A Novel Method of Deinterleaving Radar Pulse Sequences Based on a Modified DBSCAN Algorithm

A modified DBSCAN algorithm is presented for deinterleaving of radar pulses in modern EW environments.A main characteristic of the proposed method is that using only time of arrival of pulses,the method can sort the pulses efficiently.Other PDW information such as rise time,carrier frequency,pulse width,modulation on pulse,fall time and direction of arrival are not required.To identify the valid PRIs in a set of interleaved pulses,an innovative modification of the DBSCAN algorithm is introduced which is accurate and easy to implement.The proposed method determines valid PRIs more accurately and neglects the spurious ones more efficiently as compared to the classical histogram based algorithms such as SDIF.Furthermore,without specifying any input parameter,the proposed method can deinterleave radar pulses while up to 30%jitter is present in the associated PRI.The accuracy and efficiency of the proposed method are verified by computer simulations and real data results.Experimental simulations are based on different real and operational scenarios where the presence of missing and spurious pulses are also considered.So,the simulation results can be of practical significance.

Dynamic responses under the excitation of pulse sequences

This paper studies the dynamic responses of SDOF system under pulse-dominant excitations.The purpose of the study is to prepare for scrutiny of some near-field pulse-dominantground motions and their potential to cause structural damage.Extending the single pulse dynamics,we consider the effect of pulse sequences.This kind of excitation was particularly obvious in some of previous earthquakes such as Northridge (1994) and Chi-Chi (1995).Based on the duration, peak and rise and decay era of the main pulse as well as its relationship with the predecessor and successor pulses,we propose a classification for the pulse sequences.Consequent studies have been canied out for acceleration,velocity and displacement response spectra of the main pulse with either a predecessor or a successor pulse.The analysis also includes general response behaviors in different fundamental period segments and special aspects of response at certain points (e.g.,the corresponding peak points).

Magnetic resonance imaging with three-dimensional fast imaging employing steady-state acquisition with phase-cycled and short T1 inversion recovery pulse sequence for evaluating brachial plexus injury

There is a large amount of fat in the postganglionic segment of the brachial plexus nerve.The use of short T1 inversion recovery pulse sequence may improve signal strength of the brachial plexus postganglionic segment.The present study revealed that the combination of three-dimensional fast imaging employing steady-state acquisition with phase-cycled and short T1 inversion recovery pulse sequence clearly displayed the anatomical morphology and structure of the brachial plexus nerve,together with maximum intensity projection,volume rendering and other three-dimensional reconstruction techniques.Our results suggested that this method is also suitable for providing accurate assessment and diagnosis of the site,severity and scope of brachial plexus injury.

Design of control sequence of pulses for the population transfer of high dimensional spin 1/2 quantum systems

On the basis of the relationship between the Hamiltonian of spin 1/2 quantum system under control and the energy level structure and transitions, a radio frequency pulse sequence is designed using intuitive and half counter-intuitive sequences of pulse to transfer the population of the 3-qubit system coherently. The effectiveness of the designed control sequence is verified through the system simulation experiment of the evolution of state. In principle, the design method of the control pulse sequence proposed can be generalized to use in the quantum systems of higher dimension.

Assessment the Optimal Effect of Time of Repetition: Extrinsic Pulse Parameter on Gd-DTPA Enhanced, Spin-Echo T1-Weighted MR Images under Low Magnetic Field Strength

The contrast agent concentration, the time of repetition (TR) and magnetic field strength are significant parameters that influence for the accurate signal intensity (SI) in quantitative Magnetic Resonance Imaging (MRI). Therefore, this study was conducted to investigate and refine the dependence and the optimal effect of Time of Repetition (TR) on the relationship between signal intensity and Gd-DTPA (Gadolinium-diethylene-triaminepenta-acetic acid) concentration, after applying two-dimensional (2D) Spin Echo (SE) pulse sequence under low-field MRI. In addition to that, the optimal concentration of Gd-DTPA at given sequence parameters at low-field MRI was also evaluated. A water-filled phantom was constructed for a range of Gd-DTPA concentrations (0 - 6 mmol/L) and the mean signal intensities (SIs) were assessed in the defined region of interest on T1-weighted images with different TR values (40 - 2000 ms). The generated signal-concentration curves for Gd-DTPA revealed that increasing TR was associated with the increase of the overall SIs and the maximum relationship between SI to concentration. Moreover, the required Gd-DTPA concentration to produce the maximum SI was associated to decrease with the increase of TR. In addition to this, the application of beyond 100 ms TR values in this study with relatively higher concentrations (beyond 1 - 2 mmol/L) has resulted predominantly non-linear patterns in the signal-concentration curves and it appears the saturation or decay of the SIs due to T2 effect. From these results, it can be suggested that the selection of relatively lower Gd-DTPA concentration ( mmol/L) with less than 800 ms (<800 ms) TR values can produce a better linear relationship between the concertation and SIs in T1-weighted SE low field contrast-enhanced MRI. Furthermore, this study also outlined the significance and necessity of the optimization of TR in SE sequence in low field MRI prior to a particular examination.

NMR fluid analyzer applying to petroleum industry

Tremendous progress of developing nuclear magnetic resonance(NMR)fluid analyzer has been witnessed in the oil industry for last two decades.This device allows extensive and accurate exploration of fluid properties,such as its hydrogen content,composition,viscosity,hydrogen index(HI),mud filtrate invasion,gas to oil ratio,average velocity,velocity distribution etc.,in the situations of in situ downhole or surface Petro-pipelines.In this review article,we focus on the design principle,manufacturing,implementation,methodology and applications of NMR fluid analyzer to oil and gas industry.A detailed description of the state-of-art NMR fluid analyzers was firstly given to exhibit their respective characteristics.With these experiences on hand,we introduced a series of NMR fluid analyzers designed by us at China University of Petroleum-Beijing with continuous optimizations,in terms of magnet construction,antenna layout,circuit design and operating surroundings.These systems discussed in this article have been demonstrated to achieve multiple NMR parameter acquisition when the fluid is in stationary or flowing state.In the end,a prototype was fabricated and validated considering a vast of engineering influences,such as variable temperatures in a large range,high pressure,limited volume,detection efficiency,etc.A particular emphasis of this paper is to expedite the measurement efficiency of the NMR fluid analyzer to reduce the operation costs.This dilemma can be Figured out by upgrading both pulse sequence and observational mode.For different fluid states,two rapid pulse sequences were proposed to sufficiently obtain the multi-dimensional NMR correlation map.Meanwhile,two observational modes were developed to take full advantage of the polarization time,during which the individual antenna was systematically switched.Another domain of interest in this review concerns the applications of this new tool.For stationary fluids case,accurate identification of fluid properties is of great value for scheme building in oil and gas exploration process.Particularly,it can acquire the fluid content by different NMR responses of different components.In addition,with Bloembergen theory and Stokes-Einstein equation,not only molecular dynamics and composition,but also oil viscosity can be readily evaluated.Moreover,HI information of crude oils will be speculated through partial least square regression.As for flowing fluids case,velocity is a significant parameter to understand the in situ fluid exploitation and therefore evaluate the productivity of certain oil wells or pipelines.Regarding to the unique magnet and antenna designs in our NMR fluid analyzer;this review adopts two distinct methods to obtain flow velocity at a wide rating scale.The first one is a time-of-flight method adaptive in a homogeneous magnetic field,which is suitable in the case of fluid at high flow velocity.The other one relies on the adjacent echo phase difference at a magnetic field with constant gradient,which is preferred for relatively low flow velocity.In the near future,this tool will be tested underground to offer individual fluid velocities by combining both the stationary and flowing analysis methods.

Practical pulse engineering： Gradient ascent without matrix exponentiation

Since 2005, there has been a huge growth in the use of engineered control pulses to perform desired quantum operations in systems such as nuclear magnetic resonance quantum information processors. These approaches, which build on the original gradient ascent pulse engineering algorithm, remain computationally intensive because of the need to calculate matrix exponentials for each time step in the control pulse. In this study, we discuss how the propagators for each time step can be approximated using the Trotter-Suzuki formula, and a further speedup achieved by avoiding unnecessary operations. The resulting procedure can provide substantial speed gain with negligible costs in the propagator error, providing a more practical approach to pulse en-ineerinK.

Three-dimensional-fast imaging employing steady-state acquisition and T2-weighted fast spin-echo magnetic resonance sequences on visualization of cranial nerves Ⅲ-Ⅻ

Because of the small diameter and complex anatomic course of the cranial nerves except for the optic nerve, trigeminal nerve, facial nerve, and cochlear and vestibular nerve, other cranial nerves are difficult to be visualized in magnetic resonance imaging （MRI） scanning with conventional thickness （5-10 mm）. With the rapid development of MRI technology high spatial resolution, three-dimensional and two-dimensional magnetic resonance imaging technologies have been used in recent years in the observation of normal and abnormal cranial nerves, including three-dimensional constructive interference in steady state （3D CISS） sequence, three- dimensional magnetization-prepared rapid gradient-echo （3D MP-RAGE） sequence, three-dimensional fast inflow with steady-state precession （3D FISP） seohuence, and some fast spin-echo （FSE） sequences. - Threedimensional fast imaging employing steady-state acquisition （3D-FIESTA） is a fast three-dimensional steady-state imaging sequence with high spatial resolution and contrast between the organizational structures. And this sequence was reportedly used in the study on the diseases in the cerebellopontine angle; inner ear and posterior fossa tumors.7＇8 However, the reports about the value of 3D-FIESTA sequence for the visualization of normal cranial nerves are still rare.

Propagation of quasi-periodic random sound pulse sequence signals in shallow-water waveguides

It is an efficient method to model ship radiated noise as quasi-periodic random sound pulse sequences. Based on the model, this paper discusses the characteristics change of ship noise after through shallow-water waveguides. Theoretical analysis and numerical simulation show that random waveguides and multi-path effects can bring much additional transmission loss for the noise line spectra, demonstrating the instability of ship radiated noise line spectra to a certain extent, and providing some theoretical support for advanced studies of ship radiated noise.