A numerical study on dual-phase-lag model of bio-heat transfer during hyperthermia treatment

The success of hyperthermia in the treatment of cancer depends on the precise prediction and control of temperature. It was absolutely a necessity for hyperthermia treatment planning to understand the temperature distribution within living biological tissues. In this paper, dual-phase-lag model of bio-heat transfer has been studied using Gaussian distribution source term under most generalized boundary condition during hyperthermia treatment. An approximate analytical solution of the present problem has been done by Finite element wavelet Galerkin method which uses Legendre wavelet as a basis function. Multi-resolution analysis of Legendre wavelet in the present case localizes small scale variations of solution and fast switching of functional bases. The whole analysis is presented in dimensionless form. The dual-phase-lag model of bio-heat transfer has compared with Pennes and Thermal wave model of bio-heat transfer and it has been found that large differences in the temperature at the hyperthermia position and time to achieve the hyperthermia temperature exist, when we increase the value of τ_T. Particular cases when surface subjected to boundary condition of 1st, 2nd and 3rd kind are discussed in detail. The use of dual-phase-lag model of bio-heat transfer and finite element wavelet Galerkin method as a solution method helps in precise prediction of temperature. Gaussian distribution source term helps in control of temperature during hyperthermia treatment. So, it makes this study more useful for clinical applications.     

Impulsive SUI epidemic model for HIV/AIDS with chronological age and infection age

This paper develops an impulsive SUI model of human immunodeficiency virus/acquired immunodeficiency syndrome(HIV/AIDS) epidemic for the first time to study the dynamic behavior of this model. The SUI model is described by impulsive partial differential equations. First, the well-posedness of the model is attained by the method of characteristic lines and iterative method. Secondly, the basic reproduction number R₀(q,T) of the epidemic which depends on the impulsive HIV-finding period T and the HIV-finding proportion q is obtained by mathematical analysis. Our result shows that HIV/AIDS epidemic can be theoretically eradicated if we can have the suitable HIV-finding proportion q and the impulsive HIV-finding period T such that R₀(q,T)<1. We also conjecture that the infection-free periodic solution of the SUI model is unstable when R₀(q,T)>1.     

Kinetics of polymerization of deoxyhemoglobin S and mixtures of hemoglobin A and hemoglobin S at high hemoglobin concentrations

Transverse water proton relaxation times (T₂) have been measured as a function of time after deoxygenation of solutions containing hemoglobin S. The shortened T₂ values observed upon deoxygenation of hemoglobin S result from an increase in the correlation time (τ_c) of the water fraction irrotationally bound to deoxyhemoglobin S as it polymerizes. Therefore, the change in τ_c as a function of time after deoxygenation can be used to measure the rate of polymer formation. The change in τ_c observed is reasonably fit by the first-order equation τ = τ₀ (1 ? e^?kt) + τ_oxy. At a total hemoglobin concentration of approximately 300 mg/ml, the pseudo-first-order rate constant in a heterozygous AS sample is 25 times slower than in a homozygous S sample, k = 0.019 and 0.47 s^?1, respectively. Since the transit time for an erythrocyte in vivo is approximately 15 s, these results suggest that the heterozygous A/S erythrocyte would traverse the circulation and become reoxygenated before extensive polymerization and, therefore, cell sickling could occur. For the homozygous S/S erythrocyte, there is ample time for polymerization and for cell sickling during circulation.     

Stacks in canonical RNA pseudoknot structures

In this paper we study the distribution of stacks/loops in k-non-crossing, τ-canonical RNA pseudoknot structures (〈k,τ〉-structures). Here, an RNA structure is called k-non-crossing if it has no more than k-1 mutually crossing arcs and τ-canonical if each arc is contained in a stack of length at least τ. Based on the ordinary generating function of 〈k,τ〉-structures [G. Ma, C.M. Reidys, Canonical RNA pseudoknot structures, J. Comput. Biol. 15 (10) (2008) 1257] we derive the bivariate generating function , where T_k,τ(n,t) is the number of 〈k,τ〉-structures having exactly t stacks and study its singularities. We show that for a specific parametrization of the variable u, T_k,τ(x,u) exhibits a unique, dominant singularity. The particular shift of this singularity parametrized by u implies a central limit theorem for the distribution of stack-numbers. Our results are of importance for understanding the ‘language’ of minimum-free energy RNA pseudoknot structures, generated by computer folding algorithms.     

Dynamical types of bacteria and bacteriophages interaction: shielding by debris

The dynamics of the bacteria and bacteriophages interaction process was explored in depth, and laid on a firm basis through simulation and analysis. A modified Campbell model of phage-bacteria interaction was used to simulate three interacting species: bacteria, phages and bacterial debris, and their time behavior in terms of three parameters, in selected range values: the phages burst size (β), the dissolution rate of the bacterial debris (q), and the lysing time delay (τ). Six types of dynamical behavior were identified, occupying various zones in the two-dimensional (2D) plane (q, β) for several values of τ, allowing the determination of the region where shielding by bacterial debris is in effect. The problem of the occurrence of stability transitions between stable and unstable dynamical regimes was also addressed analytically, and compared with simulation results.     

Molecular mobilities of soluble components in the aqueous phase of chromaffin granules

NMR relaxation times have been used to characterize molecular motion and intermolecular complexes in the aqueous phase of bovine chromaffin granules. Partially relaxed ¹³C and proton spectra have been obtained at 3 and 25°C. T₁ measurements of five protonated carbons on epinephrine (C₂, C₅, C₆ CHOH and NCH₃) give a correlation time of 0.15 (10^?9) s at 25°C for the catechol ring and methine carbon, while the effective correlation time for the NCH₃ group is somewhat shorter due to its internal degree of rotational freedom. Resonances of protonated carbons on the soluble protein chromogranin give very similar corerlation times: 0.20 (10^?9) s for the peptide α-carbon and 0.2 (10^?9) s for the methylene sidechain carbons of glutamic acid. The correlation time (τ_R) of ATP was not measured direrctly using ¹³C T₁ data due to the weakness of its spectrum, but its reorinetation appears to be substantially slower than that of epinephrine or chromogranin. This conclusion is based on three observations: (1) the qualitative temperature dependence of T₁ for H₂ and H₈ on the adenine ring places τ_R for ATP to the right of the T₁ minimum, or τ_R ? 1.0 (10^?9) s; (2) ¹³C resonances of ATP have anomalously low amplitudes compared with epinphrine resonances, a fact that is readily explained only if ATP undergoes substantially slower reorientation; and (3) a comparision of the T₁ data on H₈ on chromaffin granules and in a dilute aqueous solution, where ρ_R for ATP cam be measured directly, indicates that τ_R ～ 1.0 (10^?9 s at 25°C in the granules. The relaxation data are consistent with the concept of a storage complex based on electrostatic interaction between a polyion (chromogranin) and its counterious (ATP and epinephrine), in which ATP cross-links cationic sidechains of the protein.     

Regression imputation of missing values in longitudinal data sets

A stand-alone, menu-driven PC program, written in GAUSS, which can be used to estimate missing observations in longitudinal data sets is described and made available to interested readers. The program is limited to the situation in which we have complete data on N cases at each of the planned times of measurement t₁, t₂,…, t_T; and we wish to use this information, together with the non-missing values for n additional cases, to estimate the missing values for those cases. The augmented data matrix may be saved in an ASCII file and subsequently imported into programs requiring complete data. The use of the program is illustrated. Ten percent of the observations in a data set consisting of mandibular ramus height measurements for N = 12 young male rhesus monkeys measured at T = 5 time points are randomly discarded. The augmented data matrix is used to determine the lowest degree polynomial adequate to fit the average growth curve (AGC); the regression coefficients are estimated and confidence intervals for them are determined; and confidence bands for the AGC are constructed. The results are compared with those obtained when the original complete data set is used.     

The consequences of contact pressure in phyllotaxis

To determine the consequences of contact pressure in phyllotaxis, a mathematical model is constructed in which a leaf distribution is represented by a point lattice of n + 1 lattice points at equal intervals on a helix wound around a cylinder. The model is normalized by taking the girth of the cylinder as 1 and by measuring time T in plastochrones, so that n = [T]. r stands for the normalized internode distance (component of the distance between two consecutive lattice points that is parallel to the axis of the cylinder). d stands for the divergence (fraction of a turn between consecutive lattice points). It is assumed that r is a monotonic decreasing function of T such that r(T) → 0 as T → ∞. Contact pressure is represented by the assumption that the minimum geodesic distance between lattice points is maximized. It is shown that if (p, q), with p < q, is the contact phyllotaxis determined when contact pressure first becomes effective, then the continuation of contact pressure requires that the advance to higher phyllotaxis as r decreases must proceed via successive pairs of consecutive terms of the Fibonacci sequence generated by the numbers p and q, namely, p, q, p + q, p + 2q, 2p + 3q, …. The divergence, starting from some value $\text{d =}\text{1}\text{t}\text{+}\text{1}\text{a}{}_2\text{+ … +}\text{1}\text{(a}{}_{\mathrm{n}}\text{+ x)}$ determined by p and q converges to an ideal angle $\text{1}\text{t}\text{+}\text{1}\text{a}{}_2\text{+ … +}\text{1}\text{a}{}_{\mathrm{n}}\text{+}\text{1}\text{τ}$, where τ is the golden section. A necessary and sufficient condition for the ideal angle to be $\text{1}\text{2}\text{+}\text{1}\text{τ}\text{= τ}{}^{\mathrm{?2}}$ is that the p and q of the initial contact phyllotaxis be consecutive Fibonacci numbers of the sequence 1, 2, 3, 5, 8, …. It is proved that a sufficient condition for convergence to the ideal angle τ^?2 of normal phyllotaxis is that contact pressure begin before T = 5 or before $\text{r <}\text{3}\text{38}\text{1}\text{2}$ with d initially between $\text{1}\text{3}$ and $\text{1}\text{2}$.     

Effect of divergence angle of ejector nozzle on aerosolisation of powdered nanoparticles

A combined experimental-numerical study was performed to reveal the mechanisms of powdered SiO₂ nanoparticle (NP) breakage and establish the relationship between the divergent angle (α) of a convergent-divergent (C-D) nozzle and nanoparticle size distribution. All distributions of aerosolised SiO₂ NPs obtained through ejectors with varied α were identically log-normal and unimodal. As α increased (from 8° to 20°), there were identified decreases in Geometric Mean Distribution (GMD)(from 216 to 189?nm), mode diameter, and median diameter, while Geometric Standard Deviation (GSD) increased slightly (from 1.59 to 1.65). The parallel negative growth trends of D25 and D75, with slightly decreasing interquartile (D25–D75) ranges, indicated that an increase in α could result in a clear shift of Particle Sizes Distribution(PSD) towards smaller particle sizes. This implied that NP deagglomeration was strengthened and the ejector became more efficient as α increased. Three cross-sections including the C-D nozzle outlet (Section 1), mixer tube inlet (Section 2), and central section (Section 3) were selected to estimate the influence of shear stress (|τ|) distribution in the ejector on NP aerosolisation. Increasing α hardly changed the location of the two inner peaks, but it significantly decreased the values of inner peaks and smoothened |τ| distributions. |τ| in Section 2 with different α exhibited a flat bimodal distribution and the two outer steep peaks (from Section 1) disappeared. For |τ0|?=?0.5 and |τ0|?=?1?Pa, the ratio of the |τ| distribution range of |τ| > |τ0| (0.5?Pa < |τ0|< 5?Pa) to the entire section span, η, increased significantly as α increased. The growth rate of η decreased apparently for |τ0| ranging from 2 to 4?Pa, but for |τ0|?≥?5?Pa, η stopped growing in Section 1. The maximum value of |τ| exerted no significant influence on NP dispersion. The smoothness and flatness of the |τ| distribution determined whether the powdered NPs could experience enough shear aerodynamics and be dispersed thoroughly. This played a crucial role in NP aerosolisation. The mechanism of the effect of α on NP dispersion resulted in smooth and flat |τ| distributions. This helped expand |τ| distribution to increase the possibility of powdered NPs experiencing stronger shear flow as α increased.     

Method for resolution and quantification of components of the non-photochemical quenching (<Emphasis Type="Italic">q</Emphasis><Subscript>N</Subscript>)

A new method of the chlorophyll (Chl) a fluorescence quenching analysis is described, which allows the calculation of values of (at least) three components of the non-photochemical quenching of the variable Chl a fluorescence (q _N) using a non-linear regression of a multi-exponential function within experimental data. Formulae for coefficients of the “energy”-dependent (ΔpH-dependent) quenching (q _E), the state-transition quenching (q _T) and the photo/inhibitory quenching (q _I) of Chl a fluorescence were found on the basis of three assumptions: (i) the dark relaxation kinetics of q _N, as well as of all its components, is of an exponential nature, (ii) the superposition principle is valid for individual Chl a fluorescence quenching processes and (iii) the same reference fluorescence level (namely the maximum variable Chl a fluorescence yield in the dark-adapted state, F _V) is used to define both q _N and its components. All definitions as well as the algorithms for analytical recognition of the q _N components are theoretically clarified and experimentally tested. The described theory results in a rather simple equation allowing to compute values for all q _N components (q _E, q _T, q _I) as well as the half-times of relaxation (τ_1/2) of corresponding quenching processes. It is demonstrated that under the above assumptions it holds: q _N = q _E + q _T + q _I. The theoretically derived equations are tested, and the results obtained are discussed for non-stressed and stressed photosynthetically active samples. Semi-empirical formulae for a fast estimation of values of the q _N components from experimental data are also given.     

Statistical inference on markov process of neuronal impulse sequences

To clarify the stochastic properties of the neuronal impulse sequences, we have proposed a measure of statistical dependency d _i (T=τ) and an equation ? _m of the matrices of the serial correlation coefficients. Markov properties of the interval sequences could be provided with d _i (T=τ) and ? _m , which represent the necessary and sufficient condition for the statistical dependence. A method to estimate the order of Markov process with the use of d _i (T=τ) and ? _m was found to be useful in practice. This was proved by the interval sequences of the 0-th, 1-st, and 2nd order semi-Markov process generated by computer. It was also found that the order of Markov process of neuronal impulse sequence is an important parameter representing the pattern of the sequence. This was proved with computer simulation by semi-Markov model of impulse sequence.     

Analysis of low angle light scattering results from T7 DNA

Selected light scattering data, obtained in earlier studies on T7 DNA in 0.195 M Na⁺, are analyzed by comparison with calculations from the theory of wormlike coils, both with and without excluded volume effects. The results confirm the conclusion from an earlier criticism, that linear extrapolations of data from the 10° to 20° angular range give incorrect values for the limiting molecular weight, M_T, and for the limiting root-mean-square radius, R_T. Further, it is shown that the excluded volume parameter, ?, must be used to provide a proper fit of calculated curves to experimental data. The revised analysis gives the following parameters for T7 DNA: M_T = 25.5 × 10⁶ ;R_T= 587 nm; ? = 0.08; and the statistical segment length, 1/λ = 120 nm. These parameters agree well with other values in the literature. The method of analysis, therefore, provides reliable results from light scattering data on high-molecular-weight, native DNA.     

Statistical uncertainty and its propagation in the analysis of quantitative polymerase chain reaction data: Comparison of methods

Most methods for analyzing real-time quantitative polymerase chain reaction (qPCR) data for single experiments estimate the hypothetical cycle 0 signal y₀ by first estimating the quantification cycle (C_q) and amplification efficiency (E) from least-squares fits of fluorescence intensity data for cycles near the onset of the growth phase. The resulting y₀ values are statistically equivalent to the corresponding C_q if and only if E is taken to be error free. But uncertainty in E usually dominates the total uncertainty in y₀, making the latter much degraded in precision compared with C_q. Bias in E can be an even greater source of error in y₀. So-called mechanistic models achieve higher precision in estimating y₀ by tacitly assuming E = 2 in the baseline region and so are subject to this bias error. When used in calibration, the mechanistic y₀ is statistically comparable to C_q from the other methods. When a signal threshold y_q is used to define C_q, best estimation precision is obtained by setting y_q near the maximum signal in the range of fitted cycles, in conflict with common practice in the y₀ estimation algorithms.     

The effect of the cryoprotectants,dimethylsulfoxide and glycerol on water transport in the human red blood cell

The response of human red blood cells to the cryoprotective agents, DMSO and glycerol, has been investigated using a pulsed NMR method. The experimentally determined parameters are: (1) the intracellular transverse relaxation time, T_2a; (2) the mean residence time of intracellular water, τ_a, which is effectively a reciprocal measure of the rate of water transport across the red blood cell membrane; and (3) the activation energy for this process. The quantitative data indicate that the observed effects are colligative rather than species-specific in origin.     

Nonnative protein polymers: structure, morphology, and relation to nucleation and growth

Thermally induced aggregates of α-chymotrypsinogen A and bovine granulocyte-colony stimulating factor in acidic solutions were characterized by a combination of static and dynamic light scattering, spectroscopy, transmission electron microscopy, and monomer loss kinetics. The resulting soluble, high-molecular weight aggregates (∼10³-10⁵ kDa) are linear, semiflexible polymer chains that do not appreciably associate with one another under the conditions at which they were formed, with classic power-law scaling of the radius of gyration and hydrodynamic radius with weight-average molecular weight (M_w). Aggregates in both systems are composed of nonnative monomers with elevated levels of β-sheet secondary structure, and bind thioflavine T. In general, the aggregate size distributions showed low polydispersity by light scattering. Together with the inverse scaling of M_w with protein concentration, the results clearly indicate that aggregation proceeds via nucleated (chain) polymerization. For α-chymotrypsinogen A, the scaling behavior is combined with the kinetics of aggregation to deduce separate values for the characteristic timescales for nucleation (τ_n) and growth (τ_g), as well as the stoichiometry of the nucleus (x). The analysis illustrates a general procedure to noninvasively and quantitatively determine τ_n, τ_g, and x for soluble (chain polymer) aggregates, as well as the relationship between τ_n/τ_g and aggregate M_w.     

Activation of Type II Adenylyl Cyclase by the Cloned μ-Opioid Receptor: Coupling to Multiple G Proteins

Abstract: Opioid receptors are multifunctional receptors that utilize G proteins for signal transduction. The cloned δ-opioid receptor has been shown recently to stimulate phospholipase C, as well as to inhibit or stimulate different isoforms of adenylyl cyclase. By using transient transfection studies, the ability of the cloned μ-opioid receptor to stimulate type II adenylyl cyclase was examined. Coexpression of the μ-opioid receptor with type II adenylyl cyclase in human embryonic kidney 293 cells allowed the μ-selective agonist, [d -Ala², N-Me-Phe⁴,Gly⁵-ol]enkephalin, to stimulate cyclic AMP accumulation in a dose-dependent manner. The opioid-induced stimulation of type II adenylyl cyclase was mediated via pertussis toxin-sensitive G_i proteins, because it was abolished completely by the toxin. Possible coupling between the μ-opioid receptor and various G protein α subunits was examined in the type II adenylyl cyclase system. The opioid-induced response became pertussis toxin-insensitive and was enhanced significantly upon co-expression with the α subunit of G_z, whereas those of G_q, G₁₂, or G₁₃ inhibited the opioid response. When pertussis toxin-sensitive G protein α subunits were tested under similar conditions, all three forms of α_i and both forms of α_o were able to enhance the opioid response to various extents. Enhancement of type II adenylyl cyclase responses by the co-expression of α subunits reflects a functional coupling between α subunits and the μ-opioid receptor, because such potentiations were not observed with the constitutively activated α subunit mutants. These results indicate that the μ-opioid receptor can couple to G_i1–3, G_o1–2, and G_z, but not to G_s, G_q, G₁₂, G₁₃, or G_t.     

Child Mortality Estimation: A Global Overview of Infant and Child Mortality Age Patterns in Light of New Empirical Data

Background

The under-five mortality rate (the probability of dying between birth and age 5 y, also denoted in the literature as U5MR and ₅ q ₀) is a key indicator of child health, but it conceals important information about how this mortality is distributed by age. One important distinction is what amount of the under-five mortality occurs below age 1 y (₁ q ₀) versus at age 1 y and above (₄ q ₁). However, in many country settings, this distinction is often difficult to establish because of various types of data errors. As a result, it is common practice to resort to model age patterns to estimate ₁ q ₀ and ₄ q ₁ on the basis of an observed value of ₅ q ₀. The most commonly used model age patterns for this purpose are the Coale and Demeny and the United Nations systems. Since the development of these models, many additional sources of data for under-five mortality have become available, making possible a general evaluation of age patterns of infant and child mortality. In this paper, we do a systematic comparison of empirical values of ₁ q ₀ and ₄ q ₁ against model age patterns, and discuss whether observed deviations are due to data errors, or whether they reflect true epidemiological patterns not addressed in existing model life tables.

Methods and Findings

We used vital registration data from the Human Mortality Database, sample survey data from the World Fertility Survey and Demographic and Health Surveys programs, and data from Demographic Surveillance Systems. For each of these data sources, we compared empirical combinations of ₁ q ₀ and ₄ q ₁ against combinations provided by Coale and Demeny and United Nations model age patterns. We found that, on the whole, empirical values fall relatively well within the range provided by these models, but we also found important exceptions. Sub-Saharan African countries have a tendency to exhibit high values of ₄ q ₁ relative to ₁ q ₀, a pattern that appears to arise for the most part from true epidemiological causes. While this pattern is well known in the case of western Africa, we observed that it is more widespread than commonly thought. We also found that the emergence of HIV/AIDS, while perhaps contributing to high relative values of ₄ q ₁, does not appear to have substantially modified preexisting patterns. We also identified a small number of countries scattered in different parts of the world that exhibit unusually low values of ₄ q ₁ relative to ₁ q ₀, a pattern that is not likely to arise merely from data errors. Finally, we illustrate that it is relatively common for populations to experience changes in age patterns of infant and child mortality as they experience a decline in mortality.

Conclusions

Existing models do not appear to cover the entire range of epidemiological situations and trajectories. Therefore, model life tables should be used with caution for estimating ₁ q ₀ and ₄ q ₁ on the basis of ₅ q ₀. Moreover, this model-based estimation procedure assumes that the input value of ₅ q ₀ is correct, which may not always be warranted, especially in the case of survey data. A systematic evaluation of data errors in sample surveys and their impact on age patterns of ₁ q ₀ and ₄ q ₁ is urgently needed, along with the development of model age patterns of under-five mortality that would cover a wider range of epidemiological situations and trajectories. Please see later in the article for the Editors'' Summary.     

Dielectric properties of two diastereoisomers of the arabinose and their equimolar mixture

Dielectric relaxation measurements were performed on two enantiomers, d- and l-arabinose and their equimolar mixture, and compared to dielectric data obtained for d-ribose. d-Arabinose differs from d-ribose by having the opposite configuration at C2. This study reveals that both d- and l- of arabinose exhibit α-relaxation peaks with the same shape for the same α-relaxation time τ_α, and the same steepness index for the T_g-scale T-dependence of τ_α. However, the two isomers have slightly different glass transition temperatures T_g’s, and their secondary γ-relaxation times also differ slightly from the previously observed γ-relaxation in d-ribose at the same temperature. However, when samples of both investigated monosaccharides are annealed at higher temperatures, their glass transition temperatures become nearly identical. This is an effect of the mutarotation process, which leads to the formation of pairs of the enantiomers and accordingly they should have the same physical properties. The width of the α-relaxation of d- and l-arabinose is broader than that of d-ribose, as reflected by the smaller stretch exponent in the Kohlrausch-Williams-Watts function used to fit the data of the former (β_KWW = 0.46 ± 0.01) than the latter (β_KWW = 0.55 ± 0.01). The width of the α-relaxation of racemic mixture of the d- and l-arabinose is slightly broader than that of the pure isomers. While the dielectric loss data of d-ribose in the glassy state at ambient and elevated pressures show an inflexion indicating the presence of the JG β-relaxation, the data of d- and l-arabinose show no such feature for identification of the supposedly universal JG β-relaxation. Nevertheless, on comparing the loss spectra of d-arabinose with that of d-ribose, the presence of the JG β-relaxation in d-arabinose has been rationalized.     

Dark recovery of the Chl a fluorescence transient (OJIP) after light adaptation: The qT-component of non-photochemical quenching is related to an activated photosystem I acceptor side

The dark recovery kinetics of the Chl a fluorescence transient (OJIP) after 15 min light adaptation were studied and interpreted with the help of simultaneously measured 820 nm transmission. The kinetics of the changes in the shape of the OJIP transient were related to the kinetics of the qE and qT components of non-photochemical quenching. The dark-relaxation of the qE coincided with a general increase of the fluorescence yield. Light adaptation caused the disappearance of the IP-phase (20-200 ms) of the OJIP-transient. The qT correlated with the recovery of the IP-phase and with a recovery of the re-reduction of P700⁺ and oxidized plastocyanin in the 20-200 ms time-range as derived from 820 nm transmission measurements. On the basis of these observations, the qT is interpreted to represent the inactivation kinetics of ferredoxin-NADP⁺-reductase (FNR). The activation state of FNR affects the fluorescence yield via its effect on the electron flow. The qT therefore represents a form of photochemical quenching. Increasing the light intensity of the probe pulse from 1800 to 15000 μmol photons m⁻² s⁻¹ did not qualitatively change the results. The presented observations imply that in light-adapted leaves, it is not possible to ‘close’ all reaction centers with a strong light pulse. This supports the hypothesis that in addition to Q_A a second modulator of the fluorescence yield located on the acceptor side of photosystem II (e.g., the occupancy of the Q_B-site) is needed to explain these results. Besides, some of our results indicate that in pea leaves state 2 to 1 transitions may contribute to the qI-phase.     

Steering by echolocation: a paradigm of ecological acoustics

1. Flights of three big brown bats (Eptesicus fuscus) landing on a hand and catching a suspended mealworm were video analysed.
2. Results were consistent with the bats using the same basic control procedure in the quite different approach tasks — namely keeping τ(r) = k _rand τ(a)τ(r) = k _αr. Here r is the current distance to the destination; α is the angle between the current direction of the destination and the goal direction of final approach (β _min); τ(r) = r/r, $\tau (\alpha ) = \alpha /\dot \alpha $ ; and k _r, k _αr are constants.
3. The bats were each quite consistent on a particular task (hand or mealworm) in the values they used for the control parameters k _r, k _αrand β _min. However, different values were used in the two tasks, which reflected the different behaviour required at the destination. Flights to hand required twisting and landing upside down and approach angle β _min was closer to vertical and k _rwas smaller and corresponded to decelerating nearly to a stop. In contrast, the mealworms were caught in mid flight and approach angle β _min was shallower and speed of approach was about constant.
4. τ(r) might be registered acoustically by τ(echo-delay) or by τ(echo-intensity). τ(α) might be registered by the bat's directional hearing and gravity sense.
5. The bats learned the tasks easily, suggesting that the control procedure they used in the experiments was part and parcel of the natural skills they had developed in the wild.