Momentum of an electromagnetic wave in dielectric media

Almost a hundred years ago, two different expressions were proposed for the energy--momentum tensor of an electromagnetic wave in a dielectric. Minkowski's tensor predicted an increase in the linear momentum of the wave on entering a dielectric medium, whereas Abraham's tensor predicted its decrease. Theoretical arguments were advanced in favour of both sides, and experiments proved incapable of distinguishing between the two. Yet more forms were proposed, each with their advocates who considered the form that they were proposing to be the one true tensor. This paper reviews the debate and its eventual conclusion: that no electromagnetic wave energy--momentum tensor is complete on its own. When the appropriate accompanying energy--momentum tensor for the material medium is also considered, experimental predictions of all the various proposed tensors will always be the same, and the preferred form is therefore effectively a matter of personal choice.Comment: 23 pages, 3 figures, RevTeX 4. Removed erroneous factor of mu/mu_0 from Eq.(44

A Mouse Model of Post-Arthroplasty Staphylococcus aureus Joint Infection to Evaluate In Vivo the Efficacy of Antimicrobial Implant Coatings

Post-arthroplasty infections represent a devastating complication of total joint replacement surgery, resulting in multiple reoperations, prolonged antibiotic use, extended disability and worse clinical outcomes. As the number of arthroplasties in the U.S. will exceed 3.8 million surgeries per year by 2030, the number of post-arthroplasty infections is projected to increase to over 266,000 infections annually. The treatment of these infections will exhaust healthcare resources and dramatically increase medical costs.To evaluate novel preventative therapeutic strategies against post-arthroplasty infections, a mouse model was developed in which a bioluminescent Staphylococcus aureus strain was inoculated into a knee joint containing an orthopaedic implant and advanced in vivo imaging was used to measure the bacterial burden in real-time. Mice inoculated with 5x10(3) and 5x10(4) CFUs developed increased bacterial counts with marked swelling of the affected leg, consistent with an acute joint infection. In contrast, mice inoculated with 5x10(2) CFUs developed a low-grade infection, resembling a more chronic infection. Ex vivo bacterial counts highly correlated with in vivo bioluminescence signals and EGFP-neutrophil fluorescence of LysEGFP mice was used to measure the infection-induced inflammation. Furthermore, biofilm formation on the implants was visualized at 7 and 14 postoperative days by variable-pressure scanning electron microscopy (VP-SEM). Using this model, a minocycline/rifampin-impregnated bioresorbable polymer implant coating was effective in reducing the infection, decreasing inflammation and preventing biofilm formation.Taken together, this mouse model may represent an alternative pre-clinical screening tool to evaluate novel in vivo therapeutic strategies before studies in larger animals and in human subjects. Furthermore, the antibiotic-polymer implant coating evaluated in this study was clinically effective, suggesting the potential for this strategy as a therapeutic intervention to combat post-arthroplasty infections

Interaction Between Convection and Pulsation

This article reviews our current understanding of modelling convection dynamics in stars. Several semi-analytical time-dependent convection models have been proposed for pulsating one-dimensional stellar structures with different formulations for how the convective turbulent velocity field couples with the global stellar oscillations. In this review we put emphasis on two, widely used, time-dependent convection formulations for estimating pulsation properties in one-dimensional stellar models. Applications to pulsating stars are presented with results for oscillation properties, such as the effects of convection dynamics on the oscillation frequencies, or the stability of pulsation modes, in classical pulsators and in stars supporting solar-type oscillations.Comment: Invited review article for Living Reviews in Solar Physics. 88 pages, 14 figure

Asteroseismology and Interferometry

Asteroseismology provides us with a unique opportunity to improve our understanding of stellar structure and evolution. Recent developments, including the first systematic studies of solar-like pulsators, have boosted the impact of this field of research within Astrophysics and have led to a significant increase in the size of the research community. In the present paper we start by reviewing the basic observational and theoretical properties of classical and solar-like pulsators and present results from some of the most recent and outstanding studies of these stars. We centre our review on those classes of pulsators for which interferometric studies are expected to provide a significant input. We discuss current limitations to asteroseismic studies, including difficulties in mode identification and in the accurate determination of global parameters of pulsating stars, and, after a brief review of those aspects of interferometry that are most relevant in this context, anticipate how interferometric observations may contribute to overcome these limitations. Moreover, we present results of recent pilot studies of pulsating stars involving both asteroseismic and interferometric constraints and look into the future, summarizing ongoing efforts concerning the development of future instruments and satellite missions which are expected to have an impact in this field of research.Comment: Version as published in The Astronomy and Astrophysics Review, Volume 14, Issue 3-4, pp. 217-36

Axial deformity correction in children via distraction osteogenesis

We performed a retrospective analysis of the results of 62 tibial and 54 femoral lengthenings in 88 consecutive patients. The patients mean age was 13.5 years and mean follow-up was four years. There was a significant difference between metaphyseal (27±1.2 days/cm) and diaphyseal (39.4±1.7 days/cm), tibial (34±1.7 days/cm) and femoral (31±1.4 days/cm) lengthening (P<0.05), but no significant difference among the lengthening indexes when treating one-, two-, or three-dimensional deformities, congenital (34±2.4 days/cm) and acquired (32±1.0 days/cm) limb length discrepancy (LLD) (P>0.05). The lengthening index was 33±1.1 days/cm, distraction regenerate length 6±0.4 cm, and lengthening percentage 21±2.1. The scatter plots of new regenerate length against time and the scatter plots of neurological complication, residual deformities, broken pins, joint contractures, and hypertension rate against lengthening percentage showed a positive linear relationship (r=0.8). We found the correlations between quantitative and qualitative parameters that should help to predict the treatment outcomes. Lengthening index depends on the amount of length gained. Higher length of new bone regenerate leads to a decrease in lengthening index. Expected gain in bone length can aid in estimating the duration of treatment. The lengthening percentage correlates very well with the complication rate and can be used to predict the complication rate

Covalently attached vancomycin provides a nanoscale antibacterial surface

Despite improved strategies for treating periprosthetic infection, current antibiotic delivery approaches are imperfect and can result in bacterial resistance and recalcitrant bio-films. To address the issues, we developed a covalently linked vancomycin-titanium implant interface that prevents and possibly eliminates bacterial colonization. We determined the amount of vancomycin immobilized on the titanium surface and assessed vancomycin stability and activity over time. When incubated with Staphylococcus aureus, the vancomycin-titanium surface showed an almost complete absence of adherent bacteria. To determine if continual exposure to vancomycin-titanium would cause decreased susceptibility to the antibiotic, S. aureus was incubated with vancomycin-titanium for 1 week or 4 weeks; these bacteria did not show an increased minimum inhibitory concentration for vancomycin. We tested the long-term stability of the vancomycin-titanium surface by incubation in phosphate-buffered saline for 11 months and then challenging the surface with S. aureus. Fluorescent staining for bacteria indicated the vancomycin-titanium retained its bactericidal activity. Finally, osteoblasts seeded on the vancomycin-titanium surface exhibited no change in viability, indicating the surface supports bone cell adhesion. Based on these observations, covalent modification of the titanium surface with an antibiotic may be viewed as a potential new tool in preventing or eliminating periprosthetic infection. © 2007 Lippincott Williams & Wilkins, Inc

In vitro and in vivo bactericidal effect of sol-gel/antibiotic thin films on fixation devices

Beneficial properties of room temperature processed silica sol-gels as resorbable and biocompatible materials for the controlled release of drugs and macromolecules have been described before. Recently, it was shown that a thin sol-gel film can be used for the controlled delivery of antibiotics such as vancomycin. It was also demonstrated that the release and degradation properties of the sol-gel films can be tailored via processing parameters. In this work, we evaluated the in vitro and in vivo bactericidal effects of vancomycin-containing thin sol-gel films applied on Ti-alloy intramedullary nails. Both the in vitro and the in vivo results demonstrate a pronounced bactericidal effect of the sol-gel/antibiotic films. This study suggests that thin antibiotic-containing sol-gel film holds great promise for the prevention and treatment of bone infections

Controlled release of vancomycin from thin sol-gel films on implant surfaces successfully controls osteomyelitis

Peri-prosthetic infection remains a serious complication of joint replacement surgery. Herein, we demonstrate that a vancomycin-containing sol-gelfilm on Ti alloy rods can successfully treat bacterial infections in an animal model. The vancomycin-containing sol-gel films exhibited predictable release kinetics, while significantly inhibiting S. aureus adhesion. When evaluated in a rat osteomyelitis model, microbiological analysis indicated that the vancomycin-containing sol-gel film caused a profound decrease in S. aureus number. Radiologically, while the control side showed extensive bone degradation, including abscesses and an extensive periosteal reaction, rods coated with the vancomycin-containing sol-gel film resulted in minimal signs of infection. mCT analysis confirmed the radiological results, while demonstrating that the vancomycin-containing sol-gel film significantly protected dense bone from resorption and minimized remodeling. These results clearly demonstrate that this novel thin sol-gel technology can be used for the targeted delivery of antibiotics for the treatment of periprosthetic as well as other bone infections. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc

Vancomycin covalently bonded to titanium alloy prevents bacterial colonization

Periprosthetic infection is a devastating consequence of implant insertion and can arise from hematogenous sources or surgical contamination. Microbes can preferentially colonize the implant surface and, by forming a biofilm, escape immune surveillance. We hypothesized that if an antibiotic can be tethered to a titanium alloy (Ti) surface, it will inhibit bacterial colonization, prevent biofilm formation, and avert late-stage infection. To test this hypothesis, a Ti rod was covalently derivatized with vancomycin. Reaction efficiencies were evaluated by colorimetric and spectrophotometric measurements. The vancomycin-modified surface was stable in aqueous solutions over extended time periods and maintained antibiotic coverage, even after press-fit insertion into a cadaverous rat femora. When evaluated using fluorescently labeled bacteria, or by direct colony counts, the surface-bound antibiotic prevented bacterial colonization in vitro after: (1) exposure to high levels of S. aureus; (2) extended incubation in physiological buffers; and (3) repeated bacterial challenges. Importantly, whereas the vancomycin-derivitized pins prevented bacterial colonization, S. aureus adhered to control pins, even in the presence of concentrations of vancomycin that exceeded the strain MIC. These results demonstrate that we have effectively engineered a stable, bactericidal Ti surface. This surface holds great promise in terms of mitigating or preventing periprosthetic infection. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc