42 research outputs found
Study of pressure effect on the magnetic penetration depth in MgB
A study of the pressure effect on the magnetic penetration depth in
polycrystalline MgB was performed by measuring the temperature dependence
of the magnetization under an applied pressure of 0.15 and 1.13 GPa. We found
that at low temperature is only slightly affected by pressure
[], in contrast to cuprate
superconductors, where, in the same range of pressure, a very large effect on
was found. Theoretical estimates indicate that most of the
pressure effect on in MgB arises from the electron-phonon
interaction.Comment: 5 pages, 2 figure
Pressure induced softening of YB_6: pressure effect on the Ginzburg-Landau parameter \kappa=\lambda/\xi
Measurements of the transition temperature T_c, the second critical filed
H_{c2} and the magnetic penetration depth \lambda under hydrostatic pressure
(up to 9.2 kbar) in the YB_6 superconductor were carried out. A pronounced and
{\it negative} pressure effects (PE) on T_c and H_{c2} with dT_c/dp=-0.0547(4)
K/kbar and \mu_0dH_{c2}(0)/dp =-4.84(20) mT/kbar, and zero PE on \lambda(0)
were observed. The PE on the coherence length d\xi(0)/dp=0.28(2) nm/kbar was
calculated from the measured pressure dependence of H_{c2}(0). Together with
the zero PE on the magnetic penetration depth \lambda(0), our results imply
that the Ginzburg-Landau parameter \kappa(0)=\xi(0)/\lambda(0) depends on
pressure and that pressure "softens" YB_6, e.g. moves it to the type-I
direction.Comment: 4 pages, 2 figure
Finite-size and pressure effects in YBa_2Cu_4O_8 probed by magnetic field penetration depth measurements
We explore the combined pressure and finite-size effects on the in-plane
penetration depth \lambda_{ab} in YBa_2Cu_4O_8. Even though this cuprate is
stoichiometric the finite-size scaling analysis of \lambda_{ab}^{-2}(T)
uncovers the granular nature and reveals domains with nanoscale size L_{c}
along the c-axis. L_{c} ranges from 33.2 Angstrom to 28.9 Angstrom at pressures
from 0.5 to 11.5 kbar. These observations raise serious doubts on the existence
of a phase coherent macroscopic superconducting state in cuprate
superconductors.Comment: 7 pages, 6 figure
Pressure effects on the transition temperature and the magnetic field penetration depth in the pyrochlore superconductor RbOs_2O_6
We report magnetization measurements under high hydrostatic pressure in the
newly discovered pyrochlore superconductor RbOs_2O_6 (T_c\simeq6.3K at p=0). A
pronounced and {\it positive} pressure effect (PE) on T_c with dT_c/dp
=0.090(1)K/kbar was observed, whereas no PE on the magnetic penetration depth
\lambda was detected. The relative pressure shift of T_c [ dlnT_c/dp \simeq
1.5%/kbar] is comparable with the highest values obtained for highly underdoped
high-temperature cuprate superconductors. Our results suggest that RbOs_2O_6 is
an adiabatic BCS-type superconductor.Comment: 11 pages, 4 figure
Influence of virtual reality soccer game on walking performance in robotic assisted gait training for children
BACKGROUND: Virtual reality (VR) offers powerful therapy options within a functional, purposeful and motivating context. Several studies have shown that patients' motivation plays a crucial role in determining therapy outcome. However, few studies have demonstrated the potential of VR in pediatric rehabilitation. Therefore, we developed a VR-based soccer scenario, which provided interactive elements to engage patients during robotic assisted treadmill training (RAGT). The aim of this study was to compare the immediate effect of different supportive conditions (VR versus non-VR conditions) on motor output in patients and healthy control children during training with the driven gait orthosis Lokomat*.
METHODS: A total of 18 children (ten patients with different neurological gait disorders, eight healthy controls) took part in this study. They were instructed to walk on the Lokomat in four different, randomly-presented conditions: (1) walk normally without supporting assistance, (2) with therapists' instructions to promote active participation, (3) with VR as a motivating tool to walk actively and (4) with the VR tool combined with therapists' instructions. The Lokomat gait orthosis is equipped with sensors at hip and knee joint to measure man-machine interaction forces. Additionally, subjects' acceptance of the RAGT with VR was assessed using a questionnaire.
RESULTS: The mixed ANOVA revealed significant main effects for the factor CONDITIONS (p < 0.001) and a significant interaction CONDITIONS x GROUP (p = 0.01). Tests of between-subjects effects showed no significant main effect for the GROUP (p = 0.592). Active participation in patients and control children increased significantly when supported and motivated either by therapists' instructions or by a VR scenario compared with the baseline measurement "normal walking" (p < 0.001).
CONCLUSIONS: The VR scenario used here induces an immediate effect on motor output to a similar degree as the effect resulting from verbal instructions by the therapists. Further research needs to focus on the implementation of interactive design elements, which keep motivation high across and beyond RAGT sessions, especially in pediatric rehabilitation
Are isomeric alkenes used in species recognition among neo-tropical stingless bees (Melipona spp)
The majority of our understanding of the role of cuticular hydrocarbons (CHC) in recognition is based largely on temperate ant species and honey bees. The stingless bees remain relatively poorly studied, despite being the largest group of eusocial bees, comprising more than 400 species in some 60 genera. The Meliponini and Apini diverged between 80-130 Myr B.P. so the evolutionary trajectories that shaped the chemical communication systems in ants, honeybees and stingless bees may be very different. Therefore, the main aim of this study was to study if a unique species CHC signal existed in Neotropical stingless bees, as shown for many temperate species, and if so what compounds are involved. This was achieved by collecting CHC data from 24 colonies belonging to six species of Melipona from North-eastern Brazil and comparing this new data with all previously published CHC studies on Melipona. We found that each of the eleven Melipona species studied so far each produced a unique species CHC signal based around their alkene isomer production. A remarkable number of alkene isomers, up to 25 in M. asilvai, indicated the diversification of alkene positional isomers among the stingless bees. The only other group to have really diversified in alkene isomer production are the primitively eusocial Bumblebees (Bombus spp), which are the sister group of the stingless bees. Furthermore, among the eleven Neotropical Melipona species we could detect no effect of the environment on the proportion of alkane production as has been suggested for some other species
Co-founding ant queens prevent disease by performing prophylactic undertaking behaviour
Abstract Background Social insects form densely crowded societies in environments with high pathogen loads, but have evolved collective defences that mitigate the impact of disease. However, colony-founding queens lack this protection and suffer high rates of mortality. The impact of pathogens may be exacerbated in species where queens found colonies together, as healthy individuals may contract pathogens from infectious co-founders. Therefore, we tested whether ant queens avoid founding colonies with pathogen-exposed conspecifics and how they might limit disease transmission from infectious individuals. Results Using Lasius niger queens and a naturally infecting fungal pathogen Metarhizium brunneum, we observed that queens were equally likely to found colonies with another pathogen-exposed or sham-treated queen. However, when one queen died, the surviving individual performed biting, burial and removal of the corpse. These undertaking behaviours were performed prophylactically, i.e. targeted equally towards non-infected and infected corpses, as well as carried out before infected corpses became infectious. Biting and burial reduced the risk of the queens contracting and dying from disease from an infectious corpse of a dead co-foundress. Conclusions We show that co-founding ant queens express undertaking behaviours that, in mature colonies, are performed exclusively by workers. Such infection avoidance behaviours act before the queens can contract the disease and will therefore improve the overall chance of colony founding success in ant queens
Introduction: exploring and explaining the Asia-Pacific Partnership on Clean Development and Climate
This introduction lays the groundwork for this Special Issue by providing an overview of the Asia-Pacific Partnership on Clean Development and Climate (APP), and by introducing three main analytical themes. The first theme concerns the emergence and continuation of the APP. The contributions show that the emergence of the APP can be attributed to international factors, including the United States' rejection of the Kyoto Protocol, and its search for an alternative arena for global climate governance, and other countries' wish to maintain good relations with the US; as well as domestic factors, such as the presence of bureaucratic actors in favour of the Partnership, alignment with domestic priorities, and the potential for reaping economic benefits through participation. The second theme examines the nature of the Partnership, concluding that it falls on the very soft side of the hard-soft law continuum and that while being branded as a public-private partnership, governments remain in charge. Under the third theme, the influence which the APP exerts on the post-2012 United Nations (UN) climate change negotiations is scrutinised. The contributions show that at the very least, the APP is exerting some cognitive influence on the UN discussions through its promotion of a sectoral approach. The introduction concludes with outlining areas for future research. © Springer Science+Business Media B.V. 2009