On the Efficiency Enhancement of an Actively Tunable MEMS Energy Harvesting Device

In this paper, we propose an active control method to adjust the resonance frequency of a capacitive energy harvester. To this end, the resonance frequency of the harvester is tuned using an electrostatic force, which is actively controlled by a voltage source. The spring softening effect of the electrostatic force is used to accommodate the dominant frequency of the ambient mechanical vibration within the bandwidth of the resonance region. A single degree of freedom is considered, and the nonlinear equation of motion is numerically integrated over time. Using a conventional proportional–integral–derivative (PID) control mechanism, the results demonstrated that our controller could shift the resonance frequency leftward on the frequency domain and, as a result, improve the efficiency of the energy harvester, provided that the excitation frequency is lower than the resonance frequency of the energy harvester. Application of the PID controller in the resonance zone resulted in pull-in instability, adversely affecting the harvester’s performance. To tackle this problem, we embedded a saturation mechanism in the path of the control signal to prevent a sudden change in motion amplitude. Outside the pull-in band, the saturation of the control signal resulted in the reduction of harvested power compared to the non-saturated signal; this is a promising improvement in the design and analysis of energy harvesting devices

First record of the loach fish Paracobitis cf. malapterura in the Kavir basin, northern Iran

The loach fish Paracobitis cf. malapterura Valenciennes, 1846 (Nemacheilidae), formerly believed to be an endemic species in the Caspian Sea basin, was recorded for the first time in the upper Kavir basin. This extension of its recorded range makes it likely that it has been overlooked in other parts of the Kavir basin

Osteological characteristics of Turkmenian stone loach, Paraschistura cristata (Cypriniformes: Nemacheilidae)

Formerly the Turkmenian stone loach was the only member of the genus Metaschistura based on osteological characters. But recently, it is placed in the genus Paraschistura based on mtDNA COI data. To provide a detailed description of the osteological characteristics of Paraschistura cristata (Berg 1898), ten specimens of P. cristata were collected from the Hari River basin in Iran and their osteological characteristics were examined. According to the results, P. cristata is osteologically characterized by a foramen in the ventral part of the exoccipital, two extra urohyals, sesamoid ossifications, trapezoid-shaped prevomer, three basibranchials, five hypural, lack of bony bridge between the parietal and pterotic, having over 20 procurrent rays supporting the adipose crest. The detailed skeletal description of P. cristata showed that this species can be easily distinguished from the related genera. Despite the mtDNA COI result, the osteological data of this species showed some features to describe it as a distinctive genus, but this needs the osteological data of the all other Paraschistura species to be compared

Threatened fishes of the world: Paracobitis vignai Nalbant and Bianco, 1998 (Nemacheilidae)

Paracobitis vignai is a Nemacheilid loach endemic to the Sistan basin. It occurs in Helmand River and its related reservoirs in Sistan-va-Baluchistan Province in southeastern Iran and probably in Afghanistan. This species is currently endangered due to habitat loss or degradation, damming and droughts. Therefore, this paper reviews the available data on taxonomy and distribution of P. vignai, provides its morphometric features, and recommends actions for its conservation

On the nonlinear dynamics of a piezoresistive based mass switch based on catastrophic bifurcation

This research investigates the feasibility of mass sensing in piezoresistive MEMS devices based on catastrophic bifurcation and sensitivity enhancement due to the orientation adjustment of the device with respect to the crystallographic orientation of the silicon wafer. The model studied is a cantilever microbeam at the end of which an electrostatically actuated tip mass is attached. The piezoresistive layers are bonded to the vicinity of the clamped end of the cantilever and the device is set to operate in the resonance regime by means of harmonic electrostatic excitation. The nonlinearities due to curvature, shortening and electrostatic excitation have been considered in the modelling process. It is shown that once the mass is deposited on the tip mass, the system undergoes a cyclic fold bifurcation in the frequency domain, which yields a sudden jump in the output voltage of the piezoresistive layers; this bifurcation is attributed to the nonlinearities governing the dynamics of the response. The partial differential equations of the motion are derived and discretized to give a finite degree of freedom model based on the Galerkin method, and the limit cycles are captured in the frequency domain by using the shooting method. The effect of the orientation of the device with respect to the crystallographic coordinates of the silicon and the effect of the orientation of the piezoresistive layers with respect to the microbeam length on the sensitivity of the device is also investigated. Thanks to the nonlinearity and the orientation adjustment of the device and piezoresistive layers, a twofold sensitivity enhancement due to the added mass was achieved. This achievement is due to the combined amplification of the sensitivity in the vicinity of the bifurcation point, which is attributed to the nonlinearity and maximizing the sensitivity by orientation adjustment of the anisotropic piezoresistive coefficients

Corporate Life Cycle and the Explanatory Power of Risk Measures versus Performance Measures

The major aim of this paper is to compare the explanatory power of risk measures versus performance measures in different life-cycle stages. To test the hypotheses, first, sample firms were classified into three life-cycle stages (Growth, Mature and Decline). Then, using regression models and Vuong's Z-statistic, the hypotheses were investigated. In this study, financial information of 75 firms which were accepted at Tehran’s Stock Exchange (TSE) from 2003 to 2008 (450 firm-years) was examined. The results of this study show that in growth and decline stages, the explanatory power of risk measures is significantly higher than performance measures and in mature stage, the opposite is true

L’hemorragie grave du peripartum en milieu de reanimation dans un centre universitaire tunisien de niveau 3: épidémiologie et facteurs de risque de mortalité maternelle

L'hémorragie grave du péripartum demeure une des causes principales de mortalité maternelle. L'objectif de notre étude était de décrire le profil épidémiologique des patientes qui ont été prises en charge en milieu de réanimation suite à une hémorragie grave du péripartum et de rechercher d'éventuels facteurs de risque de mortalité. Notre étude est rétrospective descriptive et analytique. Nous avons inclus tous  les cas  d'hémorragie du péripartum ayant séjourné en unité de réanimation obstétricale du centre de maternité et de néonatologie de Tunis (CMNT) au cours de la période allant de janvier 2010 à Décembre 2013. Nous avons  recueilli les paramètres démographiques, obstétricaux, ceux relatifs à la prise en charge chirurgicale et  réanimatoire, les scores de gravité SAPS obstétrical et APACHEII, ainsi que la morbi-mortalité. Au total nous avons colligé 322 cas sur quatre ans. La répartition annuelle des patientes ainsi que les caractéristiques  démographiques et obstétricales étaient comparables dans leur globalité sur les quatre années. Les pratiques thérapeutiques étaient également comparables. Le taux global de mortalité par hémorragie dans notre unité était à 4,7%, avec un taux annuel de mortalité stable. L'analyse des facteurs de risque de mortalité par  hémorragie en milieu de réanimation a montré une association statistiquement significative entre la survenue du décès et les facteurs suivants : recours aux catécholamines, survenue de sepsis, oedème pulmonaire aigu, coagulation intravasculaire disséminée, insuffisance rénale aigue avec recours à l'hémodialyse, SDRA ou TRALI, atteinte neurologique grave, défaillance multiviscérale et arrêt cardiaque récupéré.Key words: Mortalité maternelle, hémorragie du péripartum, réanimation, morbidit

Body shape variation of Garra rufa (Teleostei, Cyprinidae) populations in the Tigris basin in Iran using geometric morphometric analysis

Geometric morphometric method was used to examine the body shape variations among the six populations of Garra rufa, in Iranian part of Tigris basin. A total of 15 landmark-points was used for 170 specimens to hypothesize population differentiation of G. rufa in the six rivers and reservoir. In discriminant function analysis, 85.9% of original grouped cases correctly classified. Principal component analysis (PCA) and canonical variates analysis (CVA) confirmed the significant difference between the populations. The results revealed that the studied populations are divided into three clades based on differences in body depth, caudal peduncle length, backward moving of anal fin. Caudal peduncle showed shortening trend in five populations. Narrower body shape was dominated among specimens of four regions. Studies on body shape provide supporting data on fisheries, stock management, and conservative programs

Insights into seeds priming effects using a magnetic field and algal treatments on growth and productivity of faba bean under salinity stress conditions

Soil fertility and crop productivity in the Nile Delta are severely threatened by soil salinization. Hence, the development of reliable techniques to enhance the salinity tolerance of plants is an essential prerequisite for the desirable sustainable agricultural development in Egypt. In the present study, we evaluated the influence of seeds priming using a magnetic field (MF) at different exposure times (0, 15, 30, and 45 min), either alone or combined with seeds pre-soaking or foliar spraying with seaweed extracts of Hydroclathrus clathratus and Acanthophora spicifera. The effects on soil properties, growth, yield, and seed quality of Vicia faba grown in saline soil were assessed. Results indicated that MF-treated seeds (MFTS), either alone or coupled with seaweed treatments, distinctly improved soil characterization by decreasing EC and pH niches, and also increased the availability of soil macro- and micronutrient elements, particularly at MF long exposure time (≥30 min). MFTS and/or MFTS with seaweed treatments at 30 min improved soil fertility indices (CO2 evolution and nitrogenase activity) and induced the highest increases of macro- and micro-nutrient contents in seeds, plant growth and seed quality. Additionally, enhancement of chlorophyll a and b, carbohydrates and amino acids, and decreasing proline levels were the bases of salinity stress alleviation. Conclusively, seed priming in the MF coupled with foliar spraying of seaweed extracts could be a sustainable and affordable approach for cultivating V. faba plants under salinity stress conditions

Hygrothermal Performance of Cool Roofs Subjected to Saudi Climates

In regions with hot climatic conditions such as that in Saudi Arabia, a substantial share of energy is used for cooling the buildings. Many studies have shown that cool (white) roofs can help reduce the cooling energy load and thus the demand for energy over time. Also, cool roofs help reduce the urban heat island during the summer time. This research study focused on determining: (a) whether cool roofs lead to risk of condensation and mold growth in Saudi climates, (b) the amount of energy savings as result of using cool roofs instead of black roofs of same insulation amount, and (c) the reduction in the amount of insulation in cool roof having the same energy performance level as the black roof. As such, numerical simulations were conducted for a roofing system that is commonly used in low-rise buildings in Saudi Arabia in order to asses and compare the energy and hygrothermal performance of cool and black roofs. The roof was subjected to weather conditions of the Eastern Province of Saudi Arabia. The indoor conditions were taken based simple method of ASHRAE Standard 160. The results showed no moisture accumulation occurred from year-to-year after 6 years and 7 years for the black roof and cool roof, respectively, and the highest relative humidities in the black and cool roofs were well below 80% resulting in no risk of condensation and mold growth occurred in these roofs. The main outcome of this study has shown the capabilities of using reflective materials with different short-wave solar absorption coefficients for enhancing the energy performance of roofs and/or reducing the amount of insulation that resulted in same energy performance as black roofs. This study can be used in future for upgrading the Saudi Building Code so as to allow less roof insulation if cool roof is installed