Guanine‐Based Biogenic Photonic‐Crystal Arrays in Fish and Spiders

Biological photonic systems composed of anhydrous guanine crystals evolved separately in several taxonomic groups. Here, two such systems found in fish and spiders, both of which make use of anhydrous guanine crystal plates to produce structural colors, are examined. Measurements of the photonic‐crystal structures using cryo‐SEM show that the crystal plates in both fish skin and spider integument are ～20‐nm thick. The reflective unit in the fish comprises stacks of single plates alternating with ～230‐nm‐thick cytoplasm layers. In the spiders the plates are formed as doublet crystals, cemented by 30‐nm layers of amorphous guanine, and are stacked with ～200 nm of cytoplasm between crystal doublets. They achieve light reflective properties through the control of crystal morphology and stack dimensions, reaching similar efficiencies of light reflectivity in both fish skin and spider integument. The structure of guanine plates in spiders are compared with the more common situation in which guanine occurs in the form of relatively unorganized prismatic crystals, yielding a matt white coloration.     

Residual porosity and optical properties of spark plasma sintered transparent polycrystalline cerium-doped YAG

Transparent cerium-doped yttrium aluminum garnet (Ce:YAG) phosphors are promising candidates for high-power white light emitting diode applications. In the present study, Ce:YAG powder was synthesized by a co-precipitation method and highly transparent ceramics were fabricated by spark plasma sintering. The effects of temperature and pressure, as well as post-sintering treatments (annealing or hot isostatic pressing), on residual porosity were studied by electron and confocal laser microscopy. Correlation between residual porosity characteristics (pore size and volume fraction) and optical properties (in-line transmittance and photoluminescence intensity) of the luminescent transparent ceramics was established.     

Decomposition products of petn in post explosion analysis

TLC of post-explosion debris showed that in some cases PETN was accompanied by other compounds which reacted with Griess reagent. The possibility that these compounds could be lower nitrate esters of pentaerythritol (tri-, di- and mononitrate) was examined. Lower nitrate esters were obtained by hydrolysis of PETN and their structures were determined–following separation–by mass spectrometry and NMR. Chromatographic data of these esters matched data of the compounds which accompanied PETN in certain post-explosion cases. The dinitrate and trinitrate esters of pentaerythritol were isolated from post-explosion extracts and their structures confirmed by mass spectrometry and NMR.     

Sound scattering by free surface piercing and fluid-loaded cylindrical shells

A vertical flexible, thin, cylindrical shell is considered to be clamped to a rigid base in shallow water and piercing its surface. The shell is composed of an isotropic and homogeneous material and may be empty inside or filled with compressible fluid. Linear acoustics and structural dynamics are used to model sound scattering caused by an external incident sound wave. A solution is derived using a Fourier transform in the tangential and vertical directions. A collocation technique coupled with an orthogonalization procedure is used to account for the edge conditions of the shell. It is shown that zero sound scattering, indicating acoustic invisibility, is theoretically attainable and can be achieved when a continuous distribution of an oscillating pressure load is applied on the shell's wall. Similarly, zero sound transmission into the shell's inner fluid can also be considered. The possibility of using a pre-determined discrete distribution of the applied pressure load is also discussed. The derived equations are numerically solved to examine sound scattering by a thin aluminium shell in shallow water.     

Response of MCF7 human breast cancer to tamoxifen: evaluation by the three-time-point, contrast-enhanced magnetic resonance imaging method

Variations in the cellular volume fraction and in the microvascular permeability of MCF7 human breast tumors were used to assess response to tamoxifen. These pathophysiological features were mapped by applying the three-time-point, contrast-enhanced, high resolution magnetic resonance imaging method (H. Degani et al, Nat. Med., 3: 780-782, 1997). Short-term treatment with tamoxifen caused a highly significant increase in the fraction of pixels displaying intermediate contrast agent clearance pattern and a significant increase in the fraction of pixels displaying high rate of contrast agent entrance. These changes resulted from a marked rise in the extracellular volume fraction, indicating increased necrosis, and from an augmentation in the microvascular permeability, predominantly in the vicinity of the high extracellular volume fraction areas, as a result of stress-induced angiogenesis.     

Alternative genres in information systems research

In this special issue, we advocate a critical stance toward the presentational conventions that we – as authors, reviewers, and editors – accept as the academic article genre. We seek to highlight and illustrate the generative capacity and the significant role of genres in the production of knowledge. Furthermore, we wish to encourage Information Systems (IS) scholars to leverage a wider array of alternative genres to present their research in order to develop new insights on subject matters of interest to the IS discipline, as well as expand on how contemporary and emergent phenomena of interest are conceived and studied. Adopting a broad view of alternative genres, we solicited articles that apply unconventional presentational modalities to expand or challenge the prevailing modus operandi of communicating IS scholarship and practice. Six articles survived a rather lengthy and challenging review process. We briefly discuss the nature of the academic article genre and the role of alternative ways of writing. We also introduce the six exemplars of alternative genres in the special issue, namely conversation, French new novel, meditation, memoir, allegory, and crowdsourced research. We highlight key insights and contemplate their implications for current and future IS research.     

Valence Bond-Based Hybrid Quantum Mechanics Molecular Mechanics Approaches and Proper Inclusion of the Effect of the Surroundings

The pioneering development of multiscale models for complex chemical systems by Karplus, Levitt, and Warshel, including the hybrid quantum mechanics molecular mechanics (QM/MM) approach and its application to enzymes, established a new field in chemistry that allows the modeling of reactivity within complex chemical systems. Inspired by the potential of such methods, many groups developed different QM/MM variants. Valence bond (VB) theory, which always was and still is an important conceptual tool for chemists, is well suited to deal with problems of chemical reactivity. Hence, here we review VB-based QM/MM methods, including the early semi-empirical methods that utilize VB concepts and more recent ab initio VB-based QM/MM methods. Special emphasis is given to the different ways to include effects of the surroundings on the solute. It is shown that within the VB framework, simple mechanical embedding for each diabatic state, followed by mixing of the states, accounts for most of these effects.     

Knowledge-based structure prediction of MHC class I bound peptides: a study of 23 complexes

BACKGROUND: The binding of T-cell antigenic peptides to MHC molecules is a prerequisite for their immunogenicity. The ability to identify binding peptides based on the protein sequence is of great importance to the rational design of peptide vaccines. As the requirements for peptide binding cannot be fully explained by the peptide sequence per se, structural considerations should be taken into account and are expected to improve predictive algorithms. The first step in such an algorithm requires accurate and fast modeling of the peptide structure in the MHC-binding groove. RESULTS: We have used 23 solved peptide-MHC class I complexes as a source of structural information in the development of a modeling algorithm. The peptide backbones and MHC structures were used as the templates for prediction. Sidechain conformations were built based on a rotamer library, using the 'dead end elimination' approach. A simple energy function selects the favorable combination of rotamers for a given sequence. It further selects the correct backbone structure from a limited library. The influence of different parameters on the prediction quality was assessed. With a specific rotamer library that incorporates information from the peptide sidechains in the solved complexes, the algorithm correctly identifies 85% (92%) of all (buried) sidechains and selects the correct backbones. Under cross-validation, 70% (78%) of all (buried) residues are correctly predicted and most of all backbones. The interaction between peptide sidechains has a negligible effect on the prediction quality. CONCLUSIONS: The structure of the peptide sidechains follows from the interactions with the MHC and the peptide backbone, as the prediction is hardly influenced by sidechain interactions. The proposed methodology was able to select the correct backbone from a limited set. The impairment in performance under cross-validation suggests that, currently, the specific rotamer library is not satisfactorily representative. The predictions might improve with an increase in the data.