A method for analyzing the δ18O of resin-extractable soil inorganic phosphate

Improved tools for tracing phosphate transformations in soils are much needed, and can lead to a better understanding of the terrestrial phosphorus cycle. The oxygen stable isotopes in soil phosphate are still not exploited in this regard. Here we present a method for measuring the oxygen stable isotopes in a fraction of the soil phosphate which is rapidly available to plants, the resin-extractable P. This method is based on extracting available phosphate from the soil with anion-exchange membranes, soil organic matter removal by a resin, purification by precipitation as cerium phosphate, and finally precipitation as silver phosphate. The purified silver phosphate samples are then measured by a high-temperature elemental analyzer (HT-EA) coupled in continuous flow mode to an isotope ratio mass spectrometer. Testing the method with Mediterranean and semi-arid soils showed no artifacts, as well as good reproducibility in the same order as that of the HT-EA analytical uncertainty (0.3‰).     

Cellulose Nanocrystals (CNCs) Induced Crystallization of Polyvinyl Alcohol (PVA) Super Performing Nanocomposite Films

This study is aimed to explore the properties of cellulose nanocrystals (CNC)/polyvinyl alcohol (PVA) composite films with and without 1,2,3,4‐butane tetracarboxylic acid (BTCA), a nontoxic crosslinker. CNC and CNC‐PVA nanocomposite films are prepared using solution‐casting technique. Differential scanning calorimetry (DSC) analyses show that crosslinking increased the glass transition temperature but reduced the melting temperature and crystallinity. Furthermore, high CNC concentrations in the PVA matrix interfere with PVA crystallinity, whereas in specific ratio between CNC and PVA, two different crystalline structures are observed within the PVA matrix. Film surfaces and fracture topographies characterized using scanning electron microscope indicate that at certain CNC‐PVA ratios, micron‐sized needle‐like crystals have formed. These crystalline structures correlate with the remarkable improvement in mechanical properties of the CNC‐PVA nanocomposite films, that is, enhanced tensile strain and toughness to 570% and 202 MJ m^?3, respectively, as compared to pristine PVA. BTCA enhances the tensile strain, ultimate tensile stress, toughness, and modulus of CNC films compared to pristine CNC films. Water absorption of crosslinked CNC and CNC‐PVA nanocomposite films is significantly reduced, while film transparency is significantly improved as a function of PVA and crosslinker content. The presented results indicate that CNC‐PVA nanocomposite films may find applications in packaging, and though materials applications.     

Immobilization of quantum dots of cadmium selenide on the matrix of a graft liquid-crystalline polymer

A new luminescent composite based on quantum dots of CdSe immobilized on the polymer LC matrix prepared through the graft polymerization of the monomer of 4-(ω-acryloyloxyhexyloxy)benzoic acid on a fluorocarbon support after its preliminary irradiation with vacuum ultraviolet light is elaborated. The structure, composition, and optical characteristics of the prepared composite are studied via the methods of the FTIR spectroscopy, energy-dispersive and wave-dispersive analyses, and luminescence spectroscopy. The CdSe particles are shown to interact with the carboxyl groups of mesogenic fragments of the LC polymer, and this interaction leads to the integration of quantum dots into the ordered LC structure of the composite. As a result of immobilization, the luminescence peak of the quantum dots is shifted toward lower wavelengths owing to the interaction between the nanoparticles and the polymer LC matrix.     

Polynomial-time key recovery attack on the Faure–Loidreau scheme based on Gabidulin codes

Encryption schemes based on the rank metric lead to small public key sizes of order of few thousands bytes which represents a very attractive feature compared to Hamming metric-based encryption schemes where public key sizes are of order of hundreds of thousands bytes even with additional structures like the cyclicity. The main tool for building public key encryption schemes in rank metric is the McEliece encryption setting used with the family of Gabidulin codes. Since the original scheme proposed in 1991 by Gabidulin, Paramonov and Tretjakov, many systems have been proposed based on different masking techniques for Gabidulin codes. Nevertheless, over the years most of these systems were attacked essentially by the use of an attack proposed by Overbeck. In 2005 Faure and Loidreau designed a rank-metric encryption scheme which was not in the McEliece setting. The scheme is very efficient, with small public keys of size a few kiloBytes and with security closely related to the linearized polynomial reconstruction problem which corresponds to the decoding problem of Gabidulin codes. The structure of the scheme differs considerably from the classical McEliece setting and until our work, the scheme had never been attacked. We show in this article that for a range of parameters, this scheme is also vulnerable to a polynomial-time attack that recovers the private key by applying Overbeck’s attack on an appropriate public code. As an example we break in a few seconds parameters with 80-bit security claim. Our work also shows that some parameters are not affected by our attack but at the cost of a lost of efficiency for the underlying schemes.     

Spatial encoding and the single-scan acquisition of high definition MR images in inhomogeneous fields

We have recently proposed a protocol for retrieving multidimensional magnetic resonance spectra and images within a single scan, based on a spatial encoding of the spin interactions. The spatial selectivity of this encoding process also opens up new possibilities for compensating magnetic field inhomogeneities; not by demanding extreme uniformities from the B(0) fields, but by compensating for their effects at an excitation and/or refocusing level. This potential is hereby discussed and demonstrated in connection with the single-scan acquisition of high-definition multidimensional images. It is shown that in combination with time-dependent gradient and radiofrequency manipulations, the new compensation approach can be used to counteract substantial field inhomogenities at either global or local levels over relatively long periods of time. The new compensation scheme could find uses in areas where heterogeneities in magnetic fields present serious obstacles, including rapid studies in regions near tissue/air interfaces. The principles of the B(0) compensation method are reviewed for one- and higher-dimensional cases, and experimentally demonstrated on a series of 1D and 2D single-scan MRI experiments on simple phantoms.     

Methods for scalable optical quantum computation

We propose a scalable method for implementing linear optics quantum computation using the "linked-state" approach. Our method avoids the two-dimensional spread of errors occurring in the preparation of the linked state. Consequently, a proof is given for the scalability of this modified linked-state model, and an exact expression for the efficiency of the method is obtained. Moreover, a considerable improvement in the efficiency, relative to the original linked-state method, is achieved. The proposed method is applicable to Nielsen's optical "cluster-state" approach as well.     

pH‐Responsive Pillar[6]arene‐based Water‐Soluble Supramolecular Hexagonal Boxes

We describe the preparation of the first water‐soluble pH‐responsive supramolecular hexagonal boxes (SHBs) based on multiple charge‐assisted hydrogen bonds between peramino‐pillar[6]arenes 2 with the molecular “lid” mellitic acid ( 1 a ). The interaction between 2 and 1 a , as well as the other “lids” pyromellitic and trimesic acids ( 1 b and 1 c , respecively) were studied by a combination of experimental and computational methods. Interestingly, the addition of 1 a to the complexes of the protonated form of pillar[6]arene 2 , that is, 3 , with bis‐sulfonate 4 a or 4 b , immediately led to guest escape along with the formation of closed 1 a₂2 supramolecular boxes. Moreover, the process of the openning and closing of the supramolecular boxes along with threading and escaping of the guests, respectively, was found to be reversible and pH‐responsive. This study paves the way for the easy and modular preparation of different SHBs that may have myriad applications.     

Ozonolysis of olfefins and acetylenes adsorbed on silica gel

Ozonation of phenyl ethylenes adsorbed on untreated silica gel results in aromatic aldehydes and on dried silica gel in ozonides and aldehydes. On the other hand ozonation of alkyl ethylenes on both types of silica gel results in a mixture of ozonides or polymeric peroxides similar to that obtained in aprotic solvents.     

Supramolecular Translation of Enzymatically Triggered Disassembly of Micelles into Tunable Fluorescent Responses

The need for advanced fluorescent imaging and delivery platforms has motivated the development of smart probes that change their fluorescence in response to external stimuli. Here a new molecular design of fluorescently labeled PEG–dendron hybrids that self‐assemble into enzyme‐responsive micelles with tunable fluorescent responses is reported. In the assembled state, the fluorescence of the dyes is quenched or shifted due to intermolecular interactions. Upon enzymatic cleavage of the hydrophobic end‐groups, the labeled polymeric hybrids become hydrophilic, and the micelles disassemble. This supramolecular change is translated into a spectral response as the dye–dye interactions are eliminated and the intrinsic fluorescence is regained. We demonstrate the utilization of this molecular design to generate both Turn‐On and spectral shift responses by adjusting the type of the labeling dye. This approach enables transformation of non‐responsive labeling dyes into smart fluorescent probes.     

Nonlinear phase shifts of modulated light waves with slow and superluminal group delay in stimulated Brillouin scattering

Brillouin amplification with counterpropagating modulated pump and Stokes light leads to nonlinear modulation-phase shifts of the interacting intensity waves. This is due to a partial transformation of the nonmodulated light component at the input into modulated light at the output as a result of a mixing process with the counterpropagating modulated component of the pump and results in an advance or delay of the input modulation. This occurs for interactions over less than half of a modulation wavelength. Milliwatts of power in a kilometer of standard single-mode fiber give significant tunability of the modulation phase.