Dimensional analysis of spring-wing systems reveals performance metrics for resonant flapping-wing flight

Flapping-wing insects, birds and robots are thought to offset the high power cost of oscillatory wing motion by using elastic elements for energy storage and return. Insects possess highly resilient elastic regions in their flight anatomy that may enable high dynamic efficiency. However, recent experiments highlight losses due to damping in the insect thorax that could reduce the benefit of those elastic elements. We performed experiments on, and simulations of, a dynamically scaled robophysical flapping model with an elastic element and biologically relevant structural damping to elucidate the roles of body mechanics, aerodynamics and actuation in spring-wing energetics. We measured oscillatory flapping-wing dynamics and energetics subject to a range of actuation parameters, system inertia and spring elasticity. To generalize these results, we derive the non-dimensional spring-wing equation of motion and present variables that describe the resonance properties of flapping systems: N, a measure of the relative influence of inertia and aerodynamics, and K^, the reduced stiffness. We show that internal damping scales with N, revealing that dynamic efficiency monotonically decreases with increasing N. Based on these results, we introduce a general framework for understanding the roles of internal damping, aerodynamic and inertial forces, and elastic structures within all spring-wing systems.     

Photovoltaic technology development: A perspective from patent growth analysis

To catch up with the need for utilizing sunlight as an alternative energy source, photovoltaic technology has developed considerably fast in the last thirty-plus years. This article examines this technology's development from the perspective of patent growth analysis. Patent data are analyzed to find the photovoltaic technology growth trajectory. Mainly affected by environmental factors such as the price of crude oil, we observe two long-term waves of development trajectories. The current wave is found to be in the later growth stage of its life-cycle. After examining the correlation between technology development and crude oil price, a significant correlation is found between crude oil price's growth rate and photovoltaic patents' growth rate. As far as the market is concerned, it lags 10 years behind photovoltaic technology development.With the assistance of keyword co-occurrence analysis, one can classify photovoltaic patents into five groups, with each carrying a characteristic of competing photovoltaic technologies: Emerging PV, CdTe, CIS/CIGS, Group III–V, and Silicon technologies. This research observes the patent growth trajectories for each technology. Among these competing technologies, Emerging PV, Group III–V, and Silicon are still growing strong, while CdTe and CIS/CIGS are in the mature stage. This result hints at a paradigm shift for photovoltaic technology development. Sustainability is added to the technical regime in addition to efficiency, cost, and reliability.A policy other than the existing mechanism such as a feed-in tariff is suggested to stabilize photovoltaic technology development through the means of removing oil price fluctuations. Finally, several strategic issues are discussed from the technology development community's point of view.     

Sidewall defects of AlGaN/GaN HEMTs evaluated by low frequency noise analysis

The traditional dry etching isolation process in AlGaN/GaN HEMTs causes the gate metal to contact the mesa sidewalls region, forming a parasitic gate leakage path. In this paper, we suppress the gate leakage current from the mesa-sidewall to increase the gate-to-drain breakdown voltage and thereby reduce the interface trap density by using the ion implantation (I/I) isolation technology. According to the capacitance–voltage (C–V) measured curve, the hysteresis voltage was 9.3 mV and the interface state density was 5.26 × 10¹² cm⁻² for the I/I isolation sample. The 1/f noise phenomena and Schottky characteristics are particularly studied to indicate device linearity, which is sensitive to the semiconductor surface. The fluctuation that causes trapping/detrapping of free carriers near the gate interface can be reduced because side-wall plasma-induced damages were eliminated. The reduced DC and flicker noise variation of I/I isolation HEMTs is beneficial for high power transistor applications.     

Keeping baby safe: A randomized trial of a parent training program for infant and toddler motor vehicle injury prevention

Motor vehicle crashes are responsible for much death and disability among infants and toddlers. This study evaluated Keeping Baby Safe In and Around the Car, a multimedia DVD designed to improve knowledge about car seat installation among parents of infants and toddlers. The randomized controlled trial was conducted with 195 parents of children aged 0–24 months. Effective car seat use was evaluated via a written knowledge quiz and car seat simulation. Results from analyses of covariance models show that posttest scores for the intervention condition were significantly higher than those of the control condition on both knowledge and car seat simulation measures. The results, consistent across outcome measures and regardless of child age, suggest that viewing the Keeping Baby Safe In and Around the Car DVD resulted in significant gains in parents’ car seat knowledge and their ability to discriminate the critical elements of correct car seat installation. Dissemination of engaging multimedia DVDs such as this program might reduce motor vehicle crash-related injuries to infants and toddlers.     

Selection of an optimal set of cutting-tools for a general triangular pocket

The size(s) of the cutting-tool (end-mill) chosen for machining a given pocket has a significant impact on the machining time. However, the selection of cutting-tool sizes is typically based on human judgment and estimates, and is therefore prone to be conservative and non-optimal. The focus of this paper is on the development of a procedure for selection of an optimal set of cutting-tools for staircase milling of general triangular pockets with round corners, such that the machining time is minimized. We first derive analytical models for determining the time for machining the pocket using a given cutting-tool. Subsequently, we employ a dynamicprogramming based approach that utilizes these analytical models to determine the best set of cutting-tools, from the available inventory of cutting-tools, to machine the pocket. The proposed approach can be extended for optimal selection of cutting-tools for rough-machining of 3-D sculptured cavities.     

Issues in patch-by-patch machining of compound sculptured surfaces

Sculptured surfaces are widely used in commercial products and industrial designs because of their aesthetically pleasing shape characteristics. In such instances, it often becomes necessary to model the part using compound surfaces that consist of several individual sculptured surface patches. In comparison to single surface patches, compound surfaces give rise to additional challenges in making process planning decisions. In this paper, several fundamental issues relevant to patch-by-patch finish machining of compound sculptured surfaces are examined. In particular, efficient procedures for determination of the maximum gouge-free tool size, detection and avoidance of gouging, identification of the best isoparametric cutter path, and determination of an efficient machining sequence of the composing patches are presented.     

An improved reduced-rank CFAR space-time adaptive radar detectionalgorithm

The CFAR test developed in previous work is a normalized ratio test for signals in nonwhite Gaussian noise. However, in the airborne radar environment, the noise consists of strong interference and a relatively weak thermal noise, in the case of a large interference-to-thermal noise ratio, this test can be simplified to the reduced-rank CFAR test developed previously, which operates in an interference-free subspace without the need for matrix inversion operations. This test is extended in this paper to one that includes both the primary and secondary data as defined by Bose and Steinhardt (see ibid., vol.43, p.2164-75, 1995), it is also shown that this test can be modified to obtain a dramatically improved performance. A much smaller amount of sample data is needed in this new improved algorithm to achieve a given probability of detection than is required by this test. Finally, the performance of this new reduced-rank CFAR test statistic is analyzed, and a simulation is performed for an example scenario in order to validate the theoretical results     

Novel fully symmetrical inductor

Differential inductors have significant advantages over single-end inductors. But the conventional differential inductors are not really symmetrical in geometry. Here, we present a novel differential inductor that is fully symmetrical in its layout. Some measurement data will be shown to prove it.     

Concurrently searching for mobile users in cellular networks

In today's systems, upon arrival of calls to mobile users, the system attempts to locate the users sequentially (one by one) through a paging operation. In this letter, we propose to concurrently search for a number of mobile users in a mobile network, significantly reducing the cost of locating mobile users. The reduction in the paging costs due to such a concurrent search can be quite substantial, depending on the knowledge of the probabilities of the users' locations, the number of cells in the network, and the number of mobiles to be located. Additionally, we propose a low-complexity heuristic that reduces the average paging cost by 25%, in the case of no knowledge of probabilities of the mobiles' locations. With such knowledge, further reduction in the average paging costs of up to 90% can be achieved.     

Photovoltaic characteristics of silicon nanowire arrays synthesized by vapor-liquid-solid process

Silicon nanowire (SiNW) arrays were grown directly on a P type Si substrate, pre-deposited with gold catalyst, and then made into solar cell for photovoltaic characteristic measurement. Different growth conditions of SiNWs, including variation of the flow rate ratio of SiH₄ versus N₂, and the thickness of Au film, which can be sputtered into different size of nanoparticles, will be made in order to obtain an optimum photovoltaic conversion efficiency. The morphologies and crystalline structure of the nanowires are studied by SEM, TEM and XRD. The SiNW array surface is shown to have good antireflection property, and is expected to raise light absorption and short circuit current. The photovoltaic performance of the solar cells with SiNWs grown at different conditions is measured and discussed. More effort is still needed to raise the performance of SiNW solar cells.