Impact of iliac crest bone graft harvesting on fusion rates and postoperative pain during instrumented posterolateral lumbar fusion

This study aims to evaluate the influence of bone harvesting on postoperative pain and fusion rates. Group 1 patients received iliac crest bone graft (ICBG) either alone or augmented with local bone. Group 2 received only local bone. No statistical significance was found in radiological union or in the Oswestry Disability Index scores. Visual Analogue Scale scores showed less pain in group 2. Logistic regression showed no correlation between residual pain and occurrence of fusion. Harvesting ICBG did not appear to increase fusion rates and no relation was found between radiological non-union and pai

Posterolateral lumbar spine fusion using a novel demineralized bone matrix: a controlled case pilot study

Introduction: Intertransverse posterolateral fusion along with instrumentation is a common technique used for spinal fusion. Iliac crest bone graft (ICBG) offers good fusion success rates with a low risk for disease transmission but is, however, linked with certain morbidity. In an effort to eliminate or reduce the amount of iliac graft needed, bone substitutes including demineralized bone matrix (DBM) have been developed. This study evaluates a novel DBM (Accell Connexus®) used in one or two-level instrumented posterolateral lumbar fusion. Materials and methods: A total of 59 consecutive patients were studied as two groups. Group 1 consisted of 33 patients having Accell Connexus® used to augment either ICBG or local decompression material. Group 2 consisted of 26 consecutive patients, operated prior to the introduction of this novel DBM, having either ICBG alone or local decompression material. Fusion was assessed by two independent observers, blinded to graft material, using standardized criteria found in the literature. All adverse events were recorded prospectively. Results: The results show no statistically significant differences between the two groups in fusion rates, complications, surgery duration, ODI, or pain on VAS. Logistical regression showed no relation between fusion and age, smoking status or comorbidities. Furthermore, no adverse events related to the use of the novel DBM were observed. Conclusion: The results from this study demonstrate that the novel DBM presented performs equally as well as that of autologous bone, be it either ICBG or a local decompression material, and can therefore be used as a graft extende

Quadratic-in-Spin Hamiltonian at O(G2)\mathcal{O}(G^2) from Scattering Amplitudes

We obtain the quadratic-in-spin terms of the conservative Hamiltonian describing the interactions of a binary of spinning bodies in General Relativity through $\mathcal{O}(G^2)$ and to all orders in velocity. Our calculation extends a recently-introduced framework based on scattering amplitudes and effective field theory to consider non-minimal coupling of the spinning objects to gravity. At the order that we consider, we establish the validity of the formula proposed in \cite{Bern:2020buy} that relates the impulse and spin kick in a scattering event to the eikonal phase.Comment: 21 pages + references, 5 figures, 1 ancillary fil

Gravitational Self Force from Scattering Amplitudes in Curved Space

We employ scattering amplitudes in curved space to model the dynamics of a light probe particle with mass $m$ orbiting in the background spacetime induced by a heavy gravitational source with mass $M$. Observables are organized as an expansion in $m/M$ to all orders in $G$ -- the gravitational self-force expansion. An essential component of our analysis is the backreaction of the heavy source which we capture by including the associated light degrees of freedom. As illustration we consider a Schwarzschild background and verify geodesic motion as well as the first-order self-force correction to two-body scattering through ${\cal O}(G^3)$. Amplitudes in curved space offer several advantages, and further developments along these lines may advance the computation of gravitational-wave signals for extreme-mass-ratio inspirals.Comment: Published version, 30 pages, 11 figure

Gravitational Effective Field Theory Islands, Low-Spin Dominance, and the Four-Graviton Amplitude

We analyze constraints from perturbative unitarity and crossing on the leading contributions of higher-dimension operators to the four-graviton amplitude in four spacetime dimensions, including constraints that follow from distinct helicity configurations. We focus on the leading-order effect due to exchange by massive degrees of freedom which makes the amplitudes of interest infrared finite. In particular, we place a bound on the coefficient of the $R^3$ operator that corrects the graviton three-point amplitude in terms of the $R^4$ coefficient. To test the constraints we obtain nontrivial effective field-theory data by computing and taking the large-mass expansion of the one-loop minimally-coupled four-graviton amplitude with massive particles up to spin 2 circulating in the loop. Remarkably, we observe that the leading EFT coefficients obtained from both string and one-loop field-theory amplitudes lie in small islands. The shape and location of the islands can be derived from the dispersive representation for the Wilson coefficients using crossing and assuming that the lowest-spin spectral densities are the largest. Our analysis suggests that the Wilson coefficients of weakly-coupled gravitational physical theories are much more constrained than indicated by bounds arising from dispersive considerations of $2 \to 2$ scattering. The one-loop four-graviton amplitudes used to obtain the EFT data are computed using modern amplitude methods, including generalized unitarity, supersymmetric decompositions and the double copy.Comment: 123 pages, 23 figure, 2 Mathematica ancillary file

Motion-Based Sign Language Video Summarization using Curvature and Torsion

An interesting problem in many video-based applications is the generation of short synopses by selecting the most informative frames, a procedure which is known as video summarization. For sign language videos the benefits of using the $t$-parameterized counterpart of the curvature of the 2-D signer's wrist trajectory to identify keyframes, have been recently reported in the literature. In this paper we extend these ideas by modeling the 3-D hand motion that is extracted from each frame of the video. To this end we propose a new informative function based on the $t$-parameterized curvature and torsion of the 3-D trajectory. The method to characterize video frames as keyframes depends on whether the motion occurs in 2-D or 3-D space. Specifically, in the case of 3-D motion we look for the maxima of the harmonic mean of the curvature and torsion of the target's trajectory; in the planar motion case we seek for the maxima of the trajectory's curvature. The proposed 3-D feature is experimentally evaluated in applications of sign language videos on (1) objective measures using ground-truth keyframe annotations, (2) human-based evaluation of understanding, and (3) gloss classification and the results obtained are promising.Comment: This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessibl

Quantum Field Theory, Worldline Theory, and Spin Magnitude Change in Orbital Evolution

A previous paper~\cite{Bern:2022kto} identified a puzzle stemming from the amplitudes-based approach to spinning bodies in general relativity: additional Wilson coefficients appear compared to current worldline approaches to conservative dynamics of generic astrophysical objects, including neutron stars. In this paper we clarify the nature of analogous Wilson coefficients in the simpler theory of electrodynamics. We analyze the original field-theory construction, identifying definite-spin states some of which have negative norms, and relating the additional Wilson coefficients in the classical theory to transitions between different quantum spin states. We produce a new version of the theory which also has additional Wilson coefficients, but no negative-norm states. We match, through $\mathcal O(\alpha^2)$ and $\mathcal O(S^2)$, the Compton amplitudes of these field theories with those of a modified worldline theory with extra degrees of freedom introduced by releasing the spin supplementary condition. We build an effective two-body Hamiltonian that matches the impulse and spin kick of the modified field theory and of the worldline theory, displaying additional Wilson coefficients compared to standard worldline approaches. The results are then compactly expressed in terms of an eikonal formula. Our key conclusion is that, contrary to standard approaches, while the magnitude of the spin tensor is still conserved, the magnitude of the spin vector can change under conserved Hamiltonian dynamics and this change is governed by the additional Wilson coefficients. For specific values of Wilson coefficients the results are equivalent to those from a definite spin obeying the spin supplementary condition, but for generic values they are physically inequivalent. These results warrant detailed studies of the corresponding issues in general relativity.Comment: 95 pages, 3 figure

La reconfiguration politique en Grèce, 2010-2014

This thesis analyzes the political upheaval in Greece during 2010-2014, a period marked by the economic crisis and the implementation of structural adjustment programs. Based on an empirical study, we demonstrate that the collapse of PASOK and the resulting political change are conditioned both by the internal structure of the party and the adopted policies. Our study focuses on the loss of the social anchors of PASOK, a loss which precedes and decides the electoral fall. The breakdown of socialist party is analyzed correlatively to the emergence of an alternative political offer that is formed through the anti- Memorandum mobilizations. Finally, we analyze how the Memorandum is becoming a major wedge issue determining both the political offer and the electoral alignments. This work is therefore part of a broader perspective that articulates the study of party politics with political crisis’ processes.Cette thèse analyse le bouleversement politique en Grèce pendant les années 2010-2014, période marquée par la crise économique et la mise en œuvre des programmes d’ajustement structurel. En nous appuyant sur une étude empirique, nous démontrons que l’effondrement du PASOK et la mutation du jeu politique sont conditionnés tant par la structuration interne du parti que par les politiques adoptées. Notre étude est attentive à la perte des ressorts sociaux du PASOK qui précède et conditionne la chute électorale. L’effondrement des socialistes est analysé de manière corrélative à l’émergence d’une offre politique de remplacement qui se forme autour des mobilisations contre le Mémorandum. Enfin, nous analysons la manière dont la question du Mémorandum s’impose comme enjeu principal déterminant aussi bien l’offre politique que les alignements électoraux. Ce travail s’inscrit donc dans une perspective large qui articule l’étude du phénomène partisan avec les processus des crises politiques