Retrieval of transverse relaxation time distribution from spin-echo data by recurrent neural network

Inversion of transverse relaxation time decay curve from spin-echo experiments was carried out using Hopfield neural network, to obtain the transverse relaxation time distribution. The performance of this approach was tested against simulated and experimental data. The initial guess, necessary for the integration procedure, was established as the analytical Laplace inversion. Together with errors in the simulated data, inversion was also carried out with errors in this initial guess. The probability density function, calculated by the neural network, is used in multiple sclerosis diagnostics.     

Liver metastases from unknown primary site: demonstration on MR images

To demonstrate the MR imaging features of liver metastases in patients with the clinical and histologic diagnosis of tumors of unknown primary tumors, a retrospective 7-year study was performed that included a total of 14 consecutive patients (7 men and 7 women; age range, 39-82 years; mean age, 60.6 years) with liver metastases from unknown primary site who had undergone MR imaging. The following lesion features were evaluated: a) number, b) diameter, c) signal intensity on T1 and T(2)-weighted images, and d) pattern of enhancement on immediate, 45 s and 90 s post gadolinium images. Lesions were classified as hypovascular, hypervascular and nearly isovascular relative to liver parenchyma as shown on immediate post gadolinium images. Patients were separated into four major groups, related to the histologic diagnosis of the lesions: (I) poorly differentiated neoplasms; (II) well-differentiated and moderately differentiated adenocarcinoma; (III) squamous cell carcinoma; (IV) combined poorly differentiated carcinoma and poorly differentiated adenocarcinoma. MRI findings were correlated with histologic information obtained by chart review and confirmed by retrospective histopathology review. All patients had the histologic diagnosis of adenocarcinoma: 8 patients belonged to group II (1 patient with the subtype well-differentiated and 7 patients with the subtype moderately differentiated) and 6 patients to group IV. Eleven patients (79%) presented with multiple lesions distributed throughout both hepatic lobes; 3 patients exhibited solitary lesions. All solitary metastases possessed a diameter equal or larger than 5 cm. Patients with multiple metastases demonstrated a wide range of diameter, ranging from less than 1.5 cm to more than 5 cm. Regarding lesion vascularity, 4 of 13 of the patients had hypovascular metastases and 9 of 13 of the patients had hypervascular lesions. One patient demonstrated both types of lesions. Five of six patients with the histopathologic diagnosis of poorly differentiated adenocarcinoma demonstrated hypervascular metastases. Solitary metastases were most often hypovascular (2 of 3); however no correlation with the histologic subtype was possible. Liver metastases from unknown primary site are often multiple and often hypervascular. Poorly differentiated tumors are the most common histologic type. Metastases are not uncommonly hypovascular, and these are often solitary.     

Mechanochemical preparation of hydrogen-bonded adducts between the diamine 1,4-diazabicyclo[2.2.2]octane and dicarboxylic acids of variable chain length: an X-ray diffraction and solid-state NMR study

Mechanical mixing of solid dicarboxylic acids of variable chain length HOOC(CH(2))(n)COOH (n = 1-7) with solid 1,4-diazabicyclo[2.2.2]octane generates the corresponding salts or co-crystals of the formula [N(CH(2)CH(2))(3)N]-H-[OOC(CH(2))(n)COOH] (n=1-7). Preparation of the same systems from solution has been instrumental for a full characterization of the mechanochemical products by means of single-crystal and powder-diffraction X-ray analyses, as well as by solid-state NMR. The acid-base adducts, whether involving proton transfer from the COOH group to the N-acceptor, that is having ((-))O...H-N((+)) interactions, or the formation of neutral O-H...N hydrogen bonds, show a melting point alternation phenomenon analogous to that shown by the neutral carboxylic acids. The carbon chemical shift tensors of the COOH group obtained from the sideband intensity of low speed spinning NMR spectra provide a reliable criterion for assigning the protonation state of the adducts.     

A simple and general preparation of vinylic sulfides, selenides and tellurides

A general method for the synthesis of vinylic chalcogenides by nucleophilic and Ni-catalyzed vinylic substitution on vinylic halides by phenyl chalcogenolates is described. The reactions were regio and stereoselective for the nickel catalyzed substitution, and mixture of isomers was observed for some examples in the thermal process in DMF.     

Bidentate phosphines as ligands in the palladium-catalyzed intramolecular arylation: the intermolecular base-assisted proton abstraction mechanism

The palladium-catalyzed arylation of aryl bromides can be carried out in the presence of bidentate phosphines, such as dppm, dppe, dppf, and Xantphos under mild conditions. The experimental results and the DFT calculations fully support for this reaction a mechanism proceeding by an intermolecular proton abstraction.     

A note on tilting sequences

We discuss the existence of tilting modules which are direct limits of finitely generated tilting modules over tilted algebras.      

Solvent- and metal-free selective oxidation of thiols to disulfides using I2/DMSO catalytic system

We describe herein a simple, fast and inexpensive protocol for the oxidative coupling of thiols employing a stoichiometric amount of DMSO and iodine as the catalyst. Various aromatic disulfides were obtained in good to excellent yields in short reaction times at room temperature, while aliphatic disulfides were achieved in good yields when the reactions were conducted under microwave irradiation.     

Synthesis of 5′-seleno-xylofuranosides

The synthesis of selenium derivatives of naturally occurring chiral molecules is becoming increasingly important in recent years. In this context, we describe herein an easy, straightforward synthetic route for the preparation of a series of chiral seleno-furanosides, starting from the readily available carbohydrate d-xylose. In addition, selected compounds were screened as inhibitors of the δ-aminolevulinate dehydratase (δ-ALA-D) enzyme. Diselenide 4 was found to reduce significantly the enzymatic activity, while seleno-furanoside 1a increased δ-ALA-D activity.     

New class of amino-phosphinite chiral catalysts for the highly enantioselective addition of arylzinc reagents to aldehydes

A new class of amino-phosphinite chiral ligands was prepared and applied in zinc-catalyzed addition of aryl boronic acids to aldehydes; the reaction furnished the diarylmethanols in excellent yields and with a high level of enantioselectivity (up to 93% ee).     

Diamond/porous titanium three-dimensional hybrid electrodes

Hybrid three-dimensional electrodes produced from microcrystalline boron-doped diamond (BDD) and/or nanocrystalline diamond films were grown on porous titanium (Ti) substrate by hot filament chemical vapor deposition (HFCVD) technique. Powder metallurgy technique was used to obtain the Ti substrates provided by interconnected and open pores among its volume. Diamond growth parameters were optimized in order to provide the entire substrate surface covering including the deeper surfaces, pore bottoms, and walls. The morphology and structure of these electrodes were studied by scanning electron microscopy (SEM) and visible Raman spectroscopy techniques, respectively. Electrochemical response was characterized by cyclic voltammetry measurements. Results showed a wide working potential window and low background current characteristic of the diamond electrodes. The kinetic parameters also pointed out to a quasi-reversible behavior for these hybrid three-dimensional diamond/Ti electrodes.