6,110 research outputs found
A Putative Multiple-Demand System in the Macaque Brain.
UNLABELLED: In humans, cognitively demanding tasks of many types recruit common frontoparietal brain areas. Pervasive activation of this "multiple-demand" (MD) network suggests a core function in supporting goal-oriented behavior. A similar network might therefore be predicted in nonhuman primates that readily perform similar tasks after training. However, an MD network in nonhuman primates has not been described. Single-cell recordings from macaque frontal and parietal cortex show some similar properties to human MD fMRI responses (e.g., adaptive coding of task-relevant information). Invasive recordings, however, come from limited prespecified locations, so they do not delineate a macaque homolog of the MD system and their positioning could benefit from knowledge of where MD foci lie. Challenges of scanning behaving animals mean that few macaque fMRI studies specifically contrast levels of cognitive demand, so we sought to identify a macaque counterpart to the human MD system using fMRI connectivity in 35 rhesus macaques. Putative macaque MD regions, mapped from frontoparietal MD regions defined in humans, were found to be functionally connected under anesthesia. To further refine these regions, an iterative process was used to maximize their connectivity cross-validated across animals. Finally, whole-brain connectivity analyses identified voxels that were robustly connected to MD regions, revealing seven clusters across frontoparietal and insular cortex comparable to human MD regions and one unexpected cluster in the lateral fissure. The proposed macaque MD regions can be used to guide future electrophysiological investigation of MD neural coding and in task-based fMRI to test predictions of similar functional properties to human MD cortex. SIGNIFICANCE STATEMENT: In humans, a frontoparietal "multiple-demand" (MD) brain network is recruited during a wide range of cognitively demanding tasks. Because this suggests a fundamental function, one might expect a similar network to exist in nonhuman primates, but this remains controversial. Here, we sought to identify a macaque counterpart to the human MD system using fMRI connectivity. Putative macaque MD regions were functionally connected under anesthesia and were further refined by iterative optimization. The result is a network including lateral frontal, dorsomedial frontal, and insular and inferior parietal regions closely similar to the human counterpart. The proposed macaque MD regions can be useful in guiding electrophysiological recordings or in task-based fMRI to test predictions of similar functional properties to human MD cortex
3D-MHD simulations of an accretion disk with star-disk boundary layer
We present global 3D MHD simulations of geometrically thin but unstratified
accretion disks in which a near Keplerian disk rotates between two bounding
regions with initial rotation profiles that are stable to the MRI. The inner
region models the boundary layer between the disk and an assumed more slowly
rotating central, non magnetic star. We investigate the dynamical evolution of
this system in response to initial vertical and toroidal fields imposed in a
variety of domains contained within the near Keplerian disk. Cases with both
non zero and zero net magnetic flux are considered and sustained dynamo
activity found in runs for up to fifty orbital periods at the outer boundary of
the near Keplerian disk. Simulations starting from fields with small radial
scale and with zero net flux lead to the lowest levels of turbulence and
smoothest variation of disk mean state variables. For our computational set up,
average values of the Shakura & Sunyaev (1973) parameter in the
Keplerian disk are typically Magnetic field eventually always
diffuses into the boundary layer resulting in the build up of toroidal field
inward angular momentum transport and the accretion of disk material. The mean
radial velocity, while exhibiting large temporal fluctuations is always
subsonic. Simulations starting with net toroidal flux may yield an average
While being characterized by one order of magnitude larger
average , simulations starting from vertical fields with large radial
scale and net flux may lead to the formation of persistent non-homogeneous,
non-axisymmetric magnetically dominated regions of very low density.Comment: Accepted for publication in Ap
The Second Conference on Lunar Bases and Space Activities of the 21st Century, volume 1
These papers comprise a peer-review selection of presentations by authors from NASA, LPI industry, and academia at the Second Conference (April 1988) on Lunar Bases and Space Activities of the 21st Century, sponsored by the NASA Office of Exploration and the Lunar Planetary Institute. These papers go into more technical depth than did those published from the first NASA-sponsored symposium on the topic, held in 1984. Session topics covered by this volume include (1) design and operation of transportation systems to, in orbit around, and on the Moon, (2) lunar base site selection, (3) design, architecture, construction, and operation of lunar bases and human habitats, and (4) lunar-based scientific research and experimentation in astronomy, exobiology, and lunar geology
The Second Conference on Lunar Bases and Space Activities of the 21st Century, volume 2
These 92 papers comprise a peer-reviewed selection of presentations by authors from NASA, the Lunar and Planetary Institute (LPI), industry, and academia at the Second Conference on Lunar Bases and Space Activities of the 21st Century. These papers go into more technical depth than did those published from the first NASA-sponsored symposium on the topic, held in 1984. Session topics included the following: (1) design and operation of transportation systems to, in orbit around, and on the Moon; (2) lunar base site selection; (3) design, architecture, construction, and operation of lunar bases and human habitats; (4) lunar-based scientific research and experimentation in astronomy, exobiology, and lunar geology; (5) recovery and use of lunar resources; (6) environmental and human factors of and life support technology for human presence on the Moon; and (7) program management of human exploration of the Moon and space
Resolving the Formation of Protogalaxies. II. Central Gravitational Collapse
Numerous cosmological hydrodynamic studies have addressed the formation of
galaxies. Here we choose to study the first stages of galaxy formation,
including non-equilibrium atomic primordial gas cooling, gravity and
hydrodynamics. Using initial conditions appropriate for the concordance
cosmological model of structure formation, we perform two adaptive mesh
refinement simulations of ~10^8 M_sun galaxies at high redshift. The
calculations resolve the Jeans length at all times with more than 16 cells and
capture over 14 orders of magnitude in length scales. In both cases, the dense,
10^5 solar mass, one parsec central regions are found to contract rapidly and
have turbulent Mach numbers up to 4. Despite the ever decreasing Jeans length
of the isothermal gas, we only find one site of fragmentation during the
collapse. However, rotational secular bar instabilities transport angular
momentum outwards in the central parsec as the gas continues to collapse and
lead to multiple nested unstable fragments with decreasing masses down to
sub-Jupiter mass scales. Although these numerical experiments neglect star
formation and feedback, they clearly highlight the physics of turbulence in
gravitationally collapsing gas. The angular momentum segregation seen in our
calculations plays an important role in theories that form supermassive black
holes from gaseous collapse.Comment: Replaced with accepted version. To appear in ApJ v681 (July 1
Crystallographic and magnetic identification of secondary phase in orientated Bi5Fe0.5Co0.5Ti3O15 ceramics
Oxide materials which exhibit both ferroelectricity
and ferromagnetism are of great interest for sensors and memory
applications. Layered bismuth titanates with an Aurivillius
structure, (BiFeO3)nBi4Ti3O12, can possess ferroelectric and
ferromagnetic order parameters simultaneously. It has recently
been demonstrated that one such example,
Bi5Fe0.5Co0.5Ti3O15,where n = 1 with half the Fe3+ sites substituted
by Co3+ ions, exhibits both ferroelectric and ferromagnetic
properties at room temperature. Here we report the fabrication
of highly-oriented polycrystalline ceramics of this material,
prepared via molten salt synthesis and uniaxial pressing of high
aspect ratio platelets. Electron backscatter images showed that
there is a secondary phase within the ceramic matrix which is
rich in cobalt and iron, hence this secondary phase could
contribute in the main phase ferromagnetic property. The
concentration of the secondary phase obtained from secondary
electron microscopy is estimated at less than 2.5 %, below the
detection limit of XRD. TEM was used to identify the
crystallographic structure of the secondary phase, which was
shown to be cobalt ferrite, CoFe2O4. It is inferred from the data
that the resultant ferromagnetic response identified using VSM
measurements was due to the presence of the minor secondary
phase. The Remanent magnetization at room temperature was
Mr â 76 memu/g which dropped down to almost zero (Mr â 0.8
memu/g) at 460 oC, far lower than the anticipated for CoFe2O4
Banking from Leeds, not London: regional strategy and structure at the Yorkshire Bank, 1859â1952
Industrial philanthropist Edward Akroyd created the Yorkshire Penny Savings Bank in 1859. Despite competition from the Post Office Savings Bank after 1861 and a serious reserve problem in 1911, it sustained his overall strategy to become a successful regional bank. Using archival and contemporary sources to build on recent scholarship illustrating how savings banks were integrated into local economies and the complementary roles of philanthropy and paternalism, we analyse an English regional bank's strategy, including an assessment of strategic innovation, ownership changes and management structure. This will demonstrate that the founder's vision continued, even though the 1911 crisis radically altered both strategy and structure
Common Representation of Information Flows for Dynamic Coalitions
We propose a formal foundation for reasoning about access control policies
within a Dynamic Coalition, defining an abstraction over existing access
control models and providing mechanisms for translation of those models into
information-flow domain. The abstracted information-flow domain model, called a
Common Representation, can then be used for defining a way to control the
evolution of Dynamic Coalitions with respect to information flow
Evidence for a very slow X-ray pulsar in 2S0114+650 from RXTE All-Sky Monitor Observations
Rossi X-ray Timing Explorer (RXTE) All-Sky Monitor (ASM) observations of the
X-ray binary 2S0114+650 show modulations at periods close to both the optically
derived orbital period (11.591 days) and proposed pulse period (~ 2.7 hr). The
pulse period shows frequency and intensity variability during the more than 2
years of ASM observations analyzed. The pulse properties are consistent with
this arising from accretion onto a rotating neutron star and this would be the
slowest such period known. The shape of the orbital light curve shows
modulation over the course of the entire orbit and a comparison is made with
the orbital light curve of Vela X-1. However, the expected phase of eclipse,
based on an extrapolation of the optical ephemeris, does not correspond with
the observed orbital minimum. The orbital period derived from the ASM light
curve is also slightly longer than the optical period.Comment: To be published in the Astrophysical Journal, 1999, volume 511. 9
figure
Towards an understanding of the rapid decline of the cosmic star formation rate
We present a first analysis of deep 24 micron observations with the Spitzer
Space Telescope of a sample of nearly 1500 galaxies in a thin redshift slice,
0.65<z<0.75. We combine the infrared data with redshifts, rest-frame
luminosities, and colors from COMBO-17, and with morphologies from Hubble Space
Telescope images collected by the GEMS and GOODS projects. To characterize the
decline in star-formation rate (SFR) since z~0.7, we estimate the total thermal
infrared (IR) luminosities, SFRs, and stellar masses for the galaxies in this
sample. At z~0.7, nearly 40% of intermediate and high-mass galaxies (with
stellar masses >2x10^10 solar masses) are undergoing a period of intense star
formation above their past-averaged SFR. In contrast, less than 1% of
equally-massive galaxies in the local universe have similarly intense star
formation activity. Morphologically-undisturbed galaxies dominate the total
infrared luminosity density and SFR density: at z~0.7, more than half of the
intensely star-forming galaxies have spiral morphologies, whereas less than
\~30% are strongly interacting. Thus, a decline in major-merger rate is not the
underlying cause of the rapid decline in cosmic SFR since z~0.7. Physical
properties that do not strongly affect galaxy morphology - for example, gas
consumption and weak interactions with small satellite galaxies - appear to be
responsible.Comment: To appear in the Astrophysical Journal 1 June 2005. 14 pages with 8
embedded figure
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