Spectroscopic Tracers Research Articles

Asymmetrical flow field-flow fractionation with multi-angle light scattering detection for the analysis of structured nanoparticles

Synthesis and applications of new functional nanoparticles are topics of increasing interest in many fields of nanotechnology. Chemical modifications of inorganic nanoparticles are often necessary to improve their features as spectroscopic tracers or chemical sensors, and to increase water solubility and biocompatibility for applications in nano-biotechnology. Analysis and characterization of structured nanoparticles are then key steps for their synthesis optimization and final quality control. Many properties of structured nanoparticles are size-dependent. Particle size distribution analysis then provides fundamental analytical information. Asymmetrical flow field-flow fractionation (AF4) with multi-angle light scattering (MALS) detection is able to size-separate and to characterize nanosized analytes in dispersion. In this work we focus on the central role of AF4-MALS to analyze and characterize different types of structured nanoparticles that are finding increasing applications in nano-biotechnology and nanomedicine: polymer-coated gold nanoparticles, fluorescent silica nanoparticles, and quantum dots. AF4 not only size-fractionated these nanoparticles and measured their hydrodynamic radius ( r h ) distribution but it also separated them from the unbound, relatively low- M r components of the nanoparticle structures which were still present in the sample solution. On-line MALS detection on real-time gave the gyration radius ( r g ) distribution of the fractionated nanoparticles. Additional information on nanoparticle morphology was then obtained from the r h / r g index. Stability of the nanoparticle dispersions was finally investigated. Aggregation of the fluorescent silica nanoparticles was found to depend on the concentration at which they were dispersed. Partial release of the polymeric coating from water-soluble QDs was found when shear stress was induced by increasing flowrates during fractionation.

Measurement of Temperature, Density, and Particle Transport with Localized Dopants in Wire-ArrayZPinches

Axially localized NaF dopants are coated onto Al cylindrical wire arrays in order to act as spectroscopic tracers in the stagnated z-pinch plasma. Non-local-thermodynamic-equilibrium kinetic models fit to Na K-shell lines provide an independent measurement of the density and temperature that is consistent with spectroscopic analysis of K-shell emissions from Al and an alloyed Mg dopant. Axial transport of the Na dopant is observed, enabling quantitative study of instabilities in dense z-pinch plasmas.

The effects of successive high-energy shock-wave tumor administration on tumor blood flow

The effects of repeated high-energy shock wave (HESW) tumor administration on tumor blood flow (TBF) were studied in NU-1 human kidney cancer xenografts. Deuteriated water was used as a magnetic resonance spectroscopic detectable tracer for measuring tumor blood flow. Tumors were exposed twice to 800 electromagnetically generated HESW, with a 24-h interval or sham exposed. No changes in TBF occurred after sham exposure to HESW. TBF levels 2 h after the first and second HESW application were, respectively, 46% and 37% lower than the mean preexposure TBF value and returned to normal levels within 16 h. There was statistically no difference found between the effects on tumor blood flow after the first and second HESW exposure. These observations are in agreement with earlier studies and provide a rationale to shorten the time interval between HESW monotreatments to 2 to 3 h.

Recent results on Nova

On the Nova Laser at LLNL, we have recently demonstrated many of the key elements required for assuring that the next proposed laser, the National Ignition Facility (NIF) will reach ignition. In particular, we have achieved a drive of 300 eV in laser heated hohlraums; have shown good understanding and control of symmetry in hohlruams; created large NIF-Scale plasmas with plasma and irradiation conditions relevant to NIF targets that showed low levels of plasma instabilities; demonstrated a good understanding of hydrodynamic instability and subsequent pusher/fuel mix in implosions by means of spectroscopic tracers; and performed integrated implosion experiments that have performed well even under stringent convergences of order 25, which is well into the NIF ignition target regime.

Characterization of sodium transport in Acholeplasma laidlawii B cells and in lipid vesicles containing purified A. laidlawii (Na+-Mg2+)-ATPase by using nuclear magnetic resonance spectroscopy and 22Na tracer techniques.

The active transport of sodium ions in live Acholeplasma laidlawii B cells and in lipid vesicles containing the (Na+-Mg2+)-ATPase from the plasma membrane of this microorganism was studied by 23Na nuclear magnetic resonance spectroscopic and 22Na tracer techniques, respectively. In live A. laidlawii B cells, the transport of sodium was an active process in which metabolic energy was harnessed for the extrusion of sodium ions against a concentration gradient. The process was inhibited by low temperatures and by the formation of gel state lipid in the plasma membrane of this organism. In reconstituted proteoliposomes containing the purified (Na+-Mg2+)-ATPase, the hydrolysis of ATP was accompanied by the transport of sodium ions into the lipid vesicles, and the transport process was impaired by reagents known to inhibit ATPase activity. At the normal growth temperature (37 degrees C), this transport process required a maximum of 1 mol of ATP per mol of sodium ion transported. Together, these results provide direct experimental evidence that the (Na+-Mg2+)-ATPase of the Acholeplasma laidlawii B membrane is the cation pump which maintains the low levels of intracellular sodium characteristic of this microorganism.

Plasma motion in umbrae and the surrounding photosphere derived from spectroscopic Doppler measurements and tracer measurements of spots

The rotational velocity of the Sun is determined by sunspot tracings and by spectroscopic measurements of the photospheric plasma using the non-Zeeman-split line Fe i 5576 and absolute iodine reference. Stationary line shifts as limb-effect and longperiodical shifts introduced by supergranulation are discussed. The dependence on solar activity as Ca+ emissivity and magnetic fields is investigated including line asymmetries. The results are: (a) The non active photospheric regions rotate with 1995 ± 30 m s-1. Solar active regions yield a 60 m s-1 higher value. (b) In quiet regions the absolute limb shift varies between 170 m s-1 at the line core and 310 m s-1 at I/I cont ≈ 0.8 (C-shape); thus the limb shift is mainly due to entire line shifts. (c) In solar active regions (close to spots) asymmetries are widely reduced in line cores; this effect cannot be associated with a variation of the limb effect due to a large scatter of Doppler shifts near spots. (d) A reduced limb shift of 50 m s-1 is found in network boundaries and is mainly due to a small scale downflow. (e) Observations with a smaller influence of stray light yield symmetric profiles in umbrae. (f) Differences between umbral rotation rates from tracer and spectroscopic measurements do not exceed 20 m s-1, when considering straylight. The rotational velocity from umbrae exceeds that from the photosphere by 30–60 m s-1. Some individual spots yield nearly the same rotation rate as the photosphere.