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排序方式: 共有413条查询结果,搜索用时 15 毫秒
21.
Johan Plomp Mikko Heiskanen Mika Hillukkala Tapio Heikkilä Jari Rehu Niek Lambert Victor van Acht Tom Ahola 《International Journal of Wireless Information Networks》2011,18(4):280-294
In this paper, we highlight considerations for synchronization issues in body area networks. Requirements for the synchronization
accuracy in body area networks depend on the application at hand. Synchronization may be needed for power management, sample
ordering, calculation of stimulus responses and for sensor fusion. This paper provides a theoretical exercise to help understand
the accuracy required for typical human motion sensing. It gives an overview of various synchronisation strategies used and
implemented in prototype systems. Lessons learnt from practical implementations using Bluetooth, an IEEE 802.15.4 proprietary
network and Nanonet are presented to illustrate the principles involved. The discussion provides some considerations and the
requirements for typical WBAN applications. 相似文献
22.
Katja M?enp?? Ville Ell? Jari Mauno Minna Kellom?ki Riitta Suuronen Timo Ylikomi Susanna Miettinen 《Journal of the Royal Society Interface》2010,7(42):177-188
There is currently no suitable replacement for damaged temporomandibular joint (TMJ) discs after discectomy. In the present study, we fabricated bilayer biodegradable polylactide (PLA) discs comprising a non-woven mat of poly(L/D)lactide (P(L/D)LA) 96/4 and a P(L/DL)LA 70/30 membrane plate. The PLA disc was examined in combination with adipose stem cells (ASCs) for tissue engineering of the fibrocartilaginous TMJ disc in vitro. ASCs were cultured in parallel in control and chondrogenic medium for a maximum of six weeks. Relative expression of the genes, aggrecan, type I collagen and type II collagen present in the TMJ disc extracellular matrix increased in the ASC-seeded PLA discs in the chondrogenic medium. The hypertrophic marker, type X collagen, was moderately induced. Alcian blue staining showed accumulation of sulphated glycosaminoglycans. ASC differentiation in the PLA discs was close to that observed in pellet cultures. Comparison of the mRNA levels revealed that the degree of ASC differentiation was lower than that in TMJ disc-derived cells and tissue. The pellet format supported the phenotype of the TMJ disc-derived cells under chondrogenic conditions and also enhanced their hyalinization potential, which is considered part of the TMJ disc degeneration process. Accordingly, the combination of ASCs and PLA discs has potential for the development of a tissue-engineered TMJ disc replacement. 相似文献
23.
Jari Lyytimäki 《Water and Environment Journal》2012,26(3):405-414
The mass media shape the public and policy agenda by giving prominence to certain ecosystem changes and risks, as well as by framing some policy measures as the preferred ones. Based on longitudinal analysis of the leading Finnish newspaper, this study considers the media coverage of eutrophication. The results show an increase of reporting in the late 1990s as a result of intertwined ecological and social factors – i.e. intense algal occurrences and establishment of a national communication system. The news coverage has highlighted the harmful algal blooms and health risks of algal toxins and has framed short‐term weather conditions as the key factor regulating algal occurrences. This creates a challenge for environmental management aimed at reduction in the nutrient discharges that influence the state of the environment in the long term. 相似文献
24.
Marko Lyytikäinen Taija Hämäläinen Jari Hämäläinen 《International Journal of Heat and Mass Transfer》2009,52(5-6):1132-1137
In this study, the depth-averaged flow and energy equations for plate heat exchangers are presented. The equations are derived by integrating the original 3D flow and energy equations over the height of the gap between the bottom and top plates. This approach reduces the equations from 3D to 2D but still takes into account the frictions on the surfaces and heat transfer through the plates. The depth-averaging reduces the elapsed time of CFD simulations from hours to minutes. Thus, it is very practicable modelling method in real time design work. 2D CFD simulations with depth-averaged equations are compared with full 3D models for five different corrugation angles and corrugation lengths. The simulation results show that the 2D model predicts with relatively good accuracy the profile of the pressure drop and the temperature change as a function of the corrugation angle and the function of the corrugation length. In order to get more extensive information about the significance of the different geometry parameters on the efficiency of the heat exchanger, we simulated 30 different geometries with the fast 2D model. The results suggest that the temperature change is not as sensitive for the geometrical modifications as the pressure drop. 相似文献
25.
Myllykangas T Nissinen TK Rantakokko P Martikainen PJ Vartiainen T 《Water research》2002,36(12):3045-3053
The effects of ozone, chlorine, hydrogen peroxide, and permanganate on the aquatic humic matter with different molecular size fractions and the organic acid formation in drinking water treatment were studied. Aquatic humus in lake water (LW), artificially recharged groundwater (AW), and purified artificially recharged groundwater (PW) were fractionated by high-pressure size-exclusion chromatography (HP-SEC) with UV-254nm detection before and after oxidation, a technique which resulted generally in seven peaks. The sum of the molecular size fractions (SMSF) of the LW was reduced by 47% during the bank filtration process, and the SMSF of the AW was reduced by 55% during the process in the water treatment plant. The oxidation of the AW resulted in reductions in the range of 18-35% of the SMSF; the respective range of the PW was 15-69%. However, the content of the total organic carbon (TOC) reduced only slightly, and a high correlation between the TOC and the SMSF (0.911) was observed in the whole material. The greatest decreases appeared in the highest-molecular-weight fractions while the low-molecular-weight fractions remained nearly unchanged. The total content of the six organic small-molecular-weight acids (sum of the organic acids, SOA) (formate, acetate, propionate, pyruvate, oxalate, and citrate) varied between 0.1-5.1% and 0.1-9.7% of the reduced TOC in the AW and the PW, respectively. The formation of the SOA, especially of oxalate, was the greatest after hydrogen peroxide combined with ozonation (as much as 1,100 microg/L), while chlorination resulted in the SOA of < 50 microg/L. 相似文献
26.
Repokari Leena; Punam?ki Raija-Leena; Poikkeus Piia; Tiitinen Aila; Vilska Sirpa; Unkila-Kallio Leila; Sinkkonen Jari; Almqvist Frederick; Tulppala Maija 《Canadian Metallurgical Quarterly》2006,20(4):670
In this prospective controlled study, the authors examined (a) parenting experiences among couples with successful assisted reproduction treatment (ART; n = 367) and fertile spontaneously conceiving controls (n = 371) and (b) the impact of ante- and perinatal factors and child characteristics on parenting experiences. The results show that positive mothering experiences increased more during the 1st year of parenting and were generally higher among ART mothers than control mothers. No differences were found between ART fathers and controls in their fathering experience. Unpleasant birth experiences, low birth weight, and difficulty soothing the child were associated with high levels of parental stress in the control group, but this was not so among the ART parents. Psychosocial interventions in maternal care should take into account the various meanings that couples give to the history of infertility and conception and ante- and perinatal experiences. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
27.
28.
Fantuzzi E Alves JG Ambrosi P Janzekovic H Vartiainen E 《Radiation protection dosimetry》2004,112(1):3-44
A large number of standards are available for radiation protection and individual monitoring purposes. They are published by various organisations, international and national. Moreover, the increasing policy of "Quality" applied to individual monitoring requires the implementation of standards on Quality Assurance (QA) both in technical and management aspects of a dosimetric service. Implementation of standards is not mandatory; therefore, varying degrees of implementation can be found in different European countries. However, for a number of good reasons, a degree of harmonisation within the European Union (EU) of the requirements and procedures for individual monitoring would be desirable. Harmonisation as applied to dosimetric services does not mean that they should all follow exactly the same procedures, but that they should aim to meet the same general requirements, and their results should be comparable. This article aims to compile information on the use of all standards applied within individual monitoring practices, be it on the calibration of dosemeters or on the QA procedures to be applied to the overall dose evaluation process. Both "technical standards" and "quality standards" will be discussed. A list of documents of relevance to subjects such as recommendations and requirements in the field of individual monitoring, whose application could help in the harmonisation of procedures, will also be given. As it is agreed that implementation of quality standards is a relevant framework within which harmonisation can be achieved, guidance on the implementation of quality standards in a dosimetric service is given. Accreditation and approval of dosimetric services will be of relevance in the process of harmonisation of individual monitoring within the EU. In this article, a discussion of various procedures and the meaning of both forms of recognition is also provided. Although most of the text applies to the monitoring of internal and external exposure to ionising radiation, the emphasis of this practical guidance is on monitoring for external radiation with passive dosemeters. 相似文献
29.
A new local elementary interface approximation is introduced for the modeling of wave propagation through interfaces between homogeneous media. The incident wave and the surface profile are approximated locally by a spherical wave and a spherical surface, respectively. The wave field travels through the modulated structure according to the laws of geometrical optics, being refracted by the surface and propagating to the output plane locally as a geometric spherical wave. Diffraction theory is applied to propagate the field from the output plane onwards. We provide comparisons of the method with the thin-element approximation, the local plane-wave and interface approach, and rigorous diffraction theory using a sinusoidal surface-relief grating as an example. We illustrate the power of the new method by applying it to the analysis of a diffractive beam splitter. 相似文献
30.
In this paper, we present an efficient variable neighborhood search heuristic for the capacitated vehicle routing problem. The objective is to design least cost routes for a fleet of identically capacitated vehicles to service geographically scattered customers with known demands. The variable neighborhood search procedure is used to guide a set of standard improvement heuristics. In addition, a strategy reminiscent of the guided local search metaheuristic is used to help escape local minima. The developed solution method is specifically aimed at solving very large scale real-life vehicle routing problems. To speed up the method and cut down memory usage, new implementation concepts are used. Computational experiments on 32 existing large scale benchmarks, as well as on 20 new very large scale problem instances, demonstrate that the proposed method is fast, competitive and able to find high-quality solutions for problem instances with up to 20,000 customers within reasonable CPU times. 相似文献