Experimental Protection of the Spin Coherence of a Molecular Qubit Exceeding a Millisecond

Molecular qubits are promising as they can benefit from tailoring and versatile design of chemistry. It is essential to reduce the decoherence of molecular qubits caused by their interactions with the environment. Herein the dynamical decoupling(DD) technique is utilized to combat such decoherence. The coherence time for a transitionmetal complex(PPh_4)_2[Cu(mnt)_2] is prolonged from 6.8 μs to 1.4 ms. The ratio of the coherence time and the length of π/2 pulse, defined as the single qubit figure of merit(Q_M), reaches 1.4 × 10~5, which is 40 times greater than what previously reported for this molecule. Our results show that molecular qubits, with milliseconds coherence time, are promising candidates for quantum information processing.     

Experimental study of the dependences of retrieval efficiencies on time delay between magneto-optical-trap being turned off and optical storage

We report an experimental study of electromagnetically induced transparency(EIT)-based light storage in a cloud of cold atoms loaded into a magneto-optical-trap(MOT). After the MOT is turned off, the retrieval efficiencies of rightand left-circularly polarized signal light fields each as a function of storage time are measured for different time delays between MOT off and the storage event, respectively. The results show that in the delay ranging from 0.015 ms to 3.5 ms,the retrieval efficiency for a zero-storage time(0.2 μs) and the storage lifetime can exceed 15% and 1.4 ms, respectively.The measured results will provide important help for optimizing the storage of the polarized entanglement photons in cold atomic ensembles.     

Refractivity estimation from radar sea clutter

This paper addresses the problem of estimating lower atmospheric refractivity under the nonstandard propagation conditions frequently encountered in low altitude maritime radar applications. The vertical structure of the refractive environment is modeled by using a five-parameter model, and the horizontal structure is modeled as range-independent. The electromagnetic propagation in the troposphere is simulated by using a split-step fast Fourier transform based on parabolic approximation to the wave equation. A global search marked as a modified genetic algorithm (MGA) for the 5 environmental parameters is performed by using a genetic algorithm (GA) integrated with a simulated annealing technique. The retrieved results from simulated runs demonstrate the ability of this method to make atmospheric refractivity estimations. A comparison with the classical GA and the Bayesian Markov Chain Monte Carlo (Bayesian-MCMC) technique shows that the MGA can not only shorten the inverse time but also improve the inverse precision. For real data cases, the inversion values do not match the reference data very well. The inverted profile, however, can be used to synoptically describe the real refractive structure.     

Photoacoustic Imaging of Animals with an Annular Transducer Array

A photoacoustic system with an annular transducer array is presented for rapid, high-resolution photoacoustic tomography of animals. An eight-channel data acquisition system is applied to capture the photoacoustic signals by using multiplexing and the total time of data acquisition and transferring is within 3 s. A limited-view filtered back projection algorithm is used to reconstruct the photoacoustic images. Experiments are performed on a mouse head and a rabbit head and clear photoacoustic images are obtained. The experimental results demonstrate that this imaging system holds the potential for imaging the human brain.     

EFFECT OF DIELECTRIC CONSTANT ON THE EXCITON GROUND STATE ENERGY OF CdSe QUANTUM DOTS

The B-spline technique is used in the calculation of the exciton ground state energy based on the effective mass approximation (EMA) model. The exciton is confined in CdSe microspherical crystallites with a finite-height potential wall (dots). In this approach, (a) the wave function is allowed to penetrate to the outside of the dots; (b) the dielectric constants of the quantum dot and the surrounding material are considered to be different; and (c) the dielectric constant of the dots are size-dependent. The exciton energies as functions of radii of the dots in the range 0.5-3.5 nm are calculated and compared with experimental and previous theoretical data. The results show that: (1) The exciton energy is convergent as the radius of the dot becomes very small. (2) A good agreement with the experimental data better than other theoretical results is achieved. (3) The penetration (or leaking) of the wave function and the difference of the dielectric constants in different regions are necessary for correcting the Coulomb interaction energy and reproducing experimental data. (4) The EMA model with B-spline technique can describe the status of excition confined in quantum dot very well.     

Time—Frequency Analysis of Electromagnetic Pulse Response from a Spherical Target

Transient backscattering from a spherical target under incidence of an electromagnetic pulse is studied.The target can be a perfectly conducting sphere,a dielectric sphere or a dielectric spherical shell.To understand the scattering mechanism from transient impulse echoes for target detection,both the short-time Fourier transform(STFT) and the wavelet transfrom(WT) are applied to retrieval of scattering information from the backscattering data.Analysis in both the time and frequency domains demonstrates that the WT is more feasible than the STFT to clarifying scattering process of the scatterer because of its excellent multi-resolution characteristic.This technique shall be helpful for scattering analysis and detection of more complex single or multi-targets.     

Effect of Pulse Width and Fluence of Femtosecond Laser on Electron--Phonon Relaxation Time

The electron phonon relaxation time as functions of pulse width and fluence of femtosecond laser is studied based on the two-temperature model. The two-temperature model is solved using a finite difference method for copper target. The temperature distribution of the electron and the lattice along with space and time for a certain laser fluence is presented. The time-dependence of lattice and electron temperature of the surface for different pulse width and different laser fluence are also performed, respectively. Moreover, the variation of heat-affected zone per pulse with laser Auence is obtained. The satisfactory agreement between our numerical results and experimental data indicates that the electron-phonon relaxation time is reasonably accurate with the influences of pulse width and Auence of femtosecond laser.     

Feasibility of similarity coefficient map for improving morphological evaluation of T2* weighted MRI for renal cancer

The purpose of this paper is to investigate the feasibility of using a similarity coefficient map(SCM) in improving the morphological evaluation of T2* weighted(T2*W) magnatic resonance imaging(MRI) for renal cancer.Simulation studies and in vivo 12-echo T2*W experiments for renal cancers were performed for this purpose.The results of the first simulation study suggest that an SCM can reveal small structures which are hard to distinguish from the background tissue in T2*W images and the corresponding T2* map.The capability of improving the morphological evaluation is likely due to the improvement in the signal-to-noise ratio(SNR) and the carrier-to-noise ratio(CNR) by using the SCM technique.Compared with T2* W images,an SCM can improve the SNR by a factor ranging from 1.87 to 2.47.Compared with T2* maps,an SCM can improve the SNR by a factor ranging from 3.85 to 33.31.Compared with T2*W images,an SCM can improve the CNR by a factor ranging from 2.09 to 2.43.Compared with T2* maps,an SCM can improve the CNR by a factor ranging from 1.94 to 8.14.For a given noise level,the improvements of the SNR and the CNR depend mainly on the original SNRs and CNRs in T2*W images,respectively.In vivo experiments confirmed the results of the first simulation study.The results of the second simulation study suggest that more echoes are used to generate the SCM,and higher SNRs and CNRs can be achieved in SCMs.In conclusion,an SCM can provide improved morphological evaluation of T2*W MR images for renal cancer by unveiling fine structures which are ambiguous or invisible in the corresponding T2*W MR images and T2* maps.Furthermore,in practical applications,for a fixed total sampling time,one should increase the number of echoes as much as possible to achieve SCMs with better SNRs and CNRs.     

Finite-time Mittag-Leffler synchronization of fractional-order delayed memristive neural networks with parameters uncertainty and discontinuous activation functions

The finite-time Mittag-Leffler synchronization is investigated for fractional-order delayed memristive neural networks(FDMNN)with parameters uncertainty and discontinuous activation functions.The relevant results are obtained under the framework of Filippov for such systems.Firstly,the novel feedback controller,which includes the discontinuous functions and time delays,is proposed to investigate such systems.Secondly,the conditions on finite-time Mittag-Leffler synchronization of FDMNN are established according to the properties of fractional-order calculus and inequality analysis technique.At the same time,the upper bound of the settling time for Mittag-Leffler synchronization is accurately estimated.In addition,by selecting the appropriate parameters of the designed controller and utilizing the comparison theorem for fractional-order systems,the global asymptotic synchronization is achieved as a corollary.Finally,a numerical example is given to indicate the correctness of the obtained conclusions.     

Chaos game representation （CGR）-walk model for DNA sequences

Chaos game representation (CGR) is an iterative mapping technique that processes sequences of units, such as nucleotides in a DNA sequence or amino acids in a protein, in order to determine the coordinates of their positions in a continuous space. This distribution of positions has two features: one is unique, and the other is source sequence that can be recovered from the coordinates so that the distance between positions may serve as a measure of similarity between the corresponding sequences. A CGR-walk model is proposed based on CGR coordinates for the DNA sequences. The CGR coordinates are converted into a time series, and a long-memory ARFIMA (p, d, q) model, where ARFIMA stands for autoregressive fractionally integrated moving average, is introduced into the DNA sequence analysis. This model is applied to simulating real CGR-walk sequence data of ten genomic sequences. Remarkably long-range correlations are uncovered in the data, and the results from these models are reasonably fitted with those from the ARFIMA (p, d, q) model.     

Robust time reversal focusing based on Maximin criterion in a waveguide with uncertain water depth

Time reversal processing(TRP) might be regarded as matched field processing with known environmental knowledge.However,the performance of TRP is degraded in an uncertain environment.A technique based on the Maximin criterion is proposed for enhancing the robustness of TRP in a waveguide with uncertain water depth.The relationship between the water depth and the focal spot translation is examined based on the waveguide-invariant theory.Then the time reversal transmission scheme with the Maximin criterion is performed to maximize the minimum transmission power on a target of interest.At the receiving end,coherent summation operation is carried out over the received data by a reception focusing bank.If it is necessary to enhance the target echo further,the iterative time reversal can be considered where the target echo corresponding to the first time reversal transmission is regarded as a secondary source.Numerical simulations and experimental results of the target localization in a waveguide tank have verified the effectiveness of robust TRP.     

Chirp-coded robust synthetic aperture technique for medical endoscopic ultrasonography

A chirp-coded robust synthetic aperture(CRSA) technique for medical endoscopic ultrasonography is presented.The technique uses chirp-coded excitation and pulse compression to enhance the robustness of synthetic aperture technique.The effect of resolution enhancement by the CRSA technique is demonstrated by both Field II simulation and practical experiment. Data for 6 point targets is simulated and the performance of CRSA is compared with that of conventional barker-coded synthetic aperture technique(BSA).Nylon ropes are examined by a single element transducer centered at 8 MHz.Both simulation and experimental results indicated that CRSA can improve resolution of ultrasound images with good robustness as compared with the conventional BSA technique.The lateral resolution is upgraded to 1.4 mm from 1.8 mm.The main-lobe broadening and SNR degradation are 0.04 mm and 0.2 dB respectively,which are 0.95 mm and 3.6 dB lower than those of BSA,when the sound speed error is 6%of the true value 1540 m/s.It therefore can be concluded that CRSA has more robustness than BSA against the disturbance caused by sound speed errors.     

Curvelet-based palm vein biometric recognition

<正>A novel personal recognition system utilizing palm vein patterns and a novel technique to analyze these vein patterns is presented.The technique utilizes the curvelet transform to extract features from vein patterns to facilitate recognition.This technique provides optimally sparse representations of objects along the edges.Principal component analysis(PCA) is applied on curvelet-decomposed images for dimensionality reduction.A simple distance-based classifier,such as the nearest-neighbor(NN) classifier,is employed. The experiments are performed using our palm vein database.Experimental results show that the algorithm reaches a recognition accuracy of 99.6%on the database of 500 distinct subjects.     

Experimental research of circular incoherently synthetic aperture imaging ladar using chirped-laser and heterodyne detection

Synthetic aperture imaging ladar (SAIL) technique belongs fully coherent processing in both the time domain and space domain and has a rather high implement difficulty. To solve this problem, the concept of circular incoherently SAIL is introduced. A speckle version image of a two-dimensional (2D) letter ’E’ target is reconstructed from E-field projection data detected by a circular incoherently SAIL system. The experimental system is constructed by three subsystems using chirped-pulse laser as the light source and heterodyne detection to get the range information of the target. The reconstruction of the image and the noise effect are also discussed in detail.     

Image reconstruction for cone-beam computed tomography using total p-variation plus Kullback-Leibler data divergence

Accurate reconstruction from a reduced data set is highly essential for computed tomography in fast and/or low dose imaging applications. Conventional total variation(TV)-based algorithms apply the L1 norm-based penalties, which are not as efficient as Lp(0 p 1) quasi-norm-based penalties. TV with a p-th power-based norm can serve as a feasible alternative of the conventional TV, which is referred to as total p-variation(TpV). This paper proposes a TpV-based reconstruction model and develops an efficient algorithm. The total p-variation and Kullback-Leibler(KL) data divergence, which has better noise suppression capability compared with the often-used quadratic term, are combined to build the reconstruction model. The proposed algorithm is derived by the alternating direction method(ADM) which offers a stable, efficient, and easily coded implementation. We apply the proposed method in the reconstructions from very few views of projections(7 views evenly acquired within 180°). The images reconstructed by the new method show clearer edges and higher numerical accuracy than the conventional TV method. Both the simulations and real CT data experiments indicate that the proposed method may be promising for practical applications.     

Wavelength-selective switch based on a high fill-factor micromirror array

A novel design and fabrication approach for a high fill-factor micro-electro-mechanical system(MEMS) micromirror array-based wavelength-selective switch(WSS) is presented. The WSS is composed of a polarization-independent transmission grating and a high fill-factor micromirror array. The WSS is suc-cessfully demonstrated based on the fabricated high fill-factor micromirror array. Test results show that the polarization-dependent loss(PDL) is less than 0.3 dB and that the insertion loss(IL) of the wavelength channel is about -6 dB. The switching function between the two output ports of WSS is measured. The forward switching time is recorded to be about 0.5 ms,whereas the backward switching time is about 7 ms.     

Numerical Simulation of the Two—State Decoherence Model of Nano—Spin Systems

We have studied the two-state random decoherence model of the V15 system (Phys.Rev.Lett.84(2000)3458) with the k‘partial tracing of the environment’ method.The linearity relation between the averaged decoherence time and the random dipolar interaction amplitude is verified.The distribution function of decoherence time spreads more widely as the amplitude of the random field is decreased,hence it is difficult to define a decoherence time for the system.     

Simulation research on effect of magnetic nanoparticles on physical process of magneto–acoustic tomography with magnetic induction

Magneto–acoustic tomography with magnetic induction(MAT-MI) is a multiphysics coupled imaging technique that is combined with electrical impedance tomography and ultrasound imaging. In order to study the influence of adding magnetic nanoparticles as a contrast agent for MAT-MI on its physical process, firstly, we analyze and compare the electromagnetic and acoustical properties of MAT-MI theoretically before and after adding magnetic nanoparticles, and then construct a two-dimensional(2 D) planar model. Under the guidance of space-time separation theory, we determine the reasonable simulation conditions and solve the electromagnetic field and sound field physical processes in the two modes by using the finite element method. The magnetic flux density, sound pressure distribution, and related one-dimensional(1 D), 2 D, and three-dimensional(3 D) images are obtained. Finally, we make a qualitative and quantitative analysis based on the theoretical and simulation results. The research results show that the peak time of the time item separated from the sound source has a corresponding relationship with the peak time of the sound pressure signal. At this moment, MAMPTMI produces larger sound pressure signals, and the sound pressure distribution of the MAMPT-MI is more uniform, which facilitates the detection and completion of sound source reconstruction. The research results may lay the foundation for the MAT-MI of magnetically responsive nanoparticle in subsequent experiments and even clinical applications.     

Phase shift monitoring of delay-line interferometer and its application in phase-shift keying signal system

The relation between the phase shift and the mean optical power(MOP) output from a delay-line interferometer (DLI) port applied for phase-shift keying(PSK) signal demodulation is proven of a cosine law irrelevant to signal modulation condition.The variation amplitude of the MOP is proportional to the transition duration of the modulation pulses.This phenomenon is interpreted as the result of the statistical and waveform characteristics of the PSK.The conclusions verified by simulation and experiment are generalized to other modulation formats and then applied to phase detuning monitoring,delay time judgment of DLI,and independence of modulation data assessment.     

Monte Carlo tuning for the BESⅢ time-of-flight system

Using experimental data, Monte Carlo tuning is implemented for performance parameters associated with the scintillation counters and readout electronics of the BESⅢ time-of-flight(TOF) system, as part of the full simulation model. The implementation of the tuning is described for simulations designed to reproduce the performance of a number of TOF system parameters, including pulse height, hit efficiency, time resolution, dead channels and background. In addition, comparisons with experimental data are presented.