Binding between endohedral Na atoms in Si clathrate I; a first principles study

We investigate the binding nature of the endohedral sodium atoms with the ensity functional theory methods, presuming that the clathrate I consists of a sheaf of one-dimensional connections of Na@Si$_{24}$ cages interleaved in three perpendicular directions. Each sodium atom loses 30% of the 3s$^1$ charge to the frame, forming an ionic bond with the cage atoms; the rest of the electron contributes to the covalent bond between the nearest Na atoms. The presumption is proved to be valid; the configuration of the two Na atoms in the nearest Si$_{24}$ cages is more stable by 0.189 eV than that in the Si$_{20}$ and Si$_{24}$ cages. The energy of the beads of the two distorted Na atoms is more stable by 0.104 eV than that of the two infinitely separated Na atoms. The covalent bond explains both the preferential occupancies in the Si$_{24}$ cages and the low anisotropic displacement parameters of the endohedral atoms in the Si$_{24}$ cages in the [100] directions of the clathrate I.Comment: First page: Affiliation added to PDF and PS versio

Robust Processing of Natural Language

Previous approaches to robustness in natural language processing usually treat deviant input by relaxing grammatical constraints whenever a successful analysis cannot be provided by ``normal'' means. This schema implies, that error detection always comes prior to error handling, a behaviour which hardly can compete with its human model, where many erroneous situations are treated without even noticing them. The paper analyses the necessary preconditions for achieving a higher degree of robustness in natural language processing and suggests a quite different approach based on a procedure for structural disambiguation. It not only offers the possibility to cope with robustness issues in a more natural way but eventually might be suited to accommodate quite different aspects of robust behaviour within a single framework.Comment: 16 pages, LaTeX, uses pstricks.sty, pstricks.tex, pstricks.pro, pst-node.sty, pst-node.tex, pst-node.pro. To appear in: Proc. KI-95, 19th German Conference on Artificial Intelligence, Bielefeld (Germany), Lecture Notes in Computer Science, Springer 199

Two-level relationships and Scale-Free Networks

Through the distinction between ``real'' and ``virtual'' links between the nodes of a graph, we develop a set of simple rules leading to scale-free networks with a tunable degree distribution exponent. Albeit sharing some similarities with preferential attachment, our procedure is both faster than a na\"ive implementation of the Barab\'asi and Albert model and exhibits different clustering properties. The model is thoroughly studied numerically and suggests that reducing the set of partners a node can connect to is important in seizing the diversity of scale-free structures

IMPLEMENTING TARIFF RATE QUOTAS IN CGE MODELS: AN APPLICATION TO SUGAR TRADE POLICIES IN OECD COUNTRIES

We use Mixed-Complementarity-Problem programming to implement tariff rate quotas (TRQ) in the global CGE LINKAGE model. We apply the approach to tariff rate quotas in sugar markets in OECD countries. We calibrate the model on 2000 policy levels for OECD countries to reflect the full implementation of their World Trade Organization commitments. We look at reforms of TRQ and TRQ-like schemes in the EU, the United States, and Japan, as well as multilateral trade liberalization. We derive the impact of reforms on welfare, bilateral trade flows, and terms of trade. A 33-percent multilateral decrease of ad-valorem tariffs, combined with a 33-percent increase in imports under TRQ-like schemes in the EU, the United States, and Japan, induces a global welfare gain of about 889 million dollars. These three countries' trade policies create substantial trade diversion, which excludes many low-cost producers from trading opportunities. An expansion of their import quotas alone, without multilateral trade liberalization, induces welfare gains but preserves most of the trade diversion patterns. The latter diversion benefits some Least Developed Countries' producers because of granted bilateral TRQ allocations. In the context of greater market access, reductions in tariffs in the EU and the United States, and in border "surcharges" in Japan will have to be dramatic before they can significantly affect trade flows as compared to TRQ expansion. Full multilateral trade liberalization induces global welfare gains of about $3 billion.International Relations/Trade,

Textiles and apparel in NAFTA : a case of constrained liberalization

The authors examine the changes that Mexico's textile and clothing industry is likely to face under the North American Free Trade Agreement (NAFTA). They compare pre-NAFTA and probable post-NAFTA scenarios for Mexican exports. The U.S. clothing and textile industry is likely to remain among the most protected of U.S. industries, so this is essentially a comparison of two protectionist situations, not of protection and free trade. The authors trace how current quota and tariff restrictions on U.S. imports from Mexico will be replaced by rules of origin designed to protect U.S. industry. Mexican textile and clothing exports will enjoy greater access to the U.S. market if most inputs originate in North America. Under the triple transformation requirements, for example, a cotton shirt would have to be made in the NAFTA region from yarn and fabric of NAFTA origin. Mexican compliance with this rule would not prove onerous. Proximity and long-standing production-sharing arrangements have made Mexico heavily dependent on U.S. inputs. Roughly 53 percent of Mexican textile and apparel exports to the United States fall under production-sharing programs, with an average 69 percent of value added of U.S. origin. Only 15 percent of input requirements for the other 47 percent of trade is imported into Mexico - only 8 percent from non-NAFTA countries. What about future trade? The authors estimate that these Mexican exports to the United States will increase only modestly - partly because of the low level of protection already associated with production-sharing arrangements. Rules oforigin under the NAFTA are small. How much investment from outside North America will be attracted to Mexico under stringent input-sourcing requirements is open to question. The competitiveness of Mexico's apparel industry in non-NAFTA markets will depend to some extent on the international competitiveness of the U.S. textile industry.TF054105-DONOR FUNDED OPERATION ADMINISTRATION FEE INCOME AND EXPENSE ACCOUNT,Economic Theory&Research,Environmental Economics&Policies,Textiles, Apparel&Leather Industry,Trade Policy

Modification of thin films induced by slow heavy ions analysed with PIXE and SRIM

In the present work the particle induced X-rays (PIXE) emitted during interaction of inert and active slow heavy (HI) ions with specially prepared thin films were measured. Kinematics of the interaction was simulated numerically with SRIM in grazing incident-exit angle geometry and in time sequence in order to determine dynamics of formation of the subsurface region damaged through implantation, sputtering and interface mixing. It was shown that the structure and composition of films and surfaces are not stable against HI irradiation due to preferential sputtering and implantation of ions and recoils and that dynamics of such a modification can be in-situ monitored with PIXE and analyzed with SRIM

Dissociation of sensitivity to spatial frequency in word and face preferential areas of the fusiform gyrus

Different cortical regions within the ventral occipitotemporal junction have been reported to show preferential responses to particular objects. Thus, it is argued that there is evidence for a left-lateralized visual word form area and a right-lateralized fusiform face area, but the unique specialization of these areas remains controversial. Words are characterized by greater power in the high spatial frequency (SF) range, whereas faces comprise a broader range of high and low frequencies. We investigated how these high-order visual association areas respond to simple sine-wave gratings that varied in SF. Using functional magnetic resonance imaging, we demonstrated lateralization of activity that was concordant with the low-level visual property of words and faces; left occipitotemporal cortex is more strongly activated by high than by low SF gratings, whereas the right occipitotemporal cortex responded more to low than high spatial frequencies. Therefore, the SF of a visual stimulus may bias the lateralization of processing irrespective of its higher order properties