Shallow Holes Research Articles

Why Healthy Pine Seedlings Die after They Leave the Nursery

Artificial regeneration is successful when high-performing seedlings are transported with care to the planting site, stored for a short period in an environment without desiccation or fungal growth, and planted in a deep hole, so roots are in contact with moist soil. One of the requirements for success is the ability to avoid common planting mistakes. Due, in part, to the use of container stock plus an increase in rainfall, the average first-year survival of pine seedlings (89%) in the southern United States is about 15% greater now than 45 years ago. However, when survival is less than 50% six months after planting, some landowners seek reimbursement for their loss. Some assume poor seedling quality was the cause without realizing that anaerobic soils or sudden freeze events, shallow planting holes, pruning roots, a lack of rain or underground insects can kill pines. With a focus on pines planted in the southern United States, we list non-nursery factors that have killed seedlings in North America, Africa and Europe.

Chemical Defects and Impurities Introduce Charge Traps to Silicone Rubber: a Quantum Chemistry Study

The distributions of charge trap energy levels in polymer insulation material have an important influence on the charge transport characteristics and breakdown field strength of the polymer insulation, which thus has attracted considerable attention. Based on the quantum chemistry calculations, the characteristics of charge traps induced by different chemical defects and additives in silicone rubber materials are investigated. The projected density of states, and frontier molecular orbital distribution of defective silicone rubber and additive molecules are analyzed. The carbonyl defect, carboxyl defect and diethyl maleate additive all introduce deep electron traps (more than 1eV) in PDMS materials. The carbonyl defect and KH550 additive introduce shallow hole traps (less than 1eV) in PDMS materials. If chemical defects have a dominant contribution to the frontier molecular orbital of polymer is the key factor of whether they can introduce charge traps.

Removal of polyester fibre microplastics from wastewater using a UV/H2O2 oxidation process

Plastic microfibres originating from laundry wastewater are released in significant numbers to the environment due to a current lack of suitable removal technology. Advanced oxidation processes could offer a promising option to mitigate the problem due to their ability to destruct organic pollutants rather than transferring them to other forms. In this study, the effect of UV irradiation and hydrogen peroxide treatment on the removal of microplastics (MPs) was determined. MPs mass loss, carbonyl index (CI) change, and physical changes on their surface, as characterised by Fourier transform infra-red spectroscopy, scanning electron microscopy and atomic force microscopy were monitored. Additionally, the chemical oxygen demand (COD) of the water was monitored to examine the release and degradation of soluble organic material from MPs. The effect of varied UVC dose and H2O2 concentration was investigated. A dose of 500 mg L-1 H2O2 under 4.0 mW cm-2 UVC irradiation resulted in mass loss of 52.7% after 48 h (with a calculated half life of 45.3 h). Also, it was observed that degradation of fibres occurred through the formation of shallow holes, pits and cracks across their surface as well as changes in the relative abundance of oxygen containing functional groups. This chemical change was evidenced by the CI of treated MPs, which was increased up to 10.6% compared to untreated fibres. Moreover, the proposed UVC/H2O2 treatment could degrade 15.2% MPs and completely remove COD in real hospital laundry wastewater matrix within 9 h and 3 h of treatment, respectively.

Vacancy-Regulated Charge Carrier Dynamics and Suppressed Nonradiative Recombination in Two-Dimensional ReX2 (X = S, Se).

Point defects in semiconductors usually act as nonradiative charge carrier recombination centers, which severely limit the performance of optoelectronic devices. In this work, by combining time-domain density functional theory with nonadiabatic molecular dynamics simulations, we demonstrate suppressed nonradiative charge carrier recombination and prolonged carrier lifetime in two-dimensional (2D) ReX2 (X = S, Se) with S/Se vacancies. In particular, a S vacancy introduces a shallow hole trap state in ReS2, while a Se vacancy introduces both hole and electron trap states in ReSe2. Photoexcited electrons and holes can be rapidly captured by these defect states, while the release process is slow, which contributes to an elongated photocarrier lifetime. The suppressed charge carrier recombination lies in the vacancy-induced low-frequency phonon modes that weaken electron-phonon coupling, as well as the reduced overlap between electron and hole wave functions that decreases nonadiabatic coupling. This work provides physical insights into the charge carrier dynamics of 2D ReX2, which may stimulate considerable interest in using defect engineering for future optoelectronic nanodevices.

Spectroscopic Investigation of Shallow Hole Traps in Ga- and B-doped Czochralski Silicon: Insight into Light-Induced Degradation

Spectroscopic Investigation of Shallow Hole Traps in Ga- and B-doped Czochralski Silicon: Insight into Light-Induced Degradation

Traps in the spotlight: How traps affect the charge carrier dynamics in Cs2AgBiBr6 perovskite

Suitable optoelectronic properties of lead halide perovskites make these materials interesting semiconductors for many applications. Toxic lead can be substituted by combining monovalent and trivalent cations, such as in Cs 2 AgBiBr 6 . However, efficiencies of Cs 2 AgBiBr 6 -based photovoltaics are still modest. To elucidate the loss mechanisms, in this report, we investigate charge dynamics in Cs 2 AgBiBr 6 films by double-pulse excitation time-resolved microwave conductivity (DPE-TRMC). By exciting the sample with two laser pulses with identical wavelengths, we found a clear photoconductance enhancement induced by the second pulse even 30 μs after the first laser pulse. Modeling the DPE-TRMC results, complemented by photoluminescence and transient absorption, we reveal the presence of deep emissive electron traps, while shallow hole trapping is responsible for the long-lived transient absorption signals. These long-lived carriers offer interesting possibilities for X-ray detectors or photocatalysis. The DPE-TRMC methodology offers unique insight into the times involved in charge trapping and depopulation in Cs 2 AgBiBr 6 . • Double-pulse excitation TRMC is developed to study trapping processes • Cs 2 AgBiBr 6 shows high photoconductance up to 30 μs after the first excitation • A high yield of free charges results from populated trap states by the first pulse • Emission of holes residing in shallow states extends over many microseconds Trap-assisted electron recombination in Cs 2 AgBiBr 6 thin films, combined with low hole mobility and shallow trapping, can be a major drawback of Cs 2 AgBiBr 6 in photovoltaic devices. Caselli et al. reveal that the long-lived charge carriers in Cs 2 AgBiBr 6 can offer a suitable, lead-free alternative for other applications, such as X-ray detectors or photocatalysis.

First observation of paired microseismic signals during solution salt mining

To monitor the status of cavern roof instability induced by solution salt mining, we deployed a surface microseismic monitoring system for Dongxing salt mine, Dingyuan county, China. The microseismic monitoring system consists of 11 three-component geophones installed in shallow holes of 5 m deep. From 7-month continuous monitoring data, we have detected a novel type of signal that consists of two events. The first event has a long duration (>15 s) and generally has higher frequencies at the beginning. The 2nd event has a shorter duration of ∼3 s with lower frequencies. The two events are separated by ∼30–90 s in time. From May 2017 to November 2017, there are a total of 88 distinct paired signals with two events in sequence. We propose the first event corresponds to a series of fracturing processes on the cavern roof, and microseismic signals associated with different fractures are mixed and overlapped to produce a mixed signal with a longer duration. Due to a series of fracturing processes, some zones of cavern roof become instable and some rock debris may fall from the roof and collide on the cavern floor. This collision can produce a short duration signal, which corresponds to the 2nd event of the paired signal. The further analysis of polarities of the first arrivals for the 2nd event further proves its collision origin. The time interval between two events is related to the time for the falling rock debris through the brine, which is controlled by the cavern height and various physical properties of the rock debris and brine. Through the detailed analysis of paired signals, we can have a better understanding of the cavity development status for solution salt mining.

Spectra Stable Quantum Dots Enabled by Band Engineering for Boosting Electroluminescence in Devices

The band level landscape in quantum dots is of great significance toward achieving stable and efficient electroluminescent devices. A series of quantum dots with specific emission and band structure of the intermediate layer is designed, including rich CdS (R-CdS), thick ZnSe (T-ZnSe), thin ZnSe (t-ZnSe) and ZnCdS (R-ZnCdS) intermediate alloy shell layers. These quantum dots in QLEDs show superior performance, including maximum current efficiency, external quantum efficiencies and a T50 lifetime (at 1000 cd/m2) of 47.2 cd/A, 11.2% and 504 h for R-CdS; 61.6 cd/A, 14.7% and 612 h for t-ZnSe; 70.5 cd/A, 16.8% and 924 h for T-ZnSe; and 82.0 cd/A, 19.6% and 1104 h for R-ZnCdS. Among them, the quantum dots with the ZnCdS interlayer exhibit deep electron confinement and shallow hole confinement capabilities, which facilitate the efficient injection and radiative recombination of carriers into the emitting layer. Furthermore, the optimal devices show a superior T50 lifetime of more than 1000 h. The proposed novel methodology of quantum dot band engineering is expected to start a new way for further enhancing QLED exploration.

Air‐Degradation Mechanisms in Mixed Lead‐Tin Halide Perovskites for Solar Cells

AbstractOwing to the bandgap‐bowing effect, mixed lead‐tin halide perovskites provide ideal bandgaps for the bottom subcell of all‐perovskite tandem photovoltaic devices that offer fundamentally elevated power‐conversion efficiencies. However, these materials suffer from degradation in ambient air, which worsens their optoelectronic properties and hinders their usability for photovoltaic applications. Such degradation pathways are not yet fully understood, especially for the perovskites in the middle of the APbxSn1‐xI3 solid solution line, which offer the narrowest bandgaps across the range. This study unravels the degradation mechanisms of APbxSn1‐xI3 perovskites, reporting clear differences between mixed lead‐tin (x = 0.5) and tin‐only (x = 0) perovskites. The dynamic optoelectronic properties, electronic structure, crystal structure, and decomposition products of the perovskite thin films are examined in situ during air exposure. Both perovskite compositions suffer from the formation of defects over the timescale of hours, as indicated by a significant reduction in their charge‐carrier diffusion lengths. For tin‐only perovskite, degradation predominantly causes the formation of energetically shallow tin vacancies and hole doping. However, for mixed lead‐tin perovskite, deep trap states are formed that significantly accelerate charge‐carrier recombination, yet leave mobilities relatively unaffected. These findings highlight the need for passivation strategies tailored specifically to mixed lead‐tin iodide perovskites.

A novel cross‐coupled filter with triangular resonators

In this article, a novel isosceles right triangle resonators filter is presented based on cross-coupling technology. The whole filter is a square structure and it consists of four isosceles right triangle resonators. By introducing negative cross-coupling between two resonators, a fourth-order cross-coupling dielectric waveguide filter with two out-of-band transmission zeros (TZs) is implemented. By changing the sign of the coupling coefficient, the TZ can be changed around the passband. Positive coupling is achieved through a coupling partition and shallow coupling blind holes, and negative coupling is achieved through symmetrical upper and lower blind holes. The new resonator structure is introduced and the design, simulation, and physical measurement of the filter are discussed. The results show that the center frequency of the filter is 3.5 GHz and the relative bandwidth is 5.7%. The passband return loss is more than 14 dB, the insertion loss is less than 0.1 dB.

Ultrastructure of setae of a planktonic diatom, Chaetoceros coarctatus

Silica frustules of most planktonic diatoms have many shallow holes in which the length (L) is smaller than the width (W). The present study focuses on a silica ultrastructure of setae of a planktonic diatom having deep (L/W > 1) holes. Here, we characterized microscopically patterned nanoholes on the silica walls of thick, robust, and hollow setae of a colony of Chaetoceros coarctatus. Basically, tetragonal poroid arrangements with and without a costa pattern are observed on the inner and outer surfaces, respectively, for three kinds of curving hollow setae attached to the anterior, intercalary, and posterior parts of the colony. The seta structures including specific poroid arrangements and continuity of deep nanoholes depend on the location. The deep nanoholes ∼90 nm wide are elongated from 150 to 1500 nm (L/W ∼17) with an increase in the wall thickness of the polygonal tubes of the setae. The inside poroid array, with a period of 190 nm in the extension direction of setae, is lined by parallel plates of the costae. However, the poroid arrangement on the outer surface is disordered, with several holes obstructed with increasing wall thickness of the posterior terminal setae. According to the movement of a colony in a fluid microchannel, the thick curving terminal setae is suggested to involve attitude control and mechanical protection. Using an optical simulation, the patterned deep through-holes on the intercalary setae were suggested to contribute anti-reflection of blue light in the wavelength range of 400 to 500 nm for the promotion of photosynthesis in seawater.

Low-temperature large-scale hydrothermal synthesis of optically active PEG-200 capped single domain MnFe2O4 nanoparticles

Herein, we report an intrinsic fluorescence in polyethylene glycol (PEG) coated manganese ferrite (MnFe2O4) magnetic nano particles (MNPs). Generally, nano ferrites (NFs) do not show fluorescence characteristics, however, imparting fluorescence in these materials can be valuable for many applications as the stipulation of external control over the properties by external field provides an opportunity to develop active-controlled devices. In the present work, PEG-200 coated MnFe2O4 MNPs have been synthesized by a large-scale, facile one-pot hydrothermal method. The optical properties of MnFe2O4 MNPs have been by photoluminescence (PL) spectroscopy suggest that the prepared sample is showing sharp emission spectra at 422 nm, corresponding to the violet band, and second at 458 nm corresponding to the blue band. The presence of oxygen vacancy created at both tetrahedral and octahedral sites and shallow hole defects are responsible for the PL behavior in the PEG-coated MnFe2O4. The time-resolved PL (TRPL) results suggest that the MnFe2O4 MNPs have two decay times τ1=1.29ns and τ2=6.85ns which are non-correlated and correspond to different defect states. The electronic bandgap of the MNPs is 3 eV obtained from the Tauc plot using UV absorption spectra. Moreover, the structural analysis has been carried out using X-ray diffraction and various optical and magnetic properties have been correlated to structural parameters and cation distribution. The ferromagnetic resonance (FMR) spectra of the MnFe2O4 MNPs sample show a broad single peak which confirms the ferromagnetic characteristics of the sample and the g-value obtained for the sample is 1.98 which suggests that the super exchange interactions (SEI) dominates over the dipolar interaction. The M-H loop confirms the single domain nature of the sample and the saturation magnetization (SM) is 68 emu/g. The obtained value of SM is higher than the previously reported literature due to an increase in the occupancy of Fe3+ and Mn2+ ions at octahedral sites (Neel’s model). Further, the FTIR spectra confirm the spinel phase formation, and the size distribution and average size are obtained using electron microscopy analysis. The intrinsic fluorescent PEG-coated MnFe2O4 are highly suitable for a diverse range of biomedical (bio-imaging, sensing, magnetic resonance imaging (MRI) contrast agent), optoelectronics, and optical applications.

High-frequency EPR spectroscopy of paramagnetic manganese centers in GaAs : Mn crystals

High-frequency electron paramagnetic resonance (EPR) is used to study the unique properties of manganese centers in a GaAs : Mn crystal in strong magnetic fields at low temperatures. At frequencies of 94 and 130 GHz, EPR transitions were recorded in the MnGa2+-SH complex, which is a manganese ion with spin S=5/2, which replaces gallium (MnGa2+) and an ionized acceptor (A-) associated via an isotropic antiferromagnetic exchange interaction with a shallow hole (SH) with angular momentum J=3/2. A complex system of energy levels of this complex in a magnetic field and the possibility of accurately determining exchange interactions from EPR spectra are analyzed. Another complex was investigated, in which an ionized acceptor MnGa2+ interacts with a localized hole center in the form of a diamagnetic ion O2- replacing As. This complex, MnGa2+-OAs2-, is characterized by axial symmetry along the <111> axis of the cubic GaAs crystal and an anisotropic EPR spectrum. Due to the high Boltzmann factor, in our studies, the order of the fine structure spin levels of this complex was determined. The effect of the Boltzmann populations of the energy levels on the high-frequency EPR spectra was also demonstrated for the MnGa2+-SH complex. Keywords: high-frequency EPR, GaAs crystal, Mn acceptor, shallow hole, exchange interaction.

High-frequency EPR spectroscopy of paramagnetic manganese centers in GaAs : Mn crystals

High-frequency electron paramagnetic resonance (EPR) is used to study the unique properties of manganese centers in a GaAs : Mn crystal in strong magnetic fields at low temperatures. At frequencies of 94 and 130 GHz, EPR transitions were recorded in the MnGa2+-SH complex, which is a manganese ion with spin S=5/2, which replaces gallium (MnGa2+) and an ionized acceptor (A-) associated via an isotropic antiferromagnetic exchange interaction with a shallow hole (SH) with angular momentum J=3/2. A complex system of energy levels of this complex in a magnetic field and the possibility of accurately determining exchange interactions from EPR spectra are analyzed. Another complex was investigated, in which an ionized acceptor MnGa2+ interacts with a localized hole center in the form of a diamagnetic ion O2- replacing As. This complex, MnGa2+-OAs2-, is characterized by axial symmetry along the <111> axis of the cubic GaAs crystal and an anisotropic EPR spectrum. Due to the high Boltzmann factor, in our studies, the order of the fine structure spin levels of this complex was determined. The effect of the Boltzmann populations of the energy levels on the high-frequency EPR spectra was also demonstrated for the MnGa2+-SH complex. Keywords: high-frequency EPR, GaAs crystal, Mn acceptor, shallow hole, exchange interaction.

Bioerosive traces in fossil penguin bones (Aves, Sphenisciformes) from the Eocene of Marambio/Seymour Island (West Antarctica)

ABSTRACT We examined a set of penguin bones from different Eocene levels of the Submeseta Formation in Marambio/Seymour Island (James Ross Basin, Antarctic Peninsula) and found the bioerosive traces fossils presented here. Traces were assigned to ?Machichnus bohemicus, Machichnus indeterminate, Nihilichnus nihilicus, Centrichnidae indeterminate, and other ambiguous structures grouped into morphologic descriptive categories such as ‘shallow pits with radial scratches’, ‘indeterminate tunnels’, ‘rounded to sub-rounded shallow holes’, ‘oval deep traces’. According to the possible interpretations of these trace fossils, the taphonomic history of the remains, although different in all the cases, would include the primary deposition in a marine environment, transportation and subaerial exposure.

Circular cross‐coupling dielectric waveguide filter based on 90‐degree sectoral resonators

AbstractIn this study, a circular cross‐coupled dielectric waveguide (DW) filter was realized based on 90‐degree sectoral resonators. The filter is formed by splicing four 90‐degree sectoral DW resonators (SDWRs). A shallow blind hole (BH) was set at the center of each 90‐degree SDWR to adjust the resonant frequency. The magnetic coupling between the resonators was realized through the rectangular wall and shallow BH. Electrical coupling between the resonators was achieved through deep BHs. The overall structure was designed, simulated, and fabricated. The measured results demonstrate that the designed filter has a center frequency of 3.6 GHz, bandwidth of 200 MHz, insertion loss less than 1 dB, in‐band return loss greater than 15 dB, and two out‐of‐band transmission zeros at 3.38 and 3.82 GHz.

Control the shallow trap states concentration during the formation of luminescent Ag2S and Ag2S/SiO2 core/shell quantum dots

The paper presents the results of a study of shallow non-radiative trap states in colloidal Ag2S QDs and Ag2S/SiO2 core/shell QDs, passivated with 2-mercaptopropionic acid in ethylene glycol carried out the thermally stimulated luminescence technique. For Ag2S QDs, the presence of thermoluminescence peaks in the region of 150–330 K was established. The formation of the SiO2 shells leads to the disappearance of the thermoluminescence peak at 250 K. It is interpreted as a “healing” of defects, localized on Ag2S QD surface. The depths of the detected trap states were estimated using a kinetic model. They showed that the observed thermoluminescence bands are due to the presence of shallow holes trap states in Ag2S QDs with depths of 0.117 eV and 0.135 eV for the thermoluminescence peaks at 190 K and 250 K, respectively.

The man who thought he was kicked from behind.

A 53-year-old man presented with a painful swollen right calf. The day before, he was walking uphill on a cold afternoon after finishing work. Suddenly, he stepped on a shallow hole in the pavement, his foot went up and his knee straightened backwards. At the same time, he felt someone had kicked

Exciton–polaritons in GaAs-based slab waveguide photonic crystals

We report the observation of bandgaps for low loss exciton–polaritons propagating outside the light cone in GaAs-based planar waveguides patterned into two-dimensional photonic crystals. By etching square lattice arrays of shallow holes into the uppermost layer of our structure, we open gaps on the order of 10 meV in the photonic mode dispersion, whose size and light–matter composition can be tuned by proximity to the strongly coupled exciton resonance. We demonstrate gaps ranging from almost fully photonic to highly excitonic. Opening a gap in the exciton-dominated part of the polariton spectrum is a promising first step toward the realization of quantum-Hall-like states arising from topologically nontrivial hybridization of excitons and photons.

Residual stress determination using full-field optical methods

Residual stresses are created in engineering components during fabrication and processing. Such stresses can strongly influence structural behavior. They are generally found by experimental means. A widely used way of finding residual stresses is removal of a small volume of material containing stresses and measurement of the strains that develop in surrounding material as a result of stresses being released. The strains can then be used to compute residual stresses. Drilling a small shallow hole is the most common way of implementing this approach, with strains measured by nearby strain gages adhered to the surface. This paper provides an overview of how full-field optical methods can be used instead of strain gages with hole drilling, overcoming limitations associated with gages and expanding capabilities of the hole drilling approach. The methods considered are holographic and electronic speckle pattern interferometry, Moire interferometry and digital image correlation. Advantages of using optical methods to find residual stresses are shown. A variety of applications is presented, ranging from determination of stresses in underground piping to stresses in microscale specimens. In addition, optical approaches employing different ways of material removal for stress release are reviewed, as well as several non-destructive optical methods for determining residual stresses.