Infantile encephalitic beriberi (IEBB) is a rare form of thiamine deficiency and is poorly descri... more Infantile encephalitic beriberi (IEBB) is a rare form of thiamine deficiency and is poorly described. A proportion of Leigh's disease (LD) patients have similar clinical picture and response to thiamine as beriberi, leading to confusion in diagnosis and management. Data on IEBB and LD is scarce and status of thiamine deficiency in India is controversial. We report several infants with life-threatening respiratory and central nervous system symptoms that overlap between IEBB and LD. Majority had low erythrocyte transketolase levels and responded dramatically to thiamine supplementation suggesting a diagnosis of IEBB. However, presence of characteristic lesions on brain imaging and residual damage in several patients on follow-up does not rule out LD completely. Our study highlights the importance of thiamine deficiency in India, especially in the breast-feds and its overlapping features with LD. Awareness of this common mode of presentation may save patients' lives by early diagnosis and timely thiamine supplementation.
Few studies have investigated the association between genetic variation and obesity traits in Ind... more Few studies have investigated the association between genetic variation and obesity traits in Indian populations or the role of environmental factors as modifiers of these relationships. In the context of rapid urbanisation, resulting in significant lifestyle changes, understanding the aetiology of obesity is important. We investigated associations of FTO and MC4R variants with obesity traits in 3390 sibling pairs from four Indian cities, most of whom were discordant for current dwelling (rural or urban). The FTO variant rs9939609 predicted increased weight (0.09 Z-scores, 95% CI: 0.03, 0.15) and BMI (0.08 Z-scores, 95% CI: 0.02, 0.14). The MC4R variant rs17782313 was weakly associated with weight and hip circumference (P < .05). There was some indication that the association between FTO and weight was stronger in urban than that in rural dwellers (P for interaction = .03), but no evidence for effect modification by diet or physical activity. Further studies are needed to investigate ways in which urban environment may modify genetic risk of obesity.
Earlier version of an indigenously developed Pressure Wave Generator (PWG) could not develop the ... more Earlier version of an indigenously developed Pressure Wave Generator (PWG) could not develop the necessary pressure ratio to satisfactorily operate a pulse tube cooler, largely due to high blow by losses in the piston cylinder seal gap and due to a few design deficiencies. Effect of different parameters like seal gap, piston diameter, piston stroke, moving mass and the piston back volume on the performance is studied analytically. Modifications were done to the PWG based on analysis and the performance is experimentally measured. A significant improvement in PWG performance is seen as a result of the modifications. The improved PWG is tested with the same pulse tube cooler but with different inertance tube configurations. A no load temperature of 130 K is achieved with an inertance tube configuration designed using Sage software. The delivered PV power is estimated to be 28.4 W which can produce a refrigeration of about 1 W at 80 K.
A moving magnet linear motor compressor or pressure wave generator (PWG) of 2 cc swept volume wit... more A moving magnet linear motor compressor or pressure wave generator (PWG) of 2 cc swept volume with dual opposed piston configuration has been developed to operate miniature pulse tube coolers. Prelimnary experiments yielded only a no-load cold end temperature of 180 K. Auxiliary tests and the interpretation of detailed modeling of a PWG suggest that much of the PV power has been lost in the form of blow-by at piston seals due to large and non-optimum clearance seal gap between piston and cylinder. The results of experimental parameters simulated using Sage provide the optimum seal gap value for maximizing the delivered PV power.
Substrates for 2D materials are important for tailoring their fundamental properties and realizin... more Substrates for 2D materials are important for tailoring their fundamental properties and realizing device applications. Aluminum nitride films on silicon are promising large-area substrates for such devices in view of their high surface phonon energies and reasonably large dielectric constants. In this paper epitaxial layers of AlN on 2" Si wafers have been investigated as a necessary first step to realize devices from exfoliated or transferred atomic layers. Significant thickness dependent contrast enhancements are both predicted and observed for monolayers of graphene and MoS 2 on AlN films as compared to the conventional SiO 2 films on silicon, with calculated contrast values approaching 100% for graphene on AlN as compared to 8% for SiO 2 at normal incidences. Quantitative estimates of experimentally measured contrast using reflectance spectroscopy show very good agreement with calculated values. Transistors of monolayer graphene on AlN films are demonstrated, indicating the feasibility of complete device fabrication on the identified layers.
Monolayers of transition metal dichalcogenides like MoS 2 have attracted a lot of attention for t... more Monolayers of transition metal dichalcogenides like MoS 2 have attracted a lot of attention for their potential applications in electronic and optoelectronic devices. However, reports on controlled growth of high quality MoS 2 layers are limited. Here, we demonstrate chemical vapor deposition (CVD) growth of uniform single to few-layers of MoS 2 . A back-gated field effect transistor based on MoS 2 shows p-type behavior with average mobility of 10 cm 2 V -1 s -1 .
Layered transition metal dichalcogenides (TMDs), such as MoS 2 , are candidate materials for next... more Layered transition metal dichalcogenides (TMDs), such as MoS 2 , are candidate materials for next generation 2-D electronic and optoelectronic devices. The ability to grow uniform, crystalline, atomic layers over large areas is the key to developing such technology. We report a chemical vapor deposition (CVD) technique which yields n-layered MoS 2 on a variety of substrates. A generic approach suitable to all TMDs, involving thermodynamic modeling to identify the appropriate CVD process window, and quantitative control of the vapor phase supersaturation, is demonstrated. All reactant sources in our method are outside the growth chamber, a significant improvement over vapor-based methods for atomic layers reported to date. The as-deposited layers are p-type, due to Mo deficiency, with field effect and Hall hole mobilities of up to 2.4 cm 2 V −1 s −1 and 44 cm 2 V −1 s −1 respectively. These are among the best reported yet for CVD MoS 2 . † Electronic supplementary information (ESI) available: Methodology for thermodynamic modeling, supersaturation calculation, Raman, optical microscopy and AFM analysis of MoS 2 single layers are available in the ESI. See
Infantile encephalitic beriberi (IEBB) is a rare form of thiamine deficiency and is poorly descri... more Infantile encephalitic beriberi (IEBB) is a rare form of thiamine deficiency and is poorly described. A proportion of Leigh's disease (LD) patients have similar clinical picture and response to thiamine as beriberi, leading to confusion in diagnosis and management. Data on IEBB and LD is scarce and status of thiamine deficiency in India is controversial. We report several infants with life-threatening respiratory and central nervous system symptoms that overlap between IEBB and LD. Majority had low erythrocyte transketolase levels and responded dramatically to thiamine supplementation suggesting a diagnosis of IEBB. However, presence of characteristic lesions on brain imaging and residual damage in several patients on follow-up does not rule out LD completely. Our study highlights the importance of thiamine deficiency in India, especially in the breast-feds and its overlapping features with LD. Awareness of this common mode of presentation may save patients' lives by early diagnosis and timely thiamine supplementation.
Few studies have investigated the association between genetic variation and obesity traits in Ind... more Few studies have investigated the association between genetic variation and obesity traits in Indian populations or the role of environmental factors as modifiers of these relationships. In the context of rapid urbanisation, resulting in significant lifestyle changes, understanding the aetiology of obesity is important. We investigated associations of FTO and MC4R variants with obesity traits in 3390 sibling pairs from four Indian cities, most of whom were discordant for current dwelling (rural or urban). The FTO variant rs9939609 predicted increased weight (0.09 Z-scores, 95% CI: 0.03, 0.15) and BMI (0.08 Z-scores, 95% CI: 0.02, 0.14). The MC4R variant rs17782313 was weakly associated with weight and hip circumference (P < .05). There was some indication that the association between FTO and weight was stronger in urban than that in rural dwellers (P for interaction = .03), but no evidence for effect modification by diet or physical activity. Further studies are needed to investigate ways in which urban environment may modify genetic risk of obesity.
Earlier version of an indigenously developed Pressure Wave Generator (PWG) could not develop the ... more Earlier version of an indigenously developed Pressure Wave Generator (PWG) could not develop the necessary pressure ratio to satisfactorily operate a pulse tube cooler, largely due to high blow by losses in the piston cylinder seal gap and due to a few design deficiencies. Effect of different parameters like seal gap, piston diameter, piston stroke, moving mass and the piston back volume on the performance is studied analytically. Modifications were done to the PWG based on analysis and the performance is experimentally measured. A significant improvement in PWG performance is seen as a result of the modifications. The improved PWG is tested with the same pulse tube cooler but with different inertance tube configurations. A no load temperature of 130 K is achieved with an inertance tube configuration designed using Sage software. The delivered PV power is estimated to be 28.4 W which can produce a refrigeration of about 1 W at 80 K.
A moving magnet linear motor compressor or pressure wave generator (PWG) of 2 cc swept volume wit... more A moving magnet linear motor compressor or pressure wave generator (PWG) of 2 cc swept volume with dual opposed piston configuration has been developed to operate miniature pulse tube coolers. Prelimnary experiments yielded only a no-load cold end temperature of 180 K. Auxiliary tests and the interpretation of detailed modeling of a PWG suggest that much of the PV power has been lost in the form of blow-by at piston seals due to large and non-optimum clearance seal gap between piston and cylinder. The results of experimental parameters simulated using Sage provide the optimum seal gap value for maximizing the delivered PV power.
Substrates for 2D materials are important for tailoring their fundamental properties and realizin... more Substrates for 2D materials are important for tailoring their fundamental properties and realizing device applications. Aluminum nitride films on silicon are promising large-area substrates for such devices in view of their high surface phonon energies and reasonably large dielectric constants. In this paper epitaxial layers of AlN on 2" Si wafers have been investigated as a necessary first step to realize devices from exfoliated or transferred atomic layers. Significant thickness dependent contrast enhancements are both predicted and observed for monolayers of graphene and MoS 2 on AlN films as compared to the conventional SiO 2 films on silicon, with calculated contrast values approaching 100% for graphene on AlN as compared to 8% for SiO 2 at normal incidences. Quantitative estimates of experimentally measured contrast using reflectance spectroscopy show very good agreement with calculated values. Transistors of monolayer graphene on AlN films are demonstrated, indicating the feasibility of complete device fabrication on the identified layers.
Monolayers of transition metal dichalcogenides like MoS 2 have attracted a lot of attention for t... more Monolayers of transition metal dichalcogenides like MoS 2 have attracted a lot of attention for their potential applications in electronic and optoelectronic devices. However, reports on controlled growth of high quality MoS 2 layers are limited. Here, we demonstrate chemical vapor deposition (CVD) growth of uniform single to few-layers of MoS 2 . A back-gated field effect transistor based on MoS 2 shows p-type behavior with average mobility of 10 cm 2 V -1 s -1 .
Layered transition metal dichalcogenides (TMDs), such as MoS 2 , are candidate materials for next... more Layered transition metal dichalcogenides (TMDs), such as MoS 2 , are candidate materials for next generation 2-D electronic and optoelectronic devices. The ability to grow uniform, crystalline, atomic layers over large areas is the key to developing such technology. We report a chemical vapor deposition (CVD) technique which yields n-layered MoS 2 on a variety of substrates. A generic approach suitable to all TMDs, involving thermodynamic modeling to identify the appropriate CVD process window, and quantitative control of the vapor phase supersaturation, is demonstrated. All reactant sources in our method are outside the growth chamber, a significant improvement over vapor-based methods for atomic layers reported to date. The as-deposited layers are p-type, due to Mo deficiency, with field effect and Hall hole mobilities of up to 2.4 cm 2 V −1 s −1 and 44 cm 2 V −1 s −1 respectively. These are among the best reported yet for CVD MoS 2 . † Electronic supplementary information (ESI) available: Methodology for thermodynamic modeling, supersaturation calculation, Raman, optical microscopy and AFM analysis of MoS 2 single layers are available in the ESI. See
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Papers by Kranthi Kumar