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41.
In this study we describe a mechanism for supporting a community of learning scientists who are exploring educational technologies
by helping them to share and collaboratively build design knowledge. The Design Principles Database (DPD) is intended to be
built and used by this community to provide an infrastructure for participants to publish, connect, discuss and review design
ideas, and to use these ideas to create new designs. The potential of the DPD to serve as a collaborative knowledge-building
endeavor is illustrated by analysis of a CSCL study focused on peer-evaluation. The analysis demonstrates how the DPD was
used by the researchers of the peer-evaluation study in three phases. In the first phase, design principles were articulated
based on a literature review and contributed to the DPD. In the second phase, a peer-evaluation activity was designed based
on these principles, and was enacted and revised in a three-iteration study. In the third phase, lessons learned through these
iterations were fed back to the DPD. The analysis indicates that such processes can contribute to collaborative development
of design knowledge in a community of the learning sciences. Readers of ijCSCL are invited to take part in this endeavor and
share their design knowledge with the community. 相似文献
42.
Control of Polymorph Selection in Amorphous Calcium Carbonate Crystallization by Poly(Aspartic Acid): Two Different Mechanisms 下载免费PDF全文
Zhaoyong Zou Luca Bertinetti Yael Politi Peter Fratzl Wouter J. E. M. Habraken 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(21)
Poly(aspartic acid) (pAsp) is known to stabilize amorphous calcium carbonate (ACC) and affect its crystallization pathways. However, little is known about the mechanisms behind these phenomena. Here it is shown that ACC is stabilized by pAsp molecules in the solution rather than by the amount of pAsp incorporated into the ACC bulk, and that the effect of pAsp on the polymorph selection is entirely different at low and high concentration of pAsp. At low concentrations, pAsp is more effective in inhibiting the nucleation and growth of vaterite than calcite. At high concentrations, when calcite formation is prevented, the crystallization of vaterite proceeds via a pseudomorphic transformation of ACC nanospheres, where vaterite nucleates on the surface of ACC nanospheres and grows by a local transformation of the bulk ACC phase. These results shed some light on the function of pAsp during an ACC‐mediated biomineralization process and provide an explanation for the presence of metastable vaterite at conditions where calcite is thermodynamically favored. 相似文献
43.
Development of a sweet pepper harvesting robot 总被引:3,自引:0,他引:3
Boaz Arad Jos Balendonck Ruud Barth Ohad Ben‐Shahar Yael Edan Thomas Hellstrm Jochen Hemming Polina Kurtser Ola Ringdahl Toon Tielen Bart van Tuijl 《野外机器人技术杂志》2020,37(6):1027-1039
This paper presents the development, testing and validation of SWEEPER, a robot for harvesting sweet pepper fruit in greenhouses. The robotic system includes a six degrees of freedom industrial arm equipped with a specially designed end effector, RGB‐D camera, high‐end computer with graphics processing unit, programmable logic controllers, other electronic equipment, and a small container to store harvested fruit. All is mounted on a cart that autonomously drives on pipe rails and concrete floor in the end‐user environment. The overall operation of the harvesting robot is described along with details of the algorithms for fruit detection and localization, grasp pose estimation, and motion control. The main contributions of this paper are the integrated system design and its validation and extensive field testing in a commercial greenhouse for different varieties and growing conditions. A total of 262 fruits were involved in a 4‐week long testing period. The average cycle time to harvest a fruit was 24 s. Logistics took approximately 50% of this time (7.8 s for discharge of fruit and 4.7 s for platform movements). Laboratory experiments have proven that the cycle time can be reduced to 15 s by running the robot manipulator at a higher speed. The harvest success rates were 61% for the best fit crop conditions and 18% in current crop conditions. This reveals the importance of finding the best fit crop conditions and crop varieties for successful robotic harvesting. The SWEEPER robot is the first sweet pepper harvesting robot to demonstrate this kind of performance in a commercial greenhouse. 相似文献
44.
Maryam Tadayon Osnat Younes‐Metzler Yaniv Shelef Paul Zaslansky Alon Rechels Alex Berner Emil Zolotoyabko Friedrich G. Barth Peter Fratzl Benny Bar‐On Yael Politi 《Advanced functional materials》2020,30(32)
In the absence of minerals as stiffening agents, insects and spiders often use metal‐ion cross‐linking of protein matrices in their fully organic load‐bearing “tools.” In this comparative study, the hierarchical fiber architecture, elemental distribution, and the micromechanical properties of the manganese‐ and calcium‐rich cuticle of the claws of the spider Cupiennius salei, and the Zn‐rich cuticle of the cheliceral fangs of the same animal are analyzed. By correlating experimental results to finite element analysis, functional microstructural and compositional adaptations are inferred leading to remarkable damage resilience and abrasion tolerance, respectively. The results further reveal that the incorporation of both zinc and manganese/calcium correlates well with increased biomaterial's stiffness and hardness. However, the abrasion‐resistance of the claw material cross‐linked by incorporation of Mn/Ca‐ions surpasses that of many other non‐mineralized biological counterparts and is comparable to that of the fang with more than triple Zn content. These biomaterial‐adaptation paradigms for enhanced wear‐resistance may serve as novel design principles for advanced, high‐performance, functional surfaces, and graded materials. 相似文献
45.
Yael Abraham Carmen Tamburu Eugenia Klein John W. C. Dunlop Peter Fratzl Uri Raviv Rivka Elbaum 《Journal of the Royal Society Interface》2012,9(69):640-647
The sessile nature of plants demands the development of seed-dispersal mechanisms to establish new growing loci. Dispersal strategies of many species involve drying of the dispersal unit, which induces directed contraction and movement based on changing environmental humidity. The majority of researched hygroscopic dispersal mechanisms are based on a bilayered structure. Here, we investigate the motility of the stork''s bill (Erodium) seeds that relies on the tightening and loosening of a helical awn to propel itself across the surface into a safe germination place. We show that this movement is based on a specialized single layer consisting of a mechanically uniform tissue. A cell wall structure with cellulose microfibrils arranged in an unusually tilted helix causes each cell to spiral. These cells generate a macroscopic coil by spiralling collectively. A simple model made from a thread embedded in an isotropic foam matrix shows that this cellulose arrangement is indeed sufficient to induce the spiralling of the cells. 相似文献
46.
Biologically active complexes such as ribosomes and bacteriophages are formed through the self-assembly of proteins and nucleic acids. Recapitulating these biological self-assembly processes in a cell-free environment offers a way to develop synthetic biodevices. To visualize and understand the assembly process, a platform is required that enables simultaneous synthesis, assembly and imaging at the nanoscale. Here, we show that a silicon dioxide grid, used to support samples in transmission electron microscopy, can be modified into a biochip to combine in situ protein synthesis, assembly and imaging. Light is used to pattern the biochip surface with genes that encode specific proteins, and antibody traps that bind and assemble the nascent proteins. Using transmission electron microscopy imaging we show that protein nanotubes synthesized on the biochip surface in the presence of antibody traps efficiently assembled on these traps, but pre-assembled nanotubes were not effectively captured. Moreover, synthesis of green fluorescent protein from its immobilized gene generated a gradient of captured proteins decreasing in concentration away from the gene source. This biochip could be used to create spatial patterns of proteins assembled on surfaces. 相似文献
47.
Pyrene removal by polycation-montmorillonite (MMT) composites and granulated activated carbon (GAC) in the presence of humic acid (HA) was examined. Pyrene, HA, and sorbent interactions were characterized by FTIR, fluorescence and zeta measurements, adsorption, and column filtration experiments. Pyrene binding coefficients to the macromolecules were in the order of PVPcoS (poly-4-vinylpiridine-co-styrene) > HA > PDADMAC (poly diallyl-dimethyl-ammonium-chloride), correlating to pyrene-macromolecules compatibility. Electrostatic interactions explained the high adsorption of HA to both composites (~100%), whereas HA adsorption by GAC was low. Pyrene removal by the composites, unlike GAC, was enhanced in the presence of HA; removal by PDADMAC-MMT increased from ~50 (k(d) = 2.2 × 10(3) kg/L) to ~70% (k(d) = 2.4 × 10(3) kg/L) in the presence of HA. This improvement was attributed to the adsorption of pyrene-HA complexes. PVPcoS-MMT was most efficient in removing pyrene (k(d) = 1.1 × 10(4) kg/L, >95% removal) which was explained in terms of specific π donor-π acceptor interactions. Pyrene uptake by column filters of GAC reached ~50% and decreased to ~30% in the presence of HA. Pyrene removal by the PVPcoS-MMT filter was significantly higher (100-85% removal), exhibiting only a small decrease in the presence of HA. The utilization of HA as an enhancing agent in pollutant removal is novel and of major importance in water treatment. 相似文献
48.
Sara R. Jaeger Jeremy F. McRae Yael Salzman Liam Williams Richard D. Newcomb 《Food quality and preference》2010,21(1):121-131
Odour perception is controlled by environmental and genetic influences. Most people can discriminate over 10,000 different odours, but the molecular basis of this ability is poorly understood. Little is known about which odorant receptors (ORs) detect what odour compounds, and additional research is required to gain knowledge of why detection thresholds for some odorants vary 1000-fold, or more, across people. The primary purpose of this paper is to describe a research strategy for investigating the genetic basis of human odour perception. Background information on human olfaction, human genetics and the associated research approaches is presented. This is followed by a case study on cis-3-hexen-1-ol, a compound which contributes to the ‘green leaf’ odour (and flavour) in fruit, vegetables and wine. Odour detection threshold data for 48 participants were obtained using the rating R-index methodology. The ability to perceive cis-3-hexen-1-ol odour was tested for association with genetic variability on a genome-wide scale by microarray probe genotyping. A group of significant SNPs on chromosome 6 around the SNP rs9295791 was identified and these localise with a cluster of OR genes which could potentially be involved in perception of cis-3-hexen-1-ol. Further steps required to identify genes and alleles that encode the different ability to perceive cis-3-hexen-1-ol are outlined. 相似文献
49.
Daniel S Moran Yuval Heled Yael Arbel Eran Israeli Aharon S Finestone Rachel K Evans Ran Yanovich 《Journal of the International Society of Sports Nutrition》2012,9(1):1-7
Background
We examined the effect of four weeks of ??-alanine supplementation on isometric endurance of the knee extensors at 45% maximal voluntary isometric contraction (MVIC).Methods
Thirteen males (age 23?±?6 y; height 1.80?±?0.05?m; body mass 81.0?±?10.5?kg), matched for pre-supplementation isometric endurance, were allocated to either a placebo (n?=?6) or ??-alanine (n?=?7; 6.4?g·d-1 over 4?weeks) supplementation group. Participants completed an isometric knee extension test (IKET) to fatigue, at an intensity of 45% MVIC, before and after supplementation. In addition, two habituation tests were completed in the week prior to the pre-supplementation test and a further practice test was completed in the week prior to the post-supplementation test. MVIC force, IKET hold-time, and impulse generated were recorded.Results
IKET hold-time increased by 9.7?±?9.4?s (13.2%) and impulse by 3.7?±?1.3 kN·s-1 (13.9%) following ??-alanine supplementation. These changes were significantly greater than those in the placebo group (IKET: t (11)?=?2.9, p ??0.05; impulse: t (11)?=?3.1, p????0.05). There were no significant changes in MVIC force in either group.Conclusion
Four weeks of ??-alanine supplementation at 6.4?g·d-1 improved endurance capacity of the knee extensors at 45% MVIC, which most likely results from improved pH regulation within the muscle cell as a result of elevated muscle carnosine levels. 相似文献50.
Wearable computers and PDA's are physically close to, or are in contact with, the user during most of the day. This proximity would seemingly limit the amount of heat such a device may generate, conflicting with user demands for increasing processor speeds and wireless capabilities. However, this paper explores significantly increasing the heat dissipation capability per unit surface area of a mobile computer by thermally coupling it to the user. In particular, a heat dissipation model of a forearmmounted wearable computer is developed, and the model is verified experimentally. In the process, this paper also provides tools and novel suggestions for heat dissipation that may influence the design of a wearable computer. 相似文献