Minimum-wear characteristics for boundary friction between solids

A new parameter is proposed for characterizing boundary friction between solids—the probability Q that some contact spot will be converted to a wear particle as the real contact area shifts by one mean contact-spot diameter. A method is proposed for the phenomenological detection of optimum regimes of boundary friction, which are characterized by the minimum wear intensity of the sample material, and for measuring the corresponding quantity Q=Q ^opt. For babbitt, one of the most frictionless materials, the value of Q ^opt is found to be ≈2×10⁻¹⁰. When data on the linear wear intensity I _h , the contact pressure p _n , and the hardness H are available, Q can be calculated for the given test conditions. Deviations of Q from the value Q ^opt (for a given material) can serve as a criterion for how closely a prepared surface structure approaches the optimal. Zh. Tekh. Fiz. 68, 48–52 (April 1998)     

Tailored TEMp0 beams for large size 3-D laser prototyping

The Laser-Lithography technique allows the fabrication of complex objects having microsizes by selectively solidifying polymeric materials layer by layer upon exposure to a focused Gaussian laser beam having a beam propagation factor M²=1. We can expect that extension of this technique to large sizes 3-D prototyping comes up against a large increase in the design time. A possible solution is the increase in the focused spot size, but unfortunately at the price of a great reduction in the longitudinal resolution due to the resulting increase in the depth of focus. To overcome these difficulties, we propose the use of a rectified TEM_p0 beam allowing the obtaining of a Gaussian beam intensity profile in the focus plane of a lens. The reshaped TEM_p0 beam has a beam propagation factor M²≈(2p+1), and this yields to a relative improvement of the longitudinal resolution although the spot size is increased for reducing the processing time.     

Self-pulsation and optical chaos in self-pumped photorefractive BaTiO3

Sinusoidal intensity oscillations of the phase conjugated wave reflected from a self-pumped photorefractive BaTiO₃ crystal have been observed. The oscillation amplitude is shown to be increased by providing optical feedback of the light scattered during grating formation. The oscillation frequency ? can be tuned from 0.024 Hz to 2 Hz by changing the light intensity I₀ of the object beam from 0.7 W/cm² to 100 W/cm². A power law ? ∝ I^β₀ ∝ σ with β = 0.89 was observed over this range of intensities (σ = photoconductivity). Transitions to a chaotically oscillating or a stable reflecting state have been observed at higher power levels or with increased optical feedback. An additional pump beam near the entrance face of the signal beam can decrease the build-up time for the self-pumping process by a factor of five or more.     

Experimental study of a broad-band XeCl double-pass amplifier with SBS mirror

An oscillator-amplifier XeCl laser system has been used to experimentally investigate the effectiveness of a liquid stimulated Brillouin scattering (SBS) mirror for correcting the spatial aberrations of broad-band laser radiation in a double-pass amplifier. It has been found that the SBS amplifier performance is strongly dependent on the intensity I _p exciting the Brillouin medium. A good beam reconstruction has been attained at I _p1GW/cm², whereas highly aberrated output beams have been delivered by the SBS amplifier for I _p>1 GW/cm². By comparing the broad-band SBS amplifier performance to that of the same amplifier with a dielectrically coated flat mirror at one end, it has been found that the use of a SBS mirror is advantageous to obtain lower divergence output beams only for low energy pump beams (<1 mJ).     

Novel compact 60-kV Mott detector for spin-polarization electron spectroscopy

A compact 60-kV Mott polarimeter designed specially for the local analysis of surface and two-dimensional magnetism by spin-resolved electron spectroscopy is developed and tested. The use of a design which combines a spherical accelerating field and the absence of a retarding potential after scattering of the electron beam ensures high stability of the measured polarization even when the potential and diameter of the beam being investigated vary. As a result of optimization of the scattering angle (118°) and the use of surface-barrier detectors with a large collection angle (∼48°), the efficiency or figure of merit of the polarimeter, which determines the signal-to-noise ratio ɛ=(I/I ₀)·(S _eff)², equals 2.5×10⁻⁴. Specially developed electronic circuits and optimum positioning of the detectors provide a maximum electron counting rate as high as 5×10⁶ counts/s. Consequently, it is possible to calibrate the polarimeter (to find the effective Sherman function S _eff) by extrapolating the measured asymmetry to a high discrimination level. This instrument can also be used in other areas of solid-state physics, atomic physics, and high-energy physics. Zh. Tekh. Fiz. 68, 125–130 (August 1998)     

Infrared intensity analysis of CHCl3 and CDCl3

IR intensity formulae can be derived in the formI=L′ A; I being square root of intensityI ², has sign ambiguity. Equations likeI′ I=A′ LL′ A=A′ GA have been used to solve the sign ambiguity. There is only one equation for each species. This position has now been improved by introducing a new concept about this sign ambiguity and solved for electro-optical parameters taking a pair of molecules CHCl₃ and CDCl₃ for demonstration. This incidentally solves the sign ambiguity problem of polar tensors which are calculated for these molecules.     

Production of secondary radioactive beams from 44 MeV/u Ar projectiles

Secondary beams have been produced through interaction of a 1760 MeV Ar beam with a 99 mg/cm² Be target. An achromatic spectrometer is used to select the magnetic rigidity corresponding to a given beam, and to transport this beam over a distance of about 18m. The beam purity is studied using a solid state ΔE-E telescope. Beams of³⁸S and³⁹Cl are produced with a purity of about 80%, and production rates of 1.5·10^?6 I₀ and 5·10^?5 I_o respectively. Here I₀ denotes the primary beam intensity. Beams of³⁸Ar,³⁹Ar and⁴¹K are produced with about the same abundances as³⁹Cl but with lower purities. It is shown that, by setting properly the experimental parameters, the beam production can be improved by a factor 2 to 5. This could lead to intensities of about 2·10⁶ pps for³⁸S, and of 10⁷ to 10⁸ pps for the four other beams. The possibility of purifying these beams by placing a degrader between the two dipoles of the spectrometer is shown experimentally.     

Developments in quantum information processing by nuclear magnetic resonance: Use of quadrupolar and dipolar couplings

Use of dipolar and quadrupolar couplings for quantum information processing (QIP) by nuclear magnetic resonance (NMR) is described. In these cases, instead of the individual spins being qubits, the 2 ⁿ energy levels of the spin-system can be treated as an n-qubit system. It is demonstrated that QIP in such systems can be carried out using transition-selective pulses, in CH₃CN, ¹³CH₃CN, ⁷Li (I=3/2) and ¹³³Cs (I=7/2), oriented in liquid crystals yielding 2 and 3 qubit systems. Creation of pseudopure states, implementation of logic gates and arithmetic operations (half-adder and subtractor) have been carried out in these systems using transition-selective pulses.     

Laser-induced spark for simultaneous ignition and fuel-to-air ratio measurements

This work investigates the use of laser-induced gas breakdown for simultaneously igniting and measuring fuel-to-air ratio of CH₄–air and H₂–air combustible mixtures. The fuel-to-air ratio is determined using the measured spectral peak ratio I_o,Hα/I_o,OI. Sparks are produced using a single-mode, Q-switched Nd–YAG laser. The laser produces a beam of 6 mm in diameter at the wavelength of 1064 nm and pulse duration of 5.5 ns. The beam optics is designed to have mainly a beam splitter and a focusing lens. The beam splitter is coated to reflect the laser beam and transmit emission lines with wavelengths from 600 to 900 nm which are then collected by a fiberoptic cable and detected by an imaging spectrometer–detector assembly. The results showed a linear dependence of the spectral peak ratio on the equivalence ratio that can be generally expressed by φ=a(I_o,Hα/I_o,OI)+b, where a and b are the parameters that depend on the gas pressure. Using the least-square curve fitting technique to fit the experimental data, a calibration curve for calculating the equivalence ratio as a function of the ratio of (I_o,Hα/I_o,OI) was generated.     

Focusing effect of a laser beam on the power dependence of multiphoton processes

The effect of focusing a laser beam on the intensity (I) dependence of multiphoton processes was examined. A general method is given to deduce a genuine intensity dependence from the focused-beam experiment. In addition, some typical examples were examined in detail. For the dependence of the type ofI ⁿ, an apparent relation ofI ^3/2 appears only when there is a change of dependence asI ⁿI^m, withn>3/2 andm<3/2. A genuine intensity dependence can be obtained directly from the focused beam experiment ifn does not change throughout the irradiated volume, or if the conditionn>3/2>m does not hold. The case of gradually decreasingn, as is common for the infrared multiphoton reaction probability (P), was also analyzed taking the Arrhenius-type dependence,P exp(–/I), as an example. A simple method is proposed to obtain a genuine relation betweenP andI for this type of intensity dependence.     

Study of the influence of the injection section on the stability of a high-current relativistic electron beam propagating through the gaseous medium of a plasmochemical reactor

Results are presented from experimental study of the influence of the injection section on the stability of a high-current relativistic electron beam (REB) propagating through the gaseous medium of a plasmochemical reactor (PR). An REB with the electron energy E _e =1 MeV, beam current I _b =10–22 kA, and pulse duration t=60 ns was generated by the Tonus accelerator and, then, injected into a 0.1-m-diameter PR filled with air. The PR consisted of two sections with lengths L ₁= 0.3–1.0 m and L ₂=1.1–2.5 m; the total length of the system was no longer than 3.5 m. The first section was filled with air at a pressure of P ₁=0.8–1.5 torr, and the pressure in the second section was varied within the range P ₂=0.1–760 torr. The current I _b of an REB passed through both sections of the PR was measured with the help of a sectioned vacuum Faraday cup. The transportation efficiency of the beam was determined as the ratio I _b /I _inj, where I _inj is the beam current measured at the point of injection into the PR. It is shown that, for the optimal dimensions of the first PR section, it has a stabilizing action on the REB with a current density of up to 3 kA/cm², which makes it possible to increase the effective length of the second (working) PR section, which is filled with a gas at various pressures, to L ₂=(25–35)L _bet, where L _bet is the beam betatron length.     

Massive spin-momentum entanglement measured in an atomic beam spin echo experiment

In this paper we present an experiment performed with an atomic beam spin echo interferometer, in which massive intraparticle entanglement is demonstrated. In the longitudinal Stern-Gerlach arrangement the nuclear spin and linear momentum of ³He particles are inextricably linked, such that the overall system state cannot be written as the tensor product of the corresponding Hilbert spaces. The measured data show maximal entanglement between ℋ _I and ℋ _p . This hybrid system of one quantum and one classical degree of freedom is a textbook example of entanglement between discrete and continuous observables.     

Separation of quadrupolar and magnetic contributions to spin-lattice relaxation in the case of a single isotope

We present a NMR pulse double-irradiation method which allows one to separate magnetic from quadrupolar contributions in the spin–lattice relaxation. The pulse sequence fully saturates one transition while another is observed. In the presence of a Δm = 2 quadrupolar contribution, the intensity of the observed line is altered compared to a standard spin-echo experiment. We calculated analytically this intensity change for spins I = 1, , , thus providing a quantitative analysis of the experimental results. Since the pulse sequence we used takes care of the absorbed radiofrequency power, no problems due to heating arise. The method is especially suited when only one NMR sensitive isotope is available. Different cross-checks were performed to prove the reliability of the results obtained. The applicability of this method is demonstrated by a study of the plane oxygen ¹⁷O (I = ) in the high-temperature superconductor YBa₂Cu₄O₈: the ¹⁷O spin–lattice relaxation rate consists of magnetic as well as quadrupolar contributions.     

Spreading of an SR beam spot (diameter 0.5 μm, 95 eV) photoelectron image on the surface of WO<Subscript>3 − <Emphasis Type="Italic">x</Emphasis></Subscript> films

The 2D-photoemission image of the beam spot was obtained for the first time for the W⁵⁺ oxidation state on the preliminary irradiated WO_{3 − x} thin film surface, created by scanning of the SR beam over the film surface. The W⁵⁺ beam profile intensity was found to spread up to a distance of 3.2 μm for an amorphous film and 5.5 μm for a polycrystalline film, it exceeds considerably the beam spot size. The image saturation dose was reached faster for a polycrystalline film. Among the possible mechanisms explaining this phenomenon, for the case of an almost unchangeable O2s state under irradiation, a choice was made in favor of a photon-generated charge diffusion due to low-energy secondary electrons from photoemission, which produce the “coloration” effect, e⁻ + W⁶⁺ (W⁵⁺) W⁵⁺ → W⁵⁺(W⁴⁺). The O512-eV Auger peak was found to degrade at the distance of 1.5–2 mm outside the beam spot under long-time electron beam irradiation, which is attributed to electron-stimulated oxygen desorption and outdiffusion.     

Reactive scattering of oxygen atoms: O+I2, ICl,Br2

Angular and velocity distribution measurements of IO reactive scattering from crossed beams of O atoms and halogen molecules I₂, ICl are reported. Angular distribution measurements are reported for BrO from O + Br₂. The O atom beam was generated at ～350 K from a microwave discharge source and the halogen molecule beam from a supersonic nozzle source at ～380 K. The product time-of-flight distribution was recorded at each laboratory scattering angle by a mini-computer. The scattering data are found to be in excellent agreement with the RRKM-AM model of reactive scattering via a long-lived collision complex. The observation of IO product from O + ICl identifies the complex with a bound O-I-Cl triplet state, previously observed for O-Cl-Cl in matrix isolation studies, as proposed by Herschbach. The maximum centrifugal barrier B _m′ for dissociation of the long-lived complex can be accurately determined, particularly for O + I₂. The B _m′ values indicate that both the entrance and exit valleys of the potential energy surface are governed by centrifugal barriers in the region of long-range van der Waals potentials. The comparatively small reaction cross section (e.g. Q ～ 2 Ų for O + Br₂ from discharge flow measurements) is attributed primarily to an orientation requirement for reaction. The RRKM-AM model indicates a ‘tight linear’ transition state for dissociation of the O-I-I complex, corresponding to significant long-range IO orienting forces in the exit valley of the potential energy surface.     

Coherence transfer between nuclear spins in paramagnetic systems: effects of nucleus—electron dipole—dipole cross-correlation

In nuclear magnetic resonance of paramagnetic systems, cross-correlations between the fluctuations of a nucleus—nucleus dipole—dipole coupling I^k I^l and a nucleus—electron dipole coupling I^kS induces cross-relaxation and makes it possible to generate bilinear terms in the density matrix of the type 2I^k _xI^l _z from coherence I^k _x that can lead to ‘relaxation-allowed’ coherence transfer between two nuclei I^k and I^l . In this paper these effects are demonstrated in a complex involving a fragment of double-stranded DNA and two chromomycin molecules complexing a paramagnetic cobalt ion. Analytical expressions are given for the cross-correlation rates in particular conditions, while the extension to anisotropic g tensors or zero field splittings are addressed. It is shown that relaxation-allowed coherence transfer leads to characteristic signals in double-quantum filtered correlation spectroscopy (DQF—COSY), but not in total correlation spectroscopy (TOCSY). Analytical expressions are unable to reproduce the observed cross-peak patterns. A careful numerical study reveals that in the high spin Co(II) complex studied here, the cross-correlation dynamic shift contribution is of the same order of magnitude as the cross-correlation rate, a value much larger than what can be computed assuming isotropic Brownian motion and complete separation between the electron spin and the lattice.     

Reactive scattering of a supersonic oxygen atom beam O + I2

Reactive scattering of O atoms with I₂ molecules has been studied at an initial translational energy E = 43 kJ mol^-1 using a supersonic beam of O atoms seeded in He and E = 18 kJ mol^-1 using O atoms seeded in Ne. Velocity distributions of OI product were measured by cross-correlation time-of-flight analysis. Full contour maps of the differential reaction cross section were obtained which show predominantly rebound scattering at both initial translational energies. Scattering in the forward direction has a product translational energy distribution similar to that predicted for a long-lived collision complex but scattering in the backward direction has a much higher product translational energy. The greater predominance of rebound scattering observed for O + I₂ compared with O + Br₂ may be attributed to the greater exoergicity of the O + I₂ reaction. However, comparison with the O + IBr reaction which exhibits a long-lived collision complex mechanism indicates that the predominance of backward scattering for O + I₂ also arises from diminished forward scattering from larger impact parameter collisions.     

Gadolinium scandate as an alternative gate dielectric in field effect transistors on conventional and strained silicon

Long channel n-type metal oxide semiconductor field effect transistors on thin conventional and strained silicon on insulator substrates have been prepared by integrating gadolinium scandate as high-κ gate dielectric in a gate last process. The GdScO₃ films were deposited by electron beam evaporation and subsequently annealed in oxygen atmosphere. Electrical characterization of readily processed devices reveals well behaved output and transfer characteristics with high I _on/I _off ratios of 10⁶–10⁸, and steep inverse subthreshold slopes down to 66 mV/dec. Carrier mobilities of 155 cm²/Vs for the conventional and 366 cm²/Vs for the strained silicon substrates were determined.     

A Computer Program to Help Resolution of Complex and Poorly Resolved Cu2+ and VO2+ Ions Doped Single Crystals Electron Paramagnetic Resonance Spectra

Complex and poorly resolved Cu²⁺ and VO²⁺ doped single-crystal electron paramagnetic resonance (EPR) spectra are some of the serious problems that exist in this area. In order to help the resolution of this sort of spectra, and for easily resolvable spectra as well, a versatile computer program known as EPR RESolution, or EPRES, is presented. All detectable line positions in the single-crystal spectra taken in three mutually perpendicular planes are given as input. The program plots these line positions. The user then manually determines the lines by selecting the true data points on the plot and fitting them to a well-known variation function. If selection is not suitable, the process is canceled and renewed. By this process, as many resolvable lines as in the spectra can be resolved and determined. The user then groups the resolved lines according to the paramagnetic center to which they belong. This includes the attribution of correct nuclear spin I and M _I to correct lines. After this step, hyperfine and g tensor elements can be found, constructed, and diagonalized.

[Supplemental materials are available for this article. Go to the publisher's online edition of Spectroscopy Letters for the following free supplemental resource: a copy of the EPRES computer program.]