Many-body Green's function approach to attosecond nonlinear X-ray spectroscopy

Closed expressions are derived for resonant multidimensional X-ray spectroscopy using the quasiparticle nonlinear exciton representation of optical response. This formalism is applied to predict coherent four wave mixing signals which probe single and two core-hole states. Nonlinear X-ray signals are compactly expressed in terms of one- and two- particle Green's functions which can be obtained from the solution of Hedin-like equations at the $GW$ level.Comment: 10 pages and 3 figures (To appear in Physical Review B

Excitation Dynamics and Relaxation in a Molecular Heterodimer

The exciton dynamics in a molecular heterodimer is studied as a function of differences in excitation and reorganization energies, asymmetry in transition dipole moments and excited state lifetimes. The heterodimer is composed of two molecules modeled as two-level systems coupled by the resonance interaction. The system-bath coupling is taken into account as a modulating factor of the energy gap of the molecular excitation, while the relaxation to the ground state is treated phenomenologically. Comparison of the description of the excitation dynamics modeled using either the Redfield equations (secular and full forms) or the Hierarchical quantum master equation (HQME) is demonstrated and discussed. Possible role of the dimer as an excitation quenching center in photosynthesis self-regulation is discussed. It is concluded that the system-bath interaction rather than the excitonic effect determines the excitation quenching ability of such a dimer

Disseminated enterogenous cells at the cervicomedullary junction causing communicating hydrocephalus

The authors present a unique case of a patient with communicating hydrocephalus and repeated ventriculoperitoneal shunt obstructions resulting from mucin-secreting enterogenous cell deposits at the cervicomedullary junction. Pathological examinations revealed that these cellular deposits lacked characteristic cystic architecture and the patient had no history of previous cyst with dissemination. Because of the repeated shunt obstructions and inability to surgically resect the lesion in its entirety, the authors elected radiation therapy to the cervicomedullary junction, encompassing the radiological abnormality. As of this writing, the patient has remained at neurological baseline and has not required further shunt revisions for obstruction.</jats:p