91 research outputs found
Effect of Particle Concentration and AC Electric Field Strength on Particle Trapping in Rapid Electrokinetic Patterning (REP)
Rapid Electrokinetic Patterning (REP) is an optoelectric technique for trapping and translating micro- and nanoparticles non-invasively. It uses a combination of laser-induced AC electrothermal flow and particle-electrode interactions in the presence of a uniform AC electric field. The trapping is governed by laser power, electric field strength, AC frequency and dielectric properties of the particle and the medium. A REP trap has an AC frequency, termed critical frequency, above which particles cannot be trapped. It is expected to be dependent on dielectric properties of the particle and the medium. However, we propose that the particle concentration and AC field strength also influence the critical frequency. In our experiments, we test 1 µm polystyrene microspheres in REP under the condition of three particle concentrations and two electric field strengths while keeping the laser power fixed at 25mW. We find that as the particle concentration increases, the critical frequency increases. Besides, by lowering the AC field strength, the critical frequency decreases. To our best knowledge, this is the first study revealing the effect of particle concentration on critical frequency. Based on these results, by selecting proper parameters, we can separate the smaller particles and hold the larger particles in the trap, opposite to what has been achieved by other researchers. The ability to separate smaller particles will make REP a more prominent and powerful particle trapping method
Surveying the Dead Minds: Historical-Psychological Text Analysis with Contextualized Construct Representation (CCR) for Classical Chinese
In this work, we develop a pipeline for historical-psychological text
analysis in classical Chinese. Humans have produced texts in various languages
for thousands of years; however, most of the computational literature is
focused on contemporary languages and corpora. The emerging field of historical
psychology relies on computational techniques to extract aspects of psychology
from historical corpora using new methods developed in natural language
processing (NLP). The present pipeline, called Contextualized Construct
Representations (CCR), combines expert knowledge in psychometrics (i.e.,
psychological surveys) with text representations generated via
transformer-based language models to measure psychological constructs such as
traditionalism, norm strength, and collectivism in classical Chinese corpora.
Considering the scarcity of available data, we propose an indirect supervised
contrastive learning approach and build the first Chinese historical psychology
corpus (C-HI-PSY) to fine-tune pre-trained models. We evaluate the pipeline to
demonstrate its superior performance compared with other approaches. The CCR
method outperforms word-embedding-based approaches across all of our tasks and
exceeds prompting with GPT-4 in most tasks. Finally, we benchmark the pipeline
against objective, external data to further verify its validity
An integrated finite element analysis of CFRP laminates: from low-velocity impact to CAI strength prediction
Ph.DDOCTOR OF PHILOSOPH
Birefringence of GaN/AlGaN optical waveguides
This is the published version. Copyright © 2003 American Institute of PhysicsWe have experimentally studied the birefringence of wurtzite GaNgrown on a sapphire substrate. The measurements were done with single-mode GaN/AlGaN planar optical waveguides on c-plane grownheterostructure films. The refractive indices were found to be different for signal optical field perpendicular or parallel to the crystal c axis (n⊥≠n∥). More importantly, we found an approximately 10% change in index difference Δn=n∥−n⊥ with variation of the waveguide orientation in the a–b plane, and a 60° periodicity was clearly observed. This is attributed to the hexagonal structure of nitride materials
Ultrasonic neuromodulation mediated by mechanosensitive ion channels: current and future
Ultrasound neuromodulation technology is a promising neuromodulation approach, with the advantages of noninvasiveness, high-resolution, deep penetration and good targeting, which aid in circumventing the side effects of drugs and invasive therapeutic interventions. Ultrasound can cause mechanical effects, activate mechanosensitive ion channels and alter neuronal excitability, producing biological effects. The structural determination of mechanosensitive ion channels will greatly contribute to our understanding of the molecular mechanisms underlying mechanosensory transduction. However, the underlying biological mechanism of ultrasonic neuromodulation remains poorly understood. Hence, this review aims to provide an outline of the properties of ultrasound, the structures of specific mechanosensitive ion channels, and their role in ultrasound neuromodulation
GaN-based waveguide devices for long-wavelength optical communications
This is the published version. Copyright © 2003 American Institute of PhysicsRefractive indices of AlxGa1−xN with different Al concentrations have been measured in infrared wavelength regions. Single-mode ridged optical waveguidedevices using GaN/AlGaN heterostructures have been designed, fabricated, and characterized for operation in 1550 nm wavelength window. The feasibility of developing photonic integrated circuits based on III-nitride wide-band-gap semiconductors for fiber-optical communications has been discussed
Visualizing the Zhang-Rice singlet, molecular orbitals and pair formation in cuprate
The parent compound of cuprates is a charge-transfer-type Mott insulator with
strong hybridization between the Cu and O orbitals.
A key question concerning the pairing mechanism is the behavior of doped holes
in the antiferromagnetic (AF) Mott insulator background, which is a
prototypical quantum many-body problem. It was proposed that doped hole on the
O site tends to form a singlet, known as Zhang-Rice singlet (ZRS), with the
unpaired Cu spin. But experimentally little is known about the properties of a
single hole and the interplay between them that leads to superconductivity.
Here we use scanning tunneling microscopy to visualize the electronic states in
hole-doped , aiming to establish the atomic-scale local
basis for pair formation. A single doped hole is shown to have an in-gap state
and a clover-shaped spatial distribution that can be attributed to a localized
ZRS. When the dopants are close enough, they develop delocalized molecular
orbitals with characteristic stripe- and ladder-shaped patterns, accompanied by
the opening of a small gap around the Fermi level (). With
increasing doping, the molecular orbitals proliferate in space and gradually
form densely packed plaquettes, but the stripe and ladder patterns remain
nearly the same. The low-energy electronic states of the molecular orbitals are
intimately related to the local pairing properties, thus play a vitally
important role in the emergence of superconductivity. We propose that the
Cooper pair is formed by two holes occupying the stripe-like molecular orbital,
while the attractive interaction is mediated by the AF spin background
III-nitride-based planar lightwave circuits for long wavelength optical communications
©2005 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.Planar lightwave circuits based on III-nitride wide-bandgap semiconductors are proposed and the feasibility of developing III-nitride-based novel photonic integrated circuits for applications in fiber-optical communications is discussed. III-nitrides have low attenuation in the near-infrared wavelength region because of their wide bandgaps, while as semiconductors their refractive indexes can be modulated by carrier injection. III-nitrides are also well known for their ability to operate at high temperatures, high power levels and in harsh environments. These characteristics make III-nitrides ideal candidates for tunable optical phased-array (PHASAR) devices for optical communications. We have characterized the optical properties of AlxGa1-xN epilayers in the 1550-nm wavelength region, including the refractive indexes and the impact of Al concentrations. Single-mode ridged optical waveguide devices using GaN-AlGaN heterostructures have been designed, fabricated and characterized for operation in the 1550-nm wavelength window. The birefringence of wurtzite GaN grown on sapphire substrate has been observed. Refractive indexes were found to be different for signal optical field perpendicular and parallel to the crystal c axis (n(perpendicular to) not equal n(//)). More importantly, we found an approximately 10% change in the index difference Deltan = n(//) - n(perpendicular to) with varying the waveguide orientation within the c plane, and a 60degrees periodicity was clearly observed. This is attributed to the hexagonal structure of the nitride materials. Various functional waveguide devices have been realized, including 2 x 2 directional couplers and eight-wavelength array-waveguide gratings. Theoretical predictions of temperature sensitivity and the efficiency of carrier-induced refractive change are provided
Increased inorganic aerosol fraction contributes to air pollution and haze in China
The detailed formation mechanism of an increased number of haze events in China is still not very clear. Here, we found that reduced surface visibility from 1980 to 2010 and an increase in satellite-derived columnar concentrations of inorganic precursors from 2002 to 2012 are connected with each other. Typically, higher inorganic mass fractions lead to increased aerosol water uptake and light-scattering ability in elevated relative humidity. Satellite observation of aerosol precursors of NO2 and SO2 showed increased concentrations during the study period. Our in situ measurement of aerosol chemical composition in Beijing also confirmed increased contribution of inorganic aerosol fraction as a function of the increased particle pollution level. Our investigations demonstrate that the increased inorganic fraction in the aerosol particles is a key component in the frequently occurring haze days during the study period, and particularly the reduction of nitrate, sulfate and their precursor gases would contribute towards better visibility in China.Peer reviewe
- …