Efficient Experimental Design for Measuring Magnetic Susceptibility of Arbitrarily Shaped Materials by MRI

This work was funded by the Institute for Basic Science, under grant IBS-R015-D1. The SQUID measurement was provided by Dr. Seung-young Park from Korea Basic Science Institute (KBSI). The authors acknowledge the support from the KSMRM MR Engineering Research Group. Copyright © 2018 Korean Society of Magnetic Resonance in Medicine (KSMRM22Nkc

Operative Treatment with a Laparotomy for Anorectal Problems Arising from a Self-Inserted Foreign Body

An anorectal foreign body can cause serious complications such as incontinence, rectal perforation, peritonitis, or pelvic abscess, so it should be managed immediately. We experienced two cases of operative treatment for a self-inserted anorectal foreign body. In one, the foreign body could not be removed as it was completely impacted in the anal canal. We failed to remove it through the anus. A laparotomy and removal of the foreign body was performed by using an incision on the rectum. Primary colsure and a sigmoid loop colostomy were done. A colostomy take-down was done after three months. The other was a rectal perforation from anal masturbation with a plastic device. We performed primary repair of the perforated rectosigmoid colon, and we didea sigmoid loop colostom. A colostomy take-down was done three months later. Immediate and proper treatment for a self-inserted anorectal foreign body is important to prevent severe complications, and we report successful surgical treatments for problems caused by anorectal foreign bodies

Clinical features and outcomes of gastric variceal bleeding: retrospective Korean multicenter data

Background/AimsWhile gastric variceal bleeding (GVB) is not as prevalent as esophageal variceal bleeding, it is reportedly more serious, with high failure rates of the initial hemostasis (>30%), and has a worse prognosis than esophageal variceal bleeding. However, there is limited information regarding hemostasis and the prognosis for GVB. The aim of this study was to determine retrospectively the clinical outcomes of GVB in a multicenter study in Korea.MethodsThe data of 1,308 episodes of GVB (males:females=1062:246, age=55.0±11.0 years, mean±SD) were collected from 24 referral hospital centers in South Korea between March 2003 and December 2008. The rates of initial hemostasis failure, rebleeding, and mortality within 5 days and 6 weeks of the index bleed were evaluated.ResultsThe initial hemostasis failed in 6.1% of the patients, and this was associated with the Child-Pugh score [odds ratio (OR)=1.619; P<0.001] and the treatment modality: endoscopic variceal ligation, endoscopic variceal obturation, and balloon-occluded retrograde transvenous obliteration vs. endoscopic sclerotherapy, transjugular intrahepatic portosystemic shunt, and balloon tamponade (OR=0.221, P<0.001). Rebleeding developed in 11.5% of the patients, and was significantly associated with Child-Pugh score (OR=1.159, P<0.001) and treatment modality (OR=0.619, P=0.026). The GVB-associated mortality was 10.3%; mortality in these cases was associated with Child-Pugh score (OR=1.795, P<0.001) and the treatment modality for the initial hemostasis (OR=0.467, P=0.001).ConclusionsThe clinical outcome for GVB was better for the present cohort than in previous reports. Initial hemostasis failure, rebleeding, and mortality due to GVB were universally associated with the severity of liver cirrhosis

Retrospective evaluation of whole exome and genome mutation calls in 746 cancer samples

Funder: NCI U24CA211006Abstract: The Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC) curated consensus somatic mutation calls using whole exome sequencing (WES) and whole genome sequencing (WGS), respectively. Here, as part of the ICGC/TCGA Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium, which aggregated whole genome sequencing data from 2,658 cancers across 38 tumour types, we compare WES and WGS side-by-side from 746 TCGA samples, finding that ~80% of mutations overlap in covered exonic regions. We estimate that low variant allele fraction (VAF < 15%) and clonal heterogeneity contribute up to 68% of private WGS mutations and 71% of private WES mutations. We observe that ~30% of private WGS mutations trace to mutations identified by a single variant caller in WES consensus efforts. WGS captures both ~50% more variation in exonic regions and un-observed mutations in loci with variable GC-content. Together, our analysis highlights technological divergences between two reproducible somatic variant detection efforts

Engineering the Synthesis and Properties of Two-Dimensional Colloidal Perovskite Nanoplatelets

Colloidal semiconductor nanocrystals are among the leading material platforms for a wide range of optoelectronic applications including photovoltaics, displays, photodetectors, and thermoelectrics. Their colloidal stability enables facile device fabrication by providing solution processability, and tunability of the bandgap with particle size opens up the opportunity to independently optimize nanocrystal properties for specific applications. Recently, colloidal lead halide perovskite nanoplatelets (chemical formula: L₂[ABX₃]ₙ₋₁BX₄, L: alkylammonium, A: methylammonium or formamidinium or cesium, B: lead, X: halide, n: number of [BX₆] ⁴⁻ octahedral layers in the direction of thickness) have emerged as a promising class of novel semiconductor nanocrystals capitalizing on their strong absorption, bright emission with high color purity, strong quantum- and dielectric-confinement, and anisotropic transition dipole moment orientation. This dissertation seeks to establish a robust synthetic protocol for the preparation of colloidal perovskite nanoplatelets and further engineer their desirable properties. First, I briefly review the history of perovskite nanoplatelets and introduce a protocol for the facile synthesis of colloidal perovskite nanoplatelets at room-temperature. Monodispersity of the nanoplatelets is confirmed by optical and structural characterizations. Photoluminescence and absorption spectra reveal strongly-confined excitonic features which can be tuned in the visible range by changing nanoplatelet thickness and varying the composition of halide anions. Furthermore, I show that multiple species of surface-bound alkylammonium ligands can be introduced. This demonstrates the possibility of further optimizing the surface properties of nanoplatelets which can hugely impact the charge transport behavior inside the device as well as the operating stability. Then I focus on lead bromide nanoplatelets, whose deep-blue luminescence makes it one of the leading light-emitting platforms for the next-generation displays. I systematically investigate key factors that determine the stability of the nanoplatelets under UV excitation, which mimics the condition of hot-carrier injection into an operating device. It is shown that the freshness of the perovskite precursor solution is crucial in maintaining the stability and efficient luminescence. Then I show that the decrease in photoluminescence intensity upon UV irradiation primarily results from intrinsic instability of the perovskite lattice, whereas the moisture triggers the transformation of nanoplatelets into thicker nanostructures. Then substitution of the organic cation from formamidinium to methylammonium and the addition of excess alkylammonium bromide ligands during the synthesis are shown to be effective stabilization strategies. Lastly, doping of manganese (Mn²⁺) ions — a powerful method for manipulating excited state dynamics and altering semiconductor nanocrystal properties — in colloidal perovskite nanoplatelets is demonstrated. Substitutional doping of manganese for lead introduces bright and long-lived mid-gap Mn²⁺ atomic states, and the doped nanoplatelets exhibit dual emission from the band edge and the dopant state due to facile band edge-to-dopant excitation transfer. I show that photoluminescence quantum yields and band-edge-to-dopant photoluminescence intensity ratios exhibit strong excitation power dependence that cannot be explained by the saturation of long-lived dopant states. By developing a kinetic model combined with time-resolved spectroscopic studies, it is demonstrated that the annihilation of dopant-site excitons by interacting with band-edge excitons is responsible for the observed power dependence. Then I discuss significantly faster band edge-to-dopant excitation transfer in methylammonium-containing nanoplatelets compared to the transfer in formamidinium-containing nanoplatelets.Ph.D

Facile Synthesis of Colloidal Lead Halide Perovskite Nanoplatelets via Ligand-Assisted Reprecipitation

In this work, we demonstrate a facile method for colloidal lead halide perovskite nanoplatelet synthesis (Chemical formula: L2[ABX3]n-1BX4, L: butylammonium and octylammonium, A: methylammonium or formamidinium, B: lead, X: bromide and iodide, n: number of [BX6]4- octahedral layers in the direction of nanoplatelet thickness) via ligand-assisted reprecipitation. Individual perovskite precursor solutions are prepared by dissolving each nanoplatelet constituent salt in N,N-dimethylformamide (DMF), which is a polar organic solvent, and then mixing in specific ratios for targeted nanoplatelet thickness and composition. Once the mixed precursor solution is dropped into nonpolar toluene, the abrupt change in the solubility induces the instantaneous crystallization of nanoplatelets with surface-bound alkylammonium halide ligands providing colloidal stability. Photoluminescence and absorption spectra reveal emissive and strongly quantum-confined features. X-ray diffraction and transmission electron microscopy confirm the two-dimensional structure of the nanoplatelets. Furthermore, we demonstrate that the band gap of perovskite nanoplatelets can be continuously tuned in the visible range by varying the stoichiometry of the halide ion(s). Lastly, we demonstrate the flexibility of the ligand-assisted reprecipitation method by introducing multiple species as surface-capping ligands. This methodology represents a simple procedure for preparing dispersions of emissive 2D colloidal semiconductors.United States. Department of Energy. Office of Basic Energy Sciences (Award DE-SC0019345)National Science Foundation (U.S.) (Award DMR-08-19762

Rapid, theoretically artifact-free calculation of static magnetic field induced by voxelated susceptibility distribution in an arbitrary volume of interest

Purpose: To demonstrate a computationally efficient and theoretically artifact‐free method to calculate static field (B0) inhomogeneity in a volume of interest induced by an arbitrary voxelated susceptibility distribution. (2018 Magnetic Resonance in Medicine)ⓒ2018 International Society for Magnetic Resonance inMedicin