Nanoengineering of Flux Pinning Sites in High－Tc Superconductors

Volume pinning forces were determined for a variety of bulk high-Tc superconductors of the 123-type from magnetization measurements. By means of scaling of the pinning forces, the acting pinning mechanisms in various temperature ranges were identified. The Nd-based superconductors and some YBCO crystals exhibited a dominating pinning of the δTc-type (i.e., small, superconducting pinning sites). In contrast to this, the addition of insulating 211 particles provided pinning of the δl-type; providing effective pinning in the entire temperature range acting as a “background” pinning mechanism for the peak effect. Due to the small coherence lengths of the high-Tc compounds, effective pinning sites are defects or particles of nanometer size relative to ε^3. Integral magnetic measurements of the magnetization as a function of temperature in large applied magnetic fields (up to 7 T) revealed that practically all high-Tccompounds were spatially inhomogeneous, which could becaused by oxygen deficiency (YBCO), solid solutions of Nd/Ba (NdBCO and other light rare earth compounds), intergrowths (Bi-based superconductors), and doping by pair-breaking dopants like Zn, Pr. This implies that the superconducting sample consists of stronger and weaker superconducting areas, coupled together. In large applied fields, this coupling gets broken and the magnetization versus temperature curves revealed more than one superconducting transition. In contrast, irradiation experiments by neutrons, protons,and heavy-ions enabled the artificial introduction of very effective pinning sites into the high-Tc superconductors, thus creating a large variety of different observations using magnetic data. From all these observations, we construct a pinning diagram for bulk high-Tc superconductors explaining many featuresobserved in high-Tc samples.     

Providing QoS guarantees for self-similar traffic flows

1.INTRODUCTION Recentanalysesofvariouspacket basednetworking showthatnetworktraffichasvariabilityovermany timescales.Itsperformancedifferswithresultsof queuetheorythatisbasedonthePoissondistribu tion.Statisticalanalysesoflargetrafficdatasetshave revealedthatthestatisticalcharacteristicsofrealtraf ficmaybebestdescribedbyself similarity.Self simi larityimpliesthepresenceoflong rangedependence (LRD)inthetraffic.Thatis,thereexistnon negli giblepositivecorrelationintheburstbehaviorofthe …     

Evaluation of Surface Modification of Inorganic Filers

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近红外光谱技术鉴别海面溢油

近红外光谱技术分析速度快、效率高、成本低、重现性好,典型的无损分析;主要用于样品类别鉴定和纯度检验.近红外光谱技术结合模式识别方法,在纯品油种类的鉴别中已得到成功应用[1,2],本实验室也初步建立了纯品油近红外谱图数据库[3],但该法在实际海面溢油样品的鉴别中应用仍甚少.     

Original component of grain size index in core sediment from southwestern slope of the South China Sea and its paleoenvironmental implication

Traditional grain size analysis was basically used to discriminate sediment type based on its particle dimension for sedimentary naming[1,2] and to analyze the dynamic feature of transport medium, including water current and wind strength[3―5]. Recently, some patency advances havebeen made by using different methods to separate different grain sizes in various original composition from sediments for searching a new way of paleoenvironmental study[6―8]. Grain size analysis is even playing an …     

Predictability of Plastic Parts Behaviour Made from Rapid Manufacturing

One of the most important issues to resolve in parts manufactured from rapid manufacturing (RM) technologies is to know their behavior working under real conditions. Total quality manufacturing (TQM) is only possible if mechanical properties are well known in the design stage depending on the processing parameters. This work is mainly focused on testing of several samples made with different selective laser sintering (SLS) parameters and technologies. This procedure is the starting point to establish a basis for designing for RM and the standardization of RM testing. The experiments and the analysis of variance (ANOVA) analyzed the effects of several factors on mechanical properties. The SLS technologies were 3DSystem and EOS. The results show which factor has a large effect on the variables and the interaction between them. The conclusions are very useful for developing rules for designing (designing for RM) and creating new standard rules (ISO, AISI, and DIN) for RM materials and parts testing. The ANOVA gives a better knowledge of the effects of these factors and eliminates unimportant parameters.     

Recent temperature increase recorded in an ice core in the source region of Yangtze River

Interests on climate change in the source region of Yangtze River have been raised since it is a region with the greatest warming over the Tibetan Plateau (TP). A 70-year history of precipitation δ~(18)O has been recovered using an ice core record retrieved in a plat portion of the firn area in the Guoqu Glacier (33°34′37.8″N, 91°10′35.3″E, 5720 m a.s.l.), Mt. Geladaindong (the source region of Yangtze River), in November, 2005. By using a significant positive relationship between ice core δ~(18)O record and summer air temperature (July to September) from the nearby meteorological stations, a history of summer air temperature has been reconstructed for the last 70 years. Summer temperature was relatively low in 1940s and high in 1950s to the middle of 1960s. The lowest temperature occurred in the middle of 1970s. Temperature was low in 1980s and dramatically increased since 1990s, keeping the trend to the begin-ning of the 21st century. The warming rate recorded in the ice core with 0.5℃/10 a since 1970s is much higher that that in the central TP and the Northern Hemisphere (NH), and it becomes 1.1℃/10 a since 1990s which is also higher than these from the central TP and the NH, reflecting an accelerated warm-ing and a more sensitive response to global warming in the high elevation region.