Rigid unit modes in tetrahedral crystals

The 'rigid unit mode' (RUM) model requires unit blocks, in our case tetrahedra of SiO_4 groups, to be rigid within first order of the displacements of the O-ions. The wave-vectors of the lattice vibrations, which obey this rigidity, are determined analytically. Lattices with inversion symmetry yield generically surfaces of RUMs in reciprocal space, whereas lattices without this symmetry yield generically lines of RUMs. Only in exceptional cases as in beta-quartz a surface of RUMs appears, if inversion symmetry is lacking. The occurence of planes and bending surfaces, straight and bent lines is discussed. Explicit calculations are performed for five modifications of SiO_2 crystals.Comment: 18 pages, 6 figures, improved notatio

Drainage of the Teays-Stage Mount Vernon and Cambridge Rivers

Author Institution: U. S. Geological Survey, 85 Marconi Blvd., Columbus 15, Ohi

Oil Dries Used in Arson Scenes: New Absorbent Material

In many fire investigation cases, it is hard to find evidence that will lead to the cause or person that started the fire, especially within arson scenes. Because of this, the identification of ignitable liquids is critical to an arson investigation. Obtaining enough evidential information from the scene is key if arson is suspected. Many scenes involve ignitable liquids that have been poured onto furniture or carpets, allowing the ignitable liquid to easily be collected. However, in some investigations ignitable liquids are poured onto semi-porous surfaces such as concrete. Collection of these materials is difficult. Oil dries are absorbents commonly used to clean up spills, at scenes, involving hazardous materials. Since many hazardous material spills involve petroleum products, it is suspected that the oil dries might also absorb ignitable liquids. Studies done in the past on creating a solid absorbent have not been successful, while some household absorbent have been somewhat beneficial.1 This research will concentrate on the potential use of different solid oil dry absorbents to be used at a fire scene to assist in the collection of questioned arson samples. All analysis of samples will be conducted using a technique commonly used in forensic laboratories, gas chromatography with flame ionization detection

Prevalence, intensity, and effect of a nematode (Philometra saltatrix) in the ovaries of bluefish (Pomatomus saltatrix)

Examination of 203 adult bluefish (Pomatomus saltatrix) from Long Island, New York, in 2002 and 2003 and 66 from the Outer Banks, North Carolina, in 2003 revealed the presence of dracunculoid nematodes (Philometra saltatrix) in the ovaries of female fish. Percent prevalence reached 88% in July and then decreased after the peak of the spawning season. Bluefish contained up to 100 parasites per fish. Infection was associated with a range of disorders, including hemorrhage, inf lammation, edema, prenecrotic and necrotic changes, and follicular atresia, that may prevent proper development of oocytes and probably affect bluefish fecundity. Historical occurrences, life cycle, and geographical distribution of this nematode remain largely unknown, but may play important roles in recruitment processes of bluefish

Structure determination of disordered materials from diffraction data

We show that the information gained in spectroscopic experiments regarding the number and distribution of atomic environments can be used as a valuable constraint in the refinement of the atomic-scale structures of nanostructured or amorphous materials from pair distribution function (PDF) data. We illustrate the effectiveness of this approach for three paradigmatic disordered systems: molecular C60, a-Si, and a-SiO2 . Much improved atomistic models are attained in each case without any a-priori assumptions regarding coordination number or local geometry. We propose that this approach may form the basis for a generalised methodology for structure "solution" from PDF data applicable to network, nanostructured and molecular systems alike.Comment: 4 pages, 3 figures, set out as for PR

Dynamics from diffraction

A model-independent approach for the extraction of detailed lattice dynamical information from neutron powder diffraction data is described. The technique is based on a statistical analysis of atomistic configurations generated using reverse Monte Carlo structural refinement. Phonon dispersion curves extracted in this way are shown to reproduce many of the important features found in those determined independently using neutron triple-axis spectroscopy. The extent to which diffraction data are sensitive to lattice dynamics is explored in a range of materials. The prospect that such detailed dynamical information might be accessible using comparatively facile experiments such as neutron powder diffraction is incredibly valuable when studying systems for which established spectroscopic methods are prohibitive or inappropriate

Simulation study of pressure and temperature dependence of the negative thermal expansion in Zn(CN)(2)

12 pages, 16 figures12 pages, 16 figures12 pages, 16 figures12 pages, 16 figure

Open Letter(s) on Open Access

It is well known that one major obstacle to achieving open access (OA) is misunderstanding among stakeholders; some say it is the biggest problem of all. Throughout the supply-chain of producing and consuming scholarly literature, many participants—especially authors—understand the broader objectives of OA but not the practical steps they can take to help increase the accessibility of research. The purpose of “Open Letter(s) on Open Access” (OLOA) is to provide initial examples of communications that illustrate such steps. We do so by examining sets of well-regarded academic sources and evaluating the various paths that authors choose as a means of sharing their works with others, including Gold OA, Green OA, hybrid options, uploading to academic social media sites, deposits to institutional repositories, and so on. The letter(s) then offer commentary on the sharing practices and possibilities we discover. As the plural in the title suggests, OLOA is explicitly unexhaustive and reiterative, an example that others can copy and improve upon; thus, a key part of the project is to produce a set of processes that can be used by anyone interested in educating researchers about ways to advance sustainable accessibility. These proceedings of our presentation at the Charleston Conference 2018 articulate our central goals, summarize the work we have done so far, and suggest future directions for the project. Just as the digital information and scholarly landscape is constantly changing, our work is always in progress

Failure mechanisms of graphene under tension

Recent experiments established pure graphene as the strongest material known to mankind, further invigorating the question of how graphene fails. Using density functional theory, we reveal the mechanisms of mechanical failure of pure graphene under a generic state of tension. One failure mechanism is a novel soft-mode phonon instability of the $K_1$-mode, whereby the graphene sheet undergoes a phase transition and is driven towards isolated benzene rings resulting in a reduction of strength. The other is the usual elastic instability corresponding to a maximum in the stress-strain curve. Our results indicate that finite wave vector soft modes can be the key factor in limiting the strength of monolayer materials