Direct Hole Research Articles

Prevention and Control of Coal and Gas Outburst by Directional Hydraulic Fracturing through Seams and Its Application.

The regionalized pressure relief, permeability enhancement, and outburst prevention of "three high and one low" coal seams with high gas, high ground stress, high outburst risk, and low permeability have become important problems to be solved urgently in realizing the sustainable development of coal mines. In this study, a combination of theoretical research, RFPA2D-Flow numerical simulation, and field test was used to study the initiation mechanism and propagation law of directional hydraulic fracturing fractures through the seam. The results show that fracture initiation depends on the axial and radial horizontal stress of the fracture hole, the physical and mechanical properties of coal and rock, and the inside of the weakest layer. Single-hole hydraulic fracturing can achieve a pressure relief radius of 7-8 m, but there is a stress concentration zone outside, which is not conducive to regional pressure relief and permeability enhancement. Directional hydraulic fracturing with multiple holes produces an approximate cylindrical compression and crushing ring and a penetrating fracture surface along the center line of the pressure crack hole and the directional hole, which better eliminates the phenomenon of stress concentration in nondirectional hydraulic fracturing. The technology was applied to the 2238 auxiliary roadway of Chengzhuang Mine of Jinmei Group, and the field implementation results showed that field implementation results showed that directional hydraulic fracturing through the seam reduced the gas content in the coal seam to a great extent, and the coal seam gas content was reduced by about 42.3%, indicating that the technology can effectively reduce the risk of coal and gas outbursts.

The Sloan Digital Sky Survey Reverberation Mapping Project: The Black Hole Mass–Stellar Mass Relations at 0.2 ≲ z ≲ 0.8

We measure the correlation between black hole mass M BH and host stellar mass M * for a sample of 38 broad-line quasars at 0.2 ≲ z ≲ 0.8 (median redshift z med = 0.5). The black hole masses are derived from a dedicated reverberation mapping program for distant quasars, and the stellar masses are derived from two-band optical+IR Hubble Space Telescope imaging. Most of these quasars are well centered within ≲1 kpc from the host galaxy centroid, with only a few cases in merging/disturbed systems showing larger spatial offsets. Our sample spans two orders of magnitude in stellar mass (∼109–1011 M ⊙) and black hole mass (∼107–109 M ⊙) and reveals a significant correlation between the two quantities. We find a best-fit intrinsic (i.e., selection effects corrected) M BH–M *,host relation of , with an intrinsic scatter of dex. Decomposing our quasar hosts into bulges and disks, there is a similar M BH–M *,bulge relation with slightly larger scatter, likely caused by systematic uncertainties in the bulge–disk decomposition. The M BH–M *,host relation at z med = 0.5 is similar to that in local quiescent galaxies, with negligible evolution over the redshift range probed by our sample. With direct black hole masses from reverberation mapping and the large dynamical range of the sample, selection biases do not appear to affect our conclusions significantly. Our results, along with other samples in the literature, suggest that the locally measured black hole mass–host stellar mass relation is already in place at z ∼ 1.

Synergy of Bulk Defects and Surface Defects on TiO2 for Highly Efficient Photocatalytic Production of H2O2.

Artificial photosynthesis of H2O2 by TiO2-based semiconductors is a promising approach for H2O2 production. However, the efficiency of pristine TiO2 is still limited by rapid charge separation and low O2 adsorption capacity. Here, we found that the synergy between bulk and surface defects on TiO2 could overcome this demanding bottleneck. The introduced bulk defects act as hole acceptors to induce directional hole transfer, efficiently boosting electron-hole separation. Furthermore, the adsorption of O2 is strengthened by the introduced surface defects. Consequently, this synergy of bulk and surface defects on TiO2 significantly improves the photocatalytic performance, with a H2O2 production rate of 4560 μmol h-1 g-1, outperforming most reported TiO2-based photocatalysts. This work not only provides a new insight into the mechanism of surface/bulk defects in photocatalysis but also highlights that surface/bulk regulation holds great promise for achiveing efficient photocatalytic conversion.

COSMOS-Web: An Overview of the JWST Cosmic Origins Survey

We present the survey design, implementation, and outlook for COSMOS-Web, a 255 hr treasury program conducted by the James Webb Space Telescope in its first cycle of observations. COSMOS-Web is a contiguous 0.54 deg2 NIRCam imaging survey in four filters (F115W, F150W, F277W, and F444W) that will reach 5σ point-source depths ranging ∼27.5–28.2 mag. In parallel, we will obtain 0.19 deg2 of MIRI imaging in one filter (F770W) reaching 5σ point-source depths of ∼25.3–26.0 mag. COSMOS-Web will build on the rich heritage of multiwavelength observations and data products available in the COSMOS field. The design of COSMOS-Web is motivated by three primary science goals: (1) to discover thousands of galaxies in the Epoch of Reionization (6 ≲ z ≲ 11) and map reionization’s spatial distribution, environments, and drivers on scales sufficiently large to mitigate cosmic variance, (2) to identify hundreds of rare quiescent galaxies at z > 4 and place constraints on the formation of the universe’s most-massive galaxies (M ⋆ > 1010 M ⊙), and (3) directly measure the evolution of the stellar-mass-to-halo-mass relation using weak gravitational lensing out to z ∼ 2.5 and measure its variance with galaxies’ star formation histories and morphologies. In addition, we anticipate COSMOS-Web’s legacy value to reach far beyond these scientific goals, touching many other areas of astrophysics, such as the identification of the first direct collapse black hole candidates, ultracool subdwarf stars in the Galactic halo, and possibly the identification of z > 10 pair-instability supernovae. In this paper we provide an overview of the survey’s key measurements, specifications, goals, and prospects for new discovery.

Raman scattering and photoluminescence in In+ and As+ ion-implanted SiO2 layers encapsulated with Si3N4

Raman and photoluminescence spectra were investigated in the In+ and As+ ion-implanted SiO2 films encapsulated with Si3N4 layers as a function of annealing temperature. The optical phonon frequency, as a function of the InAs nanocrystal size, was also calculated within the confined phonon model. The Raman scattering band of around 231 cm−1, close to the low-frequency shifted longitudinal optical phonon mode in the InAs matrix, was observed as the annealing temperature increased to 900 °C. The InAs nanocrystal size of 3 nm was estimated. The strong room-temperature photoluminescence peaking at 550 nm (2.25 eV) was also obtained under the 473 nm wavelength excitation. Its intensity reached a maximum value as the annealing temperature increased to 1000 °C. Its peak position was blue-shifted as the excitation wavelength decreased. The direct irradiative electron and hole recombination in the InAs nanocrystals was proposed as a possible mechanism of this photoluminescence.

Self-introduction of carbon nitride quantum dots into carbon nitride planar structure for enhanced photocatalytic hydrogen production

The separation efficiency and migration rate of photogenerated carriers are important factors determining the activity of photocatalysts. In this work, CN/CNQDs were prepared by self-introducing carbon nitride quantum dots (CNQDs) into the planar structure of carbon nitride (CN) using a novel photo-triggered self-assembly strategy. Different from conventional interfacial modification strategies based on van der Waals forces or hydrogen bonding, CN/CNQDs atomic junctions formed chemical bonds between the two components, which have stronger interfacial interactions and facilitate efficient carrier migration between the two components. The continuous π-conjugated structure of CN/CNQDs also provided unique conditions for carrier migration. In addition, the presence of in-plane electric field (IEF) in CN/CNQDs acted as a direct driving force for the migration of electrons and holes in the opposite directions, which greatly facilitates the separation and transfer of photogenerated carriers in CN/CNQDs. This work provides an atomic-level strategy for the construction of heterojunction photocatalyst systems.

Magnetic Effects Promote Supermassive Star Formation in Metal-enriched Atomic-cooling Halos

Intermediate-mass black holes (with ≥105 M ⊙) are promising candidates for the origin of supermassive black holes (with ∼109 M ⊙) in the early universe (redshift z ∼ 6). Chon & Omukai first pointed out direct collapse black hole (DCBH) formation in metal-enriched atomic-cooling halos (ACHs), which relaxes the DCBH formation criterion. On the other hand, Hirano et al. showed that magnetic effects promote DCBH formation in metal-free ACHs. We perform a set of magnetohydrodynamical simulations to investigate star formation in magnetized ACHs with metallicities Z/Z ⊙ = 0, 10−5, and 10−4. Our simulations show that the mass accretion rate onto the protostars becomes lower in metal-enriched ACHs than in metal-free ACHs. However, many protostars form from gravitationally and thermally unstable metal-enriched gas clouds. Under such circumstances, the magnetic field rapidly increases as magnetic field lines wind up due to the spin of protostars. The region with the amplified magnetic field expands outwards due to the orbital motion of protostars and the rotation of the accreting gas. The amplified magnetic field extracts angular momentum from the accreting gas, promotes the coalescence of low-mass protostars, and increases the mass growth rate of the primary protostar. We conclude that the magnetic field amplification is always realized in metal-enriched ACHs regardless of the initial magnetic field strength, which affects the DCBH formation criterion. In addition, we find a qualitatively different trend from the previous unmagnetized simulations in that the mass growth rate is maximal for extremely metal-poor ACHs with Z/Z ⊙ = 10−5.

Magnetic Braking during Direct Collapse Black Hole Formation

Magnetic fields are expected to be efficiently amplified during the formation of the first massive black holes via the small-scale dynamo and in the presence of strong accretion shocks occurring during gravitational collapse. Here, we analyze high-resolution cosmological magnetohydrodynamical simulations of gravitational collapse in atomic cooling halos, exploring the dynamical role of magnetic fields, particularly concerning the effect of magnetic braking and angular momentum transport. We find that after the initial amplification, magnetic fields contribute to the transport of angular momentum and reduce it compared to pure hydrodynamical simulations. However, the magnetic and Reynolds torques do not fully compensate for the inward advection of angular momentum, which still accumulates over timescales of ∼1 Myr. A Jeans analysis further shows that magnetic pressure strongly contributes to suppressing fragmentation on scales of 0.1–10 pc. Overall, the presence of magnetic fields thus aids in the transport of angular momentum and favors the formation of massive objects.

Photoelectrochemical Valorization of Biomass Derivatives with Hematite Photoanodes Modified by Cocatalysts

The solar‐driven oxidation of biomass to valuable chemicals is rising as a promising anodic reaction in photoelectrochemical cells, replacing the sluggish oxygen evolution reaction and improving the added value of the energy conversion process. Herein, the photooxidation of 5‐hydroxymethylfurfural into furan dicarboxylic acid (FDCA) is performed in basic aqueous environment (borate buffer, pH 9.2), with the addition of 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) as redox mediator. Because of its good stability, cost‐effectiveness, and nontoxicity, titanium‐modified hematite (Ti:Fe2O3) photoanodes are investigated to this aim, and their performance is tuned by engineering the semiconductor surface with a thin layer of Co‐based cocatalysts, i.e., cobalt iron oxide (CoFeO x ) and cobalt phosphate (CoPi). Interestingly, the electrode modified with CoPi shows improved efficiency and selectivity toward the final product FDCA The source of this enhancement is correlated to the effect of the cocatalyst on the charge carrier dynamics, which is investigated by electrochemical impedance spectroscopy and intensity‐modulated photocurrent spectroscopy analysis. In addition, the results of the latter are interpreted through a novel approach called Lasso distribution of relaxation time, revealing that CoPi cocatalyst is effective in the suppression of the recombination processes and in the enhancement of direct hole transfer to TEMPO.

Strength enhancement and retention in magnesium subjected to uniaxial compression using centralized partial drill holes

The automotive industry approached light weighting vehicles using alloys and composites of aluminium and magnesium to improve fuel efficiency. They further introduced sensors to gain insight into real-time monitoring of their components. In the biomedical industry, reducing stiffness of implants, promoting cell proliferation, providing controlled drug delivery, and enabling real-time monitoring of implants has been the focus. With magnesium being a biocompatible material, research on improving the material properties of biocompatible magnesium alloys and composites is ongoing. However, tracking the efficiency of these implants in-vivo is essential and can be done using appropriate sensors. But the question of where to place them and would it affect the structural integrity of the implant needs to be answered. While previous research has explored the effect of through holes in different directions and materials, the effect of a controlled drill hole has not yet been explored. Hence, this study varies the drill depths in pure magnesium from 1 mm to 2.5 mm and drill diameter from 1 mm to 2.5 mm respectively in an 8 mm diameter cylinder to study the same. Further, an exploratory work on the effect of shape of the drill hole has also been taken up. Results convey that the sample with 1 mm drill diameter and 1.5 mm drill depth provided optimum results.

Axis-Dependent Conduction Polarity in WSi2 Single Crystals

Materials that demonstrate axis-dependent conduction polarity enable new technologies by integrating p- and n-type functionality into a single crystal. Certain anisotropic crystal structures give rise to this behavior by having dominant electron conduction along one crystallographic direction and dominant hole conduction along another. However, only a few materials have been experimentally shown to demonstrate this unique property. Here, we identify axis-dependent conduction polarity in tetragonal α-WSi2: a durable, thermally robust, and oxidation-resistant metal synthesized from earth-abundant elements. Two single crystals of α-WSi2 were prepared using Xe floating zone techniques, and their anisotropic conduction properties were evaluated. Simultaneous positive and negative thermopowers measured along the [100] and [001] directions, respectively, indicate that this material exhibits axis-dependent conduction polarity, which closely matches theoretical predictions. Hall measurements also show dominant p-type and n-type conduction along these respective crystallographic directions. Heat capacity measurements indicate that the density of states of these crystals is close to that of an exact α-WSi2 stoichiometry, confirming that this polarity anisotropy exists in relatively undoped crystals. In total, α-WSi2 is an excellent material platform for the future exploration of potential applications of this phenomenon.

Selective Cocatalyst Decoration of Narrow-Bandgap Broken-Gap Heterojunction for Directional Charge Transfer and High Photocatalytic Properties.

Narrow-bandgap semiconductors are promising photocatalysts facing the challenges of low photoredox potentials and high carrier recombination. Here, a broken-gap heterojunction Bi/Bi2 S3 /Bi/MnO2 /MnOx , composed of narrow-bandgap semiconductors, is selectively decorated by Bi, MnOx nanodots (NDs) to achieve robust photoredox ability. The Bi NDs insertion at the Bi2 S3 /MnO2 interface induces a vertical carrier migration to realize sufficient photoredox potentials to produce O2 •- and • OH active species. The surface decoration of Bi2 S3 /Bi/MnO2 by Bi and MnOx cocatalysts drives electrons and holes in opposite directions for optimal photogenerated charge separation. The selective cocatalysts decoration realizes synergistic surface and bulk phase carrier separation. Density functional theory (DFT) calculation suggests that Bi and MnOx NDs act as active sites enhancing the absorption and reactants activation. The decorated broken-gap heterojunction demonstrates excellent performance for full-light driving organic pollution degradation with great commercial application potential.

Engineering defects in TiO2 for the simultaneous production of hydrogen and organic products

Photoreforming ethanol to simultaneously produce hydrogen and value-added organic products was realized over defected TiO2. Chemically induced defects in TiO2 promoted light absorption and charge separation, enhancing overall photoactivity. The induced defects also regulated product selectivity, leading to greater hydrogen purity and liquid to gaseous carbon ratio. The optimal catalyst generated 0.08 mmol/hr of hydrogen with a purity greater than 99 % and 0.08 mmol/hr of liquid acetaldehyde over a 6 hr timeframe. This was three times greater than the untreated TiO2. Active species trapping revealed that the preferred ethanol oxidation pathway was direct hole transfer, indicating the selectivity relies on surface chemisorption. Surface defects decreased the acetaldehyde adsorption energy, instigating its prompt desorption and suppressing overoxidation into CO2, thus improving the selectivity towards hydrogen and liquid hydrocarbon products. The work offers an alternative approach towards sustainable energy by coupling photocatalysis with waste organic utilization.

A metal-organic framework-derived CuO microrods for fast photocatalytic degradation of methylene blue

Metal-organic frameworks-derived metal oxides with various morphology and composition have attracted enormous attention during the past years due to excellent catalytic activity. In this study, CuO microrods derived from the metal-organic framework MFUM-1(Cu) were prepared by careful calcination at different temperatures. Field emission scanning electron microscope images showed that while CuO microrods preserved their initial morphology after calcination at 500 °C, addition of Ce increased the integrity of the structure even after calcination at elevated temperatures. Moreover, the addition of Ce through a post-synthetic route (Ce-CuO-PS) affected size and specific surface area of Ce-CuO microrods, making them highly efficient photocatalysts for degradation of methylene blue under visible light irradiation. Dye removal efficiency of CuO-500 and Ce-CuO-PS were determined to be 96.65 and 100% (within 180 and 120 min), respectively. The radical trapping experiments with different scavengers showed that the photooxidation of methylene blue mainly occurs via direct hole (h+) oxidation and hydroxyl radicals (·OH).

Direct Macular Hole Manipulation Results in High Success Rate in Secondary Macular Hole Repair.

To investigate closure rates and functional outcomes of surgery for refractory and recurrent macular holes (MH) in a real-world setting. Retrospective review of secondary MH surgeries. A total of 72 eyes from 72 patients were included. Eyes had a mean of 1.51 surgeries before inclusion into the study with a mean MH size of 762 µm and a mean baseline logMAR BCVA of 1.11(∼20/260 Snellen). Closure rates were 89.3 % for tissue transplantation, 77.3 % for ILM flaps, 92.9 % for MH manipulation, and 12.5 % for repeat ILM peeling (p<0.05). BCVA changes in logMAR from baseline to postoperative month 6 were +0.29 for ILM peeling alone (15 ETDRS letters worse), -0.39 for macular hole manipulation (20 ETDRS letters improved), -0.23 for tissue transplantation (13 ETDRS letters improved), and -0.2 for ILM flaps (10 ETDRS letters improved; p<0.05). Secondary MH closure is possible using various surgical techniques with acceptable anatomical closure rates. Repeat ILM peeling is associated with the lowest closure rates and poorest functional results. To distinguish between techniques would require a large sample size of about 750 eyes.

Modification of ITO with Composite Self-Assembled Monolayer Enables Hole Injection and Transport Layer-Free TADF-OLED with Preferable Performance

A complex multilayer device structure severely obstructs the commercial development of thermally activated delayed fluorescence material-based organic light-emitting diodes (TADF-OLEDs) due to high preparation costs. Herein, simplified TADF-OLED without both hole injection layer (HIL) and hole transport layer (HTL) was obtained by embellishing indium tin oxide (ITO) with a composite self-assembled monolayer modification strategy. Perfluorobenzyl phosphoric acid with perfluoroalkyl carboxylic acids formed a denser composite monolayer on the surface of ITO. This increases the work function of ITO, improves the quality of emitting layer film, and facilitates hole injection, which realized direct hole injection without the HIL and HTL. The resultant HIL/HTL-free TADF-OLED gains favorable luminescence performance including a current efficiency (CE) of 76.9 cd A–1 and an external quantum efficiency (EQE) of 22.0% for green TADF-OLED and a CE of 21.4 cd A–1 and EQE of 13.4% for blue TADF-OLED. This work provides an effective method in simplifying TADF-OLED structures for its further commercial application.

Role of Magnetic Fields in the Formation of Direct Collapse Black Holes

Direct collapse black holes are the leading candidates for the origin of the first supermassive black holes. However, the role of magnetic fields during their formation is still unclear as none of the previous studies has been evolved long enough to assess their impact during the accretion phase. Here, we report the results from a suite of 3D cosmological magnetohydrodynamic (MHD) simulations which are evolved for 1.6 Myr comparable to the expected lifetime of supermassive stars (SMSs). Our findings suggest that magnetic fields are rapidly amplified by strong accretion shocks irrespective of the initial magnetic field strength and reach the saturation state. They stabilize the accretion disks and significantly reduce fragmentation by enhancing the Jeans mass in comparison with pure hydrodynamical runs. Although the initial clump masses are larger in MHD runs, the rapid coalescence of clumps in non-MHD cases due to the higher degree of fragmentation results in similar masses. Overall, the central clumps have masses of 105 M ⊙ and the mean mass accretion rates of ∼0.1 M ⊙ yr−1 are similar in both MHD and non-MHD cases. The multiplicity of SMSs is significantly reduced in MHD simulations. Such strongly amplified magnetic fields are expected to launch jets and outflows which may be detected with upcoming radio telescopes.

Through Space Sigma Donation π Acceptor Assisted Photocatalytic Degradation of Ciprofloxacin on TCPP Supported g‐C3N4

AbstractPhotocatalysis on pristine g‐C3N4 (CN) often suffers from fast recombination of photogenerated electrons and holes. Herein, we demonstrate the superior photocatalytic performance of free base tetrakis(4‐carboxyphenyl) porphyrin (TCPP) – g‐C3N4 (CN/TCPP) hybrids synthesised by a facile ultrasound aided impregnation. Structural and morphological characterisation confirmed the successful formation of the hybrid via noncovalent π–π stacking. Optical/electrochemical characterisation, as well as DFT study, designates the shifting of the optical absorption edge to visible range along with inhibition of carrier recombination through enhanced charge transfer. The CN/TCPP hybrids exhibited superior performance towards the degradation of persistent antibiotic ciprofloxacin under visible irradiation signifying its enhanced visible light sensitivity. The enhanced photocatalytic activity of CN/TCPP is ascribed to the charge transfer by through‐space conjugation by migration of electrons and holes in opposite directions, which minimises the possibility of electron‐hole recombination. From the LCMS data, scavenging studies, and first principles DFT analysis, the photodegradation of CIP is proposed to proceed via the destruction of the piperazine ring initiated mainly through the electrophilic attack by the holes.

Unlocking the Full Potential of Electron-Acceptor Molecules for Efficient and Stable Hole Injection.

Understanding the hole-injection mechanism and improving the hole-injection property are of pivotal importance in the future development of organic optoelectronic devices. Electron-acceptor molecules with high electron affinity (EA) are widely used in electronic applications, such as hole injection and p-doping. Although p-doping has generally been studied in terms of matching the ionization energy (IE) of organic semiconductors with the EA of acceptor molecules, little is known about the effect of the EA of acceptor molecules on the hole-injection property. In this work, the hole-injection mechanism in devices is completely clarified, and a strategy to optimize the hole-injection property of the acceptor molecule is developed. Efficient and stable hole injection is found to be possible even into materials with IEs as high as 5.8 eV by controlling the charged state of an acceptor molecule with an EA of about 5.0eV. This excellent hole-injection property enables direct hole injection into an emitting layer, realizing a pure blue organic light-emitting diode with an extraordinarily low turn-on voltage of 2.67V, a power efficiency of 29lm W-1 , an external quantum efficiency of 28% and a Commission Internationale de l'Eclairage y coordinate of less than 0.10.

Piezoelectric-enhanced photocatalytic performance of porous carbon nitride nanosheets.

Through the utilisation of mechanical energy, piezocatalysis and piezophotocatalysis have emerged as promising strategies to tackle the current energy and environmental issues. In this work, porous graphitic carbon nitride (g-C3N4) nanosheets were synthesised via a novel self-templating process followed by ultrasonic exfoliation to produce materials with a thickness of 1.5-2nm and a high specific surface area of 59.48m2/g. Piezo-response force microscopy (PFM) indicated that the as-prepared porous g-C3N4 nanosheets show excellent piezoelectric response. Moreover, the porous g-C3N4 nanosheets exhibit remarkable piezophotocatalytic degradation of Rhodamine B (RhB), showing an optimal first-order rate constant (k=0.301min-1) under visible light and ultrasonic co-excitation, which was 2.3 times the value under visible light irradiation alone and 9.7 times the value under only ultrasonic excitation. A piezoelectric field generated by ultrasonic excitation drove photogenerated electrons and holes in opposite directions to migrate towards the surface of the nanosheets, resulting in the generation of more reactive radicals and thereby accelerating RhB degradation. By highlighting the potential of porous g-C3N4 nanosheets as a piezo-semiconductor for environmental remediation applications, this study paves the way for developing a new method for converting solar and mechanical energy via a piezo-mediation photocatalytic reaction.