Resonant tunneling through ultrasmall quantum dots: zero-bias anomalies, magnetic field dependence, and boson-assisted transport

We study resonant tunneling through a single-level quantum dot in the presence of strong Coulomb repulsion beyond the perturbative regime. The level is either spin-degenerate or can be split by a magnetic field. We, furthermore, discuss the influence of a bosonic environment. Using a real-time diagrammatic formulation we calculate transition rates, the spectral density and the nonlinear $I-V$ characteristic. The spectral density shows a multiplet of Kondo peaks split by the transport voltage and the boson frequencies, and shifted by the magnetic field. This leads to zero-bias anomalies in the differential conductance, which agree well with recent experimental results for the electron transport through single-charge traps. Furthermore, we predict that the sign of the zero-bias anomaly depends on the level position relative to the Fermi level of the leads.Comment: 27 pages, latex, 21 figures, submitted to Phys. Rev.

ac Josephson effect in the resonant tunneling through mesoscopic superconducting junctions

We investigate ac Josephson effect in the resonant tunneling through mesoscopic superconducting junctions. In the presence of microwave irradiation, we show that the trajectory of multiple Andreev reflections can be closed by emitting or absorbing photons. Consequently, photon-assisted Andreev states are formed and play the role of carrying supercurrent. On the Shapiro steps, dc component appears when the resonant level is near a series of positions with spacing of half of the microwave frequency. Analytical result is derived in the limit of infinite superconducting gap, based on which new features of ac Josephson effect are revealed.Comment: 11 pages, 3 figure

Non-linear response of a Kondo system: Perturbation approach to the time dependent Anderson impurity model

Nonlinear tunneling current through a quantum dot (an Anderson impurity system) subject to both constant and alternating electric fields is studied in the Kondo regime. A systematic diagram technique is developed for perturbation study of the current in physical systems out of equilibrium governed by time - dependent Hamiltonians of the Anderson and the Kondo models. The ensuing calculations prove to be too complicated for the Anderson model, and hence, a mapping on an effective Kondo problem is called for. This is achieved by constructing a time - dependent version of the Schrieffer - Wolff transformation. Perturbation expansion of the current is then carried out up to third order in the Kondo coupling J yielding a set of remarkably simple analytical expressions for the current. The zero - bias anomaly of the direct current differential conductance is shown to be suppressed by the alternating field while side peaks develop at finite source - drain voltage. Both the direct component and the first harmonics of the time - dependent response are equally enhanced due to the Kondo effect, while amplitudes of higher harmonics are shown to be relatively small. A zero alternating bias anomaly is found in the alternating current differential conductance, that is, it peaks around zero alternating bias. This peak is suppressed by the constant bias. No side peaks show up in the differential alternating - conductance but their counterpart is found in the derivative of the alternating current with respect to the direct bias. The results pertaining to nonlinear response are shown to be valid also below the Kondo temperature.Comment: 55 latex pages 11 ps figure

Kondo effect in coupled quantum dots: a Non-crossing approximation study

The out-of-equilibrium transport properties of a double quantum dot system in the Kondo regime are studied theoretically by means of a two-impurity Anderson Hamiltonian with inter-impurity hopping. The Hamiltonian, formulated in slave-boson language, is solved by means of a generalization of the non-crossing approximation (NCA) to the present problem. We provide benchmark calculations of the predictions of the NCA for the linear and nonlinear transport properties of coupled quantum dots in the Kondo regime. We give a series of predictions that can be observed experimentally in linear and nonlinear transport measurements through coupled quantum dots. Importantly, it is demonstrated that measurements of the differential conductance ${\cal G}=dI/dV$, for the appropriate values of voltages and inter-dot tunneling couplings, can give a direct observation of the coherent superposition between the many-body Kondo states of each dot. This coherence can be also detected in the linear transport through the system: the curve linear conductance vs temperature is non-monotonic, with a maximum at a temperature $T^*$ characterizing quantum coherence between both Kondo states.Comment: 20 pages, 17 figure

The anterior temporal lobes are critically involved in acquiring new conceptual knowledge:evidence for impaired feature integration in semantic dementia

AbstractRecent evidence from multiple neuroscience techniques indicates that regions within the anterior temporal lobes (ATLs) are a critical node in the neural network for representing conceptual knowledge, yet their function remains elusive. The hub-and-spoke model holds that ATL regions act as a transmodal conceptual hub, distilling the various sensory-motor features of objects and words into integrated, coherent conceptual representations. Single-cell recordings in monkeys suggest that the ATLs are critically involved in visual associative learning; however, investigations of this region in humans have focused on existing knowledge rather than learning. We studied acquisition of new concepts in semantic dementia patients, who have cortical damage centred on the ventrolateral aspects of the ATLs. Patients learned to assign abstract visual stimuli to two categories. The categories conformed to a family resemblance structure in which no individual stimulus features were fully diagnostic; thus the task required participants to form representations that integrate multiple features into a single concept. Patients were unable to do this, instead responding only on the basis of individual features. The study reveals that integrating disparate sources of information into novel coherent concepts is a critical computational function of the ATLs. This explains the central role of this region in conceptual representation and the catastrophic breakdown of concepts in semantic dementia

Profile of micronucleus frequencies and DNA damage in different species of fish in a eutrophic tropical lake

Lake Paranoá is a tropical reservoir for the City of Brasilia, which became eutrophic due to inadequate sewage treatment associated with intensive population growth. At present, two wastewater treatment plants are capable of processing up to 95% of the domestic sewage, thereby successfully reducing eutrophization. We evaluated both genotoxic and cytotoxic parameters in several fish species (Geophagus brasiliensis, Cichla temensis, Hoplias malabaricus, Astyanax bimaculatus lacustres, Oreochromis niloticus, Cyprinus carpio and Steindachnerina insculpita) by using the micronucleus (MN) test, the comet assay and nuclear abnormality assessment in peripheral erythrocytes. The highest frequencies of MN were found in Cichla temensis and Hoplias malabaricus, which were statistically significant when compared to the other species. However, Steindachnerina insculpita (a detritivorous and lake-floor feeder species) showed the highest index of DNA damage in the comet assay, followed by C. temensis (piscivorous). Nuclear abnormalities, such as binucleated, blebbed, lobed and notched cells, were used as evidence of cytotoxicity. Oreochromis niloticus followed by Hoplias malaricus, ominivorous/detritivotous and piscivorous species, respectively, presented the highest frequency of nuclear abnormalities, especially notched cells, while the herbivorous Astyanax bimaculatus lacustres showed the lowest frequency compared to the other species studied. Thus, for biomonitoring aquatic genotoxins under field conditions, the food web should also be considered

Surveillance for pancreatic cancer in high-risk individuals

Background: Surveillance of individuals at high risk of pancreatic ductal adenocarcinoma (PDAC) and its precursors might lead to better outcomes. The aim of this study was to determine the prevalence and outcomes of PDAC and high-risk neoplastic precursor lesions among such patients participating in surveillance programmes. Methods: A multicentre study was conducted through the International CAncer of the Pancreas Screening (CAPS) Consortium Registry to identify high-risk individuals who had undergone pancreatic resection or progressed to advanced PDAC while under surveillance. High-risk neoplastic precursor lesions were defined as: pancreatic intraepithelial neoplasia (PanIN) 3, intraductal papillary mucinous neoplasia (IPMN) with high-grade dysplasia, and pancreatic neuroendocrine tumours at least 2 cm in diameter. Results: Of 76 high-risk individuals identified in 11 surveillance programmes, 71 had undergone surgery and five had been diagnosed with inoperable PDAC. Of the 71 patients who underwent resection, 32 (45 per cent) had PDAC or a high-risk precursor (19 PDAC, 4 main-duct IPMN, 4 branch-duct IPMN, 5 PanIN-3); the other 39 patients had lesions thought to be associated with a lower risk of neoplastic progression. Age at least 65 years, female sex, carriage of a gene mutation and location of a lesion in the head/uncinate region were associated with high-risk precursor lesions or PDAC. The survival of high-risk individuals with low-risk neoplastic lesions did not differ from that in those with high-risk precursor lesions. Survival was worse among patients with PDAC. There was no surgery-related mortality. Conclusion: A high proportion of high-risk individuals who had surgical resection for screening- or surveillance-detected pancreatic lesions had a high-risk neoplastic precursor lesion or PDAC

Bipolar I and bipolar II subtypes in older age: Results from the Global Aging and Geriatric Experiments in Bipolar Disorder (GAGE-BD) project

Objectives: The distinction between bipolar I disorder (BD-I) and bipolar II disorder (BD-II) has been a topic of long-lasting debate. This study examined differences between BD-I and BD-II in a large, global sample of OABD, focusing on general functioning, cognition and somatic burden as these domains are often affected in OABD. Methods: Cross-sectional analyses were conducted with data from the Global Aging and Geriatric Experiments in Bipolar Disorder (GAGE-BD) database. The sample included 963 participants aged ≥50 years (714 BD-I, 249 BD-II). Sociodemographic and clinical factors were compared between BD subtypes including adjustment for study cohort. Multivariable analyses were conducted with generalized linear mixed models (GLMMs) and estimated associations between BD subtype and (1) general functioning (GAF), (2) cognitive performance (g-score) and (3) somatic burden, with study cohort as random intercept. Results: After adjustment for study cohort, BD-II patients more often had a late onset ≥50 years (p = 0.008) and more current severe depression (p = 0.041). BD-I patients were more likely to have a history of psychiatric hospitalization (p < 0.001) and current use of anti-psychotics (p = 0.003). Multivariable analyses showed that BD subtype was not related to GAF, cognitive g-score or somatic burden. Conclusion: BD-I and BD-II patients did not differ in terms of general functioning, cognitive impairment or somatic burden. Some clinical differences were observed between the groups, which could be the consequence of diagnostic definitions. The distinction between BD-I and BD-II is not the best way to subtype OABD patients. Future research should investigate other disease specifiers in this population

ARIA 2016: Care pathways implementing emerging technologies for predictive medicine in rhinitis and asthma across the life cycle

The Allergic Rhinitis and its Impact on Asthma (ARIA) initiative commenced during a World Health Organization workshop in 1999. The initial goals were (1) to propose a new allergic rhinitis classification, (2) to promote the concept of multi-morbidity in asthma a