Phase diagrams, critical and multicritical behavior of hard-core Bose-Hubbard models

We determine the zero-temperature phase diagram of the hard-core Bose-Hubbard model on a square lattice by mean-field theory supplemented by a linear spin-wave analysis. Due to the interplay between nearest and next-nearest neighbor interaction and cubic anisotropy several supersolid phases with checkerboard, stripe domain or intermediate symmetry are stabilized. The phase diagrams show three different topologies depending on the relative strength of nearest and next-nearest neighbor interaction. We also find a rich variety of new quantum critical behavior and multicritical points and discuss the corresponding effective actions and universality classes.Comment: 19 pages, ReVTeX, 18 figures included, submitted to PR

Exposure to Violence as an Environmental Pathway Linking Low Socioeconomic Status with Altered Neural Processing of Threat and Adolescent Psychopathology

Low childhood socioeconomic status (SES) is associated with increased risk for psychopathology, in part because of heightened exposure to environmental adversity. Adverse experiences can be characterized along dimensions, including threat and deprivation, that contribute to psychopathology via distinct mechanisms. The current study investigated a neural mechanism through which threat and deprivation may contribute to socioeconomic disparities in psychopathology. Participants were 177 youths (83 girls) aged 10–13 years recruited from a cohort followed since the age of 3 years. SES was assessed using the income-to-needs ratio at the age of 3 years. At the age of 10–13 years, retrospective and current exposure to adverse experiences and symptoms of psychopathology were assessed. At this same time point, participants also com-pleted a face processing task (passive viewing of fearful and neutral faces) during an fMRI scan. Lower childhood SES was associated with greater exposure to threat and deprivation experiences. Both threat and deprivation were associated with higher depression symptoms, whereas threat experiences were uniquely linked to posttraumatic stress disorder symp-toms. Greater exposure to threat, but not deprivation, was associated with higher activation in dorsomedial pFC to fearful compared with neutral faces. The dorsomedial pFC is a hub of the default mode network thought to be involved in internally directed attention and cognition. Experiences of threat, but not deprivation, are associated with greater engagement of this region in response to threat cues. Threat-related adversity contributes to socioeconomic disparities in adolescent psychopathology through distinct mechanisms from deprivation

Contributions of Emotion Regulation and Brain Structure and Function to Adolescent Internalizing Problems and Stress Vulnerability During the COVID-19 Pandemic: A Longitudinal Study

Background: Adolescence is a period of increased vulnerability for internalizing problems, particularly following stressful life events. We examined how emotion regulation and brain structure and function were associated with internalizing problems during the COVID-19 pandemic and moderated the association between pandemic-related stressors and internalizing problems. Methods: Data are from a longitudinal sample (N = 145, age range, 10–15 years) strategically assessed at 3 crucial time points: before the COVID-19 pandemic, early during the stay-at-home order period, and again 6 months later. We examined associations of amygdala and hippocampal volume and amygdala activation during an emotional processing task before the pandemic, examined use of emotion regulation strategies before and during the pandemic, and examined pandemic-related stressors with internalizing problems. Results: Greater exposure to pandemic-related stressors was associated with higher internalizing problems both early and later in the COVID-19 pandemic. Youths who reported more frequent use of rumination before the pandemic and higher use of expressive suppression and lower use of cognitive reappraisal early in the pandemic had higher internalizing problems early in the pandemic. Higher left amygdala activation to neutral relative to fearful faces before the pandemic was associated with greater internalizing problems and a stronger link between pandemic-related stressors and internalizing problems early in the pandemic. Conclusions: Stressors related to the COVID-19 pandemic are strongly associated with adolescent internalizing problems, as are individual differences in emotional reactivity and regulation and their underlying neural mechanisms. Interventions that reduce pandemic-related stressors and foster adaptive emotion regulation skills may protect against adolescent psychopathology during this period of heightened exposure to stress

Emotionality and self-regulation, threat appraisal, and coping in children of divorce.

Abstract A model of the effects of children's temperament (negative and positive emotionality, impulsivity and attention focusing) on post-divorce threat appraisals, coping (active and avoidant), and psychological symptoms (depression and conduct problems) was investigated. The study utilized a sample of 223 mothers and children (ages 9 to 12 years) who had experienced divorce within the last two years. Evidence was found of direct effects of child-report negative emotionality on children's threat perceptions and of child-report positive emotionality and impulsivity on children's coping. Indirect effects of negative emotionality on active and avoidant coping through threat appraisal were found. Direct effects of the temperament variables on symptoms were also found. Cross group analyses indicated that the models were robust to age differences, but gender differences were found in the relation between negative emotionality and depression. The results of this study indicate that temperament and threat appraisals are important predictors of children's post-divorce symptoms, and that temperament is a predictor of children's appraisal and coping process

Quantum-Phase Transitions of Interacting Bosons and the Supersolid Phase

We investigate the properties of strongly interacting bosons in two dimensions at zero temperature using mean-field theory, a variational Ansatz for the ground state wave function, and Monte Carlo methods. With on-site and short-range interactions a rich phase diagram is obtained. Apart from the homogeneous superfluid and Mott-insulating phases, inhomogeneous charge-density wave phases appear, that are stabilized by the finite-range interaction. Furthermore, our analysis demonstrates the existence of a supersolid phase, in which both long-range order (related to the charge-density wave) and off-diagonal long-range order coexist. We also obtain the critical exponents for the various phase transitions.Comment: RevTex, 20 pages, 10 PostScript figures include

Superfluids and Supersolids on Frustrated 2D Lattices

We study the ground state of hard-core bosons with nearest-neighbor hopping and nearest-neighbor interactions on the triangular and Kagom\'e lattices by mapping to a system of spins ($S={1\over2}$), which we analyze using spin-wave theory. We find that the both lattices display superfluid and supersolid (a coexistence of superfluid and solid) order as the parameters and filling are varied. Quantum fluctuations seem large enough in the Kagom\'e system to raise the interesting possibility of a disordered ground state.Comment: Latex format, 24 figures available by email upon request. Submitted to Physical Review

Classification of a supersolid: Trial wavefunctions, Symmetry breakings and Excitation spectra

A state of matter is characterized by its symmetry breaking and elementary excitations. A supersolid is a state which breaks both translational symmetry and internal $U(1)$ symmetry. Here, we review some past and recent works in phenomenological Ginsburg-Landau theories, ground state trial wavefunctions and microscopic numerical calculations. We also write down a new effective supersolid Hamiltonian on a lattice. The eigenstates of the Hamiltonian contains both the ground state wavefunction and all the excited states (supersolidon) wavefunctions. We contrast various kinds of supersolids in both continuous systems and on lattices, both condensed matter and cold atom systems. We provide additional new insights in studying their order parameters, symmetry breaking patterns, the excitation spectra and detection methods.Comment: REVTEX4, 19 pages, 3 figure

Solid 4He and the Supersolid Phase: from Theoretical Speculation to the Discovery of a New State of Matter? A Review of the Past and Present Status of Research

The possibility of a supersolid state of matter, i.e., a crystalline solid exhibiting superfluid properties, first appeared in theoretical studies about forty years ago. After a long period of little interest due to the lack of experimental evidence, it has attracted strong experimental and theoretical attention in the last few years since Kim and Chan (Penn State, USA) reported evidence for nonclassical rotational inertia effects, a typical signature of superfluidity, in samples of solid 4He. Since this "first observation", other experimental groups have observed such effects in the response to the rotation of samples of crystalline helium, and it has become clear that the response of the solid is extremely sensitive to growth conditions, annealing processes, and 3He impurities. A peak in the specific heat in the same range of temperatures has been reported as well as anomalies in the elastic behaviour of solid 4He with a strong resemblance to the phenomena revealed by torsional oscillator experiments. Very recently, the observation of unusual mass transport in hcp solid 4He has also been reported, suggesting superflow. From the theoretical point of view, powerful simulation methods have been used to study solid 4He, but the interpretation of the data is still rather difficult; dealing with the question of supersolidity means that one has to face not only the problem of the coexistence of quantum coherence phenomena and crystalline order, exploring the realm of spontaneous symmetry breaking and quantum field theory, but also the problem of the role of disorder, i.e., how defects, such as vacancies, impurities, dislocations, and grain boundaries, participate in the phase transition mechanism.Comment: Published on J. Phys. Soc. Jpn., Vol.77, No.11, p.11101

"i'm not really afraid of Osama Bin Laden!" fear of terrorism in dutch children

We examined to what extent children in The Netherlands are affected by the threat of terrorism. For this purpose, a sample of school children living in Rotterdam or adjacent satellites (N = 216) completed a fear survey that included a number of terrorism-related items, and were confronted with ambiguous vignettes to measure threat-related interpretation bias. The results demonstrated that although a number of terrorism-related items (i.e., bombing attacks, explosions in a bus or subway) listed high in a ranking of most intense childhood fears, very few children made terrorist-related interpretations of ambiguous situations

Optimal Analysis for the Enhancement in the Thermal Variables Measurement by Smart and Modular Solid State Sensors

The proposed research aims to analyze and optimize the measurement of thermal physical variables during the operation of a hydrogen combustion engine. The optimal measurement of the flow, temperature, pressure, and volume is given over the hydrogen, which is the main fuel of the studied combustion motor. Hence, the success of the measurement is based on the polynomial analysis of the combustion motor operation, which needs nonlinear algorithms to get the optimal correlation of the measured physical variables as well as a high robustness and short response time during the transduction of the measured physical variable, which is achieved as a consequence of the anodic aluminum oxide (AAO) amorphous nanostructures properties that are modular solid state integration of the designed smart sensor. The short response time and high robustness is a good advantage for the designed smart sensor since it gives more time to execute sophisticated algorithms in order to get the optimal physical variables measurement. In fact, the proposed smart sensor keeps the possibility to be modular and solid state for the interaction with the hydrogen fuel as well as recognizing the presence of other molecules mixed in the fluid, which can alarm the user who is able to recognize whether it is joined oxygen or carbon residues. Therefore, the proposed research work toward a good compromise to care for the environment condition based on a cleaner combustion motor operation