On Detecting Spectrum Opportunities for Cognitive Vehicular Networks in the TV White Space

We overview the challenges related to spectrum awareness in the vehicular environment, with emphasis on awareness in the TV licensed band. In the vehicular environment the cognitive radio can help to: 1) satisfy capacity demand for Intelligent Transportation Systems (ITS) applications; and 2) offload time insensitive applications from the ITS dedicated spectrum. However, using simple propagation models we show that neither sensing, nor geolocation database lookup alone can provide sufficient incumbent protection. Collaboration among the sensors to take advantage of spatial diversity is difficult due to the rapidly changing network topology. Nevertheless, mobility provides the opportunity to use time diversity at each sensor. We also discuss the influence of sensing subsystem design on the vehicular cognitive network medium access (MAC) sublayer. Whenever appropriate, we evaluate applicability of the requirements imposed by the Federal Communications Commission (FCC) and the IEEE 802.22 standard to the cognitive vehicular networks.     

Influence of pre-electrophoresis on protein separations in polyacrylamide gels

Polyacrylamide gel electrophoresis (PAGE) is a widely used technique in protein separations. In this study, the effects of pre-electrophoresis (i.e., exposing polyacrylamide gels to an electrical field prior to loading samples) on the separation of a mixture of 10 standard proteins was investigated. Three different gel concentrations (based on amounts of acrylamide and bis-acrylamide, always at a 37.5:1 ratio) relative to the volume of the gel solution were tested: 6%, 9%, and 12%. For each concentration, multiple slab gels were subjected to pre-electrophoresis prior to separation of proteins, while multiple other (i.e., companion) slab gels were used but without applying the pre-electrophoresis technique. Separation results were investigated, showing that the application of the pre-electrophoresis technique had a significant effect on separations particularly for 6% and 9% gels.     

Minimum thickness of elliptical masonry arches

In this paper, we compute the minimum thickness and the location of the imminent intrados hinge of symmetric elliptical masonry arches when subjected to their weight. While this problem (Couplet’s problem) was solved rigorously for semicircular arches more than a century ago, no results have been available for elliptical arches. Motivated from the recent growing interest in identifying the limit equilibrium states of historic structures, this paper first computes two neighboring physically admissible thrust-lines which can just be located in elliptical arches by adopting either a polar or a cartesian coordinate system. These two distinguishable, physically admissible thrust-lines are neighboring thrust-lines to Hooke’s catenary which is not a physically admissible thrust-line as has been shown recently. Accordingly, the paper shows that the answer for the minimum thickness of symmetric elliptical masonry arches is not unique and that it depends on the coordinate system adopted and the associated stereotomy exercised. This result is confirmed by developing a variational formulation after selecting the appropriate directions of the rupture that initiates at the intrados hinge. The paper concludes that Hooke’s limiting catenary, although not a physically admissible thrust-line, offers a conservative value for the minimum thickness in most practical configurations.     

通风对室内外颗粒物浓度关系的影响分析

基于室内颗粒物质量平衡方程,建立了通风过滤空调系统的数学模型,对不同的通风系统以及不同粒径下的I/O比进行了理论研究。通过数值计算表明,过滤器效率对机械通风系统的I/O比影响显著;对于自然通风系统,当换气次数由1 h-1增加至6h-1,I/O比变化迅速,继续增大换气次数,则I/O比趋于平缓。     

Selected mapping with symbol re‐mapping for OFDM/TDM using MMSE‐FDE

Orthogonal frequency division multiplexing (OFDM) signals have a problem with a high peak‐to‐average power ratio (PAPR). A distortionless selected mapping (SLM) has been proposed to reduce the PAPR, but a high computational complexity prohibits its application to an OFDM system with a large number of subcarriers. Recently, we proposed OFDM combined with time division multiplexing (OFDM/TDM) using minimum mean square error frequency‐domain equalization (MMSE‐FDE) to improve the bit error rate (BER) performance of conventional OFDM with a lower PAPR. The PAPR problem, however, cannot be completely eliminated. In this paper, we present an SLM combined with symbol re‐mapping for OFDM/TDM using MMSE‐FDE. Unlike the conventional OFDM, where SLM is applied over subcarriers in the frequency domain, we exploit both time and frequency dimensions of OFDM/TDM signal to improve the performance with respect to PAPR and BER. A mathematical model for PAPR distribution of OFDM/TDM with SLM is presented to complement the computer simulation results. It is shown that proposed SLM can further reduce the PAPR without sacrificing the BER performance with the same or reduced computational complexity. Copyright © 2010 John Wiley & Sons, Ltd.     

Iterative decision‐directed estimation and compensation of nonlinear distortion effects for OFDM systems

Orthogonal frequency division multiplexing (OFDM) has been adopted for several wireless network standards due to its robustness against multipath fading. Main drawback of OFDM is its high peak‐to‐average power ratio (PAPR) that causes a signal degradation in a peak‐limiting (e.g., clipping) channel leading to a higher bit error rate (BER). At the receiver end, the effect of peak limitation can be removed to some extent to improve the system performance. In this paper, a joint iterative channel estimation/equalization and clipping noise reduction technique based on minimum mean square error (MMSE) criterion is presented. The equalization weight that minimizes the mean square error (MSE) between the signal after channel equalization and feedback signal after clipping noise reduction is derived assuming imperfect channel state information (CSI). The MSE performance of the proposed technique is theoretically evaluated. It is shown that the BER performance of OFDM with proposed technique can be significantly improved in a peak‐limited and doubly‐selective (i.e., time‐ and frequency‐selective) fading channel. Copyright © 2011 John Wiley & Sons, Ltd.     

Exploring Data-Independent Dimensionality Reduction in Sparse Representation-Based Speaker Identification

The sparse representation classification (SRC) has attracted the attention of many signal processing domains in past few years. Recently, it has been successfully explored for the speaker recognition task with Gaussian mixture model (GMM) mean supervectors which are typically of the order of tens of thousands as speaker representations. As a result of this, the complexity of such systems become very high. With the use of the state-of-the-art i-vector representations, the dimension of GMM mean supervectors can be reduced effectively. But the i-vector approach involves a high dimensional data projection matrix which is learned using the factor analysis approach over huge amount of data from a large number of speakers. Also, the estimation of i-vector for a given utterance involves a computationally complex procedure. Motivated by these facts, we explore the use of data-independent projection approaches for reducing the dimensionality of GMM mean supervectors. The data-independent projection methods studied in this work include a normal random projection and two kinds of sparse random projections. The study is performed on SRC-based speaker identification using the NIST SRE 2005 dataset which includes channel matched and mismatched conditions. We find that the use of data-independent random projections for the dimensionality reduction of the supervectors results in only 3 % absolute loss in performance compared to that of the data-dependent (i-vector) approach. It is highlighted that with the use of highly sparse random projection matrices having \(\pm \) 1 as non-zero coefficients, a significant reduction in computational complexity is achieved in finding the projections. Further, as these matrices do not require floating point representations, their storage requirement is also very small compared to that of the data-dependent or the normal random projection matrices. These reduced complexity sparse random projections would be of interest in context of the speaker recognition applications implemented on platforms having low computational power.     

Material characterization of blended epoxy resins related to fracture toughness

The present study describes the effect of the macromolecular modifications on the fracture toughness of an epoxy system. We synthesized epoxy networks by the reaction of diglycidyl ether of bisphenol A (DGEBA) with methyl-tetrahydro-phthalic anhydride (MTHPA), initiated by a tertiary amine. Several materials were obtained by adding a high molecular weight monomer to one with low molecular weight (both based on DGEBA) at different concentrations. In every case, a stoichiometric amount of MTHPA was employed. The glass transition temperature and the Angell’s fragility index, derived from thermo-viscoelastic properties, were used to characterize the materials. Relationship between these two parameters and the fracture properties, including the fracture toughness and the microscopic roughness of the fracture surfaces observed by atomic force microscope (AFM), was then investigated. We found that there were direct correlations among the glass transition temperature, the fragility, the fracture toughness, and the roughness. This study revealed that both the glass transition temperature and the fragility are effective for characterizing material in relation to the fracture toughness of the blended epoxy resins.     

Renewable energy sources and rationale use of energy development in the countries of GCC: Myth or reality?

The large oil and natural gas resource base and the greater competitiveness of conventional energy supply technologies based on oil and gas is a key energy characteristic in the countries of the GCC. Until today, mostly pilot and research Renewable Energy Sources (RES) and Rational Use of Energy (RUE) activities were conducted. However, these countries seem to be ready to take a more active part in the development of environmental friendly energy technologies. RES are expected to play a greater role in the future based on the rich natural potential of the region. In addition, appropriate efforts to formulate strategic RUE policies are initiated for assuring buildings sustainability and providing guidelines for future architecture. In this context, GCC countries are realizing the inevitability of putting climate change issues on the top of the list of priorities in the process of economic and social development. This paper includes an analytical review of the current RES and RUE development status in the GCC region, giving special emphasis to the business opportunities that the region offers for regional and international companies involved in this market.