Force Probe (force + probe)

Distribution by Scientific Domains


Selected Abstracts


Accessing Time,Varying Forces on the Vibrating Tip of the Dynamic Atomic Force Microscope to Map Material Composition

ISRAEL JOURNAL OF CHEMISTRY, Issue 2 2008
Ozgur Sahin
In dynamic atomic force microscopes the primary physical quantities being measured are the amplitude/phase or amplitude/frequency of the vibrating force probe. Topographic images with spatial resolutions down to the atomic scale can be obtained by mapping these measurements across the sample surface under feedback control. During the imaging process the vibrating tip is observing tip,sample interaction potentials (force,distance relationships) at every point on the surface. The interaction potential is a superposition of short- and long,distance interactions of various origins determined by the material compositions of the tip, sample, and the medium of imaging. In principle, measurement of tip,sample interaction potential should allow determination and mapping of material composition of the sample. However, a single measurement of amplitude/phase or amplitude/frequency in dynamic atomic force microscopes is not enough to characterize a complicated tip,sample interaction potential. Recent developments in the understanding of dynamics of the vibrating force probe (cantilever), together with specially designed cantilevers that utilize torsional vibrations in addition to conventional vertical vibrations, enable the recovery of tip,sample interaction potentials at a timescale less than a millisecond. Here, with theory and experiments, we discuss how these cantilevers recover the information about the tip,sample interaction forces and give an example of compositional mapping on a polymeric material system. [source]


Comparison of the validity of periodontal probing measurements in smokers and non-smokers

JOURNAL OF CLINICAL PERIODONTOLOGY, Issue 8 2001
A. J. Biddle
Abstract Aim: To determine whether the reduced inflammation and bleeding and increased fibrosis reported in tobacco smokers affect the validity of clinical probing measurements by altering probe tip penetration. Method: A constant force probe was used to measure probing depths and sound bone levels at six sites on 64 molar teeth (384 sites) in 20 smoking and 20 non-smoking patients from grooves made with a bur at the gingival margin prior to extraction. Connective tissue attachment levels were measured from the grooves with a dissecting microscope following extraction. Data were analysed using robust regression with sites clustered within subjects. Results: Sites in smokers showed more calculus but less bleeding than sites in non-smokers (p<0.05). The mean clinical probing depth was not significantly different (smokers: 5.54 mm, confidence intervals=4.81 to 6.28; non-smokers: 6.05 mm, ci=5.38 to 6.72). The corresponding post-extraction pocket depth measurements (smokers: 4.95 mm, ci=4.30 to 5.61; non-smokers: 5.23 mm, ci=4.49 to 5.96) were less than clinical probing depth in sites from both smokers and non-smokers (p<0.01). However, the proportional difference was less in smokers (p<0.05), particularly in deeper pockets, indicating that clinical probe tip penetration of tissue was greater in non-smokers. Regression analysis indicated that the presence of calculus and bleeding also influenced the difference in clinical probe penetration (p<0.05). Conclusion: Clinical probing depth at molar sites exaggerates pocket depth, but the probe tip may be closer to the actual attachment level in smokers due to less penetration of tissue. This may be partly explained by the reduced inflammation and width of supra-bony connective tissue in smokers. These findings have clinical relevance to the successful management of periodontal patients who smoke. Zusammenfassung Ziel: Bestimmung, ob die reduzierte Entzündung und Blutung und verstärkte Fibrosierung, die bei Rauchern berichtet wird, die Gültigkeit der klinischen Messung der Sondierungstiefen durch Veränderung der Penetration der Sondenspitze beeinflußt. Methoden: Eine konstante Sondierungskraft wurde genutzt, um die Sondierungstiefen und das Knochenniveau (sounding) an 6 Flächen von 64 Molaren (384 Flächen) bei 20 Rauchern und 20 Nichtrauchern von einer Furche, die mit einem Fräser in der Höhe des gingivalen Randes vor der Extraktion angelegt wurde, zu messen. Das Niveau des bindegewebigen Attachments wurde von der Furche mit einem trennenden Mikroskop nach der Extraktion gemessen. Die Daten wurden unter Nutzung einer robusten Regission mit den Flächen in den Personen zusammengefaßt analysiert. Ergebnisse: Die Flächen von Rauchern zeigten mehr Zahnstein, aber weniger Blutung als die Flächen von Nichtrauchern (p<0.05). Die mittleren Sondierungstiefen unterschieden sich nicht signifikant (Raucher: 5.54 mm, Konfidenzinterval (ci)=4.81 zu 6.28; Nichtraucher: 6.05 mm, ci=5.38 zu 6.72). Die korrespondierenden Taschenmessungen nach der Extraktion (Raucher: 4.95 mm, ci=4.30 zu 5.61; Nichtraucher: 5.23 mm, ci=4.49 zu 5.96) waren geringer als die klinischen Messungen sowohl bei den Flächen bei Rauchern als auch bei Nichtrauchern (p<0.01). Jedoch war die proportionale Differenz bei Rauchern geringer (p<0.05), besonders bei tiefen Taschen, was zeigt, daß die Penetration der Sonde ins Gewebe bei der klinischen Messung bei Nichtrauchern größer war. Die Regressionsanalyse zeigte, daß das Vorhandensein von Zahnstein und Blutung die Differenz in der klinischen Sondenpenetration beeinflußte (p<0.05). Zusammenfassung: Die klinische Sondierung an Molarenflächen überschätzt die Taschentiefe, aber die Sondenspitze liegt bei Rauchern näher am wirklichen Stützgewebelevel aufgrund der geringeren Gewebepenetration. Dies mag teilweise durch die reduzierte Entzündung und die Breite des supra-alveolären Bindegewebes bei Rauchern erklärt werden. Diese Ergebnisse haben klinische Bedeutung bei der erfolgreichen Behandlung von rauchenden parodontalen Patienten. Résumé But: L'objectif de cette étude est de déterminer si la diminution de l'inflammation et du saignement, ainsi que l'augmentation de la fibrose rapportées chez les fumerus affecte la validité des mesures de sondage parodontal en modifiant la pénétration de la sonde. Methode: Une sonde a pression constante a été utilisée pour mesurer la profondeur au sondage et pour sonder le niveau osseux sur les 6 sites de 64 molaires (384 sites) chez 20 patients fumeurs et 20 patients non-fumeurs à partir de rainures faites à la fraise au niveau de la gencive marginale avant extraction. Les niveaux d'attache du tissus conjonctif furent mesurés à partir de la rainure sous microscope de dissection après extraction. Les données furent analysées par régression avec les sites groupés par patients. Résultats: Les sites des fumerus montraient plus de tartre mais moins de saignement que les sites des non-fumeurs (p<0.05). La profondeur moyenne de sondage clinique n'était pas significativement différente (fumeurs: 5.54 mm, interval de confiance=4.81 à 6.28; non-fumeurs: 6.05 mm, ci=5.38 à 6.72). Les mesures de profondeur de poche correspondantes aprés extraction (fumeurs: 4.95 mm, interval de confiance=4.30 à 5.61; non-fumeurs: 5.23 mm, ci=4.49 à 5.96) ètaient moindre que les profondeurs de sondage clinique des sites des fumeurs et des non-fumeurs ensemble (p<0.01). Cependant, la différence proportionnelle était moindre chez les fumeurs (p<0.05), particulièrement pour les poches profondes, ce qui indique que la pénétration tissulaire de la pointe de la sonde était plus importante chez les non-fumeurs. L'analyse de régression indique que la présence de tartre et le saignement influencent aussi la différence clinique de pénétration (p<0.05). Conclusion: La profondeur clinique de sondage sur des sites molaires exaggère la profondeur de poche, mais la pointe de la sonde pourrait être plus proche de l'actuel niveau d'attache chez les fumeurs en raison de la moindre pénétration des tissus. Cela peut être partiellement expliqué par l'inflammation réduite et l'épaisseur du tissus conjonctif supra-osseux chez les fumeurs. Ces résultats ont une signification clinique pour la bonne gestion des patients fumeurs atteints de maladies parodontales. [source]


The assessment of microscopic charging effects induced by focused electron and ion beam irradiation of dielectrics

MICROSCOPY RESEARCH AND TECHNIQUE, Issue 3 2007
Marion A. Stevens-Kalceff
Abstract Energetic beams of electrons and ions are widely used to probe the microscopic properties of materials. Irradiation with charged beams in scanning electron microscopes (SEM) and focused ion beam (FIB) systems may result in the trapping of charge at irradiation induced or pre-existing defects within the implanted microvolume of the dielectric material. The significant perturbing influence on dielectric materials of both electron and (Ga+) ion beam irradiation is assessed using scanning probe microscopy (SPM) techniques. Kelvin Probe Microscopy (KPM) is an advanced SPM technique in which long-range Coulomb forces between a conductive atomic force probe and the silicon dioxide specimen enable the potential at the specimen surface to be characterized with high spatial resolution. KPM reveals characteristic significant localized potentials in both electron and ion implanted dielectrics. The potentials are observed despite charge mitigation strategies including prior coating of the dielectric specimen with a layer of thin grounded conductive material. Both electron- and ion-induced charging effects are influenced by a delicate balance of a number of different dynamic processes including charge-trapping and secondary electron emission. In the case of ion beam induced charging, the additional influence of ion implantation and nonstoichiometric sputtering from compounds is also important. The presence of a localized potential will result in the electromigration of mobile charged defect species within the irradiated volume of the dielectric specimen. This electromigration may result in local modification of the chemical composition of the irradiated dielectric. The implications of charging induced effects must be considered during the microanalysis and processing of dielectric materials using electron and ion beam techniques. Microsc. Res. Tech., 2007. © 2007 Wiley-Liss, Inc. [source]


What is the biological relevance of the specific bond properties revealed by single-molecule studies?,

JOURNAL OF MOLECULAR RECOGNITION, Issue 6 2007
Philippe Robert
Abstract During the last decade, many authors took advantage of new methodologies based on atomic force microscopy (AFM), biomembrane force probes (BFPs), laminar flow chambers or optical traps to study at the single-molecule level the formation and dissociation of bonds between receptors and ligands attached to surfaces. Experiments provided a wealth of data revealing the complexity of bond response to mechanical forces and the dependence of bond rupture on bond history. These results supported the existence of multiple binding states and/or reaction pathways. Also, single bond studies allowed us to monitor attachments mediated by a few bonds. The aim of this review is to discuss the impact of this new information on our understanding of biological molecules and phenomena. The following points are discussed: (i) which parameters do we need to know in order to predict the behaviour of an encounter between receptors and ligands, (ii) which information is actually yielded by single-molecule studies and (iii) is it possible to relate this information to molecular structure? Copyright © 2007 John Wiley & Sons, Ltd. [source]


Fluorophores as Optical Sensors for Local Forces,

CHEMPHYSCHEM, Issue 12 2009
Stefan Marawske
Abstract The main aim of this study is to investigate correlations between the impact of an external mechanical force on the molecular framework of fluorophores and the resultant changes in their fluorescence properties. Taking into account previous theoretical studies, we designed a suitable custom-tailored oligoparaphenylenevinylene derivative (OPV5) with a twisted molecular backbone. Thin foils made of PVC doped with 100 nM OPV were prepared. By applying uniaxial force, the foils were stretched and three major optical effects were observed simultaneously. First, the fluorescence anisotropy increased, which indicates a reorientation of the fluorophores within the matrix. Second, the fluorescence lifetime decreased by approximately 2.5,% (25 ps). Finally, we observed an increase in the emission energy of about 0.2,% (corresponding to a blue-shift of 1.2 nm). In addition, analogous measurements with Rhodamine 123 as an inert reference dye showed only minor effects, which can be attributed to matrix effects due to refractive index changes. To relate the observed spectroscopic changes to the underlying changes in molecular properties, quantum-chemical calculations were also performed. Semiempirical methods had to be used because of the size of the OPV5 chromophore. Two conformers of OPV5 (C2 and Cisymmetry) were considered and both gave very similar results. Both the observed blue-shift of fluorescence and the reduced lifetime of OPV5 under tensile stress are consistent with the results of the semiempirical calculations. Our study proves the feasibility of fluorescence-based local force probes for polymers under tension. Improved optical sensors of this type should in principle be able to monitor local mechanical stress in transparent samples down to the single-molecule level, which harbors promising applications in polymer science and nanotechnology. [source]