85 research outputs found
Review on possible gravitational anomalies
This is an updated introductory review of 2 possible gravitational anomalies
that has attracted part of the Scientific community: the Allais effect that
occur during solar eclipses, and the Pioneer 10 spacecraft anomaly,
experimented also by Pioneer 11 and Ulysses spacecrafts. It seems that, to
date, no satisfactory conventional explanation exist to these phenomena, and
this suggests that possible new physics will be needed to account for them. The
main purpose of this review is to announce 3 other new measurements that will
be carried on during the 2005 solar eclipses in Panama and Colombia (Apr. 8)
and in Portugal (Oct.15).Comment: Published in 'Journal of Physics: Conferences Series of the American
Institute of Physics'. Contribution for the VI Mexican School on Gravitation
and Mathematical Physics "Approaches to Quantum Gravity" (Playa del Carmen,
Quintana Roo, Mexico, Nov. 21-27, 2004). Updates to this information will be
posted in http://www.lsc-group.phys.uwm.edu/~xavier.amador/anomalies.htm
Point-contact spectroscopy on URuSi
Tunnel and point contact experiments have been made in a URuSi single
crystal along the c-axis. The experiments were performed changing temperature
and contact size in a low temperature scanning tunneling microscope. A
resonance develops at the Fermi level at K. This resonance splits
and becomes asymmetric when the 17.5 K phase transition is crossed. These
results are consistent with the existence of Kondo like bound states of the
U ionic configurations and the conduction electrons. Below the
transition, these configurations are split by the development of quadrupolar
ordering. The peak separation can be interpreted as a direct measurement of the
order parameter. Measurements on a policrystalline UAu_2Si_2$ sample are also
reported, with a comparative study of the behavior of both materials.Comment: 4 pages (Latex) + 2 postscript figure
Onset of dissipation in ballistic atomic wires
Electronic transport at finite voltages in free-standing gold atomic chains
of up to 7 atoms in length is studied at low temperatures using a scanning
tunneling microscope (STM). The conductance vs voltage curves show that
transport in these single-mode ballistic atomic wires is non-dissipative up to
a finite voltage threshold of the order of several mV. The onset of dissipation
and resistance within the wire corresponds to the excitation of the atomic
vibrations by the electrons traversing the wire and is very sensitive to
strain.Comment: Revtex4, 4 pages, 3 fig
Primordial magnetic fields at preheating
Using lattice techniques we investigate the generation of long range
cosmological magnetic fields during a cold electroweak transition. We will show
how magnetic fields arise, during bubble collisions, in the form of magnetic
strings. We conjecture that these magnetic strings originate from the alignment
of magnetic dipoles associated with EW sphaleron-like configurations. We also
discuss the early thermalisation of photons and the turbulent behaviour of the
scalar fields after tachyonic preheating.Comment: 7 pages. Talk presented at Lattice200
Andreev reflection and order parameter symmetry in heavy-fermion superconductors: the case of CeCoIn
We review the current status of Andreev reflection spectroscopy on the heavy
fermions, mostly focusing on the case of CeCoIn, a heavy-fermion
superconductor with a critical temperature of 2.3 K. This is a well-established
technique to investigate superconducting order parameters via measurements of
the differential conductance from nanoscale metallic junctions. Andreev
reflection is clearly observed in CeCoIn as in other heavy-fermion
superconductors. The measured Andreev signal is highly reduced to the order of
maximum 13% compared to the theoretically predicted value (100%).
Analysis of the conductance spectra using the extended BTK model provides a
qualitative measure for the superconducting order parameter symmetry, which is
determined to be -wave in CeCoIn. A phenomenological model is
proposed employing a Fano interference effect between two conductance channels
in order to explain both the conductance asymmetry and the reduced Andreev
signal. This model appears plausible not only because it provides good fits to
the data but also because it is highly likely that the electrical conduction
occurs via two channels, one into the heavy electron liquid and the other into
the conduction electron continuum. Further experimental and theoretical
investigations will shed new light on the mechanism of how the coherent
heavy-electron liquid emerges out of the Kondo lattice, a prototypical strongly
correlated electron system. Unresolved issues and future directions are also
discussed.Comment: Topical Review published in JPCM (see below), 28 pages, 9 figure
Point contact spectroscopy of the electron-doped cuprate superconductor Pr{2-x}Ce{x}CuO4: The dependence of conductance-voltage spectra on cerium doping, barrier strength and magnetic field
We present conductance-voltage (G-V) data for point contact junctions between
a normal metal and the electron doped cuprate superconductor Pr{2-x}Ce{x}CuO4
(PCCO). We observe a zero bias conductance peak (ZBCP) for the under-doped
composition of this cuprate (x=0.13) which is consistent with d-wave pairing
symmetry. For optimally-doped (x=0.15) and over-doped (x=0.17) PCCO, we find
that the G-V characteristics indicate the presence of an order parameter
without nodes. We investigate this further by obtaining point contact
spectroscopy data for different barrier strengths and as a function of magnetic
field.Comment: 13 pages, 9 figure
Retrospective evaluation of the Dutch pre-newborn screening cohort for propionic acidemia and isolated methylmalonic acidemia:What to aim, expect, and evaluate from newborn screening?
Evidence for effectiveness of newborn screening (NBS) for propionic acidemia (PA) and isolated methylmalonic acidemia (MMA) is scarce. Prior to implementation in the Netherlands, we aim to estimate the expected health gain of NBS for PA and MMA. In this national retrospective cohort study, the clinical course of 76/83 Dutch PA and MMA patients, diagnosed between January 1979 and July 2019, was evaluated. Five clinical outcome parameters were defined: adverse outcome of the first symptomatic phase, frequency of acute metabolic decompensations (AMD), cognitive function, mitochondrial complications, and treatment-related complications. Outcomes of patients identified by family testing were compared with the outcomes of their index siblings. An adverse outcome due to the first symptomatic phase was recorded in 46% of the clinically diagnosed patients. Outcome of the first symptomatic phase was similar in 5/9 sibling pairs and better in 4/9 pairs. Based on the day of diagnosis of the clinically diagnosed patients and sibling pair analysis, a preliminary estimated reduction of adverse outcome due to the first symptomatic phase from 46% to 36%-38% was calculated. Among the sibling pairs, AMD frequency, cognitive function, mitochondrial, and treatment-related complications were comparable. These results suggest that the health gain of NBS for PA and MMA in overall outcome may be limited, as only a modest decrease of adverse outcomes due to the first symptomatic phase is expected. With current clinical practice, no reduced AMD frequency, improved cognitive function, or reduced frequency of mitochondrial or treatment-related complications can be expected
Observation of multiple superconducting gaps in Fe1+yTe1-xSex via a nano-scale approach to point-contact spectroscopy
We report a distinct experimental approach to point-contact Andreev
reflection spectroscopy with diagnostic capability via a unique design of
nano-scale normal metal/superconductor devices with excellent thermo-mechanical
stability, and have employed this method to unveil the existence of two
superconducting energy gaps in iron chalcogenide Fe1+yTe1-xSex which is crucial
for understanding its pairing mechanism. This work opens up new opportunities
to study gap structures in superconductors and elemental excitations in solids.Comment: 18 pages (5 figures) plus supplementary materials (5 pages). J.
Phys.: Cond. Matter, in pres
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