Exploration and Exploitation in Latin American Firms: The Determinants of Organizational Ambidexterity and The Country Effect

In this article, we explore the determinants of organizational ambidexterity across Latin American countries -Chile, Ecuador, and Peru- from innovation surveys of 2,786 manufacturing companies. The study introduces valuable information on ambidextrous organizations in emerging economies, contrasting to traditional literature frequently focusing on developed countries. Findings confirm the importance to measure ambidexterity in a multidimensional perspective, relating exploration to radical innovation, and breaking down exploitation into incremental exploitation, related to incremental innovation and repetitive exploitation related to operational efficiency. This work also finds that higher GDP per capita relates to higher exploration and exploitation ability of firms and supported our hypotheses that political and economic uncertainty of each country impact on organizational ambidexterity. Additionally, we expand on Diaz-Molina´s model (2018), on the relationship between strategic and operational absorptive capacity on ambidexterity by validating his findings across several countries and uncovering a positive interaction term between strategic and operational absorptive capacity when both impact on ambidexterity

The Role of Absorptive Capacity in Innovation and Productivity in Chilean Companies: An Adapted CDM Model Across Industries

Drawing on an adapted CDM model, we present evidence on the role of strategic and operational absorptive capacity on innovation and productivity across industries in developing economies. Using a pooled cross-sectional sample from Chilean innovation surveys, we find that greater absorptive capacity (ACAP) helps firms to increase their innovative investment and the probability of producing technological innovations, which then increases firms’ labor productivity. Additionally, the effect of the strategic dimension is stronger than the operational dimension aspect, which means that the strategy of reaching these external sources might be more important than the skill of a firm´ internal units to acquire and transform external information. We find that while strategic ACAP is a stronger predictor of investment and technological innovation in both manufacturing and services companies, but operational ACAP has differing effects

Relationship between ethanol-induced activity and anxiolysis in the open field, elevated plus maze, light-dark box, and ethanol intake in adolescent rats

It is yet unclear if ethanol-induced motor stimulation in the open field (OF) merely reflects psychomotor stimulating effects of the drug or if this stimulation is driven or modulated by ethanol's antianxiety properties. In the present study, adolescent rats were administered with different ethanol doses or remained untreated. They were sequentially assessed in the OF, elevated plus maze (EPM), and light-dark box (LDB) and then assessed for ethanol intake. The aims were to assess the relationship between measures of ethanol-induced activity and anxiolysis, analyze ethanol intake as a function of prior ethanol exposure, and associate behavioral responsiveness in these apparatus with ethanol intake during adolescence. The results suggested that the enhanced exploration of the OF observed after 2.5 and 3.25. g/kg ethanol reflected a motor-stimulating effect that appeared to be relatively independent of anxiolysis. The 1.25. g/kg dose induced motor stimulation in the OF and anti-anxiety effects in the EPM, but these effects were relatively independent. The 0.5. g/kg ethanol dose exerted significant anxiolytic effects in the EPM in the absence of stimulating effects in the OF. A multivariate regression analysis indicated that adolescents with a higher frequency of rearing behavior in the OF, higher percentage of open arm entries in the EPM, and lower propensity to enter the central area of the OF exhibited greater ethanol intake. These results indicate that the OF is a valid procedure for the measurement of ethanol-induced stimulation, and provide information toward characterizing subpopulations of adolescents at risk for initiating alcohol drinking. © 2014 Elsevier B.V.Fil: Acevedo, María Belén. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra. Universidad Nacional de Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra; ArgentinaFil: Nizhnikov, M. E.. State University of New York; Estados UnidosFil: Molina, Juan Carlos. Universidad Nacional de Córdoba. Facultad de Psicología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra. Universidad Nacional de Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra; ArgentinaFil: Pautassi, Ricardo Marcos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra. Universidad Nacional de Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra; Argentina. Universidad Nacional de Córdoba. Facultad de Psicología; Argentin

Estilosde crianza y rendimiento académico en un grupo de estudiantes de básica primariade un Centro Educativo del corregimiento Altavista, Medellín 2020

Determinar la relación entre los estilos parentales y el rendimiento académico en un grupo de niños del grado primero a quinto en el Centro Educativo el Manzanillo, Altavista, Antioquia, Colombia en 2020-1.El presente trabajo tiene como objetivo analizar la correlación existente entre el rendimiento académico y el estilo de crianza implementado en los hogares en un grupode 38 estudiantes de primero a quinto grado, con edades entre los 6 y los 13 años, del Centro Educativo el Manzanillo ubicado en la ciudad de Medellín. Esta investigación se realizó bajo un enfoque cuantitativo, con alcance correlacional, de carácter no probabilístico. Se utilizó la versión chilena del Cuestionario de Dimensiones y Estilos de Crianza de Robinson y Cols (1995) y una encuesta sociodemográfica. Se encontró que, el estilo de crianza menos utilizado es el permisivo y el más empleado es autoritativo; el cual influye en el incremento del promedio académico según los datos

Phenology and mortality of embryos in a Colombian population of Nymphargus grandisonae (Anura: Centrolenidae)

Fenologia e mortalidade de embriões em uma população colombiana de Nymphargus grandisonae (Anura: Centrolenidae). Estudos de fenologia e história natural dos anuros fornecem informações úteis para sua conservação. Isso é particularmente importante nos cenários atuais de doenças emergentes, altas taxas de desmatamento e mudanças climáticas. Monitoramos a época de reprodução da perereca-de-vidro Nymphargus grandisonae (Centrolenidae) e sua relação com a precipitação e a temperatura ambiental durante quatro anos em uma população localizada nos Andes Centrais da Colômbia, América do Sul. Além disso, registramos as causas de mortalidade nas desovas dessa espécie. Quantificamos a infestação por larvas de moscas e seus efeitos na sobrevivência dos embriões. Descobrimos que a atividade reprodutiva de N. grandisonae (número de machos vocalizando) foi sazonal e ocorreu nos meses de maior precipitação. A principal causa de mortalidade embrionária nas desovas esteve associada à infestação por uma mosca do gênero c.f. Cladochaeta (Drosophilidae). A sobrevivência de embriões em desovas infestadas foi significativamente menor do que naquelas não infestadas pelas larvas da mosca. Nossos achados fornecem dados básicos para o monitoramento da dinâmica populacional de anuros na região Andina usando a perereca-de-vidro N. grandisonae como modelo de estudo.Phenology and mortality of embryos in a Colombian population of Nymphargus grandisonae (Anura: Centrolenidae). Studies of phenology and natural history of anurans provide information useful for its conservation. This is particularly important in current scenarios of emergent diseases, high rates of deforestation, and climate change. We recorded the timing of breeding of the Glass Frog Nymphargus grandisonae and its relationship to precipitation and environmental temperature for four years in a population located in the Central Andes of Colombia, South America. In addition, we recorded the causes of mortality in egg clutches of this species. We quantified infestation by fly larvae and its impact on the survival of embryos. We found that the reproductive activity of N. grandisonae (number of males calling) was seasonal and occurred in months with highest precipitation. The main cause of embryo mortality in clutches was associated with the infestation by a spittlebug fly of the genus c.f. Cladochaeta (Drosophilidae). The survival of embryos in infested clutches was significantly lower than in those clutches not infested by fly larvae. Our results provide baseline data for the monitoring of anuran population dynamics in the Andean region using the glass frog N. grandisonae as a model system

Perchlorate-Reducing Bacteria from Hypersaline Soils of the Colombian Caribbean

[EN] Perchlorate (ClO4¿) has several industrial applications and is frequently detected in environmental matrices at relevant concentrations to human health. Currently, perchlorate-degrading bacteria are promising strategies for bioremediation in polluted sites. The aim of this study was to isolate and characterize halophilic bacteria with the potential for perchlorate reduction. Ten bacterial strains were isolated from soils of Galerazamba-Bolivar, Manaure-Guajira, and Salamanca Island-Magdalena, Colombia. Isolates grew at concentrations up to 30% sodium chloride. The isolates tolerated pH variations ranging from 6.5 to 12.0 and perchlorate concentrations up to 10000¿mg/L. Perchlorate was degraded by these bacteria on percentages between 25 and 10. 16S rRNA gene sequence analysis indicated that the strains were phylogenetically related to Vibrio, Bacillus, Salinovibrio, Staphylococcus, and Nesiotobacter genera. In conclusion, halophilic-isolated bacteria from hypersaline soils of the Colombian Caribbean are promising resources for the bioremediation of perchlorate contamination.This research received support from the Vice Presidency of Research, University of Cartagena; and Colciencias-University of Cartagena (Grant: RC-758-2011/1107-521-29360).Acevedo-Barrios, R.; Bertel-Sevilla, A.; Alonso Molina, JL.; Olivero-Verbel, J. (2019). Perchlorate-Reducing Bacteria from Hypersaline Soils of the Colombian Caribbean. International Journal of Microbiology. 2019:1-13. https://doi.org/10.1155/2019/6981865S1132019Cole-Dai, J., Peterson, K. M., Kennedy, J. A., Cox, T. S., & Ferris, D. G. (2018). Evidence of Influence of Human Activities and Volcanic Eruptions on Environmental Perchlorate from a 300-Year Greenland Ice Core Record. Environmental Science & Technology, 52(15), 8373-8380. doi:10.1021/acs.est.8b01890Acevedo-Barrios, R., Sabater-Marco, C., & Olivero-Verbel, J. (2018). Ecotoxicological assessment of perchlorate using in vitro and in vivo assays. Environmental Science and Pollution Research, 25(14), 13697-13708. doi:10.1007/s11356-018-1565-6Maffini, M. V., Trasande, L., & Neltner, T. G. (2016). Perchlorate and Diet: Human Exposures, Risks, and Mitigation Strategies. Current Environmental Health Reports, 3(2), 107-117. doi:10.1007/s40572-016-0090-3Knight, B. A., Shields, B. M., He, X., Pearce, E. N., Braverman, L. E., Sturley, R., & Vaidya, B. (2018). Effect of perchlorate and thiocyanate exposure on thyroid function of pregnant women from South-West England: a cohort study. Thyroid Research, 11(1). doi:10.1186/s13044-018-0053-xSmith, P. N. (s. f.). The Ecotoxicology of Perchlorate in the Environment. Perchlorate, 153-168. doi:10.1007/0-387-31113-0_7Steinmaus, C., Pearl, M., Kharrazi, M., Blount, B. C., Miller, M. D., Pearce, E. N., … Liaw, J. (2016). Thyroid Hormones and Moderate Exposure to Perchlorate during Pregnancy in Women in Southern California. Environmental Health Perspectives, 124(6), 861-867. doi:10.1289/ehp.1409614Ghosh, A., Pakshirajan, K., Ghosh, P. K., & Sahoo, N. K. (2011). Perchlorate degradation using an indigenous microbial consortium predominantly Burkholderia sp. Journal of Hazardous Materials, 187(1-3), 133-139. doi:10.1016/j.jhazmat.2010.12.130Nerenberg, R., Rittmann, B. E., & Najm, I. (2002). Perchlorate reduction in a HYDROGEN-BASED MEMBRANE-BIOFILM REACTOR. Journal - American Water Works Association, 94(11), 103-114. doi:10.1002/j.1551-8833.2002.tb10234.xXu, J., & Logan, B. E. (2003). Measurement of chlorite dismutase activities in perchlorate respiring bacteria. Journal of Microbiological Methods, 54(2), 239-247. doi:10.1016/s0167-7012(03)00058-7Logan, B. E., Wu, J., & Unz, R. F. (2001). Biological Perchlorate Reduction in High-Salinity Solutions. Water Research, 35(12), 3034-3038. doi:10.1016/s0043-1354(01)00013-6Matsubara, T., Fujishima, K., Saltikov, C. W., Nakamura, S., & Rothschild, L. J. (2016). Earth analogues for past and future life on Mars: isolation of perchlorate resistant halophiles from Big Soda Lake. International Journal of Astrobiology, 16(3), 218-228. doi:10.1017/s1473550416000458Okeke, B. C., Giblin, T., & Frankenberger, W. T. (2002). Reduction of perchlorate and nitrate by salt tolerant bacteria. Environmental Pollution, 118(3), 357-363. doi:10.1016/s0269-7491(01)00288-3Vijaya Nadaraja, A., Gangadharan Puthiya Veetil, P., & Bhaskaran, K. (2012). Perchlorate reduction by an isolatedSerratia marcescensstrain under high salt and extreme pH. FEMS Microbiology Letters, 339(2), 117-121. doi:10.1111/1574-6968.12062Murray, C. W., & Bolger, P. (2014). Environmental Contaminants: Perchlorate. Encyclopedia of Food Safety, 337-341. doi:10.1016/b978-0-12-378612-8.00200-6Xu, J., Song, Y., Min, B., Steinberg, L., & Logan, B. E. (2003). Microbial Degradation of Perchlorate: Principles and Applications. Environmental Engineering Science, 20(5), 405-422. doi:10.1089/109287503768335904Wang, O., & Coates, J. (2017). Biotechnological Applications of Microbial (Per)chlorate Reduction. Microorganisms, 5(4), 76. doi:10.3390/microorganisms5040076Xiao, Y., & Roberts, D. J. (2013). Kinetics Analysis of a Salt-Tolerant Perchlorate-Reducing Bacterium: Effects of Sodium, Magnesium, and Nitrate. Environmental Science & Technology, 47(15), 8666-8673. doi:10.1021/es400835tNozawa-Inoue, M., Scow, K. M., & Rolston, D. E. (2005). Reduction of Perchlorate and Nitrate by Microbial Communities in Vadose Soil. Applied and Environmental Microbiology, 71(7), 3928-3934. doi:10.1128/aem.71.7.3928-3934.2005Shimkets, L. J., & Rafiee, H. (1990). CsgA, an extracellular protein essential for Myxococcus xanthus development. Journal of Bacteriology, 172(9), 5299-5306. doi:10.1128/jb.172.9.5299-5306.1990Acevedo-Barrios, R., Bertel-Sevilla, A., Alonso-Molina, J., & Olivero-Verbel, J. (2016). Perchlorate tolerant bacteria from saline environments at the Caribbean region of Colombia. Toxicology Letters, 259, S103. doi:10.1016/j.toxlet.2016.07.257Iizuka, T., Tokura, M., Jojima, Y., Hiraishi, A., Yamanaka, S., & Fudou, R. (2006). Enrichment and Phylogenetic Analysis of Moderately Thermophilic Myxobacteria from Hot Springs in Japan. Microbes and Environments, 21(3), 189-199. doi:10.1264/jsme2.21.189Wu, Z.-H., Jiang, D.-M., Li, P., & Li, Y.-Z. (2005). Exploring the diversity of myxobacteria in a soil niche by myxobacteria-specific primers and probes. Environmental Microbiology, 7(10), 1602-1610. doi:10.1111/j.1462-2920.2005.00852.xHuang, X. (1999). CAP3: A DNA Sequence Assembly Program. Genome Research, 9(9), 868-877. doi:10.1101/gr.9.9.868The neighbor-joining method: a new method for reconstructing phylogenetic trees. (1987). Molecular Biology and Evolution. doi:10.1093/oxfordjournals.molbev.a040454Felsenstein, J. (1981). Evolutionary trees from DNA sequences: A maximum likelihood approach. Journal of Molecular Evolution, 17(6), 368-376. doi:10.1007/bf01734359Fitch, W. M. (1971). Toward Defining the Course of Evolution: Minimum Change for a Specific Tree Topology. Systematic Biology, 20(4), 406-416. doi:10.1093/sysbio/20.4.406Tamura, K., Stecher, G., Peterson, D., Filipski, A., & Kumar, S. (2013). MEGA6: Molecular Evolutionary Genetics Analysis Version 6.0. Molecular Biology and Evolution, 30(12), 2725-2729. doi:10.1093/molbev/mst197Kimura, M. (1980). A simple method for estimating evolutionary rates of base substitutions through comparative studies of nucleotide sequences. Journal of Molecular Evolution, 16(2), 111-120. doi:10.1007/bf01731581Felsenstein, J. (1985). CONFIDENCE LIMITS ON PHYLOGENIES: AN APPROACH USING THE BOOTSTRAP. Evolution, 39(4), 783-791. doi:10.1111/j.1558-5646.1985.tb00420.xAlbuquerque, L., Tiago, I., Taborda, M., Nobre, M. F., Verissimo, A., & da Costa, M. S. (2008). Bacillus isabeliae sp. nov., a halophilic bacterium isolated from a sea salt evaporation pond. INTERNATIONAL JOURNAL OF SYSTEMATIC AND EVOLUTIONARY MICROBIOLOGY, 58(1), 226-230. doi:10.1099/ijs.0.65217-0Gholamian, F., Sheikh-Mohseni, M. A., & Salavati-Niasari, M. (2011). Highly selective determination of perchlorate by a novel potentiometric sensor based on a synthesized complex of copper. Materials Science and Engineering: C, 31(8), 1688-1691. doi:10.1016/j.msec.2011.07.017Donachie, S. P., Bowman, J. P., & Alam, M. (2006). Nesiotobacter exalbescens gen. nov., sp. nov., a moderately thermophilic alphaproteobacterium from an Hawaiian hypersaline lake. International Journal of Systematic and Evolutionary Microbiology, 56(3), 563-567. doi:10.1099/ijs.0.63440-0Ling, J., Zhang, G., Sun, H., Fan, Y., Ju, J., & Zhang, C. (2011). Isolation and characterization of a novel pyrene-degrading Bacillus vallismortis strain JY3A. Science of The Total Environment, 409(10), 1994-2000. doi:10.1016/j.scitotenv.2011.02.020Romano, I., Gambacorta, A., Lama, L., Nicolaus, B., & Giordano, A. (2005). Salinivibrio costicola subsp. alcaliphilus subsp. nov., a haloalkaliphilic aerobe from Campania Region (Italy). Systematic and Applied Microbiology, 28(1), 34-42. doi:10.1016/j.syapm.2004.10.001Ali Amoozegar, M., Zahra Fatemi, A., Reza Karbalaei-Heidari, H., & Reza Razavi, M. (2007). Production of an extracellular alkaline metalloprotease from a newly isolated, moderately halophile, Salinivibrio sp. strain AF-2004. Microbiological Research, 162(4), 369-377. doi:10.1016/j.micres.2006.02.007Dubert, J., Romalde, J. L., Prado, S., & Barja, J. L. (2016). Vibrio bivalvicida sp. nov., a novel larval pathogen for bivalve molluscs reared in a hatchery. Systematic and Applied Microbiology, 39(1), 8-13. doi:10.1016/j.syapm.2015.10.006Paek, J., Shin, J. H., Shin, Y., Park, I.-S., Kim, H., Kook, J.-K., … Chang, Y.-H. (2016). Vibrio injenensis sp. nov., isolated from human clinical specimens. Antonie van Leeuwenhoek, 110(1), 145-152. doi:10.1007/s10482-016-0810-6Kumar, P. S., Paulraj, M. G., Ignacimuthu, S., Al-Dhabi, N. A., & Sukumaran, D. (2017). IN VITRO ANTAGONISTIC ACTIVITY OF SOIL STREPTOMYCES COLLINUS DPR20 AGAINST BACTERIAL PATHOGENS. Journal of Microbiology, Biotechnology and Food Sciences, 7(3), 317-324. doi:10.15414/jmbfs.2017/18.7.3.317-324Bruce, R. A., Achenbach, L. A., & Coates, J. D. (1999). Reduction of (per)chlorate by a novel organism isolated from paper mill waste. Environmental Microbiology, 1(4), 319-329. doi:10.1046/j.1462-2920.1999.00042.xWaller, A. S., Cox, E. E., & Edwards, E. A. (2004). Perchlorate-reducing microorganisms isolated from contaminated sites. Environmental Microbiology, 6(5), 517-527. doi:10.1111/j.1462-2920.2004.00598.xChaudhuri, S. K., O’Connor, S. M., Gustavson, R. L., Achenbach, L. A., & Coates, J. D. (2002). Environmental Factors That Control Microbial Perchlorate Reduction. Applied and Environmental Microbiology, 68(9), 4425-4430. doi:10.1128/aem.68.9.4425-4430.2002Liebensteiner, M. G., Oosterkamp, M. J., & Stams, A. J. M. (2015). Microbial respiration with chlorine oxyanions: diversity and physiological and biochemical properties of chlorate- and perchlorate-reducing microorganisms. Annals of the New York Academy of Sciences, 1365(1), 59-72. doi:10.1111/nyas.12806Zhu, Y., Gao, N., Chu, W., Wang, S., & Xu, J. (2016). Bacterial reduction of highly concentrated perchlorate: Kinetics and influence of co-existing electron acceptors, temperature, pH and electron donors. Chemosphere, 148, 188-194. doi:10.1016/j.chemosphere.2015.10.130Giblin, T., & Frankenberger, W. T. (2001). Perchlorate and nitrate reductase activity in the perchlorate-respiring bacterium perclace. Microbiological Research, 156(4), 311-315. doi:10.1078/0944-5013-00111Sevda, S., Sreekishnan, T. R., Pous, N., Puig, S., & Pant, D. (2018). Bioelectroremediation of perchlorate and nitrate contaminated water: A review. Bioresource Technology, 255, 331-339. doi:10.1016/j.biortech.2018.02.005Wang, C., Lippincott, L., & Meng, X. (2008). Kinetics of biological perchlorate reduction and pH effect. Journal of Hazardous Materials, 153(1-2), 663-669. doi:10.1016/j.jhazmat.2007.09.01

Statistics of the purse seine Spanish fleet in the Indian Ocean (1990-2011)

This document presents summary statistics of the purse seiner Spanish fleet fishing in the Indian Ocean from 1990 to 2011. Data include catch and effort statistics as well as some fishery index by species and fishing mode. Information about the sampling scheme and the coverage of sampling, together with maps and diagrams representing the fishing pattern of this fleet by time and area strata is also included

Image processing and machine learning in the morphological analysis of blood cells

Introduction: This review focuses on how image processing and machine learning can be useful for the morphological characterization and automatic recognition of cell images captured from peripheral blood smears. Methods: The basics of the 3 core elements (segmentation, quantitative features, and classification) are outlined, and recent literature is discussed. Although red blood cells are a significant part of this context, this study focuses on malignant lymphoid cells and blast cells. Results: There is no doubt that these technologies may help the cytologist to perform efficient, objective, and fast morphological analysis of blood cells. They may also help in the interpretation of some morphological features and may serve as learning and survey tools. Conclusion: Although research is still needed, it is important to define screening strategies to exploit the potential of image-based automatic recognition systems integrated in the daily routine of laboratories along with other analysis methodologies.Peer ReviewedPostprint (published version

Labor Law in Colombia: Emergence of a Local Socialist Perspective (1930-1945)

Este artículo controvierte la tesis generalizada sobre el origen del derecho laboral en Colombia, que lo explica como una concesión del presidente Alfonso López al movimiento obrero por su apoyo durante el intento de golpe de 1944. Mediante un análisis histórico basado en la revisión de fuentes primarias, se argumenta que desde comienzos de la década de 1930 existieron diversas corrientes académicas y políticas que proponían desarrollar esta rama del derecho. Se profundiza en la apropiación crítica de teorías jurídicas transnacionales por los socialistas locales para poner en cuestión la supuesta insularidad y aislamiento intelectuales de la academia en Colombia y de este grupo en particular. Se concluye que el derecho laboral, entendido como derecho social por los socialistas, se nutrió de, al menos, cuatro fuentes: las corrientes antiformalistas, el materialismo dialectico y su expresión en el derecho soviético, el constitucionalismo social francés y el laboralismo inglés.This article challenges the general thesis on the origin of labor law in Colombia, explaining it as a concession given by president AlfonsoLópez to the workers movement for its support during the coup d’état attempt in 1944. Through a historical analysis based on the revision of primary sources, the article states that there were several academic and political currents early in the 1930’s that proposed the development of this branch of law. The article goes deeper in the critical appropriation of translational legal theories by local socialists intended to question the presumable intellectual isolation of the Colombian academicians and particularly this group. The article concludes that the labor law, understood as social right by socialists, was based at least on four sources: antiformalist currents; dialectic materialism and its expression in the Soviet law; the French social constitutionalism; and the English labor movement