Liquid-induced damping of mechanical feedback effects in single electron tunneling through a suspended carbon nanotube

In single electron tunneling through clean, suspended carbon nanotube devices at low temperature, distinct switching phenomena have regularly been observed. These can be explained via strong interaction of single electron tunneling and vibrational motion of the nanotube. We present measurements on a highly stable nanotube device, subsequently recorded in the vacuum chamber of a dilution refrigerator and immersed in the 3He/4He mixture of a second dilution refrigerator. The switching phenomena are absent when the sample is kept in the viscous liquid, additionally supporting the interpretation of dc-driven vibration. Transport measurements in liquid helium can thus be used for finite bias spectroscopy where otherwise the mechanical effects would dominate the current.Comment: 4 pages, 3 figure

Negative frequency tuning of a carbon nanotube nano-electromechanical resonator

A suspended, doubly clamped single wall carbon nanotube is characterized as driven nano-electromechanical resonator at cryogenic temperatures. Electronically, the carbon nanotube displays small bandgap behaviour with Coulomb blockade oscillations in electron conduction and transparent contacts in hole conduction. We observe the driven mechanical resonance in dc-transport, including multiple higher harmonic responses. The data shows a distinct negative frequency tuning at finite applied gate voltage, enabling us to electrostatically decrease the resonance frequency to 75% of its maximum value. This is consistently explained via electrostatic softening of the mechanical mode.Comment: 4 pages, 4 figures; submitted for the IWEPNM 2013 conference proceeding

Magnetic damping of a carbon nanotube NEMS resonator

A suspended, doubly clamped single wall carbon nanotube is characterized at cryogenic temperatures. We observe specific switching effects in dc-current spectroscopy of the embedded quantum dot. These have been identified previously as nano-electromechanical self-excitation of the system, where positive feedback from single electron tunneling drives mechanical motion. A magnetic field suppresses this effect, by providing an additional damping mechanism. This is modeled by eddy current damping, and confirmed by measuring the resonance quality factor of the rf-driven nano-electromechanical resonator in an increasing magnetic field.Comment: 8 pages, 3 figure

A relação de ajuda ao doente em fim de vida e família: o enfermeiro e o cuidar em fim de vida

Os cuidados ao doente em fim de vida tornam-se difíceis de suportar pelas pessoas envolvidas, pois, para além da sobrecarga física, existe um grande desgaste psicológico e emocional, pelo que se torna importante um acompanhamento e apoio por parte dos profissionais de saúde. A relação de ajuda é um elemento decisivo na atividade dos enfermeiros, desempenhando um papel central na resposta às necessidades concretas do doente em fim de vida e sua família. O objectivo do estudo foi identificar necessidades e dificuldades que os enfermeiros enfrentam no contexto da relação de ajuda ao doente em fim de vida e família. A metodologia utilizada foi a Revisão Sistemática da Literatura sendo aplicada a metodologia PICO. Recorreu-se às bases de dados B-on, LILACS e Scielo, tendo sido reunidos 14 artigos e analisados 7. Os resultados mostraram que muitos enfermeiros sentem dificuldade em comunicar com doentes terminais, apesar de valorizarem as relações interpessoais relacionadas com a comunicação, o conforto, o apoio e acompanhamento e as técnicas de alívio do sofrimento do doente e família, direcionadas para a gestão da dor e sofrimento. A falta de formação em cuidados paliativos é evidente, sendo que o desempenho das competências relacionais de ajuda está correlacionado com a formação que os enfermeiros desenvolvem acerca da relação de ajuda. As principais conclusões a que o estudo chegou foram que apesar da dedicação dos enfermeiros a relação de ajuda ao doente terminal e família nem sempre é conseguida. O desenvolvimento pessoal e profissional, o modo como gerem as dificuldades pessoais e relacionais com o doente e família no contexto de fim de vida, são considerados como os ingredientes major ao nível do cuidar e da relação de ajuda profissional.info:eu-repo/semantics/publishedVersio

Co-sputtered MoRe thin films for carbon nanotube growth-compatible superconducting coplanar resonators

Molybdenum rhenium alloy thin films can exhibit superconductivity up to critical temperatures of $T_c=15\mathrm{K}$. At the same time, the films are highly stable in the high-temperature methane / hydrogen atmosphere typically required to grow single wall carbon nanotubes. We characterize molybdenum rhenium alloy films deposited via simultaneous sputtering from two sources, with respect to their composition as function of sputter parameters and their electronic dc as well as GHz properties at low temperature. Specific emphasis is placed on the effect of the carbon nanotube growth conditions on the film. Superconducting coplanar waveguide resonators are defined lithographically; we demonstrate that the resonators remain functional when undergoing nanotube growth conditions, and characterize their properties as function of temperature. This paves the way for ultra-clean nanotube devices grown in situ onto superconducting coplanar waveguide circuit elements.Comment: 8 pages, 6 figure

Atmospheric Effects of Energetic Particle Precipitation in the Arctic Winter 1978-1979 Revisted

[1] The Limb Infrared Monitor of the Stratosphere (LIMS) measured polar stratospheric enhancements of NO2 mixing ratios due to energetic particle precipitation (EPP) in the Arctic winter of 1978–1979. Recently reprocessed LIMS data are compared to more recent measurements from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) and the Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) to place the LIMS measurements in the context of current observations. The amount of NOx (NO + NO2) entering the stratosphere that has been created by EPP in the mesosphere and lower thermosphere (EPP-NOx) has been quantified for the 1978–1979 and 2002–2003 through 2008–2009 Arctic winters. The NO2 enhancements in the LIMS data are similar to those in MIPAS and ACE-FTS data in the Arctic winters of 2002–2003, 2004–2005, 2006–2007, and 2007–2008. The largest enhancement by far is in 2003–2004 (∼2.2 Gmol at 1500 K), which is attributed to a combination of elevated EPP and unusual dynamics that led to strong descent in the upper stratosphere/lower mesosphere in late winter. The enhancements in 2005–2006 and 2008–2009, during which large stratospheric NOx enhancements were caused by a dynamical situation similar to that in 2003–2004, are larger than in all the other years (except 2003–2004) at 3000 K. However, by 2000 K the enhancements in 2005–2006 (2008–2009) are on the same order of magnitude as (smaller than) all other years. These results highlight the importance of the timing of the descent in determining the potential of EPP-NOx for reaching the middle stratosphere

Circulation anomalies in the Southern Hemisphere and ozone changes

We report results from two pairs of chemistryclimate model simulations using the same climate model but different chemical perturbations. In each pair of experiments an ozone change was triggered by a simple change in the chemistry. One pair of model experiments looked at the impact of polar stratospheric clouds (PSCs) and the other pair at the impact of short-lived halogenated species on composition and circulation. The model response is complex with both positive and negative changes in ozone concentration, depending on location. These changes result from coupling between composition, temperature and circulation. Even though the causes of the modelled ozone changes are different, the high latitude Southern Hemisphere response in the lower stratosphere is similar. In both pairs of experiments the high-latitude circulation changes, as evidenced by N2O differences, are suggesting a slightly longer-lasting/stronger stratospheric descent in runs with higher ozone destruction (a manifestation of a seasonal shift in the circulation). We contrast the idealised model behaviour with interannual variability in ozone and N2O as observed by the MIPAS instrument on ENVISAT, highlighting similarities of the modelled climate equilibrium changes to the year 2006–2007 in observations. We conclude that the climate system can respond quite sensitively in its seasonal evolution to small chemical perturbations, that circulation adjustments seen in the model can occur in reality, and that coupled chemistry-climate models allow a better assessment of future ozone and climate change than recent CMIP-type models with prescribed ozone fields

Broken SU(4) symmetry in a Kondo-correlated carbon nanotube

Understanding the interplay between many-body phenomena and non-equilibrium in systems with entangled spin and orbital degrees of freedom is a central objective in nano-electronics. We demonstrate that the combination of Coulomb interaction, spin-orbit coupling and valley mixing results in a particular selection of the inelastic virtual processes contributing to the Kondo resonance in carbon nanotubes at low temperatures. This effect is dictated by conjugation properties of the underlying carbon nanotube spectrum at zero and finite magnetic field. Our measurements on a clean carbon nanotube are complemented by calculations based on a new approach to the non-equilibrium Kondo problem which well reproduces the rich experimental observations in Kondo transport.Comment: 8 pages, 6 figures; appendix of 14 pages, 7 figure

The strength of the meridional overturning circulation of the stratosphere.

The distribution of gases such as ozone and water vapour in the stratosphere - which affect surface climate - is influenced by the meridional overturning of mass in the stratosphere, the Brewer-Dobson circulation. However, observation-based estimates of its global strength are difficult to obtain. Here we present two calculations of the mean strength of the meridional overturning of the stratosphere. We analyze satellite data that document the global diabatic circulation between 2007- 2011, and compare these to three re-analysis data sets and to simulations with a state-of-the-art chemistry-climate model. Using measurements of sulfur hexafluoride (SF6) and nitrous oxide, we calculate the global mean diabatic overturning mass flux throughout the stratosphere. In the lower stratosphere, these two estimates agree, and at a potential temperature level of 460 K (about 20 km or 60 hPa in tropics), the global circulation strength is 6.3-7.6 × 109 kg/s. Higher in the atmosphere, only the SF6-based estimate is available, and it diverges from the re-analysis data and simulations. Interpretation of the SF6 data-based estimate is limited because of a mesospheric sink of SF6; however, the reanalyses also differ substantially from each other. We conclude that the uncertainty in the mean meridional overturning circulation strength at upper levels of the stratosphere amounts to at least 100 %

Partially and Fully Frustrated Coupled Oscillators With Random Pinning Fields

We have studied two specific models of frustrated and disordered coupled Kuramoto oscillators, all driven with the same natural frequency, in the presence of random external pinning fields. Our models are structurally similar, but differ in their degree of bond frustration and in their finite size ground state properties (one has random ferro- and anti-ferromagnetic interactions; the other has random chiral interactions). We have calculated the equilibrium properties of both models in the thermodynamic limit using the replica method, with emphasis on the role played by symmetries of the pinning field distribution, leading to explicit predictions for observables, transitions, and phase diagrams. For absent pinning fields our two models are found to behave identically, but pinning fields (provided with appropriate statistical properties) break this symmetry. Simulation data lend satisfactory support to our theoretical predictions.Comment: 37 pages, 7 postscript figure