External Variability Research Articles

Nonreciprocal homeostatic compensation in Drosophila potassium channel mutants.

Homeostatic control of intrinsic excitability is important for long-term regulation of neuronal activity. In conjunction with many other forms of plasticity, intrinsic homeostasis helps neurons maintain stable activity regimes in the face of external input variability and destabilizing genetic mutations. In this study, we report a mechanism by which Drosophila melanogaster larval motor neurons stabilize hyperactivity induced by the loss of the delayed rectifying K+ channel Shaker cognate B (Shab), by upregulating the Ca2+-dependent K+ channel encoded by the slowpoke (slo) gene. We also show that loss of SLO does not trigger a reciprocal compensatory upregulation of SHAB, implying that homeostatic signaling pathways utilize compensatory pathways unique to the channel that was mutated. SLO upregulation due to loss of SHAB involves nuclear Ca2+ signaling and dCREB, suggesting that the slo homeostatic response is transcriptionally mediated. Examination of the changes in gene expression induced by these mutations suggests that there is not a generic transcriptional response to increased excitability in motor neurons, but that homeostatic compensations are influenced by the identity of the lost conductance.NEW & NOTEWORTHY The idea that activity-dependent homeostatic plasticity is driven solely by firing has wide credence. In this report we show that homeostatic compensation after loss of an ion channel conductance is tailored to identity of the channel lost, not its properties.

Soil erosion assessment—Mind the gap

AbstractAccurate assessment of erosion rates remains an elusive problem because soil loss is strongly nonunique with respect to the main drivers. In addressing the mechanistic causes of erosion responses, we discriminate between macroscale effects of external factors—long studied and referred to as “geomorphic external variability”, and microscale effects, introduced as “geomorphic internal variability.” The latter source of erosion variations represents the knowledge gap, an overlooked but vital element of geomorphic response, significantly impacting the low predictability skill of deterministic models at field‐catchment scales. This is corroborated with experiments using a comprehensive physical model that dynamically updates the soil mass and particle composition. As complete knowledge of microscale conditions for arbitrary location and time is infeasible, we propose that new predictive frameworks of soil erosion should embed stochastic components in deterministic assessments of external and internal types of geomorphic variability.

International Space Science Institute (ISSI) Workshop on Integrative Study of the Mean Sea Level and its Components

Because it integrates changes in several components of the climate system in response to external forcing factors and internal climate variability, sea level is one of the best indicators of global climate change.

European Randomized Study of Screening for Prostate Cancer Risk Calculator: External Validation, Variability, and Clinical Significance

To externally validate the European Randomized Study of Screening for Prostate Cancer (ERSPC) risk calculator (RC) and to evaluate its variability between 2 consecutive prostate-specific antigen (PSA) values. We prospectively catalogued 1021 consecutive patients before prostate biopsy for suspicion of prostate cancer (PCa). The risk of PCa and significant PCa (Gleason score ≥7) from 749 patients was calculated according to ERSPC-RC (digital rectal examination-based version 3 of 4) for 2 consecutive PSA tests per patient. The calculators' predictions were analyzed using calibration plots and the area under the receiver operating characteristic curve (area under the curve). Cohen kappa coefficient was used to compare the ability and variability. Of 749 patients, PCa was detected in 251 (33.5%) and significant PCa was detected in 133 (17.8%). Calibration plots showed an acceptable parallelism and similar discrimination ability for both PSA levels with an area under the curve of 0.69 for PCa and 0.74 for significant PCa. The ERSPC showed 226 (30.2%) unnecessary biopsies with the loss of 10 significant PCa. The variability of the RC was 16% for PCa and 20% for significant PCa, and a higher variability was associated with a reduced risk of significant PCa. We can conclude that the performance of the ERSPC-RC in the present cohort shows a high similitude between the 2 PSA levels; however, the RC variability value is associated with a decreased risk of significant PCa. The use of the ERSPC in our cohort detects a high number of unnecessary biopsies. Thus, the incorporation of ERSPC-RC could help the clinical decision to carry out a prostate biopsy.

DOWNTURN AS A BASIS OF A COMPANY’S PROPERTY COMPLEX INSOLVENCY

The paper gives reasons for co-relation of downturn and a company’s property complex insolvency; the factors which define it are determined. The co-relation between the concepts of insolvency and bankruptcy has been observed. The necessity of a strategic crisis management of a company’s property complex in order to adapt it to the conditions of internal and external environment variability has been explained. The objective: to prove the downturn influence on a company’s property complex insolvency; to set up the co-relation between the concepts of insolvency and bankruptcy. Method and methodology of work: the study rests on dialectical and systemic approaches; analysis, synthesis, comparison, deduction, and induction are applied. Findings: factors contributing to downturn and a company’s insolvency appearance are outlined; co-relation of insolvency and bankruptcy concepts is stated; insolvency concept is specified. Application of the findings: the findings extend theoretical ideas about a company’s property complex insolvency and can be used to justify anti-crisis management, as well as in conceptual models of its further development in conditions of high internal and external environment variability.

How does reach‐scale stream‐hyporheic transport vary with discharge? Insights from rSAS analysis of sequential tracer injections in a headwater mountain stream

AbstractThe models of stream reach hyporheic exchange that are typically used to interpret tracer data assume steady‐flow conditions and impose further assumptions about transport processes on the interpretation of the data. Here we show how rank Storage Selection (rSAS) functions can be used to extract “process‐agnostic” information from tracer breakthrough curves about the time‐varying turnover of reach storage. A sequence of seven slug injections was introduced to a small stream at base flow over the course of a diel fluctuation in stream discharge, providing breakthrough curves at discharges ranging from 0.7 to 1.2 L/s. Shifted gamma distributions, each with three parameters varying stepwise in time, were used to model the rSAS function and calibrated to reproduce each breakthrough curve with Nash‐Sutcliffe efficiencies in excess of 0.99. Variations in the fitted parameters over time suggested that storage within the reach does not uniformly increase its turnover rate when discharge increases. Rather, changes in transit time are driven by both changes in the average rate of turnover (external variability) and changes in the relative rate that younger and older water contribute to discharge (internal variability). Specifically, at higher discharge, the turnover rate increased for the youngest part of the storage (corresponding to approximately 5 times the volume of the channel), while discharge from the older part of the storage remained steady, or declined slightly. The method is shown to be extensible as a new approach to modeling reach‐scale solute transport that accounts for the time‐varying, discharge‐dependent turnover of reach storage.

Transit time distributions and StorAge Selection functions in a sloping soil lysimeter with time‐varying flow paths: Direct observation of internal and external transport variability

AbstractTransit times through hydrologic systems vary in time, but the nature of that variability is not well understood. Transit times variability was investigated in a 1 m3 sloping lysimeter, representing a simplified model of a hillslope receiving periodic rainfall events for 28 days. Tracer tests were conducted using an experimental protocol that allows time‐variable transit time distributions (TTDs) to be calculated from data. Observed TTDs varied with the storage state of the system, and the history of inflows and outflows. We propose that the observed time variability of the TTDs can be decomposed into two parts: “internal” variability associated with changes in the arrangement of, and partitioning between, flow pathways; and “external” variability driven by fluctuations in the flow rate along all flow pathways. These concepts can be defined quantitatively in terms of rank StorAge Selection (rSAS) functions, which is a theory describing lumped transport dynamics. Internal variability is associated with temporal variability in the rSAS function, while external is not. The rSAS function variability was characterized by an “inverse storage effect,” whereby younger water is released in greater proportion under wetter conditions than drier. We hypothesize that this effect is caused by the rapid mobilization of water in the unsaturated zone by the rising water table. Common approximations used to model transport dynamics that neglect internal variability were unable to reproduce the observed breakthrough curves accurately. This suggests that internal variability can play an important role in hydrologic transport dynamics, with implications for field data interpretation and modeling.

Morphological variability, chromosome polymorphism, and problems of identifying individual species of gobies of the group Ponticola (Gobiidae) and assessing taxonomic relations of local populations

In connection with the problems of identification of certain species of the genus Ponticola, and especially their juveniles, morphological and genetic studies of gobies collected in the northwestern part of the Black Sea basin were carried out using literature data and museum collections. Karyological data indicate a distinct species status of western (P. odessicus) and eastern (P. eurycephalus) mushroom gobies; the range of the latter includes not only the Sea of Azov but also waters of the Black Sea coast of the Crimean Peninsula; these conclusions are supported by preliminary molecular genetic studies. Based on the obtained results of intraspecific morphological variability of species, we propose morphological characteristics for identification of adult P. syrman and P. odessicus, as well as a specific set of characteristics to identify juvenile (body length less than 50 mm) P. syrman, P. kessleri, and P. odessicus. We reveal differences in the karyotype structure of P. syrman from populations of the Sasyk Lake and the Don River, which do not differ in terms of external morphological characteristics and variability of cytochrome b haplotypes. The need for further research of phylogeography and morphological and karyological variability of P. syrman sensu lato is assumed.

Theoretical connections between mathematical neuronal models corresponding to different expressions of noise

Identifying the right tools to express the stochastic aspects of neural activity has proven to be one of the biggest challenges in computational neuroscience. Even if there is no definitive answer to this issue, the most common procedure to express this randomness is the use of stochastic models. In accordance with the origin of variability, the sources of randomness are classified as intrinsic or extrinsic and give rise to distinct mathematical frameworks to track down the dynamics of the cell. While the external variability is generally treated by the use of a Wiener process in models such as the Integrate-and-Fire model, the internal variability is mostly expressed via a random firing process. In this paper, we investigate how those distinct expressions of variability can be related. To do so, we examine the probability density functions to the corresponding stochastic models and investigate in what way they can be mapped one to another via integral transforms. Our theoretical findings offer a new insight view into the particular categories of variability and it confirms that, despite their contrasting nature, the mathematical formalization of internal and external variability is strikingly similar.

The efficiency of areal units in spatial analysis: Assessing the performance of functional and administrative regions

Abstract An attempt to provide a procedure for the assessment of the efficiency of various regional systems for the purposes of spatial analysis is presented in this paper. Functional regions as well as approximated functional regions and the existing administrative regions in the Czech Republic are evaluated, as examples of regional systems to be compared and assessed. Functional regions and approximated functional regions are defined according to the adjusted third variant of the CURDS regionalisation algorithm, using the latest knowledge on the operation of the constraint function. The comparisons of individual regional systems are based on LISA maps and particularly on the assessment of regional variability, including the measures of internal homogeneity and external variability in the regional systems.

Austral winter external and internal atmospheric variability between 1980 and 2014

AbstractWe examine the interannual variability of the seasonal mean atmospheric circulation in the Southern Hemisphere during austral winter. The three major modes are identified by rotated empirical orthogonal function (REOF) analysis. As expected, REOF1 is associated with the Southern Annular Mode which is dominated by internal atmospheric dynamics. REOF2 displays a wave train, linked to the western North Pacific monsoon and the Pacific‐Japan pattern in East Asia in the same season; REOF3 resembles the Pacific‐South American pattern. Externally forced variability strongly projects on both REOF2 and REOF3 so that in the ensemble mean, an atmospheric model with prescribed observed sea surface temperature captures considerable parts of the time evolution of REOF2 (50%) and REOF3 (25%), suggesting a potential predictability for the two modes.

Modeling and Monitoring for Transitions Based on Local Kernel Density Estimation and Process Pattern Construction

Usually, industrial processes have multiple operational modes due to different production strategies, external environmental variability, or changes in product specifications. Monitoring of multimode processes constitutes a challenging problem considering multiple steady-state operational regions and dynamic transitions. This paper proposes a novel method for the offline identification of stable modes and transitions based on a local kernel density estimation algorithm. The online monitoring scheme is based on mode identification and transition tracking. The Tennessee Eastman (TE) benchmark process is used as a case study to evaluate the performance of the proposal. As a result, stable modes are successfully isolated from transitions, even when these involve complex changes in the production mode. The results also demonstrate that the proposed scheme is capable of tracking mode changes, and finally, results monitored during transitions confirm the validity and efficacy of the new approach compared with pr...

Water exchange between the continental shelf and the cavity beneath Nioghalvfjerdsbræ (79 North Glacier)

AbstractThe mass loss at Nioghalvfjerdsbræ is primarily due to rapid submarine melting. Ocean data obtained from beneath the Nioghalvfjerdsbræ ice tongue show that melting is driven by the presence of warm (1°C) Atlantic Intermediate Water (AIW). A sill prevents AIW from entering the cavity from Dijmphna Sund, requiring that it flow into the cavity via bathymetric channels to the south at a pinned ice front. Comparison of water properties from the cavity, Dijmphna Sund, and the continental shelf support this conclusion. Overturning circulation rates inferred from observed melt rates and cavity stratification suggest an exchange flow between the cavity and the continental shelf of 38mSv, sufficient to flush cavity waters in under 1 year. These results place upper bounds on the timescales of external variability that can be transmitted to the glacier via the ice tongue cavity.

A new species of the genus Sovia (Lepidoptera: Hesperiidae) from Qinling-Daba Mountains of China.

In this paper, a new species Sovia lii spec. nov. is described from Qinling-Daba Mountains in S. Gansu province and S. Shaanxi province, W. China. Variability of wing pattern, differences with its similar congeners and some biological information of this new taxon are introduced. External variability of Sovia lucasii, which is discovered from Shaanxi for the first time and is sympatric with the new species there, is illustrated and discussed. A brief analysis of the distributional pattern of the genus Sovia is provided. A key to the genus is given.

Magnetic resonance elastography and transient elastography as non-invasive analyses for liver fibrosis: can they obviate the need for liver biopsy in psoriasis patients treated with methotrexate?

The liver biopsy has been regarded as the reference standard method of monitoring hepatic fibrosis in psoriasis patients treated with methotrexate. It has also been subject to concerns over sampling error, internal and external variability, and potential for morbidity and mortality. During the past two decades, two imaging techniques, magnetic resonance elastography and transient elastography, have been developed and approved by the US Food and Drug Administration (FDA) for the assessment of hepatic fibrosis. Although high-quality, psoriasis-specific data are lacking, both methods have been shown to have outstanding efficacy in the detection of hepatic fibrosis, particularly the more advanced stages which may warrant the choice of a therapeutic alternative to methotrexate. Dermatologists should be aware of the availability of these tests and understand their limitations. Prospective studies in psoriasis and methotrexate management using these techniques are needed.

Los rafidiópteros de la Península Ibérica (Insecta, Neuropterida: Raphidioptera)

The present contribution revises the snake-fly species present in the fauna of the Iberian Peninsula where, to date, is represented by 16 species belonging to 9 genera of both actual families. After a diagnosis of the order and its paleontological history, there are exposed some general data on its morphology and biology, juvenile stages, behavior and distribution, as well as the used terminology, and is commented a brief introduction on the history in the knowledge of the order, and in particular in the Iberian Peninsula. It is included a list of the species belonging to the Iberian fauna and an identification key of families, genera, and species listed in the Iberian Peninsula. For every one of these taxa are compiled and annotated all the existing bibliographic general references, as those relating to the species present in the studied area, both with the currently accepted name, their synonyms and/ or any other nomenclatural combinations under which they have been recorded. Of each species is also detailed the present knowledge of its external morphology, genital variability, juvenile stages, biology, phenology and altitudinal and geographic distribution in the Peninsula, providing the now studied material, mostly unrecorded (1,073 studied specimens), and the corresponding distribution maps of these species in the studied area.

Genetic and morphological variability of the European mudminnow Umbra krameri (Teleostei, Umbridae) in Serbia and in Bosnia and Herzegovina, a basis for future conservation activities.

As a basis for future conservation activities, the genetic and external body morphology variability of the European mudminnow Umbra krameri, a highly endangered fish species in Serbia and in Bosnia and Herzegovina, was determined for existing populations with the use of molecular markers (mitochondrial and microsatellite DNA) and geometric morphometric methods. Mitochondrial DNA cytochrome b gene analysis revealed two previously undescribed haplotypes: Da1 (the Lugomir population from the Danube River basin) and Sa1 (the Bakreni Batar and the Gromiželj populations from the Sava River system), with a corresponding genetic distance of 0·7%. Paired values of FST and DAS distances for microsatellite marker data show that the difference between the Danube and the Sava populations is seven to nine times higher than the difference between the populations within the Sava River system. Geometric morphometric analyses also support a clear separation of the Lugomir population from the Bakreni Batar and the Gromiželj populations. The analysis of the body shape variation, however, indicates a significant difference between the two genetically indistinguishable Sava populations. The observed genetic and phenetic relationships of the analysed mudminnow populations most probably represent a consequence of historical, geographical and ecological factors. These results will offer guidelines for future protection, conservation and sustainable management of this species in the region.

Observed and simulated inter-decadal changes in the structure of Southern Hemisphere large-scale circulation

Several studies have identified that, in the mid-1970s to early 1980s, a major shift occurred in the structure of the large-scale circulation in both hemispheres. This work employs the CSIRO Mk3L general circulation model in ensemble simulations with observed sea surface temperatures (SSTs) and historical time-evolving carbon dioxide (CO2) concentrations to investigate the inter-decadal changes found observationally in the jet streams, temperature, Hadley circulation, mean sea level pressure and precipitation. First, the performance of the model in simulating these changes for the mean July climate fields of 1949–1968 and 1975–1994, in comparison with the corresponding observations (NCEP/NCAR Reanalysis I and the Twentieth Century Reanalysis V2), is investigated. We find that the model is quite skilful in reproducing the broad features of the important inter-decadal changes that occurred in the mid-1970s. The model simulations and the NCEP/NCAR and twentieth century reanalyses agree in the eastern hemisphere; whereas in the western hemisphere the reanalyses show differences, and the simulations combine aspects of these two datasets. The role of the direct radiative forcing due to CO2 in driving the inter-decadal changes is also examined. Results indicate that, in comparison with the indirect effect of CO2 carried by the changing SSTs, there is little additional impact of the direct radiative forcing due to CO2 on the changes in the latter period. However, our simulations with fixed CO2 concentration have shown clearly that the atmospheric simulations with historical time-evolving CO2 concentrations are more skilful in reproducing the inter-decadal changes. The sensitivity of the ensemble results to employing the same or different time evolving sea ice boundary conditions in the ensemble members is also studied. The contributions of internal and external variability are discussed.

Effect of anxiety on the function of the cardiorespiratory system

The effects of anxiety on the external respiration system and respiratory sinus arrhythmia (RSA) were studied in healthy subjects in real-life conditions. Changes in external respiration parameters and heart rate variability (HRV) in students going to take their end-of-term exams were assessed relative to a midterm period, and the cardiorespiratory system was monitored in a longitudinal study for 50 days. The function of the cardiorespiratory system was characterized by measuring external respiration parameters and calculating HRV parameters. State anxiety (SA) was assessed using Spielberger’s scale. An increase in SA before an exam was accompanied by a higher breathing rate, a higher tidal volume, and lower HRV indices, especially those related to respiratory sinus arrhythmia (HF and HF norm). The changes in the parameters depended on the increase in SA. A negative correlation was observed between midterm HF and pre-exam SA. The longitudinal study revealed a distinct negative correlation between respiratory sinus arrhythmia parameters and peak expiratory flow (PEF) and a positive correlation between SA and PEF in the majority of subjects. Changes in cardiorespiratory parameters depended on the changes in SA in the longitudinal study. An increase in SA was accompanied by substantial changes in respiratory sinus arrhythmia (RAS) and external respiration parameters, and their correlation was assumed to indicate that modification of parasympathetic activity plays a leading role in increasing PEF.

Source and regulation of flux variability in Escherichia coli.

BackgroundMetabolic responses are essential for the adaptation of microorganisms to changing environmental conditions. The repertoire of flux responses that the metabolic network can display in different external conditions may be quantified applying flux variability analysis to genome-scale metabolic reconstructions.ResultsA procedure is developed to classify and quantify the sources of flux variability. We apply the procedure to the latest Escherichia coli metabolic reconstruction, in glucose minimal medium, with an additional constraint to account for the mechanism coordinating carbon and nitrogen utilization mediated by α-ketoglutarate. Flux variability can be decomposed into three components: internal, external and growth variability. Unexpectedly, growth variability is the only significant component of flux variability in the physiological ranges of glucose, oxygen and ammonia uptake rates. To obtain substantial increases in metabolic flexibility, E. coli must decrease growth rate to suboptimal values. This growth-flexibility trade-off gives a straightforward interpretation to recent work showing that most overall cell-to-cell flux variability in a population of E. coli can be attained sampling a small number of enzymes most likely to constrain cell growth. Importantly, it provides an explanation for the global reorganization occurring in metabolic networks during adaptations to environmental challenges. The calculations were repeated with a pathogenic strain and an old reconstruction of the commensal strain, having less than 50% of the reactions of the latest reconstruction, obtaining the same general conclusions.ConclusionsIn E. coli growing on glucose, growth variability is the only significant component of flux variability for all physiological conditions explored. Increasing flux variability requires reducing growth to suboptimal values. The growth-flexibility trade-off operates in physiological and evolutionary adaptations, and provides an explanation for the global reorganization occurring during adaptations to environmental challenges. The results obtained do not rely on the knowledge of kinetic and regulatory details of the system and are highly robust to incomplete or incorrect knowledge of the reaction network.