Coopetition spectrum trading in cognitive radio networks

Spectrum trading is a promising method to improve spectrum usage efficiency. Several issues must be addressed, however, to enable spectrum trading that goes beyond conservative trading idle bands and achieve cooperation between primary and secondary users. In this paper, we argue that spectrum holes should be explicitly endogenous and negotiated by spectrum trading participants. To this end, we proposed an a Vickery auction based, coopetive framework to foster cooperation, while allowing competition for spectrum sharing. Incentive schemes and penalty for revocable spectrum are proposed to increase the spectrum access opportunities for SUs while protecting PUs spectrum value. A simultation study shows that the proposed framework outperforms conservative trading approaches, in a variety of scenarios with different levels of cooperation and bidding strategies. © 2013 IEEE

Enhanced large-scale production of laccases from Coriolopsis polyzona for use in dye bioremediation

Pollution from synthetic dyes, released by textile and paper pulping plants, draws major concern. Textile effluents have negative impact both on the environment and human health because they are toxic and some are carcinogenic. Apart from the textile industry, dyes are also widely used in manufacturing industries for leather products, cosmetics, pharmaceuticals, foods and beverages. It is known that white rot fungi can decolourise and detoxify various industrial effluents through the production of extracellular lignin modifying enzymes, a major class of which are laccases (EC 1.10.3.2). Considering the above, three strains of white rot fungi, Coriolopsis polyzona (MUCL 38443), Pleurotus ostreatus (ATCC no. MYA-2306) and Pycnoporus sanguineus (MUCL 41582) were studied for their ability to produce laccases in liquid media. The effects of mannan oligosaccharides (MO) as elicitor and ferulic acid as inducer were studied using central composite experimental design in liquid cultures of the three strains. The results showed that MO, either added alone or combined with ferulic acid, enhanced laccase activity in the three different cultures and the enhancement was species specific. The highest increase was in liquid cultures of P. sanguineus (88-fold) followed by P. ostreatus (3-fold) and C. polyzona (2-fold), among which C. polyzona resulted in the highest laccase activity. The combined addition of 150 mg/l of MO and 1 mM ferulic acid resulted in the optimal laccase activity by C. polyzona, whereas additions of 75 mg/l MO to the cultures of P. sanguineus and P. ostreatus led to the optimal activity. Extracellular laccase activity was considerably increased when C. polyzona was grown in glucose-bactopetone based culture medium induced by ferulic acid. The effect of inoculum conditions on laccase production was studied at reactor scales. Laccase activity achieved with conidia inoculation was higher compared with mycelium inoculation at the early stage of fermentation. However, the laccase levels were similar after 23 days of fermentation (110 U/ml and 100 U/ml for the conidia and mycelia pre-culture respectively). The conidia inoculation is preferred in scale-up when time-cost is considered. The maximal laccase activity with conidia inoculation in a 2 litre stirred tank reactor was 27% higher compared to that in shaken flasks. This showed that C. polyzona cultures have the potential to be scaled-up for increased laccase activity by applying conidia inoculum. The fermentation of C. polyzona was scaled-up to 20 litre and 150 litre stirred tank reactors applying fed-bath strategy. This resulted in 100 % enhancement of laccase activity. Addition of oak wood powder in the culture medium increased total laccase activity indicating the potential of lignocellulosic wastes as alternative substrates for enhanced laccase production with reducing cost. In order to investigate the application of laccases in dye decolourisation, two major laccase isozymes (Lac I & II) from C. polyzona were purified to apparent eletrophoretic homogenetity using hydrophobic interaction chromatography and ionexchange chromatography. Both enzymes were found to be monomeric proteins with the same molecular mass of 63 kDa, and isoelectronic point of 4.3. Their catalytic activities were studied under various substrates, pHs and temperatures. The highest enzyme affinity and efficiency were obtained with 2,2′-azino-bis- (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). Compared with other fungal laccases, the laccases from C. polyzona have very low Km values with ABTS as a susbtrate. The optimum pHs were 2.8, 3.0 and 5.0 on ABTS, 2, 6-dimethoxyphenol (DMP) and syringaldazine, respectively. Both isozymes had acidic optimal pH values. However, they were more stable in netural pH rather than at acidic pH. Moreover, mass spectrometry (MS) analysis of tryptic digestion products of the two isozymes was performed, which showed further similarity of these two isozymes. As common physical or chemical methods for dye removal are expensive, have low efficiency and sometimes generate other pollutants, the decolourisation of industrial effluents containing single and mixed dyes was investigated using purified laccase (Lac I) from C. polyzona as well as whole cell culture. The method appeared to be an attractive alternative for dye removal. Anthraquinone dyes were found to be more easily decolourised by Lac I compared to azo dyes. The addition of redox mediator ABTS and violuric acid (VA) improved considerably the catalytic efficiencies of azo dyes. Decolourisation, 40-50 %, was achieved for the reactive and the direct dye baths. Response surface technology (RSM) was applied to optimise the decolourisation of the diazo dye reactive black 5 (RB 5) by Lac I. Box-Behnken experimental design with three variables including laccase activity (100, 200, 300 U/l), pH (5, 7, 9) and VA concentration (0, 1.25, 2.5 mM) was studied to identify a significant correlation between the effect of these variables on decolourisation of RB5. The experimental values were in good agreement with the predicted values with the correlation coefficient of 97.4%

On model selection criteria for climate change impact studies

Climate change impact studies inform policymakers on the estimated damages of future climate change on economic, health and other outcomes. In most studies, an annual outcome variable is observed, e.g. annual mortality rate, along with higher-frequency regressors, e.g. daily temperature and precipitation. Practitioners use summaries of the higher-frequency regressors in fixed effects panel models. The choice over summary statistics amounts to model selection. Some practitioners use Monte Carlo cross-validation (MCCV) to justify a particular specification. However, conventional implementation of MCCV with fixed testing-to-full sample ratios tends to select over-fit models. This paper presents conditions under which MCCV, and also information criteria, can deliver consistent model selection. Previous work has established that the Bayesian information criterion (BIC) can be inconsistent for non-nested selection. We illustrate that the BIC can also be inconsistent in our framework, when all candidate models are misspecified. Our results have practical implications for empirical conventions in climate change impact studies. Specifically, they highlight the importance of a priori information provided by the scientific literature to guide the models considered for selection. We emphasize caution in interpreting model selection results in settings where the scientific literature does not specify the relationship between the outcome and the weather variables.Comment: Additional simulation results available from authors by reques

Coexistence of the antiferromagnetic and superconducting order and its effect on spin dynamics in electron-doped high-TcT_{c} cuprates

In the framework of the slave-boson approach to the $t-t'-t''-J$ model, it is found that for electron-doped high-$T_c$ cuprates, the staggered antiferromagnetic (AF) order coexists with superconducting (SC) order in a wide doping level ranged from underdoped to nearly optimal doping at the mean-field level. In the coexisting phase, it is revealed that the spin response is commensurate in a substantial frequency range below a crossover frequency $\omega_{c}$ for all dopings considered, and it switches to the incommensurate structure when the frequency is higher than $\omega_{c}$. This result is in agreement with the experimental measurements. Comparison of the spin response between the coexisting phase and the pure SC phase with a $d_{x^{2}-y^{2}}$-wave pairing plus a higher harmonics term (DP+HH) suggests that the inclusion of the two-band effect is important to consistently account for both the dispersion of the spin response and the non-monotonic gap behavior in the electron-doped cuprates.Comment: 6 pages, 5 figure

Spectroscopic signatures of the Larkin-Ovchinnikov state in the conductance characteristics of a normal-metal/superconductor junction

Using a discrete-lattice approach, we calculate the conductance spectra between a normal metal and an s-wave Larkin-Ovchinnikov (LO) superconductor, with the junction interface oriented {\em along} the direction of the order-parameter (OP) modulation. The OP sign reversal across one single nodal line can induce a sizable number of zero-energy Andreev bound states around the nodal line, and a hybridized midgap-states band is formed amid a momentum-dependent gap as a result of the periodic array of nodal lines in the LO state. This band-in-gap structure and its anisotropic properties give rise to distinctive features in both the point-contact and tunneling spectra as compared with the BCS and Fulde-Ferrell cases. These spectroscopic features can serve as distinguishing signatures of the LO state.Comment: 8 pages, 5 figures; version as publishe

Coil combination using linear deconvolution in k-space for phase imaging

Background: The combination of multi-channel data is a critical step for the imaging of phase and susceptibility contrast in magnetic resonance imaging (MRI). Magnitude-weighted phase combination methods often produce noise and aliasing artifacts in the magnitude images at accelerated imaging sceneries. To address this issue, an optimal coil combination method through deconvolution in k-space is proposed in this paper. Methods: The proposed method firstly employs the sum-of-squares and phase aligning method to yield a complex reference coil image which is then used to calculate the coil sensitivity and its Fourier transform. Then, the coil k-space combining weights is computed, taking into account the truncated frequency data of coil sensitivity and the acquired k-space data. Finally, combining the coil k-space data with the acquired weights generates the k-space data of proton distribution, with which both phase and magnitude information can be obtained straightforwardly. Both phantom and in vivo imaging experiments were conducted to evaluate the performance of the proposed method. Results: Compared with magnitude-weighted method and MCPC-C, the proposed method can alleviate the phase cancellation in coil combination, resulting in a less wrapped phase. Conclusions: The proposed method provides an effective and efficient approach to combine multiple coil image in parallel MRI reconstruction, and has potential to benefit routine clinical practice in the future