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Vamsi Krishna Kukkapalli,Jin Ho Kim,Sunwoo Kim 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.10
Two-phase closed thermosyphons have been employed in roadway embankments in the arctic regions to prevent permafrost from thawing. Thermosyphons installed in the embankment reject heat during the cold season and help maintain the ground temperature below freezing. Despite their proven effectiveness, the use of thermosyphons is limited due to high installation cost. In this research, roadway embankments in permafrost regions were numerically investigated to seek an optimal spacing between neighboring thermosyphons. First, this work focused on the conventional evaporator design of a horizontal straight pipe. Additionally, the constructal theory-inspired Y- and T-shaped evaporators were studied. The volumeaveraged ground temperature was computed for each design. The simulations showed that there exists an optimal spacing and that the proposed Y- and T-shaped designs outperform the conventional design. A Y- and T-shaped design with a higher bifurcation level showed better cooling performance than designs with a single bifurcation level.
Dual-Transmission-Line Microstrip Equiripple Lowpass Filter with Sharp Roll-Off
Vamsi Krishna Velidi,Subrata Sanya 한국전자통신연구원 2011 ETRI Journal Vol.33 No.6
A novel application of a dual-transmission line is proposed to design a lowpass filter (LPF). The proposed structure uses only transmission line elements to produce an equiripple LPF response with sharp roll-off. Design equations are derived using a lossless transmission line model. Controlling the electrical lengths, three transmission-zeros are realized in the stopband to obtain a sharp roll-off rate and wide stopband bandwidth. A single unit microstrip LPF with a 3-dB cut-off frequency at 1.0 GHz having a roll-off of 135 dB/GHz along with a stopband bandwidth of 69.5% is designed for validation.
Microstrip Coupled-Line Lowpass Filter with Wide Stopband for RF/Wireless Systems
Vamsi Krishna Velidi,Subrara Sanyal,Mrinal Kanti Mandal 한국전자통신연구원 2009 ETRI Journal Vol.31 No.3
We present the design of a compact microstrip lowpass filter with a wide stopband which is up to ten times the cutoff frequency. The filter is based on a coupled-line configuration and shunt open stubs. The open stubs create additional transmission zeros, which are used to extend the stopband of the filter without any additional components or cascaded units. A prototype lowpass filter with a 3 dB cutoff frequency of 0.428 GHz and a 15 dB stopband extended up to 4.77 GHz is fabricated to validate the theoretical predictions.
Vamsi Krishna Velidi,Subrara Sanyal 한국전자통신연구원 2010 ETRI Journal Vol.32 No.1
This letter presents the design of a compact bandstop filter (BSF) operating at two frequencies. The proposed BSF consists of open-ended stepped impedance resonators (OSIR) and an end-shorted parallel-coupled microstrip line (E-PCML). The OSIRs are used to achieve the impedance-controlled stopband positions. The wide BSF bandwidths are achieved through enhanced coupling of the E-PCML. Explicit design guidelines are derived using a lossless transmission line model. To validate theoretical predictions, a prototype dual-band BSF operating at 900 MHz and 2,100 MHz with fractional bandwidths of 72% and 36%, respectively, is implemented in microstrip.
Bulk electrolysis of Zn-phthalocyanine unveils self assembled nanospheres via anion binding
Narra Vamsi Krishna,Botta Bhavani,Madoori Mrinalini,K.S. Srivishnu,Lingamallu Giribabu,Seelam Prasanthkumar 한국물리학회 2020 Current Applied Physics Vol.20 No.6
Stimuli responsive π-conjugated macrocyclic systems has shown significant attention in organic electronics, however, amongst them, porphyrins and phthalocyanines unveiled remarkable growth towards materials and biological applications. Herein, we report bulk electrolysis of Zn-phthalocyanine system (ZnPc-OMe) under potential difference of 1.5 V in chloroform results anion binding mechanism directs the formation of self-assembled nanospheres by diffusion controlled approach. Electrochemical and UV–Vis absorption studies of ZnPc- OMe suggest that anion (Cl−) binding ability towards ‘Zn‘ whilst applied potential leads to the formation of H+[(Cl)ZnPc-OMe]- promote the enhanced current and charge generation. Microscopic analysis revealed that ZnPc-OMe and H+[(Cl)ZnPc-OMe]- exhibit the nanosheets and spheres with an average diameter of 0.5–1 μm and 300–500 nm, respectively. Powder X-ray diffraction analysis and raman spectra revealed the changes in crystalline phase transitions via ion-dipole and π-π stacking interactions. Thus, these unique features are atypical for phthalocyanine derivative hitherto unknown.
FE Modeling and Experimental Analysis of Residual Stresses in Vibration Assisted Turning of Ti6Al4V
Naresh Kumar Maroju,Vamsi Krishna Pasam 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.20 No.3
Titanium alloys are widely employed in aerospace, marine and biomedical industries due to their durability and ability to sustain elevated operating temperature. Vibration assisted turning (VAT) is found to be an effective alternative to machine hard materials and promises significant process improvements compared to conventional turning (CT). This paper presents experimental studies and finite element simulations in turning of Ti6Al4V alloy with uncoated carbide tools. The influence of VAT on residual stress is evaluated in both experiment and simulation. The residual stresses are evaluated experimentally along the direction of cutting and perpendicular to the direction of cutting using X-ray diffraction analysis. 3-D finite element model is developed to predict cutting forces, temperature, and machining-induced stress field and the residual stresses. It is observed that the nature of residual stresses is predominantly compressive in VAT compared to CT, due to the reduced the cutting forces, effective stresses, and temperature.