MRI dynamic range and its compatibility with signal transmission media

As the number of MRI phased array coil elements grows, interactions among cables connecting them to the system receiver become increasingly problematic. Fiber optic or wireless links would reduce electromagnetic interference, but their dynamic range (DR) is generally less than that of coaxial cables. Raw MRI signals, however, have a large DR because of the high signal amplitude near the center of k-space. Here, we study DR in MRI in order to determine the compatibility of MRI multicoil imaging with non-coaxial cable signal transmission. Since raw signal data are routinely discarded, we have developed an improved method for estimating the DR of MRI signals from conventional magnitude images. Our results indicate that the DR of typical surface coil signals at 3 T for human subjects is less than 88 dB, even for three-dimensional acquisition protocols. Cardiac and spine coil arrays had a maximum DR of less than 75 dB and head coil arrays less than 88 dB. The DR derived from magnitude images is in good agreement with that measured from raw data. The results suggest that current analog fiber optic links, with a spurious-free DR of 60–70 dB at 500 kHz bandwidth, are not by themselves adequate for transmitting MRI data from volume or array coils with DR 90 dB. However, combining analog links with signal compression might make non-coaxial cable signal transmission viable.     

Sub-100 nm structuring of indium-tin-oxide thin films by sub-15 femtosecond pulsed near-infrared laser light

In magnetron sputtered indium-tin-oxide thin films of varying oxygen content, nanostructures were formed using tightly focused high-repetition rate near-infrared sub-15 femtosecond pulsed laser light. At radiant exposure well beyond the ablation threshold, cuts of 280-350 nm in width were generated. Illumination close to the ablation threshold resulted in periodic cuts of typically 20 nm in width at periodicities between 50 nm and 180 nm, as well as single sub-20 nm cuts. Subthreshold exposure, in combination with hydrochloric acid etching, yielded nanowires of 50 nm minimum lateral dimensions.     

Microtubule‐Templated Cadmium Sulfide Nanotube Assemblies

This paper describes the use of microtubules (MTs) as nanoscale templates for the biologically directed growth and assembly of cadmium sulfide (CdS) nanotubes. CdS is a wide bandgap semiconductor with valuable optical, electronic, and chemical properties, and the organization of CdS nanostructures is critical to their widespread utility. The present work explores a bioinspired, biomediated approach to the formation and assembly of CdS nanotubes. In particular, a biomimetic synthetic strategy is used to control the uniform growth of cubic zinc blende CdS nanocrystals on MT templates, replicating the MTs' tubular morphology with dense CdS only a single nanocrystal thick. Furthermore, specific interactions between MTs and functional microtubule‐associated proteins (MAPs) are exploited to manipulate the secondary organization of these MT templates. The subsequent directed growth of CdS nanotubes on these structures produces specific biomediated architectures including linear arrays, 3D asters, and rings. Finally, cathodoluminescence from MT‐templated CdS structures verifies that the valuable semiconducting character of these materials is exhibited. These demonstrations of nanoscale materials synthesis and assembly illustrate a new level of complexity and control over materials synthesis that may be achieved using such biological tools and processes.     

Immobilization of lipase from Candida rugosa on layered double hydroxides for esterification reaction

Synthesis of layered double hydroxides (LDHs) of Zn/Al-NO3- hydrotalcite (HIZAN) and Zn/Al-diocytyl sodium sulfosuccinate (DSS) nanocomposite (NAZAD) with a molar ratio of Zn/Al of 4:1 were carried out by coprecipitation through continuous agitation. Their structures were determined using X-ray diffractometer spectra, which showed that basal spacing for LDH synthesized by both methods was about 8.89 A. An expansion of layered structure of about 27.9 A was observed to accommodate the surfactant anion between the interlayer. This phenomenon showed that the intercalation process took place between the LDH interlayer. Lipase from Candida rugosa was immobilized onto these materials by physical adsorption method. It was found that the protein loading onto NAZAD is higher than HIZAN. The activity of immobilized lipase was investigated through esterification of oleic acid and 1-butanol in hexane. The effects of pore size, surface area, reaction temperature, thermostability of the immobilized lipases, storage stability in organic solvent, and leaching studies were investigated. Stability was found to be the highest in the nanocomposite NAZAD.     

Micellar electrokinetic chromatography with amperometric detection and off-line solid-phase extraction for analysis of carbamate insecticides

Six selected primary carbamate insecticides, methomyl, carbaryl, carbofuran, propoxur, isoprocarb, and promecarb, were hydrolyzed in alkaline solution, resulting in electroactive derivatives detectable at a platinum (Pt) electrode poised at +0.8 V vs Ag/AgCl (3 M NaCl). The Pt electrode was inserted into a small electrochemical cell and positioned close to the capillary outlet as an end-column detector to detect the carbamate derivatives after electrophoretic separation. Based on their predicted pK_a values and aqueous solubilities, micellar electrokinetic chromatography (MEKC) was optimized for baseline separation of the derivatives using 20 mM borate, pH 10.2 containing 20 mM sodium dodecyl sulfate as a running buffer. When combined with solid-phase extraction (SPE) on octadecyl silica, a preconcentration factor of 100-fold achieved detection to 0.5 μM methomyl and to 0.01 μM for the remaining five pesticides, significantly below the level regulated by government agencies of most countries. The SPE-MEKC method when applied to the separation and analysis of spiked river water and soil samples, yielded results with excellent reproducibility, recovery and selectivity.     

Quantifying Polymer Swelling Employing a Linear Variable Differential Transformer: CO2 Effects on SBS Triblock Copolymer

A linear variable differential transformer (LVDT) was employed to evaluate CO₂‐polymer plasticization. Preliminary results on polystyrene‐block‐polybutadiene‐block‐polystyrene (SBS) elastomer are presented. At 22 °C under CO₂ pressure, SBS undergoes compression due to hydrostatic pressure. However, sample expansion occurs upon depressurization. At 45 °C, SBS undergoes swelling of 0.7% due to CO₂ plasticization, while no post‐pressurization expansion is observed. The contrasting result is explained by change in PS domain mobility and discontinuity in the density‐pressure relationship.

Linear displacement of SBS as a function of time at 56 and 134 bar CO₂.     

Mathematics and Science Teachers' Use of and Confidence in Empirical Reasoning: Implications for STEM Teacher Preparation

The recent trend to unite mathematically related disciplines (science, technology, engineering, and mathematics) under the broader umbrella of STEM education has advantages. In this new educational context of integration, however, STEM teachers need to be able to distinguish between sufficient proof and reasoning across different disciplines, particularly between the status of inductive and deductive modes of reasoning in mathematics. Through a specific set of mathematical conjectures, researchers explored differences between mathematics (n = 24) and science (n = 23) teachers' reasoning schemes, as well as the confidence they had in their justifications. Results from the study indicate differences between the two groups in terms of their levels of mathematical proof, as well as correlational trends that inform their confidence across these levels. Implications particularly for teacher training and preparation within the context of an integrated STEM education model are discussed.     

Equilibrium phase diagrams of aqueous mixtures of malonic acid and sulfate/ammonium salts

Tropospheric aerosols are usually complex mixtures of inorganic and organic components. Although the thermodynamic properties of inorganic aerosols have been widely studied, the effect of organics on such properties is still under discussion. In this study, solubility in water, water activity (a(w)) of aqueous solutions, deliquescence relative humidity (DRH), eutonic composition, and eutonic DRH were determined for bulk mixtures of malonic acid (MA) with ammonium sulfate (AS) and ammonium bisulfate (ABS) at 25 degrees C over the full range of composition (from 0 wt % to the solubility limit of the mixture components). The data were used to construct equilibrium phase diagrams, which show the phase of the mixtures as a function of total composition, dry mixture composition, water content, and ambient relative humidity (RH). This work complements previous reports on the thermodynamic properties of AS/MA mixtures because the range of concentrations investigated is larger than in any other published single study. On the other hand, this is the first report on the a(w), deliquescence, and water absorption of ABS/MA mixtures. The eutonic composition for AS/MA mixtures was found to be 66.8 MA dry wt % (MA dry wt % = MA mass x 100/(AS mass + MA mass) with a DRH of 0.437. The eutonic composition for the ABS/MA mixtures was lower than for the AS/MA mixtures: 20.9 MA dry wt % with a DRH of 0.327. Measured a(w) of liquid AS/MA and ABS/MA solutions is compared with an extended Zdanovskii-Stokes-Robinson expression, obtaining a good agreement (error < 5-6%). The expression was used to predict water uptake of mixtures and might be useful to interpret particle hygroscopic growth experiments. Comparison of the AS/MA and ABS/MA systems indicates that ABS reduces the DRH and enhances water uptake, relative to mixtures with AS. The results confirm that ambient particles containing sulfate and water-soluble organic compounds can remain liquid or partially liquid at very low ambient RH conditions, especially if the sulfate is not completely neutralized.