Electronic State Unfolding for Plane Waves: Energy Bands, Fermi Surfaces, and Spectral Functions

Present day computing facilities allow for first-principles density functional theory studies of complex physical and chemical phenomena. Often such calculations are linked to large supercells to adequately model the desired property. However, supercells are associated with small Brillouin zones in the reciprocal space, leading to folded electronic eigenstates that make the analysis and interpretation extremely challenging. Various techniques have been proposed and developed to reconstruct the electronic band structures of super cells unfolded into the reciprocal space of an ideal primitive cell. Here we propose an unfolding scheme embedded directly in the Vienna Ab initio Simulation Package (VASP) that requires modest computational resources and allows for an automatized mapping from the reciprocal space of the supercell to the primitive cell Brillouin zone. This algorithm can compute band structures, Fermi surfaces, and spectral functions by using an integrated postprocessing tool (bands4vasp). Here the method is applied to a selected variety of complex physical situations: the effect of doping on the band dispersion in the BaFe2(1-x)Ru2xAs2 superconductor, the interaction between adsorbates and polaronic states on the TiO2(110) surface, and the band splitting induced by noncollinear spin fluctuations in EuCd2As2

In Parkinson's disease on a probabilistic Go/NoGo task deep brain stimulation of the subthalamic nucleus only interferes with withholding of the most prepotent responses

The evidence on the impact of subthalamic nucleus deep brain stimulation (STN-DBS) on action restraint on Go/NoGO reaction time (RT) tasks in Parkinson's disease (PD) is inconsistent; with some studies reporting no effect and others finding that STN stimulation interferes with withholding of responses and results in more commission errors relative to STN-DBS off. We used a task in which the probability of Go stimuli varied from 100 % (simple RT task) to 80, 50 and 20 % (probabilistic Go/NoGo RT task), thus altering the prepotency of the response and the difficulty in withholding it on NoGo trials. Twenty PD patients with STN-DBS, ten unoperated PD patients and ten healthy controls participated in the study. All participants were tested twice; the order of on versus off stimulation for STN-DBS PD patients was counterbalanced. Both STN-DBS and unoperated PD patients were tested on medication. The results indicated that STN-DBS selectively decreased discriminability when the response was most prepotent (high-80 %, as compared to low Go probability trials-50 and 20 %). Movement times were faster with STN stimulation than with DBS off across different Go probability levels. There was neither an overall nor a selective effect of STN-DBS on RTs depending on the level of Go probability. Furthermore, compared to healthy controls, both STN-DBS and unoperated PD patients were more prone to making anticipatory errors; which was not influenced by STN stimulation. The results provide evidence for 'load-dependent' effects of STN stimulation on action restraint as a function of the prepotency of the Go response

Exciton fine structure splitting and linearly polarized emission in strained transition-metal dichalcogenide monolayers

We study theoretically effects of an anisotropic elastic strain on the exciton energy spectrum fine structure and optical selection rules in atom-thin crystals based on transition-metal dichalcogenides. The presence of strain breaks the chiral selection rules at the $\bm K$-points of the Brillouin zone and makes optical transitions linearly polarized. The orientation of the induced linear polarization is related to the main axes of the strain tensor. Elastic strain provides an additive contribution to the exciton fine structure splitting in agreement with experimental evidence obtained from uniaxially strained WSe$_2$ monolayer. The applied strain also induces momentum-dependent Zeeman splitting. Depending on the strain orientation and magnitude, Dirac points with a linear dispersion can be formed in the exciton energy spectrum. We provide a symmetry analysis of the strain effects and develop a microscopic theory for all relevant strain-induced contributions to the exciton fine structure Hamiltonian.Comment: 12 pages, 5 figure

The substantia nigra pars compacta and temporal processing

The basal ganglia and cerebellum are considered to play a role in timing, although their differential roles in timing remain unclear. It has been proposed that the timing of short milliseconds-range intervals involves the cerebellum, whereas longer seconds-range intervals engage the basal ganglia (Ivry, 1996). We tested this hypothesis using positron emission tomography to measure regional cerebral blood flow in eight right-handed males during estimation and reproduction of long and short intervals. Subjects performed three tasks: (1) reproduction of a short 500 ms interval, (2) reproduction of a long 2 s interval, and (3) a control simple reaction time (RT) task. We compared the two time reproduction tasks with the control RT task to investigate activity associated with temporal processing once additional cognitive, motor, or sensory processing was controlled. We found foci in the left substantia nigra and the left lateral premotor cortex to be significantly more activated in the time reproduction tasks than the control RT task. The left caudate nucleus and right cerebellum weremoreactive in the short relative to the long interval, whereas greater activation of the right putamen and right cerebellum occurred in the long rather than the short interval. These results suggest that the basal ganglia and the cerebellum are engaged by reproduction of both long and short intervals but play different roles. The fundamental role of the substantia nigra in temporal processing is discussed in relation to previous animal lesion studies and evidence for the modulating influence of dopamine on temporal processing

Push-pull thiophene chromophores for electro-optic applications: from 1D linear to beta-branched structures

We report the synthesis and characterization of a novel series of push-pull chromophores bearing 1D linear and beta-branched thiophenes as pi-conjugated spacers between a 2, 2, 4, 7-tetramethyl-1, 2, 3, 4-tetrahydroquinoline electron donor unit and dicyano- and tricyanovinylene electron acceptor groups. The effect of the introduction of beta-thiophenes on the linear and nonlinear (NLO) optical properties as well as electrochemical and thermal data is studied in detail by performing a comparative study between the branched and 1D linear systems. In addition, a parallel DFT computational study is used to evaluate structure-property relationships. The non-linear optical behavior of the molecules both in solution and in solid state as electro-optic (EO) films using a guest-host approach shows very promising performance for electro-optic applications with high molecular first hyperpolarizabilities (mu beta) of 4840 x 10(-48) esu and electro-optic coefficients r(33) reaching 650 pm V-1. One highlight is that the electro-optic films of the beta-branched chromophores are superior in terms of thermal stability in device operation as measured by a transmissive modified reflective Teng-Man method. This work provides guidelines for the design of improved electro-optic materials including beta-branched chromophores which could be useful for practical EO applications, where both enhanced beta and r(33) values together with chemical and thermal stability are necessary

Tuning spontaneous emission through waveguide cavity effects in semiconductor nanowires

The ability to tailor waveguide cavities and couple them with quantum emitters has developed a realm of nanophotonics encompassing, for example, highly efficient single photon generation or the control of giant photon nonlinearities. Opening new grounds by pushing the interaction of the waveguide cavity and integrated emitters further into the deep subwavelength regime, however, has been complicated by nonradiative losses due to the increasing importance of surface defects when decreasing cavity dimensions. Here, we show efficient suppression of nonradiative recombination for thin waveguide cavities using core-shell semiconductor nanowires. We experimentally reveal the advantages of such nanowires, which host mobile emitters, that is, free excitons, in a one-dimensional (1D) waveguide, highlighting the resulting potential for tunable, active, nanophotonic devices. In our experiment, controlling the nanowire waveguide diameter tunes the luminescence lifetime of excitons in the nanowires across 2 orders of magnitude up to 80 ns. At the smallest wire diameters, we show that this luminescence lifetime can be manipulated by engineering the dielectric environment of the nanowires. Exploiting this unique handle on the spontaneous emission of mobile emitters, we demonstrate an all-dielectric spatial control of the mobile emitters along the axis of the 1D nanowire waveguide

Signaling of Human Frizzled Receptors to the Mating Pathway in Yeast

Frizzled receptors have seven membrane-spanning helices and are considered as atypical G protein-coupled receptors (GPCRs). The mating response of the yeast Saccharomyces cerevisiae is mediated by a GPCR signaling system and this model organism has been used extensively in the past to study mammalian GPCR function. We show here that human Frizzled receptors (Fz1 and Fz2) can be properly targeted to the yeast plasma membrane, and that they stimulate the yeast mating pathway in the absence of added Wnt ligands, as evidenced by cell cycle arrest in G1 and reporter gene expression dependent on the mating pathway-activated FUS1 gene. Introducing intracellular portions of Frizzled receptors into the Ste2p backbone resulted in the generation of constitutively active receptor chimeras that retained mating factor responsiveness. Introducing intracellular portions of Ste2p into the Frizzled receptor backbone was found to strongly enhance mating pathway activation as compared to the native Frizzleds, likely by facilitating interaction with the yeast Gα protein Gpa1p. Furthermore, we show reversibility of the highly penetrant G1-phase arrests exerted by the receptor chimeras by deletion of the mating pathway effector FAR1. Our data demonstrate that Frizzled receptors can functionally replace mating factor receptors in yeast and offer an experimental system to study modulators of Frizzled receptors

Action selection and action awareness

Human actions are often classified as either internally generated, or externally specified in response to environmental cues. These two modes of action selection have distinct neural bases, but few studies investigated how the mode of action selection affects the subjective experience of action. We measured the experience of action using the subjective compression of the interval between actions and their effects, known as ‘temporal binding’. Participants performed either a left or a right key press, either in response to a specific cue, or as they freely chose. Moreover, the time of each keypress could either be explicitly cued to occur in one of two designated time intervals, or participants freely chose in which interval to act. Each action was followed by a specific tone. Participants judged the time of their actions or the time of the tone. Temporal binding was found for both internally generated and for stimulus-based actions. However, the amount of binding depended on whether or not both the choice and the timing of action were selected in the same way. Stronger binding was observed when both action choice and action timing were internally generated or externally specified, compared to conditions where the two parameters were selected by different routes. Our result suggests that temporal action–effect binding depends on how actions are selected. Binding is strongest when actions result from a single mode of selection

Statistical organelle dissection of Arabidopsis guard cells using image database LIPS

To comprehensively grasp cell biological events in plant stomatal movement, we have captured microscopic images of guard cells with various organelles markers. The 28,530 serial optical sections of 930 pairs of Arabidopsis guard cells have been released as a new image database, named Live Images of Plant Stomata (LIPS). We visualized the average organellar distributions in guard cells using probabilistic mapping and image clustering techniques. The results indicated that actin microfilaments and endoplasmic reticulum (ER) are mainly localized to the dorsal side and connection regions of guard cells. Subtractive images of open and closed stomata showed distribution changes in intracellular structures, including the ER, during stomatal movement. Time-lapse imaging showed that similar ER distribution changes occurred during stomatal opening induced by light irradiation or femtosecond laser shots on neighboring epidermal cells, indicating that our image analysis approach has identified a novel ER relocation in stomatal opening