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 podrían 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 políticas 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 políticas 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 Nd$_{0.5}$Sr$_{0.5}$MnO3 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

Experimental Sonic Boom Measurements on a Mach 1.6 Cruise Low-Boom Configuration

A wind tunnel test has been conducted by Gulfstream Aerospace Corporation (GAC) to measure the sonic boom pressure signature of a low boom Mach 1.6 cruise business jet in the Langley Unitary Plan Wind Tunnel at Mach numbers 1.60 and 1.80. Through a cooperative agreement between GAC and the National Aeronautics and Space Administration (NASA), GAC provided NASA access to some of the experimental data and NASA is publishing these data for the sonic boom research community. On-track and off-track near field sonic boom pressure signatures were acquired at three separation distances (0.5, 1.2, and 1.7 reference body lengths) and three angles of attack (-0.26deg, 0.26deg, and 0.68deg). The model was blade mounted to minimize the sting effects on the sonic boom signatures. Although no extensive data analysis is provided, selected data are plotted to illustrate salient features of the data. All of the experimental sonic boom pressure data are tabulated. Schlieren images of the configuration are also included