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1.
3D laser ultramicroscopy (3D LUM) is intended specially for determining the concentration and size distribution of submicron inclusions in the bulk samples of high-purity materials for visible and IR fiber optics. In this work the 3D LUM technique is shown to be able to identify the nature of individual inclusions detected. The measurement of the light scattered by an inclusion at a varied probe beam wavelength and polarization and at a varied scattered light collection angle makes it possible to determine the inclusion refractive index. The 3D LUM possibilities are illustrated by the example of studying the inclusion nature in the As2S3 glass samples prepared by the direct synthesis from elements in a quartz container at elevated temperatures. 相似文献
2.
3.
Shift in thinking to address the 21st century hunger gap 总被引:1,自引:1,他引:0
Malin Falkenmark 《Water Resources Management》2007,21(1):3-18
The present water policy debate is dominated by the 30 yr old mission to secure water supply and sanitation to all people.
The water needed to produce a nutritionally acceptable diet for one person is however 70 times as large as the amount needed
for domestic water supply. The food security dilemma is largest in arid climate regions, a situation constituting a formidable
challenge. It is suggested that an additional 5 600 km3/yr of consumptive water use will be needed to produce an adequate amount of food by 2050 – i.e almost a doubling of today’s
consumptive use of 6800 km3/yr. Past misinterpretations and conceptual deficiencies show the importance of a shift in thinking. Combining the scale of
the challenge and the time scale of the efforts to feed humanity and eradicate hunger leads to an impression of great urgency.
This urgency strengthens the call for international research both for supporting agricultural upgrading, and for much better
handling of issues of environmental sustainability. What stands out is the need of a new generation of water professionals,
able to handle complexity and able to incorporate water implications of land use and of ecosystem health in integrated water
resources management. It will for those reasons be essential and urgent to upgrade the educational system to producing this
new generation. 相似文献
4.
Near saturation steam undergoing rapid expansion, with homogeneous nucleation of water droplets, is numerically studied in a series of converging/diverging nozzles with and without shocks. To understand loss mechanisms in such flows a numerical model is presented to calculate thermodynamic losses, which is further used to quantify associated total aerodynamic losses. For the converging/diverging nozzle configuration, the model shows that the overall thermodynamic loss is only mildly influenced by increasing shock strength, while the aerodynamic losses follow that of the single phase flow, and are of the same magnitude as the thermodynamic loss only in the case of very weak shocks. The thermodynamic losses can be attributed to two influences, the homogeneous nucleation event, and the post-shock thermal oscillations in the two-phase system. The calculations rely on a new two-phase CFD model, previously reported, for non-equilibrium phase change with droplet nucleation applicable to general 3D flow configurations. 相似文献
5.
The primary purpose of this work is to review the literature about what is and is not known about using ethylene vinyl acetate (EVA0 copolymer as the encapsulant (or pottant) material in photovoltaic (PV) modules. Secondary purposes include elucidating the complexity of the encapsulation problem, providing an overview about encapsulation of PV cells and modules, providing a historical overview of the relevant research and development on EVA, summarizing performance losses reported for PV systems deployed since ca. 1981, and summarizing the general problems of polymer stability in a solar environment. We also provide a critical review of aspects of reported work for cases that we believe are important.Failure modes resolved in the early work to establish reliability of deployed modules and the purposes and properties of pottants, are summarized. Typical performance losses in large field-deployed, large-scale systems ranging from 1% to 10% per year are given quantitatively, and qualitative reports of EVA discoloration are summarized with respect to ultraviolet (UV), world-wide location and site dependence.The general stability of polymers and their desirable bulk properties for solar utilization are given. The stabilization formulation for EVA, its effectiveness, and changes in it during degradation are discussed. The degradation mechanisms for the base resin, e.g., unstabilized Elvax 150TM, and stabilized EVA are indicated for literature dating to the early 1950s, and the role played by unsaturated chromophores is indicated. The limited number of studies relating discoloration and PV cell efficiency are summarized.Observed degradation of EVA or the unstabilized base resin in the laboratory and examples used to measure the degradation are summarized in sections entitled: (1) thermally-induced degradation; (2) photodegradation and photothermal degradation of EVA in different temperature regimes; (3) photobleaching and photodegradation of the UV absorber and cross-linking agent; (4) acetic acid and metal and metal-oxide catalyzed oxidative degradation; and (5) discolaration and PV cell efficiency losses.Processing effects/influences on EVA stability are discussed in sections entitled: (1) EVA raw materials and extruded, uncured films; (2) thermal encapsulation processes; (3) effects of lamination, curing, and curing peroxide on gel content and chromophores formed; and (4) incomplete shielding of curing-generated chromophores. A summary is given for the limited number of accelerated lifetime testing efforts and examples of erroneous service lifetime predictions for EVA are discussed. The known factors that effect the discoloration rate of several EVA formulations are discussed in which the reduction in rate by using UV-absorbing superstrates is a prime example. A summary is given of what is and is not known about EVA degradation mechanisms, degradation from exposures in field-deployed modeules and/or laboratory testing, and factors that contribute to EVA stability or degradation. Finally, conclusions about using Elvax 150 in EVA formulations are summarized, and future prospects for developing the next-generation pottant for encapsulating PV modules are discussed. 相似文献
6.
7.
研究具有随机丢包的网络化多自主体系统的均方一致性问题,其中不同自主体间的通信通道具有相同的丢包情况并且均服从马尔可夫(Markov)分布。首先,利用系统变换和迭代方法,得到了系统达到均方一致的一个初等充要条件。然后,利用矩阵理论和图论知识,如果拓扑图含有有向生成树,则可以将系统的均方一致性转化成一个线性Markov跳变系统的均方稳定性,并且可以建立线性矩阵不等式形式的均方可镇定准则。最后,通过相应的仿真实例说明了所得结论的可行性。 相似文献
8.
Operational optimization of a building-level
integrated energy system considering
additional potential benefits of energy
storage
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Sai Liu Cheng Zhou Haomin Guo Qingxin Shi Tiancheng E. Song Ian Schomer Yu Liu 《电力系统保护与控制》2021,6(1):55-64
As a key component of an integrated energy system (IES), energy storage can effectively alleviate the problem of
the times between energy production and consumption. Exploiting the benefits of energy storage can improve the
competitiveness of multi-energy systems. This paper proposes a method for day-ahead operation optimization of a
building-level integrated energy system (BIES) considering additional potential benefits of energy storage. Based on
the characteristics of peak-shaving and valley-filling of energy storage, and further consideration of the changes in
the system’s load and real-time electricity price, a model of additional potential benefits of energy storage is
developed. Aiming at the lowest total operating cost, a bi-level optimal operational model for day-ahead operation
of BIES is developed. A case analysis of different dispatch strategies verifies that the addition of the proposed
battery scheduling strategy improves economic operation. The results demonstrate that the model can exploit
energy storage’s potential, further optimize the power output of BIES and reduce the economic cost. 相似文献
9.
Damping forced oscillations in power system via interline power flow controller with additional repetitive control
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With the continuous expansion of power systems and the application of power electronic equipment, forced oscillation has become one of the key problems in terms of system safety and stability. In this paper, an interline power flow controller (IPFC) is used as a power suppression carrier and its mechanism is analyzed using the linearized state-space method to improve the system damping ratio. It is shown that although the IPFC can suppress forced oscillation with well-designed parameters, its capability of improving the system damping ratio is limited. Thus, combined with the repetitive control method, an additional repetitive controller (ARC) is proposed to further dampen the forced power oscillation. The ARC control scheme is characterized by outstanding tracking performance to a system steady reference value, and the main IPFC controller with the ARC can provide higher damping, and further reduce the amplitude of oscillations to zero compared with a supplementary damping controller (SDC). Simulation results show that the IPFC with an ARC can not only greatly reduce the oscillation amplitude, but also actively output the compensation power according to the reference value of the ARC tracking system. 相似文献
10.
Nitrous oxide emission from upland crops and crop-soil systems in northeastern China 总被引:2,自引:0,他引:2
X. Chen M.L. Cabrera L. Zhang J. Wu Y. Shi W.T. Yu S.M. Shen 《Nutrient Cycling in Agroecosystems》2002,62(3):241-247
Although it is known that crops can directly emit N2O, their contribution to the total N2O emission from crop-soil systems under field conditions is not well understood. This study was conducted to study the contribution
of crops to total N2O emission from soybean-soil and maize-soil systems in northeastern China. The effects of N fertilization on N2O emission and NO
3
−
-N concentration in plants were also studied. The emission from crop-soil systems was measured with the closed chamber method,
whereas the direct emission from crops was measured with the soil surface-sealed method. The addition of fertilizer N significantly
increased the NO
3
−
-N concentration in crops and enhanced the N2O emission from crop-soil systems and from crops alone. The amount of N2O emitted directly from soybean plants accounted for 6 to 11% of the total soybean-soil emission. Similarly, the amount of
N2O emitted directly from maize plants accounted for 8.5 to 16% of the total maize-soil emission. The proportion of the applied
N lost through direct N2O emission from plants ranged from 0.19 to 0.34%, whereas the proportion of the applied N lost through N2O emission from the crop-soil system ranged from 1.1 to1.9%. These results suggest that the use of chambers that do not include
plants may lead to an underestimation of the total N2O emission from crop-soil systems.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献