Atomic Clouds as Spectrally-Selective and Tunable Delay Lines for Single Photons from Quantum Dots

We demonstrate a compact, spectrally-selective, and tunable delay line for single photons emitted by quantum dots. This is achieved by fine-tuning the wavelength of the optical transitions of such "artificial atoms" into a spectral window in which a cloud of natural atoms behaves as slow-light medium. By employing the ground-state fine-structure-split exciton confined in an InGaAs/GaAs quantum dot as a source of single photons at different frequencies and the hyperfine-structure-split $D_1$ transition of Cs-vapors as a tunable delay-medium, we achieve a differential delay of up 2.4 ns on a 7.5 cm long path for photons that are only 60 \mu eV (14.5 GHz) apart. To quantitatively explain the experimental data we develop a theoretical model that accounts for both the inhomogeneously broadening of the quantum-dot emission lines and the Doppler-broadening of the atomic lines. The concept we proposed here may be used to implement time-reordering operations aimed at erasing the "which-path" information that deteriorates entangled-photon emission from excitons with finite fine-structure-splitting.Comment: 29 pages, 5 figure

EC 10246−2707: an eclipsing subdwarf B + M dwarf binary★

We announce the discovery of a new eclipsing hot subdwarf B + M dwarf binary, EC 10246-2707, and present multi-colour photometric and spectroscopic observations of this system. Similar to other HW Vir-type binaries, the light curve shows both primary and secondary eclipses, along with a strong reflection effect from the M dwarf; no intrinsic light contribution is detected from the cool companion. The orbital period is 0.118 507 993 6 ± 0.000 000 000 9 days, or about three hours. Analysis of our time- series spectroscopy reveals a velocity semi-amplitude of K1 = 71.6 ± 1.7 km s−1 for the sdB and best-fitting atmospheric parameters of Teff = 28900 ± 500 K, log g = 5.64 ± 0.06, and log N(He)/N(H) = -2.5 ± 0.2. Although we cannot claim a unique solution from modeling the light curve, the best–fitting model has an sdB mass of 0.45 M⊙ and a cool companion mass of 0.12 M⊙. These results are roughly consistent with a canonical–mass sdB and M dwarf separated by a ∼ 0.84 R⊙. We find no evidence of pulsations in the light curve and limit the amplitude of rapid photometric oscillations to 7.2×10−12. If EC 10246- 2707 evolves into a cataclysmic variable, its period should fall below the famous CV period gap

EC 10246-2707: a new eclipsing sdB + M dwarf binary⋆

We announce the discovery of a new eclipsing hot subdwarf B + M dwarf binary, EC 10246-2707, and present multi-colour photometric and spectroscopic observations of this system. Similar to other HW Vir-type binaries, the light curve shows both primary and secondary eclipses, along with a strong reflection effect from the M dwarf; no intrinsic light contribution is detected from the cool companion. The orbital period is 0.118 507 993 6 ± 0.000 000 000 9 days, or about three hours. Analysis of our time- series spectroscopy reveals a velocity semi-amplitude of K1 = 71.6 ± 1.7 km s−1 for the sdB and best-fitting atmospheric parameters of Teff = 28900 ± 500 K, log g = 5.64 ± 0.06, and log N(He)/N(H) = -2.5 ± 0.2. Although we cannot claim a unique solution from modeling the light curve, the best–fitting model has an sdB mass of 0.45 M⊙ and a cool companion mass of 0.12 M⊙. These results are roughly consistent with a canonical–mass sdB and M dwarf separated by a ∼ 0.84 R⊙. We find no evidence of pulsations in the light curve and limit the amplitude of rapid photometric oscillations to < 0.08%. Using 15 years of eclipse timings, we construct an O-C diagram but find no statistically significant period changes; we rule out | ˙P | > 7.2×10−12. If EC 10246- 2707 evolves into a cataclysmic variable, its period should fall below the famous CV period gap.Web of Scienc

Evidence for Diffuse Central Retinal Edema In Vivo in Diabetic Male Sprague Dawley Rats

Background: Investigations into the mechanism of diffuse retinal edema in diabetic subjects have been limited by a lack of animal models and techniques that co-localized retinal thickness and hydration in vivo. In this study we test the hypothesis that a previously reported supernormal central retinal thickness on MRI measured in experimental diabetic retinopathy in vivo represents a persistent and diffuse edema. Methodology/Principal Findings: In diabetic and age-matched control rats, and in rats experiencing dilutional hyponatremia (as a positive edema control), whole central retinal thickness, intraretinal water content and apparent diffusion coefficients (ADC, ‘water mobility’) were measured in vivo using quantitative MRI methods. Glycated hemoglobin and retinal thickness ex vivo (histology) were also measured in control and diabetic groups. In the dilutional hyponatremia model, central retinal thickness and water content were supernormal by quantitative MRI, and intraretinal water mobility profiles changed in a manner consistent with intracellular edema. Groups of diabetic (2, 3, 4, 6, and 9 mo of diabetes), and age-matched controls were then investigated with MRI and all diabetic rats showed supernormal whole central retinal thickness. In a separate study in 4 mo diabetic rats (and controls), MRI retinal thickness and water content metrics were significantly greater than normal, and ADC was subnormal in the outer retina; the increase in retinal thickness was not detected histologically on sections of fixed and dehydrated retinas from these rats

Logo designs for the Oxford Research Archive

Various files and test images using the logo for the Oxford Research Archive

OAI-ORE, PRESERV2 and digital preservation

The new framework for the description and exchange of aggregations of Web resources, OAI-ORE, had its European release in April 2008 [1]. Amongst its practical uses, OAI-ORE has a role to play in digital preservation and continued access to files. This article describes the basic outline of the framework and how it can support the PRESERV2 project digital preservation model of provision of preservation services and interoperability for digital repositories. The PRESERV approach recognises that effective preservation is founded on three fundamental actions on data: copy, move and monitor. This includes the copying and movement of data between different repositories which is where OAI-ORE has a role to play. OAI-ORE also plays a part in interoperability to ensure that repositories and other tools and services can communicate and share information and data. In this way the project is creating and testing a flexible framework for an emerging range of services and tools, to ensure support for long-term access to the data deposited in repositories

Dynamically honest displays: Courtship locomotor performance indicates survival in guppies

1. The indicator theory of sexual selection suggests that mating displays honestly signal aspects of fitness. While rarely studied, kinematic (locomotor) performance is an excellent candidate for an honest indicator, as mating displays of many animals include rapid or extended locomotion that may be physiologically correlated with performance traits that impact survival. 2. We investigate the indicator value of display locomotion of wild-caught male guppies, Poecilia reticulata, by examining relationships between mating display kinematic traits, anti-predator kinematic traits, and survival during a subsequent staged encounter with a natural predator, the pike cichlid Crenicichla alta. 3. We first compared guppy display kinematics with subsequent survival, and found that display body angle and angular speed positively predicted survival. We next compared anti-predator kinematic and tactical traits with survival, to identify traits that might link mating displays to survival. We measured anti-predator traits in two tests, first in response to a standardized stimulus (fast start test), and second in response to the live predator (encounter test). Guppy fast start speed and encounter speed, time in refuges, and approach distance (response distance) all positively predicted survival, while encounter swim duration negatively predicted survival. These data provided our final hypothesis, that these particular anti-predator traits would be correlated with mating display kinematics. However, we detected only one of eight predicted correlations, a negative relationship between display body angle and encounter swim duration that may reflect an energy trade-off. 4. We conclude that courtship locomotor performance can be an honest survival indicator in guppies, and that the mechanism linking courtship to survival merits further study. These results suggest that courtship locomotion may contribute to viability impacts on the evolution of animal mate choice, and support others in suggesting that these traits may reward greater attention in sexual and natural selection studies

OAI-ORE, PRESERV2 and Digital Preservation

The new framework for the description and exchange of aggregations of Web resources, OAI-ORE, had its European release in April 2008 [1]. Amongst its practical uses, OAI-ORE has a role to play in digital preservation and continued access to files. This article describes the basic outline of the framework and how it can support the PRESERV2 project digital preservation model of provision of preservation services and interoperability for digital repositories. The PRESERV approach recognises that effective preservation is founded on three fundamental actions on data: copy, move and monitor. This includes the copying and movement of data between different repositories which is where OAI-ORE has a role to play. OAI-ORE also plays a part in interoperability to ensure that repositories and other tools and services can communicate and share information and data. In this way the project is creating and testing a flexible framework for an emerging range of services and tools, to ensure support for long-term access to the data deposited in repositories