3,437 research outputs found
Insights into the Role of Transient Chiral Mediators and Pyridone Ligands in Asymmetric Pd-Catalyzed C–H Functionalization
Mechanistic investigations uncover a novel role for 2-pyridone ligands and interrogate the origin of enantioselectivity in the (+)-norbornene-mediated Pd-catalyzed meta-C(aryl)–H functionalization of diarylmethylamines. Observations from kinetic analysis in concert with in situ ¹⁹F NMR monitoring allow us to propose that the pyridone ligand plays a role in enhancing the rate- and enantio-determining insertion of an arylpalladium species into a chiral norbornene derivative. The unprecedented features of 2-pyridone ligands in asymmetric 1,2 migratory insertion, and norbornene as a transient chiral mediator in relay chemistry, provide new insights into this ligand scaffold for future developments in stereoselective transition-metal-catalyzed C–H functionalization
Insights into the Role of Transient Chiral Mediators and Pyridone Ligands in Asymmetric Pd-Catalyzed C–H Functionalization
Mechanistic investigations uncover a novel role for 2-pyridone ligands and interrogate the origin of enantioselectivity in the (+)-norbornene-mediated Pd-catalyzed meta-C(aryl)–H functionalization of diarylmethylamines. Observations from kinetic analysis in concert with in situ ¹⁹F NMR monitoring allow us to propose that the pyridone ligand plays a role in enhancing the rate- and enantio-determining insertion of an arylpalladium species into a chiral norbornene derivative. The unprecedented features of 2-pyridone ligands in asymmetric 1,2 migratory insertion, and norbornene as a transient chiral mediator in relay chemistry, provide new insights into this ligand scaffold for future developments in stereoselective transition-metal-catalyzed C–H functionalization
Electromagnetic counterparts of high-frequency gravitational waves in a rotating laboratory frame system and their detection
We consider the perturbative photon flows (PPFs, i.e., electromagnetic (EM)
counterparts) generated by the EM resonance response to high-frequency
gravitational waves (HFGWs) with additional polarization states in a rotating
laboratory frame system. It is found that when the propagating direction of the
HFGWs and the symmetrical axis of the laboratory frame system are the same, the
PPFs have the maximum value. In this case, using the rotation (the rotation of
azimuth ) of the EM detection system, all six possible polarization
states of the HFGWs can be separated and displayed. For the current
experimental conditions, it is quite prospective to detect the PPFs generated
by the HFGWs predicted in the braneworld models, the primordial black hole
theories and the interaction mechanism between astrophysical plasma and intense
EM radiation, etc., due to the large amplitudes (or high spectral densities)
and spectral characteristics of these HFGWs. Detecting the primordial HFGWs
from inflation faces great challenges at present, but it is not impossible.Comment: 29 pages, 8 figures, 1 table; corrected some minor typos; added
reference
Neural Network Based Edge Detection for Automated Medical Diagnosis
Edge detection is an important but rather difficult task in image processing and analysis. In this research, artificial neural networks are employed for edge detection based on its adaptive learning and nonlinear mapping properties. Fuzzy sets are introduced during the training phase to improve the generalization ability of neural networks. The application of the proposed neural network approach to the edge detection of medical images for automated bladder cancer diagnosis is also investigated. Successful computer simulation results are obtained
Diagnostic value of two dimensional shear wave elastography combined with texture analysis in early liver fibrosis.
BACKGROUND: Staging diagnosis of liver fibrosis is a prerequisite for timely diagnosis and therapy in patients with chronic hepatitis B. In recent years, ultrasound elastography has become an important method for clinical noninvasive assessment of liver fibrosis stage, but its diagnostic value for early liver fibrosis still needs to be further improved. In this study, the texture analysis was carried out on the basis of two dimensional shear wave elastography (2D-SWE), and the feasibility of 2D-SWE plus texture analysis in the diagnosis of early liver fibrosis was discussed.
AIM: To assess the diagnostic value of 2D-SWE combined with textural analysis in liver fibrosis staging.
METHODS: This study recruited 46 patients with chronic hepatitis B. Patients underwent 2D-SWE and texture analysis; Young\u27s modulus values and textural patterns were obtained, respectively. Textural pattern was analyzed with regard to contrast, correlation, angular second moment (ASM), and homogeneity. Pathological results of biopsy specimens were the gold standard; comparison and assessment of the diagnosis efficiency were conducted for 2D-SWE, texture analysis and their combination.
RESULTS: 2D-SWE displayed diagnosis efficiency in early fibrosis, significant fibrosis, severe fibrosis, and early cirrhosis (AUC \u3e 0.7, P \u3c 0.05) with respective AUC values of 0.823 (0.678-0.921), 0.808 (0.662-0.911), 0.920 (0.798-0.980), and 0.855 (0.716-0.943). Contrast and homogeneity displayed independent diagnosis efficiency in liver fibrosis stage (AUC \u3e 0.7, P \u3c 0.05), whereas correlation and ASM showed limited values. AUC of contrast and homogeneity were respectively 0.906 (0.779-0.973), 0.835 (0.693-0.930), 0.807 (0.660-0.910) and 0.925 (0.805-0.983), 0.789 (0.639-0.897), 0.736 (0.582-0.858), 0.705 (0.549-0.883) and 0.798 (0.650-0.904) in four liver fibrosis stages, which exhibited equivalence to 2D-SWE in diagnostic efficiency (P \u3e 0.05). Combined diagnosis (PRE) displayed diagnostic efficiency (AUC \u3e 0.7, P \u3c 0.01) for all fibrosis stages with respective AUC of 0.952 (0.841-0.994), 0.896 (0.766-0.967), 0.978 (0.881-0.999), 0.947 (0.835-0.992). The combined diagnosis showed higher diagnosis efficiency over 2D-SWE in early liver fibrosis (P \u3c 0.05), whereas no significant differences were observed in other comparisons (P \u3e 0.05).
CONCLUSION: Texture analysis was capable of diagnosing liver fibrosis stage, combined diagnosis had obvious advantages in early liver fibrosis, liver fibrosis stage might be related to the hepatic tissue hardness distribution
Testing the spatial geometry of the universe with TianQin: the prospect of using supermassive black hole binaries
The determination of the spatial geometry of the universe plays an important
role in modern cosmology. Any deviation from the cosmic curvature
would have a profound impact on the primordial inflation paradigm and
fundamental physics. In this paper, we carry out a systematic study of the
prospect of measuring cosmic curvature with the inspiral signal of supermassive
black hole binaries (SMBHBs) that could be detected with TianQin. The study is
based on a cosmological-model-independent method that extended the application
of gravitational wave (GW) standard sirens in cosmology. By comparing the
distances from future simulated GW events and simulated data, we
evaluate if TianQin would produce robust constraints on the cosmic curvature
parameter . More specifically, we consider 3-yr to 10-yr
observations of supermassive black hole binaries with total masses ranging from
to . Our results show that in the future, with
the synergy of 10-yr high-quality observations, we can tightly constrain the
curvature parameter at the level of .
Moreover, our findings indicate that the total mass of SMBHB does influence the
estimation of cosmic curvature, implied by the analysis performed on different
subsamples of gravitational wave data. Therefore, TianQin is expected to
provide a powerful and competitive probe of the spatial geometry of the
universe, compared to future spaced-based detectors such as DECIGO.Comment: This article has been accepted by Astronomy & Astrophysic
Heat statistics in the relaxation process of the Edwards-Wilkinson elastic manifold
The stochastic thermodynamics of systems with a few degrees of freedom has
been studied extensively so far. We would like to extend the study to systems
with more degrees of freedom and even further-continuous fields with infinite
degrees of freedom. The simplest case for a continuous stochastic field is the
Edwards-Wilkinson elastic manifold. It is an exactly solvable model of which
the heat statistics in the relaxation process can be calculated analytically.
The cumulants require a cutoff spacing to avoid ultra-violet divergence. The
scaling behavior of the heat cumulants with time and the system size as well as
the large deviation rate function of the heat statistics in the large size
limit is obtained
The synthesis and characterization of 1111-type diluted magnetic semiconductors (La1-xSrx)(Zn1-xTMx)AsO (TM = Mn, Fe, Co)
The doping effect of Sr and transition metals Mn, Fe, Co into the direct-gap
semiconductor LaZnAsO has been investigated. Our results indicate that the
single phase ZrCuSiAs-type tetragonal crystal structure is preserved in
(La1-xSrx)(Zn1-xTMx)AsO (TM = Mn, Fe, Co) with the doping level up to x = 0.1.
While the system remains semiconducting, doping with Sr and Mn results in
ferromagnetic order with TC ~ 30K, and doping with Sr and Fe results in a spin
glass like state below ~6K with a saturation moment of ~0.02 muB/Fe, an order
of magnitude smaller than the ~0.4 muB/Mn of Sr and Mn doped samples. The same
type of magnetic state is observed neither for (Zn,Fe) substitution without
carrier doping, nor for Sr and Co doped specimens.Comment: Accepted for publication in EP
- …