[show abstract][hide abstract] ABSTRACT: This article presents numerical recipes for simulating high-temperature and non-equilibrium quantum spin systems that are continuously measured and controlled. The notion of a spin system is broadly conceived, in order to encompass macroscopic test masses as the limiting case of large-j spins. The simulation technique has three stages: first the deliberate introduction of noise into the simulation, then the conversion of that noise into an equivalent continuous measurement and control process, and finally, projection of the trajectory onto a state-space manifold having reduced dimensionality and possessing a Kahler potential of multi-linear form. The resulting simulation formalism is used to construct a positive P-representation for the thermal density matrix. Single-spin detection by magnetic resonance force microscopy (MRFM) is simulated, and the data statistics are shown to be those of a random telegraph signal with additive white noise. Larger-scale spin-dust models are simulated, having no spatial symmetry and no spatial ordering; the high-fidelity projection of numerically computed quantum trajectories onto low-dimensionality Kahler state-space manifolds is demonstrated. The reconstruction of quantum trajectories from sparse random projections is demonstrated, the onset of Donoho-Stodden breakdown at the Candes-Tao sparsity limit is observed, a deterministic construction for sampling matrices is given, and methods for quantum state optimization by Dantzig selection are given.
New Journal of Physics 06/2008; · 4.06 Impact Factor
[show abstract][hide abstract] ABSTRACT: This study characterizes the healing response of the glenoid after spherical reaming and prosthetic humeral head replacement in a canine model of glenohumeral hemiarthroplasty. The right glenoid of twelve skeletally mature female dogs was reamed to a uniform radius of curvature, removing all cartilage down to bleeding subchondral bone. The glenoid was not resurfaced. The humeral head was replaced with a stemmed metal prosthesis. Post-surgery, the operated limbs were immobilized for seven days, with motion allowed ad libitum thereafter. Fluorescent bone labels were administered to identify bone formation. These procedures were not complicated by instability, infection or death. Six animals were euthanized at 10 week and six more at 24 week. The intact glenohumeral joints were evaluated by gross examination, assessment of glenoid concavity, and light microscopy of methylmethacrylate sections. At 10 week, vascular fibrous tissue partially covered the glenoid, maintaining a concave surface congruent with the prosthetic humeral head. New bone formed at the margin of the glenoid, and the density of the periarticular trabecular bone increased. At 24 week, the healing was more advanced; thick fibrocartilaginous tissue covered the entire glenoid surface. These results demonstrate that spherical glenoid reaming produced a consistent healing response characterized by remodelling of the reamed bony concavity to a congruent, living, smooth, securely attached interface articulating with the humeral prosthesis.
Journal of Orthopaedic Research 02/2005; 23(1):18-26. · 2.88 Impact Factor
[show abstract][hide abstract] ABSTRACT: We tested the hypothesis that articular cartilage adjacent to experimental osteochondral defects is not subject to unusual strains under load. A 2.5-mm drill hole was made in the medial femoral condyle of 15 knees from 10 adult rabbits. Experimental joints were loaded with simulated quadriceps force, then frozen under load and preserved by freeze-substitution fixation. Deformation in the region of the defect was evaluated by scanning electron and light microscopy and compared with nondrilled and nonloaded control knees. To simulate blood clot, alginate was placed into some defects before loading. In loaded knees, articular cartilage at the edge of the drill hole was abnormally flattened and folded into the defect. Opposing tibial cartilage or meniscus intruded into the femoral defect beyond the cement line. Alginate did not prevent incursion of opposing cartilage. In this standard drill-hole model, the articular cartilage defect is occupied by the opposing surface when a joint is loaded. Any tissue growing or surgically implanted in the defect is subject to loading and displacement, therefore complicating attempts to characterize the healing or regenerative potential in similar drill-hole models. Deformation of cartilage at the defect edge suggests load concentration or increased compliance. Either phenomenon would contribute to subsequent degeneration of the cartilage adjacent to defects.
Clinical Orthopaedics and Related Research 02/2005; · 2.79 Impact Factor
[show abstract][hide abstract] ABSTRACT: Exact reconstruction of an osteochondral defect by autogenous transplantation (mosaicplasty) is difficult given the variation in joint surface contour. Clinical and experimental studies do not show the extent to which incongruity can be tolerated in autografting.
Grafted articular cartilage will hypertrophy to correct the incongruity created by recession of the transplanted surface.
Controlled laboratory study.
To test the response of grafts to incongruities, osteochondral autografts were transplanted from the trochlea to the femoral condyle in adult male sheep stifle joints. In groups of 6 animals, graft surfaces were placed flush, countersunk 1 mm or countersunk 2 mm, then histologically analyzed 6 weeks after surgery. Cartilage thickness, condition of the articular surfaces, and preservation of hyaline characteristics were the primary features compared.
Bony union, vascularization, and new bone formation were present in all grafts. Cartilage-to-cartilage healing did not occur. In flush specimens, cartilage changed minimally in thickness and histologic architecture. The specimens countersunk 1 mm demonstrated significant cartilage thickening (54.7% increase, P <.05). Chondrocyte hyperplasia, tidemark advancement, and vascular invasion occurred at the chondroosseous junction, and the surface remained smooth. Cartilage necrosis and fibrous overgrowth were observed in all grafts countersunk 2 mm.
Minimally countersunk autografts possess a capacity for remodeling that can correct initial incongruities while preserving hyaline characteristics. Grafts placed deeper do not restore the contour or composition of the original articular surface.
If preservation of normal hyaline cartilage is the objective, thin grafted articular cartilage can remodel, but the tolerance for incongruity is limited and probably less than that reported for an intra-articular fracture.
The American Journal of Sports Medicine 01/2005; 32(8):1842-8. · 4.44 Impact Factor
[show abstract][hide abstract] ABSTRACT: Previous work suggests that the labrum helps center the humeral head. We hypothesized that detachment of the labrum alone would shift the head from its centered position toward the detachment, and repair would restore its centered position. Five young shoulders were used, and glenoids were potted with the articular surfaces oriented horizontally. Unconstrained humeral heads were subjected to 30-N compressive loads and no displacing force. Using a technique with 10-micrometer resolution, we quantified head and glenoid positions before and after anteroinferior labral detachment and after three types of repair. Detachment was associated with humeral head shift toward the labral lesion in all specimens, averaging 0.74 mm (range, 0.51-1.00 mm) (P <.005). Repair to the lip restored the labrum's centering effect variably. Repair with suture anchors on the glenoid face over-reduced the humeral head, shifting it posterosuperiorly by a mean of 3.47 mm (range, 0.71-6.7 mm) (P <.05). The labrum is important for humeral head centering, even without displacing loads.
Journal of Shoulder and Elbow Surgery 01/2003; 12(1):53-8. · 2.32 Impact Factor
[show abstract][hide abstract] ABSTRACT: quantum microscope performance. In order to define a specific target for the design of next- generation quantum microscopes, and also in order to begin defining more clearly how quantum microscopes might be used in practice, this article considers the suitability of the HIV reverse transcriptase inhibitor Nevirapine as a design target. The literature from 1990-1994 is reviewed, spanning the period from the discovery of Nevirapine's anti-HIV activity to the elucidation of the structural basis for this activity. An analysis of this literature indicates that quantum microscopy could significantly shorten the duration and improve the reliability of Nevirapine- type drug development. From a physics point of view, Nevirapine's carbon-carbon nuclear dipole interactions are shown to be well-matched to testing and developing next-generation quantum simulation algorithms, being neither unrealistically simple nor intractably complex. It is noted that if the present rapid pace of advance in ab initio quantum chemical calculations continues, such that these calculations can be interfaced to the pipeline of structural information emerging from quantum microscopes, a new resource frontier will be opened biological science and medicine.
[show abstract][hide abstract] ABSTRACT: This article presents numerical techniques for simulating high-temperature and non-equilibrium quan- tum spin systems that are continuously measured and controlled. The notion of a "spin system" is broadly conceived, to encompass test masses as the limiting case of large-j spins, and in general the systems simulated are spatially inhomogeneous. The simulation technique has three stages: first the deliberate introduction of noise into the simulation, then the conversion of that noise into a informat- ically equivalent continuous measurement and control processes, and finally, projection of the trajec- tory onto a K¨ ahlerian state-space manifold having reduced dimensionality and possessing a Kahler potential of multilinear (i.e., product-sum) functional form; these state-spaces can be regarded as ruled algebraic varieties. To provide a unifying geometric context for this technique, the sectional curvature of ruled state-spaces is analyzed, and proved to be non-positive upon all sections that contain a rule. It is further shown that ruled state-spaces include the Slater determinant wave-functions of quantum chemistry as a special case and that these Slater determinant manifolds possess a K¨ ahler-Einstein met- ric. It is suggested that the Riemannian curvature properties of ruled state-spaces generically account for the fidelity, efficiency, and robustness of projective trajectory simulation on these state-spaces. The resulting formalism is used to construct a positive P-representation for the thermal density matrix, and then to prove a formal equivalence between Caves' amplifier noise limit and the standard quantum limit in test-mass monitoring. Single-spin detection by magnetic resonance force microscopy (MRFM) is then simulated, and the data statistics are shown to be those of a random telegraph signal with ad- ditive white noise, to all orders, in excellent agreement with experimental results. Then a larger-scale spin-dust model is simulated, having no spatial symmetry and no spatial ordering; the high-fidelity projection of numerically computed quantum trajectories onto low-dimensionality K¨ ahler state-space manifolds is demonstrated. Finally, a method for accomplishing public key exchange via spin-dust simulations is demonstrated; this method establishes the geometric equivalence of a set of problems in physics, engineering, and information theory.