528 research outputs found
Beggar Thy Thrifty Neighbour: The International Spillover Effects of Pensions Under Population Ageing
This paper explores the international spillover effects of ageing through capital markets when countries have different pension systems.We use a two-country twoperiod overlapping-generations model, where the two countries only differ in their pension schemes.Two forms of population ageing are considered, namely an increase in longevity and a fall in fertility.It is shown that in the long run a country using a funded pension system experiences negative spillovers from the fact that the other country uses a PAYG system.The short-run spillovers, however, are opposite to the spillovers in the long run.ageing;pensions;spillovers
CRAFT: A library for easier application-level Checkpoint/Restart and Automatic Fault Tolerance
In order to efficiently use the future generations of supercomputers, fault
tolerance and power consumption are two of the prime challenges anticipated by
the High Performance Computing (HPC) community. Checkpoint/Restart (CR) has
been and still is the most widely used technique to deal with hard failures.
Application-level CR is the most effective CR technique in terms of overhead
efficiency but it takes a lot of implementation effort. This work presents the
implementation of our C++ based library CRAFT (Checkpoint-Restart and Automatic
Fault Tolerance), which serves two purposes. First, it provides an extendable
library that significantly eases the implementation of application-level
checkpointing. The most basic and frequently used checkpoint data types are
already part of CRAFT and can be directly used out of the box. The library can
be easily extended to add more data types. As means of overhead reduction, the
library offers a build-in asynchronous checkpointing mechanism and also
supports the Scalable Checkpoint/Restart (SCR) library for node level
checkpointing. Second, CRAFT provides an easier interface for User-Level
Failure Mitigation (ULFM) based dynamic process recovery, which significantly
reduces the complexity and effort of failure detection and communication
recovery mechanism. By utilizing both functionalities together, applications
can write application-level checkpoints and recover dynamically from process
failures with very limited programming effort. This work presents the design
and use of our library in detail. The associated overheads are thoroughly
analyzed using several benchmarks
Dependable Computing on Inexact Hardware through Anomaly Detection.
Reliability of transistors is on the decline as transistors continue to shrink in size. Aggressive voltage scaling is making the problem even worse. Scaled-down transistors are more susceptible to transient faults as well as permanent in-field hardware failures. In order to continue to reap the benefits of technology scaling, it has become imperative to tackle the challenges risen due to the decreasing reliability of devices for the mainstream commodity market. Along with the worsening reliability, achieving energy efficiency and performance improvement by scaling is increasingly providing diminishing marginal returns. More than any other time in history, the semiconductor industry faces the crossroad of unreliability and the need to improve energy efficiency.
These challenges of technology scaling can be tackled by categorizing the target applications in the following two categories: traditional applications that have relatively strict correctness requirement on outputs and emerging class of soft applications, from various domains such as multimedia, machine learning, and computer vision, that are inherently inaccuracy tolerant to a certain degree. Traditional applications can be protected against hardware failures by low-cost detection and protection methods while soft applications can trade off quality of outputs to achieve better performance or energy efficiency.
For traditional applications, I propose an efficient, software-only application analysis and transformation solution to detect data and control flow transient faults. The intelligence of the data flow solution lies in the use of dynamic application information such as control flow, memory and value profiling. The control flow protection technique achieves its efficiency by simplifying signature calculations in each basic block and by performing checking at a coarse-grain level. For soft applications, I develop a quality control technique. The quality control technique employs continuous, light-weight checkers to ensure that the approximation is controlled and application output is acceptable. Overall, I show that the use of low-cost checkers to produce dependable results on commodity systems---constructed from inexact hardware components---is efficient and practical.PhDComputer Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/113341/1/dskhudia_1.pd
Pipelined Algorithms to Detect Cheating in Long-Term Grid Computations
This paper studies pipelined algorithms for protecting distributed grid
computations from cheating participants, who wish to be rewarded for tasks they
receive but don't perform. We present improved cheater detection algorithms
that utilize natural delays that exist in long-term grid computations. In
particular, we partition the sequence of grid tasks into two interleaved
sequences of task rounds, and we show how to use those rounds to devise the
first general-purpose scheme that can catch all cheaters, even when cheaters
collude. The main idea of this algorithm might at first seem
counter-intuitive--we have the participants check each other's work. A naive
implementation of this approach would, of course, be susceptible to collusion
attacks, but we show that by, adapting efficient solutions to the parallel
processor diagnosis problem, we can tolerate collusions of lazy cheaters, even
if the number of such cheaters is a fraction of the total number of
participants. We also include a simple economic analysis of cheaters in grid
computations and a parameterization of the main deterrent that can be used
against them--the probability of being caught.Comment: Expanded version with an additional figure; ISSN 0304-397
Aerospace applications of SINDA/FLUINT at the Johnson Space Center
SINDA/FLUINT has been found to be a versatile code for modeling aerospace systems involving single or two-phase fluid flow and all modes of heat transfer. Several applications of SINDA/FLUINT are described in this paper. SINDA/FLUINT is being used extensively to model the single phase water loops and the two-phase ammonia loops of the Space Station Freedom active thermal control system (ATCS). These models range from large integrated system models with multiple submodels to very detailed subsystem models. An integrated Space Station ATCS model has been created with ten submodels representing five water loops, three ammonia loops, a Freon loop and a thermal submodel representing the air loop. The model, which has approximately 800 FLUINT lumps and 300 thermal nodes, is used to determine the interaction between the multiple fluid loops which comprise the Space Station ATCS. Several detailed models of the flow-through radiator subsystem of the Space Station ATCS have been developed. One model, which has approximately 70 FLUINT lumps and 340 thermal nodes, provides a representation of the ATCS low temperature radiator array with two fluid loops connected only by conduction through the radiator face sheet. The detailed models are used to determine parameters such as radiator fluid return temperature, fin efficiency, flow distribution and total heat rejection for the baseline design as well as proposed alternate designs. SINDA/FLUINT has also been used as a design tool for several systems using pressurized gasses. One model examined the pressurization and depressurization of the Space Station airlock under a variety of operating conditions including convection with the side walls and internal cooling. Another model predicted the performance of a new generation of manned maneuvering units. This model included high pressure gas depressurization, internal heat transfer and supersonic thruster equations. The results of both models were used to size components, such as the heaters and gas bottles and also to point to areas where hardware testing was needed
Multiscale Universal Interface: A Concurrent Framework for Coupling Heterogeneous Solvers
Concurrently coupled numerical simulations using heterogeneous solvers are
powerful tools for modeling multiscale phenomena. However, major modifications
to existing codes are often required to enable such simulations, posing
significant difficulties in practice. In this paper we present a C++ library,
i.e. the Multiscale Universal Interface (MUI), which is capable of facilitating
the coupling effort for a wide range of multiscale simulations. The library
adopts a header-only form with minimal external dependency and hence can be
easily dropped into existing codes. A data sampler concept is introduced,
combined with a hybrid dynamic/static typing mechanism, to create an easily
customizable framework for solver-independent data interpretation. The library
integrates MPI MPMD support and an asynchronous communication protocol to
handle inter-solver information exchange irrespective of the solvers' own MPI
awareness. Template metaprogramming is heavily employed to simultaneously
improve runtime performance and code flexibility. We validated the library by
solving three different multiscale problems, which also serve to demonstrate
the flexibility of the framework in handling heterogeneous models and solvers.
In the first example, a Couette flow was simulated using two concurrently
coupled Smoothed Particle Hydrodynamics (SPH) simulations of different spatial
resolutions. In the second example, we coupled the deterministic SPH method
with the stochastic Dissipative Particle Dynamics (DPD) method to study the
effect of surface grafting on the hydrodynamics properties on the surface. In
the third example, we consider conjugate heat transfer between a solid domain
and a fluid domain by coupling the particle-based energy-conserving DPD (eDPD)
method with the Finite Element Method (FEM).Comment: The library source code is freely available under the GPLv3 license
at http://www.cfm.brown.edu/repo/release/MUI
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