Generation of unipolar pulses in nonlinear media

Methods recently proposed for generating unipolar pulses in nonlinear media in terahertz and optical electromagnetic ranges are reviewed. Such pulses have nonzero “electric area” (time integral of the field strength over the entire duration of a pulse) and, correspondingly, a significant component of the field with zero frequency, thus exhibiting quasistatic properties. Effective generation of unipolar pulses would allow, e.g., transferring mechanical momentum to charged particles and, thereby, controlling the motion of wave packets of matter, which can be useful for compact accelerators of charged particles and for other applications.     

Continuity of operators in separable constructive metric spaces

We construct an everywhere defined continuous operator on a separable CMS having the following property: it is not possible to cover the domain of this operator by denumerably many balls such that the oscillation of the operator in each ball of the covering is less than 1.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova Akad. Nauk SSSR, Vol. 60, pp. 194–196, 1976. Results announced October 16, 1975.     

Intrinsic ferromagnetism in insulating cobalt doped anatase TiO2

Using complementary experiments we show that the room temperature ferromagnetism observed in anatase Co:TiO(2) films is not carrier mediated, but coexists with the dielectric state. TEM and x-ray absorption spectroscopy reveal a solid solution of Co in anatase, where Co is not metallic but in the +2 state substituting for Ti. Measurements at 300 K yield a M(S) of 1.1 mu(B)/Co atom, while all films are highly insulating. The evidence of intrinsic ferromagnetism in the dielectric ground state of Co:TiO(2) leads to new considerations for the origin of ferromagnetism in transition metal doped oxides.     

Narrow α + <Superscript>28</Superscript>Si elastic-scattering states at high excitation in <Superscript>32</Superscript>S

The excitation function and angular distributions of elastic α-particle scattering on ²⁸Si have been measured in the laboratory energy range 6-28 MeV using a backscattering technique on a thick target, yielding a continuous energy distribution. More than 200 narrow states are observed, with widths in the range ∼ 30-100 keV at excitation energies E ^* = 13-32 MeV. Angular distributions at backward angles were measured, and angular momentum values of more than 83 states have been deduced. The analysis gives spin-parities J ^π, α-partial widths Γ_α and reduced widths of the narrow high-lying resonant states in ³²S. The experimentally observed states display both the negative- and the positive-parity rotational-like sequences with seemingly no parity splitting, a finding which is at variance with most potential-model predictions. The deduced effective moment of inertia indicates a more extended structure than the ground-state configuration. The observed strength of each ℓ-value is analyzed in terms of an underlying split doorway state of Lorentzian form, which yields an interpretation as fragmented rotational α + ²⁸Si states. Received: 26 June 2000 / Accepted: 16 September 2002 / Published online: 4 February 2003 RID="a" ID="a"e-mail: kkallman@abo.fi RID="b" ID="b"Present address: Swedish Polytechnic, FIN-65200 Vasa, Finland. Communicated by D. Guerreau     

The NUCLEON experiment: The current status

The main purpose of the NUCLEON experiment is direct measurements of the energy spectra of cosmic rays in the range 10¹¹–10¹⁵ eV with the use of the lightweight facility during a prolonged orbital flight. The energy is determined using a technique based on the measurement of the spatial density of secondary particles produced in the initial event of inelastic interaction. The schematic diagram of the NUCLEON facility, the current status of the project, the results of testing the prototype, and plans are presented.     

Investigation of the dielectric properties of polymer composite films with a ferroelectric filler using the bridge and thermal noise methods

Thin films of composite polymers based on polyvinylidenfluoride (PVDF), with ferroelectric fillers of No-Zr-Ti-Pb (NZTP-l) were used to study the dielectric properties of the composites; specifically, we obtained the temperature dependence of the dielectric permittivity at various frequencies at various contents of filler piezoceramic in the polymers. Measurements were conducted using the bridge method and with the thermal noise method. In the studies with the bridge method, the range of the frequencies was 25 Hz-1 MHz; in the studies with the thermal noise method, the frequencies varied from 1 to 100 kHz.     

Effect of photoexcited carriers on Raman spectra of a hydrogenated GaAs crystal implanted with silicon

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 53, No. 1, pp. 116–121, July, 1990.