Dissipation in nanocrystalline-diamond nanomechanical resonators

We have measured the dissipation and frequency of nanocrystalline-diamond nanomechanical resonators with resonant frequencies between 13.7 MHz and 157.3 MHz, over a temperature range of 1.4–274 K. Using both magnetomotive network analysis and a time-domain ring-down technique, we have found the dissipation in this material to have a temperature dependence roughly following T^(0.2), with Q^(–1) ≈ 10^(–4) at low temperatures. The frequency dependence of a large dissipation feature at ~35–55 K is consistent with thermal activation over a 0.02 eV barrier with an attempt frequency of 10 GHz

Sensitive cytokine assay based on optical fiber allowing localized and spatially resolved detection of interleukin-6

We demonstrated a cytokine detection device based on gold nanoparticle modified silica optical fiber for the monitoring of locally variable cytokine interleukin-6 (IL-6) concentrations using a sandwich immunoassay scheme. The fiber is designed to be introduced into an intrathecal catheter with micrometer-sized holes drilled along its length to enable fluid exchange between the outside and inside of the catheter. An exposed optical fiber (diameter 125 μm) modified with a layer of gold nanoparticles was functionalized with the IL-6 capture antibody to form the sensing interface. The immunocapture device was incubated with a cytokine solution to capture the analyte. The device was then exposed to the IL-6 detection antibody which was loaded on the fluorescently labeled magnetic nanoparticles, making it possible to quantify the cytokine concentration based on the intensity of fluorescence. A reliable method for quantifying the fluorescent signal on a 3D structure was developed. This device was applied to the detection of cytokine IL-6 with the low limit of detection of 1 pg mL⁻¹ in a sample volume of 1 μL. The device has the linear detection range of 1–400 pg mL⁻¹ and spatial resolution on the order of 200–450 μm, and it is capable of detecting localized IL-6 secreted by live BV2 cells following their liposaccharide stimulation. This biological detection system is suitable for monitoring multiple health conditions.Guozhen Liu, Kaixin Zhang, Annemarie Nadort, Mark R. Hutchinson, and Ewa M. Goldy

Excitation spectrum in a cylindrical Bose-Einstein gas

Whole excitation spectrum is calculated within the Popov approximation of the Bogoliubov theory for a cylindrical symmetric Bose-Einstein gas trapped radially by a harmonic potential. The full dispersion relation and its temperature dependence of the zero sound mode propagating along the axial direction are evaluated in a self-consistent manner. The sound velocity is shown to depend not only on the peak density, but also on the axial area density. Recent sound velocity experiment on Na atom gas is discussed in light of the present theory.Comment: 4 pages, 5 eps figure

Coping with stressors in late adolescence/young adulthood : a salutogenic perspective

Literature indicates that globally young people are increasingly experiencing life as hopeless and meaningless. It is thus beneficial to investigate factors facilitating well-being in young people, as they are required to cope with multiple stressors whilst simultaneously negotiating the transition from childhood to adulthood. Health practitioners need to establish ways to enhance adequate coping in young people in order to minimise stress and ward off negative consequences such as addiction, depression and other pathologies that compromise health. This study aimed to ascertain whether discovering meaning in life and developing a strong sense of coherence may predict coping with stressors in a group of male and female South Africans in late adolescence/young adulthood (N=258). Three self-report measures were used: the Purpose in Life Questionnaire to measure the extent to which one has found meaning, the Sense of Coherence Scale to assess the extent to which individuals view life as comprehensible, manageable and meaningful, and the Adolescent Coping Scale to determine ability to cope. Logistic regression analysis results indicate that the extent to which one has discovered meaning in life and developed a sense of coherence predict ability to cope in young people. This suggests that intervention strategies that encourage individuals to search for meaning and strengthen sense of coherence may be effective in facilitating coping and may contribute positively to the overall health of young people

Excitations of a Bose-condensed gas in anisotropic traps

We investigate the zero-temperature collective excitations of a Bose-condensed atomic gas in anisotropic parabolic traps. The condensate density is determined by solving the Gross-Pitaevskii (GP) equation using a spherical harmonic expansion. The GP eigenfunctions are then used to solve the Bogoliubov equations to obtain the collective excitation frequencies and mode densities. The frequencies of the various modes, classified by their parity and the axial angular momentum quantum number, m, are mapped out as a function of the axial anisotropy. Specific emphasis is placed upon the evolution of these modes from the modes in the limit of an isotropic trap.Comment: 7 pages Revtex, 9 Postscript figure

Cumulative stress restricts niche filling potential of habitat-forming kelps in a future climate

1. Climate change is driving range contractions and local population extinctions across the globe. When this affects ecosystem engineers the vacant niches left behind are likely to alter the wider ecosystem unless a similar species can fulfil them. 2. Here, we explore the stress physiology of two coexisting kelps undergoing opposing range shifts in the Northeast Atlantic and discuss what differences in stress physiology may mean for future niche filling. 3. We used chlorophyll florescence (Fv/Fm) and differentiation of the heat shock response (HSR) to determine the capacity of the expanding kelp, Laminaria ochroleuca, to move into the higher shore position of the retreating kelp, Laminaria digitata. We applied both single and consecutive exposures to immersed and emersed high and low temperature treatments, replicating low tide exposures experienced in summer and winter. 4. No interspecific differences in HSR were observed which was surprising given the species? different biogeographic distributions. However, chlorophyll florescence revealed clear differences between species with L. ochroleuca better equipped to tolerate high immersed temperatures but showed little capacity to tolerate frosts or high emersion temperatures. 5. Many patterns observed were only apparent after consecutive exposures. Such cumulative effects have largely been overlooked in tolerance experiments on intertidal organisms despite being more representative of the stress experienced in natural habitats. We therefore suggest future experiments incorporate consecutive stress into their design. 6. Climate change is predicted to result in fewer ground frosts and increased summer temperatures. Therefore, L. ochroleuca may be released from its summer cold limit in winter but still be prevented from moving up the shore due to desiccation in the summer. Laminaria ochroleuca will, however, likely be able to move into tidal pools. Therefore, only partial niche filling by L. ochroleuca will be possible in this system as climate change advancespublishersversionPeer reviewe

A Geophysical Atlas for Interpretation of Satellite-derived Data

A compilation of maps of global geophysical and geological data plotted on a common scale and projection is presented. The maps include satellite gravity, magnetic, seismic, volcanic, tectonic activity, and mantle velocity anomaly data. The Bibliographic references for all maps are included

Observation of harmonic generation and nonlinear coupling in the collective dynamics of a Bose condensate

We report the observation of harmonic generation and strong nonlinear coupling of two collective modes of a condensed gas of rubidium atoms. Using a modified TOP trap we changed the trap anisotropy to a value where the frequency of the m=0 high-lying mode corresponds to twice the frequency of the m=0 low-lying mode, thus leading to strong nonlinear coupling between these modes. By changing the anisotropy of the trap and exciting the low-lying mode we observed significant frequency shifts of this fundamental mode and also the generation of its second harmonic.Comment: 4 pages,3 figure

Thermodynamics of a Trapped Bose-Fermi Mixture

By using the Hartree-Fock-Bogoliubov equations within the Popov approximation, we investigate the thermodynamic properties of a dilute binary Bose-Fermi mixture confined in an isotropic harmonic trap. For mixtures with an attractive Bose-Fermi interaction we find a sizable enhancement of the condensate fraction and of the critical temperature of Bose-Einstein condensation with respect to the predictions for a pure interacting Bose gas. Conversely, the influence of the repulsive Bose-Fermi interaction is less pronounced. The possible relevance of our results in current experiments on trapped $^{87}{\rm Rb}-^{40}${\rm K} mixtures is discussed.Comment: 5 pages + 4 figures; minor changes, final version to appear in Phys. Rev. A; the extension work on the finite-temperature low-lying excitations can be found in cond-mat/030763