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  • 1
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    The soft X‐ray and XUV split‐and‐delay unit at beamlines FL23/24 at FLASH2 (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2024-01-12
    Description: A split‐and‐delay unit for the extreme ultraviolet and soft X‐ray spectral regions has been built which enables time‐resolved experiments at beamlines FL23 and FL24 at the Free‐electron LASer in Hamburg (FLASH). Geometric wavefront splitting at a sharp edge of a beam splitting mirror is applied to split the incoming soft X‐ray pulse into two beams. Ni and Pt coatings at grazing incidence angles have been chosen in order to cover the whole spectral range of FLASH2 and beyond, up to hν = 1800 eV. In the variable beam path with a grazing incidence angle of ϑd = 1.8°, the total transmission (T) ranges are of the order of 0.48 〈 T 〈 0.84 for hν 〈 100 eV and T 〉 0.50 for 100 eV 〈 hν 〈 650 eV with the Ni coating, and T 〉 0.06 for hν 〈 1800 eV for the Pt coating. For a fixed beam path with a grazing incidence angle of ϑf = 1.3°, a transmission of T 〉 0.61 with the Ni coating and T 〉 0.23 with a Pt coating is achieved. Soft X‐ray pump/soft X‐ray probe experiments are possible within a delay range of −5 ps 〈 Δt 〈 +18 ps with a nominal time resolution of tr = 66 as and a measured timing jitter of tj = 121 ± 2 as. First experiments with the split‐and‐delay unit determined the averaged coherence time of FLASH2 to be τc = 1.75 fs at λ = 8 nm, measured at a purposely reduced coherence of the free‐electron laser.
    Description: The properties of the recently installed split‐and‐delay unit at beamlines FL23 and FL24 at FLASH2 are presented. Its operational range, performance parameters and results of a first experiment are described. image
    Keywords: ddc:550.724 ; time‐resolved pump–probe ; XUV ; soft X‐rays ; free‐electron laser
    Language: English
    Type: doc-type:article
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  • 2
    Electronic Resource
    Electronic Resource
    How a collision causes misalignment: alignment decay in acetylene 21 (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 13611-13619 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100037a007
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  • 3
    Electronic Resource
    Electronic Resource
    Collisional effects on angular momentum orientation in acetylene X˜ 1Σg+ (ν2″=1,j″). II. Disorientation by rotationally elastic and multiple inelastic collisions (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 9749-9758 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This is the second of two papers about collisionally induced changes in molecular orientation. In the first paper [A. D. Rudert, J. Martin, W. B. Gao, J. B. Halpern, and H. Zacharias, J. Chem. Phys. 111, 9549 (1999)] the orientation was measured in the prepared state and in other states populated by collisional transfer from the initially excited one. It was shown that a significant amount of the initial orientation is retained in collisions, even for large changes in the rotational quantum number. In this paper the decay of the orientation due to elastic and multiple inelastic collisions is investigated. The measurements clearly show that for acetylene self-collisions the orientation decay [〈koritotal〉=7.6±1.0 (μs Torr)−1] is much slower than the depopulation of the prepared rotational state [〈ktot〉=25±1.8 (μs Torr)−1]. By using a set of master equations, rate constants are derived which describe the effects of both rotationally elastic and multiple inelastic collisions. From this model rate constants for orientation decay due to rotationally elastic collisions, korielastic, can be derived. These rate constants decrease from korielastic=10.7 (μs Torr)−1 for j″=1 to korielastic=3.8 (μs Torr)−1 for j″=15. The rate constants for orientation decay are found to be equal to previously measured rate constants for the alignment decay. A model describing the collisionally induced change of the direction of the molecular angular momentum vector is presented which reconciles both alignment and orientation decay measurements. It is shown that mj-changing, rotationally elastic collisions completely destroy any orientation or alignment and probably occur perpendicular to the plane of molecular rotation. This is in contrast to rotationally inelastic collisions which occur primarily in the plane of rotation. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481612
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  • 4
    Electronic Resource
    Electronic Resource
    Collisional effects on angular momentum orientation in acetylene X˜ 1Σg+ (ν2″=1,j″). I. Preparation, detection and conservation in single collisions (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 9549-9559 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effect of rotationally inelastic collisions on the orientation of the angular momentum is investigated for C2H2 (ν2=1, j). The orientation of the angular momentum in initial rotational states ji=7 to 13 is prepared by stimulated Raman pumping using circularly polarized light and S-branch transitions. After allowing an appropriate time for collisions to occur the orientation is probed by laser-induced fluorescence in the A˜ 1Au←X˜ 1Σg transition. For acetylene the theoretically calculated and the measured initial orientation, A0(1), ranges between 0.7 and 0.9. A substantial part of the orientation is conserved in rotationally inelastic collisions, which could be measured up to |Δj|=6 with sufficient signal-to-noise ratio. These results are compared with previous measurements on the conservation of alignment in collisions. Rotationally inelastic collisions with |Δj|=2 result in an average rotation of the orientation vector by about 30°. The amount of orientation that remains after a rotationally inelastic collision is found to depend primarily on |Δj|. A Δmj=0 propensity rule often used in models of rotational energy transfer is found to be inconsistent with the measurements. Also a model which proposes a minimum change of the classical angle φ between j(vector) and the quantization axis does not reproduce well the experimental data. Finally, a microscopic model for Δmj-transitions is presented which reconciles both alignment and orientation measurements. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480286
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  • 5
    Electronic Resource
    Electronic Resource
    Tracking early arrivals on the Nature trail (2007)
    [s.l.] : Nature Publishing Group
    Nature 450 (2007), S. 1156-1156 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Sir Following the 'History of Nature' timeline on your website to 1875, I arrived at the section on 'Continental copycats', which lists European publications with the same name that appeared after the birth of Nature in 1869 ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/4501156d
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  • 6
    Electronic Resource
    Electronic Resource
    Sex-linked difference in DNA content of a polytene chromosome in Prodiamesa (Chironomidae) (1981)
    Springer
    Chromosoma 82 (1981), S. 657-672 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The chironomid Prodiamesa olivacea possesses 3 pairs of chromosomes. The underreplication of the right arm in the polytene 3rd was presented earlier and is here shown to affect in females the cell nuclei of salivary glands, Malpighian tubules and the hindgut. The same somatic nuclei in males exhibit also a polytene 3rd with specific characteristics inasmuch as it contains half the relative DNA value of the female nuclei (3% instead of 6% complemental portion). — In male meiocytes the two partners in each of the 3 diakinetic bivalents were recognized to be homomorphic. In view of this morphological criterium the polytene situation in males must be due either to an unknown elimination process or to the underreplication of both right arms and further one left arm of the 3rd chromosomes. The latter model interprets the elements of the 3rd pair as differently polytenizing heterosomes in P. olivacea.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00285774
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  • 7
    Electronic Resource
    Electronic Resource
    Functional significance of changes in the shape of the polytene X chromosome in Phryne (1977)
    Springer
    Chromosoma 63 (1977), S. 359-384 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract In contrast to the autosomes, the salivary gland X chromosome of Phryne has distinctly different shapes in different cells (Wolf, 1957). These changes in shape are not correlated with alterations of the nucleic acid synthetic activities. The X in males and females always replicates in step with the autosomes, and the XB and the autosomes always have the same relative DNA contents (the Y is under-replicated). The transcriptive activity of the X is always about the same as that of the autosomes in the same cell. Breeding conditions which cause larvae to attain higher final polyteny levels enhance the stretching of the X, but the polyteny is not directly correlated with the degree of stretching; Xs with the same polyteny vary considerably in shape. — The DNA content of 2C female nuclei is 0.34×10−12 g.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00399496
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  • 8
    Electronic Resource
    Electronic Resource
    Underreplication of a polytene chromosome arm in the chironomid Prodiamesa olivacea (1979)
    Springer
    Chromosoma 72 (1979), S. 23-51 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The genome of Prodiamesa olivacea (Diptera, Chironomidae) has a 2 C DNA content of 0.25 pg. Mitotic metaphases reveal 3 pairs of chromosomes: 2 metacentric ones and one submetacentric. The latter comprises 20.8% of total Feulgen DNA. During larval polytenization the complemental portion of the 3rd falls to 6.5%. Concomitantly the polytene 3rd chromosome is much shorter than expected. It has no constriction and is shaped like a ball sector. — Underreplication is understood as suppression of DNA syntheses mainly in the long arm of the 3rd chromosome at the first to third endoreplicative cycle. Most of the dense heterochromatin seen in the apex of the 3rd polytene element is not itself underreplicated; it conceals the underreplicated long arm of this chromosome. — In ovarian nurse cells which are closely connected with the germ line the longer heterochromatic arm of the 3rd polyneme chromosome is fully replicated. — Underreplication is discussed in the context of “DNA silencing”.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00286428
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  • 9
    Electronic Resource
    Electronic Resource
    Allocyclic behaviour and underreplication of the nucleolus chromosome in Pseudodiamesa (Chironomidae) (1984)
    Springer
    Chromosoma 89 (1984), S. 263-273 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The chironomid midge Pseudodiamesa branickii shows three polytene, banded elements in salivary gland and Malpighian tubule cells, none of which carry a nucleolar organizer. The present investigation revealed four chromosome pairs in mitotic metaphases, the nucleolus was localized in the tiny chromosome 4. Microphotometric determinations of the DNA contents in mitotic and salivary gland nuclei of Ps. branickii yielded a 2C value of 0.23 pg DNA and a maximum level of 12 endoreplications. In both salivary glands and Malpighian tubules, chromosome 4 appeared as a nonbanded network of chromatin in Feulgen preparations. Indirect immunofluorescent staining with antibodies specific for RNA·DNA hybrids indicated that this structure was transcriptionally active. Its reaction to heavy metal staining suggested that it included the nucleolar organizer, and this was conclusively demonstrated by in situ hybridization with 125I-rRNA. Chromosome pair 4 comprises about 11.4% of the total DNA in metaphase, but only 3.7% in the highly polytene salivary gland complement. According to a numerical simulation, the degree of underrepresentation suggests that about 70% of chromosome 4 is precluded from polytenization. The allocyclic aspect is probably due to this underreplication, with the nucleolar activity causing a structural loosening of the rest of the chromosome. The possible nature of the underreplicated sequences is discussed in the light of recent work on molecular aspects of rDNA structure in various Diptera.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00292473
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  • 10
    Electronic Resource
    Electronic Resource
    Heteropycnosis of an underreplicating chromosome (1990)
    Springer
    Chromosoma 99 (1990), S. 24-35 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Drosophila nasutoides has an extraordinary genome since 62% of its DNA resides in chromosome4. This element mainly consists of constitutive heterochromatin which does not polytenize. Earlier studies of heterochromatin attributed little attention to the fact that “condensed” chromosomes often vary in condensation. This paper reports that chromosomes of the same complement display different degrees and kinetics of condensation. InD. nasutoides, even sex specific differences can be observed. The results of a comparative microphotometric study on neuroblast metaphases in both sexes revealed the following picture. The process of chromosome condensation is not restricted to mitotic prophase but continues into the metaphase. The mean condensation is not equal for all chromosomes. In the metaphase of the female, Feulgen density increases from theX chromosome, via3 and2, to chromosome4. In the male, the order isX, 2, 3, Y, and4. During the metaphase of the male, chromosomes condense with similar kinetics. In contrast, chromosomes of the female display asynchrony as monitored by area and length determinations. TheX chromosomes of the female probably have enhanced shortening during prophase. This would explain the metaphase of the female where theX chromosomes shorten less than the autosomes, and why each of theX chromosomes is 15% shorter than theX chromosome in the metaphase of the male. Further differences were observed in the longitudinal and lateral compaction of the chromosomes in males and females. The sex chromosomes and chromosome3 condense by shortening, while chromosomes2 and4 preferentially reduce their diameter. The large amount of DNA engaged in heteropycnosis and the isochromosome nature allow the identification of chromosome4 during interphase. At this stage, a new category of extreme DNA packaging was detected. The interphase density of chromosome4 can exceed that of metaphase by a factor of up to 8. Two events account for this high degree of condensation:(1) the homologues are particularly associated due to somatic pairing and (2) the arms are further tightened as a result of pericentric folding. The features of the isochromosome suggest that the interaction of chromatids during interphase is essentially caused by specific DNA sequences. The data confirm that heteropycnosis not only interferes with gene expression but also strongly inhibits DNA synthesis in endocycles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01737286
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