129 research outputs found
Comparative study on making loans to large companies and SME's in China
Thesis (S.M.)--Massachusetts Institute of Technology, Sloan School of Management, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (p. 41-45).The SME financing problem in China has been widely acknowledged during the recent financial crisis. The SMEs compose 99% of all registered enterprises and employ more than 60% of labors in China. They contributed significantly to the economic vitality, as well as to ensuring stable employment and sustainable development of China. However, the SMEs have been short of external funding because they are considered to be riskier than large companies which maintained closer relationships to the governments and state-own-commercial-banks, which are the main financial source under the current banking system in China. Are the SMEs riskier than the large companies in terms of loan issuance? The thesis explores the issue by discussing the current banking structure in China and explaining the reasons from political, economic, social and technological perspectives. Comparing the financial indicators including ROE (return on equity), ROA (return on assets), NPM (net profit margin), ICR (interest coverage ratio), CR (current ratio) and revenue growth of selected SMEs and large companies before and after they received the commercial loans, I find that SMEs did not necessarily demonstrate worse performance than the large companies. Contrarily, the SMEs could more effectively utilize their loans to realize better business outcomes than the large companies did. To further improve the financing issue of SMEs, the thesis will raise recommendations from the perspectives of the government regulatory bodies and the local commercial banks.by Michael Jiaming Tian.S.M
SIMBA: scalable inversion in optical tomography using deep denoising priors
Two features desired in a three-dimensional (3D) optical tomographic image reconstruction algorithm are the ability to reduce imaging artifacts and to do fast processing of large data volumes. Traditional iterative inversion algorithms are impractical in this context due to their heavy computational and memory requirements. We propose and experimentally validate a novel scalable iterative mini-batch algorithm (SIMBA) for fast and high-quality optical tomographic imaging. SIMBA enables highquality imaging by combining two complementary information sources: the physics of the imaging system characterized by its forward model and the imaging prior characterized by a denoising deep neural net. SIMBA easily scales to very large 3D tomographic datasets by processing only a small subset of measurements at each iteration. We establish the theoretical fixedpoint convergence of SIMBA under nonexpansive denoisers for convex data-fidelity terms. We validate SIMBA on both simulated and experimentally collected intensity diffraction tomography (IDT) datasets. Our results show that SIMBA can significantly reduce the computational burden of 3D image formation without sacrificing the imaging quality.https://arxiv.org/abs/1911.13241First author draf
Efficient Generation of Intense Broadband Terahertz Pulses from Quartz
The intense terahertz (THz) pulses facilitate the observation of various
nonlinear optical effects and manipulation of material properties. In this
work, we report a convenient approach that can produce strong broadband
terahertz pulses with center frequency tunable between 2-4 THz. The coherent
THz light source with pulse energy of 1.2 microjoule can be generated from a
low-cost crystalline quartz pumped by an ultrashort tilted wave-front pulse.
Thanks to the wide transparent spectral window and high damage threshold, our
theoretical analysis and experiment show that the optical rectification in
quartz is as efficient as that in LiNbO3, but covers much broader spectral
range. This work not only provides the light source that is urgently needed for
nonlinear THz spectroscopy beyond 1 THz, but offers an alternative route in the
selection of nonlinear optical crystals for optical frequency conversion
A Comprehensive Comparison of Projections in Omnidirectional Super-Resolution
Super-Resolution (SR) has gained increasing research attention over the past
few years. With the development of Deep Neural Networks (DNNs), many
super-resolution methods based on DNNs have been proposed. Although most of
these methods are aimed at ordinary frames, there are few works on
super-resolution of omnidirectional frames. In these works, omnidirectional
frames are projected from the 3D sphere to a 2D plane by Equi-Rectangular
Projection (ERP). Although ERP has been widely used for projection, it has
severe projection distortion near poles. Current DNN-based SR methods use 2D
convolution modules, which is more suitable for the regular grid. In this
paper, we find that different projection methods have great impact on the
performance of DNNs. To study this problem, a comprehensive comparison of
projections in omnidirectional super-resolution is conducted. We compare the SR
results of different projection methods. Experimental results show that
Equi-Angular cube map projection (EAC), which has minimal distortion, achieves
the best result in terms of WS-PSNR compared with other projections. Code and
data will be released.Comment: Accepted to ICASSP202
CABM: Content-Aware Bit Mapping for Single Image Super-Resolution Network with Large Input
With the development of high-definition display devices, the practical
scenario of Super-Resolution (SR) usually needs to super-resolve large input
like 2K to higher resolution (4K/8K). To reduce the computational and memory
cost, current methods first split the large input into local patches and then
merge the SR patches into the output. These methods adaptively allocate a
subnet for each patch. Quantization is a very important technique for network
acceleration and has been used to design the subnets. Current methods train an
MLP bit selector to determine the propoer bit for each layer. However, they
uniformly sample subnets for training, making simple subnets overfitted and
complicated subnets underfitted. Therefore, the trained bit selector fails to
determine the optimal bit. Apart from this, the introduced bit selector brings
additional cost to each layer of the SR network. In this paper, we propose a
novel method named Content-Aware Bit Mapping (CABM), which can remove the bit
selector without any performance loss. CABM also learns a bit selector for each
layer during training. After training, we analyze the relation between the edge
information of an input patch and the bit of each layer. We observe that the
edge information can be an effective metric for the selected bit. Therefore, we
design a strategy to build an Edge-to-Bit lookup table that maps the edge score
of a patch to the bit of each layer during inference. The bit configuration of
SR network can be determined by the lookup tables of all layers. Our strategy
can find better bit configuration, resulting in more efficient mixed precision
networks. We conduct detailed experiments to demonstrate the generalization
ability of our method. The code will be released.Comment: Accepted to CVPR202
Probing Interface of Perovskite Oxide Using Surface-specific Terahertz Spectroscopy
The surface/interface species in perovskite oxides play an essential role in
many novel emergent physical phenomena and chemical processes. With low
eigen-energy in the terahertz region, such species at buried interfaces remain
poorly understood due to the lack of feasible experimental techniques. Here, we
show that vibrational resonances and two-dimensional electron gas at the
interface can be characterized using surface-specific nonlinear spectroscopy in
the terahertz range. This technique uses intra-pulse difference frequency
mixing (DFM) process, which is allowed only at surface/interface of a medium
with inversion symmetry. Sub-monolayer sensitivity can be achieved using the
state-of-the-art detection scheme for the terahertz emission from
surface/interface. As a demonstration, Drude-like nonlinear response from the
two-dimensional electron gas emerging at LaAlO3/SrTiO3 or Al2O3/ SrTiO3
interface was successfully observed. Meanwhile, the interfacial vibrational
spectrum of the ferroelectric soft mode of SrTiO3 at 2.8 THz was also obtained
that was polarized by the surface field in the interfacial region. The
corresponding surface/interface potential, which is a key parameter for
SrTiO3-based interface superconductivity and photocatalysis, can now be
determined optically via quantitative analysis on the polarized phonon
spectrum. The interfacial species with resonant frequencies in the THz region
revealed by our method provide more insights into the understanding of physical
properties of complex oxides.Comment: arXiv admin note: substantial text overlap with arXiv:2207.1461
Single-pixel imaging based on deep learning
Single-pixel imaging can collect images at the wavelengths outside the reach
of conventional focal plane array detectors. However, the limited image quality
and lengthy computational times for iterative reconstruction still impede the
practical application of single-pixel imaging. Recently, deep learning has been
introduced into single-pixel imaging, which has attracted a lot of attention
due to its exceptional reconstruction quality, fast reconstruction speed, and
the potential to complete advanced sensing tasks without reconstructing images.
Here, this advance is discussed and some opinions are offered. Firstly, based
on the fundamental principles of single-pixel imaging and deep learning, the
principles and algorithms of single-pixel imaging based on deep learning are
described and analyzed. Subsequently, the implementation technologies of
single-pixel imaging based on deep learning are reviewed. They are divided into
super-resolution single-pixel imaging, single-pixel imaging through scattering
media, photon-level single-pixel imaging, optical encryption based on
single-pixel imaging, color single-pixel imaging, and image-free sensing
according to diverse application fields. Finally, major challenges and
corresponding feasible approaches are discussed, as well as more possible
applications in the future
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