Surface Height Fluctuations Research Articles

Study on the Influence of Strengthening Grinding Process on the Surface Integrity of 30CrMnSiA

30CrMnSiA, as a high-strength steel with excellent toughness and superior hardenability, was extensively used in the aerospace industry. At the same time, its lower surface hardness limits its application in impact and vibration environments. The surface of 30CrMnSiA was enhanced using the strengthening grinding process (SGP) technique in this work. The influence of SGP jet pressure on the surface integrity of 30CrMnSiA steel was studied, such as morphology, microstructure, roughness, and hardness. The study indicated that 30CrMnSiA samples treated by SGP reduced surface flatness, primarily due to the formation of plenty of irregular micro-pits by SGP. The greater the jet pressure leads to the more acute surface height fluctuation and the larger surface roughness. Furthermore, SGP notably enhanced the surface hardness and induced the formation of a strengthened layer. This improvement can be attributed to promoting martensite content and grain refinement within the surface layer structure facilitated by the SGP. The harder the surface hardness with the finer grain size, the thicker the strengthening layer with higher jet pressure.

Sea surface height fluctuations relevant to Indian summer monsoon over the northwestern Indian Ocean

We examined the interannual variations in sea surface height (SSH) over the northwestern Indian Ocean during 1993–2016, by using in situ observations along the east coast of the Arabian Peninsula together with satellite observations, objective analysis, and reanalysis. Focusing on the impacts of the Indian summer monsoon relative to the El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) modes, we found that the monsoon predominantly controls the summertime SSH variations at the in situ observatories, consistent with satellite observations. The monsoon is closely related to the SSH at a specific observatory in almost all seasons, whereas the wintertime SSH is strongly influenced by ENSO and IOD at other observatories. These SSH variations with local modulations in the coastal area were accompanied by basin-scale variations. The reduced southwesterly monsoon wind, for example, is found with the reduced ocean upwelling narrowly confined near the coast and the upper ocean temperature rise implying reduced meridional heat transport over the south of the Arabian Peninsula.

Electrochemically Imaging the Response of Ion-Selective Membranes with an Ultralow Detection Limit

The development of ion-selective membranes for the selective response of a particular ion has been studied for many years; however, imaging the response of the membrane with a low detection limit is challenging. Here, high spatial-resolution electrochemical imaging of this response down to picomolar is achieved using scanning ion conductive microscopy. The detection strategy relies on the exclusion of a small amount of counter ions from the membrane in the presence of a low concentration of target ions in the solution. These excluded counter ions are adsorbed at the membrane-solution interface, leading to more positive charges at the surface. The resultant elevation of the ionic current in the approach curve behaves as the response for the target ions down to 10-11 M, which is much more sensitive than that using potentiometric measurement. The constant-current scanning of the membrane exhibits the fluctuation of the apparent surface height that is correlated with the ionic concentration, permitting the imaging of the response at the nanoscale. The achievement of highly sensitive and spatial-resolution imaging for the ionic response enable the collection of spatial response at the ion-selective membrane, which will greatly advance the study of ion-selective electrodes.

Analysis of coherent laser echo characteristics back scattered from rough Gaussian target

The surface property of rough target can cause the decoherence and depolarization effects, which is among the main limiting factors in heterodyne detection. In the decoherence analyses, the phase fluctuation model of laser echo from rough target is established based on the spectral density method, and the phase fluctuations under typical roughness conditions are obtained by Monte Carlo method. The distribution properties of heterodyne signal amplitudes are analyzed under different surface height fluctuation σ and correlation length T. Then the corresponding experiments are carried out, which show that the phase fluctuations of laser echo satisfy the Gaussian distribution, and the decoherence effect induces the reductions and fluctuations of heterodyne signal amplitudes, especially with larger roughness surface. For typical rough metal targets, the depolarization characteristics of laser echoes from different scattering positions are obtained, which suggest that the depolarization effect increases with the rise of roughness. The positive correlation between the decoherence and depolarization effects provides a reference for the design of heterodyne lidar system, and the statistics can also be adopted for target roughness inference and target type identification.

Landscape dynamics facilitated non-point source pollution control and regional water security of the Three Gorges Reservoir area, China

Land use changes would significantly affect the hydrologic process at the regional scale, bringing both positive and negative ecological impacts. Estimating landscape dynamics and their effects on non-point source pollution are critical for understanding the magnitude and direction of ecological effects caused by various human demands, which is beneficial for relevant authorities to get more useful information on regional water security and provide practical guidance for land use planning. In this paper, the InVEST model was used to estimate the nitrogen loss during 1990–2015 of the Three Gorges Reservoir (TGR) area in China, and the driving mechanism of non-point source pollution was explored by spatial analysis. Meanwhile, we designed three scenarios to dissociate the impacts of afforestation and urbanization on water quality in the reservoir area. The results documented that the nitrogen loss rate of the TGR area decreased from 171.09 kg/km2 in 1990 to 108.81 kg/km2 in 2015. The nitrogen loss reduced significantly after the implementation of the reforestation project in particular. The spatial analysis demonstrated that the variation of nitrogen loss was positively related to annual total precipitation, annual mean temperature, the proportion of developed land, elevation and slope, but was negatively related to the surface height fluctuation and soil pH. The scenario analysis showed that the land use changes in the TGR area effectively control the non-point source pollution, which could provide some references for the watershed management of water sacurity. Forest restoration would reduce the nitrogen loss by 3.76 × 106 kg, while urbanization would aggravate the nitrogen loss with the annual amount of 0.20 × 105 kg for the whole TGR area. These results demonstrated significant differences in the impact of various land use patterns on nonpoint source pollution and regional water security, providing a theoretical basis for policy decisions and regional ecosystem management. To properly handle the relationship between environmental protection and economic development in ecologically fragile areas, we made some land use proposals such as reducing the discharge of industrial wastewater and the abuse of high nitrogen fertilizers. We also designed a landscape planning scheme regarding revegetation in the intermittent streams and water-level-fluctuation zone, thus improving regional water security in the TGR area.

Microswimmers near corrugated, periodic surfaces.

We explore hydrodynamic interactions between microswimmers and corrugated, or rough, surfaces, as found often in biological systems and microfluidic devices. Using the Lorentz reciprocal theorem for viscous flows we derive exact expressions for the roughness-induced velocities up to first order in the surface-height fluctuations and provide solutions for the translational and angular velocities valid for arbitrary surface shapes. We apply our theoretical predictions to elucidate the impact of a periodic, wavy surface on the velocities of microswimmers modeled in terms of a superposition of Stokes singularities. Our findings, valid in the framework of a far-field analysis, show that the roughness-induced velocities vary non-monotonically with the wavelength of the surface. For wavelengths comparable to the swimmer-surface distance a pusher can experience a repulsive contribution due to the reflection of flow fields at the edge of a surface cavity, which decreases the overall attraction to the wall.

Cera alba-assisted ultraclean graphene transfer for high-performance PbI2 UV photodetectors

Large polymer residues introduced by the graphene transfer process is still a major obstacle limiting the integration of chemical vapor deposition (CVD)-grown graphene into next-generation electronic and photoelectronic devices. Here we use cera alba, a natural and environmental-friendly material that derives from honeycomb, as the supporting layer for ultraclean graphene transfer. The transferred graphene has a low surface roughness with a surface height fluctuation within 5 nm and an only 80.08% average sheet resistance of the polymethyl methacrylate (PMMA)-transferred graphene. Further, the ultraclean graphene is used as electrodes for the PbI2-based UV photodetector and enables a 135% improvement on responsivity. The cera alba assisted transfer method reported here could achieve clean and damage-free graphene transfer, promoting the application of CVD-grown two-dimensional (2D) materials in large-area thin-film electronic and optoelectronic devices.

Analyzing the fractal feature of nickel thin films surfaces modified by low energy nitrogen ion

SummaryFractal concepts are used to explore how different energies (10, 20 and 50 keV) and fluence of 5 × 1017 N+ cm−2 affect the morphology of nickel thin film. The nickel thin film with thickness of 100 nm is prepared by electron beam evaporation technique at room temperature on stainless steel (AISI 316) substrates. The nanoscale three‐dimensional (3‐D) surface micro‐morphologies are investigated by atomic force microscopy (AFM). Interface width is used to describe the surface height fluctuations. The autocorrelation function with height‐height correlation function give the quantitative data about the morphology of surface. The value of roughness exponent and fractal dimension is computed by height‐height correlation function. Fractal measure is an important analysis which provides fundamental insights into the texture characteristics and a direct way of testing their functional role.

Immotile Active Matter: Activity from Death and Reproduction.

Unlike equilibrium atomic solids, biofilms-soft solids composed of bacterial cells-do not experience significant thermal fluctuations at the constituent level. However, living cells stochastically reproduce and die, provoking a mechanical response. We investigate the mechanical consequences of cellular death and reproduction by measuring surface-height fluctuations of biofilms containing two mutually antagonistic strains of Vibrio cholerae that kill one another on contact via the type VI secretion system. While studies of active matter typically focus on activity via constituent mobility, here, activity is mediated by reproduction and death events in otherwise immobilized cells. Biofilm surface topography is measured in the nearly homeostatic limit via white light interferometry. Although biofilms are far from equilibrium systems, measured surface-height fluctuation spectra resemble the spectra of thermal permeable membranes but with an activity-mediated effective temperature, as predicted by Risler, Peilloux, and Prost [Phys. Rev. Lett. 115, 258104 (2015)PRLTAO0031-900710.1103/PhysRevLett.115.258104]. By comparing the activity of killer strains of V. cholerae with that of genetically modified strains that cannot kill each other and validating with individual-based simulations, we demonstrate that extracted effective temperatures increase with the amount of death and reproduction and that death and reproduction can fluidize biofilms. Together, these observations demonstrate the unique physical consequences of activity mediated by death and reproduction events.

Surface switching statistics of rotating fluid: Disk-rim gap effects.

We examined the influence of internal noise on the irregular switching of the shape of the free surface of fluids in an open cylindrical vessel driven by a bottom disk rotating at constant speed [Suzuki, Iima, and Hayase, Phys. Fluids 18, 101701 (2006)PHFLE61070-663110.1063/1.2359740]. A slight increase in the disk-rim gap (less than 3% of the disk radius) was established experimentally to cause significant changes in this system, specifically, frequent appearance of the surface descending event connecting a nonaxisymmetric shape in strong mixing flow (turbulent flow) and an axisymmetric shape in laminar flow, as well as a shift in critical Reynolds number that define the characteristic states. The physical mechanism underlying the change is analyzed in terms of flow characteristics in the disk-rim gap, which acts as a noise source, and a mathematical model established from measurements of the surface height fluctuations with noise term.

Random fractal surface analysis of disordered organic thin films

Study of surface morphologies reveals useful information about interfacial contacts and materials properties such as charge carrier mobility, optical absorption and adhesion that directly affect system performance. The total effective interface area and root mean square (rms) of surface height fluctuations are among the common parameters often used to corroborate device performance upon surface modification. In this paper, random fractal surface analysis is used to characterize geometrical features of microstructure morphologies in disordered organic nickel tetrasulfonated phthalocyanine (NiTsPc) films under different solvent treatment. The different but complementary approaches are used, namely the power spectral density analysis, variogram method based on generalized Cauchy process (GCP) and grayscale fractal box counting approach. It is shown that each of these approaches offers certain perspective about the complex morphologies often found in disordered thin films and thus joint interpretation of these approaches offer better characterization of the surface properties, filling the gap left by others. The morphologies are also interpreted in the context of percolation network supported by the photocurrent density measurements.

Surface Fluctuations of Polymer Brushes Swollen in Good Solvent Vapor

Swollen polymer brushes are found in various applications including biomedical coatings where the brush provides stability against harsh environmental conditions and mediates interactions with the surroundings. The surface height fluctuations of planar polystyrene brushes (0.04–0.61 chains/nm2) highly swollen in toluene vapor are so strongly slowed by the tethering of the chains that they are unobservable in the current experimental window of length and time. This is the case despite the fact that the segmental dynamics of the brush chains should be very fast due to the substantial plasticization by the solvent. With respect to thermally stimulated fluctuations, the surfaces of these swollen brushes are solidlike on time scales and length scales pertinent to many practical applications.

Lagrangian Surface Wave Motion and Stokes Drift Fluctuations

AbstractNonlinear effects in Lagrangian sea surface motions are important to understanding variability in wave-induced mass transport, wave-driven diffusion processes, and the interpretation of measurements obtained with moored or free-drifting buoys. This study evaluates the Lagrangian vertical and horizontal motions of a particle at the surface in a natural, random sea state using second-order, finite-depth wave theory. In deep water, the predicted low-frequency (infragravity) surface height fluctuations are much larger than Eulerian bound wave motions and of the opposite sign. Comparison to surface elevation bispectra observed with a moored buoy in steady, high-wind conditions shows good agreement and confirms that—in contrast to the Eulerian sea surface motion with predominant phase coupling between the spectral peak and double-frequency harmonic components—nonlinearity in Lagrangian wave observations is dominated by phase-coupled infragravity motions. Sea surface skewness estimates obtained from moored buoys in deep and shallow sites, over a wide range of wind–sea and swell conditions, are in good agreement with second-order theory predictions. Theory and field data analysis of surface drift motions in deep water reveal energetic [O(10) cm s−1] infragravity velocity fluctuations that are several orders of magnitude larger and 180° out of phase with Eulerian infragravity motions. These large fluctuations in Stokes drift may be important in upper-ocean diffusion processes.

Effect of tethering on the surface dynamics of a thin polymer melt layer.

The surface height fluctuations of a layer of low molecular weight (2.2k) untethered perdeuterated polystyrene (dPS) chains adjacent to a densely grafted polystyrene brush are slowed dramatically. Due to the interpenetration of the brush with the layer of "untethered chains" a hydrodynamic continuum theory can only describe the fluctuations when the effective thickness of the film is taken to be that which remains above the swollen brush. The portion of the film of initially untethered chains that interpenetrates with the brush becomes so viscous as to effectively play the role of a rigid substrate. Since these hybrid samples containing a covalently tethered layer at the bottom do not readily dewet, and are more robust than thin layers of untethered short chains on rigid substrates, they provide a route for tailoring polymer layer surface properties such as wetting, adhesion and friction.

STUDY ON THE CORRECT TILT OF THE NAVIGATION OF AGRICULTURAL MACHINERY BASED ON GPS

In recent years, the development of GPS navigation technology is very fast, has been applied to almost everywhere in life, especially in the field of agricultural production in recent years is more important. In foreign countries, GPS navigation application in agricultural production development has been very mature, but in China, the application of GPS in agricultural machinery navigation is still in the stage of research and development, application in agricultural machinery navigation, the GPS navigation technology to achieve accurate positioning: the most important thing is to tilt, lateral posture correction, pure line operation and a series of work based on path tracking. The GPS carrier phase measurement technology, static positioning can not only realize agricultural accurate and real-time dynamic positioning; but also can achieve high-precision attitude measurement based on observation of carrier phase receiver. Through the vector in the process of operation because of the navigation error of surface height fluctuation generated by the tilt correction algorithm, can be derived on the agricultural machinery navigation correction, because in the process of agricultural navigation operation, positioning error vector produced by the inclination will directly affect the pure path tracking algorithm based on the trajectory of the straight line thus, effects of mechanization and efficiency of intelligent agricultural production, so the research of calibration for the error caused by the tilt is of great significance. Considering the difficulty of the experiment, our research is a double side antenna attitude, so in the original location of the next step is to collect model cars some simulation of agricultural operations process data, and then use MATLAB to carry out simulation on the PC machine, according to before and after correction for the navigation of agricultural machinery industry to observe the trajectory correction effect. .

Asymptotics of uniformly random lozenge tilings of polygons. Gaussian free field

We study large-scale height fluctuations of random stepped surfaces corresponding to uniformly random lozenge tilings of polygons on the triangular lattice. For a class of polygons (which allows arbitrarily large number of sides), we show that these fluctuations are asymptotically governed by a Gaussian free (massless) field. This complements the similar result obtained in Kenyon [Comm. Math. Phys. 281 (2008) 675-709] about tilings of regions without frozen facets of the limit shape. In our asymptotic analysis we use the explicit double contour integral formula for the determinantal correlation kernel of the model obtained previously in Petrov [Asymptotics of random lozenge tilings via Gelfand-Tsetlin schemes (2012) Preprint].

Grain boundary crack growth in metastable titanium β alloys

Ductile crack growth in a grain boundary layer is modeled under mode I plane-strain, small-scale yielding conditions. The calculations are carried out for planar polycrystals using an elastic–viscoplastic constitutive relation for a progressively cavitating solid with two populations of void nucleating second-phase particles. The material properties in the grain boundary layers are taken to be representative of those for the α phase boundaries in metastable Ti β alloys, while the grain properties are homogenized representations of the grain properties in such alloys. Void nucleation is taken to occur rather early in the deformation history in the grain boundary α phase layers by a stress-controlled nucleation criterion. Subsequent strain-controlled void nucleation occurs within the grains as well as in the grain boundary α layers. The effects of grain flow strength, average grain size, grain morphology and grain boundary α layer continuity on the crack growth resistance and on the plastic dissipation during fracture are considered. The main effects on the crack growth resistance are found to be the grain morphology and the α layer continuity. The fracture surface roughness is characterized in terms of the fracture surface height fluctuations and the computed small-scale regime Hurst exponents in the crack growth direction are consistent with the “universal” values found for other materials and loading conditions. A model for the estimation of the crack growth resistance is also presented. The model gives a very good representation of the crack growth resistance when crack branching does not occur. The model also shows that the crack path taken in the calculations is not necessarily the path of least resistance.

Seasonal barotropic sea surface height fluctuation in relation to regional ocean mass variation

A consistency between seasonal fluctuation of actual sea surface height (SSH) and those caused by mass and density variations in gyre-scale regions is examined. The SSH obtained from satellite altimetry (altimetric SSH) is adopted as the actual SSH. SSH caused by mass variation (mass-related SSH) is simulated using a barotropic global ocean model forced by water flux, wind stress and surface pressure. SSH caused by density variation (steric SSH) is calculated from water density profile, i.e. temperature and salinity profiles. The model SSH well represents mass-related SSH for gyre-scale regional means, and seasonal fluctuation of the altimetric SSH corrected for the model SSH is similar to that of steric SSH above a pressure level larger than 300 dbar. The results indicate that the mass-related SSH does not much respond to the baroclinic adjustment to the seasonally varying wind stress curl. The mass-related SSH forced by wind stress and surface pressure should be accounted for regional evaluation, though it is not necessary for global mean evaluation. Detection of steric SSH from altimetric SSH would be useful for assimilation approaches in which the altimetric SSH is treated as the variable reflecting subsurface temperature and salinity.

Stochastic and fractal properties of silicon and porous silicon rough surfaces

In this paper, we investigate the stochastic properties and fractal behavior of Si and porous silicon (PS) rough surfaces to characterize the complexity of their morphology. To this end, height fluctuations of these rough surfaces are determined by Atomic Force Microscopy (AFM) and then roughness and correlation length of the surfaces are calculated. The generalized Hurst exponent, h(q) and singularity spectrum, f(α) are obtained by using two dimensional MF-DFA method for both rough surfaces; Our results show that both mentioned surfaces are multifractal and have different scaling exponents. To investigate the reason of the observed multifractality behavior, we determine height distribution, skewness and kurtosis measures and show that the deviation from the Gaussian distribution for the height fluctuations of the surfaces can be a reason for the observed multifractality behavior.

Smoothness assessment of corneal stromal surfaces

To assess the accuracy of the scanning electron microscopy (SEM) and present alternative approaches to quantify surface roughness based on numerical analysis. Department of Ophthalmology, Maisonneuve-Rosemont Hospital, University of Montreal, Montreal, Quebec, Canada. Experimental study. Lamellar stromal cuts were performed on human corneas using a femtosecond laser or a microkeratome. The photodisrupted stromal surfaces were processed for SEM, and images were acquired at ×1000 magnification. First, images were evaluated by independent observers. Second, images were analyzed based on first-order and second-order statistics of gray-level intensities. Third, 3-dimensional (3-D) surface reconstructions were generated from pairs of SEM images acquired at 2 angles. Results show that traditional assessment of roughness based on evaluating SEM images by independent observers can be replaced by computer-image texture analysis; an algorithm was developed to avoid subjective and time-consuming observations. The 3-D reconstructions allowed additional characterization of surface properties that was not possible with SEM images alone. Significant fluctuations in surface height were lost, although they could be retrieved using 3-D reconstructions. Image texture analysis allowed objective and repeatable assessment of stromal surface roughness; however, full assessments of surface-height fluctuations required 3-D reconstruction. These complementary methodologies offer a more comprehensive assessment of corneal surface roughness in clinical applications.