Random Photon Absorption Model Elucidates How Early Gain Control in Fly Photoreceptors Arises from Quantal Sampling

Many diurnal photoreceptors encode vast real-world light changes effectively, but how this performance originates from photon sampling is unclear. A 4-module biophysically-realistic fly photoreceptor model, in which information capture is limited by the number of its sampling units (microvilli) and their photon-hit recovery time (refractoriness), can accurately simulate real recordings and their information content. However, sublinear summation in quantum bump production (quantum-gain-nonlinearity) may also cause adaptation by reducing the bump/photon gain when multiple photons hit the same microvillus simultaneously. Here, we use a Random Photon Absorption Model (RandPAM), which is the 1st module of the 4-module fly photoreceptor model, to quantify the contribution of quantum-gain-nonlinearity in light adaptation. We show how quantum-gain-nonlinearity already results from photon sampling alone. In the extreme case, when two or more simultaneous photon-hits reduce to a single sublinear value, quantum-gain-nonlinearity is preset before the phototransduction reactions adapt the quantum bump waveform. However, the contribution of quantum-gain-nonlinearity in light adaptation depends upon the likelihood of multi-photon-hits, which is strictly determined by the number of microvilli and light intensity. Specifically, its contribution to light-adaptation is marginal (≤1%) in fly photoreceptors with many thousands of microvilli, because the probability of simultaneous multi-photon-hits on any one microvillus is low even during daylight conditions. However, in cells with fewer sampling units, the impact of quantum-gain-nonlinearity increases with brightening light

Modeling elucidates how refractory period can provide profound nonlinear gain control to graded potential neurons

Refractory period (RP) plays a central role in neural signaling. Because it limits an excitable membrane's recovery time from a previous excitation, it can restrict information transmission. Classically, RP means the recovery time from an action potential (spike), and its impact to encoding has been mostly studied in spiking neurons. However, many sensory neurons do not communicate with spikes but convey information by graded potential changes. In these systems, RP can arise as an intrinsic property of their quantal micro/nanodomain sampling events, as recently revealed for quantum bumps (single photon responses) in microvillar photoreceptors. Whilst RP is directly unobservable and hard to measure, masked by the graded macroscopic response that integrates numerous quantal events, modeling can uncover its role in encoding. Here, we investigate computationally how RP can affect encoding of graded neural responses. Simulations in a simple stochastic process model for a fly photoreceptor elucidate how RP can profoundly contribute to nonlinear gain control to achieve a large dynamic range. [Abstract copyright: © 2017 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.

Phonology

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Yksityisen elinkeinonharjoittajan riskienhallinta

Tämän opinnäytetyön tarkoituksena oli selvittää yksityisen elinkeinonharjoittajan riskejä ja kehittää kohdeyrityksen riskienhallintaa. Asiaa käsiteltiin Tmi Arirent -nimisen yksityisen elinkeinonharjoittajan näkökulmasta. Opinnäytetyöprosessin aikana luotiin myös riskienhallintatyökalu, jonka avulla riskienhallinta on dokumentoitua ja järjestelmällistä. Opinnäytetyön kokonaistavoitteena oli siis luoda riittävän yksinkertainen, mutta toimiva malli yksityisen elinkeinonharjoittajan riskienhallintaan. Teoreettisessä viitekehyksessä käytettiin lähteenä alan kirjallisuutta, riskienhallintastandardeja ja luotettaviksi arvioituja verkkolähteitä. Riskienhallintatyökalun rakenne perustuu SFS ISO 31000 standardin riskienhallintamalliin. Opinnäytetyön keskeisimmät käsitteet olivat yksityinen elinkeinonharjoittaja, riskit ja niiden luokittelu sekä riskienhallinta. Kyseiset käsitteet loivat kehyksen koko opinnäytetyölle. Kohdeyrityksen perustietoja ja riskienhallinnan nykytilaa selvitettiin teemahaastattelun avulla. Tämän jälkeen tehtiin riskianalyysi työpaja-tyylisissä aivoriihitapaamisissa ja samalla selvitettiin myös kohdeyrityksen riskienhallinnan tavoitetila ja keinot sen saavuttamiseksi. Riskienhallintatyökalun alustava versio annettiin koekäyttöön ja testattavaksi potentiaalisille tuleville käyttäjille. Heiltä saatujen palautteiden perusteella työkalu muokattiin lopulliseen muotoonsa. Yksityisen elinkeinonharjoittajan keskeisimmiksi ja kriittisimmiksi riskeiksi nousivat henkilöriskit ja kalustoriskit. Yrittäjän työkyky ja kaluston kunnossa pysyminen ovat elinehto yksityisyrittäjän liiketoiminnassa. Toteutuessaan riskit voivat aiheuttaa suuria taloudellisia tappioita ja heikentää yrityksen mainetta, ja pahimmassa tapauksessa johtavat jopa liiketoiminnan lopettamiseen. Opinnäytetyöprosessissa luodun riskienhallintatyökalun avulla yrityksen riskienhallinta on hallittua, järjestelmällistä ja dokumentoitua. Työkalun tuomat hyödyt eivät rajoitu pelkästään yrityksen oman liiketoiminnan jatkuvuuden hallintaan, sillä riskienhallintatyökalun käyttämisestä saattaa olla etua myös esimerkiksi yrityskauppatilanteissa tai rahoitus- ja vakuutusneuvotteluissa. Jatkossa olisi mielenkiintoista selvittää, päteekö tämän opinnäytetyön tulokset myös muiden yksityisyrittäjien kohdalla. Lisäksi riskienhallintatyökalua voisi testata eri kokoisilla yrityksillä.The purpose of this thesis was to investigate the risks of a sole trader and to develop the risk management of the target company. The issue was discussed from the perspective of a single proprietor named Arirent. During the thesis process, a risk management tool was also created, which enables risk management to be documented and systematic. The overall aim of the Master´s Thesis was to create a sufficiently simple but functional model for the sole trader's risk management. The theoretical framework consisted of literature, risk management standards and reliable online sources. The risk management tool is based on the SFS ISO 31000 standard risk management model. The key concepts of the thesis were the sole trader, the risks and their classification and risk management. These concepts created a framework for the whole thesis. The basic information of the target company and the current state of risk management were clarified by means of theme interviews. Thereafter, a risk analysis was carried out in workshop-style brainstorming sessions, and at the same time the target company's risk management target mode and the means to achieve it were investigated. The preliminary version of the risk management tool was given for trial use and tested for potential future users. Based on their feedback, the tool was edited into its final shape. The most important and most critical risks to the sole trader were personal risks and equipment risks. The ability of an entrepreneur to work and keep the stock fit is a lifeline in a private entrepreneur's business. When implemented, the risks can lead to large financial losses and weaken the company's reputation, and in the worst case, even lead to business closures. The risk management tool created in the thesis process enables enterprise risk management to be managed, systematized and documented. The benefits of the tool are not limited to controlling the company's own business continuity, as the use of a risk management tool may also benefit, for example, from acquisitions or financial and insurance negotiations. In the future, it would be interesting to find out whether the results of this thesis also apply to other private entrepreneurs. In addition, the risk management tool could be tested by companies of different sizes

Conclusions

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Morphology

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Notes on the Aramaic Sections of Havdalah de-Rabbi Aqiba

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Introduction

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Bibliography

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