The science of the total environment

About Dendrimers: Structure, Physical Properties, and Applications

Dendrimers in Supramolecular Chemistry: From Molecular Recognition to Self-Assembly.

With the goal of developing a pH-responsive micelle system, linear-dendritic block copolymers comprising poly(ethylene oxide) and either a polylysine or polyester dendron were prepared and hydrophobic groups were attached to the dendrimer periphery by highly acid-sensitive cyclic acetals. These copolymers were designed to form stable micelles in aqueous solution at neutral pH but to disintegrate into unimers at mildly acidic pH following loss of the hydrophobic groups upon acetal hydrolysis. Micelle formation was demonstrated by encapsulation of the fluorescent probe Nile Red, and the micelle sizes were determined by dynamic light scattering. The structure of the dendrimer block, its generation, and the synthetic method for linking the acetal groups to its periphery all had an influence on the critical micelle concentration and the micelle size. The rate of hydrolysis of the acetals at the micelle core was measured for each system at pH 7.4 and pH 5, and it was found that all systems were stable at neutral pH but underwent significant hydrolysis at pH 5 over several hours. The rate of hydrolysis at pH 5 was dependent on the structure of the copolymer, most notably the hydrophobicity of the core-forming block. To demonstrate the potential of these systems for controlled release, the release of Nile Red as a "model payload" was examined. At pH 7.4, the fluorescence of micelle-encapsulated Nile Red was relatively constant, indicating it was retained in the micelle, while at pH 5, the fluorescence decreased, consistent with its release into the aqueous environment. The rate of release was strongly correlated with the rate of acetal hydrolysis and was therefore controlled by the chemical structure of the copolymer. The mechanism of Nile Red release was investigated by monitoring the change in size of the micelles over time at acidic pH. Dynamic light scattering measurement showed a size decrease over time, eventually reaching the size of a unimer, thus providing evidence for the proposed micelle disintegration.

Stimuli-responsive supramolecular assemblies of linear-dendritic copolymers.

Every three years the IAU Working Group on Cartographic Coordinates and Rotational Elements revises tables giving the directions of the poles of rotation and the prime meridians of the planets, satellites, minor planets, and comets. This report takes into account the IAU Working Group for Planetary System Nomenclature (WGPSN) and the IAU Committee on Small Body Nomenclature (CSBN) definition of dwarf planets, introduces improved values for the pole and rotation rate of Mercury, returns the rotation rate of Jupiter to a previous value, introduces improved values for the rotation of five satellites of Saturn, and adds the equatorial radius of the Sun for comparison. It also adds or updates size and shape information for the Earth, Mars’ satellites Deimos and Phobos, the four Galilean satellites of Jupiter, and 22 satellites of Saturn. Pole, rotation, and size information has been added for the asteroids (21) Lutetia, (511) Davida, and (2867) Steins. Pole and rotation information has been added for (2) Pallas and (21) Lutetia. Pole and rotation and mean radius information has been added for (1) Ceres. Pole information has been updated for (4) Vesta. The high precision realization for the pole and rotation rate of the Moon is updated. Alternative orientation models for Mars, Jupiter, and Saturn are noted. The Working Group also reaffirms that once an observable feature at a defined longitude is chosen, a longitude definition origin should not change except under unusual circumstances. It is also noted that alternative coordinate systems may exist for various (e.g. dynamical) purposes, but specific cartographic coordinate system information continues to be recommended for each body. The Working Group elaborates on its purpose, and also announces its plans to occasionally provide limited updates to its recommendations via its website, in order to address community needs for some updates more often than every 3 years. Brief recommendations are also made to the general planetary community regarding the need for controlled products, and improved or consensus rotation models for Mars, Jupiter, and Saturn.

/pdf/report-of-the-iau-working-group-on-cartographic-coordinates-vrwl6kjvps.pdf

Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2009

Plume composition as observed by the Cassini Ion Neutral Mass Spectrometer

/pdf/enceladus-and-titan-emerging-worlds-of-the-solar-system-3jmzzshh1i.pdf

Enceladus and Titan: emerging worlds of the Solar System

/pdf/titan-lake-probe-the-ongoing-nasa-decadal-study-preliminary-35fxhuyltg.pdf

Titan Lake Probe: The Ongoing NASA Decadal Study Preliminary Report

The final report for NAGW-1657 (SwRI Project 15-2783) is presented. Several distinctly different areas of research are discussed: (1) studies of the thermal structure of polar outflows; (2) Prognoz-8 data analysis; and (3) the Ulysses Jupiter encounter.

/pdf/studies-of-interactive-plasma-processes-in-the-polar-cusp-1hcucpatjv.pdf

Studies of interactive plasma processes in the polar cusp

The purpose is twofold: to report the programmatic issues of the project as to accomplishments and anticipated work statement for the next six months and to report the technical findings of the project. From the programmatic point of view the study was a clear success. Four talks were given on the work: (1) a talk on electron Bremsstrahlung X ray production at the annual American Astronomical Society, Division of Planetary Studies meeting in October of 1990 in Charlottesville, Virginia; (2) a poster on proton precipitation at the May, 1991 American Geophysical Union in Baltimore, Maryland; (3) an invited paper on multispectral time dependent modeling at the International Union of Geodosy and Geomagnetism in Vienna in August of 1991; and (4) a paper at the annual Division of Planetary Studies of the American Astronomical Society held in Palo Alto in November of 1991 entitled 'Jovian Bremsstrahlung X Rays: A Ulysses Prediction' which predicted the Jovian auroral X ray flux that should be measured by the Ulysses Gamma Ray Burst experiment during the Ulysses spacecraft's closest encounter with Jupiter in February 1992. The Ulysses' prediction paper generated much interest from people studying the Jovian aurora and from experimenters on the Ulysses spacecraft. As a result of this interest two things happened: (1) a paper of the same title was submitted and accepted for publication in the January issue of the Geophysical Research Letters; and (2) a massive observing campaign was organized to provide supporting ultraviolet and infrared observations at the time of the Ulysses encounter. This observational interest allowed personnel at the Southwest Research Institute (SwRI) (Alan Stern, PI; Hunter Waite Co-I) to obtain director's discretionary time on the Hubble Space Telescope to support the Ulysses encounter by obtaining ultraviolet observations. Once the multiple wavelength observations are obtained in February, the auroral model developed under this project will be used to analyze the data with hopes of providing new insight into the physical processes responsible for the Jovian aurora.

/pdf/aeronomical-modeling-of-the-outer-planets-2av1mh80sk.pdf

J. Hunter Waite

Papers

Plume composition as observed by the Cassini Ion Neutral Mass Spectrometer

Enceladus and Titan: emerging worlds of the Solar System

Titan Lake Probe: The Ongoing NASA Decadal Study Preliminary Report

Studies of interactive plasma processes in the polar cusp

Aeronomical modeling of the outer planets