6,797 research outputs found
Spin Seebeck effect from antiferromagnetic magnons and critical spin fluctuations in epitaxial FeF2 films
We report a longitudinal spin Seebeck effect (SSE) study in epitaxially grown
FeF2(110) antiferromagnetic (AFM) thin films with strong uniaxial anisotropy
over the temperature range of 3.8 - 250 K. Both the magnetic field- and
temperature-dependent SSE signals below the N\'eel temperature (TN=70 K) of the
FeF2 films are consistent with a theoretical model based on the excitations of
AFM magnons without any net induced static magnetic moment. In addition to the
characteristic low-temperature SSE peak associated with the AFM magnons, there
is another SSE peak at TN which extends well into the paramagnetic phase. All
the SSE data taken at different magnetic fields up to 12 T near and above the
critical point TN follow the critical scaling law very well with the critical
exponents for magnetic susceptibility of 3D Ising systems, which suggests that
the AFM spin correlation is responsible for the observed SSE near TN
Enhancing solar chimney performance in urban tunnels: Investigating the impact factors through experimental and theoretical model analysis
Efficient and sustainable ventilation in urban tunnels is crucial for combating air pollution and safeguarding human health. This study investigates the design factors impacting solar chimney performance in urban tunnels to optimize ventilation efficiency. Experimental trials analyzed the effects of blockage ratio, chimney height, and solar radiation on temperature distribution and ventilation rate. The results demonstrate that increased chimney height and solar radiation positively influence airflow velocity at the chimney outlet, enhancing ventilation. The temperature rise near absorber is higher than that closed to glazing wall. Temperature distribution within the chimney follows a distinctive horizontal two-piecewise semi-parabolic decay pattern, enabling accurate prediction of temperature profiles along the cavity depth. Novel analytical models predict temperature distribution, airflow velocity, and ventilation rate within the solar chimney system, aiding precise design and optimization. Remarkably, the blockage ratio has limited impact on ventilation rate, allowing for disregarding vehicle blockage effects in solar chimney design for urban tunnels. Matching chimney width to tunnel width and ensuring a relatively high chimney height are emphasized for optimal functionality. The study holds substantial implications for ventilation system design in urban environments, promoting healthier and more sustainable cities
Performance evaluation of solar chimney in tunnel for passive ventilation and smoke exhaustion: A numerical approach
Solar chimney applied in building ventilation can passively regulate indoor air quality without electricity cost and carbon emissions, but its application in tunnel is limited. This study conducted a numerical modelling and theoretical analysis to investigate the volumetric flow rate through multi-channel solar chimney group in tunnel under normal and fire conditions. The influences of the solar chimney arrangements on ventilation and smoke exhaustion capacity were analyzed. Results show that the solar chimney group can afford natural ventilation in tunnel without compromising the performance of smoke exhaustion through shaft. With absorbed more solar energy, increasing cavity amount and cavity width can effectively improve the ventilation performance but limited effect on smoke exhaustion. The volumetric flow rate increases with cavity height and cavity depth that is proportional to hc1/3 and L2/3 under natural ventilation. The volumetric flow rate under natural ventilation and smoke exhaustion both increase with total chimney channel area. A theoretical model considering horizontally semi-parabolic temperature distribution inside each channel was developed to correlate the volumetric flow rate, the predictions agree reasonably with numerical results under normal and fire conditions. This study contributes to the application of solar chimney group in urban tunnels and guides extraction design
Comparing the Host Galaxies of Type Ia, Type II and Type Ibc Supernovae
We compare the host galaxies of 902 supernovae, including SNe Ia, SNe II and
SNe Ibc, which are selected by cross-matching the Asiago Supernova Catalog with
the SDSS Data Release 7. We further selected 213 galaxies by requiring the
light fraction of spectral observations 15%, which could represent well the
global properties of the galaxies. Among them, 135 galaxies appear on the
Baldwin-Phillips-Terlevich diagram, which allows us to compare the hosts in
terms of star-forming, AGNs (including composites, LINERs and Seyfert 2s) and
"Absorp" (their related emission-lines are weak or non-existence) galaxies. The
diagrams related to parameters D(4000), H, stellar masses, SFRs
and specific SFRs for the SNe hosts show that almost all SNe II and most of SNe
Ibc occur in SF galaxies, which have a wide range of stellar mass and low
D(4000). The SNe Ia hosts as SF galaxies follow similar trends. A
significant fraction of SNe Ia occurs in AGNs and Absorp galaxies, which are
massive and have high D(4000). The stellar population analysis from
spectral synthesis fitting shows that the hosts of SNe II have a younger
stellar population than hosts of SNe Ia. These results are compared with those
of the 689 comparison galaxies where the SDSS fiber captures less than 15% of
the total light. These comparison galaxies appear biased towards higher
12+log(O/H) (0.1dex) at a given stellar mass. Therefore, we believe the
aperture effect should be kept in mind when the properties of the hosts for
different types of SNe are discussed.Comment: 15 pages, 9 figure
Theoretical models for predicting ventilation performance of vertical solar chimneys in tunnels
Solar chimney as a reliable renewable energy system has been primarily utilized for building ventilation, but its application in the tunnel is rarely explored. This study develops theoretical models to predict the ventilation performance of vertical solar chimney in urban tunnel. Five temperature distribution types within the chimney cavity are analyzed, including uniform, vertically linear, horizontally semi-parabolic, two piecewise semi-parabolic in the depth direction, and three-dimensional parabolic profiles. The theoretical models consider the effect of chimney configuration, tunnel geometry, glazing materials, and solar radiation intensity on airflow rate through solar chimney. Validation against experimental data and numerical simulation shows that considering three-dimensional temperature distributions results in an average 11 % deviation from validation data, outperforming assumptions of uniform (29.3 % deviation) or lower-dimensional profiles. The volumetric flow rate through solar chimney exponentially decreased with h/w and h/d that the optimum ratio of h/d is 10. The airflow rate linearly increased with 0.14 power of glazing absorptivity. This analysis provides technical guidance for optimizing solar chimney design in tunnels, enhancing natural ventilation, and reducing energy consumption for mechanical ventilation systems
Spin Seebeck effect from antiferromagnetic magnons and critical spin fluctuations in epitaxial FeF2 films
We report a longitudinal spin Seebeck effect (SSE) study in epitaxially grown
FeF2(110) antiferromagnetic (AFM) thin films with strong uniaxial anisotropy
over the temperature range of 3.8 - 250 K. Both the magnetic field- and
temperature-dependent SSE signals below the N\'eel temperature (TN=70 K) of the
FeF2 films are consistent with a theoretical model based on the excitations of
AFM magnons without any net induced static magnetic moment. In addition to the
characteristic low-temperature SSE peak associated with the AFM magnons, there
is another SSE peak at TN which extends well into the paramagnetic phase. All
the SSE data taken at different magnetic fields up to 12 T near and above the
critical point TN follow the critical scaling law very well with the critical
exponents for magnetic susceptibility of 3D Ising systems, which suggests that
the AFM spin correlation is responsible for the observed SSE near TN
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