Luminescence properties of poly‐ (phenylene vinylene) derivatives

BACKGROUND: Conjugated polymers, especially those of the poly(phenylene vinylene) (PPV) family, are promising candidates as emission material in light‐emitting devices. The aim of this work was to investigate the dependence of the luminescence properties of PPV‐based derivatives on their polymer structure, especially side groups. RESULTS: Three PPV derivatives, BEHPPV, MEHPPV and MEHSPPV, were synthesised and characterised by photoluminescence (PL) and cathodoluminescence (CL) spectroscopies in the temperature range 10–300 K. PL and CL spectra of the polymers exhibit similar luminescence peaks, which undergo a blue shift with increasing temperature. The shift in wavelength is accompanied by variations in the relative intensities of emission peaks. Both BEHPPV and MEHPPV display emission characteristics of the PPV backbone, but the peak of MEHPPV shifts to a longer wavelength in comparison with the corresponding peak of BEHPPV at the same temperature. The luminescence spectra of MEHSPPV, which has a sulfanyl incorporated in the side chain, are considerably different from those of the two other derivatives. CONCLUSIONS: The results demonstrate that the luminescence properties depend strongly on the chain conformations of the conjugated backbone, which are affected by polymer side chains. Copyright © 2007 Society of Chemical Industry     

The Scholarly Database and its utility for scientometrics research

The Scholarly Database aims to serve researchers and practitioners interested in the analysis, modelling, and visualization of large-scale data sets. A specific focus of this database is to support macro-evolutionary studies of science and to communicate findings via knowledge-domain visualizations. Currently, the database provides access to about 18 million publications, patents, and grants. About 90% of the publications are available in full text. Except for some datasets with restricted access conditions, the data can be retrieved in raw or pre-processed formats using either a web-based or a relational database client. This paper motivates the need for the database from the perspective of bibliometric/scientometric research. It explains the database design, setup, etc., and reports the temporal, geographical, and topic coverage of data sets currently served via the database. Planned work and the potential for this database to become a global testbed for information science research are discussed at the end of the paper.     

功率与控制的结合使LED照明方案灵活、简便

嵌入式电源控制器——PowerPSoC集成了多通道LED恒流通道系统,可为客户降低BOM成本,提供更大的设计灵活性。其不仅提供光的智能控制,也是LED恒流电源,可有效用来处理通信、调光、输入电压及恒定电流控制等问题。     

Structure, conformations, and repair of DNA adducts from dibenzo[a, l]pyrene: 32P-postlabeling and fluorescence studies

The nature of stable DNA adducts derived from the very potent carcinogen dibenzo[a,l]pyrene (DB[a,l]P) in the presence of rat liver microsomes in vitro and in mouse skin in vivo has been studied using 32P-postlabeling and laser-based fluorescence techniques. Analysis of DB[a,l]P-DNA adducts via 32P-postlabeling has been obtained by comparison of the adduct patterns to those obtained from reactions of synthetic (+/-)-anti-, (+)-anti-, (-)-anti-, and (+/-)-syn-DB[a,l]P-11,12-diol 13,14-epoxide (DB[a,l]PDE) with single nucleotides and calf thymus DNA. anti-DB[a,l]PDE-dA adducts derived from the (-)-enantiomer are the major adducts formed in calf thymus DNA and in mouse skin DNA. The ratio of deoxyadenosine to deoxyguanosine modification is approximately 2:1 in mouse skin exposed to DB[a,l]P; activation by rat liver microsomes leads to a similar profile of adducts but with two additional spots. The conformations of DB[a,l]P adducts in native DNA, as well as the possibility of conformation-dependent repair, have been explored by low-temperature fluorescence spectroscopy. These studies have been performed using polynucleotides and calf thymus DNA reacted in vitro with DB[a,l]PDE and native DNA from mouse epidermis exposed to DB[a, l]P. The results show that adducts are heterogeneous, possess different structures, and adopt different conformations. External, external but base-stacked and intercalated adduct conformations are observed in calf thymus DNA and in mouse skin DNA samples. Differences in adduct repair rates are also revealed; namely, the analysis of mouse skin DNA samples obtained at 24 and 48 h after exposure to DB[a,l]P clearly shows that external adducts are repaired more efficiently than intercalated adducts. These results, taken together with those for B[a]P-DNA adducts [Suh et al. (1995) Carcinogenesis 16, 2561-2569], indicate that the repair of DNA damage resulting from PAH diol epoxides is conformation-dependent.     

Receptors involved in nerve-mediated vasoconstriction in small arteries of the rat hepatic mesentery

Systemic inhibition of nitric oxide synthase (NOS) with NG-monomethyl-L-arginine (L-NMMA) causes acute insulin resistance (IR), but the mechanism is unknown. We tested whether L-NMMA-induced IR occurs via NOS blockade in the central nervous system (CNS). Six groups of Sprague-Dawley rats were studied after chronic implantation of an intracerebroventricular (ICV) catheter into the lateral ventricle and catheters into the carotid artery and jugular vein. Animals were studied after overnight food deprivation, awake, unrestrained, and unstressed; all ICV infusion of L-NMMA or D-NMMA (control) were performed with artificial cerebrospinal fluid. ICV administration of L-NMMA resulted in a 30% rise in the basal glucose level after 2 h, while ICV D-NMMA had no effect on glucose levels. Insulin, epinephrine, and norepinephrine levels were unchanged from baseline in both groups. Tracer (3H-3-glucose)-determined glucose disposal rates during 2 h euglycemic hyperinsulinemic (300 microU/ml) clamps performed after ICV administration of L-NMMA were reduced by 22% compared with D-NMMA. Insulin secretory responses to a hyperglycemic clamp and to a superimposed arginine bolus were reduced by 28% in L-NMMA-infused rats compared with D-NMMA. In conclusion, ICV administration of L-NMMA causes hyperglycemia via the induction of defects in insulin secretion and insulin action, thus recapitulating abnormalities observed in type 2 diabetes. The data suggest the novel concept that central NOS-dependent pathways may control peripheral insulin action and secretion. This control is not likely to be mediated via adrenergic mechanisms and could occur via nonadrenergic, noncholinergic nitrergic neural and/or endocrine pathways. These data support previously published data suggesting that CNS mechanisms may be involved in the pathogenesis of some forms of insulin resistance and type 2 diabetes independent of adiposity.     

Sequence heterogeneity in Parkinsonian speech

Parkinson's disease (PD) is a neurodegenerative movement disorder primarily due to basal ganglia dysfunction. While much research has been conducted on Parkinsonian deficits in the traditional arena of musculoskeletal limb movement, research in other functional motor tasks is lacking. The present study examined articulation in PD with increasingly complex sequences of articulatory movement. Of interest was whether dysfunction would affect articulation in the same manner as in limb-movement impairment. In particular, since very similar (homogeneous) articulatory sequences (the tongue twister effect) are more difficult for healthy individuals to achieve than dissimilar (heterogeneous) gestures, while the reverse may apply for skeletal movements in PD, we asked which factor would dominate when PD patients articulated various grades of artificial tongue twisters: the influence of disease or a possible difference between the two motor systems. Execution was especially impaired when articulation involved a sequence of motor program heterogeneous in terms of place of articulation. The results are suggestive of a hypokinesic tendency in complex sequential articulatory movement as in limb movement. It appears that PD patients do show abnormalities in articulatory movement which are similar to those of the musculoskeletal system. The present study suggests that an underlying disease effect modulates movement impairment across different functional motor systems.     

Estimating forage quantity and quality using aerial hyperspectral imagery for northern mixed-grass prairie

Sustainable rangeland stewardship calls for synoptic estimates of rangeland biomass quantity (kg dry matter ha^− 1) and quality [carbon:nitrogen (C:N) ratio]. These data are needed to support estimates of rangeland crude protein in forage, either by percent (CP_c) or by mass (CP_m). Biomass derived from remote sensing data is often compromised by the presence of both photosynthetically active (PV) and non-photosynthetically active (NPV) vegetation. Here, we explicitly quantify PV and NPV biomass using HyMap hyperspectral imagery. Biomass quality, defined as plant C:N ratio, was also estimated using a previously published algorithm. These independent algorithms for forage quantity and quality (both PV and NPV) were evaluated in two northern mixed-grass prairie ecoregions, one in the Northwestern Glaciated Plains (NGGP) and one in the Northwestern Great Plains (NGP). Total biomass (kg ha^− 1) and C:N ratios were mapped with 18% and 8% relative error, respectively. Outputs from both models were combined to quantify crude protein (kg ha^− 1) on a pasture scale. Results suggest synoptic maps of rangeland vegetation mass (both PV and NPV) and quality may be derived from hyperspectral aerial imagery with greater than 80% accuracy.