2,406 research outputs found
Functional Subdomains within Human FFA
Cataloged from PDF version of article.The fusiform face area (FFA) is a well-studied human brain region that shows strong activation for faces. In functional MRI studies, FFA is often assumed to be a homogeneous collection of voxels with similar visual tuning. To test this assumption, we used natural movies and a quantitative voxelwise modeling and decoding framework to estimate category tuning profiles for individual voxels within FFA. We find that the responses in most FFA voxels are strongly enhanced by faces, as reported in previous studies. However, we also find that responses of individual voxels are selectively enhanced or suppressed by a wide variety of other categories and that these broader tuning profiles differ across FFA voxels. Cluster analysis of category tuning profiles across voxels reveals three spatially segregated functional subdomains within FFA. These subdomains differ primarily in their responses for nonface categories, such as animals, vehicles, and communication verbs. Furthermore, this segregation does not depend on the statistical threshold used to define FFA from responses to functional localizers. These results suggest that voxels within FFA represent more diverse information about object and action categories than generally assumed. © 2013 the authors
Extinction of the N=20 neutron-shell closure for 32Mg examined by direct mass measurements
The 'island of inversion' around Mg is one of the most important
paradigm for studying the disappearance of the stabilizing 'magic' of a shell
closure. We present the first Penning-trap mass measurements of the exotic
nuclides Na and Mg, which allow a precise determination of
the empirical shell gap for Mg. The new value of 1.10(3) MeV is the
lowest observed shell gap for any nuclide with a canonical magic number.Comment: 6 pages, 4 figures, submitted to Physical Review
Low-Background In-Trap Decay Spectroscopy with TITAN at TRIUMF
An in-trap decay spectroscopy setup has been developed and constructed for
use with the TITAN facility at TRIUMF. The goal of this device is to observe
weak electron-capture (EC) branching ratios for the odd-odd intermediate nuclei
in the decay process. This apparatus consists of an up-to 6 Tesla,
open-access spectroscopy ion-trap, surrounded radially by up to 7 planar Si(Li)
detectors which are separated from the trap by thin Be windows. This
configuration provides a significant increase in sensitivity for the detection
of low-energy photons by providing backing-free ion storage and eliminating
charged-particle-induced backgrounds. An intense electron beam is also employed
to increase the charge-states of the trapped ions, thus providing storage times
on the order of minutes, allowing for decay-spectroscopy measurements. The
technique of multiple ion-bunch stacking was also recently demonstrated, which
further extends the measurement possibilities of this apparatus. The current
status of the facility and initial results from a In measurement are
presented.Comment: Proceedings for the 2nd International Conference on Advances in
Radioactive Isotope Science (ARIS2014
Breakdown of the Isobaric Multiplet Mass Equation for the A = 20 and 21 Multiplets
Using the Penning trap mass spectrometer TITAN, we performed the first direct
mass measurements of 20,21Mg, isotopes that are the most proton-rich members of
the A = 20 and A = 21 isospin multiplets. These measurements were possible
through the use of a unique ion-guide laser ion source, a development that
suppressed isobaric contamination by six orders of magnitude. Compared to the
latest atomic mass evaluation, we find that the mass of 21Mg is in good
agreement but that the mass of 20Mg deviates by 3{\sigma}. These measurements
reduce the uncertainties in the masses of 20,21Mg by 15 and 22 times,
respectively, resulting in a significant departure from the expected behavior
of the isobaric multiplet mass equation in both the A = 20 and A = 21
multiplets. This presents a challenge to shell model calculations using either
the isospin non-conserving USDA/B Hamiltonians or isospin non-conserving
interactions based on chiral two- and three-nucleon forces.Comment: 5 pages, 2 figure
Highly charged ions in Penning traps, a new tool for resolving low lying isomeric states
The use of highly charged ions increases the precision and resolving power,
in particular for short-lived species produced at on-line radio-isotope beam
facilities, achievable with Penning trap mass spectrometers. This increase in
resolving power provides a new and unique access to resolving low-lying
long-lived ( ms) nuclear isomers. Recently, the keV
(determined from -ray spectroscopy) isomeric state in Rb has
been resolved from the ground state, in a charge state of with the TITAN
Penning trap at the TRIUMF-ISAC facility. The excitation energy of the isomer
was measured to be keV above the ground state. The extracted
masses for both the ground and isomeric states, and their difference, agree
with the AME2003 and Nuclear Data Sheet values. This proof of principle
measurement demonstrates the feasibility of using Penning trap mass
spectrometers coupled to charge breeders to study nuclear isomers and opens a
new route for isomer searches.Comment: 8 pages, 6 figure
Trapped-ion decay spectroscopy towards the determination of ground-state components of double-beta decay matrix elements
A new technique has been developed at TRIUMF's TITAN facility to perform
in-trap decay spectroscopy. The aim of this technique is to eventually measure
weak electron capture branching ratios (ECBRs) and by this to consequently
determine GT matrix elements of decaying nuclei. These branching
ratios provide important input to the theoretical description of these decays.
The feasibility and power of the technique is demonstrated by measuring the
ECBR of Cs.Comment: 9 pages, 9 figure
Noise and Nonlinearity in Measles Epidemics: Combining Mechanistic and Statistical Approaches to Population Modeling
We present and evaluate an approach to analyzing population dynamics data using semimechanistic models. These models incorporate reliable information on population structure and underlying dynamic mechanisms but use nonparametric surface-fitting methods to avoid unsupported assumptions about the precise form of rate equations. Using historical data on measles epidemics as a case study, we show how this approach can lead to better forecasts, better characterizations of the dynamics, and better understanding of the factors causing complex population dynamics relative to either mechanistic models or purely descriptive statistical time-series models. The semimechanistic models are found to have better forecasting accuracy than either of the model types used in previous analyses when tested on data not used to fit the models. The dynamics are characterized as being both nonlinear and noisy, and the global dynamics are clustered very tightly near the border of stability (dominant Lyapunov exponent λ < 0). However, locally in state space the dynamics oscillate between strong short-term stability and strong short-term chaos (i.e., between negative and positive local Lyapunov exponents). There is statistically significant evidence for short-term chaos in all data sets examined. Thus the nonlinearity in these systems is characterized by the variance over state space in local measures of chaos versus stability rather than a single summary measure of the overall dynamics as either chaotic or nonchaotic
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