41,906 research outputs found
A quantum mechanical approach to establishing the magnetic field orientation from a maser Zeeman profile
Recent comparisons of magnetic field directions derived from maser Zeeman
splitting with those derived from continuum source rotation measures have
prompted new analysis of the propagation of the Zeeman split components, and
the inferred field orientation. In order to do this, we first review differing
electric field polarization conventions used in past studies. With these
clearly and consistently defined, we then show that for a given Zeeman
splitting spectrum, the magnetic field direction is fully determined and
predictable on theoretical grounds: when a magnetic field is oriented away from
the observer, the left-hand circular polarization is observed at higher
frequency and the right-hand polarization at lower frequency. This is
consistent with classical Lorentzian derivations. The consequent interpretation
of recent measurements then raises the possibility of a reversal between the
large-scale field (traced by rotation measures) and the small-scale field
(traced by maser Zeeman splitting).Comment: 10 pages, 5 Figures, accepted for publication in MNRA
Beyond recurrent costs: an institutional analysis of the unsustainability of donor-supported reforms in agricultural extension
International donors have spent billions of dollars over the past four decades in developing and/or reforming the agricultural extension service delivery arrangements in developing countries. However, many of these reforms, supported through short-term projects, became unsustainable once aid funding had ceased. The unavailability of recurrent funding has predominantly been highlighted in the literature as the key reason for this undesirable outcome, while little has been written about institutional factors. The purpose of this article is to examine the usefulness of taking an institutional perspective in explaining the unsustainability of donor-supported extension reforms and derive lessons for improvement. Using a framework drawn from the school of institutionalism in a Bangladeshi case study, we have found that a reform becomes unsustainable because of poor demands for extension information and advice; missing, weak, incongruent, and perverse institutional frameworks governing the exchange of extension goods (services); and a lack of institutional learning and change during the reform process. Accordingly, we have argued that strategies for sustainable extension reforms should move beyond financial considerations and include such measures as making extension goods (services) more tangible and monetary in nature, commissioning in-depth studies to learn about local institutions, crafting new institutions and/or reforming the weak and perverse institutions prevailing in developing countries. We emphasize the need to address three categories of institutions – regulative, normative, and cultural-cognitive – and call for an alignment among them. We further argue that, in order to be sustainable, a reform should take a systemic approach in institutional capacity building and, for this to be possible, adopt a long-term program approach, as opposed to a short-term project approach
Spectroscopic measurements of temperature and plasma impurity concentration during magnetic reconnection at the Swarthmore Spheromak Experiment
Electron temperature measurements during counterhelicity spheromak merging studies at the Swarthmore Spheromak Experiment (SSX) [M. R. Brown, Phys. Plasmas 6, 1717 (1999)] are presented. VUV monochromator measurements of impurity emission lines are compared with model spectra produced by the non-LTE excitation kinematics code PRISMSPECT [J. J. MacFarlane et al., in Proceedings of the Third Conference on Inertial Fusion Science and Applications (2004)] to yield the electron temperature in the plasma with 1 µs time resolution. Average T_e is seen to increase from 12 to 19 eV during spheromak merging. Average C III ion temperature, measured with a new ion Doppler spectrometer (IDS) [C. D. Cothran et al., Rev. Sci. Instrum. 77, 063504 (2006)], likewise rises during spheromak merging, peaking at ~22 eV, but a similar increase in T_i is seen during single spheromak discharges with no merging. The VUV emission line measurements are also used to constrain the concentrations of various impurities in the SSX plasma, which are dominated by carbon, but include some oxygen and nitrogen. A burst of soft x-ray emission is seen during reconnection with a new four-channel detector (SXR). There is evidence for spectral changes in the soft x-ray emission as reconnection progresses, although our single-temperature equilibrium spectral models are not able to provide adequate fits to all the SXR data
Microwave oven fabricated hybrid memristor devices for non-volatile memory storage
© 2014 IOP Publishing Ltd. Novel hybrid non-volatile memories made using an ultra-fast microwave heating method are reported for the first time. The devices, consisting of aligned ZnO nanorods embedded in poly (methyl methacrylate), require no forming step and exhibit reliable and reproducible bipolar resistive switching at low voltages and with low power usage. We attribute these properties to a combination of the high aspect ratio of the nanorods and the polymeric hybrid structure of the device. The extremely easy, fast and low-cost solution based method of fabrication makes possible the simple and quick production of cheap memory cells
Orbital Characteristics of the Subdwarf-B and F V Star Binary EC~20117-4014(=V4640 Sgr)
Among the competing evolution theories for subdwarf-B (sdB) stars is the
binary evolution scenario. EC~20117-4014 (=V4640~Sgr) is a spectroscopic binary
system consisting of a pulsating sdB star and a late F main-sequence companion
(O'Donoghue et al. 1997), however the period and the orbit semi-major axes have
not been precisely determined. This paper presents orbital characteristics of
the EC 20117-4014 binary system using 20 years of photometric data. Periodic
Observed minus Calculated (O-C) variations were detected in the two highest
amplitude pulsations identified in the EC 20117-4014 power spectrum, indicating
the binary system's precise orbital period (P = 792.3 days) and the
light-travel time amplitude (A = 468.9 s). This binary shows no significant
orbital eccentricity and the upper limit of the eccentricity is 0.025 (using 3
as an upper limit). This upper limit of the eccentricity is the lowest
among all wide sdB binaries with known orbital parameters. This analysis
indicated that the sdB is likely to have lost its hydrogen envelope through
stable Roche lobe overflow, thus supporting hypotheses for the origin of sdB
stars. In addition to those results, the underlying pulsation period change
obtained from the photometric data was = 5.4 (0.7)
d d, which shows that the sdB is just before the end of the
core helium-burning phase
Conformally Einstein Products and Nearly K\"ahler Manifolds
In the first part of this note we study compact Riemannian manifolds (M,g)
whose Riemannian product with R is conformally Einstein. We then consider
compact 6--dimensional almost Hermitian manifolds of type W_1+W_4 in the
Gray--Hervella classification admitting a parallel vector field and show that
(under some regularity assumption) they are obtained as mapping tori of
isometries of compact Sasaki-Einstein 5-dimensional manifolds. In particular,
we obtain examples of inhomogeneous locally (non-globally) conformal nearly
K\"ahler compact manifolds
Force dipoles and stable local defects on fluid vesicles
An exact description is provided of an almost spherical fluid vesicle with a
fixed area and a fixed enclosed volume locally deformed by external normal
forces bringing two nearby points on the surface together symmetrically. The
conformal invariance of the two-dimensional bending energy is used to identify
the distribution of energy as well as the stress established in the vesicle.
While these states are local minima of the energy, this energy is degenerate;
there is a zero mode in the energy fluctuation spectrum, associated with area
and volume preserving conformal transformations, which breaks the symmetry
between the two points. The volume constraint fixes the distance , measured
along the surface, between the two points; if it is relaxed, a second zero mode
appears, reflecting the independence of the energy on ; in the absence of
this constraint a pathway opens for the membrane to slip out of the defect.
Logarithmic curvature singularities in the surface geometry at the points of
contact signal the presence of external forces. The magnitude of these forces
varies inversely with and so diverges as the points merge; the
corresponding torques vanish in these defects. The geometry behaves near each
of the singularities as a biharmonic monopole, in the region between them as a
surface of constant mean curvature, and in distant regions as a biharmonic
quadrupole. Comparison of the distribution of stress with the quadratic
approximation in the height functions points to shortcomings of the latter
representation. Radial tension is accompanied by lateral compression, both near
the singularities and far away, with a crossover from tension to compression
occurring in the region between them.Comment: 26 pages, 10 figure
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