Replacement of R22 in tube-and-shell condensers: experiments and simulations

An investigation of the change in condenser overall heat transfer coefficient when replacing R22 with one of the three mixtures R407C, R404A and R410B was made, both experimentally and theoretically. Measurements have been carried out on a full-scale test plant consisting of a horizontal shell-side condenser. According to the measurements the decrease in overall heat transfer coefficient for the non-azeotropic mixture R407C was very large, up to 70% compared to R22, while for the near-azeotropic mixture R404A the decrease was less than 15%. Simulations of the condenser were done with a comprehensive computer program, calculating the condensation heat transfer with an approximate method including a correction for mass resistance. The calculation model was not able to predict this large degradation for the non-azeotropic mixture, while the predictions agreed rather well with the measurements for the pure fluid and the near-azeotropic mixtures.     

Tension of reinforced concrete prisms. Bond properties of reinforcement bars embedded in concrete tie elements. Summary of a RILEM round-robin investigation arranged by TC 147-FMB ‘Fracture Mechanics to Anchorage and Bond’

Results are presented from a RILEM Round Robin Investigation. It deals with tension stiffening of reinforcement bars embedded in concrete tie elements. Seven groups of researchers have performed some 50 tests and analyses. Parameters discussed are: cover thickness, crack spacing, bar size, tension stiffening of naked reinforcing bars, and influence of concrete strain softening.     

Recursive input-output and state-space solutions for continuous-time linear estimation problems

A general linear least-squares estimation problem is considered. It is shown how the optimal filters for filtering and smoothing can be recursively and efficiently calculated under certain structural assumptions about the covariance functions involved. This structure is related to an index known as the displacement rank, which is a measure of non-Toeplitzness of a covariance kernel. When a state space type structure is added, it is shown how the Chandrasekhar equations for determining the gain of the Kalman-Bucy filter can be derived directly from the covariance function information; thus we are able to imbed this class of state-space problems into a general input-output framework.     

Occurrence and removal of pharmaceuticals in a municipal sewage treatment system in the south of Sweden

The occurrence and removal rate of seven pharmaceuticals (ibuprofen, naproxen, diclofenac, fluoxetine, ofloxacin, norfloxacin, ciprofloxacin), two metabolites (norfluoxetine, clofibric acid), one degradation product (4-isobutylacetophenone) and 3 estrogens (17α-ethinylestradiol, 17β-estradiol, estrone) were studied in the inlet and outlet of a tertiary sewage treatment plant (STP) in Sweden as well as between different treatment steps in the STP which includes a conventional activated sludge step. Pharmaceuticals in raw household and raw hospital sewage streams leading to the STP were as well investigated. Hydraulic retention times (HRT) of each treatment step was considered for sampling and for the calculation of the removal rates. These rates were above 90%, except for diclofenac, clofibric acid, estrone and ofloxacin. However, only diclofenac and naproxen showed significant effluent loads (> 145 mg/d/1000 inh). Diclofenac was not eliminated during the treatment and in fact even higher concentrations were found at the effluent than in the inlet of the STP. 17α-Ethinylestradiol was not detected in any of the samples. Results indicate that a STP such as the one in Kristianstad, Sweden, with a tertiary treatment is sufficient to remove significantly most of the investigated pharmaceuticals. The chemical treatment improved the removal of several pharmaceuticals especially the antibiotics, which showed step removal rates between 55 and 70%. The expected concentration levels of the pharmaceuticals in the surface water (dilution 1 to 10) close to the outlet of the STP are below the no-observed effect-concentration (NOEC). However, despite that this would imply no important effects in the aquatic environment one cannot rule out negative consequences nearby the STP because most of the NOEC values are derived from acute toxicity data. This may underestimate the real impact of pharmaceuticals in the aquatic ecosystem.     

Molecular Recognition of Two 2,4‐syn‐Functionalized (S)‐Glutamate Analogues by the Kainate Receptor GluK3 Ligand Binding Domain

The kainate receptors are the least studied subfamily of ionotropic glutamate receptors. These receptors are thought to have a neuromodulatory role and have been associated with a variety of disorders in the central nervous system. This makes kainate receptors interesting potential drug targets. Today, structures of the ligand binding domain (LBD) of the kainate receptor GluK3 are only known in complex with the endogenous agonist glutamate, the natural product kainate, and two synthetic agonists. Herein we report structures of GluK3 LBD in complex with two 2,4‐syn‐functionalized (S)‐glutamate analogues to investigate their structural potential as chemical scaffolds. Similar binding affinities at GluK3 were determined for the 2‐(methylcarbamoyl)ethyl analogue (K_i=4.0 μM ) and the 2‐(methoxycarbonyl)ethyl analogue (K_i=1.7 μM ), in agreement with the similar positioning of the compounds within the binding pocket. As the binding affinity is similar to that of glutamate, this type of Cγ substituent could be used as a scaffold for introduction of even larger substituents reaching into unexplored binding site regions to achieve subtype selectivity.     

Scalable Grid‐wide capacity allocation with the SweGrid Accounting System (SGAS)

The SweGrid Accounting System (SGAS) allocates capacity in collaborative Grid environments by coordinating enforcement of Grid‐wide usage limits as a means to offer usage guarantees and prevent overuse. SGAS employs a credit‐based allocation model where Grid capacity is granted to projects via Grid‐wide quota allowances that can be spent across the Grid resources. The resources collectively enforce these allowances in a soft, real‐time manner. SGAS is built on service‐oriented principles with a strong focus on interoperability and Web services standards. This article covers the SGAS design and implementation, which, besides addressing inherent Grid challenges (scale, security, heterogeneity, decentralization), emphasizes generality and flexibility to produce a customizable system with lightweight integration into different middleware and scheduling system combinations. We focus the discussion around the system design, a flexible allocation model, middleware integration experiences and scalability improvements via a distributed virtual banking system, and finally, an extensive set of testbed experiments. The experiments evaluate the performance of SGAS in terms of response times, request throughput, overall system scalability, and its performance impact on the Globus Toolkit 4 job submission software. We conclude that, for all practical purposes, the quota enforcement overhead incurred by SGAS on job submissions is not a limiting factor for the job‐handling capacity of the job submission software. Copyright © 2008 John Wiley & Sons, Ltd.     

抑制次同步谐振的TCSC主动阻尼控制

采用同步电压反转(synchronous voltage reversal,SVR)触发控制的可控串联补偿电容(thristor controlled series compensator,TCSC)本身不会诱发系统的次同步谐振(sub- synchronous resonance SSR),而且因为其在次同步频率范围内固有的感性阻抗特性,一直以来工程中都把TCSC作为一种缓解SSR的有效措施。虽然采用SVR触发的TCSC可缓解系统SSR的压力,但其本身却无法主动抑制SSR,该文提出一种TCSC的附加控制--主动阻尼控制,通过调节TCSC的触发,可使系统在危险振荡模式下向机组提供正值的电气阻尼,从而更好地抑制SSR。时域及频域的仿真也验证了该主动阻尼控制的有效性。     

Phenolic acids in fresh and retted jute plants (Corchorus capsularis and Corchorus olitorius)

Fresh and retted bark and stem of the Corchorus capsularis and Corchorus olitorius species of jute plant were analysed for their phenolic acid contents. Free and bound phenolic acids were identified and quantitatively determined by means of HPLC. Ferulic and p-coumaric acids were the main components, whereas p-hydroxybenzoic, protocatechuic, vanillic and caffeic acids were present in varying amounts in different jute fractions. The stem contained more free phenolic acids than the bark, and the differences were very pronounced in the retted samples. On the other hand, the bark from all four samples contained more extractable ester-bound phenolic acid than the stem. The stem of fresh C. olitorius and retted bark (fibre) of both species contained more non-extractable bound phenolic acids, in particular p-coumaric acid, than the other fractions.