Sawtooth Structure Research Articles

Delay-partitioning approach to stability analysis of state estimation for neutral-type neural networks with both time-varying delays and leakage term via sampled-data control

ABSTRACTThis paper mainly focuses on further improved stability analysis of state estimation for neutral-type neural networks with both time-varying delays and leakage delay via sampled-data control by delay-partitioning approach. Instead of the continuous measurement, the sampled measurement is used to estimate the neuron states and a sampled-data estimator is constructed. To fully use the sawtooth structure characteristics of the sampling input delay, sufficient conditions are derived such that the system governing the error dynamics is asymptotically stable. The design method of the desired state estimator is proposed. We construct a suitable Lyapunov–Krasovskii functional (LKF) with triple and quadruple integral terms then by using a novel free-matrix-based integral inequality (FMII) including well-known integral inequalities as special cases. Moreover, the design procedure can be easily achieved by solving a set of linear matrix inequalities (LMIs), which can be easily facilitated by using the standard numerical software. Finally, two numerical examples are given to demonstrate the effectiveness of the proposed results.

Critical heat flux enhancement of HFE-7100 flow boiling in a minichannel heat sink with saw-tooth structures

A heat sink with convective boiling in micro- or mini-channels is with great potential to meet the requirement of the high heat dissipation of the electronic devices. This study investigates the flow boiling of HFE-7100, having a suitable boiling temperature at atmospheric pressure and dielectric property, in the minichannel heat sink with the modified surface (namely, the saw-tooth structure). The effect of the system pressure on the boiling characteristics was also studied. The results reveal that the critical heat flux can be significantly improved by introducing the saw-tooth structures on the channel surface or boosting the system pressure as well as by increasing the mass flux. Compared to the non-modified channel, the enhancements of the critical heat flux for the parallel and counter saw-tooth channels are 44% and 36%, respectively, at the small mass flux. The boiling visualization further indicates that the minichannels with the saw-tooth structures interrupt the boundary layer and restrain the coalescence of the bubble, which may be the reason for the critical heat flux enhancement. Moreover, the degree of the critical heat flux enhancement, contributed by the saw-tooth modification of the channel, decreases with an increase in the mass flux.

A Compact High-Precision GNSS Antenna With a Miniaturized Choke Ring

This letter presents a miniaturized geodetic choke ring antenna for high-precision Global Navigation Satellite System applications. The antenna consists of crossed dipoles that are fed by two coaxial feedlines, a resonant ring over the dipoles, a cavity-backed reflector with a saw-tooth structure, and a miniaturized choke ring. The choke ring alongside the saw-tooth structure can improve the front-to-back ratio (FBR) by almost 10 dB. The proposed antenna achieves a gain of over 7 dBic, a high FBR of greater than 25 dB, and an operating band covering 1.17–1.60 GHz in which the return loss is lower than −10 dB and the axial ratio is lower than 3 dB when zenith angle θ < 70°.

Microfluidic Air Sampler for Highly Efficient Bacterial Aerosol Collection and Identification.

The early warning capability of the presence of biological aerosol threats is an urgent demand in ensuing civilian and military safety. Efficient and rapid air sample collection in relevant indoor or outdoor environment is a key step for subsequent analysis of airborne microorganisms. Herein, we report a portable battery-powered sampler that is capable of highly efficient bioaerosol collection. The essential module of the sampler is a polydimethylsiloxane (PDMS) microfluidic chip, which consisted of a 3-loop double-spiral microchannel featuring embedded herringbone and sawtooth wave-shaped structures. Vibrio parahemolyticus (V. parahemolyticus) as a model microorganism, was initially employed to validate the bioaerosol collection performance of the device. Results showed that the sampling efficacy reached as high as >99.9%. The microfluidic sampler showed greatly improved capturing efficiency compared with traditional plate sedimentation methods. The high performance of our device was attributed to the horizontal inertial centrifugal force and the vertical turbulence applied to airflow during sampling. The centrifugation field and turbulence were generated by the specially designed herringbone structures when air circulated in the double-spiral microchannel. The sawtooth wave-shaped microstructure created larger specific surface area for accommodating more aerosols. Furthermore, a mixture of bacterial aerosols formed by V. parahemolyticus, Listeria monocytogenes, and Escherichia coli was extracted by the microfluidic sampler. Subsequent integration with mass spectrometry conveniently identified the multiple bacterial species captured by the sampler. Our developed stand-alone and cable-free sampler shows clear advantages comparing with conventional strategies, including portability, easy-to-use, and low cost, indicating great potential in future field applications.

A high-performance broadband terahertz absorber based on sawtooth-shape doped-silicon

Perfect absorbers with broadband absorption of terahertz (THz) radiation are promising for applications in imaging and detection to enhance the contrast and sensitivity, as well as to provide concealment. Different from previous two-dimensional structures, here we put forward a new type of THz absorber based on sawtooth-shape doped-silicon with near-unit absorption across a broad spectral range. Absorbance over 99% is observed numerically from 1.2 to 3 THz by optimizing the geometric parameters of the sawtooth structure. Our absorbers can operate over a wide range of incident angle and are polarization insensitive. The underlying mechanisms due to the combination of an air-cavity mode and mode-matching resonance on the air-sawtooth interface are analyzed in terms of the field patterns and electromagnetic power loss features.

Magnetization of interacting electrons in anisotropic quantum dots with Rashba spin–orbit interaction

Magnetization of anisotropic quantum dots in the presence of the Rashba spin–orbit interaction has been studied for three and four interacting electrons in the dot for non-zero values of the applied magnetic field. We observe unique behaviors of magnetization that are direct reflections of the anisotropy and the spin–orbit interaction parameters independently or concurrently. In particular, there are saw-tooth structures in the magnetic field dependence of the magnetization, as caused by the electron–electron interaction, that are strongly modified in the presence of large anisotropy and high strength of the spin–orbit interactions. We also report the temperature dependence of magnetization that indicates the temperature beyond which these structures due to the interactions disappear. Additionally, we found the emergence of a weak sawtooth structure in magnetization for three electrons in the high anisotropy and large spin–orbit interaction limit that was explained as a result of merging of two low-energy curves when the level spacings evolve with increasing values of the anisotropy and the spin–orbit interaction strength.

Fabrication of circular sawtooth gratings using focused UV lithography

This paper presents a novel micro-fabrication method using focused ultraviolet (UV) light to manufacture three-dimensional sawtooth structures in ultra-thick negative photoresist to fabricate a novel multi-prism x-ray lens. The method uses a lens to shape the UV beam instead of the photomask conventionally used in UV lithography. Benefits of this method include the ability to manufacture sawtooth structures in free form, for example in circular shapes as well as arrays of these shapes, and in resist that is up to 76 μm thick.To verify the method, initially a simple simulation based on Fourier optics was done to predict the exposure energy distribution in the photoresist. Furthermore, circular sawtooth gratings were manufactured in a 76 μm SU-8 resist. The UV lens was fabricated using electron beam lithography and then used to expose the SU-8 with UV light. This paper details the complete developed process, including pre-exposure with an e-beam and cold development, which creates stable sawtooth structures. The measured profile was compared to the ideal sawtooth and the simulation. The main discrepancy was in the smallest feature size, the sawtooth tips, which were wider than the desired structures, as would be expected by simulation.

The scission point configuration of fissioning nuclei

We define the optimal shape which fissioning nuclei attain just before the scission and calculate the deformation energy as function of the mass asymmetry at the scission point. The calculated deformation energy is used in quasi-static approximation for the estimation of mass distribution, total kinetic and excitation energy of fission fragments, and the total number of prompt neutrons. The calculated results reproduce rather well the experimental data on the position of the peaks in the mass distribution of fission fragments, the total kinetic and excitation energy of fission fragments. The calculated value of neutron multiplicity is somewhat larger than experimental results. The saw-tooth structure of neutron multiplicity is qualitatively reproduced.

Sampled-Data Synchronization Analysis of Markovian Neural Networks With Generally Incomplete Transition Rates.

This paper investigates the problem of sampled-data synchronization for Markovian neural networks with generally incomplete transition rates. Different from traditional Markovian neural networks, each transition rate can be completely unknown or only its estimate value is known in this paper. Compared with most of existing Markovian neural networks, our model is more practical because the transition rates in Markovian processes are difficult to precisely acquire due to the limitations of equipment and the influence of uncertain factors. In addition, the time-dependent Lyapunov-Krasovskii functional is proposed to synchronize drive system and response system. By applying an extended Jensen's integral inequality and Wirtinger's inequality, new delay-dependent synchronization criteria are obtained, which fully utilize the upper bound of variable sampling interval and the sawtooth structure information of varying input delay. Moreover, the desired sampled-data controllers are obtained. Finally, two examples are provided to illustrate the effectiveness of the proposed method.

On designing stochastic sampled-data controller for master–slave synchronization of chaotic Lur’e system via a novel integral inequality

This study investigates the problem of designing stochastic sampled-data controller for master–slave synchronization of chaotic Lur’e systems (CLSs) via a novel approach. Specially, first, we assume that the occurrence probabilities of the sampling intervals are fixed constants and satisfy a Bernoulli distribution. In order to take full advantage of the sawtooth structure characteristics of the sampling input delay, we construct a newly augmented Lyapunov–Krasovskii functional (LKF) based on the extended Wirtinger inequality. Second, by using a novel free-matrix-based integral inequality (FMBII) including well-known integral inequalities as special cases, an exponentially mean-square synchronization criterion is proposed for analyzing the corresponding synchronization error system. Third, the desired estimator gain can be designed in terms of the solution to linear matrix inequalities (LMIs) which can be solved effectively by using available software. Finally, three numerical simulation examples of Chua’s circuit and neural network are given to illustrate the effectiveness and superiorities of the proposed method.

Sampled-data synchronization for complex networks based on discontinuous LKF and mixed convex combination

This paper investigates the sampled-data synchronization problem of delayed complex networks with aperiodic sampling interval based on enhanced input delay approach. By introducing an improved discontinuous Lyapunov–Krasovskii functional (LKF), new delay-dependent synchronization criteria are obtained using Wirtinger׳s integral inequality and mixed convex combination, which fully utilize the upper bound on variable sampling interval and the sawtooth structure information of varying input delay. The derived criteria are less conservative than the existing ones. In addition, the desired sampled-data controllers are obtained by solving a set of linear matrix inequalities. Finally, numerical examples are provided to demonstrate the feasibility of the proposed method.

Synthesis and structural control of silicon and silicide nanowires/microrods using metal chloride sources

Si and silicide nanowires/microrods were synthesized using metal-chloride-based sources by the CVD technique. In the case of Si nanowire synthesis, the morphological structures of the products depended on the distance from the source material. The distance dependence of the morphological and structural properties of the nanostructures was investigated to systemically clarify the shape modification phenomena in Si nanowire synthesis. The modification of the cross-sectional shape of the Si nanowires/microrods was successfully demonstrated. The triangular nanowire has a sawtooth faceting structure on its sidewall. In addition, the synthesis of Mn-silicide phases over the entire range of the Mn–Si system was examined. The effect of adding an impurity to the source materials on the structural modifications of the resulting nanowires/microrods was also investigated. It is expected that the morphological and structural control of the nanowires/microrods will be improved by a simple thermal treatment using a metal chloride as the source material.

Synchronisation control of dynamical networks subject to variable sampling and actuators saturation

This study investigates aperiodic sampled-data synchronisation of complex dynamical network (CDN) incorporate dynamics of actuators saturation. The sampling intervals considered here are time-varying which allowed to be variable within the lower and upper bounds. In order to fully captures the sawtooth structure characteristic of the sampled-data systems, a novel time-dependent continuous Lyapunov functional is employed to obtain less conservative criteria. Furthermore, the generalised sector bound condition is utilised for the estimate about the basin of the attraction. Based on the local stability condition, the sampled-data controller is constructed to guarantee the synchronisation of CDN in the presence of actuators saturation. The obtained sufficient conditions can be cast in two optimisation cases to maximise the admissible upper bound of sampling instants or enlarge estimate about the domain of attraction for the closed-loop systems. Subsequently, the validity and applicability of the criteria are verified through numerical examples.

Interfacial pattern selection in miscible liquids under vibration.

We explore the peculiar behaviour of an interface between two miscible liquids of similar (but non-identical) viscosities and densities under horizontal vibration with a frequency less than 25 Hz. Significant differences in the structure of the formed patterns were found between microgravity and ground experiments. In a gravity field, a spatially periodic saw-tooth frozen structure is generated in the interface which dissipates at long times. By contrast, under the low gravity conditions of a parabolic flight, the long lived pattern consists of a series of vertical columns of alternating liquids.

Prompt neutron multiplicity in correlation with fragments from spontaneous fission ofCf252

The spontaneous fission of $^{252}\mathrm{Cf}$ serves as an excellent benchmark of prompt emission in fission since experimental data can be obtained without the need of an incident beam. With the purpose of providing experimental data on the prompt fission neutron properties in correlation with fission-fragment characteristics, an experiment on $^{252}\mathrm{Cf}$(SF) has been performed. In addition, the experiment serves as a benchmark of setup and analysis procedures for measurements of fluctuations in the prompt-neutron properties as a function of incident neutron energy in fission of the major actinides $^{235}\mathrm{U}$ and $^{239}\mathrm{Pu}$. The experiment employs a twin Frisch grid ionization chamber as fission-fragment detector while neutrons were counted by using a liquid scintillator placed along the symmetry axis of the ionization chamber. Average neutron multiplicity has been obtained as a function of fission-fragment mass and total kinetic energy (TKE). The average multiplicity as a function of mass agrees well with available data in the literature in the mass range from 80 to 170 u. The existence of additional sawtooth structures in the far asymmetric mass region could not be confirmed, although the statistical accuracy of the present experiment is as good as the previous study where such structures have been reported [Nucl. Phys. A 490, 307 (1988).]. The available data in the literature on the TKE dependence of the multiplicity show strong deviations. Therefore, effort was focused on investigating experimental factors in low-efficiency neutron-counting experiments that may lead to faulty determination of this dependence. Taking these factors into account, a result that agrees well with data from high-efficiency neutron-counting experiments is obtained. The experimental arrangement allows determination of the angle between the detected neutron and the fission axis, which permits the neutron properties to be transformed into the fission-fragment rest frame. Fission neutron emission spectra in the fragment center-of-mass frame have thereby been obtained as a function of the fission-fragment mass and TKE.

Do nonlinear waves evolve in a universal manner in dusty and other plasma environments?

Using a fluid theory approach, this article provides a comparative study on the evolution of nonlinear waves in dusty plasmas, as well as other plasma environments, viz electron-ion, and electron-positron plasmas. Where applicable, relevance to satellite measurements is pointed out. A range of nonlinear waves from low frequency (ion acoustic and ion cyclotron waves), high frequency (electron acoustic and electron cyclotron waves) in electron-ion plasmas, ultra-low frequency (dust acoustic and dust cyclotron waves) in dusty plasmas and in electron-positron plasmas are discussed. Depending upon the plasma parameters, saw-tooth and bipolar structures are shown to evolve.

Chip Formation in High-Speed Milling of Titanium Alloy with PCD Tools

This paper presents a detailed analysis of chip morphology through an experimental study of high-speed milling of Ti-6Al-4V alloy with PCD tools. Milling tests were conducted for cutting speed range from 125 m/min to 2000 m/min with water-soluble cutting fluid. The collected chips were firstly examined with a digital cameras and the free surface of the chips was analyzed by a scanning electron microscope (SEM). Geographical parameters of chip morphologies were described in saw-tooth/lamella frequency on the free surface and chip width. Experimental results show that the variation of chips in high-speed end milling of Ti-6Al-4V alloy is as follows, long and straight-shaped → spiral-shaped → curly-shaped → irregular-shaped. The free surface of chips exhibits saw-tooth lamella structures. The lamella becomes clearer and more obvious at higher cutting speeds. Within the same measurement distance, there is a sharp decrease in the lamella number within same measuring range. This should be attributed to the enhancement of the thermal mechanical coupled field applied to the chip formation processes.

Valveless Micropump with Saw-Tooth Microchannel

The micropump is the executive component in a microfluidic chip which impels the sample to flow. Its performance directly affects the precision and reliability of Micro Total Analysis Systems (μTAS), and it also plays a key role in the targeting transport of trace substances. The single and double chamber valveless micropumps with saw-tooth microchannel were designed. The saw-tooth diffuser/nozzle pipe was fabricated on chrome glass substrate using MEMS technology and the pump diaphragm was manufactured by PMMA material. The piezoelectric bimorph with cantilever beam was adopted as driving pump actuator and PDMS material as pump diaphragm. The valveless micropumps for both single and double chambers were formed with different saw-tooth structure parameters. The flow rate increased about 25% when the sidewall of microchannel changed from smooth to saw-tooth, and with the driving voltage increasing, the positive and negative flow difference of saw-tooth diffuser/nozzle pipe increased significantly, so does the micro pump flow rate. The best diffused angle θ was determined by the microchannel length L of saw-tooth diffuser/nozzle pipe, and the micro pump operated with its maximum flow rate only when the length-width ratio A reached the best value. The flow rate of a saw-tooth diffuser/nozzle valveless micropump with parallel double chambers increased approximately 30% than that of a single chamber.

An enhanced input-delay approach to sampled-data stabilization of T–S fuzzy systems via mixed convex combination

The problem of sampled-data control is investigated for Takagi–Sugeno (T–S) fuzzy systems with aperiodic sampling intervals based on an enhanced input-delay approach. Delay-dependent stability and stabilizability conditions for the closed-loop continuous nonuniformly sampled-data fuzzy systems are derived by constructing a novel discontinuous Lyapunov–Krasovskii (L–K) functional, which makes good use of not only the upper bound on the variable sampling interval, but also its sawtooth structure information about varying input delay often ignored in previous results. A bounding technique combined by reciprocally convex technics and linear convex combination is presented for acquiring the time derivative of the functional, wherein Jensen’s inequality and Wirtinger’s inequality are integratively employed. And a feasible solution of the obtained criterion formulated as parameterized linear matrix inequalities is ultimately conceived. A numerical example is given to show the effectiveness of the proposed method.

Network-Based Robust Passive Control for Fuzzy Systems With Randomly Occurring Uncertainties

This paper investigates the problem of robust passive control for networked fuzzy systems, where randomly occurring uncertainties, variable sampling intervals, and constant network-induced delay are taken into account. A discontinuous Lyapunov functional is introduced for the closed-loop systems, which takes full advantage of the sawtooth structure of the time-varying interval delay induced by sample-and-hold and signal transmission. A sufficient condition is proposed to ensure the closed-loop system to be robustly stochastically passive. Then, the problem of robust passive control is solved. Two examples are utilized to illustrate the advantages and effectiveness of the results that are proposed in this paper.