Transmission Velocity Research Articles

Visualizing near-field coupling in terahertz dolmens

Strong interactions between resonant structures in the near-field occur at length scales shorter than the wavelength, and can be exploited for modifying the propagation of electromagnetic radiation. Dolmen-like structures, formed by a rod supporting a dipolar (bright) resonance and two orthogonal rods with a quadrupolar (dark) resonance at the same frequency, represent a geometry of significant interest for near-field electromagnetic coupling. These structures demonstrate electromagnetically induced transparency (EIT) through coupling between these resonances, concurrently providing a sharp spectral selectivity in transmission and large group velocity reduction. We use near-field terahertz scanning microscopy to map the electric fields in the vicinity of a metallic dolmen in both amplitude and phase. In this way, we directly measure the interaction between bright and dark modes in the time-domain, revealing the physics resulting in EIT. We experimentally demonstrate the hybridization of bright and dark modes accompanying the near-field coupling, as well as the excitation of the dark mode at the frequency of the far-field transparency.

The performance of a waterborne zinc-rich coating from sodium silicate solution catalyzed by ammonium acetate

Through general property tests, rheological measurements, SEM observations and weight changes after immersion, electrochemical methods and water vapor transmission tests, a waterborne zinc-rich coating from sodium silicate solution catalyzed by ammonium acetate was characterized. Results showed that the formula catalyzed by ammonium acetate overcame the poor water resistance of other non-catalyzed coatings, while binding the zinc powder in the film. The zinc-rich film had the basic features required for a zinc-rich primer to be useful and was electrochemically cathodically protective during tests. The acetate anion from ammonium acetate resulted not only in little early corrosion while catalyzing the formation of zinc silicate before cure but also stronger corrosion protection during the immersion test on the cured film. The velocity of water vapor transmission and the amount of acetate anions present decreased with time until a stable value was achieved after approximately 6 days.

Time, computational complexity, and probability in the analysis of distance-bounding protocols

Many security protocols rely on the assumptions on the physical properties in which its protocol sessions will be carried out. For instance, Distance Bounding Protocols take into account the round trip time of messages and the transmission velocity to infer an upper bound of the distance between two agents. We classify such security protocols as Cyber-Physical. Time plays a key role in design and analysis of many of these protocols. This paper investigates the foundational differences and the impacts on the analysis when using models with discrete time and models with dense time. We show that there are attacks that can be found by models using dense time, but not when using discrete time. We illustrate this with a novel attack that can be carried out on most Distance Bounding Protocols. In this attack, one exploits the execution delay of instructions during one clock cycle to convince a verifier that he is in a location different from his actual position. We additionally present a probabilistic analysis of this novel attack. As a formal model for representing and analyzing Cyber-Physical properties, we propose a Multiset Rewriting model with dense time suitable for specifying cyber-physical security protocols. We introduce Circle-Configurations and show that they can be used to symbolically solve the reachability problem for our model, and show that for the important class of balanced theories the reachability problem is PSPACE-complete. We also show how our model can be implemented using the computational rewriting tool Maude, the machinery that automatically searches for such attacks.

Time of flight measurements of unirradiated and irradiated nuclear graphite under cyclic compressive load

The time-of-flight technique has been used to investigate the stiffness of nuclear graphite with respect to the grade and grain direction. A loading rig was developed to collect time-of-flight measurements during cycled compressive loading up to 80% of the material's compressive strength and subsequent unloading of specimens along the axis of the applied stress. The transmission velocity (related to Young's modulus), decreased with increasing applied stress; and depending on the graphite grade and orientation, the modulus then increased, decreased or remained constant upon unloading. These tests were repeated while observing the microstructure during the load/unload cycles. Initial decreases in transmission velocity with compressive load are attributed to microcrack formation within filler and binder phases. Three distinct types of behaviour occur on unloading, depending on the grade, irradiation, and loading direction. These different behaviours can be explained in terms of the material microstructure observed from the microscopy performed during loading.

The model of radiation-induced conductivity in silicon

In this paper, we consider the conduction current excited in a silicon obstacle by the action of an external flux of penetrating radiation. We use quantum kinetic equations for distribution functions of conduction band electrons and holes of the valence band in the phase space of coordinates and quasi-momentums. Effective masses, densities of states, and group velocities of particles are determined on the base of band theory of a crystal. The approximation of the continuous momentum losses due to scattering on lattice defects is performed. The applicability of the model is validated by the comparison with the experimental data for the electron average-velocity dependence on the electric-field strength and on the velocity of the electron-energy transmission to the lattice. The silicon radiation conductivity excited by a free-electron current is calculated and the compliance of the results with the theoretical estimates is demonstrated.

Nurturing user creative performance in social media networks

Purpose– Creative performance relies on the capability of developing and presenting an original concept or idea, and the collaborative production of creative content which enhances feeling of connection with others and formation of strong community. The purpose of this paper is to apply the theory of work performance containing four dimensions (capacity, opportunities, willingness, and performance) to investigate how the capabilities of social network sites enhance user creative performance through collective social capital and information capital (opportunities) for and individual habit of use (willingness) of the user to engage in social learning process.Design/methodology/approach– Many measurement items are adapted from the literature, except those measuring the constructs of social media capabilities (i.e. transmission velocity (TV), parallelism, symbol sets, rehearsability, and reprocessability) and user creative performance. The study uses survey method to collect data from social media network (SMN) users in Taiwan. Facebook is chosen as the source because it is the most prevalent and sophisticated social media platform that provides a home for users to interact and communicate. Structural equation modeling with partial least square is used to analyze the usable data collected from 533 Facebook users.Findings– The results show that the constructs are significantly and positively correlated, meaning that social media capabilities enable social capital, information capital, and habit of use to improve user creative performance in SMNs. Three out of five social media capabilities (i.e. TV, parallelism, and rehearsability) are identified as the key enablers.Research limitations/implications– Because of the sampled surveyed subjects and the single research method, there are some limitations in this study. The research results may lack generalizability that should be taken into account when they are interpreted. The authors encourage researchers to test the proposed theoretical model further with additional subjects, variables, and linkages.Practical implications– The findings of this research shed light for managers of SMN platforms on how to manage the platforms more effectively. A healthy SMN platform must implement at least these three media capabilities: the functions of news feed (i.e. TV), chat (i.e. parallelism), edit (i.e. rehearsability), in order to sustain its service.Social implications– This study confirmed that user creative performance can be increased in various ways through social capital, information capital, and habit of use. Company management should use SMNs (e.g. Facebook or Twitter) to enable employees to interact and exchange ideas and promote “coopetition” among employees across the company. If the organizational culture supports free expression of ideas and sharing of opinions, the development and robustness of group creativity can be enhanced, leading to higher competitive advantage for a company against its competitors.Originality/value– Past studies related to individual creativity have mostly discussed it as a personality trait or talent; yet, personality trait or talent is implicit until it is shown by one’s behavior. Thus, for the collective performance of user creativity on SMNs, the authors elicit individual creativity through the creative performance manifested by user behavior. Furthermore, the authors confirm that social capital, information capital, and habit of use are the critical antecedents of user creative performance, and that the five social media capabilities are the enablers of social capital, information capital, and habit of use on SMNs.

Watching online videos interactively: the impact of media capabilities in Chinese Danmaku video sites

In China, the implementation of a Danmaku social media system to sustain and raise user interest in online video sites is an increasingly widespread phenomenon. Danmaku technology is used to display users’ messages in written text on the online video stream. Little is known about the effects of this form of interactive enhancement. The aim of this empirical study is to evaluate the evolving media capabilities of the Danmaku system and their effects on users’ perceptions of interactivity and their intentions to continue using Danmaku. We draw on media synchronicity theory and apply it to a stimulus-organism-response model. Using this framework, we hypothesize that the media capabilities of the Danmaku system, namely its transmission velocity, parallelism, symbol sets, rehearsability, and reprocessability, elicit increased interactivity, which influences users’ instantaneous intentions to share and to continue the use of the Danmaku system. The results showed that both users’ instantaneous intention to share and their intention to continue to use were significantly affected by the perceived interactivity. Unlike the results of previous studies, our findings showed that all five media capabilities positively affected the users’ perceptions of interactivity. The potential theoretical and practical implications of our findings are discussed.

A tunable acoustic metamaterial with double-negativity driven by electromagnets.

With the advance of the research on acoustic metamaterials, the limits of passive metamaterials have been observed, which prompts the studies concerning actively tunable metamaterials with adjustable characteristic frequency bands. In this work, we present a tunable acoustic metamaterial with double-negativity composed of periodical membranes and side holes, in which the double-negativity pass band can be controlled by an external direct-current voltage. The tension and stiffness of the periodically arranged membranes are actively controlled by electromagnets producing additional stresses, and thus, the transmission and phase velocity of the metamaterial can be adjusted by the driving voltage of the electromagnets. It is demonstrated that a tiny direct-current voltage of 6V can arise a shift of double-negativity pass band by 40% bandwidth, which exhibits that it is an easily controlled and highly tunable acoustic metamaterial, and furthermore, the metamaterial marginally causes electromagnetic interference to the surroundings.

Dynamic Modulation of Myelination in Response to Visual Stimuli Alters Optic Nerve Conduction Velocity.

Myelin controls the time required for an action potential to travel from the neuronal soma to the axon terminal, defining the temporal manner in which information is processed within the CNS. The presence of myelin, the internodal length, and the thickness of the myelin sheath are powerful structural factors that control the velocity and fidelity of action potential transmission. Emerging evidence indicates that myelination is sensitive to environmental experience and neuronal activity. Activity-dependent modulation of myelination can dynamically alter action potential conduction properties but direct functional in vivo evidence and characterization of the underlying myelin changes is lacking. We demonstrate that in mice long-term monocular deprivation increases oligodendrogenesis in the retinogeniculate pathway but shortens myelin internode lengths without affecting other structural properties of myelinated fibers. We also demonstrate that genetically attenuating synaptic glutamate neurotransmission from retinal ganglion cells phenocopies the changes observed after monocular deprivation, suggesting that glutamate may constitute a signal for myelin length regulation. Importantly, we demonstrate that visual deprivation and shortened internodes are associated with a significant reduction in nerve conduction velocity in the optic nerve. Our results reveal the importance of sensory input in the building of myelinated fibers and suggest that this activity-dependent alteration of myelination is important for modifying the conductive properties of brain circuits in response to environmental experience. Oligodendrocyte precursor cells differentiate into mature oligodendrocytes and are capable of ensheathing axons with myelin without molecular cues from neurons. However, this default myelination process can be modulated by changes in neuronal activity. Here, we show, for the first time, that experience-dependent activity modifies the length of myelin internodes along axons altering action potential conduction velocity. Such a mechanism would allow for variations in conduction velocities that provide a degree of plasticity in accordance to environmental needs. It will be important in future work to investigate how these changes in myelination and conduction velocity contribute to signal integration in postsynaptic neurons and circuit function.

Effect of Vibration Properties of a Resonance Board on Piano Timbre

Abstract The resonance board is one of the most important components of a piano and greatly affects the piano's timbre. The vibration properties of eight resonance boards made from Picea glehnii, Picea jezoensis, Picea spinulosa, and Picea sitchensis were analyzed using the spectrum analysis method of the fast Fourier transform following vibration theory. The modulus of elasticity (E) and velocity of vibration transmission (C) of each resonance board were calculated. After the resonance boards were incorporated into pianos, the mean amplitude, ratio of maximum to minimum amplitudes, and mean ratio of successive amplitudes of resonant frequencies for 36 typical keys of each piano were obtained from the frequency spectrum. The correlation between a piano's timbre and the resonance board's vibration properties was analyzed. The results show that the piano timbre improves with increasing E and C, especially in the y direction of the resonance board.

Seismic analysis of underground tunnels by the 2.5D finite/infinite element approach

A procedure for the seismic analysis of underground tunnels using recorded free-field earthquakes based on the 2.5D finite/infinite element approach is presented. The near and far fields of the half space are modeled by finite and infinite elements, respectively. Using the 1D wave theory, the nodal force and displacement on the near-field boundary are computed for each spectral frequency of the earthquake. Then, equivalent seismic forces are computed for the near-field boundary for the earthquake spectrum. By assuming the soil-tunnel system to be uniform along the tunnel axis, the 2.5D approach can account for the wave transmission along the tunnel axis, which reduces to the 2D case for infinite transmission velocity. The horizontal and vertical components of the 1999 Chi-Chi Earthquake (TCU068) are adopted as the free-field motions in the numerical analysis. The maximal stresses and distribution patterns of the tunnel section under the P- and SV-waves are thoroughly studied by the 2.5D and 2D approaches, which should prove useful to the design of underground tunnels.

Groins and submerged breakwaters – new modeling and empirical experience

Abstract The relationship between the effectiveness of groins and their technical condition was studied. The supporting role of groins in artificial shore nourishment was tested using the theoretical modeling of hydrodynamic and morphodynamic processes in the nearshore zone. This modeling scheme was developed as to represent the actual coastal situation occurring on the shores of the Hel Peninsula (the Gulf of Gdańsk, the southern Baltic Sea). Based on the results of computations and the results of field observations, recommendations were prepared on the design and maintenance of groins. The second part of the paper is devoted to submerged breakwaters. The theoretical modeling of wave-current fields near the segmented submerged breakwaters led to the determination of coefficients of wave transmission and rip current velocities, which finally yielded a piece of design advice. In all numerical simulations, the Delft3D software was used.

Monitoring the setting process of eco-binders by ultrasonic P-wave and S-wave transmission velocity measurement: Mortar vs concrete

Current environmental imperatives have motivated much research on the possibilities of substitution of clinker, responsible for substantial emissions of CO2, by by-products of various industries.The concretes investigated are designed as to limit the early age cracking risk despite a massive substitution of up to 75% of clinker. In this framework, interest has been shown to mix designs combining the benefits of ground granulated blast-furnace slag and limestone microfiller. The aim of this study is to evaluate the impact of environmentally friendly cement-based binders on the initial and final setting time of mortars and concretes by means of a standard method (ASTM C403), early age compressive strength, elastic modulus, and ultrasonic transmission velocity measurements of P-waves and S-waves. This last method was observed to be a relevant setting indicator for both mortar and concrete samples. Critical influence of both the binder’s composition and the aggregate content has been observed on the setting process.

Comparison of conventional twist drill protocol and piezosurgery for implant insertion: an ex vivo study on different bone types

The aim of this exvivo study was to compare implant insertion procedures using piezosurgery and conventional drilling in different qualities of bone. Implant bed preparation time, generated heat, and primary implant stability were analyzed. Fresh exvivo porcine bone block samples (cancellous, mixed, and cortical bone) were obtained. The bone quality was quantified by ultrasound transmission velocity (UTV). Each bone sample received three implants of the same diameter using each of the techniques of piezosurgery and conventional twist drills. Time for preparation was taken and the temperature while performing the osteotomy was measured using infrared spectroscopy. The primary implant stability after osteotomy was measured using resonance frequency analysis (RFA) and extrusion torque (ET). ANOVA with post hoc Tukey test was carried out to compare the values for the three different groups. The UTV values strongly correlated with the density of the bone samples. There was a significant increase in time (threefold, P<0.05 [302s vs. 122s in cortical bone]) but no difference in the temperature for the piezo group (~37°C in cortical bone). Regardless of the osteotomy technique, there was a statistically significant increase in RFA and ET values in implants inserted in cancellous bone (RFA: piezo 77, drill 76; ET: piezo 22, drill 21), mixed bone (RFA: piezo 85, drill 86; ET: piezo 105, drill 61), and cortical bone (RFA: piezo 90, drill 87; ET piezo 184, drill 79) samples, respectively (P<0.05). In between the different osteotomy groups, there was no difference in the RFA values but significant higher ET values in mixed/cortical bone samples in favor for the piezosurgery group. Piezosurgery and conventional implant bed drilling procedure do have similar mechanical outcomes regarding primary stability with high RFA values, but the preparation does need more time for piezosurgery group, so that piezosurgery might be a valuable tool in only very specific cases for implant bed preparation.

How social media applications affect B2B communication and improve business performance in SMEs

Social Media Apps (SMA) are widely used to facilitate individual communications. In company situations, they are utilized as a channel to communicate with their customers. However, studies examining how SMA have been utilized in the Business-to-Business (Social Media Benchmarking Report, 2014) context are lacking. Using a model based on Media Synchronicity Theory (MST), we present one of the first empirical studies investigating the relationship between the capabilities of SMA (transmission velocity, parallelism, symbol sets, rehearsability, and reprocessability) and B2B communication and business performance. Five case studies based on face-to-face interviews with the senior managers/owners of SME (Small and Medium Enterprises) were conducted. The data were analyzed and the findings confirmed the SMA media capabilities as explained by MST. The findings also revealed a missing SMA capability, that of information security and control, which has been added to the proposed model and which may be an important addition to MST. This study calls for more research to verify this finding.

Comparison of Ordinary Pores with Internal Cured Pores Produced by Superabsorbent Polymers

Porous cementitious mixtures were prepared with two different spherical particles: expanded polystyrene (EPS) and superabsorbent polymer (SAP). The effect of EPS and SAP on the compressive strength, ultrasonic transmission, internal relative humidity and hydration degree under different volume fraction were studied. Results indicated that SAP matrix possessed much higher compressive strength (30-60%, 28d), ultrasonic transmission velocity, internal humidity (11-13%RH, 28d) and hydration degree (13-21%, 28d) than EPS matrix, which indicated that the desorption of SAP accelerated the hydration and increased the compactness of the surrounding cement paste. The internal cured pores left by SAP might have been strengthened which was different from ordinary pores produced by EPS.

Controlling of group velocity via terahertz signal radiation in a defect medium doped by four-level InGaN/GaN quantum dot nanostructure

In this paper, we propose a novel scheme for controlling the group velocity of transmitted and reflected pulse from defect medium doped with four-level InGaN/GaN quantum dot nanostructure. Quantum dot nanostructure is designed numerically by Schrödinger and Poisson equations which solve self consistently. By size control of quantum dot and external voltage, one can design a four-level quantum dot with appropriate energy levels which can be suitable for controlling the group velocity of pulse transmission and reflection from defect slab with terahertz signal field. It is found that in the presence and absence of terahertz signal field the behaviors of transmission and reflection pulses are completely different. Moreover, it is shown that for strong terahertz signal field, by changing the thickness of the slab, simultaneous peak and dip for transmission and reflection pulse are obtained.

Seismic wave propagation through an in-situ stressed rock mass

This paper presents an analytical study of seismic wave propagation through an in-situ stressed rock mass. The joint deformation is assumed to satisfy the nonlinear Bandis–Barton (B–B) deformational model. The displacement discontinuity method (DDM) is introduced to take account of the effect of in-situ stress. The amplitude- and frequency-dependence of seismic wave propagation through an in-situ stressed rock mass are analyzed. The effects of in-situ stress on seismic attenuation, energy transmission and effective seismic velocity are discussed. The results show that seismic attenuation, energy transmission and effective seismic velocity are influenced by seismic wave amplitude and frequency, and in-situ stress. Moreover, the amplitude- and frequency-dependence of a seismic wave obtained by conventional DDM are special cases when in-situ stress is not considered. The effect of in-situ stress on seismic attenuation, energy transmission and effective seismic velocity can be neglected when either the amplitude or the frequency is sufficiently large. When the frequency is sufficiently small, the effect of in-situ stress on seismic attenuation and energy transmission can also be neglected, but its effect on the effective seismic velocity cannot be ignored.

Monitoring the setting process of mortars by ultrasonic P and S-wave transmission velocity measurement

Until now, the standardized methods developed for the detection of initial and final setting are destructive and non-continuous. The well-established ultrasonic pulse transmission velocity (UPV) method can be correlated to the setting process of mortar by the measurement of P-waves. However, S-waves seem to be better indicators of the setting of cement-based materials, since they are more sensitive to the solid matrix connectivity. This study proposes a new methodology, based on the combined monitoring of P- and S-waves, to determine the setting time of mortars containing two types of fly ashes. The S-waves velocity and dynamic elastic properties seem to be the most accurate indicators of the setting process, allowing capturing microstructural evolutions that isothermal calorimetry or usual UPV methods do not detect.

Signal Simulation and Experimental Research on Acoustic Emission using LS - DYNA

To calculate sound wave velocity, we performed the Hsu-Nielsen lead break experiment using the ANSYS/LS-DYNA finite element software. First, we identified the key problems in the finite element analysis, such as selecting the exciting force, dividing the grid density, and setting the calculation steps. Second, we established the finite element model of the sound wave transmission in a plate under the lead break simulation. Results revealed not only the transmission characteristics of the sound wave but also the simulation and calculation of the transmission velocity of the longitudinal and transverse waves through the time travel curve of the vibration velocity of the sound wave at various nodes. Finally, the Hsu-Nielsen lead break experiment was implemented. The results of the theoretical calculation and simulation analysis were consistent with the experimental results, thus demonstrating that the research method using the ANSYS/LS-DYNA software to simulate sound wave transmissions in acoustic emission experiments is feasible and effective.