5,000 research outputs found
Charter School Replication: Growing a Quality Charter School Sector
NACSA's Policy Guide series is intended to support state legislatures and charter school advocates in creating policy environments that result in high quality authorizing and high quality schools. This guide outlines key considerations for policymakers committed to supporting the replication of existing successful charter school models
Containerless protein crystal growth technology: Electrostatic multidrop positioner
A brief discussion of containerless protein crystal growth in space and a diagram of the electrostatic multidrop positioner are presented. A picture of lysome crystals growing in a drop and a graph of levitation voltage versus time (minutes) are also presented
Noncontact electrical resistivity measurement technique for molten metals
A noncontact technique of measuring the changes in electrical conductivity (or resistivity) of conducting liquids is reported. The technique is based on a conducting drop that is levitated by the high-temperature electrostatic levitator in a high vacuum. This technique, which utilizes the principle of the asynchronous induction motor, measures the relative changes in torque as a function of temperature by applying a rotating magnetic field to the sample. Changes in electrical resistivity are related to the changes in measured torque using the formula developed for the induction motor. Validity of this technique was demonstrated using a pure aluminum sample around its melting temperature. When the measurement results were calibrated by a literature value of resistivity at the melting point, our resistivity data around the melting point could be expressed by rliq = 24.19 + 1.306 × 10–2(T – Tm) µOmega cm over Tm ~ 1160 K, rsolid = 10.77 + 1.421 × 10–2(T – Tm) µOmega cm over 700 K ~ Tm, and the thermal conductivity as determined by the Wiedemann–Franz–Lorenz law from the resistivity data was given by kappaliq(T) = 94.61 + 4.41 × 10–2(T – Tm) W m – 1 K – 1, kappasolid(T) = 211.13 – 7.57 × 10–2(T – Tm) W m – 1 K – 1. Both electrical resistivity and thermal conductivity are in close agreement with the literature, confirming the validity of the present technique
Keep Ballots Secret: On the Futility of Social Learning in Decision Making by Voting
We show that social learning is not useful in a model of team binary decision
making by voting, where each vote carries equal weight. Specifically, we
consider Bayesian binary hypothesis testing where agents have any
conditionally-independent observation distribution and their local decisions
are fused by any L-out-of-N fusion rule. The agents make local decisions
sequentially, with each allowed to use its own private signal and all precedent
local decisions. Though social learning generally occurs in that precedent
local decisions affect an agent's belief, optimal team performance is obtained
when all precedent local decisions are ignored. Thus, social learning is
futile, and secret ballots are optimal. This contrasts with typical studies of
social learning because we include a fusion center rather than concentrating on
the performance of the latest-acting agents
Classification of flat bands according to the band-crossing singularity of Bloch wave functions
We show that flat bands can be categorized into two distinct classes, that
is, singular and nonsingular flat bands, by exploiting the singular behavior of
their Bloch wave functions in momentum space. In the case of a singular flat
band, its Bloch wave function possesses immovable discontinuities generated by
the band-crossing with other bands, and thus the vector bundle associated with
the flat band cannot be defined. This singularity precludes the compact
localized states from forming a complete set spanning the flat band. Once the
degeneracy at the band crossing point is lifted, the singular flat band becomes
dispersive and can acquire a finite Chern number in general, suggesting a new
route for obtaining a nearly flat Chern band. On the other hand, the Bloch wave
function of a nonsingular flat band has no singularity, and thus forms a vector
bundle. A nonsingular flat band can be completely isolated from other bands
while preserving the perfect flatness. All one-dimensional flat bands belong to
the nonsingular class. We show that a singular flat band displays a novel
bulk-boundary correspondence such that the presence of the robust boundary mode
is guaranteed by the singularity of the Bloch wave function. Moreover, we
develop a general scheme to construct a flat band model Hamiltonian in which
one can freely design its singular or nonsingular nature. Finally, we propose a
general formula for the compact localized state spanning the flat band, which
can be easily implemented in numerics and offer a basis set useful in analyzing
correlation effects in flat bands.Comment: 23 pages, 13 figure
Distributed Hypothesis Testing with Social Learning and Symmetric Fusion
We study the utility of social learning in a distributed detection model with
agents sharing the same goal: a collective decision that optimizes an agreed
upon criterion. We show that social learning is helpful in some cases but is
provably futile (and thus essentially a distraction) in other cases.
Specifically, we consider Bayesian binary hypothesis testing performed by a
distributed detection and fusion system, where all decision-making agents have
binary votes that carry equal weight. Decision-making agents in the team
sequentially make local decisions based on their own private signals and all
precedent local decisions. It is shown that the optimal decision rule is not
affected by precedent local decisions when all agents observe conditionally
independent and identically distributed private signals. Perfect Bayesian
reasoning will cancel out all effects of social learning. When the agents
observe private signals with different signal-to-noise ratios, social learning
is again futile if the team decision is only approved by unanimity. Otherwise,
social learning can strictly improve the team performance. Furthermore, the
order in which agents make their decisions affects the team decision.Comment: 10 pages, 7 figure
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