Imaging mesoscopic nuclear spin noise with a diamond magnetometer

Magnetic resonance imaging can characterize and discriminate among tissues using their diverse physical and biochemical properties. Unfortunately, submicrometer screening of biological specimens is presently not possible, mainly due to lack of detection sensitivity. Here we analyze the use of a nitrogen-vacancy center in diamond as a magnetic sensor for nanoscale nuclear spin imaging and spectroscopy. We examine the ability of such a sensor to probe the fluctuations of the "classical" dipolar field due to a large number of neighboring nuclear spins in a densely protonated sample. We identify detection protocols that appropriately take into account the quantum character of the sensor and find a signal-to-noise ratio compatible with realistic experimental parameters. Through various example calculations we illustrate different kinds of image contrast. In particular, we show how to exploit the comparatively long nuclear spin correlation times to reconstruct a local, high-resolution sample spectrum.     

Interactions modes and physical properties in transition metal chalcogenolene-based molecular materials

Molecule-based materials are extremely versatile materials as they can be built from specifically designed building blocks with the desired size, shape, charge and electronic properties which determine their intermolecular interactions and, thus, their organization in the solid. The intermolecular interactions, therefore, in particular van der Waals interactions, π–π and π–d interactions, H-bonding, etc., play a crucial role in self-assembling these pre-designed molecular units and may provide a powerful way to afford layered mono- and multifunctional molecular materials with new or unknown physical properties. In this review the relationship between interaction modes and physical properties of organic/inorganic hybrids based on transition metal complexes with chalcogenolene ligands will be examined and an outlook will be proposed. With this goal, magnetic materials, highly conducting and metallic single-component materials containing dithiolene complex building blocks, multifunctional materials where the dithiolene complex is the magnetic or conducting component in addition to more complex systems involving other types of building block such as the metal oxalate complexes, will be discussed.     

Snx[BPO4]1−x composites as negative electrodes for lithium ion cells: Comparison with amorphous SnB0.6P0.4O2.9 and effect of composition

A comparative study of two Sn-based composite materials as negative electrode for Li-ion accumulators is presented. The former SnB_0.6P_0.4O_2.9 obtained by in-situ dispersion of SnO in an oxide matrix is shown to be an amorphous tin composite oxide (ATCO). The latter Sn_0.72[BPO₄]_0.28 obtained by ex-situ dispersion of Sn in a borophosphate matrix consists of Sn particles embedded in a crystalline BPO₄ matrix. The electrochemical responses of ATCO and Sn_0.72[BPO₄]_0.28 composite in galvanostatic mode show reversible capacities of about 450 and 530 mAh g⁻¹, respectively, with different irreversible capacities (60% and 29%). Analysis of these composite materials by ¹¹⁹Sn Mössbauer spectroscopy in transmission (TMS) and emission (CEMS) modes confirms that ATCO is an amorphous Sn^II composite oxide and shows that in the case of Sn_0.72[BPO₄]_0.28, the surface of the tin clusters is mainly formed by Sn^II in an amorphous interface whereas the bulk of the clusters is mainly formed by Sn⁰. The determination of the recoilless free fractions f (Lamb-Mössbauer factors) leads to the effective fraction of both Sn⁰ and Sn^II species in such composites. The influence of chemical composition and especially of the surface-to-bulk tin species ratio on the electrochemical behaviour has been analysed for several Sn_x[BPO₄]_1−x composite materials (0.17<x<0.91). The cell using the compound Sn_0.72[BPO₄]_0.28 as active material exhibits interesting electrochemical performances (reversible capacity of 500 mAh g⁻¹ at C/5 rate).     

Characterization of bacterial lipid profiles by using rapid sample preparation and fast comprehensive two‐dimensional gas chromatography in combination with mass spectrometry

The bacteria fatty acid profile has been extensively studied for taxonomic classification purposes, since bacteria, in general, contain particular and rare fatty acids, compared with animal and plant tissues. As for any real‐world sample type, the development of rapid and reliable methods for (i) sample identification (in this case, bacterium type), and (ii) constituent identification (in this instance, the fatty acid profile) is desirable. In this research, a half‐an‐hour procedure, to analyze bacteria, was developed: a 2‐min one‐step sample preparation step was followed by a relatively fast comprehensive 2D GC‐MS separation (25 min). Furthermore, dedicated MS libraries were constructed for the identification of bacteria and fatty acids. Finally, data processing, only qualitative at this stage, was carried out with the support of a novel comprehensive 2D GC software.     

Thorough evaluation of the validity of conventional enantio-gas chromatography in the analysis of volatile chiral compounds in mandarin essential oil: A comparative investigation with multidimensional gas chromatography

The present research is focused on the determination of the enantiomeric distribution of chiral compounds, contained in mandarin essential oils, by means of conventional chiral gas chromatography with flame ionization detection (enantio-GC-FID); the results attained were compared with those derived from heart-cutting multidimensional GC-mass spectrometry (MDGC/MS), to evaluate the reliability of the monodimensional technique as a tool for quality control. The Deans-switch MDGC system was equipped with two GC ovens, which were connected via a heated transfer line, a flame ionization detector (FID1) in the first dimension and a quadrupole MS as second-dimension detector. The a priori knowledge of potential co-elutions concerning target compounds (an enantiomer and an interfering compound), when using enantio-GC-FID, could enable the use of corrected enantiomer excess values. Correction factors could be calculated through a preliminary GC-FID analysis (using an apolar column), considering the peak areas of the known interferences. The method used for the calculation of a so-called “coelution correction factor” is described, along with some examples.     

A tail dependence-based dissimilarity measure for financial time series clustering

In this paper we propose a clustering procedure aimed at grouping time series with an association between extremely low values, measured by the lower tail dependence coefficient. Firstly, we estimate the coefficient using an Archimedean copula function. Then, we propose a dissimilarity measure based on tail dependence coefficients and a two-step procedure to be used with clustering algorithms which require that the objects we want to cluster have a geometric interpretation. We show how the results of the clustering applied to financial returns could be used to construct defensive portfolios reducing the effect of a simultaneous financial crisis.     

Context-specific acoustic differences between Peruvian and Iberian Spanish vowels

This paper examines four acoustic properties (duration F0, F1, and F2) of the monophthongal vowels of Iberian Spanish (IS) from Madrid and Peruvian Spanish (PS) from Lima in various consonantal contexts (/s/, /f/, /t/, /p/, and /k/) and in various phrasal contexts (in isolated words and sentence-internally). Acoustic measurements on 39 speakers, balanced by dialect and gender, can be generalized to the following differences between the two dialects. The vowel /a/ has a lower first formant in PS than in IS by 6.3%. The vowels /e/ and /o/ have more peripheral second-formant (F2) values in PS than in IS by about 4%. The consonant /s/ causes more centralization of the F2 of neighboring vowels in IS than in PS. No dialectal differences are found for the effect of phrasal context. Next to the between-dialect differences in the vowels, the present study finds that /s/ has a higher spectral center of gravity in PS than in IS by about 10%, that PS speakers speak slower than IS speakers by about 9%, and that Spanish-speaking women speak slower than Spanish-speaking men by about 5% (irrespective of dialect).