Design of Minimum Nonlinear Distortion Reconfigurable Antennas for Next-Generation Communication Systems.

Nonlinear effects in the radio front-end can degrade communication quality and system performance. In this paper we present a new design technique for reconfigurable antennas that minimizes the nonlinear distortion and maximizes power efficiency through the minimization of the coupling between the internal switching ports and the external feeding ports. As a nonlinear design and validation instance, we present the nonlinear characterization up to 50 GHz of a PIN diode commonly used as a switch for reconfigurable devices in the microwave band. Nonlinear models are extracted through X-parameter measurements supported by accurate calibration and de-embedding procedures. Nonlinear switch models are validated by S-parameter measurements in the low power signal regime and by harmonic measurements in the large-signal regime and are further used to predict the measured nonlinearities of a reconfigurable antenna. These models have the desired particularity of being integrated straightforwardly in the internal multi-port method formulation, which is used and extended to account for the power induced on the switching elements. A new figure of merit for the design of reconfigurable antennas is introduced-the power margin, that is, the power difference between the fed port and the switching elements, which combined with the nonlinear load models directly translates into nonlinearities and power-efficiency-related metrics. Therefore, beyond traditional antenna aspects such as port match, gain, and beam orientation, switch power criteria are included in the design methodology. Guidelines for the design of reconfigurable antennas and parasitic layers of minimum nonlinearity are provided as well as the inherent trade-offs. A particular antenna design suitable for 5G communications in the 3.5 GHz band is presented according to these guidelines, in which the specific switching states for a set of target performance metrics are obtained via a balancing of the available figures of merit with multi-objective separation criteria, which enables good control of the various design trade-offs. Average Error Vector Magnitude (EVM) and power efficiency improvement of 12 and 6 dB, respectively, are obtained with the application of this design approach. In summary, this paper introduces a new framework for the nonlinear modeling and design of reconfigurable antennas and provides a set of general-purpose tools applicable in cases beyond those used as examples and validation in this work. Additionally, the use of these models and guidelines is presented, demonstrating one of the most appealing advantages of the reconfigurable parasitic layer approach, their low nonlinearity.

A frequency reconfigurable antenna based on digital microfluidics.

We present a novel antenna reconfiguration mechanism relying on electrowetting based digital microfluidics to implement a frequency reconfigurable antenna operating in the X-band. The antenna built on a quartz substrate (εr = 3.9, tan δ = 0.0002) is a coplanar waveguide fed annular slot antenna, which is monolithically integrated with a microfluidic chip. This chip establishes an electrowetting on dielectric platform with a mercury droplet placed in it. The base contact area of the mercury droplet can be spread out by electrostatic actuation resulting in a change of loading capacitance. This in turn changes the resonant frequency of the antenna enabling a reversible reconfigurable impedance property. This reconfigurable antenna has been designed, fabricated and measured. The frequency of operation is tuned from around 11 GHz to 13 GHz as demonstrated by simulations and measurements. The design methodology, fabrication processes and the experimental results are given and discussed.

Clinical description of children with HIV/AIDS admitted at a referral hospital in Addis Ababa.

Seventy-seven definitely HIV infected children were identified at Ethio-Swedish Children's Hospital in Addis Ababa, Ethiopia, between January 1990 and April 2000. There were 39 females and 38 males. Their age ranged from 15 months to 12 years and their median age was 3.8 years. Most commonly diagnosed diseases included disseminated tuberculosis seen in 28 patients, pneumonia in 27, pulmonary tuberculosis in 19, persistent or chronic diarrhoeal disease in 21, otitis media in 17 and marasmus in 17 patients. Pneumocystic carinii pneumonia was considered in 11 patients. One patient was suspected to have lymphoid interstitial pneumonitis. Sixteen children (21%) died in hospital. There was an abandoned child and 20 children were already orphans. All patients presented with clinical opportunistic infections and thus there is a need to develop a pediatric clinical guideline for patient management. Primary prevention of HIV infection in women of the child bearing age is of paramount importance and reduction of mother-to-child transmission of HIV infection by antiretroviral drug needs to be considered as a primary prevention for a child.

Pseudoexfoliation syndrome in Ethiopian glaucoma patients.

BACKGROUND: Pseudoexfoliation syndrome (PXS) has variable prevalence rates in the glaucoma population depending on geographic location and racial composition of the population studied. There is no data available on this subject in Ethiopia. OBJECTIVE: To determine the prevalence of PXS among Ethiopian glaucoma clinic population. DESIGN: A prospective study. SETTING: The Glaucoma Clinic of Menelik-II-Hospital, which is a tertiary eye care centre in Addis Ababa, Ethiopia. PARTICIPANTS: All new patients with glaucoma or ocular hypertension (ocular HPN) seen during the study period from 1st April to 30th September 1996 were included in the study. RESULTS: Our of the 432 new patients of glaucoma or ocular HPN seen during the study, 108 patients (25%) had PXS. The age of PXS cases ranged from 32 years to 86 years (mean 62.3 years). There were 80 males and 28 females. Of the PXS patients, 104 (96.3%) were cases of chronic open angle glaucoma, while angle closure glaucoma and ocular HPN were rare comprising only two patients (1.85%) each. CONCLUSION: The relatively high prevalence rate of PXS among Ethiopian glaucoma clinic population found in this study stresses the need for further community-based research in order to prevent blindness due to glaucoma associated with PXS.

Kangaroo mother care for low birthweight infants: a randomized controlled trial in different settings.

A randomized controlled trial was carried out for 1 y in three tertiary and teaching hospitals, in Addis Ababa (Ethiopia), Yogyakarta (Indonesia) and Merida (Mexico), to study the effectiveness, feasibility, acceptability and cost of kangaroo mother care (KMC) when compared to conventional methods of care (CMC). About 29% of 649 low birthweight infants (LBWI; 1000-1999 g) died before eligibility. Of the survivors, 38% were excluded for various reasons, 149 were randomly assigned to KMC (almost exclusive skin-to-skin care after stabilization), and 136 to CMC (warm room or incubator care). There were three deaths in each group and no difference in the incidence of severe disease. Hypothermia was significantly less common in KMC infants in Merida (13.5 vs 31.5 episodes/100 infants/d) and overall (10.8 vs 14.6). Exclusive breastfeeding at discharge was more common in KMC infants in Merida (80% vs 16%) and overall (88% vs 70%). KMC infants had a higher mean daily weight gain (21.3 g vs 17.7 g) and were discharged earlier (13.4 vs 16.3 d after enrolment). KMC was considered feasible and presented advantages over CMC in terms of maintenance of equipment. Mothers expressed a clear preference for KMC and health workers found it safe and convenient. KMC was cheaper than CMC in terms of salaries (US$ 11,788 vs US$ 29,888) and other running costs (US$ 7501 vs US$ 9876). This study confirms that hospital KMC for stabilized LBWI 1000-1999 g is at least as effective and safe as CMC, and shows that it is feasible in different settings, acceptable to mothers of different cultures, and less expensive. Where exclusive breastfeeding is uncommon among LBWI, KMC may bring about an increase in its prevalence and duration, with consequent benefits for health and growth. For hospitals in low-income countries KMC may represent an appropriate use of scarce resources.

Ocular manifestations of leukaemia in Ethiopians.

A prospective ophthalmic evaluation of 74 newly diagnosed and 34 old (on follow-up) leukaemic patients, carried out from March 1990 to December 1995 is described. Primary ocular involvement, that is leukaemic retinal infiltrates, were detected in 32% of the newly diagnosed. In contrast, none of the old leukaemic patients had this lesion. In 69% of the new and 21% of the old cases, secondary ocular manifestations of leukaemia were observed. The major secondary ocular manifestation of leukaemia in both groups was intra-retinal haemorrhage. A variety of miscellaneous ocular findings, such as cataract, pterygium, pingeculae, etc. were detected in 36% of all leukemics. These findings indicate the importance of a complete ophthalmologic evaluation in the diagnosis, follow-up and management of leukaemic patients.

Sociodemographic profile of children affected by AIDS in Addis Abeba.

A survey was conducted in Addis Abeba between October 2, 1993 and December 10, 1993 to assess orphanhood due to AIDS deaths. It was possible to trace only 1,047 AIDS cases among residents of Addis Abeba. During the survey, 59% of the cases and 16% of their spouses were already dead. The total number of children born to the index cases were 2186, among which, 883 (40.4%) were below 15 years of age. Two hundred eighty (30.4%) of these children had lost either one or both parents. Other social problems include ill health in 10.5% among which 3.9% had AIDS; 14.1% were school dropouts. There were also children who faced abandonment, displacement and who lacked medical care at the time of their illness. The existing coping mechanism seems to be relying on the extended family, which is an important social support system. However, there is a need to raise community awareness and strengthen the system to enhance the effort in protecting and supporting children affected by AIDS.

PIP: A survey was conducted in Addis Abeba between October 2 and December 10, 1993, to assess the extent of orphanhood due to AIDS mortality. Only 1047 AIDS cases could be traced among residents. During the survey 59% of cases and 16% of their spouses were already dead. There were 2186 children born to the index cases, 883 who were below age 15 years. 280 of these 883 children had lost either one or both parents. 3.9% of the 10.5% who were in poor health had AIDS. 14.1% had dropped out of school. Children were also identified who faced abandonment, displacement, and a lack of medical care at the time of their illness. Reliance upon the extended family is an important coping mechanism in this setting. The authors point to the need to raise the level of community awareness and strengthen the system to enhance efforts to protect and support children affected by AIDS.

Idiopathic thrombocytopenic purpura (ITP) in Ethiopian children: clinical findings and response to therapy.

This retrospective study provides information on the clinical findings and response to therapy in Ethiopian children with idiopathic thrombocytopenic purpura. Forty-nine cases of idiopathic thrombocytopenic purpura admitted to the teaching hospital, Ethio-Swedish Children's Hospital (ESCH) in Addis Abeba, Ethiopia between January 1982 and December 1993 were studied. Among these were 31 females and 18 males with a female to male ratio of 1.9:1. The age range was three to 12 years with a mean of seven years. The commonest presenting clinical features were petechiae, epistaxis, gingival and gastro-intestinal bleeding. Twenty-nine patients were treated with prednisolone, out of whom, 27 attained absolute remission. Twenty patients were observed and managed conservatively and attained spontaneous remission. One child went on to develop chronic idiopathic thrombocytopenic purpura and underwent splenectomy after immunosuppressive treatment failure, while another child is still being followed up with recurrent episodes of thrombocytopenia and epistaxis. No mortality was noted in the review of these series of patients.

6-Phosphofructo-2-kinase and fructose-2,6-bisphosphatase from Saccharomyces cerevisiae.

In permeabilized yeast cells 6-phosphofructo-2-kinase and fructose-2,6-bisphosphatase are studied during growth. It is shown that in yeast at least two fructose 2,6-bisphosphate degrading enzyme activities occur, differing in pH profile and in their substrate affinities. The activities of 6-phosphofructo-2-kinase and of fructose-2,6-bisphosphatases drop in the exponential and the transition phase while the activity of the alkaline phosphatases steadily increases. In the stationary phase the activities of 6-phosphofructo-2-kinase and of the low Km fructose-2,6-bisphosphatase increase again. Yeast 6-phosphofructo-2-kinase and fructose-2,6-bisphosphatase were purified and separated from each other. The purified 6-phosphofructo-2-kinase was found to exhibit a very high specific activity (1.3 U/mg). The enzyme is efficiently inhibited by ATP. The ATP inhibition is most pronounced at low concentrations of magnesium and fructose-6-phosphate. Phosphoenolpyruvate and sn-glycerol 3-phosphate are inhibitors of the enzyme. The high-affinity yeast fructose-2,6-bisphosphatase releases inorganic phosphate from the 2-position of fructose 2,6-bisphosphate. It displays hyperbolic kinetics towards fructose 2,6-bisphosphate (Km = 0.3 microM) and is strongly inhibited by fructose 6-phosphate. The inhibition is counteracted by sn-glycerol 3-phosphate. The enzyme is shown to be inactivated by cAMP-dependent phosphorylation and reactivated by the action of protein phosphatase 2A.

Kinetics of 6-phosphofructo-2-kinase from Saccharomyces cerevisiae: inhibition of the enzyme by ATP.

6-Phosphofructo-2-kinase (PFK-2) was purified from yeast and separated from fructose-2,6-biphosphatase (FBPase-2). The purification procedure involved polyethylene glycol fractionation followed by chromatography on DEAE-Sephacel. PFK-2 and FBPase-2 were copurified in these steps. Separation of the two enzymes resulted from Sephacryl S-300 Blue chromatography. Then, PFK-2 was chromatographed on CM-Sephadex and eluted with a gradient of KCl. Finally, PFK-2 was rechromatographed at CM-Sephadex and specifically eluted with fructose 6-phosphate. PFK-2 (specific activity 1.3 U/mg) was purified about 25,000-fold. The enzyme is inhibited by ATP which is particularly pronounced at low concentrations of magnesium and fructose 6-phosphate. Phosphoenolpyruvate and sn-glycerol 3-phosphate are inhibitors of the enzyme.