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

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