5,903 research outputs found
Efficiently Learning from Revealed Preference
In this paper, we consider the revealed preferences problem from a learning
perspective. Every day, a price vector and a budget is drawn from an unknown
distribution, and a rational agent buys his most preferred bundle according to
some unknown utility function, subject to the given prices and budget
constraint. We wish not only to find a utility function which rationalizes a
finite set of observations, but to produce a hypothesis valuation function
which accurately predicts the behavior of the agent in the future. We give
efficient algorithms with polynomial sample-complexity for agents with linear
valuation functions, as well as for agents with linearly separable, concave
valuation functions with bounded second derivative.Comment: Extended abstract appears in WINE 201
Revealed cardinal preference
I prove that as long as we allow the marginal utility for money (lambda) to
vary between purchases (similarly to the budget) then the quasi-linear and
the ordinal budget-constrained models rationalize the same data. However, we know that lambda is approximately constant. I provide a simple constructive proof for the necessary and sufficient condition for the constant lambda rationalization, which I argue should replace the Generalized Axiom of
Revealed Preference in empirical studies of consumer behavior.
'Go Cardinals!'
It is the minimal requirement of any scientifi c theory that it is consistent with
the data it is trying to explain. In the case of (Hicksian) consumer theory it was
revealed preference -introduced by Samuelson (1938,1948) - that provided an
empirical test to satisfy this need. At that time most of economic reasoning was
done in terms of a competitive general equilibrium, a concept abstract enough
so that it can be built on the ordinal preferences over baskets of goods - even if
the extremely specialized ones of Arrow and Debreu. However, starting in the
sixties, economics has moved beyond the 'invisible hand' explanation of how
-even competitive- markets operate. A seemingly unavoidable step of this
'revolution' was that ever since, most economic research has been carried out
in a partial equilibrium context. Now, the partial equilibrium approach does
not mean that the rest of the markets are ignored, rather that they are held
constant. In other words, there is a special commodity -call it money - that
reflects the trade-offs of moving purchasing power across markets. As a result,
the basic building block of consumer behavior in partial equilibrium is no longer
the consumer's preferences over goods, rather her valuation of them, in terms
of money. This new paradigm necessitates a new theory of revealed preference
Movement Patterns in Resident and Translocated Three-Toed Box Turtles (Terrapene Carolina Triunguis)
Wildlife relocations, repatriations, and translocations (RRTs) are strategies that are often used for by conservation managers as a method of reestablishing viable animal populations. The effectiveness of RRT studies has been called into question by some researchers, but more data are needed on the strategy to fully understand its utility. I compared the movement patterns, home range sizes, and body condition between a group of resident and translocated adult three-toed box turtles (Terrapene carolina triunguis). Each turtle from both groups was radio-tracked at least 2-3 times per month except during the winter months. Minimum convex polygons home range sizes estimated with Geographic Information System (GIS) showed no statistical difference between resident (7.89 ± 9.17 ha) and translocated (14.22 ± 7.13 ha) groups (t = 1.43, df = 10, P = 0.18). Similarly, no statistical difference was seen in mean distance moved (t = 0.27, df = 10, P = 0.79), or maximum distance moved (t = 01.0, df = 10, P = 0.34) between the two groups. After eighteen months of radio-tracking none of the translocated turtles left the study site. These results suggest that translocation may be a viable conservation strategy for three-toed box turtles
Fuel Injector: Air swirl characterization aerothermal modeling, phase 2, volume 2
A well integrated experimental/analytical investigation was conducted to provide benchmark quality data relevant to prefilming type airblast fuel nozzle and its interaction with combustor dome air swirler. The experimental investigation included a systematic study of both single-phase flows that involved single and twin co-axial jets with and without swirl. A two-component Phase Doppler Particle Analyzer (PDPA) equipment was used to document the interaction of single and co-axial air jets with glass beads that simulate nonevaporating spray and simultaneously avoid the complexities associated with fuel atomization processes and attendant issues about the specification of relevant boundary conditions. The interaction of jets with methanol spray produced by practical airblast nozzle was also documented in the spatial domain of practical interest. Model assessment activities included the use of three turbulence models (k-epsilon, algebraic second moment (ASM) and differential second moment (DSM)) for the carrier phase, deterministic or stochastic Lagrangian treatment of the dispersed phase, and advanced numerical schemes. Although qualitatively good comparison with data was obtained for most of the cases investigated, the model deficiencies in regard to modeled dissipation rate transport equation, single length scale, pressure-strain correlation, and other critical closure issues need to be resolved before one can achieve the degree of accuracy required to analytically design combustion systems
Activity Dependent Branching Ratios in Stocks, Solar X-ray Flux, and the Bak-Tang-Wiesenfeld Sandpile Model
We define an activity dependent branching ratio that allows comparison of
different time series . The branching ratio is defined as . The random variable is the value of the next signal given
that the previous one is equal to , so . If
, the process is on average supercritical when the signal is equal to
, while if , it is subcritical. For stock prices we find
within statistical uncertainty, for all , consistent with an ``efficient
market hypothesis''. For stock volumes, solar X-ray flux intensities, and the
Bak-Tang-Wiesenfeld (BTW) sandpile model, is supercritical for small
values of activity and subcritical for the largest ones, indicating a tendency
to return to a typical value. For stock volumes this tendency has an
approximate power law behavior. For solar X-ray flux and the BTW model, there
is a broad regime of activity where , which we interpret as an
indicator of critical behavior. This is true despite different underlying
probability distributions for , and for . For the BTW model the
distribution of is Gaussian, for sufficiently larger than one, and
its variance grows linearly with . Hence, the activity in the BTW model
obeys a central limit theorem when sampling over past histories. The broad
region of activity where is close to one disappears once bulk dissipation
is introduced in the BTW model -- supporting our hypothesis that it is an
indicator of criticality.Comment: 7 pages, 11 figure
Leadership for Learning Improvement in Urban Schools
Examines urban school leaders' efforts to improve the quality of teaching and learning by supporting progress for diverse students, sharing leadership work, and aligning resources. Analyzes school environments and coordination of various leadership roles
Large Magnetoresistance in Co/Ni/Co Ferromagnetic Single Electron Transistors
We report on magnetotransport investigations of nano-scaled ferromagnetic
Co/Ni/Co single electron transistors. As a result of reduced size, the devices
exhibit single electron transistor characteristics at 4.2K. Magnetotransport
measurements carried out at 1.8K reveal tunneling magnetoresistance (TMR)
traces with negative coercive fields, which we interpret in terms of a
switching mechanism driven by the shape anisotropy of the central wire-like Ni
island. A large TMR of about 18% is observed within a finite source-drain bias
regime. The TMR decreases rapidly with increasing bias, which we tentatively
attribute to excitation of magnons in the central island.Comment: 12 pages (including 4 figures). Accepted for publishing on AP
Socially Optimal Mining Pools
Mining for Bitcoins is a high-risk high-reward activity. Miners, seeking to
reduce their variance and earn steadier rewards, collaborate in pooling
strategies where they jointly mine for Bitcoins. Whenever some pool participant
is successful, the earned rewards are appropriately split among all pool
participants. Currently a dozen of different pooling strategies (i.e., methods
for distributing the rewards) are in use for Bitcoin mining.
We here propose a formal model of utility and social welfare for Bitcoin
mining (and analogous mining systems) based on the theory of discounted
expected utility, and next study pooling strategies that maximize the social
welfare of miners. Our main result shows that one of the pooling strategies
actually employed in practice--the so-called geometric pay pool--achieves the
optimal steady-state utility for miners when its parameters are set
appropriately.
Our results apply not only to Bitcoin mining pools, but any other form of
pooled mining or crowdsourcing computations where the participants engage in
repeated random trials towards a common goal, and where "partial" solutions can
be efficiently verified
Electronic transport in Si nanowires: Role of bulk and surface disorder
We calculate the resistance and mean free path in long metallic and
semiconducting silicon nanowires (SiNWs) using two different numerical
approaches: A real space Kubo method and a recursive Green's function method.
We compare the two approaches and find that they are complementary: depending
on the situation a preferable method can be identified. Several numerical
results are presented to illustrate the relative merits of the two methods. Our
calculations of relaxed atomic structures and their conductance properties are
based on density functional theory without introducing adjustable parameters.
Two specific models of disorder are considered: Un-passivated, surface
reconstructed SiNWs are perturbed by random on-site (Anderson) disorder whereas
defects in hydrogen passivated wires are introduced by randomly removed H
atoms. The un-passivated wires are very sensitive to disorder in the surface
whereas bulk disorder has almost no influence. For the passivated wires, the
scattering by the hydrogen vacancies is strongly energy dependent and for
relatively long SiNWs (L>200 nm) the resistance changes from the Ohmic to the
localization regime within a 0.1 eV shift of the Fermi energy. This high
sensitivity might be used for sensor applications.Comment: 9 pages, 7 figures, submitted to Phys. Rev.
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