Effects of odor flux and pulse rate on chemosensory tracking in turbulent odor plumes by the blue crab, Callinectes sapidus

The ability of animals to track through chemical plumes is often related to properties of evanescent odor bursts and to small-scale mixing process that determine burst properties. However, odor plumes contain variation over a range of scales, and little is known about how variation in the properties of the odor signal on the scale of one to several seconds affects foraging performance. We examined how flux and pulse rate interact to modulate the search behavior of blue crabs, Callinectes sapidus, locating odor sources in controlled flume flows. Experimental treatments consisted of continuous plumes and plumes with discrete odor pulses at intervals of 2.5 s and 4 s at two fluxes. Crabs experienced diminished search success and reduced search efficiency as flux decreased and the inter-pulse interval lengthened. There often were significant interactions between flux and pulse length, and neither property completely determined search behavior. Thus, over the time span of several seconds, the blue crab chemosensory system is not a simple flux detector. The sensitivity of blue crabs to inter-pulse intervals in the range of several seconds indicates that larger-scale mixing processes, which create odor variation on comparable scales, may exert a significant impact on foraging success in nature.     

Quantification of electroporative uptake kinetics and electric field heterogeneity effects in cells

We have conducted experiments quantitatively investigating electroporative uptake kinetics of a fluorescent plasma membrane integrity indicator, propidium iodide (PI), in HL60 human leukemia cells resulting from exposure to 40 μs pulsed electric fields (PEFs). These experiments were possible through the use of calibrated, real-time fluorescence microscopy and the development of a microcuvette: a specialized device designed for exposing cell cultures to intense PEFs while carrying out real-time microscopy. A finite-element electrostatic simulation was carried out to assess the degree of electric field heterogeneity between the microcuvette's electrodes allowing us to correlate trends in electroporative response to electric field distribution. Analysis of experimental data identified two distinctive electroporative uptake signatures: one characterized by low-level, decelerating uptake beginning immediately after PEF exposure and the other by high-level, accelerating fluorescence that is manifested sometimes hundreds of seconds after PEF exposure. The qualitative nature of these fluorescence signatures was used to isolate the conditions required to induce exclusively transient electroporation and to discuss electropore stability and persistence. A range of electric field strengths resulting in transient electroporation was identified for HL60s under our experimental conditions existing between 1.6 and 2 kV/cm. Quantitative analysis was used to determine that HL60s experiencing transient electroporation internalized between 50 and 125 million nucleic acid-bound PI molecules per cell. Finally, we show that electric field heterogeneity may be used to elicit asymmetric electroporative PI uptake within cell cultures and within individual cells.     

Brain damage and global stereopsis.

When a single object lies in front of or beyond the plane of fixation its retinal image lies on disparate positions in the two eyes. This 'local' retinal disparity is an excellent cue to depth, and retinal disparties of a few seconds of arc are detectable by people and monkeys. However, most visual scenes produce a complex array of contours in each eye and we can detect the disparity in the arrays despite the ambiguous nature of the disparities, i.e. each contour in one eye could be related to any of several similar contours in the other eye. This ability, known as 'global' stereopsis, may be selectively impaired following brain damage in man. Global stereopsis was measured in rhesus monkeys before and after removing a different cortical visual area in different groups of animals. Only removal of the inferotemporal cortex impaired global stereopsis. The result is related to the findings with human patients and to receptive field properties of neurons in the inferotemporal cortex of monkeys.     

Long term effects of cryosurgery on cutaneous sensation.

In a study of the time course and nature of the sensory loss after cryosurgery the forearms of nine normal subjects were treated with liquid nitrogen using freeze times currently employed in clinical practice in Britain. Ability to appreciate touch, pinprick, and cold in the treated areas was tested at regular intervals and biopsy samples taken to investigate the pathogenesis. Appreciation of all three modalities of sensation was initially reduced in all nine subjects for all freeze times, yet complete recovery occurred in the seven patients completing follow up. This recovery, however, took up to one and a half years for the longest freeze, with even a 10 second freeze taking up to 10 months. Patients may be reassured that sensory loss after cryosurgery for up to two periods of 30 seconds will almost certainly recover, though it may take up to 18 months to do so.     

Decapitation in rats: latency to unconsciousness and the 'wave of death'

The question whether decapitation is a humane method of euthanasia in awake animals is being debated. To gather arguments in this debate, obsolete rats were decapitated while recording the EEG, both of awake rats and of anesthetized rats. Following decapitation a fast and global loss of power of the EEG was observed; the power in the 13-100 Hz frequency band, expressing cognitive activity, decreased according to an exponential decay function to half the initial value within 4 seconds. Whereas the pre-decapitation EEG of the anesthetized animals showed a burst suppression pattern quite different from the awake animals, the power in the postdecapitation EEG did not differ between the two groups. This might indicate that either the power of the EEG does not correlate well with consciousness or that consciousness is briefly regained in the anesthetized group after decapitation. Remarkably, after 50 seconds (awake group) or 80 seconds (anesthetized group) following decapitation, a high amplitude slow wave was observed. The EEG before this wave had more power than the signal after the wave. This wave might be due to a simultaneous massive loss of membrane potentials of the neurons. Still functioning ion channels, which keep the membrane potential intact before the wave, might explain the observed power difference. Two conclusions were drawn from this experiment. It is likely that consciousness vanishes within seconds after decapitation, implying that decapitation is a quick and not an inhumane method of euthanasia. It seems that the massive wave which can be recorded approximately one minute after decapitation reflects the ultimate border between life and death. This observation might have implications in the discussions on the appropriate time for organ donation.     

Acute effects of different stretching exercises on muscular endurance

This study aims to evaluate the acute effects of different stretching exercises on muscular endurance in men, in terms of the number of sets, set duration, and type of stretching. Two experiments were conducted; in the first one (E1), the subjects (n = 19) were evaluated to test the effect on the number of sets, and, in the second one (E2), the subjects (n = 15) were tested for the effect of set duration and type of stretching. After a warm-up of 10-15 repetitions of a bench press (BP) with submaximal effort, a one-repetition maximum (1RM) test was applied. For E1, BP endurance was evaluated after static stretching comprising one set of 20 seconds (1 x 20), two sets of 20 seconds (2 x 20), and three sets of 20 seconds (3 x 20). For E2, BP endurance was evaluated after static stretching comprising one set of 20 seconds (1 x 20), one set of 40 seconds (1 x 40), and proprioceptive neuromuscular facilitation (PNF) stretching. All tests were performed 48-72 hours apart, at which time the muscular endurance was assessed through the maximal number of repetitions (NR) of BP at 85% of 1RM until fatigue. The NR and the overload volume (OV) were compared among tests through repeated-measures analysis of variance. No significant effect of the number of sets on muscular endurance was observed because no statistically significant difference was found when comparing all stretching exercises of E1 in terms of NS (p = 0.5377) and OV (p = 0.5723). However, significant reductions were obtained in the set duration and PNF on NR (p < 0.0001) and OV (p < 0.0001), as observed in E2. The results suggest that a stretching protocol can influence BP endurance, whereas a decrease in endurance is suggested to be attributable to set duration and PNF. On the other hand, a low volume of static stretching does not seem to have a significant effect on muscular endurance.     

Characterization of distinct early assembly units of different intermediate filament proteins

We have determined the mass-per-length (MPL) composition of distinct early assembly products of recombinant intermediate filament (IF) proteins from the four cytoplasmic sequence homology classes, and compared these values with those of the corresponding mature filaments. After two seconds under standard assembly conditions (i.e. 25 mM Tris-HCl (pH 7.5), 50 mM NaCl, 37 degrees C), vimentin, desmin and the neurofilament triplet protein NF-L aggregated into similar types of "unit-length filaments" (ULFs), whereas cytokeratins (CKs) 8/18 already yielded long IFs at this time point, so the ionic strength had to be reduced. The number of molecules per filament cross-section, as deduced from the MPL values, was lowest for CK8/18, i.e. 16 and 25 at two seconds compared to 16 and 21 at one hour. NF-L exhibited corresponding values of 26 and 30. Vimentin ULFs yielded a pronounced heterogeneity, with major peak values of 32 and 45 at two seconds and 30, 37 and 44 after one hour. Desmin formed filaments of distinctly higher mass with 47 molecules per cross-section, at two seconds and after one hour of assembly. This indicates that individual types of IF proteins generate filaments with distinctly different numbers of molecules per cross-section. Also, the observed significant reduction of apparent filament diameter of ULFs compared to the corresponding mature IFs is the result of a "conservative" radial compaction-type reorganization within the filament, as concluded from the fact that both the immature and mature filaments contain very similar numbers of subunits per cross-section. Moreover, the MPL composition of filaments is strikingly dependent on the assembly conditions employed. For example, vimentin fibers formed in 0.7 mM phosphate (pH 7.5), 2.5 mM MgCl2, yield a significantly increased number of molecules per cross-section (56 and 84) compared to assembly under standard conditions. Temperature also strongly influences assembly: above a certain threshold temperature "pathological" ULFs form that are arrested in this state, indicating that the system is forced into strong but unproductive interactions between subunits. Similar "dead-end" structures were obtained with vimentins mutated to introduce principal alterations in subdomains presumed to be of general structural importance, indicating that these sequence changes led to new modes of intermolecular interactions.     

激光、~(60)Co—r射线对草毒生物效应的研究

本实验用CO_2激光功率密度10.44W/cm~2、3.40W/cm~2,一次10秒及再次6、10、14秒处理草莓、茎尖外植体,可使多数处理的无性后代,产量提高或品质改善。He—Ne激光输出功率10.6mW,原光斑照射30、40秒,也有与CO_2激光相似效应。~(60)Co—r射线吸收剂量193Gy,单独处理及与He—Ne激光30秒复合处理,可改善果实品质,He—Ne激光对~(60)Co—r射线的辐射损伤有修复作用。     

Oxygen Evolution and Oxygen Uptake by Isolated Chloroplasts of Wheat Irradiated with Monochromatic Light, without the Addition of an Oxidant

The oxygen exchange obtained when isolated chloroplasts of wheat are irradiated, without the addition of a Hill oxidant, has been investigated. Depending on the wavelength, two types of oxygen exchange are obtained. In light absorbed by both photosystems an oxygen gush appears directly upon irradiation. This oxygen evolving reaction is soon replaced by an oxygen uptake which is present until the end of the irradiation period. In light absorbed mainly in photosystem I, no oxygen gush can be observed, instead an oxygen uptake appears directly upon irradiation. An oxygen evolving process can also be observed in irradiations performed with photo-system I light, but this process appears after 10–15 seconds of irradiation. The influence of various external factors on the oxygen gush and the oxygen uptake, e.g. different wavelengths, light intensity, length of the dark periods between irradiations, was studied. The results show that the oxygen evolving reaction appearing upon irradiation with light absorbed by photosystem II and I, reflect the reduction of an oxidant, probably plasto-quinone, in the electron transport chain between the two photosystems. The reoxidation of this oxidant can be brought about after irradiating with light absorbed in photosystem I, or by prolonging the dark period between irradiations, or through some unknown process connected to photosystem II. The oxygen uptake which consists of two components, one appearing directly upon irradiation and the other one appearing after about 10 seconds of irradiation, confirms earlier observations that oxygen can be reduced in photosystem I. The electrons for the oxygen uptake appearing directly upon irradiation, are obtained from the reduced intermediates in the electron transport chain between the two photosystems. The electrons for the other oxygen uptake process are obtained from a reductant in the chloroplasts with access to the carrier chain between the photosystems. Whether the two oxygen uptake reactions reflect two sites of interaction of oxygen with the electron transport chain or only one site is discussed.     

General population growth models with Allee effects in a random environment

Allee effects on population growth are quite common in nature, usually studied through deterministic models with a specific growth rate function.In order to seek the qualitative behaviour of populations induced by such effects, one should avoid model-specific behaviours. So, we use as a basis a general deterministic model, i.e. a model with a general growth rate function, to which we add the effect on the growth rate of the random fluctuations in environmental conditions. The resulting model is the general stochastic differential equation (SDE) model that we propose here.We consider two possible cases, weak Allee effects and strong Allee effects, which lead to different qualitative behaviours of the model.We will study the model properties for both cases in terms of existence and uniqueness of the solution, extinction and stationary behaviour of the population. The two cases will be compared with each other and with the general density-dependent SDE model without Allee effects.We then consider as an example the particular case of the classic logistic model and an Allee effect version of it.     

A Safe Spore Stain for Class Use

In looking for an efficient method of pre-treating bacterial spores for staining with carbol fuchsin, the author found that the ammonia in Lagerberg's formula and the chromic acid in Moeller's formula were both fairly effective in increasing permeability. Combining the two proved highly successful; and the following method has been used for four years by classes of beginners in the study of spore-formers isolated from soil by the students.

Cover the heat-fixed smear with five percent chromic acid and after thirty seconds add twice the amount of concentrated ammonia to the acid. After two minutes rinse and steam with carbol fuchsin for two or three minutes. Rinse, destain with one percent sulphuric acid for fifteen to thirty seconds, rinse again and flood slide with tap water. Add to this a few drops of Loeffler's methylene blue and allow to counter-stain for ten to thirty seconds. Rinse, blot, dry and examine. If instructions are followed the results are always good.     

Effects of parametric manipulation of inter-stimulus similarity on 3D object categorization

To explore the nature of the representation space of 3D objects, we studied human performance in forced-choice categorization of objects composed of four geon-like parts emanating from a common center. Two categories were defined by prototypical objects, distinguished by qualitative properties of their parts (bulging vs waist-like limbs). Subjects were trained to discriminate between the two prototypes (shown briefly, from a number of viewpoints, in stereo) in a 1-interval forced-choice task, until they reached a 90% correct-response performance level. After training, in the first experiment, 11 subjects were tested on shapes obtained by varying the prototypical parameters both orthogonally (ORTHO) and in parallel (PARA) to the line connecting the prototypes in the parameter space. For the eight subjects who performed above chance, the error rate increased with the ORTHO parameter-space displacement between the stimulus and the corresponding prototype; the effect of the PARA displacement was weaker. Thus, the parameter-space location of the stimuli mattered more than the qualitative contrasts, which were always present. To find out whether both prototypes or just the nearest one to the test shape influenced the decision, in the second experiment we varied the similarity between the categories. Specifically, in the test stage trials the distance between the two prototypes could assume one of three values (FAR, INTERMEDIATE, and NEAR). For the 13 subjects who performed above chance, the error rate (on physically identical stimuli) in the NEAR condition was higher than in the other two conditions. The results of the two experiments contradict the prediction of theories that postulate exclusive reliance on qualitative contrasts, and support the notion of a representation space in which distances to more than one reference point or prototype are encoded (Edelman, 1998).     

The singularities of the visual mapping

In this article we treat purely metrical properties of the visual image, e.g. the time changes of the relative positions and orientations of image details. Self-induced movements of an observer relative to rigid bodies in his environment generate charactertistic motion parallax fields. The observer may regard those fields as proprioceptive and interprete the geometrical invariants of the fields as indicators of solid shape. In this way his perceptions become object-oriented, which is the normal case as the many constancy-phenomena show. Similar arguments apply to the disparity field of binocular vision. In this paper we treat the qualitative nature of such fields. [In this case the qualitative nature is basic. Compare the case of an equation with a single unknown. Often one is interested primarily in the qualitative solution (are there roots? How many?), and only slightly in the quantitative information (the numerical value of a root).] The qualitative nature of the fields is fixed if their singularities are known. It is shown that the singularities are of two types: isolated points (so-called specular points) and line-singularities (so-called folds, cusps and T-junctions). It is shown that for most vantage points that an observer can occupy, the topological structure of the set of singularities does not change if the observer performs small exploratory movements. That is most vantage points are stable. At an unstable vantage point the set of singularities changes and the observer experiences an event. Because certain properties of the set of singularities are shown to be preserved, only a few simple types of event are possible. A complete list is presented. The occurrence of an event is shown to be simply related to the solid shape of the objects of vision. Our geometrical theory enables us to understand the structure of the observer's internal models of external bodies.     

Kinetics of electron transfer between the primary and the secondary electron acceptor in reaction centers from Rhodopseudomonas sphaeroides.

Photoreduction of the two ubiquinone molecules, UQ1 and UQ2, bound to purified reaction center from Rhodopseudomonas sphaeroides induces different absorption band shifts of bacteriochlorophyll and bacteriopheophytin molecules depending on which ubiquinone is photoreduced. This allows us to study electron transfer between UQ1 and UQ2 directly by absorption spectrometry. The results support a model in which electrons are transferred one by one from UQ1 to UQ2 with a half-time 200 micro seconds, and two by two from fully reduced UQ2 to the secondary acceptor pool.     

Use of a modified oxygen microelectrode and laser-Doppler flowmetry to monitor changes in oxygen tension and microcirculation in a flap

Flap failure is a clinical problem in free tissue transfer, and there is no reliable device for monitoring the tissue. Differentiating between an arterial occlusion and venous congestion is also a problem. A study was undertaken to monitor viability in a pedicled groin flap and to compare two different monitoring methods. The oxygen tension in the flap, measured with a modified Clark-type microelectrode (tip diameter = 3 to 8 microm; 90 percent response within 2.6 +/- 0.5 seconds), was compared with changes in blood flow in the flap, measured with a laser-Doppler probe. In 11 Sprague-Dawley rats, the changes in oxygen tension and blood flow in the pedicled groin flap were studied after clamping and subsequent reperfusion of the artery or vein. After occlusion of the artery to the flap, oxygen tension decreased to a stable value (i.e., the recording level remained unchanged for 30 seconds), from 19.7 +/- 1.8 to 0.3 +/- 0.1 mmHg, after 193 +/-25 seconds; blood flow decreased to a stable value, from 117 +/- 21 to 54 +/- 18 perfusion units, after 26 +/- 6 seconds. Clamping of the vein resulted in a decrease in oxygen tension, from 17.1 +/- 1.8 to 1.4 +/- 0.7 mmHg, after 416 +/- 67 seconds, and blood flow decreased to a stable value, from 90 +/- 14 to 35 +/- 6 perfusion units, after 107 +/- 27 seconds. The results of this study show that there is a difference in oxygen tension and blood flow responses between arterial and venous occlusion and that it may be possible with both methods to distinguish arterial from venous occlusion. However, although oxygen tension measurements are slightly slower in response than laser-Doppler measurements, the values are more reliable as a diagnostic tool for interpretation of a vessel occlusion.     

濒危植物独花兰的传粉生物学初步观察

独花兰(Changnienia amoena Chien)为我国特有的单种属植物,近年因生境破碎化和过度采挖,其野生资源日渐减少.迄今对独花兰极为有限的研究表明,其结实率很低或根本不结实,其传粉媒介也一直未被发现.2002年3～4月,我们对神农架2个移植居群和5个天然居群进行了传粉生物学的定点观察,发现雌性三条熊蜂(Bombus(Diversobombus)trifasciatus Smith)、仿熊蜂(Bombus(Tricornibombus)imitator Pittion)和蜜蜂均访问独花兰,但只有三条熊蜂身体粘有花粉块,是独花兰的有效传粉者.三条熊蜂的访问频率很低,在113 h的观察中只有9次访问,但在一个天然居群(population 3)中曾观察到一天4次的最高访问频率;访问主要在12:00～15:00出现,但在花上停留时间很短,不超过10 s.在未被授粉的情况下,独花兰花朵大约3周后自然枯萎,但受粉后3、4 d内即出现一系列形态和颜色的变化,包括花梗逐渐伸长,子房在花梗逐渐停止伸长后开始膨大等,表明花梗伸长可作为结实(授粉成功)的指标.人工授粉实验表明,自花、异花受粉后花梗均伸长,而套袋隔离花的则花梗不伸长,说明独花?兰是自交亲和的异交种,需要昆虫传粉.根据传粉者的访问频率、居群中果实的分布,尤其是花距内无花蜜等特征,我们认为独花兰是种欺骗性传粉的兰花.相对于其他欺骗性传粉的兰花,独花兰的自然结实率并不很低(26.98%),这与居群规模小会提高欺骗性传粉兰花结实率这一观点吻合.花粉块的输出数远高于结实数,这说明独花兰存在一定的花粉浪费.     

Consequential classes of resources: Subtle global bifurcation with dramatic ecological consequences in a simple population model

Numerous situations exist in which a consumer uses two different kinds of resources, one fixed, the other renewable, e.g., nesting resources and food resources. With an elementary modification of the basic Lotka-Volterra consumer resource equations, we investigate the population dynamics of a consumer dependent on two resources, one fixed, the other renewable. Emerging from this structure is a situation of alternative attractors that remain qualitatively robust over a significant range of parameter values. However, a dramatic change in basins of attraction is induced by very small changes in parameters due to a global bifurcation. Noteworthy is the fact that the qualitative nature of the alternative equilibria remains constant but the dramatic change in the basins does not arise from subtle differences in initial conditions. Rather, there is a major restructuring of the vector field such that a permanent change involving large sets of initial conditions results from very small changes in parameters.     

Biological Time Series Analysis Using a Context Free Language: Applicability to Pulsatile Hormone Data

We present a novel approach for analyzing biological time-series data using a context-free language (CFL) representation that allows the extraction and quantification of important features from the time-series. This representation results in Hierarchically AdaPtive (HAP) analysis, a suite of multiple complementary techniques that enable rapid analysis of data and does not require the user to set parameters. HAP analysis generates hierarchically organized parameter distributions that allow multi-scale components of the time-series to be quantified and includes a data analysis pipeline that applies recursive analyses to generate hierarchically organized results that extend traditional outcome measures such as pharmacokinetics and inter-pulse interval. Pulsicons, a novel text-based time-series representation also derived from the CFL approach, are introduced as an objective qualitative comparison nomenclature. We apply HAP to the analysis of 24 hours of frequently sampled pulsatile cortisol hormone data, which has known analysis challenges, from 14 healthy women. HAP analysis generated results in seconds and produced dozens of figures for each participant. The results quantify the observed qualitative features of cortisol data as a series of pulse clusters, each consisting of one or more embedded pulses, and identify two ultradian phenotypes in this dataset. HAP analysis is designed to be robust to individual differences and to missing data and may be applied to other pulsatile hormones. Future work can extend HAP analysis to other time-series data types, including oscillatory and other periodic physiological signals.