5,463 research outputs found
Stability for an inverse problem for a two speed hyperbolic pde in one space dimension
We prove stability for a coefficient determination problem for a two velocity
2x2 system of hyperbolic PDEs in one space dimension.Comment: Revised Version. Give more detail and correct the proof of
Proposition 4 regarding the existence and regularity of the forward problem.
No changes to the proof of the stability of the inverse problem. To appear in
Inverse Problem
Anatomy of an Encounter
The project Anatomy of an Encounter was driven by the idea that we should not take for granted that we already know what ‘encounters’ are. What does ‘meeting’ another person — with a different cultural or disciplinary background — mean? How much of an encounter is in all actuality a ‘finding one another’? How much of ‘being in touch’ is depending on the work of the imagination — fed by assumptions, existing cultural frames, stereotypes, fantasies about the other?Encounters are at the heart of every ethnographic project: anthropologists no longer claim to be speaking about the other (define the other in his/her otherness; know the other). They study what occurs between themselves and others when they meet. Encounters are also at the heart of the ENCOUNTERS project, where artistically inclined ethnographers and ethnographically inclined artists meet each other. The project Anatomy of an Encounter was driven by the idea that we should not take for granted that we already know what ‘encounters’ are. What does ‘meeting’ another person — with a different cultural or disciplinary background — mean? How much of an encounter is in all actuality a ‘finding one another’? How much of ‘being in touch’ is depending on the work of the imagination — fed by assumptions, existing cultural frames, stereotypes, fantasies about the other
Nanometer Scale Mapping of the Density of States in an Inhomogeneous Superconductor
Using high speed scanning tunneling spectroscopy, we perform a full mapping
of the quasiparticle density of states (DOS) in single crystals of
BiPbSrCaCuO(2212). The measurements carried out at 5 K showed a complex spatial
pattern of important variations of the local DOS on the nanometer scale.
Superconducting areas are co-existing with regions of a smooth and larger
gap-like DOS structure. The superconducting regions are found to have a minimum
size of about 3 nm. The role of Pb-introduced substitutional disorder in the
observed spatial variations of the local DOS is discussed.Comment: 4 page Letter with 3 figures (2 color figures
Probing the superconducting condensate on a nanometer scale
Superconductivity is a rare example of a quantum system in which the
wavefunction has a macroscopic quantum effect, due to the unique condensate of
electron pairs. The amplitude of the wavefunction is directly related to the
pair density, but both amplitude and phase enter the Josephson current : the
coherent tunneling of pairs between superconductors. Very sensitive devices
exploit the superconducting state, however properties of the {\it condensate}
on the {\it local scale} are largely unknown, for instance, in unconventional
high-T cuprate, multiple gap, and gapless superconductors.
The technique of choice would be Josephson STS, based on Scanning Tunneling
Spectroscopy (STS), where the condensate is {\it directly} probed by measuring
the local Josephson current (JC) between a superconducting tip and sample.
However, Josephson STS is an experimental challenge since it requires stable
superconducting tips, and tunneling conditions close to atomic contact. We
demonstrate how these difficulties can be overcome and present the first
spatial mapping of the JC on the nanometer scale. The case of an MgB film,
subject to a normal magnetic field, is considered.Comment: 7 pages, 6 figure
Nodal liquid and s-wave superconductivity in transition metal dichalcogenides
We explore the physical properties of a unified microscopic theory for the
coexistence of superconductivity and charge density waves in two-dimensional
transition metal dichalcogenides. In the case of particle-hole symmetry the
elementary particles are Dirac fermions at the nodes of the charge density wave
gap. When particle-hole symmetry is broken electron (hole) pockets are formed
around the Fermi surface. The superconducting ground state emerges from the
pairing of nodal quasi-particles mediated by acoustic phonons via a
piezoelectric coupling. We calculate several properties in the s-wave
superconducting phase, including specific heat, ultra-sound absorption, nuclear
magnetic relaxation, thermal, and optical conductivities. In the case with
particle-hole symmetry, the specific heat jump at the transition deviates
strongly from ordinary superconductors. The nuclear magnetic response shows an
anomalous anisotropy due to the broken time-reversal symmetry of the
superconducting gap, induced by the triple charge density wave state. The loss
of lattice inversion symmetry in the charge density wave phase leads to
anomalous coherence factors in the optical conductivity and to the appearance
of an absorption edge at the optical gap energy. Furthermore, optical and
thermal conductivities display anomalous peaks in the infrared when
particle-hole symmetry is broken.Comment: 23 pages, 16 figures. Published versio
Pointwise consistency of the kriging predictor with known mean and covariance functions
This paper deals with several issues related to the pointwise consistency of
the kriging predictor when the mean and the covariance functions are known.
These questions are of general importance in the context of computer
experiments. The analysis is based on the properties of approximations in
reproducing kernel Hilbert spaces. We fix an erroneous claim of Yakowitz and
Szidarovszky (J. Multivariate Analysis, 1985) that the kriging predictor is
pointwise consistent for all continuous sample paths under some assumptions.Comment: Submitted to mODa9 (the Model-Oriented Data Analysis and Optimum
Design Conference), 14th-19th June 2010, Bertinoro, Ital
"How May I Help You?": Modeling Twitter Customer Service Conversations Using Fine-Grained Dialogue Acts
Given the increasing popularity of customer service dialogue on Twitter,
analysis of conversation data is essential to understand trends in customer and
agent behavior for the purpose of automating customer service interactions. In
this work, we develop a novel taxonomy of fine-grained "dialogue acts"
frequently observed in customer service, showcasing acts that are more suited
to the domain than the more generic existing taxonomies. Using a sequential
SVM-HMM model, we model conversation flow, predicting the dialogue act of a
given turn in real-time. We characterize differences between customer and agent
behavior in Twitter customer service conversations, and investigate the effect
of testing our system on different customer service industries. Finally, we use
a data-driven approach to predict important conversation outcomes: customer
satisfaction, customer frustration, and overall problem resolution. We show
that the type and location of certain dialogue acts in a conversation have a
significant effect on the probability of desirable and undesirable outcomes,
and present actionable rules based on our findings. The patterns and rules we
derive can be used as guidelines for outcome-driven automated customer service
platforms.Comment: 13 pages, 6 figures, IUI 201
Dielectric breakdown characteristics of a high current metal vapor plasma
Time- and spatially-resolved spectroscopy is used to study the early-time spectral features of the plasmas produced by high-current, capacitive discharges through thin silver films. Spectra are compared for several support gases including CO2, He, and an Ar/O2 mixture. All measurements were made during the first 40 [mu]s of the discharge. At atmospheric pressure for all three gases, spectra from support gas species show intense lines for only a brief interval between 10 and 30 [mu]s after the start of the discharge. Greatest intensity from silver lines always occurs at the film surface; while greatest intensity from support gas species occurs about 2.0 mm from the film surface. A magnetic field of a few kG normal to the electric field in the plasma and parallel to the thin film surface almost completely eliminates spectral lines from the support gas species.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26994/1/0000561.pd
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