137 research outputs found
Universality of BSW mechanism for spinning particles
Ba\~nados (BSW) found that Kerr black holes can act as particle
accelerators with collisions at arbitrarily high center-of-mass energies.
Recently, collisions of particles with spin around some rotating black holes
have been discussed. In this paper, we study the BSW mechanism for spinning
particles by using a metric ansatz which describes a general rotating black
hole. We notice that there are two inequivalent definitions of center-of-mass
(CM) energy for spinning particles. We mainly discuss the CM energy defined in
terms of the worldline of the particle. We show that there exists an
energy-angular momentum relation that causes collisions with
arbitrarily high energy near-extremal black holes. We also provide a simple but
rigorous proof that the BSW mechanism breaks down for nonextremal black holes.
For the alternative definition of the CM energy, some authors find a new
critical spin relation that also causes the divergence of the CM mass. However,
by checking the timelike constraint, we show that particles with this critical
spin cannot reach the horizon of the black hole. Further numerical calculation
suggests that such particles cannot exist anywhere outside the horizon. Our
results are universal, independent of the underlying theories of gravity.Comment: 8 pages, 1 figure
Aerobic exercise training at maximal fat oxidation intensity improves body composition, glycemic control, and physical capacity in older people with type 2 diabetes
Background: Aerobic training has been used as one of the common treatments for type 2 diabetes; however, further research on the individualized exercise program with the optimal intensity is still necessary. The purpose of this study was to investigate the effects of supervised exercise training at the maximal fat oxidation (FATmax) intensity on body composition, glycemic control, lipid profile, and physical capacity in older people with type 2 diabetes. Methods: Twenty-four women and 25 men with type 2 diabetes, aged 60–69 years. The exercise groups trained at the individualized FATmax intensity for 1 h/day for 3 days/week over 16 weeks. No dietary intervention was introduced during the experimental period. Whole body fat, abdominal fat, oral glucose tolerance test, lipid profile, and physical capacity were measured before and after the interventions. Results: FATmax intensity was at 41.3 ± 3.2% VO2max for women and 46.1 ± 10.3% VO2max for men. Exercise groups obtained significant improvements in body composition, with a special decrease in abdominal obesity; decreased resting blood glucose concentration and HbA1c; and increased VO2max, walking ability, and lower body strength, compared to the non-exercising controls. Daily energy intake and medication remained unchanged for all participants during the experimental period. Conclusion: Beside the improvements in the laboratory variables, the individualized FATmax training can also benefit daily physical capacity of older people with type 2 diabetes
Measurement of the complex polar magneto-optical Kerr effect using weak measurement
Polar magneto-optical Kerr effect (PMOKE) is one of the most widely being
applied magneto-optical Kerr effects (MOKE) due to the induced complex MOKE
signal, consisting of the Kerr rotation angle and the ellipticity, is very
sensitive to the magnetization component perpendicular to the magnetic surface.
However, the Kerr rotation angle and the ellipticity invariably coexist and
pose a challenge in their separation. This dual presence plays a pivotal role
in defining the light intensity detected, ultimately restricting the
advancements in the measurement precision. In this paper, we propose a weak
measurement (WM) scheme to measure the complex MOKE in the pure polar
configuration. Unlike the traditional MOKE or WM method using a
quarter-wave-plate to measure the Kerr rotation angle and the ellipticity
separately, we realize the simultaneous measurement of these two parameters in
a single WM process using two new pointers, which possesses a larger linear
response region compared with the previous amplified shift pointer. The
measurement precision for the complex PMOKE angle reaches to deg in
our experiment. Besides, the complex magneto-optical constant Q is also
calculated. This work is of great significance for the measurement of the
complex PMOKE with high efficiency, ultra-precision, low cost, and is an
important attempt to obtain complex physical quantities using WM
Fast Color-guided Depth Denoising for RGB-D Images by Graph Filtering
Depth images captured by off-the-shelf RGB-D cameras suffer from much
stronger noise than color images. In this paper, we propose a method to denoise
the depth images in RGB-D images by color-guided graph filtering. Our iterative
method contains two components: color-guided similarity graph construction, and
graph filtering on the depth signal. Implemented in graph vertex domain,
filtering is accelerated as computation only occurs among neighboring vertices.
Experimental results show that our method outperforms state-of-art depth image
denoising methods significantly both on quality and efficiency.Comment: 5 pages, 4 figure
V2C MXene-modified g-C3N4 for enhanced visible-light photocatalytic activity
Increasing the efficiency of charge transfer and separation efficiency of
photogenerated carriers are still the main challenges in the field of
semiconductor-based photocatalysts. Herein, we synthesized g-C3N4@V2C MXene
photocatalyst by modifying g-C3N4 using V2C MXene. The prepared photocatalyst
exhibited outstanding photocatalytic performance under visible light. The
degradation efficiency of methyl orange by g-C3N4@V2C MXene photocatalyst was
as high as 94.5%, which is 1.56 times higher than that by g-C3N4. This was
attributed to the V2C MXene inhibiting the rapid recombination of
photogenerated carriers and facilitating rapid transfer of photogenerated
electrons (e) from g-C3N4 to MXene. Moreover, g-C3N4@V2C MXene photocatalyst
showed good cycling stability. The photocatalytic performance was higher than
85% after three cycles. Experiments to capture free radicals revealed that
superoxide radicals (02) are the main contributors to the photocatalytic
activity. Thus, the proposed g-C3N4@V2C MXene photocatalyst is a promising
visible-light catalyst.Comment: 20 pages, 9 figure
Market investigation of basic parameters for exposure assessment of contact materials for nut-seed food in China
Objective To establish the basic parameters for exposure assessment of contact materials for nut-seed food in China. Methods The contact area method was used to study the contact materials of nut-seed food in this study. Based on the contact area values, ratio of contact areas and unit mass were obtained. Results Through investigation and analysis, 114 kinds of nut-seed food were sampled, and 3 648 related data were obtained. Food contact materials of nut-seed food on the market mainly included aluminum, polyethylene, polyethylene terephthalate, polypropylene, polystyrene and coating. The average contact area per unit mass or volume (S/V) was 21.29 dm2/kg, the median was 13.40 dm2/kg, P5 was 1.11 dm2/kg, and P95 was 67.46 dm2/kg. Conclusion The basic parameters of nut-seed food contact materials could provide data support for the safety assessment in China
Efficient and ultra-stable perovskite light-emitting diodes
Perovskite light-emitting diodes (PeLEDs) have emerged as a strong contender
for next-generation display and information technologies. However, similar to
perovskite solar cells, the poor operational stability remains the main
obstacle toward commercial applications. Here we demonstrate ultra-stable and
efficient PeLEDs with extraordinary operational lifetimes (T50) of 1.0x10^4 h,
2.8x10^4 h, 5.4x10^5 h, and 1.9x10^6 h at initial radiance (or current
densities) of 3.7 W/sr/m2 (~5 mA/cm2), 2.1 W/sr/m2 (~3.2 mA/cm2), 0.42 W/sr/m2
(~1.1 mA/cm2), and 0.21 W/sr/m2 (~0.7 mA/cm2) respectively, and external
quantum efficiencies of up to 22.8%. Key to this breakthrough is the
introduction of a dipolar molecular stabilizer, which serves two critical roles
simultaneously. First, it prevents the detrimental transformation and
decomposition of the alpha-phase FAPbI3 perovskite, by inhibiting the formation
of lead and iodide intermediates. Secondly, hysteresis-free device operation
and microscopic luminescence imaging experiments reveal substantially
suppressed ion migration in the emissive perovskite. The record-long PeLED
lifespans are encouraging, as they now satisfy the stability requirement for
commercial organic LEDs (OLEDs). These results remove the critical concern that
halide perovskite devices may be intrinsically unstable, paving the path toward
industrial applications.Comment: This is a preprint of the paper prior to peer review. New and updated
results may be available in the final version from the publishe
Establishment and application of health risk ranking model for heavy metals in aquatic products
Objective To develop a scientific and rapid risk ranking model that is suitable for the analysis of data from food chemicals surveillance system. Methods Based on the principles of food safety risk assessment, a series of index were developed for the contamination and toxicity characteristics of chemicals in food, food consumption characteristics of population, and standards violation rate, respectively. Then the logical operation relationship and the standards for assigning scores were set. The model was verified using real surveillance data. Results Total risk scores were calculated using the equation: total risk score = toxicity adjusted content score × violation rate score × consumption score. This model was applied to the risk classification of arsenic, cadmium, mercury and lead in aquatic products in China. The ranking result were in line with those estimated by the classical risk assessment model. Conclusion The model could rank the health risk of heavy metals in aquatic products properly, and can provide a scientific foundation for regulatory priority
A new method for the characterization of microcracks based on seepage characteristics
Microcracks are the main seepage channels and reservoir space for oil and gas in dense sandstone reservoirs, and the degree of development dominates the reservoir’s high and stable production capacity. A new method has been devised to address the lack of quantitative identification and characterization methods for microcrack networks. The method is based on core stress sensitivity, permeability anisotropy, and two-phase seepage rule testing. By improving upon the traditional black oil model, this method can accurately calculate the impact that microcracks of varying degrees of development have on the capacity of tight oil reservoirs. The study shows that 1) the higher the degree of microcrack development, the stronger the reservoir stress sensitivity and the greater the permeability anisotropy. As the degree of microcrack development increases, the irreducible water saturation decreases, the residual oil saturation gradually increases, and the oil–water two-phase co-infiltration zone becomes more extensive and smaller. The degree of microcrack development in tight reservoirs can be characterized based on the seepage characteristic parameters; 2) a microcrack characterization method and classification criteria have been established. It is based on stress sensitivity coefficients, permeability anisotropy parameters, and phase seepage characteristics in cores with different microcrack development degrees. For the first time, the method enables a macroscopic-level description of microcrack seepage; 3) numerical calculations show that the degree of microcrack development significantly affects the reservoir’s oil production and water production. The higher the degree of microcrack development, the higher the reservoir’s initial oil production and cumulative oil production. However, when the degree of microcrack development is too high, the microcracks are connected, thus exhibiting the nature of large fractures. This strengthens the bypassing communication effect and causes the microscopic inhomogeneity to strengthen, the oil production decreases rapidly, and water production increases quickly at the later stage. This research result enriches the reservoir microcrack characterization and evaluation system, which has essential theoretical guidance and practical significance for the rational and effective development of tight oil and tight sandstone gas
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