914 research outputs found
Phase transitions of nematic rubbers
Single crystal nematic elastomers undergo a transition from a strongly
ordered phase N to an "isotropic" phase I. We show that: (a) samples produced
under tension by the Finkelmann procedure are intrinsically anisotropic and
should show a small (temperature dependent) birefringence in the high
temperature I phase. (b) for the I->Ntransition via cooling there is a spinodal
limit but for the N->I transition via heating there is no soft mode at the
standard spinodal temperature. (c) the N->I transition is reminiscent of a
martensitic transformation: nucleation of the I phase should occur in the form
of platelets, making a well defined angle with the director.Comment: 7 pages, 3 figures (To appear in Europhys. Lett.
Efeitos gerais nos distritos escolares do uso de dados em sala de aula
In the present study, an examination is conducted in three school districts of how data are used to improve classroom practice. In doing so, we explore the effects that attitudes toward data, principal leadership, and computer data systems have on how data are used to affect classroom practice. Findings indicate that educators are ambivalent about data: they see how data could support classroom practice, but their data use operates in the presence of numerous barriers. Many of these barriers are due to principal leadership and computer data systems; these barriers often have negative effects on attitudes toward data and disrupt the progression from using data to inform classroom practice. It is hypothesized that many of these barriers can be removed through effective district policies to improve structures and supports for using data.En el presente estudio, se examinan como tres distritos escolares usan datos para mejorar la práctica docente. Se exploraron que efectos tienen las actitudes hacia los datos, el liderazgo de los directores/as, y los sistemas de procesamiento de datos para modificar prácticas en el aula. Los resultados indican que los educadores son ambivalentes acerca de los datos: ven cómo los datos podrÃan apoyar prácticas en el aula, pero el uso de datos funciona en presencia de numerosas barreras. Muchas de estas barreras se deben al liderazgo de directores/as y a los sistemas de procesamiento de datos informáticos. Estas barreras suelen tener efectos negativos en las actitudes hacia los datos e interrumpen la incorporación de datos para mejorar prácticas en el aula. Se formula la hipótesis de que muchas de estas barreras pueden ser removidas a través de polÃticas distritales eficaces que mejoren las estructuras y brinden apoyos para el uso de datos.Neste estudo, examinamos como três distritos escolares utilizaram dados para melhorar a prática docente. Foram explorados os efeitos de atitudes em relação aos dados, a liderança dos/as diretores/as, e os sistemas de processamento de dados para alterar as práticas de sala de aula. Os resultados indicam que os educadores são ambivalentes respeito a o uso dos dados: observam como os dados podem apoiar as práticas de sala de aula, mas o uso de dados se faz na presença de muitas barreiras. Muitas dessas barreiras são devidas a liderança dos/as diretores/as e aos sistemas e processamento de dados informáticos. Essas barreiras tendem a ter efeitos negativos nas atitudes com o uso dos dados e interrompem os processos de incorporar dados para melhorar as práticas de sala de aula. Se formula a hipótese de que que muitas dessas barreiras podem ser removidas através de polÃticas distritais eficazes que melhoram as estruturas e fornecendo suporte para o uso de dados
Catastrophic Fermi surface reconstruction in the shape-memory alloy AuZn
AuZn undergoes a shape-memory transition at 67 K. The de Haas van Alphen
effect persists to 100 K enabling the observation of a change in the quantum
oscillation spectrum indicative of a catastrophic Fermi surface reconstruction
at the transition. Coexistence of both Fermi surfaces at low temperatures is
suggestive of an intrinsic phase separation in the bulk of the material. In
addition, a Dingle analysis reveals a sharp change in the scattering mechanism
at a threshold cyclotron radius, which we suggest to be related to the
underlying microstructure that drives the shape-memory effect.Comment: 4 pages, 4 figure
Zebrafish Reproduction: Revisiting In Vitro Fertilization to Increase Sperm Cryopreservation Success
Although conventional cryopreservation is a proven method for long-term, safe storage of genetic material, protocols used by the zebrafish community are not standardized and yield inconsistent results, thereby putting the security of many genotypes in individual laboratories and stock centers at risk. An important challenge for a successful zebrafish sperm cryopreservation program is the large variability in the post-thaw in vitro fertilization success (0 to 80%). But how much of this variability was due to the reproductive traits of the in vitro fertilization process, and not due to the cryopreservation process? These experiments only assessed the in vitro process with fresh sperm, but yielded the basic metrics needed for successful in vitro fertilization using cryopreserved sperm, as well. We analyzed the reproductive traits for zebrafish males with a strict body condition range. It did not correlate with sperm volume, or motility (P>0.05), but it did correlate with sperm concentration. Younger males produced more concentrated sperm (P<0.05). To minimize the wastage of sperm during the in vitro fertilization process, 106 cells/ml was the minimum sperm concentration needed to achieve an in vitro fertilization success of ≥ 70%. During the in vitro process, pooling sperm did not reduce fertilization success (P>0.05), but pooling eggs reduced it by approximately 30 to 50% (P<0.05). This reduction in fertilization success was due not to the pooling of the females' eggs, but to the type of tools used to handle the eggs. Recommendations to enhance the in vitro process for zebrafish include: 1) using males of a body condition closer to 1.5 for maximal sperm concentration; 2) minimizing sperm wastage by using a working sperm concentration of 106 motile cells/ml for in vitro fertilization; and 3) never using metal or sharp-edged tools to handle eggs prior to fertilization
Size of Orbital Ordering Domain Controlled by the Itinerancy of the 3d Electrons in a Manganite Thin Film
An electronic effect on a macroscopic domain structure is found in a strongly
correlated half-doped manganite film NdSrMnO3 grown on a (011)
surface of SrTiO3. The sample has a high-temperature (HT) phase free from
distortion above 180K and two low-temperature (LT) phases with a large
shear-mode strain and a concomitant twin structure. One LT phase has a large
itinerancy (A-type), and the other has a small itinerancy (CE-type), while the
lattice distortions they cause are almost equal. Our x ray diffraction
measurement shows that the domain size of the LT phase made by the HT-CE
transition is much smaller than that by the HT-A transition, indicating that
the difference in domain size is caused by the electronic states of the LT
phases.Comment: 9 pages, 4 figure
Crystallographic structure of ultrathin Fe films on Cu(100)
We report bcc-like crystal structures in 2-4 ML Fe films grown on fcc Cu(100)
using scanning tunneling microscopy. The local bcc structure provides a
straightforward explanation for their frequently reported outstanding magnetic
properties, i.e., ferromagnetic ordering in all layers with a Curie temperature
above 300 K. The non-pseudomorphic structure, which becomes pseudomorphic above
4 ML film thickness is unexpected in terms of conventional rules of thin film
growth and stresses the importance of finite thickness effects in ferromagnetic
ultrathin films.Comment: 4 pages, 3 figures, RevTeX/LaTeX2.0
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