排序方式: 共有104条查询结果,搜索用时 15 毫秒
71.
Vasilis G. Salis Sotirios A. Mallios Ioannis G. Tigelis Aristidis S. Theodorou 《International Journal of Infrared and Millimeter Waves》2007,28(4):291-298
Optimized models for 90° polarization shift step twists for Ku, K and Ka bands are presented. The cross-section of the waveguide
employed is similar to that of a rectangular one, with the difference that the walls of the shorter side are part of a circular
one with the proper diameter. The optimized models have been found using the CST Microwave Studio simulation tool and in all
cases the return loss is kept below -20 dB for a wide range of frequency spectrum. Two examples are given, one for Ku band
and the other for K and Ka ones. 相似文献
72.
A highly sensitive compact hydrophone, based on a pi-phase-shifted fiber Bragg grating, has been developed for the measurement of wideband ultrasonic fields. The grating exhibits a sharp resonance, whose centroid wavelength is pressure sensitive. The resonance is monitored by a continuous-wave (CW) laser to measure ultrasound-induced pressure variations within the grating. In contrast to standard fiber sensors, the high finesse of the resonance--which is the reason for the sensor's high sensitivity--is not associated with a long propagation length. Light localization around the phase shift reduces the effective size of the sensor below that of the grating and is scaled inversely with the resonance spectral width. In our system, an effective sensor length of 270 μm, pressure sensitivity of 440 Pa, and effective bandwidth of 10 MHz were achieved. This performance makes our design attractive for medical imaging applications, such as optoacoustic tomography, in which compact, sensitive, and wideband acoustic detectors are required. 相似文献
73.
N Lozano WT Al-Jamal A Taruttis N Beziere NC Burton J Van den Bossche M Mazza E Herzog V Ntziachristos K Kostarelos 《Journal of the American Chemical Society》2012,134(32):13256-13258
The design of liposome-nanoparticle hybrids offers a rich toolbox for the fabrication of multifunctional modalities. A self-assembled liposome-gold nanorod hybrid vesicular system that consists of lipid-bilayer-associated gold nanorods designed to allow deep tissue detection, therapy, and monitoring in living animals using multispectral optoacoustic tomography has been fabricated and characterized in vitro and in vivo. 相似文献
74.
Stephan Kellnberger Dmitry Bozhko Andrei Chekkoury Murad Omar Daniel Razansky Vasilis Ntziachristos 《Laser \u0026amp; Photonics Reviews》2014,8(3):450-457
Miniaturized optical detectors of ultrasound represent a promising alternative to piezoelectric technology and may enable new minimally invasive clinical applications, particularly in the field of optoacoustic imaging. However, the use of such detectors has so far been limited to controlled lab environments, and has not been demonstrated in the presence of mechanical disturbances, common in clinical imaging scenarios. Additionally, detection sensitivity has been inherently limited by laser noise, which hindered the use of sensing elements such as optical fibers, which exhibit a weak response to ultrasound. In this work, coherence‐restored pulse interferometry (CRPI) is introduced – a new paradigm for interferometric sensing in which shot‐noise limited sensitivity may be achieved alongside robust operation. CRPI is implemented with a fiber‐based resonator, demonstrating over an order of magnitude higher sensitivity than that of conventional 15 MHz intravascular ultrasound probes. The performance of the optical detector is showcased in a miniaturized all‐optical optoacoustic imaging catheter. 相似文献
75.
In this Letter we present a simple and novel theoretical approach for modeling the intensity distribution from an arbitrarily shaped turbid volume in a noncontact geometry by considering diffuse light propagation in free space. This theory is validated with experiments for a diffusive volume of known geometry in a noncontact situation, both with and without the presence of an embedded absorber. The implications of this new formulation in the context of optical tomography in turbid media are discussed. 相似文献
76.
Experimental three-dimensional fluorescence reconstruction of diffuse media by use of a normalized Born approximation 总被引:5,自引:0,他引:5
We present a normalized Born expansion that facilitates fluorescence reconstructions in turbid, tissuelike media. The algorithm can be particularly useful for tissue investigations of fluorochrome distributionin vivo, since it does not require absolute photon-field measurements or measurements before contrast-agent administration. This unique advantage can be achieved only in fluorescence mode. We used this algorithm to three-dimensionally image and quantify an indocyanine fluorochrome phantom, using a novel fluorescence tomographic imager developed for animals. 相似文献
77.
Vasilis G. Gregoriou Isao Noda Anthony E. Dowrey Curtis Marcott James L. Chao Richard A. Palmer 《Journal of Polymer Science.Polymer Physics》1993,31(12):1769-1777
Dynamic mechanical analysis coupled with polarized step-scan FTIR transmission and two-dimensional correlation analysis (2D FTIR) has been used to monitor the submolecular orientational responses of the components of a semicrystalline 50 : 50 blend of low-density polyethylene (LDPE) and perdeuterated high-density polyethylene (d*-HDPE) to a small amplitude uniaxial 23.47 Hz sinusoidal mechanical strain. Perdeuteration of the HDPE component allowed the distinction of its response from that of the LDPE in the blend samples. The experiments were carried out at room temperature. Analysis of the data indicates that the crystalline parts of the two components reorient at different rates, with the functional groups of the high-density portion reorienting faster, in general, than those of the LDPE in response to the mechanical strain. © 1993 John Wiley & Sons, Inc. 相似文献
78.
Kamariotaki Maria Karaliota Alexandra Hatzipanayioti Despina Aletras Vasilis 《Transition Metal Chemistry》1998,23(5):541-546
The reaction of Vv with 3,4–dihydroxyphenylethanoic acid (3,4–DHPE) was studied by various spectroscopic techniques. Vanadium-catechol complexation is the first step, and is followed by stepwise ligand degradation, leading to several products, including AcOH. The mechanism of this degradation is investigated. 相似文献
79.
Tangoulis V Malamatari DA Soulti K Stergiou V Raptopoulou CP Terzis A Kabanos TA Kessissoglou DP 《Inorganic chemistry》1996,35(17):4974-4983
Two mixed-valence Mn(III)Mn(II) complexes and a homo-valence Mn(II) trinuclear manganese complex of stoichiometry Mn(III)Mn(II)Mn(III)(5-Cl-Hsaladhp)(2)(AcO)(4)(MeOH)(2).4CH(3)OH (1a), Mn(III)Mn(II)Mn(III) (Hsaladhp)(2)(AcO)(2)(5-Cl-Sal)(2)(thf)(2) (3a) and Mn(II)Mn(II)Mn(II) (AcO)(6)(pybim)(2) (1b) where H(3)saladhp is a tridentate Schiff base ligand and pybim a neutral bidentate donor ligand, have been structurally characterized by using X-ray crystallography. The structurally characterized mixed-valence complexes have strictly 180 degrees Mn(III)-Mn(II)-Mn(III) angles as required by crystallographic inversion symmetry. The complexes are valence trapped with two terminal Mn(III) ions showing Jahn-Teller distortion along the acetate or salicylate-Mn(III)-X axis. The Mn.Mn separation is 3.511 ? and 3.507 ? respectively. The mixed-valence complexes have S = (3)/(2) ground state and the homovalence complex S = (5)/(2), with small antiferromagnetic exchange J couplings, -5.6 and -1.8 cm(-1), respectively, while the powder ESR spectra at 4 K show a broad low field signal with g approximately 4.3 for Mn(III)Mn(II)Mn(III) and a broad temperature-dependent signal at g = 2 for Mn(II)Mn(II)Mn(II). Crystal data for 1a: [C(36)H(60)O(20)N(2)Cl(2)Mn(3)], triclinic, space group P&onemacr;, a = 9.272(7) ?, b = 11.046(8) ?, c = 12.635(9) ?, alpha = 76.78(2) degrees, beta = 81.84(2) degrees, gamma = 85.90(2) degrees, Z = 1. Crystal data for 3a: [C(48)H(56)O(18)N(2)Cl(2)Mn(3)], monoclinic, space group P2(1)/n, a = 8.776(3) ?, b = 22.182(7) ?, c = 13.575(4) ?, beta = 94.44(1) degrees, Z = 2. Crystal data for 1b: [C(36)H(36)O(12)N(6)Mn(3)], triclinic, space group P&onemacr;, a = 13.345(6) ?, b = 8.514(4) ?, c = 9.494(4) ?, alpha = 75.48(1) degrees, beta = 75.83(1) degrees, gamma = 76.42(1) degrees, Z = 1. 相似文献
80.
A new 4-(N-methylpiperazine)-N-allyl-1,8-naphthalimide with intense yellow-green fluorescence has been synthesized. Then it has been copolymerized with styrene and methylmetacrylate. The photophysical characteristics of the fluorescent dye and its copolymers (poly(St-co-NI) and poly(MAA-co-NI)) have been determined viewing their sensor properties for protons and transition metal cations (Cu2+, Fe3+ and Zn2+). Fluorescence enhancement is the photophysical response of the 4-(N-methylpiperazine)-N-allyl-1,8-naphthalimide to the presence of metal cations and protons, while fluorescence quenching is observed for both copolymers. 相似文献