Umesh Kumar - Academia.edu (original) (raw)
Papers by Umesh Kumar
Microelectronics Journal, 1980
MOS transistors in electronic technology have attained major importance in recent years. A vast a... more MOS transistors in electronic technology have attained major importance in recent years. A vast amount of literature exists illustrating the great attention that has been focused on this device. Models that characterise its terminal behaviour are essential for the analysis and design of MOS devices and circuits. Several equivalent circuits and various methods of calculating the small signal properties of a MOSFET are available. A comprehensive review is presented of the attempts approximating a MOSFET channel as a one dimensional distributed structure.
The Journal of Physical Chemistry C, 2009
The fate of bioactivity of biomolecules such as enzymes, proteins, and even drug molecules is gre... more The fate of bioactivity of biomolecules such as enzymes, proteins, and even drug molecules is greatly affected by the conformational changes in the proximity of the solid surfaces. This interaction is the key to the potential of their further applications as biosensors, in drug delivery, etc. ...
The Journal of Physical Chemistry B, 2009
The study of elastic properties of microbial and mammalian cells using atomic force microscopy, w... more The study of elastic properties of microbial and mammalian cells using atomic force microscopy, with forcesensitivity as high as pico-Newtons and spatial resolution of a few nanometers, is proving to be a great tool for the real-time observation of the effects of drugs, biomolecules, metal ions, and nanoparticles on cell physiology in their natural environment. It has been shown that the Young's modulus of the cell surfaces is extremely sensitive to the surrounding environment. Recently, a broad array of microbes have been used successfully to synthesize nanocrystals of several metal and metal oxides in a controlled manner at room temperature after exposing them to various metal ion precursors. However, so far there is no report on the fate of their elastic properties and cell topography etc. during and after their exposure to the metal ions during the microbial synthesis of nanomaterials. Additionally, this information is also found to be extremely relevant to areas such as bioremediation, bioleaching, and biomineralization, where it is important to study the direct influence on the cell physiology in the presence of metal ions. Here, we report, for the first time, the use of AFM force-distance curves on live cells, to directly monitor (in real time) the changes in the surface-topography, surface-adhesion, indentation-depth, and Young's modulus of a metal-tolerant marine bacterium, BreVibacterium casei, isolated from the coast of the Arabian Sea, after its exposure to the Co 2+ ions during the process of biosynthesis of nanoparticles. We earlier reported that this bacterium is capable of using the cobalt acetate as a precursor to synthesize protein-functionalized Co 3 O 4 nanoparticles with very high crystallinity. Our study indicates a significant change in the morphology as well as elastic and adhesive properties of the BreVibacterium casei, where we found an increase in the adhesive properties and the indentation depth of the bacterial surfaces and a decrease in the cell stiffness after several hours of exposure to the cobalt acetate. We have discussed both qualitative and quantitative analysis of the force-spectroscopy data in detail.
IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 1996
Multilayer piezoelectric resonators were fabricated and the dependance of the electrical impedanc... more Multilayer piezoelectric resonators were fabricated and the dependance of the electrical impedance and the coupling coefficient were measured as a function of the number of layers, for N=1,...20 layers. The magnitude of the electrical impedance followed the theoretical predicted 1/N 2 relation, and the coupling coefficient, K t , remained relatively constant out to N=15 layers. These cofired resonators are suitable for medical ultrasound transducers.
Applied Catalysis A: General, 2009
InTaO 4 is a photocatalyst with visible-light response that is used to split water and produce hy... more InTaO 4 is a photocatalyst with visible-light response that is used to split water and produce hydrogen. InTaO 4 is traditionally prepared by solid-state fusion of In 2 O 3 and Ta 2 O 5 at ≥1100 °C. A solgel procedure was developed to synthesize InTaO 4 from In(NO 3 ) 3 ...
Microelectronics Journal, 1980
MOS transistors in electronic technology have attained major importance in recent years. A vast a... more MOS transistors in electronic technology have attained major importance in recent years. A vast amount of literature exists illustrating the great attention that has been focused on this device. Models that characterise its terminal behaviour are essential for the analysis and design of MOS devices and circuits. Several equivalent circuits and various methods of calculating the small signal properties of a MOSFET are available. A comprehensive review is presented of the attempts approximating a MOSFET channel as a one dimensional distributed structure.
The Journal of Physical Chemistry C, 2009
The fate of bioactivity of biomolecules such as enzymes, proteins, and even drug molecules is gre... more The fate of bioactivity of biomolecules such as enzymes, proteins, and even drug molecules is greatly affected by the conformational changes in the proximity of the solid surfaces. This interaction is the key to the potential of their further applications as biosensors, in drug delivery, etc. ...
The Journal of Physical Chemistry B, 2009
The study of elastic properties of microbial and mammalian cells using atomic force microscopy, w... more The study of elastic properties of microbial and mammalian cells using atomic force microscopy, with forcesensitivity as high as pico-Newtons and spatial resolution of a few nanometers, is proving to be a great tool for the real-time observation of the effects of drugs, biomolecules, metal ions, and nanoparticles on cell physiology in their natural environment. It has been shown that the Young's modulus of the cell surfaces is extremely sensitive to the surrounding environment. Recently, a broad array of microbes have been used successfully to synthesize nanocrystals of several metal and metal oxides in a controlled manner at room temperature after exposing them to various metal ion precursors. However, so far there is no report on the fate of their elastic properties and cell topography etc. during and after their exposure to the metal ions during the microbial synthesis of nanomaterials. Additionally, this information is also found to be extremely relevant to areas such as bioremediation, bioleaching, and biomineralization, where it is important to study the direct influence on the cell physiology in the presence of metal ions. Here, we report, for the first time, the use of AFM force-distance curves on live cells, to directly monitor (in real time) the changes in the surface-topography, surface-adhesion, indentation-depth, and Young's modulus of a metal-tolerant marine bacterium, BreVibacterium casei, isolated from the coast of the Arabian Sea, after its exposure to the Co 2+ ions during the process of biosynthesis of nanoparticles. We earlier reported that this bacterium is capable of using the cobalt acetate as a precursor to synthesize protein-functionalized Co 3 O 4 nanoparticles with very high crystallinity. Our study indicates a significant change in the morphology as well as elastic and adhesive properties of the BreVibacterium casei, where we found an increase in the adhesive properties and the indentation depth of the bacterial surfaces and a decrease in the cell stiffness after several hours of exposure to the cobalt acetate. We have discussed both qualitative and quantitative analysis of the force-spectroscopy data in detail.
IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 1996
Multilayer piezoelectric resonators were fabricated and the dependance of the electrical impedanc... more Multilayer piezoelectric resonators were fabricated and the dependance of the electrical impedance and the coupling coefficient were measured as a function of the number of layers, for N=1,...20 layers. The magnitude of the electrical impedance followed the theoretical predicted 1/N 2 relation, and the coupling coefficient, K t , remained relatively constant out to N=15 layers. These cofired resonators are suitable for medical ultrasound transducers.
Applied Catalysis A: General, 2009
InTaO 4 is a photocatalyst with visible-light response that is used to split water and produce hy... more InTaO 4 is a photocatalyst with visible-light response that is used to split water and produce hydrogen. InTaO 4 is traditionally prepared by solid-state fusion of In 2 O 3 and Ta 2 O 5 at ≥1100 °C. A solgel procedure was developed to synthesize InTaO 4 from In(NO 3 ) 3 ...