Low temperature ferromagnetic properties of the diluted magnetic semiconductor Sb2-xCrxTe3

We report on magnetic and electrical transport properties of Sb2-xCrxTe3 single crystals with 0 <= x <= 0.095 over temperatures from 2 K to 300 K. A ferromagnetic state develops in these crystals at low temperatures with Curie temperatures that are proportional to x (for x > 0.014), attaining a maximum value of 20 K for x = 0.095. Hysteresis below TC for applied field parallel to the c-axis is observed in both magnetization and Hall effect measurements. Magnetic as well as transport data indicate that Cr takes the 3+ (3d3) valence state, substituting for antimony in the host lattice structure, and does not significantly affect the background hole concentration. Analysis of the anomalous Hall effect reveals that skew scattering is responsible for its presence. These results broaden the scope of ferromagnetism in the V2-VI3 diluted magnetic semiconductors (DMS) and in ferromagnetic DMS structures generallyComment: 24 pages, 5 figures, submitted to PR

Enhancing Network Intrusion Detection by Correlation of Modularly Hashed Sketches

The rapid development of network technologies entails an increase in traffic volume and attack count. The associated increase in computational complexity for methods of deep packet inspection has driven the development of behavioral detection methods. These methods distinguish attackers from valid users by measuring how closely their behavior resembles known anomalous behavior. In real-life deployment, an attacker is flagged only on very close resemblance to avoid false positives. However, many attacks can then go undetected. We believe that this problem can be solved by using more detection methods and then correlating their results. These methods can be set to higher sensitivity, and false positives are then reduced by accepting only attacks reported from more sources. To this end we propose a novel sketch-based method that can detect attackers using a correlation of particular anomaly detections. This is in contrast with the current use of sketch-based methods that focuses on the detection of heavy hitters and heavy changes. We illustrate the potential of our method by detecting attacks on RDP and SSH authentication by correlating four methods detecting the following anomalies: source network scan, destination network scan, abnormal connection count, and low traffic variance. We evaluate our method in terms of detection capabilities compared to other deployed detection methods, hardware requirements, and the attacker’s ability to evade detection

nn-type to pp-type crossover in quaternary BixSbyPbzSe3BixSbyPbzSe3 single crystals

We report on the preparation and some physical properties of a quaternary system based on Bi2Se3Bi2Se3 codoped with Sb and Pb. Single-crystal samples were prepared using the Bridgman technique and were characterized by measurements of the lattice parameters, electrical resistivity, Hall coefficient, Seebeck coefficient, and thermal conductivity. Atomic emission spectroscopy was used to find the concentration profiles of Sb and Pb along the single-crystalline ingots. Progressive codoping of the Bi2Se3Bi2Se3 crystal lattice with Sb and Pb leads to a crossover of the initially nn-type conduction to that of the pp type. It is assumed that both Sb and Pb enter the Bi sublattice. Physical properties as well as the change in the dominant carrier type are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87555/2/103720_1.pd

The kinetic studies of the solvent-promoted aggregation of a steroid-porphyrin derivative

The study of the aggregation of a steroid-functionalised porphyrin derivative shows the formation of chiral suprastuctures. Kinetic studies indicate that the mechanism of the aggregation strongly depends on both the nature of the media and on the concentration of the tetrapyrrolic macrocycle

Synthesis and spectral-luminescence properties of the conjugate of 24-epibrassinolide with porphyrin

The synthesis of a previously unknown conjugate of 24-epibrassinolide with porphyrin is described. Four molecules of 24-epibrassinolide are bonded to a molecule of porphyrin by selective formation of cyclical boric ethers in diol groups of the side chain. Electronic spectra of the synthesized conjugate of 24-epibrassinolide with porphyrin are measured and analyzed. The spectral and luminescence characteristics of the initial porphyrin and the conjugate are found to be similar. The quantum yield and fluorescence lifetime of the conjugate in tetrahydrofuran are 0.06 and 10.6 ns, respectively. The extinction coefficient of the conjugate in tetrahydrofuran is 385,000 (Mbullet operatorcm)-1 at a wavelength of 418 nm. © 2009 Springer Science+Business Media, Inc

Synthesis and spectral-luminescence properties of the conjugate of 24-epibrassinolide with porphyrin

The synthesis of a previously unknown conjugate of 24-epibrassinolide with porphyrin is described. Four molecules of 24-epibrassinolide are bonded to a molecule of porphyrin by selective formation of cyclical boric ethers in diol groups of the side chain. Electronic spectra of the synthesized conjugate of 24-epibrassinolide with porphyrin are measured and analyzed. The spectral and luminescence characteristics of the initial porphyrin and the conjugate are found to be similar. The quantum yield and fluorescence lifetime of the conjugate in tetrahydrofuran are 0.06 and 10.6 ns, respectively. The extinction coefficient of the conjugate in tetrahydrofuran is 385,000 (Mbullet operatorcm)-1 at a wavelength of 418 nm. © 2009 Springer Science+Business Media, Inc

Steroidal ribbons from (3α,5β,20S)-3-hydroxy-20-methyl-pregnan-21-oic acid

Background: Steroidal ribbons (or steroid containing ribbons) are being studied for several reasons, firstly, they may be included in the lipid bilayer, especially if they have suitable size (as "extended cholesterol"), and they are interesting in binding to steroidal receptors, gelators, and/or superassembly synthons. Bile acids seem to be very suitable as their components have natural tendency to form supramolecular assemblies. Methods: Synthesis of ester bonded tetramer of (3α,5β,20S)-3-hydroxy-20-methyl-pregnan-21-oic acid was achieved using 2,6-dichlorobenzoyl chloride and DMAP in toluene. To prepare shortened side chain steroid, the oxidative decarboxylation of protected lithocholic acid was used, followed by oxidation of thus formed terminal double bond. Aggregation properties of the prepared steroidal ribbon were studied alone and after binding with copper(II) ions. Results: There was synthesized 3α-{3α-{3α-[(3α,5β,20S)-3-hydroxy-pregnane-20-carbonyl)oxy]-[(5β,20S)-pregnane-20-carbonyl)oxy]}-[(5β,20S)-pregnane-20-carbonyl)oxy]}-(5β,20S)pregnane-20-carboxylate as a steroidal ribbon derived from bile acid, however, with the shortened side chain. The aggregation of the ribbon prepared in chloroform after binding of Cu(II) ions was monitored by absorption and circular dichroism spectroscopy at different ratios [tetramer]/[Cu(II)]. A positive bisignate band centered at 280 nm emerges; whose intensity increases with the [tetramer]/[Cu(II)] ratio. This result suggests that chiral aggregates are obtained as a consequence of Cu(II) complexation. Time dependent experiments did not show any variation in both UV-Vis and CD spectra. Conclusion: Prepared and documented new type of tetrasteroidal ribbon is unique one for the length of the connecting steroidal side chain. Its construction was done aiming to have more rigid ribbon than the one of lithocholic acid, and on the other hand, less rigid than the one derived from etienic acid. Contrary to the fact that no (chiral) aggregation was found by studying the ribbon itself, absorption and CD spectra showed defined aggregates formed after binding of Cu(II) on tetramer