Scalability and performance of an agent‐based network management middleware

Rapid growth of computer network sizes and uses necessitate analysis of network application middleware in terms of its scalability as well as performance. In this paper we analyze a distributed network management middleware based on agents that can be dispatched to locations where they can execute close to the managed nodes. The described middleware operates between the network protocol layer and the application layer and uses standard TCP protocol and SNMP probes to interface the network. By aggregating requests from many users into a single agent, our system allows multiple managers to probe problem areas with minimal management traffic overhead. We discuss and quantify the benefits of the described middleware by implementing real‐time network managers using our system. The main result of this paper is a comparison of scalability and efficiency of our agent‐based management middleware and traditional SNMP‐based data collection. To this end, we measured traffic in both real and simulated networks. In the latter case, we designed, used and described here a method of separating simulated application flow into separate subflows to simplify design of simulations. Copyright © 2004 John Wiley & Sons, Ltd.     

PPTC元件为电子设备提供价廉可靠的端口保护

高分子正温度系数(PPTC)电路保护元件主要是对有破坏性的电流过载冲击进行保护,通常称之为“可恢复式保险丝”。PPTC元件被广泛应用于计算机和外部设备的电路保护,以确保在发生意外连接中断或短路的情况下,不会导致永久性且代价巨大的内部和外部电路受损。这种元件已经成为了I/O(输入/输出)保护的工业标准,广泛应用于USB、IEEE1394、CPU和VGA等方面。在USB和IEEE1394的规范说明中都特别提及这种元件。在计算机工业中,应用PPTC元件较其它类似技术,如一次性保险丝具有更多优点。最主要的是PPTC元件是可恢复式的,减少了由于保…     

Alkaline isomerization of methyl crepenynate

Methyl crepenynate (methyl-cis-9-octadecen-12-ynoate) is readily isomerized by potassium hydroxide in ethylene glycol to an 8,10,12-octadecatrienoic acid in good yield. A reaction carried out at 120C for 1 hr in 10% base is sufficient to convert the nonconjugated enyne system completely to conjugated triene systems. Presented at AOCS Meeting in New Orleans, 1964. A laboratory of the No. Utiliz. Res. & Der. Div., ARS, USDA.     

Oxygenated fatty acids of oil from sunflower seeds after prolonged storage

Chemical analysis of a number of sunflower (Helianthus annuus) seed oil samples revealed a low and variable percentage of hydrogen bromide-reactive material. To characterize the compounds responsible for this reactivity, oil was extracted from selected introductions from Uruguay, Turkey, and Yugoslavia that had been subjected to prolonged storage. Two epoxy fatty acids and two conjugated dienolic acids were isolated from the methyl esters derived from these sunflower seed oils by using a combination of column chromatography and countercurrent distribution. The epoxy acids arecis-9,10-epoxystearic acid (0.5%) andcis-9,10-epoxy-cis-12-octadecenoic (coronaric) acid (2.2%). Characterization of the dienols revealed that they are 9-hydroxy-trans-10,cis-12-octadecadienoic acid (1.2%) and 13-hydroxy-cis-9,trans-11-octadecadienoic acid (1.3%). Fresher seed of some of these introductions contained less of the oxygenated components. Oil from recently produced seed of selected high-oil Russian sunflower varieties, including some currently grown in the United States, contained no more than trace amounts of oxygenated acids. Though the relative contributions of genetic and environmental factors toward genesis of oxygenated acids are not established, increase of those acids in some sunflower lines as a result of storage has been demonstrated. Presented at the AOCS-AACC Joint Meeting, Washington, D. C., April 1968. No. Utiliz. Res. Dev. Div., ARS, USDA.     

On reliability of a certain elementary safety system

The paper deals with the determination of reliability of an elementary safety system which consists of two identical elements used simultaneously (hot reserve) whereas for correct system operation is enough when one out of it is good. The operation time is so short that is assumed it is of zero length. Knowing the reliability of element, reliability of system is found.     

Functional Warsaw: A challenge from the past

This article describes the planning concept known as ‘Functional Warsaw’ (Warszawa Funkejonalna) prepared in 1934 by the architects and urban planners Jan Chmielewski and Szymon Syrkus. This planning exercise can be considered both as a most spectacular example of progressive trends in Polish urban planning thought in the inter‐war period, and as an attempt to respond to the challenge created by the widely known ‘Charter of Athens’ regarding the postulates of the functional urban region.

The article is divided into four sections. The first considers the national background in which circumstances conducive to development of urban thought in Poland created favourable conditions for the relatively early practice of regional planning. The next section deals with the international context, the influence of the foreign avant garde movement as represented in CIAM (the International Congresses of Modern Architecture). In the third section, the authors’ model of the functional urbanized region is described; some critical comments are offered. In the last section the impact of Functional Warsaw is considered against the development of spatial planning not only of Warsaw but of the country as well.     

Purification of erucic acid by low-temperature crystallization

Purification of crucic acid for laboratory use by low-temperature crystallization from aqueous acetone, ethanol, and methanol has been investigated. Two crystallizations of technical grade commercial acid (76–86%) from acetone-water (5∶1) provided products of 94–98% purity, depending on the original composition; residual impurities were primarily C₂₀ monoene and C₂₂ saturated acids. A laboratory of the Northern Utilization Research and Development Division, Agricultural Research Service, USDA.     

Cyanolipids of kusum (schleichera trijuga) seed oil

A cyanolipid, consisting of two fatty acid moieties esterified with 1-cyano-2-hydroxymethylprop-2-ene-1-ol, constitutes 58% ofSchleichera trijuga (Kusum) seed oil. No Utiliz. Res. Dev. Div., ARS, USDA.