Almost linear upper bounds on the length of general davenport—schinzel sequences

Davenport—Schinzel sequences are sequences that do not contain forbidden subsequences of alternating symbols. They arise in the computation of the envelope of a set of functions. We obtain almost linear upper bounds on the length λ_s(n) of Davenport—Schinzel sequences composed ofn symbols in which no alternating subsequence is of length greater thans+1. These bounds are of the formO(nα(n)^O(α(n)5-3)), and they generalize and extend the tight bound Θ(nα(n)) obtained by Hart and Sharir for the special cases=3 (α(n) is the functional inverse of Ackermann’s function), and also improve the upper boundO(n log*n) due to Szemerédi. Work on this paper has been supported in part by a grant from the U.S. — Israeli Binational Science Foundation.     

Off-axis metallic diffractive lens for terahertz beams

A diffractive optical element for off-axis focusing of terahertz radiation is presented. It was designed in a nonparaxial regime and manufactured in a metal slab by laser cutting of curved stripes. The optical function of the structure includes focusing and deflecting the illuminating beam of a chosen frequency in a particular place. Therefore, the element acts as both a spatial and a spectral filter; hence it is especially suitable for separating the terahertz signal from a broadband thermal load in passive detection devices. The experimental evaluation of the proposed diffractive lens by means of time-domain spectroscopy is presented and discussed.     

Fluorescence Spectroscopy as Tool for Bone Development Monitoring in Newborn Rats

Autofluorescence of the mandible and femur bones taken from newborn rats (7-, 14- and 28-day old) was studied. Endogenous fluorophores were excited with 231 nm, 291 nm, 340 nm and 360 nm wavelengths. Modifications in content and microenvironment of both noncolagenous and collagenous constituents of bone tissue as well as metabolic coenzymes during the bone formation with age were reflected in fluorescence emission spectra. The increase of emission from peptide bonds and tryptophan residues was noted with rat age while for collagen and metabolic coenzymes at the first 2 weeks only. After maternal administration of indinavir the changes in fluorescence intensity and shifts in position of peak maximum were found. The distinct drop of emission from peptide bonds and tryptophan residues in studied bones was detected. In the case of collagen and metabolic coenzymes the red shift of peak maximum was revealed. Fluorescence spectroscopy could be used to follow bone development in newborn rats and effect of maternal indinavir administration on offspring.     

Backtracking the movements of a migratory bird: a case study of a white-fronted goose (Anser albifrons)

The occurrence of avian influenza has brought attention to migrating birds and their migratory routes as possible carriers and gates, respectively, of the pathogenic influenza virus. There is a need to verify migration routes and to back-track the migration routes of infected animals. Stable isotope analysis of bird feathers is a valuable tool for studying the migratory pattern of birds, by gaining information about the environmental conditions during the growth of the feathers. Ideally, if different feathers that have grown during different periods are investigated, not only can information about the molting region be extracted, but also some clues can be obtained about stop-overs during the migration of individual animals, enabling the reconstruction of the pathway. In the presented case study the hydrogen, carbon nitrogen and sulfur stable isotope ratios of different types of feathers (primaries, down feathers and blood pinfeathers) from one white-fronted goose specimen have been determined. These ratios differ significantly for some elements. By taking into account the different time of growth of the respective feathers, the isotope data can be interpreted with respect to the animal migration route from the summer (and molting) to the wintering region. This is the first paper to attempt to map the migration pathway using different types of feather from a single individual.     

Determination of iodine concentration in aqueous solutions by proton activation analysis: preliminary results for digested human thyroids

The aim of our studies is to check the possibilities of using proton activation analysis as a competitive method over other analytical techniques applied for iodine determination. It is well known that long-term irradiation of biological samples leads to their decomposition and formation of gaseous radiolysis products, which increase the pressure inside the sample container. In case of using proton beam another problem with liquid samples appears. It is the production of ⁷Be via spallation reactions ¹⁶O(p, spall)⁷Be. The Compton effect from ⁷Be γ-line increases the detection limits for isotopes with low-energy γ-lines. AIC-144 cyclotron at The Niewodniczański Institute of Nuclear Physics Polish Academy of Science can accelerate protons up to energy of 60 MeV which is sufficient for (p,5n) reaction needed to obtain ¹²³I (T _1/2 = 13.27 h, Eγ = 159 keV, I = 83%) from stable ¹²⁷I, thus the Compton effect from ⁷Be was the main factor perturbing the analysis. Separation and removal of ⁷Be is required to improve the detection limit. The paper presents a method and an example of its application to the determination of iodine concentration in digested fragments of human thyroids obtained during surgical treatment of patients with different types of thyroid tumor.     

An isomerization—1,3-dipolar cycloaddition tandem reaction towards the synthesis of 3-aryl-4-methyl-5-O-substituted isoxazolines from O-allyl compounds

A new strategy for the synthesis of 3-aryl-4-methyl-5-O-substituted isoxazolines via tandem catalytic isomerization of O-allyl systems to O-(1-propenyl) systems—1,3-dipolar cycloaddition (1,3-DC) to nitrile oxides is presented. The influence of the heteroatom in Ph-X-CHCHCH₃ (X=O, S, or Se) on the regio- and stereoselectivity of ArCNO 1,3-cycloaddition to these dipolarophiles is analyzed as well. The dipolarophiles were obtained via [RuClH(CO)(PPh₃)₃]–, [RuH₂(CO)(PPh₃)]– or base (KOH/18-crown-6)-catalyzed double bond migration in corresponding allyl ethers, O-allyl acetals, PhS– and PhSe–allyl systems. Cycloadditions of nitrile oxides to O-(1-propenyl) systems were fully regioselective whereas in the reactions of ArCNO with the PhS–(1-propenyl) and PhSe–(1-propenyl) systems both possible regioisomers were formed. It was established that within the majority of dipolarophiles of ROCHCHCH₃ type 1,3-DC is concerted, while for some dipolarophiles of RXCHCHCH₃ (X=O and R=Ph₃C, 2,3-dihydroxypropyl, tetrahydropyran-2-yl; X=S or Se and R=Ph) type 1,3-DC turns into a two-step reaction with simultaneous rotation about C–C bond. The results of the experiments have been analyzed theoretically using DFT calculations. The results of these calculations agreed well with the experimental data.     

d-Glucosamine based-phosphine for Suzuki-Miyaura cross-coupling reactions in the supported aqueous phase catalysis system

A d-glucosamine-based phosphine/Pd(OAc)₂ complex has been applied to the Suzuki-Miyaura coupling reaction of aryl bromides with arylboronic acids using the supported aqueous phase catalysis, SAPC, concept. The recyclability of the catalyst was investigated and revealed a very high activity during the 4 runs.     

Sol–gel synthesis of iron oxide–silica composite microstructures

Spherical silica particles doped with iron oxide have been synthesized via base-catalyzed one-pot sol?Cgel process using tetraethoxysilane (TEOS) and iron(III) ethoxide (ITE) as co-precursors. In the modified St?ber process adopted, depending on the concentration of ITE in the starting composition, materials of various morphologies were observed under a scanning electron microscope and an atomic force microscope. The presence of ITE significantly affected the formation process of particulate silica; the spherical particles were formed accompanied by the co-presence of irregular-shaped finer aggregates. The fraction of the aggregates with rough surfaces increased with an increase of the ITE content in the reaction mixture. Both the spherical particles and irregular-shaped aggregates contained iron hydroxide and they exhibited paramagnetic behavior. The chemical composition and physicochemical properties of the materials were determined using various complementary spectroscopic methods.     

Diastereo- and enantioselective intramolecular C(sp3)-H arylation for the synthesis of fused cyclopentanes

All C-H bonds are not equal: The intramolecular arylation of unactivated C(sp(3))-H bonds in the presence of a chiral Pd/binepine catalyst allows the synthesis of fused cyclopentanes efficiently and in an diastereo- and enantioselective manner (see scheme).     

Photophysics of indole-2-carboxylic acid in an aqueous environment studied by fluorescence spectroscopy in combination with ab initio calculations

The photo-physics and -chemistry of indoles are known to be highly complex and strongly dependent on their precise molecular structure and environment. Combination of spectroscopic analysis with quantum chemical calculations should be a powerful tool to unravel precise excited state deactivation mechanisms. At the same time, combined studies are seldom and likely far from trivial. In this work we explore the feasibility of combining spectroscopic and quantum-chemical data into one consistent model. The molecule of choice is indole-2-carboxylic acid (ICA) in aqueous media. Excited state dynamics are determined by time-resolved fluorescence experiments, while excited state reaction pathways of ICA-H(2)O clusters are explored by ab initio calculations.