4,572 research outputs found
Characterization of a planar microcoil for implantable microsystems
This paper discusses the modelling, design and characterization of planar microcoils to be used in telemetry systems that supply energy to miniaturized implants. Parasitic electrical effects that may become important at a.c. frequencies of several megahertz are evaluated. The fabrication process and electrical characterization of planar receiver microcoils will be described, and it will be shown that a power of a few milliwatts is feasible.\u
Fowler-Nordheim-like local injection of photoelectrons from a silicon tip
Tunneling between a photo-excited p-type silicon tip and a gold surface is
studied as a function of tip bias, tip/sample distance and light intensity. In
order to extend the range of application of future spin injection experiments,
the measurements are carried out under nitrogen gas at room temperature. It is
found that while tunneling of valence band electrons is described by a standard
process between the semiconductor valence band and the metal, the tunneling of
photoelectrons obeys a Fowler-Nordheim-like process directly from the
conduction band. In the latter case, the bias dependence of the photocurrent as
a function of distance is in agreement with theoretical predictions which
include image charge effects. Quantitative analysis of the bias dependence of
the dark and photocurrent spectra gives reasonable values for the distance, and
for the tip and metal work functions. For small distances image charge effects
induce a vanishing of the barrier and the bias dependence of the photocurrent
is exponential. In common with many works on field emission, fluctuations in
the tunneling currents are observed. These are mainly attributed to changes in
the prefactor for the tunneling photocurrent, which we suggest is caused by an
electric-field-induced modification of the thickness of the natural oxide layer
covering the tip apex.Comment: 12 pages, 11 figures. Submitted to Phys. Rev.
Relationships between perceived teacher and peer support on motivation and achievement in high school mathematics
One hundred fourteen US students were surveyed to test a model of the relationships among motivational variables resulting from students’ first experiences as they transitioned from middle school to high school, and math achievement. Key malleable factors impacting motivation and achievement included perceived supportiveness of respondents’ teacher and peers. Longitudinal Path Analysis revealed that teacher support can impact students’ beliefs about the supportiveness of their peers, but that these social factors are mediated through students developing personal interest in mathematics to ultimately impact achievement
Better Nonlinear Models from Noisy Data: Attractors with Maximum Likelihood
A new approach to nonlinear modelling is presented which, by incorporating
the global behaviour of the model, lifts shortcomings of both least squares and
total least squares parameter estimates. Although ubiquitous in practice, a
least squares approach is fundamentally flawed in that it assumes independent,
normally distributed (IND) forecast errors: nonlinear models will not yield IND
errors even if the noise is IND. A new cost function is obtained via the
maximum likelihood principle; superior results are illustrated both for small
data sets and infinitely long data streams.Comment: RevTex, 11 pages, 4 figure
Spin-splitting in the quantum Hall effect of disordered GaAs layers with strong overlap of the spin subbands
With minima in the diagonal conductance G_{xx} and in the absolute value of
the derivative |dG_{xy}/dB| at the Hall conductance value G_{xy}=e^{2}/h,
spin-splitting is observed in the quantum Hall effect of heavily Si-doped GaAs
layers with low electron mobility 2000 cm^2/Vs in spite of the fact that the
spin-splitting is much smaller than the level broadening. Experimental results
can be explained in the frame of the scaling theory of the quantum Hall effect,
applied independently to each of the two spin subbands.Comment: 4 pages, 4 figure
Analytic Metaphysics versus Naturalized Metaphysics: The Relevance of Applied Ontology
The relevance of analytic metaphysics has come under criticism: Ladyman & Ross, for instance, have suggested do discontinue the field. French & McKenzie have argued in defense of analytic metaphysics that it develops tools that could turn out to be useful for philosophy of physics. In this article, we show first that this heuristic defense of metaphysics can be extended to the scientific field of applied ontology, which uses constructs from analytic metaphysics. Second, we elaborate on a parallel by French & McKenzie between mathematics and metaphysics to show that the whole field of analytic metaphysics, being useful not only for philosophy but also for science, should continue to exist as a largely autonomous field
XMM-Newton Witness of M86 X-ray Metamorphosis
The environmental influence of cluster media on its member galaxies, known as
Butcher--Oemler effect, has recently been subject to revision due to numerous
observations of strong morphological transformations occurring outside the
cluster virial radii, caused by some unidentified gas removal processes. In
this context we present new XMM-Newton observations of M86 group. The unique
combination of high spatial and spectral resolution and large field of view of
XMM-Newton allows an in-depth investigation of the processes involved in the
spectacular disruption of this object. We identify a possible shock with Mach
number of ~1.4 in the process of crushing the galaxy in the North-East
direction. The latter is ascribed to the presence of a dense X-ray emitting
filament, previously revealed in the RASS data. The shock is not associated
with other previously identified features of M86 X-ray emission, such as the
plume, the north-eastern arm and the southern extension, which are found to
have low entropy, similar to the inner 2 kpc of M86. Finally, mere existence of
the large scale gas halo around the M86 group, suggests that the disruptions of
M86's X-ray halo may be caused by small-scale types of interactions such as
galaxy-galaxy collisions.Comment: 11 pages, A&A in pres
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