Finite-Time Stabilization of Differential Systems with Incommensurable Delays

Differential Equations - For a spectrally controllable linear autonomous system with incommensurable delays, we construct a dynamic state feedback in the form of a differential-difference...     

Onset of crater formation during short pulse laser ablation

We report morphologic changes of metallic surfaces at the onset of ablation, starting from gentle ablation to the emergence of ablation craters. The evolution of both observed melting zones and of ablation craters therein are investigated in dependence of the ablation laser fluence for nanosecond ultraviolet laser pulses. Further, consequences of crater formation for cluster synthesis within the released atomic vapor are pointed out. PACS 52.38.Mf; 79.20.Ds; 65.40.De     

Green function renormalization in SU(2)L ⊗ U(1) four-fermion model

Using the Dyson-Schwinger equation, the four-fermion Green functions in one-loop approximation to the SU(2)_L U(1) four-fermion model are found, as well as corrections to them. An expression is obtained for the collective field propagator in the one-loop approximation, and its regularization is performed. In the model under consideration, collective excitations are identified with a massless Goldstone field and a massive scalar field. It is shown that as a result of the reconstruction of the vacuum, one fermion (the analog of the neutrino) is massless, while the other (the analog of the electron), massive.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 19–23, January, 1984.     

Laser-Cooled Ions and Atoms in a Storage Ring

Hyperfine Interactions - We review recent experiments at the Heidelberg Test Storage Ring which apply advanced laser cooling techniques to stored ion beams. Very high phase-space densities are...     

Acoustic wave propagation through the boundary between a liquid and the Heusler ferromagnetic alloy

Incidence of an acoustic wave upon a plane boundary between a liquid and a ferromagnetic crystal is considered. The ferromagnet is the Ni_2+x+y Mn_1−x Ga_1−y Heusler alloy with a shape memory, which is in the region of the premartensite or martensite phase transition in temperature. The directions of propagation and polarization and the amplitudes of the reflected and transmitted quasilongitudinal and quasitransverse waves in the (110) plane of the crystal are determined. Starting from a certain critical angle of incidence, a longitudinal wave in the crystal becomes inhomogeneous and gliding along the boundary with an accompanying surface oscillation. In the vicinity of the phase transition point, this wave may be radiated into the crystal bulk. Proceeding from the experimental data by Trivisonno for ultrasonic velocities and absorption in a Ni₂MnGa crystal, numerical estimates are obtained for the aforementioned acoustic effects.     

Bunched laser cooling of a stored weak 7Li+ ion beam in a pure triplet state

A preparation scheme for a 7Li+ ion beam in a storage ring is presented which provides ions in the metastable triplet states with well controlled longitudinal phase space properties. For both state selective preparation and beam cooling, laser- and electron-cooler forces are applied. The spatial- and momentum distributions of the ions are directly detected by a time resolved measurement of the fluorescence light. At low beam intensities, the remaining heating rate of such a beam is completely determined by residual gas scattering. This revised version was published online in July 2006 with corrections to the Cover Date.     

Spatially resolved ultra-trace analysis of elements combining resonance ionization with a MALDI-TOF spectrometer

A combined setup for spatially resolved mass analysis of trace amounts of elements and macromolecules is presented. Using a MALDI-TOF mass spectrometer, a laser spectroscopic setup for resonant ionization of neutral atoms has been implemented. This allows for an efficient and selective detection of trace elements by means of resonance ionization mass spectrometry (RIMS). The instrumental scheme is described, and methodological developments are presented. In a first application pure, laser desorption/ionization with TOF-MS was used to measure mass distributions of cosmic nanodiamonds. For further applications regarding the spatially resolved ultra-trace analysis of elements in solid samples, an implanted target was used to characterize both laser desorption/ionization and laser desorption/resonance ionization for the detection of trace elements within. A perspective of the setup is given and future investigations are outlined.     

High-pressure synthesis and magnetic properties of Bi<Subscript>0.5</Subscript>D<Subscript>0.5</Subscript>MnO<Subscript>3</Subscript> (<Emphasis Type="Italic">D</Emphasis> = Pb,Ba) solid solutions

Perovskites Bi_0.5D_0.5MnO₃(D = Pb, Ba) were prepared under high pressure (4 GPa) at 1200–1300°C. According to the X-ray diffraction data, crystalline Bi_0.5Pb_0.5MnO₃ has a tetragonal unit cell with the parameters a = 3.940 Å and c = 3.800 Å, whereas Bi_0.5Ba_0.5MnO₃ crystals are cubic with a = 3.940 Å. It is concluded from magnetic studies that lead-containing manganite is an antiferromagnet with T_N = 120 K, whereas Bi_0.5Ba_0.5MnO₃ is a spin glass with spin-freezing temperature T _f = 38 K. Both compounds are decomposed upon heating in air at temperatures above 500°C. With the use of synthesis in air, Bi_0.5Ca_{0.5 ? x}D _x MnO₃ solid solutions with x as high as 0.25 were obtained.     

Preparation of 5‐methyl‐2‐sulfanyl‐7h‐1,3,4‐thiadiazolo[3,2‐a]‐pyrimidin‐7‐ones

7H‐1,3,4‐Thiadiazolo[3,2‐a]pyrimidin‐7‐ones can be prepared by the acylation of 5‐amino‐1,3,4‐thiadiazoles with diketene and subsequent ring closure (dehydration). Whereas arylthio substituents (SC₆H₅) can be introduced in 2‐position by the replacement of Br, alkylthio groups (SC₂H₅) have to be already presentin the starting 5‐amino‐1,3,4‐thiadiazole. The ambident nucleophile 2‐thiazolidinethione reacts in the Br substitution reaction on the N atom.