scholarly journals Thermal Effects on Pull-Off Force in the Johnson–Kendall–Roberts Model

2021 ◽  
Vol 69 (1) ◽  
Author(s):  
Yunong Zhou
Keyword(s):  
Thermal Effects ◽  
Thermal Fluctuations ◽  
Increasing Temperature

AbstractIn this study, we investigate the effects of thermal fluctuations on the generalized Johnson–Kendall–Roberts (JKR) model. We show that the distribution of pull-off forces in this model is similar to that of the Bradley model, and is also consistent with the experiment result observed in Wierez-Kien et al. (Nanotechnology 29(15):155704 2018). Increasing temperature leads to a broadening of the distribution, while leads to a reduction of the pull-off force. Additionally, the pull-off force, which is separated into an athermal term and a thermal-induced reduction term, is measured by using spring velocity ranging over 5 orders of magnitude. We show that for compliant spring, the pull-off force is significantly enhanced with increasing velocity, which is mainly attributed to the contribution of the thermal-induced reduction term, while the athermal term is barely sensitive to changes in velocity.

QUANTUM AND THERMAL EFFECTS IN THE MATTER-GRAVITY SYSTEM

1994 ◽  
Vol 03 (01) ◽  
pp. 309-312
Author(s):  
G. VENTURI
Keyword(s):  
Path Integral ◽  
Thermal Effects ◽  
Unstable Mode ◽  
Thermal Fluctuations ◽  
Integral Approach ◽  
Small Radius ◽  
Complex Time ◽  
Gravity System ◽  
The Universe ◽  
Friedmann Robertson Walker

The matter-gravity system is examined in a path integral approach for the case of conformal matter coupled to a Friedmann-Robertson-Walker space time. In particular the case of gravitational potentials of interest in cosmology for which the universe tunnels from a small radius is examined. It is observed that in the presence of such gravitational horizons the universe evolves in a complex time and it is shown how a classical time and temperature emerge. Correspondingly one will have compensating quantum and thermal fluctuations for the matter and gravity system and it is noted that the unstable mode of gravity corresponding to the universe tunnelling into existence will be compensated by analogous modes for matter corresponding to its creation.

EFFECT OF TEMPERATURE ON THE PENETRATION OF HEAVY keV IONS IN MONOCRYSTALLINE SOLIDS: II. VARIOUS IONS IN GOLD, ALUMINIUM, AND TUNGSTEN

1967 ◽  
Vol 45 (8) ◽  
pp. 2467-2482 ◽  
Author(s):  
L. M. Howe ◽  
D. A. Channing
Keyword(s):  
Temperature Effect ◽  
Thermal Effects ◽  
Effect Of Temperature ◽  
Nuclear Stopping ◽  
Slowing Down ◽  
The Difference ◽  
The Stability ◽  
Increasing Temperature ◽  
Thermal Vibrations ◽  
And Tungsten

The influence of atomic thermal motion on the penetration of various heavy keV ions incident along low index channels of single crystals of gold, aluminium, and tungsten has been investigated over the temperature range 15–295 °K. In general, in gold and aluminium the effect of thermal vibrations on the slowing down of the bombarding ions was quite pronounced, whereas a less marked effect was observed in tungsten. The magnitude of the temperature effect was dependent upon the type of bombarding ion and it is suggested that this is due, to a large extent, to the difference in the relative importance of electronic to nuclear stopping along the channel in the various systems. Thermal effects on the stability of the channeled trajectories are also believed to be important. The penetration of the channeled ions was observed to decrease exponentially with increasing temperature. In addition, the magnitude of the temperature effect was found to be relatively insensitive to the bombardment direction for incidence along the more open channels.

Thermal Effects on Charge Transport in Conjugated Polymers

2013 ◽  
Vol 811 ◽  
pp. 14-18
Author(s):  
Yu Qiu
Keyword(s):  
Electric Field ◽  
Polymer Chain ◽  
Thermal Effects ◽  
Dynamical Evolution ◽  
Thermal Fluctuations ◽  
Disturbed Region ◽  
Field Range ◽  
Local Lattice ◽  
Polaron Mobility ◽  
The Right

Field dependent polaron transport in a conjugated polymer chain is studied numerically with local thermal fluctuations taken into account. Within a dynamical evolution method, a polaron moves from the left to the right side of the polymer chain in the presence of an applied electric field. Local lattice fluctuations are assumed to occur in a random way. The local thermal fluctuations are found to be equivalent to a potential barrier for the polaron. The range of the thermally disturbed region in the molecule and the effective temperature difference resulted from asymmetric thermal absorptions determine the height of the barrier. The intra-molecule polaron mobility obeys a logarithmic law in low electric field range provided that there exist asymmetric thermal absorptions within the molecule.

EFFECTS OF QUANTUM AND THERMAL FLUCTUATIONS ON COLLECTIVE PINNING AND CRITICAL CURRENT DENSITY IN TYPE-II SUPERCONDUCTING BULK MATERIALS

2011 ◽  
Vol 25 (04) ◽  
pp. 609-618
Author(s):  
MING JU CHOU ◽  
HERNG ER HORNG
Keyword(s):  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Thermal Fluctuations ◽  
Quantum Limit ◽  
Type Ii ◽  
Type Ii Superconductors ◽  
Collective Pinning ◽  
Fluctuation Temperature ◽  
Increasing Temperature

The effects of quantum and thermal fluctuations on collective pinning and critical current density Jc are investigated for bulk type-II superconductors by utilizing quantum statistics. It is shown that for a constant magnetic field, Jc is nearly independent of temperature in the quantum limit; however, in the classical limit, Jc decreases weakly with increasing temperature when T < Tdp (depinning temperature); when Tdp < T < Tf (boundary fluctuation temperature), Jc is power-law-decaying, and when T > Tf, Jc decays exponentially. For constant temperature, Jc first decreases, then increases after reaching a maximum, and finally decreases again. These results are in agreement with the experiments.

Thermal Considerations in Lens Regulator Systems

1970 ◽  
Vol 28 ◽  
pp. 358-359
Author(s):  
K.C. Newton
Keyword(s):  
Electron Microscope ◽  
Thermal Effects ◽  
Environmental Control ◽  
Reference Networks ◽  
Better Than

Thermal effects in lens regulator systems have become a major problem with the extension of electron microscope resolution capabilities below 5 Angstrom units. Larger columns with immersion lenses and increased accelerating potentials have made solutions more difficult by increasing the power being handled. Environmental control, component choice, and wiring design provide answers, however. Figure 1 indicates with broken lines where thermal problems develop in regulator systemsExtensive environmental control is required in the sampling and reference networks. In each case, stability better than I ppm/min. is required. Components with thermal coefficients satisfactory for these applications without environmental control are either not available or priced prohibitively.

Direct measurement of electron-diffraction-pattern intensities using an energy loss spectrometer

1989 ◽  
Vol 47 ◽  
pp. 668-669
Author(s):  
A. G. Jackson ◽  
M. Rowe
Keyword(s):  
Thermal Effects ◽  
Dynamic Range ◽  
Scattering Amplitude ◽  
Dynamical Theory ◽  
Site Symmetry ◽  
Proof Of Concept ◽  
Parallel Acquisition ◽  
Kinematic Approximation ◽  
Speed Up ◽  
Structure Calculations

Diffraction intensities from intermetallic compounds are, in the kinematic approximation, proportional to the scattering amplitude from the element doing the scattering. More detailed calculations have shown that site symmetry and occupation by various atom species also affects the intensity in a diffracted beam. [1] Hence, by measuring the intensities of beams, or their ratios, the occupancy can be estimated. Measurement of the intensity values also allows structure calculations to be made to determine the spatial distribution of the potentials doing the scattering. Thermal effects are also present as a background contribution. Inelastic effects such as loss or absorption/excitation complicate the intensity behavior, and dynamical theory is required to estimate the intensity value.The dynamic range of currents in diffracted beams can be 104or 105:1. Hence, detection of such information requires a means for collecting the intensity over a signal-to-noise range beyond that obtainable with a single film plate, which has a S/N of about 103:1. Although such a collection system is not available currently, a simple system consisting of instrumentation on an existing STEM can be used as a proof of concept which has a S/N of about 255:1, limited by the 8 bit pixel attributes used in the electronics. Use of 24 bit pixel attributes would easily allowthe desired noise range to be attained in the processing instrumentation. The S/N of the scintillator used by the photoelectron sensor is about 106 to 1, well beyond the S/N goal. The trade-off that must be made is the time for acquiring the signal, since the pattern can be obtained in seconds using film plates, compared to 10 to 20 minutes for a pattern to be acquired using the digital scan. Parallel acquisition would, of course, speed up this process immensely.

Theoretical study of the prestressing strand's stress by computer modeling methods

2020 ◽  
Vol 76 (11) ◽  
pp. 1139-1148
Author(s):  
A. G. Korchunov ◽  
E. M. Medvedeva ◽  
E. M. Golubchik
Keyword(s):  
Residual Stresses ◽  
High Strength ◽  
Pearlitic Steel ◽  
Internal Stresses ◽  
Steel Microstructure ◽  
Compressive Stresses ◽  
Wide Range ◽  
Prestressing Strands ◽  
Increasing Temperature ◽  
Wire Strand

The modern construction industry widely uses reinforced concrete structures, where high-strength prestressing strands are used. Key parameters determining strength and relaxation resistance are a steel microstructure and internal stresses. The aim of the work was a computer research of a stage-by-stage formation of internal stresses during production of prestressing strands of structure 1х7(1+6), 12.5 mm diameter, 1770 MPa strength grade, made of pearlitic steel, as well as study of various modes of mechanical and thermal treatment (MTT) influence on their distribution. To study the effect of every strand manufacturing operation on internal stresses of its wires, the authors developed three models: stranding and reducing a 7-wire strand; straightening of a laid strand, stranding and MTT of a 7-wire strand. It was shown that absolute values of residual stresses and their distribution in a wire used for strands of a specified structure significantly influence performance properties of strands. The use of MTT makes it possible to control in a wide range a redistribution of residual stresses in steel resulting from drawing and strand laying processes. It was established that during drawing of up to 80% degree, compressive stresses of 1100-1200 MPa degree are generated in the central layers of wire. The residual stresses on the wire surface accounted for 450-500 MPa and were tension in nature. The tension within a range of 70 kN to 82 kN combined with a temperature range of 360-380°С contributes to a two-fold decrease in residual stresses both in the central and surface layers of wire. When increasing temperature up to 400°С and maintaining the tension, it is possible to achieve maximum balance of residual stresses. Stranding stresses, whose high values entail failure of lay length and geometry of the studied strand may be fully eliminated only at tension of 82 kN and temperature of 400°С. Otherwise, stranding stresses result in opening of strands.

Low Reynolds number flow around and heat transfer from a heated circular cylinder

2010 ◽  
Vol 1 (1-2) ◽  
pp. 15-20 ◽  
Author(s):  
B. Bolló
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Reynolds Number Flow ◽  
Two Dimensional Flow ◽  
Number Flow ◽  
Low Reynolds ◽  
Increasing Temperature

Abstract The two-dimensional flow around a stationary heated circular cylinder at low Reynolds numbers of 50 < Re < 210 is investigated numerically using the FLUENT commercial software package. The dimensionless vortex shedding frequency (St) reduces with increasing temperature at a given Reynolds number. The effective temperature concept was used and St-Re data were successfully transformed to the St-Reeff curve. Comparisons include root-mean-square values of the lift coefficient and Nusselt number. The results agree well with available data in the literature.

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