Bulk and surface switching in Mn-Fe-based Prussian blue analogues

Many Prussian Blue Analogues are known to show a thermally induced phase transition close to room temperature and a reversible, photo-induced phase transition at low temperatures. This work reports on magnetic measurements, X-ray photoemission and Raman spectroscopy on a particular class of these molecular heterobimetallic systems, specifically on Rb0.81Mn[Fe(CN)6]0.95_1.24H2O, Rb0.97Mn[Fe(CN)6]0.98_1.03H2O and Rb0.70Cu0.22Mn0.78[Fe(CN)6]0.86_2.05H2O, to investigate these transition phenomena both in the bulk of the material and at the sample surface. Results indicate a high degree of charge transfer in the bulk, while a substantially reduced conversion is found at the sample surface, even in case of a near perfect (Rb:Mn:Fe=1:1:1) stoichiometry. Thus, the intrinsic incompleteness of the charge transfer transition in these materials is found to be primarily due to surface reconstruction. Substitution of a large fraction of charge transfer active Mn ions by charge transfer inactive Cu ions leads to a proportional conversion reduction with respect to the maximum conversion that is still stoichiometrically possible and shows the charge transfer capability of metal centers to be quite robust upon inclusion of a neighboring impurity. Additionally, a 532 nm photo-induced metastable state, reminiscent of the high temperature Fe(III)Mn(II) ground state, is found at temperatures 50-100 K. The efficiency of photo-excitation to the metastable state is found to be maximized around 90 K. The photo-induced state is observed to relax to the low temperature Fe(II)Mn(III) ground state at a temperature of approximately 123 K.

Photo-dissolution of flocculent, detrital material in aquatic environments: Contributions to the dissolved organic matter pool

This study shows that light exposure of flocculent material (floc) from the Florida Coastal Everglades (FCE) results in significant dissolved organic matter (DOM) generation through photo-dissolution processes. Floc was collected at two sites along the Shark River Slough (SRS) and irradiated with artificial sunlight. The DOM generated was characterized using elemental analysis and excitation emission matrix fluorescence coupled with parallel factor analysis. To investigate the seasonal variations of DOM photo-generation from floc, this experiment was performed in typical dry (April) and wet (October) seasons for the FCE. Our results show that the dissolved organic carbon (DOC) for samples incubated under dark conditions displayed a relatively small increase, suggesting that microbial processes and/or leaching might be minor processes in comparison to photo-dissolution for the generation of DOM from floc. On the other hand, DOC increased substantially (as much as 259 mgC gC−1) for samples exposed to artificial sunlight, indicating the release of DOM through photo-induced alterations of floc. The fluorescence intensity of both humic-like and protein-like components also increased with light exposure. Terrestrial humic-like components were found to be the main contributors (up to 70%) to the chromophoric DOM (CDOM) pool, while protein-like components comprised a relatively small percentage (up to 16%) of the total CDOM. Simultaneously to the generation of DOC, both total dissolved nitrogen and soluble reactive phosphorus also increased substantially during the photo-incubation period. Thus, the photo-dissolution of floc can be an important source of DOM to the FCE environment, with the potential to influence nutrient dynamics in this system.

Electrical study of impurity states in conjugated polymers

Schottky diodes resulting from an intimate contact of aluminum on electro-deposited poly(3-methylthiopene), PMeT, have been studied by admittance spectroscopy, capacitance-voltage and current-voltage measurements, and optically-induced current transients. The loss-tangents show the existence of interface states that can be removed by vacuum annealing, also visible in the transients. Furthermore, the CV curves don't substantiate the idea of movement of the dopant ions.

Electrical characterization of semiconducting polymers

Schottky diodes resulting from an intimate contact of aluminum on electrodeposited poly(3-methylthiopene) were studied by admittance spectroscopy, capacitance-voltage measurements and voltaic and optically-induced current and capacitance transients. The loss tangents show the existence of interface states that can be removed by vacuum annealing. Furthermore, the C-V curves contradict the idea of movement of the dopant ions.

Minority-carrier effects in poly-phenylenevinylene as studied by electrical characterization

Electrical measurements have been performed on poly[2-methoxy, 5 ethyl (2' hexyloxy) paraphenylenevinylene] in a pn junction with silicon. These included current-voltage measurements, capacitance-voltage measurements, capacitance-transient spectroscopy, and admittance spectroscopy. The measurements show evidence for large minority-carrier injection into the polymer possibly enabled by interface states for which evidence is also found. The shallow acceptor level depth (0.12 eV) and four deep trap level activation energies (0.30 and 1.0 eV majority-carrier type; 0.48 and 1.3 eV minority-carrier type) are found. Another trap that is visible at room temperature has point-defect nature. (C) 2001 American Institute of Physics.

Electrical study of impurity states in conjugated polymers

Schottky diodes resulting from an intimate contact of aluminum on electro-deposited poly(3-methylthiopene), PMeT, have been studied by admittance spectroscopy, capacitance-voltage and current-voltage measurements, and optically-induced current transients. The loss-tangents show the existence of interface states that can be removed by vacuum annealing, also visible in the transients. Furthermore, the CV curves don't substantiate the idea of movement of the dopant ions.

Electrical characterization of semiconducting polymers

Schottky diodes resulting from an intimate contact of aluminum on electrodeposited poly(3-methylthiopene) were studied by admittance spectroscopy, capacitance-voltage measurements and voltaic and optically-induced current and capacitance transients. The loss tangents show the existence of interface states that can be removed by vacuum annealing. Furthermore, the C-V curves contradict the idea of movement of the dopant ions.

Improved generation lifetime model for the electrical characterization of single- and double-gate SOI nMOSFETs

This work proposes a refined technique for the extraction of the generation lifetime in single- and double-gate partially depleted SOI nMOSFETs. The model presented in this paper, based on the drain current switch-off transients, takes into account the influence of the laterally non-uniform channel doping, caused by the presence of the halo implanted region, and the amount of charge controlled by the drain and source junctions on the floating body effect when the channel length is reduced. The obtained results for single- gate (SG) devices are compared with two-dimensional numerical simulations and experimental data, extracted for devices fabricated in a 0.1 mu m SOI CMOS technology, showing excellent agreement. The improved model to determine the generation lifetime in double-gate (DG) devices beyond the considerations previously presented also consider the influence of the silicon layer thickness on the drain current transient. The extracted data through the improved model for DG devices were compared with measurements and two-dimensional numerical simulations of the SG devices also presenting a good adjustment with the channel length reduction and the same tendency with the silicon layer thickness variation.

Anharmonic effects on a phonon-number measurement of a quantum-mesoscopic-mechanical oscillator

We generalize a proposal for detecting single-phonon transitions in a single nanoelectromechanical system (NEMS) to include the intrinsic anharmonicity of each mechanical oscillator. In this scheme two NEMS oscillators are coupled via a term quadratic in the amplitude of oscillation for each oscillator. One NEMS oscillator is driven and strongly damped and becomes a transducer for phonon number in the other measured oscillator. We derive the conditions for this measurement scheme to be quantum limited and find a condition on the size of the anharmonicity. We also derive the relation between the phase diffusion back-action noise due to number measurement and the localization time for the measured system to enter a phonon-number eigenstate. We relate both these time scales to the strength of the measured signal, which is an induced current proportional to the position of the read-out oscillator.

An ATP-sensitive K+ conductance in dissociated neurones from adult rat intracardiac ganglia

1. An ATP-sensitive K+ (K-ATP) conductance has been identified using the perforated patch recording configuration in a population (52%) of dissociated neurones from adult rat intracardiac ganglia. The presence of the sulphonylurea receptor in approximately half of the intracardiac neurones was confirmed by labelling with fluorescent glibenclamide-BODIPY. 2. Under current clamp conditions in physiological solutions, leveromakalim (10 muM) evoked a hyperpolarization, which was inhibited by the sulphonylurea drugs glibenclamide and tolbutamide. 3. Under voltage clamp conditions in symmetrical (140 mM) K+ solutions, hath application of levcromakalim evoked an inward current with a density of similar to8 pA pF(-1) at -50 mV and a slope conductance of similar to9 nS, which reversed close to the potassium equilibrium potential (E-K). Cell dialysis with an ATP-free intracellular solution also evoked an inward current, which was inhibited by tolbutamide. 4. Bath application of either glibenclamide (10 muM) or tolbutamide (100 muM) depolarized adult intracardiac neurones by 3-5 mV, suggesting that a K-ATP conductance is activated under resting conditions and contributes to the resting membrane potential. 5. Activation of a membrane current by levcromakalim leas concentration dependent, with an EC50 of 1.6 muM. Inhibition of the levcromakalim-activated current by glibenclamide leas also concentration dependent, with an IC50 of 55 nM. 6. Metabolic inhibition with 2,4-dinitrophenol and iodoacetic acid or superfusion with hypoxic solution (P-O2 similar to 16 mmHg) also activated a membrane current. These currents exhibited similar I-P characteristics to the levcroinakalim-induced current and were inhibited by glibenclamide. 7. Activation of K-ATP channels in mammalian intracardiac neurones may contribute to changes in neural regulation of the mature heart and. cardiac function during ischaemia-reperfusion.

Ionic selectivity of native ATP-activated (P2X) receptor channels in dissociated neurones from rat parasympathetic ganglia

1. The relative permeability of the native P2X receptor channel to monovalent and divalent inorganic and organic cations was determined from reversal potential measurements of ATP-evoked currents in parasympathetic neurones dissociated from rat submandibular ganglia using the dialysed whole-cell patch clamp technique. 2. The P2X receptor-channel exhibited weak selectivity among the alkali metals with a selectivity sequence of Na+ > Li+ > Cs+ > Rb+ > K+, and permeability ratios relative to Cs+ (P-X/P-Cs) ranging from 1. 11 to 0.86. 3. The selectivity for the divalent alkaline earth cations was also weak with the sequence Ca2+ > Sr2+ > Ba2+ > Mn2+ > Mg2+. ATP-evoked currents were strongly inhibited when the extracellular divalent cation concentration was increased. 4, The calculated permeability ratios of different ammonium cations are higher than those of the alkali metal cations. The permeability sequence obtained for the saturated organic cations is inversely correlated with the size of the cation. The unsaturated organic cations have a higher permeability than that predicted by molecular size. 5. Acidification to pH 6.2 increased the ATP-induced current amplitude twofold, whereas alkalization to 8.2 and 9.2 markedly reduced current amplitude. Cell dialysis with either anti-P2X(2) and/or anti-P2X(4) but not anti-P2X(1) antibodies attenuated the ATP-evoked current amplitude. Taken together, these data are consistent with homomeric and/or heteromeric P2X(2) and P2X(4) receptor subtypes expressed in rat submandibular neurones. 6. The permeability ratios for the series of monovalent organic cations, with the exception of unsaturated cations, were approximately related to the ionic size. The relative permeabilities of the monovalent inoganic and organic cations tested are similar to those reported previously for cloned rat P2X2 receptors expressed in mammalian cells.

A synthetic xylanase as a novel reporter in plants

Transient gene expression assays are often used to screen promoters before stable transformation. Current transient quantification methods have several problems, including a lack of reporter gene stability and expense. Here we report a synthetic, codon-optimised xylanase gene (sXynA) as a reporter gene for quantitative transient analyses in plants. Azurine-crosslinked xylan (AZCL-xylan) was used as a substrate for assaying xylanase activity. The enzymatic nature of the protein allows for sensitive assays at the low levels of transgene protein found in transiently transformed tissue extracts. The xylanase (XYN) protein is stable, activity slopes are linear over long time periods and assays are cost-effective. Coupled with the GUSPlus reporter gene, the XYN reporter allows sensitive and accurate quantification of gene control sequences in transient expression systems.

Surge damping analysis in pipe systems: modelling and experiments

The current study focuses on the analysis of pressure surge damping in single pipeline systems generated by a fast change of flow, conditions. A dimensionless form of pressurised transient flow equations was developed. presenting the main advantage of being independent of the system characteristics. In lack of flow velocity profiles. the unsteady friction in turbulent regimes is analysed based on two new empirical corrective-coefficients associated with local and convective acceleration terms. A new, surge damping approach is also presented taking into account the pressure peak time variation. The observed attenuation effect in the pressure wave for high deformable pipe materials can be described by a combination of the non-elastic behaviour of the pipe-wall with steady and unsteady friction effects. Several simulations and experimental tests have been carried out. in order to analyse the dynamic response of single pipelines with different characteristics, such as pipe materials. diameters. thickness. lengths and transient conditions.

Novel structure for large area image sensing

This work presents preliminary results in the study of a novel structure for a laser scanned photodiode (LSP) type of image sensor. In order to increase the signal output, a stacked p-i-n-p-i-n structure with an intermediate light-blocking layer is used. The image and the scanning beam are incident through opposite sides of the sensor and their absorption is kept in separate junctions by an intermediate light-blocking layer. As in the usual LSP structure the scanning beam-induced photocurrent is dependent on the local illumination conditions of the image. The main difference between the two structures arises from the fact that in this new structure the image and the scanner have different optical paths leading to an increase in the photocurrent when the scanning beam is incident on a region illuminated on the image side of the sensor, while a decreasing in the photocurrent was observed in the single junction LSP. The results show that the structure can be successfully used as an image sensor even though some optimization is needed to enhance the performance of the device.

Ultrasensitive reporter protein detection in genetically engineered bacteria.

We demonstrate the use of laser-induced fluorescence confocal spectroscopy to measure analyte-stimulated enhanced green fluorescent protein (egfp) synthesis by genetically modified Escherichia coli bioreporter cells. Induction is measured in cell lysates and, since the spectroscopic focal volume is approximately the size of one bioreporter cell, also in individual live bacteria. This is, to our knowledge, the first ever proof-of-concept work utilizing instrumentation with single-molecule detection capability to monitor bioreporter response. Although we use arsenic inducible bioreporters here, the method is extensible to gfp/egfp bioreporters that are responsive to other substances.