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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1255-1264 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electron dynamics in gold nanoparticles with an average diameter between 9 and 48 nm have been studied by femtosecond transient absorption spectroscopy. Following the plasmon bleach recovery after low power excitation indicates that a non-Fermi electron distribution thermalizes by electron–electron relaxation on a time scale of 500 fs to a Fermi distribution. This effect is only observed at low excitation power and when the electron distribution is perturbed by mixing with the intraband transitions within the conduction band (i.e., when the excitation wavelength is 630 or 800 nm). However, exciting the interband transitions at 400 nm does not allow following the early electron thermalization process. Electron thermalization with the lattice of the nanoparticle by electron–phonon interactions occurs within 1.7 ps under these conditions, independent of the excitation wavelength. In agreement with the experiments, simulations of the optical response arising from thermalized and nonthermalized electron distributions show that a non-Fermi electron distribution leads to a less intense bleach of the plasmon absorption. Furthermore, the difference between the response from the two electron distributions is greater for small temperature changes of the electron gas (low excitation powers). No size dependence of the electron thermalization dynamics is observed for gold nanoparticles with diameters between 9 and 48 nm. High-resolution transmission electron microscopy (HRTEM) reveals that these gold nanoparticles possess defect structures. The effect of this on the electron–phonon relaxation processes is discussed. 18 nm gold–silver alloy nanoparticles with a gold mole fraction of 0.8 are compared to 15 nm gold nanoparticles. While mixing silver leads to a blue-shift of the plasmon absorption in the ground-state absorption spectrum, no difference is observed in the femtosecond dynamics of the system. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 2362-2368 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Gold nanorods in colloidal solution can be melted into spherical nanoparticles by excitation with intense femtosecond laser pulses of the proper energy. The threshold of the laser pulse energy for the complete melting of the nanorods with a mean aspect ratio of 4.1 in solution is determined by observing the change in the absorption intensity of the longitudinal absorption band (measure of the rod concentration) at 800 nm with increasing number of laser pulses of known energy. The number of laser pulses needed to reduce the band intensity (rod concentration) by 1/e of its initial value is determined as the laser energy per pulse increases. For pulses of lower energy than threshold, it is found that the number of pulses required to melt the gold nanorods present in solution increases significantly with decreasing laser pulse energy. Above threshold, this number is constant since the additional absorbed laser energy will only further heat the particles to temperatures above their melting point. The gold concentration in the colloidal solution is measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES), from which the gold nanorod concentration is determined from the known shape and size distribution obtained from transmission electron microscopy (TEM) results. A simple analysis using the determined threshold energy and the nanorod concentration showed that it takes an average of ∼ 60 femtojoule (fJ) to melt a single gold nanorod. Experiments using 820 nm as well as 410 nm femtosecond laser pulses yield similar values, indicating that the laser induced shape transformation of the nanorods is independent of the irradiation wavelength and that this process is therefore photothermal in origin. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 13 (1990), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Pressure-volume measurements were made on Artemisia tridentata Nutt. ssp. tridentata samples rehydrated for 0, 1.5, 3, 6 or 24 h. Increasing rehydration time caused a significant increase in osmotic potential at turgor loss, cell elasiticity, and the relative water content at turgor loss, and a significant decrease in pressure potential at saturation. Osmotic potential at saturation was changed significantly by rehydration, but no consistent trend was observed. The symplastic water fraction did not differ significantly among treatments. The increase in the osmotic potential at turgor loss did not correspond with decreasing cell elasticity or synthesis of solutes. Instead, the leaf solute content remained constant suggesting a redistribution of solutes between the symplast and apoplast. Using non-rehydrated samples for pressure-volume analysis introduced errors in estimates of the symplastic water fraction, osmotic potential at full turgor, and the relative water content at turgor loss. These errors are due to uncertainties in the determination of saturated weights.
    Type of Medium: Electronic Resource
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  • 4
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    Berlin : Periodicals Archive Online (PAO)
    Klio. 75 (1993) 493 
    ISSN: 0075-6334
    Topics: History , Classical Studies
    Description / Table of Contents: Besprechungen und Anzeigen
    Notes: Literaturkritik
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  • 5
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Photosynthetic CO2 dependencies were measured for six lichen species, representing a variety of morphologies and collected from widely different habitats. All curves exhibited a linear increase in photosynthesis with increasing CO2 concentrations at the lower range of CO2 values, but little photosynthetic variation with increasing CO2 concentrations at the upper range of CO2 values. Half maximal CO2 concentration estimates varied from 147–440 μl CO2·l1, but had broadly overlapping confidence intervals. We conclude that lichen CO2 dependencies are basically similar to those reported for higher plants and discuss the reasons why widely varying results have previously been published.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-0630
    Keywords: PACS: 78.47.+p; 73.20.-r; 73.20.At; 79.60.-i; 79.60.Bm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract. We have investigated the population dynamics of image-potential states on the clean Pt(111) surface. The first two image-potential states have been resolved exhibiting lifetimes of 26±7 fs and 62±7 fs. Those lifetimes are in contrast to the (111) surfaces of Ag and Cu, where the n=2 state is degenerate with bulk states leading to lifetimes shorter than 20 fs.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Tetrahedron Letters 14 (1973), S. 1155-1158 
    ISSN: 0040-4039
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1433-0423
    Keywords: Schlüsselwörter Katarakt ; Offenwinkelglaukom ; Senkung des IOD ; Phakoemulsifikation ; IOL-Implantation ; Key words Cataract ; Open angle glaucoma ; IOP-reduction ; Phacoemulsification ; IOL-implantation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary Background. Many of the previous studies which dealt with the influence of cataract surgery on intraocular pressure, were performed retrospectively and based on heterogenous groups of patients. Therefore, the purpose of our study was to prospectively assess the effect of phacoemulsification and posterior chamber intraocular-lens (IOL)-implantation on intraocular pressure (IOP) under standardized conditions in patients with and without open-angle-glaucoma. Patients and methods. Overall 52 patients were recruited for the study. 34 eyes with normal IOP and 16 eyes with open-angle-glaucoma were operated with the same technique. Results. Mean IOP in patients with cataract and without glaucoma was preoperatively 15,1 mmHg. 6 months postoperatively these patients showed a mean decrease of IOP of 11,9% (1,8 mmHg+/−3,8; p=0.027) ; after 12 months IOP showed a decrease of 18,5% (2,8 mmHg+/−3,5; p=0.0001). In patients with glaucoma mean IOP was preoperatively 17,3 mmHg. IOP was reduced by 23,7% (4,1 mmHg+/−6,0; p=0.017) 6 months after cataract surgery and 22,6% (3,9 mmHg+/−4,5; p=0.005) 12 months after the operation. In 6 of 16 eyes the antiglaucoma medication could be suspended. Conclusion. Reduction of IOP is a positive side effect of phacoemulsification and posterior chamber IOL implantation and should be considered when indicating cataract surgery in patients with glaucoma and only slight elevation of IOP.
    Notes: Zusammenfassung Hintergrund. Bei vielen der bisherigen Studien, die über eine Senkung des Intraokulardrucks nach Kataraktchirurgie berichten, handelt es sich um retrospektive Untersuchungen mit einem z. T. sehr heterogenen Patientenkollektiv. Ziel unserer Untersuchung war es daher, prospektiv unter standardisierten Bedingungen bei Patienten mit und ohne Offenwinkelglaukom den mittel- und langfristigen Einfluss der Phakoemulsifikation und Hinterkammerlinsen-(HKL-)Implantation auf den Intraokulardruck (IOD) zu bestimmen. Material und Methode. Bei 52 Patienten wurde an 36 Augen mit Normaldruck und 16 mit Offenwinkelglaukom eine Kataraktoperation in standardisierter Technik durchgeführt. Ergebnisse. Bei den Normaldruckpatienten fand sich präoperativ ein durchschnittlicher Augeninnendruck von 15,1 mmHg. Sechs Monate postoperativ war durchschnittlich eine Senkung des IOD um 11,9% (1,8 mmHg +/−3,8; p=0,027), nach 12 Monaten um 18,5% (2,8 mmHg +/−3,5; p=0,0001) feststellbar. Die Patienten mit Offenwinkelglaukom wiesen präoperativ einen Augeninnendruck von 17,3 mmHg auf. Postoperativ war nach 6 Monaten bei den Glaukompatienten eine IOD-Senkung um 23,7% (4,1 mmHg +/−6,0; p=0,017) feststellbar, nach 12 Monaten um 22,6% (3,9 mmHg +/−4,5; p=0,005). Bei 6 von 16 Patienten konnte postoperativ auf eine drucksenkende Lokaltherapie verzichtet werden. Schlussfolgerung. Als positiver Nebeneffekt ist bei der Phakoemulsifikation mit HKL-Implantation eine signifikante Minderung des IOD festzustellen, was besonders bei der Indikationsstellung bei Patienten mit geringem Glaukomschaden und leicht erhöhtem Intraokulardruck berücksichtigt werden sollte.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 64 (1984), S. 204-210 
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Net photosynthetic rates for the lichen Parmelia praesignis Nyl. were obtained as a function of 5 light levels, 5 temperature levels, and of water content as thalli dried from saturated conditions. Data are described as second order polynomials in the light, and as saturation curves in the dark. Rates in the light were depressed at high water contents reaching maximal rates between 110% and 180% water content and declining as thalli dried. Physiological parameters were derived from the drying curves to investigate temperature and light interactions. Dark respiration parameters are the maximal rate, the water content where the rate is half-maximal, the water content at which respiration is zero, and the maximal water efficiency. In the light, parameters are the maximal net photosynthetic rate, the water content at the maximal rate, the water compensation point, the maximal water efficiency, and the sensitivity of net photosynthesis to change in water content. Values of half-maximal rate water contents for respiration were found to increase as temperatures increased. The greatest maximal net photosynthetic rate occurred at higher temperatures as the light intensity increased. In the light, maximal water efficiency and the sensitivity to changes in water content were generally maximal at temperatures yielding the greatest maximal net photosynthetic rates.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Psychometrika 40 (1975), S. 77-105 
    ISSN: 1860-0980
    Source: Springer Online Journal Archives 1860-2000
    Topics: Psychology
    Notes: Abstract A theory of discrimination which assumes that subjects compare psychological values evoked by a stimulus to a subjective referent is proposed. Momentary differences between psychological values for the stimulus and the referent are accumulated over time until one or the other of two response thresholds is first exceeded. The theory is analyzed as a random walk bounded between two absorbing barriers. A general solution to response conditioned expected response times is computed and the important role played by the moment generating function (mgf) for increments to the random walk is examined. From considerations of the mgf it is shown that unlike other random walk models [Stone, 1960; Laming, 1968] the present theory does not imply that response conditioned mean correct and error times must be equal. For two fixed stimuli and a fixed referent it is shown that by controlling values of response thresholds, subjects can produce Receiver Operating Characteristics similar or identical to those predicted by Signal Detection Theory, High Threshold Theory, or Low Threshold Theory.
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