RC-loaded bow-tie antenna for improved pulse radiation

In this paper, a loading technique for improving pulse radiation from bow-tie antennas is introduced. This technique allows transmission of short transient pulses with very small late-time ringing and relatively high radiation efficiency. It makes use of a combination of a constant resistive loading along the antenna and a capacitive loading with linearly increasing reactance toward the antenna ends. The constant resistive loading is applied using volumetric microwave absorbers to cover one side of the antenna and the linear capacitive loading is realized by constructing narrow slots on the antenna surface. Relatively high radiation efficiency is achieved by choosing the location of the slot nearest to the feed point in such a way that radiation from it combines constructively with radiation from the feed point. Using a 0.8-ns monocycle for excitation, the technique results in a level of late-time ringing of lower than -40 dB and at the same time the peak value of the transmitted pulse is 54% higher than that of the same antenna without loading.     

Impairment in shifting attention in autistic and cerebellar patients.

Magnetic resonance imaging (MRI) and autopsy evidence of early maldevelopment of cerebellar vermis and hemispheres in autism raises the question of how cerebellar maldevelopment contributes to the cognitive and social deficits characteristic of autism. Compared with 18 normal controls, 8 autistic patients (mean age 13.9 yrs) and 6 patients (mean age 8.6 yrs) with acquired cerebellar lesions were similarly impaired in a task requiring rapid and accurate shifts of attention between auditory and visual stimuli. Neurophysiologic and behavioral evidence rules out motor dysfunction as the cause of this deficit. These findings are consistent with the proposal that in autism cerebellar maldevelopment may contribute to an inability to execute rapid attention shifts, which in turn undermines social and cognitive development. Findings support the proposal that the human cerebellum is involved in the coordination of rapid attention shifts in a fashion analogous to its role in the coordination of movement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Vacuum evaporation of KCl-NaCl salts: Part II. vaporization-rate model and experimental results

A model based on the Hertz-Langmuir relation is used to describe how evaporation rates of the binary KCl-NaCl system change with time. The effective evaporation coefficient (α), which is a ratio of the actual evaporation rate to the theoretical maximum, was obtained for the KCl-NaCl system using this model. In the temperature range of 640 °C to 760 °C, the effective evaporation coefficient ranges from ～0.4 to 0.1 for evaporation experiments conducted at 0.13 Pa. At temperatures below the melting point, the lower evaporation coefficients are suggested to result from the more complex path that a molecule needs to follow before escaping to the gas phase. At the higher liquid temperatures, the decreasing evaporation coefficients result from a combination of the increasing vaporflow resistances and the heat-transfer effects at the evaporation surface and the condensate layer. The microanalysis of the condensate verified that composition of the condensate changes with time, consistent with the model calculation. The microstructural examination revealed that the vaporate may have condensed as a single solution phase, which upon cooling forms fine lamellar structures of the equilibrium KCl and NaCl phases. In conclusion, the optimum design of the evaporation process and equipment must take the mass and heat transfer factors and equipment materials issues into consideration.     

Multi‐“Color” Delineation of Bone Microdamages Using Ligand‐Directed Sub‐5 nm Hafnia Nanodots and Photon Counting CT Imaging

The early detection of bone microdamages is crucial to make informed decisions about the therapy and taking precautionary treatments to avoid catastrophic fractures. Conventional computed tomography (CT) imaging faces obstacles in detecting bone microdamages due to the strong self‐attenuation of photons from bone and poor spatial resolution. Recent advances in CT technology as well as novel imaging probes can address this problem effectively. Herein, the bone microdamage imaging is demonstrated using ligand‐directed nanoparticles in conjunction with photon counting spectral CT. For the first time, Gram‐scale synthesis of hafnia (HfO₂) nanoparticles is reported with surface modification by a chelator moiety. The feasibility of delineating these nanoparticles from bone and soft tissue of muscle is demonstrated with photon counting spectral CT equipped with advanced detector technology. The ex vivo and in vivo studies point to the accumulation of hafnia nanoparticles at microdamage site featuring distinct spectral signal. Due to their small sub‐5 nm size, hafnia nanoparticles are excreted through reticuloendothelial system organs without noticeable aggregation while not triggering any adverse side effects based on histological and liver enzyme function assessments. These preclinical studies highlight the potential of HfO₂‐based nanoparticle contrast agents for skeletal system diseases due to their well‐placed K‐edge binding energy.     

Benefits of ESA Gravity-Related Hands-on Programmes for University Students’ Careers

The Education Office of the European Space Agency (ESA) offers university students, from ESA Member and Cooperating States, the opportunity to perform investigations in physical sciences, life sciences, and technology, under different gravity conditions through three educational programmes. The “Fly Your Thesis!” (FYT) programme makes use of parabolic flights and the “Drop Your Thesis!” (DYT) programme utilizes a drop tower as microgravity carriers, while the “Spin Your Thesis!” (SYT) programme uses a large centrifuge to create hypergravity. To date, more than hundred university students had the chance to participate in the design, development, and performance of one or more experiments during dedicated campaigns. In the following paper, we examine demographics of past participants of the ESA Education Office gravity-related opportunities over the past seven years and evaluate the benefits of these educational programmes for the participants’ studies and careers. Student teams that participated in one of the programmes between 2009 and 2013 were contacted to fill in a questionnaire. The feedback from the students demonstrate significant benefits extending far beyond the primary educational objectives of these programmes.     

High-Temperature Failure of an Alumina-Silicon Carbide Composite under Cyclic loads: Mechanisms of Fatigue Crack-Tip Damage

Experimental results are presented on the mechanisms of tensile cyclic fatigue crack growth in an A1₂0₃-33-vol%-SiC-whisker composite at 1400°C. The ceramic composite exhibits subcritical fatigue crack propagation at stress-intensity-fator values far below the fracture toughness. The fatigue characterized by the stressintensity-factor range, ΔK, and crack propagation rates are found to be strongly sensitive to the mean stress (load ratio) and the frequency of the fatigue cycle. Detailed transmission electron microscopy of the fatigue crack-tip region, in conjunction with optical microscopy, reveals that the principal mechanism of permanent damage ahead of the advancing crack is the nucleation and growth of interfacial flaws. The oxidation of Sic whiskers in the crack-tip region leads to the formation of a silica-glass phase in the 1400°C air environment. The viscous flow of glass causes debonding of the whisker-matrix interface; the nucleation, growth, and coalescence of interfacial cavities aids in developing a diffuse microcrack zone at the fatigue crack tip. The shielding effect and periodic crack branching promoted by the microcracks result in an apparently benefcial fatigue crack-growth resistance in the A1₂0₃—SiC composite, as compared with the unreinforced alumina with a comparable grain size. A comparison of static and cyclic load crack velocities is provided to gain insight into the mechanisms of elevated temperature fatigue in ceramic composites.     

Lane-changing behavior on urban streets: a focus group-based study

As lane-changing behavior has received increasing attention during the recent years, various algorithms have been developed. However, most of these models were derived and validated using data such as vehicle trajectories, with no consideration of driver characteristics. In this research, focus group studies were conducted to obtain driver-related information so that the driver characteristics can be incorporated into lane-changing models. Different urban lane-changing scenarios were examined and discussed in the focus group meetings. The likelihood for initiating lane changes under each scenario was obtained. The participating drivers were categorized according to their background information and verbal responses, so that the lane-changing behavior can be related to driver characteristics for each group. Two types of information, quantitative and qualitative responses from participants, were used to establish this relationship. The paper concludes by providing recommendations related to the implementation of study findings into micro-simulators to better replicate driver behavior in urban street networks.     

Dow Launches First Sustainability Report in China

<正> The Dow Chemical Company announced itslaunch of the inaugural issue of the "2009Dow Greater China Sustainability Report"on April 1st.The first launched "2009 Dow Greater ChinaSustainability Report" aims to introduceDow's sustainability strategies as well as the     

The social shaping of educational technologies in Saudi Arabia: An examination of how the social fabric shapes the construction and use of technologies

This article is organised around the research question: To what extent has the social fabric shaped the way in which educational technologies are constructed at the institutional level in a specific social context? This question is addressed through a naturalistic study of a state university in the Eastern Province of Saudi Arabia. Guided by the grounded theory approach, the data analysis demonstrated that Saudi society was committed to many established relationships, structures and identities, a commitment that has resulted in the social shaping of educational technologies.