351,456 research outputs found
Experimental and computational investigation of confined laser-induced breakdown spectroscopy
This paper presents an experimental and computational study on laser-induced breakdown spectroscopy (LIBS) for both unconfined flat surface and confined cavity cases. An integrated LIBS system is employed to acquire the shockwave and plasma plume images. The computational model consists of the mass, momentum, and energy conservation equations, which are necessary to describe shockwave behaviors. The numerical predictions are validated against shadowgraphic images in terms of shockwave expansion and reflection. The three-dimensional (3D) shockwave morphology and velocity fields are displayed and discussed
Discharge precipitate's impact in Li-air battery: Comparison of experiment and model predictions
This paper presents a fundamental study on the precipitate formation/morphology and impact of discharge precipitates in Li-air batteries and compares the voltage loss with two Li-air battery models, namely a film-resistor model and surface coverage model. Toray carbon cloth is selected as cathode, which serves as large-porosity electrodes with an approximately planar reaction surface. Imaging analysis shows film formation of precipitates is observed in all the experiments. In addition, toroidal and aggregate morphologies are present under lower currents as well. Specially, toroidal or partially toroidal deposit is observed for 0.06 A/cm2. Aggregates, which consist of small particles with grain boundaries, are shown for 0.03 A/cm2. We found that the film-resistor model is unable to predict the discharge voltage behaviors under the two lower currents due to the presence of the deposit morphologies other than the film formation. The coverage model's prediction shows acceptable agreement with the experimental data because the model accounts for impacts of various morphologies of precipitates
Environmental Dependence of Cold Dark Matter Halo Formation
We use a high-resolution -body simulation to study how the formation of
cold dark matter (CDM) halos is affected by their environments, and how such
environmental effects produce the age-dependence of halo clustering observed in
recent -body simulations. We estimate, for each halo selected at redshift
, an `initial' mass defined to be the mass enclosed by the
largest sphere which contains the initial barycenter of the halo particles and
within which the mean linear density is equal to the critical value for
spherical collapse at . For halos of a given final mass, , the
ratio has large scatter, and the scatter is larger for
halos of lower final masses. Halos that form earlier on average have larger
, and so correspond to higher peaks in the initial density
field than their final masses imply. Old halos are more strongly clustered than
younger ones of the same mass because their initial masses are larger. The
age-dependence of clustering for low-mass halos is entirely due to the
difference in the initial/final mass ratio. Low-mass old halos are almost
always located in the vicinity of big structures, and their old ages are
largely due to the fact that their mass accretions are suppressed by the hot
environments produced by the tidal fields of the larger structure. The
age-dependence of clustering is weaker for more massive halos because the
heating by large-scale tidal fields is less important.Comment: 18 pages,19 figures, accepted by MNRA
Measuring the cosmic proper distance from fast radio bursts
The cosmic proper distance is a fundamental distance in the Universe.
Unlike the luminosity and angular diameter distances, which correspond to the
angular size, the proper distance is the length of light path from the source
to observer. However, the proper distance has not been measured before. The
recent redshift measurement of a repeat fast radio burst (FRB) can shed light
on the proper distance. We show that the proper distance-redshift relation can
indeed be derived from dispersion measures (DMs) of FRBs with measured
redshifts. From Monte Carlo simulations, we find that about 500 FRBs with DM
and redshift measurements can tightly constrain the proper distance-redshift
relation. We also show that the curvature of our Universe can be constrained
with a model-independent method using this derived proper distance-redshift
relation and the observed angular diameter distances. Owing to the high event
rate of FRBs, hundreds of FRBs can be discovered in the future by upcoming
instruments. The proper distance will play an important role in investigating
the accelerating expansion and the geometry of the Universe.Comment: 9 pages, 4 figures, proof versio
Extracting and Stabilizing the Unstable State of Hysteresis Loop
A novel perturbation method for the stabilization of unstable intermediate
states of hysteresis loop (i.e. S-shaped curve) is proposed. This method only
needs output signals of the system to construct the perturbation form without
delay-coordinate embedding technique, it is more practical for real-world
systems. Stabilizing and tracking the unstable intermediate branch are
demonstrated through the examples of a bistable laser system and delay feedback
system. All the numerical results are obtained by simulating each of the real
experimential conditions.Comment: 6 pages, REVTEX, 4 ps figure
DISCHARGE OXIDE STORAGE CAPACITY AND VOLTAGE LOSS IN LI-AIR BATTERY
Air cathodes, where oxygen reacts with Li ions and electrons with discharge oxide stored in their pore structure, are often considered as the most challenging component in nonaqueous Lithium-air batteries. In non-aqueous electrolytes, discharge oxides are usually insoluble and hence precipitate at local reaction site, raising the oxygen transport resistance in the pore network. Due to their low electric conductivity, their presence causes electrode passivation. This study aims to investigate the air cathode's performance through analytically obtaining oxygen profiles, modeling electrode passivation, evaluating the transport polarization raised by discharge oxide precipitate, and developing analytical formulas for insoluble Li oxides storage capacity. The variations of cathode quantities, including oxygen content and temperature, are evaluated and related to a single dimensionless parameter - the Damköhler Number (Da). An approximate model is developed to predict discharge voltage loss, along with validation against two sets of experimental data. Air cathode properties, including tortuosity, surface coverage factor and the Da number, and their effects on the cathode's capacity of storing Li oxides are formulated and discussed
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