489 research outputs found
Design of sustainable supply chains for the agrifood sector: a holistic research framework
Agrifood sector is one of the most important economic and political areas within the European Union, with key implications for sustainability such as the fulfillment of human needs, the support of employment and economic growth, and its impact on the natural environment. Â Growing environmental, social and ethical concerns and increased awareness of the impacts of the agrifood sector have led to increased pressure by all involved supply chain stakeholders, while at the same time the European Union has undertaken a number of relevant regulatory interventions. Â This paper aims to present a methodological framework for the design of green supply chains for the agrifood sector. Â The framework aims towards the optimization of the agrifood supply chain design, planning and operations through the implementation of appropriate green supply chain management and logistics principles. Â More specifically, focus is put on the minimization of the environmental burden and the maximization of supply chain sustainability of the agrifood supply chain. Â The application of such a framework could result into substantial reduction of CO2 emissions both by the additional production of other biofuels from waste, as well as the introduction of a novel intelligent logistics network, in order to reduce the harvest and transportation energy input. Â Moreover, the expansion of the biomass feedstock available for biofuel production can provide adequate support towards avoidance of food/fuel competition for land use. Â Keywords: supply chain management, green supply chains, sustainable development, agrifood secto
Scanning probe microscopy techniques for mechanical characterization at nanoscale
Three atomic force microscopy (AFM)-based techniques are reviewed that allow one to conduct accurate measurements of mechanical properties of either stiff or compliant materials at a nanometer scale. Atomic force acoustic microscopy, AFM-based depth sensing indentation, and torsional harmonic AFM are briefly described. Examples and results of quantitative characterization of stiff (an ultrathin SeSn film), soft polymeric (polyaniline fibers doped with detonation nanodiamond) and biological (collagen fibers) materials are reported
Variability and spectral modeling of the hard X-ray emission of GX 339-4 in a bright low/hard state
We study the high-energy emission of the Galactic black hole candidate GX
339-4 using INTEGRAL/SPI and simultaneous RXTE/PCA data. By the end of January
2007, when it reached its peak luminosity in hard X-rays, the source was in a
bright hard state. The SPI data from this period show a good signal to noise
ratio, allowing a detailed study of the spectral energy distribution up to
several hundred keV. As a main result, we report on the detection of a variable
hard spectral feature (>150 keV) which represents a significant excess with
respect to the cutoff power law shape of the spectrum. The SPI data suggest
that the intensity of this feature is positively correlated with the 25 - 50
keV luminosity of the source and the associated variability time scale is
shorter than 7 hours. The simultaneous PCA data, however, show no significant
change in the spectral shape, indicating that the source is not undergoing a
canonical state transition. We analyzed the broad band spectra in the lights of
several physical models, assuming different heating mechanisms and properties
of the Comptonizing plasma. For the first time, we performed quantitative model
fitting with the new versatile Comptonization code BELM, accounting
self-consistently for the presence of a magnetic field. We show that a
magnetized medium subject to pure non-thermal electron acceleration provides a
framework for a physically consistent interpretation of the observed 4 - 500
keV emission. Moreover, we find that the spectral variability might be
triggered by the variations of only one physical parameter, namely the magnetic
field strength. Therefore, it appears that the magnetic field is likely to be a
key parameter in the production of the Comptonized hard X-ray emission.Comment: 14 pages, 9 figures, 3 tables, uses emulateApj.cls, accepted for
publication in Ap
New Method for Phase transitions in diblock copolymers: The Lamellar case
A new mean-field type theory is proposed to study order-disorder transitions
(ODT) in block copolymers. The theory applies to both the weak segregation (WS)
and the strong segregation (SS) regimes. A new energy functional is proposed
without appealing to the random phase approximation (RPA). We find new terms
unaccounted for within RPA. We work out in detail transitions to the lamellar
state and compare the method to other existing theories of ODT and numerical
simulations. We find good agreements with recent experimental results and
predict that the intermediate segregation regime may have more than one scaling
behavior.Comment: 23 pages, 8 figure
Protein kinase Cι is required for Ras transformation and colon carcinogenesis in vivo
Protein kinase C ι (PKCι) has been implicated in Ras signaling, however, a role for PKCι in oncogenic Ras-mediated transformation has not been established. Here, we show that PKCι is a critical downstream effector of oncogenic Ras in the colonic epithelium. Transgenic mice expressing constitutively active PKCι in the colon are highly susceptible to carcinogen-induced colon carcinogenesis, whereas mice expressing kinase-deficient PKCι (kdPKCι) are resistant to both carcinogen- and oncogenic Ras-mediated carcinogenesis. Expression of kdPKCι in Ras-transformed rat intestinal epithelial cells blocks oncogenic Ras-mediated activation of Rac1, cellular invasion, and anchorage-independent growth. Constitutively active Rac1 (RacV12) restores invasiveness and anchorage-independent growth in Ras-transformed rat intestinal epithelial cells expressing kdPKCι. Our data demonstrate that PKCι is required for oncogenic Ras- and carcinogen-mediated colon carcinogenesis in vivo and define a procarcinogenic signaling axis consisting of Ras, PKCι, and Rac1
Lattice-gas simulations of Domain Growth, Saturation and Self-Assembly in Immiscible Fluids and Microemulsions
We investigate the dynamical behavior of both binary fluid and ternary
microemulsion systems in two dimensions using a recently introduced
hydrodynamic lattice-gas model of microemulsions. We find that the presence of
amphiphile in our simulations reduces the usual oil-water interfacial tension
in accord with experiment and consequently affects the non-equilibrium growth
of oil and water domains. As the density of surfactant is increased we observe
a crossover from the usual two-dimensional binary fluid scaling laws to a
growth that is {\it slow}, and we find that this slow growth can be
characterized by a logarithmic time scale. With sufficient surfactant in the
system we observe that the domains cease to grow beyond a certain point and we
find that this final characteristic domain size is inversely proportional to
the interfacial surfactant concentration in the system.Comment: 28 pages, latex, embedded .eps figures, one figure is in colour, all
in one uuencoded gzip compressed tar file, submitted to Physical Review
The Wetting Behavior of Polymer Droplets: Effects of Droplet Size and Chain Length
Monte
Carlo computer simulations were utilized to probe the behavior
of homopolymer droplets adsorbed at solid surfaces as a function of
the number of chains making up the droplets and varying droplet sizes.
The wetting behavior is quantified via the ratio of the perpendicular
to the parallel component of the effective radii of gyration of the
droplets and is analyzed further in terms of the adsorption behavior
of the polymer chains and the monomers that constitute the droplets.
This analysis is complemented by an account of the shape of the droplets
in terms of the principal moments of the radius of gyration tensor.
Single-chain droplets are found to lie flatter and wet the substrate
more than chemically identical multichain droplets, which attain a
more globular shape and wet the substrate less. The simulation findings
are in good agreement with atomic force microscopy experiments. The
present investigation illustrates a marked dependence of wetting and
adsorption on certain structural arrangements and proposes this dependence
as a technique through which polymer wetting may be tuned
Local re-acceleration and a modified thick target model of solar flare electrons
The collisional thick target model (CTTM) of solar hard X-ray (HXR) bursts
has become an almost 'Standard Model' of flare impulsive phase energy transport
and radiation. However, it faces various problems in the light of recent data,
particularly the high electron beam density and anisotropy it involves.} {We
consider how photon yield per electron can be increased, and hence fast
electron beam intensity requirements reduced, by local re-acceleration of fast
electrons throughout the HXR source itself, after injection.} {We show
parametrically that, if net re-acceleration rates due to e.g. waves or local
current sheet electric () fields are a significant fraction of
collisional loss rates, electron lifetimes, and hence the net radiative HXR
output per electron can be substantially increased over the CTTM values. In
this local re-acceleration thick target model (LRTTM) fast electron number
requirements and anisotropy are thus reduced. One specific possible scenario
involving such re-acceleration is discussed, viz, a current sheet cascade (CSC)
in a randomly stressed magnetic loop.} {Combined MHD and test particle
simulations show that local fields in CSCs can efficiently
accelerate electrons in the corona and and re-accelerate them after injection
into the chromosphere. In this HXR source scenario, rapid synchronisation and
variability of impulsive footpoint emissions can still occur since primary
electron acceleration is in the high Alfv\'{e}n speed corona with fast
re-acceleration in chromospheric CSCs. It is also consistent with the
energy-dependent time-of-flight delays in HXR features.Comment: 8 pages, 2 figure
Nowcasting Solar Energetic Particle Events Using Principal Component Analysis
We perform a principal component analysis (PCA) on a set of six solar variables (i.e. width/size () and velocity () of a coronal mass ejection, logarithm of the solar flare (SF) magnitude (), SF longitude (), duration (), and rise time ()). We classify the solar energetic particle (SEP) event radiation impact (in terms of the National Oceanic and Atmospheric Administration scales) with respect to the characteristics of their parent solar events. We further attempt to infer the possible prediction of SEP events. In our analysis, we use 126 SEP events with complete solar information, from 1997 to 2013. Each SEP event is a vector in six dimensions (corresponding to the six solar variables used in this work). The PCA transforms the input vectors into a set of orthogonal components. By mapping the characteristics of the parent solar events, a new base defined by these components led to the classification of the SEP events. We furthermore applied logistic regression analysis with single, as well as multiple explanatory variables, in order to develop a new index () for the nowcasting (short-term forecasting) of SEP events. We tested several different schemes for and validated our findings with the implementation of categorical scores (probability of detection (POD) and false-alarm rate (FAR)). We present and interpret the obtained scores, and discuss the strengths and weaknesses of the different implementations. We show that holds prognosis potential for SEP events. The maximum POD achieved is 77.78% and the relative FAR is 40.96%
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