Raman excitation spectroscopy of carbon nanotubes: effects of pressure medium and pressure

Raman excitation and emission spectra for the radial breathing mode (RBM) are reported, together with a preliminary analysis. From the position of the peaks on the two-dimensional plot of excitation resonance energy against Raman shift, the chiral indices (m, n) for each peak are identified. Peaks shift from their positions in air when different pressure media are added - water, hexane, sulphuric acid - and when the nanotubes are unbundled in water with surfactant and sonication. The shift is about 2 - 3 cm-1 in RBM frequency, but unexpectedly large in resonance energy, being spread over up to 100meV for a given peak. This contrasts with the effect of pressure. The shift of the peaks of semiconducting nanotubes in water under pressure is orthogonal to the shift from air to water. This permits the separation of the effects of the pressure medium and the pressure, and will enable the true pressure coefficients of the RBM and the other Raman peaks for each (m, n) to be established unambiguously.Comment: 6 pages, 3 Figures, Proceedings of EHPRG 2011 (Paris

Pressure coefficients of Raman modes of carbon nanotubes resolved by chirality: Environmental effect on graphene sheet

Studies of the mechanical properties of single-walled carbon nanotubes are hindered by the availability only of ensembles of tubes with a range of diameters. Tunable Raman excitation spectroscopy picks out identifiable tubes. Under high pressure, the radial breathing mode shows a strong environmental effect shown here to be largely independent of the nature of the environment . For the G-mode, the pressure coefficient varies with diameter consistent with the thick-wall tube model. However, results show an unexpectedly strong environmental effect on the pressure coefficients. Reappraisal of data for graphene and graphite gives the G-mode Grueuneisen parameter gamma = 1.34 and the shear deformation parameter beta = 1.34.Comment: Submitted to Physical Review

Recognizing and managing a malignant hyperthermia crisis: guidelines from the European Malignant Hyperthermia Group

Survival from a malignant hyperthermia (MH) crisis is highly dependent on early recognition and prompt action. MH crises are very rare and an increasing use of total i.v. anaesthesia is likely to make it even rarer, leading to the potential risk of reduced awareness of MH. In addition, dantrolene, the cornerstone of successful MH treatment, is unavailable in large areas around the world thereby increasing the risk of MH fatalities in these areas. The European Malignant Hyperthermia Group collected and reviewed all guidelines available from the various MH centres in order to provide a consensus document. The guidelines consist of two textboxes: Box 1 on recognizing MH and Box 2 on the treatment of an MH crisi

Graphene under hydrostatic pressure

In-situ high pressure Raman spectroscopy is used to study monolayer, bilayer and few-layer graphene samples supported on silicon in a diamond anvil cell to 3.5 GPa. The results show that monolayer graphene adheres to the silicon substrate under compressive stress. A clear trend in this behaviour as a function of graphene sample thickness is observed. We also study unsupported graphene samples in a diamond anvil cell to 8 GPa, and show that the properties of graphene under compression are intrinsically similar to graphite. Our results demonstrate the differing effects of uniaxial and biaxial strain on the electronic bandstructure.Comment: Accepted in Physical Review B with minor change

Energy levels in polarization superlattices: a comparison of continuum strain models

A theoretical model for the energy levels in polarization superlattices is presented. The model includes the effect of strain on the local polarization-induced electric fields and the subsequent effect on the energy levels. Two continuum strain models are contrasted. One is the standard strain model derived from Hooke's law that is typically used to calculate energy levels in polarization superlattices and quantum wells. The other is a fully-coupled strain model derived from the thermodynamic equation of state for piezoelectric materials. The latter is more complete and applicable to strongly piezoelectric materials where corrections to the standard model are significant. The underlying theory has been applied to AlGaN/GaN superlattices and quantum wells. It is found that the fully-coupled strain model yields very different electric fields from the standard model. The calculated intersubband transition energies are shifted by approximately 5 -- 19 meV, depending on the structure. Thus from a device standpoint, the effect of applying the fully-coupled model produces a very measurable shift in the peak wavelength. This result has implications for the design of AlGaN/GaN optical switches.Comment: Revtex

The CMS Tracker Readout Front End Driver

The Front End Driver, FED, is a 9U 400mm VME64x card designed for reading out the Compact Muon Solenoid, CMS, silicon tracker signals transmitted by the APV25 analogue pipeline Application Specific Integrated Circuits. The FED receives the signals via 96 optical fibers at a total input rate of 3.4 GB/sec. The signals are digitized and processed by applying algorithms for pedestal and common mode noise subtraction. Algorithms that search for clusters of hits are used to further reduce the input rate. Only the cluster data along with trigger information of the event are transmitted to the CMS data acquisition system using the S-LINK64 protocol at a maximum rate of 400 MB/sec. All data processing algorithms on the FED are executed in large on-board Field Programmable Gate Arrays. Results on the design, performance, testing and quality control of the FED are presented and discussed

The role of the global cryosphere in the fate of organic contaminants

The cryosphere is an important component of global organic contaminant cycles. Snow is an efficient scavenger of atmospheric organic pollutants while a seasonal snowpack, sea ice, glaciers and ice caps are contaminant reservoirs on time scales ranging from days to millennia. Important physical and chemical processes occurring in the various cryospheric compartments impact contaminant cycling and fate. A variety of interactions and feedbacks also occur within the cryospheric system, most of which are susceptible to perturbations due to climate change. In this article, we review the current state of knowledge regarding the transport and processing of organic contaminants in the global cryosphere with an emphasis on the role of a changing climate. Given the complexity of contaminant interactions with the cryosphere and limitations on resources and research capacity, interdisciplinary research and extended collaborations are essential to close identified knowledge gaps and to improve our understanding of contaminant fate under a changing climate

Host-plant acceptance on mineral soil and humus by the pine weevil Hylobius abietis (L.)

1 The pine weevil Hylobius abietis (L.) (Coleoptera, Curculionidae) is an economically important pest of conifer forest regeneration in Europe and Asia. 2 Soil scarification, which usually exposes mineral soil, is widely used to protect seedlings from weevil attack. However, the mechanism behind this protective effect is not yet fully understood. 3 Field experiments were conducted to determine the pine weevil's responses to visual and odour stimuli from seedlings when moving on mineral soil and on undisturbed humus surface. 4 One experiment measured the number of pine weevils approaching seedlings, with and without added host odour, on mineral soil and undisturbed humus. Seedlings with added host odour attracted more weevils on both soil types. Unexpectedly, somewhat more weevils approached seedlings surrounded by mineral soil. 5 In a similar experiment, feeding attacks on seedlings planted directly in the soil were recorded. Only half as many seedlings were attacked on mineral soil as on undisturbed humus. 6 In the first experiment, the weevils were trapped 2.5 cm from the bases of the seedlings' stems, whereas they could reach the seedlings in the experiment where seedlings were planted directly in the soil. We conclude that the pine weevils' decision on whether or not to feed on a seedling is strongly influenced by the surrounding soil type and that this decision is taken in the close vicinity of the seedling. The presence of pure mineral soil around the seedling strongly reduces the likelihood that an approaching pine weevil will feed on it

A novel albumin gene mutation (R222I) in familial dysalbuminemic hyperthyroxinemia

Context: Familial dysalbuminemic hyperthyroxinemia, characterized by abnormal circulating albuminwith increased T4 affinity, causes artefactual elevation of free T4 concentrations in euthyroid individuals. Objective: Four unrelated index cases with discordant thyroid function tests in different assay platforms were investigated. Design and Results: Laboratory biochemical assessment, radiolabeled T4 binding studies, and ALB sequencing were undertaken. 125I-T4 binding to both serum and albumin in affected individuals was markedly increased, comparable with known familial dysalbuminemic hyperthyroxinemia cases. Sequencing showed heterozygosity for a novel ALB mutation (arginine to isoleucine at codon 222, R222I) in all four cases and segregation of the genetic defect with abnormal biochemical phenotype in one family. Molecular modeling indicates that arginine 222 is located within a high-affinity T4 binding site in albumin, with substitution by isoleucine, which has a smaller side chain predicted to reduce steric hindrance, thereby facilitating T 4 and rT3 binding. When tested in current immunoassays, serum free T4 values from R222I heterozygotes were more measurably abnormal in one-step vs two-step assay architectures. Total rT3 measurements were also abnormally elevated. Conclusions: A novel mutation (R222I) in the ALB gene mediates dominantly inherited dysalbuminemic hyperthyroxinemia. Susceptibility of current free T4 immunoassays to interference by this mutant albumin suggests likely future identification of individuals with this variant binding protein

Determined learning approach: Implications of heutagogy society based learning

Recently, within the higher education system in the United Kingdom, there has been close examination of the way institutions teach and assess students. This scrutiny has been intensified by central government with the proposed introduction of the Teaching Excellence Framework (TEF). The anticipated TEF demands that higher education institutions evaluate their teaching and learning practices and think of new ways to develop excellent student experience. Self-determined learning has resurfaced as a popular approach in the higher education sector. At the centre of self-determined learning is the concept of heutagogy. This approach enables the student to apply what they have learned in an education setting and relate it to the workplace. The aim of this paper is to critically explore the theoretical framework behind the self-determined learning approach. The authors of this paper argue that, from a social science perspective, a determined learning approach is in the best place to provide a contemporary, exciting teaching and learning experience in a competitive higher education market