Tirupati, India
Tirupati, India

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El Aroudi A.,Rovira i Virgili University | Giaouris D.,Center for Research and Technology Hellas | Mandal K.,Physical Science | Banerjee S.,Physical Science | And 3 more authors.
IET Power Electronics | Year: 2016

Distributed power systems are considered to be a key element of future power grids. Their main characteristic is the local production and consumption of energy that is accomplished using a number of power converters that interconnect local sources and loads. In this paper, a current mode controlled dc-dc converter which feeds another current mode controlled dc-dc converter is considered to meet the demands of the load. It shows that the existence of the second converter at the output has destabilising effect on the overall system. Such a system may also exhibit interactions of various types of instability that conventional modeling methods cannot predict. Slow-timescale oscillation in standalone switching converters is usually attributed to the occurrence of a Neimark-Sacker bifurcation of the fundamental periodic orbit of the discrete-time model of the system. But in the studied cascaded system, the underlying mechanism is quite different. This paper fully explains the mechanisms as well as the conditions of the occurrence of such instabilities by employing the analytical and numerical tools of the exact switched model of the system. These results can be useful for developing design guidelines to avoid such problems. Finally, the results have been validated experimentally. © The Institution of Engineering and Technology 2016.


Raghavendra Rao T.,Acharya Nagarjuna University | Venkata Reddy C.,Acharya Nagarjuna University | Venkata Reddy C.,Koneru Lakshmaiah College of Engineering | Udaychandran Thampy U.S.,Acharya Nagarjuna University | And 5 more authors.
Optoelectronics and Advanced Materials, Rapid Communications | Year: 2013

The spectral studies on 20ZnO+xLi2O+(30-x)Na2O+50B2O3 (5≤ x ≥25) doped with 0.1 mol% of paramagnetic CuO impurity are carried out. XRD patterns of powder glass samples confirm the amorphous nature. Urbach energies are shown the structural stability of the systems. The optical band gap energies varies non-linearly within the range of 3.818 - 4.073 eV for direct and 3.770 - 4.024 eV for indirect transitions with the increase of Li2O content. The FT-IR spectral studies show that the glass systems contain BO3 and BO4 units in disordered manner. The structural changes have been observed with alkali contents of the systems. It is observed that the system is more stable at x = 20 mol%. Mixed Alkali Effect phenomenon has been explained in the glass host.


Venkata Reddy Ch.,Acharya Nagarjuna University | Rama Krishna Ch.,Acharya Nagarjuna University | Raghavendra Rao T.,Acharya Nagarjuna University | Udayachandran Thampy U.S.,Acharya Nagarjuna University | And 3 more authors.
Journal of Molecular Structure | Year: 2012

Fe 3+ doped β-BaB 2O 4 nano crystallite powder is synthesized and characterized by spectroscopic techniques. From the Powder X-ray diffraction data, Fe 3+ doped β-BBO material is observed to be monoclinic. Its average crystallite size is evaluated about 75 nm. The particle-like morphology has been observed from SEM images. The EPR spectrum shows two resonance signals at g = 4.23 and g = 2.07, respectively which are indicative of Fe 3+ ions in tetragonally distorted octahedral site symmetry. Crystal field parameter (Dq) and Racah parameters (B and C) are evaluated. Fe 3+ doped β-BaB 2O 4 nano crystallite powder luminescence properties have been studied. The emission of β-BaB 2O 4:Fe 3+ sample is exhibited two main peaks at 419 and 443 nm. FT-IR spectrum shows the characteristic vibrations of host lattice. © 2012 Elsevier B.V. All rights reserved.


Rao T.R.,Acharya Nagarjuna University | Krishna C.R.,Acharya Nagarjuna University | Thampy U.S.U.,Acharya Nagarjuna University | Reddy C.V.,Acharya Nagarjuna University | And 3 more authors.
Applied Magnetic Resonance | Year: 2011

Physical and spectral studies on 20ZnO + xLi2O + (30-x)Na2O + 50B2O3 (5 ≤ x ≥ 25) doped with 0.1 mol% of paramagnetic CuO impurity are carried out. Powder X-ray diffraction patterns of the glass samples confirm the amorphous nature. The physical parameters of all the glasses were also evaluated with respect to the composition. The electron paramagnetic resonance spectra of all these glasses exhibit resonance signals that are characteristic of Cu2+ ions. The optical absorption spectra also confirm the Cu2+ ion in tetragonally elongated octahedral site. Various crystal field, spin-Hamiltonian and bonding parameters are evaluated. It is observed that the mixed alkali effect is significant. © 2011 Springer-Verlag.


Raghavendra Rao T.,Acharya Nagarjuna University | Rama Krishna C.,Acharya Nagarjuna University | Udayachandran Thampy U.S.,Acharya Nagarjuna University | Venkata Reddy C.,Acharya Nagarjuna University | And 3 more authors.
Physica B: Condensed Matter | Year: 2011

The effect of Li 2O content in vanadyl doped 20ZnOxLi 2O(30-x)Na 2O50B 2O 3 (5≤x≥25) glasses has been studied with respect to their physical and structural properties. The absence of sharp peaks in XRD spectra of these glass samples confirms the amorphous nature. The physical parameters like density, refractive index, ionic concentration and electronic polarizability vary non-linearly with x mol% depending on the diffusivities of alkali ions. EPR and optical absorption spectra reveal that the resonance signals are characteristics of VO 2 ions in tetragonally compressed octahedral site. Spin-Hamiltonian, crystal field, tetragonal field and bonding parameters are found to be in good agreement with the other reported glass systems. The tetragonal distortion (g ⊥g ∥) and Dt reveals that their values vary non-linearly with Li 2O content and reaches a minimum at x=10 mol%. An anomaly of character has been observed in all the properties of vanadyl doped glass systems, which gives a clear indication of mixed alkali effect. © 2011 Elsevier B.V. All rights reserved.


Rama Krishna C.H.,Acharya Nagarjuna University | Venkata Reddy C.H.,Acharya Nagarjuna University | Udayachandran Thampy U.S.,Acharya Nagarjuna University | Chandrasekhar A.V.,Physics Research Center | And 3 more authors.
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2012

Chlorocadmiumphosphate Cd(HPO 4)Cl·[H 3N(CH 2) 6NH 3] 0.5 crystals containing Cu(II) ions have been successfully synthesized at room temperature by using organic amine 1,6-diamino hexane as a template. The samples are characterized by X-ray powder diffraction, Thermal and spectroscopic studies. These are crystallizes in the monoclinic crystal system with cell dimensions: a = 1.7697, b = 0.6576, c = 1.9026 nm and β = 106.5°. FT-IR spectrum showed the absorption bands related to PO 4, NH 3 + ions and other organic molecule vibrations originated from the templated molecule. The prepared crystals are stable at room temperature and as well as up to around 300 °C which were confirmed by thermal analysis. Optical absorption and EPR studies suggest that Cu(II) ion enters in to the lattice as tetragonally distorted octahedral symmetry, for which crystal field and spin-Hamiltonian parameters are calculated. Bonding parameters are suggesting that there exists partial covalent nature between Cu(II) ions and ligands. © 2011 Elsevier B.V. All rights reserved.


Rama Krishna C.H.,Acharya Nagarjuna University | Udayachandran Thampy U.S.,Acharya Nagarjuna University | Sathish D.V.,Acharya Nagarjuna University | Venkata Reddy C.H.,Acharya Nagarjuna University | And 4 more authors.
Journal of Coordination Chemistry | Year: 2011

Chlorocadmiumphosphate CdHPO 4Cl·[H 3N(CH 2) 6NH 3] 0.5 crystals doped with Mn(II) are grown at room temperature via organic amine template method and characterized by spectroscopic techniques to obtain information on the nature of the incorporated Mn(II). Powder X-ray diffraction patterns of the sample are indexed to monoclinic cell and average crystalline size is found to be around 55 nm. The optical absorption spectrum exhibits various bands which are characteristic of Mn(II) in distorted octahedral site symmetry, confirmed by characteristic resonance signal at g=2.018 observed in the EPR spectrum. Fourier transform infrared spectrum shows the specific vibrations of phosphate and organic molecules. Thermal curves indicate that the crystal is stable at 307°C; above this temperature crystal structure disintegrates due to removal of the organic amine template. © 2011 Taylor & Francis.


Rama Krishna Ch.,Acharya Nagarjuna University | Venkata Reddy Ch.,Acharya Nagarjuna University | Udayachandran Thampy U.S.,Acharya Nagarjuna University | Reddy Y.P.,Physical science | And 2 more authors.
Inorganic Chemistry Communications | Year: 2011

This paper mainly reports on the structural investigations of Fe 3+ doped chlorocadmiumphosphate CdHPO 4Cl·[H 3N(CH 2) 6NH 3] 0.5 nanocrystals prepared at room temperature by organic amine templated method. Synthesized crystals are characterized by various spectroscopic techniques. From the powder X-ray diffraction patterns, the crystal system is indexed to monoclinic unit cell with lattice parameters a = 13.533, b = 15.008, c = 10.363 Å and β = 118.3°. The average size of the crystallite evaluated is 110 nm. FT-IR spectrum contains absorption bands related to organic amine and phosphate ions. The thermal analysis indicates that the inorganic framework collapses above 300°C, after the removal of the organic amine template. From optical absorption and EPR studies the crystal field, Racah parameters and g values suggested that the doped Fe 3+ ions entered the network at distorted octahedral site. © 2011 Elsevier B.V.


Pushpa Manjari V.,Acharya Nagarjuna University | Rama Krishna Ch.,Acharya Nagarjuna University | Rama Krishna Ch.,Koneru Lakshmaiah College of Engineering | Venkata Reddy Ch.,Acharya Nagarjuna University | And 4 more authors.
Journal of Luminescence | Year: 2014

Undoped and Fe(III) ions doped NaCaAlPO4F3 phosphor has been synthesized using solid state reaction method. The prepared phosphor material was characterized by powder X-ray diffraction (XRD), SEM with EDS, optical absorption, photoluminescence (PL), electron paramagnetic resonance (EPR) and FT-IR techniques. The average crystallite size was calculated from powder XRD data. SEM micrographs show the presence of several irregular shaped particles. Optical absorption spectrum exhibited the characteristic absorption bands of Fe(III) ions in distorted octahedral site symmetry. EPR spectrum exhibited two resonance signals at g=4.25 and g=2.00. PL spectrums of both undoped phosphor exhibits emission peaks at 407, 413 and 469 nm and Fe(III) ions doped phosphor gave the emission peaks at 373 and 450 nm under UV excitation. The Commission Internationale deI'Eclairage (CIE) chromaticity coordinates for undoped and Fe(III) ions doped NaCaAlPO4F3 phosphor material are calculated from the emission spectrum. Vibrational bands related to phosphate molecules, P-O-H and hydroxyl ions are observed in the FT-IR spectrum. © 2013 Elsevier B.V. All rights reserved.


Grant
Agency: Department of Defense | Branch: Office of the Secretary of Defense | Program: SBIR | Phase: Phase II | Award Amount: 749.96K | Year: 2011

Physical Sciences, Inc. (PSI) has demonstrated that electroactive polymer coatings (EAP) may be applied to the surface of the cathode materials for lithium-ion batteries to protect against catastrophic cell failure. These EAP coatings form an electrochemical"switch"that can prevent catastrophic failure in lithium-ion batteries by reversibly changing from a conductor to an insulator on overdischarge or short-circuit of a cell. During a Phase II program PSI proposes to optimize and demonstrate on a prototype scale the EAP coatings. Laboratory scale batteries will be used to evaluate the cycling and rate performance of the coatings and select the optimal combination for scale-up. Pouch cells will then be constructed to demonstrate the safety benefits offered by the EAP coatings. Upon demonstration in a pouch cell, material will be delivered to SAFT America for the construction of cylindrical cells. The performance of these cells will be fully characterized and utilized to further optimize the coating before construction of additional cylindrical cells for delivery to the Air Force. Successful construction of the cylindrical cells and demonstration of improved battery safety will demonstrate the readiness of the EAP coatings for transition to a commercial or military application.

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