Continuous-wave and femtosecond laser operation of Yb:CaGdAlO4 under high-power diode pumping

We demonstrate the generation of 68 fs secant hyperbolic pulses at a 105 MHz repetition rate with an average power of 520 mW from a diode-pumped Yb(3+):CaGdAlO(4) mode-locked laser. A semiconductor saturable absorber allows passive mode locking, and a 15 W diode laser is used to pump directly the crystal. To our knowledge this represents the highest average power ever obtained for a sub-100 fs diode-pumped Yb-bulk laser.     

Kidney exchange simulation and optimization

One of the challenges in a kidney exchange program (KEP) is to choose policies that ensure an effective and fair management of all participating patients. In order to understand the implications of different policies of patient allocation and pool management, decision makers should be supported by a simulation tool capable of tackling realistic exchange pools and modeling their dynamic behavior. In this paper, we propose a KEP simulator that takes into consideration the wide typology of actors found in practice (incompatible pairs, altruistic donors, and compatible pairs) and handles different matching policies. Additionally, it includes the possibility of evaluating the impact of positive crossmatch of a selected transplant, and of dropouts, in a dynamic environment. Results are compared to those obtained with a complete information model, with knowledge of future events, which provides an upper bound to the objective values. Final results show that shorter time intervals between matches lead to higher number of effective transplants and to shorter waiting times for patients. Furthermore, the inclusion of compatible pairs is essential to match pairs of specific patient–donor blood type. In particular, O-blood type patients benefit greatly from this inclusion.     

Synthesis of (Z)-tributylstannyl enynes: systematic studies of Sonogashira cross-coupling reactions between (E)-1-iodovinyl-1-tributylstannanes and terminal acetylenes using amines or tetrabutylammonium hydroxide (TBAOH) as activator

Sonogashira cross-coupling reactions involving (E)-iodo vinyl stannanes and terminal acetylenes were carried out in the presence of Pd(PPh₃)₄, CuI and several amines, affording (Z)-tributylstannyl enynes in moderate to good yields (62-91%). Utilizing the catalytic system containing Pd(PPh₃)₄ (5%), CuI (10%), and TBAOH (40% in aqueous media) as activator, better yields (72-91%) and lower reaction times were achieved.     

Dynamical properties of a particle in a wave packet: Scaling invariance and boundary crisis

Some dynamical properties present in a problem concerning the acceleration of particles in a wave packet are studied. The dynamics of the model is described in terms of a two-dimensional area preserving map. We show that the phase space is mixed in the sense that there are regular and chaotic regions coexisting. We use a connection with the standard map in order to find the position of the first invariant spanning curve which borders the chaotic sea. We find that the position of the first invariant spanning curve increases as a power of the control parameter with the exponent 2/3. The standard deviation of the kinetic energy of an ensemble of initial conditions obeys a power law as a function of time, and saturates after some crossover. Scaling formalism is used in order to characterise the chaotic region close to the transition from integrability to nonintegrability and a relationship between the power law exponents is derived. The formalism can be applied in many different systems with mixed phase space. Then, dissipation is introduced into the model and therefore the property of area preservation is broken, and consequently attractors are observed. We show that after a small change of the dissipation, the chaotic attractor as well as its basin of attraction are destroyed, thus leading the system to experience a boundary crisis. The transient after the crisis follows a power law with exponent −2.     

Symmetry Studies for Data Analysis

This paper describes some of the basic applications of the algebraic theory of canonical decomposition to the analysis of data. The notions of structured data and symmetry studies are discussed and applied to demonstrate their role in well known principles of analysis of variance and their applicability in more general experimental settings.      

Microwave-promoted synthesis of chiral pyridinium salts

The synthesis of several chiral pyridinium salts via Zincke’s reaction can be easily accomplished by domestic microwave oven irradiation. Yield enhancements, reduction of reaction time, and less racemization were observed under microwave heating when compared to conventional heating in similar conditions.     

Size-controllable synthesis of nanosized-TiO2 anatase using porous Vycor glass as template

In this paper we report the synthesis and characterization of TiO₂ nanocrystal dispersed into a porous Vycor glass. We have obtained very small TiO₂ nanocrystals in the anatase form. The nanocrystal size is controlled via the mass increment only thus preventing the growth through the coalescence process. The nanocrystal size was monitored through transmission electron microscope and Raman scattering. The␣coalescence control is attributed due to the obtention of nanocrystals dispersed into the host and to the terminal bonds present in the porous which act as an anchor thus resulting in a low diffusion of the nanocrystals through the porous network.     

Electrochemistry and chromatographic detection of monosaccharides,disaccharides, and related compounds at an electrocatalytic chemically modified electrode

Many carbohydrate compounds undergo electro-oxidation at modest positive potentials at chemically modified electrodes (CMEs) made by adding cobalt phthalocyanine (CoPC) electrocatalyst to a conventional carbon paste mixture. The active carbohydrates which were oxidized at the CME at +0.4 to 0.5 V vs. Ag/AgCl under the very basic pH conditions required, included not only monosaccharides but also oligosaccharides, deoxy sugars, and even simple polyalcohols such as glycerol. When used for carbohydrate detection after liquid chromatography, the CoPC CME yielded detection limits in the 10–50 pmol range. Electrode stability and selectivity was such that no sample preparation other than dilution and particulate filtration was required for carbohydrate determinations in sample matrices including food products and physiological fluids.     

A critical experimental study of the classical tactile threshold theory

Background  

The tactile sense is being used in a variety of applications involving tactile human-machine interfaces. In a significant number of publications the classical threshold concept plays a central role in modelling and explaining psychophysical experimental results such as in stochastic resonance (SR) phenomena. In SR, noise enhances detection of sub-threshold stimuli and the phenomenon is explained stating that the required amplitude to exceed the sensory threshold barrier can be reached by adding noise to a sub-threshold stimulus. We designed an experiment to test the validity of the classical vibrotactile threshold. Using a second choice experiment, we show that individuals can order sensorial events below the level known as the classical threshold. If the observer's sensorial system is not activated by stimuli below the threshold, then a second choice could not be above the chance level. Nevertheless, our experimental results are above that chance level contradicting the definition of the classical tactile threshold.