985 research outputs found
Panoramic-reconstruction temporal imaging for seamless measurements of slowly-evolved femtosecond pulse dynamics
Single-shot real-time characterization of optical waveforms with
sub-picosecond resolution is essential for investigating various ultrafast
optical dynamics. However, the finite temporal recording length of current
techniques hinders comprehensive understanding of many intriguing ultrafast
optical phenomena that evolve over a time scale much longer than their fine
temporal details. Inspired by the space-time duality and by stitching of
multiple microscopic images to achieve a larger field of view in the spatial
domain, here a panoramic-reconstruction temporal imaging (PARTI) system is
devised to scale up the temporal recording length without sacrificing the
resolution. As a proof-of-concept demonstration, the PARTI system is applied to
study the dynamic waveforms of slowly-evolved dissipative Kerr solitons in an
ultrahigh-Q microresonator. Two 1.5-ns-long comprehensive evolution portraits
are reconstructed with 740-fs resolution and dissipative Kerr soliton
transition dynamics, in which a multiplet soliton state evolves into stable
singlet soliton state, are depicted
The Connections between QSO Absorption Systems and Galaxies: Low-Redshift Observations
Quasar absorption lines have long been recognized to be a sensitive probe of
the abundances, physical conditions, and kinematics of gas in a wide variety of
environments including low-density intergalactic regions that probably cannot
be studied by any other means. While some pre-Hubble Space Telescope (HST)
observations indicated that Mg II absorption lines arise in gaseous galactic
halos with a large covering factor, many early QSO absorber studies were
hampered by a lack of information about the context of the absorbers and their
connections with galaxies. By providing access to crucial ultraviolet resonance
lines at low redshifts, deployment of HST and the Far Ultraviolet Spectroscopic
Explorer enabled detailed studies of the relationships between QSO absorbers
and galaxies. The advent of large surveys such as the Sloan Digital Sky Survey
(SDSS) has also advanced the topic by greatly improving the size of absorber
and galaxy samples. This paper briefly reviews some observational results on
absorber-galaxy connections that have been obtained in the HST/SDSS era,
including Mg II absorbers, the low-z Lyman alpha forest, Lyman limit and damped
Lyman alpha absorbers, and O VI systems.Comment: Review paper presented at IAU Colloquium 199, Probing Galaxies
through Quasar Absorption Lines, eds. P. R. Williams, C. Shu, and B. Menard.
19 pages, 10 figure
Combating Unknown Bias with Effective Bias-Conflicting Scoring and Gradient Alignment
Models notoriously suffer from dataset biases which are detrimental to
robustness and generalization. The identify-emphasize paradigm shows a
promising effect in dealing with unknown biases. However, we find that it is
still plagued by two challenges: A, the quality of the identified
bias-conflicting samples is far from satisfactory; B, the emphasizing
strategies just yield suboptimal performance. In this work, for challenge A, we
propose an effective bias-conflicting scoring method to boost the
identification accuracy with two practical strategies -- peer-picking and
epoch-ensemble. For challenge B, we point out that the gradient contribution
statistics can be a reliable indicator to inspect whether the optimization is
dominated by bias-aligned samples. Then, we propose gradient alignment, which
employs gradient statistics to balance the contributions of the mined
bias-aligned and bias-conflicting samples dynamically throughout the learning
process, forcing models to leverage intrinsic features to make fair decisions.
Experiments are conducted on multiple datasets in various settings,
demonstrating that the proposed solution can alleviate the impact of unknown
biases and achieve state-of-the-art performance
Automatic fracture optimization for shale gas reservoirs based on gradient descent method and reservoir simulation
In shale gas reservoir development, determination of hydraulic fracture geometry for horizontal wells is a demanding yet challenging task. One type of approach for hydraulic fracture optimization is based on reservoir simulation. To improve optimization efficiency and accuracy, an automatic and robust procedure integrating the gradient descent method with gas reservoir simulation has been developed. Fractured reservoir models were constructed using the “Multiple INteracting Continua” method, whereby an in-house shale gas reservoir simulator was implemented to model multiple gas transport mechanisms including non-Darcy flow, gas desorption, Klinkenberg effect, and geomechanical effect. The optimization procedure was first validated against two ideal cases and then applied to two realistic cases to optimize fracture spacing, half-length, and dimensionless fracture conductivity. It showed that the optimization results depend on optimization objective, reservoir property, natural fractures, economics and termination criteria. This gradient descent assisted fracture optimization procedure can achieve significant computational reduction and high prediction accuracy for various shale gas reservoir cases.Cited as: Chen, J., Wang, L., Wang, C., Yao, B., Tian, Y., Wu, Y.-S. Automatic fracture optimization for shale gas reservoirs based on gradient descent method and reservoir simulation. Advances in Geo-Energy Research, 2021, 5(2): 191-201, doi: 10.46690/ager.2021.02.0
Axigluon as Possible Explanation for Forward-Backward Asymmetry
A flavor-nonuniversal chiral color model is introduced. It is used for
comparison to the recent data on . We concluded that
the data are consistent with interpretation as an axigluon exchange within
1 and a unique rise and fall behavior is predicated with regard to the
asymmetry as a function of invariant mass, which can
distinguish our model from others before one discovers the axigluon resonance.
Further aspects of the model are discussed.Comment: reference update
Cytidine-phosphate-guanosine oligodeoxynucleotides in combination with CD40 ligand decrease periodontal inflammation and alveolar bone loss in a TLR9-independent manner
Local administration of toll-like receptor 9 (TLR9), agonist cytidine-phosphate-guanosine oligodeoxynucleotide (CpG ODNs), and CD40 ligand (CD40L) can decrease ligature-induced periodontal inflammation and bone loss in wild type (WT) mouse. Objective: This study aimed to explore whether such effect is dependent on TLR9 signaling. Material and Methods: Purified spleen B cells isolated from WT C57BL/6J mice and TLR9 knockout (KO) mice were cultured for 48 hours under the following conditions: CD40L, CpG+CD40L, CpG at low, medium and high doses. We determined B cell numbers using a hemocytometer at 24 h and 48 h. Percentages of CD1dhiCD5+ B cells were detected by flow cytometry. Interleukin-10 (IL-10) mRNA expression and protein secretion were measured by quantitative real-time polymerase chain reaction (qRT-PCR) and by ELISA, respectively. The silk ligature was tied around the maxillary second molars for 14 days, during which the CpG+CD40L mixture or PBS was injected into palatal gingiva on days 3, 6, and 9. Results: For both WT and TLR9 KO mice, CpG significantly induced B cell proliferation, increased IL-10 mRNA expression and protein secretion of IL-10 but reduced CD1dhiCD5+ B cells population; local injection of CpG+CD40L mixture significantly decreased alveolar bone loss and the number of TRAP-positive cells adjacent to the alveolar bone surface, and significantly increased the gingival mRNA expression of IL-10 and decreased RANKL and IFN-γ mRNA expression. Conclusions: These results indicated that CpG plus CD40L decreased periodontal inflammation and alveolar bone loss in a TLR9-independent manner in ligature-induced experimental periodontitis
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Relative timing jitter in a counterpropagating all-normal dispersion dual-comb fiber laser
The counterpropagating all-normal dispersion (CANDi) fiber laser is an emerging high-energy single-cavity dual-comb laser source. Its relative timing jitter (RTJ), a critical parameter for dual-comb timing precision and spectral resolution, has not been comprehensively investigated. In this paper, we enhance the state-of-the-art CANDi fiber laser pulse energy from 1 nJ to 8 nJ. We then introduce a reference-free RTJ characterization technique that provides shot-to-shot measurement capability at femtosecond precision. The measurement noise floor reaches 1.6×10−7fs2/Hz, and the corresponding integrated measurement precision is only 1.8 fs (1 kHz, 20 MHz). With this characterization tool, we are able to study the physical origin of the CANDi laser’s RTJ in detail. We first verify that the cavity length fluctuation does not contribute to the RTJ. Then we measure the integrated RTJ to be 39 fs (1 kHz, 20 MHz) and identify the pump relative intensity noise (RIN) to be the dominant factor responsible for it. In particular, pump RIN is coupled to the RTJ through the Gordon–Haus effect. Finally, solutions to reduce the free-running CANDi laser’s RTJ are discussed. This work provides a general guideline to improve the performance of compact single-cavity dual-comb systems such as the CANDi laser, benefitting various dual-comb applications.</p
Spherically Symmetric Noncommutative Spacetime via Exotic Atomic Transitions
In discussing non-commutative spacetime, the generally studied
-Poincare model is inconsistent with bound states. In this Letter, we
develop the formalism and study the phenomenology of another model
by the twisted permutation algebra and extend the
Pauli Exclusion Principle(PEP) into non-commutative spacetime. The model also
implies time quantization and can avoid UV/IR mixing. Applying it to atomic
systems, we show that the model with newly induced phase factors can cause
exotic transitions consisting of three electrons in the 1S orbit of atoms. The
transition rate is derived, and the upper bound of non-commutative parameter
is thus set by utilizing data from the low-energy and low-background
experiments, where strongest constraint eV
at 90\% C.L. is given by XENONnT, with the time quanta , equivalent to twenty times smaller than the Planck time.Comment: 6 pages, 4 figure
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