Fano Effect through Parallel-coupled Double Coulomb Islands

By means of the non-equilibrium Green function and equation of motion method, the electronic transport is theoretically studied through a parallel-coupled double quantum dots(DQD) in the presence of the on-dot Coulomb correlation, with an emphasis put on the quantum interference. It has been found that in the Coulomb blockage regime, the quantum interference between the bonding and antiboding DQD states or that between their Coulomb blockade counterparts may result in the Fano resonance in the conductance spectra, and the Fano peak doublet may be observed under certain non-equilibrium condition. The possibility of manipulating the Fano lineshape is predicted by tuning the dot-lead coupling and magnetic flux threading the ring connecting the dots and leads. Similar to the case without Coulomb interaction, the direction of the asymmetric tail of Fano lineshape can be flipped by the external field. Most importantly, by tuning the magnetic flux, the function of four relevant states can be interchanged, giving rise to the swap effect, which might play a key role as a qubit in the quantum computation.Comment: 7 pages, 5 figure

A functional spiking-neuron model of activity-silent working memory in humans based on calcium-mediated short-term synaptic plasticity

In this paper, we present a functional spiking-neuron model of human working memory (WM). This model combines neural firing for encoding of information with activity-silent maintenance. While it used to be widely assumed that information in WM is maintained through persistent recurrent activity, recent studies have shown that information can be maintained without persistent firing; instead, information can be stored in activity-silent states. A candidate mechanism underlying this type of storage is short-term synaptic plasticity (STSP), by which the strength of connections between neurons rapidly changes to encode new information. To demonstrate that STSP can lead to functional behavior, we integrated STSP by means of calcium-mediated synaptic facilitation in a large-scale spiking-neuron model and added a decision mechanism. The model was used to simulate a recent study that measured behavior and EEG activity of participants in three delayed-response tasks. In these tasks, one or two visual gratings had to be maintained in WM, and compared to subsequent probes. The original study demonstrated that WM contents and its priority status could be decoded from neural activity elicited by a task-irrelevant stimulus displayed during the activity-silent maintenance period. In support of our model, we show that it can perform these tasks, and that both its behavior as well as its neural representations are in agreement with the human data. We conclude that information in WM can be effectively maintained in activity-silent states by means of calcium-mediated STSP

Histopathological Features of Early Onset Indonesian Breast Cancer Pointing to Brca1/2 Germline Mutations

Background: Breast cancer under 40 years concerns a relatively small subgroup of cases that tend to display a more aggressive phenotype. Compatible with this, early age of onset has been known as one of clinical characteristic of hereditary breast cancers associated with germline BRCA1 or BRCA1 mutations. As early onset breast cancer is frequent in Indonesia, we investigated the histopathological and immunohistochemical characteristics of early onset (< 40 years) Indonesian breast cancer patients, as such features can be used to distinguish between BRCA and non-BRCA germline mutation carriers among these young women.Method: Thirty-five formalin-fixed and paraffin-embedded tissue sections of young women (mean 36 years, range 22-40 years) who underwent surgical resection at the Department of Surgery of the Sardjito Hospital Yogyakarta were examined for pathological features, estrogen and progesterone receptor status, proliferation as determined by Ki67 labeling, EGFR and CK5/6 and the presence of HER-2/neu and p53 protein. Additionally, mutation analysis for BRCA1 and BRCA2 was performed in 30 young women. The control group consisted ofcarcinomas from women above 50 years (mean 59.02, range 50-80 years).Result: Carcinomas occurring in women aged below 40 years were more often advanced stage and higher proliferating (p=0.006). Among the early onset breast cancer patients, ductal type, grade 3, ER and HER-2/neu negativity, high Ki67 index and CK5/6 and EGFR positivity were typical for BRCA1 patients. Unfortunately, there were no typical phenotypical features for BRCA2 carriers. However, grade I and lobular cases were never BRCA1/2 germline mutated.Conclusion: Early onset Indonesian breast cancer shows increased proliferation compared to late onset patients. Within the early onset group, the strongest features pointing to a sporadic cancer seem to be grade I and lobular differentiation. Features increasing the chance of a germline BRCA1/2 mutation are CK5/6 and EGFR expression, p53 accumulation and high proliferation as measured by Ki67 labeling. This is potentially useful to optimize selection of early onset breast cancer patients for BRCA1/2 mutation testing

Resonant Tunneling through Multi-Level and Double Quantum Dots

We study resonant tunneling through quantum-dot systems in the presence of strong Coulomb repulsion and coupling to the metallic leads. Motivated by recent experiments we concentrate on (i) a single dot with two energy levels and (ii) a double dot with one level in each dot. Each level is twofold spin-degenerate. Depending on the level spacing these systems are physical realizations of different Kondo-type models. Using a real-time diagrammatic formulation we evaluate the spectral density and the non-linear conductance. The latter shows a novel triple-peak resonant structure.Comment: 4 pages, ReVTeX, 4 Postscript figure

Histopathological Features of Early Onset Indonesian Breast Cancer Pointing to Brca1/2 Germline Mutations

Background: Breast cancer under 40 years concerns a relatively small subgroup of cases that tend to display a more aggressive phenotype. Compatible with this, early age of onset has been known as one of clinical characteristic of hereditary breast cancers associated with germline BRCA1 or BRCA1 mutations. As early onset breast cancer is frequent in Indonesia, we investigated the histopathological and immunohistochemical characteristics of early onset (< 40 years) Indonesian breast cancer patients, as such features can be used to distinguish between BRCA and non-BRCA germline mutation carriers among these young women.Method: Thirty-five formalin-fixed and paraffin-embedded tissue sections of young women (mean 36 years, range 22-40 years) who underwent surgical resection at the Department of Surgery of the Sardjito Hospital Yogyakarta were examined for pathological features, estrogen and progesterone receptor status, proliferation as determined by Ki67 labeling, EGFR and CK5/6 and the presence of HER-2/neu and p53 protein. Additionally, mutation analysis for BRCA1 and BRCA2 was performed in 30 young women. The control group consisted ofcarcinomas from women above 50 years (mean 59.02, range 50-80 years).Result: Carcinomas occurring in women aged below 40 years were more often advanced stage and higher proliferating (p=0.006). Among the early onset breast cancer patients, ductal type, grade 3, ER and HER-2/neu negativity, high Ki67 index and CK5/6 and EGFR positivity were typical for BRCA1 patients. Unfortunately, there were no typical phenotypical features for BRCA2 carriers. However, grade I and lobular cases were never BRCA1/2 germline mutated.Conclusion: Early onset Indonesian breast cancer shows increased proliferation compared to late onset patients. Within the early onset group, the strongest features pointing to a sporadic cancer seem to be grade I and lobular differentiation. Features increasing the chance of a germline BRCA1/2 mutation are CK5/6 and EGFR expression, p53 accumulation and high proliferation as measured by Ki67 labeling. This is potentially useful to optimize selection of early onset breast cancer patients for BRCA1/2 mutation testing.Keywords: breast cancer, early onset, histopathology, immunohistochemistry, BRCA1, BRCA

Evidence for the involvement of tyrosine-69 in the control of stereospecificity of porcine pancreatic phospholipase A2

We have studied the role of Tyr-69 of porcine pancreatic phospholipase A2 in catalysis and substrate binding, using site-directed mutagenesis. A mutant was constructed containing Phe at position 69. Kinetic characterization revealed that the Phe-69 mutant has retained enzymatic activity on monomeric and micellar substrates, and that the mutation has only minor effects on kcat and Km. This shows that Tyr-69 plays no role in the true catalytic events during substrate hydrolysis. In contrast, the mutation has a profound influence on the stereospecificity of the enzyme. Whereas the wild-type phospholipase A2 is only able to catalyse the degradation of sn-3 phospholipids, the Phe-69 mutant hydrolyses both the sn-3 isomers and, at a low (1-2%) rate, the sn-1 isomers. Despite the fact that the stereospecificity of the mutant phospholipase has been altered, Phe-69 phospholipase still requires Ca2+ ions as a cofactor and also retains its specificity for the sn-2 ester bond. Our data suggest that in porcine pancreatic phospholipase A2 the hydroxyl group of Tyr-69 serves to fix and orient the phosphate group of phospholipid monomers by hydrogen bonding. Because no such interaction can occur between the Phe-69 side-chain and the phosphate moiety of the substrate monomer, the mutant enzyme loses part of its stereospecificity but not its positional specificity

Level statistics of XXZ spin chains with a random magnetic field

The level-spacing distribution of a spin 1/2 XXZ chain is numerically studied under random magnetic field. We show explicitly how the level statistics depends on the lattice size L, the anisotropy parameter $\Delta$, and the mean amplitude of the random magnetic field h. In the energy spectrum, quantum integrability competes with nonintegrability derived from the randomness, where the XXZ interaction is modified by the parameter $\Delta$. When $\Delta \ne 0$, the level-spacing distribution mostly shows Wigner-like behavior, while when $\Delta$=0, Poisson-like behavior appears although the system is nonintegrable due to randomness. Poisson-like behavior also appears for $\Delta \ne 0$ in the large h limit. Furthermore, the level-spacing distribution depends on the lattice size L, particularly when the random field is weak.Comment: 4 pages, 3 figures, to be published in Phys. Rev.

Unexpected non-Wigner behavior in level-spacing distributions of next-nearest-neighbor coupled XXZ spin chains

The level-spacing distributions of XXZ spin chains with next-nearest-neighbor couplings are studied under periodic boundary conditions. We confirm that integrable XXZ spin chains mostly have the Poisson distribution as expected. On the contrary, the level-spacing distributions of next-nearest-neighbor coupled XXZ chains are given by non-Wigner distributions. It is against the expectations, since the models are nonintegrable.Comment: 4 pages, 4 figures, to be published in Physical Review

Suppression of level hybridization due to Coulomb interactions

We investigate an ensemble of systems formed by a ring enclosing a magnetic flux. The ring is coupled to a side stub via a tunneling junction and via Coulomb interaction. We generalize the notion of level hybridization due to the hopping, which is naturally defined only for one-particle problems, to the many-particle case, and we discuss the competition between the level hybridization and the Coulomb interaction. It is shown that strong enough Coulomb interactions can isolate the ring from the stub, thereby increasing the persistent current. Our model describes a strictly canonical system (the number of carriers is the same for all ensemble members). Nevertheless for small Coulomb interactions and a long side stub the model exhibits a persistent current typically associated with a grand canonical ensemble of rings and only if the Coulomb interactions are sufficiently strong does the model exhibit a persistent current which one expects from a canonical ensemble.Comment: 19 pages, 6 figures, uses iop style files, version as publishe