821 research outputs found
Effect of Different Water-Binder Ratios and Fiber Contents on the Fluidity and Mechanical Properties of PVA-ECC Materials
With the development of fiber-reinforced cement composites, the diversity and complexity of application scenarios require enhanced strength and ductility and tough materials in practical engineering. To explore the effects of different water-binder ratios and fiber contents on the fluidity, bending resistance, tensile properties, fracture toughness, and fracture behavior of polyvinyl alcohol (PVA) fiber cement composites, several groups of high ductility test blocks (PVA-engineering cementitious composites (ECC)) with different mixing ratios were designed in this study. Based on the expansion degree, the mechanical experimental data, and the electron microscopy scanning image results, K-value analysis was performed on the strain hardening strength criterion. The effect of the water–binder ratio and the fiber dosing on the PVA-ECC material was determined. Results show that the greater the water-binder ratio is, the better the fluidity of the ECC matrix is. In the same cement system and at the same water-binder ratio, the fluidity of the ECC paste gradually deteriorates with the increase of the fiber content. The water-binder ratio significantly affects the flexural tensile strength of the composite. The flexural and tensile strengths of the PVA-ECC gradually increase as the water-binder ratio decreases, but the ductility gradually decreases. The water-binder ratio of the substrate directly influences the damage behavior of the fibers within the substrate. With the gradual increase of the water-binder ratio, the fiber at the crack interface gradually changes from pull-out morphology to fracture morphology. The strain capacity and the multi-crack cracking performance decrease. To achieve improved working performance in the actual project, the matrix water-binder ratio should be controlled at approximately 0.45, and the PVA fiber dose of 1.7% is optimal. This study can provide a good reference for the optimization of practical engineering components
Different Coalescence Sources of Light Nuclei Production in Au-Au Collisions at GeV
We study the production of light nuclei in the coalescence mechanism in Au-Au
collisions at midrapidity at GeV. We derive analytic formulas
of momentum distributions of two bodies, three bodies and four nucleons
coalescing into light nuclei, respectively. We naturally explain the transverse
momentum spectra of the deuteron (), triton (), helium-3 (He) and
helium-4 (He). We reproduce the data of yield rapidity densities and
averaged transverse momenta of , , He and He. We give proportions
of contributions from different coalescence sources for , He and He
in their productions. We find that besides nucleon coalescence,
nucleonnucleus coalescence and nucleusnucleus coalescence may play
requisite roles in light nuclei production in Au-Au collisions at
GeV.Comment: 5 figures, 6 table
Pressure-stabilized divalent ozonide CaO3 and its impact on Earth's oxygen cycles.
High pressure can drastically alter chemical bonding and produce exotic compounds that defy conventional wisdom. Especially significant are compounds pertaining to oxygen cycles inside Earth, which hold key to understanding major geological events that impact the environment essential to life on Earth. Here we report the discovery of pressure-stabilized divalent ozonide CaO3 crystal that exhibits intriguing bonding and oxidation states with profound geological implications. Our computational study identifies a crystalline phase of CaO3 by reaction of CaO and O2 at high pressure and high temperature conditions; ensuing experiments synthesize this rare compound under compression in a diamond anvil cell with laser heating. High-pressure x-ray diffraction data show that CaO3 crystal forms at 35 GPa and persists down to 20 GPa on decompression. Analysis of charge states reveals a formal oxidation state of -2 for ozone anions in CaO3. These findings unravel the ozonide chemistry at high pressure and offer insights for elucidating prominent seismic anomalies and oxygen cycles in Earth's interior. We further predict multiple reactions producing CaO3 by geologically abundant mineral precursors at various depths in Earth's mantle
Towards the Properties of Long Gamma-Ray Burst Progenitors with Swift Data
We investigate the properties of both the prompt and X-ray afterglows of
gamma-ray bursts (GRBs) in the burst frame with a sample of 33 Swift GRBs.
Assuming that the steep decay segment in the canonical X-ray afterglow
lightcurves is due to the curvature effect, we fit the lightcurves with a
broken power-law to derive the zero time of the last emission epoch of the
prompt emission (t1) and the beginning as well as the end time of the shallow
decay segment (t2 and t3).We show that both the isotropic peak gamma-ray
luminosity and gamma-ray energy are correlated with the isotropic X-ray energy
of the shallow decay phase and the isotropic X-ray luminosity at t2. We infer
the properties of the progenitor stars based on a model proposed by Kumar et
al. who suggested that both the prompt gamma-rays and the X-ray afterglows are
due to the accretions of different layers of materials of the GRB progenitor
star by a central black hole (BH). We find that most of the derived masses of
the core layers are 0.1-5 solar mass with a radius of 10^8-10^10 cm. The
rotation parameter is correlated with the burst duration, being consistent with
the expectation of collapsar models. The estimated radii and the masses of the
fall-back materials for the envelope layers are 10^10-10^12 cm and 10^-3~1
solar mass, respectively. The average accretion rates in the shallow decay
phase are correlated with those in the prompt gamma-ray phase, but they are
much lower. The derived radii of the envelope are smaller than the photospheric
radii of Wolf-Rayet (WR) stars. It is interesting that the assembled mass
density profile for the bursts in our sample is also well consistent with the
simulation for a pre-supernova star with 25 solar mass.Comment: 12 pages in MNRAS two-column style, 8 figures, 3 tables, accepted for
publication in MNRA
Tuning Properties of External Cavity Violet Semiconductor Laser
National Natural Science Foundation of China [91023048, 61106044, 61274052]A tunable grating-coupled external cavity (EC) laser is realized by employing a GaN-based laser diode as the gain device. A tuning range of 4.47 nm from 403.82 to 408.29 nm is achieved. Detailed investigations reveal that the injection current strongly influences the performance of the EC laser. Below the free-running lasing threshold, EC laser works stably. While above the free-running lasing threshold, a Fabry-Perot (F-P) resonance peak in the emission spectrum and a smooth kink in the output power-injection current characteristic curve are observed, suggesting the competition between the inner F-P cavity resonance and EC resonance. Furthermore, the tuning range is found to be asymmetric and occurs predominantly on the longer wavelength side. This is interpreted in terms of the asymmetric gain distribution of GaN-based quantum well material
Search for the radiative transitions and
By using a 2.92 fb data sample taken at GeV with
the BESIII detector operating at the BEPCII collider, we search for the
radiative transitions and
through the hadronic decays . No
significant excess of signal events above background is observed. We set upper
limits at a 90% confidence level for the product branching fractions to be
and
. Combining our result with world-average
values of , we find the
branching fractions
and at a 90%
confidence level.Comment: 10 pages, 4 figure
Search for C-parity violation in and
Using events recorded in
collisions at 3.686 GeV with the BESIII at the BEPCII collider, we
present searches for C-parity violation in and decays via . No significant
signals are observed in either channel. Upper limits on the branching fractions
are set to be and
at the 90\%
confidence level. The former is one order of magnitude more stringent than the
previous upper limit, and the latter represents the first limit on this decay
channel.Comment: 7 pages, 2 figure
Observation of at BESIII
Using events collected with the BESIII detector
at the BEPCII storage rings, we observe for the first time the process
,
with a significance of ( including systematic
uncertainties). The product branching fraction of is measured to be
, where the first error is statistical and the
second is systematic. This measurement provides information on the
production near threshold coupling to and improves the understanding
of the dynamics of decays to four body processes.Comment: 8 pages, 7 figure
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