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Search Results: 1 - 10 of 593591 matches for " García-Pérez "
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A Matching Model on the Use of Immigrant Social Networks and Referral Hiring  [PDF]
Mónica García-Pérez
Theoretical Economics Letters (TEL) , 2012, DOI: 10.4236/tel.2012.24070
Abstract: Using a simple search model, with urn-ball derived matching function, this paper investigates the effect of firm owner’s and coworkers’ nativity on hiring patterns and wages. In the model, social networks reduce search frictions and wages are derived endogenously as a function of the efficiency of the social ties of current employees. As a result, individuals with more efficient connections tend to receive higher wages and lower unemployment rate. However, because this efficiency depends on matching with same-type owners and coworkers, there is also a differential effect among workers’ wages in the same firm. This analysis highlights the potential importance of social connections and social capital for understanding employment opportunities and wage differentials between these groups.
Statistical Conclusion Validity: Some Common Threats and Simple Remedies
Miguel A. García-Pérez
Frontiers in Psychology , 2012, DOI: 10.3389/fpsyg.2012.00325
Abstract: The ultimate goal of research is to produce dependable knowledge or to provide the evidence that may guide practical decisions. Statistical conclusion validity (SCV) holds when the conclusions of a research study are founded on an adequate analysis of the data, generally meaning that adequate statistical methods are used whose small-sample behavior is accurate, besides being logically capable of providing an answer to the research question. Compared to the three other traditional aspects of research validity (external validity, internal validity, and construct validity), interest in SCV has recently grown on evidence that inadequate data analyses are sometimes carried out which yield conclusions that a proper analysis of the data would not have supported. This paper discusses evidence of three common threats to SCV that arise from widespread recommendations or practices in data analysis, namely, the use of repeated testing and optional stopping without control of Type-I error rates, the recommendation to check the assumptions of statistical tests, and the use of regression whenever a bivariate relation or the equivalence between two variables is studied. For each of these threats, examples are presented and alternative practices that safeguard SCV are discussed. Educational and editorial changes that may improve the SCV of published research are also discussed.
Structural Elucidation of Condensed Tannin from Picea mariana Bark  [PDF]
Papa Niokhor Diouf, Carmen Mihaela Tibirna, Martha-Estrella García-Pérez, Mariana Royer, Pascal Dubé, Tatjana Stevanovic
Journal of Biomaterials and Nanobiotechnology (JBNB) , 2013, DOI: 10.4236/jbnb.2013.43A001
Abstract:

The aim of this work was to determine the structural characteristics of the condensed tannins isolated from the aqueous extract of black spruce (Picea mariana Mill) bark. This is the first report on the structural characterization of condensed tannins from black spruce bark. The condensed tannins from the hot water extract prepared from Picea mariana bark were isolated by column chromatography on Sephadex LH-20 media. In this study, UV-visible and 13C-NMR spectroscopic techniques, along with pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and liquid chromatogramphy analyses were applied to determine the structural characteristics of black spruce bark tannins. We have confirmed for the first time the presence of methoxylated B-rings in the flavanol units of condensed tannins from black spruce bark, which could be regarded as further contribution to the chemotaxonomy of the genus Picea. The methoxylation of Norway spruce bark condensed tannins have been demonstrated previously.

Visual Contrast Processing is Largely Unaltered during Saccades
Miguel A. García-Pérez,Eli Peli
Frontiers in Psychology , 2011, DOI: 10.3389/fpsyg.2011.00247
Abstract: Saccadic suppression refers to a reduction in visual sensitivity during saccadic eye movements. This reduction is conventionally regarded as mediated by either of two sources. One is a simple passive process of motion smear during saccades also accompanied by visual masking exerted by high-contrast pre- and post-saccadic images. The other is an active process exerted by a neural mechanism that significantly reduces visual processing so that the perception of a stable visual environment is not disrupted during saccades. Some studies have actually shown that contrast sensitivity is significantly lower during saccades than under fixation, but these experiments were not designed in a way that could weigh the differential contribution of active and passive sources of saccadic suppression. We report the results of measurements of psychometric functions for contrast detection using stimuli that are only visible during saccades, thus effectively isolating any visual processing that actually takes place during the saccades and also preventing any pre- and post-saccadic visual masking. We also report measurements of psychometric functions for detection under fixation for stimuli that are comparable in duration and spatio-temporal characteristics to the intrasaccadic retinal stimulus. Whether during saccades or under fixation, the psychometric functions for detection turned out to be very similar, leaving room only for a small amount of sensitivity reduction during saccades. This suggests that contrast processing is largely unaltered during saccades and, thus, that no neural mechanism seems to be actively involved in saccadic suppression.
Florescimento e frutifica??o de lichieiras em fun??o do anelamento de ramos
García-Pérez, Eliseo;Martins, Antonio Baldo Geraldo;
Revista Brasileira de Fruticultura , 2006, DOI: 10.1590/S0100-29452006000100007
Abstract: the effects of girdling of branches on flowering and fruiting of 17 years old 'bengal' lychee trees were evaluated. the treatments consisted of girdling of main branches, and branches with 6, 4 and 2 cm of diameter and the control. the experiment was conducted in a randomized block design, with 5 replicates. the evaluations in relation to flowering were: flowering per tree and per quadrant and length of flower panicles; in relation to fruiting were: fruit set per panicle, fruit weight, longitudinal and equatorial diameters, soluble solids, harvest time and production. the girdling in the main branches induced larger flowering, without influence on the flower panicles characteristics, there were no differences in the fruit set, but with an increasing in the flowering, it increased the production, with significant anticipation of the harvest.
Cuando el coito produce dolor: una exploración de la sexualidad femenina en el noroeste de México
García-Pérez,Hilda; Harlow,Sioban D;
Salud Pública de México , 2010, DOI: 10.1590/S0036-36342010000200007
Abstract: objective: to determine the prevalence of dyspareunia among women aged 25-54 and its associated risk factors. material and methods: a cross-sectional population-based study was carried out in the city of hermosillo, sonora and data from 1183 sexually active women were analyzed. a multiple logistic regression was computed to analyze the association between dyspareunia and sociodemographic characteristics, medical conditions and sexual violence. results: the 12-month prevalence of dyspareunia was estimated to be 12.3% (95% ci 10.5, 14.4). after adjustment for working conditions, dyspareunia was associated with younger ages (25-34 years), history of sexually transmitted diseases/pelvic inflammatory disease, chronic urinary tract infections, colitis and history of sexual violence. conclusion: increased attention to this condition by reproductive health programs and primary care services is urgently needed in mexico.
Crustal structure of the Arteaga Complex, Michoacán, southern Mexico, from gravity and magnetics
Frank García-Pérez,Jaime Urrutia-Fucugauchi
Geofísica internacional , 1997,
Abstract: The Arteaga region, Michoacán, southern Mexico is one of the few areas with basement outcrops in the Guerrero ter rane. The Zihuatanejo subterrane is characterized by Late Jurassic-Early Cretaceous island-arc volcanosedimentary se quences that rest unconformably on metamorphosed rocks of the Arteaga Complex, of possible Triassic-Jurassic age. Gravity and total field magnetic measurements were taken along two SW-NE profiles across the metamorphic and igneous complex. Spectral analysis is used to estimate depths to the Moho and major crustal interfaces. The crustal thickness in creases to the N and NE away from the margin and is in the order of 28-32 km. The metamorphic complex has an average thickness of 15 km. In the southern sector near Arteaga, the uppermost metamorphic units present a lower density contrast possibly due to regional alteration. The granitic and granodioritic batholith has a thickness of up to 8 km in the SE sector. The gravity and magnetic models are consistent with proposals that the Arteaga Complex constitutes the basement of the Zihuatanejo subterrane.
Fluorosis and Dental Caries in the Hydrogeological Environments of Southeastern Communities in the State of Morelos, Mexico  [PDF]
Gricelda G. Varela-González, Alvaro García-Pérez, Rafael Huizar-Alvarez, Maria Esther Irigoyen-Camacho, Maria M. Espinoza-Jaramillo
Journal of Environmental Protection (JEP) , 2013, DOI: 10.4236/jep.2013.49115
Abstract:

Objectives: 1) To identify the hydrogeological characteristics and fluoride (F-) concentration in drinking water in the southeast of the state of Morelos, Mexico, and 2) to estimate the association between the prevalence and severity of fluorosis, dental caries, and water F- concentration. Methods: A hydrogeological model was developed to determine the vertical distribution of lithostratigraphic units, rocks’ hydraulic conductivities, and groundwater flow characteristics. A total of 649 schoolchildren from two communities received oral examinations. One community was located in an area with 0.75 mg F-/L in the water supply and the other in an area with 1.6 mg F-/L. Fluorosis was assessed using the Thylstrup & Fejerskov Index (TFI) and the dental caries were assessed with the decayed, missing, and filled teeth (DMFT) index. The region groundwater was extracted from an inter-granular aquifer consisting of volcano clasts of intermediate volcanic chemical composition. Results: Oral examinations showed that 32.35% of the children had severe forms of fluorosis (TFI ≥ 4) in the community with 1.60 mg F-/L and 7.8% in the 0.75 mg F-/L community (p < 0.0001).

Nylon/Porphyrin/Graphene Oxide Fiber Ternary Composite, Synthesis and Characterization  [PDF]
César García-Pérez, Carmina Menchaca-Campos, Miguel A. García-Sánchez, Elsa Pereyra-Laguna, Ociel Rodríguez-Pérez, Jorge Uruchurtu-Chavarín
Open Journal of Composite Materials (OJCM) , 2017, DOI: 10.4236/ojcm.2017.73009
Abstract: This research was based on the manufacture of new composite materials that offer technological possibilities in the development of new devices with greater efficiency. Electrospinning was used to form nylon 66/-tetra-(para-aminophenyl) porphyrin (H2T(p-NH2)PP)/graphene oxide (GO) composite film. Graphene oxide coatings were obtained from graphite, through mechanical exfoliation followed by calcination and ultrasonic agitation in an oxidant solution. These samples were characterized under SEM, FTIR, Raman spectroscopy, UV-vis and R-X techniques. On the other hand, H2T(p-NH2)PP was synthesized in two steps?process by the Rothemun reaction and the Adler Method and it was integrated within nylon polyamide fibers by direct addition of a hexamethylenediamine/adipoyl chloride reactant mixture. The polymerization of the nylon/H2T(p-NH2)PP species occurs in such a way that it starts or ends on the four peripherals-NH2 groups, connected and located in the same molecular plane of H2T(p-NH2)PP, forming nylon chains at the periphery of the macrocycle. The association of GO with nylon/H2T(p-NH2)PP fibers is performed
Physicians' migration in Europe: an overview of the current situation
Miguel A García-Pérez, Carlos Amaya, ángel Otero
BMC Health Services Research , 2007, DOI: 10.1186/1472-6963-7-201
Abstract: Search of secondary databases about the presence of european doctors working abroad, through two search engines in the Internet (Google and Pubmed) and a survey of professional organisations and regulators in countries of the European Union.The United Kingdom has more foreign doctors than all other European countries for which figures are available (Ireland, France, Germany, Norway, Portugal, Italy, Austria and Poland). Some 74,031 foreign doctors are registered in the UK, 30.94% of the total. European countries with the highest percentage of doctors working abroad are Ireland (47.5%, or 10,065 doctors) and Malta (23.1%, 376 doctors). The data obtained from Norway, France and Germany do not indicate an increase in the migration of professionals from countries recently incorporated into the EU.There is significant mobility and heterogeneous distribution of doctors within the EEA and it should be cause for concern among health care authorities. However, there is no evidence about a possible increase in this phenomenon after the recent expansion of the EU.A key factor in providing medical care is the availability of qualified and motivated health care professionals [1-4]. However, a extended perception exists in Europe that there is an inadequate provision and/or a poor distribution of them [5-7].The current process of political and economic globalisation, in which European legislation on free movement of persons take place, has caused significant migratory tensions. Developed countries generally act as polls of attraction for medical professionals resulting in the risk of a "brain drain" or loss of professional capital in less developed countries [1,8-11]. The recent expansion of the European Union (EU) has caused concern among authorities in recently integrated countries about the loss of professionals, although figures for previous expansions do not seem to support this concern [9,12,13].There is, however, a significant lack of information. Existing analyses of the
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