scholarly journals Seasonality in a temperate zone bird can be entrained by near equatorial photoperiods

2006 ◽  
Vol 274 (1610) ◽  
pp. 721-725 ◽  
Author(s):  
Alistair Dawson
Keyword(s):  
Rate Of Change ◽  
Annual Change ◽  
Calendar Time ◽  
Seasonal Timing ◽  
Gonadal Maturation ◽  
Wide Range ◽  
Circannual Cycles ◽  
Time Of Breeding ◽  
Testicular Size ◽  
Long Photoperiod

Birds use photoperiod to control the time of breeding and moult. However, it is unclear whether responses are dependent on absolute photoperiod, the direction and rate of change in photoperiod, or if photoperiod entrains a circannual clock. If starlings ( Sturnus vulgaris ) are kept on a constant photoperiod of 12 h light : 12 h darkness per day (12 L : 12 D), then they can show repeated cycles of gonadal maturation, regression and moult, which is evidence for a circannual clock. In this study, starlings kept on constant 11.5 L : 12.5 D for 4 years or 12.5 L : 11.5 D for 3 years showed no circannual cycles in gonadal maturation or moult. So, if there is a circannual clock, it is overridden by a modest deviation in photoperiod from 12 L : 12 D. The responses to 11.5 L : 12.5 D and 12.5 L : 11.5 D were very different, the former perceived as a short photoperiod (birds were photosensitive for most of the time) and the latter as a long photoperiod (birds remained permanently photorefractory). Starlings were then kept on a schedule which ranged from 11.5 L : 12.5 D in mid-winter to 12.5 L : 11.5 D in mid-summer (simulating the annual cycle at 9 °N) for 3 years. These birds entrained precisely to calendar time and changes in testicular size and moult were similar to those of birds under a simulated cycle at 52 °N. These data show that birds are very sensitive to changes in photoperiod but that they do not simply respond to absolute photoperiod nor can they rely on a circannual clock. Instead, birds appear to respond to the shape of the annual change in photoperiod. This proximate control could operate from near equatorial latitudes and would account for similar seasonal timing in individuals of a species over a wide range of latitudes.

Haemorheological Effects on Thrombocyte Adhesion and Aggregation Found Under Controlled Flow Conditions

1979 ◽  
Author(s):  
P.D. Richardson
Keyword(s):  
Rate Of Change ◽  
Continuous Observation ◽  
Flow Conditions ◽  
Wide Range ◽  
Stream Migration ◽  
Local Shear ◽  
Videotape Recording ◽  
Controlled Flow ◽  
A Site

Thrombocyte adhesion and aggregation in a vessel or on a chamber wall can be measured most readily if the flow is controlled and steady, and continuous observation is used. Videotape recording is very helpful for subsequent quantification of the dynamics. The adhesion of each thrombocyte can occur for a finite time interval:this interval has been observed to have a wide range. Platelets which escape often leave open a site which attracts other platelets preferentially. The rate of change of adhesion density (platelets/mm2) is affected by the local shear rate and the shear history upstream. Aggregation is affected similarly, and also proceeds with some platelet turnover. The role of erythrocytes in facilitating cross-stream migration of thrombocytes (which can enhance the growth rate of large thrombi) appears due in part to convective flow fields induced by the motion of erythrocytes in a shear flow, which can be demonstrated theoretically and experimentally. Observations of the phenomenlogy of adhesion and aggregation under controlled flow conditions and comparison with fLu id-dynamically based theory allows representation in terras of a small number of parameters with prospects of prediction of behaviour over a wide range of haemodynamic conditions; biochemical changes lead to changes in values of the parameters, so that activating agents and inhibiting agents modify values in different directions.

scholarly journals The relationship between aerosol and cloud drop number concentrations in a global aerosol microphysics model

2009 ◽  
Vol 9 (1) ◽  
pp. 3207-3241 ◽  
Author(s):  
K. J. Pringle ◽  
K. S. Carslaw ◽  
D. V. Spracklen ◽  
G. M. Mann ◽  
M. P. Chipperfield
Keyword(s):  
Size Distribution ◽  
Cloud Droplet ◽  
Global Scale ◽  
Rate Of Change ◽  
The Arctic ◽  
Aerosol Size Distribution ◽  
Percentage Error ◽  
Empirical Relationships ◽  
Wide Range ◽  
Global Mean

Abstract. Empirical relationships that link cloud droplet number (CDN) to aerosol number or mass are commonly used to calculate global fields of CDN for climate forcing assessments. In this work we use a sectional global model of sulfate and sea-salt aerosol coupled to a mechanistic aerosol activation scheme to explore the limitations of this approach. We find that a given aerosol number concentration produces a wide range of CDN concentrations due to variations in the shape of the aerosol size distribution. On a global scale, the dependence of CDN on the size distribution results in regional biases in predicted CDN (for a given aerosol number). Empirical relationships between aerosol number and CDN are often derived from regional data but applied to the entire globe. In an analogous process, we derive regional "correlation-relations" between aerosol number and CDN and apply these regional relations to calculations of CDN on the global scale. The global mean percentage error in CDN caused by using regionally derived CDN-aerosol relations is 20 to 26%, which is about half the global mean percentage change in CDN caused by doubling the updraft velocity. However, the error is as much as 25–75% in the Southern Ocean, the Arctic and regions of persistent stratocumulus when an aerosol-CDN correlation relation from the North Atlantic is used. These regions produce much higher CDN concentrations (for a given aerosol number) than predicted by the globally uniform empirical relations. CDN-aerosol number relations from different regions also show very different sensitivity to changing aerosol. The magnitude of the rate of change of CDN with particle number, a measure of the aerosol efficacy, varies by a factor 4. CDN in cloud processed regions of persistent stratocumulus is particularly sensitive to changing aerosol number. It is therefore likely that the indirect effect will be underestimated in these important regions.

Some Observations on the Compressive Buckling of Rectangular Plates

1963 ◽  
Vol 14 (1) ◽  
pp. 17-30 ◽  
Author(s):  
W. H. Wittrick
Keyword(s):  
Rate Of Change ◽  
Infinite Strip ◽  
Rectangular Plates ◽  
Buckling Mode ◽  
Simply Supported ◽  
Side Ratio ◽  
Buckling Stress ◽  
Stress Coefficient ◽  
Wide Range ◽  
Elastically Restrained

SummaryThe problem considered is the buckling of a rectangular plate under uniaxial compression. The ends may be either both clamped, both simply-supported or a mixture of the two. The sides may be elastically restrained against both deflection and rotation with any stiffnesses whatsoever. It is shown that the curve of buckling stress coefficient versus side ratio can be deduced in a simple manner from that of a plate with the same end conditions but with both sides simply-supported, provided only that the buckling stress coefficient and wavelength for an infinite strip with the same side conditions are known. Some correlations between the curves for the three types of end condition are discussed. It is also shown that if, for some given side ratio, the buckling mode is known, then it is always possible to deduce the rate of change of buckling stress coefficient with side ratio at that point. The argument is based upon an assumption which is shown to give very accurate results in a wide range of cases.

Development of a Semi-Implicit Solver for Detailed Chemistry in I.C. Engine Simulations

2005 ◽  
Author(s):  
Long Liang ◽  
Chulhwa Jung ◽  
Song-Charng Kong ◽  
Rolf D. Reitz
Keyword(s):  
Chemical Kinetic ◽  
Rate Of Change ◽  
Operating Conditions ◽  
Explicit Methods ◽  
Implicit Methods ◽  
Specific Internal Energy ◽  
Detailed Chemistry ◽  
Key Species ◽  
Wide Range ◽  
Implicit Solver

An efficient semi-implicit numerical method is developed for solving the detailed chemical kinetic source terms in I.C. engine simulations. The detailed chemistry system is a group of coupled extremely stiff O.D.E.s, which presents a very stringent timestep limitation when solved by standard explicit methods, and is computationally expensive when solved by iterative implicit methods. The present numerical solver uses a stiffly-stable noniterative semi-implicit method, in which the numerical solution to the stiff O.D.E.s never blows up for arbitrary large timestep. The formulation of numerical integration exploits the physical requirement that the species density and specific internal energy in the computational cells must be nonnegative, so that the Lipschitz timestep constraint is not present [1,2], and the computation timestep can be orders of magnitude larger than that possible in standard explicit methods and can be formulated to be of high formal order of accuracy. The solver exploits the characteristics of the stiffness of the O.D.E.s by using a sequential sort algorithm that ranks an approximation to the dominant eigenvalues of the system to achieve maximum accuracy. Subcycling within the chemistry solver routine is applied for each computational cell in engine simulations, where the subcycle timestep is dynamically determined by monitoring the rate of change of concentration of key species which have short characteristic time scales and are also important to the chemical heat release. The chemistry solver is applied in the KIVA-3V code to diesel engine simulations. Results are compared with those using the CHEMKIN package which uses the VODE implicit solver. Very good agreement was achieved for a wide range of engine operating conditions, and 40∼70% CPU time savings were achieved by the present solver compared to CHEMKIN.

scholarly journals The Extrapolar SWIFT model (version 1.0): fast stratospheric ozone chemistry for global climate models

2018 ◽  
Vol 11 (2) ◽  
pp. 753-769 ◽  
Author(s):  
Daniel Kreyling ◽  
Ingo Wohltmann ◽  
Ralph Lehmann ◽  
Markus Rex
Keyword(s):  
Polynomial Function ◽  
Stratospheric Ozone ◽  
Ozone Layer ◽  
Rate Of Change ◽  
Polynomial Functions ◽  
Mixing Ratio ◽  
Fourth Degree ◽  
Stratospheric Chemistry ◽  
Wide Range ◽  
Atlas Model

Abstract. The Extrapolar SWIFT model is a fast ozone chemistry scheme for interactive calculation of the extrapolar stratospheric ozone layer in coupled general circulation models (GCMs). In contrast to the widely used prescribed ozone, the SWIFT ozone layer interacts with the model dynamics and can respond to atmospheric variability or climatological trends. The Extrapolar SWIFT model employs a repro-modelling approach, in which algebraic functions are used to approximate the numerical output of a full stratospheric chemistry and transport model (ATLAS). The full model solves a coupled chemical differential equation system with 55 initial and boundary conditions (mixing ratio of various chemical species and atmospheric parameters). Hence the rate of change of ozone over 24 h is a function of 55 variables. Using covariances between these variables, we can find linear combinations in order to reduce the parameter space to the following nine basic variables: latitude, pressure altitude, temperature, overhead ozone column and the mixing ratio of ozone and of the ozone-depleting families (Cly, Bry, NOy and HOy). We will show that these nine variables are sufficient to characterize the rate of change of ozone. An automated procedure fits a polynomial function of fourth degree to the rate of change of ozone obtained from several simulations with the ATLAS model. One polynomial function is determined per month, which yields the rate of change of ozone over 24 h. A key aspect for the robustness of the Extrapolar SWIFT model is to include a wide range of stratospheric variability in the numerical output of the ATLAS model, also covering atmospheric states that will occur in a future climate (e.g. temperature and meridional circulation changes or reduction of stratospheric chlorine loading). For validation purposes, the Extrapolar SWIFT model has been integrated into the ATLAS model, replacing the full stratospheric chemistry scheme. Simulations with SWIFT in ATLAS have proven that the systematic error is small and does not accumulate during the course of a simulation. In the context of a 10-year simulation, the ozone layer simulated by SWIFT shows a stable annual cycle, with inter-annual variations comparable to the ATLAS model. The application of Extrapolar SWIFT requires the evaluation of polynomial functions with 30–100 terms. Computers can currently calculate such polynomial functions at thousands of model grid points in seconds. SWIFT provides the desired numerical efficiency and computes the ozone layer 104 times faster than the chemistry scheme in the ATLAS CTM.

scholarly journals A change-point model for detecting heterogeneity in ordered survival responses

2017 ◽  
Vol 27 (12) ◽  
pp. 3595-3611 ◽  
Author(s):  
Olivier Bouaziz ◽  
Grégory Nuel
Keyword(s):  
Disease Onset ◽  
Estimation Method ◽  
Survival Times ◽  
Time To Event ◽  
Calendar Time ◽  
Wide Range ◽  
Change Point Model ◽  
Hidden States ◽  
Number Of Segments ◽  
Selection Of

In this article, we suggest a new statistical approach considering survival heterogeneity as a breakpoint model in an ordered sequence of time-to-event variables. The survival responses need to be ordered according to a numerical covariate. Our estimation method will aim at detecting heterogeneity that could arise through the ordering covariate. We formally introduce our model as a constrained Hidden Markov Model, where the hidden states are the unknown segmentation (breakpoint locations) and the observed states are the survival responses. We derive an efficient Expectation-Maximization framework for maximizing the likelihood of this model for a wide range of baseline hazard forms (parametrics or nonparametric). The posterior distribution of the breakpoints is also derived, and the selection of the number of segments using penalized likelihood criterion is discussed. The performance of our survival breakpoint model is finally illustrated on a diabetes dataset where the observed survival times are ordered according to the calendar time of disease onset.

scholarly journals Disease Modelling of Cognitive Outcomes and Biomarkers in the European Prevention of Alzheimer’s Dementia Longitudinal Cohort

2021 ◽  
Vol 4 ◽  
Author(s):  
James Howlett ◽  
Steven M. Hill ◽  
Craig W. Ritchie ◽  
Brian D. M. Tom
Keyword(s):  
Disease Process ◽  
Alzheimer’S Dementia ◽  
Rate Of Change ◽  
Cognitive Outcomes ◽  
Disease Modelling ◽  
Data Set ◽  
Alzheimer's Dementia ◽  
Longitudinal Cohort ◽  
Wide Range

A key challenge for the secondary prevention of Alzheimer’s dementia is the need to identify individuals early on in the disease process through sensitive cognitive tests and biomarkers. The European Prevention of Alzheimer’s Dementia (EPAD) consortium recruited participants into a longitudinal cohort study with the aim of building a readiness cohort for a proof-of-concept clinical trial and also to generate a rich longitudinal data-set for disease modelling. Data have been collected on a wide range of measurements including cognitive outcomes, neuroimaging, cerebrospinal fluid biomarkers, genetics and other clinical and environmental risk factors, and are available for 1,828 eligible participants at baseline, 1,567 at 6 months, 1,188 at one-year follow-up, 383 at 2 years, and 89 participants at three-year follow-up visit. We novelly apply state-of-the-art longitudinal modelling and risk stratification approaches to these data in order to characterise disease progression and biological heterogeneity within the cohort. Specifically, we use longitudinal class-specific mixed effects models to characterise the different clinical disease trajectories and a semi-supervised Bayesian clustering approach to explore whether participants can be stratified into homogeneous subgroups that have different patterns of cognitive functioning evolution, while also having subgroup-specific profiles in terms of baseline biomarkers and longitudinal rate of change in biomarkers.

pH Effects on Measurements of Ionized Calcium and Ionized Magnesium in Blood

2002 ◽  
Vol 126 (8) ◽  
pp. 947-950 ◽  
Author(s):  
Sihe Wang ◽  
Elizabeth H. McDonnell ◽  
Frank A. Sedor ◽  
John G. Toffaletti
Keyword(s):  
Whole Blood ◽  
Rate Of Change ◽  
Ionized Calcium ◽  
Magnesium Concentration ◽  
Blood Gas ◽  
Ph Change ◽  
Ionized Magnesium ◽  
Ph Values ◽  
Wide Range ◽  
Blood Specimens

Abstract Context.—It is well known that the concentration of ionized calcium in blood is affected by the pH of the specimen, since hydrogen ions compete with calcium for binding sites on albumin and other proteins. However, the relationship between pH and ionized magnesium concentration is not as well characterized. Objective.—To determine the effects of pH on ionized magnesium concentration over a wide range of pH values in serum or plasma. Design.—Both ionized calcium and ionized magnesium concentrations were measured in 3 sets of samples. (1) Pools of serum or whole blood at different pH values (7.20–7.60) achieved by adding a constant volume of acid or base (diluted solutions of either hydrochloric acid or sodium hydroxide) plus saline. These pools consisted of 2 serum and 3 heparinized whole blood pools collected from leftover blood remaining in clinical specimens in the Clinical Chemistry and Blood Gas Laboratories, respectively, at Duke University Medical Center. (2) Five whole blood specimens obtained from apparently healthy individual donors. (3) Twenty-six whole blood specimens obtained from individual patients (leftover blood from the Blood Gas Laboratory) in which pH was varied by in vitro loss or gain of carbon dioxide. Results.—Both ionized calcium and ionized magnesium concentrations decreased as the pH in the specimen increased, indicating the stronger binding of these ions with proteins in the more alkaline environment. Conclusion.—We conclude that the rate of change of ionized magnesium concentration with pH change (0.12 mmol/L per pH unit) is significantly less than that of ionized calcium (0.36 mmol/L per pH unit). Furthermore, our findings indicate that if adjustment to pH 7.40 is necessary, the ionized magnesium test results need to be adjusted when pH is markedly abnormal, as is sometimes done for ionized calcium.

Advances And Enhancements in Light Element EDXRF

1987 ◽  
Vol 31 ◽  
pp. 449-454
Author(s):  
James R. Bogert
Keyword(s):  
Line Intensity ◽  
Light Element ◽  
Rate Of Change ◽  
Light Elements ◽  
Detectable Amount ◽  
X Ray ◽  
Wide Range ◽  
Minimum Detectable Amount ◽  
Excitation Conditions ◽  
System Geometry

One of the strongest analytical qualities of energy-dispersive x-ray fluorescence (EDXRF) is the wide range of analyte elements that can be detected and analyzed. Historically, the technique has covered all the elements from sodium (Z=11) and above. A useful measure of specific spectrometer performance is analyte sensitivity. X-ray spectrometric sensitivity is usually expressed in terms of minimum detectable amount of analyte or rate of change of analyte line intensity with change in amount of analyte. Many factors affect analyte sensitivity in EDXRF. These include excitation conditions, specimen conditions, system geometry, atmosphere, detector and readout conditions, and of course the specific analyte line. Typically, EDXRF sensitivity is very good, and low ppm concentrations of analytes are routinely analyzed–until one encounters the light elements.

Application of TMA for Rapid Evaluation of Low-Temperature Properties of Elastomer Vulcanizates

1979 ◽  
Vol 52 (4) ◽  
pp. 735-747
Author(s):  
D. W. Brazier ◽  
G. H. Nickel
Keyword(s):  
Thermal Expansion ◽  
Glass Transition ◽  
Low Temperature ◽  
Linear Thermal Expansion ◽  
Dimensional Change ◽  
Rate Of Change ◽  
Transition Range ◽  
Free Expansion ◽  
Wide Range ◽  
Scan Rate

Abstract Static thermomechanical analysis has been investigated as a method for determining the low-temperature properties of vulcanizates. Dimensional changes of a sample in free expansion, indentation, or tension are monitored as the sample is heated at a known and reproducible rate. The first derivative of the dimensional change is simultaneously recorded. TMA/DTMA data obtained in free expansion gives the linear thermal expansion coefficient at any temperature during the experiment. The glass transition is observed as a change in slope as in dilatometric determinations. In the indentation mode, the thermogram is the result of competition between thermal expansion and indentation. For tension measurements, the thermogram records the additive sum of thermal expansion and tensional strain development. For indentation and tension, the glass transition is obtained by a standard extrapolation method. A maximum in the DTMA thermogram is also observed which represents the maximum rate of change as the sample is heated through the glass transition range. The temperature of this maximum, Tgd, is characteristic of a vulcanizate. Variation in scan rate between 2 and 20°C/min has little effect on Tgo and no effect on Tgd. At 50°C/min, thermal gradient effects predominate. For a wide range of vulcanizates in tension or indentation, Tgo or Tgd versus the Gehman rigidity modulus gives a linear relationship. Exact temperature agreement is not observed because of differences in the experimental techniques. In blends, several Tgd values are observed. Plasticizer effects can either be observed by a shift in the Tgo or by a change in the thermogram profile, the extent of indentation and temperature range over which it occurs. The extent of indentation correlates with vulcanizate hardness as expected. The indentation of a rubber sample by a flat probe has been treated mathematically in the literature, and the determination of Young's modulus by TMA/DTMA is now being investigated. In conclusion, the ease of sample preparation and the rapidity of TMA/DTMA measurements offers a quick approach to assessing the low-temperature properties of vulcanizates. At 20°C/min scan rate, runs can be completed in as little as four minutes (80°C total scan) if the sample has a single transition.

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