Anisotropic optical property of ferroelectric Bi2O2X(X = S,Se,Te) monolayer and strain engineering.

Based on the first-principles calculations, ferroelectricBi2O2X(X=S,Se,Te)monolayers with unequivalent in-plane lattice constants are confirmed to be the ground state, which is consistent with the experiment result (Ghoshet al2019Nano Lett.195703-09), and the anisotropic optical property is firstly investigated. We find that the polarizations ofBi2O2Xmonolayers points along the direction ofa-axis, andBi2O2Temonolayer process the largest polarization. Furthermore, both the biaxial and uniaxial strains are favor for the enhancement of polarization ofBi2O2Xmonolayers. It should be mentioned that the type of band gap will convert from indirect to direct forBi2O2Temonolayer when thea-axial tensile strain is larger than 2%. At last, the optical absorption coefficient forBi2O2Xmonolayers are calculated, and we obtain thatBi2O2Temonolayer has the strongest optical absorption within the range of visible light, the anisotropy and possible strain engineering to improve the optical absorption are discussed in detail. Our findings are significant in fields of optoelectronics and photovoltaics.

Giant tunneling magnetoresistance in in-plane double-barrier magnetic tunnel junctions based on MXene Cr2C.

The discovery of two-dimensional (2D) magnetic materials makes it possible to realize in-plane magnetic tunnel junctions. In this study, the transport characteristics of an in-plane double barrier magnetic tunnel junction (IDB-MTJ) based on Cr2C have been studied by density functional theory combined with the nonequilibrium Green's function method. The results showed its maximum tunneling magnetoresistance ratio (TMR) value reached 6.58 × 1010. Its minimum TMR value (3.86 × 106) was also comparable to those of conventional field effect transistors (FETs). Due to its giant TMR and unique structural characteristics, the IDB-MTJ based on Cr2C has great potential applications in magnetic random access memory (MRAM) and logic computing.

Carbon phosphide nanoribbons with spatial inversion symmetry: robust generators of pure spin current with a photogalvanic effect.

Our recent work has demonstrated that the spin-dependent photogalvanic effect (PGE) is an ideal way to induce pure spin current in certain centrosymmetric systems (X. Tao, P. Jiang, H. Hao, X. Zheng, L. Zhang and Z. Zeng, Phys. Rev. B, 2020, 102, 081402), and thus the search for appropriate materials or structures is the key to realize it. Here, we theoretically propose a spin optoelectric device with α-phase carbon phosphide nanoribbons (α-CPNRs) to generate pure spin current by PGE using density functional theory simulation. By designing an α-CPNR based device with a centrosymmetric structure, due to the structural inversion symmetry and real space spin polarization antisymmetry of the system, the PGE induced pure spin current without any accompanying charge current can be always obtained, independent of polarization type and polarization angle of the photons. Furthermore, the magnitude of pure spin current can be greatly increased (nearly by an order of magnitude) by applying antiparallel electrical fields in the two leads to tune the spin density and band structure. Furthermore, by applying parallel electrical fields, a fully spin-polarized photocurrent can be produced in this system, suggesting a fantastic scheme to achieve half-metallic transport, another important goal in spintronics. These investigations suggest that the optoelectric devices constructed by α-CPNRs will have great potential in spintronics.

Tunable tunneling magnetoresistance in in-plane double barrier magnetic tunnel junctions based on B vacancy h-NB nanoribbons.

Magnetic tunnel junctions (MTJs) have attained new opportunities due to the emergence of two-dimensional (2D) magnetic materials after they were proposed more than forty years ago. Here, an in-plane double barrier magnetic tunnel junction (IDB-MTJ) based on B vacancy h-NB nanoribbons has been proposed firstly, and the transport properties have been studied using density functional theory combined with the nonequilibrium Green's function method. Due to its unique structural characteristics, the tunneling magnetoresistance (TMR) ratio can be tuned and the maximum TMR can reach 1.86 × 105. The potential applications of the IDB-MTJ in magnetic random-access memories and logical computation have also been discussed. We find that the IDB-MTJs have great potential in magnetic random-access memories and logical computation applications.

Graphene-based nano-devices: high spin Seebeck and pure spin photogalvanic effects.

We investigate the magnetic, thermoelectric transport, and photogalvanic effect (PGE) properties of two nano-devices based on sawtooth edged graphene nanoribbons (SGNRs). It is found that a robust spin-semiconducting property exists in SGNRs. When SGNRs are arranged in a configuration, a large spin Seebeck coefficient is obtained, indicating a high Seebeck effect under a temperature difference. In addition, we also propose a new spatial inversion symmetry nano-device, which is constructed by two head to head semi-infinite SGNRs in a configuration. The results show that spin-up and spin-down currents are generated by the PGE with opposite flowing directions and the same magnitude. As a result, only a finite pure spin current arises without an accompanying charge current. More importantly, the pure spin current is robustly induced by photons and is independent of the photon energy, polarization angle and the model of polarization (linear or elliptical polarization), which is attributed to the symmetry of the spatial inversion and anti-symmetry of the spin density inversion. The results presented here provide a useful insight into the real application of both spin caloritronics and photoelectric carbon-based nano-devices.

Transition metal-containing molecular devices: controllable single-spin negative differential thermoelectric resistance effects under gate voltages.

Based on the non-equilibrium Green function method combined with density functional theory, we investigate the spin-resolved transport through transition metal (TM) (= Cr, Mn, Fe and Ru)-containing molecular devices in the presence of zigzag graphene nanoribbon (ZGNR) electrodes. The wave-function mismatch for the single-spin component results in a perfect spin-filtering property near the Fermi level. Moreover, we also observe Fano and Breit-Wigner resonance peaks in the transmission spectrum. Under a temperature gradient, the single-spin electric current exhibits a remarkable negative differential thermoelectric resistance (NDTR) in the Ru-complex molecular device, which originates from the Fano asymmetry of the single-spin transmission peak near the Fermi level. A gate voltage allows for a precise control of the single-spin NDTR in the Ru-complex molecular device.

Giant magnetoresistance and spin Seebeck coefficient in zigzag α-graphyne nanoribbons.

We investigate the spin-dependent electric and thermoelectric properties of ferromagnetic zigzag α-graphyne nanoribbons (ZαGNRs) using density-functional theory combined with non-equilibrium Green's function method. A giant magnetoresistance is obtained in the pristine even-width ZαGNRs and can be as high as 10(6)%. However, for the doped systems, a large magnetoresistance behavior may appear in the odd-width ZαGNRs rather than the even-width ones. This suggests that the magnetoresistance can be manipulated in a wide range by the dopants on the edges of ZαGNRs. Another interesting phenomenon is that in the B- and N-doped even-width ZαGNRs the spin Seebeck coefficient is always larger than the charge Seebeck coefficient, and a pure-spin-current thermospin device can be achieved at specific temperatures.

High performance current and spin diode of atomic carbon chain between transversely symmetric ribbon electrodes.

We demonstrate that giant current and high spin rectification ratios can be achieved in atomic carbon chain devices connected between two symmetric ferromagnetic zigzag-graphene-nanoribbon electrodes. The spin dependent transport simulation is carried out by density functional theory combined with the non-equilibrium Green's function method. It is found that the transverse symmetries of the electronic wave functions in the nanoribbons and the carbon chain are critical to the spin transport modes. In the parallel magnetization configuration of two electrodes, pure spin current is observed in both linear and nonlinear regions. However, in the antiparallel configuration, the spin-up (down) current is prohibited under the positive (negative) voltage bias, which results in a spin rectification ratio of order 10(4). When edge carbon atoms are substituted with boron atoms to suppress the edge magnetization in one of the electrodes, we obtain a diode with current rectification ratio over 10(6).

Minimal incisions for treating zygomatic complex fractures.

OBJECTIVE: The objective was to study the clinical application and effects of minimal incisions for treating zygomatic complex (ZMC) fractures. METHODS: A retrospective study was conducted on the 155 patients who underwent reduction of surgical injury by minimal incision for treating ZMC fractures. RESULTS: The outcomes after treatment were satisfactory functionally and aesthetically in most patients. The clinical results were good in 150 patients. No obvious scars were noticed in all the patients. After a follow-up of average 18 months, zygomatic asymmetry was present in 2 cases, numbness in the infraorbital area in 2 cases, and limitation of mouth opening in 1 patient. Plate removal was conducted in 3 patients. CONCLUSIONS: Repositioning of ZMC fractures via minimal incisions can get satisfactory results. With this kind of approach, the surgical injury can be reduced, and clear field of operation, convenient manipulation, less bleeding, high accuracy of reduction, and inconspicuous scar can be achieved as well. It is an ideal method and deserves to be recommended in clinical procedures.

[Clinical study of muscular rehabilitation after sagittal split ramus osteotomy].

OBJECTIVE: To investigate the effect of muscular rehabilitation on recovery after sagittal split ramus osteotomy. METHODS: Twenty-seven patients undergoing sagittal split ramus osteotomy received passive motion training and muscle endurance training after surgery using the new-developed mouth-opening trainer. The passive motion training began 2-3 days after the removal of inter-maxillary elastraction. The instrument was inserted into the inter-maxillary space for 5 min per time, 3-4 times per day. When the mouth opening reached a range of 20-25 mm, the muscle endurance training initiated. The results of the training were compared with another 20 cases who received the same surgery. RESULTS: The mouth opening of the patients who received muscular rehabilitation achieved the pre-surgical level 4 weeks after surgery [(34.72 ± 3.75) mm], the bite force reached the pre-surgical level 8 weeks after surgery [(231.08 ± 62.52) N], but in the 20 cases without training the mouth opening [(28.42 ± 4.11) mm] in 4 weeks and the bite force in 8 weeks [(210.90 ± 73.40) N] were lower after surgery than before surgery. CONCLUSIONS: The systematic and standard muscle function training, accompanied with the use of the new-developed mouth-opening trainer could improve the functional recovery of the patients who receive sagittal split ramus osteotomies.

Evaluation of force degradation characteristics of orthodontic latex elastics in vitro and in vivo.

OBJECTIVE: To evaluate the characteristics of force degradation of latex elastics in clinical applications and in vitro studies. MATERIALS AND METHODS: Samples of 3/16-inch latex elastics were investigated, and 12 students between the ages of 12 and 15 years were selected for the intermaxillary and intramaxillary tractions. The elastics in the control groups were set in artificial saliva and dry room conditions and were stretched 20 mm. The repeated-measure two-way analysis of variance and nonlinear regression analysis were used to identify statistical significance. RESULTS: Overall, there were statistically significant differences between the different methods and observation intervals. At 24- and 48-hour time intervals, the force decreased during in vivo testing and in artificial saliva (P < .001), whereas there were no significant differences in dry room conditions (P > .05). In intermaxillary traction the percentage of initial force remaining after 48 hours was 61%. In intramaxillary traction and in artificial saliva the percentage of initial force remaining was 71%, and in room conditions 86% of initial force remained. Force degradation of latex elastics was different according to their environmental conditions. There was significantly more force degradation in intermaxillary traction than in intramaxillary traction. The dry room condition caused the least force loss. CONCLUSIONS: There were some differences among groups in the different times to start wearing elastics in intermaxillary traction but no significant differences in intramaxillary traction.

Coronal incision for treating zygomatic complex fractures.

OBJECTIVES: To study the value of coronal incisions for treating zygomatic complex fractures. PATIENTS AND METHODS: A retrospective study was conducted on 69 out of 83 patients regarding the indications and complications of scalp incisions for treating zygomatic complex fractures (the other 14 patients were treated by local incisions and approaches). RESULTS: In the early postoperative period, 5 patients suffered from haemorrhage, 2 had infections, 24 patients reported immediate postoperative anaesthesia and paraesthesia affecting the supraorbital region. Six had symptoms and signs of facial nerve injury: difficulty with wrinkling the forehead or to closing the eyes. After a follow-up of 3-5 years, 6 cases suffered from a scar wider than 0.5 cm, paraesthesia in 2 cases (parietal region and temporal region), depression of the temporal fossa in 2 and 1 patient had (persistent) palsy of the temporal branch of the facial nerve. CONCLUSION: On one hand, coronal incisions offer advantages such as: extensive exposure to ensure exact anatomical reduction. On the other hand, this incision has disadvantages such as obvious scars, long operating time, infections, haemorrhage, paraesthesia in the operative region, palsy of the facial nerve and depression of the temporal fossa. Therefore, the indications for coronal incisions should be strictly applied, and this incision should not be overused.

[Clinical study of surgical treatment of ankylosis of temporomandibular joint].

OBJECTIVE: To analyze the clinical feature of temporomandibular joint (TMJ) ankylosis and to investigate the advantage and disadvantage of all kind of surgery methods of TMJ ankylosis for supplying references to the treatment of TMJ ankylosis. METHODS: Aetiology, sex, age at time of treatment, clinical features, radiographic findings, surgical treatment was reviewed and analyzed. RESULTS: Trauma (66.86%, n = 117) and infection (24.57%, n = 43) were the primary causes of TMJ ankylosis. The 10 approximately 19 years age group (44.57%, n =78) occupied the highest frequency in five age groups, one hundred and fourteen (65.14%, n = 114) of the patients presented with lateral ankylosis. They were carried out different surgery method according to their difference of age, aetiology, and so on. CONCLUSIONS: The person at 10 approximately 19 years old had the more feasibility of TMJ ankylosis than others. Trauma was the commonest cause of ankylosis. Different surgical method should be choose according to the different patient.

[Function of disk reposition in the treatment of traumatogenic temporomandibular joint ankylosis].

OBJECTIVE: To investigate the method and results of disk reposition in the treatment of traumatogenic TMJ ankylosis. METHODS: In 19 cases of traumatogenic ankylosis of TMJ, the dislocated disks were repositioned during anthroplasty. In the operation, the dissection of dislocated disk was performed carefully around the TMJ. The disk was repositioned to its anatomic location over the top of condylar stump, then the lateral aspect of the disk was sutured to the soft tissue of zygomatic root. RESULTS: At the last follow-up examination, interincisal opening distance ranged from 24 to 43 mm in all cases (mean 32.63 mm), which approached or reached the normal level. No recurrence and TMJ symptom were found during the period of follow-up. CONCLUSIONS: The disk repositioning in treatment of traumatogenic TMJ ankylosis is a feasible and effective approach to reconstruct the structure and function and prevent recurrence.

[A clinical investigation on the surgical approach and fixation in operative treatment zygomatic fractures].

OBJECTIVE: To investigate the effect of soft tissue incision and rigid internal fixation in the treatment of zygomatic fracture. METHODS: 70 cases with zygomatic fracture were entered into the study. The clinical data of 65 patients who were performed operations in the treatment were analyzed. The study focused on the incision, number and locations of Titanium plate. The facial contour, reduction,fixation, healing of incision, facial bisymmetry and complications of the operation were followed up 3 - 24 months after surgery. RESULTS: All the incisions were primary healing. Clinical and radiologic assessment of reduction was symmetric and stable in 91.5% of all cases, asymmetric in 8.5% of all cases. Subcutaneous hematoma happened in 5 cases, Ti plate exposure 1 in case, scalp scar width was more than 0.5 cm in 6 cases, frontal part or scalp paresthesia 8 cases. CONCLUSIONS: Coronal scalp incision has advantages such as good exposure, precise removal of the bone block and good symmetry of both sides. RIF can improve the stability of fracture, promotes fracture healing and guarantees the rehabilitation of zygomatic complex. direct reduction and rigid internal fixation with Titanium microplate or miniplate are satisfactory in zygomatic fracture.

[The orthognathic treatment of mandibular asymmetry].

OBJECTIVE: To evaluate the methods of orthognathic treatment for mandibular asymmetry. METHODS: 110 cases of mandibular asymmetry had been treated in past thirteen years. The type of deformity, the management of the cases, and the effects of orthognathic treatment were summarized in this paper. Orthodontic therapy was taken before and after operation to keep the treatment effect. RESULTS: According to the type of the asymmetry deformity, different methods were used. After treatment, all the patients obtained satisfactory facial appearances and oral function. CONCLUSION: It should be diagnosed before surgery whether the development of deformity is steady or not. If it is steady, the effects of orthognathic and orthodontic therapy will be satisfactory; if not, we should remove the affected condyles and simulataneously ameliorate facial appearance.

[Management of disk displacement with condylar fracture].

OBJECTIVE: To investigate clinical features of disk displacement during the course of condylar fracture and to explore the techniques of disk reposition and suturation. METHODS: 32 patients (10 females and 22 males) who had disk displacements with condylar fractures were followed up. Reduction and reposition of the dislocated disks simultaneously with fixation of fractures were performed. 7 patients underwent intermaxillary fixation with elastic bands for 1 to 2 weeks. RESULTS: The occlusions were satisfactory in all cases but one for the reason of ramus height loss. No TMJ symptom was found when examined 3 months post operation. CONCLUSIONS: Anterior disk displacements were most occurred with high condylar process fractures. Surgical reposition and suturation of disk play an important role for the later TMJ-function.