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An important question in turbulent Rayleigh–Bénard convection is the scaling of the Nusselt number with the Rayleigh number in the so-called ultimate state, corresponding to asymptotically high Rayleigh numbers. A related but separate question is whether the measurements support the so-called Kraichnan law, according to which the Nusselt number varies as the square root of the Rayleigh number (modulo a logarithmic factor). Although there have been claims that the Kraichnan regime has been observed in laboratory experiments with low aspect ratios, the totality of existing experimental results presents a conflicting picture in the high-Rayleigh-number regime. We analyse the experimental data to show that the claims on the ultimate state leave open an important consideration relating to non-Oberbeck–Boussinesq effects. Thus, the nature of scaling in the ultimate state of Rayleigh–Bénard convection remains open.
In this paper we investigate methods to characterize angular current density from atomically defined gas field ion sources. We show that the ion beam emitted from a single apex atom is described by a two-dimensional Gaussian profile. Owing to the Gaussian shape of the beam and the requirement to collect the majority of the ion current, fixed apertures have inhomogeneous illumination. Therefore, angular current density measurements through a fixed aperture record averaged angular current density. This makes comparison of data difficult as averaged angular current density depends on aperture size. For the same reasons, voltage normalization cannot be performed for fixed aperture measurements except for aperture sizes that are infinitely small. Consistent determination of angular current density and voltage normalization, however, can be achieved if the beam diameter as well as total ion current are known. In cases where beam profile cannot be directly imaged with a field ion microscope, the beam profile could be extracted from measurements taken at multiple acceleration voltages and/or with multiple aperture sizes.
In many biological applications, such as cell therapy and drug delivery, there is a need to enhance diffusion by enabling chemical transport in all three dimensions. We highlight this need by comparing diffusion in a conventional two-dimensional (2D) microwell with diffusion in a three-dimensional (3D) cubic microwell using numerical simulations. We also describe the fabrication of hollow polymeric (and biocompatible) cubic microwells and microwell arrays. We emphasize that since the assembly process is compatible with 2D lithographic patterning, porosity can be precisely patterned in all three dimensions. Hence, this platform provides considerable versatility for a variety of applications.
We present model calculations of the atmospheric transmission for
DOME C in Antarctica for frequencies up to 10 THz (30 μm) using
the forward model MOLIERE-5. Measurements of precipitable water vapor
(pwv), obtained by the SUMMIT radiometer installed at the Concordia
station during 2008 and working at a wavelength of 200 μm, are
translated into atmospheric transmission using MOLIERE. Quartiles of
transmission, calculated from 200 μm data are extrapolated to
350 μm and compared to the CCAT (Cornell-Caltech Atacama
Telescope) site in Chile. It turns out that for 25% of the time at
DOME C (CCAT), the transmission is around 20% (5%) at
200 μm. This corresponds to a pwv of 0.18 mm for DOME C. At
350 μm, for 50% of time at DOME C (CCAT) the transmission is
around 55% (25%). This corresponds to a pwv of 0.22 mm for
DOME C. These results show that DOME C is one of the best observing
sites on Earth for submm-astronomy with respect to high atmospheric
transmission over long time periods.
We present preliminary results of the measurements of sky transparency conducted at Dome C during the winter 2008. Using MOLIERE modeling, we estimate a low precipitable water vapour content above Concordia station, which is very promising for future submillimetre wave observations on the Antarctic Plateau.
A continuation of this WG was voted for at the IAU GA 2006 in Prague. The International Celestial Reference Frame (ICRF) is defined by the positions of 212 distant quasars at radio wavelengths. The primary, optical reference frame is the Hipparcos Celestial Reference Frame (HCRF), which is the Hipparcos Catalog without astrometric ‘problem’ stars (in: H. Rickman (ed.) 2001, Proceedings IAU XXIV General Assembly, Transactions IAU XXIVB (San Francisco: ASP), Resolution B1.2). The Tycho-2 catalog with its 2.5 million brightest stars forms the first step in the densification of the optical reference frame. However, the limiting magnitude of about V = 12 of the Tycho-2 catalog is not sufficient for most applications in astronomy and the goal of this IAU Working Group is to further extend the grid of highly accurate positions and motions toward more and fainter stars. The web site of this WG is at <ad.usno.navy.mil/dens_wg/>.
2D-crystallization in combination with transmission electron microscopy (TEM) is one of the few methods for the structural analysis of membrane proteins in their native state. However, the parameters for the generation of large crystalline sheets are typically difficult to identify for a given protein. Many repetitive and time consuming screening steps by TEM are therefore necessary to find the best crystallization and preparation conditions. Although several software packages offer the possibility to control an electron microscope, none is completely adapted for a fully automated and completely integrated acquisition and analysis of 2D crystals. Here we report on the development of a fully automatic screening and on-line analysis software for the fast and automatic survey of large quantities of negatively stained EM samples for 2D crystallography.
The fast rate of the globalisation process and huge technological changes are leading to increased uncertainty. Risk (considered either as a threat or as an opportunity) is correlated to uncertainty. That means that the socio-economic environment may be considered as ambiguous, and the reaction of players complex, unforeseeable and difficult to handle. In such conditions one looks for simple formulae or tricks to manage the necessary change in human behaviour, institutional structures, production and trade methods. ‘Flexibility’ seems to be a magic keyword – both a performance driver and an expression of freedom. Labour market flexibility is currently the focus of ideological and political debate. This paper aims to clarify some points in the debate, especially in the European Union context. First, we give some brief information about the EU framework with regard to the labour market flexibility and its performance. Second, we try to understand how labour market flexibility is dependent on decisions of enterprises (in search of competitiveness). But this point of view needs to be enlarged to a more systemic approach; flexibility is only one of the socio-economic performance variables. A flexibility paradigm is related to a new political and humanistic project, and is a serious consideration for a number of industrial and financial companies, scientific associations and bodies.
A species checklist is presented for a stretch of the seasonally flooded Macal River in the Cayo District of Belize, together with preliminary phytosociological data for the primary riverine communities. A total of 229 species were recorded in the seasonally flooded riparian zone, representing 7% of the flora of Belize. Results of quantitative sampling indicate that Inga vera subsp. vera dominates the river corridor. Other important woody associates include Cuphea calophylla, C. utriculosa, Calyptranthes bartlettii, C. lindeniana, Lindenia rivalis, Pleuranthodendron lindenii, Calliandra tergemina and Nectandra salicifolia. One of the most significant threats to riparian vegetation in the region is the Chalillo Dam upstream of the study site. The current work provides baseline floristic and ecological data for this threatened riparian habitat and documents the structure and composition of vegetation that exists downstream from the dam before its construction.
Between January 1994 and October 1997, we interviewed 2576 black in-patients with newly diagnosed cancer in Johannesburg and Soweto, South Africa. Blood was tested for HIV-1 and HHV-8 antibodies and the study was restricted to 2191 HIV-1 antibody-negative patients. We examined the relationship between infection with HHV-8 and sociodemographic and behavioural factors using unconditional logistic regression models. Of the 2191 HIV-1 negative patients who did not have Kaposi's sarcoma, 854 (39·1%) were positive for antibodies against the latent nuclear antigen of HHV-8 encoded by orf73 in a immunofluorescence assay. Infection with HHV-8 was independently associated with increasing age (P trend=0·02). For females, independent risk factors also included working in a paid domestic capacity (OR 1·63, 95% CI 1·09–2·44, P=0·02), defining occupational status as economically non-active unemployed (OR 1·70, 95% CI 1·06–2·72, P=0·03), having a state pension or being on a disability grant (OR 1·49, 95% CI 1·05–2·11, P=0·02), using oral contraceptives (OR 1·43, 95% CI 1·03–1·99, P=0·03) and having a delayed age at menarche (P trend=0·04). The relationship between these variables and HHV-8 antibody status requires further, prospective study.
Extended abstract of a paper presented at the Pre-Meeting Congress: Materials Research in an Aberration-Free Environment, at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, July 31 and August 1, 2004.