共查询到20条相似文献,搜索用时 31 毫秒
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Rheinstädter MC Ollinger C Fragneto G Demmel F Salditt T 《Physical review letters》2004,93(10):108107
We have studied the collective short wavelength dynamics in deuterated 1,2-dimyristoyl-sn-glycero-3-phoshatidylcholine (DMPC) bilayers by inelastic neutron scattering. The corresponding dispersion relation variant Planck's over 2pi omega(Q) is presented for the gel and the fluid phase of this model system. The temperature dependence of the inelastic excitations indicates a phase coexistence between the two phases over a broad range and leads to a different assignment of excitations from that reported in a preceding inelastic x-ray scattering study [Phys. Rev. Lett. 86, 740 (2001)]]. As a consequence, we find that the minimum in the dispersion relation is actually deeper in the gel than in the fluid phase. Finally, we can clearly identify an additional nondispersive (optical) mode predicted by molecular dynamics simulations [Phys. Rev. Lett. 87, 238101 (2001)]]. 相似文献
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We demonstrate that chromatic dispersion and group delay ripple limit the performance of all-optical regeneration based on self-phase modulation. The level of degradation depends in detail on the type of phase distortions introduced. The regenerator performance is measured using the optical signal to noise ratio (OSNR) margin provided to the system for a given bit error ratio. The addition of chromatic dispersion and group delay ripple induces a significant reduction in this OSNR margin. 相似文献
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An analytical expression was proposed to analyze the influence of group-delay ripple (GDR) on timing jitter induced by self-phase modulation (SPM) and intra-channel cross-phase modulation (IXPM) in pseudolinear transmission systems when dispersion was compensated by chirped fiber Bragg grating (CFBG).Effects of ripple amplitude, period, and phase on timing jitter were discussed by theoretical and numerical analysis in detail. The results show that the influence of GDR on timing jitter changes linearly with the amplitude of GDR and whether it decreases or increases the timing jitter relies on the ripple period and ripple phase. Timing jitter induced by SPM and IXPM could be suppressed totally by adjusting the relative phase between the center frequency of the pulse and the ripples. 相似文献
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Fernández P. Aguado J.C. Blas J. Durán R. Durán J. De Miguel I. Lorenzo R. Abril E. 《Optical and Quantum Electronics》2004,36(1-3):57-66
We present an optimization process for the apodization strength factor of fiber Bragg grating dispersion compensators. It will be demonstrated that a proper choice of the apodization strength factor results in minimum deviation of the dispersion from the required level, maximum reflection bandwidth and minimum group delay ripple impact, thus leading to a reduction of the Q-factor penalty of the dispersion compensating system. We also discuss the influence of the fiber link length in the determination of the optimum apodization strength factor, taking into account that shorter links minimize the group delay ripple amplitude, whereas the longer ones maximize the bandwidth of interest. It is determined that a fiber link length of ~80 km can balance the requirements of group delay ripple impact and bandwidth. The results obtained through this analysis allow a faster modeling of the Bragg grating parameters in order to achieve an improved spectral performance, as well as a cost-effective fabrication process. 相似文献
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A. S. T. Pires 《Brazilian Journal of Physics》2018,48(6):543-547
We study quantum phase transitions in the easy-plane spin-one Heisenberg model on a zigzag square lattice with next-nearest-neighbor interactions at zero temperature using the SU(3) Schwinger boson formalism in a mean field approximation. We present the phase diagram and the dispersion relation for several values of the parameters. A magnetically disordered region in the phase diagram is found, even when the anisotropy parameter vanishes. 相似文献
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Supin AYa Popov VV Milekhina ON Tarakanov MB 《The Journal of the Acoustical Society of America》1999,106(5):2800-2804
Depth resolution of spectral ripples was measured in normal humans using a phase-reversal test. The principle of the test was to find the lowest ripple depth at which an interchange of peak and trough position (the phase reversal) in the rippled spectrum is detectable. Using this test, ripple-depth thresholds were measured as a function of ripple density of octave-band rippled noise at center frequencies from 0.5 to 8 kHz. The ripple-depth threshold in the power domain was around 0.2 at low ripple densities of 4-5 relative units (center-frequency-to-ripple-spacing ratio) or 3-3.5 ripples/oct. The threshold increased with the ripple density increase. It reached the highest possible level of 1.0 at ripple density from 7.5 relative units at 0.5 kHz center frequency to 14.3 relative units at 8 kHz (5.2 to 10.0 ripple/oct, respectively). The interrelation between the ripple depth threshold and ripple density can be satisfactorily described by transfer of the signal by frequency-tuned auditory filters. 相似文献
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脉冲激光辐照硅材料引起表面波纹的特性研究 总被引:5,自引:4,他引:5
叙述了激光与材料相互作用过程中引起相干受激光散射的机制,以及形成材料表面波纹的特性。在激光波长1.06μm、能量15mJ、光斑直径2mm、脉冲半峰全宽约10ns和入射方向为布儒斯特角的条件下,进行了脉冲激光辐照硅材料形成表面波纹的实验研究。在脉冲激光辐照硅材料表面功率密度略大于材料损伤阈值的条件下,发现了硅材料表面形成的平行等间距直线条纹结构。用光学显微镜和原子力显微镜分别测量了被辐照硅材料表面的波纹形貌特征。在假设硅材料表面波纹的产生与声波在材料中的传播速度有关的条件下,由声波传播速度和激光辐照硅材料的脉冲宽度较好地解释了材料表面形成条纹的宽度.并认为在形成表面波纹的过程中,热应力起主要作用。 相似文献
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光纤光栅非线性时延对啁啾的电视信号的影响 总被引:1,自引:1,他引:0
分析了有线电视系统中,用作色散补偿的光纤光栅因色散抖动对信号载波互调比产生的影响,结果显示色散抖动对有线电视信号互调比的影响随拦动幅度、抖动周期、信道数目的加而增加,信道频率的分布也对其的影响。对光栅的色散特性进行数值估算,发现常耦合系数线性啁啾光栅不能用的有线电视系统中进行色散补偿。 相似文献
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A model for ripple instabilities in granular media 总被引:1,自引:0,他引:1
O. Terzidis P. Claudin J.-P. Bouchaud 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):245-249
We extend the model of surface granular flow proposed in [#!bcre!#] to account for the effect of an external `wind', which
acts as to dislodge particles from the static bed, such that a stationary state of flowing grains is reached. We discuss in
detail how this mechanism can be described in a phenomenological way, and show that a flat bed is linearly unstable against
ripple formation in a certain region of parameter space. We focus in particular on the (realistic) case where the migration
velocity of the instability is much smaller than the grains' velocity. In this limit, the full dispersion relation can be
established. We relate the critical wave vector to the mean hopping length and to the ratio of the flight time to the `stick'
time. We provide an intuitive interpretation of the instability.
Received: 30 January 1998 / Revised: 12 May 1998 / Accepted: 8 June 1998 相似文献
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Multistage dispersion compensator using ring resonators 总被引:5,自引:0,他引:5
Madsen CK Lenz G Bruce AJ Capuzzo MA Gomez LT Nielsen TN Brener I 《Optics letters》1999,24(22):1555-1557
A compact, multichannel dispersion-compensating filter is demonstrated with D=-4200ps/nm, a +/-5-ps group delay ripple, <3-dB loss, and a 4.5-GHz passband width out of a 12.5-GHz free spectral range. We show that multistage designs can achieve a substantial increase in passband width and peak dispersion for a given group-delay ripple compared with single-stage designs. The dispersion-compensation effectiveness was demonstrated in a 320-km, seven-channel nonlinear system simulation for OC48 signals. 相似文献
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《Physics letters. A》1988,127(3):188-190
We discuss the dynamics of an interface separating two phases of a fluid close to its critical point and in the presence of a third, inert phase regarded as a solid wall. The dispersion relation for the interface undulations is derived and compared with the predictions of the theories of capillary waves and interfacial motion for a conserved order parameter. 相似文献
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Kletzing CA Bounds SR Martin-Hiner J Gekelman W Mitchell C 《Physical review letters》2003,90(3):035004
Measurements of the dispersion relation for shear Alfvén waves as a function of the perpendicular wave number are reported for the regime in which V(A) approximately V(Te). By measuring the parallel phase velocity of the waves, the measurements can be compared directly to theoretical predictions of the dispersion relation for a parameter regime in which particle kinetic effects become important. The comparison shows that the best agreement between theory and experiment is achieved when a fully complex, warm plasma dispersion relation is used. 相似文献
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de Kleine E Wit HP Avan P van Dijk P 《The Journal of the Acoustical Society of America》2001,110(2):973-980
Click-evoked and stimulus frequency otoacoustic emissions (CEOAEs and SFOAEs, respectively) were studied in humans during and after postural changes. The subjects were tilted from upright to a recumbent position (head down 30 deg) and upright again. Due to the downward posture change, CEOAEs showed a phase increase (80 deg at 1 kHz) and a level decrease (0.5 at 1 kHz), especially for frequency components below 2 kHz. For SFOAEs, the typical ripple pattern showed a positive shift along the frequency axis, which can be interpreted as a phase shift of the inner-ear component of the microphone signal (90 deg at 1 kHz). This also occurred mainly for frequencies below 2 kHz. The altered posture is thought to cause an increase of the intracranial pressure, and consequently of the intracochlear fluid pressure, which results in an increased stiffness of the stapes system. The observed emission changes are in agreement with predictions from a model in which the stiffness of the cochlear windows was altered. For CEOAEs, the time to regain stability after a downward turn was of the order of 30 s, while this took about 20 s after an upward turn. For SFOAEs, this asymmetry was not found to be present (about 11 s, both for up- and downward turns). 相似文献
17.
Chen K.-R. Dawson J.M. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1993,21(1):151-155
The ion-ripple laser (IRL) is an advanced scheme for generating coherent high-power radiation, in which a relativistic electron beam propagates obliquely through an ion ripple in a plasma. Its amplification mechanism is described by a low gain theory, while the linear growth rate is given by the dispersion relation. The efficiency of the lasing is determined by the nonlinear saturation mechanism discussed. By proper choice of device parameters, sources of microwaves, optical, and perhaps even X-rays can be made. The availability of tunable sources for wide wavelength regimes, coherence and high-power, as well as lower cost and simplicity of equipment, are emphasized 相似文献
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This paper presents an overview of fiber Bragg gratings (FBGs) fabrication principles and applications with emphasis on the
chirped FBG used for dispersion compensation in high-speed optical communication systems. We discuss the range of FBG parameters
enabled by current fabrication methods, as well as the relation between the accuracy of FBG parameters and the performance
of FBG-based dispersion compensators. We describe the theory of the group delay ripple (GDR) generated by apodized chirped
fiber gratings using the analogy between noisy gratings and superstructure Bragg gratings. This analysis predicts the fundamental
cutoff of the high frequency spatial noise of grating parameters in excellent agreement with the experimental data. We review
the iterative GDR correction technique, which further improves the FBG quality and potentially enables consistent fabrication
of FBG-based dispersion compensators and tunable dispersion compensators with unprecedented performance. 相似文献
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Pozo-Navas B Raghunathan VA Katsaras J Rappolt M Lohner K Pabst G 《Physical review letters》2003,91(2):028101
We have observed a discontinuous unbinding transition of lipid bilayer stacks composed of phosphatidylethanolamine and phosphatidylglycerol using x-ray diffraction. The unbinding is reversible and coincides with the main (L(beta)-->L(alpha)) transition of the lipid mixture. Interbilayer interaction potentials deduced from the diffraction data reveal that the bilayers in the L(beta) phase are only weakly bound. The unbinding transition appears to be driven by an abrupt increase in steric repulsion resulting from increased thermal undulations of the bilayers upon entering the fluid L(alpha) phase. 相似文献
20.
It is proposed that the high dispersion at the transmission band edges of uniform long period gratings (LPG) fabricated on relatively high Δ fibers can be used for efficient dispersion compensation. Since the transmission of LPG varies with length of the grating or refractive index modulation, we show that it is possible to tailor the transmission spectrum to obtain high transmission with constant dispersion and negligible delay ripple over a reasonable bandwidth. Since the proposed structure works in transmission it should be suitable for fiber optic communication links. 相似文献