In situ dual-beam coincidence second harmonic generation as a probe of spatially resolved dynamics at electrochemical interfaces

In situ dual-beam coincidence second harmonic generation was used to monitor spatially resolved dynamics at the Pt(111)/CO-saturated 0.1 M HClO4 interface. The results obtained showed that, for potential steps from 30 to about 870 mV vs RHE, the full electrooxidation of CO as evidenced from SHG occurred at different times for the two areas of the Pt(111) surface probed by the beams. On this basis, the diffusional rates of adsorbed CO cannot be assumed to be generally large enough as to render the entire surface in a homogeneous state, as invoked by the mean field approximation model.     

Comparative study of hydroxyapatite and octacalcium phosphate coatings deposited on metallic implants by PLD method

The aim of the presented study was an analysis of two apatite coatings: hydroxyapatite (HA) and octacalcium phosphate (OCP) as coatings materials for metallic implants. Both layers were deposited by means of the PLD method. As a target material, synthetic, powdered and pressed hydroxyapatite was used. HA was deposited on 316L steel substrate in two temperature ranges for obtaining different coatings: 150±30°C and 430±30°C for OCP and HA, respectively. As an intermediate layer, the nanocrystalline diamond layer (NCD) was deposited. Examined calcium phosphate layers were tested for adhesion of osteoblast cell culture (MG-63). Analytical methods (AFM, FTIR) showed the usefulness of the PLD method for deposition of the apatite layers on metallic implants. Both examined layers showed biocompatibility with human osteoblast cells and presented favorable conditions for their proliferation.     

A Compact Violet Diode Laser-Based Fluorescence Lifetime Microscope

We have constructed a time-correlated single-photon counting (TCSPC) microscope system using a pulsed violet-laser diode for measuring fluorescence lifetimes below 1 ns. These compact; cool, and fast-pulsed laser diodes are much more suitable for lifetime measurements than the traditional mode-locked lasers used in the past. The laser source (LDH-400, PicoQuant GmbH) is mounted on an optical table above the microscope, and the laser beam is directed into an Olympus BX-60 microscope by means of a dichroic beamsplitter set at 45 degrees. The system operates in backscattering mode with the fluorescence emission passing back through the dichroic beamsplitter and focused into a 100 mm focal length monochromator with a PMT detector. This prototype instrument is compact (80 × 70 × 70 cm) and is nearly fully computer controlled by means of a SPC-730 (Becker & Hickl) PC card. We include preliminary results showing the instrument response function (IRF) of the system, and some of the factors have been adjusted to minimize the temporal width of the IRF. The instrument has been validated using a series of standard fluorophores at different emission wavelengths.     

The logarithmic sobolev inequality for discrete spin systems on a lattice

For finite range lattice gases with a finite spin space, it is shown that the Dobrushin-Shlosman mixing condition is equivalent to the existence of a logarithmic Sobolev inequality for the associated (unique) Gibbs state. In addition, implications of these considerations for the ergodic properties of the corresponding Glauber dynamics are examined.During the period of this research, both authors were partially supported by NSF grant DMS 8913328     

On cylindrical symmetric flows through pipe-like domains

We prove existence of cylindrical symmetric solutions to the steady Navier-Stokes equations in bounded pipe-like domains in with the slip boundary conditions. The result is shown for any large flows across the boundary assuming only a geometrical constraint on the shape of the domain which is independent of data. The simply connectedness of the domain is not required. The technique is based on a reformulation of the original problem and delivers us a new type of estimates in the Hölder spaces for this class of the solutions.     

Convertible pneumatic actuator for magnetic resonance elastography of the brain

Here we present a novel pneumatic actuator design for brain magnetic resonance elastography (MRE). Magnetic resonance elastography is a phase contrast technique capable of tracing strain wave propagation and utilizing this information for the calculation of mechanical properties of materials and living tissues. In MRE experiments, the acoustic waves are generated in a synchronized way with respect to image acquisition, using various types of mechanical actuators. The unique feature of the design is its simplicity and flexibility, which allows reconfiguration of the actuator for different applications ranging from in vivo brain MRE to experiments with phantoms. Phantom and in vivo data are presented to demonstrate actuator performance.     

Poly(3-alkylthiophenes): new sorption materials for solid phase microextraction of drugs isolated from human plasma

A novel sorbent in solid phase microextraction (SPME) method based on poly(3-alkylthiophenes) was used in the isolation of linezolid from human plasma samples following liquid chromatography determination. The effect of extraction time on the sorption capacity of the SPME process was studied and pointed at 10 min both for adsorption and desorption. Poly(3-methylthiophene) and poly(3-nonylthiophene) were applied for the extraction of linezolid from water solutions. In plasma samples, four coatings including polythiophene and poly(3-penthylthiophene) were investigated. With these measurements, correlation coefficients were calculated in the range from 0.9820 to 0.9995, and the relative standard deviations were below 15%. That allowed claiming that the synthesized and described materials can be successfully applied in the analysis of linezolid also from other matrices such as urine or blood.     

Electrochemical reactivity of urea at Pt(100) surface in 0.5 M H2SO4 by AC impedance spectroscopy

The present paper reports an alternate current impedance spectroscopic study on adsorption of urea (U) at Pt(100) single-crystal surface, examined in 0.5 M H₂SO₄ supporting electrolyte. The resulted information provided confirmation of the role of electrosorption of urea on the Pt(100) plane through evaluation of the associated charge transfer resistance and capacitance parameters. Obtained impedance results were compared to those previously recorded for guanidinium cation (G⁺) under analogous experimental conditions, especially with respect to the so-called ion pairing mechanism, as originally proposed for the G⁺ ion and bi(sulfate)/OH species, based on the voltammetric and in situ Fourier transform infrared spectroscopy results.     

Single-point imaging with a variable phase encoding interval

A modified single-point imaging (SPI) technique using a variable phase encoding interval is proposed. This method is based on the minimization of the phase encoding interval for further signal-to-noise ratio (SNR) optimization. This is particularly beneficial when the maximum gradient amplitude limits an optimal phase encoding interval, and the resulting SNR suffers from T(2)-related signal attenuation. Theoretical calculation of the SNR and simulation of the point spread function (PSF) for the different experimental parameters are presented. Experiments using a rubber sample (T(2)* approximately 73 micros) and a tooth (bi-exponential relaxation: T(2,1)*=111 micros and T(2,1)*=872 micros) showed a significant increase in SNR (>3 and >2, respectively) when compared with images acquired with conventional SPI.