Smaller classes promote equitable student participation in STEM

Under embargo until: 2020-07-24As science, technology, engineering, and mathematics (STEM) classrooms in higher education transition from lecturing to active learning, the frequency of student interactions in class increases. Previous research documents a gender bias in participation, with women participating less than would be expected on the basis of their numeric proportions. In the present study, we asked which attributes of the learning environment contribute to decreased female participation: the abundance of in-class interactions, the diversity of interactions, the proportion of women in class, the instructor's gender, the class size, and whether the course targeted lower division (first and second year) or upper division (third or fourth year) students. We calculated likelihood ratios of female participation from over 5300 student–instructor interactions observed across multiple institutions. We falsified several alternative hypotheses and demonstrate that increasing class size has the largest negative effect. We also found that when the instructors used a diverse range of teaching strategies, the women were more likely to participate after small-group discussions.acceptedVersio

Systèmes inductifs pouvant servir de creuset froid

L'invention concerne un système inductif comprenant un premier enroulement conducteur (12) formant une bobine, et un deuxième enroulement conducteur creux (10) entourant le premier enroulement tout en laissant un espace entre eux, le deuxième enroulement comportant des spires isolées quasi-jointives

X-RAY AND MAGNETIZATION STUDIES OF THE GEOMETRICAL PARAMETERS OF THE GRAINS OF A FERROFLUID

On présente une étude par microscopie électronique, par diffusion centrale des rayons X et par aimantation, de la distribution en taille, de la structure et des corrélations magnétiques entre les grains de colloïdes magnétiques. Pour les colloïdes à base d'eau (Fe3O4 dans l'eau), les grains se comportent comme des sphères dures dispersées dans un fluide porteur. Pour les colloïdes à base de toluène (grains de cobalt) on propose un modèle où le grain est constitué d'un noyau de cobalt pur entouré d'une couche non magnétique. Dans les colloïdes de cobalt, des corrélations ont été observées qui mettent en évidence une périodicité dans la distance entre grains. Une forte anisotropie magnétique est observée pour les deux types de colloïdes.The size distribution, structure and magnetic correlations between the grains of magnetic colloids are studied by electron microscopy, small angle scattering of X-rays and magnetic measurements. For water-base colloids (Fe3O4 in water) the grains behave as hard spheres dispersed in a carrier liquid. For toluene-base colloids (Co grains) a model of a grain constituted by a core of pure cobalt and a non magnetic sheath surrounding it is proposed. In toluene-base colloids, correlations have been observed which reveal a periodicity in the intergrain spacing. Strong magnetic anisotropy is reported for both colloids

Experimental Investigation of the Hydrodynamic Interactions between a Sphere and a Large Spherical Obstacle

The hydrodynamic interactions between a spherical particle embedded in a very viscous fluid and a large close spherical obstacle are investigated experimentally. The displacement of the particle is followed by laser interferometry with a 100 nm resolution. The large obstacle is either convex, plane or concave. The experimental results for the drag coefficient on the particle are compared to the theoretical results written as three terms expansions for small gaps, viz. the result of Cox and Brenner (1967) for a plane obstacle, the result of Jeffrey (1982) and Jeffrey and Onishi (1984) for a convex obstacle and an extension of Cooley and O'Neill (1969) for a concave obstacle. Excellent agreement is found between the experimental and the theoretical results for all cases

Etude de la transition globule-forme étirée des polyamines tertiaires partiellement quaternisées par diffusion centrale des rayons X

Q-P(TDAE) X bifunctional polybases are constituted of a poly[thioether] backbone carrying both pendent tertiary amine groups, and quaternary ammonium groups resulting from partial N-methylation (X %) of some of the tertiary amine groups. These macromolecules are soluble in water whatever the pH, in contrast to the non-methylated precursor. Members of the series with X ≤ 25, have revealed an unusual polyelectrolytic behaviour characterized by very low viscosity for total deprotonation of tertiary amine residues, linear variation of the reduced viscosity as a function of the apparent degree of protonation βa, and the presence of a plateau of pH in potentiometric titration curves (high buffering effect). In order to bear out the mechanism based on a globule-toextended coil cooperative conformational transition of the all-or-none type which has been proposed previously to account for the particular physico-chemical characteristics of Q-P(TDAE) X, SAXS was investigated of Q-P(TDAE) 19 salt-free aqueous solutions at various concentrations and states of protonation for two counter-ions (Cl- and Br-). All the I(s) = f(s) curves show a peak. For low degree of protonation, the peak is narrow and periodic oscillations are observed in the high |s| range. The radius of the scattering particles is evaluated from intrinsic viscosity, from the effective potential model regarding the homogeneous sphere, from the minima position of the SAXS curves and in the other hand by using the Porod's law. The différent values thus obtained are in good agreement (R ≃ 38 A for Br- and R ≃ 36 A for Cl-). For high degrees of protonation, the peak is larger and no oscillation was detected. The variations of the position |sm| of the maximum I(sm) with polymer concentration bears out the présence of an extended coil form (|sm| ∼ Cp-1/2). It is also shown that, in the high buffering zone, the experimental intensity curves for given βa values can be deduced directly from intensity curves corresponding to the extreme conformational forms according to the respective weights of these forms. Data bear out the partition of macromolecules in two populations at equilibrium.Les polybases bifonctionnelles Q-P(TDAE) X, sont constituées d'un squelette poly[thioéther] portant à la fois des groupements latéraux amine tertiaire et des groupements ammonium quaternaire obtenus par N-méthylation d'une partie (X %) des groupes amine tertiaire. Elles sont solubles dans l'eau quel que soit le pH, contrairement à la polyamine tertiaire précurseur. Les membres de la série ayant X ≤ 25, ont révélé un comportement polyélectrolytique inhabituel caractérisé notamment par une très faible viscosité à déprotonation totale des groupes amine tertiaire, une variation linéaire de la viscosité réduite en fonction du degré de protonation apparent βa et la présence d'un plateau de pH dans les courbes de titrage potentiométrique (effet tampon). Afin de confirmer le mécanisme de transition conformationnelle coopérative globule-forme étirée proposé précédemment pour rendre compte de ces caractéristiques particulières, l'intensité des rayons X diffusée aux petits angles a été mesurée dans l'eau en absence de sel pour des solutions de Q-P(TDAE) 19 à diverses concentrations et à divers états de protonation pour deux contre-ions (Cl- et Br-). Les courbes I(s) = f (s) présentent toutes un maximum. A faible protonation, le pic est étroit et des oscillations périodiques sont observées pour les grandes valeurs de |s |. Le rayon des particules diffusantes est évalué à partir de la viscosité intrinsèque, à partir d'un modèle de potentiel effectif pour des particules homogènes et à partir de la position des minima d'oscillations des courbes de diffusion et de la loi de Porod dans l'hypothèse d'un modèle de sphères dures. Les différentes valeurs obtenues sont en bon accord (R ≃ 38 A pour Br- et R ≃ 36 A pour Cl-). A forte protonation, le pic est plus large et aucune oscillation n'est détectée. Les déplacements de la position |Sm | du maximum I(Sm) en fonction de la concentration en polymère confirment la présence d'une forme étirée (| Sm|∼C-1/2). Il est également montré que, dans la zone du palier de pH, les courbes d'intensité diffusée à un degré de protonation apparent βa donné se déduisent directement des courbes d'intensité diffusée des formes extrêmes selon les poids relatifs de ces dernières. Ces résultats confirment l'existence d'un partage des macromolécules en deux populations en équilibre

Precise measurement of particle-wall hydrodynamic interactions at low Reynolds number using laser interferometry

International audienceThe motion of a spherical particle (with radius 1 to 6 mm) in a viscous fluid is measured using laser interferometry. The typical sensitivity on the measured displacement of the sphere is of the order of 50 nm. The particle is moving on the axis of a closed cylinder. The hydrodynamic interactions between the particle and the walls of the cylinder are compared with the theoretical result of Sano [J. Phys. Soc. Jpn. 56, 2713 (1987)] valid for a very small sphere. The agreement is excellent for the smallest sphere used in the experiment. The experiment also agrees with the result from the theory of lubrication when the sphere is close to a plane end wall. The effect of the particle roughness appears at small distances. Laser interferometry appears as a useful tool to study particle–wall hydrodynamic interactions when the geometry is cumbersome

Before remodel-04

Main floor and second floor before the remodel.https://scholar.csl.edu/libraryreno/1033/thumbnail.jp

ETUDE DES CORRELATIONS DANS LES FERROFLUIDES PAR DIFFUSION CENTRALE ALTERNEE DES RAYONS X SUR LE FAISCEAU SYNCHROTRON

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Small-angle X-ray diffraction study of the thermotropic and lyotropic phases of five alkyl cyclic and acyclic disaccharides: Influence of the linkage between the hydrophilic and hydrophobic moieties

We present a comparative study of the thermotropic and lyotropic phases of 5 surfactants with an aliphatic chain of 12 carbon atoms and a cyclic or acyclic sugar head with different linkages between the two moieties. These linkages can concern different chemical groups or different orientations between the head and the chain. The compounds included the $\alpha$- and $\beta$-N dodecyl-D-maltosides, N-dodecylamino-1-deoxylactitol, N-dodecyl lactobionamide and N-acetyl N-dodecyl lactosylamine. The influence of the polar head (with closed- and opened-type sugars) and the linkage with the hydrocarbon chain on the phases obtained by the heating of the anhydrous compounds and after addition of water was studied by X-ray diffraction and optical microscopy. In the anhydrous state, the surfactants were either crystalline or amorphous. On heating, they went through a liquid crystal smectic phase which, in some cases, was preceded by solid-to-solid transitions. On addition of water, the sequence of phases from the micellar phase to the lamellar phase was accounted for in terms of the geometric model of Sadoc and Charvolin. However, with certain surfactants this sequence was not complete, and the domains of existence of phases were altered

Small angle neutron and X-ray scattering study of the formation and structure of micelles of CTAB in formamide

Small angle neutron and X-ray scattering was used to study micellization of cetyltrimethylammonium bromide (CTAB) in partially deuterated or hydrogenated formamide from the absolute values of scattered intensities,). Highly charged aggregates of around 6 monomers were observed at CTAB concentrations above the cmc (2.8 % wt at 60 $^{\circ}$C). These aggregates along with spherical particles (2 nm radius) containing 29 monomers were consistently observed at concentrations above 8 %. These particles were considered to be micelles as they had similar structure, albeit of smaller size to those observed in water (2.7 nm, aggregation number 90). They also had a higher charge in formamide than in water (degree of ionization 0.55 in formamide and 0.14 in water). With increase in surfactant concentration, the micelles elongated, although the radius of the cylinders in the two dimensional hexagonal phase remained close to 2 nm. The importance of interactions of polar head with solvent molecules of high dipole moment and dielectric constant is discussed. The less spontaneous self-association of surfactant molecules in formamide than in water poses the problem of the cmc