Particle-hole symmetry protects spin-valley blockade in graphene quantum dots.

Particle-hole symmetry plays an important role in the characterization of topological phases in solid-state systems1. It is found, for example, in free-fermion systems at half filling and it is closely related to the notion of antiparticles in relativistic field theories2. In the low-energy limit, graphene is a prime example of a gapless particle-hole symmetric system described by an effective Dirac equation3,4 in which topological phases can be understood by studying ways to open a gap by preserving (or breaking) symmetries5,6. An important example is the intrinsic Kane-Mele spin-orbit gap of graphene, which leads to a lifting of the spin-valley degeneracy and renders graphene a topological insulator in a quantum spin Hall phase7 while preserving particle-hole symmetry. Here we show that bilayer graphene allows the realization of electron-hole double quantum dots that exhibit near-perfect particle-hole symmetry, in which transport occurs via the creation and annihilation of single electron-hole pairs with opposite quantum numbers. Moreover, we show that particle-hole symmetric spin and valley textures lead to a protected single-particle spin-valley blockade. The latter will allow robust spin-to-charge and valley-to-charge conversion, which are essential for the operation of spin and valley qubits.

[Lesions of the triceps tendon : Diagnostics, management, treatment]. / Läsionen der Trizepssehne : Diagnostik, Management, Therapie.

The triceps brachii muscle is the main extender of the elbow joint. Triceps tendon rupture or tearing presents a rare injury pattern in general. Distal tendon ruptures occur most commonly in the area of the insertion of the olecranon. Fractures of the radial head are reported as the most common concomitant injury. In many cases, pre-existing degenerative damage predisposes for tendon injury. These include local steroid injections, anabolic steroid abuse, renal insufficiency requiring dialysis, hyperparathyroidism, lupus erythematosus and Marfan's syndrome. However, the most frequent trauma mechanism is a direct fall onto the extended forearm or a blow to the elbow. Beside clinical examination and sonography, magnetic resonance imaging is the diagnostic gold standard. The treatment of triceps tendon injuries includes conservative as well as operative approaches, whereby the indications for surgical treatment must be generously considered depending on the patient's age, functional demands of the patient, involvement of the dominant extremity as well as on the extent of the tendon rupture.

Probing Two-Electron Multiplets in Bilayer Graphene Quantum Dots.

We report on finite bias spectroscopy measurements of the two-electron spectrum in a gate defined bilayer graphene (BLG) quantum dot for varying magnetic fields. The spin and valley degree of freedom in BLG give rise to multiplets of six orbital symmetric and ten orbital antisymmetric states. We find that orbital symmetric states are lower in energy and separated by ≈ 0.4-0.8 meV from orbital antisymmetric states. The symmetric multiplet exhibits an additional energy splitting of its six states of ≈ 0.15-0.5 meV due to lattice scale interactions. The experimental observations are supported by theoretical calculations, which allow to determine that intervalley scattering and "current-current" interaction constants are of the same magnitude in BLG.

Electron-Hole Crossover in Gate-Controlled Bilayer Graphene Quantum Dots.

Electron and hole Bloch states in bilayer graphene exhibit topological orbital magnetic moments with opposite signs, which allows for tunable valley-polarization in an out-of-plane magnetic field. This property makes electron and hole quantum dots (QDs) in bilayer graphene interesting for valley and spin-valley qubits. Here, we show measurements of the electron-hole crossover in a bilayer graphene QD, demonstrating opposite signs of the magnetic moments associated with the Berry curvature. Using three layers of top gates, we independently control the tunneling barriers while tuning the occupation from the few-hole regime to the few-electron regime, crossing the displacement-field-controlled band gap. The band gap is around 25 meV, while the charging energies of the electron and hole dots are between 3 and 5 meV. The extracted valley g-factor is around 17 and leads to opposite valley polarization for electrons and holes at moderate B-fields. Our measurements agree well with tight-binding calculations for our device.

[Rupture of the distal biceps tendon]. / Rupturen der distalen Bizepssehne.

With an incidence of 3% of all biceps tendon injuries, rupture of the distal biceps tendon is a rare injury but can be associated with significant functional impairment of the elbow. In case of a complete rupture, the diagnosis can be made clinically with a pronounced power deficit, in particular for supination of the forearm. In cases of unclear symptoms magnetic resonance imaging should be included. Regarding the therapeutic approach, there is general consensus in the current literature that surgical treatment with anatomical reconstruction of the tendon footprint is superior to the conservative approach. Various surgical techniques with good biomechanical and clinical results are currently available but no clear superiority of a single technique has so far been demonstrated.

Graphene-based charge sensors.

We discuss graphene nanoribbon-based charge sensors and focus on their functionality in the presence of external magnetic fields and high frequency pulses applied to a nearby gate electrode. The charge detectors work well with in-plane magnetic fields of up to 7 T and pulse frequencies of up to 20 MHz. By analyzing the step height in the charge detector's current at individual charging events in a nearby quantum dot, we determine the ideal operation conditions with respect to the applied charge detector bias. Average charge sensitivities of 1.3 × 10(-3)e Hz(-1/2) can be achieved. Additionally, we investigate the back action of the charge detector current on the quantum transport through a nearby quantum dot. By varying the charge detector bias from 0 to 4.5 mV, we can increase the Coulomb peak currents measured at the quantum dot by a factor of around 400. Furthermore, we can completely lift the Coulomb blockade in the quantum dot.

Fabrication of coupled graphene-nanotube quantum devices.

We report on the fabrication and characterization of all-carbon hybrid quantum devices based on graphene and single-walled carbon nanotubes. We discuss both carbon nanotube quantum dot devices with graphene charge detectors and nanotube quantum dots with graphene leads. The devices are fabricated by chemical vapor deposition growth of carbon nanotubes and subsequent structuring of mechanically exfoliated graphene. We study the detection of individual charging events in the carbon nanotube quantum dot by a nearby graphene nanoribbon and show that they lead to changes of up to 20% of the conductance maxima in the graphene nanoribbon, acting as a well performing charge detector. Moreover, we discuss an electrically coupled graphene-nanotube junction, which exhibits a tunneling barrier with tunneling rates in the low GHz regime. This allows us to observe Coulomb blockade on a carbon nanotube quantum dot with graphene source and drain leads.

Coherent charge oscillations in a bilayer graphene double quantum dot.

The coherent dynamics of a quantum mechanical two-level system passing through an anti-crossing of two energy levels can give rise to Landau-Zener-Stückelberg-Majorana (LZSM) interference. LZSM interference spectroscopy has proven to be a fruitful tool to investigate charge noise and charge decoherence in semiconductor quantum dots (QDs). Recently, bilayer graphene has developed as a promising platform to host highly tunable QDs potentially useful for hosting spin and valley qubits. So far, in this system no coherent oscillations have been observed and little is known about charge noise in this material. Here, we report coherent charge oscillations and [Formula: see text] charge decoherence times in a bilayer graphene double QD. The charge decoherence times are measured independently using LZSM interference and photon assisted tunneling. Both techniques yield [Formula: see text] average values in the range of 400-500 ps. The observation of charge coherence allows to study the origin and spectral distribution of charge noise in future experiments.

Electronic excited states in bilayer graphene double quantum dots.

We report tunneling spectroscopy experiments on a bilayer graphene double quantum dot device that can be tuned by all-graphene lateral gates. The diameter of the two quantum dots are around 50 nm and the constrictions acting as tunneling barriers are 30 nm in width. The double quantum dot features additional energies on the order of 20 meV. Charge stability diagrams allow us to study the tunable interdot coupling energy as well as the spectrum of the electronic excited states on a number of individual triple points over a large energy range. The obtained constant level spacing of 1.75 meV over a wide energy range is in good agreement with the expected single-particle energy spacing in bilayer graphene quantum dots. Finally, we investigate the evolution of the electronic excited states in a parallel magnetic field.

Spin relaxation in a single-electron graphene quantum dot.

The relaxation time of a single-electron spin is an important parameter for solid-state spin qubits, as it directly limits the lifetime of the encoded information. Thanks to the low spin-orbit interaction and low hyperfine coupling, graphene and bilayer graphene (BLG) have long been considered promising platforms for spin qubits. Only recently, it has become possible to control single-electrons in BLG quantum dots (QDs) and to understand their spin-valley texture, while the relaxation dynamics have remained mostly unexplored. Here, we report spin relaxation times (T1) of single-electron states in BLG QDs. Using pulsed-gate spectroscopy, we extract relaxation times exceeding 200 µs at a magnetic field of 1.9 T. The T1 values show a strong dependence on the spin splitting, promising even longer T1 at lower magnetic fields, where our measurements are limited by the signal-to-noise ratio. The relaxation times are more than two orders of magnitude larger than those previously reported for carbon-based QDs, suggesting that graphene is a potentially promising host material for scalable spin qubits.

Spin-valley coupling in single-electron bilayer graphene quantum dots.

Understanding how the electron spin is coupled to orbital degrees of freedom, such as a valley degree of freedom in solid-state systems, is central to applications in spin-based electronics and quantum computation. Recent developments in the preparation of electrostatically-confined quantum dots in gapped bilayer graphene (BLG) enable to study the low-energy single-electron spectra in BLG quantum dots, which is crucial for potential spin and spin-valley qubit operations. Here, we present the observation of the spin-valley coupling in bilayer graphene quantum dots in the single-electron regime. By making use of highly-tunable double quantum dot devices we achieve an energy resolution allowing us to resolve the lifting of the fourfold spin and valley degeneracy by a Kane-Mele type spin-orbit coupling of ≈ 60 µeV. Furthermore, we find an upper limit of a potentially disorder-induced mixing of the [Formula: see text] and [Formula: see text] states below 20 µeV.

[Obstructive pulmonary diseases and pulmonary hypertension]. / Obstruktive Lungenerkrankungen und pulmonale Hypertonie.

Pulmonary hypertension is a frequent complication of chronic obstructive pulmonary disease. Especially in patients with concurrent sleep apnoe syndrome (so called "overlap syndrome"), the risk for pulmonary hypertension is high. Pathophysiologically, both toxic effects (cigarette smoke) and alveolar hypoventilation can induce dysfunction of the pulmonary endothelium. Genetic factors and cytokines/growth factors released by inflammatory cells may induce remodeling of the pulmonary vessels. Pulmonary hypertension results, which is initially reversible, but gradually worsens over time. At present, therapeutic options include long term oxygen in addition to the treatment of the underlying disease. A subgroup of patients may profit of a specific therapy with sildenafil and other new substances. However, studies that define these subgroups need to be performed.

Specific immune recognition of pancreatic carcinoma by patient-derived CD4 and CD8 T cells and its improvement by interferon-gamma.

Pancreatic carcinoma is a very aggressive disease and little is known about its immunobiology. We here describe the presence in pancreatic cancer patients of spontaneously induced functional CD4 and CD8 memory/effector T cells reactive to autologous tumor cells or to the pancreatic cancer associated antigen, MUC-1. Such specific cells were present in the bone marrow or peripheral blood of most of the 23 tested patients. Low dose stimulation of primary cultures of pancreatic cancer cells with 500 IU/ml IFN-gamma for 72 h enhanced HLA-I expression and induced the de novo expression of HLA-II molecules. This led to a much better immune recognition by autologous HLA-I restricted and purified CD8 T cells and allowed tumor cell recognition by HLA-II restricted purified CD4 T-helper cells. Thus, interferon-gamma appears to be a useful adjuvant cytokine to enhance the immunogenicity of a patients' tumor cells and their recognition by tumor reactive immune cells.

A proton-translocating H+-ATPase is involved in C6 glial pH regulation.

Glial cells extrude acid equivalents to maintain pHi. Although four mechanisms have been described so far, pHi-control under physiological conditions is still not sufficiently explained. We therefore investigated whether a H+-translocating ATPase is involved in glial pHi homeostasis using an established glial cell line (C6 glioma). In the absence of bicarbonate, the inhibition of H+-ATPases by NEM led to a pHi decrease. The application of a more specific inhibitor (NBD-Cl) showed that the H+-ATPase involved is of the vacuolar type. Inhibition went along with delayed cell swelling. Together with the fact that glial acidification was far more pronounced in Na+-free media, this may serve as evidence for a secondary activation of Na+/H+-exchange once an activation setpoint is reached, which in turn causes secondary swelling from Na+-uptake. Stimulation of Na+/H+-exchange by PMA can increase the setpoint. pHi-recovery after an acid load was blocked by the inhibition of v-type H+-ATPase, if pHi did not reach 6.6 during the acid load. The inhibition of Na+/H+-exchange by amiloride inhibited recovery only if acidification was below the threshold. Finally, in bicarbonate-free media a v-type H+-ATPase contributes to pH-regulation in glial cells, especially during pH-homeostasis at physiological conditions, while Na+/H+-exchange gains significance during severe acid loads.

Decreased somal size of deep layer 3 pyramidal neurons in the prefrontal cortex of subjects with schizophrenia.

BACKGROUND: Schizophrenia is associated with deficits in working memory, a cognitive function that depends on the connections of the prefrontal cortex (PFC) with the thalamus and other cortical regions. Pyramidal neurons in PFC deep layer 3 play a central role in both thalamocortical and corticocortical circuitry. Given that somal size tends to be associated with both the dendritic and axonal architecture of a neuron, abnormalities in these circuits in schizophrenia may be associated with a change in the somal size of deep layer 3 pyramidal neurons. METHODS: We used design-based stereology to estimate the somal volume of pyramidal neurons in deep layer 3 of PFC area 9 in 28 subjects with schizophrenia, each of whom was matched to 1 normal comparison subject for sex, age, and postmortem interval. RESULTS: The geometric mean of the somal volume estimates in the subjects with schizophrenia was significantly (P =.02) decreased by 9.2%. This decrease was associated with a shift in the distribution of somal volumes toward smaller sizes. Neither antipsychotic medication treatment history nor duration of illness was associated with somal size. CONCLUSIONS: These findings independently replicate previous reports of decreased somal size in the PFC in schizophrenia. The reduction in size of deep layer 3 pyramidal neurons is consistent with abnormalities in thalamocortical and corticocortical circuitry, suggesting that disruption of these circuits may contribute to cognitive abnormalities in schizophrenia.

Effect of disinfectants on microbial ecology in model distribution systems.

This research was conducted to assess the impact of various disinfectants on bacterial water quality within model distribution systems (i.e. annular reactors). After colonization with non-disinfected water, annular reactors were treated with relatively low doses of chlorine (0.4 mg/l), chlorine dioxide (0.15 mg/l), or chloramines (0.9 mg/l). Under the tested conditions, bacterial inactivation varied as a function of disinfectant type (ranking by efficiency per mg of oxidant: ClO2 > Cl2 > ClNH2) and sample type (bulk water vs. biofilm). Depending on the disinfectant, the log inactivation of suspended and attached bacteria were 0.7-1.2 and 0.5-1.0, respectively. The characterization of microbial communities in drinking water can be performed using biochemical and/or molecular methods. In this study, biochemical tests were used, showing that pseudomonad and pseudomonad-like bacteria, as in other studies, were the most predominant micro-organisms (e.g. Pseudomonas fluorescens, Brevundimonas vescularis). The ratio Gram-positive to Gram-negative organisms was 1 to 3. No drastic differences were observed between the non-treated and disinfected pipes. Based on the bacteriological data presented in these experiments, chlorine dioxide represents an alternative to chlorine for certain distribution systems.

Association of breakpoint 14q23 with uterine leiomyoma.

A chromosomal study of short-term cultured tumor cells from a benign uterine leiomyoma showed a clonal insertion, dir ins(14;6)(q23;p23p25) as a unique change. This finding supports the hypothesis of a specific association of the breakpoint 14q23 with uterine leiomyoma.

Chromosomes in Ewing's sarcoma. I. An evaluation of 85 cases of remarkable consistency of t(11;22)(q24;q12).

Since our initial reports on chromosomal studies in eight Ewing's sarcomas (ES), we have carried out similar investigations on 23 additional ES specimens following short-term culture of tumor cells (16 cases), and established in vitro cell lines (three cases) and on xenografted tumors in nude mice (four cases). We demonstrated the presence of the reciprocal t(11;22)(q24;q12) in every case except one that exhibited a complex t(11;22;14)(q24;q12;q11). On the basis of results from these additional 23 cases, we confirm the consistency of the t(11;22)(q24;q12) in ES. Moreover, we reviewed 54 ES cases reported by other investigators; when added to our 31 cases, this brings the total number to 85 unrelated cases of ES available for an evaluation of the frequency of involvement of bands 11q24 and 22q12 in translocations in ES. The standard t(11;22)(q24;q12) proved to be a remarkably consistent event, present in 83% of the cases. Five percent of the cases exhibited complex translocations involving a third chromosome in addition to chromosomes #11 and #22. In 4% of the cases variant translocations involved 22q12 but with a chromosome(s) other than #11. The breakpoint on chromosome 22q12 appears to be the most consistently observed event in 92% of the cases, whereas, the breakpoint at chromosome 11q24 was observed in 88% of the cases.

Inhibition of lactate export by quercetin acidifies rat glial cells in vitro.

The relationship between glial lactate release and glial intracellular pH (pHi) regulation is studied using C6 glioma cells and rat astrocytes in vitro, and the lactate transport inhibitors quercetin and alpha-cyano-4-hydroxycinnamate (CHC). pHi is measured using 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF). The results show that lactate release is mediated partly by a specific lactate transport system inhibitable by quercetin (50 microM), but not by CHC (5 mM). Inhibition by quercetin results in a significant 3-4-fold increase of intracellular lactate and a decrease of intracellular pH to 6.9. A participation of quercetin-inhibitable lactate transport in glial pHi-regulation is suggested by the observation that pHi-homeostasis after acidification by diffusion of undissociated lactic acid into the cell is inhibited by quercetin. The existence of a system controlling lactate release in glial cells may also reflect a function of astrocytes to supply neurons with lactate.