667 research outputs found
The role of inhibitory G proteins and regulators of G protein signaling in the in vivo control of heart rate and predisposition to cardiac arrhythmias
Inhibitory heterotrimeric G proteins and the control of heart rate. The activation of cell signaling pathways involving inhibitory heterotrimeric G proteins acts to slow the heart rate via modulation of ion channels. A large number of Regulators of G protein signalings (RGSs) can act as GTPase accelerating proteins to inhibitory G proteins and thus it is important to understand the network of RGS\G-protein interaction. We will review our recent findings on in vivo heart rate control in mice with global genetic deletion of various inhibitory G protein alpha subunits. We will discuss potential central and peripheral contributions to the phenotype and the controversies in the literature
Epitaxy of Fe3O4 on Si(001) by pulsed laser deposition using a TiN/MgO buffer layer
Epitaxy of oxide materials on silicon (Si) substrates is of great interest
for future functional devices using the large variety of physical properties of
the oxides as ferroelectricity, ferromagnetism, or superconductivity. Recently,
materials with high spin polarization of the charge carriers have become
interesting for semiconductor-oxide hybrid devices in spin electronics. Here,
we report on pulsed laser deposition of magnetite (Fe3O4) on Si(001) substrates
cleaned by an in situ laser beam high temperature treatment. After depositing a
double buffer layer of titanium nitride (TiN) and magnesium oxide (MgO), a high
quality epitaxial magnetite layer can be grown as verified by RHEED intensity
oscillations and high resolution x-ray diffraction.Comment: submitte
Ground-ice stable isotopes and cryostratigraphy reflect late Quaternary palaeoclimate in the Northeast Siberian Arctic (Oyogos Yar coast, Dmitry Laptev Strait)
To reconstruct palaeoclimate and palaeoenvironmental conditions in the northeast Siberian Arctic, we studied late Quaternary permafrost at the Oyogos Yar coast (Dmitry Laptev Strait). New infrared-stimulated luminescence ages for distinctive floodplain deposits of the Kuchchugui Suite (112.5 ± 9.6 kyr) and thermokarst-lake deposits of the Krest Yuryakh Suite (102.4 ± 9.7 kyr), respectively, provide new substantial geochronological data and shed light on the landscape history of the Dmitry Laptev Strait region during Marine Isotope Stage (MIS) 5. Ground-ice stable-isotope data are presented together with cryolithological information for eight cryostratigraphic units and are complemented by data from nearby Bol'shoy Lyakhovsky Island. Our combined record of ice-wedge stable isotopes as a proxy for past winter climate conditions covers about 200 000 years and is supplemented by stable isotopes of pore and segregated ice which reflect annual climate conditions overprinted by freezing processes. Our ice-wedge stable-isotope data indicate substantial variations in northeast Siberian Arctic winter climate conditions during the late Quaternary, in particular between glacial and interglacial times but also over the last millennia to centuries. Stable isotope values of ice complex ice wedges indicate cold to very cold winter temperatures about 200 kyr ago (MIS7), very cold winter conditions about 100 kyr ago (MIS5), very cold to moderate winter conditions between about 60 and 30 kyr ago, and extremely cold winter temperatures during the Last Glacial Maximum (MIS2). Much warmer winter conditions are reflected by extensive thermokarst development during MIS5c and by Holocene ice-wedge stable isotopes. Modern ice-wedge stable isotopes are most enriched and testify to the recent winter warming in the Arctic. Hence, ice-wedge-based reconstructions of changes in winter climate conditions add substantial information to those derived from paleoecological proxies stored in permafrost and allow a distinction between seasonal trends of past climate dynamics. Future progress in ice-wedge dating and an improved temporal resolution of ice-wedge-derived climate information may help to fully explore the palaeoclimatic potential of ice wedges
Magnetic and structural properties of GeMn films: precipitation of intermetallic nanomagnets
We present a comprehensive study relating the nanostructure of Ge_0.95Mn_0.05
films to their magnetic properties. The formation of ferromagnetic nanometer
sized inclusions in a defect free Ge matrix fabricated by low temperature
molecular beam epitaxy is observed down to substrate temperatures T_S as low as
70 deg. Celsius. A combined transmission electron microscopy (TEM) and electron
energy-loss spectroscopy (EELS) analysis of the films identifies the inclusions
as precipitates of the ferromagnetic compound Mn_5Ge_3. The volume and amount
of these precipitates decreases with decreasing T_S. Magnetometry of the films
containing precipitates reveals distinct temperature ranges: Between the
characteristic ferromagnetic transition temperature of Mn_5Ge_3 at
approximately room temperature and a lower, T_S dependent blocking temperature
T_B the magnetic properties are dominated by superparamagnetism of the Mn_5Ge_3
precipitates. Below T_B, the magnetic signature of ferromagnetic precipitates
with blocked magnetic moments is observed. At the lowest temperatures, the
films show features characteristic for a metastable state.Comment: accepted for publication in Phys. Rev. B 74 (01.12.2006). High
resolution images ibide
Magnetic interference patterns in 0-Pi SIFS Josephson junctions: effects of asymmetry between 0 and Pi regions
We present a detailed analysis of the dependence of the critical current I_c
on the magnetic field B of 0, Pi, and 0-Pi
superconductor-insulator-ferromagnet-superconductor Josephson junctions. I_c(B)
of the 0 and Pi junction closely follows a Fraunhofer pattern, indicating a
homogeneous critical current density j_c(x). The maximum of I_c(B) is slightly
shifted along the field axis, pointing to a small remanent in-plane
magnetization of the F-layer along the field axis. I_c(B) of the 0-Pi junction
exhibits the characteristic central minimum. I_c however has a finite value
here, due to an asymmetry of j_c in the 0 and Pi part. In addition, this I_c(B)
exhibits asymmetric maxima and bumped minima. To explain these features in
detail, flux penetration being different in the 0 part and the Pi part needs to
be taken into account. We discuss this asymmetry in relation to the magnetic
properties of the F-layer and the fabrication technique used to produce the
0-Pi junctions
Enhanced Electron-Phonon Coupling and its Irrelevance to High T Superconductivity
It is argued that the origin of the buckling of the CuO planes in
certain cuprates as well as the strong electron-phonon coupling of the
phonon is due to the electric field across the planes induced by atoms with
different valence above and below. The magnitude of the electric field is
deduced from new Raman results on YBaCuO and
BiSr(CaY)CuO with different O and Y
doping, respectively. In the latter case it is shown that the symmetry breaking
by replacing Ca partially by Y enhances the coupling by an order of magnitude,
while the superconducting drops to about two third of its original value.Comment: 4 pages, 2 figures. This and other papers can be downloaded from
http://gwis2.circ.gwu.edu/~tp
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