5,257 research outputs found
Recommended from our members
Indirect long-term global radiative cooling from NOx emissions
Anthropogenic emissions of short‐lived, chemically reactive gases, such as NO x and CO, are known to influence climate by altering the chemistry of the global troposphere and thereby the abundance of the greenhouse gases O3, CH4 and the HFCs. This study uses the characteristics of the natural modes of the tropospheric chemical system to decompose the greenhouse effect of NO x and CO emissions into (i) short‐lived modes involving predominantly tropospheric O3 and (ii) the long‐lived mode involving a global coupled CH4‐CO‐O3 perturbation. Combining these two classes of greenhouse perturbations—large, short‐lived, regional O3 increases and smaller, long‐lived, global decreases in CH4 and O3—we find that most types of anthropogenic NO x emissions lead to a negative radiative forcing and an overall cooling of the earth
Giant viscosity enhancement in a spin-polarized Fermi liquid
The viscosity is measured for a Fermi liquid, a dilute He-He mixture,
under extremely high magnetic field/temperature conditions ( T, mK). The spin splitting energy is substantially greater than
the Fermi energy ; as a consequence the polarization tends to unity
and s-wave quasiparticle scattering is suppressed for . Using a
novel composite vibrating-wire viscometer an enhancement of the viscosity is
observed by a factor of more than 500 over its low-field value. Good agreement
is found between the measured viscosity and theoretical predictions based upon
a -matrix formalism.Comment: 4 pages, 4 figure
Observation of strong electron dephasing in disordered CuGeAu thin films
We report the observation of strong electron dephasing in a series of
disordered CuGeAu thin films. A very short electron dephasing
time possessing very weak temperature dependence around 6 K, followed by an
upturn with further decrease in temperature below 4 K, is found. The upturn is
progressively more pronounced in more disordered samples. Moreover, a ln
dependent, but high-magnetic-field-insensitive, resistance rise persisting from
above 10 K down to 30 mK is observed in the films. These results suggest a
nonmagnetic dephasing process which is stronger than any known mechanism and
may originate from the coupling of conduction electrons to dynamic defects.Comment: to appear in Phys. Rev. Let
Dynamical Instability and Transport Coefficient in Deterministic Diffusion
We construct both normal and anomalous deterministic biased diffusions to
obtain the Einstein relation for their time-averaged transport coefficients. We
find that the difference of the generalized Lyapunov exponent between biased
and unbiased deterministic diffusions is related to the normalized velocity
based on the ensemble average. By Hopf's ergodic theorem, the ratios between
the time-averaged velocity and the Lyapunov exponent for single trajectories
converge to a universal constant, which is proportional to the strength of the
bias. We confirm this theory using numerical simulations.Comment: 5 pages, 3 figure
Recommended from our members
Chemical transport model ozone simulations for spring 2001 over the western Pacific:comparisons with TRACE-P lidar, ozonesondes, and Total Ozone Mapping Spectrometer columns
Two closely related chemical transport models (CTMs) employing the same high-resolution meteorological data (similar to180 km x similar to180 km x similar to600 m) from the European Centre for Medium-Range Weather Forecasts are used to simulate the ozone total column and tropospheric distribution over the western Pacific region that was explored by the NASA Transport and Chemical Evolution over the Pacific (TRACE-P) measurement campaign in February-April 2001. We make extensive comparisons with ozone measurements from the lidar instrument on the NASA DC-8, with ozonesondes taken during the period around the Pacific Rim, and with TOMS total column ozone. These demonstrate that within the uncertainties of the meteorological data and the constraints of model resolution, the two CTMs (FRSGC/UCI and Oslo CTM2) can simulate the observed tropospheric ozone and do particularly well when realistic stratospheric ozone photochemistry is included. The greatest differences between the models and observations occur in the polluted boundary layer, where problems related to the simplified chemical mechanism and inadequate horizontal resolution are likely to have caused the net overestimation of about 10 ppb mole fraction. In the upper troposphere, the large variability driven by stratospheric intrusions makes agreement very sensitive to the timing of meteorological features
A qualitative comparative survey of first cycle radiography programmes in Europe and Japan
Purpose: To qualitatively compare First Cycle Radiography programmes in Europe
and Japan.
Methods: This qualitative survey was conducted via a series of case-studies of university-based
radiography curricula in Europe and Japan.
Findings and conclusions: The main themes arising from the survey were that: (a) in Europe the
freedom that most universities have in setting their own curricula and examinations means
that in practice there is still a wide variability in curricula between and within states. On
the other hand in Japan curricula are more uniform owing to central government guidelines
regarding radiography education and a centrally administered national radiography examina-
tion. This means that student and worker mobility is much easier for Japanese radiographers.
(b) in some countries in Europe principles of reporting and healthcare management are being
expanded at the expense of the more technological aspects of radiography. Physical science
competences on the other hand are considered highly in Japanese culture and form a major
part of the curriculum. This may indicate that Japanese students would be in a much better
position to cope with role developments linked to changes in imaging technology. Pragmati-
cally oriented studies need to be carried out to determine ways in which radiographers can
enhance their role without sacrificing their technological competences. The profession cannot
afford to lose its technological expertise e it is neither in the interest of the profession itself
and even less of the patient.peer-reviewe
Generalized Arcsine Law and Stable Law in an Infinite Measure Dynamical System
Limit theorems for the time average of some observation functions in an
infinite measure dynamical system are studied. It is known that intermittent
phenomena, such as the Rayleigh-Benard convection and Belousov-Zhabotinsky
reaction, are described by infinite measure dynamical systems.We show that the
time average of the observation function which is not the function,
whose average with respect to the invariant measure is finite, converges to
the generalized arcsine distribution. This result leads to the novel view that
the correlation function is intrinsically random and does not decay. Moreover,
it is also numerically shown that the time average of the observation function
converges to the stable distribution when the observation function has the
infinite mean.Comment: 8 pages, 8 figure
Ultraslow Convergence to Ergodicity in Transient Subdiffusion
We investigate continuous time random walks with truncated -stable
trapping times. We prove distributional ergodicity for a class of observables;
namely, the time-averaged observables follow the probability density function
called the Mittag--Leffler distribution. This distributional ergodic behavior
persists for a long time, and thus the convergence to the ordinary ergodicity
is considerably slower than in the case in which the trapping-time distribution
is given by common distributions. We also find a crossover from the
distributional ergodic behavior to the ordinary ergodic behavior.Comment: 4 pages, 3 figure
Distributional Response to Biases in Deterministic Superdiffusion
We report on a novel response to biases in deterministic superdiffusion. For
its reduced map, we show using infinite ergodic theory that the time-averaged
velocity (TAV) is intrinsically random and its distribution obeys the
generalized arc-sine distribution. A distributional limit theorem indicates
that the TAV response to a bias appears in the distribution, which is an
example of what we term a distributional response induced by a bias. Although
this response in single trajectories is intrinsically random, the
ensemble-averaged TAV response is linear.Comment: 13 pages, 5 figure
- …