Arbitrage in Energy Markets: Competing in the Incumbent's Shadow

This paper studies the welfare implications of using market mechanisms to allocate transmission capacity in recently liberalized electricity markets. It questions whether access to this essential facility should be traded on a market, or whether the incumbent should retain exclusive usage rights. We show that granting exclusive use to the incumbent might be optimal, if the capacity of the essential facility is small and the incumbent can reduce production costs by taking advantage of interregional production-cost differences. This result counters the intuition that arbitrage will improve the social surplus when there is no output contraction. The reason is that when competition is imperfect, arbitrage might reduce production efficiency. We advise policymakers to introduce market mechanisms for the allocation of transmission capacity only if sufficient investment in the network is ensured or if the market power of the incumbent is broken in at least one of the markets in which it is active.Arbitrage;electricity sector;price discrimination

Arbitrage in Energy Markets: Competing in the Incumbent's Shadow

This paper studies the welfare implications of using market mechanisms to allocate transmission capacity in recently liberalized electricity markets. It questions whether access to this essential facility should be traded on a market, or whether the incumbent should retain exclusive usage rights. We show that granting exclusive use to the incumbent might be optimal, if the capacity of the essential facility is small and the incumbent can reduce production costs by taking advantage of interregional production-cost differences. This result counters the intuition that arbitrage will improve the social surplus when there is no output contraction. The reason is that when competition is imperfect, arbitrage might reduce production efficiency. We advise policymakers to introduce market mechanisms for the allocation of transmission capacity only if sufficient investment in the network is ensured or if the market power of the incumbent is broken in at least one of the markets in which it is active.Arbitrage;electricity sector;price discrimination

Creating long-lived neutral-atom traps in a cryogenic environment

We describe techniques for creating long-lived magneto-optical and magnetostatic traps for neutral atoms. These traps exist in a sealed cryogenic environment with a temperature near 4 K, where the background gas pressure can be extremely low. To date we have observed cesium magneto-optical traps with background-limited lifetimes in excess of 1 h, and magnetostatic traps with lifetimes of nearly 10 min. From these observations we use the known He-Cs van der Waals collision cross section to infer typical background gas pressures in our apparatus below 4×10^(-12) Torr. With hardware improvements we expect this pressure can be made much lower, extending the magnetostatic-trap lifetimes one to two orders of magnitude. Furthermore, with a cryogenic system one can use superconducting magnets and SQUID detectors to trap and to nondestructively sense spin-polarized atoms. With superconducting microstructures one can achieve very large magnetic-field gradients and curvatures, as high as ∼10^6 G/cm and ∼10^9 G/cm^2, respectively, for use in magnetic and magneto-optical traps

Bit-interleaved coded modulation in the wideband regime

The wideband regime of bit-interleaved coded modulation (BICM) in Gaussian channels is studied. The Taylor expansion of the coded modulation capacity for generic signal constellations at low signal-to-noise ratio (SNR) is derived and used to determine the corresponding expansion for the BICM capacity. Simple formulas for the minimum energy per bit and the wideband slope are given. BICM is found to be suboptimal in the sense that its minimum energy per bit can be larger than the corresponding value for coded modulation schemes. The minimum energy per bit using standard Gray mapping on M-PAM or M^2-QAM is given by a simple formula and shown to approach -0.34 dB as M increases. Using the low SNR expansion, a general trade-off between power and bandwidth in the wideband regime is used to show how a power loss can be traded off against a bandwidth gain.Comment: Submitted to IEEE Transactions on Information Theor

Bit-Interleaved Coded Modulation Revisited: A Mismatched Decoding Perspective

We revisit the information-theoretic analysis of bit-interleaved coded modulation (BICM) by modeling the BICM decoder as a mismatched decoder. The mismatched decoding model is well-defined for finite, yet arbitrary, block lengths, and naturally captures the channel memory among the bits belonging to the same symbol. We give two independent proofs of the achievability of the BICM capacity calculated by Caire et al. where BICM was modeled as a set of independent parallel binary-input channels whose output is the bitwise log-likelihood ratio. Our first achievability proof uses typical sequences, and shows that due to the random coding construction, the interleaver is not required. The second proof is based on the random coding error exponents with mismatched decoding, where the largest achievable rate is the generalized mutual information. We show that the generalized mutual information of the mismatched decoder coincides with the infinite-interleaver BICM capacity. We also show that the error exponent -and hence the cutoff rate- of the BICM mismatched decoder is upper bounded by that of coded modulation and may thus be lower than in the infinite-interleaved model. We also consider the mutual information appearing in the analysis of iterative decoding of BICM with EXIT charts. We show that the corresponding symbol metric has knowledge of the transmitted symbol and the EXIT mutual information admits a representation as a pseudo-generalized mutual information, which is in general not achievable. A different symbol decoding metric, for which the extrinsic side information refers to the hypothesized symbol, induces a generalized mutual information lower than the coded modulation capacity.Comment: submitted to the IEEE Transactions on Information Theory. Conference version in 2008 IEEE International Symposium on Information Theory, Toronto, Canada, July 200

Stability of Magneto-optical Traps with Large Field Gradients: Limits on the Tight Confinement of Single Atoms

We report measurements of the stability of magneto-optical traps (MOTs) for neutral atoms in the limit of tight confinement of a single atom. For quadrupole magnetic field gradients at the trap center greater than ∼1 kG/cm, we find that stochastic diffusion of atoms out of the trapping volume becomes the dominant particle loss mechanism, ultimately limiting the MOT size to greater than ∼5 μm. We measured and modeled the diffusive loss rate as a function of laser power, detuning, and field gradient for trapped cesium atoms. In addition, for as few as two atoms, the collisional loss rates become very high for tightly confined traps, allowing the direct observation of isolated two-body atomic collisions in a MOT

Angular momentum losses and the orbital period distribution of cataclysmic variables below the period gap: effects of circumbinary disks

The population synthesis of cataclysmic variables below the period is investigated. A grid of detailed binary evolutionary sequences has been calculated and included in the simulations to take account of additional angular momentum losses beyond that associated with gravitational radiation and mass loss, due to nova outbursts, from the system. As a specific example, we consider the effect of a circumbinary disk to gain insight into the ingredients necessary to reproduce the observed orbital period distribution. The resulting distributions show that the period minimum lies at about 80 minutes with the number of systems monotonically increasing with increasing orbital period to a maximum near 90 minutes. There is no evidence for an accumulation of systems at the period minimum which is a common feature of simulations in which only gravitational radiation losses are considered. The period distribution is found to be fairly flat for orbital periods ranging from about 85 to 120 minutes. The steepness of the lower edge of the period gap can be reproduced, for example, by an input of systems at periods near 2.25 hrs due to a flow of cataclysmic variable binary systems from orbital periods longer than 2.75 hrs. The good agreement with the cumulated distribution function of observed systems within the framework of our model indicates that the angular momentum loss by a circumbinary disk or a mechanism which mimics its features coupled with a weighting factor to account for selection effects in the discovery of such systems and a flow of systems from above the period gap to below the period gap are important ingredients for understanding the overall period distribution of cataclysmic variable binary systems.Comment: Accepted for publication in Ap

Observation of enhanced optical spring damping in a macroscopic mechanical resonator and application for parametric instability control in advanced gravitational-wave detectors

We show that optical spring damping in an optomechanical resonator can be enhanced by injecting a phase delay in the laser frequency-locking servo to rotate the real and imaginary components of the optical spring constant. This enhances damping at the expense of optical rigidity. We demonstrate enhanced parametric damping which reduces the Q factor of a 0.1-kg-scale resonator from 1.3×10^5 to 6.5×10^3. By using this technique adequate optical spring damping can be obtained to damp parametric instability predicted for advanced laser interferometer gravitational-wave detectors

<i>Gwynia capsula</i> (Jeffreys, 1859) and other recent brachiopods from submarine caves in Croatia

Recent brachiopods were co1lected in submarine caves along the Croatian coast of the Adriatic Sea. In a karstic cave at U Privlaka, Losinj Island, the micromorphic brachiopod Gwynia capsula (JEFFREYS, 1859) has been found for the first time in the Mediterranean Sea. In the same cave, the rhynchonellid brachiopod, Tethyrhynchia mediterranea LOGAN, 1994, is also abundant. The geographic distribution of these two species is now considerably extended