A solvent-free Diels-Alder reaction of graphite into functionalized graphene nanosheets

A solvent-free Diels-Alder reaction was carried out by heating a mixture of graphite and a typical dienophile, maleic anhydride (MA) or maleimide (MI), in a sealed glass ampoule of argon. The functionalization of graphite with dienophiles was confirmed by various characterization techniques, suggesting the efficient functionalization and delamination of graphite into a few layers of graphitic nanosheets.close0

Higgs phenomenology in the Peccei-Quinn invariant NMSSM

We study the Higgs phenomenology in the Peccei-Quinn invariant NMSSM (PQ-NMSSM) where the low energy mass parameters of the singlet superfield are induced by a spontaneous breakdown of the Peccei-Quinn symmetry. In the generic NMSSM, scalar mixing among CP-even Higgs bosons is constrained by the observed properties of the SM-like Higgs boson, as well as by the LEP bound on the chargino mass and the perturbativity bound on the singlet Yukawa coupling. In the minimal PQ-NMSSM, scalar mixing is further constrained due to the presence of a light singlino-like neutralino. It is noticed that the $2\sigma$ excess of the LEP $Zb\bar b$ events at $m_{b\bar b}\simeq$ 98 GeV can be explained by a singlet-like 98 GeV Higgs boson in the minimal PQ-NMSSM with low $\tan\beta$, stops around or below 1 TeV, and light doublet-higgsinos around the weak scale.Comment: 31 pages, 4 figures; v2: references added, light stop effects discussed, bound on the Higgs invisible decay rate correcte

TWO-DIMENSIONAL CARBON-BASED LAYERED MATERIALS: SYNTHESIS AND MODIFICATION

Department of Energy Engineeringgraphene and covalent organic framework (COF). In the first half of this thesis, I discuss postsynthetic modification of graphite into graphene nanoplatelets via solvent-free Diels-Alder reaction. The one-pot Diels-Alder reaction of pristine graphite enables to functionalize dienophiles at the edge of graphite, which facilitate to delaminate into graphene nanoplatelets by dispersing them into common organic solvent. The second half of this thesis focuses on synthesis and presynthetic modification of COFs. Firstly, I describe the presynthetic modification of imine-linked COF with high crystallinity and porosity. To improve the reactivity of COF, I designed small-pore crystalline COF using specific triamine building block including hydroxy groups. The resultant imine-linked COF showed high crystallinity and microporosity, and it exhibited high thermal stability. Secondly, I explore synthesis of imide-linked COF. Because of the irreversible second step imidization, the imide-linked COF shows high thermal and chemical stability along with the 1D polyimide analogues. The last part of this thesis, I briefly summarize my Ph.D. studies.The synthetic modification of two-dimensional (2D) layered materials as well as its chemical production represents an attractive challenge which is driven by their potential applications. Synthetic modification can tailor the physical and chemical properties by introducing or changing the functionality into the materials, hence improve their processability and performance of practical applications. The development of chemical modification for 2D layered materials has generally lagged way behind compared with other 1D and 3D analogues. Therefore, synthetic modification of 2D layered materials can be considered as a challenge for synthetic chemists. The focus of the thesis is on the synthesis and modification of 2D layered materials, which allow to enhance processability for practical applications. Before discussing my Ph.D. studies, I give a brief overview of progress on the development of 2D layered materials. Studies of this thesis is mainly divided into two kinds of materials; graphene and covalent organic framework (COF). In the first half of this thesis, I discuss postsynthetic modification of graphite into graphene nanoplatelets via solvent-free Diels-Alder reaction. The one-pot Diels-Alder reaction of pristine graphite enables to functionalize dienophiles at the edge of graphite, which facilitate to delaminate into graphene nanoplatelets by dispersing them into common organic solvent. The second half of this thesis focuses on synthesis and presynthetic modification of COFs. Firstly, I describe the presynthetic modification of imine-linked COF with high crystallinity and porosity. To improve the reactivity of COF, I designed small-pore crystalline COF using specific triamine building block including hydroxy groups. The resultant imine-linked COF showed high crystallinity and microporosity, and it exhibited high thermal stability. Secondly, I explore synthesis of imide-linked COF. Because of the irreversible second step imidization, the imide-linked COF shows high thermal and chemical stability along with the 1D polyimide analogues. The last part of this thesis, I briefly summarize my Ph.D. studies.ope

String theoretic QCD axions in the light of PLANCK and BICEP2

The QCD axion solving the strong CP problem may originate from antisymmetric tensor gauge fields in compactified string theory, with a decay constant around the GUT scale. Such possibility appears to be ruled out now by the detection of tensor modes by BICEP2 and the PLANCK constraints on isocurvature density perturbations. A more interesting and still viable possibility is that the string theoretic QCD axion is charged under an anomalous U(1)A gauge symmetry. In such case, the axion decay constant can be much lower than the GUT scale if moduli are stabilized near the point of vanishing Fayet-Illiopoulos term, and U(1)A-charged matter fields get a vacuum value v ∼ (mSUSYMnPl)1/(n+1) (n ≥ 0) induced by a tachyonic SUSY breaking mass mSUSY. We examine the symmetry breaking pattern of such models during the inflationary epoch with HI ≃ 1014 GeV, and identify the range of the QCD axion decay constant, as well as the corresponding relic axion abundance, consistent with known cosmological constraints. In addition to the case that the PQ symmetry is restored during inflation, i.e. v(tI ) = 0, there are other viable scenarios, including that the PQ symmetry is broken during inflation with v(tI ) ∼ (4HIMnPl)1/(n+1) ∼ 1016–1017 GeV due to the Hubble-induced D-term DA ∼ 82H2 I , while v(t0) ∼ (mSUSYMnPl)1/(n+1) ∼ 109–5×1013 GeV in the present universe, where v(t0) above 1012 GeV requires a fine-tuning of the axion misalignment angle. We also discuss the implications of our results for the size of SUSY breaking soft masses.131211Nsciescopu

Microspinning: Local Surface Mixing via Rotation of Magnetic Microparticles for Efficient Small-Volume Bioassays

The need for high-throughput screening has led to the miniaturization of the reaction volume of the chamber in bioassays. As the reactor gets smaller, surface tension dominates the gravitational or inertial force, and mixing efficiency decreases in small-scale reactions. Because passive mixing by simple diffusion in tens of microliter-scale volumes takes a long time, active mixing is needed. Here, we report an efficient micromixing method using magnetically rotating microparticles with patterned magnetization induced by magnetic nanoparticle chains. Because the microparticles have magnetization patterning due to fabrication with magnetic nanoparticle chains, the microparticles can rotate along the external rotating magnetic field, causing micromixing. We validated the reaction efficiency by comparing this micromixing method with other mixing methods such as simple diffusion and the use of a rocking shaker at various working volumes. This method has the potential to be widely utilized in suspension assay technology as an efficient mixing strategy

An unusual cause of duodenal perforation due to a lollipop stick

Children have a natural tendency to explore objects with their mouths; this can result in the swallowing of foreign objects. Most ingested foreign bodies pass uneventfully through the gastrointestinal tract. However, some foreign bodies cause obstruction or perforation of the gastrointestinal tract, requiring surgical intervention. Perforation of the gastrointestinal tract may be associated with considerable morbidity and mortality. The most common sites of intestinal foreign body perforation are the ileocecal and rectosigmoid regions. Foreign body perforation of the duodenum is relatively uncommon. We report the first Korean case of duodenal perforation by an ingested 8-cm lollipop stick. Lollipops are popular with the children and fairly accessible to them, as most parents are not aware of their potential harm. Pediatric clinicians should be aware of the risks associated with lollipop stick ingestion. Our report also describes the feasibility and safety of laparoscopic diagnosis and management of pediatric patients with peritonitis induced by the ingestion of foreign bodies