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  • 1
    Electronic Resource
    Electronic Resource
    Reactions of size-selected positively charged nickel clusters with carbon monoxide in molecular beams (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 3492-3497 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Reactions of small thermalized positively charged nickel clusters with carbon monoxide were studied in a molecular beam experiment. The nickel clusters were produced in a high intensity cluster ion source and thermalized in a large helium-filled quadrupole ion guide. The clusters were size selected by a quadrupole mass spectrometer. The mass- and charge-selected nickel clusters then passed through a linear quadrupole drift tube filled with a mixture of helium buffer gas and carbon monoxide. The reaction products were then analyzed by a quadrupole mass-spectrometer. Using this technique, saturation limits for Nin+ clusters with n=4–31 were measured and the competitive reaction channels were identified. Under certain experimental conditions carbide formation was observed in the case of the nickel tetramer, pentamer, and hexamer. The structure of the nickel carbonyl clusters is discussed within the framework of the polyhedral skeletal electron pair theory. The cluster growth may be explained by a pentagonal sequence of structures for n=4–7, capping of the pentagonal bipyramid to buildup an icosahedron at Ni13+, and further capping of this icosahedron to form a double icosahedron at Ni19+. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474688
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  • 2
    Electronic Resource
    Electronic Resource
    The relaxation from linear to triangular Ag3 probed by femtosecond resonant two-photon ionization (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1017-1021 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present extended NeNePo (negative to neutral to positive) measurements on the ultrafast dynamics in the ground state of neutral, mass-selected Ag3 molecules. A vibrational wave packet in the neutral molecule is created with an ultrashort laser pulse by photodetachment of the excess electron from the corresponding mass-selected anion. The subsequent molecular rearrangement is probed by photoionization after a selected time delay. Complementary to our previous investigations of this process, we now use two-photon photoionization via a resonant state in the probe step. Here, a bound–bound excitation to a well-known state followed by one-photon ionization is used instead of the nonresonant bound/free transition into the ionic continuum. Using radiation with wavelengths near 370 nm for resonant ionization, we observe a fast bending motion of the initially linear Ag3, followed by an ultrafast intramolecular vibrational energy redistribution, interpretable as an intramolecular collision process. The signal shows an apparent loss of vibrational coherence after the collision, which can be explained by the finite temperature of the anionic clusters in our experiment. Additionally, we describe a previously unknown resonance in the linear neutral molecule around 500 nm. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479382
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  • 3
    Electronic Resource
    Electronic Resource
    Retinal blood flow in diabetic children and adolescents (1991)
    Springer
    Graefe's archive for clinical and experimental ophthalmology 229 (1991), S. 336-340 
    Details
    ISSN: 1435-702X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A total of 209 diabetic children and adolescents aged 6–17 years (mean, 12.6 ± 2.3 years) were examined by ophthalmoscopy, video fluorescein angiography and hemoglobin (HbA1c) tests. Microaneurysms were found in 26% of the children (ophthalmoscopy, 11%; angiography, 23%). The prevalence of retinopathy was 16% in patients aged 6–10 years, 27% in those aged 11–13 years and 36% in those aged 14–17 years. Only five diabetics aged 11–17 years showed lesions other than microaneurysms (hard exudates, intraretinal hemorrhages or retinal capillar leakage). Retinal blood flow was quantified using video fluorescein angiography. The arm-retina time (ART) and the arteriovenous passage time (AVP) as parameters of the retinal microcirculation were obtained using an image analysing system. The mean value for ART was 9.7±2.5 s and that for AVP was 1.43±0.52 s. AVP was significantly shorter in diabetic children and adolescents with good glycemic control (HbAlc, 〈7%; AVP, 1.35±0.44 s) than in those with bad glycemic control (HbA1c, ≥ 9 % ; AVP, 1.65 ±0.51 s).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00170691
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  • 4
    Electronic Resource
    Electronic Resource
    Hemodilution therapy in central retinal vein occlusion (1994)
    Springer
    Graefe's archive for clinical and experimental ophthalmology 232 (1994), S. 33-39 
    Details
    ISSN: 1435-702X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Systemic hemorheologic abnormalities may play a part in the pathogenesis of central retinal vein occlusions. A statistically significant elevation of plasma viscosity was found in patients with acute central retinal vein occlusion compared with control patients. Local retinal blood flow parameters including arteriovenous passage time and mean arterial dye bolus velocity were significantly altered in the central retinal vein occlusion patients compared with age-matched controls at baseline examination. We performed a randomized, prospective, single-blind clinical investigation to determine the effect of hemorheological manipulation on the clinical course and retinal blood flow of eyes with central vein occlusion. Hemodilution included plasma expansion with hydroxyethyl-starch, withdrawal of whole blood if the hematocrit was above 42%, and rheologic manipulation with parenteral pentoxifylline. We found a statistically significant improvement in visual acuity at 1 year post-treatment for the treated group compared with the control group (increase of visual acuity of 1.5 lines vs decrease of 1.5 lines). The retinal blood flow parameters were markedly improved soon after the institution of therapy, and this may have contributed to the improvement in visual acuity in the treated group. There was no statistically significant difference between the two groups in the progression to ischemic central vein occlusion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00176435
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  • 5
    Electronic Resource
    Electronic Resource
    Perifoveal microcirculation with non-insulin-dependent diabetes mellitus (1994)
    Springer
    Graefe's archive for clinical and experimental ophthalmology 232 (1994), S. 225-231 
    Details
    ISSN: 1435-702X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Fluorescein angiograms were performed to evaluate perifoveal capillary blood velocities (v), capillary density (perifoveal intercapillary areas: PIA) and the foveal avascular zone (FAZ) by means of the scanning laser technique (SLO-101 Rodenstock). The angiograms were digitally stored and the data quantified off-line with an image analyzing system (IBAS). In the present study 46 patients with non-insulin-dependent diabetes mellitus (NIDDM) were examined and their data compared with that of 31 healthy volunteers. The perifoveal capillary flow velocity of the NIDDM subjects (v = 2.33±0.36 mm/s) was significantly (P 〈0.01) decreased as compared to healthy subjects (v = 2.86 ±0.41 mm/s). The perifoveal intercapillary areas in the foveal avascular zone were significantly increased in patients with NIDDM (PIA=10029 ± 3402 μm2; FAZ = 0.415 ± 0.272 mm2) as compared with healthy subjects (PIA = 3965 ± 467 μm2; FAZ=0.221 ± 0.071 mm2). These data suggest the possibility that a decrease in perifoveal capillary blood velocities in combination with decreased capillary density (enlarged PIA) and an enlargement of the foveal avascular zone may occur in patients with NIDDM. The determination of these parameters could help in monitoring the progress of diabetic retinopathy and diabetic maculopathy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00184010
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  • 6
    Electronic Resource
    Electronic Resource
    Haemorheology in patients with branch retinal vein occlusion with and without risk factors (1996)
    Springer
    Graefe's archive for clinical and experimental ophthalmology 234 (1996), S. S8 
    Details
    ISSN: 1435-702X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract • Purpose: The study was carried out to ascertain the role of blood viscosity in patients with branch retinal vein occlusion (BR-VO) with and without risk factors. • Methods: In 292 patients with acute BRVO (mean age 65 ± 10 years) and 292 controls matched for gender, age, and cardiovascular risk factors, haematocrit, plasma viscosity, erythrocyte aggregation and erythrocyte rigidity were measured. A subgroup analysis in patients with and without risk factors was performed. • Results: Haematocrit and plasma viscosity values were significantly higher in BRVO patients than in controls, but erythrocyte rigidity and erythrocyte aggregaton did not differ. Subgroup analysis revealed no differences in haematocrit and plasma viscosity values between patients with and those without cardioavascular risk factors. • Conclusions: This study shows increased plasma viscosity and haematocrit values in patients with BRVO which are not associated with the presence of other cardiovascular risk factors. Thus, changes in blood fluidity appear to be important factors in the pathogenesis of BRVO.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02343041
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  • 7
    Electronic Resource
    Electronic Resource
    Einfluß unterschiedlicher antihypertensiver Monotherapien auf die perifoveale Mikrozirkulation bei Patienten mit arterieller Hypertonie * (1996)
    Springer
    Der Ophthalmologe 93 (1996), S. 699-702 
    Details
    ISSN: 1433-0423
    Keywords: Schlüsselwörter Arterielle Hypertonie ; Mikrozirkulation ; Antihypertensive Monotherapie ; Kapillardichte ; Kapillare Fließgeschwindigkeit ; Key words Arterial hypertension ; Microcirculation ; Antihypertensive monotherapy ; Capillary density ; Capillary flow velocity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Purpose. Arterial hypertension is known to be an important risk factor for cerebral and cardiovascular disease. Previous studies have demonstrated alterations in the perifoveal microcirculation in patients with essential hypertension. During follow-up a progression of these alterations has been reported. In the present study we quantified the retinal microcirculation of patients with hypertension under different systemic antihypertensive medication. Methods. The patients were divided into three groups according to their medication. Group 1 was treated with β-blocker (n = 17), group 2 with ACE inhibitors (n = 10), and group 3 with calcium channel blockers (n = 11). All patients underwent fluorescein angiographic studies with a scanning laser ophthalmoscope. Perifoveal intercapillary areas (PIA) and the mean perifoveal capillary velocity were quantified from the angiograms. Results. Compared with reference values, all three groups of patients with essential hypertension showed significantly increased PIA and significantly decreased capillary velocity. No difference could be detected between the three groups of patients treated with β-blocker, ACE inhibitor or calcium channel blocker. Conclusion. Alterations of the perifoveal network are found in patients with arterial hypertension. These alterations are similar under antihypertensive monotherapy using β-blocker, ACE inhibitor or calcium channel blocker.
    Notes: Die arterielle Hypertonie ist als Risikofaktor für das Auftreten zerebraler und kardiovaskulärer Gefäßerkrankungen bekannt. Vorhergehende Studien haben bei Patienten mit arterieller Hypertonie Veränderungen in der perifovealen Mikrozirkulation festgestellt. In dieser Studie wurde die perifoveale Mikrozirkulation bei Patienten mit arterieller Hypertonie untersucht, die mit verschiedenen Antihypertensiva therapiert wurden. Patienten: Ihrer antihypertensiven Medikation entsprechend wurden die Patienten in 3 Gruppen eingeteilt. Gruppe 1 wurde mit β-Blocker (n = 17), Gruppe 2 mit ACE-Hemmer (n = 10), und Gruppe 3 mit Kalziumantagonisten (n = 11) behandelt. Bei allen Patienten wurde eine Videofluoreszenzangiographie mit einem Scanning-Laserophthalmoskop durchgeführt. Aus den Videofluoreszenzangiogrammen wurden die mittlere Fläche der kapillarfreien Zonen (KFZ) sowie die mittlere kapillare Fließgeschwindigkeit bestimmt. Ergebnisse: Im Vergleich zu gesunden Probanden zeigten alle 3 Gruppen mit arterieller Hypertonie eine signifikant vergrößerte KFZ und eine signifi-kant herabgesetzte mittlere kapillare Fließgeschwindigkeit. Zwischen den einzelnen Patientengruppen, die mit β-Blocker, ACE-Hemmer oder Kalziumantagonisten behandelt wurden, zeigten sich keine Unterschiede. Schlußfolgerung: Bei Patienten mit arterieller Hypertonie zeigen sich Veränderungen im perifovealen Kapillarnetz. Diese Veränderungen unterscheiden sich nicht bei unterschiedlicher antihypertensiver Monotherapie mit β-Blocker, ACE-Hemmer oder Kalziumantagonisten.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003470050061
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  • 8
    Electronic Resource
    Electronic Resource
    Subretinale Chirurgie bei choroidalen Neovaskularisationen (1997)
    Springer
    Der Ophthalmologe 94 (1997), S. 929-932 
    Details
    ISSN: 1433-0423
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Zusammenfassung Choroidale Neovaskularisationen (CNV) in Folge einer altersabhängigen Makulopathie oder entzündlicher Netz- bzw. Aderhauterkrankungen sind in der westlichen Welt die häufigste Ursache für einen schweren Visusverlust. Es konnte in großen Studien zwar gezeigt werden, daß die Laserphotokoagulation von choroidalen Neovaskularisationen den Visusverlust aufhalten kann, jedoch ist die Zahl der Patienten, bei denen diese Behandlung in Frage kommt, klein. Darüber hinaus ist die Rezidivrate trotz primär erfolgreicher Laserphotokoagulation sehr hoch. Aus diesen Gründen hat die chirurgische Entfernung von choroidalen Neovaskularisationen zunehmend an Bedeutung gewonnen. Insbesondere bei Patienten mit subfovealen CNV in Folge von chorioretinalen Entzündungen scheint die chirurgische Entfernung Vorteile gegenüber anderen Therapiemöglichkeiten zu haben. Bei der altersabhängigen Makuladegeneration sind die Ergebnisse nicht ganz so überzeugend, jedoch ist zu erwarten, daß durch neue, bisher nur experimentell eingesetzte chirurgische Verfahren die operative Therapie sich auch für dieses Krankheitsbild durchsetzen wird.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003470050224
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  • 9
    Electronic Resource
    Electronic Resource
    Retinal circulation times in quantitative fluorescein angiography (1990)
    Springer
    Graefe's archive for clinical and experimental ophthalmology 228 (1990), S. 442-446 
    Details
    ISSN: 1435-702X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We tried to obtain an overview of the quantitative state of the retinal circulation. Optical density measurements by an image analyzer were performed on video fluorescein angiograms for the determination of dye-dilution curves. To ensure that curves with a sharp peak were obtained, 1 ml sodium fluorescein 10% was flushed with 20 ml physiological saline. From dilution curves of a retinal arteriole and the corresponding venule, various retinal circulation times, T (x) (x=1, 25, 50, 75, and 100) and Tm, were calculated. T(1) corresponds to the difference in the time of initial dye appearance; T(50), to the so-called half-maxim time difference; T(100), to the difference in the time to peak intensity; and Tm, to the mean circulation time. T(50) showed the best reproducibility when it was examined at 49 retinal regions of 10 healthy volunteers with a double video-fluorescein angiogram that was obtained within 1 min. Normal values (mean ± SD) at the temporal superior region of 37 healthy volunteers were as follows: T (1) = 0.87 ± 0.66 s, T(25)=1.52±0.48 s, T(50)=1.83±0.50 s, T(75)=2.12±0.56 s, T(t00) = 2.73±0.76 s, and Tm = 2.69±1.25 s. We believe that these values give a general overview of the quantitative state of normal retinal circulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00927258
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  • 10
    Electronic Resource
    Electronic Resource
    Macular capillary particle velocities: a blue field and scanning laser comparison (1995)
    Springer
    Graefe's archive for clinical and experimental ophthalmology 233 (1995), S. 244-249 
    Details
    ISSN: 1435-702X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract • Background: Two different techniques are available for measurement of macular capillary particle velocities. The psychophysical blue field simulation technique gives data on macular leukocyte flow velocities, while the scanning laser technique provides information on capillary blood velocities of hypofluorescent segments in the macular network. Published velocity data differ considerably between the two methods. The current study was undertaken to compare the two measuring techniques in a group of healthy volunteers. • Methods: Thirty-two healthy subjects (12 man, 20 women, mean age 27 years) participated in this study. All subjects underwent entoptic leukocyte visualization by means of blue field simulation followed by fluorescein angiography using scanning laser ophthalmoscopy. • Results: The capillary blood velocities measured using the scanning laser technique were significantly higher (P 〈 0.01) than the flow velocities estimated with the blue field simulation technique (2.68 ± 0.3 mm/s vs 0.89 ±0.2 mm/s). No significant correlation between the flow velocities was found (r = −0.22). • Conclusion: The differences may be related to different measuring locations and/or measurements of different phenomena. The blue field technique estimates average leukocyte flow in the macular network, whereas the scanning laser technique quantifies the velocity of erythrocyte aggregates in the capillary lumen of the para- and perifoveal network. A combination of both techniques may be helpful in interpreting physiological responsiveness and altered velocity pattern in diseased eyes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00183599
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