Zur Mäusenahrung des Fischreihers

Ohne Zusammenfassung     

Diffusion

Summary Diffusion can occur in a porous swelling material, such as wood, under three different types of gradients through different parts of the structure. Duffusion of a solute can occur under a concentration gradient through the microscopically visible solvent filled void structure, irrespective of whether the wood swells. When it does swell the wood, additional diffusion can occur through the bound part of the liquid. Diffusion of nonswelling gases and vapors is confined to the microscopically visible voids. It occurs under a vapor pressure gradient. Bound swelling liquids can diffuse through the cell walls under a bound liquid gradient. It is also possible for continuous vapor diffusion through the coarse capillary structure to occur in parallel with continuous bound liquid diffusion through the cell walls. The two may also be in series combination. This necessitates condensation of vapor on a cell wall after passing through the voids under a vapor pressure gradient followed by passage through the cell wall under a bound liquid gradient and re-evaporation into the next void.These complex combinations of diffusion paths under different motivating gradients have been theoretically analyzed on the basis of diffusion being analogous to electrical conduction where conductivities in parallel are additive and reciprocals of conductivities (resistances) in series are additive. It is thus possible to combine the cross sections and lengths of the different diffusion paths together with separately determined diffusion coefficients on simpler systems in parallel and series combination so as to obtain theoretical combined effective diffusion coefficients.All, or only part, of the six different structures shown in equation (6) may be involved in diffusion through wood. In the case of diffusion of a solute through wood saturated with a swelling solvent, all of the structures are effective. Solution of the equation for diffusion in the fiber direction shows that the fractional fiber cavity cross section almost entirely controls the rate, whereas in the transverse directions the rate is largely controlled by the communicating structure. This is in agreement with experimental diffusion and electrical conductivity measurements, which give diffusion coefficients relative to that of the solute in bulk solvent equal to the fractional fiber cavity cross-section, corrected for the taper of the fibers. The experimental diffusion coefficients, relative to that through the solvent in bulk in the transverse directions, ranged from 0.01...0.06 compared to the elctrical conductivity values of 0.02...0.033, and a theoretical value of 0.0445 over a similar range in specific gravities.Relative diffusion coefficients for the diffusion of a solute through wood saturated with a non-swelling solvent will be less due to the fact that the terms C _a , C _e and C _c in equation (6) will be zero. These same terms are also eliminated in the diffusion of gases and non-swelling vapors through wood. When all of the diffusion is considered to be free vapor diffusion, the theoretical values are about 30 times the experimental values for transverse diffusion of carbon dioxide, but only about twice for longitudinal diffusion. If the discrepancies are considered to be entirely due to hindered diffusion occurring through the pit membrane openings, hindered diffusion coefficients 1/40 and 1/30 of the free diffusion are obtained, due to the fact that many of the openings are smaller than the mean free path of the gas.Measurements of the continuous bound water diffusion in the wood substance have been made by filling the voids of the wood with a low fusion metal that expands slightly upon solidification. These values vary but slightly between species and are independent of the specific gravity of the wood, as the E values of equation (14) take the specific gravity into account. The values in the fiber direction are about twice those in the radial direction and three times those in the tangential direction. The diffusion coefficients increase with an increase in temperature in proportion to the vapor pressure of water. This indicates that bound water diffusion must be a molecular phenomenon involving many single molecular jumps rather than being a mass movement of liquid. This is similar to the previously observed diffusion of various bound liquids through polymers [Bagley, Long 1955]. Under conditions where the rate of movement is diffusion controlled, the diffusion coefficients also increase exponentially with an increase in moisture content.All of the possible paths through wood may be effective both for steady state and dynamic diffusion through wood. The general equation (6) becomes equation (17) which involves free vapor diffusion, hindered vapor diffusion, and bound water diffusion. The logarithm of the theoretically calculated diffusion coefficient varies inversely with the reciprocal of the absolute temperature for a given specific gravity, indicating that a constant activation energy is involved. Experimental diffusion coefficients calculated from moisture gradient, steady state and rate of drying data give values only slightly lower than the theoretical values when corrected to the same specific gravity. When the drying temperatures are corrected from oven temperatures to effective drying temperatures, the agreement is further improved. The fact that the experimental values determined by rate of drying are in quite good agreement with the steady state values, is a good indication that the rate measurements are diffusion controlled.The evidence here presented clearly indicates the complexity of fluid movement in wood and points out the areas in which further experimentation is desired.

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Zusammenfassung Diffusion tritt in einem porigen quellfähigen Material, wie z. B. Holz, auf, und zwar je nach Art des unterschiedlichen Materialgefüges mit drei verschiedenen Gradienten-Typen. Diffusion eines gelösten Stoffes kann aufgrund eines Konzentrationsgefälles durch die mikroskopisch sichtbaren, mit Lösung gefüllten Hohlräume des Gefüges hindrurch stattfinden, ohne Rücksicht darauf, ob die Lösung das Holz zum Quellen bringt. Bringt sie das Holz zum Quellen, so kann eine zusätzliche Diffusion durch den bis dahin gebundenen Teil der Flüssigkeit stattfinden. Die Diffusion nichtquellender Gase und Dämpfe ist auf die mikroskopisch sichtbaren Hohlräume beschränkt. Sie entsteht durch das Dampfdruckgefälle. Gebundene, quellende Flüssigkeiten können durch Zellwände diffundieren, wenn ein Gefälle gegen die gebundene Flüssigkeit entsteht. Ebenso besteht die Möglichkeit, daß eine kontinuierliche Dampfdiffusion durch die grobe Kapillarstruktur hindurch gleichzeitig mit einer kontinuierlichen Diffusion des gebundenen Flüssigkeitsanteils durch die Zellwand hindurch stattfindet. Beide Erscheinungen können auch in hintereinander folgender Kombination auftreten. Dies setz die Kondensation des Dampfes an der Zellwand nach Durchströmen eines Hohlraumes aufgrund eines Druckgefälles voraus, gefolgt vom Durchtritt durch die Zellwand aufgrund des Gefälles gegen den gebundenen Flüssigkeitsanteil und anschließende neuerliche Verdampfung in den nächsten Hohlraum hinein.Diese komplexen Kombinationen von Diffusionswegen bei jeweils unterschiedlichen Gefällebedingungen wurden analysiert unter der Annahme einer Analogie zwischen Diffusion und elektrischer Leitfähigkeit, wobei parallelgeschaltete Leitfähigkeiten als additiv und reziproke Leitfähigkeiten, d. h. Widerstände, hintereinandergeschaltet als ebenfalls additiv gelten. Es ist auf diese Weise möglich, Querschnitte und Längen der verschiedenen Diffusionswege zusammen mit gesondert bestimmten Diffusionskoeffizienten auf einfachere Systeme in Parallel-oder Serienanordnung zu übertragen, um dadurch theoretisch ermittelte, kombinierte, effektive Diffusionskoeffizienten zu erhalten.Bei der Diffusion durch Holz können entweder alle der sechs in Gl. (16) aufgeführten Konstanten oder nur ein Teil von ihnen beteiligt sein. Inden Fällen, bei denen ein gelöster Stoff durch Holz diffundiert, das mit einem quellenden Lösungsmittel gesättigt ist, sind alle Konstanten beteiligt. Die Auflösung der Gleichung für die Diffusion in Faserrichtung zeigt aber, daß der anteilige Querschnitt des Faserhohlraumes nahezu vollständig die Diffusionsgesch windigkeit bestimmt, wogegen bei der Diffusion in den Querrichtungen die Geschwindigkeit weitgehend durch die verbindenden Gefügeteile in dieser Richtung geregelt wird. Diese Erwägungen stehen in Übereinstimmung mit experimentellen Diffusions- und elektrischen Leitfähigkeits-messungen, aus denen sich Diffusionskoeffizienten errechnen lassen, die jenen entsprechen, die für die Diffusion eines gelösten Stoffes im reinen Lösungsmittel zutreffen, was dem anteiligen Querschnitt eines Faserhohlraumes, korrigiert hinsichtlich der spitz zulaufenden Faserenden, gleichzusetzen ist. Die experimentell ermittelten Diffusionskoeffizienten, entsprechend jenen für das reine Lösungsmittel und für Querdiffusion, bewegten sich zwischen 0,01 und 0,06, die elektrischen Leitfähigkeitszahlen liegen im Vergleich dazu zwischen 0,02 und 0,033; schließlich ergibt sich ein theoretischer Wert von 0,0445 für einen vergleichbaren Dichtebereich.Die entsprechenden Diffusionskoeffizienten für die Diffusion eines gelösten Stoffes durch Holz, das mit einem nichtquellenden Lösungsmittel gesättigt ist, liegen niedriger, weil die Konstanten C _a , C _e und C _c in Gl.(6) Null werden. Sie entfallen ebenso bei der Diffusion von Gasen und nichtquellenden Dämpfen durch Holz. Wird die gesamte Diffusion als freie Dampfdiffusion betrachtet, so erreichen die theoretischen Werte etwa das 30fache der experimentell ermittelten Werte für die Querdiffusion von Kohlendioxyd, allerdings nur das zweifache der experimentellen Werte für die Längsdiffusion. Sofern man sich entschließt, die eben erwähnten Unterschiede gänzlich auf die durch die Tüpfelmembranöffnungen behinderte Diffusion zurückzuführen, so erhält man Koeffizienten der behinderten Diffusion, die 1/40 und 1/30 der freien Diffusion betragen. Dies ist der Tatsache zuzuschreiben, daß viele der in Rechnung gestellten Öffnungen kleiner sind als der angenommene mittlere Durchtrittsquerschnitt. Messungen zur Diffusion des gebundenen Wassers in die Holzsubstanz wurden in der Weise durchgeführt, daß man die Hohlräume des Holzes mit einem leicht schmelzenden Metall füllte, das sich bei der Verfestigung nur sehr wenig ausdehnt. Die erhaltenen Werte schwanken nur wenig zwischen den einzelnen Holzarten und erweisen sich als unabhängig von der Dichte des Holzes, da die E-Werte der Gl. (14) die Dichte in Rechnung stellen. Die Diffusionswerte in Faserrichtung betragen etwa das zweifache jener in Radialrichtung und das dreifache jener in Tagentialrichtung. Die Diffusionskeoffizienten wachsen mit steigender Temperatur proportional zum Dampfdruck des Wassers an. Dies gibt einen Hinweis darauf, daß die Diffusion gebundenen Wassers eher den Charakter einer molekularen Erscheinung hat, die ihrerseits eine Reihe von einfachen molekularen Verbindungsschritten einschließt, als denjenigen der Bewegung einer Flüssigkeitsmasse. Diese Vorgänge besitzen also Ähnlichkeit mit der schon früher beobachteten und geschilderten Diffusion verschiedener gebundener Flüssigkeiten durch Polymere [Bagley, Long 1955]. Unter der Bedingung, daß die Bewegungsgesch windigkeit durch Diffusion gesteuert wird, wachsen die Diffusionskoeffizienten ebenfalls exponentiell mit dem Anstieg des Feuchtigkeitsgehaltes.Alle der möglichen Diffusionswege durch das Holz sind sowohl bei ruhender und dynamischer Diffusion wirksam. Die allgemeine Gleichung (6) wird zur Gl. (17), welche die freie Dampfdiffusion, die behinderte Dampfdiffusion und die Duffusion gebundenen Wassers einschließt. Der Logarithmus des theoretisch errechneten Diffusionskoeffizienten ändert sich im umgekehreten Sinne mit dem reziproken Wert der absoluten Temperature bei einer gegebenen Dichte, was darauf hinweist, daß an dem Vorgang eine konstante Aktivierungsenergie beteiligt ist. Experimentelle Diffusionskoeffizienten, die mit Hilfe des Feuchtigkeitsgefälles, des Fauchtigkeitsgleichgewichts und der Trocknungsgeschwindigkeit errechnet wurden, ergeben Werte, die nur wenig unter den theoretischen Werten liegen, soferndiese auf die gleiche Dichte korrigiert wurden. Korrigiert man ferner die Trocknungstemperturen, und zwar von den Kammertemperaturen auf die tatsächlichen Trocknungstemperaturen, so wird die Übereinstimmung der Werte nochmals verbessert. Die Tatsache, daß die experimentell mit Hilfe der Trocknungsgeschwindigkeit bestimmten Werte gut mit den Feuchtigkeits-Gleichgewichtswerten übereinstimmen, gibt einen deutlichen Hinweis darauf, daß die Messungen der Trocknungsgeschwindigkeit durch die Diffusion bestimmt sind.Die hier angegebenen Beweise zeigen ziemlich klar die Komplexität der Flüssigkeitsbewegung in Holz auf und lassen jene Gebiete erkennen, in denen weitere experimentelle Forschung sinnvoll erscheint.

     

Dimensional stabilization of wood with water soluble fire retardant bulking chemicals compared with polyethylene glycol-1000

Summary Mono and diammonium acid phosphate, ammonium sulfamate, and sodium silicate were compared with polyethylene glycol-1000 as bulking dimension stabilizing agents using Engelmann spruce cross sectional wafers. Limiting antiswell efficiencies are equal to the volume fraction of chemical in a saturated solution. The experimental antiswell efficiencies due to bulking are the percent increase in the dry cross sectional area of the wafers caused by deposition of dry chemical within the cell walls divided by the percent swelling in water. These values for the phosphates, the sulfamate, and the polyethylene glycol approach the limiting values from solubility indicating that chemical continues to diffuse into the cell walls as the wood is dried to virtually attain a saturated solution within that structure. The sodium silicate gave an apparent negative antiswell efficiency as collapse of the fibers on drying exceeded the actual bulking. Antiswell efficiencies between 0 and 30% relative humidity, 0 and 90% relative humidity and 30 and 90% relative humidity were in general still lower. This is largely due to the treated systems taking up more water than the controls, especially at the higher relative humidity. Antiswell efficiencies for the mono ammonium acid phosphate ranged from 20 to 27%, for the diammonium acid phosphate from 28 to 37%, the ammonium sulfamate from 51 to 66% and the polyethylene glycol from 63 to 77%.Paper No. 4245 of the Journal Series of North Carolina State University Agricultural Experiment Station, Raleigh, North Carolina     

Variations of maximum tracheid and pit pore dimensions from pith to bark for ponderosa pine and redwood before and after drying determined by liquid displacement

Summary Measurements of the gas pressure just required to displace saturating liquids and allow a slow continuous stream of gas to pass through ponderosa pine and redwood cross sections over a broad range of thicknesses at varying distances from pith to bark, together with the surface tensions of the liquids, have been used to calculate: (1) maximum lumen radii and maximum fiber lengths from the data for the thinner specimens, and (2) maximum pit pore radii for the specimens thicker than the maximum fiber lengths. Maximum lumen radii and maximum fiber lengths both increase from pith to bark and with increasing height in the tree. Maximum effective pit pore radii increase from the pith to the sapwood transition point, then increase abruptly followed by a variable zone in the sapwood. Displacement of water or a wetting agent solution gave comparable results for never-dried wood. Drying from water and resoaking reduced the maximum effective pit pore size. Drying from a wetting agent soaked condition followed by resoaking reduced the loss in permeability but not to the degree anticipated. ponderosa pine sapwood, that had been exposed to bacterial action, showed a large increase in the maximum effective communicating opening sizes.     

Maximum effective lumen and pit pore sizes of the earlywood and the latewood of never dried loblolly pine sapwood

Summary Measurements of the air pressure required to initially displace a saturating liquid and allow a slow continuous stream of air bubbles to pass through wood cross sections of different thickness, together with the equilibrium surface tension of the saturating liquid, make it possible to calculate the maximum effective opening radii. Previous measurements were made for wood as a whole over complete annual rings. Measurements reported here were made separately for earlywood and latewood. Extrapolating plots of the maximum effective opening radius-cross section thickness, for thicknesses below the maximum fiber length, to zero thickness gave maximum lumen radii of 16 m for the earlywood and 10.3 m for the latewood. The values are only slightly greater than the calculated average values. Extrapolating the plots in the opposite direction to zero opening radius gave approximate maximum lumen or fiber lengths for the earlywood of 6 mm and for the latewood of 5 mm. The maximum effective opening radii for cross sections thicker than the maximum fiber length give maximum effective communicating pore radii. These values continue to decrease, with increasing thickness of the cross sections due to the decreasing probability of the largest openings falling in any one series path through the structures. The maximum effective pit pore radius for passage through fifty pits in series was 0.8 m for the earlywood and 0.28 m for the latewood.Paper No. 3787 of the Journal Series of North Carolina State University Agricultural Experiment Station, Releigh, N. C.     

Antimicrobial drug resistance as determined by the E-test in Campylobacter jejuni, C. coli, and C. lari isolates from the ceca of broiler and layer chickens in Grenada

One hundred and twenty five chickens from Grenada, consisting of 77 broilers and 48 layers were examined for carriage of thermophilic campylobacters in their ceca by culture. Seventy nine percent of chickens were positive for campylobacters, with an isolation rate of 93.5% for broilers and 56.3% for layers, the difference being significant. Sixty-four pure cultures comprising 39 Campylobacter coli, 21 Campylobacter jejuni, and 4 Campyilobacter lari isolates were tested for their resistance against 7 antibiotics using the E-test. None of the isolates were resistant to chloramphenicol and gentamicin. Resistance rates to other drugs were: ampicillin, 9.4%; ciprofloxacin, 12.5%; erythromycin, 3.1%; metronidazole, 9.4%, and tetracycline, 50% with MICs of >or=256 microg/mL for tetracycline. There were no significant differences in resistance rates between C. coli and C. jejuni. Multiple resistance to >or=2 drugs was seen in 15.6% of total isolates. All C. lari isolates were resistant to ciprofloxacin, and 3 of 4 isolates had multiple drug resistance. Overall, erythromycin, which is the drug of choice for treatment of Campylobacter infections in humans, is effective in vitro against 97% of chicken isolates in Grenada.     

Perfluorooctanoate (PFO) in Forest Soils near a Fluoropolymer Manufacturing Facility

After elevated concentrations of perfluorooctanoate (PFO) were found in river and groundwater in the vicinity of a fluoropolymer manufacturing facility, numerous soils at adjacent sites were sampled in 2007. Within a 5-km northeast-oriented sector around a probable point source, 20 forest sites were investigated and compared to deposition and groundwater data. PFO concentrations up to 600 µg/kg were detected in the soils, and PFO concentrations typically decreased toward deeper soil depths. In mixed or deciduous forests, maximum concentrations of PFO occurred in the topsoil, pointing to the favorable decomposition and incorporation of deciduous litter. PFO concentrations of the organic layer over the 20 sampling sites were interpolated using ordinary kriging. Highest PFO content in the organic layer was located about 500 m away from the point source in the regional wind direction, decreasing asymptotically outwards. Long-term monitoring data pointed to an accumulation of PFO over time in the organic layer. The data suggest that PFO might be released in the course of litter decomposition and transported toward deeper soil regions only gradually. The soils’ PFO concentrations reflect the deposition data. The transport link toward groundwater is currently established in lysimeter studies.     

Investigations concerning the prevalence of Coxiella burnetii and Chlamydia abortus in sheep in correlation with management systems and abortion rate in Lower Saxony in 2004

The intracellular bacteria Coxiella (C) burnetii and Chlamydia (Chl) abortus induce abortion in sheep and also affect humans. While Chl. abortus only infrequently infects humans, C burnetii is the aetiological agent of numerous Q fever outbreaks during the last decades. There is only limited knowledge about the prevalence of both pathogens in sheep, although sheep are involved in almost all Q fever outbreaks in Germany. The aim of our study was to investigate the prevalence of both pathogens in flocks located in Lower Saxony, Germany, in correlation to the management form and abortion rate. Serum samples of 1714 sheep from 95 flocks located in Lower Saxony were investigated by ELISA. 2.7% of these samples were positive, 1.3% showed inconclusive results in the C. burnetii-ELISA. Elevated intra-flock seroprevalences were only detected in three migrating flocks. Chlamydia-specific antibodies could be detected in 15.1% serum samples of mainly shepherded and migrating flocks. In one of these flocks with a high intra-flock seroprevalence for C burnetii (27%) and Chlamydia (44.9%), C burnetii was detected in 21.6% of the placenta samples of normal births and in 12.5% of the colostrum samples by PCR. Aborted fetuses and the corresponding placentas were negative in C burnetii-PCR, but in most of them and also in many other placenta samples Chl. abortus could be detected by PCR and DNA microarray. This survey shows a low overall prevalence of C. burnetii in sheep in Lower Saxony in the year 2004. However, three migrating flocks with a high intra-flock prevalence are localized in the southern parts of Lower Saxony. Spreading of C burnetii could occur, because of the large radius of grazing of all three flocks.     

Effect of omeprazole paste on intragastric pH in clinically normal neonatal foals

OBJECTIVE: To evaluate the efficacy of omeprazole paste, a commonly used antiulcer drug, on intragastric pH in clinically normal neonatal foals. ANIMALS: 6 clinically normal foals between 5 and 14 days of age. PROCEDURE: Intragastric pH was recorded in each foal by use of a disposable antimony pH electrode with internal reference. Values for intragastric pH were recorded every 4 seconds by use of an ambulatory pH monitor. There were two 24-hour recordings of intragastric pH for each foal, with 24 hours between recordings. Foals were not administered any drugs during the first recording. Foals were administered omeprazole paste (4 mg/kg, PO) 1 hour after the start of the second recording. Mean pH was calculated for each hour of each 24-hour recording session. Hourly mean values were compared between the first and second 24-hour recordings. RESULTS: Complete data were obtained from 4 of 6 foals during the first 24-hour recording and 6 of 6 foals during the second 24-hour recording. Foals had significantly higher mean hourly intragastric pH for hours 2 to 22 following omeprazole administration, compared with corresponding hourly pH values in foals during the first recording. CONCLUSION AND CLINICAL RELEVANCE: Omeprazole paste can effectively increase intragastric pH in clinically normal neonatal foals within 2 hours after oral administration of the first dose and can be administered to neonatal foals at the rate of 4 mg/kg, PO, every 24 hours.