Excess loop delay cancellation in sigma–delta modulators

Excess loop delay in sigma–delta ( $\Sigma\Delta$ ) modulators, especially by increasing the level of noise in signal bandwidth in continuous kind of them, leads to a dramatic decrease in their efficiency. In this paper, the error originated from the loop delay is calculated analytically and a new structure for sigma–delta modulators is presented based upon this calculation. This new structure can compensate the effect of loop-delay error completely independent of amount of delay. So by changing in loop delay during system working, the proposed structure has ability to consistent itself with new conditions and re-eliminate the error. This ability is independent of being multi-bit and the order of modulator. To evaluate the efficiency of the proposed method and the corresponding structure, first and second order modulators with capability of eliminating the error of loop delay, have been designed and simulated. All of simulations show the correctness of proposed analysis. Comparison of the proposed structures with the previous works shows the effectiveness of our technique.     

Study on dynamic and mechanical characteristics of carbon fiber- and polyamide fiber-reinforced seismic isolators

Seismic isolators are used to decrease the energy and forces of earthquakes. The weight of conventional steel-reinforced elastomeric isolators (SREIs) is high, mostly due to the use of multiple steel shim plates. On the contrary, the damping ratio of SREIs is relatively low. Accordingly, this research utilizes a new approach in which the steel shim plates are replaced by carbon and polyamide fibers. This study attempts to obtain the dynamic and mechanical properties of such carbon fiber- and polyamide fiber-reinforced elastomeric isolators, in comparison with SREIs. In this work, a number of specimens were initially designed and manufactured. Afterwards, compression and cyclic shear tests were performed on them. In the shear tests, due to the limitations of the testing machine, a constant vertical load was not applied. All three types of isolator specimen were cylindrical, with identical diameter and height. The steel-, carbon fiber-, and polyamide fiber-reinforced elastomeric isolator specimens had 16, 23, and 23 reinforcement layers, respectively. To decrease the effect of manufacturing errors on the dynamic and mechanical characteristics of the specimens, 6 samples of each isolator type were manufactured, i.e., a total of 18 samples. The outcome of the experiments revealed that the use of flexible reinforcement resulted in a damping increase of up to 20 and 30 % for the carbon fiber- and polyamide fiber-reinforced elastomeric isolators, respectively. Furthermore, the carbon fiber design provides more reasonable performance for the isolators compared with the use of polyamide fiber.     

Fatigue tests on SMA bars in span control

The estimation of the fatigue lifetime of copper-based shape memory alloy (SMA) specimens in the form of bars is investigated in view of their use in passive devices for structural control applications. In the envisaged application, the pre-stress value assigned to the SMA bars is selected so that it is only slightly modified when strain variations occur within an operative range. This condition requires that the fatigue cycles are performed in span control, conversely to the common practice of driving the tests in load control to study the fatigue behaviour of traditional metals such as steel. Several experiments are carried out at different temperatures for different strain ranges and the results are arranged with the aim of building suitable fatigue models.     

Use of an edible coating containing galbanum gum and cumin essential oil for quality preservation in sweet cherries

Nowadays, the use of natural compounds is considered as an effective strategy for maintaining the quality and heath promoting capacity of fresh products. Changes in quality parameters, main phenolics and antioxidants of sweet cherries in response to coating with a novel bioactive edible coating were studied. Fruit were treated with different concentrations of galbanum gum (GG), cumin essential oil (CEO) and CaCl₂ (CA) and stored at 2 ± 1°C with 90–95% RH for 30 days plus 1 day at ambient condition, and were subjected to quality analysis. All phenolic constituents and antioxidants of fruit juice were substantially decreased during storage in control fruit and a bioactive coating containing 1 or 2% GG + 100 or 200 µL L⁻¹ CEO + 1% CA maintained main fruit phytochemicals including phenolics, phenolic acids, flavonols, anti-stress and antioxidant enzymes activities. The coating significantly (P ≤ 0.01) enhanced fruit total antioxidant activity, flavonoids and ferulic acid contents. The results showed that it is possible to enhance the sweet cherry fruit health-promoting phytochemicals and shelf life by the use of a natural edible coating containing GG and CEO.     

Effect of hydrocolloids on physicochemical,sensory and textural properties of reconstructed rice grain by extrusion cooking technology

Cracked or broken rice grains followed by lower rice efficiency during processing and milling of rice paddy are a major challenge contributing to the reduced economic productivity of this branch of industry. Therefore, the extrusion process for turning flour from broken rice or wastes into complete rice grains can bring about value-added for producers. In addition, an optimized formulation can improve product diversity and nutritional value. In this study, the effect of addition of Guar and Arabic gums on physicochemical, texture and sensory profiles of extruded rice grains was analyzed. Both gums were used in four concentrations (0.1, 0.2, 0.3 and 0.4 w/w %, d.b), and the effect of their different levels on properties of extruded rice was studied. Results from physicochemical tests on extruded rice samples showed that moisture content, water solubility index, water absorption index and bulk density were increased in samples containing higher concentration of Guar than Arabic gum and initial moisture content of 30% compared to no-gum samples, whereas lateral expansion, cooking loss, and total color change (ΔE) were reduced. Furthermore, results showed that higher levels of Guar than Arabic gum led to an improvement in sensory and textural properties.