5,180 research outputs found
Encoding of temporal probabilities in the human brain
Anticipating the timing of future events is a necessary precursor to preparing actions and allocating resources to sensory processing. This requires elapsed time to be represented in the brain and used to predict the temporal probability of upcoming events. While neuropsychological, imaging, magnetic stimulation studies, and single-unit recordings implicate the role of higher parietal and motor-related areas in temporal estimation, the role of earlier, purely sensory structures remains more controversial. Here we demonstrate that the temporal probability of expected visual events is encoded not by a single area but by a wide network that importantly includes neuronal populations at the very earliest cortical stages of visual processing. Moreover, we show that activity in those areas changes dynamically in a manner that closely accords with temporal expectations
Internal Migration and Regional Population Dynamics in Europe: Romanian Case Study
The report analyses population migration and change in Romania over the period 1984-1994. The analysis of population change is conducted for 2948 communes and towns, the finest administrative division for which population data are available. The lack of migration data on the level of communes and towns makes in-depth analysis of the migration for small spatial units impossible. For that reason analysis of the patterns of migration is conducted for 40 Judete (also referred to as counties or regions) and the capital city of Bucharest, i.e. 41 units altogether.
Council of Europe Publishing,
F-67075 Strasbourg - Cedex,
France
Postcard: John D Knox & Company
This black and white printed postcard contains correspondence from John D. Knox & Co. in Topeka, Kansas to a man serving as treasurer in Minneapolis, Kansas. Printed text and handwriting are on the front of the card. Handwriting is on the back of the card.https://scholars.fhsu.edu/tj_postcards/2162/thumbnail.jp
The development of chemical language usage by “non-traditional” students: the interlanguage analogy
Students commonly find specialist scientific language problematic. This study investigated developments in chemical language usage by six non-traditional students over the course of 1 to 4 years. The students participated in semi-structured interviews and were asked to explain specific chemical scenarios. Interviews were transcribed and analysed for the correct use of macroscopic and sub-microscopic scientific language and occurrences of interlanguage. Results indicate that students experienced difficulties incorporating sub-microscopic language into their explanations. Students also demonstrated potential chemical interlanguage, which we characterise as transitioning from vague to defined use, combining everyday and scientific language, interchanging terms and omission of terms and formulaic phrases. Implications of these findings are discussed in relation to science pedagogy
Modeling interaction of relativistic and nonrelativistic winds in binary system PSR 1259-63/SS2883. I.Hydrodynamical limit
In this paper, we present a detailed hydrodynamical study of the properties
of the flow produced by the collision of a pulsar wind with the surrounding in
a binary system. This work is the first attempt to simulate interaction of the
ultrarelativistic flow (pulsar wind) with the nonrelativistic stellar wind.
Obtained results show that the wind collision could result in the formation of
an "unclosed" (at spatial scales comparable to the binary system size) pulsar
wind termination shock even when the stellar wind ram pressure exceeds
significantly the pulsar wind kinetical pressure. Moreover, the post-shock flow
propagates in a rather narrow region, with very high bulk Lorentz factor
(). This flow acceleration is related to adiabatical losses,
which are purely hydrodynamical effects. Interestingly, in this particular
case, no magnetic field is required for formation of the ultrarelativistic bulk
outflow. The obtained results provide a new interpretation for the orbital
variability of radio, X-ray and gamma-ray signals detected from binary pulsar
system PSR 1259-63/SS2883.Comment: 11 pages, 13 figures, submitted to MNRA
Temporal Variability of the X-ray Emission of the Crab Nebula Torus
We have analyzed five ROSAT HRI images of the Crab Nebula spanning the years
1991 to 1997 and have found significant changes in the emission structure of
the X-ray torus surrounding the pulsar. Certain regions increase in brightness
by about 20% over the six years, while others show decreases in surface
brightness. The origin of these changes is unclear, but a possible explanation
is that the bulk velocity of the synchrotron radiating electrons has decreased
on the order of 20% as well.Comment: 15 pages plus 6 figures, figure 1 and figure 6 are in color, to
appear in The Astrophysical Journal, Jan 1, 1999, Vol. 510, #
The Accretion of Lyman Alplha Clouds onto Gas-Rech Protogalaxies; A Scenario for the Formation of Globular Star Clusters
A satisfactory theory for the formation of globular star clusters (GCs) has
long been elusive, perhaps because their true progenitors had not yet been
guessed. In this paper I propose a causal relationship between the strongly
decreasing densities of Lyman alpha (LyA) clouds at high redshift and the
formation of GCs - namely that GCs were created by the accretion of LyA clouds
onto protogalaxies. I describe a scenario which involves an inherently stable
and orderly cycling of compression and cooling in the central cores of clouds
during the extended period of dissipation in the outer regins of gas-rich proto
galaxies, culminating in a burst of efficient star formation. I demonstrate
that the comoving density of GCs is comparable to that of LyA clouds at high
redshift, that the energetic requirements for compression to core GC densities
can be met, and that the time-scale for cooling is within obvious limits
imposed by dynamical stability.
This dissipative process requires there to be a large column of dissipated
gas about the attractor in order to form GCs. In addition, the energy
requirements for compression requires attractor masses greater than that
capable of sustaining circular velocities of ~40 km/s. If this scenario is
supported by numerical simulations, then by implication, the GCs were formed at
modest redshifts of z~1-3. This knowledge could help to break the degeneracy
between lookback time and redshift. The model is consistent with a picture of
hierarchical galaxy growth over time scales of many billions of years.Comment: 7 pages. Accepted, 10 June 1999 Astrophysical Journa
Acceptability of the female condom in different groups of women in South Africa - A multicentred study to inform the national female condom introductory strategy
Objectives. To assess the acceptability of the female condom to different groups of women and their partners in South Africa. Design. Descriptive, cross-sectional study. Setting. Multicentre study conducted in five sites. Subjects. The study recruited 678 women from five centres-to an acceptability trial of the female condom. Acceptability and successful use varied between the centres. Outcome measures. Factors affecting successful use and willingness and intention to use the method again. Results. In total, 209 women used the condom at least once. Discontinuation rates were high, with partner reluctance to try the method as the main reason given for discontinuation at all sites. Women who had previous experience with the male condom or who received a more intensive training session generally found the device easier to use. The main issues concerning women were over-lubrication (27%) and concern that the device was too large (28%). The majority of women said that they would be interested in using the method again (86%) and would recommend it to friends (95%). Conclusions. Overcoming partner opposition is an important issue to address when introducing the method. The study was used to address the national introductory strategy of the female condom, which began in 1998
A gamma ray burst with small contamination
We present a scenario (SupraNova) for the formation of GRBs occurring when a
supramassive neutron star (SMNS) loses so much angular momentum that
centrifugal support against self--gravity becomes impossible, and the star
implodes to a black hole. This may be the baryon--cleanest environment proposed
so far, because the SN explosion in which the SMNS formed swept the medium
surrounding the remnant, and the quickly spinning remnant loses energy through
magnetic dipole radiation at a rate exceeding its Eddington luminosity by some
four orders of magnitude. The implosion is adiabatic because neutrinos have
short mean free paths, and silent, given the prompt collapse of the polar caps.
However, a mass ~ 0.1 M_solar in the equatorial belt can easily reach
centrifugal equilibrium. The mechanism of energy extraction is via the
conversion of the Poynting flux (due to the large--scale magnetic field locked
into the minitorus) into a magnetized relativistic wind. Occasionally this
model will produce quickly decaying, or non--detectable afterglows.Comment: To appear in The Astrophysical Journal Letters. AASTeX LateX, no
figure
MOONS : the new Multi-Object Spectrograph for the VLT
MOONS is the new Multi-Object Optical and Near-infrared Spectrograph currently under construction for the Very Large Telescope (VLT) at ESO. This remarkable instrument combines, for the first time, the collecting power of an 8-m telescope, 1000 fibres with individual roboticp ositioners, and both low- and high-resolution simultaneous spectral coverage across the 0.64–1.8 μm wavelength range. This facility will provide the astronomical community with a powerful, world-leading instrument able to serve a wide range of Galactic, extragalactic and cosmological studies. Construction is now proceeding full steam ahead and this overview article presents some of the science goals and the technical description of the MOONS instrument. More detailed information on the MOONS surveys is provided in the other dedicated articles in this Messenger issue.Publisher PD
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