3,112 research outputs found
Heating of solar chromosphere by electromagnetic wave absorption in a plasma slab model
The heating of solar chromospheric inter-network regions by means of the
absorption of electromagnetic (EM) waves that originate from the photospheric
blackbody radiation is studied in the framework of a plasma slab model. The
absorption is provided by the electron-neutral collisions in which electrons
oscillate in the EM wave field and electron-neutral collisions damp the EM
wave. Given the uncertain nature of the collision cross-section due to the
plasma micro-turbulence, it is shown that for plausible physical parameters,
the heating flux produced by the absorption of EM waves in the chromosphere is
between % of the chromospheric radiative loss flux requirement. It is
also established that there is an optimal value for the collision
cross-section, m, that produces the maximal heating
flux of 1990 W m.Comment: Physics of Plasmas, in press, April 2011 issue (final printed
version, typos in proofs corrected
Simple analysis of off-axis solenoid fields using the scalar magnetostatic potential: application to a Zeeman-slower for cold atoms
In a region free of currents, magnetostatics can be described by the Laplace
equation of a scalar magnetic potential, and one can apply the same methods
commonly used in electrostatics. Here we show how to calculate the general
vector field inside a real (finite) solenoid, using only the magnitude of the
field along the symmetry axis. Our method does not require integration or
knowledge of the current distribution, and is presented through practical
examples, including a non-uniform finite solenoid used to produce cold atomic
beams via laser cooling. These examples allow educators to discuss the
non-trivial calculation of fields off-axis using concepts familiar to most
students, while offering the opportunity to introduce important advancements of
current modern research.Comment: 6 pages. Accepted in the American Journal of Physic
On the use of low-cost computer peripherals for the assessment of motor dysfunction in Parkinson’s disease – Quantification of bradykinesia using target tracking tasks
The potential of computer games peripherals to measure the motor dysfunction in Parkinson’s diseases is assessed. Of particular interest is the quantification of bradykinesia. Previous studies used modified or custom haptic interfaces, here an unmodified force feedback joystick and steering wheel are used with a laptop. During testing an on screen cursor moves in response to movements of the peripheral, the user has to track a continuously moving target (pursuit tracking), or move to a predetermined target (step tracking). All tasks use movement in the horizontal axis, allowing use of joystick or steering wheel. Two pursuit tracking tasks are evaluated, pseudo random movement, and a swept frequency task. Two step tracking tasks are evaluated, movement between two or between two of five fixed targets. Thirteen patients and five controls took part on a weekly basis. Patients were assessed for bradykinesia at each session using standard clinical measures. A range of quantitative measures was developed to allow comparison between and within patients and controls using ANOVA. Both peripherals are capable of discriminating between controls and patients, and between patients with different levels of bradykinesia. Recommendations for test procedures and peripherals are given
Grain boundary ferromagnetism in vanadium-doped InO thin films
Room temperature ferromagnetism was observed in InO\,^{\circ}{\rm C}_2_3$ host lattice, thus excluding the existence of secondary phases
of vanadium compounds. Magnetic measurements based on SQUID magnetometry and
magnetic circular dichroism confirm that the magnetism is at grain boundaries
and also in the grains. The overall magnetization originates from the competing
effects between grains and grain boundaries.Comment: 12 pages, 7 figures, 1 table, accepted by Europhysics Letter
The Parkes HI Zone of Avoidance Survey
A blind HI survey of the extragalactic sky behind the southern Milky Way has
been conducted with the multibeam receiver on the 64-m Parkes radio telescope.
The survey covers the Galactic longitude range 212 < l < 36 and Galactic
latitudes |b| < 5, and yields 883 galaxies to a recessional velocity of 12,000
km/s. The survey covers the sky within the HIPASS area to greater sensitivity,
finding lower HI-mass galaxies at all distances, and probing more completely
the large-scale structures at and beyond the distance of the Great Attractor.
Fifty-one percent of the HI detections have an optical/NIR counterpart in the
literature. A further 27% have new counterparts found in existing, or newly
obtained, optical/NIR images. The counterpart rate drops in regions of high
foreground stellar crowding and extinction, and for low-HI mass objects. Only
8% of all counterparts have a previous optical redshift measurement. A notable
new galaxy is HIZOA J1353-58, a possible companion to the Circinus galaxy.
Merging this catalog with the similarly-conducted northern extension (Donley et
al. 2005), large-scale structures are delineated, including those within the
Puppis and Great Attractor regions, and the Local Void. Several
newly-identified structures are revealed here for the first time. Three new
galaxy concentrations (NW1, NW2 and NW3) are key in confirming the diagonal
crossing of the Great Attractor Wall between the Norma cluster and the CIZA
J1324.7-5736 cluster. Further contributors to the general mass overdensity in
that area are two new clusters (CW1 and CW2) in the nearer Centaurus Wall, one
of which forms part of the striking 180 deg (100/h Mpc) long filament that
dominates the southern sky at velocities of ~3000 km/s, and the suggestion of a
further Wall at the Great Attractor distance at slightly higher longitudes.Comment: Published in Astronomical Journal 9 February 2016 (accepted 26
September 2015); 42 pages, 7 tables, 18 figures, main figures data tables
only available in the on-line version of journa
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