Is there theoretical evidence for a metallic carbon polymorph with space group symmetry at ambient conditions?

Quantum mechanical calculations based on density functional theory and the generalised gradient approximation show that the equilibrium lattice parameter of a carbon polymorph with space group symmetry would be 3.08 Å, and hence very different from that of diamond. No local minimum in the dependence of the total energy on the lattice parameter has been found. Such a polymorph would be approximately 5 eV atom⁻¹ less stable than diamond, suggesting that its synthesis is very unlikely. This finding is consistent with older density functional calculations and contradicts recent results of LCAO calculations, which have been used to support the interpretation of experimental data as showing the existence of a metallic carbon polymorph with space group symmetry .     

Sensitivity of the backscattering Mueller matrix to particle shape and thermodynamic phase

The Mueller matrix (M) corresponding to the phase matrix in the backscattering region (scattering angles ranging from 175 degrees to 180 degrees) is investigated for light scattering at a 0.532-microm wavelength by hexagonal ice crystals, ice spheres, and water droplets. For hexagonal ice crystals we assume three aspect ratios (plates, compact columns, and columns). It is shown that the contour patterns of the backscattering Mueller matrix elements other than M11, M44, M14, and M41 depend on particle geometry; M22 and M33 are particularly sensitive to the aspect ratio of ice crystals. The Mueller matrix for spherical ice particles is different from those for nonspherical ice particles. In addition to discriminating between spherical and nonspherical particles, the Mueller matrix may offer some insight as to cloud thermodynamic phase. The contour patterns for large ice spheres with an effective size of 100 microm are substantially different from those associated with small water droplets with an effective size of 4 microm.     

Chiral discrimination of basic and hydrophobic molecules by chemical force spectroscopy

Chemical force spectroscopy (CFS) is becoming a powerful technique with which to measure intermolecular forces. The prime advantage over other techniques is the ability to map spatial distribution of ligands on the surface. We have used CFS to explore the binding force of a variety of different chiral molecules in order to understand more about the nature of what is a fundamental aspect of chemical biology and of central importance in pharmacology.     

Automation for High-throughput Identification and Picking of GFP Expressing Colonies

Green fluorescent protein (GFP) has many applications as a marker in living cells, and has become widely used as a reporter gene in microbial, plant and animal cells. Screening microbial colonies for GFP expression enables various types of assays (e.g. for secretory mutations). However, this is laborious, non-quantitative and potentially hazardous to the operator (due to UV illumination) when performed manually. In order to address this the GloPix robot was developed. The imaging system discriminates between colonies based on the level of fluorescence activity and the picking function automatically transfers cells to microplate wells. Measuring fluorescent activity allows quantitation of fluorescent tag concentration/expression.     

Post-pass partitioning of signal processing programs

Symmetric multiprocessor systems are increasingly common, not only as high-throughput servers, but as a vehicle for executing a single application in parallel in order to reduce its execution latency. This article presents Pedigree, a compilation tool that employs a new partitioning heuristic based on the program dependence graph (PDG). Pedigree creates overlapping, potentially interdependent threads, each executing on a subset of the SMP processors that matches the thread’s available parallelism. A unified framework is used to build threads from procedures, loop nests, loop iterations, and smaller constructs. Pedigree does not require any parallel language support; it is post-compilation tool that reads in object code. The SDIO Signal and Data Processing Benchmark Suite has been selected as an example of real-time, latency-sensitive code. Its coarse-grained data flow parallelism is naturally exploited by Pedigree to achieve speedups of 1.63×/2.13× (mean/max) and 1.71×/2.41× on two and four processors, respectively. There is roughly a 20% improvement over existing techniques that exploit only data parallelism. By exploiting the unidirectional flow of data for coarse-grained pipelining, the synchronization overhead is typically limited to less than 6% for synchronization latency of 100 cycles, and less than 2% for 10 cycles. This research was supported by ONR contract numbers N00014-91-J-1518 and N00014-96-1-0347. We would like to thank the Pittsburgh Supercomputing Center for use of their Alpha systems.     

Towards quality requirements via animated formal specifications

Assuring a high quality requirements specification document involves both an early validation process and an increased level of participation. An approach and its supporting environment which combines the benefits of a formal system specification and its subsequent execution via a rapid prototype is reported. The environment assists in the construction, clarification, validation and visualisation of a formal specification. An illustrative case study demonstrates the consequences of assertions about system properties at this early stage of software development. Our approach involves the pragmatic combination of technical benefits of formal systems engineering based techniques with the context‐sensitive notions of increased participation of both developer and user stakeholders to move us closer towards a quality requirements specification document.     

An investigation of multiphase CFD modelling of a lateral sloshing tank

A near-resonant, sway-induced sloshing flow in a rectangular tank is used to compare a homogeneous and inhomogeneous multiphase approach for fluid density and viscosity in a commercial CFD code. Dimensional analysis of the relative motion between the phases suggests the application of an inhomogeneous multiphase model whereas previous published work has used the computationally cheaper homogeneous (or average property) approach. The comparison between the computational and experimental results shows that the homogeneous model tends to underestimate the experimental peak pressures by up to 50%. The inhomogeneous multiphase model gives good agreement with the experimental pressure data. Examination of the relative velocity at the fluid interface confirms that the inhomogeneous model is the appropriate model to use for the simulation of a violent sloshing flow.     

Research on visual word recognition: From verbal learning to parallel distributed processing.

Over the past 30 yrs, research on visual word recognition has contributed greatly to the understanding of how information is processed, represented, and accessed in the cognitive system. Today, word recognition continues to serve as a rich domain for modelling and investigating core issues in cognition. In addition, research on word recognition has been used to improve assessment and instruction of reading for children and adults. This article provides a brief overview of some trends and developments in word recognition research over the past few decades. This overview is not meant to be exhaustive (or unbiased); it is intended to give readers from outside the area a feel for why word recognition is such an important domain for cognitive research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The interaction of alumina with HCl: An infrared spectroscopy, temperature-programmed desorption and inelastic neutron scattering study

The interaction of HCl with an η-alumina catalyst has been investigated by a combination of diffuse reflectance infrared spectroscopy, temperature-programmed desorption and inelastic neutron scattering (INS) spectroscopy. Infrared spectra provide evidence for dissociative adsorption of HCl and for a process in which hydroxyl groups terminally bound to Al are replaced by chlorine. Temperature-programmed desorption experiments show HCl to desorb over the temperature range 350–>970 K, indicating dissociative HCl adsorption to occur on a wide range of active sites. INS experiments show the residual alumina hydroxyl groups to exhibit an out-of-plane deformation feature, γ(OH), at ca. 200 cm⁻¹, while the in-plane deformation mode, δ(OH), is seen at ca. 1000 cm⁻¹. The formation of new surface hydroxyl groups via the adsorption of hydrogen chloride yields a δ(OH) feature that can be resolved into two bands at 990 and 1050 cm⁻¹. Hydrogen bonding within the alumina/HCl system is responsible for the observation of an Evans transmission window in the infrared spectrum, that occurs via a Fermi resonance interaction between (i) the ν(OH) mode of hydrogen bonded hydroxyl groups and chemisorbed water with (ii) the overtone of the δ(OH) mode of surface hydroxyl groups. The INS technique is able to discriminate among different hydroxyl group bonding geometries on the basis of the local symmetry of the active sites.