2,810,724 research outputs found
Physiological adaptation of two unicellular green algae to pH stress.
No full textTwo marine algae, Dunaliella parva and Chlorococcum submarinum were selected to study the effect of pH stress on single celled algae. D. parva has been well characterised physiologically, but not with regards to pH stress. C submarinum has not been so extensively studied, but is known to grow over a wide pH range from pH 4.5 to 10.5. It was of prime importance that the algal cells were grown at the desired extreme values of external pH. Problems were encountered at high levels of pH but were overcome by growing the algae in a fermenter set up as a batch culture. This method of growth was used for both algae at extreme values of external pH and it allowed the accurate control of the media pH by the automatic addition of acid or alkali. pH 7.5 cells were grown in normal flask batch culture. The cell number, cell volume, and chlorophyll content of both algae were determined over a wide range of pH values, showing that differences in external pH had significant effects on individual cells. Protein concentrations were measured and were shown to increase in pH 9.0 grown cells. Determination of cell volume, internal pH and membrane potential have been carried out using radiolabelled isotopes for algae grown over a wide pH range. Cell volume was shown to increase at both acid and alkaline pH values. The internal pH of both algae was found to be at a more neutral pH than the external pH. For both D. parva and C submarinum, the membrane potential increased with increasing external pH. Enzyme activities in crude extracts were measured to establish the effects of external pH changes on metabolic pathways. The activity of these enzymes, taken from different organelles in the cell, was used to investigate the uniformity of internal pH
The Final Frontier of pH and the Undiscovered Country Beyond
No full textThe comparison of volumes of cells and subcellular structures with the pH values reported for them leads to a conflict with
the definition of the pH scale. The pH scale is based on the ionic product of water, Kw = [H+]6[OH2].We used Kw [in a
reversed way] to calculate the number of undissociated H2O molecules required by this equilibrium constant to yield at
least one of its daughter ions, H+ or OH2 at a given pH. In this way we obtained a formula that relates pH to the minimal
volume VpH required to provide a physical meaning to Kw, VpH~10DpH{pKw=2D|
10pKw=2
NA
(where NA is Avogadro’s number).
For example, at pH 7 (neutral at 25uC) VpH = 16.6 aL. Any deviation from neutral pH results in a larger VpH value. Our results indicate that many subcellular structures, including coated vesicles and lysosomes, are too small to contain free H+ ions at equilibrium, thus the definition of pH based on Kw is no longer valid. Larger subcellular structures, such as mitochondria, apparently contain only a few free H+ ions. These results indicate that pH fails to describe intracellular conditions, and that water appears to be dissociated too weakly to provide free H+ ions as a general source for biochemical reactions. Consequences of this finding are discussed
Photonic porous silicon as a pH sensor
No full textChronic wounds do not heal within 3 months, and during the lengthy healing process, the wound is invariably exposed to bacteria, which can colonize the wound bed and form biofilms. This alters the wound metabolism and brings about a change of pH. In this work, porous silicon photonic films were coated with the pH-responsive polymer poly(2-diethylaminoethyl acrylate). We demonstrated that the pH-responsive polymer deposited on the surface of the photonic film acts as a barrier to prevent water from penetrating inside the porous matrix at neutral pH. Moreover, the device demonstrated optical pH sensing capability visible by the unaided eye
Impact of Age and Body Site on Adult Female Skin Surface pH
No full textBackground: pH is known as an important parameter in epidermal barrier function and homeostasis. Aim: The impact of age and body site on skin surface pH (pH(SS)) of women was evaluated in vivo. Methods: Time domain dual lifetime referencing with luminescent sensor foils was used for pH(SS) measurements. pH(SS) was measured on the forehead, the temple, and the volar forearm of adult females (n = 97, 52.87 +/- 18.58 years, 20-97 years). Every single measurement contained 2,500 pH values due to the luminescence imaging technique used. Results: pH(SS) slightly increases with age on all three investigated body sites. There are no significant differences in pH(SS) between the three investigated body sites. Conclusion: Adult pH(SS) on the forehead, the temple and the volar forearm increases slightly with age. This knowledge is crucial for adapting medical skin care products. Copyright (C) 2012 S. Karger AG, Base
Panorama vom Bodensee : von Lindau bis Rorschach : gezeichnet auf dem Hoyerberg bei Lindau
No full textN. d. Nat. gez. von Ph. Poeppel ; [Jean] Jacottet lith.KreidelithographiePanorama, unten, rechts: "Lindau bei J. Th. Stettner
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
THE pH VALUE CHANGES IN THE PERIODONTAL POCKETS
No full textMany studies have been done of the pH values in periodontal pockets These studies have suggested that the pH value was influenced by the condition of the surrounding tissue. Thus, the measurement of pH in the periodontal pockets would be effective data to use for diagnosis in periodontal tissue. The sensors which have been used for measuring pH had many disadvantages, however, such as large size, slow response speed, instability in chemical substances, weak physical strength, thermal drift, and so on. Therefore, there have been few reliable data on the pH values in periodontal pockets.
We developed a new type of pH sensor, which was designed for use in the periodontal pocket.
The sensor was made by D.C. reactive sputtering of iridium oxide on solid substances. This sensor was easy to miniaturize, had quick response speed, and was stable with respect to chemical interfere, physical shock, thermal changes, and low electrical resistance. It was used in the present study to measure the pH values in the periodontal pockets of 16 subjects for 7-73 weeks.
Our results showed that the pH values in the periodontal pockets differed among the measuring points and were changeable. The pattern of change was similar in the same subject. The pH value changed depending on tooth condition. The salivary pH showed no correlation with that in the periodontal pockets.journal articl
Performance of miniaturised thick-film solid state pH sensors
No full textThe performance of novel solid-state Thick-Film pH sensor for water quality sampling suitable for deployment in remote catchment areas is described. These miniaturised screen printed planar pH sensors are an alternative to glass pH electrodes, which have many disadvantages such as high-cost, large size, mechanical fragility and limited shape. One of the approaches for improvement of the ruggedness of the pH electrode is the implementation of metal oxides as ion selective electrodes used in combination with screen printed silver/silver chloride (Ag/AgCl) reference electrodes. Various materials of Thick-Film pH sensors have been evaluated, these give a sensitivity close to the theoretical Nernstian value of 59 mV/pH at 25ºC
- …
