4,862 research outputs found
Linear Programming as a Technique for Least Cost Furnish Analysis
This study was a limited laboratory scale investigation of whether or not linear programming was a viable technique for determining the least cost furnish blends. It is original in that it used actual laboratory developed data for input to determine the linear programming model, and the results were actually produced in the laboratory to see if constraints were met. The materials used were a bleached hardwood, a bleached softwood, tab cards, clay and TiO2. It was found that requirements of linearity and averaging inherent in the linear programming caused results which were not as accurate as needed. However, by using the technique several times in a successive approximation type procedure, readjusting between uses to compensate for the problems previously noted, results of sufficient accuracy to be realistically depended upon were obtained. It is felt this justifies considerable optimism for this technique as a means of constantly economizing furnish costs
Connectivity and interference in device-to-device networks in Poisson-Voronoi cities
To study the overall connectivity in device-to-device networks in cities, we
incorporate a signal-to-interference-plus-noise connectivity model into a
Poisson-Voronoi tessellation model representing the streets of a city. Relays
are located at crossroads (or street intersections), whereas (user) devices are
scattered along streets. Between any two adjacent relays, we assume data can be
transmitted either directly between the relays or through users, given they
share a common street. Our simulation results reveal that the network
connectivity is ensured when the density of users (on the streets) exceeds a
certain critical value. But then the network connectivity disappears when the
user density exceeds a second critical value. The intuition is that for longer
streets, where direct relay-to-relay communication is not possible, users are
needed to transmit data between relays, but with too many users the
interference becomes too strong, eventually reducing the overall network
connectivity. This observation on the user density evokes previous results
based on another wireless network model, where transmitter-receivers were
scattered across the plane. This effect disappears when interference is removed
from the model, giving a variation of the classic Gilbert model and recalling
the lesson that neglecting interference in such network models can give overly
optimistic results. For physically reasonable model parameters, we show that
crowded streets (with more than six users on a typical street) lead to a sudden
drop in connectivity. We also give numerical results outlining a relationship
between the user density and the strength of any interference reduction
techniques
On the critical free-surface flow over localised topography
Flow over bottom topography at critical Froude number is examined with a focus on steady, forced solitary wave solutions with algebraic decay in the far-field, and their stability. Using the forced Korteweg-de Vries (fKdV) equation the weakly-nonlinear steady solution space is examined in detail for the particular case of a Gaussian dip using a combination of asymptotic analysis and numerical computations. Non-uniqueness is established and a seemingly infinite set of steady solutions is uncovered. Non-uniqueness is also demonstrated for the fully nonlinear problem via boundary-integral calculations. It is shown analytically that critical flow solutions have algebraic decay in the far-field both for the fKdV equation and for the fully nonlinear problem and, moreover, that the leading-order form of the decay is the same in both cases. The linear stability of the steady fKdV solutions is examined via eigenvalue computations and by a numerical study of the initial value fKdV problem. It is shown that there exists a linearly stable steady solution in which the deflection from the otherwise uniform surface level is everywhere negative
Homophilic Protocadherin Cell-Cell Interactions Promote Dendrite Complexity
SummaryGrowth of a properly complex dendrite arbor is a key step in neuronal differentiation and a prerequisite for neural circuit formation. Diverse cell surface molecules, such as the clustered protocadherins (Pcdhs), have long been proposed to regulate circuit formation through specific cell-cell interactions. Here, using transgenic and conditional knockout mice to manipulate γ-Pcdh repertoire in the cerebral cortex, we show that the complexity of a neuron’s dendritic arbor is determined by homophilic interactions with other cells. Neurons expressing only one of the 22 γ-Pcdhs can exhibit either exuberant or minimal dendrite complexity, depending only on whether surrounding cells express the same isoform. Furthermore, loss of astrocytic γ-Pcdhs, or disruption of astrocyte-neuron homophilic matching, reduces dendrite complexity cell non-autonomously. Our data indicate that γ-Pcdhs act locally to promote dendrite arborization via homophilic matching, and they confirm that connectivity in vivo depends on molecular interactions between neurons and between neurons and astrocytes
Chaotic Escape from an Open Vase-shaped Cavity. I. Numerical and Experimental Results
We present part I in a two-part study of an open chaotic cavity shaped as a vase. The vase possesses an unstable periodic orbit in its neck. Trajectories passing through this orbit escape without return. For our analysis, we consider a family of trajectories launched from a point on the vase boundary. We imagine a vertical array of detectors past the unstable periodic orbit and, for each escaping trajectory, record the propagation time and the vertical detector position. We find that the escape time exhibits a complicated recursive structure. This recursive structure is explored in part I of our study. We present an approximation to the Helmholtz equation for waves escaping the vase. By choosing a set of detector points, we interpolate trajectories connecting the source to the different detector points. We use these interpolated classical trajectories to construct the solution to the wave equation at a detector point. Finally, we construct a plot of the detector position versus the escape time and compare this graph to the results of an experiment using classical ultrasound waves. We find that generally the classical trajectories organize the escaping ultrasound waves
Resonantly enhanced second-harmonic generation using III-V semiconductor all-dielectric metasurfaces
Nonlinear optical phenomena in nanostructured materials have been challenging
our perceptions of nonlinear optical processes that have been explored since
the invention of lasers. For example, the ability to control optical field
confinement, enhancement, and scattering almost independently, allows nonlinear
frequency conversion efficiencies to be enhanced by many orders of magnitude
compared to bulk materials. Also, the subwavelength length scale renders phase
matching issues irrelevant. Compared with plasmonic nanostructures, dielectric
resonator metamaterials show great promise for enhanced nonlinear optical
processes due to their larger mode volumes. Here, we present, for the first
time, resonantly enhanced second-harmonic generation (SHG) using Gallium
Arsenide (GaAs) based dielectric metasurfaces. Using arrays of cylindrical
resonators we observe SHG enhancement factors as large as 104 relative to
unpatterned GaAs. At the magnetic dipole resonance we measure an absolute
nonlinear conversion efficiency of ~2X10^(-5) with ~3.4 GW/cm2 pump intensity.
The polarization properties of the SHG reveal that both bulk and surface
nonlinearities play important roles in the observed nonlinear process
Hyperfine Fields in an Ag/Fe Multilayer Film Investigated with 8Li beta-Detected Nuclear Magnetic Resonance
Low energy -detected nuclear magnetic resonance (-NMR) was used
to investigate the spatial dependence of the hyperfine magnetic fields induced
by Fe in the nonmagnetic Ag of an Au(40 \AA)/Ag(200 \AA)/Fe(140 \AA) (001)
magnetic multilayer (MML) grown on GaAs. The resonance lineshape in the Ag
layer shows dramatic broadening compared to intrinsic Ag. This broadening is
attributed to large induced magnetic fields in this layer by the magnetic Fe
layer. We find that the induced hyperfine field in the Ag follows a power law
decay away from the Ag/Fe interface with power , and a field
extrapolated to T at the interface.Comment: 5 pages, 4 figure. To be published in Phys. Rev.
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