Low Energy Position Research Articles

Effects of nanocrystals on hydrogen permeation and diffusion in amorphous electroless Ni-P coatings

Amorphous electroless-plated Ni-P coatings readily form nanocrystalline at relatively low temperatures. The current efforts to investigate the impact of proportion of nanocrystals on hydrogen permeation remain relatively limited, particularly when seeking to determine the impact of surface and internal nanocrystals on hydrogen permeation. The present work addresses this issue by conducting detailed analyses for amorphous electroless-plated Ni-P coatings and heat-treated coatings with a greater nanocrystalline concentration. The results show that the plated state samples exhibit excellent hydrogen permeation barrier properties.In addition, the heat-treated coatings exhibit a greater surface free energy and lower corrosion resistance due primarily to the higher density of phase boundaries arising from the increased crystallinity. The hydrogen diffusion coefficient of the heat-treated coating remains relatively stable (between 1.148×10−11 to 1.517×10−11 cm2/s) with increasing hydrogen charging current from 1 to 10 mA/cm², while the hydrogen diffusion coefficient of the as-plated amorphous coating increases from 3.406×10−12 to 7.996×10−12 cm2/s with increasing hydrogen charging current. The diffusion of hydrogen in the amorphous coating is primarily governed by low activation energy positions (i.e., 23.16 kJ/mol) associated with gaps between short-range-ordered atomic clusters in the material. A few high-energy positions (i.e., 45.58 kJ/mol) may be related to reversible hydrogen traps. The increasing crystalline content arising under heat treatment drastically reduces the prominence of low activation energy positions.

Using iBeacon Components to Design and Fabricate Low-energy and Simple Indoor Positioning Method

Using iBeacon Components to Design and Fabricate Low-energy and Simple Indoor Positioning Method

Structural and biochemical insights into Zn2+-bound EF-hand proteins, EFhd1 and EFhd2.

EF-hand proteins, which contain a Ca2+-binding EF-hand motif, are involved in regulating diverse cellular functions. Ca2+ binding induces conformational changes that modulate the activities of EF-hand proteins. Moreover, these proteins occasionally modify their activities by coordinating metals other than Ca2+, including Mg2+, Pb2+ and Zn2+, within their EF-hands. EFhd1 and EFhd2 are homologous EF-hand proteins with similar structures. Although separately localized within cells, both are actin-binding proteins that modulate F-actin rearrangement through Ca2+-independent actin-binding and Ca2+-dependent actin-bundling activity. Although Ca2+ is known to affect the activities of EFhd1 and EFhd2, it is not known whether their actin-related activities are affected by other metals. Here, the crystal structures of the EFhd1 and EFhd2 core domains coordinating Zn2+ ions within their EF-hands are reported. The presence of Zn2+ within EFhd1 and EFhd2 was confirmed by analyzing anomalous signals and the difference between anomalous signals using data collected at the peak positions as well as low-energy remote positions at the Zn K-edge. EFhd1 and EFhd2 were also found to exhibit Zn2+-independent actin-binding and Zn2+-dependent actin-bundling activity. This suggests the actin-related activities of EFhd1 and EFhd2 could be regulated by Zn2+ as well as Ca2+.

Photocatalytic degradation and pollutant-oriented structure-activity analysis of carbamazepine, ibuprofen and acetaminophen over faceted TiO2

Photocatalytic degradation of carbamazepine, ibuprofen, acetaminophen and phenol was studied in the presence of anatase photocatalyst, exposing three different crystal facets in the majority of {0 0 1}, {1 0 0} or {1 0 1}. It was found that octahedral anatase particles exposing {1 0 1} facets allow to achieve the best degradation and mineralization of all persistent organic pollutants. This confirms that the previous findings, showing high {1 0 1} activity, are not limited to phenol and could be generalized for other water pollutants. Based on the obtained results, a correlation model including exposed TiO2 crystal facet and chemical hardness of the pollutant was developed to predict the degradation rate of pollutants with a possibly diverse electronic structure. The structure-activity analyses, based on the reactivity predictors obtained from the DFT calculations for all tested compounds, have shown that pollutants with higher chemical hardness react faster with the photocatalyst. Alternatively, a similar effect was observed for the higher HOMO-LUMO energy gap of the compound. This relation indicates that for compounds with a low energy position of LUMO orbital, e.g., carbamazepine, process efficiency is not strictly dependent on the stability of h+ generated organic radical, which is often pointed out as an initial reactive form. Based on these results, a correlation model was developed for the first time to quantitatively describe the effect of the facet-pollutant interactions based on their independent electronic properties. Finally, this was followed by the detailed degradation study of the pharmaceuticals mixture, showing the impact of the total concentration and role of active species on the degradation efficiency over facet-engineered TiO2 photocatalysts.

Investigation of Movement and Deposition Behaviors of Solid Particles in Hydraulic Water Reservoir via the CFD-DEM Coupling Method

Solid contamination existing as solid particles in power fluid transmission systems may lead to transmission performance reduction, system failures, and component damage. The hydraulic reservoir will deposit the contamination and store hydraulic fluid. To investigate its purification ability for solid contamination, experiments and simulations for the motion and deposition status of the typical hydraulic system particles are carried out to reveal the interaction of particles and fluid in hydraulic water reservoirs. The results show that the CFD-DEM coupling method could predict the accurate deposition position of iron particles and sand particles when ignoring the small-scale turbulence effect in the flow field. Besides, the particle motion traces and deposition patterns in the reservoir illustrate that the flow development on the bottom surface results in the particles turning, and particles tend to settle in the low flow energy position. The motion of particles is also linked to particles Stokes number, and the same-size sand particles are easily driven by the fluid. The contribution of this paper could provide a guide for predicting the particle motion and deposition pattern in the hydraulic reservoir.

Tracing the Location of Alzheimer\'s Patient Using Location Fingerprinting

Abstract: Alzheimer's disease is the most common type of Dementia in which the person’s memory, behavior, and thinking get affected. This work is majorly focused on helping Alzheimer's patient and the Guardians/Caretakers, who are responsible for the safety of Alzheimer's patients. Trapping the patient inside a care facility or home isn't a solution for them, but at the exact moment, we can’t let them free outside which is way riskier. Therefore, the objective of our work is to design a system that can trace the location of Alzheimer's patient using Location Fingerprinting and intimating the Guardian/caretaker about their location through a Mobile Application. Among all the available approaches in Location Fingerprinting, we are making use of Bluetooth Based Positioning for location tracing within the Apartment or Care facility premises. By using RSSI and Trilateration based techniques in Bluetooth Low Energy (BLE) positioning, we can trace the location and map it into a Map in our Mobile application in terms of Latitude and Longitude. Keywords: Location Fingerprinting, Bluetooth low energy, Trilateration, Alzheimer's, Mobile Application

First-principles study of SrSnO<sub>3</sub> as transparent conductive oxide

As a wide band gap semiconductor with perovskite structure, SnSnO<sub>3</sub> is regarded as a promising candidate of transparent conductive oxides due to its superior properties like high transparency, non-toxicity and low price. In this work, the electronic structure of SrSnO<sub>3</sub> is obtained through first-principles calculations based on HSE06 hybrid functional. Especially, we investigate the defect formation energy and transition levels of the intrinsic and external defects in SrSnO<sub>3</sub>. The intrinsic defects including the anti-site defects (Sr<sub>Sn</sub> and Sn<sub>Sr</sub>), the vacancy defects (V<sub>Sr</sub>, V<sub>Sn</sub>, and V<sub>O</sub>), and the interstitial defects (Sr<sub>i</sub>, Sn<sub>i</sub> and O<sub>i</sub>) are considered while the external doping defects are taken into account, including the substitution of Li, Na, K, Al, Ga, In for Sr site, Al, Ga, In, P, As, Sb for Sn site, and N, P at O site. Subsequently, the suitable doping elements and the corresponding experimental preparation environments are pointed out. Furthermore, we discuss the mechanism of its conductance according to the energy positions of the band edges. Our calculation results demonstrate that SrSnO<sub>3</sub> is an indirect-type semiconductor with a fundamental band gap of 3.55 eV and an optical band gap of 4.10 eV and then has a good visible light transmittance. Its valence band maximum (VBM) comes from O-2p state while its conduction band minimum (CBM) mainly originates from Sn-5s state. In consistent with the delocalized Sn-5s state at CBM, the electron effective mass is light and isotropic, which is beneficial to n-type conductance. The n-type intrinsic defects Sn<sub>Sr</sub> and V<sub>o</sub> have lower defect formation energy than the p-type intrinsic defects under O-poor condition while the n-type and p-type defects with low defect formation energy are almost equal under O-rich condition. Moreover, the transition levels of Sn<sub>Sr</sub> and V<sub>O</sub> are both deep. Therefore, SrSnO<sub>3</sub> cannot have a good conductance without external doping. Our calculations also demonstrate that it is hard to produce an efficient p-type external doping due to the compensation effect by V<sub>O</sub>. On the other hand, substitution of As or Sb for Sn site can result in an effective n-type external doping due to their low defect formation energy and shallow transition levels. According to the low energy positions of VBM (–7.5 eV) and CBM (–4.0 eV) of SrSnO<sub>3</sub>, we explain the reason why it is easy to realize an n-type conductance but hard to produce a high-performance p-type conductance, which follows the doping rules for wide band gap semiconductors. Finally, Sb-doped SrSnO<sub>3</sub> is proposed as a promising candidate for n-type transparent conductive materials.

Shape memory effect in metallic glasses

Shape memory effect in metallic glasses

Internal photoemission of electrons from 2D semiconductor/3D metal barrier structures

Understanding the energy alignment of electronic bands, which originate from ultrathin MoS2 layers and metal electrodes attached to them, is crucial for the design of MoS2-based electronic devices. We have applied internal photoemission spectroscopy (IPE) to analyze this alignment. We demonstrate that IPE can yield the barrier heights in the metal/ two-dimensional semiconductor/insulator stacks when the top metal electrode is sufficiently thin for allowing both the photoexcitation of electrons and their transport towards the insulator. The electron barrier at the interface between Al and monolayer (1ML) of MoS2 is estimated at 0.7 eV, and this value explains the experimentally observed attenuated quantum yield contribution from the aluminum. Based on the relative energies of the low-energy threshold position and the Fermi level of aluminum at the interface with the SiO2 insulator, we provide a simple explanation for the observed current photoinjection at the interface between aluminum and 1ML MoS2.

Effect of vacancy defects on photoelectric properties of K2CsSb photocathode

A variety of different vacancy defect compounds may be formed during the preparation of the K2CsSb photocathode. To better understand the action mechanism of vacancy defects, the influence of Cs vacancy, K vacancy, Sb vacancy, Cs-K vacancy, Cs-Sb vacancy, K-Sb vacancy on the electronic structures and optical properties of K-Cs-Sb cathodes were investigated by the first-principles method based on density functional theory. The band structures show that, K-Cs-Sb cathode materials with Sb vacancy, Cs-Sb vacancy, K-Sb vacancy, adjacent K double vacancies are indirect bandgap semiconductors, other models are all direct bandgap semiconductors. Besides, the Sb vacancy-contained models exhibit n-type semiconductor property, while other models with only K or Cs vacancy all exhibit p-type semiconductor property. The calculated results about formation energy and formation enthalpy indicate that the Cs vacancy defects are easier to form and more thermodynamically stable than other vacancy defects. In terms of optical properties, in the energy range of 2.4–3.2 eV produced by neutrino scintillator radiation, K2CsSb without vacancy defects possesses the maximum absorption coefficient. The Sb vacancy-contained defects cause the absorption coefficient peak to shift to the lower energy position, while other vacancy defects without Sb vacancies are just the opposite.

The 1S0 → 3P1 transition position shift of Bi3+ ion doped Ln2O3 (Ln = Lu, Gd, La) phosphors

A series of Bi3+ ion doped Ln2O3 (Ln = Lu, Gd, La) phosphors have been prepared through a simple urea-based precipitation method. The 1S0 → 3P1 transition position shift of Bi3+ ion has been investigated in Bi3+-doped Ln2O3 phosphors. This is caused by difference of covalency and coordination number. The 1S0 → 3P1 transition of Bi3+ ion in Gd2O3 crystal shifts to lower energy position than that in Lu2O3 crystal for the same site due to the larger radius of Gd3+ ion compared to Lu3+ ion. However, the 1S0 → 3P1 transition of Bi3+ ion shifts to higher energy position owing to the increase of coordination number from cubic phase Lu2O3 and Gd2O3 crystals to hexagonal phase La2O3 crystal. Our work provides a reference to achieve various photoluminesence performances of Bi3+ ion doped oxides.

Injection Coding With Spectral Shaping Capability

In digital transmission systems that involve pulse amplitude modulation (PAM), channel coding is useful for spectral shaping by concentrating the frequency energy of the transmitted information towards a predetermined range of the frequency spectrum, or making it have low power content at such frequencies, so as to suit the frequency characteristics of the communication channel. We thus present a permutation coding system with injections that can exhibit spectral shaping at rational sub-multiples of the symbol frequency. We also present a mathematical expression that allows for the prediction of low energy positions in the codebook's spectrum. Upper and lower bounds for the low energy spectrum were also determined. Due to the way the injections are introduced, it gives the scheme an advantage of achieving higher symbol rate, when compared with conventional permutation coding systems.

Investigation of localized state emissions in quaternary InGaAsSb/AlGaAsSb multiple quantum wells grown by molecular beam epitaxy

As an essential structure of infrared semiconductor lasers, the optical properties of InGaAsSb/AlGaAsSb multiple quantum wells need to be fully investigated. In this paper, the temperature and excitation power-dependent photoluminescence (PL) spectra of the InGaAsSb/AlGaAsSb MQWs are measured. A strong free exciton emission with a photon energy of 0.631 eV was observed at room temperature. Besides the main peak, an obvious shoulder peak, located at the low photon energy position under low temperature range (T≤90 K), was confirmed to be an emission of defect related localized carriers by power-dependent PL spectra. The power-dependent PL spectra were dominated by the localized carriers emission under low excitation power (Iex≤20 mW), while the free-exciton emission dominated the PL spectra gradually when excitation power higher than 40 mW. This phenomenon is ascribed to the dissociation of localized states. Our work is of great significance for the device applications of InGaAsSb/AlGaAsSb multiple quantum wells.

Quasiparticle energies and excitonic effects of chromium trichloride: From two dimensions to bulk

Layered van der Waals (vdW) magnetic materials have attracted significant research interest to date. In this work, we employ the first-principles many-body perturbation theory to calculate excited-state properties of a prototype vdW magnet, chromium trichloride (CrCl3), covering monolayer, bilayer, and bulk structures. Unlike usual non-magnetic vdW semiconductors, in which many-electron interactions and excited states are sensitive to dimensionality, many-electron interactions are always enhanced and dominate quasiparticle energies and optical responses of both two-dimensional and bulk CrCl3. The electron-hole (e-h) binding energy can reach 3 eV in monolayer and remains as high as 2 eV in bulk. Because of the cancellation effect between self-energy corrections and e-h binding energies, the lowest-energy exciton (optical gap) is almost not affected by the change of dimensionality. Besides, for the excitons with similar e-h binding energies, their dipole oscillator strength can differ by a few orders of magnitude.Our analysis shows that such a big difference is from a unique interference effect between complex exciton wavefunctions and interband transitions. Finally, we find that the interlayer stacking sequence and magnetic coupling barely change quasiparticle band gaps and optical absorption spectra of CrCl3. Our calculated low-energy exciton peak positions agree with available measurements. These findings give insight into the understanding of many-electron interactions and the interplay between magnetic orders and optical excitations in vdW magnetic materials.

Giant optical absorption and ferroelectric polarization of BiCoO2S perovskite oxysulfide by first principles prediction.

Obtaining an ideal ferroelectric photovoltaic (FE-PV) material with a narrow bandgap and a large ferroelectric polarization value can enable us to achieve great practical FE-PV performance. By the introduction of sulfur into the tetragonal BiCoO3 perovskite with a C-type antiferromagnetic ordering, it is found that the bandgap of BiCoO2S decreases significantly (about 1.2 eV) while maintaining a large polarization value (about 1.86 C m-2) that is similar to the value of 1.793 C m-2 of BiCoO3. Most noteworthy is that the optical absorption of BiCoO2S is remarkably higher than those of BiCoO3 and other FE-PV materials. The decrease of the BiCoO2S bandgap originates from the movement of Co 3d states to a low-energy position due to the reduction of the Co ionicity when the less electronegative sulfur is introduced into BiCoO3 to substitute oxygen. The narrow bandgap and the high optical absorption of the BiCoO2S films grown on different substrates are favorable for FE-PV applications. In addition, the bandgap of BiCoO2S can be modulated by the doping amount of sulfur, which can help us fabricate multilayer FE-PV devices based on different bandgaps from different layers.

Ξ hyperons in the nuclear medium described by chiral NLO interactions

Properties of the baryon-baryon interactions in the strangeness $S=-2$ sector of chiral effective field theory at the next-to-leading order (NLO) level are explored by calculating $\Xi$ single-particle potentials in symmetric nuclear matter. The results are transformed to the $\Xi$ potential in finite nuclei by a local-density approximation with convolution by a Gaussian form factor to simulate finite-range effects. The $\Xi$ potential is repulsive in a central region, and attractive in a surface area when the $\Xi$ energy is low. The attractive pocket can lower the $\Xi^-$ $s$ and $p$ atomic states. The obtained binding energies in $^{12}$C and $^{14}$N are found to be conformable with those found in emulsion experiments at Japan's National Laboratory for High Energy Physics (KEK). $K^+$ spectra of $(K^-, K^+)$ $\Xi$ production inclusive processes on $^9$Be and $^{12}$C are also evaluated, using a semi-classical distorted wave method. The absolute values of the cross section are properly reproduced for $^9$Be, but the peak locates at a lower energy position than that of the experimental data. The calculated spectrum of $^{12}$C should be compared with the forthcoming result from the new experiments recently carried out at KEK with better resolution than before. The comparison would be valuable to improve the understanding of the $\Xi N$ interaction, the parametrization of which has still large uncertainties.

Low-energy PSO-based node positioning in optical wireless sensor networks

In this paper, Particle Swarm Optimization (PSO) is introduced into Optical Wireless Sensor Networks. We consider the impact of node location on energy consumption when communicating over the network. The algorithm use PSO to optimize the position of nodes with the lowest energy consumption. The proposed method converges faster. By optimizing the positioning of node, energy consumption of the node is effectively reduced and the overall performance of the network is improved. An energy-saving optical wireless sensor network is obtained.

Stable Structural Phase of Potassium-Doped p-Terphenyl and Its Semiconducting State

The potassium-doped p-terphenyl compounds were synthesized in recent experiments and the superconductivity with high transition temperatures were reported, but the atomic structure of potassium-doped p-terphenyl is unclear. In this paper, we studied the structural and electronic properties of potassium-doped p-terphenyl with various doping levels by the first-principles simulation. We first find out the low energy position of K atom in intralayer interstitial space of the molecular layer, then examine whether two rows of K atoms can be accommodated in this one space, at last the effect of the interlayer arrangement between adjacent two molecular layers on total energy is taken into account. Our results show that the doped K atoms prefer to stay at the bridge site of single C-C bond connected two phenyls instead of locating at the site above the phenyl ring, distinct from the situation of K-doped picene and phenanthrene. Among the possible structural phases of Kx-p-terphenyl, the K2-p-terphenyl phase with P212121 group symmetry is determined to be most appropriate, which is different from the one in recent report. The stable K 2 -p-terphenyl phase is semiconducting with an energy gap of 0.3 eV and the bands from the lowest unoccupied molecular orbitals are just fully filled by the electrons transferred from K atoms.

Indoor Positioning Based on Bluetooth Low-Energy Beacons Adopting Graph Optimization.

Bluetooth Low-Energy (BLE) beacons-based indoor positioning is a promising method for indoor positioning, especially in applications of position-based services (PbS). It has low deployment cost and it is suitable for a wide range of mobile devices. Existing BLE beacon-based positioning methods can be categorized as range-based methods and fingerprinting-based methods. For range-based methods, the positions of the beacons should be known before positioning. For fingerprinting-based methods, a pre-requisite is the reference fingerprinting map (RFM). Many existing methods focus on how to perform the positioning assuming the beacon positions or RFM are known. However, in practical applications, determining the beacon positions or RFM in the indoor environment is normally a difficult task. This paper proposed an efficient and graph optimization-based way for estimating the beacon positions and the RFM, which combines the range-based method and the fingerprinting-based method. The method exists without need for any dedicated surveying instruments. A user equipped with a BLE-enabled mobile device walks in the region collecting inertial readings and BLE received signal strength indication (RSSI) readings. The inertial measurements are processed through the pedestrian dead reckoning (PDR) method to generate the constraints at adjacent poses. In addition, the BLE fingerprints are adopted to generate constraints between poses (with similar fingerprints) and the RSSIs are adopted to generate distance constraints between the poses and the beacon positions (according to a pre-defined path-loss model). The constraints are then adopted to form a cost function with a least square structure. By minimizing the cost function, the optimal user poses at different times and the beacon positions are estimated. In addition, the RFM can be generated through the pose estimations. Experiments are carried out, which validates that the proposed method for estimating the pre-requisites (including beacon positions and the RFM). These estimated pre-requisites are of sufficient quality for both range-based and fingerprinting-based positioning.

Understanding the Activation and Stabilization of Electrocatalytic Single Atom Catalysts

The discovery of single atom catalysts (SACs) paths new frontier in heterogeneous catalysis. Recently, increasing interests have been focused on the construction of atomically-dispersed transition metal centers in nitrogen doped carbon through supports-assisted pyrolytic synthesis for various applications, such as electrocatalysis, CO oxidation, and organic synthesis. However, the evolution, activation and stabilization of SAC in synthesis and catalysis, which is critical for its applications, still remain unexplored yet. Here, we examined the critical importance of supports and anions for the single-atom transition-metal-sites(Co, Fe, and Ni) construction and modification, combing synchrotron X-ray absorption studies, and the electron microscopic characterizations, and electrochemical measurements. The supports and anions are essential parts which are involved in the pyrolytic synthesis. However, both of them are often excluded from construction of catalytic sites in SACs. The formation of atomic metal sites is often accompanies with the evolution of metallic metal/metal carbide nanoparticles encased by graphite layers. Here, we demonstrate a versatile anions-regulated selective generation of metal sites in carbon and demonstrate the metal-sites dependence catalytic performances for oxygen reduction reaction (ORR) and hydrogen evolution reaction. Besides achieving the controlled evolution of atomically-dispersed metal sites, we also demonstrate the roles of supports on the structural reconstruction and activation of SAC and the functional relationship between the electrocatalytic activity and electrochemical stability in SAC. Different from the previous models of integration of fragments on carbon, we initially reveal the supports-assisted structural reconstruction on the evolution of electrocatalytic SAC. More importantly, the enhanced catalytic activity and selectivity are found to result from more unoccupied 3d orbitals at low energy positions for single-atom-dispersed metal sites within non-planar coordination. This is mainly due to the facilitated interactions between metal sites and adsorbates. More importantly, such activity descriptors can further modified through controlling the atomic coordination geometry or structures. Interestingly, decreasing the atomic coordination numbers enhances the ORR activity, however, also damages the electrochemical stability of atomically dispersed metal sites under potentials, demonstrating the coordination-structure sensitivity of its electrochemical stability. Therefore, we present a functional relationship between the catalytic activity and electrochemical stability of SAC for electrocatalysis. Our studies offer molecular insights on the evolution of SAC, pathing new directions to SAC engineering with improved activity and stability for various reactions, such as ORR, water splitting, and CO2 reduction. Figure 1