Radial Structure in the TW Hya Circumstellar Disk

We present new near-infrared interferometric data from the CHARA array and the Keck Interferometer on the circumstellar disk of the young star, TW Hya, a proposed "transition disk." We use these data, as well as previously published, spatially resolved data at 10 μm and 7 mm, to constrain disk models based on a standard flared disk structure. We find that we can match the interferometry data sets and the overall spectral energy distribution with a three-component model, which combines elements at spatial scales proposed by previous studies: optically thin, emission nearest the star, an inner optically thick ring of emission at roughly 0.5 AU followed by an opacity gap and, finally, an outer optically thick disk starting at ~4 AU. The model demonstrates that the constraints imposed by the spatially resolved data can be met with a physically plausible disk but this requires a disk containing not only an inner gap in the optically thick disk as previously suggested, but also a gap between the inner and outer optically thick disks. Our model is consistent with the suggestion by Calvet et al. of a planet with an orbital radius of a few AU. We discuss the implications of an opacity gap within the optically thick disk

GJ 900: A new hierarchical system with low-mass components

Speckle interferometric observations made with the 6 m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences in 2000 revealed the triple nature of the nearby ($\pi_{Hip}=51.80\pm1.74$ mas) low-mass young ($\approx200$ Myr) star GJ 900. The configuration of the triple system allowed it to be dynamically unstable. Differential photometry performed from 2000 through 2004 yielded $I$- and $K$-band absolute magnitudes and spectral types for the components to be $I_{A}$=6.66$\pm$0.08, $I_{B}$=9.15$\pm$0.11, $I_{C}$=10.08$\pm$0.26, $K_{A}$=4.84$\pm$0.08, $K_{B}$=6.76$\pm$0.20, $K_{C}$=7.39$\pm$0.31, $Sp_{A}$$\approx$K5--K7, $Sp_{B}$$\approx$M3--M4, $Sp_{C}$$\approx$M5--M6. The ``mass--luminosity'' relation is used to estimate the individual masses of the components: $\mathcal{M}_{A}$$\approx0.64\mathcal{M}_{\odot}$, $\mathcal{M}_{B}$$\approx0.21\mathcal{M}_{\odot}$, $\mathcal{M}_{C}$$\approx0.13\mathcal{M}_{\odot}$. From the observations of the components relative motion in the period 2000--2006, we conclude that GJ 900 is a hierarchical triple star with the possible orbital periods P$_{A-BC}$$\approx$80 yrs and P$_{BC}$$\approx$20 yrs. An analysis of the 2MASS images of the region around GJ 900 leads us to suggest that the system can include other very-low-mass components.Comment: 7 pages, 5 figure

FU Orionis resolved by infrared long baseline interferometry at a 2-AU scale

We present the first infrared interferometric observations of a young stellar object with a spatial projected resolution better than 2 AU. The observations were obtained with the Palomar Testbed Interferometer. FU Ori exhibits a visibility of V^2 =0.72 +/- 0.07 for a 103 +/- 5 m projected baseline at lambda = 2.2 microns. The data are consistent on the spatial scale probed by PTI both with a binary system scenario (maximum magnitude difference of 2.7 +/- 0.5 mag and smallest separation of 0.35 +/- 0.05 AU) and a standard luminous accretion disk model (approx. accretion rate of 6e-5 Mo/yr) where the thermal emission dominates the stellar scattering, and inconsistent with a single stellar photosphere.Comment: 13 pages, 4 figures, accepted for publication in ApJ

A π-Extended Donor-Acceptor-Donor Triphenylene Twin linked via a Pyrazine-bridge

Beta-amino triphenylenes can be accessed via palladium catalyzed amination of the corresponding triflate using benzophe-none imine. Transformation of amine 6 to benzoyl amide 18 is also straightforward and its wide mesophase range demon-strates that the new linkage supports columnar liquid crystal formation. Amine 6 also undergoes clean aerobic oxidation to give a new twinned structure linked through an electron-poor pyrazine ring. The new discotic liquid crystal motif contains donor and acceptor fragments, and is more oval in shape rather than disk-like. It forms a wide range columnar mesophase. Absorption spectra are strong and broad; emission is also broad and occurs with a Stokes shift of ca. 0.7 eV, indicative of charge-transfer characte

A review of recent perspectives on biomechanical risk factors associated with anterior cruciate ligament injury

There is considerable evidence to support a number of biomechanical risk factors associated with non-contact anterior cruciate ligament (ACL) injury. This paper aimed to review these biomechanical risk factors and highlight future directions relating to them. Current perspectives investigating trunk position and relationships between strength, muscle activity and biomechanics during landing/cutting highlight the importance of increasing hamstring muscle force during dynamic movements through altering strength, muscle activity, muscle length and contraction velocity. In particular, increased trunk flexion during landing/cutting and greater hamstring strength are likely to increase hamstring muscle force during landing and cutting which have been associated with reduced ACL injury risk. Decision making has also been shown to influence landing biomechanics and should be considered when designing tasks to assess landing/cutting biomechanics. Coaches should therefore promote hamstring strength training and active trunk flexion during landing and cutting in an attempt to reduce ACL injury risk.Peer reviewe

First Space-Based Microlens Parallax Measurement: Spitzer Observations of OGLE-2005-SMC-001

We combine Spitzer and ground-based observations to measure the microlens parallax of OGLE-2005-SMC-001, the first such space-based determination since S. Refsdal proposed the idea in 1966. The parallax measurement yields a projected velocity \tilde v ~ 230 km/s, the typical value expected for halo lenses, but an order of magnitude smaller than would be expected for lenses lying in the Small Magellanic Cloud (SMC) itself. The lens is a weak (i.e., non-caustic-crossing) binary, which complicates the analysis considerably but ultimately contributes additional constraints. Using a test proposed by Assef et al. (2006), which makes use only of kinematic information about different populations but does not make any assumptions about their respective mass functions, we find that the likelihood ratio is L_halo/L_SMC = 20. Hence, halo lenses are strongly favored but SMC lenses are not definitively ruled out. Similar Spitzer observations of additional lenses toward the Magellanic Clouds would clarify the nature of the lens population. The Space Interferometry Mission could make even more constraining measurements.Comment: ApJ, in press. Text and figures are updated to match the journal versio

Moebius strip enterprises and expertise in the creative industries: new challenges for lifelong learning?

The paper argues that the emergence of a new mode of production – co-configuration is generating new modes of expertise that EU policies for lifelong learning are not designed to support professionals to develop. It maintains that this change can be seen most clearly when we analyse Small and Medium Size (SMEs) enterprises in the creative industries. Drawing on concepts from Political Economy - ‘Moebius strip enterprise/expertise’ and Cultural Historical Activity Theory - project-object’ and the ‘space of reasons’, the paper highlights conceptually and through a case study of an SME in the creative industries what is distinctive about the new modes of expertise, before moving on to reconceptualise expertise and learning and to consider the implications of this reconceptualisation for EU policies for lifelong learning. The paper concludes that the new challenge for LLL is to support the development of new forms expertise that are difficult to credentialise, yet, are central to the wider European goal of realising a knowledge economy

Following the Formation of Synaptonemal Complex Formation in Wheat and Barley by High-Resolution Microscopy

International audienceWheat and barley have large genomes of 15 Gb and 5.1 Gb, respectively, which is much larger than the human genome (3.3 Gb). The release of their respective genomes has been a tremendous advance the understanding of the genome organization and the ability for deeper functional analysis in particular meiosis. Meiosis is the cell division required during sexual reproduction. One major event of meiosis is called recombination, or the formation of crossing over, a tight link between homologous chromosomes, ensuring gene exchange and faithful chromosome segregation. Recombination is a major driver of genetic diversity but in these large genome crops, the vast majority of these events is constrained at the end of their chromosomes. It is estimated that in barley, about 30% of the genes are located within the poor recombining centromeric regions, making important traits, such as resistance to pest and disease for example, difficult to access. Increasing recombination in these crops has the potential to speed up breeding program and requires a good understand of the meiotic mechanism. However, most research on recombination in plant has been carried in Arabidopsis thaliana which despite many of the advantages it brings for plant research, has a small genome and more spread out of recombination compare to barley or wheat. Advance in microscopy and cytological procedures have emerged in the last few years, allowing to follow meiotic events in these crops. This protocol provides the steps required for cytological preparation of barley and wheat pollen mother cells for light microscopy, highlighting some of the differences between the two cereals

Dynamical Measurements of the Young Upper Scorpius Triple NTTS 155808-2219

The young, low-mass, triple system NTTS 155808-2219 (ScoPMS 20) was previously identified as a ~17-day period single-lined spectroscopic binary with a tertiary component at 0.21 arcseconds. Using high-resolution infrared spectra, acquired with NIRSPEC on Keck II, both with and without adaptive optics, we measured radial velocities of all three components. Reanalysis of the single-lined visible light observations, made from 1987 to 1993, also yielded radial velocity detections of the three stars. Combining visible light and infrared data to compute the orbital solution produces orbital parameters consistent with the single-lined solution and a mass ratio of q = 0.78 +/- 0.01 for the SB. We discuss the consistency between our results and previously published data on this system, our radial-velocity analysis with both observed and synthetic templates, and the possibility that this system is eclipsing, providing a potential method for the determination of the stars' absolute masses. Over the ~20 year baseline of our observations, we have measured the acceleration of the SB's center-of-mass in its orbit with the tertiary. Long-term, adaptive optics imaging of the tertiary will eventually yield dynamical data useful for component mass estimates.Comment: 6 Tables, 8 Figures, updated to match published tex