Investigation for Thermoelectric Properties of the MoS2 Monolayer-Graphene Heterostructure: Density Functional Theory Calculations and Electrical Transport Measurements.

We investigated the thermoelectric (TE) properties of the MoS2 monolayer-graphene heterostructure which consists of the MoS2 monolayer and graphene. The electronic structures of the MoS2 monolayer-graphene heterostructure are mainly contributed from graphene and the MoS2 monolayer for the valence band maximum and conduction band minimum, respectively. The change in the electronic structures near the Fermi level is responsible for the fact that the calculated Seebeck coefficients S and electrical conductivity σ/τ of MoS2 monolayer-graphene are largely affected from those of graphene and the MoS2 monolayer. Its power factor S 2σ/τ is increased compared to those of graphene and the MoS2 monolayer at an electron concentration of 1011 to 1012 cm-2, which corresponds to a three-dimensional concentration of 3 × 1018 to 3 × 1019 cm-3. We also demonstrated that the MoS2 monolayer shows the p-type TE behavior, while the MoS2 monolayer-graphene heterostructure is given to the n-type TE material. The current study provides a strategy to improve TE properties of the MoS2 monolayer through the formation of the MoS2 monolayer-graphene heterostructure.

Magnetic Structure and Origin of Insulating Behavior in the Ba2CuOsO6 System, and the Role of A-Site Ionic Size in Its Bandgap Opening: Density Functional Theory Approaches.

The magnetic structure and the origin of band gap opening for Ba2CuOsO6 were investigated by exploring the spin exchange interactions and employing the spin-orbit coupling effect. It revealed that the double-perovskite Ba2CuOsO6, composed of the 3d (Cu2+) and 5d (Os6+) transition metal magnetic ions is magnetic insulator. The magnetic susceptibilities of Ba2CuOsO6 obey the Curie-Weiss law, with an estimated Weiss temperature of -13.3 K, indicating AFM ordering. From the density functional theory approach, it is demonstrated that the spin exchange interaction between Cu ions plays a major role in exhibiting an antiferromagnetic behavior in the Ba2CuOsO6 system. An important factor to understand regarding the insulating behavior on Ba2CuOsO6 is the structural distortion shape of OsO6 octahedron, which should be closely connected with the ionic size of the A-site ion. Since the d-block of Os6+ (d2) ions of Ba2CuOsO6 is split into four states (xy < xz, yz < x2-y2 < z2), the crucial key is separation of doubly degenerated xz and yz levels to describe the magnetic insulating states of Ba2CuOsO6. By orbital symmetry breaking, caused by the spin-orbit coupling, the t2g level of Os6+ (d2) ions is separated into three sublevels. Two electrons of Os6+ (d2) ions occupy two levels of the three spin-orbit-coupled levels. Since Ba2CuOsO6 is a strongly correlated system, and the Os atom belongs to the heavy element group, one speculates that it is necessary to take into account both electron correlation and the spin-orbit coupling effect in describing the magnetic insulating states of Ba2CuOsO6.

Ternary selenides A2Sb4Se8 (A = K, Rb and Cs) as an n-type thermoelectric material with high power factor and low lattice thermal conductivity: importance of the conformationally flexible Sb-Se-Se-Sb bridges.

We investigated the thermoelectric properties of the layered ternary selenides A2Sb4Se8 (A = K, Rb and Cs) and the lattice thermal conductivity of K2Sb4Se8 on the basis of DFT calculations, to find that these selenides are a high-performance n-type thermoelectric material. The Seebeck coefficients and power factors calculated for the electron carriers of A2Sb4Se8 (A = K, Rb and Cs) are greater than those of the well-known thermoelectric materials Bi2Te3 and PbTe. The lattice thermal conductivity κ latt of K2Sb4Se8 is comparable to that of PbTe, well-known for its low lattice thermal conductivity. In terms of both electronic and phonon structures, the structural parts of the A2Sb4Se8 (A = K, Rb and Cs) phases crucial for their thermoelectric properties are the conformationally-flexible Sb-Se-Se-Sb bridges that interlink between their structurally rigid units.

Gigantic Phonon-Scattering Cross Section To Enhance Thermoelectric Performance in Bulk Crystals.

In thermoelectric energy conversions, thermal conductivity reduction is essential for enhancing thermoelectric performance while maintaining a high power factor. Herein, we propose an approach based on coated-grain structures to effectively reduce the thermal conductivity to a much greater degree when compared to that done by conventional nanodot nanocomposite. By incorporating CdTe coated layers on the surface of SnTe grains, the thermal conductivity is as low as 1.16 W/m-K at 929 K, resulting in a thermoelectric figure of merit, i.e., zT, of 1.90. According to our developed theory, phonons scatter coherently due to the phase lag between phonons passing through and around the coated grain. Such scattering is induced by the acoustic impedance mismatch between the coated layer and the grain, resulting in a gigantic phonon-scattering cross section. The phonon-scattering cross section of the coated grains is several orders of magnitude larger than that of the nanodots with the same impurity concentration. The power factor was also slightly increased by the energy filtering effect at the coated surface and additional minority carrier blocking by the heterointerfaces. This scheme can be utilized for various bulk crystals, meaning a broad range of materials can be considered for thermoelectric applications.

Cause for the Orbital Ordering of Cs2AgF4 and Its Effect on Thermoelectric Properties.

The cause for the orbital-ordered structure of orthorhombic Cs2AgF4 and its effect on thermoelectric properties were probed by density functional theory calculations. The orbital-ordered structure of orthorhombic Cs2AgF4 has been regarded as caused by a cooperative Jahn-Teller (JT) distortion of the AgF6 octahedra of tetragonal Cs2AgF4. However, each AgF6 octahedron of tetragonal Cs2AgF4 is axially compressed and hence has no JT instability. The orbital-ordering transition of Cs2AgF4 is best described as a metal-to-insulator transition driven by a bandgap opening at the Fermi level. The orbital-ordering opens a bandgap at the Fermi level and generates peaks in the density of states at the conduction band minimum (CBM) and valence band maximum (VBM). Consequently, orthorhombic Cs2AgF4 has strongly enhanced Seebeck coefficients as compared to tetragonal Cs2AgF4.

Outcome of balloon kyphoplasty for the treatment of osteoporotic vertebral compression fracture in patients with rheumatoid arthritis.

BACKGROUND: Osteoporosis and osteoporotic fractures are widely known as complications of rheumatoid arthritis. Kyphoplasty (KP) is known as an effective treatment modality for reducing pain and correcting kyphotic deformity in osteoporotic vertebral compression fracture (OVCF). However, cutcomes of KP in rheumatoid patients are not well known. The purpose of the study was to investigate the clinical and radiological outcomes of balloon KP on OVCF in patients with rheumatoid arthritis. METHODS: A total of 23 patients (31 vertebral bodies) with rheumatoid arthritis who received KP for OVCF and could be followed up for at least 1 year were examined. For clinical outcomes, visual analogue scale (VAS) and the Korean version of the Oswestry disability index (KODI) were evaluated. For radiological outcomes, changes in anterior vertebral height and local kyphotic angle were measured, alongside cement leakage, adjacent fracture, and the recollapse of cemented vertebra. RESULTS: The anterior vertebral height was significantly restored after surgery compared with prior to surgery (p < 0.001). Cement leakage was found in 14 cases (45.1 %), and disc space leakage was prevalent (50 %), while vascular cement leakage was found in one case. Adjacent fracture was found in 3 patients (11.5 %). VAS for lumbago showed a significant decrease (p < 0.001) after surgery (VAS = 2.4) compared with that before (VAS = 8.1); it was somewhat increased after the 1-year follow-up (VAS = 2.8; p = 0.223). KODI also decreased (48.8 %) after surgery compared with before (84.6 %). However, it increased somewhat (49.9 %) after the 1-year follow-up. CONCLUSION: KP on rheumatoid arthritis patients for OVCF was effective for reducing pain in the early stage and restoring vertebral body height. Recollapse of the treated vertebral body was found relatively frequently alongside the correction loss of local kyphotic angle.

Comparative Effects of Dexmedetomidine and Propofol on US-Guided Radiofrequency Ablation of Hepatic Neoplasm Under Monitored Anesthesia Care: A Randomized Controlled Study.

Percutaneous radiofrequency ablation (RFA) is a useful and safe procedure for treating hepatic neoplasm. However, liver RFA causes severe pain, which thereby increases the demand for monitored anesthesia care (MAC). Here, we compared the efficacy and safety of propofol and dexmedetomidine, which are commonly administered during MAC when performing RFA to assess hepatic neoplasm.In this randomized controlled trial, 40 patients were randomly allocated to 2 groups for elective RFA. Patients received either dexmedetomidine (group D) or propofol (group P). Both groups received the continuous infusion of remifentanil for pain control. The primary outcomes were opioid consumption and differences in partial pressure of arterial carbon dioxide (PaCO2) between pre- and postprocedure RFA. In addition, hemodynamic parameters, patient satisfaction, and interventional radiologist satisfaction were determined.There were significant differences in opioid consumption (50.1 ±â€Š16.8 ng/kg/min [group D] vs 71.2 ±â€Š18.7 ng/kg/min [group P]; P = 0.001) and delta PaCO2 (10.4 ±â€Š6.4 mm Hg vs 17.2 ±â€Š9.2 mm Hg, respectively; P = 0.016). Moreover, respiratory rates were significantly different between groups during RFA (P < 0.001). However, blood pressure and heart rate did not significantly change during RFA. Neither patient nor interventional radiologist satisfaction was significantly different between groups.Dexmedetomidine provides better respiratory stability and reduces opioid consumption in comparison with propofol when administered under MAC when performing RFA for hepatic neoplasm.

Comparison of the rate of successful endotracheal intubation between the "sniffing" and "ramped" positions in patients with an expected difficult intubation: a prospective randomized study.

BACKGROUND: Optimal head and neck positioning and clinical experience are important factors for successful endotracheal intubation in patients with a difficult airway. This study aimed to investigate the rate of successful endotracheal intubation between the sniffing and ramped positions in patients with an expected difficult intubation. METHODS: The study included 204 patients with an expected difficult intubation (airway difficulty score ≥ 8) based on the preoperative airway assessment. The patients were randomized into the following groups: group S was placed in the sniffing position, and group R was placed in the ramped position during direct laryngoscopy. The primary outcome was successful endotracheal intubation and the secondary measure was laryngeal view in the ramped or sniffing position when the operating table was placed at two different heights. RESULTS: Group R showed a higher rate of successful endotracheal intubation and better laryngeal view than group S (P < 0.05). The rate of successful endotracheal intubation was higher in group R than in group S at both heights of the operating table; but, it was not different within each group. Laryngeal view was not different between the two groups and within each group when the two heights of the operating table were used. Fully trained and experienced attending anesthesiologists achieved a higher rate of successful endotracheal intubation than less experienced residents in group R (P < 0.05) but not in group S. CONCLUSIONS: Ramped position and clinical experience can be important factors for laryngeal view and success rate of endotracheal intubation in patients with an expected difficult intubation.

Usefulness of the korean knee score for evaluation of the results of total knee arthroplasty.

PURPOSE: The Korean Knee score (KKS) was designed to reflect the floor-sitting lifestyle that necessitates high knee flexion. The purpose of this study is to assess whether the KKS reflects the floor-sitting lifestyle more accurately than the previously developed Knee Society clinical rating system. In addition, the presence of ceiling effects was compared between the two rating systems. MATERIALS AND METHODS: Eighty-one consecutive patients (120 knees) who were assessed regularly after total knee arthroplasty (TKA) on an outpatient basis between January 2012 and December 2012 were enrolled. All patients were asked to complete a questionnaire to assess the Knee Society Knee score (KSKS), Knee Society Function score (KSFS), and KKS. RESULTS: At the final follow-up, the mean KSKS, KSFS, and KKS were 91.2, 86.0, and 70.1, respectively, and the scores were similar between the ≥125° maximum flexion group and <125° maximum flexion group. However, the 'floor life' subdomain score of the KKS was significantly higher in the >125° maximum flexion group (15.13 vs. 11.24, p=0.001). The number of cases with the highest possible score was 24 (20%) for the KSKS and 47 (39%) for the KSFS, whereas none of the cases obtained the highest possible KKS. According to the standard deviation method, more substantial ceiling effects were present in the KSKS (83 cases, 69.1%) and KSFS (67 cases, 55.8%) than in the KKS (23 cases, 19.2%). CONCLUSIONS: Although, the KKS was effective in reducing the ceiling effect, it demonstrated limited improvement in assessing the ability to perform high knee flexion after TKA. However, the 'floor life' subdomain of KSS appeared to be valid for evaluating high flexion of the knee.