A method of fundamental solutions for radially symmetric and axisymmetric backward heat conduction problems

We propose and investigate an application of the method of fundamental solutions (MFS) to the radially symmetric and axisymmetric backward heat conduction problem (BHCP) in a solid or hollow cylinder. In the BHCP, the initial temperature is to be determined from the temperature measurements at a later time. This is an inverse and ill-posed problem, and we employ and generalize the MFS regularization approach [B.T. Johansson and D. Lesnic, A method of fundamental solutions for transient heat conduction, Eng. Anal. Boundary Elements 32 (2008), pp. 697–703] for the time-dependent heat equation to obtain a stable and accurate numerical approximation with small computational cost.

Eigen-Adaptation and Distributed Representation of 2-D Phase, Energy, Scale and Orientation in Spatial Vision

Distributed representations (DR) of cortical channels are pervasive in models of spatio-temporal vision. A central idea that underpins current innovations of DR stems from the extension of 1-D phase into 2-D images. Neurophysiological evidence, however, provides tenuous support for a quadrature representation in the visual cortex, since even phase visual units are associated with broader orientation tuning than odd phase visual units (J.Neurophys.,88,455–463, 2002). We demonstrate that the application of the steering theorems to a 2-D definition of phase afforded by the Riesz Transform (IEEE Trans. Sig. Proc., 49, 3136–3144), to include a Scale Transform, allows one to smoothly interpolate across 2-D phase and pass from circularly symmetric to orientation tuned visual units, and from more narrowly tuned odd symmetric units to even ones. Steering across 2-D phase and scale can be orthogonalized via a linearizing transformation. Using the tiltafter effect as an example, we argue that effects of visual adaptation can be better explained by via an orthogonal rather than channel specific representation of visual units. This is because of the ability to explicitly account for isotropic and cross-orientation adaptation effect from the orthogonal representation from which both direct and indirect tilt after-effects can be explained.

Információs paradoxon a vállalkozások hitelezésében nem fizető vevő esetén (An innovation paradox in enterprise financing where buyers fail to pay)

Cikkünkben a vállalkozók külső finanszírozásának modelljét terjesztjük ki arra az - irodalom által eddig nem tárgyalt - esetre, amikor a vállalkozónak van nem fizető vevője. Szerződéselméleti megközelítésünkben a vállalkozó hitelképességére vonatkozó információ aszimmetrikus a tranzakcióban részt vevő felek között, s ez morális kockázatnak ad teret. Megfigyelhető, hogy ilyenkor a pontosan fizető vevők számára is hitelszűke lép fel. A vállalkozó és a finanszírozó közötti optimális szerződés nem fizető vevő hatására további hitelszűkösséget generál. Két esetet vizsgálunk: az egyikben a vállalkozó információs előnyben van a vevő nemfizetésére vonatkozóan, a másikban nincs ilyen előny. A két modellváltozat alapján információs paradoxon jellemzi a kialakuló finanszírozási helyzetet: a vállalkozó kisebb összegű hitelhez jut az említett információs előnye esetén, mint amikor közte és a finanszírozó között szimmetrikus az információ. A modell azt a - magyar kis- és középvállalkozóknál látott - jelenséget írja le, amikor nem transzparens a szállító-vevő viszonya, és a finanszírozó bank e miatt az információs hátrány miatt kevesebb hitelt nyújt kis- és középvállalati ügyfeleinek. _____ The model of external financing of the firm is extended here to cases where there may be defaults on account receivables. Information asymmetry between entrepreneur and lender on a firm's creditworthiness leads to moral hazard and credit rationing, even in the absence of default risk. The authors show an optimal debt contract that formulates the situation, and focus on two cases: where the entrepreneur has an information advantage on defaults on receivables, and where the information is symmetric. A comparison of these cases revealed a paradoxical knowledge issue in external financing: a better informed entrepreneur may be able to afford a smaller financing ability. The model describes a frequent phenomenon in small businesses, when the relationship between buyer and seller lacks transparency, and lenders offer lower amount of lending to small and medium-sized enterprises.

Ranked search on data graphs

Graph-structured databases are widely prevalent, and the problem of effective search and retrieval from such graphs has been receiving much attention recently. For example, the Web can be naturally viewed as a graph. Likewise, a relational database can be viewed as a graph where tuples are modeled as vertices connected via foreign-key relationships. Keyword search querying has emerged as one of the most effective paradigms for information discovery, especially over HTML documents in the World Wide Web. One of the key advantages of keyword search querying is its simplicity—users do not have to learn a complex query language, and can issue queries without any prior knowledge about the structure of the underlying data. The purpose of this dissertation was to develop techniques for user-friendly, high quality and efficient searching of graph structured databases. Several ranked search methods on data graphs have been studied in the recent years. Given a top-k keyword search query on a graph and some ranking criteria, a keyword proximity search finds the top-k answers where each answer is a substructure of the graph containing all query keywords, which illustrates the relationship between the keyword present in the graph. We applied keyword proximity search on the web and the page graph of web documents to find top-k answers that satisfy user’s information need and increase user satisfaction. Another effective ranking mechanism applied on data graphs is the authority flow based ranking mechanism. Given a top- k keyword search query on a graph, an authority-flow based search finds the top-k answers where each answer is a node in the graph ranked according to its relevance and importance to the query. We developed techniques that improved the authority flow based search on data graphs by creating a framework to explain and reformulate them taking in to consideration user preferences and feedback. We also applied the proposed graph search techniques for Information Discovery over biological databases. Our algorithms were experimentally evaluated for performance and quality. The quality of our method was compared to current approaches by using user surveys.

Structure of international cooperation in trade, investment and environment

This dissertation analyzes the obstacles against further cooperation in international economic relations. The first essay explains the gradual nature of trade liberalization. I show that existence of asymmetric information between governments provides a sufficient reason for gradualism to exist. Governments prefer starting small to reduce the cost of partner’s betrayal when there is sufficient degree of information asymmetry regarding the partner’s type. Learning about partner’s incentive structure enhances expectations, encouraging governments to increase their current level of cooperation. Specifically, the uninformed government’s subjective belief for the trading partner being good is improved as the partner acts cooperatively. This updated belief, in turn, lowers the subjective probability of future betrayal, enabling further progress in cooperation. The second essay analyzes the relationship between two countries facing two policy dilemmas in an environment with two way goods and capital flows. When issues are independent and countries are symmetric, signing separate agreements for tariffs (Free Trade Agreements-FTA) and for taxes (Tax Treaties-TT) provides the identical level of enforcement as signing a linked agreement. However, linkage can still improve the joint welfare by transferring the slack enforcement power in a case of asymmetric issues or countries. I report non-results in two cases where the policy issues are interconnected due to technological spillover effect of FDI. Moreover, I show that linking the agreements actually reduces enforcement when agreements are linked under a limited punishment rule and policy variables are strategic substitutes. The third essay investigates the welfare/enforcement consequences of linking trade and environmental agreements. In the standard literature, linking the agreements generate non-trivial results only when there is structural relation between the issues. I focus on institutional design of the linkage and show that even if environmental aspects of international trade are negligible linking the agreements might still have some interesting welfare implications under current GATT Rules. Specifically, when traded goods are substitutes in consumption, linking the environmental agreement with trade agreement under the Withdrawal of Equivalent Concession Rule (Article XXVIII) will reduce the enforcement. However, enforcement in environmental issue increases when the same rule is implemented in the absence of linkage.