Narrow Range Of Variation Research Articles

Ligand and solvent effects on the catalytic activity and lifetime of zwitterionic Nickel(II) catalysts for alternating CO-Ethylene copolymerization

A series of zwitterionic nickel(II) compounds with anionic diphosphine ligands having varied substituents have been synthesized and studied as catalysts for CO-ethylene copolymerization. The electron-donating abilities of the ligands are assessed on the basis of the infrared absorptions of the CO-stretching vibrations of their Ni(0) carbonyl compounds. The equilibriums between Ni(II)-methyl and Ni(II)-acetyl and 4-coordinate and 5-coordinate Ni(II)-acetyls are studied using NMR and IR spectroscopies. With respect to the catalytic performances, a certain degree of steric hindrance around the Ni(II) center is required to achieve a high polymerization activity. The steric hindrance likely disfavors the 5-coordinate catalytically dormant state. Further increased steric congestion decreases the catalytic activity. The electron-donating ability of the ligand on the catalytic activity is modest within the relatively narrow range of variation of the present study. The catalyst lifetime and overall productivity are markedly improved by the presence of o-methoxy ancillaries on the phenyl group of the ligand although the o-methoxy decreases the activity of the catalyst. A comparison of the o-methoxy- and o-methyl-substituted ligands attributes the stabilization to the coordinating ability of the o-methoxy group rather than a steric or inductive electronic origin. The present catalysts are several times faster and more productive in THF than in toluene at room temperature. The increased activity is attributable to the coordinating ability of THF as opposed to polarity. The polymer products are strictly alternating copolymers of CO and ethylene.

Analysis and Synthesis in the Design of Magnetic Switching Electric Machines

A systematic approach to the design of electrical machines is implemented by solving problems of analysis and synthesis in various combinations at different stages and stages of design. The questions of the formulation and implementation of synthesis and analysis problems in the study and design of modular-type magnetically commutated electrical machines are considered. They are aimed at reducing weight, size and cost while improving the performance of these newly designed machines. A complex method of parametric synthesis and an automated program containing a calculated mathematical model of an electric machine has been developed. On the basis of numerical full factorial experiments, the optimization parameter is determined, and a regression analysis is performed with the construction of an optimization model. It allows you to find a narrow range of variation of significant factors, at which the optimization parameter satisfies the specified conditions. On the example of studying an inductor generator of axial-radial configuration, new approaches to the formulation and solution of typical problems of analysis and synthesis of modular-type electrical machines are shown. The use of complex parametric synthesis makes it possible to significantly reduce the masses of the designed modular machines in comparison with drum-type inductor machines of the same power.

System scheme design of electric expander cycle for LOX/LCH4 variable thrust liquid rocket engine

With the development of both cryogenic and motor pump technologies, the cryogenic variable thrust liquid rocket engines that using motor pumps have gained considerable attention. However, the heavy battery limits its performance if engine operates for high thrust. To address this challenge, the electric expander cycle system scheme for variable thrust liquid rocket engines is creatively proposed and designed. Subsequently, the system parameters are calculated based on mass and energy conservation with chamber heat transfer considered. As well, the distribution of this novel system state parameters is investigated. Further, a comparison is conducted between the electric expander cycle system, electric pump, and expander cycle systems. The comparison results demonstrate that this innovative system scheme has advantages of simple structure, low battery mass, convenient throttling, and high reusability. The system state parameters distribution indicates that the feed system can achieve the propellants' pressurization requirements throughout the designed 5:1 throttle range, which suggests the feasibility of this system scheme. Moreover, although the proposed system requires more battery power than does the turbine, the turbine power proportion in the entire system increases with thrust. However, the turbine efficiency drops steeply with a decrease in thrust, whereas the double pump efficiency presents a narrow variation range.

Molybdenum isotopic evidence for anoxic marine conditions during the end-Permian mass extinction

The end-Permian mass extinction was the most severe biotic crisis of the Phanerozoic. Oceanic anoxia has long been considered one of the main drivers of the biotic crisis. We examined the molybdenum isotope compositions of bulk carbonate samples from two Permian–Triassic boundary sections in southern China: the Meishan Global Stratotype Section and Point and the Dajiang section (an isolated carbonate platform). We also measured the Mo contents of the carbonate phases, oxides, and sulfides of the carbonate samples via sequential extraction to investigate the samples' Mo-bearing minerals. In the Meishan section, from Bed 23 to the middle of Bed 24, the δ98/95Mocorr.Al values decrease slowly from +0.89‰ to +0.35‰, while from the middle of Bed 24 to Bed 25, the δ98/95Mocorr.Al values abruptly increase from +0.35‰ to +1.78‰. In the Dajiang section, samples below the mass extinction boundary have relatively low δ98/95Mocorr.Al values with a narrow variation range (−0.05‰ to +0.46‰; average + 0.19‰); the δ98/95Mocorr.Al values of the five samples directly above the extinction boundary increase abruptly (vary from +1.38‰ to +1.63‰; average of +1.53‰), and the δ98/95Mocorr.Al values of other samples above the mass extinction boundary fluctuate slightly before returning to pre-extinction values. The results of the sequential extraction procedure indicate that carbonate-phase Mo accounts for a small portion of the total Mo (average of 13.6 and 18.4 wt% for the Meishan and Dajiang sections, respectively), oxidized and sulfided Mo are the dominant forms in the carbonate samples. Moreover, the carbonate samples with high δ98/95Mo values tend to have high contents of sulfided Mo. We suggest that marine carbonate sediments record paleo-ocean Mo isotopic signals by a mechanism similar to that of other open-ocean sediments (e.g., shales): higher δ98/95Mo values in the sediments indicate a more reducing sedimentary environment. Based on this assumption, the δ98/95Mo values of the studied sections indicate that during the Permian–Triassic transition, oceanic anoxia coincided with or slightly predated the mass extinction, and the ocean anoxic event lasted for a relatively short time, likely less than 0.061 Myr.

Multistage gold mineralization in the Hadamengou gold deposit in the northern margin of the North China Craton: Insights from in-situ trace element contents and sulfur isotope analyses of pyrite

Abstract The Hadamengou gold deposit is one of the largest gold deposits in the Wulashan-Daqingshan gold mineralization cluster, in the northern margin of the North China Craton. The gold deposit, which is hosted by Archean gneiss, comprises potassic alteration and abundant quartz-pyrite veins, with five types of hydrothermal pyrite associated with gold, tellurides, and sulfides. The earliest stage of pyrite (Py1) occurs as random disseminations within the limited volume of modified quartz-pyrite veins and was formed during or prior to the last episode of metamorphism. Py2, from the potassic and chlorite-sericite alteration zones, is related to the activity of potassic fluids, and contains inclusions of native gold, galena, melonite, electrum, and petzite. Py3, without inclusions, occurs as randomly- disseminated grains within the limited volume of grey quartz-pyrite veins. A few native gold grains are found along fractures of quartz associated with Py3. Py4 occurs as veinlets or aggregates in the milky quartz-pyrite veins and contains the highest Au concentrations. Abundant native gold, calaverite, and electrum occur along the grain boundaries and fractures, or as inclusions within Py4 and quartz. Py5 occurs as rounded and cataclastic shapes within the limited volume of quartz-carbonate veins and is depleted in Au. LA-ICP-MS trace element analysis of the pyrite shows that Py1 has a low content of gold (median of 0.07 ppm) and other trace elements (Ag, Te, Pb, Cu, Bi, and As). Potassic alteration, grey quartz-pyrite veins, and milky quartz-pyrite veins make a very large contribution to the gold endowment, with a relatively high gold content in pyrite, including Py2 (median of 0.8 ppm), Py3 (4.3 ppm), and Py4 (2.5 ppm). Other trace elements (e.g., Ag, Te, Pb, Mo, and Bi) are also significantly enriched within Py2 to Py4. Little or no gold was detected in Py5. Thus the potassic alteration and milky quartz-pyrite veins were major contributors to gold mineralization, based on the volume and Au content of pyrite within the Hadamengou deposit. In-situ LA-MC-ICP-MS sulfur isotope analyses of pyrite show negative values and a narrow range of variation of δ34S (averages of −11.4‰, −11.8‰, −10.5‰, and −9.4‰ for Py2-Py5, respectively), indicating an oxidized magmatic sulfur source for the pyrites in Hadamengou. Additionally, the occurrence of tellurium minerals associated with various pyrites, and the high Te concentration of various pyrites, also suggest that ore-forming fluids were derived from an oxidized alkaline magma. These results, combined with published geochronological data, suggest that during two episodes, Au-rich potassic and SiO2-rich fluids separated from the deep-lying Devonian alkaline magma during ascent along the EW-trending faults, and reacted together with the wall rocks to form potassic and chlorite-sericite alteration zones, resulting in gold precipitation.

A note on a class of generalized neo-Hookean models for isotropic incompressible hyperelastic materials

In a recent paper in this journal by Anssari-Benam and Bucchi (2021), the authors have proposed a new two-parameter constitutive model for isotropic incompressible hyperelastic generalized neo-Hookean materials. The model reflects the limiting chain extensibility characteristic of non-Gaussian molecular models for rubber. A major contribution of Anssari-Benam and Bucchi (2021) is in showing that the model proposed there is superior to the well-known two-parameter Gent model when fitting with a large variety of experimental data for rubber for the homogeneous deformations of uniaxial, equi-biaxial and pure shear. Moreover, for all of these deformations, a fitting with data is achieved with a single set of values for the parameters with a narrow range of variation. In the present note, we establish a simple direct relation between the new model and the classical Gent model. The large body of research results on the mechanical behavior of rubber-like materials based on the latter model are thus readily applicable to the new model. Some other directions for widening the applicability of the new model are also suggested.

Bed nucleus of the stria terminalis modulates baroreflex cardiac activity: an interaction between alpha-1 receptors and NMDA/nitric oxide pathway.

The bed nucleus of the stria terminalis (BNST) is a forebrain structure, involved in the modulation of neuroendocrine, cardiovascular and autonomic responses. One of the responses is baroreflex activity, which consists in a neural mechanism responsible for keeping the blood pressure within a narrow range of variation. It has been reported that blockade of BNST α1-adrenoceptors increased the bradycardic component of baroreflex. In addition, such receptors are able to modulate glutamate release in this structure. Interestingly, BNST NMDA receptor antagonism and neuronal nitric oxide synthase (nNOS) inhibition led to the same effect of the α1-adrenoceptors blockade on baroreflex bradycardic response. Therefore, the hypothesis of the present study is that BNST noradrenergic transmission interacts with NMDA/NO pathway through α1 adrenoceptors to modulate the baroreflex activity. Male Wistar rats had stainless steel guide cannulas bilaterally implanted in the BNST. Subsequently, a catheter was inserted into the femoral artery for cardiovascular recordings, and into the femoral vein for assessing baroreflex activation. Injection of the noradrenaline reuptake inhibitor reboxetine in the BNST did not modify the tachycardic, but significantly decreased the bradycardic component of baroreflex. Administration of an α1, but not an α2 antagonist into the BNST prior to reboxetine prevented this effect. Likewise, previous injection of NMDA/NO pathway blockers inhibited the effect of reboxetine on bradycardic response. In conclusion, it was demonstrated for the first time the existence of an interaction between BNST noradrenergic, glutamatergic and nitrergic neurotransmissions in the modulation of bradycardic baroreflex response.

Nitrogen isotopes in nitrate aerosols collected in the remote marine boundary layer: Implications for nitrogen isotopic fractionations among atmospheric reactive nitrogen species

The nitrogen isotopic composition (δ15N) of atmospheric nitrate aerosols is determined by both the δ15N of its precursor, NOx emissions, and the isotopic fractionations during the atmospheric oxidation of NOx. However, the latter has not been well-understood nor quantified by field observations. In addition, the seasonal variations of this isotopic fractionation have not been determined. To better understand this isotopic fractionation process, in this study, we analyzed the δ15N of nitrate aerosols collected from June 30, 2015 to August 6, 2016 at Baring Head, New Zealand, where the sources of NOx are well-studied. Our results showed that the δ15N values in nitrate aerosols display a clear seasonal variation, with lower δ15N values (−12‰ to ~ -9‰) in the summer (January to March) and higher δ15N values (0‰ to 3‰) in the winter (June–August), while the δ15N values of NOx sources exhibit a narrow range of variation from −10.7 ± 1.4‰ to −9.8 ± 1.4‰. We attribute this discrepancy to the significant and variable isotopic fractionations during the oxidation processes of NOx. We then quantified the isotopic fractionation during 1) the equilibrium and kinetic isotopic fractionations between NO and NO2; and 2) the oxidation of NO2 to nitrate. Our calculations suggest that at Baring Head, the seasonal variations in the oxidation pathways of NO2 are the main driver of the seasonal variations of nitrate δ15N values. Furthermore, the overall isotopic fractionation factors of the oxidation process determined by two models (Kinetic fractionation model and Equilibrium fractionation model) are generally lower in the summer (from +6.3 ± 1.7‰ to +9.5 ± 5.2‰)and higher in the winter (from +15.8 ± 1.9‰ to +17.0 ± 2.4‰).

A generalised neo-Hookean strain energy function for application to the finite deformation of elastomers

We present a new model within the class of generalised neo-Hookean strain energy functions for application to the finite deformation of incompressible elastomers. The model has a simple form with only two parameters, namely μ and N with structural roots, and is derived within the classical framework of statistical mechanics for freely jointed molecular chains in rubber elasticity Using existing experimental datasets of uniaxial, biaxial, and pure shear deformations, including Treloar’s canonical data, we show that the proposed model captures the deformation behaviours of each elastomer specimen with a single set of μ and N values (with only a narrow variation range). We conduct qualitative and quantitative comparative analyses to highlight the advantages of the proposed model, and demonstrate improved fits versus the celebrated Gent model. Given its structural molecular basis, simplicity, small number of parameters, and its capability to describe many deformation modes of a specimen using a single set of parameter values, we propose this model for application to finite deformation of elastomers.

Investigation of the correlation between perpendicular magnetic anisotropy, spin mixing conductance and interfacial Dzyaloshinskii–Moriya interaction in CoFeB-based systems

Correlation between interfacial Dzyaloshinskii–Moriya interaction (iDMI), perpendicular magnetic anisotropy (PMA) and spin pumping-induced damping was investigated in CoFeB-based systems grown by sputtering on Si substrates, using Pt, Ta, Cu, W and MgO capping layers. Vibrating sample magnetometer, Brillouin light scattering (BLS) and broadband ferromagnetic resonance techniques were combined for this aim. The CoFeB thickness dependence of iDMI and PMA constants, in CoFeB/X (where X = Pt, Cu/Pt, Ta/Pt or W/Al), revealed that only the CoFeB/Pt system presents a measurable iDMI and that the interfacial PMA is mostly similar except for the Ta/CoFeB/Ta/Pt system. Therefore, no clear correlation between the above-mentioned interfacially-driven and spin-orbit coupling related quantities was observed due to their different origins in our systems. An efficient sample design involving various spacer layers of variable thicknesses in Ta/CoFeB(1.5 nm)/Y/Pt (where Y = Cu, Ta, MgO) allowed evidence of a linear correlation between iDMI, PMA constants and the effective spin mixing conductance. The linear dependence, which could result from the narrow variation range of PMA and/or iDMI, is attributed to the similar interface orbital hybridizations involved in PMA, iDMI and spin pumping-induced damping.

Taxonomic review of the pipefish genus Pseudophallus Herald, with the description of a new species (Syngnathiformes: Syngnathidae).

We present a taxonomic review of the genus Pseudophallus, based on morphological characters, originally described to include two freshwater pipefish species from the Pacific coastal drainages of the neotropics: P. starksii and P. elcapitanensis, with the later addition of P. mindii, described from Atlantic coastal drainages. Pseudophallus mindii was formerly recognized as a single species ranging from the Brazilian state of São Paulo to Belize in Central America. Five species are recognized in the present study: P. elcapitanensis and P. starksii from the Pacific drainages; P. mindii and P. brasiliensis, the latter so far considered a junior synonym of P. mindii, and a new species. Pseudophallus mindii is redefined to include specimens with higher meristic values and narrow range of variation compared to P. brasiliensis and is restricted to the northern coastal drainages from Venezuela to Central America including the Caribbean region. Pseudophallus brasiliensis is revalidated and occurs from the drainages east of the mouth of the Orinoco to southern Brazil. The new species, Pseudophallus galadrielae sp. nov. is endemic to Lago Izabal in Guatemala. An updated identification key to the currently recognized species is provided.

Decline of soil respiration in northeastern Tibet through the transition into the Oligocene icehouse

Soil respiration (Rs), the production of carbon dioxide in soils, increases dramatically from deserts to forested ecosystems. Rs values thus provide a potential tool to identify past ecosystems if recorded in sedimentary archives. Here, we propose a quantitative method to reconstruct past Rs values from paleosols. This method reverses the soil paleobarometer, a proxy that estimates past atmospheric CO2 concentration values (CO2atm) from paleosols while considering a narrow range of variation for Rs. We use past CO2atm values from marine proxies to reconstruct soil respiration from a 20 million year-long isotopic record from northeastern Tibet covering the transition from the Eocene greenhouse to the Oligocene icehouse. We show that Rs dropped at least 4-fold through the transition into the Oligocene icehouse, marking the spread of boreal desert-steppes of Central Asia. We show that increasing aridity and the decline of monsoonal rainfall, in parallel with global cooling, caused the fall of soil respiration. These highly dynamic Rs emphasize the need for a systematic screening of paleosol isotopic data before using the soil paleobarometer to reconstruct CO2atm

Stable-isotope and fluid inclusion constraints on the timing of diagenetic events in the dolomitized Dolomia Principale inner platform (Norian, Southern Alps of Italy)

The petrographic, cathodoluminescence (CL), stable isotope, and microthermometry investigation of inner platform facies of the pervasively dolomitized carbonate platform of the Norian (Upper Triassic) Dolomia Principale (Southern Alps, N Italy) identified two major dolomite phases. An early replacement fabric-retentive dolomite (D1 and D2, respectively replacing the sedimentary facies - from fenestral mudstone/wackestone to bioclastic packstone and mudstone and stromatolites- and early marine cements) is followed by a later, vug- and fracture-filling dolomite cement phase (D3, planar-s texture).The fabric-retentive dolomitized carbonates (<4 μm−30 μm, D1) and marine fibrous cements (30 μm−250 μm, D2) exhibit dull luminescence under CL whereas the burial dolomite cement (200 μm−500 μm, D3) exhibits zoned luminescence. Microthermometric measurements of the primary two-phase fluid inclusions in D3 yielded a mean homogenization temperature of 112.4 ± 8.2 °C. Supposing a surface seawater temperature of at least 20–25 °C and a geothermal gradient of about 40 °C/km during the Early Jurassic rifting that led to the opening of the Alpine Tethys, such temperature might be reached at reasonable burial depth ranging from 2.0 km to about 2.5 km. According to the subsidence curve this depth, compatible with the temperature recorded by the fluid inclusions, was reached during the Early Jurassic, with D3 cement precipitation causing a significant reduction of the porosity.The δ13C values of the investigated dolomites (D1, D2, and D3) show a narrow range of variation (2.0–3.1‰ VPDB), pointing toward a fluid-buffered system. Differently, the δ18O values largely varies, ranging from −12.8 to +1.9‰ VPDB. In this range, D3 values cluster distinctively between −6.0 to −12.8‰ VPDB with respect to D1 and D2, which cluster from about −4 to +1.9‰ VPDB. The estimated oxygen isotope composition of the parent fluid of D1 and D2 (~0 to −5‰ VSMOW) suggests possible contributions from marine to slightly evaporated seawater, which is consistent with the arid climate and some basin restrictions suggested by earlier studies, whereas that of D3 (+1 to +5‰ VSMOW) is consistent with burial fluids.The followed integrated approach highlights the possibility to better characterize the occurrence of multiple diagenetic events in time and space, as well as their feedback effects on the porosity evolution of dolomitized carbonate reservoirs, framing the diagenetic events at regional scale.

Donnan-ion hydration model to estimate the electroosmotic permeability of clays

Electroosmotic permeability is a soil parameter that is fundamental for designing and implementing environmental remediation, dewatering, or soil stabilization processes. It presents a narrow range of variation compared to hydraulic permeability, so that in many occasions no experimental tests are carried out to determine it. Traditionally, the Helmholtz–Smoluchowski equation has been used to estimate electroosmotic permeability, despite having several drawbacks that make it difficult to apply, as it was deduced for large capillaries (unusual in clays) and its dependence on the zeta potential of the soil, difficult to measure and dependent on a wide variety of factors. The present work describes a semi-empirical formulation that allows the estimation of the electroosmotic permeability as a function of the specific surface area and the total void ratio and is based on the Donnan equilibrium and the ion hydration models. The parameters for modeling are calibrated and validated with experimental data, obtaining better results than those given by the Helmholtz–Smoluchowski model. In addition, the expected trends in the behavior of clays that can be found in the literature are obtained in a quantitative and consistent manner for different types of clays with variable water content and pore water salinity.

Static compression of rare earth metal holmium to 282 GPa

ABSTRACT The phase transitions and equation of state measurements were carried out on rare earth metal Holmium (Ho) to 282 GPa using toroidal diamond anvils thereby doubling the pressure range to which it has been studied previously. The first set of experiment employed standard beveled diamond anvils utilizing copper as an x-ray pressure standard to 217 GPa. The second set of experiment employed toroidal diamond anvils utilizing platinum as an x-ray pressure standard to 282 GPa. The recently proposed 16-atom orthorhombic structure (oF16) appeared to be stable between 103 and 282 GPa. The scaled axial ratio (c/a) shows a narrow range of variation of 1.58 ± 0.05 for the five known crystalline phases of Ho to 282 GPa. The experimental equation of state of Ho is presented up to a threefold volume compression V/Vo = 0.322.

Generation of High-Frequency Radiation in the Conditions of Superradiance of Particles with a Constant Dipole Moment

A localized ensemble of identical particles with a constant dipole moment generates during superradiance a coherent pulse of low-frequency radiation, the pulse shape depending significantly on the number of particles in the ensemble. In particular, low-frequency radiation pulse is transformed from one-hump to two-hump shape in a narrow range of variation of ensemble parameters.

Molecular Modeling and in Silico Characterization of a Pathogenesis-Related Protein-10 (PR10) and its Coding Genes in some Oryza Species

Rice is a major staple food for more than two thirds of the world population. Pathogenesis-related proteins-10 (PR10) have a range of 154 to 163 amino acid with molecular weight ~ 17 kDa. They are acidic and generally intracellular and cytosolic proteins accumulate in plants in response to biotic and abiotic stresses. In the present study, a PR10 gene and its corresponding protein were characterized in O. sativa, O. barthii, O. glaberrima, O. glumipatula, O. meridionalis, O. nivara, O. rufipogon and O. punctata. The results revealed a narrow range of variation at both DNA and protein levels in all examined species except O. glumipatula. The latter showed a relatively obvious structural variation at protein level. Such variation may be beneficial against different types of stress that requires further elucidation to exploit in rice breeding programs.

Formation of Isotope Parameters (δD, δ18O, and d) of Glaciers and Water Runoff from Severny Island of the Novaya Zemlya Archipelago

Isotope studies (δD and δ18O) were performed for the glaciers of Severny Island (Novaya Zemlya Archipelago). The studied glaciers were characterized by narrow range-of δD and δ18O values (from –15.4 to –17.6 ‰ and from –110.9 to –127.1‰, respectively). The samples of glacier ice form a linear trend within the δD–δ18O coordinates with low slope (s < 7). The isotope signature of water runoff from Severny Island point mainly to the glacial origin of the waters. The isotope parameters of glacial ice from the Novaya Zemlya Archipelago deviated from the values expected for western transfer of air masses under the latitudinal effect compared to glacial ice from other Arctic archipelagoes (Svalbard, Severnaya Zemlya, and Franz Josef Land). These parameters were similar to those for atmospheric precipitation over the continent near the town of Amderma. The slope of the trend, deuterium excess values, and narrow variation range of δD and δ18O values of ice might be caused by seasonal freezing of meltwater in firn layers within the closed system condition.

The use of the localization method for calculation of the robust PID regulator parameters for unmanned aircraft servo motor

The problem of controlling a typical nonlinear servo motor of an unmanned aercraft with non-stationary parameters using a robust PID controller is considered. The procedure for calculating the parameters of a robust PID controller based on the localization method (further - LM PID controller) for continuous and discrete control systems is studied. The influence of disturbing factors (internal and external) acting on the servo motor is considered. It is established that the main perturbations acting on the servo drive include internal perturbations, which are changes in the time constant and its gain from the temperature of the environment and the quality of the supply voltage. The simulation in the class of linear and nonlinear continuous systems showed that a servo drive with a ML PID controller has the property of robustness in the working range of changes in both the input signal and the parameters of the servo drive and controller. Simulation results showing the research are presented. When describing a servo motor with an LM PID controller in the class of linear discrete systems, its robustness is limited by a narrow range of variation of both its parameters and the quantization period of the input signal. As the degree of uncertainty in the parameters of the servo motor increases (approaching the working range of their change), the discrete system loses stability. For the synthesis of robust control circuits of an unmanned aercraft with given characteristics, mathematical dependences of the settling time and static error of a typical servo motor with LM PID controller from the quantization period of the input signal and the degree of uncertainty in its parameters are presented.

First record of Ditrupa gracillima (Annelida, Polychaeta) from the late Pliocene of Andaman and Nicobar Basin: insights on the ultrastructure, stable isotopic signature and distribution pattern

In the present study from the late Pliocene of Neill West Coast Formation, Neil Island, serpulid tubes assignable to Ditrupa gracillima Grube have been identified with the help of tube morphological (light microscopy) and ultrastructural (SEM) studies. This is the first record of the species from the late Pliocene of India. The outer layer of D. gracillima is entirely different from other invertebrates, and the presence of Ridged Prismatic Structure (RRP) exclusively characterises this particular species. The mineralogical analysis (Raman spectroscopy and EDS) reveals a Mg-Ca skeletal for D. gracillima. Isotopic analysis indicates that there is a narrow range of variation in the delta 18 O values of D. gracillima The delta 13 C of D. gracillima shows significant variation and displays the most 13 C depleted values. Based on isotopic analysis it has been inferred that the deposition of sediments took place in a shallow marine environment and D. gracillima thrived in the proximity of hydrocarbon seepages. The present day distributional pattern of D. gracillima indicates that they are mainly confined in the Indo-Pacific region.