Detection of variable frequency signals using a fast chirp transform

The detection of signals with varying frequency is important in many areas of physics and astrophysics. The current work was motivated by a desire to detect gravitational waves from the binary inspiral of neutron stars and black holes, a topic of significant interest for the new generation of interferometric gravitational wave detectors such as LIGO. However, this work has significant generality beyond gravitational wave signal detection. We define a Fast Chirp Transform (FCT) analogous to the Fast Fourier Transform (FFT). Use of the FCT provides a simple and powerful formalism for detection of signals with variable frequency just as Fourier transform techniques provide a formalism for the detection of signals of constant frequency. In particular, use of the FCT can alleviate the requirement of generating complicated families of filter functions typically required in the conventional matched filtering process. We briefly discuss the application of the FCT to several signal detection problems of current interest

A generalization of Szebehely's inverse problem of dynamics in dimension three

Extending a previous paper, we present a generalization in dimension 3 of the traditional Szebehely-type inverse problem. In that traditional setting, the data are curves determined as the intersection of two families of surfaces, and the problem is to find a potential V such that the Lagrangian L = T - V, where T is the standard Euclidean kinetic energy function, generates integral curves which include the given family of curves. Our more general way of posing the problem makes use of ideas of the inverse problem of the calculus of variations and essentially consists of allowing more general kinetic energy functions, with a metric which is still constant, but need not be the standard Euclidean one. In developing our generalization, we review and clarify different aspects of the existing literature on the problem and illustrate the relevance of the newly introduced additional freedom with many examples.Comment: 23 pages, to appear in Rep. Math. Phy

A generalization of Szebehely's inverse problem of dynamics

The so-called inverse problem of dynamics is about constructing a potential for a given family of curves. We observe that there is a more general way of posing the problem by making use of ideas of another inverse problem, namely the inverse problem of the calculus of variations. We critically review and clarify different aspects of the current state of the art of the problem (mainly restricted to the case of planar curves), and then develop our more general approach.Comment: 21 pages, to appear in Rep. Math. Phy

Does Service Bundling Reduce Churn?

We examine whether bundling in telecommunications services reduces churn using a series of large, independent cross sections of household decisions. To identify the effect of bundling, we construct a pseudo-panel dataset and utilize a linear, dynamic panel-data model, supplemented by nearest-neighbor matching. We find bundling does reduce churn for all three "triple-play" services. However, the effect is only "visible" during times of turbulent demand. We also find evidence that broadband was substituting for pay television in 2009. This analysis highlights that bundling helps with customer retention in service industries, and may play an important role in preserving contracting markets.Bundle, Service, Churn, Triple Play, Telecommunications, Cable, Broadband, Telephone, Screen

Time-dependent kinetic energy metrics for Lagrangians of electromagnetic type

We extend the results obtained in a previous paper about a class of Lagrangian systems which admit alternative kinetic energy metrics to second-order mechanical systems with explicit time-dependence. The main results are that a time-dependent alternative metric will have constant eigenvalues, and will give rise to a time-dependent coordinate transformation which partially decouples the system

Is Dual Agency in Real Estate Transactions a Cause for Concern?

We study dual agency in residential real estate, where the same agent/agency represents both the buyer and seller. We assess the extent to which dual agency suffers from an inherent conflict of interest, where the dual agent furthers the interest of one client at the expense of the other client’s, as well as principal-agent incentive misalignment where the agent furthers her own interest at the expense of one or both clients. And, we examine how these incentive conflicts affect agent behavior and transaction outcomes. To do so, we analyze 10,891 residential real estate transactions in Long Island, NY, from 2004- 2007. Specifically, we (i) identify how dual agency is correlated with house prices and time-to-sale, (ii) describe and assess agent behaviors that could generate these correlations, and (iii) provide some intuition as to the economic effects of prohibiting dual agency in real estate transactions. We find that the incidence of dual agency is uncorrelated with sale price and negatively correlated with time-to-sale. However, on very fast deals, list prices and sale prices are significantly higher on houses sold via dual agency. These findings are consistent with first-resort selling (agents first showing houses to in-house buyer clients) and strategic pricing (agents inducing their seller clients to set a higher list price in anticipation of an internal client agreeing to it) on some deals, in conjunction with agents leaning on sellers to accept a lower sale price on other deals. First-resort selling is indicative of incentive misalignment, while the latter two behaviors reflect a conflict of interest: strategic pricing transfers surplus from the buyer to the seller, and leaning on the seller transfers surplus from the seller to the buyer. Further, our results indicate little difference between dual-agent (same agent) and within-agency (same agency, but different agent) deals. Our findings provide some evidence of distorted outcomes associated with dual agency, mainly on fast deals, but the evidence indicates mild overall effects, suggesting that prohibiting the practice is not likely to substantially increase welfare.

A new HW Vir binary from the Palomar Transient Factory: PTF1 J072455.75+125300.3 - An eclipsing subdwarf B binary with a M-star companion

We report the discovery of an eclipsing binary -- PTF1 J072456$+$125301-- composed of a subdwarf B (sdB) star ($g'=17.2^m$) with a faint companion. Subdwarf B stars are core helium-burning stars, which can be found on the extreme horizontal branch. About half of them reside in close binary systems, but few are known to be eclipsing, for which fundamental stellar parameters can be derived.\newline We conducted an analysis of photometric data and spectra from the Palomar 60'' and the 200" Hale telescope respectively. A quantitative spectral analysis found an effective temperature of $T_{\text{eff}}=33900\pm350$\,K, log g = $5.74\pm0.08$ and log($n_{\text{He}}/n_{\text{H}}) = -2.02 \pm0.07$, typical for an sdB star. The companion does not contribute to the optical light of the system, except through a distinct reflection effect. From the light curve an orbital period of 0.09980(25)\,d and a system inclination of $83.56\pm0.30\,^{\circ}$ were derived. The radial velocity curve yielded an orbital semi-amplitude of K_1=95.8\pm 8.1\,\text{km s^{-1}}. The mass for the M-type dwarf companion is $0.155\pm0.020\,M_{\odot}$. PTF1\,J072456$+$125301 has similar atmospheric parameters to those of pulsating sdB stars (V346 Hya stars). Therefore it could be a high-priority object for asteroseismology, if pulsations were detected such as in the enigmatic case of NY Vir.Comment: Accepted to A&A, 7pages, 4 figure

Do Incumbents Improve Service Quality in Response to Entry? Evidence from Airlines’ On-Time Performance

We examine if and how incumbent firms respond to entry, and entry threats, using non-price modes of competition. Our analysis focuses on service quality within the airline industry. We find that incumbent on-time performance actually worsens in response to entry, and even entry threats, by Southwest Airlines. Given Southwest’s general superiority in on-time performance, this result is consistent with equilibria of theoretical models of quality and price competition, which generally predict differentiation along quality. We corroborate this intuition with further analysis, showing there is no notable response by incumbents when an airline with average on-time performance (Continental) threatens to enter or enters a route.