Second-harmonic generation in waveguides induced by photorefractive spatial solitons

We demonstrate experimentally second-harmonic generation in waveguides induced by photorefractive solitons and show that the conversion efficiency is improved considerably. These induced waveguides are flexible and can be generated in any crystalline direction that allows soliton formation, and thus offer broad tunability (by rotation of the crystal), which cannot exist in fabricated waveguides.     

High-intensity nanosecond photorefractive spatial solitons

We report the observation of high-intensity solitons in a bulk strontium barium niobate crystal. The solitons are observed by use of 8-ns optical pulses with optical intensities greater than 100 MW/cm(2). Each soliton forms and attains its minimum width after roughly ten pulses and reaches e(-1) of the steady-state width after the first pulse. We find good agreement between experimental observations and theoretical predictions for the soliton existence curve.     

Single polymer chains as specific transducers of molecular recognition in scanning probe microscopy

A new approach for the specific detection and mapping of single molecule recognition is presented, based on the nonlinear elastic behavior of a single polymer chain. The process of molecular recognition between a ligand and a receptor is inherently accompanied by a decrease in the translational and rotational degrees of freedom of the two molecules. We show that a polymeric tether linked to the ligand can effectively transduce the configurational constraint imposed by molecular recognition into a measurable force, which is dominated by the entropic elasticity of the polymer. This force is specifically characterized by a strong nonlinearity when the extension of the polymer approaches its contour length. Thus, a polymer chain tethering the ligand to an oscillating cantilevered tip gives rise to a highly anharmonic motion upon ligand-receptor binding. Higher-harmonics atomic force microscopy allows us to detect this phenomenon in real time as a specific signature for the probing and mapping of single-molecule recognition.     

Locally connected simplicial maps

In Propositions 1.6 and 7.6 of his paper onp-group complexes of finite groups [5], Quillen establishes fundamental results comparing the homology and the fundamental group of the order complexes of posetsP, Q admitting a mapf :P →Q of posets with good local behavior. We prove the analogue of Quillen’s results for mapsf :K→L of simplicial complexesK andL in a more general setup. This work was partially supported by BSF 88-00164. The first author is partially supported by NSF DMS-8721480 and NSA MDA90-88-H-2032.     

Energy Mechanism of Charges Analyzed in Real Current Environment

We analyze in this work the energy transfer process of accelerated charges, the mass fluctuations accompanying this process, and their inertial properties. Based on a previous work, we use here the dipole antenna, which is a very convenient framework for such analysis, for analyzing those characteristics. We show that the radiation process can be viewed by two energy transfer processes: one from the energy source to the charges and the second from the charges into the surrounding space. Those processes, not being in phase, result in mass fluctuations. The same principle is true during absorption. We show that in a transient period between absorption and radiation the dipole antenna gains mass according to the amount of absorbed energy and loses this mass as radiated energy. We rigorously prove that the gain of mass, resulting from electrical interaction has inertial properties in the sense of Newton's third low. We arrive to this result by modeling the reacting spacetime region by an electric dipole.     

Exploiting locality: approximating sorting buffers

The sorting buffers problem is motivated by many applications in manufacturing processes and computer science, among them car-painting and file servers architecture. The input is a sequence of items of various types. All the items must be processed, one by one, by a service station. We are given a random-access sorting buffer with a limited capacity. Whenever a new item arrives it may be moved directly to the service station or stored in the buffer. Also, at any time items can be removed from the buffer and assigned to the service station. Our goal is to give the service station a sequence of items with minimum type transitions. We generalize the problem to allow items with different sizes and type transitions with different costs. We give a polynomial-time 9-approximation algorithm for the maximization variant of this problem, which improves the best previously known 20-approximation algorithm.     

Self-deflection and all-optical beam steering in CdZnTe

We report on the experimental observation of very large self-deflection of optical beams, along with all-optical steering, and electro-optic beam deflection. We observe as many as 27 resolvable spots of deflection at 1-W/cm2 intensity. These deflections arise from enhanced photorefractive effects in CdZnTe:V, giving rise to optically induced index changes in excess of 0.08, which is to our knowledge the strongest nonlinearity ever reported for any bulk semiconductor.     

Scale-free networks are ultrasmall

We study the diameter, or the mean distance between sites, in a scale-free network, having N sites and degree distribution p(k) proportional, variant k(-lambda), i.e., the probability of having k links outgoing from a site. In contrast to the diameter of regular random networks or small-world networks, which is known to be d approximately ln(N, we show, using analytical arguments, that scale-free networks with 23, d approximately ln(N. We also show that, for any lambda>2, one can construct a deterministic scale-free network with d approximately ln(ln(N, which is the lowest possible diameter.     

Elliptic incoherent solitons in saturable nonlinear media

We identify elliptic incoherent spatial solitons in isotropic saturable nonlinear media. These solitary states are possible, provided that their correlation function is anisotropic. The propagation dynamics of this new class of solitons are investigated by use of numerical simulations. We find that, during a collision event of two such elliptic solitons, their intensity ellipse rotates, and at the same time their centers of gravity tend to revolve around each other.     

Fluorescence Polarization as a Functional Parameter in Monitoring Living Cells: Theory and Practice

The use of fluorescence polarization as a functional parameter in monitoring cellular activation calls for the reliable and accurate measurement of the fluorescence intensity and polarization (FI and FP) of microscopic objects. The relevant experimental parameters that enter such measurements are thoroughly discussed. The possibility of executing FP measurements properly by flow-through systems is compared with that of static cytometry. Remarks on the effects of high-power excitation on markers and cells conclude the paper.