Metal-organic framework based on hinged cube tessellation as transformable mechanical metamaterial

Mechanical metamaterials exhibit unusual properties, such as negative Poisson???s ratio, which are difficult to achieve in conventional materials. Rational design of mechanical metamaterials at the microscale is becoming popular partly because of the advance in three-dimensional printing technologies. However, incorporating movable building blocks inside solids, thereby enabling us to manipulate mechanical movement at the molecular scale, has been a difficult task. Here, we report a metal-organic framework, self-assembled from a porphyrin linker and a new type of Zn-based secondary building unit, serving as a joint in a hinged cube tessellation. Detailed structural analysis and theoretical calculation show that this material is a mechanical metamaterial exhibiting auxetic behavior. This work demonstrates that the topology of the framework and flexible hinges inside the structure are intimately related to the mechanical properties of the material, providing a guideline for the rational design of mechanically responsive metal-organic frameworks

Channel-Aware Congestion Control in Vehicular Cyber-Physical Systems

In vehicular cyber-physical systems, cars are connected to create a mobile network called a vehicular ad hoc network (VANET) to perform various functions, including improved awareness of the surrounding environment. Moving vehicles continually broadcast beacon signals containing information such as position, heading, acceleration, steering angle, vehicle size, and accident notification. However, channel congestion in dense traffic conditions adversely affects network performance. To resolve congestion in VANETs, several works in the literature have studied congestion control. However, they have considered packet loss only as an indication of channel congestion regardless of channel condition. In this paper, we present a channel-aware congestion control algorithm (CACC) that controls the transmission power and data rate. We take into account the received signal strength (RSS) when diagnosing packet loss to determine channel conditions, such as severe fading or channel congestion. In the case of severe fading, we decrease the data rate for a more robust modulation and coding scheme. Additionally, we adjust the transmission power to maintain a desirable packet error rate. Our simulation results show that CACC significantly outperforms other distributed congestion control algorithms by reducing the packet loss rate and increasing the packet delivery ratio.1

Correction to: Moth-eye Structured Polydimethylsiloxane Films for High-Efficiency Perovskite Solar Cells

In the original publication, the equal contribution information was not available in first page of the article

Flake Orientation in Injection Molding of Pigmented Thermoplastics

In the present work, experimental studies are carried out to understand orientation kinematics of pigment flakes during the injection molding process. The injection molding experiments are carried out using ABS resin compounded with aluminum flakes. Thin specimens are sliced off from the injection molded sample, and then the orientation distribution is observed using transmitted microscopy. Generally, the microscopic result shows a sandwich structure where the orientation state near the mid-plane differs significantly from that around the surface. Particularly at the weldline region, locally different orientation is observed near the part surface, which is the result of fountain flow at the melt front. Also the effect of mold temperature on the flake orientation is presented

Angelica acutiloba

We examined the protective effects of Angelica acutiloba Kitagawa (AAK) extract on a murine model of acute experimental colitis. Colitis was induced by 4% dextran sulfate sodium (DSS) in the drinking water of male C57BL/6 mice, for 7 consecutive days. Oral administration of AAK extract (500 mg/kg/day) significantly alleviated DSS-induced symptoms such as anorexia, weight loss, events of diarrhea or bloody stools, and colon shortening. Histological damage was also ameliorated, as evidenced by the architectural preservation and suppression of inflammatory cell infiltration in colonic samples. Treatment improved the colonic mRNA expression of different inflammatory markers: cytokines, inducible enzymes, matrix metalloproteinases, and tight junction-related proteins. In the isolated serum, IgE levels were downregulated. Collectively, these findings indicate the therapeutic potentials of AAK as an effective complementary or alternative modality for the treatment of ulcerative colitis

Virtual Surface Characteristics of a Tactile Display Using Magneto-Rheological Fluids

Virtual surface characteristics of tactile displays are investigated to characterize the feeling of human touch for a haptic interface application. In order to represent the tactile feeling, a prototype tactile display incorporating Magneto-Rheological (MR) fluid has been developed. Tactile display devices simulate the finger’s skin to feel the sensations of contact such as compliance, friction, and topography of the surface. Thus, the tactile display can provide information on the surface of an organic tissue to the surgeon in virtual reality. In order to investigate the compliance feeling of a human finger’s touch, normal force responses of a tactile display under various magnetic fields have been assessed. Also, shearing friction force responses of the tactile display are investigated to simulate the action of finger dragging on the surface. Moreover, different matrix arrays of magnetic poles are applied to form the virtual surface topography. From the results, different tactile feelings are observed according to the applied magnetic field strength as well as the arrays of magnetic poles combinations. This research presents a smart tactile display technology for virtual surfaces

Study on fatigue experiment for transverse butt weldsunder 2G and 3G weld positions

ABSTRACTAlthough the transverse butt weld method with ceramic backing strip has been widely used in various industrial fields for its fabricational convenience, it is rarely used in offshore industries since the fatigue strength of the weld joint has not been proved sufficiently. This study conducted fatigue tests for series of butt weld specimens with horizontal (2G) and vertical (3G) welding positions in order to verify the fatigue strength compared to S-N curve by DNV (Det Norske Veritas), IIW (International Institute of Welding) and Eurocode 3. The difference of the 2G specimens and the 3G specimens are investigated in terms of angular distortion and the effect on the fatigue strength are analyzed

A Robot Operating System Framework for Secure UAV Communications

To perform advanced operations with unmanned aerial vehicles (UAVs), it is crucial that components other than the existing ones such as flight controller, network devices, and ground control station (GCS) are also used. The inevitable addition of hardware and software to accomplish UAV operations may lead to security vulnerabilities through various vectors. Hence, we propose a security framework in this study to improve the security of an unmanned aerial system (UAS). The proposed framework operates in the robot operating system (ROS) and is designed to focus on sev-eral perspectives, such as overhead arising from additional security elements and security issues essential for flight missions. The UAS is operated in a nonnative and native ROS environment. The performance of the proposed framework in both environments is verified through experiments. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.1

Effects of pair freeze-out on photon distributions in BBN epoch

We investigate the evolution of non-extensivity in the photon distribution during the Big Bang Nucleosynthesis (BBN) epoch using Tsallis statistics. Assuming a minimal deviation from the Planck distribution, we construct the perturbed Boltzmann equation for photons, including the collision terms for pair creation and annihilation processes. We analyze the possibility that these collisions could cause a slight increase in the number of high-frequency photons within the BBN era, and consequently, the primordial plasma might be temporarily placed in a state of chemical non-equilibrium. We also discuss the restoration of the photon distribution to an equilibrium state as the Universe enters the matter-dominated era. These findings, which suggest possible changes in the photon distribution during the epoch between the BBN and the recombination, offer insights that support the previously proposed ansatz solution to the primordial lithium problem in arXiv:1812.09472.Comment: 9 pages, 2 figure

A New Doherty Combiner with Wide Bandwidth for Magnitude and Phase Balance Compensation

This paper proposes a novel Doherty combiner that uses a series and parallel resonant circuit for wideband. Unlike conventional combiners, the aim of the proposed combiners is to extend bandwidth for not only the magnitude bandwidth, but also phase balance by employing series and parallel resonant circuits at the output impedance of the peaking amplifier. Considering the load impedance of the peaking amplifier, the Doherty combiners were analyzed in the theory of this study by deriving the series and parallel resonant circuit values. The output phase balances are determined for the targeted bandwidth to achieve uniform phase balance in the proposed combiner I using a series resonator. For better magnitude bandwidth, the slope of reflection coefficient (Γ) at port 3 in the combiner II using series resonator was derived using the derivative of Γ with respect to ω. Experimental results show that the proposed combiner I has 63.5% magnitude fractional bandwidth (FBW) and 118% FBW with the phase balance at ±2.5°. The proposed combiner II also has 85% magnitude FBW and 118% FBW with the phase balance at ±2.5°