Cation distribution of the system CuAlxFe2−xO4 by X-rays and Mossbauer studies

The structural and Mossbauer spectroscopy studies have been performed on the spinel solid solution series CuAl _x Fe_2–x O₄ (0.0 x 1.0). All the compounds with 0.0 x 1.0 crystallised with cubic spinel structure. Lattice constant values calculated from XRD analysis were found to decrease on increasing x, linearly obeying Vegard's law. The X-ray intensity calculations indicated that Cu²⁺ prefers to occupy octahedral (B) site, where as Al³⁺ ions replace Fe³⁺ ions from both tetrahedral (A) and octahedral (B) sites. Mossbauer spectra at room temperature display magnetic sextets corresponding to A and B-sites superimposed on each other. The data shows that Al-possesses greater preference for B-site compared to A-site, and iron exists in high spin ferric Fe³⁺ state. The hyperfine fields for both A and B-sites decrease with increasing x. The cation distribution calculated from X-ray intensity data agrees with the Mossbauer results.     

Exact self-imaging of transversely periodic fields

Conditions for exactly self-imaging nonparaxial fields that are periodic also in the transverse direction are introduced. The theory is first derived by assuming full coherence and then extended into the domain of partial coherence. Different types of solutions are discussed, and some illustrations of the existence of solutions and intensity distributions of the fields are presented.     

Theory of partially coherent electromagnetic fields in the space-frequency domain

We construct the coherent-mode representation for fluctuating, statistically stationary electromagnetic fields. The modes are shown to be spatially fully coherent in the sense of a recently introduced spectral degree of electromagnetic coherence. We also prove that the electric cross-spectral density tensor can be rigorously expressed as a correlation tensor averaged over an appropriate ensemble of strictly monochromatic vectorial wave functions. The formalism is demonstrated for partially polarized, partially coherent Gaussian Schell-model beams, but the theory applies to arbitrary random electromagnetic fields and can find applications in radiation and propagation and in inverse problems.     

A field methodology to study effects of UV radiation on fish larvae

There is a considerable lack of in situ specific information about the effects of UV-B radiation on limnic animals studied in the field. We exposed larval pike (Esox lucius L.) in two types of cuvettes (glass and quartz) placed at different depths (5 or 15 cm) to natural solar UV or to artificially enhanced UV-B (lamps on 3 h per day), simulating the scenarios for coming decades. Dose realism and comparability with earlier laboratory experiments was the main purpose, and therefore UV-B irradiances to the surface as well as underwater irradiances were directly measured. Result showed that UV-B dose rates in natural waters are low even though DOC concentration was low (4.8 mg/l) in our study lake. A slight increase in ambient UV-B dose rates was enough to cause neurobehavioral symptoms in pike larvae. However, the dose rates applied were inadequate to affect superoxide dismutase (SOD) or HSP70. While assessing the suggested risks due to increased UV, conclusions emphasize the importance of conducting field UV studies as supplements to laboratory experiments. We also recommend direct measurements of UV-radiation at sites where the target organisms are actually exposed.     

Least squares support vector regression for solving Volterra integral equations

In this paper, a numerical approach is proposed based on least squares support vector regression for solving Volterra integral equations of the first and second kind. The proposed method is based on using a hybrid of support vector regression with an orthogonal kernel and Galerkin and collocation spectral methods. An optimization problem is derived and transformed to solving a system of algebraic equations. The resulting system is discussed in terms of the structure of the involving matrices and the error propagation. Numerical results are presented to show the sparsity of resulting system as well as the efficiency of the method.

     

Comparison of bacteriological culture and PCR for detection of bacteria in ovine milk—Sheep are not small cows

Mastitis, inflammation of the mammary gland, is an important cause of disease, mortality, and production losses in dairy and meat sheep. Mastitis is commonly caused by intramammary infection with bacteria, which can be detected by bacterial culture or PCR. PathoProof (Thermo Fisher Scientific Ltd., Vantaa, Finland) is a commercially available real-time PCR system for the detection of bovine mastitis pathogens. Sheep differ from cattle in the bacterial species or bacterial strains that cause mastitis, as well as in the composition of their milk. The aim of this study was to evaluate whether the PathoProof system was suitable for detection of mastitis pathogens in sheep milk. Milk samples were collected aseptically from 219 udder halves of 113 clinically healthy ewes in a single flock. Aliquots were used for bacteriological culture and real-time PCR-based detection of bacteria. For species identified by culture, the diagnosis was confirmed by species-specific conventional PCR or by sequencing of a housekeeping gene. The majority of samples were negative by culture (74.4% of 219 samples) and real-time PCR (82.3% of 192 samples). Agreement was observed for 138 of 192 samples. Thirty-four samples were positive by culture only, mostly due to presence of species that are not covered by primers in the PCR system (e.g., Mannheimia spp.). Two samples were positive for Streptococcus uberis by culture but not by PCR directly from the milk samples. This was not due to inability of the PCR primers to amplify ovine Streptococcus uberis, as diluted DNA extracts from the same samples and DNA extracts from the bacterial isolates were positive by real-time PCR. For samples containing Staphylococcus spp., 11 samples were positive by culture and PCR, 9 by culture only, and 20 by PCR only. Samples that were negative by either method had lower bacterial load than samples that were positive for both methods, whereas no clear relation with species identity was observed. This study provides proof of principle that real-time PCR can be used for detection of mastitis pathogens in ovine milk. Routine use in sheep may require inclusion of primer sets for sheep-specific mastitis pathogens.     

Catalyst-free synthesis of silicon nanowires by oxidation and reduction process

A new process has been developed to grow silicon (Si) nanowires (NWs), and their growth mechanisms were explored and discussed. In this process, SiNWs were synthesized by simply oxidizing and then reducing Si wafers in a high temperature furnace. The process involves H₂, in an inert atmosphere, reacts with thermally grown SiO₂ on Si at 1100 °C enhancing the growth of SiNWs directly on Si wafers. High-resolution transmission electron microscopy studies show that the NWs consists of a crystalline core of ~25 nm in diameter and an amorphous oxide shell of ~2 nm in thickness, which was also supported by selected area electron diffraction patterns. The NWs synthesized exhibit a high aspect ratio of ~167 and room temperature phonon confinement effect. This simple and economical process to synthesize crystalline SiNWs opens up a new way for large scale applications.     

Charge Transport in Polycrystalline Graphene: Challenges and Opportunities

Graphene has attracted significant interest both for exploring fundamental science and for a wide range of technological applications. Chemical vapor deposition (CVD) is currently the only working approach to grow graphene at wafer scale, which is required for industrial applications. Unfortunately, CVD graphene is intrinsically polycrystalline, with pristine graphene grains stitched together by disordered grain boundaries, which can be either a blessing or a curse. On the one hand, grain boundaries are expected to degrade the electrical and mechanical properties of polycrystalline graphene, rendering the material undesirable for many applications. On the other hand, they exhibit an increased chemical reactivity, suggesting their potential application to sensing or as templates for synthesis of one‐dimensional materials. Therefore, it is important to gain a deeper understanding of the structure and properties of graphene grain boundaries. Here, we review experimental progress on identification and electrical and chemical characterization of graphene grain boundaries. We use numerical simulations and transport measurements to demonstrate that electrical properties and chemical modification of graphene grain boundaries are strongly correlated. This not only provides guidelines for the improvement of graphene devices, but also opens a new research area of engineering graphene grain boundaries for highly sensitive electro‐biochemical devices.     

Healable,Stable and Stiff Hydrogels: Combining Conflicting Properties Using Dynamic and Selective Three‐Component Recognition with Reinforcing Cellulose Nanorods

Nanocomposite hydrogels are prepared combining polymer brush‐modified ‘hard’ cellulose nanocrystals (CNC) and ‘soft’ polymeric domains, and bound together by cucurbit[8]uril (CB[8]) supramolecular crosslinks, which allow dynamic host–guest interactions as well as selective and simultaneous binding of two guests, i.e., methyl viologen (the first guest) and naphthyl units (the second guest). CNCs are mechanically strong colloidal rods with nanometer‐scale lateral dimensions, which are functionalized by surface‐initiated atom transfer radical polymerization to yield a dense set of methacrylate polymer brushes bearing naphthyl units. They can then be non‐covalently cross‐linked through simple addition of poly(vinyl alcohol) polymers containing pendant viologen units as well as CB[8]s in aqueous media. The resulting supramolecular nanocomposite hydrogels combine three important criteria: high storage modulus (G′ > 10 kPa), rapid sol–gel transition (<6 s), and rapid self‐healing even upon aging for several months, as driven by balanced colloidal reinforcement as well as the selectivity and dynamics of the CB[8] three‐component supramolecular interactions. Such a new combination of properties for stiff and self‐healing hydrogel materials suggests new approaches for advanced dynamic materials from renewable sources.     

Droplet and Fluid Gating by Biomimetic Janus Membranes

The ability to gate (i.e., allow or block) droplet and fluid transport in a directional manner represents an important form of liquid manipulation and has tremendous application potential in fields involving intelligent liquid management. Inspired by passive transport across cell membranes which regulate permeability by transmembrane hydrophilic/hydrophobic interactions, macroscopic hydrophilic/hydrophobic Janus‐type membranes are prepared by facile vapor diffusion or plasma treatments for liquid gating. The resultant Janus membrane shows directional water droplet gating behavior in air‐water systems. Furthermore, membrane‐based directional gating of continuous water flow is demonstrated for the first time, enabling Janus membranes to act as facile fluid diodes for one‐way flow regulation. Additionally, in oil‐water systems, the Janus membranes show directional gating of droplets with integrated selectivity for either oil or water. The above remarkable gating properties of the Janus membranes could bring about novel applications in fluid rectifying, microchemical reaction manipulation, advanced separation, biomedical materials and smart textiles.