Spectrum analysis of turbulence in the canine ascending aorta measured with a hot-film anemometer

We measured turbulence velocity in the canine ascending aorta using a hot-film anemometer. Blood flow velocity was measured at various points across the ascending aorta approximately 1.5-2 times the diameter downstream from the aortic valve. The turbulence spectrum was calculated and its characteristics were examined in connection with the mean Reynolds number and/or measuring positions. In the higher wave number range the values of the turbulence spectra were higher at larger mean Reynolds number. In the higher wave number range, the values of the turbulence spectra were higher at points closer to the centerline of the aorta, when the mean Reynolds number was relatively large. The patterns of the turbulence spectra at various points outside the boundary layer on the aortic wall were similar.     

Phenotype-phenotype analysis: field application of the gene-for-gene hypothesis in host-pathogen relations

The frequency of occurrence of a virulence phenotype in a pathogen population is equivalent to its probability of occurrence in that population. From the compound probability law it can thus be shown that the expected frequency of occurrence of phenotypes with combined virulences is a product of the observed frequencies of the individual virulences. In many host-pathogen interactions, observed and expected frequencies of combined virulences are closely similar. Deviations from expectation, in both directions, do occur however, and these may be of crucial importance in disease control.     

Effect of couple stresses on the unsteady convective diffusion in fluid flow through a channel

A generalized dispersion model is used to obtain exact solution for unsteady convective diffusion in the presence of couple stresses. The effect of the couple stress parameter 'a' on the most dominant dispersion coefficient is clearly depicted. The dimensionless mean concentration distribution is obtained as a function of dimensionless axial distance, time and 'a'. The results for 'pure convection' are also reported. It is shown that the effect of couple stress is predominant only for small values of 'a' and when a----infinity the flow characteristics tend to their equivalents in Newtonian theory. The results of Taylor's dispersion model are recovered as a particular case in the limit tau----infinity.     

Neural reapportionment: an hypothesis to account for the function of sleep

Sleep is a ubiquitous component of animal life, and prolonged sleep deprivation is fatal in both vertebrates and invertebrates. The physiologic function of sleep, however, is not known. We propose here that sleep provides a period of time necessary to reapportion resources within neurons and neural systems that become sub-optimally distributed during active waking. Three specific examples of such reapportionment during sleep are suggested: (1) the return of the neurotransmitter, glutamate, to synaptic vesicles at presynaptic sites most active during waking, (2) the intracellular movement of mitochondria from neuronal processes to the cells soma where mitochondrial replication can occur, and (3) the readjustment of the level and distribution of neurotransmitters within the brainstem modulatory systems and elsewhere that must function in an integrated fashion during waking. Experimental approaches that might be utilized to test these hypotheses are suggested.     

A field test of the stress‐gradient hypothesis along an aridity gradient

Aims: The stress‐gradient hypothesis (SGH) predicts how plant interactions change along environmental stress gradients. We tested the SGH in an aridity gradient, where support for the hypothesis and the specific shape of its response curve is controversial. Location: Almería, Cáceres and Coimbra, three sites in the Iberian Peninsula that encompass the most arid and wet habitats in the distribution range of a nurse shrub species –Retama sphaerocarpa L. (Boiss) – in Europe. Methods: We analysed the effect of Retama on its understorey plant community and measured the biomass and species richness beneath Retama and in gaps. We estimated the frequency (changes in species richness), importance and intensity of the Retama effects, and derived the severity–interaction relationship pattern, analysing how these interaction indices changed along this aridity gradient. Results and conclusions: The intensity and frequency of facilitation by Retama increased monotonically with increasing environmental severity, and the importance tended to have a similar pattern, overall supporting the SGH. Our data did not support predictions from recent revisions of the SGH, which may not apply to whole plant communities like those studied here or when interactions are highly asymmetrical. Facilitation by Retama influenced community composition and species richness to the point that a significant fraction of species found at the most arid end of the gradient were only able to survive beneath the nurse shrub, whereas some of these species were able to thrive in gaps at more mesic sites, highlighting the ecological relevance of facilitation by nurse species in mediterranean environments, especially in the driest sites.     

Application of the Hodgkin-Huxley equations to an electric field model for interaction between excitable cells

We previously described a model for the electrical transfer of excitation from one cell to the next which utilized the electric potential generated in the junctional cleft between the cells. Low-resistance connections between the cells were not used in the model, and it was assumed that the junctional membranes were excitable. This model was analyzed for the static case without capacitances and for the dynamic case in which capacitances were part of the circuit elements. For simplicity, the Na⁺ resistance (R_Na), after a threshold potential was exceeded, was allowed to decrease exponentially (to 1% of its initial value) within 0·25–1·0 ms, and possible changes in the K⁺ resistance were ignored. In this paper, we have incorporated the Hodgkin-Huxley equations into the operation of the lumped membrane units for the electrical equivalent circuit of the cell membrane. The parameters varied are the membrane capacitances, resistances, maximum Na⁺ conductance ($\text{g}{}_{\mathrm{<mtext>Na</mtext>}}$), and the radial cleft resistance (R_jc). We demonstrated that our model worked very well, i.e. the successful transfer of action potentials was achieved, with the membrane units following Hodgkin-Huxley dynamics for changes in g_Na and g_K. The calculations indicate that transmission is facilitated when the junctional units have a higher $\text{g}{}_{\mathrm{<mtext>Na</mtext>}}$ and a lower capacitance and when R_jc is elevated. Lowering the resistance of the junctional membrane units several fold, relative to the surface membrane units, also facilitated transmission; however, the absolute resistance of the junctional membrane was still well above the maximum value that would allow sufficient local-circuit current to flow to effect transmission. Thus, the electric field model provides an alternative means of cell-to-cell propagation between myocardial cells which is electrical in nature but does not require the presence of low-resistance connections between cells.     

Investigating microscale patchiness of motile microbes under turbulence in a simulated convective mixed layer

Microbes play a primary role in aquatic ecosystems and biogeochemical cycles. Spatial patchiness is a critical factor underlying these activities, influencing biological productivity, nutrient cycling and dynamics across trophic levels. Incorporating spatial dynamics into microbial models is a long-standing challenge, particularly where small-scale turbulence is involved. Here, we combine a fully 3D direct numerical simulation of convective mixed layer turbulence, with an individual-based microbial model to test the key hypothesis that the coupling of gyrotactic motility and turbulence drives intense microscale patchiness. The fluid model simulates turbulent convection caused by heat loss through the fluid surface, for example during the night, during autumnal or winter cooling or during a cold-air outbreak. We find that under such conditions, turbulence-driven patchiness is depth-structured and requires high motility: Near the fluid surface, intense convective turbulence overpowers motility, homogenising motile and non-motile microbes approximately equally. At greater depth, in conditions analogous to a thermocline, highly motile microbes can be over twice as patch-concentrated as non-motile microbes, and can substantially amplify their swimming velocity by efficiently exploiting fast-moving packets of fluid. Our results substantiate the predictions of earlier studies, and demonstrate that turbulence-driven patchiness is not a ubiquitous consequence of motility but rather a delicate balance of motility and turbulent intensity.     

Influence of electric field on the unsteady dispersion coefficient in couple-stress flow

The influence of electric field on unsteady convective diffusion in couple stress flow is studied using a time dependent dispersion model. The electric field, arising as a body couple in the governing equations, is shown to increase the axial dispersion coefficient. This is useful in the control of haemolysis caused by artificial organs implanted or extracorporeal. The contribution of pure convection in the dispersion of concentration is singled out and investigated in detail. The results obtained are compared with those in the absence of electric field and some important conclusions are drawn.     

棉花品种抗绿盲蝽特性的田间光谱诊断

调查了生长期14个不同棉花品种上绿盲蝽Apolygus lucorum Meyer-Dür的危害情况。亚洲棉表现为高抗,冀丰杂7号等12个品种表现为中抗,灵-17表现为敏感。田间采用ASD光谱仪对14个棉花品种生长期的冠层光谱进行了测定,发现相同品种不同时期的光谱反射率的一阶微分具有明显差异(P<0.05),在近红外717 nm波段处一阶微分光谱值与棉花抗绿盲蝽级别显著相关(R2=0.89,P=0.01),可较好的表征绿盲蝽危害指数,可利用这个波段的光谱指标对棉花品种的抗绿盲蝽特性进行初步诊断,为棉花抗盲蝽评价选育提供参考。     

Measurement of turbulence intensity in the center of the canine ascending aorta with a hot-film anemometer

The blood flow velocity near the central axis of the canine ascending aorta was measured with a hot-film anemometer. The cardiac output and the heart rate were controlled at will by means of an extracorporeal circulation and by atrial pacing. The turbulent component of the blood flow velocity was calculated using an ensemble average technique. Ensemble average turbulent intensity was also calculated to show the time course of turbulence in the aorta. The ratio of the mean turbulence intensity to the time mean sectional average velocity in the aorta was constant in most animals regardless of the changes in fluid mechanical parameters. The correlation between the frequency parameter and the relative mean turbulence intensity was weakly positive. The power spectrum of the turbulence was also calculated.     

The choice of the wavelengths in spectral analysis: an application to determine the composition of a tetraribonucleotide mixture

We present a simple program running on a pocket computer allowing us to determine the order of importance of the wavelengths (regarding the accuracy of the results) in spectral analysis and to evaluate the absolute errors made on the determination of the concentrations of the constituents. We have applied this programme to the determination of the composition of a tetraribonucleotide mixture and have compared our results with other results published.     

Effect of the external magnetic field on the MHD turbulence spectra

The turbulent properties of conducting fluids in an external constant magnetic field are known to change with increasing field strength. A study is made of the behavior of the second-order structural function of the velocity field in a homogeneous incompressible turbulent fluid in the presence of an external uniform magnetic field. It is shown that, depending on the magnetic field strength, there may be different governing parameters of the system in both the inertial and dissipative intervals of turbulence. This leads to new spectral scalings that are consistent with experimental ones.     

Computational analysis of blood flow in an integrated model of the left ventricle and the aorta

To study the effects of intraventricular flow dynamics on the aortic flow, we created an integrated model of the left ventricle and aorta and conducted a computer simulation of diastolic and systolic blood flow within this model. The results demonstrated that the velocity profile at the aortic annulus changed dynamically, and was influenced by the intraventricular flow dynamics. The profile was almost flat in early systole but became nonuniform as systole progressed, and was skewed toward the posterior side in midsystole and toward the anterior side in later systole. At a distance from the aortic annulus, a different velocity profile was induced by the twisting and torsion of the aorta. In the ascending aorta, the fastest flow was initially located in the posteromedial sector, and it moved to the posterior section along the circumference as systole progressed. The nonuniformity of the aortic inflow gave rise to a complex wall shear stress (WSS) distribution in the aorta. A comparison of the WSS distribution obtained in this integrated analysis with that obtained in flow calculations using an isolated aorta model with Poiseuille and flat inlet conditions showed that intraventricular flow affected the WSS distribution in the ascending aorta. These results address the importance of an integrated analysis of flow in the left ventricle and aorta.     

Correction to: An empirical test of bet-hedging polyandry hypothesis in the field cricket Gryllus bimaculatus

Journal of Ethology -     

Quantitative analysis of an inhibitory gradient field in the hydrozoan stolon

Summary An inhibitory field which emanates from the mobile tips of elongating stolons of colonial hydroids has been identified and analyzed. It extends proximally with decreasing intensity for about 400–700 m and ensures that branching sites occur at appropriate distances along the stolon. The local strengths of inhibition within the field have been measured with a new method which permits high temporal and spatial resolution. Kinetic studies reveal three characteristics. First, inhibition decays rather rapidly after removal of its source. The half life is about 30 min. Second, loss of inhibition immediately triggers initiation of future tip formation. Third, restoration and spreading of inhibition are slow processes which take 8–24 h to recover 90% of the original inhibitory levels.     

Support for the allotonic frequency hypothesis in an insectivorous bat community

The allotonic frequency hypothesis proposes that certain insectivorous bat species can prey upon moths that can hear bat echolocation calls by using echolocation frequencies outside the sensitivity range of moth ears. The hypothesis predicts that the peak frequencies of bat echolocation calls are correlated with the incidence of moths in the diets of these bats. The aim of this study was to test this prediction on a bat community dominated by bats using low duty cycle echolocation calls, i.e. aerial foraging, insectivorous species using frequency modulated calls. The community consisted of nine species, two molossids, Sauromys petrophillus and Tadarida aegyptiaca, five vespertilionids, Eptesicus capensis, Eptesicus hottentotus, Miniopteris schreibersii, Myotis tricolor, and Myotis lesueuri, one rhinolophid, Rhinolophus clivosus, and one nycterid, Nycteris thebaica. The insect fauna in the habitat used by the bat community was suited to the testing of the allotonic frequency hypothesis because more than 90% of the moths comprising the insect fauna were tympanate. These included Pyralidae (3.8%), Geometridae (44.9%), Notodontidae (3.8%), Arctiidae (4.6%), Lymantriidae (0.8%) and Noctuidae (32.4%). As predicted, peak echolocation frequency was correlated with the incidence of moths in the diets of these nine species (r=0.98, df=7, P<0.01). Furthermore, multivariate analysis revealed that echolocation frequency (t=9.91, n=129, P<0.001) was a better predictor of diet than forearm length (t=5.51, n=129, P<0.001) or wing area (t=-3.41, n=129, P<0.001). This suggests that the selection pressure exerted by moth hearing might have acted directly on call frequency and secondarily on body size and wing morphology, as part of the same adaptive complex. It is unlikely that dietary differences were due to temporal and spatial differences in the availability of prey because the pattern of differences in skull morphology of the nine species supported our dietary analyses. The skull morphology of a bat represents a historical record of the kind of diet it has become adapted to over its evolutionary history. These results suggest that prey defences may mediate other factors structuring bat communities, e.g. competition. Competition may be reduced for those species of bats that can circumvent prey defences.     

Coarctation of the aorta in an elderly man

An active, 74-year-old man with coarctation of the aorta is described. This case is rarely found in patients over the age of 70, and the patient had been in good health.     

Map-invariant spectral analysis for the identification of DNA periodicities

Many signal processing based methods for finding hidden periodicities in DNA sequences have primarily focused on assigning numerical values to the symbolic DNA sequence and then applying spectral analysis tools such as the short-time discrete Fourier transform (ST-DFT) to locate these repeats. The key results pertaining to this approach are however obtained using a very specific symbolic to numerical map, namely the so-called Voss representation. An important research problem is to therefore quantify the sensitivity of these results to the choice of the symbolic to numerical map. In this article, a novel algebraic approach to the periodicity detection problem is presented and provides a natural framework for studying the role of the symbolic to numerical map in finding these repeats. More specifically, we derive a new matrix-based expression of the DNA spectrum that comprises most of the widely used mappings in the literature as special cases, shows that the DNA spectrum is in fact invariable under all these mappings, and generates a necessary and sufficient condition for the invariance of the DNA spectrum to the symbolic to numerical map. Furthermore, the new algebraic framework decomposes the periodicity detection problem into several fundamental building blocks that are totally independent of each other. Sophisticated digital filters and/or alternate fast data transforms such as the discrete cosine and sine transforms can therefore be always incorporated in the periodicity detection scheme regardless of the choice of the symbolic to numerical map. Although the newly proposed framework is matrix based, identification of these periodicities can be achieved at a low computational cost.