622 research outputs found
Non-linear temperature-dependent curvature of a Phase Change Composite Bimorph beam
Bimorph films curl in response to temperature. The degree of curvature
typically varies linearly with temperature and in proportion to the difference
in thermal expansion of the individual layers. In many applications, such as
controlling a thermostat, this gentle linear behavior is acceptable. In other
cases, such as opening or closing a valve or latching a deployable column into
place, an abrupt motion at a fixed temperature is preferred. To achieve this
non-linear motion, we describe the fabrication and performance of a new bilayer
structure we call 'Phase Change Composite Bimorph (PCBM)'. In a PCBM, one layer
in the bimorph is a composite containing small inclusions of phase change
materials. When the inclusions melt, their large (generally positive and >1%)
expansion coefficient induces a strong, reversible step function jump in
bimorph curvature. The measured jump amplitude and thermal response is
consistent with theory.Comment: 17 pages, 8 figures including one appendi
Method and device for providing prepaid 800/900 telecommunications service
A method and device for providing prepaid 800 and/or 900-type caller services. A caller provides a call request to a telecommunications service provider that can include an 800 or 900 telephone number and an account number for a prepaid account associated with the 800 or 900 telephone number. A determination is made if the prepaid account is authorized for the desired 800 or 900-type call, and if the account is authorized, the caller is connected to the called party associated with the 800 or 900 telephone number. When the call is completed, charges associated with the call are determined and charged to the prepaid account or other party, as desired. The prepaid account is then adjusted to reflect the determined charges.Published versio
Non-local electron transport and cross-resistance peak in NSN heterostructures
We develop a microscopic theory describing the peak in the temperature
dependence of the non-local resistance of three-terminal NSN devices. This peak
emerges at sufficiently high temperatures as a result of a competition between
quasiparticle/charge imbalance and subgap (Andreev) contributions to the
conductance matrix. Both the height and the shape of this peak demonstrate the
power law dependence on the superconductor thickness in contrast to the
zero-temperature non-local resistance which decays (roughly) exponentially with
increasing . A similar behavior was observed in recent experiments.Comment: 4 pages, 3 figure
Directional tunnelling spectroscopy of a normal metal--wave superconductor junction
We calculate the normal metal--wave superconductor tunnelling spectrum
for various junction orientations and for two forms of the superconducting gap,
one which allows for point nodes and the other which allows for line nodes. For
a junction oriented with its normal parallel to the ab plane of the tetragonal
superconductor, we find that the tunnelling spectrum is strongly dependent on
orientation in the plane. The spectrum contains two peaks at energies
equivalent to the magnitudes of the gap function in the direction parallel to
the interface normal and in the direction making a angle with the
normal. These two peaks appear in both superconductors with point nodes and
line nodes, but are more prominent in the latter. For the tunnelling along the
c axis, we find a sharp peak at the gap maximum in the conductance spectrum of
the superconductor with line nodes, whereas with point nodes we find a peak
occurring at the value of the gap function along the c axis. We discuss the
relevance of our result to borocarbide systems.Comment: 16 pages, 10 figure
Functional diversity metrics using kernel density n-dimensional hypervolumes
The use ofn-dimensional hypervolumes in trait-based ecology is rapidly increasing. By representing the functional space of a species or community as a Hutchinsonian niche, the abstract Euclidean space defined by a set of independent axes corresponding to individuals or species traits, these multidimensional techniques show great potential for the advance of functional ecology theory. In the panorama of existing methods for delineating multidimensional spaces, therpackagehypervolume(Global Ecology and Biogeography, 23, 2014, 595-609) is currently the most used. However, functions for calculating the standard set of functional diversity (FD) indices-richness, divergence and regularity-have not been developed within thehypervolumeframework yet. This gap is delaying its full exploitation in functional ecology, meanwhile preventing the possibility to compare its performance with that of other methods. We develop a set of functions to calculate FD indices based onn-dimensional hypervolumes, including alpha (richness), beta (and respective components), dispersion, evenness, contribution and originality. Altogether, these indices provide a coherent framework to explore the primary mathematical components of FD within a multidimensional setting. These new functions can work either with hypervolume objects or with raw data (species presence or abundance and their traits) as input data, and are versatile in terms of input parameters and options. These functions are implemented withinbat(Biodiversity Assessment Tools), anrpackage for biodiversity assessments. As a coherent corpus of functional indices based on a common algorithm, it opens the possibility to fully explore the strengths of the Hutchinsonian niche concept in community ecology research.Peer reviewe
Spin polarized tunneling in ferromagnet/unconventional superconductor junctions
We study tunneling in ferromagnet/unconventional superconductor (F/S)
junctions. We include the effects of spin polarization, interfacial resistance,
and Fermi wavevector mismatch (FWM) between the F and S regions. Andreev
reflection (AR) at the F/S interface, governing tunneling at low bias voltage,
is strongly modified by these parameters. The conductance exhibits a very wide
variety of features as a function of applied voltage.Comment: Revision includes new figures with angular averages and correction of
minor error
The effects of a magnetic barrier and a nonmagnetic spacer in tunnel structures
The spin-polarized transport is investigated in a new type of magnetic tunnel
junction which consists of two ferromagnetic electrodes separated by a magnetic
barrier and a nonmagnetic metallic spacer. Based on the transfer matrix method
and the nearly-free-electron-approximation the dependence of the tunnel
magnetoresistance (TMR) and electron-spin polarization on the nonmagnetic layer
thickness and the applied bias voltage are studied theoretically. The TMR and
spin polarization show an oscillatory behavior as a function of the spacer
thickness and the bias voltage. The oscillations originate from the quantum
well states in the spacer, while the existence of the magnetic barrier gives
rise to a strong spin polarization and high values of the TMR. Our results may
be useful for the development of spin electronic devices based on coherent
transport.Comment: 15 pages, 5 figure
Methods for making mirrors
A turning mirror in an optical waveguide structure is made by etching in the upper surface of the structure a cavity (18) that intercepts the path of light propagated by the waveguide (15, 16, 13). Preferably, the cavity is made to be asymmetric with the side (25) of the cavity remote from the waveguide sloping at typically a forty-five degree angle. The asymmetry can be introduced by using mask and etch techniques and treating the surface of the structure such that the etchant undercuts the mask on the side of the cavity remote from the waveguide to a greater extent than it undercuts the mask on the side of the cavity adjacent the waveguide.Published versio
DC current through a superconducting two-barrier system
We analyze the influence of the structure within a SNS junction on the
multiple Andreev resonances in the subgap I-V characteristics. Coherent
interference processes and incoherent propagation in the normal region are
considered. The detailed geometry of the normal region where the voltage drops
in superconducting contacts can lead to observable effects in the conductance
at low voltages.Comment: 11 pages, including 7 postscript file
Theory of anomalous magnetic interference pattern in mesoscopic SNS Josephson junctions
The magnetic interference pattern in mesoscopic SNS Josephson junctions is
sensitive to the scattering in the normal part of the system. In this paper we
investigate it, generalizing Ishii's formula for current-phase dependence to
the case of normal scattering at NS boundaries in an SNS junction of finite
width. The resulting flattening of the first diffraction peak is consistent
with experimental data for S-2DEG-S mesoscopic junctions.Comment: 6 pages, 5 figures. Phys. Rev. B 68, 144514 (2003
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