基于分层神经网络的分类算法

分类知识发现是数据挖掘的一项重要内容,研究各种高性能、高速度的分类算法是数据挖掘面临的主要问题之一。大多分类问题由于各特征之间存在交互性等不确定性问题。使得一般的神经网络分类算法难以取得好的分类效果。本文通过构造一种分层神经网络的分类方法。明显地提高了分类精度。     

Subgroup-specific structural variation across 1,000 medulloblastoma genomes

Medulloblastoma, the most common malignant paediatric brain tumour, is currently treated with nonspecific cytotoxic therapies including surgery, whole-brain radiation, and aggressive chemotherapy. As medulloblastoma exhibits marked intertumoural heterogeneity, with at least four distinct molecular variants, previous attempts to identify targets for therapy have been underpowered because of small samples sizes. Here we report somatic copy number aberrations (SCNAs) in 1,087 unique medulloblastomas. SCNAs are common in medulloblastoma, and are predominantly subgroup-enriched. The most common region of focal copy number gain is a tandem duplication of SNCAIP, a gene associated with Parkinson's disease, which is exquisitely restricted to Group 4α. Recurrent translocations of PVT1, including PVT1-MYC and PVT1-NDRG1, that arise through chromothripsis are restricted to Group 3. Numerous targetable SCNAs, including recurrent events targeting TGF-β signalling in Group 3, and NF-κB signalling in Group 4, suggest future avenues for rational, targeted therapy.     

Opportunities and challenges for a sustainable energy future

Access to clean, affordable and reliable energy has been a cornerstone of the world's increasing prosperity and economic growth since the beginning of the industrial revolution. Our use of energy in the twenty-first century must also be sustainable. Solar and water-based energy generation, and engineering of microbes to produce biofuels are a few examples of the alternatives. This Perspective puts these opportunities into a larger context by relating them to a number of aspects in the transportation and electricity generation sectors. It also provides a snapshot of the current energy landscape and discusses several research and development opportunities and pathways that could lead to a prosperous, sustainable and secure energy future for the world.     

不同产地不同部位云黄连生物碱成分累积研究

 研究不同产地云黄连不同部位中盐酸小檗碱、药根碱和巴马汀3种生物碱积累量差异,旨在寻找云黄连优质产区及为非药用部位综合利用提供理论依据.在云黄连采收期,分别采集泸水、贡山、福贡、腾冲4县共10个地区的云黄连居群,测定云黄连根茎、须根和叶片3个部位的生物量,采用HPLC法测定样品不同部位中盐酸小檗碱、药根碱和巴马汀的含量.结果显示,云黄连不同部位3种生物碱含量大小依次为根茎>叶>须根.云黄连根茎中3种生物碱在不同产地间差异显著,其中贡山县后山、贡山县丙中洛神山、贡山县普拉底乡3个地区所产云黄连生物碱含量、生物量、生物积累量较高.其中贡山县普拉底乡积累量最高,其盐酸小檗碱、药根碱和巴马汀单株平均积累量分别为46.899,2.76,1.708 mg.结论:在云黄连种植生产过程中,在考察其有效成分含量的同时,还应考虑其生物量.综合比较不同产地不同部位生物量、3种生物碱含量及其积累量等因素,确定贡山县后山、贡山县丙中洛神山、贡山县普拉底乡为云黄连优质产区.非药用部位中3种生物碱的积累量较大,应收集后进行有效成分的提取,达到云黄连资源综合利用的目的.     

Phase transitions in the incoherent lattice fluctuations in YBa2Cu3O(7-delta)

The growing body of experimental evidence for the existence of complex textures of charges and spins in the high-temperature superconductors has drawn attention to the so-called 'stripe-phase' models as a possible basis for the mechanism of superconductivity in these materials. Such observations have until now been restricted to systems where the texture dynamics are slow or suppressed altogether, and do not include the important case of YBa2Cu3O(7-delta). It seems likely that the dynamic behaviour of stripes, which has been suggested to undergo several phase transitions as a function of temperature, should also be reflected in the lattice properties of the host materials, and this forms the motivation for our present experiments. Specifically, we use MeV helium ion channelling, an ultrafast real-space probe of atomic displacements (with sub-picometre resolution), to probe incoherent lattice fluctuations in YBa2Cu3O(7-delta) as a function of temperature and oxygen doping. We detect lattice fluctuations that are larger than the expected thermal vibration component, and which show anomalies characteristic of the phase transitions anticipated for a dynamic stripe phase. Comparison of our lattice results with single-particle-tunnelling and photoemission data highlights the importance of spin-charge separation phenomena in the copper oxide superconductors.     

Sap flow response of Eucaylyptus （Eucalyptus urophyila） to environmental stress in South China

Sap flow and environmental conditions were monitored at two Eucalyptus (Eucalyptus urophylla S.T.Blake) plantations at Hetou and Jijia, located in Leizhou, Zhanjiang, Guangdong Province. It was found that daily sap flux density (SFD) of Eucalyptus was closely related to daily atmospheric vapor pressure deficit (VPD) (R2 = 0.76, P = 0.01 at Hetou and R2 = 0.7021, P = 0.01 at Jijia) at both sites. No significant relationship existed between daily SFD and mean daily air temperature at both sites. Daily SFD varied with wind speed Y = -17585X3 + 15147X2 - 1250.7X + 2278.4 (R2 = 0.68; P = 0.01) at Hetou and Y = -101.67X3 - 1.65X2 - 376.4X + 1914.8 (R2 = 0.40, P = 0.05) at Jijia, where Y was daily SFD, X was daily wind speed. Experimental observations yielded the following data: (1) the critical lower and upper daily VPD threshold were 0 and 2 kPa, within which daily SFD varied from 540+/-70 L/(m2.d) to 4739+/-115 L/(m2.d) at Hetou site, from 397+/-26 L/(m2.d) to 3414+/-191 L/(m2.d) at Jijia site; (2) Diurnal SFDs at Hetou site were much higher under low relative humidity (< 30%) and slightly lower under high relative humidity (> 80%) compared with those at the Jijia site; (3) The upper and lower threshold of daily and diurnal RAD for the optimal water use of E. urophylla plantations were 18+/-2.7 and 2+/-1 MJ/(m2.d), 669 and 0 J/(cm2.h) during the observation period.     

R gene expression induced by a type-III effector triggers disease resistance in rice

Disease resistance (R) genes in plants encode products that specifically recognise incompatible pathogens and trigger a cascade of events leading to disease resistance in the host plant. R-gene specificity is dictated by both host R genes and cognate avirulence (avr) genes in pathogens. However, the basis of gene-for-gene specificity is not well understood. Here, we report the cloning of the R gene Xa27 from rice and the cognate avr gene avrXa27 from Xanthomonas oryzae pv. oryzae. Resistant and susceptible alleles of Xa27 encode identical proteins. However, expression of only the resistant allele occurs when a rice plant is challenged by bacteria harbouring avrXa27, whose product is a nuclear localized type-III effector. Induction of Xa27 occurs only in the immediate vicinity of infected tissue, whereas ectopic expression of Xa27 resulted in resistance to otherwise compatible strains of the pathogen. Thus Xa27 specificity towards incompatible pathogens involves the differential expression of the R gene in the presence of the AvrXa27 effector.     

Kinetics of transformation of aflatoxin B1 into aflatoxin M1 in lactating mouse: an ELISA analysis

A new enzyme-linked immunosorbent assay (ELISA) was used to study the kinetics of transformation of aflatoxin B1 into aflatoxin M1 in lactating mice. Aflatoxin M1 concentration in the milk samples reached a maximum 30 min after injection of aflatoxin B1 and decreased thereafter. At the maximum time, the levels of aflatoxin M1 in the samples were proportional to the dosages administered. Aflatoxin B1 was also detected in the milk samples but at a lower concentration.     

单柱式阶梯浇注系统的实验研究

本文在考虑了分配直浇道内下落流体造成的冲击当量压头基础上运用近似平均法推导出液体金属在阶梯浇注系统内流动的数学模型,并通过模拟实验测定了数学模型要求的一些参数及变化规律,得出了上层内浇道不产生反灌的条件和各层内浇道截面的最佳比例等。最后用低熔点合金验证了理论分析结果。