9,634 research outputs found
The role of long-range forces in the phase behavior of colloids and proteins
The phase behavior of colloid-polymer mixtures, and of solutions of globular
proteins, is often interpreted in terms of a simple model of hard spheres with
short-ranged attraction. While such a model yields a qualitative understanding
of the generic phase diagrams of both colloids and proteins, it fails to
capture one important difference: the model predicts fluid-fluid phase
separation in the metastable regime below the freezing curve. Such demixing has
been observed for globular proteins, but for colloids it appears to be
pre-empted by the appearance of a gel. In this paper, we study the effect of
additional long-range attractions on the phase behavior of spheres with
short-ranged attraction. We find that such attractions can shift the
(metastable) fluid-fluid critical point out of the gel region. As this
metastable critical point may be important for crystal nucleation, our results
suggest that long-ranged attractive forces may play an important role in the
crystallization of globular proteins. However, in colloids, where refractive
index matching is often used to switch off long-ranged dispersion forces,
gelation is likely to inhibit phase separation.Comment: EURO-LATEX, 6 pages, 2 figure
Structural modification of polysaccharides: A biochemical-genetic approach
Polysaccharides have a wide range of industrial and biomedical applications. An industry trend is underway towards the increased use of bacteria to produce polysaccharides. Long term goals of this work are the adaptation and enhancement of saccharide properties for electronic and optic applications. In this report we illustrate the application of enzyme-bearing bacteriophage on strains of the enteric bacterium Klebsiella pneumoniae, which produces a polysaccharide with the relatively rare rheological property of drag-reduction. This has resulted in the production of new polysaccharides with enhanced rheological properties. Our laboratory is developing techniques for processing and structurally modifying bacterial polysaccharides and oligosaccharides which comprise their basic polymeric repeat units. Our research has focused on bacteriophage which produce specific polysaccharide degrading enzymes. This has lead to the development of enzymes generated by bacteriophage as tools for polysaccharide modification and purification. These enzymes were used to efficiently convert the native material to uniform-sized high molecular weight polymers, or alternatively into high-purity oligosaccharides. Enzyme-bearing bacteriophage also serve as genetic selection tools for bacteria that produce new families of polysaccharides with modified structures
Phase closure nulling of HD 59717 with AMBER/VLTI . Detection of the close faint companion
Aims: The detection of close and faint companions is an essential step in
many astrophysical fields, including the search for planetary companions. A new
method called "phase closure nulling" has been proposed for the detection of
such faint and close companions based on interferometric observations when the
system visibility amplitude is close to zero due to the large diameter of the
primary star. We aim at demonstrating this method by analyzing observations
obtained on the spectroscopic binary HD 59717. Methods: Using the AMBER/VLTI
instrument in the K-band with ~1500 spectral resolution, we record the
spectrally dispersed closures phases of the SB1 binary HD 59717 with a
three-baseline combination adequate for applying phase closure methods. After a
careful data reduction, we fit the primary diameter, the binary flux ratio, and
the separation using the phase closure data. Results: We detect the 5-mag
fainter companion of HD 59717 at a distance of 4 stellar radii from the
primary. We determine the diameter of the primary, infer the secondary's
spectral type and determine the masses and sizes of the stars in the binary
system. This is one of the highest contrasts detected by interferometry between
a companion and its parent star. Based on observations collected at the
European Southern Observatory, Paranal, Chile, within the commissioning
programme 60.A-9054(A)
Bread board float zone experiment system for high purity silicon
A breadboard float zone experimental system has been established at Westech Systems for use by NASA in the float zone experimental area. A used zoner of suitable size and flexibility was acquired and installed with the necessary utilities. Repairs, alignments and modifications were made to provide for dislocation free zoning of silicon. The zoner is capable of studying process parameters used in growing silicon in gravity and is flexible to allow trying of new features that will test concepts of zoning in microgravity. Characterizing the state of the art molten zones of a growing silicon crystal will establish the data base against which improvements of zoning in gravity or growing in microgravity can be compared. 25 mm diameter was chosen as the reference size, since growth in microgravity will be at that diameter or smaller for about the next 6 years. Dislocation free crystals were growtn in the 100 and 111 orientations, using a wide set of growth conditions. The zone shape at one set of conditions was measured, by simultaneously aluminum doping and freezing the zone, lengthwise slabbing and delineating by etching. The whole set of crystals, grown under various conditions, were slabbed, polished and striation etched, revealing the growth interface shape and the periodic and aperiodic natures of the striations
A Human-Centered Approach for Designing Decision Support Systems
The choice to include the human in the decision process affects four key areas of system design: problem representation, system analysis and design, solution technique selection, and interface requirements specification. I introduce a design methodology that captures the necessary choices associated with each of these areas. In particular I show how this methodology is applied to the design of an actual decision Support system for satellite operations scheduling. Supporting the user\u27s ability to monitor the actions of the system and to guide the decision process of the system are two key considerations in the successful design of a decision support system. Both of these points rely on the correct specification of human-computer interaction points. Traditional, computer-centered system design approaches do not do this well, if at all, and are insufficient for the design of decision support systems. These approaches typically leave the definition of human-computer interaction points till after the component and system level designs are complete. This is too late however since the component and system level design decisions can impose inflexible constraints on the choice of the human-computer interaction points. This often leads to the design of human-computer interaction points that are only good enough. These approaches result in ill-conceived problem representations and poor user-system interaction points because the system lacks the underlying architecture to support these constructs efficiently. Decision support systems require a new, human-centered design approach rather than the traditional computer-centered approaches
Kondo effect of Co adatoms on Ag monolayers on noble metal surfaces
The Kondo temperature of single Co adatoms on monolayers of Ag on Cu
and Au(111) is determined using Scanning Tunneling Spectroscopy. of Co on
a single monolayer of Ag on either substrate is essentially the same as that of
Co on a homogenous Ag(111) crystal. This gives strong evidence that the
interaction of surface Kondo impurities with the substrate is very local in
nature. By comparing found for Co on Cu, Ag, and Au (111)-surfaces we
show that the energy scale of the many-electron Kondo state is insensitive to
the properties of surface states and to the energetic position of the projected
bulk band edges.Comment: 4 pages, 3 figure
Till The Clouds Roll By
https://digitalcommons.library.umaine.edu/mmb-vp/6282/thumbnail.jp
- …