Synthesis, structure and physical properties of Ru ferrites: BaMRu5O11 (M=Li and Cu) and BaM′2Ru4O11 (M′=Mn, Fe and Co)

The synthesis, structure, and physical properties of five R-type Ru ferrites with chemical formula BaMRu₅O₁₁ (M=Li and Cu) and BaM′₂Ru₄O₁₁ (M′=Mn, Fe and Co) are reported. All the ferrites crystallize in space group P6₃/mmc and consist of layers of edge sharing octahedra interconnected by pairs of face sharing octahedra and isolated trigonal bipyramids. For M=Li and Cu, the ferrites are paramagnetic metals with the M atoms found on the trigonal bipyramid sites exclusively. For M′=Mn, Fe and Co, the ferrites are soft ferromagnetic metals. For M′=Mn, the Mn atoms are mixed randomly with Ru atoms on different sites. The magnetic structure for BaMn₂Ru₄O₁₁ is reported.     

Simple Sulfinate Synthesis Enables C?H Trifluoromethylcyclopropanation

A simple method to convert readily available carboxylic acids into sulfinate salts by employing an interrupted Barton decarboxylation reaction is reported. A medicinally oriented panel of ten new sulfinate reagents was created using this method, including a key trifluoromethylcyclopropanation reagent, TFCS‐Na. The reactivity of six of these salts towards C H functionalization was field‐tested using several different classes of heterocycles.     

Enantioselective Synthesis of Quaternary Carbon Stereocenters: Addition of 3‐Substituted Oxindoles to Vinyl Sulfone Catalyzed by Pentanidiums

A pentanidium‐catalyzed highly enantioselective conjugate addition of 3‐alkyloxindoles to phenyl vinyl sulfone has been demonstrated. This approach allows the construction of 3,3‐dialkyl‐substituted oxindole frameworks with high yield and excellent enantioselectivity (up to 99 %) under simple phase‐transfer conditions. A variety of oxindoles bearing all‐carbon quaternary stereogenic centers were obtained in the presence of 0.25 mol % pentanidium. Meanwhile, practicality was illustrated by a gram‐scale asymmetric synthesis of two 3,3‐dialkyl‐substituted oxindoles. The resulting adduct can be smoothly transformed to the natural product analogue in a short synthetic route.     

Development and validation of an ELISA kit for the detection of ricin toxins from biological specimens and environmental samples

Ricin is a toxin that can be easily extracted from seeds of Ricinus communis plants. Ricin is considered to be a major bio-threat as it can be freely and easily acquired in large quantities. A deliberate release of such toxin in civilian populations would very likely overwhelm existing public health systems, resulting in public fear and social unrest. There is currently no commercially available or FDA-approved prophylaxis such as vaccines, or therapeutic antitoxins or antidotes, available for ricin intoxication. Patient treatment is typically supportive care based on symptoms, often designed to reinforce the body’s natural response. This paper describes the development and validation of a robust ELISA test kit, which can be used to screen for ricin in biological specimens such as whole blood and faeces. Faecal specimens are shown in this study to have better diagnostic sensitivity and a wider diagnostic window compared to whole blood. From these results, it is concluded that faeces is the most suitable clinical specimen for diagnosis of ricin poisoning via the oral route. The ELISA test kit can also detect ricin in environmental samples. An advantage of this ELISA kit over other commercial off-the-shelf (COTS) detection kits currently on the market that are developed to screen environmental samples only is its ability to diagnose ricin poisoning from clinical specimens as well as detect ricin from environmental samples.     

Phase calibration of sonar systems using standard targets and dual-frequency transmission pulses

The phase angle component of the complex frequency response of a sonar system operating near transducer resonance is usually distorted. Interpretation and classification of the received sonar signal benefits from the preservation of waveform fidelity over the full bandwidth. A calibration process that measures the phase response in addition to the amplitude response is thus required. This paper describes an extension to the standard-target calibration method to include phase angle, without affecting the experimental apparatus, by using dual-frequency transmission pulses and frequency-domain data processing. This approach reduces the impact of unknown range and sound speed parameters upon phase calibration accuracy, as target phase is determined from the relationship of the two frequency components instead of relying on a local phase reference. Tungsten carbide spheres of various sizes were used to simultaneously calibrate the amplitude and phase response of an active sonar system in a laboratory tank. Experimental measurements of target phase spectra are in good agreement with values predicted from a theoretical model based upon full-wave analysis, over an operating frequency of 50-125 kHz.     

Studies on the self- and laser-initiated discharge characteristicsat dielectric/gas interfaces

Two main issues are discussed: (i) the study of arc initiation and propagation in a compressed nitrogen gas spark-gap, initiated by a low-energy (90 μJ) pulsed N₂ laser (600 ps FWHM) and (ii) the modification of the discharge characteristics due to the presence of a solid insulating space made of Plexiglas (PMMA). The studies are carried out over a pressure range of 0.1 to 0.4 MPa, and for space diameters of 1, 4 and 6 cm, in a planar uniform field gap with 1-cm spacing. Coordinated measurements of discharge current and luminosity with nanosecond response times provide data on discharge current and luminosity risetimes, delay times to the onset of discharge from the instant of laser initiation, and the threshold (minimum) voltage for the onset of discharge due to laser initiation. The results point to some basic processes involving the interaction of the insular surface with : (a) the electron avalanches in the formative stage, and (b) the streamer in the discharge growth phase leading to full conduction. The results demonstrate that the insulator surface impedes the development of both the avalanche and streamer phases of the discharge development     

Solution behavior of synthetic silk peptides and modified recombinant silk proteins

Spider dragline silk from Nephila clavipes possesses impressive mechanical properties derived in part from repetitive primary sequence containing polyalanine regions that self-assemble into crystalline β-sheets. In the present study, we have sought to understand more details of redox responses related to conformational transitions of modified silk peptides and a recombinant protein containing encoded methionine triggers. Regardless of the position of the methionine trigger relative to the polyalanine domain, chemical oxidation was rapid and slight increases in the α-helical structure and decreases in the β-sheet and random coil content were observed by CD and FTIR in the assembled silk-like peptides and the recombinant protein. CD results indicated that the decrease in β-sheet and random coil conformations, coupled with the increase in helical content during oxidation, occurred during the first 30 min of the reaction. No further conformational changes occurred after this time and the response was independent of methionine trigger location relative to the penta-alanine domain. These results were confirmed with fluorescence studies. The design, processing and utility of these modified redox triggered silk-like peptides and proteins suggest a range of potential utility, from biomaterials to engineered surface coatings with chemically alterable secondary structure and, thus, properties. PACS 87.14.Ee; 87.64.-t; 87.6.+2.     

Vibration of rectangular plates subjected to in-plane forces by the finite strip method

The finite strip method is applied to the vibration analysis of rectangular plates subjected to in-plane forces. Several numerical examples are presented and comparison with available solutions clearly indicates the accuracy and efficiency of the method.     

Flow of polymer chains and segregation in a flow field with a hybrid simulation

Effects of a flow field (E) on segregation and flow of polymer chains are studied in two dimensions using a hybrid (discrete‐to‐continuum) simulation. The flow rate (j) of polymer chains is found to increase monotonically with E, a linear response in the low field regime followed by a slow approach to saturation in the high field regime. The effective chain permeability (ϕ_c = j/E) varies nonmonotonically on increasing the field E, with a maximum (ϕ_cm) at a characteristic value of the field (in the range 0.2 < E < 2); ϕ_cm depends on the chain length. Chain aggregates exhibit an anisotropic mass distribution due to the field with a molecular bridging at high fields. The longitudinal component of the radius of gyration (R_gx) exhibits a crossover from a random walk (RW) (R_gx ˜ L_c^1/2) at E = 0 to an elongated conformation (R_gx ˜L_c) at E ⪈ 0.2; the transverse component changes from R_gy ˜ L_c^1/2 to R_gy ˜ L_c^1/3. The width of the radial distribution function (ρ(r)) of the monomers increases while its peak varies nonmonotonically with E and is consistent with the observation of anisotropic mass distribution.