Quantification of optical pulsed-plane-wave-shaping by chiral sculptured thin films

The durations and average speeds of ultrashort optical pulses transmitted through chiral sculptured thin films (STFs) were calculated using a finite-difference time-domain algorithm. Chiral STFs are a class of nanoengineered materials whose microstructure comprises parallel helicoidal nanowires grown normal to a substrate. The nanowires are $\sim$10-300 nm in diameter and $\sim1-10 \mu$m in length. Durations of transmitted pulses tend to increase with decreasing (free-space) wavelength of the carrier plane wave, while average speeds tend to increase with increasing wavelength. An increase in nonlinearity, as manifested by an intensity-dependent refractive index in the frequency domain, tends to increase durations of transmitted pulses and decrease average speeds. The circular Bragg phenomenon exhibited by a chiral STFs manifests itself in the frequency domain as high reflectivity for normally incident carrier plane waves whose circular polarization state is matched to the structural handedness of the film and whose wavelength falls in a range known as the Bragg regime; films of the opposite structural handedness reflect such plane waves little. This effect tends to distort the shapes of transmitted pulses with respect to the incident pulses, and such shaping can cause sharp changes in some measures of average speed with respect to carrier wavelength. A local maximum in the variation of one measure of the pulse duration with respect to wavelength is noted and attributed to the circular Bragg phenomenon. Several of these effects are explained via frequency-domain arguments. The presented results serve as a foundation for future theoretical and experimental studies of optical pulse propagation through causal, nonlinear, nonhomogeneous, and anisotropic materials.Comment: To appear in Journal of Modern Optic

The Evolution of Compact Binary Star Systems

We review the formation and evolution of compact binary stars consisting of white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and BHs are thought to be the primary astrophysical sources of gravitational waves (GWs) within the frequency band of ground-based detectors, while compact binaries of WDs are important sources of GWs at lower frequencies to be covered by space interferometers (LISA). Major uncertainties in the current understanding of properties of NSs and BHs most relevant to the GW studies are discussed, including the treatment of the natal kicks which compact stellar remnants acquire during the core collapse of massive stars and the common envelope phase of binary evolution. We discuss the coalescence rates of binary NSs and BHs and prospects for their detections, the formation and evolution of binary WDs and their observational manifestations. Special attention is given to AM CVn-stars -- compact binaries in which the Roche lobe is filled by another WD or a low-mass partially degenerate helium-star, as these stars are thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure

The Paradox of Engagement: Land Stewardship and Invasive Weeds in Amenity Landscapes

In New South Wales, Australia, rural landscapes are undergoing profound change as a result of exurbanization. Newcomers-amenity migrants-are drawn to the scenic beaches, forests, and open landscape character of this part of Australia near Sydney and they join existing communities of long-term residents, notably ranchers involved in dairy, beef, and other types of primary agricultural production. The rural to exurban transition is stimulating both intended and unintended socio-ecological changes, especially the proliferation of invasive weeds, which are considered to be a top national priority as they threaten Australia\u27s agricultural economy. Drawing on interview and survey research from three case studies in New South Wales, locations where an influx of exurbanites has led to mixed landscapes of production and consumption, we explore landowners\u27 diverse environmental ideologies, the degree to which they collaborate with one another, and their specific land-use practices. Results show that an overwhelming majority of both exurbanites and ranchers express concerns about weeds, but there is a marked lack of coordinated engagement on invasive species between the two types of groups. This chapter is an example of social disengagement over land-use and land-cover change, rather than competition or cooperation, and contributes to a political ecological understanding of the co-construction of social relations and land management regimes

Behavioral genetics and taste

This review focuses on behavioral genetic studies of sweet, umami, bitter and salt taste responses in mammals. Studies involving mouse inbred strain comparisons and genetic analyses, and their impact on elucidation of taste receptors and transduction mechanisms are discussed. Finally, the effect of genetic variation in taste responsiveness on complex traits such as drug intake is considered. Recent advances in development of genomic resources make behavioral genetics a powerful approach for understanding mechanisms of taste

A Ctf4 trimer couples the CMG helicase to DNA polymerase α in the eukaryotic replisome

Efficient duplication of the genome requires the concerted action of helicase and DNA polymerases at replication forks(1), to avoid stalling of the replication machinery and consequent genomic instability(2-4). In eukaryotes, the physical coupling between helicase and DNA polymerases remains poorly understood. Here we define the molecular mechanism by which the yeast Ctf4 protein links the Cdc45-MCM-GINS (CMG) DNA helicase to DNA polymerase α (Pol α) within the replisome. We use X-ray crystallography and electron microscopy to show that Ctf4 self-associates in a constitutive disk-shaped trimer. Trimerization depends on a β-propeller domain in the carboxy-terminal half of the protein, which is fused to a helical extension that protrudes from one face of the trimeric disk. Critically, Pol α and the CMG helicase share a common mechanism of interaction with Ctf4. We show that the N-terminal tails of the catalytic subunit of Pol α and the Sld5 subunit of GINS contain a conserved Ctf4-binding motif that docks onto the exposed helical extension of a Ctf4 protomer within the trimer. Accordingly, we demonstrate that one Ctf4 trimer can support binding of up to three partner proteins, including the simultaneous association with both Pol α and GINS. Our findings indicate that Ctf4 can couple two molecules of Pol α to one CMG helicase within the replisome, providing a new paradigm for lagging-strand synthesis in eukaryotes that resembles the emerging model for the simpler replisome of E. coli(5-8). The ability of Ctf4 to act as a platform for multivalent interactions illustrates a mechanism for the concurrent recruitment of factors that act together at the fork