Effects of the topology of social networks on information transmission

Social behaviours cannot be fully understood without considering the network structures that underlie them. Developments in network theory provide us with relevant modelling tools. The topology of social networks may be due to selection for information transmission. To investigate this, we generated network topologies with varying proportions of random connections and degrees of preferential attachment. We simulated two social tasks on these networks: a spreading innovation model and a simple market. Results indicated that non-zero levels of random connections and low levels of preferential attachment led to more efficient information transmission. Theoretical and practical implications are discussed

Shape optimization of tibial prosthesis components

NASA technology and optimal design methodologies originally developed for the optimization of composite structures (engine blades) are adapted and applied to the optimization of orthopaedic knee implants. A method is developed enabling the shape tailoring of the tibial components of a total knee replacement implant for optimal interaction within the environment of the tibia. The shape of the implant components are optimized such that the stresses in the bone are favorably controlled to minimize bone degradation, to improve the mechanical integrity of the implant/interface/bone system, and to prevent failures of the implant components. A pilot tailoring system is developed and the feasibility of the concept is demonstrated and evaluated. The methodology and evolution of the existing aerospace technology from which this pilot optimization code was developed is also presented and discussed. Both symmetric and unsymmetric in-plane loading conditions are investigated. The results of the optimization process indicate a trend toward wider and tapered posts as well as thicker backing trays. Unique component geometries were obtained for the different load cases

Predicting the absorption of perforated panels backed by resistive textiles

This paper studies the diffuse field sound absorption coefficient of a system consisting of a rigid perforated panel with a thin porous woven/matted material glued to its back, which is placed in front of an air cavity with a rigid backing. To cut the cost of trial and error diffuse field sound absorption coefficient measurements, a prediction method was developed. Measurements were made in a two-microphone impedance tube of the complex specific acoustic impedances of the unperforated rigid panel materials and of the thin porous materials in front of a rigidly terminated air cavity. These values were used in the transfer matrix method to predict the complex specific acoustic impedances of the perforated panels systems as a function of the angle of incidence of the sound. These calculations assumed the systems to have infinite or finite lateral extent. The measured diffuse field sound absorption coefficient values usually lay between the infinite and finite predictions. The most important variables are the perforation factor of the panel, the acoustic resistance of the thin porous material and the cavity depth

The prediction of the diffuse field sound absorption of perforated panel systems

This paper studies the diffuse field sound absorption coefficient of a system consisting of a rigid perforated panel with a thin porous woven/matted material glued to its back, which is placed in front of an air cavity with a rigid backing. To cut the cost of trial and error diffuse field sound absorption coefficient measurements, a prediction method was developed. Measurements were made in a two-microphone impedance tube of the complex specific acoustic impedances of the un-perforated rigid panel materials, and of the thin porous materials in front of a rigidly terminated air cavity. These values were used in the transfer matrix method to predict the complex specific acoustic impedances of the perorated panels systems as a function of the angle of incidence of the sound. These calculations assumed the systems to have infinite or finite lateral extent. The measured diffuse field absorption values usually lay between the infinite and finite predictions. The most important variables are the perforation factor of the panel, the acoustic resistance of the thin porous material and the cavity depth

Probing Spatial Variation Of The Fine-Structure Constant Using The CMB

The fine-structure constant, α, controls the strength of the electromagnetic interaction. There are extensions of the standard model in which α is dynamical on cosmological length and time scales. The physics of the cosmic microwave background (CMB) depends on the value of α. The effects of spatial variation in α on the CMB are similar to those produced by weak lensing: smoothing of the power spectrum, and generation of non-Gaussian features. These would induce a bias to estimates of the weak-lensing potential power spectrum of the CMB. Using this effect, Planck measurements of the temperature and polarization power spectrum, as well as estimates of CMB lensing, are used to place limits (95% C.L.) on the amplitude of a scale-invariant angular power spectrum of α fluctuations relative to the mean value (CαL=AαSI/[L(L+1)]) of AαSI≤1.6×10−5. The limits depend on the assumed shape of the α-fluctuation power spectrum. For example, for a white-noise angular power spectrum (CαL=AαWN), the limit is AαWN≤2.3×10−8. It is found that the response of the CMB to α fluctuations depends on a separate-universe approximation, such that theoretical predictions are only reliable for α multipoles with L≲100. An optimal trispectrum estimator can be constructed and it is found that it is only marginally more sensitive than lensing techniques for Planck but significantly more sensitive when considering the next generation of experiments. For a future CMB experiment with cosmic-variance limited polarization sensitivity (e.g., CMB-S4), the optimal estimator could detect α fluctuations with AαSI\u3e1.9×10−6 and AαWN\u3e1.4×10−9

Annular interdigital transducer focuses piezoelectric surface waves to a single point

We propose and demonstrate experimentally the concept of the annular interdigital transducer that focuses acoustic waves on the surface of a piezoelectric material to a single, diffraction-limited, spot. The shape of the transducing fingers follows the wave surface. Experiments conducted on lithium niobate substrates evidence that the generated surface waves converge to the center of the transducer, producing a spot that shows a large concentration of acoustic energy. This concept is of practical significance to design new intense microacoustic sources, for instance for enhanced acouto-optical interactions

The acoustic radiation impedance of a rectangular panel

This paper extends the definition of the one sided radiation impedance of a panel mounted in an infinite rigid baffle which was previously used by the authors so that it can be applied to all transverse velocity wave types on the panel rather than just to the possibly forced travelling plane transverse velocity waves considered previously by the authors. For the case of travelling plane waves on a rectangular panel with anechoic edge conditions, and for the case of standing waves on a rectangular panel with simply supported edge conditions, the equations resulting from one of the standard reductions from quadruple to double integrals are given. These double integral equations can be reduced to single integral equations, but the versions of these equations given in the literature did not always converge when used with adaptive integral routines and were sometimes slower than the double integral versions. This is because the terms in the integrands in the existing equations have singularities. Although these singularities cancel, they caused problems for the adaptive integral routines. This paper rewrites these equations in a form which removes the singularities and enables the integrals in these equations to be evaluated with adaptive integral routines. Approximate equations for the azimuthally averaged one sided radiation impedance of a rectangular panel mounted in an infinite baffle are given for all the cases considered in this paper and the values produced by these equations are compared with numerical calculations

The prediction of the complex characteristic acoustic impedance of porous materials

Modeling the complex characteristic acoustic impedance and complex wavenumber of porous materials allows the prediction of the complex specific acoustic impedance of a system consisting of porous absorbers and air cavities in front of a rigid surface. By using the transfer matrix method, the complex characteristic acoustic impedance and complex wavenumber of a porous material can be predicted by using the measured complex specific acoustic impedance of two different systems of the porous material and an air cavity, performed in a two-microphone impedance tube. Depending on the method, the material can be measured with either a rigidly terminated back plate at the back of the material, or a rigidly terminated air cavity at the back. This paper looks at why predictions using the single and double thickness method break down for thinner, less dense materials