Science.gov

Sample records for huxley correspondence letters

  1. Early Literacy: Making Letter-Sound Correspondence

    ERIC Educational Resources Information Center

    Neuman, Susan B.

    2006-01-01

    One of the most important skills for children to develop in the kindergarten year is the recognition that letters and sounds are related. It is often called "the alphabetic principle"--the notion that speech sounds can be connected to letters in a predictable way. To grasp the alphabetic principle, children need to understand that: (1) letters…

  2. A correspondence between the models of Hodgkin-Huxley and FitzHugh-Nagumo revisited

    NASA Astrophysics Data System (ADS)

    Postnikov, Eugene B.; Titkova, Olga V.

    2016-11-01

    We present the discussion on the possibility to scale the classical dimensionless FitzHugh-Nagumo model of neuronal self-sustained oscillations to the range of variables corresponding to the results, which are provided by the biophysically relevant reduced two-dimensional Hodgkin-Huxley equations (the Rinzel model). It is shown that there exists a relatively simple choice of affine transformation, which results in time-dependent solutions, which reproduce with a high accuracy the time course of the recovery variable and the sharp onsets (intervals of fast motions on a phase trajectories) of the voltage spikes. As for the latter, the reasons for unavoidable difference are discussed as well as a necessity of taking into account applied current values during such a scaling procedure.

  3. Plaidoyer pour la video-correspondance (Argument for Video Letters).

    ERIC Educational Resources Information Center

    Camilleri, Clara; Morelli, Rita

    1992-01-01

    A discussion of the second-language teaching technique of creating "video letters" responds to the questions commonly asked by skeptics about the technique's effectiveness and place in the curriculum. Advantages cited include development of learner autonomy, use of a medium familiar to students, and potential for skill development. (MSE)

  4. The Genesis of Reading Ability: What Helps Children Learn Letter-Sound Correspondences?

    ERIC Educational Resources Information Center

    Castles, Anne; Coltheart, Max; Wilson, Katherine; Valpied, Jodie; Wedgwood, Joanne

    2009-01-01

    Knowledge of letter-sound correspondences underpins successful reading acquisition, and yet little is known about how young children acquire this knowledge and what prior information they bring to the learning process. In this study, we used an experimental training design to examine whether either prior letter awareness or prior phonemic…

  5. The Genesis of Reading Ability: What Helps Children Learn Letter-Sound Correspondences?

    ERIC Educational Resources Information Center

    Castles, Anne; Coltheart, Max; Wilson, Katherine; Valpied, Jodie; Wedgwood, Joanne

    2009-01-01

    Knowledge of letter-sound correspondences underpins successful reading acquisition, and yet little is known about how young children acquire this knowledge and what prior information they bring to the learning process. In this study, we used an experimental training design to examine whether either prior letter awareness or prior phonemic…

  6. 19 CFR 145.3 - Opening of letter class mail; reading of correspondence prohibited.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 19 Customs Duties 2 2010-04-01 2010-04-01 false Opening of letter class mail; reading of... HOMELAND SECURITY; DEPARTMENT OF THE TREASURY (CONTINUED) MAIL IMPORTATIONS General Provisions § 145.3 Opening of letter class mail; reading of correspondence prohibited. (a) Matter in addition...

  7. 19 CFR 145.3 - Opening of letter class mail; reading of correspondence prohibited.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 19 Customs Duties 2 2012-04-01 2012-04-01 false Opening of letter class mail; reading of... HOMELAND SECURITY; DEPARTMENT OF THE TREASURY (CONTINUED) MAIL IMPORTATIONS General Provisions § 145.3 Opening of letter class mail; reading of correspondence prohibited. (a) Matter in addition...

  8. 19 CFR 145.3 - Opening of letter class mail; reading of correspondence prohibited.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 19 Customs Duties 2 2011-04-01 2011-04-01 false Opening of letter class mail; reading of... HOMELAND SECURITY; DEPARTMENT OF THE TREASURY (CONTINUED) MAIL IMPORTATIONS General Provisions § 145.3 Opening of letter class mail; reading of correspondence prohibited. (a) Matter in addition...

  9. 19 CFR 145.3 - Opening of letter class mail; reading of correspondence prohibited.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 19 Customs Duties 2 2013-04-01 2013-04-01 false Opening of letter class mail; reading of... HOMELAND SECURITY; DEPARTMENT OF THE TREASURY (CONTINUED) MAIL IMPORTATIONS General Provisions § 145.3 Opening of letter class mail; reading of correspondence prohibited. (a) Matter in addition...

  10. 19 CFR 145.3 - Opening of letter class mail; reading of correspondence prohibited.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 19 Customs Duties 2 2014-04-01 2014-04-01 false Opening of letter class mail; reading of... HOMELAND SECURITY; DEPARTMENT OF THE TREASURY (CONTINUED) MAIL IMPORTATIONS General Provisions § 145.3 Opening of letter class mail; reading of correspondence prohibited. (a) Matter in addition...

  11. Instruction in Letter-Sound Correspondences for Children with Autism and Limited Speech

    ERIC Educational Resources Information Center

    Benedek-Wood, Elizabeth; McNaughton, David; Light, Janice

    2016-01-01

    This study used a multiple probe across participants' research design to evaluate the effects of instruction on the acquisition of letter-sound correspondences (LSCs) by three young children with autism spectrum disorder and limited speech. All three children (ages 3-5 years) reached criterion for identifying the LSCs targeted during instruction,…

  12. The Case for Teaching Sound-to-Letter Correspondences in Spelling.

    ERIC Educational Resources Information Center

    Hodges, Richard E.

    1966-01-01

    In an attempt to resolve the controversy about the nature of our spelling system, researchers conducted a study of American English orthography which reaffirmed the case for teaching spelling on the basis of patterns of sound-to-letter correspondences. The controversy involved the Paul Hanna-James Moore study and Ernest Horn's critique of their…

  13. Instruction in Letter-Sound Correspondences for Children with Autism and Limited Speech

    ERIC Educational Resources Information Center

    Benedek-Wood, Elizabeth; McNaughton, David; Light, Janice

    2016-01-01

    This study used a multiple probe across participants' research design to evaluate the effects of instruction on the acquisition of letter-sound correspondences (LSCs) by three young children with autism spectrum disorder and limited speech. All three children (ages 3-5 years) reached criterion for identifying the LSCs targeted during instruction,…

  14. Where have all the copy letters gone? A review of current practice in professional-patient correspondence.

    PubMed

    Baxter, Susan; Farrell, Kathleen; Brown, Caroline; Clarke, Jayne; Davies, Helena

    2008-05-01

    This article reviews the literature in relation to patients receiving copies of health professional correspondence. It examines progress in adopting the practice 3 years on from its introduction as policy in the UK, and considers potential benefits and obstacles to implementation. A review of the literature on copy correspondence, accessed via Medline, PubMed, CINAHL and also online resources, using the search terms "patient letter", "copy letter", "copy correspondence" and "doctor letter". Studies describe a range of benefits from copying letters, but implementation remains inconsistent, ranging from 8 to 87% of patients reporting receiving copy correspondence. A number of concerns are identified which may be delaying whole scale adoption of the policy by health professionals. This review suggests that researchers should move from examining the benefits and concerns around copying letters to patients, and instead focus on exploring the quality of correspondence and the optimum process of implementing the practice. As patients can "opt out" of receiving copy correspondence, audit of service delivery may be better assessed by whether patients have been offered a letter, rather than the current measure of whether one has been received. Copying letters to patients may have a number of important benefits and should be routine practice where patients wish to receive correspondence. Further discussion regarding the style and content of letters would be beneficial, together with attention paid to the mechanisms for recording patient preference. There is also a need for studies in non-medical professions.

  15. Comparison of fixed and gradual array when teaching sound-letter correspondence to two children with autism who use AAC.

    PubMed

    Johnston, Susan S; Buchanan, Sara; Davenport, Lisa

    2009-06-01

    The purpose of this study was to compare two conditions for teaching two children with autism (ages 4;10 and 5;4) who used Augmentative and Alternative Communication (AAC) to point to the printed letter that corresponded to the spoken letter sounds of /t/ and /m/. In one condition (gradual array), the printed letter was first presented in isolation and then distracter letters were gradually introduced. In the other condition (fixed array), the printed letter was immediately presented in combination with seven distracter letters. Using an alternating treatment design, results revealed that the fixed array condition resulted in a faster rate of acquisition of target skills for both participants. Implications and directions for future research are discussed.

  16. Thomas Birch's 'Weekly Letter' (1741-66): correspondence and history in the mid-eighteenth-century Royal Society.

    PubMed

    Ellis, Markman

    2014-09-20

    Thomas Birch (1705-66), Secretary of the Royal Society from 1752 to 1765, and Philip Yorke, second Earl of Hardwicke (1720-90), wrote a 'Weekly Letter' from 1741 to 1766, an unpublished correspondence of 680 letters now housed in the British Library (Additional Mss 35396-400). The article examines the dimensions and purposes of this correspondence, an important conduit of information for the influential coterie of the 'Hardwicke circle' gathered around Yorke in the Royal Society. It explores the writers' self-conception of the correspondence, which was expressed in deliberately archaic categories of seventeenth-century news exchange, such as the newsletter, aviso and a-la-main. It shows how the letter writers negotiated their difference in status through the discourse of friendship, and concludes that the 'Weekly Letter' constituted for the correspondents a form of private knowledge, restricted in circulation to their discrete group, and as such unlike the open and networked model of Enlightenment science.

  17. Letters from Dom Pedro II to professor Brown-Séquard: imperial correspondence and neurophysiology.

    PubMed

    Teive, Hélio A G; Germiniani, Francisco M B; Munhoz, Renato P; Lees, Andrew J

    2012-08-01

    The authors have analyzed the content of a selection of letters written by Dom Pedro II, the Emperor of Brazil, and sent to Doctor Charles Brown-Séquard, the famous neurologist, between 1876 and 1885. The content of those letters focuses mainly on his wife's, Princess Thereza Cristina, health issues and Dom Pedro's personal desire to foster the research into the physiological study of the nervous system.

  18. Friendly Letters on the Correspondence of Helen Keller, Anne Sullivan, and Alexander Graham Bell.

    ERIC Educational Resources Information Center

    Blatt, Burton

    1985-01-01

    Excerpts from the letters between Alexander Graham Bell and Anne Sullivan and Helen Keller are given to illustrate the educational and personal growth of Helen Keller as well as the educational philosophy of Bell regarding the education of the deaf blind. (DB)

  19. Friendly Letters on the Correspondence of Helen Keller, Anne Sullivan, and Alexander Graham Bell.

    ERIC Educational Resources Information Center

    Blatt, Burton

    1985-01-01

    Excerpts from the letters between Alexander Graham Bell and Anne Sullivan and Helen Keller are given to illustrate the educational and personal growth of Helen Keller as well as the educational philosophy of Bell regarding the education of the deaf blind. (DB)

  20. Letters

    NASA Astrophysics Data System (ADS)

    2001-03-01

    The Editor welcomes letters, by e-mail to ped@iop.org or by post to Dirac House, Temple Back, Bristol BS1 6BE Contents: Force on a pendulum Sound slows down Bond is back Force on a pendulum The simple pendulum has been used by several educationalists for investigating the patterns of thinking among students and their observations that Aristotelian thinking persists among students at college level. I had also considered the simple pendulum in my 1985 letter in Physics Today [1], so I was interested to read the test given by Lenka Czudková and Jana Musilová [2]. When students were asked to draw net forces acting on the particle at various positions, 31.9% of students believed that the net force was tangential to the particle's path the whole time. To me this is no surprise because in our derivation of the equation for the period of a simple pendulum we assume that the unbalanced sine component provides the restoring force for the harmonic motion of the bob. Of course, Czudková and Musilová's question asked students for the net force on the particle, not the component. The student's answer fits well with the logic of the equilibrium of forces and the parallelogram law. Lastly, let me bring out the similarity between the student's answer and the thinking of George Gamow. He used to call positrons 'donkey' electrons because of their displacement against the applied force, before Paul Dirac termed them positrons. Victor Weisskeptf told me this anecdote in a letter in May 1982. References [1] Sathe D 1985 Phys. Today 38 144 [2] Czudková L and Musilová J 2000 Phys. Educ. 35 428 Dileep V Sathe Dadawala Jr College, Pune, India Sound slows down Without wanting to stir up more trouble amongst the already muddy waters of Physics teaching, consider how many times you have heard (or, more worryingly, read) this: 'Sound waves travel faster in a denser material' But...The velocity of simple longitudinal waves in a bulk medium is given by v = (K/ρ)1/2 where K is

  1. Teaching sound letter correspondence and consonant-vowel-consonant combinations to young children who use augmentative and alternative communication.

    PubMed

    Johnston, Susan S; Davenport, Lisa; Kanarowski, Betsy; Rhodehouse, Sara; McDonnell, Andrea P

    2009-06-01

    The purpose of this study was to provide a preliminary examination of an intervention strategy designed to teach sound-letter correspondence and spelling of consonant-vowel-consonant (CVC) combinations to young children who use Augmentative and Alternative Communication (AAC). A multiple baseline probe design across behaviors was used to assess the effects of the intervention on the percentage of correct responses provided by two participants on the target skills during free-choice play activities in the literacy center of inclusive classrooms. The results of this study provide preliminary support for the use of the intervention strategy within inclusive classrooms.

  2. Letter to the Editor of Communications in Statistics and Copies of Documenting Correspondence.

    DTIC Science & Technology

    1980-06-01

    snowboard data from the total network yet in any of our own papers. We have restricted our publications to date to data from the permanently manned...better than others). We are comparing snowboard data (7 years) with corresponding shielded precipitation gages at the respective sites (2 years only

  3. The correspondence of Thomas Dale (1700-1750): Botany in the transatlantic Republic of Letters.

    PubMed

    Cook, William J

    2012-03-01

    This paper seeks to provide a full account of the life and career of Dr. Thomas Dale (1700-1750), with particular reference to his botanical works and correspondence. Born in Hoxton, London, Dale studied medicine at Leiden and engaged fully in the social, literary and epistolary network in which botany was practised in eighteenth-century England. In 1730, however, Dale relocated to the British colonial port of Charles Town, South Carolina. Here he continued to engage in a transatlantic network of botanical exchange and discussion, corresponding on equal and reciprocal terms with his former colleagues in England. Where Dale differs from naturalists in South Carolina before him is that his motives for pursuing botany and for corresponding with English naturalists were located firmly in the New World. Such a conclusion forms a valuable, albeit small contribution to models for the development of national scientific cultures in the imperial world. Similarly, Dale's pursuit of botanical information in South Carolina provides a small amount of material with which to illustrate currently fashionable models for the mediated exchange and circulation of scientific knowledge. Copyright © 2011 Elsevier Ltd. All rights reserved.

  4. Letters

    NASA Astrophysics Data System (ADS)

    2001-07-01

    The Editor welcomes letters, by e-mail to ped@iop.org or by post to Dirac House, Temple Back, Bristol BS1 6BE, UK. Contents: Alternative view of education in Zambia Pedantry or compromise Alternative view of education in Zambia I have just read the 'On the Map' report of the International School of Lusaka with very mixed feelings (Physics Education, March 2001). I have recently spent some time in Zambia, in Lusaka, and share Sue Pears' love for the country and the Zambians. The ISL is indeed a good, prestigious school, similar to International Schools in many other countries. But, as in most other developing countries, there is enormous variation between the different types of schooling, and the ISL is at one end of the spectrum. Most schools in Zambia are less favoured. Zambia is a wonderful, beautiful country full of the most friendly and resourceful people I know. It is also a very poor country. It is a country of enormous contrasts and its schools reflect that variation. It has a tiny, affluent 'middle' class of professionals, politicians, businessmen, employees of international businesses and NGOs—nearly all paid from overseas budgets. It has an enormous majority of poor folk, cheerfully living in very basic conditions but sharing their lives in extended families without complaint. The government is virtually bankrupt, and consequently those paid by the government—teachers, police, nurses etc—get a pittance. The wage for a teacher in a typical school is #20 per month (compared to a typical teacher in the UK who gets 100 times more, about #2000 per month). The GNP in Zambia is about 1 per day per person, and this has to pay for all the schools, hospitals, police, and the civic infrastructure that we take so much for granted (the GNP in UK is about 60 per day per person). Consequently most state schools do not have resources; they have a classroom and a teacher but little else. What resources the school has will be paid for by the school fees that every

  5. Letters

    NASA Astrophysics Data System (ADS)

    2001-01-01

    The Editor welcomes letters, by e-mail to ped@iop.org or by post to Dirac House, Temple Back, Bristol BS1 6BE, UK. Contents: Maths for physics? Help! Fire! Energy and mass Maths for physics? As a maths graduate working as a university research associate I should be well qualified to support my daughter, who has just started AS-level physics, with the maths she needs for the course. There seems to be little integration between the maths and physics departments, so that maths needed for physics has not yet been covered in maths lessons. This is a problem I remember from my own school days, but the shorter timescale and modular nature of the AS and A2 levels means that it is essential that this mismatch of knowledge is resolved now. I would like to know whether physics teachers in the UK have encountered this problem and whether there is a deficiency in the maths syllabus in relation to the requirements of the AS and A2 levels in Physics or whether this is a problem peculiar to my daughter's school. Eleanor Parent of A-level student, Sheffield, UK Help! Fire! Is there a crisis in physics education? Is physics didactics coming to an end? Yes and no. Being a delegate from Norway at the on-going conference Physics on Stage (6-10 November 2000) at CERN in Geneva, I have had the opportunity to discuss this with people from all over Europe. Yes, there is a crisis. (Look at the proceedings for details on this.) I'd like to take a broader look at this situation. Like Hari Seldon in Isaac Asimov's Foundation Trilogy, I believe that there is nothing like a real crisis to get things going... Famous is the quote from the American Patent Office around 1890: 'Everything has been invented that could be invented'. Fortunately, this spurred action. The Michelson and Morley experiment heralded a most exciting period for physics. Just a cosmic blink later we put a person on the Moon. Coming back to the crisis - I am certain that in the near future we will see an interesting development

  6. Letters

    NASA Astrophysics Data System (ADS)

    2001-09-01

    The Editor welcomes letters, by e-mail to ped@iop.org or by post to Dirac House, Temple Back, Bristol BS1 6BE, UK. Contents: M-set as metaphor The abuse of algebra M-set as metaphor 'To see a World in a Grain of Sand And a Heaven in a Wild Flower Hold Infinity in the palm of your hand And Eternity in an hour' William Blake's implied relativity of spatial and temporal scales is intriguing and, given the durability of this worlds-within-worlds concept (he wrote in 1803) in art, literature and science, the blurring of distinctions between the very large and the very small must strike some kind of harmonious chord in the human mind. Could this concept apply to the physical world? To be honest, we cannot be absolutely sure. Most cosmological thinking still retains the usual notions of a finite universe and an absolute size scale extending from smallest to largest objects. In the boundless realm of mathematics, however, the story is quite different. The M-set was discovered by the French mathematician Benoit Mandelbrot in 1980, created by just a few simple lines of computer code that are repeated recursively. As in Blake's poem, this 'world' has no bottom we have an almost palpable archetype for the concept of infinity. I would use the word 'tangible', but one of the defining features of the M-set is that nowhere in the labyrinth can one find a surface smooth enough for a tangent. Upon magnification even surfaces that appeared to be smooth explode with quills and scrolls and lightning bolts and spiral staircases. And there is something more, something truly sublime. Observe a small patch with unlimited magnifying power and, as you observe the M-set on ever-smaller scales, down through literally endless layers of ornate structure, you occasionally come upon a rapidly expanding cortex of dazzling colour with a small black structure at its centre. The black spot appears to be the M-set itself! There is no end to the hierarchy, no bottom-most level, just endless recursive

  7. Letters

    NASA Astrophysics Data System (ADS)

    2001-05-01

    The Editor welcomes letters, by e-mail to ped@iop.org or by post to Dirac House, Temple Back, Bristol BS1 6BE, UK. Contents: Quantum uncertainties Reflections in a plastic box A brief history of quantum physics Correction Grammar and gender Quantum uncertainties Whilst I enjoyed Gesche Pospiech's article ('Uncertainty and complementarity: the heart of quantum physics' 2000 Phys. Educ. 35 393 9) I would like to expand on two comments he makes. Firstly the author claims that QM is linear, and a consequence of this is that any two superimposed states form an admissible third state. This is rather too sweeping, as it is true only for degenerate states. Otherwise quantum mechanics would allow a continuum of energies between states by a simple admixture of levels. The proof of this statement is trivial. For a Hamiltonian H and two orthogonal wavefunctions, ψ1 and ψ2 with energies E1 and E2 then (ψ1 + ψ2) is not an eigenfunction of that Hamiltonian as H(ψ1 + ψ2) = E1ψ1 + E2ψ2 ≠ E(ψ1 + ψ2) for any value of E, unless E1 = E2. Secondly Pospiech states that quantum objects show wave- or particle-like behaviour, depending on the measuring apparatus, and that occasionally experiments (such as Taylor's) reveal both. I would contest the validity of this type of thinking. All experiments on quantum objects reveal both types of behaviour—even ones which simply show straight line motion of photons. What is important, in addition, is our interpretation of the results. It takes an understanding of QED, for example, to see that an experiment which otherwise shows particle behaviour is, in fact, showing quantum behaviour. More contentiously though I would suggest that detection apparatus is incapable of detecting anything other than particles. Wave-like behaviour is revealed only by an analysis of the paths the particle could have taken. In other words, the interference of continuous fields sometimes predicts the same results when the detection is averaged over many events

  8. The Effectiveness of a Multi Sensory Approach in Improving Letter-Sound Correspondence among Mild Intellectual Disabled Students in State of Kuwait

    ERIC Educational Resources Information Center

    Moustafa, Amr; Ghani, Mohd Zuri

    2016-01-01

    This research examines the effectiveness of multi sensory approach for the purpose of improving the knowledge on English Letter sound correspondence among mild disabled students in the state of Kuwait. The discussion in this study is based on the multisensory approach that could be applied in the teaching of reading skills as well as phonemic…

  9. Supplemental Flashcard Drill Methods for Efficiently Helping At-Risk Kindergartners Make Letter-Sound Correspondences: Does Presentation Arrangement of Words Matter?

    ERIC Educational Resources Information Center

    Griffin, Crystal; Joseph, Laurice M.

    2015-01-01

    Variations of supplemental flashcard drill and practice instructional procedures (i.e., massed practice and interspersal presentation arrangements of words) were examined for six kindergartners who struggled making letter-sound correspondences. Findings revealed that the children demonstrated the highest learning rates when the presentation…

  10. Supplemental Flashcard Drill Methods for Efficiently Helping At-Risk Kindergartners Make Letter-Sound Correspondences: Does Presentation Arrangement of Words Matter?

    ERIC Educational Resources Information Center

    Griffin, Crystal; Joseph, Laurice M.

    2015-01-01

    Variations of supplemental flashcard drill and practice instructional procedures (i.e., massed practice and interspersal presentation arrangements of words) were examined for six kindergartners who struggled making letter-sound correspondences. Findings revealed that the children demonstrated the highest learning rates when the presentation…

  11. Circles of Confidence in Correspondence: Modeling Confidentiality and Secrecy in Knowledge Exchange Networks of Letters and Drawings in the Early Modern Period.

    PubMed

    van den Heuvel, Charles; Weingart, Scott B; Spelt, Nils; Nellen, Henk

    2016-01-01

    Science in the early modern world depended on openness in scholarly communication. On the other hand, a web of commercial, political, and religious conflicts required broad measures of secrecy and confidentiality; similar measures were integral to scholarly rivalries and plagiarism. This paper analyzes confidentiality and secrecy in intellectual and technological knowledge exchange via letters and drawings. We argue that existing approaches to understanding knowledge exchange in early modern Europe--which focus on the Republic of Letters as a unified entity of corresponding scholars--can be improved upon by analyzing multilayered networks of communication. We describe a data model to analyze circles of confidence and cultures of secrecy in intellectual and technological knowledge exchanges. Finally, we discuss the outcomes of a first experiment focusing on the question of how personal and professional/official relationships interact with confidentiality and secrecy, based on a case study of the correspondence of Hugo Grotius.

  12. Correspondence standards

    NASA Technical Reports Server (NTRS)

    1992-01-01

    This revised handbook covers the drafting, preparation, and review of NASA letters, memorandums, informal communications, electronic communications, envelopes and mailing, and classified correspondence. The appendices address specific guidelines for administrator's correspondence, White House and Congressional correspondance, Privacy Act correspondence, and foreign correspondence. Also incorporated as appendices are quick references for forms of address, compound words, and capitalization of words frequently used at NASA.

  13. Correspondencia (Correspondence).

    ERIC Educational Resources Information Center

    Brannan, Robert

    The language of Spanish correspondence possesses particular characteristics that lie somewhere between the everyday conversational style and the more formal literary style. This minicourse contains three lessons intended to enable the student to learn the letter-writing style and to write letters in Spanish. It is also intended to encourage and…

  14. Evolution and Education: Lessons from Thomas Huxley

    ERIC Educational Resources Information Center

    Lyons, Sherrie Lynne

    2010-01-01

    Thomas Huxley more than anyone else was responsible for disseminating Darwin's theory in the western world and maintained that investigating the history of life should be regarded as a purely scientific question free of theological speculation. The content and rhetorical strategy of Huxley's defense of evolution is analyzed. Huxley argued that the…

  15. Evolution and Education: Lessons from Thomas Huxley

    ERIC Educational Resources Information Center

    Lyons, Sherrie Lynne

    2010-01-01

    Thomas Huxley more than anyone else was responsible for disseminating Darwin's theory in the western world and maintained that investigating the history of life should be regarded as a purely scientific question free of theological speculation. The content and rhetorical strategy of Huxley's defense of evolution is analyzed. Huxley argued that the…

  16. Heuristics for the Hodgkin-Huxley system.

    PubMed

    Hoppensteadt, Frank

    2013-09-01

    Hodgkin and Huxley (HH) discovered that voltages control ionic currents in nerve membranes. This led them to describe electrical activity in a neuronal membrane patch in terms of an electronic circuit whose characteristics were determined using empirical data. Due to the complexity of this model, a variety of heuristics, including relaxation oscillator circuits and integrate-and-fire models, have been used to investigate activity in neurons, and these simpler models have been successful in suggesting experiments and explaining observations. Connections between most of the simpler models had not been made clear until recently. Shown here are connections between these heuristics and the full HH model. In particular, we study a new model (Type III circuit): It includes the van der Pol-based models; it can be approximated by a simple integrate-and-fire model; and it creates voltages and currents that correspond, respectively, to the h and V components of the HH system.

  17. [Short-, middle and long-term effects of training in phonological awareness and letter-sound correspondence on phonological awareness and on reading and spelling].

    PubMed

    Blaser, Regula; Preuss, Ulrich; Groner, Marina; Groner, Rudolf; Felder, Wilhelm

    2007-07-01

    The present study intended to evaluate the short-, middle and long-term effects of preschool training in phonological awareness and letter-sound correspondence, conducted in Swiss dialect in Swiss kindergartens, on the basis of the outcome variables phonological awareness and reading and spelling competence. From a total sample of 109 children with complete datasets over all measurement points, a paired sample of 26 children each from the experimental and from the control group was selected for statistical analyses. Evaluated on the one hand were the short- middle and longer-term effects of the training on the development of the phonological awareness, while on the other, the average reading and spelling competencies and the percentage of reading-and-spelling disabled children in the training and in the control group were compared for the 1st and 2nd grades. Effects of the training on phonological awareness could be documented up to the beginning of the 1st grade. The average reading and spelling competencies did not differ be-tween the groups, whereas the percentage of spelling-disabled children was markedly reduced in the training group. As a whole, the results are seen as a confirmation of the efficacy of the training in the primary prevention of reading and writing disorders.

  18. [Prevention of dyslexia – short-term and intermediate effects of promoting phonological awareness and letter-sound correspondence with at-risk preschool children].

    PubMed

    Höse, Anna; Wyschkon, Anne; Moraske, Svenja; Eggeling, Marie; Quandte, Sabine; Kohn, Juliane; Poltz, Nadine; von Aster, Michael; Esser, Günter

    2016-09-01

    This study assesses the short-term and intermediate effects of preschool training stimulating phonological awareness and letter-sound correspondence for children at risk of developing dyslexia. Moreover, we examined whether training reduced the frequency of subsequent dyslexic problems. 25 children at risk of developing dyslexia were trained with Hören, Lauschen, Lernen 1 und 2 (Küspert & Schneider, 2008; Plume & Schneider, 2004) by their kindergarten teachers and were compared with 60 untrained at-risk children. The training revealed a significant short-term effect: The phonological awareness of trained at-risk children increased significantly over that of untrained at-risk children. However, there were no differences in phonological awareness, spelling, and reading ability between the first-graders in the training and control group. Furthermore, reading problems were reduced in the training group. In the future, phonological awareness as well as additional predictors should be included when identifying children vulnerable to developing dyslexia. Moreover, in order to prevent dyslexia, additional prerequisite deficits need to be identified, alleviated, and their effects evaluated.

  19. Letters and Letter Writing.

    ERIC Educational Resources Information Center

    Frese, Millie K., Ed.

    1998-01-01

    "The Goldfinch" is a periodical that introduces young children to various facets of Iowa history. Each issue has a different theme topic and a number of articles covering diverse aspects of the topic being addressed. This issue focuses on letters and letter writing. Featured articles discuss letters that illuminate historical events. The…

  20. How a Neurologically Integrated Approach Which Teaches Sound-Symbol Correspondence and Legible Letter Formations Impacts At-Risk First Graders

    ERIC Educational Resources Information Center

    Shaw, Donita Massengill; Sundberg, Mary Lou

    2008-01-01

    The setting of this study took place in an inner city. The purpose was to determine the effectiveness of a neurologically integrated approach in teaching 43 at-risk pre-first graders their letter sounds and formations during 45-50 hours of summer school. There were four sequential phases to teaching this alphabetic approach: imagery, auditory,…

  1. Population Encoding With Hodgkin–Huxley Neurons

    PubMed Central

    Lazar, Aurel A.

    2013-01-01

    The recovery of (weak) stimuli encoded with a population of Hodgkin–Huxley neurons is investigated. In the absence of a stimulus, the Hodgkin–Huxley neurons are assumed to be tonically spiking. The methodology employed calls for 1) finding an input–output (I/O) equivalent description of the Hodgkin–Huxley neuron and 2) devising a recovery algorithm for stimuli encoded with the I/O equivalent neuron(s). A Hodgkin–Huxley neuron with multiplicative coupling is I/O equivalent with an Integrate-and-Fire neuron with a variable threshold sequence. For bandlimited stimuli a perfect recovery of the stimulus can be achieved provided that a Nyquist-type rate condition is satisfied. A Hodgkin–Huxley neuron with additive coupling and deterministic conductances is first-order I/O equivalent with a Project-Integrate-and-Fire neuron that integrates a projection of the stimulus on the phase response curve. The stimulus recovery is formulated as a spline interpolation problem in the space of finite length bounded energy signals. A Hodgkin–Huxley neuron with additive coupling and stochastic conductances is shown to be first-order I/O equivalent with a Project-Integrate-and-Fire neuron with random thresholds. For stimuli modeled as elements of Sobolev spaces the reconstruction algorithm minimizes a regularized quadratic optimality criterion. Finally, all previous recovery results of stimuli encoded with Hodgkin–Huxley neurons with multiplicative and additive coupling, and deterministic and stochastic conductances are extended to stimuli encoded with a population of Hodgkin–Huxley neurons. PMID:24194625

  2. Population Encoding With Hodgkin-Huxley Neurons.

    PubMed

    Lazar, Aurel A

    2010-02-01

    The recovery of (weak) stimuli encoded with a population of Hodgkin-Huxley neurons is investigated. In the absence of a stimulus, the Hodgkin-Huxley neurons are assumed to be tonically spiking. The methodology employed calls for 1) finding an input-output (I/O) equivalent description of the Hodgkin-Huxley neuron and 2) devising a recovery algorithm for stimuli encoded with the I/O equivalent neuron(s). A Hodgkin-Huxley neuron with multiplicative coupling is I/O equivalent with an Integrate-and-Fire neuron with a variable threshold sequence. For bandlimited stimuli a perfect recovery of the stimulus can be achieved provided that a Nyquist-type rate condition is satisfied. A Hodgkin-Huxley neuron with additive coupling and deterministic conductances is first-order I/O equivalent with a Project-Integrate-and-Fire neuron that integrates a projection of the stimulus on the phase response curve. The stimulus recovery is formulated as a spline interpolation problem in the space of finite length bounded energy signals. A Hodgkin-Huxley neuron with additive coupling and stochastic conductances is shown to be first-order I/O equivalent with a Project-Integrate-and-Fire neuron with random thresholds. For stimuli modeled as elements of Sobolev spaces the reconstruction algorithm minimizes a regularized quadratic optimality criterion. Finally, all previous recovery results of stimuli encoded with Hodgkin-Huxley neurons with multiplicative and additive coupling, and deterministic and stochastic conductances are extended to stimuli encoded with a population of Hodgkin-Huxley neurons.

  3. [R. Goldschmidt and J. Huxley: creative parallelisms].

    PubMed

    Golubovskiĭ, M D; Gall, Ia M

    2003-01-01

    The comparative analysis of scientific heritage of Richard Goldschmidt and Julian Huxley shows convincingly the resemblance of these two scientists' views over the core problems of evolutionary theory, genetics and development biology. They both contributed to developing a triad "genetics--development--evolution". The problem of a relative growth of animals was the central point in both Goldschmidt's and Huxley's works. Huxley developed a formula of the allometric growth (law of constant differential growth) while Goldschmidt was the first to draw up the broad interpretation of the consequences of that phenomenon. Both scientists belonged to initiators of development genetics and used the "non-morganian" genetics in their efforts of solving problems of macroevolution. Goldschmidt tended toward an idea of an important role of macromutation in the process of macroevolution, though Huxley adhered to more moderate views. But at the same time the concept of preadaptive mutations proposed by Huxley was close to Goldschmidt's idea of macromutants. It is shown that both scientists analyzed profoundly the changes in early stages of embryogenesis in respect to macroevolution. It is not likely to be reasonable to oppose firmly Goldschmidt's saltationism to the evolutionary synthesis of Huxley. They developed the larger biological problems in a similar way, and undoubtedly their works in the field helped to enrich the development of the views over genetics and evolution. The open-minded analysis of Goldschmidt's and Huxley's concepts leads to creating modern and up-to-date views over the theory of evolution where seemingly incompatible things go together rather well and supplement each other. Evo-Devo rediscovered Goldshmidt's Biology and Huxley's Synthesis.

  4. Hugh E. Huxley: the compleat biophysicist.

    PubMed

    Hitchcock-DeGregori, Sarah E; Irving, Thomas C

    2014-10-07

    The sliding filament model of muscle contraction, put forward by Hugh Huxley and Jean Hanson in 1954, is 60 years old in 2014. Formulation of the model and subsequent proof was driven by the pioneering work of Hugh Huxley (1924-2013). We celebrate Huxley's integrative approach to the study of muscle contraction; how he persevered throughout his career, to the end of his life at 89 years, to understand at the molecular level how muscle contracts and develops force. Here we show how his life and work, with its focus on a single scientific problem, had impact far beyond the field of muscle contraction to the benefit of multiple fields of cellular and structural biology. Huxley introduced the use of x-ray diffraction to study the contraction in living striated muscle, taking advantage of the paracrystalline lattice that would ultimately allow understanding contraction in terms of single molecules. Progress required design of instrumentation with ever-increasing spatial and temporal resolution, providing the impetus for the development of synchrotron facilities used for most protein crystallography and muscle studies today. From the time of his early work, Huxley combined electron microscopy and biochemistry to understand and interpret the changes in x-ray patterns. He developed improved electron-microscopy techniques, thin sections and negative staining, that enabled answering major questions relating to the structure and organization of thick and thin filaments in muscle and the interaction of myosin with actin and its regulation. Huxley established that the ATPase domain of myosin forms the crossbridges of thick filaments that bind actin, and introduced the idea that myosin makes discrete steps on actin. These concepts form the underpinning of cellular motility, in particular the study of how myosin, kinesin, and dynein motors move on their actin and tubulin tracks, making Huxley a founder of the field of cellular motility.

  5. Hugh E. Huxley: The Compleat Biophysicist

    PubMed Central

    Hitchcock-DeGregori, Sarah E.; Irving, Thomas C.

    2014-01-01

    The sliding filament model of muscle contraction, put forward by Hugh Huxley and Jean Hanson in 1954, is 60 years old in 2014. Formulation of the model and subsequent proof was driven by the pioneering work of Hugh Huxley (1924–2013). We celebrate Huxley’s integrative approach to the study of muscle contraction; how he persevered throughout his career, to the end of his life at 89 years, to understand at the molecular level how muscle contracts and develops force. Here we show how his life and work, with its focus on a single scientific problem, had impact far beyond the field of muscle contraction to the benefit of multiple fields of cellular and structural biology. Huxley introduced the use of x-ray diffraction to study the contraction in living striated muscle, taking advantage of the paracrystalline lattice that would ultimately allow understanding contraction in terms of single molecules. Progress required design of instrumentation with ever-increasing spatial and temporal resolution, providing the impetus for the development of synchrotron facilities used for most protein crystallography and muscle studies today. From the time of his early work, Huxley combined electron microscopy and biochemistry to understand and interpret the changes in x-ray patterns. He developed improved electron-microscopy techniques, thin sections and negative staining, that enabled answering major questions relating to the structure and organization of thick and thin filaments in muscle and the interaction of myosin with actin and its regulation. Huxley established that the ATPase domain of myosin forms the crossbridges of thick filaments that bind actin, and introduced the idea that myosin makes discrete steps on actin. These concepts form the underpinning of cellular motility, in particular the study of how myosin, kinesin, and dynein motors move on their actin and tubulin tracks, making Huxley a founder of the field of cellular motility. PMID:25296301

  6. Intermittency in the Hodgkin-Huxley model.

    PubMed

    Cano, Gaspar; Dilão, Rui

    2017-06-14

    We show that action potentials in the Hodgkin-Huxley neuron model result from a type I intermittency phenomenon that occurs in the proximity of a saddle-node bifurcation of limit cycles. For the Hodgkin-Huxley spatially extended model, describing propagation of action potential along axons, we show the existence of type I intermittency and a new type of chaotic intermittency, as well as space propagating regular and chaotic diffusion waves. Chaotic intermittency occurs in the transition from a turbulent regime to the resting regime of the transmembrane potential and is characterised by the existence of a sequence of action potential spikes occurring at irregular time intervals.

  7. Time to first spike in stochastic Hodgkin Huxley systems

    NASA Astrophysics Data System (ADS)

    Tuckwell, Henry C.; Wan, Frederic Y. M.

    2005-06-01

    The time to first spike is an experimentally observed quantity in laboratory experiments. In the auditory, somatic and visual sensory modalities, the times of first spikes in the corresponding cortical neurons have been implicated as coding much of the information about stimulus properties. We describe an analytical approach for determining the time to first spike from a given initial state which may be applied to a general nonlinear stochastic model neuron. We illustrate with a standard Hodgkin-Huxley model with a Gaussian white-noise input current whose drift parameter is μ and whose variance parameter is σ. Partial differential equations (PDEs) of second order are obtained for the first two moments of the time taken for the depolarization to reach a threshold value from rest state, as functions of the initial values. Simulation confirms that for small noise amplitudes a 2-component model is reasonably accurate. For small values of the noise parameter σ, including the deterministic case σ=0, perturbation methods are used to find the moments of the firing time and the results compare favorably with those from simulation. The approach is accurate for almost all σ when μ is above threshold for action potentials in the absence of noise and over a considerable range of values of σ when μ is as small as 2. The same methods may be applied to models similar to Hodgkin-Huxley which involve channels for additional or different ionic currents.

  8. Evolution and Education: Lessons from Thomas Huxley

    NASA Astrophysics Data System (ADS)

    Lyons, Sherrie Lynne

    2010-05-01

    Thomas Huxley more than anyone else was responsible for disseminating Darwin’s theory in the western world and maintained that investigating the history of life should be regarded as a purely scientific question free of theological speculation. The content and rhetorical strategy of Huxley’s defense of evolution is analyzed. Huxley argued that the classification of humans should be determined independent of any theories of origination of species. Besides providing evidence that demonstrated the close relationship between apes and humans, he also argued that a pithecoid ancestry in no way degraded humankind. In his broader defense of evolution he drew on his agnosticism to define what science could and could not explain. Theology made empirical claims and needed to be subject to the same standards of evidence as scientific claims. He maintained that even most scientific objections to evolution were religiously based. The objections to the theory fundamentally remain the same as in the nineteenth century and much can be learned from Huxley to develop effective strategies for educating the public about evolution. Huxley’s own scientific articles as well as his popular writings provide numerous examples that could be harnessed not only for the teaching of evolution, but also for understanding science as a process.

  9. Brave new world revisited revisited: Huxley's evolving view of behaviorism

    PubMed Central

    Newman, Bobby

    1992-01-01

    Aldous Huxley's Brave New World has served as a popular and powerful source of antibehavioral sentiment. Several of Huxley's works are examined in order to ascertain his true thoughts regarding behaviorism. Early in his career Huxley failed to appreciate aspects of behavioral theory (e.g., an appreciation of heredity) or the good ends to which it could be employed. Huxley's later works portrayed behaviorism in a much more positive light, and he believed that behavioral science, along with spiritual enlightenment, might help save humanity from the Brave New World he predicted. PMID:22478115

  10. Brave new world revisited revisited: Huxley's evolving view of behaviorism.

    PubMed

    Newman, B

    1992-01-01

    Aldous Huxley's Brave New World has served as a popular and powerful source of antibehavioral sentiment. Several of Huxley's works are examined in order to ascertain his true thoughts regarding behaviorism. Early in his career Huxley failed to appreciate aspects of behavioral theory (e.g., an appreciation of heredity) or the good ends to which it could be employed. Huxley's later works portrayed behaviorism in a much more positive light, and he believed that behavioral science, along with spiritual enlightenment, might help save humanity from the Brave New World he predicted.

  11. Randomised trial of the effects of structuring clinic correspondence.

    PubMed

    Melville, C; Hands, S; Jones, P

    2002-05-01

    We performed a randomised controlled crossover trial of clinic letters. Structured letters were compared with conventional letters containing problem lists. There were 32 participants; 25 preferred the structured letter. Median rating and items identified were higher for the structured letter. Structured clinical correspondence with paragraph headings is strongly preferred and increases comprehension.

  12. The Hodgkin-Huxley heritage: from channels to circuits.

    PubMed

    Catterall, William A; Raman, Indira M; Robinson, Hugh P C; Sejnowski, Terrence J; Paulsen, Ole

    2012-10-10

    The Hodgkin-Huxley studies of the action potential, published 60 years ago, are a central pillar of modern neuroscience research, ranging from molecular investigations of the structural basis of ion channel function to the computational implications at circuit level. In this Symposium Review, we aim to demonstrate the ongoing impact of Hodgkin's and Huxley's ideas. The Hodgkin-Huxley model established a framework in which to describe the structural and functional properties of ion channels, including the mechanisms of ion permeation, selectivity, and gating. At a cellular level, the model is used to understand the conditions that control both the rate and timing of action potentials, essential for neural encoding of information. Finally, the Hodgkin-Huxley formalism is central to computational neuroscience to understand both neuronal integration and circuit level information processing, and how these mechanisms might have evolved to minimize energy cost.

  13. Whistles, bells, and cogs in machines: Thomas Huxley and epiphenomenalism.

    PubMed

    Greenwood, John

    2010-01-01

    In this paper I try to shed some historical light upon the doctrine of epiphenomenalism, by focusing on the version of epiphenomenalism championed by Thomas Huxley, which is often treated as a classic statement of the doctrine. I argue that it is doubtful if Huxley held any form of metaphysical epiphenomenalism, and that he held a more limited form of empirical epiphenomenalism with respect to consciousness but not with respect to mentality per se. Contrary to what is conventionally supposed, Huxley's empirical epiphenomenalism with respect to consciousness was not simply based upon the demonstration of the neurophysiological basis of conscious mentality, or derived from the extension of mechanistic and reflexive principles of explanation to encompass all forms of animal and human behavior, but was based upon the demonstration of purposive and coordinated animal and human behavior in the absence of consciousness. Given Huxley's own treatment of mentality, his characterization of animals and humans as "conscious automata" was not well chosen.

  14. A Stimulus Sampling Theory of Letter Identity and Order

    ERIC Educational Resources Information Center

    Norris, Dennis; Kinoshita, Sachiko; van Casteren, Maarten

    2010-01-01

    Early on during word recognition, letter positions are not accurately coded. Evidence for this comes from transposed-letter (TL) priming effects, in which letter strings generated by transposing two adjacent letters (e.g., "jugde") produce large priming effects, more than primes with the letters replaced in the corresponding position (e.g.,…

  15. A Stimulus Sampling Theory of Letter Identity and Order

    ERIC Educational Resources Information Center

    Norris, Dennis; Kinoshita, Sachiko; van Casteren, Maarten

    2010-01-01

    Early on during word recognition, letter positions are not accurately coded. Evidence for this comes from transposed-letter (TL) priming effects, in which letter strings generated by transposing two adjacent letters (e.g., "jugde") produce large priming effects, more than primes with the letters replaced in the corresponding position (e.g.,…

  16. Remembrance of Hugh E. Huxley, a founder of our field.

    PubMed

    Pollard, Thomas D; Goldman, Yale E

    2013-09-01

    Hugh E. Huxley (1924-2013) carried out structural studies by X-ray fiber diffraction and electron microscopy that established how muscle contracts. Huxley's sliding filament mechanism with an ATPase motor protein taking steps along an actin filament, established the paradigm not only for muscle contraction but also for other motile systems using actin and unconventional myosins, microtubules and dynein and microtubules and kinesin.

  17. Alternative Models to Hodgkin-Huxley Equations.

    PubMed

    Deng, Bo

    2017-06-01

    The Hodgkin and Huxley equations have served as the benchmark model in electrophysiology since 1950s. But it suffers from four major drawbacks. Firstly, it is only phenomenological not mechanistic. Secondly, it fails to exhibit the all-or-nothing firing mechanism for action potential generation. Thirdly, it lacks a theory for ion channel opening and closing activation across the cell membrane. Fourthly, it does not count for the phenomenon of voltage-gating which is vitally important for action potential generation. In this paper, a mathematical model for excitable membranes is constructed by introducing circuit characteristics for ion pump exchange, ion channel activation, and voltage-gating. It is demonstrated that the model is capable of re-establishing the Nernst resting potentials, explicitly exhibiting the all-or-nothing firing mechanism, and most important of all, filling the long-lasting theoretical gap by a unified theory on ion channel activation and voltage-gating. It is also demonstrated that the new model has one half fewer parameters but fits significantly better to experiment than the HH model does. The new model can be considered as an alternative template for neurons and excitable membranes when one looks for simpler models for mathematical studies and for forming large networks with fewer parameters.

  18. The Hodgkin-Huxley Heritage: From Channels to Circuits

    PubMed Central

    Catterall, William A.; Raman, Indira M.; Robinson, Hugh P. C.; Sejnowski, Terrence J.; Paulsen, Ole

    2012-01-01

    The Hodgkin-Huxley studies of the action potential, published 60 years ago, are a central pillar of modern neuroscience research, ranging from molecular investigations of the structural basis of ion channel function to the computational implications at circuit level. In this Symposium Review, we aim to demonstrate the ongoing impact of Hodgkin’s and Huxley’s ideas. The Hodgkin-Huxley model established a framework in which to describe the structural and functional properties of ion channels, including the mechanisms of ion permeation, selectivity, and gating. At a cellular level, the model is used to understand the conditions that control both the rate and timing of action potentials, essential for neural encoding of information. Finally, the Hodgkin-Huxley formalism is central to computational neuroscience to understand both neuronal integration and circuit level information processing, and how these mechanisms might have evolved to minimize energy cost. PMID:23055474

  19. Schizophrenia, evolution and the borders of biology: on Huxley et al.'s 1964 paper in Nature.

    PubMed

    De Bont, Raf

    2010-06-01

    In October 1964, Julian Huxley, Ernst Mayr, Humphrey Osmond and Abram Hoffer co-published a controversial paper in Nature, in which they tried to explain the persistence of schizophrenia from an evolutionary perspective. This article will elucidate how the reputed authors composed this paper to make it a strong argument for biological psychiatry. Through a close reading of their correspondence, it will furthermore clarify the elements which remained unspoken in the paper, but which were elementary in its genesis. The first was the dominance of psychoanalytical theory in (American) psychiatry--a dominance which the authors wanted to break. The second was the ongoing discussion on the boundaries of biological determinism and the desirability of a new kind of eugenics. As such, the Huxley et al. paper can be used to study the central issues of psychiatry in a pivotal era of its history.

  20. Challenging normative orthodoxies in depression: Huxley's Utopia or Dante's Inferno?

    PubMed

    Cutcliffe, John R; Lakeman, Richard

    2010-04-01

    Although there appears to be a widespread consensus that depression is a ubiquitous human experience, definitions of depression, its prevalence, and how mental health services respond to it have changed significantly over time, particularly during recent decades. Epistemological limitations notwithstanding, it is now estimated that approximately 121 million people experience depression. At the same time, it should be acknowledged that the last two decades have seen the widespread acceptance of depression as a chemical imbalance and a massive corresponding increase in the prescription of antidepressants, most notably of selective serotonin reuptake inhibitors (SSRIs). However, questions have been raised about the effectiveness and iatrogenic side effects of antidepressants; related questions have also been asked about whose interests are served by the marketing and sales of these drugs. Accordingly, this article attempts to problematize the normative orthodoxy concerning depression and creates a "space" in which an alternative can be articulated and enacted. In so doing, the article finds that the search for a world where the automatic response to depression is a pharmacological intervention not only ignores the use of alternative efficacious treatment options but may also inhibit the persons' chance to explore the meaning of their experience and thus prevent people from individual growth and personal development. Interestingly, in worlds analogous to this pharmacologically induced depression-free state, such as utopias like that in Huxley's Brave New World, no "properly conditioned citizen" is depressed or suicidal. Yet, in the same Brave New World, no one is free to suffer, to be different, or crucially, to be independent. Copyright 2010 Elsevier Inc. All rights reserved.

  1. Models of Discourse in the Letter of Complaint

    ERIC Educational Resources Information Center

    Hartford, Beverly; Mahboob, Ahmar

    2004-01-01

    In both the Outer Circle and the Expanding Circle countries, books which provide examples of letters written in English and guidelines for writing these letters are available for students, business people, and any others who have an interest or need for writing such letters. These model letters are not only for business correspondence, but also…

  2. Models of Discourse in the Letter of Complaint

    ERIC Educational Resources Information Center

    Hartford, Beverly; Mahboob, Ahmar

    2004-01-01

    In both the Outer Circle and the Expanding Circle countries, books which provide examples of letters written in English and guidelines for writing these letters are available for students, business people, and any others who have an interest or need for writing such letters. These model letters are not only for business correspondence, but also…

  3. Julian Huxley, Uca pugnax and the allometric method.

    PubMed

    Packard, Gary C

    2012-02-15

    The allometric method, which often is attributed to Julian Huxley, entails fitting a straight line to logarithmic transformations of the original bivariate data and then back-transforming the resulting equation to form a power function in the arithmetic scale. Development of the technique was strongly influenced by Huxley's own research on growth by the enlarged 'crusher' claw in male fiddler crabs (Uca pugnax). Huxley reported a discontinuity in the log-log plot of chela mass vs body mass, which he interpreted as an abrupt change in relative growth of the chela at about the time crabs attain sexual maturity. My analysis of Huxley's arithmetic data indicates, however, that the discontinuity was an artifact caused by logarithmic transformation and that dynamics of growth by the crusher claw do not change at any point during development. Arithmetic data are well described by a power function fitted by nonlinear regression but not by one estimated by back-transforming a line fitted to logarithms. This finding and others like it call into question the continued reliance on the allometric method in contemporary research.

  4. Huxley College of Environmental Studies, Western Washington University.

    ERIC Educational Resources Information Center

    Miles, John C.

    1987-01-01

    Describes the programs of Huxley College (Washington) which were designed to provide an environmental studies thread through all of its academic endeavors. Addresses the development of the curriculum of both the undergraduate and graduate levels. Discusses its research focal points and its prospects for the future. (TW)

  5. Dartington: A Principal Source of Inspiration behind Aldous Huxley's "Island".

    ERIC Educational Resources Information Center

    Parsons, David

    1987-01-01

    Describes Dartington Hall School in Devon, England, which between the 1920s and 1970s implemented an educational system combining traditional Hindu religious philosophy and ideals of living and Western scientific knowledge and work experience. Considers ways Dartington educationally and socially resembled Aldous Huxley's utopia in…

  6. Jules Janssen's in and out correspondence

    NASA Astrophysics Data System (ADS)

    Launay, Françoise

    2001-10-01

    When she died in 1924, Miss Antoinette Janssen, the only daughter of Jules Janssen (1824-1907), bequeathed all the letters her parents had received at home to the Library of the Institut de France in Paris. That correspondence is still preserved there, in guard-books containing about 1700 letters, the transcription of which is in progress. It is not so easy to trace the outgoing letters and transcribe them, and any help would be much appreciated!

  7. Correspondence analysis

    USDA-ARS?s Scientific Manuscript database

    Correspondence analysis is a powerful exploratory multivariate technique for categorical variables with many levels. It is a data analysis tool that characterizes associations between levels of 2 or more categorical variables using graphical representations of the information in a contingency table...

  8. Correspondence Journals: Talk That Matters

    ERIC Educational Resources Information Center

    Bloem, Patricia L.

    2004-01-01

    Correspondence journals between adults and elementary-school students promote child-centered discussion and learning that is often squeezed out of the curricula. Through an extended example of an exchange of letters between a fifth-grade classroom, including several English-language learners and a university classroom of preservice teachers, the…

  9. Correspondence Journals: Talk That Matters

    ERIC Educational Resources Information Center

    Bloem, Patricia L.

    2004-01-01

    Correspondence journals between adults and elementary-school students promote child-centered discussion and learning that is often squeezed out of the curricula. Through an extended example of an exchange of letters between a fifth-grade classroom, including several English-language learners and a university classroom of preservice teachers, the…

  10. Statistical mechanics of the Huxley-Simmons model

    NASA Astrophysics Data System (ADS)

    Caruel, M.; Truskinovsky, L.

    2016-06-01

    The chemomechanical model of Huxley and Simmons (HS) [A. F. Huxley and R. M. Simmons, Nature 233, 533 (1971), 10.1038/233533a0] provides a paradigmatic description of mechanically induced collective conformational changes relevant in a variety of biological contexts, from muscles power stroke and hair cell gating to integrin binding and hairpin unzipping. We develop a statistical mechanical perspective on the HS model by exploiting a formal analogy with a paramagnetic Ising model. We first study the equilibrium HS model with a finite number of elements and compute explicitly its mechanical and thermal properties. To model kinetics, we derive a master equation and solve it for several loading protocols. The developed formalism is applicable to a broad range of allosteric systems with mean-field interactions.

  11. Statistical mechanics of the Huxley-Simmons model.

    PubMed

    Caruel, M; Truskinovsky, L

    2016-06-01

    The chemomechanical model of Huxley and Simmons (HS) [A. F. Huxley and R. M. Simmons, Nature 233, 533 (1971)NATUAS0028-083610.1038/233533a0] provides a paradigmatic description of mechanically induced collective conformational changes relevant in a variety of biological contexts, from muscles power stroke and hair cell gating to integrin binding and hairpin unzipping. We develop a statistical mechanical perspective on the HS model by exploiting a formal analogy with a paramagnetic Ising model. We first study the equilibrium HS model with a finite number of elements and compute explicitly its mechanical and thermal properties. To model kinetics, we derive a master equation and solve it for several loading protocols. The developed formalism is applicable to a broad range of allosteric systems with mean-field interactions.

  12. Parameter estimation of the Huxley cross-bridge muscle model in humans.

    PubMed

    Vardy, Alistair N; de Vlugt, Erwin; van der Helm, Frans C T

    2012-01-01

    The Huxley model has the potential to provide more accurate muscle dynamics while affording a physiological interpretation at cross-bridge level. By perturbing the wrist at different velocities and initial force levels, reliable Huxley model parameters were estimated in humans in vivo using a Huxley muscle-tendon complex. We conclude that these estimates may be used to investigate and monitor changes in microscopic elements of muscle functioning from experiments at joint level.

  13. Analytical solutions of the Frankenhaeuser-Huxley equations I: minimal model for backpropagation of action potentials in sparsely excitable dendrites.

    PubMed

    Poznanski, Roman R

    2004-09-01

    Hodgkin and Huxley's ionic theory of the nerve impulse embodies principles, applicable also to the impulses in vertebrate nerve fibers, as demonstrated by Bernhard Frankenhaeuser and Andrew Huxley 40 years ago. Frankenhaeuser and Huxley reformulated the classical Hodgkin-Huxley equations, in terms of electrodiffusion theory, and computed action potentials specifically for saltatory conduction in myelinated axons. In this paper, we obtain analytical solutions to the most difficult nonlinear partial differential equations in classical neurophysiology. We solve analytically the Frankenhaeuser-Huxley equations pertaining to a model of sparsely excitable, nonlinear dendrites with clusters of transiently activating, TTX-sensitive Na(+) channels, discretely distributed as point sources of inward current along a continuous (non-segmented) leaky cable structure. Each cluster or hot-spot, corresponding to a mesoscopic level description of Na(+) ion channels, includes known cumulative inactivation kinetics observed at the microscopic level. In such a third-order system, the 'recovery' variable is an electrogenic sodium-pump imbedded in the passive membrane, and the system is stabilized by the presence of a large leak conductance mediated by a composite number of ligand-gated channels permeable to monovalent cations Na(+) and K(+). In order to reproduce antidromic propagation and attenuation of action potentials, a nonlinear integral equation must be solved (in the presence of suprathreshold input, and a constant-field equation of electrodiffusion at each hot-spot with membrane gates controlling the flow of current). A perturbative expansion of the non-dimensional membrane potential (Phi) is used to obtain time-dependent analytical solutions, involving a voltage-dependent Na(+) activation (micro) and a state-dependent inactivation (eta) gating variables. It is shown that action potentials attenuate in amplitude in accordance with experimental findings, and that the spatial

  14. An efficient method for solving fractional Hodgkin-Huxley model

    NASA Astrophysics Data System (ADS)

    Nagy, A. M.; Sweilam, N. H.

    2014-06-01

    In this paper, we present an accurate numerical method for solving fractional Hodgkin-Huxley model. A non-standard finite difference method (NSFDM) is implemented to study the dynamic behaviors of the proposed model. The Grünwald-Letinkov definition is used to approximate the fractional derivatives. Numerical results are presented graphically reveal that NSFDM is easy to implement, effective and convenient for solving the proposed model.

  15. EXPONENTIAL TIME DIFFERENCING FOR HODGKIN-HUXLEY-LIKE ODES.

    PubMed

    Börgers, Christoph; Nectow, Alexander R

    2013-01-01

    Several authors have proposed the use of exponential time differencing (ETD) for Hodgkin-Huxley-like partial and ordinary differential equations (PDEs and ODEs). For Hodgkin-Huxley-like PDEs, ETD is attractive because it can deal effectively with the stiffness issues that diffusion gives rise to. However, large neuronal networks are often simulated assuming "space-clamped" neurons, i.e., using the Hodgkin-Huxley ODEs, in which there are no diffusion terms. Our goal is to clarify whether ETD is a good idea even in that case. We present a numerical comparison of first- and second-order ETD with standard explicit time-stepping schemes (Euler's method, the midpoint method, and the classical fourth-order Runge-Kutta method). We find that in the standard schemes, the stable computation of the very rapid rising phase of the action potential often forces time steps of a small fraction of a millisecond. This can result in an expensive calculation yielding greater overall accuracy than needed. Although it is tempting at first to try to address this issue with adaptive or fully implicit time-stepping, we argue that neither is effective here. The main advantage of ETD for Hodgkin-Huxley-like systems of ODEs is that it allows underresolution of the rising phase of the action potential without causing instability, using time steps on the order of one millisecond. When high quantitative accuracy is not necessary and perhaps, because of modeling inaccuracies, not even useful, ETD allows much faster simulations than standard explicit time-stepping schemes. The second-order ETD scheme is found to be substantially more accurate than the first-order one even for large values of Δt.

  16. EXPONENTIAL TIME DIFFERENCING FOR HODGKIN–HUXLEY-LIKE ODES

    PubMed Central

    Börgers, Christoph; Nectow, Alexander R.

    2013-01-01

    Several authors have proposed the use of exponential time differencing (ETD) for Hodgkin–Huxley-like partial and ordinary differential equations (PDEs and ODEs). For Hodgkin–Huxley-like PDEs, ETD is attractive because it can deal effectively with the stiffness issues that diffusion gives rise to. However, large neuronal networks are often simulated assuming “space-clamped” neurons, i.e., using the Hodgkin–Huxley ODEs, in which there are no diffusion terms. Our goal is to clarify whether ETD is a good idea even in that case. We present a numerical comparison of first- and second-order ETD with standard explicit time-stepping schemes (Euler’s method, the midpoint method, and the classical fourth-order Runge–Kutta method). We find that in the standard schemes, the stable computation of the very rapid rising phase of the action potential often forces time steps of a small fraction of a millisecond. This can result in an expensive calculation yielding greater overall accuracy than needed. Although it is tempting at first to try to address this issue with adaptive or fully implicit time-stepping, we argue that neither is effective here. The main advantage of ETD for Hodgkin–Huxley-like systems of ODEs is that it allows underresolution of the rising phase of the action potential without causing instability, using time steps on the order of one millisecond. When high quantitative accuracy is not necessary and perhaps, because of modeling inaccuracies, not even useful, ETD allows much faster simulations than standard explicit time-stepping schemes. The second-order ETD scheme is found to be substantially more accurate than the first-order one even for large values of Δt. PMID:24058276

  17. Tracking and control of neuronal Hodgkin-Huxley dynamics.

    PubMed

    Ullah, Ghanim; Schiff, Steven J

    2009-04-01

    Nonlinear ensemble state estimation offers a paradigm-shifting improvement in our ability to observe, predict, and control the state of spiking neuronal systems. We use an ensemble Kalman filter to predict hidden states and future trajectories in the Hodgkin-Huxley equations, reconstruct ion dynamics, control neuronal activity including a strategy for dynamic conductance clamping, and show the feasibility of controlling pathological cellular activity such as seizures.

  18. In-phase and anti-phase synchronization in noisy Hodgkin-Huxley neurons.

    PubMed

    Ao, Xue; Hänggi, Peter; Schmid, Gerhard

    2013-09-01

    We numerically investigate the influence of intrinsic channel noise on the dynamical response of delay-coupling in neuronal systems. The stochastic dynamics of the spiking is modeled within a stochastic modification of the standard Hodgkin-Huxley model wherein the delay-coupling accounts for the finite propagation time of an action potential along the neuronal axon. We quantify this delay-coupling of the Pyragas-type in terms of the difference between corresponding presynaptic and postsynaptic membrane potentials. For an elementary neuronal network consisting of two coupled neurons we detect characteristic stochastic synchronization patterns which exhibit multiple phase-flip bifurcations: The phase-flip bifurcations occur in form of alternate transitions from an in-phase spiking activity towards an anti-phase spiking activity. Interestingly, these phase-flips remain robust for strong channel noise and in turn cause a striking stabilization of the spiking frequency. Copyright © 2013 Elsevier Inc. All rights reserved.

  19. Temperature Effects on Information Capacity and Energy Efficiency of Hodgkin-Huxley Neuron

    NASA Astrophysics Data System (ADS)

    Wang, Long-Fei; Jia, Fei; Liu, Xiao-Zhi; Song, Ya-Lei; Yu, Lian-Chun

    2015-10-01

    Recent experimental and theoretical studies show that energy efficiency, which measures the amount of information processed by a neuron with per unit of energy consumption, plays an important role in the evolution of neural systems. Here, we calculated the information rates and energy efficiencies of the Hodgkin-Huxley (HH) neuron model at different temperatures in a noisy environment. We found that both the information rate and energy efficiency are maximized by certain temperatures. Though the information rate and energy efficiency cannot be maximized simultaneously, the neuron holds a high information processing capacity at the temperature corresponding to maximal energy efficiency. Our results support the idea that the energy efficiency is a selective pressure that influences the evolution of nervous systems.

  20. Action Potential Initiation in the Hodgkin-Huxley Model

    PubMed Central

    Colwell, Lucy J.; Brenner, Michael P.

    2009-01-01

    A recent paper of B. Naundorf et al. described an intriguing negative correlation between variability of the onset potential at which an action potential occurs (the onset span) and the rapidity of action potential initiation (the onset rapidity). This correlation was demonstrated in numerical simulations of the Hodgkin-Huxley model. Due to this antagonism, it is argued that Hodgkin-Huxley-type models are unable to explain action potential initiation observed in cortical neurons in vivo or in vitro. Here we apply a method from theoretical physics to derive an analytical characterization of this problem. We analytically compute the probability distribution of onset potentials and analytically derive the inverse relationship between onset span and onset rapidity. We find that the relationship between onset span and onset rapidity depends on the level of synaptic background activity. Hence we are able to elucidate the regions of parameter space for which the Hodgkin-Huxley model is able to accurately describe the behavior of this system. PMID:19148265

  1. Hippocampus minor, calcar avis, and the Huxley-Owen debate.

    PubMed

    Owen, Christopher M; Howard, Allyson; Binder, Devin K

    2009-12-01

    On the bicentennial of Darwin's birth, we describe the origin of the calcar avis and summarize the debate around this structure, which played a central role in the evolution debate in the mid-19th century. We performed a comprehensive review of relevant neuroanatomic literature, bibliographic sources, and 19th century primary sources. Once known as the hippocampus minor, the structure now known as the calcar avis is an involution of the ventricular wall produced by the calcarine fissure. A heated debate raged between 2 prominent scientific theorists, Sir Richard Owen and Thomas Henry Huxley, over the presence of the hippocampus minor in apes versus humans. Owen put forward the lack of an identifiable hippocampus minor in humans as part of an attempt to debunk evolution. A bitter personal and academic rivalry ensued, as Huxley conducted his own dissections to refute Owen's claims. Huxley ultimately dismantled Owen's premises, securing the epithet "Darwin's bulldog" for his defense of the theory of evolution. Thus, this relatively obscure neuroanatomic landmark served as a pivotal point of contention in the most popularized and acrimonious evolutionary debate of the 19th century.

  2. Action potential initiation in the hodgkin-huxley model.

    PubMed

    Colwell, Lucy J; Brenner, Michael P

    2009-01-01

    A recent paper of B. Naundorf et al. described an intriguing negative correlation between variability of the onset potential at which an action potential occurs (the onset span) and the rapidity of action potential initiation (the onset rapidity). This correlation was demonstrated in numerical simulations of the Hodgkin-Huxley model. Due to this antagonism, it is argued that Hodgkin-Huxley-type models are unable to explain action potential initiation observed in cortical neurons in vivo or in vitro. Here we apply a method from theoretical physics to derive an analytical characterization of this problem. We analytically compute the probability distribution of onset potentials and analytically derive the inverse relationship between onset span and onset rapidity. We find that the relationship between onset span and onset rapidity depends on the level of synaptic background activity. Hence we are able to elucidate the regions of parameter space for which the Hodgkin-Huxley model is able to accurately describe the behavior of this system.

  3. Letter to a Young Writer.

    ERIC Educational Resources Information Center

    Mitchell, Susan

    2001-01-01

    Presents Part Two of the ongoing series Letters to a Young Writer where poet and professor Susan Mitchell corresponds with a contemporary composer as a means of exploring the relationship between poetry and the human voice. Reflects on the role of the poet in a civilization, a "habitat," under attack. (SG)

  4. On universality in human correspondence activity.

    PubMed

    Malmgren, R Dean; Stouffer, Daniel B; Campanharo, Andriana S L O; Amaral, Luís A Nunes

    2009-09-25

    The identification and modeling of patterns of human activity have important ramifications for applications ranging from predicting disease spread to optimizing resource allocation. Because of its relevance and availability, written correspondence provides a powerful proxy for studying human activity. One school of thought is that human correspondence is driven by responses to received correspondence, a view that requires a distinct response mechanism to explain e-mail and letter correspondence observations. We demonstrate that, like e-mail correspondence, the letter correspondence patterns of 16 writers, performers, politicians, and scientists are well described by the circadian cycle, task repetition, and changing communication needs. We confirm the universality of these mechanisms by rescaling letter and e-mail correspondence statistics to reveal their underlying similarity.

  5. Einstein/Roosevelt Letters: A Unit.

    ERIC Educational Resources Information Center

    Bodle, Walter S.

    1985-01-01

    The letters in this unit of study intended for secondary students are facsimile reproductions of the correspondence between Albert Einstein and President Roosevelt on the possibility of constructing an atomic bomb. Classroom activities are also suggested. (RM)

  6. Einstein/Roosevelt Letters: A Unit.

    ERIC Educational Resources Information Center

    Bodle, Walter S.

    1985-01-01

    The letters in this unit of study intended for secondary students are facsimile reproductions of the correspondence between Albert Einstein and President Roosevelt on the possibility of constructing an atomic bomb. Classroom activities are also suggested. (RM)

  7. From the Hodgkin-Huxley axon to the virtual heart

    PubMed Central

    Noble, Denis

    2007-01-01

    Experimentally based models of the heart have been developed since 1960, starting with the discovery and modelling of potassium channels. The early models were based on extensions of the Hodgkin–Huxley nerve impulse equations. The first models including calcium balance and signalling were made in the 1980s and have now reached a high degree of physiological detail. During the 1990s these cell models have been incorporated into anatomically detailed tissue and organ models to create the first virtual organ, the Virtual Heart. With over 40 years of interaction between simulation and experiment, the models are now sufficiently refined to begin to be of use in drug development. PMID:17023502

  8. Design in Letters.

    ERIC Educational Resources Information Center

    Hiller, Peter

    2000-01-01

    Discusses an art project in which sixth grade students design alphabets by transforming the shapes of the letters into new designs that are still recognizable. Explains that students brainstorm ideas for their own lettering style. (CMK)

  9. Letter to jane addams.

    PubMed

    Bloom, M

    1995-06-01

    This letter, written to one of the founding figures in social work, draws parallels between primary prevention at the beginning and the end of the twentieth century. As expected, the letter remains unanswered.

  10. Memristor, Hodgkin-Huxley, and edge of chaos.

    PubMed

    Chua, Leon

    2013-09-27

    From a pedagogical point of view, the memristor is defined in this tutorial as any 2-terminal device obeying a state-dependent Ohm's law. This tutorial also shows that from an experimental point of view, the memristor can be defined as any 2-terminal device that exhibits the fingerprints of 'pinched' hysteresis loops in the v-i plane. It also shows that memristors endowed with a continuum of equilibrium states can be used as non-volatile analog memories. This tutorial shows that memristors span a much broader vista of complex phenomena and potential applications in many fields, including neurobiology. In particular, this tutorial presents toy memristors that can mimic the classic habituation and LTP learning phenomena. It also shows that sodium and potassium ion-channel memristors are the key to generating the action potential in the Hodgkin-Huxley equations, and that they are the key to resolving several unresolved anomalies associated with the Hodgkin-Huxley equations. This tutorial ends with an amazing new result derived from the new principle of local activity, which uncovers a minuscule life-enabling 'Goldilocks zone', dubbed the edge of chaos, where complex phenomena, including creativity and intelligence, may emerge. From an information processing perspective, this tutorial shows that synapses are locally-passive memristors, and that neurons are made of locally-active memristors.

  11. Memristor, Hodgkin-Huxley, and Edge of Chaos

    NASA Astrophysics Data System (ADS)

    Chua, Leon

    2013-09-01

    From a pedagogical point of view, the memristor is defined in this tutorial as any 2-terminal device obeying a state-dependent Ohm’s law. This tutorial also shows that from an experimental point of view, the memristor can be defined as any 2-terminal device that exhibits the fingerprints of ‘pinched’ hysteresis loops in the v-i plane. It also shows that memristors endowed with a continuum of equilibrium states can be used as non-volatile analog memories. This tutorial shows that memristors span a much broader vista of complex phenomena and potential applications in many fields, including neurobiology. In particular, this tutorial presents toy memristors that can mimic the classic habituation and LTP learning phenomena. It also shows that sodium and potassium ion-channel memristors are the key to generating the action potential in the Hodgkin-Huxley equations, and that they are the key to resolving several unresolved anomalies associated with the Hodgkin-Huxley equations. This tutorial ends with an amazing new result derived from the new principle of local activity, which uncovers a minuscule life-enabling ‘Goldilocks zone’, dubbed the edge of chaos, where complex phenomena, including creativity and intelligence, may emerge. From an information processing perspective, this tutorial shows that synapses are locally-passive memristors, and that neurons are made of locally-active memristors.

  12. RED-LETTER DAYS

    EPA Science Inventory

    The word "red-letter" is an adjective meaning "of special significance." It's origin is from the practice of marking Christian holy days in red letters on calendars. The "red-letter days" to which I refer occurred while I was a graduate student of ...

  13. Van: An Open Letter

    ERIC Educational Resources Information Center

    Tieman, John Samuel

    2011-01-01

    This essay is an open letter from a classroom teacher to a concerned citizen. The letter lists a variety of problems caused largely by standardization and the more corrosive effects of positivism. Many of these problems are unknown to those outside the immediate school setting. While the letter focuses on a specific setting, an inner city school…

  14. Developmental letter position dyslexia.

    PubMed

    Friedmann, Naama; Rahamim, Einav

    2007-09-01

    Letter position dyslexia (LPD) is a peripheral dyslexia that causes errors of letter order within words. So far, only cases of acquired LPD have been reported. This study presents selective LPD in its developmental form, via the testing of II Hebrew-speaking individuals with developmental dyslexia. The study explores the types of errors and effects on reading in this dyslexia, using a variety of tests: reading aloud, lexical decision, same-different decision, definition and letter naming. The findings indicate that individuals with developmental LPD have a deficit in the letter position encoding function of the orthographic visual analyser, which leads to underspecification of letter position within words. Letter position errors occur mainly in adjacent middle letters, when the error creates another existing word. The participants did not show an output deficit or phonemic awareness deficit. The selectivity of the deficit, causing letter position errors but no letter identity errors and no migrations between words, supports the existence of letter position encoding function as separate from letter identification and letter-to-word binding.

  15. Van: An Open Letter

    ERIC Educational Resources Information Center

    Tieman, John Samuel

    2011-01-01

    This essay is an open letter from a classroom teacher to a concerned citizen. The letter lists a variety of problems caused largely by standardization and the more corrosive effects of positivism. Many of these problems are unknown to those outside the immediate school setting. While the letter focuses on a specific setting, an inner city school…

  16. Learning to Write Letters: Examination of Student and Letter Factors

    PubMed Central

    Puranik, Cynthia S.; Petscher, Yaacov; Lonigan, Christopher J.

    2016-01-01

    Learning to write the letters of the alphabet is an important part of learning how to write conventionally. In this study, we investigated critical factors in the development of letter-writing skills using exploratory item response models to simultaneously account for variance in responses due to differences between students and between letters. Letter-writing skills were assessed in 415 preschool children aged 3 to 5 years. At the student level, we examined the contribution of letter-name knowledge, letter-sound knowledge, and phonological awareness to letter-writing skills. At the letter level, we examined seven intrinsic and extrinsic factors in understanding how preschool children learn to write alphabet letters: first letter of name, letters in name, letter order, textual frequency, number of strokes, symmetry, and letter type. Results indicated that variation in letter-writing skills was accounted for more by differences between students rather than by differences between letters, with most of the variability accounted for by letter-name knowledge and age. Although significant, the contribution of letter-sound knowledge and phonological awareness was relatively small. Student-level mechanisms underlying the acquisition of letter-writing skills are similar to the mechanisms underlying the learning of letter sounds. However, letter characteristics, which appear to play a major role in the learning of letter names and letter sounds, did not appear to influence learning how to write letters in a substantial way. The exception was if the letter was in the child’s name. PMID:25181463

  17. Learning to write letters: examination of student and letter factors.

    PubMed

    Puranik, Cynthia S; Petscher, Yaacov; Lonigan, Christopher J

    2014-12-01

    Learning to write the letters of the alphabet is an important part of learning how to write conventionally. In this study, we investigated critical factors in the development of letter-writing skills using exploratory item response models to simultaneously account for variance in responses due to differences between students and between letters. Letter-writing skills were assessed in 415 preschool children aged 3 to 5 years. At the student level, we examined the contribution of letter-name knowledge, letter-sound knowledge, and phonological awareness to letter-writing skills. At the letter level, we examined seven intrinsic and extrinsic factors in understanding how preschool children learn to write alphabet letters: first letter of name, letters in name, letter order, textual frequency, number of strokes, symmetry, and letter type. Results indicated that variation in letter-writing skills was accounted for more by differences between students rather than by differences between letters, with most of the variability accounted for by letter-name knowledge and age. Although significant, the contribution of letter-sound knowledge and phonological awareness was relatively small. Student-level mechanisms underlying the acquisition of letter-writing skills are similar to the mechanisms underlying the learning of letter sounds. However, letter characteristics, which appear to play a major role in the learning of letter names and letter sounds, did not appear to influence learning how to write letters in a substantial way. The exception was if the letter was in the child's name.

  18. Hodgkin-Huxley revisited: reparametrization and identifiability analysis of the classic action potential model with approximate Bayesian methods.

    PubMed

    Daly, Aidan C; Gavaghan, David J; Holmes, Chris; Cooper, Jonathan

    2015-12-01

    As cardiac cell models become increasingly complex, a correspondingly complex 'genealogy' of inherited parameter values has also emerged. The result has been the loss of a direct link between model parameters and experimental data, limiting both reproducibility and the ability to re-fit to new data. We examine the ability of approximate Bayesian computation (ABC) to infer parameter distributions in the seminal action potential model of Hodgkin and Huxley, for which an immediate and documented connection to experimental results exists. The ability of ABC to produce tight posteriors around the reported values for the gating rates of sodium and potassium ion channels validates the precision of this early work, while the highly variable posteriors around certain voltage dependency parameters suggests that voltage clamp experiments alone are insufficient to constrain the full model. Despite this, Hodgkin and Huxley's estimates are shown to be competitive with those produced by ABC, and the variable behaviour of posterior parametrized models under complex voltage protocols suggests that with additional data the model could be fully constrained. This work will provide the starting point for a full identifiability analysis of commonly used cardiac models, as well as a template for informative, data-driven parametrization of newly proposed models.

  19. Hodgkin–Huxley revisited: reparametrization and identifiability analysis of the classic action potential model with approximate Bayesian methods

    PubMed Central

    Daly, Aidan C.; Holmes, Chris

    2015-01-01

    As cardiac cell models become increasingly complex, a correspondingly complex ‘genealogy’ of inherited parameter values has also emerged. The result has been the loss of a direct link between model parameters and experimental data, limiting both reproducibility and the ability to re-fit to new data. We examine the ability of approximate Bayesian computation (ABC) to infer parameter distributions in the seminal action potential model of Hodgkin and Huxley, for which an immediate and documented connection to experimental results exists. The ability of ABC to produce tight posteriors around the reported values for the gating rates of sodium and potassium ion channels validates the precision of this early work, while the highly variable posteriors around certain voltage dependency parameters suggests that voltage clamp experiments alone are insufficient to constrain the full model. Despite this, Hodgkin and Huxley's estimates are shown to be competitive with those produced by ABC, and the variable behaviour of posterior parametrized models under complex voltage protocols suggests that with additional data the model could be fully constrained. This work will provide the starting point for a full identifiability analysis of commonly used cardiac models, as well as a template for informative, data-driven parametrization of newly proposed models. PMID:27019736

  20. Response of autaptic Hodgkin-Huxley neuron with noise to subthreshold sinusoidal signals

    NASA Astrophysics Data System (ADS)

    Wang, Hengtong; Chen, Yong

    2016-11-01

    In this work, we investigated the response of a stochastic Hodgkin-Huxley (HH) neuron with an autapse to subthreshold sinusoidal signals. It is found that the autapse not only adjusts the stochastic responses, but also improves the detection of subthreshold signals. In the case of weak noise, the autapse facilitates the response of neuron to the subthreshold sinusoidal signals with a small parameter region in tdelay- ω space. The increased noise intensity enlarges this parameter region and increases the corresponding response frequency in such range. As the autaptic intensity increases, however, this parameter region shrunks. We also observed that there is an optimal range of the delay time of autapse, within which the stochastic HH neuron fires action potentials with high frequency. The corresponding response spike train for the optimal delay time is nearly a regular sequence with the interspike intervals approximated to the delay time. The current results reveal a novel resonance phenomenon facilitated by autapse, named autaptic delay-induced coherence resonance.

  1. Mud, Blood, and Bullet Holes: Teaching History with War Letters

    ERIC Educational Resources Information Center

    Carroll, Andrew

    2013-01-01

    From handwritten letters of the American Revolution to typed emails from Iraq and Afghanistan, correspondence from U.S. troops offers students deep insight into the specific conflicts and experiences of soldiers. Over 100,000 correspondences have been donated to the Legacy Project, a national initiative launched in 1998 to preserve war letters by…

  2. Mud, Blood, and Bullet Holes: Teaching History with War Letters

    ERIC Educational Resources Information Center

    Carroll, Andrew

    2013-01-01

    From handwritten letters of the American Revolution to typed emails from Iraq and Afghanistan, correspondence from U.S. troops offers students deep insight into the specific conflicts and experiences of soldiers. Over 100,000 correspondences have been donated to the Legacy Project, a national initiative launched in 1998 to preserve war letters by…

  3. Edge detection based on Hodgkin-Huxley neuron model simulation.

    PubMed

    Yedjour, Hayat; Meftah, Boudjelal; Lézoray, Olivier; Benyettou, Abdelkader

    2017-04-03

    In this paper, we propose a spiking neural network model for edge detection in images. The proposed model is biologically inspired by the mechanisms employed by natural vision systems, more specifically by the biologically fulfilled function of simple cells of the human primary visual cortex that are selective for orientation. Several aspects are studied in this model according to three characteristics: feedforward spiking neural structure; conductance-based model of the Hodgkin-Huxley neuron and Gabor receptive fields structure. A visualized map is generated using the firing rate of neurons representing the orientation map of the visual cortex area. We have simulated the proposed model on different images. Successful computer simulation results are obtained. For comparison, we have chosen five methods for edge detection. We finally evaluate and compare the performances of our model toward contour detection using a public dataset of natural images with associated contour ground truths. Experimental results show the ability and high performance of the proposed network model.

  4. Hodgkin-Huxley neurons with defective and blocked ion channels

    NASA Astrophysics Data System (ADS)

    Pang, James Christopher S.; Bantang, Johnrob Y.

    2015-03-01

    We utilize the original Hodgkin-Huxley (HH) model to consider the effects of defective ion channels to the temporal response of neurons. Statistics of firing rate and inter-spike interval (ISI) reveal that production of action potentials (APs) in neurons is not sensitive to changes in membrane conductance for sodium and potassium ions, as well as to the reversal potential for sodium ions, as long as the relevant parameters do not exceed 13% from their normal levels. We also found that blockage of a critical fraction of either sodium or potassium channels (dependent on constant input current) respectively limits the firing activity or increases spontaneous spiking activity of neurons. Our model may be used to guide experiment designs related to ion channel control drug development.

  5. The foundations of literacy: learning the sounds of letters.

    PubMed

    Treiman, R; Tincoff, R; Rodriguez, K; Mouzaki, A; Francis, D J

    1998-12-01

    Learning the sounds of letters is an important part of learning to read and spell. To explore the factors that make some letter-sound correspondences easier for children to learn than others, we first analyzed knowledge of letters' sounds (and names) by 660 children between 3 1/2 and 7 1/2 years old. A second study examined pre-schoolers' (M age 4 years, 11 months) ability to learn various sound-letter mappings. Together, the results show that an important determinant of letter-sound knowledge is whether the sound occurs in the name of the letter and, if so, whether it is at the beginning or the end. The properties of the sound itself (consonant versus vowel, sonorant versus obstruent, stop versus continuant) appear to have little or no influence on children's learning of basic letter-sound correspondences. The findings show that children use their knowledge of letters' names when learning the letters' sounds rather than memorizing letter-sound correspondences as arbitrary pairings.

  6. A study of the application of the Hodgkin-Huxley and the Frankenhaeuser-Huxley model for electrostimulation of the acoustic nerve.

    PubMed

    Motz, H; Rattay, F

    1986-07-01

    By means of electrostimulation of the acoustic nerve profoundly deaf patients can, in the best cases, reach almost complete speech understanding without lip reading. In this paper the information content of the signals supplied to patients is examined by a study of action potential generation by means of the Hodgkin-Huxley and the Frankenhaeuser-Huxley equations solved by means of a digitally controlled analogue computer. The response to sinusoidal signals and to signals with the wave shape of certain vowels is investigated and compared with results from animal experiments and observation on patients.

  7. Stochastic Hodgkin-Huxley equations with colored noise terms in the conductances.

    PubMed

    Güler, Marifi

    2013-01-01

    The excitability of cells is facilitated by voltage-gated ion channels. These channels accommodate a multiple number of gates individually. The possible impact of that gate multiplicity on the cell's function, specifically when the membrane area is of limited size, was investigated in the author's prior work (Güler, 2011 ). There, it was found that a nontrivially persistent correlation takes place between the transmembrane voltage fluctuations (also between the fluctuations in the gating variables) and the component of open channel fluctuations attributed to the gate multiplicity. This nontrivial phenomenon was found to be playing a major augmentative role for the elevation of excitability and spontaneous firing in small cells. In addition, the same phenomenon was found to be enhancing spike coherence significantly. Here we extend Fox and Lu's ( 1994 ) stochastic Hodgkin-Huxley equations by incorporating colored noise terms into the conductances there to obtain a formalism capable of capturing the addressed cross-correlations. Statistics of spike generation, spike coherence, firing efficiency, latency, and jitter from the articulated set of equations are found to be highly accurate in comparison with the corresponding statistics from the exact microscopic Markov simulations. This way, it is demonstrated vividly that our formulation overcomes the inherent inadequacy of the Fox and Lu equations. Finally, a recently proposed diffusion approximation method (Linaro, Storace, & Giugliano, 2011 ) is taken into consideration, and a discussion on its character is pursued.

  8. Metamorphopsia and letter recognition

    PubMed Central

    Wiecek, Emily; Dakin, Steven C.; Bex, Peter

    2014-01-01

    Acuity is the most commonly used measure of visual function, and reductions in acuity are associated with most eye diseases. Metamorphopsia—a perceived distortion of visual space—is another common symptom of visual impairment and is currently assessed qualitatively using Amsler (1953) charts. In order to quantify the impact of metamorphopsia on acuity, we measured the effect of physical spatial distortion on letter recognition. Following earlier work showing that letter recognition is tuned to specific spatial frequency (SF) channels, we hypothesized that the effect of distortion might depend on the spatial scale of visual distortion just as it depends on the spatial scale of masking noise. Six normally sighted observers completed a 26 alternate forced choice (AFC) Sloan letter identification task at five different viewing distances, and the letters underwent different levels of spatial distortion. Distortion was controlled using spatially band-pass filtered noise that spatially remapped pixel locations. Noise was varied over five spatial frequencies and five magnitudes. Performance was modeled with logistic regression and worsened linearly with increasing distortion magnitude and decreasing letter size. We found that retinal SF affects distortion at midrange frequencies and can be explained with the tuning of a basic contrast sensitivity function, while object-centered distortion SF follows a similar pattern of letter object recognition sensitivity and is tuned to approximately three cycles per letter (CPL). The interaction between letter size and distortion makes acuity an unreliable outcome for metamorphopsia assessment. PMID:25453116

  9. From Shape to Letters.

    ERIC Educational Resources Information Center

    Schiller, Hillel A.

    In order to make letter shape recognition an integral part of perception training, the use of the line in its two basic shapes is proposed. Letter shapes may seem exceedingly complex linear shapes to young minds. Thus instead of instruction in configuration, instruction involving transformational activities to manipulate and create the…

  10. Metamorphopsia and letter recognition.

    PubMed

    Wiecek, Emily; Dakin, Steven C; Bex, Peter

    2014-12-01

    Acuity is the most commonly used measure of visual function, and reductions in acuity are associated with most eye diseases. Metamorphopsia--a perceived distortion of visual space--is another common symptom of visual impairment and is currently assessed qualitatively using Amsler (1953) charts. In order to quantify the impact of metamorphopsia on acuity, we measured the effect of physical spatial distortion on letter recognition. Following earlier work showing that letter recognition is tuned to specific spatial frequency (SF) channels, we hypothesized that the effect of distortion might depend on the spatial scale of visual distortion just as it depends on the spatial scale of masking noise. Six normally sighted observers completed a 26 alternate forced choice (AFC) Sloan letter identification task at five different viewing distances, and the letters underwent different levels of spatial distortion. Distortion was controlled using spatially band-pass filtered noise that spatially remapped pixel locations. Noise was varied over five spatial frequencies and five magnitudes. Performance was modeled with logistic regression and worsened linearly with increasing distortion magnitude and decreasing letter size. We found that retinal SF affects distortion at midrange frequencies and can be explained with the tuning of a basic contrast sensitivity function, while object-centered distortion SF follows a similar pattern of letter object recognition sensitivity and is tuned to approximately three cycles per letter (CPL). The interaction between letter size and distortion makes acuity an unreliable outcome for metamorphopsia assessment.

  11. Stability of synchronous oscillations in a system of Hodgkin-Huxley neurons with delayed diffusive and pulsed coupling

    NASA Astrophysics Data System (ADS)

    Rossoni, Enrico; Chen, Yonghong; Ding, Mingzhou; Feng, Jianfeng

    2005-06-01

    We study the synchronization dynamics for a system of two Hodgkin-Huxley (HH) neurons coupled diffusively or through pulselike interactions. By calculating the maximum transverse Lyapunov exponent, we found that, with diffusive coupling, there are three regions in the parameter space, corresponding to qualitatively distinct behaviors of the coupled dynamics. In particular, the two neurons can synchronize in two regions and desynchronize in the third. When excitatory and inhibitory pulse coupling is considered, we found that synchronized dynamics becomes more difficult to achieve in the sense that the parameter regions where the synchronous state is stable are smaller. Numerical simulations of the coupled system are presented to validate these results. The stability of a network of coupled HH neurons is then analyzed and the stability regions in the parameter space are exactly obtained.

  12. Stability of synchronous oscillations in a system of Hodgkin-Huxley neurons with delayed diffusive and pulsed coupling.

    PubMed

    Rossoni, Enrico; Chen, Yonghong; Ding, Mingzhou; Feng, Jianfeng

    2005-06-01

    We study the synchronization dynamics for a system of two Hodgkin-Huxley (HH) neurons coupled diffusively or through pulselike interactions. By calculating the maximum transverse Lyapunov exponent, we found that, with diffusive coupling, there are three regions in the parameter space, corresponding to qualitatively distinct behaviors of the coupled dynamics. In particular, the two neurons can synchronize in two regions and desynchronize in the third. When excitatory and inhibitory pulse coupling is considered, we found that synchronized dynamics becomes more difficult to achieve in the sense that the parameter regions where the synchronous state is stable are smaller. Numerical simulations of the coupled system are presented to validate these results. The stability of a network of coupled HH neurons is then analyzed and the stability regions in the parameter space are exactly obtained.

  13. The time course of visual influences in letter recognition.

    PubMed

    Madec, Sylvain; Le Goff, Kévin; Riès, Stéphanie K; Legou, Thierry; Rousselet, Guillaume; Courrieu, Pierre; Alario, F-Xavier; Grainger, Jonathan; Rey, Arnaud

    2016-06-01

    This study builds on a specific characteristic of letters of the Roman alphabet-namely, that each letter name is associated with two visual formats, corresponding to their uppercase and lowercase versions. Participants had to read aloud the names of single letters, and event-related potentials (ERPs) for six pairs of visually dissimilar upper- and lowercase letters were recorded. Assuming that the end product of processing is the same for upper- and lowercase letters sharing the same vocal response, ERPs were compared backward, starting from the onset of articulatory responses, and the first significant divergence was observed 120 ms before response onset. Given that naming responses were produced at around 414 ms, on average, these results suggest that letter processing is influenced by visual information until 294 ms after stimulus onset. This therefore provides new empirical evidence regarding the time course and interactive nature of visual letter perception processes.

  14. Which Children Benefit from Letter Names in Learning Letter Sounds?

    ERIC Educational Resources Information Center

    Treiman, Rebecca; Pennington, Bruce F.; Shriberg, Lawrence D.; Boada, Richard

    2008-01-01

    Typical U.S. children use their knowledge of letters' names to help learn the letters' sounds. They perform better on letter sound tests with letters that have their sounds at the beginnings of their names, such as v, than with letters that have their sounds at the ends of their names, such as m, and letters that do not have their sounds in their…

  15. [Thomas H.Huxley--the naval doctor who became Darwin's bulldog].

    PubMed

    Hauge, A

    2000-12-10

    Thomas H. Huxley (1825-1895) was an English physician and biologist who had a deep impact on the Victorian age. More than any other at his time he introduced scientifically based values. As a member of London's school board he brought science into the curriculum, encouraging school-children to ask questions and to make their own observations. Huxley came from a lower middle class family with little money. By sheer determination and hard work he managed to get a medical education at Charing Cross Hospital Medical School. He then obtained a posting on H.M.S. Rattlesnake, which gave him a chance to explore the southern seas and to study marine species. The results were published by the Royal Society of which Huxley became a member at the age of 26, and later its president. After several years of uncertainty he secured a position at the Royal School of Mines, which he transformed into the Imperial College of Science. He was a prolific scientist with wide interests, doing valuable work in paleontology, taxonomy and ethnology. Huxley wrote numerous essays on philosophy and scientific subjects. He coined the word agnostic to explain his attitude to Christian dogma. His style was clear and direct, and his essays still read very well. However, Huxley is now mostly, perhaps unfairly, remembered for his defence of Darwin's theory of evolution. In his book Evidence as to man's place in nature, Huxley, in contrast to Darwin, deals with the evolution of humans, mainly based on comparative anatomy. Huxley advocated a firmly held belief that scientific truths will have a liberating effect on the minds of men. His lectures on scientific subjects attracted large audiences of people who had not had the benefit of a higher education.

  16. Resumes, Applications, and Cover Letters.

    ERIC Educational Resources Information Center

    Crosby, Olivia

    1999-01-01

    Offers guidelines for creating resumes, job applications, and cover letters. Includes examples of resumes and cover letters, additional resources, and information on preparing scannable resumes. (JOW)

  17. The ISI distribution of the stochastic Hodgkin-Huxley neuron

    PubMed Central

    Rowat, Peter F.; Greenwood, Priscilla E.

    2014-01-01

    The simulation of ion-channel noise has an important role in computational neuroscience. In recent years several approximate methods of carrying out this simulation have been published, based on stochastic differential equations, and all giving slightly different results. The obvious, and essential, question is: which method is the most accurate and which is most computationally efficient? Here we make a contribution to the answer. We compare interspike interval histograms from simulated data using four different approximate stochastic differential equation (SDE) models of the stochastic Hodgkin-Huxley neuron, as well as the exact Markov chain model simulated by the Gillespie algorithm. One of the recent SDE models is the same as the Kurtz approximation first published in 1978. All the models considered give similar ISI histograms over a wide range of deterministic and stochastic input. Three features of these histograms are an initial peak, followed by one or more bumps, and then an exponential tail. We explore how these features depend on deterministic input and on level of channel noise, and explain the results using the stochastic dynamics of the model. We conclude with a rough ranking of the four SDE models with respect to the similarity of their ISI histograms to the histogram of the exact Markov chain model. PMID:25339894

  18. Blind Deconvolution of Hodgkin-Huxley neuronal model.

    PubMed

    Lankarany, M; Zhu, W-P; Swamy, M N S; Toyoizumi, Taro

    2013-01-01

    Neuron transforms information via a complex interaction between its previous states, its intrinsic properties, and the synaptic input it receives from other neurons. Inferring synaptic input of a neuron only from its membrane potential (output) that contains both sub-threshold and action potentials can effectively elucidate the information processing mechanism of a neuron. The term coined blind deconvolution of Hodgkin-Huxley (HH) neuronal model is defined, for the first time in this paper, to address the problem of reconstructing the hidden dynamics and synaptic input of a single neuron modeled by the HH model as well as estimating its intrinsic parameters only from single trace of noisy membrane potential. The blind deconvolution is accomplished via a recursive algorithm whose iterations contain running an extended Kalman filtering followed by the expectation maximization (EM) algorithm. The accuracy and robustness of the proposed algorithm have been demonstrated by our simulations. The capability of the proposed algorithm makes it particularly useful to understand the neural coding mechanism of a neuron.

  19. Spontaneous spiking in an autaptic Hodgkin-Huxley setup

    NASA Astrophysics Data System (ADS)

    Li, Yunyun; Schmid, Gerhard; Hänggi, Peter; Schimansky-Geier, Lutz

    2010-12-01

    The effect of intrinsic channel noise is investigated for the dynamic response of a neuronal cell with a delayed feedback loop. The loop is based on the so-called autapse phenomenon in which dendrites establish connections not only to neighboring cells but also to its own axon. The biophysical modeling is achieved in terms of a stochastic Hodgkin-Huxley model containing such a built in delayed feedback. The fluctuations stem from intrinsic channel noise, being caused by the stochastic nature of the gating dynamics of ion channels. The influence of the delayed stimulus is systematically analyzed with respect to the coupling parameter and the delay time in terms of the interspike interval histograms and the average interspike interval. The delayed feedback manifests itself in the occurrence of bursting and a rich multimodal interspike interval distribution, exhibiting a delay-induced reduction in the spontaneous spiking activity at characteristic frequencies. Moreover, a specific frequency-locking mechanism is detected for the mean interspike interval.

  20. The ISI distribution of the stochastic Hodgkin-Huxley neuron.

    PubMed

    Rowat, Peter F; Greenwood, Priscilla E

    2014-01-01

    The simulation of ion-channel noise has an important role in computational neuroscience. In recent years several approximate methods of carrying out this simulation have been published, based on stochastic differential equations, and all giving slightly different results. The obvious, and essential, question is: which method is the most accurate and which is most computationally efficient? Here we make a contribution to the answer. We compare interspike interval histograms from simulated data using four different approximate stochastic differential equation (SDE) models of the stochastic Hodgkin-Huxley neuron, as well as the exact Markov chain model simulated by the Gillespie algorithm. One of the recent SDE models is the same as the Kurtz approximation first published in 1978. All the models considered give similar ISI histograms over a wide range of deterministic and stochastic input. Three features of these histograms are an initial peak, followed by one or more bumps, and then an exponential tail. We explore how these features depend on deterministic input and on level of channel noise, and explain the results using the stochastic dynamics of the model. We conclude with a rough ranking of the four SDE models with respect to the similarity of their ISI histograms to the histogram of the exact Markov chain model.

  1. Spontaneous spiking in an autaptic Hodgkin-Huxley setup.

    PubMed

    Li, Yunyun; Schmid, Gerhard; Hänggi, Peter; Schimansky-Geier, Lutz

    2010-12-01

    The effect of intrinsic channel noise is investigated for the dynamic response of a neuronal cell with a delayed feedback loop. The loop is based on the so-called autapse phenomenon in which dendrites establish connections not only to neighboring cells but also to its own axon. The biophysical modeling is achieved in terms of a stochastic Hodgkin-Huxley model containing such a built in delayed feedback. The fluctuations stem from intrinsic channel noise, being caused by the stochastic nature of the gating dynamics of ion channels. The influence of the delayed stimulus is systematically analyzed with respect to the coupling parameter and the delay time in terms of the interspike interval histograms and the average interspike interval. The delayed feedback manifests itself in the occurrence of bursting and a rich multimodal interspike interval distribution, exhibiting a delay-induced reduction in the spontaneous spiking activity at characteristic frequencies. Moreover, a specific frequency-locking mechanism is detected for the mean interspike interval.

  2. Energy and information in Hodgkin-Huxley neurons.

    PubMed

    Moujahid, A; d'Anjou, A; Torrealdea, F J; Torrealdea, F

    2011-03-01

    The generation of spikes by neurons is energetically a costly process and the evaluation of the metabolic energy required to maintain the signaling activity of neurons a challenge of practical interest. Neuron models are frequently used to represent the dynamics of real neurons but hardly ever to evaluate the electrochemical energy required to maintain that dynamics. This paper discusses the interpretation of a Hodgkin-Huxley circuit as an energy model for real biological neurons and uses it to evaluate the consumption of metabolic energy in the transmission of information between neurons coupled by electrical synapses, i.e., gap junctions. We show that for a single postsynaptic neuron maximum energy efficiency, measured in bits of mutual information per molecule of adenosine triphosphate (ATP) consumed, requires maximum energy consumption. For groups of parallel postsynaptic neurons we determine values of the synaptic conductance at which the energy efficiency of the transmission presents clear maxima at relatively very low values of metabolic energy consumption. Contrary to what could be expected, the best performance occurs at a low energy cost.

  3. Suicide letters in Singapore.

    PubMed

    Chia, Boon-Hock; Chia, Audrey; Tai, Bee-Choo

    2008-01-01

    The contents of suicide letters provide insight into the reasons for suicide and the mental states of victims. Coroner court records of 1,721 Singaporean suicides occurring between 2000 and 2004 were reviewed, 398 (23%) of whom left suicide letters. Letter writers tended to be younger, single, and less likely to have mental or physical illness. A reason for suicide was evident in 58%. Major reasons included school and relationship problems in the young, financial and marital problems in adults and physical illnesses in the elderly. Positive sentiment (care/concern) was expressed in 59%. Negative emotions in 45% of which despondency/agony (60%) was the most common, followed by emptiness (25%), guilt/shame (15%), hopelessness (10%), and anger (3%). The study of these letters suggests that there are combinations of social, psychological and physical factors that influence a person to suicide, all of which are important in the prevention, assessment, and management of suicide.

  4. Letter to My Students.

    ERIC Educational Resources Information Center

    Puccio, Paul M.

    2002-01-01

    Presents the author's ideas about teaching in the form of a letter to his students. Gives his message in the form of a story. Focuses on a reverence for questions, an acceptance of solitude, and a commitment to reflectiveness. (SG)

  5. Homestead Determination Letter

    EPA Pesticide Factsheets

    This July 10, 2017 letter from EPA responds to the petition from Homestead for an advanced biofuel pathway for yellow grease used as heating oil under the Clean Air Act and the Renewable Fuel Standard Program.

  6. Reasons for Letter Contracts.

    DTIC Science & Technology

    1980-09-01

    supplies and services for the national defense. But, excessive use of letter contracts leads to charges of poor planning and may deter effective ...definitive contract. But, excessive use of letter contracts leads to charges of poor planning and may deter effective negotiation of definitized...unilateral determination because of the impact on relationships with the contractor. There are cases where, as a matter of principle, the Government must take

  7. Launch of Zoological Letters.

    PubMed

    Fukatsu, Takema; Kuratani, Shigeru

    2016-02-01

    A new open-access journal, Zoological Letters, was launched as a sister journal to Zoological Science, in January 2015. The new journal aims at publishing topical papers of high quality from a wide range of basic zoological research fields. This review highlights the notable reviews and research articles that have been published in the first year of Zoological Letters, providing an overview on the current achievements and future directions of the journal.

  8. Copies of clinic letters to the family.

    PubMed

    Bartle, D G; Diskin, L; Finlay, F

    2004-11-01

    In April 2004 guidelines were introduced advising that letters to the GP should be copied to parents of young people. A study was carried out to ascertain the views of young people and their parents as to who they felt should receive correspondence after an outpatient appointment.

  9. Phonological awareness and the use of phonological similarity in letter-sound learning.

    PubMed

    de Jong, Peter F

    2007-11-01

    The effects of the phonological similarity between a letter sound and the sound in a spoken word, and phonological awareness on letter-sound learning were examined. Two groups of 41 kindergartners were taught four letter sounds. First, both groups had to learn the associations between four symbols and four familiar words. Next, both groups were taught the letter sounds that were paired to these same symbols. Each letter sound corresponded to the first sound of the word that was previously associated with that symbol in the phonological similarity group, whereas such a relation was absent in the other group. In addition, measures of vocabulary, letter knowledge, and phonological awareness were administered. Phonological similarity facilitated letter-sound learning. Individual differences in phonological awareness had a strong effect on letter-sound learning even after current letter knowledge was controlled. Unexpectedly, the effects of phonological awareness and the ability to use phonological similarity on letter-sound learning were found to be independent.

  10. Writing effective consultation letters: 12 tips for teachers.

    PubMed

    Keely, Erin; Dojeiji, Suzan; Myers, Kathryn

    2002-11-01

    Written correspondence is the standard mode of communication between healthcare providers. Despite the importance of this skill and increased emphasis on ambulatory care, communication skills and professionalism in training programs, there has been very little written on the teaching and evaluation of consultation letter writing. Consultation letter writing is an essential skill that cannot be learned simply by reading others' letters and should be taught in a formal manner. This article describes the authors' experience in teaching the skill of writing effective consultation letters to residents and describes strategies for evaluating this skill.

  11. Neural substrates of sensorimotor processes: letter writing and letter perception

    PubMed Central

    James, Karin H.

    2015-01-01

    Writing and perceiving letters are thought to share similar neural substrates; however, what constitutes a neural representation for letters is currently debated. One hypothesis is that letter representation develops from sensorimotor experience resulting in an integrated set of modality-specific regions, whereas an alternative account suggests that letter representations may be abstract, independent of modality. Studies reviewed suggest that letter representation consists of a network of modality-responsive brain regions that may include an abstract component. PMID:26203115

  12. Letter Recognition and Sound Identification.

    ERIC Educational Resources Information Center

    Prior, Jennifer

    This lesson, which is most appropriate for kindergartners, reviews letter names and their sounds through a group letter recognition activity, a picture book activity, and alphabet practice with several online activities. During three 30-minute sessions, students will: identify the letters of the alphabet; identify the sounds of letters; identify…

  13. Letter Names, Letter Sounds and Phonological Awareness: An Examination of Kindergarten Children across Letters and of Letters across Children

    ERIC Educational Resources Information Center

    Evans, Mary Ann; Bell, Michelle; Shaw, Deborah; Moretti, Shelley; Page, Jodi

    2006-01-01

    In this study 149 kindergarten children were assessed for knowledge of letter names and letter sounds, phonological awareness, and cognitive abilities. Through this it examined child and letter characteristics influencing the acquisition of alphabetic knowledge in a naturalistic context, the relationship between letter-sound knowledge and…

  14. Students' Perceptions of Reference Letters

    ERIC Educational Resources Information Center

    Payne, Brian K.; Appel, Jonathan; Smith, Donald H.; Hoofnagle, Kara

    2006-01-01

    This study examines students' perceptions of reference letters. Students (n = 444) were asked to describe how they perceived reference letters. Four themes were uncovered. First, some students perceived reference letters as useful for employers. Second, some students perceived the letters as important for students seeking employment or admission…

  15. Thomas Huxley and the rat placenta in the early debates on evolution.

    PubMed

    Pijnenborg, R; Vercruysse, L

    2004-01-01

    The 19th century debates on mammalian classification in the light of the new evolutionary thinking led to controversies between Thomas Huxley and Richard Owen concerning the value of the placenta as a representative key organ. As a main point in his argument, Huxley provided a detailed description of a sectioned rat placenta, highlighting the importance of decidualization of the uterus as an argument supporting an evolutionary relationship between rodents, insectivores and primates, an idea hotly contested by Owen. In addition, he illustrated and correctly interpreted the maternal blood supply from uterus to placenta in striking detail. During the succeeding decades the key role of trophoblast in placenta formation was discovered, and the decidua became neglected in later comparative studies. Nevertheless, at the present time trophoblast-decidual interaction is regarded as an extremely important feature of placental development in both primates and rodents, and Huxley can therefore rightfully be considered as an early pioneer in placental research.

  16. A note on the asymptotic reduction of the Hodgkin-Huxley equations for nerve impulses.

    PubMed

    Hinch, Robert

    2005-09-01

    The (standard) FitzHugh reduction of the Hodgkin-Huxley equations for the propagation of nerve impulses ignores the dynamics of the activation gates. This assumption is invalid and leads to an over-estimation of the wave speed by a factor of 5 and the wrong dependence of wave speed on sodium channel conductance. The error occurs because a non-dimensional parameter, which is assumed to be small in the FitzHugh reduction, is in fact large (approximately 18). We analyse the Hodgkin-Huxley equations for propagating nerve impulses in the limit that this non-dimensional parameter is large, and show that the analytical results are consistent with numerical simulations of the Hodgkin-Huxley equations.

  17. Temporal processing deficits in letter-by-letter reading.

    PubMed

    Ingles, Janet L; Eskes, Gail A

    2007-01-01

    Theories of the cognitive impairment underlying letter-by-letter reading vary widely, including prelexical and lexical level deficits. One prominent prelexical account proposes that the disorder results from difficulty in processing multiple letters simultaneously. We investigated whether this deficit extends to letters presented in rapid temporal succession. A letter-by-letter reader, G.M., was administered a rapid serial visual presentation task that has been used widely to study the temporal processing characteristics of the normal visual system. Comparisons were made to a control group of 6 brain-damaged individuals without reading deficits. Two target letters were embedded at varying temporal positions in a stream of rapidly presented single digits. After each stream, the identities of the two letters were reported. G.M. required an extended period of time after he had processed one letter before he was able to reliably identify a second letter, relative to the controls. In addition, G.M.'s report of the second letter was most impaired when it immediately followed the first letter, a pattern not seen in the controls, indicating that G.M. had difficulty processing the two items together. These data suggest that a letter-by-letter reading strategy may be adopted to help compensate for a deficit in the temporal processing of letters.

  18. T.H. Huxley's criticism of German cell theory: an epigenetic and physiological interpretation of cell structure.

    PubMed

    Richmond, M L

    2000-01-01

    In 1853, the young Thomas Henry Huxley published a long review of German cell theory in which he roundly criticized the basic tenets of the Schleiden-Schwann model of the cell. Although historians of cytology have dismissed Huxley's criticism as based on an erroneous interpretation of cell physiology, the review is better understood as a contribution to embryology. "The Cell-theory" presents Huxley's "epigenetic" interpretation of histological organization emerging from changes in the protoplasm to replace the "preformationist" cell theory of Schleiden and Schwann (as modified by Albert von Kolliker), which posited the nucleus as the seat of organic vitality. Huxley's views influenced a number of British biologists, who continued to oppose German cell theory well into the twentieth century. Yet Huxley was pivotal in introducing the new German program of "scientific zoology" to Britain in the early 1850s, championing its empiricist methodology as a means to enact broad disciplinary and institutional reforms in British natural history.

  19. Principal Dynamic Mode Analysis of the Hodgkin–Huxley Equations

    PubMed Central

    Eikenberry, Steffen E.; Marmarelis, Vasilis Z.

    2015-01-01

    We develop an autoregressive model framework based on the concept of Principal Dynamic Modes (PDMs) for the process of action potential (AP) generation in the excitable neuronal membrane described by the Hodgkin–Huxley (H–H) equations. The model's exogenous input is injected current, and whenever the membrane potential output exceeds a specified threshold, it is fed back as a second input. The PDMs are estimated from the previously developed Nonlinear Autoregressive Volterra (NARV) model, and represent an efficient functional basis for Volterra kernel expansion. The PDM-based model admits a modular representation, consisting of the forward and feedback PDM bases as linear filterbanks for the exogenous and autoregressive inputs, respectively, whose outputs are then fed to a static nonlinearity composed of polynomials operating on the PDM outputs and cross-terms of pair-products of PDM outputs. A two-step procedure for model reduction is performed: first, influential subsets of the forward and feedback PDM bases are identified and selected as the reduced PDM bases. Second, the terms of the static nonlinearity are pruned. The first step reduces model complexity from a total of 65 coefficients to 27, while the second further reduces the model coefficients to only eight. It is demonstrated that the performance cost of model reduction in terms of out-of-sample prediction accuracy is minimal. Unlike the full model, the eight coefficient pruned model can be easily visualized to reveal the essential system components, and thus the data-derived PDM model can yield insight into the underlying system structure and function. PMID:25630480

  20. Principal dynamic mode analysis of the Hodgkin-Huxley equations.

    PubMed

    Eikenberry, Steffen E; Marmarelis, Vasilis Z

    2015-03-01

    We develop an autoregressive model framework based on the concept of Principal Dynamic Modes (PDMs) for the process of action potential (AP) generation in the excitable neuronal membrane described by the Hodgkin-Huxley (H-H) equations. The model's exogenous input is injected current, and whenever the membrane potential output exceeds a specified threshold, it is fed back as a second input. The PDMs are estimated from the previously developed Nonlinear Autoregressive Volterra (NARV) model, and represent an efficient functional basis for Volterra kernel expansion. The PDM-based model admits a modular representation, consisting of the forward and feedback PDM bases as linear filterbanks for the exogenous and autoregressive inputs, respectively, whose outputs are then fed to a static nonlinearity composed of polynomials operating on the PDM outputs and cross-terms of pair-products of PDM outputs. A two-step procedure for model reduction is performed: first, influential subsets of the forward and feedback PDM bases are identified and selected as the reduced PDM bases. Second, the terms of the static nonlinearity are pruned. The first step reduces model complexity from a total of 65 coefficients to 27, while the second further reduces the model coefficients to only eight. It is demonstrated that the performance cost of model reduction in terms of out-of-sample prediction accuracy is minimal. Unlike the full model, the eight coefficient pruned model can be easily visualized to reveal the essential system components, and thus the data-derived PDM model can yield insight into the underlying system structure and function.

  1. Stimulus-dependent refractoriness in the Frankenhaeuser-Huxley model.

    PubMed

    Morse, R P; Allingham, D; Stocks, N G

    2015-10-07

    Phenomenological neural models, such as the leaky integrate-and-fire model, normally have a fixed refractory time-course that is independent of the stimulus. The recovery of threshold following an action potential is typically based on physiological experiments that use a two-pulse paradigm in which the first pulse is suprathreshold and causes excitation and the second pulse is used to determine the threshold at various intervals following the first. In such experiments, the nerve is completely unstimulated between the two pulses. This contrasts the receptor stimuli in normal physiological systems and the electrical stimuli used by cochlear implants and other neural prostheses. A numerical study of the Frankenhaeuser-Huxley conductance-based model of nerve fibre was therefore undertaken to investigate the effect of stimulation on refractoriness. We found that the application of a depolarizing stimulus during the later part of what is classically regarded as the absolute refractory period could effectively prolong the absolute refractory period, while leaving the refractory time-constants and other refractory parameters largely unaffected. Indeed, long depolarizing pulses, which would have been suprathreshold if presented to a resting nerve fibre, appeared to block excitation indefinitely. Stimulation during what is classically regarded as the absolute refractory period can therefore greatly affect the temporal response of a nerve. We conclude that the classical definition of absolute refractory period should be refined to include only the initial period following an action potential when an ongoing stimulus would not affect threshold; this period was found to be about half as long as the classical absolute refractory period. We further conclude that the stimulus-dependent nature of the relative refractory period must be considered when developing a phenomenological nerve model for complex stimuli.

  2. Half a Century of Physical Review Letters

    SciTech Connect

    Garisto, Robert

    2008-10-15

    Fifty years ago, Sam Goudsmit started an experiment: the journal Physical Review Letters. Since 1958, the experiment has thrived. PRL has gone through many changes, published many important papers, and become a leader in international scientific publication. I will trace the rise of PRL from its early 20th century roots as 'Letters to the Editor,' through changes in editorial process and advents of new technology. Along the way I'll show what has gone on behind the scenes, and give a glimpse of our plans for the future. I'll also give some advice to would-be authors and referees, illustrated with interesting correspondence we've received.

  3. An investigation of the stochastic Hodgkin-Huxley models under noisy rate functions.

    PubMed

    Güler, Marifi

    2013-09-01

    The effects of ion channel fluctuations on the transmembrane voltage activity are potentially profound in small-size excitable membrane patches. Different groups have extended Hodgkin-Huxley equations into stochastic differential equations to capture the effects of ion channel noise analytically (Fox & Lu, 1994; Linaro, Storace, & Giugliano, 2011; Güler, 2013). Studies have shown that the accuracy of spiking statistics by Fox and Lu's model does not match well with the corresponding statistics from the exact microscopic simulations. The models of both Linaro et al. and Güler, however, were found to produce highly accurate statistics. Here we extend the examination of these models to the case in which the rate functions for the opening and closing of gates are under the influence of noise. For that purpose, the usual rate functions are accompanied additively by Ornstein-Uhlenbeck-type stochastic angular variables. Moreover, we argue that the existence of such noise in the rate functions is a plausible physiological phenomenon for finite-size membranes. It is observed that the presence of noise in the rates is not effective on the degree of inaccuracies within the Fox and Lu model. Güler model's accuracy is found to remain high as in the case of noise free rates. But the performance of Linaro et al.'s model is seen to degrade seriously with the increasing strength of the introduced rate function noise. We attribute this failure of Linaro et al.'s model to the use of the covariance function of open channels at the steady state, in its derivation.

  4. Spike latency and jitter of neuronal membrane patches with stochastic Hodgkin-Huxley channels.

    PubMed

    Ozer, Mahmut; Uzuntarla, Muhammet; Perc, Matjaz; Graham, Lyle J

    2009-11-07

    Ion channel stochasticity can influence the voltage dynamics of neuronal membrane, with stronger effects for smaller patches of membrane because of the correspondingly smaller number of channels. We examine this question with respect to first spike statistics in response to a periodic input of membrane patches including stochastic Hodgkin-Huxley channels, comparing these responses to spontaneous firing. Without noise, firing threshold of the model depends on frequency-a sinusoidal stimulus is subthreshold for low and high frequencies and suprathreshold for intermediate frequencies. When channel noise is added, a stimulus in the lower range of subthreshold frequencies can influence spike output, while high subthreshold frequencies remain subthreshold. Both input frequency and channel noise strength influence spike timing. Specifically, spike latency and jitter have distinct minima as a function of input frequency, showing a resonance like behavior. With either no input, or low frequency subthreshold input, or input in the low or high suprathreshold frequency range, channel noise reduces latency and jitter, with the strongest impact for the lowest input frequencies. In contrast, for an intermediate range of suprathreshold frequencies, where an optimal input gives a minimum latency, the noise effect reverses, and spike latency and jitter increase with channel noise. Thus, a resonant minimum of the spike response as a function of frequency becomes more pronounced with less noise. Spike latency and jitter also depend on the initial phase of the input, resulting in minimal latencies at an optimal phase, and depend on the membrane time constant, with a longer time constant broadening frequency tuning for minimal latency and jitter. Taken together, these results suggest how stochasticity of ion channels may influence spike timing and thus coding for neurons with functionally localized concentrations of channels, such as in "hot spots" of dendrites, spines or axons.

  5. Epistolary and Emotional Education: The Letters of an Irish Father to His Daughter, 1747-1752

    ERIC Educational Resources Information Center

    Ruberg, Willemijn

    2008-01-01

    The letters Bishop Edward Synge (1691-1762) wrote to his daughter Alicia (1733-1807) in 1747-1752 are discussed to show how correspondence from a father to a daughter could be used to teach a teenage girl how to spell and write letters. Moreover, these letters are an excellent source to show how emotional behaviour was taught. Instructions on…

  6. Epistolary and Emotional Education: The Letters of an Irish Father to His Daughter, 1747-1752

    ERIC Educational Resources Information Center

    Ruberg, Willemijn

    2008-01-01

    The letters Bishop Edward Synge (1691-1762) wrote to his daughter Alicia (1733-1807) in 1747-1752 are discussed to show how correspondence from a father to a daughter could be used to teach a teenage girl how to spell and write letters. Moreover, these letters are an excellent source to show how emotional behaviour was taught. Instructions on…

  7. Learning to recognize letters in the periphery: Effects of repeated exposure, letter frequency, and letter complexity

    PubMed Central

    Husk, Jesse S.; Yu, Deyue

    2017-01-01

    Patients with central vision loss must rely on their peripheral vision for reading. Unfortunately, limitations of peripheral vision, such as crowding, pose significant challenges to letter recognition. As a result, there is a need for developing effective training methods for improving crowded letter recognition in the periphery. Several studies have shown that extensive practice with letter stimuli is beneficial to peripheral letter recognition. Here, we explore stimulus-related factors that might influence the effectiveness of peripheral letter recognition training. Specifically, we examined letter exposure (number of letter occurrences), frequency of letter use in English print, and letter complexity and evaluated their contributions to the amount of improvement observed in crowded letter recognition following training. We analyzed data collected across a range of training protocols. Using linear regression, we identified the best-fitting model and observed that all three stimulus-related factors contributed to improvement in peripheral letter recognition with letter exposure being the most important factor. As an important explanatory variable, pretest accuracy was included in the model as well to avoid estimate biases and was shown to have influence on the relationship between training improvement and letter exposure. When developing training protocols for peripheral letter recognition, it may be beneficial to not only consider the overall length of training, but also to tailor the number of stimulus occurrences for each letter according to its initial performance level, frequency, and complexity. PMID:28265651

  8. Significance of conductances in Hodgkin-Huxley models.

    PubMed

    Foster, W R; Ungar, L H; Schwaber, J S

    1993-12-01

    1. We explore the roles of conductances in Hodgkin-Huxley (HH) models using a method that allows the explicit linking of HH model input-output behavior to parameter values for maximal conductances, voltage shifts, and time constants. The procedure can be used to identify not only the parameter values most critical to supporting a neuronal activity pattern of interest but also the relationships between parameters which may be required, e.g., limited ranges of relative magnitudes. 2. The method is the repeated use of stochastic search to find hundreds or even thousands of different sets of model parameter values that allow a HH model to produce a desired behavior, such as current-frequency transduction, to within a desired tolerance, e.g., frequency match to within 10 Hz. Graphical or other analysis may then be performed to reveal the shape and boundaries of the parameter solution regions that support the desired behavior. 3. The shape of these parameter regions can reveal parameter values and relationships essential to the behavior. For instance, graphical display may reveal covariances between maximal conductance values, or a much wider range of variation in some maximal conductance values than in others. 4. We demonstrate the use of these techniques with simple, representative HH models, primarily that of Connor et al. for crustacean walking leg axons, but also some extensions of the results are explored using the more complex model of McCormick and Huguenard for thalamocortical relay neurons. Both models are single compartment. Behaviors studied include current-to-frequency transduction, the time delay to first action potential in response to current steps, and the timing of action potential occurrences in response to both square-wave current injection and the injection of currents derived from in vitro records of excitatory postsynaptic currents. 5. Using these simple models, we find that relatively general behaviors such as current-frequency (I/F) curves may be

  9. The costs of being a restless intellect: Julian Huxley's popular and scientific career in the 1920s.

    PubMed

    Erlingsson, Steindór J

    2009-06-01

    Julian Huxley's (1887-1975) contribution to twentieth-century biology and science popularisation is well documented. What has not been appreciated so far is that despite Huxley's eminence as a public scientific figure and the part that he played in the rise of experimental zoology in Britain in the 1920s, his own research was often heavily criticised in this period by his colleagues. This resulted in numerous difficulties in getting his scientific research published in the early 1920s. At this time, Huxley started his popular science career. Huxley's friends criticised him for engaging in this actively and attributed the publication difficulties to the time that he allocated to popular science. The cause might also have its roots in his self-professed inability to delve deeply into the particularities of research. This affected Huxley's standing in the scientific community and seems to have contributed to the fact that Huxley failed twice in the late 1920s to be elected to the Royal Society. This picture undermines to some extent Peter J. Bowler's recent portrayal of Huxley as a science populariser.

  10. Letter to Doxiadis

    ERIC Educational Resources Information Center

    Fuller, Buckminster

    1969-01-01

    The second half of a lengthy letter to Dr. Constantine Doxiadis (published in full in Main Currents in Modern Thought, XXV, March-April 1969) summarizes Buckminster Fuller's personal reflections on the impact of industrialization and on the effect of technological change in uniting mankind. (MF)

  11. Letters in this Issue

    NASA Astrophysics Data System (ADS)

    1998-01-01

    Reforming the General Chemistry Textbook individual letters by Edward T. Samulski; Stephen J. Hawkes; Stephen J. Fisher; J. Stephen Hartman; A. R. H. Cole; Stanley Pine, Ronald Archer, and Herbert Kaesz; Jimmy Reeves; Robert Hill; and Brock Spencer, C. Bradley Moore and Nedah Rose. Re: article by R. J. Gillespie The author replies

  12. Harvard Education Letter, 2001.

    ERIC Educational Resources Information Center

    Gordon, David, T., Ed.

    2001-01-01

    This document is comprised of the six issues in volume 17 of the Harvard Education Letter, a bimonthly newsletter addressing current issues in elementary and secondary education. Articles in this volume include the following: (1) January-February--"Charters and Districts: Three Stages in an Often Rocky Relationship" (Kelly) and "'We…

  13. Harvard Education Letter, 2002.

    ERIC Educational Resources Information Center

    Gordon, David T., Editor

    2002-01-01

    This document is comprised of the 6 issues in volume 18 of the Harvard Education Letter, a bimonthly newsletter addressing current issues in elementary and secondary education. Articles in this volume include the following: (1) January/February--"Curriculum Access in the Digital Age" (David T. Gordon) and "Using Charters To Improve…

  14. Letters from a suicide.

    PubMed

    Barnes, Donna Holland; Lawal-Solarin, Foluso Williams; Lester, David

    2007-08-01

    A linguistic analysis of a series of letters written by a young man who died by suicide to 1 friend over a period of 2 years prior to his death revealed several trends, including a decrease in negative emotion words and an increase in death words. The implication of these trends was discussed.

  15. The Fuzzy Scarlet Letter

    ERIC Educational Resources Information Center

    Pallas, Aaron M.

    2012-01-01

    Critics of the public release of teacher evaluation scores sometimes liken these ratings to the scarlet letter worn by Hester Prynne in Nathaniel Hawthorne's classic novel. The comparison is apt. But public school teachers who are subjected to public shaming because of their students' test scores can rarely expect the opportunities for redemption…

  16. Five Long Letters.

    ERIC Educational Resources Information Center

    Bone, Eric

    1990-01-01

    Describes the life of former Louisiana governor Huey Long through five fictitious letters. Discusses Long's experiences as a state public service commissioner, governor, and senator. Attributes Long's assassination to his killer's personal motives. Concludes that Long's life showed how much personal power could be gained even in a democracy. (SG)

  17. Harvard Education Letter, 1999.

    ERIC Educational Resources Information Center

    Graves-Desai, Kelly, Ed.

    1999-01-01

    This document is comprised of the six issues in volume 15 of the Harvard Education Letter, a bimonthly newsletter addressing current issues in elementary and secondary education. Articles in this volume include the following: (1) January-February--"Retention vs. Social Promotion: Schools Search for Alternatives" (Kelly), and "School…

  18. Letters and American Literacy.

    ERIC Educational Resources Information Center

    Kevis, David E.

    The work itself should help a person who is going to teach reading and writing. Practical suggestions are offered in the final two chapters, while the opening three give intellectual perspectives. A theme binds the work of letting the consciousness of writing as a visual system be increased and of breaking the spell by which letter phonetics can…

  19. Letter to Doxiadis

    ERIC Educational Resources Information Center

    Fuller, Buckminster

    1969-01-01

    The second half of a lengthy letter to Dr. Constantine Doxiadis (published in full in Main Currents in Modern Thought, XXV, March-April 1969) summarizes Buckminster Fuller's personal reflections on the impact of industrialization and on the effect of technological change in uniting mankind. (MF)

  20. Inside the Letter

    ERIC Educational Resources Information Center

    Duke, Roger; Graham, Alan

    2007-01-01

    In this article, the authors describe how a Java applet can help to build learners' intuitions about basic ideas of algebra. "Matchbox Algebra" is a Java applet the authors have designed to enable learners to grasp a key idea in learning algebra: that the letter "x" may be thought of as representing an as-yet-unknown number. They describe the…

  1. Letters and American Literacy.

    ERIC Educational Resources Information Center

    Kevis, David E.

    The work itself should help a person who is going to teach reading and writing. Practical suggestions are offered in the final two chapters, while the opening three give intellectual perspectives. A theme binds the work of letting the consciousness of writing as a visual system be increased and of breaking the spell by which letter phonetics can…

  2. The Fuzzy Scarlet Letter

    ERIC Educational Resources Information Center

    Pallas, Aaron M.

    2012-01-01

    Critics of the public release of teacher evaluation scores sometimes liken these ratings to the scarlet letter worn by Hester Prynne in Nathaniel Hawthorne's classic novel. The comparison is apt. But public school teachers who are subjected to public shaming because of their students' test scores can rarely expect the opportunities for redemption…

  3. Inside the Letter

    ERIC Educational Resources Information Center

    Duke, Roger; Graham, Alan

    2007-01-01

    In this article, the authors describe how a Java applet can help to build learners' intuitions about basic ideas of algebra. "Matchbox Algebra" is a Java applet the authors have designed to enable learners to grasp a key idea in learning algebra: that the letter "x" may be thought of as representing an as-yet-unknown number. They describe the…

  4. Five Long Letters.

    ERIC Educational Resources Information Center

    Bone, Eric

    1990-01-01

    Describes the life of former Louisiana governor Huey Long through five fictitious letters. Discusses Long's experiences as a state public service commissioner, governor, and senator. Attributes Long's assassination to his killer's personal motives. Concludes that Long's life showed how much personal power could be gained even in a democracy. (SG)

  5. Wilberforce, Huxley and the Use of History in Teaching about Evolution.

    ERIC Educational Resources Information Center

    Gauld, Colin

    1992-01-01

    Author asserts that many historical anecdotes used in science instruction have little basis in reality. The purpose of this paper is to provide a critique of the way in which the "Wilberforce and Huxley debate at Oxford" anecdote is employed in the teaching of evolution and to suggest a more positive role for this incident in science…

  6. Wilberforce, Huxley and the Use of History in Teaching about Evolution.

    ERIC Educational Resources Information Center

    Gauld, Colin

    1992-01-01

    Author asserts that many historical anecdotes used in science instruction have little basis in reality. The purpose of this paper is to provide a critique of the way in which the "Wilberforce and Huxley debate at Oxford" anecdote is employed in the teaching of evolution and to suggest a more positive role for this incident in science…

  7. Tunicates: exploring the sea shores and roaming the open ocean. A tribute to Thomas Huxley.

    PubMed

    Lemaire, Patrick; Piette, Jacques

    2015-06-01

    This review is a tribute to the remarkable contributions of Thomas Huxley to the biology of tunicates, the likely sister group of vertebrates. In 1851, the great biologist and philosopher published two landmark papers on pelagic tunicates in the Philosophical Transactions of the Royal Society. They were dedicated to the description of the adult anatomy and life cycle of thaliaceans and appendicularians, the pelagic relatives of ascidians. In the first part of this review, we discuss the novel anatomical observations and evolutionary hypotheses made by Huxley, which would have a lasting influence on tunicate biology. We also briefly comment on the more philosophical reflections of Huxley on individuality. In the second part, we stress the originality and relevance of past and future studies of tunicates in the resolution of major biological issues. In particular, we focus on the complex relationship between genotype and phenotype and the phenomenon of developmental system drift. We propose that more than 150 years after Huxley's papers, tunicate embryos are still worth studying in their own right, independently of their evolutionary proximity to vertebrates, as they provide original and crucial insights into the process of animal evolution. Tunicates are still at the forefront of biological research.

  8. Tunicates: exploring the sea shores and roaming the open ocean. A tribute to Thomas Huxley

    PubMed Central

    Lemaire, Patrick; Piette, Jacques

    2015-01-01

    This review is a tribute to the remarkable contributions of Thomas Huxley to the biology of tunicates, the likely sister group of vertebrates. In 1851, the great biologist and philosopher published two landmark papers on pelagic tunicates in the Philosophical Transactions of the Royal Society. They were dedicated to the description of the adult anatomy and life cycle of thaliaceans and appendicularians, the pelagic relatives of ascidians. In the first part of this review, we discuss the novel anatomical observations and evolutionary hypotheses made by Huxley, which would have a lasting influence on tunicate biology. We also briefly comment on the more philosophical reflections of Huxley on individuality. In the second part, we stress the originality and relevance of past and future studies of tunicates in the resolution of major biological issues. In particular, we focus on the complex relationship between genotype and phenotype and the phenomenon of developmental system drift. We propose that more than 150 years after Huxley's papers, tunicate embryos are still worth studying in their own right, independently of their evolutionary proximity to vertebrates, as they provide original and crucial insights into the process of animal evolution. Tunicates are still at the forefront of biological research. PMID:26085517

  9. The "History" of Victorian Scientific Naturalism: Huxley, Spencer and the "End" of natural history.

    PubMed

    Lightman, Bernard

    2016-08-01

    As part of their defence of evolutionary theory, T. H. Huxley and Herbert Spencer argued that natural history was no longer a legitimate scientific discipline. They outlined a secularized concept of life from biology to argue for the validity of naturalism. Despite their support for naturalism, they offered two different responses to the decline of natural history. Whereas Huxley emphasized the creation of a biological discipline, and all that that entailed, Spencer was more concerned with constructing an entire intellectual system based on the idea of evolution. In effect, Spencer wanted to create a new scientific worldview based on evolutionary theory. This had consequences for their understanding of human history, especially of how science had evolved through the ages. It affected their conceptions of human agency, contingency, and directionality in history. Examining Huxley's and Spencer's responses to the "end" of natural history reveals some of the deep divisions within scientific naturalism and the inherent problems of naturalism in general. Whereas Huxley chose to separate the natural and the historical, Spencer opted to fuse them into a single system. Crown Copyright © 2016. Published by Elsevier Ltd. All rights reserved.

  10. The What and Where of Adding Channel Noise to the Hodgkin-Huxley Equations

    PubMed Central

    Goldwyn, Joshua H.; Shea-Brown, Eric

    2011-01-01

    Conductance-based equations for electrically active cells form one of the most widely studied mathematical frameworks in computational biology. This framework, as expressed through a set of differential equations by Hodgkin and Huxley, synthesizes the impact of ionic currents on a cell's voltage—and the highly nonlinear impact of that voltage back on the currents themselves—into the rapid push and pull of the action potential. Later studies confirmed that these cellular dynamics are orchestrated by individual ion channels, whose conformational changes regulate the conductance of each ionic current. Thus, kinetic equations familiar from physical chemistry are the natural setting for describing conductances; for small-to-moderate numbers of channels, these will predict fluctuations in conductances and stochasticity in the resulting action potentials. At first glance, the kinetic equations provide a far more complex (and higher-dimensional) description than the original Hodgkin-Huxley equations or their counterparts. This has prompted more than a decade of efforts to capture channel fluctuations with noise terms added to the equations of Hodgkin-Huxley type. Many of these approaches, while intuitively appealing, produce quantitative errors when compared to kinetic equations; others, as only very recently demonstrated, are both accurate and relatively simple. We review what works, what doesn't, and why, seeking to build a bridge to well-established results for the deterministic equations of Hodgkin-Huxley type as well as to more modern models of ion channel dynamics. As such, we hope that this review will speed emerging studies of how channel noise modulates electrophysiological dynamics and function. We supply user-friendly MATLAB simulation code of these stochastic versions of the Hodgkin-Huxley equations on the ModelDB website (accession number 138950) and http://www.amath.washington.edu/~etsb/tutorials.html. PMID:22125479

  11. The what and where of adding channel noise to the Hodgkin-Huxley equations.

    PubMed

    Goldwyn, Joshua H; Shea-Brown, Eric

    2011-11-01

    Conductance-based equations for electrically active cells form one of the most widely studied mathematical frameworks in computational biology. This framework, as expressed through a set of differential equations by Hodgkin and Huxley, synthesizes the impact of ionic currents on a cell's voltage--and the highly nonlinear impact of that voltage back on the currents themselves--into the rapid push and pull of the action potential. Later studies confirmed that these cellular dynamics are orchestrated by individual ion channels, whose conformational changes regulate the conductance of each ionic current. Thus, kinetic equations familiar from physical chemistry are the natural setting for describing conductances; for small-to-moderate numbers of channels, these will predict fluctuations in conductances and stochasticity in the resulting action potentials. At first glance, the kinetic equations provide a far more complex (and higher-dimensional) description than the original Hodgkin-Huxley equations or their counterparts. This has prompted more than a decade of efforts to capture channel fluctuations with noise terms added to the equations of Hodgkin-Huxley type. Many of these approaches, while intuitively appealing, produce quantitative errors when compared to kinetic equations; others, as only very recently demonstrated, are both accurate and relatively simple. We review what works, what doesn't, and why, seeking to build a bridge to well-established results for the deterministic equations of Hodgkin-Huxley type as well as to more modern models of ion channel dynamics. As such, we hope that this review will speed emerging studies of how channel noise modulates electrophysiological dynamics and function. We supply user-friendly MATLAB simulation code of these stochastic versions of the Hodgkin-Huxley equations on the ModelDB website (accession number 138950) and http://www.amath.washington.edu/~etsb/tutorials.html.

  12. EPA Void Letter for Suzuki

    EPA Pesticide Factsheets

    When a certificate is voided, EPA issues a void letter to the manufacturer.November 30, 2016, letter from Byron Bunker to Suzuki Motor America Inc., voiding certificate of conformity for highway motorcycle engine family CSKXC.652VR1.

  13. Taxicab Correspondence Analysis.

    PubMed

    Choulakian, V

    2006-06-01

    Taxicab correspondence analysis is based on the taxicab singular value decomposition of a contingency table, and it shares some similar properties with correspondence analysis. It is more robust than the ordinary correspondence analysis, because it gives uniform weights to all the points. The visual map constructed by taxicab correspondence analysis has a larger sweep and clearer perspective than the map obtained by correspondence analysis. Two examples are provided.

  14. Letters to a Young Writer.

    ERIC Educational Resources Information Center

    Wright, C. D.; Schulman, Grace

    2001-01-01

    Presents two letters to a young writer, modeled on the influential "Letters to a Young Poet" by Rainer Maria Rilke. Notes the first letter situates itself when a young writer first turns toward poetry; and the second addresses the relationship between mentorship and the imagination, questioning the right of any writer to presume to guide the…

  15. Letters: Windows to the Past.

    ERIC Educational Resources Information Center

    Collier-Seiter, Claudia; Seiter, David M.

    1992-01-01

    Presents a lesson plan utilizing personal letters of ordinary people to teach U.S. history. Suggests that the lesson can teach about the historical information available in personal letters, develop analytical skills through use of primary sources, and increase students' understanding of minority issues. Includes four letters to use as handouts.…

  16. Letters to the Editor

    NASA Astrophysics Data System (ADS)

    1997-03-01

    All the Letters to the Editor in this issue are in the same PostScript or PDF file. Contents Criticisms of hands-on pseudoscience David J Fisher 27 Elderberry Road, Cardiff CF5 3RG, UK Measuring varying fields Don Koks Adelaide University, Australia Relativity at A-level: a comment David Sang 3 Ellasdale Road, Bognor Regis, PO21 2SG, UK

  17. A comparison of letter and digit processing in letter-by-letter reading.

    PubMed

    Ingles, Janet L; Eskes, Gail A

    2008-01-01

    The extent to which letter-by-letter reading results from a specific orthographic deficit, as compared with a nonspecific disturbance in basic visuoperceptual mechanisms, is unclear. The current study directly compared processing of letters and digits in a letter-by-letter reader, G.M., using a rapid serial visual presentation (RSVP) task and a speeded matching task. Comparisons were made to a group of six brain-damaged individuals without reading deficits. In the RSVP task, G.M. had increased difficulty reporting the target identities when they were letters, as compared with digits. Although this general pattern was also evident in the control group, the magnitude of the letter-digit accuracy difference was greater in G.M. Similarly, in the matching task, G.M. was slower to match letters than digits, relative to the control group, although his response times to both item types were increased. These data suggest that letter-by-letter reading, at least in this case, results from a visuoperceptual encoding deficit that particularly affects letters, but also extends to processing of digits to a lesser extent. Results are consistent with the notion that a left occipitotemporal area is specialized for letter processing with greater bilaterality in the visual processing of digits.

  18. Human dynamics: Darwin and Einstein correspondence patterns.

    PubMed

    Oliveira, João Gama; Barabási, Albert-László

    2005-10-27

    In an era when letters were the main means of exchanging scientific ideas and results, Charles Darwin (1809-82) and Albert Einstein (1879-1955) were notably prolific correspondents. But did their patterns of communication differ from those associated with the instant-access e-mail of modern times? Here we show that, although the means have changed, the communication dynamics have not: Darwin's and Einstein's patterns of correspondence and today's electronic exchanges follow the same scaling laws. However, the response times of their surface-mail communication is described by a different scaling exponent from e-mail communication, providing evidence for a new class of phenomena in human dynamics.

  19. Taxicab Correspondence Analysis

    ERIC Educational Resources Information Center

    Choulakian, V.

    2006-01-01

    Taxicab correspondence analysis is based on the taxicab singular value decomposition of a contingency table, and it shares some similar properties with correspondence analysis. It is more robust than the ordinary correspondence analysis, because it gives uniform weights to all the points. The visual map constructed by taxicab correspondence…

  20. Allographic Agraphia for Single letters

    PubMed Central

    Menichelli, Alina; Machetta, Francesca; Zadini, Antonella; Semenza, Carlo

    2012-01-01

    The case is reported of a patient (PS) who, following acute encephalitis with residual occipito-temporal damage, showed a selective deficit in writing cursive letters in isolation, but no difficulty to write cursive-case words and non-words. Notably, he was able to recognize the same allographs he could not write and to produce both single letters and words in print. In addition to this selective single letter writing difficulty, the patient demonstrated an inability to correctly perform a series of imagery tasks for cursive letters. PS’s performance may indicate that single letter production requires explicit imagery. Explicit imagery may not be required, instead, when letters have to be produced in the context of a word: letter production in this case may rely on implicit retrieval of well learned scripts in a procedural way. PMID:22713390

  1. Vowel Cluster-Phoneme Correspondences in 20,000 English Words.

    ERIC Educational Resources Information Center

    Johnson, Dale D.

    The symbol-sound correspondence status of vowel-cluster (two or more adjacent vowel letters) spelling in American English was investigated. The source of the study was Venezky's 1963 revision of the Thorndike Frequency Count. A computer print-out of the 20,000 word corpus was analyzed to determine the letter-sound correspondence of vowel cluster…

  2. Which children benefit from letter names in learning letter sounds?

    PubMed

    Treiman, Rebecca; Pennington, Bruce F; Shriberg, Lawrence D; Boada, Richard

    2008-03-01

    Typical U.S. children use their knowledge of letters' names to help learn the letters' sounds. They perform better on letter sound tests with letters that have their sounds at the beginnings of their names, such as v, than with letters that have their sounds at the ends of their names, such as m, and letters that do not have their sounds in their names, such as h. We found this same pattern among children with speech sound disorders, children with language impairments as well as speech sound disorders, and children who later developed serious reading problems. Even children who scored at chance on rhyming and sound matching tasks performed better on the letter sound task with letters such as v than with letters such as m and h. Our results suggest that a wide range of children use the names of letters to help learn the sounds and that phonological awareness, as conventionally measured, is not required in order to do so.

  3. How to write effective business letters: scribing information for pharmacists.

    PubMed

    Hamilton, C W

    1993-11-01

    Pharmacists frequently write letters but lack specific training on how to do it well. This review summarizes strategies for improving business correspondence, emphasizes basic writing guidelines, and offers practical advice for pharmacists. The first steps for effective communication are careful planning and identifying the main message to be conveyed. The purpose for writing should be stated in the opening paragraph of the letter. To ensure a successful outcome, actions needed should be clearly summarized and visually highlighted. The tone of the letter should reflect a reasonable speech pattern, not the cryptic writing found in many scientific papers. The layout of the letter should be inviting, which is readily achievable through judicious use of word processing. Many delivery options are available, such as traditional postal services, express mail, and facsimile transmission. Readers are encouraged to test these basic writing principles and decide for themselves whether these recommendations affect the success of business correspondence.

  4. Young Children's Letter-Sound Knowledge.

    ERIC Educational Resources Information Center

    Dodd, Barbara; Carr, Alex

    2003-01-01

    This study with 83 normally developing children (ages 4-6) compared three essential skills in early literacy, letter-sound recognition, letter-sound recall, and letter reproduction. Children performed better in letter-sound recognition than in letter-sound recall and letter reproduction. There were no performance differences due to sex or age.…

  5. Controlling the onset of Hopf bifurcation in the Hodgkin-Huxley model

    NASA Astrophysics Data System (ADS)

    Xie, Yong; Chen, Luonan; Kang, Yan Mei; Aihara, Kazuyuki

    2008-06-01

    It is a challenging problem to establish safe and simple therapeutic methods for various complicated diseases of the nervous system, particularly dynamical diseases such as epilepsy, Alzheimer’s disease, and Parkinson’s disease. From the viewpoint of nonlinear dynamical systems, a dynamical disease can be considered to be caused by a bifurcation induced by a change in the values of one or more regulating parameter. Therefore, the theory of bifurcation control may have potential applications in the diagnosis and therapy of dynamical diseases. In this study, we employ a washout filter-aided dynamic feedback controller to control the onset of Hopf bifurcation in the Hodgkin-Huxley (HH) model. Specifically, by the control scheme, we can move the Hopf bifurcation to a desired point irrespective of whether the corresponding steady state is stable or unstable. In other words, we are able to advance or delay the Hopf bifurcation, so as to prevent it from occurring in a certain range of the externally applied current. Moreover, we can control the criticality of the bifurcation and regulate the oscillation amplitude of the bifurcated limit cycle. In the controller, there are only two terms: the linear term and the nonlinear cubic term. We show that while the former determines the location of the Hopf bifurcation, the latter regulates the criticality of the Hopf bifurcation. According to the conditions of the occurrence of Hopf bifurcation and the bifurcation stability coefficient, we can analytically deduce the linear term and the nonlinear cubic term, respectively. In addition, we also show that mixed-mode oscillations (MMOs), featuring slow action potential generation, which are frequently observed in both experiments and models of chemical and biological systems, appear in the controlled HH model. It is well known that slow firing rates in single neuron models could be achieved only by type-I neurons. However, the controlled HH model is still classified as a type

  6. Task switching and response correspondence in the psychological refractory period paradigm

    NASA Technical Reports Server (NTRS)

    Lien, Mei-Ching; Schweickert, Richard; Proctor, Robert W.

    2003-01-01

    Three experiments examined the effects of task switching and response correspondence in a psychological refractory period paradigm. A letter task (vowel-consonant) and a digit task (odd-even) were combined to form 4 possible dual-task pairs in each trial: letter-letter, letter-digit, digit-digit, and digit-letter. Foreknowledge of task transition (repeat or switch) and task identity (letter or digit) was varied across experiments: no foreknowledge in Experiment 1, partial foreknowledge (task transition only) in Experiment 2, and full foreknowledge in Experiment 3. For all experiments, the switch cost for Task 2 was additive with stimulus onset asynchrony, and the response-correspondence effect for Task 2 was numerically smaller in the switch condition than in the repeat condition. These outcomes suggest that reconfiguration for Task 2 takes place after the central processing of Task 1 and that the crosstalk correspondence effect is due to response activation by way of stimulus-response associations.

  7. Task switching and response correspondence in the psychological refractory period paradigm

    NASA Technical Reports Server (NTRS)

    Lien, Mei-Ching; Schweickert, Richard; Proctor, Robert W.

    2003-01-01

    Three experiments examined the effects of task switching and response correspondence in a psychological refractory period paradigm. A letter task (vowel-consonant) and a digit task (odd-even) were combined to form 4 possible dual-task pairs in each trial: letter-letter, letter-digit, digit-digit, and digit-letter. Foreknowledge of task transition (repeat or switch) and task identity (letter or digit) was varied across experiments: no foreknowledge in Experiment 1, partial foreknowledge (task transition only) in Experiment 2, and full foreknowledge in Experiment 3. For all experiments, the switch cost for Task 2 was additive with stimulus onset asynchrony, and the response-correspondence effect for Task 2 was numerically smaller in the switch condition than in the repeat condition. These outcomes suggest that reconfiguration for Task 2 takes place after the central processing of Task 1 and that the crosstalk correspondence effect is due to response activation by way of stimulus-response associations.

  8. Stochastic resonance, coherence resonance, and spike timing reliability of Hodgkin-Huxley neurons with ion-channel noise

    NASA Astrophysics Data System (ADS)

    Yu, Haitao; Galán, Roberto F.; Wang, Jiang; Cao, Yibin; Liu, Jing

    2017-04-01

    The random transitions of ion channels between open and closed states are a major source of noise in neurons. In this study, we investigate the stochastic dynamics of a single Hodgkin-Huxley (HH) neuron with realistic, physiological channel noise, which depends on the channel number and the voltage potential of the membrane. Without external input, the stochastic HH model can generate spontaneous spikes induced by ion-channel noise, and the variability of inter-spike intervals attains a minimum for an optimal membrane area, a phenomenon known as coherence resonance. When a subthreshold periodic input current is added, the neuron can optimally detect the input frequency for an intermediate membrane area, corresponding to the phenomenon of stochastic resonance. We also investigate spike timing reliability of neuronal responses to repeated presentations of the same stimulus with different realizations of channel noise. We show that, with increasing membrane area, the reliability of neuronal response decreases for subthreshold periodic inputs, and attains a minimum for suprathreshold inputs. Furthermore, Arnold tongues of high reliability arise in a two-dimensional plot of frequency and amplitude of the sinusoidal input current, resulting from the resonance effect of spike timing reliability.

  9. Dynamics from seconds to hours in Hodgkin-Huxley model with time-dependent ion concentrations and buffer reservoirs.

    PubMed

    Hübel, Niklas; Dahlem, Markus A

    2014-12-01

    The classical Hodgkin-Huxley (HH) model neglects the time-dependence of ion concentrations in spiking dynamics. The dynamics is therefore limited to a time scale of milliseconds, which is determined by the membrane capacitance multiplied by the resistance of the ion channels, and by the gating time constants. We study slow dynamics in an extended HH framework that includes time-dependent ion concentrations, pumps, and buffers. Fluxes across the neuronal membrane change intra- and extracellular ion concentrations, whereby the latter can also change through contact to reservoirs in the surroundings. Ion gain and loss of the system is identified as a bifurcation parameter whose essential importance was not realized in earlier studies. Our systematic study of the bifurcation structure and thus the phase space structure helps to understand activation and inhibition of a new excitability in ion homeostasis which emerges in such extended models. Also modulatory mechanisms that regulate the spiking rate can be explained by bifurcations. The dynamics on three distinct slow times scales is determined by the cell volume-to-surface-area ratio and the membrane permeability (seconds), the buffer time constants (tens of seconds), and the slower backward buffering (minutes to hours). The modulatory dynamics and the newly emerging excitable dynamics corresponds to pathological conditions observed in epileptiform burst activity, and spreading depression in migraine aura and stroke, respectively.

  10. Breaking Object Correspondence Across Saccadic Eye Movements Deteriorates Object Recognition

    PubMed Central

    Poth, Christian H.; Herwig, Arvid; Schneider, Werner X.

    2015-01-01

    Visual perception is based on information processing during periods of eye fixations that are interrupted by fast saccadic eye movements. The ability to sample and relate information on task-relevant objects across fixations implies that correspondence between presaccadic and postsaccadic objects is established. Postsaccadic object information usually updates and overwrites information on the corresponding presaccadic object. The presaccadic object representation is then lost. In contrast, the presaccadic object is conserved when object correspondence is broken. This helps transsaccadic memory but it may impose attentional costs on object recognition. Therefore, we investigated how breaking object correspondence across the saccade affects postsaccadic object recognition. In Experiment 1, object correspondence was broken by a brief postsaccadic blank screen. Observers made a saccade to a peripheral object which was displaced during the saccade. This object reappeared either immediately after the saccade or after the blank screen. Within the postsaccadic object, a letter was briefly presented (terminated by a mask). Observers reported displacement direction and letter identity in different blocks. Breaking object correspondence by blanking improved displacement identification but deteriorated postsaccadic letter recognition. In Experiment 2, object correspondence was broken by changing the object’s contrast-polarity. There were no object displacements and observers only reported letter identity. Again, breaking object correspondence deteriorated postsaccadic letter recognition. These findings identify transsaccadic object correspondence as a key determinant of object recognition across the saccade. This is in line with the recent hypothesis that breaking object correspondence results in separate representations of presaccadic and postsaccadic objects which then compete for limited attentional processing resources (Schneider, 2013). Postsaccadic object recognition

  11. Breaking Object Correspondence Across Saccadic Eye Movements Deteriorates Object Recognition.

    PubMed

    Poth, Christian H; Herwig, Arvid; Schneider, Werner X

    2015-01-01

    Visual perception is based on information processing during periods of eye fixations that are interrupted by fast saccadic eye movements. The ability to sample and relate information on task-relevant objects across fixations implies that correspondence between presaccadic and postsaccadic objects is established. Postsaccadic object information usually updates and overwrites information on the corresponding presaccadic object. The presaccadic object representation is then lost. In contrast, the presaccadic object is conserved when object correspondence is broken. This helps transsaccadic memory but it may impose attentional costs on object recognition. Therefore, we investigated how breaking object correspondence across the saccade affects postsaccadic object recognition. In Experiment 1, object correspondence was broken by a brief postsaccadic blank screen. Observers made a saccade to a peripheral object which was displaced during the saccade. This object reappeared either immediately after the saccade or after the blank screen. Within the postsaccadic object, a letter was briefly presented (terminated by a mask). Observers reported displacement direction and letter identity in different blocks. Breaking object correspondence by blanking improved displacement identification but deteriorated postsaccadic letter recognition. In Experiment 2, object correspondence was broken by changing the object's contrast-polarity. There were no object displacements and observers only reported letter identity. Again, breaking object correspondence deteriorated postsaccadic letter recognition. These findings identify transsaccadic object correspondence as a key determinant of object recognition across the saccade. This is in line with the recent hypothesis that breaking object correspondence results in separate representations of presaccadic and postsaccadic objects which then compete for limited attentional processing resources (Schneider, 2013). Postsaccadic object recognition is

  12. Letter to an ethicist

    PubMed Central

    Silver, Malcolm; Crelinsten, Gordon

    1995-01-01

    Just as issues have arisen in court that cause the public to question whether the rights of criminals are taking precedence over the rights of victims, some physicians wonder if ethicists are placing the rights of some patients ahead of the rights of society and the common good. Pathologist Malcolm Silver raised this issue in a letter to the editor of CMAJ. With his permission, it was forwarded to Dr. Gordon Crelinsten, past chair of the ethics committee at the Royal Victoria Hospital in Montreal. PMID:7697584

  13. Letters to the Editor

    NASA Astrophysics Data System (ADS)

    1998-01-01

    All the Letters to the Editor in this issue are in the same PostScript or PDF file. Contents Physics and history Arthur I Miller Department of Science & Technology Studies, University College London, Gower Street, London WC1E 6BT, UK Physics and history: a reply David Miller Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK Cathode rays, the electron and Thomson's discovery John Harris 33 Glentham Road, London SW13 9JD, UK Vectors: swallow them whole! David Wheeler Mahanakorn University of Technology, Bangkok, Thailand

  14. Letters to the Editor

    NASA Astrophysics Data System (ADS)

    1998-03-01

    All the Letters to the Editor in this issue are in the same PostScript or PDF file. Contents Comment on `Magnetic and electric field strengths of high voltage power lines and household appliances' José Luis Giordano Dept. de Ciencia y Tecnología de Materiales y Fluidos, CPSI, Universidad de Zaragoza, Spain Twins paradox S R Carson Norton College, Malton, North Yorkshire, UK On alternative ways of finding the ratio of specific heats of gases Tomas Ficker Physics Department, Technical University of Brno, Czech Republic

  15. Letters to the Editor

    NASA Astrophysics Data System (ADS)

    1998-09-01

    All the Letters to the Editor in this issue are in the same PostScript or PDF file. Contents Science spreadsheets Richard Beare Institute of Education, University of Warwick, Coventry, UK Calculating the `lost energy' Zhang Yongzhao and Zhang Shuyan Police Frontier Guard Patrol Boat Institute, Zhejiang, Ningbo 315801, People's Republic of China Cartesian diver solves the inverse sprinkler problem Boris M Valiyov and Vladimir D Yegorenkov Department of Physics, Kharkov State University, 4 Svobody sq., 310077, Kharkov, Ukraine Update excellence Karen Barker Lytham St Annes, Lancs, UK

  16. Letters to the Editor

    NASA Astrophysics Data System (ADS)

    1997-01-01

    All the Letters to the Editor in this issue are in the same PostScript or PDF file. Contents Software teaching of modular physics: SToMP Stephen Hearn Head of Science, Charterhouse, Godalming, Surrey GU7 2DX Bridging the gap or avoiding a chasm? R W West York Strengths and weaknesses of science John Bausor Christians in Science Education, Edgware, London HA8 6RR Addressing the issues Philip Britton Head of Physics, Leeds Grammar School Modern syllabuses and old textbooks: a useful synthesis Richard Barrass St Mary's College, Doncaster DN1 2ES

  17. How the Hodgkin-Huxley equations inspired the Cardiac Physiome Project.

    PubMed

    Noble, Denis; Garny, Alan; Noble, Penelope J

    2012-06-01

    Early modelling of cardiac cells (1960-1980) was based on extensions of the Hodgkin-Huxley nerve axon equations with additional channels incorporated, but after 1980 it became clear that processes other than ion channel gating were also critical in generating electrical activity. This article reviews the development of models representing almost all cell types in the heart, many different species, and the software tools that have been created to facilitate the cardiac Physiome Project.

  18. Solving the Hodgkin-Huxley equations by a random walk method

    SciTech Connect

    Sherman, A.S.; Peskin, C.S.

    1988-01-01

    A numerical method is describes for solving the Hodgkin-Huxley cable equations, set up as an initial boundary value problem. The method uses a gradient random walk combined with creation and destruction of the diffusing elements. It is designed to be efficient in the presence of sharp wavefronts. Details of implementation are given with particular emphasis on satisfying the boundary conditions without introducing excessive noise.

  19. Stochastic sensitivity analysis of noise-induced suppression of firing and giant variability of spiking in a Hodgkin-Huxley neuron model

    NASA Astrophysics Data System (ADS)

    Bashkirtseva, Irina; Neiman, Alexander B.; Ryashko, Lev

    2015-05-01

    We study the stochastic dynamics of a Hodgkin-Huxley neuron model in a regime of coexistent stable equilibrium and a limit cycle. In this regime, noise may suppress periodic firing by switching the neuron randomly to a quiescent state. We show that at a critical value of the injected current, the mean firing rate depends weakly on noise intensity, while the neuron exhibits giant variability of the interspike intervals and spike count. To reveal the dynamical origin of this noise-induced effect, we develop the stochastic sensitivity analysis and use the Mahalanobis metric for this four-dimensional stochastic dynamical system. We show that the critical point of giant variability corresponds to the matching of the Mahalanobis distances from attractors (stable equilibrium and limit cycle) to a three-dimensional surface separating their basins of attraction.

  20. Stochastic sensitivity analysis of noise-induced suppression of firing and giant variability of spiking in a Hodgkin-Huxley neuron model.

    PubMed

    Bashkirtseva, Irina; Neiman, Alexander B; Ryashko, Lev

    2015-05-01

    We study the stochastic dynamics of a Hodgkin-Huxley neuron model in a regime of coexistent stable equilibrium and a limit cycle. In this regime, noise may suppress periodic firing by switching the neuron randomly to a quiescent state. We show that at a critical value of the injected current, the mean firing rate depends weakly on noise intensity, while the neuron exhibits giant variability of the interspike intervals and spike count. To reveal the dynamical origin of this noise-induced effect, we develop the stochastic sensitivity analysis and use the Mahalanobis metric for this four-dimensional stochastic dynamical system. We show that the critical point of giant variability corresponds to the matching of the Mahalanobis distances from attractors (stable equilibrium and limit cycle) to a three-dimensional surface separating their basins of attraction.

  1. Computational and Electronic Analog Implementation of the Hodgkin-Huxley Model of Action Potentials in Neurons

    NASA Astrophysics Data System (ADS)

    Smith, Peter; Link, Justin

    2012-02-01

    Alan Loyd Hodgkin and Andrew Huxley's mathematical model of action potential initiation and propagation in neurons is one of the greatest hallmarks of biophysics. Two techniques for implementing the Hodgkin-Huxley model were explored: computational and electronic analog. Computational modeling was done using NEURON 7.1. NEURON is a free, robust, and relatively user friendly simulation environment that enables quantitatively accurate computational modeling of neurons and neural networks. An analog electronic circuit was built using field-effect transistors (FETs) to simulate the non-linear, voltage-dependent (sodium and potassium) conductances that are responsible for membrane excitability. While the electronic analog qualitatively reproduces many of the key features of the action potential including overall shape, inactivation period, and propagation, it was difficult to quantitatively reproduce the Hodgkin-Huxley model. In addition, while the relative cost to build circuits equivalent to small membrane patches is minimal (˜50), implementation of larger cells or networks would prove uneconomical. Still, both techniques are viable avenues toward introducing interdisciplinary research into either a computational or electronics lab setting at the undergraduate level.

  2. Past as Prediction: Newcomb, Huxley, The Eclipse of Thales, and The Power of Science

    NASA Astrophysics Data System (ADS)

    Stanley, Matthew

    2009-12-01

    The ancient eclipse of Thales was an important, if peculiar, focus of scientific attention in the 19th century. Victorian-era astronomers first used it as data with which to calibrate their lunar theories, but its status became strangely malleable as the century progressed. The American astronomer Simon Newcomb re-examined the eclipse and rejected it as the basis for lunar theory. But strangely, it was the unprecedented accuracy of Newcomb's calculations that led the British biologist T.H. Huxley to declare the eclipse to be the quintessential example of the power of science. Huxley argued that astronomy's ability to create "retrospective prophecy” showed how scientific reasoning was superior to religion (and incidentally, helped support Darwin's theories). Both Newcomb and Huxley declared that prediction (of past and future) was what gave science its persuasive power. The eclipse of Thales's strange journey through Victorian astronomy reveals how these two influential scientists made the case for the social and cultural authority of science.

  3. Extending the conditions of application of an inversion of the Hodgkin-Huxley gating model.

    PubMed

    Raba, Ashley E; Cordeiro, Jonathan M; Antzelevitch, Charles; Beaumont, Jacques

    2013-05-01

    We present an inversion of the Hodgkin-Huxley formalism to estimate initial conditions and model parameters, including functions of voltage, from the solutions of the underlying ordinary differential equation (ODE) subjected to multiple voltage step stimulations. As such, the procedure constitutes a means to estimate the parameters including functions of voltage of an Hodgkin-Huxley formalism from experimental data.The basic idea was developed in a previous communication (SIAM J. Appl. Math. 64:1264-1274, 2009). The inversion in question applies to currents exhibiting activation and inactivation, but the version, as published previously, cannot estimate the unknowns for channels that rapidly inactivate just after a brief opening. In such cases, the amplitude of the current, in a given voltage range, is too small to be detectable by the instrumentation using previously applied experimental protocols. This is, for example, the case for the sodium channels in a number of excitable tissue for potential in the vicinity of the cell resting potential. The current communication extends the inversion procedure in a manner to overcome this limitation.Furthermore, within the inversion framework, we can determine whether the data at the basis of the estimation sufficiently constrains the estimation problem, i.e., whether it is complete. We exploit this element of our method to document a set of stimulation protocols that constitute a complete data set for the purpose of inverting the Hodgkin-Huxley formalism.

  4. Thomas Henry Huxley (1825-1895) puts us in our place.

    PubMed

    Weiss, Kenneth M

    2004-05-15

    Thomas Huxley was one of the 19th century's most active defenders of Darwin's idea that life has evolved through natural processes. An anatomist and paleontologist, he extended his energies to science and education policy, the democratization of science, and the broad societal implications of evolution. Since his time the fossil record has greatly improved and the genetic 'revolution' has occurred, deepening our understanding of primate and human evolution in ways that would please Huxley: improved systematics relies heavily on genetic data, and molecular technologies are opening our understanding of the genetic basis of complex traits of traditional anthropological interest-but in ways that are thoroughly dependent on the fact of evolution. A more unified biological synthesis is forming that unites genes, developmental process, structure, and inheritance. But the tempo and mode of evolution remain unresolved. Huxley was one of many who have had trouble accepting Darwin's gradual natural selection as the central evolutionary mechanism, and views spanning the antipodes of gradualism and saltation find advocates even in our genetic era.

  5. Extending the Conditions of Application of an Inversion of the Hodgkin–Huxley Gating Model

    PubMed Central

    Cordeiro, Jonathan M.; Antzelevitch, Charles; Beaumont, Jacques

    2013-01-01

    We present an inversion of the Hodgkin–Huxley formalism to estimate initial conditions and model parameters, including functions of voltage, from the solutions of the underlying ordinary differential equation (ODE) subjected to multiple voltage step stimulations. As such, the procedure constitutes a means to estimate the parameters including functions of voltage of an Hodgkin–Huxley formalism from experimental data. The basic idea was developed in a previous communication (SIAM J. Appl. Math. 64:1264–1274, 2009). The inversion in question applies to currents exhibiting activation and inactivation, but the version, as published previously, cannot estimate the unknowns for channels that rapidly inactivate just after a brief opening. In such cases, the amplitude of the current, in a given voltage range, is too small to be detectable by the instrumentation using previously applied experimental protocols. This is, for example, the case for the sodium channels in a number of excitable tissue for potential in the vicinity of the cell resting potential. The current communication extends the inversion procedure in a manner to overcome this limitation. Furthermore, within the inversion framework, we can determine whether the data at the basis of the estimation sufficiently constrains the estimation problem, i.e., whether it is complete. We exploit this element of our method to document a set of stimulation protocols that constitute a complete data set for the purpose of inverting the Hodgkin–Huxley formalism. PMID:23595789

  6. Demonstrating the Correspondence Bias

    ERIC Educational Resources Information Center

    Howell, Jennifer L.; Shepperd, James A.

    2011-01-01

    Among the best-known and most robust biases in person perception is the correspondence bias--the tendency for people to make dispositional, rather than situational, attributions for an actor's behavior. The correspondence bias appears in virtually every social psychology textbook and in many introductory psychology textbooks, yet the authors'…

  7. Demonstrating the Correspondence Bias

    ERIC Educational Resources Information Center

    Howell, Jennifer L.; Shepperd, James A.

    2011-01-01

    Among the best-known and most robust biases in person perception is the correspondence bias--the tendency for people to make dispositional, rather than situational, attributions for an actor's behavior. The correspondence bias appears in virtually every social psychology textbook and in many introductory psychology textbooks, yet the authors'…

  8. Michael Maier--nine newly discovered letters.

    PubMed

    Lenke, Nils; Roudet, Nicolas; Tilton, Hereward

    2014-02-01

    The authors provide a transcription, translation, and evaluation of nine newly discovered letters from the alchemist Michael Maier (1568-1622) to Gebhardt Johann von Alvensleben (1576-1631), a noble landholder in the vicinity of Magdeburg. Stemming from the final year of his life, this correspondence casts new light on Maier's biography, detailing his efforts to secure patronage amid the financial crisis of the early Thirty Years' War. While his ill-fated quest to perfect potable gold continued to form the central focus of his patronage suits, Maier also offered his services in several arts that he had condemned in his printed works, namely astrology and "supernatural" magic. Remarks concerning his previously unknown acquaintance with Heinrich Khunrath call for a re-evaluation of Maier's negotiation of the discursive boundaries between Lutheran orthodoxy and Paracelsianism. The letters also reveal Maier's substantial contribution to a work previously ascribed solely to the English alchemist Francis Anthony.

  9. Half a Century of Physical Review Letters

    SciTech Connect

    Garisto, Robert

    2008-10-15

    Fifty years ago, Sam Goudsmit started an experiment: the journal Physical Review Letters.  Since 1958, the experiment has thrived. PRL has gone through many changes, published many important papers, and become a leader in international scientific publication.  I will trace the rise of PRL from its early 20th century roots as "Letters to the Editor," through changes in editorial process and advents of new technology. Along the way I'll show what has gone on behind the scenes, and give a glimpse of our plans for the future.  I'll also give some advice to would-be authors and referees, illustrated with interesting correspondence we've received.

  10. Half a Century of Physical Review Letters

    ScienceCinema

    Garisto, Robert

    2016-07-12

    Fifty years ago, Sam Goudsmit started an experiment: the journal Physical Review Letters.  Since 1958, the experiment has thrived. PRL has gone through many changes, published many important papers, and become a leader in international scientific publication.  I will trace the rise of PRL from its early 20th century roots as "Letters to the Editor," through changes in editorial process and advents of new technology. Along the way I'll show what has gone on behind the scenes, and give a glimpse of our plans for the future.  I'll also give some advice to would-be authors and referees, illustrated with interesting correspondence we've received.

  11. What Can Reduce Letter Migrations in Letter Position Dyslexia?

    ERIC Educational Resources Information Center

    Friedmann, Naama; Rahamim, Einav

    2014-01-01

    Letter position dyslexia (LPD) is a peripheral dyslexia that causes errors of letter position within words, such as reading "cloud" as "could." In this study, we assessed the effect of various display manipulations and reading methods on the reading of 10 Hebrew readers with developmental LPD. These manipulations included…

  12. What Can Reduce Letter Migrations in Letter Position Dyslexia?

    ERIC Educational Resources Information Center

    Friedmann, Naama; Rahamim, Einav

    2014-01-01

    Letter position dyslexia (LPD) is a peripheral dyslexia that causes errors of letter position within words, such as reading "cloud" as "could." In this study, we assessed the effect of various display manipulations and reading methods on the reading of 10 Hebrew readers with developmental LPD. These manipulations included…

  13. The Visuo-Haptic and Haptic Exploration of Letters Increases the Kindergarten-Children's Understanding of the Alphabetic Principle

    ERIC Educational Resources Information Center

    Bara, Florence; Gentaz, Edouard; Cole, Pascale; Sprenger-Charolles, Liliane

    2004-01-01

    This study examined the effect of incorporating a visuo-haptic and haptic (tactual-kinaesthetic) exploration of letters in a training designed to develop phonemic awareness, knowledge of letters and letter/sound correspondences, on 5-year-old children's understanding and use of the alphabetic principle. Three interventions, which differed in the…

  14. Complex Correspondence Principle

    SciTech Connect

    Bender, Carl M.; Meisinger, Peter N.; Hook, Daniel W.; Wang Qinghai

    2010-02-12

    Quantum mechanics and classical mechanics are distinctly different theories, but the correspondence principle states that quantum particles behave classically in the limit of high quantum number. In recent years much research has been done on extending both quantum and classical mechanics into the complex domain. These complex extensions continue to exhibit a correspondence, and this correspondence becomes more pronounced in the complex domain. The association between complex quantum mechanics and complex classical mechanics is subtle and demonstrating this relationship requires the use of asymptotics beyond all orders.

  15. A survey of patient views on receiving vascular outpatient letters.

    PubMed

    Brodie, T; Lewis, D R

    2010-01-01

    To assess the attitude of patients to receiving a copy of vascular outpatient clinic letters. 100 patients attending an outpatient vascular clinic at Christchurch Hospital were sent a copy of their outpatient letter along with a questionnaire. This gathered information on the content of the letter, their understanding of it, how useful they found it and whether they would want this practice to continue. The response rate was 68%. Ninety four percent of the responders believed receiving a copy of the letter was a good reinforcement of the information they received at the consultation. Ninety three percent of responders also found being copied into correspondence helpful and 96% understood the contents of the letters. Ninety seven percent wished to receive more letters in the future. These results suggest that vascular surgery patients both value and understand clinic letters, and that health professionals should consider adopting this practice into their vascular outpatient clinics. Copyright 2009 European Society for Vascular Surgery. Published by Elsevier Ltd. All rights reserved.

  16. The rhetoric of patient voice: reported talk with patients in referral and consultation letters.

    PubMed

    Spafford, Marlee M; Schryer, Catherine F; Lingard, Lorelei

    2008-01-01

    Referral and consultation letters are written to enable the exchange of patient information and facilitate the trajectory of patients through the healthcare system. Yet, these letters, written about yet apart from patients, also sustain and constrain professional relationships and influence attitudes towards patients. We analysed 35 optometry referral letters and 35 corresponding ophthalmology consultation letters for reported 'patient voice' coded as 'experience' or 'agenda' and we interviewed 15 letter writers (eight optometry students, six optometrists, and one community ophthalmologist). There were 80 instances of reported 'patient voice' in 35 letters. The majority (68%) of the instances occurred in referral letters, likely due to differences in both 'letter function' and 'professional stance.' Reported 'patient voice' occurred predominantly as 'experience' (81%) rather than 'agenda' instances. Letters writers focused on their readers' needs, thus a biomedical voice dominated the letters and instances of reported 'patient voice' were recontextualized for the professional audience. While reporting 'patient voice' was not the norm in these letters, its inclusion appeared to accomplish specific work: to persuade reader action, to question patient credibility, and to highlight patient agency. These letter strategies reflect professional attitudes about patients and their care.

  17. Anomalous Retinal Correspondence

    DTIC Science & Technology

    1988-10-01

    angle of anomaly is in the op- occur. Possible adaptations include amblyopia . suppress posite or noncompensating direction, the correspondence is and...When than the angle of squint, then it is described as unharmon- strabismus occurs in early childhood, certain adaptations can ious ARC (UHAC). If the...correspond- ence. However. it is clear that strict isolation of the possible THREE COMMON TESTING TEC-NIQUES adaptations is difficult. A variety of

  18. Letters in Biographies and Novels.

    ERIC Educational Resources Information Center

    Paterra, Elizabeth

    1997-01-01

    This is an annotated bibliography of biographies, historical fiction, contemporary stories, and discussion questions related to letter writing. A sidebar suggests an activity that involves reading a book about Ludwig van Beethoven, listening to Beethoven's music, and discussing letters in the story. (DGM)

  19. T-SENSE a millimeter wave scanner for letters

    NASA Astrophysics Data System (ADS)

    Nüßler, Dirk; Heinen, Sven; Sprenger, Thorsten; Hübsch, Daniel; Würschmidt, Tobais

    2013-10-01

    Letter bombs are an increasing problem for public authorities, companies and public persons. Nowadays every big company uses in his headquarters inspection system to check the incoming correspondence. Generally x-ray systems are used to inspect complete baskets or bags of letters. This concept which works very fine in big company with a large postal center is not usable for small companies or private persons. For an office environment with a small number of letters x-ray systems are too expensive and oversized. X-ray systems visualize the wires and electric circuits inside the envelope. If a letter contains no metallic components but hazard materials or drugs, the dangerous content is invisible for the most low-cost x-ray systems. Millimeter wave imagining systems offer the potential to close this gap.

  20. Multiclass Continuous Correspondence Learning

    NASA Technical Reports Server (NTRS)

    Bue, Brian D,; Thompson, David R.

    2011-01-01

    We extend the Structural Correspondence Learning (SCL) domain adaptation algorithm of Blitzer er al. to the realm of continuous signals. Given a set of labeled examples belonging to a 'source' domain, we select a set of unlabeled examples in a related 'target' domain that play similar roles in both domains. Using these 'pivot samples, we map both domains into a common feature space, allowing us to adapt a classifier trained on source examples to classify target examples. We show that when between-class distances are relatively preserved across domains, we can automatically select target pivots to bring the domains into correspondence.

  1. Multiclass Continuous Correspondence Learning

    NASA Technical Reports Server (NTRS)

    Bue, Brian D,; Thompson, David R.

    2011-01-01

    We extend the Structural Correspondence Learning (SCL) domain adaptation algorithm of Blitzer er al. to the realm of continuous signals. Given a set of labeled examples belonging to a 'source' domain, we select a set of unlabeled examples in a related 'target' domain that play similar roles in both domains. Using these 'pivot samples, we map both domains into a common feature space, allowing us to adapt a classifier trained on source examples to classify target examples. We show that when between-class distances are relatively preserved across domains, we can automatically select target pivots to bring the domains into correspondence.

  2. Students as Letter Writers: How Letters Inform Instructors

    NASA Astrophysics Data System (ADS)

    Kirms, Lynn M.

    2004-07-01

    The enhancement of faculty understanding of students through student letter writing is explored. Two short letter-writing assignments are described and their value in the teaching process is outlined. An argument is presented for gaining a realistic picture of who our students are so as to enrich our communication and teaching effectiveness in the classroom. The letter-writing assignments were made in an organic chemistry lecture setting, but could be applied throughout a chemical curriculum, at the high school and at the university level.

  3. Rival Visions: J.J. Rousseau and T.H. Huxley on the Nature (or Nurture) of Inequality and What It Means for Education

    ERIC Educational Resources Information Center

    Currie-Knight, Kevin

    2011-01-01

    Jean-Jacques Rousseau (1712-1778) and Thomas Huxley (1852-1895) had different, but substantial, effects on the history of education. Rousseau's educational theories supplied the intellectual foundation for pedagogical progressivism. Huxley's educational writings helped to enlarge the scope of the British curriculum to include such things as…

  4. Summer Correspondence Program.

    ERIC Educational Resources Information Center

    Sulphur Springs Union Elementary School District, Canyon Country, CA.

    THE FOLLOWING IS THE FULL TEXT OF THIS DOCUMENT: The goals of the Summer Correspondence Program have been to help students maintain their basic skills and avoid summer fall-out, as well as to promote parent involvement and positive community relations. After Proposition 13 left no funds for continuation of summer school programs, Sulphur Springs…

  5. The Correspondence Principle Revisited.

    ERIC Educational Resources Information Center

    Liboff, Richard L.

    1984-01-01

    Addresses the question of frequency correspondence in the domain of large quantum numbers, with reference to periodic systems. Provides two simple counterexamples (a particle in a cubical box and a rigid rotator) to show that the classical result is not always recovered in the limit of large quantum numbers. (JM)

  6. Subjective contours along truncated letters.

    PubMed

    Gillam, Barbara; Vecellio, Elia

    2012-01-01

    The truncation of upper-case words can result in a subjective contour along the truncated ends of the letters. We explored this effect in two experiments designed to tease apart the processes responsible: in particular, the possible role of letter recognition. Such a role would indicate an unprecedented involvement of "high-level vision" in the genesis of subjective contours. In experiment 1, we confirmed the basic effect of word truncation in eliciting a subjective contour, using only letters where truncation does not eliminate any critical features. In experiment 2, we showed that the effect is not confined to words/letters but is equally strong for controlled non-letter stimuli that, like words, have many forms that have an inflection or an intersection near the centre. Truncation at one end then introduces proportional imbalance between upper and lower sections of the figures. We conclude from the two experiments that part of the effect is due to vertical shortening per se and the rest to the proportional imbalance introduced by the truncation. The effect of proportional imbalance, a novel determinant of subjective contours, may result from experience with letters, although the effect is not "high level" in requiring the recognition of specific letters.

  7. Feature detection and letter identification.

    PubMed

    Pelli, Denis G; Burns, Catherine W; Farell, Bart; Moore-Page, Deborah C

    2006-12-01

    Seeking to understand how people recognize objects, we have examined how they identify letters. We expected this 26-way classification of familiar forms to challenge the popular notion of independent feature detection ("probability summation"), but find instead that this theory parsimoniously accounts for our results. We measured the contrast required for identification of a letter briefly presented in visual noise. We tested a wide range of alphabets and scripts (English, Arabic, Armenian, Chinese, Devanagari, Hebrew, and several artificial ones), three- and five-letter words, and various type styles, sizes, contrasts, durations, and eccentricities, with observers ranging widely in age (3 to 68) and experience (none to fluent). Foreign alphabets are learned quickly. In just three thousand trials, new observers attain the same proficiency in letter identification as fluent readers. Surprisingly, despite this training, the observers-like clinical letter-by-letter readers-have the same meager memory span for random strings of these characters as observers seeing them for the first time. We compare performance across tasks and stimuli that vary in difficulty by pitting the human against the ideal observer, and expressing the results as efficiency. We find that efficiency for letter identification is independent of duration, overall contrast, and eccentricity, and only weakly dependent on size, suggesting that letters are identified by a similar computation across this wide range of viewing conditions. Efficiency is also independent of age and years of reading. However, efficiency does vary across alphabets and type styles, with more complex forms yielding lower efficiencies, as one might expect from Gestalt theories of perception. In fact, we find that efficiency is inversely proportional to perimetric complexity (perimeter squared over "ink" area) and nearly independent of everything else. This, and the surprisingly fixed ratio of detection and identification

  8. Channel noise effects on first spike latency of a stochastic Hodgkin-Huxley neuron.

    PubMed

    Maisel, Brenton; Lindenberg, Katja

    2017-02-01

    While it is widely accepted that information is encoded in neurons via action potentials or spikes, it is far less understood what specific features of spiking contain encoded information. Experimental evidence has suggested that the timing of the first spike may be an energy-efficient coding mechanism that contains more neural information than subsequent spikes. Therefore, the biophysical features of neurons that underlie response latency are of considerable interest. Here we examine the effects of channel noise on the first spike latency of a Hodgkin-Huxley neuron receiving random input from many other neurons. Because the principal feature of a Hodgkin-Huxley neuron is the stochastic opening and closing of channels, the fluctuations in the number of open channels lead to fluctuations in the membrane voltage and modify the timing of the first spike. Our results show that when a neuron has a larger number of channels, (i) the occurrence of the first spike is delayed and (ii) the variation in the first spike timing is greater. We also show that the mean, median, and interquartile range of first spike latency can be accurately predicted from a simple linear regression by knowing only the number of channels in the neuron and the rate at which presynaptic neurons fire, but the standard deviation (i.e., neuronal jitter) cannot be predicted using only this information. We then compare our results to another commonly used stochastic Hodgkin-Huxley model and show that the more commonly used model overstates the first spike latency but can predict the standard deviation of first spike latencies accurately. We end by suggesting a more suitable definition for the neuronal jitter based upon our simulations and comparison of the two models.

  9. Channel noise effects on first spike latency of a stochastic Hodgkin-Huxley neuron

    NASA Astrophysics Data System (ADS)

    Maisel, Brenton; Lindenberg, Katja

    2017-02-01

    While it is widely accepted that information is encoded in neurons via action potentials or spikes, it is far less understood what specific features of spiking contain encoded information. Experimental evidence has suggested that the timing of the first spike may be an energy-efficient coding mechanism that contains more neural information than subsequent spikes. Therefore, the biophysical features of neurons that underlie response latency are of considerable interest. Here we examine the effects of channel noise on the first spike latency of a Hodgkin-Huxley neuron receiving random input from many other neurons. Because the principal feature of a Hodgkin-Huxley neuron is the stochastic opening and closing of channels, the fluctuations in the number of open channels lead to fluctuations in the membrane voltage and modify the timing of the first spike. Our results show that when a neuron has a larger number of channels, (i) the occurrence of the first spike is delayed and (ii) the variation in the first spike timing is greater. We also show that the mean, median, and interquartile range of first spike latency can be accurately predicted from a simple linear regression by knowing only the number of channels in the neuron and the rate at which presynaptic neurons fire, but the standard deviation (i.e., neuronal jitter) cannot be predicted using only this information. We then compare our results to another commonly used stochastic Hodgkin-Huxley model and show that the more commonly used model overstates the first spike latency but can predict the standard deviation of first spike latencies accurately. We end by suggesting a more suitable definition for the neuronal jitter based upon our simulations and comparison of the two models.

  10. Two New Letters by Denning

    NASA Astrophysics Data System (ADS)

    Beech, Martin

    2010-06-01

    Two letters written by W. F. Denning to R. P. Greg in March and April of 1879 that had been tucked into the folds of an 1876 edition of the British Association for the Advancement of Science Reports were recently found at the Carnegie Institution in Washington D.C. The letters are wonderfully preserved, and offer us a snap-shot of the work being performed by a young Denning at the time when his influence in the field of meteor studies was in its ascendency. The contents of these two letters is analyzed and placed within context to Denning's other publications and private life.

  11. Communicating safety information to physicians: an examination of dear doctor letters.

    PubMed

    Mazor, Kathleen M; Andrade, Susan E; Auger, Jill; Fish, Leslie; Gurwitz, Jerry H

    2005-12-01

    Recent research suggests that letters to healthcare providers may not effectively communicate safety-related information. This study examined whether content, organization, and formatting of dear doctor letters (DDLs) influences physicians' responses to the letters. Drugs with warning label changes during 2000 and 2001 were identified, and corresponding DDLs were obtained. Letters were coded for content, organization, and formatting. Ten physicians rated letters on presentation, criticalness of the information, and likelihood of changing practice as a result of the letter. Areas of deficiency were identified. The relationships between key characteristics of the letters and physicians' ratings were examined using correlations; reliability of physicians' ratings was estimated using generalizability theory. For 2000 and 2001, 124 drugs were identified as having had changes to the warning section of the label; DDLs were sent in 32 (25.8%) instances. Letters varied in terms of the placement of key information, use of formatting, and length. Physicians' ratings suggested 25% of the letters were deficient in clarity, 28% in readability, 36% in the ratio of relevant information to supporting information, 36% in key information easily discernable, and 28% in overall effectiveness of communication. Letters with formatting highlighting key information were preferred. Letter length and placement of key information were not correlated with physicians' ratings. Many DDLs do not communicate labeling changes clearly and effectively. If DDLs are used to communicate safety information to physicians, special formatting and explicit wording should be used to emphasize new information. Copyright (c) 2005 John Wiley & Sons, Ltd.

  12. Non-Gaussian Colored Noise Optimized Spatial Coherence of a Hodgkin—Huxley Neuronal Network

    NASA Astrophysics Data System (ADS)

    Sun, Xiao-Juan; Lu, Qi-Shao

    2014-02-01

    We numerically study how non-Gaussian colored noise affects the spatial coherence of a Hodgkin—Huxley neuronal network. From the simulation results, we find that there exists some intermediate noise intensities, correlation time of the colored noise, and the deviation from Gaussian colored noise, for which an ordered pattern with a characteristic spatial frequency of the system comes forth in a resonant manner. Namely, under certain conditions, spatial coherence of the studied neuronal network can be optimized by the non-Gaussian colored noise, which indicates the occurrence of spatial coherence resonance.

  13. Stochastic resonance in Hodgkin-Huxley neuron induced by unreliable synaptic transmission.

    PubMed

    Guo, Daqing; Li, Chunguang

    2012-09-07

    We systematically investigate the stochastic dynamics of a single Hodgkin-Huxley neuron driven by stochastic excitatory and inhibitory input spikes via unreliable synapses in this paper. Based on the mean-filed theory, a novel intrinsic neuronal noise regulation mechanism stemming from unreliable synapses is presented. Our simulation results show that, under certain conditions, the stochastic resonance phenomenon is able to be induced by the unreliable synaptic transmission, which can be well explained by the theoretical prediction. To a certain degree, the results presented here provide insights into the functional roles of unreliable synapses in neural information processing. Copyright © 2012 Elsevier Ltd. All rights reserved.

  14. Grandletters--A Correspondence Program for Grandparents and Their Grandchildren.

    ERIC Educational Resources Information Center

    Smith, Charles A.; Gutsch, Gayla

    This collection of materials presents "Grandletters," a correspondence program designed to strengthen the relationship between grandparents and grandchildren separated by distance, by having them exchange 10 letters on special topics, keep a scrapbook and a journal, and do other optional activities. The materials include three separate…

  15. The Syllabic Bridge: The First Step in Learning Spelling-to-Sound Correspondences

    ERIC Educational Resources Information Center

    Doignon-Camus, Nadege; Zaga, Daniel

    2014-01-01

    It is widely agreed that learning to read starts with the establishment of letter-to-phoneme correspondences. However, it is also widely agreed that prereaders do not have access to phoneme units. Here we show that the building of associations between letters and syllables, which we call the "syllabic bridge", might be a faster and more…

  16. Teacher Candidates' Mastery of Phoneme-Grapheme Correspondence: Massed versus Distributed Practice in Teacher Education

    ERIC Educational Resources Information Center

    Sayeski, Kristin L.; Earle, Gentry A.; Eslinger, R. Paige; Whitenton, Jessy N.

    2017-01-01

    Matching phonemes (speech sounds) to graphemes (letters and letter combinations) is an important aspect of decoding (translating print to speech) and encoding (translating speech to print). Yet, many teacher candidates do not receive explicit training in phoneme-grapheme correspondence. Difficulty with accurate phoneme production and/or lack of…

  17. The Syllabic Bridge: The First Step in Learning Spelling-to-Sound Correspondences

    ERIC Educational Resources Information Center

    Doignon-Camus, Nadege; Zaga, Daniel

    2014-01-01

    It is widely agreed that learning to read starts with the establishment of letter-to-phoneme correspondences. However, it is also widely agreed that prereaders do not have access to phoneme units. Here we show that the building of associations between letters and syllables, which we call the "syllabic bridge", might be a faster and more…

  18. A correspondence principle

    NASA Astrophysics Data System (ADS)

    Hughes, Barry D.; Ninham, Barry W.

    2016-02-01

    A single mathematical theme underpins disparate physical phenomena in classical, quantum and statistical mechanical contexts. This mathematical "correspondence principle", a kind of wave-particle duality with glorious realizations in classical and modern mathematical analysis, embodies fundamental geometrical and physical order, and yet in some sense sits on the edge of chaos. Illustrative cases discussed are drawn from classical and anomalous diffusion, quantum mechanics of single particles and ideal gases, quasicrystals and Casimir forces.

  19. The Complaint Letter and Response.

    ERIC Educational Resources Information Center

    Shukla, P. K.

    1998-01-01

    Describes an assignment in which students write a letter of complaint, and discusses how this assignment aids students in seeing the importance of effective written communication to their daily lives. (SR)

  20. Letter from the Friends Chairman

    MedlinePlus

    ... Home Current Issue Past Issues Letter from the Friends Chairman Past Issues / Fall 2006 Table of Contents ... FNLM Chairman Paul Rogers converse at a recent Friends function at the National Library of Medicine. Photo ...

  1. Letters to a Young Writer.

    ERIC Educational Resources Information Center

    Waldman, Anne; Becker, Robin

    2002-01-01

    Presents words of encouragement to a young poet. Includes empathetic words and motivating ideas. Presents a letter including a quote from "Tintern Abbey" by William Wordsworth and ideas about that quote. (SG)

  2. Morphology and Spelling in French Students with Dyslexia: The Case of Silent Final Letters

    ERIC Educational Resources Information Center

    Quémart, Pauline; Casalis, Séverine

    2017-01-01

    Spelling is a challenge for individuals with dyslexia. Phoneme-to-grapheme correspondence rules are highly inconsistent in French, which make them very difficult to master, in particular for dyslexics. One recurrent manifestation of this inconsistency is the presence of silent letters at the end of words. Many of these silent letters perform a…

  3. 19 CFR Policy Statement to Part 145 - Examination of Sealed Letter Class Mail

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... contained in any letter class mail unless there has been obtained in advance either a search warrant or... territory of the United States, unless a search warrant or written authorization of the sender or addressee... letter class mail which appears to contain only correspondence unless a search warrant or...

  4. 19 CFR Policy Statement to Part 145 - Examination of Sealed Letter Class Mail

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... contained in any letter class mail unless there has been obtained in advance either a search warrant or... territory of the United States, unless a search warrant or written authorization of the sender or addressee... letter class mail which appears to contain only correspondence unless a search warrant or...

  5. William Stewart Halsted: letters to a young female admirer.

    PubMed

    Cameron, J L; Gordon, T A; Kehoe, M W; McCall, N

    2001-11-01

    To present the first new information in the past 25 years concerning the life of Dr. William Stewart Halsted. This paper reports on recently discovered personal correspondence of Dr. Halsted, beginning at age 66, to a young lady, Elizabeth Blanchard Randall, 40 years his junior. Dr. William Stewart Halsted is generally considered the most important and influential surgeon that this country has produced. During his Hopkins days in Baltimore (1886-1922) he was rather reclusive, and little is known of his personal life. He was married but had no children. Several biographies written by Halsted's contemporaries constitute the bulk of what is known about Halsted's personal life. All extant letters from Dr. Halsted to Miss Randall were reviewed. Archival materials were consulted to understand the context for this friendship. The correspondence between Halsted and Randall took place during a 3-year period, although their acquaintance was probably long-standing. The letters reveal Dr. Halsted and Miss Randall's great and warm affection for each other, despite their 40-year age difference. The letters have a playful nature absent in Halsted's other correspondence. This relationship has not been previously noted. Late in Halsted's life, he developed a warm and affectionate relationship with a young lady 40 years his junior, as revealed in Halsted's correspondence. Halsted's warm, personal, and playful letters are in stark contrast to his biographers' portrayals of him as a more serious and reclusive person.

  6. Readability of standard appointment letters.

    PubMed

    Bennett, Daniel M; Gilchrist, Anne

    2010-06-01

    Introduction and aims The first contact a clinical service has with a patient is often an appointment letter and thus it is important that this letter is written in a way which is accessible. One concern is to write in language which is easily able to be read by the majority of recipients. A simple initial way to assess this is by using measures of readability of text.Methods We applied measures to examine the readability of appointment and administrative letters sent to young people by clinicians in the Young People's Department at the Royal Cornhill Hospital in Aberdeen.Results Many letters were unlikely to be understood by our youngest patients. We revised the letters to meet an agreed standard of readability, and agreed their routine use within the team. All letters were significantly improved on standard measures of readability and were preferred by patients.Conclusions The methods used are feasible, easily available and may be helpful to clinicians working in other specialties to improve the level of readability of written communication. This will help patients and families in their first contact with any clinical service.

  7. Correspondence: Searching sequence space

    SciTech Connect

    Youvan, D.C.

    1995-08-01

    This correspondence debates the efficiency and application of genetic algorithms (GAs) to search protein sequence space. The important experimental point is that such sparse searches utilize physically realistic syntheses. In this regard, all GA-based technologies are very similar; they {open_quotes}learn{close_quotes} from their initial sparse search and then generate interesting new proteins within a few iterations. Which GA-based technology is best? That probably depends on the protein and the specific engineering goal. Given the fact that the field of combinatorial chemistry is still in its infancy, it is probably wise to consider all of the proven mutagenesis methods. 19 refs.

  8. Color associations for days and letters across different languages

    PubMed Central

    Rouw, Romke; Case, Laura; Gosavi, Radhika; Ramachandran, Vilayanur

    2014-01-01

    While colors are commonplace in everyday metaphors, relatively little is known about implicit color associations to linguistic or semantic concepts in a general population. In this study, we test color associations for ordered linguistic concepts (letters and days). The culture and language specificity of these effects was examined in a large group (457) of Dutch-speaking participants, 92 English-speaking participants, and 49 Hindi-speaking participants. Non-random distributions of color choices were revealed; consistencies were found across the three language groups in color preferences for both days and letters. Interestingly, while the Hindi-speaking participants were presented with letter stimuli matched on phonology, their pattern of letter-to-color preferences still showed similarities with Dutch- and English-speaking participants. Furthermore, we found that that the color preferences corresponded between participants indicating to have conscious color experiences with letters or days (putative synesthetes) and participants who do not (non-synesthetes). We also explored possible mechanisms underlying the color preferences. There were a few specific associations, including red for “A,” red for “Monday,” and white for “Sunday.” We also explored more general mechanisms, such as overall color preferences as shown by Simner et al. (2005). While certainly not all variation can be explained or predicted, the results show that regularities are present in color-to-letter or color-to-day preferences in both putative synesthetes and non-synesthetes across languages. Both letter-to-color and day-to-color preferences were influenced by multiple factors. The findings support a notion of abstract concepts (such as days and letters) that are not represented in isolation, but are connected to perceptual representational systems. Interestingly, at least some of these connections to color representations are shared across different language/cultural groups. PMID

  9. The Fragility of the Alphabetic Principle: Children's Knowledge of Letter Names Can Cause Them to Spell Syllabically Rather Than Alphabetically

    PubMed

    Treiman; Tincoff

    1997-03-01

    The present research was designed to investigate how children's early-acquired knowledge of letter names affects their spelling. Specifically, we asked whether kindergartners and first graders sometimes spell a sequence of phonemes such as /bi/ (the name of the letter b) or /zi/ (the name of the letter z) with the corresponding consonant letter rather than spelling the sequence alphabetically, with a consonant letter followed by a vowel letter. Children made a number of letter-name spelling errors, especially when the consonant and vowel formed a complete syllable. These results show that children's knowledge of letter names can cause them to deviate from the alphabetic principle-the principle that each phoneme should be represented with a single grapheme. The findings further suggest that syllables play a special role in early writing.

  10. Solutions of the Hodgkin-Huxley equations modified for potassium accumulation in a periaxonal space.

    PubMed

    Adelman, W J; Fitzhugh, R

    1975-04-01

    Hodgkin and Huxley equations were modified to include the properties of an external diffusion barrier separated from the axolemma by a thin periaxonal space in which potassium ions accumulate as a function of membrane activity. Further modifications in the equations took into account new values for gK and new functions for alphan, betan, alphah, and betah derived from voltage clamp experiments on Loligo pealei giant axons. Equations were solved on a PDP-11 computer using the Gear predictor-corrector numerical method. In comparison with the original Hodgkin and Huxley equations, the modified equations for membrane potentials gave: 1) more accurate representations of the falling and undershoot phases of the membrane action potential, 2) more accurate representation of thresholds and latencies, 3) increases in the periaxonal space potassium ion concentration, Ks, of about 1 mM/impulse, 4) proper predictions of the time course and magnitude of either undershoot decline or periaxonal potassium ion accumulation during trains of membrane action potentials elicited by repetitivie short duration stimuli, and5) a somewhat more accurate representation of adaptation (finite train and nonrepetitive responses) during long duration constant current stimulation.

  11. Soliton-like solutions to the generalized Burgers-Huxley equation with variable coefficients

    NASA Astrophysics Data System (ADS)

    Triki, Houria; Wazwaz, Abdul-Majid

    2013-12-01

    In this paper, we consider the generalized Burgers-Huxley equation with arbitrary power of nonlinearity and timedependent coefficients. We analyze the traveling wave problem and explicitly find new soliton-like solutions for this extended equation by using the ansatz of Zhao et al. [X. Zhao, D. Tang, L. Wang, Phys. Lett. A 346 (2005) 288-291]. We also employ the solitary wave ansatz method to derive the exact bright and dark soliton solutions for the considered evolution equation. The physical parameters in the soliton solutions are obtained as function of the time-dependent model coefficients. The conditions of existence of solitons are presented. As a result, rich exact travelling wave solutions, which contain new soliton-like solutions, bell-shaped solitons and kink-shaped solitons for the generalized Burgers-Huxley equation with time-dependent coefficients, are obtained. The methods employed here can also be used to solve a large class of nonlinear evolution equations with variable coefficients.

  12. "No Country for Old Men": Huxley's Brave New World and the Value of Old Age.

    PubMed

    Linett, Maren

    2017-08-17

    This article inserts Aldous Huxley's Brave New World (1932) into a bioethical conversation about the value of old age and old people. Exploring literary treatments of bioethical questions can supplement conversations within bioethics proper, helping to reveal our existing assumptions and clear the way for more considered views; indeed, as Peter Swirski has argued, literary texts can serve as thought experiments that illuminate the ramifications of philosophical ideas. This essay examines the novel's representation of a society without old people in conjunction with ideas about aging and life narratives put forward by philosophers and bioethicists such as Ezekiel Emanuel, Gilbert Meilaender, and Alasdair MacIntyre. While critics, and Huxley himself, view the Brave New World as dystopian primarily because of its depiction of a totalitarian society where art, truth, and meaning are sacrificed to pleasure and distraction and where the ruled are programmed not to question the values of their rulers, the novel also makes clear that the excision of old age has significant political, moral, and emotional costs.

  13. Embedded Picture Mnemonics to Learn Letters

    ERIC Educational Resources Information Center

    Shmidman, Adina; Ehri, Linnea

    2010-01-01

    Can embedded mnemonics ease the task of learning a foreign alphabet? English-speaking preschoolers (N = 36, M = 5;2 years) were taught 10 Hebrew letter-sound relations. Experimental letters were learned with mnemonics that embedded letter shapes in drawings of objects whose shapes resembled the letters and whose English names began with the…

  14. Letter Writing: A Tool for Counselor Educators

    ERIC Educational Resources Information Center

    Hoffman, Rachel M.

    2008-01-01

    Letter writing is an integral component of narrative therapy practice. In addition to the benefits of letter writing in counseling practice, letter writing may hold interesting possibilities for use in counselor education. This article provides a brief review of the benefits of letter writing in counseling practice and discusses the potential use…

  15. Precision of Position Signals for Letters

    PubMed Central

    Chung, Susana T.L.; Legge, Gordon E.

    2009-01-01

    Accurate reading of words and text relies on reliable identification of letters in left to right order. Previous studies have shown that people often make letter-reversal errors when identifying strings of letters away from fixation. These errors contribute to a decline in letter identification performance away from fixation. This study tests the hypothesis that these errors are due to decreased precision (increased position noise) in the coding of letter position in the periphery. To test our hypothesis, we measured observers' performance for identifying pairs of adjacent letters presented within 8 letter positions left and right of fixation. The task was to name the two letters of each pair, from left to right. Responses were scored in two ways for each letter position: (1) letters were identified correctly and in the correct position, and (2) letters were identified correctly but in the wrong position. The ratio of these two scores, when subtracted from 1, gives the empirical rate of mislocation errors. Our primary finding shows that the coding of letter position becomes increasingly imprecise with distance from fixation. A model in which the encoded position of each letter is independent and Gaussian distributed, and in which the spread of the distribution governs the precision of localizing the letter accounts for the empirical rate of mislocation errors. We also found that precision of letter position coding scales with letter size but the precision does not improve with the use of a pre-cue. PMID:19460396

  16. Essay: Physical Review Letters; Sam Goudsmit's Vision.

    PubMed

    Adair, Robert K

    2008-01-18

    Sam Goudsmit implemented his vision of converting the Letters section of Physical Review into a distinct journal fifty years ago. Physical Review Letters was designed to publish "only papers that really deserve rapid communication." The new journal became so successful with physicists throughout the world that Physical Review Letters now publishes 3500 Letters per year.

  17. 46 CFR 115.306 - Stability letter.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 4 2013-10-01 2013-10-01 false Stability letter. 115.306 Section 115.306 Shipping COAST... of Certificates, Permits, and Stability Letters § 115.306 Stability letter. When, in accordance with § 170.120 in subchapter S of this chapter, a vessel must be provided with a stability letter, the...

  18. 46 CFR 115.306 - Stability letter.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 4 2010-10-01 2010-10-01 false Stability letter. 115.306 Section 115.306 Shipping COAST... of Certificates, Permits, and Stability Letters § 115.306 Stability letter. When, in accordance with § 170.120 in subchapter S of this chapter, a vessel must be provided with a stability letter, the...

  19. 46 CFR 115.306 - Stability letter.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 4 2011-10-01 2011-10-01 false Stability letter. 115.306 Section 115.306 Shipping COAST... of Certificates, Permits, and Stability Letters § 115.306 Stability letter. When, in accordance with § 170.120 in subchapter S of this chapter, a vessel must be provided with a stability letter, the...

  20. 46 CFR 115.306 - Stability letter.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 4 2012-10-01 2012-10-01 false Stability letter. 115.306 Section 115.306 Shipping COAST... of Certificates, Permits, and Stability Letters § 115.306 Stability letter. When, in accordance with § 170.120 in subchapter S of this chapter, a vessel must be provided with a stability letter, the...

  1. 46 CFR 115.306 - Stability letter.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 4 2014-10-01 2014-10-01 false Stability letter. 115.306 Section 115.306 Shipping COAST... of Certificates, Permits, and Stability Letters § 115.306 Stability letter. When, in accordance with § 170.120 in subchapter S of this chapter, a vessel must be provided with a stability letter, the...

  2. Business Letter Writing: English, French, and Japanese.

    ERIC Educational Resources Information Center

    Jenkins, Susan; Hinds, John

    1987-01-01

    Examination of business letters in English, French, and Japanese, focusing on prescriptive accounts in the respective languages, found that, despite amazingly similar surface characteristics, American business letters were reader-oriented, French business letters were writer-oriented, and Japanese business letters were oriented to the space…

  3. A Common Left Occipito-Temporal Dysfunction in Developmental Dyslexia and Acquired Letter-By-Letter Reading?

    PubMed Central

    Richlan, Fabio; Sturm, Denise; Schurz, Matthias; Kronbichler, Martin; Ladurner, Gunther; Wimmer, Heinz

    2010-01-01

    Background We used fMRI to examine functional brain abnormalities of German-speaking dyslexics who suffer from slow effortful reading but not from a reading accuracy problem. Similar to acquired cases of letter-by-letter reading, the developmental cases exhibited an abnormal strong effect of length (i.e., number of letters) on response time for words and pseudowords. Results Corresponding to lesions of left occipito-temporal (OT) regions in acquired cases, we found a dysfunction of this region in our developmental cases who failed to exhibit responsiveness of left OT regions to the length of words and pseudowords. This abnormality in the left OT cortex was accompanied by absent responsiveness to increased sublexical reading demands in phonological inferior frontal gyrus (IFG) regions. Interestingly, there was no abnormality in the left superior temporal cortex which—corresponding to the onological deficit explanation—is considered to be the prime locus of the reading difficulties of developmental dyslexia cases. Conclusions The present functional imaging results suggest that developmental dyslexia similar to acquired letter-by-letter reading is due to a primary dysfunction of left OT regions. PMID:20711448

  4. The syllabic bridge: the first step in learning spelling-to-sound correspondences*.

    PubMed

    Doignon-Camus, Nadege; Zagar, Daniel

    2014-09-01

    It is widely agreed that learning to read starts with the establishment of letter-to-phoneme correspondences. However, it is also widely agreed that prereaders do not have access to phoneme units. Here we show that the building of associations between letters and syllables, which we call the 'syllabic bridge', might be a faster and more direct way of learning spelling-to-sound correspondences in French. After a few minutes of exposure, prereaders are able to learn the statistical properties of letter co-occurrences. Statistical learning is boosted by explicit instructions about the associations between letter clusters and syllables. Building the syllabic bridge from available phonological syllables and frequent letter clusters may therefore be the first step in learning to read.

  5. Effects of Letter-Identification Training on Letter Naming in Prereading Children

    ERIC Educational Resources Information Center

    Hayashi, Yusuke; Schmidt, Anna C.; Saunders, Kathryn J.

    2013-01-01

    Three prereading children who named 0 to 3 of 20 targeted letters were taught to select the 20 printed letters when they heard spoken letter names. For all participants, letter-identification training resulted in naming for the majority of letters.

  6. Language General and Specific Factors in Letter Acquisition: Considering Child and Letter Characteristics in Korean

    ERIC Educational Resources Information Center

    Kim, Young-Suk; Petscher, Yaacov

    2013-01-01

    In the present study we investigated the extent to which child level factors (i.e., phonological awareness) and letter level factors (i.e., letter name structures, letter frequency, visual similarity, and letter order) contributed to letter name and sound acquisition, using data from Korean-speaking children (N = 169) and cross-classified…

  7. Effects of Letter-Identification Training on Letter Naming in Prereading Children

    ERIC Educational Resources Information Center

    Hayashi, Yusuke; Schmidt, Anna C.; Saunders, Kathryn J.

    2013-01-01

    Three prereading children who named 0 to 3 of 20 targeted letters were taught to select the 20 printed letters when they heard spoken letter names. For all participants, letter-identification training resulted in naming for the majority of letters.

  8. Unconscious letter discrimination is enhanced by association with conscious color perception in visual form agnosia.

    PubMed

    Aglioti, S; Bricolo, E; Cantagallo, A; Berlucchi, G

    1999-12-02

    Adaptive behavior guided by unconscious visual cues occurs in patients with various kinds of brain damage as well as in normal observers, all of whom can process visual information of which they are fully unaware [1] [2] [3] [4] [5] [6] [7] [8]. Little is known on the possibility that unconscious vision is influenced by visual cues that have access to consciousness [9]. Here we report a 'blind' letter discrimination induced through a semantic interaction with conscious color processing in a patient who is agnosic for visual shapes, but has normal color vision and visual imagery. In seeing the initial letters of color names printed in different colors, it is normally easier to name the print color when it is congruent with the initial letter of the color name than when it is not [10]. The patient could discriminate the initial letters of the words 'red' and 'green' printed in the corresponding colors significantly above chance but without any conscious accompaniment, whereas he performed at chance with the reverse color-letter mapping as well as in standard tests of letter reading. We suggest that the consciously perceived colors activated a representation of the corresponding word names and their component letters, which in turn brought out a partially successful, unconscious processing of visual inputs corresponding to the activated letter representations.

  9. Letters from ainsworth: contesting the 'organization' of attachment.

    PubMed

    Landa, Sophie; Duschinsky, Robbie

    2013-05-01

    As Main (1999) noted in her obituary for Mary Ainsworth, 'she was interacting weekly by letter and manuscript with her mentor and friend, John Bowlby, and their academic correspondence formed an important part of her, and implicitly our, life.' These letters of Ainsworth to John Bowlby during the 1980s, available in the Wellcome Trust Library in London, contain valuable reflections on the work of her pupils to extend her system of classifying infant behaviour in the Strange Situation Procedure. Mary Main proposed a D classification and interpreted such behaviour as a breakdown in an ABC strategy caused by a conflict between a disposition to approach and flee from the caregiver. Patricia Crittenden extended the subtypes of A and C, using a developmental model of information processing, and observed that they could be used together in A/C combinations. These letters offer insight into Ainsworth's intellectual rationale for encouraging both Main and Crittenden in their conflicting endeavours.

  10. Differences between Good and Poor Child Writers on fMRI Contrasts for Writing Newly Taught and Highly Practiced Letter Forms

    ERIC Educational Resources Information Center

    Richards, Todd L.; Berninger, Virginia W.; Stock, Pat; Altemeier, Leah; Trivedi, Pamala; Maravilla, Kenneth R.

    2011-01-01

    During fMRI imaging, 12 good and 8 poor writers aged 11 wrote a newly taught pseudoletter and a highly practiced letter. Both letters were formed from the same components, but the pseudoletter had a novel configuration not corresponding to a written English letter form. On the first fMRI contrast between the newly taught pseudoletter and highly…

  11. Differences between Good and Poor Child Writers on fMRI Contrasts for Writing Newly Taught and Highly Practiced Letter Forms

    ERIC Educational Resources Information Center

    Richards, Todd L.; Berninger, Virginia W.; Stock, Pat; Altemeier, Leah; Trivedi, Pamala; Maravilla, Kenneth R.

    2011-01-01

    During fMRI imaging, 12 good and 8 poor writers aged 11 wrote a newly taught pseudoletter and a highly practiced letter. Both letters were formed from the same components, but the pseudoletter had a novel configuration not corresponding to a written English letter form. On the first fMRI contrast between the newly taught pseudoletter and highly…

  12. Bifurcation analysis of mode-locking structure in a Hodgkin-Huxley neuron under sinusoidal current

    NASA Astrophysics Data System (ADS)

    Lee, Sang-Gui; Kim, Seunghwan

    2006-04-01

    Nervous systems under periodic stimuli display rich dynamical states including mode-locking and chaotic responses, which have been a subject of intense studies in neurodynamics. The bifurcation structure of the Hodgkin-Huxley neuron under sinusoidal stimulus is studied in detail. The mechanisms of the firing onset and rich firing dynamics are studied with the help of the codimension-2 bifurcations, which play the role of the organizing center for myriads of saddle-node, period-doubling, and inverse-flip bifurcations forming the boundaries of the complex mode-locking structure. This study provides a useful insight into the organization of similar bifurcation structures in excitable systems such as neurons under periodic forcing.

  13. Enhancing the Hodgkin-Huxley Equations: Simulations Based on the First Publication in the Biophysical Journal.

    PubMed

    Moore, John W

    2015-10-06

    The experiments in the Cole and Moore article in the first issue of the Biophysical Journal provided the first independent experimental confirmation of the Hodgkin-Huxley (HH) equations. A log-log plot of the K current versus time showed that raising the HH variable n to the sixth power provided the best fit to the data. Subsequent simulations using n(6) and setting the resting potential at the in vivo value simplifies the HH equations by eliminating the leakage term. Our article also reported that the K current in response to a depolarizing step to ENa was delayed if the step was preceded by a hyperpolarization. While the interpretation of this phenomenon in the article was flawed, subsequent simulations show that the effect completely arises from the original HH equations.

  14. A novel approach to simulate Hodgkin-Huxley-like excitation with COMSOL Multiphysics.

    PubMed

    Martinek, Johannes; Stickler, Yvonne; Reichel, Martin; Mayr, Winfried; Rattay, Frank

    2008-08-01

    A proof of concept for the evaluation of external nerve and muscle fiber excitation with the finite element software COMSOL Multiphysics, formerly known as FEMLAB, is presented. This software allows the simultaneous solution of fiber excitation by 1D models of the Hodgkin-Huxley type which are embedded in a volume conductor where the electric field is mainly dominated by the electrode currents. This way the presented bidomain model includes the interaction between electrode currents and transmembrane currents during the excitation process. Especially for direct muscle fiber stimulation (cardiac muscle, denervated muscle) the effects from secondary currents from large populations of excited fibers seem to be significant. The method has many applications, for example, the relation between stimulus parameters and fiber recruitment can be analyzed.

  15. Mathematical description of a bursting pacemaker neuron by a modification of the Hodgkin-Huxley equations.

    PubMed Central

    Plant, R E; Kim, M

    1976-01-01

    Modifications based on experimental results reported in the literature are made to the Hodgkin-Huxley equations to describe the electrophysiological behavior of the Aplysia abdominal ganglion R15 cell. The system is then further modified to describe the effects with the application of the drug tetrodotoxin (TTX) to the cells' bathing medium. Methods of the qualitative theory of differential equations are used to determine the conditions necessary for such a system of equations to have an oscillatory solution. A model satisfying these conditions is shown to preduct many experimental observations of R15 cell behavior. Numerical solutions are obtained for differential equations satisfying the conditions of the model. These solutions are shown to have a form similar to that of the bursting which is characteristic of this cell, and to preduct many results of experiments conducted on this cell. The physiological implications of the model are discussed. Images FIGURE 6 PMID:1252578

  16. Strange nonchaotic oscillations in the quasiperiodically forced Hodgkin-Huxley neuron

    NASA Astrophysics Data System (ADS)

    Lim, Woochang; Kim, Sang-Yoon

    2009-07-01

    We numerically study dynamical behaviors of the quasiperiodically forced Hodgkin-Huxley neuron and compare the dynamical responses with those for the case of periodic stimulus. In the periodically forced case, a transition from a periodic to a chaotic oscillation was found to occur via period doublings in previous numerical and experimental works. We investigate the effect of the quasiperiodic forcing on this period-doubling route to chaotic oscillation. In contrast to the case of periodic forcing, a new type of strange nonchaotic (SN) oscillating states (that are geometrically strange but have no positive Lyapunov exponents) is found to exist between the regular and chaotic oscillating states as intermediate ones. Their strange fractal geometry leads to aperiodic 'complex' spikings. Various dynamical routes to SN oscillations are identified, as in the quasiperiodically forced logistic map. These SN spikings are expected to be observed in experiments of the quasiperiodically forced squid giant axon.

  17. The response of a classical Hodgkin–Huxley neuron to an inhibitory input pulse

    PubMed Central

    Krupa, Martin; Gielen, Stan

    2010-01-01

    A population of uncoupled neurons can often be brought close to synchrony by a single strong inhibitory input pulse affecting all neurons equally. This mechanism is thought to underlie some brain rhythms, in particular gamma frequency (30–80 Hz) oscillations in the hippocampus and neocortex. Here we show that synchronization by an inhibitory input pulse often fails for populations of classical Hodgkin–Huxley neurons. Our reasoning suggests that in general, synchronization by inhibitory input pulses can fail when the transition of the target neurons from rest to spiking involves a Hopf bifurcation, especially when inhibition is shunting, not hyperpolarizing. Surprisingly, synchronization is more likely to fail when the inhibitory pulse is stronger or longer-lasting. These findings have potential implications for the question which neurons participate in brain rhythms, in particular in gamma oscillations. PMID:20387110

  18. Effects of nanosecond pulsed electric fields on the activity of a Hodgkin and Huxley neuron model.

    PubMed

    Camera, F; Paffi, A; Merla, C; Denzi, A; Apollonio, F; Marracino, P; d'Inzeo, G; Liberti, M

    2012-01-01

    The cell membrane poration is one of the main assessed biological effects of nanosecond pulsed electric fields (nsPEF). This structural change of the cell membrane appears soon after the pulse delivery and lasts for a time period long enough to modify the electrical activity of excitable membranes in neurons. Inserting such a phenomenon in a Hodgkin and Huxley neuron model by means of an enhanced time varying conductance resulted in the temporary inhibition of the action potential generation. The inhibition time is a function of the level of poration, the pore resealing time and the background stimulation level of the neuron. Such results suggest that the neuronal activity may be efficiently modulated by the delivery of repeated pulses. This opens the way to the use of nsPEFs as a stimulation technique alternative to the conventional direct electric stimulation for medical applications such as chronic pain treatment.

  19. Noise-induced synchronization in a lattice Hodgkin-Huxley neural network

    NASA Astrophysics Data System (ADS)

    Pang, James Christopher S.; Monterola, Christopher P.; Bantang, Johnrob Y.

    2014-01-01

    We examine how the synchronization of the series of action potentials (APs) of realistic neurons interconnected in a lattice is influenced by variations of both the direction and magnitude of neuron-neuron connectivity in a noisy environment. We first demonstrate the existence of an optimal noise level that brings about the highest average number of APs per unit time, for a single Hodgkin-Huxley neuron. We then show that synchronization, as a collective response of interconnected neurons forming an N×N lattice, is optimal at different noise strengths σc=σc(p), depending on the degree of random-link malfunction parameterized by flipping direction probability p. Thus, even without the scale-free structure of neuronal networks, proper combinations of both randomness in reconnection (flipping) and noisy environment can be beneficial to the collective functioning of neurons.

  20. Effect of Random Link Malfunctions to Synchronization of Hodgkin-Huxley Neurons in a Lattice Network

    NASA Astrophysics Data System (ADS)

    Pang, James Christopher S.; Bantang, Johnrob Y.; Monterola, Christopher P.

    2012-04-01

    We study the synchronization of Hodgkin-Huxley (HH) neurons connected in a directed lattice network under the influence of varying coupling strength (g) and random link malfunctions in the form of probabilistic deletion (probability q) and link direction flipping (p). We quantify the extent of synchronization of the neurons in the network by averaging the fraction of firing neurons that produce action potentials (exceeding a threshold potential of Vth) across the entire observation time. By extensively scanning over the values of g, synchronization of this network type can be enhanced by increasing g until it reaches a threshold value wherein synchronization will deteriorate abruptly due to suppression of neural firings. We also extensively probe the interplay of p and q and show that there are certain combinations for which the synchronization will improve, defying negative notions of how we perceive random malfunctions.

  1. Autaptic activity-induced synchronization transitions in Newman-Watts network of Hodgkin-Huxley neurons.

    PubMed

    Wu, Yanan; Gong, Yubing; Wang, Qi

    2015-04-01

    In this paper, we numerically study the effect of autapse on the synchronization of Newman-Watts small-world Hodgkin-Huxley neuron network. It is found that the neurons exhibit synchronization transitions as autaptic self-feedback delay is varied, and the phenomenon becomes strongest when autaptic self-feedback strength is optimal. This phenomenon also changes with the change of coupling strength and network randomness and become strongest when they are optimal. There are similar synchronization transitions for electrical and chemical autapse, but the synchronization transitions for chemical autapse occur more frequently and are stronger than those for electrical synapse. The underlying mechanisms are briefly discussed in quality. These results show that autaptic activity plays a subtle role in the synchronization of the neuronal network. These findings may find potential implications of autapse for the information processing and transmission in neural systems.

  2. Enhancing the Hodgkin-Huxley Equations: Simulations Based on the First Publication in the Biophysical Journal

    PubMed Central

    Moore, John W.

    2015-01-01

    The experiments in the Cole and Moore article in the first issue of the Biophysical Journal provided the first independent experimental confirmation of the Hodgkin-Huxley (HH) equations. A log-log plot of the K current versus time showed that raising the HH variable n to the sixth power provided the best fit to the data. Subsequent simulations using n6 and setting the resting potential at the in vivo value simplifies the HH equations by eliminating the leakage term. Our article also reported that the K current in response to a depolarizing step to ENa was delayed if the step was preceded by a hyperpolarization. While the interpretation of this phenomenon in the article was flawed, subsequent simulations show that the effect completely arises from the original HH equations. PMID:26445431

  3. Control of bursting synchronization in networks of Hodgkin-Huxley-type neurons with chemical synapses

    NASA Astrophysics Data System (ADS)

    Batista, C. A. S.; Viana, R. L.; Ferrari, F. A. S.; Lopes, S. R.; Batista, A. M.; Coninck, J. C. P.

    2013-04-01

    Thermally sensitive neurons present bursting activity for certain temperature ranges, characterized by fast repetitive spiking of action potential followed by a short quiescent period. Synchronization of bursting activity is possible in networks of coupled neurons, and it is sometimes an undesirable feature. Control procedures can suppress totally or partially this collective behavior, with potential applications in deep-brain stimulation techniques. We investigate the control of bursting synchronization in small-world networks of Hodgkin-Huxley-type thermally sensitive neurons with chemical synapses through two different strategies. One is the application of an external time-periodic electrical signal and another consists of a time-delayed feedback signal. We consider the effectiveness of both strategies in terms of protocols of applications suitable to be applied by pacemakers.

  4. Autaptic activity-induced synchronization transitions in Newman-Watts network of Hodgkin-Huxley neurons

    NASA Astrophysics Data System (ADS)

    Wu, Yanan; Gong, Yubing; Wang, Qi

    2015-04-01

    In this paper, we numerically study the effect of autapse on the synchronization of Newman-Watts small-world Hodgkin-Huxley neuron network. It is found that the neurons exhibit synchronization transitions as autaptic self-feedback delay is varied, and the phenomenon becomes strongest when autaptic self-feedback strength is optimal. This phenomenon also changes with the change of coupling strength and network randomness and become strongest when they are optimal. There are similar synchronization transitions for electrical and chemical autapse, but the synchronization transitions for chemical autapse occur more frequently and are stronger than those for electrical synapse. The underlying mechanisms are briefly discussed in quality. These results show that autaptic activity plays a subtle role in the synchronization of the neuronal network. These findings may find potential implications of autapse for the information processing and transmission in neural systems.

  5. Dynamic range in small-world networks of Hodgkin-Huxley neurons with chemical synapses

    NASA Astrophysics Data System (ADS)

    Batista, C. A. S.; Viana, R. L.; Lopes, S. R.; Batista, A. M.

    2014-09-01

    According to Stevens' law the relationship between stimulus and response is a power-law within an interval called the dynamic range. The dynamic range of sensory organs is found to be larger than that of a single neuron, suggesting that the network structure plays a key role in the behavior of both the scaling exponent and the dynamic range of neuron assemblies. In order to verify computationally the relationships between stimulus and response for spiking neurons, we investigate small-world networks of neurons described by the Hodgkin-Huxley equations connected by chemical synapses. We found that the dynamic range increases with the network size, suggesting that the enhancement of the dynamic range observed in sensory organs, with respect to single neurons, is an emergent property of complex network dynamics.

  6. Dynamic Behavior of Artificial Hodgkin-Huxley Neuron Model Subject to Additive Noise.

    PubMed

    Kang, Qi; Huang, BingYao; Zhou, MengChu

    2016-09-01

    Motivated by neuroscience discoveries during the last few years, many studies consider pulse-coupled neural networks with spike-timing as an essential component in information processing by the brain. There also exists some technical challenges while simulating the networks of artificial spiking neurons. The existing studies use a Hodgkin-Huxley (H-H) model to describe spiking dynamics and neuro-computational properties of each neuron. But they fail to address the effect of specific non-Gaussian noise on an artificial H-H neuron system. This paper aims to analyze how an artificial H-H neuron responds to add different types of noise using an electrical current and subunit noise model. The spiking and bursting behavior of this neuron is also investigated through numerical simulations. In addition, through statistic analysis, the intensity of different kinds of noise distributions is discussed to obtain their relationship with the mean firing rate, interspike intervals, and stochastic resonance.

  7. Studies of phase return map and symbolic dynamics in a periodically driven Hodgkin—Huxley neuron

    NASA Astrophysics Data System (ADS)

    Ding, Jiong; Zhang, Hong; Tong, Qin-Ye; Chen, Zhuo

    2014-02-01

    How neuronal spike trains encode external information is a hot topic in neurodynamics studies. In this paper, we investigate the dynamical states of the Hodgkin—Huxley neuron under periodic forcing. Depending on the parameters of the stimulus, the neuron exhibits periodic, quasiperiodic and chaotic spike trains. In order to analyze these spike trains quantitatively, we use the phase return map to describe the dynamical behavior on a one-dimensional (1D) map. According to the monotonicity or discontinuous point of the 1D map, the spike trains are transformed into symbolic sequences by implementing a coarse-grained algorithm — symbolic dynamics. Based on the ordering rules of symbolic dynamics, the parameters of the external stimulus can be measured in high resolution with finite length symbolic sequences. A reasonable explanation for why the nervous system can discriminate or cognize the small change of the external signals in a short time is also presented.

  8. Langevin approach with rescaled noise for stochastic channel dynamics in Hodgkin-Huxley neurons

    NASA Astrophysics Data System (ADS)

    Huang, Yan-Dong; Xiang, Li; Shuai, Jian-Wei

    2015-12-01

    The Langevin approach has been applied to model the random open and closing dynamics of ion channels. It has long been known that the gate-based Langevin approach is not sufficiently accurate to reproduce the statistics of stochastic channel dynamics in Hodgkin-Huxley neurons. Here, we introduce a modified gate-based Langevin approach with rescaled noise strength to simulate stochastic channel dynamics. The rescaled independent gate and identical gate Langevin approaches improve the statistical results for the mean membrane voltage, inter-spike interval, and spike amplitude. Project supported by the National Natural Science Foundation for Distinguished Young Scholars of China (Grant No. 11125419), the National Natural Science Foundation of China (Grant No. 10925525), and the Funds for the Leading Talents of Fujian Province, China.

  9. Rhythmic Oscillations of Excitatory Bursting Hodkin-Huxley Neuronal Network with Synaptic Learning.

    PubMed

    Shi, Qi; Han, Fang; Wang, Zhijie; Li, Caiyun

    2016-01-01

    Rhythmic oscillations of neuronal network are actually kind of synchronous behaviors, which play an important role in neural systems. In this paper, the properties of excitement degree and oscillation frequency of excitatory bursting Hodkin-Huxley neuronal network which incorporates a synaptic learning rule are studied. The effects of coupling strength, synaptic learning rate, and other parameters of chemical synapses, such as synaptic delay and decay time constant, are explored, respectively. It is found that the increase of the coupling strength can weaken the extent of excitement, whereas increasing the synaptic learning rate makes the network more excited in a certain range; along with the increasing of the delay time and the decay time constant, the excitement degree increases at the beginning, then decreases, and keeps stable. It is also found that, along with the increase of the synaptic learning rate, the coupling strength, the delay time, and the decay time constant, the oscillation frequency of the network decreases monotonically.

  10. Emergent Central Pattern Generator Behavior in Gap-Junction-Coupled Hodgkin-Huxley Style Neuron Model

    PubMed Central

    Memelli, Heraldo; Solomon, Irene C.

    2012-01-01

    Most models of central pattern generators (CPGs) involve two distinct nuclei mutually inhibiting one another via synapses. Here, we present a single-nucleus model of biologically realistic Hodgkin-Huxley neurons with random gap junction coupling. Despite no explicit division of neurons into two groups, we observe a spontaneous division of neurons into two distinct firing groups. In addition, we also demonstrate this phenomenon in a simplified version of the model, highlighting the importance of afterhyperpolarization currents (IAHP) to CPGs utilizing gap junction coupling. The properties of these CPGs also appear sensitive to gap junction conductance, probability of gap junction coupling between cells, topology of gap junction coupling, and, to a lesser extent, input current into our simulated nucleus. PMID:23365558

  11. Emergent central pattern generator behavior in gap-junction-coupled Hodgkin-Huxley style neuron model.

    PubMed

    Horn, Kyle G; Memelli, Heraldo; Solomon, Irene C

    2012-01-01

    Most models of central pattern generators (CPGs) involve two distinct nuclei mutually inhibiting one another via synapses. Here, we present a single-nucleus model of biologically realistic Hodgkin-Huxley neurons with random gap junction coupling. Despite no explicit division of neurons into two groups, we observe a spontaneous division of neurons into two distinct firing groups. In addition, we also demonstrate this phenomenon in a simplified version of the model, highlighting the importance of afterhyperpolarization currents (I(AHP)) to CPGs utilizing gap junction coupling. The properties of these CPGs also appear sensitive to gap junction conductance, probability of gap junction coupling between cells, topology of gap junction coupling, and, to a lesser extent, input current into our simulated nucleus.

  12. Predicting the past: ancient eclipses and Airy, Newcomb, and Huxley on the authority of science.

    PubMed

    Stanley, Matthew

    2012-06-01

    Greek historical accounts of ancient eclipses were an important, if peculiar, focus of scientific attention in the nineteenth century. Victorian-era astronomers tried to correct the classical histories using scientific methods, then used those histories as data with which to calibrate their lunar theories, then rejected the histories as having any relevance at all. The specific dating of these eclipses--apparently a simple exercise in celestial mechanics--became bound up with tensions between scientific and humanistic approaches to the past as well as with wider social debates over the power and authority of science in general. The major figures discussed here, including G. B. Airy, Simon Newcomb, and T. H. Huxley, argued that the critical question was whether science could speak authoritatively about the past. To them, the ability of science to talk about the past indicated its power to talk about the future; it was also the fulcrum of fierce boundary disputes among science, history, and religion.

  13. Hodgkin-Huxley model based on ionic transport in axoplasmic fluid.

    PubMed

    Bhatia, Suman; Singh, Phool; Sharma, Prabha

    2017-01-01

    Hodgkin-Huxley model has been reframed to incorporate the physical parameters of fluid inside the axon. The reframed model comprises of set of partial differential equations containing the physical parameters: density, mass fraction of sodium, potassium and chlorine ions, longitudinal diffusivity of ions and rate of additions of ions along with the temperature. Obtained conduction velocity of 19.5m/sec at a temperature of 18.5 degree celcius and conduction velocity dependency on temperature within the range 5 to 25 degree celcius are two important results that strongly validate the proposed model. The behavior of all the physical parameters has been characterized with respect to the action potential. Action potential conduction velocity along with axoplasmic fluid viscosity has been characterized with respect to different temperatures. Longitudinal diffusivity of ions is also quantified.

  14. Hodgkin-Huxley type modelling and parameter estimation of GnRH neurons.

    PubMed

    Csercsik, Dávid; Farkas, Imre; Szederkényi, Gábor; Hrabovszky, Erik; Liposits, Zsolt; Hangos, Katalin M

    2010-06-01

    In this paper a simple one compartment Hodgkin-Huxley type electrophysiological model of GnRH neurons is presented, that is able to reasonably reproduce the most important qualitative features of the firing pattern, such as baseline potential, depolarization amplitudes, sub-baseline hyperpolarization phenomenon and average firing frequency in response to excitatory current. In addition, the same model provides an acceptable numerical fit of voltage clamp (VC) measurement results. The parameters of the model have been estimated using averaged VC traces, and characteristic values of measured current clamp traces originating from GnRH neurons in hypothalamic slices. The resulting parameter values show a good agreement with literature data in most of the cases. Applying parametric changes, which lead to the increase of baseline potential and enhance cell excitability, the model becomes capable of bursting. The effects of various parameters to burst length have been analyzed by simulation.

  15. The response of a classical Hodgkin-Huxley neuron to an inhibitory input pulse.

    PubMed

    Börgers, Christoph; Krupa, Martin; Gielen, Stan

    2010-06-01

    A population of uncoupled neurons can often be brought close to synchrony by a single strong inhibitory input pulse affecting all neurons equally. This mechanism is thought to underlie some brain rhythms, in particular gamma frequency (30-80 Hz) oscillations in the hippocampus and neocortex. Here we show that synchronization by an inhibitory input pulse often fails for populations of classical Hodgkin-Huxley neurons. Our reasoning suggests that in general, synchronization by inhibitory input pulses can fail when the transition of the target neurons from rest to spiking involves a Hopf bifurcation, especially when inhibition is shunting, not hyperpolarizing. Surprisingly, synchronization is more likely to fail when the inhibitory pulse is stronger or longer-lasting. These findings have potential implications for the question which neurons participate in brain rhythms, in particular in gamma oscillations.

  16. Control of bursting synchronization in networks of Hodgkin-Huxley-type neurons with chemical synapses.

    PubMed

    Batista, C A S; Viana, R L; Ferrari, F A S; Lopes, S R; Batista, A M; Coninck, J C P

    2013-04-01

    Thermally sensitive neurons present bursting activity for certain temperature ranges, characterized by fast repetitive spiking of action potential followed by a short quiescent period. Synchronization of bursting activity is possible in networks of coupled neurons, and it is sometimes an undesirable feature. Control procedures can suppress totally or partially this collective behavior, with potential applications in deep-brain stimulation techniques. We investigate the control of bursting synchronization in small-world networks of Hodgkin-Huxley-type thermally sensitive neurons with chemical synapses through two different strategies. One is the application of an external time-periodic electrical signal and another consists of a time-delayed feedback signal. We consider the effectiveness of both strategies in terms of protocols of applications suitable to be applied by pacemakers.

  17. High-order accurate difference schemes for the Hodgkin-Huxley equations

    NASA Astrophysics Data System (ADS)

    Amsallem, David; Nordström, Jan

    2013-11-01

    A novel approach for simulating potential propagation in neuronal branches with high accuracy is developed. The method relies on high-order accurate difference schemes using the Summation-By-Parts operators with weak boundary and interface conditions applied to the Hodgkin-Huxley equations. This work is the first demonstrating high accuracy for that equation. Several boundary conditions are considered including the non-standard one accounting for the soma presence, which is characterized by its own partial differential equation. Well-posedness for the continuous problem as well as stability of the discrete approximation is proved for all the boundary conditions. Gains in terms of CPU times are observed when high-order operators are used, demonstrating the advantage of the high-order schemes for simulating potential propagation in large neuronal trees.

  18. Noise-induced spatiotemporal patterns in Hodgkin-Huxley neuronal network.

    PubMed

    Wu, Ying; Li, Jiajia; Liu, Shaobao; Pang, Jiazhi; Du, Mengmeng; Lin, Pan

    2013-10-01

    The effect of noise on the pattern selection in a regular network of Hodgkin-Huxley neurons is investigated, and the transition of pattern in the network is measured from subexcitable to excitable media. Extensive numerical results confirm that kinds of travelling wave such as spiral wave, circle wave and target wave could be developed and kept alive in the subexcitable network due to the noise. In the case of excitable media under noise, the developed spiral wave and target wave could coexist and new target-like wave is induced near to the border of media. The averaged membrane potentials over all neurons in the network are calculated to detect the periodicity of the time series and the generated traveling wave. Furthermore, the firing probabilities of neurons in networks are also calculated to analyze the collective behavior of networks.

  19. Optimal stimulus current waveshape for a Hodgkin-Huxley model neuron.

    PubMed

    Tahayori, Bahman; Dokos, Socrates

    2012-01-01

    Traditionally, rectangular Lilly-type current pulses have been employed to electrically stimulate a neuron. In this paper, we utilize a least squares optimisation approach to assess the optimality of rectangular pulses in the context of electrical current stimulation. To this end, an appropriate cost function to minimise the total charge delivered to a neuron while keeping the waveshape sufficiently smooth, is developed and applied to a Hodgkin-Huxley ionic model of the neural action potential. Cubic spline parameters were utilized to find the optimal stimulation profile for a fixed peak current. Simulation results demonstrate that the optimal stimulation profile for a specified single neuron is a non-rectangular pulse whose shape depends upon the maximum allowable current as well as the stimulus duration.

  20. Optimal decoding and information transmission in Hodgkin-Huxley neurons under metabolic cost constraints.

    PubMed

    Kostal, Lubomir; Kobayashi, Ryota

    2015-10-01

    Information theory quantifies the ultimate limits on reliable information transfer by means of the channel capacity. However, the channel capacity is known to be an asymptotic quantity, assuming unlimited metabolic cost and computational power. We investigate a single-compartment Hodgkin-Huxley type neuronal model under the spike-rate coding scheme and address how the metabolic cost and the decoding complexity affects the optimal information transmission. We find that the sub-threshold stimulation regime, although attaining the smallest capacity, allows for the most efficient balance between the information transmission and the metabolic cost. Furthermore, we determine post-synaptic firing rate histograms that are optimal from the information-theoretic point of view, which enables the comparison of our results with experimental data. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

  1. Rhythmic Oscillations of Excitatory Bursting Hodkin-Huxley Neuronal Network with Synaptic Learning

    PubMed Central

    Shi, Qi; Han, Fang; Wang, Zhijie; Li, Caiyun

    2016-01-01

    Rhythmic oscillations of neuronal network are actually kind of synchronous behaviors, which play an important role in neural systems. In this paper, the properties of excitement degree and oscillation frequency of excitatory bursting Hodkin-Huxley neuronal network which incorporates a synaptic learning rule are studied. The effects of coupling strength, synaptic learning rate, and other parameters of chemical synapses, such as synaptic delay and decay time constant, are explored, respectively. It is found that the increase of the coupling strength can weaken the extent of excitement, whereas increasing the synaptic learning rate makes the network more excited in a certain range; along with the increasing of the delay time and the decay time constant, the excitement degree increases at the beginning, then decreases, and keeps stable. It is also found that, along with the increase of the synaptic learning rate, the coupling strength, the delay time, and the decay time constant, the oscillation frequency of the network decreases monotonically. PMID:27073393

  2. Homoclinic bifurcation in a Hodgkin-Huxley model of thermally sensitive neurons

    SciTech Connect

    Feudel, Ulrike; Neiman, Alexander; Pei, Xing; Wojtenek, Winfried; Braun, Hans; Huber, Martin; Moss, Frank

    2000-03-01

    We study global bifurcations of the chaotic attractor in a modified Hodgkin-Huxley model of thermally sensitive neurons. The control parameter for this model is the temperature. The chaotic behavior is realized over a wide range of temperatures and is visualized using interspike intervals. We observe an abrupt increase of the interspike intervals in a certain temperature region. We identify this as a homoclinic bifurcation of a saddle-focus fixed point which is embedded in the chaotic attractors. The transition is accompanied by intermittency, which obeys a universal scaling law for the average length of trajectory segments exhibiting only short interspike intervals with the distance from the onset of intermittency. We also present experimental results of interspike interval measurements taken from the crayfish caudal photoreceptor, which qualitatively demonstrate the same bifurcation structure. (c) 2000 American Institute of Physics.

  3. The Harvard Education Letter, 1998.

    ERIC Educational Resources Information Center

    Graves-Desai, Kelly, Ed.; Eaton, Susan, Ed.; Walser, Nancy, Ed.

    1998-01-01

    This document is comprised of volume 14 of the Harvard Education Letter, published bimonthly and addressing current issues in elementary and secondary education. Articles in the six issues of this volume include the following: (1) January-February--"Multi-Age Classrooms: An Age-Old Grouping Method Is Still Evolving" (Walser), "Teachers Wanted:…

  4. Resumes, Applications, and Cover Letters

    ERIC Educational Resources Information Center

    Crosby, Olivia

    2009-01-01

    Good resumes, applications, and cover letters broadcast one's abilities. They tell employers how one's qualifications match a job's responsibilities. If these critical preliminaries are constructed well, one has a better chance of landing interviews--and, eventually, a job. This article provides some guidelines for creating resumes and cover…

  5. Letter to a Young Writer.

    ERIC Educational Resources Information Center

    Hirsch, Edward

    2002-01-01

    Describes, in the form of a letter to a young writer, how the author celebrates the pendulous life of the poet: from arrogance to uncertainty, from misstep to breakthrough. Emphasizes the sustaining force of reading and the need to be initiated into one's own work by the work of others. (SG)

  6. "The Scarlet Letter". [Lesson Plan].

    ERIC Educational Resources Information Center

    Discovery Communications, Inc., Bethesda, MD.

    Based on Nathaniel Hawthorne's novel "The Scarlet Letter," this lesson plan presents activities designed to help students understand that the ending of a novel does not resolve all of the questions that may occur to readers; and that readers may imagine characters living out their lives beyond the ending the author gave to a novel. The main…

  7. The Harvard Education Letter, 1995.

    ERIC Educational Resources Information Center

    Miller, Edward, Ed.

    1995-01-01

    This document is comprised of volume 11 of the Harvard Education Letter, published bimonthly and addressing current issues in elementary and secondary education. Articles in the volume's six issues are: (1) January-February--"The Old Model of Staff Development Survives in a World Where Everything Else Has Changed" (Miller), "Giving Voice to Our…

  8. The Harvard Education Letter, 1997.

    ERIC Educational Resources Information Center

    Graves-Desai, Kelly, Ed.; Maloney, Karen, Ed.

    1997-01-01

    This document is comprised of volume 13 of the Harvard Education Letter, published bimonthly and addressing current issues in elementary and secondary education. Articles in the six issues of this volume include: (1) January-February --"Making Detracking Work" (Lynn and Wheelock), "Developing a Culture of High Expectations for…

  9. Curriculum Vitae and Related Letters.

    ERIC Educational Resources Information Center

    Peterson, Sharyl Bender

    This booklet, which was developed by a college career center, explains the purpose of and procedures for writing curriculum vitae (CV) and related letters. The following topics are covered: when a CV is appropriate, points to consider when writing a CV, items usually included, possible sections to include in a CV, and steps in writing cover…

  10. Resource Letter RC-1: Cosmology

    ERIC Educational Resources Information Center

    Ryan, Michael P., Jr.; Shepley, L. C.

    1976-01-01

    This is one of a series of resource letters on different topics intended to guide college physicists, astronomers, and other scientists to some of the literature and other teaching aids that may help improve course content in specified fields. (Author/CP)

  11. A Letter to Giuseppe Garibaldi.

    ERIC Educational Resources Information Center

    Gent, Kathryn

    1979-01-01

    Describes four suggested junior high or senior high school teaching activities to use in conjunction with a letter written to Giuseppe Garibaldi during the Civil War. Activities encourage skills such as information gathering, reading and oral skills, creative expression, and critical thinking. (CK)

  12. Letter to the next President

    ERIC Educational Resources Information Center

    Rotherham, Andrew J.; Mikuta, Julie; Freeland, Julia

    2008-01-01

    This article takes the form of a letter to the 44th president of the United States, urging the president to pursue an aggressive agenda to improve teacher quality. The authors assert that because teacher quality is the single most important factor shown to impact student outcomes, the next administration must dedicate resources to human capital…

  13. Letters from a Nightingale nurse.

    PubMed

    Denny, E

    1996-01-01

    Mary Cadbury was one of six daughters in a wealthy Birmingham family, all of whom took up professional or unpaid philanthropic work. In 1873 Mary began nurse training at the Nightingale School, St Thomas's Hospital, and regularly sent letters to family and friends, which provide a graphic account of the experience of a nurse in the latter half of the nineteenth century.

  14. Resource Letter N-1: Nanotechnology

    NASA Astrophysics Data System (ADS)

    Cela, Devin; Dresselhaus, Mildred; Helen Zeng, Tingying; Terrones, Mauricio; Souza Filho, Antonio G.; Ferreira, Odair P.

    2014-01-01

    This Resource Letter provides a guide to the literature on Nanotechnology. Journal articles, books, websites, and other documents are cited on the following topics: attributes of various types of nanomaterials, nanotechnology in the context of different academic fields, and the effects of nanotechnology on society.

  15. The Harvard Education Letter, 1996.

    ERIC Educational Resources Information Center

    Miller, Edward Ed.; Graves-Desai, Kelly, Ed.; Maloney, Karen, Ed.

    1996-01-01

    This document is comprised of volume 12 of the Harvard Education Letter, published bimonthly and addressing current issues in elementary-secondary education. Articles in this volume include the following: (1) January-February--"Early Reports From Kentucky on Cash Rewards for 'Successful' Schools Reveal Many Problems" (Miller), "New…

  16. Caring Letters Project: a military suicide-prevention pilot program.

    PubMed

    Luxton, David D; Kinn, Julie T; June, Jennifer D; Pierre, Laura W; Reger, Mark A; Gahm, Gregory A

    2012-01-01

    The Caring Letters Project (CLP) is a suicide prevention program that involves sending brief caring letters to discharged inpatients following psychiatric hospitalization. Several studies suggest that repeatedly sending caring messages may reduce suicides and suicide attempts in high-risk populations. The aims of this study were to (1) evaluate feasibility of use in the military setting, (2) explore trends toward reduction of psychiatric rehospitalizations, (3) assess preference for and test e-mail correspondence, and (4) identify best practices and gather data to inform a randomized controlled study. A total of 110 psychiatric inpatients at a military treatment facility consented, were interviewed, and then received personalized handwritten letters or e-mails at regular intervals following discharge. Data collected included demographics, clinical characteristics, preference for e-mail versus postal mail, rates of undeliverable and return correspondence, rehospitalizations, and adverse events requiring safety procedures. A total of 436 letters and e-mails have been sent to date. Most participants indicated preference for e-mail versus postal mail. Fifteen participants were readmitted for treatment compared to 20 patients in usual care. Twenty participants sent responses and all were positive statements about the program. There were no adverse events. This program is feasible for use at a military treatment facility. A randomized controlled trial is needed to determine whether the intervention can reduce suicide rates among military and veteran populations.

  17. Letter to Russia

    SciTech Connect

    Tobin, J G

    2012-03-15

    find it puzzling that the authors nonetheless claim in their conclusions that 'An evaluation of state occupations supports the proposal that the occupation of the 5f levels in bulk Pu must be near 5'. Apart from the aforementioned conceptual inconsistencies, there are a number of more technical aspects that are not discussed in sufficient detail. Among these are: (1) The authors use LDA to approximate the electron correlations. A lively debate takes place in the literature whether this approximation can adequately describe the electronic structure of Pu metal or not, yet the authors do not discuss the choice of the approximation at all, which they should, in my opinion. They should also specify if their solutions are spin polarized or whether they use spin-restricted LDA. (2) The quality of the employed basis set is not clear. Are the results converged with respect to the basis size? What is the estimated magnitude of the residual errors? (3) There are statements in the manuscript indicating that the cluster calculations depend somehow on the calculations of the diatomic molecule. Namely: 'Underpinning these calculations, there is a geometry optimization of diatomic molecules...' and 'Underlying the Pu cluster simulations is the calculation of the electronic structure of a Pu2 dimer with the bond length 3.28 {angstrom} corresponding to the inter-atomic distances in delta-Pu.' What does this underpinning/underlying mean in more technical terms? What role does the geometry optimization play when the cluster calculations seem to be performed at a fixed geometry corresponding to the delta-Pu? Lastly, the manuscript contains a lot of material that was previously (and often multiple times) published elsewhere, including the Physical Review journals. For instance, the experimental part of Fig. 2 was shown already in Refs. 26, 27 and 28 in essentially the same graphical form; the top part of Fig. 9 appeared in Refs. 19, 4 and in PRL 90, 196404 (2003). I think that reprinting

  18. Letters of Reprimand: The Important Questions.

    ERIC Educational Resources Information Center

    Zirkel, Perry A.; Gluckman, Ivan B.

    1986-01-01

    Outlines two legal cases involving letters of reprimand written by administrators and put in teachers' files. Shows how in these cases the letters did not constitute defamation or a violation of First or Fourteenth Amendment rights. (MD)

  19. Analysis of inverse stochastic resonance and the long-term firing of Hodgkin-Huxley neurons with Gaussian white noise

    NASA Astrophysics Data System (ADS)

    Tuckwell, Henry C.; Jost, Jürgen

    2012-11-01

    In order to explain the occurrence of a minimum in firing rate which occurs for certain mean input levels μ as noise level σ increases (inverse stochastic resonance, ISR) in Hodgkin-Huxley (HH) systems, we analyze the underlying transitions from a stable equilibrium point to limit cycle and vice-versa. For a value of μ at which ISR is pronounced, properties of the corresponding stable equilibrium point are found. A linearized approximation around this point has oscillatory solutions from whose maxima spikes tend to occur. A one dimensional diffusion is also constructed for small noise. Properties of the basin of attraction of the limit cycle (spike) are investigated heuristically. Long term trials of duration 500000 ms are carried out for values of σ from 0 to 2.0. The graph of mean spike count versus σ is divided into 4 regions R1,…,R4, where R3 contains the minimum associated with ISR. In R1 transitions to the basin of attraction of the rest point are not observed until a small critical value of σ=σ is reached, at the beginning of R2. The sudden decline in firing rate when σ is just greater than σ implies that there is only a small range of noise levels 0<σ<σ where repetitive spiking is safe from annihilation by noise. The firing rate remains small throughout R3. At a larger critical value σ=σ which signals the beginning of R4, the probability of transitions from the basin of attraction of the equilibrium point to that of the limit cycle apparently becomes greater than zero and the spike rate thereafter increases with increasing σ. The quantitative scheme underlying the ISR curve is outlined in terms of the properties of exit time random variables. In the final subsection, several statistical properties of the main random variables associated with long term spiking activity are given, including distributions of exit times from the two relevant basins of attraction and the interspike interval.

  20. Written Communications Simulation: Write Me a Letter.

    ERIC Educational Resources Information Center

    North Carolina State Dept. of Public Instruction, Raleigh. Div. of Vocational Education.

    This simulation is intended for use as a culminating activity after students have been exposed to personal and/or business letter writing, use of reference manuals, typing of letters, mailing procedures, typing of numbers, punctuation practice, and filing procedures. Stated objectives are to enable students to type a mailable letter; to inspect,…

  1. 48 CFR 316.603 - Letter contracts.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 48 Federal Acquisition Regulations System 4 2010-10-01 2010-10-01 false Letter contracts. 316.603 Section 316.603 Federal Acquisition Regulations System HEALTH AND HUMAN SERVICES CONTRACTING METHODS AND CONTRACT TYPES TYPES OF CONTRACTS Time-and-Materials, Labor-Hour, and Letter Contracts 316.603 Letter...

  2. Beyond Zebra: Preschoolers' Knowledge about Letters.

    ERIC Educational Resources Information Center

    Treiman, Rebecca; Richmond-Welty, E. Daylene; Tincoff, Ruth

    1997-01-01

    Argues that an important type of child knowledge about letters is knowledge of the phonological structure of the letters' names in English. Concludes that learning the alphabet forms the basis for generalizations about the structure of letter names. (22 references) (Author/CK)

  3. 48 CFR 3416.603 - Letter contracts.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 48 Federal Acquisition Regulations System 7 2013-10-01 2012-10-01 true Letter contracts. 3416.603... CONTRACTING METHODS AND CONTRACT TYPES TYPES OF CONTRACTS Time-and-Materials, Labor-Hour, and Letter Contracts 3416.603 Letter contracts. ...

  4. 48 CFR 3016.603 - Letter contracts.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 48 Federal Acquisition Regulations System 7 2013-10-01 2012-10-01 true Letter contracts. 3016.603... ACQUISITION REGULATION (HSAR) CONTRACT METHODS AND CONTRACT TYPES TYPES OF CONTRACTS Time-and-Materials, Labor-Hour, and Letter Contracts 3016.603 Letter contracts. ...

  5. 7 CFR 1773.33 - Management letter.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 7 Agriculture 12 2014-01-01 2013-01-01 true Management letter. 1773.33 Section 1773.33 Agriculture... (CONTINUED) POLICY ON AUDITS OF RUS BORROWERS RUS Reporting Requirements § 1773.33 Management letter. The CPA must prepare a management letter that includes, at a minimum, comments on: (a) Audit procedures....

  6. 7 CFR 1773.33 - Management letter.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 7 Agriculture 12 2013-01-01 2013-01-01 false Management letter. 1773.33 Section 1773.33... AGRICULTURE (CONTINUED) POLICY ON AUDITS OF RUS BORROWERS RUS Reporting Requirements § 1773.33 Management letter. The CPA must prepare a management letter that includes, at a minimum, comments on: (a)...

  7. 7 CFR 1773.33 - Management letter.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 7 Agriculture 12 2012-01-01 2012-01-01 false Management letter. 1773.33 Section 1773.33... AGRICULTURE (CONTINUED) POLICY ON AUDITS OF RUS BORROWERS RUS Reporting Requirements § 1773.33 Management letter. The CPA must prepare a management letter that includes, at a minimum, comments on: (a)...

  8. Beyond Zebra: Preschoolers' Knowledge about Letters.

    ERIC Educational Resources Information Center

    Treiman, Rebecca; Richmond-Welty, E. Daylene; Tincoff, Ruth

    1997-01-01

    Argues that an important type of child knowledge about letters is knowledge of the phonological structure of the letters' names in English. Concludes that learning the alphabet forms the basis for generalizations about the structure of letter names. (22 references) (Author/CK)

  9. 7 CFR 1773.33 - Management letter.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 7 Agriculture 12 2010-01-01 2010-01-01 false Management letter. 1773.33 Section 1773.33... AGRICULTURE (CONTINUED) POLICY ON AUDITS OF RUS BORROWERS RUS Reporting Requirements § 1773.33 Management letter. The CPA must prepare a management letter that includes, at a minimum, comments on: (a) Audit...

  10. Making Routine Letters Have Positive Effects.

    ERIC Educational Resources Information Center

    Walsh, S. M.

    While few business people dispute the importance of carefully crafting persuasive, demanding, conciliatory, and bad-news letters, the regular flow of routine communications receives very little meaningful consideration or scrutiny. These routine communications (letters, inquiries, requests, collection letters, complaints, confirmations,…

  11. Letter Recognition Difficulties: Their Real Nature.

    ERIC Educational Resources Information Center

    Cohn, Marvin

    This paper examines the letter recognition difficulties of 322 primary grade students with decoding problems. Each student was asked to name all of the lower case letters, which were presented in non-alphabetical order. Each response was accurately recorded to determine which letters were taken for others. All responses were then tallied, and an…

  12. Are Letter Detection and Proofreading Tasks Equivalent?

    ERIC Educational Resources Information Center

    Saint-Aubin, Jean; Losier, Marie-Claire; Roy, Macha; Lawrence, Mike

    2015-01-01

    When readers search for misspellings in a proofreading task or for a letter in a letter detection task, they are more likely to omit function words than content words. However, with misspelled words, previous findings for the letter detection task were mixed. In two experiments, the authors tested the functional equivalence of both tasks. Results…

  13. 19 CFR 354.7 - Charging letter.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 19 Customs Duties 3 2010-04-01 2010-04-01 false Charging letter. 354.7 Section 354.7 Customs... VIOLATION OF AN ANTIDUMPING OR COUNTERVAILING DUTY ADMINISTRATIVE PROTECTIVE ORDER § 354.7 Charging letter. (a) Contents of Letter. The Deputy Under Secretary will initiate proceedings by issuing a...

  14. 7 CFR 1773.33 - Management letter.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 7 Agriculture 12 2011-01-01 2011-01-01 false Management letter. 1773.33 Section 1773.33... AGRICULTURE (CONTINUED) POLICY ON AUDITS OF RUS BORROWERS RUS Reporting Requirements § 1773.33 Management letter. The CPA must prepare a management letter that includes, at a minimum, comments on: (a) Audit...

  15. Are Letter Detection and Proofreading Tasks Equivalent?

    ERIC Educational Resources Information Center

    Saint-Aubin, Jean; Losier, Marie-Claire; Roy, Macha; Lawrence, Mike

    2015-01-01

    When readers search for misspellings in a proofreading task or for a letter in a letter detection task, they are more likely to omit function words than content words. However, with misspelled words, previous findings for the letter detection task were mixed. In two experiments, the authors tested the functional equivalence of both tasks. Results…

  16. 46 CFR 176.306 - Stability letter.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 7 2010-10-01 2010-10-01 false Stability letter. 176.306 Section 176.306 Shipping COAST...) INSPECTION AND CERTIFICATION Posting of Certificates, Permits, and Stability Letters § 176.306 Stability letter. When, in accordance with § 178.210 of this chapter, a vessel must be provided with a stability...

  17. 46 CFR 176.306 - Stability letter.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 7 2011-10-01 2011-10-01 false Stability letter. 176.306 Section 176.306 Shipping COAST...) INSPECTION AND CERTIFICATION Posting of Certificates, Permits, and Stability Letters § 176.306 Stability letter. When, in accordance with § 178.210 of this chapter, a vessel must be provided with a stability...

  18. 46 CFR 176.306 - Stability letter.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 7 2012-10-01 2012-10-01 false Stability letter. 176.306 Section 176.306 Shipping COAST...) INSPECTION AND CERTIFICATION Posting of Certificates, Permits, and Stability Letters § 176.306 Stability letter. When, in accordance with § 178.210 of this chapter, a vessel must be provided with a stability...

  19. 46 CFR 176.306 - Stability letter.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 7 2013-10-01 2013-10-01 false Stability letter. 176.306 Section 176.306 Shipping COAST...) INSPECTION AND CERTIFICATION Posting of Certificates, Permits, and Stability Letters § 176.306 Stability letter. When, in accordance with § 178.210 of this chapter, a vessel must be provided with a stability...

  20. 46 CFR 176.306 - Stability letter.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 7 2014-10-01 2014-10-01 false Stability letter. 176.306 Section 176.306 Shipping COAST...) INSPECTION AND CERTIFICATION Posting of Certificates, Permits, and Stability Letters § 176.306 Stability letter. When, in accordance with § 178.210 of this chapter, a vessel must be provided with a stability...

  1. 7 CFR 3560.709 - Demand letter.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 7 Agriculture 15 2010-01-01 2010-01-01 false Demand letter. 3560.709 Section 3560.709 Agriculture... DIRECT MULTI-FAMILY HOUSING LOANS AND GRANTS Unauthorized Assistance § 3560.709 Demand letter. (a) If a... repayment schedule, the Agency will send the borrower a demand letter specifying: (1) The amount of...

  2. 31 CFR 29.511 - Demand letters.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 31 Money and Finance: Treasury 1 2010-07-01 2010-07-01 false Demand letters. 29.511 Section 29.511... Overpayments § 29.511 Demand letters. Except as provided in § 29.516(e), before starting collection action to recover an overpayment, the Benefits Administrator must send a demand letter that informs the debtor in...

  3. Letter Writing in the College Classroom.

    ERIC Educational Resources Information Center

    Fredericksen, Elaine

    2000-01-01

    Suggests that beginning writers can improve skills when they exchange letters with peers, teachers, and others. Offers a brief historical perspective on the use of letters as a pedagogical device. Outlines current applications of letter writing and exchanges in: English as a second language; technical and business writing; composition and…

  4. 24 CFR 200.1505 - Warning letter.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... URBAN DEVELOPMENT GENERAL INTRODUCTION TO FHA PROGRAMS Multifamily Accelerated Processing (MAP): MAP... letter, which specifies problems or violations identified by HUD, to a MAP lender. (b) Effect of warning letter. The warning letter: (1) Does not suspend a lender's MAP privileges; (2) May impose a higher level...

  5. 24 CFR 200.1505 - Warning letter.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... URBAN DEVELOPMENT GENERAL INTRODUCTION TO FHA PROGRAMS Multifamily Accelerated Processing (MAP): MAP... letter, which specifies problems or violations identified by HUD, to a MAP lender. (b) Effect of warning letter. The warning letter: (1) Does not suspend a lender's MAP privileges; (2) May impose a higher level...

  6. 24 CFR 200.1505 - Warning letter.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... URBAN DEVELOPMENT GENERAL INTRODUCTION TO FHA PROGRAMS Multifamily Accelerated Processing (MAP): MAP... letter, which specifies problems or violations identified by HUD, to a MAP lender. (b) Effect of warning letter. The warning letter: (1) Does not suspend a lender's MAP privileges; (2) May impose a higher level...

  7. 24 CFR 200.1505 - Warning letter.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... URBAN DEVELOPMENT GENERAL INTRODUCTION TO FHA PROGRAMS Multifamily Accelerated Processing (MAP): MAP... letter, which specifies problems or violations identified by HUD, to a MAP lender. (b) Effect of warning letter. The warning letter: (1) Does not suspend a lender's MAP privileges; (2) May impose a higher level...

  8. 24 CFR 200.1505 - Warning letter.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... URBAN DEVELOPMENT GENERAL INTRODUCTION TO FHA PROGRAMS Multifamily Accelerated Processing (MAP): MAP... letter, which specifies problems or violations identified by HUD, to a MAP lender. (b) Effect of warning letter. The warning letter: (1) Does not suspend a lender's MAP privileges; (2) May impose a higher level...

  9. Cover Letters Can Make All the Difference.

    ERIC Educational Resources Information Center

    Skoog, Gary L.

    1989-01-01

    Discusses importance of the cover letter that accompanies mailed resume to introduce job candidate and his/her background to potential employer. Presents some guidelines that career planning and placement personnel can use in explaining the whys and hows of cover letters to students. Four steps to a good cover letter are given and examples of…

  10. Letter names and phonological awareness help children to learn letter-sound relations.

    PubMed

    Cardoso-Martins, Cláudia; Mesquita, Tereza Cristina Lara; Ehri, Linnea

    2011-05-01

    Two experimental training studies with Portuguese-speaking preschoolers in Brazil were conducted to investigate whether children benefit from letter name knowledge and phonological awareness in learning letter-sound relations. In Experiment 1, two groups of children were compared. The experimental group was taught the names of letters whose sounds occur either at the beginning (e.g., the letter /be/) or in the middle (e.g., the letter /'eli/) of the letter name. The control group was taught the shapes of the letters but not their names. Then both groups were taught the sounds of the letters. Results showed an advantage for the experimental group, but only for beginning-sound letters. Experiment 2 investigated whether training in phonological awareness could boost the learning of letter sounds, particularly middle-sound letters. In addition to learning the names of beginning- and middle-sound letters, children in the experimental group were taught to categorize words according to rhyme and alliteration, whereas controls were taught to categorize the same words semantically. All children were then taught the sounds of the letters. Results showed that children who were given phonological awareness training found it easier to learn letter sounds than controls. This was true for both types of letters, but especially for middle-sound letters. Copyright © 2011. Published by Elsevier Inc.

  11. An Attempt to Simulate Letter-by-Letter Dyslexia in Normal Readers

    ERIC Educational Resources Information Center

    Fiset, Stephanie; Arguin, Martin; Fiset, Daniel

    2006-01-01

    We attempted to simulate the main features of letter-by-letter (LBL) dyslexia in normal readers through stimulus degradation (i.e. contrast reduction and removal of high spatial frequencies). The results showed the word length and the letter confusability effects characteristic of LBL dyslexia. However, the interaction of letter confusability and…

  12. An Attempt to Simulate Letter-by-Letter Dyslexia in Normal Readers

    ERIC Educational Resources Information Center

    Fiset, Stephanie; Arguin, Martin; Fiset, Daniel

    2006-01-01

    We attempted to simulate the main features of letter-by-letter (LBL) dyslexia in normal readers through stimulus degradation (i.e. contrast reduction and removal of high spatial frequencies). The results showed the word length and the letter confusability effects characteristic of LBL dyslexia. However, the interaction of letter confusability and…

  13. Learning Letter Names and Sounds: Effects of Instruction, Letter Type, and Phonological Processing Skill

    ERIC Educational Resources Information Center

    Piasta, Shayne B.; Wagner, Richard K.

    2010-01-01

    Preschool-age children (N = 58) were randomly assigned to receive instruction in letter names and sounds, letter sounds only, or numbers (control). Multilevel modeling was used to examine letter name and sound learning as a function of instructional condition and characteristics of both letters and children. Specifically, learning was examined in…

  14. What Do Letter Migration Errors Reveal About Letter Position Coding in Visual Word Recognition?

    ERIC Educational Resources Information Center

    Davis, Colin J.; Bowers, Jeffrey S.

    2004-01-01

    Dividing attention across multiple words occasionally results in misidentifications whereby letters apparently migrate between words. Previous studies have found that letter migrations preserve within-word letter position, which has been interpreted as support for position-specific letter coding. To investigate this issue, the authors used word…

  15. Learning Letter Names and Sounds: Effects of Instruction, Letter Type, and Phonological Processing Skill

    ERIC Educational Resources Information Center

    Piasta, Shayne B.; Wagner, Richard K.

    2010-01-01

    Preschool-age children (N = 58) were randomly assigned to receive instruction in letter names and sounds, letter sounds only, or numbers (control). Multilevel modeling was used to examine letter name and sound learning as a function of instructional condition and characteristics of both letters and children. Specifically, learning was examined in…

  16. The Lyttleton-Hoyle correspondence 1939-42

    NASA Astrophysics Data System (ADS)

    Mitton, S.

    2005-12-01

    Fred Hoyle started to collaborate with his older colleague Raymond Lyttleton in 1938. Hoyle's doctoral research had been in nuclear physics, and his supervisors were Rudolph Peierls and Paul Dirac. His first papers were in quantum electrodynamics. When Hoyle decided to change his research field to astronomy, Lyttleton acted as a mentor, and it was he who suggested that Hoyle should look at the physics of accretion. From late-1939, Lyttleton and Hoyle were both scientific civil servants drafted in for war work. They were in different establishments and could communicate only by the postal service. Some 70 letters from Lyttleton to Hoyle have survived, but we do not have any copies of Hoyle's correspondence. Many letters are undated, so it required detective work to assemble them in the correct sequence. The correspondence shows that Lyttleton played the senior role in determining what problems they should tackle, and in what order. Apart from the scientific content, these letters are remarkable for the sharp personal remarks Lyttleton makes of other colleagues, and particularly the Council of the Royal Astronomical Society. I make the suggestion that the poisonous and prolonged nature of the correspondence considerably influenced Hoyle's subsequent attitude to the establishment, to government-employed astronomers, and to the RAS. This was detrimental when Hoyle found, later in his career, that he would have to provide answers to these stakeholders. This research has been supported by St Edmund's College, Cambridge, UK.

  17. The standard Hodgkin-Huxley model and squid axons in reduced external Ca++ fail to accommodate to slowly rising currents.

    PubMed Central

    Jakobsson, E; Guttman, R

    1980-01-01

    Accommodation may be defined as an increase in the threshold of an excitable membrane when the membrane is subjected to a sustained subthreshold depolarizing stimulus. Some excitable membranes show accommodation in response to currents which rise linearly at a very slow rate. In this report we point out a theoretical and an experimental counterexample, i.e., a nerve model and an axon which do not accommodate. The nerve model is the standard Hodgkin-Huxley axon, which Hodgkin and Huxley expected not to be excited by a very slowly rising current. This expectation is often quoted as fact, in spite of contrary calculations which we confirm. We have found that squid axons in seawater with reduced divalent cation concentration also do not accommodate to slowly rising currents. Images FIGURE 2 PMID:7260290

  18. 50 years of JETP Letters

    NASA Astrophysics Data System (ADS)

    Pastukhov, V. P.

    2015-04-01

    This paper briefly traces the 50-year history of the journal Pis'ma v Zhurnal Eksperimental'noi i Teoreticheskoi Fiziki (JETP Letters), whose first issue was published on 1 April 1965. The journal is intended for a wide circle of physicists-readers as a fast publication channel for short communications on new results from research of the highest significance and highest priority in all areas of experimental and theoretical physics. Today, the journal celebrates numerous important contributions to the development of physics both in Russia and worldwide. Over a historically short period, JETP Letters developed into a highly authoritative and influential source for physicists engaged in a wide range of fields. Due to the wise and well-timed editorial policy, the journal continues to retain its leadership position, despite the difficulties the entire science periodical literature - and indeed the whole of science - is currently experiencing in Russia.

  19. Open letter to the Vatican.

    PubMed

    1999-01-01

    An open letter was published by Latin American and Caribbean women during the Special Session of the UN General Assembly on the International Conference on Population and Development. The letter generally focused on the Church¿s stand on women's reproductive rights. In particular, it questioned the Church on the following aspects of reproductive health, which include: 1) maternal death related to lack of access to reproductive health care; 2) Vatican representatives insisting that only parents can supervise their children education and health, which also lead to many cases of sexual abuse and incest; 3) women's sexual inequality and daily violence; 4) the Vatican delegation blocking the advances of contraception, sexual education, and HIV prevention; 5) problems of migrants and allocation of resources; and 6) the Church failing to recognize the capacity of young people to make decisions based on their own conscience.

  20. A Fragmentary Archive: Migratory Feelings in Early Anglo-Saxon Women's Letters.

    PubMed

    Watt, Diane

    2017-01-01

    The letters by Anglo-Saxon women in the Boniface correspondence are connected by cultural practices and emotions centered on the conversion mission that functioned to maintain connections between the Anglo-Saxon diaspora. A striking recurring focus of these letters is on loss and isolation, which connects them to the Old English elegies. Many of the letters describe the writers' traumatic experiences that result from the death or absence of kin. These are women who endured the trauma of being left behind when others migrated overseas or who, in traveling away from their homeland, found themselves isolated in an alien environment, displaced in time as well as space. This article offers an analysis of the letters, focusing on the queer temporalities they explore, the queer emotions they evoke, and the queer kinships that they forge. It argues that the women's letters represent fragments of an early queer archive of migratory feelings.

  1. William Stewart Halsted: Letters to a Young Female Admirer

    PubMed Central

    Cameron, John L.; Gordon, Toby A.; Kehoe, Marjorie Winslow; McCall, Nancy

    2001-01-01

    Objective To present the first new information in the past 25 years concerning the life of Dr. William Stewart Halsted. This paper reports on recently discovered personal correspondence of Dr. Halsted, beginning at age 66, to a young lady, Elizabeth Blanchard Randall, 40 years his junior. Summary Background Data Dr. William Stewart Halsted is generally considered the most important and influential surgeon that this country has produced. During his Hopkins days in Baltimore (1886–1922) he was rather reclusive, and little is known of his personal life. He was married but had no children. Several biographies written by Halsted’s contemporaries constitute the bulk of what is known about Halsted’s personal life. Methods All extant letters from Dr. Halsted to Miss Randall were reviewed. Archival materials were consulted to understand the context for this friendship. The correspondence between Halsted and Randall took place during a 3-year period, although their acquaintance was probably long-standing. Results The letters reveal Dr. Halsted and Miss Randall’s great and warm affection for each other, despite their 40-year age difference. The letters have a playful nature absent in Halsted’s other correspondence. This relationship has not been previously noted. Conclusions Late in Halsted’s life, he developed a warm and affectionate relationship with a young lady 40 years his junior, as revealed in Halsted’s correspondence. Halsted’s warm, personal, and playful letters are in stark contrast to his biographers’ portrayals of him as a more serious and reclusive person. PMID:11685036

  2. Letter Migration in Word Perception.

    DTIC Science & Technology

    1983-04-01

    reading . In P. A. Kolers, M. E. Wrol- stad, & H. Bouma (Eds.), Processing of visual language . New York: Plenum Press, 1979. Morton, J. Interaction of...THIS PAGE (When Daee Entered) PAGE READ INSTRUCTIONS REPORT DOCUMENTATION BEFORE COMPLETING FORM I. REPORT NUMBER 2. GOVT ACCESSION NO. 3...block number) Multiple Word Perception Human Performance Perceptual Illusions Word Perception 0 Letter Migration Reading 20. ABSTRACT (Continue on

  3. Spatio-temporal properties of letter crowding

    PubMed Central

    Chung, Susana T. L.

    2016-01-01

    Crowding between adjacent letters has been investigated primarily as a spatial effect. The purpose of this study was to investigate the spatio-temporal properties of letter crowding. Specifically, we examined the systematic changes in the degradation effects in letter identification performance when adjacent letters were presented with a temporal asynchrony, as a function of letter separation and between the fovea and the periphery. We measured proportion-correct performance for identifying the middle target letter in strings of three lowercase letters at the fovea and 10° in the inferior visual field, for a range of center-to-center letter separations and a range of stimulus onset asynchronies (SOA) between the target and flanking letters (positive SOAs: target preceded flankers). As expected, the accuracy for identifying the target letters reduces with decreases in letter separation. This crowding effect shows a strong dependency on SOAs, such that crowding is maximal between 0 and ∼100 ms (depending on conditions) and diminishes for larger SOAs (positive or negative). Maximal crowding does not require the target and flanking letters to physically coexist for the entire presentation duration. Most importantly, crowding can be minimized even for closely spaced letters if there is a large temporal asynchrony between the target and flankers. The reliance of letter identification performance on SOAs and how it changes with letter separations imply that the crowding effect can be traded between space and time. Our findings are consistent with the notion that crowding should be considered as a spatio-temporal, and not simply a spatial, effect. PMID:27088895

  4. Spatio-temporal properties of letter crowding.

    PubMed

    Chung, Susana T L

    2016-01-01

    Crowding between adjacent letters has been investigated primarily as a spatial effect. The purpose of this study was to investigate the spatio-temporal properties of letter crowding. Specifically, we examined the systematic changes in the degradation effects in letter identification performance when adjacent letters were presented with a temporal asynchrony, as a function of letter separation and between the fovea and the periphery. We measured proportion-correct performance for identifying the middle target letter in strings of three lowercase letters at the fovea and 10° in the inferior visual field, for a range of center-to-center letter separations and a range of stimulus onset asynchronies (SOA) between the target and flanking letters (positive SOAs: target preceded flankers). As expected, the accuracy for identifying the target letters reduces with decreases in letter separation. This crowding effect shows a strong dependency on SOAs, such that crowding is maximal between 0 and ∼100 ms (depending on conditions) and diminishes for larger SOAs (positive or negative). Maximal crowding does not require the target and flanking letters to physically coexist for the entire presentation duration. Most importantly, crowding can be minimized even for closely spaced letters if there is a large temporal asynchrony between the target and flankers. The reliance of letter identification performance on SOAs and how it changes with letter separations imply that the crowding effect can be traded between space and time. Our findings are consistent with the notion that crowding should be considered as a spatio-temporal, and not simply a spatial, effect.

  5. Similar Sound Separation and Cumulative Introduction in Learning Letter-Sound Correspondences

    ERIC Educational Resources Information Center

    Carnine, Douglas W.

    1976-01-01

    Since similarity inhibits learning, children will have greater difficulty learning responses that are more similar to each other; the instructional procedure of separating similar sounds was evaluated in two experiments. (DMT)

  6. Teaching Letter-Sound Correspondence to Students with Moderate Intellectual Disabilities

    ERIC Educational Resources Information Center

    Flores, Margaret M.; Shippen, Margaret E.; Alberto, Paul; Crowe, Lee

    2004-01-01

    This study examined the efficacy of systematic and explicit instruction in phonic decoding for 6 elementary students with moderate intellectual disabilities. A multiple probe across behaviors with embedded changing conditions design was employed in order to analyze the effect of Direct Instruction on teaching the following skills with regard to…

  7. Similar Sound Separation and Cumulative Introduction in Learning Letter-Sound Correspondences

    ERIC Educational Resources Information Center

    Carnine, Douglas W.

    1976-01-01

    Since similarity inhibits learning, children will have greater difficulty learning responses that are more similar to each other; the instructional procedure of separating similar sounds was evaluated in two experiments. (DMT)

  8. Teaching Letter-Sound Correspondence to Students with Moderate Intellectual Disabilities

    ERIC Educational Resources Information Center

    Flores, Margaret M.; Shippen, Margaret E.; Alberto, Paul; Crowe, Lee

    2004-01-01

    This study examined the efficacy of systematic and explicit instruction in phonic decoding for 6 elementary students with moderate intellectual disabilities. A multiple probe across behaviors with embedded changing conditions design was employed in order to analyze the effect of Direct Instruction on teaching the following skills with regard to…

  9. A Nerve Model of Greatly Increased Energy-Efficiency and Encoding Flexibility over the Hodgkin-Huxley Model

    PubMed Central

    Fohlmeister, Jurgen F.

    2009-01-01

    A mammalian “RGC model” (retinal ganglion cells) is distinguished from the Hodgkin-Huxley model by the virtual absence of K-current during, and the virtual absence of Na-current after, the regenerative (rising) phase of the action potential. Both Na- and K-currents remain negligible throughout the interspike interval, whose control is therefore relinquished to stimulus currents. These properties yield a highly flexible and energy-efficient nerve impulse encoder. For the Hodgkin-Huxley model, in contrast, only 15 % of the Na-ions enter the axon regeneratively during the action potential (squid giant axon); a wasteful 85 % enter during the falling phase. Further, early activation of K-current causes the Na- and K-currents of the action potential to dominate over stimulus currents in controlling the sub-threshold membrane potential (interspike interval). This property makes the Hodgkin-Huxley model an intractable high frequency oscillator, which cannot be converted to flexible impulse encoding. The temperature difference between the squid giant axon (6.3° C) and RGCs (37° C) is bridged by a Q10 analysis, which suggests that an additional molecular gating mechanism of high Q10 – which is not present in the squid – is active in RGCs. PMID:19596283

  10. A nerve model of greatly increased energy-efficiency and encoding flexibility over the Hodgkin-Huxley model.

    PubMed

    Fohlmeister, Jürgen F

    2009-11-03

    A mammalian "RGC model" (retinal ganglion cells) is distinguished from the Hodgkin-Huxley model by the virtual absence of K-current during, and the virtual absence of Na-current after, the regenerative (rising) phase of the action potential. Both Na- and K-currents remain negligible throughout the interspike interval, whose control is therefore relinquished to stimulus currents. These properties yield a highly flexible and energy-efficient nerve impulse encoder. For the Hodgkin-Huxley model, in contrast, only 15% of the Na-ions enter the axon regeneratively during the action potential (squid giant axon); a wasteful 85% enter during the falling phase. Further, early activation of K-current causes the Na- and K-currents of the action potential to dominate over stimulus currents in controlling the sub-threshold membrane potential (interspike interval). This property makes the Hodgkin-Huxley model an intractable high frequency oscillator, which cannot be converted to flexible impulse encoding. The temperature difference between the squid giant axon (6.3 degrees C) and RGCs (37 degrees C) is bridged by a Q10 analysis, which suggests that an additional molecular gating mechanism of high Q10 - which is not present in the squid - is active in RGCs.

  11. Updated Principle of Corresponding States

    ERIC Educational Resources Information Center

    Ben-Amotz, Dor; Gift, Alan D.; Levine, R. D.

    2004-01-01

    The rule of corresponding states, which shows the connection between the thermodynamic properties of various liquids is re-examined. The overall likeness is observed by using an updated scaling technique of Lennard-Jones corresponding states (LJ-CS).

  12. Letter Knowledge in Parent–Child Conversations

    PubMed Central

    Robins, Sarah; Treiman, Rebecca; Rosales, Nicole

    2014-01-01

    Learning about letters is an important component of emergent literacy. We explored the possibility that parent speech provides information about letters, and also that children’s speech reflects their own letter knowledge. By studying conversations transcribed in CHILDES (MacWhinney, 2000) between parents and children aged one to five, we found that alphabetic order influenced use of individual letters and letter sequences. The frequency of letters in children’s books influenced parent utterances throughout the age range studied, but children’s utterances only after age two. Conversations emphasized some literacy-relevant features of letters, such as their shapes and association with words, but not letters’ sounds. Describing these patterns and how they change over the preschool years offers important insight into the home literacy environment. PMID:25598577

  13. Writing More Informative Letters of Reference

    PubMed Central

    Wright, Scott M; Ziegelstein, Roy C

    2004-01-01

    Writing a meaningful and valuable letter of reference is not an easy task. Several factors influence the quality of any letter of reference. First, the accuracy and reliability of the writer's impressions and judgment depend on how well he knows the individual being described. Second, the writer's frame of reference, which is determined by the number of persons at the same level that he has worked with, will impact the context and significance of his beliefs and estimations. Third, the letter-writing skills of the person composing the letter will naturally affect the letter. To support the other components of a candidate's application, a letter of reference should provide specific examples of how an individual's behavior or attitude compares to a reference group and should assess “intangibles” that are hard to glean from a curriculum vitae or from test scores. This report offers suggestions that should help physicians write more informative letters of reference. PMID:15109330

  14. Letters

    NASA Astrophysics Data System (ADS)

    1999-04-01

    Winter's Entertainment by Terry L. Helser Ammonia-Air Mixtures Can Be Explosive by David Tudela Re: article by S. Toby The author replies Teaching Statistical Methods by Ken Muranaka Re: article by K. Thomasson, S. Lofthus-Merschman, M. Humbert, and N. Kulevsky The author K. A. Thomasson replies Properties of Zeolite A Obtained from Powdered Laundry Detergent by Pamela J. Davis, Herman van Bekkum, and Eric N. Coker Re: article by D. A. Lindquist and A. L. Smoot The author D. A. Lindquist replies Photon-Initiated Hydrogen-Chlorine Reaction by Richard W. Schwenz and Lynn Geiger Re: article by L. M. Egolf and J. T. Keiser (J. Chem. Educ. 1993, 70, A208) Precision and Accuracy in Measurements by Volker B. E. Thomsen Re: article by R. Treptow The author replies

  15. Letters

    NASA Astrophysics Data System (ADS)

    1999-12-01

    Levels of Description in Chemistry by P. G. Nelson Re: articles by W. B. Jensen in June, July, and August of 1998. The author replies Inexpensive Variable Path-Length Cells for Discovery-Based Investigation of the Beer-Lambert Law by Jonathan Mitschele Re: article by S. A. Stewart and A. J. Sommer CD Spectroscope by Lanny Whitten Re: Classroom Activity (CD Light: An Introduction to Spectroscopy) Correction The Literature Cited section was unfortunately omitted from the October 1999 NSF Highlights column, "Organic Chemistry Course Development in a Forensic Science Program: Use of FT-NMR" by Ronald Callahan, Lawrence Kobilinsky and Robert Rothchild (J. Chem. Educ. 1999, 76, 1332-1333). The references are provided in the PDF version.

  16. Letters

    NASA Astrophysics Data System (ADS)

    2000-02-01

    Inflection at the Triple Point by R. Thomas Myers Author's reply: Stephen J. Hawkes Correction Figure 1 of the article Using Overhead Projector to Simulate X-ray Diffraction Experiments by Veljko Dragojlovic (J. Chem. Educ. 1999, 76, 1240-1241) had the images for the red filter and the blue filter reversed. The correctly labeled images are shown below. These images are shown in color in the JCE Online PDF version of this article. Figure 2. Diffraction patterns obtained with (a) red filter, (b) blue filter, and (c) without a filter.

  17. Letters

    NASA Astrophysics Data System (ADS)

    1999-01-01

    A Coordination Geometry Table by Francisco J. Arnáiz Re: article by D. Venkataraman, Y. Du, S. R. Wilson, K. A. Hirsch, P. Zhang, and J. S. Moore The authors reply Cut-Out Molecular Models by A. L. Silva, C. Fernandes, O. Wasterlain, S. Costa, and A. M. Mendes Re: article by R. J. Kashmar Kinetics Lesson for College Deans by Fred Hadley

  18. Letters

    NASA Astrophysics Data System (ADS)

    1999-11-01

    Survey of Binary Azeotropes by Paul C. Yates Re: article by R. J. Glinski, C. W. Smith, and J. B. Cooke Cheating Probabilities? Probably Not by David J. Miller Re: a criticism by C. Jonah and a note by G. T. Rizzuto and F. Walters trans-Cyclohexane-1,2-diamine by Richard S. Treptow Re: article by P. J. Walsh, D. K. Smith, and C. Castello Micropreparation of [RuH2PPh3)4] by Francisco J. Arnáiz Re: article by D. E. Linn, Jr. The author replies D. E. Linn's response follows

  19. Letters

    NASA Astrophysics Data System (ADS)

    1998-12-01

    Beer's Law: The Real Hazards by S. R. Logan Re: article by M. A. Muyskens and E. T. Sevy The author replies Photodimerization of Maleic Anhydride by Zhijun Zhang Re: article by D. Todd and M. Pickering (J. Chem. Educ. 1988, 65, 1100) Qual from a Different Viewpoint by Francisco J. Arnáiz Re: article by M. Laing (J. Chem. Educ. 1993, 70, 666)

  20. Letters

    NASA Astrophysics Data System (ADS)

    1999-10-01

    Copper Content in Synthetic Copper Carbonate: A Statistical Comparison of Experimental and Expected Results by H. Gamsjäger and W. Preis Re: article by D. Sheeran The author replies The Amateur Mineral Chemist by Dana Martin Morong More on Double Replacement by George B. Kauffman Re: article by R. B. Martin

  1. FROM THE HISTORY OF PHYSICS: Correspondence between G A Gamow and P L Kapitza

    NASA Astrophysics Data System (ADS)

    Frenkel', Viktor Ya

    1994-08-01

    The letters exchanged between Peter Kapitza and George Gamow are published here for the first time. The correspondence throws light on the active support accorded by Kapitza to his Russian colleagues and on his work as the coeditor of a prestigious series of physics monographs published by Clarendon Press, Oxford. Gamow comes over in his letters, relating to one of the most interesting periods of his creative activity (1929 - 1934), in full blaze of his personality.

  2. ["Professor is well". The correspondence between Max Schur and Marie Bonaparte].

    PubMed

    Stouten, Hanna

    2012-01-01

    The correspondence between Freud's doctor and his "Princess" spans the period 1929-1962, and comprises over 90 letters, mostly concerned with Freud's health but also touching upon Schur's permanent dilemma--to emigrate or to stay with Freud--and upon the dire situation of his family and friends on behalf of whom he appeals to Marie for help. After Freud's death the letters change in focus.

  3. Teaching letter sounds to kindergarten English language learners using incremental rehearsal.

    PubMed

    Peterson, Meredith; Brandes, Dana; Kunkel, Amy; Wilson, Jennifer; Rahn, Naomi L; Egan, Andrea; McComas, Jennifer

    2014-02-01

    Proficiency in letter-sound correspondence is important for decoding connected text. This study examined the effects of an evidence-based intervention, incremental rehearsal (IR), on the letter-sound expression of three kindergarten English language learners (ELLs) performing below the district benchmark for letter-sound fluency. Participants were native speakers of Hmong, Spanish, and Polish. A multiple-baseline design across sets of unknown letter sounds was used to evaluate the effects of IR on letter-sound expression. Visual analysis of the data showed an increase in level and trend when IR was introduced in each phase. Percentage of all non-overlapping data (PAND) ranged from 95% to 100%. All participants exceeded expected growth and reached the spring district benchmark for letter-sound fluency. Results suggest that IR is a promising intervention for increasing letter-sound expression for ELLs who evidence delays in acquiring letter sounds. Copyright © 2013 Society for the Study of School Psychology. Published by Elsevier Ltd. All rights reserved.

  4. Functional communication within a perceptual network processing letters and pseudoletters.

    PubMed

    Herdman, Anthony T

    2011-10-01

    Many studies have identified regions within human ventral visual stream to be important for object identification and categorization; however, knowledge of how perceptual information is communicated within the visual network is still limited. Current theories posit that if a high correspondence between incoming sensory information and internal representations exists, then the object is rapidly identified, and if there is not, then the object requires extra detailed processing. Event-related responses from the present magnetoencephalography study showed two main effects. The N1m peak latencies were approximately 15 milliseconds earlier to familiar letters than to unfamiliar pseudoletters, and the N2m was more negative to pseudoletters than to letters. Event-related beamforming analyses identified these effects to be within bilateral visual cortices with a right lateralization for the N2m effect. Furthermore, functional connectivity analyses revealed that gamma-band (50-80 Hz) oscillatory phase synchronizations among occipital regions were greater to letters than to pseudoletters (around 85 milliseconds). However, during a later time interval between 245 and 375 milliseconds, pseudoletters elicited greater gamma-band phase synchronizations among a more distributed occipital network than did letters. These findings indicate that familiar object processing begins by at least 85 milliseconds, which could represent an initial match to an internal template. In addition, unfamiliar object processing persisted longer than that for familiar objects, which could reflect greater attention to inexperienced objects to determine their identity and/or to consolidate a new template to aid in future identification.

  5. Synesthesia for manual alphabet letters and numeral signs in second-language users of signed languages.

    PubMed

    Atkinson, Joanna; Lyons, Tanya; Eagleman, David; Woll, Bencie; Ward, Jamie

    2016-08-01

    Many synesthetes experience colors when viewing letters or digits. We document, for the first time, an analogous phenomenon among users of signed languages who showed color synesthesia for fingerspelled letters and signed numerals. Four synesthetes experienced colors when they viewed manual letters and numerals (in two cases, colors were subjectively projected on to the hands). There was a correspondence between the colors experienced for written graphemes and their manual counterparts, suggesting that the development of these two types of synesthesia is interdependent despite the fact that these systems are superficially distinct and rely on different perceptual recognition mechanisms in the brain.

  6. The letter: private text or public place? The Mattioli-Gesner controversy about the aconitum primum.

    PubMed

    Delisle, Candice

    2004-01-01

    From 1555 to 1565, Pietro Andrea Mattioli and Conrad Gesner were locked in controversy over the veracity of Mattioli's picture of aconitum primum. This dispute led to numerous vehement publications and to intensive exchanges of letters, not only between the protagonists but also within their own and sometimes inter-connected networks of correspondence. This dispute illustrates how 16th-century scholars played upon the ambiguous place of these letters between private and public space to deal with controversy in the Republic of Letters.

  7. Teacher candidates' mastery of phoneme-grapheme correspondence: massed versus distributed practice in teacher education.

    PubMed

    Sayeski, Kristin L; Earle, Gentry A; Eslinger, R Paige; Whitenton, Jessy N

    2017-04-01

    Matching phonemes (speech sounds) to graphemes (letters and letter combinations) is an important aspect of decoding (translating print to speech) and encoding (translating speech to print). Yet, many teacher candidates do not receive explicit training in phoneme-grapheme correspondence. Difficulty with accurate phoneme production and/or lack of understanding of sound-symbol correspondence can make it challenging for teachers to (a) identify student errors on common assessments and (b) serve as a model for students when teaching beginning reading or providing remedial reading instruction. For students with dyslexia, lack of teacher proficiency in this area is particularly problematic. This study examined differences between two learning conditions (massed and distributed practice) on teacher candidates' development of phoneme-grapheme correspondence knowledge and skills. An experimental, pretest-posttest-delayed test design was employed with teacher candidates (n = 52) to compare a massed practice condition (one, 60-min session) to a distributed practice condition (four, 15-min sessions distributed over 4 weeks) for learning phonemes associated with letters and letter combinations. Participants in the distributed practice condition significantly outperformed participants in the massed practice condition on their ability to correctly produce phonemes associated with different letters and letter combinations. Implications for teacher preparation are discussed.

  8. Chimera states in a Hodgkin-Huxley model of thermally sensitive neurons.

    PubMed

    Glaze, Tera A; Lewis, Scott; Bahar, Sonya

    2016-08-01

    Chimera states occur when identically coupled groups of nonlinear oscillators exhibit radically different dynamics, with one group exhibiting synchronized oscillations and the other desynchronized behavior. This dynamical phenomenon has recently been studied in computational models and demonstrated experimentally in mechanical, optical, and chemical systems. The theoretical basis of these states is currently under active investigation. Chimera behavior is of particular relevance in the context of neural synchronization, given the phenomenon of unihemispheric sleep and the recent observation of asymmetric sleep in human patients with sleep apnea. The similarity of neural chimera states to neural "bump" states, which have been suggested as a model for working memory and visual orientation tuning in the cortex, adds to their interest as objects of study. Chimera states have been demonstrated in the FitzHugh-Nagumo model of excitable cells and in the Hindmarsh-Rose neural model. Here, we demonstrate chimera states and chimera-like behaviors in a Hodgkin-Huxley-type model of thermally sensitive neurons both in a system with Abrams-Strogatz (mean field) coupling and in a system with Kuramoto (distance-dependent) coupling. We map the regions of parameter space for which chimera behavior occurs in each of the two coupling schemes.

  9. Pseudo-Lyapunov exponents and predictability of Hodgkin-Huxley neuronal network dynamics.

    PubMed

    Sun, Yi; Zhou, Douglas; Rangan, Aaditya V; Cai, David

    2010-04-01

    We present a numerical analysis of the dynamics of all-to-all coupled Hodgkin-Huxley (HH) neuronal networks with Poisson spike inputs. It is important to point out that, since the dynamical vector of the system contains discontinuous variables, we propose a so-called pseudo-Lyapunov exponent adapted from the classical definition using only continuous dynamical variables, and apply it in our numerical investigation. The numerical results of the largest Lyapunov exponent using this new definition are consistent with the dynamical regimes of the network. Three typical dynamical regimes-asynchronous, chaotic and synchronous, are found as the synaptic coupling strength increases from weak to strong. We use the pseudo-Lyapunov exponent and the power spectrum analysis of voltage traces to characterize the types of the network behavior. In the nonchaotic (asynchronous or synchronous) dynamical regimes, i.e., the weak or strong coupling limits, the pseudo-Lyapunov exponent is negative and there is a good numerical convergence of the solution in the trajectory-wise sense by using our numerical methods. Consequently, in these regimes the evolution of neuronal networks is reliable. For the chaotic dynamical regime with an intermediate strong coupling, the pseudo-Lyapunov exponent is positive, and there is no numerical convergence of the solution and only statistical quantifications of the numerical results are reliable. Finally, we present numerical evidence that the value of pseudo-Lyapunov exponent coincides with that of the standard Lyapunov exponent for systems we have been able to examine.

  10. Global Bifurcation Structure and Parameter Dependence of the Hodgkin-Huxley Equations

    NASA Astrophysics Data System (ADS)

    Pan, Zhenxing; Doi, Shinji

    The Hodgkin-Huxley (HH) equations of a squid giant axon are the most important mathematical model in electrophysiology and biology, and are also important in the development of various biologically inspired intelligent devices such as artificial neuron device and neural networks. The HH equations, however, include various constants or parameters whose values were determined based on physiological experiments, and thus the values possess inherent ambiguities. Also, the ‘constants’ are not really constant but change temporally. Thus, in this paper, we study the effects of the change of the constants or parameters on the dynamics of the HH equations and consider the parameter dependence and sensitivity of the equations; we study the bifurcation structure of the HH equations by changing their various parameters. In particular, we take the voltage-dependency of the dynamics of so-called gating variables as typical bifurcation parameters and show that the HH dynamics is very sensitive to the steady-state functions but not sensitive to the time ‘constants’ of gating variables.

  11. Giant squid-hidden canard: the 3D geometry of the Hodgkin-Huxley model.

    PubMed

    Rubin, Jonathan; Wechselberger, Martin

    2007-07-01

    This work is motivated by the observation of remarkably slow firing in the uncoupled Hodgkin-Huxley model, depending on parameters tau( h ), tau( n ) that scale the rates of change of the gating variables. After reducing the model to an appropriate nondimensionalized form featuring one fast and two slow variables, we use geometric singular perturbation theory to analyze the model's dynamics under systematic variation of the parameters tau( h ), tau( n ), and applied current I. As expected, we find that for fixed (tau( h ), tau( n )), the model undergoes a transition from excitable, with a stable resting equilibrium state, to oscillatory, featuring classical relaxation oscillations, as I increases. Interestingly, mixed-mode oscillations (MMO's), featuring slow action potential generation, arise for an intermediate range of I values, if tau( h ) or tau( n ) is sufficiently large. Our analysis explains in detail the geometric mechanisms underlying these results, which depend crucially on the presence of two slow variables, and allows for the quantitative estimation of transitional parameter values, in the singular limit. In particular, we show that the subthreshold oscillations in the observed MMO patterns arise through a generalized canard phenomenon. Finally, we discuss the relation of results obtained in the singular limit to the behavior observed away from, but near, this limit.

  12. Neural Energy Supply-Consumption Properties Based on Hodgkin-Huxley Model.

    PubMed

    Wang, Yihong; Wang, Rubin; Xu, Xuying

    2017-01-01

    Electrical activity is the foundation of the neural system. Coding theories that describe neural electrical activity by the roles of action potential timing or frequency have been thoroughly studied. However, an alternative method to study coding questions is the energy method, which is more global and economical. In this study, we clearly defined and calculated neural energy supply and consumption based on the Hodgkin-Huxley model, during firing action potentials and subthreshold activities using ion-counting and power-integral model. Furthermore, we analyzed energy properties of each ion channel and found that, under the two circumstances, power synchronization of ion channels and energy utilization ratio have significant differences. This is particularly true of the energy utilization ratio, which can rise to above 100% during subthreshold activity, revealing an overdraft property of energy use. These findings demonstrate the distinct status of the energy properties during neuronal firings and subthreshold activities. Meanwhile, after introducing a synapse energy model, this research can be generalized to energy calculation of a neural network. This is potentially important for understanding the relationship between dynamical network activities and cognitive behaviors.

  13. Theoretical Analysis of Transcranial Magneto-Acoustical Stimulation with Hodgkin-Huxley Neuron Model.

    PubMed

    Yuan, Yi; Chen, Yudong; Li, Xiaoli

    2016-01-01

    Transcranial magneto-acoustical stimulation (TMAS) is a novel stimulation technology in which an ultrasonic wave within a magnetostatic field generates an electric current in an area of interest in the brain to modulate neuronal activities. As a key part of the neural network, neurons transmit information in the nervous system. However, the effect of TMAS on the neuronal firing pattern remains unknown. To address this problem, we investigated the stimulatory mechanism of TMAS on neurons, by using a Hodgkin-Huxley neuron model. The simulation results indicated that the magnetostatic field intensity and ultrasonic power affect the amplitude and interspike interval of neuronal action potential under a continuous wave ultrasound. The simulation results also showed that the ultrasonic power, duty cycle and repetition frequency can alter the firing pattern of neural action potential under pulsed wave ultrasound. This study may help to reveal and explain the biological mechanism of TMAS and to provide a theoretical basis for TMAS in the treatment or rehabilitation of neuropsychiatric disorders.

  14. Channel-based Langevin approach for the stochastic Hodgkin-Huxley neuron

    NASA Astrophysics Data System (ADS)

    Huang, Yandong; Rüdiger, Sten; Shuai, Jianwei

    2013-01-01

    Stochasticity in ion channel gating is the major source of intrinsic neuronal noise, which can induce many important effects in neuronal dynamics. Several numerical implementations of the Langevin approach have been proposed to approximate the Markovian dynamics of the Hodgkin-Huxley neuronal model. In this work an improved channel-based Langevin approach is proposed by introducing a truncation procedure to limit the state fractions in the range of [0, 1]. The truncated fractions are put back into the state fractions in the next time step for channel noise calculation. Our simulations show that the bounded Langevin approaches combined with the restored process give better approximations to the statistics of action potentials with the Markovian method. As a result, in our approach the channel state fractions are disturbed by two terms of noise: an uncorrelated Gaussian noise and a time-correlated noise obtained from the truncated fractions. We suggest that the restoration of truncated fractions is a critical process for a bounded Langevin method.

  15. FPGA implementation of a biological neural network based on the Hodgkin-Huxley neuron model

    PubMed Central

    Yaghini Bonabi, Safa; Asgharian, Hassan; Safari, Saeed; Nili Ahmadabadi, Majid

    2014-01-01

    A set of techniques for efficient implementation of Hodgkin-Huxley-based (H-H) model of a neural network on FPGA (Field Programmable Gate Array) is presented. The central implementation challenge is H-H model complexity that puts limits on the network size and on the execution speed. However, basics of the original model cannot be compromised when effect of synaptic specifications on the network behavior is the subject of study. To solve the problem, we used computational techniques such as CORDIC (Coordinate Rotation Digital Computer) algorithm and step-by-step integration in the implementation of arithmetic circuits. In addition, we employed different techniques such as sharing resources to preserve the details of model as well as increasing the network size in addition to keeping the network execution speed close to real time while having high precision. Implementation of a two mini-columns network with 120/30 excitatory/inhibitory neurons is provided to investigate the characteristic of our method in practice. The implementation techniques provide an opportunity to construct large FPGA-based network models to investigate the effect of different neurophysiological mechanisms, like voltage-gated channels and synaptic activities, on the behavior of a neural network in an appropriate execution time. Additional to inherent properties of FPGA, like parallelism and re-configurability, our approach makes the FPGA-based system a proper candidate for study on neural control of cognitive robots and systems as well. PMID:25484854

  16. Playing the devil's advocate: is the Hodgkin-Huxley model useful?

    PubMed

    Meunier, Claude; Segev, Idan

    2002-11-01

    Hodgkin and Huxley (H-H) model for action potential generation has held firm for half a century because this relatively simple and experimentally testable model embodies the major features of membrane nonlinearity: namely, voltage-dependent ionic currents that activate and inactivate in time. However, experimental and theoretical developments of the past 20 years force one to re-evaluate its usefulness. First, the H-H model is, in its original form, limited to the two voltage-dependent currents found in the squid giant axon and it must be extended significantly if it is to deal with the excitable soma and dendrites of neurons. Second, the macroscopic and deterministic H-H model does not capture correctly the kinetics of the Na(+) channel and it cannot account for the stochastic response to current injection that arises from the discrete nature of ion channels. Third, much simpler integrate-and-fire-type models seem to be more useful for exploring collective phenomena in neuronal networks. Is the H-H model threatened, or will it continue to set the fundamental framework for exploring neuronal excitability?

  17. Bistability and resonance in the periodically stimulated Hodgkin-Huxley model with noise

    NASA Astrophysics Data System (ADS)

    Borkowski, L. S.

    2011-05-01

    We describe general characteristics of the Hodgkin-Huxley neuron’s response to a periodic train of short current pulses with Gaussian noise. The deterministic neuron is bistable for antiresonant frequencies. When the stimuli arrive at the resonant frequency the firing rate is a continuous function of the current amplitude I0 and scales as (I0-Ith)1/2, characteristic of a saddle-node bifurcation at the threshold Ith. Intervals of continuous irregular response alternate with integer mode-locked regions with bistable excitation edge. There is an even-all multimodal transition between the 2 : 1 and 3 : 1 states in the vicinity of the main resonance, which is analogous to the odd-all transition discovered earlier in the high-frequency regime. For I0

  18. Theoretical Analysis of Transcranial Magneto-Acoustical Stimulation with Hodgkin-Huxley Neuron Model

    PubMed Central

    Yuan, Yi; Chen, Yudong; Li, Xiaoli

    2016-01-01

    Transcranial magneto-acoustical stimulation (TMAS) is a novel stimulation technology in which an ultrasonic wave within a magnetostatic field generates an electric current in an area of interest in the brain to modulate neuronal activities. As a key part of the neural network, neurons transmit information in the nervous system. However, the effect of TMAS on the neuronal firing pattern remains unknown. To address this problem, we investigated the stimulatory mechanism of TMAS on neurons, by using a Hodgkin-Huxley neuron model. The simulation results indicated that the magnetostatic field intensity and ultrasonic power affect the amplitude and interspike interval of neuronal action potential under a continuous wave ultrasound. The simulation results also showed that the ultrasonic power, duty cycle and repetition frequency can alter the firing pattern of neural action potential under pulsed wave ultrasound. This study may help to reveal and explain the biological mechanism of TMAS and to provide a theoretical basis for TMAS in the treatment or rehabilitation of neuropsychiatric disorders. PMID:27148032

  19. Multiple coherence resonance induced by time-periodic coupling in stochastic Hodgkin-Huxley neuronal networks

    NASA Astrophysics Data System (ADS)

    Lin, Xiu; Gong, Yubing; Wang, Li

    2011-12-01

    In this paper, we study the effect of time-periodic coupling strength (TPCS) on the spiking coherence of Newman-Watts small-world networks of stochastic Hodgkin-Huxley (HH) neurons and investigate the relations between the coupling strength and channel noise when coherence resonance (CR) occurs. It is found that, when the amplitude of TPCS is varied, the spiking induced by channel noise can exhibit CR and coherence bi-resonance (CBR), and the CR moves to a smaller patch area (bigger channel noise) when the amplitude increases; when the frequency of TPCS is varied, the intrinsic spiking can exhibit CBR and multiple CR, and the CR always occurs when the frequency is equal to or multiple of the spiking period, manifesting as the locking between the frequencies of the intrinsic spiking and the coupling strength. These results show that TPCS can greatly enhance and optimize the intrinsic spiking coherence, and favors the spiking with bigger channel noise to exhibit CR. This implies that, compared to constant coupling strength, TPCS may play a more efficient role for improving the time precision of the information processing in stochastic neuronal networks.

  20. Neural Energy Supply-Consumption Properties Based on Hodgkin-Huxley Model

    PubMed Central

    2017-01-01

    Electrical activity is the foundation of the neural system. Coding theories that describe neural electrical activity by the roles of action potential timing or frequency have been thoroughly studied. However, an alternative method to study coding questions is the energy method, which is more global and economical. In this study, we clearly defined and calculated neural energy supply and consumption based on the Hodgkin-Huxley model, during firing action potentials and subthreshold activities using ion-counting and power-integral model. Furthermore, we analyzed energy properties of each ion channel and found that, under the two circumstances, power synchronization of ion channels and energy utilization ratio have significant differences. This is particularly true of the energy utilization ratio, which can rise to above 100% during subthreshold activity, revealing an overdraft property of energy use. These findings demonstrate the distinct status of the energy properties during neuronal firings and subthreshold activities. Meanwhile, after introducing a synapse energy model, this research can be generalized to energy calculation of a neural network. This is potentially important for understanding the relationship between dynamical network activities and cognitive behaviors. PMID:28316842

  1. Dynamical response of the Hodgkin-Huxley model in the high-input regime

    NASA Astrophysics Data System (ADS)

    Luccioli, Stefano; Kreuz, Thomas; Torcini, Alessandro

    2006-04-01

    The response of the Hodgkin-Huxley neuronal model subjected to stochastic uncorrelated spike trains originating from a large number of inhibitory and excitatory post-synaptic potentials is analyzed in detail. The model is examined in its three fundamental dynamical regimes: silence, bistability, and repetitive firing. Its response is characterized in terms of statistical indicators (interspike-interval distributions and their first moments) as well as of dynamical indicators (autocorrelation functions and conditional entropies). In the silent regime, the coexistence of two different coherence resonances is revealed: one occurs at quite low noise and is related to the stimulation of subthreshold oscillations around the rest state; the second one (at intermediate noise variance) is associated with the regularization of the sequence of spikes emitted by the neuron. Bistability in the low noise limit can be interpreted in terms of jumping processes across barriers activated by stochastic fluctuations. In the repetitive firing regime a maximization of incoherence is observed at finite noise variance. Finally, the mechanisms responsible for the different features appearing in the interspike-interval distributions (like multimodality and exponential tails) are clearly identified in the various regimes.

  2. Bifurcation analysis of delay-induced patterns in a ring of Hodgkin-Huxley neurons.

    PubMed

    Kantner, Markus; Yanchuk, Serhiy

    2013-09-28

    Rings of delay-coupled neurons possess a striking capability to produce various stable spiking patterns. In order to reveal the mechanisms of their appearance, we present a bifurcation analysis of the Hodgkin-Huxley (HH) system with delayed feedback as well as a closed loop of HH neurons. We consider mainly the effects of external currents and communication delays. It is shown that typically periodic patterns of different spatial form (wavenumber) appear via Hopf bifurcations as the external current or time delay changes. The Hopf bifurcations are shown to occur in relatively narrow regions of the external current values, which are independent of the delays. Additional patterns, which have the same wavenumbers as the existing ones, appear via saddle-node bifurcations of limit cycles. The obtained bifurcation diagrams are evidence for the important role of communication delays for the emergence of multiple coexistent spiking patterns. The effects of a short-cut, which destroys the rotational symmetry of the ring, are also briefly discussed.

  3. Channel-noise-induced critical slowing in the subthreshold Hodgkin-Huxley neuron

    NASA Astrophysics Data System (ADS)

    Bukoski, Alex; Steyn-Ross, D. A.; Steyn-Ross, Moira L.

    2015-03-01

    The dynamics of a spiking neuron approaching threshold is investigated in the framework of Markov-chain models describing the random state-transitions of the underlying ion-channel proteins. We characterize subthreshold channel-noise-induced transmembrane potential fluctuations in both type-I (integrator) and type-II (resonator) parametrizations of the classic conductance-based Hodgkin-Huxley equations. As each neuron approaches spiking threshold from below, numerical simulations of stochastic trajectories demonstrate pronounced growth in amplitude simultaneous with decay in frequency of membrane voltage fluctuations induced by ion-channel state transitions. To explore this progression of fluctuation statistics, we approximate the exact Markov treatment with a 12-variable channel-based stochastic differential equation (SDE) and its Ornstein-Uhlenbeck (OU) linearization and show excellent agreement between Markov and SDE numerical simulations. Predictions of the OU theory with respect to membrane potential fluctuation variance, autocorrelation, correlation time, and spectral density are also in agreement and illustrate the close connection between the eigenvalue structure of the associated deterministic bifurcations and the observed behavior of the noisy Markov traces on close approach to threshold for both integrator and resonator point-neuron varieties.

  4. Quantification of degeneracy in Hodgkin-Huxley neurons on Newman-Watts small world network.

    PubMed

    Man, Menghua; Zhang, Ya; Ma, Guilei; Friston, Karl; Liu, Shanghe

    2016-08-07

    Degeneracy is a fundamental source of biological robustness, complexity and evolvability in many biological systems. However, degeneracy is often confused with redundancy. Furthermore, the quantification of degeneracy has not been addressed for realistic neuronal networks. The objective of this paper is to characterize degeneracy in neuronal network models via quantitative mathematic measures. Firstly, we establish Hodgkin-Huxley neuronal networks with Newman-Watts small world network architectures. Secondly, in order to calculate the degeneracy, redundancy and complexity in the ensuing networks, we use information entropy to quantify the information a neuronal response carries about the stimulus - and mutual information to measure the contribution of each subset of the neuronal network. Finally, we analyze the interdependency of degeneracy, redundancy and complexity - and how these three measures depend upon network architectures. Our results suggest that degeneracy can be applied to any neuronal network as a formal measure, and degeneracy is distinct from redundancy. Qualitatively degeneracy and complexity are more highly correlated over different network architectures, in comparison to redundancy. Quantitatively, the relationship between both degeneracy and redundancy depends on network coupling strength: both degeneracy and redundancy increase with complexity for small coupling strengths; however, as coupling strength increases, redundancy decreases with complexity (in contrast to degeneracy, which is relatively invariant). These results suggest that the degeneracy is a general topologic characteristic of neuronal networks, which could be applied quantitatively in neuroscience and connectomics.

  5. Effect of autaptic activity on the response of a Hodgkin-Huxley neuron

    NASA Astrophysics Data System (ADS)

    Wang, Hengtong; Wang, Longfei; Chen, Yueling; Chen, Yong

    2014-09-01

    An autapse is a special synapse that connects a neuron to itself. In this study, we investigated the effect of an autapse on the responses of a Hodgkin-Huxley neuron to different forms of external stimuli. When the neuron was subjected to a DC stimulus, the firing frequencies and the interspike interval distributions of the output spike trains showed periodic behaviors as the autaptic delay time increased. When the input was a synaptic pulse-like train with random interspike intervals, we observed low-pass and band-pass filtering behaviors. Moreover, the region over which the output ISIs are distributed and the mean firing frequency display periodic behaviors with increasing autaptic delay time. When specific autaptic parameters were chosen, most of the input ISIs could be filtered, and the response spike trains were nearly regular, even with a highly random input. The background mechanism of these observed dynamics has been analyzed based on the phase response curve method. We also found that the information entropy of the output spike train could be modified by the autapse. These results also suggest that the autapse can serve as a regulator of information response in the nervous system.

  6. A study of quantum mechanical probabilities in the classical Hodgkin-Huxley model.

    PubMed

    Moradi, N; Scholkmann, F; Salari, V

    2015-03-01

    The Hodgkin-Huxley (HH) model is a powerful model to explain different aspects of spike generation in excitable cells. However, the HH model was proposed in 1952 when the real structure of the ion channel was unknown. It is now common knowledge that in many ion-channel proteins the flow of ions through the pore is governed by a gate, comprising a so-called "selectivity filter" inside the ion channel, which can be controlled by electrical interactions. The selectivity filter (SF) is believed to be responsible for the selection and fast conduction of particular ions across the membrane of an excitable cell. Other (generally larger) parts of the molecule such as the pore-domain gate control the access of ions to the channel protein. In fact, two types of gates are considered here for ion channels: the "external gate", which is the voltage sensitive gate, and the "internal gate" which is the selectivity filter gate (SFG). Some quantum effects are expected in the SFG due to its small dimensions, which may play an important role in the operation of an ion channel. Here, we examine parameters in a generalized model of HH to see whether any parameter affects the spike generation. Our results indicate that the previously suggested semi-quantum-classical equation proposed by Bernroider and Summhammer (BS) agrees strongly with the HH equation under different conditions and may even provide a better explanation in some cases. We conclude that the BS model can refine the classical HH model substantially.

  7. Chimera states in a Hodgkin-Huxley model of thermally sensitive neurons

    NASA Astrophysics Data System (ADS)

    Glaze, Tera A.; Lewis, Scott; Bahar, Sonya

    2016-08-01

    Chimera states occur when identically coupled groups of nonlinear oscillators exhibit radically different dynamics, with one group exhibiting synchronized oscillations and the other desynchronized behavior. This dynamical phenomenon has recently been studied in computational models and demonstrated experimentally in mechanical, optical, and chemical systems. The theoretical basis of these states is currently under active investigation. Chimera behavior is of particular relevance in the context of neural synchronization, given the phenomenon of unihemispheric sleep and the recent observation of asymmetric sleep in human patients with sleep apnea. The similarity of neural chimera states to neural "bump" states, which have been suggested as a model for working memory and visual orientation tuning in the cortex, adds to their interest as objects of study. Chimera states have been demonstrated in the FitzHugh-Nagumo model of excitable cells and in the Hindmarsh-Rose neural model. Here, we demonstrate chimera states and chimera-like behaviors in a Hodgkin-Huxley-type model of thermally sensitive neurons both in a system with Abrams-Strogatz (mean field) coupling and in a system with Kuramoto (distance-dependent) coupling. We map the regions of parameter space for which chimera behavior occurs in each of the two coupling schemes.

  8. FPGA implementation of a biological neural network based on the Hodgkin-Huxley neuron model.

    PubMed

    Yaghini Bonabi, Safa; Asgharian, Hassan; Safari, Saeed; Nili Ahmadabadi, Majid

    2014-01-01

    A set of techniques for efficient implementation of Hodgkin-Huxley-based (H-H) model of a neural network on FPGA (Field Programmable Gate Array) is presented. The central implementation challenge is H-H model complexity that puts limits on the network size and on the execution speed. However, basics of the original model cannot be compromised when effect of synaptic specifications on the network behavior is the subject of study. To solve the problem, we used computational techniques such as CORDIC (Coordinate Rotation Digital Computer) algorithm and step-by-step integration in the implementation of arithmetic circuits. In addition, we employed different techniques such as sharing resources to preserve the details of model as well as increasing the network size in addition to keeping the network execution speed close to real time while having high precision. Implementation of a two mini-columns network with 120/30 excitatory/inhibitory neurons is provided to investigate the characteristic of our method in practice. The implementation techniques provide an opportunity to construct large FPGA-based network models to investigate the effect of different neurophysiological mechanisms, like voltage-gated channels and synaptic activities, on the behavior of a neural network in an appropriate execution time. Additional to inherent properties of FPGA, like parallelism and re-configurability, our approach makes the FPGA-based system a proper candidate for study on neural control of cognitive robots and systems as well.

  9. Biophysical synaptic dynamics in an analog VLSI network of Hodgkin-Huxley neurons.

    PubMed

    Yu, Theodore; Cauwenberghs, Gert

    2009-01-01

    We study synaptic dynamics in a biophysical network of four coupled spiking neurons implemented in an analog VLSI silicon microchip. The four neurons implement a generalized Hodgkin-Huxley model with individually configurable rate-based kinetics of opening and closing of Na+ and K+ ion channels. The twelve synapses implement a rate-based first-order kinetic model of neurotransmitter and receptor dynamics, accounting for NMDA and non-NMDA type chemical synapses. The implemented models on the chip are fully configurable by 384 parameters accounting for conductances, reversal potentials, and pre/post-synaptic voltage-dependence of the channel kinetics. We describe the models and present experimental results from the chip characterizing single neuron dynamics, single synapse dynamics, and multi-neuron network dynamics showing phase-locking behavior as a function of synaptic coupling strength. The 3mm x 3mm microchip consumes 1.29 mW power making it promising for applications including neuromorphic modeling and neural prostheses.

  10. Effects of maximal sodium and potassium conductance on the stability of Hodgkin-Huxley model.

    PubMed

    Zhang, Yue; Wang, Kuanquan; Yuan, Yongfeng; Sui, Dong; Zhang, Henggui

    2014-01-01

    Hodgkin-Huxley (HH) equation is the first cell computing model in the world and pioneered the use of model to study electrophysiological problems. The model consists of four differential equations which are based on the experimental data of ion channels. Maximal conductance is an important characteristic of different channels. In this study, mathematical method is used to investigate the importance of maximal sodium conductance gNA and maximal potassium conductance gK. Applying stability theory, and taking gNA and gK as variables, we analyze the stability and bifurcations of the model. Bifurcations are found when the variables change, and bifurcation points and boundary are also calculated. There is only one bifurcation point when gNA is the variable, while there are two points when gK is variable. The (gNA,  gK) plane is partitioned into two regions and the upper bifurcation boundary is similar to a line when both gNA and gK are variables. Numerical simulations illustrate the validity of the analysis. The results obtained could be helpful in studying relevant diseases caused by maximal conductance anomaly.

  11. Effects of Maximal Sodium and Potassium Conductance on the Stability of Hodgkin-Huxley Model

    PubMed Central

    Wang, Kuanquan; Yuan, Yongfeng; Zhang, Henggui

    2014-01-01

    Hodgkin-Huxley (HH) equation is the first cell computing model in the world and pioneered the use of model to study electrophysiological problems. The model consists of four differential equations which are based on the experimental data of ion channels. Maximal conductance is an important characteristic of different channels. In this study, mathematical method is used to investigate the importance of maximal sodium conductance g-Na and maximal potassium conductance g-K. Applying stability theory, and taking g-Na and g-K as variables, we analyze the stability and bifurcations of the model. Bifurcations are found when the variables change, and bifurcation points and boundary are also calculated. There is only one bifurcation point when g-Na is the variable, while there are two points when g-K is variable. The (g-Na,  g-K) plane is partitioned into two regions and the upper bifurcation boundary is similar to a line when both g-Na and g-K are variables. Numerical simulations illustrate the validity of the analysis. The results obtained could be helpful in studying relevant diseases caused by maximal conductance anomaly. PMID:25104970

  12. Robust observer-based tracking control of hodgkin-huxley neuron systems under environmental disturbances.

    PubMed

    Chen, Bor-Sen; Li, Cheng-Wei

    2010-12-01

    A nervous system consists of a large number of highly interconnected nerve cells. Nerve cells communicate by generation and transmission of short electrical pulses (action potential). In addition, membrane voltage is the only measurable state in nervous systems. A robust observer-based model reference tracking control is proposed for Hodgkin-Huxley (HH) neuron systems to generate a desired reference response in spite of environmental noises, uncertain initial values, and diffusion currents from other interconnected nerve cells. In order to simplify the robust tracking control design of nonlinear stochastic HH neuron systems, a fuzzy interpolation method is employed to interpolate several linear stochastic systems to approximate a nonlinear stochastic HH neuron system so that the nonlinear robust tracking control problem can be solved by the linear matrix inequality (LMI) technique with the help of Robust Control Toolbox in Matlab. The proposed robust observer-based tracking control scheme can provide new methods for desired action potential generation, suppression of oscillations, and blockage of action potential transmission under environmental noise and diffusion currents. These new methods are useful for patients with different neuron system dysfunctions. Finally, three simulation examples of tracking control of nervous systems are given to illustrate the design procedure and confirm the tracking performance of the proposed method.

  13. On the noise-enhancing ability of stochastic Hodgkin-Huxley neuron systems.

    PubMed

    Chen, Bor-Sen; Li, Cheng-Wei

    2010-07-01

    Recently noise has been shown to be useful in enhancing neuron sensitivity by stochastic resonance. In this study, in order to measure the noise-enhancing factor (NEF), a nonlinear stochastic model is introduced for the Hodgkin-Huxley (HH) neuron system with synaptic noise input stimulation and channel noises in the sodium and potassium channels. The enhancing factor of the HH neuron system is measured from the point of view of the noise-exploiting level of nonlinear stochastic H(infinity) signal processing. Since the nonlinear stochastic-enhancing measure problem of HH neuron systems requires a solution for the difficulty presented by the Hamilton Jacobi inequality (HJI), a fuzzy interpolation of locally linearized systems is employed to simplify the nonlinear noise-enhancing problems by solving only a set of linear matrix inequalities. The NEF of the HH neuron system is found to be related to the locations of eigenvalues of linearized HH neuron systems and can be estimated through the H(infinity) signal processing method. Based on a stochastic fuzzy linearized HH neuron system, we found that channel noises are enhanced by the active eigenvalues of ionic channels while synaptic noises are attenuated by the passive eigenvalues of synaptic process.

  14. Non-Gaussian noise optimized spiking activity of Hodgkin-Huxley neurons on random complex networks.

    PubMed

    Gong, Yubing; Hao, Yinghang; Xie, Yanhang; Ma, Xiaoguang; Yang, Chuanlu

    2009-09-01

    In this paper, we numerically study how the NGN's deviation q from Gaussian noise (q=1) affects the spike coherence and synchronization of 60 coupled Hodgkin-Huxley (HH) neurons driven by a periodic sinusoidal stimulus on random complex networks. It is found that the effect of the deviation depends on the network randomness p (the fraction of random shortcuts): for larger p (p>0.15), the spiking regularity keeps being improved with increasing q; while, for smaller p (p< 0.15), the spiking regularity can reach the best performance at an optimal intermediate q value, indicating the occurrence of "deviation-optimized spike coherence". The synchronization becomes enhanced with decreasing q, and the enhancing extent for a random HH neuron network is stronger than for a regular one. These behaviors show that the spike coherence and synchronization of the present HH neurons on random networks can be more strongly enhanced by various other types of external noise than by Gaussian noise, whereby the neuron firings may behave more periodically in time and more synchronously in space. Our results provide the constructive roles of the NGN on the spiking activity of the present system of HH neuron networks.

  15. Multiple coherence resonance induced by time-periodic coupling in stochastic Hodgkin-Huxley neuronal networks.

    PubMed

    Lin, Xiu; Gong, Yubing; Wang, Li

    2011-12-01

    In this paper, we study the effect of time-periodic coupling strength (TPCS) on the spiking coherence of Newman-Watts small-world networks of stochastic Hodgkin-Huxley (HH) neurons and investigate the relations between the coupling strength and channel noise when coherence resonance (CR) occurs. It is found that, when the amplitude of TPCS is varied, the spiking induced by channel noise can exhibit CR and coherence bi-resonance (CBR), and the CR moves to a smaller patch area (bigger channel noise) when the amplitude increases; when the frequency of TPCS is varied, the intrinsic spiking can exhibit CBR and multiple CR, and the CR always occurs when the frequency is equal to or multiple of the spiking period, manifesting as the locking between the frequencies of the intrinsic spiking and the coupling strength. These results show that TPCS can greatly enhance and optimize the intrinsic spiking coherence, and favors the spiking with bigger channel noise to exhibit CR. This implies that, compared to constant coupling strength, TPCS may play a more efficient role for improving the time precision of the information processing in stochastic neuronal networks.

  16. Determining the contributions of divisive and subtractive feedback in the Hodgkin-Huxley model.

    PubMed

    Sengül, Sevgi; Clewley, Robert; Bertram, Richard; Tabak, Joël

    2014-12-01

    The Hodgkin-Huxley (HH) model is the basis for numerous neural models. There are two negative feedback processes in the HH model that regulate rhythmic spiking. The first is an outward current with an activation variable n that has an opposite influence to the excitatory inward current and therefore provides subtractive negative feedback. The other is the inactivation of an inward current with an inactivation variable h that reduces the amount of positive feedback and therefore provides divisive feedback. Rhythmic spiking can be obtained with either negative feedback process, so we ask what is gained by having two feedback processes. We also ask how the different negative feedback processes contribute to spiking. We show that having two negative feedback processes makes the HH model more robust to changes in applied currents and conductance densities than models that possess only one negative feedback variable. We also show that the contributions made by the subtractive and divisive feedback variables are not static, but depend on time scales and conductance values. In particular, they contribute differently to the dynamics in Type I versus Type II neurons.

  17. Channel-based Langevin approach for the stochastic Hodgkin-Huxley neuron.

    PubMed

    Huang, Yandong; Rüdiger, Sten; Shuai, Jianwei

    2013-01-01

    Stochasticity in ion channel gating is the major source of intrinsic neuronal noise, which can induce many important effects in neuronal dynamics. Several numerical implementations of the Langevin approach have been proposed to approximate the Markovian dynamics of the Hodgkin-Huxley neuronal model. In this work an improved channel-based Langevin approach is proposed by introducing a truncation procedure to limit the state fractions in the range of [0, 1]. The truncated fractions are put back into the state fractions in the next time step for channel noise calculation. Our simulations show that the bounded Langevin approaches combined with the restored process give better approximations to the statistics of action potentials with the Markovian method. As a result, in our approach the channel state fractions are disturbed by two terms of noise: an uncorrelated Gaussian noise and a time-correlated noise obtained from the truncated fractions. We suggest that the restoration of truncated fractions is a critical process for a bounded Langevin method.

  18. Response of a Hodgkin-Huxley neuron to a high-frequency input.

    PubMed

    Borkowski, L S

    2009-11-01

    We study the response of a Hodgkin-Huxley neuron stimulated by a periodic sequence of conductance pulses arriving through the synapse in the high-frequency regime. In addition to the usual excitation threshold there is a smooth crossover from the firing to the silent regime for increasing pulse amplitude gsyn. The amplitude of the voltage spikes decreases approximately linearly with gsyn. In some regions of parameter space the response is irregular, probably chaotic. In the chaotic regime between the mode-locked regions 3:1 and 2:1 near the lower excitation threshold, the output interspike interval histogram (ISIH) undergoes a sharp transition. If the driving period is below the critical value, TT* even multiples of Ti also appear in the histogram, starting from the largest values. Near T* the ISIH scales logarithmically on both sides of the transition. The coefficient of variation of ISIH has a cusp singularity at T*. The average response period has a maximum slightly above T*. Near the excitation threshold in the chaotic regime the average firing rate rises sublinearly from frequencies of order 1 Hz.

  19. Effect of autaptic activity on the response of a Hodgkin-Huxley neuron.

    PubMed

    Wang, Hengtong; Wang, Longfei; Chen, Yueling; Chen, Yong

    2014-09-01

    An autapse is a special synapse that connects a neuron to itself. In this study, we investigated the effect of an autapse on the responses of a Hodgkin-Huxley neuron to different forms of external stimuli. When the neuron was subjected to a DC stimulus, the firing frequencies and the interspike interval distributions of the output spike trains showed periodic behaviors as the autaptic delay time increased. When the input was a synaptic pulse-like train with random interspike intervals, we observed low-pass and band-pass filtering behaviors. Moreover, the region over which the output ISIs are distributed and the mean firing frequency display periodic behaviors with increasing autaptic delay time. When specific autaptic parameters were chosen, most of the input ISIs could be filtered, and the response spike trains were nearly regular, even with a highly random input. The background mechanism of these observed dynamics has been analyzed based on the phase response curve method. We also found that the information entropy of the output spike train could be modified by the autapse. These results also suggest that the autapse can serve as a regulator of information response in the nervous system.

  20. Minimal Hodgkin-Huxley type models for different classes of cortical and thalamic neurons.

    PubMed

    Pospischil, Martin; Toledo-Rodriguez, Maria; Monier, Cyril; Piwkowska, Zuzanna; Bal, Thierry; Frégnac, Yves; Markram, Henry; Destexhe, Alain

    2008-11-01

    We review here the development of Hodgkin-Huxley (HH) type models of cerebral cortex and thalamic neurons for network simulations. The intrinsic electrophysiological properties of cortical neurons were analyzed from several preparations, and we selected the four most prominent electrophysiological classes of neurons. These four classes are "fast spiking", "regular spiking", "intrinsically bursting" and "low-threshold spike" cells. For each class, we fit "minimal" HH type models to experimental data. The models contain the minimal set of voltage-dependent currents to account for the data. To obtain models as generic as possible, we used data from different preparations in vivo and in vitro, such as rat somatosensory cortex and thalamus, guinea-pig visual and frontal cortex, ferret visual cortex, cat visual cortex and cat association cortex. For two cell classes, we used automatic fitting procedures applied to several cells, which revealed substantial cell-to-cell variability within each class. The selection of such cellular models constitutes a necessary step towards building network simulations of the thalamocortical system with realistic cellular dynamical properties.

  1. Channel-noise-induced critical slowing in the subthreshold Hodgkin-Huxley neuron.

    PubMed

    Bukoski, Alex; Steyn-Ross, D A; Steyn-Ross, Moira L

    2015-03-01

    The dynamics of a spiking neuron approaching threshold is investigated in the framework of Markov-chain models describing the random state-transitions of the underlying ion-channel proteins. We characterize subthreshold channel-noise-induced transmembrane potential fluctuations in both type-I (integrator) and type-II (resonator) parametrizations of the classic conductance-based Hodgkin-Huxley equations. As each neuron approaches spiking threshold from below, numerical simulations of stochastic trajectories demonstrate pronounced growth in amplitude simultaneous with decay in frequency of membrane voltage fluctuations induced by ion-channel state transitions. To explore this progression of fluctuation statistics, we approximate the exact Markov treatment with a 12-variable channel-based stochastic differential equation (SDE) and its Ornstein-Uhlenbeck (OU) linearization and show excellent agreement between Markov and SDE numerical simulations. Predictions of the OU theory with respect to membrane potential fluctuation variance, autocorrelation, correlation time, and spectral density are also in agreement and illustrate the close connection between the eigenvalue structure of the associated deterministic bifurcations and the observed behavior of the noisy Markov traces on close approach to threshold for both integrator and resonator point-neuron varieties.

  2. Bistability and resonance in the periodically stimulated Hodgkin-Huxley model with noise.

    PubMed

    Borkowski, L S

    2011-05-01

    We describe general characteristics of the Hodgkin-Huxley neuron's response to a periodic train of short current pulses with Gaussian noise. The deterministic neuron is bistable for antiresonant frequencies. When the stimuli arrive at the resonant frequency the firing rate is a continuous function of the current amplitude I(0) and scales as (I(0)-I(th))(1/2), characteristic of a saddle-node bifurcation at the threshold I(th). Intervals of continuous irregular response alternate with integer mode-locked regions with bistable excitation edge. There is an even-all multimodal transition between the 2 : 1 and 3 : 1 states in the vicinity of the main resonance, which is analogous to the odd-all transition discovered earlier in the high-frequency regime. For I(0)

  3. Texture-Based Correspondence Display

    NASA Technical Reports Server (NTRS)

    Gerald-Yamasaki, Michael

    2004-01-01

    Texture-based correspondence display is a methodology to display corresponding data elements in visual representations of complex multidimensional, multivariate data. Texture is utilized as a persistent medium to contain a visual representation model and as a means to create multiple renditions of data where color is used to identify correspondence. Corresponding data elements are displayed over a variety of visual metaphors in a normal rendering process without adding extraneous linking metadata creation and maintenance. The effectiveness of visual representation for understanding data is extended to the expression of the visual representation model in texture.

  4. Van Gogh's disease in the light of his correspondence.

    PubMed

    Voskuil, Piet H A

    2013-01-01

    The literary quality of Vincent van Gogh's correspondence is widely recognized. He wrote expressively and evocatively, and had great literary knowledge. In this essay we follow his medical history in many quotes from in his letters to see how Vincent expressed his complaints, knowledge, and emotions connected with his disease. The symptoms became most clear after December 1888. In the beginning, Van Gogh hesitated to tell much about his ailment, but gradually painted in the letters his experiences, making use of the intermittent course of his cycloid psychoses. We will see an indication that, in the network that mediated Van Gogh's brain (dys)function, elements of synesthesia, prosopagnosia, and spatial agnosia might have been activated. Van Gogh's affinity for poetry, already in his early twenty's, makes the hypothesis of a, by epileptic discharges, kindled temporal lobe at most only part of the complex interpretation of this creative and suffering mind. Copyright © 2013 S. Karger AG, Basel.

  5. Comparison of the validity of Hill and Huxley muscle-tendon complex models using experimental data obtained from rat m. soleus in situ.

    PubMed

    Lemaire, Koen K; Baan, Guus C; Jaspers, Richard T; van Soest, A J Knoek

    2016-04-01

    The relationship between mechanical and metabolic behaviour in the widely used Hill muscle-tendon complex (MTC) model is not straightforward, whereas this is an integral part of the Huxley model. In this study, we assessed to what extent Huxley- and Hill-type MTC models yield adequate predictions of mechanical muscle behaviour during stretch-shortening cycles (SSCs). In fully anaesthetized male Wistar rats (N=3), m. soleus was dissected completely free, except for the insertion. Cuff electrodes were placed over the n. ischiadicus. The distal end of the tendon was connected to a servo motor, via a force transducer. The setup allowed for full control over muscle stimulation and length, while force was measured. Quick-release and isovelocity contractions (part 1), and SSCs (part 2) were imposed. Simulations of part 2 were made with both a Hill and a Huxley MTC model, using parameter values determined from part 1. Modifications to the classic two-state Huxley model were made to incorporate series elasticity, activation dynamics, and active and passive force-length relationships. Results were similar for all rats. Fitting of the free parameters to the data of part 1 was near perfect (R(2)>0.97). During SSCs, predicted peak force and force during relaxation deviated from the experimental data for both models. Overall, both models yielded similarly adequate predictions of the experimental data. We conclude that Huxley and Hill MTC models are equally valid with respect to mechanical behaviour. © 2016. Published by The Company of Biologists Ltd.

  6. Crowding affects letters and symbols differently.

    PubMed

    Grainger, Jonathan; Tydgat, Ilse; Isselé, Joanna

    2010-06-01

    Five experiments examined crowding effects with letter and symbol stimuli. Experiments 1 through 3 compared 2-alternative forced-choice (2AFC) identification accuracy for isolated targets presented left and right of fixation with targets flanked either by 2 other items of the same category or a single item situated to the right or left of targets. Interference from flankers (crowding) was significantly stronger for symbols than letters. Single flankers generated performance similar to the isolated targets when the stimuli were letters but closer to the 2-flanker condition when the stimuli were symbols. Experiment 4 confirmed this pattern using a partial-report bar probe procedure. Experiment 5 showed that another measure of crowding, critical spacing, was greater for symbols than for letters. The results support the hypothesis that letter-string processing involves a specialized system developed to limit the spatial extent of crowding for letters in words.

  7. [Protestant clergymen among Hahnemann's clientele. Patient histories in letters].

    PubMed

    Kreher, Simone; Schlott, Melanie; Schlott, Thilo

    2016-01-01

    As part of the research project, developments in the history of science and in the regional and ecclesiastic history of the late feudal petty state of Köthen-Anhalt have been assessed and numerous documents of the Nagel and Mühlenbein family histories examined that place the transcribed patient letters of the two Protestant clergymen within the context of the Hahnemann Archives. These findings complement and extend previous insights into Hahnemann's Köthen clientele, especially when it comes to the structure and milieu of the local clerical elite. Inspired by the interpretive methods of sequential textual analysis, form and content of the letters of the two clergymen and their relatives were also investigated as methodically structured lines of communication. The body of sources published here presents--embedded in the body-image (of sickness and health) prevalent at the time--the medical cultures of educated patients as well as the increasingly professionalized medical practices of Samuel Hahnemann in a flourishing urban doctor's surgery. The correspondence between the pastors Albert Wilhelm Gotthilf Nagel (1796-1835) and August Carl Ludwig Georg Mühlenbein (1797-1866), presented here in a standard edition, has been investigated at Fulda University as part of the project 'Homöopathisches Medicinieren zwischen alltäglicher Lebensführung und professioneller Praxis' ('Homeopathic medicine between everyday use and professional practice'). Of the altogether 78 transcribed documents, 53 are letters written by either of the two pastors, 16 are patient journals by Samuel Hahnemann, 9 letters by the pastors' wives and Mühlenbein's mother. The two series of letters, originally composed between 1831 and 1833 in old German cursive script, can now be used as sources for research into the history of homeopathy.

  8. QKZ-Ruijsenaars correspondence revisited

    NASA Astrophysics Data System (ADS)

    Zabrodin, A.; Zotov, A.

    2017-09-01

    We discuss the Matsuo-Cherednik type correspondence between the quantum Knizhnik-Zamolodchikov equations associated with GL (N) and the n-particle quantum Ruijsenaars model, with n being not necessarily equal to N. The quasiclassical limit of this construction yields the quantum-classical correspondence between the quantum spin chains and the classical Ruijsenaars models.

  9. Letter to the Editor on Robert Yaes's Letter

    NASA Technical Reports Server (NTRS)

    Krisher, T. P.

    1993-01-01

    In his letter on page 13 of the March 1993 issue, Robert Yaes raised the question of whether the existence of the cosmic microwave background (CMB), now observed so precisely with COBE, is compatible with the principle of relativity: The laws by which the states of physical systems undergo change are not affected, whether these changes of state be referred to the one or other of two systems of coordinates in uniform translatory motion. Although I do not claim to provide an xpertresponse to this question, as desired by Yaes, it is my understanding that the principle of relativity is not necessarily violated by the mere existence of a universal reference frame. The laws of physics can still be invariant under some transformation of coordinates. This transformation is not specified by the principle of relativity itself, although we have discovered so far that Nature respects Lorentz invariance (principle of the constancy of the velocity of light).

  10. 1999 Children's Health Protection Advisory Committee Letters

    EPA Pesticide Factsheets

    These letters, most of which are addressed to Administrator Carol Browner, are regarding a children's longitudinal cohort study, acute dietary exposure, cancer risk assessment, and residential exposure assessments.

  11. On Becoming a Doctor of Humane Letters.

    PubMed

    Tribble Md, Curt

    2016-08-19

    In an era of rapid, cheap, and efficient electronic communication, the practice-and art-of letter writing has faded. There are many reasons for us as physicians and surgeons to resist this evolution. And, there are many opportunities to employ letter writing to the benefit of ourselves, our patients, and our colleagues. A true Doctor of Humane Letters is an honorary degree, generally awarded for significant contributions to society.  However, given that humane can be defined as showing compassion, understanding, mercy, and tolerance, we can all strive to be worthy of such a distinction. There are many mundane letters familiar to us all, such as letters of recommendation, letters of thanks, and letters of commendation. However, I would like to offer some suggestions about other less common, but useful, types of letters that might prove valuable to physicians both in training and in practice. These include letters of inquiry, condolence, reflection, and explanation, as well as some notes about missives that are often best written but not sent.

  12. Letter report: Evaluation of dryer/calciner technologies for testing

    SciTech Connect

    Sevigny, G.

    1996-02-01

    This letter report describes some past experiences on the drying and calcination of radioactive materials or corresponding simulants; and the information needed from testing. The report also includes an assessment of informational needs including possible impacts to a full-scale plant. This includes reliability, maintenance, and overall size versus throughput. Much of the material was previously compiled and reported by Mike Elliott of PNL {open_quotes}Melter Performance Assessment{close_quotes} and Larry Eisenstatt of SEG on contract to WHC in a letter to Rod Powell. Also, an annotated bibliography was prepared by Reagan Seymour of WHC. Descriptions of the drying and calciner technologies, development status, advantages and disadvantages of using a WFE or calciner, and recommendations for future testing are discussed in this report.

  13. Learning Letter Names and Sounds: Effects of Instruction, Letter Type, and Phonological Processing Skill

    PubMed Central

    Piasta, Shayne B.; Wagner, Richard K.

    2010-01-01

    Preschool-aged children (n = 58) were randomly assigned to receive instruction in letter names and sounds, letter sounds only, or numbers (control). Multilevel modeling was used to examine letter name and sound learning as a function of instructional condition and characteristics of both letters and children. Specifically, learning was examined in light of letter name structure, whether letter names included cues to their respective sounds, and children’s phonological processing skills. Consistent with past research, children receiving letter name and sound instruction were most likely to learn the sounds of letters whose names included cues to their sounds, regardless of phonological processing skills. Only children with higher phonological skills showed a similar effect in the control condition. Practical implications are discussed. PMID:20097352

  14. Learning letter names and sounds: effects of instruction, letter type, and phonological processing skill.

    PubMed

    Piasta, Shayne B; Wagner, Richard K

    2010-04-01

    Preschool-age children (N=58) were randomly assigned to receive instruction in letter names and sounds, letter sounds only, or numbers (control). Multilevel modeling was used to examine letter name and sound learning as a function of instructional condition and characteristics of both letters and children. Specifically, learning was examined in light of letter name structure, whether letter names included cues to their respective sounds, and children's phonological processing skills. Consistent with past research, children receiving letter name and sound instruction were most likely to learn the sounds of letters whose names included cues to their sounds regardless of phonological processing skills. Only children with higher phonological skills showed a similar effect in the control condition. Practical implications are discussed.

  15. Effect of Orthographic Processes on Letter Identity and Letter-Position Encoding in Dyslexic Children

    PubMed Central

    Reilhac, Caroline; Jucla, Mélanie; Iannuzzi, Stéphanie; Valdois, Sylviane; Démonet, Jean-François

    2012-01-01

    The ability to identify letters and encode their position is a crucial step of the word recognition process. However and despite their word identification problem, the ability of dyslexic children to encode letter identity and letter-position within strings was not systematically investigated. This study aimed at filling this gap and further explored how letter identity and letter-position encoding is modulated by letter context in developmental dyslexia. For this purpose, a letter-string comparison task was administered to French dyslexic children and two chronological age (CA) and reading age (RA)-matched control groups. Children had to judge whether two successively and briefly presented four-letter strings were identical or different. Letter-position and letter identity were manipulated through the transposition (e.g., RTGM vs. RMGT) or substitution of two letters (e.g., TSHF vs. TGHD). Non-words, pseudo-words, and words were used as stimuli to investigate sub-lexical and lexical effects on letter encoding. Dyslexic children showed both substitution and transposition detection problems relative to CA-controls. A substitution advantage over transpositions was only found for words in dyslexic children whereas it extended to pseudo-words in RA-controls and to all type of items in CA-controls. Letters were better identified in the dyslexic group when belonging to orthographically familiar strings. Letter-position encoding was very impaired in dyslexic children who did not show any word context effect in contrast to CA-controls. Overall, the current findings point to a strong letter identity and letter-position encoding disorder in developmental dyslexia. PMID:22661961

  16. Letter Names and Phonological Awareness Help Children to Learn Letter-Sound Relations

    ERIC Educational Resources Information Center

    Cardoso-Martins, Claudia; Mesquita, Tereza Cristina Lara; Ehri, Linnea

    2011-01-01

    Two experimental training studies with Portuguese-speaking preschoolers in Brazil were conducted to investigate whether children benefit from letter name knowledge and phonological awareness in learning letter-sound relations. In Experiment 1, two groups of children were compared. The experimental group was taught the names of letters whose sounds…

  17. Priming for letters and pseudoletters in mid-fusiform cortex: examining letter selectivity and case invariance.

    PubMed

    Burgund, E Darcy; Guo, Yi; Aurbach, Elyse L

    2009-03-01

    A large body of research indicates a critical role for the left mid-fusiform cortex in reading, however, the extent to which this area is dedicated exclusively to the processing of words and letters has been debated. Two questions regarding left mid-fusiform function are critical to this debate: (1) Are letters stored preferentially compared to visually equivalent non-letters (letter selectivity)? (2) Are letter representations abstract with respect to changes in letter case (e.g., A/a; case invariance)? The present study addressed these questions by comparing priming for letters and pseudoletters in left and right mid-fusiform regions using functional magnetic resonance imaging while subjects performed a same/different matching task. Results revealed priming for letters but not pseudoletters in the left mid-fusiform region, suggesting that representations are letter selective. However, no priming for different-case-primed letters was observed in this region, indicating that representations are not case invariant. In addition, priming for pseudoletters but not letters was observed in the homologous right mid-fusiform region. Overall, findings contradict strongly modular theories of letter/word processing and suggest that left and right mid-fusiform regions support generic object processes that are differentially effective for representing disparate types of visual stimuli.

  18. Letter-Name Letter-Sound and Phonological Awareness: Evidence from Greek-Speaking Kindergarten Children

    ERIC Educational Resources Information Center

    Manolitsis, George; Tafa, Eufimia

    2011-01-01

    The purpose of this study was to examine longitudinally the development of letter-sound and letter-name knowledge and their relation to each other and to various aspects of phonological awareness in a sample of Greek kindergarten children who did not know how to read. One hundred twenty children aged 58-69 months were assessed on letter-sound and…

  19. Letters from the Future: Suggestions for Using Letter Writing as a School Counselling Intervention

    ERIC Educational Resources Information Center

    Kress, Victoria E.; Hinkle, Michelle Gimenez; Protivnak, Jake J.

    2011-01-01

    This article presents a school counselling intervention that utilises letters written from the future. Few peer-reviewed articles have addressed the use of letter writing in a school counselling context, and none have focused on the use of letters from the future as a means of school counsellor intervention. The authors present a theoretical…

  20. Letter Names and Phonological Awareness Help Children to Learn Letter-Sound Relations

    ERIC Educational Resources Information Center

    Cardoso-Martins, Claudia; Mesquita, Tereza Cristina Lara; Ehri, Linnea

    2011-01-01

    Two experimental training studies with Portuguese-speaking preschoolers in Brazil were conducted to investigate whether children benefit from letter name knowledge and phonological awareness in learning letter-sound relations. In Experiment 1, two groups of children were compared. The experimental group was taught the names of letters whose sounds…

  1. Letter Names: Effect on Letter Saying, Spelling, and Word Recognition in Hebrew.

    ERIC Educational Resources Information Center

    Levin, Iris; Patel, Sigal; Margalit, Tamar; Barad, Noa

    2002-01-01

    Examined whether letter names, which bridge the gap between oral and written language among English speaking children, have a similar function in Hebrew. In findings from studies of Israeli kindergartners and first graders, children were found to rely on letter names in performing a number of letter saying, spelling, and word recognition tasks.…

  2. Disentangling the Developmental Trajectories of Letter Position and Letter Identity Coding Using Masked Priming

    ERIC Educational Resources Information Center

    Kezilas, Yvette; McKague, Meredith; Kohnen, Saskia; Badcock, Nicholas A.; Castles, Anne

    2017-01-01

    Masked transposed-letter (TL) priming effects have been used to index letter position processing over the course of reading development. Whereas some studies have reported an increase in TL priming over development, others have reported a decrease. These findings have led to the development of 2 somewhat contradictory accounts of letter position…

  3. Disentangling the Developmental Trajectories of Letter Position and Letter Identity Coding Using Masked Priming

    ERIC Educational Resources Information Center

    Kezilas, Yvette; McKague, Meredith; Kohnen, Saskia; Badcock, Nicholas A.; Castles, Anne

    2017-01-01

    Masked transposed-letter (TL) priming effects have been used to index letter position processing over the course of reading development. Whereas some studies have reported an increase in TL priming over development, others have reported a decrease. These findings have led to the development of 2 somewhat contradictory accounts of letter position…

  4. Osler and the Infected Letter

    PubMed Central

    2005-01-01

    The spread of infectious agents through the mail has concerned public health officials for 5 centuries. The dissemination of anthrax spores in the US mail in 2001 was a recent example. In 1901, two medical journals reported outbreaks of smallpox presumably introduced by letters contaminated with variola viruses. The stability and infectivity of the smallpox virus are reviewed from both a historical (anecdotal) perspective and modern virologic studies. Bubonic plague was the contagious disease that led to quarantines as early as the 14th century in port cities in southern Europe. Later, smallpox, cholera, typhus, and yellow fever were recognized as also warranting quarantine measures. Initially, attempts were made to decontaminate all goods imported from pestilential areas, particularly mail. Disinfection of mail was largely abandoned in the early 20th century with newer knowledge about the spread and stability of these 5 infectious agents. PMID:15890120

  5. The influence of reading expertise in mirror-letter perception: Evidence from beginning and expert readers

    PubMed Central

    Duñabeitia, Jon Andoni; Dimitropoulou, María; Estévez, Adelina; Carreiras, Manuel

    2013-01-01

    The visual word recognition system recruits neuronal systems originally developed for object perception which are characterized by orientation insensitivity to mirror reversals. It has been proposed that during reading acquisition beginning readers have to “unlearn” this natural tolerance to mirror reversals in order to efficiently discriminate letters and words. Therefore, it is supposed that this unlearning process takes place in a gradual way and that reading expertise modulates mirror-letter discrimination. However, to date no supporting evidence for this has been obtained. We present data from an eye-movement study that investigated the degree of sensitivity to mirror-letters in a group of beginning readers and a group of expert readers. Participants had to decide which of the two strings presented on a screen corresponded to an auditorily presented word. Visual displays always included the correct target word and one distractor word. Results showed that those distractors that were the same as the target word except for the mirror lateralization of two internal letters attracted participants’ attention more than distractors created by replacement of two internal letters. Interestingly, the time course of the effects was found to be different for the two groups, with beginning readers showing a greater tolerance (decreased sensitivity) to mirror-letters than expert readers. Implications of these findings are discussed within the framework of preceding evidence showing how reading expertise modulates letter identification. PMID:24273596

  6. Stochastic differential equation models for ion channel noise in Hodgkin-Huxley neurons.

    PubMed

    Goldwyn, Joshua H; Imennov, Nikita S; Famulare, Michael; Shea-Brown, Eric

    2011-04-01

    The random transitions of ion channels between conducting and nonconducting states generate a source of internal fluctuations in a neuron, known as channel noise. The standard method for modeling the states of ion channels nonlinearly couples continuous-time Markov chains to a differential equation for voltage. Beginning with the work of R. F. Fox and Y.-N. Lu [Phys. Rev. E 49, 3421 (1994)], there have been attempts to generate simpler models that use stochastic differential equation (SDEs) to approximate the stochastic spiking activity produced by Markov chain models. Recent numerical investigations, however, have raised doubts that SDE models can capture the stochastic dynamics of Markov chain models.We analyze three SDE models that have been proposed as approximations to the Markov chain model: one that describes the states of the ion channels and two that describe the states of the ion channel subunits. We show that the former channel-based approach can capture the distribution of channel noise and its effects on spiking in a Hodgkin-Huxley neuron model to a degree not previously demonstrated, but the latter two subunit-based approaches cannot. Our analysis provides intuitive and mathematical explanations for why this is the case. The temporal correlation in the channel noise is determined by the combinatorics of bundling subunits into channels, but the subunit-based approaches do not correctly account for this structure. Our study confirms and elucidates the findings of previous numerical investigations of subunit-based SDE models. Moreover, it presents evidence that Markov chain models of the nonlinear, stochastic dynamics of neural membranes can be accurately approximated by SDEs. This finding opens a door to future modeling work using SDE techniques to further illuminate the effects of ion channel fluctuations on electrically active cells.

  7. Coarse-grained event tree analysis for quantifying Hodgkin-Huxley neuronal network dynamics.

    PubMed

    Sun, Yi; Rangan, Aaditya V; Zhou, Douglas; Cai, David

    2012-02-01

    We present an event tree analysis of studying the dynamics of the Hodgkin-Huxley (HH) neuronal networks. Our study relies on a coarse-grained projection to event trees and to the event chains that comprise these trees by using a statistical collection of spatial-temporal sequences of relevant physiological observables (such as sequences of spiking multiple neurons). This projection can retain information about network dynamics that covers multiple features, swiftly and robustly. We demonstrate that for even small differences in inputs, some dynamical regimes of HH networks contain sufficiently higher order statistics as reflected in event chains within the event tree analysis. Therefore, this analysis is effective in discriminating small differences in inputs. Moreover, we use event trees to analyze the results computed from an efficient library-based numerical method proposed in our previous work, where a pre-computed high resolution data library of typical neuronal trajectories during the interval of an action potential (spike) allows us to avoid resolving the spikes in detail. In this way, we can evolve the HH networks using time steps one order of magnitude larger than the typical time steps used for resolving the trajectories without the library, while achieving comparable statistical accuracy in terms of average firing rate and power spectra of voltage traces. Our numerical simulation results show that the library method is efficient in the sense that the results generated by using this numerical method with much larger time steps contain sufficiently high order statistical structure of firing events that are similar to the ones obtained using a regular HH solver. We use our event tree analysis to demonstrate these statistical similarities.

  8. Power-Law Dynamics of Membrane Conductances Increase Spiking Diversity in a Hodgkin-Huxley Model

    PubMed Central

    Teka, Wondimu; Stockton, David; Santamaria, Fidel

    2016-01-01

    We studied the effects of non-Markovian power-law voltage dependent conductances on the generation of action potentials and spiking patterns in a Hodgkin-Huxley model. To implement slow-adapting power-law dynamics of the gating variables of the potassium, n, and sodium, m and h, conductances we used fractional derivatives of order η≤1. The fractional derivatives were used to solve the kinetic equations of each gate. We systematically classified the properties of each gate as a function of η. We then tested if the full model could generate action potentials with the different power-law behaving gates. Finally, we studied the patterns of action potential that emerged in each case. Our results show the model produces a wide range of action potential shapes and spiking patterns in response to constant current stimulation as a function of η. In comparison with the classical model, the action potential shapes for power-law behaving potassium conductance (n gate) showed a longer peak and shallow hyperpolarization; for power-law activation of the sodium conductance (m gate), the action potentials had a sharp rise time; and for power-law inactivation of the sodium conductance (h gate) the spikes had wider peak that for low values of η replicated pituitary- and cardiac-type action potentials. With all physiological parameters fixed a wide range of spiking patterns emerged as a function of the value of the constant input current and η, such as square wave bursting, mixed mode oscillations, and pseudo-plateau potentials. Our analyses show that the intrinsic memory trace of the fractional derivative provides a negative feedback mechanism between the voltage trace and the activity of the power-law behaving gate variable. As a consequence, power-law behaving conductances result in an increase in the number of spiking patterns a neuron can generate and, we propose, expand the computational capacity of the neuron. PMID:26937967

  9. Comparison between Hodgkin-Huxley and Markov formulations of cardiac ion channels.

    PubMed

    Carbonell-Pascual, Beatriz; Godoy, Eduardo; Ferrer, Ana; Romero, Lucia; Ferrero, Jose M

    2016-06-21

    When simulating the macroscopic current flowing through cardiac ion channels, two mathematical formalisms can be adopted: the Hodgkin-Huxley model (HHM) formulation, which describes openings and closings of channel 'gates', or the Markov model (MM) formulation, based on channel 'state' transitions. The latter was first used in 1995 to simulate the effects of mutations in ionic currents and, since then, its use has been extended to wild-type channels also. While the MMs better describe the actual behavior of ion channels, they are mathematically more complex than HHMs in terms of parameter estimation and identifiability and are computationally much more demanding, which can dramatically increase computational time in large-scale (e.g. whole heart) simulations. We hypothesize that a HHM formulation obtained from classical patch-clamp protocols in wild-type and mutant ion channels can be used to correctly simulate cardiac action potentials and their static and dynamic properties. To validate our hypothesis, we selected two pivotal cardiac ionic currents (the rapid delayed rectifier K(+) current, IKr, and the inward Na(+) current, INa) and formulated HHMs for both wild-type and mutant channels (LQT2-linked T474I mutation for IKr and LQT3-linked ΔKPQ mutation for INa). Action potentials were then simulated using the MM and HHM versions of the currents, and the action potential waveforms, biomarkers and action potential duration rate dependence properties were compared in control conditions and in the presence of physiological variability. While small differences between ionic currents were found between the two models (correlation coefficient ρ>0.92), the simulations yielded almost identical action potentials (ρ>0.99), suggesting that HHMs may also be valid to simulate the effects of mutations affecting IKr and INa on the action potential.

  10. Power-Law Dynamics of Membrane Conductances Increase Spiking Diversity in a Hodgkin-Huxley Model.

    PubMed

    Teka, Wondimu; Stockton, David; Santamaria, Fidel

    2016-03-01

    We studied the effects of non-Markovian power-law voltage dependent conductances on the generation of action potentials and spiking patterns in a Hodgkin-Huxley model. To implement slow-adapting power-law dynamics of the gating variables of the potassium, n, and sodium, m and h, conductances we used fractional derivatives of order η≤1. The fractional derivatives were used to solve the kinetic equations of each gate. We systematically classified the properties of each gate as a function of η. We then tested if the full model could generate action potentials with the different power-law behaving gates. Finally, we studied the patterns of action potential that emerged in each case. Our results show the model produces a wide range of action potential shapes and spiking patterns in response to constant current stimulation as a function of η. In comparison with the classical model, the action potential shapes for power-law behaving potassium conductance (n gate) showed a longer peak and shallow hyperpolarization; for power-law activation of the sodium conductance (m gate), the action potentials had a sharp rise time; and for power-law inactivation of the sodium conductance (h gate) the spikes had wider peak that for low values of η replicated pituitary- and cardiac-type action potentials. With all physiological parameters fixed a wide range of spiking patterns emerged as a function of the value of the constant input current and η, such as square wave bursting, mixed mode oscillations, and pseudo-plateau potentials. Our analyses show that the intrinsic memory trace of the fractional derivative provides a negative feedback mechanism between the voltage trace and the activity of the power-law behaving gate variable. As a consequence, power-law behaving conductances result in an increase in the number of spiking patterns a neuron can generate and, we propose, expand the computational capacity of the neuron.

  11. Library-based numerical reduction of the Hodgkin-Huxley neuron for network simulation.

    PubMed

    Sun, Yi; Zhou, Douglas; Rangan, Aaditya V; Cai, David

    2009-12-01

    We present an efficient library-based numerical method for simulating the Hodgkin-Huxley (HH) neuronal networks. The key components in our numerical method involve (i) a pre-computed high resolution data library which contains typical neuronal trajectories (i.e., the time-courses of membrane potential and gating variables) during the interval of an action potential (spike), thus allowing us to avoid resolving the spikes in detail and to use large numerical time steps for evolving the HH neuron equations; (ii) an algorithm of spike-spike corrections within the groups of strongly coupled neurons to account for spike-spike interactions in a single large time step. By using the library method, we can evolve the HH networks using time steps one order of magnitude larger than the typical time steps used for resolving the trajectories without the library, while achieving comparable resolution in statistical quantifications of the network activity, such as average firing rate, interspike interval distribution, power spectra of voltage traces. Moreover, our large time steps using the library method can break the stability requirement of standard methods (such as Runge-Kutta (RK) methods) for the original dynamics. We compare our library-based method with RK methods, and find that our method can capture very well phase-locked, synchronous, and chaotic dynamics of HH neuronal networks. It is important to point out that, in essence, our library-based HH neuron solver can be viewed as a numerical reduction of the HH neuron to an integrate-and-fire (I&F) neuronal representation that does not sacrifice the gating dynamics (as normally done in the analytical reduction to an I&F neuron).

  12. Stochastic differential equation models for ion channel noise in Hodgkin-Huxley neurons

    NASA Astrophysics Data System (ADS)

    Goldwyn, Joshua H.; Imennov, Nikita S.; Famulare, Michael; Shea-Brown, Eric

    2011-04-01

    The random transitions of ion channels between conducting and nonconducting states generate a source of internal fluctuations in a neuron, known as channel noise. The standard method for modeling the states of ion channels nonlinearly couples continuous-time Markov chains to a differential equation for voltage. Beginning with the work of R. F. Fox and Y.-N. Lu [Phys. Rev. EMTHDE91539-375510.1103/PhysRevE.49.3421 49, 3421 (1994)], there have been attempts to generate simpler models that use stochastic differential equation (SDEs) to approximate the stochastic spiking activity produced by Markov chain models. Recent numerical investigations, however, have raised doubts that SDE models can capture the stochastic dynamics of Markov chain models.We analyze three SDE models that have been proposed as approximations to the Markov chain model: one that describes the states of the ion channels and two that describe the states of the ion channel subunits. We show that the former channel-based approach can capture the distribution of channel noise and its effects on spiking in a Hodgkin-Huxley neuron model to a degree not previously demonstrated, but the latter two subunit-based approaches cannot. Our analysis provides intuitive and mathematical explanations for why this is the case. The temporal correlation in the channel noise is determined by the combinatorics of bundling subunits into channels, but the subunit-based approaches do not correctly account for this structure. Our study confirms and elucidates the findings of previous numerical investigations of subunit-based SDE models. Moreover, it presents evidence that Markov chain models of the nonlinear, stochastic dynamics of neural membranes can be accurately approximated by SDEs. This finding opens a door to future modeling work using SDE techniques to further illuminate the effects of ion channel fluctuations on electrically active cells.

  13. A nonlinear autoregressive Volterra model of the Hodgkin-Huxley equations.

    PubMed

    Eikenberry, Steffen E; Marmarelis, Vasilis Z

    2013-02-01

    We propose a new variant of Volterra-type model with a nonlinear auto-regressive (NAR) component that is a suitable framework for describing the process of AP generation by the neuron membrane potential, and we apply it to input-output data generated by the Hodgkin-Huxley (H-H) equations. Volterra models use a functional series expansion to describe the input-output relation for most nonlinear dynamic systems, and are applicable to a wide range of physiologic systems. It is difficult, however, to apply the Volterra methodology to the H-H model because is characterized by distinct subthreshold and suprathreshold dynamics. When threshold is crossed, an autonomous action potential (AP) is generated, the output becomes temporarily decoupled from the input, and the standard Volterra model fails. Therefore, in our framework, whenever membrane potential exceeds some threshold, it is taken as a second input to a dual-input Volterra model. This model correctly predicts membrane voltage deflection both within the subthreshold region and during APs. Moreover, the model naturally generates a post-AP afterpotential and refractory period. It is known that the H-H model converges to a limit cycle in response to a constant current injection. This behavior is correctly predicted by the proposed model, while the standard Volterra model is incapable of generating such limit cycle behavior. The inclusion of cross-kernels, which describe the nonlinear interactions between the exogenous and autoregressive inputs, is found to be absolutely necessary. The proposed model is general, non-parametric, and data-derived.

  14. Medicines in the correspondence of the Mozart family.

    PubMed

    Nieznanowska, J

    2001-12-01

    The most famous members of the Mozart family were musicians - not physicians. In spite of that, the family correspondence of the Mozarts contains much noteworthy information on 18th century medicine. It comes mainly from Leopold, the famous composer's father, which is why the vast majority of the medical data presented in the letters cannot be found in the popular editions of the correspondence. One of the medicine-related subjects usually omitted or presented briefly in such editions concerns the medicaments used in the Mozart family. Out of more than 100 remedies mentioned in the correspondence the article's author chose and described a few that seem to have played a particularly significant role in the life of the Mozart family.

  15. From Numbers to Letters: Feedback Regularization in Visual Word Recognition

    ERIC Educational Resources Information Center

    Molinaro, Nicola; Dunabeitia, Jon Andoni; Marin-Gutierrez, Alejandro; Carreiras, Manuel

    2010-01-01

    Word reading in alphabetic languages involves letter identification, independently of the format in which these letters are written. This process of letter "regularization" is sensitive to word context, leading to the recognition of a word even when numbers that resemble letters are inserted among other real letters (e.g., M4TERI4L). The present…

  16. From Numbers to Letters: Feedback Regularization in Visual Word Recognition

    ERIC Educational Resources Information Center

    Molinaro, Nicola; Dunabeitia, Jon Andoni; Marin-Gutierrez, Alejandro; Carreiras, Manuel

    2010-01-01

    Word reading in alphabetic languages involves letter identification, independently of the format in which these letters are written. This process of letter "regularization" is sensitive to word context, leading to the recognition of a word even when numbers that resemble letters are inserted among other real letters (e.g., M4TERI4L). The present…

  17. 48 CFR 2416.603 - Letter contracts.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 48 Federal Acquisition Regulations System 6 2010-10-01 2010-10-01 true Letter contracts. 2416.603 Section 2416.603 Federal Acquisition Regulations System DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT CONTRACTING METHODS AND CONTRACTING TYPES TYPES OF CONTRACTS Time-And-Materials, Labor-Hour, and Letter...

  18. Linguistic Prescriptivism in Letters to the Editor

    ERIC Educational Resources Information Center

    Lukac, Morana

    2016-01-01

    The public's concern with the fate of the standard language has been well documented in the history of the complaint tradition. The print media have for centuries featured letters to the editor on questions of language use. This study examines a corpus of 258 language-related letters to the editor published in the English-speaking print media. By…

  19. Developing a Standardized Letter of Recommendation

    ERIC Educational Resources Information Center

    Walters, Alyssa M.; Kyllonen, Patrick C.; Plante, Janice W.

    2006-01-01

    The Standardized Letter of Recommendation (SLR) is a Web-based admission tool designed to replace traditional, narrative letters of recommendation with a more systematic and equitable source of information about applicants to institutions of higher education. The SLR includes a rating scale and open-ended response space that prompt evaluators to…

  20. 48 CFR 18.112 - Letter contracts.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 48 Federal Acquisition Regulations System 1 2011-10-01 2011-10-01 false Letter contracts. 18.112 Section 18.112 Federal Acquisition Regulations System FEDERAL ACQUISITION REGULATION CONTRACTING METHODS AND CONTRACT TYPES EMERGENCY ACQUISITIONS Available Acquisition Flexibilities 18.112 Letter contracts...

  1. 48 CFR 16.603 - Letter contracts.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 48 Federal Acquisition Regulations System 1 2011-10-01 2011-10-01 false Letter contracts. 16.603 Section 16.603 Federal Acquisition Regulations System FEDERAL ACQUISITION REGULATION CONTRACTING METHODS AND CONTRACT TYPES TYPES OF CONTRACTS Time-and-Materials, Labor-Hour, and Letter Contracts 16.603...

  2. Statistical Learning, Letter Reversals, and Reading

    ERIC Educational Resources Information Center

    Treiman, Rebecca; Gordon, Jessica; Boada, Richard; Peterson, Robin L.; Pennington, Bruce F.

    2014-01-01

    Reversal errors play a prominent role in theories of reading disability. We examined reversal errors in the writing of letters by 5- to 6-year-old children. Of the 130 children, 92 had a history of difficulty in producing speech sounds, a risk factor for reading problems. Children were more likely to reverse letter forms that face left, such as…

  3. Cognitive Determinants of Early Letter Knowledge

    ERIC Educational Resources Information Center

    Helal, Suha; Weil-Barais, Annick

    2015-01-01

    The present study investigated the general cognitive determinants of alphabetic letter knowledge. It involved 60 French kindergarten children (mean age: five years six months). Two test batteries were used: the CMS to evaluate general cognitive abilities (memory, attention, and learning), and the LKT to assess letter knowledge and its various…

  4. 17 CFR 38.711 - Warning letters.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 17 Commodity and Securities Exchanges 1 2014-04-01 2014-04-01 false Warning letters. 38.711 Section 38.711 Commodity and Securities Exchanges COMMODITY FUTURES TRADING COMMISSION DESIGNATED CONTRACT MARKETS Disciplinary Procedures § 38.711 Warning letters. Where a rule violation is found to have occurred...

  5. 17 CFR 38.711 - Warning letters.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 17 Commodity and Securities Exchanges 1 2013-04-01 2013-04-01 false Warning letters. 38.711 Section 38.711 Commodity and Securities Exchanges COMMODITY FUTURES TRADING COMMISSION DESIGNATED CONTRACT MARKETS Disciplinary Procedures § 38.711 Warning letters. Where a rule violation is found to have occurred...

  6. Genre Analysis of Business Letters of Negotiation.

    ERIC Educational Resources Information Center

    dos Santos, V. B. M. Pinto

    2002-01-01

    Reports findings of a survey on genre analysis of 117 commercial letters in English exchanged by fax between a Brazilian company and two European companies. The letters were analyzed in terms of shared communicative purposes and rhetorical features that together contribute to the building-up of the resulting generic structure named "Business…

  7. An Open Letter to Premier Wen Jiabao

    ERIC Educational Resources Information Center

    Chinese Education and Society, 2008

    2008-01-01

    This article is an open letter of a group of early childhood education (ECE) practitioners to Premier Wen Jiabao. This open letter was written with one goal in mind: to ask Premier Wen's government to take measures to protect young children and support early childhood education. These practitioners have become worried about the many accidents that…

  8. Cognitive Determinants of Early Letter Knowledge

    ERIC Educational Resources Information Center

    Helal, Suha; Weil-Barais, Annick

    2015-01-01

    The present study investigated the general cognitive determinants of alphabetic letter knowledge. It involved 60 French kindergarten children (mean age: five years six months). Two test batteries were used: the CMS to evaluate general cognitive abilities (memory, attention, and learning), and the LKT to assess letter knowledge and its various…

  9. Letter-Sound Relationships of Phonic Cells.

    ERIC Educational Resources Information Center

    Gates, Louis

    Using 17, 211 words drawn from the word list compiled for the Stanford Spelling Study (1963) and drawing upon the "American Heritage Dictionary of the American Language" as the pronunciation reference, a researcher approached the language as if little was known about its letter-sound relationships and examined by computer the letter-sound…

  10. Letters in Time and Retinotopic Space

    ERIC Educational Resources Information Center

    Adelman, James S.

    2011-01-01

    Various phenomena in tachistoscopic word identification and priming (WRODS and LTRS are confused with and prime WORDS and LETTERS) suggest that position-specific channels are not used in the processing of letters in words. Previous approaches to this issue have sought alternative matching rules because they have assumed that these phenomena reveal…

  11. Essay: the origin of physical review letters.

    PubMed

    Trigg, George L

    2008-11-21

    When Sam Goudsmit, then Editor of Physical Review, decided to publish the Letters separately, he asked me to become Assistant Editor of the new journal. I wound up staying at PRL for a quarter of a century. I describe some of the new techniques we developed to speed up review and production so that Letters could be quickly published.

  12. Letter to, and Paintings by, George Catlin

    ERIC Educational Resources Information Center

    Rosenbaum, David; Potter, Lee Ann; Eder, Elizabeth K.

    2008-01-01

    Letters received and sent by Secretary of War Lewis Cass in the 1830s reveal much about relations between the U.S. government and Native Americans. In the immediate aftermath of the Indian Removal Act, signed into law on May 28, 1830, by President Andrew Jackson, some letters came from interpreters and school teachers seeking payment for their…

  13. An Open Letter to Tomorrow's Secondary Teachers

    ERIC Educational Resources Information Center

    Worthy, Jeff

    2016-01-01

    The article takes the form of a letter written to pre-service or beginning teachers at the secondary level in the public school system. The letter acknowledges the attributes they bring to the profession (enthusiasm, optimism, creativity, and open-mindedness) and calls on them to make the most of and work to sustain these traits as they begin…

  14. Individualized Instruction and the Letter Grade System.

    ERIC Educational Resources Information Center

    Leuba, Richard J.

    The relationship between individualized instruction (II) and letter grades is an issue of considerable debate. Ultimately, II and the letter grade system are incompatible. Grading has been a traditional form for ranking or comparing students with respect to performance criteria. The scale typically has been A to F, whereas with individualized…

  15. An Open Letter to Tomorrow's Secondary Teachers

    ERIC Educational Resources Information Center

    Worthy, Jeff

    2016-01-01

    The article takes the form of a letter written to pre-service or beginning teachers at the secondary level in the public school system. The letter acknowledges the attributes they bring to the profession (enthusiasm, optimism, creativity, and open-mindedness) and calls on them to make the most of and work to sustain these traits as they begin…

  16. 48 CFR 18.112 - Letter contracts.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 48 Federal Acquisition Regulations System 1 2014-10-01 2014-10-01 false Letter contracts. 18.112 Section 18.112 Federal Acquisition Regulations System FEDERAL ACQUISITION REGULATION CONTRACTING METHODS AND CONTRACT TYPES EMERGENCY ACQUISITIONS Available Acquisition Flexibilities 18.112 Letter...

  17. 48 CFR 18.112 - Letter contracts.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 48 Federal Acquisition Regulations System 1 2013-10-01 2013-10-01 false Letter contracts. 18.112 Section 18.112 Federal Acquisition Regulations System FEDERAL ACQUISITION REGULATION CONTRACTING METHODS AND CONTRACT TYPES EMERGENCY ACQUISITIONS Available Acquisition Flexibilities 18.112 Letter...

  18. 48 CFR 18.112 - Letter contracts.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 48 Federal Acquisition Regulations System 1 2010-10-01 2010-10-01 false Letter contracts. 18.112 Section 18.112 Federal Acquisition Regulations System FEDERAL ACQUISITION REGULATION CONTRACTING METHODS AND CONTRACT TYPES EMERGENCY ACQUISITIONS Available Acquisition Flexibilities 18.112 Letter...

  19. 48 CFR 18.112 - Letter contracts.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 48 Federal Acquisition Regulations System 1 2012-10-01 2012-10-01 false Letter contracts. 18.112 Section 18.112 Federal Acquisition Regulations System FEDERAL ACQUISITION REGULATION CONTRACTING METHODS AND CONTRACT TYPES EMERGENCY ACQUISITIONS Available Acquisition Flexibilities 18.112 Letter...

  20. Letters in Time and Retinotopic Space

    ERIC Educational Resources Information Center

    Adelman, James S.

    2011-01-01

    Various phenomena in tachistoscopic word identification and priming (WRODS and LTRS are confused with and prime WORDS and LETTERS) suggest that position-specific channels are not used in the processing of letters in words. Previous approaches to this issue have sought alternative matching rules because they have assumed that these phenomena reveal…

  1. Letters to the Editor: What Is Stuttering?

    ERIC Educational Resources Information Center

    Yairi, Ehud; Watkins, Ruth; Ambrose, Nicoline; Paden, Elaine

    2001-01-01

    The authors of a research report (1999) on the diagnosis of stuttering in young children respond to a critical letter by questioning the accuracy, validity, credibility, and internal consistency of the letter writer's criticisms. The reply goes on to clarify the evaluation of stuttering-like disfluencies and single-syllable word repetitions in…

  2. 46 CFR 170.120 - Stability letter.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 7 2010-10-01 2010-10-01 false Stability letter. 170.120 Section 170.120 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) SUBDIVISION AND STABILITY STABILITY REQUIREMENTS FOR ALL INSPECTED VESSELS Stability Instructions for Operating Personnel § 170.120 Stability letter. (a...

  3. 46 CFR 170.120 - Stability letter.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 7 2012-10-01 2012-10-01 false Stability letter. 170.120 Section 170.120 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) SUBDIVISION AND STABILITY STABILITY REQUIREMENTS FOR ALL INSPECTED VESSELS Stability Instructions for Operating Personnel § 170.120 Stability letter. (a...

  4. 46 CFR 170.120 - Stability letter.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 7 2014-10-01 2014-10-01 false Stability letter. 170.120 Section 170.120 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) SUBDIVISION AND STABILITY STABILITY REQUIREMENTS FOR ALL INSPECTED VESSELS Stability Instructions for Operating Personnel § 170.120 Stability letter. (a...

  5. 46 CFR 170.120 - Stability letter.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 7 2013-10-01 2013-10-01 false Stability letter. 170.120 Section 170.120 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) SUBDIVISION AND STABILITY STABILITY REQUIREMENTS FOR ALL INSPECTED VESSELS Stability Instructions for Operating Personnel § 170.120 Stability letter. (a...

  6. 46 CFR 170.120 - Stability letter.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 7 2011-10-01 2011-10-01 false Stability letter. 170.120 Section 170.120 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) SUBDIVISION AND STABILITY STABILITY REQUIREMENTS FOR ALL INSPECTED VESSELS Stability Instructions for Operating Personnel § 170.120 Stability letter. (a...

  7. Letter to, and Paintings by, George Catlin

    ERIC Educational Resources Information Center

    Rosenbaum, David; Potter, Lee Ann; Eder, Elizabeth K.

    2008-01-01

    Letters received and sent by Secretary of War Lewis Cass in the 1830s reveal much about relations between the U.S. government and Native Americans. In the immediate aftermath of the Indian Removal Act, signed into law on May 28, 1830, by President Andrew Jackson, some letters came from interpreters and school teachers seeking payment for their…

  8. An Open Letter to Premier Wen Jiabao

    ERIC Educational Resources Information Center

    Chinese Education and Society, 2008

    2008-01-01

    This article is an open letter of a group of early childhood education (ECE) practitioners to Premier Wen Jiabao. This open letter was written with one goal in mind: to ask Premier Wen's government to take measures to protect young children and support early childhood education. These practitioners have become worried about the many accidents that…

  9. Linguistic Prescriptivism in Letters to the Editor

    ERIC Educational Resources Information Center

    Lukac, Morana

    2016-01-01

    The public's concern with the fate of the standard language has been well documented in the history of the complaint tradition. The print media have for centuries featured letters to the editor on questions of language use. This study examines a corpus of 258 language-related letters to the editor published in the English-speaking print media. By…

  10. Genre Analysis of Business Letters of Negotiation.

    ERIC Educational Resources Information Center

    dos Santos, V. B. M. Pinto

    2002-01-01

    Reports findings of a survey on genre analysis of 117 commercial letters in English exchanged by fax between a Brazilian company and two European companies. The letters were analyzed in terms of shared communicative purposes and rhetorical features that together contribute to the building-up of the resulting generic structure named "Business…

  11. The Case of the Purloined Letter.

    ERIC Educational Resources Information Center

    Zirkel, Perry A.

    2003-01-01

    Analyzes Arkansas case wherein the Eighth Circuit held 6-5 that letter written by seventh-grade student threatening violence against his former girl friend was not protected by the First Amendment even though a friend took the letter from student's home without his knowledge and gave it to the girl. Upheld board's decision to expel student.…

  12. Samuel Hartlib on the death of Descartes: a rediscovered letter to Henry More

    PubMed Central

    Penman, Leigh T. I.

    2015-01-01

    This paper discloses the content of a previously overlooked epistle by the Anglo-Prussian intelligencer Samuel Hartlib to Henry More concerning the death of René Descartes. After a discussion situating the letter within the sequence of the More–Hartlib correspondence, an analysis of the rhetorical structure of the epistle is offered, followed by a brief assessment of Hartlib's attitude towards Descartes, and the identification of his source concerning the news of the philosopher's death. An account of the transmission of the letter via a nineteenth-century periodical is also provided. The text of Hartlib's letter and an overlooked passage of Hartlib's diary concerning Descartes's death, which draws on the content of the More letter, are presented as appendixes.

  13. Evolutionary theory in letters to the editor.

    PubMed

    Silva, Eric Orion; Lowe, Clayton Cory

    2015-05-01

    This research note presents the results of a content analysis of 234 letters to the editors that discuss evolutionary theory and were published in American newspapers. We find that letters to the editor both support and hinder the cause of teaching evolutionary theory in American secondary schools. On the one hand, anti-evolutionary theory messages are marginalized in the letters section. This marginalization signals a low level of legitimacy for creationism. It might also contribute to the sense of tension that sustains creationist identities. On the other hand, relatively few letters explicitly note the fact that scientists or the scientific community accept evolution. Interestingly, the obscuration of the scientific community's support for evolutionary theory occurs both in letters supporting and opposing evolutionary theory.

  14. Letter perception: from pixels to pandemonium.

    PubMed

    Grainger, Jonathan; Rey, Arnaud; Dufau, Stéphane

    2008-10-01

    In 1959, Oliver Selfridge proposed a model of letter perception, the Pandemonium model, in which the central hypothesis was that letters are identified via their component features. Although a consensus developed around this general approach over the years, key evidence in its favor remained lacking. Recent research has started to provide important evidence in favor of feature-based letter perception, describing the nature of the features, and the time-course of processes involved in mapping features onto abstract letter identities. There is now hope that future 'pandemonium-like' models will be able to account for the rich empirical database on letter identification that has accumulated over the past 50 years, hence solving one key component of the reading process.

  15. Letter identification and the neural image classifier.

    PubMed

    Watson, Andrew B; Ahumada, Albert J

    2015-02-12

    Letter identification is an important visual task for both practical and theoretical reasons. To extend and test existing models, we have reviewed published data for contrast sensitivity for letter identification as a function of size and have also collected new data. Contrast sensitivity increases rapidly from the acuity limit but slows and asymptotes at a symbol size of about 1 degree. We recast these data in terms of contrast difference energy: the average of the squared distances between the letter images and the average letter image. In terms of sensitivity to contrast difference energy, and thus visual efficiency, there is a peak around ¼ degree, followed by a marked decline at larger sizes. These results are explained by a Neural Image Classifier model that includes optical filtering and retinal neural filtering, sampling, and noise, followed by an optimal classifier. As letters are enlarged, sensitivity declines because of the increasing size and spacing of the midget retinal ganglion cell receptive fields in the periphery.

  16. [The professor and his student. The correspondence between Lorenz Heister and Christoph Jacob Trew].

    PubMed

    Ruisinger, Marion Maria; Schnalke, Thomas

    2004-01-01

    Letters were the central medium of communication in the medical scientific community of the 18th century. Professional as well as personal relationships were established among the various correspondents. These relationships constituted the smallest units of communication which contributed to the regional and international scientific network of the Republic of Letters. A correspondence that grew out of a trusted teacher-student relationship could gain an especially intense character both intellectually and personally. This contribution offers an analysis of an example of just such a correspondence. Lorenz Heister (1683--1758), medical professor at the universities of Altdorf and Helmstedt, and his disciple, Christoph Jacob Trew (1695--1769), who became a renowned physician and natural scientist in Nuremberg, communicated in letters to one another over a span of almost forty years. Their correspondence started as a rather asymmetrical dialogue. Over time, however, Heister and Trew came to meet as equals in almost every field of their competence. Their letters reveal a broad spectrum of scientific, organisational, professional, medical and personal issues which formed the basis of a stable and lasting learned correspondence in the age of Enlightenment.

  17. Quantum Painleve-Calogero correspondence

    SciTech Connect

    Zabrodin, A.; Zotov, A.

    2012-07-15

    The Painleve-Calogero correspondence is extended to auxiliary linear problems associated with Painleve equations. The linear problems are represented in a new form which has a suggestive interpretation as a 'quantized' version of the Painleve-Calogero correspondence. Namely, the linear problem responsible for the time evolution is brought into the form of non-stationary Schroedinger equation in imaginary time, {partial_derivative}{sub t}{psi}=((1/2) {partial_derivative}{sub x}{sup 2}+V(x,t)){psi}, whose Hamiltonian is a natural quantization of the classical Calogero-like Hamiltonian H=(1/2) p{sup 2}+V(x,t) for the corresponding Painleve equation. In present paper, we present explicit constructions for the first five equations from the Painleve list.

  18. Three Dimensional Tropical Correspondence Formula

    NASA Astrophysics Data System (ADS)

    Parker, Brett

    2017-07-01

    A tropical curve in R3 contributes to Gromov-Witten invariants in all genus. Nevertheless, we present a simple formula for how a given tropical curve contributes to Gromov-Witten invariants when we encode these invariants in a generating function with exponents of {λ} recording Euler characteristic. Our main modification from the known tropical correspondence formula for rational curves is as follows: a trivalent vertex, which before contributed a factor of n to the count of zero-genus holomorphic curves, contributes a factor of {2sin(nλ/2)}. We explain how to calculate relative Gromov-Witten invariants using this tropical correspondence formula, and how to obtain the absolute Gromov-Witten and Donaldson-Thomas invariants of some 3-dimensional toric manifolds including {CP3}. The tropical correspondence formula counting Donaldson-Thomas invariants replaces n by {i^{-(1+n)}q^{n/2}+i^{1+n}q^{-n/2}}.

  19. The effect of letter string length and report condition on letter recognition accuracy.

    PubMed

    Raghunandan, Avesh; Karmazinaite, Berta; Rossow, Andrea S

    Letter sequence recognition accuracy has been postulated to be limited primarily by low-level visual factors. The influence of high level factors such as visual memory (load and decay) has been largely overlooked. This study provides insight into the role of these factors by investigating the interaction between letter sequence recognition accuracy, letter string length and report condition. Letter sequence recognition accuracy for trigrams and pentagrams were measured in 10 adult subjects for two report conditions. In the complete report condition subjects reported all 3 or all 5 letters comprising trigrams and pentagrams, respectively. In the partial report condition, subjects reported only a single letter in the trigram or pentagram. Letters were presented for 100ms and rendered in high contrast, using black lowercase Courier font that subtended 0.4° at the fixation distance of 0.57m. Letter sequence recognition accuracy was consistently higher for trigrams compared to pentagrams especially for letter positions away from fixation. While partial report increased recognition accuracy in both string length conditions, the effect was larger for pentagrams, and most evident for the final letter positions within trigrams and pentagrams. The effect of partial report on recognition accuracy for the final letter positions increased as eccentricity increased away from fixation, and was independent of the inner/outer position of a letter. Higher-level visual memory functions (memory load and decay) play a role in letter sequence recognition accuracy. There is also suggestion of additional delays imposed on memory encoding by crowded letter elements. Copyright © 2016 Spanish General Council of Optometry. Published by Elsevier España, S.L.U. All rights reserved.

  20. Liouville Correspondences between Integrable Hierarchies

    NASA Astrophysics Data System (ADS)

    Kang, Jing; Liu, Xiaochuan; Olver, Peter J.; Qu, Changzheng

    2017-05-01

    In this paper, we study explicit correspondences between the integrable Novikov and Sawada-Kotera hierarchies, and between the Degasperis-Procesi and Kaup-Kupershmidt hierarchies. We show how a pair of Liouville transformations between the isospectral problems of the Novikov and Sawada-Kotera equations, and the isospectral problems of the Degasperis-Procesi and Kaup-Kupershmidt equations relate the corresponding hierarchies, in both positive and negative directions, as well as their associated conservation laws. Combining these results with the Miura transformation relating the Sawada-Kotera and Kaup-Kupershmidt equations, we further construct an implicit relationship which associates the Novikov and Degasperis-Procesi equations.