Scent marking in wild banded mongooses: 2. Intrasexual overmarking and competition between males

Sexual selection has resulted in the elaboration of secondary sexual characteristics in many animals. Although mammalian scent glands, secretions and marking behaviour are commonly sexually dimorphic, these traits have received little attention compared to avian plumage and mammalian weaponry. Overmarking, when one individual places a scent mark directly over that of another individual, is of particular interest. Owing to the costs of repeatedly monitoring and covering the scent marks of rivals, overmarking may provide an honest indication of a male's resource-holding potential, perhaps explaining why female rodents exposed to experimental overmarks subsequently prefer to associate with males whose scent mark was on top. This study on wild banded mongooses, Mungos mungo, suggests that overmarking may primarily affect behavioural mating success through male competition not by female mate choice. First, chemical analyses of anal gland secretions demonstrated that males had individually distinctive scents, and a field experiment confirmed that mongooses were able to discriminate between scents from different individuals. Observations of overmarking patterns showed a relationship between overmarking score and behavioural mating success, but we found no evidence that females actively chose to mate with males with high overmarking scores. Instead, we found that males with higher overmarking scores first mate-guarded females at a significantly younger age than males with lower overmarking scores. Since mate-guarding males obtain the vast majority of matings, this suggests that overmarking may be an important component of intrasexual competition for mating opportunities in this species.

Siphon flow in a cool magnetic loop

We investigate the properties of a structure in the solar chromosphere in an active region to find out whether the feature is consistent with a siphon flow in a magnetic loop filled with chromospheric material

A study of velocity fields in the transition region of Epsilon Eri (K2 V)

Analyses of the widths and shifts of optically thin emission lines in the ultraviolet spectrum of the active dwarf Epsilon Eri (K2 V) are presented. The spectra were obtained using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope and the Far Ultraviolet Spectroscopic Explorer. The line widths are used to find the non-thermal energy density and its variation with temperature from the chromosphere to the upper transition region. The energy fluxes that could be carried by Alfven and acoustic waves are investigated, to test their possible roles in coronal heating. Acoustic waves do not appear to be a viable means of coronal heating. There is, in principle, ample flux in Alfven waves, but detailed calculations of wave propagation are required before definite conclusions can be drawn about their viability. The high sensitivity and spectral resolution of the above instruments have allowed two-component Gaussian fits to be made to the profiles of the stronger transition region lines. The broad and narrow components which result share some similarities with those observed in the Sun, but in Epsilon Eri the broad component is redshifted relative to the narrow component and contributes more to the total line flux. The possible origins of the two components and the energy fluxes implied are discussed. On balance our results support the conclusion of Wood, Linsky & Ayres, that the narrow component is related to Alfven waves reaching to the corona, but the origin of the broad component is not clear.Comment: 19 pages, 16 figures. Accepted for publication by MNRA

Image-Guided Surgical Robotic System for Percutaneous Reduction of Joint Fractures

Complex joint fractures often require an open surgical procedure, which is associated with extensive soft tissue damages and longer hospitalization and rehabilitation time. Percutaneous techniques can potentially mitigate these risks but their application to joint fractures is limited by the current sub-optimal 2D intra-operative imaging (fluoroscopy) and by the high forces involved in the fragment manipulation (due to the presence of soft tissue, e.g., muscles) which might result in fracture malreduction. Integration of robotic assistance and 3D image guidance can potentially overcome these issues. The authors propose an image-guided surgical robotic system for the percutaneous treatment of knee joint fractures, i.e., the robot-assisted fracture surgery (RAFS) system. It allows simultaneous manipulation of two bone fragments, safer robot-bone fixation system, and a traction performing robotic manipulator. This system has led to a novel clinical workflow and has been tested both in laboratory and in clinically relevant cadaveric trials. The RAFS system was tested on 9 cadaver specimens and was able to reduce 7 out of 9 distal femur fractures (T- and Y-shape 33-C1) with acceptable accuracy (≈1 mm, ≈5°), demonstrating its applicability to fix knee joint fractures. This study paved the way to develop novel technologies for percutaneous treatment of complex fractures including hip, ankle, and shoulder, thus representing a step toward minimally-invasive fracture surgeries

Intra-operative fiducial-based CT/fluoroscope image registration framework for image-guided robot-assisted joint fracture surgery

Purpose Joint fractures must be accurately reduced minimising soft tissue damages to avoid negative surgical outcomes. To this regard, we have developed the RAFS surgical system, which allows the percutaneous reduction of intra-articular fractures and provides intra-operative real-time 3D image guidance to the surgeon. Earlier experiments showed the effectiveness of the RAFS system on phantoms, but also key issues which precluded its use in a clinical application. This work proposes a redesign of the RAFS’s navigation system overcoming the earlier version’s issues, aiming to move the RAFS system into a surgical environment. Methods The navigation system is improved through an image registration framework allowing the intra-operative registration between pre-operative CT images and intra-operative fluoroscopic images of a fractured bone using a custom-made fiducial marker. The objective of the registration is to estimate the relative pose between a bone fragment and an orthopaedic manipulation pin inserted into it intra-operatively. The actual pose of the bone fragment can be updated in real time using an optical tracker, enabling the image guidance. Results Experiments on phantom and cadavers demonstrated the accuracy and reliability of the registration framework, showing a reduction accuracy (sTRE) of about 0.88 ±0.2mm (phantom) and 1.15±0.8mm (cadavers). Four distal femur fractures were successfully reduced in cadaveric specimens using the improved navigation system and the RAFS system following the new clinical workflow (reduction error 1.2±0.3mm, 2±1∘). Conclusion Experiments showed the feasibility of the image registration framework. It was successfully integrated into the navigation system, allowing the use of the RAFS system in a realistic surgical application

Systematic errors of skin-friction measurements by oil-film interferometry

In recent years, the independent measurement of wall shear stress with oil-film or oil-drop interferometry has become a cornerstone of turbulent-boundary-layer research as many arguments depend critically on a precise knowledge of the skin friction ${\it\tau}_{w}^{\ast }$ . To our knowledge, all practitioners of oil-drop interferometry have so far used the leading-order similarity solution for asymptotically thin, wedge-shaped, two-dimensional oil films established by Tanner & Blows (J. Phys. E: Sci. Instrum., vol.9, 1976, pp.194-202) to relate the evolution of drop thickness to ${\it\tau}_{w}^{\ast }$ . It is generally believed that this procedure, if carefully implemented, yields the true time-averaged ${\it\tau}_{w}^{\ast }$ within $\pm 1\,\%$ or possibly better, but the systematic errors due to the finite thickness of the oil film have never been determined. They are analysed here for oil films with a thickness of the order of a viscous unit in a zero-pressure-gradient turbulent boundary layer. Neglecting spanwise surface curvature and surface tension effects, corrections due to the secondary air boundary layer above the oil film are derived with a linearised triple-layer approach that accounts for the turbulent shear-stress perturbation by means of modified van-Driest-type closure models. In addition, the correction due to processing oil drops with a slight streamwise surface curvature as if they were exact wedges is quantified. Both corrections are evaluated for oil-drop interferograms acquired in a zero-pressure-gradient turbulent boundary layer at a Reynolds number of around 3500, based on displacement thickness, and are shown to produce a reduction of the friction velocity relative to the basic Tanner and Blows theory of between $-0.1\,\%$ and $-1.5\,\%$ , depending on the mixing-length model. Despite the uncertainty about the true correction, the analysis allows the formulation of some guidelines on where and when to analyse interference fringes in order to minimise the error on the measured wall shear stres