Persistent left superior vena cava: Two case reports and a review from nephrologists’ perspective

Thoracic venous anomalies without congenital heart anomalies are present in minority of the population, but they are frequent enough to be encountered while placing hemodialysis catheters through the jugular or subclavian veins. Persistent left superior vena cava is the most commonly seen anomaly and it is rarely noticed before the observation of an unusual course of hemodialysis catheter or guidewire on chest X‐ray. We present two patients with previously unspotted persistent left superior vena cava and uncomplicated hemodialysis catheter insertions through the internal jugular veins with good catheter functions. Review of the relevant literature from a nephrologists’ perspective with technical aspects is provided.     

The reform in the Turkish natural gas market: A critical evaluation

Turkey is in a strategically advantageous position in terms of its natural gas market. Being in the middle of Europe and energy-rich countries of Central Asia, it can be an energy corridor between these two regions. It can import gas from a number of countries and diversify its sources. This situation may also provide motivation for a competitive gas market. The recent reform in the market, which began in 2001, was an attempt to strengthen the natural gas market to this end. However, the reform has not worked out as expected so far. This article discusses recent restructuring efforts in the Turkish natural gas market. We focus on the legal structure and economic consequences of the legal change within the international economic relations. After presenting a detailed discussion of the legal framework, we draw attention to the problems of the industry and difficulties in the transition to a more competitive market structure. In the end, we touch upon some regulatory issues and potential conflicts.     

25th Anniversary Article: High‐Mobility Hole and Electron Transport Conjugated Polymers: How Structure Defines Function

The structural organization of three different families of semicrystalline π‐conjugated polymers is reported (poly(3‐hexylthiophene) (P3HT), poly[2,6‐(4,4‐bis‐alkyl‐4H‐cyclopenta‐[2,1‐b;3,4‐b0]‐dithiophene)‐alt‐4,7‐(2,1,3‐benzothiadiazole)](cyclopentadithiophene‐benzothiadiazole) (CDT‐BTZ) and poly(N,N"‐bis‐2‐octyldodecylnaphtalene‐1,4,5,8‐bis‐dicarboximide‐2,6‐diyl‐alt‐5,5–2,2‐bithiophene (P(NDI2OD‐T2))). These have triggered significant interest for their remarkable charge‐transport properties. By performing molecular mechanics/dynamics simulations with carefully re‐parameterized force fields, it is illustrated in particular how the supramolecular organization of these conjugated polymers is driven by an interplay between the length and nature of the conjugated monomer unit and the packing of their alkyl side chains, and to what extent it impacts the charge‐carrier mobility, as monitored by quantum‐chemical calculations of the intermolecular hopping transfer integrals. This Progress Report is concluded by providing generic guidelines for the design of materials with enhanced degrees of supramolecular organization.     

Matrix-geometric solutions of M/G/1-type Markov chains: a unifyinggeneralized state-space approach

We present an algorithmic approach to find the stationary probability distribution of M/G/1-type Markov chains which arise frequently in performance analysis of computer and communication networks. The approach unifies finite- and infinite-level Markov chains of this type through a generalized state-space representation for the probability generating function of the stationary solution. When the underlying probability generating matrices are rational, the solution vector for level k, x_k, is shown to be in the matrix-geometric form x_k+1=gF^kH, k⩾0, for the infinite-level case, whereas it takes the modified form x_k+1=g₁F^k₁H₁+g ₂F^K-k-1₂H₂, 0⩽k⩽K, for the finite-level case. The matrix parameters in the above two expressions can be obtained by decomposing the generalized system into forward and backward subsystems, or, equivalently, by finding bases for certain generalized invariant subspaces of a regular pencil λE-A. We note that the computation of such bases can efficiently be carried out using advanced numerical linear algebra techniques including matrix-sign function iterations with quadratic convergence rates or ordered generalized Schur decomposition. The simplicity of the matrix-geometric form of the solution allows one to obtain various performance measures of interest easily, e.g., overflow probabilities and the moments of the level distribution, which is a significant advantage over conventional recursive methods     

Digital Image Analysis to Determine Pore Opening Size Distribution of Nonwoven Geotextiles

The filtration performance of a geotextile is controlled by its pore opening size distribution (PSD). Current methods for determining PSD are mostly indirect and contain inherent disadvantages. Recent technological advancements in image analysis offer great potential for a more accurate and direct way of determining the PSD of nonwoven geotextiles. A new and accurate method of image analysis for PSD determination of nonwoven geotextiles is presented in this paper. The image analysis method was developed using various mathematical morphology algorithms to provide a complete PSD curve for each geotextile. The two characteristic pore opening sizes, O95 and O50, were determined from image analysis and were compared to the results from laboratory tests, analytical equations, as well as manufacturer’s reported apparent opening sizes (AOS). The image-based O95 pore opening size of various geotextiles was comparable to the manufacturer’s reported AOS as well as to those determined from the laboratory dry sieving test. However, the measured O50 pore opening size was lower than the one determined using the analytical equations developed by two previous researchers. Overall, the image analysis method presented provides a unique and accurate method that can measure fiber thickness and pore opening sizes in a cross-sectional image of a woven geotextile.     

TELPACK: an advanced teletraffic analysis package

The performance evaluation of computer and communication networks gives rise to teletraffic problems of potentially large dimensionality. We summarize a unifying system theoretic approach to efficient solution of a diversity of such problems, and introduce TELPACK, a publicly available software that implements this approach     

Macroporous poly(N-isopropylacrylamide) networks

Summary Effects of the gel preparation temperature T _prep and the initial monomer concentration c on the swelling and the porosity properties of poly(N-isopropylacrylamide) (PNIPA) networks are described. PNIPA networks were prepared by free-radical crosslinking copolymerization of N-isopropylacrylamide and N,N'-methylene(bis)acrylamide (BAAm) in aqueous solutions. The crosslinker (BAAm) concentration in the initial monomer mixture was kept constant at 30 wt %. It was shown that macroporous PNIPA networks with a stable porous structure can be prepared at T _prep = 22.5°C and at an initial monomer concentration c > 5 w/v %. The PNIPA networks contain pores of about 0.1 μm in radius, corresponding to the interstices between the microspheres. The experimental data also show collapse of the porous structure in PNIPA networks formed at higher temperatures. Received: 30 January 2002 / Revised version: 16 May 2002 / Accepted: 1 June 2002     

Swelling and elasticity of poly (N‐isopropylacrylamide‐co‐4‐vinyl benzene sulfonic acid sodium salt) hydrogels

The mechanical properties and the swelling behavior of hydrogels based on N‐isopropylacrylamide (NIPA) and 4‐vinylbenzenesulfonic acid sodium salt (styrene sulfonate, SSA) monomers were investigated. The mole fraction of SSA in the comonomer feed varied between 0 and 1, whereas the crosslinker ratio was fixed at 1/85. Both the swelling and the elasticity data of the hydrogels swollen in water show that they are in the non‐Gaussian regime. The exponents found for the charge density dependence of the equilibrium swelling ratio as well as for the volume dependence of the gel elastic modulus are in good agreement with the predicted course of the non‐Gaussian elasticity of swollen hydrogels. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 135–141, 2004     

Gallium nitride heterostructures on 3D structured silicon

We investigated GaN-based heterostructures grown on three-dimensionally patterned Si(111) substrates by metal organic vapour phase epitaxy, with the goal of fabricating well controlled high quality, defect reduced GaN-based nanoLEDs. The high aspect ratios of such pillars minimize the influence of the lattice mismatched substrate and improve the material quality. In contrast to other approaches, we employed deep etched silicon substrates to achieve a controlled pillar growth. For that a special low temperature inductively coupled plasma etching process has been developed. InGaN/GaN multi-quantum-well structures have been incorporated into the pillars. We found a pronounced dependence of the morphology of the GaN structures on the size and pitch of the pillars. Spatially resolved optical properties of the structures are analysed by cathodoluminescence.     

雾霾之后的反思

新年过后的第二个周末,浓重的雾霾已在全国多个城市肆虐,这让人们的心情变得糟糕。数据显示,截至1月13日零时,全国有33个城市的部分监测点PM2.5浓度超过300微克/立方米,个别城市出现PM2.5"爆表",比如北京的PM2.5浓度最高达到950微克/立方米。环保专家称,如此严重的空气质量污染,可以说已近人类所能承受的极限。于是,人们看到了政府有关方面发布的紧急预案,比如通知市民减少户外活动,要求学校停止户外体育锻炼,这体现了政府的责任意识。但我们是满足于制定完美的灾情应对预案,还是谋求从根本上消除灾难?