Pancyclicity of Strong Products of Graphs

We prove that the strong product of graphs G₁××G_n is pancyclic, in particular hamiltonian, for nc for any cln(25/12)+1/640.75 whenever all G_i are connected graphs with the maximum degree at most .This research was supported by KONTAKT ME 337 as a part of REU programme and in part by GACR 201/99/0242The author acknowledges partial support by NSF grant DMS-9900969 and by Institute for Theoretical Computer ScienceThe author acknowledges partial support by Institute for Theoretical Computer ScienceInstitute for Theoretical Computer Science is supported by Ministry of Education of Czech Republic as project LN00A056Final version received: August 6, 2003     

Probing the wave function of shallow Li and Na donors in ZnO nanoparticles

Electron paramagnetic resonance and electron nuclear double resonance (ENDOR) experiments on ZnO nanoparticles reveal the presence of shallow donors related to interstitial Li and Na atoms. The shallow character of the wave function is evidenced by the multitude of 67Zn ENDOR lines and further by the hyperfine interactions with the 7Li and 23Na nuclei that are much smaller than for atomic lithium and sodium. In the case of the Li-doped nanoparticles, an increase of the hyperfine interaction with the 7Li nucleus and with the 1H nuclei in the Zn(OH)(2) capping layer is observed when reducing the size of the nanoparticles. This effect is caused by the confinement of the shallow-donor 1s-type wave function that has a Bohr radius of about 1.5 nm, i.e., comparable to the dimension of the nanoparticles.     

Overhauser effect of 67Zn nuclear spins in ZnO via cross relaxation induced by the zero-point fluctuations of the phonon field

Hole burning in and displacements of the magnetic-resonance absorption line of the electron spin of the shallow hydrogen-related donor in ZnO are observed upon resonant irradiation with microwaves at 275 GHz and at 4.5 K in a magnetic field of 10 T. These effects arise from an almost complete polarization of the many 67Zn (I=5/2) nuclear spins that have an isotropic hyperfine interaction with the electron spin of the shallow donor. It is proposed that this huge dynamic nuclear polarization is caused by a spontaneous-emission-type cross relaxation in the coupled electron-spin nuclear-spin system induced by the zero-point fluctuations of the phonon field.     

Passive stabilization of a passively mode-locked laser by nonlinear absorption in indium phosphide

A diode-pumped Nd:KGd(WO4)2 laser mode locked by a saturable Bragg reflector (SBR) is passively stabilized to suppress Q-switched mode locking and to extend the parameter range of continuous-wave mode locking. An indium phosphide plate exhibiting two-photon absorption and free-carrier absorption is used for passive stabilization. The intracavity pulse energy for the onset of stable continuous-wave mode locking is reduced by a factor of 4 compared with the laser without stabilization. By increasing the modulation depth of the SBR, pulse shortening by 30% is achieved and bandwidth-limited 6.2-ps pulses are measured.     

Low-pressure gradient micro-ion chromatography with ultra-short monolithic anion exchange column

A 1.0 x 0.4 cm silica based monolithic anion exchanger has been produced and evaluated for use within a miniature gradient suppressed ion chromatography system based upon low-pressure micro-scale peristaltic pumps.     

Highly efficient 1063-nm continuous-wave laser emission in Nd:GdVO4

Highly efficient 1-microm continuous-wave laser emission in 3-mm-thick, 0.5- and 1.0-at. % Nd:GdVO4 crystals longitudinally pumped at 879 nm into the laser emitting level is reported. Under Ti:sapphire pumping, the slope efficiency in absorbed power is approximately 80% for both crystals, while the slope efficiency, the optical-to-optical efficiency (at 1700-mW pump power), and the laser threshold in incident power are 79%, 78%, and 31 mW for 0.5-at. % Nd and 80%, 77%, and 40 mW for 1.0-at. % Nd, respectively. The slope efficiency is close to the quantum defect limit, the difference being fully accounted for by the residual optical losses. Under 879-nm diode laser pumping, the slope efficiency and the optical-to-optical efficiency in absorbed power of the 0.5-at. % Nd:GdVO4 crystal are 60% and 53%, owing to poorer superposition of the pumped and the laser mode volumes.     

Absolute Continuity in Periodic Thin Tubes and Strongly Coupled Leaky Wires

Using a perturbative argument, we show that in any finite region containing the lowest transverse eigenmode, the spectrum of a periodically curved smooth Dirichlet tube in two or three dimensions is absolutely continuous provided the tube is sufficiently thin. In a similar way we demonstrate absolute continuity at the bottom of the spectrum for generalized Schrödinger operators with a sufficiently strongly attractive interaction supported by a periodic curve in R^d = 2, 3.     

An Inverse Problem for an Harmonic Oscillator Perturbed by Potential: Uniqueness

Consider the perturbed harmonic oscillator Ty = -y" + x²y + q(x)y on L²(R) where the real potential q satisfy some assumption on infinity (the case q L²(R), (t+1)^-rdt), r < 1 is covered).     

Electronic absorption spectra of CCS and CCS in neon matrices

Mass selected C₂S⁻ ions have been co-deposited with neon to grow a matrix at 6 K. The and electronic absorption spectra of the linear CCS⁻ anion have been identified with origin band at 10 606 and 22 273 cm⁻¹, respectively. After exposure to UV radiation a new electronic transition of CCS is observed (origin band at 30 563 cm⁻¹) in addition to its known band system. Ab initio calculations provide support for the symmetry assignment of the upper electronic states of CCS⁻, CCS and of the vibrational structure in the spectra.     

Landau theory of shape phase transitions in the cranked interacting boson model

Landau theory of phase transitions is applied to quadrupole shapes of rotating atomic nuclei within the interacting boson model (IBM) with cranking. It is shown that the coherent-state method must be generalized to allow for non-Hermitian quadrupole tensors of the coherent-state coefficients, which results in important modifications of the cranking shape-phase diagram compared to previous non-IBM studies of rotating nuclei. The parameter space has two surfaces of the first-order phase transitions and a curve of the second-order phase transition at their intersection. The phase structure of the cranked IBM closely resembles systems with competing superconducting and normal phases.