14,584 research outputs found
Coulomb Oscillations in Antidots in the Integer and Fractional Quantum Hall Regimes
We report measurements of resistance oscillations in micron-scale antidots in
both the integer and fractional quantum Hall regimes. In the integer regime, we
conclude that oscillations are of the Coulomb type from the scaling of magnetic
field period with the number of edges bound to the antidot. Based on both
gate-voltage and field periods, we find at filling factor {\nu} = 2 a tunneling
charge of e and two charged edges. Generalizing this picture to the fractional
regime, we find (again, based on field and gate-voltage periods) at {\nu} = 2/3
a tunneling charge of (2/3)e and a single charged edge.Comment: related papers at http://marcuslab.harvard.ed
Assessing composition gradients in multifilamentary superconductors by means of magnetometry methods
We present two magnetometry-based methods suitable for assessing gradients in
the critical temperature and hence the composition of multifilamentary
superconductors: AC magnetometry and Scanning Hall Probe Microscopy. The
novelty of the former technique lies in the iterative evaluation procedure we
developed, whereas the strength of the latter is the direct visualization of
the temperature dependent penetration of a magnetic field into the
superconductor. Using the example of a PIT Nb3Sn wire, we demonstrate the
application of these techniques, and compare the respective results to each
other and to EDX measurements of the Sn distribution within the sub-elements of
the wire.Comment: 7 pages, 8 figures; broken hyperlinks are due to a problem with arXi
Full-field structured-illumination super-resolution X-ray transmission microscopy
Modern transmission X-ray microscopy techniques provide very high resolution at low and medium X-ray energies, but suffer from a limited field-of-view. If sub-micrometre resolution is desired, their field-of-view is typically limited to less than one millimetre. Although the field-of-view increases through combining multiple images from adjacent regions of the specimen, so does the required data acquisition time. Here, we present a method for fast full-field super-resolution transmission microscopy by structured illumination of the specimen. This technique is well-suited even for hard X-ray energies above 30 keV, where efficient optics are hard to obtain. Accordingly, investigation of optically thick specimen becomes possible with our method combining a wide field-of-view spanning multiple millimetres, or even centimetres, with sub-micron resolution and hard X-ray energies
Cardio-audio synchronization drives neural surprise response.
Successful prediction of future events depends on the brain's capacity to extract temporal regularities from sensory inputs. Neuroimaging studies mainly investigated regularity processing for exteroceptive sensory inputs (i.e. from outside the body). Here we investigated whether interoceptive signals (i.e. from inside the body) can mediate auditory regularity processing. Human participants passively listened to sound sequences presented in synchrony or asynchrony to their heartbeat while concomitant electroencephalography was recorded. We hypothesized that the cardio-audio synchronicity would induce a brain expectation of future sounds. Electrical neuroimaging analysis revealed a surprise response at 158-270 ms upon omission of the expected sounds in the synchronous condition only. Control analyses ruled out that this effect was trivially based on expectation from the auditory temporal structure or on differences in heartbeat physiological signals. Implicit neural monitoring of temporal regularities across interoceptive and exteroceptive signals drives prediction of future events in auditory sequences
Single electron capacitance spectroscopy of vertical quantum dots using a single electron transistor
We have incorporated an aluminum single electron transistor (SET) directly on
top of a vertical quantum dot, enabling the use of the SET as an electrometer
that is extremely responsive to the motion of charge into and out of the dot.
Charge induced on the SET central island from single electron additions to the
dot modulates the SET output, and we describe two methods for demodulation that
permit quantitative extraction of the quantum dot capacitance signal. The two
methods produce closely similar results for the determined single electron
capacitance peaks.Comment: Submitted to Applied Physics Letters (reformatted to fit correctly on
a page
Electron Beam Deflection Without Off-Axis Aberrations
A novel focusing/deflection system for high accuracy, high throughput E-beam lithography, denoted as Variable Axis Immersion Lens (VAIL), has been successfully demonstrated. The main attributes of this system include: l) Perpendicular landing at all points of a deflection field \u3e (10 x 10 mm), 2) Elimination of transverse chromatic aberration, 3) High resolution ( \u3c 0.2μm edge slope) over the entire deflection field, 4) Elimination of eddy current effects in the target area, and 5) Total magnetic shielding of the target from external fields
Foot and mouth disease in Zambia: Spatial and temporal distributions of outbreaks, assessment of clusters and implications for control
Zambia has been experiencing low livestock productivity as well as trade restrictions owing to the occurrence of foot and mouth disease (FMD), but little is known about the epidemiology of the disease in these endemic settings. The fundamental questions relate to the spatio-temporal distribution of FMD cases and what determines their occurrence. A retrospective review of FMD cases in Zambia from 1981 to 2012 was conducted using geographical information systems and the SaTScan software package. Information was collected from peer-reviewed journal articles, conference proceedings, laboratory reports, unpublished scientific reports and grey literature. A space–time permutation probability model using a varying time window of one year was used to scan for areas with high infection rates. The spatial scan statistic detected a significant purely spatial cluster around the Mbala–Isoka area between 2009 and 2012, with secondary clusters in Sesheke–Kazungula in 2007 and 2008, the Kafue flats in 2004 and 2005 and Livingstone in 2012. This study provides evidence of the existence of statistically significant FMD clusters and an increase in occurrence in Zambia between 2004 and 2012. The identified clusters agree with areas known to be at high risk of FMD. The FMD virus transmission dynamics and the heterogeneous variability in risk within these locations may need further investigation
Critical current diffraction pattern of SIFS Josephson junctions with step-like F-layer
We present the latest generation of
superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions
with a step-like thickness of the ferromagnetic (F) layer. The F-layer
thicknesses and in both halves were varied to obtain different
combinations of positive and negative critical current densities and
. The measured dependences of the critical current on applied magnetic
field can be well described by a model which takes into account different
critical current densities (obtained from reference junctions) and different
net magnetization of the multidomain ferromagnetic layer in both halves.Comment: 7 pages, 3 figure
A spin foam model for pure gauge theory coupled to quantum gravity
We propose a spin foam model for pure gauge fields coupled to Riemannian
quantum gravity in four dimensions. The model is formulated for the
triangulation of a four-manifold which is given merely combinatorially. The
Riemannian Barrett--Crane model provides the gravity sector of our model and
dynamically assigns geometric data to the given combinatorial triangulation.
The gauge theory sector is a lattice gauge theory living on the same
triangulation and obtains from the gravity sector the geometric information
which is required to calculate the Yang--Mills action. The model is designed so
that one obtains a continuum approximation of the gauge theory sector at an
effective level, similarly to the continuum limit of lattice gauge theory, when
the typical length scale of gravity is much smaller than the Yang--Mills scale.Comment: 18 pages, LaTeX, 1 figure, v2: details clarified, references adde
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