Rubber friction and the rheology of viscoelastic contact

The phenomena accompanying friction at low speeds (1–1500 μm/s) of a clean glass hemisphere (R = 2 mm) on a plate of soft, transparent, natural vulcanized rubber (E' = 1.6 × 10⁷dynes/cm²) were studied using an optical microscope equipped with Nomarski interference contrast (× 150) and with a device to form Newton's rings around the area of contact. The friction force under loads of zero, 1 and 2 × 10³ dynes was recorded, and its variation on the appearance of Schallamach waves was assessed. The elastic adhesion between both surfaces was specially studied, and Johnson's theory verified. The profile of the deformed rubber surface was determined, in static as well as in dynamic conditions, and the geometric process of the formation of detachment waves was demonstrated. The contact angle between rubber and glass was measured in the case of zero load.Relaxation phenomena were observed for the free surface and the bound surface (interfacial relaxation), and the corresponding characteristic relaxation times roughly estimated.Some conditions for the appearance of Schallamach waves were established and hypotheses made concerning their eventual role in the problems of tyre and seal friction. The need for a new theoretical approach to these questions is briefly discussed.     

An infrared interferometer for investigating subthermonuclear plasma in the GOL-3 multimirror trap

A simple Michelson CO₂ interferometer for measuring the high-temperature plasma density within one interference fringe (n _e l = 10¹⁶ cm^?2) at two points (0.8 and 9.0 m) of the long (L = 12 m) GOL-3 corrugated trap was used. A piezoelectric element that provides displacements of the mirror in the reference arm of the interferometer is used to calibrate the interferometer and perform remote control of the initial measurement phase. The interferometer is manufactured from dielectric materials, thus excluding a mechanical action of stray magnetic fields on its elements. The time resolution of the interferometer is determined by a HgCdTe diode and equals ??1 ns. The sensitivity of the interferometer is ??5 × 10^?4 of a fringe (n _e l = 2 × 10¹³ cm^?2).     

A study of Ar + C2H4 and Xe + CF4 gas mixtures

Mixtures of Ar + 40 ppm C₂H₄ and 50% Xe + 50%CF₄ have been investigated. The spatial distributions of photoelectron clouds produced by primary scintillations on α- and β-particle tracks, as well as the distributions of photoelectron clouds due to photons from avalanches at the pin anode, have been measured for the first time. For a mixture of 50% Xe + 50%CF₄, it has been shown for the first time that CF₄ is a photosensitive dopant in a mixture with Xe. For a mixture of Xe + CF₄ (1: 1), the maximum electron multiplication factors at the pin anode are K(β)^max = 3 × 10⁴ and K(α)^max = 3 × 10³ at a pressure of 1 atm (abs.) and K(β)^max = 10⁴ and K(α)^max = 4 × 10³ at a pressure of 10 atm (abs.)     

A calorimeter for detecting hadrons with energies of 10–100 GeV

A calorimeter for detecting hadrons in the energy range 10–100 GeV is described. It is used at CERN in the NA58 (COMPASS) experiment aimed at studying the nucleon structure and spectroscopy measurements of charmed particles. The calorimeter is composed of 480 modules with a cross section of 15×15 cm², assembled in a matrix with dimensions of 4.2×3 m² and a central window of area 1.2×0.6 m². In each module are 40 iron and scintillator layers of a total thickness of 4.8 interaction lengths. The energy resolution of the calorimeter for hadrons (pions) and electrons and the spatial resolution, determined on the test beams, are $\frac{{\sigma _\pi (E)}}{{E[GeV]}} = \frac{{59.4 \pm 2.9}}{{\sqrt E }} \oplus (7.6 \pm 0.4)\% ;\frac{{\sigma _e (E)}}{{E[GeV]}} = \frac{{24.6 \pm 0.7}}{{\sqrt E }} \oplus (0.7 \pm 0.4)\% $ , and σ _x,y ≈ 15 mm, respectively. The average value of the e/π ratio that characterizes the amplitude responses of the calorimeter to electrons and pions with equal energies from the above range is 1.2 ± 0.1. This study was performed at the JINR Laboratory for Particle Physics.     

Flow visualization and transient behavior analysis of luminescent mini-tufts after a backward-facing step

Luminescent mini-tufts method has been used for surface flow visualization for a long time. One major challenging point of this method is quantitative analysis of transient flows and the dynamic structures. This study is focused on the application of luminescent mini-tufts method in transient flows. A backward-facing step (BFS) is used in this analysis, which is one classic model that consists both flow separation and re-attachment processes. In this study, the instantaneous mini-tufts recognition, image averaging and tuft inclination angle/tuft angle estimation processes are introduced for the analysis of luminescent mini-tufts for the first time on backward-facing step flow (Re_m = 2.0 × 10⁵–7.9 × 10⁵ and Re_h = 1.3 × 10⁴–5.3 × 10⁴). Detailed transient features and characterization process for the backward-facing step model are explained in this study. The combination of optical-oil flow and hot-wire anemometry methods with luminescent mini-tufts are also shown useful to give comprehensive flow field information, including the surface flow behaviors, boundary layer, re-attachment position identification, etc. In addition, the decomposition of the luminescent mini-tufts visualization data is also conducted to give the power spectral density (PSD) and characteristic frequencies for the mini-tufts behaviors under transient fluctuating flow conditions.     

An improved method for predicting discharge of homogeneous compound channels based on energy concept

Accurate estimation of flow discharge in a compound river channel is increasingly important in river management and hydro-environment design. In this paper, a new model is developed to improve the prediction of flow based on Energy Concept Method (ECM) and Weighted Divided Channel Method (WDCM) along with the apparent shear stress at the interface between main channel and floodplain. The new model is compared with a wide range of our experimental data and the data available in the literature. The 27 datasets used include homogenous symmetric channels (22 datasets) and asymmetric channels (5 datasets) with various aspect ratios [channel total width (B) at bankfull / main channel bottom (b) =1.5–15.8], and bed slopes (S_o = 4.3 × 10⁻⁴–1.3 × 10⁻²). It was found that the new model has significantly improved the accuracy of flow prediction compared with the traditional Divided Channel Method (DCM), and has also considerably better results than the ECM and WDCM methods against all the datasets, particularly for relatively low flow depths of floodplain where the flow discharges are most difficult to predict correctly. The new model predicts the total discharge well for both symmetric and asymmetric channels, within an averaged relative error of about 5%.     

Measuring the 14C isotope concentration in a liquid organic scintillator at a small-volume setup

A low-background scintillation setup situated in the Gran Sasso National Laboratory is described. The facility is composed of nine identical cells, each 2 L in volume. The ¹⁴C content of a PXE-based scintillator has been measured using this setup; the value obtained is R(¹⁴C/¹²C) = (12.6 ± 0.4) × 10^?18. This result can be used for comprehensive investigation of possible ¹⁴C production channels in organic scintillators.     

Radiation detectors based on PbSnTe:In films,sensitive in the terahertz range of the spectrum

This paper presents a review of studies of the photoelectric properties of PbSnTe:In films obtained by molecular beam epitaxy and photosensitive structures in the far infrared and submillimeter ranges based on these films. The parameters of photodetector arrays of this type and detectors based on doped semiconductors and superconductors are compared. One-dimensional (2×128 elements) and two-dimensional (128 × 128 elements) PbSnTe:In based arrays with a sensitivity threshold of ~22 μm and an operating temperature of T ≤ 16 K are implemented. Under background-free conditions, the noise equivalent power (NEP) was NEP ≤ ^10?18 W/Hz^0.5 at T = 7 K for a black body radiation source at T_BB = 77 K. In the submillimeter range of the spectrum, sensitivity to laser radiation with a wavelength λ ≤ 205 μm and a value NEP ≤ 10^?12 W/Hz^0.5 was observed without optimization of the design of the photosensitive element and minimization of the measurement circuit noise. The directions of the development of PbSnTe:In based radiation detectors are considered..     

Potential of a sensitive uric acid biosensor fabricated using hydroxyapatite nanowire/reduced graphene oxide/gold nanoparticle

In this study, a ternary nanocomposite consisting of gold nanoparticles (AuNPs), hydroxyapatite (HAP) nanowires, and reduced graphene oxide (rGO) is synthesized by a simple one‐step hydrothermal method, which is used to modify glassy carbon electrode (GCE) for detecting uric acid. The nanocomposite is characterized through various methods such as scanning electron microscopy, transmission electron microscopy, and X‐ray diffraction. Electrochemical measurements of the modified GCE are performed in a conventional three‐electrode system. Experimental results show that the obtained HAP nanowire and rGO are mixed homogeneously, and the AuNPs are deposited into this matrix. The GCE modified by the nanocomposites have superior electrocatalytic activities for uric acid. The peak current intensities of UAO (uricase)/HAP‐rGO/AuNPs sensing system linearly increase as the uric acid concentration increases substantially in a range of 1.95 × 10^?5 to 6.0 × 10^?3 M (R² = .9943), with a detection limit of 3.9 × 10^?6 M (S/N = 3) and analytical sensitivity of 13.86 mA/M. The biosensor performs well in determining uric acid concentration in human urine samples.     

High-performance 320 × 256 long-wavelength infrared photodetector arrays based on CdHgTe layers grown by molecular beam epitaxy

This paper gives the parameters of 320 × 256 element long-wavelength infrared photodetectors fabricated by a new improved technology based on heteroepitaxial mercury-cadmium-tellur structures. In these photodetectors, the variation of the photodiode bias voltage over the area of the array is minimized; inefficient photodiode regions related to both hybridization and spike-shaped growth defects of epitaxial films are eliminated; the current-voltage characteristics of the diodes in the resulting photodetectors are homogeneous and are limited by the diffusion current component up to ?400 mV. The dark current is 0.25–0.45 nA, and R ₀ A = (0.6–3) · 10² Ω · cm². The voltage sensitivity, the threshold irradiance, and the average NETD at the maximum sensitivity are 11.8 · 10⁸ V/W, 3.7 · 10^?8 W/cm², and 26.8 mK, respectively. The percentage of defective elements is 1.5%.     

Fast-response thermistors made of synthetic single-crystal diamonds

Miniature thermistors are produced from boron-doped synthetic single-crystal diamonds grown under pressure using the thermal gradient method. It is shown that heavily doped diamonds with a boron concentration of 10¹⁹ cm^?3 or higher are most suitable for this purpose. In the temperature range of 300–700 K, coefficient β = ln(R ₁/R ₂)/(1/T ₁ ? 1/T ₂) is 2500 K. The characteristic response time of temperature-sensitive elements based on crystals with dimensions of 1 × 1 × 0.3 mm is ～100 µs; i.e., they can be used in monitoring systems with a response speed of up to 10 kHz.     

Batch and Flow‐Injection Determination of Catecholamines Using Ion Selective Electrodes

Abstract

New epinephrine (EP), dopamine (DA), and L‐Dopa (LD) ion selective PVC membrane electrodes based on ion‐pairs of catecholamines with tetraphenylborate (TPhB) are prepared. In the present work, plastic membrane selective electrodes have been constructed. They are based on the incorporation of EP‐TPhB, DA‐TPhB, or LD‐TPhB ion exchangers in poly(vinylchloride) (PVC) membranes plasticized with di(2‐ethylhexyl)sebacate (DES). The electrodes show a near – Nernstian response in the concentration ranges: 1.0×10^?4—1.0×10^?2 mol/L (epinephrine), 5.0×10^?5–1.0×10^?2 mol/L (dopamine), and 5.0×10^?4–1.0×10^?2 mol/L (L‐Dopa). The electrodes selective for epinephrine and L‐Dopa are used as detectors in the flow injection system. The proposed methods allow determination of catecholamines in pharmaceutical preparations.     

Multichannel wire gas electron multipliers

A simple technique for manufacturing electrodes of multichannel wire gas electron multipliers was developed. The maximum proportional multiplication factor of ionization electrons K ^max = 10³ was obtained when the chamber containing a multichannel wire gas electron multiplier was filled with a mixture of Ar + 10%C₂H₄ at a pressure of 1 atm (abs.) and the drift (ionization) gap of the chamber was irradiated with β particles (⁶³Ni). Under irradiation with α particles, K ^max = 10³ at a pressure of 1 atm (abs.) and 3 × 10³ at 0.4 atm (abs.). When the chamber was filled with a mixture of Ne + 10%C₂H₄ at a pressure of 1 atm (abs.) and exposed to β particles, K ^max = 4 × 10³ was obtained.     

Observations of Stick-Slip Friction in Velcro®

Friction, and in particular stick-slip friction, occurs on every length scale, from the movement of atomic force microscope tips at the nanoscale to the movement of tectonic plates of the Earth’s crust. Even with this ubiquity, there still appears to be outstanding fundamental questions, especially on the way that frictional motion varies generally with the mechanical parameters of a system. In this study, the frictional dynamics of the hook-and-loop system of Velcro^® in shear is explored by varying the typical parameters of driving velocity, applied load, and apparent contact area. It is demonstrated that in Velcro^® both the maximum static frictional force and the average kinetic frictional force vary linearly with apparent contact area (hook number), and moreover, in the kinetic regime, stick-slip dynamics are evident. Surprisingly, the average kinetic friction force is independent of velocity over nearly two-and-a-half orders of magnitude (~2 × 10^?4 to ~6 × 10^?2 m/s). The frictional force varies as a power law on the applied load with an exponent of 0.28 and 0.24 for the maximum static and kinetic frictional forces, respectively. Furthermore, the evolution of stick-slip friction to more smooth sliding, as controlled by contact area, is demonstrated by both a decrease in the spread of the kinetic friction and the spread of the fluctuations of the average kinetic friction when normalized to the average kinetic friction; these decreases follow power-law behaviors with respect to the increasing contact area with exponents of approximately ?0.3 and ?0.8, respectively. Lastly, we note that the coefficients of friction μ _s and μ _k are not constant with applied load but rather decrease monotonically with power-law behavior with an exponent of nearly ?0.8. Phenomenologically, this system exhibits interesting physics whereby in some instances it follows classical Amontons–Coulomb (AC) behavior and in others lies in stark contrast and hopefully will assist in the understanding of the friction behavior in dry surfaces.     

低强度中子流电视摄像系统

本文介绍了低强度(3～4×10³n/cm²s)中子流电视摄像系统。它利用SEC摄像机独特的积累性能,将一个用人眼直接观察什么也看不见的、不连续光点的低照度(1×10^-4Lx)中子流像转换成一个能在监视器上观察的可视图像。     

A time-of-flight mass spectrometer for monitoring the inhalational anesthesia concentration in the real-time mode

The use of a medical mass spectrometer for measuring the concentration of the gas mixture components in the breathing circuit of an inhalational anesthesia machine in the real-time mode is described. The resolution of the mass spectrometer is M/ΔM = 200, and the detection threshold in terms of the partial pressure of the analyzed gases is 2 × 10^?12 mbar. The mass spectrometer is capable of measuring the volumetric content of CO₂, O₂, and inhalational anesthetic sevoflurane. The respiratory coefficient (CO₂/O₂) was measured during anesthesia to estimate the patient’s stress reaction to a surgical injury.     

Nucleation of two-dimensional Si islands near a monatomic step on an atomically clean Si(111)-(7×7) surface

The process of nucleation of 2D islands near a monatomic step at the initial stage of growing of a silicon film on the Si(111)-(7 × 7) surface is studied by means of in situ ultrahighvacuum reflection electron microscopy. The dependence of the depletion region width W near the step, where no islands are formed, on the deposition rate R is described by the expression W² ∝ R^-χ with the exponent χ = 1.18 and χ = 0.63 at temperatures of 650 and 680 °C, respectively. It is demonstrated that the change in χ is associated with the step structure, which provides the transformation from the growth kinetics limited by attachment of adatoms to the step to that limited by diffusion of adatoms. A competition of the processes of nucleation and attachment to the step leads to an increase in the critical size of the island nucleus from i = 1 far from the step to i = 3–5 near the step and to i = 6–8 on the terrace of critical width for 2D nucleation.     

Mass-separated microbeam system with a liquid-metal-ion source

This paper describes the developement of a mass-separated focusing column, consisting of a liquid-meta-ion (LMI) source, two lenses, an E×B mass filter, and a post-deflector. This system has the ability to produce sub-μm beams with energies up to 20 keV and a maximum current ranging from 10⁻² to 1 nA, depending on the source characteristics. Preliminary operation of this focusing system was demonstrated by scanning ion microscope (SIM) images. An image resolution of less than 0.1 μm has been achieved for focused beams of ⁶⁹Ga⁺ and ¹¹B⁺, which were respectively extracted from Ga-LMI and eutectic alloy LMI sources.     

A cooling system for samples for studying their surfaces in ultrahigh vacuum

The device described is designed to cool samples with liquid nitrogen to T=?165°C during low-energy electron diffraction (LEED) studies at an ultra-high-vacuum MALTIPROBE Compact system (Omicron) and versions thereof equipped with a scanning tunneling microscope and an LEED system. The efficiency of the system is demonstrated using the example of a low-temperature 2×1 ? c(4×2) phase transition on a (100)-oriented silicon surface observed using the LEED technique.     

Simultaneous Determination of Six Trace Elements in Plant Medicines by Derivative Adsorption Waves in Conjunction with a Microwave Technique

Abstract

Complex adsorption waves of Cu(II), Pb(II), Cd(II), Ni(II), Co(II), and Zn(II) in substrate solution (pH=9.26) of diacetyldioxime‐ammonia‐ammonium chloride‐sodium citrate‐gelatin‐sodium sulfite were studied and a new method for determination of the six trace elements in aqueous solutions was developed. The results show that there are sensitive adsorption waves of Cu(II), Pb(II), Cd(II), Ni(II), Co(II), and Zn(II) complexes at about ?0.45, ?0.61,?0.78, ?1.07, ?1.23, and ?1.38 V, respectively. The method is easy to operate and is able to determine these trace elements in aqueous solutions rapidly and simultaneously. When the signal‐to‐noise ratio equals 3, the detection limits of copper, lead, cadmium, nickel, cobalt, and zinc are 3.2×10^?4, 4.8×10^?3, 1.9×10^?3, 1.7×10^?5, 2.1×10^?6, and 1.0×10^?3 µg/cm³. Good linear relationships exist between the concentrations and the current peaks when copper, lead, cadmium, nickel, cobalt, and zinc concentrations are within 6.5×10^?4～10⁰, 9.3×10^?3～10, 4.1×10^?3～10, 3.2×10^?5～10^?1, 4.0×10^?6～10^?2, and 2.1×10^?3～10 µg/cm³, respectively. In conjunction with a microwave assimilation technique, the method has been used in the rapid and simultaneous determination of these trace elements in some plant medicines with satisfactory results.