221 research outputs found
Influence of milk source on transplantability of histocompatible mammary tumours in mice.
It is confirmed that C3H mammary tumours are much more easily transplantable in histocompatible recipients when these have been reared on C3H milk, than when they have been reared on milk from the inbred Swiss/B strain. By contrast, A.CA mammary tumours transplanted in histocompatible hosts reared on A.CA or Swiss/B milk, grow almost equally well in both sorts of recipient. Thus, rearing on Swiss/B milk has different effects on the transplantability of mammary tumours of C3H and A.CA. On the other hand, recipients which were reared on C3H or A.CA milks accept grafts of C3H mammary tumours about equally, suggesting that milks from A.CA and C3H have the same effect on the transplantability of C3H mammary tumours. The different action of Swiss/B milk on tumours of C3H and A.CA seems best attributed to differences between C3H and A.CA tumours or between mouse strain genotypes. By contrast, the transplantability of C3H mammary tumours is significantly changed when the recipients were reared on milk from the RIII strain instead of C3H. These facts suggest that the milk from RIII has an action which differs from that of both C3H and A.CA in this respect. The data are discussed on the basis of a differential tollerance-inducing action of mammary tumour viruses (MTVs) which infect C3H, A.CA and RIII, and have an important role in tumour induction
Source Spectra and Site Response from S Waves of Intermediate-Depth Vrancea, Romania, Earthquakes
Seismograms from 55 intermediate-depth Vrancea earthquakes (M 4:0–
7:1) recorded at 43 stations of an accelerometric network in Romania are used to
derive source spectra and site amplification functions from S waves in the frequency
range 0.5–20 Hz with the generalized inversion technique (GIT) (Castro et al., 1990).
Attenuation is taken into account using the nonparametric attenuation functions derived
by Oth et al. (2008) from the same dataset, and the attenuation-corrected data are
then split into source and site contributions. The source spectra follow the ω 2 model
(Brune, 1970, 1971) with high corner frequencies and a related Brune stress drop of
the order of 100 MPa. The site amplification functions are separately determined for
both horizontal and vertical components. Contrary to widespread expectation, the
vertical component shows significant amplification effects at high frequencies. The
H=Z ratios determined from the GIT results compare well with H=V ratios computed
directly from the S-wave window of the accelerograms (Lermo and Chávez-García,
1993). The basic assumption for the determination of site effects from H=V ratios is
that the vertical component is not or only little affected by site effects. For Vrancea
earthquakes, this assumption is incorrect; consequently, site effects should not be
estimated from H=V ratios. The reason for this peculiar fact is the geometry of
intermediate-depth seismicity that leads to almost vertical ray paths beneath the
stations
S-Wave Attenuation Characteristics beneath the Vrancea Region in Romania: New Insights from the Inversion of Ground-Motion Spectra
The S-wave attenuation characteristics beneath the Vrancea region in
Romania are analyzed from the spectra (frequency range 0.5–20 Hz) of more than
850 recordings at 43 accelerometric stations of 55 intermediate-depth earthquakes
(M 4:0–7:1) that occurred in the Vrancea seismogenic zone. The method commonly
chosen for this type of investigation in the case of crustal earthquakes is the generalized
inversion technique (GIT) (e.g., Andrews, 1986; Castro et al., 1990). Yet the
Vrancea dataset is entirely different from common crustal datasets. Because of the
strong clustering of the hypocenters within a very small focal volume, there are only
few crossing ray paths from sources to receivers. As a consequence, inhomogeneities
in the attenuation properties are not averaged out, which leads to unphysical results if
the standard GIT approach is adopted. The problem is discussed qualitatively by performing
tests with synthetic data and solved quantitatively by adapting the GIT technique
in view of these peculiarities.With the optimally adapted inversion scheme, it is
possible to unravel differences in the attenuation characteristics between two (or more)
sets of stations. The results show that the attenuation of seismic waves is roughly
comparable in the low frequency range (<4–5 Hz) but stronger by up to an order
of magnitude at higher frequencies within the Carpathian mountain arc as compared
with the foreland area. Modeling this strongly frequency-dependent lateral variation of
seismic attenuation by a significantly lower Q beneath Vrancea (1) provides a very
good fit of observed strong-motion characteristics, (2) sheds new light on the distribution
of intensities of the previous strong earthquakes, (3) will have strong implications
for future hazard assessment, and (4) is fully compatible with structural models
from deep seismic sounding, tomography, and teleseismic attenuation
Toward a cross-border early-warning system for central Asia
Rapidly expanding urban areas in Central Asia are increasingly vulnerable to seismic risk; but at present, no earthquake early warning (EEW) systems exist in the region despite their successful implementation in other earthquake-prone areas. Such systems aim to provide short (seconds to tens of seconds) warnings of impending disaster, enabling the first risk mitigation and damage control steps to be taken. This study presents the feasibility of a large scale cross-border regional system for Central Asian countries. Genetic algorithms are used to design efficient EEW networks, computing optimal station locations and trigger thresholds in recorded ground acceleration. Installation of such systems within 3 years aims to both reducing the endemic lack of strong motion data in Central Asia that is limiting the possibility of improving seismic hazard assessment, and at providing the first regional earthquake early warning system in the are
Designing efficient earthquake early warning systems: Case study of Almaty, Kazakhstan
Rapidly expanding urban areas in Central Asia are increasingly vulnerable to seismic risk; but at present, no earthquake early warning (EEW) systems exist in the region despite their successful implementation in other earthquake-prone areas. Such systems aim to provide short (seconds to tens of seconds) warnings of impending disaster, enabling the first risk mitigation and damage control steps to be taken. This study presents the feasibility of such a system for Almaty, Kazakhstan. Genetic algorithms are used to design efficient EEW networks, computing optimal station locations and trigger thresholds in recorded ground acceleration. Factors like the possibility of station failure, elevation and access difficulty to a potential site, and the potential usefulness of existing stations in the region are considered. We present a large set of possible efficient networks, to which further selection criteria can be applied by both the installation teams and the end user, such as authorities in Almaty
Intra-Crater Eruption Dynamics at Nyiragongo (D.R. Congo), 2002–2021
Nyiragongo is one of the rare volcanoes on Earth hosting a lava lake. However, the understanding of its plumbing and lava lake systems remains limited, with, until recently, only sporadic or time-limited historical observations and measurements. Combining dense accurate lava lake and crater floor level measurements based on 1,703 satellite radar images and topographic reconstructions using photogrammetry, we obtain the first reliable picture and time evolution of intra-crater erupted lava volumes between the two last flank eruptions in January 2002 and May 2021. The filling of the crater by lava, initiated in 2002 and continued up to May 2021, is seen as an evidence of a long-term pressure build up of the magmatic system. This filling occurs through irregular pulsatory episodes of rising lava lake level, some of which overflow and solidify on the surrounding crater floor. Pauses of stable molten lava lake level and sudden numerous level drops also marked the summit's eruptive activity. The joint analysis with seismic records available since 2015 revealed that the largest lava lake drops are synchronous with seismic swarms associated with deep magma intrusions, generally preceded by an increase of extrusion rate within the crater. The appearance of a spatter cone in the summit crater in 2016, most likely superficially branched to the lava lake, was a clear marker of the change in eruption dynamics. This first long-term time series of Nyiragongo's crater topography between two hazardous flank eruptions might further help to better decipher Nyiragongo's past and future behavior using multi-parameter observations
Existence of a rotating wave pattern in a disk for a wave front interaction model
[[abstract]]We study the rotating wave patterns in an excitable medium in a disk. This wave pattern is rotating along the given disk boundary with a constant angular speed. To study this pattern we use the wave front interaction model proposed by Zykov in 2007. This model is derived from the FitzHugh-Nagumo equation and it can be described by two systems of ordinary differential equations for wave front and wave back respectively. Using a delicate shooting argument with the help of the comparison principle, we derive the existence and uniqueness of rotating wave patterns for any admissible angular speed with convex front in a given disk.[[incitationindex]]SCI[[booktype]]紙本[[booktype]]電子
Health-related factors correlate with behavior trends in physical activity level in old age: longitudinal results from a population in São Paulo, Brazil
<p>Abstract</p> <p>Background</p> <p>Physical inactivity in leisure time is common among elderly in Brazil and this finding is particularly alarming considering that this population is greatly affected by chronic diseases. The identification of health factors that influence physical activity level (PAL) will help in the development of strategies for increasing PAL older adults. The current research aimed to identify variables that independently affect behavior trends in PAL over the course of two years among elderly.</p> <p>Methods</p> <p>A survey entitled the Epidoso Project ("Epidemiology of aging") studied 1,667 community-based older individuals in São Paulo city, Brazil over the course of two years. Physical activity level was determined through questions about frequency and duration of physical activities. Body Mass Index was calculated; functional capacity was assessed through the ADL (activities of daily living) scale; cognition was assessed by Mini-Mental State Examination; and mental health was assessed through the Dysthymia Screening. Experiences of falls and fractures were also assessed. Subjects were divided into three groups according to their self-report of Physical Activity Level: a - Regularly Active; b - Insufficiently Active and c - Physically Inactive. Behavior trends in PAL were also measured after two years. Multivariate regression model methodology was used to test associations longitudinally.</p> <p>Results</p> <p>Results from the final model demonstrated that the risk of a not favorable behavior trend in PAL, which included the group who remained physically inactive and the group that displayed decreased PAL, in this cohort of older adults was significantly increased if the individual was female (OR = 2.50; 95% CI = 1.60-3.89; <it>P < 0.01</it>), older (80 y vs. 65 y, OR = 6.29, 95% CI = 2.69-14.67; <it>P < 0.01</it>), dependent on help from others for activities in the ADL scale (moderate-severe = 4-7+ vs. 0 ADLs) (OR = 2.25, 95% CI = 1.20-4.21; <it>P < 0.011</it>) or had experienced a history of falls with consequences (OR = 6.88, 95% CI = 0.91-52.01; <it>P < 0.062</it>).</p> <p>Conclusions</p> <p>Age, gender, ADL scores and falls were associated with a not favorable behavior trend in PAL. Promotion programs should target these factors, reducing barriers to achieve desired changes in PAL.</p
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