246 research outputs found
Raman fingerprint of semi-metal WTe2 from bulk to monolayer
Tungsten ditelluride (WTe2), a layered transition-metal dichalcogenide (TMD),
has recently demonstrated an extremely large magnetoresistance effect, which is
unique among TMDs. This fascinating feature seems to be correlated with its
special electronic structure. Here, we report the observation of 6 Raman peaks
corresponding to the A_2^4, A_1^9, A_1^8, A_1^6, A_1^5 and A_1^2 phonons, from
the 33 Raman-active modes predicted for WTe2. This provides direct evidence to
distinguish the space group of WTe2 from that of other TMDs. Moreover, the
Raman evolution of WTe2 from bulk to monolayer is clearly revealed. It is
interesting to find that the A_2^4 mode, centered at ~109.8 cm-1, is forbidden
in a monolayer, which may be attributable to the transition of the point group
from C2v (bulk) to C2h (monolayer). Our work characterizes all observed Raman
peaks in the bulk and few-layer samples and provides a route to study the
physical properties of two-dimensional WTe2.Comment: 19 pages, 4 figures and 2 table
Essays on Empirical Monetary and Financial Economics
In chapter one, I find that currency carry trade, which is borrowing money from a low interest rate country and lending it into a high interest rate country, can generate high excess profits in both developed and emerging markets. Emerging market (EM) data are more favorable to the UIP hypothesis, but G-10 countries are the opposite. In addition, the higher interest rate differential is usually associated with the exchange rate crash of the high interest rate currency. By decomposition, we find that the profit from G-10 country carry trade is mainly from strong exchange rates, while most of the emerging markets carry trade’s profits are from the huge interest rate differential. By using quantile regression, I also find out that carry trade portfolios are exposed to multiple risk factors. Those factors are more significant at the low tail distribution of returns. Commodities prices and emerging market equities index are positively associated with next month’s carry trade return. Liquidity condition in the U.S. is negatively related to G-10 country carry trade, but not related to emerging markets. Finally, by studying Bloomberg country specific risk data, we find that better financial, economic, and political conditions in each country predict lower carry trade return, but not statistically significant. In chapter two, I study the response of asset prices to the monetary policy shock in Federal Reserve Bank. As the most important monetary policy transmission channel, the financial markets behavior around interest rate decision of the Federal Reserve of U.S. have been widely discussed by people in academia and the industrial world. This paper uses an event study of macroeconomics to examine the casual relationship of the monetary policy shock on asset prices.We find that treasury bills, exchange rates of developed countries are significantly influenced by the unexpected component of the monetary policy in U.S. from 1989 to 2008. In addition, emerging market exchange rates respond weakly to the policy surprise. We also pointed out that international equity markets and commodities prices are not sensitive to the rate decision of the Federal Reserve Bank in one day to very significant in 5 days after rate decision. The pre and post-FOMC meeting day’s Treasury bill yields also respond to the anticipated and unanticipated of the rate decisions
Palladium-catalyzed difluoromethylation of heteroaryl chlorides, bromides and iodides.
A palladium-catalyzed difluoromethylation of a series of heteroaryl chlorides, bromides and iodides under mild conditions is described. A wide range of heteroaryl halides such as pyridyl, pyrimidyl, pyrazyl, funanyl, thienyl, pyazolyl, imidazolyl, thiazolyl, and oxazolyl halides were efficiently difluoromethylated, thus providing medicinal chemists an alternative choice for the preparation of drug candidates with the difluoromethylated heteroarene unit
Effective Seed-Guided Topic Discovery by Integrating Multiple Types of Contexts
Instead of mining coherent topics from a given text corpus in a completely
unsupervised manner, seed-guided topic discovery methods leverage user-provided
seed words to extract distinctive and coherent topics so that the mined topics
can better cater to the user's interest. To model the semantic correlation
between words and seeds for discovering topic-indicative terms, existing
seed-guided approaches utilize different types of context signals, such as
document-level word co-occurrences, sliding window-based local contexts, and
generic linguistic knowledge brought by pre-trained language models. In this
work, we analyze and show empirically that each type of context information has
its value and limitation in modeling word semantics under seed guidance, but
combining three types of contexts (i.e., word embeddings learned from local
contexts, pre-trained language model representations obtained from
general-domain training, and topic-indicative sentences retrieved based on seed
information) allows them to complement each other for discovering quality
topics. We propose an iterative framework, SeedTopicMine, which jointly learns
from the three types of contexts and gradually fuses their context signals via
an ensemble ranking process. Under various sets of seeds and on multiple
datasets, SeedTopicMine consistently yields more coherent and accurate topics
than existing seed-guided topic discovery approaches.Comment: 9 pages; Accepted to WSDM 202
Encoder-Decoder-Based Intra-Frame Block Partitioning Decision
The recursive intra-frame block partitioning decision process, a crucial
component of the next-generation video coding standards, exerts significant
influence over the encoding time. In this paper, we propose an encoder-decoder
neural network (NN) to accelerate this process. Specifically, a CNN is utilized
to compress the pixel data of the largest coding unit (LCU) into a fixed-length
vector. Subsequently, a Transformer decoder is employed to transcribe the
fixed-length vector into a variable-length vector, which represents the block
partitioning outcomes of the encoding LCU. The vector transcription process
adheres to the constraints imposed by the block partitioning algorithm. By
fully parallelizing the NN prediction in the intra-mode decision, substantial
time savings can be attained during the decision phase. The experimental
results obtained from high-definition (HD) sequences coding demonstrate that
this framework achieves a remarkable 87.84\% reduction in encoding time, with a
relatively small loss (8.09\%) of coding performance compared to AVS3 HPM4.0
Epigenetic regulation in tomato fruit ripening
Fruit ripening is a crucial stage in quality development, influenced by a diverse array of internal and external factors. Among these factors, epigenetic regulation holds significant importance and has garnered substantial research attention in recent years. Here, this review aims to discuss the breakthrough in epigenetic regulation of tomato (Solanum lycopersicum) fruit ripening, including DNA methylation, N6-Methyladenosine mRNA modification, histone demethylation/deacetylation, and non-coding RNA. Through this brief review, we seek to enhance our understanding of the regulatory mechanisms governing tomato fruit ripening, while providing fresh insights for the precise modulation of these mechanisms
Dilemma in All-optical Characterization of Single-layer NiI2 Multiferroics
Matters Arising in Nature on "Evidence for a single layer van der Waals
multiferroic". The search for two dimensional multiferroic materials is an
exciting yet challenging endeavor. Recently, Song reported the exciting
discovery of type II multiferroic order in an antiferromagnetic (AFM) NiI2
single layer and concluded the ferroelectric (FE) polarization induced by a
helical magnetic order1. Their finding was presented from all optical
experimental evidence, based on the methods of second harmonic generation (SHG)
and linear dichroism (LD). However, the all optical characterizations cannot
serve as unanimous evidence of the FE existence, particularly in conjunction
with magnetic orders in a single layer NiI2 multiferroic. We have designed and
built a Magneto-Optical-Electric Joint-measurement Scanning Imaging system
(MOEJSI) for identification of two-dimensional vdW multiferroic.Comment: 7 page
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