5,299 research outputs found
Explanation of the Normal Winter Anomaly from the Seasonal Variation of Short Wave Absorption
The frequency dependence of the winter anomaly (WA) of radio wave absorption indicates the altitude range where the considered seasonal variation of absorption, L, takes place: 75-95 km. In this height region considerable seasonal variations of ionic composition and effective recombination coefficient, alpha sub e, exist, which can cause seasonal variations of electron concentration, N, and absorption, L. An attempt to render a qualitative estimation of the normal WA, i.e., the increased ratio of winter over summer absorption, L sub w/L sub s, at medium latitudes 40 deg and 50 deg, for solar zenith angles CHi = 60 deg and 75 deg is made. This is compared with existing experimental data
Phase and Intensity Distributions of Individual Pulses of PSR B0950+08
The distribution of the intensities of individual pulses of PSR B0950+08 as a
function of the longitudes at which they appear is analyzed. The flux density
of the pulsar at 111 MHz varies strongly from day to day (by up to a factor of
13) due to the passage of the radiation through the interstellar plasma
(interstellar scintillation). The intensities of individual pulses can exceed
the amplitude of the mean pulse profile, obtained by accumulating 770 pulses,
by more than an order of magnitude. The intensity distribution along the mean
profile is very different for weak and strong pulses. The differential
distribution function for the intensities is a power law with index n = -1.1 +-
0.06 up to peak flux densities for individual pulses of the order of 160 Jy
Construction of a two-parameter empirical model of left ventricle wall motion using cardiac tagged magnetic resonance imaging data
Abstract
Background
A one-parameter model was previously proposed to characterize the short axis motion of the LV wall at the mid-ventricle level. The single parameter of this model was associated with the radial contraction of myocardium, but more comprehensive model was needed to account for the rotation at the apex and base levels. The current study developed such model and demonstrated its merits and limitations with examples.
Materials and methods
The hearts of five healthy individuals were visualized using cardiac tagged magnetic resonance imaging (tMRI) covering the contraction and relaxation phases. Based on the characteristics of the overall dynamics of the LV wall, its motion was represented by a combination of two components - radial and rotational. Each component was represented by a transformation matrix with a time-dependent variable α or β.
Image preprocessing step and model fitting algorithm were described and applied to estimate the temporal profiles of α and β within a cardiac cycle at the apex, mid-ventricle and base levels. During this process, the tagged lines of the acquired images served as landmark reference for comparing against the model prediction of the motion. Qualitative and quantitative analyses were performed for testing the performance of the model and thus its validation.
Results
The α and β estimates exhibited similarities in values and temporal trends once they were scaled by the radius of the epicardium (r
epi
)and plotted against the time scaled by the period of the cardiac cycle (T
cardiac
) of each heart measured during the data acquisition. α/r
epi
peaked at about Δt/T
cardiac
=0.4 and with values 0.34, 0.4 and 0.3 for the apex, mid-ventricle and base level, respectively. β/r
epi
similarly maximized in amplitude at about Δt/T
cardiac
=0.4, but read 0.2 for the apex and - 0.08 for the base level. The difference indicated that the apex twisted more than the base.
Conclusion
It is feasible to empirically model the spatial and temporal evolution of the LV wall motion using a two-parameter formulation in conjunction with tMRI-based visualization of the LV wall in the transverse planes of the apex, mid-ventricle and base. In healthy hearts, the analytical model will potentially allow deriving biomechanical entities, such as strain, strain rate or torsion, which are typically used as diagnostic, prognostic or predictive markers of cardiovascular diseases including diabetes.Peer Reviewe
Asymmetry Function of Interstellar Scintillations of Pulsars
A new method for separating intensity variations of a source's radio emission
having various physical natures is proposed. The method is based on a joint
analysis of the structure function of the intensity variations and the
asymmetry function, which is a generalization of the asymmetry coefficient and
characterizes the asymmetry of the distribution function of the intensity
fluctuations on various scales for the inhomogeneities in the diffractive
scintillation pattern. Relationships for the asymmetry function in the cases of
a logarithmic normal distribution of the intensity fluctuations and a normal
distribution of the field fluctuations are derived. Theoretical relationships
and observational data on interstellar scintillations of pulsars (refractive,
diffractive, and weak scintillations) are compared. Pulsar scintillations match
the behavior expected for a normal distribution of the field fluctuations
(diffractive scintillation) or logarithmic normal distribution of the intensity
fluctuations (refractive and weak scintillation). Analysis of the asymmetry
function is a good test for distinguishing scintillations against the
background of variations that have different origins
Interstellar Plasma Turbulence Spectrum Toward the Pulsars PSR B0809+74 and B0950+08
Interstellar scintillations of pulsars PSR B0809+74 and B0950+08 have been
studied using observations at low frequencies (41, 62, 89, and 112 MHz).
Characteristic temporal and frequency scales of diffractive scintillations at
these frequencies have been determined. The comprehensive analysis of the
frequency and temporal structure functions reduced to the same frequency has
shown that the spectrum of interstellar plasma inhomogeneities toward both
pulsars is described by a power law. The exponent of the spectrum of
fluctuations of interstellar plasma inhomogeneities toward PSR B0950+08 (n =
3.00 +- 0.05) appreciably differs from the Kolmogorov exponent. Toward PSR
B0809+74 the spectrum is a power law with an exponent n = 3.7 +- 0.1. A strong
angular refraction has been detected toward PSR B0950+08. The distribution of
inhomogeneities along the line of sight has been analyzed; it has been shown
that the scintillations of PSR B0950+08 take place on a turbulent layer with
enhanced electron density, which is localized at approximately 10 pc from the
observer. For PSR B0809+74 the distribution of inhomogeneities is
quasi-uniform. Mean-square fluctuations of electron density on inhomogeneities
with a characteristic scale rho_0 = 10^7 m toward four pulsars have been
estimated. On this scale the local turbulence level in the 10-pc layer is 20
times higher than in an extended region responsible for the scintillations of
PSR B0809+74.Comment: 13 pages, 11 figure
Scattering and Diffraction in Magnetospheres of Fast Pulsars
We apply a theory of wave propagation through a turbulent medium to the
scattering of radio waves in pulsar magnetospheres. We find that under
conditions of strong density modulation the effects of magnetospheric
scintillations in diffractive and refractive regimes may be observable. The
most distinctive feature of the magnetospheric scintillations is their
independence on frequency.
Results based on diffractive scattering due to small scale inhomogeneities
give a scattering angle that may be as large as 0.1 radians, and a typical
decorrelation time of seconds.
Refractive scattering due to large scale inhomogeneities is also possible,
with a typical angle of radians and a correlation time of the order
of seconds. Temporal variation in the plasma density may also result
in a delay time of the order of seconds. The different scaling of the
above quantities with frequency may allow one to distinguish the effects of
propagation through a pulsar magnetosphere from the interstellar medium. In
particular, we expect that the magnetospheric scintillations are relatively
more important for nearby pulsars when observed at high frequencies.Comment: 19 pages, 1 Figur
Construction of a two-parameter empirical model of left ventricle wall motion using cardiac tagged magnetic resonance imaging data
Background
A one-parameter model was previously proposed to characterize the short axis motion of the LV wall at the mid-ventricle level. The single parameter of this model was associated with the radial contraction of myocardium, but more comprehensive model was needed to account for the rotation at the apex and base levels. The current study developed such model and demonstrated its merits and limitations with examples.
Materials and methods
The hearts of five healthy individuals were visualized using cardiac tagged magnetic resonance imaging (tMRI) covering the contraction and relaxation phases. Based on the characteristics of the overall dynamics of the LV wall, its motion was represented by a combination of two components - radial and rotational. Each component was represented by a transformation matrix with a time-dependent variable α or β.
Image preprocessing step and model fitting algorithm were described and applied to estimate the temporal profiles of α and β within a cardiac cycle at the apex, mid-ventricle and base levels. During this process, the tagged lines of the acquired images served as landmark reference for comparing against the model prediction of the motion. Qualitative and quantitative analyses were performed for testing the performance of the model and thus its validation.
Results
The α and β estimates exhibited similarities in values and temporal trends once they were scaled by the radius of the epicardium (repi)and plotted against the time scaled by the period of the cardiac cycle (Tcardiac) of each heart measured during the data acquisition. α/repi peaked at about Δt/Tcardiac=0.4 and with values 0.34, 0.4 and 0.3 for the apex, mid-ventricle and base level, respectively. β/repi similarly maximized in amplitude at about Δt/Tcardiac=0.4, but read 0.2 for the apex and - 0.08 for the base level. The difference indicated that the apex twisted more than the base.
Conclusion
It is feasible to empirically model the spatial and temporal evolution of the LV wall motion using a two-parameter formulation in conjunction with tMRI-based visualization of the LV wall in the transverse planes of the apex, mid-ventricle and base. In healthy hearts, the analytical model will potentially allow deriving biomechanical entities, such as strain, strain rate or torsion, which are typically used as diagnostic, prognostic or predictive markers of cardiovascular diseases including diabetes
Draft genome sequence of Methyloferula stellata AR4, an obligate methanotroph possessing only a soluble methane monooxygenase
Methyloferula stellata AR4 is an aerobic acidophilic methanotroph, which, in contrast to most known methanotrophs but similar to Methylocella spp., possesses only a soluble methane monooxygenase. However, it differs from Methylocella spp. by its inability to grow on multicarbon substrates. Here, we report the draft genome sequence of this bacterium
Methodology of adipose tissue type detection in mammals
Nowadays, an interest in studying the composition, properties and functions of adipose tissue (AT) is growing among researchers, which is conditioned by its important role in the normal functioning of the body. Due to different types of adipose tissue (AT) in mammals (white, beige, brown and pink) and different physiological tasks performed by each type of AT, rapid, correct and effective detection of an AT type is highly topical. Methods used today are labor consuming and in the case of NMR and CT expensive, which limits possibilities of scientists. In this connection, the aim of this research was to develop a methodological approach allowing rapid and effective detection of an adipose tissue type. A methodology was formed based on the concept, formalized requirements for the method, step-wise structure of investigations and interpretation of results. The concept is based on differences in the structure of the adipose cell (adipocyte) of different AT types. The method is based on extraction of heme containing proteins. To this end, solvents and parameters of extraction that facilitate their better extraction have been chosen. An AT type has been determined by the total content of iron contained in the cytochrome fragment. Our own modification was selected. This modification includes preliminary mincing of a sample with the ice-cold TES buffer (pH 8.5) in a ratio of 1:5 (g: mL), homogenization at 9,000 rpm for 2 min with the following centrifugation at 10,000 g and 4 °C for 15 min. Effectiveness of the proposed method was confirmed by the histological and electrophoretic analyses. Therefore, the new methodology of identification and differentiation of adipocytes was proposed for rapid and effective detection of an adipose tissue type.Nowadays, an interest in studying the composition, properties and functions of adipose tissue (AT) is growing among researchers, which is conditioned by its important role in the normal functioning of the body. Due to different types of adipose tissue (AT) in mammals (white, beige, brown and pink) and different physiological tasks performed by each type of AT, rapid, correct and effective detection of an AT type is highly topical. Methods used today are labor consuming and in the case of NMR and CT expensive, which limits possibilities of scientists. In this connection, the aim of this research was to develop a methodological approach allowing rapid and effective detection of an adipose tissue type. A methodology was formed based on the concept, formalized requirements for the method, step-wise structure of investigations and interpretation of results. The concept is based on differences in the structure of the adipose cell (adipocyte) of different AT types. The method is based on extraction of heme containing proteins. To this end, solvents and parameters of extraction that facilitate their better extraction have been chosen. An AT type has been determined by the total content of iron contained in the cytochrome fragment. Our own modification was selected. This modification includes preliminary mincing of a sample with the ice-cold TES buffer (pH 8.5) in a ratio of 1:5 (g: mL), homogenization at 9,000 rpm for 2 min with the following centrifugation at 10,000 g and 4 °C for 15 min. Effectiveness of the proposed method was confirmed by the histological and electrophoretic analyses. Therefore, the new methodology of identification and differentiation of adipocytes was proposed for rapid and effective detection of an adipose tissue type
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