sandeep reddy - Academia.edu (original) (raw)

Papers by sandeep reddy

Journal of Renewable and Sustainable Energy, 2014

Wave power calculations for a wave energy conversion device connected to a drogue A lack of field... more Wave power calculations for a wave energy conversion device connected to a drogue A lack of field data, visible dominant wave activity in the northern division of Fiji Islands particularly off the southern coast of Taveuni, and increasing cost of nonrenewable energy sources coupled with associated harmful effects to the environment have led to initial wave energy resource assessment. The present work involved twelve months of on-site wave measurements commencing July 2012. The measured data were compared with a 30 yr hindcast WW3 model data from a joint project between the Bureau of Metrology, Australia (BoM) and The Pacific Australia Climate Change Science and Adaption Planning. The model was used to relate to the site characteristic in terms of significant wave-height and period in representation of Fiji's overall wave climate and at the same time validating the model with site measurements. The swell and wind wave components together with its prevailing direction was studied in detail. The calculated average power output was 12 kW/m for an average wave-height of 1 m while a peak wave-height of 3.75 m yielded power output of 24 kW/m. Comparison of the wave climate was also made with in situ wave assessment that was performed off the southern coast of Kadavu in 1994. In addition, two offshore wave energy converters' performance data (power matrix) were used to estimate the expected power generation based on the average sea states to briefly examine the site's potential with current technology. The summer and winter variation in wave power was calculated and wave power statistics such as percentile occurrence were also discussed. The results of the present study provide sufficient evidence of the potential of wave energy on site for future feasibility studies and subsequent power extraction. V C 2014 AIP Publishing LLC. [http://dx.

The Journal of Physical Chemistry B, 2012

A density functional theory based Car−Parrinello molecular dynamics simulation of liquid dimethyl... more A density functional theory based Car−Parrinello molecular dynamics simulation of liquid dimethyl carbonate, an environmentally benign solvent, has been carried out to study its structure and dynamics. Conformational excitations of the molecule have been probed in both its gas and liquid phases. While the cis−cis conformer is the global energy minimum and, thus, the most predominant, at ambient conditions a few percent of molecules are present in the cis−trans conformation as well. The latter possesses a dipole moment of around 4.5 D in the liquid state, a value that is nearly five times as large as that for the cis−cis conformer. Dipole− dipole interactions play a crucial role in the formation of small hydrogen bonded clusters of cis−trans conformers in the liquid. The vibrational spectrum of liquid dimethyl carbonate has been obtained from the trajectory and is shown to agree quite well with available experimental data.

The Journal of Physical Chemistry A, 2012

Gas phase quantum chemical calculations of linear, hydrogen bonded oligomers of carbonic acid hav... more Gas phase quantum chemical calculations of linear, hydrogen bonded oligomers of carbonic acid have been carried out to examine the feasibility for such species to be the building blocks of crystalline carbonic acid. Infrared and Raman vibrational spectra have been calculated and are compared against experimentally known spectra for two polymorphs of carbonic acid. The calculated anharmonic frequencies of the linear oligomer agree well with the experimental data for the centrosymmetric β-carbonic acid, rather than with that for the α polymorph. These calculations strongly suggest that β-carbonic acid should consist of one-dimensional hydrogen bonded carbonic acid molecules in the anti-anti conformation.

IEEE Information Assurance Workshop, 2003

VPOE (virtual private operation environment) is an infrastructure to provide customized services ... more VPOE (virtual private operation environment) is an infrastructure to provide customized services for applications in large-scale heterogeneous networks. In this infrastructure, the programmable network devices - called "middleware boxes" can be deployed at some functional locations in the network and provide services effectively corresponding to the service requirements. The basic functionality of middleware box is to execute customized policies. With the number of applications increasing and new services becoming popular, the policy matching and processing have been becoming a bottleneck for the middleware box performance. We focus on designing a scalable policy processing architecture, aiming to deal with this issue. Particularly, our technologies include: (1) a distributed policy processing architecture for the middleware box; (2) two policy partitioning algorithms to achieve conflict-free policies for the distributed policy processing architecture and guarantee the correctness of the policy execution. We conduct extensive performance evaluations on different architectures and algorithms. The evaluation results show that the distributed architecture can achieve over 70 percent increase of performance/price ratio with proper assignment of the policy distribution degree. The experimental results also demonstrate that to make the policy both partition capable and conflict free, more new policies have to be generated, which can be effectively reduced by using the policy compression schemes.

The Journal of Chemical Physics, 2011

Using multiple computational tools, we examine five candidate crystal structures for β-carbonic a... more Using multiple computational tools, we examine five candidate crystal structures for β-carbonic acid, a molecular crystal of environmental and astrophysical significance. These crystals comprise of hydrogen bonded molecules in either sheetlike or chainlike topologies. Gas phase quantum calculations, empirical force field based crystal structure search, and periodic density functional theory based calculations and finite temperature simulations of these crystals have been carried out. The infrared spectrum calculated from density functional theory based molecular dynamics simulations compares well with experimental data. Results suggest crystals with one-dimensional hydrogen bonding topologies (chainlike) to be more stable than those with two-dimensional (sheetlike) hydrogen bonding networks. We predict that these structures can be distinguished on the basis of their far infrared spectra.

International Journal of Bifurcation and Chaos, 2012

We investigate the origin of various convective patterns for Prandtl number P = 6.8 (for water at... more We investigate the origin of various convective patterns for Prandtl number P = 6.8 (for water at room temperature) using bifurcation diagrams that are constructed using direct numerical simulations (DNS) of Rayleigh-Bénard convection (RBC). Several complex flow patterns resulting from normal bifurcations as well as various instances of "crises" have been observed in the DNS. "Crises" play vital roles in determining various convective flow patterns. After a transition of conduction state to convective roll states, we observe time-periodic and quasiperiodic rolls through Hopf and Neimark-Sacker bifurcations at r 80 and r 500 respectively (where r is the normalized Rayleigh number). The system becomes chaotic at r 750, and the size of the chaotic attractor increases at r 840 through an "attractor-merging crisis" which results in traveling chaotic rolls. For 846 ≤ r ≤ 849, stable fixed points and a chaotic attractor coexist as a result of an inverse subcritical Hopf bifurcation. Subsequently the chaotic attractor disappears through a "boundary crisis" and only stable fixed points remain. These fixed points later become periodic and chaotic through another set of bifurcations which ultimately leads to turbulence. As a function of Rayleigh number, |W 101 | ∼ (r − 1) 0.62 and |θ 101 | ∼ (r − 1) −0.34 (velocity and temperature Fourier coefficient for (1, 0, 1) mode). However the Nusselt number scales as (r − 1) 0.33 .

Inorganic Chemistry, 2012

A three-dimensional (3D) pillared-layer metal-organic framework, [Cd(bipy)(0.5)(Himdc)](DMF)](n) ... more A three-dimensional (3D) pillared-layer metal-organic framework, [Cd(bipy)(0.5)(Himdc)](DMF)](n) (1), (bipy =4,4'-bipyridine and Himdc = 4,5-imidazoledicarboxylate) has been synthesized and structurally characterized. The highly rigid and stable framework contains a 3D channel structure with highly polar pore surfaces decorated with pendant oxygen atoms of the Himdc linkers. The desolvated framework [Cd(bipy)(0.5)(Himdc)](n) (1') is found to exhibit permanent porosity with high H(2) and CO(2) storage capacities. Two H(2) molecules occluded per unit formula of 1' and the corresponding heat of H(2) adsorption (ΔH(H2)) is about ∼9.0 kJ/mol. The high value of ΔH(H2) stems from the preferential electrostatic interaction of H(2) with the pendent oxygen atoms of Himdc and aromatic bipy linkers as determined from first-principles density functional theory (DFT) based calculations. Similarly, DFT studies indicate CO(2) to preferentially interact electrostatically (C(δ+)···O(δ-)) with the uncoordinated pendent oxygen of Himdc. It also interacts with bipy through C-H···O bonding, thus rationalizing the high heat (ΔH(CO2) ∼ 35.4 kJ/mol) of CO(2) uptake. Our work unveiled that better H(2) or CO(2) storage materials can be developed through the immobilization of reactive hetero atoms (O, N) at the pore surfaces in a metal-organic framework.

Chemical Communications, 2014

Carbonic acid (CA) is a crucial species in the equilibrium between carbon dioxide, water and many... more Carbonic acid (CA) is a crucial species in the equilibrium between carbon dioxide, water and many minerals. Yet many of its properties have either not been studied at all, or have been misunderstood. Its short lifetime in the presence of moisture has been a major stumbling block in efforts to studying it. Over the last two decades, there has been a sustained, albeit slow progress in the detection, synthesis and investigations of CA in its various phases - as a molecule in gas phase, in its crystalline state, as an adsorbate on mineral surfaces and in aqueous solutions. For instance, ultrafast time resolved spectroscopic experiments as well as molecular dynamics based free energy calculations using Kohn-Sham density functional theory have shown the pKa of CA to be around 3.5 which makes its acidity comparable to that of formic acid. The composition of its gas phase in terms of its conformer and oligomer population have also been examined. Thin films of crystalline carbonic acid polymorphs have been synthesized and characterized using infrared and Raman spectra. Given the difficulties associated in the conduct of experiments to investigate CA, computational modelling has played a significant role. Using a multi-tiered modelling approach, we have been able to examine several model crystal structures possessing distinctive hydrogen bonding motifs. Their vibrational spectra were compared against those obtained from experiments. A model crystal consisting of hydrogen bonded molecules in a chain-like fashion fits the experimental vibrational spectra of β-carbonic acid better than one in which the motif is two-dimensional (sheet-like). Under dry conditions, we predict such a crystal to be stable below 359 K at 1 atm. In this feature article, we provide a summary of our work on carbonic acid as well as review contributions from others.

Journal of Renewable and Sustainable Energy, 2014

Wave power calculations for a wave energy conversion device connected to a drogue A lack of field... more Wave power calculations for a wave energy conversion device connected to a drogue A lack of field data, visible dominant wave activity in the northern division of Fiji Islands particularly off the southern coast of Taveuni, and increasing cost of nonrenewable energy sources coupled with associated harmful effects to the environment have led to initial wave energy resource assessment. The present work involved twelve months of on-site wave measurements commencing July 2012. The measured data were compared with a 30 yr hindcast WW3 model data from a joint project between the Bureau of Metrology, Australia (BoM) and The Pacific Australia Climate Change Science and Adaption Planning. The model was used to relate to the site characteristic in terms of significant wave-height and period in representation of Fiji's overall wave climate and at the same time validating the model with site measurements. The swell and wind wave components together with its prevailing direction was studied in detail. The calculated average power output was 12 kW/m for an average wave-height of 1 m while a peak wave-height of 3.75 m yielded power output of 24 kW/m. Comparison of the wave climate was also made with in situ wave assessment that was performed off the southern coast of Kadavu in 1994. In addition, two offshore wave energy converters' performance data (power matrix) were used to estimate the expected power generation based on the average sea states to briefly examine the site's potential with current technology. The summer and winter variation in wave power was calculated and wave power statistics such as percentile occurrence were also discussed. The results of the present study provide sufficient evidence of the potential of wave energy on site for future feasibility studies and subsequent power extraction. V C 2014 AIP Publishing LLC. [http://dx.

The Journal of Physical Chemistry B, 2012

A density functional theory based Car−Parrinello molecular dynamics simulation of liquid dimethyl... more A density functional theory based Car−Parrinello molecular dynamics simulation of liquid dimethyl carbonate, an environmentally benign solvent, has been carried out to study its structure and dynamics. Conformational excitations of the molecule have been probed in both its gas and liquid phases. While the cis−cis conformer is the global energy minimum and, thus, the most predominant, at ambient conditions a few percent of molecules are present in the cis−trans conformation as well. The latter possesses a dipole moment of around 4.5 D in the liquid state, a value that is nearly five times as large as that for the cis−cis conformer. Dipole− dipole interactions play a crucial role in the formation of small hydrogen bonded clusters of cis−trans conformers in the liquid. The vibrational spectrum of liquid dimethyl carbonate has been obtained from the trajectory and is shown to agree quite well with available experimental data.

The Journal of Physical Chemistry A, 2012

Gas phase quantum chemical calculations of linear, hydrogen bonded oligomers of carbonic acid hav... more Gas phase quantum chemical calculations of linear, hydrogen bonded oligomers of carbonic acid have been carried out to examine the feasibility for such species to be the building blocks of crystalline carbonic acid. Infrared and Raman vibrational spectra have been calculated and are compared against experimentally known spectra for two polymorphs of carbonic acid. The calculated anharmonic frequencies of the linear oligomer agree well with the experimental data for the centrosymmetric β-carbonic acid, rather than with that for the α polymorph. These calculations strongly suggest that β-carbonic acid should consist of one-dimensional hydrogen bonded carbonic acid molecules in the anti-anti conformation.

IEEE Information Assurance Workshop, 2003

VPOE (virtual private operation environment) is an infrastructure to provide customized services ... more VPOE (virtual private operation environment) is an infrastructure to provide customized services for applications in large-scale heterogeneous networks. In this infrastructure, the programmable network devices - called "middleware boxes" can be deployed at some functional locations in the network and provide services effectively corresponding to the service requirements. The basic functionality of middleware box is to execute customized policies. With the number of applications increasing and new services becoming popular, the policy matching and processing have been becoming a bottleneck for the middleware box performance. We focus on designing a scalable policy processing architecture, aiming to deal with this issue. Particularly, our technologies include: (1) a distributed policy processing architecture for the middleware box; (2) two policy partitioning algorithms to achieve conflict-free policies for the distributed policy processing architecture and guarantee the correctness of the policy execution. We conduct extensive performance evaluations on different architectures and algorithms. The evaluation results show that the distributed architecture can achieve over 70 percent increase of performance/price ratio with proper assignment of the policy distribution degree. The experimental results also demonstrate that to make the policy both partition capable and conflict free, more new policies have to be generated, which can be effectively reduced by using the policy compression schemes.

The Journal of Chemical Physics, 2011

Using multiple computational tools, we examine five candidate crystal structures for β-carbonic a... more Using multiple computational tools, we examine five candidate crystal structures for β-carbonic acid, a molecular crystal of environmental and astrophysical significance. These crystals comprise of hydrogen bonded molecules in either sheetlike or chainlike topologies. Gas phase quantum calculations, empirical force field based crystal structure search, and periodic density functional theory based calculations and finite temperature simulations of these crystals have been carried out. The infrared spectrum calculated from density functional theory based molecular dynamics simulations compares well with experimental data. Results suggest crystals with one-dimensional hydrogen bonding topologies (chainlike) to be more stable than those with two-dimensional (sheetlike) hydrogen bonding networks. We predict that these structures can be distinguished on the basis of their far infrared spectra.

International Journal of Bifurcation and Chaos, 2012

We investigate the origin of various convective patterns for Prandtl number P = 6.8 (for water at... more We investigate the origin of various convective patterns for Prandtl number P = 6.8 (for water at room temperature) using bifurcation diagrams that are constructed using direct numerical simulations (DNS) of Rayleigh-Bénard convection (RBC). Several complex flow patterns resulting from normal bifurcations as well as various instances of "crises" have been observed in the DNS. "Crises" play vital roles in determining various convective flow patterns. After a transition of conduction state to convective roll states, we observe time-periodic and quasiperiodic rolls through Hopf and Neimark-Sacker bifurcations at r 80 and r 500 respectively (where r is the normalized Rayleigh number). The system becomes chaotic at r 750, and the size of the chaotic attractor increases at r 840 through an "attractor-merging crisis" which results in traveling chaotic rolls. For 846 ≤ r ≤ 849, stable fixed points and a chaotic attractor coexist as a result of an inverse subcritical Hopf bifurcation. Subsequently the chaotic attractor disappears through a "boundary crisis" and only stable fixed points remain. These fixed points later become periodic and chaotic through another set of bifurcations which ultimately leads to turbulence. As a function of Rayleigh number, |W 101 | ∼ (r − 1) 0.62 and |θ 101 | ∼ (r − 1) −0.34 (velocity and temperature Fourier coefficient for (1, 0, 1) mode). However the Nusselt number scales as (r − 1) 0.33 .

Inorganic Chemistry, 2012

A three-dimensional (3D) pillared-layer metal-organic framework, [Cd(bipy)(0.5)(Himdc)](DMF)](n) ... more A three-dimensional (3D) pillared-layer metal-organic framework, [Cd(bipy)(0.5)(Himdc)](DMF)](n) (1), (bipy =4,4'-bipyridine and Himdc = 4,5-imidazoledicarboxylate) has been synthesized and structurally characterized. The highly rigid and stable framework contains a 3D channel structure with highly polar pore surfaces decorated with pendant oxygen atoms of the Himdc linkers. The desolvated framework [Cd(bipy)(0.5)(Himdc)](n) (1') is found to exhibit permanent porosity with high H(2) and CO(2) storage capacities. Two H(2) molecules occluded per unit formula of 1' and the corresponding heat of H(2) adsorption (ΔH(H2)) is about ∼9.0 kJ/mol. The high value of ΔH(H2) stems from the preferential electrostatic interaction of H(2) with the pendent oxygen atoms of Himdc and aromatic bipy linkers as determined from first-principles density functional theory (DFT) based calculations. Similarly, DFT studies indicate CO(2) to preferentially interact electrostatically (C(δ+)···O(δ-)) with the uncoordinated pendent oxygen of Himdc. It also interacts with bipy through C-H···O bonding, thus rationalizing the high heat (ΔH(CO2) ∼ 35.4 kJ/mol) of CO(2) uptake. Our work unveiled that better H(2) or CO(2) storage materials can be developed through the immobilization of reactive hetero atoms (O, N) at the pore surfaces in a metal-organic framework.

Chemical Communications, 2014

Carbonic acid (CA) is a crucial species in the equilibrium between carbon dioxide, water and many... more Carbonic acid (CA) is a crucial species in the equilibrium between carbon dioxide, water and many minerals. Yet many of its properties have either not been studied at all, or have been misunderstood. Its short lifetime in the presence of moisture has been a major stumbling block in efforts to studying it. Over the last two decades, there has been a sustained, albeit slow progress in the detection, synthesis and investigations of CA in its various phases - as a molecule in gas phase, in its crystalline state, as an adsorbate on mineral surfaces and in aqueous solutions. For instance, ultrafast time resolved spectroscopic experiments as well as molecular dynamics based free energy calculations using Kohn-Sham density functional theory have shown the pKa of CA to be around 3.5 which makes its acidity comparable to that of formic acid. The composition of its gas phase in terms of its conformer and oligomer population have also been examined. Thin films of crystalline carbonic acid polymorphs have been synthesized and characterized using infrared and Raman spectra. Given the difficulties associated in the conduct of experiments to investigate CA, computational modelling has played a significant role. Using a multi-tiered modelling approach, we have been able to examine several model crystal structures possessing distinctive hydrogen bonding motifs. Their vibrational spectra were compared against those obtained from experiments. A model crystal consisting of hydrogen bonded molecules in a chain-like fashion fits the experimental vibrational spectra of β-carbonic acid better than one in which the motif is two-dimensional (sheet-like). Under dry conditions, we predict such a crystal to be stable below 359 K at 1 atm. In this feature article, we provide a summary of our work on carbonic acid as well as review contributions from others.