2,799 research outputs found
A comparative study of some models of incoherence at the mesoscopic scale
The pre-existing literature on phenomena at the mesoscopic scale is concerned
among other things with phase coherent transport. Phase coherent transport
dominates at very low temperatures. With increase in temperature, as the system
size becomes comparable to the inelastic mean free path phase incoherence sets
in. This incoherence further leads to dephasing, and as a consequence purely
quantum effects in electron transport give way to classical macroscopic
behavior. In this work we consider two distinct phenomenological models of
incoherent transport, the Coherent Absorption and Wave Attenuation models. We
reveal some physical problems in the Coherent Absorption model as opposed to
the Wave Attenuation model. We also compare our proposed model with experiments
in case of the much studied peak to valley ratios in resonant tunneling diodes,
magneto-conductance oscillations and Fano resonances in case of Aharonov-Bohm
rings.Comment: 20 pages, 9 figure
A reduction in self-reported confidence accompanies the recall of memories distorted by prototypes
When we recall a past event, we reconstruct the event based on a combination of episodic details and semantic knowledge (e.g., prototypes). Though prototypes can impair the veracity of recall, it remains unclear whether we are metacognitively aware of the distortions they introduce. To address this, we conducted six experiments in which participants learned object-colour/object-location pairs and subsequently recalled the colour/location when cued with the object. Leveraging unsupervised machine learning algorithms, we extracted participant-specific prototypes and embedded responses in two-dimensional space to quantify prototype-based distortions in individual memory traces. Our findings reveal robust and conceptually replicable evidence to suggest that prototype-based distortion is accompanied by a reduction in self-reported confidence - an implicit measure of metacognitive awareness. Critically, we find evidence to suggest that it is prototype-based distortion of a memory trace that undermines confidence, rather than a lack of confidence biasing reconstruction towards the use of prototypes. Collectively, these findings suggest that we possess metacognitive awareness of distortions embedded in our memories
A reduction in self-reported confidence accompanies the recall of memories distorted by prototypes
When we recall a past event, we reconstruct the event based on a combination of episodic details and semantic knowledge (e.g., prototypes). Though prototypes can impair the veracity of recall, it remains unclear whether we are metacognitively aware of the distortions they introduce. To address this, we conducted six experiments in which participants learned object-colour/object-location pairs and subsequently recalled the colour/location when cued with the object. Leveraging unsupervised machine learning algorithms, we extracted participant-specific prototypes and embedded responses in two-dimensional space to quantify prototype-based distortions in individual memory traces. Our findings reveal robust and conceptually replicable evidence to suggest that prototype-based distortion is accompanied by a reduction in self-reported confidence - an implicit measure of metacognitive awareness. Critically, we find evidence to suggest that it is prototype-based distortion of a memory trace that undermines confidence, rather than a lack of confidence biasing reconstruction towards the use of prototypes. Collectively, these findings suggest that we possess metacognitive awareness of distortions embedded in our memories
Milky Way Disk-Halo Transition in HI: Properties of the Cloud Population
Using 21cm HI observations from the Parkes Radio Telescope's Galactic All-Sky
Survey, we measure 255 HI clouds in the lower Galactic halo that are located
near the tangent points at 16.9 < l < 35.3 degrees and |b| < 20 degrees. The
clouds have a median mass of 700 Msun and a median distance from the Galactic
plane of 660 pc. This first Galactic quadrant (QI) region is symmetric to a
region of the fourth quadrant (QIV) studied previously using the same data set
and measurement criteria. The properties of the individual clouds in the two
quadrants are quite similar suggesting that they belong to the same population,
and both populations have a line of sight cloud-cloud velocity dispersion of
sigma_cc ~ 16 km/s. However, there are three times as many disk-halo clouds at
the QI tangent points and their scale height, at h=800 pc, is twice as large as
in QIV. Thus the observed line of sight random cloud motions are not connected
to the cloud scale height or its variation around the Galaxy. The surface
density of clouds is nearly constant over the QI tangent point region but is
peaked near R~4 kpc in QIV. We ascribe all of these differences to the
coincidental location of the QI region at the tip of the Milky Way's bar, where
it merges with a major spiral arm. The QIV tangent point region, in contrast,
covers only a segment of a minor spiral arm. The disk-halo HI cloud population
is thus likely tied to and driven by large-scale star formation processes,
possibly through the mechanism of supershells and feedback.Comment: 14 pages, 20 figures, to be published in ApJ (accepted August 3 2010
Magnetized gas in the smith high velocity cloud
We report the first detection of magnetic fields associated with the Smith High Velocity Cloud. We use a catalog of Faraday rotation measures toward extragalactic radio sources behind the Smith Cloud, new H I observations from the Robert C. Byrd Green Bank Telescope, and a spectroscopic map of Hα from the Wisconsin H-Alpha Mapper Northern Sky Survey. There are enhancements in rotation measure (RM) of =100 rad m-2 which are generally well correlated with decelerated Hα emission. We estimate a lower limit on the line-of-sight component of the field of =8 μG along a decelerated filament; this is a lower limit due to our assumptions about the geometry. No RM excess is evident in sightlines dominated by H I or Hα at the velocity of the Smith Cloud. The smooth Hα morphology of the emission at the Smith Cloud velocity suggests photoionization by the Galactic ionizing radiation field as the dominant ionization mechanism, while the filamentary morphology and high (=1 Rayleigh) Hα intensity of the lower-velocity magnetized ionized gas suggests an ionization process associated with shocks due to interaction with the Galactic interstellar medium. The presence of the magnetic field may contribute to the survival of high velocity clouds like the Smith Cloud as they move from the Galactic halo to the disk. We expect these data to provide a test for magnetohydrodynamic simulations of infalling gas
Laser writing of individual atomic defects in a crystal with near-unity yield
Atomic defects in wide band gap materials show great promise for development
of a new generation of quantum information technologies, but have been hampered
by the inability to produce and engineer the defects in a controlled way. The
nitrogen-vacancy (NV) color center in diamond is one of the foremost
candidates, with single defects allowing optical addressing of electron spin
and nuclear spin degrees of freedom with potential for applications in advanced
sensing and computing. Here we demonstrate a method for the deterministic
writing of individual NV centers at selected locations with high positioning
accuracy using laser processing with online fluorescence feedback. This method
provides a new tool for the fabrication of engineered materials and devices for
quantum technologies and offers insight into the diffusion dynamics of point
defects in solids.Comment: 16 pages, 8 figure
Rhythmic interactions between the mediodorsal thalamus and prefrontal cortex precede human visual perception
The thalamus is much more than a simple sensory relay. High-order thalamic nuclei, such as the mediodorsal thalamus, exert a profound influence over animal cognition. However, given the difficulty of directly recording from the thalamus in humans, next-to-nothing is known about thalamic and thalamocortical contributions to human cognition. To address this, we analysed simultaneously-recorded thalamic iEEG and whole-head MEG in six patients (four female, two male; plus MEG recordings from twelve healthy controls) as they completed a visual detection task. We observed that the phase of both ongoing mediodorsal thalamic and prefrontal low-frequency activity was predictive of perceptual performance. Critically however, mediodorsal thalamic activity mediated prefrontal contributions to perceptual performance. These results suggest that it is thalamocortical interactions, rather than cortical activity alone, that is predictive of upcoming perceptual performance and, more generally, highlights the importance of accounting for the thalamus when theorising about cortical contributions to human cognition
Measurement of a Magnetic Field in a Leading Arm High Velocity Cloud
Using a recent catalogue of extragalactic Faraday rotation derived from the
NRAO VLA Sky Survey we have found an agreement between Faraday rotation
structure and the HI emission structure of a High Velocity Cloud (HVC)
associated with the Leading Arm of the Magellanic System. We suggest that this
morphological agreement is indicative of Faraday rotation through the HVC.
Under this assumption we have used 48 rotation measures through the HVC,
together with estimates of the electron column density from H-\alpha\
measurements and QSO absorption lines to estimate a strength for the
line-of-sight component of the coherent magnetic field in the HVC of >
6 {\rm \mu G}B_{r}/B_{||} < 0.8$, which suggests that the random field does not dominate
over the coherent field as it does in the Magellanic Clouds from which this HVC
likely originates.Comment: 17 pages, 3 figure
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