Guidance to assess ventilation performance of a classroom based on CO2 monitoring

Since the COVID-19 pandemic, the ventilation of school buildings has attracted considerable attention from the general public and researchers. However, guidance to assess the ventilation performance in classrooms, especially during a pandemic, is still lacking. Therefore, aiming to fill this gap, this study conducted a full-scale laboratory study to monitor the CO2 concentrations at 18 locations in a classroom setting under four different ventilation regimes. Additionally, a field study was carried out in two Dutch secondary schools to monitor the CO2 concentrations in the real classrooms with different ventilation regimes. Both the laboratory and field study findings showed that CO2 concentrations varied a lot between different locations in the same room, especially under natural ventilation conditions. The outcome demonstrates the need of monitoring the CO2 concentration at more than one location in a classroom. Moreover, the monitored CO2 concentration patterns for different ventilation regimes were used to determine the most representative location for CO2 monitoring in classrooms. For naturally ventilated classrooms, the location on the wall opposite to windows and the location on the front wall (nearby the teacher) were recommended. For mechanically ventilated classrooms, one measurement location seemed enough because CO2 was well-mixed under this ventilation regime.

Analysis of Tube-to-Tubesheet Welding in Carbon Steel Heat Exchangers of a Double Plate Header Box

The rear wall of the header box serves as a tubesheet in heat exchangers of double plate header box. Tube-to-tubesheet welding must be performed using orbital Gas Tungsten Arc Welding (GTAW) with a head extension, which is passed through the corresponding hole in the front wall (plugsheet) of the header box, where the welding machine is supported. In this project, the effect of parallelism deviations between the plugsheet and the tubesheet of carbon steel header box is analyzed to evaluate its influence on the quality of the tube-to-tubesheet welding. Welded tube (SA-210 Gr. A1) to tubesheet (SA-516 Gr. 70) coupons are manufactured simulating the parallelism deviations previously analyzed in two double plate header boxes of air-cooled heat exchangers using two different preheating temperatures. Macrographic analysis is performed in order to evaluate the weld penetration (minimum leak path) and length of the weld leg in tube-to-tubesheet joints. The results obtained show important variations in those parameters when the parallelism deviations are equal to or greater than −1 mm over the theoretical distance as well as when the distance approaches +1 mm or more. Finally, the incorporation of dimensional controls prior to the welding process is discussed and the implementation of improvements in orbital GTAW equipment is recommended as an optimal solution for this kind of heat exchangers.

Elastic Bottom Effects on Ocean Water Wave Scattering by a Composite Caisson-Type Breakwater Placed Upon a Rock Foundation in a Two-Layer Fluid

The association of oblique surface gravity waves with a caisson-type multi-chamber porous breakwater fitted with a perforated front wall in a two-layer fluid is studied in finite ocean depth with an elastic bottom. This study focuses on the influence of porous parameters of the interface-piercing structure on wave attenuation in surface and interfacial modes. The flexural gravity wave motion establishes the influence of the elastic bottom. The reflection coefficients for waves in both modes are evaluated to show their effects on the free surface and interface elevations and the waveloads. Consequently, the appropriateness of various configurations of the structure on the wave scattering is studied. Due to wave dissipation by the structure, less waveload is detected on the stiff wall and less elevation is noticed in the porous zone. The structure’s multi-chamber division allows it to have more dissipative and reflective properties. Adjustment of the structure’s height, breadth, and porous parameter leads to achieving good amount of wave reflection and maximum energy dissipation. An optimal width can be determined for a suitable configuration of the structure so that a breakwater can be built with an acceptable level of reflection and dissipation characteristics. The shear force and bottom deflection show how elastic parameters of the sea-floor affect wave scattering.

Extending FMC Based Ultrasonic Imaging Practices to Smaller Wall Thickness

During the construction of pipelines for the transportation of oil and gas, the inspection of girth welds is a critical step to ensure the integrity and thereby the safety and durability of the pipeline. In this paper we present an advanced technology ‘IWEX’ for the non-destructive testing of welds based on 2D and 3D ultrasonic imaging. This technology allows for safe, fast, and accurate inspection whereby the results are presented comprehensively. This will be illustrated with results from a recent project. The IWEX technology is based on an ultrasonic inspection concept, whereby ‘fingerprints’ of ultrasonic signals are recorded, also referred to as ‘full matrix capture’ (FMC) data. Then, an image area is defined, consisting out of pixels over an area large enough to cover the inspection volume. With the FMC data, image amplitudes are calculated for each pixel so that the shape of geometry (back wall, front wall, cap, and root) and possible indications are revealed. As opposed to traditional ultrasonic testing strategies, the detection and sizing of indications is therefore less dependent on its orientation. The project concerned the inspection of J and V welds from a 5.56″ diameter carbon steel pipe with an 8.4mm wall thickness. The wall thickness is relatively thin compared to common inspection scopes. Therefore, the inspection set-up was adapted, and procedural changes were proposed. Consequently, additional validation efforts were required to demonstrate compliance with the required inspection standard; DNVGL-ST-F101: 2017. As part of this, welds were scanned with seeded indications and the reported locations were marked for macro slicing under witnessing of an independent representative from DNVGL. The resulting images from the indications in the welds showed great detail with respect to the position, orientation and height of the indications. A quantitative comparison with the results from the macro slices was performed, including a statistical analysis of the height sizing and depth positioning accuracies. From the analysis, it could be observed that the expected improvements with respect to the resolution and sizing accuracy were indeed achieved. Thereby, the procedure has proven to be adequate for the inspection of carbon steel girth welds within the thin wall thickness range (~6mm to ~15mm). The IWEX technology is a member of the upcoming inspection strategy based on imaging of ultrasonic FMC data. This strategy can be considered as the next step in the evolution of inspection strategies after phased array inspection. The IWEX technology has been witnessed and qualified by independent 3rd parties like DNVGL, this makes the IWEX technology unique in its kind and it opens opportunities for further acceptance in the industry and other inspection applications.

Mental imagery of object motion in weightlessness

Mental imagery represents a potential countermeasure for sensorimotor and cognitive dysfunctions due to spaceflight. It might help train people to deal with conditions unique to spaceflight. Thus, dynamic interactions with the inertial motion of weightless objects are only experienced in weightlessness but can be simulated on Earth using mental imagery. Such training might overcome the problem of calibrating fine-grained hand forces and estimating the spatiotemporal parameters of the resulting object motion. Here, a group of astronauts grasped an imaginary ball, threw it against the ceiling or the front wall, and caught it after the bounce, during pre-flight, in-flight, and post-flight experiments. They varied the throwing speed across trials and imagined that the ball moved under Earth’s gravity or weightlessness. We found that the astronauts were able to reproduce qualitative differences between inertial and gravitational motion already on ground, and further adapted their behavior during spaceflight. Thus, they adjusted the throwing speed and the catching time, equivalent to the duration of virtual ball motion, as a function of the imaginary 0 g condition versus the imaginary 1 g condition. Arm kinematics of the frontal throws further revealed a differential processing of imagined gravity level in terms of the spatial features of the arm and virtual ball trajectories. We suggest that protocols of this kind may facilitate sensorimotor adaptation and help tuning vestibular plasticity in-flight, since mental imagery of gravitational motion is known to engage the vestibular cortex.

Influence of the Perforated Rate on the Wave Attenuation Performance of Perforated Caisson Set on a Rubble Bed

A Jarlan-type perforated caisson (JTPC) was an important form of structure in offshore and coastal engineering and its wave attenuation performance was greatly affected by μ (the perforated rate). In the present research, a numerical model based on VARANS equations was tested by comparing the simulation results with physical experiments and then adopted to study the effect of a larger range of μ on wave attenuation performance which included both the horizontal wave forces and the reflection coefficients. Conclusions were drawn that the total horizontal wave force and the reflection coefficient both tended to decrease and then increase with increasing μ; when the reflection coefficient reached its minimum value as about μ=0.2, the wave force at the seaward side of the perforated front wall tended to be equal to that at the solid rear wall; the total horizontal wave force reached its minimum value as about μ=0.3.

Scar Tissue after a Cesarean Section—The Management of Different Complications in Pregnant Women

The definition of a cesarean scar pregnancy (CSP) is the localization of the gestational sac (GS) in the cicatrix tissue, which is created in the front wall of the uterus after a previous cesarean section (CS). The worldwide prevalence of CSP has been growing rapidly. However, there are no general recommendations regarding prophylaxis and treatment of the abnormalities of the anterior wall of the uterus discovered in a non-pregnant myometrium, or how to deal with existing cases of CSP. We present the latest knowledge, a holistic approach to the biology, histology, imaging, and management concerning post-CS scars based on our cases, which were treated in the Department of Pregnancy and Pathology of Pregnancy in the Medical University of Lublin, Poland. In our study, we present images of tissue samples of areas with a cicatrix in the uterus, and ultrasound and MRI images of CSP. We discuss the advances in the biology of the post-CS scar tissue, the prevention techniques used to repair the scar defect (niche) before the pregnancy, and the treatment of different complications of CSP, such as the rupture of the gravid uterus or the dehiscence of the myometrium.

Numerical and Geometrical Analysis of the Onshore Oscillating Water Column Wave Energy with a Ramp

This study is about a two-dimensional numerical analysis of the influence of a ramp in front on an oscillating water column wave energy converter (OWC-WEC). The main purpose was to evaluate, numerically and geometrically, the effect of using a ramp variation in relation to the frontal wall on the hydropneumatic power of the OWC-WEC. The constructal design method was applied for geometric analysis. The problem had a geometric constraint: the area of the ramp (A2) and two degrees of freedom: H2 / L2 (ratio of the height and length of the ramp) and L4 (the distance of the ramp concerning the OWC-WEC front wall). In numerical simulations, the equations of conservation of mass, momentum, and an equation for the transport of volumetric fraction were solved using the finite volume method (FVM). The multiphase model volume of fluid (VOF) was applied for the air-water interaction. Thus, the increase in the H2/L2 ratio resulted in a decrease of the root mean square (RMS) of the available hydropneumatic power (Phyd). By varying the distance L4, the better case was = 6 m and / = 0.025 and the worst case was = 1 m and / = 0.2. The relative difference between the better RMS Phyd = 150.7957 W and the worst Phyd = 73.1164 W reached up to a hundred and six percent.

Exploration of Comparative Concepts in the Ethnomathematics of The Buton Traditional House

The Buton community has practiced mathematical culture in the form of a Buton traditional house called banua tadha (right house). The purpose of this study was to explore the comparative concepts in the ethnomathematics of the Buton traditional house. This research is qualitative research with an ethnographic approach. The results of this study indicate that every Buton traditional house contains several comparative concepts in the ethnomathematical: (1) the width of the door and the width of the stairs, (2) the walls of the house and the tutumbu, (3) the width of the house and tutumbu, (4) wall and pillar heights, (5) the height of the bhate and the length of the limana bathe, (6) the height of the front wall to the height of the side walls, (7) the width of the stair post with the size of the rungs of the stairs, and (8) wall height and house pole height, and (9) the shape of a right triangle formed by a crutch (konta), a pole (ariy), and a buffer (tadha). These comparisons can be used in learning mathematics to pass on the ethnomathematical local wisdom of the Buton traditional house.