169,943 research outputs found
Development of peptide inhibitors of lipases and phospholipases by phage display technology
No full textBiološke knjižnice naključnih peptidov, predstavljenih na površini organizmov, nam omogočajo sistematično proučevanje interakcij ciljnih makromolekul. Peptidni modulatorji terapevtsko zanimivih ciljnih proteinov imajo v sodobnem načrtovanju učinkovin vse pomembnejšo vlogo.
V prvem delu smo vpeljali, razvili in optimirali metodologijo bioloških kombinatoričnih knjižnic z uporabo streptavidina kot modelne ciljne makromolekule. V drugem delu pa smo jo uporabili kot orodje za identifikacijo strukturno in funkcionalno optimalnih peptidnih ligandov izbranih ciljnih makromolekul. Primerjalno smo ovrednotili dva tipa bioloških knjižnic, bakterijsko in bakteriofagno predstavitveno knjižnico. Na podlagi lastnih eksperimentov in podatkov, objavljenih v literaturi, smo zaključili, da so bakteriofagne predstavitvene knjižnice sicer tehnično zahtevnejše, vendar v večini primerov vodijo v uspešnejšo selekcijo. Za rešetanje in ovrednotenje posameznih bakteriofagnih klonov smo primerjali dve metodi, encimskoimunski test na trdnem nosilcu in površinsko plazmonsko resonanco. Obe metodi je mogoče uspešno uporabiti za določanje vezavnih lastnosti bakteriofagnih klonov, izbira pa temelji na naravi in količini ciljne makromolekule ter nenazadnje na opremi, ki nam je na voljo. Predvsem kadar je količina ciljne makromolekule omejujoč dejavnik, je metoda izbora površinska plazmonska resonanca, saj raznoliki senzoski čipi omogočajo pritrditev katerekoli makromolekule, ne glede na njene fizikalno-kemijske lastnosti. V tehnologijo bakterifagnega prikaza smo vpeljali uporabo ultrazvoka, ki pri eluciji pripomore tako k pretrganju interakcij med tarčo in peptidom na bakteriofagu, kot tudi desorpciji tarčnega proteina skupaj z bakteriofagom s trdnega nosilca. Uvedba tega inovativnega postopka v afinitetne selekcije bo brez dvoma prispevala k razvoju tehnologije bakteriofagnih predstavitvenih knjižnic. Tehnologijo bioloških peptidnih knjižnic smo uporabili za razvoj novih ligandov in potencialnih inhibitorjev encimov, ki sodelujejo pri razgradnji in absorpciji maščob v prebavnem traktu (pankreasne lipaze, pankreasne fosfolipaze A2). Uporabili smo knjižnico naključnih, cikličnih heptapeptidov in linearnih dodekapetidov izraženih na bakteriofagih. Naredili smo več neodvisnih selekcij, pri katerih smo spreminjali načine spiranja in elucije. Inhibicijo pankreasne lipaze smo dosegli s peptidom D23 (navidezna konstanta inhibicije 16 μM). Ligandi pankreasne fosfolipaze A2 in sorodne fosfolipaze, amoditoksina C, ki smo jih izolirali z različnimi selekcijskimi protokoli, jasno kažejo afiniteto do obeh encimov, neodvisno od ciljne molekule uporabljene pri selekciji. Navkljub vezavi na tarčna proteina, pa peptidi ne vplivajo na njuno aktivnost. Peptidi, pridobljeni s to metodologijo, so ligandi določenih mest ciljnega proteina in lahko predstavljajo spojine vodnice pri razvoju novih učinkovin. Njihova uporabna vrednost je predvsem v sposobnosti selektivnih interakcij s ciljnimi proteinskimi makromolekulami.Libraries of random peptides displayed on the surface of biological systems are an essential tool that enables systematic study of target molecule interactions. Peptide modulators of therapeutically interesting target proteins are gaining an increasingly important role in drug discovery and development. First part comprises of introduction, development and optimization of biological display libraries with the use of a model target molecule, streptavidin. The second part describes the use of such libraries and optimized procedures in a search of novel peptide ligands of selected targets. Bacterial and phage display libraries were compared for their efficiency in the search of model target protein (streptavidin) binding motif. Under similar conditions, phage display library, although technically more demanding, proved to be convincingly better. Efficiency and convenience of enzyme linked immunosorbent assay and surface plasmon resonance were compared for determining the binding properties of peptide-displaying phage clones using streptavidin as a model protein target. Both methods can be successfully used for affinity ranking. The choice therefore depends on the nature and the amount of target protein and the equipment available. Versatile sensor chips enable immobilization of almost any target molecule, regardless of their physiochemical properties and when there is only a small amount of target molecule available, surface plasmon resonance would be a method of choice. An improved non-specific elution strategy was introduced to the phage display technology. This procedure employs ultrasound to break the interaction of high affinity clones with the target and also to detach the target molecule from the immobilization surface. This new approach is able to surmount the incapability of other commonly used non-specific elution techniques and represents an important improvement in a search for novel specific ligands. Phage display technology was used to develop new ligands and potential inhibitors of lipid digestion and absorption enzymes (pancreatic lipase, pancreatic phospholipase A2) in gastrointestinal tract. A random, cyclic heptapetide and a linear dodecapeptide phage display library were used. Several independent selections were performed, differing in washing and elution steps. Inhibition of pancreatic lipase was achieved by peptide D23 (apparent inhibition constant of 16 μM). Peptide ligands of pancreatic phospholipase A2 and structurally related ammodytoxin C, selected by different selection protocols, clearly indicate affinity towards both enzymes, regardless which of the two proteins was used as a target in the selection procedure. Despite clear affinity, none of the peptides had inhibitory activity in vitro.Peptides selected and discovered by screening biological libraries target only a few sites on a given protein, often associated with biological activity. These peptides are modulators of protein function and are a starting point in drug development, their main advantage being the ability of highly specific interaction with protein macromolecules
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Mitomycin C in highly myopic eyes - Author reply
No full textOphthalmology. 2005 Feb;112(2):208-18; discussion 219.
Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes.
Gambato C, Ghirlando A, Moretto E, Busato F, Midena E.
SourceRefractive Surgery Service and Antimetabolite Therapy Research Unit, Department of Ophthalmology, University of Padova, Padova, Italy.
Abstract
PURPOSE: To evaluate the role of topical mitomycin C in corneal wound healing (CWH) after photorefractive keratectomy (PRK) in highly myopic eyes.
DESIGN: Prospective, double-masked, randomized clinical trial.
PARTICIPANTS: Seventy-two eyes of 36 patients affected by high (>7 diopters) myopia.
METHODS: In each patient, one eye was randomly assigned to PRK with intraoperative topical 0.02% mitomycin C application, and the fellow eye was treated with a placebo. Postoperatively, mitomycin C-treated eyes received artificial tears (3 times daily, tapered in 3 months), whereas the fellow eye was treated with fluorometholone sodium 2% and artificial tears (3 times daily, tapered in 3 months).
MAIN OUTCOME MEASURES: Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA), contrast sensitivity, manifest refraction, and biomicroscopy. Contrast sensitivity was determined using the Pelli-Robson chart. Corneal confocal microscopy documented CWH.
RESULTS: Mean follow-up was 18 months (range, 12-36). No side effects or toxic effects were documented. At 12-month follow-up examination, UCVAs (logarithm of the minimum angle of resolution) were 0.4+/-0.48 and 0.5+/-0.53 (P = .03) in mitomycin C-treated eyes and corticosteroid-treated eyes, respectively. At 1 year, corneal haze developed in 20% of corticosteroid-treated eyes, versus 0% of mitomycin C-treated eyes. At 12, 24, and 36 months, corneal confocal microscopy showed activated keratocytes and extracellular matrix significantly more evident in untreated eyes (Ps = 0.004, 0.024, and 0.046, respectively).
CONCLUSION: Topical intraoperative application of 0.02% mitomycin C can reduce haze formation in highly myopic eyes undergoing PRK.
Comment in
Ophthalmology. 2006 Feb;113(2):357; author reply 357-8
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Chromate-free Pre-treatment of Aluminium for Adhesive Bonding
No full textThe increasing use of aluminium in automotive and transport applications is primarily driven by its high strength to weight ratio, enabling substantially improved fuel economy and reduced CO2 emissions when substituted for heavier materials. However, the change of material presents new challenges with respect to design and methods of joining. Structural adhesive bonding offers several advantages compared with welding, but a major limitation is concern about the durability of joints in wet and corrosive environments. The pre-treatment of the aluminium surface prior to bonding is the key to long service life. Pre-treatments successfully employed by the aerospace industry cannot be used in automotive production, where cheaper and more environmentally friendly pre-treatments are required. Specifically, the use of chromates is unacceptable. Hence, there is a need to develop chromate-free pre-treatments that will consistently provide the required level of performance, while being acceptable both in terms of general engineering practice and economy. To accomplish this task, basic knowledge of the processes occurring on the aluminium surface during pre-treatment, properties of the modified surface, and mechanisms of joint degradation are necessary.
The purpose of the present work has therefore been to contribute to a better understanding of how the aluminium substrate affects the formation and properties of conversion coatings for adhesive bonding. In particular, a commercial chromate-free fluorotitanate/zirconate based process has been investigated and compared with conventional chromate treatment. The materials chosen for this work were commercially extruded AA6060-T6 aluminium and a structural single-part epoxy adhesive. To complement the studies of the commercial alloy, model analogues of the AA6060 aluminium matrix and α-Al(Fe,Mn)Si phase particles present in the commercial alloy were also investigated.
It was observed that the α-Al(Fe,Mn)Si particles played an essential role in the formation and properties of Ti-Zr oxide conversion coatings on AA6060 aluminium. The particles were significantly nobler than the aluminium matrix in the pre-treatment solution. An alkaline diffusion layer therefore developed around the particles during pre-treatment due to oxygen reduction and hydrogen evolution reactions. As Ti-Zr oxide precipitation was favoured at high pH, the conversion layers normally deposited at and in the vicinity of the cathodic particles. The conversion layers formed consequently exhibited considerable lateral variations in thickness. In addition to substrate microstructure, bulk pH and agitation of the conversion bath were important factors controlling the extent of Ti-Zr oxide deposition and its distribution on the surface. On areas well away from the cathodic particles coverage was generally very poor, although a high density of small (<50 nm) oxide particles was deposited, presumably with a composition similar to the continuous conversion layer close to the α-Al(Fe,Mn)Si particles. The cathodic activity of the particles was only slightly reduced by formation of the Ti-Zr oxide conversion coating. In combination with poor coverage of the aluminium matrix, these conversion coatings are therefore not expected to improve the corrosion resistance of aluminium significantly.
In contrast to the above mechanism, the chromate conversion coating (CCC) formed by a redox reaction between chromate ions and aluminium. A relatively thick, porous chromium oxide layer developed over the aluminium matrix of AA6060, while a significantly thinner film was formed on the α-Al(Fe,Mn)Si particles. The morphology of the CCC covering the matrix was influenced by the hardening Mg2Si phase, primarily by promoting nucleation of the CCC. Despite the thin film (<50 nm) formed on the α-Al(Fe,Mn)Si particles by chromating, the cathodic activity was significantly reduced. Inhibition of the cathodic reactivity at these particles is suggested as an important factor contributing to the high performance of chromate pretreatments on aluminium.
Testing of epoxy-bonded AA6060 aluminium joints in humid environment showed that Ti-Zr based pre-treatment provided improved adhesion relative to alkaline etching and deoxidation only. However, Ti-Zr based pre-treatment was inferior to chromating. Rapid, interfacial crack growth during wedge testing was particularly observed for adherends with a relatively thick Ti-Zr oxide deposit, suggesting that excessive Ti-Zr oxide deposition should be avoided. Furthermore, as the substrate microstructure (i.e. type, area fraction and distribution of cathodic sites) strongly affected the Ti-Zr oxide deposition, the pre-treatment conditions should be adapted to the specific alloy in order to achieve optimum performance.
In the presence of chlorides, degradation of adhesive-bonded joints may be accelerated by a filiform corrosion (FFC) type of mechanism. The α-Al(Fe,Mn)Si particles in AA6060 played a crucial role in promoting FFC, as demonstrated by complete FFC immunity of the iron-free AA6060 model analogue alloy. Ti-Zr based pre-treatment provided less protection against FFC relative to chromate pre-treatment. The good FFC resistance of CCCs was partly attributed to a better inhibition of the cathodic activity at the α-Al(Fe,Mn)Si particles.
The cathodic α-Al(Fe,Mn)Si particles present on the surface of AA6060 aluminium could be effectively removed by different etch treatments. However, selective removal of surface intermetallics did not prevent FFC because filament growth was supported by cathodic activity on particles that become exposed in the filament tail as a result of the corrosion process.
Based on lap shear testing, hot AC anodising in sulphuric acid to a film thickness of about 0.2 µm showed promise as another chromate-free pretreatment for durable adhesive bonding. The performance was better than a conventional chromic-sulphuric acid based etch treatment. While hot AC anodising did not significantly inhibit the cathodic activity on the α-Al(Fe,Mn)Si particles, good resistance against FFC was still obtained due to the oxide film covering the whole aluminium matrix. Based also on separate durability data recently available, hot AC anodising is considered as a robust alternative to chromating for adhesive bonding of aluminium in certain industrial applications.dr.ing.dr.ing
A Multi-Language Comparison of Influences on Author Verification using Character N-Grams
No full textWe create a new multi-language corpus for author verification based on Wikipedia talkpages, and evaluate the influence that differences in topic and time have on character n-gram author profiles. Topic alignment between two texts is found to increase author verification precision, and an authors writing style is found to change over time, but not more significantly after 3 years than after 1 year.Information ArchitectureWISElectrical Engineering, Mathematics and Computer Scienc
A 0.12mm<sup>2</sup> Wien-Bridge Temperature Sensor with 0.1°C (3σ) Inaccuracy from -40°C to 180°C
No full text Resistor-based temperature sensors can achieve much higher resolution and energy efficiency than conventional BJT-based sensors [1], but they typically occupy more area (> 0.25 mm 2 ) and have lower operating temperatures (le 125 {circ} {C}) [2]-[4]. This work describes a 0.12mm 2 resistor-based sensor that uses a Wien-bridge (WB) filter to achieve 0.1 {circ} {C} (3 sigma) inaccuracy from - 40 {circ} {C} to 180 {circ} {C}. Compared to a state-of-the-art WB sensor [4], it occupies 6 × less area and achieves comparable relative accuracy over a 76% wider operating range. Session 10.3 Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic InstrumentationMicroelectronic
A ±25A Versatile Shunt-Based Current Sensor with 10kHz Bandwidth and ±0.25% Gain Error from -40°C to 85°C Using 2-Current Calibration
No full textAccurate current sensing is critical in many industrial applications, such as battery management and motor control. Precise shunt-based current sensors have been reported with gain errors of less than 1% over the industrial temperature range (-40°C to 85°C) [1]–[4]. However, since they are intended for coulomb counting, their bandwidth is limited to a few tens of Hz, making them unsuitable for battery impedance or motor-current sensing. This paper presents a current sensor with a wide (10kHz) bandwidth and a tunable temperature compensation scheme (TCS), which allows it to be flexibly used with different types of shunts while maintaining high accuracy. A low-cost room-temperature calibration scheme is proposed to optimize gain flatness over temperature by exploiting the shunt's self-heating at large currents. Over the industrial temperature range and a ±25A current range, it achieves state-of-the-art gain error (±0.25%) with both low-cost PCB and stable metal-alloy shunts.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic InstrumentationMicroelectronic
An Article About Albertus C. Van Raalte, Author Unknown, Except for Parts Taken from an Article by Anna C. Post
No full textAn article about Albertus C. Van Raalte, author unknown, except for parts taken from an article by Anna C. Post. The author knew first generation persons in the Holland settlement and therefore, the article has some value.https://digitalcommons.hope.edu/vrp_1890s/1012/thumbnail.jp
Gas fluxes and biological and physiochemical measurements made across an Arctic forefield.
No full textHalocarbon fluxes measured using dynamic flux chambers across a retreating glacier's forefield, at Midtre Lovenbreen, Svalbard. Also included in this dataset, are physiochemical and biological parameters of the soil where each chamber measurement was conducted. If using this data, please cite: Macdonald, M.L., Wadham, J.L., Young, D., O'Dohery, S., Lunder, C., Hermansen, O., Lamarche-Gagnon, G., (2019). Consumption of CH3Cl, CH3Br and CH3I and emission of CHCl3, CHBr3 and CH2Br2 from a retreating Arctic glacier’s forefield. JOURNAL, VOL, ISSUE. doi: XXX
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