恒热源下平表面层流膜态沸腾的分析和计算

对沿恒热源传导下平表面层流流动的膜态沸腾进行研究。指出如何应用流线迭代法,对沿流动方向各截面上流体的速度分布和温度分布数值解的求法,并举例说明它的应用。最后对计算结果进行分析和讨论。     

Intravascular inhomogeneous oxygen distribution in microvessels: theory

Cross-sectional oxygen distribution in microvessels in most previous studies has been assumed to be homogeneous. Recent studies using phosphorescence quenching microscopy or microspectrophotometry showed a decline in oxygen profile near the arterial wall. In this study we performed theoretical analysis of intravascular P(O(2)) and S(O(2)) profiles in arterioles by using a radial diffusion model with a constant oxygen efflux from the vascular lumen, taking intravascular flow distribution into account. Theoretical calculations indicated that radial oxygen diffusion and a laminar flow pattern would create inhomogeneous intravascular oxygen profile with a decline toward the arterial wall. As mean blood flow velocity became lower, the difference between the centerline oxygen level and the inner surface level became larger. In conclusion, it is suggested that oxygen efflux from the vascular lumen and less convective supply near the vascular wall create a decline in P(O(2)) as well as S(O(2)) toward the arterial wall.     

Two-Dimensional Chemotherapy Simulations Demonstrate Fundamental Transport and Tumor Response Limitations Involving Nanoparticles

Zheng et al. (2004) developed a multiscale, two-dimensional tumor simulator with the capability of showing tumoral lesion progression through the stages of diffusion-limited dormancy, neo-vascularization (angiogenesis) and consequent rapid growth and tissue invasion. In this paper we extend their simulator to describe delivery of chemotherapeutic drugs to a highly perfused tumoral lesion and the tumor cells' response to the therapy. We perform 2-D simulations based on a self-consistent parameter estimation that demonstrate fundamental convective and diffusive transport limitations in delivering anticancer drug into tumors, whether this delivery is via free drug administration (e.g., intravenous drip), or via 100 nm nanoparticles injected into the bloodstream, extravasating and releasing the drug that then diffuses into the tumoral tissue, or via smaller 1-10 nm nanoparticles that are capable of diffusing directly and targeting the individual tumor cell.Even in a best-case scenario involving: constant ("smart") drug release from the nanoparticles; a homogenous tumor of one cell type, which is drug-sensitive and does not develop resistance; targeted nanoparticle delivery, with resulting low host tissue toxicity; and for model parameters calibrated to ensure sufficient drug or nanoparticle blood concentration to rapidly kill all cells in vitro ; our analysis shows that fundamental transport limitations are severe and that drug levels inside the tumor are far less than in vitro , leaving large parts of the tumor with inadequate drug concentration. A comparison of cell death rates predicted by our simulations reveals that the in vivo rate of tumor shrinkage is several orders of magnitude less than in vitro for equal chemotherapeutic carrier concentrations in the blood serum and in vitro, and after some shrinkage the tumor may achieve a new mass equilibrium far above detectable levels. We also demonstrate that adjuvant anti-angiogenic therapy "normalizing" the vasculature may ameliorate transport limitations, although leading to unwanted tumor fragmentation. Finally, our results suggest that small nanoparticles equipped with active transport mechanisms (e.g., chemotaxis) would overcome the predicted limitations and result in improved tumor response.     

Convective heat transfer area of the human body

In order to clarify the heat transfer area involved in convective heat exchange for the human body, the total body surface area of six healthy subjects was measured, and the non-convective heat transfer area and floor and chair contact areas for the following nine common body positions were measured: standing, sitting on a chair, sitting in the seiza position, sitting cross-legged, sitting sideways, sitting with both knees erect, sitting with a leg out, and the lateral and supine positions. The main non-convective heat transfer areas were: the armpits (contact between the upper arm and trunk regions), contact between the two legs, contacts between the fingers and toes, and contact between the hands and the body surface. Also, when sitting on the floor with some degree of leg contact (sitting in the seiza position, cross-legged, or sideways), there was a large non-convective heat transfer area on the thighs and legs. Even when standing or sitting in a chair, about 6–8% of the body surface did not transfer heat by convection. The results showed that the effective thermal convective area factor for the naked whole body in the standing position was 0.942. While sitting in a chair this factor was 0.860, while sitting in a chair but excluding the chair contact area it was 0.918, when sitting in the seiza position 0.818, when sitting cross-legged 0.843, in the sideways sitting position 0.855, when sitting with both knees erect 0.887, in the leg-out sitting position 0.906, while in the lateral position it was 0.877 and the supine position 0.844. For all body positions, the effective thermal convective area factor was greater than the effective thermal radiation area factor, but smaller than the total body surface area.     

多囊卵巢综合征患者卵丘形态与未成熟卵母细胞发育潜能关系

目的 研究多囊卵巢综合征患者无刺激周期取出的不同形态未成熟卵母细胞的发育潜能。方法 43例PCOS不孕患者进行了47个未成熟卵母细胞体外成熟培养（IVM）周期。所有患者均未经促卵泡素刺激,予以HCG36h后取卵。根据取出的卵-冠-丘复合物形态将其分为3组：卵丘紧密组、卵丘松散组、无卵丘组。比较3组的体外成熟率、受精率和优质胚胎率。结果 47个IVM周期共收集未成熟卵母细胞874枚,体外成熟率61.19%,受精率71.07%,着床率13.13%。卵丘松散组的体外成熟率明显高于卵丘紧密组（72.26%vs49.54%,P〈0.05）,受精率、优质胚胎率三组间无差异。结论 PCOS患者无刺激周期取出的未成熟卵母细胞中,卵丘松散、扩张的卵母细胞具有更好的体外成熟潜力。     

Novel demonstration of a physiologic/pharmacologic role of insulin-like growth factor-1 in ovulation in rats and action on cumulus oophorus

Gonadotropins are well known to be the most important stimulus for ovarian follicular development. More recently, there is indirect evidence that insulin-like growth factor-1 (IGF-1) is also a very important autocrine/paracrine factor in folliculogenesis. We had access to an analog of IGF-1, LR³IGF-1, which binds very poorly to IGF-1 binding proteins and therefore was shown by previous investigators to have biologic effects. We studied rats that were superovulated with the use of gonadotropins. We showed that the addition of LR³IGF-1 by infusion further increased the ovulation rate (statistically significant) and increased the ovarian weight in two of three strains of rats. We demonstrated that infusion of LR³IGF-1 or injection of equine chorionic gonadotropin or a combination of these two were associated with oocytes with reduced number of cumulus cells (statistically significant). We conducted an experiment to determine whether in vitro culturing with varying dosage of IGF-1 may stimulate cumulus cell replication to improve the quality of oocyte cumulus complex. IGF-1 did not show any change in this respect. Through these physiologic (pharmacologic) studies, we have shown that IGF-1 (analog) can further increase the ovulation rate induced by gonadotropins. Presented at the 46th Annual Meeting of the Canadian Fertility and Andrology Society. September 13–16, 2000, St. John’s Newfoundland.     

In Vitro Stimulation of Cumulus-Cell Expansion by Human Cord Serum in Mouse Oocyte–Cumulus Complexes

Purpose: The aim of this study was to test whether human cord serum (HCS) containing gonadotropins has an effect on the expansion ofoocyte—cumulus complexes (OCCs). Methods: The concentration of follicle stimulating hormone (FSH) and luteinizing hormone (LH) was measured in HCS by radioimmunoassay (RIA). After short-term culture (4 hr) with or without OCCs, medium containing 0.4% bovine serum albumin (BSA) as control or 10% HCS was collected and analyzed for its concentration of estradiol, progesterone, and testosterone. Results: The FSH concentration was at the basal level, but the LH level was as high as 142.4 mILU/ml in both natured and denatured serum. Undetectable levels of steroids were observed in control media with or without OCCs. In contrast, a moderate amount of steroid hormones was detected in culture medium containing HCS. OCCs secreted a minute amount of steroid hormones in response to HCS. Similar patterns of cumulus expansion were observable by treatment with HCS, human chorionic gonadotropin (hCG), or HCS plus hCG after 4, 8, or 22 hr of culture. However, no cumulus expansion was observed in controls. Conclusion: These results suggest that LH in HCS induces cumulus expansion but does not affect the secretion of steroid hormones by OCCs during culture.     

Factors affecting survival of reconstructed mouse embryos after nuclear transfer

Reconstruction of mouse embryos was performed by injection of donor genetic material from differentiated cells of various types (cumulus cells, cardiomyocytes, and epithelial cells) into recipient cells (mature oocytes and zygotes). A medium for microsurgery was selected, which enhanced survival of both embryonic and somatic cells during the reconstructive manipulations. Special preparation of somatic cells to transplantation was carried out, which employed factors synchronizing the cells in a certain phase of the cell cycle in order to enhance their capacity to maintain the development of reconstructed embryos. The processes of nucleus reprogramming in specialized cells under the action of cytoplasmic factors of oocytes and zygotes were examined. During in vitro culturing of reconstructed embryos, the most successful development was observed in embryos implanted with donor material from cumulus cells. Mouse embryos reconstructed with a certain genome and subsequent production and use of stem cells are considered as the model system for developing the basic principles of replacement therapy.__________This revised version was published online in July 2005 with the addition of the issue title and article categoryTranslated from Kletochnye Tekhnologii v Biologii i Meditsine, Vol. 1, No. 1, pp. 47–51, January, 2005     

Inhibition by human embryos of mouse granulosa cell progesterone production: development of a sensitive bioassay

Reproduction technologies could be improved by the development of methods to evaluate oocyte or embryo quality in a non-invasive, quantitative manner. Since human embryos secrete a factor that inhibits granulosa cell progesterone production, an interspecies bioassay was established to investigate whether the presence of this progesterone-inhibitory factor (PIF) in human embryo-conditioned (HEC) media is related to the health and developmental capacity of the embryos. Oocytes were microsurgically removed from oocyte-cumulus complexes isolated from superovulated mouse ovaries, and the oocytectomized complexes were cultured in HEC media in the presence of follicle stimulating hormone and testosterone. Progesterone accumulation in the media was determined by radioimmunoassay. Despite the potential limitations of very small volumes of HEC media to evaluate, and the need to freeze these media at the source, the bioassay was able to detect PIF activity in HEC media. Most embryos produced PIF activity, but the degree of inhibition was not correlated with the ability of oocytes to be fertilized, nor with embryo morphology or ability to cleave and develop after transfer. These results demonstrate that secretion of PIF by human embryos can be measured by this bioassay and that human PIF can inhibit murine granulosa cell steroidogenesis; however, PIF activity is not correlated with human embryo quality or developmental competence.     

Enhanced enstrophy generation for turbulent convection in low-Prandtl-number fluids

Turbulent convection is often present in liquids with a kinematic viscosity much smaller than the diffusivity of the temperature. Here we reveal why these convection flows obey a much stronger level of fluid turbulence than those in which kinematic viscosity and thermal diffusivity are the same; i.e., the Prandtl number Pr is unity. We compare turbulent convection in air at Pr = 0.7 and in liquid mercury at Pr = 0.021. In this comparison the Prandtl number at constant Grashof number Gr is varied, rather than at constant Rayleigh number Ra as usually done. Our simulations demonstrate that the turbulent Kolmogorov-like cascade is extended both at the large- and small-scale ends with decreasing Pr. The kinetic energy injection into the flow takes place over the whole cascade range. In contrast to convection in air, the kinetic energy injection rate is particularly enhanced for liquid mercury for all scales larger than the characteristic width of thermal plumes. As a consequence, mean values and fluctuations of the local strain rates are increased, which in turn results in significantly enhanced enstrophy production by vortex stretching. The normalized distributions of enstrophy production in the bulk and the ratio of the principal strain rates are found to agree for both Prs. Despite the different energy injection mechanisms, the principal strain rates also agree with those in homogeneous isotropic turbulence conducted at the same Reynolds numbers as for the convection flows. Our results have thus interesting implications for small-scale turbulence modeling of liquid metal convection in astrophysical and technological applications.Turbulent convection depends strongly on the material properties of the working fluid that are quantified by the Prandtl number, the ratio of kinematic viscosity of the fluid to thermal diffusivity of the temperature, Pr = ν/κ. Compared with the vast number of investigations at Pr ≥ 1 (1, 2), the very-low-Pr regime appears almost as a “terra incognita” despite many applications. Turbulent convection in the Sun is present at Prandtl numbers Pr < 10^?3 (3–5). The Prandtl number in the liquid metal core of the Earth is Pr ～ 10^?2 (6). Convection in material processing (7), nuclear engineering (8), or liquid metal batteries (9) has Prandtl numbers between 3 × 10^?2 and 10^?3. Rayleigh–Bénard convection (RBC), a fluid flow in a layer that is cooled from above and heated from below, is a paradigm for all of these examples. One reason for significantly fewer low-Pr RBC studies is that laboratory measurements have to be conducted in opaque liquid metals such as mercury or gallium at Pr = 0.021 (10–12). The lowest value for a Prandtl number that can be obtained in optically transparent fluids is Pr = 0.2 for binary gas mixtures (13), i.e., an order of magnitude larger than in liquid metals. Direct numerical simulations (DNS) are currently the only way to gain access to the full 3D convective turbulent fields in low-Pr convection (14–18). These simulations turn out to become very demanding if the small-scale structure of turbulence is to be studied, even for moderate Rayleigh number Ra, the parameter that quantifies the thermal driving in turbulent convection (19, 20). Whereas heat transport is reduced in low-Pr convection, the production of vorticity and shear are enhanced significantly, which amplifies the small-scale intermittency in these flows. An analysis of vorticity generation mechanisms in such flows and a comparison with other turbulent flows, which requires the resolution of spatial derivatives of the turbulent fields, is still missing. These details are, however, essential to improve parameterizations of the small-scale turbulence in low-Prandtl-number fluids such as algebraic heat flux and other subgrid-scale models (21, 22).In the present work, we investigate the reasons for this enhanced vorticity generation in low-Pr convection and compare and contrast the enstrophy production to turbulent convection at Pr ～ 1. Our studies are based on high-resolution 3D DNS. Rather than studying the Pr dependence of convection at a fixed Rayleigh number Ra, as is usually done, we compare two simulations at the same Grashof number Gr, which is defined byGr=gαΔTH3ν2=RaPr.[1]Here, g is the acceleration due to gravity, α is the thermal expansion coefficient, and ΔT is the total temperature difference across the cell height H. In such a comparison, Ra and Pr are varied now simultaneously and the corresponding dimensionless momentum equations (Eq. 4) remain unchanged. This implies that the strongly differing Prandtl numbers show up only in the advection–diffusion equation [5] for temperature. We demonstrate this perspective for two simulations at one Grashof number. We also mention that a similar discussion was emphasized in 2D quasi-geostrophic DNS (20). Fig. 1 illustrates our point of view. In Fig. 1 A and C, we show snapshots of temperature (Fig. 1 A and C, Left) and velocity magnitude (Fig. 1 A and C, Right) for the two runs. Compared with convection in air (Fig. 1 A), the temperature field in the liquid metal flow is much more diffusive, which is indicated by the smoother changes in color. The thickness of the thermal boundary layerδT=H2Nu[2]is significantly enhanced with Nu being the Nusselt number that measures turbulent heat transfer. This large thermal diffusivity is in line with an enhanced fluid turbulence level as seen by a comparison of Fig. 1 A and C, Right. The red line in Fig. 1B illustrates our pathway in the plane, which is spanned by the Prandtl and Rayleigh numbers.Open in a separate windowFig. 1.Comparison of two turbulent convection runs. (A, Left) Vertical slice cut of temperature; (A, Right) corresponding velocity magnitude. Data are for run RB1 at Pr = 0.7. (B) Sketch of the Prandtl–Rayleigh-number plane illustrating our parameter variation between runs RB1 and RB2 (more details in 相似文献