Saturation in cascaded optical amplifier free-space optical communication systems

The performance of a free-space optical (FSO) communication system in a turbulent atmosphere employing an optical amplifier (OA) cascade to extend reach is investigated. Analysis of both single and cascaded OA FSO communication links is given and the implications of using both adaptive (to channel state) and non-adaptive decision threshold schemes are analysed. The benefits of amplifier saturation, for example in the form of effective scintillation reduction when a non-adaptive decision threshold scheme is utilised at the receiver for different atmospheric turbulence regimes, are presented. Monte Carlo simulation techniques are used to model the probability distributions of the optical signal power, noise and the average bit error rate due to scintillation for the cascade. The performance of an adaptive decision threshold is superior to a non-adaptive decision threshold for both saturated and fixed gain preamplified receivers and the ability of a saturated gain OA to suppress scintillation is only meaningful for system performance when a non-adaptive decision threshold is used at the receiver. An OA cascade can be successfully used to extend reach in FSO communication systems and specific system implementations are presented. The optimal cascade scheme with a non-adaptive receiver would use frequent low gain saturated amplification

Performance evaluation of turbulence-accentuated interchannel crosstalk for hybrid fibre and free-space optical wavelength-division-multiplexing systems using digital pulse-position modulation

A hybrid fibre and free-space optical communication link using digital pulse-position modulation (DPPM) in a wavelength-division-multiplexing system is proposed. Such a system, which could provide a power efficient, robust and flexible solution to high-speed access networks, is a contender for a passive optical network solution and could readily be deployed in areas with restrictions in optical fibre installation, or alternatively as a disaster recovery network. Interchannel crosstalk and atmospheric turbulence are major impairments in such a system and could combine in some cases to degrade the system. Both impairments are investigated here and the results are presented in the form of bit error probability, required optical transmission power and power penalties. Depending on the position of the interferer relative to the desired user, power penalties of about 0.2–3.0 dB for weak turbulence and above 20 dB for strong turbulence regimes are reported for bit error rate of 10−6. DPPM scheme with a coding level of 2 show about 2 dB improvements over on–off-keying scheme

Evaluating the efficacy of probiotic on treatment in patients with small intestinal bacterial overgrowth (SIBO) - A pilot study

Background & objectives: Small intestinal bacterial overgrowth (SIBO) leads to several gastrointestinal (GI) problems and complications leading to malabsorption. The effectiveness of probiotics in the treatment of SIBO syndrome has not been well studied. This pilot study was aimed to assess the efficacy of a probiotic consisting of lactobacilli in the treatment of SIBO. Methods: In this study, 30 cases suffering from chronic abdominal pain or diarrhoea and with a positive hydrogen breath test were randomized in a double-blind manner into two groups: probiotic drug user and control group. After an initial 3-week aggressive therapy with broad-spectrum antibiotics, a 15-day maintenance antibiotic therapy with lactol was administered for the study group and the same regimen without lactol for the control group. After six months the HBT result and the GI symptoms were analyzed and compared between the two groups. Results: The result of hydrogen breath test and the clinical symptoms in patients receiving the maintenance regimen with lactol probiotic showed a better response. The hydrogen breath test turned negative in 93.3 per cent of those receiving lactol compared to 66.7 per cent of the controls. In all the cases receiving lactol, the abdominal pain disappeared completely ( p =0.002). In addition, other GI problems including flatulence, belching and diarrhoea significantly improved in the study group ( p <0.05). Interpretation & conclusions: Based on the preliminary data it seems that adding lactol probiotic to the maintenance therapy of small intestinal bacterial overgrowth patients on routine antibiotic therapy will be beneficial in preventing the complications of this syndrome

Prenatal Exposure to Phthalic Acid Induces Increased Blood Pressure, Oxidative Stress, and Markers of Endothelial Dysfunction in Rat Offspring

Previous studies have reported the harmful effects of exposure to phthalic acid (PA) on heart. No studies have reported the effects of prenatal PA exposure on the structure or function of heart. The current study aimed to investigate the effects of prenatal PA exposure on the markers of oxidative stress and cardiac structure in rats' offspring. Twenty-four pregnant rats were randomly categorized into three groups of control, exposed to 2.5 and 5 PA. The morphometric properties of coronary arteries, markers of oxidative stress, and NOS activity were measured in offspring rats. By a dose-dependent manner, the body weight (BW), heart weight (HW), and HW/BW of the intervention groups were reduced and their heart rate and blood pressure were conversely increased compared to the control group. Also, the wall thickness, cross-sectional area of the aorta and septal branch of the descending left coronary artery were significantly increased in the intervention group. In addition, PA significantly increased the level of malondialdehyde and decreased the level of superoxide dismutase and glutathione peroxidase, compared to the control group. This study revealed that prenatal exposure of rats to PA causes vascular dysfunction, increasing oxidative stress, and reduction in cardiac nitric oxide synthetase activity among offspring rats

Perfluorocarbon attenuates inflammatory cytokines, oxidative stress and histopathologic changes in paraquat-induced acute lung injury in rats

The effects of perfluorocarbon (PFC) on paraquat (PQ) induced acute lung injury (ALI) was evaluated among rats. Twenty four Wistar rats were divided into 4 groups: control group injected by saline physiologic 0.9, PFC group injected by Perfluorocarbon, PQ group injected by PQ and PQ+ PFC group injected by PFC one hour after receiving paraquat. Bronchoalveular fluid content, inflammatory cytokines, oxidative and histopathologic changes were measured after 72 h. The levels of interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta(TGF-beta 1) in the PQ group were increased compared to either control or PFC groups, but their levels decreased in PQ+ PFC group significantly (p <0.05). Also, histopathologic evaluation revealed an increase in malondialdehyde (MDA) and hydroxyproline (HP) in the PQ group but a decrease in PQ+PFC group significantly (p < 0.01). PFC emulsion by its anti-inflammatory, anti-oxidative and anti-fibrotic properties can reduce the inflammatory and fibrotic alterations, pulmonary oedema, and pulmonary histopathologic changes created by PQ (C)2015 Elsevier B.V. All rights reserved

Petal: a reliable explant for direct bulblet regeneration of endangered wild populations of Fritillaria imperialis L.

Wild populations of Fritillaria imperialis L. are facing extinction and need urgent conservation. This paper presents an efficient system for in vitro direct bulblet regeneration of these populations by petal culturing of flower buds. Petals at different developmental stages, green-closed flower bud (before nectar secretion) and red-closed flower bud (beginning of nectar secretion), were used as explants, and the effects of various proportions of cytokinin to auxin on direct bulblet regeneration pathway were evaluated. More explants switched on direct regeneration pathway in combination of auxins (0.6 mg l−1 NAA + 0.4 mg l−1 IAA) with higher level of cytokinin (1 mg l−1 BAP). In contrast, auxins (0.6 mg l−1 NAA + 0.4 mg l−1 IAA) with lower level of cytokinin (0.1 mg l−1 BAP) produced more bulblets per regenerated explant. In green-closed flower bud stage, direct bulblets regenerated from the end of petal where it was connected to the receptacle, while nectar secretion site was the place of bulblet formation in red-closed flower bud stage. In addition, genotype-dependency of direct bulblet regeneration pathway was investigated by using two different wild populations of Fritillaria imperialis. This plant regeneration procedure was applicable to different Fritillaria genotypes and regenerated bulblets were normal.Manijeh Mohammadi-Dehcheshmeh, Ahmad Khalighi, Roohangiz Naderi, Manoochehr Sardari, Esmaeil Ebrahimi