Circularly polarized light at the mirror: Caveats and opportunities

Moving from the simple concept that reflection onto a mirror surface changes the handedness of circularly polarized light, we describe what happens to the emergent polarization in two different cases after reflection on a back mirror. In the first case, a regular emitter is taken into account, where reflection has the effect to destroy the emergent polarization. In the second case, we show what could happen when a hypothetical apparently non-reciprocal emitting material undergoes a similar experiment. These simple concepts have important implications in the design of efficient circularly polarized emitting devices.     

Improved automated monitoring and new analysis algorithm for circadian phototaxis rhythms in Chlamydomonas

Automated monitoring of circadian rhythms is an efficient way of gaining insight into oscillation parameters like period and phase for the underlying pacemaker of the circadian clock. Measurement of the circadian rhythm of phototaxis (swimming towards light) exhibited by the green alga Chlamydomonas reinhardtii has been automated by directing a narrow and dim light beam through a culture at regular intervals and determining the decrease in light transmittance due to the accumulation of cells in the beam. In this study, the monitoring process was optimized by constructing a new computer-controlled measuring machine that limits the test beam to wavelengths reported to be specific for phototaxis and by choosing an algal strain, which does not need background illumination between test light cycles for proper expression of the rhythm. As a result, period and phase of the rhythm are now unaffected by the time a culture is placed into the machine. Analysis of the rhythm data was also optimized through a new algorithm, whose robustness was demonstrated using virtual rhythms with various noises. The algorithm differs in particular from other reported algorithms by maximizing the fit of the data to a sinusoidal curve that dampens exponentially. The algorithm was also used to confirm the reproducibility of rhythm monitoring by the machine. Machine and algorithm can now be used for a multitude of circadian clock studies that require unambiguous period and phase determinations such as light pulse experiments to identify the photoreceptor(s) that reset the circadian clock in C. reinhardtii.     

Entrainment of the human circadian system by light

The periodic light-dark cycle is the dominant environmental synchronizer used by humans to entrain to the geophysical 24-h day. Entrainment is a fundamental property of circadian systems by which the period of the internal clock (tau) is synchronized to the period of the entraining stimuli (T cycle). An important aspect of entrainment in humans is the maintenance of an appropriate phase relationship between the circadian system, the timing of sleep and wakefulness, and environmental time (a.k.a. the phase angle of entrainment) to maintain wakefulness throughout the day and consolidated sleep at night. In this article, we review these concepts and the methods for assessing circadian phase and period in humans, as well as discuss findings on the phase angle of entrainment in healthy adults. We review findings from studies that examine how the phase, intensity, duration, and spectral characteristics of light affect the response of the human biological clock and discuss studies on entrainment in humans, including recent studies of the minimum light intensity required for entrainment. We briefly review conditions and disorders in which failure of entrainment occurs. We provide an integrated perspective on circadian entrainment in humans with respect to recent advances in our knowledge of circadian period and of the effects of light on the biological clock in humans.     

Acceptance angles of butterfly ommatidia

The ommatidial acceptance angle (angular sensitivity) of seven species of butterflies was determined by a novel technique. Measurements were based upon the fact that light adaptation produces a graded contraction of specific retinula cells with a concomitant reduction in the brillance of the observed reflection (glow). Measurements were, therefore, based upon the changes in the intensity of the reflections as an adapting light was moved to various spatial positions. Measurements were also made on the angle of illumination that would produce reflections, as well as the angle through which reflections could be observed. Average angles so determined were: half-linear sensitivity, 1°16′; reflection (acceptance), 2°47′; reflection (viewing), 9–10°; inter-ommatidial, 1°47′. These results suggest that the butterfly eye may have greater acuity than those of previously studied insects.     

EcoPred: an educational individual based model to explain biological control,a case study within an arable land

ABSTRACT

Individual based models (IBMs) are up-to-date tools both in research and educational areas. Here we introduce an IBM built on NetLogo platform that simulates a top-down trophic cascade controlled by the pressure exerted by two model predators (web-building spiders and ground runner spiders) on a model pest (the olive fruit fly) within a hypothetical agricultural landscape (the olive crop). EcoPred is an IBM that aims to be an educational tool that can help teachers to explain concepts related to ecology in a modern, enjoyable and comprehensive way. EcoPred reflects the changes on a fly population within a simulated olive crop according to (1) the mortality rate caused by the predation of two spider species and energy loss, (2) the energy gain by feeding on flowers and (3) the reproduction rate in olive trees. The model was tested with 26 students achieving very good results in terms of acceptance and interest on the learning method. EcoPred can be used for educational purposes with 16 year old students and older to explain ecological concepts such as trophic level, species interactions, limiting factor and biological control in an interactive way simultaneously introducing students to biology oriented programming languages.     

Miniaturization capable, very sensitive polarimeter as detector of an implantable glucose probe. I. Optical amplification of the measuring value]

From a clinical point of view, an implantable telemetric probe for monitoring the blood glucose profile is highly desirable. It should be capable of monitoring the blood glucose level continuously or at regular brief intervals, if necessary requirement-controlled. Apart from blood, measurement can also be made in intercellular tissue fluid, for example, in subcutaneous connective and fatty tissue, because this fluid accurately reflects blood glucose levels after only a brief, but negligible, time lag. Since the functional lifespan of an implantable probe is of decisive importance, only physical sensors, but not bio-sensors can be considered. We are in the process of developing a very sensitive miniaturised detector based on polarimetry, capable of determining the measuring parameter--the spatial orientation of the in-plane vibration of a polarised light beam--with extreme accuracy. This is a very important point, since the physiological and pathological glucose levels modify the in-plane vibration by only a very tiny angle of rotation. The high level of accuracy is achieved by various specific optical amplification mechanisms, and amplification of the electric signal. Two purely optical amplification methods are described here. Simple linear elongation of the optical path of a laser beam within the sample, resulting in a proportional amplification of the measuring signal, is obviously strictly limited in an implantable probe. We therefore developed a technique that preserves the polarisation state of the light beam during reflection. This technique makes possible multiple passage of the light beam through the fluid being sensed, thus elongating the optical path by "folding" the light beam without the need to enlarge the measuring cuvette. In a second possibility, enlargement of the rotation angle can be achieved by reflecting the light beam from a suitable surface, when the orthogonal components of the polarised light beam are reflected to different extents.     

Intrinsic period and light intensity determine the phase relationship between melatonin and sleep in humans

The internal circadian clock and sleep-wake homeostasis regulate the timing of human brain function, physiology, and behavior so that wakefulness and its associated functions are optimal during the solar day and that sleep and its related functions are optimal at night. The maintenance of a normal phase relationship between the internal circadian clock, sleep-wake homeostasis, and the light-dark cycle is crucial for optimal neurobehavioral and physiological function. Here, the authors show that the phase relationship between these factors-the phase angle of entrainment (psi)-is strongly determined by the intrinsic period (tau) of the master circadian clock and the strength of the circadian synchronizer. Melatonin was used as a marker of internal biological time, and circadian period was estimated during a forced desynchrony protocol. The authors observed relationships between the phase angle of entrainment and intrinsic period after exposure to scheduled habitual wakefulness-sleep light-dark cycle conditions inside and outside of the laboratory. Individuals with shorter circadian periods initiated sleep and awakened at a later biological time than did individuals with longer circadian periods. The authors also observed that light exposure history influenced the phase angle of entrainment such that phase angle was shorter following exposure to a moderate bright light (approximately 450 lux)-dark/wakefulness-sleep schedule for 5 days than exposure to the equivalent of an indoor daytime light (approximately 150 lux)-dark/wakefulness-sleep schedule for 2 days. These findings demonstrate that neurobiological and environmental factors interact to regulate the phase angle of entrainment in humans. This finding has important implications for understanding physiological organization by the brain's master circadian clock and may have implications for understanding mechanisms underlying circadian sleep disorders.     

Elementary education majors experience hands-on learning in introductory biology

Faculty members from the University of South Dakota attended the Curriculum Reform Institute offered by the University of Wisconsin at Oshkosh, WI, during the summer of 2002 to design a course sequence for elementary education majors that better meets their needs for both content and pedagogy based on the science education standards. The special section of introductory biology that resulted from this workshop is designed to use laboratories and activities that either help students learn major concepts in the life sciences or model how to teach these concepts to their future K-8 students. This study describes how the active, hands-on learning opportunity for preservice teachers with its emphasis on both content and performance-based assessment was implemented in an introductory biology course for elementary education majors during the spring of 2004. During the initial offering of this course, student perceptions about what helped them to learn in the special section was compared with their nonscience major peers in the large lecture-intensive class that they would have taken. Each group of students completed early and late web-based surveys to assess their perceptions about learning during the courses. After the completion of the course, students in the special section appreciated how the relevance of science and conducting their own scientific experimentation helped them learn, enjoyed working and studying in small groups, valued diverse class time with very little lecture, were more confident in their abilities in science, and were more interested in discussing science with others. This course format is recommended for science classes for preservice teachers.     

Modeling the molecular regulatory mechanism of circadian rhythms in Drosophila

Thanks to genetic and biochemical advances on the molecular mechanism of circadian rhythms in Drosophila, theoretical models closely related to experimental observations can be considered for the regulatory mechanism of the circadian clock in this organism. Modeling is based on the autoregulatory negative feedback exerted by a complex between PER and TIM proteins on the expression of per and tim genes. The model predicts the occurrence of sustained circadian oscillations in continuous darkness. When incorporating light-induced TIM degradation, the model accounts for damping of oscillations in constant light, entrainment of the rhythm by light-dark cycles of varying period or photoperiod, and phase shifting by light pulses. The model further provides a molecular dynamical explanation for the permanent or transient suppression of circadian rhythmicity triggered in a variety of organisms by a critical pulse of light. Finally, the model shows that to produce a robust rhythm the various clock genes must be expressed at the appropriate levels since sustained oscillations only occur in a precise range of parameter values. BioEssays 22:84-93, 2000.     

The reflectance properties of plant internodes modify elongation responses to lateral far-red radiation

The quality and quantity of light reflected from Nicotinia tabacum L. internodes was monitored as the angle of incidence was varied. Reflectance of incident light, which was either normal or longitudinal to the internode axis, was investigated. Increasing the angle of incidence caused a greater proportion of incident light to be reflected. Light striking N. tabacum internodes was always modified prior to reflection, and smaller incident angles produced greater modification of the reflected light quality. At larger angles, interactions with the internode were reduced. As a parallel investigation, the extension growth rate of light-grown Sinapis alba L. seedlings was monitored continuously using sensitive linear displacement transducers. When the angle of illumination by fibre-optic probes, presenting far-red light to the growing internode, was changed from 0° to 45°, an increase was observed in stem extension rate. There is a possibility that this rate increase was the result of a fall in the red:far-red ratio (R:FR) present inside the plant internode as the angle of incidence was altered. However, it is more likely that it was due to the larger surface area of stem being illuminated. The consequences of these observations are discussed in relation to the potential influence of such modified reflections on canopy light environments and resultant shade responses which may occur when light of known R:FR impinges on plant internodes at angles other than 0°. The possibility is discussed that plants may perceive the quality of reflected radiation from neighbouring plants to be substantially different dependent upon the angle at which it is reflected.     

Performing Evolution: Role-Play Simulations

By simulating evolution through performance, students become physically, as well as mentally, engaged in thinking about evolutionary concepts. This instructional strategy redirects tension around the subject toward metacognitive reflection. Non-verbal performances like those presented here also avoid the pitfalls of relying on difficult-to-use language. This paper describes a teachable unit including the learning goals and outcomes as well as rubrics to aid assessment. Through two performance-based activities, the unit introduces the fundamental evolutionary concepts that evolution lacks forethought and that natural selection is a sorting process. By reflecting on the performances, students learn other sophisticated evolutionary concepts like hitchhiking, the effects of environmental change, and the extinction of traits. They also become aware of the scientific process, articulating hypotheses about the outcome of the simulations, collecting data, and revising their hypotheses. Discussions and homework about the performances reveal how learning progresses, and detailed rubrics help both instructors and students assess conceptual learning. This unit concludes with the opportunity for students to transfer what they have learned to new concepts: they design new performances to simulate other mechanisms of evolution, such as genetic drift, mutation, and migration.     

Data-driven modelling captures dynamics of the circadian clock of Neurospora crassa

Eukaryotic circadian clocks are based on self-sustaining, cell-autonomous oscillatory feedback loops that can synchronize with the environment via recurrent stimuli (zeitgebers) such as light. The components of biological clocks and their network interactions are becoming increasingly known, calling for a quantitative understanding of their role for clock function. However, the development of data-driven mathematical clock models has remained limited by the lack of sufficiently accurate data. Here we present a comprehensive model of the circadian clock of Neurospora crassa that describe free-running oscillations in constant darkness and entrainment in light-dark cycles. To parameterize the model, we measured high-resolution time courses of luciferase reporters of morning and evening specific clock genes in WT and a mutant strain. Fitting the model to such comprehensive data allowed estimating parameters governing circadian phase, period length and amplitude, and the response of genes to light cues. Our model suggests that functional maturation of the core clock protein Frequency causes a delay in negative feedback that is critical for generating circadian rhythms.     

Exploring continuity equation via a modeling activity: in the context of crowd science

Abstract

Using problems from real life contexts which is related to learners’ environment or their culture plays an important role in their learning that concept. In this regard, science educators especially physics educators search for real-life domain of theoretical concepts for effective science teaching and they consider analogical and physical models as an opportunity in their instruction. In the presented activity, we worked with 66 senior pre-service science teachers from our science teaching methods course. We used crowd movements as a real-life domain of our analogical models to scientifically explain a stampede case, then utilized physical model to explore continuity equation. Real life problem based scenarios could be used while taking advantage of the 3?D modeling in teaching of scientific principle. As a result, we found that pre-service teachers were able to make scientific explanation for causes of stampedes by using modeling activity. High school teachers and upper-level instructors could benefit from including the modeling activity introduced in this study to help their students understand the concepts related to continuity equation by designing a physical model based on an analogical model. Via the physical model, students are able to make predictions, observations, interpretations and explanations of a complex and abstract scientific phenomenon.     

How can dragonflies discern bright and dark waters from a distance? The degree of polarisation of reflected light as a possible cue for dragonfly habitat selection

SUMMARY 1. Based on the findings that some dragonflies prefer either ‘dark’ or ‘bright’ water (as perceived by the human eye viewing downwards perpendicularly to the water surface), while others choose both types of water bodies in which to lay their eggs, the question arises: How can dragonflies distinguish a bright from a dark pond from far away, before they get sufficiently close to see it is bright or dark? 2. Our hypothesis is that certain dragonfly species may select their preferred breeding sites from a distance on the basis of the polarisation of reflected light. Is it that waters viewed from a distance can be classified on the basis of the polarisation of reflected light? 3. Therefore we measured, at an angle of view of 20° from the horizontal, the reflection‐polarisation characteristics of several ponds differing in brightness and in their dragonfly fauna. 4. We show that from a distance, at which the angle of view is 20° from the horizontal, dark water bodies cannot be distinguished from bright ones on the basis of the intensity or the angle of polarisation of reflected light. At a similar angle of view, however, dark waters reflect light with a significantly higher degree of linear polarisation than bright waters in any range of the spectrum and in any direction of view with respect to the sun. 5. Thus, the degree of polarisation of reflected light may be a visual cue for the polarisation‐sensitive dragonflies to distinguish dark and bright water bodies from far away. Future experimental studies should prove if dragonflies do indeed use this cue for habitat selection.     

Individual Intelligence in the Context of Modern Psycholinguistic Studies

The article reports a comparative study on university students’ linguistic consciousness and world-view. An attempt is made to integrate psycholinguistics with the study of intelligence. Psycholinguistic tools are combined to diagnose indicators of intelligence. A special focus is on linguistic tools for reflection, generalization, and transformation of reality.     

同时应用近场光学显微镜的透射和反射模式研究单个细胞的光学性质

通常认为．在近场光学显微技术的光收集模式中,观察透光性好的样品时采用透射模式．研究不透明样品时采用反射模式。本文同时采用透射和反射两种模式观察透明性较好的PCI2细胞和淋巴细胞样品．初步研究单个细胞的反射、吸收、透射和荧光等光学性质,以促进组织光学和激光生物医学等领域的进一步发展。细胞光学的时代就要到来。     

Eliminating Unwanted Far-Field Excitation in Objective-Type TIRF. Part II. Combined Evanescent-Wave Excitation and Supercritical-Angle Fluorescence Detection Improves Optical Sectioning

Azimuthal beam scanning makes evanescent-wave (EW) excitation isotropic, thereby producing total internal reflection fluorescence (TIRF) images that are evenly lit. However, beam spinning does not fundamentally address the problem of propagating excitation light that is contaminating objective-type TIRF. Far-field excitation depends more on the specific objective than on cell scattering. As a consequence, the excitation impurities in objective-type TIRF are only weakly affected by changes of azimuthal or polar beam angle. These are the main results of the first part of this study (Eliminating unwanted far-field excitation in objective-type TIRF. Pt.1. Identifying sources of nonevanescent excitation light). This second part focuses on exactly where up beam in the illumination system stray light is generated that gives rise to nonevanescent components in TIRF. Using dark-field imaging of scattered excitation light we pinpoint the objective, intermediate lenses and, particularly, the beam scanner as the major sources of stray excitation. We study how adhesion-molecule coating and astrocytes or BON cells grown on the coverslip surface modify the dark-field signal. On flat and weakly scattering cells, most background comes from stray reflections produced far from the sample plane, in the beam scanner and the objective lens. On thick, optically dense cells roughly half of the scatter is generated by the sample itself. We finally show that combining objective-type EW excitation with supercritical-angle fluorescence (SAF) detection efficiently rejects the fluorescence originating from deeper sample regions. We demonstrate that SAF improves the surface selectivity of TIRF, even at shallow penetration depths. The coplanar microscopy scheme presented here merges the benefits of beam spinning EW excitation and SAF detection and provides the conditions for quantitative wide-field imaging of fluorophore dynamics at or near the plasma membrane.     

Eliminating Unwanted Far-Field Excitation in Objective-Type TIRF. Part II. Combined Evanescent-Wave Excitation and Supercritical-Angle Fluorescence Detection Improves Optical Sectioning

Azimuthal beam scanning makes evanescent-wave (EW) excitation isotropic, thereby producing total internal reflection fluorescence (TIRF) images that are evenly lit. However, beam spinning does not fundamentally address the problem of propagating excitation light that is contaminating objective-type TIRF. Far-field excitation depends more on the specific objective than on cell scattering. As a consequence, the excitation impurities in objective-type TIRF are only weakly affected by changes of azimuthal or polar beam angle. These are the main results of the first part of this study (Eliminating unwanted far-field excitation in objective-type TIRF. Pt.1. Identifying sources of nonevanescent excitation light). This second part focuses on exactly where up beam in the illumination system stray light is generated that gives rise to nonevanescent components in TIRF. Using dark-field imaging of scattered excitation light we pinpoint the objective, intermediate lenses and, particularly, the beam scanner as the major sources of stray excitation. We study how adhesion-molecule coating and astrocytes or BON cells grown on the coverslip surface modify the dark-field signal. On flat and weakly scattering cells, most background comes from stray reflections produced far from the sample plane, in the beam scanner and the objective lens. On thick, optically dense cells roughly half of the scatter is generated by the sample itself. We finally show that combining objective-type EW excitation with supercritical-angle fluorescence (SAF) detection efficiently rejects the fluorescence originating from deeper sample regions. We demonstrate that SAF improves the surface selectivity of TIRF, even at shallow penetration depths. The coplanar microscopy scheme presented here merges the benefits of beam spinning EW excitation and SAF detection and provides the conditions for quantitative wide-field imaging of fluorophore dynamics at or near the plasma membrane.     

珠江口水体的光学特征及分析

通过2003年1月份对珠江口水体中的光谱分布,衰减系数,光反射率以及浮游植物对光吸收的研究结果显示:红光、蓝光衰减较快,绿光衰减较小,越向水体下层,绿光的相对含量越大,这主要是由于浮游植物在蓝光和红光波段处有吸收峰以及非藻颗粒对蓝紫光吸收较多的缘故;从总体来讲,绿光的辐亮度漫反射率(Lu/Ed)较蓝光和红光大:在上层水体中有一个反射强度较大的区域,可能是由于浮游植物在这一层的分布较多。     

Assessing understanding in biology

This paper discusses several new assessment strategies that encourage meaningful learning and conceptual understanding in the biological sciences. Our purpose is to introduce a handful of evaluation and measurement techniques that help students assimilate well-integrated, strongly cohesive frameworks of interrelated concepts as a way of facilitating ‘real understanding’ of natural phenomena. Among these methods are concept maps, V diagrams, SemNet software, image-based test items, clinical interviews, portfolios, written products, performance measures, and conceptual diagnostic tests. Evidence suggests that these methods are most useful at highlighting ‘alternative conceptions’ and assisting students who wish to ‘learn how to learn’.