Shape Of Envelope Research Articles

Effects of the closed domain area on the dynamics of a closed flexible filament behind a rigid plate

In this study, the effects of the closed domain area on the dynamics of a coupling system consisting of a plate and a flexible filament were investigated. Numerical simulations were performed utilizing the immersed boundary method and a penalty method was adopted to conserve the closed domain area. The drag variation was investigated across various length ratio (Lr) and area reduction (Ar), and the maximum drag reduction of 30.26% was achieved at Lr=2.0 and Ar=0%. For a small area reduction like Ar≤10%, the drag of the system with Lr<1.75 was lower than that of a fully filled state, but it had a significant increase because of vortex shedding variation for Lr≥1.75. When Ar exceeded 30%, the system drag closely approached that of the bare plate. Furthermore, the maximum width of the shape envelope was employed to renormalize the drag and considered to roughly estimate drag. In addition, the effects of the bending coefficient (γ) on filament shapes were concluded. For γ<0.01, the filament was closer to the plate as Ar increased. However, for γ≥0.01, the filament globally bent and flapped like an elastic rod for high Ar avoiding the occurrence of large curvature.

Generation of dual and quad-optical frequency combs in the injected radiation free mode-locked frequency-shifted feedback laser

The results of an optoelectronic system—frequency-shifted feedback (FSF) laser experimental examination are presented. The considered FSF laser is seeded only with optical amplifier spontaneous emission (ASE) and operates in the mode-locked regime, whereby the output radiation is sequence of short pulses with a repetition rate determined by the delay time in its optical feedback circuit. In the frequency domain, the spectrum of such a pulse sequence is an optical frequency comb (OFC). These OFCs we call initial. We consider the possibility of tunable acousto-optic (AO) dual and quad-comb frequency spacing downconversion in the FSF laser seeded with ASE and operating in the mode-locked regime. The examined system applies a single frequency shifting loop with single AO tunable filter as the frequency shifter that is fed with several radio frequency signals simultaneously. The initial OFCs with frequency spacing of about 6.5 MHz may be obtained in the wide spectral range and their width, envelope shape and position in the optical spectrum may be tuned. The dual-combs are obtained with a pair of initial OFCs aroused by two various ultrasound waves in the acousto-optic tunable filter (AOTF). The dual-combs frequency spacing is determined by the frequency difference of the signals applied to the AOTF piezoelectric transducer and can be tuned simply. The quad-combs are obtained with three initial OFCs, forming a pair of dual-combs, appearing when three ultrasound frequencies feed the AOTF transducer. The quad-combs frequency spacing is defined by the difference between the frequency spacing of dual-combs. Quad-combs with more than 5000 spectral lines and tunable frequency spacing are observed. The successive frequency downconversion gives the possibility to reduce the OFC frequency spacing form several MHz for initial OFC to tens of kHz for quad-combs.Graphical abstract

Mapping the Seismicity of Mars With InSight

AbstractThe InSight seismometers have recorded more than 1,300 events. Ninety‐eight of these, named the low‐frequency (LF) family, show energy predominantly below 1 Hz down to ∼0.1 Hz. The Marsquake Service identified seismic phases and computed distances for 42 of these marsquakes, 24 of which have backazimuths. Hence, the locations of the majority of LF family events remain undetermined. Here, we use an envelope shape similarity approach to determine event classes and distances, and introduce an alternative method to estimate the backazimuth. In our analysis, we use the highest quality marsquakes with known distances as templates, including the largest event S1222a, and assign new distances to similar group of events for which distance estimates were not previously available. We find the Tharsis region to be more active than initially perceived on the basis of 5 newly located events near Valles Marineris and Olympus Mons. We relocate two marsquakes with little or no S‐wave energy in the NE of the Elysium Bulge. The event epicenters in Cerberus Fossae follow a north‐south trend due to uncertainties in location, while the fault system is in the NW‐SE direction; therefore, these events are re‐projected along the observed fault system based on our interpretations. The marsquakes in our interpreted catalog are predominantly observed in the northern hemisphere of Mars above the equatorial dichotomy boundary.

Experimental investigation on the interaction between mode-2 internal solitary wave and horizontal transverse cylinder

The experimental study on the interaction between a mode-2 internal solitary wave (ISW) and a horizontal transverse cylinder has been carried out in a large gravity-stratified fluid flume. One kind of making-wave method of “rotating-blade-gate” is proposed to achieve the experimental simulation of the standard mode-2 ISW in the laboratory flume. The conductivity probe array and particle image velocimetry are used to measure the mode-2 ISW and its wave-flow structure of the interaction with the horizontal transverse cylinder, and the micro-amplitude force sensor is used to measure the forces of the mode-2 ISW on the cylinder model. It is shown that the mode-2 ISW geometric structure is characterized by a convex and concave oval wave envelope shape and the counterclockwise and clockwise circulations are formed in its convex and concave domains, respectively. The resulting pair of upper and lower antisymmetric circulations moves forward together, which causes a horizontal strong flow at the symmetric center of the wave envelope consistent with the wave propagation direction. The horizontal transverse cylinder is subjected to the combined action of horizontal flow, vertical flow, and density change induced by the mode-2 ISW, in which the horizontal strong flow, induced flow separation, and vortex structure located at the symmetric center of the wave envelope are the signature features that are different from other positions. The theoretical analysis model of the forces exerted by the mode-2 ISW on a horizontal transverse cylinder is established. The spatial distribution characteristic of the force exerted by the mode-2 ISW on a horizontal cylinder is obtained, and the essential reason for the maximum horizontal and vertical loads on the cylinder is revealed. The horizontal maximum load corresponds to the inhomogeneous change of the horizontal velocity along the depth, and the vertical maximum load depends on the maximum density change along the depth, of which variation trend corresponds to the linear change of wave amplitudes.

Experimental study of intrinsic localized mode mobility in a cyclic, balanced, 1D nonlinear transmission line.

Mobile intrinsic localized modes (ILMs) in balanced nonlinear capacitive-inductive cyclic transmission lines are studied by experiment, using a spatiotemporal driver under damped steady-state conditions. Without nonlinear balance, the experimentally observed resonance between the traveling ILM and normal modes of the nonlinear transmission line generates lattice drag via the production of a lattice backwave. In our experimental study of a balanced running ILM in a steady state, it is observed that the fundamental resonance can be removed over extended, well-defined driving frequency intervals and strongly suppressed over the complete ILM driving frequency range. Because both of these nonlinear capacitive and inductive elements display hysteresis our observation demonstrates that the experimental system, which is only partially self-dual, is surprisingly tolerant, regarding the precision necessary to eliminate the ILM backwave. It appears that simply balancing the cell dual nonlinearities makes the ILM envelope shape essentially the same at the two locations in the cell, so that the effective lattice discreteness seen by the ILM nearly vanishes.

A previously uncharacterized divisome-associated lipoprotein, DalA, is needed for normal cell division in Rhodobacterales.

The bacterial cell envelope is a key subcellular compartment with important roles in antibiotic resistance, nutrient acquisition, and cell morphology. We seek to gain a better understanding of proteins that contribute to the function of the cell envelope in Alphaproteobacteria. Using Rhodobacter sphaeroides, we show that a previously uncharacterized protein, RSP_1200, is an outer membrane (OM) lipoprotein that non-covalently binds peptidoglycan (PG). Using a fluorescently tagged version of this protein, we find that RSP_1200 undergoes a dynamic repositioning during the cell cycle and is enriched at the septum during cell division. We show that the position of RSP_1200 mirrors the location of FtsZ rings, leading us to propose that RSP_1200 is a newly identified component of the R. sphaeroides' divisome. Additional support for this hypothesis includes the co-precipitation of RSP_1200 with FtsZ, the Pal protein, and several predicted PG L,D-transpeptidases. We also find that a ∆RSP_1200 mutation leads to defects in cell division, sensitivity to PG-active antibiotics, and results in the formation of OM protrusions at the septum during cell division. Based on these results, we propose to name RSP_1200 DalA (for division-associated lipoprotein A) and postulate that DalA serves as a scaffold to position or modulate the activity of PG transpeptidases that are needed to form envelope invaginations during cell division. We find that DalA homologs are present in members of the Rhodobacterales order within Alphaproteobacteria. Therefore, we propose that further analysis of this and related proteins will increase our understanding of the macromolecular machinery and proteins that participate in cell division in Gram-negative bacteria. IMPORTANCE Multi-protein complexes of the bacterial cell envelope orchestrate key processes like growth, division, biofilm formation, antimicrobial resistance, and production of valuable compounds. The subunits of these protein complexes are well studied in some bacteria, and differences in their composition and function are linked to variations in cell envelope composition, shape, and proliferation. However, some envelope protein complex subunits have no known homologs across the bacterial phylogeny. We find that Rhodobacter sphaeroides RSP_1200 is a newly identified lipoprotein (DalA) and that loss of this protein causes defects in cell division and changes the sensitivity to compounds, affecting cell envelope synthesis and function. We find that DalA forms a complex with proteins needed for cell division, binds the cell envelope polymer peptidoglycan, and colocalizes with enzymes involved in the assembly of this macromolecule. The analysis of DalA provides new information on the cell division machinery in this and possibly other Alphaproteobacteria.

A design framework for a kinetic shading device system for building envelopes

This paper presents a design framework of a shading device applied on a building envelope, with a scheduled automatic activation logic, based on a sun path diagram. This proposal aims to balance the direct sun indoor exposure by evaluating the envelope area exposed to direct sun rays and the hourly activation rate of shading devices. These procedures are over the parametric modeling and simulation platform using raytracing, structural finite element analysis, and Computer Numerical Control (CNC) prototyping. The design process of building envelopes equipped with kinetic devices can use all these design resources. The kinetic device's activation logic relies on the feed-forward paradigm, scheduling the activation from the parametric modeling and the sun path diagram, using an angle threshold between the device post and the sun vector as a parameter. The design framework showed the preliminary path to develop shading devices considering the building envelope shape with a feed-forward activation logic based on local sun path characteristics.

Robust RPPG Method Based on Reference Signal Envelope to Improve Wave Morphology

Remote physiological monitoring has become increasingly important in improving quality of life, with remote photoplethysmography (RPPG) being a popular choice. This paper introduces an envelope–based method for RPPG channels to improve wave morphology of the collected signal based on the reference signal from finger PPG. Using a model consistent with physiological and optical principles, the authors divided the signal into linear superpositions, comprising pulse, constant, and disturbance components. The correlation coefficients were used to calculate a linear combination of Red–Green–Blue (RGB) channels to approximate the envelope shape of the reference PPG signal. Experiments with different light intensities and stability were designed to compare the envelope approximation ability and robustness of the proposed method with some common methods. Analysis of variance demonstrated the stable performance of the envelopment–based approach in most cases. Additionally, it improved the morphology of the Green (G) channel, including changing trends and directions, adjusting wave sizes, reducing noise, and reinforcing details of the single waveform. The envelope–based linear model approach has the ability to flexibly improve RPPG signals, which helps RPPG play a full role in many fields such as medicine.

An algorithm for spectrally matching bi-directional ground motions to a target RotD100 spectrum while maintaining the radial spectral acceleration pattern

An integrated algorithm to spectrally match two seed-recorded horizontal bi-directional ground motion components to a maximum-direction response spectrum (RotD100) while maintaining the radial spectral acceleration pattern (RadSAP) at target natural periods is presented. The algorithm is based on the complex-discrete-Fourier-transform (CDFT) and iterative manipulation of the seed-recorded bi-directional ground motions. Initially, a population of candidate bi-directional ground motion pairs is generated, and the candidate resulting in the minimum error in RadSAP is picked. Subsequently, the CDFT coefficients of the picked bi-directional ground motion near the target natural periods are rotated to modify the orientation angle, which contributes to the modification of RadSAP. Then, a double iterative method is introduced to modify the bi-directional ground motion after CDFT coefficients rotation to be spectral and envelope shape compatible in the frequency and time domain. In order to show the effectiveness of the proposed algorithm, two target response spectra are determined following the current ASCE/SEI 7-16 and CJJ 166-2011 specifications, and 10 bi-directional ground motions are selected based on the resemblance in response spectrum for each target spectrum. It is shown that with the proposed algorithm, the RotD100 response spectra estimated from the modified bi-directional ground motions closely match the smooth target RotD100 response spectrum, and the RadSAPs at these target natural periods show an improved match with the seed-recorded bi-directional ground motions than the previous version method. Furthermore, the waveforms of the results obtained using the proposed method are similar to that of the scaled seed records in terms of acceleration, velocity, and displacement. Thus, the generated bi-directional ground motions can be used for future seismic risk assessment of buildings considering the directionality effects.

Research on Passive Design Strategies for Low-Carbon Substations in Different Climate Zones

In the energy-saving design of substations, the building envelope thermal parameters, window-to-wall ratio, and shape factor are three crucial influencing factors. They not only affect the building’s appearance but also have an important impact on the total building energy consumption. In this paper, we applied the energy consumption simulation software DeST-c to study the influence of the above three elements on the total energy consumption of the building in a representative city with different thermal zones. The optimal envelope thermal parameters, optimal window-to-wall ratio, and optimal shape factor were derived through combination with economic analysis. Finally, the sensitivity analysis of different elements was carried out to determine the suitable passive design solutions for substations in different climate zones. It was found that the thickness of roof insulation has the greatest influence on the energy consumption of substation buildings among all envelopes. The optimal window-to-wall ratios were 0.4, 0.4~0.5, 0.3, 0.3~0.4, and 0.5 for severe cold, cold, hot summer and cold winter, hot summer and warm winter, and mild regions, respectively; and the optimal shape factors were 0.29, 0.30, 0.23, 0.31, and 0.33, respectively. The conclusions of this study can provide architects with energy-saving design strategies and suggestions for substations in different climate zones, and provide references for building energy-saving designs and air conditioning and heating equipment selection.

Cell envelope growth of Gram‐negative bacteria proceeds independently of cell wall synthesis

All bacterial cells must expand their envelopes during growth. The main load‐bearing and shape‐determining component of the bacterial envelope is the peptidoglycan cell wall. Bacterial envelope growth and shape changes are often thought to be controlled through enzymatic cell wall insertion. We investigated the role of cell wall insertion for cell shape changes during cell elongation in Gram‐negative bacteria. We found that both global and local rates of envelope growth of Escherichia coli remain nearly unperturbed upon arrest of cell wall insertion—up to the point of sudden cell lysis. Specifically, cells continue to expand their surface areas in proportion to biomass growth rate, even if the rate of mass growth changes. Other Gram‐negative bacteria behave similarly. Furthermore, cells plastically change cell shape in response to differential mechanical forces. Overall, we conclude that cell wall‐cleaving enzymes can control envelope growth independently of synthesis. Accordingly, the strong overexpression of an endopeptidase leads to transiently accelerated bacterial cell elongation. Our study demonstrates that biomass growth and envelope forces can guide cell envelope expansion through mechanisms that are independent of cell wall insertion.

A parametric design approach for multi-lobed hybrid airships

AbstractIn recent years, there has been an increasing interest in the research and development of hybrid airships for various applications. Airship design involves multiple design parameters from various disciplines that interact mutually. Existing design methodologies, however, are often limited to fixed shapes and geometry. This paper provides a comprehensive parametric design approach for the sizing of multi-lobed hybrid air vehicles for low- and high-altitude applications. The proposed design techniques are robust so that the designer has the freedom to change the number of lobes, the relative location of lobes, the envelope profile, and the optimiser for the design optimisation process. The outcomes of the proposed methodology are envelope volume, wetted surface area, length and span of the envelope, sizing and layout of the solar array, and sizing and layout of the fins. The modeling techniques highlighted in this paper are very efficient for the design and optimisation of multi-lobed airships in the conceptual design phase with a large design exploration space. The robustness of the shape generation algorithms is tested on some of the standard envelope profiles of airships. The effect of the shape and geometry of the multi-lobed envelope on added mass is demonstrated through the added mass estimation using Boundary Element Method.

Updated Zone of Intrusion Envelopes in the Manual for Assessing Safety Hardware Impact Conditions

Roadside barriers are used to shield fixed objects near the roadway and are designed to mitigate the severity of run-off-road crashes near those fixed objects. The zone of intrusion (ZOI) defines the potential location of a vehicle component above and beyond the top face of the barrier during an impact, and therefore indicates if there is a potential that a fixed object located behind a barrier could interact with the vehicle during redirection. Previous ZOI envelope guidelines were based on older vehicle models and test results. Further review was required to update the guidelines for contemporary vehicles and impact conditions in accordance with the American Association of State Highway and Transportation Officials (AASHTO) Manual for Assessing Safety Hardware (MASH). A literature review of full-scale crash tests and computer simulations were used to identify the ZOI envelope shapes for MASH test levels 2–5. Simulations were calibrated using test data and were used to investigate gaps in the full-scale test data. Conservative guidelines were developed from the combined simulation and test data, and recommended ZOI envelope shapes were developed that conservatively bounded the ZOI results. Results were presented for potential revision of ZOI envelope guidelines in the AASHTO Roadside Design Guide. Future recommendations to improve ZOI measurements in test data and simulation modeling were also presented.

Effects of the skirt length and embedment depth on the capacity of a skirted spudcan foundation under combined loading

Skirted spudcan foundations can provide a considerable bearing capacity and moment fixity for resisting the complex combined vertical, horizontal, and moment loadings arising from the harsh environment in the offshore oil and gas industry. These potential benefits are conducive to the extension of mobile jack-up drilling rigs into deep water. In this study, a series of probe tests were carried out using finite element analysis to investigate the effects of the skirt length and embedment depth on the bearing capacity of skirted spudcan foundations in soft clay under combined loading. The results indicate that both the skirt length and the embedment depth can significantly affect the behavior of a skirted spudcan and apparently improve the various bearing capacities under combined loading. As the skirt length and embedment depth increase, the failure envelope's size gradually expands and the failure envelope's shape changes accordingly. A spudcan with a skirt length of 0.25D embedded in about 2D of sediments is suggested to obtain an optimal application in practice. A closed-form algebraic expression was derived to interpret and predict the behavior of skirted spudcan foundations, which properly considers the effects of the skirt length and embedment depth.

Dynamics of Gas Ionization by Laser Pulses with Different Envelope Shapes

The properties of the dynamics of gas ionization under the action of femtosecond ionizing laser pulses with various envelope shapes are studied. It is shown that the duration of ionization in the saturation regime (at a high final degree of ionization) can either increase or decrease with an increase in the peak intensity of the ionizing pulse, depending on the shape of its envelope. We also determined the influence of the pulse shape on the spectrum of Brunel harmonics and the terahertz yield when two-color pulses are used.

Feasibility of Time-Dependent Amplitude in Pulse-Compressed Broadband Acoustic Signals for Determining the Dorsal Orientation of Fish

Fish body orientation significantly influences the size obtained with hydroacoustic signals, and thus the estimate of fish size and biomass. For this reason, each characteristic of a target’s echo can be advantageous for developing algorithms to refine acoustic fish estimates. We measured pulse-compressed broadband acoustic signals from tethered fish (common bream Abramis brama) in different dorsal positions. Based on generalized additive mixed models (GAMM), we initially tested the influence of the fish dorsal aspect on the amplitude echo envelope and amplitude echo descriptors (amplitude maximum and amplitude echo length at seven different levels below the maximum) by altering the fish dorsal orientation. Our study confirmed that the dorsal aspect influenced the shapes of the amplitude echo envelopes in both fast- and slow-tapered pulses. Furthermore, we found that echo lengths approximately 15 dB below the amplitude maximum, especially for fast-tapered signals, could provide good characteristics of the echo-envelope shape for determining the fish dorsal aspect and facilitating thus the conversion between acoustic target strength and true fish length.

Search for the optimal shape of the envelope of a microwave pulse of a powerful generator in the maximum permissible radiation mode

In the article, the problem of choosing the shape of the envelope of the microwave pulse of a powerful generator, which provides the maximum radiated surface antenna energy in the pre-breakdown mode, is formulated in the form of an isoperimetric problem of the calculus of variations, and its solution is obtained. Optimization was carried out at a fixed effective duration of the envelope. It has been established that the optimal shape depends on the effective pulse duration and is a truncated oval. As the pulse duration increases, the optimal shape tends to be rectangular. Analytical expressions are obtained that relate the effective duration and maximum allowable energy to the breakdown field for pulses with optimal, rectangular, Gaussian, and triangular envelopes. The dependences of the breakdown field and the maximum allowable energy of pulses with the indicated envelope shapes on the effective pulse duration are calculated in the range of realizable durations of powerful relativistic microwave generators. A comparative analysis of the obtained results is given.

An Early Forecast of Long‐Period Ground Motions of Large Earthquakes Based on Deep Learning

AbstractLong‐period (LP; approximately 2–10 s) ground motions generated by large earthquakes are amplified in large basins and threaten high‐rise buildings in modern cities. In this study, we accomplished an early forecast of LP ground motions in distant basins based on deep learning technology using waveforms observed near the epicenter. A Temporal Convolutional Network was first trained using waveform data from past large earthquakes in the Japan Trench. LP ground motions of recent large earthquakes, including the 2011 Off the Pacific coast of Tohoku earthquake (Mw 9.0), were forecasted in the Kanto (Tokyo) and Osaka basins. This study effectively forecasted LP ground motions of large earthquakes regarding amplitude, waveform envelope shape, spectral characteristics, and duration. Faster forecasts (in 0.05 s or less) allow for updating forecasts as data is acquired, improving forecast accuracies and ensuring 1–2 min of lead time before large and prolonged shakes occur.

End-effects mitigation in empirical mode decomposition using a new correlation-based expansion model

The real-time analysis of time-varying data has become extremely significant in mechanical systems. The Hilbert–Huang transform (HHT) is a recent development in signal processing based on time–frequency distribution for analyzing complex signals. The HHT permits instantaneous attributes to be used to study signals that display complex behavior and stochastically vary with time. This transform combines empirical mode decomposition (EMD) and Hilbert transform (HT). The EMD converts a signal of time into various intrinsic mode functions (IMF), which are subsequently used by the HT to insert into the same time–frequency space. However, the restriction of the end-effect is an important problem when employing the EMD method. End-effect causes several issues such as changing the shapes of envelopes, deviating IMF, computational instabilities at the signal borders, and modal aliasing. To mitigate the end-effects, this study presents a correlation-based expansion model at both ends of the signal. Motivated by end-effects mitigation, data outside of the signal boundaries are predicted based on the similarity of the signal’s start and end segments with the signal's inner segment. Correlation techniques are a reliable method to find signal pattern similarities. Seven simulated signals are used to verify the method's performance. The seven signals include six monovarietal signals with various amplitude modulation-frequency modulation behaviors and a one-channel functional near-infrared spectroscopy (fNIRS) signal. The comparison results of the proposed technique with standard EMD and EMD coupled with other expansion methods show that the end-effect in the EMD method by correlation expansion can effectively reduce.

Interaural time difference sensitivity under binaural cochlear implant stimulation persists at high pulse rates up to 900 pps

Spatial hearing remains one of the major challenges for bilateral cochlear implant (biCI) users, and early deaf patients in particular are often completely insensitive to interaural time differences (ITDs) delivered through biCIs. One popular hypothesis is that this may be due to a lack of early binaural experience. However, we have recently shown that neonatally deafened rats fitted with biCIs in adulthood quickly learn to discriminate ITDs as well as their normal hearing litter mates, and perform an order of magnitude better than human biCI users. Our unique behaving biCI rat model allows us to investigate other possible limiting factors of prosthetic binaural hearing, such as the effect of stimulus pulse rate and envelope shape. Previous work has indicated that ITD sensitivity may decline substantially at the high pulse rates often used in clinical practice. We therefore measured behavioral ITD thresholds in neonatally deafened, adult implanted biCI rats to pulse trains of 50, 300, 900 and 1800 pulses per second (pps), with either rectangular or Hanning window envelopes. Our rats exhibited very high sensitivity to ITDs at pulse rates up to 900 pps for both envelope shapes, similar to those in common clinical use. However, ITD sensitivity declined to near zero at 1800 pps, for both Hanning and rectangular windowed pulse trains. Current clinical cochlear implant (CI) processors are often set to pulse rates ≥ 900 pps, but ITD sensitivity in human CI listeners has been reported to decline sharply above ~ 300 pps. Our results suggest that the relatively poor ITD sensitivity seen at > 300 pps in human CI users may not reflect the hard upper limit of biCI ITD performance in the mammalian auditory pathway. Perhaps with training or better CI strategies good binaural hearing may be achievable at pulse rates high enough to allow good sampling of speech envelopes while delivering usable ITDs.