Progressive Transactional Memory in Time and Space

Transactional memory (TM) allows concurrent processes to organize sequences of operations on shared \emph{data items} into atomic transactions. A transaction may commit, in which case it appears to have executed sequentially or it may \emph{abort}, in which case no data item is updated. The TM programming paradigm emerged as an alternative to conventional fine-grained locking techniques, offering ease of programming and compositionality. Though typically themselves implemented using locks, TMs hide the inherent issues of lock-based synchronization behind a nice transactional programming interface. In this paper, we explore inherent time and space complexity of lock-based TMs, with a focus of the most popular class of \emph{progressive} lock-based TMs. We derive that a progressive TM might enforce a read-only transaction to perform a quadratic (in the number of the data items it reads) number of steps and access a linear number of distinct memory locations, closing the question of inherent cost of \emph{read validation} in TMs. We then show that the total number of \emph{remote memory references} (RMRs) that take place in an execution of a progressive TM in which $n$ concurrent processes perform transactions on a single data item might reach $\Omega(n \log n)$, which appears to be the first RMR complexity lower bound for transactional memory.Comment: Model of Transactional Memory identical with arXiv:1407.6876, arXiv:1502.0272

Interaction of whispering gallery modes in integrated optical micro-ring or -disk circuits: Hybrid CMT model

Whispering gallery modes supported by open circular dielectric cavities are embedded into a nonparametric two-dimensional frequency domain hybrid coupled mode theory framework. Regular aggregates of these cavities, including straight access channels, are investigated. The model enables convenient studies of the guided wave scattering process, the response of the circuit to guided wave excitation. Transmission resonances can be characterized directly in terms of resonance frequency and linewidth by computing supermodes of the entire composite circuits, comprising both cavities and bus waveguides. Examples of single ring and disk filters, a coupled-resonator optical waveguide, and a three-cavity photonic molecule in a reflector configuration allow the approach to be assessed

A modified molecular beam instrument for the imaging of radicals interacting with surfaces during plasma processing

A new instrument employing molecular beam techniques and laser induced fluorescence(LIF) for measuring the reactivity of gas phase radicals at the surface of a depositing film has been designed and characterized. The instrument uses an inductively coupled plasma source to create a molecular beam containing essentially all plasma species. A tunable excimer pumped dye laser is used to excite a single species in this complex molecular beam.LIF signals are imaged onto a gated, intensified charge coupled device (ICCD) to provide spatial resolution. ICCD images depict the fluorescence from molecules both in the molecular beam and scattering from the surface of a depositing film. Data collected with and without a substrate in the path of the molecular beam provide information about the surface reactivity of the species of interest. Here, we report the first measurements using the third generation imaging of radicals interacting with surfaces apparatus. We have measured the surface reactivity of SiH molecules formed in a 100% SiH_4 plasma during deposition of an amorphous hydrogenated silicon film. On a 300 K Si (100) substrate, the reactivity of SiH is near unity. The substrate temperature dependence (300–673 K) of the reactivity is also reported. In addition, reactivity measurements for OH molecules formed in a water plasma are presented. In contrast to the SiH molecule, the reactivity of OH radicals is 0.55±0.05 on the surface of a Si (100) substrate

Plasma enhanced chemical vapor deposition of SiO_2 using novel alkoxysilane precursors

This communication describes our results using these novel alkoxysilane precursors for PECVD of SiO_2 films in an inductively coupled rf plasma reactor. The effects of deposition time, rf power, and organosilane pressure on the films’ characteristics are described

Geologic Mapping of the Guinevere Planitia Quadrangle of Venus

The Guinevere Planitia quadrangle of Venus (0-25degN, 300-330deg) covers a lowland region east of Beta Regio and west of Eistla Regio, including parts of Guinevere and Undine Planitiae. The V-30 quadrangle is dominated by low-lying plains interpreted to be of volcanic origin and exhibiting numerous wrinkle ridges. Using Pioneer Venus, Goldstone, and Arecibo data, previous investigators have described radar bright, dark, and mottled plains units in the Guinevere Planitia region, as well as arcuate fracture zones and lineament belt segments that define the Beta-Eistla deformation zone [1-5]. Magellan SAR images show that volcanic landforms compose the majority of the surface units in V-30 [6-7]. The quadrangle contains parts of four major volcanoes: Atanua (9degN, 307deg), Rhpisunt (3degN, 302deg), Tuli (13degN, 314deg), and Var (3degN, 316deg) Montes, and three coronae: Hulda (12degN, 308deg), Madderakka (9degN, 316deg), and Poloznitsa (1degN, 303deg). Seymour crater, located at 18degN, 327deg, is associated with extensive crater outflow deposits

Why are plant–soil feedbacks so unpredictable, and what to do about it?

1.The study of feedbacks between plants and soils (plant‐soil feedbacks; PSFs) is receiving increased attention. However, PSFs have been mostly studied in isolation of abiotic and biotic drivers that could affect their strength and direction. This is problematic because it has led to limited predictive power of PSFs in ‘the real world’, leaving large knowledge gaps in our ability to predict how PSFs contribute to ecosystem processes and functions. 2.Here, we present a synthetic framework to elucidate how abiotic and biotic drivers affect PSFs. We focus on two key abiotic drivers (temperature and soil moisture) and two key biotic drivers (aboveground plant consumers and belowground top‐down control of pathogens and mutualists). We focus on these factors because they are known drivers of plants and soil organisms and the ecosystem processes they control, and hence would be expected to strongly influence PSFs. 3.Our framework describes the proposed mechanisms behind these drivers and explores their effects on PSFs. We demonstrate the impacts of these drivers using the fast‐ to slow‐growing plant economics spectrum. We use this well‐established paradigm because plants on opposite ends of this spectrum differ in their relationships with soil biota and have developed contrasting strategies to cope with abiotic and biotic environmental conditions. 4.Finally, we present suggestions for improved experimental designs and scientific inference that will capture and elucidate the influence of above‐ and belowground drivers on PSFs. By establishing the role of abiotic and biotic drivers of PSFs, we will be able to make more robust predictions of how PSFs impact on ecosystem function