On ergodic operator means in Banach spaces

We consider a large class of operator means and prove that a number of ergodic theorems, as well as growth estimates known for particular cases, continue to hold in the general context under fairly mild regularity conditions. The methods developed in the paper not only yield a new approach based on a general point of view, but also lead to results that are new, even in the context of the classical Cesaro means

Quasi-K\"ahler Bestvina-Brady groups

A finite simple graph \G determines a right-angled Artin group G_\G, with one generator for each vertex v, and with one commutator relation vw=wv for each pair of vertices joined by an edge. The Bestvina-Brady group N_\G is the kernel of the projection G_\G \to \Z, which sends each generator v to 1. We establish precisely which graphs \G give rise to quasi-K\"ahler (respectively, K\"ahler) groups N_\G. This yields examples of quasi-projective groups which are not commensurable (up to finite kernels) to the fundamental group of any aspherical, quasi-projective variety.Comment: 11 pages, accepted for publication by the Journal of Algebraic Geometr

Non-finiteness properties of fundamental groups of smooth projective varieties

For each integer n\ge 2, we construct an irreducible, smooth, complex projective variety M of dimension n, whose fundamental group has infinitely generated homology in degree n+1 and whose universal cover is a Stein manifold, homotopy equivalent to an infinite bouquet of n-dimensional spheres. This non-finiteness phenomenon is also reflected in the fact that the homotopy group \pi_n(M), viewed as a module over Z\pi_1(M), is free of infinite rank. As a result, we give a negative answer to a question of Koll'ar on the existence of quasi-projective classifying spaces (up to commensurability) for the fundamental groups of smooth projective varieties. To obtain our examples, we develop a complex analog of a method in geometric group theory due to Bestvina and Brady.Comment: 16 page

Alexander polynomials: Essential variables and multiplicities

We explore the codimension one strata in the degree-one cohomology jumping loci of a finitely generated group, through the prism of the multivariable Alexander polynomial. As an application, we give new criteria that must be satisfied by fundamental groups of smooth, quasi-projective complex varieties. These criteria establish precisely which fundamental groups of boundary manifolds of complex line arrangements are quasi-projective. We also give sharp upper bounds for the twisted Betti ranks of a group, in terms of multiplicities constructed from the Alexander polynomial. For Seifert links in homology 3-spheres, these bounds become equalities, and our formula shows explicitly how the Alexander polynomial determines all the characteristic varieties.Comment: 27 page

Topology and geometry of cohomology jump loci

We elucidate the key role played by formality in the theory of characteristic and resonance varieties. We define relative characteristic and resonance varieties, V_k and R_k, related to twisted group cohomology with coefficients of arbitrary rank. We show that the germs at the origin of V_k and R_k are analytically isomorphic, if the group is 1-formal; in particular, the tangent cone to V_k at 1 equals R_k. These new obstructions to 1-formality lead to a striking rationality property of the usual resonance varieties. A detailed analysis of the irreducible components of the tangent cone at 1 to the first characteristic variety yields powerful obstructions to realizing a finitely presented group as the fundamental group of a smooth, complex quasi-projective algebraic variety. This sheds new light on a classical problem of J.-P. Serre. Applications to arrangements, configuration spaces, coproducts of groups, and Artin groups are given.Comment: 41 pages; this is a major revision of arXiv:math/0512480; accepted for publication in Duke Mathematical Journa

Universities` Role in Knowledge-Based Economy and Society. Implications for Romanian Economics Higher Education

The main objective of the article is to analyse the extent to which Romanian universities and, particularly, those in economics higher education field can face the demands of knowledge-based economy and society. The specific objectives of the work mainly consisted of: (a) reviewing the literature outlining the theoretical, methodological and conceptual boundaries; (b) identifying methods for assessing universities’ intellectual capital and examples of good practice; and (c) presenting our research results. The research methodology was based on a structured questionnaire applied in the Academy of Economic Studies, Bucharest, Faculty of Business Administration in foreign languages. Examples of good practice in European universities and international reports of prestigious international organizations were considered as well. The research highlighted the key role of universities as main investors in lifelong learning education, by including the opinions of the direct beneficiars-students, within the context of the Romanian society and knowledge-based economy.Knowledge-based economy, knowledge-based society, investment in lifelong learning education, intellectual capital, sustainable competitive advantage

Cloud Computing as Evolution of Distributed Computing – A Case Study for SlapOS Distributed Cloud Computing Platform

The cloud computing paradigm has been defined from several points of view, the main two directions being either as an evolution of the grid and distributed computing paradigm, or, on the contrary, as a disruptive revolution in the classical paradigms of operating systems, network layers and web applications. This paper presents a distributed cloud computing platform called SlapOS, which unifies technologies and communication protocols into a new technology model for offering any application as a service. Both cloud and distributed computing can be efficient methods for optimizing resources that are aggregated from a grid of standard PCs hosted in homes, offices and small data centers. The paper fills a gap in the existing distributed computing literature by providing a distributed cloud computing model which can be applied for deploying various applications

Hybrid VLC Communications System for Increased Security Based on Raspberry Pi Microcomputer

VLC (Visible Light Communications) technology represents nowadays a new paradigm that could have a significant impact on future wireless communications. Although this technology has many advantages, one of the most common problem generated by the use of optical communication systems (based on the light in the visible spectrum), is the increased degree of disruption of the communication channel under the direct sunlight influence. The purpose of this article is to present the technological developments specific to the VLC/IR-RF (Visible Light Communication / Infrared - Radio-Frequency) hybrid system developed in the framework of a scientific research project started in 2017, which were recorded during the first half of 2019. This system based on multiple sensory devices such as temperature, motion, light intensity, dust, IR and microbolometer sensors will present the ability of intelligent monitoring and control of indoor environments (houses, office buildings, universities, campuses, etc.). From the point of view of the final purpose of the project, this will result in a hybrid bidirectional optical communication system capable of supporting high transfer rates, increased resistance to the specific sunlight disturbance, and the possibility of transmitting sensory information over long distances. The previous experimentation activities undertaken during the project were based on the use of the Arduino UNO development boards. Currently, it has been chosen to replace them with the development boards based on the ARM Cortex-A53 processor, in order to improve the system’s performance. The Arduino development boards have limited the performance of the communications system from the point of view of the transfer speeds and distances. The new Raspberry Pi development boards, being a complete operating and control system, presents high operational performances that can be used in favor of the final goal of the project.</p