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1
Nakagawa, Kosuke, Takahiro Tsukahara e Takahiro Ishida. "DNS Study on Turbulent Transition Induced by an Interaction between Freestream Turbulence and Cylindrical Roughness in Swept Flat-Plate Boundary Layer". Aerospace 10, n. 2 (30 gennaio 2023): 128. http://dx.doi.org/10.3390/aerospace10020128.
Testo completoAbstract (sommario):
Laminar-to-turbulent transition in a swept flat-plate boundary layer is caused by the breakdown of the crossflow vortex via high-frequency secondary instability and is promoted by the wall-surface roughness and the freestream turbulence (FST). Although the FST is characterized by its intensity and wavelength, it is not clear how the wavelength affects turbulent transitions and interacts with the roughness-induced transition. The wavelength of the FST depends on the wind tunnel or in-flight conditions, and its arbitrary control is practically difficult in experiments. By means of direct numerical simulation, we performed a parametric study on the interaction between the roughness-induced disturbance and FST in the Falkner–Skan–Cooke boundary layer. One of our aims is to determine the critical roughness height and its dependence on the turbulent intensity and peak wavelength of FST. We found a suppression and promotion in the transition process as a result of the interaction. In particular, the immediate transition behind the roughness was delayed by the long-wavelength FST, where the presence of FST suppressed the high-frequency disturbance emanating from the roughness edge. Even below the criticality, the short-wavelength FST promoted a secondary instability in the form of the hairpin vortex and triggered an early transition before the crossflow-vortex breakdown with the finger vortex. Thresholds for the FST wavelengths that promote or suppress the early transition were also discussed to provide a practically important indicator in the prediction and control of turbulent transitions due to FST and/or roughness on the swept wing.
2
OVCHINNIKOV, VICTOR, MEELAN M. CHOUDHARI e UGO PIOMELLI. "Numerical simulations of boundary-layer bypass transition due to high-amplitude free-stream turbulence". Journal of Fluid Mechanics 613 (1 ottobre 2008): 135–69. http://dx.doi.org/10.1017/s0022112008003017.
Testo completoAbstract (sommario):
Direct numerical simulations (DNS) of bypass transition due to high-amplitude free-stream turbulence (FST) are carried out for a flat-plate boundary layer. The computational domain begins upstream of the plate leading edge and extends into the fully turbulent region. Thus, there is noad hoctreatment to account for the initial ingestion of FST into the laminar boundary layer. We study the effects of both the FST length scale and the disturbance behaviour near the plate leading edge on the details of bypass transition farther downstream. In one set of simulations, the FST parameters are chosen to match the ERCOFTAC benchmark case T3B. The inferred FST integral length scaleL11is significantly larger (RL=UL11/ν = 6580) than that employed in previous simulations of bypass transition (RL≃ 1000). An additional set of simulations was performed atRL= 1081 to compare the transition behaviour in the T3B case with that of a smaller value of FST length scale. The FST length scale is found to have a profound impact on the mechanism of transition. While streamwise streaks (Klebanoff modes) are observed at both values of the FST length scale, they appear to have clear dynamical significance only at the smaller value ofRL, where transition is concomitant with streak breakdown. For the T3B case, turbulent spots form upstream of the region where streaks could be detected. Spot precursors are traced to quasi-periodic spanwise structures, first observed as short wavepackets in the wall-normal velocity component inside the boundary layer. These structures are reoriented to become horseshoe vortices, which break down into young turbulent spots. Two of the four spots examined for this case had a downstream-pointing shape, similar to those found in experimental studies of transitional boundary layers. Additionally, our simulations indicate the importance of leading-edge receptivity for the onset of transition. Specifically, higher fluctuations of the vertical velocity at the leading edge of the plate result in higher levels of streamwise Reynolds stress inside the developing boundary layer, facilitating breakdown to turbulence.
3
Verberck, B., A. V. Nikolaev e K. H. Michel. "Theoretical Model for the Structural Phase Transition and the Metal–Insulator Transition in Polymerized KC60". Fullerenes, Nanotubes and Carbon Nanostructures 12, n. 1-2 (2 gennaio 2005): 243–52. http://dx.doi.org/10.1081/fst-120027164.
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Hosseinverdi, Shirzad, e Hermann F. Fasel. "Role of Klebanoff modes in active flow control of separation: direct numerical simulations". Journal of Fluid Mechanics 850 (10 luglio 2018): 954–83. http://dx.doi.org/10.1017/jfm.2018.489.
Testo completoAbstract (sommario):
Our previous research has shown that an active flow control strategy using two-dimensional (2-D) harmonic blowing and suction with properly chosen frequency and amplitude can significantly reduce the separation region, delay transition to turbulence and can even relaminarize the flow. How such effective flow control for transition delay and relaminarization is affected by free-stream turbulence (FST) remains an open question. In order to answer this question, highly resolved direct numerical simulations (DNS) are carried out where very low-amplitude isotropic FST fluctuations are introduced at the inflow boundary of the computational domain. With FST the effectiveness of the flow control is not diminished, and the extent of the separated flow region is reduced by the same amount as for the zero FST case. However, a striking difference observed in the DNS is the fact that in the presence of even very low levels of FST, the flow transitions shortly downstream of the reattachment location of the bubble, contrary to the case without FST. It appears that this different behaviour for even very small levels of FST is caused by an interaction between the high-amplitude 2-D disturbances introduced by the flow control forcing and 3-D Klebanoff modes (K-modes) that are generated by the FST. The streamwise elongated streaks due to the K-modes cause a spanwise-periodic modulation of the basic flow and subsequently of the primary 2-D wave. The disturbances associated with this modulation exhibit strong growth and initiate the breakdown process to turbulence. Linear secondary instability investigations with respect to low-frequency 3-D disturbances are carried out based on the linearized Navier–Stokes equations. The response of the forced flow to the low-frequency 3-D disturbances reveals that the time-periodic base flow is unstable with respect to a wide range of 3-D modes. In particular, the wavelength associated with the spanwise spacing of the K-mode falls into the range of, and is in fact very close to, the most unstable 3-D disturbances. Results from the secondary instability analysis and the comparison with DNS results, support the conjecture that the forcing amplitude has a major impact on the onset and amplification rate of the K-modes: lowering the forcing amplitude postpones the onset of the growth of the K-modes and reduces the growth rate of the K-modes for a given FST intensity. The net effect of these two events is a delay of the transition onset. Nevertheless, the instability mechanism that governs the transition process is the same as previously identified, i.e. interaction of the K-mode and 2-D primary wave. Furthermore, for low levels of FST, the amplitude of the low-frequency K-modes scales linearly with the FST intensity in the approach boundary layer up to the secondary instability regime.
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Hosseinverdi, Shirzad, e Hermann F. Fasel. "Numerical investigation of laminar–turbulent transition in laminar separation bubbles: the effect of free-stream turbulence". Journal of Fluid Mechanics 858 (12 novembre 2018): 714–59. http://dx.doi.org/10.1017/jfm.2018.809.
Testo completoAbstract (sommario):
The role of free-stream turbulence (FST) in the hydrodynamic instability mechanisms and transition to turbulence in laminar separation bubbles (LSBs) was investigated using direct numerical simulations (DNS). Towards this end, a set of highly resolved DNS have been carried out, where isotropic FST fluctuations with intensities from 0.1 % to 3 % are introduced to investigate the relevant physical mechanisms governing the interaction of separation and transition in LSBs. For disturbance-free simulations, i.e. without FST, laminar–turbulent transition involves a Kelvin–Helmholtz (KH) instability of the separated shear layer. For LSBs subjected to FST, vortical FST fluctuations penetrate the approaching attached laminar boundary layer upstream of the separation location and induce slowly growing low-frequency disturbances, so-called Klebanoff (K) modes, which cause a spanwise modulation with a distinct spanwise wavelength. Simultaneously, the FST enhances the initial levels of instability waves with frequencies in the frequency range of the KH instability, but at much smaller amplitude levels compared to the K-modes. Results from the calculations based on the linearized Navier–Stokes equations and comparison with DNS results reveal that the K-mode exhibits exponential growth in the separated shear layer until it reaches a peak amplitude. At the same time, two-dimensional (2D) disturbance waves are also exponentially amplified, in fact at larger growth rate compared to the K-mode, due to the primary (convective) shear-layer instability mechanism until they saturate downstream of the peak amplitude associated with the K-mode. Therefore, based on detailed spectral analysis and modal decompositions for the separation bubbles investigated, the transition process is the result of two different mechanisms: (i) strong amplification of high-frequency (order of the shedding frequency), essentially 2D or weakly oblique fluctuating disturbances and (ii) low-frequency, three-dimensional K-modes caused by FST. Depending on the intensity of the FST, one of these mechanisms would dominate the transition process, or both mechanisms act together and contribute simultaneously. The net effect of these two events is an acceleration of transition for an increased level of FST intensity, which in turn leads to a reduction of the extent of the separation bubble in streamwise and wall-normal directions. The ‘roll-up’ into spanwise large-scale vortical structures resulting from the shear-layer instability, and the eventual breakdown of these structures, strongly contribute to the reattachment process. The spanwise coherence of these ‘rollers’ deteriorates due to the presence of large-amplitude K-modes, thus effectively weakening their strength for high levels of FST intensities ($Tu>1\,\%$).
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Gall, N. R., E. V. Rut'kov e A. Ya Tontegode. "C60DECOMPOSITION ON SOME TRANSITION METAL AND SEMICONDUCTOR SURFACES". Fullerene Science and Technology 9, n. 2 (15 aprile 2001): 241–46. http://dx.doi.org/10.1081/fst-100102971.
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Konarev, Dmitri V., Gunzi Saito e Rimma N. Lyubovskaya. "Singlet‐Triplet Transition in the C60 2− Dianion". Fullerenes, Nanotubes and Carbon Nanostructures 12, n. 1-2 (2 gennaio 2005): 147–54. http://dx.doi.org/10.1081/fst-120027148.
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Balzer, Wolfgang, e H. F. Fasel. "Numerical investigation of the role of free-stream turbulence in boundary-layer separation". Journal of Fluid Mechanics 801 (21 luglio 2016): 289–321. http://dx.doi.org/10.1017/jfm.2016.424.
Testo completoAbstract (sommario):
The aerodynamic performance of lifting surfaces operating at low Reynolds number conditions is impaired by laminar separation. In most cases, transition to turbulence occurs in the separated shear layer as a result of a series of strong hydrodynamic instability mechanisms. Although the understanding of these mechanisms has been significantly advanced over the past decades, key questions remain unanswered about the influence of external factors such as free-stream turbulence (FST) and others on transition and separation. The present study is driven by the need for more accurate predictions of separation and transition phenomena in ‘real world’ applications, where elevated levels of FST can play a significant role (e.g. turbomachinery). Numerical investigations have become an integral part in the effort to enhance our understanding of the intricate interactions between separation and transition. Due to the development of advanced numerical methods and the increase in the performance of supercomputers with parallel architecture, it has become feasible for low Reynolds number application ($O(10^{5})$) to carry out direct numerical simulations (DNS) such that all relevant spatial and temporal scales are resolved without the use of turbulence modelling. Because the employed high-order accurate DNS are characterized by very low levels of background noise, they lend themselves to transition research where the amplification of small disturbances, sometimes even growing from numerical round-off, can be examined in great detail. When comparing results from DNS and experiment, however, it is beneficial, if not necessary, to increase the background disturbance levels in the DNS to levels that are typical for the experiment. For the current work, a numerical model that emulates a realistic free-stream turbulent environment was adapted and implemented into an existing Navier–Stokes code based on a vorticity–velocity formulation. The role FST plays in the transition process was then investigated for a laminar separation bubble forming on a flat plate. FST was shown to cause the formation of the well-known Klebanoff mode that is represented by streamwise-elongated streaks inside the boundary layer. Increasing the FST levels led to accelerated transition, a reduction in bubble size and better agreement with the experiments. Moreover, the stage of linear disturbance growth due to the inviscid shear-layer instability was found to not be ‘bypassed’.
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He, S., e M. Seddighi. "Turbulence in transient channel flow". Journal of Fluid Mechanics 715 (9 gennaio 2013): 60–102. http://dx.doi.org/10.1017/jfm.2012.498.
Testo completoAbstract (sommario):
AbstractDirect numerical simulations (DNS) are performed of a transient channel flow following a rapid increase of flow rate from an initially turbulent flow. It is shown that a low-Reynolds-number turbulent flow can undergo a process of transition that resembles the laminar–turbulent transition. In response to the rapid increase of flow rate, the flow does not progressively evolve from the initial turbulent structure to a new one, but undergoes a process involving three distinct phases (pre-transition, transition and fully turbulent) that are equivalent to the three regions of the boundary layer bypass transition, namely, the buffeted laminar flow, the intermittent flow and the fully turbulent flow regions. This transient channel flow represents an alternative bypass transition scenario to the free-stream-turbulence (FST) induced transition, whereby the initial flow serving as the disturbance is a low-Reynolds-number turbulent wall shear flow with pre-existing streaky structures. The flow nevertheless undergoes a ‘receptivity’ process during which the initial structures are modulated by a time-developing boundary layer, forming streaks of apparently specific favourable spacing (of about double the new boundary layer thickness) which are elongated streamwise during the pre-transitional period. The structures are stable and the flow is laminar-like initially; but later in the transitional phase, localized turbulent spots are generated which grow spatially, merge with each other and eventually occupy the entire wall surfaces when the flow becomes fully turbulent. It appears that the presence of the initial turbulent structures does not promote early transition when compared with boundary layer transition of similar FST intensity. New turbulent structures first appear at high wavenumbers extending into a lower-wavenumber spectrum later as turbulent spots grow and join together. In line with the transient energy growth theory, the maximum turbulent kinetic energy in the pre-transitional phase grows linearly but only in terms of ${u}^{\ensuremath{\prime} } $, whilst ${v}^{\ensuremath{\prime} } $ and ${w}^{\ensuremath{\prime} } $ remain essentially unchanged. The energy production and dissipation rates are very low at this stage despite the high level of ${u}^{\ensuremath{\prime} } $. The pressure–strain term remains unchanged at that time, but increases rapidly later during transition along with the generation of turbulent spots, hence providing an unambiguous measure for the onset of transition.
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Zhang, Guangsheng, Chenghao Wang, Lingmei Jiang, Yibo Wang, Bing Wang, Xiaoxu Wang, Haoran Liu, Lishuai Zong, Jinyan Wang e Xigao Jian. "Low Dielectric Constant Photocurable Fluorinated Poly (Phthalazinone Ether) Ink with Excellent Mechanical Properties and Heat Resistance". Polymers 15, n. 6 (20 marzo 2023): 1531. http://dx.doi.org/10.3390/polym15061531.
Testo completoAbstract (sommario):
The photosensitive resins for 3D printing technology have been widely applied throughout the advanced communication field due to their merits of high molding accuracy and fast processing speed. Regardless, they, in particular, should have better mechanical properties, heat resistance, and dielectric properties. Herein, photocurable fluorinated poly (phthalazinone ether) (FSt-FPPE) was utilized as a prepolymer to improve the performance of photosensitive resin. A series of UV-curable inks named FST/DPGs were prepared with FSt-FPPE and acrylic diluents of different mass fractions. The FST/DPGs were cured into films by UV curing and post-treatment. After curing, their properties were characterized in detail. In terms of heat resistance, glass transition temperature (Tg) could reach 233 °C and the 5% thermal decomposition temperature (Td5%) was 371 °C. The tensile strength surprisingly reached 61.5 MPa, and the dielectric constant (Dk) could be significantly reduced to 2.75. Additionally, FST/DPGs were successfully employed in UV-assisted direct writing (DIW) to print 3D objects that benefited from their commendable fluidity and rapid curing speed. A stiff cylinder sample with a smooth surface and distinct pattern was ultimately obtained, indicating their remarkable 3D printing adaptation. Such photosensitive resin for UV-assisted DIW exhibits tremendous potential in the electronic industry.
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AKTAŞ, Nesimi, e Kamil Emre GERÇEKASLAN. "Glass transition and sorption properties of Köftür: a dehydrated fruit-based product". Food Science and Technology 40, suppl 2 (dicembre 2020): 503–11. http://dx.doi.org/10.1590/fst.34419.
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Kondrin, M. V., A. G. Lyapin, S. V. Popova e V. V. Brazhkin. "Kinetic Properties of Orientational Phase Transition in Polymerized States of Fullerites C60". Fullerenes, Nanotubes and Carbon Nanostructures 12, n. 1-2 (2 gennaio 2005): 259–62. http://dx.doi.org/10.1081/fst-120027166.
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Stevenson, J. P. J., K. P. Nolan e E. J. Walsh. "Particle image velocimetry measurements of induced separation at the leading edge of a plate". Journal of Fluid Mechanics 804 (9 settembre 2016): 278–97. http://dx.doi.org/10.1017/jfm.2016.532.
Testo completoAbstract (sommario):
The free shear layer that separates from the leading edge of a round-nosed plate has been studied under conditions of low (background) and elevated (grid-generated) free stream turbulence (FST) using high-fidelity particle image velocimetry. Transition occurs after separation in each case, followed by reattachment to the flat surface of the plate downstream. A bubble of reverse flow is thereby formed. First, we find that, under elevated (7 %) FST, the time-mean bubble is almost threefold shorter due to an accelerated transition of the shear layer. Quadrant analysis of the Reynolds stresses reveals the presence of slender, highly coherent fluctuations amid the laminar part of the shear layer that are reminiscent of the boundary-layer streaks seen in bypass transition. Instability and the roll-up of vortices then follow near the crest of the shear layer. These vortices are also present under low FST and in both cases are found to make significant contributions to the production of Reynolds stress over the rear of the bubble. But their role in reattachment, whilst important, is not yet fully clear. Instantaneous flow fields from the low-FST case reveal that the bubble of reverse flow often breaks up into two or more parts, thereby complicating the overall reattachment process. We therefore suggest that the downstream end of the ‘separation isoline’ (the locus of zero absolute streamwise velocity that extends unbroken from the leading edge) be used to define the instantaneous reattachment point. A histogram of this point is found to be bimodal: the upstream peak coincides with the location of roll-up, whereas the downstream mode may suggest a ‘flapping’ motion.
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Watmuff, Jonathan H. "Effects of Weak Free Stream Nonuniformity on Boundary Layer Transition". Journal of Fluids Engineering 128, n. 2 (4 aprile 2005): 247–57. http://dx.doi.org/10.1115/1.2169813.
Testo completoAbstract (sommario):
Experiments are described in which well-defined weak Free Stream Nonuniformity (FSN) is introduced by placing fine wires upstream of the leading edge of a flat plate. Large amplitude spanwise thickness variations form in the boundary layer as a result of the interaction between the steady laminar wakes from the wires and the leading edge. The centerline of a region of elevated layer thickness is aligned with the centerline of the wake in the freestream and the response is shown to be remarkably sensitive to the spanwise length-scale of the wakes. The region of elevated thickness is equivalent to a long narrow low speed streak in the layer. Elevated Free Stream Turbulence (FST) levels are known to produce randomly forming arrays of long narrow low speed streaks in laminar boundary layers. Therefore the characteristics of the streaks resulting from the FSN are studied in detail in an effort to gain some insight into bypass transition that occurs at elevated FST levels. The shape factors of the profiles in the vicinity of the streak appear to be unaltered from the Blasius value, even though the magnitude of the local thickness variations are as large as 60% of that of the undisturbed layer. Regions of elevated background unsteadiness appear on either side of the streak and it is shown that they are most likely the result of small amplitude spanwise modulation of the layer thickness. The background unsteadiness shares many of the characteristics of Klebanoff modes observed at elevated FST levels. However, the layer remains laminar to the end of the test section (Rx≈1.4×106) and there is no evidence of bursting or other phenomena associated with breakdown to turbulence. A vibrating ribbon apparatus is used to examine interactions between the streak and Tollmien-Schlichting (TS) waves. The deformation of the mean flow introduced by the streak is responsible for substantial phase and amplitude distortion of the waves and the breakdown of the distorted waves is more complex and it occurs at a lower Reynolds number than the breakdown of the K-type secondary instability that is observed when the FSN is not present.
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Thompson, David M., John H. Brownie e Michael C. Baird. "Spectroscopic Evidence for Anionic Coordination Complexes of the Transition Metals with C70and the Higher Fullerenes C76, C78, C82, C84, C86, C90, and C92". Fullerenes, Nanotubes and Carbon Nanostructures 12, n. 3 (26 dicembre 2004): 697–713. http://dx.doi.org/10.1081/fst-200029881.
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Phani Kumar, P., A. C. Mandal e J. Dey. "Effect of a mesh on boundary layer transitions induced by free-stream turbulence and an isolated roughness element". Journal of Fluid Mechanics 772 (7 maggio 2015): 445–77. http://dx.doi.org/10.1017/jfm.2015.203.
Testo completoAbstract (sommario):
Streamwise streaks, their lift-up and streak instability are integral to the bypass transition process. An experimental study has been carried out to find the effect of a mesh placed normal to the flow and at different wall-normal locations in the late stages of two transitional flows induced by free-stream turbulence (FST) and an isolated roughness element. The mesh causes an approximately 30 % reduction in the free-stream velocity, and mild acceleration, irrespective of its wall-normal location. Interestingly, when located near the wall, the mesh suppresses several transitional events leading to transition delay over a large downstream distance. The transition delay is found to be mainly caused by suppression of the lift-up of the high-shear layer and its distortion, along with modification of the spanwise streaky structure to an orderly one. However, with the mesh well away from the wall, the lifted-up shear layer remains largely unaffected, and the downstream boundary layer velocity profile develops an overshoot which is found to follow a plane mixing layer type profile up to the free stream. Reynolds stresses, and the size and strength of vortices increase in this mixing layer region. This high-intensity disturbance can possibly enhance transition of the accelerated flow far downstream, although a reduction in streamwise turbulence intensity occurs over a short distance downstream of the mesh. However, the shape of the large-scale streamwise structure in the wall-normal plane is found to be more or less the same as that without the mesh.
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Westin, K. J. A., A. V. Boiko, B. G. B. Klingmann, V. V. Kozlov e P. H. Alfredsson. "Experiments in a boundary layer subjected to free stream turbulence. Part 1. Boundary layer structure and receptivity". Journal of Fluid Mechanics 281 (25 dicembre 1994): 193–218. http://dx.doi.org/10.1017/s0022112094003083.
Testo completoAbstract (sommario):
The modification of the mean and fluctuating characteristics of a flat-plate boundary layer subjected to nearly isotropic free stream turbulence (FST) is studied experimentally using hot-wire anemometry. The study is focussed on the region upstream of the transition onset, where the fluctuations inside the boundary layer are dominated by elongated flow structures which grow downstream both in amplitude and length. Their downstream development and scaling are investigated and the results are compared with those obtained by previous authors. This allows some conclusions about the parameters which are relevant for the modelling of the transition process. The mechanisms underlying the transition process and the relative importance of the Tollmien–Schlichting wave instability in this flow are treated in an accompanying paper (part 2 of the present report).
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Gahtori, Archana, e Abhishek Singh. "Ligand-based Pharmacophore Model for Generation of Active Antidepressant- like Agents from Substituted 1,3,5 Triazine Class". Current Computer-Aided Drug Design 16, n. 2 (25 marzo 2020): 167–75. http://dx.doi.org/10.2174/1573409915666181219125415.
Testo completoAbstract (sommario):
Introduction: Although the transition of a lead candidate into a drug is currently structured by well-defined milestone, it is still most challenging and offers no guarantee in success to the end. In fact, ligand-based pharmacophore modeling has become a key motive force for retrieving potential leads across several therapeutic areas. Methods: An urgent need towards the development of novel antidepressant agents led us to generate a pharmacophore model from an existing 44 compounds dataset. The best model with one hydrophobic, two ring aromatic, and one positive ionization features was chosen on behalf of the correlation coefficient, sensitivity, specificity, yield of actives and accuracy measures using HypoGen module of Discovery Studio. In house library consisting of 10,000 substituted 1,3,5 triazine derivatives were shortlisted to select four insilico hits. All shortlisted compounds were synthesized and characterized by FTIR, 1H-& 13C-NMR spectroscopy and finally tested for antidepressant-like activity using behavioral models on rats viz. Forced Swim Test (FST) and Elevated Plus Maze (EPM). Results: Two shortlisted compounds with optimal fit values showed a significant decrease in the duration of immobility as compared to standard drug Imipramine in FST while time spent in open arm in enhanced in case of EPM.
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Fan, Fan, Xianping Zhang, Chuanbing Cai e Yanwei Ma. "Angular dependence of the critical current density in FeSe0.5Te0.5 thin films on metal substrates". Superconductor Science and Technology 34, n. 12 (9 novembre 2021): 125015. http://dx.doi.org/10.1088/1361-6668/ac2e5c.
Testo completoAbstract (sommario):
Abstract Biaxially textured FeSe0.5Te0.5 (FST) thin films were fabricated on ion-beam assisted-deposition LaMnO3 (LMO) buffered metal substrate with additional CeO2 as a buffer layer. Profiting from the implementation of CeO2 layers, the resultant FST films show a small out-of-plane misalignment of about 2.04° and an in-plane misalignment around 4.02°. In addition, the films have a high superconducting transition temperature (T c) ∼ 17 K and a comparatively high critical current density (J c) of 0.78 MA cm−2 in self-field at 4.2 K. On the other hand, a high J c peak for H//c above H//ab at temperatures below 10 K was observed, which results from grain boundaries along the c-axis. In addition, J c peaks for H//ab emerge above 10 K and become more pronounced than those for H//c at 12 K, indicating both a temperature- and field-dependent pinning mechanism. Moreover, J c(θ) data except for in the vicinity of H//ab and H//c can be successfully scaled using the anisotropic Ginzburg–Landau approach with an appropriate J c anisotropy ratio of γJ c ∼ 1.5, implying the presence of both ab-plane and c-axis correlated flux pinning centers in FST films.
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Nielsen, Einar E., Peter Grønkjær, Dorte Meldrup e Helge Paulsen. "Retention of juveniles within a hybrid zone between North Sea and Baltic Sea Atlantic cod (Gadus morhua)". Canadian Journal of Fisheries and Aquatic Sciences 62, n. 10 (1 ottobre 2005): 2219–25. http://dx.doi.org/10.1139/f05-139.
Testo completoAbstract (sommario):
Elucidating the relative roles of dispersal and retention of juvenile stages is an important issue for understanding population structure and evolution in marine organisms. We investigated the genetic population structure of juvenile Atlantic cod (Gadus morhua) within the transition zone between the North Sea and the Baltic Sea, employing nine microsatellite loci, and compared our data with adult cod data from the same area. Small but statistically significant overall differentiation (Fst = 0.003) was found among juvenile samples. Samples of juveniles grouped genetically with adult samples from the same geographical regions. Individual admixture analysis of a large sample of juveniles taken within the transition zone showed that the patterns of genetic differentiation could not be explained by mixing of pure North Sea and Baltic Sea individuals. Instead, the high number of juveniles with intermediate genotypes was compatible with a scenario of exclusive local (transition zone) origin. The results support the hypothesis that population structure in marine fishes is maintained by the retention of juveniles.
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de Kloet, E. R., e M. L. Molendijk. "Coping with the Forced Swim Stressor: Towards Understanding an Adaptive Mechanism". Neural Plasticity 2016 (2016): 1–13. http://dx.doi.org/10.1155/2016/6503162.
Testo completoAbstract (sommario):
In the forced swim test (FST) rodents progressively show increased episodes of immobility if immersed in a beaker with water from where escape is not possible. In this test, a compound qualifies as a potential antidepressant if it prevents or delays the transition to this passive (energy conserving) behavioural style. In the past decade however the switch from active to passive “coping” was used increasingly to describe the phenotype of an animal that has been exposed to a stressful history and/or genetic modification. A PubMed analysis revealed that in a rapidly increasing number of papers (currently more than 2,000) stress-related immobility in the FST is labeled as a depression-like phenotype. In this contribution we will examine the different phases of information processing during coping with the forced swim stressor. For this purpose we focus on the action of corticosterone that is mediated by the closely related mineralocorticoid receptors (MR) and glucocorticoid receptors (GR) in the limbic brain. The evidence available suggests a model in which we propose that the limbic MR-mediated response selection operates in complementary fashion with dopaminergic accumbens/prefrontal executive functions to regulate the transition between active and passive coping styles. Upon rescue from the beaker the preferred, mostly passive, coping style is stored in the memory via a GR-dependent action in the hippocampal dentate gyrus. It is concluded that the rodent’s behavioural response to a forced swim stressor does not reflect depression. Rather the forced swim experience provides a unique paradigm to investigate the mechanistic underpinning of stress coping and adaptation.
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Shen, Luyu, e Changgen Lu. "On the Generation of Instability Tollmien-Schlichting Waves by Free-Stream Turbulence". Advances in Applied Mathematics and Mechanics 9, n. 2 (9 gennaio 2017): 429–38. http://dx.doi.org/10.4208/aamm.2015.m998.
Testo completoAbstract (sommario):
AbstractThe beginning of the transition from the laminar to a turbulent flow is usually the generation of instability Tollmien-Schlichting (T-S) waves in the boundary layer. Previously, most numerical and experimental researches focused on generating instability T-S waves through the external disturbances such as acoustic waves and vortical disturbances interacting with wall roughness or at the leading-edge of flatplate, whereas only a few paid attention to the excitation of the T-S waves directly by free-stream turbulence (FST). In this study, the generating mechanism of the temporal mode T-S waves under free-stream turbulence is investigated by using direct numerical simulation (DNS) and fast Fourier transform. Wave packets superposed by a group of stability, neutral and instability T-S waves are discovered in the boundary layer. In addition, the relation between the amplitude of the imposed free-stream turbulence and the amplitude of the excited T-S wave is also obtained.
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Wennerström, Lovisa, Nils Ryman, Jean-Luc Tison, Anna Hasslow, Love Dalén e Linda Laikre. "Genetic landscape with sharp discontinuities shaped by complex demographic history in moose ( Alces alces )". Journal of Mammalogy 97, n. 1 (23 settembre 2015): 1–13. http://dx.doi.org/10.1093/jmammal/gyv146.
Testo completoAbstract (sommario):
Abstract The moose ( Alces alces ) is the most intensely managed game species in Fennoscandia; approximately one-third of the population, ca. 160,000 animals, is harvested annually. Despite the species’ biological and socioeconomic importance, there are knowledge gaps with respect to its intraspecific diversity and genetic structure. Recent studies of moose in neighboring countries report 2 genetic groups in Finland, 3 in Norway with one of them suggested to be of ancient origin, and no indications of bottlenecks. To delineate the spatial genetic landscape of the Swedish moose, we used allozyme variability from over 20,000 georeferenced moose collected all over Sweden in combination with 12 microsatellites ( n > 1,200) and mitochondrial DNA (mtDNA) sequences ( n = 44). We combined individual-based and traditional statistical approaches with coalescence-based simulations. The results indicate a complex history with bottlenecks and recent expansions that is consistent with historical records. Swedish moose are separated into 2 major genetic groups, a northern and a southern one, where the southern group is further divided into 3 subgroups. The 2 main subpopulations are moderately differentiated ( FST = 0.1; RST = 0.07) and separated by sharp genetic discontinuities occurring over a relatively narrow transition zone in central Sweden that coincides with a similar, previously reported transition zone in Norway. This differentiation is not reflected in mtDNA variation, where no significant divergence was observed. Together with the FST and RST similarities, this suggests that the 2 major subpopulations in Sweden reflect divergence shaped after the postglacial recolonization of Scandinavia. Neighborhood size assessments indicate that gene flow is relatively restricted with an estimated average dispersal distance of 3.5–11.1 km, and spatial autocorrelograms suggest that genetic similarity decreases almost linearly over space resulting in continuous genetic clines within major subgroups. Management areas largely coincide with genetic clusters, simplifying the integration of genetic information into management.
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Hamilton, M. G., P. A. Tilyard, D. R. Williams, R. E. Vaillancourt, T. J. Wardlaw e B. M. Potts. "The genetic variation in the timing of heteroblastic transition in Eucalyptus globulus is stable across environments". Australian Journal of Botany 59, n. 2 (2011): 170. http://dx.doi.org/10.1071/bt10313.
Testo completoAbstract (sommario):
Eucalyptus globulus is one of the best known examples of a heteroblastic plant. It exhibits a dramatic phase change from distinctive juvenile to adult leaves, but the timing of this transition varies markedly. We examined the genetic variation in the timing of heteroblastic transition using five large open-pollinated progeny trials established in north-western Tasmania. We used univariate and multi-variate mixed models to analyse data on the presence/absence of adult or intermediate foliage at age 2 years from a total of 14 860 trees across five trials, as well as height to heteroblastic phase change from one trial. Up to 566 families and 15 geographic subraces of E. globulus were represented in the trials. The timing of the heteroblastic transition was genetically variable and under strong genetic control at the subrace and within-subrace level, with single-trial narrow-sense heritability estimates for the binary trait averaging 0.50 (range 0.44–0.65). The degree of quantitative trait differentiation in the timing of heteroblastic transition among subraces, as measured by QST, exceeded the published level of neutral molecular marker (FST) differentiation in all cases, arguing that diversifying selection has contributed to shaping broad-scale patterns of genetic differentiation. Most inter-trial genetic correlations were close to one at the subrace and additive genetic levels, indicating that the genetic variation in this important developmental change is expressed in a stable manner and that genotype-by-environment interaction is minimal across the environments studied.
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Qin, Ning-Xin, Yi-Ran Zhao, Wei-Hui Shi, Zhi-Yang Zhou, Ke-Xin Zou, Chuan-Jin Yu, Xia Liu et al. "Anxiety and depression-like behaviours are more frequent in aged male mice conceived by ART compared with natural conception". Reproduction 162, n. 6 (1 dicembre 2021): 437–48. http://dx.doi.org/10.1530/rep-21-0175.
Testo completoAbstract (sommario):
The number of children born after assisted reproductive technology (ART) is accumulating rapidly, and the health problems of the children are extensively concerned. This study aims to evaluate whether ART procedures alter behaviours in male offspring. Mouse models were utilized to establish three groups of offspring conceived by natural conception (NC), in vitro fertilization and embryo transfer (IVF-ET), and frozen-thawed embryo transfer (IVF-FET), respectively. A battery of behaviour experiments for evaluating anxiety and depression levels, including the open field test (OFT), elevated plus maze (EPM) test, light/dark transition test (L/DTT), tail suspension test (TST), forced swimming test (FST), and sucrose preference test (SPT) was carried out. Aged (18 months old), but not young (3 months old), male offspring in the IVF-ET and IVF-FET groups, compared with those in the NC group, exhibited increased anxiety and depression-like behaviours. The protein expression levels of three neurotrophins in PFC or hippocampus in aged male offspring from the IVF-ET and IVF-FET groups reduced at different extent, in comparison to NC group. RNA sequencing (RNA-Seq) was performed in the hippocampus of 18 months old offspring to further explore the gene expression profile changes in the three groups. KEGG analyses revealed the coexisted pathways, such as PI3K-Akt signalling pathway, which potentially reflected the similarity and divergence in anxiety and depression between the offspring conceived by IVF-ET and IVF-FET. Our research suggested the adverse effects of advanced age on the psychological health of children born after ART should be highlighted in the future.
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Han, Sang-Kap, Min-Kyung Joo, Jeon-Kyung Kim, Woonhee Jeung, Heerim Kang e Dong-Hyun Kim. "Bifidobacteria-Fermented Red Ginseng and Its Constituents Ginsenoside Rd and Protopanaxatriol Alleviate Anxiety/Depression in Mice by the Amelioration of Gut Dysbiosis". Nutrients 12, n. 4 (26 marzo 2020): 901. http://dx.doi.org/10.3390/nu12040901.
Testo completoAbstract (sommario):
Gut dysbiosis is closely connected with the outbreak of psychiatric disorders with colitis. Bifidobacteria-fermented red ginseng (fRG) increases the absorption of ginsenoside Rd and protopanxatriol into the blood in volunteers and mice. fRG and Rd alleviates 2,4,6-trinitrobenzenesulfonic acid-induced colitis in mice. Therefore, to understand the gut microbiota-mediated mechanism of fRG against anxiety/depression, we examined the effects of red ginseng (RG), fRG, ginsenoside Rd, and protopanaxatriol on the occurrence of anxiety/depression, colitis, and gut dysbiosis in mice. Mice with anxiety/depression were prepared by being exposed to two stressors, immobilization stress (IS) or Escherichia coli (EC). Treatment with RG and fRG significantly mitigated the stress-induced anxiety/depression-like behaviors in elevated plus maze, light-dark transition, forced swimming (FST), and tail suspension tasks (TST) and reduced corticosterone levels in the blood. Their treatments also suppressed the stress-induced NF-κB activation and NF-κB+/Iba1+ cell population in the hippocampus, while the brain-derived neurotrophic factor (BDNF) expression and BDNF+/NeuN+ cell population were increased. Furthermore, treatment with RG or fRG suppressed the stress-induced colitis: they suppressed myeloperoxidase activity, NF-κB activation, and NF-κB+/CD11c+ cell population in the colon. In particular, fRG suppressed the EC-induced depression-like behaviors in FST and TST and colitis more strongly than RG. fRG treatment also significantly alleviated the EC-induced NF-κB+/Iba1+ cell population and EC-suppressed BDNF+/NeuN+ cell population in the hippocampus more strongly than RG. RG and fRG alleviated EC-induced gut dysbiosis: they increased Bacteroidetes population and decreased Proteobacteria population. Rd and protopanaxatriol also alleviated EC-induced anxiety/depression and colitis. In conclusion, fRG and its constituents Rd and protopanaxatriol mitigated anxiety/depression and colitis by regulating NF-κB-mediated BDNF expression and gut dysbiosis.
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Muli, Joshua Kiilu, Johnstone O. Neondo, Peter K. Kamau, George N. Michuki, Eddy Odari e Nancy L. M. Budambula. "Genetic diversity and population structure of wild and cultivated Crotalaria species based on genotyping-by-sequencing". PLOS ONE 17, n. 9 (1 settembre 2022): e0272955. http://dx.doi.org/10.1371/journal.pone.0272955.
Testo completoAbstract (sommario):
Crotalaria is a plant genus that is found all over the world, with over 700 species of herbs and shrubs. The species are potential alternative food and industrial crops due to their adaptability to different environments. Currently, information on the genetic diversity and population structure of these species is scanty. Genotyping-by-sequencing (GBS) is a cost-effective high-throughput technique in diversity evaluation of plant species that have not been fully sequenced. In the current study, de novo GBS was used to characterize 80 Crotalaria accessions from five geographical regions in Kenya. A total of 9820 single nucleotide polymorphism (SNP) markers were obtained after thinning and filtering, which were then used for the analysis of genetic diversity and population structure in Crotalaria. The proportion of SNPs with a minor allele frequency (maf) > = 0.05 was 45.08%, while the Guanine-Cytosine (GC) content was 0.45, from an average sequence depth of 455,909 reads per base. The transition vs transversion ratio was 1.81 and Heterozygosity (He) ranged between 0.01–0.07 in all the sites and 0.04 to 0.52 in the segregating sites. The mean Tajima’s D value for the population was -0.094, suggesting an excess of rare alleles. The fixation index (Fst) between the different populations based on the Wright Fst (1943) ranged from 0.0119 to 0.066 for the Eastern-Western and Nairobi-Western populations. Model based techniques of population structure analysis including structure, k-means and cross-entropy depicted eight clusters in the study accessions. Non-model based techniques especially DAPC depicted poor population stratification. Correspondence Analysis (CA), Principal coordinate analyses (PCoA) and phylogenetic analysis identified a moderate level of population stratification. Results from this study will help conservationists and breeders understand the genetic diversity of Crotalaria. The study also provides valuable information for genetic improvement of domesticated species.
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Woodley, Michael A., Shameem Younuskunju, Bipin Balan e Davide Piffer. "Holocene Selection for Variants Associated With General Cognitive Ability: Comparing Ancient and Modern Genomes". Twin Research and Human Genetics 20, n. 4 (20 luglio 2017): 271–80. http://dx.doi.org/10.1017/thg.2017.37.
Testo completoAbstract (sommario):
Human populations living during the Holocene underwent considerable microevolutionary change. It has been theorized that the transition of Holocene populations into agrarianism and urbanization brought about culture-gene co-evolution that favored via directional selection genetic variants associated with higher general cognitive ability (GCA). To examine whether GCA might have risen during the Holocene, we compare a sample of 99 ancient Eurasian genomes (ranging from 4.56 to 1.21 kyr BP) with a sample of 503 modern European genomes (Fst= 0.013), using three different cognitive polygenic scores (130 SNP, 9 SNP and 11 SNP). Significant differences favoring the modern genomes were found for all three polygenic scores (odds ratios = 0.92,p= 001; .81,p= 037; and .81,p= .02 respectively). These polygenic scores also outperformed the majority of scores assembled from random SNPs generated via a Monte Carlo model (between 76.4% and 84.6%). Furthermore, an indication of increasing positive allele count over 3.25 kyr was found using a subsample of 66 ancient genomes (r= 0.22,pone-tailed= .04). These observations are consistent with the expectation that GCA rose during the Holocene.
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Williams, Samuel M., Michael B. Bennett, Julian G. Pepperell, Jess A. T. Morgan e Jennifer R. Ovenden. "Spatial genetic subdivision among populations of the highly migratory black marlin Istiompax indica within the central Indo-Pacific". Marine and Freshwater Research 67, n. 8 (2016): 1205. http://dx.doi.org/10.1071/mf14370.
Testo completoAbstract (sommario):
The black marlin Istiompax indica is a highly migratory species and as a result is expected to show little genetic population structure throughout its broad geographic range. Tissue samples from 183 I. indica were collected from three geographic regions within the central Indo-Pacific and analysed using mitochondrial and nuclear DNA markers. Nuclear genetic heterogeneity was found among populations in the south-western Pacific Ocean, eastern Indian Ocean and South China Sea (significant FST values of 0.013–0.037). Combining information from nuclear markers with published movement and reproductive data suggests that reproductive philopatry plays a role in maintaining contemporary I. indica population structure. Analyses of the mitochondrial control region did not reflect this pattern; however, it identified historical population structure. Differing patterns of genetic population structure revealed by mitochondrial and nuclear markers demonstrated that a transition must have occurred between historical and contemporary population structures. This restructuring presumably reflects a species whose populations have become genetically isolated before experiencing a period of secondary contact. The spatial subdivision evident among populations indicates that I. indica in this central Indo-Pacific region should be managed as three independent stocks, to guide the sustainability of this fisheries resource.
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Rocha-Olivares, Axayácatl, e Russell D. Vetter. "Effects of oceanographic circulation on the gene flow, genetic structure, and phylogeography of the rosethorn rockfish (Sebastes helvomaculatus)". Canadian Journal of Fisheries and Aquatic Sciences 56, n. 5 (1 maggio 1999): 803–13. http://dx.doi.org/10.1139/f99-004.
Testo completoAbstract (sommario):
The genetic structure and phylogeography of 88 rosethorn rockfish (Sebastes helvomaculatus) from five localities (California, Oregon, British Columbia, and two in the Gulf of Alaska) were analyzed using DNA sequences from the mitochondrial control region. High levels of genetic diversity (h > 85%) and significant population genetic structure (FST = 0.13, P < 0.001; AMOVA ΦST = 0.15, P << 0.001) were found. A significant genetic break was detected (ΦCT = 0.22, P << 0.001) coinciding with the transition zone between the Oregonian and Aleutian zoogeographic provinces and consistent with retention and dispersal mechanisms associated with the oceanographic circulation of the region. A correlation between geographic distance and population genetic distance supported the hypothesis of gene flow dominated by pelagic-phase dispersal. Oregonian province populations had higher haplotype diversity, with >70% of the individuals representing a recent lineage absent in the Aleutian province. This suggests a limited northward dispersal across the zoogeographic boundary. The phylogeographic stucture may be due to a founder effect in the Aleutian province or an ocean circulation driven pseudo-vicariance. These results demonstrate that organisms with protracted pelagic-phase stages and high dispersal capability can exhibit population genetic structure that reflects their historical demography and present dispersal patterns.
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Кукушкин, С. А., e А. В. Осипов. "Пути политипных превращений в карбиде кремния". Физика твердого тела 61, n. 8 (2019): 1443. http://dx.doi.org/10.21883/ftt.2019.08.47967.452.
Testo completoAbstract (sommario):
In this work, two main polytypic transformations in silicon carbide, namely, 2H→6H and 3C→6H, were studied using ab initio methods. It is shown that intermediate states with trigonal symmetry P3m1 and monoclinic symmetry Cm greatly simplify the movement of close-packed layers during such transitions, breaking them up into separate stages. It was found that the two polytypic transformations occur quite differently. During the 2H→6H transition, the displaceable bonds are noticeably tilted compared to the initial position, which makes it possible to reduce the compression of SiC bonds in the (112 ̅0) plane. The 3C→6H transition takes place through the formation of auxiliary Si – Si and C – C bonds that live for a short time and help the tightly packed layers exchange places. As a result, the activation barrier for the conversion of 2H→6H (1.7 eV/atom) is significantly less than the activation barrier for the conversion of 3C→6H (3.6 eV/atom), which means that the second transition must occur at temperatures of 750-800 ℃ higher than the first one. The energy profiles of these polytypic transformations, as well as the geometry of all intermediate and transitional phases, are calculated. It is shown that all transition states have monoclinic symmetry.
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Yesigat, Anteneh, e P. singh. "The Study of Coexistance of Superconductivity and Spin Glass in Fe Pnictide(Fe1+YSeXTe1−X)". Journal of Advances in Nanotechnology 1, n. 2 (26 giugno 2020): 19–41. http://dx.doi.org/10.14302/issn.2689-2855.jan-19-3048.
Testo completoAbstract (sommario):
Superconductivity and magnetism were previously thought as incompatible until the discovery of some rare earth ternary compounds that shows the coexistence of superconductivity and magnetism. In some of the recently discovered iron based layered superconductors superconductivity and diamagnetic order system are coexist. That occurs in only 11 and 122 family. The present works we examine the possibility of coexistence of superconductivity and disorder of magnetic spin is called spin glass when freeze the system that can show the superconductivity and spin glass coexist. In this present work we can examine the possibility of coexistence of superconductivity and spin glass in detailed 11 family of Fe1+ySexTe1−x compound. We show that spin glass like behavior is present in FST for x = 0.1 - 0.15 we present evidence form magnetization measurement and characterized the short-range order with neutron scattering. One of our main results is that the short-range order is structural as well as magnetic order. The factor of magnetic order exchange in long range depend on temperature, pressure, number of doping and other external factor discussed it. We found mathematical expression for superconductor transition TC, spin glass temperature TgSusceptibility x(q), and retardation time τ using for born approximation and digamma function depend on wave vector(q) and cut off frequency(ω) in the region coexistence of superconductivity and spin glass in Fe1+ySexTe1−xcompound.
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Алиев, А. Р., И. Р. Ахмедов, М. Г. Какагасанов e З. А. Алиев. "Предпереходные явления в области фазовых переходов первого рода в ионно-молекулярных кристаллах". Физика твердого тела 62, n. 6 (2020): 890. http://dx.doi.org/10.21883/ftt.2020.06.49344.34m.
Testo completoAbstract (sommario):
Raman spectroscopy was used to study the molecular relaxation processes in sulfates Li2SO4, Na2SO4, K2SO4, carbonates Li2CO3, Na2CO3, K2CO3, perchlorates NaClO4, KClO4 and nitrates Ca(NO3)2, Sr(NO3)2, Ba(NO3)2. It has been established that in the systems under study, phase transitions of the first kind are stretched in nature (diffuse phase transition): in sulfates, carbonates and perchlorates they are structural phase transitions, and in nitrates this is a crystal-melt phase transition. The existence of a pre-transition region was found in all the crystals studied.
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Вальков, В. И., В. И. Каменев, А. В. Головчан, И. Ф. Грибанов, В. В. Коледов, В. Г. Шавров, В. И. Митюк e П. Дуда. "Магнитные и магнитокалорические эффекты в системах с реверсивными переходами первого рода". Физика твердого тела 63, n. 5 (2021): 628. http://dx.doi.org/10.21883/ftt.2021.05.50813.271.
Testo completoAbstract (sommario):
Within the framework of the model of interacting parameters of magnetic and structural orders, a theoretical analysis of magnetostructural reversible first-order phase transitions is carried out. Reversible phase transitions are characterized by a jump-like appearance of magnetic order with decreasing temperature (as in a first-order phase transition), and with a reverse increase in temperature, the magnetic order gradually disappears (as in a second-order phase transition). Such transitions are observed in some alloys of the Mn_{1-x}Cr_{x}NiGe magnetocaloric system under pressure (x = 0.11) and without (x = 0.18) and are accompanied by specific magnetic and magnetocaloric features. A phenomenological description of these features is carried out within the concept of a soft mode for the structural subsystem undergoing first-order structural phase transition (P6_{3}/mmc-P_{nma}) and the Heisenberg model for the spin subsystem. For systems with magnetostructural instability within the molecular field approximation for the spin subsystem and the shifted harmonic oscillator approximation for the lattice subsystem, it is shown that the reversible phase transitions arise when the temperature of magnetic disordering is in the temperature hysteresis region of the 1st order structural phase transition P6_{3}/mmc-P_{nma}. It is also shown that the two-peak form of the isothermal entropy, which is characteristic of reversible transitions, is due to the separation of the structural and magnetic entropy contributions.
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Егоров, В. М., e П. Н. Якушев. "Фазовые и релаксационные переходы в политетрафторэтилене". Физика твердого тела 60, n. 9 (2018): 1824. http://dx.doi.org/10.21883/ftt.2018.09.46405.060.
Testo completoAbstract (sommario):
AbstractComparative analysis of phase and relaxation transitions in poly(tetrafluoroethylene) by differential scanning calorimetry and dynamic mechanical analysis has been carried out. Elimination of procedural errors in the first case has allowed us to obtain true values of thermodynamic parameters for phase transitions and reveal their nature. Quantitative analysis of heat capacity peak profile was performed on the basis of smeared first-order phase transition theory and relaxation glass transition has been characterized.
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Moncrieff, Lisa, Ievgeniia Kocherova, Artur Bryja, Wiesława Kranc, Joanna Perek, Magdalena Kulus, Michal Jeseta et al. "Transcriptomic profile of genes encoding proteins responsible for regulation of cells differentiation and neurogenesis in vivo and in vitro – an oocyte model approach". Medical Journal of Cell Biology 8, n. 1 (29 aprile 2020): 1–11. http://dx.doi.org/10.2478/acb-2020-0001.
Testo completoAbstract (sommario):
AbstractThe growth and development of the oocyte is essential for the ovarian follicle. Cumulus cells (CCs) - a population of granulosa cells - exchange metabolites, proteins and oocyte-derived paracrine factors with the oocyte through gap junctions, to contribute to the competency and health of the oocyte. This bi-directional communication of the cumulus-oocyte complex could be better understood through the micro-analysis of a porcine oocyte gene expression before in vitro maturation (IVM) and after. Additionally, the study of the somatic and gamete cells differentiation capability into neuronal lineage would be promising for future stem cell research as granulosa cells are easily accessible waste material from in vitro fertilization (IVF) procedures. Therefore, in this study, the oocytes of 45 pubertal Landrace gilts were isolated and the protein expression of the COCs were analyzed through micro-analysis techniques. Genes belonging to two ontological groups: neuron differentiation and negative regulation of cell differentiation have been identified which have roles in proliferation, migration and differentiation. Twenty identified porcine oocyte genes (VEGFA, BTG2, MCOLN3, EGR2, TGFBR3, GJA1, FST, CTNNA2, RTN4, MDGA1, KIT, RYK, NOTCH2, RORA, SMAD4, ITGB1, SEMA5A, SMARCA1, WWTR1 and APP) were found to be down-regulated after the transition of IVM compared to in vitro. These results could be applied as gene markers for the proliferation, migration and differentiation occurring in the bi-directional communication between the oocyte and CCs.Running title: Differentiation and neurogenesis in oocyte cells
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Загребин, М. А., М. В. Матюнина, А. Б. Кошкин, В. Д. Бучельников e В. В. Соколовский. "Фазовые превращения в сплавах Fe-=SUB=-100-x-=/SUB=-Si-=SUB=-x-=/SUB=-: исследования ab initio". Физика твердого тела 62, n. 5 (2020): 655. http://dx.doi.org/10.21883/ftt.2020.05.49224.24m.
Testo completoAbstract (sommario):
In present work, on the basis of structural and magnetic phase transition temperatures estimated theoretically from the first principles, the concentration phase diagram for Fe100-xSix (9.375 ≤ x ≤ 25.0 at.%) was plotted. Structural phase transition temperatures for the experimentally observed crystal structures were obtained from the structural optimization. The Curie temperatures were estimated from mean field approximation using ab initio calculated exchange coupling constants. Both structural and magnetic phase transitions temperatures are found in qualitative agreement with the experiment. For the whole considered concentration range, structural transitions from the ordered cubic to fully disordered through partially disordered one are appeared with temperature increasing. As for magnetic transformations, ferromagnetic-paramagnetic transition is observed for all compositions, however, it happens in different crystal phases.
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Васин, М. Г., e В. М. Винокур. "Калибровочная теория стекольного перехода в трехмерной XY-модели с вмороженным беспорядком". Физика твердого тела 60, n. 6 (2018): 1183. http://dx.doi.org/10.21883/ftt.2018.06.45998.26m.
Testo completoAbstract (sommario):
AbstractThe gauge theory of phase transitions in a three-dimensional XY-model with a hardened disorder is considered. It is shown that the topological phase transition occurring in the vortex subsystem of this model is a transition in the state of spin glass.
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Милинский, А. Ю., С. В. Барышников, Е. В. Чарная, И. В. Егорова e Н. И. Ускова. "Влияние наноконфайнмента на кинетику фазовых переходов в органическом сегнетоэлектрике DIPAI". Физика твердого тела 62, n. 7 (2020): 1059. http://dx.doi.org/10.21883/ftt.2020.07.49473.036.
Testo completoAbstract (sommario):
The results of studying the linear and nonlinear dielectric properties of a new organic ferroelectric diisopropylammonium iodide (DIPAI), embedded in porous alumina films, in comparison with bulk DIPAI, are presented. It was found, for DIPAI in pores 300 and 60 nm in diameter the ferroelectric phase is formed in the heating and cooling modes in the temperature interval between two structural phase transitions above room temperature. No noticeable temperature hysteresis was observed for both phase transitions. It was shown that the boundaries of the intermediate polar phase for nanostructured DIPAI shift to low temperatures with decreasing pore size. For bulk DIPAI, two structural transitions were revealed during heating with the formation of an intermediate polar phase and only one transition during cooling, below which ferroelectricity occurred. The temperature of this transition was much lower than the corresponding temperature during heating. It is assumed that the observed differences in phase transitions for DIPAI in pores and bulk DIPAI are associated with acceleration of the phase transitions kinetics under conditions of nanoconfinement.
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Juárez-Miranda, Aldo Isaac, Amelia Cornejo-Romero e Carlos Fabián Vargas-Mendoza. "Population expansion and genetic structure in Cephalocereus nizandensis (Cactaceae), a microendemic cactus of rocky outcrops of the Tehuantepec basin, Mexico". Plant Ecology and Evolution 154, n. 2 (24 giugno 2021): 217–30. http://dx.doi.org/10.5091/plecevo.2021.1773.
Testo completoAbstract (sommario):
Background and aims – Cephalocereus nizandensis is a microendemic columnar cactus that grows isolated in xerophytic enclaves associated with rocky outcrops in the Isthmus of Tehuantepec, in the south of Mexico. Its demographic history and genetic structure were assessed to determine the main events that shaped its current restricted distribution.Material and methods – Chloroplast intergenic sequences of 40 individuals and inter simple sequence repeats (ISSRs) of 45 individuals from four isolated populations were used to estimate haplotypic and nucleotide diversity, using expected heterozygosity and the Shannon index. AMOVA, population pair-wise FST, and Bayesian clustering analyses were performed to explore the genetic structure. Demographic history was estimated with neutrality tests, mismatch distribution analysis, and Bayesian skyline plots. Phylogenetic relationships and divergence times were determined using a median joining network and a Bayesian molecular clock.Key results – C. nizandensis has a high diversity and moderate genetic differentiation. The lowest elevation locality was found to be the most genetically distinct. The species has undergone a process of population expansion that began 150,000 years ago and has remained without evidence of a population contraction in the transition from the Pleistocene to the Holocene (11,700 years ago).Conclusions – C. nizandensis presents moderate but significant genetic differentiation, which may be due to an early divergence of its populations. Currently observed levels of genetic diversity are the result of historical maintenance of high population sizes and a population expansion approximately in the last 150,000 years, which was sustained independently of the climatic fluctuations of the Early Quaternary, due in part to the stability of the rocky habitat.
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Wei, Caihong, Li Li, Hongwei Su, Lingyang Xu, Jian Lu, Li Zhang, Wenzhong Liu, Hangxing Ren e Lixin Du. "Identification of the crucial molecular events during the large-scale myoblast fusion in sheep". Physiological Genomics 46, n. 12 (15 giugno 2014): 429–40. http://dx.doi.org/10.1152/physiolgenomics.00184.2013.
Testo completoAbstract (sommario):
It is well known that in sheep most myofibers are formed before birth; however, the crucial myogenic stage and the cellular and molecular mechanisms underpinning phenotypic variation of fetal muscle development remain to be ascertained. We used histological, microarray, and quantitative real-time PCR (qPCR) methods to examine the developmental characteristics of fetal muscle at 70, 85, 100, 120, and 135 days of gestation in sheep. We show that day 100 is an important checkpoint for change in muscle transcriptome and histomorphology in fetal sheep and that the period of 85–100 days is the vital developmental stage for large-scale myoblast fusion. Furthermore, we identified the cis-regulatory motifs for E2F1 or MEF2A in a list of decreasingly or increasingly expressed genes between 85 and 100 days, respectively. Further analysis demonstrated that the mRNA and phosphorylated protein levels of E2F1 and MEF2A significantly declined with myogenic progression in vivo and in vitro. qRT-PCR analysis indicated that PI3K and FST, as targets of E2F1, may be involved in myoblast differentiation and fusion and that downregulation of MEF2A contributes to transition of myofiber types by differential regulation of the target genes involved at the stage of 85–100 days. We clarify for the first time the timing of myofiber proliferation and development during gestation in sheep, which would be beneficial to meat sheep production. Our findings present a repertoire of gene expression in muscle during large-scale myoblast fusion at transcriptome-wide level, which contributes to elucidate the regulatory network of myogenic differentiation.
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Behera, Bijay Kumar, Vishwamitra Singh Baisvar, Ajaya Kumar Rout, Prasenjit Paria, Pranaya Kumar Parida, Dharmendra Kumar Meena, Pronob Das, Brundaban Sahu, Basanta Kumar Das e Joykrushna Jena. "Genetic diversity study of three Indian major carps from four riverine ecosystems". Aquatic Ecosystem Health & Management 25, n. 2 (1 aprile 2022): 15–24. http://dx.doi.org/10.14321/aehm.025.02.15.
Testo completoAbstract (sommario):
Abstract The wild stock of Indian major carps is declining in major rivers of India due to pollution, overexploitation, and inbreeding depression. In the present study, the comparative population structure, genetic diversity, and historical demographics of IMCs, Labeo rohita, Labeo catla, and Cirrhinus mrigala were characterized by analyzing partial 307bp sequences of Cytochrome b gene of 357 individuals collected from seven geographically isolated sites from Indian river basins and two culture zones. The DNA sequences alignment among three species revealed comparative divergence and evolution in these heterogeneous species in terms of over transition to transversion ratio of 6.25. The study implicated the occurrence of 35 haplotypes with haplotype diversity of 0.7333 in L. rohita at Brahmaputra basin showing allelic richness, while no nucleotide diversity (π) 0.000 was observed in L. catla of two geographically isolated locations of Rivers Ganga and Narmada. The analysis of molecular variance (AMOVA) revealed the genetic diversity of IMCs is to be very low (9.40%) within the species, as compared to among the three species (80.76%). The Fst scores ranged between 0.000 and 0.996, indicating low to high genetic structure of IMCs. The Haplotype-1, Haplotype-13, and Haplotype-19 in L. rohita, L. catla, and C. mrigala were considered as ancestral haplotypes, respectively. The expansion factor was found to be 0.45000 and 0.90000 for L. rohita stocks at Farakka-Ganga and Allahabad-Ganga, respectively. The present study provides the first report on genealogical biogeography, evolutionary divergence, and expansion of three IMCs, which could help to formulate the strategies for conservation of fisheries biodiversity in the Indian riverine ecosystems.
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Рамазанов, М. К., А. К. Муртазаев, М. А. Магомедов e Т. Р. Ризванова. "Фазовые переходы в двумерной антиферромагнитной модели Поттса на решетке кагоме". Физика твердого тела 64, n. 12 (2022): 2016. http://dx.doi.org/10.21883/ftt.2022.12.53655.436.
Testo completoAbstract (sommario):
The phase transitions and thermodynamic properties of the two-dimensional antiferromagnetic Potts model with the number of spin states q = 4 on the kagome lattice are studied by the Monte Carlo method, taking into account the exchange interactions of the first J1 and second J2 nearest neighbors. The studies were carried out for the value of the interaction of the second nearest neighbors in the interval -1.0 ≤ J2 ≤ 0.0. An analysis of the character of phase transitions has been carried out. It is shown that in the interval -1.0 ≤ J2 ≤ -0.1, a second-order phase transition is observed, while at J2 = 0.0, frustrations disturb the order in the system and lead to the disappearance of the phase transition.
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Муртазаев, А. К., Д. Р. Курбанова e М. К. Рамазанов. "Фазовые переходы и термодинамические свойства модели Поттса с числом состояний спина q=4 на треугольной решетке". Физика твердого тела 61, n. 11 (2019): 2195. http://dx.doi.org/10.21883/ftt.2019.11.48428.520.
Testo completoAbstract (sommario):
The Wang-Landau Monte Carlo algorithm has been used to study the phase transitions and thermodynamic properties of the two-dimensional ferromagnetic q = 4 Potts model on a triangular lattice. A nature of phase transition has estimated using the methods of the fourth order Binder cumulants and the histogram analysis. It has been established that a first-order phase transition is observed in the model under study.
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Иванов, К. А., Е. И. Гиршова e М. А. Калитеевский. "Моделирование ангармонических блоховских осцилляций: численные проблемы и нелинейные эффекты". Письма в журнал технической физики 47, n. 1 (2021): 42. http://dx.doi.org/10.21883/pjtf.2021.01.50458.18441.
Testo completoAbstract (sommario):
The work presents robust and fast numerical method for calculation of complex-valued energies and wave functions of carriers in one-dimensional electrically biased periodic structures. Using this method optical transitions were studied in a superlattice (Bloch oscillations). Transition probabilities were shown to disobey linear dependence from applied field when it is large enough; in this case transitional with double and triple Bloch frequency can be more intensive than on single frequency. In a superlattice with a split miniband the same holds, with non-linearity being more pronounced in wider split case.
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Муртазаев, А. К., М. К. Бадиев, М. К. Рамазанов e М. А. Магомедов. "Влияние магнитного поля на фазовые переходы в модели Гейзенберга на треугольной решетке". Физика твердого тела 63, n. 8 (2021): 1141. http://dx.doi.org/10.21883/ftt.2021.08.51168.068.
Testo completoAbstract (sommario):
The Monte Carlo method was used to study phase transitions, magnetic and thermodynamic properties of the three-dimensional antiferromagnetic Heisenberg model on a layered triangular lattice in a magnetic field. The studies were carried out in the range of variation of the magnetic field value 0≤h≤12. The magnetic structures of the ground state are obtained in a wide range of magnetic field values. The character of phase transitions is determined on the basis of the histogram method of data analysis. It was found that in the range 0≤h≤10, a first-order phase transition is realized. It is shown that a further increase in the magnetic field value removes the degeneracy of the ground state and smears out the phase transition.
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Муртазаев, А. К., М. К. Рамазанов, Д. Р. Курбанова e М. К. Бадиев. "Фазовые переходы в атиферромагнитной модели Гейзенберга на объемно-центрированной кубической решетке с учетом взаимодействий следующих ближайших соседей". Физика твердого тела 60, n. 6 (2018): 1162. http://dx.doi.org/10.21883/ftt.2018.06.45993.15m.
Testo completoAbstract (sommario):
AbstractBased on the replica exchange Monte Carlo algorithm and histogram analysis of data, the phase transitions in the three-dimensional antiferromagnetic Heisenberg model on a body-centered cubic lattice with allowance for the next-nearest-neighbor interaction are studied. The study is performed for the nextnearest- neighbor exchange interaction ratio of r = 1. It is established that, for this model, the transition from the antiferromagnetic to paramagnetic phase is a first-order phase transition.
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Муртазаев, А. К., Т. Р. Ризванова, М. К. Рамазанов e М. А. Магомедов. "Фазовые переходы и термодинамические свойства модели Поттса с числом состояний спина q=4 на решетке кагоме". Физика твердого тела 62, n. 8 (2020): 1278. http://dx.doi.org/10.21883/ftt.2020.08.49614.043.
Testo completoAbstract (sommario):
Phase transitions and thermodynamic properties of the 2D ferromagnetic Potts model with the number of spin states q = 4 on a kagome lattice are investigated by the Mote Carlo method based on the Wang-Landau algorithm. The orders of the phase transitions are investigated using the Binder fourth-order cumulant method and histogram analysis of data. It is established that a first-order transition is observed in the model being investigated.
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Wagman, Jeffrey B., Matthew D. Langley e Valeri Farmer-Dougan. "Carrying their own weight: Dogs perceive changing affordances for reaching". Quarterly Journal of Experimental Psychology 71, n. 5 (1 gennaio 2018): 1040–44. http://dx.doi.org/10.1080/17470218.2017.1322990.
Testo completoAbstract (sommario):
Choices about when to transition between two modes of behaviour are determined by the fit between action capabilities and environmental properties. However, such transitions typically occur not at the absolute limits of action capabilities but rather based on the relative stability of each mode. People transition from an arm-only to an arm-plus-torso-reach, not when object distance exceeds arm length but when the stability of reaching with the arm-plus-torso exceeds that of reaching with the arm-only. To the extent that perception is supported by detection of invariant stimulation patterns, such a transition ought to reflect both the fit between action capabilities and environmental properties and the relative stability of modes regardless of species. We investigated the height at which dogs transitioned from reaching with the head-only to rearing when wearing a weighted backpack – a manipulation expected to decrease the stability of a head-only reach. As expected, the transition occurred at taller heights for tall than for short dogs but at the same ratio of treat-height-to-shoulder-height for both groups. This transition also occurred at shorter heights and smaller ratios of treat-height-to-shoulder-height when dogs wore a weighted backpack. The results suggest that stimulation patterns that support control of behaviour may be invariant across species.
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Heckotter, J., J. Thewes, D. Frohlich, M. Abmann e M. Bayer. "Landau-level quantization of the yellow excitons in cuprous oxide". Физика твердого тела 60, n. 8 (2018): 1585. http://dx.doi.org/10.21883/ftt.2018.08.46252.20gr.
Testo completoAbstract (sommario):
AbstractLately, the yellow series of P -excitons in cuprous oxide could be resolved up to the principal quantum number n = 25. Adding a magnetic field, leads to additional confinement normal to the field. Thereby, the transition associated with the exciton n is transformed into the transition between the electron and hole Landau levels with quantum number n , once the associated magnetic length becomes smaller than the related exciton Bohr radius. The magnetic field of this transition scales roughly as n ^–3. As a consequence of the extended exciton series, we are able to observe Landau level transitions with unprecedented high quantum numbers of more than 75.