Micromechanical models to guide the development of synthetic ‘brick and mortar’ composites

This paper describes a micromechanical analysis of the uniaxial response of composites comprising elastic platelets (bricks) bonded together with thin elastic perfectly plastic layers (mortar). The model yields closed-form results for the spatial variation of displacements in the bricks as a function of constituent properties, which can be used to calculate the effective properties of the composite, including elastic modulus, strength and work-to-failure. Regime maps are presented which indicate critical stresses for failure of the bricks and mortar as a function of constituent properties and brick architecture. The solution illustrates trade-offs between elastic modulus, strength and dissipated work that are a result of transitions between various failure mechanisms associated with brick rupture and rupture of the interfaces. Detailed scaling relationships are presented with the goal of providing material developers with a straightforward means to identify synthesis targets that balance competing mechanical behaviors and optimize material response. Ashby maps are presented to compare potential brick and mortar composites with existing materials, and identify future directions for material development.     

A low-power highly digitized receiver for 2.4-GHz-band GFSK applications

This paper describes the design and measurement results of a low-power highly digitized receiver for Gaussian frequency-shift keying modulated input signals at 2.4 GHz. The RF front-end has been based on a low-IF architecture and does not require any variable gain or filtering blocks. The full dynamic range of the low-IF signal is converted into the digital domain by a low-power high-resolution time-continuous SigmaDelta analog-to-digital converter (ADC). This leads to a linear receive chain without limiters. A fifth-order poly-phase loop filter is used in the complex SigmaDelta ADC. The digital block performs filtering and demodulation. Channel filtering is combined with matched filtering and the suppression of noise resulting from the SigmaDelta ADC. The high degree of digitization leads to design flexibility with respect to changing standards and scalability in future CMOS generations. The receiver has been realized in a standard 0.18-mum CMOS process and measures 3.5 mm². The only external components are an antenna filter and a crystal. The power consumption is only 32 mW in the continuous mode, which is at least a factor of two lower than state-of-the-art CMOS receivers     

TG-MS characterization of the reaction products of cadmium yellow and malachite artist’s pigments

The deleterious interaction of some traditional sulphide artists pigments and copper ions results in the formation of black copper sulphides, in particular, covellite (CuS), and, hence, the discolouration of valuable artworks. In this paper the interaction of malachite, a source of copper(II) ions, with the pigment cadmium yellow, a sulphide pigment comprising of a solid solution of cadmium and zinc sulphides, is investigated by XRD and TG-MS. XRD showed the presence of the copper sulphide and cadmium carbonate phases, produced by a simple ion exchange mechanism. TG-MS showed the complexity of the range of metastable phases produced. The identification of these phases, however, requires further work.     

The influence of normal stress anisotropy in predicting scalar dispersion with the v–f model

A numerical study of scalar dispersion is presented to investigate the effectiveness of pairing the v²–f turbulence model with algebraic models for the scalar flux. This approach is contrasted with utilizing a full Second Moment Closure (SMC) as the flow field input to the scalar model. Predictions of scalar transport in a turbulent channel and over a wavy wall are compared to available DNS databases. The latter case includes a scalar release from a point source and therefore detailed comparisons of the three-component turbulent scalar flux are reported. It is found that the transported variable v², representing the near wall turbulent velocity fluctuation scale, can be used to increase the level of normal stress anisotropy provided to algebraic scalar models and thereby improve mean scalar prediction over that of the Standard Gradient Diffusion Hypothesis (SGDH). Improvement is most significant in the near wall region. Three specifications of the normal stresses, derived from v², are considered to provide the link from the v²–f model to the algebraic flux models used to close the scalar transport equation. Barycentric maps are used to examine the state of turbulence anisotropy in each case. As the anisotropy in the normal stress specification becomes more accurate, improvements are realized in the prediction of the spanwise flux as well as the mean concentration.     

Echolocation in the Risso's dolphin,Grampus griseus

The Risso's dolphin (Grampus griseus) is an exclusively cephalopod-consuming delphinid with a distinctive vertical indentation along its forehead. To investigate whether or not the species echolocates, a female Risso's dolphin was trained to discriminate an aluminum cylinder from a nylon sphere (experiment 1) or an aluminum sphere (experiment 2) while wearing eyecups and free swimming in an open-water pen in Kaneohe Bay, Hawaii. The dolphin completed the task with little difficulty despite being blindfolded. Clicks emitted by the dolphin were acquired at average amplitudes of 192.6 dB re 1 microPa, with estimated sources levels up to 216 dB re 1 microPa-1 m. Clicks were acquired with peak frequencies as high as 104.7 kHz (Mf(p) = 47.9 kHz), center frequencies as high as 85.7 kHz (Mf(0) = 56.5 kHz), 3-dB bandwidths up to 94.1 kHz (M(BW) = 39.7 kHz), and root-mean-square bandwidths up to 32.8 kHz (M(RMS) = 23.3 kHz). Click durations were between 40 and 70 micros. The data establish that the Risso's dolphin echolocates, and that, aside from slightly lower amplitudes and frequencies, the clicks emitted by the dolphin were similar to those emitted by other echolocating odontocetes. The particular acoustic and behavioral findings in the study are discussed with respect to the possible direction of the sonar transmission beam of the species.     

Integrated lens with dielectric horn antenna

A dielectric lens is integrated into a dielectric loaded horn antenna to produce a high efficiency feed for reflectors. The lens is designed using simple ray theory and analysed using modal matching techniques. Aperture efficiencies of up to 78% are achieved while retaining good crosspolar performance.<>     

Photofission of heavy nuclei at energies up to 4 GeV

Total photofission cross sections for 238U, 235U, 233U, 237Np, 232Th, and natPb have been measured simultaneously, using tagged photons in the energy range Egamma=0.17-3.84 GeV. This was the first experiment performed using the Photon Tagging Facility in Hall B at Jefferson Lab. Our results show that the photofission cross section for 238U relative to that for 237Np is about 80% over the entire energy range, implying the presence of important processes which compete with fission. If we assume that for 237Np the photofission probability is equal to unity, we observe a significant shadowing effect, starting below 1.5 GeV.     

Lossless quantization of Hadamard transform coefficients

This paper shows that an nx1 integer vector can be exactly recovered from its Hadamard transform coefficients, even when 0.5n log (2)(n) of the (less significant) bits of these coefficients are removed. The paper introduces a fast "lossless" dequantization algorithm for this purpose. To investigate the usefulness of the procedure in data compression, the paper investigates an embedded block image coding technique called the "LHAD" based on the algorithm. The results show that lossless compression ratios close to the state of the art can be achieved, but that techniques such as CALIC and S+P still perform better.