1,955 research outputs found
Somatic stem cells and the origin of cancer
Most human cancers derive from a single cell targeted
by genetic and epigenetic alterations that initiate
malignant transformation. Progressively, these
early cancer cells give rise to different generations
of daughter cells that accumulate additional mutations,
acting in concert to drive the full neoplastic
phenotype1,2. As we have currently deciphered
many of the gene pathways disrupted in cancer, our
knowledge about the nature of the normal cells
susceptible to transformation upon mutation has
remained more elusive.
Adult stem cells are those that show long-term
replicative potential, together with the capacities of
self-renewal and multi-lineage differentiation. These
stem cell properties are tightly regulated in normal
development, yet their alteration may be a critical
issue for tumorigenesis. This concept has arisen
from the striking degree of similarity noted between
somatic stem cells and cancer cells, including
the fundamental abilities to self-renew and differentiate.
Given these shared attributes, it has been
proposed that cancers are caused by transforming
mutations occurring in tissue-specific stem cells3-9.
This hypothesis has been functionally supported by
the observation that among all cancer cells within a
particular tumor, only a minute cell fraction has the
exclusive potential to regenerate the entire tumor
cell population3,10-13; these cells with stem-like
properties have been termed cancer stem cells.
Cancer stem cells can originate from mutation in
normal somatic stem cells that deregulate their
physiological programs. Alternatively, mutations
may target more committed progenitor cells or
even mature cells, which become reprogrammed to
acquire stem-like functions14,15 In any case, mutated
genes should promote expansion of stem/progenitor
cells, thus increasing their predisposition to
cancer development by expanding self-renewal and
pluripotency over their normal tendency towards
relative quiescency and proper differentiation
Uniform semiclassical wave function for coherent 2D electron flow
We find a uniform semiclassical (SC) wave function describing coherent
branched flow through a two-dimensional electron gas (2DEG), a phenomenon
recently discovered by direct imaging of the current using scanned probed
microscopy. The formation of branches has been explained by classical
arguments, but the SC simulations necessary to account for the coherence are
made difficult by the proliferation of catastrophes in the phase space. In this
paper, expansion in terms of "replacement manifolds" is used to find a uniform
SC wave function for a cusp singularity. The method is then generalized and
applied to calculate uniform wave functions for a quantum-map model of coherent
flow through a 2DEG. Finally, the quantum-map approximation is dropped and the
method is shown to work for a continuous-time model as well.Comment: 9 pages, 7 figure
Magnetism in Dense Quark Matter
We review the mechanisms via which an external magnetic field can affect the
ground state of cold and dense quark matter. In the absence of a magnetic
field, at asymptotically high densities, cold quark matter is in the
Color-Flavor-Locked (CFL) phase of color superconductivity characterized by
three scales: the superconducting gap, the gluon Meissner mass, and the
baryonic chemical potential. When an applied magnetic field becomes comparable
with each of these scales, new phases and/or condensates may emerge. They
include the magnetic CFL (MCFL) phase that becomes relevant for fields of the
order of the gap scale; the paramagnetic CFL, important when the field is of
the order of the Meissner mass, and a spin-one condensate associated to the
magnetic moment of the Cooper pairs, significant at fields of the order of the
chemical potential. We discuss the equation of state (EoS) of MCFL matter for a
large range of field values and consider possible applications of the magnetic
effects on dense quark matter to the astrophysics of compact stars.Comment: To appear in Lect. Notes Phys. "Strongly interacting matter in
magnetic fields" (Springer), edited by D. Kharzeev, K. Landsteiner, A.
Schmitt, H.-U. Ye
Influence of nominal composition variation on phase evolution and creep life of Type 316H austenitic stainless steel components
AbstractThe present work aims to understand the influence of variation in chemical composition in the long term evolution of secondary phases. Three samples with nominal composition of Type 316H but different specific composition have been exposed to 505°C during 150, 145 and 300 kh. The percentage of ferrite and M23C6 carbide have been measured using EBSD and compared with Thermo-Calc predictions. In addition, thin foils were prepared and characterized to identify secondary phases in the samples. The discussion is focused on the influence of the secondary phases on creep deformation and failure
Changes in Number and Weight of Wheat and Triticale Grains to Manipulation in Source-Sink Relationship
The source-sink ratio experimental manipulation has helped to define whether a crop is limited by source or sink or co-limited by both. There is no evidence in triticale of source-sink manipulations effects on yield and yield components. Two experiments were accomplished during 2008 and 2009 growing seasons at the Universidad AutĂłnoma del Estado de MĂ©xico, MĂ©xico, and one in 2010 at the National Institute of Agricultural Technology in Pergamino, Argentina. Two triticale cultivars (line 4 and 7) and one wheat cultivar (Tollocan) were used. Source-sink relations were modified at anthesis by thinning, degraining, shading, and total defoliation procedures. Changes in the source-sink relation affected yields in both species differentially. The changes in yield due to cultivars and treatments were explained mainly by the number of grains rather than by their individual grain weight. The number of grains was affected by all treatments in both species, while the individual grain weight was increased by thinning and degraining mainly in triticale. A greater number of fertile florets in triticale were associated with their higher rate of abortion compared to wheat. These results could help to better understand crop management and genetic improvement.Fil: Ballesteros Rodriguez, E.. Universidad Nacional AutĂłnoma de MĂ©xico; MĂ©xicoFil: Martinez Rueda, C.G.. Universidad Nacional AutĂłnoma de MĂ©xico; MĂ©xicoFil: Morales Rosales, E.J.. Universidad Nacional AutĂłnoma de MĂ©xico; MĂ©xicoFil: Estrada Campuzano, G.. Universidad Nacional AutĂłnoma de MĂ©xico; MĂ©xicoFil: GonzĂĄlez, Fernanda Gabriela. Instituto Nacional de TecnologĂa Agropecuaria. Centro Regional Buenos Aires Norte. EstaciĂłn Experimental Agropecuaria Pergamino; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentin
Ab initio molecular dynamics simulations of Aluminum solvation
The solvation of Al and its hydrolyzed species in water clusters has been
studied by means of ab initio molecular dynamics simulations. The hexa-hydrate
aluminum ion formed a stable complex in the finite temperature cluster
simulation of one aluminum ion and 16 waters. The average dipole moment of
strongly polarized hydrated water molecules in the first solvation shell of the
hexa-hydrate aluminum ion was found to be 5.02 Debye. The deprotonated
hexa-hydrate complex evolves into a tetra-coordinated aluminate ion with two
water molecules in the second solvation shell forming hydrogen bonds to the
hydroxyl groups in agreement with the observed coordination.Comment: 12 pages in Elsevier LaTeX, 5 figures in Postscript, 2 last figures
are in color, submitted to Chemical Physics Letter
Expression of adrenomedullin and its receptor during embryogenesis suggests autocrine or paracrine modes of action
The present study reports the developmental patterns of expression of adrenomedullin (AM) in rat and mouse embryos. AM is a novel multifunctional peptide recently isolated from a human pheochromocytoma, which has been shown to promote growth in a variety of mammalian cell lines. We have applied several techniques to investigate the localization of both the AM peptide and its receptor throughout development. Immunocytochemical detection has been performed using different specific antibodies against AM and its gene-related peptide pro-AM N-terminal 20 peptide. In situ hybridization showed the localization of the messenger RNAs for AM and its receptor. Western blot analysis together with reverse transcription-PCR gave further support to the localization of AM and its receptor in a variety of embryonic tissues. The localization of the receptor paralleled that of AM itself, suggesting an autocrine or paracrine mode of action. The spatio-temporal pattern of expression of AM in cardiovascular, neural, and skeletal-forming tissues as well as in the main embryonic internal organs is described. The primitive placenta, especially the giant trophoblastic cells, shows high levels of AM and AM receptor. The heart is the first organ that expresses AM during development. The kidney, lung, and developing tooth, in which epithelial-mesenchymal interactions are taking place, show specific patterns of AM expression. In several regions of the embryo, the patterns of AM expression correspond to the degree of differentiation. The possible involvement of AM in the control of embryonic invasion, proliferation, and differentiation is discussed
The Implications of Fabrication and Cast-to-Cast Variability on Thermal Aging in the Creep Range for AISI Type 316H Stainless Steel Components
Constraints on the pMSSM from LAT Observations of Dwarf Spheroidal Galaxies
We examine the ability for the Large Area Telescope (LAT) to constrain
Minimal Supersymmetric Standard Model (MSSM) dark matter through a combined
analysis of Milky Way dwarf spheroidal galaxies. We examine the Lightest
Supersymmetric Particles (LSPs) for a set of ~71k experimentally valid
supersymmetric models derived from the phenomenological-MSSM (pMSSM). We find
that none of these models can be excluded at 95% confidence by the current
analysis; nevertheless, many lie within the predicted reach of future LAT
analyses. With two years of data, we find that the LAT is currently most
sensitive to light LSPs (m_LSP < 50 GeV) annihilating into tau-pairs and
heavier LSPs annihilating into b-bbar. Additionally, we find that future LAT
analyses will be able to probe some LSPs that form a sub-dominant component of
dark matter. We directly compare the LAT results to direct detection
experiments and show the complementarity of these search methods.Comment: 24 pages, 9 figures, submitted to JCA
LFI 30 and 44 GHz receivers Back-End Modules
The 30 and 44 GHz Back End Modules (BEM) for the Planck Low Frequency
Instrument are broadband receivers (20% relative bandwidth) working at room
temperature. The signals coming from the Front End Module are amplified, band
pass filtered and finally converted to DC by a detector diode. Each receiver
has two identical branches following the differential scheme of the Planck
radiometers. The BEM design is based on MMIC Low Noise Amplifiers using GaAs
P-HEMT devices, microstrip filters and Schottky diode detectors. Their
manufacturing development has included elegant breadboard prototypes and
finally qualification and flight model units. Electrical, mechanical and
environmental tests were carried out for the characterization and verification
of the manufactured BEMs. A description of the 30 and 44 GHz Back End Modules
of Planck-LFI radiometers is given, with details of the tests done to determine
their electrical and environmental performances. The electrical performances of
the 30 and 44 GHz Back End Modules: frequency response, effective bandwidth,
equivalent noise temperature, 1/f noise and linearity are presented
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