Absorbance characterization of microsphere-based ion-selective optodes

Ionophore-based microsphere sensors are characterized here in transmission mode. These sensors contain a lipophilic ionophore for the analyte cation, a chromoionophore for recognizing H⁺, and a lipophilic cation-exchanger. They function on the basis of an ion-exchange equilibration step where an increased concentration of analyte ion leads to increased level of extraction into the bulk of the microsphere, expelling protons in return and deprotonating the chromoionophore. Since the path length is variable across the microsphere, such bead-based sensors are normally characterized in fluorescence mode. In this paper, the response of the sensing microspheres is calculated from the ratio of transmitted light intensities at the absorbance peak maxima of the protonated and unprotonated forms of the chromoionophore. At a fixed position of the particle, the resulting responses are found to be independent of light scattering, incident light intensity and the shape or size of the microsphere. The responses of potassium-selective microspheres obtained by this method agree quantitatively with corresponding fluorescence-based data.     

Effect of Air-excess on Blends of RON70 Partially Premixed Combustion

Partially Premixed Combustion (PPC) is a combustion concept that aims to provide combustion with low smoke and NOx emissions and a high thermal efficiency. Extending the ignition delay to enhance premixing, avoiding spray-driven combustion, and controlling temperature at an optimum level through use of suitable dilution levels has been recognized as a key factor to achieve such a concept. Fuels with high auto-ignition resistance do extend ignition delay. In this work three ternary blends of an alcohol (ethanol or n-butanol), n-heptane and iso-octane with a target research octane number (RON) of 70 are studied. RON70 was earlier found to be close to optimal for PPC over a large load range. The objective of this research is to analyze the sensitivity of the combustion parameters to changes in air-excess ratio when using these three blends. The engine was operated at 1250 rpm and 1000 bar injection pressure with a single injection strategy. Results revealed that efficiency was increased from rich to lean combustion, and these three blends show distinct premixed combustion even in lean PPC operation. The premixed fraction of combustion however reduces with the increase of air-excess ratio, which is especially apparent for PRF70 which consists of n-heptane and iso-octane alone.     

Scattering Amplitudes Interpolating Between Instant Form and Front Form of Relativistic Dynamics

Among the three forms of relativistic Hamiltonian dynamics proposed by Dirac in 1949, the front form has the largest number of kinematic generators. This distinction provides useful consequences in the analysis of physical observables in hadron physics. Using the method of interpolation between the instant form and the front form, we introduce the interpolating scattering amplitude that links the corresponding time-ordered amplitudes between the two forms of dynamics and provide the physical meaning of the kinematic transformations as they allow the invariance of each individual time-ordered amplitude for an arbitrary interpolation angle. We discuss the rationale for using front form dynamics, nowadays known as light-front dynamics (LFD), and present a few explicit examples of hadron phenomenology that LFD uniquely can offer from first-principles quantum chromodynamics. In particular, model-independent constraints are provided for the analyses of deuteron form factors and the N Δ transition form factors at large momentum transfer squared Q ². The swap of helicity amplitudes between the collinear and non-collinear kinematics is also discussed in deeply virtual Compton scattering.     

Vibrational spectroscopy of gas-phase neutral and cationic phenanthrene in their electronic groundstates

Various experimental methods are applied to retrieve the vibrational structure of phenanthrene in its neutral and cationic groundstates. The linear infrared (IR) absorption spectra in the 400-1650 cm(-1) range of jet-cooled phenanthrene and its cation, both clustered with either an argon or a neon atom, are obtained via photo-induced cluster dissociation spectroscopy. The spectra observed are in good agreement with calculated spectra of the bare species. However, the observed spectrum of cationic phenanthrene shows more lines and lines with different intensities in the 900-1400 cm(-1) range than expected from calculations. Additional spectra of the perdeuterated phenanthrene Ar cation, and the warm (T approximately > room temperature) bare phenanthrene cation are recorded. Also the mass-analyzed threshold ionization spectra of bare phenanthrene and phenanthrene-Ar are recorded and compared with each other. Comparison of the spectral data recorded to calculated spectra of bare neutral, cationic and cationic perdeuterated phenanthrene, as well as to IR spectra recorded in matrix-isolation experiments, explicitly demonstrates that cluster dissociation spectroscopy is a valid and powerful method to obtain IR spectroscopic information of bare neutral and cationic jet-cooled poly-aromatic hydrocarbons.     

Selective depiction of susceptibility transitions using Laplace-filtered phase maps

In this work, we aim to demonstrate the ability of Laplace-filtered three-dimensional (3D) phase maps to selectively depict the susceptibility transitions in an object. To realize this goal, it is first shown that both the Laplace derivative of the z component of the static magnetic field in an object and the Laplacian of the corresponding phase distribution may be expected to be zero in regions of constant or linearly varying susceptibility and to be nonzero when there is an abrupt change in susceptibility, for instance, at a single point, a ridge, an interface, an edge or a boundary. Next, a method is presented by which the Laplace derivative of a 3D phase map can be directly extracted from the complex data, without the need for phase unwrapping or subtraction of a reference image. The validity of this approach and of the theory behind it is subsequently demonstrated by simulations and phantom experiments with exactly known susceptibility distributions. Finally, the potential of the Laplace derivative analysis is illustrated by simulations with a Shepp-Logan digital brain phantom and experiments with a gel phantom containing positive and negative focal susceptibility deviations.     

Review of inventory systems with deterioration since 2001

This paper presents an up-to-date review of the advances made in the field of inventory control of perishable items (deteriorating inventory). The last extensive review on this topic dates back to 2001 (Goyal S.K. and Giri B.C., Recent trends in modeling of deteriorating inventory, European Journal of Operational Research, 134, 1–16). Since then, over two hundred articles on this subject have been published in the major journals on inventory control, indicating the need for a new review. We use the classification of Goyal and Giri based on shelf life characteristics and demand characteristics. Contributions are highlighted by discussing main system characteristics, including price discounts, backordering or lost sales, single or multiple items, one or two warehouses, single or multi-echelon, average cost or discounted cash flow, and payment delay.     

Structure and dynamics of water in nonionic reverse micelles: A combined time-resolved infrared and small angle x-ray scattering study

We study the structure and reorientation dynamics of nanometer-sized water droplets inside nonionic reverse micelles (water/Igepal-CO-520/cyclohexane) with time-resolved mid-infrared pump-probe spectroscopy and small angle x-ray scattering. In the time-resolved experiments, we probe the vibrational and orientational dynamics of the O-D bonds of dilute HDO:H(2)O mixtures in Igepal reverse micelles as a function of temperature and micelle size. We find that even small micelles contain a large fraction of water that reorients at the same rate as water in the bulk, which indicates that the polyethylene oxide chains of the surfactant do not penetrate into the water volume. We also observe that the confinement affects the reorientation dynamics of only the first hydration layer. From the temperature dependent surface-water dynamics, we estimate an activation enthalpy for reorientation of 45 ± 9 kJ mol(-1) (11?±?2 kcal mol(-1)), which is close to the activation energy of the reorientation of water molecules in ice.     

UV-B absorbance and UV-B absorbing compounds (para-coumaric acid) in pollen and sporopollenin: the perspective to track historic UV-B levels.

UV-B absorbance and UV-B absorbing compounds (UACs) of the pollen of Vicia faba, Betula pendula, Helleborus foetidus and Pinus sylvestris were studied. Sequential extraction demonstrated considerable UV-B absorbance both in the soluble (acid methanol) and insoluble sporopollenin (acetolysis resistant residue) fractions of UACs, while the wall-bound fraction of UACs was small. The UV-B absorbance of the soluble and sporopollenin fraction of pollen of Vicia faba plants exposed to enhanced UV-B (10 kJ m(-2) day(-1) UV-B(BE)) was higher than that of plants that received 0 kJ m(-2) day(-1) UV-B(BB). Pyrolysis gas chromatography-mass spectrometry (py-GC-MS) analysis of pollen demonstrated that p-coumaric acid and ferulic acid formed part of the sporopollenin fraction of the pollen. The amount of these aromatic monomers in the sporopollenin of Vicia faba appeared to increase in response to enhanced UV-B (10 kJ m(-2) day(-1) UV-B(BE)). The detection limit of pyGC-MS was sufficiently low to quantify these phenolic acids in ten pollen grains of Betula and Pinus. The experimental data presented provide evidence for the possibility that polyphenolic compounds in pollen of plants are indicators of solar UV-B and may be applied as a new proxy for the reconstruction of historic variation in solar UV-B levels.     

Real-time probing of the growth dynamics of nanoparticles using potentiometric ion-selective electrodes

This Communication demonstrates the ability of potentiometric ion-selective electrodes (ISE) to probe the growth dynamics of metal nanoparticles in real-time. The new monitoring capability is illustrated using a solid-contact silver ISE for monitoring the hydroquinone-induced precipitation of silver on gold nanoparticle seeds. Potential-time recordings obtained under different conditions are used to monitor the depletion of the silver ion during the nanoparticle formation and shed useful insights into the growth dynamics of the nanoparticles. Such potentiometric profiles correlate well with the analogous optical measurements. The new real-time electrochemical probing of the particle growth process reflects the direct, rapid and sensitive response of modern ISE to changes in the level of the precipitated metal ion from the bulk solution and holds considerable promise for probing the preparation of different nanoscale materials.     

Bonding and redox properties of [Os(3)(CO)(9)(tmbp)(L)] (tmbp=4,4',5,5'-tetramethyl-2,2'-biphosphinine; L=CO, PPh(3)) clusters with an unprecedented electron-deficient metallic core and doubly bridging biphosphinine dianion

Herein we describe in detail the bonding properties and electrochemical behavior of the first known triosmium carbonyl clusters with a coordinated redox-active ligand 4,4',5,5'-tetramethyl-2,2'-biphosphinine (tmbp), the phosphorus derivative of 2,2'-bipyridine. The clusters investigated were [Os(3)(CO)(10)(tmbp)] (1) and its derivative [Os(3)(CO)(9)(PPh(3))(tmbp)] (2). The crystal structures of both clusters are compared with those of relevant compounds; they served as the basis for density functional theory (DFT and time-dependent DFT) calculations. The experimental and theoretical data reveal an unexpected and unprecedented bridging coordination mode of tmbp, with each P atom bridging two metal atoms. The tmbp ligand is formally reduced by transfer of two electrons from the triangular cluster core that consequently lacks one of the metal-metal bonds. Both 1 and 2 therefore represent 50e(-) clusters with a coordinated 8e(-) donor, [tmbp](2-). The HOMO and LUMO of 1 and 2 possess a predominant contribution from different pi*(tmbp) orbitals, implying that the lowest energy excited state possesses a significant intraligand character. This is in agreement with the photostability of these clusters. DFT calculations also predict the experimentally observed structure of 1 to be the most stable one in a series of several plausible structural isomers. Stepwise two-electron electrochemical reduction of 1 and 2 results in dissociation of CO and PPh(3), respectively, and formation of the [Os(3)(CO)(9)(tmbp)](2-) ion. The initially produced radical anions of the parent clusters, in which the odd electron is predominantly localized on the tmbp ligand, are sufficiently stable at low temperatures and can be observed with IR spectroelectrochemistry. The electron-deficiency of the cluster core in 1 permits facile electrocatalytic substitution of a CO ligand by tertiary phosphane and phosphite donors.