75 research outputs found
Experimental and numerical investigation of the effects of porosity on the in-plane shear properties of CFRPs using the V-notched rail shear test method
No full textVoids occurred after the manufacturing process are a common defect of composite materials. They appear to have a negative impact on the matrix-dominated material properties, the gravity of which depends upon the porosity content, the shape and the volume of pores. In the present work, the effects of porosity on the shear mechanical properties of unidirectional carbon fiber-reinforced plastic composites are evaluated via mechanical testing and numerical simulation. In this framework, the V-Notched Rail Shear test method is applied on carbon fiber reinforced plastic specimens of four porosity levels. Moreover, two finite element methodologies are utilized for simulating this particular mechanical test namely the progressive damage model (PDM) and the Virtual Crack Closing Technique (VCCT). Double cantilever beam (mode I) and end notched flexure tests (mode II) are also conducted for the development of the VCCT model. The results from the shear mechanical tests reveal a considerable drop in both the elastic properties and strength. In addition to that, for larger porosity contents, more cracks are present and crack initiation and propagation occur at a faster pace. Finally, the advantages and disadvantages of the two numerical methods are presented and assessed revealing a satisfying consistency with the results obtained by the mechanical tests
Evaluation of porosity effects on the mechanical properties of carbon fiber-reinforced plastic unidirectional laminates by X-ray computed tomography and mechanical testing
No full textThe effects of porosity on the matrix-dominated mechanical properties of unidirectional carbon fiber-reinforced plastic composites were evaluated using X-ray computed tomography and mechanical testing. Carbon fiber-reinforced plastic plates of four porosity levels were manufactured by implementing different curing cycles. Porosity was detected by X-ray computed tomography tests, conducted on samples taken from the plates, and quantified by analyzing the computed tomography scans using the VGStudio Max software. Four different types of mechanical tests were conducted; namely, transverse tension, V-notched rail shear, three-point bending, and short-beam shear tests. The porosity analysis showed that with increasing the porosity volume fraction, the number of pores decreases, their volume increases while their shape changes from spherical or ellipsoidal to a needle-shape. The results from mechanical tests reveal that the presence of pores reduces all matrix-dominated material properties of the UniDirectional (UD) carbon fiber-reinforced plastic material. The reduction in strength is greater than the reduction in the elastic properties. Moreover, the reduction in the in-plane shear and interlaminar properties is greater than the tensile properties of the UD carbon fiber-reinforced plastic material. Between porosity contents of similar volume fraction, the one with the few large pores proved more severe than the one with the many small pores. The large standard deviation observed for some of the tests is attributed to the non-uniform dispersion of pores
Does the extracorporeal circulation worsen anemia in hemodialysis patients? Investigation with advanced microscopes of red blood cells drawn at the beginning and end of dialysis
No full textDimosthenis Stamopoulos,1 Nerantzoula Bakirtzi,2,3 Efthymios Manios,1 Eirini Grapsa41Institute of Advanced Materials, Physicochemical Processes, Nanotechnology and Microsystems, National Center for Scientific Research 'Demokritos,' Athens, Greece; 2Department of Nephrology, Hospital 'G. Gennimatas,' Athens, Greece; 3Renal Unit, Hospital 'Alexandra,' Athens, Greece; 4Renal Unit, Hospital 'Aretaieion,' Athens, GreeceBackground: In hemodialysis (HD) patients, anemia relates to three main factors: insufficient production of erythropoietin; impaired management of iron; and decreased lifespan of red blood cells (RBCs). The third factor can relate to structural deterioration of RBCs due to extrinsic (extracorporeal circuit; biochemical activation and/or mechanical stress during dialysis) and intrinsic (uremic milieu; biochemical interference of the RBC membrane constituents with toxins) mechanisms. Herein, we evaluate information accessed with advanced imaging techniques at the cellular level.Methods: Atomic force and scanning electron microscopes were employed to survey intact RBCs (iRBCs) of seven HD patients in comparison to seven healthy donors. The extrinsic factor was investigated by contrasting pre- and post-HD samples. The intrinsic environment was investigated by comparing the microscopy data with the clinical ones.Results: The iRBC membranes of the enrolled HD patients were overpopulated with orifice-like (high incidence; typical size within 100–1,000 nm) and crevice-like (low incidence; typical size within 500–4,000 nm) defects that exhibited a statistically significant (P < 0.05) relative increase (+55% and +350%, respectively) in respect to healthy donors. The relative variation of the orifice and crevice indices (mean population of orifices and crevices per top membrane surface) between pre- and post-HD was not statistically significant (−3.3% and +4.5%, respectively). The orifice index correlates with the concentrations of urea, calcium, and phosphorus, but not, however, with that of creatinine.Conclusion: Extracorporeal circulation is not detrimental to the structural integrity of RBC membranes. Uremic milieu is a candidate cause of RBC membrane deterioration, which possibly worsens anemia.Keywords: hemodialysis, anemia, red blood cells, atomic force microscopy, scanning electron microscop
Universal Expressions for the Polarization and the Depolarization Factor in Homogeneous Dielectric and Magnetic Spheres Subjected to an External Field of Any Form
No full textSpherical structures of dielectric and magnetic materials are studied intensively in basic research and employed widely in applications. The polarization, (Figure presented.) (P for dielectric and M for magnetic materials), is the parent physical vector of all relevant entities (e.g., moment, (Figure presented.), and force, F), which determine the signals recorded by an experimental setup or diagnostic equipment and configure the motion in real space. Here, we use classical electromagnetism to study the polarization, (Figure presented.), of spherical structures of linear and isotropic—however, not necessarily homogeneous—materials subjected to an external vector field, (Figure presented.) (Eext for dielectric and Hext for magnetic materials), dc (static), or even ac of low frequency (quasistatic limit). We tackle an integro-differential equation on the polarization, (Figure presented.), able to provide closed-form solutions, determined solely from (Figure presented.), on the basis of spherical harmonics, (Formula presented.). These generic equations can be used to calculate analytically the polarization, (Figure presented.), directly from an external field, (Figure presented.), of any form. The proof of concept is studied in homogeneous dielectric and magnetic spheres. Indeed, the polarization, (Figure presented.), can be obtained by universal expressions, directly applicable for any form of the external field, (Figure presented.). Notably, we obtain the relation between the extrinsic, (Figure presented.), and intrinsic, (Figure presented.), susceptibilities ((Formula presented.) and (Formula presented.) for dielectric and (Formula presented.) and (Formula presented.) for magnetic materials) and clarify the nature of the depolarization factor, (Figure presented.), which depends on the degree l—however, not on the order m of the mode (Formula presented.) of the applied (Figure presented.). Our universal approach can be useful to understand the physics and to facilitate applications of such spherical structures. © 2025 by the author
Electromagnetism in Linear, Homogeneous and Isotropic Materials: The Analogy Between Electricity and Magnetism in the Susceptibility and Polarization
No full textThrough the years, the asymmetry in the constitutive relations that define the electric and magnetic polarization, P and M, respectively, by the relevant vector field, E and H, has been imprinted, rather arbitrarily, in Maxwell’s equations. Accordingly, in linear, homogeneous, and isotropic (LHI) materials, the electric and magnetic polarization are defined via P = χeε0E (‘P-E, χe’ formulation; 0 ≤ χe < ∞) and M = χmH (‘M-H, χm’ formulation; −1 ≤ χm < ∞), respectively. Recently, the constitutive relation of the polarization was revisited in LHI dielectrics by introducing an electric susceptibility, χε, which couples linearly the reverse polarization, P~ = −P, with the electric displacement D through P~ = χεD (‘P-D, χε’ formulation; −1 ≤ χε ≤ 0). Here, the ‘P-D, χε’ formulation is generalized for the time-dependent case. It is documented that the susceptibility and polarization of LHI dielectric and magnetic materials can be described by the ‘P-D, χε’ and ‘M-H, χm’ formulation, respectively, on a common basis. To this end, the depolarizing effect is taken into account, which unavoidably emerges in realistic specimens of limited size, by introducing a series scheme to describe the evolution of polarization and calculate the extrinsic susceptibility. The engagement of the depolarizing factor N (0 ≤ N≤ 1) with the accompanying convergence conditions dictates that the intrinsic susceptibility of LHI materials, whether electric or magnetic, should range within [−1, 1]. The ‘P-D, χε’ and ‘M-H, χm’ formulations conform with this expectation, while the ‘P-E, χe’ does not. Remarkably, Maxwell’s equations are unaltered by the ‘P-D, χε’ formulation. Thus, all time-dependent processes of electromagnetism described by the standard ‘P-E, χe’ approach, are reproduced equivalently, or even advantageously, by the alternative ‘P-D, χε’ formulation
Electrostatics in Materials Revisited: The Case of Free Charges Combined with Linear, Homogeneous, and Isotropic Dielectrics
No full textHere we revisit the electrostatics of material systems comprising of free charges and linear, homogeneous, and isotropic (LHI) dielectrics. We focus on D(r) suggesting that this is the primary vector field of electrostatics. We show that D(r) is sufficient to conceptually describe all underlying physics and to mathematically accomplish all necessary calculations, beforehand, independently of the secondary vector fields P(r) and E(r) that, if needed, can be easily calculated from D(r). To this effect, we introduce a P-D electric susceptibility, χε, with −1≤χε≤0, that couples linearly P(r) with D(r) (instead of the standard P-E electric susceptibility, χe, with 0≤χe<∞, that couples linearly P(r) with E(r)). This concept restores the somehow misleading causality/feedback between P(r) and E(r) of the standard formulation, captures efficiently the underlying physics, enables electrostatics to obtain a form analogous to that of magnetostatics, and facilitates analytical/computational calculations in relevant systems. To document these claims, we provide technical means, among others, the free scalar potential, Ufr, and clarify the conditions that enable the calculation of D(r) on a standalone basis, directly from the free charge density, ρf, and the electric susceptibility, χε, of the LHI dielectrics. Our concept sets interesting perspectives for the treatment of all dielectrics
Influence of the Tegument of Phaseolus Vulgaris Seeds and of Larval Density on the Development of Acanthoscelides Obtectus Say
No full textImmunocompatibility of a new dual modality contrast agent based on radiolabeled iron-oxide nanoparticles
No full textRadiolabeled magnetic nanoparticles are promising candidates as dual-modality-contrast-agents (DMCA) for diagnostic applications. The immunocompatibility of a new DMCA is a prerequisite for subsequent in vivo applications. Here, a new DMCA, namely Fe3O4 nanoparticles radiolabeled with 68Ga, is subjected to immunocompatibility tests both in vitro and in vivo. The in vitro immunocompatibility of the DMCA relied on incubation with donated human WBCs and PLTs (five healthy individuals). Optical microscopy (OM) and atomic force microscopy (AFM) were employed for the investigation of the morphological characteristics of WBCs and PLTs. A standard hematology analyzer (HA) provided information on complete blood count. The in vivo immunocompatibility of the DMCA was assessed through its biodistribution among the basic organs of the mononuclear phagocyte system in normal and immunodeficient mice (nine in each group). In addition, Magnetic Resonance Imaging (MRI) data were acquired in normal mice (three). The combined OM, AFM and HA in vitro data showed that although the DMCA promoted noticeable activation of WBCs and PLTs, neither degradation nor clustering were observed. The in vivo data showed no difference of the DMCA biodistribution between the normal and immunodeficient mice, while the MRI data prove the efficacy of the particular DMCA when compared to the non-radiolabeled, parent CA. The combined in vitro and in vivo data prove that the particular DMCA is a promising candidate for future in vivo applications. © 2021, The Author(s)
Control of superconductivity by means of electric-field-induced strain in superconductor/piezoelectric hybrids
No full textThe controlled modification of superconductivity by any means, specifically in hybrid systems, has attracted much interest in the recent decades. Here, we present experimental data and phenomenological modeling on the control of TC of superconducting (SC) Nb thin films, with thickness 3 nm ≤ dNb≤50 nm, under the application of in-plane strain, S(Eex) induced by an external out-of-plane electric field, Eex to piezoelectric (PE) single crystals, namely, (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT), with x = 0.27 and 0.31. We report experimental modification of TC of Nb by Eex, accurately described by a phenomenological model that incorporates the constitutive relation S(Eex) of PMN-xPT. The systematic experimental-phenomenological modeling approach introduced here is generic and paves the way for an understanding of the underlying physical mechanisms in any SC/PE hybrid. © 2018 Author(s)
Pronounced and reversible modulation of the piezoelectric coefficients by a low magnetic field in a magnetoelectric PZT-5%Fe 3 O 4 system
No full textComposite magnetoelectric compounds that combine ferroelectricity/piezoelectricity and ferromagnetism/magnetostriction are investigated intensively for room-temperature applications. Here, we studied bulk composites of a magnetostrictive constituent, ferromagnetic Fe 3 O 4 nanoparticles, homogeneously embedded in a ferroelectric/piezoelectric matrix, Pb(Zr 0.52 Ti 0.48 )O 3 (PZT). Specifically, we focused on PZT-5%Fe 3 O 4 samples which are strongly insulating and thus sustain a relatively high out-of-plane external electric field, E ex,z . The in-plane strain-electric field curve (S(E ex,z )) was carefully recorded upon successive application and removal of an out-of-plane external magnetic field, H ex,z . The obtained S(E ex,z ) data exhibited two main features. First, the respective in-plane piezoelectric coefficients, d(E ex,z ) = 200–250 pm/V, show a dramatic decrease, 50–60%, upon application of a relatively low H ex,z = 1 kOe. Second, the process is completely reversible since the initial value of d(E ex,z ) is recovered upon removal of H ex,z . Polarization data, P(E ex,z ), evidenced that the Fe 3 O 4 nanoparticles introduced static structural disorder that made PZT harder. Taken together, these results prove that the Fe 3 O 4 nanoparticles, except for static structural disorder, introduce reconfigurable magnetic disorder that modifies the in-plane S(E ex,z ) curve and the accompanying d(E ex,z ) of PZT when an external magnetic field is applied at will. The room-temperature feasibility of these findings renders the PZT-x%Fe 3 O 4 system a solid basis for the development of magnetic-field-controlled PE devices. © 2019, The Author(s)
- …
