3,941 research outputs found
Symmetry Classes in Graphene Quantum Dots: Universal Spectral Statistics, Weak Localization, and Conductance Fluctuations
We study the symmetry classes of graphene quantum dots, both open and closed,
through the conductance and energy level statistics. For abrupt termination of
the lattice, these properties are well described by the standard orthogonal and
unitary ensembles. However, for smooth mass confinement, special time-reversal
symmetries associated with the sublattice and valley degrees of freedom are
critical: they lead to block diagonal Hamiltonians and scattering matrices with
blocks belonging to the unitary symmetry class even at zero magnetic field.
While the effect of this structure is clearly seen in the conductance of open
dots, it is suppressed in the spectral statistics of closed dots, because the
intervalley scattering time is shorter than the time required to resolve a
level spacing in the closed systems but longer than the escape time of the open
systems.Comment: 4 pages, 4 figures, RevTex, submitted to Phys. Rev. Let
Understanding young people's transitions in university halls through space and time
This article contributes to the theoretical discussion about young people's transitions through space and time. Space and time are complex overarching concepts that have creative potential in deepening understanding of transition. The focus of this research is young people's experiences of communal living in university halls. It is argued that particular space-time concepts draw attention to different facets of experience and in combination deepen the understanding of young people's individual and collective transitions. The focus of the article is the uses of the space-time concepts 'routine', 'representation', 'rhythm' and 'ritual' to research young people's experiences. The article draws on research findings from two studies in the North of England. © 2010 SAGE Publications
How do proteins search for their specific sites on coiled or globular DNA
It is known since the early days of molecular biology that proteins locate
their specific targets on DNA up to two orders of magnitude faster than the
Smoluchowski 3D diffusion rate. It was the idea due to Delbruck that they are
non-specifically adsorbed on DNA, and sliding along DNA provides for the faster
1D search. Surprisingly, the role of DNA conformation was never considered in
this context. In this article, we explicitly address the relative role of 3D
diffusion and 1D sliding along coiled or globular DNA and the possibility of
correlated re-adsorbtion of desorbed proteins. We have identified a wealth of
new different scaling regimes. We also found the maximal possible acceleration
of the reaction due to sliding, we found that the maximum on the
rate-versus-ionic strength curve is asymmetric, and that sliding can lead not
only to acceleration, but in some regimes to dramatic deceleration of the
reaction.Comment: 16 pages, 5 figure
Reputation Agent: Prompting Fair Reviews in Gig Markets
Our study presents a new tool, Reputation Agent, to promote fairer reviews
from requesters (employers or customers) on gig markets. Unfair reviews,
created when requesters consider factors outside of a worker's control, are
known to plague gig workers and can result in lost job opportunities and even
termination from the marketplace. Our tool leverages machine learning to
implement an intelligent interface that: (1) uses deep learning to
automatically detect when an individual has included unfair factors into her
review (factors outside the worker's control per the policies of the market);
and (2) prompts the individual to reconsider her review if she has incorporated
unfair factors. To study the effectiveness of Reputation Agent, we conducted a
controlled experiment over different gig markets. Our experiment illustrates
that across markets, Reputation Agent, in contrast with traditional approaches,
motivates requesters to review gig workers' performance more fairly. We discuss
how tools that bring more transparency to employers about the policies of a gig
market can help build empathy thus resulting in reasoned discussions around
potential injustices towards workers generated by these interfaces. Our vision
is that with tools that promote truth and transparency we can bring fairer
treatment to gig workers.Comment: 12 pages, 5 figures, The Web Conference 2020, ACM WWW 202
Occupying wide open spaces? Late Pleistocene hunterâgatherer activities in the Eastern Levant
With a specific focus on eastern Jordan, the Epipalaeolithic Foragers in Azraq Project explores changing hunter-gatherer strategies, behaviours and adaptations to this vast area throughout the Late Pleistocene. In particular, we examine how lifeways here (may have) differed from surrounding areas and what circumstances drew human and animal populations to the region. Integrating multiple material cultural and environmental datasets, we explore some of the strategies of these eastern Jordanian groups that resulted in changes in settlement, subsistence and interaction and, in some areas, the occupation of substantial aggregation sites. Five years of excavation at the aggregation site of Kharaneh IV suggest some very intriguing technological and social on-site activities, as well as adaptations to a dynamic landscape unlike that of today. Here we discuss particular aspects of the Kharaneh IV material record within the context of ongoing palaeoenvironmental reconstructions and place these findings in the wider spatial and temporal narratives of the Azraq Basin
Status of the LHC Superconducting Cable Mass Production
Six contracts have been placed with industrial companies for the production of 1200 tons of the superconducting (SC) cables needed for the main dipoles and quadrupoles of the Large Hadron Collider (LHC). In addition, two contracts have been placed for the supply of 470 tons of NbTi and 26 tons of Nb sheets. The main characteristic of the specification is that it is functional. This means that the physical, mechanical and electrical properties of strands and cables are specified without defining the manufacturing processes. Facilities for the high precision measurements of the wire and cable properties have been implemented at CERN, such as strand and cable critical current, copper to superconductor ratio, interstrand resistance, magnetisation, RRR at 4.2 K and 1.9 K. The production has started showing that the highly demanding specifications can be fulfilled. This paper reviews the organisation of the contracts, the test facilities installed at CERN, the various types of measurements and the results of the main physical properties obtained on the first batches. The status of the deliveries is presented
The solvation and dissociation of 4-benzylaniline hydrochloride in chlorobenzene
A reaction scheme is proposed to account for the liberation of 4-benzylaniline from 4-benzylaniline hydrochloride, using chlorobenzene as a solvent at a temperature of 373 K. Two operational regimes are explored: âclosedâ reaction conditions correspond to the retention of evolved hydrogen chloride gas within the reaction medium, whereas an âopenâ system permits gaseous hydrogen chloride to be released from the reaction medium. The solution phase chemistry is analyzed by 1H NMR spectroscopy. Complete liberation of solvated 4-benzylaniline from solid 4-benzylaniline hydrochloride is possible under âopenâ conditions, with the entropically favored conversion of solvated hydrogen chloride to the gaseous phase thought to be the thermodynamic driver that effectively controls a series of interconnecting equilibria. A kinetic model is proposed to account for the observations of the open system
Heterogeneous Diffusion in Highly Supercooled Liquids
The diffusivity of tagged particles is demonstrated to be very heterogeneous
on time scales comparable to or shorter than the relaxation time
( the stress relaxation time) in a highly supercooled
liquid via 3D molecular dynamics simulation. The particle motions in the
relatively active regions dominantly contribute to the mean square
displacement, giving rise to a diffusion constant systematically larger than
the Einstein-Stokes value. The van Hove self-correlation function is
shown to have a long distance tail which can be scaled in terms of
for t \ls 3\tau_{\alpha}. Its presence indicates heterogeneous diffusion in
the active regions. However, the diffusion process eventually becomes
homogeneous on time scales longer than the life time of the heterogeneity
structure ().Comment: 4 pages, 5 figure
Rutherford cables with anisotropic transverse resistance
Putting a resistive core into the center of a Rutherford cable increases resistance between strands in the crossover direction, which greatly reduces the coupling currents, even when the resistance to adjacent turns remains small. This allows one to improve stability by soldering strands together or using porous metal, without incurring a penalty of increased coupling. We describe our manufacturing methods and an experimental measurement of coupling
Diacetylene polymerization on a bulk insulator surface
Richter A, Haapasilta V, Venturini C, et al. Diacetylene polymerization on a bulk insulator surface. Physical Chemistry Chemical Physics. 2017;19(23):15172-15176.Molecular electronics has great potential to surpass known limitations in conventional silicon-based technologies. The development of molecular electronics devices requires reliable strategies for connecting functional molecules by wire-like structures. To this end, diacetylene polymerization has been discussed as a very promising approach for contacting single molecules with a conductive polymer chain. A major challenge for future device fabrication is transferring this method to bulk insulator surfaces, which are mandatory to decouple the electronic structure of the functional molecules from the support surface. Here, we provide experimental evidence for diacetylene polymerization of 3,30-(1,3-butadiyne-1,4-diyl) bisbenzoic acid precursors on the (10.4) surface of calcite, a bulk insulator with a band gap of around 6 eV. When deposited on the surface held at room temperature, ordered islands with a (1 x 3) superstructure are observed using dynamic atomic force microscopy. A distinct change is revealed upon heating the substrate to 485 K. After heating, molecular stripes with a characteristic inner structure are formed that excellently match the expected diacetylene polymer chains in appearance and repeat distance. The corresponding density functional theory computations reveal molecular-level bonding patterns of both the (1 x 3) superstructure and the formed striped structure, confirming the assignment of on-surface diacetylene polymerization. Transferring the concept of using diacetylene polymerization for creating conductive connections to bulk insulator surfaces paves the way towards application-relevant systems for future molecular electronic devices
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