5,958 research outputs found
Witten index, axial anomaly, and Krein's spectral shift function in supersymmetric quantum mechanics
A new method is presented to study supersymmetric quantum mechanics. Using relative scattering techniques, basic relations are derived between Krein’s spectral shift function, the Witten index, and the anomaly. The topological invariance of the spectral shift function is discussed. The power of this method is illustrated by treating various models and calculating explicitly the spectral shift function, the Witten index, and the anomaly. In particular, a complete treatment of the two‐dimensional magnetic field problem is given, without assuming that the magnetic flux is quantized
Switched Control of Electron Nuclear Spin Systems
In this article, we study control of electron-nuclear spin dynamics at
magnetic field strengths where the Larmor frequency of the nucleus is
comparable to the hyperfine coupling strength. The quantization axis for the
nuclear spin differs from the static B_0 field direction and depends on the
state of the electron spin. The quantization axis can be switched by flipping
the state of electron spin, allowing for universal control on nuclear spin
states. We show that by performing a sequence of flips (each followed by a
suitable delay), we can perform any desired rotation on the nuclear spins,
which can also be conditioned on the state of the electron spin. These
operations, combined with electron spin rotations can be used to synthesize any
unitary transformation on the coupled electron-nuclear spin system. We discuss
how these methods can be used for design of experiments for transfer of
polarization from the electron to the nuclear spins
Effect of a rotating propeller on the separation angle of attack and distortion in ducted propeller inlets
The present study represents an extension of an earlier wind tunnel experiment performed with the P&W 17-in. Advanced Ducted Propeller (ADP) Simulator operating at Mach 0.2. In order to study the effects of a rotating propeller on the inlet flow, data were obtained in the UTRC 10- by 15-Foot Large Subsonic Wind Tunnel with the same hardware and instrumentation, but with the propeller removed. These new tests were performed over a range of flow rates which duplicated flow rates in the powered simulator program. The flow through the inlet was provided by a remotely located vacuum source. A comparison of the results of this flow-through study with the previous data from the powered simulator indicated that in the conventional inlet the propeller produced an increase in the separation angle of attack between 4.0 deg at a specific flow of 22.4 lb/sec-sq ft to 2.7 deg at a higher specific flow of 33.8 lb/sec-sq ft. A similar effect on separation angle of attack was obtained by using stationary blockage rather than a propeller
Electroweak form factors of heavy-light mesons -- a relativistic point-form approach
We present a general relativistic framework for the calculation of the
electroweak structure of heavy-light mesons within constituent-quark models. To
this aim the physical processes in which the structure is measured, i.e.
electron-meson scattering and semileptonic weak decays, are treated in a
Poincar\'e invariant way by making use of the point-form of relativistic
quantum mechanics. The electromagnetic and weak meson currents are extracted
from the 1- and 1--exchange amplitudes that result from a
Bakamjian-Thomas type mass operator for the respective systems. The covariant
decomposition of these currents provides the electromagnetic and weak
(transition) form factors. Problems with cluster separability, which are
inherent in the Bakamjian-Thomas construction, are discussed and it is shown
how to keep them under control. It is proved that the heavy-quark limit of the
electroweak form factors leads to one universal function, the Isgur-Wise
function, confirming that the requirements of heavy-quark symmetry are
satisfied. A simple analytical expression is given for the Isgur-Wise function
and its agreement with a corresponding front-form calculation is verified
numerically. Electromagnetic form factors for and and weak
-decay form factors are calculated with a simple
harmonic-oscilllator wave function and heavy-quark symmetry breaking due to
finite masses of the heavy quarks is discussed.Comment: 20 pages, 14 figure
Tunable multi-photon Rabi oscillations in an electronic spin system
We report on multi-photon Rabi oscillations and controlled tuning of a
multi-level system at room temperature (S=5/2 for Mn2+:MgO) in and out of a
quasi-harmonic level configuration. The anisotropy is much smaller than the
Zeeman splittings, such as the six level scheme shows only a small deviation
from an equidistant diagram. This allows us to tune the spin dynamics by either
compensating the cubic anisotropy with a precise static field orientation, or
by microwave field intensity. Using the rotating frame approximation, the
experiments are very well explained by both an analytical model and a
generalized numerical model. The calculated multi-photon Rabi frequencies are
in excellent agreement with the experimental data
Universal Control of Nuclear Spins Via Anisotropic Hyperfine Interactions
We show that nuclear spin subsystems can be completely controlled via
microwave irradiation of resolved anisotropic hyperfine interactions with a
nearby electron spin. Such indirect addressing of the nuclear spins via
coupling to an electron allows us to create nuclear spin gates whose
operational time is significantly faster than conventional direct addressing
methods. We experimentally demonstrate the feasibility of this method on a
solid-state ensemble system consisting of one electron and one nuclear spin.Comment: RevTeX4, 8 pages, 8 figure
Quenching Spin Decoherence in Diamond through Spin Bath Polarization
We experimentally demonstrate that the decoherence of a spin by a spin bath
can be completely eliminated by fully polarizing the spin bath. We use electron
paramagnetic resonance at 240 gigahertz and 8 Tesla to study the spin coherence
time of nitrogen-vacancy centers and nitrogen impurities in diamond from
room temperature down to 1.3 K. A sharp increase of is observed below the
Zeeman energy (11.5 K). The data are well described by a suppression of the
flip-flop induced spin bath fluctuations due to thermal spin polarization.
saturates at below 2 K, where the spin bath polarization
is 99.4 %.Comment: 5 pages and 3 figure
Electromagnetic meson form factor from a relativistic coupled-channel approach
Point-form relativistic quantum mechanics is used to derive an expression for
the electromagnetic form factor of a pseudoscalar meson for space-like momentum
transfers. The elastic scattering of an electron by a confined quark-antiquark
pair is treated as a relativistic two-channel problem for the and
states. With the approximation that the total velocity of the
system is conserved at (electromagnetic) interaction vertices this
simplifies to an eigenvalue problem for a Bakamjian-Thomas type mass operator.
After elimination of the channel the electromagnetic meson
current and form factor can be directly read off from the one-photon-exchange
optical potential. By choosing the invariant mass of the electron-meson system
large enough, cluster separability violations become negligible. An equivalence
with the usual front-form expression, resulting from a spectator current in the
reference frame, is established. The generalization of this
multichannel approach to electroweak form factors for an arbitrary bound
few-body system is quite obvious. By an appropriate extension of the Hilbert
space this approach is also able to accommodate exchange-current effects.Comment: 30 pages, 5 figure
3D printing of ultra‐thin veneers made of lithium disilicate using the LCM method in a digital workflow: A feasibility study
Objective
This article highlights the feasibility of the additive fabrication of ultra-thin veneers made of lithium disilicate using the lithography-based ceramic manufacturing (LCM) method.
Clinical Considerations
An esthetical appealing restoration of anterior teeth with thin ceramic veneers is considered one of the ultimate challenges in restorative dental prosthetics. These sophisticated restorations can be fabricated in different ways. Both analog and digital subtractive manufacturing processes have been used to date. Either of the methods is highly demanding for the dental technician and dental engineering due to the required low ceramic layer thickness.
Conclusion
Modern additive manufacturing methods, for example LCM technology, enable the production of ultra-thin lithium disilicate veneers with layer thicknesses of down to 0.2 mm and could therefore represent a viable alternative for this indication in the future.
Clinical Significance
Digital technologies can help streamline workflows, make the outcome more predictable and reproducible, and even further optimize therapeutic restorative options such as highly esthetic veneers for anterior teeth. The reduced material thickness allows for a true non-prep solution or minimally invasive preparation
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