Shear band formation in granular media as a variational problem

Strain in sheared dense granular material is often localized in a narrow region called shear band. Recent experiments in a modified Couette cell provided localized shear flow in the bulk away from the confining walls. The non-trivial shape of the shear band was measured as the function of the cell geometry. First we present a geometric argument for narrow shear bands which connects the function of their surface position with the shape in the bulk. Assuming a simple dissipation mechanism we show that the principle of minimum dissipation of energy provides a good description of the shape function. Furthermore, we discuss the possibility and behavior of shear bands which are detached from the free surface and are entirely covered in the bulk.Comment: 4 pages, 5 figures; minor changes, typos and journal-ref adde

Capillary Electrochromatography – Challenges and Opportunities for Coupling with Mass Spectrometry

Capillary electrochromatography (CEC) has attracted considerable interest within recent years because of its potential to generate very high efficiencies within relatively short analysis time. Since CEC combines the attributes of both capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC), neutral as well as charged analytes can be separated. Usually, CEC is performed with UV detection, but mass spectrometry (MS) is becoming a more common detection method because additional information about the molecular weight and the structure of an analyte can be obtained. Due to the low flow rates in the packed capillary and the small sample amounts that are required, CEC is ideally suited for the implementation into miniaturized systems and for coupling with MS. While numerous advantages have been made in CEC/MS, the coupling technique is still in a development and growth stage. So far, the development of the technique seems to be limited by the lack of robust and automated specially designed CEC instruments and CEC interfaces. As soon as these practical constraints have been solved, CEC/MS will be a powerful separation/detection technique with unrivaled sensitivity and specifity. This article aims at highlighting the potential of CEC as coupling technique with mass spectrometry

Strategies for Overcoming Common Obstacles in the Online Environment: Issues in Virtual School Teaching

K-12 online learning or virtual schooling has seen substantial growth in the United States over the past two decades. While the practice of virtual schooling has exploded, the availability of research-based best practices to guide teachers working in these environments is lacking. This chapter presents four cases from Michigan Virtual School (MVS) teachers that examine a variety of issues that virtual school teachers face when facilitating K-12 student learning in the online environment, including strategies to provide substantive feedback in English Language Arts, methods for addressing the demonstration of mathematical computations, using Web 2.0 tools to increase interaction in an online environment, and a five-step process for incorporating reading and writing to increase science literacy. Each case follows a similar format, outlining why the problem exists in the virtual school environment, followed by what strategies each MVS teacher uses, and how that strategy is implemented in virtual schooling

Liver carcinogenesis in a non-migratory fish: The association with polycyclic aromatic hydrocarbon exposure

Field and laboratory studies indicate a strong positive association between exposure to chemical pollutants in aquatic environments and development of neoplasia in fishes. This brief communication reviews some of the more important North American and European studies that have been conducted on this relationship. We then review work conducted on a small nonmigratory estuarine cyprinodontid teleost fish, the mummichog (Fundulus heteroclitus) in the industrialized Elizabeth River, Virginia USA. Histopathological surveys of mummichogs from variously degraded habitats indicate an association between PAH exposure and development of neoplasia. We have observed non-neoplastic lesions, preneoplasms and hepatic, biliary, exocrine pancreatic and vascular neoplasms in mummichogs inhabiting Virginia and Maryland estuaries. These lesions track a sediment PAH gradient with highest prevalence occurring in fish from PAI-I-contaminated sites in the industrialized portions of the Elizabeth River, Virginia. Liver metabolizing enzyme profiles typical of those observed in carcinogen-challenged laboratory rodents (e.g., depressed phase I enzymes, elevated phase II enzymes, elevated p-glycoprotein) provided additional support of a chemical etiology for the neoplasms occurring in these fish. Long-term laboratory exposure of mummichogs to creosote-contaminated sediments resulted in development of altered hepatocellular foci and hepatic neoplasms. Biomarkers of fish exposure and effects (e.g., CYPlA induction, bile FA C\u27s, DNA adducts, liver histopathology) are presently used in the Puget Sound, Washington USA and Elizabeth River, Virginia USA to track long-term environmental recovery following habitat remediation

Teachers\u27 Perceptions of K-12 Online: Impacting the Design of a Graduate Course Curriculum

While K-12 online learning in the United States has increased exponentially, the ability of teacher education programs to adequately prepare teachers to design, deliver, and support has been deficient. A small number of universities have begun to address this deficit through the introduction of graduate certificates in online teaching. This article examines curricular changes focused on introducing in-service teachers to K-12 online learning. This design-based research study examined changes in teacher perceptions after having completed a systematic curriculum focused on K-12 online learning, as well as track revisions to that curriculum based on the data collected. The results indicate that even in a jurisdiction where online learning has become a graduation requirement, teachers often have many misconceptions about K-12 online learning. Further, planned exposure to K-12 online learning content can have significant impact on student understanding of and interest in the design, delivery, and support of K-12 online learning

Single-frame Regularization for Temporally Stable CNNs

Convolutional neural networks (CNNs) can model complicated non-linear relations between images. However, they are notoriously sensitive to small changes in the input. Most CNNs trained to describe image-to-image mappings generate temporally unstable results when applied to video sequences, leading to flickering artifacts and other inconsistencies over time. In order to use CNNs for video material, previous methods have relied on estimating dense frame-to-frame motion information (optical flow) in the training and/or the inference phase, or by exploring recurrent learning structures. We take a different approach to the problem, posing temporal stability as a regularization of the cost function. The regularization is formulated to account for different types of motion that can occur between frames, so that temporally stable CNNs can be trained without the need for video material or expensive motion estimation. The training can be performed as a fine-tuning operation, without architectural modifications of the CNN. Our evaluation shows that the training strategy leads to large improvements in temporal smoothness. Moreover, for small datasets the regularization can help in boosting the generalization performance to a much larger extent than what is possible with na\"ive augmentation strategies

In vivo measurement of afferent activity with axon-specific calcium imaging.

In vivo calcium imaging from axons provides direct interrogation of afferent neural activity, informing the neural representations that a local circuit receives. Unlike in somata and dendrites, axonal recording of neural activity-both electrically and optically-has been difficult to achieve, thus preventing comprehensive understanding of neuronal circuit function. Here we developed an active transportation strategy to enrich GCaMP6, a genetically encoded calcium indicator, uniformly in axons with sufficient brightness, signal-to-noise ratio, and photostability to allow robust, structure-specific imaging of presynaptic activity in awake mice. Axon-targeted GCaMP6 enables frame-to-frame correlation for motion correction in axons and permits subcellular-resolution recording of axonal activity in previously inaccessible deep-brain areas. We used axon-targeted GCaMP6 to record layer-specific local afferents without contamination from somata or from intermingled dendrites in the cortex. We expect that axon-targeted GCaMP6 will facilitate new applications in investigating afferent signals relayed by genetically defined neuronal populations within and across specific brain regions