1,009 research outputs found
Temperature-heat uncertainty relation for quantum thermometry
We investigate the resource theory for temperature estimation. We demonstrate
that it is the fluctuation of heat that fundamentally determines temperature
precision through the temperature-heat uncertainty relation. Specifically, we
find that heat is divided into trajectory heat and correlation heat, which are
associated with the heat exchange along thermometer's evolution path and the
correlation between the thermometer and the sample, respectively. Based on two
type of thermometers, we show that both of these heat terms are resources for
enhancing temperature precision. Additionally, we demonstrate that the
temperature-heat uncertainty relation is consistent with the well known
temperature-energy uncertainty relation in thermodynamics. By clearly
distinguishing the resources for enhancing estimation precision, our findings
not only explain why various quantum features are crucial for accurate
temperature sensing but also provide valuable insights for designing
ultrahigh-sensitive quantum thermometers.Comment: 6 pages, 1 figur
Improved PSO algorithm based on chaos theory and its application to design flood hydrograph
AbstractThe deficiencies of basic particle swarm optimization (bPSO) are its ubiquitous prematurity and its inability to seek the global optimal solution when optimizing complex high-dimensional functions. To overcome such deficiencies, the chaos-PSO (COSPSO) algorithm was established by introducing the chaos optimization mechanism and a global particle stagnation-disturbance strategy into bPSO. In the improved algorithm, chaotic movement was adopted for the particles' initial movement trajectories to replace the former stochastic movement, and the chaos factor was used to guide the particles' path. When the global particles were stagnant, the disturbance strategy was used to keep the particles in motion. Five benchmark optimizations were introduced to test COSPSO, and they proved that COSPSO can remarkably improve efficiency in optimizing complex functions. Finally, a case study of COSPSO in calculating design flood hydrographs demonstrated the applicability of the improved algorithm
Silicon nitride metalenses for unpolarized high-NA visible imaging
As one of nanoscale planar structures, metasurface has shown excellent
superiorities on manipulating light intensity, phase and/or polarization with
specially designed nanoposts pattern. It allows to miniature a bulky optical
lens into the chip-size metalens with wavelength-order thickness, playing an
unprecedented role in visible imaging systems (e.g. ultrawide-angle lens and
telephoto). However, a CMOS-compatible metalens has yet to be achieved in the
visible region due to the limitation on material properties such as
transmission and compatibility. Here, we experimentally demonstrate a divergent
metalens based on silicon nitride platform with large numerical aperture
(NA~0.98) and high transmission (~0.8) for unpolarized visible light,
fabricated by a 695-nm-thick hexagonal silicon nitride array with a minimum
space of 42 nm between adjacent nanoposts. Nearly diffraction-limit virtual
focus spots are achieved within the visible region. Such metalens enables to
shrink objects into a micro-scale size field of view as small as a single-mode
fiber core. Furthermore, a macroscopic metalens with 1-cm-diameter is also
realized including over half billion nanoposts, showing a potential application
of wide viewing-angle functionality. Thanks to the high-transmission and
CMOS-compatibility of silicon nitride, our findings may open a new door for the
miniaturization of optical lenses in the fields of optical fibers,
microendoscopes, smart phones, aerial cameras, beam shaping, and other
integrated on-chip devices.Comment: 16 pages, 7 figure
tert-Butyl 4-isopropyl-2-oxo-6-phenyl-3,4-dihydro-2H-pyran-3-carboxylate
In the title compound, C19H24O4, the six-membered lactone ring adopts an envelope conformation with the tert-butoxycarbonyl and isopropyl substituents in axial positions, and the phenyl group in an equatorial position. In the crystal structure, weak intermolecular C—H⋯O hydrogen bonds link the molecules into centrosymmetric dimers
A Security and Efficient Routing Scheme with Misbehavior Detection in Delay-Tolerant Networks
Due to the unique network characteristics, the security and efficient routing in DTNs are considered as two great challenges. In this paper, we design a security and efficient routing scheme, called SER, which integrates the routing decision and the attacks detection mechanisms. In SER scheme, each DTNs node locally maintains a one-dimensional vector table to record the summary information about the contact with other nodes and the trust degree of other nodes. To obtain the global status and the contact relationship among all nodes, the trusted routing table consisting of vectors of all nodes is built in each DTNs node. The method for detecting malicious nodes and selfish nodes is proposed, which exploits the global summary information to analyze the history forwarding behavior of node and judge whether it is a malicious node or selfish node. The routing decision method is proposed based on trust degree of forwarding messages between nodes, which adopts trust degree as relay node selection strategy. Simulation results show that compared with existing schemes SER scheme could detect the attacks behavior of malicious nodes and selfish nodes, at the same time, with higher delivery rate and lower average delivery delay
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