The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
Xiaolin Zhong - One of the best experts on this subject based on the ideXlab platform.
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An evaluation of shock-capturing methods on a hypersonic boundary layer Receptivity problem
47th AIAA Aerospace Sciences Meeting including The New Horizons Forum and Aerospace Exposition, 2009Co-Authors: Syed F. Rehman, Xiaolin ZhongAbstract:Understanding of transition of hypersonic boundary layers is critical for future development of re-entry vehicles. The Receptivity of such a boundary layer to external flow disturbances is not well understood, particularly when the surface has finite-sized roughness. In this work, we explore the use of shock capturing for study of hypersonic boundary layer Receptivity. In such problems, the interaction of the low-amplitude disturbances with shock structures may not be properly accounted for due to the localized dissipation inherent in the method. Previously-developed previously-developed WENO-based third- and fifth order shock capturing methods are applied to a Receptivity problem, the Mach 4.5 flow past a flat plate with a sharp leading edge. This problem has been studied previously with a high-order shock fitting scheme. The shock-fitted solution is used to evaluate shock capturing schemes in terms of accuracy, eciency and stability. Also, the significance of the leading edge singularity will be studied, which was not possible with a shock fitting method.
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Receptivity of a supersonic boundary layer over a flat plate part 3 effects of different types of free stream disturbances
Journal of Fluid Mechanics, 2005Co-Authors: Xiaolin ZhongAbstract:Supersonic boundary-layer Receptivity to different types of free-stream disturbance is studied for a Mach 4.5 boundary-layer flow over a flat plate by using the approaches of both direct numerical simulation and linear stability theory. This paper is Part 3 of a three-part study of the Receptivity of supersonic boundary layers to free-stream disturbances. The present paper investigates Receptivity to four types of different free-stream disturbances, i.e. slow and fast acoustic waves, entropy waves, and vorticity waves. A high-order shock-fitting scheme is used in the numerical simulation in order to accurately account for the effects of interactions between free-stream disturbance waves and the oblique shock wave. Numerical results on the generation of fast acoustic waves by free-stream entropy waves or vorticity waves are compared with those of a linear theory. Good agreement is obtained in both wave angles and amplitudes immediately behind the bow shock. It is found that the second-mode Receptivity to free-stream slow acoustic waves is several times stronger than that to free-stream fast acoustic waves. This is because free-stream slow acoustic waves can directly induce and interact with the first and second Mack modes, while free-stream fast acoustic waves cannot. Instead, the free-stream fast acoustic waves can only induce and interact with stable mode I waves, which in turn induce unstable Mack modes. In the cases of Receptivity to free-stream entropy waves and vorticity waves, it is found that the oblique shock wave created by the displacement of the boundary layer plays an important role because boundary-layer disturbances are mainly induced by fast acoustic waves generated behind the shock by free-stream forcing waves. As a result, mechanisms of the Receptivity to free-stream entropy and vorticity waves are very similar to those of the Receptivity to free-stream fast acoustic waves.
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Receptivity of a supersonic boundary layer over a flat plate part 2 Receptivity to free stream sound
Journal of Fluid Mechanics, 2003Co-Authors: Xiaolin ZhongAbstract:In this paper, we continue to study the mechanisms of the Receptivity of the supersonic boundary layer to free-stream disturbances by using both direct numerical simulation and linear stability theory. Specifically, the Receptivity of a Mach 4.5 flow over a flat plate to free-stream fast acoustic waves is studied. The Receptivity to free-stream slow acoustic waves, entropy waves and vorticity waves will be studied in the future. The oblique shock wave induced by the boundary-layer displacement plays an important role in the Receptivity because the free-stream disturbance waves first pass through the shock before entering the boundary layer. A high-order shock-fitting scheme is used in the numerical simulations in order to account for the effects of interactions between free-stream disturbance waves and the oblique shock wave. The results show that the Receptivity of the flat-plate boundary layer to free-stream fast acoustic waves leads to the excitation of both Mack modes and a family of stable modes, i.e. mode I, mode II, etc. It is found that the forcing fast acoustic waves do not interact directly with the unstable Mack modes. Instead, the stable mode I waves play an important role in the Receptivity process because they interact with both the forcing acoustic waves and the unstable Mack-mode waves. Through the interactions, the stable mode I waves transfer wave energy from the forcing fast acoustic waves to the second Mack-mode waves. The effects of incident wave angles, forcing wave frequencies, and wall temperature perturbation conditions on the Receptivity are studied. The results show that the Receptivity mechanisms of the second mode are very different from those of modes I and II, which leads to very different Receptivity properties of these discrete wave modes to free-stream fast acoustic waves with different incident wave angles, frequencies, and different wall boundary conditions. The maximum receptivities of the second mode, mode I and mode II to planar free-stream fast acoustic waves are obtained when incident wave angles approximately equal 26 ◦ ,4 5 ◦ , and 18 ◦ ,r espectively. The results of Receptivity to a beam of free-stream fast acoustic waves show that the leading edge is one of the most efficient regions for Receptivity.
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Receptivity of a supersonic boundary layer over a flat plate part 1 wave structures and interactions
Journal of Fluid Mechanics, 2003Co-Authors: Xiaolin ZhongAbstract:This paper is the first part of a two-part study on the mechanisms of the Receptivity to disturbances of a Mach 4.5 flow over a flat plate by using both direct numerical simulations (DNS) and linear stability theory (LST). The main objective of the current paper is to study the linear stability characteristics of the boundary-layer wave modes and their mutual resonant interactions. The numerical solutions of both steady base flow and unsteady flow induced by forcing disturbances are obtained by using a fifth-order shock-fitting method. Meanwhile, the LST results are used to study the supersonic boundary-layer stability characteristics relevant to the Receptivity study. It is found that, in addition to the conventional first and second modes, there exist a family of stable wave modes in the supersonic boundary layer. These modes play a very important role in the Receptivity process of excitation of the unstable Mack modes, especially the second mode. These stable modes are termed mode I, mode II, etc., in this paper. Though mode I and mode II waves are linearly stable, they can have resonant (synchronization) interactions with both acoustic waves and the Mack-mode waves. Therefore, the stable wave modes such as mode I and mode II are critical in transferring wave energy between the acoustic waves and the unstable second mode. The effects of frequencies and wall boundary conditions for the temperature perturbations on the boundary-layer stability and Receptivity are also studied.
Carlos Simon - One of the best experts on this subject based on the ideXlab platform.
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Human endometrial Receptivity: a genomic
2020Co-Authors: José Remohí, Francisco Domínguez, A. Pellicer, Carlos SimonAbstract:The endometrium is a specialized tissue, hormonally-regulated, that is non-adhesive for embryos throughout most of the menstrual cycle in humans and other primates. Thus, endometrial Receptivity is a self-limited period in which the endometrial epithelium (EE) acquires a functional and transient ovarian steroid-dependent status. The luminal EE acquires the ability to adhere (Receptivity) the developing human blastocyst during this period due mainly to the presence of progesterone after appropriate 17β-oestradiol priming. This status is a key element for embryonic implantation and appears to be closely associated with morphological and biochemical changes of EE cells. This specific time window is thought to be open after 4–5 days and closes after 9–10 days of progesterone production or administration, creating a physiological window of Receptivity limited to days 19–24 of the menstrual cycle in humans. The scientific knowledge of the endometrial Receptivity process is fundamental for the understanding of the human reproduction, but, so far, none of the proposed biochemical markers for endometrial Receptivity have been proved clinically useful. In this work new strategies are presented based on molecular biology technologies that aim to clarify the fragmented information in this field using differential display, quantitative PCR and cDNA microarray analysis of endometrial epithelial-derived cell lines and endometrial samples to investigate the hierarchy at the mRNA level of molecules implicated in the process of endometrial Receptivity.
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Endometrial Receptivity by Endometrial Receptivity Analysis (ERA) for Infertility
Endometrial Gene Expression, 2019Co-Authors: María Ruiz-alonso, Jose Miravet-valenciano, Pilar López, Carlos SimonAbstract:The endometrial factor plays a key role in implantation, being one of the responsible for recurrent implantation failure (RIF). Along years, many molecules implied in the acquisition of endometrial Receptivity have been proposed as markers of this status, but as this phenotype is the consequence of several biological changes, it was needed to change to a more holistic point of view. In this sense, the development of new technologies, such as microarrays and next-generation sequencing, allowed to develop a transcriptomic tool able to identify the endometrial status of each patient in a specific moment. This improvement has allowed a better clinical management of infertility with an endometrial origin.
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Clinical management of endometrial Receptivity.
Seminars in reproductive medicine, 2014Co-Authors: David Blesa, María Ruiz-alonso, Carlos SimonAbstract:The endometrial window of implantation (WOI), the cycle days during which normal embryo implantation can occur, has generally been assumed to begin on cycle day 19 or 20 of an idealized 28 days cycle and last for 4 to 5 days. Noyes et al took the first steps in defining the WOI by establishing a set of morphological criteria to evaluate endometrial development and Receptivity, but recent studies have invalidated their use in the routine evaluation of infertility. Based on greater than 10 years of extensive research, our group has developed a molecular diagnostic tool (the endometrial Receptivity array [ERA] test) based on the specific transcriptomic signature that identifies the receptive endometrium in natural and artificial (hormonal replacement therapy) cycles. The ERA test has shown that some patients have a delayed WOI, others have an advanced WOI, and others can have unusually short windows of Receptivity. This identification and characterization of the WOI allows the personalization of the embryo transfer. In this review, we describe the ERA and our experience with its use in assessment of the endometrial Receptivity in patients undergoing assisted reproduction.
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profiling the gene signature of endometrial Receptivity clinical results
Fertility and Sterility, 2013Co-Authors: Tamara Garridogomez, Maria Ruizalonso, David Blesa, Patricia Diazgimeno, Felipe Vilella, Carlos SimonAbstract:This article highlights the need for methods to objectively diagnose endometrial Receptivity as a factor contributing to infertility in female patients. The correct identification of the appropriate window of implantation in a given patient, by using endometrial Receptivity biomarkers, can help to prevent reproductive failure resulting from misplaced timing of the endometrial window of implantation (WOI). Although to date no single, clinically relevant morphologic, molecular, or histologic marker capable of indicating endometrial Receptivity status has been identified, global transcriptomic analysis of human endometria performed in the last decade has given us insights into a genomic signature that is capable of identifying endometrial Receptivity. As a consequence, a genomic tool named the Endometrial Receptivity Array (ERA), based on a customized microarray, was developed, and along with it a specially trained bioinformatic prediction computer algorithm was created to identify WOI timing in the endometrium. This tool has proven more accurate and consistent than histologic (Noyes) dating at identifying the personalized WOI day, thus leading to the new clinical concept of personalized ET on the optimum day of endometrial Receptivity, identified individually case by case.
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Ovarian stimulation and endometrial Receptivity
Human Reproduction, 1999Co-Authors: Diana Valbuena, José Remohí, Melinda J. Jasper, Antonio Pellicer, Carlos SimonAbstract:Endometrial Receptivity is a limiting step in the success of in-vitro fertilization (IVF). To investigate this issue, we selected a specific population of high responder patients in whom implantation was impaired, even when good quality embryos were transferred. We present a series of studies showing that high oestradiol concentrations on the day of human chorionic gonadotrophin (HCG) administration are detrimental to uterine Receptivity. In addition, we suggest clinical strategies to improve endometrial Receptivity in high responder patients using a step-down regimen.
S Hamamah - One of the best experts on this subject based on the ideXlab platform.
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insights into human endometrial Receptivity from transcriptomic and proteomic data
Reproductive Biomedicine Online, 2012Co-Authors: D Haouzi, H Dechaud, S Assou, S HamamahAbstract:Abstract The appreciation of endometrial Receptivity is a crucial step in assisted reproductive technology as implantation failures are thought to result, in large part, from abnormal endometrial Receptivity. Using emerging omics technologies, investigators have begun to define both molecular signatures and specific biomarkers of receptive endometrium. The aim of this review was to analyse the new perspectives brought to the appreciation of endometrial Receptivity by transcriptomic and proteomic technologies, involving the analysis of gene- or protein-expression-profile shifts between the pre-receptive and receptive secretory stages and how they might lead to new strategies for endometrial Receptivity assessments. The use of omics as molecular tools to determine the effects of stimulation protocols on endometrial gene expression and clinical outcomes has also been investigated. The appreciation of endometrial Receptivity is a crucial step in assisted reproductive technology as implantation failures are thought to result, in large part, from abnormal endometrial Receptivity. Using emerging omics technologies, investigators have begun to define both molecular signatures and specific biomarkers of receptive endometrium. The aim of this review is to analyse the new perspectives brought to the appreciation of endometrial Receptivity by omics technologies, involving the analysis of gene- or protein-expression-profile shifts between the pre-receptive and receptive secretory stages, and how they might lead to new strategies for endometrial Receptivity assessments. The use of omics during IVF procedures as molecular tools to determine the effects of stimulation protocols on endometrial gene expression and clinical outcomes has also been investigated.
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controlled ovarian hyperstimulation for in vitro fertilization alters endometrial Receptivity in humans protocol effects
Biology of Reproduction, 2010Co-Authors: D Haouzi, H Dechaud, S Assou, Clothilde Dechanet, T Anahory, S HamamahAbstract:The impact of gonadotropin-releasing hormone (GnRH) agonist long compared with GnRH antagonist protocols, under in vitro fertilization conditions on endometrial Receptivity, is still debated. Therefore, we compared the effect of both GnRH antagonist and agonist long protocols on the endometrial Receptivity by analyzing, to our knowledge for the first time, the global gene expression profile shift during the prereceptive and receptive stages of stimulated cycles under the two GnRH analogue protocols compared with natural cycles in the same patients. For the same normal-responder patients, endometrial biopsies were collected on the day of oocyte retrieval and on the day of embryo transfer after human chorionic gonadotropin administration of a stimulated cycle with either GnRH agonist long or GnRH antagonist protocols and compared with the prereceptive and receptive stages of a natural cycle. Samples were analyzed using DNA microarrays. Gene expression profiles and biological pathways involved during the prereceptive stage to the receptive endometrial transition of stimulated and natural cycles were analyzed and compared for each patient. Both protocols affect endometrial Receptivity in comparison with their natural cycle in the same patients. Major differences in endometrial chemokines and growth factors under stimulated cycles in comparison with natural cycles were observed. Such an effect has been associated with gene expression alterations of endometrial Receptivity. However, the endometrial Receptivity under the GnRH antagonist protocol was more similar to the natural cycle Receptivity than that under the GnRH agonist protocol.
Ariel Revel - One of the best experts on this subject based on the ideXlab platform.
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defective endometrial Receptivity
Fertility and Sterility, 2012Co-Authors: Ariel RevelAbstract:The endometrium is one of the most fascinating tissues in the human body. Its sole purpose is to enable implantation of an embryo during a relatively short window of opportunity in the menstrual cycle. It is becoming clear that overcoming the current bottleneck in improvements to assisted reproductive techniques will require a closer look at the interface between uterus and embryo. Indeed, embryo implantation requires a cross talk with a receptive endometrium. Using sonography, hysteroscopy and endometrial biopsy we can learn about anatomical and functional markers of endometrial Receptivity. This article reviews the factors which might cause defective endometrial Receptivity. These include uterine polyps, septa, leiomyomata and adhesions. The effect of thin endometrium, endometriosis and hydrosalpinx is also described. Finally contemporary investigation of molecular markers of endometrial Receptivity is described. Improving embryo implantation by a closer look inside the uterus is the key to increasing pregnancy rates in IVF.
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endometrial Receptivity markers the journey to successful embryo implantation
Human Reproduction Update, 2006Co-Authors: Hanna Achache, Ariel RevelAbstract:Human embryo implantation is a three-stage process (apposition, adhesion and invasion) involving synchronized crosstalk between a receptive endometrium and a functional blastocyst. This ovarian steroid-dependant phenomenon can only take place during the window of implantation, a self-limited period of endometrial Receptivity spanning between days 20 and 24 of the menstrual cycle. Implantation involves a complex sequence of signalling events, consisting in the acquisition of adhesion ligands together with the loss of inhibitory components, which are crucial to the establishment of pregnancy. Histological evaluation, now considered to add little clinically significant information, should be replaced by functional assessment of endometrial Receptivity. A large number of molecular mediators have been identified to date, including adhesion molecules, cytokines, growth factors, lipids and others. Thus, endometrial biopsy samples can be used to identify molecules associated with uterine Receptivity to obtain a better insight into human implantation. In addition, development of functional in vitro systems to study embryo–uterine interactions will lead to better definition of the interactions existing between the molecules involved in this process. The purpose of this review was not only to describe the different players of the implantation process but also to try to portray the relationship between these factors and their timing in the process of uterine Receptivity.
A P Roschektaev - One of the best experts on this subject based on the ideXlab platform.
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Receptivity coefficients at excitation of cross flow waves due to scattering of free stream vortices on surface vibrations
Journal of Fluid Mechanics, 2016Co-Authors: V I Borodulin, A V Ivanov, Y S Kachanov, A P RoschektaevAbstract:This paper is devoted to an experimental investigation of Receptivity of a laminar swept-wing boundary layer due to scattering of free-stream vortices on localized (in the streamwise direction) surface vibrations. The experiments were conducted under completely controlled disturbance conditions by means of a hot-wire anemometer on a model of a swept wing with a sweep angle of 25°. Both the free-stream vortices and the surface vibrations were generated by disturbance sources; their frequency–wavenumber spectra were measured thoroughly. The free-stream vorticity vectors were directed perpendicular to the incident-flow velocity vector and parallel to the swept-wing-model surface. The linearity of the Receptivity mechanism under investigation (in a sense that the corresponding Receptivity coefficients are independent of the disturbances amplitudes) has been checked carefully. The main goal of this experiment was to estimate the vibration-vortex Receptivity coefficients as functions of the disturbance frequency, spanwise wavenumber and vortex offset parameter. This goal has been attained. Being defined in Fourier space, the obtained Receptivity coefficients are independent of the specific surface vibration shape and can be used for verification of various Receptivity theories.
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Receptivity coefficients at excitation of cross flow waves by free stream vortices in the presence of surface roughness
Journal of Fluid Mechanics, 2013Co-Authors: V I Borodulin, A V Ivanov, Y S Kachanov, A P RoschektaevAbstract:The present experimental study is devoted to examination of the vortex Receptivity mechanism associated with excitation of unsteady cross-flow (CF) waves due to scattering of unsteady free-stream vortices on localized steady surface non-uniformities (roughness). The measurements are carried out in a low-turbulence wind tunnel by means of a hot-wire anemometer in a boundary layer developing over a $25\textdegree $ swept-wing model. The harmonic-in-time free-stream vortices were excited by a thin vibrating wire located upstream of the experimental-model leading edge and represented a kind of small-amplitude von Karman vortex street with spanwise orientation of the generated instantaneous vorticity vectors. The controlled roughness elements (the so-called ‘phased roughness’) were placed on the model surface. This roughness had a special shape, which provided excitation of CF-waves having basically some predetermined (required) spanwise wavenumbers. The linearity of the stability and Receptivity mechanisms under study was checked accurately by means of variation of both the free-stream-vortex amplitude and the surface roughness height. These experiments were directed to obtaining the amplitudes and phases of the vortex-roughness Receptivity coefficients for a number of vortex disturbance frequencies. The vortex street position with respect to the model surface (the vortex offset parameter) was also varied. The Receptivity characteristics obtained experimentally in Fourier space are independent of the particular roughness shape, and can be used for validation of Receptivity theories.
