Search

Two recent experiments for adsorbed acrylonitrile on the Si(001) surface reported different adsorption structures at 110 and 300 K. We investigate the reaction of acrylonitrile on Si(001) by first-principles density-functional calculations. We find that the so-called [4+2] structure in which acrylonitrile resides between two dimer rows is not only thermodynamically favored over other structural models but also easily formed via a precursor where the N atom of acrylonitrile is attached to the down atom of the Si dimer. The additional initial-state theory calculation for the C 1s core levels of adsorbed acrylonitrile provides an interpretation for the observed low- and room-temperature adsorption configurations in terms of the precursor and [4+2] structures, respectively. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The adsorption and reaction of acetonitrile (CH[sub 3]CN) on the Si(001) surface are investigated by first-principles density-functional calculations within the generalized gradient approximation. We find that two di-σ configurations in which CH[sub 3]CN bonds on top of a Si dimer and across the ends of two adjacent Si dimers in the same dimer row have adsorption energies of 1.43 and 1.35 eV, respectively. On the other hand, our calculated adsorption energy for the cross-row bridging structure (in which CH[sub 3]CN adsorbs between two dimer rows) is 0.52 eV, much smaller than that (0.91 eV) of a precursor state where the N atom bonds to the down-buckled atom of the Si dimer. This result does not support the conclusion drawn from a combination of temperature programmed desorption spectroscopy and density functional cluster calculations, where one of the two observed desorption states was assigned to the cross-row bridging structure. Based on our results for the energetics of various adsorption configurations and the energy profile of the reaction pathways, we provide a reinterpretation for the observed desorption states. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A theoretical analysis was conducted on the characteristics and performance of an optically combined dual-loop optoelectronic oscillator (OC-DOEO) based on an open-loop response method. The OC-DOEO utilizes the Vernier effect to eliminate spurious tones while accompanying the optical interference among the dual-loop signals. It was determined that the optical interference in the OC-DOEO significantly affected the OEO performances, including loop efficiency, phase noise, and spurious tones. It was demonstrated that DOEO performances can be maximized by controlling dual-loop parameters, such as the phase delay and power-split ratio, without spurious tones. [ABSTRACT FROM AUTHOR]

The phase modulation (PM) and amplitude modulation (AM) of optical signals can be achieved using a direct-modulated (DM) optical injection-locked (OIL) semiconductor laser. We propose and theoretically analyze a simple method to extract the phase component of a PM signal produced by a DM-OIL semiconductor laser. The pure AM component of the combined PM–AM signal can be isolated by square-law detection in a photodetector and can then be used to compensate for the PM–AM signal based on an optical homodyne method. Using the AM compensation technique, we successfully developed a simple and cost-effective phase extraction method applicable to the PM–AM optical signal of a DM-OIL semiconductor laser. [ABSTRACT FROM AUTHOR]

To improve the detection rate of gastrointestinal tumors, image-enhanced endoscopy has been widely used during screening and surveillance endoscopy in Korea. In addition to narrow band imaging (NBI) with/without magnification, various types of electronic chromoendoscopies have been used, including autofluorescence imaging, I-scan, and flexible spectral imaging color enhancement. These technologies enable the accurate characterization of tumors because they enable visualization of microvascular and microsurface patterns. The present review focuses on understanding the principle and clinical applications of advanced imaging technologies other than NBI. [ABSTRACT FROM AUTHOR]

The search for one-dimensional electron systems with a giant Rashba-type spin splitting is of importance for the application of spin transport. Here we report, based on a first-principles density-functional-theory calculation, that Bi zigzag chains formed on a heterogeneous GaAs(110) surface have a giant spin splitting of surface states. This giant spin splitting is revealed to originate from spin-orbit coupling (SOC) and electric dipole interaction that are significantly enhanced by (i) the asymmetric surface charge distribution due to the strong SOC-induced hybridization of the Bi px, py, and pz orbitals and (ii) the large out-of-plane and in-plane potential gradients generated by two geometrically and electronically inequivalent Bi atoms bonding to Ga and As atoms. The results demonstrate an important implication of the in-plane and out-of-plane asymmetry of the Bi/GaAs(110) interface system in producing the giant spin splitting with the in-plane and out-of-plane spin components. [ABSTRACT FROM AUTHOR]

Background and study aim: This study aimed to evaluate the feasibility of a novel laser system for endoscopic submucosal dissection (ESD) of gastric epithelial neoplasia. Patients and methods: A total of 10 patients underwent ESD by a single expert endoscopist. A thulium 2-μm wavelength laser system was used for ESD procedures. Instead of using endoscopy knives, a 550-μm flexible silica fiber was inserted through the working channel of the endoscope. Results: In all patients, ESD was completed using only the thulium laser, without the need for endoscopy knives. The median total procedure time was 49 minutes (range 35-203). In 8/10 patients (80 %), no active bleeding was observed during ESD. The final pathologic mapping revealed low-grade dysplasia (n=4), differentiated adenocarcinoma (n=5), and signet ring cell carcinoma (n=1). Curative resection was achieved in 9/10 patients (90 %). There were no significant complications, such as delayed bleeding or perforation. Conclusions: The thulium laser system was feasible in ESD of gastric epithelial neoplasia. [ABSTRACT FROM AUTHOR]

Recent experimental evidence that fluorinated graphene creates local magnetic moments around F adatoms has not been supported by semilocal density-functional theory (DFT) calculations where the adsorption of an F adatom induces no magnetic moment in graphene. Here, we show that such an incorrect prediction of the nonmagnetic ground state is due to the self-interaction error inherent in semilocal exchange-correlation functionals. The present hybrid DFT calculation for an F adatom on graphene predicts not only a spin-polarized ground state with a spin moment of ∼1 μB, but also a long-range spin polarization caused by the bipartite nature of the graphene lattice as well as the induced spin polarization of the graphene states. The results provide support for the experimental observations of local magnetic moments in fluorinated graphene. [ABSTRACT FROM AUTHOR]

The precise driving force of the phase transition in indium nanowires on Si(111) has been controversial whether it is driven by a Peierls instability or by a simple energy lowering due to a periodic lattice distortion. The present van der Waals (vdW) corrected hybrid density functional calculation predicts that the low-temperature 8 x 2 structure whose building blocks are indium hexagons is energetically favored over the room-temperature 4 x 1 structure. We show that the correction of self-interaction error and the inclusion of vdW interactions play crucial roles in describing the covalent bonding, band-gap opening, and energetics of hexagon structures. The results manifest that the formation of hexagons occurs by a simple energy lowering due to the lattice distortion, not by a charge density wave formation arising from Fermi surface nesting. [ABSTRACT FROM AUTHOR]

Background/Aims: In hospitalized patients with acute steroid-refractory UC, infliximab has been demonstrated to be one of the medical rescue therapies to avoid colectomy. We report the result of a retrospective observational study to find the efficacy and safety of infliximab as a rescue therapy in our hospital. Methods: Between January 2007 and January 2010, 9 hospitalized patients with steroid-refractory UC were selected to receive three infusions of infliximab (5 mg/kg), at weeks 0, 2, and 6. Efficacy of treatment was evaluated at 8 weeks after the first infliximab infusion and at the end of follow-up period. Adverse events related to infliximab rescue therapy were also collected. Results: Seven patients (77.8%) had completed 3 infusions of infliximab and achieved clinical response at 8 weeks after the first infliximab infusion. Clinical remission rate and the rate of mucosal healing at 8 weeks were 57.1% (4/7) and 71.4% (5/7), respectively. They were followed up for median time of 24.9 months (19.5-53.6 months). One patient underwent emergency colectomy at weeks 2, due to colon perforation, while another patient had discontinued infliximab treatment at weeks 4, because of Clostridium difficile-associated colitis. Finally, colectomy was avoided in 77.8% (7/9) of cases. There was no mortality. Conclusions: Rescue therapy with infliximab has sustained clinical benefit in 88.9% of our hospitalized patients with acute steroid-refractory UC. Future prospective and long-term follow-up trials with a large number of patients are needed to confirm the efficacy and safety of the treatment. [ABSTRACT FROM AUTHOR]

We present theoretical investigations of the self-assembled growth of one-dimensional (1D) molecular lines directed across the dimer rows on the H-terminated Si(001)-(2 × 1) surface. Based on density-functional theory calculations, a growth approach of the 1D acetylacetone line is proposed, which involves the radical chain reaction initiated at two dangling-bond sites on one side of two adjacent Si dimers. It is also enabled that, if an H-free Si dimer were employed as the initial reaction site, a 1D acetylacetone line can grow along the dimer row. Our findings represent a novel insight into the growth of 1D molecular lines not only across but also along the dimer rows on the H-terminated Si(001)-(2 × 1) surface. [ABSTRACT FROM AUTHOR]

Using first-principles density-functional calculations, we investigate the structure and growth mechanism of allyl mercaptan lines on the H-terminated Si(100)-2 × 1 surface. The earlier structural model (termed the linear structure), where the terminal C atom of the C=C bond initially reacts with a single Si dangling bond, has been competing with a new structural model (termed the branched structure) where the medial C atom of the C=C bond initially reacts with a single Si dangling bond. We find that formation of the branched structure is kinetically unfavored over that of the linear structure. Moreover, the simulated scanning tunneling microscopy (STM) image of the branched structure cannot reproduce the features observed in the STM experiment, such as the position and origin of the bright protrusion. Thus, the present results do not support the branched structure in many respects. [ABSTRACT FROM AUTHOR]

Using first-principles density-functional calculations, we investigated two competing pathways for the dissociation of water and ammonia on a Si(001) surface. For both systems, we found that, in addition to the conventionally accepted intradimer transfer of the H atom, the interdimer transfer of the H atom can be equally probable with the same reaction mechanism. Our analysis shows that the two dissociation pathways occur through the Lewis acid−base reaction between the partially positive H ion and the electron-abundant up atom of the buckled Si dimer. The result of the interdimer H transfer not only supports a recently proposed model for C-defect on Si(001) but also corresponds to the recent scanning tunneling microscopy data of ammonia dissociation on Si(001). [ABSTRACT FROM AUTHOR]

A 59-year-old Asian woman suffered from a TCH followed by sudden, binocular blurred vision, mimicking pituitary apoplexy. The diagnostic workup (including fluorescein angiography, MRI of the brain, and CSF analysis) showed severe optic disc swelling and dye leakage of multiple faint hyperfluorescent spots at retinal pigment epithelium level, diffuse pachymeningeal hypertrophy, and monocytic pleocytosis, respectively. VKH disease should be considered in the differential diagnosis of patients presenting with a TCH followed by sudden, bilateral decreased visual acuity. [ABSTRACT FROM AUTHOR]

A recent scanning tunneling microscope nanolithography technique can fabricate one-dimensional “dangling-bond (DB) wire” by the selective removal of H atoms from a H-passivated Si(001) surface along the Si dimer row. We here theoretically investigate the bonding geometry, band structure, and binding mechanism of an armchair (3,3) single-walled carbon nanotube (CNT) adsorbed on the DB wire. We find that the formation of C–Si bonds between the CNT and the DB wire gives rise to hybridization between the carbon π-bond states and the Si dangling-bond states. This hybridization breaks the rotational symmetry of the (3,3) CNT whose π-bonding and π-antibonding bands cross at the Fermi level. As a result, the adsorbed CNT opens an energy gap of ∼0.1 eV, yielding a metal-to-semiconductor transition. [ABSTRACT FROM AUTHOR]

The dissociative adsorption of an H2 molecule on the Si(001) surface, which has been experimentally identified in terms of dissociation on one side of two adjacent Si dimers, is investigated by spin polarized density-functional calculations within the generalized-gradient approximation. In contrast to the prevailing nonmagnetic configuration of charge ordering, we propose a new ground state where the two single dangling bonds (DBs) created by H2 dissociation are antiferromagnetically coupled with each other. Such a spin ordering is found to be energetically favored over the previously proposed charge ordering. In the latter configuration, the buckling of the two DBs amounts to a height difference (Δh) of 0.63 Å, caused by a Jahn–Teller-like distortion, while in the former configuration, their buckling is almost suppressed to be Δh=0.03 Å as a consequence of spin polarization. [ABSTRACT FROM AUTHOR]

Using first-principles density-functional calculations, we investigate the reaction of acetone on the Si(001) surface, which exhibits the conversion from a kinetically controlled reaction to thermodynamically controlled one by means of thermal anneal or the highly confined electron beam of the scanning tunneling microscopy (STM) tip. We identified the four different reaction pathways forming not only two kinds of di-σ structures on top of a single Si dimer (termed as the [2+2] cycloaddition structure) and across the ends of two adjacent Si dimers but also two bridge-bonded dissociative structures (termed the “end-bridge” and “dimer-bridge” structures) involving two adjacent Si dimers. Our calculated energy profiles for the reaction pathways show not only that formation of the [2+2] cycloaddition structure is kinetically favored because of its low-energy barrier, but also that, as temperature increases, the kinetically favored [2+2] cycloaddition structure is converted to the more thermodynamically stable end-bridge and dimer-bridge structures via an intermediate state where the O atom forms a dative bond to the down Si atom of the buckled dimer. In addition, we find that the Si–C bonding (antibonding) states of the [2+2] cycloaddition structure appear at about 1–2 (2–3) eV below (above) the Fermi level, in which injected holes (electrons) through the STM tip can be created (trapped) to give rise to a Si–C bond breakage. These results manifest that the kinetically controlled reaction of acetone on Si(001) is associated with the [2+2] cycloaddition structure, rather than the α-H cleavage structure proposed by a recent STM experiment. [ABSTRACT FROM AUTHOR]

Sedation, defined as the depressed level of consciousness, induced by drug administration, is widely used for gastrointestinal endoscopy to relieve a patient's anxiety and discomfort. In addition, successful procedure is anticipated with control of unintended movements. Endoscopic sedation, however, cannot be free from the risk of serious adverse events, e.g., cardiopulmonary compromise. Therefore, principles on personnel, facility and equipment, as well as performance itself, should be followed to prevent unfavorable incidents. In this article, sedation guidelines for the Accreditation of Qualified Endoscopy Units, issued by the Korean Society of Gastrointestinal Endoscopy, are presented [ABSTRACT FROM AUTHOR]

As a prototypical one-dimensional electron system, self-assembled indium (In) nanowires on the Si(111) surface have been believed to drive a metal-insulator transition by a charge-density-wave (CDW) formation due to Fermi surface nesting. Here, our first-principles calculations demonstrate that the structural phase transition from the high-temperature 4×1 phase to the low-temperature 8×2 phase occurs through an exothermic reaction with the consecutive bond-breaking and bond-making processes, giving rise to an energy barrier between the two phases as well as a gap opening. This atomistic picture for the phase transition not only identifies its first-order nature but also solves a long-standing puzzle of the origin of the metal-insulator transition in terms of the ×2 periodic lattice reconstruction of In hexagons via bond breakage and new bond formation, not by the Peierls-instability-driven CDW formation. [ABSTRACT FROM AUTHOR]

The article discusses the Peierls instability in one-dimensional borine wire. The dangling bond (DB) wire is generated by the selective removal of H atoms from an H-passivated Si(001) surface using the scanning tunneling microscope (STM) nanolithography technique. The DB wire can be utilized as a template for the fabrication of a molecular wire.

The article reports on the theoretical prediction of heterogeneous molecular wires on the Si(001) surface. Hybrid organic molecular silicon surfaces have potential application for new sensor and molecular device technologies. Feedback controlled lithography was used to generate arbitrary arrays of individual dangling bonds on the silicon surface.

Background/Aims: Currently, a new over-the-scope clip (OTSC) system has been introduced. This system has been used for gastrointestinal perforations and fistulas in other countries. The aim of our study is to examine the therapeutic success rate of endoscopic treatment using the OTSC system in Korea. Methods: This was a multicenter prospective study. A total of seven endoscopists at seven centers performed this procedure. Results: A total of 19 patients were included, with gastrointestinal leakages from anastomosis sites, fistulas, or esophageal perforations due to Boerhaave's syndrome. Among these, there were three gastrojejunostomy sites, three esophagojejunostomy sites, four esophagogastrostomy sites, one esophagocolonostomy site, one jejuno-jejunal site, two endoscopic full thickness resection site closures, one Boerhaave's syndrome, two esophago-bronchial fistulas, one gastrocolonic fistula, and one colonopseudocyst fistula. The size of the leakage ranged from 5 to 30 mm. The median procedure time was 16 min. All cases were technically successful. Complete closure of the leak was achieved in 14 of 19 patients using OTSC alone. Conclusions: The OTSC system is a safe and effective method for the management of gastrointestinal leakage, especially in cases of anastomotic leakage after surgery. [ABSTRACT FROM AUTHOR]

A recent density-functional calculation for fcc C60Hn (n = odd) [K. W. Lee and C. E. Lee, Phys. Rev. Lett. 106, 166402 (2011)] proposed the existence of Stoner ferromagnetism based on an itinerant band model. However, our density-functional calculation shows that the antiferromagnetic (AFM) configuration is slightly more stable than the ferromagnetic (FM) one. This preference for antiferromagnetism over ferromagnetism is analogous to the case of a dimer (C60H)2, where each C60H is spin polarized by an intramolecular exchange and the two magnetic moments are antiferromagnetically coupled with each other. The results demonstrate that the underlying mechanism of the magnetic order in fcc C60Hn is associated with the AFM superexchange between the magnetic moments created by H dopants. [ABSTRACT FROM AUTHOR]

Using a hybrid density-functional theory (DFT) calculation including spin-orbit coupling (SOC), we predict that the zigzag antiferromagnetic (AFM) ground state of the honeycomb layered compound Na2IrO3 opens the observed insulating gap through a long-range magnetic order. We show that the effect of SOC and the correction of self-interaction error inherent in previous local or semilocal DFT calculations play crucial roles in predicting the band gap formation in Na2IrO3. It is revealed that the itinerant AFM order with a strong suppression of the Ir magnetic moment is attributed to a considerable hybridization of the Ir 5d orbitals with the O 2p orbitals. Thus, our results suggest that the insulating phase of Na2IrO3 can be represented as a Slater insulator driven by itinerant magnetism. [ABSTRACT FROM AUTHOR]

We perform semilocal and hybrid density-functional theory (DFT) studies of the Sn/Ge(111) surface to identify the origin of the observed insulating √3×√3 phase below ~30  K. In contrast with the semilocal DFT calculation predicting a metallic 3×3 ground state, the hybrid DFT calculation including van der Waals interactions shows that the insulating ferrimagnetic structure with a ~3×√3 structural symmetry is energetically favored over the metallic 3×3 structure. It is revealed that the correction of the self-interaction error with a hybrid exchange-correlation functional gives rise to a band gap opening induced by a ferrimagnetic order. The results show that the observed insulating phase is attributed to the Slater mechanism via itinerant magnetic order rather than the hitherto accepted Mott-Hubbard mechanism via electron correlations. [ABSTRACT FROM AUTHOR]

van der Waals energy-corrected density functional theory (DFT + vdW) as well as the exact exchange with electron correlation in the random-phase approximation are used to study the adsorption of benzene on the Si(001) surface with respect to two controversial adsorption structures (termed "butterfly" and "tight bridge"). Our finding that the tight-bridge structure is energetically favored over the butterfly structure agrees with standard DFT but conflicts with previous vdW-inclusive calculations. However, the inclusion of zero-point energy and thermal vibrations reverses the stability of the two structures with increasing temperature. Our results provide an explanation for the recent experimental observation that both structures coexist at room temperature. [ABSTRACT FROM AUTHOR]

First-principles calculations combined with kinetic Monte Carlo simulations are carried out to unambiguously demonstrate the vital role of van der Waals (vdW) interactions in the self-assembly of styrene nanowires on H-terminated Si(100) surfaces. We find that, only with the inclusion of London dispersion forces, accounting for the attractive parts of vdW interactions, are the effective intermolecular interactions reversed from repulsive to attractive. Such attractive interactions, in turn, ensure the preferred growth of long wires under physically realistic conditions as observed experimentally. We further propose a cooperative scheme, invoking the application of an electric field and the selective creation of Si dangling bonds, to drastically improve the ordered arrangement of the molecular nanowires. The present paper represents a significant step forward in the fundamental understanding and precise control of molecular self-assembly guided by London dispersion forces. [ABSTRACT FROM AUTHOR]

Using first-principle density-functional calculations, we investigate the competition between Peierls instability and spin ordering in a zigzag C chain generated in an H-passivated graphene. We find that such a quasi-one-dimensional (1D) C chain of infinite length stabilizes a Peierls instability showing bond alternation with a band-gap opening. As the chain length becomes finite, the Peierls distortion is enhanced at even-numbered chains, while a ferrimagnetic spin ordering with the atomic structure of a topological soliton is stabilized at odd-numbered chains. These results indicate the existence of complex interplay between electron-lattice and electron-electron interactions with respect to the parity of the quasi-1D C chains. [ABSTRACT FROM AUTHOR]

Background/Aims: The aim of this in vivo animal study was to evaluate the effectiveness and safety of dedicated cold snare (DCS) compared with those of traditional snare (TS) for cold snare polypectomy (CSP). Methods: A total of 36 diminutive (5 mm) and 36 small (9 mm) pseudolesions were made by electrocoagulation in the colons of mini-pigs. Results: For the diminutive lesions, there were no significant differences in technical success rate, procedure time, or complete resection rate between the DCS and TS groups; the rate of uneven resection margin in the DCS group was significantly lower than that of the TS group. For small lesions, technical success rate and complete resection rate were significantly higher in the DCS group than in the TS group (100% [18/18] vs. 55.6% [10/18], p=0.003; 94.4% [17/18] vs. 40% [4/10], p=0.006). In addition, the procedure duration was significantly shorter, and the rate of uneven resection margin was significantly lower in the DCS group (28.5 sec vs. 66.0 sec, p=0.006; 11.1% [2/18] vs. 100% [10/10], p<0.001). Two cases of perforation occurred in the DCS group. Multivariate analysis revealed that DCS use was independently associated with complete resection. Conclusions: DCS is superior to TS in terms of technical success, complete resection, and reducing the duration of the procedure for CSP of small polyps. [ABSTRACT FROM AUTHOR]

Background/Aims: Neutrophil to lymphocyte ratio (NLR) and platelet to lymphocyte ratio (PLR) can serve as biomarkers for diagnosing and assessing disease activity in ulcerative colitis (UC). We investigated their clinical significance in UC. Methods: We analyzed 48 patients with UC who underwent measurement of fecal calprotectin (FC) and endoscopy and 96 age- and sexmatched healthy controls. NLR and PLR were compared between the patients and healthy controls. The endoscopic activity was divided into 2 groups: group 1 (mild to moderate inflammation) and group 2 (severe inflammation) according to the Mayo endoscopic subscore in UC. Results: To diagnose UC, the optimal cutoff of NLR and PLR was 2.26 (sensitivity 54.2%; specificity 90.6%; positive likelihood ratio 5.778, 95% confidence interval [CI] 2.944–11.339; area under the curve [AUC] 0.774, 95% CI, 0.690–0.859) and 179.8 (sensitivity 35.4%; specificity 90.6%; positive likelihood ratio 3.778, 95% CI 1.821–7.838; AUC 0.654, 95% CI 0.556–0.753), respectively. The optimal cutoff to differentiate group 1 and group 2 was 3.44, 175.9, and 453 µg/g for NLR, PLR, and FC, respectively (sensitivity, 63.6% vs. 90.9% vs. 81.8%; specificity, 81.1% vs. 78.4% vs. 73.0%; positive likelihood ratio, 3.364 vs. 4.205 vs. 3.027; AUC, 0.714 vs. 0.897 vs. 0.813). PLR had the highest AUC and positive likelihood ratio. Conclusions: NLR and PLR help differentiate patients with UC from healthy controls. NLR, PLR, and FC indicate endoscopic activity and may reflect intestinal mucosal conditions. [ABSTRACT FROM AUTHOR]

We present first-principles density-functional calculations for the electronic properties of nitrogen(N)-doped as well as carbon(C)-doped titanium dioxide (TiO2). We find that the bands originating from N (C) 2p states appear in the band gap of TiO2, but the mixing of N (C) with O 2p states is too weak to produce a significant band-gap narrowing. Our results are consistent with several recent experimental data of N-doped TiO2, where the absorption of visible light is due to isolated N 2p states above the valence-band maximum of TiO2 rather than due to a band-gap narrowing. [ABSTRACT FROM AUTHOR]

Two-dimensional layered transition-metal-dichalcogenide (TMDC) materials often exhibit exotic quantum phases due to the delicate coupling and competitions of charge, lattice, orbital, and spin degrees of freedom. Surprisingly, we here present, based on first-principles density-functional theory calculations, the incorporation of all such degrees of freedom in a charge density wave (CDW) of monolayer (ML) TMDC 1T - TaS2. We reveal that this CDW accompanying the lattice distortion to the "David-star" (DS) superstructure constituted of one cental, six nearest-neighbor, and six next-nearest-neighbor Ta atoms is driven by the formation of quasimolecular orbitals due to a strong hybridization of Ta t2g orbitals. The resulting weakly overlapped nonbonding orbitals between the DS clusters form a narrow half-filled band at the middle of the CDW gap, leading to the Stoner-type magnetic instability caused by an intramolecular exchange interaction. It is thus demonstrated that the Stoner parameter I corresponding to the effective on-site Coulomb interaction U opens a Mott gap. Our finding of the intricate charge-lattice-orbital-spin coupling in ML 1T - TaS2 provides a framework for the exploration of various CDW phases observed in few-layer or bulk 1T - TaS2. [ABSTRACT FROM AUTHOR]

Low-dimensional electron systems often show a delicate interplay between electron-phonon and electron-electron interactions, giving rise to interesting quantum phases such as the charge density wave (CDW) and magnetism. Using the density-functional theory (DFT) calculations with the semilocal and hybrid exchange-correlation functionals as well as the exact-exchange plus correlation in the random-phase approximation (EX+cRPA), we systematically investigate the ground state of the metallic atom wires containing dangling-bond (DB) electrons, fabricated by partially hydrogenating the GaN(10 ¯ 1 0) and ZnO(10 ¯ 1 0) surfaces. We find that the CDW or antiferromagnetic (AFM) order has an electronic energy gain due to a band-gap opening, thereby being more stabilized compared to the metallic state. Our semilocal DFT calculation predicts that both DB wires in GaN(10 ¯ 1 0) and ZnO(10 ¯ 1 0) have the same CDW ground state, whereas the hybrid DFT and EX+cRPA calculations predict the AFM ground state for the former DB wire and the CDW ground state for the latter one. It is revealed that more localized Ga DB electrons in GaN(10 ¯ 1 0) prefer the AFM order, while less localized Zn DB electrons in ZnO(10 ¯ 1 0) the CDW formation. Our findings demonstrate that the drastically different ground states are competing in the DB wires created on the two representative compound semiconductor surfaces. [ABSTRACT FROM AUTHOR]

Background/Aims: Although the role of capsule endoscopy (CE) in Crohn's disease (CD) has expanded, CE is not used routinely for diagnosing and evaluating CD in Korea. We aimed to investigate current patterns of practice and evaluate the clinical significance of the use of CE in CD in Korean patients. Methods: Among 651 CE procedures performed for various indications, we retrospectively analyzed the medical records of patients who underwent CE in 57 cases of suspected CD (sCD) and 14 cases of established CD (eCD). Results: In the sCD group, CE was most commonly used for the initial diagnosis of CD (54.4%). Capsule retention was found in only 1 patient in the eCD group (1/71, 1.4%). In the sCD group, 28.1% of patients were diagnosed with CD on the basis of CE findings; other diseases diagnosed included tuberculous enteritis (7.0%), non-steroidal anti-inflammatory drug-induced enteropathy (5.3%), and other enteritis (17.5%). Only 11.5% of patients with eCD (14/122) underwent CE. The indication for CE in the 14 patients with eCD was to assess disease extent and activity. The overall diagnostic yield of CE was 59.7%. Therapeutic strategies were changed in 70.2% of patients in the sCD group and 50% of those in the eCD group based on CE findings. Conclusions: In clinical practice, CE was most commonly indicated for the initial diagnosis of CD and was not generally performed in patients with eCD. CE appears to be an effective diagnostic modality for evaluating sCD and is useful for determining therapeutic strategies for patients with sCD and those with eCD. [ABSTRACT FROM AUTHOR]

Background/Aims: We evaluated whether manometric subtype is associated with treatment outcome in patients with achalasia treated by peroral endoscopic myotomy (POEM). Methods: High-resolution manometry data and Eckardt scores were collected from 83 cases at two tertiary referral centers where POEM is performed. Manometric tracings were classified according to the three Chicago subtypes. Results: Among the 83 cases, 48 type I, 24 type II, and 11 type III achalasia cases were identified. No difference was found in pre-POEM Eckardt score, basal lower esophageal sphincter (LES) pressure, or integrated relaxation pressure (IRP) among the type I, type II, and type III groups. All three patient groups showed a significant improvement in post-POEM Eckardt score (6.1±2.1 to 1.5±1.5, p=0.001; 6.8±2.2 to 1.2±0.9, p=0.001; 6.6±2.0 to 1.6±1.4, p=0.011), LES pressure (26.1±13.8 to 15.4±6.8, p=0.018; 32.3±19.0 to 19.2±10.4, p=0.003; 36.8±19.2 to 17.5±9.7, p=0.041), and 4s IRP (21.5±11.7 to 12.0±8.7, p=0.007; 24.5±14.8 to 12.0±7.6, p=0.002; 24.0±15.7 to 11.8±7.1, p=0.019) at a median follow-up of 16 months. Conclusions: POEM resulted in a good clinical outcome for all manometric subtypes. [ABSTRACT FROM AUTHOR]

Quantum growth refers to the phenomena in which the quantum mechanically confined motion of electrons in metallic wires, islands, and films determines their overall structural stability as well as their physical and chemical properties. Yet to date, there has been a lack of a unified understanding of quantum growth with respect to the dimensionality of the nanostructures as well as the valency of the constituent atoms. Based on a first-principles approach, we investigate the stability of nanowires, nanoislands, and ultrathin films of prototypical metal elements. We reveal that the Friedel oscillations generated at the edges (or surfaces) of the nanostructures cause corresponding oscillatory behaviors in their stability, leading to the existence of highly preferred lengths (or thicknesses). Such magic lengths of the nanowires are further found to depend on both the number of valence electrons and the radial size, with the oscillation period monotonously increasing for alkali and group IB metals, and monotonously decreasing for transition and group IIIA-VA metals. When the radial size of the nanowires increases to reach ∼10 Å, the systems equivalently become nanosize islands, and the oscillation period saturates to that of the corresponding ultrathin films. These findings offer a generic perspective of quantum growth of different classes of metallic nanostructures. [ABSTRACT FROM AUTHOR]

The exploration of topological states is of significant fundamental and practical importance in contemporary condensed matter physics, for which the extension to two-dimensional (2D) organometallic systems is particularly attractive. Using first-principles calculations, we show that a 2D hexagonal triphenyl-lead lattice composed of only main group elements is susceptible to a magnetic instability, characterized by a considerably more stable antiferromagnetic (AFM) insulating state rather than the topologically nontrivial quantum spin Hall state proposed recently. Even though this AFM phase is topologically trivial, it possesses an intricate emergent degree of freedom, defined by the product of spin and valley indices, leading to Berry curvature-induced spin and valley currents under electron or hole doping. Furthermore, such a trivial band insulator can be tuned into a topologically nontrivial matter by the application of an out-of-plane electric field, which destroys the AFM order, favoring instead ferrimagnetic spin ordering and a quantum anomalous Hall state with a nonzero topological invariant. These findings further enrich our understanding of 2D hexagonal organometallic lattices for potential applications in spintronics and valleytronics. [ABSTRACT FROM AUTHOR]

Background/Aims: Pneumoperitoneum is recognized as a benign and self-limiting finding after the insertion of a percutaneous endoscopic gastrostomy (PEG) tube, while complicated pneumoperitoneum is rarely reported. The aim of this study was to reappraise pneumoperitoneum following PEG. Methods: We retrospectively reviewed 193 patients who underwent PEG from May 2008 to May 2014. All patients had a follow-up upright chest or simple abdominal radiograph after PEG. Pneumoperitoneum was quantified by measuring the height of the air column under the diaphragm and graded as small (<2 cm), moderate (2−4 cm), or large (>4 cm). Clinically significant signs were defined as fever, abdominal tenderness or leukocytosis occurring after PEG insertion. Results: Of the 193 study patients, 9 (4.6%) had a pneumoperitoneum visualized by radiographic imaging, graded as small in 5 patients, moderate in 2 patients and large in 2 patients. Clinically significant signs were observed in 5 (55.5%) patients with fever reported in 4 patients, abdominal tenderness in 4 patients and leukocytosis in 4 patients. The time to resolution of free air was 2−18 days. Two patients (22.2%) with moderate or large pneumoperitoneum after PEG died from either pneumonia or septic shock. Conclusions: The clinical course of pneumoperitoneum after PEG is not always benign and self-limiting. These findings suggest that clinicians should not neglect a moderate or large pneumoperitoneum, particularly in patients who have an altered mental status or received antibiotics, since peritoneal irritation cannot be observed under these circumstances. [ABSTRACT FROM AUTHOR]

Background/Aims: Currently, the videofluoroscopic swallowing study (VFSS) is the standard tool for evaluating dysphagia. We evaluated whether the addition of endoscopist-directed flexible endoscopic evaluation of swallowing (FEES) to VFSS could improve the detection rates of penetration, aspiration, and pharyngeal residue, compared the diagnostic efficacy between VFSS and endoscopist-directed FEES and assessed the adverse events of the FEES. Methods: In single tertiary referral center, a retrospective analysis of prospectively collected data was conducted. Fifty consecutive patients suspected of oropharyngeal dysphagia were enrolled in this study between January 2012 and July 2012. Results: The agreement in the detection of penetration and aspiration between VFSS and FEES of viscous food (κ=0.34; 95% confidence interval [CI], 0.15 to 0.53) and liquid food (κ=0.22; 95% CI, 0.02 to 0.42) was “fair.” The agreement in the detection of pharyngeal residue between the two tests was “substantial” with viscous food (κ=0.63; 95% CI, 0.41 to 0.94) and “fair” with liquid food (κ=0.37; 95% CI, 0.10 to 0.63). Adding FEES to VFSS significantly increased the detection rates of penetration, aspiration, and pharyngeal residue. No severe adverse events were noted during FEES, except for two cases of epistaxis, which stopped spontaneously without requiring any packing. Conclusions: This study demonstrated that the addition of endoscopist-directed FEES to VFSS increased the detection rates of penetration, aspiration, and pharyngeal residue. [ABSTRACT FROM AUTHOR]

The insulating ground state of the 5d transition metal oxide CaIrO3 has been classified as a Mott-type insulator. Based on a systematic density functional theory (DFT) study with local, semilocal, and hybrid exchange-correlation functionals, we reveal that the Ir t2g states exhibit large splittings and one-dimensional electronic states along the c axis due to a tetragonal crystal field. Our hybrid DFT calculation adequately describes the antiferromagnetic (AFM) order along the c direction via a superexchange interaction between Ir4+ spins. Furthermore, the spin-orbit coupling (SOC) hybridizes the t2g states to open an insulating gap. These results indicate that CaIrO3 can be represented as a spin-orbit Slater insulator, driven by the interplay between a long-range AFM order and the SOC. Such a Slater mechanism for the gap formation is also demonstrated by the DFT + dynamical mean field theory calculation, where the metal-insulator transition and the paramagnetic to AFM phase transition are concomitant with each other. [ABSTRACT FROM AUTHOR]

It was recently proposed that the stress state of a material can also be altered via electron or hole doping, a concept termed electronic stress (ES), which is different from the traditional mechanical stress (MS) due to lattice contraction or expansion. Here we demonstrate the equivalence of ES and MS in structural stabilization, using In wires on Si(l 11) as a prototypical example. Our systematic density-functional theory calculations reveal that, first, for the same degrees of carrier doping into the In wires, the ES of the high-temperature metallic 4 × 1 structure is only slightly compressive, while that of the low-temperature insulating 8 × 2 structure is much larger and highly anisotropic. As a consequence, the intrinsic energy difference between the two phases is significantly reduced towards electronically phase-separated ground states. Our calculations further demonstrate quantitatively that such intriguing phase tunabilities can be achieved equivalently via lattice-contraction induced MS in the absence of charge doping. We also validate the equivalence through our detailed scanning tunneling microscopy experiments. The present findings have important implications for understanding the underlying driving forces involved in various phase transitions of simple and complex systems alike. [ABSTRACT FROM AUTHOR]

Exploration and manipulation of electronic states in low-dimensional systems are of great importance in the fundamental and practical aspects of nanomaterial and nanotechnology. Here, we demonstrate that the incorporation of vacancy defects into monatomic indium wires on n-type Si(111) can stabilize electronically phase-separated ground states where the insulating 8 × 2 and metallic 4 × 1 phases coexist. Furthermore, the areal ratio of the two phases in the phase-separated states can be tuned reversibly by electric field or charge doping, and such tunabilities can be quantitatively captured by first principles-based modeling and simulations. The present results extend the realm of electronic phase separation from strongly correlated d-electron materials typically in bulk form to weakly interacting sp-electron systems in reduced dimensionality. [ABSTRACT FROM AUTHOR]

Background/Aims: Providers may be hesitant to perform double-balloon enteroscopy (DBE) in the elderly because the increased number of co-morbidities in this population poses a greater risk of complications resulting from sedation. There are limited data on the use of DBE in the elderly. Here, we assessed the safety and efficacy of DBE in the elderly compared to those in younger patients. Methods: We retrospectively analyzed the medical records of 158 patients who underwent 218 DBEs. Patients were divided into an elderly group (age =65 years; mean 71.4±5.4; n=34; 41 DBEs) and a younger group (age <65 years; mean 39.5±13.5; n=124; 177 DBEs). Results: In both groups, the most common indication for DBE was obscure gastrointestinal bleeding. Mucosal lesions (33.3% vs. 60.9%; P=0.002) were the most common finding in both groups, followed by tumors (30.8% vs. 14.1%; P=0.036). The elderly were more likely to receive interventional therapy (51.3% vs. 23.5%; P=0.001). The diagnostic yield of DBE was slightly higher in the elderly group (92.3% vs. 86.5%; P=0.422), but was not statistically significant. The thera- peutic success rate of DBE was 100% in the elderly group compared to 87.5% in the younger group (P=0.536). The overall DBE complication rate was 1.8% overall, and this rate did not differ significantly between the groups (2.6% vs. 1.7%; P=0.548). Conclusions: DBE is safe and effective in the elderly, and has a high diagnostic yield and high therapeutic success rate. [ABSTRACT FROM AUTHOR]

The Sn overlayer on the Si (111) surface has been considered as a prototypical system for exploring two- dimensional (2D) correlated physics on the triangular lattice. Most of the previous theoretical studies were based on the presumption that the surface state dominantly originates from Sn dangling-bond (DB) electrons, leading to a strongly correlated 2D electronic system. By contrast, our density-functional theory calculations show that the Sn DB state significantly hybridizes with Si substrate states to form a resonant state. The strong resonance between the Sn 5pz and Si 3pz orbitals facilitates the recently observed antiferromagnetic order through superexchange interactions, giving rise to a band-gap opening. It is thus demonstrated that the insulating ground state of Sn/Si(111) can be characterized as a Slater-type insulator via band magnetism. [ABSTRACT FROM AUTHOR]

We report a case of a 70-year-old man harboring a wide-necked thrombosed giant aneurysm of the left middle cerebral artery (MCA) on the M1 segment. The patient presented with generalized tonic-clonic seizures. A computerized tomography scan showed a calcified aneurysmal wall with perianeurysmal swelling. The aneurysm was successfully embolized using closed-cell nitinol stent-assisted coiling (Leo, BALT Co., Montmorency, France). [ABSTRACT FROM AUTHOR]

Recently, two-dimensional layered electrides have emerged as a new class of materials which possess anionic electrons in the interstitial spaces between cationic layers. Here, based on first-principles calculations, we discover a time-reversal-symmetry-breaking Weyl semimetal phase in a unique two-dimensional layered ferromagnetic (FM) electride Gd2C. It is revealed that the crystal field mixes the interstitial electron states and Gd-5d orbitals near the Fermi energy to form band inversions. Meanwhile, the FM order induces two spinful Weyl nodal lines (WNLs), which are converted into multiple pairs of Weyl nodes through spin-orbit coupling. Further, we not only identify Fermi-arc surface states connecting the Weyl nodes but also predict a large intrinsic anomalous Hall conductivity due to the Berry curvature produced by the gapped WNLs. Our findings demonstrate the existence of Weyl fermions in the room-temperature FM electride Gd2C, therefore offering a new platform to investigate the intriguing interplay between electride materials and magnetic Weyl physics. [ABSTRACT FROM AUTHOR]

A flatband representing a highly degenerate and dispersionless manifold state of electrons may offer unique opportunities for the emergence of exotic quantum phases. To date, definitive experimental demonstrations of flatbands remain to be accomplished in realistic materials. Here, we present the first experimental observation of a striking flatband near the Fermi level in the layered Fe3Sn2 crystal consisting of two Fe kagome lattices separated by a Sn spacing layer. The band flatness is attributed to the local destructive interferences of Bloch wave functions within the kagome lattices, as confirmed through theoretical calculations and modelings. We also establish high-temperature ferromagnetic ordering in the system and interpret the observed collective phenomenon as a consequence of the synergetic effect of electron correlation and the peculiar lattice geometry. Specifically, local spin moments formed by intramolecular exchange interaction are ferromagnetically coupled through a unique network of the hexagonal units in the kagome lattice. Our findings have important implications to exploit emergent flat-band physics in special lattice geometries. [ABSTRACT FROM AUTHOR]

Contemporary science is witnessing a rapid expansion of the two-dimensional (2D) materials family, each member possessing intriguing emergent properties of fundamental and practical importance. Using the particle-swarm optimization method in combination with first-principles density functional theory calculations, here we predict a new category of 2D monolayers named tellurene, composed of the metalloid element Te, with stable 1T-MoS2-like (α-Te), and metastable tetragonal (β-Te) and 2H-MoS2-like (γ-Te) structures. The underlying formation mechanism is inherently rooted in the multivalent nature of Te, with the central-layer Te behaving more metal-like (e.g., Mo), and the two outer layers more semiconductorlike (e.g., S). We also show that the α-Te phase can be spontaneously obtained from the magic thicknesses divisible by three layers truncated along the [001] direction of the trigonal structure of bulk Te, and both the α- and β-Te phases possess electron and hole mobilities much higher than MoS2. Furthermore, we present preliminary but convincing experimental evidence for the layering behavior of Te on HOPG substrates, and predict the importance of multivalency in the layering behavior of Se. These findings effectively extend the realm of 2D materials to group-VI elements. [ABSTRACT FROM AUTHOR]

Tuning band gaps in two-dimensional (2D) materials is of great interest for the fundamental and practical aspects of contemporary material sciences. Recently, black phosphorus (BP) consisting of stacked layers of phosphorene was experimentally observed to show a widely tunable band gap by means of the deposition of potassium (K) atoms on the surface, thereby allowing great flexibility in the design and optimization of electronic and optoelectronic devices. Here, based on density-functional theory calculations, we demonstrates that the donated electrons from K dopants are mostly localized in the topmost BP layer and this surface charging efficiently screens the K ion potential. It is found that, as the K doping increases, the extreme surface charging and its screening of K atoms shift the conduction bands down in energy, i.e., towards a higher binding energy, because they have more charge near the surface, while it has little influence on the valence bands having more charge in the deeper layers. This result provides a different explanation for the observed tunable band gap compared to the previously proposed giant Stark effect where a vertical electric field from the positively ionized K overlayer to the negatively charged BP layers shifts the conduction band minimum Γ1c (valence band minimum Γ8v) downwards (upwards). The present prediction of Γ1c and Γ8v as a function of the K doping reproduces well the widely tunable band gap, anisotropic Dirac semimetal state, and band-inverted semimetal state, as observed in an angle-resolved photoemission spectroscopy experiment. Our findings shed new light on a route for tunable band gap engineering of 2D materials through the surface doping of alkali metals. [ABSTRACT FROM AUTHOR]