35,151 research outputs found
The Tragedy and Promise of Self-Determination
The principle of self-determination, like Janus, has two faces: negative and positive. Often understood as enabling the fracture of states into national components, the principle is better seen as facilitating the creation of multinational frameworks that foster toleration and human rights
Exact symmetries in the velocity fluctuations of a hot Brownian swimmer
Symmetries constrain dynamics. We test this fundamental physical principle,
experimentally and by molecular dynamics simulations, for a hot Janus swimmer
operating far from thermal equilibrium. Our results establish scalar and
vectorial steady-state fluctuation theorems and a thermodynamic uncertainty
relation that link the fluctuating particle current to its entropy production
at an effective temperature. A Markovian minimal model elucidates the
underlying non-equilbrium physics.Comment: 5 pages, 3 figure
On the Dynamics of Active Aging
The conceptual basis of active aging is extended with a dynamic systems model, called Janus. The Janus model accounts for the life-course dynamics of simple and more complex growth and decline functions, on the strength of three principles. The first principle of transition states that the unitary lifespan trajectory of development and aging is the product of two complementary forces, growth and senescence, which are effective from conception until death. The first principle solves the traditional problem of the age at which development ends and the process of aging starts. The second and third principles of peak capacity and peak time refer, respectively, to the impact of growth rate (peak capacity) and rate of senescence (peak time) on the life-course of dynamic systems. The validity of the Janus model is demonstrated by simulating the empirical lifespan trajectories of functional capacity, intelligence, and mortality. The Janus model contributes to the concept of active aging by underlining the dynamic limits of human nature, by stimulating effective policies for promoting active aging in the first half of life, and by emphasizing the growth potential of older people in the second half
Janus II: a new generation application-driven computer for spin-system simulations
This paper describes the architecture, the development and the implementation
of Janus II, a new generation application-driven number cruncher optimized for
Monte Carlo simulations of spin systems (mainly spin glasses). This domain of
computational physics is a recognized grand challenge of high-performance
computing: the resources necessary to study in detail theoretical models that
can make contact with experimental data are by far beyond those available using
commodity computer systems. On the other hand, several specific features of the
associated algorithms suggest that unconventional computer architectures, which
can be implemented with available electronics technologies, may lead to order
of magnitude increases in performance, reducing to acceptable values on human
scales the time needed to carry out simulation campaigns that would take
centuries on commercially available machines. Janus II is one such machine,
recently developed and commissioned, that builds upon and improves on the
successful JANUS machine, which has been used for physics since 2008 and is
still in operation today. This paper describes in detail the motivations behind
the project, the computational requirements, the architecture and the
implementation of this new machine and compares its expected performances with
those of currently available commercial systems.Comment: 28 pages, 6 figure
Spin-splitting in electric-potential-difference antiferromagnetism
The antiferromagnetic (AFM) materials are robust to external magnetic
perturbation due to missing any net magnetic moment. In general, the spin
splitting in the band structures disappears in these antiferromagnets. However,
the altermagnetism can achieve spin-split bands in collinear
symmetry-compensated antiferromagnet with special magnetic space group. Here,
we propose a new mechanism that can achieve spin splitting in two-dimensional
(2D) Janus A-type AFM materials. Since the built-in electric field caused by
Janus structure creates a layer-dependent electrostatic potential, the
electronic bands in different layers will stagger, producing the spin
splitting, which can be called electric-potential-difference antiferromagnetism
(EPD-AFM). We demonstrate that Janus monolayer is a possible
candidate to achieve the EPD-AFM by the first-principles calculations. It is
proposed that the spin splitting can be tuned in EPD-AFM by piezoelectric
effect. Our works provide a new design principle for generating spin
polarization in 2D AFM materials.Comment: 6 pages, 6 figure
JANUS: an FPGA-based System for High Performance Scientific Computing
This paper describes JANUS, a modular massively parallel and reconfigurable
FPGA-based computing system. Each JANUS module has a computational core and a
host. The computational core is a 4x4 array of FPGA-based processing elements
with nearest-neighbor data links. Processors are also directly connected to an
I/O node attached to the JANUS host, a conventional PC. JANUS is tailored for,
but not limited to, the requirements of a class of hard scientific applications
characterized by regular code structure, unconventional data manipulation
instructions and not too large data-base size. We discuss the architecture of
this configurable machine, and focus on its use on Monte Carlo simulations of
statistical mechanics. On this class of application JANUS achieves impressive
performances: in some cases one JANUS processing element outperfoms high-end
PCs by a factor ~ 1000. We also discuss the role of JANUS on other classes of
scientific applications.Comment: 11 pages, 6 figures. Improved version, largely rewritten, submitted
to Computing in Science & Engineerin
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