490 research outputs found
Resonant speed meter for gravitational wave detection
Gravitational-wave detectors have been well developed and operated with high
sensitivity. However, they still suffer from mirror displacement noise. In this
paper, we propose a resonant speed meter, as a displacement noise-canceled
configuration based on a ring-shaped synchronous recycling interferometer. The
remarkable feature of this interferometer is that, at certain frequencies,
gravitational-wave signals are amplified, while displacement noises are not.Comment: 4 pages, 4 figure
Longitudinal Stress-Buffering Effects of Social Integration for Late-Life Functional Health
Stress can negatively affect multiple aspects of health, including functional health, among older adults, who are likely to face unique, age-related stressful experiences. Previous research has addressed the protective effects of social relations (i.e., social ties, social participation, and social integration) for physical and mental health outcomes, yet few studies have examined functional health. This study aimed to investigate the longitudinal stress-buffering effects of social integration on late-life functional health. Using three-wave data from 399 older adults (aged older than 60 years), two-level hierarchical linear modeling analysis was conducted and the results indicated that in addition to its main effect on functional (activity of daily living) limitations, social integration moderated the negative effect of stress on the longitudinal trajectory of functional limitations. The findings suggest important directions of future research to identify the mechanisms of such buffering effects over time and develop effective interventions to enhance late-life functional health while promoting social integration
Quasinormal ringing of acoustic black holes in Laval nozzles: Numerical simulations
Quasinormal ringing of acoustic black holes in Laval nozzles is discussed.
The equation for sounds in a transonic flow is written into a
Schr\"{o}dinger-type equation with a potential barrier, and the quasinormal
frequencies are calculated semianalytically. From the results of numerical
simulations, it is shown that the quasinormal modes are actually excited when
the transonic flow is formed or slightly perturbed, as well as in the real
black hole case. In an actual experiment, however, the purely-outgoing boundary
condition will not be satisfied at late times due to the wave reflection at the
end of the apparatus, and a late-time ringing will be expressed as a
superposition of "boxed" quasinormal modes. It is shown that the late-time
ringing damps more slowly than the ordinary quasinormal ringing, while its
central frequency is not greatly different from that of the ordinary one. Using
this fact, an efficient way for experimentally detecting the quasinormal
ringing of an acoustic black hole is discussed.Comment: 9 pages, 8 figures, accepted for publication in Physical Review
What Controls Activity Trends of Electrocatalytic Hydrogen Evolution Reaction?-Activation Energy Versus Frequency Factor
Renewable energy storage via water electrolysis strongly depends on the design of electrified electrode–electrolyte interfaces at which electricity is converted into chemical energy. At the core of the hydrogen evolution reaction (HER) and the oxygen evolution reaction conversion efficiency are interfacial processes with complex dynamic mechanisms, whose further acceleration is practically impossible without a thorough fundamental understanding of electrocatalysis. Here, we communicate new experimental insights into HER, which will potentially further deepen our general understanding of electrocatalysis. Of special note is the very surprising observation that the most active metals (i.e., noble metals) for HER, which exhibit the lowest overpotentials at a defined current density, exhibit the highest activation energies in comparison to the other metals from the d-block. This suggests a major, if not dominant, impact of the frequency factor on activity trends and the need for deeper reconsideration of the origins of electrocatalytic activity
The Effect of Iron Impurities on Transition Metal Catalysts for the Oxygen Evolution Reaction in Alkaline Environment: Activity Mediators or Active Sites?
There is an ongoing debate on elucidating the actual role of Fe impurities in alkaline water electrolysis, acting either as reactivity mediators or as co-catalysts through synergistic interaction with the main catalyst material. This perspective summarizes the most prominent oxygen evolution reaction (OER) mechanisms mostly for Ni-based oxides as model transition metal catalysts and highlights the effect of Fe incorporation on the catalyst surface in the form of impurities originating from the electrolyte or co-precipitated in the catalyst lattice, in modulating the OER reaction kinetics, mechanism and stabilit
Study of the genetic homogeneity of Albarino (Vitis vinifera L.) growing in Galicia (Spain) using isozyme and RAPD markers
Research NoteAn evaluation of the genetic diversity of cv. Albarino (Vitis vinifera L.) was carried out. Centenarian and young plants were selected from vineyards, some of them showing slight ampelographic differences. Using ELISA tests 5 out of 24 plants were found to be infected with grapevine leafroll-associated virus 3 (GLRaV-3). In order to evaluate genetic polymorphism, 10 enzyme systems and 42 RAPD primers were used. The 73 isozyme and 308 RAPD markers were common in the samples tested. The results show the existence of a genetic homogeneity within Albarino cultivated in Galicia. Minor ampelographic differences among samples could be due to external factors rather than to genetic differences
Electrocatalysis Beyond 2020: How to Tune the Preexponential Frequency Factor
After a century of research on electrocatalytic reactions, a universal theory of electrocatalysis is still not established due to limited understanding of complex energy conversion processes at electrified electrode-electrolyte interfaces. Most of the research efforts directed toward the acceleration of important electrocatalytic reactions (e. g. hydrogen evolution reaction) were in the direction of minimizing activation energy by tuning the adsorption energies of key intermediates. This kind of approach is well-established and, importantly, in some cases it was valuable by predicting the design of electrocatalysts with advanced properties. However, in some very important research endeavors, advancement in performance of newly designed electrocatalysts could not be attributed to altered/minimized activation energy. Important to note is that modern electrocatalysis almost completely disregards influence of the preexponential factor on reaction rate. In this work, we open some important questions relevant for future of electrocatalysis and electrochemical energy conversion, with special focus on preexponential factor as major contributor to electrocatalytic reaction rate
High Ratio of 44Ti/56Ni in Cas A and Axisymmetric Collapse-Driven Supernova Explosion
The large abundance ratio of in Cas A is puzzling. In fact,
the ratio seems to be larger than the theoretical constraint derived by Woosley
& Hoffman (1991). However, this constraint is obtained on the assumption that
the explosion is spherically symmetric, whereas Cas A is famous for the
asymmetric form of the remnant. Recently, Nagataki et al. (1997) calculated the
explosive nucleosynthesis of axisymmetrically deformed collapse-driven
supernova. They reported that the ratio of was enhanced by
the stronger alpha-rich freezeout in the polar region. In this paper, we apply
these results to Cas A and examine whether this effect can explain the large
amount of and the large ratio of . We demonstrate
that the conventional spherically symmetric explosion model can not explain the
Ti mass produced in Cas A if its lifetime is shorter than 80
years and the intervening space is transparent to the gamma-ray line from the
decay of Ti. On the other hand, we show the axisymmetric explosion
models can solve the problem. We expect the same effect from a three
dimensionally asymmetric explosion, since the stronger alpha-rich freezeout
will also occur in that case in the region where the larger energy is
deposited.Comment: 10 pages, LaTeX text and 3 postscript figure
Dark-field transmission electron microscopy and the Debye-Waller factor of graphene
Graphene's structure bears on both the material's electronic properties and
fundamental questions about long range order in two-dimensional crystals. We
present an analytic calculation of selected area electron diffraction from
multi-layer graphene and compare it with data from samples prepared by chemical
vapor deposition and mechanical exfoliation. A single layer scatters only 0.5%
of the incident electrons, so this kinematical calculation can be considered
reliable for five or fewer layers. Dark-field transmission electron micrographs
of multi-layer graphene illustrate how knowledge of the diffraction peak
intensities can be applied for rapid mapping of thickness, stacking, and grain
boundaries. The diffraction peak intensities also depend on the mean-square
displacement of atoms from their ideal lattice locations, which is
parameterized by a Debye-Waller factor. We measure the Debye-Waller factor of a
suspended monolayer of exfoliated graphene and find a result consistent with an
estimate based on the Debye model. For laboratory-scale graphene samples,
finite size effects are sufficient to stabilize the graphene lattice against
melting, indicating that ripples in the third dimension are not necessary.Comment: 10 pages, 4 figure
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