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Processing and characterization of sintered reaction bonded Si<sub>3</sub>N<sub>4</sub> ceramics
Golla, B.R.,Ko, J.W.,Kim, H.D. Elsevier 2017 INTERNATIONAL JOURNAL OF REFRACTORY METALS AND HAR Vol.68 No.-
<P>The present contribution reports the influence of nitridation and sintering conditions on the densification, microstructure, mechanical and thermal conductivity properties of sintered reaction bonded Si3N4 (SRBSN) mixed with 3.5% Y2O3-1.5% MgO. The nitridation of samples was carried out at 1450 and 1500 degrees C for different time schedules (2.5, 8 and 16 h) in order to increase beta Si3N4 phase and subsequently sintering was performed at various temperatures (1850, 1900 and 1950 degrees C) for 10 h to enhance densification and properties of SRBSN ceramics. It was observed that the density of the samples slightly decreased and beta Si3N4 phase significantly increased to 87% with increasing nitridation temperature and time. The density of gas pressure sintered (GPS) samples increased with increasing sintering temperature, almost full density was measured for all the samples at the respective sintering temperature (except those samples which were given nitridation at 1500 degrees C for 16 h). The microstructure of SRBSN samples were characterized by bimodal microstructure with equiaxed and rod like elongated grains and average grain size of SRBSN samples varied between 1.62 and 2.43 mu m and aspect ratio of grains varied from 3.78 to 6.88 with varying the sintering temperature. Depending on the sintering density and microstructure, the SRBSN samples exhibited hardness (16.69 to 19.47 GPa), fracture toughness (7.02 to 9.20 MPa.m(1/2)) and thermal conductivity (77.32 to 98.52 W/m.K). The coarsening of grain size and aspect ratio negatively affected hardness and fracture toughness, on the contrary the thermal conductivity increased. Among all samples, the SRBSN (which was subjected to nitridation at 1500 degrees C for 16 h; GPS at 1950 degrees C for 10 h) measured with good combination of hardness: 17.32 GPa, fracture toughness: 8.36 MPa.m(1/2) and thermal conductivity: 98.52 W/m.K.</P>
LINEAR MAPS PRESERVING 𝓐𝓝-OPERATORS
Golla, Ramesh,Osaka, Hiroyuki Korean Mathematical Society 2020 대한수학회보 Vol.57 No.4
Let H be a complex Hilbert space and T : H → H be a bounded linear operator. Then T is said to be norm attaining if there exists a unit vector x<sub>0</sub> ∈ H such that ║Tx<sub>0</sub>║ = ║T║. If for any closed subspace M of H, the restriction T|M : M → H of T to M is norm attaining, then T is called an absolutely norm attaining operator or 𝓐𝓝-operator. In this note, we discuss linear maps on B(H), which preserve the class of absolutely norm attaining operators on H.
Linear maps preserving AN-operators
Ramesh Golla,Hiroyuki Osaka 대한수학회 2020 대한수학회보 Vol.57 No.4
Let $H$ be a complex Hilbert space and $T : H\rightarrow H$ be a bounded linear operator. Then $T$ is said to be \textit{norm attaining} if there exists a unit vector $x_0\in H$ such that $\|Tx_0\|=\|T\|$. If for any closed subspace $M$ of $H$, the restriction $T|M : M \rightarrow H$ of $T$ to $M$ is norm attaining, then $T$ is called an \textit{absolutely norm attaining} operator or $\mathcal{AN}$-operator. In this note, we discuss linear maps on $\mathcal B(H)$, which preserve the class of absolutely norm attaining operators on $H$.
Kaliki, Sravan Kumar,Golla, Shiva Prasad,Kurukundu, Rama Naidu Electronics and Telecommunications Research Instit 2021 ETRI Journal Vol.43 No.1
Noncontiguous orthogonal frequency division multiplexing (NC-OFDM)-based cognitive radio (CR) systems achieve highly efficient spectrum utilization by transmitting unlicensed users' data on subcarriers of licensed users' data when they are free. However, there are two disadvantages to the NC-OFDM system: out-of-band power (OBP) and a high peak-to-average power ratio (PAPR). OBP arises due to side lobes of an NC-OFDM signal in the frequency domain, and it interferes with the spectrum for unlicensed users. A high PAPR occurs due to the inverse fast Fourier transform (IFFT) block used in an NC-OFDM system, and it induces nonlinear effects in power amplifiers. In this study, we propose an algorithm called "Alternative Projections onto Convex and Non-Convex Sets" that reduces the OBP and PAPR simultaneously. The alternate projections are performed onto these sets to form an iteration, and it converges to the specified limits of in-band-power, peak amplitude, and OBP. Furthermore, simulations show that the bit error rate performance is not degraded while reducing OBP and PAPR.
The Densification and Photoluminescence Characteristics of Ca-α-SiAlON:Eu2+ Plate Phosphor
박영조,이재욱,김진명,Brahma Raju Golla,윤창번,윤철수 한국세라믹학회 2013 한국세라믹학회지 Vol.50 No.4
Plate-type phosphor is a promising substitute in overcoming the issues related to the powder phosphor paste mixed with resin. In this research, Ca-α-SiAlON:Eu2+ plate phosphor (CaxSi12-(m+n)Alm+nOnN16-n:Euy) was investigated for the varied compositions (m,n) of the host crystal with the fixed Eu content (y). Densification was promoted for the compositions with increasing ‘m’ values for the m=2n relationship. Dictated by the Eu concentration inside the phosphor crystal, photoluminescence intensity was stronger in α2 specimen (m = 3.0, n = 1.5) containing the second phases when compared to α1 specimen (m = 1.5, n = 0.75) comprising a single-phase α-SiAlON. The concentration of Eu in the non-emitting amorphous interfacial glass phase was 2~4 times of the designed Eu concentration inside the α-SiAlON crystal.
Park, Young-Jo,Lee, Jae-Wook,Kim, Jin-Myung,Golla, Brahma Raju,Yoon, Chang-Bun,Yoon, Chulsoo The Korean Ceramic Society 2013 한국세라믹학회지 Vol.50 No.4
Plate-type phosphor is a promising substitute in overcoming the issues related to the powder phosphor paste mixed with resin. In this research, $Ca-{\alpha}-SiAlON:Eu^{2+}$ plate phosphor ($Ca_xSi_{12-(m+n)}Al_{m+n}O_nN_{16-n}:Eu_y$) was investigated for the varied compositions (m,n) of the host crystal with the fixed Eu content (y). Densification was promoted for the compositions with increasing 'm' values for the m=2n relationship. Dictated by the Eu concentration inside the phosphor crystal, photoluminescence intensity was stronger in ${\alpha}2$ specimen (m = 3.0, n = 1.5) containing the second phases when compared to ${\alpha}1$ specimen (m = 1.5, n = 0.75) comprising a single-phase ${\alpha}$-SiAlON. The concentration of Eu in the non-emitting amorphous interfacial glass phase was 2~4 times of the designed Eu concentration inside the ${\alpha}$-SiAlON crystal.
Peeyush Kumar,Sudheer K. Vuyyuru,Prasenjit Das,Bhaskar Kante,Mukesh Kumar Ranjan,David Mathew Thomas,Sandeep Mundhra,Pabitra Sahu,Pratap Mouli Venigalla,Saransh Jain,Sandeep Goyal,Rithvik Golla,Shubi 대한장연구학회 2023 Intestinal Research Vol.21 No.4
Background/Aims: Evidence on predictors of primary nonresponse (PNR), and secondary loss of response (SLR) to anti-tumor necrosis factor (anti-TNF) agents in inflammatory bowel disease is scarce from Asia. We evaluated clinical/biochemical/molecular markers of PNR/SLR in ulcerative colitis (UC) and Crohn’s disease (CD).Methods: Inflammatory bowel disease patients treated with anti-TNF agents (January 2005–October 2020) were ambispectively included. Data concerning clinical and biochemical predictors was retrieved from a prospectively maintained database. Immunohistochemistry for expression of oncostatin M (OSM), OSM receptor (OSM-R), and interleukin-7 receptor (IL-7R) were done on pre anti-TNF initiation mucosal biopsies.Results: One-hundred eighty-six patients (118 CD, 68 UC: mean age, 34.1±13.7 years; median disease duration at anti-TNF initiation, 60 months; interquartile range, 28–100.5 months) were included. PNR was seen in 17% and 26.5% and SLR in 47% and 28% CD and UC patients, respectively. In CD, predictors of PNR were low albumin (<i>P</i><0.001), postoperative recurrence (<i>P</i>=0.001) and high IL-7R expression (<i>P</i><0.027) on univariate; and low albumin alone (hazard ratio [HR], 0.09; 95% confidence interval [CI], 0.03–0.28; <i>P</i><0.001) on multivariate analysis respectively. Low albumin (HR, 0.31; 95% CI, 0.15–0.62; <i>P</i>=0.001) also predicted SLR. In UC, predictors of PNR were low albumin (<i>P</i><0.001), and high C-reactive protein (<i>P</i><0.001), OSM (<i>P</i><0.04) and OSM-R (P=0.07) stromal expression on univariate; and low albumin alone (HR, 0.11; 95% CI, 0.03–0.39; <i>P</i>=0.001) on multivariate analysis respectively. Conclusions: Low serum albumin at baseline significantly predicted PNR in UC and PNR/SLR in CD patients. Mucosal markers of PNR were high stromal OSM/OSM-R in UC and high IL-7R in CD patients.