Rate adaptation using acknowlegement feedback: throughput upper bounds

We consider packet-by-packet rate adaptation to maximize the throughput over a finite-state Markov channel. To limit the amount of feedback data, we use past packet acknowledgements (ACKs) and past rates as channel state information. It is known that the maximum achievable throughput is computationally prohibitive to determine. Thus, in this paper we derive two upper bounds on the maximum achievable throughput, which are tighter than previously known ones. We compare the upper bounds with a known myopic rate-adaptation policy. Numerical studies over a wide range of SNR suggest that the myopic rate-adaptation policy is close to the upper bounds and may be adequate in slowly time-varying channels

Rate adaptation using acknowlegement feedback: throughput upper bounds

We consider packet-by-packet rate adaptation to maximize the throughput over a finite-state Markov channel. To limit the amount of feedback data, we use past packet acknowledgements (ACKs) and past rates as channel state information. It is known that the maximum achievable throughput is computationally prohibitive to determine. Thus, in this paper we derive two upper bounds on the maximum achievable throughput, which are tighter than previously known ones. We compare the upper bounds with a known myopic rate-adaptation policy. Numerical studies over a wide range of SNR suggest that the myopic rate-adaptation policy is close to the upper bounds and may be adequate in slowly time-varying channels

"Low-state" Black Hole Accretion in Nearby Galaxies

I summarize the main observational properties of low-luminosity AGNs in nearby galaxies to argue that they are the high-mass analogs of black hole X-ray binaries in the "low/hard" state. The principal characteristics of low-state AGNs can be accommodated with a scenario in which the central engine is comprised of three components: an optically thick, geometrically accretion disk with a truncated inner radius, a radiatively inefficient flow, and a compact jet.Comment: 8 pages. To appear in From X-ray Binaries to Quasars: Black Hole Accretion on All Mass Scales, ed. T. J. Maccarone, R. P. Fender, and L. C. Ho (Dordrecht: Kluwer

Phonological representations and early literacy in Chinese

Phonological processing skills predict early reading development, but what underlies developing phonological processing skills? Phonological representations of 140 native Cantonese-speaking Chinese children (age 4–10) were assessed with speech gating, mispronunciation detection, and nonword repetition tasks; their nonverbal IQ, reading, and phonological processing were assessed with standard tests. Results indicated that even without explicit script-sound correspondence at the phonemic level in Chinese orthography, young Chinese speakers developed representations segmented at this level, and such representations were more fine-grained for older children. Further, the quality of kindergarteners’ phonological representations (specified by sensitivity to mispronunciation in lexical judgment) significantly predicted their emergent reading abilities, and this relation was fully mediated by phonological processing skills, with rapid naming showing the strongest mediation effect. Such mediation was no longer found with the primary-school sample, suggesting plausible developmental changes in the relations between phonological representations, phonological processing, and reading during early reading development.postprin

Variability of organic and elemental carbon, water soluble organic carbon, and isotopes in Hong Kong

International audienceTo determine the levels and variations of carbonaceous aerosol in Hong Kong, PM2.5 and PM10 samples were collected by high volume (Hi-vol) samplers at three monitoring stations (representing middle-scale roadside, urban-, and regional-scale environments) during winter (November 2000 to February 2001) and summer (June 2001 to August 2001) periods. The highest concentrations of organic carbon (OC), elemental carbon (EC), and water-soluble organic carbon (WSOC) were found at the middle-scale roadside site with the lowest at the regional-scale site. The percentages of WSOC in total carbon at these sites were inversely correlated with their concentrations (i.e., the highest percentages of WSOC were observed at the regional-scale site). A high WSOC fraction may be associated with aged aerosol because of the secondary formation by photochemical oxidation of organic precursors of anthropogenic pollutants during transport. The annual average of isotope abundances (?13C) of OC and EC were ?26.9±0.5? and ?25.6±0.1?, respectively. There were no notable differences for seasonal distributions of carbon isotopic composition, consistent with motor vehicle emissions being the main source contributors of carbonaceous aerosol in Hong Kong. OC 13C abundances at the regional-scale site were higher than those at the middle-scale roadside and urban sites, consistent with secondary organic aerosols of biogenic origin

The role of Schizosaccharomyces pombe SUMO ligases in genome stability

SUMOylation is a post-translational modification that affects a large number of proteins, many of which are nuclear. While the role of SUMOylation is beginning to be elucidated, it is clear that understanding the mechanisms that regulate the process is likely to be important. Control of the levels of SUMOylation is brought about through a balance of conjugating and deconjugating activities, i.e. of SUMO (small ubiquitin-related modifier) conjugators and ligases versus SUMO proteases. Although conjugation of SUMO to proteins can occur in the absence of a SUMO ligase, it is apparent that SUMO ligases facilitate the SUMOylation of specific subsets of proteins. Two SUMO ligases in Schizosaccharomyces pombe, Pli1 and Nse2, have been identified, both of which have roles in genome stability. We report here on a comparison between the properties of the two proteins and discuss potential roles for the proteins

Study of heterogeneous nucleation of eutectic Si in high-purity Al-Si alloys with Sr addition

The official published version can be accessed from the link below - Copyright @ 2010 The Minerals, Metals & Materials Society and ASM InternationalAl-5 wt pct Si master-alloys with controlled Sr and/or P addition/s were produced using super purity Al 99.99 wt pct and Si 99.999 wt pct materials in an arc melter. The master-alloy was melt-spun resulting in the production of thin ribbons. The Al matrix of the ribbons contained entrained Al-Si eutectic droplets that were subsequently investigated. Differential scanning calorimetry, thermodynamic calculations, and transmission electron microscopy techniques were employed to examine the effect of the Sr and P additions on eutectic undercoolings and nucleation phenomenon. Results indicate that, unlike P, Sr does not promote nucleation. Increasing Sr additions depressed the eutectic nucleation temperature. This may be a result of the formation of a Sr phase that could consume or detrimentally affect potent AlP nucleation sites.This work is financially supported by the Higher Education Commission of Pakistan and managerially supported from the OAD

Exhaled nitric oxide measurements with dynamic flow restriction in children aged 4-8 yrs

Fractional exhaled nitric oxide concentration (FENO) depends on exhalation flow; however, children often are unable to perform controlled flow procedures. Therefore, a device was developed for off-line FENO sampling, with dynamic flow restriction (DFR). The authors compared off-line w

Induced circular dichroism of stereoregular vinyl polymers

Stereoregular vinyl polymers, poly(2-vinyl pyridine)s (P2VPs), were synthesized to examine the tacticity effect on the induced circular dichroism (ICD) via association with chiral acids. The ICD was found to be strongly dependent on the isotacticity of the P2VPs and the acidity of chiral acid in addition to its bulkiness