An Experimental and Analytical Study on the Deflection Behavior of Precast Concrete Beams with Joints

The use of precast concrete modular construction in the replacement and rebuilding of old structures has recently increased. However, the joints between modules in this type of construction exhibit special behavior that should be considered when analyzing the behavior of modular members. Both stability and serviceability should be studied; however, existing research has only addressed the former. Research regarding serviceability, involving deflection and crack development and propagation, is lacking. This study considers the difference in strength between on-site cast and precast segmental concrete to accurately evaluate the deflection of precast concrete flexural members with joints within the lapped splice. In addition, to reflect an initial crack, the deflection is calculated and evaluated by reflecting the effect of tension-stiffening and subsequently redefining the attached transmission lengths of the left and right sides of the cracked surface as a new cracked region. As a result of explicitly including joint behavior which is considered attached transmission length and characteristic by concrete strength, a more accurate calculation of deflection is developed

Effect of the carbon nanotube type on the thermoelectric properties of CNT/Nafion nanocomposites

The effect of different carbon nanotube (CNT) types on the thermoelectric performance of CNT/polymer nanocomposites was studied. Three different kinds of CNTs, single( SWCNTs), few-(FWCNTs) and multi-walled CNTs (MWCNTs), were effectively dispersed in an aqueous solution of Nafion. The electrical properties of the CNT/Nafion nanocomposites were primarily affected by the CNTs since the Nafion acts as an electrically non-conducting matrix, while the thermal conductivity of the nanocomposites was dominated by the Nafion mainly due to weak van der Waals interaction. In this way, electrical and thermal transport can be separated. In all three types of CNTs, both the electrical conductivity and Seebeck coefficient increased as the concentration of CNTs was increased. While the electrical conductivity depends on the type of CNT, the behavior of the Seebeck coefficient was relatively insensitive of the CNT type at high CNT loading. This indicates that high-energy-charges can participate in transport processes irrespective of the type of CNT. It is suggested that FWCNTs and MWCNTs are preferred over SWCNTs in CNT/Nafion nanocomposites for thermoelectric applications

High performance H2O2 production achieved by sulfur-doped carbon on CdS photocatalyst via inhibiting reverse H2O2 decomposition

Solar production of hydrogen peroxide (H2O2) from oxygen gas and water using photocatalysts is a safe, cost-effective, and eco-friendly method. However, the development of efficient photocatalysts has been impeded by their high decomposition rate of photogenerated H2O2 on the surface of photocatalysts. Here we report CdS/sulfur-doped carbon nanocomposites prepared by adopting a Cd- and S-containing metal-organic framework as a precursor. The intimate contact between the two components provoked their synergetic effect for much better H2O2 production performance than that of commercial CdS, where the hydrophobic sulfur-doped carbon prevent the approach of H2O2 and suppress its decomposition. Resultingly, it recorded H2O2 concentration of 17.1 mM under visible light irradiation in KOH solution with 2-propanol as a hole scavenger, which is the highest value among all the reported photocatalysis systems. This value is sufficiently high to be directly utilized in area of bleaching and acidic waste treatments

Dry Transient Electronic Systems by Use of Materials that Sublime

The recent emergence of materials for electronic systems that are capable of programmable self-destruction and/or bio/eco-resorption creates the potential for important classes of devices that cannot be easily addressed using conventional technologies, ranging from temporary biomedical implants to enviromentally benign environmental monitors to hardware secure data systems. Although most previous demonstrations rely on wet chemistry to initiate transient processes of degradation/decomposition, options in "dry transient electronic systems" could expand the range of possible uses. The work presented here introduces materials and composite systems in which sublimation under ambient conditions leads to mechanical fragmentation and disintegration of active devices upon disappearance of a supporting substrate, encapsulation layer, interlayer dielectric and/or gate dielectric. Examples span arrays of transistors based on silicon nanomembranes with specialized device designs to solar cells adapted from commercial components

Dry Transient Electronic Systems by Use of Materials that Sublime

The recent emergence of materials for electronic systems that are capable of programmable self-destruction and/or bio/eco-resorption creates the potential for important classes of devices that cannot be easily addressed using conventional technologies, ranging from temporary biomedical implants to enviromentally benign environmental monitors to hardware secure data systems. Although most previous demonstrations rely on wet chemistry to initiate transient processes of degradation/decomposition, options in "dry transient electronic systems" could expand the range of possible uses. The work presented here introduces materials and composite systems in which sublimation under ambient conditions leads to mechanical fragmentation and disintegration of active devices upon disappearance of a supporting substrate, encapsulation layer, interlayer dielectric and/or gate dielectric. Examples span arrays of transistors based on silicon nanomembranes with specialized device designs to solar cells adapted from commercial components

Three-Dimensional Silicon Electronic Systems Fabricated by Compressive Buckling Process

Recently developed approaches in deterministic assembly allow for controlled, geometric transformation of two-dimensional structures into complex, engineered three-dimensional layouts. Attractive features include applicability to wide ranging layout designs and dimensions along with the capacity to integrate planar thin film materials and device layouts. The work reported here establishes further capabilities for directly embedding high-performance electronic devices into the resultant 3D constructs based on silicon nanomembranes (Si NMs) as the active materials in custom devices or microscale components released from commercial wafer sources. Systematic experimental studies and theoretical analysis illustrate the key ideas through varied 3D architectures, from interconnected bridges and coils to extended chiral structures, each of which embed n-channel Si NM MOSFETs (nMOS), Si NM diodes, and p-channel silicon MOSFETs (pMOS). Examples in stretchable/deformable systems highlight additional features of these platforms. These strategies are immediately applicable to other wide-ranging classes of materials and device technologies that can be rendered in two-dimensional layouts, from systems for energy storage, to photovoltaics, optoelectronics, and others. © 2018 American Chemical Society.1

Binodal, wireless epidermal electronic systems with in-sensor analytics for neonatal intensive care

Existing vital sign monitoring systems in the neonatal intensive care unit (NICU) require multiple wires connected to rigid sensors with strongly adherent interfaces to the skin. We introduce a pair of ultrathin, soft, skin-like electronic devices whose coordinated, wireless operation reproduces the functionality of these traditional technologies but bypasses their intrinsic limitations. The enabling advances in engineering science include designs that support wireless, battery-free operation; real-time, in-sensor data analytics; time-synchronized, continuous data streaming; soft mechanics and gentle adhesive interfaces to the skin; and compatibility with visual inspection and with medical imaging techniques used in the NICU. Preliminary studies on neonates admitted to operating NICUs demonstrate performance comparable to the most advanced clinical-standard monitoring systems. Copyright © 2019, American Association for the Advancement of Science.1