Searching for new two-dimensional (2D) Dirac cone materials has been popular since the discovery of graphene with a Dirac cone structure. Based on density functional theory (DFT) calculations, we ...theoretically designed a HfB2 monolayer as a new 2D Dirac material by introducing the transition metal Hf into a graphene-like boron framework. This newly predicted HfB2 monolayer has pronounced thermal and kinetic stabilities along with a Dirac cone with a massless Dirac fermion and Fermi velocities (3.59 × 105 and 6.15 × 105 m s−1) comparable to that of graphene (8.2 × 105 m s−1). This study enriches the diversity and promotes the application of 2D Dirac cone materials.
•The first study showing a new model for casing strength under combined load.•Hoop stress distribution is shown under combined load based on the energy method.•Critical shear load can enhance casing ...strength under radial non-uniform load.•The results presented in this paper may provide a new concept for casing design.
In studies of casing strength in oil and gas wells, the focus has largely been on the influence of the non-uniformity of the external load on the casing strength. However, most equations for calculating casing strengths in the analysis of non-uniformities focus on the radial non-uniform load while neglecting the effect of shear load. To address this, the possible effects of shear load on the outer casing is discussed. A study is carried out on the hoop stress, which is the primary factor affecting casing yield failure, and this stress can be obtained by the energy method. As a result, the yield failure mechanism for the inner wall of the casing is determined under combined load. Based on these results, a new equation for calculating medium-thickness casing collapse strength under combined load is proposed. In addition, the results indicate that the casing collapse strength reaches a maximum when the shear load constant is close to the corresponding critical shear load constant of the casing, which can effectively eliminate the negative effects on casing strength caused by the radial non-uniform load. Compared with the traditional methods of increasing the casing grade and wall thickness, the results presented here provide a new concept for casing design and casing rehabilitation in complicated strata of deep and ultra-deep wells (e.g., salt and gypsum rock).
Searching for new two-dimensional (2D) Dirac cone materials has been popular since the discovery of graphene with a Dirac cone structure. Based on density functional theory (DFT) calculations, we ...theoretically designed a HfB
monolayer as a new 2D Dirac material by introducing the transition metal Hf into a graphene-like boron framework. This newly predicted HfB
monolayer has pronounced thermal and kinetic stabilities along with a Dirac cone with a massless Dirac fermion and Fermi velocities (3.59 × 10
and 6.15 × 10
m s
) comparable to that of graphene (8.2 × 10
m s
). This study enriches the diversity and promotes the application of 2D Dirac cone materials.
The improvement of high‐performance narrow‐band green phosphors in backlight display applications is still a major challenge. Based on the UCr4C4 type of oxide phosphor, the high‐performance ...narrow‐band green phosphors Rb3M(Li3SiO4)4:Eu2+ (M = Rb or Na) are studied in different luminous positions. Benefiting from the replacement of Rb by Na, the change of the local environment in the crystal structure of Rb3Na(Li3SiO4)4:Eu2+ (R3NLSO:Eu2+) leads to the decrease of Stokes shift, which improves the quantum efficiency. Moreover, change in the local environment enhances the structural rigidity, which makes the thermal and chemical stability better. The R3NLSO:8%Eu2+ phosphor presents a narrow‐band green emission centered at 527 nm, excellent thermal stability (102% @150 °C of the integrated emission intensity at room temperature), and high internal/external quantum efficiency (85.3%/40.4%). The white light‐emitting diode (wLED) using R3NLSO:8%Eu2+ phosphor presents a superior luminous efficiency of 128.3 lm W‐1 and a wide color gamut. All the results indicate that R3NLSO:8%Eu2+ green phosphor has great application prospects in the field of liquid crystal display. This work also provides important guiding significance for the optimization of alkali metal element type of phosphors.
The strategy of replacing Rb with Na is used to obtain a high‐performance green phosphor Rb3Na(Li3SiO4)4:8%Eu2+ with high internal/external quantum efficiency of 85.3%/40.4% and excellent thermal stability. The white light‐emitting diode using the phosphor presents a superior luminous efficiency of 128.3 lm W−1 and a wide color gamut. Furthermore, surface modification can effectively improve the chemical stability of the phosphor.
Composites of porous Co
0.5
Zn
0.5
zeolitic imidazolate framework (CZ-ZIF)-derived binary Co/ZnO with reduced graphene oxide (RGO) have been prepared by a wet chemical method and carbonization ...process. CZ-ZIF-derived Co/ZnO microframes with diameter of about 250 nm were dispersed onto the surface of RGO nanosheets. The impedance matching of the composite could be adjusted by controlling the weight ratio of RGO to Co/ZnO microframes. Due to its porous structure, excellent impedance matching, and dielectric loss characteristics, the Co/ZnO/RGO composite exhibited maximum reflection loss (RL) of − 52.2 dB at 10.96 GHz. Coatings with thickness of 2.0 mm to 4.0 mm showed bandwidth of 5.6 GHz (from 8.72 GHz to 14.32 GHz) for RL of − 10 dB (90% absorption). Additionally, the amount of composite added into paraffin matrix was only 8 wt.%, less than for most electromagnetic (EM) wave absorbers in previous reports. Therefore, such Co/ZnO/RGO composites may be promising candidate EM wave absorbing materials.
This systematic review aimed to evaluate the effects of different theta burst stimulation (TBS) protocols on improving upper extremity motor functions in patients with stroke, their associated ...modulators of efficacy, and the underlying neural mechanisms. We conducted a meta-analytic review of 29 controlled trials published from January 1, 2000, to August 29, 2023, which investigated the effects of TBS on upper extremity motor, neurophysiological, and neuroimaging outcomes in poststroke patients. TBS significantly improved upper extremity motor impairment (Hedge's
= 0.646,
= 0.003) and functional activity (Hedge's
= 0.500,
< 0.001) compared to controls. Meta-regression revealed a significant relationship between the percentage of patients with subcortical stroke and the effect sizes of motor impairment (
= 0.015) and functional activity (
= 0.018). Subgroup analysis revealed a significant difference in the improvement of upper extremity motor impairment between studies using 600-pulse and 1200-pulse TBS (
= 0.002). Neurophysiological studies have consistently found that intermittent TBS increases ipsilesional corticomotor excitability. However, evidence to support the regional effects of continuous TBS, as well as the remote and network effects of TBS, is still mixed and relatively insufficient. In conclusion, TBS is effective in enhancing poststroke upper extremity motor function. Patients with preserved cortices may respond better to TBS. Novel TBS protocols with a higher dose may lead to superior efficacy compared with the conventional 600-pulse protocol. The mechanisms of poststroke recovery facilitated by TBS can be primarily attributed to the modulation of corticomotor excitability and is possibly caused by the recruitment of corticomotor networks connected to the ipsilesional motor cortex.
The role of the counter electrode (CE) in dye-sensitized solar cell (DSSC) is to collect electrons from the external circuit and reduce
I
3
−
to
I
−
in the electrolyte. In this paper, the ...perovskite-phase La
0.5
Sr
0.5
CoO
2.91
(LSCO) nanoparticles were synthesized through a sol–gel method and used as the CE for DSSC. The cell showed a power conversion efficiency (
PCE
) of 3.24 %. To further improve the PCE of CE of the LSCO nanoparticles, the nanocomposites of the LSCO nanoparticles with reduced graphene oxide (LSCO@RGO) have been prepared via a simply physical mixing method and served as the efficient CE for DSSC. The LSCO@RGO nanocomposites exhibit excellent electrocatalytic performance for reduction of triiodide, owing to the positive synergetic effect between LSCO nanoparticles and RGO sheets. As a consequence, the DSSC with the LSCO@RGO nanocomposites CE yielded a PCE of 6.32 %, which is observably higher than that of using pristine LSCO CE (3.24 %) or RGO CE (4.54 %) alone, and up to 88 % of the Pt CE (7.18 %).
The role of the counter electrode (CE) in dye-sensitized solar cell (DSSC) is to collect electrons from the external circuit and reduce I sub(3) super(-) to I super(-) in the electrolyte. In this ...paper, the perovskite-phase La sub(0.5)Sr sub(0.5)CoO sub(2.91) (LSCO) nanoparticles were synthesized through a sol-gel method and used as the CE for DSSC. The cell showed a power conversion efficiency (PCE) of 3.24 %. To further improve the PCE of CE of the LSCO nanoparticles, the nanocomposites of the LSCO nanoparticles with reduced graphene oxide (LSCOGO) have been prepared via a simply physical mixing method and served as the efficient CE for DSSC. The LSCOGO nanocomposites exhibit excellent electrocatalytic performance for reduction of triiodide, owing to the positive synergetic effect between LSCO nanoparticles and RGO sheets. As a consequence, the DSSC with the LSCOGO nanocomposites CE yielded a PCE of 6.32 %, which is observably higher than that of using pristine LSCO CE (3.24 %) or RGO CE (4.54 %) alone, and up to 88 % of the Pt CE (7.18 %).
Searching for new two-dimensional (2D) Dirac cone materials has been popular since the discovery of graphene with a Dirac cone structure. Based on density functional theory (DFT) calculations, we ...theoretically designed a HfB
2
monolayer as a new 2D Dirac material by introducing the transition metal Hf into a graphene-like boron framework. This newly predicted HfB
2
monolayer has pronounced thermal and kinetic stabilities along with a Dirac cone with a massless Dirac fermion and Fermi velocities (3.59 × 10
5
and 6.15 × 10
5
m s
−1
) comparable to that of graphene (8.2 × 10
5
m s
−1
). This study enriches the diversity and promotes the application of 2D Dirac cone materials.
A novel 2D boron-based Dirac cone material: a HfB
2
monolayer.
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