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Online learning in higher education requires the effective promotion of autonomous learning, active commitment, and the development of digital competencies. The current article researches the relationships among these variables through a systematic review of the literature on the links among motivation, self-regulated learning, and digital competency. Following a search for articles on Web of Science and Scopus, a qualitative analysis with a thematic focus was completed. Seminal theoretical perspectives in common were observed, but few experiences addressed these dimensions in an integrated manner. The results show initial development of research on the topic in teaching contexts using educational platforms, with a recognition of the bilateral relationships between constructs, and relevant repercussions in academic performance and the willingness to learn. [ABSTRACT FROM AUTHOR]

In exchange for extrafloral nectar, ants deter herbivores from the plants decreasing the herbivore damage, and increasing plant performance in terms of growth and survival. Plants of different sexes may exhibit differences in the investment of resources for defence, thereby differentially decreasing the amount of energy available to other physiological processes. In this context, little is known about sex‐related differences in the outcome of ant–plant interactions in plants bearing extrafloral nectaries (EFNs).In the present study, we conducted ant‐exclusion experiments in the field to test for sex‐related differences in the outcome of ant–plant interactions in vegetative and reproductive buds of Opuntia robusta in individuals of different sexes in two populations: trioecious and dioecious. We applied tanglefoot to some plant and others were allowed ant access, and measured herbivory, relative growth rates and survival probabilities of buds during the growing season when EFNs are active. We counted the number of ants foraging in EFNs of flowers and cladodes of different sexes. We hypothesized that differences in resource investment to defence between sexes change the outcome of ant–plant interactions in terms of the number of ants foraging on EFNs, herbivory, growth, and survival probabilities.Our results suggest sex‐specific strategies in the investment of resources for defence mediated by EFNs in O. robusta, wherein males, females and hermaphrodites from both populations respond differentially to ant presence and herbivores. These sex‐related differences affected the outcome of the ant–plant interactions, influencing changes in number of ants foraging on EFNs, and the resulting herbivory, growth and survival of flowers and cladodes among the different sexes and among populations. Our results suggest that the maintenance of EFNs in O. robusta is costly, reflecting some trade‐offs between growth/survival and defence. Buds visited by ants tended to grow slowly and survive worse in the trioecious population; in the dioecious population they grew slower but survived better. Overall, a greater number of ants visiting EFNs was related to lower herbivore damage, greater growth and survival of flowers and cladodes. Our study underscores the importance of considering plant sex in the outcome of ant–plant interactions. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

A growing body of research investigates how changes in weather shape individual choices about migration, yet highly variable results continue to challenge our understanding of the weather-migration nexus. We use a data-driven approach to identify which weather variables best predicted migration decisions of 54,986 individuals originating in Mexico between 1989 and 2016. Using supervised machine learning, we fit random forests to model migration choices based on individual, household, and community attributes in training data (three-fourths of the sample) from the Mexican Migration Project. We aggregated 36 annual weather variables at the community level and applied k-fold cross-validation to evaluate which models best predicted migration decisions. The top performing models were then applied to the test data (one-fourth of our sample). Three weather variables consistently out-performed others across models: minimum temperature during day, maximum temperature at night, and 'growing degree days' – the number of days with optimal growth temperatures for corn (the major crop for most communities). Our results demonstrate that weather is related to individual choices about migration and illustrate the utility of using principled variable selection which revealed that both customized (growing degree days for a particular crop) and generic (max-min temperatures) metrics can be predictive of migration behaviors. [ABSTRACT FROM AUTHOR]

We study the spectrum and transmission coefficient of plane waves propagating along square ribbons of varying widths, containing a square-shaped, PT -symmetric impurity region. We start with a zero-width ribbon (1D chain) and place a PT symmetric dimer. The spectrum is computed numerically and the instability gain is computed as a function of the gain/loss dimer strength. The transmission coefficient is obtained in closed form and examined as a function of wavevector and the gain/loss parameter. Next, we study a ribbon in a narrow ladder configuration containing a square PT impurity. As before, we compute the instability gain numerically and the transmission coefficient in closed form for the two possible input modes. Finally, we repeat the calculations for a wider ladder ribbon containing a Lieb-like impurity in a PT configuration. For all cases and transmission channels, we obtain transmission divergences in wavevector-gain/loss parameter space, whose number increases with the width of the ribbon. • PT -symmetry. • Ribbon lattice. • Square-shaped PT impurity. • Instability rate. • Transmission coefficient. [ABSTRACT FROM AUTHOR]

We examine a fractional discrete nonlinear Schrodinger dimer, where the usual first-order derivative in the time evolution is replaced by a non integer-order derivative. The dimer is nonlinear (Kerr) and PT -symmetric, and for localized initial conditions we examine the exchange dynamics between both sites. By means of the Laplace transformation technique, the linear PT dimer is solved in closed form in terms of Mittag–Leffler functions, while for the nonlinear regime, we resort to numerical computations using the direct explicit Grunwald algorithm. In general, we see that the main effect of the fractional derivative is to produce a monotonically decreasing time envelope for the amplitude of the oscillatory exchange. In the presence of PT symmetry, the oscillations experience some amplification for gain/loss values below some threshold, while beyond threshold, the amplitudes of both sites grow unbounded. The presence of nonlinearity can arrest the unbounded growth and lead to a selftrapped state. The trapped fraction decreases as the nonlinearity is increased past a critical value, in marked contrast with the standard (non-fractional) case. [ABSTRACT FROM AUTHOR]

We studied HCl uptake by MgCl2 and sea salt over a relative humidity (RH) range from 0% to 34% at 278–313 K using a differential bead‐filled flow tube coupled to a high‐pressure chemical ionization mass spectrometer. The results showed that dry MgCl2 and sea salt are essentially inert to gaseous HCl with a probability of less than 10−6. However, under humid conditions, HCl was found to be efficiently taken up by wet inorganic surfaces. The HCl uptake coefficient for MgCl2 and sea salt increased squarely with RH, reaching a value of 0.00123 and 0.00171, respectively, at 29% RH and 298 K. Such wetting behavior is even enhanced at elevated temperatures, with the coefficient reaching 0.00208 and 0.00239, respectively, at 313 K. Based on the study of the dependence of γHCl on the initial HCl concentration, we estimate γHCl as 0.012 at 24% RH at a typical HCl concentration in the troposphere. In addition, the observation of the remarkable enhancement in the OH uptake by the HCl‐treated salts agrees with the results of our previous investigation, which suggested that water absorption on salts enhances γOH by lowering the surface pH. The proposed mechanism of HCl uptake by sea salt aerosol has implications for ozone production in the marine boundary layer. [ABSTRACT FROM AUTHOR]

This paper identifies the relationship between the health management of the COVID-19 pandemic and the economic outcomes. It shows economic and mortality indicators as well as other social and cultural variables affecting the results. It takes into account the effect of oil prices upon the exporting countries leeway. It also shows how the disruption in international trade affected global value chains. Countries with better health results during the pandemic showed better results in economic growth in the second quarter of 2020. The best predictor of economic success was the health system strengh measured by number of beds prior to the pandemic. [ABSTRACT FROM AUTHOR]

Foraging activity of bees depends on a combination of their biology, floral traits attractive for bees and environmental factors. We carried out this study to determine whether the variation of floral aperture, floral display and environmental factors throughout the day influence the foraging activity and composition of bee visitors in Kallstroemia pubescens (G. Don) Dandy. This research was conducted at the Chamela Biological Station, UNAM, Jalisco, Mexico. During anthesis, we collected bees and recorded the foraging behavior hourly. We measured hourly the environmental factors (temperature, relative humidity, and light intensity), floral aperture, floral display and floral reward. Using generalized linear mixed-effects models we tested which of the factors have more influence on floral aperture and foraging activity. To determine the dissimilarity of the species composition between the hours sampled, we used a one-way analysis of similarity (ANOSIM). We found that light intensity and humidity affected the floral aperture. Likewise, floral aperture, light intensity, temperature and time of day had a higher influence on the frequency of visitation and composition of bee species. When flowers were fully open, we recorded a greater number of bees and species. We observed two types of foraging behavior: bees collecting resources from the top of the flower (pollen gatherers) and bees within the flower avoiding the anthers and stigma (nectar gatherers). The total number of pollen gatherers recorded during our observations was greater than nectar gatherers, suggesting that this is the main floral reward. The species that had the pollen gathering behavior were mainly big bees, Apis mellifera and Exomalopsis zexmeniae, these are the potential pollinators because of their direct contact with the reproductive parts of the flower. Our results show floral aperture and environmental factors in combination influenced the foraging activity of bees, promoting changes in bee community composition throughout the day. [ABSTRACT FROM AUTHOR]

We study the transport properties of an initially localized excitation in several flat band lattices, in the presence of nonlinear (Kerr) disorder. In the weak nonlinearity regime, the dynamics is controlled by the degeneracy of the bands leading to a linear form of selftrapping. In the strong nonlinearity regime, the dynamics of the excitations depends strongly on the local environment around the initial excitation site that leads to a highly fluctuating selfrapping profile. For a binary nonlinear disorder, it is shown that the spreading of the flat band fundamental mode, is completely inhibited for a finite fraction of all cases. This fraction corresponds to the fraction of times the same value of (random) nonlinearity is assigned to all sites of the fundamental mode. [ABSTRACT FROM AUTHOR]

Machine learning is a field at the intersection of statistics and computer science that uses algorithms to extract information and knowledge from data. Its applications increasingly find their way into economics, political science, and sociology. We offer a brief introduction to this vast toolbox and illustrate its current uses in the social sciences, including distilling measures from new data sources, such as text and images; characterizing population heterogeneity; improving causal inference; and offering predictions to aid policy decisions and theory development. We argue that, in addition to serving similar purposes in sociology, machine learning tools can speak to long-standing questions on the limitations of the linear modeling framework, the criteria for evaluating empirical findings, transparency around the context of discovery, and the epistemological core of the discipline. [ABSTRACT FROM AUTHOR]

To our knowledge, there are no studies about the structure and ecological function of extrafloral nectaries (EFNs) in Opuntia robusta. This is the first description of EFNs in O. robusta, where young spines have an interesting structure and a secreting function, which are different from EFNs described in other Cactaceae species. We used light, scanning-electron, and transmission-electron microscopy to examine morphology, anatomy, and ultrastructure of the secretory spines in areoles in female and hermaphrodite individuals of O. robusta. Young cladodes develop areoles with modified and secretory spines as EFNs only active during the early growth phase. EFNs are non-vascularized structures, with no stomata, that consist of a basal meristematic tissue, a middle elongation region, and an apical secretory cone formed by large globular epidermal cells, containing nectar and medullar elongated cells. We observed the presence of Golgi apparatus, vesicles and plastids in the medullar and sup-epidermal cells of the spine. We propose that the nectar is stored in the globular cells at the apex of the spine and secreted by breaking through the globular cells or by pores. We recorded a more frequent presence of ants on younger cladode sprouts producing young secreting spines: this result is parallel with the predictions of Optimal Defense Hypothesis, which states that younger plant organs should be better defended than older ones because their loss produces a higher fitness impairment. Although Diaz-Castelazo’s hypothesis states that a more complex structure of EFNs correlates with their lower among-organs dispersion, comparing to less complex EFNs, non-vascularized structure of EFNs in O. robusta is not associated with their higher among-organs dispersion likened to O. stricta, which produces vascularized EFNs. We provide evidence that this characteristic is not a good taxonomic feature of Opuntia genus. Moreover, the comparison of EFNs of O. robusta and O. stricta suggests that the hypothesis of Diaz-Castelazo should be revised: it is rather a rule but not a law. [ABSTRACT FROM AUTHOR]

This essay analyzes three elections that had unexpected results: the exit of the United Kingdom from the European Union, the rejection of the peace agreement in Colombia and the election of Trump as president of the United States. It emphasizes three aspects: the predictions were made in a situation of uncertainty based on rules or conventions, the campaigns involved strong emotional elements and the results were affected by cultural factors (identity and religious) and not only economic ones. Standard economics omits such factors although it should take them into account. [ABSTRACT FROM AUTHOR]

Most research on the relation between steroid hormones and risky behavior has been done for Caucasian populations using 2D:4D. Some articles with ethnically mixed samples were not conclusive. We studied the relation between prenatal exposure to testosterone (T) and financial risk in a Colombian population (89 male, 34 female). Colombian population is the result of miscegenation among Amerindian, Spanish and African groups. Prenatal exposure to T was proxied by 2D:4D and rel 2 digit ratios. Risk behavior was elicited by the choice of a lottery in a 50%–50% Eckel and Grossman task with actual monetary payoffs. People with higher prenatal T exposure (lower left-hand 2D:4D, rel 2 ratios) tend to choose more risky lotteries, although the effect is weak and better captured in binary-choice than in ordered-logit models. Results are statistically significant for the left hand but not for the right hand. An increment of one standard deviation in the 2D:4D/ rel 2 of the left hand diminishes the probability of taking the riskier lotteries by 8%/10%. [ABSTRACT FROM AUTHOR]

In supercooled aqueous solutions, ice nucleation is the initial stage of the freezing process. In this paper, we present experimental results that indicate that during the freezing of aqueous solutions, freeze-induced phase separation (FIPS) into pure ice and a freeze-concentrated solution (FCS) takes place. Our observations involve the use of an optical cryo-microscope (OC-M) to record images and movies. The results visually indicate for the first time that there are two freezing processes for (NH4)3H(SO4)2/H2O solutions: (i) contact freezing, as is the case for pure water drops, and (ii) the Wegener-Bergeron-Findeisen process, which is the growth of frozen drops (ice) at the expense of liquid ones. We also present OC-M images of frozen micrometer-scaled H2SO4/H2O drops that support our previous finding that freezing of these solutions generates mixed-phase particles, namely an ice core coated with a FCS. These results are relevant for atmospheric as well as for pharmaceutical sciences. [ABSTRACT FROM AUTHOR]

Although freeze-induced phase separation and the ice/FCS (freeze-concentration solution) morphology of aqueous solutions play an important role in fields ranging from life sciences and biotechnology to geophysics and high-altitude ice clouds, their understanding is far from complete. Herein, using differential scanning calorimetry (DSC) and optical cryo-microscope (OC-M), we have studied the freezing and glass transition behavior and the ice/FCS morphology of emulsified 10–60 wt% CA (citric acid) solutions in the temperature region of ∼308 and 153 K. We have obtained a lot of new result which are understandable and unclear. The most essential understandable results are as follows: (i) similar to bulk CA/H 2 O, emulsified CA/H 2 O also freezes upon cooling and warming and (ii) the ice/FCS morphology of frozen drops smaller than ∼3–4 μm is less ramified than that of frozen bulk solutions. Unclear results, among others, are as follows: (i) in contrast to bulk solutions, which produce one freezing event, emulsified CA/H 2 O produces two freezing events and (ii) in emulsions, drop concentration is not uniform. Our results demonstrate that DSC thermograms and OC-M images/movies are mutually supplementary and allow us to extract important information which cannot be gained when DSC and OC-M techniques are used alone. [ABSTRACT FROM AUTHOR]

• Fractional calculus. • PT-symmetry. • Fractionality drives the system into instability eventually, for fixed gain/loss. • Gain/loss drives the system into instability eventually, for fixed fractionality. • Increase in system's size drives the system into instability eventually. We examine the stability domains of a 1D discrete Schrödinger equation in the simultaneous presence of parity-time (PT) symmetry and fractionality. Direct numerical examination of the eigenvalues of the system reveals that, as the fractional exponent is decreased away from unity (the standard case), the instability gain increases abruptly past a critical value. Also, as the length of the system increases, the stable fraction decreases as well. Also, for a fixed fractional exponent and lattice size, an increase in gain/loss also brings about an abrupt increase in the instability gain. Finally, the participation ratio of the modes is seen to decrease with an increase of the gain/loss parameter and with a decrease of the fractional exponent, evidencing a tendency towards localization. [ABSTRACT FROM AUTHOR]

We examine the interplay between disorder and fractionality in a one-dimensional tight-binding Anderson model. In the absence of disorder, we observe that the two lowest energy eigenvalues detach themselves from the bottom of the band, as fractionality s is decreased, becoming completely degenerate at s = 0 , with a common energy equal to a half bandwidth, V. The remaining N − 2 states become completely degenerate forming a flat band with energy equal to a bandwidth, 2 V. Thus, a gap is formed between the ground state and the band. In the presence of disorder and for a fixed disorder width, a decrease in s reduces the width of the point spectrum while for a fixed s , an increase in disorder increases the width of the spectrum. For all disorder widths, the average participation ratio decreases with s showing a tendency towards localization. However, the average mean square displacement (MSD) shows a hump at low s values, signaling the presence of a population of extended states, in agreement with what is found in long-range hopping models. • Fractional calculus. • 1D Anderson model. • Localization increases with decreasing fractality exponent. • Hump in mean square displacement. • Long-range hopping. [ABSTRACT FROM AUTHOR]

Radical uncertainty has been defined as non-probabilistic; however this definition is insufficient as there is no unique notion of probability. The article makes a historical presentation of equiprobabilistic, frequentist and Bayesian definitions of probability and proposes a notion of uncertainty resulting from these definitions. Keynes theory of animal spirits is presented as an explanation of human action in an uncertain social world. [ABSTRACT FROM AUTHOR]

Financial institutions show a characteristic risk exposure and vulnerability, making them prone to instability. Financial systems in Latin America, however, were left largely unscathed by the global financial crisis starting in 2008. This state-of-the-art survey provides an in-depth analysis on the identification and regulation of systemically important financial institutions (SIFIs). While Latin America benefits from its rich historical experience in managing systemic risks, we find the problem of SIFIs to be still underestimated. However, there are first efforts to cope with SIFIs in science and particularly Latin American supervisors and regulators are starting to take the threat posed by SIFIs seriously. [ABSTRACT FROM AUTHOR]

Calorimetric and optical cryo-microscopemeasurements of 10–64wt % citric acid (CA) solutions subjected to moderate (3 K/min) andslow (0.5 and 0.1 K/min) cooling/warming rates and also to quenching/moderatewarming between 320 and 133 K are presented. Depending on solutionconcentration and cooling rate, the obtained thermograms show onefreezing event and from one to three liquid–glass transitionsupon cooling and from one to six liquid–glass and reverse glass–liquidtransitions, one or two freezing events, and one melting event uponwarming of frozen/glassy CA/H2O. The multiple freezingevents and glass transitions pertain to the mother CA/H2O solution itself and two freeze-concentrated solution regions, FCS1and FCS2, of different concentrations. The FCS1and FCS2(or FCS22) are formed duringthe freezing of CA/H2O upon cooling and/or during the freezingupon warming of partly glassy or entirely glassy mother CA/H2O. The formation of two FCS1and FCS22regionsduring the freezing upon warming to our best knowledge has never beenreported before. Using an optical cryo-microscope, we are able toobserve the formation of a continuous ice framework (IF) and its morphologyand reciprocal distribution of IF/(FCS1+ FCS2). Our results provide a new look at the freezing and glass transitionbehavior of aqueous solutions and can be used for the optimizationof lyophilization and freezing of foods and biopharmaceutical formulations,among many other applications where freezing plays a crucial role. [ABSTRACT FROM AUTHOR]

The freezing of aqueous solutions and reciprocal distribution of ice and a freeze-concentrated solution (FCS) are poorly understood in spite of their importance in fields ranging from biotechnology and life sciences to geophysics and climate change. Using an optical cryo-miscroscope and differential scanning calorimetry, we demonstrate that upon cooling of citric acid and sucrose solutions a fast freezing process results in a continuous ice framework (IF) and two freeze-concentrated solution regions of different concentrations, FCS1 and FCS2. The FCS1 is maximally freeze-concentrated and interweaves with IF. The less concentrated FCS2 envelops the entire IF/FCS1.We find that upon further cooling, the FCS1 transforms to glass, whereas the slow freezing of FCS2 continues until it is terminated by a FCS2-glass transition. We observe the resumed slow freezing of FCS2 upon subsequent warming. The net thermal effect of the resumed freezing and a reverse glass-FCS1 transition produces the Ttr2-transition which before has only been observed upon warming of frozen hydrocarbon solutions and which nature has remained misunderstood for decades. [ABSTRACT FROM AUTHOR]

In the present work, we revisit the issue of the self-trapping dynamical transition at a nonlinear impurity embedded in an otherwise linear lattice. For our Schrödinger chain example, we present rigorous arguments that establish necessary conditions and corresponding parametric bounds for the transition between linear decay and nonlinear persistence of a defect mode. The proofs combine a contraction mapping approach applied to the fully dynamical problem in the case of a 3D-lattice, together with variational arguments for the derivation of parametric bounds for the creation of stationary states associated with the expected fate of the self-trapping dynamical transition. The results are relevant for both power law nonlinearities and saturable ones. The analytical results are corroborated by numerical computations. The latter are performed for cases of different dimension. [ABSTRACT FROM AUTHOR]

We introduce the novel concept of a bound state in the continuum (BIC) for a binary lattice satisfying the [ABSTRACT FROM AUTHOR]

• Electrical lattice. • Electro-inductive waves. • Excitation transport. • Transmission coefficient. • Fano resonances. We study the scattering properties of an electrical lattice consisting of a one-dimensional array of inductively-coupled LC units. For an initially localized electrical excitation, and in the absence of any impurity, we compute in closed form the mean square displacement of an initially localized electrical excitation for the cases of an infinite and semi-infinite lattice, obtaining a ballistic propagation under very general conditions. For the transport of extended excitations, we compute in closed form the transmission coefficient of electro-inductive plane waves across an impurity region, containing a number of side-coupled units, or a single internal impurity in the presence of coupling to first-and second nearest neighbors, looking for the presence of Fano resonances (FRs). For all cases examined, we obtain a closed-form expression for the position of the FR in terms of the relative strengths of the inductive couplings involved. For the case of two, identical side-coupled impurities, the position of the single FR turns out to be independent of the relative distance between the two impurities. [ABSTRACT FROM AUTHOR]

• A fractional version of 2D discrete Laplacian is inserted into the DNLS equation. • Spectrum of linear waves and root mean square displacement are computed in closed form. • Insertion of single general nonlinear surface impurity at the edge and at a corner. • Use of Green functions: method of images. • Compute the mode energy and bound state profile. We study the formation of localized modes around a generalized nonlinear impurity which is located at the boundary of a semi-infinite square lattice, and where we replace the standard discrete Laplacian by a fractional one, characterized by a fractional exponent 0 < α < 1 where α = 1 marks the standard, non-fractional case. We specialize to two impurity cases: impurity at an "edge" and impurity at a "corner" and use the formalism of lattice Green functions to obtain in closed form the bound state energy and its mode amplitude. It is found that, for any fractional exponent and for impurity strengths above a certain threshold, there is always a single bound state for the linear impurity, while for the nonlinear (cubic) case, up to two bound states are possible. At small fractional exponents, the energy of the impurity mode becomes directly proportional to the impurity strength. [ABSTRACT FROM AUTHOR]

• Embedded mode. • Embedded soliton. • Discrete breathers. For a one-dimensional linear lattice, earlier work has shown how to systematically construct a slowly- decaying linear potential bearing a localized eigenmode embedded in the continuous spectrum. Here, we extend this idea in two directions: The first one is in the realm of the discrete nonlinear Schrödinger, where the linear operator of the Schrödinger type is considered in the presence of a Kerr focusing or defocusing nonlinearity and the embedded linear mode is continued into the nonlinear regime as a discrete solitary wave. The second case is the Klein-Gordon setting, where the presence of a cubic nonlinearity leads to the emergence of embedded-in-the-continuum discrete breathers. In both settings, it is seen that the stability of the modes near the linear limit turns into instability as nonlinearity is increased past a critical value, leading to a dynamical delocalization of the solitary wave (or breathing) state. Finally, we suggest a concrete experiment to observe these embedded modes using a bi-inductive electrical lattice. [ABSTRACT FROM AUTHOR]

We examine the PT-symmetry-breaking transition for a magnetic metamaterial of a finite extent, modeled as an array of coupled split-ring resonators in the equivalent circuit model approximation. Small-size arrays are solved completely in closed form, while for arrays larger than N = 5 results were computed numerically for several gain and loss spatial distributions. In all cases, it is found that the parameter stability window decreases rapidly with the size of the array, until at N = 20 approximately it is not possible to support a stable PT-symmetric phase. [ABSTRACT FROM AUTHOR]

Abstract: A two-dimensional lattice model based on Cellular Automata theory and swarm intelligence is used to study the spatial and population dynamics of a theoretical ecosystem. It is found that the social interactions among predators provoke the formation of clusters, and that by increasing the mobility of predators the model enters into an oscillatory behavior. [Copyright &y& Elsevier]

El artículo discurre sobre el economista británico Ronald Coase y sus ideas sobre la teoría económica durante el siglo 20. Los autores comentan específicamente sobre las teorías de Keynes y las de Hayek así como la crítica de Coase. También se considera el concepto del mercado de las ideas.

In this paper, we examine a nonlinear magnetoinductive dimer and compute its linear and nonlinear symmetric, antisymmetric and asymmetric modes in closed-form, in the rotating-wave approximation. A linear stability analysis of these modes reveals that the asymmetric mode is always stable, for any allowed value of the coupling param-eter and for both, hard and soft nonlinearity. An exact numerical computation of the dimer dynamics reveals a magnetic energy self-trapping whose threshold increases for increasing dimer coupling, decreases for increasing nonlinearity response and is robust against asymmetrical nonlinear responses and resonant frequencies mismatch. [ABSTRACT FROM AUTHOR]

• A fractional version of discrete Laplacian is inserted into the DNLS equation. • Spectrum of linear waves and root mean square displacement computed in closed form. • Insertion of single general nonlinear impurity. • Use of Green functions to compute the mode energy and profile and the transmission of plane waves. • Effect of fractional exponent on all of the above phenomenology. We use a lattice Green function approach to study the stationary modes of a linear/nonlinear (Kerr) impurity embedded in a periodic one-dimensional lattice where we replace the standard discrete Laplacian by a fractional one. The energies and the mode profiles are computed in closed form, for different fractional exponents and different impurity strengths. The energies of the impurity mode lie outside the linear band whose bandwidth decreases steadily as the fractional exponent decreases. For any fractional exponent values, there is always a single bound state for the linear impurity while for the nonlinear (Kerr) case, up to two bound states are possible, for impurity strengths above certain threshold. The energy of the linear mode (or that of the upper energy nonlinear one), becomes directly proportional to the impurity strength at large impurity strengths. The transmission of plane waves is also computed in closed form for several fractional exponents, and various impurity strengths. We observe that fractionality tends to increase the overall transmission. The selftrapping transition for the nonlinear impurity shifts to lower nonlinearity values as the fractional exponent is decreased. In both cases, linear and nonlinear, we observe a form of trapping at zero impurity strength, which can be explained by the near-degeneracy of the spectrum in the limit of a small fractional exponent. [ABSTRACT FROM AUTHOR]

Abstract: We examine localization of light in nonlinear (Kerr) kagome lattices in the shape of narrow strips of varying width. For the narrowest ribbon, the band structure features a flat band leading to linear dynamical trapping of an initially localized excitation. We also find a geometry-induced bistability of the nonlinear modes as the width of the strip is changed. A crossover from one to two dimensions localization behavior is observed as the width is increased, attaining two-dimensional behavior for relatively narrow ribbons. [Copyright &y& Elsevier]

We prove that for a one-dimensional, infinite periodic lattice, with long-range coupling among sites, the diffusion of an initial delta-like pulse in the bulk is ballistic at all times, with a 'speed' that depends on the 'smoothness' of the dispersion relation. We obtain a closed-form expression for the mean square displacement (MSD), and showsome relevant examples including finiterange coupling, exponentially decreasing coupling and power-law decreasing coupling. For the case of an initial excitation at the edge of the lattice, we find an approximate expression for the MSD that predicts ballistic behavior at long times in agreement with numerical results. [ABSTRACT FROM AUTHOR]

We introduce a novel concept of surface bound states in the continuum, i.e., surface modes embedded into the linear spectral band of a discrete lattice. We suggest an efficient method for creating such surface modes and the local bounded potential necessary to support the embedded modes. We demonstrate that the surface embedded modes are structurally stable, and the position of their eigenvalues inside the spectral band can be tuned continuously by adding weak nonlinearity. [ABSTRACT FROM AUTHOR]

The author reflects on the problems of the Colombian health care system which are based on a simplified economic perception. The author states that the affirmations that deny the existence of flaws both of the State and of the market system ignore the complexity of true decisions. The author says that a usual error in the discourses of economic systems and public policy is made when the comparisons are made between practical real schemes and an ideal schemes.

Polar stratospheric clouds (PSCs) are extremely efficient at catalysing the transformation of photostable chlorine reservoirs into photolabile species, which are actively involved in springtime ozone-depletion events. Why PSCs are such efficient catalysts, however, is not well understood. Here, we investigate the freezing behaviour of ternary HNO3–H2SO4–H2O droplets of micrometric size, which form type II PSC ice particles. We show that on freezing, a phase separation into pure ice and a residual solution coating occurs; this coating does not freeze but transforms into glass below ∼150 K. We find that the coating, which is thicker around young ice crystals, can still be approximately 30 nm around older ice crystals of diameter about 10 µm. These results affect our understanding of PSC microphysics and chemistry and suggest that chlorine-activation reactions are better studied on supercooled HNO3–H2SO4–H2O solutions rather than on a pure ice surface. [ABSTRACT FROM AUTHOR]

The purpose of this investigation was to study basal cerebral glucose absorption patterns associated to long-term post-traumatic stress disorder. Fluorodeoxyglucose positron emission tomography (FDG-PET) and statistic parametric mapping (SPM) were used to compare regional cerebral glucose absorption between 15 war veterans (Hispanic men, aged 39-41 (M = 39.5, SD = 0.84)) diagnosed with post-traumatic stress disorder (PTSD) based on DSM-IV criteria, and a matching control group of six asymptomatic veterans. This study was conducted 20 years after the traumatic events. PTSD patients presented relatively diminished activity ( P<0.005) in: cingulate gyri, precuneus, insula, hippocampus; frontal, pre-frontal and post-central regions; lingual, calcarine, occipital medial and superior gyri, and verbal and paraverbal areas. Relativeley augmented activity ( P<0.005) was observed in PTSD patients in: fusiform, temporal superior, medial, and inferior gyri; occipital medial, inferior and lingual gyri; precuneus, and cerebellum. The amygdala and the thalamus showed normal metabolic activity. Various brain regions that showed diminished activity (limbic, frontal and prefrontal cortex, multimodal parieto-occipital areas and verbal and paraverbal areas) have evolved lately, and sub-serve highly complex cognitive and behavioural functions. Metabolic activity patterns are comparable to those observed in personality disorders of the borderline type. [ABSTRACT FROM AUTHOR]

Current emissions of anthropogenic greenhouse gases (GHGs) have already committed the planet to an increase in average surface temperature by the end of the century that may be above the critical threshold for tipping elements of the climate system into abrupt change with potentially irreversible and unmanageable consequences. This would mean that the climate system is close to entering if not already within the zone of "dangerous anthropogenic interference" (DAI). Scientific and policy literature refers to the need for "early," "urgent," "rapid," and "fast-action" mitigation to help avoid DAI and abrupt climate changes. We define "fast-action" to include regulatory measures that can begin within 2-3 years, be substantially implemented in 5-10 years, and produce a climate response within decades. We discuss strategies for short-lived non-CO2 GHGs and particles, where existing agreements can be used to accomplish mitigation objectives. Policy makers can amend the Montreal Protocol to phase down the production and consumption of hydrofluorocarbons (HFCs) with high global warming potential. Other fast-action strategies can reduce emissions of black carbon particles and precursor gases that lead to ozone formation in the lower atmosphere, and increase biosequestration, including through biochar. These and other fast-action strategies may reduce the risk of abrupt climate change in the next few decades by complementing cuts in CO2 emissions. [ABSTRACT FROM AUTHOR]

Abstract: We study localized modes on a single magnetic impurity positioned in the bulk or at the surface of a one-dimensional chain, in the presence of a magnetic field B acting at the impurity site. The strong on-site nonlinear interaction U between two electrons of opposite spin at the impurity site, modelled here as a nonlinear local term, and the presence of the external field induce a strong correlation between parallel and antiparallel spin bound states. We find that, for an impurity in the bulk, a localized vector mode (with up and down spin components) is always possible for any given value of U and B, while for a surface impurity, a minimum value of both, U and B is needed to create a vector mode. In this case, up to two localized modes are possible, but only one of them is stable. The presence of the surface seems to destabilize the bulk mode in the parameter region , creating a “forbidden strip” region in parameter space, bounded by and , approximately. [Copyright &y& Elsevier]

Abstract: We study localized modes on a single Ablowitz–Ladik impurity embedded in the bulk or at the surface of a one-dimensional linear lattice. Exact expressions are obtained for the bound state profile and energy. Dynamical excitation of the localized mode reveals exponentially-high amplitude oscillations of the spatial profile at the impurity location. The presence of a surface increases the minimum nonlinearity to effect a dynamical selftrapping. [Copyright &y& Elsevier]

• 2D split-ring resonator array with resonant frequency disorder. • Localized modes and magnetic transport for uncorrelated and correlated disorder in 2D. • Correlated disorder can create sub-diffusive propagation. We study the effect of a resonant frequency disorder on the eigenstates and the transport of magnetic energy in a two-dimensional (square) array of split-ring resonators (SRRs). In the absence of disorder, we find the dispersion relation of magneto-inductive waves and the mean square displacement (MSD) in closed form, showing that at long times the MSD is ballistic. When disorder is present, we consider two types: the usual Anderson distribution (uncorrelated monomers) and 2 × 2 units assigned at random to lattice sites (correlated tetramers). This is a direct extension to two dimensions of the one-dimensional random dimer model (RDM). For the uncorrelated case, we see saturation of the MSD for all disorder widths, while for the correlated case we find a disorder window, inside which the MSD does not saturate at long times, with an asymptotic sub-diffusive behavior M S D ∼ t 0.26. Outside this disorder window, the MSD shows the same kind of saturation as in the monomer case. We conjecture that the sub-diffusive behavior is a remanent of a weak resonant transmission of a 2D plane wave across a tetramer unit. [ABSTRACT FROM AUTHOR]

Objective: To perform the economic evaluation and analyze the financial sustainability of the primary health care model (APS) of the Suba Hospital II Level - State Social Company (ESE). Methodology: This is a cost effective analysis in which the effectiveness units were life years gained by reduction in maternal and infant mortality caused by acute diarrheic disease. Cost units were expressed in monetary units, and the threshold level of cost effectiveness was the Gross Domestic Income (PIB) per capita. Epidemiologic data was used from the Suba locality (2002-2003, 2005-2006); from the Ciudad Bolivar locality (2005-2006); and from Bogota (2005-2006). The sustainability analysis was also performed from the qualitative behavior expected from the income and costs result of the implementation of the APS and considering accounting data from 2004 to 2006. Results: The annual cost effective increment was $6'473,091 pesos for 2006. The implementation of the model in the Suba locality was cost effective. The model generated 412.8 years of life gained for the locality. The implementation of the APS eventually decreases some of the costs and income at the same time. It does not generate losses, but it does decrease billing. Conclusions: The implementation of the APS generates benefits for society, which nonetheless, are not susceptible to being translated into monetary income for the hospital. This can generate contradictory incentives in the actual system, which incentives and principles lean more to the treatment of disease, instead of achieving health results [ABSTRACT FROM AUTHOR]

Abstract: We study the properties of localized impurity modes and the transmission of plane waves across a general nonlinear impurity embedded in an infinite one-dimensional linear chain. Using the formalism of the lattice Green function, we obtain nonlinear equations for the bound state energy and the transmission coefficient, for a wide class of nonlinear impurities. We specialize to a saturable nonlinear impurity, obtaining closed form expressions for the bound state energy and transmission coefficient. [Copyright &y& Elsevier]

The efficacy of tax reforms is estimated for the period 1973-2000 using three ARIMAX models for the real revenue and the revenue/GDP ratio. The analysis, including only those reforms changing tax bases and/or tariffs, or that aim to increase revenue or reduce evasion, shows that only two out of the fifteen reforms considered managed to have an impact upon revenue, those of 1974 and 1990, whose effect is permanent. [ABSTRACT FROM AUTHOR]

About half of the world's population now lives in urban areas because of the opportunity for a better quality of life. Many of these urban centers are expanding rapidly, leading to the growth of megacities, which are defined as metropolitan areas with populations exceeding 10 million inhabitants. These concentrations of people and activity are exerting increasing stress on the natural environment, with impacts at urban, regional and global levels. In recent decades, air pollution has become one of the most important problems of megacities. Initially, the main air pollutants of concern were sulfur compounds, which were generated mostly by burning coal. Today, photochemical smog--induced primarily from traffic, but also from industrial activities, power generation, and solvents--has become the main source of concern for air quality, while sulfur is still a major problem in many cities of the developing world. Air pollution has serious impacts on public health, causes urban and regional haze, and has the potential to contribute significantly to climate change. Yet, with appropriate planning, megacities can efficiently address their air quality problems through measures such as application of new emission control technologies and development of mass transit systems. This review is focused on nine urban centers, chosen as case studies to assess air quality from distinct perspectives: from cities in the industrialized nations to cities in the developing world. While each city--its problems, resources, and outlook--is unique, the need for a holistic approach to the complex environmental problems is the same. There is no single strategy in reducing air pollution in megacities; a mix of policy measures will be needed to improve air quality. Experience shows that strong political will coupled with public dialog is essential to effectively implement the regulations required to address air quality problems. [ABSTRACT FROM AUTHOR]

Based on literary sources and following Marshall Berman and Benedict Anderson's theory, this article outlines some key tendencies of English society prior to World War I. Economic modernization and political imperialism emerged while the cultural avant garde (i.e. modernism) was pushed into the background. Religious, sexual and political repression completed the picture and supported the fear of inner ruptures and discontinuities related to the experience of modernity; in contrast, conventions and other mechanisms were used to create the illusion of continuity in their place. [ABSTRACT FROM AUTHOR]