17,788 research outputs found
The Chaotic Regime of D-Term Inflation
We consider D-term inflation for small couplings of the inflaton to matter
fields. Standard hybrid inflation then ends at a critical value of the inflaton
field that exceeds the Planck mass. During the subsequent waterfall transition
the inflaton continues its slow-roll motion, whereas the waterfall field
rapidly grows by quantum fluctuations. Beyond the decoherence time, the
waterfall field becomes classical and approaches a time-dependent minimum,
which is determined by the value of the inflaton field and the self-interaction
of the waterfall field. During the final stage of inflation, the effective
inflaton potential is essentially quadratic, which leads to the standard
predictions of chaotic inflation. The model illustrates how the decay of a
false vacuum of GUT-scale energy density can end in a period of `chaotic
inflation'.Comment: 15 pages, 6 figures. v3: matches version published in JCA
Reducing AC impedance measurement errors caused by the DC voltage dependence of broadband high-voltage bias-tees
During the AC impedance characterization of devices, from the kHz-range up to the GHz-range, accuracy can be lost when a DC voltage is applied. Commercial high-voltage broadband bias-tees are often voltage-dependent, which can cause inaccuracies at low frequencies. A calibration technique with applied bias significantly improves the measurement accuracy.\ud
Additionally, a bias-tee has been developed with a voltageindependent capacitor, suitable for DC voltages up to 500 V showing excellent performance up to several gigahertz. PIN diode limiters protect the measurement equipment from damage in case of a device breakdown.\u
On the Trade-Off Between Quality Factor and Tuning Ratio in Tunable High-Frequency Capacitors
A benchmark of tunable and switchable devices at microwave frequencies is presented on the basis of physical limitations to show their potential for reconfigurable cellular applications. Performance limitations are outlined for each given technology focusing on the quality factor (Q) and tuning ratio (eta) as figures of merit. The state of the art in terms of these figures of merit of several tunable and switchable technologies is visualized and discussed. If the performance of these criteria is not met, the application will not be feasible. The quality factor can typically be traded off for tuning ratio. The benchmark of tunable capacitor technologies shows that transistor-switched capacitors, varactor diodes, and ferroelectric varactors perform well at 2 GHz for tuning ratios below 3, with an advantage for GaAs varactor diodes. Planar microelectromechanical capacitive switches have the potential to outperform all other technologies at tuning ratios higher than 8. Capacitors based on tunable dielectrics have the highest miniaturization potential, whereas semiconductor devices benefit from the existing manufacturing infrastructure
Monopoly and the incentive to innovate when adoption involves switchover disruptions
When considering the incentive of a monopolist to adopt an innovation, the textbook model assumes that it can instantaneously and seamlessly introduce the new technology. In fact, firms often face major problems in integrating new technologies. In some cases, firms have to (temporarily) produce at levels substantially below capacity upon adoption. We call such phenomena switchover disruptions, and present extensive evidence on them. If firms face switchover disruptions, then they may temporarily lose some unit sales upon adoption. If the firm loses unit sales, then a cost of adoption is the foregone rents on the sales of those units. Hence, greater market power will mean higher prices on those lost units of output, and hence a reduced incentive to innovate. We introduce switchover disruptions into some standard models in the literature, show they can overturn some famous results, and then show they can help explain evidence that firms in more competitive environments are more likely to adopt technologies and increase productivity.
- …