949 research outputs found
Derivation and characterization of monkey embryonic stem cells
Embryonic stem (ES) cell based therapy carries great potential in the treatment of neurodegenerative diseases. However, before clinical application is realized, the safety, efficacy and feasibility of this therapeutic approach must be established in animal models. The rhesus macaque is physiologically and phylogenetically similar to the human, and therefore, is a clinically relevant animal model for biomedical research, especially that focused on neurodegenerative conditions. Undifferentiated monkey ES cells can be maintained in a pluripotent state for many passages, as characterized by a collective repertoire of markers representing embryonic cell surface molecules, enzymes and transcriptional factors. They can also be differentiated into lineage-specific phenotypes of all three embryonic germ layers by epigenetic protocols. For cell-based therapy, however, the quality of ES cells and their progeny must be ensured during the process of ES cell propagation and differentiation. While only a limited number of primate ES cell lines have been studied, it is likely that substantial inter-line variability exists. This implies that diverse ES cell lines may differ in developmental stages, lineage commitment, karyotypic normalcy, gene expression, or differentiation potential. These variables, inherited genetically and/or induced epigenetically, carry obvious complications to therapeutic applications. Our laboratory has characterized and isolated rhesus monkey ES cell lines from in vitro produced blastocysts. All tested cell lines carry the potential to form pluripotent embryoid bodies and nestin-positive progenitor cells. These ES cell progeny can be differentiated into phenotypes representing the endodermal, mesodermal and ectodermal lineages. This review article describes the derivation of monkey ES cell lines, characterization of the undifferentiated phenotype, and their differentiation into lineage-specific, particularly neural, phenotypes. The promises and limitations of primate ES cell-based therapy are also discussed
Exceptionally Slow Rise in Differential Reflectivity Spectra of Excitons in GaN: Effect of Excitation-induced Dephasing
Femtosecond pump-probe (PP) differential reflectivity spectroscopy (DRS) and
four-wave mixing (FWM) experiments were performed simultaneously to study the
initial temporal dynamics of the exciton line-shapes in GaN epilayers. Beats
between the A-B excitons were found \textit{only for positive time delay} in
both PP and FWM experiments. The rise time at negative time delay for the
differential reflection spectra was much slower than the FWM signal or PP
differential transmission spectroscopy (DTS) at the exciton resonance. A
numerical solution of a six band semiconductor Bloch equation model including
nonlinearities at the Hartree-Fock level shows that this slow rise in the DRS
results from excitation induced dephasing (EID), that is, the strong density
dependence of the dephasing time which changes with the laser excitation
energy.Comment: 8 figure
Angle-resonant stimulated polariton amplifier
We experimentally demonstrate resonant coupling between photons and excitons in microcavities which can efficiently generate enormous single-pass optical gains approaching 100. This new parametric phenomenon appears as a sharp angular resonance of the incoming pump beam, at which the moving excitonic polaritons undergo very large changes in momentum. Ultrafast stimulated scattering is clearly identified from the exponential dependence on pump intensity. This device utilizes boson amplification
induced by stimulated energy relaxation
The role of social networks in students’ learning experiences
The aim of this research is to investigate the role of social networks in computer science education. The Internet shows great potential for enhancing collaboration between people and the role of social software has become increasingly relevant in recent years. This research focuses on analyzing the role that social networks play in students’ learning experiences. The construction of students’ social networks, the evolution of these networks, and their effects on the students’ learning experience in a university environment are examined
Rapid and high throughput molecular identification of diverse mosquito species by igh resolution melting analysis
Mosquitoes are a diverse group of invertebrates, with members that are among the most important vectors of diseases. The correct identification of mosquitoes is paramount to the control of the diseases that they transmit. However, morphological techniques depend on the quality of the specimen and often unavailable taxonomic expertise, which may still not be able to distinguish mosquitoes among species complexes (sibling and cryptic species). High resolution melting (HRM) analyses, a closed-tube, post-polymerase chain reaction (PCR) method used to identify variations in nucleic acid sequences, has been used to differentiate species within the Anopheles gambiae and Culex pipiens complexes. We validated the use of PCR-HRM analyses to differentiate species within Anopheles and within each of six genera of culicine mosquitoes, comparing primers targeting cytochrome b (cyt b), NADH dehydrogenase subunit 1 (ND1), intergenic spacer region (IGS) and cytochrome c oxidase subunit 1 (COI) gene regions. HRM analyses of amplicons from all the six primer pairs successfully differentiated two or more mosquito species within one or more genera (Aedes (Ae. vittatus from Ae. metallicus), Culex (Cx. tenagius from Cx. antennatus, Cx. neavei from Cx. duttoni, cryptic Cx. pipiens species), Anopheles (An. gambiae s.s. from An. arabiensis) and Mansonia (Ma. africana from Ma. uniformis)) based on their HRM profiles. However, PCR-HRM could not distinguish between species within Aedeomyia (Ad. africana and Ad. furfurea), Mimomyia (Mi. hispida and Mi. splendens) and Coquillettidia (Cq. aurites, Cq. chrysosoma, Cq. fuscopennata, Cq. metallica, Cq. microannulatus, Cq. pseudoconopas and Cq. versicolor) genera using any of the primers. The IGS and COI barcode region primers gave the best and most definitive separation of mosquito species among anopheline and culicine mosquito genera, respectively, while the other markers may serve to confirm identifications of closely related sub-species. This approach can be employed for rapid identification of mosquitoes
Intermediate and extreme mass-ratio inspirals — astrophysics, science applications and detection using LISA
Black hole binaries with extreme (gtrsim104:1) or intermediate (~102–104:1) mass ratios are among the most interesting gravitational wave sources that are expected to be detected by the proposed laser interferometer space antenna (LISA). These sources have the potential to tell us much about astrophysics, but are also of unique importance for testing aspects of the general theory of relativity in the strong field regime. Here we discuss these sources from the perspectives of astrophysics, data analysis and applications to testing general relativity, providing both a description of the current state of knowledge and an outline of some of the outstanding questions that still need to be addressed. This review grew out of discussions at a workshop in September 2006 hosted by the Albert Einstein Institute in Golm, Germany
Ultraspinning instability of anti-de Sitter black holes
Myers-Perry black holes with a single spin in d>5 have been shown to be
unstable if rotating sufficiently rapidly. We extend the numerical analysis
which allowed for that result to the asymptotically AdS case. We determine
numerically the stationary perturbations that mark the onset of the
instabilities for the modes that preserve the rotational symmetries of the
background. The parameter space of solutions is thoroughly analysed, and the
onset of the instabilities is obtained as a function of the cosmological
constant. Each of these perturbations has been conjectured to represent a
bifurcation point to a new phase of stationary AdS black holes, and this is
consistent with our results.Comment: 22 pages, 7 figures. v2: Reference added. Matches published versio
Pyrolysis of medium-density fiberboard: optimized search for kinetics scheme and parameters via a genetic algorithm driven by Kissinger's method
The pyrolysis kinetics of charring
materials plays an important
role in understanding material combustions especially for construction
materials with complex degradation chemistry. Thermogravimetric analysis
(TGA) is frequently used to study the heterogeneous kinetics of solid
fuels; however, there is no agreed method to determine the pyrolysis
scheme and kinetic parameters for charring polymers with multiple
components and competing reaction pathways. This study develops a
new technique to estimate the possible numbers of species and sub-reactions
in pyrolysis by analyzing the second derivatives of thermogravimetry
(DDTG) curves. The pyrolysis of a medium-density fiberboard (MDF)
in nitrogen is studied in detail, and the DDTG curves are used to
locate the temperature of the peak mass-loss rate for each sub-reaction.
Then, on the basis of the TG data under multiple heating rates, Kissinger’s
method is used to quickly find the possible range of values of the
kinetic parameters (<i>A</i> and <i>E</i>). These
ranges are used to accelerate the optimization of the inverse problem
using a genetic algorithm (GA) for the kinetic and stoichiometric
parameters. The proposed method and kinetic scheme found are shown
to match the experimental data and are able to predict accurately
results at different heating rates better than Kissinger’s
method. Moreover, the search method (K–K method) is highly
efficient, faster than the regular GA search alone. Modeling results
show that, as the TG data available increase, the interdependence
among kinetic parameters becomes weak and the accuracy of the first-order
model declines. Furthermore, conducting TG experiment under multiple
heating rates is found to be crucial in obtaining good kinetic parameters
Quantum nature of a strongly-coupled single quantum dot-cavity system
Cavity quantum electrodynamics (QED) studies the interaction between a
quantum emitter and a single radiation-field mode. When an atom is in strong
coupling with a cavity mode1,2, it is possible to realize key quantum
information processing (QIP) tasks, such as controlled coherent coupling and
entanglement of distinguishable quantum systems. Realizing these tasks in the
solid state is clearly desirable, and coupling semiconductor self-assembled
quantum dots (QDs) to monolithic optical cavities is a promising route to this
end. However, validating the efficacy of QDs in QIP applications requires
confirmation of the quantum nature of the QD-cavity system in the strong
coupling regime. Here we find a confirmation by observing quantum correlations
in photoluminescence (PL) from a photonic crystal (PC) nanocavity3-5
interacting with one, and only one, QD located precisely at the cavity electric
field maximum. When off-resonance, photon emission from the cavity mode and QD
excitons is anti-correlated at the level of single quanta, proving that the
mode is driven solely by the QD despite an energy mis-match between cavity and
excitons. When tuned into resonance, the exciton and photon enter the
strong-coupling regime of cavity-QED and the QD lifetime reduces by a factor of
120. The photon stream from the cavity becomes anti-bunched, proving that the
coupled exciton/photon system is in the quantum anharmonic regime. Our
observations unequivocally show that QIP tasks requiring the quantum nonlinear
regime are achievable in the solid state.Comment: 14 pages 4 figure
Transient Expression of Hemagglutinin Antigen from Low Pathogenic Avian Influenza A (H7N7) in Nicotiana benthamiana
The influenza A virus is of global concern for the poultry industry, especially the H5 and H7 subtypes as they have the potential to become highly pathogenic for poultry. In this study, the hemagglutinin (HA) of a low pathogenic avian influenza virus of the H7N7 subtype isolated from a Swedish mallard Anas platyrhynchos was sequenced, characterized and transiently expressed in Nicotiana benthamiana. Recently, plant expression systems have gained interest as an alternative for the production of vaccine antigens. To examine the possibility of expressing the HA protein in N. benthamiana, a cDNA fragment encoding the HA gene was synthesized de novo, modified with a Kozak sequence, a PR1a signal peptide, a C-terminal hexahistidine (6×His) tag, and an endoplasmic retention signal (SEKDEL). The construct was cloned into a Cowpea mosaic virus (CPMV)-based vector (pEAQ-HT) and the resulting pEAQ-HT-HA plasmid, along with a vector (pJL3:p19) containing the viral gene-silencing suppressor p19 from Tomato bushy stunt virus, was agro-infiltrated into N. benthamiana. The highest gene expression of recombinant plant-produced, uncleaved HA (rHA0), as measured by quantitative real-time PCR was detected at 6 days post infiltration (dpi). Guided by the gene expression profile, rHA0 protein was extracted at 6 dpi and subsequently purified utilizing the 6×His tag and immobilized metal ion adsorption chromatography. The yield was 0.2 g purified protein per kg fresh weight of leaves. Further molecular characterizations showed that the purified rHA0 protein was N-glycosylated and its identity confirmed by liquid chromatography-tandem mass spectrometry. In addition, the purified rHA0 exhibited hemagglutination and hemagglutination inhibition activity indicating that the rHA0 shares structural and functional properties with native HA protein of H7 influenza virus. Our results indicate that rHA0 maintained its native antigenicity and specificity, providing a good source of vaccine antigen to induce immune response in poultry species
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