476 research outputs found
Measurement of volumetric lesion load in multiple sclerosis: moving from normal- to dirty-appearing white matter
No full textDiffusion-weighted imaging parameters to track success of pyogenic brain abscess therapy
No full textSeed ecology in dry sandy grasslands - an approach to patterns and mechanisms
No full textDry sandy grasslands occur throughout Central Europe and Southern Germany, and they host many rare and endangered plant species. To date, insufficient data on seed ecological aspects of this endangered vegetation type exist. Seed ecological studies attempt to develop ecological knowledge by identifying patterns and underlying mechanisms. To bring all results together, it can be pointed out that environmental factors strongly shape seed ecological patterns. Species with special mechanisms like those creating persistent seed banks for small sized seeds, faster germination speed and the development of physiological dormancy may tolerate sandy grasslands habitat conditions. Filtering effect of aluminum toxicity for germination of species from calcareous soil indicates the importance of regeneration niches in community assembly. Developing seed ecological traits as easy measurable traits would help to elucidate community assembly rules. Different factors like habitat conditions and seed responses to these environmental factors, seed reserves and germination limitations should be considered in restoration ecology and conservation issues. Seed ecological studies can help in habitat restoration planning and species reintroduction design making
Experimental investigation into gas migration mechanism in submarine sandy sediments at pore-scale
Get PDFThe dissociation of natural gas hydrate usually induces gas migration within shallow marine sediments, which has been widely reported to trigger geological hazards and submarine facility failure. To date, the mechanisms by which gas migration governs internal structural evolution and seafloor morphological changes remain poorly understood. This study investigates the gas migration behavior and associated morphological changes in sandy sediments using a novel experimental setup that integrates X-ray computed tomography scanning technology with a custom-built seepage apparatus. The apparatus enables gas injection with constant flow rate and real-time observation of the occurrence and migration process of gas within sediments. Experiments were conducted on Fujian sand with different particle sizes and gas flow rates, demonstrating that gas migration follows a particle-displacement pattern in fine-grained sediments and a pore-invasion pattern otherwise. The study further explores the dynamics of gas pocket formation, as well as the channel healing and re-opening behavior. The results demonstrate the porescale mechanism governing morphological evolution of seabed, with pockmarks and knolls at the surface and elongated chimney-like channels underneath. This work also highlights the advantage of X-ray computed tomography techniques for understanding gas migration processes in marine sediments.Document Type: Original articleCited as: Sun, W., Kong, D., Li, Z., Peng, Y., Chen, Y., Cheng, Y. P., Zhu, B. Experimental investigation into gas migration mechanism in submarine sandy sediments at pore-scale. Advances in Geo-Energy Research, 2025, 17(1): 30-42. https://doi.org/10.46690/ager.2025.07.0
The Resilience of Biofilm‐Bound Sandy Systems to Cyclic Changes in Shear Stress
No full textSand-attached benthic biofilms drive many important biogeological processes and serve as cooperative “ecosystem engineers”. In aquatic environments, biofilms undergo periodic detachment and re-colonization due to the regular changes in hydrodynamic forcing. However, legacy impacts of past microbial actions on current biofilm formation and the biostabilization of the substratum sands are yet to be fully understood. In this study, a systematic set of flume experiments were conducted to investigate the effects of different depositional histories. Changes in the erosion threshold and rate of erosion were determined from the time sequences of suspended sediment concentrations. The contents of extracellular polymeric substances (EPS) and particle morphology of the biofilm-bound sandy matrix were analyzed. Surprisingly, biostabilization is disturbance-stimulated, rather than disturbance-limited, as previously thought. Bio-sandy beds cultivated under intensive disturbance presented an EPS accumulation in each cycle, and showed a more rapid increase in bed strength and stability than when rarely disturbed. All colonies from previous cycles exhibited traces of EPS as “footprints”. These stimulated and possibly accelerated the process of recolonization, thereby enhancing the erosion resistance of the bed. In contrast, a stabilized bed was better suited to mature microbial communities. A modified “Windows of Opportunity” framework was therefore put forward. Although biostabilization was not established within short quiescent periods, the system created the “opportunity” to become established in subsequent “windows” by seeding the colonization process. The stabilization, destabilization and re-stabilization of biofilm may imply a much more important role as ecosystem engineers and is relevant for a range of engineered bio-systems
[[alternative]]THE EFFECT OF REPEATED MAXIMAL ISOKINETIC VOLUNTARY ECCENTRIC
No full text[[abstract]]不論是運動選手或一般大眾從事運動時，所引起之延遲性肌肉酸痛(
DOMS)現象，是一 個很普遍且又不會感到陌生的經驗。當肌纖維發
生DOMS時，是否可以再繼續從事高強度的劇烈運動呢? 或是應等到 DOMS
的情況完全復原才可以再作運動呢? 此一問題亦是大家所關心的問題。所
以本研究的目的在於探討從事反覆最大自主等速離心收縮運動，對已受到
損傷且還未完全恢復之肌纖維的影響。受試者為24名大學健康男性學生，
平均年齡為22.9±2.3歲，身高173.6±6.9公分，體重68.2±5.1公斤。本
研究是以隨機分派的方式將受試者分成反覆離心運動組和控制組，每組各
十二名。所有受試者一開始須從事一回合共30次最大自主等速離心收縮
(是以Cybex 6000機器，將轉速設定在60度/秒之情形下)，來誘發其非慣
用手的肱二頭肌產生DOMS之狀態。其中反覆離心運動組在第一回合運動後
的第三和第六天時，各再作一回合的最大自主等速離心運動。本研究的依
變項為肘關節活動範圍、肌肉酸痛指數、最大屈肘等長肌力、CK 和 GOT
活性值。所有受試者在第一回合運動前及 運動後第 1-9 天之間，每天
各接受一次肌肉酸痛指數測量及一次抽血(共十次);在第一回合運動前及
運動後的第0、1、2、3、4、5、6、7、8、9 天時，各接受一次肘關節活
動範圍及最大屈肘等長肌力的測驗(實驗組之所有依變項均統一在每回合
的運動前測量)。 結果:發現不同兩組在所有DOMS的評估指標中，皆僅在
時間方面有達到顯著水準(P<.05)而已;換言之，反覆離心運動組在從事第
一回合離心運動後的第三和第六天時，再繼續各作一回合高強度的離心收
縮運動後，發現並沒有進一步加重肌纖維受到損傷或阻礙肌肉損傷之恢復
的情形，所以當肌纖維因從事離心運動進而引起DOMS的情形時，可能不須
等到DOMS完全恢復，即可再繼續從事高強度的運動。 結論:因從事運動所
引起之DOMS，在肌肉酸痛情況、關節活動範圍、肌肉力量、血液中之 CK
和 GOT 活性還未恢復之前，再繼續從事高強度之離心運動，可能不會進
一步加重肌纖維之損傷情形，所以在此一情況下，可能可以繼續從事運動
或訓練，而不會產生額外的肌肉損傷。
Delayed onset muscle soreness (DOMS) is commonly caused by
unaccustomedor novel exercise in both recreational and elite
athletes. Should one make the muscle do strenuous exercise when
it has already produced DOMS ? Thisis a question that everybody
cares about needs to know the answer. The purpose of this study
was to investigate whether performing repeated boutsof
isokinetic voluntary eccentric exercise when muscles had not
recovered from previous exercise would have a positive influence
on DOMS recovery. Agroup of of 24 male university students
(22.9±2.3 yrs,173.6±6.9 cm,68.2±5.1 kg) were placed in one of
two groups. The control group (n=12) and ex-ercise group (n=12)
performed three sets of 10 maximal isokinetic voluntary
eccentric actions (ECC1) of the non-dominant forearm flexors. A
Cybex 6000that was set at a speed of 60
Delayed onset muscle soreness (DOMS) is commonly caused by
Experimental Study on Static Characteristics of Sandy Pebble Soil
No full textThrough the consolidation drained triaxial shear test of sandy pebble soil, the stress-strain curve of sandy pebble soil is obtained, analysis manifest that in the shearing process, shear dilatancy deformation and shear contraction deformation of sandy pebble soil are intercoupling, making asymptote of the curve after peak stress nearly a horizontal line. Meanwhile, based on the Duncan-Chang model, elastic modulus and Poisson ratio features of sandy pebble soil are analyzed, and Duncan-Chang model parameters are obtained.</jats:p
[[alternative]]The Effects of The Repeated Bout Effect on Muscle Damage
No full text[[abstract]]BACKGROUND: Previous studies have shown that repeating the same bouts of 30 maximal voluntary eccentric contractions at 1 to 6 days or 3 and 6 days after the first maximal eccentric exercise (ECC1) did not cause further muscle damage. This is referred to as the “repeated bout effect”. However, the amount of total work done during each of the subsequent bouts could only reach about 57%-76% of that done during the ECC1. It may be possible that the repeated bout of 30 maximal eccentric contractions was not stressful enough to produce further damage. What if one were to do the subsequent bout of intensive eccentric exercise, at what intensity would this second bout produce no further muscle damage or retard the recovery process? PURPOSE: This study examined the effects of the repeated bout effect after second bout of intensive eccentric exercise (80%, 90%, and 100% of the pre-ECC1 MVC level) on the indicators of muscle damage. METHODS: Fifty-one college-age males and females were randomly assigned into 100% maximal isometric voluntary contraction strength (MVC)(E100; n =12), 90% MVC (E90; n =13), 80% MVC (E80; n =14), and control (CON; n = 12) groups. The initial exercise was 30 maximal eccentric contraction (ECC1) on non-dominant elbow flexors using a dumbbell that was set at 100% of the pre-ECC1 MVC level. Three days after ECC1, the E80, E90, and E100 groups repeated this same exercise of 30 repetitions, but using a dumbbell that was set at 80%, 90%, and 100%, respectively, of the pre-ECC1 MVC level. This second bout was hereafter referred to as ECC2. Upper arm circumference (CIR), range of motion (ROM), MVC, serum creatine kinase (CK) and lactate dehydrogenase (LDH) activities were measured before, immediately after, and every 24 hours or 9 consecutive days after ECC1. In the E80, E90, and E100 groups, CIR, ROM, MVC, CK, and LDH were also tested immediately after ECC2. Muscle soreness was assessed before and for 9 consecutive days after ECC1. Ultrasound imagines were taken from the upper arm immediately before ECC1, and at 2, 4, and 9 days after ECC1 for all groups. RESULTS: There were significant changes (p < 0.05) in all criterion measures following ECC1 for all groups. Moreover, the E80 to E100 subjects who repeated the second bout of eccentric contraction training at varying intensities 3 days after ECC1, no further muscle damage was observed when the indirect indicators of muscle damage were used. However, the ultrasound imagine showed a significant increased (p < 0.05) in muscle damaged area after ECC2 for the E100 group when compared to the E80, E90, and CON groups. CONCLUSION: 1.When the indirect indicators of muscle damage (e.g. MVC, ROM, CIR, soreness, CK, LDH) were used for the evaluation of eccentric-training effect after repeating a second bout of eccentric exercise on the damaged muscle, at the intensity of 80~100% pre-ECC1 MVC level, no signs of deterioration or retardation in the recovery process were observed. 2.However, when ultrasound images were used for the evaluation of eccentric-training at 100% of pre-ECC1 MVC level, the damage was much more evident. This suggest that the upper limit of repeated bout effect is approximately at 90% of pre-ECC1 MVC. 3.The results of this study may provide new information and serve as a practical reference to strength training for coaches, athletes and the general public during muscle damage and muscle soreness.
KEY WORDS: eccentric contraction training, repeated bout effect, ultrasound imagines,
muscle damage.
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