Avian metapneumovirus(aMPV),a paramyxovirus,causes acute respiratory diseases in turkeys and swollen head syndrome in chickens.This study established a reverse genetics system for aMPV subtype B LN16-A strain based on...Avian metapneumovirus(aMPV),a paramyxovirus,causes acute respiratory diseases in turkeys and swollen head syndrome in chickens.This study established a reverse genetics system for aMPV subtype B LN16-A strain based on T7 RNA polymerase.Full-length cDNA of the LN16-A strain was constructed by assembling 5 cDNA fragments between the T7 promoter and hepatitis delta virus ribozyme.Transfection of this plasmid,along with the supporting plasmids encoding the N,P,M2-1,and L proteins of LN16-A into BSR-T7/5 cells,resulted in the recovery of aMPV subtype B.To identify an effective insertion site,the enhanced green fluorescent protein(EGFP)gene was inserted into different sites of the LN16-A genome to generate recombinant LN16-As.The results showed that the expression levels of EGFP at the site between the G and L genes of LN16-A were significantly higher than those at the other two sites(between the leader and N genes or replacing the SH gene).To verify the availability of the site between G and L for foreign gene expression,the VP2 gene of very virulent infectious bursal disease virus(vvIBDV)was inserted into this site,and recombinant LN16-A(rLN16A-vvVP2)was successfully rescued.Single immunization of specificpathogen-free chickens with rLN16A-vvVP2 induced high levels of neutralizing antibodies and provided 100%protection against the virulent aMPV subtype B and vvIBDV.Establishing a reverse genetics system here provides an important foundation for understanding aMPV pathogenesis and developing novel vector vaccines.展开更多
On-chip devices for generating pre-designed vectorial optical fields(VOFs)under surface wave(SW)excitations are highly desired in integrated photonics.However,conventional devices are usually of large footprints,low e...On-chip devices for generating pre-designed vectorial optical fields(VOFs)under surface wave(SW)excitations are highly desired in integrated photonics.However,conventional devices are usually of large footprints,low efficiencies,and limited wave-control capabilities.Here,we present a generic approach to design ultra-compact on-chip devices that can efficiently generate pre-designed VOFs under SW excitations,and experimentally verify the concept in terahertz(THz)regime.We first describe how to design SW-excitation metasurfaces for generating circularly polarized complex beams,and experimentally demonstrate two meta-devices to realize directional emission and focusing of THz waves with oppo-site circular polarizations,respectively.We then establish a systematic approach to construct an integrated device via merging two carefully designed metasurfaces,which,under SW excitations,can separately produce pre-designed far-field patterns with different circular polarizations and generate target VOF based on their interference.As a proof of con-cept,we demonstrate experimentally a meta-device that can generate a radially polarized Bessel beam under SW excita-tion at~0.4 THz.Experimental results agree well with full-wave simulations,collectively verifying the performance of our device.Our study paves the road to realizing highly integrated on-chip functional THz devices,which may find many ap-plications in biological sensing,communications,displays,image multiplexing,and beyond.展开更多
To the Editor:We read with interest the article by Wang et al.,titled"Modeling the spread risk of dengue vector Aedes albopictus caused by environmental factors in Shanghai,China"[1].The use of ensemble ecol...To the Editor:We read with interest the article by Wang et al.,titled"Modeling the spread risk of dengue vector Aedes albopictus caused by environmental factors in Shanghai,China"[1].The use of ensemble ecological niche models to map Aedes albopictus distribution in urban Shanghai is both timely and methodologically sound.The identified drivers-vegetation index,temperature,and proximity to water-are well-known contributors to vector proliferation.However,one dimension remains notably underrepresented:human behavioral factors.展开更多
The development of clinical candidates that modify the natural progression of sporadic Parkinson's disease and related synucleinopathies is a praiseworthy endeavor,but extremely challenging.Therapeutic candidates ...The development of clinical candidates that modify the natural progression of sporadic Parkinson's disease and related synucleinopathies is a praiseworthy endeavor,but extremely challenging.Therapeutic candidates that were successful in preclinical Parkinson's disease animal models have repeatedly failed when tested in clinical trials.While these failures have many possible explanations,it is perhaps time to recognize that the problem lies with the animal models rather than the putative candidate.In other words,the lack of adequate animal models of Parkinson's disease currently represents the main barrier to preclinical identification of potential disease-modifying therapies likely to succeed in clinical trials.However,this barrier may be overcome by the recent introduction of novel generations of viral vectors coding for different forms of alpha-synuclein species and related genes.Although still facing several limitations,these models have managed to mimic the known neuropathological hallmarks of Parkinson's disease with unprecedented accuracy,delineating a more optimistic scenario for the near future.展开更多
Prestack reverse time migration（PSTM） is a common imaging method; however low-frequency noises reduce the structural imaging precision. Thus, the suppression of migration noises must be considered. The generation me...Prestack reverse time migration（PSTM） is a common imaging method; however low-frequency noises reduce the structural imaging precision. Thus, the suppression of migration noises must be considered. The generation mechanism of low-frequency noises is analyzed and the up-, down-, left-, and right-going waves are separated using the Poynting vector of the acoustic wave equation. The computational complexity and memory capacitance of the proposed method are far smaller than that required when using the conventional separation algorithm of 2D Fourier transform. The normalized wavefield separation crosscorrelation imaging condition is used to suppress low-frequency noises in reverse time migration and improve the imaging precision. Numerical experiments using the Marmousi model are performed and the results show that the up-, down-, left-, and right-going waves are well separated in the continuation of the wavefield using the Poynting vector. We compared the imaging results with the conventional method, Laplacian filtering, and wavefield separation with the 2D Fourier transform. The comparison shows that the migration noises are well suppressed using the normalized wavefield separation cross-correlation imaging condition and higher precision imaging results are obtained.展开更多
The laser gyro is most su it able for building the strap down inertial navigation system (SINS), and its acc uracy of attitude algorithm can enormously affect that of the laser SINS. This p aper develops three improv...The laser gyro is most su it able for building the strap down inertial navigation system (SINS), and its acc uracy of attitude algorithm can enormously affect that of the laser SINS. This p aper develops three improved algorithmal expressions for strap down attitude ut ilizing the angular increment output by the laser gyro from the last two and cur rent updating periods according to the number of gyro samples, and analyses the algorithm error in the classical coning motion. Compared with the conventional algorithms, simulational results show that this improved algorithm has higher precision. A new way to improve the rotation vector algorithms is provided.展开更多
In order to solve the fatigue damage identification problem of helicopter moving components, a new approach for acoustic emission （AE） source type identification based on the harmonic wavelet packet （HWPT） feature...In order to solve the fatigue damage identification problem of helicopter moving components, a new approach for acoustic emission （AE） source type identification based on the harmonic wavelet packet （HWPT） feature extraction and the hierarchy support vector machine （H-SVM） classifier is proposed. After a four-level decomposition of the HWPT, the energy feature of AE signals in different frequency bands is extracted, which overcomes the shortcomings of the traditional wavelet packet including energy leakage, and inflexible frequency band selection and different frequency resolutions on different levels. The H-SVM classifier is trained with a subset of the experimental data for known AE source types and tested using the remaining set of data. The results of pressure-off experiments on the specimens of carbon fiber materials indicate that the proposed approach can effectively implement the AE source type identification, and has a better performance in terms of computational efficiency and identification accuracy than the wavelet packet （WPT） feature extraction.展开更多
A heavy rain process of the Changjiang-Huaihe Meiyu front (MYF) is diagnosed by the agency of the traditional Q vector partitioning (QVP) method to decompose the wet Q vector (Q) in a natural coordinate system that fo...A heavy rain process of the Changjiang-Huaihe Meiyu front (MYF) is diagnosed by the agency of the traditional Q vector partitioning (QVP) method to decompose the wet Q vector (Q) in a natural coordinate system that follows the isoentropes and by using the numerical simulation results of the revised MM4 meso-scale model. The technique shows that the partitioned wet Q vectors can lead to a significant scale separation of vertical motion related to the torrential rain. The results not only verify the existing conclusion that different scales interact throughout the rainstorm but also indicate the largely different roles of these scales during differing phases of the heavy ramfall on a quantitative basis. Specifically, during the developing stage, the large-scale plays a predominant role in forcing vertical motion, while frontal-scale forcing is secondary; during the intense stage, the frontal-scale evolves into the primary factor of forcing vertical motion, whereas the large-scale forcing is minor and plays a diminishing role and can even be ignored; and during the decaying stage, the large-scale once again serves as the main forcing of vertical motion in such a way that the forcing of the frontal-scale decays quickly and is of secondary importance. Furthermore, the partitioned wet Q vectors are suggested to be more suitable than the total wet Q vector for evaluating the potential physical mechanism of rainstorm genesis. The first step is that the forcing of large-scale $2?bla cdot {? Q}_s^*$ gives rise to the genesis of meso-scale $2?bla cdot {? Q}_n^*$ forcing; and then, accordingly as $2?bla cdot {? Q}_n^*$ forcing increases, whereby the secondary circulation is reinforced, the intensity of the rainfall is strengthened; and at last, the secondary circulation caused by $2?bla cdot {? Q}_n^*$ forcing is directly responsible for generation of the MYF heavy rainfall.展开更多
Summary： Intraventricular hydrodynamics is considered an important component of cardiac function assessment. Vector flow mapping （VFM） is a novel flow visualization method to describe cardiac pathophysiological con...Summary： Intraventricular hydrodynamics is considered an important component of cardiac function assessment. Vector flow mapping （VFM） is a novel flow visualization method to describe cardiac pathophysiological condition. This study examined use of new VFM and flow field for assessment of left ventricular （LV） systolic hemodynamics in patients with simple hyperthyroidism （HT）. Thirty-seven simple HT patients were enrolled as HT group, and 38 gender- and age-matched healthy volunteers as control group. VFM model was used to analyze LV flow field at LV apical long-axis view. The follow- ing flow parameters were measured, including peak systolic velocity （Vs）, peak systolic flow （Fs）, total systolic negative flow （SQ） in LV basal, middle and apical level, velocity gradient from the apex to the aortic valve （AV）, and velocity according to half distance （V1/2）. The velocity vector in the LV cavity, stream line and vortex distribution in the two groups were observed. The results showed that there were no significant differences in the conventional parameters such as left ventricular ejection fraction （LVEF）, left ventricular end-diastolic diameter （LVEDD） and left atrium diameter （LAD） between HT group and control group （P〉0.05）. Compared with the control group, a brighter flow and more vortexes were detected in HT group. Non-uniform distribution occurred in the LV flow field, and the stream lines were discontinuous in HT group. The values of Vs and Fs in three levels, SQ in middle and basal levels, AV and V1/2 were higher in HT group than in control group （P〈0.01）. AV was positively correlated with serum free thyroxin （FT4） （r=0.48, P〈0.01）. Stepwise multiple regression analysis showed that LVEDD, FT4, and body surface area （BSA） were the influence factors of △V. The unstable left ventricular sys- tolic hydrodynamics increased in a compensatory manner in simple PIT patients. The present study in- dicated that VFM may be used for early detection of abnormal ventricle contraction in clinical settings.展开更多
Engine spark ignition is an important source for diagnosis of engine faults.Based on the waveform of the ignition pattern,a mechanic can guess what may be the potential malfunctioning parts of an engine with his/her e...Engine spark ignition is an important source for diagnosis of engine faults.Based on the waveform of the ignition pattern,a mechanic can guess what may be the potential malfunctioning parts of an engine with his/her experience and handbooks.However,this manual diagnostic method is imprecise because many spark ignition patterns are very similar.Therefore,a diagnosis needs many trials to identify the malfunctioning parts.Meanwhile the mechanic needs to disassemble and assemble the engine parts for verification.To tackle this problem,an intelligent diagnosis system was established based on ignition patterns.First,the captured patterns were normalized and compressed.Then wavelet packet transform（WPT） was employed to extract the representative features of the ignition patterns.Finally,a classification system was constructed by using multi-class support vector machines（SVM） and the extracted features.The classification system can intelligently classify the most likely engine fault so as to reduce the number of diagnosis trials.Experimental results show that SVM produces higher diagnosis accuracy than the traditional multilayer feedforward neural network.This is the first trial on the combination of WPT and SVM to analyze ignition patterns and diagnose automotive engines.展开更多
Ship floating condition in regular waves is calculated. New equations controlling any ship＇s floating condition are proposed by use of the vector operation. This form is a nonlinear optimization problem which can be ...Ship floating condition in regular waves is calculated. New equations controlling any ship＇s floating condition are proposed by use of the vector operation. This form is a nonlinear optimization problem which can be solved using the penalty function method with constant coefficients. And the solving process is accelerated by dichotomy. During the solving process, the ship＇s displacement and buoyant centre have been calculated by the integration of the ship surface according to the waterline. The ship surface is described using an accumulative chord length theory in order to determine the displacement, the buoyancy center and the waterline. The draught forming the waterline at each station can be found out by calculating the intersection of the ship surface and the wave surface. The results of an example indicate that this method is exact and efficient. It can calculate the ship floating condition in regular waves as well as simplify the calculation and improve the computational efficiency and the precision of results.展开更多
To make the modulation classification system more suitable for signals in a wide range of signal to noise rate （SNR）, a feature extraction method based on signal wavelet packet transform modulus maxima matrix （WPT...To make the modulation classification system more suitable for signals in a wide range of signal to noise rate （SNR）, a feature extraction method based on signal wavelet packet transform modulus maxima matrix （WPTMMM） and a novel support vector machine fuzzy network （SVMFN） classifier is presented. The WPTMMM feature extraction method has less computational complexity, more stability, and has the preferable advantage of robust with the time parallel moving and white noise. Further, the SVMFN uses a new definition of fuzzy density that incorporates accuracy and uncertainty of the classifiers to improve recognition reliability to classify nine digital modulation types （i.e. 2ASK, 2FSK, 2PSK, 4ASK, 4FSK, 4PSK, 16QAM, MSK, and OQPSK）. Computer simulation shows that the proposed scheme has the advantages of high accuracy and reliability （success rates are over 98% when SNR is not lower than 0dB）, and it adapts to engineering applications.展开更多
For the navigation algorithm of the strapdown inertial navigation system,by comparing to the equations of the dual quaternion and quaternion,the superiority of the attitude algorithm based on dual quaternion over the ...For the navigation algorithm of the strapdown inertial navigation system,by comparing to the equations of the dual quaternion and quaternion,the superiority of the attitude algorithm based on dual quaternion over the ones based on rotation vector in accuracy is analyzed in the case of the rotation of navigation frame.By comparing the update algorithm of the gravitational velocity in dual quaternion solution with the compensation algorithm of the harmful acceleration in traditional velocity solution,the accuracy advantage of the gravitational velocity based on dual quaternion is addressed.In view of the idea of the attitude and velocity algorithm based on dual quaternion,an improved navigation algorithm is proposed,which is as much as the rotation vector algorithm in computational complexity.According to this method,the attitude quaternion does not require compensating as the navigation frame rotates.In order to verify the correctness of the theoretical analysis,simulations are carried out utilizing the software,and the simulation results show that the accuracy of the improved algorithm is approximately equal to the dual quaternion algorithm.展开更多
The energy preserving average vector field （AVF） method is applied to the coupled Schr6dinger-KdV equations. Two energy preserving schemes are constructed by using Fourier pseudospectral method in space direction di...The energy preserving average vector field （AVF） method is applied to the coupled Schr6dinger-KdV equations. Two energy preserving schemes are constructed by using Fourier pseudospectral method in space direction discretization. In order to accelerate our simulation, the split-step technique is used. The numerical experiments show that the non-splitting scheme and splitting scheme are both effective, and have excellent long time numerical behavior. The comparisons show that the splitting scheme is faster than the non-splitting scheme, but it is not as good as the non-splitting scheme in preserving the invariants.展开更多
In this study, singular vectors related to a heavy rainfall case over the Korean Peninsula were calculated using the fifth-generation Pennsylvania State University-National Center for Atmospheric Research Mesoscale Mo...In this study, singular vectors related to a heavy rainfall case over the Korean Peninsula were calculated using the fifth-generation Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model （MM5） adjoint modeling system. Tangent linear and adjoint models include moist physical processes, and a moist basic state and a moist total energy norm were used for the singular-vector calculations. The characteristics and nonlinear growth of the first singular vector were analyzed, focusing on the relationship between the basic state and the singular vector. The horizontal distribution of the initial singular vector was closely related to the baroclinicity index and the moisture availability of the basic state. The temperature-component energy at a lower level was dominant at the initial time, and the kinetic energy at upper levels became dominant at the final time in the energy profile of the singular vector. The nonlinear growth of the singular vector appropriately reflects the temporal variations in the basic state. The moisture-component energy at lower levels was dominant at earlier times, indicating continuous moisture transport in the basic state. There were a large amount of precipitation and corresponding latent heat release after that period because the continuous moisture transport created favorable conditions for both convective and nonconvective precipitation. The vertical propagation of the singular-vector energy was caused by precipitation and the corresponding latent heating in the basic state.展开更多
This paper presents a novel method for radar emitter signal recognition. First, wavelet packet transform （WPT） is introduced to extract features from radar emitter signals. Then, rough set theory is used to select t...This paper presents a novel method for radar emitter signal recognition. First, wavelet packet transform （WPT） is introduced to extract features from radar emitter signals. Then, rough set theory is used to select the optimal feature subset with good discriminability from original feature set, and support vector machines （SVMs） are employed to design classifiers. A large number of experimental results show that the proposed method achieves very high recognition rates for 9 radar emitter signals in a wide range of signal-to-noise rates, and proves a feasible and valid method.展开更多
In order to accurately predict bus travel time, a hybrid model based on combining wavelet transform technique with support vector regression(WT-SVR) model is employed. In this model, wavelet decomposition is used to e...In order to accurately predict bus travel time, a hybrid model based on combining wavelet transform technique with support vector regression(WT-SVR) model is employed. In this model, wavelet decomposition is used to extract important information of data at different levels and enhances the forecasting ability of the model. After wavelet transform different components are forecasted by their corresponding SVR predictors. The final prediction result is obtained by the summation of the predicted results for each component. The proposed hybrid model is examined by the data of bus route No.550 in Nanjing, China. The performance of WT-SVR model is evaluated by mean absolute error(MAE), mean absolute percent error(MAPE) and relative mean square error(RMSE), and also compared to regular SVR and ANN models. The results show that the prediction method based on wavelet transform and SVR has better tracking ability and dynamic behavior than regular SVR and ANN models. The forecasting performance is remarkably improved to obtain within 6% MAPE for testing section Ⅰ and 8% MAPE for testing section Ⅱ, which proves that the suggested approach is feasible and applicable in bus travel time prediction.展开更多
基金supported by the grants from the National Key Research and Development Program of China(2022YFD1800604)the China Agriculture Research System(CARS-41)the Heilongjiang Touyan Innovation Team Program,China。
文摘Avian metapneumovirus(aMPV),a paramyxovirus,causes acute respiratory diseases in turkeys and swollen head syndrome in chickens.This study established a reverse genetics system for aMPV subtype B LN16-A strain based on T7 RNA polymerase.Full-length cDNA of the LN16-A strain was constructed by assembling 5 cDNA fragments between the T7 promoter and hepatitis delta virus ribozyme.Transfection of this plasmid,along with the supporting plasmids encoding the N,P,M2-1,and L proteins of LN16-A into BSR-T7/5 cells,resulted in the recovery of aMPV subtype B.To identify an effective insertion site,the enhanced green fluorescent protein(EGFP)gene was inserted into different sites of the LN16-A genome to generate recombinant LN16-As.The results showed that the expression levels of EGFP at the site between the G and L genes of LN16-A were significantly higher than those at the other two sites(between the leader and N genes or replacing the SH gene).To verify the availability of the site between G and L for foreign gene expression,the VP2 gene of very virulent infectious bursal disease virus(vvIBDV)was inserted into this site,and recombinant LN16-A(rLN16A-vvVP2)was successfully rescued.Single immunization of specificpathogen-free chickens with rLN16A-vvVP2 induced high levels of neutralizing antibodies and provided 100%protection against the virulent aMPV subtype B and vvIBDV.Establishing a reverse genetics system here provides an important foundation for understanding aMPV pathogenesis and developing novel vector vaccines.
基金the financial support from National Natural Science Foundation of China (Nos. 62192771, 12374344, 12221004)National Key Research and Development Program of China (2022YFA1204700, 2020YFA0710100)+1 种基金Natural Science Foundation of Shanghai (Grant No. 23dz2260100)China Postdoctoral Science Foundation 2021TQ0077
文摘On-chip devices for generating pre-designed vectorial optical fields(VOFs)under surface wave(SW)excitations are highly desired in integrated photonics.However,conventional devices are usually of large footprints,low efficiencies,and limited wave-control capabilities.Here,we present a generic approach to design ultra-compact on-chip devices that can efficiently generate pre-designed VOFs under SW excitations,and experimentally verify the concept in terahertz(THz)regime.We first describe how to design SW-excitation metasurfaces for generating circularly polarized complex beams,and experimentally demonstrate two meta-devices to realize directional emission and focusing of THz waves with oppo-site circular polarizations,respectively.We then establish a systematic approach to construct an integrated device via merging two carefully designed metasurfaces,which,under SW excitations,can separately produce pre-designed far-field patterns with different circular polarizations and generate target VOF based on their interference.As a proof of con-cept,we demonstrate experimentally a meta-device that can generate a radially polarized Bessel beam under SW excita-tion at~0.4 THz.Experimental results agree well with full-wave simulations,collectively verifying the performance of our device.Our study paves the road to realizing highly integrated on-chip functional THz devices,which may find many ap-plications in biological sensing,communications,displays,image multiplexing,and beyond.
基金supported by Three-Year Initiative Plan for Strengthening Public Health System Construction in Shanghai(2023-2025)Key Discipline Project(No.GWVI-11.1-12).
文摘To the Editor:We read with interest the article by Wang et al.,titled"Modeling the spread risk of dengue vector Aedes albopictus caused by environmental factors in Shanghai,China"[1].The use of ensemble ecological niche models to map Aedes albopictus distribution in urban Shanghai is both timely and methodologically sound.The identified drivers-vegetation index,temperature,and proximity to water-are well-known contributors to vector proliferation.However,one dimension remains notably underrepresented:human behavioral factors.
基金supported by grants PID2020-120308RB-I00 and PID2023-147802OB-I00 funded by MICIU/AEI/10.13039/501100011033FEDER,UE,by Aligning Science Across Parkinson’s(ref.ASAP-020505)through the Michael J.Fox Foundation for Parkinson’s Research+1 种基金by CiberNed Intramural Collaborative Projects(ref.PI2020/09)by the Spanish Fundación Mutua Madrile?a de Investigación Médica(to JLL)。
文摘The development of clinical candidates that modify the natural progression of sporadic Parkinson's disease and related synucleinopathies is a praiseworthy endeavor,but extremely challenging.Therapeutic candidates that were successful in preclinical Parkinson's disease animal models have repeatedly failed when tested in clinical trials.While these failures have many possible explanations,it is perhaps time to recognize that the problem lies with the animal models rather than the putative candidate.In other words,the lack of adequate animal models of Parkinson's disease currently represents the main barrier to preclinical identification of potential disease-modifying therapies likely to succeed in clinical trials.However,this barrier may be overcome by the recent introduction of novel generations of viral vectors coding for different forms of alpha-synuclein species and related genes.Although still facing several limitations,these models have managed to mimic the known neuropathological hallmarks of Parkinson's disease with unprecedented accuracy,delineating a more optimistic scenario for the near future.
基金supported by the National Natural Science Foundation of China(No.41174087,41204089)the National Oil and Gas Major Project(No.2011ZX05005-005)
文摘Prestack reverse time migration（PSTM） is a common imaging method; however low-frequency noises reduce the structural imaging precision. Thus, the suppression of migration noises must be considered. The generation mechanism of low-frequency noises is analyzed and the up-, down-, left-, and right-going waves are separated using the Poynting vector of the acoustic wave equation. The computational complexity and memory capacitance of the proposed method are far smaller than that required when using the conventional separation algorithm of 2D Fourier transform. The normalized wavefield separation crosscorrelation imaging condition is used to suppress low-frequency noises in reverse time migration and improve the imaging precision. Numerical experiments using the Marmousi model are performed and the results show that the up-, down-, left-, and right-going waves are well separated in the continuation of the wavefield using the Poynting vector. We compared the imaging results with the conventional method, Laplacian filtering, and wavefield separation with the 2D Fourier transform. The comparison shows that the migration noises are well suppressed using the normalized wavefield separation cross-correlation imaging condition and higher precision imaging results are obtained.
文摘The laser gyro is most su it able for building the strap down inertial navigation system (SINS), and its acc uracy of attitude algorithm can enormously affect that of the laser SINS. This p aper develops three improved algorithmal expressions for strap down attitude ut ilizing the angular increment output by the laser gyro from the last two and cur rent updating periods according to the number of gyro samples, and analyses the algorithm error in the classical coning motion. Compared with the conventional algorithms, simulational results show that this improved algorithm has higher precision. A new way to improve the rotation vector algorithms is provided.
基金The Natural Science Foundation of Heilongjiang Province ( No. F201018)the National Natural Science Foundation of China( No. 60901042)
文摘In order to solve the fatigue damage identification problem of helicopter moving components, a new approach for acoustic emission （AE） source type identification based on the harmonic wavelet packet （HWPT） feature extraction and the hierarchy support vector machine （H-SVM） classifier is proposed. After a four-level decomposition of the HWPT, the energy feature of AE signals in different frequency bands is extracted, which overcomes the shortcomings of the traditional wavelet packet including energy leakage, and inflexible frequency band selection and different frequency resolutions on different levels. The H-SVM classifier is trained with a subset of the experimental data for known AE source types and tested using the remaining set of data. The results of pressure-off experiments on the specimens of carbon fiber materials indicate that the proposed approach can effectively implement the AE source type identification, and has a better performance in terms of computational efficiency and identification accuracy than the wavelet packet （WPT） feature extraction.
基金This work was supported by the National Natural Science Foundation of China under Grant Nos.40075009 and 40205008,and by Project 37020 of the Social Public Special Research Grant of the Ministry of Science and Technology of China.
文摘A heavy rain process of the Changjiang-Huaihe Meiyu front (MYF) is diagnosed by the agency of the traditional Q vector partitioning (QVP) method to decompose the wet Q vector (Q) in a natural coordinate system that follows the isoentropes and by using the numerical simulation results of the revised MM4 meso-scale model. The technique shows that the partitioned wet Q vectors can lead to a significant scale separation of vertical motion related to the torrential rain. The results not only verify the existing conclusion that different scales interact throughout the rainstorm but also indicate the largely different roles of these scales during differing phases of the heavy ramfall on a quantitative basis. Specifically, during the developing stage, the large-scale plays a predominant role in forcing vertical motion, while frontal-scale forcing is secondary; during the intense stage, the frontal-scale evolves into the primary factor of forcing vertical motion, whereas the large-scale forcing is minor and plays a diminishing role and can even be ignored; and during the decaying stage, the large-scale once again serves as the main forcing of vertical motion in such a way that the forcing of the frontal-scale decays quickly and is of secondary importance. Furthermore, the partitioned wet Q vectors are suggested to be more suitable than the total wet Q vector for evaluating the potential physical mechanism of rainstorm genesis. The first step is that the forcing of large-scale $2?bla cdot {? Q}_s^*$ gives rise to the genesis of meso-scale $2?bla cdot {? Q}_n^*$ forcing; and then, accordingly as $2?bla cdot {? Q}_n^*$ forcing increases, whereby the secondary circulation is reinforced, the intensity of the rainfall is strengthened; and at last, the secondary circulation caused by $2?bla cdot {? Q}_n^*$ forcing is directly responsible for generation of the MYF heavy rainfall.
基金supported by Independent Innovation Fund of Huazhong University of Science and Technology for Clinical Skills,China(No.2015-01-18-53028)
文摘Summary： Intraventricular hydrodynamics is considered an important component of cardiac function assessment. Vector flow mapping （VFM） is a novel flow visualization method to describe cardiac pathophysiological condition. This study examined use of new VFM and flow field for assessment of left ventricular （LV） systolic hemodynamics in patients with simple hyperthyroidism （HT）. Thirty-seven simple HT patients were enrolled as HT group, and 38 gender- and age-matched healthy volunteers as control group. VFM model was used to analyze LV flow field at LV apical long-axis view. The follow- ing flow parameters were measured, including peak systolic velocity （Vs）, peak systolic flow （Fs）, total systolic negative flow （SQ） in LV basal, middle and apical level, velocity gradient from the apex to the aortic valve （AV）, and velocity according to half distance （V1/2）. The velocity vector in the LV cavity, stream line and vortex distribution in the two groups were observed. The results showed that there were no significant differences in the conventional parameters such as left ventricular ejection fraction （LVEF）, left ventricular end-diastolic diameter （LVEDD） and left atrium diameter （LAD） between HT group and control group （P〉0.05）. Compared with the control group, a brighter flow and more vortexes were detected in HT group. Non-uniform distribution occurred in the LV flow field, and the stream lines were discontinuous in HT group. The values of Vs and Fs in three levels, SQ in middle and basal levels, AV and V1/2 were higher in HT group than in control group （P〈0.01）. AV was positively correlated with serum free thyroxin （FT4） （r=0.48, P〈0.01）. Stepwise multiple regression analysis showed that LVEDD, FT4, and body surface area （BSA） were the influence factors of △V. The unstable left ventricular sys- tolic hydrodynamics increased in a compensatory manner in simple PIT patients. The present study in- dicated that VFM may be used for early detection of abnormal ventricle contraction in clinical settings.
基金supported by University of Macao Research Grant,China (Grant No. RG057/08-09S/VCM/FST, Grant No. UL011/09-Y1/ EME/ WPK01/FST)
文摘Engine spark ignition is an important source for diagnosis of engine faults.Based on the waveform of the ignition pattern,a mechanic can guess what may be the potential malfunctioning parts of an engine with his/her experience and handbooks.However,this manual diagnostic method is imprecise because many spark ignition patterns are very similar.Therefore,a diagnosis needs many trials to identify the malfunctioning parts.Meanwhile the mechanic needs to disassemble and assemble the engine parts for verification.To tackle this problem,an intelligent diagnosis system was established based on ignition patterns.First,the captured patterns were normalized and compressed.Then wavelet packet transform（WPT） was employed to extract the representative features of the ignition patterns.Finally,a classification system was constructed by using multi-class support vector machines（SVM） and the extracted features.The classification system can intelligently classify the most likely engine fault so as to reduce the number of diagnosis trials.Experimental results show that SVM produces higher diagnosis accuracy than the traditional multilayer feedforward neural network.This is the first trial on the combination of WPT and SVM to analyze ignition patterns and diagnose automotive engines.
基金financially supported by the Science Fund for Creative Research Groups of the National Natural Science Foundation of China(Grant No.51321065)the Research Fund of State Key Laboratory of Ocean Engineering of Shanghai Jiao Tong University(Grant No.1104)
文摘Ship floating condition in regular waves is calculated. New equations controlling any ship＇s floating condition are proposed by use of the vector operation. This form is a nonlinear optimization problem which can be solved using the penalty function method with constant coefficients. And the solving process is accelerated by dichotomy. During the solving process, the ship＇s displacement and buoyant centre have been calculated by the integration of the ship surface according to the waterline. The ship surface is described using an accumulative chord length theory in order to determine the displacement, the buoyancy center and the waterline. The draught forming the waterline at each station can be found out by calculating the intersection of the ship surface and the wave surface. The results of an example indicate that this method is exact and efficient. It can calculate the ship floating condition in regular waves as well as simplify the calculation and improve the computational efficiency and the precision of results.
文摘To make the modulation classification system more suitable for signals in a wide range of signal to noise rate （SNR）, a feature extraction method based on signal wavelet packet transform modulus maxima matrix （WPTMMM） and a novel support vector machine fuzzy network （SVMFN） classifier is presented. The WPTMMM feature extraction method has less computational complexity, more stability, and has the preferable advantage of robust with the time parallel moving and white noise. Further, the SVMFN uses a new definition of fuzzy density that incorporates accuracy and uncertainty of the classifiers to improve recognition reliability to classify nine digital modulation types （i.e. 2ASK, 2FSK, 2PSK, 4ASK, 4FSK, 4PSK, 16QAM, MSK, and OQPSK）. Computer simulation shows that the proposed scheme has the advantages of high accuracy and reliability （success rates are over 98% when SNR is not lower than 0dB）, and it adapts to engineering applications.
基金supported by the National Natural Science Foundation of China(No.61174126)
文摘For the navigation algorithm of the strapdown inertial navigation system,by comparing to the equations of the dual quaternion and quaternion,the superiority of the attitude algorithm based on dual quaternion over the ones based on rotation vector in accuracy is analyzed in the case of the rotation of navigation frame.By comparing the update algorithm of the gravitational velocity in dual quaternion solution with the compensation algorithm of the harmful acceleration in traditional velocity solution,the accuracy advantage of the gravitational velocity based on dual quaternion is addressed.In view of the idea of the attitude and velocity algorithm based on dual quaternion,an improved navigation algorithm is proposed,which is as much as the rotation vector algorithm in computational complexity.According to this method,the attitude quaternion does not require compensating as the navigation frame rotates.In order to verify the correctness of the theoretical analysis,simulations are carried out utilizing the software,and the simulation results show that the accuracy of the improved algorithm is approximately equal to the dual quaternion algorithm.
基金supported by the National Natural Science Foundation of China(Grant No.91130013)the Open Foundation of State Key Laboratory of HighPerformance Computing of China
文摘The energy preserving average vector field （AVF） method is applied to the coupled Schr6dinger-KdV equations. Two energy preserving schemes are constructed by using Fourier pseudospectral method in space direction discretization. In order to accelerate our simulation, the split-step technique is used. The numerical experiments show that the non-splitting scheme and splitting scheme are both effective, and have excellent long time numerical behavior. The comparisons show that the splitting scheme is faster than the non-splitting scheme, but it is not as good as the non-splitting scheme in preserving the invariants.
基金funded by the Korea Meteorological Administration Research and Development Program (Grant No.RACS 2010-2016)supported by Leading Foreign Research Institute Recruitment Program through the National Research Foundation of Korea (NRF)funded by the Ministry of Education,Science and Technology (MEST) (2010-00715)the Brain Korea 21Project
文摘In this study, singular vectors related to a heavy rainfall case over the Korean Peninsula were calculated using the fifth-generation Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model （MM5） adjoint modeling system. Tangent linear and adjoint models include moist physical processes, and a moist basic state and a moist total energy norm were used for the singular-vector calculations. The characteristics and nonlinear growth of the first singular vector were analyzed, focusing on the relationship between the basic state and the singular vector. The horizontal distribution of the initial singular vector was closely related to the baroclinicity index and the moisture availability of the basic state. The temperature-component energy at a lower level was dominant at the initial time, and the kinetic energy at upper levels became dominant at the final time in the energy profile of the singular vector. The nonlinear growth of the singular vector appropriately reflects the temporal variations in the basic state. The moisture-component energy at lower levels was dominant at earlier times, indicating continuous moisture transport in the basic state. There were a large amount of precipitation and corresponding latent heat release after that period because the continuous moisture transport created favorable conditions for both convective and nonconvective precipitation. The vertical propagation of the singular-vector energy was caused by precipitation and the corresponding latent heating in the basic state.
文摘This paper presents a novel method for radar emitter signal recognition. First, wavelet packet transform （WPT） is introduced to extract features from radar emitter signals. Then, rough set theory is used to select the optimal feature subset with good discriminability from original feature set, and support vector machines （SVMs） are employed to design classifiers. A large number of experimental results show that the proposed method achieves very high recognition rates for 9 radar emitter signals in a wide range of signal-to-noise rates, and proves a feasible and valid method.
基金Sponsored by the Projects of International Cooperation and Exchange of the National Natural Science Foundation of China(Grant No.51561135003)the Scientific Research Foundation of Graduated School of Southeast University(Grant No.YBJJ1842)
文摘In order to accurately predict bus travel time, a hybrid model based on combining wavelet transform technique with support vector regression(WT-SVR) model is employed. In this model, wavelet decomposition is used to extract important information of data at different levels and enhances the forecasting ability of the model. After wavelet transform different components are forecasted by their corresponding SVR predictors. The final prediction result is obtained by the summation of the predicted results for each component. The proposed hybrid model is examined by the data of bus route No.550 in Nanjing, China. The performance of WT-SVR model is evaluated by mean absolute error(MAE), mean absolute percent error(MAPE) and relative mean square error(RMSE), and also compared to regular SVR and ANN models. The results show that the prediction method based on wavelet transform and SVR has better tracking ability and dynamic behavior than regular SVR and ANN models. The forecasting performance is remarkably improved to obtain within 6% MAPE for testing section Ⅰ and 8% MAPE for testing section Ⅱ, which proves that the suggested approach is feasible and applicable in bus travel time prediction.
