Fractal morphology, imaging and mass spectrometry of single aerosol particles in flight

The morphology of micrometre-size particulate matter is of critical importance in fields ranging from toxicology to climate science, yet these properties are surprisingly difficult to measure in the particles' native environment. Electron microscopy requires collection of particles on a substrate; visible light scattering provides insufficient resolution; and X-ray synchrotron studies have been limited to ensembles of particles. Here we demonstrate an in situ method for imaging individual sub-micrometre particles to nanometre resolution in their native environment, using intense, coherent X-ray pulses from the Linac Coherent Light Source free-electron laser. We introduced individual aerosol particles into the pulsed X-ray beam, which is sufficiently intense that diffraction from individual particles can be measured for morphological analysis. At the same time, ion fragments ejected from the beam were analysed using mass spectrometry, to determine the composition of single aerosol particles. Our results show the extent of internal dilation symmetry of individual soot particles subject to non-equilibrium aggregation, and the surprisingly large variability in their fractal dimensions. More broadly, our methods can be extended to resolve both static and dynamic morphology of general ensembles of disordered particles. Such general morphology has implications in topics such as solvent accessibilities in proteins, vibrational energy transfer by the hydrodynamic interaction of amino acids, and large-scale production of nanoscale structures by flame synthesis.     

Bromus invasions on the Nevada Test Site: present status of B. rubens and B. tectorum with notes on their relationship to disturbance and altitude

Bromus rubens and Bromus tectorum are now nearly ubiquitous components of the Nevada Test Site (NTS) flora. Introduced to the western United States in the late 1800s, they spread through the Mojave and Great Basin deserts in the early twentieth century. Since quantitative studies began on the NTS in 1957; Bromus spp. have greatly increased in frequency and density. By 1988 both species occurred in many places at densities exceeding 1000 individuals per square meter. They may significantly increase flammability of the vegetation and reduce success of native ephemeral species.     

The effect of an ethanol extract of catnip (Nepeta cataria) on the behavior of the young chick.

The alcohol extract of catnip has a biphasic effect on the behavior of young chicks. Low and moderate dose levels (25--1800 mg/kg) cause increasing numbers of chicks to sleep, while high dose levels (i.e. above 2 g/kg) cause a decreasing number of chicks to sleep.     

Dimerization inhibits the activity of receptor-like protein-tyrosine phosphatase-alpha.

Protein-tyrosine phosphatases (PTPs) are vital for regulating tryosine phosphorylation in many processes, including growth and differentiation. The regulation of receptor-like PTP (RPTP) activity remains poorly understood, but based on the crystal structure of RPTPalpha domain 1 we have proposed that dimerization can negatively regulate activity, through the interaction of an inhibitory 'wedge' on one monomer with the catalytic cleft of domain 1 in the other monomer. Here we show that dimerization inhibits the activity of a full-length RPTP in vivo. We generated stable disulphide-bonded full-length RPTPalpha homodimers by expressing mutants with single cysteines at different positions in the ectodomain juxtamembrane region. Expression of wild-type RPTPalpha and Phe135Cys and Thr141Cys mutants in RPTPalpha-null mouse embryo cells increased dephosphorylation and activity of Tyr 529 in the protein tyrosine kinase c-Src; in contrast, expression of a Pro137Cys mutant did not. Mutation of Pro 210/211 to leucine in the inhibitory wedge of the Pro137Cys mutant restored its ability to activate c-Src, indicating that dimerization may inhibit full-length RPTPalpha activity in a manner stereochemically consistent with RPTPalpha crystal structures. Our results suggest that RPTPalpha activity can in principle be negatively regulated by dimerization in vivo.     

The Lost Papers of Robert Boyle

Although the volume of the surviving papers of Robert Boyle is substantial (over 20,000 leaves), a considerable amount of the written material left by Boyle at his death in 1691 has not survived in the Boyle archive. This paper gauges the scale and identity of these losses using the surviving inventories made by the Rev. Henry Miles in the 1740s when he was collecting and sorting Boyle's literary remains in conjunction with Thomas Birch's preparation of his 1744 Life and Works of Boyle. These detailed lists (edited as appendices to this paper), together with other sources, indicate losses due to a variety of reasons, some deliberate, others accidental. The losses involved the disposal of both items judged (in the eighteenth century) to be peripheral to Boyle's archive and, ironically, those in the most finished state from Boyle's hand, which were perhaps abortively destined for the Birch edition. These losses have significantly altered the character of the Boyle Papers, and thus the view of Boyle that is derived from them.