Impact of Hammock Formations on Vertical Obstructions

2004 ◽  
Author(s):  
Stanislav A. Vershinin ◽  
Pavel A. Truskov ◽  
Konstantin V. Kouzmitchev
Keyword(s):  
Initial Phase ◽  
Dynamic Effect ◽  
Local Stress ◽  
Second Phase ◽  
Spatial Effects ◽  
Dynamic Effects ◽  
Cyclic Pattern ◽  
Perfectly Plastic ◽  
Spherical Element ◽  
Plane Slab

The paper considers scenarios of head-on impact on vertical obstacles and destruction of hummock subsurface parts represented as a discrete spherical-element medium. The issues analyzed include the 2-phase nature of interaction and destruction of a loose and connected medium and also the cyclic pattern of loading and dynamic effects emerging in interaction with the hummock keel. The contact local stress in the subsurface part is determined by solving the Hertz equation which describes the indent of a sphere into a plane slab. Structural bonds are destructed when cohesion vanishes over the sliding plane. In the initial phase, a frozen ice ridge disintegrates as an perfectly plastic body with small angle of cohesion, while the second phase is viewed as dozing the sliding prism as a loose discrete body. This model allows for spatial effects in distortion of the subsurface part of an ice ridge. The dynamic effect is noted to increase with the size of hummock fragments, hummock speed and size.

scholarly journals Force maintenance and myosin filament assembly regulated by Rho-kinase in airway smooth muscle

2015 ◽  
Vol 308 (1) ◽  
pp. L1-L10 ◽  
Author(s):  
Bo Lan ◽  
Linhong Deng ◽  
Graham M. Donovan ◽  
Leslie Y. M. Chin ◽  
Harley T. Syyong ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Initial Phase ◽  
Rho Kinase ◽  
Myosin Filament ◽  
Second Phase ◽  
Minimal Effect ◽  
Kinase Inhibition ◽  
Myosin Filaments ◽  
Force Maintenance

Smooth muscle contraction can be divided into two phases: the initial contraction determines the amount of developed force and the second phase determines how well the force is maintained. The initial phase is primarily due to activation of actomyosin interaction and is relatively well understood, whereas the second phase remains poorly understood. Force maintenance in the sustained phase can be disrupted by strains applied to the muscle; the strain causes actomyosin cross-bridges to detach and also the cytoskeletal structure to disassemble in a process known as fluidization, for which the underlying mechanism is largely unknown. In the present study we investigated the ability of airway smooth muscle to maintain force after the initial phase of contraction. Specifically, we examined the roles of Rho-kinase and protein kinase C (PKC) in force maintenance. We found that for the same degree of initial force inhibition, Rho-kinase substantially reduced the muscle's ability to sustain force under static conditions, whereas inhibition of PKC had a minimal effect on sustaining force. Under oscillatory strain, Rho-kinase inhibition caused further decline in force, but again, PKC inhibition had a minimal effect. We also found that Rho-kinase inhibition led to a decrease in the myosin filament mass in the muscle cells, suggesting that one of the functions of Rho-kinase is to stabilize myosin filaments. The results also suggest that dissolution of myosin filaments may be one of the mechanisms underlying the phenomenon of fluidization. These findings can shed light on the mechanism underlying deep inspiration induced bronchodilation.

Creep Relaxation of an Elastic–Perfectly Plastic Hemisphere in Fully Plastic Contact

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
Andreas Goedecke ◽  
Randolf Mock
Keyword(s):  
Creep Behavior ◽  
Contact Area ◽  
Geometrical Parameters ◽  
Second Phase ◽  
Perfectly Plastic ◽  
Area Increase ◽  
Accelerated Creep ◽  
Material Creep ◽  
Evolution Laws ◽  
Elastic Perfectly Plastic

A set of finite element simulations was performed to analyze the creep behavior of an elastic–perfectly plastic hemisphere in contact with a rigid flat. This study focuses on the time-dependent stress relaxation of a fully plastic asperity. Assuming a Garofalo (hyperbolic sine) type material creep law, the asperity shows two distinct phases of relaxation. In the first phase, the asperity creeps with an accelerated creep rate and shows a contact area increase similar to that of a cylindrical geometry. In the second phase, no contact area change can be measured and the asperity creeps with a slower rate. Empirical evolution laws for the asperity creep behavior are presented, analyzing the influence of both material and geometrical parameters. The results are interpreted in terms of transient friction.

The Roman Road-Station at Thenadassa (Ain Wif)

1982 ◽  
Vol 13 ◽  
pp. 73-80 ◽  
Author(s):  
D. J. Mattingly
Keyword(s):  
Initial Phase ◽  
Indigenous Population ◽  
Second Century ◽  
Third Century ◽  
Second Phase ◽  
The Third ◽  
Military Presence ◽  
Two Phases ◽  
The Military ◽  
New Evidence

AbstractA reappraisal of the Roman period ruins at Ain Wif has been made following the identification there of traces of defensive walls. These walls are interpreted as being the robbed-out remains of a Roman fortlet and possibly also a tort on the same site. Two phases of military occupation were also evident in modern drain trenches being cut across the site and are attested epigraphically for the military bath-house by the spring. Ceramic evidence from the site suggests that the initial phase lies within the second century, whilst the Severan occupation, known from an inscription to begin early in the third century, represents a second phase. The previous view of the site as an undefended road-station, with a military presence only under the Severan emperors is no longer tenable. Moreover, the new evidence indicates that there was some measure of military organisation in the hinterland of the Emporia prior to the accession of Septimius Severus at the very end of the second century AD. The importance of the site also lies in its large civilian and indigenous population who continued to occupy the site long after the military had departed.

scholarly journals Magnetic relaxation and the Taylor conjecture

2015 ◽  
Vol 81 (6) ◽  
Author(s):  
H. K. Moffatt
Keyword(s):  
Magnetic Field ◽  
Initial Phase ◽  
Magnetic Relaxation ◽  
Magnetic Energy ◽  
Magnetic Pressure ◽  
Second Phase ◽  
One Dimensional ◽  
Induction Equation ◽  
Two Phases ◽  
The Magnetic Field

A one-dimensional model of magnetic relaxation in a pressureless low-resistivity plasma is considered. The initial two-component magnetic field $\boldsymbol{b}(\boldsymbol{x},t)$ is strongly helical, with non-uniform helicity density. The magnetic pressure gradient drives a velocity field that is dissipated by viscosity. Relaxation occurs in two phases. The first is a rapid initial phase in which the magnetic energy drops sharply and the magnetic pressure becomes approximately uniform; the helicity density is redistributed during this phase but remains non-uniform, and although the total helicity remains relatively constant, a Taylor state is not established. The second phase is one of slow diffusion, in which the velocity is weak, though still driven by persistent weak non-uniformity of magnetic pressure; during this phase, magnetic energy and helicity decay slowly and at constant ratio through the combined effects of pressure equalisation and finite resistivity. The density field, initially uniform, develops rapidly (in association with the magnetic field) during the initial phase, and continues to evolve, developing sharp maxima, throughout the diffusive stage. Finally it is proved that, if the resistivity is zero, the spatial mean $\langle (\boldsymbol{b}\boldsymbol{\cdot }\boldsymbol{{\rm\nabla}}\times \boldsymbol{b})/b^{2}\rangle$ is an invariant of the governing one-dimensional induction equation.

scholarly journals e-Pedagogy: the pedagogies of e-learning

2004 ◽  
Vol 12 (3) ◽  
Author(s):  
Wassila Naamani Mehanna
Keyword(s):  
Data Collection ◽  
Quantitative Data ◽  
Initial Phase ◽  
Qualitative Data ◽  
Second Phase ◽  
Postgraduate Programme ◽  
Data Collection And Analysis ◽  
Online Classrooms ◽  
E Learning ◽  
Effect Size Calculation

The aim of this research was to establish effective e-learning practice in higher education. This was achieved by looking at examples of different pedagogic techniques employed in several cases. The effectiveness of these techniques was established by looking at the students’ outcomes on these courses. This study has adopted a sequential mixed methodology characterized by an initial phase of qualitative data collection and analysis, which was followed by a phase of quantitative data collection and analysis. The first phase of the study involved collecting a year of data from a postgraduate programme. A grounded approach was used to analyse one million words of online conferences or discussions, and led to the emergence of 29 pedagogic behaviours. These pedagogic behaviours were then developed into a coding instrument. The second phase, hypothetico-deductive analysis, confirmed their presence in three other cases, five million words of online interactions, and established their associations with students’ learning and outcomes. The findings suggest seven clusters of pedagogies correlated with students’ grades and the effect size calculation revealed an educational significance for all of them. This indicates that if they are employed in online classrooms they are likely to enhance students’ learning and outcomes.DOI: 10.1080/0968776042000259582

scholarly journals Requerimientos de humedad relativa y tiempos de incubación para la infección de conidios de Colletotrichum gloeosporioides en frutos de papaya.

2016 ◽  
Vol 9 (1) ◽  
pp. 81 ◽  
Author(s):  
Alfredo Durán ◽  
Lenín Ramírez ◽  
Dennis Mora
Keyword(s):  
Relative Humidity ◽  
Incubation Time ◽  
Initial Phase ◽  
Colletotrichum Gloeosporioides ◽  
Disease Incidence ◽  
Hot Water ◽  
Second Phase ◽  
Damage Level ◽  
The University ◽  
Erratic Behavior

The research was carried out at the University of Costa Rica's phytopathology laboratory between October 1995 and March 1996. In an initial phase, some creole papaya fruits from Gu.cimo (Limón province) were used. In order to eliminate latent infections, they were washed and immersed in hot water (49° C for 20 minutes). The fruits were then randomly placed in groups of 20, which conformed each treatment. Finally, they were inoculated by spraying with 5.5 ml of a 10.000 Colletotrichum gloeosporioides spores per mililiter suspension; then they were placed in plastic boxes and stored in containers with a 30°C temperature and relative humidities of 70%, 80%, and 90%. Fruits were kept in the compartments for periods of 5, l0, 15, 20 and 25 hours. Temperature and relative humidity were monitored during the experiment through the incubator's sensors and with a portable hydrothermograph. Finally, the incidence and severity of anthracnose was evaluated. During the second phase, fruits of the Hawaiian sunrise variety were used, following the same procedures applied to the native fruits. In native fruits, 100% of those placed at 80% and 90% relative humidity were contaminated after being in the compartment for five hours. The incidence decreased in the group with 70% relative humidity. The damage level increased with increases in relative humidity, although some erratic behavior was observed. In the test with Hawaiian fruit, the disease incidence increased according with incubation time. Severity showed a similar behavour; however, there was also erratic behavour here.

A Theoretically-Based Statistical Model of Transition Toughness

2007 ◽  
Author(s):  
Marjorie A. EricksonKirk ◽  
Matthew Wagenhofer
Keyword(s):  
Temperature Dependence ◽  
Phase Particle ◽  
Local Stress ◽  
Quantitative Model ◽  
Second Phase ◽  
Dislocation Mechanics ◽  
Deformation And Fracture ◽  
Wide Range ◽  
Local Stresses ◽  
Macroscopic Crack

A program was undertaken to develop a fully predictive model of the scatter in toughness across a wide range of transition temperatures based on a physical understanding of deformation and fracture behavior. The temperature dependence of the proposed model is taken from previous work in which the local mechanisms of cleavage fracture were used to define the plastic work to fracture. The local to global stress transference is achieved by a dislocation-mechanics based examination of the interaction between the globally applied stresses, a macroscopic crack and a nearby accumulation of dislocations blocked by a second phase particle, i.e. slip band, whose position relative to the macroscopic crack tip is variable. The scatter of toughness values at each temperature is captured through variation of this macro-crack / micro-crack geometry, and of the particle size. Once the local stress field is determined using the dislocation-based transference equations, an energy balance criterion for fracture is applied that incorporates the temperature-dependent fracture work term and the local stresses determined from the transference equations. This paper summarizes this multiscale fracture model, which serves as a foundation for more detailed descriptions of the mathematics of the quantitative model, its temperature dependence and scatter characteristics and coding efforts. These latter topics will be addressed in greater detail in subsequent papers.

scholarly journals Polarized Response of East Asian Winter Temperature Extremes in the Era of Arctic Warming

2018 ◽  
Vol 31 (14) ◽  
pp. 5543-5557 ◽  
Author(s):  
Shuangmei Ma ◽  
Congwen Zhu ◽  
Boqi Liu ◽  
Tianjun Zhou ◽  
Yihui Ding ◽  
...  
Keyword(s):  
Global Warming ◽  
East Asia ◽  
Winter Season ◽  
Surface Air Temperature ◽  
Dynamic Effect ◽  
Arctic Amplification ◽  
Dynamic Effects ◽  
North Asia ◽  
Thermodynamic Effects ◽  
Cold Extremes

Abstract It has been argued that fewer cold extremes will be expected to occur over most midlatitude areas, because of anthropogenic-induced global warming. However, East Asia repeatedly suffered from unexpected cold spells during the winter of 2015/16, and the low surface air temperature (SAT) during 21–25 January 2016 broke the previous calendar record from 1961. We hypothesize that cold extremes such as these occur because of Arctic amplification (AA) of global warming. To test this hypothesis, we analyzed the changes of SAT variability in the winter season over East Asia. Our results show that the SAT variability (measured by the standard deviation of the winter season daily mean SAT) over East Asia has significantly increased in the era of AA during 1988/89–2015/16 and exhibits a polarization between warm and cold extremes, popularly dubbed as “weather whiplash.” This phenomenon is driven by both the thermodynamic effects of global warming and the dynamic effects of AA. Global warming favors a rising SAT and more frequent warm extremes. The AA phenomenon strengthens the wavy components of midlatitude circulation, leading to more frequent blockings over the Ural region and a stronger Siberian high in north Asia. This dynamic effect of AA enhances the intrusion of cold air from Siberia into East Asia and causes cold extremes. Because there is a comparable increase of frequency of both warm and cold extremes, the SAT variability significantly increases in unison with AA, but little change is observed in the seasonal mean SAT of East Asia. This implies increased risks of both cold and warm extremes over East Asia exist even during global warming.

BODY HEAT STORAGE, METABOLISM AND RESPIRATION OF COWS ABRUPTLY EXPOSED AND ACCLIMATIZED TO COLD AND 18 °C ENVIRONMENTS

1984 ◽  
Vol 64 (3) ◽  
pp. 641-653 ◽  
Author(s):  
J. A. McLEAN ◽  
W. T. WHITMORE ◽  
B. A. YOUNG ◽  
R. WEINGARDT
Keyword(s):  
Initial Phase ◽  
Heat Storage ◽  
The Body ◽  
Second Phase ◽  
Mean Body Temperature ◽  
Cyclic Patterns ◽  
Cyclic Temperature ◽  
Two Phases ◽  
Body Heat ◽  
Effective Buffer

Six cows were alternated between cold (−30 to 0 °C) and 18 °C environments. Rectal (Tr), mean skin (Ts) and mean body (Tb = 0.86 Tr + 0.14 Ts) temperatures, respiration rate (RR) and metabolism per unit body size (M) were measured on first exposure and after acclimatization to each environment. Cows acclimatized to the cold had the same Tr as when acclimatized to 18 °C, but Ts and RR were lower and M was higher in the cold than in the 18 °C environment. Acclimatization appeared to occur in two phases. In the initial phase, lasting less than a day, new 24-h cyclic patterns (greater in the cold than in 18 °C) were established in body temperatures, respiration and metabolism. In the second phase which took longer than 2 days new levels were established in these parameters. The change in heat stored in the body between the two environments was not as great as previously found in an environment with a relatively small but cyclic temperature variation. It is suggested that changes in body heat storage are associated with cyclic or sudden changes in the environment, when it can act as an effective buffer against thermal stress. Key words: Cattle, mean body temperature, body heat storage, acclimatization

Effect of Ca2+ deprivation on release of luteinizing hormone induced by luteinizing hormone releasing hormone from female rat pituitary glands in vitro

1982 ◽  
Vol 94 (1) ◽  
pp. 11-20 ◽  
Author(s):  
J. de Koning ◽  
A. M. I. Tijssen ◽  
J. A. M. J. van Dieten ◽  
G. P. van Rees
Keyword(s):  
Protein Synthesis ◽  
Initial Phase ◽  
Phase Response ◽  
Ovariectomized Rats ◽  
Second Phase ◽  
Pituitary Glands ◽  
Lh Release ◽  
Lh Rh ◽  
Intact Rats

Continuous exposure of hemi-pituitary glands from intact female rats to LH releasing hormone (LH-RH) in vitro displayed three phases in the pattern of LH release: during the first hour release of LH was low (first phase response), then it increased to a higher level during the second hour and remained constant during the next 2 h (second phase response), after which there was a refractoriness of LH release (third phase response). The initial phase response of pituitary glands from intact rats was blocked by EGTA (a Ca2+ chelator) but there was a small but significant increase in the rate of LH release during the second phase response. This increase could be prevented by inhibition of protein synthesis by cycloheximide. Cycloheximide and EGTA did not affect basal release of LH by glands from intact rats, neither did EGTA affect the high basal release of LH by glands from ovariectomized rats. However, the LH-RH-induced release of LH from pituitary glands of ovariectomized rats, which did not show the initial phase of low LH release, was completely suppressed by EGTA throughout a 4-h incubation period. The pattern of LH release stimulated by the combination of N6-monobutyryl cyclic AMP and theophylline (mbcAMP/theophylline) showed an initial phase of low LH release lasting 4 h after which it increased. The magnitude of the effect was small compared with the action of LH-RH. As it did with LH-RH, EGTA completely blocked the initial response, but allowed a small increase in the rate of LH release thereafter; this increase could also be blocked by inhibition of protein synthesis. Addition of EGTA to media during pretreatment of pituitary glands from intact rats with either LH-RH or mbcAMP/theophylline did not impair the facilitatory effect of these secretagogues on the responsiveness of the glands to subsequent exposure to LH-RH and cycloheximide and normal Ca2+ levels. The restoration of Ca2+ levels after withdrawal neither affected basal nor LH-RH-induced release of LH. Exclusion of Ca2+ from the media during a 6-h incubation of pituitary glands from intact rats with LH-RH prevented the glands from becoming refractory to subsequent stimulation by LH-RH, which occurs when normal Ca2+ concentrations are present. The results suggested that extracellular Ca2+ is obligatory for LH release and the induction of refractoriness by LH-RH. In contrast, that part of the action of LH-RH which is cyclic AMP-mediated and protein synthesis-dependent is not affected by withdrawal of extracellular Ca2+.

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