3,339 research outputs found
Osteoblast interactions within a biomimetic apatite microenvironment.
Numerous reports have shown that accelerated apatites can mediate osteoblastic differentiation in vitro and bone formation in vivo. However, how cells interact within the apatite microenvironment remains largely unclear, despite the vast literature available today. In response, this study evaluates the in vitro interactions of a well-characterized osteoblast cell line (MC3T3-E1) with the apatite microenvironment. Specifically, cell attachment, spreading, and viability were evaluated in the presence and absence of serum proteins. Proteins were found to be critical in the mediation of cell-apatite interactions, as adherence of MC3T3-E1 cells to apatite surfaces without protein coatings resulted in significant levels of cell death within 24 h in serum-free media. In the absence of protein-apatite interaction, cell viability could be "rescued" upon treatment of MC3T3-E1 cells with inhibitors to phosphate (PO(4) (3-)) transport, suggesting that PO(4) (3-) uptake may play a role in viability. In contrast, rescue was not observed upon treatment with calcium (Ca(2+)) channel inhibitors. Interestingly, a rapid "pull-down" of extracellular Ca(2+) and PO(4) (3-) ions onto the apatite surface could be measured upon the incubation of apatites with α-MEM, suggesting that cells may be subject to changing levels of Ca(2+) and PO(4) (3-) within their microenvironment. Therefore, the biomimetic apatite surface may significantly alter the microenvironment of adherent osteoblasts and, as such, be capable of affecting both cell survival and differentiation
Direct observation of acoustic phonon mediated relaxation between coupled exciton states in a single quantum dot molecule
We probe acoustic phonon mediated relaxation between tunnel coupled exciton
states in an individual quantum dot molecule in which the inter-dot quantum
coupling and energy separation between exciton states is continuously tuned
using static electric field. Time resolved and temperature dependent optical
spectroscopy are used to probe inter-level relaxation around the point of
maximum coupling. The radiative lifetimes of the coupled excitonic states can
be tuned from ~2 ns to ~10 ns as the spatially direct and indirect character of
the wavefunction is varied by detuning from resonance. Acoustic phonon mediated
inter-level relaxation is shown to proceed over timescales comparable to the
direct exciton radiative lifetime, indicative of a relaxation bottleneck for
level spacings in the range $\Delta E\$ ~3-6 meV.Comment: 6 pages, 4 figures, submitted for publicatio
High-accuracy standard specimens for the line-focus-beam ultrasonicmaterial characterization system
科研費報告書収録論文(課題番号:13555085・基盤研究(B)(2) ・H13~H14/研究代表者:櫛引, 淳一/超高品質人工水晶の超音波マイクロスペクトロスコピー
Enhanced photoluminescence emission from two-dimensional silicon photonic crystal nanocavities
We present a temperature dependent photoluminescence study of silicon optical
nanocavities formed by introducing point defects into two-dimensional photonic
crystals. In addition to the prominent TO phonon assisted transition from
crystalline silicon at ~1.10 eV we observe a broad defect band luminescence
from ~1.05-1.09 eV. Spatially resolved spectroscopy demonstrates that this
defect band is present only in the region where air-holes have been etched
during the fabrication process. Detectable emission from the cavity mode
persists up to room-temperature, in strong contrast the background emission
vanishes for T > 150 K. An Ahrrenius type analysis of the temperature
dependence of the luminescence signal recorded either in-resonance with the
cavity mode, or weakly detuned, suggests that the higher temperature stability
may arise from an enhanced internal quantum efficiency due to the
Purcell-effect
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Carotenoids are the likely precursor of a significant fraction of marine dissolved organic matter.
The ocean's biota sequester atmospheric carbon dioxide (CO2) in part by producing dissolved organic matter (DOM) that persists in the ocean for millennia. This long-term accumulation of carbon may be facilitated by abiotic and biotic production of chemical structures that resist degradation, consequently contributing disproportionately to refractory DOM. Compounds that are selectively preserved in seawater were identified in solid-phase extracted DOM (PPL-DOM) using comprehensive gas chromatography (GC) coupled to mass spectrometry (MS). These molecules contained cyclic head groups that were linked to isoprenoid tails, and their overall structures closely resembled carotenoid degradation products (CDP). The origin of these compounds in PPL-DOM was further confirmed with an in vitro β-carotene photooxidation experiment that generated water-soluble CDP with similar structural characteristics. The molecular-level identification linked at least 10% of PPL-DOM carbon, and thus 4% of total DOM carbon, to CDP. Nuclear magnetic resonance spectra of experimental CDP and environmental PPL-DOM overlapped considerably, which indicated that even a greater proportion of PPL-DOM was likely composed of CDP. The CDP-rich DOM fraction was depleted in radiocarbon (14C age > 1500 years), a finding that supports the possible long-term accumulation of CDP in seawater. By linking a specific class of widespread biochemicals to refractory DOM, this work provides a foundation for future studies that aim to examine how persistent DOM forms in the ocean
Toward unification of the multiscale modeling of the atmosphere
As far as the representation of deep moist convection is concerned, only two kinds of model physics are used at present: highly parameterized as in the conventional general circulation models (GCMs) and explicitly simulated as in the cloud-resolving models (CRMs). Ideally, these two kinds of model physics should be unified so that a continuous transition of model physics from one kind to the other takes place as the resolution changes. With such unification, the GCM can converge to a global CRM (GCRM) as the grid size is refined. This paper suggests two possible routes to achieve the unification. ROUTE I continues to follow the parameterization approach, but uses a unified parameterization that is applicable to any horizontal resolutions between those typically used by GCMs and CRMs. It is shown that a key to construct such a unified parameterization is to eliminate the assumption of small fractional area covered by convective clouds, which is commonly used in the conventional cumulus parameterizations either explicitly or implicitly. A preliminary design of the unified parameterization is presented, which demonstrates that such an assumption can be eliminated through a relatively minor modification of the existing mass-flux based parameterizations. Partial evaluations of the unified parameterization are also presented. ROUTE II follows the "multi-scale modeling framework (MMF)" approach, which takes advantage of explicit representation of deep moist convection and associated cloud-scale processes by CRMs. The Quasi-3-D (Q3-D) MMF is an attempt to broaden the applicability of MMF without necessarily using a fully three-dimensional CRM. This is accomplished using a network of cloud-resolving grids with large gaps. An outline of the Q3-D algorithm and highlights of preliminary results are reviewed
Development of the line-focus-beam ultrasonic materialcharacterization system
科研費報告書収録論文(課題番号:13555085・基盤研究(B)(2) ・H13~H14/研究代表者:櫛引, 淳一/超高品質人工水晶の超音波マイクロスペクトロスコピー
A Correlation between the Emission Intensity of Self-Assembled Germanium Islands and the Quality Factor of Silicon Photonic Crystal Nanocavities
We present a comparative micro-photoluminescence study of the emission
intensity of self-assembled germanium islands coupled to the resonator mode of
two-dimensional silicon photonic crystal defect nanocavities. The emission
intensity is investigated for cavity modes of L3 and Hexapole cavities with
different cavity quality factors. For each of these cavities many nominally
identical samples are probed to obtain reliable statistics. As the quality
factor increases we observe a clear decrease in the average mode emission
intensity recorded under comparable optical pumping conditions. This clear
experimentally observed trend is compared with simulations based on a
dissipative master equation approach that describes a cavity weakly coupled to
an ensemble of emitters. We obtain evidence that reabsorption of photons
emitted into the cavity mode is responsible for the observed trend. In
combination with the observation of cavity linewidth broadening in power
dependent measurements, we conclude that free carrier absorption is the
limiting effect for the cavity mediated light enhancement under conditions of
strong pumping.Comment: 8 pages, 5 figure
The application of ultrasonic NDT techniques in tribology
The use of ultrasonic reflection is emerging as a technique for studying tribological contacts. Ultrasonic waves can be transmitted non-destructively through machine components and their behaviour at an interface describes the characteristics of that contact. This paper is a review of the current state of understanding of the mechanisms of ultrasonic reflection at interfaces, and how this has been used to investigate the processes of dry rough surface contact and lubricated contact. The review extends to cover how ultrasound has been used to study the tribological function of certain engineering machine elements
Dust Migration and Morphology in Optically Thin Circumstellar Gas Disks
We analyze the dynamics of gas-dust coupling in the presence of stellar
radiation pressure in circumstellar gas disks, which are in a transitional
stage between the gas-dominated, optically thick, primordial nebulae, and the
dust-dominated, optically thin Vega-type disks. Dust undergo radial migration,
seeking a stable equilibrium orbit in corotation with gas. The migration of
dust gives rise to radial fractionation of dust and creates a variety of
possible observed disk morphologies, which we compute by considering the
equilibrium between the dust production and the dust-dust collisions removing
particles from their equilibrium orbits. Sand-sized and larger grains are
distributed throughout most of the gas disk, with concentration near the gas
pressure maximum in the inner disk. Smaller grains (typically in the range of
10 to 200 micron) concentrate in a prominent ring structure in the outer region
of the gas disk (presumably at radius 100 AU), where gas density is rapidly
declining with radius. The width and density, as well as density contrast of
the dust ring with respect to the inner dust disk depend on the distribution of
gas. Our results open the prospect for deducing the distribution of gas in
circumstellar disks by observing their dust. We have qualitatively compared our
models with two observed transitional disks around HR 4796A and HD 141569A.
Dust migration can result in observation of a ring or a bimodal radial dust
distribution, possibly very similar to the ones produced by gap-opening
planet(s) embedded in the disk, or shepherding it from inside or outside. We
conclude that a convincing planet detection via dust imaging should include
specific non-axisymmetric structure following from the dynamical simulations of
perturbed disks.Comment: 27 pages, 16 figures, submitted to Ap
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