Low-frequency wide band-gap elastic/acoustic meta-materials using the K-damping concept

The terms "acoustic/elastic meta-materials" describe a class of periodic structures with unit cells exhibiting local resonance. This localized resonant structure has been shown to result in negative effective stiffness and/or mass at frequency ranges close to these local resonances. As a result, these structures present unusual wave propagation properties at wavelengths well below the regime corresponding to band-gap generation based on spatial periodicity, (i.e. "Bragg scattering"). Therefore, acoustic/elastic meta-materials can lead to applications, especially suitable in the low-frequency range. However, low frequency range applications of such meta-materials require very heavy internal moving masses, as well as additional constraints at the amplitudes of the internally oscillating locally resonating structures, which may prohibit their practical implementation. In order to resolve this disadvantage, the K-Damping concept will be analyzed. According to this concept, the acoustic/elastic meta-materials are designed to include negative stiffness elements instead or in addition to the internally resonating added masses. This concept removes the need for the heavy locally added heavy masses, while it simultaneously exploits the negative stiffness damping phenomenon. Application of both Bloch's theory and the classical modal analysis at the one-dimensional mass-in-mass lattice is analyzed and corresponding dispersion relations are derived. The results indicate significant advantages over the conventional mass-in-a mass lattice, such as broader band-gaps and increased damping ratio and reveal significant potential in the proposed solution. Preliminary feasibility analysis for seismic meta-structures and low frequency acoustic isolation-damping confirm the strong potential and applicability of this concept.Comment: Keywords: Acoustic meta-materials, elastic meta-materials, low-frequency vibration absorption, seismic meta-structures, noise absorptio

ATRA mechanically reprograms pancreatic stellate cells to suppress matrix remodelling and inhibit cancer cell invasion

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive malignancy with a dismal survival rate. Persistent activation of pancreatic stellate cells (PSCs) can perturb the biomechanical homoeostasis of the tumour microenvironment to favour cancer cell invasion. Here we report that ATRA, an active metabolite of vitamin A, restores mechanical quiescence in PSCs via a mechanism involving a retinoic acid receptor beta (RAR-β)-dependent downregulation of actomyosin (MLC-2) contractility. We show that ATRA reduces the ability of PSCs to generate high traction forces and adapt to extracellular mechanical cues (mechanosensing), as well as suppresses force-mediated extracellular matrix remodelling to inhibit local cancer cell invasion in 3D organotypic models. Our findings implicate a RAR-β/MLC-2 pathway in peritumoural stromal remodelling and mechanosensory-driven activation of PSCs, and further suggest that mechanical reprogramming of PSCs with retinoic acid derivatives might be a viable alternative to stromal ablation strategies for the treatment of PDAC

Low-frequency wide band-gap elastic/acoustic metamaterials using the K-damping concept

The terms “acoustic/elastic meta-materials” describe a class of periodic structures with unit cells exhibiting local resonance. This localized resonant structure has been shown to result in negative effective stiffness and/or mass at frequency ranges close to these local resonances. As a result, these structures present unusual wave propagation properties at wavelengths well below the regime corresponding to band-gap generation based on spatial periodicity, (i.e. “Bragg scattering”). Therefore, acoustic/elastic meta-materials can lead to applications, especially suitable in the low-frequency range. However, low frequency range applications of such meta-materials require very heavy internal moving masses, as well as additional constraints at the amplitudes of the internally oscillating locally resonating structures, which may prohibit their practical implementation. In order to resolve this disadvantage, the KDamping concept will be analyzed. According to this concept, the acoustic/elastic meta-materials are designed to include negative stiffness elements instead or in addition to the internally resonating added masses. This concept removes the need for the heavy locally added heavy masses, while it simultaneously exploits the negative stiffness damping phenomenon. Application of both Bloch’s theory and the classical modal analysis at the one-dimensional mass-in-mass lattice is analyzed and corresponding dispersion relations are derived. The results indicate significant advantages over the conventional mass-in-a mass lattice, such as broader band-gaps and increased damping ratio and reveal significant potential in the proposed solution. Preliminary feasibility analysis for seismic meta-structures and low frequency acoustic isolation-damping confirm the strong potential and applicability of this concept

Syndecan-4 tunes cell mechanics by activating the kindlin-integrin-RhoA pathway

A mechanism of cell response to localized tension shows that syndecan-4 synergizes with EGFR to elicit a mechanosignalling cascade that leads to adaptive cell stiffening through PI3K/kindlin-2 mediated integrin activation. Extensive research over the past decades has identified integrins to be the primary transmembrane receptors that enable cells to respond to external mechanical cues. We reveal here a mechanism whereby syndecan-4 tunes cell mechanics in response to localized tension via a coordinated mechanochemical signalling response that involves activation of two other receptors: epidermal growth factor receptor and beta 1 integrin. Tension on syndecan-4 induces cell-wide activation of the kindlin-2/beta 1 integrin/RhoA axis in a PI3K-dependent manner. Furthermore, syndecan-4-mediated tension at the cell-extracellular matrix interface is required for yes-associated protein activation. Extracellular tension on syndecan-4 triggers a conformational change in the cytoplasmic domain, the variable region of which is indispensable for the mechanical adaptation to force, facilitating the assembly of a syndecan-4/alpha-actinin/F-actin molecular scaffold at the bead adhesion. This mechanotransduction pathway for syndecan-4 should have immediate implications for the broader field of mechanobiology.Peer reviewe

Detecting gravitational waves from precessing binaries of spinning compact objects: Adiabatic limit

Black-hole (BH) binaries with single-BH masses m=5--20 Msun, moving on quasicircular orbits, are among the most promising sources for first-generation ground-based gravitational-wave (GW) detectors. Until now, the development of data-analysis techniques to detect GWs from these sources has been focused mostly on nonspinning BHs. The data-analysis problem for the spinning case is complicated by the necessity to model the precession-induced modulations of the GW signal, and by the large number of parameters needed to characterize the system, including the initial directions of the spins, and the position and orientation of the binary with respect to the GW detector. In this paper we consider binaries of maximally spinning BHs, and we work in the adiabatic-inspiral regime to build families of modulated detection templates that (i) are functions of very few physical and phenomenological parameters, (ii) model remarkably well the dynamical and precessional effects on the GW signal, with fitting factors on average >~ 0.97, but (iii) might require increasing the detection thresholds, offsetting at least partially the gains in the fitting factors. Our detection-template families are quite promising also for the case of neutron-star--black-hole binaries, with fitting factors on average ~ 0.93. For these binaries we also suggest (but do not test) a further template family, which would produce essentially exact waveforms written directly in terms of the physical spin parameters.Comment: 38 pages, 16 figures, RevTeX4. Final PRD version. Lingering typos corrected. Small corrections to GW flux terms as per Blanchet et al., PRD 71, 129902(E)-129904(E) (2005

Bilateral giant femoropopliteal artery aneurysms: a case report

<p>Abstract</p> <p>Introduction</p> <p>Popliteal artery aneurysms are the most common peripheral arterial aneurysms, and are frequently bilateral. Acute limb ischemia, rupture and compression phenomena can complicate these aneurysms when the diameter exceeds 2 cm.</p> <p>Case Presentation</p> <p>We report an 82-year-old male patient with two giant femoropopliteal aneurysms, 10.5 and 8.5 cm diameters, managed in our institution. Both aneurysms were resected and a polytetrafluoroethylene (PTFE) femoropopliteal interposition graft was placed successfully. Management and literature review are discussed.</p> <p>Conclusion</p> <p>We believe this is the first report in the medical literature of bilateral giant femoropopliteal aneurysms.</p

African Americans, Gentrification, and Neoliberal Urbanization: the Case of Fort Greene, Brooklyn

This article examines the gentrification of Fort Greene, which is located in the western part of black Brooklyn, one of the largest contiguous black urban areas in the USA. Between the late 1960s and 2003, gentrification in Fort Greene followed the patterns discovered by scholars of black neighborhoods; the gentrifying agents were almost exclusively black and gentrification as a process was largely bottom-up because entities interested in the production of space were mostly not involved. Since 2003, this has changed. Whites have been moving to Fort Greene in large numbers and will soon represent the numerical majority. Public and private interventions in and around Fort Greene have created a new top-down version of gentrification, which is facilitating this white influx. Existing black residential and commercial tenants are replaced and displaced in the name of urban economic development

The Politics of Race and Class and the Changing Spatial Fortunes of the McCarren Pool in Brooklyn, New York, 1936-2010

This paper explores the changing spatial properties of the McCarren Pool and connects them to the politics of race and class. The pool was a large liberal government project that sought to improve the leisure time of working class Brooklynites and between 1936 and the early 1970s it was a quasi-public functional space. In the 1970s and the early 1980s, the pool became a quasi-public dysfunctional space because the city government reduced its maintenance and staffing levels. Working class whites of the area engaged into neighborhood defense in order to prevent the influx of Latinos and African Americans into parts of Williamsburg and Greenpoint and this included the environs of the McCarren Pool. The pool was shut down in 1983 because of a mechanical failure. Its restoration did not take place because residents and storekeepers near the vicinity of the pool complained that by the 1970s, it was only African Americans and Latinos who patronized the pool and that their presence in the neighborhood undermined white exclusivity. For two decades, the McCarren Pool became a multi-use alternative space frequented by homeless people, graffiti artists, heroin users, teenagers, and drug dealers. Unlike previous decades, during this period, people of various racial and ethnic backgrounds frequented the pool area in a relatively harmonious manner. In the early part of the twenty-first century, a neoliberal city administration allowed a corporation to organize music concerts in the pool premises and promised to restore the facility into an operable swimming pool. The problem with this restoration project is that the history of the pool between the early 1970s and the early 2000s is downplayed and this does not serve well former or future users of the poo