Now showing items 26325-26344 of 49060

    • L-Arginine-Incorporated Cement Mortar as Sustainable Artificial Reefs

      Hyun-Min Yang; Nosang V. Myung; Han-Seung Lee; Jitendra Kumar Singh (MDPI AG, 2020-08-01)
      L-arginine is one of the amino acids found in plant seeds. In the present study, various amounts (i.e., 3%, 5%, 10%) of L-arginine were added to cement mortar to investigate the compressive strength, workability, leaching behavior, and pH change in distilled and natural seawater, as well as dissolved nitrogen and growth of chlorophyll-a (Chl-a) by immersion in natural seawater. The compressive strength of the cement mortar is decreased with increase in L-arginine content owing to the high flow/slump and air content. A concentration of 10% L-arginine significantly promoted the growth of Chl-a on the cement mortar for up to 56 days of immersion in natural seawater. This is due to the availability of high dissolved nitrogen and pH inside the pores. This study recommends the use of L-arginine in artificial reef structures where marine ecosystems can be maintained.
    • L2 Motivational Self System, International Posture and the Sustainable Development of L2 Proficiency in the COVID-19 Era: A Case of English Majors in China

      Xi Zhao; Wei Xiao; Jiajia Zhang (MDPI AG, 2022-07-01)
      The L2 motivation self system (L2MSS) has been extensively researched in a variety of contexts, but few studies have delved into its relationship with international posture and the sustainable development of L2 proficiency in the COVID-19 era. To address this issue, we surveyed 156 English majors in China and analyzed their response data with structural equation modelling. The results show that the ideal L2 self positively predicts the L2 learning experience, while the ought-to L2 self has a negative predictive power. The international posture exerts a positive influence on the ideal L2 self and L2 experience, and a negative insignificant influence on the ought-to L2 self. The L2 experience and ideal L2 self have a positive influence on L2 proficiency, while the ought-to L2 self has a negative influence. Our results not only contribute to the generalizability of L2MSS but also deepen the understanding of possible contextual variations of L2 motivation, as well as the uniqueness in the sustainable development of English majors in China during the COVID-19 pandemic.
    • Lab-at-Home: Hands-On Green Analytical Chemistry Laboratory for New Normal Experimentation

      Chonnipa Yeerum; Piyanat Issarangkura Na Ayutthaya; Kullapon Kesonkan; Kanokwan Kiwfo; Siripat Suteerapataranon; Piyatida Panitsupakamol; Pathinan Paengnakorn; Dujrudee Chinwong; Surarong Chinwong; Chalermpong Saenjum (MDPI AG, 2022-03-01)
      The COVID-19 pandemic has forced analytical chemistry educators in Thailand to change methods of teaching and learning to new normal ones. Higher education has faced additional challenges because of a lack of hands-on experiments and an increasing number of students in foundation chemistry courses being hindered from practicing skills. This work aimed to develop a Lab-at-Home (LAH) for new normal, analytical chemistry experimentation. The LAH implemented a hands-on green chemistry experiment, i.e., colorimetric determination of iron using non-hazardous reagents (supporting Sustainable Development Goal (SDG) 12-responsible consumption and production). The LAH was sent to students at their location before the synchronous class, where the instructors were prompt to supervise. Thus, this supports SDG4-quality education and SDG10-reduced inequalities. The learning outcome achievements, i.e., the analytical characteristics and colorimetry principles comprehension, as well as the ability to perform data analysis, were evaluated by a quiz and laboratory report. LAH satisfaction was assessed by questionnaire and focus group discussion. The learning outcomes were successfully achieved, although students who performed the experiment individually received higher scores than those who did in groups. Students were very satisfied with the LAH as a tool for new normal experimentation, yet some students faced a poor Internet connection during the synchronous online class.
    • Labor Contracts, Wages and SME Failure

      Nico Dewaelheyns; Cynthia Van Hulle; Yannick Van Landuyt; Mathias Verreydt (MDPI AG, 2021-07-01)
      Although employment protection and employee remuneration has been shown to affect many aspects of a firm’s performance, evidence of their ability to explain firm failure is very limited. This paper examines the effect of different types of labor contracts and wages on the probability of corporate failure between 2012 and 2019 using a sample of 29,596 Belgian SMEs. Using discrete time hazard regression models, we find that the use of contract types with lower employment protection and paying lower wages are significant predictors of failure.
    • Labor Market Determinants of Migration Flows in Europe

      Elvira Nica (MDPI AG, 2015-01-01)
      Considerable research attention has focused on the labor market impacts of immigration, the operation and competitiveness of the European Union (EU) labor market, and the expenditures and advantages of labor circulation for sending and receiving economies. The aim of the present study is to examine and evaluate the negative social consequences arising from the mobility of workers, the social and economic drivers of migration, and the effect of immigration on natives’ labor market results such as wages and employment.
    • Labor Markets and Sustainability: Short-Run Dynamics and Long-Run Equilibrium

      João Ricardo Faria; Franklin G. Mixon (MDPI AG, 2022-04-01)
      Many of the world’s economies experienced rapid structural changes due to globalization and other forces over the past 50 years. During this period, developing countries were the recipients of massive foreign direct investment, and their industrialization was accompanied by urbanization, city gigantism, and related environmental issues, such as pollution. Over time, investments in the education of the urban poor allowed their move from the industrial sector to the service sector. This growth of the service sector came at the expense of the industrial sector, which implied structural changes in cities and massive cleaning efforts. The objective of this study is to model these transitions in a simple dynamic framework. The economic model indicates that in the short run, urban growth is negatively impacted by environmental degradation and agglomeration costs, while service sector growth is negatively impacted by environmental cleaning costs. In the long run, optimal city and service sizes are both decreasing functions of environmental degradation and agglomeration and cleaning costs. Thus, sustainability ultimately determines the optimal city size.
    • Labor Union Effects on Innovation and Commercialization Productivity: An Integrated Propensity Score Matching and Two-Stage Data Envelopment Analysis

      Dongphil Chun; Yanghon Chung; Chungwon Woo; Hangyeol Seo; Hyesoo Ko (MDPI AG, 2015-04-01)
      Research and development (R&D) is a critical factor in sustaining a firm’s competitive advantage. Accurate measurement of R&D productivity and investigation of its influencing factors are of value for R&D productivity improvements. This study is divided into two sections. The first section outlines the innovation and commercialization stages of firm-level R&D activities. This section analyzes the productivity of each stage using a propensity score matching (PSM) and two-stage data envelopment analysis (DEA) integrated model to solve the selection bias problem. Second, this study conducts a comparative analysis among subgroups categorized as labor unionized or non-labor unionized on productivity at each stage. We used Korea Innovation Survey (KIS) data for analysis using a sample of 400 Korean manufacturers. The key findings of this study include: (1) firm innovation and commercialization productivity are balanced and show relatively low innovation productivity; and (2) labor unions have a positive effect on commercialization productivity. Moreover, labor unions are an influential factor in determining manufacturing firms’ commercialization productivity.
    • Laboratory and In-Situ Measurements for Thermal and Acoustic Performance of Straw Bales

      Stefano Cascone; Gianpiero Evola; Antonio Gagliano; Gaetano Sciuto; Chiara Baroetto Parisi (MDPI AG, 2019-10-01)
      This paper investigates the performance of timber-framed walls insulated with straw bales, and compares them with similar walls containing expanded polystyrene (EPS) instead of straw bales. First, thermal conductivity, initial water content, and density of the straw bales were experimentally measured in a laboratory set-up, and the dependence of the thermal conductivity of the dry material on temperature was described. Then, the two insulation solutions were compared by looking at their steady and periodic thermal transmittance, decrement factor, phase shift, internal areal heat capacity and surface mass. Finally, the acoustic performance of both wall typologies was analyzed by means of in situ measurements in two-story buildings built in Southern Italy. The weighted apparent sound reduction index for the partition wall between two houses and the weighted standardized level difference for the façades were assessed based on ISO Standard 16283. The results indicate that the dry straw bales have an average thermal conductivity of <i>k</i> = 0.0573 W/(m·K), and their density is around 80 kg/m<sup>3</sup>. In addition, straw bale walls have good steady thermal performance, but they still lack sufficient thermal inertia, as witnessed by the low phase shift and the high periodic thermal transmittance. Finally, according to the on-site measurements, the results underline that the acoustic performance of the straw bale walls is far better than the walls adopting traditional EPS insulation. Overall, the straw bales investigated are a promising natural and sustainable solution for thermal and sound insulation of buildings.
    • Laboratory Assessment of the Infiltration Capacity Reduction in Clogged Porous Mixture Surfaces

      Valerio C. Andrés-Valeri; Mariana Marchioni; Luis Angel Sañudo-Fontaneda; Filippo Giustozzi; Gianfranco Becciu (MDPI AG, 2016-08-01)
      Permeable pavements have been used widely across the world to manage urban stormwater. The hydrological behaviour of permeable surfaces is a complex process affected by many factors, such as rainfall intensity, rainfall duration, pavement geometrical conditions, and clogging level of the permeable surface, amongst others. This laboratory study was carried out to assess the influence of clogging level and rainfall intensity on the infiltration capacity of porous mixture surfaces used in Permeable Pavement Systems (PPS). Porous Concrete (PC) and Porous Asphalt (PA) mixtures with different air void contents (15%, 20%, and 25%) were subject to different clogging scenarios by using varying sediment loads (0, 500, and 1000 g/m2). Permeability experiments were carried out for each clogging scenario through a new rainfall simulator specially developed, tailored, and calibrated for the laboratory simulation of a wide range of rainfall events. Permeability measurements were taken under all different scenarios as a result of the combination of the different rainfall events (50, 100, and 150 mm/h) simulated over the specimens of porous mixtures and the sediment loads applied to them. The results showed that the PC mixtures tested perform better than the PA ones in terms of infiltration capacity, showing less potential for clogging and being more easily cleaned by the wash-off produced by the simulated rainfall events.
    • Laboratory Characterization of a Liquid Metal MHD Generator for Ocean Wave Energy Conversion

      José Carlos Domínguez-Lozoya; Sergio Cuevas; David Roberto Domínguez; Raúl Ávalos-Zúñiga; Eduardo Ramos (MDPI AG, 2021-04-01)
      Harnessing ocean wave energy is an old challenge that has gained momentum in recent years. In this paper, we present the flow and electrical characterization of a prototype of an alternate liquid metal magnetohydrodynamic (MHD) generator at a laboratory scale which has the potential to make use of the energy of marine waves for its conversion into electrical energy. The eutectic alloy Galinstan, used as a working fluid, was driven in oscillatory motion in a duct of a rectangular cross-section exposed to a transverse magnetic field generated by permanent neodymium magnets. The electric current induced by the motion of the liquid metal in the magnetic field was collected through copper electrodes and delivered to the load. The oscillatory axial velocity component along the duct was measured using ultrasonic Doppler velocimetry for different oscillation frequencies. In turn, the output currents and voltages were measured for different operation conditions and the electric power and efficiency were estimated from experimental measurements. The coupling of this generator to a wave energy converter (WEC) is discussed.
    • Laboratory Evaluation of Finely Milled Brick Debris as a Soil Stabilizer

      Cesar Hidalgo; GLORIA CARVAJAL; Fredy Muñoz (MDPI AG, 2019-02-01)
      Brick is one of the most common building materials, and it is also one of the largest components of waste generated from both construction and demolition. Reuse of this waste would reduce the environmental and social impacts of construction. One potential bulk use of such waste is as a cementing agent for soil stabilization. However, this is currently limited by the need to mill the residue to a particle size below 0.035 mm. In this study, the behavior of two soil types stabilized using alkali-activated brick dust was investigated. The unconfined compression strength at different curing temperatures and moistures and the use of different types and concentrations of alkaline activators were investigated. It was found that the addition of brick dust resulted in an increase in the soil strength between 1.7⁻2.3 times with respect to the non-stabilized material, suggesting that the resulting materials will find practical applications in construction.
    • Laboratory Evaluation of Hot Asphalt Concrete Properties with Cuban Recycled Concrete Aggregates

      Debora Acosta Alvarez; Anadelys Alonso Aenlle; Antonio José Tenza-Abril (MDPI AG, 2018-07-01)
      Recycled Aggregates (RA) from construction and demolition waste (CDW) are a technically viable alternative to manufacture of asphalt concrete (AC). The main objective of this work is to evaluate the properties of hot asphalt mixtures that have been manufactured with different sources of CDW (material from concrete test specimens, material from the demolition of sidewalks and waste from prefabrication plants) from Cuba. Dense asphalt mixtures were manufactured with a maximum aggregate size of 19 mm, partially replacing (40%) the natural aggregate fraction measured between 5 mm and 10 mm with three types of RA from Cuba. Marshall specimens were manufactured to determine the main properties of the AC in terms of density, voids, stability and deformation. Additionally, the stiffness modulus of the AC was evaluated at 7 °C, 25 °C and 50 °C. The results corroborate the potential for using these sources of CDW from Cuba as a RA in asphalt concrete, thereby contributing an important environmental and economic benefit.
    • Laboratory Evaluation of Storage Stability for CRM Asphalt Binders

      Jihyeon Yun; Navid Hemmati; Moon-Sup Lee; Soon-Jae Lee (MDPI AG, 2022-06-01)
      This paper conveys the laboratory investigation of the storage stability of CRM binder as a basic study. The CRM binder was produced through the wet process in the laboratory. The percentages of crumb rubber used for rubberized binder were 5%, 10%, 15% and 20%. The samples were prepared according to ASTM D7173. In order to evaluate the properties of each part of the binders, tests were carried out through the rotational viscosity and viscoelasticity, and the separation index was assessed with the G*/sin δ and %rec. In general, the results of this study revealed that (1) the conditioned CRM binders appeared to have higher viscosity in the bottom part compared to the middle and top parts.; (2) similar to the viscosity results, the CRM binders after conditioning showed the highest G*/sin δ value in the bottom part; (3) from the MSCR test, Jnr and % rec values are observed to have a similar trend with G*/sin δ results, although some of the data were not measured due to the higher load than the DSR test; and (4) it was discovered that the SI from G*/sin δ generally used was suitable for evaluating the storage stability of CRM asphalt binders, compared to the SI from % rec.
    • Laboratory Evaluation of Sustainable PMA Binder Containing Styrene-Isoprene-Styrene (SIS) and Thermoplastic Polyurethane

      Hyun Hwan Kim; Mithil Mazumder; Soon-Jae Lee; Moon-Sup Lee (MDPI AG, 2020-12-01)
      In this study, thermoplastic polyurethane (TPU) and styrene-isoprene-styrene (SIS) were utilized to enhance asphalt binder properties. Superpave asphalt binder tests and multiple stress creep recovery (MSCR) were conducted to evaluate the physical and rheological performance (viscosity, rutting, and cracking properties) of the asphalt binders before and after short-term aging and after the long-term aging process. The results showed that (i) TPU has a positive effect on workability, including the mixing and compaction processes, which was evident from the reduced binder viscosity; (ii) asphalt binders with TPU and SIS showed better rutting resistance compared to the SIS binders without TPU; (iii) the cracking resistance of asphalt binders was found to be improved significantly with the addition of TPU; and (iv) TPU has the potential to be considered as a sustainable polymer modifier for producing bearable asphalt binders by improving rutting and crack resistance without increasing the melting temperature of the asphalt binders.
    • Laboratory Evaluation of the Residue of Rubber-Modified Emulsified Asphalt

      Dongdong Ge; Xiaodong Zhou; Siyu Chen; Dongzhao Jin; Zhanping You (MDPI AG, 2020-10-01)
      Emulsified asphalt has been widely used in various surface treatment methods such as chip seal for low-volume road preservation. Using modified emulsified asphalt made it possible to use chip seal technology on medium- and even high-volume traffic pavements. The main objective of the study is to quantify the residue characteristics of rubber-modified emulsified asphalt and to assess the effectiveness of using crumb rubber to modify emulsified asphalt binder. The four emulsified asphalt residues used the distillation procedure. Then, the rheology characteristics of emulsified asphalt residue were evaluated. The Fourier transform infrared spectroscopy (FTIR) test analyzed the chemical change of emulsified asphalt during the aging procedure. The results indicate that the evaporation method cannot remove all the water in emulsified asphalt. The mass change during the rolling thin film oven (RTFO) process only represented the component change of emulsified asphalt binder residue. Both the high-temperature and low-temperature performance grade of the two emulsified asphalt binders with rubber were lower. The original asphalt binder adopted to emulsification had a crucial influence on the performance of emulsified asphalt. The rubber modification enhanced the property of the emulsified asphalt binder at low temperatures, and the improvement effect was enhanced as the rubber content in the emulsified asphalt was raised. The C=O band was more effective in quantifying the aging condition of the residue. The findings of this study may further advance the emulsified asphalt technology in pavement construction and maintenance.
    • Laboratory Evaluation on Performance of Recycled Asphalt Binder and Mixtures under Short-Term Aging Conditions

      Yuefeng Zhu; Jiawei Zhang; Chundi Si; Tao Yan; Yanwei Li (MDPI AG, 2021-03-01)
      As asphalt materials are exposed to very high temperatures before construction, such as in the transportation stage or the storage stage, short-term aging of asphalt material occurs. At these stages, diffusion or blending between RAP (reclaimed asphalt pavement) binder and virgin binder may occur. In this study, recycled blends, incorporating SBS modified binder, RAP binder and recycling agents, were prepared with incremental RAP binders of up to 40%, and RTFO (Rolling Thin-Film Oven) tests in condition times of 300 and 600 min were conducted on the recycled blends. Characterization tests included Δ<i>T</i><sub>cr</sub>, complex modulus master curve, a G-R (Glover-Rowe) parameter on recycled blends, and dynamic modulus, fracture test, and midpoint bending fatigue tests on mixtures. The Δ<i>T</i><sub>cr</sub> and the G-R parameter results showed that aging time significantly affected the cracking resistance of the recycled blends. Compared to the virgin SBS modified asphalt binder, the recycled blends tended to be more sensitive to the aging process. The complex modulus master curve of binders and the dynamic modulus and phase angle results of mixtures show that the binder/mixtures appear to be stiffer with an increase in the RAP binder dosage. Generally, the low temperature cracking and fatigue cracking resistance of virgin mixtures is better than that of RAP mixtures, especially for high RAP binder dosage mixtures, and longer aging times have a negative impact on the cracking resistance of mixture. However, when we extend RTFO aging time, the higher dosage of RAP mixtures show better cracking resistance than the lower dosage of RAP mixtures. The reason for this could be that the chemical process may occur between the virgin SBS modified asphalt binder and the RAP binder at high temperatures.
    • Laboratory Experimental Laws for the Radon Exhalation of Similar Uranium Samples with Low-Frequency Vibrations

      Zi-qi Cai; Xiang-yang Li; Bo Lei; Jing-fan Yuan; Chang-shou Hong; Hong Wang (MDPI AG, 2018-08-01)
      It is the fact that there are lots of hazard incidents in underground uranium mines caused by radon but in-suit uranium samples were difficult to collect. Based on closed chamber method, three similar samples in different sealed ways were made in a laboratory with different material rations, namely uranium tailings, quartz sand, cement, iron powder and silicon powder to measure the radon concentrations with and without low-frequency vibrations, which was used by the experimental device for low-frequency vibration diffusion of radon. The results showed that the radon exhalation coming from the similar samples was influenced by the low frequency vibration; the results are presented as two-stage variations compared with the blank group. The radon exhalation increased with the rising vibration frequency when the frequency was 50 to 70 Hz, but fell slowly after reaching the peak radon exhalation rate. Analyses of the relations between the rock damage degree, changes in porosity and the occurrence of an inflection point in the radon exhalation rate in the samples found that they also increased when the frequency was between 0 to 80 in sample 3. The maximum porosity of the third samples was about 4.8% with a low-frequency vibration 60 Hz, while the maximum damage degree was about 0.07 at 50 Hz.
    • Laboratory Experiments of Tradable Development Rights: A Synthesis of Different Treatments

      Till Proeger; Lukas Meub; Kilian Bizer (MDPI AG, 2018-06-01)
      Tradable development rights (TDR) are considered by scholars and regulators in various countries as a means of reducing land consumption efficiently. Similar to the development of CO2-certificate trading schemes, the methodology of experimental economics can be used to derive empirical evidence on the core parameters and problems of TDR schemes, thus extending theoretical modelling and evidence from case studies. Building on a common laboratory experimental framework, we discuss results from five distinct experiments that consider mechanisms of allocation, resilience against external shocks, political business cycles, communication and collusion, and risk. These results provide initial empirical directions for the further study and introduction of TDR schemes for managing and reducing environmental issues related to land consumption for building projects.
    • Laboratory Investigation of Compaction Characteristics of Plant Recycled Hot-Mix Asphalt Mixture

      Jiangang Yang; Chen Sun; Wenjie Tao; Jie Gao; Bocheng Huang; Jian Zhang (MDPI AG, 2021-03-01)
      In this study, the compaction characteristics of recycled hot-mix asphalt (RHMA) were evaluated using the void content (<i>VV</i>), compaction energy index (<i>CEI</i>), slope of accumulated compaction energy (<i>K</i>), and lock point (<i>LP</i>). Then, the effects of the compaction parameters, including the gradation of the RHMA, reclaimed asphalt pavement (RAP) content, temperature of gyrations, and number of gyrations, on the compaction characteristics of RHMA were investigated. An orthogonal experiment was designed and the data collected were analyzed via range analysis; then, a regression model was generated relying on a quadratic polynomial. Furthermore, the regression model was used for the comparison and prediction of the mixture’s compactability during the material design. Finally, the compaction mechanism of RHMA was discussed from the perspective of the void content of RAP particles. The results showed that a finer aggregate gradation, a higher gyration temperature, a greater number of gyrations, and a higher RAP content were effective for increasing the compactability of RHMA. The range analysis results suggest that the gradation of RHMA has the greatest influence on compactability, followed by the RAP content. The RAP aggregate cannot diffuse to a new mixture completely, so the remained RAP particle reduces the void content of RHMA. Therefore, a higher RAP content up to 50% can help RHMA to achieve the designed void content with higher efficiency.
    • Laboratory Model Tests of Leachate Drawdown Using Vertical Drainage Wells with Vacuum Pumping in Municipal Solid Waste Landfills with High Leachate Levels

      Xiaobing Xu; Guangyao Li; Da Ni; Cheng Feng; Sifa Xu (MDPI AG, 2022-07-01)
      Municipal solid waste (MSW) landfills in China generally have high leachate mounds, which potentially induce severe geotechnical and environmental issues. In this study, laboratory model tests were carried out to preliminarily investigate the performance of vertical drainage wells accompanied with vacuum pumping (VDW-VP) on leachate drawdown in MSW landfills with high leachate levels. Leachate drawdown tests through VDW-VP under conditions with and without gas injection were performed. Different vacuum pressures (0~−9.5 kPa) were imposed during the tests. Results indicated that the leachate pumping processes for both the two conditions were characterized by a stage of continuous effluent followed by a stage of discontinuous effluent, corresponding to the periods before and after the leachate level in the vertical well dropped to the bottom, respectively. During the stage of continuous effluent, as the vacuum pressure increased, the effluent rate decreased and the leachate level in the vertical well needed a longer time to reach the bottom. During the stage of discontinuous effluent, the leachate level in the MSW gradually approached that in the vertical well. A higher vacuum pressure rendered a larger cumulative leachate pumping volume for the condition with a gas injection, but this was not the case for the condition without a gas injection. In addition, some local pore water pressures were observed to suddenly increase and drop under the condition with the gas injection, attributed to the migration of entrapped gas zones. The increase in vacuum pressure might promote the migration of entrapped gas zones and hence increase the cumulative leachate pumping volume.