Effect of content and fineness of slag as high volume cement replacement on strength and durability of ultra-high performance mortar

Replacement of cement by slag in ultra-high performance concrete (UHPC) makes it a green material for building and construction application. However, slag hydrates slower which delay strength gain in UHPC which can be addressed by using slag of high fineness. In this study, cement is replaced by slag at 20% and 60% by weight. Slag of three different fineness is used: 400±4 m2/kg, 556±5 m2/kg and 750± 5 m2/kg at constant water-binder ratio of 0.25 for all mixes. Compressive and flexural strength were measured for mechanical performance while water penetration test and chloride migration test were conducted to enumerate durability. Results show that early and late compressive strength and flexural strength are improved significantly by incorporation of slag with fineness 556 ± 5 m2/kg compared to reference and slag of 400 m2/kg fineness. However, at similar fineness 20% slag incorporation is found to produce higher early strength compared to 60% slag although 90 day strength for both replacement percentages are similar. On durability aspects it is found that slag with fineness of 556 m2/kg and 750 m2/kg demonstrates significantly lower penetration depth and very high resistance to chloride migration at 28 day and 90 day age irrespective of slag replacement percentage. The study suggests that slag of high fineness (about 556 m2/kg based on the study) and 20-60% cement replacement can significantly accelerate hydration and improve long term durability of UHPC mortar

Modeling of electron mobility of gan at low temperature and low electric field

An analytical model at low temperature and low field electron mobility of GaN has been developed. The electron mobility in GaN have been calculated using Relaxation Time Approximation method considering elastic process of acoustic phonon deformation potential scattering, acoustic piezoelectric scattering and ionized impurity scattering, neutral impurity scattering, dislocation scattering. Ionized impurity scattering has been treated beyond the Born approximation using Dingle and Brooks- Herring analysis. The compensation ratio is used as a parameter with a realistic charge neutrality condition. Degeneracy is very important factor as it is used to imply different statistics (Maxwell – Boltzmann or Fermi – Dirac) at different temperature. Generalized M-B statistics are used throughout because the samples we have used to compare our results are highly Non-degenarate. The result shows that, the proposed model can accurately predict the electron mobility as a function of both the carrier concentration and the temperature upto 200 K. The discrepancy of this model above temperature 200 K presumably results from the following factors: ignoring the role of optical phonon, at low temperature consideration of parabolic band i.e. neglecting the effect of inter-velly scattering and ignoring the effect of very few interfacial charges in the degenerate layer at the GaN-substrate interface. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2791

Biochar-mortar composite: manufacturing, evaluation of physical properties and economic viability

Singapore generates about half a million ton of wood waste annually, which constitutes a major fraction of disposed waste. Pyrolysis of wood waste to produce biochar, which can be used as additive in cement mortar, is a viable alternative to increase recycling rate of woody residues. This study explores the influence of biochar, prepared from mixed wood saw dust, on strength, elastic modulus, drying shrinkage and permeability of cement mortar. Biochar prepared by pyrolysis at 300 oC (BC 300) and 500 oC (BC 500) was added to mortar at 1–8% by weight of cement. Results show that addition of 1–2 wt% BC 300 and BC 500 improve early age (7-day) compressive strength of mortar, which is related to high water retention of 7.50 g/g and 8.78 g/g by dry BC 300 and BC500 respectively. However, addition of biochar did not significantly influence flexural strength, drying shrinkage and modulus of elasticity. Mortar with 1% addition of BC 300 and BC 500 showed about 58% and 66% reduction in water absorption and depth of water penetration respectively compared to control. Based on the experimental findings, it is concluded that 1–2 wt% addition of biochar may be recommended to improve strength and reduce permeability of cement mortar. Added at these proportions, we showed that the price of biochar mortar is still reasonably close to that of conventional mortar. Therefore, this study suggests that biochar from wood waste has the potential to be deployed as carbon sequestering admixture to improve performance of cementitious mortar at a price that is likely to be acceptable to the building industry

Bound states in the dynamics of a dipole in the presence of a conical defect

In this work we investigate the quantum dynamics of an electric dipole in a $(2+1)$-dimensional conical spacetime. For specific conditions, the Schr\"odinger equation is solved and bound states are found with the energy spectrum and eigenfunctions determined. We find that the bound states spectrum extends from minus infinity to zero with a point of accumulation at zero. This unphysical result is fixed when a finite radius for the defect is introduced.Comment: 4 page

Biochar-based adsorbents for carbon dioxide capture: a critical review

Carbon dioxide (CO2) is the main anthropogenic greenhouse gas contributing to global warming, causing tremendous impacts on the global ecosystem. Fossil fuel combustion is the main anthropogenic source of CO2 emissions. Biochar, a porous carbonaceous material produced through the thermochemical conversion of organic materials in oxygen-depleted conditions, is emerging as a cost-effective green sorbent to maintain environmental quality by capturing CO2. Currently, the modification of biochar using different physico-chemical processes, as well as the synthesis of biochar composites to enhance the contaminant sorption capacity, has drawn significant interest from the scientific community, which could also be used for capturing CO2. This review summarizes and evaluates the potential of using pristine and engineered biochar as CO2 capturing media, as well as the factors influencing the CO2 adsorption capacity of biochar and issues related to the synthesis of biochar-based CO2 adsorbents. The CO2 adsorption capacity of biochar is greatly governed by physico-chemical properties of biochar such as specific surface area, microporosity, aromaticity, hydrophobicity and the presence of basic functional groups which are influenced by feedstock type and production conditions of biochar. Micropore area (R2 = 0.9032, n = 32) and micropore volume (R2 = 0.8793, n = 32) showed a significant positive relationship with CO2 adsorption capacity of biochar. These properties of biochar are closely related to the type of feedstock and the thermochemical conditions of biochar production. Engineered biochar significantly increases CO2 adsorption capacity of pristine biochar due to modification of surface properties. Despite the progress in biochar development, further studies should be conducted to develop cost-effective, sustainable biochar-based composites for use in large-scale CO2 capture

The effect of soil incubation on bio self-healing of cementitious mortar

Successful implementation of bacteria-based self-healing in cracked cementitious materials requires the provision of a suitable incubation environment, which can activate the bacteria to produce e.g. calcium carbonate sealing the cracks. Research to date has focused on the self-healing process in humid air and water. However, almost all structures are built on or in the ground, thus, significant amounts of concrete are exposed to ground conditions. To investigate the effect of soil incubation on the self-healing process, laboratory experiments were conducted on mortar impregnated with Bacillus subtilis (encapsulated in calcium alginate). The mortar specimens were initially cracked and subdivided into three groups and each group was incubated for 28 days within different incubation environments, namely, partially-saturated soil, full-saturated soil, and water. Supported by Scanning Electron Microscope (SEM) and Energy Dispersive X-Ray Spectrometry (EDX), the results revealed that the bio self-healing can be activated within the cracks under the saturated regime of soil as far as the matric suction is smaller than the capillary pressure of the cracks. Moreover, the results indicated there was no evidence suggesting the influence of naturally existing bacteria in the soil on the self-healing process within the considered incubation period.European Union’s Horizon 2020 research and innovation programm

First narrow-band search for continuous gravitational waves from known pulsars in advanced detector data

Spinning neutron stars asymmetric with respect to their rotation axis are potential sources of continuous gravitational waves for ground-based interferometric detectors. In the case of known pulsars a fully coherent search, based on matched filtering, which uses the position and rotational parameters obtained from electromagnetic observations, can be carried out. Matched filtering maximizes the signalto- noise (SNR) ratio, but a large sensitivity loss is expected in case of even a very small mismatch between the assumed and the true signal parameters. For this reason, narrow-band analysis methods have been developed, allowing a fully coherent search for gravitational waves from known pulsars over a fraction of a hertz and several spin-down values. In this paper we describe a narrow-band search of 11 pulsars using data from Advanced LIGO’s first observing run. Although we have found several initial outliers, further studies show no significant evidence for the presence of a gravitational wave signal. Finally, we have placed upper limits on the signal strain amplitude lower than the spin-down limit for 5 of the 11 targets over the bands searched; in the case of J1813-1749 the spin-down limit has been beaten for the first time. For an additional 3 targets, the median upper limit across the search bands is below the spin-down limit. This is the most sensitive narrow-band search for continuous gravitational waves carried out so far

Sensitivity of the Advanced LIGO detectors at the beginning of gravitational wave astronomy

The Laser Interferometer Gravitational Wave Observatory (LIGO) consists of two widely separated 4 km laser interferometers designed to detect gravitational waves from distant astrophysical sources in the frequency range from 10 Hz to 10 kHz. The first observation run of the Advanced LIGO detectors started in September 2015 and ended in January 2016. A strain sensitivity of better than 10−23/Hz−−−√ was achieved around 100 Hz. Understanding both the fundamental and the technical noise sources was critical for increasing the astrophysical strain sensitivity. The average distance at which coalescing binary black hole systems with individual masses of 30  M⊙ could be detected above a signal-to-noise ratio (SNR) of 8 was 1.3 Gpc, and the range for binary neutron star inspirals was about 75 Mpc. With respect to the initial detectors, the observable volume of the Universe increased by a factor 69 and 43, respectively. These improvements helped Advanced LIGO to detect the gravitational wave signal from the binary black hole coalescence, known as GW150914

Search for post-merger gravitational waves from the remnant of the binary neutron star merger GW170817

In Advanced LIGO, detection and astrophysical source parameter estimation of the binary black hole merger GW150914 requires a calibrated estimate of the gravitational-wave strain sensed by the detectors. Producing an estimate from each detector's differential arm length control loop readout signals requires applying time domain filters, which are designed from a frequency domain model of the detector's gravitational-wave response. The gravitational-wave response model is determined by the detector's opto-mechanical response and the properties of its feedback control system. The measurements used to validate the model and characterize its uncertainty are derived primarily from a dedicated photon radiation pressure actuator, with cross-checks provided by optical and radio frequency references. We describe how the gravitational-wave readout signal is calibrated into equivalent gravitational-wave-induced strain and how the statistical uncertainties and systematic errors are assessed. Detector data collected over 38 calendar days, from September 12 to October 20, 2015, contain the event GW150914 and approximately 16 of coincident data used to estimate the event false alarm probability. The calibration uncertainty is less than 10% in magnitude and 10 degrees in phase across the relevant frequency band 20 Hz to 1 kHz