Two-dimensional Fourier transform of scaled Dirac delta curves

We obtain a Fourier transform scaling relation to find analytically, numerically, or experimentally the spectrum of an arbitrary scaled two-dimensional Dirac delta curve from the spectrum of the nonscaled curve. An amplitude factor is derived and given explicitly in terms of the scaling factors and the angle of the forward tangent at each point of the curve about the positive x axis. With the scaling relation we determine the spectrum of an elliptic curve by a circular geometry instead of an elliptical one. The generalization to N-dimensional Dirac delta curves is also included.     

都市理论和中国的城市化

这期《国外城市规划》的文集中收录的文章．展现了我对于都市理论探索的一个总体面貌，时间跨越了30年．从1972年首次发表的法语版《城市问题》到1996至2004年间关于流动空间和地方空间的理论著作。很显然．它们并不是一成不变的．理论在数十年间发生了变化。实际上．在早期理论中的一些基本要素与后期概念的发展是相互抵触的。或许这正是它应该呈现的样子．因为从根本上来说我是一名研究者，而不是哲学家，对我来说，理论的建构是用来理解、修正社会和空间过程的工具。在研究实践中．我对这些概念去伪存精．并发展了一些新的概念和新的理论解释来说明我所观察到的现象。     

发达资本主义的集体消费与城市矛盾

不同社会群体在生产体系中所处的地位决定了产品在他们之间的分配．这就使得社会不平等成为所有阶级社会最显著的特征；一旦我们否认了社会层级体系（the system of socialstratification．涉及生产的经济和象征性的分配）与社会阶级体系（the system of socialclasses，基于生产体系以及各阶级之间的权力关系）之间的固有联系．并且认为前者依赖于后者，那么就有必要从生产方式的阶段和社会体系的历史形成过程出发，阐明这种社会不平等的具体形态。因而，以主流阶级总是有好结局的宿命论为基础的“富人”与”穷人”永不平等的历史．便让位于消费层面上关于社会生产分化的精确分析和对于一定类型的社会关系基本逻辑的研究．而这种社会关系的体验形式则是沉重的日常生活。     

Effects of indoor drinking water handling on trihalomethanes and haloacetic acids

In this study, different tap water handling strategies were investigated to evaluate the effects on two principal chlorinated DBPs, trihalomethanes (THMs) and haloacetic acids (HAAs). Tap water samples collected in the Quebec City (Canada) distribution system on a spatio-temporal basis were subjected to diverse indoor handling scenarios: storing water in the refrigerator, boiling water followed by storage and, finally, filtering water with a point-of-use commercial pitcher also followed by storage. In the first two cases, the use of covered and uncovered pitchers was investigated separately, while in the last case, both the use of new and used filters was compared. In all cases, maximum storage time was 48h. Results demonstrated that in some cases, water handling scenarios have considerable effect, and in other cases, little or no effect. Removal of THM concentrations by simple storage was high (on average 30%) and very high by boiling and filtering with subsequent storage in the refrigerator (on average, 87% and 92%, respectively). In scenarios where water was stored in uncovered pitchers (with or without previous boiling and filtering), the THM decrease was higher for increased storage times. However, storage did not have any effect on HAAs, whereas boiling decreased levels of trichloroacetic acid (TCAA) (on average 42%) and increased levels of dichloroacetic acid (DCAA) (on average 35%), resulting in unchanged average levels of total HAAs. The use of the filtration pitcher decreased HAA levels dramatically (on average 66%). Percentages of change in chlorinated DBPs in the different scenarios varied according to initial concentrations in tap water (baseline water), that is, according to the spatio-temporal variations of these substances in the distribution system. On the basis of these results, the paper discusses implications regarding public health protection and exposure assessment for epidemiological studies.     

High-Strength and High-Fracture-Toughness Ceramics in the Al2O3/LaAl11O18 Systems

Control of microstructure in the Al₂O₃/LaAl₁₁O₁₈ system was performed. Elongated alumina grains were formed by doping with small addition of silica, and 20 vol% lanthana- luminate was formed in situ by the reaction of LaAlO₃- A1₂O₃ in an alumina matrix. Strengths of over 600 MPa and a high fracture toughness (6 MPa.m^1/2) were achieved in the material with both elongated A1₂O₃ grains and LaAl₁₁O₁₈ platelets. Generally antagonistic properties such as strength and fracture toughness have been made compatible in the same ceramic system.     

Synthesis and characterization of poly(1-sila-cis-pent-3-enes) substituted with pendant pyridinyl groups

Poly[1-methyl-1-[3-(3-pyridinyl)propyl]-1-sila-cis-pent-3-ene], poly[1-phenyl-1-[3-(3-pyridinyl)propyl)-1-sila-cis-pent-3-ene], and poly[1-phenyl-1-(4-pyridinyl)-1-sila-cis-pent-3-ene] were synthesized by the anionic ring-opening polymerization of 1-methyl-1-[3-(3-pyridinyl)propyl]-1-silacyclopent-3-ene, 1-phenyl-1-[3-(3-pyridinyl)propyl]-1-silacyclopent-3-ene, and 1-phenyl-1-(4-pyridinyl)-1-silacyclopent-3-ene, respectively. These are the first polycarbosilanes which contain heterocyclic pyridine units as side-chain substituents. These polymers were characterized by¹H,¹³C, and²⁹Si NMR as well as by IR and UV spectroscopy. The molecular weight distributions were determined by gel permeation chromatography, glass transition temperatures, by differential seanning calorimetry: (DSC) and thermal behavior, by thermogravimetric analysis. (TGA).     

Preparation and Characterization of NTC Thermistors: Nickel Manganites Doped with Lithium

Oxides of the form Ni_xMn_3-x O₄ present properties that make them useful as NTC thermistors. Nickel manganites doped with lithium were synthesized by two methods: insertion with n -BuLi and reaction of nickel-manganese formates with lithium formate. XPS and XRD studies showed that both procedures led to oxides with spinel structure, although with different cation distributions. Dilatometry established that a cationic reordering took place on manganites doped by insertion with n -BuLi during sintering. SEM mapping studies showed that a segregation on grain boundaries took place, leading to an increase in Mn content and a decrease in nickel on the particle surface. Finally, electrical studies showed the nickel manganites doped with lithium, Ni_xMn_3-x-yLi_yO₄, had similar resistivities and sensitivity indexes to nickel manganites, Ni_xMn_3-xO₄, but higher electrical stability.     

Processing Strategy for Producing Highly Anisotropic Silicon Nitride

Silicon nitride with a preferred orientation of large elongated grains was obtained by tape casting of raw powder slurry seeded with rodlike β-Si₃N₄ particles, followed by a gas pressure sintering under 1 MPa nitrogen pressure. The large elongated grains developed from seeds lay in planes parallel to the casting direction in a two-dimensional distribution. Increased fracture toughness (11.1 MPa·m^1/2) and bending strength (1100 MPa) were achieved in the direction perpendicular to the grains alignment compared to specimens with a random distribution of elongated grains. Morover, the specimens exhibited a high Weibull modulus of 46 due to the uniform distribution of large grains.     

A new approach for project control under uncertainty. Going back to the basics

In this paper we propose a new methodology for project control under uncertainty. In particular, we integrate Earned Value Methodology (EVM) with project risk analysis. The methodology helps project managers to know whether the project deviations from planned values are within the “expected” deviations derived from activity planned variability. Although the methodology is new and innovative, we only go back to the fundamentals of project simulation to generate the “universe” of possible projects, according to the assumed variability of project activities. Then we organize and gather the information in order to make the data coherent with EVM. We explain the steps to implement the methodology and we show three case studies. The methodology makes explicit that the schedule and budget resulting from traditional methods like PERT are statistically very optimistic.