Analysis of equiangular spiral antennas

In this work, equiangular spiral antennas are analyzed with the well-known method of moments in conjunction with triangular patch modeling. In particular, the analysis focuses on the validity of several generic guidelines hitherto available for designing such antennas. In our study, numerical results indicate that increasing the number of spiral arm turns broadens the radiation pattern (i.e., the axial ratio increases), but that tapering the outermost portion of the arms has little effect. Furthermore, as a spiral is wrapped tighter, the radiation pattern broadens and the gain increases. We also show that the useful frequency range of the spiral antenna depends not only on the spiral arm length and the inner radius near the spiral center, but also on the wrap tightness. Finally, numerically determined input impedance differed considerably from the 188-Ω impedance expected for these self-complementary type antennas. © 1996 John Wiley & Sons, Inc.     

Oat lipids

Oats are a significant world crop. While nutritional interest in food oats has concentrated on oats as a source of dietary fiber, the lipid component has both nutritional and technological potential. Thus, the lipid fraction of the oat grain determines in large measure its energy content and has a significant impact on nutritional quality. The oat lipids mediate the pasting properties of oat starch and hence influence functionality. Lipids are also implicated in the flavor/off-flavor attributes of oats. These aspects of oat lipids are reviewed together with analytical methods for assessing the lipid content of oats.     

Effect of Coordinating Solvents on Solution Speciation and the Crystallisation via ROP of a Triphos-Silver Coordination Cage

There is a general lack of understanding of how coordination polymers (metal-organic frameworks) form. Some insight can be gained from observations of formal ROP (ring-opening polymerisation) relationships between coordination polymers and their discrete soluble precursors. Most ROP examples reported previously have involved bidentate bridging ligands. Here we present an unusual example of a ROP relationship based on a tripodal ligand. In particular, 1,3,5-tris(diphenylphosphino)benzene (L1) is found to form a symmetrical coordination cage of stoichiometry Ag₃(L1)₂ in solution in acetonitrile. This contrasts with previous observations in less-coordinating solvents in which higher nuclearity cages are also formed, and shows that the coordinating acetonitrile solvent reduces anion-templating effects. On crystallization from acetonitrile a one-dimensional polymeric structure [Ag₃(L1)₂(NCCH₃)(OTf)₃] _n is obtained. The structure is noteworthy in being a ROP isomer of the trinuclear cage observed in solution. The structure also exhibits solvent-filled channels (maximum diameter 6.1 Å) but the material is not stable to desolvation. The structure of the polymer contrasts with that obtained from less-coordinating solvents, the latter being a stable hexagonal 2-dimensional structure with nanoporosity.     

Salmonella in uncooked retail meats in New Zealand

A national quantitative survey of Salmonella in five types of uncooked retail meats in New Zealand was undertaken from August 2003 to May 2005 to establish baseline proportionality data. The overall prevalence of Salmonella in 1,108 meat samples was 1.1% (95% confidence interval, 0.6 to 1.9). Low prevalences of Salmonella in each meat type were observed, with 3% (1.2 to 6.1) in chicken, 1.3% (0.3 to 3.8) in lamb and mutton, 0.5% (0 to 3.0) in unweaned veal, 0.4% (0 to 2.4) in beef, and 0% (0 to 1.6) in pork. The Salmonella serotypes isolated were Salmonella Infantis from beef; Salmonella Typhimurium PT1 from unweaned veal and chicken; Salmonella sp. 6,7:k:-, Salmonella Enteritidis PT9a, Salmonella sp. 4,5,12:-:-, Salmonella sp. 4,12:-:-, and Salmonella Typhimurium PT160 from chicken; and Salmonella sp. 4:-:2 and Salmonella Brandenburg from lamb. Four of the isolates from chicken, Salmonella sp. 4,5,12:-:- (two isolates), Salmonella sp. 4,12:-:-, and Salmonella Typhimurium PT1, were very similar phenotypically and serologically to the attenuated Salmonella vaccine strain used in MeganVacl for poultry. One lamb sample yielded a count of Salmonella Brandenburg of 4.24 most probable number (MPN)/g, while all other positive samples were <1.0 MPN/g. The results provide baseline proportionality data for Salmonella in retail uncooked meats that will contribute invaluably toward future risk assessment in light of other information, such as consumption data that can be used for risk characterization.     

Classical and Differential Thermal Analysis Studies of the Glass-Ceramic Transformation in a YSiAlON Glass

Nucleation and crystallization studies were conducted on a YSiAlON glass that contained 17 equiv.% nitrogen (7.5 at.%) by using a two-stage nucleation-and-growth treatment. Classical and differential thermal analysis (DTA) techniques were both used to study the crystallization process, to ensure that the optimum heat-treatment schedule that yielded a fine microstructure and minimum residual glass was applied. The optimum nucleation and crystallization temperatures were determined from DTA traces that were recorded from isothermal heat treatments at different nucleating temperatures, ranging between T _g - 40°C and T _g+ 100°C for 1 h and crystal-growth temperatures in the range of 1170°-1310°C for 0.5 h, respectively. The activation energy for the crystallization process was determined, based on the analysis of the variation of peak temperature at five different heating rates. Specimens heat treated in a tube furnace under nitrogen gas were subjected to microscopical investigation, and results showed variations in the volume fraction of crystalline phases and crystal size with nucleation temperature. The nucleation temperature, T _g+ 40°C (1025°C), which corresponded to the maximum volume fraction of crystalline phases and minimum crystal size, was consistent with the optimum nucleation temperature, T _g+ 35°C (1020°C), as determined from DTA. The time and temperature of nucleation and crystal growth dictated the nature and size of the crystalline phases. Properties such as hardness and density were assessed and correlated to the nucleation temperature. The influence of sample specific surface on the devitrification mechanisms was estimated, and bulk nucleation was observed to be the dominant nucleation mechanism.     

The stress response of a semi-infinite micropolar granular material subject to a concentrated force normal to the boundary

We consider the problem of a two dimensional semi-infinite granular material subject to a concentrated or point force normal to the boundary. This boundary value problem was originally solved for a classical elastic material by Flamant in 1892 and, hence, is also known as the Flamant problem (Johnson [8]). In this paper, the granular material is considered as an elastic micropolar or Cosserat continuum and is represented by a particular form of the general constitutive law derived in Walsh and Tordesillas [29]. The stress distribution predicted by the model is in good agreement with experimental data for small strains. In particular, two important features that are captured by the proposed model are: (i) the presence of tensile stress response regions, and (ii) the dependence of the stresses on the microstructural properties, i.e. the particles normal, tangential and rotational stiffness constants. The proposed analysis utilizes two new stress functions, similar to Airys stress functions in classical elastic theory.The support of the US Army Research Office through a grant to AT (Grant No. DAAD19-02-1-0216) and the Melbourne Research and Development Grant scheme is gratefully acknowledged. We thank our reviewers for their useful suggestions and insightful comments.     

Revealing Nanomechanical Domains and Their Transient Behavior in Mixed-Halide Perovskite Films

Halide perovskites are a versatile class of semiconductors employed for high performance emerging optoelectronic devices, including flexoelectric systems, yet the influence of their ionic nature on their mechanical behavior is still to be understood. Here, a combination of atomic-force, optical, and compositional X-ray microscopy techniques is employed to shed light on the mechanical properties of halide perovskite films at the nanoscale. Mechanical domains within and between morphological grains, enclosed by mechanical boundaries of higher Young's Modulus (YM) than the bulk parent material, are revealed. These mechanical boundaries are associated with the presence of bromide-rich clusters as visualized by nano-X-ray fluorescence mapping. Stiffer regions are specifically selectively modified upon light soaking the sample, resulting in an overall homogenization of the mechanical properties toward the bulk YM. This behavior is attributed to light-induced ion migration processes that homogenize the local chemical distribution, which is accompanied by photobrightening of the photoluminescence within the same region. This work highlights critical links between mechanical, chemical, and optoelectronic characteristics in this family of perovskites, and demonstrates the potential of combinational imaging studies to understand and design halide perovskite films for emerging applications such as photoflexoelectricity.     

A Murine Oral‐Exposure Model for Nano‐ and Micro‐Particulates: Demonstrating Human Relevance with Food‐Grade Titanium Dioxide

Human exposure to persistent, nonbiological nanoparticles and microparticles via the oral route is continuous and large scale (10¹²–10¹³ particles per day per adult in Europe). Whether this matters or not is unknown but confirmed health risks with airborne particle exposure warns against complacency. Murine models of oral exposure will help to identify risk but, to date, lack validation or relevance to humans. This work addresses that gap. It reports i) on a murine diet, modified with differing concentrations of the common dietary particle, food grade titanium dioxide (fgTiO₂), an additive of polydisperse form that contains micro‐ and nano‐particles, ii) that these diets deliver particles to basal cells of intestinal lymphoid follicles, exactly as is reported as a “normal occurrence” in humans, iii) that confocal reflectance microscopy is the method of analytical choice to determine this, and iv) that food intake, weight gain, and Peyer's patch immune cell profiles, up to 18 weeks of feeding, do not differ between fgTiO₂‐fed groups or controls. These findings afford a human‐relevant and validated oral dosing protocol for fgTiO₂ risk assessment as well as provide a generalized platform for application to oral exposure studies with nano‐ and micro‐particles.     

Multifrequency ultrasound transducers for conformal interstitial thermal therapy

Control over the pattern of thermal damage generated by interstitial ultrasound heating applicators can be enhanced by changing the ultrasound frequency during heating. The ability to change transmission frequency from a single transducer through the use of high impedance front layers was investigated in this study. The transmission spectrum of multifrequency transducers was calculated using the KLM equivalent circuit model and verified with experimental measurements on prototype transducers. The addition of a quarter-wavelength thick PZT (unpoled) front layer enabled the transmission of ultrasound at two discrete frequencies, 4.7 and 9.7 MHz, from a transducer with an original resonant frequency of 8.4 MHz. Three frequency transmission at 3.3, 8.4, and 10.8 MHz was possible for a transducer with a half-wavelength thick front layer. Calculations of the predicted thermal lesion size at each transmission frequency indicated that the depth of thermal lesion could be varied by a factor of 1.6 for the quarter-wavelength front layer. Heating experiments performed in excised liver tissue with a dual-frequency applicator confirmed this ability to control the shape of thermal lesions during heating to generate a desired geometry. Practical interstitial Designs that enable the generation of shaped thermal lesions are feasible.     

Wavelet decomposition of cardiovascular signals for baroreceptor function tests in pigs

In this paper, the discrete wavelet transform (DWT) was applied to analyze the fluctuations in RR interval and systolic arterial pressure (SAP) recorded from eight alpha-chloralose anesthetized pigs. Our aim was to characterize the autonomic modulation before and after cardiac autonomic blockade and during baroreflex function tests. The instantaneous power of decomposed low-frequency (LF) and high-frequency (HF) components was used for a time-variant spectral analysis. Our results suggested that transient events and changes in autonomic modulation were detected with high temporal resolution. A nonlinear relationship between RR interval and SAP during pharmacologically induced changes in blood pressure was found, when the superimposed effect of respiratory sinus arrhythmia was removed. In addition, the baroslopes were nearly linear when both the LF and HF components were removed using DWT decomposition.