New electronic and magnetic properties emerging from adsorption of organized organic layers

New electronic and magnetic properties are induced by the adsorption of closed packed monolayers on solid substrates. For many thiolated molecules self-assembled on gold, a surprisingly large paramagnetism is observed. In the case where the layers are made from chiral molecules, in addition an unexpectedly large electronic dichroism is observed, which manifests itself as spin specific electron transmission. This dichroism was observed for monolayers made from polyalanine and from DNA. Self-assembled monolayers of double-stranded DNA oligomers on gold interact with polarized electrons similarly to a strong and oriented magnetic field. The direction of the field for right-handed DNA is away from the substrate. Moreover, the layer shows very high paramagnetic susceptibility. Interestingly, thiolated single-stranded DNA oligomers on gold do not show this effect. All the observations can be rationalized by assuming organization induced charge transfer between the substrate and the organic layer. The charge transfer results in spin alignment of the transferred electrons/holes. While for achiral molecules the spin alignment varies among the domains, in the case of monolayer made from chiral molecules the alignment is the same across the entire sample. When magnetic field is applied, large magnetic moment is observed that results from orbital magnetism.     

Second-order semilinear elliptic inequalities in exterior domains

We study the problem of existence and nonexistence of positive solutions of the semilinear elliptic inequalities in divergence form with measurable coefficients in exterior domains in . For W(x)?|x|^−σ at infinity we compute the critical line on the plane (p,σ), which separates the domains of existence and nonexistence, and reveal the class of potentials V that preserves the critical line. Example are provided showing that the class of potentials is maximal possible, in certain sense. The case of (p,σ) on the critical line has also been studied.     

Determination of volatile biogenic amines in muscle food products by ion mobility spectrometry

The extent of spoilage of muscle food products was determined through measurement of volatile biogenic amines that emanated from food samples. The release of the amines was enhanced by addition of a few drops of an alkaline solution and the amines were monitored by ion mobility spectrometry (IMS). The limit of detection of the method for trimethylamine (TMA) was 2 ng and the measurement was completed within <2 min with short and long term reproducibility of 15 and 25%, respectively, for replicate samples. The method provides qualitative information as it distinguishes between different amines, as well as quantitative data for the key compounds. A good correlation was found between the IMS results and the microorganism populations in microbiological cultures. The effects of storage time and temperature and of the type of meat on the formation of biogenic amines were examined, and as expected, the higher the storage temperature the faster the spoilage. Thus, this pilot study shows that the measurement of biogenic amines can serve as an indicator for food spoilage or freshness.     

Calcium ion fluorescence detection using liposomes containing Alexa-labeled calmodulin

This paper describes the preparation and characterization of calcium ion sensitive fluorescent liposomes and their application for the determination of calcium ions in aqueous samples. Calmodulin (CaM), a calcium ion-binding protein labeled with the fluorophore Alexa-488 is embedded in the membrane of unilamellar liposomes. Upon calcium ion binding, calmodulin undergoes a conformational change that exposes its hydrophobic core and affects the fluorescence intensity of the attached fluorophore. Characterization studies of Alexa-CaM-containing liposomes reveal that embedding calmodulin molecules in the bilayer membrane of liposomes extends the lifetime of the calcium ion binding activity of calmodulin by about fourfold compared to the lifetime of its calcium-binding activity in free solution. Moreover, the calcium ion response of Alexa-CaM-containing liposomes is about threefold higher than the calcium ion response of Alexa-CaM in solution. The improvement in the calcium ion detection properties is attributed to the interaction between calmodulin, a membranal protein, and the hydrophobic phospholipids of the liposomes. The analytical properties of the calcium ion sensitive fluorescent liposomes are discussed.     

New Developments in Activation Analysis for Material and Environmental Sciences

Activation analysis in general and mainly reactor neutron activation analysis (NAA) has been used extensively for measuring trace elements in high purity materials, particularly semiconductor materials. The advantages of NAA in determination of trace elements differ from one semiconductor material to another. For all of them the inherent properties of activation analysis especially those of non contamination with the reagents, low blanks and high sensitivity are the reasons for the choice of NAA as the main analytical procedure. These inherent properties are essential for analysis of high-purity materials where concentrations of ppb's and sub ppb's have to be measured. NAA is specially suitable for the determination of trace elements in silicon due to the very short lived very low activity induced by neutron reaction in silicon. This enables easy instrumental (i.e. without chemical separations) determination of trace elements in silicon. In the HFR reactor at Peten, Netherlands, a special facility was constructed for irradiation of silicon samples of Philips, in which silicon wafers of up to 15 cm diameter can be irradiated with 4 × 10¹³n. cm^?2. sec^?1 and the irradiation is done for 72–96 hours. using large Ge(Li) detectors (100 to 150cc) and long counting time (8–16 hours) they measured 22 elements in concentrations below ppb and 10 others between ppb and 300 ppm. Trace elements in germanium have been determined both instrumentally after very long decay time (100 days) or after short decay time removing the activities from the matrix by chemical separation. Trace elements in GaAs are determined only after chemical separtion. Several other semiconductor material such as Sc, Te, GaP and CuInS₂ were also determined by NAA. Some trace elements cannot be determined by neutron activation. Carbon, nitrogen and oxygen are determined by activation with protons, alphas or ³He particles. Boron and hydrogen are determined by prompt emission induced by charged particle activation, which gives not only the total concentration but also the depth profile. Carbon, nitrogen, oxygen and phosphorus were also determined by prompt proton activation analysis. The environmental samples studied by activation analysis can be divided into three categories: atmospheric aerosols, water samples and solid wastes. NAA of atmospheric aerosols have been used for their posible toxicological hazards, their source identification and for studies of atmospheric transport processes.     

The chemistry of polycyclic arene imines. V. Reactions of phenanthrene 9,10-imine with nucleophiles under phase transfer conditions

Reactions of phenanthrene 9,10-imine (1) with alkyl halides, sodium azide and ammonium thiocyanate in two liquid phase systems were investigated. In the presence of aqueous sodium hydroxide and alkyl halides triethylbenzylammonium (TEBA) salts promote N-alkylation of 1 with preservation of the aziridine ring. Tetrabutylammonium (TBA) salts catalyze nucleophilic substitutions in which the three membered ring is cleaved. Aqueous sodium azide reacts with 1 to give trans-10-azido-9,10-dihydro-9-phenanthrenamine (2) . Ammonium and potassium thiocyanate cause expansion of the aziridine ring; while the unsubstituted imine 1 yields the 2-thiazolamine derivative 4 , N-butylphenanthrene 9,10-imine (8) froms trans-3a,11b-dihydro-3-butylphenanthro[9,10-d]thiazol-2-imine (9) with an exocyclic CN bond. The structure of 9 was established by X-ray crystal analysis.     

A Critical Phenomenon for Sublinear Elliptic Equations in Cone-Like Domains

The authors of this paper study positive supersolutions to theelliptic equation -u = c|x|^–su^p in Cone-like domains ofR^N (N 2), where p, s R and c > 0. They prove that in thesublinear case p < 1 there exists a critical exponent p_*> 1 such that the equation has a positive supersolution ifand only if – < p < p_*. The value of p_* is determinedexplicitly by s and the geometry of the cone. 2000 MathematicsSubject Classification 35J60 (primary), 35B05, 35R45 (secondary).     

Spatial information transmission using orthogonal mutual coherence coding

We use the coherence of a light beam to encode spatial information. We apply this principle to obtain spatial superresolution in a limited aperture system. The method is based on shaping the mutual intensity function of the illumination beam in a set of orthogonal distributions, each one carrying the information for a different frequency bandpass or spatial region of the input object. The coherence coding is analogous to time multiplexing but with multiplexing time slots that are given by the coherence time of the illumination beam. Most images are static during times much longer than this coherence time, and thus the increase of resolution in our system is obtained without any noticeable cost.     

Asymptotic expansions for parabolic systems

We consider a parabolic system in a half space. A theorem, similar to one proved by Meyers and Pazy for elliptic equations outside the unit ball is proved, namely, if the coefficients, the right side, and the initial conditions of the parabolic system have asymptotic expansions at infinity with respect to the space variable, then so does the solution of the corresponding Cauchy problem. Some generalizations and examples are given.