121 research outputs found
Gravitational waves from oscillations of compact stars: what can we learn from current observations?
No full textOscillating compact stars are promising sources of gravitational radiation. Upper limits on gravitational-wave (GW) burst emission associated with a Vela timing glitch and in coincidence with electromagnetic triggers from magnetars were set recently by the LIGO and Virgo Collaborations. Those searches targeted f-modes of neutron stars with standard equations of state. Indeed, the f-modes are believed to be the principal GW emitters of conventional neutron stars; their high frequencies, though, imply that we would be able to detect only very energetic nearby events. Exotic equations of state, on the other hand, which predict elastic quark matter cores, may be much more interesting. LIGO and Virgo continuous-wave searches are already able to put constraints on the physics of such objects by comparing theoretical models with data analysis (DA) results. In this presentation, we consider this scenario from the GW burst (and not the continuous-wave) point of view. We review the properties of oscillation modes of exotic compact stars with elastic cores. We make estimates on the GW energy output after a corequake and we discuss if/how we can use the latest burst DA results to extract information about the deep interiors of compact stars and/or the underlying physical mechanisms producing glitches and/or flares
Development of a nanoporous and multilayer drug-delivery platform for medical implants
No full textVarvara Karagkiozaki,1 Eleftherios Vavoulidis,1 Panagiotis G Karagiannidis,1 Maria Gioti,1 Dimitrios G Fatouros,2 Ioannis S Vizirianakis,3 Stergios Logothetidis11Lab for Thin Films–Nanosystems and Nanometrology, Physics Department, 2Department of Pharmaceutical Technology, 3Laboratory of Pharmacology, School of Pharmacy, Aristotle University of Thessaloniki, GreeceAbstract: Biodegradable polymers can be applied to a variety of implants for controlled and local drug delivery. The aim of this study is to develop a biodegradable and nanoporous polymeric platform for a wide spectrum of drug-eluting implants with special focus on stent-coating applications. It was synthesized by poly(DL-lactide-co-glycolide) (PLGA 65:35, PLGA 75:25) and polycaprolactone (PCL) in a multilayer configuration by means of a spin-coating technique. The antiplatelet drug dipyridamole was loaded into the surface nanopores of the platform. Surface characterization was made by atomic force microscopy (AFM) and spectroscopic ellipsometry (SE). Platelet adhesion and drug-release kinetic studies were then carried out. The study revealed that the multilayer films are highly nanoporous, whereas the single layers of PLGA are atomically smooth and spherulites are formed in PCL. Their nanoporosity (pore diameter, depth, density, surface roughness) can be tailored by tuning the growth parameters (eg, spinning speed, polymer concentration), essential for drug-delivery performance. The origin of pore formation may be attributed to the phase separation of polymer blends via the spinodal decomposition mechanism. SE studies revealed the structural characteristics, film thickness, and optical properties even of the single layers in the triple-layer construct, providing substantial information for drug loading and complement AFM findings. Platelet adhesion studies showed that the dipyridamole-loaded coatings inhibit platelet aggregation that is a prerequisite for clotting. Finally, the films exhibited sustained release profiles of dipyridamole over 70 days. These results indicate that the current multilayer phase therapeutic approach constitutes an effective drug-delivery platform for drug-eluting implants and especially for cardiovascular stent applications.Keywords: drug delivery, implants, stents, polymers, spin-coating, atomic force microscop
Torsional oscillations of slowly rotating relativistic stars
No full textWe study the effects of rotation on the torsional modes of oscillating relativistic stars with a solid crust. Earlier works in Newtonian theory provided estimates of the rotational corrections for the torsional modes and suggested that they should become Chandrasekhar–Friedman–Schutz unstable, even for quite low rotation rates. In this work, we study the effect of rotation in the context of general relativity using elasticity theory and in the slow-rotation approximation. We find that the Newtonian picture does not change considerably. The inclusion of relativistic effects leads only to quantitative corrections. The degeneracy of modes for different values of m is removed, and modes with ℓ = m are shifted towards zero frequencies and become secularly unstable at stellar rotational frequencies ~20–30 Hz
Erratum: All-sky search for gravitational-wave bursts in the first joint LIGO-GEO-Virgo run (Physical Review D - Particles, Fields, Gravitation and Cosmology (2010) 81 (102001))
No full textThis paper was published online on 5 May 2010 with an omission in the Collaboration author list. S. Dwyer has been
added as of 12 April 2012. The Collaboration author list is incorrect in the printed version of the journal
Erratum: Search for gravitational waves from compact binary coalescence in LIGO and Virgo data from S5 and VSR1 (Physical Review D - Particles, Fields, Gravitation and Cosmology)
No full textThis paper was published online on 5 November 2010 with an omission in the Collaboration author list. S. Dwyer has
been added as of 12 April 2012. The Collaboration author list is incorrect in the printed version of the journal
Development of a nanoporous and multilayer drug-delivery platform for medical implants
No full textBiodegradable polymers can be applied to a variety of implants for controlled and local drug delivery. The aim of this study is to develop a biodegradable and nanoporous polymeric platform for a wide spectrum of drug-eluting implants with special focus on stent-coating applications. It was synthesized by poly(DL-lactide-co-glycolide) (PLGA 65:35, PLGA 75:25) and polycaprolactone (PCL) in a multilayer configuration by means of a spin-coating technique. The antiplatelet drug dipyridamole was loaded into the surface nanopores of the platform. Surface characterization was made by atomic force microscopy (AFM) and spectroscopic ellipsometry (SE). Platelet adhesion and drug-release kinetic studies were then carried out. The study revealed that the multilayer films are highly nanoporous, whereas the single layers of PLGA are atomically smooth and spherulites are formed in PCL. Their nanoporosity (pore diameter, depth, density, surface roughness) can be tailored by tuning the growth parameters (eg, spinning speed, polymer concentration), essential for drug-delivery performance. The origin of pore formation may be attributed to the phase separation of polymer blends via the spinodal decomposition mechanism. SE studies revealed the structural characteristics, film thickness, and optical properties even of the single layers in the triple-layer construct, providing substantial information for drug loading and complement AFM findings. Platelet adhesion studies showed that the dipyridamole-loaded coatings inhibit platelet aggregation that is a prerequisite for clotting. Finally, the films exhibited sustained release profiles of dipyridamole over 70 days. These results indicate that the current multilayer phase therapeutic approach constitutes an effective drug-delivery platform for drug-eluting implants and especially for cardiovascular stent applications
Publisher's Note: Search for gravitational waves from binary black hole inspiral, merger, and ringdown
No full textThis paper was published online on 6 June 2011 with an omission in the Collaboration author list. S. Dwyer has been
added as of 12 April 2012. The Collaboration author list is incorrect in the printed version of the journal
Limitations of the time slide method of background estimation
No full textInternational audienceTime shifting the output of gravitational wave detectors operating in coincidence is a convenient way of estimating the background in a search for short-duration signals. In this paper, we show how non-stationary data affect the background estimation precision. We present a method of measuring the fluctuations of the data and computing its effects on a coincident search. In particular, we show that for fluctuations of moderate amplitude, time slides larger than the fluctuation time scales can be used. We also recall how the false alarm variance saturates with the number of time shifts
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