507 research outputs found
Implications of Public Opinion for Space Program Planning, 1980 - 2000
The effect of public opinion on future space programs is discussed in terms of direct support, apathy, or opposition, and concern about the tax burden, budgetary pressures, and national priorities. Factors considered include: the salience and visibility of NASA as compared with other issues, the sources of general pressure on the federal budget which could affect NASA, the public's opinions regarding the size and priority of NASA'S budget, the degree to which the executive can exercise leverage over NASA's budget through influencing or disregarding public opinion, the effects of linkages to other issues on space programs, and the public's general attitudes toward the progress of science
La influencia de UBER como modelo de servicio en la preferencia de los usuarios del segmento B entre los 20-25 años de Ate Vitarte en el año 2018.
Al buscar en las tiendas de App que nos ofrecen los teléfonos móviles, el nombre de “UBER” en este navegador nos devuelve una gran cantidad de buenos comentarios. Frente a este buen número de comentarios, también aparece un notorio número de App’s, donde distinguimos la aparición de los sectores de Taxi. Como si se tratara de la venta de camisetas en los estadios, antes y después del evento deportivo, mucha variedad para elegir. Pero siempre al encontrar una buena opción dejas de lado otra, como en este caso sería la preferencia de App’s sobre el uso de taxis informales, casi habitual entre un fenómeno reciente de nuestra economía y un sector con muchos años a su espalda. Modernidad y tradición se enfrentan de nuevo, cuál enfrentamiento de animales hambrientos, algo que analizaremos en este documento, no es ningún fruto de casualidad
Atmospheric Consequences of Cosmic Ray Variability in the Extragalactic Shock Model II: Revised ionization levels and their consequences
It has been suggested that galactic shock asymmetry induced by our galaxy's
infall toward the Virgo Cluster may be a source of periodicity in cosmic ray
exposure as the solar system oscillates perpendicular to the galactic plane.
Here we investigate a mechanism by which cosmic rays might affect terrestrial
biodiversity, ionization and dissociation in the atmosphere, resulting in
depletion of ozone and a resulting increase in the dangerous solar UVB flux on
the ground, with an improved ionization background computation averaged over a
massive ensemble (about 7 x 10^5) shower simulations. We study minimal and full
exposure to the postulated extragalactic background. The atmospheric effects
are greater than with our earlier, simplified ionization model. At the lower
end of the range effects are too small to be of serious consequence. At the
upper end of the range, ~6 % global average loss of ozone column density
exceeds that currently experienced due to effects such as accumulated
chlorofluorocarbons. The intensity is less than a nearby supernova or galactic
gamma-ray burst, but the duration would be about 10^6 times longer. Present UVB
enhancement from current ozone depletion ~3% is a documented stress on the
biosphere, but a depletion of the magnitude found at the upper end of our range
would double the global average UVB flux. For estimates at the upper end of the
range of the cosmic ray variability over geologic time, the mechanism of
atmospheric ozone depletion may provide a major biological stress, which could
easily bring about major loss of biodiversity. Future high energy astrophysical
observations will resolve the question of whether such depletion is likely.Comment: 22 pages, 5 figures, to be published in Journal of Geophysical
Research--Planets. This is an update and replacement for our 2008 paper, with
a much more extensive simulation of air shower ionization. Ionization effects
and ozone depletion are somewhat large
Why growth equals power - and why it shouldn't : constructing visions of China
When discussing the success of China's transition from socialism, there is a tendency to focus on growth figures as an indication of performance. Whilst these figures are
indeed impressive, we should not confuse growth with development and assume that the former necessarily automatically generates the latter. Much has been done to
reduce poverty in China, but the task is not as complete as some observers would suggest; particularly in terms of access to health, education and welfare, and also in
dealing with relative (rather than absolute) depravation and poverty. Visions of China have been constructed that exaggerate Chinese development and power in the global
system partly to serve political interests, but partly due to the failure to consider the relationship between growth and development, partly due to the failure to disaggregate
who gets what in China, and partly due to the persistence of inter-national conceptions of globalised production, trade, and financial flows
How spiking neurons give rise to a temporal-feature map
A temporal-feature map is a topographic neuronal representation of temporal attributes of phenomena or objects that occur in the outside world. We explain the evolution of such maps by means of a spike-based Hebbian learning rule in conjunction with a presynaptically unspecific contribution in that, if a synapse changes, then all other synapses connected to the same axon change by a small fraction as well. The learning equation is solved for the case of an array of Poisson neurons. We discuss the evolution of a temporal-feature map and the synchronization of the single cells’ synaptic structures, in dependence upon the strength of presynaptic unspecific learning. We also give an upper bound for the magnitude of the presynaptic interaction by estimating its impact on the noise level of synaptic growth. Finally, we compare the results with those obtained from a learning equation for nonlinear neurons and show that synaptic structure formation may profit
from the nonlinearity
Long term time variability of cosmic rays and possible relevance to the development of life on Earth
An analysis is made of the manner in which the cosmic ray intensity at Earth
has varied over its existence and its possible relevance to both the origin and
the evolution of life. Much of the analysis relates to the 'high energy' cosmic
rays () and their variability due to the changing
proximity of the solar system to supernova remnants which are generally
believed to be responsible for most cosmic rays up to PeV energies. It is
pointed out that, on a statistical basis, there will have been considerable
variations in the likely 100 My between the Earth's biosphere reaching
reasonable stability and the onset of very elementary life. Interestingly,
there is the increasingly strong possibility that PeV cosmic rays are
responsible for the initiation of terrestrial lightning strokes and the
possibility arises of considerable increases in the frequency of lightnings and
thereby the formation of some of the complex molecules which are the 'building
blocks of life'. Attention is also given to the well known generation of the
oxides of nitrogen by lightning strokes which are poisonous to animal life but
helpful to plant growth; here, too, the violent swings of cosmic ray
intensities may have had relevance to evolutionary changes. A particular
variant of the cosmic ray acceleration model, put forward by us, predicts an
increase in lightning rate in the past and this has been sought in Korean
historical records. Finally, the time dependence of the overall cosmic ray
intensity, which manifests itself mainly at sub-10 GeV energies, has been
examined. The relevance of cosmic rays to the 'global electrical circuit'
points to the importance of this concept.Comment: 18 pages, 5 figures, accepted by 'Surveys in Geophysics
Micro-finance, women’s empowerment and fertility decline in Bangladesh: How important was women’s agency?
As Nobel Prize winner Amartya Sen has argued “[Bangladesh’s development achievements have] important lessons for other countries across the globe, [in particular a focus on] reducing gender inequality”. A major avenue through which this emphasis has been manifest lies, according to this narrative, in enhancements to women’s agency for instrumental and intrinsic reasons particularly through innovations in family planning and microfinance. The “Bangladesh paradox” of improved wellbeing despite low economic growth over the last four decades is claimed as a paradigmatic case of the spread of both modern family planning programmes and microfinance leading to women’s empowerment and fertility reduction. In this paper we show that the links between microfinance, empowerment and fertility reduction, are fraught with problems, and far from robust; hence the claimed causal links between microfinance and family planning via women’s empowerment needs to be further reconsidered
Carbon fixation rates in groundwater similar to those in oligotrophic marine systems
The terrestrial subsurface contains nearly all of Earth’s freshwater reserves and harbours the majority of our planet’s total prokaryotic biomass. Although genetic surveys suggest these organisms rely on in situ carbon fixation, rather than the photosynthetically derived organic carbon transported from surface environments, direct measurements of carbon fixation in the subsurface are absent. Using an ultra-low level 14C-labelling technique, we estimate in situ carbon fixation rates in a carbonate aquifer. We find these rates are similar to those measured in oligotrophic marine surface waters and up to six-fold greater than those observed in the lower euphotic zone. Our empirical carbon fixation rates agree with nitrification rate data. Metagenomic analyses reveal abundant putative chemolithoautotrophic members of an uncharacterized order of Nitrospiria that may be behind the carbon fixation. On the basis of our determined carbon fixation rates, we conservatively extrapolate global primary production in carbonate groundwaters (10% of global reserves) to be 0.11 Pg carbon per year. These rates fall within the range found for oligotrophic marine surface waters, indicating a substantial contribution of in situ primary production to subsurface ecosystem processes. We further suggest that, just as phototrophs are for marine biogeochemical cycling, such subsurface carbon fixation is potentially foundational to subsurface trophic webs.</p
Deepwater dissolved oxygen shows little ecological memory between lake phenological seasons
Depletion of deepwater dissolved oxygen (DO) in lakes has become increasingly prevalent and severe because of many external stressors, potentially threatening human-derived ecosystem services ranging from drinking water quality to fisheries. Using year-round, high-frequency DO data from 12 dimictic lakes, we compared 3 measures of deepwater DO depletion during winter and summer: DO depletion rate, DO minimum, and hypoxia duration. Hypoxia (DO 65%) regardless of the previous summer’s DO depletion severity. This lack of ecological memory in deepwater DO depletion across seasons suggests that deepwater DO largely resets during spring and fall mixing periods in most years in these dimictic lakes. Understanding the patterns and drivers in deepwater DO depletion in both winter and summer is a key step forward for predicting future chemical and biological consequences of seasonal DO depletion and managing lake ecosystem health, as well as the effects that climate change may have on these patterns.acceptedVersio
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