Tsinghua Science and Technology最新文献

The power consumption by the data cache is important in DSP designs. This study presents an enhanced branch access LRU-SEQ (EBA-LRU-SEQ) policy for data caches in DSP designs to reduce the power consumption. The design is based on the LRU policy with embedded prefetch table to provide branch access. Tests show that the EBA-LRU-SEQ policy reduces the data cache power consumption to 54% of a system with no power control.

The idea of using a one-time-one-key design has been widely applied in conventional cryptography. With the security theory of conventional cryptology, encryption algorithms are made public while all the secrets are encoded only in the keys. This paper applies chaos theory to conventional cryptography to develop a one-time-one-algorithm design. A general theory is given to generate the clock key, substitution box, permutation box and operational sign functions for a one-time-one-algorithm scheme. This scheme is then implemented in a system to manage the tradeoff between speed and the security of the encryption algorithm.

A critical parameter of brain-computer interfaces (BCIs) is the number of dimensions a user can control independently. One way to increment this number without increasing the mental effort required to operate the system is to stimulate several sensory modalities simultaneously, and to distinguish brain activity patterns when the user focuses attention to different elements of this multisensory input. In this article we show how shifting attention between simultaneously presented tactile and visual stimuli affects the electrical brain activity of human subjects, and that this signal can be used to augment the control information from the two uni-modal BCI subsystems.

A stronger canonical model was developed to improve the performance of automatic pronunciation evaluations. Three different strategies were investigated with speaker adaptive training to normalize variations among speakers, minimum phone error training to identify easily confused phones and maximum likelihood linear regression (MLLR) adaptation to compensate for accent variations between native and non-native speakers. The three schemes were combined to improve the correlation coefficient between machine scores and human scores from 0.651 to 0.679 on the sentence level and from 0.788 to 0.822 on the speaker level.

The cluster global time can change in wireless sensor networks due to leader re-elections and node disabilities between two successive synchronizations, which will affect temporal relationships. This paper analyzes cluster global time continuity, using global time change models for the node dynamics. The results prove that defining the global time using the cluster average time (AGT) is more stable than defining it using a single node's local time (SGT). With normally distributed clock-parameter assumptions, the AGT change bounds are at most 70.7% of those for the SGT's. The impacts of the initial phase and frequency skew distributions on the global time continuity are also investigated to show that the initial phase variations may strongly influence the continuity. Simulations show that the AGT is more stable with less disabled nodes or larger clusters. The appropriate cluster size is 20–40 when there are less than 15 disabled nodes.

Cross-modal interactions between visual understanding and linguistic processing substantially contribute to the remarkable robustness of human language processing. We argue that the formation of cross-modal referential links is a prerequisite for the occurrence of cross-modal interactions between vision and language. In this paper we examine a computational model for a cross-modal reference formation with respect to its robustness against conceptual underspecification in the visual modality. This investigation is motivated by the fact that natural systems are well capable of establishing a cross-modal reference between modalities with different degrees of conceptual specification. In the investigated model, conceptually underspecified context information continues to drive the syntactic disambiguation of verb-centered syntactic ambiguities as long as the visual context contains the situation arity information of the visual scene.

The present study examined whether audiovisual integration of temporal stimulus features in humans can be predicted by the maximum likelihood estimation (MLE) model which is based on the weighting of unisensory cues by their relative reliabilities. In an audiovisual temporal order judgment paradigm, the reliability of the auditory signal was manipulated by Gaussian volume envelopes, introducing varying degrees of temporal uncertainty. While statistically optimal weighting according to the MLE rule was found in half of the participants, the other half consistently overweighted the auditory signal. The results are discussed in terms of a general auditory bias in time perception, interindividual differences, as well as in terms of the conditions and limits of statistically optimal multisensory integration.

Engineering-oriented simulations of quantum mechanical tunneling are often based on density-gradient (DG) theory. This paper presents an analytical solution to the DG equation for quantum tunneling through an ultra-thin oxide in a MOS capacitor with an n+ poly-silicon gate obtained using the method of matched asymptotic expansions. Tunneling boundary conditions extend the approximation into the entire region of the poly-silicon gate, oxide barrier, and substrate. An analytical solution in the form of an asymptotic series is obtained in each region by treating each part of the domain as a separate singular perturbation problem. The solutions are then combined through ‘matching’ to obtain an approximate solution for the whole domain. Analytical formulae are given for the electrostatic potential and the electron density profiles. The results capture the features of the quantum effects which are quite different from classical physics predictions. The analytical results compare well with exact numerical solutions over a broad range of voltages and different oxide thicknesses. The analytical results predict the enhancement of the quantum tunneling effect as the oxide thickness is reduced.

The interactions among nano-sized giant magnetoresistances (GMRs) which can affect the biosensor operation, were studied using micromagnetic simulations and micromagnetic analysis. The magnetic field energy, the magnetization distribution and the effective magnetic field were simulated for variable spacer distances, aspect ratios and external magnetic fields to study the interactions among the GMR sensors. And the spacer distance should be at least 1000 nm to eliminate interference between 1000 nm× 100 nm×9 nm or larger GMRs in an array, while the aspect ratio should be more than 10 to improve the sensor sensitivity and stability. Micromagnetic energy theory is used to explain the simulation results.

Existing methods of obtaining runtime feedback for structure data-layout optimization have several drawbacks, such as large overhead and difficulty composing training sets. As a result, structure data-layout optimization is not widely used. To overcome these drawbacks, a performance monitoring unit (PMU) sampling method was developed with much less overhead and better portability and usability. An algorithm was developed to correct incomplete and inaccurate PMU sampling. With the corrected PMU feedback, a structure data-layout optimizer achieved a 45.1% performance improvement compared to a design without data-layout optimization, which is 97.6% of the performance improvement achieved with instrumented feedback. Calculation of the PMU feedback increased the execution time by 12.3%, compared to the overhead for the instrumented feedback of 341.5%. Tests show that the PMU feedback is efficient and effective for structure data-layout optimization.