160 research outputs found
A Call to Standardize Teratoma Assays Used to Define Human Pluripotent Cell Lines
SummaryThe teratoma assay is the gold standard for documenting pluripotency of human stem cells. However, reports of new human ESC and iPSC lines vary widely in both methods and analysis of teratoma data. We call for consensus standards to be established to make this assay worthy of its “golden” status
Suppression of ferromagnetism in CeSi_1.81 under temperature and pressure
We have studied the pressure dependence of the magnetization of single
crystalline CeSi_1.81. At ambient pressure ferromagnetism develops below T_C =
9.5 Below ~ 5 K an additional shoulder in low-field hysteresis loops and a
metamagnetic crossover around 4 T suggest the appearance of an additional
magnetic modulation to the ferromagnetic state. The suppression of the magnetic
order in CeSi_1.81 as function of temperature at ambient pressure and as
function of pressure at low temperature are in remarkable qualitative
agreement. The continuous suppression of the ordered moment at p ~ 13.1 kbar
suggests the existence of a ferromagnetic quantum critical point in this
material.Comment: 9 pages, 9 figures, to be published in Physical Review
HP1 drives de novo 3D genome reorganization in early Drosophila embryos
Fundamental features of 3D genome organization are established de novo in the early embryo, including clustering of pericentromeric regions, the folding of chromosome arms and the segregation of chromosomes into active (A-) and inactive (B-) compartments. However, the molecular mechanisms that drive de novo organization remain unknown. Here, by combining chromosome conformation capture (Hi-C), chromatin immunoprecipitation with high-throughput sequencing (ChIP–seq), 3D DNA fluorescence in situ hybridization (3D DNA FISH) and polymer simulations, we show that heterochromatin protein 1a (HP1a) is essential for de novo 3D genome organization during Drosophila early development. The binding of HP1a at pericentromeric heterochromatin is required to establish clustering of pericentromeric regions. Moreover, HP1a binding within chromosome arms is responsible for overall chromosome folding and has an important role in the formation of B-compartment regions. However, depletion of HP1a does not affect the A-compartment, which suggests that a different molecular mechanism segregates active chromosome regions. Our work identifies HP1a as an epigenetic regulator that is involved in establishing the global structure of the genome in the early embryo
Entwicklung, Erprobung, Umsetzung und Evaluation von Strategien in den Bereichen Tiergesundheit, Haltung, Fütterung, Management in der ökologischen Ferkelerzeugung
Die ökologische Ferkelerzeugung weist hinsichtlich Tiergesundheit, Leistungsfähigkeit und Wirtschaftlichkeit große Defizite auf. Die Ursachen sind komplex und betreffen u.a. Fütterung, Haltung und Hygiene. Für diese Bereiche sollten durch Exakt- und Praxisversuche Lösungsansätze entwickelt werden. Teilprojekte umfassten folgende Themen: Der Einfluss unterschiedlicher Raufutter in der Fütterung tragender Sauen, die Wirkung einer Inulinzugabe sowie vom Extrudieren von Ackerbohnen in Sauen- und Ferkelfutter, die Bewertung alternativer Desinfektionsverfahren, ein Vergleich von Einzelhaltung versus kombinierte Einzel- und Gruppenhaltung säugender Sauen sowie die Optimierung des Ferkelliegebereichs in der Ferkelaufzucht.
Zentrale Ergebnisse:
- Die verschiedenen Raufuttervarianten (Kleegrassilage, Heu, Maissilage, Topinamburknollen) hatten keine negativen Effekte auf Körperkonstitution und Reproduktionsleistungen der Sauen.
- Die Saugferkel der mit Inulin versorgten Sauen entwickelten sich gegenüber der Kontrollgruppe während der Säugezeit leistungsmäßig besser, während der Ferkelaufzucht gab es keine Leistungssteigerungen. Der Einsatz von getoasteten Ackerbohnen führte zu signifikant besseren Ferkelzunahmen gegenüber dem Einsatz von extrudierten Ackerbohnen.
- Keines der getesteten alternativen Desinfektionsverfahren (HeiĂźwasserdampf, elektroaktiviertes Wasser, Abflammen) ist eine Alternative zur chemischen Desinfektion bezĂĽglich Keimreduktion, Arbeitsaufwand und Kosten.
- Gruppensäugen führt bei Sauen zu erhöhter Aktivität sowie zu spezifischen Verhaltensanpassungen. Leistungseinbußen konnten weder für Sauen noch für Ferkel dokumentiert werden. „Gruppensäugen“ führt zu einem höheren Arbeitszeitbedarf und steigenden Baukosten.
- Der Liegebereich für Aufzuchtferkel ist in vielen Betrieben nicht optimal und durch z. T. einfache Maßnahmen (Abdichten des Liegenestes, Wärmedämmung des Bodens, Bodenheizung, Anbringen einer weiteren Wärmequelle) für die Tiere zu verbessern
Super Bloch oscillations in the Peyrard-Bishop-Holstein model
Recently, polarons in the Peyrard-Bishop-Holstein model under DC electric
fields were established to perform Bloch oscillations, provided the
charge-lattice coupling is not large. In this work, we study this model when
the charge is subjected to an applied field with both DC and AC components.
Similarly to what happens in the rigid lattice, we find that the carrier
undergoes a directed motion or coherent oscillations when the AC field is
resonant or detuned with respect to the Bloch frequency, respectively. The
electric density current and its Fourier spectrum are also studied to reveal
the frequencies involved in the polaron dynamics
Tunable magnetic properties of arrays of Fe(110) nanowires grown on kinetically-grooved W(110) self-organized templates
We report a detailed magnetic study of a new type of self-organized nanowires
disclosed briefly previously [B. Borca et al., Appl. Phys. Lett. 90, 142507
(2007)]. The templates, prepared on sapphire wafers in a kinetically-limited
regime, consist of uniaxially-grooved W(110) surfaces, with a lateral period
here tuned to 15nm. Fe deposition leads to the formation of (110) 7 nm-wide
wires located at the bottom of the grooves. The effect of capping layers (Mo,
Pd, Au, Al) and underlayers (Mo, W) on the magnetic anisotropy of the wires was
studied. Significant discrepancies with figures known for thin flat films are
evidenced and discussed in terms of step anisotropy and strain-dependent
surface anisotropy. Demagnetizing coeffcients of cylinders with a triangular
isosceles cross-section have also been calculated, to estimate the contribution
of dipolar anisotropy. Finally, the dependence of magnetic anisotropy with the
interface element was used to tune the blocking temperature of the wires, here
from 50K to 200 K
Platinum Group Metal-Doped Tungsten Phosphates for Selective C-H Activation of Lower Alkanes
Platinum group metal (PGM)-based catalysts are known to be highly active in the total combustion of lower hydrocarbons. However, through an alternative catalyst design reported in this paper by isolating PGM-based active sites in a tungsten phosphate matrix, we present a class of catalysts for selective oxidation of n-butane, propane, and propylene that do not contain Mo or V as redox-active elements. Two different catalyst concepts have been pursued. Concept A: isolating Ru-based active sites in a tungsten phosphate matrix coming upon as ReO3-type structure. Concept B: dilution of PGM-based active sites through the synthesis of X-ray amorphous Ru tungsten phosphates supported on SiO2. Using a high-throughput screening approach, model catalysts over a wide compositional range were evaluated for C3 and C4 partial oxidation. Bulk crystalline and supported XRD amorphous phases with similar Ru/W/P compositions showed comparable performance. Hence, for these materials, composition is more crucial than the degree of crystallinity. Further studies for optimization on second-generation supported systems revealed even better results. High selectivity for n-butane oxidation to maleic anhydride and propane oxidation to an acrolein/acrylic acid has been achieved
Field-induced delocalization and Zener breakdown in semiconductor superlattices
We investigate the energy spectrum and the electron dynamics of a band in a semiconductor superlattice as a function of the electric field. Linear optical spectroscopy shows that, for high fields, the well-known localization of the Bloch states is followed by a field-induced delocalization, associated with Zener breakdown. Using time-resolved measurements, we observe Bloch oscillations in a regime where they are damped by Zener breakdown
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