4,776 research outputs found
Tauroursodeoxycholic acid exerts anticholestatic effects by a cooperative cPKC alpha-/PKA-dependent mechanism in rat liver.
Objective: Ursodeoxycholic acid (UDCA) exerts anticholestatic effects in part by protein kinase C (PKC)-dependent mechanisms. Its taurine conjugate, TUDCA, is a cPKCa agonist. We tested whether protein kinase A (PKA) might contribute to the anticholestatic action of TUDCA via cooperative cPKCa-/PKA-dependent mechanisms
in taurolithocholic acid (TLCA)-induced cholestasis.
Methods: In perfused rat liver, bile flow was determined gravimetrically, organic anion secretion spectrophotometrically,
lactate dehydrogenase (LDH) release enzymatically, cAMP response-element binding protein (CREB) phosphorylation by immunoblotting, and cAMP by immunoassay. PKC/PKA inhibitors were tested radiochemically. In vitro phosphorylation of the conjugate export pump, Mrp2/Abcc2, was studied in rat hepatocytes and human Hep-G2 hepatoma cells.
Results: In livers treated with TLCA (10 mmol/l)+TUDCA (25 mmol/l), combined inhibition of cPKC by the cPKCselective
inhibitor Go¨6976 (100 nmol/l) or the nonselective PKC inhibitor staurosporine (10 nmol/l) and of PKA by H89 (100 nmol/l) reduced bile flow by 36% (p,0.05) and 48% (p,0.01), and secretion of the Mrp2/
Abcc2 substrate, 2,4-dinitrophenyl-S-glutathione, by 31% (p,0.05) and 41% (p,0.01), respectively; bile flow was
unaffected in control livers or livers treated with TUDCA only or TLCA+taurocholic acid. Inhibition of cPKC or PKA alone did not affect the anticholestatic action of TUDCA. Hepatic cAMP levels and CREB phosphorylation as readout of PKA activity were unaffected by the bile acids
tested, suggesting a permissive effect of PKA for the anticholestatic action of TUDCA. Rat and human hepatocellular Mrp2 were phosphorylated by phorbol ester pretreatment and recombinant cPKCa, nPKCe, and PKA, respectively, in a staurosporine-sensitive manner.
Conclusion: UDCA conjugates exert their anticholestatic action in bile acid-induced cholestasis in part via cooperative post-translational cPKCa-/PKA-dependent
mechanisms. Hepatocellular Mrp2 may be one target of bile acid-induced kinase activation
Microscopic resolution broadband dielectric spectroscopy
Results are presented for a non-contact measurement system capable of micron level spatial resolution. It utilises the novel electric potential sensor (EPS) technology, invented at Sussex, to image the electric field above a simple composite dielectric material. EP sensors may be regarded as analogous to a magnetometer and require no adjustments or offsets during either setup or use. The sample consists of a standard glass/epoxy FR4 circuit board, with linear defects machined into the surface by a PCB milling machine. The sample is excited with an a.c. signal over a range of frequencies from 10 kHz to 10 MHz, from the reverse side, by placing it on a conducting sheet connected to the source. The single sensor is raster scanned over the surface at a constant working distance, consistent with the spatial resolution, in order to build up an image of the electric field, with respect to the reference potential. The results demonstrate that both the surface defects and the internal dielectric variations within the composite may be imaged in this way, with good contrast being observed between the glass mat and the epoxy resin
Evolution of helicity in NOAA 10923 over three consecutive solar rotations
We have studied the evolution of magnetic helicity and chirality in an active
region over three consecutive solar rotations. The region when it first
appeared was named NOAA10923 and in subsequent rotations it was numbered NOAA
10930, 10935 and 10941. We compare the chirality of these regions at
photospheric, chromospheric and coronal heights. The observations used for
photospheric and chromospheric heights are taken from Solar Vector Magnetograph
(SVM) and H_alpha imaging telescope of Udaipur Solar Observatory (USO),
respectively. We discuss the chirality of the sunspots and associated H_alpha
filaments in these regions. We find that the twistedness of superpenumbral
filaments is maintained in the photospheric transverse field vectors also. We
also compare the chirality at photospheric and chromospheric heights with the
chirality of the associated coronal loops, as observed from the HINODE X-Ray
Telescope.Comment: 8 pages, 4 figure
Ascent of volatile-rich felsic magma in dykes:a numerical model applied to deep-sourced porphyry intrusions
Dyke propagation is a mechanism for more rapid ascent of felsic magmas through the crust than is possible via diapirs or percolative flow. As it ascends, the magma undergoes complex physical and chemical transformations induced by decompression and cooling. These processes dramatically change the magma density and viscosity, which in turn affect magma ascent rate and the depth at which the dyke arrests. We present a mathematical model of dyke propagation for silicic magmas taking into account the presence of multiple volatile species (H2O and CO2), bubble growth, heat advection and loss, crystallization and latent heat release. We consider conditions for dykes associated with porphyry ore deposits, which may represent an end-member in rapid ascent of felsic magmas from depth. In particular, we simulate the propagation of dykes launched from a deep (900 MPa), volatile-saturated magma source, testing the effects of the magma H2O/CO2 content, temperature and mass on its ascent rate and final emplacement depth. The model predicts short ascent times (hours to days), with a large increase in viscosity at shallow depth, leading to stagnation and solidification of the dyke. Higher initial water content, higher temperature and larger mass of the magma in the dyke promote faster propagation and shallower arrest. Volatile loss from ascending magma remains limited until the stagnation depth, providing a potential mechanism for transfer of deep volatiles to hypabyssal blind intrusions associated with porphyry ore deposits. Our findings are applicable to the problem of silicic magma ascent through the crust more generally
An exploratory study of how a Korean chaebol’s learning culture facilitates customer service
This paper explains how the organizational learning concept is used by managers in a global Korean company to promote group work, information sharing and an open communication style in order to produce a high level of customer service. Previously collected data from a set of in-depth personal interviews undertaken with three senior managers in a Korean electronics company were analyzed and interpreted using the grounded theory approach, and a number of propositions are put forward. The research findings show that managers in a chaebol deploy organizational learning to identify skilled and knowledgeable staff, and improve the organization’s capability by placing emphasis on developing harmonious, mutually oriented relationships that permeate throughout the organization. Top management demand that staff identify with government economic objectives and align the organization’s strategy accordingly so that the products produced are marketable. To achieve this, the organization fosters continual interaction among managers throughout the organization’s hierarchy. The chaebol’s organizational learning model encapsulates a “corollary” (continual communication) and “tools” (cultural influence and relationship management), and manifests in a unique strategy that allows management systems to evolve naturally
Signal specific electric potential sensors for operation in noisy environments
Limitations on the performance of electric potential sensors are due to saturation caused by environmental electromagnetic noise. The work described involves tailoring the response of the sensors to reject the main components of the noise, thereby enhancing both the effective dynamic range and signal to noise. We show that by using real-time analogue signal processing it is possible to detect a human heartbeat at a distance of 40 cm from the front of a subject in an unshielded laboratory. This result has significant implications both for security sensing and biometric measurements in addition to the more obvious safety related applications
Partially-erupting prominences: a comparison between observations and model-predicted observables
<p><b>Aims:</b> We investigate several partially-erupting prominences to study their relationship with other CME-associated phenomena and compare these observations with observables predicted by a model of partially-expelled-flux-ropes (Gibson & Fan 2006a, ApJ, 637, L65; 2006b, J. Geophys. Res., 111, 12103).</p>
<p><b>Methods:</b> We studied 6 selected events with partially-erupting prominences using multi-wavelength observations recorded by the Extreme-ultraviolet Imaging Telescope (EIT), Transition Region and Coronal Explorer (TRACE), Mauna Loa Solar Observatory (MLSO), Big Bear Solar Observatory (BBSO), and Soft X-ray Telescope (SXT). The observational features associated with partially-erupting prominences were then compared with the predicted observables from the model.</p>
<p><b>Results:</b> The partially-expelled-flux-rope (PEFR) model can explain the partial eruption of these prominences, and in addition predicts a variety of other CME-related observables that provide evidence of internal reconnection during eruption. We find that all of the partially-erupting prominences studied in this paper exhibit indirect evidence of internal reconnection. Moreover, all cases showed evidence of at least one observable unique to the PEFR model, e.g., dimmings external to the source region and/or a soft X-ray cusp overlying a reformed sigmoid.</p>
<p><b>Conclusions:</b> The PEFR model provides a plausible mechanism to explain the observed evolution of partially-erupting-prominence-associated CMEs in our study.</p>
The role of the spin in quasiparticle interference
Quasiparticle interference patterns measured by scanning tunneling microscopy
(STM) can be used to study the local electronic structure of metal surfaces and
high temperature superconductors. Here, we show that even in non-magnetic
systems the spin of the quasiparticles can have a profound effect on the
interference patterns. On Bi(110), where the surface state bands are not
spin-degenerate, the patterns are not related to the dispersion of the
electronic states in a simple way. In fact, the features which are expected for
the spin-independent situation are absent and the observed interference
patterns can only be interpreted by taking spin-conserving scattering events
into account.Comment: 4 pages, 2 figure
CME liftoff with high-frequency fragmented type II burst emission
Aims: Solar radio type II bursts are rarely seen at frequencies higher than a
few hundred MHz. Since metric type II bursts are thought to be signatures of
propagating shock waves, it is of interest to know how these shocks, and the
type II bursts, are formed. In particular, how are high-frequency, fragmented
type II bursts created? Are there differences in shock acceleration or in the
surrounding medium that could explain the differences to the "typical" metric
type IIs? Methods: We analyse one unusual metric type II event in detail, with
comparison to white-light, EUV, and X-ray observations. As the radio event was
associated with a flare and a coronal mass ejection (CME), we investigate their
connection. We then utilize numerical MHD simulations to study the shock
structure induced by an erupting CME in a model corona including dense loops.
Results: Our simulations show that the fragmented part of the type II burst can
be formed when a coronal shock driven by a mass ejection passes through a
system of dense loops overlying the active region.To produce fragmented
emission, the conditions for plasma emission have to be more favourable inside
the loop than in the interloop area. The obvious hypothesis, consistent with
our simulation model, is that the shock strength decreases significantly in the
space between the denser loops. The later, more typical type II burst appears
when the shock exits the dense loop system and finally, outside the active
region, the type II burst dies out when the changing geometry no longer favours
the electron shock-acceleration.Comment: 7 pages, 9 figures, A&A accepte
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