Showing papers in "Journal of Tsinghua University in 2011"

Security threats and measures for the Internet of Things

Abstract: Governments,companies and research institutions are pressuring research and development of the Internet of Things.However,the development of the Internet of Things will be constrained by security and privacy threats.This paper summarizes security threats to the Internet of Things to provide a theoretical reference for study of the Internet of Things and to provide useful security measures.The architecture of the Internet of Things is used to classify threats for the perception layer,transport layer and application layer.The perception layer threats include security threats for Radio Frequency Identification,Wireless Sensor Networks and mobile intelligent terminals.Transport layer threats include data leakage or damage and security issues during massive data integration.Application layer threats include the loss of user privacy,incorrect access control policies and inadequate security standards.Finally,this paper gives security measures and recommendations for all types of security threats.

SINA microblog data retrieval

Abstract: With the large increase of SINA Microblog web users,analyses SINA Microblog data has aroused wide public concernThe data retrieval is a primary need for all these studiesThis paper presents two data retrieval techniques based on opened APIs and web crawlers with webpage extractionA program controls the methods and frequencies of the API queries for efficient data downloading via parsing of JSON objectsA traditional web crawler integrated with webpage extraction overcomes the shortcomings of opened SINA API interfaces that limit retrieval of the entire dataset without quantity and frequency limitationsTest results show that a combination of these two techniques allows complete data retrieval of SINA Microblog data

Anticipatory coarticulation in V1#C2V2 sequences in standard Chinese

Abstract: An electropalatographic and acoustic analysis was used to investigate the C2-to-V1 and V2-to-V1 anticipatory effects.The articulatory measures were obtained by the electropalatography(EPG) and the F2 trajectory by linear prediction coding(LPC).The results show that: 1) the F2 transition is significantly correlated with the posterior contact index;2) a manner difference is found for linguapalatal contact and the F2 trajectory for V1 when C2 are labial,alveolar and velar consonants;3) the anticipatory vocalic effect is significant for the F2 transition and/or EPG parameters for V1 when the C2 are labial,alveolar and velar consonants.The rounded feature of V2 tends to spread onto the V1 off-glide which affects the F2 transition of V1.The article concludes that the anticipatory effects are constrained by the articulatory constraints on the tongue body for intervocalic consonants and that the rounding feature of V2 is independent in the coarticulatory process.

High speed on-off solenoid valve with proportional control based on high frequency PWM control

Abstract: Modern automobile braking systems(such as anti-lock brake systems(ABS) and electronic stability program(ESP)) use an electronic control unit(ECU) to control the brake pressure through a two-status-two-way high-speed on/off valve to build up,hold or reduce the brake pressure.Since traditional high-speed on/off valves have only on/off states,a proportionality function was added to the high-speed on/off valve to improve the control precision.This paper describes a high-speed on/off valve MATLAB-Simulink simulation model using pulse width modulation(PWM) control with a 2～4 kHz modulation frequency used to analyze the proportionality function of the high-speed on/off valve for different duty cycles of the PWM control.The analyses extend application of the high-speed on/off valve to precise control of the brake pressure.This propositional control of the high-speed on/off valve in vehicle systems ABS and ESP makes the brake pressure increase more stable.

Cascade-based attack vulnerability in complex networks

Abstract: Traditional complex network resilience research has mainly focused on static network connectivity,while ignoring dynamic effects.This study analyzes the performance of three kinds of network models for cascading failures based on their dynamic properties,including the Erdos-Renyi random model(ER) and two scale-free models: the Barabasi-Albert model(BA) and the Positive Feedback Preferential model(PFP).Simulations show that against random attacks,the ER network is fragile,while the BA network is more vulnerable than the PFP network.Against intentional attacks,the Highest Vertex Degree First,Highest Vertex Betweenness First and Highest Edge Betweenness First,have similar performance with network collapse only by attacking a few important edges.The PFP network is more robust than the ER and BA networks.The performance results show that the dynamic network properties have a significant impact on complex network resilience.This is important when evaluating complex systems reliability,constructing reliable network topologies,and designing protection and attack strategies.

Traffic velocity distributions for different spacings

Abstract: Conventional traffic density-velocity models usually use deterministic functions.However,stochastic traffic flow fluctuations mean that the traffic velocity cannot be uniquely determined by the density.A more accurate description of the density-velocity relation was developed using NGSIM(next generation simulation) data to model the velocity distribution for different spacing.Test results show that at low traffic densities the velocity normally follows a log-normal distribution,while at high traffic densities the velocity follows a negative-exponential distribution.

UAV relay network to provide communications in mobile ad hoc networks

Abstract: Network connectivity can be affected by mobile networks mobility and extensions of the active area.This paper presents a method using an unmanned aerial vehicle(UAV) relay networks to support communication in mobile ad hoc networks.System models are given for ground node to UAV connectivity,ground node to ground node via UAV connectivity,and UAV to UAV connectivity.This paper also presents a weighted centroid UAV flight model with a flight control method for the UAV relay network.Simulations analyze the impact of the ground node active region,speed,and communication methods on the three types of network connectivity.The simulations also analyze the performance of the weighted centroid UAV flight method and the centroid UAV flight method.The simulations show that the weighted centroid UAV flight method more effectively supports ground node intra-domain communication than the centroid UAV flight method while the weighted method is less effective in supporting ground node connections to the UAV.

Multi-hazard risk assessment using GIS in urban areas

Abstract: A risk assessment method was developed for natural disasters related to technological problems to mitigate the effects of disasters.This method first describes the severity and probability of a single incident.Then,a risk map overlay is used to assess the spatial information using the geographic information system to collect vulnerability information.Integrated risks are ranked with a hazard interactions map finally produced based on disaster chains.The method was then applied to Beijing to develop a Beijing risk assessment and mapping software for the rapid estimates of multiple integrated hazards.The result gives a practical means for multi-hazard risk assessment and suggestions for safety personnel.

Hybrid excitation permanent magnet synchronous generator utilizing tooth harmonics for the excitation

Abstract: The tooth harmonic electromotive force(EMF) of the rotor windings induced by the inherent tooth harmonic magnetic field is used as the excitation of a hybrid excitation permanent magnet synchronous generatorThis not only improves material utilization,but also facilitates removal of the brushes and slip ringsThe generation mechanism of the tooth harmonic magnetic field and the tooth harmonic EMF in the rotor windings is analyzed to develop a new hybrid excitation permanent magnet synchronous generatorA prototype was manufactured to demonstrate the feasibility of a hybrid excitation permanent magnet synchronous generator utilizing the tooth harmonic magnetic field for excitationTests show that the tooth harmonic EMF of the rotor windings induced by the tooth harmonic magnetic field can be used to adjust the air-gap magnetic field in the hybrid excitation permanent magnet synchronous generator

Automated lung segmentation for chest CT images used for computer aided diagnostics

Abstract: Segmentation of lungs in chest computed tomography(CT) is often performed as a preprocessing step for computer aided diagnosis(CAD) for lung nodulesTraditional methods are based on threshold strategies which often incorrectly exclude some very important regions such as juxtapleural nodules and blood vessels when some abnormalities exist in the lungThis paper presents a method for lung parenchyma extraction including the initial border extraction,the modification of the initial border based on a 2-D convex hull and the final parenchyma extractionExperiments on over 400 clinical chest CT images of 6 patients show that the segmentation accuracies are all above 83% in both normal and lung cancer casesThis segmentation method effectively includes all juxtapleural nodules and blood vessels in chest CT images for detection of lung nodules in CAD systems

Predictions of China's passenger vehicle and commercial vehicle stocks

Abstract: The stocks of China's passenger vehicles and commercial vehicles were projected by employing Gompertz model and linear extrapolation modelThe results indicate that China's vehicle stock will reach 252—292 million in 2020 and 398—523 million in 2030The passenger vehicle stock will grow faster with some uncertainty,reaching 220—259 million in 2020 and 351—476 million in 2030The commercial vehicle stock will reach 328 million in 2020 and 469 million in 2030In spite of the fast growth of the vehicle stock in China,the vehicle ownership level of China will still be far behind developed countries

Automatic phrase boundary labeling for a Mandarin TTS corpus using the Viterbi decoding algorithm

Abstract: An automatic prosodic phrase boundary labeling method was developed for Mandarin speech synthesis corpora using the Viterbi decoding algorithm.The algorithm quickly and precisely labels the prosodic phrase boundaries of Mandarin speech,which will reduce the cost of constructing a large corpus based Mandarin unit selection speech synthesis system.The method can be divided into the model training stage and the prosody labeling stage.The training prepares a context-dependent hidden Markov model(HMM) of the spectrum,F0 and phone duration.In the labeling stage,the Viterbi decoding algorithm is used to label the prosodic phrase boundaries using the training stage models.Tests show that the system gives an F-score of 77.64% for the prosodic phrase boundary labeling.The prosodic labeling categories can be increased easily in this method.

Light weight design of a machine tool based on sensitivity analysis

Abstract: Light weight design of machine tools can reduce costs while maintaining stiffness.A high-speed horizontal machining center was analyzed using a sensitivity analysis of the mass to stiffness results for each dimension using SolidWorks and ANSYS.The light weight design procedure has the sensitivity dimensions as parameters,the mass as the goal,and the stiffness and casting technique as the constraint conditions.The simulations show that the stiffness can be maintained while reducing the mass by 312 kg(6.9%).The optimization shows the validity of the sensitivity analysis for the light weight design of structures.

Coarticulatory effect in VCV sequences in Chinese

Abstract: The V-to-V coarticulatory effect in VCV sequences involves trans-segmental effects on the onset values of the second formant(F2) by the foregoing vowels on the following ones.However,due to the long temporal separation between vowels for aspirated stops,coarticulation has little effect in the aspirated stops since aspiration is a prominent factor in blocking coarticulation.The effect of the stop place is seen with coarticulation extent of the labial exceeding that of the alveolar in the fixed vowel context of /i/.However,the interactive effect of the place of articulation and the fixed vowel context is stronger than the effect of the stop place.

Regenerative braking system based on ESP pressure modulator

Abstract: The hydraulic braking system energy regeneration efficiency was improved by a regenerative braking system based on an ESP pressure modulator.This paper describes the working principle,hardware design and the regenerative brake system test bed.Tests of the regenerative braking system verify the smoothness and braking efficiency.

Intelligent information security risk assessment based on a decision tree algorithm

Abstract: Information security risk assessments are subjective,require long modeling times and have low classification accuracy.An intelligent information security risk assessment method based on a decision tree algorithm(ISRAD) was developed using hierarchical decomposition based on the analytic hierarchy process(AHP)method with classification based on a decision tree classification algorithm using machine learning.This method used to assess risks when classifying discrete data from companies,banks and government entitles compared with support vector machine classification algorithm,this method can handle various data types with 200% better classification and fast characterization.Therefore,this method is an effective information system risk assessment method.

Decision support system for urban shelter locations

Abstract: A decision support system based on the geographic information system(GIS) and multi objective programming was developed to identify shelter locations and evacuee distributions.Candidate shelters were filtered by overlapping park locations with risk maps for different urban disasters.The city road topology was then considered to find the shortest routes among nodes calculated by the GIS network analysis function.A multi-objective programming model was then developed to optimize the number,locations and service areas of the shelters.A case study applied to a Chinese city shows that the model can be used to locate the practical urban shelter locations.

Ship detection algorithm for optical remote sensing images

Abstract: A ship detection algorithm was developed for general hardware platforms for optical remote sensing images.The system uses an adaptive threshold histogram-based segmentation technique for the land masking.Then,the sparseness of ships on the sea is used to develop an effective prescreening approach based on the tile statistical features with only the target-labeled tiles processed in the next step.A clutter rate coefficient is used to control the structural elements of the morphology Top-Hat operator for better background suppression.Finally,a pattern recognition method is used for discrimination.Tests show the effectiveness of this algorithm implemented on a hardware platform.

Analysis and measurement of carbamate,carbonate and bicarbonate in carbonated aqueous ammonia solution

Abstract: Aqueous ammonia solution is considered to be an effective and economic absorbent for CO2 capture in recent years,but the ion identification(related to carbamate,carbonate and bicarbonate) is difficult after CO2 dissolving into aqueous ammonia solution.A titration method was developed to determine the total CO2 and total ammonia in the solution using 0.1 mol/L H2SO4 and Metrohm 809 Titrando.The method shows good accuracy compared with the mass balance method and the BaCl2 precipitation method.The titration process was analyzed in detail,which shows that the titration method developed by the National Energy Technology Laboratory(NETL) of the U.S.Department of Energy is questionable.The titration method in this paper cannot determine the concentration of carbamate,carbonate and bicarbonate,respectively,compared with the Raman and NMR spectroscopy methods,but the total CO2 and total ammonia can be determined quickly and accurately according to the titration profile of pH.

Transient voltage stability of independent electric power systems with induction motors

Abstract: Independent electric power systems having induction motors can experience voltage stability problemsA multi-motor,multi-generator power system model was used to analyze transient voltage stabilityThis model effectively eliminates the zero eigenvalue of the Jacobi matrix at the equilibrium point,while guaranteeing equivalence with the original system using a purely differential equation modelA method to differentiate transient voltage in stabilities from transient angle in stabilities was presented,which is used for engineering designFinally,a transient angle stability margin index based on semi-tensor product was extended to the transient voltage stability problemSimulations show that the analysis method can effectively evaluate the transient voltage stability of independent electric power systems and predict reasonably accurate critical clearing times

Forest fuel loading estimates based on a back propagation neutral network

Abstract: Forest fuel loading is an import factor related to the fire behavior;therefore,forest fuel loading estimates are very important for forest fire management.This study used data collected in 32 Larix Gmelinii forest sample locations in the Daxing'anling region to build a multivariable regression equation and a back propagation neural network model to estimate forest fuel loadings from stand factors,such as tree age,crown cover,average tree height,and diameter at breast height.The back propagation neutral network training and simulation used for models in MATLAB with the multivariable regression equation developed using SPSS.The fitting precision of the back propagation neutral network model was 99.9% with an extrapolation precision of 65.51%.The fitting precision of the multivariable regression equation was 68.29% with an extrapolation precision of 62.1%.Thus,the back propagation neutral network model for estimating forest fuel loading from the stand factors is more accurate than the multivariable regression equation.The extrapolation accuracy of both the BP neutral network model and the multivariable regression model are less than 70% due to the small number of samples.

Optimum design of runner blades of a tubular turbine based on vorticity dynamics

Abstract: The boundary vorticity dynamics(BVD) method was used to optimize the runner blade shape of a tubular turbine.The three-dimensional full-passage turbulent simulation was performed with initial designs of the guide vanes and runner blades.The distribution of the boundary vorticity flux(BVF) on the runner blade surfaces was then analyzed to find where the flow behavior was defective.The runner blade shape was then modified based on the swirl to compare the BVF conditions near the hub and on the blade leading edge which improved the runner efficiency.The result shows that the BVF distribution on the blade surfaces effectively indicates the tubular runner performance for reliable shape optimization.

Software trustworthness evaluation based on weakness analysis and testing assessment

Abstract: This paper presents a software trustworthness evaluation method based on weakness analyses and testing assessments to evaluate the software's fitness-for-use during the development cycle.This paper focuses on five aspects of trustworthiness.To find out a weakness,the analysis starts from a weakness exposed in the software design model.The analysis considers the trustworthiness of the entire software package by evaluating the danger and influence of the software weakness.The analysis evaluates the software trustworthiness from different angles to find weaknesses early in the software design stage to improve software development quality and efficiency.

Positioning based on the Chinese digital terrestrial television broadcasting system

Abstract: The digital terrestrial television broadcasting(DTTB) system can be complement satellite positioning in urban and indoor environments.A time-frequency joint positioning method based on time-domain synchronous OFDM(TDS-OFDM) signal properties in both the time and frequency domains from the Chinese DTTB system was developed using the pseudorandom noise(PN) sequence in the frame header and the transmission parameter signaling(TPS) in the frame body.The TPS is time-division multiplexed(TDM) as orthogonal frequency-domain pilots.The frequency-domain TPS and the time-domain PN sequences are used jointly to accurately estimate the signal transmission delay.Then,the position is determinated based on the time difference of arrival(TDOA).The number of multiplies in theoretically equal to the symbol numbers used for the positioning.Simulations show an accuracy of 0.15 m when the signal-to-noise ratio(SNR) is higher than 20 dB is an AWGN channel.Thus,this system is simple and accurate.

Exciter stator current harmonics of multi-phase brushless excitation system

Abstract: Rectifier faults in brushless exciter systems are difficult to detect because the rectifier is rotating,while the harmonic characteristics of the stator field winding are more easily measured for fault detection.The fault characteristics of a rotating rectifier in a multi-phase brushless exciter system were determined by predicting the armature current and the magnetic motive force(MMF) for normal and open circuit faults of a single diode.The results were used to describe the harmonic characteristics of the exciter stator current.A system simulation was then also used to analyze the harmonics of the exciter stator current.The theoretical analysis agrees well with the simulation results to show that this method can be used to study the harmonic characteristics of the exciter stator current for various rotary rectifier faults for fault diagnosis of rotary rectifiers in multi-phase brushless exciter systems.

Projecting beam model for robot-assisted flexible needle insertion

Abstract: Needle path steering is one of the most important techniques during robotic-assisted needle insertionSoft tissue deformation,multi-layer tissue relative sliding and needle deflection can easily make the needle miss the target,which decreases the needle insertion precisionBased on the analysis of needle forces,a projecting beam model was proposed to predict the needle path through laws of needle deflection,with a flexible needle divided into finite segments with quasi-static process during needle insertion and each segment regarded as a projecting beamAn algorithm was then developed to predict the needle path in three-dimensional spaceSimulation results show that the proposed model can effectively predict the flexible needle path,which provides a theoretical fundamental for path planning and obstacle avoidance during robot-assisted needle insertion

SICGE extensions and their linkage with IESOM

Abstract: An energy-economy-environment integrated assessment model(3E model) was developed to improve evaluations of the effects of energy and climate change policies.The state information center general equilibrium model(SICGE) was extended to include a production function,carbon emission calculations and a carbon tax in a macro-economic system.The Tsinghua energy system optimization model(TESOM) was used to describe the energy system with bidirectional links to SICGE through linkage variables such as the energy service demand,various technical variables and investment costs.The converged solution gave more consistent results for the SICGE and TESOM models.

Head pose estimation based on a second order histogram of the orientation gradient

Abstract: One of the key problems of appearance based head pose estimation methods is to find the proper image descriptors which are closely related to the head pose variations.This paper describes a second order histogram of the orientation gradient(HOG) based head pose image representation for head pose estimation in still images.The image is divided into a grid of cells with the HOG computed for each cell.Then a pair wise relationship vector among the bins of neighboring HOGs is computed with all the pair wise relationship vectors then concatenated to form the final descriptor.The second order HOG is used to encode the second order statistics of the gradient orientation distribution to accurately describe the pose variations.Tests show that this method is more accurate than the two state-of-the-art methods using the original HOG and the GaFour method.

HMM-based expressive speech synthesis with a flexible Mandarin stress adaptation model

Abstract: Expressive speech synthesis has recently received much attention. Stress is one key issue which may improve the expressiveness of the synthetic speech. However, rare work was done in Mandarin stress prediction and expression. This paper presents a HMM-based expressive speech synthesis system which supports Mandarin stress synthesis. Mandarin stress was automatically predicted with textual features utilizing a Maximum Entropy Model. The linear adaptation model was extracted from a large corpus by analyzing their stress related acoustic features. The advantage of the proposed model is it can be easily modified to build a system with another speaking style or emotion. Experiments show that the proposed stress adaptation system can convey stress effectively and generate high expressive speech. The overall performance of the synthetic speech is also improved.

Stress patterns of disyllabic words terms with identical pronunciation and different morph-syntactic structures in standard Chinese

Abstract: Perceptual and acoustic analyses were used to investigate the stress patterns of Chinese disyllabic constituents with identical pronunciation and different morph-syntactic structuresTests demonstrate that the stress patterns in standard Chinese(SC) are "Strong-Weak" when the final syllable is a neutral tone and that this stress pattern can be used as the cue to discriminate meanings of the disyllabic constitutesHowever,due to the final lengthening effect,disyllabic constituents without neutral tones were inclined to be the "Weak-Strong" pattern,which exhibits no corresponding relation with the morph-syntactic structures