Comparison Sites

Web search technologies are fundamental tools to easily navigate through the huge amount of information available in the Internet. One particular type of search technologies are the so- called shopbots, or comparison sites. The emergence of Internet shopbots and their implications for price competition and market efficiency are the focus of this chapter. We develop a simple model where a price comparison site tries to attract (possibly vertically and horizontally differentiated) online retailers on the one hand, and consumers on the other hand. The analysis of the model reveals that differentiation among the products of the retailers as well as their ability to price discriminate between on- and off-comparison-site consumers play a critical role. When products are homogeneous, if online retailers cannot charge different on- and off-the-comparison- site prices, then the comparison site has incentives to charge fees so high that some firms are excluded, which generates price dispersion and an inefficient outcome. By contrast, when on- and off-comparison-site prices can be different, the comparison site attracts all the players to the platform and the allocation is efficient. A similar result obtains when products are horizontally differentiated. In that case, the comparison site becomes an aggregator of product information and no matter whether firms can price discriminate or not, the comparison site attracts all the players to the platform and an efficient outcome ensues. We argue that the lack of vertical product differentiation may also be critical for this efficiency result. In fact, we show that when quality differences are large, the comparison site may find it profitable to charge fees such that low quality producers are excluded, thereby inducing an inefficient outcome.

DEVELOPMENT OF MINIMUM COST, INCENTIVE BASED PLAN FOR THE IMPLEMENTATION OF A TECHNOLOGY STANDARD FOR COFFEE PROCESSING IN HONDURAS

In Honduras, traditional coffee processing is the cause of two problems: poor coffee quality and contaminated water. In this study we propose to replace traditional coffee processing plants with a network of improved ecological plants that would be optimally located in a sub-watershed. The method is an adaptation of a spatial integer linear programming that determines the optimal location and size of new coffee processing plants. We applied the method to a typical sub-watershed in the hillsides of western Honduras and show that coffee quality can be improved and contamination can be reduced substantially at a relatively low cost. We also calculated the incentive for small farmers to give up home processing. We find that the incentive is much lower than the premium that could be obtained from an improved coffee quality.Agribusiness,

Nonsequential Search Equilibrium with Search Cost Heterogeneity

We generalize the model of Burdett and Judd (1983) to the case where an arbitrary finite number of firms sells a homogeneous good to buyers who have heterogeneous search costs. We show that a price dispersed symmetric Nash equilibrium always exists. Numerical results show that the behavior of prices with respect to the number of firms hinges upon the shape of the search cost distribution: when search costs are relatively concentrated (dispersed), entry of firms leads to higher (lower) average prices.nonsequential search, oligopoly, arbitrary search cost distributions

On the Identification of the Costs of Simultaneous Search

This paper studies the identification of the costs of simultaneous search in a class of (portfolio) problems studied by Chade and Smith (2006). We show that aggregate data from a single market, or disaggregate data from a single market segment, do not provide sufficient information to identify the costs of simultaneous search in any reasonable interval. We then show that by pooling aggregate data from multiple markets, or disaggregate data from multiple market segments, the econometrician can identify the costs of simultaneous search in a non-empty interval. Within the context of specific examples, we illustrate that identification of the search cost distribution in its full support may easily be obtained.search costs, portfolio choice, non-parametric identification

TRADE-OFFS BETWEEN ECONOMIC EFFICIENCY AND CONTAMINATION BY COFFEE PROCESSING A BIOECONOMIC MODEL AT THE WATERSHED LEVEL IN HONDURAS

In Honduras, traditional coffee processing is the cause of two major problems: poor coffee quality and contaminated water. In this paper we present a method that determines the trade-off between economic efficiency and contamination in a Honduran sub-watershed. The method is a bioeconomic model based on mathematical programming that stimulates the functioning of the interlinked economic and ecological processes in the sub-watershed. We compare various scenarii where the model is given the possibility of replacing traditional coffee processing plants with a network of improved ecological plants. For different levels of contamination the model determines the optimal location and size of new coffee processing plants along river streams by minimizing transport, variable and fixed costs. The restrictions of the system are the volume of wet coffee to be processed, the available stream water, and in the alternative scenarii, investment capital and contaminant concentration in the river. We apply the method to a typical sub-watershed in the hillsides of western Honduras and show that coffee quality can be improved and contamination can be reduced substantially at a relatively low cost.coffee, environment, water quality, mathematical programming, transport cost, spatial analysis, watershed, Honduras., Environmental Economics and Policy,

Clinical Evolution of New Delhi Metallo-β-Lactamase (NDM) optimizes resistance under Zn(II) Deprivation

Carbapenem-resistant Enterobacteriaceae (CRE) are rapidly spreading and taking a staggering toll on all health care systems, largely due to the dissemination of genes coding for potent carbapenemases. An important family of carbapenemases are the Zn(II)-dependent β-lactamases, known as metallo-β-lactamases (MBLs). Among them, the New Delhi metallo-β-lactamase (NDM) has experienced the fastest and widest geographical spread. While other clinically important MBLs are soluble periplasmic enzymes, NDMs are lipoproteins anchored to the outer membrane in Gram-negative bacteria. This unique cellular localization endows NDMs with enhanced stability upon the Zn(II) starvation elicited by the immune system response at the sites of infection. Since the first report of NDM-1, new allelic variants (16 in total) have been identified in clinical isolates differing by a limited number of substitutions. Here, we show that these variants have evolved by accumulating mutations that enhance their stability or the Zn(II) binding affinity in vivo, overriding the most common evolutionary pressure acting on catalytic efficiency. We identified the ubiquitous substitution M154L as responsible for improving the Zn(II) binding capabilities of the NDM variants. These results also reveal that Zn(II) deprivation imposes a strict constraint on the evolution of this MBL, overriding the most common pressures acting on catalytic performance, and shed light on possible inhibitory strategies.Fil: Bahr, Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; ArgentinaFil: Vitor Horen, Luisina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; ArgentinaFil: Bethel, Christopher R.. Louis Stokes Cleveland VA Medical Center; Estados UnidosFil: Bonomo, Robert A.. Louis Stokes Cleveland VA Medical Center; Estados UnidosFil: Gonzalez, Lisandro Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; ArgentinaFil: Vila, Alejandro Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; Argentin

Magnon valley Hall effect in CrI3-based vdW heterostructures

Magnonic excitations in the two-dimensional (2D) van der Waals (vdW) ferromagnet CrI3 are studied. We find that bulk magnons exhibit a non-trivial topological band structure without the need for Dzyaloshinskii-Moriya (DM) interaction. This is shown in vdW heterostructures, consisting of single-layer CrI3 on top of different 2D materials as MoTe2, HfS2 and WSe2. We find numerically that the proposed substrates modify substantially the out-of-plane magnetic anisotropy on each sublattice of the CrI3 subsystem. The induced staggered anisotropy, combined with a proper band inversion, leads to the opening of a topological gap of the magnon spectrum. Since the gap is opened non-symmetrically at the K+ and K- points of the Brillouin zone, an imbalance in the magnon population between these two valleys can be created under a driving force. This phenomenon is in close analogy to the so-called valley Hall effect (VHE), and thus termed as magnon valley Hall effect (MVHE). In linear response to a temperature gradient we quantify this effect by the evaluation of the temperature-dependence of the magnon thermal Hall effect. These findings open a different avenue by adding the valley degrees of freedom besides the spin, in the study of magnons

Comparison sites

Web search technologies are fundamental tools for navigating the Internet. One particular type of search technology is "shopbots", or comparison sites. The emergence of Internet shopbots and their implications for price competition and market efficiency are the focus of this paper. We develop a simple model where a price comparison site tries to attract (possibly vertically and horizontally differentiated) online retailers, on the one hand, and consumers, on the other. Analysis of the model reveals that differentiation among the products of the retailers and their ability to price discriminate between on- and off-comparison-site consumers play a critical role. When products are homogeneous, if online retailers cannot charge different on- and off-the-comparison-site prices, then the comparison site has incentives to charge fees so high that some firms are excluded, which generates price dispersion and an inefficient outcome. By contrast, when on- and off-comparison-site prices can be different, the comparison site attracts all the players to the platform and the allocation is efficient. A similar result obtains when products are horizontally differentiated. In that case, the comparison site becomes an aggregator of product information and no matter whether firms can price discriminate or not, the comparison site attracts all the players to the platform and an efficient outcome ensues. We argue that the lack of vertical product differentiation may also be critical for this efficiency result. In fact, we show that when quality differences are large, the comparison site may find it profitable to charge fees that effectively exclude low quality producers, thereby inducing an inefficient outcome.shopbots; two-sided market; intermediation; price discrimination; product differentiation;

Nonparametric Estimation of the Costs of Non-Sequential Search

We study a consumer non-sequential search oligopoly model with search cost heterogeneity. We first prove that an equilibrium in mixed strategies always exists. We then examine the nonparametric identification and estimation of the costs of search. We find that the sequence of points on the support of the search cost distribution that can be identified is convergent to zero as the number of firms increases. As a result, when the econometrician has price data from only one market, the search cost distribution cannot be identified accurately at quantiles other than the lowest. To solve this pitfall, we propose to consider a richer framework where the researcher has price data from many markets with the same underlying search cost distribution. We provide conditions under which pooling the data allows for the identification of the search cost distribution at all the points of its support. We estimate the search cost density function directly by a semi-nonparametric density estimator whose parameters are chosen to maximize the joint likelihood corresponding to all the markets. A Monte Carlo study shows the advantages of the new approach and an application using a data set of online prices for memory chips is presented

Role of early extraction of odontogenic focus in deep neck infections

Odontogenic deep neck infections remain a common condition that presents a challenging issue due to the complex involvement of the neck and adjacent structures and its potential life-threatening risk. Periapical infection of the second or third molar with spread to the submandibular and parapharyngeal spaces is the most commonly observed scenario. However, the time of dental extraction of the infection focus remains controversial. The aim of this study is to provide an overview of the epidemiology, clinical and radiological features, and management in patients diagnosed with ODNI and to identify the role of early dental extraction on patient outcomes and recovery. This retrospective study included patients over 18 years old with a diagnosis of ODNI who were admitted to the University Hospital ?Dr Jose Eleuterio Gonzalez? from January 2017 to January 2022. ODNI diagnosis was based on clinical and radiological evidence of the disease supplemented by dental and maxillofacial evaluation for an odontogenic aetiology. A total of 68 patients were included in the study. The patients? mean age was 40.96 ± 14.9. Diabetes mellitus was the most common comorbidity. The submandibular space was the most common deep neck space involved (n=59, 86.8%). Mediastinitis, marginal nerve injury and orocervical fistula were observed in 7.5% of patients, with no fatality in this series. A delay of >3 days for dental extraction of the involved tooth was associated with an increased rate of mediastinitis (n=3, 100%, p= 0.022), number of surgical interventions (1.45 ± 0.61, p= 0.006), ICU stay (n=8, 40%, p= 0.019), and ICU length of stay (0.85 ± 0.8, p= 0.001). Expedited management with surgical drainage and intravenous antibiotic treatment, along with early extraction of the involved tooth, is mandatory