113,626 research outputs found
Verbal paired associates and the hippocampus: The role of scenes
It is widely agreed that patients with bilateral hippocampal damage are impaired at binding pairs of words together. Consequently, the verbal paired associates (VPA) task has become emblematic of hippocampal function. This VPA deficit is not well understood and is particularly difficult for hippocampal theories with a visuospatial bias to explain (e.g., cognitive map and scene construction theories). Resolving the tension among hippocampal theories concerning the VPA could be important for leveraging a fuller understanding of hippocampal function. Notably, VPA tasks typically use high imagery concrete words and so conflate imagery and binding. To determine why VPA engages the hippocampus, we devised an fMRI encoding task involving closely matched pairs of scene words, pairs of object words, and pairs of very low imagery abstract words. We found that the anterior hippocampus was engaged during processing of both scene and object word pairs in comparison to abstract word pairs, despite binding occurring in all conditions. This was also the case when just subsequently remembered stimuli were considered. Moreover, for object word pairs, fMRI activity patterns in anterior hippocampus were more similar to those for scene imagery than object imagery. This was especially evident in participants who were high imagery users and not in mid and low imagery users. Overall, our results show that hippocampal engagement during VPA, even when object word pairs are involved, seems to be evoked by scene imagery rather than binding. This may help to resolve the issue that visuospatial hippocampal theories have in accounting for verbal memory
Betweenness centrality correlation in social networks
Scale-free (SF) networks exhibiting a power-law degree distribution can be
grouped into the assortative, dissortative and neutral networks according to
the behavior of the degree-degree correlation coefficient. Here we investigate
the betweenness centrality (BC) correlation for each type of SF networks. While
the BC-BC correlation coefficients behave similarly to the degree-degree
correlation coefficients for the dissortative and neutral networks, the BC
correlation is nontrivial for the assortative ones found mainly in social
networks. The mean BC of neighbors of a vertex with BC is almost
independent of , implying that each person is surrounded by almost the
same influential environments of people no matter how influential the person
is.Comment: 4 pages, 4 figures, 1 tabl
orbifold compactifications in with Gauss-Bonnet term
We present a general setup for junctions of semi-infinite 4-branes in
with the Gauss-Bonnet term. The 3-brane tension at the junction of 4-branes can
be nonzero. Using the brane junctions as the origin of the discrete
rotation symmetry, we identify 3-brane tensions at three fixed points of the
orbifold in terms of the 4-brane tensions. As a result, the three
3-brane tensions can be simultaneously positive, which enables us to explain
the mass hierarchy by taking one of two branes apart from the hidden brane as
the visible brane, and hence does not introduce a severe cosmological problem.Comment: Latex file of 20 pages including 2 figure
Robustness of the avalanche dynamics in data packet transport on scale-free networks
We study the avalanche dynamics in the data packet transport on scale-free
networks through a simple model. In the model, each vertex is assigned a
capacity proportional to the load with a proportionality constant . When
the system is perturbed by a single vertex removal, the load of each vertex is
redistributed, followed by subsequent failures of overloaded vertices. The
avalanche size depends on the parameter as well as which vertex triggers
it. We find that there exists a critical value at which the avalanche
size distribution follows a power law. The critical exponent associated with it
appears to be robust as long as the degree exponent is between 2 and 3, and is
close in value to that of the distribution of the diameter changes by single
vertex removal.Comment: 5 pages, 7 figures, final version published in PR
Separation of Topographic Features from Magnetic Force Images Using Capacitive Coupling Effect
Separation of topographic features from magnetic images has been an issue for the past two decades in magnetic force microscopy (MFM). The frequent pickups of the topographic features are interpreted as transitions of the tip between bistable states of the tip-sample assembly in the noncontact and tapping regions. MFM using electrostatic force modulation demonstrates the separation of the topographic features from the magnetic images by removing the tapping state from the bistable states through the introduction of a capacitive coupling
Electron Spin Relaxation under Drift in GaAs
Based on a Monte Carlo method, we investigate the influence of transport
conditions on the electron spin relaxation in GaAs. The decay of initial
electron spin polarization is calculated as a function of distance under the
presence of moderate drift fields and/or non-zero injection energies. For
relatively low fields (a couple of kV/cm), a substantial amount of spin
polarization is preserved for several microns at 300 K. However, it is also
found that the spin relaxation rate increases rapidly with the drift field,
scaling as the square of the electron wavevector in the direction of the field.
When the electrons are injected with a high energy, a pronounced decrease is
observed in the spin relaxation length due to an initial increase in the spin
precession frequency. Hence, high-field or high-energy transport conditions may
not be desirable for spin-based devices.Comment: 4 pages, 3 figures, one table. Scheduled for publication in the May
26, 2003 issue of Applied Physics Letters (039321APL
The quantization of the chiral Schwinger model based on the BFT-BFV formalism II
We apply an improved version of Batalin-Fradkin-Tyutin (BFT) Hamiltonian
method to the a=1 chiral Schwinger Model, which is much more nontrivial than
the a>1.\delta\xi$ in the measure. As a result, we explicitly
obtain the fully gauge invariant partition function, which includes a new type
of Wess-Zumino (WZ) term irrelevant to the gauge symmetry as well as usual WZ
action.Comment: 17 pages, To be published in J. Phys.
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