On Poisson–Tweedie mixtures

Poisson-Tweedie mixtures are the Poisson mixtures for which the mixing measure is generated by those members of the family of Tweedie distributions whose support is non-negative. This class of non-negative integer-valued distributions is comprised of Neyman type A, back-shifted negative binomial, compound Poisson-negative binomial, discrete stable and exponentially tilted discrete stable laws. For a specific value of the “power” parameter associated with the corresponding Tweedie distributions, such mixtures comprise an additive exponential dispersion model. We derive closed-form expressions for the related variance functions in terms of the exponential tilting invariants and particular special functions. We compare specific Poisson-Tweedie models with the corresponding Hinde-Demétrio exponential dispersion models which possess a comparable unit variance function. We construct numerous local approximations for specific subclasses of Poisson-Tweedie mixtures and identify Lévy measure for all the members of this three-parameter family

Quantum BRST operators in the extended BRST-anti-BRST formalism

The quantum BRST-anti-BRST operators are explicitely derived and the consequences related to correlation functions are investigated. The connection with the standard formalism and the loopwise expansions for quantum operators and anomalies in Sp(2) approach are analyzed.Comment: 7 page

Carrier field shock formation of long wavelength femtosecond pulses in dispersive media

We numerically demonstrate the formation of carrier field shocks in various dispersive media for a wide variety of input conditions using two different electric field propagation models. In addition, an investigation of the impact of numerous physical effects on carrier wave shock is performed. It is shown that in many cases a field shock is essentially unavoidable and therefore extremely important in the propagation of intense long wavelength pulses in weakly dispersive nonlinear media such as noble gases, air, and single-crystal diamond. The results presented here are expected to have a significant impact in the field of ultrashort nonlinear optics, attosecond pulse generation, and wavepacket synthesis where the use of mid-IR wavelengths is becoming increasingly more important.Comment: 14 pages, 17 figure

Segmenting the cruise market: an application of multiple correspondence analysis

The cruise line industry is one of the fastest growing travel sectors, and an industry with a high rate of repeat business. This study contributes to the understanding of potential repeat visitors by segmenting cruise tourists based upon their intent to cruise in the future. The purpose of this research note is to reflect on the segmentation method applied. Respondents were asked to respond to questions about their intentions to cruise in the future, and were able to answer yes, no, or not sure, thus making a traditional factor-cluster approach using principal components analysis (or similar) not feasible. This study uses a two step method that combines Multiple Correspondence Analysis (MCA) with a k-means cluster analysis, to segment the sample based on responses to five questions about future cruising intentions

Backpacker motivations: a travel career approach

The main purpose of this study was to conceptualize backpacker motivation within the framework of the travel career pattern (TCP) theory of travel motivation. An online survey was administered to backpackers targeted in backpacker-specific online communities in order to obtain a diverse sample. The relationship between backpackers’ previous travel experience and motivations was examined, and six underlying dimensions of motivation were extracted. Four of the motivations, personal/social growth, experiential, budget travel, and independence were found to be fluid in relation to backpackers’ travel experience. Notably, two dimensions, cultural knowledge and relaxation, were found to be constant in relation to the backpackers’ travel experience, which suggest that the two dimensions constitute the core motivations for backpackers