Mott physics in 2p2p electron dioxygenyl magnet : O2_{2}MMF6_{6} (MM=Sb, Pt)

We have investigated electronic structures and magnetic properties of O$_{2}$$M$F$_{6}$ ($M$=Sb, Pt), which are composed of two building blocks of strongly correlated electrons: O$_{2}^{+}$ dioxygenyls and $M$F$_{6}^{-}$ octahedra, by employing the first-principles electronic structure band method. For O$_{2}$SbF$_{6}$, as a reference system of O$_{2}$PtF$_{6}$, we have shown that the Coulomb correlation of O(2$p$) electrons drives the Mott insulating state. For O$_{2}$PtF$_{6}$, we have demonstrated that the Mott insulating state is induced by the combined effects of the Coulomb correlation of O(2$p$) and Pt(5$d$) electrons and the spin-orbit (SO) interaction of Pt(5$d$) states. The role of the SO interaction in forming the Mott insulating state of O$_{2}$PtF$_{6}$ is similar to the case of Sr$_{2}$IrO$_{4}$ that is a prototype of a SO induced Mott system with J$_{eff}=1/2$.Comment: 5 pages, 6 figure

Das beobachtbare Erscheinungsbild von Trümmerscheiben

Debris disks are dusty circumstellar disks around main-sequence stars and natural by-products of the planet formation process. With an almost gas-free environment, dust-replenishing parent bodies orbit their host star and most likely continuously supply fine dust through mutual collisions. Thus, debris disks comprise solids ranging from kilometer-sized planetesimals down to micrometer-sized dust. Due to the large surface to volume ratio, dust grains are efficient radiators of thermal re-emission and scatterers of incident radiation from the stellar source. Dust grains are, therefore, readily detectable in a planetary system. Consequently, debris disk observables mainly depend on dust properties and the disk structure, as well as stellar properties. In this dissertation, an observational appearance of debris disks is investigated. This allows the verification of predictions made concerning the spatial structure, underlying dynamical processes, and optical properties of the dust in the debris disk system. In particular, the potential for multi-wavelength and spatially resolved observations in numerical studies are conducted to constrain the observational appearance of debris disks with the physical properties and dynamics of dust grains. To develop observational strategies of disk observations, a new tool has been developed for analytical modeling of debris disks and the interpretation of results from the collisional approach. The dependence of the observational appearance of debris disks on essential collisional parameters, such as the eccentricity of the parent belt, the dispersion of the eccentricities of parent belt bodies, and the critical specific energy for fragmentation of dust particles, is investigated. Furthermore, the feasibility of detecting water ice in typical debris disk systems, assuming various ice destruction mechanisms and dust mixtures with various internal structures, is investigated. Additionally, the multi-wavelength modeling of debris disks in η Chameleontis cluster is investigated to constrain the physical parameters and properties of the disks, such as the range of possible radial locations and total dust mass, based on observation from the APEX/LABOCA and the archival Gaia/DR2 data. Finally, a model based on a planetesimal mass distribution function is investigated to discuss the flattening of the spectral energy distribution of HD 107146 at mm wavelength with the NIKA2 observation

Adaptive Building Skin

City is made up of diversity and density. Diverse factors make activities and different relationships in a city. These are very sensitive to other factors’ changes. Their various responses make city dynamic and finally characterize the face of a city or a town. Buildings are one of dynamic factors in a city. The building facade which determines building’s identity marks the transition between outside and inside. The facade has a strong relationship between building programs and urban activities. Their looks make a huge effect on urban environment. But buildings’ configuration is fixed once design choices are made. Buildings are conceived as a rigid objects and inflexible, unresponsive, and unsustainable. Considering that buildings are the largest contributor to the city environment, building should be responsive to changes and facade performance should be more active to building programs. Adaptive building facade will be the means that can address these challenges

Optical Metrology and Beam Shaping using Active Lensing and Engineered Diffusers

This thesis encompasses three chapters that delve into innovative studies within optical experiments. The overarching motivation behind this research is to enhance the efficiency, and versatility of measurement techniques used in the field. Furthermore, by exploring novel technologies and methodologies, these studies aim to overcome existing limitations and open new avenues for optical experimentation. The first chapter addresses the challenge of accurately measuring the radius of curvature of a sample without physically moving the lens position. Conventional methods using single lenses are prone to errors caused by mechanical drift or instability. To mitigate these issues, the study introduces Tunable Focal Lenses (TFLs) as a replacement for fixed focal length lenses. By employing TFLs in Twyman-Green and Fizeau interferometry, the research demonstrates a more reliable and expeditious approach. The experimental results highlight the potential of TFLs to eliminate errors associated with physical lens movement and present a promising alternative to conventional lens configurations. In the second chapter, the focus shifts to improving diffusing systems utilized in optical experiments. The motivation behind this study lies in the need for efficient and effective replacements for pinhole-based diffusers. Engineered Diffusers (EDs), with their advanced properties, emerge as a potential solution. Specifically, the research delves into utilizing the Light Shaping Diffuser (LSD) due to its high light transmission rate. The experiment explores the spatial characteristics of a collimated beam diffused by LSD and investigates methods to mitigate speckle patterns that often arise. To this end, the research introduces the Speckle Reducer (SR), which combines liquid crystal technology and diffractive optics. Through a comprehensive analysis utilizing techniques such as CCD imaging, Shack-Hartmann wavefront measurement, and knife-edge measurement, the study provides valuable insights into beam divergence calculation, beam profile analysis, and wavefront curvature measurement. By showcasing the potential of EDs, particularly LSDs, as viable alternatives to pinhole-based diffusing systems, this research paves the way for enhanced optical experiments. The final chapter delves into the experimental exploration of LSDs and SRs for interferometry measurements. The primary motivation is to evaluate the effectiveness of this combination as an adaptive optical measurement tool. A Michelson interferometer is employed to evaluate, wherein a beam shaped by LSD and enhanced by SR is split using a beam splitter. The divided parts are directed towards a reference mirror and an adjustable mirror, respectively, before being recombined at the beam splitter. The resulting fringe pattern is captured by a CCD camera, enabling detailed analysis. Moreover, the study investigates the measurement of the refractive index of a thick glass placed between the beam splitter and mirror by utilizing the enhanced beam\u27s bull\u27s eye fringe pattern generated by the SR. The experiment aims to observe changes in fringe patterns as the glass is tilted at various angles, offering valuable insights into the potential applications of LSDs and SRs in interferometry measurements. Through these three interconnected chapters, this research project presents a comprehensive exploration of cutting-edge techniques and technologies in optical experiments. By addressing key challenges and proposing innovative solutions, this work contributes to advancing measurement methodologies, offering new perspectives and possibilities for the optical research community

Antiferromagnetic and structural transitions in the superoxide KO2 from first principles: A 2p-electron system with spin-orbital-lattice coupling

KO2 exhibits concomitant antiferromagnetic (AFM) and structural transitions, both of which originate from the open-shell 2p electrons of O$_{2}^{-}$ molecules. The structural transition is accompanied by the coherent tilting of O$_{2}^{-}$ molecular axes. The interplay among the spin-orbital-lattice degrees of freedom in KO2 is investigated by employing the first-principles electronic structure theory and the kinetic-exchange interaction scheme. We have shown that the insulating nature of the high symmetry phase of KO2 at high temperature (T) arises from the combined effect of the spin-orbit coupling and the strong Coulomb correlation of O 2p electrons. In contrast, for the low symmetry phase of KO2 at low T with the tilted O$_{2}^{-}$ molecular axes, the band gap and the orbital ordering are driven by the combined effects of the crystal-field and the strong Coulomb correlation. We have verified that the emergence of the O 2p ferro-orbital ordering is essential to achieve the observed AFM structure for KO2

Strength matters: Tie strength as a causal driver of networks’ information benefits

Studies of social networks have often taken the existence of a social tie as a proxy for the transmission of information. However, other studies of social networks in the labor market propose that the likelihood of information transmission might depend on strength of the tie; and that tie strength is a potentially important source of the tie's value. After all, even if job seekers have social ties to those who have valuable job information, the seekers will gain little information benefit when the ties do not actually transmit the information. This paper clarifies the conditions under which social ties might provide information benefits. We use a survey vignette experiment and ask MBA students about their likelihood of relaying job information via strong ties (to friends) or weak ties (to acquaintances), holding constant the structural locations spanned by the tie and job seekers' fit with the job. The results support the claim that strength of tie has a causal effect on the chances of information transmission: potential referrers are more likely to relay job information to their friends than to acquaintances. The larger implication of these findings is that whatever benefits there might be to using weak ties to reach distant non-redundant information during job search, these benefits need to be considered against the likely fact that people connected via weak ties are less likely to actually share information about job opportunities than are people to whom the job seeker is strongly tied