Direct Observation of a Fractional Charge

We performed measurements of Quantum Shot Noise in order to determine the quasiparticle charge in the Fractional Quantum Hall regime. The noise is generated by a current flow through a partially transmitting Quantum Point Contact in a 2DEG. The noise is directly proportional to the charge of the quasiparticles, thus allowing direct determination of the charge. We measured Quantum Shot Noise at a filling factor of 1/3 and found that the charge is e/3; as predicted by Laughlin.Comment: 3 pages, PostScript, 4 figures. Submitted to Natur

The Evolution of Quasiparticle Charge in the Fractional Quantum Hall Regime

The charge of quasiparticles in a fractional quantum Hall (FQH) liquid, tunneling through a partly reflecting constriction with transmission t, was determined via shot noise measurements. In the nu=1/3 FQH state, a charge smoothly evolving from e*=e/3 for t=1 to e*=e for t<<1 was determined, agreeing with chiral Luttinger liquid theory. In the nu=2/5 FQH state the quasiparticle charge evolves smoothly from e*=e/5 at t=1 to a maximum charge less than e*=e/3 at t<<1. Thus it appears that quasiparticles with an approximate charge e/5 pass a barrier they see as almost opaque.Comment: 4 pages, Correct figure 3 and caption include

Fractal-like hierarchical organization of bone begins at the nanoscale

INTRODUCTION: The components of bone assemble hierarchically to provide stiffness and toughness. Deciphering the specific organization and relationship between bone’s principal components—mineral and collagen—requires answers to three main questions: whether the association of the mineral phase with collagen follows an intrafibrillar or extrafibrillar pattern, whether the morphology of the mineral building blocks is needle- or platelet-shaped, and how the mineral phase maintains continuity across an extensive network of cross-linked collagen fibrils. To address these questions, a nanoscale level of three-dimensional (3D) structural characterization is essential and has now been performed. RATIONALE: Because bone has multiple levels of 3D structural hierarchy, 2D imaging methods that do not detail the structural context of a sample are prone to interpretation bias. Site-specific focused ion beam preparation of lamellar bone with known orientation of the analyzed sample regions allowed us to obtain imaging data by 2D high-resolution transmission electron microscopy (HRTEM) and to identify individual crystal orientations. We studied higher-level bone mineral organization within the extracellular matrix by means of scanning TEM (STEM) tomography imaging and 3D reconstruction, as well as electron diffraction to determine crystal morphology and orientation patterns. Tomographic data allowed 3D visualization of the mineral phase as individual crystallites and/or aggregates that were correlated with atomic-resolution TEM images and corresponding diffraction patterns. Integration of STEM tomography with HRTEM and crystallographic data resulted in a model of 3D mineral morphology and its association with the organic matrix. RESULTS: To visualize and characterize the crystallites within the extracellular matrix, we recorded imaging data of the bone mineral in two orthogonal projections with respect to the arrays of mineralized collagen fibrils. Three motifs of mineral organization were observed: “filamentous” (longitudinal or in-plane) and “lacy” (out-of-plane) motifs, which have been reported previously, and a third “rosette” motif comprising hexagonal crystals. Tomographic reconstructions showed that these three motifs were projections of the same 3D assembly. Our data revealed that needle-shaped, curved nanocrystals merge laterally to form platelets, which further organize into stacks of roughly parallel platelets separated by gaps of approximately 2 nanometers. These stacks of platelets, single platelets, and single acicular crystals coalesce into larger polycrystalline aggregates exceeding the lateral dimensions of the collagen fibrils, and the aggregates span adjacent fibrils as continuous, cross-fibrillar mineralization. CONCLUSION: Our findings can be described by a model of mineral and collagen assembly in which the mineral organization is hierarchical at the nanoscale. First, the data reveal that mineral particles are neither exclusively needle- nor platelet-shaped, but indeed are a combination of both, because curved acicular elements merge laterally to form slightly twisted plates. This can only be detected when the organic extracellular matrix is preserved in the sample. Second, the mineral particles are neither exclusively intrafibrillar nor extrafibrillar, but rather form a continuous cross-fibrillar phase where curved and merging crystals splay beyond the typical dimensions of a single collagen fibril. Third, in the organization of the mineral phase of bone, a helical pattern can be identified. This 3D observation, integrated with previous studies of bone hierarchy and structure, illustrates that bone (as a material, as a tissue, and as an organ) follows a fractal-like organization that is self-affine. The assembly of bone components into nested, helix-like patterns helps to explain the paradoxical combination of enhanced stiffness and toughness of bone and results in an expansion of the previously known hierarchical structure of bone to at least 12 levels

What is novel in quantum transport for mesoscopics?

The understanding of mesoscopic transport has now attained an ultimate simplicity. Indeed, orthodox quantum kinetics would seem to say little about mesoscopics that has not been revealed - nearly effortlessly - by more popular means. Such is far from the case, however. The fact that kinetic theory remains very much in charge is best appreciated through the physics of a quantum point contact. While discretization of its conductance is viewed as the exclusive result of coherent, single-electron-wave transmission, this does not begin to address the paramount feature of all metallic conduction: dissipation. A perfect quantum point contact still has finite resistance, so its ballistic carriers must dissipate the energy gained from the applied field. How do they manage that? The key is in standard many-body quantum theory, and its conservation principles.Comment: 10 pp, 3 figs. Invited talk at 50th Golden Jubilee DAE Symposium, BARC, Mumbai, 200

Regulating Access to Adult Content (with Privacy Preservation)

In the physical world we have well-established mechanisms for keeping children out of adult-only areas. In the virtual world this is generally replaced by self declaration. Some service providers resort to using heavy-weight identification mechanisms, judging adulthood as a side effect thereof. Collection of identification data arguably constitutes an unwarranted privacy invasion in this context, if carried out merely to perform adulthood estimation. This paper presents a mechanism that exploits the adult's more extensive exposure to public media, relying on the likelihood that they will be able to recall details if cued by a carefully chosen picture. We conducted an online study to gauge the viability of this scheme. With our prototype we were able to predict that the user was a child 99% of the time. Unfortunately the scheme also misclassified too many adults. We discuss our results and suggest directions for future research

Molecular Forces Governing the Biological Function of Per-Arnt-Sim-B (PAS-B) Domains: A Comparative Computational Study

\ua9 2021 by the authors.Per-Arnt-Sim (PAS) domains are evolutionarily-conserved regions found in proteins in all living systems, involved in transcriptional regulation and the response to hypoxic and xenobiotic stress. Despite having low primary sequence similarity, they show an impressively high structural conservation. Nonetheless, understanding the underlying mechanisms that drive the biological function of the PAS domains remains elusive. In this work, we used molecular dynamics simulations and bioinformatics tools in order the investigate the molecular characteristics that govern the intrinsic dynamics of five PAS-B domains (human AhR receptor, NCOA1, HIF1α, and HIF2α transcription factors, and Drosophila Suzukii (D. Suzukii) juvenile hormone receptor JHR). First, we investigated the effects of different length of N and C terminal regions of the AhR PAS-B domain, showing that truncation of those segments directly affects structural stability and aggregation propensity of the domain. Secondly, using the recently annotated PAS-B located in the methoprene-tolerant protein/juvenile hormone receptor (JHR) from D. Suzukii, we have shown that the mutation of the highly conserved “gatekeeper” tyrosine to phenylalanine (Y322F) does not affect the stability of the domain. Finally, we investigated possible redox-regulation of the AhR PAS-B domain by focusing on the cysteinome residues within PAS-B domains. The cysteines in AhR PAS-B are directly regulating the dynamics of the small molecule ligand-gating loop (residues 305 to 326). In conclusion, we comprehensibly described several molecular features governing the behaviour of PAS-B domains in solution, which may lead to a better understanding of the forces driving their biological functions

Ring diagrams and electroweak phase transition in a magnetic field

Electroweak phase transition in a magnetic field is investigated within the one-loop and ring diagram contributions to the effective potential in the minimal Standard Model. All fundamental fermions and bosons are included with their actual values of masses and the Higgs boson mass is considered in the range $75 GeV \leq m_H \leq 115 GeV$. The effective potential is real at sufficiently high temperature. The important role of fermions and $W$-bosons in symmetry behaviour is observed. It is found that the phase transition for the field strengths $10^{23} - 10^{24}$G is of first order but the baryogenesis condition is not satisfied. The comparison with the hypermagnetic field case is done.Comment: 16 pages, Latex, changed for a mistake in the numerical par

An Electronic Mach-Zehnder Interferometer

Double-slit electron interferometers, fabricated in high mobility two-dimensional electron gas (2DEG), proved to be very powerful tools in studying coherent wave-like phenomena in mesoscopic systems. However, they suffer from small fringe visibility due to the many channels in each slit and poor sensitivity to small currents due to their open geometry. Moreover, the interferometers do not function in a high magnetic field, namely, in the quantum Hall effect (QHE) regime, since it destroys the symmetry between left and right slits. Here, we report on the fabrication and operation of a novel, single channel, two-path electron interferometer that functions in a high magnetic field. It is the first electronic analog of the well-known optical Mach-Zehnder (MZ) interferometer. Based on single edge state and closed geometry transport in the QHE regime the interferometer is highly sensitive and exhibits very high visibility (62%). However, the interference pattern decays precipitously with increasing electron temperature or energy. While we do not understand the reason for the dephasing we show, via shot noise measurement, that it is not a decoherence process that results from inelastic scattering events.Comment: to appear in Natur

Theory of suppressed shot-noise at ν=2/(2p+χ)\nu=2/(2p+\chi)

We study the edge states of fractional quantum Hall liquid at bulk filling factor $\nu=2/(2p+\chi)$ with $p$ being an even integer and $\chi=\pm 1$. We describe the transition from a conductance plateau $G=\nu G_0=\nu e^2/h$ to another plateau $G=G_0/(p+\chi)$ in terms of chiral Tomonaga-Luttinger liquid theory. It is found that the fractional charge $q$ which appears in the classical shot-noise formula $S_{I}=2q$ is $q=e/(2p+\chi)$ on the conductance plateau at $G=\nu G_0$ whereas on the plateau at $G=G_0/(p+\chi)$ it is given by $q=e/(p+\chi)$. For $p=2$ and $\chi=-1$ an alternative hierarchy constructions is also discussed to explain the suppressed shot-noise experiment at bulk filling factor $\nu=2/3$.Comment: Typos in Eqs. (5-7) correcte