Growth and Characterization of Graphene on Texture-Controlled Platinum Films

Department of Materials Science EngineeringIn this study, the primary purpose of this research is to grow high quality graphene on platinum (Pt) films, especially wrinkle-free graphene as a 2-dimensional membrane for transparent conductor and hydrophobic water-distillation applications by using texture-controlled Pt films that have incorporated oxygen atoms. In order to achieve the final goals, this research primary had been focused on analysis of abnormal Pt grains through annealing process and study of graphene growth kinetics through chemical vapor deposition process. Then, a new transfer method was applied to graphene transfer by reacting graphene/Pt interface, without incurring damages and unintentional doping. The wrinkle-free graphene was synthesized by using texture-controlled Pt films (200, 220) with giant grains (GGPt) via chemical vapor deposition (CVD). The Pt films on SiO2/Si substrates could be controlled by sputtering with Ar/O2 gas mixtures and abnormal grain growth was affected by the incorporated oxygen during post-annealing process. In order to analysis of graphene growth kinetics on GGPt, each films were heated at the CVD process temperature of ~975 ºC and maintained for 10 min under CH4/H2 gas mixture (5 and 50 sccm, respectively) without cleaning treatments. Enhanced surface perfectness and limited number of grain boundary (GB) of Pt induced homogeneous C-precipitation, thus the high-crystallized monolayer graphene sheets was formed. The transferred graphene shows wrinkle-free characteristics regardless of the orientation types of Pt, probably due to much lesser difference in thermal expansion coefficient (TEC, ~11 μm m-1K-1 at 1000 °C) to graphene. The wrinkles or ripples-free graphene films showed a high crystallinity and high carrier mobility at room-temperature up to ~8,500 cm2V-1s-1. To transfer graphene, a thermal-assisted transfer method was applied by a NaOH (1 M) aqueous solution at 90 °C. The thermal-assisted transfer method was only activated by the hydroxide (OH-) in NaOH solution to separate the graphene/Pt interface. The thermal-assisted transfer process allowed the complete transfer of large-scale graphene films onto arbitrary target substrates without incurring damages and unintentional doping. Compare to bare GGPt, graphene-free GGPt showed no contamination and degradation after the graphene transfer. The fact was demonstrated by XPS data, which showed almost same binding energy of Pt-4f5/2, Pt-4f7/2 (74±0.2 eV). On the basis of these results, a recycle ability of Pt was demonstrated. Also, the result of graphene on the recycled Pt showed almost same quality as the obtained graphene from 1st Pt. Furthermore, the transfer method could be applicable to the large-scale patterned graphene on Pt films with SiO2 regions. By comparing an electrochemical transfer method, the thermal-assisted transfer method have proved to be successfully transferred onto SiO2/Si substrate for the patterned Pt films. The reason is that the reaction between Si and Na+ took place in the boiled NaOH solution to react the SiO2 surface. Through a pre-annealing step in CVD process, the porous graphene membrane could be obtained from the porous Pt texture. The density and size of pore depended on the pre-annealing time in hydrogen gas. Especially, a dense pores of Pt films was obtained with controllable density (~2×105 cm-2) and ~2.5 μm of radius by pre-annealing for 5 min. Since an oxygen was inserted during Pt film sputtered as an adhesion layer between Pt and SiO2/Si substrate, Pt sintering has occurred by oxygen diffusion during pre-annealing step in H2 atmosphere. The porous graphene membrane were successfully transferred onto SiO2/Si substrate by thermal-assisted transfer method. Surprisingly, graphene was grown direct in the pores of Pt films. It was demonstrated through that Pt particles directly formed growth of the graphene. In summary, this study shows the wrinkle-free characteristic of graphene layer by using Pt thin films with preferred orientations and giant grains. In addition, large-scale and patterned graphene films can be successfully transferred onto arbitrary substrates via thermal-assisted transfer method and the Pt substrates can be repeatedly used for the proliferation of graphene applications. Furthermore, this transfer technique shows a high tolerance to variations in types and morphologies of underlying substrates, which is essential for the various applications proposed for graphene.ope

A Passivity-based Nonlinear Admittance Control with Application to Powered Upper-limb Control under Unknown Environmental Interactions

This paper presents an admittance controller based on the passivity theory for a powered upper-limb exoskeleton robot which is governed by the nonlinear equation of motion. Passivity allows us to include a human operator and environmental interaction in the control loop. The robot interacts with the human operator via F/T sensor and interacts with the environment mainly via end-effectors. Although the environmental interaction cannot be detected by any sensors (hence unknown), passivity allows us to have natural interaction. An analysis shows that the behavior of the actual system mimics that of a nominal model as the control gain goes to infinity, which implies that the proposed approach is an admittance controller. However, because the control gain cannot grow infinitely in practice, the performance limitation according to the achievable control gain is also analyzed. The result of this analysis indicates that the performance in the sense of infinite norm increases linearly with the control gain. In the experiments, the proposed properties were verified using 1 degree-of-freedom testbench, and an actual powered upper-limb exoskeleton was used to lift and maneuver the unknown payload.Comment: Accepted in IEEE/ASME Transactions on Mechatronics (T-MECH

Revisiting the Concept of Targeting NFAT to Control T Cell Immunity and Autoimmune Diseases

The nuclear factor of activated T cells (NFAT) family of transcription factors, which includes NFAT1, NFAT2, and NFAT4, are well-known to play important roles in T cell activation. Most of NFAT proteins are controlled by calcium influx upon T cell receptor and costimulatory signaling results increase of IL-2 and IL-2 receptor. NFAT3 however is not shown to be expressed in T cells and NFAT5 has not much highlighted in T cell functions yet. Recent studies demonstrate that the NFAT family proteins involve in function of lineage-specific transcription factors during differentiation of T helper 1 (Th1), Th2, Th17, regulatory T (Treg), and follicular helper T cells (Tfh). They have been studied to make physical interaction with the other transcription factors like GATA3 or Foxp3 and they also regulate Th cell signature gene expressions by direct binding on promotor region of target genes. From last decades, NFAT functions in T cells have been targeted to develop immune modulatory drugs for controlling T cell immunity in autoimmune diseases like cyclosporine A, FK506, etc. Due to their undesirable side defects, only limited application is available in human diseases. This review focuses on the recent advances in development of NFAT targeting drug as well as our understanding of each NFAT family protein in T cell biology. We also discuss updated detail molecular mechanism of NFAT functions in T cells, which would lead us to suggest an idea for developing specific NFAT inhibitors as a therapeutic drug for autoimmune diseases

Mesenteric extraskeletal osteosarcoma with telangiectatic features: a case report

<p>Abstract</p> <p>Background</p> <p>Extraskeletal osteosarcoma is a rare malignant mesenchymal tumor, with a predominant occurrence in the extremities. Only two cases of mesenteric extraskeletal osteosarcoma have been documented. We describe an unusual case of extraskeletal osteosarcoma with telangiectatic features occurring in the mesentery.</p> <p>Case presentation</p> <p>A 67-year-old male presented with blood-tinged stool of 1-month's duration. On colonoscopy, a solid mass was detected protruding from the colon wall. Computed tomography showed a 15 × 9.7 cm heterogeneously enhancing mass, with mottled calcification and a cystic portion, occupying the left upper quadrant of the abdominal cavity. Curative resection of the tumor was performed, and the excised tumor was composed of large multilocular cysts containing old hematomas and necrotic debris. The histology revealed an osteosarcoma showing osteoid formation and blood-filled spaces lined with atypical cells. Despite postoperative chemotherapy, he developed a recurrent peritoneal mass and multiple lung metastases 3 months postoperatively.</p> <p>Conclusion</p> <p>Given the rarity of cases of mesenteric extraskeletal osteosarcoma, its biologic behavior at this location remains to be determined. However, extraskeletal osteosarcoma with telangiectatic features is an uncommon entity to be recognized because of the possible fatal outcome related to the tumors.</p

SYNGAS PRODUCTION WITH A DUAL FLUIDIZED BED GASIFIER FOR POLYGENERATION

A pilot scale dual fluidized bed gasification system was developed for polygeneration with biomass. The gasification system is designed for supplying syngas for Fischer Tropsch (F-T) synthesis of bio-diesel and power generation with a syngas engine. Characteristics of biomass steam gasification were investigated in a lab scale bubbling fluidized bed, and hydrodynamics of a dual fluidized bed were investigated in a cold flow model. Based on the results from the lab scale test and cold flow model, a pilot scale dual fluidized bed gasifier was designed. In this paper, the developing process of the gasifier and preliminary results of system operation will be presented

Optimal application of compressive palatal stents following mesiodens removal in pediatric patients:a Randomized Controlled Trial

There is no scientific evidence supporting the choice of a palatal stent in patients who underwent removal of an impacted supernumerary tooth. We aimed to investigate the effects of palatal stents in patients who underwent supernumerary tooth removal through a palatal approach and to suggest the optimal stent thickness and material. We recruited 144 patients who underwent extraction of a supernumerary tooth between the maxillary anterior teeth. Subjects were assigned to a control group (CG) or one of four compressive palatal stent groups (CPSGs) classified by the thickness and material of the thermoplastic acrylic stent used. Palatal gingival swelling and objective indices (healing, oral hygiene, gingival, and plaque) were evaluated before surgery and on postoperative days (PODs) 3, 7, and 14; pain/discomfort and the Child Oral Health Impact Profile (COHIP) were assessed as subjective indices of the effects of the stent. The CPSGs showed faster healing than did the CG on PODs 7 (P<0.001) and 14 (P=0.043); swelling was measured by 1.64±0.88 mm and 4.52±0.39 mm, respectively. Although swelling was least in the 4-mm hard group (0.92±0.33 mm), the difference compared with that in the 2-mm hard group (1.01±0.18 mm) was not significant (P=0.077). The CPSGs showed better COHIP (P<0.001-0.036) and pain scores (P<0.001) than did the CG on PODs 1-3. Compressive palatal stents reduce discomfort by decreasing pain and alleviating swelling. Although a stent is effective regardless of its thickness and material, 2-mm hard stents maximized such positive effects with minimal discomfort