Application of the Grey topological method to predict the effects of ship pitching

Ship motion,with six degrees of freedom,is a complex stochastic process.Sea wind and waves are the primary influencing factors.Prediction of ship motion is significant for ship navigation.To eliminate errors,a path prediction model incorporating ship pitching was developed using the Gray topological method,after analyzing ship pitching motions.With the help of simple introduction to Gray system theory,we selected a group of threshold values.Based on an analysis of ship pitch angle sequences over 40 second intervals,a Grey metabolism GM(1,1) model was established according to the time-series which every threshold corresponded to.Forecasting future ship motion with the GM(1,1) model allowed drawing of the forecast curve with effective forecasting points.The precision of the test results show that the model is accurate,and the forecast results are reliable.

Selective excitation of molecular mode in a mixture by femtosecond resonance-enhanced coherent anti-Stokes Raman scattering spectroscopy

Femtosecond time-resolved coherent anti-Stokes Raman scattering （CARS） spectroscopy is used to investigate gaseous molecular dynamics. Due to the spectrally broad laser pulses, usually poorly resolved spectra result from this broad spectroscopy. However, it can be demonstrated that by the electronic resonance enhancement optimization control a selective excitation of specific vibrational mode is possible. Using an electronically resonance-enhanced effect, iodine molecule specific CARS spectroscopy can be obtained from a mixture of iodine-air at room temperature and a pressure of 1 atm （corresponding to a saturation iodine vapour as low as about 35 Pa）. The dynamics on either the electronically excited state or the ground state of iodine molecules obtained is consistent with previous studies （vacuum, heated and pure iodine） in the femtoseeond time resolved CARS spectroscopy, showing that an effective method of suppressing the non-resonant CARS background and other interferences is demonstrated.

Coherent coupling between vibrational modes of C-H bonds at different positions studied by femtosecond time-resolved coherent anti-Stokes Raman scattering

We performed femtosecond time-resolved coherent anti-Stokes Raman scattering （fs-CARS） measurements on liquid toluene and PVK film. For both samples, we selectively excited the CH stretching vibrational modes and observed the expected quantum beat signals. The frequency of the well-defined beats is in good agreement with the energy difference between the two simultaneously excited modes, which demonstrates that a coherent coupling between the vibrational modes of the C H chemical bonds exists at the different positions of the molecules. The dephasing times of the excited modes are obtained simultaneously.

Theoretical and experimental investigations of coherent phonon dynamics in sapphire crystal using femto-second time-resolved coherent anti-Stokes Raman scattering

We report on the theoretical and the experimental investigations of the coherent phonon dynamics in sapphire crystal using the femtosecond time-resolved coherent anti-Stokes Raman scattering （fs-CARS） technique. The temporal chirped white-light continuum （WLC） is used for the Stokes pulse, therefore we can perform the selective excitation of the phonon modes without using a complicated laser system. The expected quantum beat phenomenon is clearly observed. The theoretical formulas consist very well with the experimental results. The dephasing times of the excited phonon modes, the wavenumber difference, and the phase shift between the simultaneously excited modes are obtained and discussed. This work opens up a way to study directly high-frequency coherent phonon dynamics in bulk crystals on a femtosecond time scale and is especially helpful for understanding the nature of coherent phonons.

Terahertz beats of vibrational modes in methanol and ethanol selectively excited by tr-CARS technique

A recently developed time-resolved coherent anti-Stokes Raman scattering(tr-CARS) technique allows the measurement of vibrational coherences with high frequency differences with the ambient environment.The method is based on the short spatial extension of femtosecond pulses with a broadband tunable nonlinear optical parametric amplifier(NOPA) and an internal time delay between the probe and pump/Stokes pulse pair in the CARS process.The different beat frequencies between Raman modes can be selectively detected as oscillations in the tr-CARS transient signal with the broadband tunable NOPA.In this work,we aim at the Raman C-H stretching vibrations from 2800 cm 1 to 3000 cm 1,within which the different vibrational modes in both ethanol and methanol are selectively excited and simultaneously detected.The high time resolution of the experimental set-up allows one to monitor the vibrational coherence dynamics and to observe the quantum beat phenomena on a terahertz scale.This investigation indicates that the femtosecond tr-CARS technique is a powerful tool for the real-time monitoring and detection of molecular and biological agents,including airborne contaminants such as bacterial spores,viruses and their toxins.

Measurements of the concentration of organic solutions by femtosecond time-resolved ERE-CARS

A variant of all-resonant CARS named electronic-resonant enhancement CARS(ERE-CARS) is applied to measure the methanol-water solution concentration at room temperature.The measurements are performed using the ERE-CARS signal of the Raman vibrations near the C-H stretching modes(at 2835 and 2942 cm 1) in methanol.By changing the timing(t>0) of the laser pulses of this non-degenerate four wave mixing technique,the concentration information based on the vibrational dynamics of the C-H bonds can be successfully detected as the frequency-spread dephasing rate during the first few hundred fs in the ERE-CARS signal with high sensitivity and accuracy.Femtosecond time-resolved ERE-CARS technique is applied to the concentration analysis of a mixture of the organic solution.This investigation indicates that femtosecond time-resolved ERE-CARS technique might be a powerful tool for real-time detection for solution concentration of different liquids.

Effect of time bin size on accuracy of streak tube imaging lidar

Streak tube imaging lidar （STIL） is an active imaging system that has a high range accuracy with tile use of a pulsed lapser transmitter and streak tube receiver to produce 3D range inlages. This work investigates the effect of tile time bin size oil the range accuracy of STIL systems based on the peak detection algorithm. The nunlerical simulation indicates that the time bin size has a significant effect on the range aceuracy, resulting in a modified analytical estimate of the range error. An indoor experilnent with a planar target is carried out to validate the theory that shows the linear relationship between tile range error and the time bin size. Finer 3D depth iinages of a fist model are acquired by using a smaller time bin size and the best range error of 0.003 In is achieved with the optimal time bin size of 0.07 ns.