Platonic crystal with low-frequency locally resonant snail structures. Wave trapping, transmission amplification and shielding

We propose a new type of platonic crystal. The proposed microstructured plate includes snail resonators with low-frequency resonant vibrations. The particular dynamic effect of the resonators are highlighted by a comparative analysis of dispersion properties of homo- geneous and perforated plates. Analytical and numerical estimates of classes of standing waves are given and the analysis on a macrocell shows the possibility to obtain localization, wave trapping and edge waves. Applications include transmission amplification within two plates separated by a small ligament. Finally we proposed a design procedure to suppress low frequency flexural vibration in an elongated plate implementing a by-pass system re- routing waves within the mechanical system.Comment: 11 figures (20 files

Hierarchical auxetic and isotropic porous medium with extremely negative Poisson's ratio

We propose a novel two-dimensional hierarchical auxetic structure consisting of a porous medium in which a homogeneous matrix includes a rank-two set of cuts characterised by different scales. The six-fold symmetry of the perforations makes the medium isotropic in the plane. Remarkably, the mesoscale interaction between the first- and second-level cuts enables the attainment of a value of the Poisson’s ratio close to the minimum reachable limit of -1. The effective properties of the hierarchical auxetic structure are determined numerically, considering both a unit cell with periodic boundary conditions and a finite structure containing a large number of repeating cells. Further, results of the numerical study are validated experimentally on a polymeric specimen with appropriately arranged rank-two cuts, tested under uniaxial tension. We envisage that the proposed hierarchical design can be useful in numerous engineering applications exploiting an extreme auxetic effect

Hierarchical auxetic and isotropic porous medium with extremely negative Poisson's ratio

We propose a novel two-dimensional hierarchical auxetic structure consisting of a porous medium in which a homogeneous matrix includes a rank-two set of cuts characterised by different scales. The six-fold symmetry of the perforations makes the medium isotropic in the plane. Remarkably, the mesoscale interaction between the first- and second-level cuts enables the attainment of a value of the Poisson's ratio close to the minimum reachable limit of -1. The effective properties of the hierarchical auxetic structure are determined numerically, considering both a unit cell with periodic boundary conditions and a finite structure containing a large number of repeating cells. Further, results of the numerical study are validated experimentally on a polymeric specimen with appropriately arranged rank-two cuts, tested under uniaxial tension. We envisage that the proposed hierarchical design can be useful in numerous engineering applications exploiting an extreme auxetic effect

The Relationship between Serum Zinc Level and Liver Elastrography Using Fibroscan in Non-Alcoholic Fatty Liver Patients

BACKGROUND AND OBJECTIVE: Zinc is one of the essential elements for many vital functions of the body, including regulation of gene expression, anti-inflammatory and antioxidant activity, protein and nucleic acids metabolism. Since, many people develop advanced liver disease, including liver cirrhosis, they have zinc deficiency. The aim of this study was to investigate the relationship between liver stiffness and serum zinc levels in patients with non-alcoholic fatty liver disease. METHODS: This cross-sectional study was performed on 40 non-alcoholic fatty liver disease Patients referring to Imam Khomeini Hospital in Ahvaz in 1395. Serum zinc levels and liver Stiffness (based on METAVIR scale) were measured by fibroscan, and Age, sex, serum zinc level and liver fibroscan were recorded. Serum zinc level at different ages and scores of Liver stiffness was compared and analyzed. FINDINGS: This study was conducted on 40 patients with non-alcoholic fatty liver disease. The number of men was 26 patients (65%). Mean age of patients was 45.077±9.4 years, mean serum zinc level was 81.4±8.1 and mean liver stiffness was 6.5±2.1 kPa. Serum zinc level had a reverse and strong correlation with liver stiffness (p=0.0001, r=0.9). Also, with age increasing, liver stiffness increased (p=0.01, r=0.5) and serum zinc level decreased (p=0.01, r=0.5). CONCLUSION: According to findings of the present study, the serum zinc level significantly decreased with fibrosis progression in patients with non-alcoholic fatty liver

Hierarchical large-scale elastic metamaterials for passive seismic wave mitigation

Large scale elastic metamaterials have recently attracted increasing interest in the scientific community for their potential as passive isolation structures for seismic waves. In particular, so-called "seismic shields"have been proposed for the protection of large areas where other isolation strategies (e.g. dampers) are not workable solutions. In this work, we investigate the feasibility of an innovative design based on hierarchical design of the unit cell, i.e. a structure with a self-similar geometry repeated at different scales. Results show how the introduction of hierarchy allows the conception of unit cells exhibiting reduced size with respect to the wavelength while maintaining the same or improved isolation efficiency at frequencies of interest for earthquake engineering. This allows to move closer to the practical realization of such seismic shields, where low-frequency operation and acceptable size are both essential characteristics for feasibility

Electron Transfer from Cyt b559 and Tyrosine-D to the S2 and S3 states of the water oxidizing complex in Photosystem II at Cryogenic Temperatures

The Mn4CaO5 cluster of photosystem II (PSII) catalyzes the oxidation of water to molecular oxygen through the light-driven redox S-cycle. The water oxidizing complex (WOC) forms a triad with Tyrosine(Z) and P-680, which mediates electrons from water towards the acceptor side of PSII. Under certain conditions two other redox-active components, Tyrosine(D) (Y-D) and Cytochrome b (559) (Cyt b (559)) can also interact with the S-states. In the present work we investigate the electron transfer from Cyt b (559) and Y-D to the S-2 and S-3 states at 195 K. First, Y-D (aEuro cent) and Cyt b (559) were chemically reduced. The S-2 and S-3 states were then achieved by application of one or two laser flashes, respectively, on samples stabilized in the S-1 state. EPR signals of the WOC (the S-2-state multiline signal, ML-S-2), Y-D (aEuro cent) and oxidized Cyt b (559) were simultaneously detected during a prolonged dark incubation at 195 K. During 163 days of incubation a large fraction of the S-2 population decayed to S-1 in the S-2 samples by following a single exponential decay. Differently, S-3 samples showed an initial increase in the ML-S-2 intensity (due to S-3 to S-2 conversion) and a subsequent slow decay due to S-2 to S-1 conversion. In both cases, only a minor oxidation of Y-D was observed. In contrast, the signal intensity of the oxidized Cyt b (559) showed a two-fold increase in both the S-2 and S-3 samples. The electron donation from Cyt b (559) was much more efficient to the S-2 state than to the S-3 state

Perfectly matched layers for flexural waves: An exact analytical model

In this paper we present an analytical model of Perfectly Matched Layers for flexural waves within elongated beam structures. The model is based on transformation optics techniques and it is shown to work both in time harmonic and transient regimes. A comparison between flexural and longitudinal waves is detailed and it is shown that the bending problem requires special interface conditions. A connection with transformation of eigenfrequencies and eigenmodes is given and the effect of the additional boundary conditions introduced at the border of the Perfectly Matched Layer domain is discussed in detailed. Such a model is particularly useful for Finite Element analyses pertaining propagating flexural waves in infinite domain

Invariance of eigenfrequencies under geometric transformation in plate structures

Geometric transformation is applied here to the problem of flexural waves in thin plates. Differently from problems governed by the Helmholtz equation, the equation of motion does not retain its form. A physical interpretation is given which involves a non homogenous anisotropic plate with axial stresses. Boundary conditions are not satisfied anymore after transformation, but some possible constraints can be applied on the transformation law in order to cancel differences at the boundary of the transformed domain. As a comparison tool, we propose the eigenfrequency analysis of rectangular plates and we show the correctness of the proposed approach for different transformations and boundary conditions

Enhancement of Y-D(center dot) spin relaxation by the CaMn4 cluster in photosystem II detected at room temperature: A new probe for the S-cycle

The long-lived, light-induced radical Y-D(.) of the Tyr161 residue in the D2 protein of Photosystem 11 (PSII) is known to magnetically interact with the CaMn4 cluster, situated similar to 30 angstrom away. In this study we report a transient step-change increase in YD EPR intensity upon the application of a single laser flash to S, state-synchronised PSII-enriched membranes from spinach. This transient effect was observed at room temperature and high applied microwave power (100 mW) in samples containing PpBQ, as well as those containing DCMU. The subsequent decay lifetimes were found to differ depending on the additive used. We propose that this flash-induced signal increase was caused by enhanced spin relaxation of YD by the OEC in the S-2 state, as a consequence of the single laser flash turnover. The post-flash decay reflected S-2 -> S-1 back-turnover, as confirmed by their correlations with independent measurements of S-2 multiline EPR signal and flash-induced variable fluorescence decay kinetics under corresponding experimental conditions. This flash-induced effect opens up the possibility to study the kinetic behaviour of S-state transitions at room temperature using YD as a probe. (c) 2006 Elsevier B.Z. All rights reserved