172,230 research outputs found
Morphologien von Partikeln in der Polaren Stratosphäre
No full textDie Morphologien von Aerosolpartikeln haben einen wichtigen Einfluss auf deren Extinktionsspektrum. Die Kenntnis dieser Spektren ist essentiell für die Identifizierung und Strukturaufklärung der Partikel. Dies gilt in besonderem Maße für Polar Stratosphärische Wolkenpartikel, die mit satellitengestützten optischen Methoden untersucht werden. In den hier vorgestellten Laborexperimenten wurden Proben präpariert, deren Phasenzusammensetzung aus Vergleichsexperimenten bereits bekannt war [1-4]. Diese Kryoproben wurden mittels einer Kryo-Transferkammer in ein environmental scanning electron microscope (ESEM) eingebracht und wurden in Temperaturabhängigkeit beobachtet. Der Vorteil dieser Technik besteht darin, dass bei Drücken bis 5 mbar gearbeitet werden kann und so eine Dehydratation der Probe vermieden wird. Für die Hydratphasen Salpetersäuretrihydrat, Salpetersäuredihydrat und deren Mischungen wurden die Morphologien bestimmt [5] und unter Zuhilfenahme der entsprechenden optischen Konstanten wurden die passenden Extinktionsspektren berechnet [6].
[1] Tizek, H.; Knözinger, E.; Grothe, H. "X-ray diffraction studies on nitric acid dihydrate" Phys. Chem. Chem. Phys., 2002 , 4, 5128-5134.
[2] Grothe, H.; Lund Myhre, C.E.; Tizek, H. "Vibrational Spectra of Nitric Acid Dihydrate (NAD)" Vibr. Spectr. 2004, 34, 55-62.
[3] Tizek, H.; Knözinger, E.; Grothe, H. "Formation and Phase Distribution of Nitric Acid Hydrates in the Mole Fraction Range xHNO3 < 0.25: a combined XRD and IR study" Phys. Chem. Chem. Phys. 2004, 6, 972-979.
[4] H. Grothe, C.E. Lund Myhre and C. J. Nielsen "Low-frequency Raman Spectra of Nitric Acid Hydrates" J. Phys. Chem. A 2006, 110, 1, 171-176.
[5] H. Grothe, H. Tizek, D. Waller and D. J. Stokes, The crystallization kinetics and morphology of nitric acid trihydrate, Phys. Chem. Chem. Phys. 2006, 8, 2232-2239.
[6] H. Grothe, H. Tizek and I. K. Ortega "Metastable Nitric Acid Hydrates - Possible Constituents of Polar Stratospheric Clouds?" Faraday Discussion 2007, 137, in print
Basic fibroblast growth factor (bFGF) in rodent testis
No full textWe have previously described a 30 kDa basic fibroblast growth factor (bFGF)-like protein in rodent testicular homogenates and have shown that pachytene spermatocytes are the sites of predominant immunoreactivity for this bFGF-like protein (Mayerhofer, A., Russell, L.D., Grothe, C., Rudolf, M. and Gratzl, M. (1991) Endocrinology 129, 921–924). We have now addressed the question whether this 30 kDa bFGF-like protein is a large bFGF form and whether it is produced by pachytene spermatocytes. We detected bFGF mRNA in homogenates of isolated mouse spermatocytes (which consisted mainly of pachytene spermatocytes) using S1 nuclease protection assays. As shown by Western blot analyses, the bFGF mRNA in mouse spermatocytes is translated into bFGF of an approximate molecular weight of 30 kDa. Neither bFGF mRNA, nor bFGF itself, was observed in isolated mouse Leydig cells. These results indicate that the immunoreactive bFGF-like protein observed previously in germ cells of the murine testis is identical to bFGF. Thus, germ cells of the testis produce bFGF, which may exert regulatory function in the process of spermatogenesis
Kinderwünsche in Deutschland: Konsequenzen für eine nachhaltige Familienpolitik
No full textHöhn C, Ette A, Ruckdeschel K, Grothe F. Kinderwünsche in Deutschland: Konsequenzen für eine nachhaltige Familienpolitik. Stuttgart: Robert-Bosch-Stiftung; 2006
Biological Ice Nucleation in the Atmosphere and the Biosphere
No full textFrom the thermodynamic point of view, ice and snow can form already at temperatures slightly below its melting point, i.e. below zero degrees Celsius. Actually, ultrapure, liquid water can be supercooled down to minus forty degrees Celsius without freezing. The reason is a kinetic activation barrier, which hinders the phase transition. However, water impurities, e.g. biological material or organic particles, can lower this activation barrier and can thus catalyze the phase transition. This process is called heterogeneous ice nucleation and it plays an important role in many biological, meteorological and technical processes, e.g. in the formation of atmospheric ice clouds [1].
The most effective ice nucleus is ice itself, since it provides the own hexagonal structure, on which water molecules from the liquid phase can be oriented to form further ice phase. The most effective heterogeneous ice nucleus is the bacterium pseudomonas syringae. The reason is a protein at its outer cell membrane, which exhibits a hexagonal, ice-like structure. Furthermore, many other bacteria, fungal spores, and pollens carry also very effective ice nuclei, many of which in fact are macromolecules.
Macromolecular ice nuclei have for a long time been neglected by atmospheric scientists. However, plants are known by biologists to produce macromolecular ice nuclei as a part of their low-temperature survival strategy. In the past, it has been shown by us that birch pollen exhibit ice nucleation active macromolecules at their surface [2, 3]. These molecules can be washed off from the pollen grains and nucleate ice independently. Only very recently, we found the same ice nuclei also on secondary and primary wood and on leafs of birch trees. The question remains if these biological ice nuclei can be dispersed through the atmosphere and can impact cloud glaciation processes.
[1] T. Bartels-Rausch, V. Bergeron, J. Cartwright, R. Escribano, J. Finney, H. Grothe, P. Gutierrez, J. Haapala, W. Kuhs, J. Pettersson, S. Price, C. Sainz-Dıaz, D Stokes, G. Strazzulla, E. Thomson, H. Trinks, and N. Uras-Aytemiz, Rev. Mod. Phys. 84 (2012)885.
[2] B.G. Pummer, H. Bauer, J. Bernardi, S. Bleicher, and H. Grothe, Atm. Chem. Phys., 12 (2012) 2541.
[3] B.G. Pummer, C. Budke, S. Augustin-Bauditz, D. Niedermeier, L. Felgitsch, C. Kampf, R. Huber, K. Liedl, T. Loerting, T. Moschen, M. Schauperl, M. Tollinger, C. Morris, H. Wex, H. Grothe, U. Pöschl, T. Koop, and J. Fröhlich-Nowoisky, Atm. Chem. Phys. 15 (2015) 4077
Biological Ice Nucleation in the Atmosphere and the Biosphere
No full textFrom the thermodynamic point of view, ice and snow can form already at temperatures slightly below its melting point, i.e. below zero degrees Celsius. Actually, ultrapure, liquid water can be supercooled down to minus forty degrees Celsius without freezing. The reason is a kinetic activation barrier, which hinders the phase transition. However, water impurities, e.g. biological material or organic particles, can lower the activation barrier and can thus catalyze the phase transition. This process is called heterogeneous ice nucleation and it plays an important role in many biological, meteorological and technical processes, e.g. in the formation of atmospheric ice clouds. The most effective ice nucleus is ice itself, since it provides the own hexagonal structure, on which water molecules from the liquid phase can be oriented in order to form further ice phase. The most effective heterogeneous ice nucleus is the bacterium Pseudomonas Syringae. The reason is a protein at its outer cell membrane, which exhibits a hexagonal, icelike structure. Furthermore, fungal spores, pollen, and carbonaceous particles are also very effective ice nuclei [1, 2]. In many cases, the physical and chemical reasons for the ice nucleation activity are understood only rudimentary. Thus, the search for the perfect ice nucleus is still an open issue [3].The talk will explain the fundamentals of heterogeneous ice nucleation and will give examples from the field and the laboratory.
[1] B.G. Pummer, H. Bauer, J. Bernardi, S. Bleicher, and H. Grothe, Atm. Chem. Phys., 12 2541 (2012).
[2] B.G. Pummer, C. Budke, S. Augustin-Bauditz, D. Niedermeier, L. Felgitsch, C. Kampf, R. Huber, K. Liedl, T. Loerting, T. Moschen, M. Schauperl, M. Tollinger, C. Morris, H. Wex, H. Grothe, U. Pöschl, T. Koop, and J. Fröhlich-Nowoisky, Atm. Chem. Phys. 15 4077 (2015).
[3] T. Bartels-Rausch, V. Bergeron, J. Cartwright, R. Escribano, J. Finney, H. Grothe, P. Gutierrez, J. Haapala, W. Kuhs, J. Pettersson, S. Price, C. Sainz-Diaz, D Stokes, G. Strazzulla, E. Thomson, H. Trinks, and N. Uras-Aytemiz, Rev. Mod. Phys. 84 885 (2012)
UTA-Jugendbücher Band 1
No full textHere is a large, deteriorating book of German fables done not too long after World War II. As the beginning T of C shows, the fables are organized by subjects. Thus the Tierfabeln, after 54 pages of Reineke Fuchs, move to some eleven fables on lions, add then fifteen on the fox, and move on thus through five more animal groups. There are then three other major categories: plants; nature and humans; and wise people and fools. The illustrations occur especially to mark the beginnings of sections. This book looks a bit as though it had gone through a war itself! Its cardboard covers have done well to hold out as long as they have. I take it that the book gives us a sense of East German productivity soon after the war. Inscribed at Christmas, 1949.Language note: GermanAuswahl und Bearbeitung von Willy Schüssle
Nukleation, Wachstum und Phasenübergänge von NAD und NAT - Untersuchungen an einem Labormodel
No full textSalpeters¨aurehydrate sind wichtige Bestandteile von festen Partikeln
in Polaren Stratosph¨arischen Wolken (PSC) und in Zirruswolken.
Entsprechend dem Phasendiagramm kommen nur
hexagonales Eis und Salpeters¨auretrihydrat (&#946;-NAT) als thermodynamisch
stabile Festk¨orperphasen in Frage. Beide Strukturen
werden in der Stratosph¨are regelm¨aßig beobachtet. Daneben
k¨onnten aber auch eine Reihe metastabiler Modifikationen
existieren: &#945;-NAD (Dihydrat), &#946;-NAD, &#945;-NAT, NAP (Pentahydrat)
und kubisches Eis. Die Existenzm¨oglichkeit dieser metastabilen
Verbindungen in der Stratosph¨are ist bisher nicht gesichert
und wird diskutiert.
Im Labor haben wir ein spezielles Modellverfahren entwickelt,
um die metastabilen Strukturen m¨oglichst rein darzustellen und
untersuchen zu k¨onnen. Als Untersuchungsmethoden wurden
die R¨ontgenpulverdiffraktion [1, 2], die FTIR-Spektroskopie [3]
und die Ramanspektroskopie [4] eingesetzt. Ziel war es, mit
der Diffraktion die Phasenzusammensetzung der Proben abzusichern
und dann an entsprechenden Proben spektroskopische
Daten zu sammeln, die f¨ur Feldmessungen und Kammerexperimente
ben¨otigt werden.
Besonderes Interesse galt dem NAD, das spezielle Nukleationseigenschaften
zeigt. F¨ur NAD und NAT wurde die Kristallisationskinetik
der Phasen¨uberg¨ange bestimmt. Dabei konnte
gezeigt werden, dass in verd¨unnten Proben hexagonales Eis
den Phasen¨ubergang von &#945;- in &#946;-NAT hemmt. Somit kann &#945;-
NAT auch bei stratosph¨arischen Temperaturen (T > 180 K)
noch mehrere Stunden existieren. Erg¨anzend wurde in ESEMMessungen
(environmental scanning electron microsocopy) der
Einfluss von Eis auf die Morphologie der Kristallite beobachtet.
Deren Kenntnis ist entscheidend, um das Streuverhalten der
Kristalle und Partikel richtig zu verstehen.
[1] H. Tizek, E. Kn¨ozinger, H. Grothe, PCCP 4 (2002), 5128.
[2] H. Tizek, E. Kn¨ozinger, H. Grothe, PCCP 6 (2004), 972.
[3] H. Grothe, C. E. Lund Myhre, H. Tizek, Vibr. Spectr. 34
(2004), 55.
[4] H. Grothe, C. E. Lund Myhre, C. J. Nielsen, J. Phys. Chem.
A 110 (2006), 2, in print
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Interaction of excitation and inhibition in processing of pure tone and amplitude-modulated stimuli in the medial superior olive of the mustached bat
No full text 1. In mammals with good low-frequency hearing, the medial superior olive (MSO) processes interaural time or phase differences that are important cues for sound localization. Its cells receive excitatory projections from both cochlear nuclei and are thought to function as coincidence detectors. The response patterns of MSO neurons in most mammals are predominantly sustained. In contrast, the MSO in the mustached bat is a monaural nucleus containing neurons with phasic discharge patterns. These neurons receive projections from the contralateral anteroventral cochlear nucleus (AVCN) and the ipsilateral medial nucleus of the trapezoid body (MNTB). 2. To further investigate the role of the MSO in the bat, the responses of 252 single units in the MSO to pure tones and sinusoidal amplitude-modulated (SAM) stimuli were recorded. The results confirmed that the MSO in the mustached bat is tonotopically organized, with low frequencies in the dorsal part and high frequencies in the ventral part. The 61-kHz region is overrepresented. Most neurons tested (88%) were monaural and discharged only in response to contralateral stimuli. Their response could not be influenced by stimulation of the ipsilateral ear. 3. Only 11% of all MSO neurons were spontaneously active. In these neurons the spontaneous discharge rate was suppressed during the stimulus presentation. 4. The majority of cells (85%) responded with a phasic discharge pattern. About one-half (51%) responded with a level-independent phasic ON response. Other phasic response patterns included phasic OFF or phasic ON-OFF, depending on the stimulus frequency. Neurons with ON-OFF discharge patterns were most common in the 61-kHz region and absent in the high-frequency region. 5. Double tone experiments showed that at short intertone intervals the ON response to the second stimulus or the OFF response to the first stimulus was inhibited. 6. In neuropharmacological experiments, glycine applied to MSO neurons (n = 71) inhibited any tone-evoked response. In the presence of the glycine antagonist strychnine the response patterns changed from phasic to sustained (n = 35) and the neurons responded to both tones presented in double tone experiments independent of the intertone interval (n = 5). The effects of strychnine were reversible. 7. Twenty of 21 neurons tested with sinusoidally amplitude-modulated (SAM) signals exhibited low-pass or band-pass filter characteristics. Tests with SAM signals also revealed a weak temporal summation of inhibition in 13 of the 21 cells tested.(ABSTRACT TRUNCATED AT 400 WORDS) </jats:p
Mitomycin C in highly myopic eyes - Author reply
No full textOphthalmology. 2005 Feb;112(2):208-18; discussion 219.
Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes.
Gambato C, Ghirlando A, Moretto E, Busato F, Midena E.
SourceRefractive Surgery Service and Antimetabolite Therapy Research Unit, Department of Ophthalmology, University of Padova, Padova, Italy.
Abstract
PURPOSE: To evaluate the role of topical mitomycin C in corneal wound healing (CWH) after photorefractive keratectomy (PRK) in highly myopic eyes.
DESIGN: Prospective, double-masked, randomized clinical trial.
PARTICIPANTS: Seventy-two eyes of 36 patients affected by high (>7 diopters) myopia.
METHODS: In each patient, one eye was randomly assigned to PRK with intraoperative topical 0.02% mitomycin C application, and the fellow eye was treated with a placebo. Postoperatively, mitomycin C-treated eyes received artificial tears (3 times daily, tapered in 3 months), whereas the fellow eye was treated with fluorometholone sodium 2% and artificial tears (3 times daily, tapered in 3 months).
MAIN OUTCOME MEASURES: Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA), contrast sensitivity, manifest refraction, and biomicroscopy. Contrast sensitivity was determined using the Pelli-Robson chart. Corneal confocal microscopy documented CWH.
RESULTS: Mean follow-up was 18 months (range, 12-36). No side effects or toxic effects were documented. At 12-month follow-up examination, UCVAs (logarithm of the minimum angle of resolution) were 0.4+/-0.48 and 0.5+/-0.53 (P = .03) in mitomycin C-treated eyes and corticosteroid-treated eyes, respectively. At 1 year, corneal haze developed in 20% of corticosteroid-treated eyes, versus 0% of mitomycin C-treated eyes. At 12, 24, and 36 months, corneal confocal microscopy showed activated keratocytes and extracellular matrix significantly more evident in untreated eyes (Ps = 0.004, 0.024, and 0.046, respectively).
CONCLUSION: Topical intraoperative application of 0.02% mitomycin C can reduce haze formation in highly myopic eyes undergoing PRK.
Comment in
Ophthalmology. 2006 Feb;113(2):357; author reply 357-8
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