2,127 research outputs found
Positive and Negative Sources of Emotional Arousal Enhance Long-Term Word-List Retention When Induced as Long as 30 Min After Learning
The consolidation of newly formed memories occurs slowly, allowing memories to be altered by experience for some time after their formation. Various treatments, including arousal, can modulate memory consolidation when given soon after learning, but the degree of time-dependency of these treatments in humans has not been studied. Thus, 212 participants learned a word list, which was followed by either a positively or negatively valenced arousing video clip (i.e., comedy or surgery, respectively) after delays of 0, 10, 30 or 45 min. Arousal of either valence induced up to 30 min after learning, but not after 45 min, significantly enhanced one-week retrieval. The findings support (1) the time-dependency of memory modulation in humans and (2) other studies that suggest that it is the degree of arousal, rather than valence that modulates memory. Important implications for developing memory intervention strategies and for preserving and validating witness testimony are discussed
Characterizing the geometrical edges of nonlocal two-qubit gates
Nonlocal two-qubit gates are geometrically represented by tetrahedron known
as Weyl chamber within which perfect entanglers form a polyhedron. We identify
that all edges of the Weyl chamber and polyhedron are formed by single
parametric gates. Nonlocal attributes of these edges are characterized using
entangling power and local invariants. In particular, SWAP (power)alpha family
of gates constitutes one edge of the Weyl chamber with SWAP-1/2 being the only
perfect entangler. Finally, optimal constructions of controlled-NOT using
SWAP-1/2 gate and gates belong to three edges of the polyhedron are presented.Comment: 11 pages, 4 figures, Phys. Rev. A 79, 052339 (2009
Epoxy/ graphene nanocomposites – processing and properties: a review
Graphene has recently attracted significant academic and industrial interest because of its excellent performance in mechanical, electrical and thermal applications. Graphene can significantly improve physical properties of epoxy at extremely small loading when incorporated appropriately. Herein, the structure, preparation and properties of epoxy/graphene nanocomposites are reviewed in general, along with detailed examples drawn from the key scientific literature. The modification of graphene and the utilization of these materials in the fabrication of nanocomposites with different processing methods have been explored. This review has been focused on the processing methods and mechanical, electrical, thermal, and fire retardant properties of the nanocomposites. The synergic effects of graphene and other fillers in epoxy matrix have been summarised as well
Scalability of Shor's algorithm with a limited set of rotation gates
Typical circuit implementations of Shor's algorithm involve controlled
rotation gates of magnitude where is the binary length of the
integer N to be factored. Such gates cannot be implemented exactly using
existing fault-tolerant techniques. Approximating a given controlled
rotation gate to within currently requires both
a number of qubits and number of fault-tolerant gates that grows polynomially
with . In this paper we show that this additional growth in space and time
complexity would severely limit the applicability of Shor's algorithm to large
integers. Consequently, we study in detail the effect of using only controlled
rotation gates with less than or equal to some . It is found
that integers up to length can be factored
without significant performance penalty implying that the cumbersome techniques
of fault-tolerant computation only need to be used to create controlled
rotation gates of magnitude if integers thousands of bits long are
desired factored. Explicit fault-tolerant constructions of such gates are also
discussed.Comment: Substantially revised version, twice as long as original. Two tables
converted into one 8-part figure, new section added on the construction of
arbitrary single-qubit rotations using only the fault-tolerant gate set.
Substantial additional discussion and explanatory figures added throughout.
(8 pages, 6 figures
Entangling characterization of (SWAP)1/m and Controlled unitary gates
We study the entangling power and perfect entangler nature of (SWAP)1/m, for
m>=1, and controlled unitary (CU) gates. It is shown that (SWAP)1/2 is the only
perfect entangler in the family. On the other hand, a subset of CU which is
locally equivalent to CNOT is identified. It is shown that the subset, which is
a perfect entangler, must necessarily possess the maximum entangling power.Comment: 12 pages, 1 figure, One more paragraph added in Introductio
Schmidt Analysis of Pure-State Entanglement
We examine the application of Schmidt-mode analysis to pure state
entanglement. Several examples permitting exact analytic calculation of Schmidt
eigenvalues and eigenfunctions are included, as well as evaluation of the
associated degree of entanglement.Comment: 5 pages, 3 figures, for C.M. Bowden memoria
Generalized Limits for Parameter Sensitivity via Quantum Ziv-Zakai Bound
We study the generalized limit for parameter sensitivity in quantum
estimation theory considering the effects of repeated and adaptive
measurements. Based on the quantum Ziv-Zakai bound, we derive some lower bounds
for parameter sensitivity when the Hamiltonian of system is unbounded and when
the adaptive measurements are implemented on the system. We also prove that the
parameter sensitivity is bounded by the limit of the minimum detectable
parameter. In particular, we examine several known states in quantum phase
estimation with non-interacting photons, and show that they can not perform
better than Heisenberg limit in a much simpler way with our result.Comment: 8pages, 5 figure
Improved Cardiorespiratory Fitness Is Associated with Increased Cortical Thickness in Mild Cognitive Impairment
Cortical atrophy is a biomarker of Alzheimer’s disease (AD) that correlates with clinical symptoms. This study examined changes in cortical thickness from before to after an exercise intervention in mild cognitive impairment (MCI) and healthy elders. Thirty physically inactive older adults (14 MCI, 16 healthy controls) underwent MRI before and after participating in a 12-week moderate intensity walking intervention. Participants were between the ages of 61 and 88. Change in cardiorespiratory fitness was assessed using residualized scores of the peak rate of oxygen consumption (V̇O2peak) from pre- to post-intervention. Structural magnetic resonance images were processed using FreeSurfer v5.1.0. V̇O2peak increased an average of 8.49%, which was comparable between MCI and healthy elders. Overall, cortical thickness was stable except for a significant decrease in the right fusiform gyrus in both groups. However, improvement in cardiorespiratory fitness due to the intervention (V̇O2peak) was positively correlated with cortical thickness change in the bilateral insula, precentral gyri, precuneus, posterior cingulate, and inferior and superior frontal cortices. Moreover, MCI participants exhibited stronger positive correlations compared to healthy elders in the left insula and superior temporal gyrus. A 12-week moderate intensity walking intervention led to significantly improved fitness in both MCI and healthy elders. Improved V̇O2peak was associated with widespread increased cortical thickness, which was similar between MCI and healthy elders. Thus, regular exercise may be an especially beneficial intervention to counteract cortical atrophy in all risk groups, and may provide protection against future cognitive decline in both healthy elders and MCI
Exercise Training and Functional Connectivity Changes in Mild Cognitive Empairment and Healthy Elders
Background: Effective interventions are needed to improve brain function in mild cognitive impairment (MCI), an early stage of Alzheimer’s disease (AD). The posterior cingulate cortex (PCC)/precuneus is a hub of the default mode network (DMN) and is preferentially vulnerable to disruption of functional connectivity in MCI and AD. Objective: We investigated whether 12 weeks of aerobic exercise could enhance functional connectivity of the PCC/precuneus in MCI and healthy elders. Methods: Sixteen MCI and 16 healthy elders (age range = 60–88) engaged in a supervised 12-week walking exercise intervention. Functional MRI was acquired at rest; the PCC/precuneus was used as a seed for correlated brain activity maps. Results: A linear mixed effects model revealed a significant interaction in the right parietal lobe: the MCI group showed increased connectivity while the healthy elders showed decreased connectivity. In addition, both groups showed increased connectivity with the left postcentral gyrus. Comparing pre to post intervention changes within each group, the MCI group showed increased connectivity in 10 regions spanning frontal, parietal, temporal and insular lobes, and the cerebellum. Healthy elders did not demonstrate any significant connectivity changes. Conclusion: The observed results show increased functional connectivity of the PCC/precuneus in individuals with MCI after 12 weeks of moderate intensity walking exercise training. The protective effects of exercise training on cognition may be realized through the enhancement of neural recruitment mechanisms, which may possibly increase cognitive reserve. Whether these effects of exercise training may delay further cognitive decline in patients diagnosed with MCI remains to be demonstrated
Role of Bell Singlet State in the Suppression of Disentanglement
The stability of entanglement of two atoms in a cavity is analyzed in this
work. By studying the general Werner states we clarify the role of Bell-singlet
state in the problem of suppression of disentanglement due to spontaneous
emission. It is also shown explicitly that the final amount of entanglement
depends on the initial ingredients of the Bell-singlet state.Comment: 5 pages, 2 figures, accepted by Phys. Rev.
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