20,219 research outputs found
Stretching single polysaccharide molecules using AFM: A potential method for the investigation of the intermolecular uronate distribution of alginate?
Illustrative examples of the way in which the molecular force-extension behaviour of polysaccharides is governed by the nature of the linkage between their constituent pyranose rings are presented for a series of standard homopolymers. These results agree with previously proposed general hypotheses regarding the possibility of generating force-induced conformational transitions, and with the predictions of a model in which the inter-conversion of pyranose conformers is assumed to be an equilibrium process on the timescale of the molecular stretching. Subsequently, we investigate the potential of the technique in the characterisation of co-polymeric polysaccharides in which the nature of the glycan linkages is different between the two distinct residue types. Specifically, we explore the possibility that the ratio of mannuronic acid (M) to guluronic acid (G) in alginate chains will be reflected in their single molecule stretching behaviour, owing to their contrasting equatorial and axial linkages. Furthermore, as the technique described interrogates the sample one polymer at a time we outline the promise of, and the obstacles to, obtaining a new level of characterisation using this methodology where differences observed in the single molecule stretching curves obtained from single alginate samples reflectsomething of the real intermolecular distribution of the M / G ratio
Prehistoric Giant Swamp Taro (Cyrtosperma chamissonis) from Henderson Island, Southeast Polynesia
Subfossilleaf fragments of giant swamp taro (Cyrtosperma chamissonis)
were recovered from archaeological contexts dating as early as A.D.
1451 (mean date) on Henderson Island (24 0 22' S, 1280 19' W), Pitcairn
group-a raised limestone (makatea) island isolated at the extreme margin of
southeastern Polynesia and the Indo-West Pacific biotic province. Comparison
of subfossil specimens and modern reference material from a range of known
cultigens under scanning electron microscopy confirms the identification. A
period of active interarchipelago voyaging between A.D. 1000 and A.D. 1500 is
known from recent summaries of the geochemical analysis of exotic finegrained
basalt artifacts from archaeological sites throughout Polynesia. If not
an initial colonization, it is during this time that Cyrtosperma should have
been introduced prehistorically to most, if not all, of the inhabitable islands of
the region, especially those island groups lying to the west of Henderson. Investigation
of subfossil plant remains adds another dimension to understanding
plant distributions, prehistoric crop use, and subsistence practices in the Indo-Pacific
region
Deployable antenna phase A study
Applications for large deployable antennas were re-examined, flight demonstration objectives were defined, the flight article (antenna) was preliminarily designed, and the flight program and ground development program, including the support equipment, were defined for a proposed space transportation system flight experiment to demonstrate a large (50 to 200 meter) deployable antenna system. Tasks described include: (1) performance requirements analysis; (2) system design and definition; (3) orbital operations analysis; and (4) programmatic analysis
Radiative Properties of the Stueckelberg Mechanism
We examine the mechanism for generating a mass for a U(1) vector field
introduced by Stueckelberg. First, it is shown that renormalization of the
vector mass is identical to the renormalization of the vector field on account
of gauge invariance. We then consider how the vector mass affects the effective
potential in scalar quantum electrodynamics at one-loop order. The possibility
of extending this mechanism to couple, in a gauge invariant way, a charged
vector field to the photon is discussed.Comment: 8 pages, new Introduction, added Reference
Investigation of ultrafast laser photonic material interactions: challenges for directly written glass photonics
Currently, direct-write waveguide fabrication is probably the most widely
studied application of femtosecond laser micromachining in transparent
dielectrics. Devices such as buried waveguides, power splitters, couplers,
gratings and optical amplifiers have all been demonstrated. Waveguide
properties depend critically on the sample material properties and writing
laser characteristics. In this paper we discuss the challenges facing
researchers using the femtosecond laser direct-write technique with specific
emphasis being placed on the suitability of fused silica and phosphate glass as
device hosts for different applications.Comment: 11 pages, 87 references, 11 figures. Article in revie
Migration of income-support recipients from non-metropolitan NSW and SA into Sydney and Adelaide
Nancy Marshall, Ian Burnley, Peter Murphy, Graeme Hug
An exploration of ebook selection behavior in academic library collections
Academic libraries have offered ebooks for some time, however little is known about how readers interact with them while making relevance decisions. In this paper we seek to address that gap by analyzing ebook transaction logs for books in a university library
Bending-wave Instability of a Vortex Ring in a Trapped Bose-Einstein Condensate
Based on a velocity formula derived by matched asymptotic expansion, we
investigate the dynamics of a circular vortex ring in an axisymmetric
Bose-Einstein condensate in the Thomas-Fermi limit. The trajectory for an
axisymmetrically placed and oriented vortex ring is entirely determined,
revealing that the vortex ring generally precesses in condensate. The linear
instability due to bending waves is investigated both numerically and
analytically. General stability boundaries for various perturbed wavenumbers
are computed. In particular, the excitation spectrum and the absolutely stable
region for the static ring are analytically determined.Comment: 4 pages, 4 figure
Structure and superconductivity of two different phases of Re3W
Two superconducting phases of Re(3)W have been found with different physical properties. One phase crystallizes in a noncentrosymmetric cubic (alpha-Mn) structure and has a superconducting transition temperature T(c) of 7.8 K. The other phase has a hexagonal centrosymmetric structure and is superconducting with a T(c) of 9.4 K. Switching between the two phases is possible by annealing the sample or remelting it. The properties of both phases of Re(3)W have been characterized by powder neutron diffraction, magnetization, and resistivity measurements. The temperature dependences of the lower and upper critical fields have been measured for both phases. These are used to determine the penetration depths and the coherence lengths for these systems
- …