9,157 research outputs found
Reducing Polarization Mode Dispersion With Controlled Polarization Rotations
One of the fundamental limitations to high bit rate, long distance,
telecommunication in optical fibers is Polarization Mode Dispersion (PMD). Here
we introduce a conceptually new method to reduce PMD in optical fibers by
carrying out controlled rotations of polarization at predetermined locations
along the fiber. The distance between these controlled polarization rotations
must be less than both the beat length and the mode coupling length of the
fiber. This method can also be combined with the method in which the fiber is
spun while it drawn. The incidence of imperfections on the efficiency of the
method is analysed.Comment: 4 page
Guidelines for fabrication of hybrid microcircuits
Document is summary of approaches that may be taken in designing hybrid microcircuits similar to those for aerospace application
Ince's limits for confluent and double-confluent Heun equations
We find pairs of solutions to a differential equation which is obtained as a
special limit of a generalized spheroidal wave equation (this is also known as
confluent Heun equation). One solution in each pair is given by a series of
hypergeometric functions and converges for any finite value of the independent
variable , while the other is given by a series of modified Bessel functions
and converges for , where denotes a regular singularity.
For short, the preceding limit is called Ince's limit after Ince who have used
the same procedure to get the Mathieu equations from the Whittaker-Hill ones.
We find as well that, when tends to zero, the Ince limit of the
generalized spheroidal wave equation turns out to be the Ince limit of a
double-confluent Heun equation, for which solutions are provided. Finally, we
show that the Schr\"odinger equation for inverse fourth and sixth-power
potentials reduces to peculiar cases of the double-confluent Heun equation and
its Ince's limit, respectively.Comment: Submitted to Journal of Mathmatical Physic
Geometric scaling of purely-elastic flow instabilities
We present a combined experimental, numerical and theoretical investigation
of the geometric scaling of the onset of a purely-elastic flow instability in a
serpentine channel. Good qualitative agreement is obtained between experiments,
using dilute solutions of flexible polymers in microfluidic devices, and
two-dimensional numerical simulations using the UCM model. The results are
confirmed by a simple theoretical analysis, based on the dimensionless
criterion proposed by Pakdel-McKinley for onset of a purely-elastic
instability
Axially open nonradiative structures: an example of single-mode resonator based on the sample holder
The concept of nonradiative dielectric resonator is generalized in order to
include axially open configurations having rotational invariance. The resulting
additional nonradiative conditions are established for the different resonance
modes on the basis of their azimuthal modal index. An approximate chart of the
allowed dielectric and geometrical parameters for the TE011 mode is given. A
practical realization of the proposed device based on commercial fused quartz
tubes is demonstrated at millimeter wavelengths, together with simple
excitation and tuning mechanisms. The observed resonances are characterized in
their basic parameters, as well as in the field distribution by means of a
finite element method. The predictions of the theoretical analysis are well
confirmed, both in the general behaviour and in the expected quality factors.
The resulting device, in which the sample holder acts itself as single-mode
resonating element, combines an extreme ease of realization with
state-of-the-art performances. The general benefits of the proposed open
single-mode resonators are finally discussed.Comment: 18 pages, 10 figure
Distal and proximal associates of academic performance at secondary level: A mediation model of personality and self-efficacy
The predictive map for personality-related measures has evolved into distal, proximal and immediate associates of academic performance. This study used distal (Five Factor Model) and proximal (Academic Self-efficacy, ASE) associates with GPA (a specific facet of academic performance) at two time points with secondary level students at sixth form college (N = 106, average age 17 and evenly balanced by gender). Openness, Conscientiousness and ASE were associated with GPA at weak to moderate levels. In a path analysis with ASE as the mediator, the three constructs explained 17% variance on academic performance at time 1 and 42% at time 2 when a direct effect from GPA1 to GPA2 was introduced, with Openness and ASE remaining statistically significant when controlling for GPA1, and all three constructs provided significant indirect effects. Findings demonstrate the salient value of Openness and Conscientiousness, when configured with ASE as the mediator. Findings are applied to the approaches that facilitate learning pathways and support ability processes in achievement
Nonlinear Induction Detection of Electron Spin Resonance
We present a new approach to the induction detection of electron spin
resonance (ESR) signals exploiting the nonlinear properties of a
superconducting resonator. Our experiments employ a yttrium barium copper oxide
(YBCO) superconducting stripline microwave (MW) resonator integrated with a
microbridge. A strong nonlinear response of the resonator is thermally
activated in the microbridge when exceeding a threshold in the injected MW
power. The responsivity factor characterizing the ESR-induced change in the
system's output signal is about 100 times larger when operating the resonator
near the instability threshold, compared to the value obtained in the linear
regime of operation. Preliminary experimental results, together with a
theoretical model of this phenomenon are presented. Under appropriate
conditions nonlinear induction detection of ESR can potentially improve upon
the current capabilities of conventional linear induction detection ESR
Weak inter-band coupling in MgB: a specific heat analysis
The superconducting state of MgB is investigated by specific
heat measurements in detail. The specific heat in the normal state is analyzed
using a recently developed computer code. This allows for an extraction of the
electronic specific heat in the superconducting state with high accuracy and a
fair determination of the main lattice features. One of the two investigated
samples shows a hump in the specific heat at low temperatures within the
superconducting state, accompanied by an unusual low value of the small gap,
, pointing to a very weak inter-band coupling. This
sample allows for a detailed analysis of the contribution from the -band
to the electronic specific heat in the superconducting state. Therefore the
usual analysis method is modified, to include the individual conservation of
entropy of both bands. From analyzing the deviation function of
MgB, the theoretically predicted weak inter-band coupling scenario is
confirmed.Comment: major revision
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