Vacuum Forces Research Articles

Vacuum-assisted vaginal delivery simulation – quantitation of subjective measures of traction and detachment forces

Objective: Excessive traction has been alleged as the cause of newborn complications associated with vacuum delivery. We sought to quantify subjective levels of physician vacuum traction in a simulated obstetric delivery model, dependent upon level of training. Methods: Three groups of physicians, based on training level applied traction (minimal, average, maximal) on a pre-applied vacuum model and forces were continually recorded. Detachment force was recorded with traction in both the pelvic axis and at an oblique angle. Results: Quantified traction force increased from subjective minimal to average to maximal pulls. Within each level, there were no differences between the groups in the average traction force. Detachment force was significantly less when traction was applied at an oblique angle as opposed to the pelvic axis (11.1 ± 0.3 vs 12.2 ± 0.3 kg). Conclusion: Providers appear to be good judges of the force being applied, as a clear escalation in force is noted with minimal, average and maximal force pulls. There appears to be a relatively short learning curve for use of the vacuum, as junior residents’ applied force was not different from those of more experienced practitioners. Using the KIWI device, detachment force is lower when traction is applied at an oblique angle.

REPULSIVE CASIMIR EFFECTS

Like Casimir's original force between conducting plates in vacuum, Casimir forces are usually attractive. But repulsive Casimir forces can be achieved in special circumstances. These might prove useful in nanotechnology. We give examples of when repulsive quantum vacuum forces can arise with conducting materials.

Exact solution for the Casimir stress in a spherically symmetric medium

We calculated the force of the quantum vacuum, the Casimir force, in a spherically symmetric medium, Maxwell's fish eye, surrounded by a perfect mirror and derived an exact analytic solution. Our solution questions the idea that the Casimir force of a spherical mirror is repulsive - we found an attractive force that diverges at the mirror.

Study on the Force of Flexible Vacuum Cup Fixture for Aircraft Skin Trimming

When the aircraft skin is in the process of trimming and on the flexible vacuum cup fixture, by analyzing the stress to the aircraft skin and studying the relationship between vacuum pressure and deformation of aircraft skin, vacuum pressure, vacuum force and cutting parameters, the relationship which between vacuum pressure of flexible fixture and cutting parameters, clamping points of flexible fixture, friction coefficient of cup and aircraft skin, the maximum deformation allowed on aircraft skin is obtained. It provides a methodology to improve the precision of trimming of aircraft skin components.

Nanofretting behaviours of ultrathin DLC coating on Si(100) substrate

Abstract Due to its excellent mechanical properties and stable chemical behaviours, the diamond-like carbon (DLC) coating has been extensively used as a low-frictional and wear-resistant protective coating in MEMS. However, its efficacy on resisting nanofretting damage of silicon substrate needs to be verified. With an atomic force microscopy, the nanofretting behaviours of ultrathin DLC coating and its Si(1 0 0) substrate against SiO2 microsphere were investigated under vacuum and air conditions. The applied normal load Fn was 2 μN and the displacement amplitudes ranged from 0.5 nm to 100 nm. The experimental results indicated that the DLC coating revealed a strong effect on the nanofretting regime, adhesion force, friction force and nanofretting damage of Si(1 0 0)/SiO2 pairs. Either in vacuum or in air condition, the coating could expand the slip regime of Si(1 0 0)/SiO2 pairs into a lower value of displacement amplitude. Owing to the absence of oxygen and water molecule in vacuum, both the adhesion and friction forces on DLC coating were similar as those on Si(1 0 0) substrate. However, while the nanofretting ran in air, the DLC coating could significantly reduce the adhesion and friction forces of Si(1 0 0) substrate. Even though the coating was only 2 nm in thickness, it could effectively protect the silicon substrate from nanofretting damage. In vacuum, the ultrathin DLC coating can prevent the formation of hillock on Si(1 0 0) substrate. In air, the wear depth on DLC coating was

Casimir-Polder repulsion near edges: Wedge apex and a screen with an aperture

Although repulsive effects have been predicted for quantum vacuum forces between bodies with nontrivial electromagnetic properties, such as between a perfect electric conductor and a perfect magnetic conductor, realistic repulsion seems difficult to achieve. Repulsion is possible if the medium between the bodies has a permittivity in value intermediate to those of the two bodies, but this may not be a useful configuration. Here, inspired by recent numerical work, we initiate analytic calculations of the Casimir-Polder interaction between an atom with anisotropic polarizability and a plate with an aperture. In particular, for a semi-infinite plate, and, more generally, for a wedge, the problem is exactly solvable, and for sufficiently large anisotropy, Casimir-Polder repulsion is indeed possible, in agreement with the previous numerical studies. In order to achieve repulsion, what is needed is a sufficiently sharp edge (not so very sharp, in fact) so that the directions of polarizability of the conductor and the atom are roughly normal to each other. The machinery for carrying out the calculation with a finite aperture is presented. As a motivation for the quantum calculation, we carry out the corresponding classical analysis for the force between a dipole and a metallic sheet with a circular aperture, when the dipole is on the symmetry axis and oriented in the same direction.

Vacuum polarization by a flat boundary in cosmic string spacetime

In this paper, we analyze the vacuum expectation values of the field squared and the energy–momentum tensor associated with a massive scalar field in a higher dimensional cosmic string spacetime, obeying Dirichlet or Neumann boundary conditions on the surface orthogonal to the string. In order to develop this analysis, the corresponding Green's function is obtained. The Green's function is given by the sum of two expressions: the first one corresponds to the standard Green's function in the boundary-free cosmic string spacetime and the second contribution is induced by the boundary. The boundary-induced parts have opposite signs for Dirichlet and Neumann scalars. Because the analysis of vacuum polarization effects in the boundary-free cosmic string spacetime has been developed in the literature, here we are mainly interested in the calculations of the effects induced by the boundary. In this way closed expressions for the corresponding expectation values are provided, as well as their asymptotic behavior in different limiting regions being investigated. We show that the non-trivial topology due to the cosmic string enhances the boundary-induced vacuum polarization effects for both the field squared and the energy–momentum tensor, compared to the case of a boundary in Minkowski spacetime. The presence of the cosmic string induces non-zero stress along the direction normal to the boundary. The corresponding vacuum force acting on the boundary is investigated.

Theoretical and experimental study of the performance of flat suction cups in the presence of tangential loads

Abstract Suction cups are used extensively throughout the packaging industry, as well as most other fields of robotics. In this present work, by means of a theoretical and experimental approach, the minimum value of the vacuum force and the adhesion coefficient able to guarantee the grasp and movement of the object with suction cups have been studied. Using a special test rig, experimental measurements regarding the slipping conditions obtained by stressing plates grasped by a flat suction cup with tangential forces and torque have been carried out. The experimental results have been compared with those obtained from a theoretical model in two suction cup–object contact pressure hypotheses (edge contact and full contact).

Casimir force between integrable and chaotic pistons

We have computed numerically the Casimir force between two identical pistons inside a very long cylinder, considering different shapes for the pistons. The pistons can be considered as quantum billiards, whose spectrum determines the vacuum force. The smooth part of the spectrum fixes the force at short distances, and depends only on geometric quantities like the area or perimeter of the piston. However, correcting terms to the force, coming from the oscillating part of the spectrum which is related to the classical dynamics of the billiard, are qualitatively different for classically integrable or chaotic systems. We have performed a detailed numerical analysis of the corresponding Casimir force for pistons with regular and chaotic classical dynamics. For a family of stadium billiards, we have found that the correcting part of the Casimir force presents a sudden change in the transition from regular to chaotic geometries.

Development of a Wall Climbing Robot

Problem statement: The problem of a wall climbing robot is holding on the wall. This is challenge for researchers. There are many factors, which effect in holding, all forces, robot movement and mechanical design. Approach: This study proposed movement step design for wall-climbing robot. In design the robot use pneumatic system as main unit to move on the wall. The robot can move in four directions, forward, backward, left and right. Results: We analyzed force acting with the wall that the wall should have only slope from 0° (parallel with the ground) to 90° (vertical line). At equilibrium condition, we expressed all forces in equilibrium by sum all forces that equal zero. Conclusion: We can choose parameter to improve the climbing efficiency that the robot can climb much slope. For the first way, we can change the wall material to increase μs and for the second way, we can improve vacuum force by means of increasing pneumatic system efficiency.

Heparinized hydroxyapatite/collagen three-dimensional scaffolds for tissue engineering

Currently, in bone tissue engineering research, the development of appropriate biomaterials for the regeneration of bony tissues is a major concern. Bone tissue is composed of a structural protein, collagen type I, on which calcium phosphate crystals are enclosed. For tissue engineering, one of the most applied strategies consists on the development and application of three dimensional porous scaffolds with similar composition to the bone. In this way, they can provide a physical support for cell attachment, proliferation, nutrient transport and new bone tissue infiltration. Hydroxyapatite is a calcium phosphate with a similar composition of bone and widely applied in several medical/dentistry fields. Therefore, in this study, hydroxyapatite three dimensional porous scaffolds were produced using the polymer replication method. Next, the porous scaffolds were homogeneously coated with a film of collagen type I by applying vacuum force. Yet, due to collagen degradability properties, it was necessary to perform an adequate crosslinking method. As a result, N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) was employed as an efficient and non-toxic crosslinking method in this research. The composites were characterized by means of SEM, DSC and TNBS. Furthermore, heparin was incorporated in order to accomplish sustained delivery of a growth factor of interest namely, bone morphogenetic proteins (BMP-2). BMP-2 binding and release of non-heparinized and heparinized scaffolds was evaluated at specific time points. The incorporation of heparin leads to a reduced initial burst phase when compared to the non heparinized materials. The results show a beneficial effect with the incorporation of heparin and its potential as a localized drug delivery system for the sustained release of growth factors.

Wool keratin-stabilized silver nanoparticles

In this paper, we explored a facile method to prepare stable silver nanoparticles (Ag NPs) using extracted wool keratin as the capping agent. The formation of Ag NPs was investigated by UV–Vis spectroscopy, X-ray photo-electron spectrometer and X-ray diffraction spectrometer. The morphology of the NPs was detected by scanning electron microscopy in vacuum and atomic force microscopy in fluid. The possible interactions between the silver core and the capping agent have been investigated using Fourier transform infrared spectroscopy. The effects of keratin concentration on the incubation of the NPs were studied by UV–Vis spectra. It was found that under alkaline condition the process of incubation was much faster than that under neutral pH condition. The photoluminescence properties of the Ag NPs were also investigated. We believe that this work is helpful for the high-value utilization of wool and other keratin-rich bioresource.

Dynamic Modeling and Analysis on a New Type Wall-climbing Robot for Ship Wall Rust Removal

A tracked wall climbing robot for ship rust removal is designed, which is adsorbed by permanent magnetic and vacuum mixed adsorption. The robot has the characteristics of heavy body and heavy load, and the load mass and the center of gravity position change with the climbing high. According to the climbing wall working principle, the kinematics models which contain the robot climbing and turning on the ship wall are established. The models are optimized by using fuzzy optimization theory and analyzed by simulation, and the safe working range is planned. Then the kinematics climbing ability is analyzed, and the relation between upward climbing height and ship wall tilt angle is discussed with theoretical torque, maximum torque and rated torque. An experimental prototype is developed for carrying out wall-climbing turning, fixed load climbing and variable load climbing tests. Simulation and test results show that the optimization model is reliable, the permanent magnetic adsorption force, vacuum force and water jet force have little effect on motion performance, but the robot body weight, wall-climbing height and ship wall tilt angle have great effect on it, and the planned safe working range is reasonable.

Vacuum Pressures during Autologous Fat Transfer (AFT): A Study of the Closed Syringe Type and other Aspirator Pressures

Objective: Vacuum pressures have long been thought to damage the lipocytes during harvest. Several studies have described this as well as the need to reduce the pressure during harvest. The goals of this article are to increase awareness of the pressures associated with the closed syringe technique and other methods of harvesting for autologous fat transfer (AFT). Methods: The closed syringe pressures are presented for 60-, 30-, and 10-mL syringes. Note that the vacuum force for any manual syringe is the plunger and the position of the plunger will dictate the pressure that will be applied to the fat. Results: The closed syringe tests on 60-, 30-, and 10-mL syringes (three brands) show that a 60-mL syringe will produce an 18.5-in mercury vacuum pressure, but only when the plunger is withdrawn to maximum. The tests also showed that when the plunger is at 30 mL, the response is 16 in of mercury; at 10 mL the response is 6 in of mercury. Thus, the smaller the syringe capacity, the lower the vacuum pressure. This lessening of the vacuum pressure is not due to the plunger losing pressure around its gasket, but it is directly related to the empty space (volume) left in the syringe. Thus, a 60-mL syringe that is half full of fat renders an identical pressure to an empty 30-mL syringe, that being 16 in of mercury. Discussion: Electrically powered vacuum sources do not respond in this manner because the motor will maintain a relatively constant pressure throughout the procedure. The economic advantages of the closed syringe technique are discussed with emphasis on the availability of generic materials and thus lessened cost. The disadvantages include the varying downward pressures during harvest, the added time to decant or centrifuge the harvested material, and the need for added transfers. Also presented are the 2 filter-type harvest units on the market today (Lipivage and TissuTrans) that will save considerable time by separating out the unwanted material during the harvest and without additional transfers. Conclusion: Knowing the pressures administered (to fat) by the syringes or reservoirs used in all types of fat harvesting equipment is important and part of the standardization process.

Attachment of the NemerteanMalacobdella arrokeanato the Mantle of the GeoduckPanopea abbreviataand Survival Outside the Host

Results of the histopathological study of mantle tissues of the commercial geoduck Panopea abbreviata hosting the nemertean Malacobdella arrokeana revealed that the normal histology of mantle tissues of the bivalve was not altered by the attachment structure of the nemertean, even when the maximum individuals per clam reached 191 nemerteans. However, the vacuum force generated by the nemertean sucker seems to elicit a slight mechanical stretching of epithelial cells and a negligible infiltration response affecting the connective tissue between inner and outer mantle epithelia beneath the point of attachment. The 99.4% bivalves examined (n ¼ 657) hosted at least 1 specimen of M. arrokeana. Adult nemerteans were able to survive outside the host for up to 3 mo at 13C. These results suggest that the relationship between M. arrokeana and P. abbreviata should be considered as a commensal rather than a parasitic relationship.

Numerical and semiclassical analysis of some generalized Casimir pistons

The Casimir force due to a scalar field on a piston in a cylinder of radius $r$ with a spherical cap of radius $R>r$ is computed numerically in the world-line approach. A geometrical subtraction scheme gives the finite interaction energy that determines the Casimir force. The spectral function of convex domains is obtained from a probability measure on convex surfaces that is induced by the Wiener measure on Brownian bridges the convex surfaces are the hulls of. The vacuum force on the piston by a scalar field satisfying Dirichlet boundary conditions is attractive in these geometries, but the strength and short-distance behavior of the force depends crucially on the shape of the piston casing. For a cylindrical casing with a hemispherical head, the force for $a/R\sim 0$ does not depend on the dimension of the casing and numerically approaches $\sim - 0.00326(4)\hbar c/a^2$. Semiclassically this asymptotic force is due to short, closed and non-periodic trajectories that reflect once off the piston near its periphery. The semiclassical estimate $-\hbar c/(96\pi a^2)(1+2\sqrt{R^2-r^2}/a)$ for the force when $a/r\ll r/R\leq 1$ reproduces the numerical results within statistical errors.

Numerical calculation of the force on some Generalized Casimir Pistons

In this talk I presented numerical calculations of the Casimir force due to a scalar field on a piston in a cylinder of radius τ with a spherical cap of radius R > τ. Geometrical subtractions give a finite interaction energy. Due to reflection positivity, the vacuum force on the piston by a scalar field satisfying Dirichlet boundary conditions is attractive for these geometries, but the strength and short-distance behavior of the force depends strongly on the shape of the piston casing. For a cylindrical casing with a hemispherical head of large radius, the attractive force on the piston is inversely proportional to the square of the height of the piston.

Size quantization effects in thin film Casimir interaction

We investigate the role of size quantization in the vacuum force between metallic films of nanometric thickness. The force is calculated by the Lifshitz formula with the film dielectric tensor derived from the one-electron energies and wavefunctions under the assumption of a constant potential inside the film and a uniform distribution of the positive ion charge. The results show that quantization effects tend to reduce the force with respect to the continuum plasma model. The reduction is more significant at low electron densities and for film size of the order of few nanometers and persists for separation distances up to 10-50 nm. Comparison with previous work indicates that the softening of the boundary potential is important in determining the amount of the reduction. The calculations are extended to treat Drude intraband absorption. It is shown that the inclusion of relaxation time enhances the size quantization effects in the force calculations.

Intrinsic and extrinsic corrugation of monolayer graphene deposited onSiO2

Using scanning tunneling microscopy in an ultrahigh vacuum and atomic force microscopy, we investigate the corrugation of graphene flakes deposited by exfoliation on a Si/SiO2 (300 nm) surface. While the corrugation on SiO2 is long range with a correlation length of about 25 nm, some of the graphene monolayers exhibit an additional corrugation with a preferential wavelength of about 15 nm. A detailed analysis shows that the long-range corrugation of the substrate is also visible on graphene, but with a reduced amplitude, leading to the conclusion that the graphene is partly freely suspended between hills of the substrate. Thus, the intrinsic rippling observed previously on artificially suspended graphene can exist as well, if graphene is deposited on SiO2.

真空中におけるアルミニウム合金(Al2024-T4)のフレッティング疲労特性(<小特集>締結・接合・接着部の評価技術)

Plain fatigue, fatigue crack growth and fretting fatigue tests of Al alloy (Al2024-T4) in air and in vacuum were carried out using a fatigue testing machine with SEM for in-situ observation. Fretting fatigue strength in vacuum was higher than that in air, while it was lower than plain fatigue strength in vacuum. High tangential force in vacuum would result in earlier fretting fatigue crack nucleation. However, high fatigue crack growth resistance would take dominant role for higher fretting fatigue strength in vacuum.