5,170 research outputs found
New insight into cataract formation -- enhanced stability through mutual attraction
Small-angle neutron scattering experiments and molecular dynamics simulations
combined with an application of concepts from soft matter physics to complex
protein mixtures provide new insight into the stability of eye lens protein
mixtures. Exploring this colloid-protein analogy we demonstrate that weak
attractions between unlike proteins help to maintain lens transparency in an
extremely sensitive and non-monotonic manner. These results not only represent
an important step towards a better understanding of protein condensation
diseases such as cataract formation, but provide general guidelines for tuning
the stability of colloid mixtures, a topic relevant for soft matter physics and
industrial applications.Comment: 4 pages, 4 figures. Accepted for publication on Phys. Rev. Let
Impact of classical forces and decoherence in multi-terminal Aharonov-Bohm networks
Multi-terminal Aharonov-Bohm (AB) rings are ideal building blocks for quantum
networks (QNs) thanks to their ability to map input states into controlled
coherent superpositions of output states. We report on experiments performed on
three-terminal GaAs/Al_(x)Ga_(1-x)As AB devices and compare our results with a
scattering-matrix model including Lorentz forces and decoherence. Our devices
were studied as a function of external magnetic field (B) and gate voltage at
temperatures down to 350 mK. The total output current from two terminals while
applying a small bias to the third lead was found to be symmetric with respect
to B with AB oscillations showing abrupt phase jumps between 0 and pi at
different values of gate voltage and at low magnetic fields, reminiscent of the
phase-rigidity constraint due to Onsager-Casimir relations. Individual outputs
show quasi-linear dependence of the oscillation phase on the external electric
field. We emphasize that a simple scattering-matrix approach can not model the
observed behavior and propose an improved description that can fully describe
the observed phenomena. Furthermore, we shall show that our model can be
successfully exploited to determine the range of experimental parameters that
guarantee a minimum oscillation visibility, given the geometry and coherence
length of a QN.Comment: 7 pages, 8 figure
Modelling a Particle Detector in Field Theory
Particle detector models allow to give an operational definition to the
particle content of a given quantum state of a field theory. The commonly
adopted Unruh-DeWitt type of detector is known to undergo temporary transitions
to excited states even when at rest and in the Minkowski vacuum. We argue that
real detectors do not feature this property, as the configuration "detector in
its ground state + vacuum of the field" is generally a stable bound state of
the underlying fundamental theory (e.g. the ground state-hydrogen atom in a
suitable QED with electrons and protons) in the non-accelerated case. As a
concrete example, we study a local relativistic field theory where a stable
particle can capture a light quantum and form a quasi-stable state. As
expected, to such a stable particle correspond energy eigenstates of the full
theory, as is shown explicitly by using a dressed particle formalism at first
order in perturbation theory. We derive an effective model of detector (at
rest) where the stable particle and the quasi-stable configurations correspond
to the two internal levels, "ground" and "excited", of the detector.Comment: 13 pages, references added, final versio
Highly nonlinear dynamics in a slowly sedimenting colloidal gel
We use a combination of original light scattering techniques and particles
with unique optical properties to investigate the behavior of suspensions of
attractive colloids under gravitational stress, following over time the
concentration profile, the velocity profile, and the microscopic dynamics.
During the compression regime, the sedimentation velocity grows nearly linearly
with height, implying that the gel settling may be fully described by a
(time-dependent) strain rate. We find that the microscopic dynamics exhibit
remarkable scaling properties when time is normalized by strain rate, showing
that the gel microscopic restructuring is dominated by its macroscopic
deformation.Comment: Physical Review Letters (2011) xxx
Current-Phase Relation of a Bose-Einstein Condensate Flowing Through a Weak Link
We study the current-phase relation of a Bose-Einstein condensate flowing
through a repulsive square barrier by solving analytically the one dimensional
Gross-Pitaevskii equation. The barrier height and width fix the current-phase
relation , which tends to for weak
barriers and to the Josephson sinusoidal relation for
strong barriers. Between these two limits, the current-phase relation depends
on the barrier width. In particular, for wide enough barriers, we observe two
families of multivalued current-phase relations. Diagrams belonging to the
first family, already known in the literature, can have two different positive
values of the current at the same phase difference. The second family, new to
our knowledge, can instead allow for three different positive currents still
corresponding to the same phase difference. Finally, we show that the
multivalued behavior arises from the competition between hydrodynamic and
nonlinear-dispersive components of the flow, the latter due to the presence of
a soliton inside the barrier region.Comment: 6 pages, 5 figure
Multi-specific calibration of the B isotope proxy in calcareous red algae for pH reconstruction
Analytical spectrum of nonlinear Thomson scattering including radiation reaction
Accelerated charges emit electromagnetic radiation and the consequent
energy-momentum loss alters their trajectory. This phenomenon is known as
radiation reaction and the Landau-Lifshitz (LL) equation is the classical
equation of motion of the electron, which takes into account radiation-reaction
effects in the electron trajectory. By using the analytical solution of the LL
equation in an arbitrary plane wave, we compute the analytical expression of
the classical emission spectrum via nonlinear Thomson scattering including
radiation-reaction effects. Both the angularly-resolved and the
angularly-integrated spectra are reported, which are valid in an arbitrary
plane wave. Also, we have obtained a phase-dependent expression of the electron
dressed mass, which includes radiation-reaction effects. Finally, the
corresponding spectra within the locally constant field approximation have been
derived.Comment: 18 pages, no figure
Institutional oversight of the graduate medical education enterprise: development of an annual institutional review
Background: The Accreditation Council for Graduate Medical Education (ACGME) fully implemented all aspects of the Next Accreditation System (NAS) on July 1, 2014. In lieu of periodic accreditation site visits of programs and institutions, the NAS requires active, ongoing oversight by the sponsoring institutions (SIs) to maintain accreditation readiness and program quality. Methods: The Ochsner Health System Graduate Medical Education Committee (GMEC) has instituted a process that provides a structured, process-driven improvement approach at the program level, using a Program Evaluation Committee to review key performance data and construct an annual program evaluation for each accredited residency. The Ochsner GMEC evaluates the aggregate program data and creates an Annual Institutional Review (AIR) document that provides direction and focus for ongoing program improvement. This descriptive article reviews the 2014 process and various metrics collected and analyzed to demonstrate the program review and institutional oversight provided by the Ochsner graduate medical education (GME) enterprise. Results: The 2014 AIR provided an overview of performance and quality of the Ochsner GME program for the 2013-2014 academic year with particular attention to program outcomes; resident supervision, responsibilities, evaluation, and compliance with duty-hour standards; results of the ACGME survey of residents and core faculty; and resident participation in patient safety and quality activities and curriculum. The GMEC identified other relevant institutional performance indicators that are incorporated into the AIR and reflect SI engagement in and contribution to program performance at the individual program and institutional levels. Conclusion: The Ochsner GME office and its program directors are faced with the ever-increasing challenges of today’s healthcare environment as well as escalating institutional and program accreditation requirements. The overall commitment of this SI to advancing our GME enterprise is clearly evident, and the opportunity for continued improvement resulting from institutional oversight is being realized
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