Effect of surface treatment on mechanical properties of glass fiber/stainless steel wire mesh reinforced epoxy hybrid composites

Karunagaran N.,Rajadurai A. 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.6

This paper investigates the effect of surface treatment for glass fiber, stainless steel wire mesh on tensile, flexural, inter-laminar shear and impact properties of glass fiber/ stainless steel wire mesh reinforced epoxy hybrid composites. The glass fiber fabric is surface treated either by 1 N solution of sulfuric acid or 1 N solution of sodium hydroxide. The stainless steel wire mesh is also surface treated by either electro dissolution or sand blasting. The hybrid composites are fabricated using epoxy resin reinforced with glass fiber and fine stainless steel wire mesh by hand lay-up technique at room temperature. The hybrid composite consisting of acid treated glass fiber and sand blasted stainless steel wire mesh exhibits a good combination of tensile, flexural, inter-laminar shear and impact behavior in comparison with the composites made without any surface treatment. The fine morphological modifications made on the surface of the glass fiber and stainless steel wire mesh enhances the bonding between the resin and reinforcement which inturn improved the tensile, flexural, inter-laminar shear and impact properties.

Effect of calcination on the crystallinity of sputtered TiO₂ thin films as studied by Raman scattering

Karunagaran, B.,Mangalaraj, D.,Kim, Kyunghae,Hong, Byungyou,Roh, Yonghan,Park, Cheon Seok,Yi, Junsin Akademie-Verlag 2005 Crystal research and technology Vol.40 No.3

<P>Titanium dioxide films have been deposited using DC magnetron sputtering technique onto silicon substrates at an ambient temperature and at an oxygen partial pressure of 7 × 10 <SUP>–5</SUP> mbar and sputtering pressure (Ar + O<SUB>2</SUB>) of 1 × 10 <SUP>–3 </SUP>mbar. The deposited films were calcinated at 673 and 773 K. The composition of the films as analyzed using Auger Electron Spectroscopy (AES) revealed the stoichiometry with an O and Ti ratio of 2.08. The influence of post-deposition calcination on the Raman scattering of the films was studied. The existence of Raman active modes A<SUB>1g</SUB>, B<SUB>1g</SUB> and E<SUB>g</SUB> corresponding to the Raman shifts are reported in this paper. The improvement of crystallinity of the TiO<SUB>2</SUB> films as shown by the Raman scattering studies has also been reported. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Low-Temperature Deposition of Silicon-Nitride Layers by Using PECVD for High Efficiency Si Solar Cells

Bojan Karunagaran,E.-K Suh,J. P Jeong,S. J. Chung,Subramaniyam Nagarajan 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.6

Silicon nitride (SiNx) films were deposited onto acid-polished and phosphorous-doped multicrystalline silicon (mc-Si) wafers by using a horizontal plasma-enhanced chemical vapour deposition (PECVD) reactor at a relatively low temperature of 300 C. High-purity silane (SiH4) and ammonia (NH3) were employed in the present work as precursor gases and by varying the ratio of the precursor gases; we were able to modify the index of refraction of the resulting SiNx films from 1.9 to 2.3, which had a direct influence on the reflectance, which is a very important factor in deciding the solar cell efficiency. In order to show the effectiveness of our low-temperature deposited SiNx layers as AR coating layers, we fabricated mc-Si solar cells by using our PECVD SiNx layers, highthroughput screen printing, and rapid thermal processing (RTP) firing. Using this sequence, we were able to obtain solar cells with efficiencies over 14 % for polished mc-Si wafers of sizes 125 mm square.

Characteristics of p-Type GaN Formed by Two Different Types of Mg Diffusion

Chung Sangjo,Karunagaran B,Muthusamy Senthil Kumar,Suh E. -K 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.1

Two different types of magnesium (Mg) diffusion onto intentionally undoped n-type GaN, resulting in p-type GaN formation, have been employed in this work. Secondary-ion mass spectroscopy (SIMS) measurements reveal a uniform Mg concentration for both methods of diffusion up to a depth of 1.5 μm in GaN. Hall measurement data indicate that all the diffused and annealed samples consistently show p-type conductivity with hole concentrations in the range of 5 7 × 1016/cm3 and with mobilities <50 cm2/V·s. The measured dark current of the samples almost exponentially increases with the reciprocal temperature with an activation energy of 144 meV or 168 meV in the temperature range from 170 K to 250 K. The photoluminescence (PL) spectra of Mg diffused GaN show a broad violet emission at around 3.15 eV. This broad peak may be attributed to Mg acceptors. In the photocurrent (PC) measurements on the Mg/Au film deposited on n-type GaN, an additional broad peak was observed at around 1.2 eV, and this peak may be related to the yellow luminescence.

Photocurrent Spectroscopy Investigations of Mg-Related Defect Levels in p-Type GaN

Chung sangjo,B. Karunagaran bojan,Hong C.-H,Lee H. J,Suh E.-K 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.3

The defect levels associated with the Mg impurity in p-type GaN films were systematically investigated in terms of doping concentration by using photocurrent spectroscopy. Mg-doped GaN samples were grown on sapphire substrates by using metal-organic chemical-vapor deposition (MOCVD) and were annealed in a nitrogen atmosphere at 850 C for 10 min. At room temperature, photocurrent (PC) spectra showed two peaks, one at 3.31 and the other at 3.15 eV, associated with acceptor levels formed at 300 and 142 meV, respectively, above the valence band in the as-grown samples. However, after thermal annealing, PC spectra exhibited various additional peaks, depending on the Mg concentration. In the GaN samples with a Mg concentration around 6 7 × 1017 cm.3, we observed PC peaks related to Mg at 3.31 and 3.02 eV and to the carbon acceptor at 3.17 eV. For moderately Mg-doped GaN samples, i.e., a hole concentration of p = 3 4 × 1017 cm.3, an additional peak was observed around 0.9 eV, which could be attributed to defects related to the Ga vacancy. For relatively low Mg-doped samples whose hole concentrations are 1 2 × 1017 cm.3, an additional broad peak was observed around 1.3 eV. This peak might be related to the yellow band luminescence. As the Mg concentration was increased, the concentration of Ga vacancies could be reduced because the Mg occupied the substitutional sites of Ga in the GaN lattice. When the hole concentration was above 6 7 × 1017 cm.3, the yellow luminescence and the Ga-vacancy-related peaks disappeared completely.

Sub-micrometer-sized Graphite As a Conducting and Catalytic Counter Electrode for Dye-sensitized Solar Cells

Veerappan, Ganapathy,Bojan, Karunagaran,Rhee, Shi-Woo American Chemical Society 2011 ACS APPLIED MATERIALS & INTERFACES Vol.3 No.3

<P>Sub-micrometer-sized colloidal graphite (CG) was tested as a conducting electrode to replace transparent conducting oxide (TCO) electrodes and as a catalytic material to replace platinum (Pt) for I<SUB>3</SUB><SUP>−</SUP> reduction in dye-sensitized solar cell (DSSC). CG paste was used to make a film via the doctor-blade process. The 9 μm thick CG film showed a lower resistivity (7 Ω/◻) than the widely used fluorine-doped tin oxide TCO (8−15 Ω/◻). The catalytic activity of this graphite film was measured and compared with the corresponding properties of Pt. Cyclic voltammetry and electrochemical impedance spectroscopy studies clearly showed a decrease in the charge transfer resistance with the increase in the thickness of the graphite layer from 3 to 9 μm. Under 1 sun illumination (100 mW cm<SUP>−2</SUP>, AM 1.5), DSSCs with submicrometer-sized graphite as a catalyst on fluorine-doped tin oxide TCO showed an energy conversion efficiency greater than 6.0%, comparable to the conversion efficiency of Pt. DSSCs with a graphite counter electrode (CE) on TCO-free bare glass showed an energy conversion efficiency greater than 5.0%, which demonstrated that the graphite layer could be used both as a conducting layer and as a catalytic layer.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2011/aamick.2011.3.issue-3/am101204f/production/images/medium/am-2010-01204f_0006.gif'></P>

Menadione (Vitamin K3) Induces Apoptosis of Human Oral Cancer Cells and Reduces their Metastatic Potential by Modulating the Expression of Epithelial to Mesenchymal Transition Markers and Inhibiting Migration

Suresh, Shruthy,Raghu, Dinesh,Karunagaran, Devarajan Asian Pacific Journal of Cancer Prevention 2013 Asian Pacific journal of cancer prevention Vol.14 No.9

Oral cancer is one of the most commonly occurring cancers worldwide, decreasing the patient's survival rate due to tumor recurrence and metastasis. Menadione (Vitamin K3) is known to exhibit cytotoxicity in various cancer cells but the present study focused on its effects on viability, apoptosis, epithelial to mesenchymal transition (EMT), anchorage independent growth and migration of oral cancer cells. The results show that menadione is more cytotoxic to SAS (oral squamous carcinoma) cells but not to non-tumorigenic HEK293 and HaCaT cells. Menadione treatment increased the expression of pro-apoptotic proteins, Bax and p53, with a concurrent decrease in anti-apoptotic proteins, Bcl-2 and p65. Menadione induced the expression of E-cadherin but reduced the expression of EMT markers, vimentin and fibronectin. Menadione also inhibited anchorage independent growth and migration in SAS cells. These findings reveal and confirm that menadione is a potential candidate in oral cancer therapy as it exhibits cytotoxic, antineoplastic and antimigratory effects besides effectively blocking EMT in oral cancer cells.

Nanometer Sized Silver Particles Embedded Silica Particles—Spray Method

Gnana kumar, G,Karunagaran, B,Nahm, KeeSuk,Nimma Elizabeth, R Springer 2009 Nanoscale research letters Vol.4 No.5

<P>Spherical shaped, nanometer to micro meter sized silica particles were prepared in a homogeneous nature by spray technique. Silver nanoparticles were produced over the surface of the silica grains in a harmonized manner. The size of silver and silica particles was effectively controlled by the precursors and catalysts. The electrostatic repulsion among the silica spheres and the electro static attraction between silica spheres and silver particles make the synchronized structure of the synthesized particles and the morphological images are revealed by transmission electron microscope. The silver ions are reduced by sodium borohydride. Infra red spectroscopy and X-ray photoelectron spectroscopy analysis confirm the formation of silver–silica composite particles. Thermal stability of the prepared particles obtained from thermal analysis ensures its higher temperature applications. The resultant silver embedded silica particles can be easily suspended in diverse solvents and would be useful for variety of applications.</P>

Case Report : Periosteal nociceptors induced hypotension and bradycardia under spinal anesthesia

( Rakesh Garg ),( Pradeep Karunagaran ),( Mridula Pawar ) 대한마취과학회 2011 Korean Journal of Anesthesiology Vol.60 No.1

The sudden hemodynamic disturbance in the perioperative period can occur because of various surgical and anesthetic reasons but hemodynamic collapse due to noxious stimulus of periosteum stripping has not been described. We report two cases of severe hypotension and bradycardia during periosteum stripping in orthopedic surgery under subarachnoid block even though the block level was adequate. In our patients, hemodynamic collapse occurred specifically at a moment when surgeons manipulated periosteum and fall in blood pressure and heart rate was sudden in onset. The hemodynamic disturbance did not appear to be related to vagally mediated or due toblockade of sympathetic fibers but appeared to be related to periosteal nociceptors. (Korean J Anesthesiol 2011; 60: 52-53)

Molecular design and synthesis of ruthenium(<small>II</small>) sensitizers for highly efficient dye-sensitized solar cells

Anthonysamy, A.,Lee, Y.,Karunagaran, B.,Ganapathy, V.,Rhee, S.-W.,Karthikeyan, S.,Kim, K. S.,Ko, M. J.,Park, N.-G.,Ju, M.-J.,Kim, J. K. Royal Society of Chemistry 2011 Journal of materials chemistry Vol.21 No.33

<P>We synthesized hydrophobic ruthenium(<SMALL>II</SMALL>) sensitizers (SY-04 and SY-05) with high molar extinction coefficient by extending the π-conjugation of 3,4- or 3-alkylthiophene-substituted bipyridine ligands. Both dyes displayed a remarkably high molar extinction coefficient of 21.7 × 10<SUP>3</SUP> M<SUP>−1</SUP> cm<SUP>−1</SUP> arising from red-shift of their metal-to-ligand charge transfer band when compared to a commonly used N3 sensitizer. The solar-to-electrical energy conversion efficiency (<I>η</I>) of the SY-04 based dye-sensitized solar cell (DSC) was 7.70%, which is 27% higher than that (6.05%) of the N3-based DSC under the same cell fabrication conditions. The increased <I>η</I> was attributed to the increase in life time and recombination half-life measured by electrochemical impedance and transition absorption spectroscopy, respectively. Density functional theory and time-dependent density functional theory calculations of two dyes in both gas phase and solution were performed. The calculated values of the highest occupied and the lowest unoccupied molecular orbitals and absorption spectra are in good agreement with the experimental results.</P> <P>Graphic Abstract</P><P>DSCs based on hydrophobic ruthenium(<SMALL>II</SMALL>) sensitizers with thiophene-substituted bipyridine ligands showed the solar-to-electrical energy conversion of 7.70%, which is 27% higher than that of N3-based DSC at the same fabrication condition. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1jm11760b'> </P>