Spin polarization of electrons in a magnetic impurity doped semiconductor quantum dot – The effect of electron–phonon interaction

A theoretical model is presented in this paper for degree of spin polarization in a light emitting diode (LED) whose epitaxial region contains quantum dots doped with magnetic impurity. The model is then used to investigate the effect of electron–phonon interaction on degree of spin polarization at different temperatures and magnetic fields. It is found that magnetic impurity increases the degree of spin polarization irrespective of temperature, while the electron–phonon interaction decreases the degree of spin polarization. Results are found to be in better agreement with experiments.     

Certain variants of multipermutohedron ideals

Multipermutohedron ideals have rich combinatorial properties. An explicit combinatorial formula for the multigraded Betti numbers of a multipermutohedron ideal and their Alexander duals are known. Also, the dimension of the Artinian quotient of an Alexander dual of a multipermutohedron ideal is the number of generalized parking functions. In this paper, monomial ideals which are certain variants of multipermutohedron ideals are studied. Multigraded Betti numbers of these variant monomial ideals and their Alexander duals are obtained. Further, many interesting combinatorial properties of multipermutohedron ideals are extended to these variant monomial ideals.     

Chemical composition,and antibacterial and antioxidant activities of essential oils from Laggera tomentosa Sch. Bip. ex Oliv. et Hiern (Asteraceae)

Laggera tomentosa Sch. Bip. ex Oliv. et Hiern (Asteraceae), an endemic Ethiopian medicinal plant, is traditionally used to treat various ailments. Previously, the chemical constituents of the essential oil (EO) of its leaves and inflorescence were documented. However, no data about the chemical compositions of other parts of the EOs of the plant have been reported to date. Moreover, there are no previous biological activity reports on any parts of the EOs of this plant. Thus, in this study, the EOs were isolated from the stem bark and roots of this plant by hydrodistillation and analyzed using gas chromatography-mass spectrometry to identify their components. In addition, antibacterial potentials of the oils were evaluated using the disc diffusion and minimal inhibitory concentration (MIC) methods. 2,2-diphenyl-1-picrylhydrazyl (DPPH) and hydrogen peroxide methods were also employed to assess their antioxidant properties. Oxygenated monoterpenes (71.82% and 77.51%), of which 2,5-dimethoxy- p -cymene (57.28% and 64.76%) and thymol methyl ether (9.51% and 8.93%) were identified as major components in the EOs of stem bark and roots of L. tomentosa and the oils, were the most potent in the DPPH (IC50, 0.33 ± 1.10 and 0.39 ± 0.97 mg/mL) assay, respectively. Moreover, the EOs demonstrated appreciable activity towards the gram+ ( S. aureus and B. cereus ) bacteria. Among these oils, the oil of the stem bark showed the greatest activity to the gram+ (MIC = 0.625 mg/mL) bacteria. Therefore, the overall results suggested that the EOs of L. tomentosa may be a promising prospect for pharmaceutical, food, and other industrial applications.     

Strichartz estimates for the Schrödinger propagator for the Laguerre operator

We obtain homogeneous Strichartz estimate for the Schrödinger propagator e $^{-itL_{\alpha}}$ for the Laguerre operator L _α on ${\mathbb R}_+^n$ . We follow regularization technique as introduced in J. Funct. Anal. 224(2) (2005) 371–385. We also establish inhomogeneous Strichartz estimates for different admissible pairs.     

An efficient parallel algorithm for non-equilibrium molecular dynamics simulations of very large systems in planar Couette flow

In this paper we present an efficient parallel domain decomposition algorithm for non-equilibrium molecular dynamics (NEMD) simulations of large systems under planar Couette flow. We propose a modified deforming cell method that permits NEMD simulations with negligible penalties due to the Lees-Edwards periodic boundary conditions. The algorithm was used to study large systems of the Weeks-Chandler-Andersen fluid in order to obtain better viscosity results at the low shear rate regimes where the signal-to-noise ratio is very small.     

A comparative study of the density of defect states in bulk samples and thin films of glassy Se<Subscript>90</Subscript>Sb<Subscript>10</Subscript>

The present paper reports the comparative study of density of defect states (DOS) between bulk samples and thin films of glassy Se₉₀Sb₁₀. These glasses have been prepared by the quenching technique. Thin films of these glasses have been prepared by vacuum evaporation technique. Space-charge-limited conduction (SCLC) has been measured at different temperatures. The density of localized states near Fermi level is calculated by fitting the data to the theory of SCLC for the case of uniform distribution of localized states for bulk as well as for thin films. A comparison has been made between the density of states calculated in these two cases.     

Differential adduction of proteins vs. deoxynucleosides by methyl methanesulfonate and 1-methyl-1-nitrosourea in vitro

The reactions of two model mutagenic and carcinogenic alkylating agents, N-methyl-N-nitrosourea (MNU) and methyl methanesulfonate (MMS), with proteins and deoxynucleosides in vitro, were investigated. The protein work used an approach involving trypsin digestion and high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC/ESI-MS/MS). This technique permitted identification of the specific location of protein adduction by both MNU and MMS with commercial apomyoglobin and human hemoglobin, under physiological conditions. MNU treatment resulted in predominantly carbamoylation adducts on the proteins, but in contrast only methylated protein adducts were found following treatment with MMS. Further analyses, using TurboSequest, and the Scoring Algorithm for Spectral Analysis (SALSA), revealed that MNU carbamoylation was specific for modification of either the N-terminal valine or the free amino group in lysine residues of apomyglobin and human hemoglobin. However, MMS methylation modified the N-terminal valine and histidine residues of the proteins. Despite their clear differences in protein modifications, MNU and MMS formed qualitatively the same methylated deoxynucleoside adduct profiles with all four deoxynucleosides in vitro under physiological conditions. In light of their different biological potencies, where MMS is considered a 'super clastogen' while MNU is a 'super mutagen', these differences in reaction products with proteins vs. deoxynucleosides may indicate that these two model alkylating agents work via different mechanisms to produce their mutagenic and carcinogenic effects.     

An efficient approach for the synthesis of novel methyl sulfones in acetic acid medium and evaluation of antimicrobial activity

A series of nine methyl sulphones ( 3a –3 i ) starting from the aldehydes ( 1a–1i ) were synthesized in two consecutive steps. In the first step, preparation of allyl alcohols ( 2a–2i ) from their corresponding aldehydes by the reaction of sodium borohydride in methanol at room temperature is reported. Finally, methyl sulphones are synthesized by condensing sodium methyl sulfinates with allyl alcohols in the presence of BF ₃ .Et ₂ O in acetic acid medium at room temperature for about 2–3 h. The reaction conditions are simple, yields are high (85%–95%), and the products were obtained with good purity. All the synthesized compounds were characterized by their ¹ H, ¹³ C NMR, and mass spectral analysis. All the title compounds were screened for antimicrobial activity. Among the compounds tested, the compound 3f has inhibited both Gram positive and Gram negative bacteria effectively and compound 3i has shown potent antifungal activity. These promising components may help to develop more potent drugs in the near future for the treatment of bacterial and fungal infections.     

Betulinic acid binding to human serum albumin: a study of protein conformation and binding affinity

Betulinic acid (BA) has anti cancer and anti-HIV activity and has been proved to be therapeutically effective against cancerous and HIV-infected cells. Human serum albumin (HSA) is the predominant protein in the blood. Most drugs that bind to HSA will be transported to other parts of the body. Using micro TOF-Q mass spectrometry, we have shown, for the first time that BA isolated from a plant (Tephrosia calophylla) binds to HSA. The binding constant of BA to HSA was calculated from fluorescence data and found to be K(BA)=1.685+/-0.01 x 10(6) M(-1), indicating a strong binding affinity. The secondary structure of the HSA-BA complex was determined by circular dichroism. The results indicate that the HSA in this complex is partially unfolded. Further, binding of BA at nanomolar concentrations of BA to free HSA was detected using micro TOF-Q mass spectrometry. The study revealed a mass increase from 65199 Da (free HSA) to 65643 Da (HSA+drug), where the additional mass of 444 Da was due to bound BA. Based on the results of this study, it is suggested that micro TOF-Q mass spectrometry is useful technique for drug binding studies.     

Synthesis and Bioactivity of Some New 2-(Alkoxy carbonyl alkyl)-6-bromo-3,4-dihydro-3-(α-methyl benzyl)-2-oxo- benzo[e] [2H-1,3,2-oxazaphosphinine] Derivatives

Synthesis of some new 2-(alkoxy carbonyl alkyl)-6-bromo-3,4-dihydro-3-(α-methyl benzyl)-2-oxo-3-benzo- [e][2H-1,3,2-oxazaphosphinine] derivatives was accomplished through a two step process, which involves the condensation of 2-[(α-methylbenzyl amino)methyl]-4-bromophenol (1) with phosphorus oxychloride in equimolar quantities in the presence of triethylamine in dry toluene in 50—55 ℃ producing the corresponding intermediate (2), and subsequent reaction with the amino acid alkyl ester in dry tetrahydrofuran in the presence of triethylamine at different temperatures. They exhibited significant antibacterial and fungal activity.