56,512 research outputs found
Mössbauer Spectrometry Study of Thermally-Activated Electronic Processes in Li_xFePO_4
The solid solution phase of Li_xFePO_4 with different Li concentrations, x, was investigated by Mössbauer spectrometry at temperatures between 25 and 210 °C. The Mössbauer spectra show a temperature dependence of their isomer shifts (E_(IS)) and electric quadrupole splittings (E_Q), typical of thermally activated, electronic relaxation processes involving ^(57)Fe ions. The activation energies for the fluctuations of E_Q and E_(IS) for Fe^(3+) are nearly the same, 570 ± 9 meV, suggesting that both originate from charge hopping. For the Fe^(2+) components of the spectra, the fluctuations of E_Q occurred at lower temperatures than the fluctuations of E_(IS), with an activation energy of 512 ± 12 meV for E_Q and one of 551 ± 7 meV for E_(IS). The more facile fluctuations of E_Q for Fe^(2+) are evidence for local motions of neighboring Li^+ ions. It appears that the electron hopping frequency is lower than that of Li^+ ions. The activation energies of relaxation did not have a measurable dependence on the concentration of lithium, x
MEG-measured auditory steady-state oscillations show high test-retest reliability: a sensor and source-space analysis
Stability of oscillatory signatures across magnetoencephalography (MEG) measurements is an important prerequisite for basic and clinical research that has been insufficiently addressed. Here, we evaluated the test–retest reliability of auditory steady-state responses (ASSRs) over two MEG sessions. The study required participants (N = 13) to detect the rare occurrence of pure tones interspersed within a stream of 5 Hz or 40 Hz amplitude-modulated (AM) tones. Intraclass correlations (ICC; Shrout and Fleiss, 1979) were derived to assess stability of spectral power changes and the inter-trial phase coherence (ITPC) of task-elicited neural responses. ASSRs source activity was estimated using eLORETA beamforming from bilateral auditory cortex. ASSRs to 40 Hz AM stimuli evoked stronger power modulation and phase-locking than 5 Hz stimulation. Overall, spectral power and ITPC values at both sensor- and source-level showed robust ICC values. Notably, ITPC measures yielded higher ICCs (~ 0.86–0.96) between sessions compared to the assessment of spectral power change (~ 0.61–0.82). Our data indicate that spectral modulations and phase consistency of ASSRs in MEG data are highly reproducible, providing support for MEG-measured oscillatory parameters in basic and clinical research
MEG sensor and source measures of visually induced gamma-band oscillations are highly reliable
High frequency brain oscillations are associated with numerous cognitive and behavioral processes. Non-invasive measurements using electro-/magnetoencephalography (EEG/MEG) have revealed that high frequency neural signals are heritable and manifest changes with age as well as in neuropsychiatric illnesses. Despite the extensive use of EEG/MEG-measured neural oscillations in basic and clinical research, studies demonstrating test–retest reliability of power and frequency measures of neural signals remain scarce. Here, we evaluated the test–retest reliability of visually induced gamma (30–100 Hz) oscillations derived from sensor and source signals acquired over two MEG sessions. The study required participants (N = 13) to detect the randomly occurring stimulus acceleration while viewing a moving concentric grating. Sensor and source MEG measures of gamma-band activity yielded comparably strong reliability (average intraclass correlation, ICC = 0.861). Peak stimulus-induced gamma frequency (53–72 Hz) yielded the highest measures of stability (ICCsensor = 0.940; ICCsource = 0.966) followed by spectral signal change (ICCsensor = 0.890; ICCsource = 0.893) and peak frequency bandwidth (ICCsensor = 0.856; ICCsource = 0.622). Furthermore, source-reconstruction significantly improved signal-to-noise for spectral amplitude of gamma activity compared to sensor estimates. Our assessments highlight that both sensor and source derived estimates of visually induced gamma-band oscillations from MEG signals are characterized by high test–retest reliability, with source derived oscillatory measures conferring an improvement in the stability of peak-frequency estimates. Importantly, our finding of high test–retest reliability supports the feasibility of pharma-MEG studies and longitudinal aging or clinical studies
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Kleshchev's decomposition numbers and branching coefficients in the Fock space
10.1090/S0002-9947-07-04202-XTransactions of the American Mathematical Society36031179-119
Ground States of S-duality Twisted N=4 Super Yang-Mills Theory
We study the low-energy limit of a compactification of N=4 U(n) super
Yang-Mills theory on with boundary conditions modified by an S-duality
and R-symmetry twist. This theory has N=6 supersymmetry in 2+1D. We analyze the
compactification of this 2+1D theory by identifying a dual weakly coupled
type-IIA background. The Hilbert space of normalizable ground states is
finite-dimensional and appears to exhibit a rich structure of sectors. We
identify most of them with Hilbert spaces of Chern-Simons theory (with
appropriate gauge groups and levels). We also discuss a realization of a
related twisted compactification in terms of the (2,0)-theory, where the recent
solution by Gaiotto and Witten of the boundary conditions describing D3-branes
ending on a (p,q) 5-brane plays a crucial role.Comment: 104 pages, 5 figures. Revisions to subsection (6.6) and other minor
corrections included in version
Achieving Effective Innovation Based On TRIZ Technological Evolution
Organised by: Cranfield UniversityThis paper outlines the conception of effective innovation and discusses the method to achieve it. Effective
Innovation is constrained on the path of technological evolution so that the corresponding path must be
detected before conceptual design of the product. The process of products technological evolution is a
technical developing process that the products approach to Ideal Final Result (IFR). During the process, the
sustaining innovation and disruptive innovation carry on alternately. By researching and forecasting potential
techniques using TRIZ technological evolution theory, the effective innovation can be achieved finally.Mori Seiki – The Machine Tool Compan
Joint perception: gaze and beliefs about social context
The way that we look at images is influenced by social context. Previously we demonstrated this phenomenon of joint perception. If lone participants believed that an unseen other person was also looking at the images they saw, it shifted the balance of their gaze between negative and positive images. The direction of this shift depended upon whether participants thought that later they would be compared against the other person or would be collaborating with them. Here we examined whether the joint perception is caused by beliefs about shared experience (looking at the same images) or beliefs about joint action (being engaged in the same task with the images). We place our results in the context of the emerging field of joint action, and discuss their connection to notions of group emotion and situated cognition. Such findings reveal the persuasive and subtle effect of social context upon cognitive and perceptual processes
The influence of atmosphere on the performance of pure-phase WZ and ZB InAs nanowire transistors
We compare the characteristics of phase-pure MOCVD grown ZB and WZ InAs
nanowire transistors in several atmospheres: air, dry pure N and O, and
N bubbled through liquid HO and alcohols to identify whether
phase-related structural/surface differences affect their response. Both WZ and
ZB give poor gate characteristics in dry state. Adsorption of polar species
reduces off-current by 2-3 orders of magnitude, increases on-off ratio and
significantly reduces sub-threshold slope. The key difference is the greater
sensitivity of WZ to low adsorbate level. We attribute this to facet structure
and its influence on the separation between conduction electrons and surface
adsorption sites. We highlight the important role adsorbed species play in
nanowire device characterisation. WZ is commonly thought superior to ZB in InAs
nanowire transistors. We show this is an artefact of the moderate humidity
found in ambient laboratory conditions: WZ and ZB perform equally poorly in the
dry gas limit yet equally well in the wet gas limit. We also highlight the
vital role density-lowering disorder has in improving gate characteristics, be
it stacking faults in mixed-phase WZ or surface adsorbates in pure-phase
nanowires.Comment: Accepted for publication in Nanotechnolog
Three-boson problem at low energy and Implications for dilute Bose-Einstein condensates
It is shown that the effective interaction strength of three bosons at small
collision energies can be extracted from their wave function at zero energy. An
asymptotic expansion of this wave function at large interparticle distances is
derived, from which is defined a quantity named three-body scattering
hypervolume, which is an analog of the two-body scattering length. Given any
finite-range interaction potentials, one can thus predict the effective
three-body force from a numerical solution of the Schr\"{o}dinger equation. In
this way the constant for hard-sphere bosons is computed, leading to the
complete result for the ground state energy per particle of a dilute
Bose-Einstein condensate (BEC) of hard spheres to order , where
is the number density. Effects of are also demonstrated in the three-body
energy in a finite box of size , which is expanded to the order ,
and in the three-body scattering amplitude in vacuum. Another key prediction is
that there is a violation of the effective field theory (EFT) in the condensate
fraction in dilute BECs, caused by short-range physics. EFT predictions for the
ground state energy and few-body scattering amplitudes, however, are
corroborated.Comment: 24 pages, no figur
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