Renegociaci?n de contratos de concesi?n en infraestructura de transporte : diagn?stico, an?lisis y propuestas de mejora

Como ha ocurrido en muchos otros pa?ses, en el Per?, tradicionalmente, el Estado ha sido el ?nico en asumir la responsabilidad de proporcionar infraestructura p?blica y de prestar los servicios asociados con esta. Vali?ndose de sus propios medios, ha tratado, durante muchos a?os, de cumplir con la responsabilidad de brindar a la poblaci?n carreteras, aeropuertos, plantas de tratamiento de agua, centrales de generaci?n el?ctrica, etc. Finalmente, el Estado peruano comprendi? que no ser?a posible lograr el desarrollo del pa?s apelando ?nicamente a sus recursos propios, sino que tambi?n era necesario contar con la inversi?n y la capacidad de la empresa privada, para incrementar las posibilidades de alcanzar sus metas. Este nuevo modelo econ?mico permiti? que el Estado delegue la gesti?n de los servicios p?blicos en una administraci?n privada, sin perjuicio de retener su titularidad y competencia para ejercer las correspondientes funciones de regulaci?n y fiscalizaci?n. Por tanto, el objetivo general del presente trabajo es proponer mejoras al dise?o inicial de los contratos de concesi?n en infraestructura de transportes. Para ello, se presenta y analiza el marco conceptual de los contratos de concesi?n en cuanto contratos administrativos, as? como las teor?as relacionadas con su renegociaci?n. Luego se describe el marco normativo e institucional del sistema de concesiones del Per?, as? como las normas aplicables a la renegociaci?n de los contratos de concesi?n en el sector Transportes. A continuaci?n se efect?a el diagn?stico, se identifican y analizan los temas considerados m?s relevantes y que con mayor frecuencia son objeto de modificaci?n contractual. Finalmente, se formulan propuestas de mejora del dise?o de los contratos de concesi?n. El objetivo es que estas permitan perfeccionar los documentos contractuales de los proyectos a partir de los cuales se originan los futuros procesos de promoci?n de la inversi?n privada, espec?ficamente en aquellos temas en los cuales resulta posible hallar una soluci?n a trav?s del dise?o contractual

Geometries of Light and Shadows, from Piero della Francesca to James Turrell

This chapter addresses the problem of representing light and shadow in the artistic culture, from its uncertain beginnings, related to the studies on conical linear perspective in the Fifteenth Century, to the applications of light projection in the installations of contemporary art. Here are examined in particular two works by two artists, representing two different conceptual approaches to the perception and symbolism of light and shadow. The first is the so-called Brera Madonna by Piero della Francesca, where the image projected from a luminous radiation is employed with a narrative purpose, supporting the apparently hidden script of the painting and according to the artist\u2019s own speculations about perspective as a means to clarify the phenomenal world. The second is one of James Turrell\u2019s Dark Spaces installations, where quantum electrodynamics interpretation of light is taken into account: for Turrell, light is physical and thus can shape spaces where the visitors, or viewers, can \u201csee themselves seeing.\u201d In his body of work, perceptual deceptions are carefullyproduced by the interaction of the senses with his phenomenal staging of light and darkness, but a strong symbolic component is always present, often related to his own speculative interests. In both cases, light and shadow, through their geometries, emphasize both phenomenal and spiritual contents of the work of art, intended as a device to expand the perception and the knowledge of the viewer

Conifers in cold environments synchronize maximum growth rate of tree-ring formation with day length

Intra-annual radial growth rates and durations in trees are reported to differ greatly in relation to species, site and environmental conditions. However, very similar dynamics of cambial activity and wood formation are observed in temperate and boreal zones. Here, we compared weekly xylem cell production and variation in stem circumference in the main northern hemisphere conifer species (genera Picea, Pinus, Abies and Larix) from 1996 to 2003. Dynamics of radial growth were modeled with a Gompertz function, defining the upper asymptote (A), x-axis placement (β) and rate of change (κ). A strong linear relationship was found between the constants β and κ for both types of analysis. The slope of the linear regression, which corresponds to the time at which maximum growth rate occurred, appeared to converge towards the summer solstice. The maximum growth rate occurred around the time of maximum day length, and not during the warmest period of the year as previously suggested. The achievements of photoperiod could act as a growth constraint or a limit after which the rate of tree-ring formation tends to decrease, thus allowing plants to safely complete secondary cell wall lignification before winter

Statistical approach for supernova matter

We formulate a statistical model for description of nuclear composition and equation of state of stellar matter at subnuclear densities and temperature up to 20 MeV, which are expected during the collapse and explosion of massive stars. The model includes nuclear, electromagnetic and weak interactions between all kinds of particles, under condition of statistical equilibrium. We emphasize importance of realistic description of the nuclear composition for understanding stellar dynamics and nucleosynthesis. It is demonstrated that the experience accumulated in studies of nuclear multifragmentation reactions can be used for better modelling properties of stellar medium.Comment: 35 pages including 23 figures, submitted to Nuclear Physics

Productivity and evapotranspiration of two contrasting semiarid ecosystems following the 2011 global carbon land sink anomaly

© 2016 Elsevier B.V. Global carbon balances are increasingly affected by large fluctuations in productivity occurring throughout semiarid regions. Recent analyses found a large C uptake anomaly in 2011 in arid and semiarid regions of the southern hemisphere. Consequently, we compared C and water fluxes of two distinct woody ecosystems (a Mulga (Acacia) woodland and a Corymbia savanna) between August 2012 and August 2014 in semiarid central Australia, demonstrating that the 2011 anomaly was short-lived in both ecosystems. The Mulga woodland was approximately C neutral but with periods of significant uptake within both years. The extreme drought tolerance of Acacia is presumed to have contributed to this. By contrast, the Corymbia savanna was a very large net C source (130 and 200gCm-2yr-1 in average and below average rainfall years, respectively), which is likely to have been a consequence of the degradation of standing, senescent biomass that was a legacy of high productivity during the 2011 anomaly. The magnitude and temporal patterns in ecosystem water-use efficiencies (WUE), derived from eddy covariance data, differed across the two sites, which may reflect differences in the relative contributions of respiration to net C fluxes across the two ecosystems. In contrast, differences in leaf-scale measures of WUE, derived from 13C stable isotope analyses, were apparent at small spatial scales and may reflect the different rooting strategies of Corymbia and Acacia trees within the Corymbia savanna. Restrictions on root growth and infiltration by a siliceous hardpan located below Acacia, whether in the Mulga woodland or in small Mulga patches of the Corymbia savanna, impedes drainage of water to depth, thereby producing a reservoir for soil moisture storage under Acacia while acting as a barrier to access of groundwater by Corymbia trees in Mulga patches, but not in the open Corymbia savanna

Effectiveness of student response systems in terms of learning environment, attitudes and achievement

In order to investigate the effectiveness of using Student Response Systems (SRS) among grade 7 and 8 science students in New York, the How Do You Feel About This Class? (HDYFATC) questionnaire was administered to 1097 students (532 students did use SRS and 565 students who did not use SRS). Data analyses attested to the sound factorial validity and internal consistency reliability of the HDYFATC, as well as its ability to differentiate between the perceptions of students in different classrooms. Very large differences between users and non-users of SRS, ranging from 1.17 to 2.45 standard deviations for various learning environment scales, attitudes and achievement, supported the efficacy of using SRS

In-Datacenter Performance Analysis of a Tensor Processing Unit

Many architects believe that major improvements in cost-energy-performance must now come from domain-specific hardware. This paper evaluates a custom ASIC---called a Tensor Processing Unit (TPU)---deployed in datacenters since 2015 that accelerates the inference phase of neural networks (NN). The heart of the TPU is a 65,536 8-bit MAC matrix multiply unit that offers a peak throughput of 92 TeraOps/second (TOPS) and a large (28 MiB) software-managed on-chip memory. The TPU's deterministic execution model is a better match to the 99th-percentile response-time requirement of our NN applications than are the time-varying optimizations of CPUs and GPUs (caches, out-of-order execution, multithreading, multiprocessing, prefetching, ...) that help average throughput more than guaranteed latency. The lack of such features helps explain why, despite having myriad MACs and a big memory, the TPU is relatively small and low power. We compare the TPU to a server-class Intel Haswell CPU and an Nvidia K80 GPU, which are contemporaries deployed in the same datacenters. Our workload, written in the high-level TensorFlow framework, uses production NN applications (MLPs, CNNs, and LSTMs) that represent 95% of our datacenters' NN inference demand. Despite low utilization for some applications, the TPU is on average about 15X - 30X faster than its contemporary GPU or CPU, with TOPS/Watt about 30X - 80X higher. Moreover, using the GPU's GDDR5 memory in the TPU would triple achieved TOPS and raise TOPS/Watt to nearly 70X the GPU and 200X the CPU.Comment: 17 pages, 11 figures, 8 tables. To appear at the 44th International Symposium on Computer Architecture (ISCA), Toronto, Canada, June 24-28, 201

Streets of resilience: Exploring the role of educational outreach projects with street connected young people in Guatemala City

We explored resilience amongst street connected young people (SCYP) in Guatemala City in relation to two community‐based educational outreach projects who work with at risk young people. We investigated (a) how these projects adapt and constructed meaningful spaces of safety and protection for SCYP and (b) how their interactions with the families of SCYP impact on well‐being amongst SCYP. We focused on resilience‐building elements and practices, rather than on the dangers of street connectedness. Using ethnographic interviews, participatory photography, and image elicitation, we worked with eight young people and four adult project volunteers. Our research yielded evidence that dwellings, market stalls, and buildings used for religious purposes are being adapted as spaces of aspiration and opportunity to promote resilience. We found evidence of rifts between education projects and parents, and evidence for strategies for repairing these rifts. Our findings highlight the importance of community educational organisations in Guatemala City and have implications for their practice