321 research outputs found
Unitary transformations for testing Bell inequalities
It is shown that optical experimental tests of Bell inequality violations can
be described by SU(1,1) transformations of the vacuum state, followed by photon
coincidence detections. The set of all possible tests are described by various
SU(1,1) subgroups of Sp(8,). In addition to establishing a common
formalism for physically distinct Bell inequality tests, the similarities and
differences of post--selected tests of Bell inequality violations are also made
clear. A consequence of this analysis is that Bell inequality tests are
performed on a very general version of SU(1,1) coherent states, and the
theoretical violation of the Bell inequality by coincidence detection is
calculated and discussed. This group theoretical approach to Bell states is
relevant to Bell state measurements, which are performed, for example, in
quantum teleportation.Comment: 3 figure
Lost and found: the radial quantum number of Laguerre-Gauss modes
We introduce an operator linked with the radial index in the Laguerre-Gauss
modes of a two-dimensional harmonic oscillator in cylindrical coordinates. We
discuss ladder operators for this variable, and confirm that they obey the
commutation relations of the su(1,1) algebra. Using this fact, we examine how
basic quantum optical concepts can be recast in terms of radial modes.Comment: Some minor typos fixed
BIOMECHANICAL STUDY ON CADAVER KNEE FOR THE EVALUATION OF CRUCIATE KNEE LIGAMENT RECONSTRUCTIONS
INTRODUCTION: Ruptures of the anterior and posterior cruciate knee ligament (ACL and PCL), alone or combined, are some of the most frequent joint injuries, especially in sports. The long-term unsatisfactory results and lack of systematic evaluation of surgical reconstructions have led us to undergo an evaluation on cadaver knees.
MATERIAL AND METHOD: A preliminary study was performed on one cadaver knee. The femur was fixed on a holder and magnetic sensors âBirdsTMâ were attached to the tibia and the femur, which tracked the kneeâs movement. A threedimensional knee analyzer GENI(1) was used to calculate kinematic parameters (tibial internal and external rotation and ab/adduction), as well as ligament combined deformation (elongation / bending / torsion) during knee flexion. This experiment was performed on an intact knee and a knee where the PCL has been cut and reconstructed using a synthetic Trevia ligament. Finally the knee was dissected to produce a combined postero-lateral instability and reconstructed with and without postero-lateral corner reconstruction. The effect of different reconstruction methods on kinematics and ligament deformation were compared.
RESULTS AND DISCUSSION: Kinematic parameters changed significantly when PCl and postero-lateral corner were dissected. The reconstruction of the PCL alone, using an âOver-the-Bottomâ method described by Krudwig(2), shifted the curves back to the initial situation and decreased the variability of the movement. Ligament deformation was 3 mm elongation, 50o femoral flexion and 90o torsion. These values are in accordance with material properties and should lead to good long-term biofunctionnality.
CONCLUSION: This study proposes an in vitro protocol for a better understanding of the clinical success or failure of different procedures. Preliminary results showed that the system and the protocol setup are sensitive to changes in kinematics following posterior cruciate ligament dissection and reconstruction. Experiments are performed at this time on several cadaver knees, in order to compare different reconstruction methods.
REFERENCES:
Sati, M. et al. (1997). Computer Assisted Knee Surgery: Diagnostics and Planning
of Knee Surgery. Computer Aided Surgery 2, 108-123.
Krudwig, W. (1997). In L'H. Yahia (Ed.), Ligaments and Ligamentoplasties.
Heidelberg: Springer Verlag
Changes in physical education teachersâ beliefs regarding motivational strategies: A quasi-experimental study
Abstract
Physical education teachers use motivational strategies that can (positively or negatively) affect their studentsâ level of motivation and engagement. Indeed, according to their experiences and beliefs, some teachers may focus on strategies that thwart, rather than support, studentsâ psychological needs (autonomy, competence, and relatedness). Effective professional development represents an excellent opportunity to help teachers use research-supported motivational strategies. Therefore, this study aimed to discover if attendance at a 2-day training course could positively affect PE teachersâ beliefs regarding empowering motivational strategies. Specifically, 11 PE teachers (experimental group = 6 [attending the training]; control group = 5 [no training]) from primary school (n = 6) and secondary school (n = 5) expressed their beliefs (effectiveness, feasibility, and normality) regarding 31 empowering motivational strategies proposed during training at the beginning (October) and the end (April) of the school year. Results of the Wilcoxon signed-rank test for related samples indicated no significant differences for the belief regarding effectiveness in either group. However, some positive significant changes (p †.05) occurred in the experimental group for two motivational strategies supporting studentsâ need for autonomy and one supporting their need for competence. Given the small sample, positive trends (p †.10) are also considered results of interest. In conclusion, the training appears likely to impact teachersâ beliefs. However, future professional development should provide additional feedback and follow-up time with teachers during experimentation with students to allow teachers to refine their understanding and use of the motivational strategies proposed
SU(N)-symmetric quasi-probability distribution functions
We present a set of N-dimensional functions, based on generalized
SU(N)-symmetric coherent states, that represent finite-dimensional Wigner
functions, Q-functions, and P-functions. We then show the fundamental
properties of these functions and discuss their usefulness for analyzing
N-dimensional pure and mixed quantum states.Comment: 16 pages, 2 figures. Updated text to reflect referee comment
A complementarity-based approach to phase in finite-dimensional quantum systems
We develop a comprehensive theory of phase for finite-dimensional quantum
systems. The only physical requirement we impose is that phase is complementary
to amplitude. To implement this complementarity we use the notion of mutually
unbiased bases, which exist for dimensions that are powers of a prime. For a
d-dimensional system (qudit) we explicitly construct d+1 classes of maximally
commuting operators, each one consisting of d-1 operators. One of this class
consists of diagonal operators that represent amplitudes (or inversions). By
the finite Fourier transform, it is mapped onto ladder operators that can be
appropriately interpreted as phase variables. We discuss the examples of qubits
and qutrits, and show how these results generalize previous approaches.Comment: 6 pages, no figure
Quantum phases of a qutrit
We consider various approaches to treat the phases of a qutrit. Although it
is possible to represent qutrits in a convenient geometrical manner by
resorting to a generalization of the Poincare sphere, we argue that the
appropriate way of dealing with this problem is through phase operators
associated with the algebra su(3). The rather unusual properties of these
phases are caused by the small dimension of the system and are explored in
detail. We also examine the positive operator-valued measures that can describe
the qutrit phase properties.Comment: 6 page
Technical considerations in lateral extra-articular reconstruction coupled with anterior cruciate ligament reconstruction: a simulation study evaluating the influence of surgical parameters on control of knee stability
Background: Surgical parameters such as the selection of tibial and femoral attachment site, graft tension, and knee flexion angle at the time of fixation may influence the control of knee stability after lateral extra-articular reconstruction. This study aimed to determine how sensitive is the control of knee rotation and translation, during simulated pivot-shift scenarios, to these four surgery settings.
Methods: A computer model was used to simulate 625 lateral extra-articular reconstructions based upon five different variations of each of the following parameters: femoral and tibial attachment sites, knee flexion angle and graft tension at the time of fixation. For each simulated surgery, the lateral extra-articular reconstruction external rotation moment at the knee joint center was computed during simulated pivot-shift scenarios. The sensitivity of the control of knee rotation and translation to a given surgery setting was assessed by calculating the coefficient of variation of the lateral extra-articular reconstruction external rotation moment.
Findings: Graft tension had minimal influence on the control of knee rotation and translation with less than 2.4% of variation across the scenarios tested. Control of knee rotation and translation was the least affected by the femoral attachment site if the knee was close to full extension at the time of graft fixation. The choice of the tibial attachment site was crucial when the femoral fixation was proximal and posterior to the femoral epicondyle since 15 to 67% of variation was observed in the control of knee rotation and translation.
Interpretation: Femoral and tibial attachment sites as well as knee flexion angle at the time of fixation should be considered by surgeons when performing lateral extra-articular reconstruction. Variation in graft tension between the ranges 20â40âŻN has minimal influence on the control of knee rotation and translation
Exchange Gate on the Qudit Space and Fock Space
We construct the exchange gate with small elementary gates on the space of
qudits, which consist of three controlled shift gates and three "reverse"
gates. This is a natural extension of the qubit case.
We also consider a similar subject on the Fock space, but in this case we
meet with some different situation. However we can construct the exchange gate
by making use of generalized coherent operator based on the Lie algebra su(2)
which is a well--known method in Quantum Optics. We moreover make a brief
comment on "imperfect clone".Comment: Latex File, 12 pages. I could solve the problems in Sec. 3 in the
preceding manuscript, so many corrections including the title were mad
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