15,791 research outputs found
Classical novae and type I X-ray bursts: challenges for the 21st century
Classical nova explosions and type I X-ray bursts are the most frequent types
of thermonuclear stellar explosions in the Galaxy. Both phenomena arise from
thermonuclear ignition in the envelopes of accreting compact objects in close
binary star systems. Detailed observations of these events have stimulated
numerous studies in theoretical astrophysics and experimental nuclear physics.
We discuss observational features of these phenomena and theoretical efforts to
better understand the energy production and nucleosynthesis in these
explosions. We also examine and summarize studies directed at identifying
nuclear physics quantities with uncertainties that significantly affect model
predictions.Comment: 40 pages, accepted for AIP Advances: Stardust - Progress and Problems
in Nuclear Astrophysic
Late biological effects of heavy charged particles: Cataracts, vascular injury and life shortening in mice
Risks associated with extended habitation in a space environment, particularly hazards to space workers that might result from exposure to high energy heavy ion particles (HZE), were studied. Biological effects of HZE were investigated in mice to assess their potential adverse health hazards. The potential effects of HZE particles on the crystalline lens of the eye and the carcinogenic effects and blood vessel (vascular) damage from radiation were evaluated by a risk assessment. Animal experiments to evaluate dose response relationships for tumor induction/promotion and for vascular injury were introduced. Cataract productions and preliminary results on cacinogenic and vascular effects are presented for perspective
Comparison of velocity-based and traditional 1RM-percent-based prescription on acute kinetic and kinematic variables
Purpose:
This study compared kinetic and kinematic data from three different velocity-based training (VBT) sessions and a 1-repetition maximum (1RM) percent-based training (PBT) session using full-depth, free-weight back squats with maximal concentric effort.
Methods:
Fifteen strength-trained men performed four randomized resistance-training sessions 96-hours apart: PBT session involved five sets of five repetitions using 80%1RM; load-velocity profile (LVP) session contained five sets of five repetitions with a load that could be adjusted to achieve a target velocity established from an individualized LVP equation at 80%1RM; fixed sets 20% velocity loss threshold (FSVL20) session that consisted of five sets at 80%1RM but sets were terminated once the mean velocity (MV) dropped below 20% of the threshold velocity or when five repetitions were completed per set; variable sets 20% velocity loss threshold (VSVL20) session comprised 25-repetitions in total, but participants performed as many repetitions in a set as possible until the 20% velocity loss threshold was exceeded.
Results:
When averaged across all repetitions, MV and peak velocity (PV) were significantly (p<0.05) faster during the LVP (MV: ES=1.05; PV: ES=1.12) and FSVL20 (MV: ES=0.81; PV: ES=0.98) sessions compared to PBT. Mean time under tension (TUT) and concentric TUT were significantly less during the LVP session compared to PBT. FSVL20 session had significantly less repetitions, total TUT and concentric TUT than PBT. No significant differences were found for all other measurements between any of the sessions.
Conclusions:
VBT permits faster velocities, avoids additional unnecessary mechanical stress but maintains similar measures of force and power output compared to strength-oriented PBT
Can a workspace help to overcome the query formulation problem in image retrieval?
We have proposed a novel image retrieval system that incorporates a workspace where users can organise their search results. A task-oriented and user-centred experiment has been devised involving design professionals and several types of realistic search tasks. We study the workspace’s effect on two aspects: task conceptualisation and query formulation. A traditional relevance feedback system serves as baseline. The results of this study show that the workspace is more useful with respect to both of the above aspects. The proposed approach leads to a more effective and enjoyable search experience
A Study of starless dark cloud LDN 1570: Distance, Dust properties and Magnetic field geometry
We wish to map the magnetic field geometry and to study the dust properties
of the starless cloud, L1570, using multi-wavelength optical polarimetry and
photometry of the stars projected on the cloud. We made R-band imaging
polarimetry of the stars projected on a cloud, L1570, to trace the magnetic
field orientation. We also made multi-wavelength polarimetric and photometric
observations to constrain the properties of dust in L1570. We estimated a
distance of 394 +/- 70 pc to the cloud using 2MASS JHKs colours. Using the
values of the Serkowski parameters namely , ,
{\lambda}max and the position of the stars on near infrared color-color
diagram, we identified 13 stars that could possibly have intrinsic polarization
and/or rotation in their polarization angles. One star, 2MASS
J06075075+1934177, which is a B4Ve spectral type, show the presence of diffuse
interstellar bands in the spectrum apart from showing H{\alpha} line in
emission. There is an indication for the presence of slightly bigger dust
grains towards L1570 on the basis of the dust grain size-indicators such as
{\lambda}max and Rv values. The magnetic field lines are found to be parallel
to the cloud structures seen in the 250{\mu}m images (also in 8{\mu}m and
12{\mu}m shadow images) of L1570. Based on the magnetic field geometry, the
cloud structure and the complex velocity structure, we believe that L1570 is in
the process of formation due to the converging flow material mediated by the
magnetic field lines. Structure function analysis showed that in the L1570
cloud region the large scale magnetic fields are stronger when compared with
the turbulent component of magnetic fields. The estimated magnetic field
strengths suggest that the L1570 cloud region is sub-critical and hence could
be strongly supported by the magnetic field lines.Comment: 26 pages, 22 figures, and 7 tables; Accepted for its publication in
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