There is no temperature dependence of net biochemical fractionation of hydrogen and oxygen isotopes in tree-ring cellulose

The isotopic composition of tree-ring cellulose was obtained over a two-year period from small diameter, riparian zone trees along an elevational transect in Big Cottonwood Canyon, Utah, USA to test for a possible temperature dependence of net biological fractionation during cellulose synthesis. The isotope ratios of stream water varied by only 3.6% and 0.2% in deltaD and delta18O, respectively, over an elevation change of 810m. The similarity in stream water and macroenvironment over the short (13km) transect produced nearly constant stem and leaf water deltaD and delta18O values. In addition, what few seasonal variations observed in the isotopic composition of source water and atmospheric water vapor or in leaf water evaporative enrichment were experienced equally by all sites along the elevational transect. The temperature at each site along the transect spanned a range of > or = 5 degrees C as calculated using the adiabatic lapse rate. Since the deltaD and delta18O values of stem and leaf water varied little for these trees over this elevation/temperature transect, any differences in tree-ring cellulose deltaD and delta18O values should have been associated with temperature effects on net biological fractionation. However, the slopes of the regressions of elevation versus the deltaD and delta18O values of tree-ring cellulose were not significantly different from zero indicating little or no temperature dependence of net biological fractionation. Therefore, cross-site climatic reconstruction studies using the isotope ratios of cellulose need not be concerned that temperatures during the growing season have influenced results.     

Integral equation formulation for buoyancy-driven convection problems

An integral equation formulation for buoyancy-driven convection problems is developed and illustrated. Buoyancy-driven convection in a bounded cylindrical geometry with a free surface is studied for a range of aspect ratios and Nusselt numbers. The critical Rayleigh number, the nature of the cellular motion, and the heat transfer enhancement are computed using linear theory. Green's functions are used to convert the linear problem into linear Fredholm integral equations. Theorems are proved which establish the properties of the eigenvalues and eigenfunctions of the linear integral operator which appears in these equations.     

Photocurrent measurements for laterally resolved interface characterization

A miniaturized optical set-up based on a CD-ROM player optic was developed for LAPS (light addressable potentiometric sensors). A focus of 2.6 μm was achieved using this easy to handle device. The lateral resolution of LAPS measurements can be improved by using GaAs as the semiconductor material instead of Si. The diffusion length of the minority charge carriers was determined to be smaller than 3.1 μm. A new method called SPIM (scanning photo-induced impedance microscopy) is described. Using this technique, the impedance of thin films can be measured with lateral resolution.     

Permanently oriented antibody immobilization for digoxin determination with a flow-through fluoroimmunosensor

This paper reports a new flow-through fluoroimmunosensor, the function of which is based on antibodies immobilized on an inmunoreactor of controlled-pore glass (CPG), for determination of digoxin, used in the treatment of congestive heart failure and artery disease. The immunosensor has a detection limit of 1.20 microg L(-1) and provides high reproducibility (RSD=4.5% for a concentration of 0.0025 mg L(-1), and RSD=6.7% for 0.01 mg L(-1)). The optimum working concentration range was found to be 1.2 x 10(-3)-4.0 x 10(-2) mg L(-1). The lifetime of the immunosensor was about 50 immunoassays; if stored unused its lifetime can be extended to three months. A sample speed of about 10-12 samples per hour can be attained. Possible interference from substances with structures similar to digoxin (morphine, heroin, tebaine, codeine, pentazocine and narcotine) was investigated. No cross-reactivity was seen at the highest digoxin: interferent ratio studied (1:100). The proposed fluoroimmunosensor was successfully used to determine digoxin concentrations in human serum samples.     

Hydrogen network fluctuations of associating liquids: dielectric relaxation of ethylene glycol oligomers and their mixtures with water

Complex dielectric spectra of ethylene glycol and of various derivatives as well as of mixtures of water with an ethylene glycol oligomer and with a poly(ethylene glycol) dimethyl ether oligomer have been measured. The spectra can be well represented by a Cole-Cole [Cole and Cole, J. Chem. Phys. 9, 341 (1941)] spectral function. The extrapolated low frequency (static) permittivity of this function has been evaluated to yield the effective dipole orientation correlation factor of the liquids. The relaxation time of the ethylene glycols displays a characteristic dependence upon the ratio of concentrations of hydrogen bond donating and accepting groups, indicating two opposing effects. With increasing availability of hydrogen bonding sites effects of association and also of dynamical destabilization increase. Both effects exist also in the mixture of water with the oligomers. They are discussed in terms of a wait-and-switch model of dipole reorientation in associating liquids. Another feature in the dependence of the dielectric relaxation time of poly(ethylene glycol)/water mixtures upon mixture composition has been tentatively assigned to precritical demixing behavior of the binary liquids in some temperature range.     

A rapid and precise method for sampling and determining the oxygen isotope ratio of atmospheric water vapor

A quantitative method for cryogenically sampling atmospheric water vapor on the temporal scale of 10 to 15 min in the field or laboratory is described. The sample apparatus is lightweight, affordable, and easy to assemble. The method allows for H2O:CO2 equilibration within the same sampling tubes and hence increases turnaround time for delta18O analysis. Quantitative analysis in the laboratory showed recovery of a vaporized, known, 18O water standard to 0.2 per thousand precision.     

Distinction of the delayed fluorescences S1 → S0 And S2 → S0 of pyrene by selective quenching Of S1 → S0

In the spectrum of the delayed fluorescence (DF) of pyrene, caused by triplet-triplet annihilation T₁ + T₁ → S_n + S_o (n = 1,2), a strong DF S₁ → S_o and a very weak DF S₂ → s₀ are observed. The DF S₁→ S_o is quenched selectively by compounds like N-diethylanine or triethylamine which do not quench T₁ of pyrene.     

Schrittweise Zweiphotonenanregung der Tetracenfluoreszenz aus angeregten oberen Singulettzuständen

Ohne Zusammenfassung     

In vivo magnetic resonance micro-imaging of the human toe at 3 Tesla.

The feasibility of in vivo high-resolution magnetic resonance micro-imaging of fine anatomic structures of human toes was tested. Five healthy subjects were investigated on an experimental 3 Tesla whole body scanner, using standard 3D gradient echo sequences. A radio-frequency surface coil was used for signal detection. Feet, toes and surface coil were comfortably fixed using a home built device for positioning and reduction of motion artifacts. The spatial resolution of 117 x 313 x 375 microm(3) allowed detailed visualization of anatomic structures like skin layers, vessels and nerves. In addition, oval structures with diameters ranging from 500 to 1000 microm were observed in all subjects, which could represent the sensory nerve endings of Vater-Pacinian bodies. Thus, high resolution MR micro-imaging at 3 Tesla may provide improved morphologic information in distal extremities of humans in vivo.