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1
Mescia, Luciano, Michele Alessandro Chiapperino, Pietro Bia, Claudio Maria Lamacchia, Johan Gielis et Diego Caratelli. « Design of Electroporation Process in Irregularly Shaped Multicellular Systems ». Electronics 8, no 1 (1 janvier 2019) : 37. http://dx.doi.org/10.3390/electronics8010037.
Texte intégralRésumé :
Electroporation technique is widely used in biotechnology and medicine for the transport of various molecules through the membranes of biological cells. Different mathematical models of electroporation have been proposed in the literature to study pore formation in plasma and nuclear membranes. These studies are mainly based on models using a single isolated cell with a canonical shape. In this work, a space–time (x,y,t) multiphysics model based on quasi-static Maxwell’s equations and nonlinear Smoluchowski’s equation has been developed to investigate the electroporation phenomenon induced by pulsed electric field in multicellular systems having irregularly shape. The dielectric dispersion of the cell compartments such as nuclear and plasmatic membranes, cytoplasm, nucleoplasm and external medium have been incorporated into the numerical algorithm, too. Moreover, the irregular cell shapes have been modeled by using the Gielis transformations.
2
Ocko, Samuel A., Kiah Hardcastle, Lisa M. Giocomo et Surya Ganguli. « Emergent elasticity in the neural code for space ». Proceedings of the National Academy of Sciences 115, no 50 (27 novembre 2018) : E11798—E11806. http://dx.doi.org/10.1073/pnas.1805959115.
Texte intégralRésumé :
Upon encountering a novel environment, an animal must construct a consistent environmental map, as well as an internal estimate of its position within that map, by combining information from two distinct sources: self-motion cues and sensory landmark cues. How do known aspects of neural circuit dynamics and synaptic plasticity conspire to accomplish this feat? Here we show analytically how a neural attractor model that combines path integration of self-motion cues with Hebbian plasticity in synaptic weights from landmark cells can self-organize a consistent map of space as the animal explores an environment. Intriguingly, the emergence of this map can be understood as an elastic relaxation process between landmark cells mediated by the attractor network. Moreover, our model makes several experimentally testable predictions, including (i) systematic path-dependent shifts in the firing fields of grid cells toward the most recently encountered landmark, even in a fully learned environment; (ii) systematic deformations in the firing fields of grid cells in irregular environments, akin to elastic deformations of solids forced into irregular containers; and (iii) the creation of topological defects in grid cell firing patterns through specific environmental manipulations. Taken together, our results conceptually link known aspects of neurons and synapses to an emergent solution of a fundamental computational problem in navigation, while providing a unified account of disparate experimental observations.
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CRESSON, JACKY. « NON-DIFFERENTIABLE DEFORMATIONS OF ℝn ». International Journal of Geometric Methods in Modern Physics 03, no 07 (novembre 2006) : 1395–415. http://dx.doi.org/10.1142/s0219887806001752.
Texte intégralRésumé :
Many problems of physics or biology involve very irregular objects like the rugged surface of a malignant cell nucleus or the structure of space-time at the atomic scale. We define and study non-differentiable deformations of the classical Cartesian space ℝn which can be viewed as the basic bricks to construct irregular objects. They are obtained by taking the topological product of n-graphs of nowhere differentiable real valued functions. Our point of view is to replace the study of a non-differentiable function by the dynamical study of a one-parameter family of smooth regularization of this function. In particular, this allows us to construct a one-parameter family of smooth coordinates systems on non-differentiable deformations of ℝn, which depend on the smoothing parameter via an explicit differential equation called a scale law. Deformations of ℝn are examples of a new class of geometrical objects called scale manifolds which are defined in this paper. As an application, we derive rigorously the main results of the scale-relativity theory developed by Nottale in the framework of a scale space-time manifold.
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Luza, J. G., R. van Gorsel, V. S. Polito et A. A. Kader. « Chilling Injury in Peaches : A Cytochemical and Ultrastructural Cell Wall Study ». Journal of the American Society for Horticultural Science 117, no 1 (janvier 1992) : 114–18. http://dx.doi.org/10.21273/jashs.117.1.114.
Texte intégralRésumé :
Fruits of mid- (`O'Henry'), late (`Airtime'), and extra-late-season (`Autumn Gem') peach [Prunus persica (L.) Batsch] cultivars were examined for changes in cell wall structure and cytochemistry that accompany the onset of mealiness and leatheriness of the mesocarp due to chilling injury. The peaches were stored at 10C for up to 18 days or at SC for up to 29 days. Plastic-embedded sections were stained by the Schiff's-periodic acid reaction, Calcofluor white MR2, and Coriphosphine to demonstrate total insoluble carbohydrates, ß-1,4 glucans, and pectins, respectively. Mealiness was characterized by separation of mesocarp parenchyma cells leading to increased intercellular spaces and accumulation of pectic substances in the intercellular matrix. Little structural change was apparent in the cellulosic component of the cell walls of these fruits. In leathery peaches, the mesocarp parenchyma cells collapsed, intercellular space continued to increase, and pectin-positive staining in the intercellular matrix increased greatly. In addition, the component of the cell walls that stained positively for ß-1,4 glucans became thickened relative to freshly harvested or mealy fruit. At the ultrastructural level, dissolution of the middle lamella, cell separation, irregular thickening of the primary wall, and plasmolysis of the mesocarp parenchyma cells were seen as internal breakdown progressed.
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Inoue, S. « Possible continuity of subplasmalemmal cytoplasmic network with basement membrane cord network : ultrastructural study ». Journal of Cell Science 108, no 5 (1 mai 1995) : 1971–76. http://dx.doi.org/10.1242/jcs.108.5.1971.
Texte intégralRésumé :
The ultrastructure of the subplasmalemmal cytoplasm of the cell and the associated basement membrane as well as the area of the cell-basement membrane border were observed with high resolution electron microscopy after preparation of the tissues with cryofixation or glutaraldehyde fixation followed by freeze substitution. The subplasmalemmal cytoplasm of the smooth muscle cells of rat epididymal tubules and the podocyte processes of the mouse glomerular visceral epithelium were found to be composed of a fine network of irregular anastomosing strands. This network closely resembled the previously characterized cord network of the basement membrane. The cords are known to be composed of a 1.5 to 3 nm thick core filament made up of type IV collagen which is surrounded by an irregular ‘sheath’ of other components. The strands in the subplasmalemmal network showed ultrastructural features similar to those of the cord network. Ribbon-like, 4.5 nm wide heparan sulfate proteoglycan ‘double tracks’ were previously reported to be associated with the cord network. Structures similar in size and appearance to the double tracks were also found in the subplasmalemmal network. At the cell-basement membrane border, the lamina densa of the basement membrane was in contact with the cell without the intervening space of a lamina lucida which was recently found to be an artefact caused by conventional tissue processing. Furthermore, the subplasmalemmal network appeared to be continuous through the plasma membrane, with the cord network of the basement membrane.(ABSTRACT TRUNCATED AT 250 WORDS)
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Et. al., Mrs M. Anline Rejula,. « Medical Image Segmentation Of Wbc Using Improved Dual Threshold Method ». Turkish Journal of Computer and Mathematics Education (TURCOMAT) 12, no 10 (28 avril 2021) : 6129–43. http://dx.doi.org/10.17762/turcomat.v12i10.5450.
Texte intégralRésumé :
segmentation of medical images is a critical method for the proper identification and diagnosis of diseases. Because of the distinction between them, the segmentation of the WBCs is an important issue.The automatic diagnosis of multiple white blood cell or leukocyte disorders plays a significant role. The suggested work is an Improved Dual-Threshold approach based on a variation of white blood cell (WBC) segmentation of different color spaces. The improved dual-threshold segmentation method consists of three stages: the pre-processing stage, the segmentation step of the threshold, and the post-procurement phase. For additional handling, two images are obtained: one is a contrast-stretched grey image and the other is an H part image from the altered colour space of YCbCr in the pre-processing step. The three main steps comprising the threshold segmentation are context separation, red blood cell extraction, and the finest threshold selection.The single-threshold method in RGB colour space is involved in the process of separation of Red Blood Cells (RBC), the H channel image is used in the step of background extraction. The Golden Section search method is used for the best threshold selection item. Finally, to eliminate the noise and the unfinished
WBCs, median filtering and arithmetical morphology are used in the post-processing stage. The image data collection for Acute Lymphoblastic Leukaemia (ALL) is used to test and segment irregular cells from test data using an overall accuracy. Compared to the current segmentation outcome, the implemented segmentation approach shows better precision performance.
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Fuchs, M., M. K. Jones et K. L. Williams. « Characterisation of an epithelium-like layer of cells in the multicellular Dictyostelium discoideum slug ». Journal of Cell Science 105, no 1 (1 mai 1993) : 243–53. http://dx.doi.org/10.1242/jcs.105.1.243.
Texte intégralRésumé :
Ultrarapid freezing (RF) followed by freeze-substitution (FS) provide superior preservation of the Dictyostelium discoideum multicellular slug tissue over conventional methods of chemical fixation at room temperature. The peripheral cells of slugs prepared by RF and FS form a tight layer of flattened cells. This cell layer resembles epithelia of other multicellular organisms in that it has close junctional contact between cells associated with the extracellular matrix (ECM, slime sheath). This is the first report that clearly demonstrates the existence of such peripheral cellular specialisation in this otherwise well-studied model system. Junctional contacts between adjacent cells mean that there is no intercellular space evident between apical membranes of apposing cells, and basally the intermembraneous space between peripheral cells is less than 10 nm. By contrast, the intercellular space between internal cells is approximately 10–25 nm. The shape of the peripheral cells varies with their location around the slug. In the posterior prespore zone, the peripheral cells are squamous and exhibit polarity along their antero-posterior axis. In the anterior prestalk zone, peripheral cells are less flattened, project irregular filipodia between internal cells, and are polarised along their apical-basal axis. Colloidal gold immunocytochemistry with the markers MUD1, MUD50 and MUD62 demonstrated that the peripheral layer is formed of prestalk cells in the anterior region and ventrum, and mostly prespore cells along the dorsum. Thus, the peripheral layer, while having specific cell classes in different regions, is not differentiation-specific. Rather, it appears that the structure of these epithelium-like cells is influenced by interaction with molecules of the ECM (sheath).
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Guio, P., et H. L. Pécseli. « Phase space structures generated by absorbing obstacles in streaming plasmas ». Annales Geophysicae 23, no 3 (30 mars 2005) : 853–65. http://dx.doi.org/10.5194/angeo-23-853-2005.
Texte intégralRésumé :
Abstract. The dynamic behavior of a collisionless plasma flowing around an obstacle is investigated by numerical methods. In the present studies, the obstacle is formed by an absorbing cylinder, and a 2-D electrostatic particle-in-cell simulation is used to study the flow characteristics, with extensions to a fully 3-D generalization of the problem demonstrated as well. The formation of irregular filamented density depletions, oblique to the flow, is observed. The structures form behind the obstacle, in a region with a strong velocity shear, but also other instability mechanisms can be identified. The dynamics of these structures is highly dependent on the physical parameters of the plasma, and they can either be quasi-stationary or undergo a dynamic evolution. The structures are found to be associated with phase-space vortices, observed especially in the phase space spanned by the velocity direction perpendicular to the flow and the spatial coordinate in the same direction. The bias of the obstacle with respect to the plasma potential is found to be an important parameter for the dynamics of the structures, but seemingly not for their formation as such. The results can be of interest in the interpretation of structures in space plasmas as observed by instrumented spacecrafts.
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TANAKA, SATOSHI, KYOKO HASEGAWA, SUSUMU NAKATA, HIDEO NAKAJIMA, TAKUYA HATTA, FREDERIKA RAMBU NGANA, TAKUMA KAWAMURA, NAOHISA SAKAMOTO et KOJI KOYAMADA. « GRID-INDEPENDENT METROPOLIS SAMPLING FOR VOLUME VISUALIZATION ». International Journal of Modeling, Simulation, and Scientific Computing 01, no 02 (juin 2010) : 199–218. http://dx.doi.org/10.1142/s1793962310000158.
Texte intégralRésumé :
We propose a method of sampling regular and irregular-grid volume data for visualization. The method is based on the Metropolis algorithm that is a type of Monte Carlo technique. Our method enables "importance sampling" of local regions of interest in the visualization by generating sample points intensively in regions where a user-specified transfer function takes the peak values. The generated sample-point distribution is independent of the grid structure of the given volume data. Therefore, our method is applicable to irregular grids as well as regular grids. We demonstrate the effectiveness of our method by applying it to regular cubic grids and irregular tetrahedral grids with adaptive cell sizes. We visualize volume data by projecting the generated sample points onto the 2D image plane. We tested our sampling with three rendering models: an X-ray model, a simple illuminant particle model, and an illuminant particle model with light-attenuation effects. The grid-independency and the efficiency in the parallel processing mean that our method is suitable for visualizing large-scale volume data. The former means that the required number of sample points is proportional to the number of 2D pixels, not the number of 3D voxels. The latter means that our method can be easily accelerated on the multiple-CPU and/or GPU platforms. We also show that our method can work with adaptive space partitioning of volume data, which also enables us to treat large-scale/complex volume data easily.
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Soroka, C. J., et M. G. Farquhar. « Characterization of a novel heparan sulfate proteoglycan found in the extracellular matrix of liver sinusoids and basement membranes. » Journal of Cell Biology 113, no 5 (1 juin 1991) : 1231–41. http://dx.doi.org/10.1083/jcb.113.5.1231.
Texte intégralRésumé :
A novel heparan sulfate proteoglycan (HSPG) present in the extracellular matrix of rat liver has been partially characterized. Proteoglycans were purified from a high salt extract of total microsomes from rat liver and found to consist predominantly (approximately 90%) of HSPG. A polyclonal antiserum raised against this fraction specifically recognized HSPG by immunoprecipitation and immunoblotting. The intact, fully glycosylated HSPG migrated as a broad smear (150-300 kD) by SDS-PAGE, but after deglycosylation with trifluoromethanesulfonic acid only a single approximately 40-kD band was seen. By immunocytochemistry this HSPG was localized in the perisinusoidal space of Disse associated with irregular clumps of basement membrane-like extracellular matrix material, some of which was closely associated with the hepatocyte sinusoidal cell surface. It was also localized in biosynthetic compartments (rough ER and Golgi cisternae) of hepatocytes, suggesting that this HSPG is synthesized and deposited in the space of Disse by the hepatocyte. The anti-liver HSPG IgG also stained basement membranes of hepatic blood vessels and bile ducts as well as those of kidney and several other organs (heart, pancreas, and intestine). An antibody that recognizes the basement membrane HSPG found in the rat glomerular basement membrane did not precipitate the 150-300-kD rat liver HSPG. We conclude that the liver sinusoidal space of Disse contains a novel population of HSPG that differs in its overall size, its distribution and in the size of its core protein from other HSPG (i.e., membrane-intercalated HSPG) previously described in rat liver. It also differs in its core protein size from HSPG purified from other extracellular matrix sources. This population of HSPG appears to be a member of the basement membrane HSPG family.
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Malik, Affan, Danqi Qu et Hui-Chia Yu. « Smoothed Boundary Method Electrochemical Simulation Framework for Complex Electrode Microstructures ». ECS Meeting Abstracts MA2022-01, no 46 (7 juillet 2022) : 1968. http://dx.doi.org/10.1149/ma2022-01461968mtgabs.
Texte intégralRésumé :
Battery and fuel cell electrodes possess highly complex microstructures: tortuous interparticle space, irregular particle surfaces, and various particle sizes. Additionally, coupled physical mechanisms, such as mass transport and electron transport, heat generation, and phase transformations, simultaneously occur during the electrode’s operations. All these combined complexity makes modeling electrochemical processes with explicit considerations of electrode microstructures very challenging. As such, electrode designs are still heavily relied on experimental trial-and-error methods even though modern computational resources have grown rapidly. Furthermore, experimental technologies have become very mature to reconstruct three-dimensional (3D) microstructures. The abundant microstructure data open a window for directly simulating the physical processes in complex microstructures. This talk will introduce an innovative simulation method using a continuous function to define complex microstructures. Since the irregular complex microstructure surfaces are implicitly described, this method no longer requires meshes conformal to the complex microstructures as in the conventional simulations. Thus, it allows us to simulate detailed electrochemical phenomena in complex electrode microstructures in an unprecedented pace with ease, especially for image-based, reconstructed microstructures. We will showcase several recent simulations to demonstrate the presented method, including phase transformations in porous graphite anode, hybrid electrodes, electrochemical impedance spectroscopy, and electrochemical processes in NMC-separator-graphite full-cell. The presented method is applicable to other electrochemical systems, and can be extended to include other physical mechanisms for further studying cycling-induced phenomena such as stress, heat, and Li-plating. Figure 1
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Brigatti, M. F., E. Galli et L. Medici. « Ba-rich celestine : new data and crystal structure refinement ». Mineralogical Magazine 61, no 406 (juin 1997) : 447–51. http://dx.doi.org/10.1180/minmag.1997.061.406.10.
Texte intégralRésumé :
AbstractA Ba-rich celestine (Sr0.87Ba0.13SO4) filling cavities of volcanoclastic rocks from Montecchio Maggiore (Vicenza, Italy) was studied. The role of the Ba content in the mineral was determined using X-ray powder data, single crystal X-ray refinement, thermal and chemical analyses. The unit cell parameters (obtained by single crystal diffraction) are a = 8.408, b = 5.372, c = 6.897 Å, and the refinement in the space group Pnma (Z = 4) gives the final R value of 0.039. The average (Sr,Ba)-oxygen bond length is 2.842 Å and agrees with an occupancy of Sr 87% and Ba 13%. Individual bond lengths (Sr,Ba)-O and bond strength calculations confirm that all twelve interactions are significant and define an irregular array around the cation.
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D. Purwaningsih, H. Sutrisno, K. H. Sugiyarto, C. Kusumawardani et N. A. Kusumaningrum. « SYNTHESIS OF LiFe1-xNixPO4/C USING THE REFLUX WITH MICROWAVE IRRADIATION METHOD ». RASAYAN Journal of Chemistry 16, no 02 (2023) : 728–34. http://dx.doi.org/10.31788/rjc.2023.1628164.
Texte intégralRésumé :
The aim of this study was to synthesize LiFe1-xNixPO4/C with x = 0; 0.05; 0.07; 0.09 using the reflux method assisted by microwave irradiation. The goal was to increase the value of the electronic conductivity and reaction rate of Li+ compounds. The results showed that the method successfully synthesized LiFePO4/C and LiFe1-xNixPO4/C with an orthorhombic crystal structure in the Pnma space group. The optimum reflux-microwave irradiation time was 10 minutes, and increasing moles of Ni doping lead to a decrease in the lattice parameters cell volume. The crystalline size ranged from 21.42–22.62 nm, and the surface of the compound particles was irregular. The compound LiFe0.93Ni0.07PO4/C had the highest conductivity (5.45 × 10-7 S/cm).
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Mezaoui, Djillali, Sabrina Belkhiri et Thierry Belkhiri. « Structure Determination of New Phases K1.65V1.78W0.22O2(AsO4)2and K2V2O2(AsO4)2 ». Acta Crystallographica Section A Foundations and Advances 70, a1 (5 août 2014) : C236. http://dx.doi.org/10.1107/s2053273314097630.
Texte intégralRésumé :
Two new phases K1.65V1.78W0.22O2(AsO4)2 and K2V2O2(AsO4)2 [1,2] belonging to KTiOPO4 family (KTP) [3] have been synthesized and characterized by single crystal X-ray diffraction. The structure of K1.65V1.78W0.22O2(AsO4)2 shows an irregular MO6 octahedra (M=78%V+22%W) with two abnormal short bonds M–O (1.774 (7) Å) and (1.824 (8) Å) which suggest that the non linear optical property could be more important. In order to show the influence of the tungsten and vanadium on the distortion of the MO6 octahedra, we substituted the tungsten by the vanadium element. The single-crystal K2V2O2(AsO4)2 consists of common VO6 octahedra with one short bond V–O (1.652(2) Å) . We used SUPERFLIP and JANA 2006 programs [4, 5] to resolve and refine these structures. The refinement by JANA 2006 led to the reliability factors: (R =0.048, Rw = 0.064) for K1.65V1.78W0.22O2(AsO4)2, and (R =0.028, Rw = 0.034) for K2V2O2(AsO4). Structure of K1.65V1.78W0.22O2(AsO4)2 Structure of K2V2O2(AsO4)2 Space group: Pc21n Space group: Pc21n Cell parameters: Cell parameters: a = 6.5322 (7) Å a = 6.5368 (2) Å b = 10.7228 (9) Å b = 10.7228 (5) Å c = 13.0782 (5) Å c = 13.0666 (4) Å
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Bidwell, V. J., et H. R. Thorpe. « Kinematic cell model of macropore flow from intermittent irrigation pulses ». Soil Research 39, no 4 (2001) : 837. http://dx.doi.org/10.1071/sr00070.
Texte intégralRésumé :
Significant fluctuations in soil water flux were observed in the drainage hydrographs from lysimeters (1220 mm diam., 900 mm deep) of undisturbed field soil, recorded at 5-min intervals, in response to intermittent 1-min pulses of irrigation water (3.4 or 6.8 mm) at irregular time intervals (4–17 min). The hypothetical process for this phenomenon was flow through soil macropores, in association with non-linear sorption into soil micropores. The kinematic wave approach to analysing macropore flow was modelled as a series of bi-continuum cells, which can be expressed as a set of non-linear ordinary differential equations. This non-linear state-space description enables the use of MATLAB software for convenient coding of the model and numerical integration of the model response to transient water flux input. Model simulation of drainage response to the irrigation pulse sequences showed good prediction of the wetting and draining fronts of the hydrograph but gave only indicative prediction of the magnitudes and wavelengths of the flow fluctuations. The model demonstrates the sensitivity of macropore flow to variations in the intervals between irrigation pulses, and supports previous evidence of fluctuations in macropore flow even for single water flux input pulses under laboratory conditions.
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Ly, Cheng, et Seth H. Weinberg. « Automaticity in ventricular myocyte cell pairs with ephaptic and gap junction coupling ». Chaos : An Interdisciplinary Journal of Nonlinear Science 32, no 3 (mars 2022) : 033123. http://dx.doi.org/10.1063/5.0085291.
Texte intégralRésumé :
Spontaneous electrical activity, or automaticity, in the heart is required for normal physiological function. However, irregular automaticity, in particular, originating from the ventricles, can trigger life-threatening cardiac arrhythmias. Thus, understanding mechanisms of automaticity and synchronization is critical. Recent work has proposed that excitable cells coupled via a shared narrow extracellular cleft can mediate coupling, i.e., ephaptic coupling, that promotes automaticity in cell pairs. However, the dynamics of these coupled cells incorporating both ephaptic and gap junction coupling has not been explored. Here, we show that automaticity and synchronization robustly emerges via a Hopf bifurcation from either (i) increasing the fraction of inward rectifying potassium channels (carrying the [Formula: see text] current) at the junctional membrane or (ii) by decreasing the cleft volume. Furthermore, we explore how heterogeneity in the fraction of potassium channels between coupled cells can produce automaticity of both cells or neither cell, or more rarely in only one cell (i.e., automaticity without synchronization). Interestingly, gap junction coupling generally has minor effects, with only slight changes in regions of parameter space of automaticity. This work provides insight into potentially new mechanisms that promote spontaneous activity and, thus, triggers for arrhythmias in ventricular tissue.
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Brzezicka-Szymczyk, Krystyna, Władysław Golinowski et Czesław Zamorski. « Cytological effect of Tilt 250 EC in the successive phases of the Triticale rust disease process caused by Puccinia recondita f. sp. tritici ». Acta Societatis Botanicorum Poloniae 66, no 2 (2014) : 153–58. http://dx.doi.org/10.5586/asbp.1997.019.
Texte intégralRésumé :
The disease process caused by rust (<em>Puccinia recondita</em> f. sp. <em>tritici</em>) in <em>Triticale</em> (<em>Triticale</em>-Wittmack cv. Bolero) and the effect of the application of the propikonazole - Tilt 250 EC are described. In plants not protected chemically one could observe the whole pathogen developmental cycle ending with the appearance of uredinia with urediniospores. The highest pathogen susceptibility to chemical agent was observed at the time of inoculation, during incubation and at the beginning of the actual disease. By inhibiting the ergosterol biosynthesis in the fungus cells the preparation (propikonazole) inhibited the development of the intra- and extracellular mycelium. The mycelium degeneration manifested itself by the irregular growth of intercellular hyphae, perforation of septa, homogenization of protoplasts and cell collapse. The thickening of the cell wall, modification of the perihaustorial space and protoplast obliteration were observed in the haustoria.
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Sahtout, Naheda, Jijin R. A. Kuttiyatveetil, Michel Fodje et David A. R. Sanders. « Putative thioredoxin Trx1 fromThermosipho africanusstrain TCF52B : expression, purification and structural determination using S-SAD ». Acta Crystallographica Section F Structural Biology Communications 72, no 6 (23 mai 2016) : 443–47. http://dx.doi.org/10.1107/s2053230x16007214.
Texte intégralRésumé :
Thioredoxin is a small ubiquitous protein that plays a role in many biological processes. A putative thioredoxin, Trx1, fromThermosipho africanusstrain TCF52B, which has low sequence identity to its closest homologues, was successfully cloned, overexpressed and purified. The protein was crystallized using the microbatch-under-oil technique at 289 K in a variety of conditions; crystals grown in 0.2 MMgCl2, 0.1 Mbis-tris pH 6.5, 25%(w/v) PEG 3350, which grew as irregular trapezoids to maximum dimensions of 1.2 × 1.5 × 0.80 mm, were used for sulfur single-wavelength anomalous dispersion analysis. The anomalous sulfur signal could be detected to 2.83 Å resolution using synchrotron radiation on the 08B1-1 beamline at the Canadian Light Source. The crystals belonged to space groupP212121, with unit-cell parametersa= 40.6,b= 41.5,c= 56.4 Å, α = β = γ = 90.0°.
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Elghoul, Mahmoud, Ramadan Kandyle et Mohamed Abumandour. « Microscopic Focus on the Different Hepatic Cells of The Young Domesticated Pig (Sus suidae) ». Alexandria Journal of Veterinary Sciences 76, no 2 (2023) : 1. http://dx.doi.org/10.5455/ajvs.94338.
Texte intégralRésumé :
The current investigation was concerned with the different hepatic cells of the liver of the young domesticated pig. This work was carried out on fresh hepatic specimens from six healthy young pigs that were gathered immediately after their slaughter at the Abdelkader abattoir, Alexandria, Egypt. In our histological results, the liver had different cells including the hepatocytes and non-parenchymal cells including, the Kupffer cells and Ito cells. The hepatocytes had a large round cell nucleus with a prominent nucleolus. The intracellular lipid droplets allowed for the identification of ito cells and were found in the perisinusoidal space. By TEM observations, Kupffer cells had an irregular nucleus with a condensed type of chromatin. Ito cells had a large flat nucleus and large fat droplets, while their cytoplasm had a rough endoplasmic reticulum intermixed with mitochondria.
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Alshammari, Adel, Fahad Alabdah, Weiguang Wang et Glen Cooper. « Virtual Design of 3D-Printed Bone Tissue Engineered Scaffold Shape Using Mechanobiological Modeling : Relationship of Scaffold Pore Architecture to Bone Tissue Formation ». Polymers 15, no 19 (28 septembre 2023) : 3918. http://dx.doi.org/10.3390/polym15193918.
Texte intégralRésumé :
Large bone defects are clinically challenging, with up to 15% of these requiring surgical intervention due to non-union. Bone grafts (autographs or allografts) can be used but they have many limitations, meaning that polymer-based bone tissue engineered scaffolds (tissue engineering) are a more promising solution. Clinical translation of scaffolds is still limited but this could be improved by exploring the whole design space using virtual tools such as mechanobiological modeling. In tissue engineering, a significant research effort has been expended on materials and manufacturing but relatively little has been focused on shape. Most scaffolds use regular pore architecture throughout, leaving custom or irregular pore architecture designs unexplored. The aim of this paper is to introduce a virtual design environment for scaffold development and to illustrate its potential by exploring the relationship of pore architecture to bone tissue formation. A virtual design framework has been created utilizing a mechanical stress finite element (FE) model coupled with a cell behavior agent-based model to investigate the mechanobiological relationships of scaffold shape and bone tissue formation. A case study showed that modifying pore architecture from regular to irregular enabled between 17 and 33% more bone formation within the 4–16-week time periods analyzed. This work shows that shape, specifically pore architecture, is as important as other design parameters such as material and manufacturing for improving the function of bone tissue scaffold implants. It is recommended that future research be conducted to both optimize irregular pore architectures and to explore the potential extension of the concept of shape modification beyond mechanical stress to look at other factors present in the body.
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Baumgärtel, K. « Coherent amplitude modulation of electron-beam-driven Langmuir waves ». Annales Geophysicae 31, no 4 (10 avril 2013) : 633–38. http://dx.doi.org/10.5194/angeo-31-633-2013.
Texte intégralRésumé :
Abstract. A linear approach to the phenomenon of irregular amplitude modulation of beam-driven Langmuir waves, developed in a previous paper, is extended to explain periodic modulation as well. It comes about by beating of the fastest growing mode of the instability with beam-aligned plasma oscillations. They are naturally generated in a uniform domain of beam–plasma interaction prior to the onset of the instability. Particle-in-cell (PIC) simulations support the results of the linear analysis.
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Nor Asmira Amaran, Norazila Ibrahim et Zakiah Mohamed. « Structural and Morphology Changes in PrMnO3 Manganite Induced by Ba (x=0.33) Doping ». Journal of Advanced Research in Applied Sciences and Engineering Technology 29, no 3 (8 février 2023) : 160–67. http://dx.doi.org/10.37934/araset.29.3.160167.
Texte intégralRésumé :
In this paper, we discuss the structural and morphology properties of the solid-state prepared Pr0.67Ba0.33MnO3 perovskite manganite X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analyses were utilised to examine the structure, morphology, and chemical composition. The compound exhibits a single phase with an orthorhombic perovskite structure with a Pnma space group without any impurities. The refined cell parameters are a = 5.504 Å, b = 7.778 Å, and c = 5.528 Å (α = β = γ = 90° and a ≠ b ≠ c), therefore the cell volume is 236.723 Å^3. The tolerance factor is used to predict the stability of the Pr0.67Ba0.33MnO3, which is τ = 0.9241. Fourier transform infrared spectroscopy (FTIR) reveals that the Mn-O bonds appear at 600 cm^(-1). In addition, morphology SEM revealed that the grain sizes are heterogeneous, and the grain shapes are irregular. Using EDX technique, the percentage elemental composition of Pr, Ba, Mn, and O was determined. The values of the atomic percentages for each element are almost identical to the ratios of the elements during sample preparation.
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Karakurt, Eyyup Murat, Yuksel Cetin, Alper Incesu, Huseyin Demirtas, Mehmet Kaya, Yasemin Yildizhan, Merve Tosun et Yan Huang. « Microstructural, Biomechanical, and In Vitro Studies of Ti-Nb-Zr Alloys Fabricated by Powder Metallurgy ». Materials 16, no 12 (8 juin 2023) : 4240. http://dx.doi.org/10.3390/ma16124240.
Texte intégralRésumé :
This study investigated the microstructures, mechanical performances, corrosion resistances, and in vitro studies of porous Ti-xNb-10Zr (x: 10 and 20; at. %) alloys. The alloys were fabricated by powder metallurgy with two categories of porosities, i.e., 21–25% and 50–56%, respectively. The space holder technique was employed to generate the high porosities. Microstructural analysis was performed by using various methods including scanning electron microscopy, energy dispersive spectroscopy, electron backscatter diffraction, and x-ray diffraction. Corrosion resistance was assessed via electrochemical polarisation tests, while mechanical behavior was determined by uniaxial compressive tests. In vitro studies, such as cell viability and proliferation, adhesion potential, and genotoxicity, were examined by performing an MTT assay, fibronectin adsorption, and plasmid-DNA interaction assay. Experimental results showed that the alloys had a dual-phase microstructure composed of finely dispersed acicular hcp α-Ti needles in the bcc β-Ti matrix. The ultimate compressive strength ranged from 1019 MPa to 767 MPa for alloys with 21–25% porosities and from 173 MPa to 78 MPa for alloys with 50–56% porosities. Noted that adding a space holder agent played a more critical role in the mechanical behaviors of the alloys compared to adding niobium. The pores were largely open and exhibited irregular shapes, with uniform size distribution, allowing for cell ingrowth. Histological analysis showed that the alloys studied met the biocompatibility criteria required for orthopaedic biomaterial use.
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Chen, Xu, Yi Shao, Shi-Nan Wu et Shan-Bi Zhou. « Potential Factors of Corneal Endothelial Cells for Progression in Children with Uveitis ». Disease Markers 2021 (28 décembre 2021) : 1–10. http://dx.doi.org/10.1155/2021/8432774.
Texte intégralRésumé :
Objective. To observe the morphological changes and abnormal structure of corneal endothelial cells in children with uveitis, to analyze the related factors affecting the morphological changes of corneal endothelial cells, and to explore the clinical application of a corneal endothelial microscope in children with uveitis. Methods. The corneal endothelial cells of 70 patients with uveitis were photographed with the Topcon SP-3000 noncontact corneal endothelial microscope, and the corneal endothelial cell density (CD), average cell area (AVE), coefficient of variation of the cell area (CV), and percentage of hexagonal cells (PHC) were measured with the IMAGEnet system. Twenty-eight patients (56 eyes) with monocular uveitis were selected, with the affected eyes (28 eyes) as the experimental group and the contralateral healthy eyes (28 eyes) as the control group. The corneal endothelial cell parameters between the two groups were statistically analyzed. The parameters of corneal endothelial cells in 70 children with uveitis were compared, and the effects of the course of the disease, inflammatory cells in the anterior chamber, and posterior corneal deposition (KP) on the parameters of corneal endothelial cells were analyzed. Results. There are four abnormal forms of the corneal endothelium in children with uveitis: enlarged cell area gap, irregular cell shape, blurred intercellular space, and cell loss. KP showed irregular high reflective white spots in the corneal endothelial microscope images, surrounded by dark areas, and existed in all the eyes with dusty KP found in slit lamp examination and a small number of eyes without obvious KP. Comparing the corneal endothelial cell parameters between the experimental group and the control group, it was found that the corneal endothelial CD and PHC of the former were lower than those of the latter, and the difference was statistically significant ( P < 0.001 and P = 0.018 , respectively). The AVE and CA of the former were higher than those of the latter ( P = 0.013 and P = 0.046 , respectively). The corneal endothelial cell density of the eyes with a course of the disease of more than 1 year was lower than that of the eyes with a course of the disease less than 1 year, the coefficient of variation of the corneal endothelial cell area of the eyes with KP was higher than that of the eyes without KP, and the difference was statistically significant ( P = 0.003 and P = 0.030 , respectively). Conclusion. Corneal endothelial microscopy is one of the important methods for the detection of uveitis with high sensitivity. The change of morphological parameters of corneal endothelial cells is one of the important indexes to assist in the diagnosis of uveitis and can be further promoted in ophthalmological examination.
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Vassilyeva, Olga Yu, Katerina V. Kasyanova, Vladimir N. Kokozay et Brian W. Skelton. « Crystal structure of dichloridobis{μ-2-methoxy-6-[(methylimino)methyl]phenolato}{2-methoxy-6-[(methylimino)methyl]phenolato}cadmium(II)cobalt(III) monohydrate ». Acta Crystallographica Section E Crystallographic Communications 74, no 11 (2 octobre 2018) : 1532–35. http://dx.doi.org/10.1107/s2056989018013610.
Texte intégralRésumé :
The title compound, [CoCd(C9H10NO2)3Cl2]·H2O, is a solvatomorph of the corresponding hemihydrate recently published by us [Nesterova et al. (2018). Appl. Cat. A, 560, 171–184]. The current structure reveals different cell parameters and space group compared with the published one while both are monoclinic with almost the same cell volume. The title compound is formed of discrete neutral dinuclear molecules with no crystallographically imposed symmetry and water molecules of crystallization. The overall geometry about the cobalt(III) ion is octahedral with an N3O3 environment; each ligand acts as a meridional ONO donor. The CdII coordination sphere approximates an irregular square pyramid with a chlorine atom at the apex. There is significant shortening of a Cd—O bond length to the oxygen atom of the methoxo group on one of the ligands [2.459 (3) Å] compared to the corresponding distance in the published structure [2.724 (7) Å], while other Cd—Cl/N/O bonds remain roughly the same. In the crystal lattice, the heterometallic molecules, which are related by the crystallographic n-glide plane and interlinked by weak hydrogen bonds to solvent water molecules, form columns along [101]. Adjacent columns lie antiparallel to each other.
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Duarte, José Lucas Costa, Wellington Martins dos Santos, Hodias Sousa de Oliveira, Gabriel Forte Paranhos, Helder Carlos Costa Pereira et Jeann Leal de Araújo. « Dilated cardiomyopathy in a green-winged saltator (Saltator similis) ». Brazilian Journal of Veterinary Pathology 17, no 1 (2024) : 46–50. http://dx.doi.org/10.24070/bjvp.1983-0246.v17i1p46-50.
Texte intégralRésumé :
Cardiovascular diseases are rarely reported in birds. Among pet birds, they are most documented in psittacine birds. Dilated cardiomyopathy is a myocardial disease frequently found in poultry but with few reports in both pet and wild birds. An elderly male green-winged saltator (Saltator similis) died suddenly after presenting intermittent clinical signs of dyspnea, weakness, and vocalization changes. A general increase in cardiac size with a bulging apex was observed at necropsy. The heart exhibited an enlarged left ventricular space and flaccid musculature on the cut section. The liver was diffusely enlarged with rounded edges. No other gross lesions were observed. Samples were collected in 10% formalin and routinely processed. Histologically, bundles of myocardial fibers were irregularly arranged, with markedly elongated myofibrils and irregular cell contours. Additionally, multifocal areas of disruption were observed between the myofibrils. Diffuse hepatic congestion of sinusoids and portal veins was observed, and diffuse edema in the interstitium and para bronchi was present in the lungs. The clinical signs observed were nonspecific and can be found in several diseases of the cardiovascular and respiratory systems of birds. The gross and histological findings are compatible with what has been described for dilated cardiomyopathy in birds; however, left ventricular dilatation is uncommon in avian patients. Heart diseases in pet birds are still underdiagnosed, and reports of cardiomyopathies are limited to psittacine birds. To the authors’ knowledge, this is the first report of a dilated cardiomyopathy in a passerine bird.
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Herndon, Aaron M., Margret L. Casal et John T. (Scott) Jaques. « Testicular Neoplasia in the Retained Testicles of an Intersex Male Dog ». Journal of the American Animal Hospital Association 48, no 2 (1 mars 2012) : 118–24. http://dx.doi.org/10.5326/jaaha-ms-5696.
Texte intégralRésumé :
This case describes the presentation and management of an 8 yr old phenotypically female intersex male dog presented for evaluation of a mass in the right inguinal region. The right inguinal space was surgically explored, and a large irregular mass resembling a fully developed testicle was identified in the right vaginal tunic. A second mass resembling an atrophied, but anatomically mature testicle, was identified in the left tunic. The larger mass was identified as a Sertoli cell tumor that had replaced all normal testicular tissue. The smaller mass was identified as a testicle that contained a small intratubular seminoma. The patient was diagnosed as having a phenotypic female sex, chromosomal male sex, and a gonadal male sex. Hormone assays completed before and after the gonadectomy and mass removal document an elevation of circulating progesterone presurgically that returned to baseline by 1 mo postsurgically. The source of the progesterone was identified to be the Leydig cells of the atrophied testicle.
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Piro, Oscar E., Gustavo A. Echeverría, Eduardo E. Castellano, Beatriz S. Parajón-Costa et Enrique J. Baran. « Structural and spectroscopic characterization of isotypic sodium, rubidium and cesium acesulfamates ». Zeitschrift für Naturforschung B 70, no 7 (1 juillet 2015) : 491–96. http://dx.doi.org/10.1515/znb-2015-0042.
Texte intégralRésumé :
AbstractThree new acesulfamate salts, NaC4H4NO4S, RbC4H4NO4S and CsC4H4NO4S, were prepared by reactions in aqueous solutions and thoroughly characterized. Their crystal and molecular structures were determined by single crystal X-ray diffraction methods. They crystallize in the monoclinic space group P21/a with a = 7.2518(2), b = 8.9414(4), c = 10.5929(4) Å, β = 99.951(3)°, V = 676.52(4) Å3 for the Na salt; a = 7.4663(3), b = 9.6962(4), c = 10.4391(4) Å, β = 95.150(3)°, V = 752.68(5) Å3 for the Rb salt and a = 7.5995(4), b = 9.9439(4), c = 10.8814(6) Å, β = 91.298(5)°, V = 822.08(7) Å3 for the Cs salt, and Z = 4 molecules per unit cell. The three compounds are isotypic to each other and to the previously reported potassium salt. The metal ions are in irregular polyhedral coordination with six neighboring acesulfamate anions through their nitrogen and carbonyl and sulfoxide oxygen atoms. The FTIR spectra of the compounds were also recorded and are briefly discussed.
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Brzezicka-Szymczyk, Krystyna, Władysław Golinowski et Czesław Zamorski. « Cytological changes observed in the successive phases of the wheat rust caused by Puccinia recondita f. sp. tritici after the treatment with Tilt 250EC ». Acta Societatis Botanicorum Poloniae 64, no 4 (2014) : 349–58. http://dx.doi.org/10.5586/asbp.1995.045.
Texte intégralRésumé :
The disease process of wheat (<i>Triticum aestivum</i>) cv. Parada caused by rust (<i>Puccinia recondita</i> Rob. ex Desm. f. sp. <i>tritici</i>) and the effect of applying the fungicide Tilt 250EC are described. The application of spraying at the time of inoculation, during incubation and at the beginning of the actual disease is most effective, thus attests to the highest pathogen susceptibility to that chemical agent at these phases of the disease. Tilt 250EC (propikonazole) inhibits the ergosterol biosynthesis in the fungus cells. Application of the preparation caused the inhibition of the development and necrosis of the intra- and extracellular mycelium. Observed were: irregular growth of intercellular hyphae, perforation of septas, homogenization of protoplasts and collapsing of cells. In the haustoria observed were: the thickening of the cell wall, modification of the perihaustorial space, protoplast degeneration and finally the haustorium obliteration.
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Wu, Gangfeng, Zhiguo He et Guohua Liu. « Development of a Cell-Centered Godunov-Type Finite Volume Model for Shallow Water Flow Based on Unstructured Mesh ». Mathematical Problems in Engineering 2014 (2014) : 1–15. http://dx.doi.org/10.1155/2014/257915.
Texte intégralRésumé :
Based on the Godunov-type cell-centered finite volume method, this paper presents a two-dimensional well-balanced shallow water model for simulating flows over arbitrary topography with wetting and drying. The central upwind scheme is used for the computation of mass and momentum fluxes on interface. The novel aspect of the present model is a robust and accurate nonnegative water depth reconstruction method which is implemented in the unstructured mesh to achieve second-order accuracy in space and to track the moving wet/dry fronts of the flow over irregular terrain. By defining the bed elevation and primary flow variables at the cell center in the nonstaggered grid system, all computational cells are either fully wet or dry to avoid the problem of being partially wetted. The developed model is capable of being well balanced and preserving the computed water depth to be nonnegative under a certain CFL restriction, which makes it robust and stable. The present model is validated against three benchmark tests and two laboratory dam-break cases. Finally, the good agreement between the numerical results by the established model and measured data of the Malpasset dam break event on a 1/400 scale physical model demonstrates the capability of the model for the real-life applications.
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Abouhamed, Marouan, Kay Grobe, Isabelle V. Leefa Chong San, Sabine Thelen, Ulrike Honnert, Maria S. Balda, Karl Matter et Martin Bähler. « Myosin IXa Regulates Epithelial Differentiation and Its Deficiency Results in Hydrocephalus ». Molecular Biology of the Cell 20, no 24 (15 décembre 2009) : 5074–85. http://dx.doi.org/10.1091/mbc.e09-04-0291.
Texte intégralRésumé :
The ependymal multiciliated epithelium in the brain restricts the cerebrospinal fluid to the cerebral ventricles and regulates its flow. We report here that mice deficient for myosin IXa (Myo9a), an actin-dependent motor molecule with a Rho GTPase–activating (GAP) domain, develop severe hydrocephalus with stenosis and closure of the ventral caudal 3rd ventricle and the aqueduct. Myo9a is expressed in maturing ependymal epithelial cells, and its absence leads to impaired maturation of ependymal cells. The Myo9a deficiency further resulted in a distorted ependyma due to irregular epithelial cell morphology and altered organization of intercellular junctions. Ependymal cells occasionally delaminated, forming multilayered structures that bridged the CSF-filled ventricular space. Hydrocephalus formation could be significantly attenuated by the inhibition of the Rho-effector Rho-kinase (ROCK). Administration of ROCK-inhibitor restored maturation of ependymal cells, but not the morphological distortions of the ependyma. Similarly, down-regulation of Myo9a by siRNA in Caco-2 adenocarcinoma cells increased Rho-signaling and induced alterations in differentiation, cell morphology, junction assembly, junctional signaling, and gene expression. Our results demonstrate that Myo9a is a critical regulator of Rho-dependent and -independent signaling mechanisms that guide epithelial differentiation. Moreover, Rho-kinases may represent a new target for therapeutic intervention in some forms of hydrocephalus.
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Cai, Gemei, Ming He, X. L. Chen, W. Y. Wang, Y. F. Lou, H. H. Chen et J. T. Zhao. « Crystal structure and luminescence properties of a novel promising phosphor Ba3ScB9O18 ». Powder Diffraction 22, no 4 (décembre 2007) : 328–33. http://dx.doi.org/10.1154/1.2770745.
Texte intégralRésumé :
A novel borate compound Ba3ScB9O18 has been synthesized by solid-state reaction and its structure has been determined and refined from powder X-ray diffraction data. This compound crystallizes in a hexagonal cell (space group P63/m) with lattice parameters a=7.1360(4) Å and c=16.5420(9) Å, and each unit cell contains two formulas. Its crystal structure is made up of planar B3O6 groups parallel to each other along the [001] direction, regular ScO6 octahedra, irregular BaO6 hexagons, and BaO9 polyhedra to form an analogue structure of Ba3YB9O18. DTA and TGA curves for Ba3ScB9O18 show that it is a chemically stable and congruent melting compound. Luminescence properties for Ba3ScB9O18 were investigated using fluorescence spectroscopy and X-ray excited luminescence measurements. Its emission spectrum upon UV excitation (330 nm) has exhibited a prominent blue-green emission band at about 490 nm, and its XEL spectra show an intense emission band in the range of 360 to 500 nm with peak center at 400 nm. The light yield of Ba3ScB9O18 powders is about 23% as large as that of BGO powders under the same measurement conditions. There seems to be a certain relationship between the scintillation properties and the structural features of Ba3ScB9O18.
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Шапеев, В. П., et В. А. Беляев. « Solving the biharmonic equation with high order accuracy in irregular domains by the least squares collocation method ». Numerical Methods and Programming (Vychislitel'nye Metody i Programmirovanie), no 4 (18 décembre 2018) : 340–55. http://dx.doi.org/10.26089/nummet.v19r431.
Texte intégralRésumé :
Предложен и реализован новый вариант метода коллокации и наименьших квадратов (КНК) повышенной точности для численного решения неоднородного бигармонического уравнения. Дифференциальная задача методом КНК проектируется в пространство полиномов четвертой и восьмой степеней. Реализованный алгоритм применяется в нерегулярных областях, границы которых заданы аналитическими кривыми, в частности сплайнами. Исходная нерегулярная область включается в прямоугольник, который покрывается регулярной сеткой с прямоугольными ячейками. На границе области используется "одинарный" слой ререгулярных ячеек (н-ячеек), отсеченных границей от прямоугольных граничных ячеек начальной регулярной сетки. Все н-ячейки разбиваются на два класса: самостоятельные, в которых находится центр содержащих их граничных ячеек, и несамостоятельные, центр содержащих их граничных ячеек которых расположен вне области. Вытянутые несамостоятельные граничные н-ячейки присоединяются к соседним самостоятельным ячейкам, и в объединенных ячейках строится свой отдельный кусок аналитического решения. При этом в граничных ячейках, которые пересекла граница, для аппроксимации дифференциальных уравнений использованы "законтурные" (расположенные вне расчетной области) точки коллокации и точки согласования решения задачи. Эти два приема позволили существенно уменьшить обусловленность системы линейных алгебраических уравнений (СЛАУ) приближенной задачи по сравнению со случаем, когда несамостоятельные н-ячейки использовались как самостоятельные для построения приближенного решения задачи и не была использована "законтурная" часть граничных ячеек. В численных экспериментах по сходимости приближенного решения различных задач на последовательности сеток установлено, что решение сходится с повышенным порядком и с высокой точностью совпадает с аналитическим решением задачи в случае, когда решение известно. Приведено сравнение полученных результатов с известными результатами других авторов, которые использовали конечно-разностный метод (FDM, Finite Difference Method) повышенного порядка аппроксимации. В качестве приложения решение неоднородного бигармонического уравнения использовано для моделирования напряженно-деформированного состояния (НДС) изотропных тонких пластин нерегулярных форм. This paper addresses a new version of the least squares collocation (LSC) method of high order accuracy proposed and implemented for the numerical solution of the nonhomogeneous biharmonic equation. The differential problem is projected onto a polynomial space of fourth and eighth degrees by the LSC method. The algorithm implemented is applied in irregular domains. The boundaries of these domains are given by analytical curves, in particular, by splines. The irregular domain is embedded in a rectangle covered by a regular grid with rectangular cells. In this paper we use the irregular cells (i-cells) which are cut off by the domain boundary from the rectangular cells of the initial regular grid. All i-cells are divided into two classes: the independent and dependent ones. The center of a dependent cell is located outside the domain by contrast with the center of an independent cell. The idea of attaching elongated dependent irregular cells to the neighboring ones is used. A separate piece of the analytical solution is constructed in the combined cells. The collocation and matching points located outside the domain are used to approximate the differential equations in the boundary cells. These two approaches allow us to essentially reduce the conditionality of the corresponding system of linear algebraic equations. It is shown that the approximate solutions obtained by the LSC method converge with an increased order and coincide with the analytical solutions of the test problems with high accuracy in the case of the known solution. The numerical results are compared with those found by other authors who used a high order finite difference method. The nonhomogeneous biharmonic equation is used to model the stress-strain state of isotropic thin irregular plates as an application.
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Mills, Stuart J., Anthony R. Kampf, Koichi Momma, Robert M. Housley et Joseph Marty. « Müllerite, the Fe-analogue of backite from Otto Mountain, California, USA ». Canadian Mineralogist 58, no 4 (1 juillet 2020) : 413–19. http://dx.doi.org/10.3749/canmin.2000026.
Texte intégralRésumé :
ABSTRACT Müllerite (IMA2019–060) is a new mineral found at several workings on Otto Mountain, 2.5 km NW of Baker, San Bernardino County, California, USA. Müllerite occurs as hexagonal tablets and thin plates up to 0.2 mm across, intergrown ball-like clusters, and scattered flakes. Crystals are yellow, tending to reddish-orange, and have a pale-yellow streak and subadamantine to greasy luster. Crystals are brittle with an irregular fracture and have a hardness of ∼2 and perfect cleavage on {001}. The main forms observed are {100} and {001}. The calculated density is 5.812 g/cm3. The empirical formula (based on 7 O + Cl + I apfu) is Pb1.83Ag0.26Fe0.93Al0.03Cu0.02Te6+0.95O5.56Cl1.30I0.14; the endmember formula is Pb2Fe3+(Te6+O6)Cl. Müllerite is trigonal, space group P312, with the unit cell parameters a = 5.2040(5), c = 8.9654(12) Å, V = 210.23(3) Å3, and Z = 1. The crystal structure of müllerite was refined using Rietveld analysis and converged to Rwp = 4.861%, S = 0.1873, RB = 1.800%, and RF = 0.691%. Müllerite is the Fe-analogue of backite, Pb2Al3+(Te6+O6)Cl.
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Sejkora, Jiří, Petr Pauliš, Luboš Vrtiška, Ondřej Pour et Zdeněk Dvořák. « Lindgrenite, monoclinic Cu3(MoO4)(OH)2, from Cínovec, Krušné hory Mountains - the first occurrence in the Czech Republic ». Bulletin Mineralogie Petrologie 31, no 1 (2023) : 41–46. http://dx.doi.org/10.46861/bmp.31.041.
Texte intégralRésumé :
A very rare mineral lindgrenite, Cu3(MoO4)2(OH)2, was found in material from the 3rd level of abandoned Cínovec mine 1 of the Cínovec Sn-W deposit, Krušné hory Mountains, northern Bohemia. This is the first occurrence of this mineral in the Czech Republic. Lindgrenite occurs there as olive green irregular coatings on the area up to 0.5 × 1 cm in size formed by hemispherical to spherical aggregates up to 0.3 mm across with crystalline surface in association with brochantite. Lindgrenite is monoclinic, space group P21/n, the unit-cell parameters refined from X-ray powder diffraction data are: a 5.3934(18), b 14.032(2), c 5.6098(15) Å, β 98.54(2)° and V 419.86(16) Å3. Chemical analyses of lindgrenite correspond to the empirical formula (Cu2.92Fe0.03)Σ2.95(MoO4)1.97(PO4)0.07(AsO4)0.01(OH)1.70 on the basis of 5 atoms pfu. Its origin is connected with simultaneous weathering of primary Cu (tennantite) and Mo (molybdenite) minerals in the conditions of supergene zone in-situ.
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Kampf, Anthony R., Joy Désor et Chi Ma. « Karlseifertite, Pb(Ga2Ge)(AsO4)2(OH)6, a new dussertite-group mineral, from Tsumeb, Namibia ». European Journal of Mineralogy 36, no 5 (24 septembre 2024) : 873–78. http://dx.doi.org/10.5194/ejm-36-873-2024.
Texte intégralRésumé :
Abstract. Karlseifertite (IMA 2024-007, International Mineralogical Association), Pb(Ga2Ge)(AsO4)2(OH)6, is a new member of the dussertite group, from Tsumeb, Namibia. It is a secondary oxidation-zone mineral found on fracture surfaces in germanite–chalcocite ore. Karlseifertite occurs in rosettes of thin, yellow, hexagonal plates up to about 0.2 mm in diameter and usually less than 0.01 mm thick. The mineral has a pale-yellow streak, subadamantine lustre, Mohs hardness of ∼ 4, brittle tenacity, irregular fracture, perfect cleavage on {001} and a calculated density of 4.993 g cm−3. Optically, karlseifertite crystals are uniaxial (+), with ω=1.890(5) and ε=1.894(calc) (white light). The empirical formula from electron probe microanalyses is Pb0.992+(Ga1.603+Ge0.684+Fe0.573+Al0.123+)Σ2.97[(As0.765+S0.156+W0.096+)Σ1.00O4]2(OH0.99)6. Karlseifertite is trigonal with space group R3‾m and unit-cell parameters a=7.2814(7), c=17.1077(12) Å, V=785.50(15) Å3 and Z=3. The mineral has an alunite-supergroup structure (R1=0.0591 for 248 reflections with I>2σI).
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M. J. Thamer et Noor A. Hameed. « The Effect of Reinforcement Weight Ratios on the Mechanical Properties of ZrO2/ Unsaturated Polyester Nanocomposites ». International Journal of Nanoelectronics and Materials (IJNeaM) 16, no 3 (22 octobre 2024) : 643–50. http://dx.doi.org/10.58915/ijneam.v16i3.1331.
Texte intégralRésumé :
This work aims to prepare ZrO2/ unsaturated polyester nanocomposites with reinforcement weight percentage ratios (1, 2, 3, 4, 5, and 6) wt.% and study the effect of this reinforcement weight ratio on some mechanical properties such as hardness, impact strength, and tensile strength. The used powder has a monoclinic structure, P2/m space group, and unit cell parameters a, b, and c = 5.313Å, 5.210 Å, and 5.145 Å, receptively, and angels α, γ = 90º and β= 99.233º according to XRD data and using Dicvol 91 indexing program. The grain size of the used powder was estimated using Scherrer’s equation to be 43.2 nm. The SEM micrograph of ZrO2 nanopowder showed the particle morphology having homogenous irregular grains and appears to be similar to a coral shape. The results of the hardness test showed that increasing the reinforcement weight ratio led to an increase in the hardness values. Impact, tensile, and flexural strength values increase with the reinforcement weight ratio and peaked at 6 wt. %, and decreased at a higher ratio.
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Jabberi, Henda, et Faouzi Ben Ammar. « New advanced concept of the flying capacitor asymmetric multilevel voltage source inverter ». COMPEL - The international journal for computation and mathematics in electrical and electronic engineering 37, no 3 (8 mai 2018) : 1166–88. http://dx.doi.org/10.1108/compel-04-2017-0168.
Texte intégralRésumé :
Purpose To improve the voltage quality in AC adjustable high-power-speed-drive applications, the purpose of the paper is to provide a large number of output levels without increasing the number of commutation cells in the three-phase, n-cells flying capacitor voltage source asymmetric Multilevel Inverter (MI). The concept is based on the selection of different ratios between the breakdown voltages of two successive power devices. The new mathematical model is developed under various ratios, allows a thorough investigation of the harmonic distortions, flying capacitor energy storage, flying capacitor voltage balancing controllability and blocking voltage insulated gate bipolar transistor (IGBT) capability. Design/methodology/approach The asymmetrical design provides a large number of output levels without increasing the number of commutation cells. The important new analytical expression of capacitors voltage distribution is derived and extended to any ratio between the switch breakdown voltages of two successive power devices. Findings The detailed simulation study of the proposed concept has been carried out using MATLAB/Simulink. The power switches control of the three-phase three-cell MI is assured by new phase-shifted-multi-carrier pulse width modulation. The space vector representation is used to show the regular and irregular step output voltage in the complex plan (α,β). Originality/value In the paper, the n cells flying capacitor inverter, which typically operates in the (n + 1) levels mode, was extended to (n + 2), (n + 3) … until 2n levels with regular or irregular step output voltage. Consequently, the claimed advantages of the asymmetric MI are to improve power quality by reducing harmonic distortions and to reduce the requirement on capacitive energy storage in the circuit.
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Mehta, Rupal I., Rajiv Mangla et Rashi I. Mehta. « Giant Arachnoid Granulations : Diagnostic Workup and Characterization in Three Symptomatic Adults ». International Journal of Molecular Sciences 24, no 14 (13 juillet 2023) : 11410. http://dx.doi.org/10.3390/ijms241411410.
Texte intégralRésumé :
Giant arachnoid granulations (GAGs) are poorly investigated. Here, we document clinical findings associated with five new GAGs and illustrate the anatomical composition of these structures as well as diagnostic considerations in three symptomatic adults. The GAGs ranged from 1.1 to 3.6 cm (mean, 2.2 cm) in maximum dimension and manifested in middle-aged individuals who presented with long-standing brain mass and/or chronic headache. On imaging examinations, the tissues appeared as irregular parasagittal and/or perisinus structures that demonstrated heterogeneous internal elements. The GAGs abutted dura, extended through calvarial marrow spaces, and impinged on dural venous sinuses, causing their stenosis. The histologic workup of two GAG specimens resected from separate individuals revealed central collagen with pronounced internal vascular proliferation. One specimen additionally exhibited reactive changes within the lesion, including venous thrombosis, hemorrhage, and conspicuous inflammation. The salient immune component consisted of a foam cell-rich infiltrate that obstructed subcapsular and internal sinusoidal GAG spaces. Within this specimen, meningothelial hyperplasia was also appreciated. Notably, proliferated lymphatic vascular elements were additionally observed within the structure, extending into deep central collagen regions and engulfing many extravasated erythrocytes in the subcapsular space. In both surgically treated patients, symptoms resolved completely following resection. This report is the first to definitively depict reactive vascular and immunological changes within GAGs that were clinically associated with headache. The frequency of reactive changes within these meningeal structures is unclear in the literature, as GAGs are rarely sampled and investigated. Further systematic analyses are warranted to elucidate the causes and consequences of GAG genesis and their roles in physiology and disease states.
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Bukhari, Mahrukh, Munazza Mohsin, Zohra Nazir Kayani, Shahzad Rasool et Rizwan Raza. « The La+3-, Nd+3-, Bi+3-Doped Ceria as Mixed Conductor Materials for Conventional and Single-Component Solid Oxide Fuel Cells ». Energies 16, no 14 (11 juillet 2023) : 5308. http://dx.doi.org/10.3390/en16145308.
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Clean energy devices are essential in today’s environment to combat climate change and work towards sustainable development. In this paper, the potential materials A2Ce2O7−δ (A = La+3, Nd+3, Bi+3) were analyzed for clean energy devices, specifically for conventional and single-component solid oxide fuel cells (SC-SOFCs). The wet chemical route has been followed for the preparation of samples. X-ray diffraction patterns showed that all three samples exhibited a defected fluorite cubic structure. It also revealed the presence of dopants in the ceria, which was confirmed by the fingerprint region of FTIR. The optical behavior, fuel cell performance and electrochemical behavior were studied by UV–vis, fuel cell testing apparatus and EIS, respectively. The SEM results showed that all samples had irregular polygons. In Raman spectra, the F2g mode corresponding to the space group (Fm3m) confirms the fluorite structure. The Raman spectra showed that A2Ce2O7−δ (A = La+3, Nd+3, Bi+3) have different trends. The conventional fuel cell performance showed that the maximum power density of Bi2Ce2O7 was 0.65 Wcm−2 at 600 °C. The performance of A2Ce2O7−δ (A = La3+, Nd3+, Bi3+) as a single-component fuel cell revealed that Nd2Ce2O7−δ is the best choice with semiconductors conductors ZnO and NCAL. The highest power density (Pmax) of the Nd2Ce2O7/ZnO was 0.58 Wcm−2, while the maximum power output (Pmax) of the Nd2Ce2O7/NCAL was 0.348 Wcm−2 at 650 °C. All the samples showed good agreement with the ZnO as compared to NCAL for SC-SOFCs.
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Zimeras, Stelios. « Exploratory Point Pattern Analysis for Modeling Biological Data ». International Journal of Systems Biology and Biomedical Technologies 2, no 1 (janvier 2013) : 1–13. http://dx.doi.org/10.4018/ijsbbt.2013010101.
Texte intégralRésumé :
Data in the form of sets of points, irregular distributed in a region of space could be identified in varies biological applications for examples the cell nuclei in a microscope section of tissue. These kinds of data sets are defined as spatial point patterns and the presentation of the positions in the space are defined as points. The spatial pattern generated by a biological process, can be affected by the physical scale on which the process is observed. With these spatial maps, the biologists will usually want a detailed description of the observed patterns. One way to achieve this is by forming a parametric stochastic model and fitting it to the data. The estimated values of the parameters could be used to compare similar data sets providing statistical measures for fitting models. Also a fitted model can provide an explanation of the biological processes. Model fitting especially for large data sets is difficult. For that reason, statistical methods can apply with main purpose to formulate a hypothesis for the implementation of biological process. Spatial statistics could be implemented using advance statistical techniques that explicitly analyses and simulates point structures data sets. Typically spatial point patterns are data that explain the location of point events. The author’s interest is the investigation of the significance of these patterns. In this work, an investigation of biological spatial data is analyzed, using advance statistical modeling techniques like kriging.
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Mancini, Rock, Amy E. Nielsen, Joseph D. Hantho et Anthony J. Burt. « Drugging drug resistance with bystander-assisted immunotherapy. » Journal of Immunology 200, no 1_Supplement (1 mai 2018) : 58.14. http://dx.doi.org/10.4049/jimmunol.200.supp.58.14.
Texte intégralRésumé :
Abstract Acquired drug resistance is a longstanding challenge that reduces the efficacy of chemotherapeutic drugs. In contrast, the efficacies of modern immunotherapies do not directly correlate to the prevalence of chemo-resistant phenotypes. Here we improve upon this paradigm by targeting the action of immunotherapeutics to two general mechanisms of acquired drug resistance: irregular metabolism and drug efflux mediated by the ABC superfamily of transport proteins. In chemo-resistant prostate cancer cells, we demonstrate that these two mechanisms act in concert to selectively metabolize our newly developed class of enzyme-directed prodrug to the Toll-Like Receptor 7 immunotherapeutic Imiquimod. Following metabolism, liberated Imiquimod undergoes drug efflux to the extracellular space where it activates bystander immune cells in local proximity. In-vitro, we characterize this process of Bystander-Assisted ImmunoTherapy (BAIT) using an AT3B-1 chemo-resistant prostate cancer model with RAW-Blue and JAWSII reporter immune cell lines. Co-culture of AT3B-1 cancer cells with reporter immune cells results in immunogenicity mediated selectively by cancer cells. This results in enhanced NF-κB transcription, expression of cell surface markers, and secreted cytokines indicative of a cell-mediated immune response. Our prodrug is non-immunogenic with healthy cells alone and the enzyme-directing groups are stable for over 3 days in serum. Taken together, our results demonstrate that BAIT co-opts common mechanisms of drug resistance to elicit immunogenicity mediated by cancer cells themselves. We anticipate that BAIT will find use as a new mechanism of action that exploits drug resistant phenotypes to generate an immune response.
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Imaliza, Nurul, Mochamad Zainuri et Febiola Lintang Valentina Priono Putri. « Influence of carbon type on the structure of Na2MnPO4F/C as cathode material ». Journal of Physics : Conference Series 2498, no 1 (1 mai 2023) : 012032. http://dx.doi.org/10.1088/1742-6596/2498/1/012032.
Texte intégralRésumé :
Abstract Energy production and storage technologies have attracted much attention for everyday applications. Sodium-ion battery (SIB) has been recognized as one of the most potent types of technology for low-cost rechargeable batteries due to its abundant sodium resource. In the following, the synthesis of Na2MnPO4F /C material with the type of carbon is Citric Acid and Glucose using the solid-state method. The structure, morphology, particle size dimensions, etc. of the prepared materials were studied by XRD, SEM-EDX, DTA-TGA, PSA, and FTIR. The result is that Na2MnO4 with P21/n space group is a monoclinic structure and there is a decrease in cell volume and crystal size due to carbon coating. The particle sizes of NMPF 0%, NMPF 5%G, and NMPF 5%CA were 1127, 730, and 532 nm, respectively, with irregular particle shapes. However, it can be observed that glucose has more carbon content than citric acid as seen from the EDX results. The functional groups FTIR results obtained were Mn-O (stretching), O-P-O (bending-asymmetry), P-O (stretching-symmetry/asymmetry), and C-C (stretching-symmetry).
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Kordan, V., O. Zaremba, P. Demchenko et V. Pavlyuk. « Synthesis and electrochemical properties of LiyM1-xCaxMnO3 (M = Pr, Eu) solid solutions ». Physics and Chemistry of Solid State 23, no 4 (18 décembre 2022) : 699–704. http://dx.doi.org/10.15330/pcss.23.4.699-704.
Texte intégralRésumé :
New Li-containing solid solutions LiyM1-xCaxMnO3 (M = Pr and Eu) were synthesized by electrochemical lithiation of the ceramics with perovskite structure. The qualitative and quantitative composition of the initial and Li-containing ceramics was determined by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The M/Ca/Mn cation ratio was confirmed by X-ray fluorescence spectroscopy. The crystal structure of theM1-xCaxMnO3solid solutions before lithiation (GdFeO3-type structure, space group Pnma, Pearson code oP20) and after lithiation (filled-up GdFeO3-type) was determined by the Rietveld method. X-ray structural analysis showed the formation of phases with increased unit cell parameters after lithiation process. In the case of Eu and Pr-containing samples X-rays diffraction patterns illustrate the amorphous halo based on the by-products of reaction between of ceramics surface and components from electrolyte. Under experimental conditions (Li-metal anode) the quantity of intercalated Li increases for ceramics: Li0.084Eu0.5Ca0.5MnO3, Li0.113Pr0.5Ca0.5MnO3, and Li0.134Pr0.7Ca0.3MnO3. Scanning electron microscopy method revealed the formation of Li-containing aggregates with dimension of 200-900 nm. The grains demonstrate block-like or irregular shape morphology with developed area surface.
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Shen, Yanfei, Yongqing Tu et Wei Huang. « Flexural Strength Evaluation of Multi-Cell Composite L-Shaped Concrete-Filled Steel Tubular Beams ». Buildings 12, no 1 (3 janvier 2022) : 39. http://dx.doi.org/10.3390/buildings12010039.
Texte intégralRésumé :
Concrete-filled steel tubular (CFST) members have been widely used in industrial structures and high-rise residential buildings. The multi-cell composite L-shaped concrete-filled steel tubular (ML-CFST) cross-section, as an innovative, special-shaped structural arrangement, may solve the issue of normal CFST members protruding from walls and result in more usable interior space. Currently, no design rules are available for the application of ML-CFST members. One of the primary objectives of the present study is to develop recommendations in line with the unified theory to evaluate the bending moment resistance of ML-CFST beams. According to the unified theory, the bending moment resistance of an ML-CFST beam is related to the compressive strength (fsc) and the flexural strength index (γm) of a composite section, in which the accuracy of γm and fsc are affected by a confinement effect factor (ξ). Nevertheless, the original expression of ξ is not suitable for ML-CFST sections, since the appreciable effect of the irregular shape on confinement is neglected. Considering the cross-sectional geometry and boundary conditions of the cells, an equivalent shape factor to modify the confinement effect was proposed in this study through dividing the infill concrete into highly confined areas and less confined areas. An adequate formula to calculate the fsc and an approximate expression of γm for the ML-CFST sections was then developed. Furthermore, four-point bending tests on eight specimens were carried out to investigate the flexural performance of the ML-CFST beams. Lastly, the proposed formulas were assessed against experimental and numerical results. The comparisons show that the proposed unified theory-based approach produced accurate and generally conservative results for the ML-CFST beams studied.
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Meidina, Dwi Winda, et Netty Laura S. « Pengaruh Kesehatan Mental Karyawan terhadap Kinerja yang Dimediasi oleh Kesejahteraan di Tempat Kerja (Studi Empiris pada Karyawan Divisi Teknologi Informasi di Masa Work From Home) ». Business Management Journal 18, no 1 (21 avril 2022) : 85. http://dx.doi.org/10.30813/bmj.v18i1.3092.
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<p><em> </em><em>The implementation of working from home has changed employees' work environment, from an office environment to a home environment. It raises many limitations, like communication and interaction space. It can negatively impact employees because it can trigger irregular working hours and long working hours. IT field is one of the jobs that can be done remotely, but it still have different with the implementation of WFH and pandemic that requires new adaptations. This study aims to determine the effect of innovation culture, self-efficacy on technostress, and technostress, burnout on performance with workplace well-being as a mediating variable for IT employees who work from home. This study uses a survey method with an online questionnaire to 295 IT employees and used as a research sample. Data analysis method used SmartPLS 3.2 program by analyzing the inner and outer models. The results of this study indicate that: innovation culture is significant to technostress, self-efficacy is significant to technostress, innovation culture and technostress is significant to WWB, but burnout to WWB is not significant, technostress, burnout and WWB is significant to performance, WWB can mediate innovation culture and technostress to its effect on performance, WWB is not able to mediate burnout on performance.<strong></strong></em></p>
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Mills, S. J., A. R. Kampf, A. G. Christy, R. M. Housley, G. R. Rossman, R. E. Reynolds et J. Marty. « Bluebellite and mojaveite, two new minerals from the central Mojave Desert, California, USA ». Mineralogical Magazine 78, no 5 (octobre 2014) : 1325–40. http://dx.doi.org/10.1180/minmag.2014.078.5.15.
Texte intégralRésumé :
AbstractBluebellite, Cu6[I5+O3(OH)3](OH)7Cl and mojaveite, Cu6[Te6+O4(OH)2](OH)7Cl, are new secondary copper minerals from the Mojave Desert. The type locality for bluebellite is the D shaft, Blue Bell claims, near Baker, San Bernardino County, California, while cotype localities for mojaveite are the E pit at Blue Bell claims and also the Bird Nest drift, Otto Mountain, also near Baker. The two minerals are very similar in their properties. Bluebellite is associated particularly with murdochite, but also with calcite, fluorite, hemimorphite and rarely dioptase in a highly siliceous hornfels. It forms bright bluishgreen plates or flakes up to ~20 mm 620 mm 65 mm in size that are usually curved. The streak is pale bluish green and the lustre is adamantine, but often appears dull because of surface roughness. It is non-fluorescent. Bluebellite is very soft (Mohs hardness ~1), sectile, has perfect cleavage on {001} and an irregular fracture. The calculated density based on the empirical formula is 4.746 g cm–3. Bluebellite is uniaxial (–), with mean refractive index estimated as 1.96 from the Gladstone-Dale relationship. It is pleochroic O (bluish green) >> E (nearly colourless). Electron microprobe analyses gave the empirical formula Cu5.82I0.99Al0.02Si0.12O3.11(OH)9.80Cl1.09based on 14 (O+Cl) a.p.f.u. The Raman spectrum shows strong iodate-related bands at 680, 611 and 254 cm–1. Bluebellite is trigonal, space group R3, with the unit-cell parameters: a = 8.3017(5), c = 13.259(1) Å , V = 791.4(1) Å 3 and Z = 3. The eight strongest lines in the powder X-ray diffraction (XRD) pattern are [dobs/Å (I) (hkl)]: 4.427(99)(003), 2.664(35)(211), 2.516(100)(212̄ ), 2.213(9)(006), 2.103(29)(033,214), 1.899(47)(312,215̄ ), 1.566(48)(140,217) and 1.479(29)(045,143̄ ,324).Mojaveite occurs at the Blue Bell claims in direct association with cerussite, chlorargyrite, chrysocolla, hemimorphite, kettnerite, perite, quartz and wulfenite, while at the Bird Nest drift, it is associated with andradite, chrysocolla, cerussite, burckhardtite, galena, goethite, khinite, mcalpineite, thorneite, timroseite, paratimroseite, quartz and wulfenite. It has also been found at the Aga mine, Otto Mountain, with cerussite, chrysocolla, khinite, perite and quartz. Mojaveite occurs as irregular aggregates of greenish-blue plates flattened on {001} and often curved, which rarely show a hexagonal outline, and also occurs as compact balls, from sky blue to medium greenish blue in colour. Aggregates and balls are up to 0.5 mm in size. The streak of mojaveite is pale greenish blue, while the lustre may be adamantine, pearly or dull, and it is non-fluorescent. The Mohs hardness is ~1. It is sectile, with perfect cleavage on {001} and an irregular fracture. The calculated density is 4.886 g cm–3, based on the empirical formulae and unit-cell dimensions. Mojaveite is uniaxial (–), with mean refractive index estimated as 1.95 from the Gladstone-Dale relationship. It is pleochroic O (greenish blue) >> E (light greenish blue). The empirical formula for mojaveite, based on 14 (O+Cl) a.p.f.u., is Cu5.92Te1.00Pb0.08Bi0.01O4(OH)8.94Cl1.06. The most intense Raman bands occur at 694, 654 (poorly resolved), 624, 611 and 254 cm–1. Mojaveite is trigonal, space group R3, with the unit-cell parameters: a = 8.316(2), c = 13.202(6) Å and V = 790.7(1) Å 3. The eight strongest lines in the powder XRD pattern are [dobs/Å (I) (hkl)]: 4.403(91)(003), 2.672(28)(211), 2.512(100)(212̄ ), 2.110(27)(033,214), 1.889(34)(312,215̄ ,223̄ ), 1.570(39)(404,140,217), 1.481(34)(045,143̄ ,324) and 1.338(14)(422). Diffraction data could not be refined, but stoichiometries and unit-cell parameters imply that bluebellite and mojaveite are very similar in crystal structure. Structure models that satisfy bondvalence requirements are presented that are based on stackings of brucite-like Cu6MX14layers, where M = (I or Te) and X = (O, OH and Cl). Bluebellite and mojaveite provide a rare instance of isotypy between an iodate containing I5+with a stereoactive lone electron pair and a tellurate containing Te6+with no lone pair.
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Evans, JR. « Carbon Fixation Profiles Do Reflect Light Absorption Profiles in Leaves ». Functional Plant Biology 22, no 6 (1995) : 865. http://dx.doi.org/10.1071/pp9950865.
Texte intégralRésumé :
Bifacial leaves contain an array of chloroplasts which are aligned along cell walls adjacent to intercellular airspaces. Cells beneath the adaxial (upper) surface are generally cylindrical in shape, forming palisade tissue and contain chloroplasts that have characteristics associated with acclimation to high irradiance. Conversely, cells near the abaxial (lower) surface are irregular in shape, forming spongy tissue and contain chloroplasts that have characteristics associated with acclimation to low irradiance. This results in a gradient of declining photosynthetic capacity per unit chlorophyll with increasing depth into the leaf. Space irradiance declines dramatically through the leaf. The profile of light absorption through the leaf has yet to be measured, but should approximate the product of space irradiance and pigment profiles. Since pigment content is highest in the middle of the leaf, light absorption peaks about one quarter of the way through the leaf. The response of leaf photosynthetic rate to irradiance reflects the interaction between the profiles of light absorption and chloroplast characteristics. Quantum yield (mol CO2 mol-1 quanta absorbed) varies for different layers in the leaf because the profile of Rubisco content per unit chlorophyll is not as steep as the light absorption profile. This skews the profile of carbon fixation away from the light absorption profile, favouring greater fixation in deeper layers. Nishio, Sun and Vogelmann (1993, Plant Cell 5, 953-961) measured profiles of 14C fixation across spinach leaves and concluded that carbon fixation was disconnected from the light gradient. Reanalysis of their data shows that carbon fixation is remarkably consistent with light absorption obeying the Beer- Lambert law when allowance is made for chlorophyll and Rubisco profiles through the leaf. This interpretation is supported by chlorophyll fluorescence properties of adaxial and abaxial surfaces. An apparent extinction coefficient of about 1500 m2 (mol Chl)-1 could be derived from leaf data which compares with 2230 m2 (mol Chl)-1 for pigment-protein complexes in solution. A possible test for this analysis would be to measure the 14C fixation profile of leaves illuminated on their abaxial surface.
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de Alexandre, Juliana Sversut, Alexandre Ninhaus-Silveira, Rosicleire Veríssimo-Silveira, Hellen Buzollo, José Augusto Senhorini et Milena Penteado Chaguri. « Structural analysis of the embryonic development in Brycon cephalus (Günther, 1869) ». Zygote 18, no 2 (27 novembre 2009) : 173–83. http://dx.doi.org/10.1017/s0967199409990190.
Texte intégralRésumé :
SummaryThe embryogenesis of Brycon cephalus was established in seven stages: zygote, cleavage, blastula, gastrula, segmentation, larval and hatching, in an incubation period of 11 h (26°C). The zygote phase was observed directly after fertilization and egg hydration. Cleavage began at 0.5 h of incubation and extended up to the morula phase (1.5 h; +100 blastomeres). Cleavage was meroblastic and underwent the following division pattern: the first five divisions were vertical and perpendicular to each other, following the model 2 × 2, 4 × 2, 4 × 4 and 4 × 8. The sixth division was horizontal and occurred at 1.25 h after fertilization, giving rise to two cell layers (4 × 8 × 2) with 64 blastomeres. At the blastula stage (1.25–1.5 h), an irregular space between the blastomeres, the blastocoele, could be detected and the periblast structure initiated. The gastrula (1.75–6.0 h) was characterized by the morphogenetic movements of epiboly, convergence and cell involution, and formation of the embryonic axis. The segmentation stage (7–9 h) comprised the development of somites, the notochord, optic, otic and Kupffer's vesicles, neural tube, primitive intestine and ended with the release of the tail. The larval stage (up to 10 h) was characterized by the presence of 30 somites and growth and elongation of the larvae. At the hatching stage, the embryos presented more than 30 somites and exhibited swimming movements and a soft chorion. The blastomeres presented euchromatic nuclei, indicating a high mitotic activity and many yolk globules in the cytoplasm. The periblast was constituted of a layer with several nuclei and many vesicles, which grew during the epiboly movement.
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Shchipalkina, Nadezhda, Igor Pekov, Sergey Britvin, Natalia Koshlyakova, Marina Vigasina et Evgeny Sidorov. « A New Mineral Ferrisanidine, K[Fe3+Si3O8], the First Natural Feldspar with Species-Defining Iron ». Minerals 9, no 12 (11 décembre 2019) : 770. http://dx.doi.org/10.3390/min9120770.
Texte intégralRésumé :
Ferrisanidine, K[Fe3+Si3O8], the first natural feldspar with species-defining iron, is an analogue of sanidine bearing Fe3+ instead of Al. It was found in exhalations of the active Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Fissure Tolbachik Eruption, Tolbachik volcano, Kamchatka Peninsula, Russia. The associated minerals are aegirine, cassiterite, hematite, sylvite, halite, johillerite, arsmirandite, axelite, aphthitalite. Ferrisanidine forms porous crusts composed by cavernous short prismatic crystals or irregular grains up to 10 μm × 20 μm. Ferrisanidine is transparent, colorless to white, the lustre is vitreous. Dcalc is 2.722 g·cm−3. The chemical composition of ferrisanidine (wt. %, electron microprobe) is: Na2O 0.25, K2O 15.15, Al2O3 0.27, Fe2O3 24.92, SiO2 60.50, in total 101.09. The empirical formula calculated based on 8 O apfu is (K0.97Na0.03)Ʃ1.00(Si3.03Fe3+0.94Al0.02)Ʃ3.99O8. The crystal structure of ferrisanidine was studied using the Rietveld method, the final R indices are: Rp = 0.0053, Rwp = 0.0075, R1 = 0.0536. Parameters of the monoclinic unit cell are: a = 8.678(4), b = 13.144(8), c = 7.337(5) Å, β = 116.39(8)°, V = 749.6(9) Å3. Space group is C2/m. The crystal structure of ferrisanidine is based on the sanidine-type “ferrisilicate” framework formed by disordered [SiO4] and [Fe3+O4] tetrahedra.