6,227 research outputs found
Childhood Psychosocial Determinants of Cardiovascular Health
Understanding risk and protective factors that impact cardiovascular health is of utmost importance. There is ample evidence that cardiovascular health begins in childhood, tracks over time, and is subject to adverse social influences. This paper reviews key studies examining the relations of psychosocial factors in childhood to cardiovascular health in adulthood. The existing literature provides evidence for both individual and cumulative effects of childhood psychosocial factors on adult cardiovascular health across the population, although the specific mechanisms underlying these relationships are not yet fully understood. This paper also includes a discussion of evidence-based strategies for prevention and treatment of childhood psychosocial problems. The extent to which these programs lead to improved cardiovascular health in high-risk groups or across the population by impacting psychosocial factors has not yet been studied, but is a clear future direction for research and policy
Flow-induced voltage and current generation in carbon nanotubes
New experimental results, and a plausible theoretical understanding thereof,
are presented for the flow-induced currents and voltages observed in
single-walled carbon nanotube samples. In our experiments, the electrical
response was found to be strongly sublinear -- nearly logarithmic -- in the
flow speed over a wide range, and its direction could be controlled by an
electrochemical biasing of the nanotubes. These experimental findings are
inconsistent with the conventional idea of a streaming potential as the
efficient cause. Here we present a new, physically appealing, Langevin-equation
based treatment of the nanotube charge carriers, assumed to be moving under
coulombic forcing by the correlated ionic fluctuations, advected by the liquid
in flow. The resulting 'Doppler-shifted' force-force correlation, as seen by
the charge carriers drifting in the nanotube, is shown to give a strongly
sublinear response, broadly in agreement with experiments.Comment: 11 pages including 3 figures. To appear in Phys. Rev B (2004
Origin of the unusual dependence of Raman D band on excitation wavelength in graphite-like materials
We have revisited the still unresolved puzzle of the dispersion of the Raman
disordered-induced D band as a function of laser excitation photon energy E
in graphite-like materials. We propose that the D-mode is a combination of an
optic phonon at the K-point in the Brillioun zone and an acoustic phonon whose
momentum is determined uniquely by the double resonance condition. The fit of
the experimental data with the double-resonance model yields the reduced
effective mass of 0.025m for the electron-hole pairs corresponding to the
A transition, in agreement with other experiments. The model can also
explain the difference between and for D and
D modes, and predicts its dependence on the Raman excitation
frequency.Comment: 4 figures in eps forma
Superorbital Period in the High Mass X-ray Binary 2S 0114+650
We report the detection of a superorbital period in the high-mass X-ray
binary 2S 0114+650. Analyses of data from the Rossi X-ray Timing Explorer
(RXTE) All-Sky Monitor (ASM) from 1996 January 5 to 2004 August 25 reveal a
superorbital period of 30.7 +/- 0.1 d, in addition to confirming the previously
reported neutron star spin period of 2.7 h and the binary orbital period of
11.6 d. It is unclear if the superorbital period can be ascribed to the
precession of a warped accretion disc in the system.Comment: 5 pages, 5 figures, submitted to MNRAS 27th January 2005. Manuscript
expanded to include discussion of evolution of periods, and hardness ratio
variability. Number of figures increased from 5 to 9. Accepted for
publication 19th December 200
Enhanced Raman and photoluminescence response in monolayer MoS due to laser healing of defects
Bound quasiparticles, negatively charged trions and neutral excitons, are
associated with the direct optical transitions at the K-points of the Brillouin
zone for monolayer MoS. The change in the carrier concentration,
surrounding dielectric constant and defect concentration can modulate the
photoluminescence and Raman spectra. Here we show that exposing the monolayer
MoS in air to a modest laser intensity for a brief period of time enhances
simultaneously the photoluminescence (PL) intensity associated with both trions
and excitons, together with 3 to 5 times increase of the Raman intensity
of first and second order modes. The simultaneous increase of PL from trions
and excitons cannot be understood based only on known-scenario of depletion of
electron concentration in MoS by adsorption of O and HO molecules.
This is explained by laser induced healing of defect states resulting in
reduction of non-radiative Auger processes. This laser healing is corroborated
by an observed increase of intensity of both the first order and second order
2LA(M) Raman modes by a factor of 3 to 5. The A mode hardens by
1.4 cm whereas the E mode softens by 1 cm.
The second order 2LA(M) Raman mode at 440 cm shows an increase in
wavenumber by 8 cm with laser exposure. These changes are a
combined effect of change in electron concentrations and oxygen-induced lattice
displacements.Comment: 15 pages, 5 figures, Journal of Raman Spectroscopy, 201
Isospin effects on the mass dependence of balance energy
We study the effect of isospin degree of freedom on balance energy throughout
the mass range between 50 and 350 for two sets of isotopic systems with N/Z =
1.16 and 1.33 as well as isobaric systems with N/Z = 1.0 and 1.4. Our findings
indicate that different values of balance energy for two isobaric systems may
be mainly due to the Coulomb repulsion. We also demonstrate clearly the
dominance of Coulomb repulsion over symmetry energy.Comment: 5 pages, 3 figures In this version the discussion is in terms of N/Z
whereas in the journal the whole discussion is in terms of N/A. The
conclusions remain unaffecte
Phonon renormalisation in doped bilayer graphene
We report phonon renormalisation in bilayer graphene as a function of doping.
The Raman G peak stiffens and sharpens for both electron and hole doping, as a
result of the non-adiabatic Kohn anomaly at the point. The bilayer has
two conduction and valence subbands, with splitting dependent on the interlayer
coupling. This results in a change of slope in the variation of G peak position
with doping, which allows a direct measurement of the interlayer coupling
strength.Comment: 5 figure
Femtosecond Photoexcited Carrier Dynamics in Reduced Graphene Oxide Suspensions and Films
We report ultrafast response of femtosecond photoexcited carriers in single
layer reduced graphene oxide flakes suspended in water as well as few layer
thick film deposited on indium tin oxide coated glass plate using pump-probe
differential transmission spectroscopy at 790 nm. The carrier relaxation
dynamics has three components: ~200 fs, 1 to 2 ps, and ~25 ps, all of them
independent of pump fluence. It is seen that the second component (1 to 2 ps)
assigned to the lifetime of hot optical phonons is larger for graphene in
suspensions whereas other two time constants are the same for both the
suspension and the film. The value of third order nonlinear susceptibility
estimated from the pump-probe experiments is compared with that obtained from
the open aperture Z-scan results for the suspension.Comment: 4 pages, 4 figures, to appear in International Journal of Nanoscience
(IJN), 201
Ultrafast photoinduced enhancement of nonlinear optical response in 15-atom gold clusters on indium tin oxide conducting film
We show that the third order optical nonlinearity of 15-atom gold clusters is
significantly enhanced when in contact with indium tin oxide (ITO) conducting
film. Open and close aperture z-scan experiments together with non-degenerate
pump-probe differential transmission experiments were done using 80 fs laser
pulses centered at 395 nm and 790 nm on gold clusters encased inside
cyclodextrin cavities. We show that two photon absorption coefficient is
enhanced by an order of magnitude as compared to that when the clusters are on
pristine glass plate. The enhancement for the nonlinear optical refraction
coefficient is ~3 times. The photo-induced excited state absorption using
pump-probe experiments at pump wavelength of 395 nm and probe at 790 nm also
show an enhancement by an order of magnitude. These results attributed to the
excited state energy transfer in the coupled gold cluster-ITO system are
different from the enhancement seen so far in charge donor-acceptor complexes
and nanoparticle-conjugate polymer composites.Comment: To appear in Optics Express (2013);
http://dx.doi.org/10.1364/OE.21.00848
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