Gravity-free hydraulic jumps and metal femtoliter cups

Hydraulic jumps created by gravity are seen everyday in the kitchen sink. We show that at small scales a circular hydraulic jump can be created in the absence of gravity by surface tension. The theory is motivated by our experimental finding of a height discontinuity in spreading submicron molten metal droplets created by pulsed-laser ablation. By careful control of initial conditions, this leads to solid femtoliter cups of gold, silver, copper, niobium, and tin.     

A theoretical prediction of rotating waves in Type-I hydraulic jumps

The rotation of polygons in a Type-II hydraulic jump prompts us to look for a rotational feature in the Type-I hydraulic jump. Coupling the radial and azimuthal flows breaks the azimuthal symmetry of the shallow-water circular jump. An unstable rotating wave along the circumference of the jump is possible with a kinematic viscosity of very small order, whose upper threshold value is less than the kinematic viscosity of water.     

Standing and travelling waves in the shallow-water circular hydraulic jump

A wave equation for a time-dependent perturbation about the steady shallow-water solution emulates the metric an acoustic white hole, even upon the incorporation of nonlinearity in the lowest order. A standing wave in the sub-critical region of the flow is stabilised by viscosity, and the resulting time scale for the amplitude decay helps in providing a scaling argument for the formation of the hydraulic jump. A standing wave in the super-critical region, on the other hand, displays an unstable character, which, although somewhat mitigated by viscosity, needs nonlinear effects to be saturated. A travelling wave moving upstream from the sub-critical region, destabilises the flow in the vicinity of the jump, for which experimental support has been given.     

Accurate measurement of pressure differences and the effect of baffle on pressure distribution in vacuum chamber during dynamic gas flow

The need to know the pressure in relatively large vacuum chambers arises at different measurements (calibration of vacuum gauges, outgassing measurements, etc.) and investigating the ways to minimize these pressure differences are of equal importance in such industrial as well as research applications. The experimental determination of the pressure differences between various gauge positions in a chamber of cylindrical shape and the effect of a baffle on pressure distribution are described in the paper. The pressure in the chamber was generated dynamically in the pressure range 0.1–133 Pa through adjustable gas flow into the chamber. Five identical capacitance diaphragm gauges (CDGs) were used in which one CDG remained fixed at the central position of the chamber while the other four (in two pairs) were mutually interchanged. The differences on the order of several percent between positions at different levels were calculated and the effect of the baffle was investigated which are specific for this chamber.     

Compact vision using circular dynamic stereoscopy with a beam splitter

Circular dynamic stereoscopy (CDS) has special advantages for 3-D measurement as it uses a single CCD camera without cumbersome settings. In CDS, annular streaks are recorded, with their size inversely proportional to the depth/distance of the measuring point from the CCD camera. Therefore three-dimensional information can be measured automatically by image processing techniques. When the measuring points are relatively dense, streaks on the image plane overlap, making automatic processing difficult. To cope with this problem, one of the coupled mirrors is replaced by a beam splitter. The annular streaks and their corresponding center positions are then recorded on the same image as the displacement. The recording of the center positions helps in resolving the overlapping annular streaks.     

Correlation between phase diagrams and spontaneous magnetization jumps in narrow-band manganites

The correlation between the phase diagrams of narrow-band manganites and the abrupt magnetization jumps observed previously at a magnetic-field-induced transition from the antiferromagnetic to ferromagnetic state has been studied. This transition occurs during several milliseconds and is related to a spontaneous thermal avalanche; however, the mechanisms of the avalanche formation and development have not been conclusively established. It has been shown that different compositions (Pr_0.67Ca_0.33MnO₃, Sm_0.55Sr_0.45Mn¹⁸O₃, and Eu_0.58Sr_0.42MnO₃) are qualitatively characterized by analogous phase diagrams with a negative incline of the antiferromagnet/ferromagnet interface in the H-T plane; apparently, this analogy determines the avalanche-like character of the transition.     

X-ray fluorescence intensity distribution in circular specimens

Summary The relative X-ray fluorescence (XRF) intensities for annular source and various annular specimen are measured with a Ge-Li detection system and calculated by the Monte Carlo numerical techniques (MCNT).Kα X-ray intensities of annular specimens with different radii prepared from a pure-molybdenum foil are measured and it is seen that the measured values are in good agreement with the values calculated by MCNT. The variation of the fluorescence intensity due to the collimator radius is also studied. The differences between the MCNT and experimental results are discussed in terms of the possible sources of errors.     

Comparison between intensity jumps in experimental,simulated and theoretical multielemental spectra

The results obtained by applying the theory developed for the SEICXRF method and applying a Monte Carlo simulation code (MCS) are compared with the experimental data in order to validate this theory. Specifically, an assay is made with the spectra corresponding to a brass sample and a soil sample. The experimental data were corrected considering the chamber efficiency and the dead time of the detection system. The considerations taken into account in order to obtain a correct comparison between theory and experiment are discussed in detail. Good agreement between spectra is observed, taking as reference the given values of the elemental composition. The experimental intensity jumps are in agreement with those predicted by the theory and by the MCS. Copyright © 2003 John Wiley & Sons, Ltd.     

The evolution of field distribution in a dynamic cavity

The results of calculations of the dynamics of a field in a cavity that consists of a stationary mirror and a periodically displacing mirror are presented. The initial distribution of the field corresponds to the equilibrium thermal (Planck) distribution. It is shown that, if conditions of a resonant excitation are implemented, pulses can be formed the degree of unipolarity of which increases from the initial zero degree to an almost maximum (unit) degree.     

The effect of couple stresses on stress distribution in a thin plate due to the pressure of a rivet on one side of a circular hole

In this paper we shall investigate the effect of couple stresses on stress distribution in an infinite plate with a circular hole subjected to pressure exerted by a rivet.     

圆环电流的磁场以及两共轴圆环电流之间的相互作用力

直接由毕奥－萨伐尔定律计算圆环电流在空间任一点产生的磁场，并由此求出两共轴圆环电流之间的相互作用力。     

Relationships between arithmetic averages of sound pressure level calculated in octave bands and Zwicker’s loudness level

Previously it has been found through a series of psychoacoustical experiments that the arithmetic average of sound pressure level calculated in octave bands is a good estimator of loudness for various kinds of environmental noise. Remarkably, the arithmetic average of sound pressure level in octave bands from 63 Hz to 4 kHz, L_m,1/1(63-4k), strongly correlates with the loudness level specified in ISO 532B, LL(Z), as well as with loudness assessment. To investigate this relationship further, a numerical study has been carried out based on Zwicker’s loudness model. As a result, practical expressions to estimate the loudness levels of general environmental noises from the sound pressure levels in octave bands from 63 Hz or 125 Hz to 4 kHz are proposed.     

Quantum jumps between macroscopic quantum states of a superconducting qubit coupled to a microscopic two-level system

We report the observation of quantum jumps between macroscopic quantum states in a superconducting phase qubit coupled to the two-level systems in the Josephson tunnel junction, and all key features of quantum jumps are confirmed in the experiments. Moreover, quantum jumps can be used to calibrate such two-level systems, which are believed to be one of the main decoherence sources in Josephson devices.     

The dynamic analysis of circular plates and shallow spherical shells

In the investigation reported here an attempt has been made to study the influence of Berger's approximation on the non-linear transient response of circular plates and shallow spherical shells. The governing equations of motion obtained from Berger's approximation are solved by using the rapidly converging Chebyshev series spacewise and the Houbolt scheme for integration in the time domain. Results calculated when using Berger's approximation are compared with exact results. It is shown that Berger's method yields very accurate values for plates and shells under transient loading, in the case of immovable edge conditions.     

Cavitation onset caused by a dynamic pressure wave in liquid pipelines

When liquids flow in the pipelines, the onset of cavitation can be characterized by a variant of the Euler number known as the cavitation number (CN), which is based on the velocity and denoted by C in this paper. Conventionally, cavitation is considered to be induced when C ~ 1. However, experimental observations and several pipe bursts indicate that the CN may incorrectly predict the onset of cavitation. For example, when leakage occurs in the pipeline or a valve in the pipeline is opened, the resultant pressure loss generates a dynamic pressure wave with a small amplitude, which may lead to bubble formation, even though C ~ 1 is not satisfied. Hence, this paper proposes another CN based on the amplitude of the generated dynamic pressure wave, rather than the velocity, for ascertaining the onset of cavitation. The validity of the proposed CN was verified through experiments and a case study. The results indicated that the proposed CN can be effectively used for cavitation prediction induced by pressure fluctuations and for investigating phenomena such as pressure fluctuation, leakage, and corrosion in liquid pipelines, tanks, and pressure vessels, as well as the safety design of liquefied natural gas tanks and tankers.