288 research outputs found
Autoimmune Pancreatitis with Associated Ulcerative Colitis in a Teenager
Autoimmune pancreatitis (AIP) is a rare entity that is extremely uncommon in children. Its diagnosis is also a clinical challenge. This form of chronic pancreatitis often presents itself with obstructive jaundice and/or a pancreatic mass and it is sometimes misdiagnosed as pancreatic cancer. We describe the case of a 13-year-old boy with obstructive jaundice and a 4 cm mass in the head of the pancreas that was diagnosed as AIP with associated ulcerative colitis.info:eu-repo/semantics/publishedVersio
First-principles modeling of the interactions of iron impurities with graphene and graphite
Results of first principles modelling of interactions graphene and graphite
with iron impurities predict the colossal difference between these two carbon
allotropes. Insertion of the iron atoms between the planes of graphite is much
more energetically favourable than adsorption of the iron adatom at graphite or
graphene surface. High mobility of iron adatom over graphite surface and within
bulk graphite is reported. Calculated values of formation energies for the
substitutional iron impurities suggest that iron is more destructive for
graphite than for graphene. This effect caused formation of uniform carbon
environment of the iron atom inside the multilayer system. In contrast to
graphene segregation of the substitutional iron impurities in graphite at the
ambient conditions is not energetically favourable. Enhancement of interlayer
bonding in contaminated graphite and purity of graphene from iron impurities
are also reported.Comment: 14 pages, 3 figures, to appear in phis. stat. solidi (b
Facile Synthesis of High Quality Graphene Nanoribbons
Graphene nanoribbons have attracted attention for their novel electronic and
spin transport properties1-6, and because nanoribbons less than 10 nm wide have
a band gap that can be used to make field effect transistors. However,
producing nanoribbons of very high quality, or in high volumes, remains a
challenge. Here, we show that pristine few-layer nanoribbons can be produced by
unzipping mildly gas-phase oxidized multiwalled carbon nanotube using
mechanical sonication in an organic solvent. The nanoribbons exhibit very high
quality, with smooth edges (as seen by high-resolution transmission electron
microscopy), low ratios of disorder to graphitic Raman bands, and the highest
electrical conductance and mobility reported to date (up to 5e2/h and 1500
cm2/Vs for ribbons 10-20 nm in width). Further, at low temperature, the
nanoribbons exhibit phase coherent transport and Fabry-Perot interference,
suggesting minimal defects and edge roughness. The yield of nanoribbons was ~2%
of the starting raw nanotube soot material, which was significantly higher than
previous methods capable of producing high quality narrow nanoribbons1. The
relatively high yield synthesis of pristine graphene nanoribbons will make
these materials easily accessible for a wide range of fundamental and practical
applications.Comment: Nature Nanotechnology in pres
Clar's Theory, STM Images, and Geometry of Graphene Nanoribbons
We show that Clar's theory of the aromatic sextet is a simple and powerful
tool to predict the stability, the \pi-electron distribution, the geometry, the
electronic/magnetic structure of graphene nanoribbons with different hydrogen
edge terminations. We use density functional theory to obtain the equilibrium
atomic positions, simulated scanning tunneling microscopy (STM) images, edge
energies, band gaps, and edge-induced strains of graphene ribbons that we
analyze in terms of Clar formulas. Based on their Clar representation, we
propose a classification scheme for graphene ribbons that groups configurations
with similar bond length alternations, STM patterns, and Raman spectra. Our
simulations show how STM images and Raman spectra can be used to identify the
type of edge termination
Etching and Narrowing of Graphene from the Edges
Large scale graphene electronics desires lithographic patterning of narrow
graphene nanoribbons (GNRs) for device integration. However, conventional
lithography can only reliably pattern ~20nm wide GNR arrays limited by
lithography resolution, while sub-5nm GNRs are desirable for high on/off ratio
field-effect transistors (FETs) at room temperature. Here, we devised a gas
phase chemical approach to etch graphene from the edges without damaging its
basal plane. The reaction involved high temperature oxidation of graphene in a
slightly reducing environment to afford controlled etch rate (\leq ~1nm/min).
We fabricated ~20-30nm wide GNR arrays lithographically, and used the gas phase
etching chemistry to narrow the ribbons down to <10nm. For the first time, high
on/off ratio up to ~10^4 was achieved at room temperature for FETs built with
sub-5nm wide GNR semiconductors derived from lithographic patterning and
narrowing. Our controlled etching method opens up a chemical way to control the
size of various graphene nano-structures beyond the capability of top-down
lithography.Comment: 18 pages, 4 figures, to appear in Nature Chemistr
Availability of substance abuse treatment services in Spanish: A GIS analysis of Latino communities in Los Angeles County, California
<p>Abstract</p> <p>Background</p> <p>The percentage of Latino clients entering outpatient substance abuse treatment (OSAT) in the United States has increased significantly in the past 10 years. Evidence suggests that a lack of services in Spanish is a significant barrier to treatment access among Latinos.</p> <p>Methods</p> <p>Using a geographic information system (GIS) approach, data from the U.S. Census Bureau and the National Survey of Substance Abuse Treatment Services (N-SSATS) were analyzed to determine the geographic distance between OSAT facilities with services in Spanish and Latino communities throughout Los Angeles County, CA. Data from N-SSATS were also analyzed using logistic regression models to examine organizational characteristics and their association with offering services in Spanish. Our GIS methods are tested in their ability to provide baseline measures to inform future analysis comparing changes in demography and service infrastructure.</p> <p>Results</p> <p>GIS analysis revealed cold spots representing high-density Latino communities with extensive travel distance to facilities offering services in Spanish. The average linear distance between Latino communities and facilities offering Spanish-language services ranged from 2 to 6 miles, while the location of the cold spots pointed to a need for services in Spanish in a particular subregion of the county. Further, secondary data analysis revealed that, on average, being privately owned (<it>OR </it>= .23, 95% CI = 0.06-0.90) was associated with a lower likelihood of providing services in Spanish compared to public facilities. Additionally, a facility with a state license (<it>OR </it>= 2.08, 95% CI = 1.12-3.88) or a higher number of Medicaid recipients (<it>OR </it>= 2.98, 95% CI = 1.76-5.05) was twice as likely to offer services in Spanish.</p> <p>Conclusion</p> <p>Despite the significant presence of Latinos in L.A. County in 2000, low capacity was found in discrete Latino communities in terms of offering OSAT services in Spanish. Funding and regulation play a significant role in facilities' capacity to offer these services. Future studies should build from our multi-method approach to compare changes in population demography and system infrastructure and inform health care policy that seeks to improve providers' capacity to provide linguistically competent care.</p
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