101 research outputs found
Enhancing infrared emission of mercury telluride (HgTe) quantum dots by plasmonic structures
The coupling of HgTe quantum dots to a gold nanobump plasmonic array can enhance the spontaneous infrared emission by a factor of five and reduce the influence of nonradiative decay channels
Suppression of nano-channel ion conductance by electro-osmotic flow in nano-channels with weakly overlapping electrical double layers
This theoretical study investigates the nonlinear ionic current-voltage
characteristics of nano-channels that have weakly overlapping electrical double
layers. Numerical simulations as well as a 1-D mathematical model are developed
to reveal that the electro-osmotic flow (EOF) interplays with the
concentration-polarization process and depletes the ion concentration inside
the channels, thus significantly suppressing the channel conductance. The
conductance may be restored at high electrical biases in the presence of
recirculating vortices within the channels. As a result of the EOF-driven ion
depletion, a limiting-conductance behavior is identified, which is
intrinsically different from the classical limiting-current behavior
Enhancing infrared emission of mercury telluride (HgTe) quantum dots by plasmonic structures
The coupling of HgTe quantum dots to a gold nanobump plasmonic array can enhance the spontaneous infrared emission by a factor of five and reduce the influence of nonradiative decay channels
Interlayer Interactions in Anisotropic Atomically-thin Rhenium Diselenide
Recently, two-dimensional (2D) materials with strong in-plane anisotropic
properties such as black phosphorus have demonstrated great potential for
developing new devices that can take advantage of its reduced lattice symmetry
with potential applications in electronics, optoelectronics and
thermoelectrics. However, the selection of 2D material with strong in-plane
anisotropy has so far been very limited and only sporadic studies have been
devoted to transition metal dichalcogenides (TMDC) materials with reduced
lattice symmetry, which is yet to convey the full picture of their optical and
phonon properties, and the anisotropy in their interlayer interactions. Here,
we study the anisotropic interlayer interactions in an important TMDC 2D
material with reduced in-plane symmetry - atomically thin rhenium diselenide
(ReSe2) - by investigating its ultralow frequency interlayer phonon vibration
modes, the layer dependent optical bandgap, and the anisotropic
photoluminescence (PL) spectra for the first time. The ultralow frequency
interlayer Raman spectra combined with the first study of polarization-resolved
high frequency Raman spectra in mono- and bi-layer ReSe2 allows deterministic
identification of its layer number and crystal orientation. PL measurements
show anisotropic optical emission intensity with bandgap increasing from 1.26
eV in the bulk to 1.32 eV in monolayer, consistent with the theoretical results
based on first-principle calculations. The study of the layer-number dependence
of the Raman modes and the PL spectra reveals the relatively weak van der Waals
interaction and 2D quantum confinement in atomically-thin ReSe2.Comment: 17 pages, 5 figures, supplementary informatio
Digital Pre-distortion Technology For Optimization Design Of VDB Transmitter
Due to the nonlinear distortion of the power amplifier, the problems of in-band distortion and Adjacent Channel Interference will occur in VDB transmitter .To address the problem ,this paper introduces a digital pre-distortion method based on memoryless polynomial model ,which can solve the coefficients of digital pre-distorter with indirect learning structure. The results show that the digital pre-distortion method can effectively improve the third-order intermodulation distortion, the adjacent channel power ratio (ACPR) and the error vector amplitude (EVM) of VDB transmitter, and it can also improve the performance and efficiency of the communication system
Do Large Language Models Know What They Don't Know?
Large language models (LLMs) have a wealth of knowledge that allows them to
excel in various Natural Language Processing (NLP) tasks. Current research
focuses on enhancing their performance within their existing knowledge. Despite
their vast knowledge, LLMs are still limited by the amount of information they
can accommodate and comprehend. Therefore, the ability to understand their own
limitations on the unknows, referred to as self-knowledge, is of paramount
importance. This study aims to evaluate LLMs' self-knowledge by assessing their
ability to identify unanswerable or unknowable questions. We introduce an
automated methodology to detect uncertainty in the responses of these models,
providing a novel measure of their self-knowledge. We further introduce a
unique dataset, SelfAware, consisting of unanswerable questions from five
diverse categories and their answerable counterparts. Our extensive analysis,
involving 20 LLMs including GPT-3, InstructGPT, and LLaMA, discovering an
intrinsic capacity for self-knowledge within these models. Moreover, we
demonstrate that in-context learning and instruction tuning can further enhance
this self-knowledge. Despite this promising insight, our findings also
highlight a considerable gap between the capabilities of these models and human
proficiency in recognizing the limits of their knowledge.Comment: 10 pages, 9 figures, accepted by Findings of ACL202
Multi-Octave Frequency Comb from an Ultra-Low-Threshold Nanophotonic Parametric Oscillator
Ultrabroadband frequency combs coherently unite distant portions of the
electromagnetic spectrum. They underpin discoveries in ultrafast science and
serve as the building blocks of modern photonic technologies. Despite
tremendous progress in integrated sources of frequency combs, achieving
multi-octave operation on chip has remained elusive mainly because of the
energy demand of typical spectral broadening processes. Here we break this
barrier and demonstrate multi-octave frequency comb generation using an optical
parametric oscillator (OPO) in nanophotonic lithium niobate with only
femtojoules of pump energy. The energy-efficient and robust coherent spectral
broadening occurs far above the oscillation threshold of the OPO and detuned
from its linear synchrony with the pump. We show that the OPO can undergo a
temporal self-cleaning mechanism by transitioning from an incoherent operation
regime, which is typical for operation far above threshold, to an ultrabroad
coherent regime, corresponding to the nonlinear phase compensating the OPO
cavity detuning. Such a temporal self-cleaning mechanism and the subsequent
multi-octave coherent spectrum has not been explored in previous OPO designs
and features a relaxed requirement for the quality factor and relatively narrow
spectral coverage of the cavity. We achieve orders of magnitude reduction in
the energy requirement compared to the other techniques, confirm the coherence
of the comb, and present a path towards more efficient and wider spectral
broadening. Our results pave the way for ultrashort-pulse and ultrabroadband
on-chip nonlinear photonic systems for numerous applications.Comment: 8 pages, 4 figure
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