Throughput and energy efficiency in IEEE 802.11 WLANs: friends or foes?

Proceedings of: 6th International ICST Conference on Heterogeneous Networking for Quality, Reliability, Security and Robustness, QShine 2009 and 3rd International Workshop on Advanced Architectures and Algorithms for Internet Delivery and Applications, AAA-IDEA 2009, Las Palmas, Gran Canaria, November 23-25, 2009Understanding and optimizing the energy consumption of wireless devices is critical to maximize network lifetime and to provide guidelines for the design of new protocols and interfaces. In this work we first provide an accurate analysis of the energy performance of an IEEE 802.11 WLAN, and then we derive the configuration to maximize it. We also analyze the impact of the energy configuration of the device on the throughput performance, and discuss in which circumstances throughput and energy efficiency can be both maximized and where they constitute different challenges.European Community's Seventh Framework ProgramPublicad

The sea urchin sns5 chromatin insulator settles a gene therapy vector into an independent domain of expression in the vertebrate genome

One of the critical aspects of introducing a transgene into the eukaryotic genome is the great variability of gene expression due to position effects (1). Chromatin-dependent repressive states could be overcome by incorporation in the transgene of chromatin insulators, functioning to establish and delimit domains of expression. We have previously demonstrated that the sea urchin sns5 DNA element has the typical features of an insulator: by acting as enhancer blocker, it shields promoters from neighboring regulatory elements, and by acting as barrier it buffers a transgene from the propagation of condensed chromatin (2,3). We have investigated the use of sns5 in the field of gene therapy. Our preliminary studies shown that the inclusion of sns5 in \uf0e3-retroviral vectors allows position-independent expression in erythroid cells (4). Moreover, transcription factors and histone modifications mark the sns5 chromatin at the integration site (4), suggesting that sns5 displays mechanisms of action common to other well characterized insulators. Here we show that sns5 increases the likelihood and the expression of a \uf062-globin/lentiviral vector integrated as a single copy in both murine cell clones and in a mouse model of \uf062-thalassemia. It has been proposed that two copies of insulators may direct the formation of a chromatin loop by interaction among protein complexes assembled on their sequences (5). Intriguingly, by using the 3C technology, we found that sns5-flanked vectors integrated at a single copy in the resident genome are specifically organized into an independent chromatin structure. Our findings highlight that sns5 could be a promising tool for improving the performance of vectors in the field of gene therapy. 1. Gaszner and Felsenfeld (2006). Nat Rev Genet 7:703-13 2. Palla et al (1997). PNAS USA 94:2272-7 3. Cavalieri et al (2009). Nucleic Acids Res 37:7407-15 4. D'Apolito et al (2009). Mol Ther 17:1434-41 5. Wallace and Felsenfeld (2007). Curr Op Genet Dev 17:400-

Turbulence in Rivers

The study of turbulence has always been a challenge for scientists working on geophysical flows. Turbulent flows are common in nature and have an important role in geophysical disciplines such as river morphology, landscape modeling, atmospheric dynamics and ocean currents. At present, new measurement and observation techniques suitable for fieldwork can be combined with laboratory and theoretical work to advance the understanding of river processes. Nevertheless, despite more than a century of attempts to correctly formalize turbulent flows, much still remains to be done by researchers and engineers working in hydraulics and fluid mechanics. In this contribution we introduce a general framework for the analysis of river turbulence. We revisit some findings and theoretical frameworks and provide a critical analysis of where the study of turbulence is important and how to include detailed information of this in the analysis of fluvial processes. We also provide a perspective of some general aspects that are essential for researchers/ practitioners addressing the subject for the first time. Furthermore, we show some results of interest to scientists and engineers working on river flows

Analytical solution of kinematic wave time of concentration for overland flow under green-ampt infiltration

In this paper the well-known kinematic wave equation for computing the time of concentration for impervious surfaces has been extended to the case of pervious hillslopes, accounting for infiltration. An analytical solution for the time of concentration for overland flow on a rectangular plane surface is derived using the kinematic wave equation under the Green-Ampt infiltration. The relative time of concentration is defined as the ratio between the time of concentration of an infiltrating plane and the soil sorptivity time scale, depending on the normalized rainfall intensity and a parameter synthesizing the soil and hillslope characteristics. It is shown that for a more complex case (corresponding to the second domain of solution domain), the time of concentration can also be estimated by two simplified approximate procedures. An error analysis for the time of concentration computed for constant and time-varying infiltration is carried out. Finally, for a hillslope under the Green-Ampt infiltration, the time of concentration obtained by the kinematic wave equation is compared with that computed by a nonlinear storage model. An application of the proposed method for two different soils is shown and discussed

Determining Probability Distribution of Hillslope Peak Discharge by Using an Analytical Solution of Kinematic Wave Time of Concentration.

Hillslope hydrology is fundamental for understanding the flood phenomenon and for evaluating the time of concentration. The latter is a key variable for predicting peak discharge at the basin outlet and for designing urban infrastructure facilities. There have been a multitude of studies on the hydrologic response at the hillslope scale, and the time of concentration has been derived for different approaches. One approach for deriving hillslope response utilizes, in a distributed form, the differential equations of unsteady overland flow, specifically developed at the hydrodynamic scale, in order to account for the spatial heterogeneity of soil characteristics, topography, roughness and vegetation cover on the hillslope. Therefore, this approach seemingly mimics the complete hydraulics of flow. However, the very complex patterns generated by spatial heterogeneity can cause considerable error in the prediction even by very sophisticated models. Another approach that directly operates at the hillslope scale is by averaging over the hillslope the soil hydraulics, the topography, and the roughness characteristics. A physically-based lumped model of hillslope response was first proposed by Horton (1938), under the assumption that the flow regime is intermediate between laminar and turbulent regimes (transitional flow regime), by applying the mass conservation equation to the hillslope as a whole and by using the kinematic wave assumption for the friction slope (Singh, 1976, 1996). Robinson et al. (1995) and Robinson and Sivapalan (1996) generalized Horton\u2019s approach, suggesting an approximate solution of the overland flow equation that is valid for all flow regimes. Agnese et al. (2001) derived an analytical solution of a nonlinear storage model of hillslope response that is valid for all flow regimes, and the associated time of concentration. Recently, the well-known kinematic wave equation for computing the time of concentration for impervious surfaces has been extended to the case of pervious hillslopes, accounting for infiltration. In particular, an analytical solution for the time of concentration for overland flow on a rectangular plane surface was derived using the kinematic wave equation under the Green-Ampt infiltration (Baiamonte and Singh, 2015). The objective of this work is to apply the latter solution to determine the probability distribution of hillslope peak discharge by combining it with the familiar rainfall duration-intensity-frequency approach

Overland Flow Times of Concentration for Hillslopes of Complex Topography

The time of concentration is an important parameter for predicting peak discharge at the basin outlet and for designing urban infrastructure facilities. In studying the hillslope response, employing hydraulic equations of flow, the shape of the hillslope geometry has often been assumed as rectangular and planar. However, natural hillslopes have complex topographies whose shapes are characterized by irregularly spaced contour lines. Recently, kinematic wave time of concentration has been derived for rectangular and curved parallel hillslopes. This paper extends this work to hillslopes of complex planform geometry, considering the degree of divergence or convergence of the hillslope. The extended formulation consists of only one equation that is valid for both divergent/convergent surfaces and for concave/convex hillslope profile, and is compared with the formulations for plane convergent and plane divergent surfaces previously introduced. Results are compared with those already available in the literature, which were obtained by using the nonlinear storage model applied to the same complex hillslopes

Determining soil hydraulic properties using infiltrometer techniques: An assessment of temporal variability in a long-term experiment under minimum-and no-tillage soil management

Conservation agriculture is increasingly accepted by farmers, but the modeling studies on agro-environmental processes that characterize these agricultural systems require accurate information on the temporal variability of the soil's main physical and hydraulic properties. Therefore, specific investigations carried out in long-term experiments can increase our knowledge on the pros and cons of different measurement techniques. In this work, the simplified falling head (SFH) technique and the Beerkan Estimation of Soil Transfer (BEST) procedure were applied to investigate the temporal variability of some main soil physical and hydraulic properties, including bulk density (BD), field saturated hydraulic conductivity (Kfs), macroporosity (Pmac), air capacity (AC), plant available water capacity (PAWC), and relative field capacity (RFC). For this purpose, a long-term experiment was selected, and the experimental information obtained was used to verify the long-term impact (fifteen years) determined by two alternative forms of soil management, minimum tillage (MT) and no tillage (NT), for the cultivation of durum wheat. The main results of the comparison between MT and NT showed: (i) A comparable temporal variability in Kfs values when SFH was considered, given that in 75% of considered cases, the same result (i.e., significant or not significant) was obtained; (ii) a comparable temporal variability in Kfs values under MT (but not under NT) when both SFH and BEST were used, as a result of a possible Kfs, SFH overestimation under NT; (iii) differences in Kfs estimations by a factor of 6 or 7 (Kfs, SFH > Kfs, BEST) when comparable soil conditions (moisture and soil density) were considered; (iv) a comparable temporal variability when other soil indicators (BD, Pmac, AC, PAWC, and RFC) were simultaneously considered. After about fifteen years of field experiments characterized by continuous soil management and conducted with the methodological rigor typical of experimental farms, the SFH-and BEST-derived experimental information showed a substantial equivalence between MT and NT for the fine-textured soil investigated