1,593 research outputs found
Effects of a radially varying electrical conductivity on 3D numerical dynamos
The transition from liquid metal to silicate rock in the cores of the
terrestrial planets is likely to be accompanied by a gradient in the
composition of the outer core liquid. The electrical conductivity of a volatile
enriched liquid alloy can be substantially lower than a light-element-depleted
fluid found close to the inner core boundary. In this paper, we investigate the
effect of radially variable electrical conductivity on planetary dynamo action
using an electrical conductivity that decreases exponentially as a function of
radius. We find that numerical solutions with continuous, radially outward
decreasing electrical conductivity profiles result in strongly modified flow
and magnetic field dynamics, compared to solutions with homogeneous electrical
conductivity. The force balances at the top of the simulated fluid determine
the overall character of the flow. The relationship between Coriolis and
Lorentz forces near the outer boundary controls the flow and magnetic field
intensity and morphology of the system. Our results imply that a low
conductivity layer near the top of Mercury's liquid outer core is consistent
with its weak magnetic field.Comment: 30 pages, 11 figures, 2 tables. To be published in Physics of Earth
and Planetary Interiors (PEPI)
Renal Transplant Survey: how standardised is a standard kidney transplant?
Aim: The primary intention of the current study was to discover if there are international standards in renal transplantation. Method: A questionnaire was created using an online survey tool (Qualtrics Âź), and distributed to a list of email addresses supplied by the unit's senior transplant surgeon. A literature review was performed on the questions and on the history of transplantation. Ethics was approved by FHS HREC number 193/2015. Results: A total of 30 surveys were completed from a total of 147 emails sent (20.4%). Two thirds of respondents work exclusively in the public sector and almost two-thirds (63.3%) of the respondents had been involved in transplantation for over 10 years. Two thirds of the surgeons estimate that their units perform more than 60 transplants per annum. Only 30% (9/30) use living donors in more than 50% of their surgeries. Most (53.3%) perfuse the kidneys both in the donor (in situ) and outside (ex situ or ex vivo). If no anatomic abnormalities were noted in open living donor nephrectomy, 63.3% would prefer to use the left kidney, and the recipient transplantation would be performed on the right side (76.7%). The majority (90%) of surgeons would preserve the vas deferens, but sacrifice the round ligament and inferior epigastric vessels (76.7% and 80% respectively). There is no marked difference for use of either the internal or external iliac artery for the arterial anastomosis, but most use the external iliac vein for venous anastomosis (86.7%). 80% use a ureteroneocystostomy with a tunnel, and 60% use a DJ stent or ureteric catheter and closed suction drain routinely. Two thirds would remove the transurethral catheter on day 4-7 post operatively. 80% routinely biopsy the kidney, and 63.3% would biopsy prior to treating for possible acute renal rejection. Discussion: These results compare with some of the studies found in the literature and operative textbooks. There do appear to be standards noted between most of the respondent's answers. Conclusion: There do appear to be standards for renal transplantation and these are appreciated globally
Die siekteprofieI van 'n geriatriese buitepasient - Afdeling
A series of 120 outpatients over the age of 75 years were assessed on a clinical, functional and social basis. The multiplicity of pathology, decrease in functional ability and social background are emphasized. This  comprehensive approach in the evaluation of the elderly sick was found to be of great value both in the clinic and in aftercare services
The initial temporal evolution of a feedback dynamo for Mercury
Various possibilities are currently under discussion to explain the observed
weakness of the intrinsic magnetic field of planet Mercury. One of the possible
dynamo scenarios is a dynamo with feedback from the magnetosphere. Due to its
weak magnetic field Mercury exhibits a small magnetosphere whose subsolar
magnetopause distance is only about 1.7 Hermean radii. We consider the magnetic
field due to magnetopause currents in the dynamo region. Since the external
field of magnetospheric origin is antiparallel to the dipole component of the
dynamo field, a negative feedback results. For an alpha-omega-dynamo two
stationary solutions of such a feedback dynamo emerge, one with a weak and the
other with a strong magnetic field. The question, however, is how these
solutions can be realized. To address this problem, we discuss various
scenarios for a simple dynamo model and the conditions under which a steady
weak magnetic field can be reached. We find that the feedback mechanism
quenches the overall field to a low value of about 100 to 150 nT if the dynamo
is not driven too strongly
Generation of directional, coherent matter beams through dynamical instabilities in Bose-Einstein condensates
We present a theoretical analysis of a coupled, two-state Bose-Einstein
condensate with non-equal scattering lengths, and show that dynamical
instabilities can be excited. We demonstrate that these instabilities are
exponentially amplified resulting in highly-directional,
oppositely-propagating, coherent matter beams at specific momenta. To
accomplish this we prove that the mean field of our system is periodic, and
extend the standard Bogoliubov approach to consider a time-dependent, but
cyclic, background. This allows us to use Floquet's theorem to gain analytic
insight into such systems, rather than employing the usual Bogoliubov-de Gennes
approach, which is usually limited to numerical solutions. We apply our theory
to the metastable Helium atom laser experiment of Dall et al. [Phys. Rev. A 79,
011601(R) (2009)] and show it explains the anomalous beam profiles they
observed. Finally we demonstrate the paired particle beams will be
EPR-entangled on formation.Comment: Corrected reference
The PGE2-Stat3 interaction in doxorubicin-induced myocardial apoptosis
Aims Both cyclooxygenase-2 (COX-2) and the transcription factor signal transducer and activator of transcription 3 (Stat3) are involved in adaptive growth and survival of cardiomyocytes. In ventricular cardiomyocytes, prostaglandin E2 (PGE2), a major COX-2 product, leads to adaptive growth via Stat3 activation, but whether this transcription factor acts as a signalling molecule in PGE2-induced cell survival is unknown. Therefore, the purpose of this study was to determine whether PGE2 counteracts cardiac apoptosis induced by doxorubicin (DOX), and if so, whether Stat3 plays a critical role in this cardioprotective effect. Methods and results Neonatal rat ventricular cardiomyocytes were incubated with DOX (0.5 ”M) and/or PGE2 (1 ”M). Apoptosis was assessed by determining caspase3 activation and apoptotic DNA fragmentation. The role of Stat3 was evaluated in vitro and in vivo by transfecting cardiomyocytes with siRNA targeting rat Stat3 and by using cardiomyocyte-restricted Stat3 knockout (Stat3 KO) mice, respectively. Incubation of ventricular cardiomyocytes with PGE2 led to a time-dependent decrease in the DOX-induced caspase3 activation, reaching a maximal inhibition of 70 ± 5% after 4 h. Similarly, PGE2 inhibited DOX-induced DNA fragmentation by 58 ± 5% after 24 h. This antiapoptotic action of PGE2 was strongly reduced by the ERK1/2 inhibitor, U0126, whereas the p38 MAP kinase inhibitor, SB203580, had no effect. Depleting Stat3 expression by 50-60% in isolated ventricular cardiomyocytes markedly reduced the protective effect of PGE2 on DOX-induced caspase3 activation and DNA fragmentation. Likewise, the stable PGE2 analogue, 16,16-dimethyl-PGE2, was unable to counteract cardiac apoptosis induced by DOX in Stat3 KO mice. Conclusion Our results demonstrate that PGE2 prevents myocardial apoptosis induced by DOX. This protection requires the activation of the prosurvival pathways of Stat3 and ERK1/
Theoretical Analysis of a Large Momentum Beamsplitter using Bloch Oscillations
In this paper, we present the implementation of Bloch oscillations in an
atomic interferometer to increase the separation of the two interfering paths.
A numerical model, in very good agreement with the experiment, is developed.
The contrast of the interferometer and its sensitivity to phase fluctuations
and to intensity fluctuations are also calculated. We demonstrate that the
sensitivity to phase fluctuations can be significantly reduced by using a
suitable arrangement of Bloch oscillations pulses
Coupled spin models for magnetic variation of planets and stars
Geomagnetism is characterized by intermittent polarity reversals and rapid
fluctuations. We have recently proposed a coupled macro-spin model to describe
these dynamics based on the idea that the whole dynamo mechanism is described
by the coherent interactions of many small dynamo elements. In this paper, we
further develop this idea and construct a minimal model for magnetic
variations. This simple model naturally yields many of the observed features of
geomagnetism: its time evolution, the power spectrum, the frequency
distribution of stable polarity periods, etc. This model has coexistent two
phases; i.e. the cluster phase which determines the global dipole magnetic
moment and the expanded phase which gives random perpetual perturbations that
yield intermittent polarity flip of the dipole moment. This model can also
describe the synchronization of the spin oscillation. This corresponds to the
case of sun and the model well describes the quasi-regular cycles of the solar
magnetism. Furthermore, by analyzing the relevant terms of MHD equation based
on our model, we have obtained a scaling relation for the magnetism for
planets, satellites, sun, and stars. Comparing it with various observations, we
can estimate the scale of the macro-spins.Comment: 16 pages, 9 figure
Optical Clocks in Space
The performance of optical clocks has strongly progressed in recent years,
and accuracies and instabilities of 1 part in 10^18 are expected in the near
future. The operation of optical clocks in space provides new scientific and
technological opportunities. In particular, an earth-orbiting satellite
containing an ensemble of optical clocks would allow a precision measurement of
the gravitational redshift, navigation with improved precision, mapping of the
earth's gravitational potential by relativistic geodesy, and comparisons
between ground clocks.Comment: Proc. III International Conference on Particle and Fundamental
Physics in Space (SpacePart06), Beijing 19 - 21 April 2006, to appear in
Nucl. Phys.
Improved Term of the Muon Anomalous Magnetic Moment
We have completed the evaluation of all mass-dependent QED
contributions to the muon , or , in two or more different
formulations. Their numerical values have been greatly improved by an extensive
computer calculation. The new value of the dominant term is 132.6823 (72), which supersedes the old value 127.50 (41).
The new value of the three-mass term
is 0.0376 (1). The term is crudely estimated to
be about 0.005 and may be ignored for now. The total QED contribution to
is , where 0.02 and
1.15 are uncertainties in the and terms and 0.85 is from
the uncertainty in measured by atom interferometry. This raises the
Standard Model prediction by , or about 1/5 of the
measurement uncertainty of . It is within the noise of current
uncertainty () in the estimated hadronic
contributions to .Comment: Appendix A has been rewritten extensively. It includes the 4th-order
calculation for illustration. Version accepted by PR
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