16 Search Results

Frequencydomain coherent multidimensional spectroscopy when dephasing rivals pulsewidth: Disentangling material and instrument response
Ultrafast spectroscopy is often collected in the mixed frequency/time domain, where pulse durations are similar to system dephasing times. In these experiments, expectations derived from the familiar driven and impulsive limits are not valid. This work simulates the mixeddomain fourwave mixing response of a model system to develop expectations for this more complex fieldmatter interaction. We also explore frequency and delay axes. We show that these line shapes are exquisitely sensitive to excitation pulse widths and delays. Near pulse overlap, the excitation pulses induce correlations that resemble signatures of dynamic inhomogeneity. We describe these line shapes using an intuitive picturemore »Cited by 2 
Quasilinear diffusion coefficients in a finite Larmor radius expansion for ion cyclotron heated plasmas
In this study, a reduced model of quasilinear velocity diffusion by a small Larmor radius approximation is derived to couple the Maxwell’s equations and the Fokker Planck equation selfconsistently for the ion cyclotron range of frequency waves in a tokamak. The reduced model ensures the important properties of the full model by KennelEngelmann diffusion, such as diffusion directions, wave polarizations, and Htheorem. The kinetic energy change (Wdot ) is used to derive the reduced model diffusion coefficients for the fundamental damping (n = 1) and the second harmonic damping (n = 2) to the lowest order of the finite Larmormore » 
SingleCrystal Thin Films of Cesium Lead Bromide Perovskite Epitaxially Grown on Metal Oxide Perovskite (SrTiO _{3})
Highquality metal halide perovskite single crystals have low defect densities and excellent photophysical properties, yet thin films are the most sought after material geometry for optoelectronic devices. Perovskite singlecrystal thin films (SCTFs) would be highly desirable for highperformance devices, but their growth remains challenging, particularly for inorganic metal halide perovskites. Herein, we report the facile vaporphase epitaxial growth of cesium lead bromide perovskite (CsPbBr _{3}) continuous SCTFs with controllable micrometer thickness, as well as nanoplate arrays, on traditional oxide perovskite SrTiO _{3}(100) substrates. Heteroepitaxial singlecrystal growth is enabled by the serendipitous incommensurate lattice match between these two perovskites, and overcomingmore »Cited by 3 
Complex and noncentrosymmetric stacking of layered metal dichalcogenide materials created by screw dislocations
The interesting and tunable properties of layered metal dichalcogenides heavily depend on their phase and layer stacking. Here, we show and explain how the layer stacking and physical properties of WSe _{2} are influenced by screw dislocations. A onetoone correlation of atomic force microscopy and high and lowfrequency Raman spectroscopy of many dislocated WSe _{2} nanoplates reveals variations in the number and shapes of dislocation spirals and different layer stackings that are determined by the number, rotation, and location of the dislocations. Plates with triangular dislocation spirals form noncentrosymmetric stacking that gives rise to strong secondharmonic generation and enhanced photoluminescence,more »Cited by 5 
Global Analysis of Perovskite Photophysics Reveals Importance of Geminate Pathways
Hybrid organicinorganic perovskites demonstrate desirable photophysical behaviors and promising applications from efficient photovoltaics to lasing, but the fundamental nature of excited state species is still under debate. We also collected timeresolved photoluminescence of singlecrystal nanoplates of methylammonium lead iodide perovskite (MAPbI3), with excitation over a range of fluences and repetition rates, to provide a more complete photophysical picture. A fundamentally different way of simulating the photophysics is developed that relies on unnormalized decays, global analysis over a large array of conditions, and inclusion of steadystate behavior; these details are critical to capturing observed behaviors. These additional constraints require inclusion ofmore »Cited by 7 
Fusion Energy Sciences Exascale Requirements Review. An Office of Science review sponsored jointly by Advanced Scientific Computing Research and Fusion Energy Sciences, January 2729, 2016, Gaithersburg, Maryland
The additional computing power offered by the planned exascale facilities could be transformational across the spectrum of plasma and fusion research — provided that the new architectures can be efficiently applied to our problem space. The collaboration that will be required to succeed should be viewed as an opportunity to identify and exploit crossdisciplinary synergies. To assess the opportunities and requirements as part of the development of an overall strategy for computing in the exascale era, the Exascale Requirements Review meeting of the Fusion Energy Sciences (FES) community was convened January 27–29, 2016, with participation from a broad range ofmore » 
Absolutemagnitude distributions of supernovae
The absolutemagnitude distributions of seven supernova (SN) types are presented. The data used here were primarily taken from the Asiago Supernova Catalogue, but were supplemented with additional data. We accounted for both foreground and hostgalaxy extinction. A bootstrap method is used to correct the samples for Malmquist bias. Separately, we generate volumelimited samples, restricted to events within 100 Mpc. We find that the superluminous events (M{sub B} < –21) make up only about 0.1% of all SNe in the biascorrected sample. The subluminous events (M{sub B} > –15) make up about 3%. The normal Ia distribution was the brightest withmore » 
Investigation of the validity of quasilinear theory for electron Landau damping in a tokamak using a broadband wave effect
The quasilinear diffusion coefficient assuming a constant magnetic field along the electron orbit is widely used to describe electron Landau damping of waves in a tokamak where the magnitude of the magnetic field varies on a flux surface. To understand the impact of violating the constant magnetic field assumption, we introduce the effect of a broadbandwidth wave spectrum which has been used in the past to validate quasilinear theory for the fast decorrelation process between resonances. By the reevaluation of the diffusion coefficient through the level of the phase integral for the tokamak geometry with the broadband wave effect included,more »