16,015 research outputs found
Chemical Evolution of the Galaxy Based on the Oscillatory Star Formation History
We model the star formation history (SFH) and the chemical evolution of the
Galactic disk by combining an infall model and a limit-cycle model of the
interstellar medium (ISM). Recent observations have shown that the SFH of the
Galactic disk violently variates or oscillates. We model the oscillatory SFH
based on the limit-cycle behavior of the fractional masses of three components
of the ISM. The observed period of the oscillation ( Gyr) is reproduced
within the natural parameter range. This means that we can interpret the
oscillatory SFH as the limit-cycle behavior of the ISM. We then test the
chemical evolution of stars and gas in the framework of the limit-cycle model,
since the oscillatory behavior of the SFH may cause an oscillatory evolution of
the metallicity. We find however that the oscillatory behavior of metallicity
is not prominent because the metallicity reflects the past integrated SFH. This
indicates that the metallicity cannot be used to distinguish an oscillatory SFH
from one without oscillations.Comment: 21 pages LaTeX, to appear in Ap
Self-Regulation of Star Formation in Low Metallicity Clouds
We investigate the process of self-regulated star formation via
photodissociation of hydrogen molecules in low metallicity clouds. We evaluate
the influence region's scale of a massive star in low metallicity gas clouds
whose temperatures are between 100 and 10000 Kelvin. A single O star can
photodissociate hydrogen molecules in the whole of the host cloud. If
metallicity is smaller than about 10^{-2.5} of the solar metallicity, the
depletion of coolant of the the host cloud is very serious so that the cloud
cannot cool in a free-fall time, and subsequent star formation is almost
quenched. On the contrary, if metallicity is larger than about 10^{-1.5} of the
solar metallicity, star formation regulation via photodissociation is not
efficient. The typical metallicity when this transition occurs is about 1/100
of the solar metallicity. This indicates that stars do not form efficiently
before the metallicity becomes larger than about 1/100 of the solar metallicity
and we considered that this value becomes the lower limit of the metallicity of
luminous objects such as galaxies.Comment: 14 pages, including 5 figures, To appear in ApJ, Vol. 53
How can the land managers and his multi-stakeholder network at the farm level influence the multifunctional transitions pathways?
The changing role of agriculture is at the core of transition pathways in many rural areas. Productivism, post-productivism and multifunctionality have been targeted towards a possible conceptualization of the transition happening in rural areas. The factors of change, including productivist and post-productivist trends, are combined in various ways and have gone in quite diverse directions and intensities, in individual regions and localities. Even, in the same holding, productivist and post-productivist strategies can co-exist spatially, temporally, structurally, leading to a higher complexity in changing patterns. In south Portugal extensive landscapes, dominated by traditionally managed agro-forestry systems under a fuzzy land use pattern, multifunctionality at the farm level is indeed conducted by different stakeholders whose interests may or not converge: a multifunctional land management may indeed incorporate post-productivist and productivist agents. These stakeholders act under different levels of ownership, management and use, reflecting a particular land management dynamic, in which different interests may exist, from commercial production to a variety of other functions (hunting, bee-keeping, subsistence farming, etc.), influencing management at the farm level and its supposed transition trajectory. This multistakeholder dynamic is composed by the main land-manager (the one who takes the main decisions), sub land-managers (land-managers under the rules of the main land-manager), workers and users (locals or outsiders), whose interest and action within the holding may vary differently according to future (policy, market, etc.) trends, and therefore reflect more or less resilient systems. The goal of the proposed presentation is to describe the multi-stakeholder relations at the farm level, its spatial expression and the factors influencing the land management system resilience in face of the transition trends in place
The role of translational invariance in non linear gauge theories of gravity
The internal structure of the tetrads in a Poincar\'e non linear gauge theory
of gravity is considered. Minkowskian coordinates becomes dynamical degrees of
freedom playing the role of Goldstone bosons of the translations. A critical
length allowing a covariant expansion similar to the weak field approach is
deduced, the zeroth order metric being maximally symmetric (Minkowskian in some
cases).Comment: 17 pages, LaTe
Modular termination verification for non-blocking concurrency
© Springer-Verlag Berlin Heidelberg 2016.We present Total-TaDA, a program logic for verifying the total correctness of concurrent programs: that such programs both terminate and produce the correct result. With Total-TaDA, we can specify constraints on a thread’s concurrent environment that are necessary to guarantee termination. This allows us to verify total correctness for nonblocking algorithms, e.g. a counter and a stack. Our specifications can express lock- and wait-freedom. More generally, they can express that one operation cannot impede the progress of another, a new non-blocking property we call non-impedance. Moreover, our approach is modular. We can verify the operations of a module independently, and build up modules on top of each other
Building thermal dynamics modeling with deep learning exploiting large residential smart thermostat dataset
In this paper, we present a deep learning approach to model building thermal dynamics with large-scale smart thermostat data collected from residential buildings. We developed a Long Short-Term Memory (LSTM) model as a baseline and compared it to a CNN-LSTM model to predict indoor air temperature in a multi-step time horizon in 164 buildings. The study showed that the proposed CNN-LSTM achieved an average of 0.26 °C Mean Absolute Error (MAE) for one-hour-ahead (12 future steps) predictions, which is over 6% of improvement comparing with the baseline. Furthermore, the results indicated that the CNN-LSTM models achieved more robust performance across different building characteristics, system configurations and locations, with a standard deviation reduction of 22%, proving the effectiveness and generalizability of the proposed approach
Improving the Knowledge on Seismogenic Sources in the Lower Tagus Valley for Seismic Hazard Purposes
The Lower Tagus Valley, that includes the metropolitan area of Lisbon, has been struck by several earthquakes which produced significant material damage and loss of lives. Their exact location remains unknown. Our goal is to shed some light into the seismogenic sources in the area using seismic reflection and geological data. In areas with no seismic coverage, potential-field data interpretation was carried out. Seismicity was overlaid to the potential seismogenic structures and high-resolution data was acquired in order to confirm which structures have been active into the Quaternary. Three major fault-zones affecting the Neogene were identified: V. F. Xira, Samora-Alcochete and Pinhal Novo. For the first fault, strong evidences suggest it is active. The other two fault-zones and other structures previously unknown can be correlated with several epicentres. Empirical relationships between maximum moment magnitude and fault area indicate that MW > 6.5 earthquakes can be expected for the larger structures
Reflecting on collaborative research into the sustainability of Mediterranean agriculture: A case study using a systematization of experiences approach
This article describes how a research institute went about reviewing the relationship between its members and external research partners in engaging in collaborative research. A systematization of experiences (SE) process was implemented to enable such review and draw implications for the institute’s strategy regarding research into the sustainability of Mediterranean agriculture. The SE exercise included four workshops attended by selected researchers, one questionnaire survey targeting the institute’s research community, and three focus group discussions with external research partners. The rate of participation by researchers decreased during the process; however, those that followed through to the end of the SE exercise found it to be useful in clarifying both individual and institutional perspectives. Further, SE was seen as a vehicle for increasing the level of understanding between researchers and their willingness to engage in collaborative actions. However, the rapid pace of today’s academic world and the dominant mode of evaluating scientific performance were identified as hindering the conditions needed to allow the necessary space and time for reflection and collaborative efforts. Therefore, the results highlight the current tension between the production of scientific knowledge according to existing patterns and the development of socially meaningful research
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