Scientific objectivity proves to be an essential tool for determining the fundamental content of the abstract paintings produced by Jackson Pollock in the late 1940s. Pollock dripped paint from a can ...onto vast canvases rolled out across the floor of his barn. Although this unorthodox technique has been recognized as a crucial advancement in the evolution of modern art, the precise quality and significance of the patterns created are controversial. Here we describe an analysis of Pollock's patterns which shows, first, that they are fractal, reflecting the fingerprint of nature, and, second, that the fractal dimensions increased during Pollock's career.
Quantum point contacts (QPCs) have shown promise as nanoscale spin-selective components for spintronic applications and are of fundamental interest in the study of electron many-body effects such as ...the 0.7 × 2e 2/h anomaly. We report on the dependence of the 1D Landé g-factor g* and 0.7 anomaly on electron density and confinement in QPCs with two different top-gate architectures. We obtain g* values up to 2.8 for the lowest 1D subband, significantly exceeding previous in-plane g-factor values in AlGaAs/GaAs QPCs and approaching that in InGaAs/InP QPCs. We show that g* is highly sensitive to confinement potential, particularly for the lowest 1D subband. This suggests careful management of the QPC’s confinement potential may enable the high g* desirable for spintronic applications without resorting to narrow-gap materials such as InAs or InSb. The 0.7 anomaly and zero-bias peak are also highly sensitive to confining potential, explaining the conflicting density dependencies of the 0.7 anomaly in the literature.
The out-of-plane g-factor g ⊥ * for quasi two-dimensional (2D) holes in a (100) GaAs heterostructure is studied using a variable width quantum wire. A direct measurement of the Zeeman splitting is ...performed in a magnetic field applied perpendicular to the 2D plane. We measure an out-of-plane g-factor up to g ⊥ * = 5, which is larger than previous optical studies of g ⊥ * and is approaching the long predicted but never experimentally verified out-of-plane g-factor of 7.2 for heavy holes.
We report a study of transport blockade features in a quantum dot single-electron transistor, based on an undoped AlGaAs/GaAs heterostructure. We observe suppression of transport through the ground ...state of the dot, as well as negative differential conductance at finite source-drain bias. The temperature and magnetic field dependences of these features indicate the couplings between the leads and the quantum dot states are suppressed. We attribute this to two possible mechanisms: spin effects which determine whether a particular charge transition is allowed based on the change in total spin, and the interference effects which arise from coherent tunnelling of electrons in the quantum dot.
We present resistively detected NMR measurements in induced and modulation-doped electron quantum point contacts, as well as induced hole quantum point contacts. While the magnitude of the resistance ...change and associated NMR peaks in n-type devices is in line with other recent measurements using this technique, the effect in p-type devices is too small to measure. This suggests that the hyperfine coupling between holes and nuclei in this type of device is much smaller than the electron hyperfine coupling, which could have implications in quantum information processing.
Disorder increasingly affects performance as electronic devices are reduced in size. The ionized dopants used to populate a device with electrons are particularly problematic, leading to ...unpredictable changes in the behavior of devices such as quantum dots each time they are cooled for use. We show that a quantum dot can be used as a highly sensitive probe of changes in disorder potential and that, by removing the ionized dopants and populating the dot electrostatically, its electronic properties become reproducible with high fidelity after thermal cycling to room temperature. Our work demonstrates that the disorder potential has a significant, perhaps even dominant, influence on the electron dynamics, with important implications for "ballistic" transport in quantum dots.
Nanopore sensors detect individual species passing through a nanoscale pore. This experimental paradigm suffers from long analysis times at low analyte concentration and non-specific signals in ...complex media. These limit effectiveness of nanopore sensors for quantitative analysis. Here, we address these challenges using antibody-modified magnetic nanoparticles ((anti-PSA)-MNPs) that diffuse at zero magnetic field to capture the analyte, prostate-specific antigen (PSA). The (anti-PSA)-MNPs are magnetically driven to block an array of nanopores rather than translocate through the nanopore. Specificity is obtained by modifying nanopores with anti-PSA antibodies such that PSA molecules captured by (anti-PSA)-MNPs form an immunosandwich in the nanopore. Reversing the magnetic field removes (anti-PSA)-MNPs that have not captured PSA, limiting non-specific effects. The combined features allow detecting PSA in whole blood with a 0.8 fM detection limit. Our 'magnetic nanoparticle, nanopore blockade' concept points towards a strategy to improving nanopore biosensors for quantitative analysis of various protein and nucleic acid species.
Communication in a doctor-patient relationship constitutes a crucial aspect in medicine, and its multiple dimensions encompass a wide variety of ethical issues. Communication is particularly relevant ...in oncology, because it requires continually dealing with sensitive topics in one of the most highly vulnerable situations as a human: illness and proximity to death. Sexuality is one of these topics because it constitutes an area that is frequently affected by cancer and cancer treatment, which may include causing significant distress, the reinforcement of a negative self-image, relationship conflicts and a permanent memory of having cancer. The objective of this research is to describe the perception of knowledge and communications practices used by oncology doctors with respect to sexual health in the care of their patients, as well as the barriers found when it comes to confronting the topic.
An exploratory quantitative, descriptive and cross-sectional study was carried out, in which a self-administered questionnaire was given to oncology doctors who practise in Chile. This questionnaire had 41 closed questions with answers on a Likert scale and was previously validated by being reviewed and applied to a pilot group of five professionals (one medical bioethics expert and four doctors in the field of oncology). The data were analysed with the SPSS statistical program v. 20, using descriptive statistics.
The main results show that the surveyed doctors consider sexuality to be an important part of patients' quality of life. However, this finding does not align with the practices given for including it as part of clinical care. The professionals refer as the main barriers those that are attributed to the structural functioning of the institution, giving little value to those barriers related to personal aspects or those associated with patient characteristics and/or behaviors.
The results of this study show that, despite oncology doctors seeing sexuality as an important aspect of the quality of life of their patients, they do not include the topic in clinical care. Given that one of the main barriers is obstacles relating to the institution, it is necessary to create political institutions that create the conditions for including this area as a relevant part of cancer patient care.
Two-dimensional (2D) electronic systems can exhibit dramatic drops in resistivity, rhoxx, as the temperature Tarrow right0, which has renewed debate as to whether 2D systems may have a metallic ...ground state. The metallic behaviour is only observed in low-disorder systems, where interactions between the carriers are strong. However, the strength of the metallic behaviour is not universal, with decreases in resistivity ranging from a few per cent to an order of magnitude as Tarrow right0. Here, we compare the metallic behaviour in 2D systems dominated by long- and short-range disorder. We thereby highlight the pivotal role played by the type of disorder in determining the strength of metallic behaviour in these systems. In doing so, we resolve recent confusion in the literature that has arisen from the application of interaction-based theories of metallic behaviour to 2D systems whose disorder environments are inconsistent with the assumptions made by these theories. PUBLICATION ABSTRACT
We report the observation of Kondo physics in a spin-3/2 hole quantum dot. The dot is formed close to pinch-off in a hole quantum wire defined in an undoped AlGaAs/GaAs heterostructure. We clearly ...observe two distinctive hallmarks of quantum dot Kondo physics. First, the Zeeman spin splitting of the zero-bias peak in the differential conductance is independent of the gate voltage. Second, this splitting is twice as large as the splitting for the lowest one-dimensional subband. We show that the Zeeman splitting of the zero-bias peak is highly anisotropic and attribute this to the strong spin-orbit interaction for holes in GaAs.
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