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Background/Objectives: The acute impact of Hibiscus sabdariffa calyces (HSC) extract on postprandial vascular function and other cardiometabolic risk factors have not been studied previously. This study investigated the acute impact of HSC extract consumption on blood pressure (BP), vascular function and other cardiometabolic risk markers. Subjects/Methods: Twenty-five men with 1% to 10% cardiovascular disease (CVD) risk (determined by QRISK&reg, 2) were randomised to consume either 250 mL of the aqueous extract of HSC or water with breakfast in a randomised, controlled, single‐blinded, 2-meal cross-over study (ClinicalTrials.gov, NTC02165553) with a two weeks washout period between study days. BP was measured at baseline and hourly for 4 h. Flow mediated dilatation (FMD) of the branchial artery was measured at baseline, 2 and 4 h post intervention drink consumption. Results: Acute consumption of aqueous extract of HSC caused a significant increase in % FMD (p &lt, 0.001), a non-significant decrease in systolic BP (SBP) and diastolic BP (DBP), non-significant increase in urinary and plasma nitric oxide (NOx) and reduced response of serum glucose, plasma insulin, serum triacylglycerol and C-reactive protein (CRP) levels, significant (p = 0.026) improvement in the area under systemic antioxidant response curve (0 to 2 h), no significant changes in arterial stiffness following the acute consumption of the extract of HSC. Gallic acid, 4-O-methylgallic acid, 3-O-methylgallic acid and hippuric acid reached a maximum plasma concentration at 1 to 2 h post consumption of the extract of HSC. Conclusion: The extract of HSC improved postprandial vascular function and may be a useful dietary strategy to reduce endothelial dysfunction and CVD risk, although this requires confirmation.

ObjectiveTo identify factors that explain variations between districts in maternal health service coverage and maternal health outcomes.MethodsIndividual key informant interviews and focus group discussions using structured topic lists were conducted in May 2015 in four purposively selected districts.ResultsThe solidarity support for poor people and the interconnectedness between local leaders and heads of health facilities were identified as enablers of health service utilization. Geographical factors, in particular location close to borders with mobile populations and migrants, and large populations with sparsely distributed health infrastructure, exacerbated by hilly topography and muddy roads were identified as barriers. Shortages of skilled health providers at the level of district hospitals were cited as contributing to poor maternal health outcomes.ConclusionThere is a need to take into account disparities between districts when allocating staff and financial resources in order to achieve universal coverage for high-quality maternal health services and better outcomes. Local innovations such as the use of SMS and WhatsApp text messages by health workers and financial protection schemes for poor patients improve solidarity and are worth to be scaled up.

Total shoulder arthroplasty (TSA) has repeatedly been shown to be an effective and durable treatment option for end-stage arthritis with good long-term survivorship. Whereas pain relief is typically the primary goal, improvements in range of motion are typically expected as well. The factors that influence postoperative motion have not been well characterized. The purpose of the study was to examine the factors that influence ultimate postoperative motion after TSA.A retrospective review was conducted of prospectively collected data of 230 patients with minimum 1-year follow-up after TSA for end-stage arthropathy with an intact rotator cuff. Analysis was focused on factors that may correlate with postoperative measured forward flexion, abduction, external rotation, and internal rotation. Included in this analysis was perception of motion, age, body mass index (BMI), comorbidities (smoking, diabetes, osteoporosis, hypercholesterolemia, inflammatory arthritis, and thyroid disease), and number of comorbidities.Preoperative motion in all directions was predictive of postoperative motion for forward flexion (R = 0.235; P.001), abduction (R = 0.363; P.001), external rotation (R = 0.325; P.001), and internal rotation (R = 0.213; P = .002). BMI and diabetes both negatively correlated with internal rotation (R = -0.134, P = .40 and R = -0.196, P = .003, respectively). Individual and total number of comorbidities were not predictive of postoperative motion. The patient's perception of preoperative motion also did not correlate with postoperative motion.Preoperative range of motion before TSA is most predictive of final motion achieved. Individual and total number of comorbidities are not predictive of postoperative motion. Patients with high diabetes and increased BMI have limited postoperative internal rotation.

While system complexity is on the rise across many product lines, the resources required to successfully design and implement complex systems remain constrained. Because financiers of complex systems development efforts actively monitor project implementation cost, project performance models are needed to help project managers predict their cost compliance and avoid cost overruns. This article describes recent research conducted by the authors to develop a cost overrun predictive model using five known drivers of complex systems development cost. The study identifies schedule and reliability, as the key determinants of whether or not a large complex systems development project will experience cost overrun.

The development of Novel cancer immunotherapies has relied on the use of immune humanized mice. The field of study can be enhanced using an immune humanized rat, which will provide several advantages over the currently available humanized mouse models. The SRG OncoRat®; A Rag2/Il2rg double-knockout rat supports the growth of larger tumors for serial fine needle biopsies to assess immune infiltration and serial blood draws for assessing human immune development and tumor biomarkers in real-time throughout an efficacy study. Using this rat, we developed a novel autologous human skin and immune cells-humanized rat model by co-engrafting full-thickness human-fetal skin and autologous fetal lymphoid organoids under the kidney capsule along with intravenous injection of autologous fetal-liver derived hematopoietic stem cells, thus termed, human skin-immune system humanized rat model (hSIS-humanized rat). We demonstrated the development of adult-like, full-thickness human skin and human lymphoid organoids along with human immune cells. Methicillin-resistant Staphylococcus aureus inoculation in the human skin results in infection and skin pathology, thus recapitulating clinical outcomes. This model will enable in vivo mechanistic studies for development and evaluation of novel therapeutics for skin infectious disease and may also provide a model for establishing skin grafts of patient-derived melanoma tumors to investigate melanoma metastasis and response to therapies. In addition, engrafting the rat with human lymphoid organs and human immune cells may provide a similar platform to the BLT mouse for immunotherapy studies. Furthermore, we demonstrated the presence of Human CD45+, CD3+, and CD20+ cells in peripheral blood, spleen, and bone marrow of the SRG OncoRat® engrafted with human PBMCs, hence humanizing the rat's immune system. These immune humanized rat models may be beneficial for evaluating immunotherapies in human cancer models, including assessment of immune cell infiltration through fine needle biopsies. Citation Format: Bisoye Towobola Adedeji, Fallon K. Noto, Tseten Yeshi Jamling, Yash Argawal, Cole Jamison Beatty, Sara Grace Ho, Antu Das, Rajeev Kishore Salunke, Moses Turkle Bility. Humanized rat model [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5621.

Endemic foot-and-mouth disease (FMD) presents a global economic challenge to the livestock industry. The progressive control pathway for FMD (PCP-FMD) specifies successive steps through which a country/region can reduce FMD virus circulation and impact. These steps are reliant on understanding and obtaining knowledge on FMD epidemiology, to inform development of appropriate disease interventions like vaccination and quarantine programs. Currently, Uganda and Tanzania are in the early stages of the PCP-FMD. This review was undertaken to determine FMDV serotype distribution in Uganda and Tanzania between 2003 and 2015. The paper also presents the vaccine strains used in both countries for the same period viz avis the circulating topotypes. The review highlights four (O, A, SAT 1 and SAT 2) and five (O, A, SAT 1, SAT 2 and SAT 3) serotypes that occurred in Uganda and Tanzania respectively in the thirteen year period. Observations revealed that reported circulating serotypes O and A in the two countries belonged to similar topotypes, East African 2 (EA-2) and AFRICA respectively. The SAT 1 viruses in Tanzania belonged to topotype I and differed from the Ugandan SAT 1s that belonged to topotype IV. Similarly, the SAT 2s in both countries belonged to different topotypes: IV in Tanzania and I in Uganda. This review additionally, underscores the spatial distribution of FMDV serotypes in Uganda and Tanzania and highlights regions in both countries that had high serotype diversity. The paper recommends definitive disease diagnoses, molecular serotype characterisation and matched vaccination deployment for improved disease control.

A major pathogenic feature associated with HIV infection is lymphoid fibrosis, which persists during antiretroviral therapy (ART). Lymphoid tissues play critical roles in the generation of antigen-specific immune response, and fibrosis disrupts the stromal network of lymphoid tissues, resulting in impaired immune cell trafficking and function, as well as immunodeficiency. Developing an animal model for investigating the impact of HIV infection–induced lymphoid tissue fibrosis on immunodeficiency and immune cell impairment is critical for therapeutics development and clinical translation. Said model will enable in vivo mechanistic studies, thus complementing the well-established surrogate model of SIV infection–induced lymphoid tissue fibrosis in macaques. We developed a potentially novel human immune system–humanized mouse model by coengrafting autologous fetal thymus, spleen, and liver organoids under the kidney capsule, along with i.v. injection of autologous fetal liver–derived hematopoietic stem cells, thus termed the BM-liver-thymus-spleen (BLTS) humanized mouse model. BLTS humanized mouse model supports development of human immune cells and human lymphoid organoids (human thymus and spleen organoids). HIV infection in BLTS humanized mice results in progressive fibrosis in human lymphoid tissues, which was associated with immunodeficiency in the lymphoid tissues, and lymphoid tissue fibrosis persists during ART, thus recapitulating clinical outcomes.

Immune humanized mice have been valuable in the development of novel cancer immunotherapies and have demonstrated stronger efficacy when combined with standard of care chemotherapy. An immune humanized rat could provide several advantages over the currently available humanized mouse models, including supporting the growth of larger tumors for serial fine needle biopsies to assess immune infiltration and serial blood draws for assessing human immune development and tumor biomarkers in real-time throughout an efficacy study. We developed a novel autologous human skin and immune cells-humanized rat model by co-engrafting full-thickness human-fetal skin and autologous fetal lymphoid organoids under the kidney capsule along with intravenous injection of autologous fetal-liver derived hematopoietic stem cells, thus termed, human skin-immune system humanized rat model (hSIS-humanized rat). hSIS-humanized rat support development of adult-like, full-thickness human skin and human lymphoid organoids along with human immune cells. Methicillin-resistant Staphylococcus aureus inoculation in the human skin results in infection and skin pathology, thus recapitulating clinical outcomes. This model will enable in vivo mechanistic studies for development and evaluation of novel therapeutics for skin infectious disease and may also provide a model for establishing skin grafts of patient-derived melanoma tumors to investigate melanoma metastasis and response to therapies. In addition, engrafting the rat with human lymphoid organs and human immune cells may provide a similar platform to the BLT mouse for immunotherapy studies. Finally, we have demonstrated humanization of the rat immune system using human PBMCs. Human CD45+, CD3+, and CD20+ cells can be found in the peripheral blood, spleen, and bone marrow of engrafted rats. These immune humanized rat models may be beneficial for evaluating immunotherapies in human cancer models, including assessment of immune cell infiltration through fine needle biopsies. Citation Format: Fallon K Noto, Bisoye Towobola Adedeji, Yash Agarwal, Cole Beatty, Sara Ho, Antu Das, Rajeev Salunke, Moses Bility, Tseten Yeshi Jamling. A Rag2/Il2rg double-knockout rat supports engraftment of human immune system for immunotherapy-based cancer efficacy studies [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr A007. doi:10.1158/1535-7163.TARG-19-A007

Chronic Opisthorchis viverrini-induced hepatobiliary disease is associated with significant leukocyte infiltration, including activated macrophages; however, the polarization of infiltrating macrophages remains to be fully characterized. In this study, we characterized macrophage polarization and phenotype in chronic O. viverrini-induced hepatobiliary disease in humans and hamsters using gene expression and histochemical analysis. Chronic O. viverrini infection and associated hepatobiliary diseases were associated with iron loaded M2-like macrophages in both humans and hamsters. This study provides suggestive evidence that iron loaded M2-like macrophages promote hepatobiliary disease in chronic O. viverrini infection.

Several utilities in Africa are planning to build Smart Distribution Management System (SDMS) to provide better customer service, improve reliability & quality of power supply and also improve commercial viability of their utilities. The SDMS architecture and design for each Utility has to be determined considering current operational status of distribution network, ability to mobilize resources to finance capital investment and anticipated benefits. This paper presents SDMS architecture and design for a Typical African Utility based on Consultant's hands on experience of working with African Utilities for more than a decade. A case study of implementing proposed SDMS for a Ghanaian utility, Northern Electricity Distribution Company (NEDCo) currently under progress is presented.

The immuno-pathogenic mechanisms of chronic hepatitis C virus (HCV) infection remain to be elucidated and pose a major hurdle in treating or preventing chronic HCV-induced advanced liver diseases such as cirrhosis. Macrophages are a major component of the inflammatory milieu in chronic HCV–induced liver disease, and are generally derived from circulating inflammatory monocytes; however very little is known about their role in liver diseases. To investigate the activation and role of macrophages in chronic HCV–induced liver fibrosis, we utilized a recently developed humanized mouse model with autologous human immune and liver cells, human liver and blood samples and cell culture models of monocyte/macrophage and/or hepatic stellate cell activation. We showed that M2 macrophage activation was associated with liver fibrosis during chronic HCV infection in the livers of both humanized mice and patients, and direct-acting antiviral therapy attenuated M2 macrophage activation and associated liver fibrosis. We demonstrated that supernatant from HCV-infected liver cells activated human monocytes/macrophages with M2-like phenotypes. Importantly, HCV-activated monocytes/macrophages promoted hepatic stellate cell activation. These results suggest a critical role for M2 macrophage induction in chronic HCV-associated immune dysregulation and liver fibrosis.

Hepatitis B virus (HBV) and hepatitis C virus (HCV) infect and replicate primarily in human hepatocytes. Few reliable and easy accessible animal models are available for studying the immune system's contribution to the liver disease progression during hepatitis virus infection. Humanized mouse models reconstituted with human hematopoietic stem cells (HSCs) have been developed to study human immunology, human immunodeficiency virus 1 infection, and immunopathogenesis. However, a humanized mouse model engrafted with both human immune and human liver cells is needed to study infection and immunopathogenesis of HBV/HCV infection in vivo. We have recently developed the humanized mouse model with both human immune and human liver cells (AFC8-hu HSC/Hep) to study immunopathogenesis and therapy of HCV infection in vivo. In this review, we summarize the current models of HBV/HCV infection and their limitations in immunopathogenesis. We will then present our recent findings of HCV infection and immunopathogenesis in the AFC8-hu HSC/Hep mouse, which supports HCV infection, human T-cell response and associated liver pathogenesis. Inoculation of humanized mice with primary HCV isolates resulted in long-term HCV infection. HCV infection induced elevated infiltration of human immune cells in the livers of HCV-infected humanized mice. HCV infection also induced HCV-specific T-cell immune response in lymphoid tissues of humanized mice. Additionally, HCV infection induced liver fibrosis in humanized mice. Anti-human alpha smooth muscle actin (αSMA) staining showed elevated human hepatic stellate cell activation in HCV-infected humanized mice. We discuss the limitation and future improvements of the AFC8-hu HSC/Hep mouse model and its application in evaluating novel therapeutics, as well as studying both HCV and HBV infection, human immune responses, and associated human liver fibrosis and cancer.

Background Foot-and-mouth disease (FMD) is endemic in Uganda in spite of the control measures used. Various aspects of the maintenance and circulation of FMD viruses (FMDV) in Uganda are not well understood; these include the role of the African buffalo (Syncerus caffer) as a reservoir for FMDV. To better understand the epidemiology of FMD at the livestock-wildlife-interface, samples were collected from young, unvaccinated cattle from 24 pastoral herds that closely interact with wildlife around Queen Elizabeth National Park in Uganda, and analysed for evidence of FMDV infection. Results In total, 37 (15 %) of 247 serum samples had detectable antibodies against FMDV non-structural proteins (NSPs) using a pan-serotypic assay. Within these 37 sera, antibody titres ≥ 80 against the structural proteins of serotypes O, SAT 1, SAT 2 and SAT 3 were detected by ELISA in 5, 7, 4 and 3 samples, respectively, while neutralizing antibodies were only detected against serotype O in 3 samples. Two FMDV isolates, with identical VP1 coding sequences, were obtained from probang samples from clinically healthy calves from the same herd and are serotype SAT 1 (topotype IV (EA-I)). Based on the VP1 coding sequences, these viruses are distinct from previous cattle and buffalo SAT 1 FMDV isolates obtained from the same area (19–30 % nucleotide difference) and from the vaccine strain (TAN/155/71) used within Uganda (26 % nucleotide difference). Eight herds had only one or a few animals with antibodies against FMDV NSPs while six herds had more substantial evidence of prior infection with FMDV. There was no evidence for exposure to FMDV in the other ten herds. Conclusions The two identical SAT 1 FMDV VP1 sequences are distinct from former buffalo and cattle isolates from the same area, thus, transmission between buffalo and cattle was not demonstrated. These new SAT 1 FMDV isolates differed significantly from the vaccine strain used to control Ugandan FMD outbreaks, indicating a need for vaccine matching studies. Only six herds had clear serological evidence for exposure to O and SAT 1 FMDV. Scattered presence of antibodies against FMDV in other herds may be due to the occasional introduction of animals to the area or maternal antibodies from past infection and/or vaccination. The evidence for asymptomatic FMDV infection has implications for disease control strategies in the area since this obstructs early disease detection that is based on clinical signs in FMDV infected animals. Electronic supplementary material The online version of this article (doi:10.1186/s12917-015-0616-1) contains supplementary material, which is available to authorized users.

Concerns about potentially irreversible non-target impacts from the importation and release of entomophagous biological control agents (BCAs) have resulted in increasingly stringent national import requirements by National Plant Protection Organizations worldwide. However, there is a divergence of opinions among regulators, researchers, environmentalists, and the general public on ways to appropriately manage associated risks. Implementation of a comprehensive and effective risk communication process might narrow the opinion gaps. Results from a comprehensive survey conducted in the United States were used to describe communication habits of stakeholders involved in biological control and identify areas that are fundamental in an efficient process. In addition, this study critically reviews risk communication practices and how phytosanitary decisions are communicated in the permitting systems for entomophagous BCAs of several countries to identify risk communication tools used in an effective risk communication framework. The following barriers to efficient risk communication were identified: absence of a formalized risk communication process, undefined risk communication goals and target audiences, lack of credibility and objectivity of information sources, inefficiency of mode of distribution of messages, insufficient public participation, and lack of transparency of decision making processes. This paper suggests the creation and/or enhancement of modes of distribution of risk messages to increase coverage, understanding, and guidance. For instance, messages should be presented in different formats such as internet, brochures, and newspapers. Surveys, public meetings, and trainings/workshops are tools that can be used to characterize stakeholders’ diversity and develop risk messages specific to the targeted audience. Implementation of a participatory decision making process will increase stakeholder involvement and trust in the risk management plan. Development of practical mechanisms, such as public hearings will increase all stakeholders’ involvement in the risk assessment process. A clear framework describing how public comments will be incorporated in the decision making process should be implemented. Finally, to ensure a streamlined risk communication process, there must be consistency in the messages disseminated by federal, state, and local agencies.

Minimizing the impact of invasive alien species (IAS) on islands and elsewhere requires researchers to provide cogent information on the environmental and socioeconomic consequences of IAS to the public and policy makers. Unfortunately, this information has not been readily available owing to a paucity of scientific research and the failure of the scientific community to make their findings readily available to decision makers. This review explores the vulnerability of islands to biological invasion, reports on environmental and socioeconomic impacts of IAS on islands and provides guidance and information on technical resources that can help minimize the effects of IAS in island ecosystems. This assessment is intended to provide a holistic perspective on island-IAS dynamics, enable biologists and social scientists to identify information gaps that warrant further research and serve as a primer for policy makers seeking to minimize the impact of IAS on island systems. Case studies have been selected to reflect the most scientifically-reliable information on the impacts of IAS on islands. Sufficient evidence has emerged to conclude that IAS are the most significant drivers of population declines and species extinctions in island ecosystems worldwide. Clearly, IAS can also have significant socioeconomic impacts directly (for example human health) and indirectly through their effects on ecosystem goods and services. These impacts are manifest at all ecological levels and affect the poorest, as well as richest, island nations. The measures needed to prevent and minimize the impacts of IAS on island ecosystems are generally known. However, many island nations and territories lack the scientific and technical information, infrastructure and human and financial resources necessary to adequately address the problems caused by IAS. Because every nation is an exporter and importer of goods and services, every nation is also a facilitator and victim of the invasion of alien species. Wealthy nations therefore need to help raise the capacity of island nations and territories to minimize the spread and impact of IAS.

Foot-and-mouth disease (FMD) is endemic in Kenya and has been well studied in cattle, but not in pigs, yet the role of pigs is recognised in FMD-free areas. This study investigated the presence of antibodies against FMD virus (FMDV) in pigs sampled during a countrywide random survey for FMD in cattle coinciding with SAT 1 FMDV outbreaks in cattle. A total of 191 serum samples were collected from clinically healthy pigs in 17 districts. Forty-two of the 191 sera were from pigs vaccinated against serotypes O/A/SAT 2 FMDV. Antibodies against FMDV non-structural proteins were found in sera from 30 vaccinated and 71 non-vaccinated pigs, altogether 101/191 sera (53 %), and 91 % of these (92/101) also had antibodies measurable by serotype-specific ELISAs, predominantly directed against SAT 1 with titres of 10–320. However, only five high titres against SAT 1 in vaccinated pigs were confirmed by virus neutralisation test (VNT). Due to high degree of agreement between the two ELISAs, it was concluded that positive pigs had been infected with FMDV. Implications of these results for the role of pigs in the epidemiology of FMD in Kenya are discussed, and in-depth studies are recommended.

Foot-and-mouth disease (FMD) is endemic in Kenya where four serotypes (O, A, SAT 1 and SAT 2) of the virus are currently in circulation. Within 2010 and 2011, the National Laboratory recorded an increase in the number of FMD outbreaks caused by serotype O virus. The characteristics of these viruses were determined to ascertain whether these were independent outbreaks or one single strain spreading throughout the country. The sequences of the complete VP1-coding region were analysed from viruses sampled within different areas of Kenya during 2010 and 2011. The results indicated that the 2010 to 2011 outbreaks in Kenya were caused by four independent strains. By comparison with earlier type O isolates from Eastern Africa, it was apparent that the outbreaks were caused by viruses from three different lineages of topotype EA-2 and a fourth virus strain belonging to topotype EA-4. The topotypes EA-1 and EA-3 were not detected from these outbreaks. Implications of these results for FMD control in Eastern Africa are discussed.

Background Accurate diagnosis is pertinent to any disease control programme. If Eastern Africa is to work towards control of foot-and-mouth disease (FMD) using the Progressive Control Pathway for FMD (PCP-FMD) as a tool, then the capacity of national reference laboratories (NRLs) mandated to diagnose FMD should match this task. This study assessed the laboratory capacity of 14 NRLs of the Eastern Africa Region Laboratory Network member countries using a semi-structured questionnaire and retrospective data from the World Reference Laboratory for FMD annual reports and Genbank® through National Centre for Biotechnology Information for the period 2006–2010. Results The questionnaire response rate was 13/14 (93%). Twelve out of the 13 countries/regions had experienced at least one outbreak in the relevant five year period. Only two countries (Ethiopia and Kenya) had laboratories at biosecurity level 3 and only three (Ethiopia, Kenya and Sudan) had identified FMD virus serotypes for all reported outbreaks. Based on their own country/region assessment, 12/13 of these countries /regions were below stage 3 of the PCP-FMD. Quarantine (77%) and vaccination (54%) were the major FMD control strategies employed. The majority (12/13) of the NRLs used serological techniques to diagnose FMD, seven used antigen ELISA and three of these (25%) also used molecular techniques which were the tests most frequently requested from collaborating laboratories by the majority (69%) of the NRLs. Only 4/13 (31%) participated in proficiency testing for FMD. Four (31%) laboratories had no quality management systems (QMS) in place and where QMS existed it was still deficient, thus, none of the laboratories had achieved accreditation for FMD diagnosis. Conclusions This study indicates that FMD diagnostic capacity in Eastern Africa is still inadequate and largely depends on antigen and antibody ELISAs techniques undertaken by the NRLs. Hence, for the region to progress on the PCP-FMD, there is need to: implement regional control measures, improve the serological diagnostic test performance and laboratory capacity of the NRLs (including training of personnel as well as upgrading of equipment and methods, especially strengthening the molecular diagnostic capacity), and to establish a regional reference laboratory to enforce QMS and characterization of FMD virus containing samples.

We present the design, fabrication, and demonstration of a 10/spl times/10 matrix-addressed vertical-cavity top-surface-emitting laser (VCSEL) array. These arrays are batch-fabricated from full 3-in diameter GaAs/AlGaAs wafers. We show that no performance-penalty is paid using top-contacted matrix addressed pixels over conventional planar VCSEL devices. A computer-controlled display system for electrically addressing the array was designed and constructed to permit video demonstration and array testing. >

Given two energy states (levels) in a quantum well formed by two potential barriers of finite thickness, elementary quantum mechanics tells us that the lower energy state is more tightly bound than the upper state. This produces a longer spatial confinement lifetime in the lower state than in the upper state. This ratio of lifetimes is opposite to that needed for laser action between these states. Furthermore, the lifetime of the lower energy state must be significantly shorter than the electron scattering time for the upper state. These facts have blocked the development of lasers based on these transitions. However, in this paper we report experimental and analytical results on a versatile type of semiconductor heterostructure that overcomes these difficulties. Unlike previous devices, this structure relies on an optical transition between two states which are both above-barrier quasibound states in the ‘classical’ continuum. The oscillator strength is large and the operation of the device clearly demonstrates coherent electron wave behavior. Such structures could represent the basis for a new room-temperature infrared semiconductor laser.

Responsivity and thermionic dark current are studied in asymmetric stepped GaAs/AlGaAs multiquantum well infrared detectors with a single bound state. Although attributed to different transport properties, both the photoexcited and the thermally emitted carriers exhibit asymmetric transport properties with respect to the voltage polarity. The experimental characteristics are explained by the minibands-quasi continuum energy structure above the barrier.

Compound semiconductors—semiconductors made when elements from Columns III and V of the Periodic Table are combined—are being used more frequently in the fabrication of integrated circuits. The evaluation and utilization of new processing technologies have enabled compound semiconductor technology to move out of the laboratory into real-world applications. Compound semiconductors, such as gallium arsenide and indium phosphide, are being used because of their inherent radiation hardness and their ability to quickly transmit electrons and because they can be utilized to make semiconductor lasers and photodetectors used in telecommunications. Although the raw chemical constituents used to make and process compound semiconductors have well-documented toxicological effects, compound semiconductor materials per se were not thought to present an acute toxicity hazard. This investigation documented the formation of arsine and phosphine—acutely toxic gaseous hydrides—which result from the handling and pro...

The transport of hot electrons in the AlxGa1−xAs barriers above the wells in a multiple quantum well (MQW) structure is investigated. The structures that are studied are asymmetric quantum well infrared detectors. The transport of the hot electrons normal to the layers is strongly dependent on both voltage and well shape. It is suggested that the key parameter which affects the transport properties is the dwell time of the electrons in the continuum, above the well region. This is most readily seen in asymmetric MQW structures, in which the dwell time under an applied bias depends very strongly on bias polarity. Calculations of electron transmission coefficient and dwell time show that the electron mean free path in asymmetric wells is much larger in positive bias than in a negative one. Employing this model, we achieve a very good fit to experimental data.

We introduce a new low-loss fast intracavity semiconductor Fabry-Perot saturable absorber operated at anti-resonance both to start and sustain stable mode locking of a cw-pumped Nd:YLF laser. We achieved a 3.3-ps pulse duration at a 220-MHz repetition rate. The average output power was 700 mW with 2 W of cw pump power from a Ti:sapphire laser. At pump powers of less than 1.6 W the laser self-Q switches and produces 4-ps pulses within a 1.4-micros Q-switched pulse at an approximately 150-kHz repetition rate determined by the relaxation oscillation of the Nd:YLF laser. Both modes of operation are stable. In terms of coupled-cavity mode locking, the intra-cavity antiresonant Fabry-Perot saturable absorber corresponds to monolithic resonant passive mode locking.

Vertical cavity zone lasers (Z-lasers) operating at 980 nm and 850 nm have been fabricated. This new class of high power (>100 mW) high efficiency (/spl eta//spl ap/ 36%) large area (70 /spl mu/m diameter) vertical cavity laser has an output that is automatically focused to a spot at a particular distance away from the laser. This is in contrast to the conventional surface or edge emitting array devices that usually have multiple far-field lobes and need external optical components for focusing purposes. Among other applications, the unique properties of 980 nm Z-lasers makes them attractive as a pump laser for fiber amplifier systems.

We report the observation of bistable polarization switching in a vertical‐cavity surface‐emitting laser under optical injection. The wavelength dependence of the switching is measured. It is found that this polarization switching is achieved through injection locking where both the wavelength and the polarization of the vertical‐cavity laser are locked to the injected optical signal.

Selectively excited room‐temperature photoluminescence spectra of InGaAs‐GaAs‐AlGaAs quantum well heterostructures reveal a broad line at midgap energies originating in the Si doped AlGaAs. When carriers are photoexcited directly in the wells, this line is dramatically enhanced at the expense of the quantum well line, indicating carriers escape from the wells. The broad emission and its enhancement can be explained in terms of recombination between electrons trapped at DX centers in AlGaAs and holes transferred into AlGaAs from the neighboring wells. We also observe the broad emission by direct over‐the‐gap photoexcitation of very highly doped Si:AlGaAs. The doping dependence consistently correlates this line to DX centers.

An asymmetric semiconductor electron wave Fabry–Perot interference filter has been designed with two above‐barrier quasibound states for optical transitions. The upper state was designed to have a spatial confinement lifetime greater than three times that of the lower state (which was designed to be less than 100 fs). Such lifetime ratios and magnitudes, which are nearly impossible for below‐barrier states, satisfy the criteria required for achieving population inversion. Furthermore, the transitions were designed to have large dipole matrix elements. Absorption measurements at multiple temperatures were used to demonstrate the first bound‐to‐quasibound transitions in an asymmetric structure. The experimental energies and dipole matrix elements are in agreement with calculated values. This type of structure could represent the basis for a new room‐temperature infrared semiconductor laser.

A new type of asymmetric stepped GaAs/AlGaAs multiquantum well infrared detector is reported. These asymmetric detectors utilize the usual bound‐to‐continuum transition. The current responsivity is remarkably asymmetric with regard to the voltage polarity. In contrast with rectangular wells, in which responsivity is saturated in both bias polarities, these wells exhibit saturation only for negative bias. The responsivity increases monotonously with positive electric field. This is attributed to changes induced by the field on the transport properties of the excited electrons. In particular, the bias affects the dwell time spent by the carrier wave packet in the well region. Employing this model, we achieve a very good fit with experimental data.

We demonstrate record high pulsed output power exceeding 530 mW from an electrically pumped phase‐coupled 8×8 vertical cavity surface emitting laser array (SELA) at room temperature. Three array types are compared: an 8×8 pixellated SELA(PSELA), an 8×8 grid contact SELA(CSELA), and a 78 μm×78 μm single broad area SEL(BSEL) emitter. The CSELA operating in a phase‐coupled supermode exhibits the lowest threshold current (100 mA) and voltage (1.6 V), highest damage threshold and a smooth L‐I characteristic with differential quantum efficiency ηd≳27%, the BSEL has the largest output power≳580 mW and a large ηd≳48%, the PSELA exhibited a large voltage with the largest ηd≳80%.

The effects of electrorefraction in quantum‐well Fabry–Perot (FP) modulators are discussed theoretically and illustrated experimentally. The large electrorefraction at the zero‐field heavy‐hole exciton is shown to produce strong modulation in FP devices operated at that wavelength. At longer operating wavelengths, the weakening electrorefraction plays a diminishing role. By taking into account the field dependent absorption α(λ,E) and dispersion n(λ,E) of the quantum‐well material, the measured reflectivity spectra are successfully modeled.

Symmetric self‐electro‐optic effect devices (S‐SEEDs) using extremely shallow GaAs/Al0.04Ga0.96As multiple quantum wells are demonstrated. By exploiting mainly exciton ionization, rather than the usual quantum‐confined Stark shift, room‐temperature optical bistability is obtained with no applied bias. The extremely shallow symmetric‐SEED (symmetric E‐SEED) exhibits contrast ratios (CRs)≂3.5, with biasses

We have devised a novel vertical‐cavity top surface‐emitting GaAs quantum well laser structure which operates at 0.84 μm. The laser combines peripheral current injection with efficient heat removal and uses only the epitaxially grown semiconductor layers for the output mirrors. The structure is obtained by a patterned deep H+ implantation and anneal cycle which maintains surface conductivity while burying a high resistance layer. Peripheral injection of current occurs from the metallized contact area into the nonimplanted nonmetallized emission window. For 10‐μm‐diam emitting windows, ∼4 mA thresholds with continuous‐wave (cw) room‐temperature output powers ≳1.5 mW are obtained. Larger diameter emitting windows have maximum cw output powers greater than 3 mW. These are the highest cw powers achieved to date in current injected vertical‐cavity surface‐emitting lasers.

A possible laser device is designed with the use of classically free quasibound electron states. An asymmetric semiconductor electron wave Fabry-Perot interference filter is designed with an upper electron state having much stronger confinement than the lower electron state. This structure also allows for direct current pumping of the upper state and rapid depletion of the lower state under the presence of a field. Spectroscopy experiments demonstrate the existence of the upper quasibound state in a test structure. This laser filter structure, designed for infrared gain with current pumping, is combined with a special injector filter for room temperature narrow energy current injection into the upper lasing state. A stack of 54 periods of this electrically pumped structure is placed within a waveguide geometry. A laser device is fabricated by etching mesa structures from 50 to 100 micrometers wide. End cleaved facets serve as reflectors for mesas from 2 to 5 mm long. Tests are performed on these devices to determine their electrical properties and suitability for lasing.

A possible laser device is designed with the use of classically free quasibound electron states. An asymmetric semiconductor electron wave Fabry-Perot interference filter is designed with an upper electron state having much stronger confinement (235f6 lifetime) than the lower electron state (76f s lifetime). This structure also allows for direct current pumping of the upper state and rapid depletion of the lower state under the presence of a field. Experiments demonstrate the existence of the upper quasibound state in this structure. Another structure, designed for infrared gain with current pumping, has improved parameters over the structure used in the spectroscopy measurement.

We discuss the potential of using coherently-coupled vertical cavity surface emitting laser arrays ashigh-intensity light sources. In particular, the design and performance of a novel two-dimensional phase-coupled grid Contact vertical cavity Surface Emitting Laser Array (C-SELA) is reported. We discuss theoptical properties of the C-SELA; in addition to the usual out-of-phase array mode, we demonstrate in-phase SELA coupling. We introduce a simple physical model to describe our experimental results. Over 1.2Watt optical power emission is obtained at room temperature from an electrically-excited lOxlO C-SELA.This laser array exhibited a low threshold current density of only 600Amps/cm2 and over 60% single-endeddifferential quantum efficiency. I . INTRODUCTION High power semiconductor lasers have a number of important commercial, medical, and military appli-cations.1'2 To date, little research has been conducted into the potential of using Vertical Cavity SurfaceEmitting Lasers (VCSELs) as a high intensity light source. The advantages of using VCSELs for highpower include ease of manufacture and testing of 2D arrays and thus low cost production, good optical pro-perties, and a buried active region beneath a distributed mirror, low surface power density due to increasedemission area and hence, the potential for low catastophic optical damage. We have studied variousapproaches to achieving large coherent output power from VCSELs.3 These include using a broad-areaemission window, a closely-spaced individually-pixellated VCSEL array, and a novel approach using a gridcontact to force coherence across the array by modulating the gain and reflectivity. We demonstrated highcoherent optical output power exceeding 0.53 W in a single coherent supermode from an 8x8 phase-coupledpatterned grid Contact vertical cavity Surface Emitting Laser Array (C-SELA).3 The C-SELA exhibits asmooth L-I and a low-voltage (1 .6V threshold voltage) electrical characteristic overcoming some of themajor problems associated with VCSELs. Another similarly-sized 8x8 SELA was studied in which all ele-ments were individually pixellated. In contrast to the C-SELA, it was found that the pixelated SELA,although exhibiting an extremely large external quantUm efficiency rj

A new type of asymmetric stepped GaAs/AlGaAs multi quantum well infrared detectors is reported. These asymmetric detectors utilize the usual bound to continuum transition. The current responsivity is remarkably asymmetric with regard to the voltage polarity. In contrast with rectangular wells, in which responsivity is saturated in both bias polarities, these wells exhibit saturation only for negative bias. The responsivity increases monotonously with positive electric field. The difference between polarities for the noise is much smaller at low temperatures. As a result, the highest D * in positive polarity is much higher than in the negative one. This is attributed to changes induced by the field on the transport properties of the excited electrons. In particular, the bias affects the dwell time spent by the carrier wave packet in the well region. Employing this model, we achieve a very good fit with experimental data. The transport asymmetry is further studied using identical asymmetric wells which were grown in opposite sequences. It is shown that the effect of the asymmetry in the interfaces is of the same order of magnitude as the structural asymmetry.

We report on Molecular Beam Epitaxial growth and properties of strained In0.2Ga0.8As-GaAs quantum well (QW) structures suitable for 980 nm lasers. The QW width was maintained at 80 A and the barrier thickness was varied from 50 A to 300 A. The effects of increasing the barrier width on the structural and optical properties of the QW were examined using double crystal x-ray diffraction rocking scans (DCXRD) and photoluminescence measurements. DCXRD rocking scans revealed satellite peaks from the strained layer quantum wells (SLQW). The linewidth of the peaks decreased as the barrier width was increased. Optical measurements indicate significant improvements in the internal luminescence efficiency in the thick barrier structures. We assign the improvements in the luminescence properties to the reduction of non-radiative centers in the thick barrier structures. The sources of the non-radiative centers are ascribed to structural defects that are generated as a result of strain relaxation in the thin barrier structures. A new broad photoluminescence feature at 0.9 eV was also observed and believed to originate in the AlGaAs:Si cladding region. We shall present these results and discuss the implications of increasing the barrier thickness of In0.2Ga0.8As-GaAs QW on the performance of 980 nm lasers.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We report batch-processed, totally planar, vertical-cavity top surface emitting GaAs/AlGaAs laser devices and arrays. Different size devices are studied experimentally. We measure continuous-wave threshold currents down to 1.7 mA and output powers > 3.7 mW at room temperature. We also discuss interesting characteristics such as differential quantum efficiencies exceeding unity and multi-transverse mode behavior. An array having 64 X 1 individually-accessed elements is characterized and shown to have uniform room-temperature continuous-wave operating characteristics in threshold current approximately equals 2.1 +/- 0.1 mA, wavelength approximately equals 849.4 +/- 0.8 nm, and output power approximately equals 0.5 +/- 0.1 mW.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Advances in epitaxial growth techniques such as molecular beam epitaxy and metal organic chemical vapor deposition have facilitated the formation of high quality III-V heterostructures with dimensional control down to atomic levels, with abrupt doping and near-defect-free interfaces. The flexibility and remarkable control offered by these techniques have resulted in the fabrication of new devices based on confinement or modulation of carriers in thin III-V heterostructures. Quantum wells and superlattice based devices are expected to be utilized in optical information processing as sources, modulators, and detectors. In this paper, we will review the general epitaxial requirements for quantum wells and superlattices based devices, and discuss the fabrication and properties of a new class of infrared photodetectors that employ intraband transitions in quantum wells.

We report on molecular beam epitaxial growth of Si doped, single and multiple quantum well structures. We have examined the effects of growth parameters such as substrate temperature, group V/III ratio, and intentional and unintentional impurities, on the electrical and optical properties of the quantum wells structures. Capacitance–voltage and secondary ion mass spectrometry analysis of the structures reveal that the net density of electrically active carriers in the wells is controlled by the number of acceptor states in the AlGaAs barrier. We have assigned the source of the acceptor state to the presence of oxygen in the AlGaAs barrier. We observe that the strength of the intersubband optical absorption from the quantum wells increases linearly with the Si‐doping in the well. Photoluminescence measurements indicate that for a given substrate temperature, a lower V/III ratio results in higher quality quantum well.

Hybrid mode locking of a broad-area semiconductor laser with a multiple-quantum-well saturable absorber in an external cavity is demonstrated. A novel method for mode control of the broad-area laser output, based on patterning of the multiple quantum well absorber into a microdot mirror structure, is presented. Pulses as short as 15 ps, at a repetition rate of 593 MHz, with an average power of 9 mW and a peak power of 1 W have been achieved.

Tho Letter reports the reduction of p-mirror electrical resistance using a very simple delta doping technique. The differentia] resistance was reduced almost by half, and the peak output power was increased by about 40% with delta doping. No significant difference was observed in threshold current and efficiency.

The Letter reports for the first time over 1 W pulsed optical power emission obtained at room temperature from an electrically-excited grid-contact vertical cavity top surface emitting laser array. This laser exhibited a low threshold current density of only 600 A/cm2 and over 60% single-ended differential quantum efficiency.

Kerr lens mode-locked (KLM) solid-state lasers are typically not self-starting. We address this problem by introducing a broadband semiconductor saturable absorber that could be used as a tunable, all-solid-state, passive starting mechanism. We extend the wavelength tunability of a semiconductor saturable absorber to more than 100 nm using a band-gap-engineered low-temperature molecular-beam-epitaxy (MBE)-grown bulk AlGaAs semiconductor saturable absorber in which the absorption edge of the saturable absorber has been artificially broadened by continuously reducing the Al concentration during the MBE growth. We demonstrate its tunability and its feasibility as a starting mechanism for KLM with a picosecond resonant passive mode-locked Ti:sapphire laser. The extension to femtosecond KLM lasers has been discussed previously.

Ion beam milling-induced damage in a 500 A AlGaAs/40 A GaAs/500 A AlGaAs single quantum well structure was investigated using low temperature cathodoluminescence spectroscopy. The ion beam energy (500-1500 eV) dependence of luminescence intensity indicated that minimum damage is introduced at a beam energy of 500 eV. Most (80-85%) of the original luminescence intensity was recovered on annealing at 400 o C for 5 min

Highly efficient (1.2 mW/mA, >70% CW differential quantum efficiency), top-surface-emitting, vertical cavity lasers are achieved at room temperature. Buried damage layers by proton implantation are used for efficient current funnelling. The CW threshold currents are 3.5–8.0 mA, at 3.7–4.2 V bias, for 10.30 μm diameter lasers. The lasing wavelengths are 845–848 nm.