126 research outputs found
Closed Superstrings in a Uniform Magnetic Field and Regularization Criterion
We summarize exact solutions of closed superstrings in a constant magnetic
field, from a view point of the regularization criterion. Some models will be
excluded according to this criterion. The spectrum-generating algebra is also
constructed in these interacting models.Comment: 13 pages, No figure
NS Open Strings with B Field and Their Interactions with NS Closed Strings
We consider interactions of a NS open string with first important states of a
NS closed string, i.e., a closed-string tachyon and a graviton, where both ends
of the NS open string are attached on a D-brane, and a constant background B
field is lying along directions parallel to the D-brane world volume. Contrary
to general expectations, there are no constraints on these vertex operators
coming from the B field. However, we point out that these vertex operators have
singularities at both ends of the NS open string when external momenta take
some values. These kinds of singularities essentially come from the Dirichlet
boundary conditions along directions transverse to the D-brane world volume.Comment: LaTex, 10 pages, no figure
Constrained Quantization of Charged Strings in Background B Field and g-Factors
The Dirac quantization is performed for the constrained system of the open
string with different charges located at both ends in the constant background B
field. Noncommutativity reveals to commutators [X, X], [P, P] and also [X,P] at
both ends of the string. We consider a dependence on the change of the
"cyclotron frequency" of the charged string. The g-factor of the charged string
is also calculated in the framework of our formulation.Comment: 21 pages, no figures, LaTe
Brans-Dicke Theory on Geometry
The gauge theory on geometry is applied to the
Brans-Dicke(BD) theory, where is the four dimensional space-time and
is a discrete space with two points. This approach had been previously
proposed by Konisi and Saito without recourse to noncommutative geometry(NCG).
Since our approach is geometrically simpler and clearer than NCG, one can see
more directly the effect of the space in obtaining the BD theory.Comment: 12 pages, LaTeX fil
Anatomic double-bundle anterior cruciate ligament reconstruction, using CT-based navigation and fiducial markers
Accurate placement of separate anteromedial and posterolateral bundle bone tunnels is crucial for anatomic, double-bundle anterior cruciate ligament (ACL) reconstruction. However, identifying the anatomic footprint at which to make the tibial and femoral bone tunnels is not a straightforward procedure. To overcome this problem, we used a CT-based navigation technique with a registration procedure based on fiducial markers (FMs). Preoperatively, 10 FM points were placed on skin around knee joint and scanned with CT. Imaging data of the knee were recorded on the computer system for preoperative registration and surgical planning. Intraoperatively, with a reference frame fixed to the distal medial aspect of femur and tibia, paired-point matching registration was performed with the use of points marked on skin through FM center holes. During tibial tunnel guide wire placement, tibial aiming guide with tracking device fed back the position of tip and direction of the guide wire on the three-dimensional (3D) tibia bone surface image and multiple image planes in real time. For the femoral side, the navigation pointer was placed at the footprint center with visual guidance of 3D image of lateral wall sagittal view on navigation monitor and marked with navigation awl. The average registration accuracy of 22 consecutive patients was 0.7 +/- A 0.2 mm and 0.6 +/- A 0.2 mm for femoral and tibial bone, respectively. Most of the bone tunnel positions evaluated with 3D-CT image were confirmed to be accurately placed in reference to the preoperative plan. There was no damage to femoral condyle cartilage and no other complication. This new CT-based computer navigation system opens the possibility for surgeons to plan bone tunnel positioning preoperatively and control it during technically demanding anatomic double-bundle ACL reconstruction.ArticleKNEE SURGERY SPORTS TRAUMATOLOGY ARTHROSCOPY. 19(3):378-383 (2011)journal articl
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