Polymorphic Students

Objective: In an effort to break away from the stale classifications of community college students that stem from the hegemonic perspective of previous literature, this work utilizes the perceptions of community college practitioners to demonstrate new ways of understanding the identities of community college students. Method: By utilizing Gee’s identity theory and Grillo’s theory of intersectionality, we analyze interviews with community college practitioners from three different community colleges on the West coast of the United States to answer these questions: What identities (i.e., natural, institutional, and discursive) do faculty and administrators recognize in community college students? In what ways do community college faculty and administrators describe and conceptualize community college students? Findings: First, community college student identities are intricate and have changed with time; there are two different institutional views held by organizational members—the educational view and the managerial view—which both shape the construction of student identities and play a prominent role in determining which students are disadvantaged. Second, organizational members constructed meanings of student achievement and value (i.e., attributes or outcomes of the ideal student, or what policy makers and institutions refer to as success) according to organizational priorities and perspectives. Conclusion: This investigation encapsulates and elucidates the portrayals and understandings of community college students held by community college administrators and faculty as a means to acknowledge the diverse identities among these students. Scholars and practitioners are encouraged to acknowledge the polymorphic identities of this diverse population to improve scholarship and practice

Spin torque contribution to the a.c. spin Hall conductivity

Using the recently proposed definition of a conserved spin-current operator [J. Shi et al., Phys. Rev. Lett. 96, 076604 (2006)] we explore the frequency dependent spin Hall conductivity for a two-dimensional electron gas with Rashba and Dresselhaus spin-orbit interaction in response to an oscillating electric field. We show that the optical spectrum of the spin Hall conductivity exhibit remarkable changes when the new definition of spin current is applied. Such behavior is mainly due to a significant contribution of the spin torque term which is absent in the conventional form of the spin current. In addition, it is observed that the magnitude and direction of the dynamic spin Hall current strongly depends on the electric field frequency as with the interplay of the spin-orbit coupling strengths.Comment: 8 pages, 4 figures, pape

Scaling of Local Slopes, Conservation Laws and Anomalous Roughening in Surface Growth

We argue that symmetries and conservation laws greatly restrict the form of the terms entering the long wavelength description of growth models exhibiting anomalous roughening. This is exploited to show by dynamic renormalization group arguments that intrinsic anomalous roughening cannot occur in local growth models. However some conserved dynamics may display super-roughening if a given type of terms are present.Comment: To appear in Phys. Rev. Lett., 4 pages in RevTeX style, no fig

Coarse grained approach for volume conserving models

Volume conserving surface (VCS) models without deposition and evaporation, as well as ideal molecular-beam epitaxy models, are prototypes to study the symmetries of conserved dynamics. In this work we study two similar VCS models with conserved noise, which differ from each other by the axial symmetry of their dynamic hopping rules. We use a coarse-grained approach to analyze the models and show how to determine the coefficients of their corresponding continuous stochastic differential equation (SDE) within the same universality class. The employed method makes use of small translations in a test space which contains the stationary probability density function (SPDF). In case of the symmetric model we calculate all the coarse-grained coefficients of the related conserved Kardar-Parisi-Zhang (KPZ) equation. With respect to the symmetric model, the asymmetric model adds new terms which have to be analyzed, first of all the diffusion term, whose coarse-grained coefficient can be determined by the same method. In contrast to other methods, the used formalism allows to calculate all coefficients of the SDE theoretically and within limits numerically. Above all, the used approach connects the coefficients of the SDE with the SPDF and hence gives them a precise physical meaning.Comment: 11 pages, 2 figures, 2 table

Detectability of simulated apical lesions on mandibular premolars and molars between radiographic intraoral and cone-beam computed tomography images: an ex vivo study.

Adequate endodontic diagnostic is essential when making a therapy decision. Radiographic imagining acquisition methods (IAMs) are fundamental apical lesions of endodontic (ALE) origin diagnose tool. Thus, the aim of this research was to compare the simulated apical lesions (SALs) diagnose potential of digital intraoral radiography (DIR) and cone-beam computed tomography (CBCT), if there is a relationship between the IAMs, SALs-depth and their correct diagnose likelihood in human mandibular specimens' datasets. 1024 SALs were prepared in cancellous and cortical bone with different penetration depths. The SALs-stages were radiographed with CBCT and DIR. The IAMs were randomly evaluated by 16 observers in two trials. Possible SAL findings were analyzed according to a five-point scale. The null hypothesis established that SALs detection accuracy does not differ between CBCT and DIR. Significantly differences (first 0.935 and second trial 0.960) were found for the CBCT area under the curve when compared with the DIR (first 0.859 and second trial 0.862) findings. SALs of smaller size were earlier detected by CBCT. In SALs without cortical involvement the probability of detection increased from 90 to 100%. The SALs-depth had the highest detectability influence on cancellous bone lesions and CBCT SALs detectability was 84.9% higher than with DIR images. The CBCT diagnose reproducibility was higher than the one of DIR (Kappa CBCT 75.7-81.4%; DIR 53.4-57.1%). Our results showed that CBCT has a higher SALs IAM diagnosing accuracy and that SALs detection accuracy incremented as the SALs-size increased

Benthic suspension feeders, key players in Antartic marine ecosystems?

Ja fa un cert temps que hom accepta, de manera general i a partir d'estudis de la columna d'aigua en mar obert, que en les comunitats marines de l'oceà Antàrtic hi ha un període prolongat d'activitat hivernal mínima que s'estén al llarg de sis mesos com a mínim, que és el temps que dura l'hivern austral. Tanmateix, investigacions recents en algunes espècies d'invertebrats suspensívors (filtradors) bentònics litorals han suggerit que el període d'inactivitat potser dura només unes poques setmanes. Això planteja una interessant qüestió: què és el que permet que aquests organismes antàrtics mengin, i per tant romanguin actius, durant períodes molt més llargs del que fins ara s'havia cregut? Hom ha suggerit adaptacions especials a menjar en concentracions molt baixes d'aliment, o bé a usar eficientment l'abundància ocasional d'aliment enmig de llargs períodes d'escassedat. Molts animals suspensívors podrien usar fonts alternatives al seu aliment usual, el fito- i el zooplàncton; per exemple, la ?fracció fina' de matèria orgànica, o microplàncton (bacteris, ciliats i flagel·lats, junt amb carboni inorgànic particulat d'orígens diversos), que hom ha demostrat recentment que té un paper molt més significatiu del que hom creia a l'hora de complementar la dieta i de subvenir a les demandes energètiques de moltes espècies de suspensívors. També s'ha esmentat el possible paper de la resuspensió de sediments i, atès l'elevat valor alimentari del component orgànic dels sediments antàrtics, àdhuc de fons pregons, serà interessant investigar més en aquesta línia. Observacions recents relacionades amb la dieta natural (captura de preses) d'algunes espècies d'aigües somes porten a suposar que alguns suspensívors antàrtics, si més no, tenen taxes de creixement i reproducció que són similars a les assenyalades per a espècies d'aigües temperades.For quite some time it was generally accepted, from water column and open sea studies, that in Antarctic marine communities there is a prolonged period of minimal winter activity which lasts for at least six months during the Southern winter. However, recent studies on certain littoral benthic suspension feeders have suggested that the period of inactivity may last only a few weeks. This raises the question of what allows these organisms to feed, and hence remain active, for considerably longer periods than previously thought. Special adaptations to feeding at low levels of food concentration, or to using occasional food abundance followed by long periods of starvation have been suggested. Many suspension feeders might use alternative food sources to phytoand zooplankton, e.g., the «fine fraction» of organic matter, or microplankton (bacteria, ciliates, and flagellates including POC of several origins), which has recently been shown to play a much more significant role than expected in complementing the diet and meeting energy demands in many species of suspension feeders. The possible role of sediment resuspension has also been reported, and given the high food value of the organic component of sediments even on deep bottoms further research would be of interest. Recent observations related to the natural diet (prey capture) of several shallow species lead to the assumption that part of Antarctic suspension feeders have similar growth and reproduction rates to those reported for temperate waters. Efficient food assimilation may contribute to our understanding of the continuous reproduction state observed in octocorals and, also, of the development of tridimensionally structured communities which are suspension-feeder dominated, highly diversified, and have a high biomass

Scaling of local interface width of statistical growth models

We discuss the methods to calculate the roughness exponent alpha and the dynamic exponent z from the scaling properties of the local roughness, which is frequently used in the analysis of experimental data. Through numerical simulations, we studied the Family, the restricted solid-on-solid (RSOS), the Das Sarma-Tamborenea (DT) and the Wolf-Villain (WV) models in one- and two dimensional substrates, in order to compare different methods to obtain those exponents. The scaling at small length scales do not give reliable estimates of alpha, suggesting that the usual methods to estimate that exponent from experimental data may provide misleading conclusions concerning the universality classes of the growth processes. On the other hand, we propose a more efficient method to calculate the dynamic exponent z, based on the scaling of characteristic correlation lengths, which gives estimates in good agreement with the expected universality classes and indicates expected crossover behavior. Our results also provide evidence of Edwards-Wilkinson asymptotic behavior for the DT and the WV models in two-dimensional substrates.Comment: To appear in Surface Scienc

Interfaces with a single growth inhomogeneity and anchored boundaries

The dynamics of a one dimensional growth model involving attachment and detachment of particles is studied in the presence of a localized growth inhomogeneity along with anchored boundary conditions. At large times, the latter enforce an equilibrium stationary regime which allows for an exact calculation of roughening exponents. The stochastic evolution is related to a spin Hamiltonian whose spectrum gap embodies the dynamic scaling exponent of late stages. For vanishing gaps the interface can exhibit a slow morphological transition followed by a change of scaling regimes which are studied numerically. Instead, a faceting dynamics arises for gapful situations.Comment: REVTeX, 11 pages, 9 Postscript figure

Absolute properties of the low-mass eclipsing binary CM Draconis

Spectroscopic and eclipsing binary systems offer the best means for determining accurate physical properties of stars, including their masses and radii. The data available for low-mass stars have yielded firm evidence that stellar structure models predict smaller radii and higher effective temperatures than observed, but the number of systems with detailed analyses is still small. In this paper we present a complete reanalysis of one of such eclipsing systems, CM Dra, composed of two dM4.5 stars. New and existing light curves as well as a radial velocity curve are modeled to measure the physical properties of both components. The masses and radii determined for the components of CM Dra are M1=0.2310+/-0.0009 Msun, M2=0.2141+/-0.0010 Msun, R1=0.2534+/-0.0019 Rsun, and R2=0.2396+/-0.0015 Rsun. With relative uncertainties well below the 1% level, these values constitute the most accurate properties to date for fully convective stars. This makes CM Dra a valuable benchmark for testing theoretical models. In comparing our measurements with theory, we confirm the discrepancies reported previously for other low-mass eclipsing binaries. These discrepancies seem likely to be due to the effects of magnetic activity. We find that the orbit of this system is slightly eccentric, and we have made use of eclipse timings spanning three decades to infer the apsidal motion and other related properties.Comment: 19 pages, 9 figures. Accepted for publication in Ap