9,380 research outputs found
WHY DO FARMERS FORWARD CONTRACT IN FACTOR MARKETS?
This study investigated farmers' incentives to forward purchase inputs. A model of farmer decision making was used to derive an optimal forward contracting rule. Explicit in the model was the tradeoff between the quantity of input to be purchased in advance, and the remaining portion to be purchased later on the spot market. Results indicated that the primary reasons farmers contract inputs are to reduce risk and to speculate on favorable price moves. A numerical example of fertilizer used in corn production indicated that the size of the price discount was the dominant factor in forward contracting decisions.Farm Management,
Creation, Coordination, and Activation of Resources in Physics and Mathematics Learning
This project seeks to study introductory college level courses in physics, mechanics, and mathematics. The research questions involve the processes by which students become able to use resources across contexts (such as between mathematics and physics), how ideas in math and physics form a resource network, and what mechanisms trigger individual resources or coordinated networks. The researcher will conduct clinical interviews, small group interviews, and statistical analysis of survey questions as well as videos from classroom and help sessions. The data being collected would be analyzed for purpose of describing the development of students as they refine skills in mathematics and physical reasoning. A small group of students (15) at the University of Maine will be the subject of the study.The outcome of this project is expected to be a better model of student reasoning and learning . The reviewers were particularly interested in the possibly useful observations about the connections between mathematics and physics learning. Papers would be prepared for all education research associations, including physics
Kernel Metric Learning for Clustering Mixed-type Data
Distance-based clustering and classification are widely used in various
fields to group mixed numeric and categorical data. A predefined distance
measurement is used to cluster data points based on their dissimilarity. While
there exist numerous distance-based measures for data with pure numerical
attributes and several ordered and unordered categorical metrics, an optimal
distance for mixed-type data is an open problem. Many metrics convert numerical
attributes to categorical ones or vice versa. They handle the data points as a
single attribute type or calculate a distance between each attribute separately
and add them up. We propose a metric that uses mixed kernels to measure
dissimilarity, with cross-validated optimal kernel bandwidths. Our approach
improves clustering accuracy when utilized for existing distance-based
clustering algorithms on simulated and real-world datasets containing pure
continuous, categorical, and mixed-type data.Comment: 23 pages, 5 tables, 2 figure
Cosmological Constraints on a Dynamical Electron Mass
Motivated by recent astrophysical observations of quasar absorption systems,
we formulate a simple theory where the electron to proton mass ratio is allowed to vary in space-time. In such a minimal theory only
the electron mass varies, with and kept constant. We find
that changes in will be driven by the electronic energy density after
the electron mass threshold is crossed. Particle production in this scenario is
negligible. The cosmological constraints imposed by recent astronomical
observations are very weak, due to the low mass density in electrons. Unlike in
similar theories for spacetime variation of the fine structure constant, the
observational constraints on variations in imposed by the weak
equivalence principle are much more stringent constraints than those from
quasar spectra. Any time-variation in the electron-proton mass ratio must be
less than one part in since redshifts This is more than
one thousand times smaller than current spectroscopic sensitivities can
achieve. Astronomically observable variations in the electron-proton must
therefore arise directly from effects induced by varying fine structure
'constant' or by processes associated with internal proton structure. We also
place a new upper bound of on any large-scale spatial
variation of that is compatible with the isotropy of the microwave
background radiation.Comment: New bounds from weak equivalence principle experiments added,
conclusions modifie
Narrow-line Laser Cooling by Adiabatic Transfer
We propose and demonstrate a novel laser cooling mechanism applicable to
particles with narrow-linewidth optical transitions. By sweeping the frequency
of counter-propagating laser beams in a sawtooth manner, we cause adiabatic
transfer back and forth between the ground state and a long-lived optically
excited state. The time-ordering of these adiabatic transfers is determined by
Doppler shifts, which ensures that the associated photon recoils are in the
opposite direction to the particle's motion. This ultimately leads to a robust
cooling mechanism capable of exerting large forces via a weak transition and
with reduced reliance on spontaneous emission. We present a simple intuitive
model for the resulting frictional force, and directly demonstrate its efficacy
for increasing the total phase-space density of an atomic ensemble. We rely on
both simulation and experimental studies using the 7.5~kHz linewidth S
to P transition in Sr. The reduced reliance on spontaneous
emission may allow this adiabatic sweep method to be a useful tool for cooling
particles that lack closed cycling transitions, such as molecules.Comment: 5 pages, 4 figure
Surveying structural complexity in quantum many-body systems
Quantum many-body systems exhibit a rich and diverse range of exotic
behaviours, owing to their underlying non-classical structure. These systems
present a deep structure beyond those that can be captured by measures of
correlation and entanglement alone. Using tools from complexity science, we
characterise such structure. We investigate the structural complexities that
can be found within the patterns that manifest from the observational data of
these systems. In particular, using two prototypical quantum many-body systems
as test cases - the one-dimensional quantum Ising and Bose-Hubbard models - we
explore how different information-theoretic measures of complexity are able to
identify different features of such patterns. This work furthers the
understanding of fully-quantum notions of structure and complexity in quantum
systems and dynamics.Comment: 9 pages, 5 figure
Assembly and use of new task rules in fronto-parietal cortex
Severe capacity limits, closely associated with fluid intelligence, arise in learning and use of new task rules. We used fMRI to investigate these limits in a series of multirule tasks involving different stimuli, rules, and response keys. Data were analyzed both during presentation of instructions and during later task execution. Between tasks, we manipulated the number of rules specified in task instructions, and within tasks, we manipulated the number of rules operative in each trial block. Replicating previous results, rule failures were strongly predicted by fluid intelligence and increased with the number of operative rules. In fMRI data, analyses of the instruction period showed that the bilateral inferior frontal sulcus, intraparietal sulcus, and presupplementary motor area were phasically active with presentation of each new rule. In a broader range of frontal and parietal regions, baseline activity gradually increased as successive rules were instructed. During task performance, we observed contrasting fronto-parietal patterns of sustained (block-related) and transient (trial-related) activity. Block, but not trial, activity showed effects of task complexity. We suggest that, as a new task is learned, a fronto-parietal representation of relevant rules and facts is assembled for future control of behavior. Capacity limits in learning and executing new rules, and their association with fluid intelligence, may be mediated by this load-sensitive fronto-parietal network
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