7,859 research outputs found
The Permeability of Network Boundaries: Strategic Alliances in the Japanese Electronics Industry in the 1990s
This paper looks at the choice of strategic partners for alliance formation in the Japanese electronics industry during the post-bubble economic period 1992-97. Results from a dyad analysis of 128 companies suggest that firms tend to look for partners within their existing vertical keiretsu networks of organizations for alliances that target the creation of resources that build on existing knowledge (production or distribution) but that this common keiretsu effect disappears for alliances that involve new knowledge creation (new product or technology development). The role of corporate networks, environmental uncertainty and their implications for our understanding of strategic alliance formation and the dynamics of social networks are discussed.
Confidence regions for the multinomial parameter with small sample size
Consider the observation of n iid realizations of an experiment with d>1
possible outcomes, which corresponds to a single observation of a multinomial
distribution M(n,p) where p is an unknown discrete distribution on {1,...,d}.
In many applications, the construction of a confidence region for p when n is
small is crucial. This concrete challenging problem has a long history. It is
well known that the confidence regions built from asymptotic statistics do not
have good coverage when n is small. On the other hand, most available methods
providing non-asymptotic regions with controlled coverage are limited to the
binomial case d=2. In the present work, we propose a new method valid for any
d>1. This method provides confidence regions with controlled coverage and small
volume, and consists of the inversion of the "covering collection"' associated
with level-sets of the likelihood. The behavior when d/n tends to infinity
remains an interesting open problem beyond the scope of this work.Comment: Accepted for publication in Journal of the American Statistical
Association (JASA
How Geometry Controls the Tearing of Adhesive Thin Films on Curved Surfaces
Flaps can be detached from a thin film glued on a solid substrate by tearing
and peeling. For flat substrates, it has been shown that these flaps
spontaneously narrow and collapse in pointy triangular shapes. Here we show
that various shapes, triangular, elliptic, acuminate or spatulate, can be
observed for the tears by adjusting the curvature of the substrate. From
combined experiments and theoretical models, we show that the flap morphology
is governed by simple geometric rules.Comment: 6 pages, 5 figure
mixtools: An R Package for Analyzing Mixture Models
The mixtools package for R provides a set of functions for analyzing a variety of finite mixture models. These functions include both traditional methods, such as EM algorithms for univariate and multivariate normal mixtures, and newer methods that reflect some recent research in finite mixture models. In the latter category, mixtools provides algorithms for estimating parameters in a wide range of different mixture-of-regression contexts, in multinomial mixtures such as those arising from discretizing continuous multivariate data, in nonparametric situations where the multivariate component densities are completely unspecified, and in semiparametric situations such as a univariate location mixture of symmetric but otherwise unspecified densities. Many of the algorithms of the mixtools package are EM algorithms or are based on EM-like ideas, so this article includes an overview of EM algorithms for finite mixture models.
The importance of inversion disorder in the visible light induced persistent luminescence in Cr doped ABO (A = Zn or Mg and B = Ga or Al)
Cr doped spinel compounds ABO with A=Zn, Mg and B=Ga, Al
exhibit a long near infrared persistent luminescence when excited with UV or
X-rays. In addition, persistent luminescence of ZnGaO and to a lesser
extent MgGaO, can also be induced by visible light excitation via
A T transition of Cr, which makes these
compounds suitable as biomarkers for in vivo optical imaging of small animals.
We correlate this peculiar optical property with the presence of antisite
defects, which are present in ZnGaO and MgGaO. By using X-ray
absorption fine structure (XAFS) spectroscopy, associated with electron
paramagnetic resonance (EPR) and optical emission spectroscopy, it is shown
that an increase in antisite defects concentration results in a decrease in the
Cr-O bond length and the octahedral crystal field energy. A part of the defects
are in the close environment of Cr ions, as shown by the increasing
strain broadening of EPR and XAFS peaks observed upon increasing antisite
disorder. It appears that ZnAlO, which exhibits the largest crystal
field splitting of Cr and the smallest antisite disorder, does not show
considerable persistent luminescence upon visible light excitation as compared
to ZnGaO and MgGaO. These results highlight the importance of
Cr ions with neighboring antisite defects in the mechanism of persistent
luminescence exhibited by Cr doped ABO spinel compounds.Comment: 10 pages + supplementary (available on request
Noise-induced volatility of collective dynamics
"Noise-induced volatility" refers to a phenomenon of increased level of
fluctuations in the collective dynamics of bistable units in the presence of a
rapidly varying external signal, and intermediate noise levels. The
archetypical signature of this phenomenon is that --beyond the increase in the
level of fluctuations-- the response of the system becomes uncorrelated with
the external driving force, making it different from stochastic resonance.
Numerical simulations and an analytical theory of a stochastic dynamical
version of the Ising model on regular and random networks demonstrate the
ubiquity and robustness of this phenomenon, which is argued to be a possible
cause of excess volatility in financial markets, of enhanced effective
temperatures in a variety of out-of-equilibrium systems and of strong selective
responses of immune systems of complex biological organisms. Extensive
numerical simulations are compared with a mean-field theory for different
network topologies
Synthesis and proton conduction properties of lanthanide amino-sulfophosphonates
Crystalline acid-functionalized metal phosphonates are potential candidates as proton conducting electrolytes. Their frameworks can be chemically modified to contain proton carriers such as acidic groups (P-OH; -SO3H, -COOH,…) and guest molecules (H2O, NH3,…) that generates hydrogen bond networks stable in a wide range of temperature [1,2].
In this work, focus is laid on properties derived from the combination of lanthanide ions with the amino-sulfophosphonate ligand (H2O3PCH2)2-N-(CH2)2-SO3H. Hightrough-put screening was followed to reach the optimal synthesis conditions under solvothermal conditions at 140 ºC. Isolated polycrystalline solids, Ln[(O3PCH2)2-NH-(CH2)2-SO3H].2H2O (Ln= La, Pr and Sm), crystallize in the monoclinic (La) and orthorhombic (Pr and Sm) systems with unit cell volume of ~2548 Å3. Preliminary proton conductivity measurements for Sm derivative have been carried out between 25º and 80 ºC at relative humidity (RH) values of 70 % and 95 %. The sample exhibits enhanced conductivity at high RH and T (Figure 1) and constant activation energies of 0.4 eV, typical of a Grothuss mechanism of proton.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. FQM-1656; MAT2013-41836-
Understanding the gastrointestinal tract of the elderly to develop dietary solutions that prevent malnutrition
Although the prevalence of malnutrition in the old age is increasing worldwide a synthetic understanding of the impact of aging on the intake, digestion, and absorption of nutrients is still lacking. This review article aims at filling the gap in knowledge between the functional decline of the aging gastrointestinal tract (GIT) and the consequences of malnutrition on the health status of elderly. Changes in the aging GIT include the mechanical disintegration of food, gastrointestinal motor function, food transit, chemical food digestion, and functionality of the intestinal wall. These alterations progressively decrease the ability of the GIT to provide the aging organism with adequate levels of nutrients, what contributes to the development of malnutrition. Malnutrition, in turn, increases the risks for the development of a range of pathologies associated with most organ systems, in particular the nervous-, muscoskeletal-, cardiovascular-, immune-, and skin systems. In addition to psychological, economics, and societal factors, dietary solutions preventing malnutrition should thus propose dietary guidelines and food products that integrate knowledge on the functionality of the aging GIT and the nutritional status of the elderly. Achieving this goal will request the identification, validation, and correlative analysis of biomarkers of food intake, nutrient bioavailability, and malnutrition.info:eu-repo/semantics/publishedVersio
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