462 research outputs found
Influence of decreasing nutrient path length on the development of engineered cartilage
SummaryObjectiveChondrocyte-seeded agarose constructs of 4mm diameter (2.34mm thickness) develop spatially inhomogeneous material properties with stiffer outer edges and a softer central core suggesting nutrient diffusion limitations to the central construct region [Guilak F, Sah RL, Setton LA. Physical regulation of cartilage metabolism. In: Mow VC, Hayes WC, Eds. Basic Orthopaedic Biomechanics, Philadelphia 1997;179–207.]. The effects of reducing construct thickness and creating channels running through the depth of the thick constructs were examined.MethodsIn Study 1, the properties of engineered cartilage of 0.78mm (thin) or 2.34mm (thick) thickness were compared. In Study 2, a single nutrient channel (1mm diameter) was created in the middle of each thick construct. In Study 3, the effects of channels on larger 10mm diameter, thick constructs were examined.ResultsThin constructs developed superior mechanical and biochemical properties than thick constructs. The channeled constructs developed significantly higher mechanical properties vs control channel-free constructs while exhibiting similar glycosaminoglycan (GAG) and collagen content. Collagen staining suggested that channels resulted in a more uniform fibrillar network. Improvements in constructs of 10mm diameter were similarly observed.ConclusionsThis study demonstrated that more homogeneous tissue-engineered cartilage constructs with improved mechanical properties can be achieved by reducing their thickness or incorporating macroscopic nutrient channels. Our data further suggests that these macroscopic channels remain open long enough to promote this enhanced tissue development while exhibiting the potential to refill with cell elaborated matrix with additional culture time. Together with reports that <3mm defects in cartilage heal in vivo and that irregular holes are associated with clinically used osteochondral graft procedures, we anticipate that a strategy of incorporating macroscopic channels may aid the development of clinically relevant engineered cartilage with functional properties
Hamiltonian light-front field theory within an AdS/QCD basis
Non-perturbative Hamiltonian light-front quantum field theory presents
opportunities and challenges that bridge particle physics and nuclear physics.
Fundamental theories, such as Quantum Chromodynmamics (QCD) and Quantum
Electrodynamics (QED) offer the promise of great predictive power spanning
phenomena on all scales from the microscopic to cosmic scales, but new tools
that do not rely exclusively on perturbation theory are required to make
connection from one scale to the next. We outline recent theoretical and
computational progress to build these bridges and provide illustrative results
for nuclear structure and quantum field theory. As our framework we choose
light-front gauge and a basis function representation with two-dimensional
harmonic oscillator basis for transverse modes that corresponds with
eigensolutions of the soft-wall AdS/QCD model obtained from light-front
holography.Comment: To appear in the proceedings of Light-Cone 2009: Relativistic
Hadronic and Particle Physics, July 8-13, 2009, Sao Jose dos Campos, Brazi
PERCEPTIONS AND ADAPTATION TO CLIMATE CHANGE AND VARIABILITY BY IMMIGRANT FARMERS IN SEMI-ARID REGIONS OF KENYA
Kenya comprises of 83% arid and semi-arid land mainly suited to
extensive livestock production. Communities living in the semi-arid
areas have been affected by serious effects of climate change and
variability. A study was carried out to evaluate farmer perceptions and
adaptation to climate change in Naro Moru and Nairutia areas (both in
Nyeri North District) and Matanya in Lamuria Division in Laikipia East
District, areas that are typically semi-arid in nature. The farmers
identified environmental destruction as the major contributor to the
visible effects of climate change and variability in the region. The
main indicators are erratic and low rainfalls, frequent droughts and
dust storms, low crop yields and high day and low night time
temperatures. The effects of climate change resulted into increased
levels of poverty, food insecurity, change in biodiversity and scarcity
of resources such as water and indigenous trees which are sources of
medicine, nectar, fuel wood, timber and fodder. Changes in biodiversity
entail disappearance of wild animals and insects such as safari ants
and an upsurge of pests (e.g. centipedes, millipedes and birds). The
reduced availability of resources has changed the people\u2019s
attitudes towards the need to conserve the natural resources and
enhance food security through self and group initiatives. The biggest
efforts have been towards tree planting and husbandry and adoption of
appropriate technologies and farming methods.Le Kenya comprend 83% de terres arides et semi arides utilis\ue9es
principalement \ue0 l\u2019\ue9levage extensif. Les
communaut\ue9s vivant dans ces r\ue9gions ont \ue9t\ue9
affect\ue9es par de s\ue9rieux effets de la variabilit\ue9 et du
changement climatique. Une \ue9tude \ue9tait men\ue9e pour
\ue9valuer les perceptions paysannes et l\u2019adaptation au
changement climatique dans les milieux de NaoMoru et Nairutia (tous
dans le district du Nyeru au Nord) et dans la Division de Lamuria
\ue0 Matanyu dans le District Est \ue0 Laikipia, milieux
typiquement \ue0 nature semi aride. Les fermiers ont identifi\ue9
la destruction environnementale comme \ue9tant la cause majeure aux
effets visibles du changement et la variabilit\ue9 climatique dans la
r\ue9gion. Les indicateurs principaux sont des pr\ue9cipitations
erratiques et faibles, de s\ue9cheresses fr\ue9quentes et pluies
orageuses, faibles rendements des cultures et des temp\ue9ratures
nocturnes \ue9lev\ue9es et basses. Des effets du changement
climatique a r\ue9sult\ue9 une augmentation \ue9lev\ue9 du
niveau de la pauvret\ue9, l\u2019ins\ue9curit\ue9 alimentaire,
le changement dans la biodiversit\ue9 et le manque des ressources
comme l\u2019eau et les arbres indig\ue8nes \ue0 usage comme
mat\ue9riel de m\ue9decine, nectar, bois de chauffe, planches et
alimentation du b\ue9tail. Le changement dans la biodiversit\ue9
signifie la disparition de la faune et insectes tels que les termites
et l\u2019apparition des pestes (centip\ue8des, millip\ue8des et
oiseaux). La disponibilit\ue9 r\ue9duite des ressources a
chang\ue9 les attitudes de la population en rapport avec le besoin
dans la conservation des ressources naturelles et
l\u2019am\ue9lioration de la s\ue9curit\ue9 alimentaire \ue0
travers des initiatives personnelles et priv\ue9es. De plus grands
efforts ont \ue9t\ue9 faits pour la plantation d\u2019arbres et
l\u2019\ue9levage ainsi que l\u2019adoption appropri\ue9e des
technologies et des m\ue9thodes d\u2019exploitation agricoles
Photon-Phonon-assisted tunneling through a single-molecular quantum dot
Based on exactly mapping of a many-body electron-phonon interaction problem
onto a one-body problem, we apply the well-established nonequilibrium Green
function technique to solve the time-dependent phonon-assisted tunneling at low
temperature through a single-molecular quantum dot connected to two leads,
which is subject to a microwave irradiation field. It is found that in the
presence of the electron-phonon interaction and the microwave irradiation
field, the time-average transmission and the nonlinear differential conductance
display additional peaks due to pure photon absorption or emission processes
and photon-absorption-assisted phonon emission processes. The variation of the
time-average current with frequency of the microwave irradiation field is also
studied.Comment: 9 pages, 6 figures, submitted to Phys. Rev. B. accepted by Phys. Rev.
Theory of Current and Shot Noise Spectroscopy in Single-Molecular Quantum Dots with Phonon Mode
Using the Keldysh nonequilibrium Green function technique, we study the
current and shot noise spectroscopy of a single molecular quantum dot coupled
to a local phonon mode. It is found that in the presence of electron-phonon
coupling, in addition to the resonant peak associated with the single level of
the dot, satellite peaks with the separation set by the frequency of phonon
mode appear in the differential conductance. In the ``single level'' resonant
tunneling region, the differential shot noise power exhibit two split peaks.
However, only single peaks show up in the ``phonon assisted''
resonant-tunneling region. An experimental setup to test these predictions is
also proposed.Comment: 5 pages, 3 eps figures embedde
Green function techniques in the treatment of quantum transport at the molecular scale
The theoretical investigation of charge (and spin) transport at nanometer
length scales requires the use of advanced and powerful techniques able to deal
with the dynamical properties of the relevant physical systems, to explicitly
include out-of-equilibrium situations typical for electrical/heat transport as
well as to take into account interaction effects in a systematic way.
Equilibrium Green function techniques and their extension to non-equilibrium
situations via the Keldysh formalism build one of the pillars of current
state-of-the-art approaches to quantum transport which have been implemented in
both model Hamiltonian formulations and first-principle methodologies. We offer
a tutorial overview of the applications of Green functions to deal with some
fundamental aspects of charge transport at the nanoscale, mainly focusing on
applications to model Hamiltonian formulations.Comment: Tutorial review, LaTeX, 129 pages, 41 figures, 300 references,
submitted to Springer series "Lecture Notes in Physics
Recommended from our members
Hamiltonian Light-front Field Theory Within an AdS/QCD Basis
Non-perturbative Hamiltonian light-front quantum field theory presents opportunities and challenges that bridge particle physics and nuclear physics. Fundamental theories, such as Quantum Chromodynamics (QCD) and Quantum Electrodynamics (QED) offer the promise of great predictive power spanning phenomena on all scales from the microscopic to cosmic scales, but new tools that do not rely exclusively on perturbation theory are required to make connection from one scale to the next. We outline recent theoretical and computational progress to build these bridges and provide illustrative results for nuclear structure and quantum field theory. As our framework we choose light-front gauge and a basis function representation with two-dimensional harmonic oscillator basis for transverse modes that corresponds with eigensolutions of the soft-wall AdS/QCD model obtained from light-front holography
Longitudinal double-spin asymmetry and cross section for inclusive neutral pion production at midrapidity in polarized proton collisions at sqrt(s) = 200 GeV
We report a measurement of the longitudinal double-spin asymmetry A_LL and
the differential cross section for inclusive Pi0 production at midrapidity in
polarized proton collisions at sqrt(s) = 200 GeV. The cross section was
measured over a transverse momentum range of 1 < p_T < 17 GeV/c and found to be
in good agreement with a next-to-leading order perturbative QCD calculation.
The longitudinal double-spin asymmetry was measured in the range of 3.7 < p_T <
11 GeV/c and excludes a maximal positive gluon polarization in the proton. The
mean transverse momentum fraction of Pi0's in their parent jets was found to be
around 0.7 for electromagnetically triggered events.Comment: 6 pages, 3 figures, submitted to Phys. Rev. D (RC
Longitudinal scaling property of the charge balance function in Au + Au collisions at 200 GeV
We present measurements of the charge balance function, from the charged
particles, for diverse pseudorapidity and transverse momentum ranges in Au + Au
collisions at 200 GeV using the STAR detector at RHIC. We observe that the
balance function is boost-invariant within the pseudorapidity coverage [-1.3,
1.3]. The balance function properly scaled by the width of the observed
pseudorapidity window does not depend on the position or size of the
pseudorapidity window. This scaling property also holds for particles in
different transverse momentum ranges. In addition, we find that the width of
the balance function decreases monotonically with increasing transverse
momentum for all centrality classes.Comment: 6 pages, 3 figure
Energy and system size dependence of \phi meson production in Cu+Cu and Au+Au collisions
We study the beam-energy and system-size dependence of \phi meson production
(using the hadronic decay mode \phi -- K+K-) by comparing the new results from
Cu+Cu collisions and previously reported Au+Au collisions at \sqrt{s_NN} = 62.4
and 200 GeV measured in the STAR experiment at RHIC. Data presented are from
mid-rapidity (|y|<0.5) for 0.4 < pT < 5 GeV/c. At a given beam energy, the
transverse momentum distributions for \phi mesons are observed to be similar in
yield and shape for Cu+Cu and Au+Au colliding systems with similar average
numbers of participating nucleons. The \phi meson yields in nucleus-nucleus
collisions, normalised by the average number of participating nucleons, are
found to be enhanced relative to those from p+p collisions with a different
trend compared to strange baryons. The enhancement for \phi mesons is observed
to be higher at \sqrt{s_NN} = 200 GeV compared to 62.4 GeV. These observations
for the produced \phi(s\bar{s}) mesons clearly suggest that, at these collision
energies, the source of enhancement of strange hadrons is related to the
formation of a dense partonic medium in high energy nucleus-nucleus collisions
and cannot be alone due to canonical suppression of their production in smaller
systems.Comment: 20 pages and 5 figure
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