Overlimiting Current in Nonuniform Arrays of Microchannels: Recirculating Flow and Anticrystallization.

Overlimiting current (OLC) through electrolytes interfaced with perm-selective membranes has been extensively researched for understanding fundamental nano-electrokinetics and developing efficient engineering applications. This work studies how a network of microchannels in a nonuniform array, which mimics a natural pore configuration, can contribute to OLC. Here, micro/nanofluidic devices are fabricated with arrays of parallel microchannels with nonuniform size distributions, which are faced with a perm-selective membrane. All cases maintain the same surface and bulk conduction to allow probing of the sensitivity only by the nonuniformity. Rigorous experimental and theoretical investigation demonstrates that overlimiting conductance has a maximum value depending on the nonuniformity. Furthermore, in operando visualization reveals that the nonuniform arrays induce flow loops across the microchannel network enhancing advective transport. This recirculating flow eliminates local salt accumulations so that it can effectively suppress undesirable salt crystallization. Therefore, these results can significantly advance not only the fundamental understanding of the driving mechanism of the OLC but also the design rule of electrochemical membrane applications.

Surface Conduction in a Microchannel.

Ionic current through a microchannel has drawn significant attention not only for fundamental electrokinetic research but also for the development of novel micro/nanofluidic applications. Among various ion transport mechanisms, surface conduction, which is a predominant mechanism in micro/nanofluidic devices, has been theoretically characterized based on two-dimensional analysis. However, its infinite axis assumption has become a barrier for direct application in practical micro/nanochannel networks. In this work, we conducted rigorous experiments to include all of the three-dimensional length scales. There, L/ A, the perimeter to area ratio of the microchannel cross-section, came up as a single parameter to quantitatively interpret the surface conductive ion transportation. Overlimiting conductance of microchannel devices increased with larger perimeter, which is equivalent to specific surface area, even with the same cross sectional area. Finally, a micro/nanofluidic diode with a different L/ A value on its forward and reverse channel was demonstrated as a simple application. The analysis presented could provide a practical guideline to design a micro/nanofluidic application.

An Enhanced LoRaWAN Security Protocol for Privacy Preservation in IoT with a Case Study on a Smart Factory-Enabled Parking System.

The Internet of Things (IoT) utilizes algorithms to facilitate intelligent applications across cities in the form of smart-urban projects. As the majority of devices in IoT are battery operated, their applications should be facilitated with a low-power communication setup. Such facility is possible through the Low-Power Wide-Area Network (LPWAN), but at a constrained bit rate. For long-range communication over LPWAN, several approaches and protocols are adopted. One such protocol is the Long-Range Wide Area Network (LoRaWAN), which is a media access layer protocol for long-range communication between the devices and the application servers via LPWAN gateways. However, LoRaWAN comes with fewer security features as a much-secured protocol consumes more battery because of the exorbitant computational overheads. The standard protocol fails to support end-to-end security and perfect forward secrecy while being vulnerable to the replay attack that makes LoRaWAN limited in supporting applications where security (especially end-to-end security) is important. Motivated by this, an enhanced LoRaWAN security protocol is proposed, which not only provides the basic functions of connectivity between the application server and the end device, but additionally averts these listed security issues. The proposed protocol is developed with two options, the Default Option (DO) and the Security-Enhanced Option (SEO). The protocol is validated through Burrows⁻Abadi⁻Needham (BAN) logic and the Automated Validation of Internet Security Protocols and Applications (AVISPA) tool. The proposed protocol is also analyzed for overheads through system-based and low-power device-based evaluations. Further, a case study on a smart factory-enabled parking system is considered for its practical application. The results, in terms of network latency with reliability fitting and signaling overheads, show paramount improvements and better performance for the proposed protocol compared with the two handshake options, Pre-Shared Key (PSK) and Elliptic Curve Cryptography (ECC), of Datagram Transport Layer Security (DTLS).

The influence of accelerometer epoch length on physical activity output in adolescent athletes.

Epoch in accelerometer measurements is an important option that affects the results of physical activity (PA) analysis. Many studies have been conducted to investigate the effect of epoch on PA output in adolescents, but few have been performed on highly active youth athletes. We aimed to examine the differences in energy expenditure and time spent in different activity intensities by applying various epoch lengths in adolescent athletes. The participants of this study comprised 31 male athletes aged 12 to 13 in basketball, soccer, and taekwondo teams. Athletes wore a tri-axial accelerometer attached to the right hip for 6 to 7 consecutive days, including sleeping time. Subsequently, the recorded data from the accelerometer were downloaded using the ActiLife software and analyzed by varying the epoch to 1, 10, 30, and 60 sec. Daily average metabolic equivalents (METs) increased as the epoch increased (F=2.918, P=0.037), showing a significant difference between 1 and 60-sec epochs. As epoch length increased, sedentary (0-1.5 METs) (F=94.001, P=0.000) and high intensity (6 METs and higher) activity time (F=3.536, P=0.017) decreased, while low (1.5-3 METs) (F=173.949, P= 0.000), moderate (3-6 METs) (F=70.792, P=0.000), and moderate-to-vigorous activity (3 METs and higher intensity) (F=34.683, P=0.000) times increased. Comparing PA among adolescent athletes by varying epoch settings of accelerometers revealed differences in PA levels and time spent in different activity intensities. Future studies should consider the characteristic changes in the PA outputs according to the epoch length in very active adolescent athletes.

Double-Layered Polymer Microcapsule Containing Non-Flammable Agent for Initial Fire Suppression.

Fire in energy storage systems, such as lithium-ion batteries, has been raised as a serious concern due to the difficulty of suppressing it. Fluorine-based non-flammable agents used as internal substances leaked through the fine pores of the polymer outer shell, leading to a degradation of fire extinguishing performance. To improve the durability of the fire suppression microcapsules and the stability of the ouster shell, a complex coacervation was used, which could be microencapsulated at a lower temperature, and the polymer shell was coated with urea-formaldehyde (UF) resin. The outermost UF resin formed elaborate bonds with the gelatin-based shell, and thus, the structure of the outer shell became denser, thereby improving the loss resistance of the inner substance and thermal stability. The double-layered microcapsules had an average particle diameter of about 309 µm, and a stable outer shell formed with a mass loss of 0.005% during long-term storage for 100 days. This study confirmed that the double-layered microcapsules significantly improved thermal stability, resistance to core material loss, core material content and fire suppression performance compared to single wall microcapsules. These results indicated that the double-layered structure was suitable for the production of microcapsules for initial fire suppression, including highly volatile non-flammable agents with a low boiling point.

Pulsed electric field-assisted overlimiting current enhancement through a perm-selective membrane.

Overlimiting current through a perm-selective membrane has been actively researched not only for the fundamental advancement of electrokinetics but also for energy/environmental applications such as electrodialysis, fuel cells, etc. In particular, various strategies were reported for the enhancement of overlimiting current because these applications demand efficient mass transport through the membrane. In this work, we presented in operando visualization and rigorous numerical study for the overlimiting current density enhancement using a pulsed electric field which is one of the most cost-effective parameters to be externally controlled. We clearly demonstrated that the current density had a peak value as a function of the pulse frequency and would suggest its correlation to a concentration profile and diffusion relaxation time ([small tau, Greek, tilde]diff). As the pulse frequency was chosen which is similar to ([small tau, Greek, tilde]diff)-1, the concentration profiles (i.e. established current paths) were maintained even in off-state due to remnant current paths helping the fast ion transportation. The fundamental evidence presented in this work would provide a strategical design of a perm-selective membrane system for a higher mass transportation efficiency.

The Effect of Hamstring Relaxation Program on Headache, Pressure Pain Threshold, and Range of Motion in Patients with Tension Headache: A Randomized Controlled Trial.

The purpose of this study was to determine if the severity of headache is reduced by decreasing hamstring tension in patients with tension headache. Thirty patients participated in this study. The participants were randomly allocated to two groups: hamstring relaxation program (HR) group (n = 15) and control group (n = 15). The participants in the HR group participated in a HR program for 25 min per day, three times per week, for a period of 4 weeks, and the control group participated in an electrotherapy for 25 min per day, three times per week, for a period of 4 weeks. Both groups participated in a self-myofacial release for 5 min per day, three times per week, for a period of 4 weeks. Headache was evaluated using the headache impact test (HIT-6) and visual analog scale (VAS). The pain pressure threshold (PPT) was evaluated using a digital pressure algometer. The range of motion (ROM) was evaluated using a goniometer and two special tests: straight leg raise test (SLRT) and popliteal angle test (PAT). The two groups showed no significant differences in terms of age, sex, height, and weight. The VAS and HIT-6 scores (p < 0.05) and neck and hamstring PPT showed significant improvements (p < 0.05). Neck flexion ROM and SLRT and PAT scores showed significant improvements (p < 0.05) in both groups, and the HR group showed significantly more improvements than the control group. This study confirmed that the HR program has positive effects on tension headache and is a good intervention for alleviating headaches in patients with tension headache.

Elimination of pseudo-negative conductance by coercive steady state in perm-selective ion transportation.

Ion concentration polarization (ICP) has drawn unprecedented attention due to its new underlying physics and engineering applications such as biomolecular preconcentrator and electrofluidic desalination. Typically, the current-voltage characteristic of ICP has three distinctive regimes with a positive slope in all regimes, but an unintentional negative slope ("overshoot current") was often observed in the Ohmic/limiting regime. This phenomenon impeded an exact estimation of electrokinetic properties of the ICP platform. Therefore, in this work, we eliminated overshoot current by limiting the length of the diffuse layer using a coercive injection of a fresh electrolyte solution. Both the visualization of ICP layer propagation and the measurement of current-voltage characteristics verifying the time for reaching the steady state within an effective length of a microchannel played a critical role. The most relevant parameter was shown to be the diffusion relaxation time which was directly correlated with the sweep rate of an external voltage. Using this new measurement platform, one can significantly reduce the time and labor for the electrokinetic studies and applications based on them.

Quantifying the pH shift induced by selective anodic electrochemical reactions in the ion concentration polarization phenomenon.

Recently, the ion concentration polarization (ICP) phenomenon has been actively utilized for low abundance biomolecular preconcentration applications. Since ICP significantly rearranges the ion distribution near a permselective membrane, its detailed investigation should be conducted for developing efficient platforms. In particular, proton transport through the membrane critically affects the pH of sample solutions so that continuous monitoring or batch measurement of pH is the priority task to be carried out. Moreover, electrochemical reactions have been overlooked, even though an overpotential is applied to preconcentrate a sample under physiological conditions, and the electrodes are in direct contact with the sample biomolecules. In this work, we experimentally visualized and directly measured how the electrochemical reaction dominated the preconcentration efficiency using two types of electrode configurations; large exposed electrode area (LEEA) and small exposed electrode area (SEEA). Interestingly, significant pH variation was confirmed only in the case of SEEA. As a result, the BSA preconcentration was impeded within a short period in the case of SEEA, but loss-free preconcentration was achieved in the case of LEEA. Therefore, one should pay careful attention to the electrode design of electrokinetic operation, especially when pH-sensitive biomolecules are involved.

Acquisition of heat shock tolerance by regulation of intracellular redox states.

In the yeast Saccharomyces cerevisiae, a mild heat treatment strongly induces Hsp104p which provides acquisition of thermotolerance. The mechanism by which Hsp104p protects cells from the severe heat shock has not yet been completely elucidated. In this study, a pivotal role of Hsp104p as an efficient scavenger of the reactive oxygen species (ROS) is investigated. In our previous study, we reported that Hsp104p acted as a regulator in the mitochondrial respiration pathway. In this report, the recombinant wild-type and hypersensitive ras mutants (ira2Delta) with the extrachromosomal plasmids wild-type and mutant hsp104 genes were studied. The resulting strains successfully expressed both wild-type and mutant Hsp104p and showed the thermotolerance phenotype in the strain with the functional wild-type Hsp104p expressed. Upon treatment with H2O2 and menadione, the strains with the functional Hsp104p expressed showed higher survival rates than the other mutants, indicating the protective role of Hsp104p from the oxidative stress. Fluorescence measurement of the oxidation-dependent probe, 2',7'-dichlorofluoroscein diacetate (H2DCFDA), also indicated that Hsp104p significantly reduced the amount of ROS. Resistance to the oxidative stress was independent of the amount of the glutathione in the hyperactivated ras mutants. Taken all together, this study confirms that Hsp104p plays a crucial role in keeping cells from being damaged by the oxidative stress, thus acting as a modulator of the intracellular redox state.