294 research outputs found
Filtering out the cosmological constant in the Palatini formalism of modified gravity
According to theoretical physics the cosmological constant (CC) is expected
to be much larger in magnitude than other energy densities in the universe,
which is in stark contrast to the observed Big Bang evolution. We address this
old CC problem not by introducing an extremely fine-tuned counterterm, but in
the context of modified gravity in the Palatini formalism. In our model the
large CC term is filtered out, and it does not prevent a standard cosmological
evolution. We discuss the filter effect in the epochs of radiation and matter
domination as well as in the asymptotic de Sitter future. The final expansion
rate can be much lower than inferred from the large CC without using a
fine-tuned counterterm. Finally, we show that the CC filter works also in the
Kottler (Schwarzschild-de Sitter) metric describing a black hole environment
with a CC compatible to the future de Sitter cosmos.Comment: 22 pages, 1 figure, discussion extended, references added, accepted
by Gen.Rel.Gra
Effects of dual task on turning ability in stroke survivors and older adults
Background: Turning is an integral component of independent mobility in which stroke survivors frequently fall. Objective: This study sought to measure the effects of competing cognitive demands on the stepping patterns of stroke survivors, compared to healthy age-match adults, during turning as a putative mechanism for falls. Methods: Walking and turning (90º) was assessed under single (walking and turning alone) and dual task (subtracting serial 3s while walking and turning) conditions using an electronic, pressure-sensitive walkway. Dependent measures were time to turn, variability in time to turn, step length, step width and single support time during three steps of the turn. Turning ability in single and dual task conditions was compared between stroke survivors (n= 17, mean ± SD: 59 ± 113 months post-stroke, 64 ± 10 years of age) and age-matched healthy counterparts (n = 15). Results: Both groups took longer, were more variable, tended to widen the second step and, crucially, increased single support time on the inside leg of the turn while turning and distracted. Conclusions. Increased single support time during turning may represent biomechanical mechanism, within stepping patterns of turning under distraction, for increased risk of falls for both stroke survivors and older adults
Viral Load Distribution in SARS Outbreak
Airborne transmission may have resulted in an outbreak of SARS in Hong Kong
Assessing Exposures from the Deepwater Horizon Oil Spill Response and Clean-up
The GuLF Study is investigating adverse health effects from work on the response and clean-up after the Deepwater Horizon explosion and oil release. An essential and necessary component of that study was the exposure assessment. Bayesian statistical methods and over 135 000 measurements of total hydrocarbons (THC), benzene, ethylbenzene, toluene, xylene, and n-hexane (BTEX-H) were used to estimate inhalation exposures to these chemicals for >3400 exposure groups (EGs) formed from three exposure determinants: job/activity/task, location, and time period. Recognized deterministic models were used to estimate airborne exposures to particulate matter sized 2.5 μm or less (PM2.5) and dispersant aerosols and vapors. Dermal exposures were estimated for these same oil-related substances using a model modified especially for this study from a previously published model. Exposures to oil mist were assessed using professional judgment. Estimated daily THC arithmetic means (AMs) were in the low ppm range (<25 ppm), whereas BTEX-H exposures estimates were generally <1000 ppb. Potential 1-h PM2.5 air concentrations experienced by some workers may have been as high as 550 μg m-3. Dispersant aerosol air concentrations were very low (maximum predicted 1-h concentrations were generally <50 μg m-3), but vapor concentrations may have exceeded occupational exposure excursion guidelines for 2-butoxyethanol under certain circumstances. The daily AMs of dermal exposure estimates showed large contrasts among the study participants. The estimates are being used to evaluate exposure-response relationships in the GuLF Study
Study of the B^0 Semileptonic Decay Spectrum at the Upsilon(4S) Resonance
We have made a first measurement of the lepton momentum spectrum in a sample
of events enriched in neutral B's through a partial reconstruction of B0 -->
D*- l+ nu. This spectrum, measured with 2.38 fb**-1 of data collected at the
Upsilon(4S) resonance by the CLEO II detector, is compared directly to the
inclusive lepton spectrum from all Upsilon(4S) events in the same data set.
These two spectra are consistent with having the same shape above 1.5 GeV/c.
From the two spectra and two other CLEO measurements, we obtain the B0 and B+
semileptonic branching fractions, b0 and b+, their ratio, and the production
ratio f+-/f00 of B+ and B0 pairs at the Upsilon(4S). We report b+/b0=0.950
(+0.117-0.080) +- 0.091, b0 = (10.78 +- 0.60 +- 0.69)%, and b+ = (10.25 +- 0.57
+- 0.65)%. b+/b0 is equivalent to the ratio of charged to neutral B lifetimes,
tau+/tau0.Comment: 14 page, postscript file also available at
http://w4.lns.cornell.edu/public/CLN
Update of the Search for the Neutrinoless Decay
We present an update of the search for the lepton family number violating
decay using a complete CLEO II data sample of 12.6 million
pairs. No evidence of a signal has been found and the
corresponding upper limit is \BR(\tau \to \mu\gamma) < 1.0 \times 10^{-6}
at 90% CL, significantly smaller than previous limits. All quoted results are
preliminary.Comment: 9 pages postscript, also available through
http://w4.lns.cornell.edu/public/CLN
Probing exotic phenomena at the interface of nuclear and particle physics with the electric dipole moments of diamagnetic atoms: A unique window to hadronic and semi-leptonic CP violation
The current status of electric dipole moments of diamagnetic atoms which
involves the synergy between atomic experiments and three different theoretical
areas -- particle, nuclear and atomic is reviewed. Various models of particle
physics that predict CP violation, which is necessary for the existence of such
electric dipole moments, are presented. These include the standard model of
particle physics and various extensions of it. Effective hadron level combined
charge conjugation (C) and parity (P) symmetry violating interactions are
derived taking into consideration different ways in which a nucleon interacts
with other nucleons as well as with electrons. Nuclear structure calculations
of the CP-odd nuclear Schiff moment are discussed using the shell model and
other theoretical approaches. Results of the calculations of atomic electric
dipole moments due to the interaction of the nuclear Schiff moment with the
electrons and the P and time-reversal (T) symmetry violating
tensor-pseudotensor electron-nucleus are elucidated using different
relativistic many-body theories. The principles of the measurement of the
electric dipole moments of diamagnetic atoms are outlined. Upper limits for the
nuclear Schiff moment and tensor-pseudotensor coupling constant are obtained
combining the results of atomic experiments and relativistic many-body
theories. The coefficients for the different sources of CP violation have been
estimated at the elementary particle level for all the diamagnetic atoms of
current experimental interest and their implications for physics beyond the
standard model is discussed. Possible improvements of the current results of
the measurements as well as quantum chromodynamics, nuclear and atomic
calculations are suggested.Comment: 46 pages, 19 tables and 16 figures. A review article accepted for
EPJ
Green and lean sustainable development path in China: Guanxi, practices and performance
Globalisation has created both drivers and pressure for Chinese organisations to enhance their business performance as well as environmental performance. Green and lean practice is emerging as a critical approach for Chinese organisations to achieve sustainable development and improve organisational performance. By conducting empirical studies from 172 respondents on green and lean practice in different Chinese organisations, this research shows how green and lean practice affects organisational performance and how this association is affected by guanxi. The findings explain that guanxi between organisational partners improves the positive effect of green and lean practice on organisational performance. The results of this paper offer helpful insights into how managers should enhance their guanxi initiatives, in order to improve environmental and business performance over their supply chains. The paper also suggests the limitations of this research, as well as directions for future research
Production of singlet P-wave and states
No spin-singlet quarkonium state has yet been observed. In this
paper we discuss the production of the singlet P-wave and
states and . We consider two possibilities. In the first the
states are produced via the electromagnetic cascades \ups(3S) \to
\eta_b(2S) + \gamma \to h_b + \gamma \gamma \to \eta_b +\gamma\gamma\gamma
and . A more promising process consists of single pion
transition to the state followed by the radiative transition to the
state: \ups(3S)\to h_b + \pi^0 \to \eta_b + \pi^0 +\gamma and . For a million \ups(3S) or
's produced we expect these processes to produce several hundred events.Comment: 13 pages, LaTeX, 1 figure, to be published Phys. Rev. D. Some
equation numbers and one table number correcte
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