Experimental observation of self-accelerating beams in quadratic nonlinear media

We present the experimental observation of 1D and 2D self-accelerating nonlinear beams in quadratic media, which are also the first nonlinear self-accelerating beams in any symmetric nonlinearity. Notably, we show that the intensity peaks of the first and second harmonics are asynchronous with respect to one another, but the coupled harmonics exhibit joint acceleration within the nonlinear medium. Finally, we demonstrate the impact of self-healing effects on the jointly accelerating first and second harmonics.     

Nondiffracting accelerating wave packets of Maxwell's equations

We present the nondiffracting spatially accelerating solutions of the Maxwell equations. Such beams accelerate in a circular trajectory, thus generalizing the concept of Airy beams to the full domain of the wave equation. For both TE and TM polarizations, the beams exhibit shape-preserving bending which can have subwavelength features, and the Poynting vector of the main lobe displays a turn of more than 90°. We show that these accelerating beams are self-healing, analyze their properties, and find the new class of accelerating breathers: self-bending beams of periodically oscillating shapes. Finally, we emphasize that in their scalar form, these beams are the exact solutions for nondispersive accelerating wave packets of the most common wave equation describing time-harmonic waves. As such, this work has profound implications to many linear wave systems in nature, ranging from acoustic and elastic waves to surface waves in fluids and membranes.     

Multisoliton ejection from an amplifying potential trap

We study theoretically the dynamics of a beam launched inside an amplifying trap potential. Raising the amplification transforms the dynamics from linear tunneling at low amplification to periodic ejection of a sequence of identical solitons (when the amplification rate exceeds the tunneling rate) and, at strong amplification, to nonperiodic multisoliton ejection.     

White-light solitons

Optical spatial solitons made from incoherent white light were experimentally observed in 1997 by Mitchell and Segev [Nature (London) 387, 880 (1997)]. We present what is believed to be the first theory describing these solitons and find the characteristic features of their spatiotemporal coherence properties and their temporal power spectrum.     

Fast screening of operational aqueous samples by gross alpha and beta counting with LSC systems

At nuclear installations a large number of samples is used to control operational tasks and health physics parameters. A fast screening process can be applied to provide immediate indication on possible contamination, and liquid scintillation counting (LSC) is the preferred method. Many LSC systems, which do not perform pulse shape analysis, are still in use. A screening procedure for these systems is presented based on three windows analysis. It may greatly reduce work and time, compared to using a proportional counter system, besides providing more accurate results.     

A theoretical understanding of the smallness of σelσT

The origin for the smallness of $\text{σ}{}_{\mathrm{el}}\text{σ}{}_{\mathrm{T}}$ is discussed within the framework of a factorizable dual bootstrap model with full t-dependence.     

“Complex” versus “free radical” mechanism for the catalytic decomposition of H2O2 by ferric ions

Kinetic and spectrophotometric measurements made during the Fe³⁺ ion catalyzed decomposition of H₂O₂ have been analyzed using the computer simulation method. Improved values of the rate constants of the “complex scheme” and of the molar absorptivities ofthe intermediates were obtained: k₃/K_M = 4.94 M^?1 min^?1, k₄ = 193 M^?1 min^?1, ε_I/K_M = 52.3 M^?2 cm^?1, ε_II = 25.7 M^?1 cm^?1. The simulation revealed details of the reaction which were unavailable by other means and which explained several features of its kinetics. The total amount of O₂ evolved in the reaction using [H₂O₂] ～ 10^?2 M has been calculated and found to be nearly stoichiometric. O₂ evolution experiments in this region cannot, thus, distinguish between the “complex mechanism” predicting nearly stoichiometric evolution of O₂ and the “free radical mechanism” predicting exactly stoichiometricamounts of O₂. There are discrepancies within the “free radical scheme” with regard to the correct values of the rate constants to fit the reactions of H₂O₂ both with Fe²⁺ and Fe³⁺ ions, as well as other reactions assumed to proceed via free radicals.     

Photoreduction of bacteriorhodopsin Schiff base at low humidity. A study with C13=C14 nonisomerizable artificial pigments

The retinal protonated Schiff base of bacteriorhodopsin is photoreactive to reducing agents such as NaBH4. In the present work we have studied the effect of different protein hydration levels on the photoreductive reaction, as well as the consequences of preventing isomerization around the critical C13=C14 retinal double bond. It was revealed that the rate of light-induced NaBH4 reaction can be fitted to three phases, between 100 and 87%, from 87 to 35% and below 35% relative humidities (r.h.). The three phases are attributed to three protein regions characterized by different water affinities. Furthermore, it is shown that the PSB reduction reaction is light catalyzed even in artificial pigments derived from retinal analogs, in which isomerization around the C13=C14 double bond is prevented. It is suggested that the protein experiences light-induced conformational alterations that are not associated with C13=C14 double bond isomerization. In the 13-cis locked pigment the rate of reduction reaction is affected by r.h. levels only below 35%. The relatively low r.h. required for withdrawing water from the protein is attributed to the increased protein-water affinity in this specific pigment.     

A heterometric micro-determination of lead with sodium diethyldithiocarbamate

The reaction between lead and sodium diethyldithiocarbamate is studied hcterometrically. The influence of the milieu, conditions of acidity and of different complexing agents, was studied. 0.02–0.04 mg lead per ml of solution can be determined either alone or in the presence of large excesses of other metals. A titration is carried out at 20°C in 8–15 minutes with an error of 0.0–1.0%. The analysed solution may contain ~ 99.5% of the following cations: Ca⁺². Sr⁺², Ba⁺², Mg⁺² Zn⁺², Mn⁺², Ni⁺², Co⁺², Al⁺³, Cr⁺³, Fe⁺³, Cd⁺². Cu⁺², Sb⁺³, Hg⁺², Ag⁺.