Endocardial versus epicardial ventricular radiofrequency ablation: utility of in vivo contact force assessment.

BACKGROUND Contact force (CF) is an important determinant of lesion formation for atrial endocardial radiofrequency ablation. There are minimal published data on CF and ventricular lesion formation. We studied the impact of CF on lesion formation using an ovine model both endocardially and epicardially. METHODS AND RESULTS Twenty sheep received 160 epicardial and 160 endocardial ventricular radiofrequency applications using either a 3.5-mm irrigated-tip catheter (Thermocool, Biosense-Webster, n=160) or a 3.5 irrigated-tip catheter with CF assessment (Tacticath, Endosense, n=160), via percutaneous access. Power was delivered at 30 watts for 60 seconds, when either catheter/tissue contact was felt to be good or when CF>10 g with Tacticath. After completion of all lesions, acute dimensions were taken at pathology. Identifiable lesion formation from radiofrequency application was improved with the aid of CF information, from 78% to 98% on the endocardium (P<0.001) and from 90% to 100% on the epicardium (P=0.02). The mean total force was greater on the endocardium (39±18 g versus 21±14 g for the epicardium; P<0.001) mainly because of axial force. Despite the force-time integral being greater endocardially, epicardial lesions were larger (231±182 mm(3) versus 209±131 mm(3); P=0.02) probably because of the absence of the heat sink effect of the circulating blood and covered a greater area (41±27 mm(2) versus 29±17 mm(2); P=0.03) because of catheter orientation. CONCLUSIONS In the absence of CF feedback, 22% of endocardial radiofrequency applications that are thought to have good contact did not result in lesion formation. Epicardial ablation is associated with larger lesions.

Estimation of tool pose based on force-density correlation during robotic drilling

The application of image-guided systems with or without support by surgical robots relies on the accuracy of the navigation process, including patient-to-image registration. The surgeon must carry out the procedure based on the information provided by the navigation system, usually without being able to verify its correctness beyond visual inspection. Misleading surrogate parameters such as the fiducial registration error are often used to describe the success of the registration process, while a lack of methods describing the effects of navigation errors, such as those caused by tracking or calibration, may prevent the application of image guidance in certain accuracy-critical interventions. During minimally invasive mastoidectomy for cochlear implantation, a direct tunnel is drilled from the outside of the mastoid to a target on the cochlea based on registration using landmarks solely on the surface of the skull. Using this methodology, it is impossible to detect if the drill is advancing in the correct direction and that injury of the facial nerve will be avoided. To overcome this problem, a tool localization method based on drilling process information is proposed. The algorithm estimates the pose of a robot-guided surgical tool during a drilling task based on the correlation of the observed axial drilling force and the heterogeneous bone density in the mastoid extracted from 3-D image data. We present here one possible implementation of this method tested on ten tunnels drilled into three human cadaver specimens where an average tool localization accuracy of 0.29 mm was observed.

A new application of emulsions to measure the gravitational force on antihydrogen

We propose to build and operate a detector based on the emulsion film technology for the measurement of the gravitational acceleration on antimatter, to be performed by the AEgIS experiment (AD6) at CERN. The goal of AEgIS is to test the weak equivalence principle with a precision of 1% on the gravitational acceleration g by measuring the vertical position of the annihilation vertex of antihydrogen atoms after their free fall while moving horizontally in a vacuum pipe. With the emulsion technology developed at the University of Bern we propose to improve the performance of AEgIS by exploiting the superior position resolution of emulsion films over other particle detectors. The idea is to use a new type of emulsion films, especially developed for applications in vacuum, to yield a spatial resolution of the order of one micron in the measurement of the sag of the antihydrogen atoms in the gravitational field. This is an order of magnitude better than what was planned in the original AEgIS proposal.

Male-male competition and nuptial-colour displacement as a diversifying force in Lake Victoria cichlid fishes

We propose a new mechanism for diversification of male nuptial–colour patterns in the rapidly speciating cichlid fishes of Lake Victoria. Sympatric closely related species often display nuptial colours at opposite ends of the spectrum with males either blue or yellow to red. Colour polymorphisms within single populations are common too. We propose that competition between males for breeding sites promotes such colour diversification, and thereby speciation. We hypothesize that male aggression is primarily directed towards males of the common colour, and that rare colour morphs enjoy a negatively frequency–dependent fitness advantage. We test our hypothesis with a large dataset on the distributions and nuptial colorations of 52 species on 47 habitat islands in Lake Victoria, and with a smaller dataset on the within–spawning–site distributions of males with different coloration. We report that territories of males of the same colour are negatively associated on the spawning site, and that the distribution of closely related species over habitat islands is determined by nuptial coloration in the fashion predicted by our hypothesis. Whereas among unrelated species those with similar nuptial colour are positively associated, among closely related species those with similar colour are negatively associated and those with different colour are positively associated. This implies that negatively frequency–dependent selection on nuptial coloration among closely related species is a sufficiently strong force to override other effects on species distributions. We suggest that male–male competition is an important and previously neglected agent of diversification among haplochromine cichlid fishes.

The UNESCO Convention on Cultural Diversity: An Appraisal Five Years after Its Entry into Force

The United Nations Educational Scientific and Cultural Organization (UNESCO) adopted in 2005 the first legally binding international instrument on culture. The Convention on the Protection and Promotion of the Diversity of Cultural Expressions was agreed upon with an overwhelming majority and after the swiftest ratification process in the history of the UNESCO entered into force on 18 March 2007. Now, five years later and with some 125 Members committed to implementing the Convention, not only observers with a particular interest in the topic but also the broader public may be eager to know what has happened and in how far has the implementation progress advanced. This is the question that animates this paper and which it seeks to answer by giving a brief background to the UNESCO Convention, clarifying its legal and political status and impact, as well as by looking at the current implementation activities in the domestic and international contexts.

The UNESCO Convention on Cultural Diversity : An Appraisal Five Years after its Entry into Force

The United Nations Educational Scientific and Cultural Organization (UNESCO) adopted in 2005 the first legally binding international instrument on culture. The Convention on the Protection and Promotion of the Diversity of Cultural Expressions was agreed upon with an overwhelming majority and after the swiftest ratification process in the history of the UNESCO entered into force on 18 March 2007. Now, five years later and with some 125 Members committed to implementing the Convention, not only observers with a particular interest in the topic but also the broader public may be eager to know what has happened and in how far has the implementation progress advanced. This is the question that animates this paper and which it seeks to answer by giving a brief background to the UNESCO Convention, clarifying its legal and political status and impact, as well as by looking at the current implementation activities in the domestic and international contexts.

Cell force measurements in 3D microfabricated environments based on compliant cantilevers.

We report the fabrication, functionalization and testing of microdevices for cell culture and cell traction force measurements in three-dimensions (3D). The devices are composed of bent cantilevers patterned with cell-adhesive spots not lying on the same plane, and thus suspending cells in 3D. The cantilevers are soft enough to undergo micrometric deflections when cells pull on them, allowing cell forces to be measured by means of optical microscopy. Since individual cantilevers are mechanically independent of each other, cell traction forces are determined directly from cantilever deflections. This proves the potential of these new devices as a tool for the quantification of cell mechanics in a system with well-defined 3D geometry and mechanical properties.

Precision of fit and retention force of cast non-precious-crowns on standard titanium implant-abutment with different design and height

OBJECTIVE The cost-effectiveness of cast nonprecious frameworks has increased their prevalence in cemented implant crowns. The purpose of this study was to assess the effect of the design and height of the retentive component of a standard titanium implant abutment on the fit, possible horizontal rotation and retention forces of cast nonprecious alloy crowns prior to cementation. MATERIALS AND METHODS Two abutment designs were examined: Type A with a 6° taper and 8 antirotation planes (Straumann Tissue-Level RN) and Type B with a 7.5° taper and 1 antirotation plane (SICace implant). Both types were analyzed using 60 crowns: 20 with a full abutment height (6 mm), 20 with a medium abutment height (4 mm), and 20 with a minimal (2.5 mm) abutment height. The marginal and internal fit and the degree of possible rotation were evaluated by using polyvinylsiloxane impressions under a light microscope (magnification of ×50). To measure the retention force, a custom force-measuring device was employed. STATISTICAL ANALYSIS one-sided Wilcoxon rank-sum tests with Bonferroni-Holm corrections, Fisher's exact tests, and Spearman's rank correlation coefficient. RESULTS Type A exhibited increased marginal gaps (primary end-point: 55 ± 20 μm vs. 138 ± 59 μm, P < 0.001) but less rotation (P < 0.001) than Type B. The internal fit was also better for Type A than for Type B (P < 0.001). The retention force of Type A (2.49 ± 3.2 N) was higher (P = 0.019) than that of Type B (1.27 ± 0.84 N). Reduction in abutment height did not affect the variables observed. CONCLUSION Less-tapered abutments with more antirotation planes provide an increase in the retention force, which confines the horizontal rotation but widens the marginal gaps of the crowns. Thus, casting of nonprecious crowns with Type A abutments may result in clinically unfavorable marginal gaps.