344 research outputs found
An improved evaluation of surface finish with a three dimensional tester
The design and programming of an automated three dimensional surface finish tester is described. The device produces a three dimensional image of the microscopic texture of the examined surface. The surface finish tester presents the following advantages over conventional profilometry: (1) more complete exploration of surface texture by successive probe sweeps; (2) automation of measuring and calculating; (3) more accurate representation of the derived parameters; (4) analysis of the degree of homogeneity of the surface; (5) three dimensional graphic representation accurately depicting the state of the surface; (6) detection of local imperfections; and (7) detection of scoring that occurred during machining
Fractionalizing a local pair density wave: a good "recipe" for opening a pseudo-gap
We give a concise version of a recently proposed concept of fractionalization
of an order parameter, thus generating a constraint through a fictitious gauge
field. We argue that this new line of approach is key to explain the
longstanding mystery of the pseudo-gap phase in cuprate superconductors. For
example, the fractionalization of a finite momentum, charge two state living on
latice bonds -- also called Pair Density Wave, into a particle-particle and a
particle-hole pair leads to the opening of a gap in the fermionic spectrum. It
induces "phase-locking" between the particle-particle and particle-hole pairs.
We describe the formation of the Fermi arcs in the spectrum and give an account
of recent Raman spectroscopy results from a minimal microscopic model. We
relate the "phase-locking" to intriguing STM experimental observations
Anomalous softening of phonon-dispersion in cuprate superconductors
A softening of phonon-dispersion has been observed experimentally in
under-doped cuprate superconductors at the charge-density wave (CDW) ordering
wave vector. Interestingly, the softening occurs below the superconducting (SC)
transition temperature T, in contrast to the metallic systems, where the
softening occurs usually below the CDW onset temperature T. An
understanding of the `anomalous' nature of the phonon-softening and its
connection to the pseudo-gap phase in under-doped cuprates remain open
questions. Within a perturbative approach, we show that a complex interplay
among the ubiquitous CDW, SC orders and life-time of quasi-particles associated
to thermal fluctuations, can explain the anomalous phonon-softening below
T. Furthermore, our formalism captures different characteristics of the
low temperature phonon-softening depending on material specificity.Comment: Supplementary include
Pairing susceptibility of the two-dimensional Hubbard model in the thermodynamic limit
We compute the diagrammatic expansion of the particle-particle susceptibility
via algorithmic Matsubara integration and compute the correlated pairing
susceptibility in the thermodynamic limit of the 2D Hubbard Model. We study the
static susceptibility and its dependence on the pair momentum for
a range of temperature, interaction strength, and chemical potential. We show
that -wave pairing is expected in the model in the
limit from direct perturbation theory. From this, we identify key second and
third-order diagrams that support pairing processes and note that the diagrams
responsible are not a part of charge or spin susceptibility expansions. We find
two key components for pairing at momenta and that can be
well fit as separate bosonic modes. We extract amplitudes and correlation
length scales where we find a predominantly local pairing and
non-local pairs and present the relative weights of these
modes for variation in temperature, doping, and interaction strength.Comment: 9 pages - 10 figure
Le pouvoir histaminopexique du serum du cheval
Grandadam A. Le pouvoir histaminopexique du sérum du cheval. In: Bulletin de l'Académie Vétérinaire de France tome 110 n°4, 1957. pp. 165-169
Electronic spectral function in fractionalized Pair Density Wave scenario
Studies of the electronic spectral function in cuprates by Angle-Resolved
Photo-Emission Spectroscopy reveal unusual features in the pseudogap phase that
persist in the superconducting phase. We address here these observations based
on the recently proposed idea that the pseudogap is due to the
fractionalization of modulated particle-particle pairs (a Pair Density Wave)
into uniform particle-particle and modulated particle-hole pairs. The
constraint that appears between these two types of pairs can be seen has an
amplitude for the pseudogap energy scale. This constraint directly modify the
electronic spectral function in the pseudogap phase. We derive a
self-consistent equation for the pseudogap amplitude and show that it leads to
the formation of Fermi arcs. The band dispersion obtained in the anti-nodal
region is in good agreement with experimental ARPES observations in
PbBiSrLaCuO (Bi2201) and present
a back-bending that goes to the Fermi level as we go away from the antinodal
region. We also discuss the temperature dependence of the ARPES spectrum in the
pseudogap and in the superconducting state
Renormalized Perturbation Theory for Fast Evaluation of Feynman Diagrams on the Real Frequency Axis
We present a method to accelerate the numerical evaluation of spatial
integrals of Feynman diagrams when expressed on the real frequency axis. This
can be realized through use of a renormalized perturbation expansion with a
constant but complex renormalization shift. The complex shift acts as a
regularization parameter for the numerical integration of otherwise sharp
functions. This results in an exponential speed up of stochastic numerical
integration at the expense of evaluating additional counter-term diagrams. We
provide proof of concept calculations within a difficult limit of the
half-filled 2D Hubbard model on a square lattice
Intermittent selective clamping improves rat liver regeneration by attenuating oxidative and endoplasmic reticulum stress.
International audienceIntermittent clamping of the portal trial is an effective method to avoid excessive blood loss during hepatic resection, but this procedure may cause ischemic damage to liver. Intermittent selective clamping of the lobes to be resected may represent a good alternative as it exposes the remnant liver only to the reperfusion stress. We compared the effect of intermittent total or selective clamping on hepatocellular injury and liver regeneration. Entire hepatic lobes or only lobes to be resected were subjected twice to 10 min of ischemia followed by 5 min of reperfusion before hepatectomy. We provided evidence that the effect of intermittent clamping can be damaging or beneficial depending to its mode of application. Although transaminase levels were similar in all groups, intermittent total clamping impaired liver regeneration and increased apoptosis. In contrast, intermittent selective clamping improved liver protein secretion and hepatocyte proliferation when compared with standard hepatectomy. This beneficial effect was linked to better adenosine-5'-triphosphate (ATP) recovery, nitric oxide production, antioxidant activities and endoplasmic reticulum adaptation leading to limit mitochondrial damage and apoptosis. Interestingly, transient and early chaperone inductions resulted in a controlled activation of the unfolded protein response concomitantly to endothelial nitric oxide synthase, extracellular signal-regulated kinase-1/2 (ERK1/2) and p38 MAPK activation that favors liver regeneration. Endoplasmic reticulum stress is a central target through which intermittent selective clamping exerts its cytoprotective effect and improves liver regeneration. This procedure could be applied as a powerful protective modality in the field of living donor liver transplantation and liver surgery
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