MIMO Underwater Visible Light Communications: Comprehensive Channel Study, Performance Analysis, and Multiple-Symbol Detection

In this paper, we analytically study the bit error rate (BER) performance of underwater visible light communication (UVLC) systems with binary pulse position modulation (BPPM). We simulate the channel fading-free impulse response (FFIR) based on Monte Carlo numerical method to take into account the absorption and scattering effects. Additionally, to characterize turbulence effects, we multiply the aforementioned FFIR by a fading coefficient which for weak oceanic turbulence can be modeled as a lognormal random variable (RV). Moreover, to mitigate turbulence effects, we employ multiple transmitters and/or receivers, i.e., spatial diversity technique over UVLC links. Closed-form expressions for the system BER are provided, when equal gain combiner (EGC) is employed at the receiver side, thanks to Gauss-Hermite quadrature formula and approximation to the sum of lognormal RVs. We further apply saddle-point approximation, an accurate photon-counting-based method, to evaluate the system BER in the presence of shot noise. Both laser-based collimated and light emitting diode (LED)-based diffusive links are investigated. Since multiple-scattering effect of UVLC channels on the propagating photons causes considerable inter-symbol interference (ISI), especially for diffusive channels, we also obtain the optimum multiple-symbol detection (MSD) algorithm to significantly alleviate ISI effects and improve the system performance. Our numerical analysis indicates good matches between the analytical and photon-counting results implying the negligibility of signal-dependent shot noise, and also between analytical results and numerical simulations confirming the accuracy of our derived closed-form expressions for the system BER. Besides, our results show that spatial diversity significantly mitigates fading impairments while MSD considerably alleviates ISI deteriorations

Actividad antihipóxica y actividad antioxidante de semilas de Hibiscus esculentus

The antihypoxic and antioxidant activities of Hibiscus esculentus seeds were investigated employing eight in vitro assay systems. Antihypoxic activity was investigated in two models, haemic and circulatory. The effects were pronounced in both models of hypoxia. The antihypoxic effects were dose-dependent. The results indicated that the extracts have a protective effect against hypoxia induced lethality in mice. The extracts showed antioxidant activity in some models. IC50 for DPPH radical-scavenging activity was 234 ± 8.9 μg ml-1. The extracts showed weak nitric oxide-scavenging activity between 0.1 and 1.6 mg ml-1. The extracts showed weak Fe2+ chelating ability. IC50 were 150 ± 13 μg ml-1. The extracts also exhibited low antioxidant activity in the linoleic acid model but were capable of scavenging hydrogen peroxide in a concentration dependent manner. The total amount of phenolic compounds in each extract was determined as gallic acid equivalents and total flavonoid contents were calculated as quercetin equivalents from a calibration curve. Pharmacological effects may be attributed, at least in part, to the presence of phenols and flavonoids in the extracts.La actividad antihipóxica y antioxidante de semillas de Hibiscus esculentus fue investigada empleando ocho ensayos in vitro. La actividad antihipóxica fue investigada en dos modelos, uno de caracter hemínico y otro circulatorio. Los efectos fueron pronunciados en ambos modelos de hipoxia. Los efectos antihipóxicos fueron dependientes de la dosis. Los resultados indican que los extractos tienen un efecto protector contra la letabilidad inducida por hipoxia en ratones. Los extractos mostraron actividad antioxidante en algunos modelos. El IC50 para la actividad captadora de radicales fue 234 ± 8.9 μg ml-1. Los extractos muestran una débil actividad captadora de óxido nítrico comprendida entre 0.1 y 1.6 mg ml-1. Los extractos muestran una débil capacidad quelatante de Fe2+. El IC50 fue de 150 ± 13 μg ml-1. Los extractos también muestran una baja actividad antioxidante en modelos con ácido linoleico aunque fueron capaces de eliminar peróxido de hidrógeno en una manera dependiente de la concentración. La concentración de compuestos fenólicos totales en cada extracto fue determinado como equivalents de ácido gálico y el contenido total de flavonoides fue calculado como equivalentes de quercitina para la curva de calibración. Los efectos farmacológicos pueden ser atribuidos, al menos en parte, a la presencia de fenoles y flavonoides en el extracto

The antioxidant activity of wild medlar (Mespilus germanica L.) fruit, stem bark and leaf

The medlar is an edible fruit. Modern medicine has recognized its healing properties in the treatment of some diseases. There is no scientific data in the literature about the antioxidant activity of methanol or aqueous extract of medlar fruit, leaf or stem bark. Antioxidant activities of these parts were evaluated by employing six test systems. Stem bark extract (aqueous and methanol) showed best activity in 1,1-diphenyl-2-picryl hydrazyl (DPPH) radical scavenging activity with IC50 = 10.7 ± 0.6 and 11.4 ± 0.8 μgml-1, respectively. All extracts showed weak Fe2+ chelating ability. Methanol extract of fruit had better activity in nitric oxide scavenging model than others (IC50 = 247 ± 12.2 μgml-1). The leaves and bark extracts showed good reducing power than fruit extract. In reducing powers, there were no significant differences (p > 0.05) among the stem bark and leaves extracts that were comparable with vitamin C (p< 0.05). Extracts exhibited good antioxidant activity in the ferric thiocyanate (FTC) method. They manifested almost the same pattern of activity as vitamin C and butylated hydroxyanisole (BHA) at different incubation times (until 72nd hour) but stem bark extract showed higher peroxidation inhibition than vitamin C and BHA at the 96th hour (p < 0.05). The extracts were capable of scavenging H2O2 in a concentration-dependent manner. Leaves methanol extract showed good activity that was comparable with quercetin (p > 0.05). Bark and leaf extracts had higher total phenolic and flavonoid contents than fruit.Keywords: Antioxidant activity, free radical scavenging, Mespilus germanica, medlar, phenolic contents, flavonoids content

Angular right symmetricity of bounded linear operators on Hilbert spaces

We introduce and characterize angular right symmetric and approximate angular right symmetric points of the algebra of all bounded linear operators defined on either real or complex Hilbert spaces

Stress Intensity Factors for Circumferential Semi-Elliptical Cracks in Cylinders Subjected to Forced Convection Heat Transfer

This paper analyzes the circumferential semi-elliptical crack on the inner surface of a thick-walled cylinder while keeping the thermal loading in steady state. Forced convection heat transfer in the inner surface and free convection in the outer surface are applied to the cylinder, which was constructed from isotropic and homogeneous materials. To this end, the thermal stress intensity factors are determined using the weight function method. To validate the results, 3-D finite element method is applied as well as API standard code. Due to the existence of two planes of symmetry, only a quarter model of the cylinder was used and along the crack front, the modelling is carried out over singular isoparametric elements. The results for stress intensity factor are obtained at different aspect ratios and relative depths of the crack. The stress intensity factors calculated via built-in J-integral solver based on the domain integral technique in the ABAQUS software. The results obtained via this method were in good agreement with the proposed weight function, demonstrating the latter’s high adequacy and efficiency

Prediction of blast-induced air overpressure using a hybrid machine learning model and gene expression programming (GEP) : a case study from an iron ore mine

Mine blasting can have a destructive effect on the environment. Among these effects, air overpressure (AOp) is a major concern. Therefore, a careful assessment of the AOp intensity should be conducted before any blasting operation in order to minimize the associated environmental detriment. Several empirical models have been established to predict and control AOp. However, the current empirical methods have many limitations, including low accuracy, poor generalizability, consideration only of linear relationships among influencing parameters, and investigation of only a few influencing parameters. Thus, the current research presents a hybrid model which combines an extreme gradient boosting algorithm (XGB) with grey wolf optimization (GWO) for accurately predicting AOp. Furthermore, an empirical model and gene expression programming (GEP) were used to assess the validity of the hybrid model (XGB-GWO). An analysis of 66 blastings with their corresponding AOp values and influential parameters was conducted to achieve the goals of this research. The efficiency of AOp prediction methods was evaluated in terms of mean absolute error (MAE), coefficient of determination (R 2 ), and root mean square error (RMSE). Based on the calculations, the XGB-GWO model has performed as well as the empirical and GEP models. Next, the most significant parameters for predicting AOp were determined using a sensitivity analysis. Based on the analysis results, stemming length and rock quality designation (RQD) were identified as two variables with the greatest influence. This study showed that the proposed XGB-GWO method was robust and applicable for predicting AOp driven by blasting operations

Antioxidant activity of different parts of Tetrataenium lasiopetalum.

In Iranian traditional medicine, different species of the genus Tetrataenium are used as antiseptic, spice and food additives.The present study examined the possible antioxidant effects of hydro-alcoholic extracts of different parts of Tetrataenium lasiopetalum (Boiss.) Manden (Apiaceae).Laminas, stems, petioles, fruits, peduncles and flowers of T. lasiopetalum were collected, dried and then extracted by ethanol and water (70:30). Antioxidant activities of extracts were examined by employing different in vitro assays, i.e., 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging, metal chelating, reducing power activities and hemoglobin-induced linoleic acid system. Also, total phenolic and flavonoid contents of the extracts were evaluated.Hydro-alcoholic extract of T. lasiopetalum flower showed the highest activity in scavenging of DPPH (IC50 = 170 ± 7 μg/mL). In metal chelating assay, lamina extract possesses a better iron ion chelating activity than other extracts (230 ± 10 μg/mL). Lamina hydro-alcoholic extract demonstrated better activity in reducing the power and hemoglobin-induced linoleic acid system than other parts of T. lasiopetalum.These results showed the antioxidant activity of different parts of T. lasiopetalum based on its usage in traditional medicine

Actividad antioxidante de extractos metanólicos de Ferula assafoetida y la composición de su aceite esencial

The antioxidant activity of the aerial parts of Ferula assafoetida was determined by employing various in vitro assay systems. IC50 for DPPH radical-scavenging activity was 380 ± 12 mg ml-1. The extracts showed good nitric oxide-scavenging activity (IC50 was 270 ± 3) and Fe2+ chelating ability (IC50 was 0.57 ± 0.02 mg ml-1). The peroxidation inhibition (antioxidant activity) of the extracts exhibited values from 82% (at 24 hrs) and 88% (at 72 hrs). The extract exhibited a fairy weak reducing power at 25-800 μg ml-1 of extracts which was not comparable with Vitamin C (p < 0.001). The tested extracts exhibited very low antioxidant activity. In addition, the chemical composition of the essential oil of the aerial parts was determined. The major compounds were phenol, 2-methyl-5-(1-methyl ethyl) (18.2 %), α.-Bisabolol (10.4%) and Arsine triethyl (8.7 %). Total phenol compounds, as determined by the Folin Ciocalteu method, were 94.8 ± 5.9 mg gallic acid equivalent/g of extract powder and the total flavonoid content (by AlCl3 method) was 90.9 ± 6.3 mg quercetin equivalent/g of extract powder.La actividad antioxidante de las partes aéreas de Ferula assafoetida se determinó empleando varios sistemas de ensayos in vitro. El IC50 de la actividad captadora de radicales de DPPH fue 380 ± 12 mg ml-1. Los extractos también mostraron una buena actividad captadora de óxido nítrico (IC50 fue 270 ± 3) y capacidad quelatante de Fe2+ (IC50 fue 0.57 ± 0.02 mg ml-1). La inhibición de la peroxidación (actividad antioxidante) de los extractos mostró valores del 82% (a las 24 horas) y 88% (a las 72 horas). El extracto mostró un ligero descenso del poder reductor con 25- 800 μg ml-1 de extracto que no fue comparable con la vitamina C (p < 0.001). Los extractos ensayados mostraron una muy baja actividad antioxidante. Además, la composición química del aceite esencial de las partes aéreas fue determinada. Los principales compuestos fueron fenol, 2-metil-5-(1-metil etilo) (18.2 %), α.-Bisabolol (10.4%) and Arsine trietilo (8.7 %). Los fenoles totales, determinados por el método de Folin-Ciocalteau, fue de 94.8 ± 5.9 mg de equivalentes de ácido gálico/g de extracto en polvo y el contenido total de flavonoides (por el método del AlCl3) fue de 90.9 ± 6.3 mg de equivalentes de quercitina/g de extracto en polvo

Granting Asylum to Truth-Seekers from the perspective of Qur'an

From the very beginning of the Islamic era, it has happened many times that a number of polytheists, in response to their call of nature, applied for a voluntary listening to the Quran. This phenomenon, which is called "Asylum-Seeking of Polytheists" in the Quran, was considered as a unique and incomparable event throughout the Islamic history in the field of propagation of the religion of Islam for non-Muslims. Asylum means seeking refugee by the idolaters. In this case, it is obligatory for the Muslims to provide the ground for realizing this important issue, to remove the possible obstacles and to accept the asylum-seeker pagan and provide him with sufficient verses and proofs so that he may be guided to the right path.In this article, while giving an objective explanation of this issue, as well as referring to examples of "granting asylum to truth-seeking pagans", we study the practical solutions in this regard, which are presented for the first time and, if realized, good conditions would be created for non-Muslims. Obviously, this kind of asylum is a cultural and religious asylum and not a political asylum