Universal collisionless transport of graphene

The impact of the electron-electron Coulomb interaction on the optical conductivity of graphene has led to a controversy that calls into question the universality of collisionless transport in this and other Dirac materials. Using a lattice calculation that avoids divergences present in previous nodal Dirac approaches, our work settles this controversy and obtains results in quantitative agreement with experiment over a wide frequency range. We also demonstrate that dimensional regularization methods agree, as long as the scaling properties of the conductivity and the regularization of the theory in modified dimension are correctly implemented. Tight-binding lattice and nodal Dirac theory calculations are shown to coincide at low energies even when the non-zero size of the atomic orbital wave function is included, conclusively demonstrating the universality of the optical conductivity of graphene.Comment: 4+ pages,4 figures; includes Supplemental Material (18 pages, 2 figures

Time-Reversal-Invariant Hofstadter-Hubbard Model with Ultracold Fermions

We consider the time-reversal-invariant Hofstadter-Hubbard model which can be realized in cold atom experiments. In these experiments, an additional staggered potential and an artificial Rashba--type spin-orbit coupling are available. Without interactions, the system exhibits various phases such as topological and normal insulator, metal as well as semi--metal phases with two or even more Dirac cones. Using a combination of real-space dynamical mean-field theory and analytical techniques, we discuss the effect of on-site interactions and determine the corresponding phase diagram. In particular, we investigate the semi--metal to antiferromagnetic insulator transition and the stability of different topological insulator phases in the presence of strong interactions. We compute spectral functions which allow us to study the edge states of the strongly correlated topological phases.Comment: 4+ pages, 4 figures; includes Supplemental Material (5 pages). Published versio

Designing objects with meaningful associations

Objects often become cherished for their ties to beliefs, experiences, memories, people, places or values that are significant to their owner. These ties can reflect the ways in which we as humans use objects to characterise, communicate and develop our sense of self. This paper outlines our approach to applying product attachment theory to design practices. We created six artefacts that were inspired by interviews conducted with three individuals who discussed details of their life stories. We then evaluated the associations that came to mind for our participants when interacting with these newly designed artefacts to determine whether these links brought meaning to them. Our findings highlight the potential of design to bring emotional value to products by embodying significant aspects of a person’s self-identity. To do so, designers must consider both the importance and authenticity of the associations formed between an object and an individual

THE IMPACT OF THE COVID-19 PANDEMIC ON SOCIAL FUCNTIONING, NEGATIVE AFFECT, AND PARANOID IDEATION

The COVID-19 pandemic has contributed to significant increases in mental health symptoms among the general population. Given greater levels of social isolation prior to the pandemic and an increased vulnerability to stress, those with psychosis spectrum disorders may be especially susceptible to the mental health impacts of the pandemic. Yet very few studies exploring the impact of the pandemic on social functioning and mental health have included individuals with psychosis spectrum disorders. Utilizing data gathered from a transdiagnostic sample of individuals spanning the spectrum of psychosis, the current study investigated the impact of the COVID-19 pandemic on perceptions of interpersonal relationships and symptomatology. Results indicated that perceived rejection and hostility were greater during COVID compared to pre-COVID levels and that average and high levels of negative COVID-related impacts helped to maintain levels of perceived hostility from pre-COVID levels. Analyses also found a relation between the number of negative COVID-related impacts and lower social support, greater social distress, greater negative affect, and greater paranoid ideation during the pandemic. Contrary to expectations, symptoms during the pandemic were not predicted by social resources before the pandemic and paranoid ideation did not change compared to pre-COVID levels. However, persecutory paranoid ideation was related to more negative perceptions of the government’s response to COVID. These findings demonstrate how the COVID-19 pandemic has impacted perceptions of social relationships and symptomatology among those with psychosis spectrum disorders and raise concerns that those high in paranoid ideation may be less willing to engage in government mandated protective health behaviors designed to limit the spread of COVID-19

THE ECONOMICS OF AGRICULTURAL LABOR EXCHANGE WITH EVIDENCE FROM INDONESIA

In agricultural labor exchange, farmers temporarily pool their labor into teams and complete a task on each team member's plot in succession. Labor time is exchanged between team members under strict reciprocity and without pay. The use of agricultural labor exchange in developing countries is widespread, but has received little attention from economists. This dissertation investigates the motivation for the formation of labor exchange teams by considering the individual farmer's decision to participate. The analysis focuses on the two most prominent motivations for labor exchange: credit and labor market imperfections and the technological benefits of teamwork. A theoretical model of demand for labor exchange under factor market imperfections generalizes existing models of the organization of agricultural production by allowing for returns to teamwork and labor exchange. This generalization accounts for empirically relevant modes of production that were previously ruled out. The model establishes positive marginal returns to teamwork as a necessary condition for labor exchange when non-household labor exhibits moral hazard. The empirical analysis tests the implications of the model using primary data on agricultural households from Indonesia. Production function estimates demonstrate positive returns to teamwork for a sample of rice and corn farmers, establishing the necessary condition for labor exchange. Estimates of the farmer's decision to participate in labor exchange subject to unobserved working capital constraints are estimated for alternative constraint status assignment rules and via the EM algorithm. Results show that the effect of working capital holdings on the probability of participating in labor exchange has the inverted-U shape predicted by the model for working capital constrained households. Also, labor exchange use is responsive to wages in the paid labor market, and is constrained by the local distribution of land and crop choice. These findings imply that labor exchange operates in conjunction with paid labor markets; that labor exchange is a source of productivity growth for poor capital constrained farmers; and that the institution of labor exchange is likely to persist much later into the process of development than suggested by previous studies

Aqueous Assembly of Zwitterionic Daisy Chains

The synthesis and characterization of zwitterionic molecular [c2]‐ and [a2]‐daisy chains are described, relying on recognition of a positively charged cyclophane and a negatively charged oligo(phenylene‐ethynylene) (OPE) rod in aqueous medium. For this purpose, syntheses of an acetylene‐functionalized macrocyclic receptor and a water‐soluble OPE‐rod as the guest component are presented, from which a heteroditopic daisy chain monomer was prepared. This monomer aggregated strongly in water/methanol 4:1 and formed molecular daisy chains, which were isolated as interlocked species from a stoppering reaction at 1 mm concentration. The cyclic dimer [c2] was the main product with an isolated yield of 30 % and consisted of a mixture of diastereomers, as evidenced by 1H NMR spectroscopy

Versatile volumetric additive manufacturing with 3D ray tracing

Tomographic volumetric additive manufacturing (VAM) is an optical 3D printing technique where an object is formed by photopolymerizing resin via tomographic projections. Currently, these projections are calculated using the Radon transform from computed tomography but it ignores two fundamental properties of real optical projection systems: finite etendue and non-telecentricity. In this work, we introduce 3D ray tracing as a new method of computing projections in tomographic VAM and demonstrate high fidelity printing in non-telecentric and higher etendue systems, leading to a 3X increase in vertical build volume than the standard Radon method. The method introduced here expands the possible tomographic VAM printing configurations, enabling faster, cheaper, and higher fidelity printing.Comment: 16 pages, 8 figure

BALANÇO AMBIENTAL SKINNERIANO: REFORÇO E PUNIÇÃO COMO GANHOS E PERDAS E REGISTRO DIGITAL

This study aimed to establish values and references through the method of inductive observation, based on human actions towards the environment, as well as nature's actions towards different types of environments. The purpose was to create a foundation for future effective and sensitive digital environmental records that consider both human and nature perspectives. Within this logical framework, the Skinnerian behavioral theory was utilized, incorporating the concepts of positive and negative reinforcement and punishment to explore various occurrences and their socio-environmental consequences. Given that this theory is based on living beings that can be stimulated, we established a correlation between the concept of nature and a human being in the early months of life, capable of feeling, reacting, and being sensitive. In this manner, we arrived at what we refer to as "Skinnerian gains and losses" (GPs), which establish values and symbols that can be recorded, defining an environmental balance with up to sixteen attributions, four for each responsible agent in relation to the affected entity, be it human or nature, within the context of the environment or society.Este estudio tuvo como objetivo establecer valores y referencias, mediante el método de observación inductiva, basados en las acciones humanas en relación con el medio ambiente, así como de la naturaleza en relación con diversos tipos de ambientes. El propósito fue crear una base para futuros registros ambientales digitales efectivos y sensibles, que consideren los puntos de vista tanto humanos como naturales. Para esta definición lógica, utilizando la teoría conductista de Skinner, se consideraron los conceptos de refuerzo y castigo positivos y negativos, para explorar diversas situaciones y sus consecuencias socioambientales. Al tratarse de una teoría basada en seres vivos que pueden ser estimulados, establecimos una correlación entre el concepto de naturaleza y un ser humano en los primeros meses de vida, que siente, reacciona y es sensible. De esta manera, llegamos a lo que llamamos "ganancias y pérdidas skinnerianas" (GPs), que establecen valores y simbologías que pueden ser registrados, definiendo un equilibrio ambiental con hasta dieciséis atribuciones, cuatro para cada agente responsable en relación con el afectado, es decir, humano o naturaleza, para el medio ambiente o la sociedad.Este estudo teve como objetivo estabelecer valores e referências, pelo método de observação indutiva, com base nas ações humanas em relação ao meio ambiente, assim como da natureza em relação aos diversos tipos de ambientes. O propósito foi criar uma base para futuros registros ambientais digitais eficazes e sensíveis, com tecnologia apropriada, que considerem a perspectiva humana ou da natureza. Para essa definição lógica, utilizando a teoria comportamental skinneriana, foram considerados os conceitos de reforço e punição positivos e negativos, para explorar diversas ocorrências e suas consequências socioambientais. Por se tratar de uma teoria baseada em ações antropogênicas e ocorrências naturais, que repercutem na sociedade e no meio ambiente, causando ganhos e perdas, aprendizados e traumas, consideramos as características particulares de cada agente, humano e natureza, sem rotulagens, números singulares, abstrações generalizadas ou atribuições antropomórficas. Dessa forma, chegamos ao que chamamos de "ganhos e perdas skinnerianos" (GPs), que estabelecem valores e simbologias que podem ser registrados, definindo um equilíbrio ambiental com até dezesseis atribuições, quatro para cada agente responsável em relação ao afetado, ou seja, humano ou natureza, para o meio ambiente ou sociedade. Palavras-chave: natureza; sociedade; meio ambiente; sustentabilidade; educação ambiental.   Skinnerian environmental balance: reinforcement and punishment as gains and losses and digital record   ABSTRACT: This study aimed to establish values and references through the method of inductive observation, based on human actions in relation to the environment, as well as nature's interactions within various types of environments. The purpose was to create a foundation for future effective and sensitive digital environmental records, utilizing appropriate technology, that considers the human or natural perspective. For this logical definition, employing the Skinnerian behavioral theory, concepts of positive and negative reinforcement and punishment were considered to explore various occurrences and their socio-environmental consequences. As this theory is rooted in anthropogenic actions and natural events, impacting society and the environment, causing gains and losses, learning, and traumas, the particular characteristics of each agent, human and nature, were considered without labels, singular numbers, generalized abstractions, or anthropomorphic attributions. In this manner, we arrived at what we refer to as "Skinnerian gains and losses" (GPs), which establish values and symbolisms that can be recorded, defining an environmental balance with up to sixteen attributions, four for each responsible agent in relation to the affected, namely, human or nature, environment, or society. Keywords: nature; society; environment; sustainability; environmental education