124 research outputs found
Threshold of microvascular occlusion: injury size defines the thrombosis scenario
Damage to the blood vessel triggers formation of a hemostatic plug, which is
meant to prevent bleeding, yet the same phenomenon may result in a total
blockade of a blood vessel by a thrombus, causing severe medical conditions.
Here, we show that the physical interplay between platelet adhesion and
hemodynamics in a microchannel manifests in a critical threshold behavior of a
growing thrombus. Depending on the size of injury, two distinct dynamic
pathways of thrombosis were found: the formation of a nonocclusive plug, if
injury length does not exceed the critical value, and the total occlusion of
the vessel by the thrombus otherwise. We develop a mathematical model that
demonstrates that switching between these regimes occurs as a result of a
saddle-node bifurcation. Our study reveals the mechanism of self-regulation of
thrombosis in blood microvessels and explains experimentally observed
distinctions between thrombi of different physical etiology. This also can be
useful for the design of platelet-aggregation-inspired engineering solutions.Comment: 7 pages, 5 figures + Supplementary informatio
Tubulin bond energies and microtubule biomechanics determined from nanoindentation in silico
Microtubules, the primary components of the chromosome segregation machinery,
are stabilized by longitudinal and lateral non-covalent bonds between the
tubulin subunits. However, the thermodynamics of these bonds and the
microtubule physico-chemical properties are poorly understood. Here, we explore
the biomechanics of microtubule polymers using multiscale computational
modeling and nanoindentations in silico of a contiguous microtubule fragment. A
close match between the simulated and experimental force-deformation spectra
enabled us to correlate the microtubule biomechanics with dynamic structural
transitions at the nanoscale. Our mechanical testing revealed that the
compressed MT behaves as a system of rigid elements interconnected through a
network of lateral and longitudinal elastic bonds. The initial regime of
continuous elastic deformation of the microtubule is followed by the transition
regime, during which the microtubule lattice undergoes discrete structural
changes, which include first the reversible dissociation of lateral bonds
followed by irreversible dissociation of the longitudinal bonds. We have
determined the free energies of dissociation of the lateral (6.9+/-0.4
kcal/mol) and longitudinal (14.9+/-1.5 kcal/mol) tubulin-tubulin bonds. These
values in conjunction with the large flexural rigidity of tubulin
protofilaments obtained (18,000-26,000 pN*nm^2), support the idea that the
disassembling microtubule is capable of generating a large mechanical force to
move chromosomes during cell division. Our computational modeling offers a
comprehensive quantitative platform to link molecular tubulin characteristics
with the physiological behavior of microtubules. The developed in silico
nanoindentation method provides a powerful tool for the exploration of
biomechanical properties of other cytoskeletal and multiprotein assemblie
The role of platelets in blood coagulation during thrombus formation in flow
Hemostatic plug covering the injury site (or a thrombus in the pathological case) is formed due to the complex interaction of aggregating platelets with biochemical reactions in plasma that participate in blood coagulation. The mechanisms that control clot growth and which lead to growth arrest are not yet completely understood. We model them with numerical simulations based on a hybrid DPD-PDE model. Dissipative particle dynamics (DPD) is used to model plasma flow with platelets while fibrin concentration is described by a simplified reaction-diffusion-convection equation. The model takes into account consecutive stages of clot growth. First, a platelet is weakly connected to the clot and after some time this connection becomes stronger due to other surface receptors involved in platelet adhesion. At the same time, the fibrin network is formed inside the clot. This becomes possible because flow does not penetrate the clot and cannot wash out the reactants participating in blood coagulation. Platelets covered by the fibrin network cannot attach new platelets. Modelling shows that the growth of a hemostatic plug can stop as a result of its exterior part being removed by the flow thus exposing its non-adhesive core to the flow
Impact of shoreline changes to pahang coastal area by using geospatial technology
Malaysia has a long coastline stretching over 4,809 km where more than 1,300 km of beaches are experiencing erosion. Coastal erosion is recognised as the permanent loss of land and habitats along the shoreline resulting in the changes of the coast. Thus, it is important to detect and monitor shoreline changes especially in Pahang coast by identifying the rate of shoreline erosion and accretion. This study used temporal data and high spatial resolution imagery (SPOT 5) using remote sensing and GIS techniques to monitor shoreline changes along 10 study locations, which is from Cherating to Pekan of the Pahang coast. The total length of shoreline changes is about 14 km (14035.10 m) where all these areas are very likely to experience erosion ranging from 0.1 to 94.7 ha. On the other hand, these coastal areas found a minimal accretion with increased sediment from 0.1 to 2.8 ha. Overall, the coastal areas are exposed to higher erosion process than accretion with a very high vulnerability of erosion rate from 1.8 to 20.9 meter per year. The findings on monitoring shoreline changes and identifying vulnerable erosion areas might be useful in the policy and decision making for sustainable coastal management
Integrasi kaedah geospatial dan pemodelan hidrodinamik untuk mengkaji impakkenaikan aras laut terhadap kawasan pantai
Kawasan pesisir pantai merupakan kawasan yang sangat terdedah dan sensitif kepada pelbagai ancaman terutamanya hakisan dan limpahan yang boleh menyebabkan impak negatif kepada kesejahteraan hidup manusia, persekitaran dan ekosistem. Kawasan pesisir pantai di Batu Pahat, Johor sangat terdedah kepada masalah banjir akibat fenomena air pasang dan sebahagian kawasan pantai lain dikategorikan sebagai kawasan hakisan pantai kritikal. Tujuan kajian ini adalah untuk mengenal pasti impak kenaikan aras laut terhadap komuniti pesisir pantai di Batu Pahat. Dengan menggunakan perisian ArcGIS dan MIKE21, kawasan banjir yang berlaku terhadap penempatan komuniti di pesisir pantai Batu Pahat dapat dikenal pasti dan meramalkan impak masa hadapan. Melalui hasil kajian, kawasan pantai di Batu Pahat mengalami kejadian hakisan pantai yang aktif dan jumlah kadar kehilangan tanah di kawasan tersebut sebanyak 415.7 hektar berbanding dengan kadar pemendapan yang hanya mendapat kira-kira 68.52 hektar. Hasil peta-peta risiko inundasi bagi kenaikan aras laut menunjukkan anggaran seramai 50 hingga 1145 populasi daripada jumlah penduduk seramai 28420 orang akan menerima impak kesan dari kenaikan aras laut pada tahun 2013, 2020 dan 2040. Selain itu, daripada 33 batang jalan raya di kawasan kajian, hanya 1 kawasan akan menghadapi kesan kenaikan aras laut pada tahun 2020 dan 2040. Justeru itu, peta risiko inundasi yang disediakan bagi pantai Batu Pahat amatlah berguna untuk mencegah hakisan pantai dan mengurangkan bencana masa depan
Correction to: Thermal decomposition of rice husk: a comprehensive artificial intelligence predictive model
Unfortunately, in the original publication of the article the third author name was misspelled as
Faisal Abnisal. The corrected author name should read as “Faisal Abnisa”. The affiliation of
third author was incorrectly published. The corrected affiliation is given below
Thermal decomposition of rice husk: a comprehensive artificial intelligence predictive model
This study explored the predictive modelling of the pyrolysis of rice husk to
determine the thermal degradation mechanism of rice husk. The study can
ensure proper modelling and design of the system, towards optimising the
industrial processes. The pyrolysis of rice husk was studied at 10, 15 and
20 °C min−1 heating rates in the presence of nitrogen using thermogravimetric
analysis technique between room temperature and 800 °C. The thermal
decomposition shows the presence of hemicellulose and some part of
cellulose at 225–337 °C, the remaining cellulose and some part of lignin were
degraded at 332–380 °C, and lignin was degraded completely at 480 °C. The
predictive capability of artificial neural network model was studied using
different architecture by varying the number of hidden neurone node, learning
algorithm, hidden and output layer transfer functions. The residual mass, initial degradation temperature and thermal degradation rate at the end of the
experiment increased with an increase in the heating rate. Levenberg–
Marquardt algorithm performed better than scaled conjugate gradient
learning algorithm. This result shows that rice husk degradation is best
described using nonlinear model rather than linear model. For hidden and
output layer transfer functions, ‘log-sigmoid and tan-sigmoid', and ‘tansigmoid
and tan-sigmoid' transfer functions showed remarkable results based
on the coefficient of determination and root mean square error values. The
accuracy of the results increases with an increasing number of hidden
neurone. This result validates the suitability of an artificial neural network
model in predicting the devolatilisation behaviour of biomass
Structural basis of nucleosome assembly by the Abo1 AAA+ ATPase histone chaperone
The fundamental unit of chromatin, the nucleosome, is an intricate structure that requires histone chaperones for assembly. ATAD2 AAA+???ATPases are a family of histone chaperones that regulate nucleosome density and chromatin dynamics. Here, we demonstrate that the fission yeast ATAD2 homolog, Abo1, deposits histone H3???H4 onto DNA in an ATP-hydrolysis-dependent manner by in vitro reconstitution and single-tethered DNA curtain assays. We present cryo-EM structures of an ATAD2 family ATPase to atomic resolution in three different nucleotide states, revealing unique structural features required for histone loading on DNA, and directly visualize the transitions of Abo1 from an asymmetric spiral (ATP-state) to a symmetric ring (ADP- and apo-states) using high-speed atomic force microscopy (HS-AFM). Furthermore, we find that the acidic pore of ATP-Abo1 binds a peptide substrate which is suggestive of a histone tail. Based on these results, we propose a model whereby Abo1 facilitates H3???H4 loading by utilizing ATP
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