334 research outputs found
Morphological expression of the left coronary artery: a direct anatomical study
The left coronary artery presents wide variability in its morphological expression.
The purpose of this work was to determine the variations in the left coronary
artery and those of its branches in heart samples taken from a group of
154 Colombian mixed-race people. Cadaveric coronary arteries were injected
with synthetic resins. Left coronary artery trunks presented 6.48 ± 2.57 mm
lengths. Left coronary arteries were bifurcated in 80 hearts (52%), trifurcated
in 65 hearts (42.2%) and tetrafurcated in 9 hearts (5.8%). A short circumflex
branch was observed in 143 hearts (92.8%), finalising as a left marginal branch
in 39 of them (25.3%). The inferior third of the posterior interventricular sulcus
was the most frequently occurring segment in anterior interventricular branch
finalisation (63.6%). The calibre of the left coronary artery trunk was 3.58 ±
± 0.59 mm, that of the anterior interventricular branch 2.94 ± 0.5 mm and
that of the circumflex branch 2.71 ± 0.54 mm. Of the total sample 86 myocardial
bridges were observed with 61 cases (70.9%) in the anterior interventricular
branch, distributed amongst all segments (proximal, intermediate and distal).
Average myocardial bridge length was 19.4 ± 10.7 mm, and no gender
differences were observed (p = 0.20). The most frequently occurring location
of the myocardial bridges, on the anterior interventricular branch (proximal
and intermediate), agreed with previous studies. Left coronary artery trunk length
and calibre and that of its branches were considerably smaller than those reported
in other populations. (Folia Morphol 2008; 67: 135–142
Combinatorics of irreducible Gelfand-Tsetlin sl(3)-modules
In this paper we present an explicit description of all irreducible sl(3)-modules which admit a Gelfand-Tsetlin tableaux realization with respect to the standard Gelfand-Tsetlin subalgebra
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Comparison of Microstructures and Mechanical Properties for Solid Cobalt-Base Alloy Components and Biomedical Implant Prototypes Fabricated by Electron Beam Melting
The microstructures and mechanical behavior of simple, as-fabricated, solid
geometries (with a density of 8.4 g/cm3), as-fabricated and fabricated and annealed
femoral (knee) prototypes all produced by additive manufacturing (AM) using electron
beam melting (EBM) of Co-26Cr-6Mo-0.2C powder are examined and compared in this
study. Microstructures and microstructural issues are examined by optical metallography,
SEM, TEM, EDS, and XRD while mechanical properties included selective specimen
tensile testing and Vickers microindentation (HV) and Rockwell C-scale (HRC) hardness
measurements. Orthogonal (X-Y) melt scanning of the electron beam during AM
produced unique, orthogonal and related Cr23C6 carbide (precipitate) cellular arrays with
dimensions of ~2μm in the build plane perpendicular to the build direction, while
connected carbide columns were formed in the vertical plane, parallel to the build
direction.Mechanical Engineerin
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Microstructure Architecture Development in Metals and Alloys By Additive Manufacturing Using Electron Beam Melting
The concept of materials with controlled microstructural architecture (MCMA) to
develop and fabricate structural materials with novel and possibly superior properties and
performance characteristics is a new paradigm or paradigm extension for materials science and
engineering. In the conventional materials science and engineering paradigm, structure
(microstructure), properties, processing, and performance features are linked in the development
of desirable materials properties and performance through processing methodologies which
manipulate microstructures. For many metal or alloy systems, thermomechanical treatment
combining controlled amounts of plastic deformation with heat treatment or aging cycles can
achieve improved mechanical properties beyond those attainable by conventional processing
alone (such as rolling or forging for example) through controlled microstructure development. In
this paper we illustrate a new concept involving the fabrication of microstructural architectures
by the process development and selective manipulation of these microstructures ideally defining
material design space. This allows for the additional or independent manipulation of material
properties by additive manufacturing (AM) using electron beam melting (EBM). Specifically we
demonstrate the novel development of a carbide (M23C6) architecture in the AM of a Co-base
alloy and an oxide (Cu2O) precipitate-dislocation architecture in the AM of an oxygen-containing Cu. While more conventional processing can produce various precipitate
microstructures in these materials, EBM produces spatial arrays of precipitate columns or
columnar-like features often oriented in the build direction. These microstructural architectures
are observed by optical microscopy and scanning and transmission electron microscopy.
Prospects for EBM architecture development in precipitation-hardenable Al alloys is also
discussed. In the EBM build process using precursor powders, the electron beam parameters
(including beam focus, scan speed and sequencing) produce localized, requisite thermodynamic
regimes which create or organize the precipitate-related spatial arrays. This feature demonstrates
the utility of AM not only in the fabrication of complex components, but also prospects for
selective property design using CAD for MCMA development: a new or extended processing-microstructure-property-performance paradigm for materials science and engineering in
advanced manufacturing involving solid free-form fabrication (SFF).Mechanical Engineerin
Leishmania infection in bats from a non-endemic region of Leishmaniasis in Brazil
Leishmaniasis is a complex of zoonotic diseases caused by parasites of the genus Leishmania, which can develop in domestic as well as wild animals and humans throughout the world. Currently, this disease is spreading in rural and urban areas of non-endemic regions in Brazil. Recently, bats have gained epidemiological significance in leishmaniasis due to its close relationship with human settlements. In this study, we investigated the presence of Leishmania spp. DNA in blood samples from 448 bats belonging to four families representing 20 species that were captured in the Triangulo Mineiro and Alto Paranaiba areas of Minas Gerais State (non-endemic areas for leishmaniasis), Brazil. Leishmania spp. DNA was detected in 8.0% of the blood samples, 41.6% of which were Leishmania infantum, 38.9% Leishmania amazonensis and 19.4% Leishmania braziliensis. No positive correlation was found between Leishmania spp. and bat food source. The species with more infection rates were the insectivorous bats Eumops perotis; 22.2% (4/18) of which tested positive for Leishmania DNA. The presence of Leishmania in the bat blood samples, as observed in this study, represents epidemiological importance due to the absence of Leishmaniasis cases in the region. © Cambridge University Press 2017
Suppression of charge-ordering and appearance of magnetoresistance in a spin-cluster glass manganite La0.3Ca0.7Mn0.8Cr0.2O3
The magnetic properties of electron-doped manganite La0.3Ca0.7MnO3 and
La0.3Ca0.7Mn0.8Cr0.2O3 polycrystalline samples prepared by sol-gel technique
have been investigated between 5 and 300 K in magnetic fields ranging from 0 to
5 T. The transition at 260 K, attributed to charge ordering in La0.3Ca0.7MnO3,
is completely suppressed in the Cr-substituted sample while the onset of a
magnetic remanence followed by the appearance of a magnetic irreversibility at
lower temperatures is observed in both samples. These features indicate that
ferromagnetic clusters coexist with either an antiferromagnetic phase for
La0.3Ca0.7MnO3 or a spin-cluster glass phase for La0.3Ca0.7Mn0.8Cr0.2O3 at the
lowest temperatures. The exponential temperature dependence of the resistivity
for the Cr-substituted sample is consistent with the small polaron hopping
model for 120 K < T < 300 K, while the data are better described by Mott's
hopping mechanism for T < 120 K. Whereas the parent compound La0.3Ca0.7MnO3 is
known to show no magnetoresistance, a large negative magnetoresistance is
observed in the La0.3Ca0.7Mn0.8Cr0.2O3 sample below 120 K. The appearance of
the CMR is attributed to spin dependent hopping between spin clusters and/or
between ferromagnetic domains
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A comparison of the mechanical behavior of AlSi7Mg alloy produced through additive manufacturing and subjected to different heat treatment and aging conditions
The versatility and adaptability of Aluminum F357 (AlSi7Mg) make it a popular material in the
aerospace and defense industries. In this study, two different laser powder bed fusion systems,
EOS M290, and SLM 280HL were used to create specimens of Aluminum F357. These
specimens were subjected to five different heat treatments: As-built, stress relief (SR), hot
isostatic pressing (HIP), T6, and HIP+T6) as per ASTM F3318-18 standard. The printed
specimens were then reduced to tensile bars through machining and tested for mechanical
properties as per ASTM E28 using an MTS Landmark tensile testing system. In addition to the
mechanical behavior analysis, the study used a JEOL JSM-IT500 SEM to observe and document
the fracture produced by the tensile test and a Qness 30 CHD Master+ microhardness testing
system to obtain hardness (HV) values of the alloy. The results showed that specimens fabricated
in the Z direction had a tendency for higher yield strengths of approximately 225 MPa and
although these results were similar between LPBF systems some variances can still be seen.
However, these differences between the LPBF systems were observed to be partially mitigated
by heat treatments. In conclusion, this study highlights the significance of heat treatment on the
mechanical properties of Aluminum F357. The results provide valuable information for the
aerospace and defense industries to optimize their processes and produce high-quality
components. The compatibility of LPBF system fabrication and the mitigation of differences
observed between LPBF machines by heat treatments, further demonstrate the potential of this
method for producing high-quality Aluminum F357 components.Mechanical Engineerin
Colossal dielectric constants in transition-metal oxides
Many transition-metal oxides show very large ("colossal") magnitudes of the
dielectric constant and thus have immense potential for applications in modern
microelectronics and for the development of new capacitance-based
energy-storage devices. In the present work, we thoroughly discuss the
mechanisms that can lead to colossal values of the dielectric constant,
especially emphasising effects generated by external and internal interfaces,
including electronic phase separation. In addition, we provide a detailed
overview and discussion of the dielectric properties of CaCu3Ti4O12 and related
systems, which is today's most investigated material with colossal dielectric
constant. Also a variety of further transition-metal oxides with large
dielectric constants are treated in detail, among them the system La2-xSrxNiO4
where electronic phase separation may play a role in the generation of a
colossal dielectric constant.Comment: 31 pages, 18 figures, submitted to Eur. Phys. J. for publication in
the Special Topics volume "Cooperative Phenomena in Solids: Metal-Insulator
Transitions and Ordering of Microscopic Degrees of Freedom
An Integrated TCGA Pan-Cancer Clinical Data Resource to Drive High-Quality Survival Outcome Analytics
For a decade, The Cancer Genome Atlas (TCGA) program collected clinicopathologic annotation data along with multi-platform molecular profiles of more than 11,000 human tumors across 33 different cancer types. TCGA clinical data contain key features representing the democratized nature of the data collection process. To ensure proper use of this large clinical dataset associated with genomic features, we developed a standardized dataset named the TCGA Pan-Cancer Clinical Data Resource (TCGA-CDR), which includes four major clinical outcome endpoints. In addition to detailing major challenges and statistical limitations encountered during the effort of integrating the acquired clinical data, we present a summary that includes endpoint usage recommendations for each cancer type. These TCGA-CDR findings appear to be consistent with cancer genomics studies independent of the TCGA effort and provide opportunities for investigating cancer biology using clinical correlates at an unprecedented scale. Analysis of clinicopathologic annotations for over 11,000 cancer patients in the TCGA program leads to the generation of TCGA Clinical Data Resource, which provides recommendations of clinical outcome endpoint usage for 33 cancer types
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