Fluorescence drainage profiles of thin liquid films.
Fluorescence drainage-profiles of thin liquid films formed from Rhodamine solutions containing anionic, cationic and non-ionic surfactants have been investigated. It is found that the influence of system variables such as electrolyte concentration, dye concentration, film environment and solution viscosity can be evaluated by means of the profiles. The addition of sodium chloride leads to the expansion (non-ionic surfactant), or contraction (anionic surfactant) of the profiles. In the case of the cationic surfactant, it reduces the number of fringes in the profiles. The height of selected fringes changes linearly with dye concentration, and no fringes are observed when the films are submerged in non-polar solvents. The influence of solution viscosity on film thickness and drainage rate is demonstrated by the number and frequency of fringes in the profile. The formation of first and second "black films" from solutions containing varying concentrations of sodium chloride can be shown.
A profile of Jim Winefordner including a bibliography and a list of co-workers
THERE are many qualitative and quantitative measures which one might use to examine a scientific career. During his 35 years at the University of Florida, Jim Winefordner has provided data for many. Perhaps the most interesting and informative measure of any scientist’s career lies in the publication record. Jim’s bibliography, at present containing some 725 publications, is included in this special issue. The sheer quantity of publication is remarkable. On average, Jim has produced a paper every 18 days for 35 years. These have been distributed among some 57 scientific journals with about 95 papers appearing in Spectrochimicu Actu B. It provides a panoramic view of his scientific interests. With few exceptions, his work falls under the broad umbrella of spectrochemistry and, within that domain, there is almost no technique to which he has not made some important contribution. Some of his favorite interests are obvious. I doubt that anyone has published or ever will publish as many papers on atomic fluorescence spectrometry. Jim was the first to use atomic fluorescence as an analytical method; his first paper on the subject appeared in 1964. About a third of Jim’s bibliography is devoted in some way to atomic fluorescence. He has considered theoretical aspects, experimental nuances and a multitude of practical applications. Every conceivable experimental permutation has been studied with many different excitation sources, atom reservoirs and detection systems. Atomic fluorescence investigations continue to form the backbone of Jim’s still vigorous research program. He quickly recognized the role that lasers could play in analytical spectroscopy and was among the first to use a pulsed dye laser as an excitation source. Laser excitation figured prominently in his atomic fluorescence work as well as in a multitude of other spectroscopic studies. Jim has shown a persistent interest in every facet of luminescence spectrometry, including molecular techniques such as low temperature and room temperature phosphorescence and fluorescence in various media and surface enhanced Raman spectrometry. Naturally, this work led to many side trips, especially into studies of a more fundamental kind. Distributed throughout the bibliography are papers addressing characterization of flames and plasmas, development of methods for plasma diagnostics, measurements of free atom fractions, temperature measurements, luminescence lifetimes, etc. Jim has always been interested in the validity of analytical measurements and so there are many publications concerning the measurement and prediction of signal and noise and upon one of his favorite topics, the rigorous definition of a limit of detection. Jim’s work has played an important role in the widespread acceptance of a standard definition of the limit of detection. Jim has maintained this extraordinary level of research productivity by relying on hard work and a prodigious appetite for the scientific literature. Over the years he has methodically accumulated some 32,000 reprints and categorized them under 144 topics, filling 40 file drawers. Even though these are cross-indexed by author, the
Failure analysis for poor solderability of Au surface of PCB
Nonwetting is one of the common problems and is always rejected in electronic assemblies. ENIG pads of a PCBA exhibited nonwetting after lead-free reflow soldering. With the aid of stereomicroscope, SEM&EDS and XRF, a series of analysis was performed. And after visual inspection, surface and cross section analysis, thickness measurement and solderability test, it can be inferred that oxidation of plating surface was the main reason for nonwetting, and corrosion in Ni plating caused an adverse impact on solderalibity.