13,024 research outputs found
FTMP data acquisition environment
The Fault-Tolerant Multi-Processing (FTMP) test-bed data acquisition environment is described. The performance of two data acquisition devices available in the test environment are estimated and compared. These estimated data rates are used as measures of the devices' capabilities. A new data acquisition device was developed and added to the FTMP environment. This path increases the data rate available by approximately a factor of 8, to 379 KW/S, while simplifying the experiment development process
Abnormal fault-recovery characteristics of the fault-tolerant multiprocessor uncovered using a new fault-injection methodology
An investigation was made in AIRLAB of the fault handling performance of the Fault Tolerant MultiProcessor (FTMP). Fault handling errors detected during fault injection experiments were characterized. In these fault injection experiments, the FTMP disabled a working unit instead of the faulted unit once in every 500 faults, on the average. System design weaknesses allow active faults to exercise a part of the fault management software that handles Byzantine or lying faults. Byzantine faults behave such that the faulted unit points to a working unit as the source of errors. The design's problems involve: (1) the design and interface between the simplex error detection hardware and the error processing software, (2) the functional capabilities of the FTMP system bus, and (3) the communication requirements of a multiprocessor architecture. These weak areas in the FTMP's design increase the probability that, for any hardware fault, a good line replacement unit (LRU) is mistakenly disabled by the fault management software
In-circuit fault injector user's guide
A fault injector system, called an in-circuit injector, was designed and developed to facilitate fault injection experiments performed at NASA-Langley's Avionics Integration Research Lab (AIRLAB). The in-circuit fault injector (ICFI) allows fault injections to be performed on electronic systems without special test features, e.g., sockets. The system supports stuck-at-zero, stuck-at-one, and transient fault models. The ICFI system is interfaced to a VAX-11/750 minicomputer. An interface program has been developed in the VAX. The computer code required to access the interface program is presented. Also presented is the connection procedure to be followed to connect the ICFI system to a circuit under test and the ICFI front panel controls which allow manual control of fault injections
A short review of "DGP Specteroscopy"
In this paper we provide a short review of the main results developed in
hep-th/0604086. We focus on linearised vacuum perturbations about the
self-accelerating branch of solutions in the DGP model. These are shown to
contain a ghost in the spectrum for any value of the brane tension. We also
comment on hep-th/0607099, where some counter arguments have been presented.Comment: Minor typos correcte
Sharing Default Information as a Borrower Discipline Device
Creditors often share information about their customers' credit record. Besides helping them to spot bad risks, this informational exchange acts as a disciplinary device. If creditors are known to exchange data about defaults, borrowers must consider that default on a current lender would disrupt their credit rating with all the other lenders. This raises their incentive to perform. But sharing more detailed information can reduce this disciplinary effect: when lenders only disclose past defaults, borrowers' incentives to perform may be greater than when lenders share all their information. In some instances, by "fine-tuning" the type and accuracy of the information shared, lenders can raise borrowers' incentives to their first-best level.Fiscal policy, national saving, contractionary fiscal expansions
The Logic & Limits of the Exceptional Circumstances Test in Magill and IMS Health
In this Article, we show that, in contrast to the Commission\u27s balancing approach in Microsoft, the ECJ\u27s narrow construction of the obligation to license IP under Article 82 of the EC Treaty is based on sound economics and constitutes appropriate public policy. The set of “exceptional circumstances” listed in Magill and IMS Health constitutes a reasonable implementation of the optimal legal standard for the assessment of refusals to licence IP: modified per se legality. In the IP context, an obligation to make property available is a requirement for compulsory licensing. The ECJ test limits compulsory licensing to those situations in which the prospective social benefits of licensing are large, while the negative effects of reducing the incentives to innovate are small. The ECJ test ensures that intervention is restricted to cases where the intervention is still likely to increase social welfare. The Commission\u27s test in Microsoft, being a balancing test, does not. As noted by Professor Gerardin, “balancing ex ante vs. ex post efficiencies is obviously a very difficult process, which even the most sophisticated economists may find daunting. The risk of mistaken decisions is therefore high.
Synergistic Gravity and the Role of Resonances in GRS-Inspired Braneworlds
We consider 5D braneworld models of quasi-localized gravity in which 4D
gravity is reproduced at intermediate scales while the extra dimension opens up
at both the very short and the very long distances, where the geometry is flat.
Our main interest is the interplay between the zero mode of these models,
whenever a normalizable zero mode exists, and the effects of zero energy
graviton resonant modes coming from the contributions of massive KK modes. We
first consider a compactified version of the GRS model and find that
quasi-localized gravity is characterized by a scale for which both the
resonance and the zero mode have significant contribution to 4D gravity. Above
this scale, gravity is primarily mediated by the zero mode, while the resonance
gives only minor corrections. Next, we consider an asymmetric version of the
standard non-compact GRS model, characterized by different cosmological
constants on each AdS side. We show that a resonance is present but the
asymmetry, through the form of the localizing potential, can weaken it,
resulting in a shorter lifetime and, thus, in a shorter distance scale for 4D
gravity. As a third model exhibiting quasi-localization, we consider a version
of the GRS model in which the central positive tension brane has been replaced
by a configuration of a scalar field propagating in the bulk.Comment: 18 pages, 3 figures, added 1 figure, revised version as published in
Class. Quant. Gra
Stealth Acceleration and Modified Gravity
We show how to construct consistent braneworld models which exhibit late time
acceleration. Unlike self-acceleration, which has a de Sitter vacuum state, our
models have the standard Minkowski vacuum and accelerate only in the presence
of matter, which we dub ``stealth-acceleration''. We use an effective action
for the brane which includes an induced gravity term, and allow for an
asymmetric set-up. We study the linear stability of flat brane vacua and find
the regions of parameter space where the set-up is stable. The 4-dimensional
graviton is only quasi-localised in this set-up and as a result gravity is
modified at late times. One of the two regions is strongly coupled and the
scalar mode is eaten up by an extra symmetry that arises in this limit. Having
filtered the well-defined theories we then focus on their cosmology. When the
graviton is quasi-localised we find two main examples of acceleration. In each
case, we provide an illustrative model and compare it to LambdaCDM.Comment: 32 pages, 5 figure
Resonance in Asymmetric Warped Geometry
We study the spectrum of an asymmetric warped braneworld model with different
AdS curvatures on either side of the brane. In addition to the RS-like modes we
find a resonance state. Its mass is proportional to the geometric mean of the
two AdS curvature scales, while the difference between them determines the
strength of the resonance peak. There is a complementarity between the RS
zero-mode and the resonance: making the asymmetry stronger weakens the
zero-mode but strengthens the resonance, and vice versa. We calculate
numerically the braneworld gravitational potential and discuss the holographic
correspondence for the asymmetric model.Comment: 17 pages, 9 figures; v2 references with comments added; v3 two
references added, JHEP versio
Ghosts in asymmetric brane gravity and the decoupled stealth limit
We study the spectrum of gravitational perturbations around a vacuum de
Sitter brane in a 5D asymmetric braneworld model, with induced curvature on the
brane. This generalises the stealth acceleration model proposed by Charmousis,
Gregory and Padilla (CGP) which realises the Cardassian cosmology in which
power law cosmic acceleration can be driven by ordinary matter. Whenever the
bulk has infinite volume we find that there is always a perturbative ghost
propagating on the de Sitter brane, in contrast to the Minkowski brane case
analysed by CGP. We discuss the implication of this ghost for the stealth
acceleration model, and identify a limiting case where the ghost decouples as
the de Sitter curvature vanishes.Comment: 21 page
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