Photolysis of allene and propyne in the 7-30 eV region probed by the visible fluorescence of their fragments

The photolysis of allene and propyne, two isomers of C(3)H(4), has been investigated in the excitation energy range of 7-30 eV using vacuum ultraviolet synchrotron radiation. The visible fluorescence excitation spectra of the excited neutral photofragments of both isomers were recorded within the same experimental conditions. Below the first ionization potential (IP), this fluorescence was too weak to be dispersed and possibly originated from C(2)H or CH(2) radicals. Above IP, three excited photofragments have been characterized by their dispersed emission spectra: the CH radical (A (2)Delta-X (2)Pi), the C(2) radical (d (3)Pi(g)-a (3)Pi(u), "Swan's bands"), and the H atom (4-2 and 3-2 Balmer lines). A detailed analysis of the integrated emission intensities allowed us to determine several apparition thresholds for these fragments, all of them being interpreted as rapid and barrierless dissociation processes on the excited potential energy surfaces. In the low energy range explored in this work, both isomers exhibit different intensity distributions in their fragment emission as a function of the photolysis energy, indicating that mutual allene<-->propyne isomerization is not fully completed before dissociation occurs. The effect of isomerization on the dissociation into excited fragments is present in the whole excitation energy range albeit less important in the 7-16 eV region; it gradually increases with increasing excitation energy. Above 19 eV, the fragment distribution is very similar for the two isomers.     

In vitro permeation of chromium species through porcine and human skin as determined by capillary electrophoresis–inductively coupled plasma–sector field mass spectrometry

Since the species that trigger chromium allergy are not yet known, it is important to gain more of an insight into the mechanism of chromium transport through the skin and into the relationship between chromium allergy and chromium species. In vitro permeation studies with porcine and human skin were performed using a Franz static diffusion cell. Investigations attempted to elucidate (i) which Cr compounds are able to permeate through skin, (ii) the influence the Cr concentration in the donor solution has on the Cr permeation, and (iii) the effect that the time of exposure to the donor solution has on Cr permeation. Capillary electrophoresis hyphenated to inductively coupled plasma–sector field mass spectrometry (CE–ICP–SFMS) was used to separate and quantify the Cr species in the receptor fluid. 50 mmol L⁻¹ phosphate buffer (pH 2.5) was used for CE separation, and two different electrophoretic runs were carried out (in the positive and negative modes). Pneumatic nebulization (PN)-ICP-SFMS was used in order to quantify the total amount of Cr absorbed by the skin after microwave-assisted acid digestion of the tissue. Cr(VI) was found to pass most easily through the skin. Nevertheless, Cr(VI) was also shown to be absorbed more efficiently by the skin than Cr(III), an observation attributed to a more pronounced rejection of the positively charged Cr(III) ions by the skin barrier. These results were in good agreement with in vitro permeation studies previously reported in the literature in which other analytical techniques were used. Differences observed in the permeation of Cr following the application of aqueous Cr donor solutions and Cr-containing simulated sweat donor solutions are also described.      

Determination of the pion charge form factor at Q2=1.60 and 2.45 (GeV/c)2

The 1H(e,e'pi+)n cross section was measured at four-momentum transfers of Q2=1.60 and 2.45 GeV2 at an invariant mass of the photon nucleon system of W=2.22 GeV. The charged pion form factor (F(pi)) was extracted from the data by comparing the separated longitudinal pion electroproduction cross section to a Regge model prediction in which F(pi) is a free parameter. The results indicate that the pion form factor deviates from the charge-radius constrained monopole form at these values of Q2 by one sigma, but is still far from its perturbative quantum chromodynamics prediction.     

Cramer-Rao lower bound for the estimation of the degree of polarization in active coherent imagery at low photon levels

The degree of polarization (DOP) is an important tool in many optical measurement and imaging applications. We address the problem of its estimation in images that are perturbed with both speckle and photon noise, by determining the Cramer-Rao lower bounds (CRLBs) when the illuminated materials are purely depolarizing. We demonstrate that the CRLBs are simply the sum of the CRLBs due to speckle noise and Poisson noise. We use this result to analyze the influence of different optical parameters on DOP estimation.     

Local existence and uniqueness of the mild solution to the 1D Vlasov–Poisson system with an initial condition of bounded variation

We propose a result of local existence and uniqueness of a mild solution to the one‐dimensional Vlasov–Poisson system. We establish the result for an initial condition lying in the space W^1,1(?²), then we extend it to initial conditions lying in the space BV(?²), without any assumption of continuity, boundedness or compact support. Copyright © 2010 John Wiley & Sons, Ltd.     

Multiple electrophilic substitution of 1,1,2,2,9,9,10,10-octafluoro

Synthetic methods for introduction of two substituents into the rings of octafluoroparacyclophane are presented. Nitration gives three isomers with nitro substituents on different rings: pseudo-ortho, pseudo-meta, and pseudo-para, in equal amounts. These dinitro compounds are shown to be precursors of a variety of other disubstituted OFP derivatives. Methods of characterization of isomeric disubstituted OFPs are extensively discussed, and the 1H and 19F NMR spectra of these derivatives are analyzed explicitly.     

Ensemble methods for classification in cheminformatics

We describe the application of ensemble methods to binary classification problems on two pharmaceutical compound data sets. Several variants of single and ensembles models of k-nearest neighbors classifiers, support vector machines (SVMs), and single ridge regression models are compared. All methods exhibit robust classification even when more features are given than observations. On two data sets dealing with specific properties of drug-like substances (cytochrome P450 inhibition and "Frequent Hitters", i.e., unspecific protein inhibition), we achieve classification rates above 90%. We are able to reduce the cross-validated misclassification rate for the Frequent Hitters problem by a factor of 2 compared to previous results obtained for the same data set with different modeling techniques.     

On the observation of the fine structure effect in non-relativistic (e, 2e) processes

The spin asymmetry arising in an (e,2e) process using spin-polarized incoming electrons with non-relativistic energies is shown to be dominated by the fine structure effect if a suitable kinematical regime is chosen. Calculations in the distorted wave Born approximation (DWBA) for both the triple differential cross-section and the spin asymmetry are presented for the inner shell ionization of argon. This process would provide an accessible target for existing experimental set-ups.