Comb Structures Research Articles

Effective diffusion along the backbone of combs with finite-span 1D and 2D fingers.

Diffusion in complex heterogeneous media, such as biological tissues or porous materials, typically involves constrained displacements in tortuous structures and sticky environments. Therefore, diffusing particles experience both entropic (excluded-volume) forces and the presence of complex energy landscapes. In this situation, one may describe transport through an effective diffusion coefficient. In this paper, we examine comb structures with finite-length 1D and finite-area 2D fingers, which act as purely diffusive traps. We find that there exists a critical width of 2D fingers, above which the effective diffusion along the backbone is faster than for an equivalent arrangement of 1D fingers. Moreover, we show that the effective diffusion coefficient is described by a general analytical form for both 1D and 2D fingers, provided the correct scaling variable is identified as a function of the structural parameters. Interestingly, this formula corresponds to the well-known general situation of diffusion in a medium with fast reversible adsorption. Finally, we show that the same formula describes diffusion in the presence of dilute potential energy traps, e.g., through a landscape of square wells. While diffusion is ultimately always the result of microscopic interactions (with particles in the fluid, other solutes, and the environment), effective representations are often of great practical use. The results reported in this paper help clarify the microscopic origins and the applicability of global, integrated descriptions of diffusion in complex media.

Behavior analysis of comb-drive actuators operating in near-zero-overlap configuration

Comb structures are widely used in micro-electromechanical systems as basic components of electrostatic actuators, capacitive sensors, resonators and energy harvesters. Typically, they are operated with a large overlap of the comb fingers, in the linear region. Here we study the behavior of comb-drive actuators during the displacement along the axis of the fingers in the unconventional regime where the fingers are slightly overlapping (around the width d of the fingers), which has recently gained attention in the MEMS community. In the intermediate region where the overlap approaches zero, fringing electric fields induce a non-linear variation of the capacitance, yielding a significant electrostatic force between the combs even without finger overlap with a maximum gradient occurring in this region. The comb capacitance variation with overlap was calculated using analytical and FEM modeling and confirmed with experimental results. We explored the implications of this condition in both static and dynamic modes, highlighting the effect of spring softening arising from the second derivative of the capacitance. These findings introduce new operational possibilities for actuators and sensors and substantial tunability in frequency for resonators.

Property-guided generation of complex polymer topologies using variational autoencoders

The complexity and diversity of polymer topologies, or chain architectures, present substantial challenges in predicting and engineering polymer properties. Although machine learning is increasingly used in polymer science, applications to address architecturally complex polymers are nascent. Here, we use a generative machine learning model based on variational autoencoders and data generated from molecular dynamics simulations to design polymer topologies that exhibit target properties. Following the construction of a dataset featuring 1342 polymers with linear, cyclic, branch, comb, star, or dendritic structures, we employ a multi-task learning framework that effectively reconstructs and classifies polymer topologies while predicting their dilute-solution radii of gyration. This framework enables the generation of polymer topologies with target size, which is subsequently validated through molecular simulation. These capabilities are then exploited to contrast rheological properties of topologically distinct polymers with otherwise similar dilute-solution behavior. This research opens avenues for engineering polymers with more intricate and tailored properties with machine learning.

Токораспределение в гребенчатых структурах биполярных и гетеробиполярных СВЧ транзисторов с учетом сопротивления дорожек металлизации

Представлен краткий анализ причин неоднородного и неустойчивого распределения тока между элементарными транзисторами в гребенчатых структурах (ГС) биполярных (БТ) и гетеробиполярных (ГБТ) СВЧ транзисторов. Получено выражение для тока, втекающего в элементарный транзистор ГС, с учетом сопротивления эмиттерной дорожки металлизации. Приведена оценка влияния технологического разброса сопротивлений эмиттерных дорожек металлизации на неравномерность распределения полного тока транзистора между элементарными транзисторами. Показано, что сопротивление эмиттерных дорожек металлизации играет стабилизирующую роль и приводит к повышению тепловой устойчивости токораспределения в ГС, при этом наименее устойчивым к тепловому пробою будет элементарный транзистор ГС с наименьшим сопротивлением эмиттерной дорожки и наибольшим тепловым сопротивлением. Предложены рекомендации по выравниванию и повышению устойчивости токораспределения в ГС БТ и ГБТ.

Токораспределение в гребенчатых структурах биполярных и гетеробиполярных СВЧ транзисторов с учетом сопротивления дорожек металлизации

A brief analysis of the causes of inhomogeneous and unstable current distribution between elementary transistors in comb structures (CS) of bipolar (BT) and heterobipolar (HBT) microwave transistors is presented. An expression for the current flowing into a CS elementary transistor, taking into account the emitter track metallization resistance, is derived. An estimation of the influence of technological variation of emitter metallization track resistances on the non-uniformity of the transistor total current distribution between elementary transistors is given. It is shown that resistance of emitter tracks of metallization plays a stabilizing role and leads to increase of thermal stability of current distribution in CS, thus the least stable to thermal breakdown will be elementary transistor of CS with the least resistance of emitter track and the greatest thermal resistance. Recommendations on equalization and increase of stability of current distribution in CS of BT and HBT are offered.

The inheritance of alternative nest architectural traditions in stingless bees

The transmission of complex behavior and culture in humans has long been attributed to advanced forms of social learning,1,2 which play a crucial role in our technological advancement.3 While similar phenomena of behavioral traditions and cultural inheritance have been observed in animals,1,2,4,5,6 including in primates,7 whales,8 birds,9 and even insects,10 the underlying mechanisms enabling the persistence of such animal traditions, particularly in insects, are less well understood. This study introduces pioneering evidence of enduring architectural traditions in the stingless bee Scaptotrigona depilis, which are maintained without any evidence for social learning. We demonstrate that S.depilis exhibits two distinct nest architectures, comprising either helicoidal or flat, stacked horizontal combs, which are transmitted across generations through stigmergy11,12,13,14,15,16,17-an environmental feedback mechanism whereby the presence of the existing comb structures guides subsequent construction behaviors-thereby leading to a form of environmental inheritance.18,19,20 Cross-fostering experiments further show that genetic factors or prior experience does not drive the observed variation in nest architecture. Moreover, the experimental introduction of corkscrew dislocations within the combs prompted helicoidal building, confirming the use of stigmergic building rules. At a theoretical level, we establish that the long-term equilibrium of building in the helicoidal pattern fits with the expectations of a two-state Markov chain model. Overall, our findings provide compelling evidence for the persistence of behavioral traditions in an insect, based on a simple mechanism of environmental inheritance and stigmergic interactions, without requiring any sophisticated learning mechanism, thereby expanding our understanding of how traditions can be maintained in non-human species.

Driving Principle and Stability Analysis of Vertical Comb-Drive Actuator for Scanning Micromirrors.

We have developed a manufacturing process for micromirrors based on microelectromechanical systems (MEMS) technology. The process involves designing an electrostatic vertically comb-driven actuator and utilizing a self-alignment process to produce a height difference between the movable comb structure and the fixed comb structure of the micromirror. To improve the stability of the micromirror, we propose four instability models in micromirror operation with the quasi-static driving principle and structure of the micromirror considered, which can provide a basic guarantee for the performance of vertical comb actuators. This analysis pinpoints factors leading to instability, including the left and right gap of the movable comb, the torsion beams of the micromirror, and the comb-to-beams distance. Ultimately, the voltages at which device failure occurs can be determined. We successfully fabricated a one-dimensional micromirror featuring a 0.8 mm mirror diameter and a 30 μm device layer thickness. The height difference between the movable and fixed comb structures was 10 μm. The micromirror was able to achieve a static mechanical angle of 2.25° with 60 V@DC. Stable operation was observed at voltages below 60 V, in close agreement with the theoretical calculations and simulations. At the driving voltage of 80 V, we observed the longitudinal displacement movement of the comb fingers. Furthermore, at a voltage of 129 V, comb adhesion occurred, resulting in device failure. This failure voltage corresponds to the lateral torsional failure voltage.

Non-ribosomal peptide synthase profiles remain structurally similar despite minimally shared features across fungus-farming termite microbiomes

Abstract Fungus-farming termites (Macrotermitinae) engage in an obligate mutualism with members of the fungal genus Termitomyces, which they maintain as a monoculture on specialized comb structures. Both these comb structures and the guts of the termites host diverse bacterial communities that are believed to assist in sustaining monoculture farming through antagonist suppression. Among candidate bacteria-derived compounds serving this function are non-ribosomal peptides (NRPs), which are a highly bioactive class of specialized metabolites, frequently produced by symbionts within eukaryotic hosts. However, our understanding of specialized metabolites in termite-associated microbiomes is limited. Here we use amplicon sequencing to characterize both bacterial composition and NRP potential. We show that bacterial and NRP diversity are correlated and that the former varies more than the latter across termite host and gut and comb samples. Compositions of the two are governed by host species and sample type, with topological similarity indicating a diverse set of biosynthetic potential that is consistent with the long evolutionary history of the Macrotermitinae. The structure of both bacterial and NRP compositional networks varied similarly between guts and combs across the Macrotermitinae albeit with auxiliary termite genus-specific patterns. We observed minimal termite species-specific cores, with essentially no Macrotermitinae-wide core and an abundance of putatively novel biosynthetic gene clusters, suggesting that there is likely no single solution to antagonist suppression via specialized NRP metabolites. Our findings contribute to an improved understanding of the distribution of NRP potential in the farming termite symbiosis and will help guide targeted exploration of specialized metabolite production.

Диагностика неоднородности токораспределения в гребенчатых структурах мощных биполярных и гетеробиполярных транзисторов по рекомбинационному излучению

A brief overview of methods for diagnosing current distribution and defects of high-power RF and microwave bipolar and heterobipolar transistors by recombination radiation is presented. An experimental setup is described for recording recombination radiation of structures of bipolar semiconductor devices with spatial resolution, which makes it possible to evaluate the inhomogeneity of current distribution in the comb structures of RF and microwave bipolar and heterobipolar transistors. The results of experimental testing of the installation on several samples of bipolar transistors of various types in the diode connection of the emitter junction are presented. It is established that the brightness of recombination radiation and, accordingly, the emitter current density monotonically decreases from the end to the base of the emitter tracks of current-carrying metallization, while the brightness inhomogeneity coefficient, defined as the ratio of the brightness of recombination radiation at the end to the beginning of the emitter tracks monotonically increases with increasing current flowing through the junction. An analytical model is proposed to explain the brightness distribution of recombination radiation along metallization paths in the comb structure of RF and microwave transistors.

A Double Differential Torsional Accelerometer With Higher Than 10-kHz Measurement Bandwidth for Vibration Monitoring

This paper reports the design, fabrication, ASIC, package, and characterization of a z-axis accelerometer with double differential torsional configuration. Compared with typical comb structures, diagonally large depth non-penetrating quad-mass has a simple structure with a large feature size. Compared with traditional unbalanced proof mass structures, the fully differential sensitive configuration theoretically eliminates the influence of common mode errors such as interference force and temperature variations. Thus a high performance structure with high sensitivity and good stability was obtained. Meanwhile, the anchor was arranged internally to make the structure more compact and less stress sensitive. The sensitive structure has a size of 2.4mm×1.8mm. An optimization of kinetic properties was done to get large bandwidth and small mechanical thermal noise. The ASIC of the double differential torsional structure was implemented, which adopted single-cycle clock double-edge multiplexing to improve C/V conversion efficiency and reduce circuit noise. At the same time, the error compensation technology used on the ASIC makes the accelerometer sensitivity error less than 1% and zero bias error less than ±0.02V. The resonance frequency is about 16kHz, the ±5% bandwidth is larger than 10kHz, the cross-axis sensitivities of the x-axis and y-axis are less than 1.5% and 1%, respectively, the bias instability is less than 700μg, the noise spectral density is better than 30μg/√ Hz above 10Hz, the normalized drift over the full temperature range (-40 °C to 60 °C ) is less than 1.78g under uncompensated conditions.

Dissipative Solitons and Switching Waves in Dispersion-Modulated Kerr Cavities

We theoretically and experimentally investigate the formation of dissipative coherent structures in Kerr nonlinear optical microresonators, whose spectrum encompasses an integrated dispersion that exceeds the cavity free-spectral range. We are able to access this regime in low-dispersion photonic chip-based microresonators by employing synchronous pulse driving, which increases the peak power over the continuous-wave-driving regime. Exploring this dispersion-folded regime, we demonstrate that the presence of periodically varying dispersion can excite higher-order comb structures, which we explore in both the normal and anomalous dispersion regimes. In the former, we observe the coexistence of switching wave fronts with Faraday instability-induced period-doubling patterns. They manifest as strong satellite microcombs highly separated either side of the core microcomb, at an offset close to half the repetition rate but while sharing the same repetition rate. In the latter, for dissipative Kerr solitons in anomalous dispersion, we observe the formation of higher-order phase-matched dispersive waves (“Kelly-like” sidebands), where the folded dispersion crosses the frequency comb grid. We observe up to the fifth higher-order dispersive wave in our experiments and show that these higher-order dispersive waves coherently extend the soliton frequency comb bandwidth significantly. For both cases, we show that our results can be understood by considering four-wave mixing in a two-dimensional Fourier transform representation. The results demonstrate the rich novel nonlinear dynamics of driven dissipative nonlinear cavities with periodically varying dispersion in the dispersion-folded pumping regime.2 MoreReceived 19 June 2022Accepted 14 February 2023DOI:https://doi.org/10.1103/PhysRevX.13.011040Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasPattern formationSpatiotemporal chaosPhysical SystemsCoherent structuresFloquet systemsFront propagationNonlinear wavesSolitonsSynchronizationNonlinear Dynamics

Optical frequency combs in dispersion-controlled doubly resonant second-harmonic generation.

We report on the experimental realization and a systematic study of optical frequency comb generation in doubly resonant intracavity second harmonic generation (SHG). The efficiency of intracavity nonlinear processes usually benefits from the increasing number of resonating fields. Yet, achieving the simultaneous resonance of different fields may be technically complicated, all the more when a phase matching condition must be fulfilled as well. In our cavity we can separately control the resonance condition for the fundamental and its second harmonic, by simultaneously acting on an intracavity dispersive element and on a piezo-mounted cavity mirror, without affecting the quasi-phase matching condition. In addition, by finely adjusting the laser-to-cavity detuning, we are able to observe steady comb emission across the whole resonance profile, revealing the multiplicity of comb structures, and the substantial role of thermal effects on their dynamics. Lastly, we report the results of numerical simulations of comb dynamics, which include photothermal effects, finding a good agreement with the experimental observations. Our system provides a framework for exploring the richness of comb dynamics in doubly resonant SHG systems, assisting the design of chip-scale quadratic comb generators.

Feynman rules for scalar conformal blocks

We complete the proof of “Feynman rules” for constructing M-point conformal blocks with external and internal scalars in any topology for arbitrary M in any spacetime dimension by combining the rules for the blocks (based on their Witten diagram interpretation) with the rules for the construction of conformal cross ratios (based on the OPE and “flow diagrams”). The full set of Feynman rules leads to blocks as power series of the hypergeometric type in the conformal cross ratios. We then provide a proof by recursion of the Feynman rules which relies heavily on the first Barnes lemma and the decomposition of the topology of interest in comb structures. Finally, we provide a nine-point example to illustrate the rules.

Analysis of a silicon comb structure using an inverse Talbot\u2013Lau neutron grating interferometer

We describe an inverse Talbot–Lau neutron grating interferometer that provides an extended autocorrelation length range for quantitative dark-field imaging. To our knowledge, this is the first report of a Talbot–Lau neutron grating interferometer (nTLI) with inverse geometry. We demonstrate a range of autocorrelation lengths (ACL) starting at low tens of nanometers, which is significantly extended compared to the ranges of conventional and symmetric setups. ACLs from a minimum of 44 nm to the maximum of 3.5 μm were presented for the designed wavelength of 4.4 Å in experiments. Additionally, the inverse nTLI has neutron-absorbing gratings with an optically thick gadolinium oxysulfide (Gadox) structure, allowing it to provide a visibility of up to 52% while maintaining a large field of view of approximately 100 mm × 100 mm. We demonstrate the application of our interferometer to quantitative dark-field imaging by using diluted polystyrene particles in an aqueous solution and silicon comb structures. We obtain quantitative structural information of the sphere size and concentration of diluted polystyrene particles and the period, height, and duty cycle of the silicon comb structures. The optically thick Gadox structure of the analyzer grating also provides improved characteristics for the correction of incoherent neutron scattering in an aqueous solution compared to the symmetric nTLI.

A compact double-inverted Ω-shaped dual-band patch antenna for WLAN/WiMAX applications

Abstract In this study, a new compact dual-band antenna with overall size of 11 × 14.46 × 1.6 mm3 has been designed, fabricated and tested. The proposed antenna consists of two inverted Ω-shaped strips loaded with two different comb structures. The fist comb of six elements connected to the first Ω-shaped radiating branch is used to decrease the second band lower cut-off frequency and cover the intended WLAN and WiMAX applications. In order to cover the 2.45 GHz WLAN band and further reduce the antenna dimensions, a second comb structure of 14 elements is attached to the upper radiating branch. The fabricated antenna covers the frequency bands from 2.42 to 2.6 GHz and from 4.25 to 6.77 GHz with a reflection coefficient of |S 11| ≤ −10 dB. The antenna shows an omnidirectional radiation pattern in the H-plane and a monopole-like radiation pattern in the E-plane. The measured results agree well with the simulated ones which indicate that the proposed antenna is suitable to be used in the WLAN/WiMAX applications.

Evolution of the frequency-comb structure and coherence from a Keldysh multiphoton into a tunneling regime.

We present a theoretical study of the characteristics of the frequency-comb structure and coherence via high-order harmonic generation (HHG) driven by the laser pulse trains when the ionization process is pushed from Keldysh multiphoton into tunneling regime. HHG is obtained by solving accurately the time-dependent Schrödinger equation by means of the time-dependent generalized pseudospectral method. We find that the nested comb structures are formed from each harmonic order in the Keldysh multiphoton ionization regime. But it is severely suppressed or even disappeared in the Keldysh tunneling ionization regime. It implies that the temporal coherence of the emitted frequency comb modes is very sensitive to the Keldysh ionization regime. To understand the evolution of frequency-comb structure and coherence, we perform the calculation of the time-dependent ionization probability and the spectral phase of frequency-comb HHG. We find that the frequency-comb HHG driven by the laser pulse trains in the Keldysh multiphoton regime has a good coherence because the ionization probability of the atom driven by each laser pulse is stable, leading to a phase-coherent frequency-comb structure rather than those cases in the Keldysh tunneling regime with high laser intensity. Our results shed light on current interest and significance to the experimental realization of controllable and frequency-comb vacuum-ultraviolet light sources.

Microporous carbon with highly dispersed nano-lanthanum oxide (La2O3) for enhanced adsorption of methylene blue

• Nano La 2 O 3 is ideal to induce extra microporosity on carbon granules by heat treatment at 873 K. • Resulted carbon retained their inherent honey comb structures where nucleated metal oxide are occupied on the edges. • Material is ideal to scavenge cationic dyes by electrostatic activation because of O 2− ions of these occupied nano La 2 O 3 with organics. • John-Sivanandan Achari isotherms of GACLaO873 has three phases identified as due to molecular sieve effects, donor–acceptor and electrostatic attraction type adsorptions in the liquid phase. Activated carbon doped with Lanthanum compounds are prepared and used as a preferred material for adsorption treatment systems. In this study, use of nano La 2 O 3 and La 3+ is attempted as tuning agents for granular activated carbons (GAC) and products are marked as GACLaX and GACLaOX series, produced under controlled activation (473–1273 K) for a Lanthanum/carbon ratio 0.04. They were tested for their physico-chemical features, textural superiority, and efficiency determined by XRD, FTIR, SEM, XPS, Raman, and N 2 /BET and t-plots. It is found that carbon GACLaO873 (GAC activated with nano lanthanum oxide at 873 K) has good microporosity and adsorption efficiency. Nano La 2 O 3 and La 3+ incorporated extra microporosity ( SA micro ) measured as 707 m 2 /g for GACLaO873 compared to native carbon GAC (589 m 2 /g). The respective surface area ( SA BET ) of these new carbons are determined as 946 m 2 /g (GACLaO873), 953 m 2 /g (GACLa1073), and 997 m 2 /g (GAC383). Suitability of the new carbon materials in solid–liquid batch reactor systems is studied for methylene blue (MB) in concentration ranges 25–1500 mg/L. Analysis of equilibrium isotherm uptake data by John-Sivanandan Achari isotherm model found distinct features of different adsorption phases (kinks) in their plots. For GACLaO873, monolayer coverage q m (J-SA) has been 256 mg/g against the basic carbon GAC383 (190 mg/g). Lanthanum activated carbon GACLa1073 has been noted with adsorption efficiency for metal ions, Mn (99.3%), Fe (99.1%), Co (96.6%), As (76.3%), Ba (63.0%), Li (50.4%), Al (71.3%), Cr (47.7%), Ni (99.2%), Cu (7.11%), Zn (24.3%), Cd (55.1%), Tl (32.6%) and Pd (94.9%) tested for a contaminated groundwater sample as a field trial. Lanthanum, La 3+ , and nano La 2 O 3 doped activated carbon series (GACLaX and GACLaOX) prepared under a controlled condition and activation temperature X, bears good microporosity and adsorption efficiency for organic and metal ion contaminants.

Realization of Three-Dimensionally MEMS Stacked Comb Structures for Microactuators Using Low-Temperature Multi-Wafer Bonding with Self-Alignment Techniques in CMOS-Compatible Processes.

A high-aspect-ratio three-dimensionally (3D) stacked comb structure for micromirror application is demonstrated by wafer bonding technology in CMOS-compatible processes in this work. A vertically stacked comb structure is designed to circumvent any misalignment issues that could arise from multiple wafer bonding. These out-of-plane comb drives are used for the bias actuation to achieve a larger tilt angle for micromirrors. The high-aspect-ratio mechanical structure is realized by the deep reactive ion etching of silicon, and the notching effect in silicon-on-insulator (SOI) wafers is minimized. The low-temperature bonding of two patterned wafers is achieved with fusion bonding, and a high bond strength up to 2.5 J/m2 is obtained, which sustains subsequent processing steps. Furthermore, the dependency of resonant frequency on device dimensions is studied systematically, which provides useful guidelines for future design and application. A finalized device fabricated here was also tested to have a resonant frequency of 17.57 kHz and a tilt angle of 70° under an AC bias voltage of 2 V.

Backbone diffusion and first-passage dynamics in a comb structure with confining branches under stochastic resetting

We study the diffusive motion of a test particle in a two-dimensional comb structure consisting of a main backbone channel with continuously distributed side branches, in the presence of stochastic Markovian resetting to the initial position of the particle. We assume that the motion along the infinitely long branches is biased by a confining potential. The crossover to the steady state is quantified in terms of a large deviation function, which is derived for the first time for comb structures in the present paper. We show that the relaxation region is demarcated by a nonlinear ‘light-cone’ beyond which the system is evolving in time. We also investigate the first-passage times along the backbone and calculate the mean first-passage time and optimal resetting rate.

Synthesis of Comb-Polyurethane-Modified Polycarboxylate at Indoor Temperature and Its Interaction With Portland Cement

According to the principle of radical polymerization reaction, different polycarboxylates with comb structures were synthesized. With the other two commercial polycarboxylates (C-PCE-1 and C-PCE-2), the effects of all the polycarboxylates on adsorption, hydration, zeta potential, liquid surface tension, and flowability in Portland cement were determined. Compared to O-PCE and C-PCEs, the adsorption value of M-PCE increased by 14.1% and the adsorption rate increased by 24% maximum. O-PCE, C-PCE-1, and C-PCE-2 have a delayed effect on the hydration of the cementitious materials, but M-PCE does not. Due to higher adsorption amount, M-PCE with siloxane groups has an excellent comprehensive performance of zeta potential, liquid surface tension, and flowability in cementitious materials.