10,248 research outputs found
The Rise of Supermarkets and Vertical Relationships in the Indonesian Food Value Chain: Causes and Consequences
This paper reviews the causes of the emergence of modern retailing and the vertical relationships in the Indonesian food value chain, and the consequences of these changes on market organization and value distribution. The findings of this paper suggest that there are both demand- and supply-side factors that contribute to the emergence of modern retailing. The evolution of vertical relationships between farmers and modern retailers observed in Indonesia is a direct response to risks and quality uncertainty. In the vertical relation, large-scale retailers may earn a monopsonistic rent, and there are risks of exclusion of small-scale farmers from the emerging food value chain. However, there are alternative channels through which farmers may sell their products, albeit at a lower price compared to the modern channels, and measures can be instituted to protect them against monopsonistic rents. The findings have important policy implications for developing countries.supermarkets, retailing, Indonesia, food value chain
A new cellular automata model for city traffic
We present a new cellular automata model of vehicular traffic in cities by
combining ideas borrowed from the Biham-Middleton-Levine (BML) model of city
traffic and the Nagel-Schreckenberg (NaSch) model of highway traffic. The model
exhibits a dynamical phase transition to a completely jammed phase at a
critical density which depends on the time periods of the synchronized signals.Comment: 6 pages, 5 figures, uses Springer Macros 'lncse', to appear in
"Traffic and Granular Flow '99: Social, Traffic, and Granular Dynamics"
edited by D. Helbing, H. J. Herrmann, M. Schreckenberg, and D. E. Wolf
(Springer, Berlin
Time-resolved measurement of single pulse femtosecond laser-induced periodic surface structure formation
Time-resolved diffraction microscopy technique has been used to observe the
formation of laser-induced periodic surface structures (LIPSS) from the
interaction of a single femtosecond laser pulse (pump) with a nano-scale groove
mechanically formed on a single-crystal Cu substrate. The interaction dynamics
(0-1200 ps) was captured by diffracting a time-delayed, frequency-doubled pulse
from nascent LIPSS formation induced by the pump with an infinity-conjugate
microscopy setup. The LIPSS ripples are observed to form sequentially outward
from the groove edge, with the first one forming after 50 ps. A 1-D analytical
model of electron heating and surface plasmon polariton (SPP) excitation
induced by the interaction of incoming laser pulse with the groove edge
qualitatively explains the time-evloution of LIPSS formation.Comment: 4 pages, 5 figure
Microscopic energy flows in disordered Ising spin systems
An efficient microcanonical dynamics has been recently introduced for Ising
spin models embedded in a generic connected graph even in the presence of
disorder i.e. with the spin couplings chosen from a random distribution. Such a
dynamics allows a coherent definition of local temperatures also when open
boundaries are coupled to thermostats, imposing an energy flow. Within this
framework, here we introduce a consistent definition for local energy currents
and we study their dependence on the disorder. In the linear response regime,
when the global gradient between thermostats is small, we also define local
conductivities following a Fourier dicretized picture. Then, we work out a
linearized "mean-field approximation", where local conductivities are supposed
to depend on local couplings and temperatures only. We compare the approximated
currents with the exact results of the nonlinear system, showing the
reliability range of the mean-field approach, which proves very good at high
temperatures and not so efficient in the critical region. In the numerical
studies we focus on the disordered cylinder but our results could be extended
to an arbitrary, disordered spin model on a generic discrete structures.Comment: 12 pages, 6 figure
Global Opportunities to Increase Agricultural Independence Through Phosphorus Recycling
Food production hinges largely upon access to phosphorus (P) fertilizer. Most fertilizer P used in the global agricultural system comes from mining of nonrenewable phosphate rock deposits located within few countries. However, P contained in livestock manure or urban wastes represents a recyclable source of P. To inform development of P recycling technologies and policies, we examined subnational, national, and global spatial patterns for two intersections of land use affording high P recycling potential: (a) manure‐rich cultivated areas and (b) populous cultivated areas. In turn, we examined overlap between P recycling potential and nation‐level P fertilizer import dependency. Populous cultivated areas were less abundant globally than manure‐rich cultivated areas, reflecting greater segregation between crops and people compared to crops and livestock, especially in the Americas. Based on a global hexagonal grid (290‐km2 grid cell area), disproportionately large shares of subnational “hot spots” for P recycling potential occurred in India, China, Southeast Asia, Europe, and parts of Africa. Outside of China, most of the remaining manure‐rich or populous cultivated areas occurred within nations that had relatively high imports of P fertilizer (net P import:consumption ratios ≥0.4) or substantial increases in fertilizer demand between the 2000s (2002–2006) and 2010s (2010–2014). Manure‐rich cultivated grid cells (those above the 75th percentiles for both manure and cropland extent) represented 12% of the global grid after excluding cropless cells. Annually, the global sum of animal manure P was at least 5 times that contained in human excreta, and among cultivated cells the ratio was frequently higher (median = 8.9). The abundance of potential P recycling hot spots within nations that have depended on fertilizer imports or experienced rising fertilizer demand could prove useful for developing local P sources and maintaining agricultural independence
Hysteresis phenomenon in deterministic traffic flows
We study phase transitions of a system of particles on the one-dimensional
integer lattice moving with constant acceleration, with a collision law
respecting slower particles. This simple deterministic ``particle-hopping''
traffic flow model being a straightforward generalization to the well known
Nagel-Schreckenberg model covers also a more recent slow-to-start model as a
special case. The model has two distinct ergodic (unmixed) phases with two
critical values. When traffic density is below the lowest critical value, the
steady state of the model corresponds to the ``free-flowing'' (or ``gaseous'')
phase. When the density exceeds the second critical value the model produces
large, persistent, well-defined traffic jams, which correspond to the
``jammed'' (or ``liquid'') phase. Between the two critical values each of these
phases may take place, which can be interpreted as an ``overcooled gas'' phase
when a small perturbation can change drastically gas into liquid. Mathematical
analysis is accomplished in part by the exact derivation of the life-time of
individual traffic jams for a given configuration of particles.Comment: 22 pages, 6 figures, corrected and improved version, to appear in the
Journal of Statistical Physic
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