329,306 research outputs found
Nanoskopie mit fokussiertem Licht (Nobel-Aufsatz).
No full textEin Bild sagt mehr als tausend Worte – dies gilt sicher nicht nur für das tägliche Leben, sondern auch für die Naturwissenschaften. Es ist daher wohl kein Zufall, dass der Beginn der modernen Naturwissenschaften historisch erkennbar mit der Erfindung des Lichtmikroskops zusammenfällt. Wie man durch einen transienten molekularen Zustandsübergang die beugungsbedingte Auflösungsgrenze radikal überwinden kann, zeigt uns S. W. Hell in seinem Nobel-Aufsatz
Measurement of the 4Pi-confocal point spread function proves 75 nm axial resolution
No full textIn a 4Pi-confocal microscope the specimen is illuminated and observed coherently from above and below such that the numerical aperture is increased [S. W Hell, European Patent Application 91121368.4 (filed 1990, published 1992), S. W Hell and E. H. K. Stelzer, J. Opt. Soc. Am. A 9, 2159 (1992)]. The point spread functions of 4Pi-confocal and confocal microscopes were measured. Our measurements prove a three- to seven-fold increase of axial resolution, thus opening the prospect for a powerful three-dimensional imaging technique with an axial resolution down to 75 nm
Equivalence of the Huygens-Fresnel and Debye approach for the calculation of high aperture point-spread-functions in the presence of refractive index mismatch.
No full textAs discussed in recent work (Sheppard, C. J. R. & Torok, P., I. Microsc.. 185, 366-384; Torok et al., J. Microsc., 188, 158-172), two approaches have been used extensively for vectorial computations of high aperture confocal point-spread functions when focusing through a dielectric interface. Whereas the equation by Hell, Reiner, Cremer & Stelzer (I. Microsc., 169, 391-405) is based on the Huygens-Fresnel principle, the more recent approach by Torok. Varga Br Booker (J. Opt. Sec. Aln. A, 12, 325-332; J. Opt. SOC. Am. A, 12, 2136-2144) is based on the Debye approximation. While the earlier theory considers a large but finite focal length the second theory is derived for an infinitely high Fresnel number, In a high aperture microscope, a high Fresnel number is equivalent to assuming that the focal length be infinitely large with respect to the wavelength. So far, the two theories are regarded as different, with the one by Torok et al, being rigorous, In this paper, we demonstrate that, if the same conditions are applied, the equation by Torok et ttl, can be analytically derived from that by Hell et nl. Producing the same results, the benefit brought about by the equation by Torok el nl. is improved flexibility and computational speed for cases with azimuthal symmetry
Nanoscopy with Focused Light
No full textFor many decades, it has been accepted that the resolution of a lens-based optical microscope is limited to about d =λ (2 NA) < 200 nm. The discovery in the 1990’s that elementary transitions between the states of a fluorophore can be used to eliminate the limiting role of diffraction has led to lens-based light microscopy concepts with resolution down to the nanometer scale1,2. Currently, all far-field fluorescence nanoscopy (superresolution) concepts that have found wider application share a common enabling element: they modulate the fluorescence capability of adjacent features such that they fluoresce sequentially3,4
Far-field fluorescence microscopy with repetitive excitation.
No full textWe introduce the concept of repeatedly exciting an excited state of a photostable
fluorescent entity to generate a nonlinear fluorescence signal which is
solely based on the linear susceptibility of the molecule. The excitation
cycle between the fluorescent state and another state prolongs the average
lifetime of , with emphasis on those molecules that are in the center of
the focus. The photons emitted by the long-lived molecules in the center
are recorded by a temporal filter and constitute fluorescence that depends
nonlinearly on the excitation intensity. Theoretical analysis reveals that
this concept can provide three-dimensional imaging and improve the spatial
resolution in far-field fluorescence microscopy. We show that despite the
presence of diffraction the effective focal waist can in principle be narrowed
down to the molecular scale at the expense of signal
Infernal imagery in Anglo-Saxon charters
No full textThis doctoral dissertation analyses depictions of hell in sanctions, i.e. threats of punishments in Anglo-Saxon charters. I am arguing that an innovative use of sanctions as pastoral and ideological instruments effected the peak of infernal imagery in the sanctions of tenth-century royal diplomas. Belonging to the genre of ritual curses, Anglo-Saxon sanctions contain the three standard ecclesiastical curses (excommunication, anathema and damnation). It cannot be established if other requirements of ritual cursing (authoritative personnel, setting and gestures) were fulfilled. A lack of evidence, together with indications of more secular punishments, suggests that sanctions were not used as legal instruments. Their pastoral function is proposed by frightening depictions of hell and the devil, as fear is an important means of achieving salvation in biblical, homiletic and theological writings available or produced in Anglo-Saxon England. The use of the infernal motifs of Hell as a Kitchen, Satan as the Mouth of Hell and winged demons in sanctions are discussed in detail. Sanctions frequently contain the overtly didactic and pastoral device of the exemplum. Notorious sinners believed to be damned in hell (e.g. Judas) are presented as negative exempla in sanctions to deter people from transgressing against charters. The repeated use of terms from classical mythology for depicting hell in Anglo-Saxon sanctions appears to correlate with the preference for hermeneutic Latin by tenth-century monastic reformers. The reasons for employing classical mythological terminology seem to agree with those suggested for the use of hermeneutic Latin (intellectual snobbery and raising the stylistic register), and glossaries constitute the main source of both types of Latinity. The sanctions of the Refoundation Charter of New Minster, Winchester, which is known to display the ‘ruler theology’ propagated by the monastic reform, are examined in their textual contexts with regard to the observations made in the earlier parts of this dissertation
1970's Southern rock and W.J. Cash's Hell uva fella
Full text link"1970's American Southern Rock was a musical phenomenon as unique, diverse, and dynamic as the politically and racially tumultuous region from which it hailed. This region has been portrayed in popular culture via a male stereotype that almost seventy years ago Southern ethnographer W.J. Cash dubbed the "hell of a fellow [hell uva fella]. Even in the post-bellum South of the late Civil Rights Era, the values of the ruggedly individualistic frontiersman survived and developed into a unique concept of regional masculinity. The Southern man portrayed in 1970's Southern Rock is a unique, regionalized aggregate of the American South's cultural heritage, its dynamic values in the 1970s, and the incorporation of characteristics found in Cash's decades older hell uva fella tradition, all of which embody an individualism that is both personally and politically self-destructive."--Abstract from author supplied metadata
Far-field optical nanoscopy
Full text linkIn 1873, Ernst Abbe discovered what was to become a well-known paradigm: the inability of a lens-based optical microscope to discern details that are closer together than half of the wavelength of light. However, for its most popular imaging mode, fluorescence microscopy, the diffraction barrier is crumbling. Here, I discuss the physical concepts that have pushed fluorescence microscopy to the nanoscale, once the prerogative of electron and scanning probe microscopes. Initial applications indicate that emergent far-field optical nanoscopy will have a strong impact in the life sciences and in other areas benefiting from nanoscale visualization
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