Theory of spin blockade, charge ratchet effect, and thermoelectrical behavior in serially coupled quantum-dot system

The charge transport of a serially coupled quantum dots (SCQD) connected to the metallic electrodes is theoretically investigated in the Coulomb blockade regime. A closed-form expression for the tunneling current of SCQD in the {\color{red} weak interdot hopping} limit is obtained by solving an extended two-site Hubbard model via the Green's function method. We use this expression to investigate spin current rectification, negative differential conductance, and coherent tunneling in the nonlinear response regime. The current rectification arising from the space symmetry breaking of SCQD is suppressed by increasing temperature. The calculation of SCQD is extended to the case of multiple parallel SCQDs for studying the charge ratchet effect and SCQD with multiple levels. In the linear response regime, the functionalities of spin filter and low-temperature current filter are demonstrated to coexist in this system. It is further demonstrated that two-electron spin singlet and triplet states can be readily resolved from the measurement of Seebeck coefficient rather than that of electrical conductance.Comment: 11 pages, 9 figures. Revised argument, results unchanged, added reference

Trion ground state, excited states and absorption spectrum using electron-exciton basis

We solve the Schr\"{o}dinger equation for two electrons plus one hole by writing it in the electron-exciton basis. The main advantage of this basis is to eliminate the exciton contribution from the trion energy in a natural way. The interacting electron-exciton system is treated using the recently developed composite boson many-body formalism which allows an exact handling of electron exchange. We numerically solve the resulting electron-exciton Schr\"{o}dinger equation, with the exciton levels restricted to the lowest $1s, 2s$ and $3s$ states, and we derive the trion ground state energy as a function of the electron-to-hole mass ratio. While our results are in reasonable agreement with those obtained through the best variational methods using free carrier basis, this electron-exciton basis is mostly suitable to easily reach the bound and unbound trion excited states. Through their wave functions, we here calculate the optical absorption spectrum in the presence of hot carriers for 2D quantum wells. We find large peaks located at the exciton levels, which are attributed to electron-exciton (unbound) scattering states, and small peaks identified with trion bound states.Comment: 16 pages; 15 figure

Pressure Dependence of Fragile-to-Strong Transition and a Possible Second Critical Point in Supercooled Confined Water

By confining water in nano-pores of silica glass, we can bypass the crystallization and study the pressure effect on the dynamical behavior in deeply supercooled state using neutron scattering. We observe a clear evidence of a cusp-like fragile-to-strong (F-S) dynamic transition. Here we show that the transition temperature decreases steadily with an increasing pressure, until it intersects the homogenous nucleation temperature line of bulk water at a pressure of 1600 bar. Above this pressure, it is no longer possible to discern the characteristic feature of the F-S transition. Identification of this end point with the possible second critical point is discussed.Comment: 4 pages, 3 figure

Observation of the Density Minimum in Deeply Supercooled Confined Water

Small angle neutron scattering (SANS) is used to measure the density of heavy water contained in 1-D cylindrical pores of mesoporous silica material MCM-41-S-15, with pores of diameter of 15+-1 A. In these pores the homogenous nucleation process of bulk water at 235 K does not occur and the liquid can be supercooled down to at least 160 K. The analysis of SANS data allows us to determine the absolute value of the density of D2O as a function of temperature. We observe a density minimum at 210+-5 K with a value of 1.041+-0.003 g/cm3. We show that the results are consistent with the predictions of molecular dynamics simulations of supercooled bulk water. This is the first experimental report of the existence of the density minimum in supercooled water

Patterns of Interactions in Complex Social Networks Based on Coloured Motifs Analysis

Coloured network motifs are small subgraphs that enable to discover and interpret the patterns of interaction within the complex networks. The analysis of three-nodes motifs where the colour of the node reflects its high – white node or low – black node centrality in the social network is presented in the paper. The importance of the vertices is assessed by utilizing two measures: degree prestige and degree centrality. The distribution of motifs in these two cases is compared to mine the interconnection patterns between nodes. The analysis is performed on the social network derived from email communication

Ganglionated plexi and ligament of Marshall ablation reduces atrial vulnerability and causes stellate ganglion remodeling in ambulatory dogs

Background Simultaneous activation of the stellate ganglion (SGNA), the ligament of Marshall (LOM) and the ganglionated plexi (GP) often precedes the onset of paroxysmal atrial tachyarrhythmias (PAT). Objective To test the hypothesis that ablation of the LOM and the superior left GP (SLGP) reduces atrial vulnerability and results in remodeling of the stellate ganglion. Methods Nerve activity was correlated to PAT and ventricular rate (VR) at baseline, after ablation of the LOM and SLGP, and after AF. Neuronal cell death was assessed with Tyrosine hydroxylase (TH) and terminal deoxynucleotidyl transferase dUTP nick end label (TUNEL) staining. Results There were 4±2 PAT episodes per day in controls. None were observed in the ablation group; even though SGNA and VR increased from 2.2 μV (95% confidence interval (CI); 1.2 – 3.3 μV) and 80 bpm (CI 68 – 92 bpm) at baseline to 3.0 μV (CI 2.6 – 3.4 μV, p=0.046) and 90 bpm (CI 75 – 108 bpm, p=0.026) after ablation, and to 3.1 μV (CI 1.7 – 4.5 μV, p=0.116) and 95 bpm (CI 79 – 110 bpm, p=0.075) after AF. There was an increase in TH-negative cells in the ablation group and a 19.7% (CI, 8.6 – 30.8%) TUNEL-positive staining in both the left and right SG. None were observed in the control group. Conclusion LOM and SLGP ablation caused LSG remodeling and cell death. There was reduced correlation of the VR response and PAT to SGNA. These findings support the importance of SLGP and LOM in atrial arrhythmogenesis

Antiarrhythmic effects of stimulating the left dorsal branch of the thoracic nerve in a canine model of paroxysmal atrial tachyarrhythmias

Background Stellate ganglion nerve activity (SGNA) precedes paroxysmal atrial tachyarrhythmia (PAT) episodes in dogs with intermittent high-rate left atrial (LA) pacing. The left dorsal branch of the thoracic nerve (LDTN) contains sympathetic nerves originating from the stellate ganglia. Objective The purpose of this study was to test the hypothesis that high-frequency electrical stimulation of the LDTN can cause stellate ganglia damage and suppress PAT. Methods We performed chronic LDTN stimulation in 6 dogs with and 2 dogs without intermittent rapid LA pacing while monitoring SGNA. Results LDTN stimulation reduced average SGNA from 4.36 μV (95% confidence interval [CI] 4.10–4.62 μV) at baseline to 3.22 μV (95% CI 3.04–3.40 μV) after 2 weeks (P = .028) and completely suppressed all PAT episodes in all dogs studied. Tyrosine hydroxylase staining showed large damaged regions in both stellate ganglia, with increased percentages of tyrosine hydroxylase–negative cells. The terminal deoxynucleotidyl transferase dUTP nick end labeling assay showed that 23.36% (95% CI 18.74%–27.98%) of ganglion cells in the left stellate ganglia and 11.15% (95% CI 9.34%–12.96%) ganglion cells in the right stellate ganglia were positive, indicating extensive cell death. A reduction of both SGNA and heart rate was also observed in dogs with LDTN stimulation but without high-rate LA pacing. Histological studies in the latter 2 dogs confirmed the presence of extensive stellate ganglia damage, along with a high percentage of terminal deoxynucleotidyl transferase dUTP nick end labeling–positive cells. Conclusion LDTN stimulation damages both left stellate ganglia and right stellate ganglia, reduces left SGNA, and is antiarrhythmic in this canine model of PAT

Using skin sympathetic nerve activity to estimate stellate ganglion nerve activity in dogs

BACKGROUND: Stellate ganglion nerve activity (SGNA) is important in cardiac arrhythmogenesis. However, direct recording of SGNA requires access to the thoracic cavity. Skin of upper thorax is innervated by sympathetic nerve fibers originating from the stellate ganglia and is easily accessible. OBJECTIVE: The purpose of this study was to test the hypothesis that thoracic skin nerve activity (SKNA) can be used to estimate SGNA. METHODS: We recorded SGNA and SKNAs using surface electrocardiogram leads in 5 anesthetized and 4 ambulatory dogs. Apamin injected into the right stellate ganglion abruptly increased both right SGNA and SKNA in 5 anesthetized dogs. We integrated nerve activities and averaged heart rate in each 1-minure window over 10 minutes. We implanted a radiotransmitter to record left SGNA in 4 ambulatory dogs (2 normal, 1 with myocardial infarction, 1 with intermittent rapid atrial pacing). After 2 weeks of recovery, we simultaneously recorded the SKNA and left SGNA continuously for 30 minutes when the dogs were ambulatory. RESULTS: There was a positive correlation [average r = 0.877, 95% confidence interval (CI) 0.732-1.000, P <.05 for each dog] between integrated skin nerve activity (iSKNA) and SGNA (iSGNA) and between iSKNA and heart rate (average r = 0.837, 95% CI 0.752-0.923, P <.05). Similar to that found in the anesthetized dogs, there was a positive correlation (average r = 0.746, 95% CI 0.527-0.964, P <.05) between iSKNA and iSGNA and between iSKNA and heart rate (average r = 0.706, 95% CI 0.484-0.927, P <.05). CONCLUSION: SKNAs can be used to estimate SGNA in dogs

Long-term intermittent high-amplitude subcutaneous nerve stimulation reduces sympathetic tone in ambulatory dogs

BACKGROUND: Reducing sympathetic efferent outflow from the stellate ganglia (SG) may be antiarrhythmic. OBJECTIVE: The purpose of this study was to test the hypothesis that chronic thoracic subcutaneous nerve stimulation (ScNS) could reduce SG nerve activity (SGNA) and control paroxysmal atrial tachycardia (PAT). METHODS: Thoracic ScNS was performed in 8 dogs while SGNA, vagal nerve activity (VNA), and subcutaneous nerve activity (ScNA) were monitored. An additional 3 dogs were used for sham stimulation as controls. RESULTS: Xinshu ScNS and left lateral thoracic nerve ScNS reduced heart rate (HR). Xinshu ScNS at 3.5 mA for 2 weeks reduced mean average SGNA from 5.32 μV (95% confidence interval [CI] 3.89-6.75) at baseline to 3.24 μV (95% CI 2.16-4.31; P = .015) and mean HR from 89 bpm (95% CI 80-98) at baseline to 83 bpm (95% CI 76-90; P = .007). Bilateral SG showed regions of decreased tyrosine hydroxylase staining with increased terminal deoxynucleotidyl transferase dUTP nick-end labeling-positive nuclei in 18.47% (95% CI 9.68-46.62) of all ganglion cells, indicating cell death. Spontaneous PAT episodes were reduced from 9.83 per day (95% CI 5.77-13.89) in controls to 3.00 per day (95% CI 0.11-5.89) after ScNS (P = .027). Left lateral thoracic nerve ScNS also led to significant bilateral SG neuronal death and significantly reduced average SGNA and HR in dogs. CONCLUSION: ScNS at 2 different sites in the thorax led to SG cell death, reduced SGNA, and suppressed PAT in ambulatory dogs