Existence of Partially Degenerate Electrical Transport in Intermetallic Cu2SnSe3 Thermoelectric System Sintered at Different Temperatures

K. Gurukrishna,H. R. Nikhita,S. M. Mallikarjuna Swamy,Ashok Rao 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.8

A detailed investigation on the temperature dependent electrical properties of Cu2SnSe3system, synthesized via conventionalsolid-state reaction at different sintering temperatures are presented in this communication. All the samples exhibit degeneratesemiconducting nature at low temperatures. The existence of small polarons and hence electron–phonon interactionsare confirmed at temperatures below 400 K. A transition was observed from degenerate to non-degenerate semiconductingbehaviour at high temperatures (T > 400 K). The study confirms the unusual transition in electrical resistivity as well asthermopower at high temperatures in all the compounds, demonstrating the existence of minority carrier excitation alongwith temperature-triggered ionisation of the defects. The transport behaviour is further supported by an upward movementof Fermi level away from the valence band. Highest weighted mobility of 8.2 cm2V−1 s−1 at 673 K was obtained for thesample sintered at 1073 K. A considerable decrease in electrical resistivity with increase in temperature (T > 400 K) hasdriven the power factor to increase exponentially, thereby achieving highest value of 188 μV/mK2 (at 673 K) for the samplesintered at 673 K.

Immobilization of Xylanase Using a Protein-Inorganic Hybrid System

( Ashok Kumar ),( Sanjay K. S. Patel ),( Bharat Mardan ),( Raviteja Pagolu ),( Rowina Lestari ),( Seong-hoon Jeong ),( Taedoo Kim ),( Jung Rim Haw ),( Sang-yong Kim ),( In-won Kim ),( Jung-kul Lee ) 한국미생물생명공학회(구 한국산업미생물학회) 2018 Journal of microbiology and biotechnology Vol.28 No.4

In this study, the immobilization of xylanase using a protein-inorganic hybrid nanoflower system was assessed to improve the enzyme properties. The synthesis of hybrid xylanase nanoflowers was very effective at 4°C for 72 h, using 0.25 mg/ml protein, and efficient immobilization of xylanase was observed, with a maximum encapsulation yield and relative activity of 78.5% and 148%, respectively. Immobilized xylanase showed high residual activity at broad pH and temperature ranges. Using birchwood xylan as a substrate, the V_max and K_m values of xylanase nanoflowers were 1.60 mg/ml and 455 μmol/min/mg protein, compared with 1.42 mg/ml and 300 μmol/min/mg protein, respectively, for the free enzyme. After 5 and 10 cycles of reuse, the xylanase nanoflowers retained 87.5% and 75.8% residual activity, respectively. These results demonstrate that xylanase immobilization using a proteininorganic hybrid nanoflower system is an effective approach for its potential biotechnological applications.

Characteristic enhancement of white LED lamp using low temperature co-fired ceramic-chip on board package

심재관,K. Ashok,라용호,임홍철,백병준,이철로 한국물리학회 2012 Current Applied Physics Vol.12 No.2

In this paper, we propose low temperature co-fired ceramic-chip on board (LTCC-COB) package with improved thermal characteristics; no insulation layer exists between the LED chip and metal base. In actual measurement as well as in thermal simulation, the proposed LED lamp structure showed excellent thermal properties, compared with surface mound device-printed circuit board (SMD-PCB) package LED lamp. The optical output power, thermal distribution, currentevoltage (IeV) and electroluminescence (EL) were measured and compared to analyze the characteristics of LTCC-COB package LED lamp with SMD-PCB package LED lamp. EL peak intensity of LTCC-COB package LED lamp is 1.75 times better than that of SDM-PCB package LED lamp. The thermal resistance between packing area and air was found to be 7.3 K/W and 7.9 K/W for LTCC-COB package and SMD-PCB package respectively. The proposed LTCCCOB packaged LED lamp is not only suitable for high power LED package due to its low thermal resistance but also a promising solution for illumination modules.

Characteristic enhancement of white LED lamp using low temperature co-fired ceramic-chip on board package

Sim, J.K.,Ashok, K.,Ra, Y.H.,Im, H.C.,Baek, B.J.,Lee, C.R. Elsevier 2012 Current Applied Physics Vol.12 No.2

In this paper, we propose low temperature co-fired ceramic-chip on board (LTCC-COB) package with improved thermal characteristics; no insulation layer exists between the LED chip and metal base. In actual measurement as well as in thermal simulation, the proposed LED lamp structure showed excellent thermal properties, compared with surface mound device-printed circuit board (SMD-PCB) package LED lamp. The optical output power, thermal distribution, current-voltage (I-V) and electroluminescence (EL) were measured and compared to analyze the characteristics of LTCC-COB package LED lamp with SMD-PCB package LED lamp. EL peak intensity of LTCC-COB package LED lamp is 1.75 times better than that of SDM-PCB package LED lamp. The thermal resistance between packing area and air was found to be 7.3 K/W and 7.9 K/W for LTCC-COB package and SMD-PCB package respectively. The proposed LTCC-COB packaged LED lamp is not only suitable for high power LED package due to its low thermal resistance but also a promising solution for illumination modules.

Investigations on magnetic and electrical properties of Zn doped Fe₂O₃ nanoparticles and their correlation with local electronic structures

Kumar, Parmod,Sharma, Vikas,Singh, Jitendra P.,Kumar, Ashish,Chahal, Surjeet,Sachdev, K.,Chae, K.H.,Kumar, Ashok,Asokan, K.,Kanjilal, D. Elsevier 2019 Journal of magnetism and magnetic materials Vol.489 No.-

<P><B>Abstract</B></P> <P>Present work aims at investigating the structural, magnetic and dielectric properties of zinc doped Fe<SUB>2</SUB>O<SUB>3</SUB> nanoparticles (pure, 10%, 20% & 30%) and correlated with their local electronic structures using X-ray absorption near-edge structure (XANES) spectroscopy. X-ray diffraction and Raman measurements infer that doping of Zn cations lead to the formation of secondary phases corresponding to ZnFe<SUB>2</SUB>O<SUB>4</SUB> along with the hematite phase of Fe<SUB>2</SUB>O<SUB>3</SUB>. Magnetic measurements show that magnetization vs magnetic field curve for 10% Zn doping exhibit maximum saturation magnetization (~2.93 × 10<SUP>−3</SUP> emu/g) as well as the coercivity (~956 Oe). The values of these parameters decrease for higher content of Zn. The temperature dependence of dielectric behaviour follows the same trend as that of the lattice parameter and magnetic measurements. The XANES spectra at Fe L- and Fe K-edges indicate partial reduction of Fe<SUP>3+</SUP> ions into Fe<SUP>2+</SUP> upon Zn doping in the Fe<SUB>2</SUB>O<SUB>3</SUB> lattice. However, divalent state is favourable for Zn (i.e. Zn<SUP>2+</SUP>) within the doping range reported in this study.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Zn doped Fe<SUB>2</SUB>O<SUB>3</SUB> nanoparticles. </LI> <LI> Study of magnetic and electrical properties. </LI> <LI> Correlation of magnetic and electrical properties with local electronic structure. </LI> </UL> </P>

Variability of Azadirachtin in Azadirachta indica (neem) and Batch Kinetics Studies of Cell Suspension Culture

Ashok K. Srivastava,Gunjan Prakash,C. J. S. K. Emmannuel 한국생물공학회 2005 Biotechnology and Bioprocess Engineering Vol.10 No.3

Seeds of neem were collected from different parts of India and analyzed for their azadirachtin content by High Performance Liquid Chromatography (HPLC). In order to assess the effects of genotypic and geographical variation on azadirachtin content in cell cultures, callus development was attempted in the seeds containing high and low concentration of azadirachtin. The concentration of azadirachtin in callus cultures was significantly affected by the explant source. Seed kernels with higher azadirachtin content produced higher azadirachtin content in callus cultures and lower azadirachtin content was seen in callus cultures produced from seed kernels with low azadirachtin content. The protocol for development of elite stock culture of Azadirachta indica was established with the objective of selecting a high azadirachtin-producing cell line. The highest azadirachtin-producing cell line was selected and the effects of different media and illumination conditions on growth and azadirachtin production were studied in shake flask suspension culture. Detailed batch growth kinetics was also established. These studies provided elite starter culture and associated protocols for cultivation of A. indica plant cell culture in the bioreactor.

Feedback control strategies for active control of noise inside a 3-D vibro-acoustic cavity

Ashok K. Bagha,Subodh V. Modak 국제구조공학회 2017 Smart Structures and Systems, An International Jou Vol.20 No.3

This paper presents and compares three feedback control strategies for active control of noise inside a 3-D vibro-acoustic cavity. These are a) control strategy based on direct output feedback (DOFB) b) control strategy based on linear quadratic regulator (LQR) to reduce structural vibrations and c) LQR control strategy with a weighting scheme based on structural-acoustic coupling coefficients. The first two strategies are indirect control strategies in which noise reduction is achieved through active vibration control (AVC), termed as AVC-DOFB and AVC-LQR respectively. The third direct strategy is based on active structural-acoustic control (ASAC). This strategy is an LQR based optimal control strategy in which the coupling between the various structural and the acoustic modes is used to design the controller. The strategy is termed as ASAC-LQR. A numerical model of a 3-D rectangular box cavity with a flexible plate (glued with piezoelectric patches) and with other five surfaces treated rigid is developed using finite element (FE) method. A single pair of collocated piezoelectric patches is used for sensing the vibrations and applying control forces on the structure. A comparison of frequency response function (FRF) of structural nodal acceleration, acoustic nodal pressure, and piezoelectric actuation voltage is carried out. It is found that the AVC-DOFB control strategy gives equal importance to all the modes. The AVC-LQR control strategy tries to consume the control effort to damp all the structural modes. It is seen that the ASAC-LQR control strategy utilizes the control effort more intelligently by adding higher damping to those structural modes that matter more for reducing the interior noise.

Herbal Mixtures Consisting of Puerarin and Either Polyenylphosphatidylcholine or Curcumin Provide Comprehensive Protection

Ashok K. Singh,Elhabib Benlhabib,Shveta Gupta,Yin Jiang 한국식품영양과학회 2007 Journal of medicinal food Vol.10 No.3

Bioprocess Strategies and Recovery Processes in Gibberellic Acid Fermentation

Ashok K. Srivastava,Ruchi Shukla,Subhash Chand 한국생물공학회 2003 Biotechnology and Bioprocess Engineering Vol.8 No.5

Gibberellic acid (GA3) is a commercially important plant growth hormone, which is gaining much more attention all over the world due to its effective use in agriculture and brewing industry. Industrially it is produced by submerged fermentation technique using Ascomycetous fungus Gibberella fujikuroi. Solid state and immobilized cell fermentation techniques had also been developed as an alternative to obtain higher yield of GA3. This review summarizes the problems of GA3 fermentation such as production of co-secondary metabolites along with GA3, substrate inhibition and degradation of GA3 to biologically inert compound gibberellenic acid, which limits the yield of GA3 in the fermentation medium. These problems can be overcome by various bioprocessing strategies e.g. two - stage and fed batch cultivation processes. Further research on bioreactor operation strategies such as continuous and / or extractive fermentation with or without cell recycle / retention system need to be investigated for improvement in yield and productivity. Down stream processing for GA3 isolation is also a challenge and procedures available for the same have been critically evaluated.

Anti-Inflammatory Potency of Nano-Formulated Puerarin and Curcumin in Rats Subjected to the Lipopolysaccharide-Induced Inflammation

Ashok K. Singh,Yin Jiang,Shveta Gupta,Mohamod Younus,Mohamod Ramzan 한국식품영양과학회 2013 Journal of medicinal food Vol.16 No.10

Puerarin (PU) and curcumin (CU), used commonly in traditional Chinese medicine and Ayurveda, have been shown to possess potent anti-inflammatory, anti-oxidation, and neuro-protective properties. Despite the experimental success of CU and PU in in vitro and animal models, their effectiveness has not yet been demonstrated in clinical trials, possibly because of their poor bioavailability. We hypothesized that gold nanoparticle (AuNP)-formulated PU (PU-AuNP), CU (CUAuNP), or a combination of PU and CU (PU-CU-AuNP) were a more effective and nontoxic alternative to their bulk (nonformulated) counterparts. To test the hypothesis, bioavailability, therapeutic potency, and toxicity of bulk CU and/or PU were compared with those of their nanotized counterparts in rats subjected to the lipopolysaccharide (LPS)-induced inflammation. This study showed that a 20-mg/kg dose of bulk PU or a mixture of PU and CU did not, while their nanotized counterparts, PU-AuNP, CU-AuNP, or PU-CU-AuNP, effectively suppressed the LPS-induced inflammation and cytotoxicity in rats. In addition, PU-CU-AuNP was more potent than PU-AuNP or CU-AuNP alone. The blank AuNP (bAuNP) at £ 40 mg/kg dose did not cause any adverse effects (blood and brain lactic acid concentrations, kidney function, and neuronal apoptosis were measured) in animals. Therefore, the present observations suggest that a bi-functional AuNP loaded with CU and PU may effectively suppress the LPS-induced inflammation and cytotoxicity provided the following conditions are met: (1) The AuNP dose is at or below the no-effect dose; (2) the nanoparticles release a therapeutic dose of CU and PU in vivo; and (3) the active ingredients are released into the intracellular component of the brain.