A fast and slippery slope for file systems

There is a vast number and variety of file systems cur-rently available, each optimizing for an ever growing number of storage devices and workloads. Users have an unprece-dented, and somewhat overwhelming, number of data man-agement options. At the same time, the fastest storage de-vices are only getting faster, and it is unclear on how well the existing file systems will adapt. Using emulation tech-niques, we evaluate five popular Linux file systems across a range of storage device latencies typical to low-end hard drives, latest high-performance persistent memory block de-vices, and in between. Our findings are often surprising. De-pending on the workload, we find that some file systems can clearly scale with faster storage devices much better than others. Further, as storage device latency decreases, we find unexpected performance inversions across file systems. Finally, file system scalability in the higher device latency range is not representative of scalability in the lower, sub-millisecond, latency range. We then focus on Nilfs2 as an especially alarming example of an unexpectedly poor scala-bility and present detailed instructions for identifying bottle-necks in the I/O stack

Walking on inclines: how do desert ants monitor slope and step length

<p>Abstract</p> <p>Background</p> <p>During long-distance foraging in almost featureless habitats desert ants of the genus <it>Cataglyphis </it>employ path-integrating mechanisms (vector navigation). This navigational strategy requires an egocentric monitoring of the foraging path by incrementally integrating direction, distance, and inclination of the path. Monitoring the latter two parameters involves idiothetic cues and hence is tightly coupled to the ant's locomotor behavior.</p> <p>Results</p> <p>In a kinematic study of desert ant locomotion performed on differently inclined surfaces we aimed at pinpointing the relevant mechanisms of estimating step length and inclination. In a behavioral experiment with ants foraging on slippery surfaces we broke the otherwise tightly coupled relationship between stepping frequency and step length and examined the animals' ability to monitor distances covered even under those adverse conditions. We show that the ants' locomotor system is not influenced by inclined paths. After removing the effect of speed, slope had only marginal influence on kinematic parameters.</p> <p>Conclusion</p> <p>From the obtained data we infer that the previously proposed monitoring of angles of the thorax-coxa joint is not involved in inclinometry. Due to the tiny variations in cycle period, we also argue that an efference copy of the central pattern generator coding the step length in its output frequency will most likely not suffice for estimating step length and complementing the pedometer. Finally we propose that sensing forces acting on the ant's legs could provide the desired neuronal correlate employed in monitoring inclination and step length.</p

Effects of Weather Related Safety Messages on the Motorway Traffic Parameters

Intelligent transport systems have a huge importance during adverse weather conditions. These systems call the drivers’ attention to possible dangers by the use of variable message signs installed along the motorways. Several researchers have dealt with the connection of weather and traffic safety in the last decades, but they have not investigated the effects of weather related messages. This paper examines the impact of weather-related warning messages on traffic in adverse weather circumstances on the Hungarian motorways. Three independent databases were analyzed in order to compare the speed-reducing effect of specific signs during different weather events and precipitate intensities

1-Click Energy: Managing Corporate Demand for Clean Power

Globally, more private businesses, especially Fortune 100 companies are generating their own electricity, investing in renewable energy facilities, and voluntarily purchasing renewable energy credits to cover their carbon footprints. This shift could have a significant impact on the existing energy delivery system. On the one hand, this shift shows positive momentum toward the incorporation of clean energy into a fossil fuel dominated grid. As the negative impacts of climate change accelerate around the globe, decreasing reliance on fossil fuels is certainly an important goal. On the other hand, corporate disruption of what has historically been a highly regulated public service industry could result in a slippery slope of market power and loosened consumer protections, lost profits and stranded costs for utilities, and increased utility bills for the remaining customers. This Article recommends changes to the current regulatory scheme that would (1) go further to protect customers from multinational corporate wholesale sellers of electricity and (2) allow utilities to plan and collaborate earlier with large corporate customers to meet their clean energy demands

Legislative Delegation and Two Conceptions of the Legislative Power

[Excerpt] The current federal government, with its burgeoning administrative agencies, does not embody what most Americans would recognize as the constitutional doctrine of separation of powers. This is, in part, due to the Congress’s frequent practice of delegating legislative powers to the executive branch, i.e., giving administrative agencies the power to promulgate rules regulating private behavior and having the force of law. Legislative delegation has been the subject of academic, legal, and political wrangling since the early congresses and clearly calls into question whether modern practice adheres to constitutional norms. This article discusses legislative delegation in terms of some core ideas that informed the writing and ratification of the Constitution, and then look at debates on legislative delegation from the early republic, the Progressive era, and modern times. Ultimately, this article argues that the no delegation doctrine – that legislative power cannot be delegated to the executive consistently with the Constitution – should be viewed as an important protector of constitutional values whose judicial enforcement is both desirable and practicable. In Part II, I discuss how the change in the conception of law and legislative power over the eighteenth century ought to influence how one appraises the propriety of legislative delegation. In Part III, I consider important debates over delegation occurring at critical moments in the history of delegation. Instead of focusing on the relatively familiar historical narrative of Supreme Court cases, I concentrate on the unchanging themes underlying arguments about delegation. In Part IV, I consider the main point of contention in modern discussions of delegation, namely judicial review, and evaluate assertions regarding its practicability and clarity

Down a slippery slope:lack of trust, coercive threats and business tax resistance in Greece, 1955-1988

Over the second half of the 20th century, Greek governments failed to tax business income in line with the country’s level of economic development. This paper uses the “slippery slope” model of tax compliance to explain why the reform of income and corporate taxation in the late 1950s met strong resistance in the business sector. We argue that the negative legacy of interwar reforms, the lack of sustained and credible investment in trust building in coincidence with the postwar reforms, and the intensification of coercive threats in tax enforcement led to an antagonistic tax climate and a degradation of enforced and voluntary compliance. Our qualitative analysis based on original primary sources shows that the arguments publicly voiced by entrepreneurs and their organizations reflected their persistent perception of tax power as unfair, arbitrary and extractive. Using aggregate tax returns data, our quantitative analysis finds evidence of systematic and increasing income underreporting both by unincorporated and incorporated businesses. This vicious circle of non-cooperation and mutual distrust explains why governments got trapped into a persistent low tax capacity equilibrium that still casts a shadow on the Greek economy

Higher-Order Physic for Modeling Ice Streams in Ice Sheets

Ice streams are transitional between inland glaciers and ice shelves. Hence no stresses can be neglected. Ice streams are important dynamic features of a glacier; it is well known that ice streams drain up to 90% of the ice from an ice sheet. Herein I model ice streams as a multiphysics system of coupled components. This includes treating ice as a non-Newtonian fluid since empirical measurements show a power law relation between stress and strain rate. Sliding is a physical feature that must be included. This is done with a novel approach to sliding by way of a slippery layer. The slippery layer is given negligible thickness and rheology is tuned to the ice stream being modeled. Testing and benchmarking verifies the model. The first comparison is made with the shallow ice approximation, a known analytical solution. The model is setup with a problem domain in which basal stress dominates. Comparison of the surface veloc- ities shows excellent agreement. A second comparison involves a problem domain where longitudinal stress dominates. In this case a floating slab of is tested for creep via Weertman thinning. The model solution shows excellent agreement with the analytical solution of Weertman thinning. Additional benchmarking tests other model parameters to ensure proper settings. These include proper discretization of the problem domain and analysis of aspect ratio effects, the ratio of width to height. The temperature solver is tested for conduction dominated problem domains as well as advection and strain heating dominated problem domains. Again the model yields expected results. The model application to a real world ice stream is made with Whillans Ice Stream, which is located in Antarctica. Model results show that temperature is dominated by advection and that velocities show nearly plug-flow, in which vertical columns of ice move. The slippery layer tuned with a uniform softening shows better agreement with measured surface velocities [17] than tuning with a progressive softening

Leg Coordination during Walking in Insects

Locomotion depends on constant adaptation to different requirements of the environment. An appropriate temporal and spatial coordination of multiple body parts is necessary to achieve a stable and adapted behavior. Until now it is unclear how the neuronal structures can achieve these meaningful adaptations. The exact role of the nervous system, muscles and mechanical constrains are not known. By using preparations in which special forms of adaptations are considered under experimental conditions that selectively exclude external influences, like mechanical interactions through the ground or differences in body mass, one can draw conclusions about the organization of the respective underlying neuronal structures. In the present thesis, four different publications are presented, giving evidence of mechanisms of temporal or spatial coordination of leg movements in the stick insect Carausius morosus and the fruit fly Drosophila melanogaster during different experimental paradigms. At first, state dependent local coordinating mechanisms are analyzed. Electromyographic measurements of the three major antagonistic leg muscle pairs of the forward and backward walking stick insect are evaluated. It becomes evident that only the motor activity of the most proximal leg joint is changed when walking direction is changed from forward to backward, which demonstrates that the neuronal networks driving movement in each individual leg seem to be organized in a modular structure. In the second part mechanisms that influence movement speed of the individual leg and coordination of speed between the different legs of the stick insect come into focus. Electrophysiological and behavioral experiments with the intact and reduced stick insect were used to examine relationships between the velocity of a stepping front leg and neuronal activity in the mesothoracic segment as well as correlations between the stepping velocities of different legs during walks with constant velocity or with distinct accelerations. It was shown that stepping velocity of single legs were not reflected in motoneuron activity or stepping velocity of another leg. Only when an increase in walking speed was induced, clear correlation in the stepping velocities of the individual legs was found. Subsequently, the analysis of changes in temporal leg coordination during different walking speeds in the fruit fly reveals that the locomotor system of Drosophila can cover a broad range of walking speeds and seems to follow the same rules as the locomotor system of the stick insect. Walking speed is increased by modifying stance duration, whereas swing duration and step amplitude remain largely unchanged. Changes in inter-leg coordination are gradually and systematically with walking speed and can adapt to major biomechanical changes in its walking apparatus. In the final part it was the aim to understand the role of neuronal mechanisms for the orientation and spatial coordination of foot placement in the stick insect. Placement of middle and hind legs with respect to the position of their respective rostrally neighboring leg were analyzed under two different conditions. Segment and state dependent differences in the aiming accuracy of the middle and hind legs could be shown, which indicate differences in the underlying neuronal structures in the different segments and the importance of movement in the target leg for the processing of the position information. Taken together, common principles in inter-leg coordination where found, like similarities between different organisms and segment specific or state dependent modifications in the walking system. They can be interpreted as evidence for a highly adaptive and modular design of the underlying neuronal structures