44 Hits in 1.5 sec

Sound induced by a simple impact oscillator [article]

S. P. Narla, Kartik Venkatraman
2021 arXiv   pre-print
Acoustic radiation due to vibration and impact of a spring-mass-damper oscillator whose motion is constrained by a barrier is analyzed at a field point in a free field. Impact between the mass and the barrier is modeled using a coefficient of restitution model. Non-linear behavior of the oscillator is observed due to motion constraint. Steady state response is studied using a bifurcation diagram. For small amplitudes of oscillation, the pressure perturbation by a vibrating mass in a
more » ... fluid is modeled as an acoustic dipole with its center at the equilibrium position of the mass and its axis aligned with the motion of the oscillator. The boundary condition for the acoustic domain is an acoustic free-field condition. It is observed that the unsteady acoustic pressure resulting from the impact force is a few orders of magnitude greater relative to the pressure field resulting from vibration alone before or after impact. We also analyzed the influence of coefficient of restitution, damping ratio, the ration of base excitation frequency to the natural frequency, and the ratio of the distance of the barrier to the base excitation amplitude on the acoustic radiation. Damping ratio and coefficient of restituion are shown to be the most significant paramters that affect the acoustic radiation from the vibro-impact oscillator.
arXiv:2108.12804v1 fatcat:sh2zk3bxzrdgbp7apqzxyojlfm

ABL modelling of complex terrain using non-neutral and canopy models

Kartik Venkatraman
2022 Zenodo  
WESC Presentation 2021
doi:10.5281/zenodo.6548245 fatcat:mnt5czqy7rbxjlmfhr7bkh5e3y

Piezo-actuated Vibration and Flutter Control

S.B. Kandagal, Kartik Venkatraman
2006 Defence Science Journal  
Kandagal and Venkatraman 25 experimentally demonstrated the viscoelastic behaviour of shunted piezoceramics.  ...  Kandagal and Venkatraman 49 studied various feedback measurement conditions for SISO feedback control and strain actuation in heave and pitch directions to quantify their effect on flutter.  ...  Dr Kartik Venkatraman is presently Assistant Professor in the Department of Aerospace Engineering, Indian Institute of Science, Bangalore. His research areas are dynamics and aeroelasticity.  ... 
doi:10.14429/dsj.56.1927 fatcat:lcysuxwsbjbn3dudmj5gkg37by

Cross-linked polymers in strain: Structure and anisotropic stress [article]

Prashant Kumar Srivastava, Kartik Venkatraman
2011 arXiv   pre-print
The study on the effect of cross-linking reveals that stress levels increase in a cross-linked polymer network as compared to a linear polymeric system Srivastava & Venkatraman (2010) .  ...  The equations of motion for the monomers which are involved in cross-linking is the same as that derived for the monomers belonging to the linear polymer chain Srivastava & Venkatraman (2010) .  ... 
arXiv:1105.0801v1 fatcat:hat4oaflurer3etgpc47hvd5sy

Vibrational Spectroscopy at Atomic Resolution with Electron Impact Scattering [article]

Kartik Venkatraman, Barnaby D.A. Levin, Katia March, Peter Rez, and Peter A. Crozier
2018 arXiv   pre-print
Atomic vibrations control all thermally activated processes in materials including diffusion, heat transport, phase transformations, and surface chemistry. Recent developments in monochromated, aberration-corrected scanning transmission electron microscopy (STEM) have enabled nanoscale probing of vibrational modes using a focused electron beam. However, to date, no experimental atomic resolution vibrational spectroscopy has been reported. Here we demonstrate atomic resolution by exploiting
more » ... ized impact excitations of vibrational modes in materials. We show that the impact signal yields high spatial resolution in both covalent and ionic materials, and atomic resolution is available from both optical and acoustic vibrational modes. We achieve a spatial resolution of better than 2 Å which is an order of magnitude improvement compared to previous work. Our approach represents an important technical advance that can be used to provide new insights into the relationship between the thermal, elastic and kinetic properties of materials and atomic structural heterogeneities.
arXiv:1812.08895v1 fatcat:gp6xv6spdzh4riuvvtm6oarnfm

What Are the Applications of meV EELS ?

Peter Rez, Katia March, Kartik Venkatraman
2020 Microscopy and Microanalysis  
The combination of high performance monochromators with energy loss spectrometers has opened up spectral windows in the visible and Infra-Red that were inaccessible in the transmission electron microscope for many years. It has been possible on occasion to achieve energy resolutions of 5 meV (~ 40 cm -1 ) in the monochromated Nion UltraSTEM with probe currents of order 10 pA, and 10 meV is achievable on a routine basis. Although this is spectacular compared to EELS in the past, the energy
more » ... tion is still significantly inferior to 0.1 cm-1 (~ 0.01 meV) energy resolution of Raman or Infra-Red spectroscopy. However these bulk characterization techniques are unable to offer nanometer spatial resolution, except in specialized circumstances. The new applications that are now possible can be broadly divided into three areas, nanophotonics, detection of point defects, and localized vibrational spectroscopy. The very small characteristic scattering angle for low energy dipole excitations means that the signal is delocalized over regions up to 10nm for signals in the optical part of the spectrum, and up to 100nm for signals in the IR region. Although this delocalization severely degrades spatial resolution it can be used to advantage in damage free vibrational spectroscopy and for probing effects of long-range electromagnetic fields that are relevant in nanophotonics. However there are significant differences, in EELS usually only the electrostatic field is significant whereas photons have related electric and magnetic fields perpendicular to each other. Although lattice resolved images in phonon modes have been demonstrated, it is unlikely that defect modes arising from differences in bonding will be detected with the present resolution. Furthermore most of the interest in materials relates to thermal transport involving low energy phonons that are difficult to separate from the tail of the zero loss peak. It is still possible to extra information from the asymmetry of the zero loss peak. Fig 1 shows the mapping of the phonon dispersion of the acoustic phonon along [111] in Ge, showing the broadening of the dispersion from anharmonic interactions. The situation is very different for organic compounds, including biological material [1]. An energy resolution of 5 meV is sufficient to make distinctions between different classes of organic compounds. It is even possible to determine the proportions of secondary structure in a protein using the technique pioneered by Byler and Susi [2] for IR spectroscopy. Fig 2 shows distinct spectra for vibrations related to the C=O on the protein backbone for bacteriorhodopsin which is largely B sheet and ompF porin that is predominately a helix. Point defects have traditionally been a "blind spot' in the TEM of materials. The ability to detect point defect states in band gaps of semiconductors and insulators is a significant advance. The first applications were color centers in alkali halides, though more recently detection of point defect states in
doi:10.1017/s1431927620019194 fatcat:yoa6o2vognhpfdr5o7yblc3q3q

Transpiration in 15 Tree Species Grown on a Phytocapped Landfill Site

Kartik Venkatraman, Nanjappa Ashwath
2016 Hydrology Current Research  
Citation: Venkatraman K, Ashwath N (2016) Transpiration in 15 Tree Species Grown on a Phytocapped Landfill Site.  ...  Citation: Venkatraman K, Ashwath N (2016) Transpiration in 15 Tree Species Grown on a Phytocapped Landfill Site.  ... 
doi:10.4172/2157-7587.1000236 fatcat:hj2gskffqvgjpfo3vrdstwhybi

Structure, molecular dynamics, and stress in a linear polymer under dynamic strain [article]

Prashant Kumar Srivastava, Kartik Venkatraman
2010 arXiv   pre-print
Venkatraman List of Tables 1 Scaled parameters 7 Nomenclature Roman Symbols b i Bond vector between the united atoms i − 1 and i f ij force on united atom G H t H H matrix consisting of edge vectors  ...  length on radius of gyration 22 31 Effect of chain length on mass ratios 23 32 Effect of chain length on mean bond angle 23 33 Effect of chain length on mean chain angle 24 Prashant Kumar Srivastava & Kartik  ... 
arXiv:1012.5588v1 fatcat:ngqa27lnpzcrfdko3nbklg32c4

Query optimization of distributed pattern matching

Jiewen Huang, Kartik Venkatraman, Daniel J. Abadi
2014 2014 IEEE 30th International Conference on Data Engineering  
Greedy algorithms for subgraph pattern matching operations are often sufficient when the graph data set can be held in memory on a single machine. However, as graph data sets increasingly expand and require external storage and partitioning across a cluster of machines, more sophisticated query optimization techniques become critical to avoid explosions in query latency. In this paper, we introduce several query optimization techniques for distributed graph pattern matching. These techniques
more » ... lude (1) a System-R style dynamic programming-based optimization algorithm that considers both linear and bushy plans, (2) a cycle detection-based algorithm that leverages cycles to reduce intermediate result set sizes, and (3) a computation reusing technique that eliminates redundant query execution and data transfer over the network. Experimental results show that these algorithms can lead to an order of magnitude improvement in query performance.
doi:10.1109/icde.2014.6816640 dblp:conf/icde/HuangVA14 fatcat:oy6twopc5jhhdhrnkizrtkntbu

Simultaneous excitation of phonons at the center and boundaries of Brillouin zones with high energy electron beams [article]

Kartik Venkatraman, Peter A. Crozier
2020 arXiv   pre-print
High energy electron beams can now be routinely focused to 1-2 Å and offer the ability to obtain vibrational information from materials using monochromated electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM). Here it is shown that long and short wavelength phonons can be probed simultaneously with on-axis vibrational STEM EELS. The advantage of using focused electron beams is that the short wavelength phonons are probed via impact scattering while the
more » ... ong-wavelength modes are probed via dipole scattering. The localized character of the short-wavelength modes is demonstrated by scanning the electron beam across the edge of a hexagonal boron nitride nanoparticle. It is found that the condition required for high spatial resolution STEM imaging also correlates with the condition to enhance the short-wavelength phonon contribution to the vibrational energy-loss spectrum. Probing short-wavelength phonons at high spatial resolution with on-axis vibrational STEM EELS will help develop a fundamental connection between vibrational excitations and bonding arrangements at atomic scale heterogeneities in materials.
arXiv:2010.14378v1 fatcat:b7zqf5j2sja5lee3if75pmu5aa

Can phytocapping technique reduce methane emission from municipal landfills?

Kartik Venkatraman, Nanjappa Ashwath
2009 International Journal of Environmental Technology and Management  
METHODS Details of establishing the Phytocapping trial are provided in Venkatraman and Ashwath (2005) , Venkatraman and Ashwath (2006) , and Venkatraman and Ashwath (2007) .  ...  include natural attenuation of landfill-generated methane through aerobic oxidation in landfill soils (Grossman et al. 2002) , and the use of 'Phytocapping' systems(Fig 2) (Ashwath and Pangahas 2005; Venkatraman  ... 
doi:10.1504/ijetm.2009.021573 fatcat:pde6nuhwqba7dkcs7evgwbjzru

Background Modelling for Quantitative Analysis in Vibrational EELS

Barnaby D.A. Levin, Kartik Venkatraman, Diane M. Haiber, Katia March, Peter A. Crozier
2019 Microscopy and Microanalysis  
Vibrational peaks in electron energy loss spectroscopy (EELS) are typically located on a rapidly falling background, arising from both the tail of the zero-loss peak, and non-characteristic phonon losses. The signal-to-background ratio is often quite small (~10-20%), which makes accurate background modelling and peak fitting essential for revealing subtle differences in characteristic peak shapes and intensities. 674
doi:10.1017/s1431927619004100 fatcat:4yp7sofbjzhpnawhwfhtyj67v4

Exploring Phononic and Photonic Excitations with Monochromated STEM EELS

Kartik Venkatraman, Qianlang Liu, Barnaby Levin, Katia March, Peter Crozier
2020 Microscopy and Microanalysis  
The enhanced energy resolution of recently developed monochromators now make it possible to use electron energy-loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) to probe materials systems in new ways. This powerful spectroscopic capability combined with the small focused electron probe opens the door to explore photonic and phononic/vibrational excitations with high spatial resolution [1-3]. Here we describe recent advances leading to atomic resolution
more » ... spectroscopy and novel approaches to probe guided photonic modes in dielectric particles.
doi:10.1017/s1431927620018310 fatcat:qspmz4kjvbfj7ca7jave2sprky

Canopy Rainfall Intercepted by Nineteen Tree Species Grown on a Phytocapped Landfill

Kartik Venkatraman, Nanjappa Ashwath
2016 International Journal of Waste Resources  
Citation: Venkatraman K, Ashwath N (2016) Canopy Rainfall Intercepted by Nineteen Tree Species Grown on a Phytocapped Landfill.  ... 
doi:10.4172/2252-5211.1000202 fatcat:k2uzidtaczcwtauwlxdp7ctmdm

Nature of the Vibrational-Loss EELS Peaks Measured from Ionic Specimens

R.F. Egerton, Katia March, Kartik Venkatraman, Peter A. Crozier
2019 Microscopy and Microanalysis  
The vibrational-loss (phonon) features measured by monochromated electron energy-loss spectroscopy of ionic or partially ionic materials are dominated by dipole scattering and characterized by a narrow Lorentzian angular distribution of scattered intensity. The same features are therefore visible in infraredabsorption spectra and are fully characterized in terms of a wavelength-dependent complex permittivity. For the case of a parallel-slab specimen, Kröger [1] provided analytical expressions
more » ... r the energy-loss probability, which are easily evaluated given dielectric data in the UV, visible or IR regions [2]. Results for MgO and SiO 2 are given in Fig. 1 , for specimen thicknesses t between 100 nm and 2500 nm. Peaks in the energy-differential probability dP/dΕ corresponding to a bulk excitation (B) scale in rough proportion to t, but more rapidly for thin specimens due to the begrenzungs effect [3]. Surface-mode excitations (S) show a sub-linear t-dependence, arising from strong coupling between the two surfaces. Plots of d 2 P/dΕdt display an opposite behavior. Surface and bulk modes can also be distinguished on the basis of their different angular dependence of scattering, and from their peak energies, which increase with specimen thickness in the case of surface modes. We have used a Nion HERMES monochromated STEM to measure the vibrational-peak intensities in several materials, at an incident energy of 60 keV and with an energy resolution of 8 -16 meV (Fig. 2) . Local thickness t was estimated by recording the low-loss region and using the log-ratio method and the Kramers-Kronig sum rule [3]. The graph in Fig. 2 shows the probability P LO = I LO /I 0 for a hexagonal-BN specimen, I 0 being the integrated zero-loss intensity and I LO the combined intensity of surface and bulk longitudinal-optical peaks (above background) in the energy range 0.15 -0.20 eV. Elastic scattering was excluded by a 10mrad spectrometer-entrance aperture. As a sum of bulk and surface peaks, P LO is seen consist of two components. One of them is proportional to thickness and arises from the first "bulk" term in the Kröger formula. The second component derives from three surface-dependent terms and is apparently independent of thickness in the close-coupling situation (t << λ LO ) that exists for thin TEM specimens. Because of the begrenzungs effect, this simple thickness scaling is not expected if intensities of the individual bulk and surface peaks are measured.
doi:10.1017/s1431927619003829 fatcat:5htnq4hlyvek7gmecmvnte4o7y
« Previous Showing results 1 — 15 out of 44 results