2,572 research outputs found
[4-(Methylsulfonyl)phenyl]acetic acid
In the crystal structure of the title compound, C9H10O4S, centrosymmetrically related molecules are linked into dimers by intermolecular O—H⋯O hydrogen bonds. Unconventional C—H⋯O hydrogen-bond interactions are also present, connecting dimers into a three-dimensional network
C2H N=1-0 and N2H+ J=1-0 observations of Planck Galactic cold clumps
A survey of C2H N=1-0 and N2H+ J=1-0 toward Planck Galactic cold clumps
(PGCCs) was performed using the Purple Mountain Observatory's 13.7 m telescope.
C2H and N2H+ were chosen to study the chemical evolutionary states of PGCCs.
Among 121 observed molecular cores associated with PGCCs, 71 and 58 are
detected with C2H N=1-0 and N2H+ J=1-0, respectively. The detected lines of
most sources can be fitted with a single component with compatible Vlsr and
line widths, which confirms that these PGCC cores are very cold (with gas
temperatures 9-21 K) and quiescent while still dominanted by turbulence. The
ratio between the column densities of C2H and N2H+ (N(C2H)/N(N2H+)) is found to
be a good tracer for the evolutionary states of PGCC cores. Gas-grain chemical
model can reproduce the decreasing trend of N(C2H)/N(N2H+) as a function of
time. The cores with the lowest abundances of N2H+ (X[N2H+] < 10^{-10}) are the
youngest, and have nearly constant abundances of C2H. In evolved cores with
X[N2H+] ~ 1E-9, abundances of C2H drop quickly as the exhaustion of carbon
atoms. Although these PGCC cores are in different evolutionary states, they are
all quite young ( N(N2H+). Mapping observations are
carried out toward 20 PGCC cores. The PGCC cores in Cepheus have lower
N(C2H)/N(N2H+) and larger line widths compared with those in Taurus. This
implies that PGCC cores in Taurus are less chemically evolved than those in
Cepheus.Comment: 23 pages, 6 figures, 5 table
The diagnostic value of elastography and ultrasound contrast in papillary thyroid microcarcinoma
目的 评估弹性成像与超声造影(CEUS)两种检查技术对鉴别诊断甲状腺微小乳头状癌(TMC)的价值。方法 对常规超声检测出且定性困难的73例80个甲状腺微小结节进行弹性成像及CEUS检查,所有结节均经手术病理证实。比较两种检查方法的准确性。结果 80个结节中CEUS诊断正确率为85.0%(68/80),其中6例TMC误诊为良性病变,6例良性结节误诊为TMC;弹性成像5分法诊断正确率为92.5%(74/80),其中3例TMC误诊为良性结节,3例良性结节误诊为TMC。性成像诊断甲状腺微小癌的敏感性94.0%,特异性90.0%,准确性92.5%;CEUS诊断甲状腺微小癌的敏感性88.0%,特异性80.0%,准确性85.0%。结论 CEUS和弹性成像对于诊断TMC方面均有价值,但弹性评分≥3作为诊断TMC的敏感性、特异性及准确性均高于CEUS。Objective: To assess the value of elastic imaging and CEUS two inspection techniques for differential diagnosis of thyroid papillary carcinoma (TMC). Method: To do elastic imaging and CEUS checks to 73 cases of 80 thyroid nodules which was tested by conventional ultrasonic and difficult to quantify. All nodules were confirmed by surgery and pathologic examination. Comparing the accuracy of both detection methods. Result: Of the 80 nodules, the accuracy of CEUS diagnosis was 85.0%(68/80), of which 6 cases were misdiagnosed as benign lesions, and 6cases of benign nodules were misdiagnosed as TMC: the accuracy of 5-point scale criteria of elastography was 92.5%(74/80), of which 3 TMC were misdiagnosed as benign nodules: and 3 benign nodules were misdiagnosed as TMC. The application of elastography in the diagnosis of thyroid microcarcinoma displayed a sensitivity of 94.0%, a specificity of 90.0% and an accuracy of 92.5%. Elastography detection was more advantagerous than CEUS in the diagnosis of thyroid microcarcinoma, and compared to CEUS , the differences were statistically significant(P <0.05).Conclusion: Elastography and Ultrasound Contrast have highly practical value to diagnosis of TMC. The sensitivity specificity and accuracy of using elastic score ≥3 as criteria of diagnosis of TMC was higher than that of CEUS
Infall, Fragmentation and Outflow in Sgr B2
Observations of HCO lines and continuum at 1.3 mm towards Sgr B2(N) and
Sgr B2(M) cores were carried out with the SMA. We imaged HCO line
absorption against the continuum cores and the surrounding line emission
clumps. The results show that the majority of the dense gas is falling into the
major cores where massive stars have been formed. The filaments and clumps of
the continuum and gas are detected outside of Sgr B2(N) and Sgr B2(M) cores.
Both the spectra and moment analysis show the presence of outflows from Sgr
B2(M) cores. The HCO gas in the red-shifted outflow of Sgr B2(M) appears
to be excited by a non-LTE process which might be related to the shocks in the
outflow.Comment: 5 pages, 3 figures, Published in J. Physics Conference Serie
Intent Contrastive Learning with Cross Subsequences for Sequential Recommendation
The user purchase behaviors are mainly influenced by their intentions (e.g.,
buying clothes for decoration, buying brushes for painting, etc.). Modeling a
user's latent intention can significantly improve the performance of
recommendations. Previous works model users' intentions by considering the
predefined label in auxiliary information or introducing stochastic data
augmentation to learn purposes in the latent space. However, the auxiliary
information is sparse and not always available for recommender systems, and
introducing stochastic data augmentation may introduce noise and thus change
the intentions hidden in the sequence. Therefore, leveraging user intentions
for sequential recommendation (SR) can be challenging because they are
frequently varied and unobserved. In this paper, Intent contrastive learning
with Cross Subsequences for sequential Recommendation (ICSRec) is proposed to
model users' latent intentions. Specifically, ICSRec first segments a user's
sequential behaviors into multiple subsequences by using a dynamic sliding
operation and takes these subsequences into the encoder to generate the
representations for the user's intentions. To tackle the problem of no explicit
labels for purposes, ICSRec assumes different subsequences with the same target
item may represent the same intention and proposes a coarse-grain intent
contrastive learning to push these subsequences closer. Then, fine-grain intent
contrastive learning is mentioned to capture the fine-grain intentions of
subsequences in sequential behaviors. Extensive experiments conducted on four
real-world datasets demonstrate the superior performance of the proposed ICSRec
model compared with baseline methods.Comment: 10pages, 5figures, WSDM2024. arXiv admin note: text overlap with
arXiv:2304.0776
Meta-optimized Contrastive Learning for Sequential Recommendation
Contrastive Learning (CL) performances as a rising approach to address the
challenge of sparse and noisy recommendation data. Although having achieved
promising results, most existing CL methods only perform either hand-crafted
data or model augmentation for generating contrastive pairs to find a proper
augmentation operation for different datasets, which makes the model hard to
generalize. Additionally, since insufficient input data may lead the encoder to
learn collapsed embeddings, these CL methods expect a relatively large number
of training data (e.g., large batch size or memory bank) to contrast. However,
not all contrastive pairs are always informative and discriminative enough for
the training processing. Therefore, a more general CL-based recommendation
model called Meta-optimized Contrastive Learning for sequential Recommendation
(MCLRec) is proposed in this work. By applying both data augmentation and
learnable model augmentation operations, this work innovates the standard CL
framework by contrasting data and model augmented views for adaptively
capturing the informative features hidden in stochastic data augmentation.
Moreover, MCLRec utilizes a meta-learning manner to guide the updating of the
model augmenters, which helps to improve the quality of contrastive pairs
without enlarging the amount of input data. Finally, a contrastive
regularization term is considered to encourage the augmentation model to
generate more informative augmented views and avoid too similar contrastive
pairs within the meta updating. The experimental results on commonly used
datasets validate the effectiveness of MCLRec.Comment: 11 Pages,8 figure
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Infall and Outflow of Molecular Gas in Sgr B2
Observations of two lines and continuum emission at 1.3 mm toward Sgr B2(N) and Sgr B2(M) have been carried out with the SMA. The mosaic maps of Sgr B2(N) and Sgr B2(M) in both continuum and lines show a complex distribution of dust and molecular gas in both clumps and filaments surrounding the compact star formation cores. We have observed a decelerating outflow originated from the Sgr B2(M) core, showing that both the redshifted and blueshifted outflow components have a common terminal velocity. This terminal velocity is . It provides an excellent method for determination of the systematic velocity of the molecular cloud. The SMA observations have also shown that a large fraction of absorption against the two continuum cores is redshifted with respect to the systematic velocities of Sgr B2(N) and Sgr B2(M), respectively, suggesting that the majority of the dense molecular gas is flowing into the two major cores where massive stars have been formed. We have solved the radiative transfer in a multilevel system with LVG approximation. The observed line intensities and their ratios can be adequately fitted with this model for the most of the gas components. However, the line intensities between the higher energy level transition and the lower energy level transition is reversed in the redshifted outflow region of Sgr B2(M), suggesting the presence of inversion in population between the ground levels in the two K ladders . The possibility of weak maser processes for the emission in Sgr B2(M) is discussed.Astronom
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