Multi-year techno-economic assessment of proposed zero-emission hybrid community microgrid in Nigeria using HOMER.

This paper presents a novel use of the HOMER Software for the multi-year economic, environmental, and energetic assessment of a proposed multi-source standalone renewable microgrid. A rural-but-rapidly-commercializing community in Nigeria's middle belt was used as a case study, with an average power demand of 975 kW and average consumption of 23.028 MWh/day. A generation mix of flat-plate photovoltaic (PV) array (3 MW nominal), concentrated solar thermal (CSP, 9 MW nominal), and small hydropower (SH, up to 200 kW), with battery storage (200 strings), system converter (2.5 MW nominal) using the Oshin River was recommended as the optimal system for minimizing the cost of electricity (LCOE) in HOMER. A diesel-based system was also simulated and a multiyear analysis for a 25-year period shows that the Net Present Cost (NPC) of $55.7 million for the renewable microgrid is vastly superior to the $408 million for the diesel microgrid, with LCOE of $0.26 and $1.01 per kWh respectively. The system also saved up to 7540 metric tons of CO2 per year in emissions. The results of the study indicate the proposed microgrid as an economically and environmentally superior alternative to diesel generators in the long term, and as deserving consideration for similar applications.

Wide multiwavelength Brillouin-Raman fiber laser assisted by an arc-shaped fiber attenuator.

A wide bandwidth, single-spacing half-open-cavity multiwavelength Brillouin-Raman fiber laser (MWBRFL) is demonstrated. The laser cavity contains a fiber loop mirror (FLM) with an arc-shaped optical fiber attenuator that is used to control the mirror reflectivity, thereby suppressing gain competition from longitudinal cavity modes. A tuning range of 45 nm with 632 lines at Raman and 1525 nm Brillouin pump powers of 1.2 W and 12 dBm can be achieved using the 10 dB arc-shaped optical fiber attenuator in the cavity. This is in comparison to 433 Stokes lines obtained over a 31 nm tuning range for the half-open MWBRFL cavity without any feedback power optimization. The MWBRFL has low power fluctuations of less than 0.1 dB over a 1 h test period. The inclusion of the arc-shaped optical fiber attenuator in the MWBRFL provides substantial control over the reflectivity of the FLM as well as improving the laser's tuning range to generate a high number of Brillouin Stokes signals.

Wide-uniform triple Brillouin frequency spacing multi-wavelength fiber laser assisted by a distributed Raman amplifier.

In this paper, we demonstrate a wide-uniform and hybrid multi-wavelength fiber laser source with triple Brillouin-shift wavelength spacing. The hybrid gains include the combination of erbium-ytterbium-doped fiber and distributed Raman amplifiers. For optimum performances, the Brillouin pump wavelength is set at 1532 nm with power at -20 dBm, erbium-ytterbium-doped fiber amplifier at 950 mW and Raman pump power at 900 mW. The highest channel count is obtained in this kind of laser design, where around 164 Stokes lines are produced within 10 dB spectral flatness. The corresponding bandwidth is 40 nm, where the average optical signal-to-noise ratio is maintained at 36 dB estimation. The outstanding total power stability indicates 0.74 dB fluctuation over a 45-minute duration. This merits the practicality for various applications especially in optical communication system and sensing. Furthermore, a reasonable wide tuning range of 36 nm is realized, beginning from 1532 nm, which is only restricted by the accessible hybrid gain bandwidth.

Enhanced flatness of 20 GHz channel spacing multiwavelength Brillouin-Raman fiber laser with sub-millimeter air gap.

We discover the technique of controlling the flatness in signal amplitude of a multiwavelength Brillouin-Raman fiber laser by employing an air-gap outside of the cavity. The structure that is adjustable within sub-millimeter length behaves as flexible optical feedback that provides modifiable portions of multiple Fresnel reflectivities. This is the main benchmark that allows the efficient management of gain competition between self-lasing modes and Brillouin Stokes waves that is vital for self-flattening initiation. When setting the Brillouin pump wavelength at 1529 nm and the air-gap distance to 0.4 mm, 296 Stokes lines are produced with a channel spacing of 0.158 nm. The lasing bandwidth is 46.60 nm that covers from 1529.16 to 1575.76 nm wavelength. In this case at Raman power of 950 mW, the intense Brillouin pump power of 2 dBm saturates the cascaded higher-orders lasing lines. As a result, the overall peak power discrepancy is maintained at just 1.8 dB where an average optical-signal-to-noise ratio of 20 dB is realized. To date, this is the widest bandwidth with the flattest spectrum attained in multiwavelength fiber lasers that incorporate a single Raman pump unit.

Independent determinants of periodontitis in Yemeni adults: A case-control study.

OBJECTIVES: The relative importance of risk factors of periodontitis varies from one population to another. In this study, we sought to identify independent risk factors of periodontitis in a Yemeni population. METHODS: One hundred and fifty periodontitis cases and 150 healthy controls, all Yemeni adults 30-60 years old, were recruited. Sociodemographic data and history of oral hygiene practices and oral habits were obtained. Plaque index (PI) was measured on index teeth. Periodontal health status was assessed using Community Periodontal Index (CPI) and Clinical Attachment Loss (CAL) according to WHO. Periodontitis was defined as having one or more sextants with a CPI score ≥ 3. Multiple logistic regression modelling was employed to identify distal, intermediate and proximal determinants of periodontitis, while ordinal regression was used to identify those of CAL scores. RESULTS: In logistic regression, PI score was associated with the highest odds of periodontitis (OR = 82.9) followed by cigarette smoking (OR = 12.8), water pipe smoking (OR = 10.2), male gender (OR = 3.4) and age (OR = 1.19); on the other hand, regular visits to the dentist (OR = 0.05), higher level of education (OR = 0.37) and daily dental flossing (OR = 0.95) were associated with lower odds. Somewhat similar associations were seen for CAL scores (ordinal regression); however, qat chewing was identified as an additional determinant (OR = 4.69). CONCLUSION: Water pipe smoking is identified as a risk factor of periodontitis in this cohort in addition to globally known risk factors. Adjusted effect of qat chewing is limited to CAL scores, suggestive of association with recession.

Flat amplitude and wide multiwavelength Brillouin/erbium fiber laser based on Fresnel reflection in a micro-air cavity design.

In this report, we demonstrate a wide multiwavelength Brillouin-erbium fiber laser (MBEFL) with improved flatness that integrates a micro-air cavity. This air-gap introduces a cavity loss to overcome the gain saturation as well as providing efficient pump recycling scheme through Fresnel back-reflection. In addition, the efficient four-wave mixing in the highly nonlinear fiber contributes to the self-flattening of the output spectra. During operation, the optimized pumping values are set at 13 dBm Brillouin power and 600 mW erbium-ytterbium doped fiber amplifier when the air-gap length is fixed at 10 µm. A total of 180 Stokes lines are produced with a channel spacing of 0.08 nm. The flat lasing bandwith is 14 nm that consists of 1557 to 1571 nm wavelengths within 3-dB span. The average optical signal-to-noise ratio is 18 dB, having high peak power of -8 dBm. To our knowledge, this is the best result attained in MBEFLs with respect to the spectral flatness. In fact, the power stability of 0.76 dB order over 45 minute durations merits it applications in optical fiber sensing and communications.

Wide bandwidth and flat multiwavelength Brillouin-erbium fiber laser.

A wide bandwidth and flat multiwavelength Brillouin-erbium fiber laser is demonstrated experimentally. In the proposed laser setup, the combination of a Brillouin mirror with feedback and a ring cavity with four-wave mixing assistance is realized. The efficiency of Brillouin Stokes lines generation is enhanced by the feedback-based Brillouin mirror structure. The effect of four-wave mixing in highly nonlinear fiber increases the generation of Brillouin Stokes lines in a wider bandwidth. The laser lines over 16 nm bandwidth (i.e 200 channels) within 4.65 dB power difference are obtained. The generated laser lines span from 1534 to 1550 nm with wavelength spacing of 0.08 nm and optical signal-to-noise ratio of at least 15 dB. The laser can also be freely tuned over 32 nm and is stable with power fluctuations of 0.7 dB over 1 hour duration.

Investigation of the fatigue behavior of adhesive bonding of the lithium disilicate glass ceramic with three resin cements using rotating fatigue method.

OBJECTIVE: To investigate the fatigue behavior of bonding interface of lithium disilicate ceramic with three different dual cure resin cements. MATERIAL AND METHODS: Forty five bar shaped ceramic-resin-ceramic specimens were prepared and divided into 3 groups (n=15) according to the resin cement used (group1: Panavia F2.0, group 2: RelyX Ultimate, group 3: Duo-Link Universal). Three specimens of each group were tested using three point bending test and the fracture strength of the resin-ceramic bond was measured. Other specimens of each group were placed in the rotating fatigue testing machine at stresses equal to 30%, 40%, 50% and 60% of the fracture strength. The cyclic loading was continued until fracture or a maximum of 10,000 cycles. For the specimens which did not fail until 10,000 cycles, the cyclic loading was stopped and the remained fracture strength of the specimens was measured. RESULTS: None of the specimens with cyclic loads of 30% and 40% of the fracture strength, have failed until 10,000 cycles. After 10,000 load cycles, the fracture strength of these specimens was significantly lower than their initial fracture strength. On the other hand, all specimens with cyclic stresses equal to 50% and 60% of the fracture strength have failed before 10,000 cycles so that the numbers of load cycles of RelyX specimens were significantly higher than those of Panavia ones and the numbers of cycles of Panavia specimens were significantly higher than those of Duo-Link specimens. CONCLUSION: The fatigue resistance of the ceramic-resin interface is significantly lower than its bond strength. Furthermore, RelyX Ultimate showed the highest fatigue resistance and Duo-Link Universal exhibited the weakest fatigue resistance. Since dental restorations are under cyclic loading caused by mastication forces, the results of this research can be used to select fatigue resistant resin cements for bonding of ceramic restorations.

Quantitative analysis of classical and new putative periodontal pathogens in subgingival biofilm: a case-control study.

BACKGROUND AND OBJECTIVES: A number of species/phylotypes have been newly implicated as putative periopathogens. The objective of this study was to explore associations among classical and new pathogens in subgingival biofilm and to assess their relative importance to chronic periodontitis. MATERIAL AND METHODS: Pooled subgingival biofilm samples were obtained from 40 patients with chronic periodontitis and 40 healthy controls. Taqman q-PCR assays were used to determine the absolute and relative counts of Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola, Parvimonas micra, Filifactor alocis, oral Synergistetes and oral TM7s. Microbial associations were assessed using cluster analysis. Different statistical models were used to explore associations between microbial parameters and periodontitis. RESULTS: The median log and relative counts were lowest for TM7s (4.4 and 0.0016%, respectively) and highest for oral Synergistetes (7.2 and 1.4%, respectively). Oral Synergistetes clustered strongly with the red complex, particularly T. forsythia (100% rescaled similarity). All species/phylotypes except TM7s were significantly associated with periodontitis (Mann-Whitney test; p ≤ 0.005). However, P. gingivalis and F. alocis lost association after adjusting for confounders (ordinal regression). In receiving operator characteristic curve analysis, the log counts of oral Synergistetes were the best markers of periodontitis (82.5% sensitivity and specificity), followed by those of T. forsythia, P. micra and T. denticola. In prediction analysis, however, P. micra was the only microbial predictor of periodontal parameters. CONCLUSIONS: Oral Synergistetes are presented here as new members of the red complex, with relative importance to periodontitis exceeding that of the classical members. P. micra is shown as an important periodontal pathogen warranting more attention.

Speed/accuracy trade-offs in target-directed movements.

This target article presents a critical survey of the scientific literature dealing with the speed/accuracy trade-offs in rapid-aimed movements. It highlights the numerous mathematical and theoretical interpretations that have been proposed in recent decades. Although the variety of points of view reflects the richness of the field and the high degree of interest that such basic phenomena attract in the understanding of human movements, it calls into question the ability of 'many models to explain the basic observations consistently reported in the field. This target article summarizes the kinematic theory of rapid human movements, proposed recently by R. Plamondon (1993b; 1993c; 1995a; 1995b), and analyzes its predictions in the context of speed/accuracy trade-offs. Data from human movement literature are reanalyzed and reinterpreted in the context of the new theory. It is shown that the various aspects of speed/accuracy trade-offs can be taken into account by considering the asymptotic behavior of a large number of coupled linear systems, from which a delta-lognormal law can be derived to describe the velocity profile of an end-effector driven by a neuromuscular synergy. This law not only describes velocity profiles almost perfectly, it also predicts the kinematic properties of simple rapid movements and provides a consistent framework for the analysis of different types of speed/accuracy trade-offs using a quadratic (or power) law that emerges from the model.

Modelling velocity profiles of rapid movements: a comparative study.

In this paper we compare 23 different models that can be used to describe the asymmetric bell-shaped velocity profiles of rapid-aimed movements. The comparison is performed with the help of an analysis-by-synthesis experiment over a database of 1052 straight lines produced by nine human subjects. For each line and for each model, a set of parameters is extracted that minimizes the error between the original and the reconstructed data. Performance analysis on the basis of the mean-square-error clearly reflects the superiority of the support-bounded lognormal model to globally describe the velocity profile characterizing rapid movements.