bluuebunny/crossref_metadata_2025 huggingface dataset:
Self‐efficacy's influence on student academic achievement in the medical anatomy curriculum
Authors: Burgoon Jennifer Marie , Meece Judith L. , Granger Noelle A.
Published: May 2012

Self‐efficacy is defined as a person's beliefs in his or her own abilities to successfully complete a task and has been shown to influence student motivation and academic behaviors. More specifically, anatomical self‐efficacy is defined as an individual's judgment of his or her ability to successfully complete tasks related to the anatomy curriculum; these include dissecting, learning anatomical concepts, and applying anatomical knowledge to clinical situations. The purpose of this study was to investigate the influence of anatomical self‐efficacy on the academic performance of students enrolled in a medical gross anatomy course. To obtain students' anatomical self‐efficacy ratings, surveys containing the same anatomical self‐efficacy instrument were completed by first‐year medical students at a southeastern United States allopathic medical school after each of four gross anatomy assessments. Additional data collected included student demographic information, Medical College Admission Test® (MCAT®) scores, and anatomy assessment scores, both written examination and laboratory practical. To investigate the potential predictive nature of self‐efficacy for academic performance on both the written examination and the laboratory practical components of medical anatomy assessments, hierarchical linear regression analyses were conducted. For these analyses, academic ability (defined as the sum of the physical sciences and biological sciences MCAT scores) was controlled. The results of the hierarchical linear regressions indicated that all four laboratory practical scores were predicted by the corresponding self‐efficacy ratings, while two (i.e., thorax/abdomen and pelvis/lower limb) of the four written examination scores were predicted by the corresponding self‐efficacy ratings (P ≤ 0.05). Anat Sci Educ. © 2012 American Association of Anatomists.
A machine‐learning approach to negation and speculation detection in clinical texts
Authors: Cruz Díaz Noa P. , Maña López Manuel J. , Vázquez Jacinto Mata , Álvarez Victoria Pachón
Published: May 2012

Detecting negative and speculative information is essential in most biomedical text‐mining tasks where these language forms are used to express impressions, hypotheses, or explanations of experimental results. Our research is focused on developing a system based on machine‐learning techniques that identifies negation and speculation signals and their scope in clinical texts. The proposed system works in two consecutive phases: first, a classifier decides whether each token in a sentence is a negation/speculation signal or not. Then another classifier determines, at sentence level, the tokens which are affected by the signals previously identified. The system was trained and evaluated on the clinical texts of the BioScope corpus, a freely available resource consisting of medical and biological texts: full‐length articles, scientific abstracts, and clinical reports. The results obtained by our system were compared with those of two different systems, one based on regular expressions and the other based on machine learning. Our system's results outperformed the results obtained by these two systems. In the signal detection task, the F‐score value was 97.3% in negation and 94.9% in speculation. In the scope‐finding task, a token was correctly classified if it had been properly identified as being inside or outside the scope of all the negation signals present in the sentence. Our proposal showed an F score of 93.2% in negation and 80.9% in speculation. Additionally, the percentage of correct scopes (those with all their tokens correctly classified) was evaluated obtaining F scores of 90.9% in negation and 71.9% in speculation.
Fungitoxic and insecticidal plant polypeptides
Authors: Becker‐Ritt Arlete Beatriz , Carlini Célia Regina
Published: May 2012

According to the World Bank and FAO, the population grows worldwide and the poorest countries are expected to double their population within the next decades, reaching ∼7.2 billion in 2015. Moreover, the food and financial crisis together with the global economic recession pushed the number of hungry and undernourished people in the world to unprecedented levels. The substitution of animal proteins by plant proteins in food and feed is a general trend because of the lower cost and better production efficiency. Pathogens and pests can reduce the crop yields up to 30%. In some places, the losses can reach 80% due to climate conditions, proliferation of insects, and fungal diseases. All together, the harvest and postharvest losses vary from 5% to 20% and depending on the commodity can be as high as 50%. Plants have a complex chemical armory for defense composed of low and high molecular mass compounds that can act over a variety of pests and pathogens, from micro‐organisms to phytophagous insects or grazing animals. Among them, plant fungitoxic and insecticidal polypeptides represent promising alternatives to increase the supply of plant‐derived proteins and tackle the hunger in a global scale. © 2012 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 98: 367‐384, 2012.
ChemInform Abstract: A Versatile Ru Catalyst for the Asymmetric Transfer Hydrogenation of Both Aromatic and Aliphatic Sulfinylimines.
Authors: Pablo Oscar , Guijarro David , Kovacs Gabor , Lledos Agusti , Ujaque Gregori , Yus Miguel
Published: May 2012

A ruthenium complex bearing an achiral amino alcohol ligand is prepared in situ.
Fast clearing RGD‐based near‐infrared fluorescent probes for in vivo tumor diagnosis
Authors: Cao Jie , Wan Shunan , Tian Junmei , Li Siwen , Deng Dawei , Qian Zhiyu , Gu Yueqing
Published: May 2012

A fast clearing hydrophilic near‐infrared (NIR) dye ICG‐Der‐02 was used to constitute tumor targeting contrast agents. Cell adhesion molecule integrin αvβ3 served as the target receptor because of its unique expression on almost all sprouting tumor vasculatures. The purpose of this study was to synthesize and compare the properties of integrin αvβ3‐targeted, fast clearing NIR probes both in vitro and in vivo for tumor diagnosis. ICG‐Der‐02 was covalently conjugated to three kinds of RGD peptide including linear, monoeric cyclic and dimeric RGD to form three RGD‐based NIR probes. The integrin receptor specificities of these probes were evaluated in vitro by confocal microscopy. The dynamic bio‐distribution and elimination ratse were in vivo real‐time monitored by a near‐infrared imaging system in normal mice. Further, the in vivo tumor targeting abilities of the RGD‐based NIR probes were compared in αvβ3‐positive MDA‐MB‐231, U87MG and αvβ3‐negtive MCF‐7 xenograft mice models. Three RGD‐based NIR probes were successfully synthesized with good optical properties. In vitro cellular experiments indicated that the probes have a clear binding affinity to αυβ3‐positive tumor cells, with a cyclic dimeric RGD probe owing the highest integrin affinity. Dynamic bio‐distributions of these probes showed a rapid clearing rate through the renal pathway. In vivo tumor targeting ability of the RGD‐based porbes was demonstrated on MDA‐MB‐231 and U87MG tumor models. As expected, the c(RGDyK)2‐ICG‐Der‐02 probe displayed the highest tumor‐to‐normal tissue contrast. The in vitro and in vivo block experiments confirmed the receptor binding specificity of the probes. The hydrophilic dye‐labeled NIR probes exhibited a fast clearing rate and deep tissue penetration capability. Further, the αυβ3 receptor affinity of the three RGD‐based NIR probes followed the order of dimer cyclic > monomer cyclic > linear. The results demonstrate potent fast clearing probes for in vivo early tumor diagnosis. Copyright © 2012 John Wiley & Sons, Ltd.
Toward absolute quantification of iron oxide nanoparticles as well as cell internalized fraction using multiparametric MRI
Authors: Girard O. M. , Ramirez R. , McCarty S. , Mattrey R. F.
Published: May 2012

Iron oxide nanoparticles (IONPs) are widely used as MR contrast agents because of their strong magnetic properties and broad range of applications. The contrast induced by IONPs typically depends on concentration, water accessibility, particle size and heterogeneity of IONP distribution within the microenvironment. Although the latter could be a tool to assess local physiological effects at the molecular level, it renders IONP quantification from relaxation measurements challenging. This study aims to quantify IONP concentration using susceptibility measurements. In addition, further analysis of relaxation data is proposed to extract quantitative information about the IONP spatial distribution. Mesenchymal stem cells were labeled with IONPs and the IONP concentration measured by mass spectroscopy. MR relaxation parameters (T1, T2, T2*) as well as magnetic susceptibility of cylindrical samples containing serial dilutions of mixtures of free and cell‐internalized IONPs were measured and correlated with IONP concentration. Unlike relaxation data, magnetic susceptibility was independent of whether IONPs were free or internalized, making it an excellent candidate for IONP quantification. Using IONP concentration derived from mass spectroscopy and measured relaxation times, free and internalized IONP fractions were accurately calculated. Magnetic susceptibility was shown to be a robust technique to measure IONP concentration in this preliminary study. Novel imaging‐based susceptibility mapping techniques could prove to be valuable tools to quantify IONP concentration directly by MRI, for samples of arbitrary shape. Combined with relaxation time mapping techniques, especially T2 and T2*, this could be an efficient way to measure both IONP concentration and the internalized IONP fraction in vivo using MRI, to gain insight into tissue function and molecular imaging paradigms. Copyright © 2012 John Wiley & Sons, Ltd.
Evaluation of manganese uptake and toxicity in mouse brain during continuous MnCl2 administration using osmotic pumps
Authors: Sepúlveda M. R. , Dresselaers T. , Vangheluwe P. , Everaerts W. , Himmelreich U. , Mata A. M. , Wuytack F.
Published: May 2012

Manganese is a vital element and cofactor of many key enzymes, but it is toxic at high levels, causing pronounced disturbances in the mammalian brain. Magnetic resonance imaging (MRI) studies using manganese ions as a paramagnetic contrast agent are often limited by the neurotoxicity of Mn2+. In this work, we have explored a new in vivo model to study Mn2+ uptake, distribution and neurotoxicity in mice by subcutaneous implantation of mini‐osmotic pumps delivering MnCl2 continuously for 21 days. Fractionated injections can reduce the toxicity; however, constant administration at very low doses using osmotic pumps caused a substantial effect on the T1 contrast in MRI while reducing toxicity. Manganese‐enhanced MRI documented fast but reversible Mn2+ deposition largely in glomerular and mitral cell layers of the olfactory bulb, in the CA3 area of the hippocampus, and in the gray matter of the cerebellum. Mn2+ accumulated as early as the first days after implantation, with a fast dispersal 9 days after stopping a 12‐days Mn2+ exposure. Prominent Mn2+ accumulation was also seen in salivary glands and in the endocrine thyroid and posterior pituitary gland. These structures with enhanced Mn2+ accumulation correlated well with those showing high expression of the secretory pathway Ca2+/Mn2+‐ATPase (SPCA1), i.e. a transporter that could take part in Mn2+ detoxification. Our new experimental model for continuous low‐dosage administration of Mn2+ is an easy alternative for enhancing Mn2+‐based contrast in MEMRI studies, and might provide insight into the etiology of neuropathologies resulting from chronic Mn2+ exposure in vivo. Copyright © 2012 John Wiley & Sons, Ltd.
Dynamics of presynaptic protein recruitment induced by local presentation of artificial adhesive contacts
Authors: Suarez Fernando , Thostrup Peter , Colman David , Grutter Peter
Published: May 2012

In this study, we introduce a novel approach to induce and observe the formation of presynaptic compartments in axons through a combination of atomic force microscopy (AFM) and fluorescence microscopy. First, we use a poly‐D‐lysine‐coated bead attached to an AFM tip to induce the recruitment of two synaptic proteins, bassoon and synaptophysin, and measure their absolute arrival times to the presynaptic department. We find that bassoon arrives before synaptophysin. Second, we observe the formation of very long (several 10s of μm), structured, protein‐containing membranous strings as the AFM tip was withdrawn from the axon. It is conceivable that these strings might be a novel mechanism by which new neurites or branch points along existing neurites may be generated in situ. © 2012 Wiley Periodicals, Inc. Develop Neurobiol, 2013
Development of ramified microglia from early macrophages in the zebrafish optic tectum
Authors: Svahn Adam J. , Graeber Manuel B. , Ellett Felix , Lieschke Graham J. , Rinkwitz Silke , Bennett Maxwell R. , Becker Thomas S.
Published: May 2012

Microglia, the resident macrophage precursors of the brain, are necessary for the maintenance of tissue homeostasis and activated by a wide range of pathological stimuli. They have a key role in immune and inflammatory responses. Early microglia stem from primitive macrophages, however the transition from early motile forms to the ramified mature resident microglia has not been assayed in real time. In order to provide such an assay, we used zebrafish transgenic lines in which fluorescent reporter expression is driven by the promoter of macrophage expressed gene 1 (mpeg1; Ellet et al. [2011]: Blood 117(4): e49–e56,). This enabled the investigation of the development of these cells in live, intact larvae. We show that microglia develop from highly motile amoeboid cells that are engaged in phagocytosis of apoptotic cell bodies into a microglial cell type that rapidly morphs back and forth between amoeboid and ramified morphologies. These morphing microglia eventually settle into a typical mature ramified morphology. Developing microglia frequently come into contact with blood capillaries in the brain, and also frequently contact each other. Up to 10 days postfertilization, microglia were observed to undergo symmetric division. In the adult optic tectum, the microglia are highly branched, resembling mammalian microglia. In addition, the mpeg1 transgene also labeled highly branched cells in the skin overlying the optic tectum from 8–9 days postfertilization, which likely represent Langerhans cells. Thus, the development of zebrafish microglia and their cellular interactions was studied in the intact developing brain in real time and at cellular resolution. © 2012 Wiley Periodicals, Inc. Develop Neurobiol, 2013
A Stable Iridium(IV) Complex Containing the Kläui Tripodal Ligand [Co(η5‐C5H5){P(O)(OEt)2}3]–
Authors: Ip Ho‐Fai , So Yat‐Ming , Lee Hung Kay , Williams Ian D. , Leung Wa‐Hung
Published: May 2012

Iridium and rhodium complexes containing the Kläui oxygen tripodal ligand [Co(η5‐C5H5){P(O)(OEt)2}3]– (LOEt–) have been synthesized and their redox chemistry investigated. Treatment of [Ir(COE)2Cl]2 (COE = cyclooctene) with [AgLOEt] afforded [Ir(LOEt)Cl2(COE)] (1), which reacted with AgNO3, 4,4′‐di‐tert‐butyl‐2,2′‐bipyridyl (dtbpy), and NH4PF6 to give [Ir(LOEt)(dtbpy)(COE)][PF6] (2). Ozonolysis of complex 1 in CH2Cl2 afforded the IrIV complex [Ir(LOEt)Cl3] (3), which exhibited an EPR signal (CH2Cl2, 4 K) with g = 1.65 and 1.06. The IrIV/IrIII reduction potential for complex 3 in acetonitrile was determined to be ca. 0 V vs. ferrocenium/ferrocene. Treatment of [Rh(bpy)Cl3(DMF)] (bpy = 2,2′‐bipyridyl; DMF = N,N‐dimethylformamide) with [AgLOEt] and Ag(OTf) (OTf– = triflate) afforded [Rh(LOEt)(bpy)Cl][OTf] (4), which reacted with AgOTf in refluxing acetone to yield [Rh(LOEt)(bpy)(acetone)][OTf]2 (5). Reaction of [RhLOEtCl2]2 with 1 equiv. or an excess of tert‐butylamine in refluxing tetrahydrofuran afforded [Rh(LOEt)Cl2(NH2tBu)] (6) or [Rh(LOEt)Cl2(NH2tBu)2] (7). Complex 7 contains one chlorido ligand and one noncoordinated chloride ion that is hydrogen‐bonded to the two tert‐butylamine ligands. The crystal structures of complexes 1, 3, and 7 were determined.
C–C Bond Formation by Sequential Intramolecular Hydrogen Atom Transfer/Intermolecular Radical Allylation Reaction in Carbohydrate Systems
Authors: León Elisa I. , Martín Ángeles , Pérez‐Martín Inés , Quintanal Luís M. , Suárez Ernesto
Published: May 2012

A tandem 1,5‐, 1,6‐ or 1,8‐intramolecular hydrogen atom transfer (HAT)/intermolecular radical allylation using mono‐ or (1→4)‐O‐disaccharide models is described. It is a simple, sequential, stereocontrolled methodology for C–C bond formation by remote free radical functionalization, giving access to interesting carbohydrate structures carrying differently functionalized tethers.
SPRY2 loss enhances ErbB trafficking and PI3K/AKT signalling to drive human and mouse prostate carcinogenesis
Authors: Gao Meiling , Patel Rachana , Ahmad Imran , Fleming Janis , Edwards Joanne , McCracken Stuart , Sahadevan Kanagasabai , Seywright Morag , Norman Jim , Sansom Owen , Leung Hing Y.
Published: May 2012

Loss of SPRY2 and activation of receptor tyrosine kinases are common events in prostate cancer (PC). However, the molecular basis of their interaction and clinical impact remains to be fully examined. SPRY2 loss may functionally synergize with aberrant cellular signalling to drive PC and to promote treatment‐resistant disease. Here, we report evidence for a positive feedback regulation of the ErbB‐PI3K/AKT cascade by SPRY2 loss in in vitro as well as pre‐clinical in vivo models and clinical PC. Reduction in SPRY2 expression resulted in hyper‐activation of PI3K/AKT signalling to drive proliferation and invasion by enhanced internalization of EGFR/HER2 and their sustained signalling at the early endosome in a PTEN‐dependent manner. This involved p38 MAPK activation by PI3K to facilitate clathrin‐mediated ErbB receptor endocytosis. Finally, in vitro and in vivo inhibition of PI3K suppressed proliferation and invasion, supporting PI3K/AKT as a target for therapy particularly in patients with PTEN‐haploinsufficient‐, low SPRY2‐ and ErbB‐expressing tumours. In conclusion, SPRY2 is an important tumour suppressor in PC since its loss drives the PI3K/AKT pathway via functional interaction with the ErbB system.
MicroRNAs are universal regulators of differentiation, activation, and polarization of microglia and macrophages in normal and diseased CNS
Authors: Ponomarev Eugene D. , Veremeyko Tatiana , Weiner Howard L.
Published: May 2012

MicroRNAs (miRNAs) are a class of small (∼22 nucleotides) noncoding RNAs involved in the regulation of gene expression at the post‐translational level. It is estimated that 30–90% of human genes are regulated by miRNAs, which makes these molecules of great importance for cell growth, activation, and differentiation. Microglia is CNS‐resident cells of a myeloid lineage that play an important role in immune surveillance and are actively involved in many neurologic pathologies. Although the exact origin of microglia remains enigmatic, it is established that primitive macrophages from a yolk sac populate the brain and spinal cord in normal conditions throughout development. During various pathological events such as neuroinflammation, bone marrow derived myeloid cells also migrate into the CNS. Within the CNS, both primitive macrophages from the yolk sac and bone marrow derived myeloid cells acquire a specific phenotype upon interaction with other cell types within the CNS microenvironment. The factors that drive differentiation of progenitors into microglia and control the state of activation of microglia and bone marrow‐derived myeloid cells within the CNS are not well understood. In this review we will summarize the role of miRNAs during activation and differentiation of myeloid cells. The role of miR‐124 in the adaptation of microglia and macrophages to the CNS microenvironment will be further discussed. We will also summarize the role of miRNAs as modulators of activation of microglia and microphages. Finally, we will describe the role of miR‐155 and miR‐124 in the polarization of macrophages towards classically and alternatively activated phenotypes. © 2012 Wiley Periodicals, Inc.
Smoking is associated with impaired bone mass development in young adult men: A 5-year longitudinal study
Authors: Rudäng Robert , Darelid Anna , Nilsson Martin , Nilsson Staffan , Mellström Dan , Ohlsson Claes , Lorentzon Mattias
Published: May 2012

It has previously been shown that smoking is associated with reduced bone mass and increased fracture risk, but no longitudinal studies have been published investigating altered smoking behavior at the time of bone mass acquisition. The aim of this study was to investigate the development of bone density and geometry according to alterations in smoking behavior in a 5-year, longitudinal, population-based study of 833 young men, age 18 to 20 years (baseline). Furthermore, we aimed to examine the cross-sectional, associations between current smoking and parameters of trabecular microarchitecture of the radius and tibia, using high-resolution peripheral quantitative computed tomography (HR-pQCT), in young men aged 23 to 25 years (5-year follow-up). Men who had started to smoke since baseline had considerably smaller increases in areal bone mineral density (aBMD) at the total body (mean ± SD, 0.020 ± 0.047 mg/cm2 versus 0.043 ± 0.040 mg/cm2, p < 0.01) and lumbar spine (0.027 ± 0.062 mg/cm2 versus 0.052 ± 0.065 mg/cm2, p = 0.04), and substantially greater decreases in aBMD at the total hip (−0.055 ± 0.058 mg/cm2 versus −0.021 ± 0.062 mg/cm2, p < 0.01) and femoral neck (−0.077 ± 0.059 mg/cm2 versus −0.042 ± 0.070 mg/cm2, p < 0.01) than men who were nonsmokers at both the baseline and follow-up visits. At the tibia, subjects who had started to smoke had a smaller increment of the cortical cross-sectional area (CSA) than nonsmokers (8.1 ± 4.3 mm2 versus 11.5 ± 8.9 mm2, p = 0.03), and a larger decrement of trabecular volumetric BMD (vBMD) than nonsmokers (−13.9 ± 20.5 mg/mm3 versus −4.1 ± 13.9 mg/mm3, p < 0.001). In the cross-sectional analysis at follow-up (23–25 years of age), smokers had significantly lower trabecular vBMD at the tibia (7.0%, p < 0.01) due to reduced trabecular thickness (8.9%, p < 0.001), as assessed using HR-pQCT, than nonsmokers. In conclusion, this study is the first to report that men who start to smoke in young adulthood have poorer development of their aBMD at clinically important sites such as the spine and hip than nonsmokers, possibly due to augmented loss of trabecular density and impaired growth of cortical cross-sectional area. © 2012 American Society for Bone and Mineral Research.
Steroid hormone receptors, matrix metalloproteinases, insulin‐like growth factor, and dystroglycans interactions in prostatic diseases in the elderly men
Authors: Hetzl A.C. , Fávaro W.J. , Billis A. , Ferreira U. , Cagnon V.H.A.
Published: May 2012

OBJECTIVES: The aim of this study was to evaluate the reactivity of steroid hormone receptors (SHRs), dystroglycans (DGs), matrix metalloproteinases (MMPs), insulin‐like growth factor receptor (IGFR‐1), and laminin (Lam) in both prostatic stromal and epithelial compartments showing different diseases in elderly men. METHODS: Sixty prostatic samples were obtained from 60‐ to 90‐year‐old patients (mean 63 years) with and without prostatic lesions from Hospital of the School of Medicine, State University of Campinas (UNICAMP). The Samples were divided into standard (no lesions); high grade prostatic intraepithelial neoplasia (HGPIN); prostatic cancer (PC); and benign prostatic hyperplasia (BPH) groups. The samples were submitted to immunohistochemistry and Western blotting analyses. Research Ethics Committee of the School of Medicine, University of Campinas/UNICAMP (number 0094.0.146.000‐08). RESULTS: The results showed increased IGFR‐1 and MMPs protein levels in the PC and HGPIN groups. Decreased αDG and βDG protein levels were verified in the PC and HGPIN groups. Androgen receptor (AR) reactivity was similar among all groups. Estrogen receptor α (Erα) immunoreactivity was more intense in the epithelium in the PC and HGPIN groups. Estrogen receptor β (ERβ) immunoreactivity was weak in the epithelium of the HGPIN and PC groups. CONCLUSIONS: To conclude, there was an association among IGFR‐1, MMPs, and SHRs, indicating IGFR‐1 as a target molecule in prostate therapy, considering the IGF proliferative properties. Also, the distinct SHRs reactivities in the lesions in both prostatic compartments indicated different paracrine signals and pointed out the importance of estrogenic pathways in the activation of these disorders. Microsc. Res. Tech. 75:1197–1205, 2012. © 2012 Wiley Periodicals, Inc.
Microcavity plasmonics: strong coupling of photonic cavities and plasmons
Authors: Ameling Ralf , Giessen Harald
Published: May 2012

The understanding of light‐matter interactions at the nanoscale lays the groundwork for many future technologies, applications and materials. The scope of this article is the investigation of coupled photonic‐plasmonic systems consisting of a combination of photonic microcavities and metallic nanostructures. In such systems, it is possible to observe an exceptionally strong coupling between electromagnetic light modes of a resonator and collective electron oscillations (plasmons) in the metal. Furthermore, the results have shown that coupled photonic‐plasmonic structures possess a considerably higher sensitivity to changes in their environment than conventional localized plasmon sensors due to a plasmon excitation phase shift that depends on the environment.
Long‐Chain Polyacetals From Plant Oils
Authors: Chikkali Samir , Stempfle Florian , Mecking Stefan
Published: May 2012

Plant oil‐derived α,ω‐diacetals are polycondensated to the novel polyacetals [OCH2O(CH2)y]n (y = 19 and 23) with molecular weight of ca. Mn = 2 × 104 g mol−1. The long methylene sequences provide substantial melt and crystallization temperatures (Tm = 88 °C and Tc = 68 °C for y = 23), and rates of hydrolytic degradation are dramatically lower for the long‐chain polyacetals versus a shorter chain analogue (y = 12) studied for comparison.
Macroscopic diffusivity in concrete determined by computational homogenization
Authors: Nilenius Filip , Larsson Fredrik , Lundgren Karin , Runesson Kenneth
Published: May 2012

Effective moisture and chloride ion diffusivity coefficients for concrete are determined by computational homogenization, where concrete is modeled on the mesoscale as a heterogenous three‐phase composite material. By imposing moisture and chloride ion gradients on a representative volume element, effective macroscale properties are obtained through finite element analysis. A parametric study of the effects of the ballast content was carried out. The numerical results correspond well with an estimate of the Hashin–Shtrikman type available in the literature. The computational homogenization strategy proposed here also includes the interfacial transition zone, and its influence on the effective diffusivity coefficients is assessed. Copyright © 2012 John Wiley & Sons, Ltd.
On the performance of high‐order finite elements with respect to maximum principles and the nonnegative constraint for diffusion‐type equations
Authors: Payette G.S. , Nakshatrala K.B. , Reddy J.N.
Published: May 2012

The main aim of this paper is to document the performance of p‐refinement with respect to maximum principles and the nonnegative constraint. The model problem is steady‐state anisotropic diffusion with decay (which is a second‐order elliptic partial differential equation). We consider the standard single‐field formulation based on the Galerkin formalism and two least squares‐based mixed formulations. We employ Lagrange polynomials with unequal‐spaced points, and polynomials of order p = 1 to p = 10 are used. It is shown that the violation of the nonnegative constraint cannot be overcome with p‐refinement alone for anisotropic diffusion. We shall illustrate the performance of p‐refinement by using several representative problems. The intended outcomes of the paper are twofold. First, this study will caution the users of high‐order approximations about their performance with respect to maximum principles and the nonnegative constraint. Second, this study will help researchers develop new methodologies for enforcing maximum principles and the nonnegative constraint under high‐order approximations. Copyright © 2012 John Wiley & Sons, Ltd.
Polyvinylidene fluoride/poly(ethylene terephthalate) conductive composites for proton exchange membrane fuel cell bipolar plates: Crystallization, structure, and through‐plane electrical resistivity
Authors: Song Jianbin , Mighri Frej , Ajji Abdellah , Lu Chunhua
Published: May 2012

Polyvinylidene fluoride/poly(ethylene terephthalate) (PVDF/PET)‐based composites for proton exchange membrane fuel cell bipolar plates (BPs) were prepared at different crystallization temperatures and characterized by X‐ray diffraction, differential scanning calorimetry, and resistivity setup. Composite conductivity was made possible by using a mixture of carbon black (CB) and graphite (GR). To improve composite processability, its viscosity was reduced by adding a small amount of cyclic butylene terephthalate (c‐BT) oligomer and thermoplastic polyolefin elastomer. In the PVDF/PET‐based composite, it was found that PVDF phase could crystallize easily but PET crystallization was difficult. Because of the CB/GR additives, the formed crystals in PVDF/PET phases had a poor perfection degree and showed a lower melting temperature when compared with pure PVDF and PET. It was observed that PET nucleation was accelerated but not that of PVDF. According to through‐plane resistivity results, composite crystallization temperature range was divided into two parts (below/above 170°C), in which a different variation behavior of through‐plane resistivity was observed. It has been proved that the resistivity was mainly governed by the network of CB/GR developed inside the PET phase, and decreasing the crystallinity of PET led to a decrease of through‐plane resistivity, which is desirable for BPs. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers
Modification of styrene–ethylene/butylene–styrene copolymer microstructure by polystyrene homopolymer and evolution of a cocontinuous blend morphology
Authors: Raha Sumanta , Kao Nhol , Bhattacharya Sati N.
Published: May 2012

Styrene–ethylene/butylene–styrene (SEBS) copolymer was blended with the homopolymer polystyrene (hPS) in a counter‐rotating twin‐screw extruder to prepare hPS/SEBS blends. The morphology of the hPS/SEBS blends was studied by environmental scanning electron microscopy (ESEM) and by transmission electron microscopy (TEM). TEM imaging of pure SEBS revealed a microphase‐separated morphology, showing ordered regions or grains where the discrete styrene blocks formed hexagonally packed cylindrical structures within the ethylene/butylene matrix. Blending of small quantities of the homopolymer hPS showed an interesting result. The TEM images of the SEBS‐rich blends revealed that the added hPS was absorbed within the bulk of the SEBS phase resulting in a new SEBS‐rich phase, and the absorbed hPS was found to join the styrene cylinders of pure SEBS thereby modifying its original microstructure. As the hPS concentration in the blends was increased further, the ESEM and TEM images showed that the excess homopolymer hPS phase separated, forming a cocontinuous morphology with the hPS‐modified SEBS‐rich phases. Linear viscoelastic tests on the SEBS‐rich blends also revealed the existence of a synergistic effect, showing increased elastic behavior compared with that of pure SEBS. Small‐angle X‐ray scattering results showed an additional periodicity in the SEBS‐rich phase because of the modification of the SEBS microstructure by hPS. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers
Synthesis and characterization of Ti(Tbse)2 and its application as a catalyst for ROP of rac‐Lactide
Authors: Hu Chengbo , Wang Yuanliang , Xiang Hongzhao , Fu Ya , Fu Chunhua , Sun Jiaoxia , Xiang Yan , Ruan Changshun , Li Xiang
Published: May 2012

A novel bis(3,5‐di‐ tert‐butylsalicylaldehyde‐co‐ethanolamine) titanium(IV) complex (Ti(Tbse)2) was synthesized and structurally characterized. The X‐ray diffraction results showed that the titanium ion was bonded with two 3,5‐di‐tert‐butylsalicylaldehyde‐co‐ethanolamine ligands (Tbse ligands) in O,N,O‐tridentate mode. Experimental results revealed that the Ti(Tbse)2 complex could efficiently catalyze the ring‐opening polymerization (ROP) of rac‐lactide and showed a well‐controlled manner at 160 °C, and the polymers obtained had a controlled molecular weight and low polydispersity indices. Kinetic studies showed that the polymerization reaction was second order in monomer concentration and first order in catalyst concentration, and the apparent activation energy (Ea = 77.0 kJ mol−1) and frequency factor (A = 3.3 × 1011) were obtained according to the Arrhenius equation. 13C nuclear magnetic resonance spectra and thermogravimetric and differential scanning calorimetry analysis indicated that the polylactide was essentially a heterotactic and thermally stable polymer. Copyright © 2012 Society of Chemical Industry
Degradable and chemically recyclable epoxy resins containing acetal linkages: Synthesis, properties, and application for carbon fiber‐reinforced plastics
Authors: Hashimoto Tamotsu , Meiji Hiroyuki , Urushisaki Michio , Sakaguchi Toshikazu , Kawabe Kazumasa , Tsuchida Chihiro , Kondo Keiichi
Published: May 2012

Four sorts of epoxy resins containing degradable acetal linkages were synthesized by the reaction of bisphenol A (BA) or cresol novolak (CN) resin with vinyl ethers containing a glycidyl group [4‐vinlyoxybutyl glycidyl ether (VBGE) and cyclohexane dimethanol vinyl glycidyl ether (CHDMVG)] and cured with known typical amine‐curing agents. The thermal and mechanical properties of the cured resins were investigated. Among the four cured epoxy resins, the CN‐CHDMVG resin (derived from CN and CHDMVE) exhibited relatively high glass transition temperature (Tg = ca. 110 °C). The treatment of these cured epoxy resins with aqueous HCl in tetrahydrofuran (THF) at room temperature for 12 h generated BA and CN as degradation main products in high yield. Carbon fiber‐reinforced plastics (CFRPs) were prepared by heating the laminated prepreg sheets with BA‐CHDMVG (derived from BA and CHDMVE) and CN‐CHDMVG, in which strands of carbon fibers are impregnated with the epoxy resins containing conventional curing agents and curing accelerators. The obtained CFRPs showed good appearance and underwent smooth breakdown with the aqueous acid treatment in THF at room temperature for 24 h to produce strands of carbon fiber without damaging their surface conditions and tensile strength. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012
Synthesis and Photovoltaic Properties of Thieno[3,4‐c]pyrrole‐4,6‐dione‐based donor–acceptor Copolymers
Authors: Wen Shanpeng , Cheng Weidong , Li Pengfei , Yao Shiyu , Xu Bin , Li Hui , Gao Yajun , Wang Zilong , Tian Wenjing
Published: May 2012

Three donor–acceptor (D–A) 1,3‐di(thien‐2‐yl)thieno [3,4‐c]pyrrole‐4,6‐dione‐based copolymers, poly{9,9‐dioctylfluorene‐2,7‐diyl‐alt‐1,3‐bis(4‐hexylthien‐2‐yl)‐5‐octylthieno[3,4‐c]pyrrole‐4,6‐dione}, poly{N‐(1‐octylnonyl)carbazole‐2,7‐diyl‐alt‐1,3‐bis(4‐hexylthien‐2‐yl)‐5‐octylthieno[3,4‐c]pyrrole‐4,6‐dione}, and poly {4,8‐bis(2‐ethylhexyloxyl) benzo[1,2‐b:3,4‐b′]dithiophene‐alt‐1,3‐bis(4‐hexylthien‐2‐yl)‐5‐octylthieno[3,4‐c] pyrrole‐4,6‐dione} were synthesized by Suzuki or Stille coupling reaction. By changing the donor segment, the bandgaps and energy levels of these copolymers could be finely tuned. Cyclic voltammetric study shows that the highest occupied molecular orbital (HOMO) energy levels of the three copolymers are deep‐lying, which implies that these copolymers have good stability in the air and the relatively low HOMO energy level assures a higher open‐circuit potential when they are used in photovoltaic cells. Bulk‐heterojunction photovoltaic cells were fabricated with these polymers as the donors and PC71BM as the acceptor. The cells based on the three copolymers exhibited power conversion efficiencies of 0.22, 0.74, and 3.11% with large open‐circuit potential of 1.01, 0.99, and 0.90 V under one sun of AM 1.5 solar simulator illumination (100 mW/cm2). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012
Solvent‐free polymerization of citric acid and hexamethylenediamine for novel carboxylated polyamides
Authors: Jiang Man , Chen Wei , Fang Ping , Chen Shangli , Bai Junxiao , Huang Yanfei , Han Miaowei , Lu Ping , Dong Jian
Published: May 2012

Copolymers of tributyl citrate (TBC) and hexamethylenediamine (HMDA) were synthesized with a solvent‐free condensation method with molar ratios of TBC to HMDA varying from 2:1 to 1:2. The reaction led to poly(succinimide‐co‐citramide) copolymers which were characterized by infrared and Raman spectroscopies, X‐ray diffraction, and thermal analyses. Hydrolysis of the copolymers resulted in water soluble polycitramides with number averaged molecular weights ranging from 1.16 × 104 to 5.00 × 103 as determined by gel permeation chromatography. 1H, 13C, and 13C‐1H‐heteronuclear single quantum coherence NMR spectroscopy has confirmed that the hydrolyzed polycitramides with COOH side chains and amide backbones are structurally similar to biodegradable poly(aspartic acid) (PASP). Interestingly, the polycitramides showed Ca2+ and Pb2+ ion chelating capabilities higher than PASP, citric acid–sorbitol copolymers, or conventional resins. Thus, the polycitramides offer promise as a totally new class of metal sequesters and renewable substitutes for PASP and poly(acrylic acid). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012
Unoriented D‐brane instantons
Authors: Bianchi M. , Inverso G.
Published: May 2012

We give a pedagogical introduction to D‐brane instanton effects in vacuum configurations with open and unoriented strings. We focus on quiver gauge theories for unoriented D‐branes at orbifold singularities and describe in some detail the ℤ3 case, where both ‘gauge’ and ‘exotic’ instantons can generate non‐perturbative super potentials, and the ℤ5 case, where supersymmetry breaking may arise from the combined effect of ‘gauge’ instantons and a FI D‐term.
Computational methods for scaffold hopping
Authors: Schuffenhauer Ansgar
Published: May 2012

It is not uncommon in drug discovery that the core fragment, typically called scaffold, of a molecule with an interesting biological activity cannot be developed further because of issues related to intellectual property, physicochemical properties, metabolic stability, or toxicity, to name only a few reasons. In this situation, it is desirable to replace this molecule with another having a different chemical connectivity, but similar shape and pharmacophore features enabling it to interact in the same way with the target as the original molecule. Such a replacement is called scaffold hopping. Several ligand‐based virtual screening and scoring methods supporting the identification of novel ligands starting from known ligands and, if known, their bound conformation, are available. Scaffold hopping capability has been demonstrated for pharmacophore searches, field‐ and shape‐based similarity searches, alignment free similarity searches using three‐dimensional (3D)‐ or connectivity‐based descriptors, and fragment‐based methods. Although for many methods successful prospective uses have been reported, rigorous systematic benchmarking of scaffold hopping is still challenging due to the lacking consensus in the definition of a scaffold. Despite their drawbacks, computational scaffold extraction methods have been frequently used in approximate benchmarks for scaffold hopping. In many systematic retrospective studies, connectivity‐based methods were shown to be at least equally effective as 3D methods, especially when the conformations of the reference structures were generated with a conformer generator. However, in prospective comparison studies, especially when a hypothesis of the 3D binding conformation was available and used, often 3D methods were found to give superior results. © 2012 John Wiley & Sons, Ltd.

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Computer and Information Science > Chemoinformatics
Synthesis, Crystal Structures, and Catalytic Properties of Silver(I) and Cobalt(II) Coordination Polymers Based on Flexible Bis(benzimidazole) with Pyridine‐2, 6‐Dicarboxylate
Authors: Geng Jian‐Chen , Qin Li , Du Xu , Xiao Shu‐Lin , Cui Guang‐Hua
Published: May 2012

Two coordination polymers, [Ag2(pydca)(bbbi)2]n (1) and [Co2(pydca)2(bbbi)3]n·nH2O (2) [pydca = pyridine‐2, 6‐dicarboxylate, bbbi = 1, 1′‐(1, 4‐butylene)bis‐1H‐benzimidazole)] were hydrothermally synthesized and characterized by elemental analysis, IR spectroscopy, TG, PXRD, and single‐crystal X‐ray diffraction. Compound 1 features a one‐dimensional helical chain structure bridged by bbbi ligand, and further assembled into a 2D supramolecular architecture through three kinds of intermolecular π–π stacking interactions. Compound 2 displays an undulated 2D (6, 3) layer structure, in which each [Co(pydca)] unit is connected by three bbbi bridge ligands. Moreover, 1 and 2 have a remarkable activity for degradation of methyl orange in a photo‐assisted Fenton‐like process.
Systematic Investigation of Porous Inorganic‐Organic Hybrid Compounds with Photo‐Switchable Properties
Authors: Modrow Antje , Feyand Mark , Zargarani Dordaneh , Herges Rainer , Stock Norbert
Published: May 2012

Four new compounds [Co2(NDC)2(AzBIPY)] (1), [Cu2(NDC)2(AzBIPY)] (2), [Zn2(BPDC)2(AzBIPY)] (3) and [Zn2(CCA)2(AzBIPY)] (4) (with H2NDC: 2, 6‐naphthalenedicarboxylic acid, AzBIPY: 3‐azo‐phenyl‐4, 4′‐bipyridine, H2BPDC: 4, 4′‐biphenyl‐dicarboxylic acid and H2CCA: 4‐carboxy‐cinnamic acid) were synthesized and characterized. All compounds have paddle‐wheel units and photo switchable linker molecules in common. In all four compounds the azo group of the AzBIPY linker molecule protrudes into the pores. For compound 1 and 2 isomerization can be accomplished upon irradiation with UV light (λ = 365 nm) to switch the thermodynamically stable trans‐isomer into the cis‐isomer. Back switching can be achieved thermally or by irradiation with visible light (λ = 455 nm).
Synthesis and Structural Characterization of ACu9Tt4 (A = Ca, Sr, Ba, Eu; Tt = Si, Ge, Sn) – Tetragonally Distorted Ternary Variants of the Cubic NaZn13 Structure Type. Improved Structure Refinement of SrCu2Ge2
Authors: Schäfer Marion C. , Yamasaki Yuki , Fritsch Veronika , Bobev Svilen
Published: May 2012

Investigations in the Cu‐rich parts of the ternary systems A–Cu–Tt (A = Ca, Sr, Ba, Eu, Yb; Tt = Si, Ge, Sn) were carried out using the molten flux method. The results indicate that using tin as a flux, several stannides with a general formula ACu9Sn4 (A = Ca, Sr, Ba, and Eu) can be readily synthesized. Their structures (space group I4/mcm, Pearson symbol tI56) are ordered ternary variants of the cubic NaZn13 structure type. In the corresponding germanium and silicon systems, only the solid solutions BaCu9–xGe4+x and BaCu9–xSi4+x (x ≈ 0.5) can be obtained from eutectic Cu:Tt mixtures with compositions approximately 2:1. Their structures are formally isotypic with the CeNi8.5Si4.5 structure type, a partially ordered variant of the same NaZn13 structure. In the remaining systems A–Cu–Tt (A = Ca, Sr, Eu, Yb; Tt = Si, Ge), the known ACu2Tt2 phases (space group I4/mmm, Pearson symbol tI10) with the ThCr2Si2 structure type were found to be the most frequently observed products. In this article we discuss the subtleties of each structure with regard to the synthetic route; the similarities and the differences in the syntheses, and the structure refinements among the studied compounds are compared and contrasted. The structure of SrCu2Ge2 was also re‐assessed.
N‐Methyl‐2, 2'‐Dipicolylamine Complexes as Potential Models for Metal‐Mediated Base Pairs
Authors: Seubert Kristof , Böhme Dominik , Kösters Jutta , Shen Wei‐Zheng , Freisinger Eva , Müller Jens
Published: May 2012

Metal‐mediated base pairs can be used to insert metal ions into nucleic acids at precisely defined positions. As structural data on the resulting metal‐modified DNA are scarce, appropriate model complexes need to be synthesized and structurally characterized. Accordingly, the molecular structures of nine transition metal complexes of N‐methyl‐2, 2'‐dipicolylamine (dipic) are reported. In combination with an azole‐containing artificial nucleoside, this tridentate ligand had recently been used to generate metal‐mediated base pairs (Chem. Commun. 2011, 47, 11041–11043). The PdII and PtII complexes reported here confirm that the formation of planar complexes (as required for a metal‐mediated base pair) comprising N‐methyl‐2, 2'‐dipicolylamine is possible. Two HgII complexes with differing stoichiometry indicate that a planar structure might also be formed with this metal ion, even though it is not favored. In the complex [Ag2(dipic)2](ClO4)2, the two AgI ions are located close to one another with an Ag···Ag distance of 2.9152(3) Å, suggesting the presence of a strong argentophilic interaction.
Constraints on the pMSSM from searches for squarks and gluinos by ATLAS
Authors: Strübig Antonia , Caron Sascha , Rammensee Michael
Published: May 2012

Abstract

We study the impact of the jets and missing transverse momentum SUSY anal- yses of the ATLAS experiment on the phenomenological MSSM (pMSSM). We investigate sets of SUSY models with a flat and logarithmic prior in the SUSY mass scale and a mass range up to 1 and 3 TeV, respectively. These models were found previously in the study ’Supersymmetry without Prejudice’. Removing models with long-lived SUSY particles, we show that 99 % of 20000 randomly generated pMSSM model points with a flat prior and 85 % for a logarithmic prior are excluded by the ATLAS results. For models with squarks and gluinos below 600 GeV all models of the pMSSM grid are excluded. We identify SUSY spectra where the current ATLAS search strategy is less sensitive and propose extensions to the inclusive jets search channel.
Hematological profile of East African short-horn zebu calves from birth to 51 weeks of age
Authors: van Wyk I. Conradie , Goddard A. , de C. Bronsvoort B. M. , Coetzer J. A. W. , Booth C. , Hanotte O. , Jennings A. , Kiara H. , Mashego P. , Muller C. , Pretorius G. , Poole E. J. , Thumbi S. M. , Toye P. G. , Woolhouse M. E. J. , Penzhorn B. L.
Published: May 2012

This paper is the first attempt to accurately describe the hematological parameters for any African breed of cattle, by capturing the changes in these parameters over the first 12 months of an animal’s life using a population-based sample of calves reared under field conditions and natural disease challenge. Using a longitudinal study design, a stratified clustered random sample of newborn calves was recruited into the IDEAL study and monitored at 5-weekly intervals until 51 weeks of age. The blood cell analysis performed at each visit included: packed cell volume; red cell count; red cell distribution width; mean corpuscular volume; mean corpuscular hemoglobin concentration; hemoglobin concentration; white cell count; absolute lymphocyte, eosinophil, monocyte, and neutrophil counts; platelet count; mean platelet volume; and total serum protein. The most significant age-related change in the red cell parameters was a rise in red cell count and hemoglobin concentration during the neonatal period. This is in contrast to what is reported for other ruminants, including European cattle breeds where the neonatal period is marked by a fall in the red cell parameters. There is a need to establish breed-specific reference ranges for blood parameters for indigenous cattle breeds. The possible role of the postnatal rise in the red cell parameters in the adaptability to environmental constraints and innate disease resistance warrants further research into the dynamics of blood cell parameters of these breeds.