An Approach to Linear Scalable DH-PHEMT Model for Millimeterwave Application

This paper describes a scalable small-signal equivalent circuit for 0.25 m gatelength Double Heterojunction delta-doped PHEMTs. The scaling rules for all elements except the pad capacitances and bondwire inductances have been determined. Good agreement is obtained between simulation results and measured results for 2 times 20 m , 2 times 40 m, 2 times 60 m, 2 times 100 m gate width (number of gate fingers times unit gate width) DH PHEMT.     

Light absorption in laser-heated cavities

The absorption of laser light in 0.25–1 mm diameter gold cavities, irradiated for the purpose of generating high-temperature blackbody radiation with intense laser radiation of either =0.44 m or =1.3 m wavelength, was investigated. For =0.44 m radiation the absorption exceeded 0.9 for all conditions, but dropped to only 0.3 for the smallest cavities irradiated at =1.3 m. Entrance hole and cavity filling with plasma seems important for the understanding of the observations.     

A new procedure for thin-film deposition by solution spraying

The major reasons for the low photovoltaic efficiency of Cu₂S/CdS cells, in which the CdS film is deposited by spraying, are due to small film thicknesses which do not exceed 4 m and the small average grain size which ranges from 0.1 to 0.5 m.A new experimental solution spraying procedure is described that prevents both restrictions by controlling the substrate temperature. Average grain sizes of more than 1 m are obtained.Work supported by Ministere Pubblica Istruzione and Centro Regionale Ricerche Nucleari e di Struttura della Materia     

Trilinear generally covariant equations

Field equations for n-frames h ^a that are possible in the theory of absolute parallelism are considered. It is shown that in three cases the equations can, after the substitution h ^a =H^pH ^a (H=det H ^a , p is an n-dependent constant), be written in a trilinear form that contains only the matrix H _a and its derivatives and not H ^a . It is shown that the equations are still regular for degenerate but finite matrices H _a if rank H _a 2.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 22–27, February, 1991.     

Probability of predissociation of mesic molecules HμHe

The probability of predissociation of the HHe mesomolecules has been calculated for different hydrogen and helium isotopes. It is shown, that for pHe molecules the predissociation is the main channel for mesomolecular decay, while for tHe mesomolecules the main channel is a radiative decay. The KEK data on the relative smallness of the yield of -quanta from the radiative decay of mesomolecules d³He as compared with d⁴He can be explained if one takes into consideration the mesomolecular predissociation channel and the difference in their production rate.     

Isotope dependence of particle-decay rates of muonic molecular ions (d3,4Heμ) J=1 below (dμ)1s-3,4He threshold

Rates of particle-emitting decay of the resonant state of the muonic molecular ion (dHe) _J=1 lying below the (d)_1s-He threshold can decay to the d-He scattering state. The resonant state is estimated by scattering calculations with the non-adiabatic coupled-rearrangement-channel method. Strong isotope dependence of the decay rates of (d³He) _J=1 and (d⁴He) _J=1 is predicted, though the calculated radiative decay rates of the states are almost the same. In (d³He) _J=1, the particle decay width is three times larger than the radiative decay width, while the two types of decay widths are almost the same in (d⁴He) _J=1. This results in a strong hindrance of the branching ratio of the radiative decay of (d³He) _J=1 compared with the case of (d⁴He) _J=1. This is consistent with a recent observation of the radiative decay of the two molecular states.     

Measurement of the refractive index and optical absorption spectra of epitaxial bismuth substituted yttrium iron garnet films at uv to near-ir wavelengths

Refractive-index and optical-absorption spectra of Bi-substituted yttrium iron garnet films, epitaxially grown by liquid-phase epitaxy, have been measured in the spectral regime 0.26 m1.9 m by thin-film interference for 0.52 m and by ellipsometry for0.52 m. The Y_3–x–y Bi _x Pb _y Fe_5–z Pt _z O₁₂ films contain bismuth in the range Ox 1.42, lead in the range 0.01 y0.08 and platinum in the range 0.005<=z0.03. There is satisfactory coincidence between the results from ellipsometry and thin-film interference in the overlapping wavelength region. The materials investigated are the same as reported earlier from this laboratory in ter mof their magnetic and magnetooptic properties.     

Positivity of entropy production in the presence of a random thermostat

We study nonequilibrium statistical mechanics in the presence of a thermostat acting by random forces, and propose a formula for the rate of entropy productione() in a state . When is a natural nonequilibrium steady state we show thate()0, and sometimes we can provee()>0.     

Determination of the Coefficient of Laser Radiation Reflection from Dielectric Targets in Vacuum

We present the results of experimental determination of the coefficients of laser radiation reflection (₁ 10.6 m and ₂ 1.06 m) from dielectric targets of complex chemical composition in vacuum with allowance for a regime of developed plasma formation.     

A μSR study of spin density wave condensation in Cr85Mo15

Zero field SR spectra from Cr₈₅Mo₁₅ are well described by the sum of a lightly damped (0.02s^–1<₁<0.2s^–1) and a heavily damped (2s^–1<₂<15s^–1) exponential. The temperature dependence of these components is discussed in relation to the condensation of the incommensurate spin density wave and the onset of the antiferromagnetic state in this Cr-like alloy below T_N=120K. Evidence is presented for the nucleation of the spin density wave at temperatures greater than 1.5T_N.     

Ultrashort in-plane semiconductor microlasers with high-reflectivity microstructured mirrors

We present very compact, as short as 20 m long, low-threshold in-plane semiconductor lasers operating at a wavelength of 980 nm, in which microstructured mirrors have been formed at both cavity ends by deep reactive ion etching (RIE). The back mirror consists of a seven-period third order Bragg reflector with a measured reflectivity of 95%. The front mirror has a similar configuration, but consists of three periods with a lower reflectivity (80%) in order to allow output coupling. Lasing has been achieved from 20 m long and 8 m wide devices exhibiting a current threshold of 7 mA. These are among the shortest in-plane Fabry–Perot electrically pumped lasers demonstrated to date. Design issues are discussed, along with experimental data from which values for the reflectivity of the mirrors are derived. State-of-the-art electron beam lithography (EBL) and high-aspect-ratio RIE have been used for device fabrication, while additional strategies are proposed for the further improvement of the device performance.     

The van der Waals limit for classical systems. I. A variational principle

We consider the thermodynamic pressurep(, ) of a classical system of particles with the two-body interaction potentialq(r)+ ^v K(r), where is the number of space dimensions, is a positive parameter, and is the chemical potential. The temperature is not shown in the notation. We prove rigorously, for hard-core potentialsq(r) and for a very general class of functionsK(s), that the limit 0 of the pressurep(, ) exists and is given by where the limit and the supremum can be interchanged. Here is a certain class of nonnegative, Riemann integrable functions,D is a cube of volume |D|, anda ⁰() is the free energy density of a system withK=0 and density . A similar result is proved for the free energy.     

Positron annihilation anomaly in the high-temperature superconductor YBa2Cu3O7−x

We have measured the ac susceptibility of a wire with a Nb core (1.27 mm diam.) and a Cu cladding (0.37 mm thickness) atT50 K andB0.1 mG. Due to its proximity to Nb, the Cu becomes fully superconducting. From the data we find a breakdown fieldH _b =1.2 (mG) and a coherence length =2.2T ^–1/2 (m) for the Cu, as well as a field penetration depth -34T ^1/2 (m) at the Cu/Nb interface.     

μ+SR in magnetically ordered BCC metals: Local fields, μ+ sites,quantum diffusion,and strain effects

The paper gives a critical discussion of the procedures for extracting from the ⁺SR signals obtainable on magnetically ordered metals information on ⁺ sites, on local lattice distortions induced by the ⁺, on the local magnetic fields felt by the ⁺, and on quantum diffusion. Results for-Fe are: ⁺ occupy O sites, the tetragonality of the elastic double-force tensor isA–B 2eV, the dipolar magnetic field acting on the ⁺ isB _dip=(0.66±0.02)T. Using this information ⁺ hopping rates and diffusivities in Fe are deduced and compared with diffusivities obtained for hydrogen and deuterium. From this it is concluded that hydrogen in Fe diffuses via the adiabatic mechanism. In addition, the paper contains a brief summary of the theoretical background required for taking advantage of the rather large ¦A– B¦ values expected for ⁺ at O sites in bcc metals in order to gain information on the effects of energy asymmetries between neighbouring ⁺ sites on the ⁺ hopping rates.     

Monte-Carlo calculation of bound-state properties

We elaborate on the role of the Green's function Monte-Carlo method in connection with quantum few-body systems and their computational treatment algorithms for calculation of bound-state properties are presented. We report results obtained from Green's function Monte-Carlo calculations both of ground-state properties of the mesic moleculesdt,dd, andpd as well as of excited states of the three-dimensional anharmonic oscillator and thedt molecule.Deceased     

Collisionless kinetic equations for massive particles with spins 1/2 and 0 in gravitational and electromagnetic fields

We define a covariant and gauge-invariant generalization of the Wigner functions of particles with spins 1/2 and 0. The collisionless kinetic equations are obtained for these particles in external gravitational and electromagnetic fields in the quasiclassical approximation; also obtained are the momentum representations of the energy-momentum tensor, current, and spin tensor, taking into account the effects of the spin's interaction with the gravitational field an electromagnetic field. The following notation is used: e and m are the charge and mass of the particles; is Planck's constant; (x) are the covariant-fixed Dirac matrices; ^,=(1/4)[, ]: a(^b)=(1/2) (a b +ab ); [A, B]=A·B – B·A; A,B=A·B+B·A; g(x)=det(g (x));R = –...; the speed of light c=1.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 47–53, September, 1990.The author wishes the thank Yu. G. Ignat'ev and members of the seminar in General Relativistic Statistics and Cosmology of the Kazan' Pedagogical Institute for useful discussions.     

Towards slow μ− production via muon catalyzed fusion

Slow ^– production via dd-CF using a two-layer arrangement is investigated. To determine its feasibility, experimental measurements are now in progress using the muonic X-ray detection method. The following experimental steps are being considered: (1) measurement of the number of ^– stopped inside a solid H₂/D₂ layer by detecting p K X-rays, (2) hot d emission detection by placing a secondary target at a distance of 10–30 mm from the layer and by detecting specific delayed X-rays, (3) measurement of the disappearance of d emission as the added D₂ layer is increased, (4) dd-CF measurement by detecting fusion protons, and (5) slow ^– emission detection. Results of the initial test experiment are presented.     

FIR gain measurements in cw laser pumped CH3OD

Direct measurements of small signal and saturated gain in cw laser pumped CH₃OD are reported for three lasing transitions of 57 m, 82 m and 103 m. The 57 m transition has a measured gain of 0.6/m, the strongest gain in methanol reported so far. Moreover small gain saturation of this line makes it to be one of the strongest known cw FIR laser lines.     

Pulsed 532 nm laser wirestripping: Removal of dye-doped polyurethane insulation

Removal of rhodamine 6G doped polyurethane insulation coated onto 50 m diameter wire is shown to proceed efficiently and cleanly by irradiation with 532 nm Q-switched pulses from a Nd:YAG laser. The stripping action produced by this method is similar in quality to excimer laser wirestripping. Several experimental parameters were explored including fluence, pulse duration, dye concentration, and the number of incident pulses. Acceptable stripping conditions were obtained for a 3–5 s exposure at 10 Hz, using a dye concentration of 10% by weight, and 12 n pulses at 650 mJ/cm². Nearly 0.5 m/pulse is removed at this fluence, which exceeds the threshold fluence of 600 mJ/cm² by only 50 mJ/cm². The measured 532 nm absorption coefficient of the 10% dye-doped polyurethane was 4×10⁴ cm^–1. Lower fluences and/or dye concentrations produced inadequate stripping, while shorter duration pulses caused unacceptable melting of the thin gold layer which covered the copper core of the wire. Pulse-by-pulse photographs of the stripping action clearly show melting of the dye/polymer insulation, and thermal rollback of the insulation near the stripped end. Regardless, excellent edge definition is obtained by this method.     

On the photo-electroluminescence of ZnS-Cu

The influence of weak ultra-violet irradiation on the brightness waves of electroluminescence is investigated for two types of ZnS-Cuphosphors. The observed effects (increase in brightness in the primary peak and its phase shift, the disappearance of the secondary peak) are explained on the basis of present-day conceptions on electroluminescence.

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ZnS-Cu

ZnS-Cu. ( , ) .