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We measured the atomic volume of Ag in a toroidal diamond anvil cell to a maximum pressure of 416 GPa and calculated the atomic volume and elastic constants of Ag up to 750 and 460 GPa, respectively. Our density functional theory calculations at 0 K utilize an all-electron fully relativistic method and agree well with our volume measurements, particularly at pressures above ∼75 GPa. We corrected our experimental results for non-hydrostaticity using a line shift analysis, and the resulting Vinet equation of state (EOS) parameters are reported. We find that the uniaxial stress sustained by Ag increases linearly up to 4.5 GPa at a pressure of 416 GPa. Our experimental results indicate that the fcc structure of Ag remains stable to at least 416 GPa at room temperature. Our theoretical results show that C44 increases as pressure increases and reaches a maximum at ∼100 GPa above which it begins to decrease, a sign that the fcc structure of Ag is becoming unstable, and at V/V0 = 0.30, the bcc structure is lower in energy than fcc. [ABSTRACT FROM AUTHOR]

Double satellite formation for gravity field exploration is a complex space virtual instrument system with high-precision, whose normal manner is threatened by the space debris environment. The normal manner of the formation based on control with prescribed performance is studied. Based on the random impact of space debris, nonlinear dynamical equations with 20 variables are established considering the relative attitude of the double satellite. The interferential characteristics and expected stability under certain disturbance conditions by the space debris in low Earth orbit are analyzed. To simplify the relative motion of the formation and the motion of the test mass (TM) relative to the cage, a prescribed performance function is introduced to constrain the relative attitude errors of transient and steady states. An adaptive attitude control design method based on a prescribed performance function is proposed. Finally, the analysis is carried out. The results show that the probability of normal manner of the formation is about 78.45% in the first year and about 45.59% in the first three years. The normal manner of the double satellite formation for gravity field exploration can be effectively simulated and analyzed based on the prescribed performance control methods. [ABSTRACT FROM AUTHOR]

Transcranial Magnetic Stimulation has the potential to treat various neurological disorders noninvasively and safely. The "Halo coil" configuration can stimulate deeper regions of the brain with lower surface to deep-brain field ratio compared to other coil configurations. The existing "Halo coil" configuration is fixed and is limited in varying the site of stimulation in the brain. We have developed a new system based on the current "Halo coil" design along with a graphical user interface system that enables the larger coil to rotate along the transverse plane. The new system can also enable vertical movement of larger coil. Thus, this adjustable "Halo coil" configuration can stimulate different regions of the brain by adjusting the position and orientation of the larger coil on the head. We have calculated magnetic and electric fields inside a MRI-derived heterogeneous head model for various positions and orientations of the coil. We have also investigated the mechanical and thermal stability of the adjustable "Halo coil" configuration for various positions and orientations of the coil to ensure safe operation of the system. [ABSTRACT FROM AUTHOR]

With a view to fabricating future flexible electronic devices, an atmospheric-pressure plasma jet driven by 13.56 MHz radio-frequency power is developed for depositing Cu thin films on polyimide, where a Cu wire inserted inside the quartz tube was used as the evaporation source. A polyimide substrate is placed on a water-cooled copper heat sink to prevent it from being thermally damaged. With the aim of preventing oxidation of the deposited Cu film, we investigated the effect of adding H2 to Ar plasma on film characteristics. Theoretical fitting of the OH emission line in OES spectrum revealed that adding H2 gas significantly increased the rotational temperature roughly from 800 to 1500 K. The LMM Auger spectroscopy analysis revealed that higher-purity Cu films were synthesized on polyimide by adding hydrogen gas. A possible explanation for the enhancement in the Cu film deposition rate and improvement of purity of Cu films by H2 gas addition is that atomic hydrogen produced by the plasma plays important roles in heating the gas to promote the evaporation of Cu atoms from the Cu wire and removing oxygen from copper oxide components via reduction reaction. [ABSTRACT FROM AUTHOR]

Both polarons and excitons, which are composite particles with internal lattice structure, play an important role in the transport and light-emitting properties of conjugated polymers for the use in, e.g., polymer based light-emitting diodes (LEDs). The scattering and recombination processes between a triplet exciton and a polaron are investigated using a nonadiabatic evolution method based on an extended Su–Schrieffer–Heeger model including interchain interactions. The results show that an excited polaron state can be formed, besides a triplet exciton is converted into a singlet exciton by the polaron. Moreover, the yields of both the singlet exciton and the excited polaron states increase with increasing interchain coupling strength. The excited polaron is luminescent due to radiative decay as is the singlet exciton. Therefore, our results indicate that the quantum efficiency of polymer LEDs could be enhanced by polaron-exciton recombination. [ABSTRACT FROM AUTHOR]

Within an extended Su–Schrieffer–Heeger model including interchain interactions and the extended Hubbard model, the dynamical relaxation of photoexcitations in two coupled conjugated polymer chains is investigated by using a nonadiabatic evolution method. Initially, one of the two chains is photoexcited and the other chain is in the dimerized ground state. Due to the interchain interactions, the electron and/or the hole can be transferred from one chain to the other chain. For weak interchain coupling, the dynamical evolution of the lattice on the photoexcited chain is similar to that found in an isolate single chain case. With interchain interactions increasing, the amplitude of the distortions on the photoexcited chain decreases, and simultaneously, that on the other chain gradually increases. Until stronger interchain coupling, the deformations of the two chains have almost the same amplitude. Besides intrachain polaron-excitons and intrachain oppositely charged polaron pairs as found in single chain case, interchain polaron-excitons and interchain separated charged polaron pairs are obtained. The results show that the yield of interchain products increases and that of intrachain products decreases with interchain coupling increasing. Totally, the yield of charged polarons (including intrachain oppositely charged polaron pairs and interchain oppositely charged polaron pairs) is about 25%, in good agreement with results from experiments. [ABSTRACT FROM AUTHOR]

Organized extremely small Ti–Sn alloy nanodots have been formed in the subsurface of SiO2 by dynamic coimplantation of isotopic 48Ti+ and 120Sn+ at a low kinetic energy of 9 keV into (0001) Z-cut quartz at different substrate temperatures. Transmission electron microscopy images show that the Ti–Sn alloy nanodots are single crystal and have been formed uniformly at room temperature. They are distributed in a two-dimensional array with similar size of ∼4 nm and constant interdot spacing between each dot. The regions beyond and below the two-dimensional array are depleted of detectable nanodots. At high temperature, the distribution and crystallinity were destroyed with much smaller amorphous nanodots in a slightly deeper region. The implantation was carried out by dynamic coimplantation, rather than the commonly used sequential implantation. These results indicate that dynamic low energy coimplantation is capable of forming well-ordered two-dimensional array of alloy nanodots. [ABSTRACT FROM AUTHOR]

A cubic phase of C3N4 was discovered. It was recovered at ambient conditions from the graphite-like C3N4 (g-C3N4) phase subjected to pressures between 21 and 38 GPa in a diamond-anvil cell, laser heated to temperatures between 1600 and 3000 K. The x-ray-diffraction data of the phase are best explained by a cubic unit cell with the lattice parameters a=3.878±0.001 Å. With an assumption of 1 molecule/unit cell (Z=1) for the cubic phase, the molar volume of the cubic phase is 35.126 cm3/mol and the density is 2.62 g/cm3. The density of the cubic phase is less than that which was predicted for the high-pressure phases but is 12% denser than the low-pressure graphitic phase (ρ=2.336 g/cm3). The cubic phase has not been predicted theoretically and represents an unknown structure in C3N4. [ABSTRACT FROM AUTHOR]

The measurement of transient temperatures less than 1000 K for samples in laser-heated diamond anvil cells remains a challenge. Here we present the design and performance characteristics of a multi-channel pyrometer that works in the near-infrared from 1200 to 2000 nm. It has a relatively small footprint, is portable, requires only low voltage power supplies, and can report temperatures down to 800 K on the millisecond scale or faster. A single data point without averaging can be acquired in 14 µs (sampling rate of 7 kilosamples per second). In conjunction with a diamond anvil cell, the system delivers accurate and rapid measurements down to ∼830 K. The pyrometer has been successfully interfaced several times with the combined x-ray diffraction and laser heating system at the High Pressure Collaborative Access Team at the Advanced Photon Source at Argonne National Laboratories. [ABSTRACT FROM AUTHOR]

We propose a nanowaveguide platform for collective atom-light interaction through evanescent field coupling. We have developed a 1 cm-long silicon nitride nanowaveguide can use evanescent fields to trap and probe an ensemble of 87Rb atoms. The waveguide has a sub-micrometer square mode area and was designed with tapers for high fiber-to-waveguide coupling efficiencies at nearinfrared wavelengths (750 nm to 1100 nm). Inverse tapers in the platform adiabatically transfer a weakly guided mode of fiber-coupled light into a strongly guided mode with an evanescent field to trap atoms and then back to a weakly guided mode at the other end of the waveguide. The coupling loss is -1 dB per facet (~80% coupling efficiency) at 760 nm and 1064 nm, which is estimated by a propagation loss measurement with waveguides of different lengths. The proposed platform has good thermal conductance and can guide high optical powers for trapping atoms in ultra-high vacuum. As an intermediate step, we have observed thermal atom absorption of the evanescent component of a nanowaveguide and have demonstrated the U-wire mirror magneto-optical trap that can transfer atoms to the proximity of the surface. [ABSTRACT FROM AUTHOR]

In this study, we report high-performance amorphous In2O3/InZnO bilayer metal-oxide (BMO) thin-film transistor (TFT) using an ultra-thin solution-processed amorphous ZrOx dielectric. A thin layer of In2O3 offers a higher carrier concentration, thereby maximizing the charge accumulation and yielding high carrier mobility. A thick amorphous layer of InZnO controls the charge conductance resulting in low off-state current and suitable threshold voltage. As a consequence, the BMO TFT showed higher filed-effect mobility (37.9 cm2/V s) than single-layer InZnO TFT (7.6 cm2/V s). Apart from that we obtain an on/off current ratio of 109, a subthreshold swing voltage of 120 mV/decade, and a voltage shift ≤ 0.4 V under positive bias stress for 2.5 h, for a gate voltage of 3 V and drain voltage of 1 V. These data demonstrate that the BMO TFT has great potential for a broad range of applications as switching low-power transistors. [ABSTRACT FROM AUTHOR]

Coherent x-ray diffraction imaging is used to map the local three dimensional strain inhomogeneity and electron density distribution of two individual LiNi0.5Mn1.5O4-δ cathode nanoparticles in both ex-situ and in-situ environments. Our reconstructed images revealed a maximum strain of 0.4%. We observed different variations in strain inhomogeneity due to multiple competing effects. The compressive/tensile component of the strain is connected to the local lithium content and, on the surface, interpreted in terms of a local Jahn-Teller distortion of Mn3+. Finally, the measured strain distributions are discussed in terms of their impact on competing theoretical models of the lithiation process. [ABSTRACT FROM AUTHOR]

We present the design and performance of an active mechanical noise cancellation scanning tunneling microscope (STM). This system features two key parts: a “twin-tip” scanner and an active mechanical noise cancellation algorithm. The twin-tip scanner functions as two independent STMs which share nearly the same mechanical transfer function, allowing both STMs to sense nearly identical background mechanical noise. Based on an adaptive digital signal processing technique, the active mechanical noise cancellation algorithm applies the noise sensed by the first STM to concurrently cancel the noise in the second STM and hence allows the second STM to acquire spectroscopy with a significantly improved signal to noise ratio. This system demonstrates long-term stability of the tip-sample tunnel junction and improved spectroscopy measurement in a mechanically noisy environment. [ABSTRACT FROM AUTHOR]

Extremely small Sn nanodots embedded in the subsurface of SiO2, i.e., Sn–SiO2 quantum dot composites, have been formed by ion implantation of the 120Sn+ isotope into (0001) Z-cut quartz at a low kinetic energy of 9 keV at room temperature. Transmission electron microscopy images show that the Sn nanodots have an average size of about 3 nm, and both single-crystal and amorphous nanodots have been observed at room temperature. The nanodots are randomly distributed in the lateral direction but confined in a narrow layer in the depth direction. The bimodal size distribution that is often observed in high energy implantation was not observed in the present study. The spatial morphology and crystallinity of the Sn nanodots can be modified by thermal annealing, and the extent of the modification is dependent on the annealing temperature. The distribution and crystallinity of the Sn nanodots in single-crystal bulk SiO2 are different from those of Sn nanocrystals in thin SiO2 films on silicon substrates. The mechanisms that could account for these phenomena are discussed. [ABSTRACT FROM AUTHOR]

NiO/Ag/CoO/Fe single crystalline films are grown epitaxially on a vicinal Ag(001) substrate using molecular beam epitaxy and investigated by photoemission electron microscopy. We find that after zero-field cooling, the in-plane Fe magnetization switches from parallel to perpendicular direction of the atomic steps of the vicinal surface at thinner CoO thickness but remains in its original direction parallel to the steps at thicker CoO thickness. CoO and NiO domain imaging result shows that both CoO/Fe and NiO/CoO spins are perpendicularly coupled, suggesting that the Fe magnetization switching may be associated with the rotatable-frozen spin transition of the CoO film. [ABSTRACT FROM AUTHOR]

CoO/Fe thin films were grown epitaxially onto vicinal Ag(001) and investigated using magneto-optic Kerr effect, x-ray magnetic circular dichroism (XMCD), and x-ray magnetic linear dichroism (XMLD) techniques. We show that the CoO film in the ultrathin regime does not induce a uniaxial magnetic anisotropy but a coercivity enhancement. This result provides a mechanism for the microscopic origin of the rotatable magnetic anisotropy. XMLD measurement further reveals that the underlying mechanism is that the CoO spins are totally rotatable in the ultrathin regime to follow the Fe magnetization. [ABSTRACT FROM AUTHOR]

In Ge2Sb2Te5 (GST), the prototype phase-change alloy for data storage, in situ x-ray diffraction experiments reveal a pressure-induced crystalline-amorphous-crystalline transition sequence, all at the same fixed composition and in one experimental cycle. A body-centered-cubic polymorph is discovered at high pressures; the formation of this phase is attributable to its high packing density rendered possible by the switch from covalent to metallic bonding as predicted by ab initio calculations. [ABSTRACT FROM AUTHOR]

Resistive switching (RS) characteristics of a Pr0.7Ca0.3MnO3 (PCMO) film sandwiched between a Pt bottom electrode and top electrodes (TE) made of various metals are found to belong to two categories. Devices with TE made of Al, Ti, and Ta exhibit a large I-V hysteresis loop and bipolar RS, but those with TE made of Pt, Ag, Au, and Cu do not. Transmission electron microscopy reveals that a thin metal-oxide layer formed at the interface between the former group of TE and PCMO, but not for the latter group of TE. Analysis shows that the categorization depends on the Gibbs free energy of oxidation of the TEs with respect to that of PCMO. [ABSTRACT FROM AUTHOR]

Passive Q-switching operation with a class of Nd:Gd[sub x]Y[sub 1-x]VO[sub 4] crystals has been demonstrated. Compared to Nd:YVO[sub 4] and Nd:GdVO[sub 4], the pulse energy produced with Nd:Gd[sub 0.64]Y[sub 0.36]VO[sub 4] under certain conditions was found to be enhanced by factors of 6.0 and 2.5, while the peak power enhanced by factors of 14.7 and 3.6, respectively. At the incident pump power of 9.6 W, 1.3 W of average output power was obtained, with the pulse energy, peak power, and pulse repetition frequency being 166 μJ, 24.5 kW, and 7.7 kHz, respectively. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Boron carbide (B4C) coatings are prepared by an RF inductively coupled plasma (ICP) torch with different amounts of hydrogen introduced into the sheath gas. The effects of the added hydrogen on the characteristics of the plasma are diagnosed by optical emission spectroscopy and high speed photography. The effects on the melting of B4C particles in the plasma are studied by scanning electron microscopy (SEM). The microstructure of the B4C coatings was determined with SEM imaging and x-ray diffraction analysis. The results show that adding hydrogen to the sheath gas leads to plasma contraction, which results in higher gas temperature of plasma. It also enhances B4C particles spheroidizing and improves the compactness of B4C coatings. Plasma processing does not change the main phase of boron carbide. The obtained results on B4C coatings on Cu substrates allows for improving the B4C coatings fabrication process. [ABSTRACT FROM AUTHOR]

Underwater shock wave technology can realize dynamic rock fracture, which is helpful to increase oil and gas reservoir permeability. It can realize the efficient exploitation of medium and low maturity oil and gas resources. In practical application, the shock wave parameters require not only high intensity but also safety and controllability. To meet these requirements, insensitive composite energetic materials driven by electrical wire explosion plasma were proposed, which is one of the most promising methods. However, when in use, the load assembly process containing wires and energetic materials is complex. In this paper, a new type of energetic material load is proposed, using non-penetrating wire to drive composite energetic material. It can simplify the production process of the energetic load and produce acceptable shock wave parameters. The test results show that both the energy deposition of the wire and the shock wave intensity decrease under a non-penetrating wire structure. However, the shock wave intensity is still higher than that of the underwater electrical wire explosion. Based on schlieren diagnosis, it is found that the composite energetic material is gradually driven, and the energy release is not concentrated. In addition, the "non-wire" structure driving condition was discussed in contrast. Under this condition, the process of ionization channel establishment in composite energetic materials is random. The shock wave intensity is weak because the composite energetic material is in the process of slow detonation., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

Validated and accurate edge profiles (temperature, density, etc.) are vitally important to the Mega Ampere Spherical Tokamak Upgrade (MAST-U) divertor and confinement effort. Density profile reflectometry has the potential to significantly add to the measurement capabilities currently available on MAST-U (e.g., Thomson scattering and Langmuir probes). This work presents the diagnostic requirements, problems, and solutions facing profile reflectometry in spherical tokamaks and MAST-U in particular. Requirements include density measurements near zero electron density in the scrape off layer region, coverage for a broad range of MAST-U plasma parameters, high time (≤10 microseconds) and spatial resolutions (≤1 cm), reliability, and identification of the plasma start frequency., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

A pulsed power supply with a short rise time and high repetition frequency is favorable to driving diffusive plasma for strongly oxidizing radical (O3, OH) generation and increasing the system's energy efficiency. In this paper, a 10-stage solid-state linear transformer driver (LTD) with a nanosecond rise time is developed to drive plasma for wastewater treatment. To decrease the rise time, a control system with low jitter is developed to improve the synchronization of pulses using an optocoupler isolation chip. A 10-stage LTD with a rise time of 6.2 ns is realized in the case that the rise time of the single-stage LTD is 5.4 ns. The results show that the LTD can generate pulses on a 300 Ω resistive load with a repetition frequency of 10 kHz, an amplitude of 8.80 kV, an overshoot less than 3.97%, and a reverse overshoot less than 4.82%. The rise time (6.2-33.0 ns), the pulse width (35.9-200.0 ns), and the fall time (10.5-27.6 ns) can be adjusted flexibly and independently by controlling the drive signals of metal oxide semiconductor field effect transistors. The pulsed generator is utilized to drive plasma in the needle-water electrode system. The preliminary experimental results show that the plasma includes abundant oxygen atoms and hydroxyl radicals with high activity, and it is suitable for wastewater treatment., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

Ultra-low noise is a critical component in the design of high-precision sensor front-ends. We introduced differential phase-sensitive detection (d-PSD) to mitigate both multiplicative and additive noise in optical sensors, aiming for an enhanced performance and cost-effectiveness. The d-PSD combines a capacitive transimpedance amplifier (C-TIA), a delta-sigma analog-to-digital converter (ΔΣ-ADC), and a software-based lock-in amplifier (s-LIA). The first two components utilize the DDC112 (a dual current input 20-bit ADC) for a minimal analog channel length, thus reducing noise efficiently, while the latter employs a cost-effective 32-bit microcontroller unit (MCU), the HC32F460. This approach was successfully implemented as the front-end for a smart optical sensor. Testing indicated that the sensor achieved an equivalent current noise level of 0.6 nA/√Hz, primarily attributed to the light source driver rather than the sensor's front-end circuit. The sensor exhibited an exceptional performance, with a 3σ measurement precision of 5.4 × 10-4 over a 1-second integration time and a dynamic range of 100 dB, leveraging the proposed method and design. Furthermore, the front-end of the sensor boasts a compact size, low power consumption, and affordability, making it an ideal, versatile solution for ultra-high precision, smart optical sensors., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

We use molecular dynamics simulations to study the frictional response of monolayers of the anionic surfactant sodium dodecyl sulfate and hemicylindrical aggregates physisorbed on gold. Our simulations of a sliding spherical asperity reveal the following two friction regimes: at low loads, the films show Amonton's friction with a friction force that rises linearly with normal load, and at high loads, the friction force is independent of the load as long as no direct solid-solid contact occurs. The transition between these two regimes happens when a single molecular layer is confined in the gap between the sliding bodies. The friction force at high loads on a monolayer rises monotonically with film density and drops slightly with the transition to hemicylindrical aggregates. This monotonous increase of friction force is compatible with a traditional plowing model of sliding friction. At low loads, the friction coefficient reaches a minimum at the intermediate surface concentrations. We attribute this behavior to a competition between adhesive forces, repulsion of the compressed film, and the onset of plowing., (© 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).)

The majority of reported measurements on high intensity ultrasound beams in air are below 40 kHz and performed on standing waves inside of a guide. Here, experimental characterization of high intensity progressive and divergent sound beams in air at 300 kHz are presented. Measurements in this frequency range are challenging. Accurate characterization of high intensity sound beams requires a measurement bandwidth at least ten times the beam's primary frequency, as high intensity soundwaves steepen and form shocks and, therefore, contain significant signal power at harmonic frequencies. Hence, a measurement bandwidth of at least 3 MHz is required. Calibrated measurement microphones are generally not available in this frequency range. This limitation has been overcome by using a hydrophone with a calibrated response from 250 kHz to 20 MHz. A narrowband piezoelectric transducer is used as the source in this study, and it is capable of generating tone burst waveforms centered at 300 kHz with 160 dB sound pressure level surface pressure. Cumulative wave steepening and shock formation are observed in on-axis measurements. The source's surface vibration profile is measured using a scanning laser Doppler vibrometer, and the vibration profile is imported into a numerical wide-angle Khokhlov-Zabolotskaya-Kuznetsov simulation for comparison against measured on-axis waveforms., (© 2023 Acoustical Society of America.)

Electrical wire explosions have many applications in scientific research and industry. Optical diagnosis is a powerful method to clarify the evolutionary process of such explosions. In this paper, an experimental platform was established to diagnose the optical radiation of electrical wire explosions. A low-jitter trigatron switch and its trigger generator were designed to ensure accurate synchronization. The spatial-temporal evolution process and the self-emission spectrum of electrical explosion plasmas from different wires (copper and tantalum) were obtained and analyzed. The optical diagnosis results indicated that the electrical explosion of copper wire was mainly characterized by the inhomogeneity of partial ionization and the rapid expansion of the discharge channel. The spectrum in the early discharge stage of the copper wire electrical explosion was a continuum, and most of the self-radiation spectral lines belonged to Cu I or Cu II. At the later stage of the plasma dissipation process, the continuous spectrum gradually transformed into a line spectrum. The development of the tantalum wire discharge channel was relatively uniform, and the plasma was mainly established in the gas-liquid mixed phase channel of the tantalum wire. The self-emission spectrum of the tantalum wire was always continuous, and the absorption process of line spectrum radiation was distinct.

X-ray diffraction indicates that the structure of the recently discovered carbonaceous sulfur hydride (C-S-H) room-temperature superconductor is derived from previously established van der Waals compounds found in the H 2 S-H 2 and CH 4 -H 2 systems. Crystals of the superconducting phase were produced by a photochemical synthesis technique, leading to the superconducting critical temperature T c of 288 K at 267 GPa. X-ray diffraction patterns measured from 124 to 178 GPa, within the pressure range of the superconducting phase, are consistent with an orthorhombic structure derived from the Al 2 Cu-type determined for (H 2 S) 2 H 2 and (CH 4 ) 2 H 2 that differs from those predicted and observed for the S-H system at these pressures. The formation and stability of the C-S-H compound can be understood in terms of the close similarity in effective volumes of the H 2 S and CH 4 components, and denser carbon-bearing S-H phases may form at higher pressures. The results are crucial for understanding the very high superconducting T c found in the C-S-H system at megabar pressures.

Nonlinear stochastic complex networks in ecological systems can exhibit tipping points. They can signify extinction from a survival state and, conversely, a recovery transition from extinction to survival. We investigate a control method that delays the extinction and advances the recovery by controlling the decay rate of pollinators of diverse rankings in a pollinators-plants stochastic mutualistic complex network. Our investigation is grounded on empirical networks occurring in natural habitats. We also address how the control method is affected by both environmental and demographic noises. By comparing the empirical network with the random and scale-free networks, we also study the influence of the topological structure on the control effect. Finally, we carry out a theoretical analysis using a reduced dimensional model. A remarkable result of this work is that the introduction of pollinator species in the habitat, which is immune to environmental deterioration and that is in mutualistic relationship with the collapsed ones, definitely helps in promoting the recovery. This has implications for managing ecological systems.

In this study, we report an oxygen-doped MoS 2 quantum dot (O-MoS 2 QD) hybrid electrocatalyst for the hydrogen evolution reaction (HER). The O-MoS 2 QDs were prepared with a one-pot microwave method by hydrazine-mediated oxygen-doping. The synthetic method is straightforward, time-saving, and can be applied in large scale preparation. Ultra-small O-MoS 2 QDs with the average size of 5.83 nm and 1-4 layers can be uniformly distributed on the surface of reduced graphene oxide (RGO). Benefited from the unique structure and the doping effect of oxygen in the MoS 2 QDs and the great number of active sites, the O-MoS 2 QD hybrid displayed outstanding electrocatalytic performance toward HER. A low overpotential of 76 mV at 10 mA/cm 2 and a Tafel slope of 58 mV/dec were obtained in an acidic solution toward HER. Additionally, the resultant O-MoS 2 QD hybrid also exhibited excellent stability and durability toward HER, displaying negligible current density loss after 1000 cycles of cyclic voltammetry. The design and synthesis of the electrocatalyst in this work open up a prospective route to prepare active and stable electrocatalysts toward substituting precious metals for hydrogen generation.

We demonstrate an integrated laser system for the mobile integrating sphere cold atom clock. Three distributed Bragg reflector diode lasers (780 nm) with custom drive circuits are used for the cooling, repumping, pumping, and probe lights. Automatic frequency-locking and relocking of the laser are presented. All of the optical elements are integrated on two sides of an aluminum base plate. The mechanical structure is simulated and optimized to minimize the deformation of the base plate. We optimize, measure, and discuss the frequency and intensity noises of the laser system. The techniques and designs used in this laser system can also be used in other mobile platforms for quantum sensing experiments.

The self-assembled multilayers have been studied by many researchers to modify the surfaces of artificial implants for increasing biocompatibility. The accurate mechanical properties of the film can only be obtained from the experimental results using appropriate theoretical models. As the film is composed of both solid polymers and fluid, this paper proposes a two-phase model. Based on the volume average method, the momentum equations are derived for both solid and liquid phases. In order to test our model, we built the porous film on the gold chip of the quartz crystal microbalance using the layer-by-layer method. The buildup process is based on the electrostatic interactions between anionic sodium hyaluronate and cationic chitosan by imitating the endothelial surface layer. By fitting our model to the experimental changes of the resonant frequency and dissipation factor, we get reasonable values of the film thickness, the porosity, the shear modulus of the solid phase, and the permeability. Compared with the existing models, the newly introduced permeability is an important property of the porous layer affecting the values of other parameters. Our model can provide more intrinsic properties of the self-assembled polymeric network and explain its interaction with the permeating fluid.

Chemical mechanical planarization (CMP) is the most widely used planarization technique in semiconductor manufacturing presently. With the aid of in situ measurement technology, CMP tools can achieve good performance and stable productivity. However, the in situ measurement has remained unexplored from a kinematic standpoint. The available related resources for the kinematic analysis are very limited due to the complexity and technical secret. In this paper, a comprehensive kinematic analysis of in situ measurement is provided, including the analysis model, the measurement trajectory, and the measurement time of each zone of wafer surface during the practical CMP process. In addition, a lot of numerical calculations are performed to study the influences of main parameters on the measurement trajectory and the measurement velocity variation of the probe during the measurement process. All the efforts are expected to improve the in situ measurement system and promote the advancement in CMP control system.

An overview of the in situ laser heating system at the High Pressure Collaborative Access Team, with emphasis on newly developed capabilities, is presented. Since its establishment at the beamline 16-ID-B a decade ago, laser-heated diamond anvil cell coupled with in situ synchrotron x-ray diffraction has been widely used for studying the structural properties of materials under simultaneous high pressure and high temperature conditions. Recent developments in both continuous-wave and modulated heating techniques have been focusing on resolving technical issues of the most challenging research areas. The new capabilities have demonstrated clear benefits and provide new opportunities in research areas including high-pressure melting, pressure-temperature-volume equations of state, chemical reaction, and time resolved studies.

In order to timely grasp a single variable nonlinear system running states, a new method called Scatter Point method is put forward in this paper. It can be used to observe or monitor the running states of a single variable nonlinear system in real-time. In this paper, the definition of the method is given at first, and then its working principle is expounded theoretically, after this, some physical experiments based on Chua's nonlinear system are conducted. At the same time, many scatter point graphs are measured by a general analog oscilloscope. The motion, number, and distribution of these scatter points shown on the oscilloscope screen can directly reflect the current states of the tested system. The experimental results further confirm that the method is effective and practical, in which the system running states are not easily lost. In addition, this method is not only suitable for single variable systems but also for multivariable systems.

In recent years, a variety of film thickness measurement techniques for copper chemical mechanical planarization (CMP) are subsequently proposed. In this paper, the eddy-current technique is used. In the control system of the CMP tool developed in the State Key Laboratory of Tribology, there are in situ module and off-line module for measurement subsystem. The in situ module can get the thickness of copper film on wafer surface in real time, and accurately judge when the CMP process should stop. This is called end-point detection. The off-line module is used for multi-points measurement after CMP process, in order to know the thickness of remained copper film. The whole control system is structured with two levels, and the physical connection between the upper and the lower is achieved by the industrial Ethernet. The process flow includes calibration and measurement, and there are different algorithms for two modules. In the process of software development, C++ is chosen as the programming language, in combination with Qt OpenSource to design two modules' GUI and OPC technology to implement the communication between the two levels. In addition, the drawing function is developed relying on Matlab, enriching the software functions of the off-line module. The result shows that the control system is running stably after repeated tests and practical operations for a long time.

The vibrational and structural properties of a hydrogen-rich group IVa hydride, Sn(CH(3))(4), have been investigated by combining Raman spectroscopy and synchrotron x-ray diffraction measurements at room temperature and at pressures up to 49.9 GPa. Both techniques allow the obtaining of complementary information on the high-pressure behaviors and yield consistent phase transitions at 0.9 GPa for the liquid to solid and 2.8, 10.4, 20.4, and 32.6 GPa for the solid to solid. The foregoing solid phases are identified to have the orthorhombic, tetragonal, monoclinic crystal structures with space groups of Pmmm for phase I, P4/mmm for phase II, P2/m for phase III, respectively. The phases IV and V coexist with phase III, resulting in complex analysis on the possible structures. These transitions suggest the variation in the inter- and intra-molecular bonding of this compound.

A new piston-cylinder-type pressurizable dilatometer controlled by a stepper motor has been developed to measure the time-dependent bulk modulus and pressure-volume-temperature (PVT) behavior of polymeric materials. The dilatometer can be operated from 35 to 230 degrees C and at pressures of up to 250 MPa. The sample cell, which contains the sample and a fluorinated oil as the confining fluid, is totally submerged into a high precision oil bath to achieve a temperature stability of better than 0.01 degrees C. The instrument is calibrated with mercury and quartz. The total instrument volume is 4.0 cm(3), of which 2.3 cm(3) is the sample cell; the total volume can be measured with an average absolute error of better than 5.0x10(-4) cm(3). To demonstrate the instrument's capabilities, the time-dependent bulk modulus and the PVT behavior of a polystyrene are obtained and compared to the literature.

We have used x-ray diffraction to determine the structure factor of water along its melting line to a static pressure of 57 GPa (570 kbar) and a temperature of more than 1500 K, conditions which correspond to the lower mantle of the Earth, and the interiors of Neptune and Uranus up to a depth of 7000 km. We have also performed corresponding first principles and classical molecular dynamics simulations. Above a pressure of 4 GPa the O-O structure factor is found to be very close to that of a simple soft sphere liquid, thus permitting us to determine the density of liquid water near the melting line. By comparing these results with the density of ice, also determined in this study, we find that the enthalpy of fusion (DeltaH(f)) increases enormously along the melting line, reaching approximately 120 kJ/mole at 40 GPa (compared to 6 kJ/mole at 0 GPa), thus revealing significant molecular dissociation of water upon melting. We speculate that an extended two-phase region could occur in planetary processes involving the adiabatic compression of water.

The effect of the exchange-attempt frequency on sampling efficiency is studied in replica exchange molecular dynamics (REMD). We show that sampling efficiency increases with increasing exchange-attempt frequency. This conclusion is contrary to a commonly expressed view in REMD. Five peptides (1-21 residues long) are studied with a spectrum of exchange-attempt rates. Convergence rates are gauged by comparing ensemble properties between fixed length test REMD simulations and longer reference simulations. To show the fundamental correlation between exchange frequency and convergence time, a simple model is designed and studied, displaying the same basic behavior of much more complex systems.