•The cavitation damage characteristics for AlCu4Mg1 and Ti6Al4V were compared.•Ultrasonic cavitation can slightly increase surface roughness to submicron scale.•Ultrasonic cavitation can raise ...surface hardness and be used for surface treatment.•The effects of time, amplitude and viscosity were quantitatively studied.
For the analysis of ultrasonic cavitation erosion on the surface of materials, the ultrasonic cavitation erosion experiments for AlCu4Mg1 and Ti6Al4V were carried out, and the changes of surface topography, surface roughness, and Vickers hardness were explored. Cavitation pits gradually expand and deepen with the increase of experiment time, and Ti6Al4V is more difficult to erode by cavitation than AlCu4Mg1. After experiments, the cavitation damage characteristics such as the single pit, the rainbow ring area, the fisheye pit, and some small pits were observed, which can be considered to be induced by a single micro-jet impact, ablation effect caused by the high temperature, micro-jet impingement with a sharp angle, and multibeam micro-jets coupling impact or negative pressure in the local area produced by micro-jet impact, respectively. The surface roughness and Vickers hardness of the material increase slowly after rapid growth at different points in time as the experiment time increases. With the increase of the ultrasonic amplitude, both of them first increase and then decrease after the ultrasonic amplitude is greater than 10.8 μm. The increases in surface roughness and Vickers hardness tend to decrease as the viscosity coefficient increases. Ultrasonic cavitation can cause submicron surface roughness and increase surface hardness by 20.36%, so it can be used as a surface treatment method.
Manganese zinc (Mn-Zn) ferrites were prepared by solid-state reaction. The sintering process was investigated in detail using differential scanning calorimetry/thermogravimetric analysis and x-ray ...diffraction characterizations. A three-step weight loss was observed and the main Mn-Zn ferrite formation reaction was detected. Two-step heat treatment was employed to achieve high density Mn-Zn ferrite. For sintering temperatures from 1300°C to 1400°C, crystal grains of Mn-Zn ferrite became uniform with larger size and more equiaxed shape. The grain boundaries changed from curved to straight. Such features were believed helpful for the magnetic domain wall movement. In addition, better diffusivity at higher sintering temperature homogenized the distribution of impurities which also facilitated the magnetic domain alignment. Thanks to the microstructure acquired by controlling the sintering process, a high-amplitude permeability of 1151, a low total loss of 411 W/kg and coercivity of 57.63 A/m at 65 kHz were simultaneously achieved on samples sintered at 1400°C.
In this work, the microstructure, crystallographic parameters and magnetic properties of polycrystalline manganese–zinc (Mn–Zn) ferrites were investigated. Mn
1−
x
Zn
x
Fe
2
O
4
(0.11 ≤
x
≤ 0.14) ...were prepared by the solid-state reaction method at 1360 °C for 2 h in air atmosphere. Phase evolution and microstructure of Mn–Zn ferrites were investigated by XRD and SEM techniques. X-ray diffraction study confirmed the formation of spinel-structured Mn
1−
x
Zn
x
Fe
2
O
4
. The magnetic properties were measured employing soft magnetic alternating current measuring instrument (MATS-3010SA). It was observed that as the zinc content (
x
) increases, the lattice constant remained stable, microstructure did not change significantly, the permeability of Mn–Zn ferrite was improved, and total loss and coercivity were reduced. Changes in crystal structure and magnetism were attributed to occupancy of non-magnetic Zn
2+
and super-exchange interactions between the metal ions of sub-lattice A and B in the spinel structure. These results indicated that the magnetic properties of Mn
1−
x
Zn
x
Fe
2
O
4
ferrites were strongly affected by the Zn content (
x
). In a brief summary, Mn
0.86
Zn
0.14
Fe
2
O
4
ferrite exhibited excellent magnetic properties with a low loss (
P
s
= 39.24 W/kg) and low coercivity (
H
c
= 39.16 A/m) measured at 200 mT and 10 kHz.
•A variety of methods are used to carry out research, include fracture mechanics, soil mechanics, physical similarity simulation and numerical calculation.•The mining-induced cracking mechanism and ...criterion of surface soil layer were first proposed.•The prediction formula of downward crack development depth of surface soil layer was put forward, and it has been verified through physical similarity simulation and numerical calculation.
In order to reveal the cracking mechanism of surface soil layer caused by coal seam mining, and explore theoretical methods for predicting the development depth of downward fractures during mining. Based on the background of the No. 1–2 upper coal seam mining in Daliuta Coal Mine, combining with fracture mechanics, soil mechanics, physical similarity simulation and numerical calculation methods. The mining-induced cracking mechanism and criterion of surface soil layer were analyzed, the crack development pattern and expansion mechanism were revealed, and the prediction formula of downward crack development depth of surface soil layer was put forward. The research results show that surface cracks mainly occur in the tensile zone, the concentrated tensile stress produced by the subsidence of overburden in the tensile zone can lead to soil cracking. When the surface maximum horizontal tensile deformation exceeds the limit horizontal deformation of soil, the soil layer cracks, and the cracking criterion of the surface soil layer was given accordingly. The soil crack of coal seam mining belongs to the mixed mode crack, and the soil cracks tip starts cracking and expanding along the direction of the maximum principal stress, therefore, the initiation crack angle of soil crack tip was obtained, and the fracture criterion of soil crack was proposed. With the crack propagation and development, the microcosmic crack becomes the macroscopic downward fracture. When the horizontal stress of the soil decreases to the cohesive force of the soil, the downward fracture stops develop, and the calculation formula for the development depth of mining-induced downward fracture was proposed. The development and evolution law of downward fracture was revealed, after the surface cracks, with the advance of the longwall face, the downward crack continues to extend and develop to the deep. Downward fracture develops on the ground surface at the open cut side, the mined-out area and in front of the longwall face, the maximum development depth of downward fracture tends to be stable when the longwall face advances to a certain distance. According to the physical simulation, numerical calculation and theoretical calculation, the development depth of downward fracture in No 1–2 upper coal seam mining is 8.11 m, 8.21 m and 8.14 m respectively. The theoretical prediction formula is reliable, and the results can provide a new method for the research of the development depth of mining-induced surface downward fracture.
•The size effect of materials should be considered in the formation of cavitation pits.•The prediction models of cavitation impact load, impact pressure and velocity of micro-jet with size effect ...were established.•A size effect coefficient 1+54hpα2μ2bdp2σJC2 was defined.•The predicted values of parameters increased by about 11%–88% for the ten typical cavitation pits when considering the size effect.
High-speed micro-jet produced by cavitation collapse near the wall is the main mechanism of material damage, and cavitation pit is the most typical damage feature. The reason why high-pressure and high-speed micro-jet can only cause nano- and microscale cavitation pit is that the micro-jet is a short-term impact load of nano- and microscale, and the material shows size effect during the formation of pits. To further explore the cavitation damage characteristics and deformation mechanism of materials, the theoretical framework of indentation test and J-C constitutive model were adopted, and the size effect of materials during the process of cavitation pit formation was mainly considered, and the prediction models of cavitation impact load, impact pressure and velocity of micro-jet were established. The results showed that the equivalent stress and strain of cavitation pit and the impact pressure and velocity of micro-jet are only related to the diameter-to-depth ratio of pit without size effect, and also to the diameter of pit with size effect. Larger diameter and deeper depth of the pit infers greater cavitation impact load, and the influence of the pit diameter is more obvious. When considering the size effect, there is an additional size effect coefficient: 1+54hpα2μ2bdp2σJC2. In the selected size range of pit, the cavitation impact load, impact pressure and velocity of micro-jet predicted with size effect increase by 0.9408%–322.5% compared with those without size effect. The maximum increase ratio appears at the minimum of diameter-to-depth ratio of pit (dp = 2 μm and dh = 2 μm), that is, the smaller the pit diameter is and the greater the depth is, the greater the increase ratio is. Ten typical cavitation pits were selected for inversion analysis. The impact pressure and velocity of micro-jet with and without size effect are 473–1131 MPa and 355–848 m/s, and 427–604 MPa and 320–453 m/s, respectively. The predicted values increase by about 11%-88% when considering the size effect, and the micro-jet velocity predicted is closer to that observed by high-speed cameras, which confirms the necessity and rationality of size effect in the inversion analysis of cavitation pits.
Antibiotic resistance represents a major threat worldwide. Gram-positive and Gram-negative opportunistic pathogens are becoming resistant to all known drugs mainly because of the overuse and misuse ...of these medications and the lack of new antibiotic development by the pharmaceutical industry. There is an urgent need to discover structurally innovative antibacterial agents for which no pre-existing resistance is known. This work describes the identification, synthesis and biological evaluation of a novel series of 1,5-diphenylpyrrole compounds active against a panel of ESKAPE bacteria. The new compounds show high activity against both wild type and drug-resistant Gram + ve and Gram-ve pathogens at concentrations similar or lower than levofloxacin. Microbiology studies revealed that the plausible target of the pyrrole derivatives is the bacterial DNA gyrase, with the pyrrole derivatives displaying similar inhibitory activity to levofloxacin against the wild type enzyme and retaining activity against the fluoroquinolone-resistant enzyme.
Display omitted
•Novel 1,5-diphenyl-pyrrole derivatives were synthesized.•The new compounds are endowed with high antibacterial activity.•The phenyl substituents at N1 and C5 of the pyrroles is essential for activity.•Protonatable guanidine/amino moieties improve the activity against Gram-ve bacteria.•Bacterial DNA gyrase was identified as a plausible target.
Staphylococcus aureus
is a common human bacterium that sometimes becomes pathogenic, causing serious infections. A key feature of
S. aureus
is its ability to acquire resistance to antibiotics. The ...presence of the staphylococcal cassette chromosome (SCC) element in serotypes of
S. aureus
has been confirmed using multiplex PCR assays. The SCC element is the only vector known to carry the
mecA
gene, which encodes methicillin resistance in
S. aureus
infections. Here, we report the genome sequence of a novel methicillin-sensitive
S. aureus
(MSSA) strain: SCC-like MSSA463. This strain was originally erroneously serotyped as methicillin-resistant
S. aureus
in a clinical laboratory using multiplex PCR methods. We sequenced the genome of SCC-like MSSA463 using pyrosequencing techniques and compared it with known genome sequences of other
S. aureus
isolates. An open reading frame (CZ049; AB037671) was identified downstream of
attL
and
attR
inverted repeat sequences. Our results suggest that a lateral gene transfer occurred between
S. aureus
and other organisms, partially changing
S. aureus
infectivity. We propose that
attL
and
attR
inverted repeats in
S. aureus
serve as frequent insertion sites for exogenous genes.
An organ unique to mammals, the mammary gland develops 90% of its mass after birth and experiences the pregnancylactation-involution cycle (PL cycle) during reproduction. To understand mammogenesis ...at the transcriptomic level and using a ribo-minus RNA-seq protocol, we acquired greater than 50 million reads each for the mouse mammary gland during pregnancy (day 12 of pregnancy), lactation (day 14 of lactation), and involution (day 7 of involution). The pregnancy-, lactation- and involution-related sequencing reads were assembled into 17344, 10160, and 13739 protein-coding transcripts and 1803, 828, and 1288 non-coding RNAs (ncRNAs), respectively. Differentially expressed genes (DEGs) were defined in the three samples, which comprised 4843 DEGs (749 up-regulated and 4094 down-regulated) from pregnancy to lactation and 4926 DEGs (4706 up-regulated and 220 down-regulated) from lactation to involution. Besides the obvious and substantive up- and down-regulation of the DEGs, we observe that lysosomal enzymes were highly expressed and that their expression coincided with milk secretion. Further analysis of transcription factors such as
Trps1, Gtf2i, Tcf7l2, Nupr1, Vdr, Rb1
, and
Aebp1
, and ncRNAs such as
mir-125b, Let7, mir-146a
, and
mir-15
has enabled us to identify key regulators in mammary gland development and the PL cycle.
Computational meta-optics brings a twist on the accelerating hardware with the benefits of ultrafast speed, ultra-low power consumption, and parallel information processing in versatile applications. ...Recent advent of metasurfaces have enabled the full manipulation of electromagnetic waves within subwavelength scales, promising the multifunctional, high-throughput, compact and flat optical processors. In this trend, metasurfaces with nonlocality or multi-layer structures are proposed to perform analog optical computations based on Green's function or Fourier transform, intrinsically constrained by limited operations or large footprints/volume. Here, we showcase a Fourier-based metaprocessor to impart customized highly flexible transfer functions for analog computing upon our single-layer Huygens' metasurface. Basic mathematical operations, including differentiation and cross-correlation, are performed by directly modulating complex wavefronts in spatial Fourier domain, facilitating edge detection and pattern recognition of various image processing. Our work substantiates an ultracompact and powerful kernel processor, which could find important applications for optical analog computing and image processing.
Metasurfaces enable a new paradigm to control electromagnetic waves by manipulating subwavelength artificial structures within just a fraction of wavelength. Despite the rapid growth, simultaneously ...achieving low‐dimensionality, high transmission efficiency, real‐time continuous reconfigurability, and a wide variety of reprogrammable functions is still very challenging, forcing researchers to realize just one or few of the aforementioned features in one design. This study reports a subwavelength reconfigurable Huygens' metasurface realized by loading it with controllable active elements. The proposed design provides a unified solution to the aforementioned challenges of real‐time local reconfigurability of efficient Huygens' metasurfaces. As one exemplary demonstration, a reconfigurable metalens at the microwave frequencies is experimentally realized, which, to the best of the knowledge, demonstrates for the first time that multiple and complex focal spots can be controlled simultaneously at distinct spatial positions and reprogrammable in any desired fashion, with fast response time and high efficiency. The presented active Huygens' metalens may offer unprecedented potentials for real‐time, fast, and sophisticated electromagnetic wave manipulation such as dynamic holography, focusing, beam shaping/steering, imaging, and active emission control.
By loading controllable active elements, a subwavelength metasurface is proposed with real‐time local reconfigurability. A reconfigurable active Huygens' metalens is experimentally realized at microwave frequencies, which demonstrates for the first time that multiple and complex focal spots can be controlled simultaneously at distinct spatial positions and reprogrammable in any desired fashion, with a fast response time of 10 µs and high efficiency.
PDF
