Network visualization with Nam, the VINT network animator

Network protocol designers face many difficult tasks, including simultaneously monitoring state in a potentially large number of nodes, understanding and analyzing complex message exchanges, and characterizing dynamic interactions with competing traffic. Traditionally they have used packet traces to accomplish these tasks, but traces have two major drawbacks: they present an incredible amount of detail, which challenges the designer's ability to comprehend the data; and they are static, which hides an important dimension of protocol behavior. As a result, detailed analysis frequently becomes tedious and error-prone. Although network simulators such as the VINT project's ns can easily generate numerous detailed traces, they provide limited help for analyzing and understanding the data. Nam, the network animator that we developed in our work at the VINT project, provides packet-level animation, protocol graphs, traditional time-event plots of protocol actions, and scenario editing capabilities. Nam benefits from a close relationship with ns, which can collect detailed protocol information from a simulation. With some preprocessing. Nam can visualize data taken directly from real network traces     

Perspectives on optimistically replicated,peer-to-peer filing

This research proposes and tests an approach to engineering distributed file systems that are aimed at wide-scale, Internet-based use. The premise is that replication is essential to deliver performance and availability, yet the traditional conservative replica consistency algorithms do not scale to this environment. Our Ficus replicated file system uses a single-copy availability, optimistic update policy with reconciliation algorithms that reliably detect concurrent updates and automatically restore the consistency of directory replicas. The system uses the peer-to-peer model in which all machines are architectural equals but still permits configuration in a client-server arrangement where appropriate. Ficus has been used for six years at several geographically scattered installations. This paper details and evaluates the use of optimistic replica consistency, automatic update conflict detection and repair, the peer-to-peer (as opposed to client-server) interaction model, and the stackable file system architecture in the design and construction of Ficus. The paper concludes with a number of lessons learned from the experience of designing, building, measuring, and living with an optimistically replicated file system. © 1998 John Wiley & Sons, Ltd.     

Calibrated models for simulation of stratified hot water heat stores

Hot water heat stores (HWHS) are generally used to overcome the diurnal or seasonal mismatch in the availability and demand of thermal energy. To enhance the system efficiency, good thermal stratification of the HWHS is required. In order to simulate different flow processes in stratified HWHS the effects of stratification on the turbulence are to be considered. Benchmark experiments have been conducted on turbulent flows into a continuously stratified HWHS. Based on these benchmark experiments, different two‐equation turbulence transport models namely the RNG (ReNormalizable Group) and the realizable k–ε turbulence models have been calibrated. The major improvement is provided to the ε‐equation by introducing the effects of the buoyancy field on the turbulence dissipation rate. It is achieved by calibrating the coefficient of the dissipation term (C_ε2 in the RNG and C₂ in the realizable k–ε model) based on the benchmark experiments. A re‐definition of the turbulent Prandtl number (Pr_t) incorporating the effects of stratification on turbulent thermal diffusivity improved the calibration further. The calibrated computational fluid dynamic models are found to predict the charging, discharging and storing processes of typical HWHS with good accuracy. Copyright © 2008 John Wiley & Sons, Ltd.     

Non-uniqueness in phase and reaction equilibrium computations

The chemical reaction equilibrium problem in a homogeneous phase is known to have an unique solution except when the thermodynamic model of the phase c     

An accelerated successive substitution algorithm

Three related proposals are made for accelerating the familiar successive substitution procedure for phase equilibrium flash calculations. Basic to the development of the acceleration procedures is the observation that successive substitution can be regarded as a method of steep descent for free energy minimization. Acceleration is obtained by choosing an optimal step length. Results show a significant decrease in the number of iterations required for convergence, even in difficult problems near the mixture critical point.     

Humoral factors in the regulation of cell proliferation in haematopoiesis. II. Erythropoiesis, megakaryopoiesis, multipotent stem cell (author's transl)

Diffusible factors probably play an important role in the control of cell proliferation during haematopoiesis. Several stimulators of erythropoiesis including erythropoietin are to be found in sera. Inhibitors are found in erythrocyte supernatants, in the urin of newborn children, and in plasma of patients with renal insufficiency. Stimulators of megakaryopoiesis have been shown to be present in conditioned media of lymphoid cells and bone marrow cells. Inhibitors have been detected in various sera. Proliferation of multipotent stem cells is probably also regulated by a humoral mechanism. Stimulators and inhibitors are present in bone marrow extracts. Clinical relevance of these factors is discussed.     

Hybrid transmission of analogue PAL and digital 64-QAM CATVchannels

A system experiment for fibre optic hybrid transmission of analogue CATV BK 300 and 1.8 Gbit/s with 64-QAM channels has been realised. It has been shown that additional transmission of 1.8 Gbit/s of compressed digital video (MPEG) using 64-QAM is possible without a significant degradation of the laser clipping rate. Measured bit error rates are compared with simulation results based on impulsive clipping noise     

The effects of momentum diffusers and flow guides on the efficiency of stratified hot water seasonal heat stores

Hot water seasonal heat stores (HWSHS) carry the solar thermal energy from energy‐rich seasons of the year over to energy‐poor seasons so as to ensure the availability of solar energy throughout the year. Momentum diffusers and flow guides are designed to charge and discharge the harvested solar thermal energy within HWSHS in a stratified manner to enhance the efficiency of the solar systems. To evaluate the efficiency of an HWSHS, a characterization scheme developed for general stratified thermal energy stores (TES) (Sol Energy 2007; 81 :1043–1054) is used. It addresses the First Law and Second Law concerns over a TES simultaneously. This study is confined to systems that use the same nozzles at fixed positions in both charging and discharging cycles. Different parameters related to axial, conical and radial diffusers as well as a variety of flow‐guide designs are studied. The results suggest that a nozzle that brings about better diffuser action by minimizing entropy generation may not necessarily improve the energy response and guarantee better overall efficiency of the HWSHS. Of all, the different nozzle designs experimented with the conical diffusers with smaller angles of diffusion produced the best overall efficiency. Copyright © 2008 John Wiley & Sons, Ltd.