Parallel Analysis: a Method for Determining Significant Principal Components

Numerous ecological studies use Principal Components Analysis (PCA) for exploratory analysis and data reduction. Determination of the number of components to retain is the most crucial problem confronting the researcher when using PCA. An incorrect choice may lead to the underextraction of components, but commonly results in overextraction. Of several methods proposed to determine the significance of principal components, Parallel Analysis (PA) has proven consistently accurate in determining the threshold for significant components, variable loadings, and analytical statistics when decomposing a correlation matrix. In this procedure, eigenvalues from a data set prior to rotation are compared with those from a matrix of random values of the same dimensionality (p variables and n samples). PCA eigenvalues from the data greater than PA eigenvalues from the corresponding random data can be retained. All components with eigenvalues below this threshold value should be considered spurious. We illustrate Parallel Analysis on an environmental data set. We reviewed all articles utilizing PCA or Factor Analysis (FA) from 1987 to 1993 from Ecology, Ecological Monographs, Journal of Vegetation Science and Journal of Ecology. Analyses were first separated into those PCA which decomposed a correlation matrix and those PCA which decomposed a covariance matrix. Parallel Analysis (PA) was applied for each PCA/FA found in the literature. Of 39 analyses (in 22 articles), 29 (74.4%) considered no threshold rule, presumably retaining interpretable components. According to the PA results, 26 (66.7%) overextracted components. This overextraction may have resulted in potentially misleading interpretation of spurious components. It is suggested that the routine use of PA in multivariate ordination will increase confidence in the results and reduce the subjective interpretation of supposedly objective methods

Crystallographic Evidence of Drastic Conformational Changes in the Active Site of a Flavin-Dependent

The soil actinomycete Kutzneria sp. 744 produces a class of highly decorated hexadepsipeptides, which represent a new chemical scaffold that has both antimicrobial and antifungal properties. These natural products, known as kutznerides, are created via nonribosomal peptide synthesis using various derivatized amino acids. The piperazic acid moiety contained in the kutzneride scaffold, which is vital for its antibiotic activity, has been shown to derive from the hydroxylated product of l-ornithine, l-N5-hydroxyornithine. The production of this hydroxylated species is catalyzed by the action of an FAD- and NAD(P)H-dependent N-hydroxylase known as KtzI. We have been able to structurally characterize KtzI in several states along its catalytic trajectory, and by pairing these snapshots with the biochemical and structural data already available for this enzyme class, we propose a structurally based reaction mechanism that includes novel conformational changes of both the protein backbone and the flavin cofactor. Further, we were able to recapitulate these conformational changes in the protein crystal, displaying their chemical competence. Our series of structures, with corroborating biochemical and spectroscopic data collected by us and others, affords mechanistic insight into this relatively new class of flavin-dependent hydroxylases and adds another layer to the complexity of flavoenzymes.National Center for Research Resources (U.S.) (P41RR012408)National Institute of General Medical Sciences (U.S.) (P41GM103473

Tendencias de la cultura y cambio organizacional: estudio de caso

La imagen corporativa en relación con el medio se evidencia en el informe de Deloitte (2018) sobre tendencias del capital humano, en donde se reportan alrededor de 11.000 cuestionarios aplicados a gerentes de 140 países y 150 líderes de empresas colombianas, el planteamiento realizado sugiere que el capital social cobra tanto importancia como el físico y el financiero. Estos aspectos están relacionados con la identidad corporativa y cómo se relaciona a su vez con la cultura y la gestión del en la organización. La cultura y la gestión del cambio han cobrado mucho interés para las personas que guían las organizaciones, los estudios realizados por Deloitte en 2017 se focalizaron en la relación de la cultura y el compromiso como elementos importantes del empleado; los resultados del estudio dejan en evidencia cómo la habilidad de las organizaciones para afrontar inconvenientes de compromiso y cultura tenían una reducción del 14% con respecto al año anterior, estos datos permiten entender la complejidad del ambiente en el ámbito laboral y dan cuenta de la importancia de desarrollar conocimiento válido que oriente a académicos y empresarios para que puedan abordar de una manera adecuada estos aspectos.1a edició

Witches' Brew and Bloodcraft An Examination of Inertial Behaviors In Laminar Flow Environments

Deterministic Lateral Displacement arrays (DLDs) utilize the properties of laminar or viscous flow to separate biological material by characteristic size. DLDs are comprised of a long, at chip through which a solution is forced. A grid of laterally offset rows of pillars determines a flow pattern throughout the length of the chip. Due to laminar behavior, particles are expected to closely follow flow patterns, separating them based on their flow mode. As the size scale of DLDs decreases in an effort to boost the resolution of separation, experimentalists find that the efficiencies are decreasing: Polymer chains that otherwise traverse the length of the array unscathed break apart in the smaller scale, and particles do not separate as expected from laminar properties. Using low Reynolds and Stokes number approximations, this paper solves the laminar case in 2 1/2 dimensions for a scalar stream function. The scalar stream function allows us to translate boundary conditions from cartesian to polar, which allows us to de fine a critical radius and characteristic displacement vector to locate regions of inertial particle behavior in an otherwise completely laminar fluid. Finally, the scalar stream function and critical radius are applied to simulated flow environments to investigate if inertial behaviors may be occurring. We find clear patterns which are compliant with experimental observations, and make claims regarding theoretical models

The Effect of Second-Language Proficiency on Second Language Reading Comprehension

Data from a first-language reading test, a second-language reading comprehension test with questions from different cognitive levels, and from the TOEFL were submitted to partial correlation analysis to detennine whether there was a significant effect of second-language proficiency on second-language reading comprehension when the influence of first-language reading comprehension was held constant. The results indicated that for factual and inference questions second-language reading comprehension may be more closely related to second-language proficiency than to first-language reading comprehension. The lack of a similar relationship for the generalization questions may be due to a substantial variation in the second-language readers' fonnal and content background knowledge which is necessary for the processing and comprehension of generalization questions. Data van 'n eerste taal-leestoets, 'n tweede taal-leesbegripstoets met vrae op verskillende kognitiewe vlakke en van die TO EFL is aan gedeeltelike korrelasie-ontleding onderworpe om vas te stel of daar 'n beduidende bei"nvloeding van tweede taal-vaardigheid op tweede taalleesbegrip was terwyl die invloed van eerste taal-leesbegrip konstant gebly het. Die resultate het aangedui dat wat feitelike en gevolgtrekkingsvrae betref, tweede taal-leesbegrip moontlik nader verwant is aan tweede taal-vaardigheid as aan eerste taal-leesbegrip. Die afwesigheid van 'n soortgelyke verhouding betreffende die veralgemeningsvrae is moontlik te IV)lte aan 'n aansienlike variasie in die tweede taal lesers se fonnele en inhoudelike agtergrondkennis wat nodig is vir die verwerking en begrip van veralgemeningsvrae