538 research outputs found
The impact of the graduated driver licence scheme on road traffic accident youth mortality in New Zealand
This paper examines the impact of the introduction of New Zealand’s Graduated Driving Licence System (GDLS) on patterns of road traffic accident mortality amongst the young driving population from 1980 to 2001. Results show that the mortality rate has declined, but that rates in New Zealand are three times greater than in England and Wales and twice those of Scotland. When the data is adjusted to take account of differences in the minimum driving age, rates remain consistently higher in New Zealand and the proportional reduction in road traffic accident youth mortality is not significantly better than that experienced in Great Britain
Scaling laws for electron kinetic effects in tokamak scrape-off layer plasmas
Tokamak edge (scrape-off layer (SOL)) plasmas can exhibit non-local transport in the direction parallel to the magnetic field due to steep temperature gradients. This effect along with its consequences has been explored at equilibrium for a range of conditions, from sheath-limited to detached, using the 1D kinetic electron code SOL-KiT, where the electrons are treated kinetically and compared to a self-consistent fluid model. Line-averaged suppression of the kinetic heat flux (compared to Spitzer-Härm) of up to 50% is observed, contrasting with up to 98% enhancement of the sheath heat transmission coefficient, γe. Simple scaling laws in terms of basic SOL parameters for both effects are presented. By implementing these scalings as corrections to the fluid model, we find good agreement with the kinetic model for target electron temperatures. It is found that the strongest kinetic effects in γe are observed at low-intermediate collisionalities, and tend to increase (keeping upstream collisionality fixed) at increasing upstream densities and temperatures. On the other hand, the heat flux suppression is found to increase monotonically as upstream collisionality decreases. The conditions simulated encompass collisionalities relevant to current and future tokamaks
Twisted plasma waves driven by twisted ponderomotive force
We present results of twisted plasma waves driven by twisted ponderomotive
force. With beating of two, co-propagating, Laguerre-Gaussian (LG) orbital
angular momentum (OAM) laser pulses with different frequencies and also
different twist indices, we can get twisted ponderomotive force.
Three-dimensional particle-in-cell simulations are used to demonstrate the
twisted plasma waves driven by lasers. The twisted plasma waves have an
electron density perturbation with a helical rotating structure. Different from
the predictions of the linear fluid theory, the simulation results show a
nonlinear rotating current and a static axial magnetic field. Along with the
rotating current is the axial OAM carried by particles in the twisted plasma
waves. Detailed theoretical analysis of twisted plasma waves is given too
Three Dimensional Secondary Ion Mass Spectrometry Imaging and Retrospective Depth Profiling
Secondary Ion Mass Spectrometry (SIMS) for three dimensional analysis of materials is an exciting and rapidly developing technique. We describe a framestore datasystem for ion microprobe instruments and present images and three dimensional SIMS data acquired and processed with this system. The concept of retrospective depth profiling is introduced, particularly as a means to optimise concentration detection limits. We examine the dependence of concentration detection limits on spatial resolution
Маркшейдерська школа Національного гірничого університету
Викладена історія створення та розвитку маркшейдерської школи в НГУ протягом 110 років.Изложена история создания и развития маркшейдерской школы в НГУ в течение 110 лет.History of creation and development ofsurveyor school is expounded in NMU during 110 years
Image-guided liver surgery: intraoperative projection of computed tomography images utilizing tracked ultrasound
AbstractBackgroundUltrasound (US) is the most commonly used form of image guidance during liver surgery. However, the use of navigation systems that incorporate instrument tracking and three-dimensional visualization of preoperative tomography is increasing. This report describes an initial experience using an image-guidance system with navigated US.MethodsAn image-guidance system was used in a total of 50 open liver procedures to aid in localization and targeting of liver lesions. An optical tracking system was employed to localize surgical instruments. Customized hardware and calibration of the US transducer were required. The results of three procedures are highlighted in order to illustrate specific navigation techniques that proved useful in the broader patient cohort.ResultsOver a 7-month span, the navigation system assisted in completing 21 (42%) of the procedures, and tracked US alone provided additional information required to perform resection or ablation in six procedures (12%). Average registration time during the three illustrative procedures was <1min. Average set-up time was approximately 5min per procedure.ConclusionsThe Explorer™ Liver guidance system represents novel technology that continues to evolve. This initial experience indicates that image guidance is valuable in certain procedures, specifically in cases in which difficult anatomy or tumour location or echogenicity limit the usefulness of traditional guidance methods
Geodetic VLBI Observations of EGRET Blazars
We present VLBI observations of the EGRET quasars 0202+149, CTA 26, and
1606+106, as well as additional analysis of VLBI observations of 1156+295
presented in Piner & Kingham (1997b). We have produced 8 and 2 GHz VLBI images
at 11 epochs, 8 epochs, and 12 epochs, spanning the years 1989 to 1996, of
0202+149, CTA 26, and 1606+106 respectively. The VLBI data have been taken from
the Washington VLBI correlator's geodetic database. We have measured the
apparent velocities of the jet components and find that CTA 26 and 1606+106 are
superluminal sources, with average apparent speeds of 8.9 and 2.9 h^{-1}c
respectively (H_{0}=100h km s^{-1} Mpc^{-1}, q_{0}=0.5). The components in
0202+149 are stationary, and we identify this source as a compact F double.
These sources all have apparently bent jets, and we detected non-radial motion
of components in CTA 26 and 1156+295. We have not yet detected any components
emerging subsequent to the gamma-ray flares in CTA 26, 1156+295, and 1606+106,
and we derive lower limits on the ejection times of any such components. The
misalignment angle distribution of the EGRET sources is compared to the
distribution for blazars as a whole, and we find that EGRET sources belong
preferentially to neither the aligned nor the misaligned population. We also
compare the average values for the apparent velocities and Doppler beaming
factors for the EGRET and non-EGRET blazars, and find no significant
differences. We thus find no indication, within the measurement errors, that
EGRET blazars are any more strongly beamed than their counterparts which have
not been detected in gamma-rays.Comment: 47 pages, including 13 figures; accepted for publication in the
Astrophysical Journa
VSOP and Ground-based VLBI Imaging of the TeV Blazar Markarian 421 at Multiple Epochs
We present thirty VLBI images of the TeV blazar Markarian 421 (1101+384) at
fifteen epochs spanning the time range from 1994 to 1997, and at six different
frequencies from 2.3 to 43 GHz. The imaged observations include a
high-resolution 5 GHz VLBI Space Observatory Programme (VSOP) observation with
the HALCA satellite on 1997 November 14; full-track VLBA observations from 1994
April, 1996 November, and 1997 May at frequencies between 5 and 43 GHz; six
epochs of VLBA snapshot observations at frequencies between 2 and 15 GHz from
Radio Reference Frame studies; and five geodetic VLBI observations at 2 and 8
GHz from the archive of the Washington VLBI Correlator Facility located at the
U.S. Naval Observatory. The dense time coverage of the images allows us to
unambiguously track components in the parsec-scale jet over the observed time
range. We measure the speeds of three inner jet components located between 0.5
and 5 mas from the core (0.3 to 3 pc projected linear distance) to be 0.19 +/-
0.27, 0.30 +/- 0.07, and -0.07 +/- 0.07 c (H_{0}=65 km s^{-1} Mpc^{-1}). If the
sole 43 GHz image is excluded, all measured speeds are consistent with no
motion. These speeds differ from tentative superluminal speeds measured by
Zhang & B\aa\aa th from three epochs of data from the early 1980's. Possible
interpretations of these subluminal speeds in terms of the high Doppler factor
demanded by the TeV variability of this source are discussed.Comment: 18 pages, including 7 figures, emulateapj.sty, accepted by The
Astrophysical Journal; modified text describing Radio Reference Frame
observation
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