Bruno Silva - Academia.edu (original) (raw)

Papers by Bruno Silva

Research paper thumbnail of Dependability models for designing disaster tolerant cloud computing systems

2013 43rd Annual IEEE/IFIP International Conference on Dependable Systems and Networks (DSN), 2013

Research paper thumbnail of Decrease in APP and CP mRNA expression supports impairment of iron export in Alzheimer’s disease patients

Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease, 2015

Alzheimer's disease (AD) is a neurodegenerative disorder of still unknown etiology and the leadin... more Alzheimer's disease (AD) is a neurodegenerative disorder of still unknown etiology and the leading cause of dementia worldwide. Besides its main neuropathological hallmarks, a dysfunctional homeostasis of transition metals has been reported to play a pivotal role in the pathogenesis of this disease. Dysregulation of iron (Fe) metabolism in AD has been suggested, particularly at the level of cellular iron efflux. Herein, we intended to further clarify the molecular mechanisms underlying Fe homeostasis in AD. In order to achieve this goal, the expression of specific Fe metabolism-related genes directly involved in Fe regulation and export was assessed in peripheral blood mononuclear cells (PBMCs) from 73 AD patients and 74 controls by quantitative PCR. The results obtained showed a significant decrease in the expression of aconitase 1 (ACO1; P = 0.007); ceruloplasmin (CP; P b 0.001) and amyloid-beta precursor protein (APP; P = 0.006) genes in AD patients compared with healthy volunteers. These observations point out to a significant downregulation in the expression of genes associated with ferroportin-mediated cellular Fe export in PBMCs from AD patients, when compared to controls. Taken together, these findings support previous studies suggesting impairment of Fe homeostasis in AD, which may lead to cellular Fe retention and oxidative stress, a typical feature of this disease.

Research paper thumbnail of An overview of molecular basis of iron metabolism regulation and the associated pathologies

Biochimica et biophysica acta, Jan 2, 2015

Iron is essential for several vital biological processes. Its deficiency or overload drive to the... more Iron is essential for several vital biological processes. Its deficiency or overload drive to the development of several pathologies. To maintain iron homeostasis, the organism controls the dietary iron absorption by enterocytes, its recycling by macrophages and storage in hepatocytes. These processes are mainly controlled by hepcidin, a liver-derived hormone which synthesis is regulated by iron levels, inflammation, infection, anemia and erythropoiesis. Besides the systemic regulation of iron metabolism mediated by hepcidin, cellular regulatory processes also occur. Cells are able to regulate themselves the expression of the iron metabolism-related genes through different post-transcriptional mechanisms, as the alternative splicing, microRNAs, the IRP/IREs system and the proteolytic cleavage. Whenever those mechanisms are disturbed, due to genetic or environmental factors, iron homeostasis is disrupted and iron related pathologies may arise.

Research paper thumbnail of GeoClouds Modcs: A perfomability evaluation tool for disaster tolerant IaaS clouds

2014 IEEE International Systems Conference Proceedings, 2014

Performance and availability are key aspects to evaluate the quality of cloud computing systems. ... more Performance and availability are key aspects to evaluate the quality of cloud computing systems. The assessment of these systems should consider the effects of queuing and failure/recovery behavior of data center subsystems and disaster occurrences. Additionally, penalties may be applied if the defined quality level of SLA contracts is not satisfied. Thus, IaaS providers need to evaluate the performability level of its environment, considering, also, the possibility of disasters. A possible approach to protect cloud systems from natural disasters corresponds to the utilization of redundant data centers located far enough apart. However, the time to back up the VM data increases with the distance. To accomplish these issues, we propose a user-friendly tool, namely GeoClouds Modcs, for evaluating distributed cloud computing systems deployed into multiple data centers considering disaster occurrence. The proposed environment adopts a hybrid heterogeneous modeling approach, which includes Reliability Block Diagrams (RBD), Stochastic Petri Nets (SPN) and Cloud System High-Level models to perform the system evaluation. For specialized users, the tool also provides specific features that enable edit and evaluate the result SPN and RBD models on external evaluation tools (i.e., Mercury and TimeNET). To illustrate the proposed tool's usability, we present a case study that evaluates a cloud computing distributed in different cities considering diverse user loads.

Research paper thumbnail of Evaluating the Power Consumption of Wireless Sensor Network Applications Using Models

Research paper thumbnail of Modeling hard real-time systems considering inter-task relations, dynamic voltage scaling and overheads

Microprocessors and Microsystems, 2008

Dynamic voltage scaling (DVS) has been adopted as an effective technique for reducing energy cons... more Dynamic voltage scaling (DVS) has been adopted as an effective technique for reducing energy consumption in embedded systems. Although several scheduling approaches have been developed to address voltage scaling together with stringent timing constraints, inter-task relations have been neglected. This work presents a pre-runtime method for hard real-time systems scheduling considering dynamic voltage scaling, overheads and inter-task relations. The proposed work considers time Petri nets as a formal model in order to provide a basis for precise schedule generation as well as to allow property analysis and verification. Experimental results depict the proposed approach feasibility, in the sense that energy consumption is minimized as well as system constraints are met.

Research paper thumbnail of Synthetic Workload Generation for Capacity Planning of Virtual Server Environments

Systems, Man and …, 2009

Capacity planning tools aim at monitoring and evaluating computational infrastructures resources ... more Capacity planning tools aim at monitoring and evaluating computational infrastructures resources in terms of workloads. The Capacity Advisor is a capacity planning tool inside the HP Virtual Server Environment-VSE. This paper describes the development and use of a synthetic workload generator named WGCap (Workload Generator for Capacity Advisor), a flexible synthetic workload generator that generates traces to be imported into the Capacity Advisor for simulating the consumption of resources like CPU demand, memory size, disk data rate and network data rate. The workload generation is reliable and flexible, allowing the generation of workloads based on actual traces or on a significant set of probability distributions and statistical summaries. Index Terms-Synthetic workload generation, capacity planning, random variates.

Research paper thumbnail of A hybrid DVS scheduling approach for hard real-time systems

Dynamic Voltage Scaling (DVS) has been largely adopted as an effective technology for reducing en... more Dynamic Voltage Scaling (DVS) has been largely adopted as an effective technology for reducing energy consumption in embedded systems. Since the usage of DVS may affect the timing constraints of a hard real-time system, over the last decade, several pre-runtime as well as runtime scheduling approaches have been developed to tackle such an issue. Nevertheless, both have drawbacks that can be mitigated using a joint approach. This paper proposes a hybrid DVS scheduling approach for energy-constrained hard real-time systems, taking into account overheads, precedence and exclusion relations. The proposed method adopts a formal model based on time Petri nets in order to provide feasible schedules that satisfy timing and energy constraints.

Research paper thumbnail of Survivability Evaluation of Disaster Tolerant Cloud Computing Systems

A prominent type of cloud service is the Infrastructure-as-a-Service (IaaS), which delivers, on-d... more A prominent type of cloud service is the Infrastructure-as-a-Service (IaaS), which delivers, on-demand, computing resources in the form of virtual machines (VMs) satisfying user needs. In such systems, penalties may be applied if the defined quality level of service level agreement (SLA) is not satisfied. Therefore, high availability is a critical requirement of these systems. A strategy to protect such systems from natural or manmade disasters corresponds to the utilization of multiple data centers located into different geographical locations to provide the service. Considering such systems, redundancy mechanisms can be adopted to receive copies of VM images during data center operation. Hence, whenever a disaster makes one data center unavailable, the VMs can be re-instantiated in other operational data center. Modeling techniques, with a strong mathematical foundation, such as Stochastic Petri Nets (SPN) can be adopted to evaluate survivability in these complex infrastructures. This work presents SPN models to evaluate survivability metrics in IaaS systems deployed into geographically distributed data centers taking into account disaster occurrences. Using the proposed models, IaaS providers can evaluate the impact of VM transmission time and the VM backup period on survivability metrics. A case study is provided to illustrate the effectiveness of the proposed work.

Research paper thumbnail of Dependability models for designing disaster tolerant cloud computing systems

2013 43rd Annual IEEE/IFIP International Conference on Dependable Systems and Networks (DSN), 2013

Research paper thumbnail of Decrease in APP and CP mRNA expression supports impairment of iron export in Alzheimer’s disease patients

Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease, 2015

Alzheimer's disease (AD) is a neurodegenerative disorder of still unknown etiology and the leadin... more Alzheimer's disease (AD) is a neurodegenerative disorder of still unknown etiology and the leading cause of dementia worldwide. Besides its main neuropathological hallmarks, a dysfunctional homeostasis of transition metals has been reported to play a pivotal role in the pathogenesis of this disease. Dysregulation of iron (Fe) metabolism in AD has been suggested, particularly at the level of cellular iron efflux. Herein, we intended to further clarify the molecular mechanisms underlying Fe homeostasis in AD. In order to achieve this goal, the expression of specific Fe metabolism-related genes directly involved in Fe regulation and export was assessed in peripheral blood mononuclear cells (PBMCs) from 73 AD patients and 74 controls by quantitative PCR. The results obtained showed a significant decrease in the expression of aconitase 1 (ACO1; P = 0.007); ceruloplasmin (CP; P b 0.001) and amyloid-beta precursor protein (APP; P = 0.006) genes in AD patients compared with healthy volunteers. These observations point out to a significant downregulation in the expression of genes associated with ferroportin-mediated cellular Fe export in PBMCs from AD patients, when compared to controls. Taken together, these findings support previous studies suggesting impairment of Fe homeostasis in AD, which may lead to cellular Fe retention and oxidative stress, a typical feature of this disease.

Research paper thumbnail of An overview of molecular basis of iron metabolism regulation and the associated pathologies

Biochimica et biophysica acta, Jan 2, 2015

Iron is essential for several vital biological processes. Its deficiency or overload drive to the... more Iron is essential for several vital biological processes. Its deficiency or overload drive to the development of several pathologies. To maintain iron homeostasis, the organism controls the dietary iron absorption by enterocytes, its recycling by macrophages and storage in hepatocytes. These processes are mainly controlled by hepcidin, a liver-derived hormone which synthesis is regulated by iron levels, inflammation, infection, anemia and erythropoiesis. Besides the systemic regulation of iron metabolism mediated by hepcidin, cellular regulatory processes also occur. Cells are able to regulate themselves the expression of the iron metabolism-related genes through different post-transcriptional mechanisms, as the alternative splicing, microRNAs, the IRP/IREs system and the proteolytic cleavage. Whenever those mechanisms are disturbed, due to genetic or environmental factors, iron homeostasis is disrupted and iron related pathologies may arise.

Research paper thumbnail of GeoClouds Modcs: A perfomability evaluation tool for disaster tolerant IaaS clouds

2014 IEEE International Systems Conference Proceedings, 2014

Performance and availability are key aspects to evaluate the quality of cloud computing systems. ... more Performance and availability are key aspects to evaluate the quality of cloud computing systems. The assessment of these systems should consider the effects of queuing and failure/recovery behavior of data center subsystems and disaster occurrences. Additionally, penalties may be applied if the defined quality level of SLA contracts is not satisfied. Thus, IaaS providers need to evaluate the performability level of its environment, considering, also, the possibility of disasters. A possible approach to protect cloud systems from natural disasters corresponds to the utilization of redundant data centers located far enough apart. However, the time to back up the VM data increases with the distance. To accomplish these issues, we propose a user-friendly tool, namely GeoClouds Modcs, for evaluating distributed cloud computing systems deployed into multiple data centers considering disaster occurrence. The proposed environment adopts a hybrid heterogeneous modeling approach, which includes Reliability Block Diagrams (RBD), Stochastic Petri Nets (SPN) and Cloud System High-Level models to perform the system evaluation. For specialized users, the tool also provides specific features that enable edit and evaluate the result SPN and RBD models on external evaluation tools (i.e., Mercury and TimeNET). To illustrate the proposed tool's usability, we present a case study that evaluates a cloud computing distributed in different cities considering diverse user loads.

Research paper thumbnail of Evaluating the Power Consumption of Wireless Sensor Network Applications Using Models

Research paper thumbnail of Modeling hard real-time systems considering inter-task relations, dynamic voltage scaling and overheads

Microprocessors and Microsystems, 2008

Dynamic voltage scaling (DVS) has been adopted as an effective technique for reducing energy cons... more Dynamic voltage scaling (DVS) has been adopted as an effective technique for reducing energy consumption in embedded systems. Although several scheduling approaches have been developed to address voltage scaling together with stringent timing constraints, inter-task relations have been neglected. This work presents a pre-runtime method for hard real-time systems scheduling considering dynamic voltage scaling, overheads and inter-task relations. The proposed work considers time Petri nets as a formal model in order to provide a basis for precise schedule generation as well as to allow property analysis and verification. Experimental results depict the proposed approach feasibility, in the sense that energy consumption is minimized as well as system constraints are met.

Research paper thumbnail of Synthetic Workload Generation for Capacity Planning of Virtual Server Environments

Systems, Man and …, 2009

Capacity planning tools aim at monitoring and evaluating computational infrastructures resources ... more Capacity planning tools aim at monitoring and evaluating computational infrastructures resources in terms of workloads. The Capacity Advisor is a capacity planning tool inside the HP Virtual Server Environment-VSE. This paper describes the development and use of a synthetic workload generator named WGCap (Workload Generator for Capacity Advisor), a flexible synthetic workload generator that generates traces to be imported into the Capacity Advisor for simulating the consumption of resources like CPU demand, memory size, disk data rate and network data rate. The workload generation is reliable and flexible, allowing the generation of workloads based on actual traces or on a significant set of probability distributions and statistical summaries. Index Terms-Synthetic workload generation, capacity planning, random variates.

Research paper thumbnail of A hybrid DVS scheduling approach for hard real-time systems

Dynamic Voltage Scaling (DVS) has been largely adopted as an effective technology for reducing en... more Dynamic Voltage Scaling (DVS) has been largely adopted as an effective technology for reducing energy consumption in embedded systems. Since the usage of DVS may affect the timing constraints of a hard real-time system, over the last decade, several pre-runtime as well as runtime scheduling approaches have been developed to tackle such an issue. Nevertheless, both have drawbacks that can be mitigated using a joint approach. This paper proposes a hybrid DVS scheduling approach for energy-constrained hard real-time systems, taking into account overheads, precedence and exclusion relations. The proposed method adopts a formal model based on time Petri nets in order to provide feasible schedules that satisfy timing and energy constraints.

Research paper thumbnail of Survivability Evaluation of Disaster Tolerant Cloud Computing Systems

A prominent type of cloud service is the Infrastructure-as-a-Service (IaaS), which delivers, on-d... more A prominent type of cloud service is the Infrastructure-as-a-Service (IaaS), which delivers, on-demand, computing resources in the form of virtual machines (VMs) satisfying user needs. In such systems, penalties may be applied if the defined quality level of service level agreement (SLA) is not satisfied. Therefore, high availability is a critical requirement of these systems. A strategy to protect such systems from natural or manmade disasters corresponds to the utilization of multiple data centers located into different geographical locations to provide the service. Considering such systems, redundancy mechanisms can be adopted to receive copies of VM images during data center operation. Hence, whenever a disaster makes one data center unavailable, the VMs can be re-instantiated in other operational data center. Modeling techniques, with a strong mathematical foundation, such as Stochastic Petri Nets (SPN) can be adopted to evaluate survivability in these complex infrastructures. This work presents SPN models to evaluate survivability metrics in IaaS systems deployed into geographically distributed data centers taking into account disaster occurrences. Using the proposed models, IaaS providers can evaluate the impact of VM transmission time and the VM backup period on survivability metrics. A case study is provided to illustrate the effectiveness of the proposed work.