar ratio 2:1 or 2:5. Raman spectra clearly show well resolved bands in the 750-800 cm-1 region and in the 950-1000 cm-1 region assigned to the nu1 modes of the (UO2)2+ units and to the (SiO4)4- tetrahedra. For example, soddyite is characterized by Raman bands at 828.0, 808.6 and 801.8 cm-1 (UO2)2+ (nu1), 909.6 and 898.0 cm-1 (UO2)2+ (nu3), 268.2, 257.8 and 246.9 cm-1 are assigned to the nu2 (delta) (UO2)2+. Coincidences of the nu1 (UO2)2+ and the nu1 (SiO4)4- is expected. Bands at 1082.2, 1071.2, 1036.3, 995.1 and 966.3 cm-1 are attributed to the nu3 (SiO4)4-. Sets of Raman bands in the 200-300 cm-1 region are assigned to nu2 (delta) (UO2)2+ and UO ligand vibrations. Multiple bands indicate the non-equivalence of the UO bonds and the lifting of the degeneracy of nu2 (delta) (UO2)2+ vibrations. The (SiO4)4- tetrahedral are characterized by bands in the 470-550 cm-1 and in the 390-420 cm-1 region. These bands are attributed to the nu4 and nu2 (SiO4)4- bending modes. The minerals show characteristic OH stretching bands in the 2900-3500 cm-1 and 3600-3700 cm-1.     

On curves on K3 surfaces,II

We study the Clifford index c of a smooth irreducible curve X in the linear series |2H| on a special K3 surface S of degree 2n in \({{\mathbb P}}^{n+1}\), with hyperplane section H, and we look for the complete and base point free linear series of S whose restrictions to X compute c. In a more general context, we discuss the features of such series, for an assigned curve on a K3 surface; this discussion is of some independent interest.     

Credit rating prediction using Ant Colony Optimization

The introduction of the Basel II Capital Accord has encouraged financial institutions to build internal rating systems assessing the credit risk of their various credit portfolios. One of the key outputs of an internal rating system is the probability of default (PD), which reflects the likelihood that a counterparty will default on his/her financial obligation. Since the PD modelling problem basically boils down to a discrimination problem (defaulter or not), one may rely on the myriad of classification techniques that have been suggested in the literature. However, since the credit risk models will be subject to supervisory review and evaluation, they must be easy to understand and transparent. Hence, techniques such as neural networks or support vector machines are less suitable due to their black box nature. Building upon previous research, we will use AntMiner+ to build internal rating systems for credit risk. AntMiner+ allows to infer a propositional rule set from a given data set, hereby using the principles from Ant Colony Optimization. Experiments will be conducted using various types of credit data sets (retail, small- and medium-sized enterprises and banks). It will be shown that the extracted rule sets are both powerful in terms of discriminatory power and comprehensibility. Furthermore, a framework will be presented describing how AntMiner+ fits into a global Basel II credit risk management system.