17,992 research outputs found
Growth of Pseudotypes of Vesicular Stomatitis Virus with N-Tropic Murine Leukemia Virus Coats in Cells Resistant to N-Tropic Viruses
Formation of pseudotypes between murine RNA tumor viruses and vesicular stomatitis virus (VSV) has been confirmed. Pseudotypes of VSV genomes coated by the surface envelope from an N-tropic tumor virus grew equally well in cells homozygous for either the Fv-1n or Fv-1b alleles. Therefore, the product of the Fv-1 locus, which restricts growth of murine RNA tumor viruses, must act on an intracellular aspect of tumor virus replication, a step after attachment and penetration
Existence and uniqueness for Mean Field Games with state constraints
In this paper, we study deterministic mean field games for agents who operate
in a bounded domain. In this case, the existence and uniqueness of Nash
equilibria cannot be deduced as for unrestricted state space because, for a
large set of initial conditions, the uniqueness of the solution to the
associated minimization problem is no longer guaranteed. We attack the problem
by interpreting equilibria as measures in a space of arcs. In such a relaxed
environment the existence of solutions follows by set-valued fixed point
arguments. Then, we give a uniqueness result for such equilibria under a
classical monotonicity assumption
Engineering Dynamical Sweet Spots to Protect Qubits from 1/ Noise
Protecting superconducting qubits from low-frequency noise is essential for
advancing superconducting quantum computation. Based on the application of a
periodic drive field, we develop a protocol for engineering dynamical sweet
spots which reduce the susceptibility of a qubit to low-frequency noise. Using
the framework of Floquet theory, we prove rigorously that there are manifolds
of dynamical sweet spots marked by extrema in the quasi-energy differences of
the driven qubit. In particular, for the example of fluxonium biased slightly
away from half a flux quantum, we predict an enhancement of pure-dephasing by
three orders of magnitude. Employing the Floquet eigenstates as the
computational basis, we show that high-fidelity single- and two-qubit gates can
be implemented while maintaining dynamical sweet-spot operation. We further
confirm that qubit readout can be performed by adiabatically mapping the
Floquet states back to the static qubit states, and subsequently applying
standard measurement techniques. Our work provides an intuitive tool to encode
quantum information in robust, time-dependent states, and may be extended to
alternative architectures for quantum information processing
Binding-incompetent adenovirus facilitates molecular conjugate-mediated gene transfer by the receptor-mediated endocytosis pathway
Molecular conjugate vectors may be constructed that accomplish high efficiency gene transfer by the receptor-mediated endocytosis pathway. In order to mediate escape from lysosomal degradation, we have incorporated adenoviruses into the functional design of the conjugate. In doing so, however, we have introduced an additional ligand, which can bind to receptors on the cell surface, undermining the potential for cell specific targeting. To overcome this, we have treated the adenovirus with a monoclonal anti-fiber antibody, which renders the virus incapable of binding to its receptor. The result is a multi-functional molecular conjugate vector, which has preserved its binding specificity while at the same time being capable of preventing lysosomal degradation of endosome-internalized conjugate-DNA complexes. This finding indicates that adenoviral binding is not a prerequisite for adenoviral-mediated endosome disruption
Using state space differential geometry for nonlinear blind source separation
Given a time series of multicomponent measurements of an evolving stimulus,
nonlinear blind source separation (BSS) seeks to find a "source" time series,
comprised of statistically independent combinations of the measured components.
In this paper, we seek a source time series with local velocity cross
correlations that vanish everywhere in stimulus state space. However, in an
earlier paper the local velocity correlation matrix was shown to constitute a
metric on state space. Therefore, nonlinear BSS maps onto a problem of
differential geometry: given the metric observed in the measurement coordinate
system, find another coordinate system in which the metric is diagonal
everywhere. We show how to determine if the observed data are separable in this
way, and, if they are, we show how to construct the required transformation to
the source coordinate system, which is essentially unique except for an unknown
rotation that can be found by applying the methods of linear BSS. Thus, the
proposed technique solves nonlinear BSS in many situations or, at least,
reduces it to linear BSS, without the use of probabilistic, parametric, or
iterative procedures. This paper also describes a generalization of this
methodology that performs nonlinear independent subspace separation. In every
case, the resulting decomposition of the observed data is an intrinsic property
of the stimulus' evolution in the sense that it does not depend on the way the
observer chooses to view it (e.g., the choice of the observing machine's
sensors). In other words, the decomposition is a property of the evolution of
the "real" stimulus that is "out there" broadcasting energy to the observer.
The technique is illustrated with analytic and numerical examples.Comment: Contains 14 pages and 3 figures. For related papers, see
http://www.geocities.com/dlevin2001/ . New version is identical to original
version except for URL in the bylin
A Therapeutic Vaccine Approach to Stimulate Axon Regeneration in the Adult Mammalian Spinal Cord
AbstractAxon growth inhibitors associated with myelin play an important role in the failure of axon regeneration in the adult mammalian central nervous system (CNS). Several inhibitors are present in the mature CNS. We now present a novel therapeutic vaccine approach in which the animals' own immune system is stimulated to produce polyclonal antibodies that block myelin-associated inhibitors without producing any detrimental cellular inflammatory responses. Adult mice immunized in this manner showed extensive regeneration of large numbers of axons of the corticospinal tracts after dorsal hemisection of the spinal cord. The anatomical regeneration led to recovery of certain hind limb motor functions. Furthermore, antisera from immunized mice were able to block myelin-derived inhibitors and promote neurite growth on myelin in vitro
Pseudospectral solution of near-singular problems using numerical coordinate transformations based on adaptivity
This is the published version, also available here: http://dx.doi.org/10.1137/S1064827595291984.The work presented here describes a method of coordinate transformation that enables spectral methods to be applied efficiently to differential problems with steep solutions. The approach makes use of the adaptive finite difference method presented by Huang and Sloan [SIAM J. Sci. Comput., 15 (1994), pp. 776--797]. This method is applied on a coarse grid to obtain a rough approximation of the solution and a suitable adapted mesh. The adaptive finite difference solution permits the construction of a smooth coordinate transformation that relates the computational space to the physical space. The map between the spaces is based on Chebyshev polynomial interpolation. Finally, the standard pseudospectral (PS) method is applied to the transformed differential problem to obtain highly accurate, nonoscillatory numerical solutions. Numerical results are presented for steady problems in one and two space dimensions
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