排序方式: 共有107条查询结果,搜索用时 31 毫秒
11.
In strong atmospheric turbulence, the asymptotic on-axis scintillation behaviors of Laguerre Gaussian (LG) beams are examined.
To arrive at the strong-turbulence solution, we utilize the existing filtering approach for weak-turbulence solutions and
our recently reported weak-turbulence scintillation index formula for LG beams. In the limiting case, our solution correctly
predicts the asymptotic strong-turbulence behavior of Gaussian beam wave scintillation. Investigation of the scintillations
versus the propagation distance, source size, wavelength and refractive index structure parameter lead to the conclusion that
the LG beams with higher order radial modes can provide less scintillation. The results are applicable to long-haul atmospheric
optical communication links. 相似文献
12.
We report the fabrication and characterization of a magnetically recyclable Fe3O4@Nico@Ag catalyst for reduction reactions in the liquid phase. Fe3O4 is a magnetic core and nicotinic acid was used as the linker for Ag. The characterization was done with X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, vibrating sample magnetometry (VSM), and ultraviolet-visible spectroscopy. VSM measurements proved the super-paramagnetic property of the catalyst. 相似文献
13.
M. Ayd?nZ. Durmus H. KavasB. Esat H. SözeriA. Baykal F. Y?lmazM.S. Toprak 《Polyhedron》2011,30(6):1120-1126
Poly(3-thiophene acetic acid)/Fe3O4 nanocomposite is synthesized by the precipitation of Fe3O4 in the presence of poly(3-thiophene acetic acid) (P3TAA). Structural, surface, morphological, thermal properties and conductivity characterization/evaluation of the nanocomposite were performed by XRD, FT-IR, TEM, TGA, and conductivity measurements, respectively. The capping of P3TAA around Fe3O4 nanoparticles was confirmed by FT-IR spectroscopy, the interaction being via bridging oxygens of the carboxylate and the nanoparticle surface through bidentate binding. The crystallite and particle size were obtained as 9 ± 2 nm and 11 ± 1 nm from XRD line profile fitting and TEM image analysis, respectively, which reveal nearly single crystalline nature of Fe3O4 nanoparticles. Magnetization measurements reveal that P3TAA coated magnetite particles do not saturate at higher fields. There is no coercivity and remanence revealing superparamagnetic character. Magnetic particle size calculated from the theoretical fitting as 9.1 nm which coincides the values determined from TEM micrographs and XRD line profile fitting. The comparison to the TEM particle size reveals slightly modified magnetically dead nanoparticle surface. 相似文献
14.
We have presented a method for the fabrication of poly(3-thiophenyl acetic acid) (P3TAA)-BaFe12O19 nanocomposites by the in situ polymerization of P3TAA in the presence of synthesized BaFe12O19 nanoparticles. The nanoparticles and the nanocomposite were analyzed by XRD, FTIR, TGA, TEM, VSM and conductivity techniques for structural and physicochemical characteristics. Crystallographic analysis revealed the phase as hexaferrite and X-ray line profile fitting yielded a crystallite size of 32 nm. The particles, observed by TEM, exhibit irregular shapes and sizes between 100 and 500 nm, revealing polycrystalline character when compared with the crystallite size from XRD. FTIR and TGA analysis results show that P3TAA is conjugated to the particle surface via a carboxylate group and that the composite has a polymer content of ∼10%. Magnetic hysteresis curves do not saturate at high fields, which is a characteristic feature of fine particle systems with grain sizes smaller than 1 μm. Conductivity measurements showed a semiconductor character of the nanocomposite. 相似文献
15.
C. Z. ?il H. T. Eyyubo?lu Y. Baykal O. Korotkova Y. Cai 《Applied physics. B, Lasers and optics》2010,98(1):195-202
Root mean square (rms) beam wander of J
0-Bessel Gaussian and I
0-Bessel Gaussian beams, normalized by the rms beam wander of the fundamental Gaussian beam, is evaluated in atmospheric turbulence.
Our formulation is based on the first and the second statistical moments obtained from the Rytov series. It is found that
after propagating in atmospheric turbulence, the collimated J
0-Bessel Gaussian and the I
0-Bessel Gaussian beams have smaller rms beam wander than that of the Gaussian beam, regardless of the choice of Bessel width
parameter. However, the extent of such an advantage depends on the chosen width parameter, Gaussian source size, propagation
distance and the wavelength. Focusing at finite distances of the considered beams causes the rms beam wander to decrease sharply
at the propagation distances equal to the focusing parameter. 相似文献
16.
Yangsheng Yuan Yangjian Cai Jun Qu Halil T. Eyyubo?lu Yahya Baykal 《Optics & Laser Technology》2010,42(8):1344-1348
Based on the extended Huygens–Fresnel integral and the second-order moments of the Wigner distribution function, an analytical formulae for the propagation factors (M2-factors) of coherent and partially coherent one-dimensional Hermite–Gaussian beams in a turbulent atmosphere are derived. Evolution properties of the M2-factor of the Hermite–Gaussian beam in a turbulent atmosphere are studied numerically in detail. Our results show that the M2-factor of the Hermite–Gaussian beam increases upon propagation in a turbulent atmosphere. The M2-factor of the Hermite–Gaussian beam with larger beam order (or lower coherence) increases slower that of the Hermite–Gaussian beam with smaller beam order (or higher coherence) in a turbulent atmosphere, which means that the Hermite–Gaussian beam with a larger beam order and lower coherence is less affected by a turbulent atmosphere. Our results will be useful in long-distance free-space optical communications. 相似文献
17.
Functionalized multiwall carbon nanotubes (MWCNT-COOH) were decorated with crystalline cobalt ferrite nanoparticles (CoFe2O4 NPs) by co-precipitation reaction to form MWCNT-COOH/CoFe2O4 hybrid. The hybrid was characterized by X-ray diffraction analysis, transmission electron microscopy (TEM), Fourier transfom infrared spectroscopy and vibrating sample magnetometry. The results confirmed that MWCNTs and CoFe2O4 NPs coexisted in the hybrid. The TEM results showed a thick layer of CoFe2O4 was intimately connected to the surface of MWCNTs. The saturation magnetization value of the hybrid was 11.5 emu/g. There has been a high frequency fluctuation in conductivity, however, above all dc conductivity changes and resulting activation energy is calculated from the Arrhenius plots. It is found to vary with the temperature regions. This can be attributed to the existence of a conventional temperature independent tunneling conduction mechanism, which can be also explained that the metallic conduction is a dominant mechanism around room temperature. The ac conductivity of MWCNT-COOH/CoFe2O4 hybrid might also be a consequence of the predictions of the universal dynamic response and the ‘n’ power exponents could be determined with lower concentration of the addition in the hybrids. 相似文献
18.
H.T. Eyyubolu Y. Baykal E. Sermutlu Y. Cai 《Applied physics. B, Lasers and optics》2008,92(2):229-235
For a weak turbulence propagation environment, the scintillation index of the lowest order Bessel–Gaussian beams is formulated.
Its triple and single integral versions are presented. Numerical evaluations show that at large source sizes and large width
parameters, when compared at the same source size, Bessel–Gaussian beams tend to exhibit lower scintillations than the Gaussian
beam scintillations. This advantage is lost however for excessively large width parameters and beyond certain propagation
lengths. Large width parameters also cause rises and falls in the scintillation index of off-axis positions toward the edges
of the received beam. Comparisons against the fundamental Gaussian beam are made on equal source size and equal power basis.
PACS 42.25.Dd; 42.25.Bs; 42.68.Bz; 42.68.-w 相似文献
19.
Laser array beam propagating through mouse liver tissue is investigated. The turbulence power spectrum of the liver tissue is employed in the extended Huygens–Fresnel method to obtain an optical intensity profile and beam broadening at the observation point in biological liver tissue. Variations of the beam profile and the beam broadening are simulated based on the number of beamlets, source size, wavelength and the ring radius of the array. A biological tissue, illuminated by the laser array beam, exhibits different beam profiles and beam spot radius variations when the number of beamlets, source size, wavelength and the ring radius of the laser array beam are varied. Examining these variations observed in the propagated optical beam and comparing them with the test cases, abnormalities such as cancer and tumor in a biological liver tissue can be diagnosed. 相似文献
20.
Tevhide Özkaya Abdulhadi Baykal Muhammet Sadaka Toprak 《Central European Journal of Chemistry》2008,6(3):465-469
Water-soluble Mn3O4 nanocrystals have been prepared through thermal decomposition in a high temperature boiling solvent, 2-pyrrolidone. The final
product was characterized with XRD, SEM, TEM, FTIR and Zeta Potential measurements. Average crystallite size was calculated
as ∼15 nm using XRD peak broadening. TEM analysis revealed spherical nanoparticles with an average diameter of 14±0.4 nm.
FTIR analysis indicated that 2-pyrrolidone coordinates with the Mn3O4 nanocrystals only via O from the carbonyl group, thus confining their growth and protecting their surfaces from interaction
with neighboring particles.
相似文献