Deep brain stimulation (DBS) has been successfully applied in various neurodegenerative diseases as an effective symptomatic treatment. However, its mechanisms of action within the brain network are ...still poorly understood. Many virtual DBS models analyze a subnetwork around the basal ganglia and its dynamics as a spiking network with their details validated by experimental data. However, connectomic evidence shows widespread effects of DBS affecting many different cortical and subcortical areas. From a clinical perspective, various effects of DBS besides the motoric impact have been demonstrated. The neuroinformatics platform The Virtual Brain (TVB) offers a modeling framework allowing us to virtually perform stimulation, including DBS, and forecast the outcome from a dynamic systems perspective prior to invasive surgery with DBS lead placement. For an accurate prediction of the effects of DBS, we implement a detailed spiking model of the basal ganglia, which we combine with TVB via our previously developed co-simulation environment. This multiscale co-simulation approach builds on the extensive previous literature of spiking models of the basal ganglia while simultaneously offering a whole-brain perspective on widespread effects of the stimulation going beyond the motor circuit. In the first demonstration of our model, we show that virtual DBS can move the firing rates of a Parkinson's disease patient's thalamus - basal ganglia network towards the healthy regime while, at the same time, altering the activity in distributed cortical regions with a pronounced effect in frontal regions. Thus, we provide proof of concept for virtual DBS in a co-simulation environment with TVB. The developed modeling approach has the potential to optimize DBS lead placement and configuration and forecast the success of DBS treatment for individual patients.
•Spiking basal ganglia network and mean-field cortical activity co-simulated•Simulated multiscale networks for a healthy control and Parkinson's disease patient•Thalamic activity normalizes during virtual DBS in multiscale model•Distributed altered cortical activity predominantly in frontal regions by DBS•Proof-of-concept study for multiscale co-simulations to individually tailor DBS
Achieving highly efficient phosphorescence in purely organic luminophors at room temperature remains a major challenge due to slow intersystem crossing (ISC) rates in combination with effective ...non‐radiative processes in those systems. Most room temperature phosphorescent (RTP) organic materials have O‐ or N‐lone pairs leading to low lying (n, π*) and (π, π*) excited states which accelerate kisc through El‐Sayed's rule. Herein, we report the first persistent RTP with lifetimes up to 0.5 s from simple triarylboranes which have no lone pairs. RTP is only observed in the crystalline state and in highly doped PMMA films which are indicative of aggregation induced emission (AIE). Detailed crystal structure analysis suggested that intermolecular interactions are important for efficient RTP. Furthermore, photophysical studies of the isolated molecules in a frozen glass, in combination with DFT/MRCI calculations, show that (σ, B p)→(π, B p) transitions accelerate the ISC process. This work provides a new approach for the design of RTP materials without (n, π*) transitions.
Efficient intersystem crossing (ISC) in combination with strong intermolecular interactions suppresses the nonradiative decay rate knr and leads to the first reported persistent room temperature phosphorescence (RTP) from purely organic triarylborane phosphors, which do not possess O‐ or N‐lone pairs. Transitions between local σ‐ and π‐excitation also accelerate kisc.
Derivatives of dipole transition moments between spin?orbit coupled (SOC) multireference configuration interaction wave functions have been used in conjunction with vibrational frequencies from ...density functional theories to compute vibronic S1?S0 (11B3u11Ag ) and T1?S0 (13B3u?11Ag) absorption spectra in Herzberg?Teller approximation. The experimentally known spectra are well reproduced. The calculations reveal unexpectedly small spin?orbit couplings between the 13B3u (3n?*) state and nearby optically bright 1B2u (1??*) states, thus explaining the absence of the 1b1g10 (v10a10 ) fundamental in the vibrational fine-structure of the T1?S0 transition. Adiabatically, two triplet states are found below the S1 state. The out-of-plane distorted T2 minimum results from a pseudo Jahn?Teller interaction between two 3??* states of B1u and B2u symmetry. At the D2h-symmetric S0 and S1 minimum geometries, the latter states are located well above S1. The S1 and T2 potentials intersect at geometries far away from the Franck?Condon region. This explains the apparently contradictory results that the linewidth in the higher energy regime above the T1?S0 origin suddenly broadens while no trace of a second triplet state, located energetically below the S1 origin, could be identified in phosphorescence excitation spectra of the ultracold isolated pyrazine molecule.
Heptazine derivatives are promising dopants for electroluminescent devices. Recent studies raised the question whether heptazines exhibit a small regular or an inverted singlet–triplet (IST) gap. It ...was argued that the S1 ← T1 reverse intersystem crossing (RISC) is a downhill process in IST emitters and therefore does not require thermal activation, thus enabling efficient harvesting of triplet excitons. Rate constants were not determined in these studies. Modeling the excited-state properties of heptazine proves challenging because fluorescence and intersystem crossing (ISC) are symmetry-forbidden in first order. In this work, we present a comprehensive theoretical study of the photophysics of heptazine and its derivative HAP-3MF. The calculations of electronic excitation energies and vibronic coupling matrix elements have been conducted at the density functional theory/multireference configuration interaction (DFT/MRCI) level of theory. We have employed a finite difference approach to determine nonadiabatic couplings and derivatives of spin–orbit coupling and electric dipole transition matrix elements with respect to normal coordinate displacements. Kinetic constants for fluorescence, phosphorescence, internal conversion (IC), ISC, and RISC have been computed in the framework of a static approach. Radiative S1 ↔ S0 transitions borrow intensity mainly from optically bright E′ π → π* states, while S1 ↔ T1 (R)ISC is mediated by E″ states of n → π* character. Test calculations show that IST gaps as large as those reported in the literature are counterproductive and slow down the S1 ← T1 RISC process. Using the adiabatic DFT/MRCI singlet–triplet splitting of −0.02 eV, we find vibronically enhanced ISC and RISC to be fast in the heptazine core compound. Nevertheless, its photo- and electroluminescence quantum yields are predicted to be very low because S1 → S0 IC efficiently quenches the luminescence. In contrast, fluorescence, IC, ISC, and RISC proceed at similar time scales in HAP-3MF.
New high precision measurements of the Collins and Sivers asymmetries of charged hadrons produced in deep-inelastic scattering of muons on a transversely polarised
6LiD target are presented. The data ...were taken in 2003 and 2004 with the COMPASS spectrometer using the muon beam of the CERN SPS at 160
GeV
/
c
. Both the Collins and Sivers asymmetries turn out to be compatible with zero, within the present statistical errors, which are more than a factor of 2 smaller than those of the published COMPASS results from the 2002 data. The final results from the 2002, 2003 and 2004 runs are compared with naive expectations and with existing model calculations.
We present a new measurement of the longitudinal spin asymmetry A1d and the spin-dependent structure function g1d of the deuteron in the range 1<Q2<100 GeV2 and 0.004<x<0.7. The data were obtained by ...the COMPASS experiment at CERN using a 160 GeV polarised muon beam and a large polarised 6LiD target. The results are in agreement with those from previous experiments and improve considerably the statistical accuracy in the region 0.004<x<0.03.
In this work, we report benchmark spin–orbit calculations for a representative set of electronic states including π → π*, n → π*, and π → σ* and Rydberg states of organic molecules. Auxiliary ...many-electron wave functions (AMEWs) have been generated from left and/or right eigenvectors of Casida’s non-Hermitian time-dependent density functional theory (TDDFT) equation. The newly developed Spoiler program has been used to evaluate spin–orbit matrix elements (SOMEs) from full linear response TDDFT and TDDFT calculations in Tamm–Dancoff approximation (TDA) in conjunction with the well-known B3-LYP and PBE0 hybrid functionals. The data thus obtained have been benchmarked against SOMEs from multireference configuration interaction calculations recently performed in our group. It turns out that the TDDFT SOMEs are rather insensitive with regard to the choice of eigenvectors (left, right, or mixed) as long as the AMEWs are normalized. To avoid problematic excitation energies of low-lying triplet excited states, the use of the TDA is recommended. With regard to SOMEs, a slight preference is found for the PBE0 functional.
We present a determination of the gluon polarization ΔG/G in the nucleon, based on the helicity asymmetry of quasi-real photoproduction events, Q2<1 (GeV/c)2, with a pair of large transverse-momentum ...hadrons in the final state. The data were obtained by the COMPASS experiment at CERN using a 160 GeV polarized muon beam scattered on a polarized 6LiD target. The helicity asymmetry for the selected events is 〈A∥/D〉=0.002±0.019(stat)±0.003(syst). From this value, we obtain in a leading-order QCD analysis ΔG/G=0.024±0.089(stat)±0.057(syst) at xg=0.095 and μ2≃3 (GeV/c)2.
Designing highly efficient purely organic phosphors at room temperature remains a challenge because of fast non‐radiative processes and slow intersystem crossing (ISC) rates. The majority of them ...emit only single component phosphorescence. Herein, we have prepared 3 isomers (o, m, p‐bromophenyl)‐bis(2,6‐dimethylphenyl)boranes. Among the 3 isomers (o‐, m‐ and p‐BrTAB) synthesized, the ortho‐one is the only one which shows dual phosphorescence, with a short lifetime of 0.8 ms and a long lifetime of 234 ms in the crystalline state at room temperature. Based on theoretical calculations and crystal structure analysis of o‐BrTAB, the short lifetime component is ascribed to the T1M state of the monomer which emits the higher energy phosphorescence. The long‐lived, lower energy phosphorescence emission is attributed to the T1A state of an aggregate, with multiple intermolecular interactions existing in crystalline o‐BrTAB inhibiting nonradiative decay and stabilizing the triplet states efficiently.
Bromo‐triarylborane o‐BrTAB exhibits dual phosphorescence at room temperature; a short‐lived higher energy emission originates from single molecules (T1M) whereas the long‐lived component at lower energy results from an aggregate (T1A). Under 365 nm UV light irradiation, crystalline o‐BrTAB emits bright pale blue light (fluorescence). After turning off the light, a persistent yellow afterglow remains for 2 s.
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