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Bessel-beam launchers are promising and established technologies for focusing applications at microwaves. Their use in time-domain leads to the definition of a new class of devices, namely, the X-wave launchers. In this work, we discuss the focusing features of such devices with a specific interest at millimeter waves. The spatial resolutions of such systems are described under a rigorous mathematical framework to derive novel operating conditions for designing X-wave launchers. These criteria might be particularly appealing for specific millimeter-wave applications. In particular, it is shown that an electrically large aperture is not strictly required, as it seemed from previous works. However, the use of an electrically small aperture would demand a considerably wideband capability. The various discussions presented here provide useful information for the design of X-wave launchers. This aspect is finally shown with reference to the practical design of two different X-wave launchers.
Accurate measurement of herbage intake rate is critical to advance knowledge of the ecology of grazing ruminants. This experiment tested the integration of behavioral and acoustic measurements of chewing and biting to estimate herbage dry matter intake (DMI) in dairy cows offered micro-swards of contrasting plant structure. Micro-swards constructed with plastic pots were offered to three lactating Holstein cows (608±24.9 kg of BW) in individual grazing sessions (n=48). Treatments were a factorial combination of two forage species (alfalfa and fescue) and two plant heights (tall=25±3.8 cm and short=12±1.9 cm) and were offered on a gradient of increasing herbage mass (10 to 30 pots) and number of bites (~10 to 40 bites). During each grazing session, sounds of biting and chewing were recorded with a wireless microphone placed on the cows’ foreheads and a digital video camera to allow synchronized audio and video recordings. Dry matter intake rate was higher in tall alfalfa than in the other three treatments (32±1.6 v. 19±1.2 g/min). A high proportion of jaw movements in every grazing session (23 to 36%) were compound jaw movements (chew-bites) that appeared to be a key component of chewing and biting efficiency and of the ability of cows to regulate intake rate. Dry matter intake was accurately predicted based on easily observable behavioral and acoustic variables. Chewing sound energy measured as energy flux density (EFD) was linearly related to DMI, with 74% of EFD variation explained by DMI. Total chewing EFD, number of chew-bites and plant height (tall v. short) were the most important predictors of DMI. The best model explained 91% of the variation in DMI with a coefficient of variation of 17%. Ingestive sounds integrate valuable information to remotely monitor feeding behavior and predict DMI in grazing cows.
Escherichia coli O157 are zoonotic bacteria for which cattle are an important reservoir. Prevalence estimates for E. coli O157 in British cattle for human consumption are over 10 years old. A new baseline is needed to inform current human health risk. The British E. coli O157 in Cattle Study (BECS) ran between September 2014 and November 2015 on 270 farms across Scotland and England & Wales. This is the first study to be conducted contemporaneously across Great Britain, thus enabling comparison between Scotland and England & Wales. Herd-level prevalence estimates for E. coli O157 did not differ significantly for Scotland (0·236, 95% CI 0·166–0·325) and England & Wales (0·213, 95% CI 0·156–0·283) (P = 0·65). The majority of isolates were verocytotoxin positive. A higher proportion of samples from Scotland were in the super-shedder category, though there was no difference between the surveys in the likelihood of a positive farm having at least one super-shedder sample. E. coli O157 continues to be common in British beef cattle, reaffirming public health policy that contact with cattle and their environments is a potential infection source.
TW Hydrae is a very young and nearby association with about 30 known members which is an excellent target for studies on stellar evolution since several of its members present a particular interest (planetary system, brown dwarfs, etc.). With the new data from TGAS and the Gaia DR1 eventually combined with others astrometric data we intend to improve our kinematic knowledge of this association.
In a recent study, we derived individual distances for a sample of pre-main sequence stars that define the comoving association of young stars in the Lupus star-forming region. Here, we use these new distances to investigate the mass and age distributions of Lupus T Tauri stars and derive the average disk lifetime in the Lupus association based on an empirical disk model.
We report on the analysis of virtual powder-diffraction patterns from serial femtosecond crystallography (SFX) data collected at an X-ray free-electron laser. Different approaches to binning and normalizing these patterns are discussed with respect to the microstructural characteristics which each highlights. Analysis of SFX data from a powder of Pr0.5Ca0.5MnO3 in this way finds evidence of other trace phases in its microstructure which was not detectable in a standard powder-diffraction measurement. Furthermore, a comparison between two virtual powder pattern integration strategies is shown to yield different diffraction peak broadening, indicating sensitivity to different types of microstrain. This paper is a first step in developing new data analysis methods for microstructure characterization from serial crystallography data.
We evaluated the concordance between assemblages of Ephemeroptera and Trichoptera to verify if they respond similarly to environmental gradients in the basin of Suiá-Missu river in Mato Grosso, central Brazil. We tested the predictions that: (i) the distributional pattern of mayfly and caddisfly larvae is concordant along the spatial and (ii) environmental variation along the basin, and if (iii) taxa are concordant between themselves along the seasons and with the environmental gradients disregarding the seasons of the year. We found a concordance between species composition of mayfly and caddisfly in fall-water and rainy period, when analyzed separately by each season. The concordance between environmental variables and the two taxa analyzed separately also was concordant, but only on the fall-water season. Finally, we found congruence when both analyzed groups disregarded the temporal effect, but it was less representative than when we consider the seasons variation. Our results suggest that the hydrological cycle could be a driver of changes in species composition of mayflies and caddisflies.
To reliably determine the main physical parameters (masses and ages) of young stars, we must know their distances. While the average distance to nearby star-forming regions (<300 pc) is often known, the distances to individual stars are usually unknown. Individual distances to members of young moving groups can be derived from their radial velocities and proper motions using the convergent-point strategy. We investigate the kinematic properties of the Lupus moving group with the primary objective of deriving individual distances to all group members.
We have conducted a program of trigonometric distance measurements to 13 members of the TW Hydrae Association (TWA), which will enable us (through back-tracking methods) to derive a convincing estimate of the age of the association, independent of stellar evolutionary models. With age, distance, and luminosity known for an ensemble of TWA stars and brown dwarfs, models of early stellar evolution (which are still uncertain for young ages and substellar masses) will then be constrained by observations over a wide range of masses (0.025 to 0.7 M⊙).
We studied the self-assembly of nanoscopic building blocks comprised of polymer-tethered nanoparticles using computer simulation and predict that these building blocks can assemble into mono- and multi-layer sheets and shells. The simulations further demonstrate that for some nanoparticle geometries and tethered nanoparticle topologies, ideas from block copolymers, surfactants and liquid crystals can be used to predict the ordered morphologies attained via self- assembly and that for specific cases the morphologies are consistent with Israelachvili packing rules.
A method to generate line pattern structures in thin organic films with embedded gold and silver nanoparticles is introduced. The films are irradiated with ultrashort, linearly polarized laser pulses. As we find out from electron microscopy (TEM, SEM), periodically arranged line-like structures are formed after the irradiation. We have used so far three different laser wavelengths (266 nm, 400 nm, 800 nm). The resulting structure periods in the range of 170 nm to 600 nm indicate a linear correlation of the period length of the line structures and the wavelength of the incident laser light. The direction of the particle lines corresponds to the linear polarization of the laser pulses. The anisotropic structure modification is mirrored in corresponding anisotropic optical film properties.
74Ge nanocrystals were formed by ion beam synthesis in SiO2. Transmission Electron Microscopy was used to characterize the structure and properties of these Ge nanocrystals before and after liberation from the matrix. The liberation from the SiO2 matrix was achieved through selective etching in a HF bath. High-resolution micrographs and selective area diffraction confirm that the crystallinity is retained in this process. Transfer of released nanocrystals is achieved through ultrasonic dispersion in methanol and deposition onto lacey carbon films via evaporation of methanol. In an effort to determine the melting point of Ge nanocrystals and observe the growth and evolution of nanocrystals embedded in the amorphous SiO2 during heat treatment, as-grown nanocrystals were heated in-situ up to 1192°C±60°C in a JEOL 200CX analytical electron microscope. Electron diffraction patterns are recorded using a Charge-Coupled Device. A large melting hysteresis was observed around the melting temperature of bulk Ge.
The uniformity and reproducibility of the CdTe QD arrays on the GaAs substrates can be improved by using a nanoporous mask. The CdTe QDs on the GaAs substrate were grown by a molecular beam epitaxy (MBE) method. The nanoporous alumina masks used for the fabrication of QD arrays have the thickness from 0.3 νm to 5 νm with the nanochannels of ∼ 80 nm diameter and the pore density of ∼ 1010cm−2. When the thickness of the alumina mask used for the CdTe QD growth was about 300 nm, the CdTe QD arrays formed as a replica of the nanochannels of the mask. Smaller self-assembled CdTe QDs located randomly were produced by using the thicker nanochannel mask than 0.5 νm. The thickness of the nanochannel mask controls the size of the CdTe/GaAs QDs.
ITO nanoparticles were synthesized by coprecipitation method in an aqueous solution and thermal method in an alcohol solution. The coprecipitate prepared at room temperature showed the crystal structure of indium oxide in X-ray diffraction when it was annealed above 300°C. In thermal method, the nanoparticles have two phase crystal structure of indium oxide hydroxide (InOOH) and indium hydroxide (In(OH)3). Annealing at the temperature above 300 °C, it showed the rhombohedral crystal structure of indium oxide (In2O3). The phase transition of ITO nanoparticle was also detected with DSC. Near IR-reflective film was prepared by spin coating using ITO sol solution. Transmission electron microsopy (TEM) and energy dispersive X-ray spectrometer (EDS) were used to characterize the morphology and composition of ITO nanoparticles. Near-IR (NIR) spectrometer was used to determine reflectance on the surface of ITO film in the NIR-radiation region.
Through control of the grain-boundary structure, principally in the nature of the nanoscale intergranular films, a silicon carbide with a fracture toughness as high as 9.1 MPa.m1/2 has been developed by hot pressing β-SiC powder with aluminum, boron, and carbon additions (ABC-SiC). Central in this material development has been systematic transmission electron microscopy (TEM) and mechanical characterizations. In particular, atomic-resolution electron microscopy and nanoprobe composition quantification were combined in analyzing grain boundary structure and nanoscale structural features. Elongated SiC grains with 1 nm-wide amorphous intergranular films were believed to be responsible for the in situ toughening of this material, specifically by mechanisms of crack deflection and grain bridging. Two methods were found to be effective in modifying microstructure and optimizing mechanical performance. First, prescribed post-annealing treatments at temperatures between 1100 and 1500°C were seen to cause full crystallization of the amorphous intergranular films and to introduce uniformly dispersed nanoprecipitates within SiC matrix grains; in addition, lattice diffusion of aluminum at elevated temperatures was seen to alter grain-boundary composition. Second, adjusting the nominal content of sintering additives was also observed to change the grain morphology, the grain-boundary structure, and the phase composition of the ABC-SiC. In this regard, the roles of individual additives in developing boundary microstructures were identified; this was demonstrated to be critical in optimizing the mechanical properties, including fracture toughness and fatigue resistance at ambient and elevated temperatures, flexural strength, wear resistance, and creep resistance.
Self-assembled nanopore templates were fabricated by anodizing aluminum in several electrolytes under specially selected conditions. The size of the nanopores was controlled, and many sizes were fabricated. Y-junction nanopore templates were also fabricated using a two-step anodization. Magnetic nanowires and Y-junction nanowires were then fabricated by electrochemical deposition of magnetic material into the nanopore templates and Y-junction nanopore templates. The magnetic properties of nanowires were investigated by VSM and compared.
Poly (vinyl alcohol) (PVA)/H3PMo12O40ultra-fine fiber aggregates contained differential weight percentage of H3PMo12O40 to PVA (20, 50 and 80 wt.%, respectively) have been successfully prepared by electrospinning technique. By means of IR spectrum, wide-angle X-ray diffraction, and scanning electron microscope (SEM) techniques, the fiber aggregates were characterized. The result from scanning electron microscopy (SEM) showed that the average diameter of the fibers was between 240-900 nm. The photochromic behavior of the fiber aggregates was investigated by means of IR, UV-Vis spectra and electron spin resonance (ESR). The results showed that the Mo atom of H3PMo12O40 was reduced via one-electron step and the PVA was oxidized to unsaturated ketone after the PVA/H3PMo12O40 fiber aggregates was irradiated under UV light. The color of the fiber aggregates changed from white to blue under ultraviolet irradiation and the photochromism of the fiber aggregates was reversible in air condition.
A honeycomb-like SiC reconstructed surface with regular, periodic porosity in the nano-scale range has been used as an effective template for the formation of monodispersed Co nanoclusters. In-situ scanning tunneling microscopy (STM) was used to study the nucleation process of the Co nanoclusters on this template. The deposition of Co at different substrate temperature was investigated by STM. It is found that the failure in the deposition of Co nanoclusters on the SiC honeycomb template with substrate temperatures higher than room temperature (RT) might be due to the high desorption rate of the adsorbed Co atoms.
Nonvolatile nanoscale memories with ultra-long retention times have been demonstrated for both binary and multilevel applications. These devices were based on nanowires functionalized with a self- assembled monolayer of redox active molecular wires, where the bit was represented by the charge stored in the redox molecules and the nanowire conductance was used as the readout. Our devices exhibited reliable operation, on/off ratios ∼ 104 and retention times ∼ one month, one of the longest retention times ever achieved with nanoscale devices. These devices were further tailored for multilevel data storage with appreciable noise margins, representing a new concept for functional devices. Our work clearly demonstrates the potential of combining nanowires and molecular wires for superior performance.