22/4/2009 - Page Rank Nedir?Pagerank metodu Google tarafından, sitelerin birbirleriyle orantılı olarak önemlerini yani kısaca popüleritelerini tespit etmek için bulundu. Bu metod oluşturulurken siteler arasındaki linkler baz alınarak internetteki topoloji örneklendi. Page Rank'in ana fikri şöyledir: Eğer bir A sitesi B sitesinin linkini yayınlamışsa bunun nedeni B sayfasının A sayfası ziyaretçileri tarafından dolaşılabilecek olarak düşünülmüş olmasıdır. Bu yapıya göre A sayfası B sayfasının pagerankini yükseltmiş olacaktır. Ancak Pagerank kavramı sadece bunlarla sınırlı değildir. Aşağıda belirttiğim iki fikir de önemli başrol oynar.
Mantığı açıkladıktan sonra, bu sistemi gelin formülize edelim. Başlamadan önce açıklayalım, bu formülü Google'ın iki kurucusundan aldık. Formül şu ana kadar değişilik geçirmiştir ancak temel mantığı halen aynıdır. A 1, A 2 , ..., An B sayfasına link veren sayfalar olsun. PR(Ak)'yı da A k sayfasının pageranki olarak kabul edelim. N(Ak) ise Ak sayfasının dış sayfalara verdiği link sayısı olsun. d ise 0 ile 1 arasında değişen ve genellikle 0.85 olan bir katsayı olsun. Bu durumda PageRank'in matematiksel değeri şöyle olacaktır: PR(B) = (1-d) + d x ( PR(A1) / N(A1) + ... + PR(An) / N(An) ) Belki bu formülün hem basit hem de karmaşık olduğunu düşünebilirsiniz. Basit çünkü sadece birkaç koşula bağlı, karmaşık çünkü hesaplamak için daha önceden başka bir sitenin pagerankini hesaplamanız gerekir. Aslında bu çok basittir, tüm pagerankleri belli bir değere sabitlerseniz olur biter. Eğer her sayfaya aynı değeri verirseniz; bu değeri kaç alırsanız alın sonuç değişmeyecektir. Formülü tekrarlamaya başladığınızda sonuç bir önceki hesaplamaya bağlı olarak tekrar hesaplanacaktır. İşlem ilerledikçe pagerank değerleri yerine oturmaya başlayacak, ve bir hesaplamadan diğerine kadar hiçbir değişiklik olmayacaktır. Rastgele Yürüme ModeliPageRank değerinin hesaplanmasında formül dışında bir başka model daha vardır. Bu model de internetde dolaşan birinin simüle edilmesiyle, rastgele linkler arasında dolaşılmasıdır. Bir düşünün, birisi bir sayfada dolaşırken bir link dikkatini çeker ve ona tıklayarak o sayfada dolaşmaya başlar. Böylece giderek birçok sayfa dolaşılır . Page Rank değeri bir ziyaretçinin sayfada harcadığı süreye de bağlı olabilir. Eğer gidilen bir sayfada geriye dönüş için de link bulunuyorsa olasılık daha da artacaktır. Bu da formülün ikinci terimine denk gelmektedir. İlk terim ise sayfadan çıkılmadan içeri de ne kadar dolaşılabileceği olasılığını modeller. Formülde ifade ettiğmiz d sembolü aslında budur. PageRank HesaplanmasıPageRank'in matematiksel formülünü elde ettikten sonra, bunları hesaplamak için şu değişkenlere ihtiyacımız vardır: B sayfasının PageRank'i üç faktöre bağlıdır:
Öyleyse B sayfasının pagerank değeri şunlarla alakalı değildir:
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22/4/2009 - Teknolojinin artıları ve eksileri
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16/4/2009 - IBM Cognos 8 ControllerIBM Cognos 8 Controller provides Finance organizations with unmatched capabilities for managing the close, consolidation, and reporting process. An automated, menu-driven application that is owned and managed by Finance, IBM Cognos 8 Controller can consolidate diverse ledgers representing thousands of operating units and accounts into a common chart-of-accounts structure.IBM Cognos 8 Controller reduces close cycle times and gives you the transparency that is essential for sustained compliance with Sarbanes-Oxley and IFRS. It supports local, regional, or global requirements, and enables you to adapt to business and regulatory changes in real time. What IBM Cognos 8 Controller Offers to Finance Leaders IBM Cognos 8 Controller offers critical benefits for the key members of your finance team—and for the CIO, who needs to ensure compatibility with existing IT investments: * For Corporate Controllers: IBM Cognos 8 Controller enables the corporate controller to automate the entire close process, from data collection to financial consolidation to output. Close cycle times are reduced while data integrity is assured. * For the CFO: IBM Cognos 8 Controller reduces risk and provides the CFO with an enterprise view of key financial ratios and results. Greater visibility improves strategic decision making across the organization, while the high quality of financial results eases external reporting and compliance. * For the CIO: IBM Cognos 8 Controller allows the CIO to leverage current IT investments while ensuring that centralized systems meet the demand for secure and reliable data. And it offers the opportunity for performance management standardization from a single vendor, with enterprise planning and business intelligence across a single architecture and platform. IBM Cognos 8 Controller is the only solution that includes more than 200 pre-configured, standard reports to satisfy the demands of management and regulators. All the reports required at key stages of the close process are available automatically—no custom report creation is needed. In addition, IBM Cognos 8 Controller is seamlessly integrated with IBM Cognos 8 Planning and IBM Cognos 8 Business Intelligence. It enables performance management to be integrated at the data, security and process level—all at a low total cost of ownership. Learn more: * Features and Benefits of IBM Cognos 8 Controller * Read the IBM Cognos 8 Controller Fact Sheet * Read about the 200+ Standard Reports available with IBM Cognos 8 Controller * Visit the Compliance Resource Center * Learn best practices thru IBM Cognos 8 Controller Performance BluePrints |
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11/4/2009 - High Flow Range Mass Coriolis Flow Meter
ACCURATE AND RELIABLE This meter has the ability to maintain high accuracy, despite changing viscosity conditions, with accuracy of +0.25% of reading. EASY CLEANING The ACM series has smooth stainless steel tubes and no moving parts, and is therefore very easy to flush and clean. MULTI-TASKING The ACM series of mass coriolis flow meters measure flow, density and temperature. MATERIAL COMPATIBILITY Because of the meter's 316 stainless steel flow tubes, the ACM series can measure a wide range of materials. VARIETY OF ELECTRONICS Electronics available for the ACM series include a local, hazardous rated display and a remote, panel-mount digital display.
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8/4/2009 - VSEPWhile membrane-based separations of liquids from solids have enjoyed increasing popularity over the last 20 years, the technology has an inherent Achilles heel that affects all membrane devices: fouling. This long-term loss in throughput capacity is due primarily to the formation of a boundary layer that builds up naturally on the membranes surface during the filtration process. In addition to cutting down on the flux performance of the membrane, this boundary or gel layer acts as a secondary membrane reducing the native design selectivity of the membrane in use. This inability to handle the buildup of solids has also limited the use of membranes to low-solids feed streams.
To help minimize this boundary layer buildup, membrane designers have used a method known as tangential-flow or cross-flow filtration that relies on high velocity fluid flow pumped across the membranes surface as a means of reducing the boundary layer effect. (See Figure 1) In cross-flow designs, it is not economic to create high shear forces, thus limiting the use of cross-flow to low-viscosity (watery) fluids. In addition, increased cross-flow velocities result in a significant pressure drop from the inlet (high pressure) to the outlet (lower pressure) end of the device, which leads to premature fouling of the membrane that creeps up the device until permeate rates drop to unacceptably low levels.
Instead of producing high cross flow, an alternative method for producing intense shear waves on the face of a membrane is developed. The technique is called Vibratory Shear Enhanced Processing (VSEP). In a VSEP System, the feed slurry remains nearly stationary, moving in a leisurely, meandering flow between parallel membrane leaf elements. Shear cleaning action is created by vigorously vibrating the leaf elements in a direction tangent to the faces of the membranes. The shear waves produced by the membrane's vibration cause solids and foulants to be lifted off the membrane surface and remixed with the bulk material flowing through the membrane stack. This high shear processing exposes the membrane pores for maximum throughput that is typically between 3 and 10 times the throughput of conventional cross-flow systems. (See Figure 2, above) The oscillation produces a shear at the membrane surface of about 150,000 inverse seconds (equivalent to over 200 G's of force), which is approximately 10 times the shear rate of the best conventional cross-flow systems. More importantly, the shear in a VSEP System is focused at the membrane surface where it is cost effective and most useful in preventing fouling, while the bulk fluid between the membrane disks moves very little.
The disc pack hold up volume of a system with 1,400 ft2 (130 sq. meters) of membrane area, is less than 50 gallons (189 liters). As a result, product recovery in batch processes can be extremely high. At startup, the VSEP system is fed with a slurry and the concentrate valve is closed. Permeate is produced and suspended solids in the feed are collected inside the VSEP filter pack. After a programmed time interval, valve on concentrate line is opened to release the accumulated concentrated solids. The valve is then closed to allow the concentration of additional feed material. This cycle repeats indefinitely.
The operating pressure is created by the feed pump. VSEP machines can routinely operate at pressures as high as 500 psig (35 bar). While higher pressures often produce increased permeate flow rates, they also use more energy. Therefore, an operating pressure is used that optimizes the balance between flow rates and energy consumption. The vibration amplitude and corresponding shear rate can also be varied which directly affects filtration rates. Shearing is produced by the torsion oscillation of the filter stack. Typically the stack oscillates with an amplitude of 3/4 to 1 1/4 inches (1.9 to 3.2 cm) peak to peak displacement at the rim of the stack. The oscillation frequency is approximately 53 Hz and produces a shear intensity of about 150,000 inverse seconds. Feed residence time is set by the frequency of the opening and closing of the exit valve (valve one). The solids level in the feed increases as the feed material remains in the machine. Occasionally, a cleaner is added to the membrane stack and continued oscillation helps clean the membrane in minutes. This process can be automated and only consumes approximately 50 gallons (189 liters) of cleaning solution thus reducing cleaner disposal problems inherent with other membrane systems. Control system VSEP systems are supplied with internationally branded Programmable Logic Controllers. All components are fully contained in a NEMA 4 rated enclosure. Various levels of control sophistication are available depending on the complexity of the application. For polishing or low solids applications simple controls having minimal outputs and inputs are provided. For high solids applications controls with more features are used to insure trouble free operation. The VSEP controller typically sets solids levels by actuating the exit valve based on operating parameters such as pressure or flow rate. Other control options available include automatic clean-in-place, automatic flush, automatic shut down, full alarm features with digital diagnostic displays, remote diagnostics and monitoring, and many others. Dunwell engineers have spent years perfecting VSEP controls to maximize reliability and to minimize operator intervention.
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