Sensors for chemicals based on electrically conductive immiscible HIPS/TPU blends containing carbon black

Carbon Black (CB)-containing immiscible polymer blends based on high-impact polystyrene/thermoplastic polyurethane (HIPS/TPU) were studied as sensing materials for an homologous series of alcohols, including, methanol, ethanol and 1-propanol. The studied immiscible blend was designed to exhibit a double-continuity structure i.e., the CB particles form chain-like network structures within the TPU phase, which forms a continuous phase within the HIPS matrix. Extruded HIPS/TPU/CB filaments produced by a capillary rheometer process at various shear rate levels were used for the sensing experiments. All filaments displayed a selective resistance changes upon exposure to the various alcohols combined with reproducibility and recovery behaviour. An attempt is made to identify the dominant mechanisms controlling the sensing process in a CB-containing immiscible polymer blend characterized by a double-continuity structure. The distinct structure and composition of the HIPS/TPU interphase region were found to have a crucial role in the sensing mechanism, determining the selectivity of the filaments toward the studied alcohols. Additionally, the sensing performance of HIPS/TPU/CB system is compared to recent results for TPU/CB compounds, polypropylene/TPU/CB and HIPS/ethylene vinyl acetate/CB immiscible polymer blends.     

Electrophysiological properties and cholinergic responses of rat ventral oral pontine reticular neurons in vitro

This study analyses the relationship between the use of rotating instruments, the production of a smear layer and the presence of alterations to enamel microstructures. The rotating instruments used were carbide (8-12 blade) and diamond tipped (30-15 m) cutters. Cavities were made in extracted teeth. Subsequently, half the sample was analysed using the rugosimeter before and after the application of ortophosphoric acid at 35% for 15 and the other half suing a Scansion Electronic microscope (SEM). The results obtained showed on the one hand that carbide cutters leave a smoother surfacer than diamond tipped cutters, and on the other that the smear layer is eliminated better by carbide cutters compared to diamond tipped cutters. Moreover, there are no major traumatic-type alterations at the level of the enamel affecting the microstructure after the use of carbide cutters.     

Using Multiple Solution Tasks for the Evaluation of Students’ Problem-Solving Performance in Geometry

Abstract

The article demonstrates that multiple solution tasks (MSTs) in the context of geometry can serve as a research instrument for evaluating geometry knowledge and creativity. Geometry knowledge is evaluated based on the correctness and connectedness of solutions, whereas creativity is evaluated based on a combination of fluency, flexibility, and originality of solutions. In this article, the MST research instrument is introduced in connection with the theoretical analysis of the research literature and then explained and analyzed using geometry students’ performance results on one MST. The analysis shows that the research instrument differentiates between students belonging to high- and regular-level instruction groups and sheds light on the interrelations between components of geometry knowledge and creativity.     

Micellization Behavior of Long-Chain Substituted Alkylguanidinium Surfactants

Surface activity and micelle formation of alkylguanidinium chlorides containing 10, 12, 14 and 16 carbon atoms in the hydrophobic tail were studied by combining conductivity and surface tension measurements with isothermal titration calorimetry. The purity of the resulting surfactants, their temperatures of Cr→LC and LC→I transitions, as well as their propensity of forming birefringent phases, were assessed based on the results of ¹H and ¹³C NMR, differential scanning calorimetry (DSC), and polarizing microscopy studies. Whenever possible, the resulting values of Krafft temperature (T_K), critical micelle concentration (CMC), minimum surface tension above the CMC, chloride counter-ion binding to the micelle, and the standard enthalpy of micelle formation per mole of surfactant (Δ_micH°) were compared to those characterizing alkyltrimethylammonium chlorides or bromides with the same tail lengths. The value of T_K ranged between 292 and 314 K and increased strongly with the increase in the chain length of the hydrophobic tail. Micellization was described as both entropy and enthalpy-driven. Based on the direct calorimetry measurements, the general trends in the CMC with the temperature, hydrophobic tail length, and NaCl addition were found to be similar to those of other types of cationic surfactants. The particularly exothermic character of micellization was ascribed to the hydrogen-binding capacity of the guanidinium head-group.     

A CMOS V-I converter with 75-dB SFDR and 360-/spl mu/W power consumption

This work describes a method for analysis of voltage-to-current converters (V-I converters or transconductors) and a novel V- I converter circuit with significantly improved linearity. The new circuit utilizes a combination of cross-coupling and local resistive feedback for a significant, simultaneous suppression of the third- and fifth-order harmonic distortion components in the transconductor characteristics. An evaluation of the optimal circuit dimensioning is shown. Simple and robust design rules are derived for the chosen operation conditions. The transistor implementation is presented and a prototype V- I converter is realized in a digital 0.18-/spl mu/m CMOS technology. The measured spurious-free dynamic range is 75 dB in a frequency band of 10 MHz. The circuit occupies less than 0.02 mm/sup 2/ and dissipates 360 /spl mu/W.     

Phytoextraction of Au: Uptake,accumulation and cellular distribution in Medicago sativa and Brassica juncea

The influence of metal concentration, solution pH and exposure time on the phytoextraction (i.e. separation using vascular plants) of Au was investigated for the known metallophytes Brassica juncea (BJ) and Medicago sativa (MS). Metal uptake was inferred using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and in vivo localisation and distribution using proton induced X-ray emission spectroscopy (μ-PIXE). MS roots accumulated a maximum of 287 mg Au g^?1 (dry biomass) and BJ roots a maximum of 227 mg Au g^?1 (dry biomass), both when exposed to a 10,000 ppm aqueous solution of KAuCl_4. MS was found to accumulate comparatively greater quantities of Au than BJ across higher substrate concentrations (40–10,000 ppm Au) whereas BJ was found to be a better accumulator of Au at lower concentrations (5–20 ppm Au). In general MS showed an increase in Au uptake with an increase in Au substrate concentration and the time exposed, whereas for BJ the maximum uptake was observed after 48 h of exposure at higher concentrations (100–10,000 ppm), and then decreased at longer exposure times. The uptake ratio (UR), defined as the ratio of Au concentration in plant tissues to the concentration in the substrate, increased with increasing concentration and exposure time, to a maximum of 995 for MS roots after 72 h exposure. Metal translocation from roots to shoots in BJ increased with increasing substrate concentration, however in the shoots, metal uptake increased from 24 to 48 h and then decreased at 72 h, indicating some threshold level had been reached and metal was then being excluded from the cells, possibly through the phloem to the Au solution. Elemental distribution maps of plant tissues measured using μ-PIXE, show Au present across the entire sample, ranging from the epidermis and cortex, with the greatest concentration occurring within the central stele. This result is suggestive of xylem loading. These results collectively suggest that the separation of Au using vascular plants for applications in mining (phytomining) and remediation (phytoremediation) are viable technologies.     

Removal of some organic pollutants in water employing ceramic membranes impregnated with cross-linked silylated dendritic and cyclodextrin polymers

Triethoxysilylated derivatives of poly(propylene imine) dendrimer, polyethylene imine and polyglycerol hyperbranched polymers and beta-cyclodextrin have been synthesized and characterized. These compounds impregnated ceramic membranes made from Al(2)O(3), SiC and TiO(2) and subsequently sol-gel reaction led to their polymerization and chemical bond formation with the ceramic substrates. The resulting organic-inorganic filters were tested for the removal of a variety of organic pollutants from water. They were found to remove of polycyclic aromatic hydrocarbons (up to 99%), of monocyclic aromatic hydrocarbons (up to 93%), trihalogen methanes (up to 81%), pesticides (up to 43%) and methyl-tert-butyl ether (up to 46%).     

The structure and electro‐mechanical properties of novel hybrid CNT/PANI nanocomposites

Electrically conductive elastomeric nanocomposites containing carbon nanotubes (CNT) and polyaniline (PANI) are reported in the present investigation. The synthesis procedure included an in situ inverse emulsion polymerization of aniline doped with dodecylbenzene sulfonic acid (DBSA) in the presence of CNT and dissolved styrene‐isoprene‐styrene (SIS) block copolymer. The PANI synthesis step was carried out by applying ultrasonic energy. The dispersions obtained were processed by two methods: a recently developed precipitation‐filtration procedure, and a conventional drop‐cast procedure. The techniques developed resulted in homogeneous exfoliated PANI coated nanotubes within the elastomeric matrix. The presence of CNT/PANI in the SIS elastomeric matrix affects thermal, mechanical, and electrical properties of the nanocomposites. The formation of continuous three‐dimensional CNT/PANI networks prepared via the precipitation‐filtration method enhances the nanocomposite properties. Contrarily, the intermittent three‐dimensional network prepared by conventional drop‐cast method leads to inferior properties. Nanocomposites produced by both techniques are observed by HRSEM. The two processing techniques result in different structures, which affect the physical properties of the materials produced. A relatively low percolation threshold for both methods was determined. The Young's modulus of the SIS/CNT/PANI significantly increased in the presence of CNT. The precipitation‐filtration technique yields an improved nanocomposite product compared to the drop‐cast route. POLYM. COMPOS., 35:788–794, 2014. © 2013 Society of Plastics Engineers     

The NSAID dexketoprofen trometamol is as potent as mu-opioids in the depression of wind-up and spinal cord nociceptive reflexes in normal rats

The aim of this study was to examine the potency of the antinociceptive effects of the non-steroidal antiinflammatory drug (NSAID), Dexketoprofen Trometamol (the active enantiomer of ketoprofen) on spinal cord nociceptive reflexes. These effects were compared with those of the mu-opioid receptor agonist fentanyl in normal animals. The experiments were performed in male Wistar rats anaesthetised with alpha-chloralose. The nociceptive reflexes were recorded as single motor units in peripheral muscles, activated by mechanical and electrical stimulation. Both dexketoprofen and fentanyl inhibited responses evoked by mechanical and electrical stimulation with doses in the same nanomolar range (dexketoprofen ID50s: 100 and 762 nmol kg-1 and fentanyl: 40 and 51 nmol kg-1, respectively). Dexketoprofen and fentanyl also significantly inhibited wind-up. Since fentanyl has been shown to be some 1000 times more potent than morphine in this type of experiments, we conclude that dexketoprofen has central analgesic actions in normal animals and depresses nociceptive responses with a potency similar to that of mu-opioid agonists.     

Pressor responses to distension of the ureter in anaesthetised rats: characterisation of a model of acute visceral pain

HIV-associated dementia is a frequent consequence of HIV infection and relates to neuronal damage, possibly as a result of increased neurotoxic kynurenine metabolites. Indoleamine-2,3-dioxygenase (IDO) activity, which regulates kynurenine metabolism, may thus be increased in HIV infection. We measured IDO activity in post-mortem brain tissue from AIDS patients, including a subgroup that exhibited dementia, and age-matched control subjects. IDO activity was increased, but not significantly, in the AIDS group as well as the non-dementia group, compared to controls. Enzyme activity was significantly increased in the dementia group when compared to control values. IDO activity is increased in HIV-associated dementia and is thus likely to increase kynurenine pathway metabolites, such as 3-hydroxykynurenine and quinolinic acid, and elevated levels of these neurotoxins may contribute to the neuronal deficits underlying HIV-associated dementia.