Solutions of the reflection equation for the vertex model

We investigate the possible regular solutions of the boundary Yang–Baxter equation for the fundamental U_q[G₂] vertex model. We find four distinct classes of reflection matrices such that half of them are diagonal while the other half are non-diagonal. The latter are parameterized by two continuous parameters but only one solution has all entries non-null. The non-diagonal solutions do not reduce to diagonal ones at any special limit of the free-parameters.     

The Gaussian effective potential and stochastic partial differential equations

We investigate arbitrary stochastic partial differential equations subject to translation invariant and temporally white noise correlations from a nonperturbative framework. The method that we expose first casts the stochastic equations into a functional integral form, then it makes use of the Gaussian effective potential approach, which is an useful tool for describing symmetry breaking. We apply this method to the Kardar-Parisi-Zhang equation and find that the system exhibits spontaneous symmetry breaking in eight="16" border="0" style="vertical-align:bottom" width="106" alt="View the MathML source" title="View the MathML source" src="http://ars.els-cdn.com/content/image/1-s2.0-S0378437107007224-si7.gif"> and (3+1) Euclidean dimensions, providing insight into the evolution of the system configuration due to the presence of noise correlations. A simple and systematic approach to the renormalization, without explicit regularization, is employed.     

Classical limit of the Casimir entropy for scalar massless field

We study the Casimir effect at finite temperature for a massless scalar field in the parallel plates geometry in <em>Nem> spatial dimensions, under various combinations of Dirichlet and Neumann boundary conditions on the plates. We show that in all these cases the entropy, in the limit where energy equipartitioning applies, is a geometrical factor whose sign determines the sign of the Casimir force.     

Surface modification of poly(propylene carbonate) by oxygen ion implantation

Poly(propylene carbonate) (PPC) was implanted by oxygen ion with energy of 40 keV. The influence of experimental parameters was investigated by varying ion fluence from 1 &times; 10¹² to 1 &times; 10¹⁵ ions/cm². XPS, SEM, surface roughness, wettability, hardness, and modulus were employed to investigate structure and properties of the as-implanted PPC samples. Eight chemical groups, i.e., carbon, Cer="0" alt="single bond" src="http://cdn.els-cdn.com/sd/entities/sbnd" class="glyphImg">H, Cer="0" alt="single bond" src="http://cdn.els-cdn.com/sd/entities/sbnd" class="glyphImg">Oer="0" alt="single bond" src="http://cdn.els-cdn.com/sd/entities/sbnd" class="glyphImg">C, Cer="0" alt="single bond" src="http://cdn.els-cdn.com/sd/entities/sbnd" class="glyphImg">O, Oer="0" alt="single bond" src="http://cdn.els-cdn.com/sd/entities/sbnd" class="glyphImg">Cer="0" alt="single bond" src="http://cdn.els-cdn.com/sd/entities/sbnd" class="glyphImg">O, Cer="0" alt="double bond; length as m-dash" src="http://cdn.els-cdn.com/sd/entities/dbnd" class="glyphImg">O, eight="43" border="0" align="middle" width="63" style="vertical-align: bottom;" alt="Image" title="Image" src="http://ars.els-cdn.com/content/image/1-s2.0-S0169433206015649-fx1.jpg">, and eight="41" border="0" align="middle" width="62" style="vertical-align: bottom;" alt="Image" title="Image" src="http://ars.els-cdn.com/content/image/1-s2.0-S0169433206015649-fx2.jpg"> groups were observed on surfaces of the as-implanted samples. The species and relative intensities of the chemical groups changed with increasing ion fluence. SEM images displayed that irradiation damage was related strongly with ion fluence. Both surface-recovering and shrunken behavior were observed on surface of the PPC sample implanted with fluence of 1 &times; 10¹⁵ ions/cm². As increasing ion fluence, the surface roughness of the as-implanted PPC samples increased firstly, reached the maximum value of 159 nm, and finally decreased down the minimum value. The water droplet contact angle of the as-implanted PPC samples changed gradually with fluence, and reached the minimum value of 70&deg; with fluence of 1 &times; 10¹⁵ ions/cm². The hardness and modulus of the as-implanted PPC samples increased with increasing ion fluence, and reached their corresponding maximum values with fluence of 1 &times; 10¹⁵ ions/cm². The experimental results revealed that oxygen ion fluence closely affected surface chemical group, morphology, surface roughness, wettability, and mechanical properties of the as-implanted PPC samples.     

Properties of the Ising magnet confined in a corner geometry

The properties of Ising square lattices with nearest neighbor ferromagnetic exchange confined in a corner geometry, are studied by means of Monte Carlo simulations. Free boundary conditions at which boundary magnetic fields ±<em>hem> are applied, <em>i.e.em>, at the two boundary rows ending at the lower left corner a field +<em>hem> acts, while at the two boundary rows ending at the upper right corner a field −<em>hem> acts. For temperatures <em>Tem> less than the critical temperature <em>Tem>_c of the bulk, this boundary condition leads to the formation of two domains with opposite orientation of the magnetization direction, separated by an interface which for <em>Tem> larger than the filling transition temperature <em>Tem>_f(<em>hem>) runs from the upper left corner to the lower right corner, while for <em>Tem><<em>Tem>_f(<em>hem>) this interface is localized either close to the lower left corner or close to the upper right corner. It is shown that for <em>Tem>=<em>Tem>_f(<em>hem>) the magnetization profile <em>mem>(<em>zem>) in the <em>zem>-direction normal to the interface simply is linear and the interfacial width scales as <em>wem>∝<em>Lem>, while for <em>Tem>><em>Tem>_f(<em>hem>) it scales as eight="17" border="0" style="vertical-align:bottom" width="53" alt="View the MathML source" title="View the MathML source" src="http://ars.els-cdn.com/content/image/1-s2.0-S0169433207009907-si11.gif">. The distribution <em>Pem>(<em>?em>) of the interface position <em>?em> (measured along the <em>zem>-direction from the corners) decays exponentially for <em>Tem><<em>Tem>_<em>fem>(<em>hem>) from either corner, is essentially flat for <em>Tem>=<em>Tem>_f(<em>hem>), and is a Gaussian centered at the middle of the diagonal for <em>Tem>><em>Tem>_f(<em>hem>). Unlike the findings for critical wetting in the thin film geometry of the Ising model, the Monte Carlo results for corner wetting are in very good agreement with the theoretical predictions.     

Dynamics of electrons and holes at surfaces

We present <em>ab initioem> calculation results for electron-phonon (e-ph) contribution to hole lifetime broadening of the eight="13" border="0" style="vertical-align:bottom" width="13" alt="View the MathML source" title="View the MathML source" src="http://ars.els-cdn.com/content/image/1-s2.0-S0169433207009816-si1.gif"> surface state on Al(0 0 1). We show that e-ph coupling in this state is significantly stronger than in bulk Al at the Fermi level. It makes the e-ph decay channel very important in the formation of the hole decay in the surface state at eight="13" border="0" style="vertical-align:bottom" width="13" alt="View the MathML source" title="View the MathML source" src="http://ars.els-cdn.com/content/image/1-s2.0-S0169433207009816-si2.gif">. We also present the results for e-e lifetime broadening in a quantum-well state in 1 ML K/Cu(1 1 1). We show that this contribution is not negligible and is much larger than that in a surface state on Ag(1 1 1).     

Laser-induced pattern formation in liquid sulfur

Liquid sulfur is a well-known liquid which exhibits a polymerization transition at T_p=159 °C. Recently, it was found from our experiments that such a transition can be induced below T_p through laser illumination and that an iridescent pattern appears under strong illumination with a pulsed laser of more than 60 mJ/cm² pulse. It is proposed that the visible change in iridescence is due to a macroscopic reconstruction of laser-generated polymers and that a laser-induced phase transition takes place from a freely expanded polymer phase to an ordered polymer phase when increasing the laser illumination. To further examine this possibility, the time variation of the iridescent pattern has been fully investigated using a macro lens, a polarized microscope and an optical microscope. In an analysis of the iridescent pattern, a rapid decrease in the area was observed after an initial slow decrease, suggesting a type of phase transition. Results from the observation of a quenched sulfur sample with a polarized microscope gave evidence that the iridescent region consists of polymers. Through observation of the liquid with a microscope, a striped pattern with micrometer sized spacing was noted in the iridescent pattern. A drastic color change was observed in the pattern from its generation to its disappearance. Sample thickness dependence of the pattern was also observed. These results were well explained by assuming the self-arrangement of laser-generated colloidal polymers.     

Adhesion of fluid vesicles at chemically structured substrates

The adhesion of fluid vesicles at chemically structured substrates is studied theoretically via Monte Carlo simulations. The substrate surface is planar and repels the vesicle membrane apart from a single surface domain γ , which strongly attracts this membrane. If the vesicle is larger than the attractive γ domain, the spreading of the vesicle onto the substrate is restricted by the size of this surface domain. Once the contact line of the adhering vesicle has reached the boundaries of the γ domain, further deflation of the vesicle leads to a regime of low membrane tension with pronounced shape fluctuations, which are now governed by the bending rigidity. For a circular γ domain and a small bending rigidity, the membrane oscillates strongly around an average spherical cap shape. If such a vesicle is deflated, the contact area increases or decreases with increasing osmotic pressure, depending on the relative size of the vesicle and the circular γ domain. The lateral localization of the vesicle's center of mass by such a domain is optimal for a certain domain radius, which is found to be rather independent of adhesion strength and bending rigidity. For vesicles adhering to stripe-shaped surface domains, the width of the contact area perpendicular to the stripe varies nonmonotonically with the adhesion strength.     

On a possible variation of the proton-to-electron mass ratio: H2 spectra in the line of sight of high-redshift quasars and in the laboratory

Recently the finding of an indication for a <em>decreaseem> of the proton-to-electron mass ratio <em>μem> = <em>mem>_p/<em>mem>_e by 0.002% in the past 12 billion years was reported in the form of a Letter [E. Reinhold, R. Buning, U. Hollenstein, P. Petitjean, A. Ivanchik, W. Ubachs, Phys. Rev. Lett. 96 (2006) 151101]. Here we will further detail the methods that led to that result and put it in perspective. Laser spectroscopy on molecular hydrogen, using a narrow-band and tunable extreme ultraviolet laser system at the Laser Centre Vrije Universiteit Amsterdam, results in transition wavelengths of spectral lines in the eight="22" border="0" style="vertical-align:bottom" width="96" alt="View the MathML source" title="View the MathML source" src="http://ars.els-cdn.com/content/image/1-s2.0-S0022285206003419-si8.gif"> Lyman and eight="22" border="0" style="vertical-align:bottom" width="97" alt="View the MathML source" title="View the MathML source" src="http://ars.els-cdn.com/content/image/1-s2.0-S0022285206003419-si9.gif"> Werner band systems at an accuracy of (4-11) &times; 10⁻⁸, depending on the wavelength region. This corresponds to an absolute accuracy of 0.000004-0.000010 nm. A database of 233 accurately calibrated H₂ lines is presented here for future reference and comparison with astronomical observations. Recent observations of the same spectroscopic features in cold hydrogen clouds at redshifts <em>zem> = 2.5947325 and <em>zem> = 3.0248970 in the line of sight of two quasar light sources (Q 0405−443 and Q 0347−383) resulted in 76 reliably determined transition wavelengths of H₂ lines at accuracies in the range 2 &times; 10⁻⁷ to 1 &times; 10⁻⁶. Those observations were performed with the Ultraviolet and Visible Echelle Spectrograph at the Very Large Telescope of the European Southern Observatory at Paranal, Chile. A third ingredient in the analysis is the calculation of an improved set of sensitivity coefficients <em>Kem>_<em>iem>, a parameter associated with each spectral line, representing the dependence of the transition wavelength on a possible variation of the proton-to-electron mass ratio <em>μem>. The new model for calculation of the <em>Kem>_<em>iem> sensitivity coefficients is based on a Dunham representation of ground state and excited state level energies, derived from the most accurate data available in literature for the eight="21" border="0" style="vertical-align:bottom" width="39" alt="View the MathML source" title="View the MathML source" src="http://ars.els-cdn.com/content/image/1-s2.0-S0022285206003419-si10.gif">ground electronic state and the presently determined level energies in the eight="19" border="0" style="vertical-align:bottom" width="38" alt="View the MathML source" title="View the MathML source" src="http://ars.els-cdn.com/content/image/1-s2.0-S0022285206003419-si11.gif"> and C¹Π_u states. Moreover, the model includes adiabatic corrections to electronic energies as well as local perturbation effects between B and C levels. The full analysis and a tabulation of the resulting <em>Kem>_<em>iem> coefficients is given in this paper. A statistical analysis of the data yields an indication for a variation of the proton-to-electron mass ratio of Δ<em>μem>/<em>μem> = (2.45 ± 0.59) &times; 10⁻⁵ for a weighted fit and Δ<em>μem>/<em>μem> = (1.99 ± 0.58) &times; 10⁻⁵ for an unweighted fit. This result, indicating the decrease of <em>μem>, has a statistical significance of 3.5<em>σem>. Mass-variations as discussed relate to <em>inertialem> or kinematic masses, rather than gravitational masses. Separate treatment of the data gives a similar positive result for each of the quasars Q 0405−443 and Q 0347−383. The statistical analysis is further documented and possible systematic shifts underlying the data, with the possibility of mimicking a non-zero Δ<em>μem>/<em>μem> value, are discussed. The observed decrease in <em>μem> corresponds to a rate of change of d ln<em>μem>/d<em>tem> = −2 &times; 10⁻¹⁵ per year, if a linear variation with time is assumed. Experiments for detecting a possible variation of <em>μem> in the modern epoch via ultra-precision experiments on H₂ quadrupole transitions are proposed.     

Discrimination of photoblinking and photobleaching on the single molecule level

Wide field observation of individual dye molecules have been performed to study fluorescence intermittency. We demonstrate a data analysis scheme, which enables us to quantify the decay of the ensemble intensity which is due to <em>onem>/<em>offem>-blinking of the molecules (photophysical bleaching) by getting rid of the effects of photochemical degradation of the dye (photochemical bleaching). Under the conditions of our experiments, photophysical and thus reversible bleaching is the dominant of the two bleaching mechanisms.