7,564,592 research outputs found

### Asymptotic States and the Definition of the S-matrix in Quantum Gravity

Viewing gravitational energy-momentum as equal by observation, but different
in essence from inertial energy-momentum naturally leads to the gauge theory of
volume-preserving diffeormorphisms of an inner Minkowski space. The generalized
asymptotic free scalar, Dirac and gauge fields in that theory are canonically
quantized, the Fock spaces of stationary states are constructed and the
gravitational limit - mapping the gravitational energy-momentum onto the
inertial energy-momentum to account for their observed equality - is
introduced. Next the S-matrix in quantum gravity is defined as the
gravitational limit of the transition amplitudes of asymptotic in- to
out-states in the gauge theory of volume-preserving diffeormorphisms. The so
defined S-matrix relates in- and out-states of observable particles carrying
gravitational equal to inertial energy-momentum. Finally generalized LSZ
reduction formulae for scalar, Dirac and gauge fields are established which
allow to express S-matrix elements as the gravitational limit of truncated
Fourier-transformed vacuum expectation values of time-ordered products of field
operators of the interacting theory. Together with the generating functional of
the latter established in an earlier paper [8] any transition amplitude can in
principle be computed to any order in perturbative quantum gravity.Comment: 35 page

### Unified model of voltage/current mode control to predict saddle-node bifurcation

A unified model of voltage mode control (VMC) and current mode control (CMC)
is proposed to predict the saddle-node bifurcation (SNB). Exact SNB boundary
conditions are derived, and can be further simplified in various forms for
design purpose. Many approaches, including steady-state, sampled-data, average,
harmonic balance, and loop gain analyses are applied to predict SNB. Each
approach has its own merits and complement the other approaches.Comment: Submitted to International Journal of Circuit Theory and Applications
on December 23, 2010; Manuscript ID: CTA-10-025

### Quantum stochastic integrals as operators

We construct quantum stochastic integrals for the integrator being a
martingale in a von Neumann algebra, and the integrand -- a suitable process
with values in the same algebra, as densely defined operators affiliated with
the algebra. In the case of a finite algebra we allow the integrator to be an
$L^2$--martingale in which case the integrals are $L^2$--martingales too

### Heat-treatment of metal parts facilitated by sand embedment

Embedding metal parts of complex shape in sand contained in a steel box prevents strains and warping during heat treatment. The sand not only provides a simple, inexpensive support for the parts but also ensures more uniform distribution of heat to the parts

### Magnetic field dependence of the antiferromagnetic phase transitions in Co-doped YbRh_2Si_2

We present first specific-heat data of the alloy Yb(Rh_(1-x)Co_x)_2Si_2 at
intermediate Co-contents x=0.18, 0.27, and 0.68. The results already point to a
complex magnetic phase diagram as a function of composition. Co-doping of
YbRh_2Si_2 (T_N^{x=0}=72 mK) stabilizes the magnetic phase due to the volume
decrease of the crystallographic unit cell. The magnetic phase transitions are
clearly visible as pronounced anomalies in C^{4f}(T)/T and can be suppressed by
applying a magnetic field. Going from x=0.18 to x=0.27 we observe a change from
two mean-field (MF) like magnetic transitions at T_N^{0.18}=1.1 K and
T_L^{0.18}=0.65 K to one sharp \lambda-type transition at T_N^{0.27}=1.3 K.
Preliminary measurements under magnetic field do not confirm the field-induced
first-order transition suggested in the literature. For x=0.68 we find two
transitions at T_N^{0.68}=1.14 K and T_L^{0.68}=1.06 K.Comment: Accepted for the ICM proceedings 200

### Bifurcation Boundary Conditions for Switching DC-DC Converters Under Constant On-Time Control

Sampled-data analysis and harmonic balance analysis are applied to analyze
switching DC-DC converters under constant on-time control. Design-oriented
boundary conditions for the period-doubling bifurcation and the saddle-node
bifurcation are derived. The required ramp slope to avoid the bifurcations and
the assigned pole locations associated with the ramp are also derived. The
derived boundary conditions are more general and accurate than those recently
obtained. Those recently obtained boundary conditions become special cases
under the general modeling approach presented in this paper. Different analyses
give different perspectives on the system dynamics and complement each other.
Under the sampled-data analysis, the boundary conditions are expressed in terms
of signal slopes and the ramp slope. Under the harmonic balance analysis, the
boundary conditions are expressed in terms of signal harmonics. The derived
boundary conditions are useful for a designer to design a converter to avoid
the occurrence of the period-doubling bifurcation and the saddle-node
bifurcation.Comment: Submitted to International Journal of Circuit Theory and Applications
on August 10, 2011; Manuscript ID: CTA-11-016

### Figure of merit for direct-detection optical channels

The capacity and sensitivity of a direct-detection optical channel are calculated and compared to those of a white Gaussian noise channel. Unlike Gaussian channels in which the receiver performance can be characterized using the noise temperature, the performance of the direct-detection channel depends on both signal and background noise, as well as the ratio of peak to average signal power. Because of the signal-power dependence of the optical channel, actual performance of the channel can be evaluated only by considering both transmit and receive ends of the systems. Given the background noise power and the modulation bandwidth, however, the theoretically optimum receiver sensitivity can be calculated. This optimum receiver sensitivity can be used to define the equivalent receiver noise temperature and calculate the corresponding G/T product. It should be pointed out, however, that the receiver sensitivity is a function of signal power, and care must be taken to avoid deriving erroneous projections of the direct-detection channel performance

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