An Energy-conscious Transport Protocol for Multi-hop Wireless Networks

We present a transport protocol whose goal is to reduce power consumption without compromising delivery requirements of applications. To meet its goal of energy efficiency, our transport protocol (1) contains mechanisms to balance end-to-end vs. local retransmissions; (2) minimizes acknowledgment traffic using receiver regulated rate-based flow control combined with selected acknowledgements and in-network caching of packets; and (3) aggressively seeks to avoid any congestion-based packet loss. Within a recently developed ultra low-power multi-hop wireless network system, extensive simulations and experimental results demonstrate that our transport protocol meets its goal of preserving the energy efficiency of the underlying network.Defense Advanced Research Projects Agency (NBCHC050053

A Two-step Statistical Approach for Inferring Network Traffic Demands (Revises Technical Report BUCS-2003-003)

Accurate knowledge of traffic demands in a communication network enables or enhances a variety of traffic engineering and network management tasks of paramount importance for operational networks. Directly measuring a complete set of these demands is prohibitively expensive because of the huge amounts of data that must be collected and the performance impact that such measurements would impose on the regular behavior of the network. As a consequence, we must rely on statistical techniques to produce estimates of actual traffic demands from partial information. The performance of such techniques is however limited due to their reliance on limited information and the high amount of computations they incur, which limits their convergence behavior. In this paper we study a two-step approach for inferring network traffic demands. First we elaborate and evaluate a modeling approach for generating good starting points to be fed to iterative statistical inference techniques. We call these starting points informed priors since they are obtained using actual network information such as packet traces and SNMP link counts. Second we provide a very fast variant of the EM algorithm which extends its computation range, increasing its accuracy and decreasing its dependence on the quality of the starting point. Finally, we evaluate and compare alternative mechanisms for generating starting points and the convergence characteristics of our EM algorithm against a recently proposed Weighted Least Squares approach.National Science Foundation (ANI-0095988, EIA-0202067, ITR ANI-0205294

On the origin of two unidentified radio/X-ray sources discovered with XMM-Newton

We aim at clarifying the nature of the emission of two spatially related unidentified X-ray sources detected with XMM-Newton telescope at intermediate-low Galactic latitude. Observations reveal a point-like source aligned with elongated diffuse emission. The X-ray spectra are best-fitted by absorbed power laws with photon indices ~1.7 for the point-like and ~2.0 for the extended one. Both sources show nonthermal radio-continuum counterparts that might indicate a physical association. From the available data, we did not detect variability on the point-like source in several timescales. Two possible scenarios are analyzed: first, based on HI line absorption, assuming a Galactic origin, we infer a distance upper bound of <2 kpc, which poses a constraint on the height over the Galactic plane of <200 pc and on the linear size of the system of 10^32 erg/s and >7.5 x 10^32 erg/s, for the point-like and extended sources, respectively; second, an extra-Galactic nature is discussed, where the point-like source might be the core of a radio galaxy and the extended source its lobe. In this case, we compare derived fluxes, spectral indices, and spatial correlation with those typical from the radio galaxy population, showing the feasibility of this alternative astrophysical scenario. From the available observational evidence, we suggest that the most promising scenario to explain the nature of these sources is a system consisting of a one-sided radio galaxy, where the point-like source is an active galactic nucleus and the extended source corresponds to the emission from its lobe. Other possibilities include a PSR/PWN origin, where the radio/X-ray emission originates from the synchrotron cooling of relativistic particles in the PSR magnetic field or a casual alignment between two unrelated sources, such as an AGN core and a Galactic X-ray blob.Comment: 6 pages, 2 figures. Accepted for publication in Astronomy and Astrophysics (A&A

The energy spectrum observed by the AGASA experiment and the spatial distribution of the sources of ultra-high energy cosmic rays

Seven and a half years of continuous monitoring of giant air showers triggered by ultra high-energy cosmic rays have been recently summarized by the AGASA collaboration. The resulting energy spectrum indicates clearly that the cosmic ray spectrum extends well beyond the Greisen-Zatsepin-Kuzmin (GZK) cut-off at $\sim 5 \times 10^{19}$ eV. Furthermore, despite the small number statistics involved, some structure in the spectrum may be emerging. Using numerical simulations, it is demonstrated in the present work that these features are consistent with a spatial distribution of sources that follows the distribution of luminous matter in the local Universe. Therefore, from this point of view, there is no need for a second high-energy component of cosmic rays dominating the spectrum beyond the GZK cut-off.Comment: 14 pages, 4 figures, Astrophys. J. Letters (submitted

Vocational Training for Disadvantaged Youth in Colombia: A Long-Term Follow-Up

We evaluate the long-term impacts of a randomized Colombian training and job placement program. Following the large short-term effects, we now find that the program effects persist, increasing formal participation and earnings contributions to social security and working in larger firms. By using a large administrative source we are also able to establish that the program improved both male and female labor market outcomes by a similar amount--a result that was not apparent with the smaller evaluation sample. The results point to a cost-effective approach to reducing informality and improving labor market outcomes in the long run

Age Structure and Sex Ratio of Thrips Scirtothrips Dorsalis Hood (Thysanoptera : Thripidae) Associate with Mango Agroecosystem in East Java, Indonesia

A research aimed to investigate the age structure and sex ratio of S. dorsalis Hood in mango agroecosystem was conducted at PT. Trigatra Rajasa farm, Situbondo, East Java, Indonesia. The research was started from April to May 2013. A Completely Randomized Design, Analysis of Variance and Least Significant Difference were used to design, knew the variance and significantly different among the treatment, respectively. Thirteen mango trees set in cross section were sampled and observed for the presence of S. dorsalis including weeds under the mango canopy and four cardinal directions of border. A weekly sample was done for four weeks. The result showed that instar one and adult were preferred to associate with weeds under the mango canopy and borders compare to mango leaves except second instar. Further, observation was presented that all the age structures were given equal male female sex ratio. Based on total population numbers, there wasn't significantly difference of age structure and sex ratio of S. dorsalis associate with weeds inside the orchard including mango leaves and borders. Twenty seven species of weeds were discovered associate with mango agroecosystem and comprehensively discused based on the most dominance and preferred by S. dorsalis

Climate change, loss of (bio)diversity, natural ressource depletion, social marginalization etc: Our adaptation and mitigation contribution

The environmental and social challenges of the planet are a sad reality. Organic Agriculture advocates often espouse its contributions to mitigating the negative effects of farming. But mitigation alone is not enough. Farmers also need to adapt to a changed climate, reduced biodiversity and depleted resources as well as to an ever-changing socio-cultural environment