143 research outputs found
Stress-Crack Separation Relationship for Macrosynthetic, Steel and Hybrid Fiber Reinforced Concrete
An experimental evaluation of the crack propaga
tion and post-cracking response of macro
fiber reinforced concrete in flexure is c
onducted. Two types of structur
al fibers, hooked end
steel fibers and continuousl
y embossed macro-synthetic fibers are used in this study. A fiber
blend of the two fibers is evaluated for spec
ific improvements in the post peak residual load
carrying response. At 0.5% volume fraction, both
steel and macrosynthetic fiber reinforced
concrete exhibits load recovery at large
crack opening. The blend of 0.2% macrosynthetic
fibers and 0.3% steel fibers shows a significa
nt improvement in the immediate post peak load
response with a significantly smaller load drop and a
constant residual load carrying capacity
equal to 80% of the peak load. An analytical
formulation to predict fle
xure load-displacement
behaviour considering a multi-linear stress-
crack separation (σ
-w) relationship is developed.
An inverse analysis is developed for obtaining the multi-
linear σ
-w relation, from the
experimental response. The
�
-w curves of the steel and
macrosynthetic fiber reinforced
concrete exhibit a stress recovery after
a significant drop with increa
sing crack opening.
Significant residual load carrying capacity is attained
only at large crack separation. The fiber
blend exhibits a constant residual
stress with increasing crack sepa
ration following an initial
decrease. The constant residual stress is
attained at a small crack separation
A Metamaterial Backed Dipole Antenna for High Gain Directional Communications
The enhanced radiation performance of a dipole antenna backed by the split ring resonator-continuous wire pair array working in the H┴ excitation scenario is presented in this paper. The H┴ excitation scenario of the metamaterial is used to get zero reflection phase resulting in enhanced gain performance. The two layer meta-structure along with the dipole is fabricated on a low cost substrate of dielectric constant 4.4 and height 1mm. The reflection properties of the metamaterial structure and its effect on the radiation performance of the dipole antenna are presented in this paper
Are lead-free relaxor ferroelectric materials the most promising candidates for energy storage capacitors?
Dielectric capacitors offer high-power density and ultrafast discharging times as compared to electrochemical capacitors and batteries, making them potential candidates for pulsed power technologies (PPT). However, low energy density in different dielectric materials such as linear dielectrics (LDs), ferroelectrics (FEs), and anti-ferroelectric (AFEs) owing to their low polarization, large hysteresis loss and low breakdown strength, respectively, limits their real time applications. Thus, achieving a material with high dielectric constant, large dielectric breakdown strength and slim hysteresis is imperative to obtain superior energy performance. In this context, relaxor ferroelectrics (RFEs) emerged as the most promising solution for energy storage capacitors. This review starts with a brief introduction of different energy storage devices and current advances of dielectric capacitors in PPT. The latest developments on lead-free RFEs including bismuth alkali titanate based, barium titanate based, alkaline niobite based perovskites both in ceramics and thin films are comprehensively discussed. Further, we highlight the different strategies used to enhance their energy storage performance to meet the requirements of the energy storage world. We also provide future guidelines in this field and therefore, this article opens a window for the current advancement in the energy storage properties of RFEs in a systematic way.This study has been partially supported by (i) DST-SERB, Govt. of India through Grant ECR/2017/000068 (KCS), (ii) UGC through grant nos. F.4-5(59-FRP)/ 2014(BSR) and (iii) Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UIDB/FIS/04650/2020 (JPBS). The author A. R. Jayakrishnan acknowledges the Central University of Tamil Nadu, India for his Ph. D fellowship. The authors acknowledge the CERIC-ERIC Consortium for access to experimental facilities and financial support under proposal 20192055
A Metamaterial Backed Dipole Antenna for High Gain Directional Communications
The enhanced radiation performance of a dipole antenna backed by the split ring resonator-continuous wire pair array working in the H┴ excitation scenario is presented in this paper. The H┴ excitation scenario of the metamaterial is used to get zero reflection phase resulting in enhanced gain performance. The two layer meta-structure along with the dipole is fabricated on a low cost substrate of dielectric constant 4.4 and height 1mm. The reflection properties of the metamaterial structure and its effect on the radiation performance of the dipole antenna are presented in this paper
Twisted large cellular fibroma of the ovary with pelvic effusion-revisiting incomplete demons Meigs’ syndrome
Fibromas of the ovary are benign tumours arising from the stromal component of the ovary. They represent 1% of ovarian neoplasms and are generally benign. The cellular subtype accounts for around 10% of these and is a tumour of uncertain malignant potential. Recurrence may occur or it could be associated with peritoneal implants. Usually these are solid tumours, sometimes with small areas of cystic degeneration. Occasionally, large fibromas may undergo torsion causing acute abdominal pain and generally tends to occur in post-menopausal women. The solid areas, ORADS and ascites simulated a malignant ovarian tumour on both MRI, USG and gross pathologic examination. Here we present a case of a postmenopausal woman presented with abdominal pain and postprandial vomiting with a large twisted ovarian fibroma leading to diagnostic and therapeutic challenges masquerading as a malignant ovarian neoplasm
Grating-based Dipole Antenna Configuration for High Gain Directional Radiation characteristics
The experimental and simulation studies of the radiation performance enhancement of a dipole antenna using metal strip grating are presented in this paper. The subwavelength imaging configuration of the metal strip grating is utilized for enhancing the radiation performance of a dipole antenna working in the S-band. The resultant design shows a gain of 9 dBi and front to back ratio of the design is found to be -23 dB at resonance. The coupling between electric and magnetic resonances provides the necessary impedance matching performance when the antenna is brought in the vicinity of the grating
Grating-based Dipole Antenna Configuration for High Gain Directional Radiation characteristics
The experimental and simulation studies of the radiation performance enhancement of a dipole antenna using metal strip grating are presented in this paper. The subwavelength imaging configuration of the metal strip grating is utilized for enhancing the radiation performance of a dipole antenna working in the S-band. The resultant design shows a gain of 9 dBi and front to back ratio of the design is found to be -23 dB at resonance. The coupling between electric and magnetic resonances provides the necessary impedance matching performance when the antenna is brought in the vicinity of the grating
Composition-dependent xBa(Zr0.2Ti0.8)O3-(1-x)(Ba0.7Ca0.3)TiO3 bulk ceramics for high energy storage applications
This work reports the composition dependent microstructure, dielectric, ferroelectric
and energy storage properties, and the phase transitions sequence of lead free
xBa(Zr0.2Ti0.8)O3-(1-x)(Ba0.7Ca0.3)TiO3 [xBZT-(1-x)BCT] ceramics, with x = 0.4, 0.5
and 0.6, prepared by solid state reaction method. The XRD and Raman scattering results
confirm the coexistence of rhombohedral and tetragonal phases at room temperature
(RT). The temperature dependence of Raman scattering spectra, dielectric permittivity
and polarization points a first phase transition from ferroelectric rhombohedral phase to
ferroelectric tetragonal phase at a temperature (TR-T) of 40 0C and a second phase
transition from ferroelectric tetragonal phase - paraelectric pseudocubic phase at a
temperature (TT-C) of 110 0C. The dielectric analysis suggests that the phase transition at
TT-C is of diffusive type and the BZT-BCT ceramics are a relaxor type ferroelectric
materials. The composition induced variation in the temperature dependence of
dielectric losses was correlated with full width half maxima (FWHM) of A1, E(LO)
Raman mode. The saturation polarization (Ps) ≈ 8.3 μC/cm2 and coercive fields ≈ 2.9
kV/cm were found to be optimum at composition x = 0.6 and is attributed to grain size
effect. It is also shown that BZT-BCT ceramics exhibit a fatigue free response up to 105
cycles. The effect of a.c. electric field amplitude and temperature on energy storage
density and storage efficiency is also discussed. The presence of high TT-C (110 0C), a
high dielectric constant (εr ≈ 12285) with low dielectric loss (0.03), good polarization
(Ps) ≈ 8.3 μC/cm2) and large recoverable energy density (W = 121 mJ/cm3) with an
energy storage efficiency (η) of 70 % at an electric field of 25 kV/cm in 0.6BZT
0.4BCT ceramics make them suitable candidates for energy storage capacitor
applications.This work was supported by (i) DST-SERB, Govt. of India through grant ECR/2017/000068 and (ii) UGC through Grant Nos. F.4-5(59-FRP/ 2014(BSR)). The authors AR Jayakrishnan acknowledges Central University of Tamil Nadu, India for his Ph.D fellowship. K.V.A. acknowledges the DST for the Inspire fellowship IF170601. J.P.B.S. is grateful for the financial support through the FCT Grant SFRH/BPD/92896/2013.The authors thank to Vivek Sudarsanan from the Central University of Kerala for XRD measurements.info:eu-repo/semantics/publishedVersio
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