Quantum to classical crossover in the 2D easy-plane XXZ model

Ground-state and thermodynamical properties of the spin-1/2 two-dimensional easy-plane XXZ model are investigated by both a Green's-function approach and by Lanczos diagonalizations on lattices with up to 36 sites. We calculate the spatial and temperature dependences of various spin correlation functions, as well as the wave-vector dependence of the spin susceptibility for all anisotropy parameters $\Delta$. In the easy--plane ferromagnetic region $(-1< \Delta < 0)$, the longitudinal correlators of spins at distance $r$ change sign at a finite temperature $T_0(\Delta, {\bf r})$. This transition, observed in the 2D case for the first time, can be interpreted as a quantum to classical crossover.Comment: 4 pages, 6 figures, Contribution to the Ising Centennial Colloquium, ICM2000, Belo Horizonte, Brazil, August 200

Moses and the Ark: exploring semantic illusions

In Part One, three experiments investigated the effects of the surface structure of semantic illusion sentences upon semantic illusion rate (Chapters 3 to 6), but only a comparison of question and statements revealed any significant effects, with questions leading to more semantic illusion responses. To explore the implications of this lack of effect, a rating scale study was designed to provide an overview of how semantic illusion sentences compare to sentences used in ordinary discourse: semantic illusion type sentences were found to differ significantly from other sentences along a number of salient dimensions. In Part Two, three further experiments related semantic illusions to problem solving and examined the processing requirements of semantic illusions. Findings indicated that semantic illusions are subject to a kind of ‘functional fixedness’, which prevents thorough processing (Chapters 9 and 10). This may in part be explained by the load that semantic illusion sentences place on working memory, as was indicated by the results of two further experiments, which investigated the role that the different components of working memory play in semantic illusion processing (Chapter 11)

Exploring the Relationship between Urban Form, Mobility and Social Well-Being: Towards an Interdisciplinary Field of Sustainable Urban Planning and Transport Development

This Special Issue focuses on exploring the relationship between urban form, mobility, and social well-being across neighbourhoods, cities, and regions. Understanding more about these relationships is helpful in shaping integrated sustainable urban planning and transport development strategies. There is a growing body of research examining changes in well-being in response to social and spatial interventions (e.g., inequality, social exclusion, the built environment, land use, and transport development) and behavioural changes (e.g., travel preferences). However, there is a lack of understanding of the different types of well-being (e.g., social, hedonic, eudaimonic, short-term/long-term, or individual/collective well-being, as well as the spatial nature of well-being) and the variations in their impact. Furthermore, limited attention has been paid to the standardised measurement of well-being in both quantitative and qualitative terms in the field of social sciences, particularly regarding social and eudaimonic well-being, since they are abstract concepts and thus difficult to assess accurately. Therefore, there is an urgent need to further explore the relationship between urban form, mobility, and social well-being, as well as to examine the ways in which different types of well-being can be measured by applying various advanced models and research approaches within the broad field of urban planning and transport

Why didn't you tag me?!: Social exclusion from Instagram posts hurts, especially those with a high need to belong

Humans are highly sensitive to ostracism experiences and thus, even very short occurrences of being excluded and ignored can threaten fundamental needs and lower mood. We investigated whether not being tagged causes similar negative responses as being excluded in real life. Using a multi-method approach, we show across five studies (total N = 1149) that not being tagged in a posted photo strongly threatens fundamental needs. This effect is moderated by individuals' need to belong, such that individuals with a higher need to belong experience not being tagged as more aversive. Results replicate across vignette studies in which participants imagine not being tagged on Instagram (Studies 2 and 3) and across studies using an alleged group task paradigm that mimicked the psychological mechanism of not being tagged outside of Instagram (Studies 4a and 4b). All experimental studies were pre-registered and we freely share all materials, code and data. Extending ostracism effects to the social media phenomenon tagging, the present research bridges real-world and digital social interactions. The results add to theoretical knowledge on social media, ostracism, and digital well-being and have practical implications for social media app design, social media interventions and our everyday interactions that increasingly happen online

Theory of short-range magnetic order for the t-J model

We present a self-consistent theory of magnetic short-range order based on a spin-rotation-invariant slave-boson representation of the 2D t-J model. In the functional-integral scheme, at the nearest-neighbour pair-approximation level, the bosonized t-J Lagrangian is transformed to a classical Heisenberg model with an effective (doping-dependent) exchange interaction which takes into account the interrelation of ``itinerant'' and ``localized'' magnetic behaviour. Evaluating the theory in the saddle-point approximation, we find a suppression of antiferromagnetic and incommensurate spiral long-range-ordered phases in the favour of a paramagnetic phase with pronounced antiferromagnetic short-range correlations.Comment: 2 pages, 1 Postscript figure, LTpaper.sty, Proc. XXI Int. Conf. on Low Temp. Phys. Prague 9

Depressed and excluded: Do depressive symptoms moderate recovery from ostracism?

Background. Prior studies show that depressed individuals react with more immediate reflexive need threat to ostracism than healthy controls. However, it remains unclear whether the observed difference between depressed individuals and healthy controls is caused by ostracism. To find out, the exclusion condition needs to be compared to a baseline condition: inclusion. Methods. We assessed depressive symptoms in N = 426 participants in an experimental study. Participants were included or excluded in Cyberball and indicated both their immediate reflexive need satisfaction level and their reflective need satisfaction level several minutes later to assess recovery. Results. Being excluded decreased reflexive need satisfaction levels for all participants. At the same time, the strength of depressive symptoms negatively predicted reflexive and reflective need satisfaction and was associated with slower recovery. Importantly, no moderation was observed: individuals with more depressive symptoms reported reduced need satisfaction levels regardless of being included or excluded in Cyberball. Limitations. The present findings were obtained with one paradigm only, albeit the most commonly used one: Cyberball. Depressive symptoms were assessed as self-report; future studies may wish to replicate the effects using structured clinical interviews. Conclusions. Depressive symptoms come with lowered need satisfaction levels, irrespective of whether individuals are socially excluded or included. Clinical practitioners should be aware of the relationship between chronic need threat and depression in order to help their patients overcome it

Patologías víricas en Ulmus laevis en el este de Alemania

Virus-like leaf symptoms and dieback were observed on elm trees in a public park near Potsdam. Infection with Cherry leaf roll virus (CLRV), Elm mottle virus (EMV), Arabis mosaic virus (ArMV) and Tobacco ringspot virus (TRSV), well known viruses to infected elm trees was excluded by bioassays and serological tests. Poty- or carlavirus- like flexible particles of approximately 750 nm in length were isolated repeatedly from diseased elms. The particles were transmissible to diverse Chenopodium species, a herbaceous indicator. The virus was not a member of the Potyviridae family, based on an ELISA and an RT-PCR assay using a potyvirus genus-specific broad-spectrum polyclonal antibody and family-specific primers, respectively. Also no potyvirus-like pinwheel inclusions were found in leaf cells of infected indicator plants in electron microscopic studies. Further molecular characterization of these virus isolates is under way.En olmos situados en un parque cercano a Postdam, se ha observado la presencia de s&iacute;ntomas foliares similares a los producidos por virus. Mediante bioensayos y pruebas serol&oacute;gicas se descart&oacute; la presencia de infecciones originados por el virus del enrollamiento de la hoja del cerezo (CLRV), el virus del moteado del olmo (EMV), el virus del mosaico de Arabis (ArMV) y el virus del anillamiento del tabaco (TRSV), todos ellos bien conocidos por afectar a los olmos. Repetidamente se aisl&oacute;, en olmos enfermos, part&iacute;culas flexibles de aproximadamente 750 mm de longitud similares a las de Potyvirus y Carlavirus. Las part&iacute;culas fueron transmisibles a diversas especies de Chenopodium, un indicador herb&aacute;ceo. Seg&uacute;n una prueba ELISA y un ensayo RT-PCR en que se usaron, respectivamente, un anticuerpo policlonal espec&iacute;fico de g&eacute;nero de Potyvirus de amplio espectro, y cebadores espec&iacute;ficos de la familia, el virus no es miembro de la familia Potyviridae. Tampoco se ha encontrado, en estudios mediante microscop&iacute;a electr&oacute;nica, inclusiones del tipo potyvirus en las c&eacute;lulas de las hojas de plantas indicadoras infectadas. En la actualidad se est&aacute;n realizando nuevas caracterizaciones moleculares de estos aislamientos v&iacute;ricos