1,007 research outputs found
Correction: Rhodium-catalyzed cycloaddition of carbonyl ylides for the synthesis of spiro[furo[2,3-<i>a</i>]xanthene-2,3′-indolin]-2′-one scaffolds
No full textCorrection for ‘Rhodium-catalyzed cycloaddition of carbonyl ylides for the synthesis of spiro[furo[2,3-a]xanthene-2,3′-indolin]-2′-one scaffolds’ by B. V. Subba Reddy et al., RSC Adv., 2016, 6, 50497–50499.</p
Narayanella, a new name for Narayana Subba Rao (hymenoptera : mymaridae)
No full textThe name Narayana was applied (Subba Rao, 1976) to a genus erected for the new species N. pilipes reared from the gaUs of Lagerstoemia flos reginae. Unfortunately the author overlooked the vulid and prior use of Narayana by Distant (1908). Narayana Distant was erected with rusticitatus as type-species (Issidae: Homoptera). Hence Narayana Subba Rao is a junior homonym which has to be replaced according to the rules of the International Zoological Nomenclature
Characterization of Red sandalwood by ICP-MS Analysis, Optical absorption and EPR spectroscopic methods
No full textRed sandalwood contains Cd, Fe, Ni, Mn, C, S, H elements. ICP-MS results indicate that the red sandalwood contains Ni (61.877), Cu (281.256), Ba (3722.064) and Sr (6365.482) ppm elements respectively. It has partial semi conducting nature. EPR spectrum of the sample is due to Fe(III) in tetragonal distortion and its ash sample also contains Mn(II) in addition to Fe(III). The g values obtained for Fe(III) in the sample are 6.52, 2.63 and 1.92 respectively. The observed g and A values for Mn (II) are 1.990 and 88.5 G respectively. Mn(II) may be low in concentration in the sample. Optical absorption spectrum clearly indicates the presence of both ferric iron and Ni(II) in octahedral geometry. NIR Spectrum is due to carbonate overtones and harmonics and water fundamentals
Characterization of Phyllanthus amarus herb by inductively coupled plasma mass spectrometric (ICP-MS) analysis, optical absorption and electron paramagnetic resonance (EPR) spectroscopic methods
No full textA powdered sample of Phyllanthus amarus herb from kadapa district of Andhra Pradesh India, is used in the present study. ICP-MS analysis indicates that copper is present in higher concentration when compared with other elements.Althought the Pb is toxic, it is within permissible limits. The evalauted soil and herb phsico-chemical properties indicate that the sample is acidic in nature in comparison with soil. An EPR study on the powdered sample confirm the presence of Fe(III), Mn(II), and Cu(II. Optical absiorption spectrum indicates that the Fe(III) is present in an octahedral position whereas the Cu(II) is in a rhombically distorted octahedral environment. MIR results are due to carbonate fundamental
Organic Farming: Status, Issues and Prospects – A Review
No full textThis review paper attempts to bring together different issues in the light of recent developments in organic farming. The after effects of green revolution have encouraged the farmers to take up organic farming. This paper has reviewed the global and Indian scenario with reference to organic farming. In India, the cultivated land under certification is 2.8 Mha only. The key issues emerging in organic farming include yield reduction in conversion to organic farm, soil fertility enhancement, integration of livestock, certification constraints, ecology, marketing and policy support. The potential for organic farming, especially in the dryland regions has been discussed. It has been argued that organic farming is productive and sustainable, but there is a need for strong support to it in the form of subsidies, agricultural extension services and research.Agricultural and Food Policy,
A New Class of Single DC-link Fed Multilevel Inverter Topologies for Grid Connected Photovoltaic Systems with Reduced Component Count and Inherent Capacitor Balancing
No full textGrid integration of photovoltaic (PV) energy sources has been mostly governed by conventional two-level voltage source inverters. These topologies have significant switching power losses, dV/dt stress and THD level at lower switching frequencies. The above issues can be solved by introducing more voltage levels through multilevel converters. Conventional multilevel converters have many issues like neutral point voltage drift in neutral point clamped (NPC) topology, floating capacitor charge balance in flying capacitor (FC) topology and large number of isolated DC sources in cascaded half bridge (CHB) topology when scaling them for higher number of voltage levels. Additionally, active power devices and its associated gate drivers, clamping diodes, flying capacitors and DC link capacitors also increase with levels. Hence, it is desirable to generate a multilevel voltage output with a single DC link and with the reduced components count. This thesis proposes a new way of generating multilevel voltage output using a single DC source and with the least components count. The thesis also proposes a new gate driver that can be operated at wide duty cycle ratios and wide band frequency.
The thesis presents five major contributions as follows,
1. 16 switch five level inverter for isolated grid tied systems
2. 12 switch five level inverter for isolated grid tied systems
3. Inherent DC link capacitor balancing
4. Extension of five level inverter topologies to higher levels
5. A Wide duty cycle range wide band high frequency isolated gate driver for multilevel power converters
First part of the research work, presents a novel five level inverter for high power isolated grid connection, which is powered by a single DC source. The proposed topology employs overall 16 active power devices, two DC link capacitors and a Scott-T transformer. Out of 16 power switches, 8 switches operate at high frequency and remaining 8 operate at the fundamental frequency. The DC link capacitors have an inherent voltage balancing which eliminates the requirement of charge balancing circuit or complex control algorithm. Additionally, necessity of expensive voltage sensors are also mitigated. The five level converter initially generate five level voltages in two phase system, and then they are transformed to three phases by using a Scott-T transformer. Operation of the proposed five level inverter (1 kW) is tested experimentally by connecting it to a three phase grid with unity power factor control. Second part follows the footsteps of the first topology.
The second topology presents a grid connected five level inverter with only 12 power devices. This topology is also powered by a single DC source. Eight (8) out of 12 power devices are switched at fundamental frequency (variable) and the remaining devices are switched at high frequency. The proposed inverter is validated experimentally by connecting it to a three phase grid. The performance of capacitor voltage balancing under steady state and transient loading conditions is verified.
Third part of the thesis discusses about the inherent charge balancing phenomenon of the DC link capacitors for the proposed inverter topologies. In both the topologies, the DC link capacitors have inherent voltage balancing capability. This feature eliminates the requirement of voltage sensors and complex control schemes which are generally employed in the conventional multilevel inverters.
In fourth part of the research work, a wide band frequency and wide duty cycle operated isolated gate driver with only a single auxiliary power supply is proposed. The proposed gate driver is specifically advantageous for multilevel inverters as all the gate drivers can be powered by a single auxiliary power supply. The integrated gate driver has features like, wide duty cycle (0 - 100%) and wide band frequency (ranging from DC to 1 MHz) operation, short circuit/over current, and miller clamp protections. The performance of the gate driver is validated experimentally followed by a LTSPICE software simulations.
Finally, a generalized multilevel inverter topology based on the proposed five level inverter topologies with only a single DC source is presented. Multilevel output is obtained by cascading H-bridge modules on either side of the five level converter after the unfolding stage. Connecting `n' number of H-bridge modules per phase to the five level converter leads to [8n+1] levels of the output voltage. Feasibility of the converter is validated by testing a nine level inverter configuration. The proposed concept uses least active power devices, DC link capacitor, flying capacitor, and diodes compared to the existing single DC link fed multilevel inverter topologies.
All the above presented topologies and circuits are extensively tested in simulation and in the experimentation in laboratory for three phase grid connected unity power factor operation. A 1 kW, 50 Hz fundamental and 10 kHz switching inverters was developed for the experimental studies. The inverter is used for the grid integration of DC sources with 192 V, 1 kW power rating. The inverter prototype consists of power semiconductor switches of rating 1200 V and 75 A insulated gate bipolar transistor (IGBT) half bridge Semikron modules (SKM75GB12T4). The proposed gate drivers were used to drive the power IGBTs. The Scott-T transformer is realized using two single phase transformers with an appropriate winding turns ratio. The current control and PWM signal generation is carried in a digital signal processor (DSP-TMS320F28335) with a clock frequency of 150 MHz. The grid voltage and currents were sensed by using LEM make voltage (LV-25P) and current (LA-55P) sensors. The sensed voltage and current data is fed to the analog to digital converter (ADC) which internally exists in the DSP. All the computations and frame transformations were also carried within the DSP. The dead time for the IGBT modules is generated as 1μs. The testing was done by connecting the proposed inverters to the grid. The inverter performance is validated at various loading conditions. The inherent capacitor balancing was also validated under steady state and transient loading conditions.
The proposed inverter topologies exhibits advantages like, reduced components count, single DC link operation, inherent capacitor voltage balancing, fundamental switching devices and inherent isolation. Overall size of the proposed inverters is less compared to the conventional five level inverters for grid connected applications where isolation is mandatory. The inherent capacitor voltage balancing also eliminates the requirement of expensive voltage sensors, complex control circuits and algorithms. The fewer active components count results in simple control architecture and improves reliability of the inverters to a large extent. The experimental validation shows that the proposed inverter topologies can be considered as viable solutions for the high power isolated grid tied photovoltaic systems
Investigations on the Corona Degradation of Polymeric Insulating Samples
No full textInsulators play an important role in the reliability and safe operation of EHV/UHV transmission lines. Recently several utilities in the country and elsewhere are using polymeric insulators for the high voltage transmission and distribution systems due to their advantages. Since, polymeric insulators are of recent origin and organic in nature, their long-term field performance is not yet fully understood. International standard organizations like CIGRE, IEC, IEEE etc, are currently working towards the development of methods for long term performance; some include resistance to corona, ozone, chemical attack, hydrophobicity etc, for the polymeric insulating samples. The present investigation focuses on two important aspects:
(1) Investigations on the corona induced degradation on different polymeric samples under normal and due to different fog conditions.
(2) Application of digital imaging techniques for the detection of corona discharges and its analysis.
An experimental facility along with a new methodology is proposed and adopted for the corona induced degradation studies on polymer insulator examples. The investigations are conducted on different polymer samples for the normal and the effect of different fog environments, some interesting results are obtained, further the treated samples are analyzed using physicochemical analysis, it was found that corona treated samples present higher hydroxylation, detection of nitric acid on sample surface which cause brittle fracture of fiberglass rod of the insulator, loss of Alumina trihydrate (ATH) filler, decrease in tensile strength on theinsulator samples.It was observed from experimental investigations that corona activity isone of the important phenomena responsible for the degradation of polymeric insulators. Hence, periodic inspection of polymeric insulators and the detection of corona discharges are important in condition monitoring. Hence an attempt is made to analyze and quantify the corona discharges using image processing techniques. A color threshold based corona plasma extraction algorithm is adopted. A luminance component ‘Y’parameter is computed from the processed corona images and is shown to correlate well with the corona released power. A physical model is proposed to explain the phenomenon and is quantified by adopting the line‐detection based image processing algorithm to compute the corona spread angle. It is observed that material degradation caused by the corona with less spread angle is higher in comparison to the wide spread corona. To overcome the limitation of conventional images,high dynamic range imaging technique is employed to accurately identify the location of corona stress on the polymeric samples. Interestingly, it is observed that the correlation between the degradation patterns estimated by the corona images and Fourier transform infrared spectroscopy(FTIR) show that HDR image provides the true correlation, whereas the conventional images resulted in pseudo‐correlation
Cloning and expression of a subfamily 1.4 lipase from Bacillus licheniformis IBRL-CHS2
No full textWe report on the cloning of the lipase gene from Bacillus licheniformis IBRLCHS2
and the expression of the recombinant lipase. DNA sequencing analysis of the
cloned lipase gene showed that it shares 99% identity with the lipase gene from
B. licheniformis ATCC 14580 and belongs to subfamily 1.4 of true lipases based on amino
acid sequence alignment of various Bacillus lipases. The 612 bp lipase gene was then
cloned into the pET-15b(+) expression vector and the construct was transformed into
E. coli BL21 (DE3) for bulk expression of the lipase. Expression was analysed by SDSPAGE
where the lipase was found to have a molecular weight of about 23 kDa
Commutativity of Prime Rings with Symmetric Biderivations
No full textThe present paper shows some results on the commutativity of R: Let R be a prime ring and for any nonzero ideal I of R, if R admits a biderivation B such that it satisfies any one of the following properties (i) B([x, y], z) = [x, y], (ii) B([x, y], m) + [x, y] = 0, (iii) B(xoy, z) = xoy, (iv) B(xoy, z) + xoy = 0, (v) B(x, y)oB(y, z) = 0, (vi)B(x, y)oB(y, z) = xoz, (vii) B(x, y)oB(y, z) + xoy = 0, for all x, y, z ∈ R, then R is a commutative ring
Analysis of High Temperature Low Sag Conductors used for High Voltage Transmission
No full textPresently there is a continuous demand for the electric power consumption across the globe, however with the existing distribution lines are reaching critical limits of ampacity and sag, it has become difficult in finding corridors to construct new overhead lines in many industrialized countries including India. Replacing the existing ACSR conductors with high temperature high current low sag (HTLS) conductors almost of the same diameter is one of the recent methods. The present work a parametric study is conducted for steady state surface temperature, thermal time constant, change of emissivity, absorptivity etc for various ACSR and HTLS conductors using the developed computer code which is in accordance with IEEE Std. 738. Some experimental study is also conducted and the results obtained are presented. (C) 2016 The Authors. Published by Elsevier Ltd
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