Item-writing Rules: Collective Wisdom

In student assessment, teachers place the greatest weight on tests they have constructed themselves and have an equally great interest in the quality of those tests. To increase the validity of teacher-made tests, many item-writing rules-of-thumb are available in the literature, but few rules have been tested experimentally. In light of the paucity of empirical studies, the validity of any given guideline might best be established by relying on experts. This study analyzed twenty classroom assessment textbooks to identify a consensus list of item-writing rules. Forty rules for which there was agreement among textbook authors are presented. The rules address four different validity concerns-potentially confusing wording or ambiguous requirements, the problem of guessing, test-taking efficiency, and controlling for testwiseness

Conteúdo fenólico in vitro em açucena durante a organogênese.

Apesar de a produção de compostos fenólicos in vitro ser associada à inibição da morfogênese, em estudos preliminares foi observado que a formação destes compostos em explantes de segmentos de bulbos de Hippeastrum aulicum antecedeu o processo organogênico. Neste sentido, o objetivo deste trabalho foi identificar a composição de ácidos fenólicos presentes nos explantes de segmentos de bulbos de H. aulicum para verificar a relação destes compostos com as respostas observadas in vitro. Foram analisados qualitativamente e quantitativamente a composição de ácidos fenólicos em tecidos de explantes com sintomas visuais de oxidação e em amostras de tecidos de bulbo intacto, por meio de cromatografia líquida de alta eficiência. Foram identificados os ácidos gálico, cinâmico e trans-cinâmico nos explantes de segmentos de bulbos e nos tecidos do bulbo com coloração natural, sendo observadas diferenças na concentração destes compostos entre as duas amostras. A presença de ácido cafeico apenas na amostra de tecidos do bulbo com coloração natural. De acordo com a literatura, estes compostos estão relacionados com o metabolismo da auxina. Assim, acredita-se que os mesmos podem ter influenciado a morfogênese em explantes de H. aulcum

Aspectos da morfogênese in vitro de açucena.

O entendimento dos aspectos relacionados a diferenciação in vitro de brotações é importante, pois auxilia na otimização do desenvolvimento de protocolos de micropropagação. Neste trabalho foi estudado o início do processo morfogênico em explantes de camadas de bulbo de H. aulicum através de observações de cortes histológicos realizadas aos 10, 15, 60, 90 dias da inoculação em meio de cultura MS suplementado com 0,1 uM de ácido naftalenoacético e 4,0 uM de benzilaminopurina. Foi verificado que o início do processo morfogênico nos explantes de segmentos de bulbo de H. aulicum, ocorreu nas células epidérmicas e subepidérmicas da região abaxial das camadas, sendo que a provável função da porção do caule na qual elas estão inseridas seja o fornecimento de fitorreguladores

Efeito de ANA e BAP na propagação in vitro de açucena.

As açucenas ou Hippeastrum produzem poucos propágulos vegetativos durante o crescimento, sendo a micropropagação uma alternativa para produção de mudas uma vez que através da técnica é possível a obtenção de plantas em larga escala em curto espaço de tempo, a partir de um mínimo de material vegetal. Assim, o objetivo deste trabalho foi avaliar o efeito de ANA e de BAP na propagação in vitro de H. aulicum. Explantes de segmentos de bulbo foram inoculados em meio de cultura MS suplementado com 0,00; 0,20; ou 1,00 uM de ANA, combinados com 0,20; 1,00 ou 4,00 uM de BAP. Após 60 dias, as brotações formadas foram transferidas para MS suplementado com 1,00 uM ANA e 10,00; 15,00 ou 30,00 uM de BAP. O meio com 1,00 uM de ANA e 4,00 uM de BAP foi o mais adequado para indução de brotações foliares e de bulbos por explante, em termos de número e vigor das mudas produzidas. Na fase de multiplicação, não foram observadas diferenças nas respostas com as doses de BAP testadas

Octupole coil configuration for the Tandem Mirror Experiment Upgrade (TMX-U)

The octupole plug concept offers the attractive possibility of reducing the length of the plug and transition sections in tandem mirror reactors. In the Tandem Mirror Experiment Upgrade (TMX-U), we are designing an octupole plug-transition that will replace our current quadrupole plug-transition. The reduction in length is made possible by the more nearly circular plasma cross section throughout the plug and transition sections. The principal physics of the design is the magnetohydrodynamic (MHD) stabilization of the core plasma in the plug by a hot electron ring in the mantle region surrounding the core. This hot electron mantle is MHD stable because of the good curvature field lines provided by the octupole. The positive radial pressure gradient in the hot electron mantle in turn stabilizes the core's plasma. Each octupole set consists of six coils replacing the transition and plug sets in the existing TMX-U experiment. The central cell coils will remain unchanged. Five of the coils for each of the new sets will be fabricated, while one, the 6-T mirror coil, will be reused from TMX-U. This paper will elaborate on the design configuration of the magnets. In particular, the configuration provides for adequate neutral beam lines-of-sight, and access for 0.615 MW of electron-cyclotron resonant heating (ECRH) on each end

Transversality of Electromagnetic Waves in the Calculus-Based Introductory Physics Course

Introductory calculus-based physics textbooks state that electromagnetic waves are transverse and list many of their properties, but most such textbooks do not bring forth arguments why this is so. Both physical and theoretical arguments are at a level appropriate for students of courses based on such books, and could be readily used by instructors of such courses. Here, we discuss two physical arguments (based on polarization experiments and on lack of monopole electromagnetic radiation), and the full argument for the transversality of (plane) electromagnetic waves based on the integral Maxwell equations. We also show, at a level appropriate for the introductory course, why the electric and magnetic fields in a wave are in phase and the relation of their magnitudes.Comment: 10 pages, 6 figure

Constructing Fresnel reflection coefficients by ruler and compass

A simple and intuitive geometical method to analyze Fresnel formulas is presented. It applies to transparent media and is valid for perpendicular and parallel polarizations. The approach gives a graphical characterization particularly simple of the critical and Brewster angles. It also provides an interpretation of the relation between the reflection coefficients for both basic polarizations as a symmetry in the plane

Fresnel coefficients as hyperbolic rotations

We describe the action of a plane interface between two semi-infinite media in terms of a transfer matrix. We find a remarkably simple factorization of this matrix, which enables us to express the Fresnel coefficients as a hyperbolic rotation.Comment: 6 pages, 3 figure

Characterization of porous low-k films using variable angle spectroscopic ellipsometry

doi:10.1063/1.2189018Variable angle spectroscopic ellipsometry (VASE™) is used as a tool to characterize properties such as optical constant, thickness, refractive index depth profile, and pore volume fraction of single and bilayer porous low-k films. The porous films were prepared using sacrificial pore generator (porogen) approach. Two sets of porous films with open- and closed-pore geometries were measured. Three models were used for data analysis: Cauchy, Bruggeman effective medium approximation (BEMA), and graded layer. Cauchy, a well-known model for transparent films, was used to obtain thickness and optical constant, whereas BEMA was utilized to calculate the pore volume fraction from the ellipsometric data. The Cauchy or BEMA models were then modified as graded layers, resulting in a better fit and a better understanding of the porous film. The depth profile of the porous film implied a more porous layer at the substrate-film interface. We found 3%-4% more porosity at the interface compared with the bulk for both films. This work shows that VASE™, a nondestructive measurement tool, can be used to characterize single- and multigraded layer porous films quickly and effectively.The authors would like to acknowledge the financial support of Semiconductor Research Corporation (SRC)