Unsteady Surfaces Research Articles

Morphological effect of fabricated surfaces obtained from fluorinated porphyrin based copolymer for oxygen and pressure sensing applications

Good oxygen sensitivity and fast response of oxygen probe is primary requirement for pressure sensing applications. Therefore in this study, porphyrin based new fluorinated oxygen probe (OP) monomer was synthesized and copolymerized with 2-(3-(6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl)ureido)ethyl methacrylate (SCMHBMA), octafluoropentyl methacrylate (OCFPM) and butyl acrylate (BA). SCMHBMA may play important biological role in cell adhesion. OCFPM and BA were used as fluorinated and non-fluorinated monomers, respectively. The synthesized oxygen sensitive copolymer (OSC) was used to fabricate spin coated film and membranes of electrospun beaded nanofibers and only nanofibers. Morphological effect of fabricated surfaces was evaluated in terms of oxygen sensitivity, response time and pressure sensitivity. The surface of beaded nanofibers was considered transition state between plain spin coated films surface and fibrous membrane. Nanofibers membrane showed highest oxygen sensitivity (I0/I 36.7) and pressure sensitivity (0.92 %) among all the surfaces. Moreover, nanofibers membrane exhibited fast response to oxygen (t95% 0.6 s). Moreover, the electrospun nanofiber membrane was found biocompatible by inherent culture of HeLa cells. Hence, the fabricated membranes may find applications in pressure mapping of biological systems and unsteady surfaces.

A Hemispherical Motor Oscillator for Experiments on Swimming and Flying of Small Animals

The propulsors of organisms from paramecia to dolphins have ball-and-socket jointed bases that allow large-amplitude, low-friction swings. Their olivo-cerebellar control also remains unchanged. Yet, the propulsive surfaces of small animals vary widely from flagellar filaments (0 < Re < 5) to flapping fins (Re > 20) with an intermediate range of Reynolds number (5 < Re < 20) where both types are present in the same swimming animal. Analysis suggests that these unsteady surfaces are mechanical oscillators coupled to their nonlinear wakes. A low-friction-driven oscillator that can interact with the oscillators of models or live swimming and flying animals could help us understand the hydro-structural events prompting the evolution of such surfaces at specific Re values. A gearless underdamped (in air) hemispherical motor oscillator is described where energetic efficiency increases by a factor of eight as the forces drop by a factor of ten from 10 N. The electrical efficiencies at 0.8 N are comparable to the total thermal efficiencies of flies, and the quality factor is comparable. The continuously varying fin oscillation of penguin fins and abruptly varying fin oscillations of Clione antarctica and flies are reproduced. When flapping at 0.3 Hz, the oscillator would respond to all wake nonlinearities. Abrupt fin turning is modeled by switching the roll and pitch phase difference between −π/2 and π/2 in successive quadrants. Defining the fish-wake lock-in error as the difference between Triantafyllou's fish Strouhal number and the tangent of the vortex-shedding angle, an experiment is discussed for measuring the minimum drag of live fish.

Standing balance on unsteady surfaces in children on the autism spectrum: The effects of IQ

BackgroundPostural stability difficulties are commonly reported in people on the autism spectrum. However, it is unclear whether unsteady surfaces may exacerbate postural stability difficulties in children and adolescents with autism spectrum disorder (ASD). Understanding balance on unsteady surfaces is important because uneven surfaces are commonly encountered in daily life. MethodsTwenty-one youth on the autism spectrum and 16 youth with typical development (ages 6–16 years, IQ ≥ 79) stood on both a fixed and unsteady (tiltable) platform, and center of pressure was measured. ResultsThe group with ASD exhibited differentially more postural sway on the unsteady surface compared to the group with typical development. However, there was substantial variability within the ASD group. Follow-up analyses suggested that much of the variability in postural sway in the ASD group was accounted for by IQ. ConclusionsClinically, these findings suggest that not all individuals with ASD struggle more with postural stability on unsteady surfaces. Instead children and adolescents with ASD and below-average IQ may have particular difficulty on unsteady surfaces and may require accommodations. Further, these findings lay the groundwork for future research to investigate the underlying mechanisms of poorer balance across the autism spectrum.

Trunk muscle activation characteristics in patients with severe haemophilia.

Recurrent bleeding episodes in patients with haemophilia (PWH) lead to joint alterations and therewith disturbed muscle coordination patterns. Major weight-bearing joints are affected most. However, possible effects on trunk muscle activity have not been examined so far. The objective of this work was to study consequences of haemarthropathy on characteristics of trunk muscles in PWH while standing on surfaces with different mechanical properties. Surface EMG of internal oblique (IO) and multifidus (MF) muscles were bilaterally recorded during a natural bilateral stance in 20 PWH with severe haemophilia A [age: 42 years (SD: 10)] and 25 non-haemophilic controls [NHC, 43 (12)]. Amplitude ratios, a symmetry index between sides and the co-activation ratio of IO over MF served as outcome measures and compared standing on three different surfaces (stable, soft, unsteady). PWH revealed markedly restricted lower extremity joints (P < 0.001), but without any hint of back pain. Neither result revealed significant main or interaction effects of 'group' (P > 0.24). Group-independent analyses showed amplitude ratios (MF: P < 0.05) as well as symmetry indices (MF: P < 0.02) significantly altered by 'surface' in NHC only. Effects of utilizing soft vs. unsteady surfaces were not detectable (P > 0.77). Utilizing unstable surfaces does not lead to altered trunk muscle activity in PWH. Differently than expected, a quite similar behaviour of lower trunk muscles in terms of applied indices can be found in PWH and NHC. Ascending alterations of muscle coordination in PWH could not be verified.

Prevalence and Impact of Bilateral Vestibular Hypofunction

Profound bilateral vestibular hypofunction (BVH) causes disabling oscillopsia, chronic disequilibrium, and postural instability, but little is known about its epidemiology and impact. To assess prevalence and functional impact of BVH in the US adult population. National cross-sectional survey using a national database and corollary validation study. Adult respondents to the 2008 Balance and Dizziness Supplement to the US National Health Interview Survey (N = 21 782). Prevalence of BVH, socioeconomic and quality-of-life impact of BVH, and fall risk. Criteria for the survey-based diagnosis of BVH included all of the following: presence of visual blurring with head movement; unsteadiness; difficulty walking in darkness or unsteady surfaces and in a straight path; and symptoms being at least "a big problem" and present for at least 1 year, in the absence of other neurologic conditions or eye pathologic conditions affecting vision. Adjusted national estimates from this survey indicate the prevalence of BVH in 2008 was 28 per 100 000 US adults (64 046 Americans). Of the participants with BVH, 44% reported changing their driving habits because of their symptoms, 56% reported reduced participation in social activities, and 58% reported difficulties with activities of daily living. Respondents with BVH had a 31-fold increase in the odds of falling in multivariate analyses compared with all respondents, with 25% reporting a recent fall-related injury. As estimated by the presence of specific symptoms in a nationally representative survey, BVH has considerable socioeconomic and quality-of-life impacts and significantly increases fall risk. These data support the need for new therapeutic strategies for BVH, including vestibular rehabilitation and implantable vestibular prostheses.

The effects of viscosity on sound radiation near solid surfaces

AbstractAlthough the acoustic analogy developed by Lighthill, Curle, and Ffowcs Williams and Hawkings for sound generation by unsteady flow past solid surfaces is formally exact, it has become accepted practice in aeroacoustics to use an approximate version in which viscous quadrupoles are neglected. Here we show that, when sound is radiated by non-rigid surfaces, and the smallest dimension is comparable to or less than the viscous penetration depth, neglect of the viscous-quadrupole term can cause large errors in the sound field. In addition, the interpretation of the viscous quadrupoles as contributing only to sound absorption is shown to be inaccurate. Comparisons are made with the scalar wave equation for linear waves in a viscous fluid, which is extended using generalized functions to describe the effects of solid surfaces. Results are also presented for two model problems, one in a half-space and one with simple cylindrical geometry, for which analytical solutions are available.

Numerical solving of incompressible Navier-Stokes equations using an original local multigrid refinement method

Numerical simulation of complex flows involving unsteady structures, boundary layers or free surfaces on a unique grid is very greedy in time and CPU because a great number of calculation point is needed to ensure a satisfactory description of the different scales of the problem. An original local multigrid method, able to refine the grid at the cell scale, is proposed to solve the Navier-Stokes and energy equations. The results obtained for the natural convection in a square cavity are compared to the one of the literature for Rayleigh numbers in the range 10 5–10 8.

Integral membrane heparan sulfate proteoglycans

Heparan sulfate is a regulatory polysaccharide. It modulates specific growth factor-receptor interactions, accelerates the formation of specific proteinase-proteinase inhibitor complexes, and mediates interactions of the cell surface with several enzymes and structural proteins. It abounds on the surfaces of embryonic cells, respecting or outlining morphogenetic rather than histological boundaries. This cell surface-associated heparan sulfate is implanted on specific integral membrane proteins, which together constitute two novel molecular families. The first family includes four syndecan-like integral membrane proteoglycans (SLIPS), with core proteins that span the membrane and shared sequence motifs in highly conserved cytoplasmic domains. The second is made up by two or more glypican-related integral membrane proteoglycans (GRIPS) that are linked to the cell surface via glycosyl phosphatidylinositol. These proteoglycans show differential expression and turnover patterns, prevailing in distinct cell types, membrane domains, and endocytotic machineries, and are subject to strict developmental controls. This suggests that each of these cell surface proteoglycans functions in a specific context, and that these functions pertain to the transduction of signals that emanate from the continuous interplay between matrix components, growth factors, and proteinases. Caution: beware of loose GRIPS and SLIPS on unsteady cell surfaces.

Three-dimensional unsteady Euler equations solution on dynamic grids

A method is presented for solving the three-dimensional unsteady Euler equations on dynamic grids based on flux vector splitting. The equations are cast in curvilinear coordinates and a finite volume discretization is used for handling arbitrary geometries. The discretized equations are solved using an explicit upwind second-order predictor corrector scheme that is stable for a CFL of 2. Characteristic variable boundary conditions are developed and used for unsteady impermeable surfaces and for the far-field boundary. Dynamic-grid results are presented for an oscillating air-foil and for a store separating from a reflection plate. For the cases considered of stores separating from a reflection plate, the unsteady aerodynamic forces on the store are significantly different from forces obtained by steady-state aerodynamics with the body inclination angle changed to account for plunge velocity.

亜音速非定常揚力面数値計算法（ＢＩＳ） ＩＩＩ 計算結果続報

This paper presents some additional numerical results to our previous papers, concerning about a new computation method for unsteady subsonic lifting surfaces, BIS (Box-in-Strip). It consists of two parts. The one is comparisons between BIS and PCKFM (Piecewise Continuous Kernel-Function Method), which seems to be appreciated as an excellent method in USA. The other is comparisons between BIS and analytical solutions for circular and/or elliptic planform wings in steady incompressible flow. As a result, it is found that PCKFM yields fairly close results to BIS in the case of the rectangular wing with AR=10 and that correlation between BIS and analytical solutions is much more excellent than VLM. Thus we confirmed again the superiority of BIS over VLM.

亜音速非定常揚力面計算法（ＢＩＳ） ＩＩ 数値計算結果

This paper concerns with numerical evaluation of a new computation method for unsteady subsonic lifting surfaces, BIS (Box-In-Strip), the formulation of which was reported minutely in our previous paper. The numerical results of BIS-QS, a refined version, are compared with those of DLM (DoubletLattice Method) and DPM (Doublet-Point Method). Three kinds of wing planform, designated as Wing R, H, and E are used for evaluating these schemes. A new criterion is used on Wing R (rectangular planform); comparison is made between the pressure distribution at the root chord of a high aspect ratio wing and that of 2-dimensional airfoils, besides the "Error-Index" is used which has been developed by our laboratory previously. The Wing H has leading and trailing edges of a smooth hyperbolic curve, while the Wing E has a swept-tapered planform and so a kink at the midspan. It is found that the convergence and accuracy of BIS-QS are superior to DLM significantly and to DPM remarkably, without increasing computation cost, even for high frequency and high subsonic Mach number.

亜音速非定常揚力面計算法（ＢＩＳ） Ｉ 定式化

A new numerical method is formulated which belongs in discrete ones rather than mode methods of unsteady subsonic lifting surfaces. This may be said a final form (revision and extension) of the DSM (Doublet Strip Method). After integrating spanwise first the kernel function across a narrow chordwise strip, there appear just similar singular terms as in the DLM-C for two-dimensional airfoils. Thus Mangler's principal value can be avoided. The following chordwise quadrature may be carried out efficiently as in the DLM-C developed by our laboratory in past. This new method is designated as BIS (Box-in-Strip) method. Authors' basic thought is stated concerning about the reason for being of efficient linearized lifting surface methods, especially at high reduced frequencies and high subsonic Mach numbers. It is often not wellunderstood in our country. It is noted that results obtained through lifting surface methods may have significant influences into some other numerical schemes, such as Surface Singularity Method.

Improved numerical method for unsteady lifting surfaces in incompressible flow

y0 6 An improved numerical method has been developed for unsteady thin rectangular wings in incompressible flow. To satisfy the wing boundary conditions, the spanwise pressure distribution is assumed to be stepwise constant, while the chordwise integral is reduced to a finite sum using several kinds of quadratures; Cauchy and logarithmic singularities are treated appropriately. The present method gives excellent results over a wide range of reduced frequency k (k = 0.0-5.0) within reasonable computer time. Extension to compressible flow and to swept tapered wings applications is discussed briefly.

Expansion series of integral functions occurring in unsteady aerodynamics

Attention is given to two real integral functions which occur in the kernel of singular integral equations for subsonic unsteady lifting surfaces. The arguments k, r, and X of the functions correspond to the reduced frequency, spanwise distance, and modified coordinate in the flow direction, respectively. The value of the parameter nu in the functions depends on geometrical conditions. The considered investigation has the objective to present a series for general values of the nonnegative integer nu in order to compute efficiently the integral functions. The approach makes it possible to avoid any approximation or numerical quadrature.

Some remarks on lifting surface theory

This paper gives a brief review of the theory of unsteady lifting surfaces as applied to ships' propellers. The possibilities and limitations of this theory are discussed, together with some results recently obtained by different authors. Mathematical methods of solution and their implications will be avoided wherever possible. The accurate measurement of unsteady forces acting on a propeller is rather difficult. Some investigations have been performed and the results of these are compared with results obtained with the lifting surface theory. Further systematic investigations are necessary and some suggestions for these are given.