16,451 research outputs found
Laboratory Evaluation of Mefluidide Effects on Elongation of Hydrilla and Eurasian Watermilfoil
The potential of mefluidide (N-(2,4-dimethyl-5[[trifluromethyl) sulfonyl] amino] phenol) acetamide) to act as a submersed aquatic plant growth regulator was evaluated using a laboratory bioassay system. Main stem elongation of hydrilla (Hydrilla verticillata (L.f.) Royle) and Eurasian watermilfoil (Myriophyllum spicatum L.) was effectively reduced by mefluidide at low concentrations. The lowest effective concentration of mefluidide that reduced stem length in Eurasian watermilfoil (100 yg a.i./L) was 5 times lower than that for hydrilla (500 yg a.i./L). Short-term net photosynthetic rates of these plants were not affected by mefluidide at concentrations as high as 1000 yg a.i./L. The minimum exposure time required to maintain an inhibitory effect for at least 28 days at a concentration of 500 yg ai.i./L was 3 to 7 days for Eurasian watermilfoil and 7 to 14 days for hydrilla. The results suggest that mefluidide is a more effective growth regulator for Eurasian watermilfoil than hydrilla. Exogenously applied gibberellic acid (GA) did not completely overcome the inhibitory effect of mefluidide even when GA was added at a high concentration (10-5 M). In addition, the internodal lengths of stems treated with mefluidide were not reduced as they were when treated with gibberellin synthesis inhibitors. The reduction of main stem elongation by mefluidide appeared to be due to the inhibition of new cell and tissue development at the stem tip rather than from inhibition of GA biosynthesis
Long String Scattering in c = 1 String Theory
We study the scattering of long strings in c = 1 string theory, both in the
worldsheet description and in the non-singlet sector of the dual matrix quantum
mechanics. From the worldsheet perspective, the scattering amplitudes of long
strings are obtained from a decoupling limit of open strings amplitudes on FZZT
branes, which we compute by integrating Virasoro conformal blocks along with
structure constants of boundary Liouville theory. In particular, we study the
tree level amplitudes of (1) a long string decaying by emitting a closed
string, and (2) the scattering of a pair of long strings. We show that they are
indeed well defined as limits of open string amplitudes, and that our results
are in striking numerical agreement with computations in the adjoint and
bi-adjoint sectors of the dual matrix model (based on proposals of Maldacena
and solutions due to Fidkowski), thereby providing strong evidence of the
duality.Comment: 42 pages, 18 figure
Wilson-Loop Characterization of Inversion-Symmetric Topological Insulators
The ground state of translationally-invariant insulators comprise bands which
can assume topologically distinct structures. There are few known examples
where this distinction is enforced by a point-group symmetry alone. In this
paper we show that 1D and 2D insulators with the simplest point-group symmetry
- inversion - have a classification. In 2D, we identify a relative
winding number that is solely protected by inversion symmetry. By analysis of
Berry phases, we show that this invariant has similarities with the first Chern
class (of time-reversal breaking insulators), but is more closely analogous to
the invariant (of time-reversal invariant insulators). Implications of
our work are discussed in holonomy, the geometric-phase theory of polarization,
the theory of maximally-localized Wannier functions, and in the entanglement
spectrum.Comment: The updated version is accepted in Physical Review
The c=1 String Theory S-Matrix Revisited
We revisit the perturbative S-matrix of c=1 string theory from the worldsheet
perspective. We clarify the origin of the leg pole factors, the non-analyticity
of the string amplitudes, and the validity as well as limitations of earlier
computations based on resonance momenta. We compute the tree level 4-point
amplitude and the genus one 2-point reflection amplitude by numerically
integrating Virasoro conformal blocks with DOZZ structure constants on the
sphere and on the torus, with sufficiently generic complex Liouville momenta,
and find agreement with known answers from the c=1 matrix model.Comment: 32 pages, 7 figures; footnote and references added, typos correcte
FROST -- Fast row-stochastic optimization with uncoordinated step-sizes
In this paper, we discuss distributed optimization over directed graphs,
where doubly-stochastic weights cannot be constructed. Most of the existing
algorithms overcome this issue by applying push-sum consensus, which utilizes
column-stochastic weights. The formulation of column-stochastic weights
requires each agent to know (at least) its out-degree, which may be impractical
in e.g., broadcast-based communication protocols. In contrast, we describe
FROST (Fast Row-stochastic-Optimization with uncoordinated STep-sizes), an
optimization algorithm applicable to directed graphs that does not require the
knowledge of out-degrees; the implementation of which is straightforward as
each agent locally assigns weights to the incoming information and locally
chooses a suitable step-size. We show that FROST converges linearly to the
optimal solution for smooth and strongly-convex functions given that the
largest step-size is positive and sufficiently small.Comment: Submitted for journal publication, currently under revie
Understanding the great trade collapse of 2008–09 and the subsequent trade recovery
This article documents the Great Trade Collapse of 2008–09, as well as the dramatic recovery in trade of 2009–10. The authors consider how three distinct policy actions — fiscal stimulus, funding for trade finance and a commitment to refrain from increasing trade barriers — might have affected both the collapse and recovery.Gross domestic product ; Trade ; Recessions
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