Unusual light spectra from a two-level atom in squeezed vacuum

We investigate the interaction of an atom with a multi-channel squeezed vacuum. It turns out that the light coming out in a particular channel can have anomalous spectral properties, among them asymmetry of the spectrum, absence of the central peak as well as central hole burning for particular parameters. As an example plane-wave squeezing is considered. In this case the above phenomena can occur for the light spectra in certain directions. In the total spectrum these phenomena are washed out.Comment: 16 pages, LaTeX, 3 figures (included via epsf

The Power of General Relativity

We study the cosmological and weak-field properties of theories of gravity derived by extending general relativity by means of a Lagrangian proportional to $R^{1+\delta}$. This scale-free extension reduces to general relativity when $\delta \to 0$. In order to constrain generalisations of general relativity of this power class we analyse the behaviour of the perfect-fluid Friedmann universes and isolate the physically relevant models of zero curvature. A stable matter-dominated period of evolution requires $\delta >0$ or $\delta <-1/4$. The stable attractors of the evolution are found. By considering the synthesis of light elements (helium-4, deuterium and lithium-7) we obtain the bound $-0.017<\delta <0.0012.$ We evaluate the effect on the power spectrum of clustering via the shift in the epoch of matter-radiation equality. The horizon size at matter--radiation equality will be shifted by $\sim 1$ for a value of $\delta \sim 0.0005.$ We study the stable extensions of the Schwarzschild solution in these theories and calculate the timelike and null geodesics. No significant bounds arise from null geodesic effects but the perihelion precession observations lead to the strong bound $\delta =2.7\pm 4.5\times 10^{-19}$ assuming that Mercury follows a timelike geodesic. The combination of these observational constraints leads to the overall bound $0\leq \delta <7.2\times 10^{-19}$ on theories of this type.Comment: 26 pages and 5 figures. Published versio

Spitzer Mid-Infrared Photometry of 500 - 750 K Brown Dwarfs

Mid-infrared data, including Spitzer warm-IRAC [3.6] and [4.5] photometry, is critical for understanding the cold population of brown dwarfs now being found, objects which have more in common with planets than stars. As effective temperature (T_eff) drops from 800 K to 400 K, the fraction of flux emitted beyond 3 microns increases rapidly, from about 40% to >75%. This rapid increase makes a color like H-[4.5] a very sensitive temperature indicator, and it can be combined with a gravity- and metallicity-sensitive color like H-K to constrain all three of these fundamental properties, which in turn gives us mass and age for these slowly cooling objects. Determination of mid-infrared color trends also allows better exploitation of the WISE mission by the community. We use new Spitzer Cycle 6 IRAC photometry, together with published data, to present trends of color with type for L0 to T10 dwarfs. We also use the atmospheric and evolutionary models of Saumon & Marley to investigate the masses and ages of 13 very late-type T dwarfs, which have H-[4.5] > 3.2 and T_eff ~ 500 K to 750 K.Comment: To be published in the on-line version of the Proceedings of Cool Stars 16 (ASP Conference Series). This is an updated version of Leggett et al. 2010 ApJ 710 1627; a photometry compilation is available at http://www.gemini.edu/staff/slegget

Timing recovery after the cretaceous/paleogene boundary: evidence from Brazos River, Texas

As part of an on-going re-assessment of the Cretaceous/ Paleogene boundary in the Brazos River area, Falls County, Texas, a number of new exposures have been described. One of these, at River Bank South, provides a near continuous record of the lowermost Paleocene. It is from this succession that stable isotope analysis of bulk organic matter (δ13C and C/N) and mono-specific samples of the benthic foraminifera Lenticulina rotulata Lamarck (δ18O and δ13C) yields an orbitally-tuned stable isotope record, which allows the timing of events adjacent to the Cretaceous/Paleogene boundary to be determined. Using this cyclicity, it is suggested that the on-set of biotic recovery began ∼40,000 years after the impact (near the base of Zone Pα) and that more significant recovery of planktic foraminifera and calcareous nannofossils began close to the base of Zone P1a, some 85,000–100,000 years post-impact. The data also appear to record the presence of the earliest Paleocene DAN-C2 and Lower C29n hyperthermal events and that these events appear to be an accentuated segment of this orbital cyclicity

Effects of Feeding Brassica Mixture Cover Crops During Backgrounding on Carcass Traits and Fresh Meat Quality

Objective: Determine effects of feeding brassica-based cover crops to cattle during backgrounding on carcass characteristics and tenderness, flavor, and juiciness of longissimus dorsi steaks