Three orbital model for the iron-based superconductors

The theoretical need to study the properties of the Fe-based high-T_c superconductors with reliable many-body techniques requires us to determine the minimum number of orbital degrees of freedom that will capture the physics of these materials. While the shape of the Fermi surface (FS) obtained with the local density approximation (LDA) can be reproduced by a two-orbital model, it has been argued that the bands that cross the chemical potential result from the strong hybridization of three of the Fe 3d orbitals. For this reason, a three-orbital Hamiltonian obtained with the Slater-Koster formalism by considering the hybridization of the As p orbitals with the Fe d_xz,d_yz, and d_xy orbitals is discussed here. This model reproduces qualitatively the FS shape and orbital composition obtained by LDA calculations for undoped pnictides when four electrons per Fe are considered. Within a mean-field approximation, its magnetic and orbital properties in the undoped case are described. With increasing Coulomb repulsion, four regimes are obtained: (1) paramagnetic, (2) magnetic (pi,0) spin order, (3) the same (pi,0) spin order but now including orbital order, and finally (4) a magnetic and orbital ordered insulator. The spin-singlet pairing operators allowed by the lattice and orbital symmetries are also constructed. It is found that for pairs of electrons involving up to diagonal nearest-neighbors sites, the only fully gapped and purely intraband spin-singlet pairing operator is given by Delta(k)=f(k)\sum_{alpha} d_{k,alpha,up}d_{-k,alpha,down} with f(k)=1 or f(k)=cos(k_x)cos(k_y) which would arise only if the electrons in all different orbitals couple with equal strength to the source of pairing

Constraints Imposed by Symmetry on Pairing Operators for the Pnictides

Considering model Hamiltonians that respect the symmetry properties of the pnictides, it is argued that pairing interactions that couple electrons at different orbitals with an orbital-dependent pairing strength inevitably lead to interband pairing matrix elements, at least in some regions of the Brillouin zone. Such interband pairing has not been considered of relevance in multiorbital systems in previous investigations. It is also observed that if, instead, a purely intraband pairing interaction is postulated, this requires that the pairing operator has the form $\Delta^+(k)=f(k) \sum_{\alpha} d^+_{k,\alpha,\uparrow}d^+_{-k, \alpha,\downarrow}$ where $\alpha$ labels the orbitals considered in the model and f(k) arises from the spatial location of the coupled electrons or holes. This means that the gaps at two different Fermi surfaces involving momenta $k_F$ and $k'_F$ can only differ by the ratio $f(k_F)/ f(k'_F)$ and that electrons in different orbitals must be subject to the same pairing attraction, thus requiring fine tuning. These results suggest that previously neglected interband pairing tendencies could actually be of relevance in a microscopic description of the pairing mechanism in the pnictides

Connection or Competence: Emotional Labor Versus Service Quality as Antecedents to Customer Loyalty

Service delivery has become increasingly important in service heavy industries and particularly within restaurants. Within this segment, the employee’s ability to display the appropriate emotions is of great concern. The axiom “service with a smile”, has been a mainstay for many years. However, a frown has the opposite effect. The question has been raised, how do frontline employees manage their emotions so as to provide the service with the appropriate emotion and the feeling of a genuine connection? This form of labor has been coined, emotional labor, and has a research stream dedicated to its understanding. This dissertation utilized a 2 (emotional labor) x 2 (service quality) x 2 (purpose of consumption) experimental design manipulating each one of the preceding variables. The results indicated that, opposed to expectations, purpose of consumption did not play a significant role in satisfaction or loyalty. Conversely, both emotional labor and service quality played a significant role on both satisfaction and loyalty. In addition the interaction of service quality and emotional labor had a significant impact on satisfaction. These results indicate that emotional labor does impact satisfaction and loyalty, however, it has a much greater impact when the more tactical service quality is in place

Menu engineering and dietary behavior impact on young adults’ kilocalorie choice

The obesity pandemic is associated with increased consumption of restaurant food. Labeling of menus is an intervention used to provide consumers with kilocalorie (calorie) information in hopes of them making healthier food choices. This study evaluated the relationship between young adults’ calorie choices on restaurant menus and menu design, dietary behaviors, and demographic characteristics. A 3 (fast-casual restaurants) × 4 (menu-designs based on menu engineering theories) between-subjects (n = 480, 18–24-year olds) experimental design was used. The relationship between the participants’ calorie choices (high versus low) and menu design, stage of change, gender, race, educational level and weight status was evaluated using logistic regression. All independent variables had at least one category that had greater odds (CI 95% ± 5%) of subjects choosing a lower calorie entree, except education level and race/ethnic group. Normal weight and overweight subjects had greater odds of choosing lower calorie entrees than those that were obese. In addition, subjects that had started to control their calorie intake for less than six months or had sustained this change for at least six months, had greater odds of choosing lower calorie entrees compared to others. Including a green symbol and calories on fast casual restaurant menus may influence some young adults to choose lower calorie entrees

Expanding the Restaurant Value Chain through Digital Delivery: a Significant Disruptor in the U.S. Restaurant Industry

The food industry has experienced enormous growth in the use of food delivery in recent years. More specifically, digitally enabled food delivery has emerged as the most disruptive force in the foodservice industry today. Increased consumer demand for convenience and variety in conjunction with the rapid pace of technological advancements are believed to be the driving factors for the emergence of this phenomenon (Carsten et al., 2016). Foot traffic at traditional dine-in establishments has dwindled as customers opt for online delivery instead, resulting in an altering of the restaurant value chain (Huang, Kohli and Lal, 2019). In particular, the emergence of third-party delivery aggregators (TPDA), such as Grubhub and Uber Eats, present traditional, brick and mortar foodservice operators with a multitude of both opportunities and challenges. Opportunities range from lower financial and logistical barriers for marketplace entrance, to accessing new and more extensive geographical markets, as well as the opportunity for increased sales volumes (Maras, 2019). However, it has been reported that large commission and services fees (5 to 40% on each delivery order) paid to the TPDAs by restaurants are consuming already narrow profit margins (Fisher, 2019). Other reported challenges include operational issues and a lack of consistency of food and service quality (Maras, 2019). On the consumer side, the added convenience of dining at home can come at a premium expense through delivery charges and higher-priced menu items. Therefore, the decision to offer food delivery service

Competing Pairing Symmetries in a Generalized Two-Orbital Model for the Pnictides

We introduce and study an extended "t-U-J" two-orbital model for the pnictides that includes Heisenberg terms deduced from the strong coupling expansion. Including these J terms explicitly allows us to enhance the strength of the (pi, 0)-(0, pi) spin order which favors the presence of tightly bound pairing states even in the small clusters that are here exactly diagonalized. The A1g and B2g pairing symmetries are found to compete in the realistic spin-ordered and metallic regime. The dynamical pairing susceptibility additionally unveils low-lying B1g states, suggesting that small changes in parameters may render any of the three channels stable.Comment: submitted PRL 10/5/1

Exploring Attitudes and Reactions to Unfamiliar Food Pairings: An Examination of the Underlying Motivations and the Impact of Culinary Education

A mixed-methodology study was conducted to better understand consumer attitudes and behaviors toward novel food pairings and the impact of culinary education. Focus groups were conducted to investigate the underlying motivational factors to the reactions and behaviors toward unfamiliar foods. The second phase of the study consisted of sensory evaluation by two separate cohorts, panelists with and without culinary education, of food products created through the novel pairings of foods. Panelists with culinary education expressed a greater overall liking for the animal-based pairing. Sensory-Affective and Ideational factors appeared to be underlying motivational factors of these hedonic reactions