Structures of Fluorinated Graphenes and Their Signatures

Recent synthesis of fluorinated graphene introduced interesting stable derivatives of graphene. In particular, fluorographene (CF), namely fully fluorinated chair conformation, is found to display crucial features, such as high mechanical strength, charged surfaces, local magnetic moments due to vacancy defects and a wide band gap rapidly reducing with uniform strain. These properties, as well as structural parameters and electronic densities of states are found to scale with fluorine coverage. However, most of the experimental data reported to date neither for CF, nor for other CnF structures complies with the results obtained from first-principles calculations. In this study, we attempt to clarify the sources of disagreements.Comment: Phys. Rev. B 83, 115432 (2011

The Numerical Comparison of Flow Patterns and Propulsive Performances for the Hydromedusae Sarsia Tubulosa and Aequorea Victoria

The thrust-generating mechanism of a prolate hydromedusa Sarsia tubulosa and an oblate hydromedusa Aequorea victoria was investigated by solving the incompressible Navier–Stokes equations in the swirl-free cylindrical coordinates. The calculations clearly show the vortex dynamics related to the thrust-generating mechanism, which is very important for understanding the underlying propulsion mechanism. The calculations for the prolate jetting hydromedusa S. tubulosa indicate the formation of a single starting vortex ring for each pulse cycle with a relatively high vortex formation number. However, the calculations for the oblate jet-paddling hydromedusa A. victoria indicate shedding of the opposite-signed vortex rings very close to each other and the formation of large induced velocities along the line of interaction as the vortices move away from the hydromedusa in the wake. In addition to this jet propulsion mechanism, the hydromedusa\u27s bell margin acts like a paddle and the highly flexible bell margin deforms in such a way that the low pressure leeward side of the bell margin has a projected area in the direction of motion. This thrust is particularly important during refilling of the subumbrella cavity where the stopping vortex causes significant pressure drag. The swimming performances based on our numerical simulations, such as swimming velocity, thrust, power requirement and efficiency, were computed and support the idea that jet propulsion is very effective for rapid body movement but is energetically costly and less efficient compared with the jet-paddling propulsion mechanism

A Case of Type I Aortic Dissection; Intravascular Fenestration Prior to Surgical Procedure

Proper clinical and radiological evaluation of aortic dissection, determination of branches being perfused by true or false lumen is necessary in constructing a correct strategy to treat this disorder. Multidisciplinary approach in experienced centers is mandatory to have satisfying results. Percutaneous fenestration of the dissection flap prior to surgery is a simple procedure that improves organ perfusion and creates a more comfortable postoperative period

Synchronous computer-mediated communication between foreign language learners and prospective teachers

Technology has proven itself as a valuable contribution to educational practices when used in a pedagogically sound manner. In this quasi-experimental study using the Interaction Hypothesis as a theoretical framework, 11 intermediate college-level learners of French and Russian and prospective language teachers had six 30-minute synchronous online chat sessions completing communicative tasks. Using a mixed-methods approach, both quantitative and qualitative data were included in the analysis. The study provides evidence for the positive effect of synchronous computer-mediated communication on second language vocabulary acquisition and prospective teachers\u27 professional development, and underlines the importance of scaffolding in online environments. Vocabulary gains of the language learners did not hold up over a two-week period, and there was a weak relationship between uptake outcome and vocabulary acquisition

Electronic and Vibrational Properties of PbI 2 : From Bulk to Monolayer

Using first-principles calculations, we study the dependence of the electronic and vibrational properties of multi-layered PbI 2 crystals on the number of layers and focus on the electronic-band structure and the Raman spectrum. Electronic-band structure calculations reveal that the direct or indirect semiconducting behavior of PbI 2 is strongly influenced by the number of layers. We find that at 3L-thickness there is a direct-to-indirect band gap transition (from bulk-to-monolayer). It is shown that in the Raman spectrum two prominent peaks, A 1g and E g , exhibit phonon hardening with increasing number of layers due to the inter-layer van der Waals interaction. Moreover, the Raman activity of the A 1g mode significantly increases with increasing number of layers due to the enhanced out-of-plane dielectric constant in the few-layer case. We further characterize rigid-layer vibrations of low-frequency inter-layer shear (C) and breathing (LB) modes in few-layer PbI 2 . A reduced mono-atomic (linear) chain model (LCM) provides a fairly accurate picture of the number of layers dependence of the low-frequency modes and it is shown also to be a powerful tool to study the inter-layer coupling strength in layered PbI 2 .Comment: To appear in Phys. Rev.