Bootstrap approximation for the exchange-correlation kernel of time-dependent density functional theory

A new parameter-free approximation for the exchange-correlation kernel $f_{\rm xc}$ of time-dependent density functional theory is proposed. This kernel is expressed as an algorithm in which the exact Dyson equation for the response as well as a further approximate condition are solved together self-consistently leading to a simple parameter-free kernel. We apply this to the calculation of optical spectra for various small bandgap (Ge, Si, GaAs, AlN, TiO$_2$, SiC), large bandgap (C, LiF, Ar, Ne) and magnetic (NiO) insulators. The calculated spectra are in very good agreement with experiment for this diverse set of materials, highlighting the universal applicability of the new kernel.Comment: 4 figures 5 page

Ab initio many-body calculation of excitons in solid Ne and Ar

Absorption spectra, exciton energy levels and wave functions for solid Ne and Ar have been calculated from first principles using many-body techniques. Electronic band structures of Ne and Ar were calculated using the GW approximation. Exciton states were calculated by diagonalizing an exciton Hamiltonian derived from the particle-hole Green function, whose equation of motion is the Bethe-Salpeter equation. Singlet and triplet exciton series up to n=5 for Ne and n=3 for Ar were obtained. Binding energies and longitudinal-transverse splittings of n=1 excitons are in excellent agreement with experiment. Plots of correlated electron-hole wave functions show that the electron-hole complex is delocalised over roughly 7 a.u. in solid Ar.Comment: 6 page

Spatio-temporal variability and principal components of the particle number size distribution in an urban atmosphere

A correct description of fine (diameter <1 μm) and ultrafine (<0.1 μm) aerosol particles in urban areas is of interest for particle exposure assessment but also basic atmospheric research. We examined the spatio-temporal variability of atmospheric aerosol particles (size range 3–800 nm) using concurrent number size distribution measurements at a maximum of eight observation sites in and around Leipzig, a city in Central Europe. Two main experiments were conducted with different time span and number of observation sites (2 years at 3 sites; 1 month at 8 sites). A general observation was that the particle number size distribution varied in time and space in a complex fashion as a result of interaction between local and far-range sources, and the meteorological conditions. To identify statistically independent factors in the urban aerosol, different runs of principal component (PC) analysis were conducted encompassing aerosol, gas phase, and meteorological parameters from the multiple sites. Several of the resulting PCs, outstanding with respect to their temporal persistence and spatial coverage, could be associated with aerosol particle modes: a first accumulation mode ("droplet mode", 300–800 nm), considered to be the result of liquid phase processes and far-range transport; a second accumulation mode (centered around diameters 90–250 nm), considered to result from primary emissions as well as aging through condensation and coagulation; an Aitken mode (30–200 nm) linked to urban traffic emissions in addition to an urban and a rural Aitken mode; a nucleation mode (5–20 nm) linked to urban traffic emissions; nucleation modes (3–20 nm) linked to photochemically induced particle formation; an aged nucleation mode (10–50 nm). Additional PCs represented only local sources at a single site, or infrequent phenomena. In summary, the analysis of size distributions of high time and size resolution yielded a surprising wealth of statistical aerosol components occurring in the urban atmosphere over one single city. A paradigm on the behaviour of sub-μm urban aerosol particles is proposed, with recommendations how to efficiently monitor individual sub-fractions across an entire city

Treating treatment-resistant patients with panic disorder and agoraphobia: A randomized controlled switching trial

Background: Nonresponsiveness to therapy is generally acknowledged, but only a few studies have tested switching to psychotherapy. This study is one of the first to examine the malleability of treatment-resistant patients using acceptance and commitment therapy (ACT). Methods: This was a randomized controlled trial that included 43 patients diagnosed with primary panic disorder and/or agoraphobia (PD/A) with prior unsuccessful state-of-the-art treatment (mean number of previous sessions = 42.2). Patients were treated with an ACT manual administered by novice therapists and followed up for 6 months. They were randomized to immediate treatment (n = 33) or a 4-week waiting list (n = 10) with delayed treatment (n = 8). Treatment consisted of eight sessions, implemented twice weekly over 4 weeks. Primary outcomes were measured with the Panic and Agoraphobia Scale (PAS), the Clinical Global Impression (CGI), and the Mobility Inventory (MI). Results: At post-treatment, patients who received ACT reported significantly more improvements on the PAS and CGI (d = 0.72 and 0.89, respectively) than those who were on the waiting list, while improvement on the MI (d = 0.50) was nearly significant. Secondary outcomes were consistent with ACT theory. Follow-up assessments indicated a stable and continued improvement after treatment. The dropout rate was low (9%). Conclusions: Despite a clinically challenging sample and brief treatment administered by novice therapists, patients who received ACT reported significantly greater changes in functioning and symptomatology than those on the waiting list, with medium-to-large effect sizes that were maintained for at least 6 months. These proof-of-principle data suggest that ACT is a viable treatment option for treatment-resistant PD/A patients. Further work on switching to psychotherapy for nonresponders is clearly needed. © 2015 S. Karger AG, Basel

Computer simulation of crystallization kinetics with non-Poisson distributed nuclei

The influence of non-uniform distribution of nuclei on crystallization kinetics of amorphous materials is investigated. This case cannot be described by the well-known Johnson-Mehl-Avrami (JMA) equation, which is only valid under the assumption of a spatially homogeneous nucleation probability. The results of computer simulations of crystallization kinetics with nuclei distributed according to a cluster and a hardcore distribution are compared with JMA kinetics. The effects of the different distributions on the so-called Avrami exponent $n$ are shown. Furthermore, we calculate the small-angle scattering curves of the simulated structures which can be used to distinguish experimentally between the three nucleation models under consideration.Comment: 14 pages including 7 postscript figures, uses epsf.sty and ioplppt.st