Refine
Year of publication
Document Type
- Article (848) (remove)
Has Fulltext
- no (848) (remove)
Is part of the Bibliography
- yes (848)
Keywords
- cybersecurity (9)
- Shodan (7)
- Censys (6)
- Maltego (6)
- OSINT (6)
- Internet of Things (4)
- IoT (4)
- security (4)
- smart home (4)
- Computational complexity (3)
Institute
Width of cluster plasmon resonances: Bulk dielectric functions and chemical interface damping
(1993)
The damping of collective electron resonances in clusters which develop into plasmon polaritons at larger sizes is investigated for free, supported, and embedded neutral metal clusters. Embedding of free 2 nm Ag clusters of 2-nm diameter into a SiO2 matrix leads to an increase of the width of the resonances by more than a factor of 3. The optical spectra are compared with the Mie theory using size-effect-modified dielectric functions of the solid state. The results corroborate the assumption that the widths of the resonances strongly depend on chemical interface effects. The results are briefly discussed with regard to limited-mean-free-path and quantum-size-effect theories and a recent approach by Persson. It is demonstrated that the widths of the spectra of supported and embedded clusters have to be interpreted with care since true intrinsic size effects of the clusters appear to be less effective than previously believed and can be obscured by the chemical interface damping.
© 1993 The American Physical Society
Laser-induced desorption of metal atoms from the surface of small metal particles has been investigated as a function of the shape of the particles and the polarization of the incident laser light. The particles were supported on LiF, quartz or sapphire substrates. In a first set of experiments, the shape of the particles was determined by recording optical transmission spectra with s- and p-polarized light incident under an angle of typically 40° with respect to the surface normal. The metal particles turn out to be oblate, the ratio of the axes perpendicular and parallel to the substrate surface being on the order of 0.5. This ratio decreases with increasing particle size. Also, the particles change shape if the temperature is raised. In further experiments, s- and p-polarized light has been used to stimulate desorption of atoms via surface plasmon excitation. It is found that the desorption rate markedly depends on the polarization of the light. This is explained by excitation of the collective electron oscillation along different axes of the non-spherical particles.
Results on laser-induced desorption of metal atoms from small metal particles are presented. Experiments have been performed on sodium, potassium, and silver particles supported on a LiF(100) single-crystal surface under ultrahigh vacuum conditions. Measurements include the determination of the desorption rate as a function of laser wavelength, laser intensity, average particle size, and substrate temperature, the determination of the kinetic energy of the desorbed atoms, the investigation of the optical spectra of the supported metal particles, and the study of the influence of adsorbate molecules on the desorption rate. Furthermore, theoretical extinction and absorption spectra of the metal particles have been calculated with the classical electrodynamical Mie theory as a function of average particle size and excitation wavelength. Also, the radial electric field at the particle surface was computed. The results of the experiments and theoretical calculations are combined to give a consistent picture of the mechanism of metal-atom desorption by electronic excitation with laser light. A realistic surface potential from which the atoms escape and nonlocal optical effects are taken into account. The latter introduce additional absorption channels by the formation of electron-hole pairs in the surface layer of the particle which relax into antibonding states before desorption occurs. Finally, the mechanism is discussed in the light of similar phenomena observed for thin metal films. Possibilities for future work are outlined.
© 1993 The American Physical Society
Beleuchtet man die Oberfläche eines Festkörpers mit Laserlicht, können darauf adsorbierte Atome oder Moleküle abgelöst werden. Solche Desorptionsprozesse sind in jüngster Zeit in zahlreichen Experimenten untersucht worden, wobei sich das Interesse sowohl auf die Erforschung der zugrundeliegenden Mechanismen als auch auf mögliche Anwendungen dieser Reaktionen, zum Beispiel zur gezielten Modifizierung von Oberflächen, konzentriert. Besonders interessant ist das laserinduzierte Aufbrechen von Bindungen zur Oberfläche dann, wenn es nicht einfach als thermischer Prozeß durch eine Temperaturerhöhung hervorgerufen wird, sondern direkt auf einer elektronischen Anregung beruht. Solche nichtthermischen Prozesse werden selbst für Metalle beobachtet, obwohl die Kopplung der elektronischen Anregung an das Substrat hier besonders schnell abläuft. Der zugrundeliegende Mechanismus beruht auf dem Zusammenspiel einer kollektiven Elektronenoszillation und einer lokalisierten Einzelelektronenanregung, wobei auch nichtlokale optische Effekte in der Metalloberfläche eine wichtige Rolle spielen.
The results of an experimental study of the optical and photoelectrical properties of Eu-containing lead chalcogenides and superlattices are presented. From both sets of experiments band offset data for the lead chalcogenide-europium chalcogenide heterojunction are derived. The results are compared with the data obtained from a linear interpolation of the band structures between those of the binaries.
On the theory of composite gauge bosons: Calculation of coupling constants and covariant derivatives
(1993)
An innovative net-based methodology to integrate qualitative and quantitative analysis of distributed software systems is outlined, and an on-going prototype implementation of a related graphic-oriented tool kit is sketched. The proposed method combines qualitative analysis, monitoring and testing as well as quantitative analysis on the basis of a net-based intermediate representation of the distributed software system under consideration. All transformations (from the distributed software system into a first Petri net model, and between the different kinds of net models) can be made formally, and therefore automated to a high degree. The evaluation of quantitative properties is based on so-called object nets which are obtained by a property-preserving structural compression and quantitative expansion of the qualitative model. In this way, the frequency and delay attributes necessary to generate quantitative models are provided by the monitoring and testing component.
Cis-diammine dichloro platinum (II) (CDDP), is a highly potent antineoplastic agent that is used in the treatment of ovarian cancer. However, the clinical use of CDDP is restricted by its severe side effects. In order to reduce these side effects and to enhance its therapeutic efficacy, we developed specific immunoconjugates consisting of the murine monoclonal antibody OC125 and CDDP, using diethylene triamine pentaacetic acid (DTPA) as a linker.
The coupling efficiencies of the different preparations synthesized, varied between 1.10±0.42 and 2.65±1.60 mol of CDDP per mol of antibody protein. Despite the chemical modification of the antibody molecule, specific binding activity of the OC125-CDDP conjugates toward the CA125 antigen was maintained as was demonstrated by means of immunohisto-/cytochemical staining of frozen sections of ovarian cancer tissue, amniotic epithelium, and the CA125 positive ovarian cancer cell line NIH:OVCAR 3.
The antiproliferative activity of the immunoconjugates was tested against the human ovarian cancer cell lines NIH:OVCAR3 and SKOV 3, applying a kinetic crystal violet microassay.
Despite the promising results obtained with the specific immuno-staining of the target cells, no significant antiproliferative activity of our immunoconjugates against the cell lines tested was observed.
One possible explanation for the lack of antitumor activity could be the fact that CA125 is released in large amounts by the NIH:OVCAR 3 cells. This may have prevented an efficient immunotargeting of the cancer cells by the formation of soluble immune complexes.
Identification of insulin and insulin-like growth factor I (IGF I) receptors in ovarian cancer
(1994)
Abstract
The objective of this study was to test if specific insulin and insulin-like growth factor I (IGF I) receptors are expressed in ovarian cancer tissue. Thirteen tissue specimens from primary ovarian cancers, 1 specimen from a primary peritoneal carcinoma, 10 specimens from metastatic lesions of ovarian carcinomas, and 4 specimens from recurrent ovarian cancers together with 13 normal ovaries were tested for their content of insulin and IGF-I receptors, by the application of specific insulin and IGF-I receptor radioimmunoassays. The insulin receptor (IR) and IGF-I receptor (IGF R) content in the primary tumors varied between 23.8-321.4 and 16.4-554.2 ng/0.1 mg DNA, respectively. Metastatic lesions contained between 12.3 and 226.7 ng IR/0.1 mg DNA and between 7.5 and 459.4 ng IGF R/0.1 mg DNA. In recurrent tumors the receptor concentrations were in the range of 41.5-79.8 and 48.9-160.9 ng/0.1 mg DNA for insulin and IGF-I receptors, respectively. Normal ovarian tissue contained between 12.2 and 150.1 ng IR and between 21.4 and 420.1 ng IGF R per 0.1 mg DNA, respectively. As both insulin and IGF-I receptors are present in ovarian cancer tissue, the effects of insulin and IGF-I as potential growth factors in ovarian cancer should be further investigated.
Copyright © 1994 Academic Press. All rights reserved.
A free boundary-value problem for a nonisothermal flow of two heavy viscous incompressible capillary liquids descibing a slot coating process is mathematically studied. The problem is stationary and two-dimensional and the Boussinesq approximation for the Navier-Stokes equations is used. The existence and uniqueness of a weak solution is proved in weighted Holder spaces for small data.
Exact solutions of generalized three-particle Bargmann-Wigner equations in the strong-coupling limit
(1994)
Small sodium and silver particles were generated on dielectric substrates like LiF, quartz and sapphire under ultrahigh vacuum conditions. The optical transmission spectra of the clusters were measured as a function of cluster size and shape, for low and high substrate temperatures as well as for s- and p- polarization of the incident light. Excitation of dipolar surface plasmon oscillations in the directions normal and parallel to the substrate surface could be identified. Furthermore, optical spectra for Na and Ag clusters were calculated with the classical Mie theory. The measured spectra vary strongly if the experimental conditions are changed and can be exploited, for example, to characterize the particles with regard to their size and shape. In particular, the axial ratio of the spheroidal clusters could be determined. Its value is considerably different for the two investigated metals and depends on the substrate material. Furthermore, the temperature of the substrate has a pronounced influence on the shape of the particles. At low temperature of T=100 K two-dimensional island growth is predominant. The particles extend only little in the direction perpendicular to the surface and coalesce readily at small coverage of metal atoms. In contrast, the clusters are truly three-dimensional at T=300 K. At this stage, sodium particles still exhibit a rather small axial ratio whereas silver clusters appear almost spherical. Thus, measurements of the optical spectra permit direct in situ monitoring of cluster growth during the nucleation of adsorbed atoms and of temperature induced shape variations. In addition to investigations of the shape of the particles, the quadrupolar surface plasmon mode was observed for Ag clusters.
Imaging Pattern Formation in Surface Reactions from Ultrahigh Vacuum up to Atmospheric Pressures
(1995)
Two optical methods that allow pattern formation to be investigated at an arbitrary pressure are here applied to image concentration patterns of adsorbed species associated with heterogeneous catalytic reactions. In contrast to most surface physical techniques, these methods are not restricted to high vacuum conditions and thus bridge the “pressure gap.” With carbon monoxide oxidation on a (110) surface of platinum as an example, the coupling mechanisms responsible for spatiotemporal self-organization in surface reactions were followed from reaction-diffusion control to the thermokinetic region, associated with phenomena not previously observed in pattern formation.
Two surface-sensitive optical imaging methods, Ellipso-Microscopy for surface Imaging (EMSI) and Reflection Anisotropy Microscopy (RAM) are introduced. They allow imaging of pattern formation on surfaces, e.g., due to submonolayer coverages of adsorbates, at any arbitrary pressure.
In spatio-temporal pattern formation during heterogeneously catalysed reactions this bridges the ‘pressure gap’ between well-defined UHV experiments and ‘real catalysis’. For the CO oxidation on Pt(110), the parameter space for pattern formation was extended up to 100 mbar, i.e., by 5 orders of magnitude compared to earlier investigations by Photo-Emission Electron Microscopy (PEEM) which had to be conducted below 10−3 mbar. With increasing pressure, the synchronisation mechanisms responsible for the observed pattern showed a gradual shift from reaction-diffusion to thermal-kinetic coupling unveiling previously unseen features of pattern formation in catalysis.
Effective dynamics in a subfermion shell model of leptons, quarks and electroweak gauge bosons
(1995)
Beschreibung finiter plastischer Deformationen von Einkristallen mittels materieller Isomorphismen
(1995)
Modular process nets are a graphical and formal notation for the representation of technical and business process models containing concurrent activities. Originally this class of Petri nets was developed for the modeling, analysis, simulation and control of workflows and computer-based process control systems, but it is also suitable for use in all other areas where a formal but comprehensible description of complex processes is needed. After a description of the basic aims and design decisions for modular process nets, the report gives a brief introduction to low-level Petri nets including different types of transition rules and aspects of the descriptive and prescriptive use of process models. The main and most innovative points which are explained in more detail are the introduction of a hierarchical module concept for nets and the definition of elementare process nets. The module concept is part of a more general ("object-based") approach to Petri nets allowing severaltypes of ab straction, whereas the main points of elementary process nets are synchronous and asynchronous communication between separately interpreted net instances via events and token passing. Modular process nets are low-level Petri nets equipped with these module and communication concepts and optionally enhanced by die use of a task concept, a method known from the areas of computer-supported cooperative work (CSCW) and work-flow management. Because the report is aimed at a systematic and easy-to-understand introduction to modular process nets, it provides a precise explanation of this net class which is kept as informal as possible and enhanced by some typical application examples
Two new optical imaging methods with submonolayer surface sensitivity are applied together to investigate pattern formation of adsorbate concentrations on surfaces during heterogeneously catalysed reactions. Ellipso-microscopy for surface imaging (EMSI) is based on an ellipsometric effect, reflection anisotropy microscopy (RAM) on the polarising properties of surface anisotropies. For the CO oxidation reaction on a Pt(110) surface features like front propagation, target patterns and spiral waves are observed, similar as in prior investigations by photoemission electron microscopy (PEEM). By applying EMSI and RAM simultaneously and imaging the same spot of the surface, supplementary information is gained on the properties of the reaction diffusion fronts. When observing a reaction front by EMSI and RAM at temperatures between 330 and 420 K the image of the front in RAM trails behind its image in EMSI. EMSI seems to display changes in the coverage of adsorbates while RAM relates to variations in surface structure.
Neutron diffraction experiments on powders are used to investigate the quantum mechanical behaviour of uniaxial rotators, i.e. NH3-molecules in Ni(NH3)6(PF6)2, Co(NH3)6(PF6)2 and Ni(NH3)6I2. A diffuse temperature dependent component of the total scattering, modulated ∼ sin QrH-H/QrH-H, is observed at a temperature of ≃ 20 K and below. This observation is due to the fact, that on cooling the sample to kT ∼ B (rotational constant) the rotational ground state is strongly populated. The ground state of a uniaxial free rotator, however, is completely polarized. As a consequence the scattering of those NH3 groups being in the ground state becomes coherent and is observable in diffraction experiments.
The single most common cause leading to the diagnosis of endometrial cancer is postmenopausal bleeding. Although most patients with early-stage disease (FIGO stage I and II) can be cured, prognosis worsens considerably with increasing stage. While serum CA 125 levels are elevated only in a significant proportion of patients with advanced disease, recently a new serum marker (OVX1) for the detection of early-stage endometrial cancer was reported. Serum OVX1 levels were measured using an OVX1 radioimmunoassay (RIA) or enzyme immunoassay (EIA) in 192 patients with endometrial cancer. CA 125 levels were measured in 112 patients using the CIS ELSA CA 125 kit. Apparently healthy females had mean serum OVX1 levels measured with the OVX1–EIA of 1.34 ± 0.74 U/ml, while patients with endometriosis had mean OVX1 serum levels of 3.15 ± 2.45 U/ml. The mean OVX1 serum level for endometrial cancer patients was 2.00 ± 1.32 U/ml. These values were 2.76 ± 1.62, 6.10 ± 4.66, and 5.37 ± 3.49, respectively, using the OVX1–RIA assay. Applying a cutoff value of 2.8 U/ml, serum OVX1–EIA levels in endometrial cancer patients were increased in 25 of 127 patients (19.7%) with stage I disease, 5 of 17 patients with stage II (29.4%), 5 of 22 patients (22.7%) with stage III, and 4 of 11 patients (36.4%) with stage IV disease. Using the OVX1–RIA and a cutoff of 7.2 U/ml, serum levels were increased in 22 of 127 (17.3%) stage I, 6 of 17 (35.3%) stage II, 5 of 22 (22.7%) stage III, and 6 of 11 (54.5%) stage IV patients. Serum CA 125 levels, determined in a total of 112 patients, were elevated above 35 U/ml in 12 of 79 patients (15.2%) with stage I, 4 of 12 patients (33.3%) with stage II, 8 of 13 patients (61.5%) with stage III, and all of 8 patients (100%) with stage IV disease. While a good correlation between serum CA 125 levels and the clinical stage of the disease was found, no correlation could be detected for OVX1 and stage.
Das deutsche Gesundheitsnetz
(1998)
Online only?
(1998)
Gespiegelt in besondern Düften …: Oasen, Seeungeheuer und weitere Spielereien der Fata Morgana
(1998)
„Wer die Natur liebt, der braucht das Beobachten ihrer Erscheinungen wie die Luft zum Atmen.” — So formulierte Marcel Minnaert das Bedürfnis der Naturbeobachtung im Vorwort seines berühmten Buchs „Licht und Farbe in der Natur” [1]. Bekannte Beispiele für Naturerscheinungen in der Atmosphäre sind Luftspiegelungen, Regenbögen und Halos. Diese optischen Phänomene bieten nicht nur faszinierende Anblicke, sondern beinhalten auch genügend Aspekte für eine interessante Physik (z. B. [2]). — Der vorliegende Artikel geht von grundlegenden physikalischen Betrachtungen aus und zeigt, daß sich alle Phänomene atmosphärischer Optik übersichtlich klassifizieren lassen. Luftspiegelungen werden exemplarisch im Detail behandelt. Viele nützliche Informationen findet man in Standardwerken [1, 3–5]; den aktuellen Stand der Forschung in Konferenzberichten, z. B. [6].
Old and new laboratory experiments on atmospheric optics with a focus on mirages, rainbows, and halos are presented. Some qualitative demonstrations serve primarily didactical purposes, e.g., by proving the existence of curved light rays in media with a gradient of the index of refraction, by directly visualizing the minimum-deviation curve for rainbow paths in water droplets, or by helping to elucidate the ray classes in hexagons that contribute to a specific halo. In addition, quantitative experiments allow a direct comparison of angular positions and intensities with analytical computations or Monte Carlo simulations of light scattering from small water droplets or ice hexagons. In particular, the latter can help us to understand complex halo phenomena.
© 1998 Optical Society of America
Die dynamische Optimierung spielt eine wichtige Rolle für die wirtschaftliche Prozeßführung von thermischen Trennverfahren in der fettchemischen Industrie. In dieser Arbeit wird eine effiziente Methode zur Ermittlung optimaler Führungsstrategien für zwei verschiedene Destillationsprozesse vorgestellt. Für die Lösung der Optimierungsprobleme werden detaillierte Modelle verwendet und die ermittelten Strategien direkt an einer Laboranlage und einer Produktionsanlage realisiert. Die experimentellen Ergebnisse der Optimierung demonstrieren die Anwendbarkeit dieser Methode. Die Führungszeit kann durch eine Realisierung der optimalen Strategien erheblich reduziert werden.
Zusammenfassung
Intrauterin wachstumsretardierte Neugeborene konnten ihr genetisches Wachstumspotential aufgrund einer intrauterinen Mangelversorgung nicht realisieren und werden deshalb zu klein oder zu leicht geboren. Das Merkmal „zu leicht” wird mit Hilfe von Gewichtsperzentilen quantifiziert. Kinder mit einem Gewicht< 10. Perzentile werden als „small for gestational age” (SGA) bezeichnet. Diese Einteilung berücksichtigt jedoch nicht die Proportionen eines Neugeborenen, so daß vor allem asymmetrisch retardierte Neugeborene, deren Gewicht zwar die 10. Perzentile noch überschreitet, die jedoch für ihre Körpergröße untergewichtig sind, nicht erfaßt werden. Der Ponderal Index (PI) dagegen berücksichtigt sowohl Gewicht als auch Länge des Neugeborenen. Kinder mit einem PI < 10. Perzentile werden als „low Ponderal Index” (LPI) klassifiziert. Aus pädiatrischen Studien ist bekannt, daß LPI-Kinder vermehrt durch Hypoglykämien, Hypothermien, Hypokalzämien und Mekoniumaspirationen/Aspirationspneumonien gefährdet sind. Langzeiterhebungen zeigten eine verzögerte körperliche Entwicklung und gehäuft motorische oder neurologische Verhaltensauffälligkeiten sowie schulische Probleme.
Fragestellung: Ziel der vorliegenden Arbeit war die Frage, ob Mangelgeborene, insbesondere LPI-Neugeborene, auch intrapartum einer erhöhten Gefährdung ausgesetzt sind.
Methoden: Hierzu wurden 3687 Neugeborene retrospektiv erfaßt, die anhand von Perzentilenkurven des betrachteten Kollektivs als SGA, LPI, SGA/LPI oder Vergleichskollektiv klassifiziert wurden.
Ergebnisse: Unterschiede im Geburtsmodus zwischen SGA- bzw. LPI-Mangelgeborenen und eutrophen Neugeborenen waren schwach ausgeprägt. Demgegenüber unterschied sich die Indikation, aufgrund deren ein geburtshilflicher Eingriff vorgenommen werden mußte deutlich. Bei 31 % aller operativ entbundenen LPI-Neugeborenen, 47 % der SGA-Neugeborenen und 52 % der SGA/LPI-Kinder erfolgte die operative Entbindung aus fetaler Indikation, im Vergleich zu 16 % des Normalkollektivs. Bezüglich des „fetal outcome”, das die Merkmale neonataler Säure-Basen-Status, Apgar-Wert, Verlegung in die Kinderklinik und perinatale Mortalität einbezog, verhielten sich die Gruppen SGA, LPI und SGA/LPI in gleicher Weise schlechter gegenüber dem Vergleichskollektiv. Die Unterschiede zwischen proportionierten (SGA) und dysproportionierten (LPI) Mangelgeborenen waren weniger deutlich.
Schlußfolgerungen: Es zeigte sich, daß das gegenwärtige engmaschige, geburtshilfliche Management mit nahezu permanenter CTG-Überwachung sub partu Probleme rechtzeitig erkennen und beherrschen ließ. Die Erfassung des niedrigen Ponderal Index war zur Erkennung und Vermeidung subpartaler geburtshilflicher Risikofaktoren nicht entscheidend.
Porträts von Naturwissenschaftlern und sachliche Darstellungen aus der Physik finden sich in zahlreichen Bereichen des täglichen Lebens, insbesondere auch auf vielen Banknoten. Die Auswahl -- vorgegeben durch die politisch inspirierte Motivwahl der Notenbanken -- stellt eine interessante Reise durch die Wissenschaftsgeschichte dar.