97 research outputs found
Deprojection technique for galaxy cluster considering point spread function
We present a new method for the analysis of Abell 1835 observed by
XMM-Newton. The method is a combination of the Direct Demodulation technique
and deprojection. We eliminate the effects of the point spread function (PSF)
with the Direct Demodulation technique. We then use a traditional depro-jection
technique to study the properties of Abell 1835. Compared to that of
deprojection method only, the central electron density derived from this method
increases by 30%, while the temperature profile is similar.Comment: accepted for publication in Sciences in China -- G, the Black Hole
special issu
Characterization and insight mechanism of an acid-adapted β-Glucosidase from Lactobacillus paracasei and its application in bioconversion of glycosides
Introduction: β-glucosidase is one class of pivotal glycosylhydrolase enzyme that can cleavage glucosidic bonds and transfer glycosyl group between the oxygen nucleophiles. Lactobacillus is the most abundant bacteria in the human gut. Identification and characterization of new β-glucosidases from Lactobacillus are meaningful for food or drug industry.Method: Herein, an acid-adapted β-glucosidase (LpBgla) was cloned and characterized from Lactobacillus paracasei. And the insight acid-adapted mechanism of LpBgla was investigated using molecular dynamics simulations.Results and Discussion: The recombinant LpBgla exhibited maximal activity at temperature of 30°C and pH 5.5, and the enzymatic activity was inhibited by Cu2+, Mn2+, Zn2+, Fe2+, Fe3+ and EDTA. The LpBgla showed a more stable structure, wider substrate-binding pocket and channel aisle, more hydrogen bonds and stronger molecular interaction with the substrate at pH 5.5 than pH 7.5. Five residues including Asp45, Leu60, Arg120, Lys153 and Arg164 might play a critical role in the acid-adapted mechanism of LpBgla. Moreover, LpBgla showed a broad substrate specificity and potential application in the bioconversion of glycosides, especially towards the arbutin. Our study greatly benefits for the development novel β-glucosidases from Lactobacillus, and for the biosynthesis of aglycones
Interactions Between Nanoparticles and Dendritic Cells: From the Perspective of Cancer Immunotherapy
Dendritic cells (DCs) are the primary antigen-presenting cells and play key roles in the orchestration of the innate and adaptive immune system. Targeting DCs by nanotechnology stands as a promising strategy for cancer immunotherapy. The physicochemical properties of nanoparticles (NPs) influence their interactions with DCs, thus altering the immune outcome of DCs by changing their functions in the processes of maturation, homing, antigen processing and antigen presentation. In this review, we summarize the recent progress in targeting DCs using NPs as a drug delivery carrier in cancer immunotherapy, the recognition of NPs by DCs, and the ways the physicochemical properties of NPs affect DCs' functions. Finally, the molecular pathways in DCs that are affected by NPs are also discussed
Type-A quasi-periodic oscillation in the black hole transient MAXI J1348-630
We present a detailed analysis of the spectral and timing characteristics of
a 7-Hz type-A quasi-periodic oscillation (QPO) detected in NICER observations
of the black hole X-ray binary MAXI J1348-630 during its high-soft state. The
QPO is broad and weak, with an integrated fractional rms amplitude of 0.9 per
cent in the 0.5-10 keV band. Thanks to the large effective area of NICER,
combined with the high flux of the source and a relatively long accumulative
exposure time, we construct the first rms and phase-lag spectra for a type-A
QPO. Our analysis reveals that the fractional rms amplitude of the QPO
increases with energy from below 1 per cent at 1 keV to 3 per cent at 6 keV.
The shape of the QPO spectrum is similar to that of the Comptonised component,
suggesting that the Comptonised region is driving the variability. The phase
lags at the QPO frequency are always soft taking the lowest energy as
reference. By jointly fitting the time-averaged spectrum of the source and the
rms and phase-lag spectra of the QPO with the time-dependent Comptonisation
model vkompthdk, we find that the radiative properties of the type-A QPO can be
explained by a vertically extended Comptonised region with a size of 2300 km.Comment: 7 pages, 5 figures, accepted for publication in MNRA
Type-A quasi-periodic oscillation in the black hole transient MAXI J1348-630
We present a detailed analysis of the spectral and timing characteristics of a 7-Hz type-A quasi-periodic oscillation (QPO) detected in NICER observations of the black hole X-ray binary MAXI J1348-630 during its high-soft state. The QPO is broad and weak, with an integrated fractional rms amplitude of 0.9 per cent in the 0.5-10 keV band. Thanks to the large effective area of NICER, combined with the high flux of the source and a relatively long accumulative exposure time, we construct the first rms and phase-lag spectra for a type-A QPO. Our analysis reveals that the fractional rms amplitude of the QPO increases with energy from below 1 per cent at 1 keV to ∼3 per cent at 6 keV. The shape of the QPO spectrum is similar to that of the Comptonized component, suggesting that the Comptonized region is driving the variability. The phase lags at the QPO frequency are always soft taking the lowest energy as reference. By jointly fitting the time-averaged spectrum of the source and the rms and phase-lag spectra of the QPO with the time-dependent Comptonization model vkompthdk, we find that the radiative properties of the type-A QPO can be explained by a vertically extended Comptonized region with a size of ∼2300 km.</p
The atomic gas of star-forming galaxies at z0.05 as revealed by the Five-hundred-meter Aperture Spherical Radio Telescope
We report new HI observations of four z0.05 star-forming galaxies
undertaken during the commissioning phase of the Five-hundred-meter Aperture
Spherical Radio Telescope (FAST). FAST is the largest single-dish telescope
with a 500 meter aperture and a 19-Beam receiver. Exploiting the unprecedented
sensitivity provided by FAST, we aim to study the atomic gas, via the HI 21cm
emission line, in low- star-forming galaxies taken from the Valpara\'iso
ALMA/APEX Line Emission Survey (VALES) project. Together with previous ALMA
CO() observations, the HI data provides crucial information to measure
the gas mass and dynamics. As a pilot HI survey, we targeted four local
star-forming galaxies at . In particular, one of them has already
been detected in HI by the Arecibo Legacy Fast ALFA survey (ALFALFA), allowing
a careful comparison. We use an ON-OFF observing approach that allowed us to
reach an rms of 0.7mJy/beam at a 1.7km/s velocity resolution within only 20
minutes ON-target integration time. We demonstrate the great capabilities of
the FAST 19-beam receiver for pushing the detectability of the HI emission line
of extra-galactic sources. The HI emission line detected by FAST shows good
consistency with the previous ALFALFA results. Our observations are put in
context with previous multi-wavelength data to reveal the physical properties
of these low- galaxies. We find that the CO() and HI emission line
profiles are similar. The dynamical mass estimated from the HI data is an order
of magnitude higher than the baryon mass and the dynamical mass derived from
the CO observations, implying that the mass probed by dynamics of HI is
dominated by the dark matter halo. In one case, a target shows an excess of
CO() in the line centre, which can be explained by an enhanced
CO() emission induced by a nuclear starburst showing high velocity
dispersion.Comment: 5 pages, 3 figures, 2 appendix, A&A Letter accepte
Ultrafast Surface-Specific Spectroscopy of Water at a Photoexcited TiO2 Model Water-Splitting Photocatalyst
A critical step in photocatalytic water dissociation is the hole-mediated oxidation reaction. Molecular-level insights into the mechanism of this complex reaction under realistic conditions with high temporal resolution are highly desirable. Here, we use femtosecond time-resolved, surface-specific vibrational sum frequency generation spectroscopy to study the photo-induced reaction directly at the interface of the photocatalyst TiO2 in contact with liquid water at room temperature. Thanks to the inherent surface specificity of the spectroscopic method, we can follow the reaction of solely the interfacial water molecules directly at the interface at timescales on which the reaction takes place. Following the generation of holes at the surface immediately after photoexcitation of the catalyst with UV light, water dissociation occurs on a sub-20 ps timescale. The reaction mechanism is similar at pH 3 and 11. In both cases, we observe the conversion of H2O into Ti−OH groups and the deprotonation of pre-existing Ti−OH groups. This study provides unique experimental insights into the early steps of the photo-induced dissociation processes at the photocatalyst-water interface, relevant to the design of improved photocatalysts
High energy Millihertz quasi-periodic oscillations in 1A 0535+262 with Insight-HXMT challenge current models
We studied the millihertz quasi-periodic oscillation (mHz QPO) in the 2020
outburst of the Be/X-ray binary 1A 0535+262 using Insight-HXMT data over a
broad energy band. The mHz QPO is detected in the 27-120 keV energy band. The
QPO centroid frequency is correlated with the source flux, and evolves in the
35-95 mHz range during the outburst. The QPO is most significant in the 50-65
keV band, with a significance of ~ 8 sigma, but is hardly detectable (<2 sigma)
in the lowest (1-27 keV) and highest (>120 keV) energy bands. Notably, the
detection of mHz QPO above 80 keV is the highest energy at which mHz QPOs have
been detected so far. The fractional rms of the mHz QPO first increases and
then decreases with energy, reaching the maximum amplitude at 50-65 keV. In
addition, at the peak of the outburst, the mHz QPO shows a double-peak
structure, with the difference between the two peaks being constant at ~0.02
Hz, twice the spin frequency of the neutron star in this system. We discuss
different scenarios explaining the generation of the mHz QPO, including the
beat frequency model, the Keplerian frequency model, the model of two jets in
opposite directions, and the precession of the neutron star, but find that none
of them can explain the origin of the QPO well. We conclude that the
variability of non-thermal radiation may account for the mHz QPO, but further
theoretical studies are needed to reveal the physical mechanism.Comment: 13 pages, 7 figures. Accepted for publication in MNRA
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