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Methodological considerations for molecular dynamics simulations of complex interfaces are presented in this article. A slab geometry is examined in the context of stationary phases where selectivity occurs predominantly in pores within silica beads. Specifically, we examine the Whelk-O1 interface with n-hexane/2-propanol, the TMA-(Pro)2-N(CH3)-tether interface with n-hexane/2-propanol, and the C18H37Si interface with water/methanol. The following methodological issues are considered in detail: The assessment of solvent density within the confined region and excluded volume of the interface; the structural equilibration of surface-bound moieties; solvent equilibration for binary mixtures; surface size effects, and periodic boundary conditions; the treatment of electrostatic interactions; and the impact of pore size. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations are employed to examine the selectivity of four proline-based chiral stationary phases in two solvent environments, a relatively apolar n -hexane/2-propanol solvent and a polar water/methanol solvent. The four chiral surfaces are based on a BOC-terminated diproline, a TMA-terminated diproline, a TMA-terminated triproline and a TMA-terminated hexaproline. This range of chiral selectors allows an analysis of the impact of oligomer length and terminal group on selectivity while the two solvent environments indicate the impact of solvent hydrogen bonding and polarity. The selector–analyte interactions are examined for six closely related analytes that each have an aromatic moiety, a hydrogen, and an alcohol group directly bonded to the stereocenter. The analytes differ in the nature of the aromatic group (phenyl or anthracyl), in the attachment point (to the central ring or a side ring in the anthracyl), and in the fourth group bonded to the carbon (CH 3 , CF 3 , or C 2 H 5 ). For each of the 48 solvent + selector + analyte systems, selectivity factors are calculated and, when possible, compared to experiment. The docking mode for these proline-based selectors is analyzed. [ABSTRACT FROM AUTHOR]

Abstract: Poly-proline chains and derivatives have been recently examined as the basis for new chiral stationary phases in high performance liquid chromatography [1–5]. The selectivity of poly-proline has been measured for peptides with up to ten proline units [1]. In this article, we employ molecular dynamics simulations to examine the interfacial structure and solvation of surface-bound poly-proline chiral selectors. Specifically, we study the interfacial structure of trimethylacetyl-terminated poly-proline chains with three-to-six prolines. The surface includes silanol groups and end-caps, to better capture the characteristics of the stationary phase, and the solvent is either a polar water/methanol or a relatively apolar n-hexane/2-propanol mixture. We begin with a comprehensive ab initio study of the conformers, their energies, and an assessment of conformer flexibility. Force fields have been developed for each poly-proline selector. Molecular dynamics simulations are employed to study the preferred backbone conformations and solvent hydrogen bonding for different poly-proline/solvent interfaces. For triproline, the effect of two different terminal groups, trimethylacetyl and t-butyl carbamate are compared. [Copyright &y& Elsevier]

Abstract: Separation of asphaltenes from three types of Iranian crude oils of different asphaltene contents, using asymmetric, ceramic monolith membranes with the pore sizes of 0.2μm and 50nm was investigated. The experiments were conducted in a batch filtration unit at a differential pressure of 200kPa and a temperature of 120°C. Two important operating parameters including flux of permeate and asphaltene rejection were monitored as a function of time. A decline in the flux of permeate and an increase in the asphaltene rejection occurred as a result of fouling the membrane. The flux of permeate did not exhibit a strong function of pore size and this phenomenon confirmed that fouling of the membrane was according to the formation of gel layer. [Copyright &y& Elsevier]

Abstract: Proline chains have generated considerable interest as a possible basis for new selectors in chiral chromatography. In this article, we employ molecular dynamics simulations to examine the interfacial structure of two diproline chiral selectors, one with a terminal trimethylacetyl group and one with a terminal t-butyl carbamate group. The solvents consist of a relatively apolar n-hexane/2-propanol and a polar water/methanol mixture. We begin with electronic structure calculations for the two chiral selectors to assess the energetics of conformational changes, particularly along the backbone where the amide bonds can alternate between cis and trans conformations. Force fields have been developed for the two selectors, based on these ab initio calculations. Molecular dynamics simulations of the selective interfaces are performed to examine the preferred backbone conformations, as a function of end-group and solvent. The full chiral surface includes the diproline selectors, trimethylsilyl end-caps, and silanol groups. Connection is made with selectivity measurements on these interfaces, where significant differences are observed between these two very similar selectors. [Copyright &y& Elsevier]

Abstract: We record and analyze small earthquakes around Tehran, Iran, using the permanent seismological network of the Institute of Geophysics of the University of Tehran and two temporary dense seismological networks installed for several weeks during 1999 and 2000. Regional seismicity is distributed throughout Central Alborz, extending from the Caspian Sea to the Iran Plain, with the highest level of activity east of Tehran related to the Mosha and to the Garmsar faults, which both dip northward and have had strong historical earthquakes. Our focal mechanisms, the first for these faults, confirm a left lateral strike slip motion. [Copyright &y& Elsevier]

Elastic modulus (E) and uniaxial compressive strength (UCS) are very important engineering parameters that is required for many engineering projects. In some projects such as well drilling for oil production, deep underground tunnels in crushed zone, due to the depth of the well and fractures of rocks, there are some problems for obtained standard core samples. In this situations various methods have been developed for determining UCS and E using drilling cutting. Indentation test is one of these methods, in this method, an indenter penetrates into the stabilized samples in the surrounding material and then Critical Transition Force (CTF) and Indentation modulus (IM) determine. In the present study in order to developing the application of indentation testing for sandstone, and investigate the effect of particles size, shape and thickness, 14 sandstone blocks were collected from different formations in Iran and their physical characteristics, UCS and, E were measured using standard methods. After crushing the blocks and preparing 600 particles with dimensions of 3 × 3 × 3 mm 3 , 5 × 5 × 3 mm 3 , 5 × 5 × 5 mm 3 , 5 × 5 × 8 mm 3 , and 8 × 8 × 8 mm 3 and irregular shape particles with a thickness of 5 mm, indentation tests were performed on each particle and CTF and IM were calculated for each particle separately. According to the tests carried out some empirical relationships were proposed between UCS - CTF (with R 2  ≥ 0.86) and E – IM (with R 2  ≥ 0.73) for different shapes and dimensions. Due to the differences in the dimensions of the produced particles, investigating the effect of surface and thickness of particle on the CTF and the IM revealed that the particle's surface had a considerable effect on the CTF and IM; however, the effect of thickness was negligible. Using the dimensionless surface parameter (S and S i ), some empirical relationships between UCS – CTF/S (with R 2  ≥ 0.80) and E – IM/S i (with R 2  ≥ 0.77) were proposed for predicting UCS and E of sandstone particles with different shapes and dimensions. The accuracy of these relations was validated by performing standard uniaxial and indentation tests on 4 sandstone blocks and comparing measured UCS and E with those predicted using these relations. This comparison showed there is a good correlation between measured and predicted values. The proposed equations in this study were compared with results of previous studies. The relationship proposed in the present study to predict sandstone UCS has a similar accuracy with those proposed in by other researchers. [ABSTRACT FROM AUTHOR]

We describe six cases from three unrelated consanguineous Egyptian families with a novel characteristic brain malformation at the level of the diencephalic-mesencephalic junction. Brain magnetic resonance imaging demonstrated a dysplasia of the diencephalic-mesencephalic junction with a characteristic 'butterfly'-like contour of the midbrain on axial sections. Additional imaging features included variable degrees of supratentorial ventricular dilatation and hypoplasia to complete agenesis of the corpus callosum. Diffusion tensor imaging showed diffuse hypomyelination and lack of an identifiable corticospinal tract. All patients displayed severe cognitive impairment, post-natal progressive microcephaly, axial hypotonia, spastic quadriparesis and seizures. Autistic features were noted in older cases. Talipes equinovarus, non-obstructive cardiomyopathy and persistent hyperplastic primary vitreous were additional findings in two families. One of the patients required shunting for hydrocephalus; however, this yielded no change in ventricular size suggestive of dysplasia rather than obstruction. We propose the term 'diencephalic-mesencephalic junction dysplasia' to characterize this autosomal recessive malformation. [ABSTRACT FROM AUTHOR]

A surveillance study was carried out to determine the prevalence of Listeria spp. in traditional dairy products in Chahar Mahal & Bakhtiyari province, Iran. From February 2009 to February 2010, a total of 290 samples of various traditional dairy products were obtained from randomly selected retail stores located in 6 major cities of the province. Using cultural method, 21 samples (7.2%) were found positive for Listeria spp. The highest prevalence of Listeria was found in traditional ice-cream (16.7%), followed by cheese (15.0%), butter (7.5%), and kashk (2.2%) samples. The overall prevalence of Listeria was 7.2%, in which L. innocua was the most commonly recovered species (66.6%); the remaining isolates were identified as L. monocytogenes (23.8%), L. murrayi (4.8%) and L. seeligeri (4.8%). All 5 Listeria strains identified as L. monocytogenes were also positive using polymerase chain reaction (PCR). Susceptibilities of the 21 strains to nine antimicrobial drugs were determined using the disk diffusion assay. All isolates were resistant to one or more antimicrobial agents. Six strains (28.6%) were resistant to a single and 5 strains (23.8%) showed resistance to two antimicrobial agents. Multi-drug resistance was established in 23.8% of Listeria strains. Resistance to nalidixic acid was the commonest finding (85.7%), followed by resistance to penicillin (47.6%), and tetracycline (33.3%). The results provide information about the contamination levels of traditional dairy products in one of the provinces of Iran and highlight the emergence of multi-drug resistant Listeria in the environment. [ABSTRACT FROM AUTHOR]

Magnetic resonance (MR) imaging studies have identified hippocampal structural alterations in the pathogenesis of schizophrenia. Brain-derived neurotrophic factor (BDNF) is one of the neurotrophins that is widely expressed in the hippocampal formation and has been implicated in the neurobiology of schizophrenia. Polymorphisms in the BDNF gene may therefore confer risk for schizophrenia through hippocampal pathogenesis and/or making the hippocampus more susceptible to environmental insults. In this study, we investigated whether val66met, a functional and abundant missense polymorphism in the coding region of the BDNF gene, was associated with the volume of the hippocampal formation in 19 patients with first-episode schizophrenia and 25 healthy volunteers. A total of 124 contiguous T1-weighted coronal MR images (slice thickness=1.5 mm) were acquired through the whole head using a 3D Fast SPGR IR Prep sequence on a 1.5 T GE imaging system. Volumes of the right and left hippocampal formation were measured manually by an operator blind to group status and genotype. All participants were genotyped for the BDNF val66met locus. Mixed model analyses revealed a main effect of BDNF val66met genotype such that in the combined sample of patients and healthy volunteers, val/val homozygotes (N=27) had larger volumes of the hippocampal formation compared to val/met heterozygotes (N=17). In separate analyses by group, however, val66met genotype accounted for a greater proportion of the variance in the volume of the hippocampal formation in patients compared to healthy volunteers. These findings implicate genetic involvement of BDNF in variation of human hippocampal volume and suggest that this effect may be greater among patients compared to healthy volunteers.Molecular Psychiatry (2005) 10, 631–636. doi:10.1038/sj.mp.4001656 Published online 15 March 2005 [ABSTRACT FROM AUTHOR]

The influence of manufacturing parameters such as compacting pressure, heat treatment and microstructure on the static and dynamic properties of Fe–1.75 Ni–1.5 Cu–0.5 Mo–0.6 C was investigated. Wear and fatigue tests were carried out on reciprocate wearing and tension compression mode, respectively. The results show that delamination wear mechanism of sintered steel is similar to that of conventional wrought or cast materials. But, in sintered material, open porosity acts as sites of generation and collection of wear debris or formation of subsurface cracks. Wear rate is decreased and fatigue strength is increased by heat treatment. [Copyright &y& Elsevier]