Rohan Bansal - Academia.edu (original) (raw)

Papers by Rohan Bansal

This paper presents recent progress on scanning laser epitaxy, a laser manufacturing technique be... more This paper presents recent progress on scanning laser epitaxy, a laser manufacturing technique being developed for achieving single crystal growth in nickel‐based superalloys. Investigations have been performed for creating monolithic deposits on like chemistry single‐crystal nickel superalloy substrates. Progress in the areas of microstructure development and process control will be discussed in the context of repairing high‐value single‐crystal turbine engine components. This work is funded by the Office of Naval Research contract #N00173‐07‐1‐G012. Introduction In the course of a single crystal (SX) airfoil’s life, damage and wear occur on the leading tip in the amount if 0.5 to 1 mm, causing the turbine's performance to eventually deviate from design specifications. Once this occurs, the damaged airfoils must be replaced at a cost of several thousand dollars each. When considering that a turbine engine contains several hundred airfoils split between the various stages, the c...

Introduction: Traumatic neglected dislocations of hip in children are rare entity. Neglected trau... more Introduction: Traumatic neglected dislocations of hip in children are rare entity. Neglected traumatic dislocations of hip in children along with heterotopic ossification are still rare. Post traumatic neglected hip dislocations are to be diagnosed as early as possible and have to be treated with precision and aggression as the outcome of treatment for the same is not predictable. Case Report: 5 year female with post-traumatic neglected hip dislocation with heterotopic ossification forming a pseudoacetabulum postero-superiorly in which femur head was lodged. The girl was operated by open reduction using Moore’s Posterior approach and showed good results. Here is a mention of a rare case with a good 18 months follow up with no complication. Conclusions: Post-traumatic neglected posterior hip dislocation mostly requires open reduction and relocation of femoral head in original acetabulum with concentric reduction. Heterotopic ossification is a rare but known complication of traumatic ...

Journal of the Asia Pacific Economy

Abstract The COVID-19 pandemic has led to major learning about the social and economic losses tha... more Abstract The COVID-19 pandemic has led to major learning about the social and economic losses that an external shock to the system can cause. In this paper, we examine some sustainability issues focusing on three key focal points of sustainable development – economic growth, poverty and inequality in the context of climate change. We focus on the inter-relationship between economic growth, investment, labour force participation, energy consumption, poverty and inequality under alternative scenarios using the global framing of Shared Socio-Economic Pathways (SSPs). An econometric model is used for estimating the relationship between GDP and its determinants along with fitting a General Quadratic and/or Beta Lorenz curve using the World Bank’s Povcal software for determining the relationship between income, poverty and inequality. Alternative GDP growth paths, redistribution assumptions and poverty lines are used for simulations which reveal the extent of sensitivity of the developmental targets to scenarios up to 2030.

2021 IEEE Symposium on Security and Privacy (SP)

Journal of biomechanical engineering, Jan 19, 2018

A subset of temporomandibular joint (TMJ) disorders are attributed to joint degeneration. The pig... more A subset of temporomandibular joint (TMJ) disorders are attributed to joint degeneration. The pig has been considered the preferred in-vivo model for the evaluation of potential therapies for TMJ disorders, and practical considerations such as cost and husbandry issues have favored the use of young, skeletally immature animals. However, the effect of growth on the biochemical and biomechanical properties of the TMJ disc and articulating cartilage has not been examined. The present study investigates the effect of age on the biochemical and biomechanical properties of healthy porcine TMJs at 3, 6, and 9 months of age. DNA , hyrdroxyproline, and glycosaminoglycan (GAG) content were determined and the discs and condyles were tested in uniaxial unconfined stress relaxation compression from 10% - 30% strain. TMJ discs were further assessed with a tensile test to failure technique, which included the ability to test multiple samples from the same region of an individual disc to minimize t...

Journal of orthopaedic case reports

Traumatic neglected dislocations of hip in children are rare entity. Neglected traumatic dislocat... more Traumatic neglected dislocations of hip in children are rare entity. Neglected traumatic dislocations of hip in children along with heterotopic ossification are still rare. Post traumatic neglected hip dislocations are to be diagnosed as early as possible and have to be treated with precision and aggression as the outcome of treatment for the same is not predictable. 5 year female with post-traumatic neglected hip dislocation with heterotopic ossification forming a pseudoacetabulum postero-superiorly in which femur head was lodged. The girl was operated by open reduction using Moore's Posterior approach and showed good results. Here is a mention of a rare case with a good 18 months follow up with no complication. Post-traumatic neglected posterior hip dislocation mostly requires open reduction and relocation of femoral head in original acetabulum with concentric reduction. Heterotopic ossification is a rare but known complication of traumatic dislocation of hip in children. Good...

Urologic Clinics of North America, 2016

The relationship between obesity and hypogonadism is complicated. The relationship is bidirection... more The relationship between obesity and hypogonadism is complicated. The relationship is bidirectional and there are numerous causative and correlative factors on both sides of the equation. Obesity is increasing in prevalence in epidemic proportions. Likewise, we are beginning to see the rapid increase in the incidence of male hypogonadism. It is only recently that we are learning the ways in which these 2 conditions exacerbate each other, and we are only beginning to understand how by treating one of these conditions, we can help to treat the other as well.

Advanced Engineering Materials, 2015

ABSTRACT This article demonstrates single-pass fabrication of thick, crack-free deposits of René ... more ABSTRACT This article demonstrates single-pass fabrication of thick, crack-free deposits of René 80, a high gamma-prime “non-weldable” superalloy, atop like-chemistry substrates through scanning laser epitaxy (SLE), a metal powder bed-based laser additive manufacturing (AM) technique. Microstructural investigations and processing zone identification are presented. Optical microscopy and scanning electron microscopy reveal the segregated dendritic microstructure with the presence of finer carbides and primary γ′ particles. Transmission electron microscopy reveals a bimodal distribution of finer secondary γ′ particles in the deposit region. Microindentation hardness measurements show an increase in the hardness value by 25% in the deposit region compared to the cast substrate due to microstructural refinement. In addition to the achievement of metallurgical continuity across the interface and improved hardness in the deposit, the crack-free deposits obtained here for René 80 represent one of the few successes reported for a non-weldable alloy of its kind. The results presented here illustrate the significant potential of SLE for the AM-based repair of existing and AM-based construction of entirely new gas turbine hot-section components utilizing powders of high γ′ nickel-based superalloys that have long been known to have high tendency for cracking under the processing conditions associated with traditional welding, joining, and cladding approaches.

ASME 2011 Dynamic Systems and Control Conference and Bath/ASME Symposium on Fluid Power and Motion Control, Volume 1, 2011

This paper describes the development of a feedback controller for rejecting wind disturbances on ... more This paper describes the development of a feedback controller for rejecting wind disturbances on a crane payload. The goal of this research is to perform in-situ parameter sensitivity testing that is specific to a given crane structure. Through experimentation, this paper evaluates the robustness of a closed-loop controller that implements station keeping on a bridge crane. A set of general trends were developed to describe how altering system parameters and operating conditions affected controller performance. Such findings are not limited to single parameter characterization and can be extended to multiple variables given specific system specifications.

International Journal of Physiotherapy and Research, 2015

Metallurgical and Materials Transactions B, 2014

Metallurgical and Materials Transactions B, 2014

ABSTRACT Part I [Metall. Mater. Trans. B, 2014, DOI:10.1007/s11663-014-0117-9] presented a compre... more ABSTRACT Part I [Metall. Mater. Trans. B, 2014, DOI:10.1007/s11663-014-0117-9] presented a comprehensive thermal, fluid flow, and solidification model that can predict the temperature distribution and flow characteristics for the processing of CMSX-4 alloy powder through scanning laser epitaxy (SLE). SLE is an additive manufacturing technology aimed at the creation of equiaxed, directionally solidified and single-crystal (SX) deposits of nickel-based superalloys using a fast-scanning laser beam. Part II here further explores the Marangoni convection-based model to predict the solidification microstructure as a function of the conditions at the trailing edge of the melt pool formed during the SLE process. Empirical values for several microstructural characteristics such as the primary dendrite arm spacing (PDAS), the columnar-to-equiaxed transition (CET) criterion and the oriented-to-misoriented transition (OMT) criterion are obtained. Optical microscopy provides visual information on the various microstructural characteristics of the deposited material such as melt depth, CET location, OMT location, PDAS, etc. A quantitative and consistent investigation of this complex set of characteristics is both challenging and unprecedented. A customized image-analysis technique based on active contouring is developed to automatically extract these data from experimental micrographs. Quantitative metallography verifies that even for the raster scan pattern in SLE and the corresponding line heat source assumption, the PDAS follows the growth relation w ~G −0.5V −0.25 (w = PDAS, G = temperature gradient and V = solidification velocity) developed for marginal stability under constrained growth. Models for the CET and OMT are experimentally validated, thereby providing powerful predictive capabilities for controlling the microstructure of SX alloys processed through SLE.

Metallurgical and Materials Transactions B, 2014

ABSTRACT Scanning laser epitaxy (SLE) is a new laser-based additive manufacturing technology unde... more ABSTRACT Scanning laser epitaxy (SLE) is a new laser-based additive manufacturing technology under development at the Georgia Institute of Technology. SLE is aimed at the creation of equiaxed, directionally solidified, and single-crystal deposits of nickel-based superalloys through the melting of alloy powders onto superalloy substrates using a fast scanning Nd:YAG laser beam. The fast galvanometer control movement of the laser (0.2 to 2 m/s) and high-resolution raster scanning (20 to 200 µm line spacing) enables superior thermal control over the solidification process and allows the production of porosity-free, crack-free deposits of more than 1000 µm thickness. Here, we present a combined thermal and fluid flow model of the SLE process applied to alloy CMSX-4 with temperature-dependent thermo-physical properties. With the scanning beam described as a moving line source, the instantaneous melt pool assumes a convex hull shape with distinct leading edge and trailing edge characteristics. Temperature gradients at the leading and trailing edges are of order 2 × 105 and 104 K/m, respectively. Detailed flow analysis provides insights on the flow characteristics of the powder incorporating into the melt pool, showing velocities of order 1 × 10–4 m/s. The Marangoni effect drives this velocity from 10 to 15 times higher depending on the operating parameters. Prediction of the solidification microstructure is based on conditions at the trailing edge of the melt pool. Time tracking of solidification history is incorporated into the model to couple the microstructure prediction model to the thermal-fluid flow model, and to predict the probability of the columnar-to-equiaxed transition. Qualitative agreement is obtained between simulation and experimental result.

Volume 2A: Advanced Manufacturing, 2013

ABSTRACT This paper investigates effects of natural and Marangoni convection on the resultant sol... more ABSTRACT This paper investigates effects of natural and Marangoni convection on the resultant solidification microstructure in the scanning laser epitaxy (SLE) process. SLE is a laser-based additive manufacturing process that is being developed at the Georgia Institute of Technology for the additive manufacturing of nickel-base superalloys components with equiaxed, directionally-solidified or single-crystal microstructures through the laser melting of alloy powders onto superalloy substrates. A combined thermal and fluid flow model of the system simulates a heat source moving over a powder bed and dynamically adjusts the thermophysical property values. The geometrical and thermal parameters of the simulated laser melt pool are used to predict the solidification behavior of the alloy. The effects of natural and Marangoni convection on the resultant microstructure are evaluated through comparison with a pure conduction model. Inclusion of Marangoni effect produces shallower melt pools compared to a pure conduction model. A detailed flow analysis provides insights into the flow characteristics of the powder, the structure of rotational vortices created in the melt pool, and the solidification phenomena in the melt pool. The modeling results are compared with measurements and observation through real-time thermal imaging and video microscopy to understand the flow phenomenon.In contrast to the single weld-bead approach, the raster scan in SLE allows every position in melt pool to be visited twice by the solid-liquid interface as the scan source progresses. To properly address this situation, time tracking is incorporated into the model to correctly couple the microstructure prediction model. An optimization study is carried out to evaluate the critical values of the transition parameters that govern the columnar-to-equiaxed transition (CET) and the oriented-to-misoriented (OMT) transition. This work is sponsored by the Office of Naval Research through grant N00014-11-1-0670.

Journal of Orthopaedic Case Reports, 2013

Osteopoikilosis or osteopathia condensans disseminata is a rare hereditary autosomal dominant scl... more Osteopoikilosis or osteopathia condensans disseminata is a rare hereditary autosomal dominant sclerosing bone dysplasia. Patients are usually asymptomatic and the diagnosis is usually made incidentally on radiographs which show presence of symmetric, multiple, well defined, small ovoid areas of increased radiodensity clustered in peri-articular osseous regions with propensity for epiphyseal and metaphyseal involvement. There are no increased risks of pathological fracture in a case of osteopoikilosis and traumatic fracture healing in a case of osteopoikilosis is similar to fracture occurring in other normal patients. A 34 years male, electrician came with history of accidental fall from height while working in office leading to development of pain and swelling over left lower leg and ankle diagnosed with Ruedi-Allgower classification type I pilon fracture(without fibula fracture) no distal neuro-vascular deficit. Patient was offered surgical treatment in form of open reduction and internal fixation of tibial fracture by plate osteosynthesis using antero-medial approach , showed complete union and was followed up for eight months. Osteopoikilosis has a benign course and it should always be kept as a possible differential diagnosis for osteoblastic metastasis to avoid diagnositic dilemma. Diagnosis can be settled by routine x-rays (for type ,extent and site of lesions, bones affected), clinical features of patient , histopathology and other systemic or pre-existing conditions.

Proceedings of the National Academy of Sciences, 2013

Legionella and Coxiella are intracellular pathogens that use the virulence-related Icm/Dot type-I... more Legionella and Coxiella are intracellular pathogens that use the virulence-related Icm/Dot type-IVB secretion system to translocate effector proteins into host cells during infection. These effectors were previously shown to contain a C-terminal secretion signal required for their translocation. In this research, we implemented a hidden semi-Markov model to characterize the amino acid composition of the signal, thus providing a comprehensive computational model for the secretion signal. This model accounts for dependencies among sites and captures spatial variation in amino acid composition along the secretion signal. To validate our model, we predicted and synthetically constructed an optimal secretion signal whose sequence is different from that of any known effector. We show that this signal efficiently translocates into host cells in an Icm/Dot-dependent manner. Additionally, we predicted in silico and experimentally examined the effects of mutations in the secretion signal, which provided innovative insights into its characteristics. Some effectors were found to lack a strong secretion signal according to our model. We demonstrated that these effectors were highly dependent on the IcmS-IcmW chaperons for their translocation, unlike effectors that harbor a strong secretion signal. Furthermore, our model is innovative because it enables searching ORFs for secretion signals on a genomic scale, which led to the identification and experimental validation of 20 effectors from Legionella pneumophila, Legionella longbeachae, and Coxiella burnetii. Our combined computational and experimental methodology is general and can be applied to the identification of a wide spectrum of protein features that lack sequence conservation but have similar amino acid characteristics.

Nastac/CFD, 2012

Abstract This paper focuses on modeling of the scanning laser epitaxy (SLE) process that is curre... more Abstract This paper focuses on modeling of the scanning laser epitaxy (SLE) process that is currently being investigated and developed at the Georgia Institute of Technology. SLE is a laser-based manufacturing process for the creation of equiaxed, directionally solidified and single-crystal deposits of nickel superalloys onto superalloy substrates through melting and resolidifícation of alloy powders using a scanning laser beam. The thermal modeling of the system, done in a commercial CFD software package, simulates a heat source moving ...

This paper presents recent progress on scanning laser epitaxy, a laser manufacturing technique be... more This paper presents recent progress on scanning laser epitaxy, a laser manufacturing technique being developed for achieving single crystal growth in nickel‐based superalloys. Investigations have been performed for creating monolithic deposits on like chemistry single‐crystal nickel superalloy substrates. Progress in the areas of microstructure development and process control will be discussed in the context of repairing high‐value single‐crystal turbine engine components. This work is funded by the Office of Naval Research contract #N00173‐07‐1‐G012. Introduction In the course of a single crystal (SX) airfoil’s life, damage and wear occur on the leading tip in the amount if 0.5 to 1 mm, causing the turbine's performance to eventually deviate from design specifications. Once this occurs, the damaged airfoils must be replaced at a cost of several thousand dollars each. When considering that a turbine engine contains several hundred airfoils split between the various stages, the c...

Introduction: Traumatic neglected dislocations of hip in children are rare entity. Neglected trau... more Introduction: Traumatic neglected dislocations of hip in children are rare entity. Neglected traumatic dislocations of hip in children along with heterotopic ossification are still rare. Post traumatic neglected hip dislocations are to be diagnosed as early as possible and have to be treated with precision and aggression as the outcome of treatment for the same is not predictable. Case Report: 5 year female with post-traumatic neglected hip dislocation with heterotopic ossification forming a pseudoacetabulum postero-superiorly in which femur head was lodged. The girl was operated by open reduction using Moore’s Posterior approach and showed good results. Here is a mention of a rare case with a good 18 months follow up with no complication. Conclusions: Post-traumatic neglected posterior hip dislocation mostly requires open reduction and relocation of femoral head in original acetabulum with concentric reduction. Heterotopic ossification is a rare but known complication of traumatic ...

Journal of the Asia Pacific Economy

Abstract The COVID-19 pandemic has led to major learning about the social and economic losses tha... more Abstract The COVID-19 pandemic has led to major learning about the social and economic losses that an external shock to the system can cause. In this paper, we examine some sustainability issues focusing on three key focal points of sustainable development – economic growth, poverty and inequality in the context of climate change. We focus on the inter-relationship between economic growth, investment, labour force participation, energy consumption, poverty and inequality under alternative scenarios using the global framing of Shared Socio-Economic Pathways (SSPs). An econometric model is used for estimating the relationship between GDP and its determinants along with fitting a General Quadratic and/or Beta Lorenz curve using the World Bank’s Povcal software for determining the relationship between income, poverty and inequality. Alternative GDP growth paths, redistribution assumptions and poverty lines are used for simulations which reveal the extent of sensitivity of the developmental targets to scenarios up to 2030.

2021 IEEE Symposium on Security and Privacy (SP)

Journal of biomechanical engineering, Jan 19, 2018

A subset of temporomandibular joint (TMJ) disorders are attributed to joint degeneration. The pig... more A subset of temporomandibular joint (TMJ) disorders are attributed to joint degeneration. The pig has been considered the preferred in-vivo model for the evaluation of potential therapies for TMJ disorders, and practical considerations such as cost and husbandry issues have favored the use of young, skeletally immature animals. However, the effect of growth on the biochemical and biomechanical properties of the TMJ disc and articulating cartilage has not been examined. The present study investigates the effect of age on the biochemical and biomechanical properties of healthy porcine TMJs at 3, 6, and 9 months of age. DNA , hyrdroxyproline, and glycosaminoglycan (GAG) content were determined and the discs and condyles were tested in uniaxial unconfined stress relaxation compression from 10% - 30% strain. TMJ discs were further assessed with a tensile test to failure technique, which included the ability to test multiple samples from the same region of an individual disc to minimize t...

Journal of orthopaedic case reports

Traumatic neglected dislocations of hip in children are rare entity. Neglected traumatic dislocat... more Traumatic neglected dislocations of hip in children are rare entity. Neglected traumatic dislocations of hip in children along with heterotopic ossification are still rare. Post traumatic neglected hip dislocations are to be diagnosed as early as possible and have to be treated with precision and aggression as the outcome of treatment for the same is not predictable. 5 year female with post-traumatic neglected hip dislocation with heterotopic ossification forming a pseudoacetabulum postero-superiorly in which femur head was lodged. The girl was operated by open reduction using Moore's Posterior approach and showed good results. Here is a mention of a rare case with a good 18 months follow up with no complication. Post-traumatic neglected posterior hip dislocation mostly requires open reduction and relocation of femoral head in original acetabulum with concentric reduction. Heterotopic ossification is a rare but known complication of traumatic dislocation of hip in children. Good...

Urologic Clinics of North America, 2016

The relationship between obesity and hypogonadism is complicated. The relationship is bidirection... more The relationship between obesity and hypogonadism is complicated. The relationship is bidirectional and there are numerous causative and correlative factors on both sides of the equation. Obesity is increasing in prevalence in epidemic proportions. Likewise, we are beginning to see the rapid increase in the incidence of male hypogonadism. It is only recently that we are learning the ways in which these 2 conditions exacerbate each other, and we are only beginning to understand how by treating one of these conditions, we can help to treat the other as well.

Advanced Engineering Materials, 2015

ABSTRACT This article demonstrates single-pass fabrication of thick, crack-free deposits of René ... more ABSTRACT This article demonstrates single-pass fabrication of thick, crack-free deposits of René 80, a high gamma-prime “non-weldable” superalloy, atop like-chemistry substrates through scanning laser epitaxy (SLE), a metal powder bed-based laser additive manufacturing (AM) technique. Microstructural investigations and processing zone identification are presented. Optical microscopy and scanning electron microscopy reveal the segregated dendritic microstructure with the presence of finer carbides and primary γ′ particles. Transmission electron microscopy reveals a bimodal distribution of finer secondary γ′ particles in the deposit region. Microindentation hardness measurements show an increase in the hardness value by 25% in the deposit region compared to the cast substrate due to microstructural refinement. In addition to the achievement of metallurgical continuity across the interface and improved hardness in the deposit, the crack-free deposits obtained here for René 80 represent one of the few successes reported for a non-weldable alloy of its kind. The results presented here illustrate the significant potential of SLE for the AM-based repair of existing and AM-based construction of entirely new gas turbine hot-section components utilizing powders of high γ′ nickel-based superalloys that have long been known to have high tendency for cracking under the processing conditions associated with traditional welding, joining, and cladding approaches.

ASME 2011 Dynamic Systems and Control Conference and Bath/ASME Symposium on Fluid Power and Motion Control, Volume 1, 2011

This paper describes the development of a feedback controller for rejecting wind disturbances on ... more This paper describes the development of a feedback controller for rejecting wind disturbances on a crane payload. The goal of this research is to perform in-situ parameter sensitivity testing that is specific to a given crane structure. Through experimentation, this paper evaluates the robustness of a closed-loop controller that implements station keeping on a bridge crane. A set of general trends were developed to describe how altering system parameters and operating conditions affected controller performance. Such findings are not limited to single parameter characterization and can be extended to multiple variables given specific system specifications.

International Journal of Physiotherapy and Research, 2015

Metallurgical and Materials Transactions B, 2014

Metallurgical and Materials Transactions B, 2014

ABSTRACT Part I [Metall. Mater. Trans. B, 2014, DOI:10.1007/s11663-014-0117-9] presented a compre... more ABSTRACT Part I [Metall. Mater. Trans. B, 2014, DOI:10.1007/s11663-014-0117-9] presented a comprehensive thermal, fluid flow, and solidification model that can predict the temperature distribution and flow characteristics for the processing of CMSX-4 alloy powder through scanning laser epitaxy (SLE). SLE is an additive manufacturing technology aimed at the creation of equiaxed, directionally solidified and single-crystal (SX) deposits of nickel-based superalloys using a fast-scanning laser beam. Part II here further explores the Marangoni convection-based model to predict the solidification microstructure as a function of the conditions at the trailing edge of the melt pool formed during the SLE process. Empirical values for several microstructural characteristics such as the primary dendrite arm spacing (PDAS), the columnar-to-equiaxed transition (CET) criterion and the oriented-to-misoriented transition (OMT) criterion are obtained. Optical microscopy provides visual information on the various microstructural characteristics of the deposited material such as melt depth, CET location, OMT location, PDAS, etc. A quantitative and consistent investigation of this complex set of characteristics is both challenging and unprecedented. A customized image-analysis technique based on active contouring is developed to automatically extract these data from experimental micrographs. Quantitative metallography verifies that even for the raster scan pattern in SLE and the corresponding line heat source assumption, the PDAS follows the growth relation w ~G −0.5V −0.25 (w = PDAS, G = temperature gradient and V = solidification velocity) developed for marginal stability under constrained growth. Models for the CET and OMT are experimentally validated, thereby providing powerful predictive capabilities for controlling the microstructure of SX alloys processed through SLE.

Metallurgical and Materials Transactions B, 2014

ABSTRACT Scanning laser epitaxy (SLE) is a new laser-based additive manufacturing technology unde... more ABSTRACT Scanning laser epitaxy (SLE) is a new laser-based additive manufacturing technology under development at the Georgia Institute of Technology. SLE is aimed at the creation of equiaxed, directionally solidified, and single-crystal deposits of nickel-based superalloys through the melting of alloy powders onto superalloy substrates using a fast scanning Nd:YAG laser beam. The fast galvanometer control movement of the laser (0.2 to 2 m/s) and high-resolution raster scanning (20 to 200 µm line spacing) enables superior thermal control over the solidification process and allows the production of porosity-free, crack-free deposits of more than 1000 µm thickness. Here, we present a combined thermal and fluid flow model of the SLE process applied to alloy CMSX-4 with temperature-dependent thermo-physical properties. With the scanning beam described as a moving line source, the instantaneous melt pool assumes a convex hull shape with distinct leading edge and trailing edge characteristics. Temperature gradients at the leading and trailing edges are of order 2 × 105 and 104 K/m, respectively. Detailed flow analysis provides insights on the flow characteristics of the powder incorporating into the melt pool, showing velocities of order 1 × 10–4 m/s. The Marangoni effect drives this velocity from 10 to 15 times higher depending on the operating parameters. Prediction of the solidification microstructure is based on conditions at the trailing edge of the melt pool. Time tracking of solidification history is incorporated into the model to couple the microstructure prediction model to the thermal-fluid flow model, and to predict the probability of the columnar-to-equiaxed transition. Qualitative agreement is obtained between simulation and experimental result.

Volume 2A: Advanced Manufacturing, 2013

ABSTRACT This paper investigates effects of natural and Marangoni convection on the resultant sol... more ABSTRACT This paper investigates effects of natural and Marangoni convection on the resultant solidification microstructure in the scanning laser epitaxy (SLE) process. SLE is a laser-based additive manufacturing process that is being developed at the Georgia Institute of Technology for the additive manufacturing of nickel-base superalloys components with equiaxed, directionally-solidified or single-crystal microstructures through the laser melting of alloy powders onto superalloy substrates. A combined thermal and fluid flow model of the system simulates a heat source moving over a powder bed and dynamically adjusts the thermophysical property values. The geometrical and thermal parameters of the simulated laser melt pool are used to predict the solidification behavior of the alloy. The effects of natural and Marangoni convection on the resultant microstructure are evaluated through comparison with a pure conduction model. Inclusion of Marangoni effect produces shallower melt pools compared to a pure conduction model. A detailed flow analysis provides insights into the flow characteristics of the powder, the structure of rotational vortices created in the melt pool, and the solidification phenomena in the melt pool. The modeling results are compared with measurements and observation through real-time thermal imaging and video microscopy to understand the flow phenomenon.In contrast to the single weld-bead approach, the raster scan in SLE allows every position in melt pool to be visited twice by the solid-liquid interface as the scan source progresses. To properly address this situation, time tracking is incorporated into the model to correctly couple the microstructure prediction model. An optimization study is carried out to evaluate the critical values of the transition parameters that govern the columnar-to-equiaxed transition (CET) and the oriented-to-misoriented (OMT) transition. This work is sponsored by the Office of Naval Research through grant N00014-11-1-0670.

Journal of Orthopaedic Case Reports, 2013

Osteopoikilosis or osteopathia condensans disseminata is a rare hereditary autosomal dominant scl... more Osteopoikilosis or osteopathia condensans disseminata is a rare hereditary autosomal dominant sclerosing bone dysplasia. Patients are usually asymptomatic and the diagnosis is usually made incidentally on radiographs which show presence of symmetric, multiple, well defined, small ovoid areas of increased radiodensity clustered in peri-articular osseous regions with propensity for epiphyseal and metaphyseal involvement. There are no increased risks of pathological fracture in a case of osteopoikilosis and traumatic fracture healing in a case of osteopoikilosis is similar to fracture occurring in other normal patients. A 34 years male, electrician came with history of accidental fall from height while working in office leading to development of pain and swelling over left lower leg and ankle diagnosed with Ruedi-Allgower classification type I pilon fracture(without fibula fracture) no distal neuro-vascular deficit. Patient was offered surgical treatment in form of open reduction and internal fixation of tibial fracture by plate osteosynthesis using antero-medial approach , showed complete union and was followed up for eight months. Osteopoikilosis has a benign course and it should always be kept as a possible differential diagnosis for osteoblastic metastasis to avoid diagnositic dilemma. Diagnosis can be settled by routine x-rays (for type ,extent and site of lesions, bones affected), clinical features of patient , histopathology and other systemic or pre-existing conditions.

Proceedings of the National Academy of Sciences, 2013

Legionella and Coxiella are intracellular pathogens that use the virulence-related Icm/Dot type-I... more Legionella and Coxiella are intracellular pathogens that use the virulence-related Icm/Dot type-IVB secretion system to translocate effector proteins into host cells during infection. These effectors were previously shown to contain a C-terminal secretion signal required for their translocation. In this research, we implemented a hidden semi-Markov model to characterize the amino acid composition of the signal, thus providing a comprehensive computational model for the secretion signal. This model accounts for dependencies among sites and captures spatial variation in amino acid composition along the secretion signal. To validate our model, we predicted and synthetically constructed an optimal secretion signal whose sequence is different from that of any known effector. We show that this signal efficiently translocates into host cells in an Icm/Dot-dependent manner. Additionally, we predicted in silico and experimentally examined the effects of mutations in the secretion signal, which provided innovative insights into its characteristics. Some effectors were found to lack a strong secretion signal according to our model. We demonstrated that these effectors were highly dependent on the IcmS-IcmW chaperons for their translocation, unlike effectors that harbor a strong secretion signal. Furthermore, our model is innovative because it enables searching ORFs for secretion signals on a genomic scale, which led to the identification and experimental validation of 20 effectors from Legionella pneumophila, Legionella longbeachae, and Coxiella burnetii. Our combined computational and experimental methodology is general and can be applied to the identification of a wide spectrum of protein features that lack sequence conservation but have similar amino acid characteristics.

Nastac/CFD, 2012

Abstract This paper focuses on modeling of the scanning laser epitaxy (SLE) process that is curre... more Abstract This paper focuses on modeling of the scanning laser epitaxy (SLE) process that is currently being investigated and developed at the Georgia Institute of Technology. SLE is a laser-based manufacturing process for the creation of equiaxed, directionally solidified and single-crystal deposits of nickel superalloys onto superalloy substrates through melting and resolidifícation of alloy powders using a scanning laser beam. The thermal modeling of the system, done in a commercial CFD software package, simulates a heat source moving ...