An analysis of various elastic net algorithms

The Elastic Net Algorithm (ENA) for solving the Traveling Salesman Problem is analyzed applying statistical mechanics. Using some general properties of the free energy function of stochastic Hopfield Neural Networks, we argue why Simic's derivation of the ENA from a Hopfield network is incorrect. However, like the Hopfield-Lagrange method, the ENA may be considered a specific dynamic penalty method, where, in this case, the weights of the various penalty terms decrease during execution of the algorithm. This view on the ENA corresponds to the view resulting from the theory on `deformable templates', where the term stochastic penalty method seems to be most appropriate. Next, the ENA is analyzed both on the level of the energy function as well as on the level of the motion equations. It will be proven and shown experimentally, why a non-feasible solution is sometimes found. It can be caused either by a too rapid lowering of the temperature parameter (which is avoidable), or by a peculiar property of the algorithm,namely, that of adhering to equidistance of the elastic net points. Thereupon, an alternative, Non-equidistant Elastic Net Algorithm (NENA) is presented and analyzed. It has a correct distance measure and it is hoped to guarantee feasibility in a more natural way. For small problem instances, this conjecture is confirmed experimentally. However, trying larger problem instances, the pictures changes: our experimental results show that the elastic net points appear to become `lumpy' which may cause non-feasibility again. Moreover, in cases both algorithms yield a feasible solution, the quality of the solution found by the NENA is often slightly worse than the one found by the original ENA. This motivated us to try an Hybrid Elastic Net Algorithm (HENA), which starts using the ENA and, after having found a good approximate solution, switches to the NENA in order to guarantee feasibility too. In practice, the ENA and HENA perform more or less the same. Up till now, we did not find parameters of the HENA, which invariably guarantee the desired feasibility of solutions

Complications in subfascial endoscopic perforating vein surgery: A report of two cases

AbstractSubfascial endoscopic perforating vein surgery is a safe method for the division of incompetent perforating veins. Nevertheless, we report two cases with unfortunate complications: the posterior tibial artery and tibial nerve were damaged during the procedures. In one patient this resulted in a reintervention, but in both patients it resulted in permanent discomfort. We then present a guideline that may prevent damage to these critical structures. (J Vasc Surg 2001;33:1108-10.

Over de bepaling van het gehalte aan pepsine in natuurlijk en kunstmatig maagsap

Mode of access: Internet

Design Management: Communication in the design process

When a client initiates a building project, he is confronted with the complexity of today’s building industry. Whether this client is a single person or a large organization, a confrontation with the industry’s complex methods and proceedings is unavoidable. Perhaps the difficulty consists of specific questions about the design, never thought of before by the client? Or it is the lack of financial control or the control over the architectural design? Due recent political and economical developments, most clients tend to focus their demands and wishes in terms of operability, flexibility and (future) economic value. Means of evaluation are often directed at the finished product, which is the eventually the finished building itself. What about the means of evaluation during the development of the project? Hardly existing, these means of evaluation of the design and construction process are severely limited. To facilitate the client, but also the process manager, additional research and aid on this issue is a warm welcome. The main focus of this research is put on the design process, because most important decisions considering the operability, financial cost and flexibility of the building are made during this process. After a study of theory and examples, it appears that communication is one of the most important thrusts in this process. However, communication within the design process remains intuitive and informal. The main question of this research is to find out if a formalization of communication can help the client and process manager to recognize, avoid or at least help to solve problems during the design process. To answer this question a three-part puzzle must be solved. It is the ability to understand the design process, to track possible problems and if necessary find ways to solve them. The puzzle is solved piece by piece. First, a model as a description of reality must be created, in order to describe the design process in its basic terms. Secondly, a script is developed to allow its operator to ask specific questions in order to determine if there is a problem. The script continues in order to determine the threat to either client or the project as a whole. It also allows the operator to strip the problem to its basic character, which can be described in terms of language problems, consistency of information, social behavior or sudden changes. Thirdly, possible steering options are to be identified and described. These tools can be used to create a solution if a problem exists. Finally, specific combinations of these tools are described as tactics. These tactics are basic approaches in solving the most common and characteristic problems. The combination of these scripts, tools and tactics is called the toolbox. The combination of the model and toolbox functions as the intended formalization. To acquire information to first create a model and consequently a toolbox, today’s practice and professional literature are studied. To study practice, the case study method and ethnographic research are used to identify situations. These situations indicate a problem or conflict, which may occur during a meeting between participants. Of course, these situations may also stretch beyond one or more meetings. Two practice cases where studied, as well as one literature case. The first case was the renovation of the tower of the main building on the campus of the Vrije Universiteit in Amsterdam, the Netherlands. The second case was the development of a medical training facility and school, called the OZW building. This project was a joint approach of the VU University and the Hoge School Holland and multiple smaller organizations. The literature case covered the development of the Guggenheim museum in Bilbao, Spain. Based on these case studies and further literature study, a model of the design process was created. This model consisted of underlying processes such as the knowledge gap and the continuous translation of hard, quantified data (such as spatial demands) to softer, variable information (such as architectural drawings) and backwards. Additional underlying processes consisted of a graphical description of a meeting (a triangle shaped balance between information, communication and participants) and a situation (a triangle shaped balance between language problems, social behavior, information inconsistency and sudden changes as an external influence). These underlying processes where compared to the expected level of communication and the total level of development of the design. Doing so, a graphical description of the total design process could be drawn. An additional typology of explaining the possible cause was also created. By turning conclusions from case and literature study around into questions, the development of several scripts could take place. The scripts consist of a situation analysis and a threat analysis. Consequently, social, organizational and administrational tools were created. The deployment of the tools can be done along a communicational network structure (by describing communication as a network of nodes). Social tools consisted of a set of options, allowing to create a certain atmosphere and/or work environment. The organizational tools are intended to help the operator to choose means of communication properly. Administrational tools are intended to structure streams of information, as well as to archive information considering the development of the design. Eventually, eight tactical approaches were formulated. Each addressed one of the problem characteristics possible within the design process. Two examples are the shadow document and the resolution format to prevent and solve language problems. Another example is the tactic of the freeze cycle, intended to solve or prevent problems information inconsistency. Conclusively, formalization can be created. With the model and toolbox, the client and process manager can hopefully better understand means of communication within the design process. However, a short handout cannot be made. The subject is still too complex to explain in just a few pages of text. Some amount of study by the client is required. Testing and evaluating the toolbox in a practice environment could however not be done within the current time span. Furthermore, due the social character of this subject, further research should be a joint approach by both management and social studies.Real Estate & HousingArchitectur