183 research outputs found
The Decay Process of an {\alpha}-configuration Sunspot
The decay of sunspot plays a key role in magnetic flux transportation in
solar active regions (ARs). To better understand the physical mechanism of the
entire decay process of a sunspot, an {\alpha}-configuration sunspot in AR NOAA
12411 was studied. Based on the continuum intensity images and vector magnetic
field data with stray light correction from Solar Dynamics
Observatory/Helioseismic and Magnetic Imager, the area, vector magnetic field
and magnetic flux in the umbra and penumbra are calculated with time,
respectively. Our main results are as follows: (1) The decay curves of the
sunspot area in its umbra, penumbra, and whole sunspot take the appearance of
Gaussian profiles. The area decay rates of the umbra, penumbra and whole
sunspot are -1.56 MSH/day, -12.61 MSH/day and -14.04 MSH/day, respectively; (2)
With the decay of the sunspot, the total magnetic field strength and the
vertical component of the penumbra increase, and the magnetic field of the
penumbra becomes more vertical. Meanwhile, the total magnetic field strength
and vertical magnetic field strength for the umbra decrease, and the
inclination angle changes slightly with an average value of about 20{\deg}; (3)
The magnetic flux decay curves of the sunspot in its umbra, penumbra, and whole
sunspot exhibit quadratic patterns, their magnetic flux decay rates of the
umbra, penumbra and whole sunspot are -9.84 * 10^19 Mx/day, -1.59 * 10^20
Mx/day and -2.60 * 10^20 Mx/day , respectively. The observation suggests that
the penumbra may be transformed into the umbra, resulting in the increase of
the average vertical magnetic field strength and the reduction of the
inclination angle in the penumbra during the decay of the sunspot
Laboratory observation of ion acceleration via reflection off laser-produced magnetized collisionless shocks
Fermi acceleration by collisionless shocks is believed to be the primary
mechanism to produce high energy charged particles in the Universe,where
charged particles gain energy successively from multiple reflections off the
shock front.Here,we present the first direct experimental evidence of ion
energization from reflection off a supercritical quasi perpendicular
collisionless shock,an essential component of Fermi acceleration in a laser
produced magnetized plasma. We observed a quasi monoenergetic ion beam with 2,4
times the shock velocity in the upstream flow using time of flight method. Our
related kinetic simulations reproduced the energy gain and showed that these
ions were first reflected and then accelerated mainly by the motional electric
field associated with the shock. This mechanism can also explain the quasi
monoenergetic fast ion component observed in the Earth's bow shock
Targeted inhibition of Wnt signaling with a Clostridioides difficile toxin B fragment suppresses breast cancer tumor growth
Wnt signaling pathways are transmitted via 10 homologous frizzled receptors (FZD1-10) in humans. Reagents broadly inhibiting Wnt signaling pathways reduce growth and metastasis of many tumors, but their therapeutic development has been hampered by the side effect. Inhibitors targeting specific Wnt-FZD pair(s) enriched in cancer cells may reduce side effect, but the therapeutic effect of narrow-spectrum Wnt-FZD inhibitors remains to be established in vivo. Here, we developed a fragment of C. difficile toxin B (TcdBFBD), which recognizes and inhibits a subclass of FZDs, FZD1/2/7, and examined whether targeting this FZD subgroup may offer therapeutic benefits for treating breast cancer models in mice. Utilizing 2 basal-like and 1 luminal-like breast cancer models, we found that TcdBFBD reduces tumor-initiating cells and attenuates growth of basal-like mammary tumor organoids and xenografted tumors, without damaging Wnt-sensitive tissues such as bones in vivo. Furthermore, FZD1/2/7–positive cells are enriched in chemotherapy-resistant cells in both basal-like and luminal mammary tumors treated with cisplatin, and TcdBFBD synergizes strongly with cisplatin in inhibiting both tumor types. These data demonstrate the therapeutic value of narrow-spectrum Wnt signaling inhibitor in treating breast cancers
Potential of Core-Collapse Supernova Neutrino Detection at JUNO
JUNO is an underground neutrino observatory under construction in Jiangmen, China. It uses 20kton liquid scintillator as target, which enables it to detect supernova burst neutrinos of a large statistics for the next galactic core-collapse supernova (CCSN) and also pre-supernova neutrinos from the nearby CCSN progenitors. All flavors of supernova burst neutrinos can be detected by JUNO via several interaction channels, including inverse beta decay, elastic scattering on electron and proton, interactions on C12 nuclei, etc. This retains the possibility for JUNO to reconstruct the energy spectra of supernova burst neutrinos of all flavors. The real time monitoring systems based on FPGA and DAQ are under development in JUNO, which allow prompt alert and trigger-less data acquisition of CCSN events. The alert performances of both monitoring systems have been thoroughly studied using simulations. Moreover, once a CCSN is tagged, the system can give fast characterizations, such as directionality and light curve
Detection of the Diffuse Supernova Neutrino Background with JUNO
As an underground multi-purpose neutrino detector with 20 kton liquid scintillator, Jiangmen Underground Neutrino Observatory (JUNO) is competitive with and complementary to the water-Cherenkov detectors on the search for the diffuse supernova neutrino background (DSNB). Typical supernova models predict 2-4 events per year within the optimal observation window in the JUNO detector. The dominant background is from the neutral-current (NC) interaction of atmospheric neutrinos with 12C nuclei, which surpasses the DSNB by more than one order of magnitude. We evaluated the systematic uncertainty of NC background from the spread of a variety of data-driven models and further developed a method to determine NC background within 15\% with {\it{in}} {\it{situ}} measurements after ten years of running. Besides, the NC-like backgrounds can be effectively suppressed by the intrinsic pulse-shape discrimination (PSD) capabilities of liquid scintillators. In this talk, I will present in detail the improvements on NC background uncertainty evaluation, PSD discriminator development, and finally, the potential of DSNB sensitivity in JUNO
Robust estimation of bacterial cell count from optical density
Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data
Ligand-Enabled β-C(sp3)–H Lactonization: A Stepping Stone for General and Practical β-C–H Functionalizations
β-C–H
functionalization of aliphatic acids is emerging as a valuable synthetic
disconnection that complements a wide range of conjugate addition reactions. Despite
two decades of effort on β-C–H functionalizations, reported reactions bear numerous
challenges, especially for industrial-scale applications due to the use of
expensive oxidants and poor scope. For example, arylation reactions are only compatible
with aryl iodides but not the more practical aryl bromides and chlorides,
alkylations are limited to primary alkyl coupling partners; fluorination and
amination reactions have not been possible using free carboxylic acids as
directing groups. The unselective formation of mono- and di-functionalized
products is another major drawback. Herein, we report an unprecedented palladium-catalyzed
β-C(sp3)–H lactonization of aliphatic acids enabled by a mono-N-protected β-amino acid ligand. The highly
strained and reactive β-lactone products are versatile linchpins for the mono-selective
installation of diverse alkyl, alkenyl, aryl, alkynyl, fluoro, hydroxyl, and
amino groups at the β position of the parent acid, thus providing a one-for-all
strategy to synthesize a myriad of carboxylic acids. The use of inexpensive tert-butyl
hydrogen peroxide (TBHP) as the oxidant, as well as the ease of product
purification without column chromatography renders this reaction amenable to
ton-scale manufacturing
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