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The network, similar to CPU and memory, is a critical and shared resource in the cloud. However, unlike other resources, it is neither shared proportionally to payment, nor do cloud providers offer minimum guarantees on network bandwidth. The reason networks are more difficult to share is because the network allocation of a virtual machine (VM) X depends not only on the VMs running on the same machine with X , but also on the other VMs that X communicates with and the cross-traffic on each link used by X . In this paper, we start from the above requirements--payment proportionality and minimum guarantees--and show that the network-specific challenges lead to fundamental tradeoffs when sharing cloud networks. We then propose a set of properties to explicitly express these tradeoffs. Finally, we present three allocation policies that allow us to navigate the tradeoff space. We evaluate their characteristics through simulation and testbed experiments to show that they can provide minimum guarantees and achieve better proportionality than existing solutions.
Abstract The work describes a novel approach for sustained photobiological production of H2 gas via the reversible hydrogenase pathway in the green alga Chlamydomonas reinhardtii. This single-organism, two-stage H2 production method circumvents the severe O2 sensitivity of the reversible hydrogenase by temporally separating photosynthetic O2 evolution and carbon accumulation (stage 1) from the consumption of cellular metabolites and concomitant H2 production (stage 2). A transition from stage 1 to stage 2 was effected upon S deprivation of the culture, which reversibly inactivated photosystem II (PSII) and O2 evolution. Under these conditions, oxidative respiration by the cells in the light depleted O2 and caused anaerobiosis in the culture, which was necessary and sufficient for the induction of the reversible hydrogenase. Subsequently, sustained cellular H2 gas production was observed in the light but not in the dark. The mechanism of H2 production entailed protein consumption and electron transport from endogenous substrate to the cytochromeb 6-f and PSI complexes in the chloroplast thylakoids. Light absorption by PSI was required for H2 evolution, suggesting that photoreduction of ferredoxin is followed by electron donation to the reversible hydrogenase. The latter catalyzes the reduction of protons to molecular H2in the chloroplast stroma.
We show that the magnetization of a single `qubit' spin weakly coupled to an otherwise isolated disordered spin chain exhibits periodic revivals in the localized regime, and retains an imprint of its initial magnetization at infinite time. We demonstrate that the revival rate is strongly suppressed upon adding interactions after a time scale corresponding to the onset of the dephasing that distinguishes many-body localized phases from Anderson insulators. In contrast, the ergodic phase acts as a bath for the qubit, with no revivals visible on the time scales studied. The suppression of quantum revivals of local observables provides a quantitative, experimentally observable alternative to entanglement growth as a measure of the `non-ergodic but dephasing' nature of many-body localized systems.
Natural photosynthetic systems collect sunlight using a vast array of light-harvesting chromophores that channel the absorbed energy to a single reaction center. Recently, it has been realized that dendritic macromolecules can exhibit similar properties, though on a more modest scale. The preparation of dendritic structures and assemblies composed of numerous light-collecting chromophores that transfer their energy to a single energy 'sink' at the core has been achieved in a number of diverse and creative ways. These novel structures are being used as model systems in light-emitting diodes, signal amplifiers, fluorescent sensors, frequency converters, and other photonic devices.
Abstract This paper exposes Hodgkin–Huxley’s “ time-varying conductance ” as an ill-conceived conceptual blunder and identifies a fundamental new physical concept dubbed “ Edge of Chaos Kernel ” as nature’s optimal mechanism for creating an “ action potential ,” aka “ all - or - none ” response. As a bonus, it also offers a precise characterization of the heretofore unresolved notion of excitability , which in turn finally resolves Galvani’s 240 year old enigma on the physical mechanism which gives rise to a near-abrupt all - or - none phenomenon, triggered by a global saddle-node bifurcation where a stable and an unstable periodic orbit grows in size while evolving their shape, ever so gently, so as to morph onto each other, until they became a single orbit, in high-dimensional state space. Even more intriguing is the Edge of Chaos Kernel ’s humble incarnation from the Chua’s Riddle , and its innate ability to exhibit both Turing instability and the yet unresolved Smale’s paradox.
The concern over climate change has motivated a search for low-carbon transportation fuels. One approach to low-carbon fuels is to exploit photosynthesis, which stores solar energy in plant biomass. I review here some aspects of the potential for making liquid fuels from biomasss. There appear to be significant amounts of currently un- or underutilized land available to raise biomass for liquid fuels. Rather than compete with feed crops, we have explored the potential of energy crops such as perennial grasses. Processes have been developed for efficient production of fuels from biomass. Lots of progress has been made but lessons are still being learned.
Aging disrupts sleep. Moreover, these sleep impairments are exaggerated in Alzheimer's disease, and are proposed to contribute to cognitive decline. Recent human studies have linked β-amyloid with non-rapid eye-movement (NREM) sleep disruption. However, the impact of tau pathology on human sleep oscillations and cognition remains uninvestigated. Here, we tested the hypothesis that tau burden within medial temporal lobe (MTL) impairs the coupled relationship between the two key NREM sleep oscillations—sleep spindles and slow waves, and their known support of hippocampal memory. In vivo tau was measured with [18F]AV1451 PET in cognitively normal older adults (n=19, mean age=75.8), together with overnight, dense-array sleep EEG recordings. A validated associative recognition task was used to measure hippocampal memory function. Analyses focused on relationships between three measurements: (i) AV1451 tau PET binding in MTL measured as the mean (L+R) standardized uptake value ratio of tracer relative to inferior cerebellar gray matter (SUVR), (ii) EEG phase-amplitude coupling between NREM spindles and slow wave oscillations, and (iii) hippocampus-dependent memory. Worse memory performance was related to greater tau burden in MTL (AV1451 SUVR; p=0.03; Fig. 1). MTL tau burden additionally predicted the severity of impaired sleep spindle-slow wave oscillation coupling over the prefrontal cortex (p=0.03; Fig. 2, top). Moreover, this tau-related sleep disruption of spindle-slow wave coupling predicted the degree of memory impairment (p=0.05; Fig. 2, bottom).
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