2,786 research outputs found
The Combined Impact Of IgLON Family Proteins Lsamp And Neurotrimin On Developing Neurons And Behavioral Profiles In Mouse
Cell surface neural adhesion proteins are critical components in the complex orchestration of cell proliferation, apoptosis, and neuritogenesis essential for proper brain construction and behavior. We focused on the impact of two plasticity-associated IgLON family neural adhesion molecules, Neurotrimin (Ntm) and Limbic system associated membrane protein (Lsamp), on mouse behavior and its underlying neural development. Phenotyping neurons derived from the hippocampi of Lsamp−/−, Ntm−/− and Lsamp−/−Ntm−/− mice was performed in parallel with behavioral testing. While the anatomy of mutant brains revealed no gross changes, the Ntm−/− hippocampal neurons exhibited premature sprouting of neurites and manifested accelerated neurite elongation and branching. We propose that Ntm exerts an inhibitory impact on neurite outgrowth, whereas Lsamp appears to be an enhancer of the said process as premature neuritogenesis in Ntm−/− neurons is apparent only in the presence of Lsamp. We also show interplay between Lsamp and Ntm in regulating tissue homeostasis: the impact of Ntm on cellular proliferation was dependent on Lsamp, and Lsamp appeared to be a positive regulator of apoptosis in the presence of Ntm. Behavioral phenotyping indicated test-specific interactions between Lsamp and Ntm. The phenotypes of single mutant lines, such as reduced swimming speed in Morris water maze and increased activity in the elevated plus maze, were magnified in Lsamp−/−Ntm−/− mice. Altogether, evidence both from behavioral experiments and cultured hippocampal cells show combined and differential interactions between Ntm and Lsamp in the formation of hippocampal circuits and behavioral profiles. We demonstrate that mutual interactions between IgLON molecules regulate the initiation of neurite sprouting at very early ages, and even cell-autonomously, independent of their regulation of cell-cell adhesion
Integer programming methods for large-scale practical classroom assignment problems
In this paper we present an integer programming method for solving the Classroom Assignment Problem in University Course Timetabling. We introduce a novel formulation of the problem which generalises existing models and maintains tractability even for large instances. The model is validated through computational results based on our experiences at the University of Auckland, and on instances from the 2007 International Timetabling Competition. We also expand upon existing results into the computational difficulty of room assignment problems
A programmable two-qubit quantum processor in silicon
With qubit measurement and control fidelities above the threshold of
fault-tolerance, much attention is moving towards the daunting task of scaling
up the number of physical qubits to the large numbers needed for fault tolerant
quantum computing. Here, quantum dot based spin qubits may offer significant
advantages due to their potential for high densities, all-electrical operation,
and integration onto an industrial platform. In this system, the
initialisation, readout, single- and two-qubit gates have been demonstrated in
various qubit representations. However, as seen with other small scale quantum
computer demonstrations, combining these elements leads to new challenges
involving qubit crosstalk, state leakage, calibration, and control hardware
which provide invaluable insight towards scaling up. Here we address these
challenges and demonstrate a programmable two-qubit quantum processor in
silicon by performing both the Deutsch-Josza and the Grover search algorithms.
In addition, we characterise the entanglement in our processor through quantum
state tomography of Bell states measuring state fidelities between 85-89% and
concurrences between 73-80%. These results pave the way for larger scale
quantum computers using spins confined to quantum dots
Vectorial Loading of Processive Motor Proteins: Implementing a Landscape Picture
Individual processive molecular motors, of which conventional kinesin is the
most studied quantitatively, move along polar molecular tracks and, by exerting
a force on a tether, drag cellular cargoes, {\em in
vivo}, or spherical beads, {\em in vitro}, taking up to hundreds of
nanometer-scale steps. From observations of velocities and the dispersion of
displacements with time, under measured forces and controlled fuel supply
(typically ATP), one may hope to obtain insight into the molecular motions
undergone in the individual steps. In the simplest situation, the load force
may be regarded as a scalar resisting force, , acting
parallel to the track: however, experiments, originally by Gittes {\em et al.}
(1996), have imposed perpendicular (or vertical) loads, , while more
recently Block and coworkers (2002, 2003) and Carter and Cross (2005) have
studied {\em assisting} (or reverse) loads, , and also sideways (or
transverse) loads
Anderson Transition in Disordered Graphene
We use the regularized kernel polynomial method (RKPM) to numerically study
the effect disorder on a single layer of graphene. This accurate numerical
method enables us to study very large lattices with millions of sites, and
hence is almost free of finite size errors. Within this approach, both weak and
strong disorder regimes are handled on the same footing. We study the
tight-binding model with on-site disorder, on the honeycomb lattice. We find
that in the weak disorder regime, the Dirac fermions remain extended and their
velocities decrease as the disorder strength is increased. However, if the
disorder is strong enough, there will be a {\em mobility edge} separating {\em
localized states around the Fermi point}, from the remaining extended states.
This is in contrast to the scaling theory of localization which predicts that
all states are localized in two-dimensions (2D).Comment: 4 page
Flexible Lipid Bilayers in Implicit Solvent
A minimalist simulation model for lipid bilayers is presented. Each lipid is
represented by a flexible chain of beads in implicit solvent. The hydrophobic
effect is mimicked through an intermolecular pair potential localized at the
``water''/hydrocarbon tail interface. This potential guarantees realistic
interfacial tensions for lipids in a bilayer geometry. Lipids self assemble
into bilayer structures that display fluidity and elastic properties consistent
with experimental model membrane systems. Varying molecular flexibility allows
for tuning of elastic moduli and area/molecule over a range of values seen in
experimental systems.Comment: 5 pages, 5 figure
Launch Vehicle Demonstrator Using Shuttle Assets
The Marshall Space Flight Center Advanced Concepts Office (ACO) has the leading role for NASA s preliminary conceptual launch vehicle design and performance analysis. Over the past several years the ACO Earth-to-Orbit Team has evaluated thousands of launch vehicle concept variations for a multitude of studies including agency-wide efforts such as the Exploration Systems Architecture Study (ESAS), Constellation, Heavy Lift Launch Vehicle (HLLV), Heavy Lift Propulsion Technology (HLPT), Human Exploration Framework Team (HEFT), and Space Launch System (SLS). NASA plans to continue human space exploration and space station utilization. Launch vehicles used for heavy lift cargo and crew will be needed. One of the current leading concepts for future heavy lift capability is an inline one and a half stage concept using solid rocket boosters (SRB) and based on current Shuttle technology and elements. Potentially, the quickest and most cost-effective path towards an operational vehicle of this configuration is to make use of a demonstrator vehicle fabricated from existing shuttle assets and relying upon the existing STS launch infrastructure. Such a demonstrator would yield valuable proof-of-concept data and would provide a working test platform allowing for validated systems integration. Using shuttle hardware such as existing RS-25D engines and partial MPS, propellant tanks derived from the External Tank (ET) design and tooling, and four-segment SRB s could reduce the associated upfront development costs and schedule when compared to a concept that would rely on new propulsion technology and engine designs. There are potentially several other additional benefits to this demonstrator concept. Since a concept of this type would be based on man-rated flight proven hardware components, this demonstrator has the potential to evolve into the first iteration of heavy lift crew or cargo and serve as a baseline for block upgrades. This vehicle could also serve as a demonstration and test platform for the Orion Program. Critical spacecraft systems, re-entry and recovery systems, and launch abort systems of Orion could also be demonstrated in early test flights of the launch vehicle demo. Furthermore, an early demonstrator of this type would provide a stop-gap for retaining critical human capital and infrastructure while affording the current emerging generation of young engineers opportunity to work with and capture lessons learned from existing STS program offices and personnel, who were integral in the design and development of the Space Shuttle before these resources are no longer available. The objective of this study is to define candidate launch vehicle demonstration concepts that are based on Space Shuttle assets and determine their performance capabilities and how these demonstration vehicles could evolve to a heavy lift capability to low earth orbit
Avian oncogenesis induced by lymphoproliferative disease virus: a neglected or emerging retroviral pathogen?
Lymphoproliferative disease virus (LPDV) is an exogenous oncogenic retrovirus that induces lymphoid tumors in some galliform species of birds. Historically, outbreaks of LPDV have been reported from Europe and Israel. Although the virus has previously never been detected in North America, herein we describe the widespread distribution, genetic diversity, pathogenesis, and evolution of LPDV in the United States. Characterization of the provirus genome of the index LPDV case from North America demonstrated an 88% nucleotide identity to the Israeli prototype strain. Although phylogenetic analysis indicated that the majority of viruses fell into a single North American lineage, a small subset of viruses from South Carolina were most closely related to the Israeli prototype. These results suggest that LPDV was transferred between continents to initiate outbreaks of disease. However, the direction (New World to Old World or vice versa), mechanism, and time frame of the transcontinental spread currently remain unknown
Segregation by thermal diffusion in granular shear flows
Segregation by thermal diffusion of an intruder immersed in a sheared
granular gas is analyzed from the (inelastic) Boltzmann equation. Segregation
is induced by the presence of a temperature gradient orthogonal to the shear
flow plane and parallel to gravity. We show that, like in analogous systems
without shear, the segregation criterion yields a transition between upwards
segregation and downwards segregation. The form of the phase diagrams is
illustrated in detail showing that they depend sensitively on the value of
gravity relative to the thermal gradient. Two specific situations are
considered: i) absence of gravity, and ii) homogeneous temperature. We find
that both mechanisms (upwards and downwards segregation) are stronger and more
clearly separated when compared with segregation criteria in systems without
shear.Comment: 8 figures. To appear in J. Stat. Mec
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