Dynamic recrystallization of austenite during hot plastic deformation

The kinetics of dynamic recrystallization is dependent on the thermomechanical conditions in which plastic deformation is taking place. To determine the timet _p needed for the onset of dynamic recrystallization, experimental work was performed on low-carbon austenite to check the validity of the equationW= 2·1 × 10^–1 Z ^–0.94, whereW= t_pexp(–Q/RT),Z represents the Zener-Hollomon parameter, and Q=276 kJ mol^–1.     

Two-photon time-resolved optogalvanic signals of neon

In this work, temporal evolution of two-photon laser optogalvanic signals of neon has been studied. Optogalvanic signals for four transitions from the metastable 2p⁵3s[3/2]₂ state to 2p⁵4d′[3/2]₁, 2p⁵4d′[3/2]₂, 2p⁵4d′[5/2]₃ and 2p⁵4d′[5/2]₂ states were recorded over a range of discharge currents (3.4–9 mA). It was found that the shape of the optogalvanic signal was strongly dependent on the discharge current so that its peak shifted to shorter times and its amplitude increased with the discharge current. The decay rates of the 4d states, calculated from the optogalvanic signals, were found to increase linearly with the discharge current in the range of 6.2–9 mA. However, for the range of 3.4–5.4 mA, the decay rates were observed to slightly decrease with the discharge current.     

Exclusive photoproduction of mesons at HERA

The exclusive photoproduction reaction γp→p has been studied with the ZEUS experiment in ep collisions at HERA using an integrated luminosity of 468 pb⁻¹. The measurement covers the kinematic range 60<W<220 GeV and Q²<1 GeV², where W is the photon–proton centre-of-mass energy and Q² is the photon virtuality. These results, which represent the analysis of the full ZEUS data sample for this channel, are compared to predictions based on perturbative QCD.     

Numerical simulation of diffusive conductivity in Rashba split two-dimensional gas

We numerically model the conductivity of a two-dimensional electron gas (2DEG) in the presence of the Rashba spin–orbit (SO) interaction in the diffusive transport regime. We performed simulation using samples which width W and length L are up to 200 and 30 000, respectively, on a tight-binding square lattice. When the system is in the diffusive regime, the quadratic increase of the conductivity with SO interaction strength λ_SO derived previously by Born approximation is reproduced except for very weak SO interaction. In order to obtain satisfactory agreement between numerical and analytical results, the sample width and length should be much larger than the mean free path ℓ but the length should be shorter than the localization length ξ, e.g. 4ℓW and 10ℓLξ. The anomaly at weak SO interaction is also observed in the conductance fluctuation and the localization length, and is attributed to the finite size crossover from symplectic to orthogonal class with decreasing SO interaction. The typical values of the SO interaction characterizing the crossover obtained for ℓ48 are λ_SO1.0/W and 0.2/W when we impose open and periodic boundary conditions, respectively.     

On the phase diagram of the Extended Hubbard Model

The phase diagram of the Extended Hubbard Model in the atomic limit (zero band width) is investigated for arbitrary values of intra-site interactionI, inter-site repulsionW and chemical potential . First the ground states and their boundaries in the plane (I/4W, –₀/4W) are determined and then using the Peierls chessboard method the existence of several kinds of long range orders, corresponding to ground states, is proven. It is conjectured that the results obtained hold for finite but sufficiently small band width. Arguments in favour of this conjecture are presented.     

Application of the Wavelet Transform for Detecting Signals of Nuclear Quadrupole Resonance

In the present study, the wavelet transform is used to increase the signal-to-noise ratio of nuclear quadrupole resonance (NQR) signals in the direct pulse method. The efficiency of the wavelet and Fourier transforms used for detecting the NQR signal component is compared. The signal consists of noise, magnetoacoustic and piezoelectric signals, noise from external sources, and NQR signal. Signals from ¹⁴ N nuclei in hexahydro-1,3,5-trinitro-s-triazine C₃H₆N₆O₆ (RDX) are investigated at a temperature of 298 K.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 47–50, January, 2005.     

New non-abelian couplings and radiative corrections to the main decay of the top quark

We calculate first order radiative corrections to the main decay of the top quark,tb+W, beyond the Standard Model, by grafting onto the standard lagrangian (using the terminology of de Rújula, Gavela, Hernandez and Massó), a new operator, which respects the gauge symmetry of the Standard Model and modifies theZ ⁰ W ⁺ W ^–,W ⁺ W ^– vertices In our renormalization scheme we use ,G _F,M _Z as input parameters. Them _t dependence is given where we use =1 TeV as a possible scale of the new physics. Form _t =150(200) GeV and =1 TeV, the maximal effect due to the new non-abelian couplings, is to change the relative size of the electroweak radiative corrections of the Standard Model by adding a value of –2.98(–6.96)%, i.e. from a value of 5.55(3.26)% to 2.57(–3.7)%.     

Detection of methane in air using diode-laser pumped difference-frequency generation near 3.2 μm

Spectroscopic detection of the methane in natural air using an 800 nm diode laser and a diode-pumped 1064 nm Nd:YAG laser to produce tunable light near 3.2 µm is reported. The lasers were pump sources for ring-cavity-enhanced tunable difference-frequency mixing in AgGaS₂. IR frequency tuning between 3076 and 3183 cm^–1 was performed by crystal rotation and tuning of the extended-cavity diode laser. Feedback stabilization of the IR power reduced intensity noise below the detector noise level. Direct absorption and wavelength-modulation (2f) spectroscopy of the methane in natural air at 10.7 kPa (80 torr) were performed in a 1 m single-pass cell with 1 µW probe power. Methane has also been detected using a 3.2 µm confocal build-up cavity in conjunction with an intracavity absorption cell. The best methane detection limit observed was 12 ppb m (Hz.)^–1/2.     

Surface properties of laser processed ductile iron

On laser melt treatment,Sliding Wear of pearlitic ductile iron reduced from severe metallic wear to oxidative mild wear by nearly two orders of magnitude at 7.5 ms^–1 over a load range of 14–31 kg cm^–2; resistance toCavitation Erosion improved by a factor ofseven in corrosive media and surface hardness increased from 20–22 to 40–58 HR_c. Laser melting could effectively reduceCorrosion rates in dilute acids by nearly 40%.These improvements were caused by the ultrafine microstructure (1–41 ,DAS), microhardness (700–900,HV _0,1) and the consequent high resistance to plastic flow and subsurface crack initiation.In this investigation, pin-on-disc adhesive wear, ultrasonic vibratory cavitation erosion and potentiodynamic corrosion in synthetic sea water and 0.01 N H₂SO₄, were assessed after laser surface melting or transformation hardening of hyper-eutectic ductile iron, typically employed in automotive and marine engine components by using CO₂ CW or Nd-YAG pulsed high power laser. Also the processing parameters viz, beam power (P), scan rate (U), and specific energy intensity (P/UD _b ² ) for threshold and specific depth of transformation hardening or melting have been determined.     

Are the sources of natural fluctuations correlated in different laser modes?

The intensity fluctuations in multimode lasers with slow relaxing laser media are theoretically investigated. The power spectra corresponding to different correlation conditions between the noise sources inserted into individual modes are calculated in the framework of a two-level homogeneously broadened laser model with spatial hole burning. The comparison of calculated spectra with the experimental data allows us conclude that the noise sources are correlated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 6, pp. 771–782, June, 1996.     

Photoelectric properties of Pb1−x−y Sn x Ge y Te:In epitaxial films

Pb_1–x–y Sn _x Ge _y Te:In epitaxial films are examined in a wide temperature interval and at various background fluxes. These films have high sensitivity to infrared radiation in the spectral range <20m. The lifetime depends exponentially on temperature and varies from several seconds at T=10 K to 10^–2 s at T=20 K. The two-electron model of Jahn-Teller centers is proposed to explain the results. Multielement photoresistors based on these films are fabricated and D*=1.7×10¹³ cm Hz^1/2 W^–1 at T=25 K is achieved. Noise of the photoresistors is independent of background flux when it varies from 10¹² cm^–2 s^–1 to 10¹⁸ cm^–2 s^–1. As compared with Si:Ga and Ge:Hg photoresistors, the responsitivity is several orders larger at the operating temperature 25–30 K.     

Studies on the preparation and ethanol gas sensing properties of spinel Zn0.6Mn0.4Fe2O4 nanomaterials

Zn_1−xMn_xFe₂O₄ (x = 0, 0.2 and 0.4) nanomaterials were synthesized by sol–gel citrate method and studied structural and gas sensing properties. The structural characteristics of synthesized nanomaterials were studied by X-ray diffraction measurement (XRD) and transmission electron microscope (TEM). The results revealed that the particle size is in the range of 30–35 nm for Mn–Zn ferrite with good crystallinity. The gas sensing properties were studied towards reducing gases like LPG, CH_4, CO and ethanol and it is observed that Mn–Zn ferrite shows high response to ethanol at relatively lower operating temperature. The Zn_0.6Mn_0.4Fe₂O₄ nanomaterial shows better sensitivity towards ethanol at an operating temperature 300 °C. Incorporation of 1.5 wt.% Pd improved the sensitivity, selectivity, response time and reduced the operating temperature from 300 °C to 230 °C for ethanol sensor. The response time of 200 ppm ethanol in air is about 10s.     

Rotating-disk diode-pumped continuous-wave Nd:YAG laser

Continuous-Wave (CW) diode-laser-pumped experiments using rotating Nd: YAG disk(s) have been performed in the input-power range of 1–6 W and rotation-speed range of 0–25 Hz. With a single Nd: YAG disk in the laser cavity, about 1.56 W of output power at 1.06 µm due to the Nd³⁺ (⁴ F _3/2–⁴ I _11/2) transition at an absorbed input power of 4.2 W has been observed, leading to an optical-to-optical conversion efficiency of over 37% and slope efficiency of 52% using 7.5% transmission output coupler. The laser output power has been observed to decrease by either increasing the number of Nd:YAG disks in the cavity or increasing the rotation speed of the disk(s).     

Parametric Frequency Converters Based on New Nonlinear Crystals

Results of investigations into the physical properties of a number of new nonlinear crystals are presented. The parameters of frequency converters manufactured on their basis are compared, and second-harmonic generation of CO₂ lasers first excited by frequency conversion in LiInSe₂, AgGa_{1– x} In_xSe₂, Ag_xGa_xGe_xS_{2(1 + x)}, and Hg_1–x Cd_xGa₂S₄ crystals is investigated. The superiority of HgGa₂S₄, Hg_1–x Cd_xGa₂S₄, and AgGa_1–x In_xSe₂ over the well-known crystals has been demonstrated for frequency conversion both within the middle-IR range and from the visible range to the middle-IR range. Advantages of LiInSe₂ and AgGa_1–x In_xSe₂ crystals are demonstrated for the direct frequency conversion of femtosecond laser radiation to the middle-IR range compared to the cascade frequency conversion and direct frequency conversion in LiInS₂ crystals.     

Measurement of the WWγ cross section and direct limits on anomalous quartic gauge boson couplings at LEP

The process e⁺e⁻→W⁺W⁻γ is analysed using the data collected with the L3 detector at LEP at a centre-of-mass energy of 188.6 GeV, corresponding to an integrated luminosity of 176.8 pb⁻¹. Based on a sample of 42 selected W⁺W⁻ candidates containing an isolated hard photon, the W⁺W⁻γ cross section, defined within phase-space cuts, is measured to be: σ_WWγ=290±80±16 fb, consistent with the Standard Model expectation. Including the process , limits are derived on anomalous contributions to the Standard Model quartic vertices W⁺W⁻γγ and W⁺W⁻Zγ at 95% CL: −0.043 GeV⁻²<a₀/Λ²<0.043 GeV⁻², −0.08 GeV⁻²<a_c/Λ²<0.13 GeV⁻², −0.41 GeV⁻²<a_n/Λ²<0.37 GeV⁻².     

Frequency- and wavelength-modulation spectroscopies: Comparison of experimental methods using an AlGaAs diode laser

Low-wavelength modulation (1 kHz), high-wavelength modulation (100 MHz) and two-tone frequency modulation (390±5 MHz) spectroscopies are systematically compared by measuring the minimum detectable absorption achieved using an AlGaAs diode laser tuned on a third-overtone methane transition at 886 nm. From the S/N behavior has been extrapolated a minimum relative absorption (1 Hz of bandwidth) of 4.5(1)×10^–7 for the LMW, 9.7(3)×10^–8 for the HWM and 6.4(2)×10^–8 for the TTFM. In the LWM case the detection-limit value is represented by the laser amplitude 1/f excess noise, while for the high-frequency detection techniques this contribution is negligible with respect to other noise sources. These detection limits well agree with the calculated quantum limited values based on measured laser power, modulation index, noise figure of the electronic components, and other parameters of the apparatus.     

Method of measurement range change in microwave radiometers with pulse-width modulation of a reference signal

A simple method for changing the measurement range in zero microwave radiometers with pulse-width modulation is proposed. This method consists in the modulation change of reference noise oscillator signals rather than in the change of their absolute values.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 8, pp. 1057–1064, August, 1996.     

230 and 492 GHz low noise sis waveguide receivers employing tuned Nb/AlOx/Nb tunnel junctions

We report results on two full height waveguide receivers that cover the 200–290 GHz and 380–510 GHz atmospheric windows. The receivers are part of the facility instrumentation at the Caltech Submillimeter Observatory on Mauna Kea in Hawaii. We have measured receiver noise temperatures in the range of 20K–35K DSB in the 200–290 GHz band, and 65–90K DSB in the 390–510 GHz atmospheric band. In both instances low mixer noise temperatures and very high quantum efficiency have been achieved. Conversion gain (3 dB) is possible with the 230 GHz receiver, however lowest noise and most stable operation is achieved with unity conversion gain.A 40% operating bandwidth is achieved by using a RF compensated junction mounted in a two-tuner full height waveguide mixer block. The tuned Nb/AlO _x /Nb tunnel junctions incorporate an end-loaded tuning stub with two quarter-wave transformer sections to tune out the large junction capacitance. Both 230 and 492 GHz SIS junctions are 0.49µm² in size and have current densities of 8 and 10 kA/cm² respectively.Fourier Transform Spectrometer (FTS) measurements of the 230 and 492 GHz tuned junctions show good agreement with the measured heterodyne waveguide response.     

Cross sections for five jet production above theW + W − threshold ine + e − annihilation

We describe the calculation of five jet production from theW ⁺ W ^– intermediate state ine ⁺ e ^– annihilation in lowest order QCD. Some results for integrated cross-sections are presented.     

Charge carriers and mobility of Cu-Ti ferrite

The concentration and drift mobility of charge carriers in Cu_1–x Ti _x Fe₂O₄ ferrite are calculated, over a wide range of temperatures (300–773 K), employing d.c. conductivity and thermoelectric power data. With increasing temperature the concentration of charge carriers decreases whilst the drift mobility exhibits an exponential increase. Over the above-mentioned temperature range, the obtained density of charge carriers varies between 10²¹ and 10²² cm^–3 whereas the drift mobility has values between 10^–8 and 10^–4 cm²/V s. The results are discussed on the basis of a small-polaron hopping conduction. The activation of the d.c. conductivity has been attributed to the thermal activation of the mobility.