Numerically flat Higgs vector bundles

After providing a suitable definition of numerical effectiveness for Higgs bundles, and a related notion of numerical flatness, in this paper we prove, together with some side results, that all Chern classes of a Higgs-numerically flat Higgs bundle vanish, and that a Higgs bundle is Higgs-numerically flat if and only if it is has a filtration whose quotients are flat stable Higgs bundles. We also study the relation between these numerical properties of Higgs bundles and (semi)stability.Comment: 11 page

Threshold Resummed Spectra in B -> Xu l nu Decays in NLO (I)

We evaluate thresholds resummed spectra in B -> Xu l nu decays in next-to-leading order. We present results for the distribution in E_X and in m_X^2/E_X^2, for the distribution in E_X and E_l and for the distribution in E_X, where E_X and m_X are the energy and the invariant mass of the final hadronic state Xu respectively and E_l is the energy of the charged lepton. We explicitly show that all these spectra (where there is no integration over the hadronic energy) can be directly related to the photon spectrum in B -> Xs gamma via short-distance coefficient functions.Comment: 33 pages, no figures. The section on the double distribution in the hadron and electron energies has been largely rewritten with an improved resummation scheme. Small stylistic changes in the remaining sections. References adde

Time Minimal Trajectories for a Spin 1/2 Particle in a Magnetic Field

In this paper we consider the minimum time population transfer problem for the $z$-component of the spin of a (spin 1/2) particle driven by a magnetic field, controlled along the x axis, with bounded amplitude. On the Bloch sphere (i.e. after a suitable Hopf projection), this problem can be attacked with techniques of optimal syntheses on 2-D manifolds. Let $(-E,E)$ be the two energy levels, and $|\Omega(t)|\leq M$ the bound on the field amplitude. For each couple of values $E$ and $M$, we determine the time optimal synthesis starting from the level $-E$ and we provide the explicit expression of the time optimal trajectories steering the state one to the state two, in terms of a parameter that can be computed solving numerically a suitable equation. For $M/E<<1$, every time optimal trajectory is bang-bang and in particular the corresponding control is periodic with frequency of the order of the resonance frequency $\omega_R=2E$. On the other side, for $M/E>1$, the time optimal trajectory steering the state one to the state two is bang-bang with exactly one switching. Fixed $E$ we also prove that for $M\to\infty$ the time needed to reach the state two tends to zero. In the case $M/E>1$ there are time optimal trajectories containing a singular arc. Finally we compare these results with some known results of Khaneja, Brockett and Glaser and with those obtained by controlling the magnetic field both on the $x$ and $y$ directions (or with one external field, but in the rotating wave approximation). As byproduct we prove that the qualitative shape of the time optimal synthesis presents different patterns, that cyclically alternate as $M/E\to0$, giving a partial proof of a conjecture formulated in a previous paper.Comment: 31 pages, 10 figures, typos correcte

Toward a universal theory of the human group: sociological systems framework applied to the comparative analysis of groups and organizations

Drawing on a sociological multi-level, dynamic systems approach – actor-system-dynamics (ASD) -- which has been developed and applied in institutional, organizational, and societal analyses, we formulate a general model for the comparative analysis of social groups and organizations. This social systems approach has not been previously applied in the group area. We claim that the approach can be systematically and fruitfully applied to small as well as large groups and organizations as a methodology to understand and analyze their structure, functioning and dynamics. A group is considered a system with three universal subsystems on which any human social organization, including small groups, depends and which motivate, shape and regulate group activities and productions. The subsystems are bases or group requisites – necessary for group “functioning” and performance in more or less orderly or coherent ways; on this basis a group may be able to realize its purposes or goals(as well as possibly some members’ personal goals) and maintain and reproduce the group. The group bases consist of: first, a rule regime (collective culture)defining group identity and purpose, shaping and regulating roles and role relationships, normative patterns and behavioral outputs; second, an agential base of group members who are socialized or partially socialized carriers of and adherents to the group’s identity and rule regime; of relevance here are involvement/participation factors motivating member to adhere to, accept, and implement key components of the rule regime; third, there is a resource base, 2 technologies and materials, self-produced and/or obtained from the environment, which are essential to group functioning and key group performances. Section I briefly presents the framework and outlines the group systems model, characterized by its three universal bases or subsystems and its finite universal production functions and their outputs as well as the particular context(s) in which groups function. For illustrative purposes, the section identifies three major ideal-type modalities of group formation: informal self-organization by agents, group construction by external agents, and group formation through more or less formal multi-agent negotiation. The general systems model presented in Section II characterizes a social group not only by its three universal bases but by its finite universal production functions (elaborated in Section IV) and its outputs as well as by its shared places (situations for interaction) and times for gathering and interacting. Group productions impact on the group itself (reflexivity) and on its environment. These outputs, among other things, maintain/adapt/develop the group bases (or possibly unintentionally undermine/destroy them) Thus, groups can be understood as action and interaction systems producing goods, services, incidents and events, experiences, developments, etc. for themselves and possibly for the larger environment on which they depend for resources, recruits, goods and services, and legitimation. The model provides a single perspective for the systematic description and comparative analysis of a wide diversity of groups (Sections III and IV). A major distinctive feature in our systems approach is the conceptualization of rules and rule regimes (Sections II, III, IV, and V). Finite universal rule categories (ten distinct categories) are specified; they characterize every functioning social group or organization. A rule regime, while an abstraction is carried, applied, adapted, and transformed by concrete human agents, who interact, exchange, exercise power, and struggle within the group, in large part based on the rule regime which they maintain and adapt as well as transform. The paper emphasizes not only the systemic character of all functioning groups – universally their three bases and their output functions together with feedback dynamics -- but also the differentiating character of any given group’s distinct rule configuration (Section IV). For illustrative purposes Section IV presents a selection of rule configurations characterizing several ideal types of groups, a military unit, a terrorist group, a recreational or social group, a research group, a corporate entity Section V considers the dynamics of groups in terms of modification and transformation of group bases and their production functions. The group system model enables us to systematically identify and explicate the internal and external factors that drive group change and transformation, exposing the complex interdependencies and dynamic potentialities of group systems. Section VI sums up the work and points out its scope and limitations. The group systems model offers a number of promising contributions: (1) a universal systems model identifies the key subsystems and their interrelationships as well as their role in group production functions/outputs and performances; (2) the work conceptualizes and applies rules and rule complexes and their derivatives in roles, role relationships, norms, group procedures and production functions; (3) it identifies the universal categories of rules making up a rule regime, a major subsystem for any functioning group; (4) the model conceptualizes particular “group rule configurations” – rule regimes with specified rules in the universal rule categories—for any given group; groups are identifiable and differentiable by their rule configurations (as well as by their resource and agency bases); (5) it conceptualizes the notion of the degree of coherence (alternatively, degree of incoherence) of rule configurations characteristic of any given group and offers an explanation of why group attention is focused on the coherence of rules in certain group areas; (6) the systems model suggests an interpretation of Erving Goffman’s “frontstage backstage” distinction in terms of alternative, differentiated rule regimes which are to a greater or lesser extent incoherent with respect to one another; moreover, the participants who are privy to the differentiation navigate using a shared rule complex to translate coherently and consistently 3 from one regime to the other, using appropriate discourses; (7) incoherence, contradiction, conflict and struggle relating to rule regimes are considered part and parcel of group functioning and development; (8)group stability and change are explicated in terms of internal mechanisms (e.g., governance, innovation, and conflict) as well as external mechanisms (resource availability, legal and other institutional developments, population conditions), pointing up the complex systemic interdependencies and dynamic potentialities of group systems; (9) given the multi-level dynamic systems framework (i.e., ASD) that has been applied in a range of special areas (economic, political, technological, environmental, bio-medical, among others) its applicataion in the field of groups is a promising step toward achieving greater synthesis in sociology and social science. This 2nd edition of the paper has been substantially rewritten and extended: the current text is twice the number of pages of the original – and there has been much restructuring of the manuscript as a whole. Tables and figures have been added. Substantively, we developed the following features of the work in the 2nd edition: (1) more attention has been given to tension, conflict, and conflict resolution in groups; (2) we also stressed group requisites for sustainability and group production functions; (3) a section on group formation with illustrations has been added; (4) we have expanded our attention to group rule configurations which differentiate groups from one another but also enable systematic comparisons; (5) we have much expanded consideration of the dynamics of group change and transformation

A universal theory of social groups: the actor-system-dynamics approach to agents, rule regimes, and interaction processes

Drawing on multi-level, dynamic systems theory in sociology which has been developed and applied in institutional, organizational, and societal analyses, we formulate a general theory of social groups. This social systems approach has not been previously applied in the group area. We claim that this particular systems approach can be systematically and fruitfully applied to small as well as large groups to understand and analyze their functioning and dynamics. In this article, we refer to a group as an aggregation of persons/social agents that is characterized by (1) shared group identity, (2) a shared rule regime (collective culture) shaping and regulating their roles and role relationships and group behavioral outputs (3) its bases of membership and adherence or commitment to the group, its identity and rule regime, (4) its technologies and material resources used in group interactions, 2 performances, and productions (5) it shared places (situations for interaction), and (6) its times for gathering and interacting. The theory identifies three universal bases on which any human group or social organization, including small groups, depends and which motivate, shape and regulate group activities and productions (Section II). The bases are group requisites – necessary for group “functioning” and interacting in more or less orderly or coherent ways, realizing group as well as possibly members’ goals and maintaining and reproducing the group. The group bases consist of, first, a rule regime or social structural base; second, an agential base of group members socialized or partially socialized carriers of and adherents to the group’s rule regime; of importance here are involvement/participation factors motivating member to adhere to, accept, and implement the rule regime; third, there is a resource base, technologies and resources self-produced and/or obtained from the environment, which are essential to key group activities. In the theory presented here in Section II, a social group is not only characterized by its three universal bases but by its universal functions, group actions and outputs -- its interactions and productions/performances and their outcomes and developments including the impact of their productions on the group itself (reflexivity) and on its environment (see Figure 1). These outputs, among other things, maintain/adapt/develop core group Bases (or possibly unintentionally undermine/destroy them). Thus, groups can be understood as action/interaction systems producing goods, services, incidents and events, experiences, developments, etc. for themselves and possibly for the larger environment on which they depend for resources, recruits, goods and services, legitimation, etc. The theory identifies the six (6) universal system functions of groups. A major distinctive feature in our systems approach is the theory of rule regimes, specifying the finite universal rule categories (ten distinct categories) that characterize every functioning social group or organization. A rule regime, while an abstraction is carried, applied, adapted, and transformed by concrete human agents, who interact, exchange, exercise power, and struggle within the group, in large part based on the rule regime which they maintain, adapt, and transform. We emphasize not only the systemic character of all functioning groups – universally their three bases and their six output functions together with feedback dynamics -- but also the differentiating character of any given group’s particular rule configuration. The article ends with a discussion of two major theoretical implications: (1) the identification and analyses of any given group’s particular rule configuration which characterize that group and is sustained under relatively stable internal and external conditions (Section III); for illustrative purposes we present in Section IV a selection of few simple rule configurations that characterize several diverse types of groups. (2) the transformation of group bases and their interaction/production functions. The theory enables from a single framework the systematic description and comparative analysis of a wide diversity of groups, as illustrated in Sections III and IV

Neoplastic tissue transfiguration in vivo by recombinant human transforming growth factor-β3

Human oral squamous cell carcinomas (hSCCs) are the most common head and neck cancers now presenting with more aggressive biological and clinical features due to smoking and alcohol together with widespread viremia. Transforming growth factor-β (TGF-β) proteins are powerful morphogens that induce rapid and substantial induction of endochondral bone formation but in primates only