Home About us Contact
|
Home About us Contact | ||
|
|
||
Exponential Growth (exponential + growth)
Terms modified by Exponential Growth Selected AbstractsNumerical experiments on dynamo action in sheared and rotating turbulenceASTRONOMISCHE NACHRICHTEN, Issue 7 2008T. A. Yousef Abstract Numerical simulations of forced turbulence in elongated shearing boxes are carried out to demonstrate that a nonhelical turbulence in conjunction with a linear shear can give rise to a mean-field dynamo. Exponential growth of magnetic field at scales larger than the outer (forcing) scale of the turbulence is found. Over a range of values of the shearing rate S spanning approximately two orders of magnitude, the growth rate of the magnetic field is proportional to the imposed shear, , , S, while the characteristic spatial scale of the field is lB , S,1/2. The effect is quite general: earlier results for the nonrotating case by Yousef et al. (2008) are extended to shearing boxes with Keplerian rotation; it is also shown that the shear dynamo mechanism operates both below and above the threshold for the fluctuation dynamo. The apparently generic nature of the shear dynamo effect makes it an attractive object of study for the purpose of understanding the generation of magnetic fields in astrophysical systems. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Exponential growth for the wave equation with compact time-periodic positive potentialCOMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 4 2009Ferruccio Colombini We prove the existence of smooth positive potentials V(t, x), periodic in time and with compact support in x, for which the Cauchy problem for the wave equation utt , ,xu + V(t, x)u = 0 has solutions with exponentially growing global and local energy. Moreover, we show that there are resonances, z , ,, |z| > 1, associated to V(t, x). © 2008 Wiley Periodicals, Inc. [source] Seasonal polydomy in a polygynous supercolony of the odorous house ant, Tapinoma sessileECOLOGICAL ENTOMOLOGY, Issue 6 2008GRZEGORZ BUCZKOWSKI Abstract 1.,The odorous house ant, Tapinoma sessile, is a native ant species common throughout North America. In its natural habitat, T. sessile is a low-key species that consists of small colonies. In invaded urban areas, T. sessile exhibits extreme polygyny and polydomy and becomes a dominant invasive pest. 2.,The current study examined: (i) the density, persistence, and the spatial distribution of nests in a large supercolony of T. sessile, (ii) trail abundance and overall colony connectivity as facilitated by the network of trails, (iii) the abundance and the spatial distribution of competing ant species, and (iv) the effect of environmental factors on the number and distribution of T. sessile nests. 3.,A distinct pattern of seasonal polydomy was observed, whereby the colony undergoes an annual fission-fusion cycle. The colony occupies one or a few nests during the winter, experiences rapid exponential growth in the spring to colonize available nesting sites, reaches maximum nest density in the summer, and again coalesces in the winter, returning to the same winter location year after year. The trails show spatio-temporal variation as well, depending on the location of nesting and foraging sites. Furthermore, nest movements may be driven by soil microclimate and proximity to man-made structures. 4.,In total, 119 ant nests were discovered in a 3.15 ha plot, 90 (76%) of which belonged to T. sessile. Tapinoma sessile exhibited strong colony connectivity as 78/90 (87%) of nests were connected to at least one other nest by a trail. Mean persistence time for T. sessile nests was 133 ± 5 days. 5.,Results indicate that T. sessile is a highly adaptable native ant species that exhibits a high degree of flexibility in its colony social structure. A high degree of polygyny and polydomy may contribute to its ecological dominance and pest status in urban environments. [source] Ricci flows and infinite dimensional algebrasFORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 6-7 2004I. Bakas The renormalization group equations of two-dimensional sigma models describe geometric deformations of their target space when the world-sheet length changes scale from the ultra-violet to the infra-red. These equations, which are also known in the mathematics literature as Ricci flows, are analyzed for the particular case of two-dimensional target spaces, where they are found to admit a systematic description as Toda system. Their zero curvature formulation is made possible with the aid of a novel infinite dimensional Lie algebra, which has anti-symmetric Cartan kernel and exhibits exponential growth. The general solution is obtained in closed form using Bäcklund transformations, and special examples include the sausage model and the decay process of conical singularities to the plane. Thus, Ricci flows provide a non-linear generalization of the heat equation in two dimensions with the same dissipative properties. Various applications to dynamical problems of string theory are also briefly discussed. Finally, we outline generalizations to higher dimensional target spaces that exhibit sufficient number of Killing symmetries. [source] Allocation of above-ground growth is related to light in temperate deciduous saplingsFUNCTIONAL ECOLOGY, Issue 4 2003D. A. King Summary 1Allocational shifts in response to light may be an important factor in allowing plants to survive in shade, while increasing their extension rates and competitive ability in sun. To investigate this response, the allocation of above-ground growth between leaves, branches and stems was studied in saplings of Acer pensylvanicum L. and Castenea dentata (Marsh.) Borkh. in the Appalachian mountains of western Virginia, USA. Measurements of current leaf biomass, current and past year leaf numbers and the growth ring widths of branches and stem were used to estimate biomass partitioning for saplings growing in locations ranging from forest understorey to large openings. 2Both species showed higher leaf area per unit leaf biomass (SLA) and higher allocation of above-ground growth to leaves in shade than in sun. 3There were no differences between species in the slopes of the relationships of allocation and SLA vs estimated irradiance, but SLA was significantly greater in A. pensylvanicum than in C. dentata at a given light level. Hence, somewhat lower production per unit leaf area is required to maintain the canopy in A. pensylvanicum, consistent with foresters' ratings of greater shade tolerance for this species. 4Greater foliar allocation in shade than sun has also been observed in broad-leaved evergreen saplings, but generally not in seedlings. This difference is probably related to differences in size and age between seedlings and saplings. Young seedlings typically show exponential growth with no immediate foliar losses, while shaded saplings lie closer to the steady state where new leaves replace old ones with little additional stem growth. 5Thus trees shift their allocation patterns in an acclimatory fashion, depending on their size and light environment, with the costs of replacing senesced leaves becoming of consequence as juveniles age. [source] Saturation and time dependence of geodynamo modelsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2010M. Schrinner SUMMARY In this study we address the question under which conditions a saturated velocity field stemming from geodynamo simulations leads to an exponential growth of the magnetic field in a corresponding kinematic calculation. We perform global self-consistent geodynamo simulations and calculate the evolution of a kinematically advanced tracer field. The self-consistent velocity field enters the induction equation in each time step, but the tracer field does not contribute to the Lorentz force. This experiment has been performed by Cattaneo and Tobias and is closely related to the test field method by Schrinner et al. We find two dynamo regimes in which the tracer field either grows exponentially or approaches a state aligned with the actual self-consistent magnetic field after an initial transition period. Both regimes can be distinguished by the Rossby number and coincide with the dipolar and multipolar dynamo regimes identified by Christensen and Aubert. Dipolar dynamos with low Rossby number are kinematically stable whereas the tracer field grows exponentially in the multipolar dynamo regime. This difference in the saturation process for dynamos in both regimes comes along with differences in their time variability. Within our sample of 20 models, solely kinematically unstable dynamos show dipole reversals and large excursions. The complicated time behaviour of these dynamos presumably relates to the alternating growth of several competing dynamo modes. On the other hand, dynamos in the low Rossby number regime exhibit a rather simple time dependence and their saturation merely results in a fluctuation of the fundamental dynamo mode about its critical state. [source] Influence of the growth phase and culture medium on the survival of Mannheimia haemolytica during storage at different temperaturesJOURNAL OF APPLIED MICROBIOLOGY, Issue 1 2004E. van Rensburg Abstract Aims:, To quantify the influence of the growth phase, storage temperature and nutritional quality of the plate count medium on the apparent viability of Mannheimia haemolytica during storage at different temperatures. Methods and Results:,Mannheimia haemolytica was grown in shake flasks and in aerobic continuous culture to investigate factors affecting cell viability during storage, which was determined using plate counts on different media and epifluorescence microscopy. The high specific death rates of cells harvested after cessation of exponential growth and stored at 22, 4, ,18 and ,75°C could be related to the rapid onset of exponential death in batch cultures. Yeast extract supplementation of the culture medium increased the viability of cells at most of the above-mentioned storage temperatures. Of the total cell count in continuous culture, only 48% could be recovered on brain,heart infusion agar, whereas supplementation of the agar medium with foetal calf serum increased the plate count to 71% of the total count. Conclusions:,Mannheimia haemolytica cells harvested from the exponential growth phase had the highest survival rate during storage at low temperatures. Plate count values also depended on the nutritional quality of the agar medium. Significance and Impact of the Study:, Results presented here impact on the procedures for culture preservation and plate count enumeration of this fastidious animal pathogen. [source] Characterization and mechanism of action of cerein 7, a bacteriocin produced by Bacillus cereus Bc7JOURNAL OF APPLIED MICROBIOLOGY, Issue 2 2000J.C. Oscáriz Cerein 7 is a peptidic antibiotic produced by Bacillus cereus Bc7 (CECT 5148) at the end of exponential growth but before sporulation onset. Cerein 7 has a broad spectrum of antibacterial activity against Gram-positive bacteria, but it is inactive against Gram-negative bacteria. The sequence of its amino-terminal end and its characteristics of hydrophobicity and molecular mass make cerein 7 unique among the bacteriocins produced by the soil bacterium B. cereus. In this paper a further characterization of cerein 7 is presented, it is shown that it can be classified as a Klaenhammer's class II bacteriocin and that its mode of action corresponds to that of a membrane-active compound. [source] The Perils of Cognitive Enhancement and the Urgent Imperative to Enhance the Moral Character of HumanityJOURNAL OF APPLIED PHILOSOPHY, Issue 3 2008INGMAR PERSSON abstract As history shows, some human beings are capable of acting very immorally.1 Technological advance and consequent exponential growth in cognitive power means that even rare evil individuals can act with catastrophic effect. The advance of science makes biological, nuclear and other weapons of mass destruction easier and easier to fabricate and, thus, increases the probability that they will come into the hands of small terrorist groups and deranged individuals. Cognitive enhancement by means of drugs, implants and biological (including genetic) interventions could thus accelerate the advance of science, or its application, and so increase the risk of the development or misuse of weapons of mass destruction. We argue that this is a reason which speaks against the desirability of cognitive enhancement, and the consequent speedier growth of knowledge, if it is not accompanied by an extensive moral enhancement of humankind. We review the possibilities for moral enhancement by biomedical and genetic means and conclude that, though it should be possible in principle, it is in practice probably distant. There is thus a reason not to support cognitive enhancement in the foreseeable future. However, we grant that there are also reasons in its favour, but we do not attempt to settle the balance between these reasons for and against. Rather, we conclude that if research into cognitive enhancement continues, as it is likely to, it must be accompanied by research into moral enhancement. [source] Frequency of Man-Made Disasters in the 20th CenturyJOURNAL OF CONTINGENCIES AND CRISIS MANAGEMENT, Issue 1 2006Les Coleman This paper analyses two disaster databases maintained by the Center for Research on the Epidemiology of Disasters and by Emergency Management Australia. The objective is to quantify the frequency, nature and changes in man-made disasters in industrialised countries during the past century. The analysis shows an exponential growth in disaster frequency, largely due to an increase in traditional hazards such as fires and explosions, rather than from new technologies. Although the number of incidents has grown, this has been offset by a decline in fatalities per incident. An important implication of these results is that regulatory oversight and internal corporate governance processes are inadequate to ensure effective management of modern industrial risks. [source] Attributed disability: a spot of local difficultyJOURNAL OF EVALUATION IN CLINICAL PRACTICE, Issue 1 2006George Peat PhD MCSP Abstract There has been an exponential growth of publications relating to the development and application of health measurement instruments. Condition-specific measures have formed a large part of this trend. This article questions the rationale behind the concept of condition-specific disability, a common domain in such measures, taking musculoskeletal medicine as an example. It argues that physical functions are seldom unique to a specific condition and that measurement specificity therefore relies on attributing functional consequences to the health condition of interest. The presence of multi-morbidity (musculoskeletal and non-musculoskeletal), and the influence of personal and environmental factors, pose problems for attribution that have seldom been empirically investigated. Furthermore, attributing disability to a specific health condition of interest potentially limits insights into important interventions such as managing co-morbid interactions and targeting barriers in the physical, social, and attitudinal environment. Efforts to identify regionally relevant item content and to measure participation in daily life are a step in the right direction. Attribution is not needed for either. [source] Valuing of firms' prior knowledge: a measure of knowledge distanceKNOWLEDGE AND PROCESS MANAGEMENT: THE JOURNAL OF CORPORATE TRANSFORMATION, Issue 2 2003Shantha Liyanage Knowledge, especially scientific and technological knowledge, grows according to knowledge trajectories and guideposts that make up the prior knowledge of an organization. We argue that these knowledge structures and their specific components lead to successful innovation. A firm's prior knowledge facilitates the absorption of new knowledge, thereby renewing a firm's systematic search, transfer and acquisition of knowledge and capabilities. In particular, the exponential growth in biotechnology is characterized by the convergence of disparate scientific and technological knowledge resources. This paper examines the shift from protein-based to DNA-based diagnostic technologies as an example, to quantify the value of a firm's prior knowledge using relative values of knowledge distance. The distance between core prior knowledge and the rate of transition from one knowledge system to another has been identified as a proxy for the value a firm's prior knowledge. The overall ,difficulty of transition' from one technology paradigm to another is discussed. We argue this transition is possible when the knowledge distance is minimal and the transition process has a correspondingly high value of absorptive capacities. Our findings show knowledge distance is a determinant of the feasibility, continuity and capture of scientific and technological knowledge. Copyright © 2003 John Wiley & Sons, Ltd. [source] Low magnetic fields behavior of photon echo in LuLiF4:Er3+LASER PHYSICS LETTERS, Issue 9 2006V. N. Lisin Abstract It is reported about the first observation and studying of the photon echo in LuLiF4:Er3+. The energy transition is 4I15/2 , 4F9/2 (, = 6536 Å). The density of ErF3 is 0.025 wt%. The operation temperature is 1.9 K. Measurements were spent at low (up to 1200 Oe) and even zero external magnetic fields. It was studied a behavior of the photon echo intensity versus the magnetic field magnitude and direction about the crystal axis C and versus the laser pulse separation t12. It was observed an exponential growth and then, after some plateau, an exponential decreasing of the photon echo intensity as a function of magnetic field with increasing of the magnetic field from zero value. The parameters describing the exponential growth and decreasing are not depended on direction of magnetic field. Value of a magnetic field at which the echo intensity accepts the maximum, and quantity of this maximum decrease with increased the pulse separation t12 and the angle , between the magnetic field and crystal axis. The echo intensity exponentially decreases with increased , . The parameter describing the exponential decreasing is not depended on the magnitude of the field. The echo intensity as a function of pulse separation shows exponential decay. The phase relaxation time is depended on the magnitude and direction of the magnetic field. T2 is equal to 202 ± 16 ns at zero magnetic field. Phenomenological formula is suggested, which qualitatively presents the mentioned dependencies. Polarization properties of the backward photon echo in this crystal are studied also. (© 2006 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Predicting the probability of progression-free survival in patients with small hepatocellular carcinomaLIVER TRANSPLANTATION, Issue 4 2002Steve J. Cheng Allocation of cadaveric livers to patients based on such objective medical urgency data as the Model for End-Stage Liver Disease (MELD) score may not benefit patients with small hepatocellular carcinomas (HCCs). To ensure that these patients have a fair opportunity of receiving a cadaveric organ, the risk for death caused by HCC and tumor progression beyond 5 cm should be considered. Using a Markov model, two hypothetical cohorts of patients with small hepatomas were assumed to have either (1) Gompertzian tumor growth, in which initial exponential growth decreases as tumor size increases; or (2) rapid exponential growth. The model tracked the number of patients who either died or had tumor progression beyond 5 cm. These results were used to back-calculate an equivalent MELD score for patients with small HCCs. All probabilities in the model were varied simultaneously using a Monte Carlo simulation. The Gompertzian growth model predicted that patients with a 1- and 4-cm tumor have 1-year progression-free survival rates of 70% (HCC-specific MELD score 6) and 66% (HCC-specific MELD score 8), respectively. When assuming rapid exponential growth, patients with a 1- and 4-cm tumor have progression-free survival rates of 69% (HCC-specific MELD score 6) and 12% (HCC-specific MELD score 24), respectively. Our model predicted that the risk for death caused by HCC or tumor progression beyond 5 cm should increase with larger initial tumor size in patients with small hepatomas. To ensure that these patients have a fair opportunity to receive a cadaveric organ, HCC-specific scores predicted by our model could be added to MELD scores of patients with HCC. [source] Dunkl transforms and Dunkl convolutions on functions and distributions with restricted growthMATHEMATISCHE NACHRICHTEN, Issue 6 2009Jorge J. Betancor Abstract In this paper we investigate Dunkl transforms and Dunkl convolutions on R in some spaces of functions and distributions with exponential growth introduced by Hasumi [12] (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Phylogeographic analysis of the red seaweed Palmaria palmata reveals a Pleistocene marine glacial refugium in the English ChannelMOLECULAR ECOLOGY, Issue 3 2005JIM PROVAN Abstract Phylogeography has provided a new approach to the analysis of the postglacial history of a wide range of taxa but, to date, little is known about the effect of glacial periods on the marine biota of Europe. We have utilized a combination of nuclear, plastid and mitochondrial genetic markers to study the biogeographic history of the red seaweed Palmaria palmata in the North Atlantic. Analysis of the nuclear rDNA operon (ITS1-5.8S-ITS2), the plastid 16S- trnI- trnA-23S-5S, rbcL- rbcS and rpl12- rps31- rpl9 regions and the mitochondrial cox2,3 spacer has revealed the existence of a previously unidentified marine refugium in the English Channel, along with possible secondary refugia off the southwest coast of Ireland and in northeast North America and/or Iceland. Coalescent and mismatch analyses date the expansion of European populations from approximately 128 000 bp and suggest a continued period of exponential growth since then. Consequently, we postulate that the penultimate (Saale) glacial maximum was the main event in shaping the biogeographic history of European P. palmata populations which persisted throughout the last (Weichselian) glacial maximum (c. 20 000 bp) in the Hurd Deep, an enigmatic trench in the English Channel. [source] Ribosome rescue: tmRNA tagging activity and capacity in Escherichia coliMOLECULAR MICROBIOLOGY, Issue 2 2005Sean D. Moore Summary When protein synthesis stalls in bacteria, tmRNA acts first as a surrogate tRNA and then as an mRNA in a series of reactions that append a peptide tag to the nascent polypeptide and ,rescue' the ribosome. The peptide tag encoded by wild-type tmRNA promotes rapid degradation of rescued proteins. Using a mutant tmRNA that encodes a tag that does not lead to degradation, we demonstrate that the synthesis of approximately 0.4% of all proteins terminates with tagging and ribosome rescue during normal exponential growth of Escherichia coli. The frequency of tagging was not significantly increased in cells expressing very high levels of tmRNA and its binding protein SmpB, suggesting that recognition of ,stalled' ribosomes does not involve competition between tmRNA and other translation factors for A-sites that are unoccupied transiently during protein synthesis. When the demand for ribosome rescue was increased artificially by overproduction of a non-stop mRNA, tmRNA levels did not increase but tmRNA-mediated tagging increased substantially. Thus, the ribosome-rescue system usually operates well below capacity. [source] DksA represses ribosomal gene transcription in Pseudomonas aeruginosa by interacting with RNA polymerase on ribosomal promotersMOLECULAR MICROBIOLOGY, Issue 4 2005Karl Perron Summary In Escherichia coli transcription of ribosomal RNA (rRNA) is regulated by the H-NS and Fis proteins, as well as by the small signal molecule ppGpp and the initiating nucleotides. During amino acid starvation, the concentration of ppGpp increases, and binding of this alarmone to RNA polymerase (RNAP) leads to inhibition of rRNA transcription, a regulatory event called stringent response. Here we show that in Pseudomonas aeruginosa DksA, a protein with pleiotropic effects, is a negative regulator of rRNA transcription both during exponential growth and stringent conditions. A dksA mutant overexpresses rRNA, without being affected in the production of ppGpp. Cell-fractionation and chromosome immunoprecipitation experiments demonstrate that DksA is associated with DNA, in particular with promoters of ribosomal genes in vivo. The binding to rRNA promoters specifically increases during stringent response, and correlates with the binding of RNAP to these regions. Moreover DksA can be copurified with RNAP subunits in vivo. DNA band shift experiments show that DksA, in synergy with ppGpp, increases the binding of RNAP to ribosomal promoters. Therefore DksA might be a new regulator of rRNA transcription in P. aeruginosa. [source] Association of mycothiol with protection of Mycobacterium tuberculosis from toxic oxidants and antibioticsMOLECULAR MICROBIOLOGY, Issue 6 2003Nancy A. Buchmeier Summary Mycothiol, MSH or 1d - myo -inosityl 2-(N -acetyl- l -cysteinyl)amido-2-deoxy- , - d -glucopyranoside, is an unusual conjugate of N -acetylcysteine (AcCys) with 1d - myo -inosityl 2-acetamido-2-deoxy-,- d -glucopyranoside (GlcN-Ins), and is the major low-molecular-mass thiol in mycobacteria. Mycothiol has antioxidant activity as well as the ability to detoxify a variety of toxic compounds. Because of these activities, MSH is a candidate for protecting Mycobacterium tuberculosis from inactivation by the host during infections as well as for resisting antituberculosis drugs. In order to define the protective role of MSH for M. tuberculosis, we have constructed an M. tuberculosis mutant in Rv1170, one of the candidate MSH biosynthetic genes. During exponential growth, the Rv1170 mutant bacteria produced , 20% of wild-type levels of MSH. Levels of the Rv1170 substrate, GlcNAc-Ins, were elevated, whereas those of the product, GlcN-Ins, were reduced. This establishes that the Rv1170 gene encodes for the major GlcNAc-Ins deacetylase activity (termed MshB) in the MSH biosynthetic pathway of M. tuberculosis. The Rv1170 mutant grew poorly on agar media lacking catalase and oleic acid, and had heightened sensitivities to the toxic oxidant cumene hydroperoxide and to the antibiotic rifampin. In addition, the mutant was more resistant to isoniazid, suggesting a role for MSH in activation of this prodrug. These data indicate that MSH contributes to the protection of M. tuberculosis from oxidants and influences resistance to two first-line antituberculosis drugs. [source] Intracellular translation initiation factor levels in Saccharomyces cerevisiae and their role in cap-complex functionMOLECULAR MICROBIOLOGY, Issue 2 2002Tobias Von Der Haar Summary Knowledge of the balance of activities of eukaryotic initiation factors (eIFs) is critical to our understanding of the mechanisms underlying translational control. We have therefore estimated the intracellular levels of 11 eIFs in logarithmically growing cells of Saccharomyces cerevisiae using polyclonal antibodies raised in rabbits against recombinant proteins. Those factors involved in 43S complex formation occur at levels comparable (i.e. within a 0.5- to 2.0-fold range) to those published for ribosomes. In contrast, the subunits of the cap-binding complex eIF4F showed considerable variation in their abundance. The helicase eIF4A was the most abundant eIF of the yeast cell, followed by eIF4E at multiple copies per ribosome, and eIF4B at approximately one copy per ribosome. The adaptor protein eIF4G was the least abundant of the eIF4 factors, with a copy number per cell that is substoichiometric to the ribosome and similar to the abundance of mRNA. The observed excess of eIF4E over its functional partner eIF4G is not strictly required during exponential growth: at eIF4E levels artificially reduced to 30% of those in wild-type yeast, growth rates and the capacity for general protein synthesis are only minimally affected. This demonstrates that eIF4E does not exercise a higher level of rate control over translation than other eIFs. However, other features of the yeast life cycle, such as the control of cell size, are more sensitive to changes in eIF4E abundance. Overall, these data constitute an important basis for developing a quantitative model of the workings of the eukaryotic translation apparatus. [source] Chromosome replication patterns in the hyperthermophilic euryarchaea Archaeoglobus fulgidus and Methanocaldococcus (Methanococcus) jannaschiiMOLECULAR MICROBIOLOGY, Issue 5 2002Sophie Maisnier-Patin Summary We analysed chromosome replication patterns in the two hyperthermophilic euryarchaea Archaeoglobus fulgidus and Methanocaldococcus (Methanococcus) jannaschii by marker frequency analysis (MFA). For A. fulgidus, the central region of the chromosomal physical map displayed a higher relative abundance in gene dosage during exponential growth, with two continuous gradients to a region of lower abundance at the diametrically opposite side of the genome map. This suggests bidirectional replication of the A. fulgidus chromosome from a single origin. The organization of the putative replication origin region relative to the cdc6, mcm and DNA polymerase genes differed from that reported for Pyrococcus species. No single replication origin or termination regions could be identified for M. jannaschii, adding to the list of unusual properties of this organism. The organization of the A. fulgidus cell cycle was characterized by flow cytometry analysis of the samples from which genomic DNA was extracted for MFA. The relative lengths of the cell cycle periods were found to be similar to those of crenarchaea. [source] Spo0A directly controls the switch from acid to solvent production in solvent-forming clostridiaMOLECULAR MICROBIOLOGY, Issue 5 2000Adriana Ravagnani The spo0A genes of Clostridium beijerinckii NCIMB 8052 and Clostridium cellulolyticum ATCC 35319 were isolated and characterized. The C-terminal DNA-binding domains of the predicted products of spo0A from these two organisms, as well as 16 other taxonomically diverse species of Bacillus and Clostridium, show extensive amino acid sequence conservation (56% identity, 65% similarity over 104 residues). A 12-amino-acid motif (SRVERAIRHAIE) that forms the putative DNA recognition helix is particularly highly conserved, suggesting a common DNA target. Insertional inactivation of spo0A in C. beijerinckii blocked the formation of solvents (as well as spores and granulose). Sequences resembling Spo0A-binding motifs (TGNCGAA) are found in the promoter regions of several of the genes whose expression is modulated at the onset of solventogenesis in Clostridium acetobutylicum and C. beijerinckii. These include the upregulated adc gene, encoding acetoacetate decarboxylase (EC 4.1.1.4), and the downregulated ptb gene, encoding phosphotransbutyrylase (EC 2.3.1.c). In vitro gel retardation experiments using C. acetobutylicum adc and C. beijerinckii ptb promoter fragments and recombinant Bacillus subtilis and C. beijerinckii Spo0A suggested that adc and ptb are directly controlled by Spo0A. The binding affinity was reduced when the 0A boxes were destroyed, and enhanced when they were modified to conform precisely to the consensus sequence. In vivo analysis of wild-type and mutagenized promoters transcriptionally fused to the gusA reporter gene in C. beijerinckii validated this hypothesis. Post-exponential phase expression from the mutagenized adc promoter was substantially reduced, whereas expression from the mutagenized ptb promoter was not shut down at the end of exponential growth. [source] Does population ecology have general laws?OIKOS, Issue 1 2001Peter Turchin There is a widespread opinion among ecologists that ecology lacks general laws. In this paper I argue that this opinion is mistaken. Taking the case of population dynamics, I point out that there are several very general law-like propositions that provide the theoretical basis for most population dynamics models that were developed to address specific issues. Some of these foundational principles, like the law of exponential growth, are logically very similar to certain laws of physics (Newton's law of inertia, for example, is almost a direct analogue of exponential growth). I discuss two other principles (population self-limitation and resource-consumer oscillations), as well as the more elementary postulates that underlie them. None of the "laws" that I propose for population ecology are new. Collectively ecologists have been using these general principles in guiding development of their models and experiments since the days of Lotka, Volterra, and Gause. [source] Inactivation of Virulent Burkholderia pseudomallei by SunlightPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2009Jose-Luis Sagripanti The goal of this study was to determine the sensitivity of virulent Burkholderia pseudomallei to natural sunlight. We describe solar dosimetry calibrated to integrate radiation between 295 and 305 nm and an exposure system that minimizes thermal effects on bacterial cells. Burkholderia pseudomallei cells were either exposed to sunlight in UV transparent dishes or maintained in the dark covered by opaque foil. The cells maintained in the dark remained at constant levels for the duration of all experiments. The exposed cells nearby were killed with a kinetic studied through 5 Log10 inactivation. We found that cells in stationary phase of growth were nearly two-fold more resistant to sunlight than cells in lag or exponential growth. A virulent strain of B. pseudomallei that produced mucoid colonies showed sensitivity to sunlight similar to both a virulent strain that produced nonmucoid colonies and a strain of B. thailandensis. The inactivation of B. pseudomallei by sunlight in different types of water of environmental relevance or inside amoebae was investigated. The sensitivity of virulent B. pseudomallei was calculated and its comparison with previous studies employing monochromatic germicidal light (254 nm) is discussed. This may be the first report in the open literature of the inactivation of a virulent biological threat agent by natural sunlight. These data should assist in estimating the risk for contracting melioidosis and in predicting the time period during which B. pseudomallei remains infectious after an accidental or intentional release in the environment. [source] Room temperature gas sensor based on porous silicon/metal oxide structurePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2007V. M. Arakelyan Abstract N-type TiO2,x and In2O3 · SnO2 thin films were deposited onto p-type porous silicon layer which was formed by common electrochemical anodization. The current-voltage characteristics of obtained structures and sensitivity to different concentrations of hydrogen in air were studied. Measurements were carried out at room temperature. As shown results of measurements, an exponential growth of the current in forward branch of the current-voltage characteristics of the device made of TiO2,xlayer was detected. Higher sensitivity to hydrogen of the TiO2,x -porous silicon sensor in comparison to structure made of In2O3 · SnO2 film was detected at room temperature (without preheating of work body of the sensor). (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Histological investigation of stripe rust (Puccinia striiformis f.sp. tritici) development in resistant and susceptible wheat cultivarsPLANT PATHOLOGY, Issue 4 2006J. Moldenhauer The wheat cultivar Kariega expresses complete adult plant resistance against stripe rust, whereas cv. Avocet S is susceptible. Using confocal laser scanning microscopy, initial fungal penetration into flag leaves was identical in both cultivars, with directional germ-tube growth towards stomata that were penetrated without the formation of an appressorium, followed by differentiation of a substomatal vesicle, infection hyphae, haustorial mother cells and haustoria. During the following 4 days, further fungal development occurred more quickly in the resistant than in the susceptible cultivar. However, by 7 days postinoculation (dpi) the situation changed, with exponential growth of the pathogen occurring only in the susceptible line. Induced cellular lignification, a typical defence reaction of cereals, was observed at 4 dpi in the resistant cultivar, and 2 days later lignified tissue completely surrounded the fungal colonies. In the susceptible cultivar, isolated lignified host cells occurred at 6 dpi, and long, unbranched fungal hyphae outgrowing the resistance reaction were observed. [source] An analytical model for the rapid intensification of tropical cyclonesTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 642 2009Chanh Q. Kieu Abstract The nonlinearity and complexity of the primitive equations have been key obstacles to our understanding of tropical cyclones (TCs), particularly in relation to the dynamical processes leading to their rapid intensification. In this study, an axisymmetric model, in which all nonlinear terms in the horizontal momentum equations are retained, is used to examine analytically the effects of organized deep convection on TC rapid intensification. By prescribing a vertical profile of the vertical motion with exponential growth in the core region, a class of exact time-dependent solutions for the primary circulations of TCs are obtained. The analytical solutions are shown to capture well many observed dynamical structures in both the core and outer regions and the rapid growth of TCs in terms of maximum winds and central pressure drops. The analytical solutions reveal that (1) the rotational flows in the inner-core region grow double-exponentially, and the central pressure drops occur at rates much faster than the rotational growth; (2) the amplification rates of the primary circulations differ profoundly from those of the secondary circulations; (3) the rotational flows tend to grow from the bottom upwards with the fastest growth occurring at the lowest levels; and (4) the TC growth rates depend critically on the vertical structure of tangential flows, with a faster rate for a lower-level peak rotation. The nonlinear dynamics are shown to play an important role in the rapid growth of TCs. It is demonstrated that the analytical solutions can also be used to construct dynamically consistent vortices for the initialization of TC models. Limitations and possible improvements of the analytical model are also discussed. Copyright © 2009 Royal Meteorological Society [source] Structure validation in chemical crystallographyACTA CRYSTALLOGRAPHICA SECTION D, Issue 2 2009Anthony L. Spek Automated structure validation was introduced in chemical crystallography about 12,years ago as a tool to assist practitioners with the exponential growth in crystal structure analyses. Validation has since evolved into an easy-to-use checkCIF/PLATON web-based IUCr service. The result of a crystal structure determination has to be supplied as a CIF-formatted computer-readable file. The checking software tests the data in the CIF for completeness, quality and consistency. In addition, the reported structure is checked for incomplete analysis, errors in the analysis and relevant issues to be verified. A validation report is generated in the form of a list of ALERTS on the issues to be corrected, checked or commented on. Structure validation has largely eliminated obvious problems with structure reports published in IUCr journals, such as refinement in a space group of too low symmetry. This paper reports on the current status of structure validation and possible future extensions. [source] The origin of our galactic magnetic fieldASTRONOMISCHE NACHRICHTEN, Issue 1 2010R.M. Kulsrud Abstract A serious difficulty with the standard alpha-omega theory of the origin of galactic magnetic fields involves the question of flux expulsion. This is intimately related to flux freezing. The alpha-omega theory is shown in the context of the giant superbubble explosions that have a large impact on the physics of the interstellar medium. It is shown that superbubbles alone can duplicate the processes of the alpha-omega dynamo and produce exponential growth of the galactic magnetic field. The possibility of the blow-out of pieces of the magnetic field is discussed and it is shown that they have the potential to solve the flux-expulsion problem. However, such an explanation must lead to apparent ,gaps' in the field in the galactic disc. These gaps are probably unavoidable in any dynamo theory and should have important observable consequences, one of which is an explanation for the escape of cosmic rays from the disc (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Biomedical applications of capillary electrophoresis with laser-induced fluorescence detectionBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 7-8 2001Ximena Páez Abstract Capillary electrophoresis (CE) is a high-efficiency analytical technique that has had a great impact as a tool in biomedical research, clinical and forensic practice in the last ten years. Only in one of the applications, the DNA analysis, it has had an explosive exponential growth in the last few years. This impact is expressed in an enormous amount of CE articles and many reviews. The CE advantages with respect to other analytical techniques: the required very small sample volume, rapid analysis, great resolution power and low costs, have made this technique ideal for the analysis of a numerous endogenous and exogenous substances present in biological fluids. The different modes of CE have been coupled to different detection techniques such as UV-absorbance, electrochemical, mass spectrometry and laser-induced fluorescence detection (LIFD) to detect different nature and molecular size separated analytes. This review focuses mostly on the applications of CE,LIFD, to measure drugs and endogenous neuroactive substances such as amino acids and monoamines, especially in microdialysis samples from experimental animals and humans. CE,LIFD trends are discussed: automated faster analysis with capillary array systems, resolution power improvement, higher detection sensitivity, and CE systems miniaturization for extremely small sample volume, in order to make CE easier and affordable to the lab bench or the clinical bed. Copyright © 2001 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||||||||