LED nonlinearity mitigation in LACO-OFDM optical communications based on adaptive predistortion and postdistortion techniques.

The preinstalled white light emitting diodes (WLEDs) inside buildings can be exploited as an optical source in visible light communications (VLC) motivated by high optical efficiency and low cost. One of the main challenges for VLC is LED nonlinear distortion, which has a detrimental effect on system performance. Estimation and compensation of the LED nonlinear behavior can be accomplished using predistortion or postdistortion techniques. Three compensation techniques are adopted to mitigate the effect of LED nonlinearity on layered asymmetrically clipped optical, orthogonal frequency division multiplexing. Their performance and efficiency are discussed and compared with the aid of error vector magnitude and bit error rate (BER) in an additive white Gaussian noise channel. The obtained results reveal that polynomial-based predistorters and postdistorters can overcome the LED nonlinear behavior with extra SNR of only 0.25 dB at BER of 10-3. Furthermore, the look-up-table-based predistorter can provide the same BER with lower SNR penalty than the previous two systems.

Exploring the effect of LED nonlinearity on the performance of layered ACO-OFDM.

Visible light communication (VLC) depends on light emitting diodes (LEDs) for data transmission. This is one of the strengths of VLC motivated by high optical efficiency and low cost. However, LEDs impose nonlinear effects on the transmitted signal and limit overall system performance, especially in the case of multicarrier modulation systems. This paper extends to the layered asymmetrically clipped optical, orthogonal frequency division multiplexing (LACO-OFDM) and investigates the impact of LED nonlinearity on system performance. The effect of the second-order nonlinear distortion in addition to the clipping noise is presented and analyzed at different power values assuming different strengths of nonlinearity. With a variable number of layers, the system performance is explored considering a nonlinear LED model. Finally, the impact of nonlinearity is investigated in the case of ACO-OFDM for the sake of comparison, bearing in mind that ACO-OFDM represents the first layer of LACO-OFDM.

In utero stem cell transplantation for radical treatment of osteogenesis imperfecta: perspectives and controversies.

Osteogenesis imperfecta (OI) is a lethal hereditary connective tissue disease that affects the synthesis of type I collagen. Current treatment options including surgical, physical, and medical treatment help to reduce pain, deformities, and rate of bone fracture. However, these choices are insufficient and are associated with many adverse effects. The development of stem cell therapy allows scientists to consider this option for radical treatment of many genetic diseases including OI. In utero stem cell transplantation provides a better opportunity for early prenatal intervention while the fetus is preimmune and before any permanent damage occurs. Few animal and human trials for treatment of OI have been published, and the results were promising but still controversial. Our objective is to review the available evidence and discuss the points of controversy including the parameters of treatment success and postnatal predictors of long-term treatment outcome.

The patterns and criteria of vaginal douching and the risk of preterm labor among upper Egypt women.

OBJECTIVES: Our study identifies vaginal douching as a risk factor for preterm labor and specifies the risk according to the method, frequency, nature, and timing of douching. MATERIALS AND METHODS: This is a hospital-based case-control study. A total of 480 women were recruited. Women were classified into case group (history of preterm labor) and control group (no history of preterm labor). An interview questionnaire was administered, which included participants' data and criteria of douching practice. RESULTS: Among participants who regularly douched (73.13%), 281 (80.06%) used it for cleanliness and religious considerations. Women who have been regularly douched were at higher risk of preterm labor (adjusted odds ratio [OR] = 1.9; 95% CI = 1.078-3.278; p = .026). The method (fingers vs pump) and the frequency of douching were significantly relevant. The risk of douching during pregnancy was borderline (adjusted OR = 2.1; 95% CI = 1.001-4.446; p =.05). Douching several times per day has an OR of 4.05 (95% CI = 1.196-13.737; p =.025) when compared with the monthly frequency. CONCLUSIONS: Vaginal douching is associated with higher risk of preterm labor. We recommend that the risk of asymptomatic bacterial vaginosis should be considered.

The laterality of ovulation: how far does it matter?

The laterality of ovulation, or the side at which ovulation occurs, was the subject of much research in the past century, but it was discussed merely as an interesting physiologic issue in all primates. In the last few years, the increasing development of infertility treatment has drawn the attention of researchers to the clinical aspects of this phenomenon. In the review, we discuss the nature of ovulation side and how far it can influence pregnancy outcome in infertile women treated with different modalities.

Twin pregnancy with complete hydatidiform mole and coexisting fetus following ovulation induction with a non-prescribed clomiphene citrate regimen: a case report.

INTRODUCTION: Twin pregnancy with complete hydatidiform mole represents a very rare obstetric problem. Management of such cases is always problematic because the possibility of fetal survival should always be weighed against the risk of complications of molar pregnancy. CASE PRESENTATION: A 34-year-old Caucasian woman presented to our center with mild vaginal bleeding. Our patient was 16 weeks pregnant after a seven-year period of primary infertility. She became pregnant following a non-prescribed regimen of clomiphene citrate extending from the second day to the 13th day of her last cycle. A transabdominal ultrasound examination revealed a twin pregnancy with complete hydatidiform mole and a coexisting fetus. Serum ß human chorionic gonadotropin was falsely low as identified by serial dilution of the sample (the 'hook effect'). Our patient refused termination of pregnancy and she was hospitalized for strict observation and follow-up. Unfortunately, she developed an attack of severe vaginal bleeding and a hysterotomy was performed. The fetus died shortly after birth. CONCLUSIONS: Twin pregnancy with complete hydatidiform mole represents a matter of controversy. We suggest that conservation should always be considered whenever tertiary care services and strict observation are available.