DNS

This paper is a summary of “What DNS Is Not”, a paper written by Paul Vixie, who is an American computer scientist and internet hall of fame. His technical contributions include Domain Name System (DNS) protocol design and procedure, mechanisms to achieve operational robustness of DNS implementations, and significant contributions to open source software principles and methodology. This review is originally published in Queue vol. 7, no. 10. And it draws upon mostly about the abuses of the Domain Name Server system. The author also discusses how much of DNS misuse can be prevented, what kind of solutions might be proposed, and what potential future improvements can be aimed. The purpose of this paper summary is to give the reader a brief overview of the original paper without changing the purpose, content and meaning of the article.

The four human IgG isotypes are highly conserved in amino acid sequence, but show differential ability to activate complement (C'): IgG3 and IgGl are very active. IgG2 is active under certain conditions, and IgG4 is inactive. Although the second constant domain (C,2) is critical for C' activation, the individual amino acids that confer isotype-specific activity have not been identified. We have generated a series of mutants between IgG2 and IgG3, resulting in the exchange of the four N-terminal and six C-terminal polymorphic residues within C"2. Mutants containing the N-terminus of the C,2 of IgG3 were as effective as wildtype IgG3 in Clq binding, Cl activation and terminal complex (MAC) formation, but had reduced ability to effect C/-mediated lysis. IgG2 and mutants containing the N-terminal portion of the CH2 of IgG2 were reduced compared to IgG3 in activating Cl, binding Clq and inducing assembly of the MAC, and were inactive in mediating lysis of target cells. Thus, the amino acid sequence differences in the N-terminus of C,,2 play a critical role in determining the relative abilities of IgG2 and IgG3 to bind Clq and activate the C' cascade although additional residues of C,2 must be involved in mediating optimal target cells lysis. The sequence of the N-terminus of C,2 was less critical in determining C4 and C3 binding. Characterization of domain exchange mutants suggests that intermediate steps may be partly dependent on domains other than C,2. IgGs that do not direct target cell lysis nevertheless activate intermediate steps in the pathway, which may contribute to immune complex-associated disorders. pi;, 1997 Elsevier Science Ltd. All rights reserved.

The initiation of turbulent non-premixed combustion of gaseous fuels through autoignition and through spark ignition is reviewed, motivated by the increasing relevance of these phenomena for new combustion technologies. The fundamentals of the associated turbulent-chemistry interactions are emphasized. Background information from corresponding laminar flow problems, relevant turbulent combustion modelling approaches, and the ignition of turbulent sprays are included. For both autoignition and spark ignition, examination of the reaction zones in mixture fraction space is revealing. We review experimental and numerical data on the stochastic nature of the emergence of autoignition kernels and of the creation of kernels and subsequent flame establishment following spark ignition, aiming to reveal the particular facet of the turbulence causing the stochasticity. In contrast to fullyfledged turbulent combustion where the effects of turbulence on the reaction are reasonably wellestablished, at least qualitatively, here the turbulence can cause trends that are not straightforward. Autoignition occurs usually away from stoichiometry at a ''most reactive mixture fraction'', which can be approximately determined from homogeneous or laminar flow autoignition calculations, and at locations in the turbulent flow with low scalar dissipation. Such locations may be the cores of vortices. Once autoignition has occurred at a time that is mostly affected by the history of the conditional scalar dissipation, the relative magnitudes of convection, diffusion and reaction can affect the stabilisation height of flames in sprays or jets. Modelling efforts based on the Conditional Moment Closure, advanced flamelet approaches, and the transported PDF method seem suitable for capturing many, but not yet all, of the trends observed in DNS or experiment. Further experiments and DNS of realistic fuels and at conditions demonstrating chemical complexities must be performed to examine more fully the effects of scalar dissipation and its fluctuations on pre-ignition reaction zones. The statistics of the first appearance of autoignition in transient problems and its connection with the mixing field must also be studied. Ignition from a localised spark has a stochastic character that depends on the mixture fraction sampled at the spark location and duration and the local scalar dissipation. The success or not of the subsequent flame depends on the development of turbulent edge or stratified flames. Only preliminary data exist on the propagation speed of such flames and on their quenching. A lot remains to be done on turbulent edge flame propagation in unreacted and partially-reacted mixtures with inhomogeneities, turbulent flame propagation in non-uniformly dispersed droplet mists, and the transient stabilisation process of recirculating flames. The nature of the flame generation process at very short timescales, i.e. before any appreciable propagation, by sparking in inhomogeneous mixtures needs also to be examined. The development of high repetition rate diagnostics, for single-and two-phase flows, and the development of modelling approaches capturing both premixed and non-premixed reaction zones in gaseous and spray combustion are necessary.

—This work presents the numerical simulation and analysis of the turbulent flow over a two-dimensional channel with a backward-facing step. The computational simulation performed in this study is based on the Reynolds equations using a technique denominated Reynolds Average Navier-Stokes (RANS). The main objective of the present work is the comparison of different models of turbulence applied to the turbulent flow over a backward-facing step. The performance of each RANS model used will be discussed and compared with the results obtained through a direct numerical simulation present in the literature. The RANS turbulence models used are k-ω, k-ε, Shear Stress Transport k-ω (SST k-ω) and the second-order closure model called Reynolds Stress Model (RSM). The Reynolds number used in all the numerical simulations constructed in this study is equal to 9000, based on the height of the step h and the inlet velocity U b. The results are the reattachment length, the mean velocity profiles and the turbulence intensities profiles. The k-ε model obtained poor results in most of the analyzed variables in this study. Among the RANS turbulence models, the SST k-ω model presented the best results of reattachment length, mean velocity profile and contour when compared to results obtained in the literature. The RSM model found the best results of turbulence intensity profile, when compared to the models of two partial differential equations that use the Boussines hypothesis.

This paper reviews the chemical and electrochemical depositions of platinum group metals (PGMs) from aqueous solutions. With a brief introduction on the fundamental aspects of chemical/electrochemical depositions, the review describes recent advances in chemical and Abbreviations: CD, cathode current density expressed as amperes per cm 2 ; CE, cathode current efficiency; dc, direct current; DMFC, direct methanol fuel cell; DNS, dinitrosulfatoplatinate; Electroforming, deposition of thick metallic coating which is later removed from cathode substrate, used for preparing thick metallic foils, halograms, duplicating complicated structures etc.; NHE, normal hydrogen electrode; PCB, printed circuit board; PGM, platinum group metal; PEMFC, polymer electrolyte membrane fuel cell; PET, polyethylene terphthalate; Pt-P-salt, cis-diammineplatinum(II)nitrite; PWB, printed wiring board; Strike, very thin metallic coating that is given prior to the main PGM coating for changing the character of base metal; SCE, saturated calomel electrode

Today, Internet offers many critical applications. So, it becomes very crucial for Internet service providers to ensure traceability of operations and to secure data exchange. Since all these communications are based on the use of the Domain Name System (DNS) protocol, it becomes necessary to think to enhance and secure it by proposing a secure version of this protocol that can correct the whole or a part of the DNS protocol weaknesses and vulnerabilities. In this context, DNSsec was created by the IETF to ensure the integrity of DNS data and authentication of the source of such data. DNSsec is based on the key cryptography public to provide different security services. In the present paper, we will present first the DNS protocol and its weaknesses. After that, we will be interested in studying the DNSsec implementation and data exchange, and then give a deep analysis of its weaknesses.

This paper details and interprets evidence of the historical shift of internet control, and particularly the control of the Domain Name System, from a public trust to private parties. It examines the ramifications of these shifts on (i) political dynamics and user autonomy in the Internet’s infrastructure, (ii) ‘freedom of speech’, and, more generally, (iii) the power of the Internet to influence individuals and to shape societies. It concludes that future policy should recognise the possibilities of non-linear and plural control structures as alternative mechanisms for promoting greater eInclusion, eAccessibility and democratisation than is permitted by the hierarchical control structures of Internet History. Within this context, the paper notes that Internet free speech and future priorities of global society are being seeded at this very moment by policies of Domain Name System and Internet architecture control that need to be more fully and more publicly monitored.

This paper reviews the models developed for the flow field inside inverse-flow cyclone separators. In a first part, traditional algebraic models and their foundations are summarized in a unified manner, including the formulae for tangential velocity and pressure drop. The immediate application to the prediction of collection efficiency is also reviewed. The approach is the classical, treating first the dilute limit (clean-gas correlations), and afterwards correcting for ''mass loading'' effects. Although all these methods have had a remarkable success, more advanced ideas are needed to model cyclones. This is put forward by exploring the work done on the so-called ''natural'' length of the cyclone, that has led to the discovery of instability and secondary flows. The resort to computational fluid dynamics (CFD) in this case is difficult, however, due to the very nature of the flow structure. A closing section on the subject reviews past and recent CFD simulations of cyclones, both single-and two-phase, steady and unsteady, aiming at delineating the state-of-the-art, present limitations and perspectives of this field of research. r

© 1999-2015 Joel Barrios Dueñas. Usted es libre de copiar, distribuir y comunicar públicamente la obra y hacer obras derivadas bajo las condiciones siguientes: a) Debe reconocer y citar al autor original. b) No puede utilizar esta obra para fines comerciales. c) Si altera o transforma esta obra o genera una obra derivada, sólo puede distribuir la obra generada bajo una licencia idéntica a ésta. Al reutilizar o distribuir la obra, tiene que dejar bien claro los términos de la licencia de esta obra. Alguna de estas condiciones puede no aplicarse si se obtiene el permiso del titular de los derechos de autor. Los derechos derivados de usos legítimos u otras limitaciones no se ven afectados por lo anterior. La información contenida en este documento y los derivados de éste se proporcionan tal cual son y los autores no asumirán responsabilidad alguna si el usuario o lector hace mal uso de éstos.

menghubungkan 3 router dengan menggunakan kabel serial DTE dengan menambah module WIC-2T dan WIC-1T pada router, mengkonfigurasi Router RIP menggunakan CLI, Mengkonfigurasi Router menggunakan CLI, mengkonfigurasi Wireless Router, mengkonfigurasi DNS dan DHCP.

PROGRAM STUDI TEKNIK INFORMATIKA JURUSAN TEKNIK ELEKTRO POLITEKNIK NEGERI SEMARANG 2013 DNS DAN PROXY I. Tujuan Instruksional Khusus : Setelah Menyelesaikan praktek ini mahasiswa dapat : 1. Mengetahui tentang DNS dan Proxy 2. Dapat melakukan seting DNS dan Proxy II. Dasar Teori A. Setting DNS Fungsi dari setting DNS adalah untuk menentukan alamat IP server yang berfungsi sebagai Domain Name Server (server ini bertugas menerjemahkan alamat domain yang anda tuju). Setting ini sebaiknya anda lakukan, walaupun bukan merupakan kerharusan karena SijiwaeNet akan secara otomatis menentukan DNS server. 1. Klik dua kali icon My Computer, lalu klik dua kali icon Dial Up Networking 2. Klik kanan icon SijiwaeNet yang sudah dibuat sebelumnya, pilih Properties 3. Setelah keluar window SijiwaeNet, klik pada Server Types Tab. Perhatikan setting pada Advanced Options, lakukan seperti terlihat pada gambar. 4. Klik tombol TCP/IP Settings. Klik pada Specify name server address, lalu isikan sebagai berikut : Masukkan Primary DNS : 202.134.0.155 Secondary DNS : 202.134.2.5 Jika telah selesai, klik OK untuk menutup dialog, lalu OK lagi untuk kembali ke awal. B. Setting Proxy Seting proxy server dapat dilakukan melalui aplikasi browser (baik Internet Explorer/ IE maupun Netscape Navigator). Untuk IE versi 5.O : 1. Jalankan IE, klik menu Tools, lalu pilih Internet Options. Maka akan muncul window Internet Options, pilih tab Connection sehingga muncul seperti dibawah. 2. Pada kotak Dial-up settings, pilih SijiwaeNet (pilihan ini seharusnya muncul bila anda telah membuat seting dial up modem sebelumnya). Kemudian tekan tombol Settings. Maka akan muncul window SijiwaeNet Settings seperti dibawah. 3. Perhatikan pada kotak Proxy Server. Pada Use a proxy server, kotak pilihan dikosongkan (tidak diberi tanda). Artinya, kita memberikan seting agar browser tidak usah menggunakan proxy. Hal ini dilakukan karena untuk akses lewat SijiwaeNet, seluruh pengguna telah diset agar secara otomatis agar menggunakan proxy Telkom secara default, sehingga tidak perlu dilakukan seting. Jangan lupa klik tombol OK. Maka seting proxy telah selesai. catatan.

Permeable reactive barrier (PRB) technology is increasingly considered for in situ treatment of contaminated groundwater; however, current design formulas for PRBs are limited and do not properly account for all major physical and attenuation processes driving remediation. This study focused on developing a simple methodology to design PRBs that is easy to implement while improving accuracy and being more conservative than the available design methodologies. An empirical design equation and a simple analytical design equation were obtained to calculate the thickness of a PRB capable of degrading a contaminant from a source contaminant concentration s C to a maximum contaminant level MCL C at a Point of compliance POC . Both equations integrate the fundamental components that drive the natural attenuation process of the aquifer and the reactive capacity of the PRB. The empirical design equation was derived from a dataset of random hypothetical cases that used the solutions of the PRB conceptual model (Solution I). The analytical design equation was derived from particular solutions of the model (Solution II) which the study showed fit the complex solutions of the model well. Using the hypothetical cases, the analytical equation has shown that it gives an estimated thickness of the PRB just 15 % lower or higher than the real thickness of the PRB 95 percent of the time. To calculate the design thickness of a PRB, Natural attenuation capacity of the aquifer can be estimated from the observed contaminant concentration changes along aquifer flowpaths prior to the installation of a PRB. Bench-scale or pilot testing can provide good estimates of the required residence times (Gavaskar et al. 2000),

The standard filter paper assay (FPA) published by the International Union of Pure and Applied Chemistry (IUPAC) is widely used to determine total cellulase activity. However, the IUPAC method is not suitable for the parallel analyses of large sample numbers. We describe here a microplate-based method for assaying large sample numbers. To achieve this, we reduced the enzymatic reaction volume to 60 Al from the 1.5 ml used in the IUPAC method. The modified 60-Al format FPA can be carried out in 96-well assay plates. Statistical analyses showed that the cellulase activities of commercial cellulases from Trichoderma reesei and Aspergillus species determined with our 60-Al format FPA were not significantly different from the activities measured with the standard FPA. Our results also indicate that the 60-Al format FPA is quantitative and highly reproducible. Moreover, the addition of excess h-glucosidase increased the sensitivity of the assay by up to 60%. B 2004 Wiley Periodicals, Inc.

This work proposes a novel approach to infer and characterize Internet-scale DNS Distributed Reflection Denial of Service (DRDoS) attacks by leveraging the darknet space. Complementary to the pioneer work on inferring Distributed Denial of Service (DDoS) activities using darknet, this work shows that we can extract DDoS activities without relying on backscattered analysis. The aim of this work is to extract cyber security intelligence related to DRDoS activities such as intensity, rate and geo-location in addition to various network-layer and flow-based insights. To achieve this task, the proposed approach exploits certain DDoS parameters to detect the attacks and the expectation maximization and k-means clustering techniques in an attempt to identify campaigns of DRDoS Attacks. We empirically evaluate the proposed approach using 1.44 TB of real darknet data collected from a/13 address space during a recent several months period. Our analysis reveals that the approach was successful in inferring significant DNS amplification DRDoS activities including the recent prominent attack that targeted one of the largest anti-spam organizations. Moreover, the analysis disclosed the mechanism of such DNS amplification attacks. Further, the results uncover high-speed and stealthy attempts that were never previously documented. The extracted insights from various validated DNS DRDoS case studies lead to a better understanding of the nature and scale of this threat and can generate inferences that could contribute in detecting, preventing, assessing, mitigating and even attributing of DRDoS activities.

Today, Internet offers many critical applications. So, it becomes very crucial for Internet service providers to ensure traceability of operations and to secure data exchange. Since all these communications are based on the use of the Domain Name System (DNS) protocol, it becomes necessary to think to enhance and secure it by proposing a secure version of this protocol that can correct the whole or a part of the DNS protocol weaknesses and vulnerabilities. In this context, DNSsec was created by the IETF to ensure the integrity of DNS data and authentication of the source of such data. DNSsec is based on the key cryptography public to provide different security services. In the present paper, we will present first the DNS protocol and its weaknesses. After that, we will be interested in studying the DNSsec implementation and data exchange, and then give a deep analysis of its weaknesses.

The semantic web remains in the early stages of development. It has not yet achieved the goals envisioned by its founders as a pervasive web of distributed knowledge and intelligence. Success will be attained when a dynamic synergism can be created between people and a sufficient number of infrastructure systems and tools for the semantic web in analogy with those for the original web. The domain name system (DNS), web browsers, and the benefits of publishing web pages motivated many people to register domain names and publish web sites on the original web. An analogous resource label system, semantic search applications, and the benefits of collaborative semantic networks will motivate people to register resource labels and publish resource descriptions on the semantic web. The Domain Ontology Oriented Resource System (DOORS) and Problem Oriented Registry of Tags and Labels (PORTAL) are proposed as infrastructure systems for resource metadata within a paradigm that can serve as a bridge between the original web and the semantic web. Registers domain names while DNS publishes domain addresses with mapping of names to addresses for the original web. Analogously, POR-TAL registers resource labels and tags while DOORS publishes resource locations and descriptions with mapping of labels to locations for the semantic web. BioPORT is proposed as a prototype PORTAL registry specific for the problem domain of biomedical computing.

Computational fluid dynamics (CFD) calculations of pump sumps are troublesome due to the nature of the flow. Pump sump flow is turbulent and unsteady, and pump sump dimensions are large compared to diameter of vortices occurring near the sump walls or in the pump column. Therefore, to capture the general and important phenomena of the flow, the computational grid should be fine enough at certain areas of the sump. Combined with unsteady calculations, this usually results in computationally expensive cases. The decision for a suitable turbulent model plays an important role in adding or reducing the computational costs. The present study first compares some different turbulent models on a fine computational grid to the published experimental model. The intention of the present work is to get an answer whether the Unsteady Reynolds Averaged Navier-Stokes (URANS) model really fails in predictions of vortex modeling, since the usage of Large Eddy Simulation (LES) model for industrial cases would represent huge computational power demands. In the second part of the paper a real case pump sump is analyzed.

Using DNS, domain names can be assigned to groups of Internet resources independent of their physical location. Without DNS, the only way to reach other computers on the Internet is to use the numerical network address. The use of IP address for locating and connecting to remote systems is tedious and is not very user friendly. A preferable and much relied upon service for retrieving an IP address just by referencing a FQDN is DNS. Several types of DNS based communications take place on the internet which are exploited by the cyber criminals for attacking systems. Although different mechanisms have been suggested by the research community to secure the DNS based communications yet it is still not fully secure. Since DNS does not necessarily require the establishment of a TCP connection it allows the attackers to redirect the response to the victims host by spoofing the source IP address as the victims IP address. By exploiting this vulnerability the attacker can launch different types of attacks like Cache Poisoning, DNS Spoofing, Protocol corruption, Zone corruptions, Session Hijacking, etc. Although the use of UDP makes the system faster, ye, it is suggested that all DNS based communications should be TCP based rather than UDP.

h i g h l i g h t s " Utilization of rice straw for the production of alcoholic biofuel. " Release of 3.9% (w/v) total sugar with 2.3% w/v of glucose by stress assisted acid hydrolysis of rice straw. " Production of ABE through clostridial fermentation of RSH. " Production of 6.24 g L À1 , 13.5 g L À1 and 0.82 g L À1 of ABE using RSH as a feedstock.

This paper reviews the chemical and electrochemical depositions of platinum group metals (PGMs) from aqueous solutions. With a brief introduction on the fundamental aspects of chemical/electrochemical depositions, the review describes recent advances in chemical and Abbreviations: CD, cathode current density expressed as amperes per cm 2 ; CE, cathode current efficiency; dc, direct current; DMFC, direct methanol fuel cell; DNS, dinitrosulfatoplatinate; Electroforming, deposition of thick metallic coating which is later removed from cathode substrate, used for preparing thick metallic foils, halograms, duplicating complicated structures etc.; NHE, normal hydrogen electrode; PCB, printed circuit board; PGM, platinum group metal; PEMFC, polymer electrolyte membrane fuel cell; PET, polyethylene terphthalate; Pt-P-salt, cis-diammineplatinum(II)nitrite; PWB, printed wiring board; Strike, very thin metallic coating that is given prior to the main PGM coating for changing the character of base metal; SCE, saturated calomel electrode

Los servicios de red como ser publicación de contenido WWW y mail entre otros, han crecido exponencialmente en los últimos años. El acceso a la red por parte de pequeñas organizaciones, e inclusive usuarios particulares, ha propiciado que la oferta de contenidos sea cada vez mayor, sin contar, en la gran mayoría de los casos, con grandes infraestructuras de hardware, redundancia y comunicaciones. Este crecimiento conlleva a la necesidad de contar con mecanismos de replicación, que garanticen alta disponibilidad. Las grandes organizaciones tienden a configurar sus servicios críticos en servidores redundantes y redes sin puntos únicos de falla con el fin de brindar elevados niveles de SLA (Service Level Agreement). Las tendencias actuales, llevan a los administradores a utilizar las técnicas anteriormente descriptas, así como también a desconsolidar los mismos en diversos centros de procesamiento de datos (CPD) con el fin de garantizar niveles mínimos de puntos únicos de falla. Histór...

The antiphishing system uses visual characteristics to identify fake and phishing sites and suspicious pages similarity to actual sites registered with the system. In the initial two sequential processes in the Site Watcher system runs on local email servers and monitors emails for keywords and suspicious URLs. The second process then compares the potential phishing pages against actual pages and assesses visual similarities between them in terms of key regions, page layouts, and overall styles. The project is a research on the Internet Utility which is mainly used for detecting the Phishing attacks which is mainly used for monitoring every popup used with another website, monitoring the authentication of every websites and use of image containing an institution's corporate logos and artwork.

In the late 1990s, the application of a well known mathematical transformation revolutionized the music industry. That process, known as Auto-Tune, relies on the ability of the Fourier Transform to identify dominant frequencies within a time-series record of a signal. Mega-stars like Madonna, Cher, Britney Spears, Tim McGraw, Kanye West, and many more heavily use Auto-Tune not only to ensure perfect pitch, but often simply for the unique sounds the function produces. Perhaps unknown to these singers, wave experts were using exactly the same mathematical functions to identify ocean wave characteristics forty years prior to the first mainstream music hit (Cher's "Believe") to use Auto-Tune. This paper presents an overview of the Fourier Transform and its application in both the music industry and the scientific study of water waves.

The Internet put the rest of the world at the reach of our computers. In the same way it also made our computers reachable by the rest of the world. Good news and bad news!. Over the last decade, the Internet has been subject to widespread security attacks. Besides the classical terms, new ones had to be found in order to designate a large collection of threats: Worms, break-ins, hackers, crackers, hijacking, phrackers, spoofing, man-in-the-middle, password-sniffing, denial-of-service, and so on.

We present an improved numerical scheme for numerical simulations of low Mach number turbulent reacting flows with detailed chemistry and transport. The method is based on a semi-implicit operator-splitting scheme with a stiff solver for integration of the chemical kinetic rates, developed by Knio et al. [O.M. Knio, H.N. Najm, P.S. Wyckoff, A semi-implicit numerical scheme for reacting flow II. Stiff, operator-split formulation, Journal of Computational Physics 154 (2) (1999) 428-467]. Using the material derivative form of continuity equation, we enhance the scheme to allow for large density ratio in the flow field. The scheme is developed for direct numerical simulation of turbulent reacting flow by employing high-order discretization for the spatial terms. The accuracy of the scheme in space and time is verified by examining the grid/time-step dependency on one-dimensional benchmark cases: a freely propagating premixed flame in an open environment and in an enclosure related to spark-ignition engines. The scheme is then examined in simulations of a two-dimensional laminar flame/vortex-pair interaction. Furthermore, we apply the scheme to direct numerical simulation of a homogeneous charge compression ignition (HCCI) process in an enclosure studied previously in the literature. Satisfactory agreement is found in terms of the overall ignition behavior, local reaction zone structures and statistical quantities. Finally, the scheme is used to study the development of intrinsic flame instabilities in a lean H 2 /air premixed flame, where it is shown that the spatial and temporary accuracies of numerical schemes can have great impact on the prediction of the sensitive nonlinear evolution process of flame instability.

Numerical prediction of an efficiency of a 6-blade Kaplan turbine is presented. At first, the results of steady state analysis performed by different turbulence models for different operating regimes are compared to the measurements. For small and optimal angles of runner blades the efficiency was quite accurately predicted, but for maximal blade angle the discrepancy between calculated and measured values was quite large. By transient analysis, especially when the Scale Adaptive Simulation Shear Stress Transport (SAS SST) model with zonal Large Eddy Simulation (ZLES) in the draft tube was used, the efficiency was significantly improved. The improvement was at all operating points, but it was the largest for maximal discharge. The reason was better flow simulation in the draft tube. Details about turbulent structure in the draft tube obtained by SST, SAS SST and SAS SST with ZLES are illustrated in order to explain the reasons for differences in flow energy losses obtained by different turbulence models.

The Internet put the rest of the world at the reach of our computers. In the same way it also made our computers reachable by the rest of the world. Good news and bad news!. Over the last decade, the Internet has been subject to widespread security attacks. Besides the classical terms, new ones had to be found in order to designate a large collection of threats: Worms, break-ins, hackers, crackers, hijacking, phrackers, spoofing, man-in-the-middle, password-sniffing, denial-of-service, and so on.

But what are GeoIP services and how do they create the most accurate geo-DNS? Find out now in our new eBook which discusses what GeoIP services are, how they direct your queries more efficiently, and how they integrate with the Constellix suite.

The present study adresses the turbulent flow over a wavy surface by direct numerical simulation (DNS). Compared to classical channel flow the wavy surface structure adds a degree of complexity to the flow by inducing streamline curvature, flow separation and flow reattachment, thus leading to flow situations which are often present in relevant technical and geophysical applications. The governing equations are discretized with a second order finite volume method on Cartesian, structured, staggered grids, and are integrated in time using the semi-implicit projection method. The wavy surface is represented with a variant of the immersed boundary method (IBM). The solution of the discretized system of linear equations is accelerated with an algebraic multigrid procedure. The simulations were performed on the Cray XT5 computer and scale well up to 128 processors. The flow over the wavy surface is particularly challenging for the IBM since the cells are cut at different angles in the regions where the most interesting phenomena like separation and reattachment takes place. In the present work, particular attention was payed on the size of the computational domain, ensuring it does not hinder the natural development of coherent structures in the considered flow. The results of the simulations compare favorably with particle image velocimetry (PIV) measurements, showing the IBM is an interesting candidate for simulating flows over wavy surfaces.

A highly accurate algorithm has been developed to study the process of spatial transition to turbulence. The algorithmic details of the direct numerical simulation (DNS) of transition to turbulence in a boundary layer based on a formulation in terms of vertical velocity and vertical vorticity are presented. Issues concerning the boundary conditions are discussed. The linear viscous terms are discretized using an implicit Crank–Nicholson scheme, and a low-storage Runge–Kutta method is used for the nonlinear terms. For the spatial discretization, fourth-order compact finite differences have been used, as these have been found to have better resolution compared to explicit differencing schemes of comparable order. The number of grid points that are needed per wavelength is close to the theoretical optimum for any numerical scheme. The resulting time-discretized fourth-order equations are split up into two second-order equations, resulting in Helmholtz- and Poisson-type equations. The boundary conditions for the Laplacian of the vertical velocity are determined using an influence matrix method. A robust multigrid algorithm has been developed to solve the resulting anisotropic elliptical equations. For the outflow boundary, a buffer domain method, which smoothly reduces the disturbances to zero, in conjunction with parabolization of the Navier–Stokes equations has been used. The validation of the results for the DNS solver is made both for linear and weakly nonlinear cases.