10,107 research outputs found
Phase-lock loop frequency control and the dropout problem
Technique automatically sets the frequency of narrow band phase-lock loops within automatic lock-in-range. It presets a phase-lock loop to a desired center frequency with a closed loop electronic frequency discriminator and holds the phase-lock loop to that center frequency until lock is achieved
Communication system features dual mode range acquisition plus time delay measurement
Communication system combines range acquisition system and time measurement system for tracking high velocity aircraft and spacecraft. The range acquisition system uses a pseudonoise code to determine range and the time measurement system reduces uncontrolled phase variations in the demodulated signal
A Hybrid Laser Ultrasonic Based Systemf ro Composite Molding
Conventional piezoelectric based ultrasonic systems have been extensively employed for material characterization. These systems however, have been challenged by the recent need to rapidly scan large areas of new materials such as composites having complex geometry. A promising candidate addressing this issue is laser ultrasonics. Though laser ultrasonics is not new and has generated considerable research interest in the past two decades, its industrial acceptance has been limited. Among its many benefits, laser ultrasonics promise the flexibility of a couplant free inspection system. Pulsed lasers, in particular, offer energy concentration at high repetition rates which can be readily directed at any location on the specimen for interrogation purposes. The detection of laser ultrasound is usually done through Michaelson or Fabry-Perot type interferometric systems. Though these detection systems have the advantage of couplant free detection, they constitute a major component of system cost owing to the precision required. The sensitivity of such systems are also not satisfactory
The geometry of manifolds and the perception of space
This essay discusses the development of key geometric ideas in the 19th
century which led to the formulation of the concept of an abstract manifold
(which was not necessarily tied to an ambient Euclidean space) by Hermann Weyl
in 1913. This notion of manifold and the geometric ideas which could be
formulated and utilized in such a setting (measuring a distance between points,
curvature and other geometric concepts) was an essential ingredient in
Einstein's gravitational theory of space-time from 1916 and has played
important roles in numerous other theories of nature ever since.Comment: arXiv admin note: substantial text overlap with arXiv:1301.064
Etch Induced Microwave Losses in Titanium Nitride Superconducting Resonators
We have investigated the correlation between the microwave loss and
patterning method for coplanar waveguide titanium nitride resonators fabricated
on Si wafers. Three different methods were investigated: fluorine- and
chlorine-based reactive ion etches and an argon-ion mill. At high microwave
probe powers the reactive etched resonators showed low internal loss, whereas
the ion-milled samples showed dramatically higher loss. At single-photon powers
we found that the fluorine-etched resonators exhibited substantially lower loss
than the chlorine-etched ones. We interpret the results by use of numerically
calculated filling factors and find that the silicon surface exhibits a higher
loss when chlorine-etched than when fluorine-etched. We also find from
microscopy that re-deposition of silicon onto the photoresist and side walls is
the probable cause for the high loss observed for the ion-milled resonator
Effect of well-width on the electro-optical properties of a quantum well
We record photoreflectance from Ge/GeSi modulation doped quantum wells
possessing V/cm perpendicular electric fields. Qualitatively very
different spectra are obtained from samples of well-width 100 \AA and 250 \AA.
Comparing the wavefunctions calculated from an \textbf{k.p}
theory, we find that while they remain confined in the narrower 100 \AA QW, the
electric field causes them to tunnel into the forbidden gap in the 250 \AA\
well. This implies that the samples should show a transition from the quantum
confined Franz-Keldysh effect to the bulk-like Franz-Keldysh effect. Close to
the band-edge where Franz-Keldysh effects are important, simulated
photoreflectance spectra reproduce the essential features of the experiment,
without any adjustable parameters.Comment: 8 pages, 8 figures. Submitted to Phys. Rev.
Coherence in a transmon qubit with epitaxial tunnel junctions
We developed transmon qubits based on epitaxial tunnel junctions and
interdigitated capacitors. This multileveled qubit, patterned by use of
all-optical lithography, is a step towards scalable qubits with a high
integration density. The relaxation time T1 is .72-.86mu sec and the ensemble
dephasing time T2 is slightly larger than T1. The dephasing time T2 (1.36mu
sec) is nearly energy-relaxation-limited. Qubit spectroscopy yields weaker
level splitting than observed in qubits with amorphous barriers in
equivalent-size junctions. The qubit's inferred microwave loss closely matches
the weighted losses of the individual elements (junction, wiring dielectric,
and interdigitated capacitor), determined by independent resonator
measurements
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