A simulation study of the effects of small center enrollment in multi -center clinical trials

Multi-center clinical trials are very common in the development of new drugs and devices. One concern in such trials, is the effect of individual investigational sites enrolling small numbers of patients on the overall result. Can the presence of small centers cause an ineffective treatment to appear effective when treatment-by-center interaction is not statistically significant?^ In this research, simulations are used to study the effect that centers enrolling few patients may have on the analysis of clinical trial data. A multi-center clinical trial with 20 sites is simulated to investigate the effect of a new treatment in comparison to a placebo treatment. Twelve of these 20 investigational sites are considered small, each enrolling less than four patients per treatment group. Three clinical trials are simulated with sample sizes of 100, 170 and 300. The simulated data is generated with various characteristics, one in which treatment should be considered effective and another where treatment is not effective. Qualitative interactions are also produced within the small sites to further investigate the effect of small centers under various conditions.^ Standard analysis of variance methods and the "sometimes-pool" testing procedure are applied to the simulated data. One model investigates treatment and center effect and treatment-by-center interaction. Another model investigates treatment effect alone. These analyses are used to determine the power to detect treatment-by-center interactions, and the probability of type I error.^ We find it is difficult to detect treatment-by-center interactions when only a few investigational sites enrolling a limited number of patients participate in the interaction. However, we find no increased risk of type I error in these situations. In a pooled analysis, when the treatment is not effective, the probability of finding a significant treatment effect in the absence of significant treatment-by-center interaction is well within standard limits of type I error. ^

Gestión de la mano de obra, flexibilidad y precariedad en el sector comercio : Heterogeneidad de situaciones. Un análisis en los shopping center

En esta ponencia presentamos un primer acercamiento exploratorio en el sector comercio. Concretamente, y a partir del análisis de un subsector -shopping centers-, buscamos observar cuestiones vinculadas con las estrategias de flexibilidad laboral, precariedad y subcontratación a través del estudio de las modalidades de gestión de mano de obra que allí operan. Para ello, analizamos algunas de las formas contractuales y las condiciones de trabajo que se presentan en un sector caracterizado por la heterogeneidad de los actores, la multiplicidad de actividades y el relevante lugar que ocupa en la economía argentina. La elección del sector mercantil parte de considerar las grandes transformaciones que la actividad ha experimentado a lo largo de su historia. E0sto se debe, entre otros factores, a los cambios económicos y sociales que impactaron directamente en las actividades comerciales. Y, a su vez, incidieron en la composición de los trabajadores y en la organización del trabajo que integran el sector. Dada la complejidad de la actividad seleccionada, distinguimos para el análisis del presente trabajo el subsector centros de compras (shopping centers). En primer lugar, nos proponemos una presentación general del sector comercio. Luego, nos focalizaremos en el subsector seleccionado a fin de identificar las principales características que operan en él

Christos C. Tsagalis. The Oral Palimsest. Exploring Intertextuality in the Homeric Epics. Center for Hellenic Studies, Harvard University Press, Cambridge, Massachusetts, and London, England, 2008, ix+325 pp.

Fil: Zecchin de Fasano, Graciela Cristina. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Christos C. Tsagalis. The Oral Palimsest. Exploring Intertextuality in the Homeric Epics. Center for Hellenic Studies, Harvard University Press, Cambridge, Massachusetts, and London, England, 2008, ix+325 pp.

Fil: Zecchin de Fasano, Graciela Cristina. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Gestión de la mano de obra, flexibilidad y precariedad en el sector comercio : Heterogeneidad de situaciones. Un análisis en los shopping center

En esta ponencia presentamos un primer acercamiento exploratorio en el sector comercio. Concretamente, y a partir del análisis de un subsector -shopping centers-, buscamos observar cuestiones vinculadas con las estrategias de flexibilidad laboral, precariedad y subcontratación a través del estudio de las modalidades de gestión de mano de obra que allí operan. Para ello, analizamos algunas de las formas contractuales y las condiciones de trabajo que se presentan en un sector caracterizado por la heterogeneidad de los actores, la multiplicidad de actividades y el relevante lugar que ocupa en la economía argentina. La elección del sector mercantil parte de considerar las grandes transformaciones que la actividad ha experimentado a lo largo de su historia. E0sto se debe, entre otros factores, a los cambios económicos y sociales que impactaron directamente en las actividades comerciales. Y, a su vez, incidieron en la composición de los trabajadores y en la organización del trabajo que integran el sector. Dada la complejidad de la actividad seleccionada, distinguimos para el análisis del presente trabajo el subsector centros de compras (shopping centers). En primer lugar, nos proponemos una presentación general del sector comercio. Luego, nos focalizaremos en el subsector seleccionado a fin de identificar las principales características que operan en él

Gestión de la mano de obra, flexibilidad y precariedad en el sector comercio : Heterogeneidad de situaciones. Un análisis en los shopping center

En esta ponencia presentamos un primer acercamiento exploratorio en el sector comercio. Concretamente, y a partir del análisis de un subsector -shopping centers-, buscamos observar cuestiones vinculadas con las estrategias de flexibilidad laboral, precariedad y subcontratación a través del estudio de las modalidades de gestión de mano de obra que allí operan. Para ello, analizamos algunas de las formas contractuales y las condiciones de trabajo que se presentan en un sector caracterizado por la heterogeneidad de los actores, la multiplicidad de actividades y el relevante lugar que ocupa en la economía argentina. La elección del sector mercantil parte de considerar las grandes transformaciones que la actividad ha experimentado a lo largo de su historia. E0sto se debe, entre otros factores, a los cambios económicos y sociales que impactaron directamente en las actividades comerciales. Y, a su vez, incidieron en la composición de los trabajadores y en la organización del trabajo que integran el sector. Dada la complejidad de la actividad seleccionada, distinguimos para el análisis del presente trabajo el subsector centros de compras (shopping centers). En primer lugar, nos proponemos una presentación general del sector comercio. Luego, nos focalizaremos en el subsector seleccionado a fin de identificar las principales características que operan en él

Major and trace element composition of melts from the Gorely volcanic center, southern Kamchatka

Melt inclusions in olivine and plagioclase phenocrysts from rocks (magnesian basalt, basaltic andesite, andesite, ignimbrite, and dacite) of various age from the Gorely volcanic center, southern Kamchatka, were studied by means of their homogenization and by analyzing the glasses in 100 melt inclusions on an electron microprobe and 24 inclusions on an ion probe. The SiO2 concentrations of the melts vary within a broad range of 45-74 wt%, as also are the concentrations of other major components. According to their SiO2, Na2O, K2O, TiO2, and P2O5 concentrations, the melts are classified into seven groups. The mafic melts (45-53 wt% SiO2) comprise the following varieties: potassic (on average 4.2 wt% K2O, 1.7 wt% Na2O, 1.0 wt% TiO2, and 0.20 wt% P2O5), sodic (3.2% Na2O, 1.1% K2O, 1.1% TiO2, and 0.40% P2O5), and titaniferous with high P2O5 concentrations (2.2% TiO2, 1.1% P2O5, 3.8% Na2O, and 3.0% K2O). The melts of intermediate composition (53-64% SiO2) also include potassic (5.6% K2O, 3.4% Na2O, 1.0% TiO2, and 0.4% P2O5) and sodic (4.3% Na2O, 2.8% K2O, 1.3% TiO2, and 0.4% P2O5) varieties. The acid melts (64-74% SiO2) are either potassic (4.5% K2O, 3.6% Na2O, 0.7% TiO2, and 0.15% P2O5) or sodic (4.5% Na2O, 3.1% K2O, 0.7% TiO2, and 0.13% P2O5). A distinctive feature of the Gorely volcanic center is the pervasive occurrence of K-rich compositions throughout the whole compositional range (silicity) of the melts. Melt inclusions of various types were sometimes found not only in a single sample but also in the same phenocrysts. The sodic and potassic types of the melts contain different Cl and F concentrations: the sodic melts are richer in Cl, whereas the potassic melts are enriched in F. We are the first to discover potassic melts with very high F concentrations (up to 2.7 wt%, 1.19 wt% on average, 17 analyses) in the Kuriles and Kamchatka. The average F concentration in the sodic melts is 0.16 wt% (37 analyses). The melts are distinguished for their richness in various groups of trace elements: LILE, REE (particularly HREE), and HFSE (except Nb). All of the melts share certain geochemical features. The concentrations of elements systematically increase from the mafic to acid melts (except only for the Sr and Eu concentrations, because of active plagioclase fractionation, and Ti, an element contained in ore minerals). The paper presents a review of literature data on volcanic rocks in the Kurile-Kamchatka area in which melt inclusions with high K2O concentrations (K2O/Na2O > 1) were found. K-rich melts are proved to be extremely widespread in the area and were found on such volcanoes as Avachinskii, Bezymyannyi, Bol'shoi Semyachek, Dikii Greben', Karymskii, Kekuknaiskii, Kudryavyi, and Shiveluch and in the Valaginskii and Tumrok Ranges.

Chemical composition of rocks and minerals from the Karymsky volcanic center, Eastern Kamchatka

The powerful eruption in the Akademii Nauk caldera on January 2, 1996 marked a new activity phase of the Karymsky volcano and became a noticeable event in the history of modern volcanism in Kamchatka. The paper reports data obtained by studying more than 200 glassy melt inclusions in phenocrysts of olivine (Fo82-72), plagioclase (An92-73), and clinopyroxene (Mg# 83-70) in basalts of the 1996 eruption. The data were used to estimate composition of the parental melt and physicochemical parameters of the magma evolution. According to our data, the parental melt corresponded to low magnesium, high aluminum basalt (SiO2 = 50.2%, MgO = 5.6%, Al2O3 = 17%) of the mildly potassium type (K2O = 0.56%) and contained much dissolved volatile components (H2O = 2.8%, S = 0.17%, and Cl = 0.11%). Melt inclusions in the minerals are similar in chemical composition, a fact testifying that the minerals crystallized simultaneously with one another. Their crystallization started at pressure ~1.5 kbar, proceeded within a narrow temperature range of 1040+/-20°C, and continued until near-surface pressure ~100 bar was reached. Degree of crystallization of the parental melt during its eruption was close to 55%. Massive crystallization was triggered by H2O degassing under pressure <1 kbar. Magma degassing in an open system resulted in escape of 82% H2O, 93% S, and 24% Cl (of their initial contents in the parental melt) to the fluid phase. Release of volatile compounds to the atmosphere during the eruption that lasted for 18 h was estimated as 1.7x10**6 t H2O, 1.4x10**5 t S, and 1.5x10**4 t Cl. Concentrations of most incompatible trace elements in the melt inclusions are close to those in the rocks and to the expected fractional differentiation trend. Melt inclusions in plagioclase were found to be selectively enriched in Li. The Li-enriched plagioclase with melt inclusions thought to originate from cumulate layers in the feeding system beneath Karymsky volcano, in which plagioclase interacted with Li-rich melts/brines and was subsequently entrapped and entrained by the magma during the 1996 eruption.