302 research outputs found
Superfluid He in globally isotropic random media
Recent theoretical and experimental studies of superfluid He in aerogels
with a global anisotropy, e.g., due to an external stress, have definitely
shown that the A-like phase with an equal spin pairing (ESP) in such aerogel
samples is in the ABM (or, axial) pairing state. In this paper, the A-like
phase of superfluid He in globally {\it isotropic} aerogel is studied in
details by assuming a weakly disordered system in which singular topological
defects are absent. Through calculation of the free energy, a disordered ABM
state is found to be the best candidate of the pairing state of the globally
isotropic A-like phase. Further, it is found through a one-loop renormalization
group calculation that the coreless continuous vortices (or, vortex-skyrmions)
are irrelevant to the long-distance behavior of the disorder-induced textures,
and that the superfluidity is maintained in spite of lack of the conventional
off-diagonal long range order. Therefore, the globally isotropic A-like phase
at weak disorder is, like in the case with a global stretched anisotropy, a
superfluid glass with the ABM pairing.Comment: Revised version accepted for publication in Phys.Rev.
NMR in Superfluid A-like Phase of He Confined in Globally Deformed Aerogel in Tilted Magnetic Field
NMR spectra in superfluid A-like phases confined in axially deformed aerogel
in presence of a magnetic field inclined with respect to deformation axis is
considered. The characteristic features of dipole frequency shift in axially
compressed and axially stretched cases are compared. In particular, it is shown
that in axially stretched aerogel environment the stability region of
coherently spin precessing mode is rather narrow due to the U(1)LIM effect.Comment: 8 pages, 2 figure
Soliton-like Spin State in the A-like Phase of 3He in Anisotropic Aerogel
We have found a new stable spin state in the A-like phase of superfluid 3He
confined to intrinsically anisotropic aerogel. The state can be formed by
radiofrequency excitation applied while cooling through the superfluid
transition temperature and its NMR properties are different from the standard
A-like phase obtained in the limit of very small excitation. It is possible
that this new state is formed by textural domain walls pinned by aerogel.Comment: 9 pages, 3 figures. Submitted to J. of Low Tem. Phys. (QFS2007
Proceedings
Orbital glass and spin glass states of 3He-A in aerogel
Glass states of superfluid A-like phase of 3He in aerogel induced by random
orientations of aerogel strands are investigated theoretically and
experimentally. In anisotropic aerogel with stretching deformation two glass
phases are observed. Both phases represent the anisotropic glass of the orbital
ferromagnetic vector l -- the orbital glass (OG). The phases differ by the spin
structure: the spin nematic vector d can be either in the ordered spin nematic
(SN) state or in the disordered spin-glass (SG) state. The first phase (OG-SN)
is formed under conventional cooling from normal 3He. The second phase (OG-SG)
is metastable, being obtained by cooling through the superfluid transition
temperature, when large enough resonant continuous radio-frequency excitation
are applied. NMR signature of different phases allows us to measure the
parameter of the global anisotropy of the orbital glass induced by deformation.Comment: 7 pages, 6 figures, Submitted to Pis'ma v ZhETF (JETP Letters
Phase diagram of superfluid 3He in "nematically ordered" aerogel
Results of experiments with liquid 3He immersed in a new type of aerogel are
described. This aerogel consists of Al2O3 strands which are nearly parallel to
each other, so we call it as a "nematically ordered" aerogel. At all used
pressures a superfluid transition was observed and a superfluid phase diagram
was measured. Possible structures of the observed superfluid phases are
discussed.Comment: 6 pages, 8 figures. Submitted to Pis'ma v ZhETF (JETP Letters
Observation of Coherent Precession of Magnetization in Superfluid 3He A-phase
We report the first observation of coherent quantum precession of
magnetization (CQP) in superfluid 3He-A in aerogel. The coherent precession in
bulk 3He A-phase is unstable due to the positive feedback of spin supercurrent
to the gradient of phase of precession. It was predicted that the homogeneous
precession will be stable if the orbital momentum of 3He-A could be oriented
along the magnetic field. We have succeeded to prepare this configuration by
emerging 3He in uniaxially-deformed anisotropic aerogel. The dissipation rate
of coherent precession states in aerogel is much larger then one in bulk 3He-B.
We propose a mechanism of this dissipation.Comment: 4 pages, 4 figure
Clinical and neural effects of six-week administration of oxytocin on core symptoms of autism
Autism spectrum disorder is a prevalent neurodevelopmental disorder with no established pharmacological treatment for its core symptoms. Although previous literature has shown that single-dose administration of oxytocin temporally mitigates autistic social behaviours in experimental settings, it remains in dispute whether such potentially beneficial responses in laboratories can result in clinically positive effects in daily life situations, which are measurable only in long-term observations of individuals with the developmental disorder undergoing continual oxytocin administration. Here, to address this issue, we performed an exploratory, randomized, double-blind, placebo-controlled, crossover trial including 20 high-functional adult males with autism spectrum disorder. Data obtained from 18 participants who completed the trial showed that 6-week intranasal administration of oxytocin significantly reduced autism core symptoms specific to social reciprocity, which was clinically evaluated by Autism Diagnostic Observation Scale (P = 0.034, PFDR < 0.05, Cohen's d = 0.78). Critically, the improvement of this clinical score was accompanied by oxytocin-induced enhancement of task-independent resting-state functional connectivity between anterior cingulate cortex and dorso-medial prefrontal cortex (rho = -0.60, P = 0.011), which was measured by functional magnetic resonance imaging. Moreover, using the same social-judgement task as used in our previous single-dose oxytocin trial, we confirmed that the current continual administration also significantly mitigated behavioural and neural responses during the task, both of which were originally impaired in autistic individuals (judgement tendency: P = 0.019, d = 0.62; eye-gaze effect: P = 0.03, d = 0.56; anterior cingulate activity: P = 0.00069, d = 0.97; dorso-medial prefrontal activity: P = 0.0014, d = 0.92; all, PFDR < 0.05). Furthermore, despite its longer administration, these effect sizes of the 6-week intervention were not larger than those seen in our previous single-dose intervention. These findings not only provide the evidence for clinically beneficial effects of continual oxytocin administration on the core social symptoms of autism spectrum disorder with suggesting its underlying biological mechanisms, but also highlight the necessity to seek optimal regimens of continual oxytocin treatment in future studies
Magnetic tunnel junctions with metastable bcc Co3Mn electrodes
We studied magnetic tunnel junctions (MTJs) with a MgO(001) barrier and metastable bcc Co3Mn(001) disordered alloy electrodes. A tunnel magnetoresistance (TMR) ratio was approximately 200{250% observed at room temperature.We successfully observed the TMR ratio greater than 600% at 10 K which was higher than the past reported value of MgO-based MTJs with ultrathin bcc Co(001) electrodes. However our experimental value was still much lower than the past theoretical prediction in bcc Co/MgO/Co(001) MTJs. We discuss some differences in the bulk band structure affecting the TMR effect for bcc Co and bcc Co3Mn
Effects of rTMS of pre-supplementary motor area on fronto basal ganglia network activity during stop-signal task
Stop-signal task (SST) has been a key paradigm for probing human brain mechanisms underlying response inhibition, and the inhibition observed in SST is now considered to largely depend on a fronto basal ganglia network consisting mainly of right inferior frontal cortex, pre-supplementary motor area (pre-SMA), and basal ganglia, including subthalamic nucleus, striatum (STR), and globus pallidus pars interna (GPi). However, causal relationships between these frontal regions and basal ganglia are not fully understood in humans. Here, we partly examined these causal links by measuring human fMRI activity during SST before and after excitatory/inhibitory repetitive transcranial magnetic stimulation (rTMS) of pre-SMA. We first confirmed that the behavioral performance of SST was improved by excitatory rTMS and impaired by inhibitory rTMS. Afterward, we found that these behavioral changes were well predicted by rTMS-induced modulation of brain activity in pre-SMA, STR, and GPi during SST. Moreover, by examining the effects of the rTMS on resting-state functional connectivity between these three regions, we showed that the magnetic stimulation of pre-SMA significantly affected intrinsic connectivity between pre-SMA and STR, and between STR and GPi. Furthermore, the magnitudes of changes in resting-state connectivity were also correlated with the behavioral changes seen in SST. These results suggest a causal relationship between pre-SMA and GPi via STR during response inhibition, and add direct evidence that the fronto basal ganglia network for response inhibition consists of multiple top-down regulation pathways in humans
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