scholarly journals Air-temperature control on diurnal variations in microseismicity at Laohugou Glacier No. 12, Qilian Mountains

2019 ◽  
Vol 60 (79) ◽  
pp. 125-136 ◽  
Author(s):  
Tao Zhang ◽  
Yuqiao Chen ◽  
Min Ding ◽  
Zhongyan Shen ◽  
Yuande Yang ◽  
...  
Keyword(s):  
Short Duration ◽  
Crack Opening ◽  
Low Frequency ◽  
Local Stress ◽  
Stress Concentrations ◽  
Night Time ◽  
Strong Negative Correlation ◽  
Near Surface ◽  
Temperature Change Rate ◽  
Trigger Algorithm

ABSTRACTWe conducted a 9-d seismic experiment in October 2015 at Laohugou Glacier No. 12. We identified microseismic signals using the short-term/long-term average trigger algorithm at four stations and classified them as long and short-duration events based on waveform, frequency, duration and magnitude characteristics. Both categories show systematical diurnal trends. The long-duration events are low-frequency tremor-like events that mainly occurred during the daytime with only several events per day. These events lasted tens of seconds to tens of minutes and are likely related to resonance of daytime meltwater. The dominant short-duration events mostly occurred during the night time with a peak occurrence frequency of ~360 h−1. Their short-duration (<0.2 s), high frequency (20–100 Hz) and dominance of Rayleigh waves are typical of events for near-surface crack opening. A strong negative correlation between the hourly event number and temperature change rate suggests that the occurrence of night-time events is controlled by the rate of night-time cooling. We estimated the near-surface tensile stress due to thermal contraction at night to be tens of kilopascals, which is enough to induce opening of surface cracks with pre-existing local stress concentrations, although we cannot exclude the effect of refreezing of meltwater produced during the day.

Plastics Sandwich Beams under Bending Loads of Short Duration

1967 ◽  
Vol 9 (5) ◽  
pp. 355-361 ◽  
Author(s):  
R. M. Ogorkiewicz ◽  
A. A. M. Sayigh
Keyword(s):  
Polyvinyl Chloride ◽  
Short Duration ◽  
Stress Function ◽  
Local Stress ◽  
Sandwich Beams ◽  
Stress Concentrations ◽  
Four Point Bending ◽  
Bending Loads ◽  
Uniformly Distributed Loads ◽  
Good Agreement

Design of plastics sandwich structures calls for methods of predicting their deformation under load, which were studied with particular reference to beams under three- and four-point bending and under uniformly distributed loads. A preliminary series of tests established the stress-strain characteristics of p.v.c. (polyvinyl chloride) and polyurethane core and rigid p.v.c. skin materials. Using stress function solutions deflections and skin strains of different beams of these materials were then calculated and compared with experimental results obtained with beams made of the same combinations of materials. Good agreement was found for loads of short duration within the limits imposed by local stress concentrations.

scholarly journals Influence of Reversed Fatigue Loading on Damage Evolution of Cross-Ply Carbon Fibre Composites

Materials ◽  
2019 ◽  
Vol 12 (7) ◽  
pp. 1153 ◽  
Author(s):  
Just ◽  
Koch ◽  
Brod ◽  
Jansen ◽  
Gude ◽  
...  
Keyword(s):  
Residual Stresses ◽  
Carbon Fibre ◽  
Crack Formation ◽  
Crack Opening ◽  
Local Stress ◽  
Fatigue Loading ◽  
Stress Concentrations ◽  
Delamination Growth ◽  
Stress Ratios ◽  
Carbon Fibre Composites

Microcrack formation and delamination growth are the main damage mechanisms in thefatigue of composites. They lead to significant stiffness loss, introduce stress concentrations andcan be the origin of subsequent damage events like buckling or fibre breakage, especially in case ofshear and compression stresses during load reversal. Fatigue experiments of carbon fibre reinforcedlaminates were conducted at several stress ratios and analysed in terms of crack and delaminationgrowth. These investigations were accompanied by microscopic imaging, digital image correlationand finite element modelling to take into account the effects of residual stresses and crack closure.It was found that residual stresses significantly change the local stress ratio in off-axis layers andlead to residual crack opening of inter fibre cracks. These cracks remain open and close under highcompression loadings only. Furthermore, crack formation under pulsating compression loadingturned out to be driven by residual stresses leading to perpendicular cracks as observed underpure tension loading. The experimental findings further confirm the severe detrimental effect oftension-compression loading on crack formation and delamination growth compared to pulsatingtension-tension or compression-compression loads.

A Simple Model for Fatigue Crack Growth Near Stress Concentrations

1991 ◽  
Vol 113 (4) ◽  
pp. 542-548 ◽  
Author(s):  
R. C. McClung
Keyword(s):  
Fatigue Crack ◽  
Simple Model ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Fatigue Cracks ◽  
Crack Opening ◽  
Local Stress ◽  
Growth Data ◽  
Stress Concentrations

Fatigue crack growth rates are often difficult to predict for short cracks growing near stress concentrations. This paper presents a simple model to predict those growth rates which incorporates the phenomenon of crack closure. Crack opening stresses are shown to change significantly as cracks grow away from notches, and the simple model is designed to describe those changes. The effective stress range ratio, U, is assumed to be dependent on the local stress at the crack tip location in a corresponding uncracked body. The value of U changes with the normalized maximum stress in unnotched bodies, and this dependence can be quantified with elastic-plastic finite element models or simpler modified-Dugdale crack analyses. The local stress distribution is estimated with a Neuber analysis. A semi-empirical stress intensity factor solution is constructed and calibrated with known exact solutions. The crack growth rate is then calculated with the modified Paris law, taking crack growth constants from long crack data. The model is illustrated with a specific case study, the growth of cracks from center notches in an SAE 1026 steel. Experimental crack growth data for notches of different sizes and shapes compare favorably with the calculations. The scheme is contrasted with previous models for notch fatigue cracks. The implications of the simple model for other fatigue design problems are explored, highlighting the simplicity and generality of the model.

scholarly journals 125 Short Duration Monoballismus

CNS Spectrums ◽  
2018 ◽  
Vol 23 (1) ◽  
pp. 79-80
Author(s):  
Davinder Dhillon ◽  
Priya Batta ◽  
Alan R. Hirsch
Keyword(s):  
Short Duration ◽  
Parietal Lobe ◽  
Focal Epilepsy ◽  
Memory Loss ◽  
Low Frequency ◽  
Normal Animal ◽  
Conversion Disorder ◽  
Huntington's Chorea ◽  
Study Objective ◽  
Alien Hand Syndrome

AbstractStudy ObjectiveWhile monoballismus has been reported to be associated with hemorrhagic lesions in the subthalamic nucleus (Ohnishi, 2009) and multiple sclerosis (MS) (Rosa, 2011), the duration has been reported to be at least six days (Soysal, 2012). A patient with epochs of monoballismus lasting for 45 minutes is presented.MethodsCase Study: A 57 year old right handed female with attention deficit hereditary disorder predominantly inattentive on amphetamine sulphate, presented with two years of memory loss. For instance, after ordering food in restaurants, by the time the food arrives, she could not recall what she ordered. At the onset of this symptom, she noted three epochs of her left arm jerking for 45 minutes. The jerking would begin with low amplitude and low frequency and rapidly progress to the forearm and arm of greater magnitude and low frequency. With her right hand she would try to hold down her left arm without success. There was no associated paresis, sensory phenomena, headaches, dizziness, presyncope, loss of consciousness, or strong emotions. She admitted to frequent jamais vu.ResultsAbnormalities: Neurological Examination: Mental Status Examination: Memory: Immediate Recall: 5 digits forward and 2 digits backwards. Cranial Nerve (CN) Examination: CN I: Alcohol Sniff Test 8 (hyposmia). CN XII: tongue tremor on protrusion. Motor Examination: Drift Test: positive right pronator drift. Gait Examination: Tandem Gait: unstable. Reflexes: 0-1 throughout. Neuropsychiatric Examination: Go-No-Go Test: 6/6 (normal). Animal Fluency Test: 15 (normal). Clock Drawing Test: 3 (abnormal). Center for Neurologic Study Lability Scale: 16 (pseudobulbar affect). Other: MRI with and without infusion: normal.ConclusionTransient tonic-clonic movements of one limb have been described with focal epilepsy associated with diabetic non-ketotic hyperglycemia (Grant, 1985). A metabolic abnormality such as transient hypoglycemia or hyperkalemia can cause a focal dystonia (Soysal, 2012), which theoretically could manifest with monoballismus. This could be a somatic manifestation of underlying conflict, conversion disorder, or as a result of a physical manifestation of panic attack with hyperventilation and tetany (Mihai, 2008). This may be the first manifestation of a generalized cerebral disorder associated with chorea or ballismus such as Wilson’s disease, or Huntington’s Chorea (Mihai, 2008). It is possible that this is a variant of Alien Hand Syndrome with parietal lobe involvement (Shrestha, 2015). But this is unlikely given the absence of hemineglect or hemiagnosia. It is possible that amphetamines may have induced a monochorea. Chronic amphetamine use has been demonstrated to cause chorea (Klawans, 1974) and it theoretically could have caused ballismus movements in this case. In patients who present with short duration monoballismus, evaluation for subthalamic nuclei function, seizure disorders and other origins of ballismus are warranted.Funding AcknowledgementsSmell & Taste Treatment and Research Foundation

scholarly journals Large Temperature Fluctuations due to Cold-Air Pool Displacement along the Lee Slope of a Desert Mountain

2017 ◽  
Vol 56 (4) ◽  
pp. 1083-1098 ◽  
Author(s):  
Matthew E. Jeglum ◽  
Sebastian W. Hoch ◽  
Derek D. Jensen ◽  
Reneta Dimitrova ◽  
Zachariah Silver
Keyword(s):  
Low Frequency ◽  
Temperature Fluctuations ◽  
Atmospheric Modeling ◽  
Large Temperature ◽  
Complex Flow ◽  
Near Surface ◽  
Cold Air ◽  
Flow Interactions ◽  
Initial Drop ◽  
Program Temperature

AbstractLarge temperature fluctuations (LTFs), defined as a drop of the near-surface temperature of at least 3°C in less than 30 min followed by a recovery of at least half of the initial drop, were frequently observed during the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) program. Temperature time series at over 100 surface stations were examined in an automated fashion to identify and characterize LTFs. LTFs occur almost exclusively at night and at locations elevated 50–100 m above the basin floors, such as the east slope of the isolated Granite Mountain (GM). Temperature drops associated with LTFs were as large as 13°C and were typically greatest at heights of 4–10 m AGL. Observations and numerical simulations suggest that LTFs are the result of complex flow interactions of stably stratified flow with a mountain barrier and a leeside cold-air pool (CAP). An orographic wake forms over GM when stably stratified southwesterly nocturnal flow impinges on GM and is blocked at low levels. Warm crest-level air descends in the lee of the barrier, and the generation of baroclinic vorticity leads to periodic development of a vertically oriented vortex. Changes in the strength or location of the wake and vortex cause a displacement of the horizontal temperature gradient along the slope associated with the CAP edge, resulting in LTFs. This mechanism explains the low frequency of LTFs on the west slope of GM as well as the preference for LTFs to occur at higher elevations later at night, as the CAP depth increases.

Dispersion relations, rays and ray splitting in magnetohelioseismology

2005 ◽  
Vol 364 (1839) ◽  
pp. 333-349 ◽  
Author(s):  
P.S Cally
Keyword(s):  
Strong Field ◽  
Mode Conversion ◽  
Low Frequency ◽  
Active Regions ◽  
Dispersion Relations ◽  
Near Surface ◽  
Wave Splitting ◽  
Proper Account ◽  
Acoustic Dispersion ◽  
Field Inclination

Local helioseismology seeks to probe the near surface regions of the Sun, and in particular of active regions. These are distinguished by their strong magnetic fields, yet current local techniques do not take proper account of this. Here, we first derive appropriate gravito-magneto-acoustic dispersion relations, and then use these to examine how acoustic rays entering regions of strong field split into fast and slow components, and the subsequent fates of each. Specifically, two types of transmission point, where wave energy can transfer from the fast to slow branch (or vice versa) are identified; one close to the equipartition level where the sound and Alfvén speeds coincide, and one higher up near the acoustic cutoff turning point. This second type only exists for rays of low frequency or low l though. In accord with recent studies of fast-to-slow mode conversion from the perspective of p-modes, magnetic field inclination is found to have significant consequences for wave splitting.

Low Cycle Fatigue Analysis of Marine Structures

2006 ◽  
Author(s):  
Xiaozhi Wang ◽  
Joong-Kyoo Kang ◽  
Yooil Kim ◽  
Paul H. Wirsching
Keyword(s):  
Welded Joints ◽  
Low Cycle Fatigue ◽  
Prediction Method ◽  
Local Stress ◽  
Cyclic Plasticity ◽  
Cycle Fatigue ◽  
Stress Concentrations ◽  
Damage Prediction ◽  
Marine Structure ◽  
Number Of Cycles

There are situations where a marine structure is subjected to stress cycles of such large magnitude that small, but significant, parts of the structural component in question experiences cyclic plasticity. Welded joints are particularly vulnerable because of high local stress concentrations. Fatigue caused by oscillating strain in the plastic range is called “low cycle fatigue”. Cycles to failure are typically below 104. Traditional welded joint S-N curves do not describe the fatigue strength in the low cycle region (< 104 number of cycles). Typical Class Society Rules do not directly address the low cycle fatigue problem. It is therefore the objective of this paper to present a credible fatigue damage prediction method of welded joints in the low cycle fatigue regime.

scholarly journals The influence of the forest on night-time snow surface temperature

2001 ◽  
Vol 32 ◽  
pp. 217-222 ◽  
Author(s):  
Peter Höller
Keyword(s):  
Surface Temperature ◽  
Open Field ◽  
Air Temperature ◽  
Forest Canopy ◽  
Small Range ◽  
Snow Surface ◽  
Net Radiation ◽  
Night Time ◽  
Near Surface ◽  
Snow Surface Temperature

AbstractSnow surface temperature (Ts) plays an important role in the formation of surface hoar or near-surface faceted crystals The goal of this study was to obtain detailed information on Ts in different forest stands nelr the timberline. The investigations were conducted during clear nights and showed that the snow surface temperature is influenced very strongly by the forest canopy. While the air temperature was very similar on the different experimental sites, Ts was higher in the forest than in the open field; on the south-facing slope the difference between the forest and the open field was 3–4.5°C, and on the north-facing slope approximately 3–7°C. Taking into account that εair is 0.7 and εtree is 0.94, the incoming radiation (I ↓) for the different experimental sites was calculated by the equation of Brunt (the canopy density was estimated using photographs taken with an 8 mm fish-eye). To calculate Ts, air temperature and averaged values of the net radiation (because the net radiation (I) has only a small range of variation during clear nights) were used. The results show that the calculated values were higher than the measured values (by approximately 2°C). However, a better correlation was found by using lower values of the emissivity (εair0.67 and εtree0.91).

Quantifying heating biases in marine air temperature observations, ~1790 - present

2021 ◽  
Author(s):  
Thomas Cropper ◽  
Elizabeth Kent ◽  
David Berry ◽  
Richard Cornes ◽  
Beatriz Recinos-Rivas
Keyword(s):  
Air Temperature ◽  
Diurnal Cycle ◽  
Surface Air Temperature ◽  
Night Time ◽  
Data Set ◽  
Near Surface ◽  
Marine Surface ◽  
Heating Model ◽  
Marine Air

<p>Accurate, long-term time series of near-surface air temperature (AT) are the fundamental datasets on which the magnitude of anthropogenic climate change is scientifically and societally addressed. Across the ocean, these (near-surface) climate records use Sea Surface Temperature (SST) instead of Marine Air Temperature (MAT) and blend the SST and AT over land to create datasets. MAT has often been overlooked as a data choice as daytime MAT observations from ships are known to contain warm biases due to the storage of accumulated solar energy. Two recent MAT datasets, CLASSnmat (1881 – 2019) and UAHNMAT (1900 – 2018), both use night-time MAT observations only. Daytime MAT observations in the International Comprehensive Ocean–Atmosphere Data Set (ICOADS) account for over half of the MAT observations in ICOADS, and this proportion increases further back in time (i.e. pre-1850s). If long-term MAT records over the ocean are to be extended, the use of daytime MAT is vital.</p><p> </p><p>To adjust for the daytime MAT heating bias, and apply it to ICOADS, we present the application of a physics-based model, which accounts for the accumulated energy storage throughout the day. As the ‘true’ diurnal cycle of MAT over the ocean has not been, to-date, adequately quantified, our approach also removes the diurnal cycle from ICOADS observations and generates a night-time equivalent MAT for all observations. We fit this model to MAT observations from groups of ships in ICOADS that share similar heating biases and metadata characteristics. This enables us to use the empirically derived coefficients (representing the physical energy transfer terms of the heating model) obtained from the fit for use in removal of the heating bias and diurnal cycle from ship-based MAT observations throughout ICOADS which share similar characteristics (i.e. we can remove the diurnal cycle from a ship which only reports once daily at noon). This adjustment will create an MAT record of night-time-equivalent temperatures that will enable an extension of the marine surface AT record back into the 18<sup>th</sup> century.</p>

TO DETERMINE THE PHYSICAL AND MECHANICAL PROPERTIES OF THE SOIL OF LANDSLIDE SLOPES FROM THE DEGREE OF POROSITY AND HUMIDITY

InterConf ◽  
2021 ◽  
pp. 917-933
Author(s):  
Аkbota Serikkyzy ◽  
A. Baimakhan ◽  
A. Makhanova ◽  
Baimakhan Baimakhan ◽  
G. Baimakhanova
Keyword(s):  
Mechanical Properties ◽  
Physical And Mechanical Properties ◽  
Local Stress ◽  
Saturated Soil ◽  
Degree Of Saturation ◽  
Stress Concentrations ◽  
Mountain Slope ◽  
Experimental Works ◽  
Water Saturated

The results of theoretical and experimental works devoted to the determination of the physical and mechanical properties of water–saturated soil are analyzed. On the basis of a comprehensive analysis, conclusions are formulated, and a method is proposed for determining the Young’s modulus and Poisson’s ratio for water-saturated soil, depending on humidity (degree of saturation) and porosity. Tables of data on the physical and mechanical properties of water–saturated soil are proposed. The study established the places of formation of local stress concentrations along the inclined layer. The values of dangerous stress concentrations found in various areas of the mountain slope that are vulnerable to collapse are shown in the tables.

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