7,294 research outputs found
Spray nozzle designs for agricultural aviation applications
Techniques of generating monodisperse sprays and information concerning chemical liquids used in agricultural aviation are surveyed. The periodic dispersion of liquid jet, the spinning disk method, and ultrasonic atomization are the techniques discussed. Conceptually designed spray nozzles for generating monodisperse sprays are assessed. These are based on the classification of the drops using centrifugal force, on using two opposing liquid laden air jets, and on operating a spinning disk at an overloaded flow. Performance requirements for the designs are described and estimates of the operational characteristics are presented
Introduction of the \u3csup\u3e305\u3c/sup\u3eArgā\u3csup\u3e305\u3c/sup\u3eSer mutation in the large extrinsic loop E of the CP43 protein of Synechocystis sp. PCC 6803 leads to the loss of cytochrome c\u3csub\u3e550\u3c/sub\u3e binding to Photosystem II
CP43, a component of Photosystem II (PSII) in higher plants, algae and cyanobacteria, is encoded by the psbC gene. Previous work demonstrated that alteration of an arginine residue occurring at position 305 to serine produced a strain (R305S) with altered PSII characteristics including lower oxygen-evolving activity, fewer assembled reaction centers, higher sensitivity to photoinactivation, etc. [Biochemistry 38 (1999) 1582]. Additionally, it was determined that the mutant exhibited an enhanced stability of its S2 state. Recently, we observed a significant chloride effect under chloride-limiting conditions. The mutant essentially lost the ability to grow photoautotrophically, assembled fewer fully functional PSII reaction centers and exhibited a very low rate of oxygen evolution. Thus, the observed phenotype of this mutation is very similar to that observed for the psbV mutant, which lacks cytochrome c550 (Biochemistry 37 (1998) 1551). A His-tagged version of the R305S mutant was produced to facilitate the isolation of PSII particles. These particles were analyzed for the presence of cytochrome c550. Reduced minus oxidized difference spectroscopy and chemiluminescence examination of Western blots indicated that cytochrome c550 was absent in these PSII particles. Whole cell extracts from the R305S mutant, however, contained a similar amount of cytochrome c550 to that observed in the control strain. These results indicate that the mutation R305S in CP43 prevents the strong association of cytochrome c550 with the PSII core complex. We hypothesize that this residue is involved in the formation of the binding domain for the cytochrome. Ā© 2002 Elsevier Science B.V. All rights reserved
Realism and the wave-function
Realism -- the idea that the concepts in physical theories refer to 'things'
existing in the real world -- is introduced as a tool to analyze the status of
the wave-function. Although the physical entities are recognized by the
existence of invariant quantities, examples from classical and quantum physics
suggest that not all the theoretical terms refer to the entities: some terms
refer to properties of the entities, and some terms have only an epistemic
function. In particular, it is argued that the wave-function may be written in
terms of classical non-referring and epistemic terms. The implications for
realist interpretations of quantum mechanics and on the teaching of quantum
physics are examined.Comment: No figure
Src, PKCĪ±, and PKCĪ“ are required for Ī±vĪ²3 integrin-mediated metastatic melanoma invasion
<p>Abstract</p> <p>Background</p> <p>Integrins, cell-surface receptors that mediate adhesive interactions between cells and the extracellular matrix (ECM), play an important role in cancer progression. Expression of the vitronectin receptor Ī±vĪ²3 integrin correlates with increased invasive and metastatic capacity of malignant melanomas, yet it remains unclear how expression of this integrin triggers melanoma invasion and metastasis.</p> <p>Results</p> <p>Two melanoma cell lines C8161.9 and M14 both express high levels of Ī±vĪ²3 integrin and adhere to vitronectin. However, only the highly metastatic C8161.9 cells are capable of invading vitronectin-enriched Matrigel in an Ī±vĪ²3-depenent manner. Elevated levels of PKCĪ± and PKCĪ“, and activated Src were detected specifically in the highly metastatic melanoma cells, but not in the low metastatic M14 cells. Inhibition of Src or PKC activity suppressed Ī±vĪ²3-dependent invasion. Furthermore, over expression of Src or PKCĪ± and PKCĪ“ was sufficient to confer Ī±vĪ²3-dependent invasiveness to M14 cells. Stress fiber formation and focal adhesion formation were almost completely absent in C8161.9 cells compared to M14 cells. Inhibition of Src signaling was sufficient to restore normal actin architecture, and resulted in decreased p190RhoGAP phosphorylation and enhanced RhoA activity. Src had no effect on Rac activity. Loss of PKCĪ± expression, but not PKCĪ“, by siRNA inhibited Rac and PAK activity as well as invasiveness. Loss of PKCĪ± restored focal adhesion formation and partially restored stress fiber formation, while loss of PKCĪ“ primarily restored stress fibers.</p> <p>Conclusion</p> <p>The misregulated expression of PKCĪ± and PKCĪ“ and elevated Src activity in metastatic melanoma cells is required for efficient Ī±vĪ²3-mediated invasion. PKCĪ± and Src enhance Ī±vĪ²3-mediated invasion in part by increasing the GTPase activity of Rac relative to RhoA. PKCĪ± influences focal adhesion formation, while PKCĪ“ controls stress fibers.</p
Teleological Essentialism
Placeholder essentialism is the view that there is a causal essence that holds category members together, though we may not know what the essence is. Sometimes the placeholder can be filled in by scientific essences, such as when we acquire scientific knowledge that the atomic weight of gold is 79. We challenge the view that placeholders are elaborated by scientific essences. On our view, if placeholders are elaborated, they are elaborated Aristotelian essences, a telos. Utilizing the same kinds of experiments used by traditional essentialistsāinvolving superficial change (study 1), transformation of insides (study 2), acquired traits (study 3) and inferences about offspring (study 4)āwe find support for the view that essences are elaborated by a telos. And we find evidence (study 5) that teleological essences may generate category judgments
Theories of Reference: What Was the Question?
The new theory of reference has won popularity. However, a number of noted philosophers have also attempted to reply to the critical arguments of Kripke and others, and aimed to vindicate the description theory of reference. Such responses are often based on ingenious novel kinds of descriptions, such as rigidified descriptions, causal descriptions, and metalinguistic descriptions. This prolonged debate raises the doubt whether different parties really have any shared understanding of what the central question of the philosophical theory of reference is: what is the main question to which descriptivism and the causal-historical theory have presented competing answers. One aim of the paper is to clarify this issue. The most influential objections to the new theory of reference are critically reviewed. Special attention is also paid to certain important later advances in the new theory of reference, due to Devitt and others
How Events Come Into Being: EEQT, Particle Tracks, Quantum Chaos, and Tunneling Time
In sections 1 and 2 we review Event Enhanced Quantum Theory (EEQT). In
section 3 we discuss applications of EEQT to tunneling time, and compare its
quantitative predictions with other approaches, in particular with
B\"uttiker-Larmor and Bohm trajectory approach. In section 4 we discuss quantum
chaos and quantum fractals resulting from simultaneous continuous monitoring of
several non-commuting observables. In particular we show self-similar,
non-linear, iterated function system-type, patterns arising from quantum jumps
and from the associated Markov operator. Concluding remarks pointing to
possible future development of EEQT are given in section 5.Comment: latex, 27 pages, 7 postscript figures. Paper submitted to Proc.
Conference "Mysteries, Puzzles And Paradoxes In Quantum Mechanics, Workshop
on Entanglement And Decoherence, Palazzo Feltrinelli, Gargnano, Garda Lake,
Italy, 20-25 September, 199
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