94 research outputs found
Stochastic homogenization of the laser intensity to improve the irradiation uniformity of capsules directly driven by thousands laser beams
Illumination uniformity of a spherical capsule directly driven by laser beams has been assessed numerically. Laser facilities characterized by ND = 12, 20, 24, 32, 48 and 60 directions of irradiation with associated a single laser beam or a bundle of NB laser beams have been considered. The laser beam intensity profile is assumed super-Gaussian and the calculations take into account beam imperfections as power imbalance and pointing errors. The optimum laser intensity profile, which minimizes the root-mean-square deviation of the capsule illumination, depends on the values of the beam imperfections. Assuming that the NB beams are statistically independents is found that they provide a stochastic homogenization of the laser intensity associated to the whole bundle, reducing the errors associated to the whole bundle by the factor  , which in turn improves the illumination uniformity of the capsule. Moreover, it is found that the uniformity of the irradiation is almost the same for all facilities and only depends on the total number of laser beams Ntot = ND × NB
Is a persistent global bias necessary for the establishment of planar cell polarity?
Planar cell polarity (PCP)–the coordinated polarisation of a whole field of cells within the plane of a tissue–relies on the interaction of three modules: a global module that couples individual cellular polarity to the tissue axis, a local module that aligns the axis of polarisation of neighbouring cells, and a readout module that directs the correct outgrowth of PCP-regulated structures such as hairs and bristles. While much is known about the molecular components that are required for PCP, the functional details of–and interactions between–the modules remain unclear. In this work, we perform a mathematical and computational analysis of two previously proposed computational models of the local module (Amonlirdviman et al., Science, 307, 2005; Le Garrec et al., Dev. Dyn., 235, 2006). Both models can reproduce wild-type and mutant phenotypes of PCP observed in the Drosophila wing under the assumption that a tissue-wide polarity cue from the global module persists throughout the development of PCP. We demonstrate that both models can also generate tissue-level PCP when provided with only a transient initial polarity cue. However, in these models such transient cues are not sufficient to ensure robustness of the resulting cellular polarisation
Exawatt-Zettawatt Pulse Generation and Applications
A new amplification method, weaving the three basic compression techniques,
Chirped Pulse Amplification (CPA), Optical Parametric Chirped Pulse
Amplification (OPCPA) and Plasma Compression by Backward Raman Amplification
(BRA) in plasma, is proposed. It is called C3 for Cascaded Conversion
Compression. It has the capability to compress with good efficiency kilojoule
to megajoule, nanosecond laser pulses into femtosecond pulses, to produce
exawatt and beyond peak power. In the future, C3 could be used at large-scale
facilities such as the National Ignition Facility (NIF) or the Laser Megajoule
(LMJ) and open the way to zettawatt level pulses. The beam will be focused to a
wavelength spot size with a f#1. The very small beam size, i.e. few
centimeters, along with the low laser repetition rate laser system will make
possible the use of inexpensive, precision, disposable optics. The resulting
intensity will approach the Schwinger value, thus opening up new possibilities
in fundamental physics.Comment: 13 pages, 4 figure
Self-Assembled Polymeric Micellar Nanoparticles as Nanocarriers for Poorly Soluble Anticancer Drug Ethaselen
A series of monomethoxy poly(ethylene glycol)-poly(lactide) (mPEG-PLA) diblock copolymers were synthesized, and mPEG-PLA micelle was fabricated and used as a nanocarrier for solubilization and delivery of a promising anticancer drug ethaselen. Ethaselen was efficiently encapsulated into the micelles by the dialysis method, and the solubility of ethaselen in water was remarkably increased up to 82 μg/mL before freeze-drying. The mean diameter of ethaselen-loaded micelles ranged from 51 to 98 nm with a narrow size distribution and depended on the length of PLA block. In vitro hemolysis study indicated that mPEG-PLA copolymers and ethaselen-loaded polymeric micelles had no hemolytic effect on the erythrocyte. The enhanced antitumor efficacy and reduced toxic effect of ethaselen-loaded polymeric micelle when compared with ethaselen-HP-β-CD inclusion were observed at the same dose in H22human liver cancer cell bearing mouse models. These suggested that mPEG-PLA polymeric micelle nanoparticles had great potential as nanocarriers for effective solubilization of poorly soluble ethaselen and further reducing side effects and toxicities of the drug
Genetic Control of Organ Shape and Tissue Polarity
A combination of experimental analysis and mathematical modelling shows how the genetic control of tissue polarity plays a fundamental role in the development and evolution of form
Photocytotoxicity of mTHPC (Temoporfin) Loaded Polymeric Micelles Mediated by Lipase Catalyzed Degradation
Purpose. To study the in vitro photocytotoxicity and cellular uptake of biodegradable polymeric micelles loaded with the photosensitizer mTHPC, including the effect of lipase-catalyzed micelle degradation. Methods. Micelles of mPEG750-b-oligo(ɛ-caprolactone)5 (mPEG750-b-OCL5) with a hydroxyl (OH), benzoyl (Bz) or naphthoyl (Np) end group were formed and loaded with mTHPC by the film hydration method. The cellular uptake of the loaded micelles, and their photocytotoxicity on human neck squamous carcinoma cells in the absence and presence of lipase were compared with free and liposomal mTHPC (Fospeg ®). Results. Micelles composed of mPEG750-b-OCL5 with benzoyl and naphtoyl end groups had the highest loading capacity up to 30 % (w/w), likely due to π–π interactions between the aromatic end group and the photosensitizer. MTHPC-loaded benzoylated micelles (0.5 mg/mL polymer) did not display photocytotoxicity or any mTHPC-uptake by the cells, in contrast to free and liposomal mTHPC. After dilution of the micelles below the critical aggregation concentration (CAC), or after micelle degradation by lipase, photocytotoxicity and cellular uptake of mTHPC were restored. Conclusion. The high loading capacity of the micelles, the high stability of mTHPC-loaded micelles above the CAC, and the lipase-induced release of the photosensitizer makes these micelles very promising carriers for photodynamic therapy in vivo. KEY WORDS: drug release; enzymatic degradation; meta-tetra(hydroxyphenyl)chlorin (mTHPC); photodynamic therapy (PDT); polymeric micelles
Propagation of LIL/LMJ beams under the interaction with contamination particles and component surface defects
This paper presents recent studies of the propagation of
high-power laser beams like Laser Integration Line (LIL) and Laser MegaJoule
(LMJ) beams, when interactions occur with environmental pollution particles
and component defects. The studies are mainly achieved with the CEA-DAM
MIRĂ“ beam propagation code. The highest intensifications in the
downstream propagation are obtained for phase objects like dielectric
particles, scratches or laser damage rather than for amplitude objects like
metallic particles. Dramatic amplification of Kerr nonlinear effect leading
to beam self-focusing inside the component is predicted depending on the
particle size. The effect of statistical distributions of end-of-line phase
defects on the LIL/LMJ 0.351-m-wavelength focal spot intensity and
size is quantified
Solid state laser design for inertial confinement fusion: Trends toward power production
Diode-pumped solid state lasers have the potential efficiency and
repetition rate required for power production. One current candidate
for laser materials is an Ytterbium doped ceramic. Yb doped
sesquioxides are promising laser materials opening new fields during
the research phase to demonstrate ignition and fusion gain
(including the fast ignitor concept). We think that cryogenically
cooled diode pumped Yb: ceramic laser is the best way to operating
at high average power an that all of the operational features of the
laser can be demonstrated at an aperture scale of only 10-15 cm
- …