51,610 research outputs found
Finding the Origin of the Pioneer Anomaly
Analysis of radio-metric tracking data from the Pioneer 10/11 spacecraft at
distances between 20 - 70 astronomical units (AU) from the Sun has consistently
indicated the presence of an anomalous, small, constant Doppler frequency
drift. The drift can be interpreted as being due to a constant acceleration of
a_P= (8.74 \pm 1.33) x 10^{-8} cm/s^2 directed towards the Sun. Although it is
suspected that there is a systematic origin to the effect, none has been found.
As a result, the nature of this anomaly has become of growing interest. Here we
present a concept for a deep-space experiment that will reveal the origin of
the discovered anomaly and also will characterize its properties to an accuracy
of at least two orders of magnitude below the anomaly's size. The proposed
mission will not only provide a significant accuracy improvement in the search
for small anomalous accelerations, it will also determine if the anomaly is due
to some internal systematic or has an external origin. A number of critical
requirements and design considerations for the mission are outlined and
addressed. If only already existing technologies were used, the mission could
be flown as early as 2010.Comment: 21 SS pages, 4+1 figures. final changes for publicatio
Distributed Convergence Verification for Gaussian Belief Propagation
Gaussian belief propagation (BP) is a computationally efficient method to
approximate the marginal distribution and has been widely used for inference
with high dimensional data as well as distributed estimation in large-scale
networks. However, the convergence of Gaussian BP is still an open issue.
Though sufficient convergence conditions have been studied in the literature,
verifying these conditions requires gathering all the information over the
whole network, which defeats the main advantage of distributed computing by
using Gaussian BP. In this paper, we propose a novel sufficient convergence
condition for Gaussian BP that applies to both the pairwise linear Gaussian
model and to Gaussian Markov random fields. We show analytically that this
sufficient convergence condition can be easily verified in a distributed way
that satisfies the network topology constraint.Comment: accepted by Asilomar Conference on Signals, Systems, and Computers,
2017, Asilomar, Pacific Grove, CA. arXiv admin note: text overlap with
arXiv:1706.0407
Impact of market deregulation on the competitiveness of commercial milk producers in East Griqualand: a unit cost ratio (UCR) analysis: 1983-2006
This study investigates the impact of dairy market deregulation on the competitiveness of milk producers who comprise the East Griqualand (EG) study group in KwaZulu-Natal and the Eastern Cape Province of South Africa. The study uses a microeconomic approach, the unit cost ratio (UCR) method of competitiveness analysis, to assess changes in the relative competitiveness of EG milk producers from 1983 – 2006. Findings of previous research indicate that dairy market deregulation in the 1980s and 1990s caused lower real milk producer prices, increased uncertainty and higher exit rates in the South African dairy industry. Results of the UCR analysis suggest that EG milk producers were not competitive based on the net local price received for milk but were competitive when dairy cattle trading income was included. This suggests that dairy cattle trading income played an important role in enhancing the profitability of EG dairy enterprises in the study period. Further UCR analysis revealed that the top one-third of EG milk producers were relatively competitive from 1983 – 2006 due to higher real milk prices and lower unit costs. A panel data study of individual EG milk producers could be used to identify other important factors affecting milk producer competitiveness over time.dairy market deregulation, East Griqualand milk producers, competitiveness, unit cost ratio analysis, Livestock Production/Industries,
FOXP3 interacts with hnRNPF to modulate pre-mRNA alternative splicing
FOXP3 promotes the development and function of regulatory T cells mainly through regulating the transcription of target genes. RNA alternative splicing has been implicated in a wide range of physiological and pathophysiological processes. We report here that FOXP3 associates with heterogeneous nuclear ribonucleoprotein (hnRNP) F through the exon 2-encoded region of FOXP3 and the second quasi-RNA recognition motif (qRRM) of hnRNPF. FOXP3 represses the ability of hnRNPF to bind to its target pre-mRNA and thus modulates RNA alternative splicing. Furthermore, overexpression of mouse hnRNPF in in vitro-differentiated regulatory T cells (Tregs) reduced their suppressive function. Thus, our studies identify a novel mechanism by which FOXP3 regulates mRNA alternative splicing to modulate the function of regulatory T cells
Perfect Andreev Reflection of Helical Edge Modes in InAs/GaSb Quantum Wells
We present an experimental study of inverted InAs/GaSb composite quantum
wells in the hybridization regime and contacted by superconducting electrodes.
A front gate is used to vary the Fermi level into the mini-gap, where recent
experiments indicate existence of helical edge modes [arXiv:1105.0137]. Zero
bias dips in differential resistance are observed across the mini-gap,
suggesting transport dominated by Andreev reflection processes. Evolution of
the mini-gap differential resistance with applied bias as well as measured
mini-gap excess current of 150 nA are in good agreement with the prediction of
perfect Andreev reflection of the helical edge modes, which is necessitated by
the absence of back-scattering channels. The perfect Andreev reflection occurs
in spite of a finite barrier at the interface and shows strong sensitivity to
time-reversal breaking - hallmarks of the helical nature of quantum spin Hall
edges
Factors influencing the long-term competitiveness of commercial milk producers: evidence from panel data in East Griqualand, South Africa
This study investigates factors influencing the long-term competitiveness of 11 commercial milk producers from East Griqualand (EG), South Africa using unbalanced panel data for the period 1990 to 2006. Results of a ridge regression analysis show that dairy herd size, the level of farm debt, annual production per cow, technology and policy changes over time, and the ratio of trading income to total milk income influence the long-term competitiveness of these milk producers. To enhance their competitiveness in a deregulated dairy market, relatively small and profitable EG milk producers should consider increasing their herd sizes, as the importance of herd size in explaining competitiveness suggests that size economies exist. All EG milk producers should consider utilising more pasture- and forage-based production systems to lower feed costs and select dairy cattle of superior genetic merit to improve milk yields on pasture.Commercial milk production, competitiveness, panel data, Production Economics,
Entanglement of separate nitrogen-vacancy centers coupled to a whispering-gallery mode cavity
We present a quantum electrodynamical model involving nitrogen-vacancy
centers coupled to a whispering-gallery mode cavity. Two schemes are considered
to create W state and Bell state, respectively. One of the schemes makes use of
the Raman transition with the cavity field virtually excited; The other enables
the Bell state preparation and quantum information transfer by virtue of dark
state evolution and adiabatic passage, which is tolerant to ambient noise and
experimental parameter fluctuations. We justify our schemes by considering the
experimental feasibility and challenge using currently available technology.Comment: 8 pages and 5 figure
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