2,622 research outputs found
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
Integral Field Unit Observations of NGC 891: Kinematics of the Diffuse Ionized Gas Halo
We present high and moderate spectral resolution spectroscopy of diffuse
ionized gas (DIG) emission in the halo of NGC 891. The data were obtained with
the SparsePak integral field unit at the WIYN Observatory. The wavelength
coverage includes the [NII]6548,6583, Halpha, and [SII]6716,6731 emission
lines. Position-velocity (PV) diagrams, constructed using spectra extracted
from four SparsePak pointings in the halo, are used to examine the kinematics
of the DIG. Using two independent methods, a vertical gradient in azimuthal
velocity is found to be present in the northeast quadrant of the halo, with
magnitude approximately 15-18 km/s/kpc, in agreement with results from HI
observations. The kinematics of the DIG suggest that this gradient begins at
approximately 1 kpc above the midplane. In another part of the halo, the
southeast quadrant, the kinematics are markedly different, and suggest rotation
at about 175 km/s, much slower than the disk but with no vertical gradient. We
utilize an entirely ballistic model of disk-halo flow in an attempt to
reproduce the kinematics observed in the northeast quadrant. Analysis shows
that the velocity gradient predicted by the ballistic model is far too shallow.
Based on intensity cuts made parallel to the major axis in the ballistic model
and an Halpha image of NGC 891 from the literature, we conclude that the DIG
halo is much more centrally concentrated than the model, suggesting that
hydrodynamics dominate over ballistic motion in shaping the density structure
of the halo. Velocity dispersion measurements along the minor axis of NGC 891
seem to indicate a lack of radial motions in the halo, but the uncertainties do
not allow us to set firm limits.Comment: 31 pages, 10 figures. Accepted for publication in the Astrophysical
Journa
HALOGAS observations of NGC 5023 and UGC 2082: Modeling of non-cylindrically symmetric gas distributions in edge-on galaxies
In recent years it has become clear that the vertical structure of disk
galaxies is a key ingredient for understanding galaxy evolution. In particular,
the presence and structure of extra-planar gas has been a focus of research.
The Hydrogen Accretion in LOcal GAlaxieS (HALOGAS) survey aims to provide a
census on the rate of cold neutral gas accretion in nearby galaxies as well as
a statistically significant set of galaxies that can be investigated for their
extra-planar gas properties.
In order to better understand the the vertical structure of the neutral
hydrogen in the two edge-on HALOGAS galaxies NGC 5023 and UGC 2082 we construct
detailed tilted ring models. The addition of distortions resembling arcs or
spiral arms significantly improves the fit of the models to these galaxies. In
the case of UGC 2082 no vertical gradient in rotational velocity is required in
either symmetric models nor non-symmetric models to match the observations. The
best fitting model features two arcs of large vertical extent that may be due
to accretion. In the case of NGC 5023 a vertical gradient is required in
symmetric models (dV/dz = km s kpc) and its
magnitude is significantly lowered when non-symmetric models are considered
(dV/dz = km s kpc). Additionally it is shown that the
underlying disk of NGC 5023 can be made symmetric, in all parameters except the
warp, in non-symmetric models. In comparison to the "classical" modeling these
models fit the data significantly better with a limited addition of free
parameters.Comment: 27 Pages, 22 Figures. Accepted for publication in MNRA
Untangling cosmic magnetic fields: Faraday tomography at metre wavelengths with LOFAR
14 pages, 6 figures. Accepted for publication in "The Power of Faraday Tomography" special issue of GalaxiesThe technique of Faraday tomography is a key tool for the study ofmagnetised plasmas in the new era of broadband radio-polarisation observations. In particular, observations at metre wavelengths provide significantly better Faraday depth accuracies compared to traditional centimetre-wavelength observations. However, the effect of Faraday depolarisationmakes the polarised signal very challenging to detect at metre wavelengths (MHz frequencies). In this work, Faraday tomography is used to characterise the Faraday rotation properties of polarised sources found in data from the LOFAR Two-Metre Sky Survey (LoTSS). Of the 76 extragalactic polarised sources analysed here, we find that all host a radio-loud AGN (Active Galactic Nucleus). The majority of the sources (~64%) are large FRII radio galaxies with a median projected linear size of 710 kpc and median radio luminosity at 144 MHz of 4 × 10 26 W Hz -1 (with ~13% of all sources having a linear size > 1 Mpc). In several cases, both hotspots are detected in polarisation at an angular resolution of ~20'. One such case allowed a study of intergalactic magnetic fields on scales of 3.4 Mpc. Other detected source types include an FRI radio galaxy and at least eight blazars. Most sources display simple Faraday spectra, but we highlight one blazar that displays a complex Faraday spectrum, with two close peaks in the Faraday dispersion function.Peer reviewe
On the exact electric and magnetic fields of an electric dipole
We derive from Jefimenko's equations a multipole expansion in order to obtain
the exact expressions for the electric and magnetic fields of an electric
dipole with an arbitrary time dependence. A few comments are also made about
the usual expositions found in most common undergraduate and graduate textbooks
as well as in the literature on this topic
Theory of Light Emission in Sonoluminescence as Thermal Radiation
Based on the model proposed by Hilgenfeldt {\it at al.} [Nature {\bf 398},
401 (1999)], we present here a comprehensive theory of thermal radiation in
single-bubble sonoluminescence (SBSL). We first invoke the generalized
Kirchhoff's law to obtain the thermal emissivity from the absorption
cross-section of a multilayered sphere (MLS). A sonoluminescing bubble, whose
internal structure is determined from hydrodynamic simulations, is then
modelled as a MLS and in turn the thermal radiation is evaluated. Numerical
results obtained from simulations for argon bubbles show that our theory
successfully captures the major features observed in SBSL experiments.Comment: 17 pages, 20 figure
Kinematics of diffuse ionized gas in the disk halo interface of NGC 891 from Fabry-P\'erot observations
The properties of the gas in halos of galaxies constrain global models of the
interstellar medium. Kinematical information is of particular interest since it
is a clue to the origin of the gas. Here we report observations of the
kinematics of the thick layer of the diffuse ionized gas in NGC 891 in order to
determine the rotation curve of the halo gas. We have obtained a Fabry-P\'erot
data cube in Halpha to measure the kinematics of the halo gas with angular
resolution much higher than obtained from HI 21 cm observations. The data cube
was obtained with the TAURUS II spectrograph at the WHT on La Palma. The
velocity information of the diffuse ionized gas extracted from the data cube is
compared to model distributions to constrain the distribution of the gas and in
particular the halo rotation curve. The best fit model has a central
attenuation tau_H-alpha=6, a dust scale length of 8.1 kpc, an ionized gas scale
length of 5.0 kpc. Above the plane the rotation curve lags with a vertical
gradient of -18.8 km/s/kpc. We find that the scale length of the H-alpha must
be between 2.5 and 6.5 kpc. Furthermore we find evidence that the rotation
curve above the plane rises less steeply than in the plane. This is all in
agreement with the velocities measured in the HI.Comment: A&A, in press. 13 pages, 19 figure
The nature of the low-frequency emission of M51: First observations of a nearby galaxy with LOFAR
The grand-design spiral galaxy M51 was observed with the LOFAR High Frequency
Antennas (HBA) and imaged in total intensity and polarisation. This observation
covered the frequencies between 115 MHz and 175 MHz. We produced an image of
total emission of M51 at the mean frequency of 151 MHz with 20 arcsec
resolution and 0.3 mJy rms noise, which is the most sensitive image of a galaxy
at frequencies below 300 MHz so far. The integrated spectrum of total radio
emission is described well by a power law, while flat spectral indices in the
central region indicate thermal absorption. We observe that the disk extends
out to 16 kpc and see a break in the radial profile near the optical radius of
the disk. Our main results, the scale lengths of the inner and outer disks at
151 MHz and 1.4 GHz, arm--interarm contrast, and the break scales of the
radio--far-infrared correlations, can be explained consistently by CRE
diffusion, leading to a longer propagation length of CRE of lower energy. The
distribution of CRE sources drops sharply at about 10 kpc radius, where the
star formation rate also decreases sharply. We find evidence that thermal
absorption is primarily caused by HII regions. The non-detection of
polarisation from M51 at 151 MHz is consistent with the estimates of Faraday
depolarisation. Future searches for polarised emission in this frequency range
should concentrate on regions with low star formation rates.Comment: 20 pages, 18 figures, accepted for publication in A&
Exploiting simultaneous observational constraints on mass and absorption to estimate the global direct radiative forcing of black carbon and brown carbon
Atmospheric black carbon (BC) is a leading climate warming agent, yet uncertainties on the global direct radiative forcing (DRF) remain large. Here we expand a global model simulation (GEOS-Chem) of BC to include the absorption enhancement associated with BC coating and separately treat both the aging and physical properties of fossil-fuel and biomass-burning BC. In addition we develop a global simulation of brown carbon (BrC) from both secondary (aromatic) and primary (biomass burning and biofuel) sources. The global mean lifetime of BC in this simulation (4.4 days) is substantially lower compared to the AeroCom I model means (7.3 days), and as a result, this model captures both the mass concentrations measured in near-source airborne field campaigns (ARCTAS, EUCAARI) and surface sites within 30%, and in remote regions (HIPPO) within a factor of 2. We show that the new BC optical properties together with the inclusion of BrC reduces the model bias in absorption aerosol optical depth (AAOD) at multiple wavelengths by more than 50% at AERONET sites worldwide. However our improved model still underestimates AAOD by a factor of 1.4 to 2.8 regionally, with the largest underestimates in regions influenced by fire. Using the RRTMG model integrated with GEOS-Chem we estimate that the all-sky top-of-atmosphere DRF of BC is +0.13 Wm[superscript −2] (0.08 Wm[superscript −2] from anthropogenic sources and 0.05 Wm[superscript −2] from biomass burning). If we scale our model to match AERONET AAOD observations we estimate the DRF of BC is +0.21 Wm[superscript −2], with an additional +0.11 Wm[superscript −2] of warming from BrC. Uncertainties in size, optical properties, observations, and emissions suggest an overall uncertainty in BC DRF of −80%/+140%. Our estimates are at the lower end of the 0.2–1.0 Wm[superscript −2] range from previous studies, and substantially less than the +0.6 Wm[superscript −2] DRF estimated in the IPCC 5th Assessment Report. We suggest that the DRF of BC has previously been overestimated due to the overestimation of the BC lifetime (including the effect on the vertical profile) and the incorrect attribution of BrC absorption to BC.United States. Environmental Protection Agency. Office of Research and Development National Center for Environmental Research Science to Achieve Results (STAR) Program (Grant RD-83503301
- …