Random walks on lattices with points of two colors. II. Some rigorous inequalities for symmetric random walks

We continue our investigation of a model of random walks on lattices with two kinds of points, black and white. The colors of the points are stochastic variables with a translation-invariant, but otherwise arbitrary, joint probability distribution. The steps of the random walk are independent of the colors. We are interested in the stochastic properties of the sequence of consecutive colors encountered by the walker. In this paper we first summarize and extend our earlier general results. Then, under the restriction that the random walk be symmetric, we derive a set of rigorous inequalities for the average length of the subwalk from the starting point to a first black point and of the subwalks between black points visited in succession. A remarkable difference in behavior is found between subwalks following an odd-numbered and subwalks following an evennumbered visit to a black point. The results can be applied to a trapping problem by identifying the black points with imperfect traps.     

The laplacian in regions with many small obstacles: Fluctuations around the limit operator

We consider the Laplacian _m in ³ (or in a bounded region of ³) with Dirichlet boundary conditions on the surfaces of some identical (small) neighborhoods ofm randomly distributed points, in the limit whenm goes to infinity and their linear size decreases as 1/m. We give here a stronger form of the result showing the convergence of the above operator to – C(x), whereC(x) is the limit density of electrostatic capacity of the obstacles. In particular results on the rate of convergence and on the fluctuations of _m around the limit operator are given.     

Early stage ageing effects and shallow positron traps in Al–Mg–Si alloys

Room temperature ageing, so-called natural ageing, of Al–Mg–Si alloys has a subtle but striking influence on the mechanical properties achievable by subsequent ageing at more elevated temperatures. Though strongly debated, different clustering processes are generally accepted to give rise to this effect. Using temperature-dependent positron lifetime measurements of naturally aged Al–Mg–Si alloys, it is shown that in the early stages of ageing, small clusters of alloying atoms without embedded vacancies take part in the decomposition process. These clusters serve as shallow positron traps with a binding energy of about 55(10) meV, grow in the course of natural ageing and transform to deep positron traps with binding energies well above thermal energies. Thus, results of positron annihilation spectroscopy techniques need to be interpreted carefully with respect to the microstructure of age-hardenable Al alloys. Moreover, it is shown that a simple approach to bind positron states using a three-dimensional potential well and (bulk) positron affinities cannot explain the present findings.     

超低渗致密储层成岩相特征及其对产能控制作用——以麻黄山西区块长8油组油藏为例

通过对鄂尔多斯盆地麻黄山西区块长8油组岩心观察,以及综合运用普通薄片、铸体薄片、扫描电镜以及压汞等分析化验资料,在对储层成岩作用类型和特征研究的基础上,结合孔渗条件,将该区目的层段成岩相划分为四类;再结合各类成岩相电测响应特征,建立成岩相测井识别标准,完成各单井成岩相识别;在此基础上对井间成岩相的空间展布状态进行预测,并对各类成岩相发育规律进行分析、总结。研究表明,麻黄山西区块长8油组储层划分为斑状溶蚀孔隙成岩相、碳酸盐致密胶结成岩相、黏土矿物致密胶结成岩相和致密压实成岩相四种成岩相类型。斑状溶蚀孔隙成岩相主要发育在水下分流河道微相中,物性最好,横向延展性和连通性好;黏土矿物致密胶结成岩相和碳酸盐致密胶结成岩相主要发育在水下分流河道、席状砂、河口坝微相中,物性次之;致密压实成岩相主要发育在分流间湾微相和前三角洲泥微相,物性最差,连片发育,为本区最发育的成岩相类型。体现优质成岩相主要发育在优势沉积微相中,成岩相对孔渗具有控制作用。斑状溶蚀孔隙成岩相碳酸盐致密胶结成岩相中试油日产和单位产能最高,是最有利于油气富集、开采的优势相带,为下一步重点开发的区域;黏土矿物致密胶结成岩相和致密压实成岩相虽然分布范围广,但整体产能较低,分析认为主要由于这两类相带物性较差,在生产开发中应采取酸化、压裂等方式进行储层改造来提高产能。     

鄂西渝东地区志留系小河坝组砂岩储层特征及成岩相研究

通过普通薄片、铸体薄片、扫描电镜、阴极发光、X-射线衍射以及流体包裹体等多种分析测试方法,对鄂西渝东地区小河坝组砂岩储层发育特征及成岩相进行了详细的研究。研究结果表明:研究区小河坝组砂岩类型主要为长石质石英砂岩,其成分成熟度和结构成熟度均为中等;储层物性较差,为典型的低孔渗致密砂岩储层,孔隙类型以粒间溶孔为主;成岩作用是控制该区储层物性的关键因素,其中压实和硅质胶结作用主要为破坏性成岩作用,碳酸盐胶结交代作用和溶蚀作用则为建设性成岩作用,其形成的次生孔隙极大的改善了储层物性;有机质反射率、古地温以及流体包裹体等资料显示,研究区总体处于中成岩B-晚成岩期;根据成岩作用对物性的影响以及成岩相综合分析,将本区小河坝组砂岩划分为强压实成岩相、黏土矿物胶结成岩相、石英次生加大成岩相、碳酸盐胶结交代成岩相等4种单因素成岩相,其中压实—黏土矿物胶结—碳酸盐交代胶结组合成岩相为本区小河坝砂岩储层最有利的储层相带。     

Transverse heating due to nonadiabatic propagation of cold atoms in an atomic guide

We study propagation of cold atoms along a curved atomic guide following an arbitrary trajectory in space. Transverse energy of the atomic beam increases as the beam propagates along the guide. Our model explains results of recent experiments on optical and magnetic guiding of cold atoms.     

孔隙性碳酸盐岩储层的储集性及成岩模式

以往对碳酸盐岩储层的研究,多偏重于其非均质性及低孔渗的储集条件,而对于大—中容量,中、高孔渗性的孔隙性碳酸盐岩储层的研究,则涉及较少。近年来我国海域油气勘探表明,生物礁、滩相的碳酸盐岩天然气储层具有优越的储集条件,已日益成为重要的天然气勘探领域。该文借鉴碎屑岩储层的一些研究方法,对孔隙性碳酸盐岩储层的储集特征、成岩作用及孔隙演化进行了研究,并建立了孔隙性碳酸盐岩储层的两种成岩模式。     

陷阱理论在聚丙烯电老化试验中的证实

以聚丙烯薄膜为试样，在真空中进行了工频电老化试验，在电老化过程中，同时测量试样的剩余击穿场强和表面电位增量，并在不同电压下测量了寿命时间，实验发现在广泛的电压范围内，在双对数坐标上，试样的的寿命曲线，剩余击穿场和表面电位增量都是折线，且具有相关性，证实了陷阱在介质击穿过程中的决定性作用和寿命的理论公式中幂指数随电场强度范围的不同而变化的理论预言。不管电老化电压如何，试样的击穿都发生在陷阱密度，自由