323 research outputs found
Mono- and Biexponential Luminescence Decays of Individual Single-Walled Carbon Nanotubes
We have studied the exciton recombination dynamics of individual (6,4) and (6,5) single-walled carbon nanotubes embedded in aqueous gels or deposited on glass surfaces. CoMoCat nanotubes systematically display short monoexponential photoluminescence (PL) decays presumably due to defects introduced during their synthesis. In contrast HiPco nanotubes can either display mono- or biexponential PL decays depending on the environmental conditions. Transition from bi- to monoexponential decays can be reproduced by a simple three level model taking into account defect-dependent nonradiative decay mechanisms
Osteoconductive properties of poly(96L/4D-lactide)/beta-tricalcium phosphate in long term animal model
The objective of this study was to determine the effect of calcium phosphate mineral content on the bone in-growth at the expense of composite of co-polylactide polymer charged with 2 different ratios of β-TCP granules (10 and 24 w-% of β-TCP). The evaluation was realized in a long term rabbit bone model. After 24, 48 and 76 weeks, the implants were examined by micro CT, scanning electron microscopy (SEM) using backscattered electron (BSE) and light microscopy (polarized and blue light microscopy). No foreign body reaction was detected during the 76 weeks follow-up in any of the test samples. Polymer hydrolysis began at approximately 24 weeks, by 76 weeks, the pure polymer implant had begun to release P(96L/4D)LA particles and show signs of peripheral localized bone resorption. A decrease in the amount of CaP was noticed between 24 and 76 weeks in both 10 wt-% and 24 wt-% β-TCP/P(96L/4D)LA composites. The study showed that the highest bone in-growth was with 24 wt-% β-TCP/P(96L/4D)LA composite. Bone in-growth and mineralization were evident for the composites associated with specific peripheral bone architecture. Fluorescent labelling demonstrated high bone in-growth and remodeling at the interface, while for pure co-polymer no bone remodeling or bone activity was maintained after 48 weeks. The study demonstrated the positive effect of calcium phosphate content into P(96L/4D)LA. This kind of composite is a suitable resorbable osteoconductive matrix, which provides long term stability required for ligament fixation device
Photoswitchable single-walled carbon nanotubes for super-resolution microscopy in the near-infrared
The design of single-molecule photoswitchable emitters was the first milestone toward the advent of single-molecule localization microscopy, setting a new paradigm in the field of optical imaging. Several photoswitchable emitters have been developed, but they all fluoresce in the visible or far-red ranges, missing the desirable near-infrared window where biological tissues are most transparent. Moreover, photocontrol of individual emitters in the near-infrared would be highly desirable for elementary optical molecular switches or information storage elements since most communication data transfer protocols are established in this spectral range. Here, we introduce a type of hybrid nanomaterials consisting of single-wall carbon nanotubes covalently functionalized with photoswitching molecules that are used to control the intrinsic luminescence of the single nanotubes in the near-infrared (beyond 1 μm). Through the control of photoswitching, we demonstrate super-localization imaging of nanotubes unresolved by diffraction-limited microscopy
Reconstruction of irradiated bone segmental defects with a biomaterial associating MBCP+®, microstructured collagen membrane and total bone marrow grafting: An experimental study in rabbits
The bone tissue engineering models used today are still a long way from any oncologic application as immediate postimplantation irradiation would decrease their osteoinductive potential. The aim of this study was to reconstruct a segmental critical size defect in a weight-bearing bone irradiated after implantation. Six white New Zealand rabbits were immediately implanted with a biomaterial associating resorbable collagen membrane EZ® filled and micro-macroporous biphasic calcium phosphate granules (MBCP+®). After a daily schedule of radiation delivery, and within 4 weeks, a total autologous bone marrow (BM) graft was injected percutaneously into the center of the implant. All the animals were sacrificed at 16 weeks. Successful osseous colonization was found to have bridged the entire length of the defects. Identical distribution of bone ingrowth and residual ceramics at the different levels of the implant suggests that the BM graft plays an osteoinductive role in the center of the defect. Periosteum-like formation was observed at the periphery, with the collagen membrane most likely playing a role. This model succeeded in bridging a large segmental defect in weight-bearing bone with immediate postimplantation fractionated radiation delivery. This has significant implications for the bone tissue engineering approach to patients with cancer-related bone defects
Modeling and Optimization of Lactic Acid Synthesis by the Alkaline Degradation of Fructose in a Batch Reactor
The present work deals with the determination of the optimal operating conditions of lactic acid synthesis by the alkaline degradation of fructose. It is a complex transformation for which detailed knowledge is not available. It is carried out in a batch
or semi-batch reactor. The ‘‘Tendency Modeling’’ approach, which consists of the development of an approximate stoichiometric and kinetic model, has been used.
An experimental planning method has been utilized as the database for model development.
The application of the experimental planning methodology allows comparison between the experimental and model response. The model is then used in an optimization procedure to compute the optimal process. The optimal control problem is converted into a nonlinear programming problem solved using the sequencial quadratic programming procedure coupled with the golden search method. The strategy developed allows simultaneously optimizing the different variables, which may be constrained. The validity of the methodology is illustrated by the determination
of the optimal operating conditions of lactic acid production
Using atomic interference to probe atom-surface interaction
We show that atomic interference in the reflection from two suitably
polarized evanescent waves is sensitive to retardation effects in the
atom-surface interaction for specific experimental parameters. We study the
limit of short and long atomic de Broglie wavelength. The former case is
analyzed in the semiclassical approximation (Landau-Zener model). The latter
represents a quantum regime and is analyzed by solving numerically the
associated coupled Schroedinger equations. We consider a specific experimental
scheme and show the results for rubidium (short wavelength) and the much
lighter meta-stable helium atom (long wavelength). The merits of each case are
then discussed.Comment: 11 pages, including 6 figures, submitted to Phys. Rev. A, RevTeX
sourc
Imaging Gold Nanoparticles in Living Cells Environments using Heterodyne Digital Holographic Microscopy
This paper describes an imaging microscopic technique based on heterodyne
digital holography where subwavelength-sized gold colloids can be imaged in
cell environment. Surface cellular receptors of 3T3 mouse fibroblasts are
labeled with 40 nm gold nanoparticles, and the biological specimen is imaged in
a total internal reflection configuration with holographic microscopy. Due to a
higher scattering efficiency of the gold nanoparticles versus that of cellular
structures, accurate localization of a gold marker is obtained within a 3D
mapping of the entire sample's scattered field, with a lateral precision of 5
nm and 100 nm in the x,y and in the z directions respectively, demonstrating
the ability of holographic microscopy to locate nanoparticles in living cells
environments
A {\mu}-TPC detector for the characterization of low energy neutron fields
The AMANDE facility produces monoenergetic neutron fields from 2 keV to 20
MeV for metrological purposes. To be considered as a reference facility,
fluence and energy distributions of neutron fields have to be determined by
primary measurement standards. For this purpose, a micro Time Projection
Chamber is being developed to be dedicated to measure neutron fields with
energy ranging from 8 keV up to 1 MeV. In this work we present simulations
showing that such a detector, which allows the measurement of the ionization
energy and the 3D reconstruction of the recoil nucleus, provides the
determination of neutron energy and fluence of these neutron fields
Optical binding of particles with or without the presence of a flat dielectric surface
Optical fields can induce forces between microscopic objects, thus giving
rise to new structures of matter. We study theoretically these optical forces
between two spheres, either isolated in water, or in presence of a flat
dielectric surface. We observe different behavior in the binding force between
particles at large and at small distances (in comparison with the wavelength)
from each other. This is due to the great contribution of evanescent waves at
short distances. We analyze how the optical binding depends of the size of the
particles, the material composing them, the wavelength and, above all, on the
polarization of the incident beam. We also show that depending on the
polarization, the force between small particles at small distances changes its
sign. Finally, the presence of a substrate surface is analyzed showing that it
only slightly changes the magnitudes of the forces, but not their qualitative
nature, except when one employs total internal reflection, case in which the
particles are induced to move together along the surface.Comment: 8 pages, 9 figures, and 1 tabl
Mandibular Segmental Defect Regenerated With Macroporous Biphasic Calcium Phosphate, Collagen Membrane, and Bone Marrow Graft in Dogs
OBJECTIVE:
To reconstruct segmental mandibulectomy using calcium phosphate ceramics and collagen membrane with a delayed bone marrow grafting in experimental animals.
DESIGN:
Defects of segmental mandibulectomy were filled with calcium phosphate granules and wrapped with a collagen membrane in 4 dogs and left empty as a control in 2 dogs. Two months later, a bone marrow graft was injected into the center of the implants. Animals were humanely killed after a 16-week delay.
SUBJECTS:
Six adult beagles were included in this study.
INTERVENTION:
Segmental mandibulectomy.
MAIN OUTCOME MEASURE:
Bone ingrowth and material resorption in the reconstructed segment.
RESULTS:
Successful osseous colonization bridged the whole length of the defects. The good new bone formation at the center and the periosteum-like formation at the periphery suggest the osteoinductive role of the bone marrow graft and the healing scaffold role of the membrane.
CONCLUSIONS:
This model succeeded in regenerating a large segmental defect in the mandible. An investigation with a postimplantation radiation delivery schedule is required with the use of this model, which should be considered as a preclinical study for a bone tissue engineering approach in patients with cancer-related bone defects
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