Periodic Planar Disk Packings

Several conditions are given when a packing of equal disks in a torus is locally maximally dense, where the torus is defined as the quotient of the plane by a two-dimensional lattice. Conjectures are presented that claim that the density of any strictly jammed packings, whose graph does not consist of all triangles and the torus lattice is the standard triangular lattice, is at most $\frac{n}{n+1}\frac{\pi}{\sqrt{12}}$, where $n$ is the number of packing disks. Several classes of collectively jammed packings are presented where the conjecture holds.Comment: 26 pages, 13 figure

The effect of advance ratio on the aerodynamics of revolving wings

Recent studies have demonstrated that a quasi-steady model closely matches the instantaneous force produced by an insect wing during hovering flight. It is not clear, however, if such methods extend to forward flight. In this study we use a dynamically scaled robotic model of the fruit fly Drosophila melanogaster to investigate the forces produced by a wing revolving at constant angular velocity while simultaneously translating at velocities appropriate for forward flight. Because the forward and angular velocities were constant wing inertia was negligible, and the measured forces can be attributed to fluid dynamic phenomena. The combined forward and revolving motions of the wing produce a time-dependent free-stream velocity profile, which suggests that added mass forces make a contribution to the measured forces. We find that the forces due added mass make a small, but measurable, component of the total force and are in excellent agreement with theoretical values. Lift and drag coefficients are calculated from the force traces after subtracting the contributions due to added mass. The lift and drag coefficients, for fixed angle of attack, are not constant for non-zero advance ratios, but rather vary in magnitude throughout the stroke. This observation implies that modifications of the quasi-steady model are required in order to predict accurately the instantaneous forces produced during forward flight. We show that the dependence of the lift and drag coefficients upon advance ratio and stroke position can be characterized effectively in terms of the tip velocity ratio – the ratio of the chordwise components of flow velocity at the wing tip due to translation and revolution. On this basis we develop a modified quasi-steady model that can account for the varying magnitudes of the lift and drag coefficients. Our model may also resolve discrepancies in past measurements of wing performance based on translational and revolving motion

Operational cost drivers

To be economically viable, the operations cost of launch vehicles must be reduced by an order of magnitude as compared to the Space Transportation System (STS). A summary of propulsion-related operations cost drivers derived from a two-year study of Shuttle ground operations is presented. Examples are given of the inordinate time and cost of launch operations caused by propulsion systems designs that did not adequately consider impacts on prelaunching processing. Typical of these cost drivers are those caused by central hydraulic systems, storable propellants, gimballed engines, multiple propellants, He and N2 systems and purges, hard starts, high maintenance turbopumps, accessibility problems, and most significantly, the use of multiple, nonintegrated RCS, OMS, and main propulsion systems. Recovery and refurbishment of SRBs have resulted in expensive crash and salvage operations. Vehicle system designers are encouraged to be acutely aware of these cost drivers and to incorporate solutions (beginning with the design concepts) to avoid business as usual and costs as usual

CIRCA 2000 operations criteria

The current Shuttle Program was used as a working model and certified data source in the identification of Space Transportation System (STS) operational cost drivers. Changes to flight hardware, processing methodologies, and identification of automation applications that would reduce costs were derived by reference to that data. The CIRCA 2000 Criteria were developed using these critical analyses of the on-going Shuttle Program. Several innovative suggestions are reviewed

Identification and Analysis of Ichthyofaunal Remains from Late Pleistocene-Holocene Deposits of Cheek Bend Cave (40MU261), Maury County, Tennessee

Knowledge of the character of the late Pleistocene-Holocene ichthyofauna of the middle Duck River was acquired as a result of identification and biostratigraphic analysis of numerous fish bone fragments from the well-stratified deposits of Cheek Bend Cave, a small rockshelter situated in the limestone bluffs along the Duck River in Maury County, Tennessee. Forty-five unequivocal fish taxa (representing 12 families) were identified, of which 25 taxa occurred in the Late Wisconsin strata, 33 in Holocene strata, and 13 in both depositional sequences. Fifteen of the Late Wisconsin taxa and 18 Holocene taxa appear to represent initial records for these periods, while 17 taxa are recorded for the first time from fossil deposits. Composing this latter group are small fish taxa from the following families: Cyprinidae, Ictaluridae, Cyprinodontidae, Percidae, and Cottidae. Of particular interest are an apparently undescribed, extinct cyprinid taxon (mid-Holocene) that presumably has close affinities with species of the modern genera Dionda and Hybognathus and an unusual form of Noturus flavus (Late Wisconsin and Holocene) which appears to be somewhat distinct from modern counterparts. Although not identified from the cave deposits, Lagochila lacera, the harelip sucker, practically unknown from prehistoric deposits, was identified from the Middle to Late Archaic Hayes Site located on the Duck River in the cave vicinity. From a distributional standpoint, one species identified from the mid-Holocene deposits, Noturus flavater, is noteworthy. Its modern range is restricted to the southern Ozark region in Missouri and Arkansas. Indirect evidence of a changing fish fauna is inferred from the concentration of certain groups of fishes in the Holocene strata, namely he Lepisosteidae, Ictaluridae, Cyprinodontidae, and the genus Lepomis. These groups may have been only marginally represented (at least locally) in the presumed middle Tennessee boreal forest region during the last glacial maximum, a distributional situation perhaps analogous to their modern distributions that appear to complement the boreal region of North America. More direct evidence was obtained as a result of the identification, from Pleistocene strata, of three species whose modern ranges are outside the Tennessee region completely (Perca flavescens, Nocomis bigutattus) or to a large extent (Esox masquinongy)

Interfacial Forces of 2D Materials at the Oil–Water Interface

Two-dimensional (2D) materials, including graphene and graphene oxide (GO), are a subject of interest for many researchers due to their exceptional properties (strength, conductivity, etc.). These materials, comprised of atomically-thin sheets, may naturally occur stacked together like sheets of paper, but their most interesting properties emerge when separated into individual layers. However, scaling up the processes used to isolate single sheets of some of these materials, particularly graphene, has proven problematic. They can be fiercely resistant to exfoliation, difficult to disperse, and have a worrying propensity to restack. All these problems contribute to the great difficulty these fascinating materials have encountered leaving the lab and entering commercial use. Existing production methods either produce minute quantities, require huge amounts of energy, or involve chemical treatments that transform their properties, typically for the worse. Here, we investigate a method that instead harnesses these difficulties. We force the material to exfoliate itself at the interface between two immiscible solvents, stabilizing the interface and acting as a surfactant with a two-dimensional morphology. In this work we investigate this method and its results in two ways. First, we describe a method we developed using optical microscopy and free software (ImageJ and Gwyddion) that rapidly and inexpensively provides full, simultaneous characterization of thousands of sheets of these materials, yielding both flake area and thickness. We then use this technique to examine the changes induced in 2D material that was exfoliated at the oil–water interface, improving our understanding of the process at the population/production level. Second, we characterize this interaction using force spectroscopy with graphene-functionalized colloidal probes at the surface of pinned droplets of heptane in water. This provides valuable insight into the not-well-understood mechanisms underlying the exfoliation process at the interfacial level. By combining the results seen across these two length scales, our results significantly enhance the understanding of this novel exfoliation process. Additionally, we examine the interactions between another 2D material, mica, and an oil-coated probe in a salt brine using force spectroscopy at high temperature (100 °C) and high pressure (100 atm). These tests are the first demonstration of force spectroscopy in this parameter space and reveal the significant impact of both temperature and pressure on interfacial forces between oil and mineral in this regime. Taken together, our results impact a wide variety of systems including the large-scale production of nanomaterials, nanocomposites, solar cells, sensors, flexible electronics, oil recovery, and catalysis

Studies in tuberculosis

The matter selected for this thesis is arranged under three headings :-(1). A Survey of Anti- Tuberculosis work in Newcastle-upon-Tyne.(2). Observations on the Deaths from Tuberculosis.(3). The Inter -Relations of Influenza and Pulmonary Tuberculosis.The first two sections deal, more or less, with the organisation and routine work of the Dispensary; special attention was paid to the subject of the third section expressly for the purpose of this Essay

The fishes of the Obion River system

A survey was conducted to determine the species composition of fishes in the Obion River system in northwest Tennessee. This system, draining most of northwest Tennessee, has largely been subjected to channelization practices within the past 50 or 60 years. Within the drainage is Reelfoot Lake, a large, shallow lake offering a unique habitat to the system. This survey was conducted at various times during 1971 and 1973, while a large number of collections were reported from the records of other investigators. Collections were reported from a large number of streams within the system, with most records coming from the Reelfoot Lake area and the principle forks of the system. Survey methods employed by the collectors included seining, chemical application, and to a small extent, hoop netting and gill netting. A total of 183 collections are reported, and the results are presented in the annotated listing of species followed by a discussion of taxonomic, zoogeographic, and ecological considerations. Of the 110 species presumed to exist in the system, 100 were verified by records. The study revealed a somewhat more diverse fauna in the • upper portion of the system than in the central and lower regions of the system. Reelfoot Lake and its tributaries and outlet (Running Reelfoot Bayou) had the richest fauna of any part of the system