THERMODYNAMIC PROPERTIES OF SILVER-CONTAINING COMPOUNDS OF THE Ag–Fe–Sn–S SYSTEM OBTAINED BY LOW-TEMPERATURE SOLID-STATE SYNTHESIS

The existence of the AgFeS2 and Ag2FeS2 compounds in the equilibrium concentration space of the Ag–Fe–S system was established by the EMF method. Investigations were performed in the electrochemical cells (ECCs) of the type (−) С | Ag | SЕ | R(Ag+) | PЕ | С (+), where C is the inert electrode (graphite), Ag is the negative (left) electrode, SE is the solid electrolyte, PE is the positive (right) electrode, R(Ag+) is the region of Ag+ diffusion into PE. Ag2GeS3 glass was used as the solid-state electrolyte with purely Ag+ ionic conductivity. The SnS2–FeS2–Ag2FeS2 (A) phase region of the Ag–Fe–Sn–S system is formed with the participation of three-component compounds. The cross-sections AgFeS2–Ag2FeSnS4, AgFeS2–Ag2FeSn3S8, and AgFeS2–SnS2 carry out the division of (A). Spatial position of the two-phases FeS2–AgFeS2, AgFeS2–Ag2FeS2 and three-phases AgFeS2–Ag2FeSn3S8–SnS2, AgFeS2–Ag2FeSnS4–Ag2FeSn3S8 regions of (A) regarding the point of silver was used to write the equations of the overall potential-forming reactions. Reactions were realized in the positive electrodes of ECCs. PE at the stage of the cell preparation is a well-mixed composition of finely ground (particle size ~5 μm) of the compounds Ag2S, FeS, FeS2 and Ag2S, FeS, FeS2, SnS2 in two- and three-phases regions of (A), respectively. The ratios of compounds in PE of ECCs were determined from the equations of the overall potential-forming reactions in respective phase regions. The decomposition of the metastable set of binary compounds and the synthesis of the equilibrium set of phases were carried out in the nanoscale region of the PE of ECC in contact with SE, i.e. in the R(Ag+) region. The Ag+ ions displaced from the left electrode to the right one for thermodynamic reasons act as nucleation centers for the equilibrium compounds. The process of forming the equilibrium set of phases in the R(Ag+) region for the particle size of the metastable phase mixture ~5 μm and Т=580 K took less than 72 h. The linear dependencies of EMF vs T of ECCs with PE of two- and three-phases regions were established in the ranges of (455–519) K and (450–514) K, respectively. Based on these dependencies, the standard thermodynamic quantities of the AgFeS2, Ag2FeS2, Ag2FeSnS4, and Ag2FeSn3S8 compounds were experimentally determined for the first time. The reliability of the established equilibrium sets of phases that provide the potential-forming reactions in ECCs was confirmed by the coincidence of the calculated and literature values of the Gibbs energy of the Ag2FeSnS4 and Ag2FeSn3S8 compounds.

Electronic transport induced by doping on the electrodes in molecular devices

The electronic transport properties of molecular device based on photochromic diarylethene with carbon nanotube electrode are investigated by density functional theory and non-equilibrium Green’s function. The devices with open and closed configurations show a switching effect. It is found that doping of different amounts of nitrogen atoms on left electrodes results in different electronic transport properties. In addition, we discuss the observed oscillation of current in the devices induced by doping using transmission eigenstates and transmission spectra of the device. The local density of states of the device is calculated to analyze the observed rectifying behavior. The results suggest that doping of nitrogen atoms on the left electrode can be considered as a factor to modulate the electronic transport properties of molecular device.

Speech changes induced by deep brain stimulation of the subthalamic nucleus in Parkinson disease: involvement of the dentatorubrothalamic tract

OBJECTIVEPatients with Parkinson disease (PD) who undergo subthalamic nucleus (STN) deep brain stimulation (DBS) often develop a deterioration in speech performance, but there is no clear consensus on the specific effects seen or the mechanism involved and little description of the impact of DBS on conversational speech. Furthermore, there has been no fiber tract connectivity analysis to identify the structures potentially modulated by DBS to cause such deficits. The main objective of this study was to quantify spontaneous speech performance and identify potential involvement of the dentatorubrothalamic tract (DRTt) in patients who underwent STN DBS, because this tract has been implicated in speech deterioration.METHODSSpontaneous speech samples were obtained with STN DBS in both on and off modes in 35 patients with PD and assessed across multiple domains. Diffusion tensor imaging tractography seeded from the therapeutic DBS contacts was performed to identify the fiber tracts involved and, specifically, the DRTt. The position of active electrode contacts was assessed relative to that of the STN.RESULTSFifteen patients with akinetic-rigid (AR) PD and 20 with tremor-dominant (TD) PD subtypes were identified. In the AR-PD subgroup of patients, in whom there was DRTt involvement, 71% demonstrated much better overall speech and largely improved or unchanged fluency in the DBS-off condition. In patients with TD PD with DRTt involvement, 50% demonstrated better overall speech in the off condition, and equivocal results regarding improved or worsened fluency were found. When there was minimal DRTt involvement, 75% of patients with AR PD had better overall speech in the DBS-on condition and better or minimal fluency changes. Similarly, 83% of patients with TD PD with minimal DRTt involvement had better or minimal overall speech and fluency changes in the on condition. More medially placed left electrode contacts were associated with more DRTt involvement in 77% of patients (10 of 13).CONCLUSIONSTo the authors' knowledge, this is the first study to have investigated a specific fiber tract involved in STN DBS in different subtypes of PD relative to its impact on spontaneous speech. At optimal therapeutic programming of STN DBS, overall spontaneous speech and fluency were affected more negatively in patients with AR PD than in those with TD PD when there was DRTt involvement. After fiber tract analysis and modeling, it was found that medially positioned left electrode contacts more often involved fibers of the DRTt. If possible, avoidance of the DRTt by using active electrode contacts that are positioned less medially, specifically in patients with AR PD, might result in less speech deterioration.