Drilling is involved in many applications of carbon fiber-reinforced plastic (CFRP) composites. Rotary ultrasonic machining (RUM) has been successfully employed to drill holes in CFRP using either ...cutting fluid or cold air as coolant. However, there are no reported studies to compare the results in RUM of CFRP using these two types of coolant. This article, for the first time, presents an experimental study to compare cutting force, torque, surface roughness, burning of machined surface, and tool wear in RUM of CFRP using these two types of coolant. This study will result in knowledge about machining conditions under which it is feasible to use cold air instead of cutting fluid and differences in machined hole quality produced using cold air vs. cutting fluid.
Carbon fiber–reinforced plastic composites have many superior properties, including low density, high strength-to-weight ratio, and good durability, which make them attractive in many industries. ...However, due to anisotropic properties, high stiffness, and high abrasiveness of carbon fibers in carbon fiber–reinforced plastic, high cutting force, high tool wear, and high surface roughness are always caused in conventional machining processes. This article reports an investigation using rotary ultrasonic machining in surface grinding of carbon fiber–reinforced plastic composites in order to develop an effective and high-quality surface grinding process. In rotary ultrasonic machining surface grinding of carbon fiber–reinforced plastic composites, tool selection is of great importance since tool variables will significantly affect output variables. In this work, the effects of tool variables, including abrasive size, abrasive concentration, number of slots, and tool end geometry, on machining performances, including the cutting force, torque, and surface roughness, are experimentally studied. The results show that lower cutting forces and torque are generated by the tool with higher abrasive size, lower abrasive concentration, and two slots. Lower surface roughness is generated by the tool with smaller abrasive size, smaller abrasive concentration, two slots, and convex end geometry. This investigation will provide guides for tool selections during rotary ultrasonic machining surface grinding of carbon fiber–reinforced plastic composites.
CrN coatings have been grown by arc ion plating (AIP) onto Ti6Al4V alloy substrate at various nitrogen pressures (PN2). The goals of this investigation are to study the influence of nitrogen pressure ...content on the composition, structure and mechanical properties of AIP CrN coatings, as well as their tribological properties. With an increase of PN2, the main phases in the coatings changed from CrN+Cr2N+Cr to CrN, and the texture of CrN was transformed from CrN (111)-oriented to (220)-oriented. Furthermore, the multi-layers including a metal Cr layer, a Cr2N layer and a CrN layer were observed by cross-sectional TEM (XTEM), besides an “unbalanced” state transition layer at the interface of CrN/substrate which was analyzed by nucleation thermodynamics subsequently. An increase in nitrogen pressure also resulted in a change of micro-hardness due to the variation in composition and structure. Finally, the tribological properties of the Ti6Al4V substrate and the CrN/Ti6Al4V coating system have also been explored, which shows that CrN coatings can act as good wear resistance layer for Ti6Al4V substrate.
► The phases change was studied the phase diagram. ► We observed and proved the existence of a thin unbalanced state transition layer. ► The hardness of CrN coatings increases with the N content during a certain range. ► The wear mechanisms of CrN/Ti6Al4V coating system were discussed.
Highlights • SIRT3 levels are elevated after OGD in PC12 cells. • SIRT3 protects PC12 cells from oxidative stress-mediated cell damage. • SIRT3 protects against cell death through PGC-1α and the ...MnSOD pathway. • SIRT3 and PGC-1α regulate each other in physiologic and hypoxic conditions.
The 2020 coronavirus pandemic and the following quarantine measures have led to significant changes in daily life worldwide. Preliminary research indicates that air quality has improved in many urban ...areas as a result of these measures. This study takes a neighborhood-scale approach to quantifying this change in pollution. Using data from a network of citizen-hosted, low-cost particulate matter (PM) sensors, called Air Quality & yoU (AQ&U), we obtained high-spatial resolution measurements compared to the relatively sparse state monitoring stations. We compared monthly average estimated PM2.5 concentrations from February 11 to May 11, 2019 at 71 unique locations in Salt Lake County, UT, USA with the same (71) sensors’ measurements during the same timeframe in 2020. A paired t-test showed significant reductions (71.1% and 21.3%) in estimated monthly PM2.5 concentrations from 2019 to 2020 for the periods from March 11-April 10 and April 11-May 10, respectively. The March time period corresponded to the most stringent COVID-19 related restrictions in this region. Significant decreases in PM2.5 were also reported by state monitoring sites during March (p < 0.001 compared to the previous 5-year average). While we observed decreases in PM2.5 concentrations across the valley in 2020, it is important to note that the PM2.5 concentrations did not improve equally in all locations. We observed the greatest reductions at lower elevation, more urbanized areas, likely because of the already low levels of PM2.5 at the higher elevation, more residential areas, which were generally below 2 μg/m3 in both 2019 and 2020. Although many of measurements during March and April were near or below the estimated detection limit of the low-cost PM sensors and the federal equivalent measurements, every low-cost sensor (51) showed a reduction in PM2.5 concentration in March of 2020 compared to 2019. These results suggest that the air quality improvement seen after March 11, 2020 is due to quarantine measures reducing traffic and decreasing pollutant emissions in the region.
•Significant reductions in PM concentration corresponded to COVID-related restrictions and traffic reductions.•Networked low-cost PM measurements identified decreases in PM levels at 50+ locations.•The low-cost PM measurements supported findings from sparse state monitors.•The greatest percent reductions occurred in locations with the most urban activity.
Abstract
In this paper, the multiwavelength data from radio to X-ray bands for 2709 blazars in the 4FGL-DR3 catalog are compiled to calculate their spectral energy distributions using a parabolic ...equation
log
(
ν
f
ν
)
=
P
1
log
ν
−
P
2
2
+
P
3
. Some important parameters including spectral curvature (
P
1
), synchrotron peak frequency (
P
2
,
log
ν
p
), and peak luminosity (
log
L
p
) are obtained. Based on those parameters, we discussed the classification of blazars using the “Bayesian classification” and investigated some mutual correlations. We came to the following results. (1) Based on the Bayesian classification of synchrotron peak frequencies, the 2709 blazars can be classified into three subclasses, i.e.,
log
(
ν
p
/
Hz
)
<
13.7
for low synchrotron peak blazars (LSPs),
13.7
<
log
(
ν
p
/
Hz
)
<
14.9
for intermediate synchrotron peak blazars (ISPs), and
log
(
ν
p
/
Hz
)
>
14.9
for high synchrotron peak blazars (HSPs), and there are 820 HSPs, 750 ISPs, and 1139 LSPs. (2) The
γ
-ray emission has the closest relationship with radio emission, followed by optical emission, while the weakest relationship is that with X-ray emission. The
γ
-ray luminosity is also correlated with the synchrotron peak luminosity. (3) There are strong positive correlations between the curvature (1/∣
P
1
∣) and the peak frequency (
log
ν
p
) for all subclasses (FSRQs, (high, intermediate, and low) BL Lacertae objects). For different subclasses, the correlation slopes are different, which implies that there are different acceleration mechanisms and emission processes for different subclasses of blazars.
Beaming Effect in Fermi Blazars Yang, W. X.; Wang, H. G.; Liu, Y. ...
Astrophysical journal/The Astrophysical journal,
02/2022, Letnik:
925, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract
Blazars show extreme observational properties that are due to the beaming effect with the jet being close to the line of sight. It was found that the observed luminosity is anticorrelated ...with the synchrotron peak frequency but the debeamed luminosity and the frequency is positively correlated. In this work, we revisit this correlation for a large sample of 255 blazars from the fourth Fermi catalog with available Doppler factors. Our analysis comes to the following conclusions. (1) The observed radio, X-ray,
γ
-ray, and synchrotron peak luminosity are all anticorrelated with the peak frequency, but the debeamed luminosity is positively correlated with the debeamed peak frequency. The anticorrelation is due to a selection effect or a beaming effect. (2) The Compton dominance parameter is correlated with both the bolometric luminosity and Doppler factor, implying that the more highly Compton-dominated sources are more luminous. (3) The bolometric luminosity can be represented by the
γ
-ray luminosity for Fermi blazars.
Drought is a major threat to agricultural production. Plants synthesize
the hormone abscisic acid (ABA) in response to drought, triggering a signalling
cascade in guard cells that results in stomatal ...closure, thus reducing water
loss. ABA triggers an increase in cytosolic calcium in guard
cells (Ca2+cyt) that
has been proposed to include Ca2+ influx across the plasma
membrane. However, direct recordings of Ca
2+ currents have been limited and the upstream activation
mechanisms of plasma membrane Ca2+ channels remain unknown.
Here we report activation of Ca2+-permeable channels in the
plasma membrane of Arabidopsis guard cells by hydrogen peroxide. The
H2O2-activated Ca2+ channels mediate
both influx of Ca2+ in protoplasts and increases in Ca
2+cyt in intact guard cells. ABA induces the production
of H2O2 in guard cells. If H2O2
production is blocked, ABA-induced closure of stomata is inhibited. Moreover,
activation of Ca2+ channels by H2O2 and
ABA- and H2O2-induced stomatal closing are disrupted
in the recessive ABA-insensitive mutant gca2. These data indicate that
ABA-induced H2O2 production and the H2O
2-activated Ca2+ channels are important mechanisms for
ABA-induced stomatal closing.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
•RSM can be successfully applied for modeling and optimizing the UV-A pelleting process.•Energy consumption increased when ultrasonic power, sieve size, and pellet weight increased.•Effects of ...pelleting pressure had no significant effects on the energy consumption in UV-A pelleting.
Cellulosic biomass can be used as a feedstock for biofuel manufacturing. Pelleting of cellulosic biomass can increase its bulk density and thus improve its storability and reduce the feedstock transportation costs. Ultrasonic vibration-assisted (UV-A) pelleting can produce biomass pellets whose density is comparable to that processed by traditional pelleting methods (e.g. extruding, briquetting, and rolling). This study applied response surface methodology to the development of a predictive model for the energy consumption in UV-A pelleting of wheat straw. Effects of pelleting pressure, ultrasonic power, sieve size, and pellet weight were investigated. This study also optimized the process parameters to minimize the energy consumption in UV-A pelleting using response surface methodology. Optimal conditions to minimize the energy consumption were the following: ultrasonic power at 20%, sieve size at 4mm, and pellet weight at 1g, and the minimum energy consumption was 2.54Wh.
► A power consumption measurement method in rotary ultrasonic machining (RUM) is proposed. ► Effects of ultrasonic power, tool rotation speed, feedrate, and type of CFRP on power consumption are ...investigated. ► Power consumption percentages of each component are studied. ► Ultrasonic power supply in RUM system is not the largest power consumer during machining.
Carbon fiber reinforced plastic (CFRP) composites are very difficult to machine. A large number of holes need to be drilled in CFRP for many applications. Therefore, it is important to develop cost-effective drilling processes. CFRP has been drilled by rotary ultrasonic machining (RUM) successfully. The literature has reports about the effects of input variables on output variables (including cutting force, torque, surface roughness, tool wear, and workpiece delamination) in RUM of CFRP. However, there are no reports on power consumption in RUM of CFRP. This paper reports the first study on power consumption in RUM of CFRP. It reports an experimental investigation on effects of input variables (ultrasonic power, tool rotation speed, feedrate, and type of CFRP) on power consumption of each component (including ultrasonic power supply, spindle motor, coolant pump, and air compressor) and the entire RUM system.
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