Tensor networks for MIMO LPV system identification

ABSTRACT

In this paper, we present a novel multiple input multiple output (MIMO) linear parameter varying (LPV) state-space refinement system identification algorithm that uses tensor networks. Its novelty mainly lies in representing the LPV sub-Markov parameters, data and state-revealing matrix condensely and in exact manner using specific tensor networks. These representations circumvent the ‘curse-of-dimensionality’ as they inherit the properties of tensor trains. The proposed algorithm is ‘curse-of-dimensionality’-free in memory and computation and has conditioning guarantees. Its performance is illustrated using simulation cases and additionally compared with existing methods.     

Carbonaceous fillers for shape memory actuation of polyurethane composites by resistive heating

The effectiveness of carbonaceous, electrically conductive fillers in shape memory actuation of polyurethane composites by resistive heating was evaluated. Specifically, the dependence of electrical resistivity on specimen temperature and imposed tensile strains encountered in shape memory test cycles was determined for shape memory polyurethane (SMPU) composites of carbon nanofiber (CNF), oxidized carbon nanofiber (ox-CNF), and carbon black (CB). The SMPU composites with crystalline soft segments were synthesized from diphenylmethane di-isocyanate, 1,4-butanediol, and poly(caprolactone)diol in a low-shear chaotic mixer and in an internal mixer. The materials synthesized in the chaotic mixer showed higher soft segment crystallinity and lower electrical percolation threshold. A reduction in soft segment crystallinity was observed in the presence of CNF and ox-CNF; the reduction was smaller in the case of ox-CNF. Only the composites of CB showed pronounced positive temperature coefficient (PTC) effects. The observed PTC effects bore a close relationship with non-linear thermal expansion during heating. The composites of CNF and ox-CNF did not show PTC effects due to low levels of soft segment crystallinity. The resistivity of composites of CB increased by several orders of magnitude with imposed tensile strain while composites of CNF and ox-CNF showed weak dependence on strain.     

A comparative study of electrical and optical properties of InN and In0.48Ga0.52N

We present results of our studies concerning electrical and optical properties of In_0.48Ga_0.52N and InN. Hall measurement were carried out at temperatures between T=77 and 300 K. Photoluminescence (PL) spectrum in InN and In_0.48Ga_0.52N. InN has a single peak at 0.77 eV at 300 K. However, the PL in In_0.48Ga_0.52N has two peaks; a prominent peak at 1.16 eV and a smaller peak at 1.55 eV. These two peaks are attributed to Indium segregation corresponding to a high Indium concentration of 48% and a low concentration of 36%. High electric field measurements indicate that drift velocity that tends to saturate at around V_d=1.0×10⁷ cm/s at 77 K in InN at an electric field of F=12 kV/cm. However, in In_0.48Ga_0.52N the I–V curve is almost linear up to an electric field of F=45 kV/cm, where the drift velocity is V_d=1.39×10⁶ cm/s. At applied electric fields above this value a S-type negative differential resistance (NDR) is observed leading to an instability in the current and to the irreversible destruction of the sample.     

Three-dimensional silk impregnated HAp/PHBV nanofibrous scaffolds for bone regeneration

Three-dimensional silk fibroin impregnated poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) nanofibrous scaffolds with or without hydroxyapatite (HAp) were prepared by wet-electrospinning method followed by freeze-drying. Scaffolds with cotton wool-like structure have the average fiber diameter of 450–850?nm with 80–85% porosity. In-vitro cell culture tests using MG-63 osteosarcoma human cells revealed improved cell viability, alkaline phosphatase (ALP) activity and total cellular protein amount on the silk impregnated scaffolds compared to PHBV and HAp/PHBV scaffolds after 10 days of cell culture. Immunohistochemical analyses on the silk impregnated scaffolds showed that HAp triggered cell penetration and type I collagen production. Besides, HAp mineralization tendency increased with a decrease in percent crystallinity of the scaffolds comprising HAp and silk after 4 weeks of incubation in simulated body fluid. Consequently, cotton wool-like HAp/PHBV-SF scaffold would be a promising candidate as a bone-filling material for tissue regeneration.     

Growth and survival of Escherichia coli O157:H7 on fresh-cut apples in modified atmospheres at abusive temperatures

The effects of reduced-O2 and elevated-CO2 modified atmospheres (MAs) and abusive temperatures on the growth and survival of E. coli O157:H7, yeast, and molds and on changes in the visual quality of fresh-cut apples were evaluated. High-CO1 and low-O2 (> or = 15% and < 1%, respectively) atmospheres inhibited the growth of the pathogen on apple slices at 15 and 20 degrees C. However, the population of the pathogen increased by 1 log cycle after 2 weeks of storage in air. The high-CO2 MA resulted in the inhibition of yeast and mold growth, less browning, and better visual quality than did air and ambient-CO2 atmospheres. The results of this study confirm that E. coli O157:H7 can grow on apple slices in air. These results also show that these organisms survive but are inhibited in MAs with high CO2 levels at abusive temperatures. An MA can increase the shelf life of fresh-cut apples by improving retention of visual quality and inhibiting yeast and molds. Thus, contamination of minimally processed apples with E. coli O157:H7 can be a safety issue for both air- and MA-packaged cut apples.     

Flexibility Based Approach for Damage Characterization: Benchmark Application

A flexibility based damage characterization technique is described and its performance is examined in the context of Phase 1 of the benchmark study developed by the IASC-ASCE SHM Task Group. Noteworthy features of the analytical development are: (1) the methodology used to extract a matrix that is proportional to the flexibility when the excitation is stochastic; (2) the technique used to interrogate the changes in flexibility (or flexibility proportional matrices) with regards to the location of the damage; and (3) the method used to quantify the damage without the use of a model. The strategy proved successful in all the cases considered.     

Bi-modal emotion recognition from expressive face and body gestures

Psychological research findings suggest that humans rely on the combined visual channels of face and body more than any other channel when they make judgments about human communicative behavior. However, most of the existing systems attempting to analyze the human nonverbal behavior are mono-modal and focus only on the face. Research that aims to integrate gestures as an expression mean has only recently emerged. Accordingly, this paper presents an approach to automatic visual recognition of expressive face and upper-body gestures from video sequences suitable for use in a vision-based affective multi-modal framework. Face and body movements are captured simultaneously using two separate cameras. For each video sequence single expressive frames both from face and body are selected manually for analysis and recognition of emotions. Firstly, individual classifiers are trained from individual modalities. Secondly, we fuse facial expression and affective body gesture information at the feature and at the decision level. In the experiments performed, the emotion classification using the two modalities achieved a better recognition accuracy outperforming classification using the individual facial or bodily modality alone.     

User behavior modeling of voice communications: an empirical study

In this study, analysis and modeling of arrival and service processes are presented in a comprehensive fashion in order to determine statistical properties of voice traffic from end‐user perspective in accordance with the queueing theory. For the first time in the literature, we introduce a user centric approach and examine these services considering both flow directions of voice traffic, the uplink and the downlink as opposed to existing studies with the network centric approach. In our study, we use experimental data composed of actual phone calls collected from 2G/3G networks. To achieve this, we designed and implemented a data collection system for mobile users and compared the results by using data from an operational cellular network. In order to determine the time correlation of voice calls, Hurst parameter estimation methods are used. On the basis of the outcomes, independency of call arrivals is shown. Additionally, it is shown that calls acquired from user and network centric approaches are both Poisson distributed. Next, looking at the problem from service process perspective, thorough analyses are performed to determine mathematical models that can best characterize call holding times. Maximum likelihood estimation and expectation maximization algorithm are used, and it is shown that the optimum mathematical model for the characterization of call holding times is the lognormal distribution family. Copyright © 2014 John Wiley & Sons, Ltd.     

Evaluation of nanoparticulate fillers for development of shape memory polyurethane nanocomposites

The effects of nano-size fillers on shape memory (SM) properties of polyurethane (PU) nanocomposites were evaluated. Organoclay, carbon nanofiber (CNF), silicon carbide (SiC), and carbon black (CB) were selected as the fillers in an attempt to reinforce the PU and to obtain significantly increased shape recovery stress. The shape memory PU was synthesized from diphenylmethane diisocyanate, 1,4-butanediol, and poly(caprolactone)diol, the latter with a molecular weight of 4000 g/mol. The composites were prepared by melt mixing of extended chain PU with the fillers. The shape memory behavior was triggered by heating the specimen above the melting point of the crystalline soft segment. Our results indicate that exfoliated organoclay significantly augments SM performance, while CNF and SiC diminish it by interfering with crystallization of the soft segment. CB destroys the shape memory properties beyond a certain loading. Better SM performance with organoclay can be attributed to mechanical reinforcement without much interference with the soft segment crystallinity. The reduction of soft segment crystallinity in the presence of CNF and SiC was analyzed. It was found that the extent of crystallinity, as well as the crystallization temperature, was significantly reduced in the presence of these fillers.