2,764 research outputs found
Increased tolerance of Litopenaeus vannamei to white spot syndrome virus (WSSV) infection after oral application of the viral envelope protein VP28
It has been generally accepted that invertebrates such as shrimp do not have an adaptive immune response system comparable to that of vertebrates. However, in the last few years, several studies have suggested the existence of such a response in invertebrates. In one of these studies, the shrimp Penaeus monodon showed increased protection against white spot syndrome virus (WSSV) using a recombinant VP28 envelope protein of WSSV. In an effort to further investigate whether this increased protection is limited to P. monodon or can be extended to other penaeid shrimp, experiments were performed using the Pacific white shrimp Litopenaeus vannamei. As found with P. monodon, a significantly lower cumulative mortality for VP28-fed shrimp was found compared to the controls. These experiments demonstrate that there is potential to use oral application of specific proteins to protect the 2 most important cultured shrimp species, P. monodon and L. vannamei, against WSSV. Most likely, this increased protection is based on a shared and, therefore, general defence mechanism present in all shrimp species. This makes the design of intervention strategies against pathogens based on defined proteins a viable option for shrimp cultur
The combinatorics of open covers (II)
We continue to investigate various diagonalization properties for sequences
of open covers of separable metrizable spaces introduced in Part I. These
properties generalize classical ones of Rothberger, Menger, Hurewicz, and
Gerlits-Nagy. In particular, we show that most of the properties introduced in
Part I are indeed distinct. We characterize two of the new properties by
showing that they are equivalent to saying all finite powers have one of the
classical properties above (Hurewicz property in one case and in the Menger
property in other). We consider for each property the smallest cardinality of
metric space which fails to have that property. In each case this cardinal
turns out to equal another well-known cardinal less than the continuum. We also
disprove (in ZFC) a conjecture of Hurewicz which is analogous to the Borel
conjecture. Finally, we answer several questions from Part I concerning
partition properties of covers
Stability domains for time-delay feedback control with latency
We generalize a known analytical method for determining the stability of
periodic orbits controlled by time-delay feedback methods when latencies
associated with the generation and injection of the feedback signal cannot be
ignored. We discuss the case of extended time-delay autosynchronization (ETDAS)
and show that nontrivial qualitative features of the domain of control observed
in experiments can be explained by taking into account the effects of both the
unstable eigenmode and a single stable eigenmode in the Floquet theory.Comment: 9 pages, 6 figures; Submitted to Physical Review
Synthesis of 2(3H)-furanones via electrophilic cyclization
The electrophilic cyclization of functionally-substituted alkynes is a very promising route to an extraordinary range of medicinally-interesting, functionally-substituted heterocycles and carbocycles. A variety of highly substituted 2(3H)-furanones are readily prepared from 3-alkynoate esters and the corresponding acids via electrophilic cyclization. This highly efficient approach proceeds under mild conditions, tolerates various functional groups, and generally provides 2(3H)-furanones in good to excellent yields. The cyclizations of 3-alkynoate esters and the corresponding acids have been performed using an excess of the electrophile at room temperature using either methylene chloride or acetonitrile as the solvent. Successful electrophiles in this process include I2, ICl, and PhSeCl. The iodine functionality introduced into the heterocycle facilitates further elaboration by Pd-catalyzed chemistry
Dynamic Response Analysis of an Icosahedron Shaped Lighter Than Air Vehicle
The creation of a lighter than air vehicle using an inner vacuum instead of a lifting gas is considered. Specifically, the icosahedron shape is investigated as a design that will enable the structure to achieve positive buoyancy while resisting collapse from the atmospheric pressure applied. This research analyzes the dynamic response characteristics of the design, and examines the accuracy of the finite element model used in previous research by conducting experimental testing. The techniques incorporated in the finite element model are confirmed based on the experimental results using a modal analysis. The experimental setup designed will allow future research on the interaction between the frame and skin of icosahedron like structures using various combinations of materials and construction methods. Additionally, a snapback behavior observed in previous static response analysis is further investigated to determine nonlinear instability issues with the design. Dynamic analysis of the structure reveals chaotic motion is present in the frame of the icosahedron under certain loads and boundary conditions. These findings provide information critical to the design of an icosahedron shaped lighter than air vehicle using an inner vacuum
Coexisting patterns of population oscillations: the degenerate Neimark Sacker bifurcation as a generic mechanism
We investigate a population dynamics model that exhibits a Neimark Sacker
bifurcation with a period that is naturally close to 4. Beyond the bifurcation,
the period becomes soon locked at 4 due to a strong resonance, and a second
attractor of period 2 emerges, which coexists with the first attractor over a
considerable parameter range. A linear stability analysis and a numerical
investigation of the second attractor reveal that the bifurcations producing
the second attractor occur naturally in this type of system.Comment: 8 pages, 3 figure
Dense, sequentially continuous maps on dyadic compacta
AbstractWe prove in ZFC that for every sequentially continuous ω-dense function f which maps a dyadic compactum onto a Tychonoff space Y, there exists a closed subspace Z ⊆ Dτ such that f[Z] = f[Dτ] and the restriction of f to Z is continuous. Moreover, the range of every such mapping f is a dyadic compactum
Visibility graphs and symbolic dynamics
Visibility algorithms are a family of geometric and ordering criteria by
which a real-valued time series of N data is mapped into a graph of N nodes.
This graph has been shown to often inherit in its topology non-trivial
properties of the series structure, and can thus be seen as a combinatorial
representation of a dynamical system. Here we explore in some detail the
relation between visibility graphs and symbolic dynamics. To do that, we
consider the degree sequence of horizontal visibility graphs generated by the
one-parameter logistic map, for a range of values of the parameter for which
the map shows chaotic behaviour. Numerically, we observe that in the chaotic
region the block entropies of these sequences systematically converge to the
Lyapunov exponent of the system. Via Pesin identity, this in turn suggests that
these block entropies are converging to the Kolmogorov- Sinai entropy of the
map, which ultimately suggests that the algorithm is implicitly and adaptively
constructing phase space partitions which might have the generating property.
To give analytical insight, we explore the relation k(x), x \in[0,1] that, for
a given datum with value x, assigns in graph space a node with degree k. In the
case of the out-degree sequence, such relation is indeed a piece-wise constant
function. By making use of explicit methods and tools from symbolic dynamics we
are able to analytically show that the algorithm indeed performs an effective
partition of the phase space and that such partition is naturally expressed as
a countable union of subintervals, where the endpoints of each subinterval are
related to the fixed point structure of the iterates of the map and the
subinterval enumeration is associated with particular ordering structures that
we called motifs
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