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The aim of this study was to develop a new phase-change material (PCM) for thermal energy storage (TES) in gypsum-based building materials. Expanded vermiculite was used as a base for a coconut oil (CtO)–vermiculite composite PCM. The maximum mass ratio of CtO retained in the vermiculate was found to be 27% for the best particle-size distribution of the vermiculite. The results showed that there were only physical interactions between oil and vermiculite in the composite. The melting temperature and latent heat of the composite were measured as 22·29°C and 24·21 J/g, respectively. Thermal cycling tests showed that there was no significant change in thermal property of the composite after 1000 thermal cycles. A gypsum-based heat-storage material was prepared by mixing the composite with gypsum. The thermal properties, compressive strength and water adsorption of the gypsum–composite mix were then measured. The results showed that the composite could be considered as a promising PCM in gypsum-based building materials for TES applications. This is due to its satisfactory physical, mechanical and thermal properties and good thermal reliability and chemical stability.

The industrial sections have always been thirsty to predict events and be aware of future sudden changes. Where using time-series forecasting based on deep learning techniques can have a significant effect on addressing this issue. In this paper, we present Stacked Long Short-Term Memory (LSTM) networks to predict significant electric consumption changes when a group of devices is activated or deactivated randomly. Three Power quadratic phases are used as a dataset. The goal is to predict multi-steps in the future minutes. The supervised learning technique is used to transform series data to supervised data for training and prediction, and then the Walk-forward cross-validation is implemented to evaluate subsequent time steps prediction and output is a vector of prediction. Finally, the root-mean-square error (RMSE) method is employed as a metric for each lead time on an output vector. Furthermore, we compared our proposed model with the Vanilla and Bidirectional LSTMs architecture, in which the performance of our method shows that it was successful. Our experimental results support the view that enough data is crucial to event detection in time series data and suggest that Stacked LSTM is a good architecture with which to address it.

Multiple people's tracking and detecting are essential and challenging tasks for monitoring vision, particularly in public places like shopping centers. We introduced a technical proposal based on the detection algorithm and tracking algorithm. In this investigation, we applied YOLOv3 as a detection algorithm and to raise the performance and velocity Kalman Filter was used as a tracking algorithm. We additionally validated the performance of the proposed detection method “YOLOv3” by performed a statistical analysis of detecting errors MSE method. The experimental results on a series of tests show that the efficiency of the proposed method is quite beneficial, and is able to detect people not only in closed space but in open space, especially when they are closer to each other as well.

In this work, activated phosphorous slag based cylindrical adsorbent was synthesized for removal of basic violet (BV) and malachite green oxalate (MGO) dyes from aqueous solution. For this purpose, the adsorbent was prepared using a mixture of silica-fume and phosphorous slag as raw precursor and different concentration of NaOH as alkaline solution under a specified curing condition. Response surface methodology has been applied to determine the optimal adsorbent composition and experimental conditions (pH, initial concentration, adsorbent dosage, and contact time). The obtained results showed that the phosphorous slag combined with 30 wt% of silica-fume and 15 mol/L of NaOH was the optimal synthesized adsorbent with an acceptable strength of 6.25 MPa. The maximum adsorption capacity was measured as 46.58 mg/g for BV and 46.36 mg/g for MGO in the optimum condition. Specific surface area for the produced shaped adsorbent is 56.59 m2/g with average pore diameter of 20 nm which was classified as a mesoporous material. It was found from adsorption/desorption test that the overall adsorption capacity decreased about 11% after seven-cycle that result in a reliable reuse of the shaped adsorbent. The resulted high removal efficiency after several desorption cycles not only could be due to the porosity of the mesoporous adsorbent but also could be due to the presence of Si–O–Si bonds in its molecular-structure that result in higher adsorption efficiency. It was also found that silica-fume could play as a structure modifying agent that affect the molecular-structure of the adsorbent by formation of more Si–O–Si bonds due to increase in Si/Al molar ratio in the adsorbent composition.

This paper focused on determining the rheological behavior and apparent activation energy of activated phosphorous slag (AAPS) with sodium silicate and NaOH at different SiO2/Na2O (S/N) and Na2O/Al2O3 (N/A) molar ratios. The results showed that the AAPS paste behaved like a shear-thinning fluid, its rheological behavior obeyed the Herschel-Bulkley model, and its apparent viscosity decreased with increasing of shear rate. The chemical composition of activator affected the rheological properties and fluidity of AAPS paste but had no significant effect on shear thinning parameters. It was found that shear thinning behavior of AAPS paste was depend upon the changes done in the nature of phosphorous slag after activation process. It was observed that the initial rest time before increase of shear stress during the time was decreased as the S/N and N/A was increased due to increase in the slag dissolution rate and more gel formation. Increase in chemical composition of the activator also caused to accelerate the geopolymerization reactions and hence increased the shear stress. Apparent activation energy of AAPS paste based on Arrhenius viscosity model at temperatures of 10, 25, and 40 °C was measured in the range of 39.2–44.5 kJ/mol. It was found that lower silica content in the activator, i.e. decrease of S/N molar ratio, and higher alkaline content in the activator, i.e. increase of N/A molar ratio, result in decrease of the apparent activation energy. The accuracy of Arrhenius viscosity model was confirmed by determining the activation energy of OPC as the blank sample that was measured as 36.7 kJ/mol.

Charge carrier dynamics in amorphous semiconductors has been a topic of intense research that has been propelled by modern applications in thin-film solar cells, transistors and optical sensors. Charge transport in these materials differs fundamentally from that in crystalline semiconductors owing to the lack of long-range order and high defect density. Despite the existence of well-established experimental techniques such as photoconductivity time-of-flight and ultrafast optical measurements, many aspects of the dynamics of photo-excited charge carriers in amorphous semiconductors remain poorly understood. Here, we demonstrate direct imaging of carrier dynamics in space and time after photo-excitation in hydrogenated amorphous silicon (a-Si:H) by scanning ultrafast electron microscopy (SUEM). We observe an unexpected regime of fast diffusion immediately after photoexcitation, together with spontaneous electron-hole separation and charge trapping induced by the atomic disorder. Our findings demonstrate the rich dynamics of hot carrier transport in amorphous semiconductors that can be revealed by direct imaging based on SUEM.

As an emerging single elemental layered material with a low symmetry in-plane crystal lattice, black phosphorus (BP) has attracted significant research interest owing to its unique electronic and optoelectronic properties, including its widely tunable bandgap, polarization dependent photoresponse and highly anisotropic in-plane charge transport. Despite extensive study of the steady-state charge transport in BP, there has not been direct characterization and visualization of the hot carriers dynamics in BP immediately after photoexcitation, which is crucial to understanding the performance of BP-based optoelectronic devices. Here we use the newly developed scanning ultrafast electron microscopy (SUEM) to directly visualize the motion of photo-excited hot carriers on the surface of BP in both space and time. We observe highly anisotropic in-plane diffusion of hot holes, with a 15-times higher diffusivity along the armchair (x-) direction than that along the zigzag (y-) direction. Our results provide direct evidence of anisotropic hot carrier transport in BP and demonstrate the capability of SUEM to resolve ultrafast hot carrier dynamics in layered two-dimensional materials., Comment: 21 pages, 6 figures

The present work is devoted to a better insight into the identification of carbonation versus efflorescence formation in alkali-activated blast-furnace slag and investigates the relation between the chemical composition of the alkali-activator and the extent of the occurrence of these two phenomena. Obtained results showed that mixes of relatively lower alkali contents suffer not only from weak compressive strength due microstructural defects, but also from carbonation during the first few days. On the other hand, mixes containing relatively higher alkali contents strongly suffer from efflorescence formation in spite of their interestingly high compressive strengths. Carbonation during the first few days can partially neutralize the alkali content of the surface layers of the material which in turn significantly affects the activation mechanism leading to the formation of binding compounds of different molecular structure.

This study focused on the evaluation of the mechanical and durability aspects of stabilized poorly graded sandy soil by activated blast furnace slag cements (ASCs) with three different acti...

Understanding the dynamics of charge carriers at the semiconductor surfaces and interfaces is fundamental to the further development of photocatalytic, photovoltaic, and optoelectronic devices. Here, we study the surface photovoltage (SPV) dynamics in intrinsic and doped silicon using scanning ultrafast electron microscopy (SUEM). SUEM is a surface sensitive technique that allows the direct imaging of carriers at ultrafast time scales, thereby elucidating their spatiotemporal response to optical excitation. We first discuss the mechanism of image formation in SUEM. We then use these images to show that carrier dynamics on the silicon surface depends strongly on the doping type and concentration, though not always dictated by SPV. The numerical simulation of the drift-diffusion model suggests that this is due to the formation of complex transport processes, driven by intrinsic and photoinduced fields in the excited volume. This work refines our current understanding of the surface-exclusive dynamics in semiconductors by introducing a means to study their evolution in space and time and providing a model to explain the underlying mechanism.

This paper investigates the kinetics of geopolymerisation in an inorganic polymeric binder based on a natural pozzolan. The heat released by the exothermic geopolymerisation reaction process is monitored under isothermal temperature conditions, maintained in a differential scanning calorimeter using a water circulation cell. Calorimetric data are obtained isothermally at 65, 75, and 85 °C with various Na2O/Al2O3 and SiO2/Na2O molar ratios and in the presence and absence of small amounts of calcium aluminate cement (used as an efflorescence control admixture in these binder systems). The first stage of reaction, which is rapid and strongly exothermic, is shortened as the temperature increases. The total heat of reaction increases in the mixes containing calcium aluminate cement, but the apparent activation energy calculated using a pseudo-first-order reaction model is lower than without added calcium aluminate cement. At a constant overall SiO2/Na2O molar ratio, the apparent activation energy is decreased as the Na2O/Al2O3 molar ratio increases. Calcium aluminate cement, therefore, reduces the minimum energy required to initiate geopolymerisation reactions of this natural pozzolan and facilitates the progress of the reactions which lead to formation of a cementitious product.

The perturbation of a semiconductor from the thermodynamic equilibrium often leads to the display of nonlinear dynamics and formation of spatiotemporal patterns due to the spontaneous generation of competing processes. Here, we describe the ultrafast imaging of nonlinear carrier transport in silicon, excited by an intense femtosecond laser pulse. We use scanning ultrafast electron microscopy (SUEM) to show that, at a sufficiently high excitation fluence, the transport of photoexcited carriers slows down by turning into an oscillatory process. We attribute this nonlinear response to the electric field, generated by the spatial separation of these carriers under intrinsic and photo-induced fields; we then provide an advection-diffusion model that mimics the experimental observation. Our finding provides a direct imaging evidence for the electrostatic oscillation of hot carriers in highly excited semiconductors and offers new insights into their spatiotemporal evolution as the equilibrium is recovered.

In this study, properties of cement composites and mortars were investigated in presence of Nano-Fe2O3 as their modifier. Cement composites were synthesized using the sol-gel method with tetraethylammonium orthosilicate as the complex legend. Subsequently, Nano-Fe2O3 was added at 2, 4, and 6 wt% dosages to the cement composite, while for mortars 2, 3 and 4 wt% of Nano-Fe2O3 dosages were used. FTIR and XRD tests were conducted to analyze the phase composition, molecular, and microstructure of cement composites, additionally, the effects of adding Nano-Fe2O3 on compressive and flexural strengths of mortars were investigated. The results indicated a change in the phase composition of the molecular-structure of cement composites, leading to stronger bonds in silicate network with more ordered arrangement in the presence of nanoparticles. The formation of three-membered silicate rings was also evident in composite samples containing higher amounts of Nano-Fe2O3 (i.e. 4 and 6 wt%). The microstructure analysis revealed that samples with Nano-Fe2O3 had a denser structure with a smaller pore size in comparison with control samples. The mechanical performance of mortar samples were enhanced with the incorporation of Nano-Fe2O3, where 3 wt% dosage was identified as the optimum.

Autonomous vehicles make the main part of the intelligent transportation system. In addition, the accident statistics illustrates that the number of accidents accrued in the night, bad weather conditions and, especially, due to the vehicles in front. This paper offers a method of image processing to tracking vehicle and brake light which includes the cascade classifier algorithm based on the classification of a collection of information. The brake light detection is based on the HSV color space algorithm. This method can be useful for mobile robots and industrial robots in terms of object detection and recognition in real time.

The present study aimed to determine the rheological behavior of activated phosphorus slag (AAPS) with a combination of Ca(OH)2 and Na2CO3 (CNC activator) or Na2SO4 (CNS activator) compared to OPC paste. The findings showed that the rheology of AAPS pastes fit with the Herschel-Bulkley model and behaved like a shear-thinning fluid. The AAPS pastes rheology is affected by concentration and nature of activator. The shear stress in AAPS pastes was lower than OPC paste, and increased with increasing the activator concentration. In early ages, reaction products of PS/CNC pastes included calcite-type compounds with the formed gel while gypsum compounds formed in the PS/CNS pastes. This resulted in higher shear stress and lower workability for PS/CNC pastes compared to PS/CNS pastes. The formed gel due to interaction between Ca2+ ions of CNC activator and Si4+ ions of Phosphorus slag caused an increase in the shear stress for PS/CNC during the time., This work was supported by the Science & Technology Park of Semnan University, Iran [grant ID: 1233/95/315, 2016]. The authors acknowledged the financial supports from the Ministry of Science, Research, and Technology of Islamic Republic of Iran who paid for the PhD scholarship and travel to Madrid for Hamideh Mehdizadeh.

Understanding the mechanical properties of organic semiconductors is essential to their electronic and photovoltaic applications. Despite a large volume of research directed toward elucidating the chemical, physical and electronic properties of these materials, little attention has been directed toward understanding their thermo-mechanical behavior. Here, we report the ultrafast imaging of surface acoustic waves (SAWs) on the surface of the Poly(3-hexylthiophene-2,5-diyl) (P3HT) thin film at the picosecond and nanosecond timescales. We then use these images to measure the propagation velocity of SAWs, which we then employ to determine the Young's modulus of P3HT. We further validate our experimental observation by performing a semi-empirical transient thermoelastic finite element analysis. Our findings demonstrate the potential of ultrafast electron microscopy to not only probe charge carrier dynamics in materials as previously reported, but also to measure their mechanical properties with great accuracy. This is particularly important when in situ characterization of stiffness for thin devices and nanomaterials is required.

The nonequilibrium dynamics of carriers in semiconductors plays a major role in the performance and efficiency of the electronic and photovoltaic devices. In this study, we use the scanning ultrafast electron microscopy (SUEM) technique to study the surface photovoltage dynamics in doped silicon samples. We observe that the optical excitation of lightly doped n-type and p-type silicon as well as heavily doped n-type silicon increases the electron density on the surface. In contrast, the optical excitation of heavily doped p-type silicon increases the hole density on the surface. Furthermore, we show that the rise and the decay timescales of these events strongly depend on the doping concentration.

In situ attenuated total-reflectance Fourier transform infrared (ATR-FTIR) spectroscopy was used to investigate the gel formation of a natural pozzolan-based geopolymer and its relation to ...

Hollow silica particles (HSPs) have become the focus of interest in many laboratories recently, because of their versatility, stemming from the ability to control their size and shape, as well as surface functionalization. Determining the mechanical stability of hollow particles is essential for their use, both in applications in which they need to retain their structure, as well as those in which they need to break down. We have synthesized a series of HSPs (inner diameter of 231 nm) with increasing wall thickness (7-25 nm), using a template approach. Their mechanical stability was measured using mercury intrusion porosimetry (MIP), which represents the novel application of the technique for these materials. The samples with complete shells break at progressively higher pressures, and samples with wall thickness ≥21 nm remain stable to the highest pressure applied (414 MPa). Other characterization methods, namely microscopy, gas adsorption, and small-angle X-ray scattering, shed light on the size parameters of the particles, as well as the porosity of the silica walls. By varying the amount of silica precursor used in the template coating step, we were able to produce hollow silicas with variable stability, thereby allowing for control of their mechanical properties.

The dynamics of photo-excited charge carriers, particularly their transport and interactions with defects and interfaces, play an essential role in determining the performance of a wide range of solar and optoelectronic devices. A thorough understanding of these processes requires tracking the motion of photocarriers in both space and time simultaneously with extremely high resolutions, which poses a significant challenge for previously developed techniques, mostly based on ultrafast optical spectroscopy. Scanning ultrafast electron microscopy (SUEM) is a recently developed photon-pump-electron-probe technique that combines the spatial resolution of scanning electron microscopes (SEM) and the temporal resolution of femtosecond ultrafast lasers. Despite many recent excellent reviews for the ultrafast electron microscopy, we dedicate this article specifically to SUEM, where we review the working principle and contrast mechanisms of SUEM in the secondary-electron-detection mode from a users' perspective and discuss the applications of SUEM to directly image photocarrier dynamics in various materials. Furthermore, we propose future theoretical and experimental directions for better understanding and fully utilizing the SUEM measurements to obtain detailed information about the dynamics of photocarriers. To conclude, we envision the potential of expanding SUEM into a versatile platform for probing photophysical processes beyond photocarrier dynamics., Comment: 23 pages, 6 figures

The C 1s inner shell excitation spectra of individual metallic and semiconducting single-walled carbon nanotubes (SWCNTs) were measured using high-resolution electron energy loss spectroscopy in an aberration-corrected transmission electron microscope (TEM-EELS). On the basis of its diameter, the metallic SWCNT is most likely a (10,10) sample, whereas (11,12) and a number of other chiral vectors are consistent with the diameter of the semiconducting SWCNTs. The C 1s X-ray absorption spectra of the same electronically pure SWCNT materials were measured as individual bundles or agglomerations of bundles by scanning transmission X-ray microscopy. Spectral differences in the C 1s → π* transitions of metallic and semiconducting species, related to differences in the van Hove singularities in their unoccupied states, are observed by both methods. The fine structure of the C 1s → π* transitions is similar to that recently reported from nonspatially resolved X-ray absorption spectroscopy of ensemble samples of high-purity metallic and semiconducting SWCNTs. The quality of the TEM-EELS spectra of individual SWCNTs is such that the line shape can be used to identify if they are metallic or semiconducting, thereby opening up the possibility to interrogate the electronic state of single-SWCNT devices. A strong X-ray linear dichroism in the C 1s → π* band of both types of SWCNTs was observed.

Momentum resolved electron energy loss (EELS) spectra of multi-walled carbon nanotubes (MWCNT) have been measured at the C 1s edge in a transmission electron microscope (TEM). We demonstrate that structurally sensitive electron linear dichroic (ELD) signals analogous to X-ray linear dichroic (XLD) signals (Najafi et al., 2008) [17] can be measured by TEM-EELS from individual MWCNT if sample tilt and deflection of the inelastic scattering signal relative to the EELS spectrometer entrance aperture are used. This method is used to map defects in MWCNT at higher spatial resolution than is currently possible with X-ray microscopy.

This paper addresses methods to reduce efflorescence in a geopolymer binder based on a pumice-type natural pozzolanic material from Taftan, Iran. Geopolymer pastes samples are analyzed for compressive strength and efflorescence formation after curing at 95% humidity for 28 days. To reduce the extent of efflorescence, Al-rich mineral admixtures such as metakaolin, ground granulated blast-furnace slag, and three types of calcium aluminate cements are incorporated into the dry binder at a range of concentrations. Hydrothermal curing at elevated temperatures also shows a positive effect in efflorescence reduction. Calcium aluminate cements show the greatest effect in efflorescence reduction, which is attributed to their dissolution in alkaline media releasing high amounts of alumina into the aluminosilicate geopolymer gel. These results confirm that it is possible to develop a more reliable geopolymer binder with improved properties either by adding a suitable amount of active alumina to precursors such as natural pozzolan, or by manipulating the curing conditions to enhance alumina release from less-reactive precursor phases.

The presence of defects in carbon nanotubes strongly modifies their electrical, mechanical, and chemical properties. It was long thought undesirable, but recent experiments have shown that introduction of structural defects using ion or electron irradiation can lead to novel nanodevices. We demonstrate a method for detecting and quantifying point defect density in individual carbon nanotubes (CNTs) based on measuring the polarization dependence (linear dichroism) of the C 1s → π* transition at specific locations along individual CNTs with a scanning transmission X-ray microscope (STXM). We show that STXM can be used to probe defect density in individual CNTs with high spatial resolution. The quantitative relationship between ion dose, nanotube diameter, and defect density was explored by purposely irradiating selected sections of nanotubes with kiloelectronvolt (keV) Ga+ ions. Our results establish polarization-dependent X-ray microscopy as a new and very powerful characterization technique for carbon nanotubes and other anisotropic nanostructures.

The C 1s X-ray absorption spectra of several isolated bundles of single-walled carbon nanotubes (SWCNT) have been measured using scanning transmission X-ray microscopy. First the C 1s and O 1s spectra of a purified but unfunctionalized SWCNT were measured. The C 1s --pi* transition at 285 eV exhibited almost as strong a dichroic effect (spectral dependence on orientation) as that found in multiwalled carbon nanotubes (Najafi; et al. Small 2008, 7, 2279-2285). Second, purified SWCNT were functionalized with dodecyl and then investigated by STXM. Spectral evidence for the dodecyl functionalization is presented and discussed in comparison to the X-ray absorption spectra of aliphatic hydrocarbons. Both orientation and functionalization mapping of an individual SWCNT bundle is demonstrated.

This paper reports the results of a study on the influence of curing conditions on compressive strength development in inorganic polymeric binder prepared from natural pozzolan. Three mixes with different chemical formulations were prepared and cured hydrothermally at different temperatures and times. In particular, the effect of a precuring at an atmosphere of more than 95% relative humidity at room temperature on compressive strength development before the application of heat was studied. Different curing regimes including hydrothermal treatment in steam-saturated atmosphere at different temperatures of 45, 65, 85 °C and for different time periods of 5, 10, 15, and 20 h after 1 and 7 days of precuring were applied. The mix exhibiting the maximum compressive strength after hydrothermal treatment was selected and cured in autoclave at temperatures of 125, 150, 180, and 210 °C for different time periods of 20, 30, 40, and 50 h for investigating the effects of higher times and temperatures of curing on strength development and also to determine the maximum achievable compressive strength. Results show that relatively long precuring in humid atmosphere is very beneficial for compressive strength development. The highest compressive strength achieved for three different regimes of curing including 28 days at an atmosphere of more than 95% relative humidity at 25 °C, 20 h hydrothermal treatment at 85 °C after 1 day precuring, and 20 h hydrothermal treatment at 85 °C after 7 days precuring were 37.5, 37.5, and 57.5 MPa, respectively. The maximum achievable compressive strength under autoclave curing at 210 °C for 30 h after 7 days of precuring was 108.7 MPa.

The polarization dependence (linear dichroism) of the C 1s X-ray absorption spectrum of individual multi-walled carbon nanotubes (MWCNTs) is measured using scanning transmission X-ray microscopy. A very strong dichroic effect is found in the C 1s --> pi* transition, with almost complete disappearance of this transition when the electric-field (E)-vector is aligned parallel to high-quality (low-defect) MWCNTs and maximum intensity when the E-vector is orthogonal to the tube axis. In contrast, there is very little dichroism in the C 1s --> sigma* transitions. The origin of this polarization effect is explained. The magnitude of the polarization dependence is found to differ in MWCNTs synthesized by different methods (arc discharge versus chemical vapor deposition). This is ascribed to differences in densities of sp(2)-type defects. The potential for use of this signal to characterize defects in single-carbon-nanotube devices is discussed.