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排序方式: 共有88条查询结果,搜索用时 31 毫秒
41.
Sergio Padovan Dr. Carla Carrera Dr. Valeria Catanzaro Dr. Cristina Grange Dr. Malvina Koni Dr. Giuseppe Digilio 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(48):12289-12293
One possibility for the non-invasive imaging of encapsulated cell grafts is to label the lumen of cell embedding capsules with a redox-responsive probe, as an increased extracellular reducing potential can be considered as a marker of hypoxia-induced necrosis. A Gd(III)-HPDO3A-like chelate has been conjugated to glycol-chitosan through a redox-responsive disulphide bond to obtain a contrast agent for Magnetic Resonance Imaging (MRI). Such a compound can be interspersed with fibroblasts within the lumen of alginate-chitosan capsules. Increasing reducing conditions within the extracellular microenvironment lead to the reductive cleavage of the disulphide bond and to the release of gadolinium in the form of a low molecular weight, non-ionic chelate. The efflux of such chelate from capsules is readily detected by a decrease of contrast enhancement in T1-weighted MR images. 相似文献
42.
We report an increase in pulse energy to 5.1 microJ obtained directly from a femtosecond diode-pumped Yb:YAG thin disk laser without external amplification. Stable passive mode locking was obtained with a semiconductor saturable absorber mirror (SESAM). The laser delivers 63 W of average output power in a nearly diffraction-limited beam (M2=1.1) at a center wavelength of 1030 nm. The pulse repetition rate is 12.3 MHz, and the pulses have a duration of 800 fs, which results in a peak power of 5.6 MW. The laser was operated in a box flooded with helium because the nonlinearity of air was found to be a limiting factor for the stability of the pulse formation at increasing pulse energies. 相似文献
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The validity of the “bubble method” is discussed for the measurements of contact angles between a crystal and its own melt and for the observations of interface morphology. Experiments were done on KCl crystals pulled in various directions. Gold decoration technique was employed to observe the surface morphology. The measurement of the contact angle a is valid for the 〈100〉 axis of pulling but lacks accuracy for the other directions. The {100} interface shows two dimensional nucleation, curved growth fronts and no trace of a liquid layer. The {110}, {310}and {111} interfaces show steps and pyramids constituted by {100} facets, completely stripped of the melt, and “structureless” regions resulting from freely frozen liquid surface. 相似文献
45.
Billia B Bergeon N Thi HN Jamgotchian H Gastaldi J Grange G 《Physical review letters》2004,93(12):126105
The dynamical interaction between columnar interface microstructure and self-stress, resulting in unforeseen mechanical deformation phenomena, is brought to light by means of in situ and real-time synchrotron x-ray topography during directional solidification of dilute aluminum alloys. Beyond long-known local mechanical stresses, global mechanical constraints are found to be active. In particular, column rotation results from deformation caused by the mechanical moments associated with the very growth shape, namely, the cumulative torque acting together with the cumulative bending moment under gravity. A basic model allowing for a qualitative explanation of the observed distinctive features of the self-stress effects on microstructure dynamics is proposed. 相似文献
46.
Semiconductor saturable absorber mirror (SESAM) devices have become a key component of ultrafast passive mode-locked laser sources. Here we describe in more detail how the key SESAM parameters such as saturation fluence, modulation depth, and nonsaturable losses are measured with a high accuracy. These parameters need to be known and controlled to obtain stable pulse generation for a given laser. A high-precision, wide dynamic range setup is required to measure this nonlinear reflectivity of saturable absorbers. The challenge to measure a low modulation depth and key measures necessary to obtain an accurate calibration are described in detail. The model function for the nonlinear reflectivity is based on a simple two-level travelling wave system. We include spatial beam profiles, nonsaturable losses and higher-order absorption, such as two-photon absorption and other induced absorption. Guidelines to extract the key parameters from the measured data are given. PACS 07.60.Hv; 42.65.Re; 42.70.Nq 相似文献
47.
R. Grange M. Haiml R. Paschotta G.J. Spühler L. Krainer M. Golling O. Ostinelli U. Keller 《Applied physics. B, Lasers and optics》2005,80(2):151-158
The reflectivity of a semiconductor saturable absorber mirror (SESAM) is generally expected to increase with increasing pulse energy. However, for higher pulse energies the reflectivity can decrease again; we call this a roll-over of the nonlinear reflectivity curve caused by inverse saturable absorption. We show for several SESAMs that the measured roll-over is consistent with two-photon absorption only for short (femtosecond) pulses, while a stronger (yet unidentified) kind of nonlinear absorption is dominant for longer (picosecond) pulses. These inverse saturable absorption effects have important technological consequences, e.g. for the Q-switching dynamics of passively mode-locked lasers. A simple equation using only measurable SESAM parameters and including inverse saturable absorption is derived for the Q-switched mode-locking threshold. We present various data and discuss the sometimes detrimental effects of this roll-over for femtosecond high repetition rate lasers, as well as the potentially very useful consequences for passively mode-locked multi-GHz lasers. We also discuss strategies to enhance or reduce this induced absorption by using different SESAM designs or semiconductor materials. PACS 42.60.Fc; 42.70.Nq; 78.20.Ci 相似文献
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Mishra A. Jahan CS A. Kesarwani S. Raval H. Kumar S. Meena J. 《The European Physical Journal A - Hadrons and Nuclei》2019,55(6):1-8
The European Physical Journal A - In this paper, we investigated the spectroscopy of heavy tetraquarks through a relativistic diquark-antidiquark model. To this aim, the two-bosonic Klein-Gordon... 相似文献
50.
Willard M Freeman Melinda E Lull Kruti M Patel Robert M Brucklacher Drake Morgan David CS Roberts Kent E Vrana 《BMC neuroscience》2010,11(1):29