Short-time Surface Research Articles

New results on robust sliding mode control for linear time-delay systems

AbstractThis work focuses on the sliding mode control (SMC) for a family of linear systems with uncertainties and time-varying delays. First, an integral switching surface is constructed to verify the robust asymptotic stability of the considered system and the results are extended to analyse the mixed $\mathscr{H}_{\infty }\big /$Passivity performance index. Thereafter, a suitable SMC law is developed to force the system state onto the predefined switching surface in short time. By using Lyapunov stability theory, some novel results are obtained, and the required stability conditions are established in terms of linear matrix inequalities which can be solved by standard Matlab toolbox. Finally, the results are validated over a Chua’s circuit model, which describes the practical application of the developed results.

Improving mechanical properties for pure irons by local surface mechanical attrition treatment

ABSTRACTAfter a short-time surface mechanical attrition treatment process, a planar uneven structure was obtained on the surface of irons. The yield strength of the sample subjected to surface mechanical attrition treatment for 60 s is almost twice than that of the annealed sample, but the ductility is still well retained. The good combination of strength and ductility is mainly due to the extra strain hardening and the coexistence of soft and hard phases. The extra strain hardening delays the annihilation of dislocations and reduces the plastic instability, while the hard phase in the planar uneven structure suppresses the crack initiation, and the soft phase delays the crack propagation.

A facile, robust and versatile finite element implementation to study the time-dependent behaviors of responsive gels

Though there are significant efforts to develop numerical platforms to simulate the dynamic behaviors of responsive gels, several challenges were not successfully resolved, including truly robust method to handle time-dependent and coupled mass diffusion and deformation fields particularly at very short-time and complicated instability. In this Letter, a facile, robust and versatile finite element method was developed to resolve these challenges by adopting ramping boundary conditions, viscous damping, and damped Newton–Raphson method. This method can be readily implemented in a commercial platform COMSOL Multiphysics. The finite element method was showcased to study several dynamic examples that possess very short-time surface wrinkles, wrinkle evolutions, and incorporation with other physics field. Given the fact that the implementation is through a commercial platform, this method can have significant contributions to the studies of gels.

Fast subsurface fingerprint imaging with full-field optical coherence tomography system equipped with a silicon camera.

Images recorded below the surface of a finger can have more details and be of higher quality than the conventional surface fingerprint images. This is particularly true when the quality of the surface fingerprints is compromised by, for example, moisture or surface damage. However, there is an unmet need for an inexpensive fingerprint sensor that is able to acquire high-quality images deep below the surface in short time. To this end, we report on a cost-effective full-field optical coherent tomography system comprised of a silicon camera and a powerful near-infrared LED light source. The system, for example, is able to record 1.7 cm×1.7 cmen face images in 0.12s with the spatial sampling rate of 2116 dots per inch and the sensitivity of 93dB. We show that the system can be used to image internal fingerprints and sweat ducts with good contrast. Finally, to demonstrate its biometric performance, we acquired subsurface fingerprint images from 240 individual fingers and estimated the equal-error-rate to be ∼0.8%. The developed instrument could also be used in other en face deep-tissue imaging applications because of its high sensitivity, such as in vivo skin imaging.

Duplex surface modification of porous poly (lactic acid) scaffold

A duplex surface modification method is used to enhance the surface and mechanical properties of porous poly (l-lactic acid) (PLLA) scaffold. The scaffold was first modified by a surface alkali hydrolysis treatment and then it underwent a short-time surface coating process. An acetic acid treatment was introduced to the traditional surface hydrolysis; the result indicates that this novel surface alkali hydrolysis treatment can further improve the hydrophilicity and surface roughness of the PLLA scaffold. Surface hydrolysis also improves the bonding strength of the scaffold with the coating significantly. The existence of the gelatin–hydroxyapatite hybrid coating increases the hydrophilicity, mechanical property and apatite-forming ability of the scaffold considerably.

Color Fading of Indigo-Dyed Cotton Denim Fabric by Laser

Laser allows short-time surface engraving of the patterns of desired variety, size, and intensity on a wide range of textile surfaces with precision and without much damaging the texture of the materials. The laser application in textile material has been applied possible to make denim fabric looked faded and worn out without the use chemical process. In this study, laser was applied on the denim fabric in order to evaluate its effect on fabric shade. The laser power density increased in response to the increase in the level of pixel time and resolution. Under the effect of high laser power density, a paler surface appearance was noted in the denim fabrics and the K/Ssum values indicated that the amount of dye on denim fabric was decreased significantly.

Observation of pre-breakdown emission sites and breakdowns of vacuum gaps under short-pulsed testing

Emission activity of the stainless steel cathode under 200 kV, 50 to 200 ns voltage pulses was studied with the use of a 4-channel, 12-bit ICCD camera. The gap was formed by a bulk cathode and a thin-foil titanium anode. Both the cathode and anode surfaces were cleaned and polished preliminary by means of electron-beam treatment in the mode of short-time surface melting in vacuum. Observations gave a ground to tell about prebreakdown emission sites of two kinds that are stable emission sites (SES's) and unstable ones (UES's), which are different in behavior and in ability to initiate breakdowns. SES's were recognized on the cathode at relatively low electric field strengths (at 0.55 MV/cm in average). Close to 1 MV/cm, UES's start to be recognized in images. An UES's pattern is changed from shot to shot without breakdowns. Often, breakdowns occur in spatial locations different from UES's recorded in the previous shot. The results obtained could be of interest in study of pre-breakdown and breakdown phenomena at extremely high electric fields in vacuum.

Formation of an epitaxial monolayer on graphite upon short-time surface contact with highly diluted aqueous solutions of 1-monostearoylglycerol

Short-time surface contact of highly diluted 1-monostearoylglycerol (1-MSG) aqueous solutions with highly oriented pyrolitic graphite results in the deposition of an epitaxial monolayer that can be detected by atomic force microscopy operating in tapping mode at the graphite–air interface. The monolayer obtained with the racemic mixture is then compared to that obtained with one of the pure enantiomers. The analogous behavior found for aqueous solutions of rac-1-MSG and 3- sn-MSG implies a two-dimensional self-assembly process with chiral discrimination. The results suggest that the monolayer originates from species located at the surface of the deposition drop. They also indicate that the simple experimental procedure reported, or more elaborate Langmuir–Schaefer methods, could be the method of choice to prepare other monolayers of similar surfactants.

Dynamical constraints on phase transitions

The numerical solutions of nonlocal and local Boltzmann kinetic equations for the simulation of central heavy ion reactions are parameterized in terms of time dependent thermodynamical variables in the Fermi liquid sense. This allows one to discuss dynamical trajectories in phase space. The nonequilibrium state is characterized by non-isobaric, non-isochoric etc. conditions, shortly called iso-nothing conditions. Therefore a combination of thermodynamical observables is constructed which allows one to locate instabilities and points of possible phase transition in a dynamical sense. We find two different mechanisms of instability, a short time surface - dominated instability and later a spinodal - dominated volume instability. The latter one occurs only if the incident energies do not exceed significantly the Fermi energy and might be attributed to spinodal decomposition. In contrast the fast surface explosion occurs far outside the spinodal region and pertains also in the cases where the system develops too fast to suffer a spinodal decomposition and where the system approaches equilibrium outside the spinodal region.

Noninvasive assessment of myocardial cell injury in dogs with suspected cardiac contusion

To determine the suitability of serologic biochemical tests to diagnose myocardial cell injury in dogs with suspected cardiac contusion. Myocardial contusion after blunt thoracic trauma will frequently be overlooked or missed unless hemo-dynamic instability or dramatic electrocardiographic findings are observed. There are no available non-invasive tests to definitely detect blunt myocardial lesions in dogs. Circulating biochemical markers of skeletal muscle and myocardial cell integrity (aspartate aminotransferase, lactate dehydrogenase, a-hydroxybutyrate dehydrogenase, creatine kinase [CK], CK isoenzyme MB, and cardiac troponins I [cTnT] and T [cTnT]) were analyzed in 33 dogs with blunt chest injury and in 40 control dogs. Results were compared with ECG abnormalities diagnosed from serial short-time surface ECGs. Cardiac TnI and CK-MB in serum were not detectable in 36 and 26 healthy dogs (median and range were 0 and 0 to 1.37 ng/ml and 0 and 0 to 3.17 ng/ml, respectively). Serum cTnT was not found in normal dogs. In dogs with thoracic trauma, circulating cTnI was elevated in 18 dogs (range 0 to 160.1 ng/ml), CK-MB in 14 dogs (range 0 to 24.9 ng/ml) and cTnT in 9 dogs (range 0 to 2.35 ng/ml), suggesting myocardial cell injury in 58% of dogs. Relevant electrocardiographic abnormalities were observed in 10/33 (30%) dogs. No differences in serum concentrations of markers of myocardial injury were found between dogs with or without relevant ECG abnormalities. Myocardial cell injury is a frequent event in dogs with blunt thoracic trauma. Analysis of serum cTnI is more sensitive in detecting myocardial abnormalities than determination of circulating cTnT and CK-MB or electrocardiography.

The vibrating electropolishing process of aluminium in phosphoric acid solution (1st Report)

This study is concerning with the electropolishing process with the vibrating anode in phosphoric acid bath based on the patents-(Jap. Pat. No. 128891, 190520, T-Nakayama)In these experiments the static method and the vibration method have been used symmetrically.(1) As a whole, the electropolished surface produced by the static method has always shown uneven surface, its reflectivity being up to 80%, but the vibration method gave an extremely smooth surface and its reflectivity reached to 90%.(2) In the vibration method, the concentration of phosphoric acid to obtain electropolished surface is higher than that in the static method, but it has been possible to perform electropolishing up to a higher concentration than that in the static.(3) Upon increase of the current density, the surface condition has changed in the order as follows:A (etched surface)-B (insufficient polished surface)-C (electropolished surface)-D (rough surface)-E (burned surface).The similar results can be obtained with each concentration as well as with both the static and the vibration method.(4) With the identical concentration of phosphoric acid, the vibration method produced electropolished surface in a higher current density than the static method, and electropolished surface also can be obtained untill reaching to a higher current density than that of the static.(5) With the same temperature, electropolished surface can be obtained at a higher current density of the vibration method than that of the static, producing electropolished surface untill reaching a higher current density.(6) While the static method produces electropolished surface in short time in comparison with the vibration method, the vibration method produces electropolished surface until reaching to a longer electrolysis time than the static.