755 research outputs found
Minority odors get equal say
The olfactory system becomes more sensitive when odor inputs are weak, and less sensitive when confronted with strong odors
Kinetic measurement of ribosome motor stalling force
We measure the ribosome motor stalling forces to unzip mRNA polymers during gene expression. An approach of using the changes in the reaction rate constants to determine the molecular motor forces is presented. Specific antisense DNA oligomers complementary to mRNA templates are used as kinetic barriers for estimating the ribosome forces using real time bioluminescence detection of luciferase gene expression. The rate constants are determined by comparing the experimental data with numerical simulation of gene expression to deduce the ribosome force (26.5Β±1 pN) required to unzip mRNA polymers. Understanding the forces generated by the ribosome may also enable the construction of information-based artificial nanoscale machines
SpikingLab: modelling agents controlled by Spiking Neural Networks in Netlogo
The scientific interest attracted by Spiking Neural Networks (SNN) has lead to the development of tools for the simulation and study of neuronal dynamics ranging from phenomenological models to the more sophisticated and biologically accurate Hodgkin-and-Huxley-based and multi-compartmental models. However, despite the multiple features offered by neural modelling tools, their integration with environments for the simulation of robots and agents can be challenging and time consuming. The implementation of artificial neural circuits to control robots generally involves the following tasks: (1) understanding the simulation tools, (2) creating the neural circuit in the neural simulator, (3) linking the simulated neural circuit with the environment of the agent and (4) programming the appropriate interface in the robot or agent to use the neural controller. The accomplishment of the above-mentioned tasks can be challenging, especially for undergraduate students or novice researchers. This paper presents an alternative tool which facilitates the simulation of simple SNN circuits using the multi-agent simulation and the programming environment Netlogo (educational software that simplifies the study and experimentation of complex systems). The engine proposed and implemented in Netlogo for the simulation of a functional model of SNN is a simplification of integrate and fire (I&F) models. The characteristics of the engine (including neuronal dynamics, STDP learning and synaptic delay) are demonstrated through the implementation of an agent representing an artificial insect controlled by a simple neural circuit. The setup of the experiment and its outcomes are described in this work
Magnetotransport of La0.70ca0.3-xsrxmno3 (Ag): A Potential Room Temperature Bolometer and Magnetic Sensor
Here we report the optimized magneto-transport properties of polycrystalline
La0.70Ca0.3-xSrxMnO3 and their composites with Ag. The optimization was carried
out by varying the Sr and Ag contents simultaneously to achieve large
temperature coefficient of resistance (TCR) as well as low field
magneto-resistance (MR) at room temperature. Sharpest paramagnetic
(PM)-ferromagnetic (FM) and insulator-metal (IM) transition is observed in the
vicinity of the room temperature (TC=300 K=TIM) for the composition
La0.70Ca0.20Sr00.10MnO3:Ag0.20. Partial substitution of larger Sr2+ ions at the
Ca2+ ions sites controls the magnitude of the FM and IM transition
temperatures, while the Ag induces the desired sharpness in these transitions.
For the optimized composition, maximum TCR and MR are tuned to room temperature
(300 K) with the former being as high as 9% and the later being 20 and 30
percent at 5 and 10 kOe magnetic fields respectively. Such sharp single peak
(TCR= 9 percent) at room temperature can be used for the bolometric and
infrared detector applications. The achievement of large TCR and low field MR
at T~300K in polycrystalline samples is encouraging and we believe that further
improvements can be achieved in thin films, which, by virtue of their low
conduction noise, are more suitable for device applications.Comment: 11 pages Text + Figures. Suggestions/comments welcome
([email protected]
Enhanced Room Temperature Coefficient of Resistance and Magneto-resistance of Ag-added La0.7Ca0.3-xBaxMnO3 Composites
In this paper we report an enhanced temperature coefficient of resistance
(TCR) close to room temperature in La0.7Ca0.3-xBaxMnO3 + Agy (x = 0.10, 0.15
and y = 0.0 to 0.40) (LCBMO+Ag) composite manganites. The observed enhancement
of TCR is attributed to the grain growth and opening of new conducting channels
in the composites. Ag addition has also been found to enhance intra-granular
magneto-resistance. Inter-granular MR, however, is seen to decrease with Ag
addition. The enhanced TCR and MR at / near room temperature open up the
possibility of the use of such materials as infrared bolometric and magnetic
field sensors respectively.Comment: 22 pages of Text +
Figs:comments/suggestions([email protected]
Radiological Society of North America expert consensus document on reporting chest CT findings related to COVID-19: Endorsed by the Society of Thoracic Radiology, the American College of Radiology, and RSNA
Routine screening CT for the identification of coronavirus disease 19 (COVID-19) pneumonia is currently not recommended by most radiology societies. However, the number of CT examinations performed in persons under investigation for COVID-19 has increased. We also anticipate that some patients will have incidentally detected findings that could be attributable to COVID-19 pneumonia, requiring radiologists to decide whether or not to mention COVID-19 specifically as a differential diagnostic possibility. We aim to provide guidance to radiologists in reporting CT findings potentially attributable to COVID-19 pneumonia, including standardized language to reduce reporting variability when addressing the possibility of COVID-19. When typical or indeterminate features of COVID-19 pneumonia are present in endemic areas as an incidental finding, we recommend contacting the referring providers to discuss the likelihood of viral infection. These incidental findings do not necessarily need to be reported as COVID-19 pneumonia. In this setting, using the term viral pneumonia can be a reasonable and inclusive alternative. However, if one opts to use the term COVID-19 in the incidental setting, consider the provided standardized reporting language. In addition, practice patterns may vary, and this document is meant to serve as a guide. Consultation with clinical colleagues at each institution is suggested to establish a consensus reporting approach. The goal of this expert consensus is to help radiologists recognize findings of COVID-19 pneumonia and aid their communication with other health care providers, assisting management of patients during this pandemic. Published under a CC BY 4.0 license
Quasi-discretization Of The Electron Continuum Emitted In Collisions Of 0.6 Mev UβΒΉ Au11+ With Noble Gases
We have measured relative doubly differential cross sections for electron emission in collisions of 0.6 MeV uβ1 Au11+ projectile ions with He, Ne and Ar targets for laboratory electron-detection angles between 17\u27 and 80\u27 and electron energies from 100 eV to well above the classical binary encounter region. The authors observe that, independent of the target Zt, the electron spectra display three characteristic peak-line structures whose energies are nearly invariant with observation angle. These structures are attributed to the diffraction of quasi-free target electrons in the potential of the projectile. Β© 1992 IOP Publishing Ltd
Automated Ensemble Modeling with modelMaGe: Analyzing Feedback Mechanisms in the Sho1 Branch of the HOG Pathway
In systems biology uncertainty about biological processes translates into
alternative mathematical model candidates. Here, the goal is to generate, fit
and discriminate several candidate models that represent different hypotheses
for feedback mechanisms responsible for downregulating the response of the Sho1
branch of the yeast high osmolarity glycerol (HOG) signaling pathway after
initial stimulation. Implementing and testing these candidate models by hand is
a tedious and error-prone task. Therefore, we automatically generated a set of
candidate models of the Sho1 branch with the tool modelMaGe.
These candidate models are automatically documented, can readily be simulated
and fitted automatically to data. A ranking of the models with respect to
parsimonious data representation is provided, enabling discrimination between
candidate models and the biological hypotheses underlying them. We conclude that
a previously published model fitted spurious effects in the data. Moreover, the
discrimination analysis suggests that the reported data does not support the
conclusion that a desensitization mechanism leads to the rapid attenuation of
Hog1 signaling in the Sho1 branch of the HOG pathway. The data rather supports a
model where an integrator feedback shuts down the pathway. This conclusion is
also supported by dedicated experiments that can exclusively be predicted by
those models including an integrator feedback
A Model of Late Long-Term Potentiation Simulates Aspects of Memory Maintenance
Late long-term potentiation (L-LTP) appears essential for the formation of
long-term memory, with memories at least partly encoded by patterns of
strengthened synapses. How memories are preserved for months or years, despite
molecular turnover, is not well understood. Ongoing recurrent neuronal
activity, during memory recall or during sleep, has been hypothesized to
preferentially potentiate strong synapses, preserving memories. This hypothesis
has not been evaluated in the context of a mathematical model representing
biochemical pathways important for L-LTP. I incorporated ongoing activity into
two such models: a reduced model that represents some of the essential
biochemical processes, and a more detailed published model. The reduced model
represents synaptic tagging and gene induction intuitively, and the detailed
model adds activation of essential kinases by Ca. Ongoing activity was modeled
as continual brief elevations of [Ca]. In each model, two stable states of
synaptic weight resulted. Positive feedback between synaptic weight and the
amplitude of ongoing Ca transients underlies this bistability. A tetanic or
theta-burst stimulus switches a model synapse from a low weight to a high
weight stabilized by ongoing activity. Bistability was robust to parameter
variations. Simulations illustrated that prolonged decreased activity reset
synapses to low weights, suggesting a plausible forgetting mechanism. However,
episodic activity with shorter inactive intervals maintained strong synapses.
Both models support experimental predictions. Tests of these predictions are
expected to further understanding of how neuronal activity is coupled to
maintenance of synaptic strength.Comment: Accepted to PLoS One. 8 figures at en
Unraveling the Design Principle for Motif Organization in Signaling Networks
Cellular signaling networks display complex architecture. Defining the design principle of this architecture is crucial for our understanding of various biological processes. Using a mathematical model for three-node feed-forward loops, we identify that the organization of motifs in specific manner within the network serves as an important regulator of signal processing. Further, incorporating a systemic stochastic perturbation to the model we could propose a possible design principle, for higher-order organization of motifs into larger networks in order to achieve specific biological output. The design principle was then verified in a large, complex human cancer signaling network. Further analysis permitted us to classify signaling nodes of the network into robust and vulnerable nodes as a result of higher order motif organization. We show that distribution of these nodes within the network at strategic locations then provides for the range of features displayed by the signaling network
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