Photoacoustic spectrometer for accurate,continuous measurements of atmospheric carbon dioxide concentration

We have developed a portable photoacoustic spectrometer that offers routine, precise and accurate measurements of the molar concentration of atmospheric carbon. The temperature-controlled spectrometer continuously samples dried atmospheric air and employs an intensity-modulated distributed feedback laser and fiber amplifier operating near 1.57 µm. For measurements of carbon dioxide in air, we demonstrate a measurement precision (60-s averaging time) of 0.15 µmol mol^?1 and achieve a standard uncertainty of 0.8 µmol mol^?1 by calibrating the analyzer response in terms of certified gas mixtures. We also investigate how water vapor affects the photoacoustic signal by promoting collisional relaxation of the carbon dioxide.     

Fluorescence lifetimes as a distinguishing property of members of drug series

The fluorescence lifetimes of antidepressant drugs, benzimidazoles, barbiturates and antimalarial drugs are reported for several different chemical environments. The quantum yields and natural fluorescence lifetimes are also reported for the latter two drug families. Structurally similar members of each drug group were qualitatively distinguished through temporal resolution, and the sensitivity of fluorescence enhanced by proper choice of chromophore environment.     

Electronic properties of metal clusters (Ni13 to Ni87) and implications for chemisorption

First principles calculations of the electronic properties of Ni clusters (up to Ni₈₇) are reported. It is found that the ionization potential (IP) converges to bulk values (work function) by Ni₄₃, whereas the electron affinity (EA) is off by 2.5 eV, even for Ni₈₇. The conduction band of ～16 eV appears converged by Ni₈₇. It is found that the electron density for surface atoms is significantly lower than the bulk value. The significance of these results for chemisorption on small metallic clusters and for modelling of chemisorption on bulk surfaces is discussed.     

The motion artifact suppression technique (MAST) in magnetic resonance imaging: clinical results

The Motion Artifact Suppression Technique (MAST) is a method which uses a series of gradient echos that are computed to cancel velocity, acceleration and pulsatility components of involuntary motion in MR imaging. A total of 916 patient studies were performed over a nine month period using MAST sequences with a TE 40, 60, 80, 100, 120, and 26/112. There was considerable improvement in long TR, long TE images. Cerebrospinal fluid flow artifacts were reduced. Body and spine images had reduced flow and respiratory artifacts. Spin rephasing in blood vessels caused increase intraluminal signal. This might be useful for cardiovascular imaging.     

A theory of gravity based on the Weyl-Eddington action

We show that the conformal Weyl-Eddington theory can yield an effective long-ranged theory of gravity in accord with observations. In the framework of induced gravity, an R² term is induced with a finite calculable coefficient with just the right sign for the theory to be free from tachyons. Our observation is not true order by order in perturbation theory.     

Gram-Schmidt orthogonalization of the Zernike polynomials on apertures of arbitrary shape

An orthonormal hexagonal Zernike basis set is generated from circular Zernike polynomials apodized by a hexagonal mask by use of the Gram-Schmidt orthogonalization technique. Results for the first 15 hexagonal Zernike polynomials are shown. The Gram-Schmidt orthogonalization technique presented can be extended to both apertures of arbitrary shape and other basis functions.     

A New Process for the Synthesis of Fentanyl

Catalytic hydrogenation of pyridinium derivative for the preparation of analgesic Fentanyl, (N-(l-phenethyl-4-piperidyl)-propionanilide) is reported. This constitutes a novel synthesis for the analogs of Fentanyl type compounds.