Infrared Spectroscopy of Organoclays Synthesized with the Surfactant Octadecyltrimethylammonium Bormide

Infrared spectroscopy using a smart endurance single bounce diamond ATR cell has been used to study the changes in the spectra of the surfactant octadecyltrimethylammonium bromide upon intercalation into a sodium montmorillonite. The wavenumbers of bands attributed to CH stretching and bending vibrations in general decrease as the concentration of the surfactant measured in terms of the cation exchange capacity (CEC) up to 1.0 CEC. After this point the bands increase approaching a value the same as that of the surfactant. Significant changes occur in the HCH deformation modes of the methyl groups of the surfactant. These changes are attributed to the methyl groups locking into the siloxane surface of the montmorillonite. Such a concept is supported by changes in the SiO stretching bands of the montmorillonite siloxane surfac

A survey of sag monitoring methods for power grid transmission lines

The transmission line is a fundamental asset in the power grid. The sag condition of the transmission line between two support towers requires accurate real-time monitoring in order to avoid any health and safety hazards or power failure. In this paper, state-of-the-art methods on transmission line sag monitoring are thoroughly reviewed and compared. Both the direct methods that use the direct video or image of the transmission line and the indirect methods that use the relationships between sag and line parameters are investigated. Sag prediction methods and relevant industry standards are also examined. Based on these investigation and examination, future research challenges are outlined and useful recommendations on the choices of sag monitoring methods in different applications are made

Biocompatible magnesium alloys for hard tissue engineering

 Novel Mg-Zr-Sr and Mg-1Zr-2Sr-xDy/yHo alloys have recently been developed for use as biodegradable implant materials. These alloys are recommended to be promising biodegradable implant materials as they have enhanced corrosion resistance and excellent biocompatibility

Security enhancement using a novel two-slot cooperative NOMA scheme

In this letter, we propose a novel cooperative non-orthogonal multiple access (NOMA) scheme to guarantee the secure transmission of a specific user via two time slots. During the first time slot, the base station (BS) transmits the superimposed signal to the first user and the relay via NOMA. Meanwhile, the signal for the first user is also decoded at the second user from the superimposed signal due to its high transmit power. In the second time slot, the relay forwards the signal to the second user while the BS retransmits the signal for the first user as interference to disrupt the eavesdropping. Due to the fact that the second user has obtained the signal for the first user in the first slot, the interference can be eliminated at the second user. To measure the performance of the proposed cooperative NOMA scheme, the outage probability for the first user and the secrecy outage probability for the second user are analyzed. Simulation results are presented to show the effectiveness of the proposed scheme

Multiple UAVs as relays : multi-hop single link versus multiple dual-hop links

Unmanned aerial vehicles (UAVs) have found many important applications in communications. They can serve as either aerial base stations or mobile relays to improve the quality of services. In this paper, we study the use of multiple UAVs in relaying. Considering two typical uses of multiple UAVs as relays that form either a single multi-hop link or multiple dual-hop links, we first optimize the placement the UAVs by maximizing the end-to-end signal-to-noise ratio for three useful channel models and two common relaying protocols. Based on the optimum placement, the two relaying setups are then compared in terms of outage and bit error rate. Numerical results show that the dual-hop multi-link option better than the multi-hop single link option when the air-to-ground path loss parameters depend on the UAV positions. Otherwise, the dual-hop option is only better when the source-to-destination distance small. Also, decode-and-forward UAVs provide better performances than amplify-and-forward UAVs. The investigation also reveals the effects of important system parameters on the optimum UAV positions and the relaying performances to provide useful design guidelines

Studies on the effect of Celastrus orbiculatus (Celastraceae) extract on chemosensitivity of liver cancer cells via Wnt/β-catenin pathway

Purpose: To examine the efficacy of Celastrus orbiculatus extract (COE) on the chemosensitivity of liver cancer (LC) cells and its mechanism of action.Methods: Hep G2/ADM cells in the logarithmic growth phase were assigned to a control group (no treatment for cell culture medium only) and a study group (120 μg/ml COE added to the culture medium). After 48 h of incubation, the biological responses were compared. The study group wasdivided into groups A and B, while control group was divided into groups C and D, with 1 μmol/L XAV939 added in groups A and C. Cell proliferation, cell invasion, cell apoptosis rate, and apoptosis protein in the four groups were evaluated.Results: The study group showed significantly lower values in terms of cell proliferation and cell invasiveness (p < 0.05) and a higher apoptotic rate than the control group (p < 0.05)). The study group also demonstrated an elevated pro-apoptotic protein Bax level and a declined anti-apoptotic protein Bcl-2  level. In contrast to group B, the proliferation and invasiveness of Hep G2/ADM cells in group A treated with the inhibitor, XAV939, were significantly lower (p < 0.05), while the apoptotic rate exhibited a significant increase (p < 0.05). There was a rise in the level of pro-apoptotic protein, Bax, and a fall in the anti-apoptotic protein Bcl-2 level in group A. Lower levels of β-catenin, c-Myc, and cyclin D1 protein were observed in the study group compared with the control group (p < 0.05). Compared with other groups, the multiplication capacity and invasiveness of cells in group A treated with COE and inhibitor XAV939 significantly declined, while the apoptotic rate increased (p < 0.05).Conclusion: COE reverses drug resistance in chemotherapy by inhibiting the expression of Wnt/β-catenin pathway in LC cells. Therefore, COE has potentials for use along with chemotherapeutic agents in the management of liver cancer

Critical Current Distribution in Spin Transfer Switched Magnetic Tunnel Junctions

The spin transfer switching current distribution within a cell was studied in magnetic tunnel junction based structures having alumina barriers with resistance-area product (RA) of 10 to 30 Ohm-um2 and tunneling magneto-resistance (TMR) of ~20%. These were patterned into current perpendicular to plane configured nano-pillars having elliptical cross-sections of area ~0.02 um2. The width of the critical current distribution (sigma/average of distribution), measured using 30 ms current pulse width, was found to be 7.5% and 3.5% for cells with thermal factor (KuV/kBT) of 40 and 65 respectively. The distribution width did not change significantly for pulse widths between 1 s and 4 ms. An analytical expression for probability density function, p(I/Ico) was derived considering the thermally activated spin transfer model, which supports the experimental observation that the thermal factor is the most significant parameter in determining the within cell critical current distribution width.Comment: 12 pages, 4 figure

Spin-Polarized Current Induced Torque in Magnetic Tunnel Junctions

We present tight-binding calculations of the spin torque in non-collinear magnetic tunnel junctions based on the non-equilibrium Green functions approach. We have calculated the spin torque via the effective local magnetic moment approach and the divergence of the spin current. We show that both methods are equivalent, i.e. the absorption of the spin current at the interface is equivalent to the exchange interaction between the electron spins and the local magnetization. The transverse components of the spin torque parallel and perpendicular to the interface oscillate with different phase and decay in the ferromagnetic layer (FM) as a function of the distance from the interface. The period of oscillations is inversely proportional to the difference between the Fermi-momentum of the majority and minority electrons. The phase difference between the two transverse components of the spin torque is due to the precession of the electron spins around the exchange field in the FM layer. In absence of applied bias and for a relatively thin barrier the perpendicular component of the spin torque to the interface is non-zero due to the exchange coupling between the FM layers across the barrier.Comment: 6 pages, 3 figure

A novel spectrum sharing scheme assisted by secondary NOMA relay

In this letter, a two-slot secondary non-orthogonal multiple access (NOMA) relay is used to assist spectrum sharing, where the primary transceivers with long distance communicate through the relay. First, the information for the primary receiver (PR) and secondary receivers (SRs) is transmitted via the NOMA relay. Then, the information for PR is re-transmitted to it through a selected SR to improve its quality of service using maximal-ratio combining, while the next data for PR is sent from the primary transmitter (PT) to the NOMA relay simultaneously. The power allocation solution is derived for the NOMA relay. Simulation results have shown the effectiveness of the proposed scheme

Spin Transfer Switching and Spin Polarization in Magnetic Tunnel Junctions with Mgo and Alox Barriers

We present spin transfer switching results for MgO based magnetic tunneling junctions (MTJs)with large tunneling magnetoresistance (TMR) ratio of up to 150% and low intrinsic switching current density of 2-3 x 10 MA/cm2. The switching data are compared to those obtained on similar MTJ nanostructures with AlOx barrier. It is observed that the switching current density for MgO based MTJs is 3-4 times smaller than that for AlOx based MTJs, and that can be attributed to higher tunneling spin polarization (TSP) in MgO based MTJs. In addition, we report a qualitative study of TSP for a set of samples, ranging from 0.22 for AlOx to 0.46 for MgO based MTJs, and that shows the TSP (at finite bias) responsible for the current-driven magnetization switching is suppressed as compared to zero-bias tunneling spin polarization determined from TMR.Comment: To appear in Appl. Phys. Lett. soo