4,859 research outputs found
Vortex Glass is a Metal: Unified Theory of the Magnetic Field and Disorder-Tuned Bose Metals
We consider the disordered quantum rotor model in the presence of a magnetic
field. We analyze the transport properties in the vicinity of the multicritical
point between the superconductor, phase glass and paramagnetic phases. We find
that the magnetic field leaves metallic transport of bosons in the glassy phase
in tact. In the vicinity of the vicinity of the superconductivity-to-Bose metal
transition, the resistitivy turns on as with . This
functional form is in excellent agreement with the experimentally observed
turn-on of the resistivity in the metallic state in MoGe, namely , . The metallic state is also shown to presist in
three spatial dimensions. In addition, we also show that the metallic state
remains intact in the presence of Ohmic dissipation in spite of recent claims
to the contrary. As the phase glass in is identical to the vortex glass,
we conclude that the vortex glass is, in actuality, a metal rather than a
superconductor at T=0. Our analysis unifies the recent experiments on vortex
glass systems in which the linear resistivity remained non-zero below the
putative vortex glass transition and the experiments on thin films in which a
metallic phase has been observed to disrupt the direct transition from a
superconductor to an insulator.Comment: Published version with an appendix showing that the claim in
cond-mat/0510380 (and cond-mat/0606522) that Ohmic dissipation in the phase
glass leads to a superconducting state is false. A metal persists in this
case as wel
Symmetry Principle Preserving and Infinity Free Regularization and renormalization of quantum field theories and the mass gap
Through defining irreducible loop integrals (ILIs), a set of consistency
conditions for the regularized (quadratically and logarithmically) divergent
ILIs are obtained to maintain the generalized Ward identities of gauge
invariance in non-Abelian gauge theories. Overlapping UV divergences are
explicitly shown to be factorizable in the ILIs and be harmless via suitable
subtractions. A new regularization and renormalization method is presented in
the initial space-time dimension of the theory. The procedure respects
unitarity and causality. Of interest, the method leads to an infinity free
renormalization and meanwhile maintains the symmetry principles of the original
theory except the intrinsic mass scale caused conformal scaling symmetry
breaking and the anomaly induced symmetry breaking. Quantum field theories
(QFTs) regularized through the new method are well defined and governed by a
physically meaningful characteristic energy scale (CES) and a physically
interesting sliding energy scale (SES) which can run from to a dynamically generated mass gap or to in the
absence of mass gap and infrared (IR) problem. It is strongly indicated that
the conformal scaling symmetry and its breaking mechanism play an important
role for understanding the mass gap and quark confinement.Comment: 59 pages, Revtex, 4 figures, 1 table, Erratum added, published
versio
Private Matchings and Allocations
We consider a private variant of the classical allocation problem: given k
goods and n agents with individual, private valuation functions over bundles of
goods, how can we partition the goods amongst the agents to maximize social
welfare? An important special case is when each agent desires at most one good,
and specifies her (private) value for each good: in this case, the problem is
exactly the maximum-weight matching problem in a bipartite graph.
Private matching and allocation problems have not been considered in the
differential privacy literature, and for good reason: they are plainly
impossible to solve under differential privacy. Informally, the allocation must
match agents to their preferred goods in order to maximize social welfare, but
this preference is exactly what agents wish to hide. Therefore, we consider the
problem under the relaxed constraint of joint differential privacy: for any
agent i, no coalition of agents excluding i should be able to learn about the
valuation function of agent i. In this setting, the full allocation is no
longer published---instead, each agent is told what good to get. We first show
that with a small number of identical copies of each good, it is possible to
efficiently and accurately solve the maximum weight matching problem while
guaranteeing joint differential privacy. We then consider the more general
allocation problem, when bidder valuations satisfy the gross substitutes
condition. Finally, we prove that the allocation problem cannot be solved to
non-trivial accuracy under joint differential privacy without requiring
multiple copies of each type of good.Comment: Journal version published in SIAM Journal on Computation; an extended
abstract appeared in STOC 201
Comparing Consumer-Produced Product Reviews across Multiple Websites
Authors show that the sentiment of the online consumer reviews could vary substantially so relying on a single data source to make purchase decision is not a wise idea
Point-contact tunneling spectroscopy measurement of CuTiSe: disorder-enhanced Coulomb effects
We performed point-contact spectroscopy tunneling measurements on
CuTiSe bulk with and at temperatures ranging from
K and observe a suppression in the density of states around zero-bias
that we attribute to enhanced Coulomb interactions due to disorder. We find
that the correlation gap associated with this suppression is related to the
zero-temperature resistivity. We use our results to estimate the disorder-free
transition temperature and find that the clean limit is close to the
experimentally observed .Comment: 4 pages, 4 figure
Quantifying Changes in Creativity: Findings from an Engineering Course on the Design of Complex and Origami Structures
Engineering educators have increasingly sought strategies for integrating the arts into their curricula. The primary objective of this integration varies, but one common objective is to improve students’ creative thinking skills. In this paper, we sought to quantify changes in student creativity that resulted from participation in a mechanical engineering course targeted at integrating engineering, technology, and the arts. The course was team taught by instructors from mechanical engineering and art. The art instructor introduced origami principles and techniques as a means for students to optimize engineering structures. Through a course project, engineering student teams interacted with art students to perform structural analysis on an origami-based art installation, which was the capstone project of the art instructor’s undergraduate origami course. Three engineering student teams extended this course project to collaborate with the art students in the final design and physical installation.
To evaluate changes in student creativity, we used two instruments: a revised version of the Reisman Diagnostic Creativity Assessment (RDCA) and the Innovative Behavior Scales. Initially, the survey contained 12 constructs, but three were removed due to poor internal consistency reliability: Extrinsic Motivation; Intrinsic Motivation; and Tolerance of Ambiguity. The nine remaining constructs used for comparison herein included:
• Originality: Confidence in developing original, innovative ideas
• Ideation: Confidence in generating many ideas
• Risk Taking: Adventurous; Brave
• Openness of Process: Engaging various potentialities and resisting closure
• Iterative Processing: Willingness to iterate on one’s solution
• Questioning: Tendency to ask lots of questions
• Experimenting/exploring: Tendency to physically or mentally take things apart
• Idea networking: Tendency to engage with diverse others in communicative acts
• Observing: Tendency to observe the surrounding world
By conducting a series of paired t-tests to ascertain if pre and post-course responses were significantly different on the above constructs, we found five significant changes. In order of significance, these included Idea Networking; Questioning; Observing; Originality; and Ideation. To help explain these findings, and to identify how this course may be improved in subsequent offerings, the discussion includes the triangulation of these findings in light of teaching observations, responses from a mid-semester student focus group session, and informal faculty reflections. We close with questions that we and others ought to address as we strive to integrate engineering, technology, and the arts. We hope that these findings and discussion will guide other scholars and instructors as they explore the impact of art on engineering design learning, and as they seek to evaluate student creativity resulting from courses with similar aims
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