Compensation for HPA nonlinearity and I/Q imbalance in MIMO beamforming systems

In this paper, we investigate the effects of high-power amplifier (HPA) nonlinearity and in-phase and quadrature-phase (I/Q) imbalance on the performance of multiple-input multiple-output (MIMO) transmit beamforming (TB) systems. Specifically, we propose a compensation method for HPA nonlinearity and I/Q imbalance together in MIMO TB systems. The performance of the MIMO TB system under study is evaluated in terms of the average symbol error probability (SEP) and system capacity, considering transmission over uncorrelated frequency-flat Rayleigh fading channels. Numerical results are provided and show the effects of several system parameters, such as the HPA parameters, image-leakage ratio, numbers of transmit and receive antennas, length of pilot symbols, and modulation order of phase-shift keying (PSK), on performance.

On the effect of I/Q imbalance on MIMO transmit-receive diversity systems

In practice, all I/Q signal processing receivers face the problem of I/Q imbalance. In this paper, we investigate the effect of I/Q imbalance on the performance of MIMO maximal ratio combining (MRC) systems that perform the combining at the radio frequency (RF) level, thereby requiring only one RF chain. Based on a system modeling that takes the I/Q imbalance into account, we evaluate the performance in terms of average symbol error probability (SEP), outage probability and system capacity, which are derived considering transmission over uncorrelated Rayleigh fading channels. Numerical results are provided to illustrate the effects of system parameters, such as the image- leakage ratio, numbers of transmit and receive antennas, and modulation order of quadrature amplitude modulation (QAM), on the system performance.

Multi-hop amplify-and-forward relaying cooperation in the presence of I/Q imbalance

In this paper, multi-hop cooperative networks implementing channel state information (CSI)-assisted amplify-and-forward (AF) relaying in the presence of in-phase and quadrature-phase (I/Q) imbalance are investigated. We propose a compensation algorithm for the I/Q imbalance. The performance of the multi-hop CSI-assisted AF cooperative networks with and without compensation for I/Q imbalance in Nakagami-m fading environment is evaluated in terms of average symbol error probability. Numerical results are provided and show that the proposed compensation method can effectively mitigate the impact of I/Q imbalance.

Synthesis of prebiotic galactooligosaccharides from lactose using bifidobacterial β-galactosidase (BbgIV) immobilised on DEAE-Cellulose, Q-Sepharose and amino-ethyl agarose

The bifidobacterial β-galactosidase BbgIV was immobilised on DEAE-Cellulose and Q-Sepharose via ionic binding and on amino-ethyl- and glyoxal-agarose via covalent attachment, and was then used to catalyse the synthesis of galactooligosaccharides (GOS). The immobilisation yield exceeded 90 % using ionic binding, while it was low using aminoethyl agarose (25 – 28 %) and very low using glyoxal agarose (< 3 %). This was due to the mild conditions and absence of chemical reagents in ionic binding, compared to covalent attachment. The maximum GOS yield obtained using DEAE-Cellulose and Q-Sepharose was similar to that obtained using free BbgIV (49 – 53 %), indicating the absence of diffusion limitation and mass transfer issues. For amino-ethyl agarose, however, the GOS yield obtained was lower (42 – 44 %) compared to that obtained using free BbgIV. All the supports tried significantly (P < 0.05) increased the BbgIV operational stability and the GOS synthesis productivity up to 55 °C. Besides, six successive GOS synthesis batches were performed using BbgIV immobilised on Q-Sepharose; all resulted in similar GOS yields, indicating the possibility of developing a robust synthesis process. Overall, the GOS synthesis operation performance using BbgIV was improved by immobilising the enzyme onto solid supports, in particular on Q-Sepharose

High-temperature order–disorder transitions in the skutterudites CoGe1.5Q1.5 (Q=S, Te)

The temperature dependence of anion ordering in the skutterudites CoGe1.5Q1.5 (Q=S, Te) has been investigated by powder neutron diffraction. Both materials adopt a rhombohedral structure at room temperature (space group R-3 ) in which the anions are ordered trans to each other within Ge2Q2 rings. In CoGe1.5S1.5, anion ordering is preserved up to the melting point of 950 °C. However, rhombohedral CoGe1.5Te1.5 undergoes a phase transition at 610 °C involving a change to cubic symmetry (space group Im-3). In the high-temperature modification, there is a statistical distribution of anions over the available sites within the Ge2Te2 rings. The structural transition involves a reduction in the degree of distortion of the Ge2Te2 rings which progressively transform from a rhombus to a rectangular shape. The effect of this transition on the thermoelectric properties has been investigated.

Differential epigenetic reprogramming in response to specific endocrine therapies promotes cholesterol biosynthesis and cellular invasion

Endocrine therapies target the activation of the oestrogen receptor alpha (ERα) via distinct mechanisms, but it is not clear whether breast cancer cells can adapt to treatment using drug-specific mechanisms. Here we demonstrate that resistance emerges via drug-specific epigenetic reprogramming. Resistant cells display a spectrum of phenotypical changes with invasive phenotypes evolving in lines resistant to the aromatase inhibitor (AI). Orthogonal genomics analysis of reprogrammed regulatory regions identifies individual drug-induced epigenetic states involving large topologically associating domains (TADs) and the activation of super-enhancers. AI-resistant cells activate endogenous cholesterol biosynthesis (CB) through stable epigenetic activation in vitro and in vivo. Mechanistically, CB sparks the constitutive activation of oestrogen receptors alpha (ERα) in AI-resistant cells, partly via the biosynthesis of 27-hydroxycholesterol. By targeting CB using statins, ERα binding is reduced and cell invasion is prevented. Epigenomic-led stratification can predict resistance to AI in a subset of ERα-positive patients

Oleaginous yeast Cryptococcus curvatus exhibits interplay between biosynthesis of intracellular sugars and lipids

Patterns of the biosynthesis ofmajor metabolites of the oleaginous yeast Cryptococcus curvatus NRRL Y-1511 were investigated during cultivation on sugar-based media. When lactose or sucrose was employed as substrate under nitrogen-limited conditions, the yeast strain accumulated high quantities of intra-cellular total sugars (ITS) at the beginning of fermentation (up to 68% w/w), with ITS values progressively decreasing to 20%, w/w, at the end of the fermentation. Decrease in ITS content and consumption of extracellular lactose led to a subsequent rise in lipid accumulation, reaching 29.8% in dry cell weight at 80 g/L of initial lactose concentration. Lactose was a more favorable substrate for lipid production than sucrose. In nitrogen-excess conditions, ITS were produced in significant quantities despite the continuous presence of nitrogen in the medium. Growth on lactose was not followed by secretion of extra-cellular b-galactosidase. High quantities of extra-cellular invertase were observed during growth on sucrose. The composition of ITS was highly influenced by the sugar used as substrate. Cellular lipids contained mainly palmitic and to lesser extent linoleic and stearic acids. This is the first report in the literature that demonstrates the interplay between the biosynthesis of intra-cellular total sugars and lipid synthesis for oleaginous yeast strains.

Evaluating glucose and xylose as cosubstrates for lipid accumulation and c-linolenic acid biosynthesis of Thamnidium elegans

Aims: To study the biotechnological production of lipids containing rich amounts of the medically and nutritionally important c-linolenic acid (GLA), during cultivation of the Zygomycetes Thamnidium elegans, on mixtures of glucose and xylose, abundant sugars of lignocellulosic biomass. Methods and Results: Glucose and xylose were utilized as carbon sources, solely or in mixtures, under nitrogen-limited conditions, in batch-flask or bioreactor cultures. On glucose, T. elegans produced 31.9 g/L of biomass containing 15.0 g/L lipid with significantly high GLA content (1014 mg/L). Xylose was proved to be an adequate substrate for growth and lipid production. Additionally, xylitol secretion occurred when xylose was utilized as carbon source, solely or in mixtures with glucose. Batch-bioreactor trials on glucose yielded satisfactory lipid production, with rapid substrate consumption rates. Analysis of intracellular lipids showed that the highest GLA content was observed in early stationary growth phase, while the phospholipid fraction was the most unsaturated fraction of T. elegans. Conclusions: Thamnidium elegans represents a promising fungus for the successful valorization of sugar-based lignocellulosic residues into microbial lipids of high nutritional and pharmaceutical interest.