2,254 research outputs found
A Note on Implementing Box-Cox Quantile Regression
Get PDFThe Box-Cox quantile regression model using the two stage method suggested by Chamberlain (1994) and Buchinsky (1995) provides a flexible and numerically attractive extension of linear quantile regression techniques. However, the objective function in stage two of the method may not exists. We suggest a simple modification of the estimator which is easy to implement. The modified estimator is still pn{consistent and we derive its asymptotic distribution. A simulation study confirms that the modified estimator works well in situations, where the original estimator is not well defined. --Box-Cox quantile regression,iterative estimator
Generating Survival Times to Simulate Cox Proportional Hazards Models
Get PDFThis paper discusses techniques to generate survival times for simulation studies regarding Cox proportional hazards models. In linear regression models, the response variable is directly connected with the considered covariates, the regression coefficients and the simulated random errors. Thus, the response variable can be generated from the regression function, once the regression coefficients and the error distribution are specified. However, in the Cox model, which is formulated via the hazard function, the effect of the covariates have to be translated from the hazards to the survival times, because the usual software packages for estimation of Cox models require the individual survival time data. A general formula describing the relation between the hazard and the corresponding survival time of the Cox model is derived. It is shown how the exponential, the Weibull and the Gompertz distribution can be used to generate appropriate survival times for simulation studies. Additionally, the general relation between hazard and survival time can be used to develop own distributions for special situations and to handle flexibly parameterized proportional hazards models. The use of other distributions than the exponential distribution only is indispensable to investigate the characteristics of the Cox proportional hazards model, especially in non-standard situations, where the partial likelihood depends on the baseline hazard
Bias of Maximum-Likelihood estimates in logistic and Cox regression models: A comparative simulation study
Get PDFParameter estimates of logistic and Cox regression models are biased for finite samples. In a simulation study we investigated for both models the behaviour of the bias in relation to sample size and further parameters. In the case of a dichotomous explanatory variable x the magnitude of the bias is strongly influenced by the baseline risk defined by the constants of the models and the risk resulting for the high risk group. To conduct a direct comparison of the bias of the two models analyses were based on the same simulated data. Overall, the bias of the two models appear to be similar, however, the Cox model has less bias in situations where the baseline risk is high
Implementing Box–Cox Quantile Regression
No full textThe Box–Cox quantile regression model introduced by Powell (1991) is a flexible and numerically attractive extension of linear quantile regression techniques. Chamberlain (1994) and Buchinsky (1995) suggest a two stage estimator for this model but the objective function in stage two of their method may not be defined in an application. We suggest a modification of the estimator which is easy to implement. A simulation study demonstrates that the modified estimator works well in situations, where the original estimator is not well defined.Box–Cox quantile regression, Iterative estimator, C13, C14,
Cultural representation of sexual dissent in comics: the "desired men" of Ralf König in Der bewegte Mann
Get PDFEn este artículo se abordará la representación de la sexualidad disidente en una de las obras inaugurales de Ralf König, el ciclo Der bewegte Mann, constituido por dos partes publicadas en los años ochenta y que nos permiten apreciar la emergencia del autor en el mercado editorial alemán, así como sus operaciones de resistencia ante los intentos de normalización y represión por parte de la heteronormatividad.In this article, the representation of sexual dissent in German author Ralf König will be adressed. The work analize the cycle Der bewegte Mann, consisting of two parts published in the eighties and that allows us to appreciate the emergence of the author in the german publishing, as well as its operations of resistance to the attempts of normalization and repression by heteronormativity.Fil: Saxe, Facundo. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación. Instituto de Investigaciones en Humanidades y Ciencias Sociales (UNLP-CONICET); Argentina
Representación cultural de la disidencia sexual en el cómic: los «hombres deseados» de Ralf König en Der bewegte Mann
Get PDFEn este artículo se abordará la representación de la sexualidad disidente en una de las obras inaugurales de Ralf König, el ciclo Der bewegte Mann, constituido por dos partes publicadas en los años ochenta y que nos permiten apreciar la emergencia del autor en el mercado editorial alemán, así como sus operaciones de resistencia ante los intentos de normalización y represión por parte de la heteronormatividad.In this article, the representation of sexual dissent in German author Ralf König will be adressed. The work analize the cycle Der bewegte Mann, consisting of two parts published in the eighties and that allows us to appreciate the emergence of the author in the german publishing, as well as its operations of resistance to the attempts of normalization and repression by heteronormativity.Facultad de Humanidades y Ciencias de la Educació
Dihydroisocoumarins, Naphthalenes, and Further Polyketides from <i>Aloe vera</i> and <i>A. plicatilis</i>: Isolation, Identification and Their 5-LOX/COX-1 Inhibiting Potency
No full textThe present study aims at the isolation and identification of diverse phenolic polyketides from Aloe vera (L.) Burm.f. and Aloe plicatilis (L.) Miller and includes their 5-LOX/COX-1 inhibiting potency. After initial Sephadex-LH20 gel filtration and combined silica gel 60- and RP18-CC, three dihydroisocoumarins (nonaketides), four 5-methyl-8-C-glucosylchromones (heptaketides) from A. vera, and two hexaketide-naphthalenes from A. plicatilis have been isolated by means of HSCCC. The structures of all polyketides were elucidated by ESI-MS and 2D 1H/13C-NMR (HMQC, HMBC) techniques. The analytical/preparative separation of 3R-feralolide, 3′-O-β-d-glucopyranosyl- and the new 6-O-β-d-glucopyranosyl-3R-feralolide into their respective positional isomers are described here for the first time, including the assignment of the 3R-configuration in all feralolides by comparative CD spectroscopy. The chromones 7-O-methyl-aloesin and 7-O-methyl-aloeresin A were isolated for the first time from A. vera, together with the previously described aloesin (syn. aloeresin B) and aloeresin D. Furthermore, the new 5,6,7,8-tetrahydro-1-O-β-d-glucopyranosyl- 3,6R-dihydroxy-8R-methylnaphtalene was isolated from A. plicatilis, together with the known plicataloside. Subsequently, biological-pharmacological screening was performed to identify Aloe polyketides with anti-inflammatory potential in vitro. In addition to the above constituents, the anthranoids (octaketides) aloe emodin, aloin, 6′-(E)-p-coumaroyl-aloin A and B, and 6′-(E)-p-coumaroyl-7-hydroxy-8-O-methyl-aloin A and B were tested. In the COX-1 examination, only feralolide (10 µM) inhibited the formation of MDA by 24%, whereas the other polyketides did not display any inhibition at all. In the 5-LOX-test, all aloin-type anthranoids (10 µM) inhibited the formation of LTB4 by about 25–41%. Aloesin also displayed 10% inhibition at 10 µM in this in vitro setup, while the other chromones and naphthalenes did not display any activity. The present study, therefore, demonstrates the importance of low molecular phenolic polyketides for the known overall anti-inflammatory activity of Aloe vera preparations
Sexuellen Dissidenz and Comic im Werk von Ralf König
Get PDFRalf König es un autor de importancia innegable para la historieta alemana desde los años ochenta al presente. El abordaje programático y sistemático de la sexualidad disidente en sus vertientes más subversivas convierten la obra de König en un conjunto de textos culturales que constituyen una suerte de "historias culturales" de los devenires de la disidencia sexual en las últimas tres décadas en el contexto europeo. Este artículo analiza dos obras de Ralf König (Kondom des Grauens, 1987; Bis auf die Knochen, 1990) que constituyen un ciclo que permiten pensar el diálogo que establece la obra de König con la crisis del VIH-Sida, la pornografía gay, la violencia y discriminación sobre las sexualidades disidentes, la influencia del movimiento queer y el colectivo LGBTIQ norteamericano en Alemania, entre otras cuestiones.Ralf König has been an author of an undeniable importance for the German comic since the 1980s. The programmatic and systematic approach to dissident sexuality in its most subversive aspects makes König's work a set of cultural texts that stand as some sort of "cultural histories" of the progressions of sexual dissidence in the last three decades in the European context. This article analyzes two works by Ralf König (Kondom des Grauens, 1987; Bis auf die Knochen, 1990) which constitute a cycle that allows us to ponder on the dialogue established by König's works with the HIV-AIDS crisis, gay pornography, violence and discrimination towards dissident sexualities, the influence of the queer movement and the American LGBTIQ collective in Germany, among other issues.Facultad de Humanidades y Ciencias de la Educació
Eelco Visser - An Exceptional SLE Researcher
Get PDFThese notes honor Eelco Visser as an exceptional member of the Software Language Engineering (SLE) community. The notes are authored from the perspective of an SLE co-founder and a continuous SLE supporter. As an inevitable side effect, a short history of SLE is captured. The commemoration begins with Eelco’s role in launching the SLE conference. The commemoration continues with Eelco’s contributions as an author and his involvement with running the conference and working towards an SLE Body of Knowledge (SLEBoK). The commemoration ends with recalling Eelco’s role as the de-facto SLE photographer
- …
