Liquid-Liquid Phase Transition for an Attractive Isotropic Potential with Wide Repulsive Range

Recent experimental and theoretical results have shown the existence of a liquid-liquid phase transition in isotropic systems, such as biological solutions and colloids, whose interaction can be represented via an effective potential with a repulsive soft-core and an attractive part. We investigate how the phase diagram of a schematic general isotropic system, interacting via a soft-core squared attractive potential, changes by varying the parameters of the potential. It has been shown that this potential has a phase diagram with a liquid-liquid phase transition in addition to the standard gas-liquid phase transition and that, for a short-range soft-core, the phase diagram resulting from molecular dynamics simulations can be interpreted through a modified van der Waals equation. Here we consider the case of soft-core ranges comparable with or larger than the hard-core diameter. Because an analysis using molecular dynamics simulations of such systems or potentials is too time-demanding, we adopt an integral equation approach in the hypernetted-chain approximation. Thus we can estimate how the temperature and density of both critical points depend on the potential's parameters for large soft-core ranges. The present results confirm and extend our previous analysis, showing that this potential has two fluid-fluid critical points that are well separated in temperature and in density only if there is a balance between the attractive and repulsive part of the potential. We find that for large soft-core ranges our results satisfy a simple relation between the potential's parameters

N=2 supersymmetric Yang-Mills theories and Whitham integrable hierarchies

We review recent work on the study of N=2 super Yang-Mills theory with gauge group SU(N) from the point of view of the Whitham hierarchy, mainly focusing on three main results: (i) We develop a new recursive method to compute the whole instanton expansion of the low-energy effective prepotential; (ii) We interpret the slow times of the hierarchy as additional couplings and promote them to spurion superfields that softly break N=2 supersymmetry down to N=0 through deformations associated to higher Casimir operators of the gauge group; (iii) We show that the Seiberg-Witten-Whitham equations provide a set of non-trivial constraints on the form of the strong coupling expansion in the vicinity of the maximal singularities. We use them to check a proposal that we make for the value of the off-diagonal couplings at those points of the moduli space.Comment: 19 pages, LaTeX, no figures; Invited talk at the Second Meeting "Trends in Theoretical Physics", held in Buenos Aires, December 199

A Configurational Approach to Comparative Corporate Governance

We seek to bring to the core of the study of comparative corporate governance analysis the idea that within countries and industries, there exist multiple configurations of firm level characteristics and governance practices leading to effective corporate governance. In particular, we propose that configurations composed of different bundles of corporate governance practices are a useful tool to examine corporate governance models across and within countries (as well as potentially to analyze over time changes). While comparative research, identifying stylized national models of corporate governance, has been fruitful to help us think about the key institutional and shareholder rights determining governance differences and similarities across countries, we believe that given the financialization of the corporate economy, current globalization trends of investment, and rapid information technology advances, it is important to shift our conceptualization of governance models beyond the dichotomous world of common-law/outsider/shareholder-oriented system vs. civil law/insider/stakeholder oriented system. Our claim is based on the empirical observation that there exists a wide range of firms that either (1) fall in the "wrong" corporate governance category; (2) are a hybrid of these two categories; or (3) should be placed into an entirely new category such as firms in emerging markets or state-owned firms. In addition, as Aguilera and Jackson (2003) argue, firms, regardless of their legal family constraints, their labor and product markets, and the development of the financial markets from which they can draw, have significant degrees of freedom to chose whether to implement different levels of a given corporate governance practice. That is, firms might chose to fully endorse a practice or simply seek to comply with the minimum requirements without truly internalizing the governance practice. An illustrative example of the different degrees of internalization of governance practices is the existing variation in firms' definition of director independence or disclosure of compensation systems. We first discuss the conceptual idea of configurations or bundles of corporate governance practices underscoring the concept of equifinal paths to given firm outcomes as well as the complementarity and substitution in governance practices. We then move to the practice level of analysis to show how three governance characteristics (legal systems, ownership and boards of directors) cannot be conceptualized independently, as each of them is contingent on the strength and prevalence of other governance practices. In the last section, we illustrate how different configurations are likely to playout across industries and countries, taking as the departing practice, corporate ownership.

A methodology for exploring emergence in learning communities

Learning communities are becoming increasingly complex in nature, often being used to drive multiple agendas. For example, there is an increasing move to develop learning cities which seek to draw on synergies to both improve citizen learning and skills as well as economic regeneration. Such synergy-driven learning communities, of which the learning cities are but one example, seek to utilise interaction to develop 'emergent products', be it at the individual level or the system-wide level, which could not be produced in isolation. Successfully enabling emergence is critical to their success. Designing for specific types of emergence is however difficult given the intrinsic unpredictability of complex systems. Insight into the intrinsic characteristics of these synergy-driven learning communities and how their interaction leads to emergence over time is required. This paper reports on the methodology developed to explore these highly complex learning communities. The approach adopted was to combine exploratory case studies which established the intrinsic characteristics of the learning communities with an exploration of emergence guided by a meta-level conceptual framework of emergence. This was augmented by secondary data to aid triangulation and provide rigour. As well as discussing the rationale for the adopted approach, implementation issues and the rich information set obtained are discussed using specific case examples. Findings from the investigations led to recommendations regarding future development of appropriate methods for seeding and managing such complex learning communities. The meta level framework means the approach may be readily adapted to other complex social system

Heterogeneous Capital, Entrepreneurship, and Economic Organization

We outline an Austrian approach to economic organization based on the entrepreneur and the Austrian idea of capital as heterogeneous and time-dimensioned, tow themes associated with Israel Kirzner's contributions. We provide a novel interpretation of capital heterogeneity based on the notion of attributes, argue that attributes are costly to measure and that this links directly to the theory of economic organization. In particular, we develop insights in economic organization based on the notion that entrepreneurs will often have to experiment with capital assets to gauge the value of these assets when deployed in production.Austrian Economics, capital, knowledge

Theories of managerial action and their impact on the conceptualisation of executive careers.

In this paper I outline one of the developments in the social sciences and macro organizational theory that could be of special profit for academic work on careers. I argue that a theory of action perspective is timely because its assumptions fit extremely well with the heterogeneity and lability of today’s structures and the plurality and unpredictability they bring to careers. I suggest there are two basic potential contributions of theories of action to the field of careers. First, they endorse the relevance of the shift in the basic image of managers’ careers, from the analogy of an ascendant trajectory of positions, to that of an idiosyncratic sequence of experiences loosely related to an organisational architecture. Second, they reinforce Weick’s arguments (1996) that careers cannot be conceived of merely as a dependent variable, as just “following” structures. Both contributions spring from a notion of management work in theories of action as essentially local, tactical, and pragmatic, with enacting or social constructionist effects on structure and organizations.executive careers; structure; organizations;

Inherent Structures for Soft Long-Range Interactions in Two-Dimensional Many-Particle Systems

We generate inherent structures, local potential-energy minima, of the "$k$-space overlap potential" in two-dimensional many-particle systems using a cooling and quenching simulation technique. The ground states associated with the $k$-space overlap potential are stealthy ({\it i.e.,} completely suppress single scattering of radiation for a range of wavelengths) and hyperuniform ({\it i.e.,} infinite wavelength density fluctuations vanish). However, we show via quantitative metrics that the inherent structures exhibit a range of stealthiness and hyperuniformity depending on the fraction of degrees of freedom that are constrained. Inherent structures in two dimensions typically contain five-particle rings, wavy grain boundaries, and vacancy-interstitial defects. The structural and thermodynamic properties of inherent structures are relatively insensitive to the temperature from which they are sampled, signifying that the energy landscape is relatively flat and devoid of deep wells. Using the nudged-elastic-band algorithm, we construct paths from ground-state configurations to inherent structures and identify the transition points between them. In addition, we use point patterns generated from a random sequential addition (RSA) of hard disks, which are nearly stealthy, and examine the particle rearrangements necessary to make the configurations absolutely stealthy. We introduce a configurational proximity metric to show that only small local, but collective, particle rearrangements are needed to drive initial RSA configurations to stealthy disordered ground states. These results lead to a more complete understanding of the unusual behaviors exhibited by the family of "collective-coordinate" potentials to which the $k$-space overlap potential belongs.Comment: 36 pages, 16 figure

Allo-network drugs: Extension of the allosteric drug concept to protein-protein interaction and signaling networks

Allosteric drugs are usually more specific and have fewer side effects than orthosteric drugs targeting the same protein. Here, we overview the current knowledge on allosteric signal transmission from the network point of view, and show that most intra-protein conformational changes may be dynamically transmitted across protein-protein interaction and signaling networks of the cell. Allo-network drugs influence the pharmacological target protein indirectly using specific inter-protein network pathways. We show that allo-network drugs may have a higher efficiency to change the networks of human cells than those of other organisms, and can be designed to have specific effects on cells in a diseased state. Finally, we summarize possible methods to identify allo-network drug targets and sites, which may develop to a promising new area of systems-based drug design