Longitudinal Absorption Research Articles

Determination of lead in whole blood: Comparison of the LeadCare blood lead testing system with Zeeman longitudinal electrothermal atomic absorption spectrometry

This study compares the efficiency of blood lead level analysis by graphite furnace atomic absorption spectrometry (GFAAS) and the portable LeadCare Blood Lead Testing System (LCS). Recoveries of two added lead concentrations of 22 and 42 micrograms/dL ranged from 102.4 to 105.5% for LCS and from 96.3 to 97.2% for GFAAS. Measurement of a certified sample (Certified Danish Whole Blood) at a blood lead concentration of 26.2 micrograms/dL gave within- and between-run coefficients of variation which were both approximately 8% by LCS and 2% by GFAAS. Comparison of the tested method (LCS) versus GFAAS from analysis of 76 samples of blood lead collected from workers in different industrial sectors showed imperfect overall correlation (r = 0.95). The LCS is quite suitable for screening purposes, but requires the use of non-frozen blood collected less than 24 h before. Conservative threshold values should be applied when using the LCS for initial screening in the field.

Spectroscopic determination of the melting energy of a gold nanorod

Gold nanorods in colloidal solution can be melted into spherical nanoparticles by excitation with intense femtosecond laser pulses of the proper energy. The threshold of the laser pulse energy for the complete melting of the nanorods with a mean aspect ratio of 4.1 in solution is determined by observing the change in the absorption intensity of the longitudinal absorption band (measure of the rod concentration) at 800 nm with increasing number of laser pulses of known energy. The number of laser pulses needed to reduce the band intensity (rod concentration) by 1/e of its initial value is determined as the laser energy per pulse increases. For pulses of lower energy than threshold, it is found that the number of pulses required to melt the gold nanorods present in solution increases significantly with decreasing laser pulse energy. Above threshold, this number is constant since the additional absorbed laser energy will only further heat the particles to temperatures above their melting point. The gold concentration in the colloidal solution is measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES), from which the gold nanorod concentration is determined from the known shape and size distribution obtained from transmission electron microscopy (TEM) results. A simple analysis using the determined threshold energy and the nanorod concentration showed that it takes an average of ∼ 60 femtojoule (fJ) to melt a single gold nanorod. Experiments using 820 nm as well as 410 nm femtosecond laser pulses yield similar values, indicating that the laser induced shape transformation of the nanorods is independent of the irradiation wavelength and that this process is therefore photothermal in origin.

Hole Scattering in p-type Wurtzite Gallium Nitride

ABSTRACTWe investigate acoustic phonon scattering processes for holes in wurtzite gallium nitride. Using a six-band Rashba-Sheka-Pikus Hamiltonian description of the valence bands of gallium nitride, total scattering rates are calculated by numerical integration over final states. An examination of the interband and intraband processes shows strong scattering rate anisotropy between holes moving parallel to and perpendicular to the hexagonal plane. Results are given for inelastic acoustic deformation potential and piezoelectric scattering processes involving both longitudinal and transverse acoustic phonon absorption.

Nonequilibrium electron distributions in a three-subband InGaAs/InAlAs quantum well studied via double resonance spectroscopy

Midinfrared optical pumping of electrons from the ground (n=1) to the first excited (n=2) subband of the quantum well produces a strongly nonthermal electron distribution which is probed spectroscopically. Two sharp induced absorption peaks appear, associated with electrons which have scattered from the upper subband via longitudinal optical (LO) phonon emission and absorption. The presence of the phonon absorption channel evidences the importance of nonequilibrium LO phonon populations (nph∼1), and the impact on the nonradiative intersubband scattering rates in quantum cascade laser devices is explored.

Metal Nanowires and Intercalated Metal Layers in Single-Walled Carbon Nanotube Bundles

Nanowires of Au, Ag, Pt, and Pd (1.0−1.4 nm diam) have been produced in the capillaries of single-walled carbon nanotubes (SWNTs). The nanowire is single-crystalline in some cases. Dispersions of the nanowires in alcohol show longitudinal plasmon absorption bands at different wavelengths, suggesting the presence of a distribution of aspect ratios. A novel phenomenon involving the intercalation of metal layers (∼0.5 nm thick) in the intertubular space of SWNT bundles has been observed. SWNTs decorated by metal nanoparticles are formed in some of the preparations.

Nonlinear absorption and refractive index measurements of silver nanorods by the Z-scan technique

We report the first measurement on the nonlinear optical coefficients of ellipsoidal silver nanoparticles in the longitudinal surface plasmon absorption region (800 nm), by using the Z-scan technique. It has been observed that the nonlinear absorption and nonlinear index of silver nanorods embedded in borosilicate glass differ remarkably from those of spheroids.

Ultrasonic Investigation of Polyurethane Gel Forming Systems

Polyurethane systems corresponding to different reaction extents of the gelation process are investigated by ultrasonic methods in order to apprehend their high-frequency dynamical properties and their evolution during formation. The longitudinal moduli M calculated from the measurement of the longitudinal velocity and absorption exhibit a relaxation behavior which is attributed to the α process. The results are analyzed by comparison with low-frequency rheological data, allowing a more complete description of this relaxation by the Tamman−Vogel−Hesse−Fulcher equation. As moduli M are obtained versus temperature at a single frequency, data are treated by a transformed Havriliak−Negami function. The α relaxation process probed by ultrasonics is larger than the rheological one, which has been interpreted in terms of the influence of a secondary relaxation merging at high temperature.

Thermal Reshaping of Gold Nanorods in Micelles

Gold nanorods are prepared in aqueous solution by an electrochemical method and are shape controlled by using capping micelles as described by Yu et al. (J. Phys. Chem. B 1997, 101 (34), 6661). Transmission electron microscopic (TEM) images are determined for these gold nanorods, taken from solutions heated to various temperatures in the range of 25−160 °C. Size and shape analysis of their TEM images showed that the mean aspect ratio of the nanorods in solution decreases with increasing temperature, mostly as a result of reduction in their length. Heating the dried nanorods themselves on a TEM slide to much higher temperatures does not produce any shape changes. This suggests that the observed relative instability of the longer nanorods in the micellar solutions is attributed to the relative instability of the micelles capping the longer gold nanorods. Following the change with time of the longitudinal surface plasmon absorption band of the gold nanorods at five different temperatures, the activation ener...

Saturated 43-μm fluorescence frequency stabilization of a sequence-band CO_2 laser

The saturated 4.3-μm fluorescence frequency stabilization method has been extended to a sequence-band CO2 laser. Owing to little photon trapping, we can detect the 4.3-μm fluorescence with a good signal-to-noise ratio by using a longitudinal CO2 absorption cell heated to 200°C. The frequency stability estimated from the residual error signal is better than 50 kHz.

Ski having improved shock absorption and vibration resistance

A ski for use on snow comprises a longitudinally extending body defining a longitudinal median plane and having a sole substantially perpendicular thereto for slidably engaging a surface. The sole has a central zone lying between front and rear contact lines. The width of the body is established by opposed lateral surfaces, and the thickness of the body is established by an upper wall opposed to the sole. A longitudinal core extends along the length of the body between front and rear ends of the ski and has a width established by lateral side walls that respectively face the lateral surfaces of the body. The thickness of the core is established by upper and lower walls. The ski also includes mechanical resistance elements, internal longitudinal shock absorption members made of a viscoelastic material, and filling elements connecting the resistance elements to the other elements. The internal shock absorption members are in the form of a pair of lateral strips of viscoelastic material, each strip being sandwiched between a lateral surface of the body and the facing lateral wall of the core. The lateral side walls of the core make respective inclination angles A and B with the sole of the body, the inclination angles being a nonconstant function of the length of the core for effecting mechanical shock absorption properties which vary longitudinally along the body.

Ultrasonic investigation of some rubber blends

AbstractCompression ultrasonic velocity, longitudinal ultrasonic absorption, and heat of mixing for NR‐BR, NR, NBR, and NR‐IIR rubber blends were measured. Results show the applicability of examining the compatibility degree by using longitudinal ultrasonic absorption techniques. Results showed that NR‐BR blends are compatible, whereas NR‐NBR and NR‐IIR blends are semicompatible and incompatible, respectively.

Characteristics of improved microwave interstitial antennas for local hyperthermia

The heating potentials of two newly-developed microwave interstitial antennas are reported in this paper. The longitudinal (parallel to the antenna) and transverse (over a plane perpendicular to the antenna) specific absorption rate (SAR) distributions of single and an array of four parallel antennas were measured in a muscle equivalent phantom and their performance characterized at 915 MHz in terms of the following parameters: peak depth (location of the profile peak with respect to the surface), 50% HL (effective heating length over which SAR > 50% of the peak normalized SAR), dead length (axial length at the antenna tip with SAR < 50% of peak normalized SAR), and the variations of the specific absorption rate pattern relative to the depth of insertion. The results are analyzed and discussed in terms of these parameters and other factors important in the clinical use of these antennas for effective interstitial hyperthermia.

The Effect of Crosslinks on Ultrasonic Properties in Glassy Epoxy Resin

Ultrasonic properties in epoxy resins cured with three different curing agents, methylnadic anhydride (MNA) and two kinds of aliphatic diamine, were investigated in the MHz region. The apparent moduli calculated from ultrasonic velocities and longitudinal absorptions in glassy resins show a decrease of elasticity with crosslinking in the MNA cured system, whereas the elasticity of rubbery resins has been reported to be proportional to the amount of crosslinks. The elasticity in glassy resins depends on the glass transition process, and we observed a similar phenomenon in the diamine system cured at high temperature.

Heating pattern of helical microwave intracavitary oesophageal applicator

Helical microwave intracavitary oesophageal (HMIO) applicators were designed to operate at frequencies of 433 MHz and 915 MHz. Heating patterns were studied within muscle-equivalent phantom by thermographic camera and fibreoptic thermometers. The results showed that frequency significantly influenced the microwave heating pattern. The 433 MHz applicator had a single power deposition region, the longitudinal specific absorption rate (SAR) distribution appeared to be nearly even, and the maximum SAR value occurred close to the centre of the active length of the applicator. The 915 MHz applicator had two power deposition regions, the peak SAR values occurred at about 1/4 and 3/4 of the active length respectively. The radial SAR distribution suggested that there is no obvious difference between the 433 MHz and 915 MHz applicators in that the average radial penetration of 50% surface SAR (RP50) was about 0.65 cm. It was also shown that power deposition was axially symmetric for both 433 MHz and 915 MHz HMIO applicators. It is shown that better impedance matching is more important for intracavitary hyperthermia than for external hyperthermia. Choosing HMIO applicators in clinical practice is also discussed.

Infrared spectra of large clusters containing small ether molecules: Liquid, crystalline, and clathrate-hydrate cluster spectra

Large clusters of different structural phases containing the small-ring ether molecules tetrahydrofuran, trimethylene oxide, and ethylene oxide have been prepared and studied spectroscopically using a simple cluster cell based on a small infrared gas cell. Pure ether clusters are formed efficiently upon loading of the precooled cell (80–130 K) to pressures of a few hundred Torr with a gaseous mixture of an ether diluted with N2. For the right choice of temperature the pure ether clusters, which tend to be exceptionally large, initially assume a supercooled liquid structure but convert to the stable crystal structure over the observation time of a few minutes. Approximate nucleation temperatures, for this phase transition, range from 125 K for tetrahydrofuran to 100 K for ethylene oxide. The crystalline-cluster absorption bands, for the ether vibrational modes having large oscillator strengths, are distorted by dominance of the longitudinal mode absorption as expected for ultrathin particles. When water is included as a third component of the gaseous mixture, with a concentration chosen to give cluster compositions appropriate to the respective clathrate hydrate structures, the clusters assume the crystalline clathrate hydrate structures for temperatures close to the optimum values for thin-film clathrate hydrate formation by vapor cocondensation methods.

Ultrasonic Viscoelasticity and Excess Absorption in Polymer Solution

Shear moduli are measured by the reflection method for many polymer-toluene solutions. The results have good agreement with theoretical values by Rouse and Lamb. Longitudinal velocity and absorption are measured for poly(vinylisobuthylether) solution in toluene by the interferometric method. Comparing both moduli, it is found that the ratio of the dynamic volume viscosity to the dynamic shear one is 20–40. The phenomena are discussed on the basis of several theories and found to be well described by the concentration fluctuation theory by V. P. Romanov and V. A. Solove’ev.

Observation of a low-temperature resonance peak in ultrasonic attenuation ofUPt3

We report measurements of the temperature dependence of the ultrasonic attenuation in normal-state UPt/sub 3/. At about 12 K a pronounced longitudinal absorption peak is observed. Such a peak does not appear for transverse-acoustic waves. Our experimental results can be well explained by a narrow resonance in the quasiparticle excitation spectrum near the Fermi energy and are consistent with the enhanced specific-heat coefficient.

NMR of textures in rotatingHe3−A

Four vortex textures in /sup 3/He-A, one analytic and three singular, are proposed as possible candidates to explain recent transverse NMR results in the Helsinki rotating cryostat. Although the analytic texture, previously discussed by Seppaaumllaauml and Volovik, has a transverse NMR shift and absorption closest to the observed values, the agreement with experiment is not wholly satisfactory. Longitudinal NMR shifts and absorption are calculated for the four textures; such measurements might determine which vortex is present.

Ultrasound absorption in liquid metals

The excess longitudinal ultrasonic absorption over and above the classical value has been attributed to the solid-like mechanisms of the interaction of sound waves with the conduction electrons and the thermal phonons in liquid metals, both exhibiting a quadratic dependence on the sound frequency.

Dynamic shear viscosity measurements in aqueous sodium deoxycholate solutions

The real component of shear impedance, RL, was measured in concentrated aqueous solutions of sodium deoxycholate, by means of different experimental techniques, in the frequency range 30KHz – 830MHz, at temperatures from 20°to 40°C. The results obtained give direct confirmation on the existence of viscoelastic effects in such a system; they allow, also, to evaluate an upper limit for the dynamic shear viscosity values. From these data it is evident that shear viscosity relaxes well below the usual frequency range of longitudinal ultrasonic experiments. As a consequence, the previously observed large longitudinal ultrasonic absorption appear to be due mainly to volume viscosity contributions.