Gravitational lensing of active galactic nuclei.

Most of the known cases of strong gravitational lensing involve multiple imaging of an active galactic nucleus. The properties of lensed active galactic nuclei make them promising systems for astrophysical applications of gravitational lensing; in particular, they show structure on scales of milliseconds of arc to tens of seconds of arc, they are variable, and they are polarized. More than 20 cases of strong gravitational lenses are now known, and about half of them are radio sources. High-resolution radio imaging is making possible the development of well-constrained lens models. Variability studies at radio and optical wavelengths are beginning to yield results of astrophysical interest, such as an independent measure of the distance scale and limits on source sizes.

The vesicular monoamine transporter 2 is present in small synaptic vesicles and preferentially localizes to large dense core vesicles in rat solitary tract nuclei.

In central neurons, monamine neurotransmitters are taken up and stored within two distinct classes of regulated secretory vesicles: small synaptic vesicles and large dense core vesicles (DCVs). Biochemical and pharmacological evidence has shown that this uptake is mediated by specific vesicular monamine transporters (VMATs). Recent molecular cloning techniques have identified the vesicular monoamine transporter (VMAT2) that is expressed in brain. This transporter determines the sites of intracellular storage of monoamines and has been implicated in both the modulation of normal monoaminergic neurotransmission and the pathogenesis of related neuropsychiatric disease. We used an antiserum against VMAT2 to examine its ultrastructural distribution in rat solitary tract nuclei, a region that contains a dense and heterogeneous population of monoaminergic neurons. We find that both immunoperoxidase and immunogold labeling for VMAT2 localize to DCVs and small synaptic vesicles in axon terminals, the trans-Golgi network of neuronal perikarya, tubulovesicles of smooth endoplasmic reticulum, and potential sites of vesicular membrane recycling. In axon terminals, immunogold labeling for VMAT2 was preferentially associated with DCVs at sites distant from typical synaptic junctions. The results provide direct evidence that a single VMAT is expressed in two morphologically distinct types of regulated secretory vesicles in central monoaminergic neurons.

A class of single-stranded telomeric DNA-binding proteins required for Rap1p localization in yeast nuclei.

We have identified a class of proteins that bind single-stranded telomeric DNA and are required for the nuclear organization of telomeres and/or telomere-associated proteins. Rlf6p was identified by its sequence similarity to Gbp1p, a single-stranded telomeric DNA-binding protein from Chlamydomonas reinhardtii. Rlf6p and Gbp1p bind yeast single-stranded G-strand telomeric DNA. Both proteins include at least two RNA recognition motifs, which are found in many proteins that interact with single-stranded nucleic acids. Disruption of RLF6 alters the distribution of repressor/activator protein 1 (Rap1p), a telomere-associated protein. In wild-type yeast cells, Rap1p localizes to a small number of perinuclear spots, while in rlf6 cells Rap1p appears diffuse and nuclear. Interestingly, telomere position effect and telomere length control, which require RAP1, are unaffected by rlf6 mutations, demonstrating that Rap1p localization can be uncoupled from other Rap1p-dependent telomere functions. In addition, expression of Chlamydomonas GBP1 restores perinuclear, punctate Rap1p localization in rlf6 mutant cells. The functional complementation of a fungal gene by an algal gene suggests that Rlf6p and Gbp1p are members of a conserved class of single-stranded telomeric DNA-binding proteins that influence nuclear organization. Furthermore, it demonstrates that, despite their unusual codon bias, C. reinhardtii genes can be efficiently translated in Saccharomyces cerevisiae cells.

Plasmid DNA entry into postmitotic nuclei of primary rat myotubes.

These studies were initiated to elucidate the mechanism of DNA nuclear transport in mammalian cells. Biotin- or gold-labeled plasmid and plasmid DNA expression vectors for Escherichia coli beta-galactosidase or firefly luciferase were microinjected into the cytoplasm of primary rat myotubes in culture. Plasmid DNA was expressed in up to 70% of the injected myotubes, which indicates that it entered intact, postmitotic nuclei. The nuclear transport of plasmid DNA occurred through the nuclear pore by a process common to other large karyophilic macromolecules. The majority of the injected plasmid DNA was sequestered by cytoplasmic elements. This understanding of plasmid DNA nuclear transport provides a basis for increasing the efficiency of gene transfer.

Fluorescent Biological Aerosol Particles in Coastal Canada and the Link to Atmospheric Ice Nuclei

Bioaerosols are a subgroup of atmospheric aerosols and are often linked to the spread of human, animal and plant diseases. Bioaerosols also may play an indirect effect on environmental processes, including the formation of precipitation and alteration of the global climate through their role as nuclei for cloud droplet formation. Several types of biological organisms (e.g., fungi and bacteria) have been shown to be effective ice nuclei (IN) and cloud condensation nuclei (CCN). During 21 days in August 2013 we participated in a collaborative international campaign at a rural, coastal site near the village of Ucluelet on the west coast of Vancouver Island, British Columbia, Canada. The experiments were conducted as part of the NETCARE project (the NETwork on Climate and Aerosols: Addressing Key Uncertainties in Remote Canadian Environments), in part to examine cloud nuclei properties of marine aerosol. The study was conducted from a mobile trailer located approximately 100 m from the coast. A suite of aerosol instrumentation was operated for approximately one month. Key instruments utilized as a part of this thesis include the wideband integrated bioaerosol sensor (WIBS-4A) and the multiple orifice uniform deposition impactor (MOUDI) coupled with an off-line droplet freezing technique (DFT) for the measurement of ice nucleation activity of particles in immersion mode. The WIBS measures the concentration and properties of individual fluorescent particles suspended in the air, which can serve as a proxy for airborne biological particle content. Particles shown to be fluorescent by the WIBS instrument were divided into seven categories based on the pattern of fluorescence each particle exhibited in the three fluorescent channels. Results of the WIBS analysis show that the fluorescent particle concentration in the region correlated well with IN number. The fluorescent particle concentration correlated well with the number of particles shown to be ice active as a function of both particle size and freezing temperature. Correlations involving marine aerosols and marine biological activity indicate that the majority of IN measured at the coastal site likely are not from have marine sources.

Total cross sections of nuclei for 280 Mev neutrons.

The measurement of 28O-Mev neutron cross sections of various nuclei is described. The neutron beam used results from 340-Mev protons in the 184-in. cyclotron striking a 2-in. Be target. The neutron detector consists of a double coincidence anthracene scintillation counter telescope which counts recoil protons scattered at 15 deg from a paraffin cylinder placed in the collimated neutron beam. A 2-in. Cu absorber placed between the counters assures that only protons of energy greater than 250 Mev are counted. The cross sections for all nuclei measured from Li to Pb are smaller than the corresponding cross sections measured at 90 Mev by factors between 0.5 and 0.6.

Analysis of (n, 2n) cross sections for nuclei of mass A>30 /

"Physics; Reactor technology--TID-4500, 36th ed."

Condensation of vapor as induced by nuclei and ions.

"The contemporaneous variations of the nucleation and the ionization of the atmosphere of Providence, by Lulu B. Joslin": p. 123-154.

Cluster cannibalism and scaling relations of galactic stellar nuclei

Recently, very massive compact stellar systems have been discovered in the intracluster regions of galaxy clusters and in the nuclear regions of late-type disk galaxies. It is unclear how these compact stellar systems - known as ultracompact dwarf (UCD) galaxies or nuclear clusters (NCs) - form and evolve. By adopting a formation scenario in which these stellar systems are the product of multiple merging of star clusters in the central regions of galaxies, we investigate, numerically, their physical properties. We find that physical correlations among velocity dispersion, luminosity, effective radius, and average surface brightness in the stellar merger remnants are quite different from those observed in globular clusters. We also find that the remnants have triaxial shapes with or without figure rotation, and these shapes and their kinematics depend strongly on the initial number and distribution of the progenitor clusters. These specific predictions can be compared with the corresponding results of ongoing and future observations of UCDs and NCs, thereby providing a better understanding of the origin of these enigmatic objects.

A comparison of surface brightness profiles for ultracompact dwarfs and dwarf elliptical nuclei: implications for the “threshing” scenario

Using imaging from the Hubble Space Telescope, we derive surface brightness profiles for ultracompact dwarfs in the Fornax Cluster and for the nuclei of dwarf elliptical galaxies in the Virgo Cluster. Ultracompact dwarfs are more extended and have higher surface brightnesses than typical dwarf nuclei, while the luminosities, colors, and sizes of the nuclei are closer to those of Galactic globular clusters. This calls into question the production of ultracompact dwarfs via threshing, whereby the lower surface brightness envelope of a dwarf elliptical galaxy is removed by tidal processes, leaving behind a bare nucleus. Threshing may still be a viable model if the relatively bright Fornax ultracompact dwarfs considered here are descended from dwarf elliptical galaxies whose nuclei are at the upper end of their luminosity and size distributions.

Infraslow (<0.1 Hz) oscillations in thalamic relay nuclei basic mechanisms and significance to health and disease states

In the absence of external stimuli, the mammalian brain continues to display a rich variety of spontaneous activity. Such activity is often highly stereotypical, is invariably rhythmic, and can occur with periodicities ranging from a few milliseconds to several minutes. Recently, there has been a particular resurgence of interest in fluctuations in brain activity occurring at <0.1 Hz, commonly referred to as very slow or infraslow oscillations (ISOs). Whilst this is primarily due to the emergence of functional magnetic resonance imaging (fMRI) as a technique which has revolutionized the study of human brain dynamics, it is also a consequence of the application of full band electroencephalography (fbEEG). Despite these technical advances, the precise mechanisms which lead to ISOs in the brain remain unclear. In a host of animal studies, one brain region that consistently shows oscillations at <0.1 Hz is the thalamus. Importantly, similar oscillations can also be observed in slices of isolated thalamic relay nuclei maintained in vitro. Here, we discuss the nature and mechanisms of these oscillations, paying particular attention to a potential role for astrocytes in their genesis. We also highlight the relationship between this activity and ongoing local network oscillations in the alpha (a; ~8-13 Hz) band, drawing clear parallels with observations made in vivo. Last, we consider the relevance of these thalamic ISOs to the pathological activity that occurs in certain types of epilepsy.