METHODOLOGIES FOR DESIGNING AND DEVELOPING HYPERMEDIA APPLICATIONS

Hypermedia design, as any other design activity, may be observed according to two points of view: methods which suggest milestones to guide the designer's work and process which concerns the actual detailed behavior of the designer at work. Cognitive studies assess that mental processes involved in any design process show widely shared human characteristics regardless to the used design method. Thereby, they provide general keys to help designers. Thus, a hypertext design environment should equally consider the two dimensions of a hypertext design activity, in particular it should support the natural design process specificities, mainly the incremental and opportunist aspects. The paper focuses on the hypertext design as a computer supported human activity. It examines what is general both in the design methods and in the design process of hypertexts in order to determine which general features are helpful to designers. This analysis has raised from the observation of the behavior of MacWeb users during design tasks. It is related to sound and well known results in cognitive science. The paper also describes how the proposed features are implemented in the MacWeb system.Information Systems Working Papers Serie

The critical Kerr non-linear optical cavity in the presence of internal loss and driving noise

We theoretically analyze the noise transformation of a high power continuouswave light field that is reflected off a critical Kerr non-linear cavity (KNLC). Our investigations are based on a rigorous treatment in the time-domain. Thereby, realistic conditions of a specific experimental environment including optical intra-cavity loss and strong classical driving noise can be modeled for any KNLC. We show that even in the presence of optical loss and driving noise considerable squeezing levels can be achieved. We find that the achievable squeezing levels are not limited by the driving noise but solely by the amount of optical loss. Amplitude quadrature squeezing of the reflected mean field is obtained if the KNLC's operating point is chosen properly. Consistently, a KNLC can provide a passive, purely optical reduction of laser power noise as experimentally demonstrated in [1]. We apply our model to this experiment and find good agreement with measured noise spectra

Observation of a kilogram-scale oscillator near its quantum ground state

We introduce a novel cooling technique capable of approaching the quantum ground state of a kilogram-scale system-an interferometric gravitational wave detector. The detectors of the Laser Interferometer Gravitational-wave Observatory (LIGO) operate within a factor of 10 of the standard quantum limit (SQL), providing a displacement sensitivity of 10(-18) m in a 100 Hz band centered on 150 Hz. With a new feedback strategy, we dynamically shift the resonant frequency of a 2.7 kg pendulum mode to lie within this optimal band, where its effective temperature falls as low as 1.4 mu K, and its occupation number reaches about 200 quanta. This work shows how the exquisite sensitivity necessary to detect gravitational waves can be made available to probe the validity of quantum mechanics on an enormous mass scale.United States National Science FoundationScience and Technology Facilities Council of the United KingdomMax-Planck-SocietyState of NiedersachsenAustralian Research CouncilCouncil of Scientific and Industrial Research of IndiaIstituto Nazionale di Fisica Nucleare of ItalySpanish Ministerio de Educacion y CienciaConselleria d’Economia Hisenda i Innovacio of the Govern de les Illes BalearsScottish Funding CouncilScottish Universities Physics AllianceNational Aeronautics and Space AdministrationCarnegie TrustLeverhulme TrustDavid and Lucile Packard FoundationResearch CorporationAlfred P. Sloan Foundatio

Ein vereinfachtes numerisches Verfahren für die mechanische Simulation in Virtual-Reality-Systemen

Derzeitige Systeme für virtuelle Realität (VR-Systeme) müssen noch in erheblichem Umfang funktional erweitert werden, wenn man mit ihrer Hilfe z.B. autonome mobile Roboter als Interaktionspartner in der VR-Welt modellieren will. Insbesondere muss zukünftig verlangt werden, dass mechanische Vorgänge in der VR-Simulation weitgehend korrekt nachbildbar sind. Mit diesem Ziel im Hintergrund wird hier ein vereinfachtes numerisches Verfahren vorgestellt, welches die dynamische und kinematische Simulation von gelenkgekoppelten Mehrkörpersystemen erlaubt. Das Verfahren ist konsequent auf der elementaren Mechanik der Massenpunktsysteme aufgebaut, umgeht die komplizierte mechanische Gleichungstheorie für Mehrkörpersysteme und führt zu extrem kurzen und durchsichtigen Simulationsprogrammen, wobei allerdings bei der Körpermodellierung zunächst nur diskrete Massenpunktverteilungen realisierbar sind, was für VR-Systeme völlig ausreichend erscheint

The status of GEO 600

The GEO 600 laser interferometer with 600m armlength is part of a worldwide network of gravitational wave detectors. GEO 600 is unique in having advanced multiple pendulum suspensions with a monolithic last stage and in employing a signal recycled optical design. This paper describes the recent commissioning of the interferometer and its operation in signal recycled mode

METHODOLOGIES FOR DESIGNING AND DEVELOPING HYPERMEDIA APPLICATIONS

Hypermedia design, as any other design activity, may be observed according to two points of view: methods which suggest milestones to guide the designer's work and process which concerns the actual detailed behavior of the designer at work. Cognitive studies assess that mental processes involved in any design process show widely shared human characteristics regardless to the used design method. Thereby, they provide general keys to help designers. Thus, a hypertext design environment should equally consider the two dimensions of a hypertext design activity, in particular it should support the natural design process specificities, mainly the incremental and opportunist aspects. The paper focuses on the hypertext design as a computer supported human activity. It examines what is general both in the design methods and in the design process of hypertexts in order to determine which general features are helpful to designers. This analysis has raised from the observation of the behavior of MacWeb users during design tasks. It is related to sound and well known results in cognitive science. The paper also describes how the proposed features are implemented in the MacWeb system.Information Systems Working Papers Serie

Astrophysically Triggered Searches for Gravitational Waves: Status and Prospects

In gravitational-wave detection, special emphasis is put onto searches that focus on cosmic events detected by other types of astrophysical observatories. The astrophysical triggers, e.g. from gamma-ray and X-ray satellites, optical telescopes and neutrino observatories, provide a trigger time for analyzing gravitational wave data coincident with the event. In certain cases the expected frequency range, source energetics, directional and progenitor information is also available. Beyond allowing the recognition of gravitational waveforms with amplitudes closer to the noise floor of the detector, these triggered searches should also lead to rich science results even before the onset of Advanced LIGO. In this paper we provide a broad review of LIGO's astrophysically triggered searches and the sources they target

Image-based Rendering: Neue Techniken der photorealistischen Bilderzeugung. Seminar, Wintersemester 1999/2000

In den letzten Jahren zeigte sich, da{\ss} einige Aufgaben im Bereich der Bilderzeugung mit rein geometriebasierten Verfahren nur schlecht oder gar nicht bew{\"a}ltigt werden k{\"o}nnen. Denkt man zum Beisp iel an ein Stofftier, so ist eine exakte geometrische Modellierung, auf deren Basis dann neue Bilder berechnet werden, sicher schwer anzugeben. \\ Schon in den 60er-Jahren wurde die Idee entwickelt, hinreichend viele Kameraaufnahmen einer Szene zu machen und bei Bedarf die zu einer bestimmten Blickrichtung geh{\"o}rende Aufnahme aus dem Vorrat zu nehmen (Movie Map). Erst heute reichen Speicher- und Rechenleistung der Computer aus, um Verfahren dieser Art zu verwirklichen. Es wird also versucht, mit Hilfe vorher von einer Szene aufgenommener Bilder neue Ansichten der Szene zu erzeugen. Dabei werden nicht nur auf schon vorhandene Aufnahmen zur{\"u}ckgegriffen und diese unver{\"a}ndert ver wendet, sondern man m{\"o}chte mit m{\"o}glichst wenig Aufnahmen auskommen und fehlende Bilder aus schon vorhandenen berechnen. Zu diesem Zweck wird keine Geometrie aus den zuvor aufgenommenen Bildern ermittelt. Es wird nur auf den Bilddaten gearbeitet, also neue Bilder aus vorhandenen berechnet: Image-based Rendering (IBR)

Numerical comparison of X-ray differential phase contrast and attenuation contrast

We present a numerical tool to compare directly the contrast-to-noise-ratio (CNR) of the attenuation- and differential phase-contrast signals available from grating-based X-ray imaging for single radiographs. The attenuation projection is differentiated to bring it into a modality comparable to the differential phase projection using a Gaussian derivative filter. A Relative Contrast Gain (RCG) is then defined as the ratio of the CNR of image values in a region of interest (ROI) in the differential phase projection to the CNR of image values in the same ROI in the differential attenuation projection. We apply the method on experimental data of human breast tissue acquired using a grating interferometer to compare the two contrast modes for two regions of interest differing in the type of tissue. Our results indicate that the proposed method can be used as a local estimate of the spatial distribution of the ratio δ/β, i.e., real and imaginary part of the complex refractive index, across a sample

Directional limits on persistent gravitational waves using LIGO S5 science data

The gravitational-wave (GW) sky may include nearby pointlike sources as well as astrophysical and cosmological stochastic backgrounds. Since the relative strength and angular distribution of the many possible sources of GWs are not well constrained, searches for GW signals must be performed in a model-independent way. To that end we perform two directional searches for persistent GWs using data from the LIGO S5 science run: one optimized for pointlike sources and one for arbitrary extended sources. The latter result is the first of its kind. Finding no evidence to support the detection of GWs, we present 90% confidence level (CL) upper-limit maps of GW strain power with typical values between 2-20x10^-50 strain^2 Hz^-1 and 5-35x10^-49 strain^2 Hz^-1 sr^-1 for pointlike and extended sources respectively. The limits on pointlike sources constitute a factor of 30 improvement over the previous best limits. We also set 90% CL limits on the narrow-band root-mean-square GW strain from interesting targets including Sco X-1, SN1987A and the Galactic Center as low as ~7x10^-25 in the most sensitive frequency range near 160 Hz. These limits are the most constraining to date and constitute a factor of 5 improvement over the previous best limits.Comment: 10 pages, 4 figure