Discussion on Barkhausen and Nyquist stability criteria

Most textbooks on analog circuits and signal processing describe the Barkhausen criterion pertaining to the determination of sinusoidal oscillations in a closed-loop system. On the other hand, the Nyquist stability criterion is well known, as discussed in most textbooks on control systems. Recently, some examples in which the Barkhausen criterion fails to produce the correct condition for startup of oscillations have been reported. In the present paper, an explanation of oscillation startup based on the Nyquist stability criterion is given and the close relationship between the Barkhausen and the Nyquist criteria highlighted. It is shown that the Nyquist criterion (which is a rigorous technique) is a more robust approach than the Barkhausen criterion concerning the determination of sinusoidal oscillations in a closed-loop system and that the Barkhausen criterion (whenever it yields the correct result) is subsumed by the Nyquist criterion as a special case. The textbooks usually describe the Barkhausen criterion as a separate topic, i.e., do not discuss the relationship of this criterion with the Nyquist criterion. It is, therefore, felt that the present discussion will go a long way to put the subject in a broader perspective.     

A 1 GHz Digital Channel Multiplexer for Satellite Outdoor Unit

A digital channel multiplexer for satellite outdoor unit running at 1 GHz clock frequency is implemented in 65 nm CMOS mixed oxide dual voltage technology. This multiplexer, based on a 1 GS/s digital signal processor (DSP) approach with 500 MHz input and output bandwidth, embeds two 8 bit 1 GS/s analog-digital converters (ADCs) and two 8 bit 1 GS/s digital-analog converter (DACs). It consumes less that 1022 mW at ambient temperature while achieving noise rejection up to 42.5 dB on a single tone, and > 37 dB on modulated satellite channels.     

Estimation of strength parameters of rock using artificial neural networks

The accurate determination of geomechanical properties such as uniaxial compressive strength and shear strength requires considerable time in collecting appropriate samples, their preparation and laboratory testing. To minimize the time and cost, a number of empirical relations have been reported which are widely used for the estimation of complex rock properties from more easily acquired data. This paper reports the use of an artificial neural network to predict the deformation properties of Coal Measure rocks using dynamic wave velocity, point load index, slake durability index and density. The results confirm the applicability of this method.     

A Simple Conceptual Model of Sediment Yield

The sediment graphs (time distribution of sediment yield) are very essential if the sediment transports the pollutants that are toxic at high concentrations, requiring determination of peak, rather than average sediment flow rate. In this paper, an effort has been made to develop a simple conceptual model of sediment yield based on Soil Conservation Service Curve Number (SCS-CN) method, instantaneous unit sediment graph (IUSG) method, and Power law and the performance is tested using real field data of Chaukhutia watershed of Ramganga river catchment (area = 452.25 km²). The proposed model is found to provide realistic estimates of temporal variation of sediment yield as well as total sediment yield during a storm event. The model is found to be most sensitive to parameter β followed by k, \upalpha\upalpha, A, and n_s. A comparison is made with the existing IUSG based models of Kumar and Rastogi (J Hydrol 95:155–163, 1987) and Raghuwanshi et al. (J Hydraul Eng ASCE 120(4):495–503, 1994) for developing sediment graphs.     

Binding of zinc to bovine and human milk proteins

Zn binding by whole bovine and human casein and by purified bovine caseins and whey proteins was investigated by equilibrium dialysis. Bovine alpha s1-casein had the greatest Zn-binding capacity (approximately 11 atoms Zn/mol). Protein aggregation was observed as Zn concentration was increased and the protein precipitated at a free Zn concentration of 1.7 mM. Zn binding increased with increasing pH in the range 5.4-7.0 and decreased with increasing ionic strength. Competition between Zn and Ca was observed for binding to alpha s1-casein indicating common binding sites for these two metals. Bovine beta-casein bound up to 8 atoms Zn/mol and precipitated at a free Zn concentration of approximately 2.5 mM, while kappa-casein bound 1-2 atoms Zn/mol. Whole bovine and human casein bound 5-8 atoms Zn/mol and precipitated at a free Zn concentration of approximately 2.0 mM. Scatchard plots for Zn binding to caseins showed upward convexity, possibly due to Zn-induced association of caseins. Apparent average association constants (Kapp) for all caseins were similar (log Kapp 3.0-3.2). Enzymic dephosphorylation of alpha s1- or whole bovine casein markedly reduced, but did not eliminate, Zn binding. Thus, phosphoserine residues appeared to be the primary Zn-binding sites in caseins. With the exception of bovine serum albumin, which bound over 8 atoms Zn/mol, the bovine whey proteins, beta-lactoglobulin, alpha-lactalbumin and lactotransferrin, had little capacity for Zn binding.     

Response of laying Japanese quails to graded levels of essential amino acids profile with reduced dietary protein

The effect on egg production of graded levels of ideal amino acids, combined with reduced protein in the diet, was investigated in 312 laying quails aged 6–18 weeks. The quails were offered six diets, each of which contained one of three levels of amino acids (85, 100 and 115% of essential amino acids (EAAs)) together with 5% or without fishmeal (FM) (3 × 2 factorial design). Each diet was offered to 26 replicated groups of two quails each. Hen‐day and hen‐housed egg production did not differ as a result of EAA level, protein type or their interaction during the overall period of egg production. Egg weight improved linearly (P < 0.01) with increased EAA levels, while egg mass output per bird per day remained similar at the 100 and 115% EAA levels. Quails fed higher (100 and 115%) EAA levels had an improved feed conversion ratio (P < 0.01) compared to birds fed 85% EAA. The gain in body weight during the laying period was higher (P < 0.01) at the 100 or 115% than at 85% EAA levels The ratio of egg mass or egg mass and live weight gain, together, to protein intake improved (P < 0.01) linearly with a decrease in EAA levels in the diets, while better (P < 0.01) energy efficiency (EE, energy intake: egg mass) and net EE (energy intake: egg mass plus gain) was obtained in higher EAA levels (100 or 115%). Protein and energy efficiencies remained similar due to protein type or interaction. Shape index, albumen index, yolk index, yolk colour and relative shell weight did not differ due to EAA levels, protein type or their interaction. Eggs laid from quails fed diets with 100% EAAs without FM and 115% EAAs with or without FM had higher shell thickness than those on 85% EAAs irrespective of protein type. The retention of nitrogen and calcium retention was higher (P < 0.01) at the 115% EAA level. The results indicated a dietary level of 100% EAA (185 g kg^?1 crude protein (CP)) with 12.13 MJ kg^?1 was suitable for laying quails of 6–18 weeks of age. Copyright © 2007 Society of Chemical Industry     

Status of dietary fiber contents in pigmented and non-pigmented rice varieties before and after parboiling

Five different varieties of paddy (four pigmented and one non-pigmented) were shelled and milled in pre and post parboiled form, their dietary fiber contents were estimated. Under similar conditions of milling, raw rice showed a high degree of polish (DOP), 9–12 g/100 g and parboiled rice showed low DOP, 4.6–6.6 g/100 g. Dietary fiber content was high in pigmented rice, 9–10 g/100 g compared to non-pigmented, ∼6 g/100 g. Soluble fiber content in pigmented head rice (dehusked) varied from 1 to 1.5 g/100 g and in its brokens varied from 0.45 to 1.45 g/100 g. Dietary fiber content was low by about 1% in parboiled rice. In the parboiled rice of pigmented varieties, the total fiber content varied from 7.95 ± 0.15 to 9.05 ± 0.25 g/100 g and the soluble fiber content varied from 0.7 to 0.9 g/100 g. In milled parboiled rice the respective values were 5 ± 0.4 to 6 ± 0.1 g/100 g and 0.85 ± 0.05 to 1.25 ± 0.05 g/100 g. However, the soluble fiber content in the non-pigmented brown rice, IR-64 remained same after parboiling, 0.75 ± 0.5 g/100 g. Milled parboiled rice showed higher soluble dietary fiber compared to milled raw rice. In conclusion, dietary fiber was high in pigmented rice varieties when compared with non-pigmented rice.     

Finite element modeling of orthogonal micromachining of anisotropic pyrolytic carbon via damaged plasticity

Engineered features on pyrolytic carbon (PyC) have been demonstrated as an approach to improve the flow hemodynamics of the cardiovascular implants such as bileaflet mechanical heart valve. PyC also finds application in thermonuclear and missile components due to its unique directional thermal properties. However, very little work has been reported on modeling of machining/micromachining of PyC. Note that PyC is a brittle anisotropic material and its machining characteristics differ from plastically deformable isotropic materials. Consequently, this study is aimed at developing a finite element model to understand the mechanics of material removal in the plane of transverse isotropy (horizontally stacked laminae) of PyC. A damaged plasticity model has been used to capture the effect of material degradation under machining. Uniaxial tension/compression tests have been carried out to calibrate the damaged plasticity model. A cohesive element layer has been used between the chip layer and the bulk material to simulate the delamination/peeling effect. The model predicts cutting force and thrust forces at different set of process parameters. The orthogonal cutting model has been validated against the experimental data for different cutting conditions for cutting and thrust forces. In addition, the chip geometry has also been compared. The prediction error in the model lies between 9% and 27%. Parametric studies have also been performed to understand the effect of the machining parameters on the process response. It is found that use of the positive rake angle decreases the cutting forces up to 75%.     

Acid Diffusion into Rice Boluses is Influenced by Rice Type,Variety, and Presence of α‐Amylase

Breakdown of rice during gastric digestion may be influenced by rice structure, presence of salivary α‐amylase, and hydrolysis by gastric acid. During mastication, saliva is mixed with rice, allowing α‐amylase to begin starch hydrolysis. This hydrolysis may continue in the gastric environment depending on the rate at which gastric acid penetrates into the rice bolus. The objective of this study was to determine the acid uptake into rice boluses with and without α‐amylase in saliva. Two types each of brown and white rice (medium and long grain), were formed into a cylindrical‐shaped bolus. Each bolus was sealed on all sides except one to allow one‐dimensional mass transfer, and incubated by immersion in simulated gastric juice at 37 °C under static conditions. Acidity of the boluses was measured by titration after 1 to 96 h of incubation. Effective diffusivity of the gastric juice through the bolus was estimated using MATLAB. Average acidity values ranged from 0.04 mg HCl/g dry matter (medium grain white rice, no incubation) to 10.01 mg HCl/g dry matter (long‐grain brown rice, 72 h incubation). The rice type, presence of α‐amylase, and incubation time all significantly influenced rice bolus acidity (P < 0.001). Effective diffusivity of gastric juice into the bolus was greater in brown rice than in white rice. These results indicate that starch hydrolysis by α‐amylase may continue in the stomach before the gastric acid penetrates the rice bolus, and the rate of acid uptake will depend on the type of rice consumed.