2,350 research outputs found
TRANSGENIC CROPS AND THE ENVIRONMENT: MISSING MARKETS AND PUBLIC ROLE
The rapidity of change has left scant opportunity for investigation of the consequences of biotechnology adoption on long-term ecosystem or economic system functioning. Economic theory suggests that, if the "Biotechnology Revolution" is left to market forces alone,there will be neglected public goods. Theory and limited empirical evidence suggests that there are significant incentives for private firms to discount and neglect certain environmental impacts and to develop products that meet only the needs of those able and willing to pay. Negative distributional impacts on rural societies and economies will not normally enter the private calculus nor will the long-term problems of insect and plant resistance. Thus, there is a strong case for enhanced public roles with respect to the use of transgenic crops. The adoption of the precautionary approach in public policies addressing transgenic crops is one alternative to better reflect public concerns.Environmental Economics and Policy, Research and Development/Tech Change/Emerging Technologies,
A pilot demonstration project of technology application from the aerospace industry to city management (four cities program)
The Four Cities Program has completed the first year of the planned two-year program. At the beginning of the first year, a variety of program initiation activities were accomplished. Contracts were negotiated; science and technology advisors were interviewed, selected and assigned; general indoctrination and integration of the advisors into city affairs occurred; technical needs were identified and related projects pursued; pilot projects for the second year were identified; inter-city coordination on technical problems began to emerge; and the general soundness of the four cities program seems to have been established. Above all, the inter-personal relationships between the advisors and their interfaces in city government appear to be functioning smoothly. The establishment of such mutual respect, trusts, and confidences are believed essential to the success of the program
Parametrization of gamma-ray production cross-sections for pp interactions in a broad proton energy range from the kinematic threshold to PeV energies
Using publicly available Monte Carlo codes as well as compilation of
published data on p--p interactions for proton kinetic energy below 2 GeV, we
parametrize the energy spectra and production rates of -rays by simple
but quite accurate () analytical expressions in a broad range from
the kinematic threshold to PeV energies.Comment: 19 pages, 15 figures, v2 version fixes the cross reference
Extensive Characterization of Seismic Laws in Acoustic Emissions of Crumpled Plastic Sheets
Statistical similarities between earthquakes and other systems that emit
cracking noises have been explored in diverse contexts, ranging from materials
science to financial and social systems. Such analogies give promise of a
unified and universal theory for describing the complex responses of those
systems. There are, however, very few attempts to simultaneously characterize
the most fundamental seismic laws in such systems. Here we present a complete
description of the Gutenberg-Richter law, the recurrence times, Omori's law,
the productivity law, and Bath's law for the acoustic emissions that happen in
the relaxation process of uncrumpling thin plastic sheets. Our results show
that these laws also appear in this phenomenon, but (for most cases) with
different parameters from those reported for earthquakes and fracture
experiments. This study thus contributes to elucidate the parallel between
seismic laws and cracking noises in uncrumpling processes, revealing striking
qualitative similarities but also showing that these processes display unique
features.Comment: Accepted for publication in EP
Resources/Services Available to the Handicapped of Southside Tidewater Virginia
Two research objectives were set up for this study. These included: 1. Accumulate and analyze data on the services and resources available to the handicapped in the Southside Tidewater area; 2. Develop a method or media for information dissemination to those who work with the targeted population
Distance to the scaling law: a useful approach for unveiling relationships between crime and urban metrics
We report on a quantitative analysis of relationships between the number of
homicides, population size and other ten urban metrics. By using data from
Brazilian cities, we show that well defined average scaling laws with the
population size emerge when investigating the relations between population and
number of homicides as well as population and urban metrics. We also show that
the fluctuations around the scaling laws are log-normally distributed, which
enabled us to model these scaling laws by a stochastic-like equation driven by
a multiplicative and log-normally distributed noise. Because of the scaling
laws, we argue that it is better to employ logarithms in order to describe the
number of homicides in function of the urban metrics via regression analysis.
In addition to the regression analysis, we propose an approach to correlate
crime and urban metrics via the evaluation of the distance between the actual
value of the number of homicides (as well as the value of the urban metrics)
and the value that is expected by the scaling law with the population size.
This approach have proved to be robust and useful for unveiling
relationships/behaviors that were not properly carried out by the regression
analysis, such as i) the non-explanatory potential of the elderly population
when the number of homicides is much above or much below the scaling law, ii)
the fact that unemployment has explanatory potential only when the number of
homicides is considerably larger than the expected by the power law, and iii) a
gender difference in number of homicides, where cities with female population
below the scaling law are characterized by a number of homicides above the
power law.Comment: Accepted for publication in PLoS ON
Scale-adjusted metrics for predicting the evolution of urban indicators and quantifying the performance of cities
More than a half of world population is now living in cities and this number
is expected to be two-thirds by 2050. Fostered by the relevancy of a scientific
characterization of cities and for the availability of an unprecedented amount
of data, academics have recently immersed in this topic and one of the most
striking and universal finding was the discovery of robust allometric scaling
laws between several urban indicators and the population size. Despite that,
most governmental reports and several academic works still ignore these
nonlinearities by often analyzing the raw or the per capita value of urban
indicators, a practice that actually makes the urban metrics biased towards
small or large cities depending on whether we have super or sublinear
allometries. By following the ideas of Bettencourt et al., we account for this
bias by evaluating the difference between the actual value of an urban
indicator and the value expected by the allometry with the population size. We
show that this scale-adjusted metric provides a more appropriate/informative
summary of the evolution of urban indicators and reveals patterns that do not
appear in the evolution of per capita values of indicators obtained from
Brazilian cities. We also show that these scale-adjusted metrics are strongly
correlated with their past values by a linear correspondence and that they also
display crosscorrelations among themselves. Simple linear models account for
31%-97% of the observed variance in data and correctly reproduce the average of
the scale-adjusted metric when grouping the cities in above and below the
allometric laws. We further employ these models to forecast future values of
urban indicators and, by visualizing the predicted changes, we verify the
emergence of spatial clusters characterized by regions of the Brazilian
territory where we expect an increase or a decrease in the values of urban
indicators.Comment: Accepted for publication in PLoS ON
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Polyamide Nanocomposites for Selective Laser Sintering
Current polyamide 11 and 12 are lacking in fire retardancy and high strength/high
heat resistance characteristics for a plethora of finished parts that are desired and required
for performance driven applications. It is anticipated that nanomodification of polyamide
11 and 12 will result in enhanced polymer performance, i.e., fire retardancy, high strength
and high heat resistance for polyamide 11 and 12. It is expected that these findings will
expand the market opportunities for polyamide 11 and 12 resin manufacturers.
The objective of this research is to develop improved polyamide 11 and 12 polymers
with enhanced flame retardancy, thermal, and mechanical properties for selective laser
sintering (SLS) rapid manufacturing (RM). A nanophase was introduced into the
polyamide 11 and 12 via twin screw extrusion to provide improved material properties of
the polymer blends. Arkema RILSAN® polyamide 11 molding polymer pellets and
Degussa VESTAMID® L1670 polyamide 12 were examined with three types of
nanoparticles: chemically modified montmorillonite (MMT) organoclays, surface
modified nanosilica, and carbon nanofibers (CNFs) to create polyamide 11 and 12
nanocomposites.
Wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM)
were used to determine the degree of dispersion. Injection molded test specimens were
fabricated for physical, thermal, mechanical properties, and flammability tests. Thermal
stability of these polyamide 11 and 12 nanocomposites was examined by TGA.
Mechanical properties such as tensile, flexural, and elongation at break were measured.
Flammability properties were also obtained using the Cone Calorimeter at an external
heat flux of 50 kW/m2. TEM micrographs, physical, mechanical, and flammability
properties are included in the paper. Polyamide 11 and 12 nanocomposites properties are
compared with polyamide 11 and 12 baseline polymers. Based on flammability and
mechanical material performance, selective polymers including polyamide 11
nanocomposites and control polyamide 11 were cryogenically ground into fine powders
and fabricated into SLS parts.Mechanical Engineerin
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