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The distribution of counterions inside urchinlike charged copolymer micelles is investigated using Monte Carlo simulation. Each highly charged arm of the micelle is fixed in a rodlike geometry. Three different categories can be distinguished in the counterion population: ions locally condensed in the vicinity of the stretched branches, ions trapped inside the globular micelle and free ions localized outside the micelle which monitor the osmotic pressure and the long range electrostatic repulsion between micelles. Comparisons with simple Poisson–Boltzmann theories in various geometries and with small-angle x-ray scattering confirm this picture. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The ultra-bright femtosecond X-ray pulses provided by X-ray Free Electron Lasers (XFELs) open capabilities for studying the structure and dynamics of a wide variety of biological and inorganic systems beyond what is possible at synchrotron sources. Although the structure and chemistry at the catalytic sites have been studied intensively in both biological and inorganic systems, a full understanding of the atomic-scale chemistry requires new approaches beyond the steady state X-ray crystallography and X-ray spectroscopy at cryogenic temperatures. Following the dynamic changes in the geometric and electronic structure at ambient conditions, while overcoming X-ray damage to the redox active catalytic center, is key for deriving reaction mechanisms. Such studies become possible by using the intense and ultra-short femtosecond X-ray pulses from an XFEL, where sample is probed before it is damaged. We have developed methodology for simultaneously collecting X-ray diffraction data and X-ray emission spectra, using an energy dispersive spectrometer, at ambient conditions, and used this approach to study the room temperature structure and intermediate states of the photosynthetic water oxidizing metallo-protein, photosystem II. Moreover, we have also used this setup to simultaneously collect the X-ray emission spectra from multiple metals to follow the ultrafast dynamics of light-induced charge transfer between multiple metal sites. A Mn–Ti containing system was studied at an XFEL to demonstrate the efficacy and potential of this method. [ABSTRACT FROM AUTHOR]

Inhalation of hypertonic saline (HS) acutely enhances mucociliary clearance (MC) in both health and disease. In patients with cystic fibrosis (CF), repeated use of HS causes a sustained improvement in MC as well as clinical benefit. The pharmacodynamic duration of activity on MC may be an important determinant of its therapeutic potential in other airways diseases. Before moving toward testing the clinical benefits of HS for non-CF indications, we sought to assess the duration of pharmacodynamic effects of HS in healthy subjects by performing radiotracer clearance studies at baseline, 30-min post-HS administration, and 4-h post-HS administration. Indeed, acceleration of MC was observed when measured 30 min after HS inhalation. This acceleration was most pronounced in the first 30 min after inhaling the radiotracer in the central lung region (mean Ave30Clr = 15.5 vs. 8.6% for 30-min post-HS treatment vs. mean baseline, respectively, P < 0.005), suggesting that acute HS effects were greatest in the larger bronchial airways. In contrast, when MC was measured 4 h after HS administration, all indices of central lung region MC were slower than at baseline: Ave30Clr = 5.9% vs. 8.6% (P < 0.10); Ave90Clr = 12.4% vs. 16.8% (P = 0.05); clearance through 3 h = 29.4 vs. 43.7% (P < 0.002); and clearance through 6 h = 39.4 vs. 50.2% (P < 0.02). This apparent slowing of MC in healthy subjects 4-h post-HS administration may reflect depletion of airway mucus following acute HS administration. [ABSTRACT FROM AUTHOR]

Two-dimensional electronic spectroscopy is a sensitive probe of solvation dynamics. Using a pump–probe geometry with a pulse shaper [Optics Express 15 (2007), 16681–16689; Optics Express 16 (2008), 17420–17428], we present temperature dependent 2D spectra of laser dyes dissolved in glass-forming solvents. At low waiting times, the system has not yet relaxed, resulting in a spectrum that is elongated along the diagonal. At longer times, the system loses its memory of the initial excitation frequency, and the 2D spectrum rounds out. As the temperature is lowered, the time scale of this relaxation grows, and the elongation persists for longer waiting times. This can be measured in the ratio of the diagonal width to the anti-diagonal width; the behavior of this ratio is representative of the frequency–frequency correlation function [Optics Letters 31 (2006), 3354–3356]. Near the glass transition temperature, the relaxation behavior changes. Understanding this change is important for interpreting temperature-dependent dynamics of biological systems. [ABSTRACT FROM AUTHOR]

Unusual and surprising features of the response of a slightly tapered, nearly rectangular membrane, or analogous medium, excited at either the wider end or the narrower end and fixed on the other three sides are examined analytically. Radical differences between the two appear for the same 'near-resonant' frequency. For excitation at the wider end, there can be a large-amplitude response in the wider half, while the narrower half remains almost undisturbed. For excitation at the narrower end, there is only small-amplitude response throughout. These peculiarities are associated with the presence of a 'turning point,' in the sense of the WKB method used in the analysis. [ABSTRACT FROM AUTHOR]

Explores the mass flight of U.S. Navy's Navy-Curtiss seaplanes. Engine power and wingspan of the seaplanes; Cruising speed of the seaplanes; Deployment of a bridge of ships to aid the navigation; Establishment of a meteorological observation network; Forecasters assigned to seaplane tenders; Weather and sea conditions for takeoff; Route of the flight; Flying time for the entire route; Lessons learned from the mass flight.

The article comments on the importance of symbols in teaching chemistry. The author found symbols to be of great assistance in the interpretation of chemical changes and storing in the memory the fundamental chemical facts of the subject. The author needed a more consistent and systematized guidance as a teacher who is not a chemist and cannot devote the whole time to any specialty.