Length Dependence Research Articles

Coupling Efficiency of a Spot Size Converter for Optical Fiber-Chip Connections

The light propagation in optical waveguide must be able to maintain low propagation loss, low coupling loss and scattering loss condition, especially in the junction. In this research, a spot size converter is proposed to preserve the lowest coupling loss. This optical converter is composed of a single mode optical fiber (SiO2) including inversed taper. The optical input signal from the optical fiber is launched into photonic integrated circuits and then coupled into the Si-Slab waveguide. Furthermore, linear form with the length dependence has been studied to obtain the optimal position of optical fiber and the chip and analyzed the coupling efficiency of it. The purpose of this research is to procure the optimal form of spot size converter. The simulation result shows the coupling loss of linear form is 0.62 dB and 0.24 dB on TE and TM mode condition respectively. Along with the increase in the taper length, the coupling loss obtained tends to decrease as well. So that, it can be assumed the design of a linear form with 100 μm taper length provides the highest coupling efficie ncy.

Predicting microplastic masses in river networks with high spatial resolution at country level

Microplastics are a ubiquitous contaminant of natural waters, and a lot of field monitoring is currently performed. However, what is missing so far is a general understanding how emissions of microplastics are linked to environmental exposure, especially on larger geographic scales such as countries. Here we coupled a high-resolution microplastic release model with a fate model in rivers and lakes and parameterized it for Switzerland on a country scale to predict masses of microplastics in each river section for seven different polymers. The results show that catchment characteristics, for example, distribution of releases within the catchment, location and size of lakes or river connections, are as important as polymer properties such as density. There is no simple linear function of microplastic retention within a catchment in dependency of river length to the outlet. Instead, we found that different catchments cover a wide range of retained fractions for microplastics. Consequently, we argue that the availability and use of spatially distributed release data and performing modelling on high spatial resolution is of importance when estimating concentrations of microplastics in large areas such as countries.

Interaction of a moving shock wave with a turbulent boundary layer

In the present study, the influence of a uniformly moving impinging shock on the resulting shock wave–turbulent boundary layer interaction is numerically investigated. The relative Mach number of the shock front travelling above a flat-plate model varied between 0 and 2.3, while the quasi-steady inflow conditions remained constant with a Mach number of 3. To quantitatively evaluate the effect of shock travelling speed, a well-known scaling method for interaction length in quasi-steady flows was applied as a reference after significant improvements in modelling the effects of Reynolds number and wall temperature using new and existing data. Moreover, previously obtained experimental results for a limited range of travelling speeds were employed to validate the obtained numerical results. Three ranges of shock travelling speeds with distinctly different properties were extracted and quantitatively described using a developed correlation-based approach built on the extended quasi-stationary scaling law. In the first range, the scaled interaction length reaches its maximum for the given interaction strength and can be directly described by the scaling law obtained for quasi-stationary interactions. In the second travelling-speed range, the dependence of the interaction length on the interaction strength is explicitly influenced by the shock movement. With increasing shock travelling speed, the scaled interaction length here decreases significantly faster than in the quasi-stationary reference case. The end of this speed range is reached when the absolute shock front speed has caught up with the maximum speed of sound in the interaction zone, and thus the interaction length has fallen to zero. This travelling-speed limit signifies the transition to the third range, where upstream influence is no longer possible.

Evolution of fluctuation conductivity of Y1Ba2Cu3O7-Δ single crystals under the influence of medium doses of electron irradiation and doping with praseodymium

The influence of medium doses (from 1019 cm–2 to 1020 cm–2) of irradiation with fast electrons and changes in the concentration of praseodymium in the interval 0.0 ≤ z ≤ 0.5 on the excess conductivity of optimally oxygen-doped Y1Ba2Cu3O7-δ single crystals was studied. It is shown that electron irradiation and an increase in the degree of doping with praseodymium leads to a significant expansion of the temperature interval of the existence of excess conductivity, thereby narrowing the region of the linear dependence of r(Т) in the ab-plane. It was established that at doses 0 ≤ D ≤ 6.5´1019 cm–2 the value of the value of the transverse coherence length ξс(0) increases with an increase in D approximately 3 times and more than four times as the praseodymium content in the sample increases to z ≈ 0.42. At the same time, in both cases, the 2D-3D crossover point is shifted by temperature. In contrast to the case of irradiation with small doses (D ≤ 1019 cm–2) and doping with praseodymium up to concentrations z ≤ 0.39, irradiation with medium doses and doping with praseodymium at higher concentrations leads to a non-monotonic dependence of the transverse coherence length xс(0) with characteristic maxima at D ~ (7-8)´1019 cm–2 and z ≈ 0.42, which may be related to the general suppression of superconducting characteristics.

Chain length dependence of structural and transport properties of single lithium-ion conducting polymer electrolytes: A molecular dynamics simulation study

In this work, the parameters affecting the performance of polymer electrolytes, for utilization in lithium-ion batteries (LiBs) are investigated. For this purpose, by using density functional theory (DFT) and molecular dynamics (MD) simulation, the structural and transport properties of single lithium-ion conducting polymer electrolytes (SLICPEs) based on boron ethylene glycol (BEG), as the anion, with the molecular structure ofBO3−−C2H4On−BO4− are evaluated. The calculated structural properties, include density, glass transition temperature, and radial distribution function (RDF). The simulated transport properties are diffusion coefficient, transference number, and ionic conductivity. In the first step, the optimization of molecular structures is obtained by DFT calculations with B3LYP functional approximation and Mullikan partial charges for the polymer chain lengths of 1, 4, 8, and 15 monomers. Then, by using MD simulations and an ten-stages compression-expansion procedure, the studied electrolyte systems are equilibrated. The results indicate that the transference numbers of these electrolytes are significantly higher than those of commonly used electrolytes based on polyethylene oxide (PEO). Inspection of the obtained results indicates that the diffusion and ionic conductivity coefficients are influenced by the interaction of Li+ with oxygen atoms in the polymer chain. Analysis of the transport properties of Li+ along the polymer chain structure reveals that the presence of a boron atom in the polymer chain backbone induces a significant non–uniform charge distribution along the polymer chain and as a result weakens the interaction between Li+ with an oxygen atom in the polymer chain. Therefore compared to the conventional electrolytes, Li+ can move more freely along the polymer chain, and as a result, the performance of LiBs is promoted significantly.

Reversible Regulation of Long-Distance Charge Transport in DNA Nanowires by Dynamically Controlling Steric Conformation.

Understanding of DNA-mediated charge transport (CT) is significant for exploring circuits at the molecular scale. However, the fabrication of robust DNA wires remains challenging due to the persistence length and natural flexibility of DNA molecules. Moreover, CT regulation in DNA wires often relies on predesigned sequences, which limit their application and scalability. Here, we addressed these issues by preparing self-assembled DNA nanowires with lengths of 30-120 nm using structural DNA nanotechnology. We employed these nanowires to plug individual gold nanoparticles into a circuit and measured the transport current in nanowires with an optical imaging technique. Contrary to the reported cases with shallow or no length dependence, a fair current attenuation was observed with increasing nanowire length, which experimentally confirmed the prediction of the incoherent hopping model. We also reported a mechanism for the reversible CT regulation in DNA nanowires, which involves dynamic transitions in the steric conformation.

Bandwidth-Decomposed Analysis of Spatial-Mode Dispersion of Coupled 2-Core Fiber Employing Linear Optical Sampling

The complex impulse responses of two types of coupled 2-core fibers, with homogeneous and heterogeneous cores, were measured by using a measurement system based on linear optical sampling. The measurements were performed over a bandwidth of 20 nm (∼2.5 THz), and the spatial-mode dispersion (SMD) was analyzed. Several lengths of both homogeneous and heterogeneous core fibers were prepared to investigate the length dependence of SMD. The SMDs for divided frequency bands were examined by numerically analyzing the measured broadband impulse response. Consequently, the power impulse response at each subband was obtained, and the variation in the SMDs was examined. In addition, the statistical distribution of the SMD was revealed to be different for each type of the 2-core fiber. The SMD observed at a specific band is handled by the receiver in space-division multiplexing transmission systems. Finally, we present a measurement of mode dependent loss (MDL) of a 2-core fiber, and discuss the impact of time axis inaccuracy to the MDL measurement. These analyses performed are expected to be beneficial for designing such systems.

Temperature Dependence of Dynamic Properties of Poly(ethylene glycol) Molecules on a MHz-Oscillating Solid–Liquid Interface

The temperature dependence of resonant molecular weights and resonant lengths of soft materials was investigated at the nanoscale for a viscous penetration depth region and a physisorption region using a quartz crystal microbalance (QCM). Poly(ethylene glycol) (PEG) was used as a model for soft materials. The study revealed that, in the viscous penetration depth and physisorption regions, the logarithmic values of the resonant molecular weights decreased linearly with those of the QCM angular frequencies and converged to a single point of 1360 g/mol at 416 MHz independently of temperature. The convergence point was consistent with that of chemisorption. In addition, in the regions of the viscous penetration depth and physisorption at each temperature, the slopes of logarithms of the resonant lengths decreased linearly with the logarithms of the QCM angular frequencies and were equal to those of chemisorption. As a result, a convergence point of the resonant length appeared at 2.87 nm and 416 MHz, where its frequency was equivalent to that of the chemisorption. These results enabled us to quantitatively establish the behavior of the resonant molecular weight and resonant length as a function of temperature and frequency.

Observation of anisotropic magneto-inductance effect

We have discovered a new phenomenon that inductance oscillates as a function of the angle between an in-plane magnetic field and an electric current direction in permalloy films, which we have named “the anisotropic magneto-inductance (AML) effect.” We have investigated the dependences of the AML effect on the size and voltage. The length, frequency, and amplitude dependences suggest that the AML effect should be evaluated in terms of “inductivity.” Inductors based on this AML effect have the potential to be variable, on-chip, and one billion times smaller than the small commercial inductor.

The effect of polymer length in liquid-liquid phase separation

Understanding the thermodynamics that drive liquid-liquid phase separation (LLPS) is quite important given the number of diverse biomolecular systems undergoing this phenomenon. Many studies have focused on condensates of long polymers, but very few systems of short-polymer condensates have been observed and studied. Here, we study a short-polymer system of various lengths of poly-adenine RNA and peptides formed by the RGRGG sequence repeats to understand the underlying thermodynamics of LLPS. Using the recently developed COCOMO coarse-grained (CG) model, we predicted condensates for lengths as short as 5-10 residues, which was then confirmed by experiment, making this one of the smallest LLPS systems yet observed. A free-energy model reveals that the length dependence of condensation is driven primarily by entropy of confinement. The simplicity of this system will provide the basis for understanding more biologically realistic systems.

Pulse length dependence of a reactive high power impulse magnetron (HiPIMS) discharge

The pulse length dependence of a reactive high power impulse magnetron sputtering (HiPIMS) discharge with a tungsten cathode in an argon+oxygen gas mixture gas was investigated. The HiPIMS discharge is operated with a variable pulse length of 20–500 µs. Discharge current measurements, optical emission spectroscopy of neutral Ar, O, and W lines, and energy-resolved ion mass spectrometry are employed. A pronounced dependence of the discharge current on pulse length is noted while the initial discharge voltage is maintained constant. Energy-resolved mass spectrometry shows that the oxygen-to-tungsten (O+/W+) and the tungsten oxide-to-tungsten (WO+/W+) ion ratio decreases with pulse length due to target cleaning. Simulation results employing the SDTrimSP program show the formation of a non-stoichiometric sub-surface compound layer of oxygen which depends on the impinging ion composition and thus on the pulse length.

Chain length dependence of ZnO nanofiller–polystyrene blend coating nanofilm: Morphology, surface mechanics, photochemistry, and chain packing

Based on that chain packing which is associated with the number of entanglements per chain and thereby chain length is an influential factor closely related to the properties of polymeric coating film, the nanothin film of zinc oxide (ZnO) nanofiller–incorporated polystyrene (PS) coated on Si substrate important to electronic packaging for protecting electronic material surface is fabricated with different PS molecular weights primarily for heat–resistant coating. Synergistically, through directly–measurable film characteristics obtained using atomic force microscopy (AFM) and spectroscopy (AFS) in conjunction with Raman spectroscopy (RS), the internal structures of the films are evaluated which helps indicate the corresponding film properties tested afterwards. Considering mechanical responses of individual nanoscale surface features together with surface morphology, the optimal PS–ZnO film is pointed out which indicates improved resistance to thermal dewetting compared to pure PS films while providing sub–nanometer roughness and the highest contact area of relatively low–surface–energy sites. Correlated with Raman analysis, chain packing structure encouraging multiple amplification of incident light is ascribed to the films made of the optimal chain length which indicates and describes the observed enhancement of photocatalytic self–cleaning. This study not only contributes to the development of PS–ZnO composite for multi–function coating but also to the design of structure and inspection of nanoparticle–reinforced polymer thin films.

Effect of in-plane alignment on selective area grown homo-epitaxial nanowires

In-plane selective area growth (SAG) of III–V nanowires (NWs) has emerged as a scalable materials platform for quantum electronics and photonics applications. Most applications impose strict requirements on the material characteristics which makes optimization of the crystal quality vital. Alignment of in-plane SAG NWs with respect to the substrate symmetry is of importance due to the large substrate-NW interface as well as to obtain nanostructures with well-defined facets. Understanding the role of mis-orientation is thus important for designing devices and interpretation of electrical performance of devices. Here we study the effect of mis-orientation on morphology of selectively grown NWs oriented along the [1 1̅ 1̅] direction on GaAs(2 1 1)B. Atomic force microscopy is performed to extract facet roughness as a measure of structural quality. Further, we evaluate the dependence of material incorporation in NWs on the orientation and present the facet evolution in between two high symmetry in-plane orientations. By investigating the length dependence of NW morphology, we find that the morphology of ≈1 μm long nominally aligned NWs remains unaffected by the unintentional misalignment associated with the processing and alignment of the sample under study. Finally, we show that using Sb as a surfactant during growth improves root-mean-square facet roughness for large misalignment but does not lower it for nominally aligned NWs.

Bulk-surface coupling in dual topological insulator Bi1Te1 and Sb-doped Bi1Te1 single crystals via electron-phonon interaction

Recently, has been proved to be a dual topological insulator (TI), a new subclass of symmetry-protected topological phases, and predicted to be higher order topological insulator (HOTI). Being a dual TI (DTI), Bi1Te1 is said to host quasi-1D surface states (SSs) due to weak TI phase and topological crystalline insulating SSs at the same time. On the other hand, HOTI supports topologically protected hinge states. So, is a unique platform to study the electrical signature of topological SS (TSS) of fundamentally different origins. Though there is a report of magneto-transport measurements on large-scale Bi1Te1 thin films, the Bi1Te1 single crystal is not studied experimentally to date. Even the doping effect in a DTI Bi1Te1 is missing in the literature. In this regard, we performed the perpendicular and parallel field magneto-transport measurement on the exfoliated microflake of Bi1Te1 and Sb-doped Bi1Te1 single crystals, grown by the modified Bridgmann method. Our metallic sample shows the weak anti-localization behavior analyzed by the multi-channel Hikami-Larkin-Nagaoka equation. We observed the presence of a pair of decoupled TSS. Further, we extracted the dephasing index (β) from temperature (T)-dependence of phase coherence length (L), following the power law equation (L). The thickness-dependent value of β indicates the transition in the dephasing mechanism from electron-electron to electron-phonon interaction with the increase in thickness, indicating the enhancement in the strength of bulk-surface coupling. Sb-doped system shows weakened bulk-surface coupling, hinted by the reduced dephasing indices.

Semiconductor-hydrophobic material interfaces as a new active site paradigm for photocatalytic degradation of perfluorocarboxylic acids

Photocatalytic degradation of long-chain perfluorocarboxylic acid (PFCA) water contaminants has been reported for numerous of semiconductors, including composite TiO2 particles decorated with graphitic carbon co-catalysts. While pristine TiO2 degrades PFCAs inefficiently, the carbon components purportedly enhance activity due to their conductive nature and resultant charge separation enhancement. Yet herein, we present evidence that the catalytic activity of a graphene oxide (GO)-TiO2 composite from the literature arose not due to from charge separation, but to a unique mode of PFCA adsorption occurring at the interface of TiO2 and hydrophobic GO. Photocatalytic degradation rates by GO-TiO2 were compared to those of composites containing nonconductive polymer microparticles (polyethylene, polytetrafluoroethylene). Results showed that polymer-TiO2 composites performed as well as GO-TiO2 in degrading both perfluorooctanoic acid and oxalate, a common hole scavenger. Thus, the enhanced activity may occur for any TiO2-hydrophobic interface, regardless of co-catalyst conductivity. Furthermore, compared to an unmodified reference catalyst, chain length dependence of PFCA degradation by a polymer-TiO2 composite was found to be less severe, with greater activity toward short-chain species indicating enhanced adsorption behavior. Potential adsorption mechanisms are presented, along with broader implications toward improving the applicability of heterogeneous processes toward a wider range of perfluoroalkyl contaminants.

Lateral charge migration in 1D semiconductor-metal hybrid photocatalytic systems.

Colloidal nanorods based on CdS or CdSe, functionalized with metal particles, have proven to be efficient catalysts for light-driven hydrogen evolution. Seeded CdSe@CdS nanorods have shown increasing performance with increasing rod length. This observation was rationalized by the increasing lifetime of the separated charges, as a large distance between holes localized in the CdSe seed and electrons localized at the metal tip decreases their recombination rate. However, the impact of nanorod length on the electron-to-tip localization efficiency or pathway remained an open question. Therefore, we investigated the photo-induced electron transfer to the metal in a series of Ni-tipped CdSe@CdS nanorods with varying length. We find that the transfer processes occurring from the region close to the semiconductor-metal interface, the rod region, and the CdSe seed region depend in different ways on the rods' length. The rate of the fastest process from excitonic states generated directly at the interface is independent of the rod length, but the relative amplitude decreases with increasing rod length, as the weight of the interface region is decreasing. The transfer of electrons to the metal tip from excitons generated in the CdS rod region depends strongly on the length of the nanorods, which indicates an electron transport-limited process, i.e., electron diffusion toward the interface region, followed by fast interface crossing. The transfer originating from the CdSe excitonic states again shows no significant length dependence in its time constant, as it is probably limited by the rate of overcoming the shallow confinement in the CdSe seed.

Spatio-temporal patterning of extensile active stresses in microtubule-based active fluids.

Microtubule-based active fluids exhibit turbulent-like autonomous flows, which are driven by the molecular motor powered motion of filamentous constituents. Controlling active stresses in space and time is an essential prerequisite for controlling the intrinsically chaotic dynamics of extensile active fluids. We design single-headed kinesin molecular motors that exhibit optically enhanced clustering and thus enable precise and repeatable spatial and temporal control of extensile active stresses. Such motors enable rapid, reversible switching between flowing and quiescent states. In turn, spatio-temporal patterning of the active stress controls the evolution of the ubiquitous bend instability of extensile active fluids and determines its critical length dependence. Combining optically controlled clusters with conventional kinesin motors enables one-time switching from contractile to extensile active stresses. These results open a path towards real-time control of the autonomous flows generated by active fluids.

Performance evaluation simulation of the optical splitters integrated with unidirectional fiber elements

Abstract This study has clarified the performance evaluation simulation of the optical splitters integrated with unidirectional fiber elements. The simulative performance evaluation of electrostatic, thermal, and piezoelectric actuation based micro electro mechanical systems. The force against the displacement based electrostatic and elastic forces for parallel plate actuator is simulated by MEMSover simulation software. The voltage with angular displacement for a torsion bar actuator is clarified. Besides the lateral displacement against voltage for a comb drive actuator is reported. The dependence of the film thickness on the deflection of a bimetallic cantilever, the dependence of passive beam length on deflection of a bimorph actuator and the transient response of a bent beam actuator are demonstrated. Moreover the piezoelectric actuator force against applied voltage and the piezoelectric actuator displacement against applied voltage variations are reported.

Study of parameters and regimes of pressureless flow in a channel with overboard overflow

There were studied the changes of pressureless flow parameters: flow rate and height of the liquid layer, within section of the overboard overflow across the side of the channel, as well as the dependence of the length of this link on the parameters of the channel and flow. It was established that when calculating with engineering accuracy the height of the overflow above the side of the channel and the flow rate along the channel from the length of existence of the overflow layer, only the effect of the effective flow coefficient should be taken into account. The dependence of the dimensionless height of the overflow above the side of the channel on the dimensionless length of the overboard overflow has a clear extreme character, and the dependence of the dimensionless flow along the channel on the dimensionless length of existence of the overboard overflow does not have a clear extreme character. The dependence of the dimensionless length of the overboard overflow on the effective flow rate is well approximated by a power function with a negative fractional exponent and it can be characterized by the absence of extrema and curvature change points, and asymptotically approaches zero at infinity.

Single-Input Broadband Hybrid Doherty Power Amplifiers Design Relying on a Phase Sliding-Mode of the Load Modulation Scheme

This work introduces a novel design theory for a single-input hybrid Doherty power amplifier (PA) inspired by the design space existing within the previously reported dual-input Doherty–Chireix (outphasing) continuum. Unlike the conventional <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda /4$ </tex-math></inline-formula> Doherty PA inverter which only performs the correct load modulation at its center frequency, the hybrid Doherty PA (HD <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\omega $ </tex-math></inline-formula> -PA) combiner network achieves a wideband load modulation using the frequency dependence of the electrical length of the output combiner lines versus frequency for sliding the PA mode of operation. A modified theory is presented in this work to allow for a single-input PA implementation. In this new design, the outphasing angle is only changing with frequency and not the input power. A transmission line phase shifter is used to provide the correct frequency-dependent input phase offset ensuring the correct wideband load modulation performed by the output combiner. A novel methodology is also proposed to select the optimal input phase offset to reduce the variation in the saturation power versus frequency and minimize the circuit size. A proof-of-concept demonstrator PA circuit is designed to operate from 2.5 to 3.3 GHz. When the fabricated PA is excited by a 20-MHz long-term evolution (LTE) modulated signal with 6-dB peak-to-average-power ratio (PAPR), an average efficiency of 45%–59% and adjacent channel leakage ratio (ACLR) less than −50 dBc are achieved after digital predistortion (DPD) across the entire band. When the fabricated PA is excited by a 5G-like 50-MHz orthogonal frequency-division multiplexing (OFDM) signal with 10-dB PAPR, an average efficiency of 33%–41% and ACLR less than −44 dBc are achieved after DPD across the entire band.