13,000 research outputs found
Anomalous Meissner effect in pnictide superconductors
The Meissner effect has been studied in Ba(Fe0.926Co0.074)2As2 and
Ba0.6K0.4Fe2As2 single crystals and compared to well known, type-II
superconductors LuNi2B2C and V3Si. Whereas flux penetration is mostly
determined by the bulk pinning (and, perhaps, surface barrier) resulting in a
large negative magnetization, the flux expulsion upon cooling in a magnetic
field is very small, which could also be due to pinning and/or surface barrier
effects. However, in stark contrast with the expected behavior, the amount of
the expelled flux increases almost linearly with the applied magnetic field, at
least up to our maximum field of 5.5 T, which far exceeds the upper limit for
the surface barrier. One interpretation of the observed behavior is that there
is a field-driven suppression of magnetic pair-breaking
ITO-Free Transparent Organic Solar Cell with Distributed Bragg Reflector for Solar Harvesting Windows
We demonstrated an indium tin oxide (ITO)-free, highly transparent organic solar cell with the potential to be integrated into window panes for energy harvesting purposes. A transparent, conductive ZnO/Ag/ZnO multilayer electrode and a Ag:Ca thin film electrode were used in this transparent device as the bottom and top electrode, respectively. To further improve the transmittance of the solar cell, the thickness of the top ZnO layer was investigated both experimentally and with simulations. An average visible transmittance of \u3e60% was reached, with a maximum transmittance of 73% at 556 nm. Both top and bottom illumination of the solar cell generated comparable power conversion efficiencies, which indicates the wide application of this solar cell structure. In addition, we fabricated distributed Bragg reflector mirrors with sputtered SiO2 and TiO2, which efficiently increased the power conversion efficiency over 20% for the solar cells on glass and poly(ethylene terephthalate) (PET) substrates
Higher moment singularities explored by the net proton non-statistical fluctuations
We use the non-statistical fluctuation instead of the full one to explore the
higher moment singularities of net proton event distributions in the
relativistic Au+Au collisions at from 11.5 to 200 GeV
calculated by the parton and hadron cascade model PACIAE. The PACIAE results of
mean (), variance (), skewness (), and kurtosis () are
consistent with the corresponding STAR data. Non-statistical moments are
calculated as the difference between the moments derived from real events and
the ones from mixed events, which are constructed by combining particles
randomly selected from different real events. An evidence of singularity at
60 GeV is first seen in the energy dependent
non-statistical and .Comment: 5 pages,5 figure
Analysis of temperature field and thermal stress of molten iron slagging-off robot arm
In this paper, the transient temperature field and thermal stress of the slagging-off robot arm were analyzed by finite element method, the temperature distribution and change of the robot arm in one working cycle were determined, and the thermal stress and thermal deformation of the slag-scraping plate after the skimming was completed were solved. The results show that the temperature of the equipment in the slagging-off process can reach 206 °C, and the heat can be transferred to the position of 200mm, which will not affect the key parts in the manipulator. Due to the direct contact with molten iron, the heat stress and deformation of the slag-scraping plate are large, which may result in the high melt loss rate of the slag-scraping plate
Quantum Mechanical Search and Harmonic Perturbation
Perturbation theory in quantum mechanics studies how quantum systems interact
with their environmental perturbations. Harmonic perturbation is a rare special
case of time-dependent perturbations in which exact analysis exists. Some
important technology advances, such as masers, lasers, nuclear magnetic
resonance, etc., originated from it. Here we add quantum computation to this
list with a theoretical demonstration. Based on harmonic perturbation, a
quantum mechanical algorithm is devised to search the ground state of a given
Hamiltonian. The intrinsic complexity of the algorithm is continuous and
parametric in both time T and energy E. More precisely, the probability of
locating a search target of a Hamiltonian in N-dimensional vector space is
shown to be 1/(1+ c N E^{-2} T^{-2}) for some constant c. This result is
optimal. As harmonic perturbation provides a different computation mechanism,
the algorithm may suggest new directions in realizing quantum computers.Comment: 6 pages, 4 figures, revtex
High-Responsivity Graphene-Boron Nitride Photodetector and Autocorrelator in a Silicon Photonic Integrated Circuit
Graphene and other two-dimensional (2D) materials have emerged as promising
materials for broadband and ultrafast photodetection and optical modulation.
These optoelectronic capabilities can augment complementary
metal-oxide-semiconductor (CMOS) devices for high-speed and low-power optical
interconnects. Here, we demonstrate an on-chip ultrafast photodetector based on
a two-dimensional heterostructure consisting of high-quality graphene
encapsulated in hexagonal boron nitride. Coupled to the optical mode of a
silicon waveguide, this 2D heterostructure-based photodetector exhibits a
maximum responsivity of 0.36 A/W and high-speed operation with a 3 dB cut-off
at 42 GHz. From photocurrent measurements as a function of the top-gate and
source-drain voltages, we conclude that the photoresponse is consistent with
hot electron mediated effects. At moderate peak powers above 50 mW, we observe
a saturating photocurrent consistent with the mechanisms of electron-phonon
supercollision cooling. This nonlinear photoresponse enables optical on-chip
autocorrelation measurements with picosecond-scale timing resolution and
exceptionally low peak powers
Optimal sequencing of a set of positive numbers with the variance of the sequence's partial sums maximized
We consider the problem of sequencing a set of positive numbers. We try to
find the optimal sequence to maximize the variance of its partial sums. The
optimal sequence is shown to have a beautiful structure. It is interesting to
note that the symmetric problem which aims at minimizing the variance of the
same partial sums is proved to be NP-complete in the literature.Comment: 12 pages;Accepted for publication in Optimization Lette
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