Miscellanea

Miscellane

Treatment of ankle osteoarthritis: arthrodesis versus total ankle replacement

While ankle arthrodesis has remained the gold standard treatment for symptomatic primary, secondary, and posttraumatic ankle arthritis, more recently, total ankle replacement (TAR) has seen considerable improvement in terms of biomechanics, function, and complication rates. However, while in the long-term degeneration of the adjacent joints is almost always found on radiographs after ankle arthrodesis, the longevity of TAR is still insufficient and does not match that of total knee and hip joints. The current review article focuses on the treatment of ankle arthritis by means of arthrodesis and TA

Energy-gap dynamics of superconducting NbN thin films studied by time-resolved terahertz spectroscopy

Using time-domain Terahertz spectroscopy we performed direct studies of the photoinduced suppression and recovery of the superconducting gap in a conventional BCS superconductor NbN. Both processes are found to be strongly temperature and excitation density dependent. The analysis of the data with the established phenomenological Rothwarf-Taylor model enabled us to determine the bare quasiparticle recombination rate, the Cooper pair-breaking rate and the electron-phonon coupling constant, \lambda = 1.1 +/- 0.1, which is in excellent agreement with theoretical estimates.Comment: 4 pages, 4 figures; final version, accepted for publication in Phys. Rev. Let

Arthrodese und Endoprothese des oberen Sprunggelenks: Indikationen, Techniken und Fallstricke

Zusammenfassung: Die symptomatische Arthrose des oberen Sprunggelenks (OSG) stellt den orthopädischen Chirurgen, nach ausgereizter konservativer bzw. gelenkerhaltender Therapie vor die Wahl der geeigneten operativen Therapie. Nach massiven Problemen der Endoprothetik des OSG in deren Anfangsjahren stellt diese aktuell eine immer häufiger angewandte Alternative zur Arthrodese des OSG dar. Wichtig für den späteren Erfolg der gewählten Methode ist die sorgfältige Patientenauswahl und deren ausführliche Information betreffend operativer Technik, zu erwartendem Ergebnis und Komplikationen. Nach wie vor besteht unter verschiedenen Autoren Einigkeit bezüglich der Wichtigkeit der Indikation hinsichtlich der Endoprothetik des OSG. Dennoch zeigt sich in der Literatur der Trend zu immer niedriger Indikationsschwelle zugunsten der Endoprothetik des OSG. Sowohl die Arthrodese als auch die Endoprothetik des OSG bleiben trotz stetig verbessertem Verständnis der Biomechanik des Rückfußes, verbesserter Operationstechnik und verbesserten Implantaten anspruchsvolle Eingriffe. Eine zusammenfassende Beschreibung der aktuellen Techniken zeigt einen Überblick der aktuellen Techniken. Ziel dieses Übersichtsartikels ist es, die aktuelle Literatur aufzuarbeiten und dem orthopädischen Chirurgen eine Entscheidungshilfe bei der Wahl des operativen Verfahrens zur Behandlung der symptomatischen endgradigen Arthrose des OSG zu gebe

Emergent Geometry and Gravity from Matrix Models: an Introduction

A introductory review to emergent noncommutative gravity within Yang-Mills Matrix models is presented. Space-time is described as a noncommutative brane solution of the matrix model, i.e. as submanifold of \R^D. Fields and matter on the brane arise as fluctuations of the bosonic resp. fermionic matrices around such a background, and couple to an effective metric interpreted in terms of gravity. Suitable tools are provided for the description of the effective geometry in the semi-classical limit. The relation to noncommutative gauge theory and the role of UV/IR mixing is explained. Several types of geometries are identified, in particular "harmonic" and "Einstein" type of solutions. The physics of the harmonic branch is discussed in some detail, emphasizing the non-standard role of vacuum energy. This may provide new approach to some of the big puzzles in this context. The IKKT model with D=10 and close relatives are singled out as promising candidates for a quantum theory of fundamental interactions including gravity.Comment: Invited topical review for Classical and Quantum Gravity. 57 pages, 5 figures. V2,V3: minor corrections and improvements. V4,V5: some improvements, refs adde

Gravity and compactified branes in matrix models

A mechanism for emergent gravity on brane solutions in Yang-Mills matrix models is exhibited. Newtonian gravity and a partial relation between the Einstein tensor and the energy-momentum tensor can arise from the basic matrix model action, without invoking an Einstein-Hilbert-type term. The key requirements are compactified extra dimensions with extrinsic curvature M^4 x K \subset R^D and split noncommutativity, with a Poisson tensor \theta^{ab} linking the compact with the noncompact directions. The moduli of the compactification provide the dominant degrees of freedom for gravity, which are transmitted to the 4 noncompact directions via the Poisson tensor. The effective Newton constant is determined by the scale of noncommutativity and the compactification. This gravity theory is well suited for quantization, and argued to be perturbatively finite for the IKKT model. Since no compactification of the target space is needed, it might provide a way to avoid the landscape problem in string theory.Comment: 35 pages. V2: substantially revised and improved, conclusion weakened. V3: some clarifications, published version. V4: minor correctio

RAId_aPS: MS/MS analysis with multiple scoring functions and spectrum-specific statistics

Statistically meaningful comparison/combination of peptide identification results from various search methods is impeded by the lack of a universal statistical standard. Providing an E-value calibration protocol, we demonstrated earlier the feasibility of translating either the score or heuristic E-value reported by any method into the textbook-defined E-value, which may serve as the universal statistical standard. This protocol, although robust, may lose spectrum-specific statistics and might require a new calibration when changes in experimental setup occur. To mitigate these issues, we developed a new MS/MS search tool, RAId_aPS, that is able to provide spectrum-specific E-values for additive scoring functions. Given a selection of scoring functions out of RAId score, K-score, Hyperscore and XCorr, RAId_aPS generates the corresponding score histograms of all possible peptides using dynamic programming. Using these score histograms to assign E-values enables a calibration-free protocol for accurate significance assignment for each scoring function. RAId_aPS features four different modes: (i) compute the total number of possible peptides for a given molecular mass range, (ii) generate the score histogram given a MS/MS spectrum and a scoring function, (iii) reassign E-values for a list of candidate peptides given a MS/MS spectrum and the scoring functions chosen, and (iv) perform database searches using selected scoring functions. In modes (iii) and (iv), RAId_aPS is also capable of combining results from different scoring functions using spectrum-specific statistics. The web link is http://www.ncbi.nlm.nih.gov/CBBresearch/Yu/raid_aps/index.html. Relevant binaries for Linux, Windows, and Mac OS X are available from the same page.Comment: 34 pages, 10 figures, 1 supplementary information file (RAId_aPS_support.pdf). To view the supplementary file, please download and extract the gzipped tar source file listed under "Other formats

Quantum Gravity from Noncommutative Spacetime

We review a novel and authentic way to quantize gravity. This novel approach is based on the fact that Einstein gravity can be formulated in terms of a symplectic geometry rather than a Riemannian geometry in the context of emergent gravity. An essential step for emergent gravity is to realize the equivalence principle, the most important property in the theory of gravity (general relativity), from U(1) gauge theory on a symplectic or Poisson manifold. Through the realization of the equivalence principle, which is an intrinsic property in symplectic geometry known as the Darboux theorem or the Moser lemma, one can understand how diffeomorphism symmetry arises from noncommutative U(1) gauge theory; thus, gravity can emerge from the noncommutative electromagnetism, which is also an interacting theory. As a consequence, a background-independent quantum gravity in which the prior existence of any spacetime structure is not a priori assumed but is defined by using the fundamental ingredients in quantum gravity theory can be formulated. This scheme for quantum gravity can be used to resolve many notorious problems in theoretical physics, such as the cosmological constant problem, to understand the nature of dark energy, and to explain why gravity is so weak compared to other forces. In particular, it leads to a remarkable picture of what matter is. A matter field, such as leptons and quarks, simply arises as a stable localized geometry, which is a topological object in the defining algebra (noncommutative $\star$-algebra) of quantum gravity.Comment: 97 pages, to be published in J. Korean Phys. So