Projections in operator ranges

If is a Hilbert space, is a positive bounded linear operator on and is a closed subspace of , the relative position between and establishes a notion of compatibility. We show that the compatibility of is equivalent to the existence of a convenient orthogonal projection in the operator range with its canonical Hilbertian structure.

     

A new strategy for respiration compensation, applied toward 3D free-breathing cardiac MRI

In thorax and abdomen imaging, image quality may be affected by breathing motion. Cardiac MR images are typically obtained while the patient holds his or her breath, to avoid respiration-related artifacts. Although useful, breath-holding imposes constraints on scan duration, which in turn limits the achievable resolution and SNR. Longer scan times would be required to improve image quality, and effective strategies are needed to compensate for respiratory motion. A novel approach at respiratory compensation, targeted toward 3D free-breathing cardiac MRI, is presented here. The method aims at suppressing the negative effects of respiratory-induced cardiac motion while capturing the heart's beating motion. The method is designed so that the acquired data can be reconstructed in two different ways: First, a time series of images is reconstructed to quantify and correct for respiratory motion. Then, the corrected data are reconstructed a final time into a cardiac-phase series of images to capture the heart's beating motion. The method was implemented, and initial results are presented. A cardiac-phase series of 3D images, covering the entire heart, was obtained for two free-breathing volunteers. The present method may prove especially useful in situations where breath-holding is not an option, for example, for very sick, mentally impaired or infant patients.     

Coacervative microextraction ultrasound-assisted back-extraction technique for determination of organophosphates pesticides in honey samples by gas chromatography–mass spectrometry

Coacervative microextraction ultrasound-assisted back-extraction technique (CME-UABE) is proposed for the first time for extracting and preconcentrating organophosphates pesticides (OPPs) from honey samples prior to gas chromatography–mass spectrometry (GC–MS) analysis. The extraction/preconcentration technique is supported on the micellar organized medium based on non-ionic surfactant. To enable coupling the proposed technique with GC, it was required to back extract the analytes into hexane. Several variables including, surfactant type and concentration, equilibration temperature and time, matrix modifiers, pH and buffers nature were studied and optimized over the relative response of the analytes. The best working conditions were as follows: an aliquot of 10 mL 50 g L⁻¹ honey blend solution was conditioned by adding 100 μL 0.1 mol L⁻¹ hydrochloric acid (pH 2) and finally extracted with 100 μL Triton X-114 100 g L⁻¹ at 85 °C for 5 min using CME technique. Under optimal experimental conditions, the enrichment factor (EF) was 167 and limits of detection (LODs), calculated as three times the signal-to-noise ratio (S/N = 3), ranged between 0.03 and 0.47 ng g⁻¹. The method precision was evaluated over five replicates at 1 ng g⁻¹ with RSDs ≤9.5%. The calibration graphs were linear within the concentration range of 0.3–1000 ng g⁻¹ for chlorpirifos; and 1–1000 ng g⁻¹ for fenitrothion, parathion and methidathion, respectively. The coefficients of correlation were ≥0.9992. Validation of the methodology was performed by standard addition method at two concentration levels (2 and 20 ng g⁻¹). The recoveries were ≥90%, indicating satisfactory robustness of the methodology, which could be successfully applied for determination of OPPs in honey samples of different Argentinean regions. Two of the analyzed samples showed levels of methidathion ranged between 1.2 and 2.3 ng g⁻¹.     

The GMSA for a hard-sphere fluid revisited: evaluation of the Henderson-Blum approximation[*

The Generalized Mean Spherical Approximation for a hard-sphere fluid developed by Waisman [E. Waisman, Mol. Phys. 25, 45 (1973)] over forty years ago is revisited. The relatively recent [C. F. Tejero and M. López de Haro, Mol. Phys. 105, 2999 (2007)] completely analytical results for the direct correlation function of such approximation are used to assess the simplification introduced by Henderson and Blum [D. Henderson and L. Blum, Mol. Phys. 32, 1627 (1976)]. The conclusion is reached that such simplification is a rather valuable compromise between simplicity and accuracy.     

Monitoring large scale wine fermentations with infrared spectroscopy

Negative effects on wine quality and productivity caused by stuck and sluggish fermentations can be reduced significantly, if such problems are detected early through periodic chemical analysis. Infrared spectroscopy (IR) has been used successfully for monitoring fermentations, since many compounds can be measured quickly from a single sample without prior treatment. Nevertheless, few applications of this technology in large scale winemaking have been reported, and these do not cover the entire fermentation from must to finished wine. In this work, we developed IR calibrations for analyzing the fermenting must at any stage of fermentation. The calibration model was obtained with multivariable partial least squares and proved effective for analyzing Cabernet Sauvignon fermentations for glucose, fructose, glycerol, ethanol, and the organic acids; malic, tartaric, succinic, lactic, acetic, and citric. Upon external validation we found an average relative predictive error of 4.8%. Malic acid showed the largest relative predictive error (8.7%). In addition, external validation found that insufficient data for these calibrations made the analysis of fermenting musts using other grape varieties less reliable.     

Palladium-catalyzed chemoselective cross-coupling of acyl chlorides and organostannanes

Chemoselective cross-coupling of aliphatic and aromatic acyl chlorides with aryl-, heteroaryl-, and alkynylstannanes proceeds in up to 98% yield using 2.5 mol % of bis(di-tert-butylchlorophosphine)palladium(II) dichloride as the precatalyst. Various functional groups including aryl chlorides and bromides that usually undergo oxidative addition to palladium complexes bearing phosphinous acid or dialkylchlorophosphine ligands are tolerated. This procedure allows convenient ketone formation and eliminates inherent limitations of Friedel-Crafts acylations such as substituent-directing effects and typical reactivity requirements of Lewis acid-catalyzed electrophilic aromatic substitutions.     

Spectroscopic analysis of imidazolidines. Part II: 1H NMR spectroscopy and conformational analysis of 1,2 and 1,3‐diarylimidazolidines

¹H NMR spectra of a series of 1,2 and 1,3‐diarylimidazolidines are analyzed and correlated with their conformational features. Results were interpreted on the basis of chemical shifts and coupling constants of hydrogen atoms and confirmed by ID nOe difference experiments. 1,3‐Diarylimidazolidines ( 1–7 ) show a fast inversion of the N‐aryl nitrogen in all studied cases. 1,2‐Diaryl‐3‐methyl (or benzyl) imidazolidines ( 8–13 ) display a preferential conformation with a transoid orientation of N₃ and C₂ substituents.     

Dediazoniation of 1-naphthalenediazonium tetrafluoroborate in aqueous acid and in micellar solutions

We have measured the rates and product yields of dediazoniation of 1-naphthalenediazonium (1ND) tetrafluoroborate in the presence and absence of sodium dodecyl sulfate (SDS) micellar aggregates by employing a combination of UV–vis spectroscopy and high-performance liquid chromatography (HPLC) measurements. Kinetic data were obtained by a derivatization procedure with product yields were determined by HPLC. HPLC chromatograms show that in aqueous acid and in micellar solutions only one dediazoniation product is formed in significant quantities, 1-naphthol (NOH), and the observed rate constants (k_obs) are the same when 1ND loss is monitored spectrometrically and when NOH formation is monitored by HPLC. Activation parameters were obtained both in the presence and absence of SDS micellar aggregates. In both the systems, the enthalpies of activation are high and the entropies of activation are positive. The enthalpy of activation in the absence of SDS is very similar to that in the presence of SDS micelles, but the entropy of activation is lower by a factor of 4. As a consequence, SDS micelles speed up the thermal decomposition of 1ND and increase k_obs by a factor of 1.5 when [SDS] = 0.02 M. In contrast, results obtained in the presence of complexing systems such as crown ethers and polyethers show significant stabilization of the parent arenediazonium ions. Kinetic and HPLC data are consistent with the heterolytic D_N + A_N mechanism that involves the rate-determining fragmentation of the arenediazonium ion into a very reactive phenyl cation that reacts competitively with available nucleophiles. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 301–309, 2008     

Entangled two-photon wave packet in a dispersive medium

We report an experimental study of group-velocity dispersion effect on an entangled two-photon wave packet, generated via spontaneous parametric down-conversion and propagating through a dispersive medium. Even in the case of using cw laser beam for pump, the biphoton wave packet and the second-order correlation function spread significantly. The study and understanding of this phenomenon is of great importance for quantum information applications, such as quantum communication and distant clock synchronization.     

Linear‐Hyperbranched Amphiphilic AB Diblock Copolymers Based on Polystyrene and Hyperbranched Polyglycerol

Summary: A convenient three‐step strategy has been developed for the preparation of well‐defined amphiphilic, linear‐hyperbranched block copolymers by hypergrafting. The synthetic procedure is based on a combination of carbanionic polymerization with the alkoxide‐based, controlled ring‐opening multibranching polymerization of glycidol. A linear AB diblock copolymer polystyrene‐block‐polybutadiene (PS‐b‐PB) with narrow polydispersity was obtained by anionic copolymerization. Subsequent hydroxylation by hydroboration led to PS₅₀₈‐b‐(PB‐OH)₅₆, used as macroinitiator for the polymerization of glycidol under slow monomer addition conditions.

Structure of the linear‐hyperbranched amphiphilic AB diblock copolymer PS₅₀₈‐b‐(PB₅₆‐hg‐PG_x) and an AFM micrograph of its micellar core–shell structure observed after solution casting.