20,768 research outputs found
Leishmania manipulation of sand fly feeding behavior results in enhanced transmission.
In nature the prevalence of Leishmania infection in whole sand fly populations can be very low (<0.1%), even in areas of endemicity and high transmission. It has long since been assumed that the protozoan parasite Leishmania can manipulate the feeding behavior of its sand fly vector, thus enhancing transmission efficiency, but neither the way in which it does so nor the mechanisms behind such manipulation have been described. A key feature of parasite development in the sand fly gut is the secretion of a gel-like plug composed of filamentous proteophosphoglycan. Using both experimental and natural parasite-sand fly combinations we show that secretion of this gel is accompanied by differentiation of mammal-infective transmission stages. Further, Leishmania infection specifically causes an increase in vector biting persistence on mice (re-feeding after interruption) and also promotes feeding on multiple hosts. Both of these aspects of vector behavior were found to be finely tuned to the differentiation of parasite transmission stages in the sand fly gut. By experimentally accelerating the development rate of the parasites, we showed that Leishmania can optimize its transmission by inducing increased biting persistence only when infective stages are present. This crucial adaptive manipulation resulted in enhanced infection of experimental hosts. Thus, we demonstrate that behavioral manipulation of the infected vector provides a selective advantage to the parasite by significantly increasing transmission
Thick film silicon growth techniques
Thick film silicon ribbons were produced by means of the edge-defined, film-fed growth (EFG) technique. EFG is a process by which single crystals may be grown having a shape controlled by the outside dimensions of a die, the growth taking place from an extremely thin film of liquid fed by capillary action from a crucible below. The principal problem to be overcome in the application of this process to the growth of thick film silicon ribbon relates to the material, such as the shaping die. For the method to operate, this die material must be wet by the liquid silicon. To preserve semiconductor quality, the liquid silicon must not react significantly with the die material. The most promising die material for this application appears to be SiC and SiC-SiO2 admixture. In this case good wetting occurs between the molten silicon and the SiC. C is a relatively unharmful contaminant of Si and additions of quartz to SiC are found to decrease the extent of reaction
Thick silicon growth techniques
Hall mobility measurements on a number of single crystal silicon ribbons grown from graphite dies have shown some ribbons to have mobilities consistent with their resistivities. The behavior of other ribbons appears to be explained by the introduction of impurities of the opposite sign. Growth of a small single crystal silicon ribbon has been achieved from a beryllia dia. Residual internal stresses of the order of 7 to 18,000 psi have been determined to exist in some silicon ribbon, particularly those grown at rates in excess of 1 in./min. Growth experiments have continued toward definition of a configuration and parameters to provide a reasonable yield of single crystal ribbons. High vacuum outgassing of graphite dies and evacuation and backfilling of growth chambers have provided significant improvements in surface quality of ribbons grown from graphite dies
Enhancing the Performance of Eye and Head Mice: A Validated Assessment Method and an Investigation into the Performance of Eye and Head Based Assistive Technology Pointing Devices
This work poses the question "Could eye and head based assistive technology device
interaction performance approach that of basic hand mouse interaction?" To this aim, the
work constructs, validates, and applies a detailed and comprehensive pointing device
assessment method suitable for assistive technology direct pointing devices, it then uses
this method to add enhancement to these devices, finally it then demonstrates that such
enhanced eye or head based pointing can approach that of basic hand mouse interaction
and be a viable and usable interaction method for people with high-level motor
disabilities.
Eye and head based pointing devices, or eye and head mice, are often used by high-level
motor disabled people to enable computer interaction in the place of a standard desktop
hand mouse. The performance of these eye and head mice pointing devices when used for
direct manipulation on a standard graphical user interface has generally been regarded as
poor in comparison to that of a standard desktop hand mouse, thus putting users of head
and eye mice at a disadvantage when interacting with computers.
The performance of eye and head based pointing devices during direct manipulation on a
standard graphical user interface has not previously been investigated in depth, and the
reasons why these devices seem to demonstrate poor performance have not been
determined in detail. Few proven methods have been demonstrated and investigated that
enhance the performance of these devices based on their performance during direct
manipulation. Importantly, and key to this work is that, no validated assessment method
has been constructed to allow such an investigation.
This work seeks to investigate the performance of eye and head based pointing devices
during direct manipulation by constructing and verifying a test method suitable for the
detailed performance assessment of eye and head based assistive technology pointing
devices. It then uses this method to determine the factors influencing the performance of eye and head mice during direct manipulation. Finally, after identifying these factors, this
work hypothesises, and then demonstrates that applying suitable methods for addressing
these factors can result in enhanced performance for eye and head mice. It shows that the
performance of these enhanced devices can approach the performance of standard desktop
hand mice with the use of highly experienced users, together with the enhancement of a
supporting modality for object manipulation, and a supporting interface enhancement for
object size magnification; thus demonstrating that these devices can approach and equal
the performance of basic hand mouse interaction
Thick film silicon growth techniques
One inch wide silicon ribbons up to 14 inches long have been produced from graphite dies. Several different techniques have been employed to improve the semiconductor purity of silicon. This has resulted in a general increase in quality although the techniques involved have not been optimized. The power factor of uncoated ribbon solar cells produced for material evaluation has increased to approximately 75% of those evaluation cells made from commercial silicon. The present limitation is believed due to low lifetime. Additional work has continued with new die materials; however, only composite dies of SiO2 and C show significant potential at this time
Thick film silicon growth techniques
Silicon ribbon growth experiments were conducted using orifices (dies) fabricated from SiC-SiO2 mixtures, fused quartz, SiC, and fine-grained, high density graphite. The best results were obtained from graphite dies. A number of different approaches was tried in modifying the thermal gradient in the dies and in holding the dies. The best results here were obtained from a 0.25-in. thick Mo disc holding a graphite die directly and fitting the die quite closely. Ribbon growths as wide as 9 mm were obtained, while the longest ribbon was 450 x 3.5 x 0.5 mm. Resistivities of ribbons grown from graphite dies have been measured over the range of 0.03 to 1.6 ohm-cm. Some thoughts and literature findings are presented regarding refractory oxide materials as potential orifices
Molecular Weight Dependence of Polymersome Membrane Elasticity and Stability
Vesicles prepared in water from a series of diblock copolymers and termed
"polymersomes" are physically characterized. With increasing molecular weight
, the hydrophobic core thickness for the self-assembled bilayers
of polyethyleneoxide - polybutadiene (PEO-PBD) increases up to 20 -
considerably greater than any previously studied lipid system. The mechanical
responses of these membranes, specifically, the area elastic modulus and
maximal areal strain are measured by micromanipulation. As expected
for interface-dominated elasticity, ( 100 ) is found to be
independent of . Related mean-field ideas also predict a limiting
value for which is universal and about 10-fold above that typical of
lipids. Experiments indeed show generally increases with
, coming close to the theoretical limit before stress relaxation is
opposed by what might be chain entanglements at the highest . The
results highlight the interfacial limits of self-assemblies at the nano-scale.Comment: 16 pages, 5 figures, and 1 tabl
The Liouville-type theorem for integrable Hamiltonian systems with incomplete flows
For integrable Hamiltonian systems with two degrees of freedom whose
Hamiltonian vector fields have incomplete flows, an analogue of the Liouville
theorem is established. A canonical Liouville fibration is defined by means of
an "exact" 2-parameter family of flat polygons equipped with certain pairing of
sides. For the integrable Hamiltonian systems given by the vector field
on where
is a complex polynomial in 2 variables, geometric properties of
Liouville fibrations are described.Comment: 6 page
- ā¦