The growth of supermassive black holes (BHs) located at the centers of their host galaxies comes mainly from the accretion of gas, but how to fuel them remains an outstanding unsolved problem in quasar evolution. This issue can be elucidated by quantifying the radiative efficiency parameter (eta) as a function of redshift, which also provides constraints on the average spin of the BHs and its possible evolution with time. We derive a formalism to link eta with the luminosity density, BH mass density, and duty cycle of quasars, quantities we can estimate from existing quasars, and galaxy survey data. We find that eta has a strong cosmological evolution: at z approximate to 2, eta approximate to 0.3, and by z approximate to 0 it has decreased by an order of magnitude, to eta approximate to 0.03. We interpret this trend as evolution in BH spin, and we appeal to episodic, random accretion as the mechanism for reducing the spin. The observation that the fraction of radio-loud quasars decreases with increasing redshift is inconsistent with the popular notion that BH spin is a critical factor for generating strong radio jets. In agreement with previous studies, we show that the derived history of BH accretion closely follows the cosmic history of star formation, consistent with other evidence that BHs and their host galaxies co-evolve.

Composite diamond anvils have been developed for high-pressure/high-temperature measurements of diamond anvil cells. The anvils are fabricated using single-crystal chemical vapor deposition (CVD) from previously used and/or slightly damaged anvils made of natural or synthetic diamond. These composite anvils can be fabricated to possess optical characteristics at least comparable to conventional diamond anvils, whereas the single-crystal CVD portion is more durable because of its enhanced toughness relative to natural diamond. The viability of such anvils is demonstrated in measurements on hydrogen at megabar pressures and high temperature.

Approaches for enhancing the strength and toughness of single-crystal diamond produced by chemical vapor deposition (CVD) at high growth rates are described. CVD processes used to grow single-crystal diamond in high density plasmas were modified to incorporate boron and nitrogen. Semi-quantitative studies of mechanical properties were carried out using Vickers indentation techniques. The introduction of boron in single-crystal CVD diamond can significantly enhance the fracture toughness of this material without sacrificing its high hardness (similar to 78 GPa). Growth conditions were varied to investigate its effect on boron incorporation and optical properties by means of photoluminescence, infrared, and ultraviolet-visible absorption spectroscopy. Boron can be readily incorporated into single-crystal diamond by the methods used, but with nitrogen addition, the incorporation of boron was hindered. The spectroscopic measurements indicate that nitrogen and boron coexist in the diamond structure, which helps explain the origin of the enhanced fracture toughness of this material. Further, low pressure/high temperature annealing can enhance the intrinsic hardness of single-crystal CVD diamond by a factor of two without appreciable loss in fracture toughness. This doping and post-growth treatment of diamond may lead to new technological applications that require enhanced mechanical properties of diamond.

Plasma-substrate interactions in diamond synthesis via microwave plasma-assisted chemical vapor deposition (CVD) are an important issue in CVD reactor optimization. The hot spot formation observed during single-crystal diamond synthesis in 2.45-GHz cylindrical cavity reactors is examined after long-run deposition.

Finding ways to routinely and reliably produce larger near-colorless and colorless single-crystal diamond needed for a variety of applications in science and technology is a major challenge. Microwave plasma assisted chemical vapor deposition (MPCVD) techniques have been refined to produce large, high-purity single crystal diamond anvils. Specifically multicarat single crystal diamond has been produced at high growth rate without annealing (around 50 mu m/h) with low impurities content. UV-visible absorption, Raman/photoluminescence spectroscopy, cathodoluminescence, and confocal Raman imaging are used to characterize the diamond. The measurements show that the material has high optical quality and clarity without layers. The large intensity ratio of the second-order Raman peak to the fluorescence background is essential for high-pressure optical windows. The origin of the residual color is also examined.

Small-angle X-ray scattering (SAXS) was performed on single-crystal chemical vapor deposition (CVD) diamonds with low nitrogen concentrations, which were fabricated by microwave plasma-assisted chemical vapor deposition at high growth rates. High optical quality undoped 500 mm-thick single-crystal CVD diamonds grown without intentional nitrogen addition proved to be excellent as windows on SAXS cells, yielding parasitic scattering no more intense than a 7.5 mm-thick Kapton film. A single-crystal CVD diamond window was successfully used in a high-pressure SAXS cell.

Single crystal diamond synthesis by microwave plasma chemical vapor deposition at rapid growth rate has considerably advanced in the past few years. Developments have been made in growth, optical quality, and mechanical properties. Of the various types of single crystal diamond that can be produced using these techniques, high quality single crystal CVD diamond can be routinely produced, and this material is playing an increasing role in research on materials under extreme conditions. This article highlights recent developments in single crystal CVD diamond synthesis and characterization, as well as various applications in high-pressure materials research.

A 75 kW, 915 MHz microwave plasma-assisted chemical vapor deposition system was adapted and utilized to scale up production of high-quality single-crystal diamonds at high growth rates. A 300 mm diameter plasma discharge was achieved with uniform temperature distributions of +/- 250 degrees C on up to 300 single-crystal diamond substrates. Diamond single crystals were synthesized from H-2/CH4/N-2 gas mixtures at pressures between 90 and 180 Torr, with recorded growth rates from 10 to 30 mu m/h. The source of N-2 was from vacuum chamber leakage, and it greatly affected synthesis chemistry. Optical emission spectroscopy was used to probe the localized plasma chemistry and plasma uniformity at different gas pressures. Production rates of up to 100 g/day of single-crystal diamonds were demonstrated, with 25% of the material categorized as colorless. Crystals up to 3.5 mm in thickness could be produced during a single deposition run. The quality of the crystals produced was assessed by photoluminescence and UV-visible absorption spectroscopies.

Background Many animals and plants acquire their coevolved symbiotic partners shortly post-embryonic development. Thus, during embryogenesis, cellular features must be developed that will promote both symbiont colonization of the appropriate tissues, as well as persistence at those sites. While variation in the degree of maturation occurs in newborn tissues, little is unknown about how this variation influences the establishment and persistence of host-microbe associations.Results The binary symbiosis model, the squid-vibrio (Euprymna scolopes-Vibrio fischeri) system, offers a way to study how an environmental gram-negative bacterium establishes a beneficial, persistent, extracellular colonization of an animal host. Here, we show that bacterial symbionts occupy six different colonization sites in the light-emitting organ of the host that have both distinct morphologies and responses to antibiotic treatment. Vibrio fischeri was most resilient to antibiotic disturbance when contained within the smallest and least mature colonization sites. We show that this variability in crypt development at the time of hatching allows the immature sites to act as a symbiont reservoir that has the potential to reseed the more mature sites in the host organ when they have been cleared by antibiotic treatment. This strategy may produce an ecologically significant resiliency to the association.Conclusion sThe data presented here provide evidence that the evolution of the squid-vibrio association has been selected for a nascent organ with a range of host tissue maturity at the onset of symbiosis. The resulting variation in physical and chemical environments results in a spectrum of host-symbiont interactions, notably, variation in susceptibility to environmental disturbance. This "insurance policy" provides resiliency to the symbiosis during the critical period of its early development. While differences in tissue maturity at birth have been documented in other animals, such as along the infant gut tract of mammals, the impact of this variation on host-microbiome interactions has not been studied. Because a wide variety of symbiosis characters are highly conserved over animal evolution, studies of the squid-vibrio association have the promise of providing insights into basic strategies that ensure successful bacterial passage between hosts in horizontally transmitted symbioses.