El objetivo de esta nota es reflexionar sobre el impacto que el COVID-19 genera y seguira generando en el proceso de produccion mundial que se articula fundamentalmente en torno a las cadenas globales de valor (CGV). Para ello, pensamos que el analisis requiere tomar en cuenta la amplia literatura internacional sobre sistemas complejos que anidan en las CGV. Desde esta perspectiva, consideramos que un sistema economico esta conformado por multiples subsistemas interrelacionados de diverso grado de desarrollo, integrados a la vez por diversas organizaciones (empresas e instituciones) que realizan interacciones entre si que van mas alla de las transacciones de compra venta coordinadas por el mercado. En especial, un sistema es complejo cuando esta compuesto por multiples actores que interactuan en una forma no lineal de modo que el agregado es mayor que la suma de las partes. En estos sistemas las propiedades del agregado son “emergentes”. Asimismo, estos sistemas son: i) modulares, porque estan formados por un conjunto de partes especificas, funcionales y conectadas; ii) abiertos, porque sus partes interactuan con ciertos grados de libertad y pueden cambiar sus conexiones y iii) jerarquicos, porque cada modulo es un sistema complejo.

Abstract The pace ,of technological, innovation ,since ,World ,War ,II is dramatically accelerating,following ,the commercial ,exploitation of the ,Internet since 1994. For example, just in the last six years fiber optics capacity (infrastructure for transmission,of information ,including ,voice and ,data) has incremented ,over one hundred times thanks to a new technology, dense wave division multiplexing, and internet traffic has increased over 1000 times. Moreover, internet traffic still continues,to duplicate,every 200 days. The dramatic,advances,in information,and communication,technologies,provide,excellent examples,of the critical relevance,of the knowledge,in the,development,of competitive,advantages. The Silicon Valley (SV) that about ,fifty years ago ,was ,an agricultural ,region ,became ,the center of dramatic technological and organizational transformations. In fact, most of the present,high-tech companies ,did ,not exist twenty ,years ,ago. Venture ,capital contribution,to the local economy,is quite important,not only due to the magnitude ofthe,financial investment ,(venture investment ,in SV during ,1999 surpassed 11.000 millions ,of dollars) but also because ,the extend ,and ,quality of networks (management teams, high-level employees, customers, providers, etc.) that bring to emerging,companies. ,How ,are new ,technologies ,developing? ,What is the ,role of private,and ,public ,investment ,in the ,financing ,of R&D? Which ,are the most dynamical,agents and how,do they,interact? How,are new,companies,created and how,do they,evolve? The discussion,of these,questions,is the focus of the,current

We study stress relaxation in a strongly segregated lamelar mesophase of diblock copolymers. We consider the extreme limit in which chains are highly stretched and with their junction points confined to narrow interfaces. A lamella can be divided into “stress blobs” at some distance z from the interface, with well defined local modulus G(z,w) at frequency w. For sliding (compressional) stress the total modulus is transmitted in series (parallel) across the layer. We evaluate the local G(z,t) which shows, for a given height, a very broad spectrum of relaxation times.

Object-Oriented technology is gaining rapid acceptance among software developers, and is becoming the preferred choice for modern computer programming projects. Should a natural scientist care? We discuss some of the main concepts in object-oriented programming and the potential of this interesting technology. The object model views the world as made of many objects interacting (exchanging messages) with each other to produce a collective behavior. This picture resembles a quantum system of interacting particles. Suggestive analogies between the object model and quantum physics are identified and exploited in this work to provide an introduction to object-oriented programming

The problems of the partial covering time (PCT) and of the random covering time (RCT) are studied in two dimensions using Monte Carlo simulations. We find that the PCT (RCT) presents a discontinuous transition at f = 1 (f = 0), where f is the fraction of visited sites by a random walker. An analysis of the time evolution of the surviving unvisited clusters reveals that they exhibit a time-dependent fractal-like structure.

The 1/d expansion method for polymer chains is examined by comparing these expansions for several thermodynamic and structural quantities with the results of standard series analysis of exact enumeration data. The comparisons cover a wide range of spatial dimensions d, including non-integer ones, and are performed for particular values of interaction energy. Good agreement is generally found for d>4, whereas discrepancies become conspicuous as d decreases to d= 2. Reasonable values are obtained for the exponents nu and gamma in d = 2 - 4 by applying the coherent-anomaly method of Suzuki to our 1/d expansions through fifth order in d-1.

We consider the statistical properties associated with the packing of p self-avoiding rods of length M on a d-dimensional hypercubic lattice with N sites and periodic boundary conditions. The exact treatment for few (p≤4) rods is combined with information derivable from the lattice cluster theory (LCT) to obtain the exact analytic form for the free energy f per site. The thermodynamic limit of this free energy f is reexpressed as a series expansion about the zeroth order Flory mean field approximation. The expansion is in powers of the rod volume fraction φ=pM/N and contributions are retained through order φp (with p=4) for any M and d. The theory is compared with previous diagram based LCT calculations and with the DiMarzio approximation. Departures (in the thermodynamic limit) from the latter successful approximation appear at order φ4 and arise from correlations of four rods in configurations where the rods are not all parallel, correlations which are absent in the DiMarzio approximation. Our method uses computer enumerations to replace the time consuming task of evaluating the many-body diagrams of the LCT. The series for d≳1 are ill behaved in the large M limit and strongly indicate that resummations are required to obtain physically meaningful results.

The lattice cluster theory for the free energy of a set of mutually avoiding rigid rod polymers is extended to treat anisotropic orientational distributions. The theory permits the systematic evaluation of corrections to the isotropic Flory mean field approximation for arbitrary rod orientational distributions, with the Flory theory being the zeroth order isotropic limit of the full theory. The corrections to the zeroth order mean field entropy are represented as a cluster expansion and may be evaluated as a series expansion in the polymer volume fraction φ. We compute all corrections through order φ3 that survive in the thermodynamic limit for the general anisotropic case, along with new fourth order results, which also extend the isotropic limit theory. The anisotropic rod lattice cluster theory represents an improvement over the DiMarzio theory for the packing entropy of rod polymers. This improvement first emerges at fourth order in φ and arises in the lattice cluster theory from inclusion of correlations between four rods lying along distinct lattice directions, four-rod correlations that are absent in DiMarzio’s theory.

The self-avoiding walk (SAW) exponents nu and gamma are computed over a range of dimensions (1 less-than-or-equal-to d < infinity) from exact expressions for the mean-square end-to-end distance [R(n)2] and the partition function Q(n) of SAWs having a limited number of steps, n less-than-or-equal-to 11. SAW exponents (nu, gamma) for arbitrary dimension d are estimated by applying standard extrapolation techniques to our direct enumeration data which has been analytically continued to variable dimension. Exponent estimates obtained from continuum theories of self-avoiding paths are compared with the SAW calculations.

We present a systematic method of evaluating the packing entropy for a set of mutually avoiding extended, hard, rigid objects on a lattice. The method generalizes a simple algebraic representation of the lattice cluster theory developed by Freed and co-workers for systems composed of flexible objects. The theory provides a power series expansion in z-1 for the corrections to the zeroth order mean field approximation partition function, where z is the lattice coordination number. We illustrate the general theory by calculating the packing entropy of four-unit rigid ''square'' objects on a hypercubic lattice as a function of the volume fraction of the squares. As a particular limiting case, we also evaluate for the packing entropy of two, three, and four squares on a two-dimensional square lattice and find agreement with the cluster expansion.

The surface tension increment is evaluated for dilute polymer solutions. The first virial coefficient is calculated to first order in excluded volume near two limiting boundary conditions: repulsive (Dirichlet) and reflecting (von Neumann). An interpolation function extends the calculations to intermediate values of the polymer–surface interaction strength and provides the surface pressure as a function of both polymer–polymer and polymer–surface interactions. Comparison with experiments for polystyrene in toluene suggest the importance of nonuniversal contributions to the surface tension increment.

Exact enumeration data in dimensions d = 2-6 is used to evaluate the exact d-dimensional mean-square end-to-end distance R(n)2 of a short (n less-than-or-equal-to 11) n-bond self-interacting self-avoiding random walk on hypercubic lattices as function of the neighbor contact energy. This exact form is transformed into a large n expansion of R(n)2 through fifth order in d-1 but to all orders in the contact energy.