紧扣三阶学段特点 助力小学写作教学

根据学生的身心发展规律、课标的设计要求以及课程的设置编排区别进行写作教学中的学段性划分,落实于教学实践中学段性特点体现为"句—段—文"的语式训练体系,文体内容范畴呈现由易到难的趋势,表达训练要求由规范到个性化,设置合理的训练梯度。教师在厘清写作教学的学段性差异,并将之作为一个具有内在逻辑性的观照体系,才能科学、合理地设置写作教学系统,提高教学实效性。

浅谈概括课文主要内容的问题与对策

在新课改的背景下,教师要全力实施素质教育,提升小学生的语文综合素养。高度的概括能力是学生语文综合素养之一,概括主要内容教学,需要基于教材,有学段要求,本文为概括内容教学提供了教学策略及方法。

Superposability of unsteady aerodynamic loads on bridge deck sections

The 2-dimensional unsteady aerodynamic forces,in the context of both a thin airfoil where theory of potential flow is always applicable and a bluff bridge-deck section where separated flow is typically induced,are investigated from a point of view of whether or not they conform to the principle of linear superposition in situations of various structural motions and wind gusts.It is shown that some basic preconditions that lead to the linear superposability of the unsteady aerodynamic forces in cases of thin airfoil sections are no longer valid for a bluff section.Theoretical models of bridge aerodynamics such as the one related to flutter-buffeting analysis and those concerning aerodynamic admittance(AA)functions,however,necessitate implicitly this superposability.The contradiction revealed in this work may throw light on the perplexing problem of AA functions pertaining to the description of buffeting loads of bridge decks.Some existing theoretical AA models derived from flutter derivatives according to interrelations valid only for thin airfoil theories,which have been employed rather extensively in bridge aerodynamics,are demonstrated to be illogical.Finally,with full understanding of the preconditions of the applicability of linear superposability of the unsteady aerodynamic forces,suggestions in regard to experiment-based AA functions are presented.

Nutritional therapy for active Crohn’s disease

Nutritional therapy for active Crohn’s disease (CD) is an underutilised form of treatment in adult patients, though its use is common in the paediatric population. There is evidence that nutritional therapy can effectively induce remission of CD in adult patients. Enteral nutrition therapy is safe and generally well tolerated. Meta-analysis data suggest that corticosteroids are superior to nutritional treatment for induction of remission in active CD. However, the potential side effects of such pharmacotherapy must be taken into consideration. This review examines the evidence for the efficacy of elemental and polymeric diets, and the use of total parenteral nutrition in active CD.

Impact of Crash Environments on Crashworthiness of Fuselage Section

In order to study the crash resistance of the civil aircraft structure in different crash environments,two environmental models of soft soil and water are established to analyze the dynamic response of the fuselage section subjected to the vertical at the impact velocity of 7 m/s.Simulation results show that the soft crash environment can have a certain cushioning effect on the structure crash,but it will prolong the crash time and change the energy absorption mode.This work suggests that soft environment may not be suitable for forced landing.

Immunohistochemical evaluation of vitamin D receptor(VDR) expression in cutaneous melanoma tissues and four VDR gene polymorphisms

Objective:Vitamin D receptor(VDR)mediates vitamin D activity.We examined whether VDR expression in excised melanoma tissues is associated with VDR gene(VDR)polymorphisms.Methods:We evaluated VDR protein expression(by monoclonal antibody immunostaining),melanoma characteristics,and carriage of VDR-Fok I-rs2228570(C>T),VDR-Bsm I-rs1544410(G>A),VDR-ApaI-rs7975232(T>G),and VDR-TaqI-rs731236(T>C)polymorphisms(by restriction fragment length polymorphism).Absence or presence of restriction site was denoted by a capital or lower letter,respectively:"F"and"f"for Fok I,"B"and"b"for Bsm I,"A"and"a"for ApaI,and "T"and"t"for TaqI endonuclease.Seventy-four Italian cutaneous primary melanomas(52.1±12.7 years old)were studied;51.4% were stage Ⅰ,21.6% stage Ⅱ ,13.5% stage Ⅲ,and 13.5% stage Ⅳ melanomas.VDR expression was categorized as follows:100% positive vs.<100%;over the median 20%(high VDR expression)vs.≤20%(low VDR expression);absence vs.presence of VDR-expressing cells.Results:Stage I melanomas,Breslow thickness of<1.00 mm,level II Clark invasion,Aa heterozygous genotype,and AaTT combined genotype were more frequent in melanomas with high vs.low VDR expression.Combined genotypes BbAA,bbAa,AATt,BbAATt,and bbAaTT were more frequent in 100%vs.<100%VDR-expressing cells.Combined genotype AATT was more frequent in melanomas lacking VDR expression(odds ratio=14.5;P=0.025).VDR expression was not associated with metastasis,ulceration,mitosis>1,regression,tumor-infiltrating lymphocytes,tumoral infiltration of vascular tissues,additional skin and non-skin cancers,and melanoma familiarity.Conclusions:We highlighted that VDR polymorphisms can affect VDR expression in excised melanoma cells.Low VDR expression in AATT carriers is a new finding that merits further study.VDR expression possibly poses implications for vitamin D supplementation against melanoma.VDR expression and VDR genotype may become precise medicinal tools for melanoma in the future.

Gd-EOB-DTPA-enhanced magnetic resonance imaging features of hepatic hemangioma compared with enhanced computed tomography

AIM:To clarify features of hepatic hemangiomas on gadolinium-ethoxybenzyl-diethylenetriaminpentaacetic acid (Gd-EOB-DTPA)-enhanced magnetic resonance imaging (MRI) compared with enhanced computed tomography (CT). METHODS:Twenty-six patients with 61 hepatic hem- angiomas who underwent both Gd-EOB-DTPA-enhanced MRI and enhanced CT were retrospectively reviewed. Hemangioma appearances (presence of peripheral nodular enhancement, central nodular enhancement, diffuse homogenous enhancement, and arterioportal shunt during the arterial phase, fill-in enhancement during the portal venous phase, and prolonged enhancement during the equilibrium phase) on Gd-EOB-DTPA-enhanced MRI and enhanced CT were evaluated.The degree of contrast enhancement at the enhancing portion within the hemangioma was visually assessed using a five-point scale during each phase. For quantitative analysis, the tumor-muscle signal intensity ratio (SIR), the liver-muscle SIR, and the attenuation value of the tumor and liver parenchyma were calculated. The McNemar test and the Wilcoxon's signed rank test were used to assess the significance of differences in the appearances of hemangiomas and in the visual grade of tumor contrast enhancement between Gd-EOB-DTPA-enhanced MRI and enhanced CT. RESULTS:There was no significant difference between Gd-EOB-DTPA-enhanced MRI and enhanced CT in the presence of peripheral nodular enhancement (85% vs 82%), central nodular enhancement (3% vs 3%), diffuse enhancement (11% vs 16%), or arterioportal shunt (23% vs 34%) during arterial phase, or fill-in enhancement (79% vs 80%) during portal venous phase. Prolonged enhancement during equilibrium phase was observed less frequently on Gd-EOB-DTPA-enhanced MRI than on enhanced CT (52% vs 100%, P < 0.001). On visual inspection, there was significantly less contrast enhancement of the enhancing portion on Gd-EOB-DTPA-enhanced MRI than on enhanced CT during the arterial (3.94 ± 0.98 vs 4.57 ± 0.64, respectively, P < 0.001), portal venous (3.72 ± 0.82 vs 4.36 ± 0.53, respectively, P < 0.001), and equilibrium phases (2.01 ± 0.95 vs 4.04 ± 0.51, respectively, P < 0.001). In the quantitative analysis, the tumor-muscle SIR and the liver-muscle SIR observed with Gd-EOB-DTPA-enhanced MRI were 0.80 ± 0.24 and 1.28 ± 0.33 precontrast, 1.92 ± 0.58 and 1.57 ± 0.55 during the arterial phase, 1.87 ± 0.44 and 1.73 ± 0.39 during the portal venous phase, 1.63 ± 0.41 and 1.78 ± 0.39 during the equilibrium phase, and 1.10 ± 0.43 and 1.92 ± 0.50 during the hepatobiliary phase, respectively. The attenuation values in the tumor and liver parenchyma observed with enhanced CT were 40.60 ± 8.78 and 53.78 ± 7.37 precontrast, 172.66 ± 73.89 and 92.76 ± 17.92 during the arterial phase, 152.76 ± 35.73 and 120.12 ± 18.02 during the portal venous phase, and 108.74 ± 18.70 and 89.04 ± 7.25 during the equilibrium phase, respectively. Hemangiomas demonstrated peak enhancement during the arterial phase, and both the SIR with Gd-EOB-DTPA-enhanced MRI and the attenuation value with enhanced CT decreased with time. The SIR of hemangiomas was lower than that of liver parenchyma during the equilibrium and hepatobiliary phases on Gd-EOB-DTPA-enhanced MRI. However, the attenuation of hemangiomas after contrast injection was higher than that of liver parenchyma during all phases of enhanced CT. CONCLUSION:Prolonged enhancement during the equilibrium phase was observed less frequently on Gd-EOB-DTPA-enhanced MRI than enhanced CT, which may exacerbate differentiating between hemangiomas and malignant tumors.

TeachingmA Way of Implementing Statistical Methods for Ordinal Data to Researchers

The use of questionnaires, rating scales and other kinds of ordered classifications is unlimited and interdisciplinary, so it can take long time before novel statistical methods presented in statistical journals reach researchers of applied sciences. Therefore. teaching is an effective way of introducing novel methods to researchers at an early stage. Assessments on scales produce ordinal data having rank-invariant properties only, which means that suitable statistical methods are non-parametric and often rank-based. These limited mathematical properties have been taken into account in the research regarding development of statistical methods for paired ordinal data. The aim is to present a statistical method for paired ordinal data that has been successfully implemented to researchers from various disciplines together with statisticians attending interactive problem solving courses of biostatistics.

A Comparative Assessment of Aerodynamic Models for Buffeting and Flutter of Long-Span Bridges

Wind-induced vibrations commonly represent the leading criterion in the design of long-span bridges. The aerodynamic forces in bridge aerodynamics are mainly based on the quasi-steady and linear unsteady theory. This paper aims to investigate different formulations of self-excited and buffeting forces in the time domain by comparing the dynamic response of a multi-span cable-stayed bridge during the critical erection condition. The bridge is selected to represent a typical reference object with a bluff con- crete box girder for large river crossings. The models are viewed from a perspective of model complexity, comparing the influence of the aerodynamic properties implied in the aerodynamic models, such as aerodynamic damping and stiffness, fluid memory in the buffeting and self-excited forces, aerodynamic nonlinearity, and aerodynamic coupling on the bridge response. The selected models are studied for a windspeed range that is typical for the construction stage for two levels of turbulence intensity. Furthermore, a simplified method for the computation of buffeting forces including the aerodynamic admittance is presented, in which rational approximation is avoided. The critical flutter velocities are also compared for the selected models under laminar flow.

Improving oil recovery in the CO2 flooding process by utilizing nonpolar chemical modifiers

By means of experiments of C02 miscibility with crude oil, four nonpolar chemicals were evaluated in order to enhance the miscibility of C02 with crude oil. Through pre-slug injection and joint injection of toluene in CO2, crude oil displacement experiments in the slim-tube were conducted to investigate effects of the toluene- enhanced C02 flooding under simulated subterranean reservoir conditions. Experimental results showed that toluene can enhance extraction of oil into C02 and dissolution of C02 into oil with the increment of 251% and 64% respectively. Addition of toluene can obviously improve the oil recovery in either pre-slug injection or joint injection, and the crude oil recovery increased with the increase of the toluene concentration. The oil recov- ery can increase by 22.5% in pre-slug injection with the high toluene concentration. Pre-slug injection was recom- mended because it can consume less toluene than joint injection. This work could be useful to development and application of the CO） flooding in the oil recoverv as well as CO2 emission reduction.

Genetics and phylogeny of genus Coilia in China based on AFLP markers

The taxonomy of Coilia has been extensively studied in China,and yet phylogenetic relationships among component taxa remain controversial.We used a PCR-based fingerprinting technique,amplified fragment length polymorphism(AFLP) to characterize and identify all four species of Coilia in China.We examined the genetic relationships of the four species of Coilia and a subspecies of Coilia nasus with AFLP.A total of 180 AFLP loci were generated from six primer combinations,of which 76.11% were polymorphic.The mean genetic distance between pairs of taxa ranged from 0.047 to 0.596.The neighbor-joining tree and UPGMA dendrogram resolved the investigated species into three separate lineages:(1) C.mystus,(2) C.grayii and(3) C.brachygnathus,C.nasus,and C.nasus taihuensis.Phylogenetic analysis of the AFLP data is inconsistent with current morphological taxonomic systems.The AFLP data indicated a close relationship among C.brachygnathus,C.nasus taihuensis,and C.nasus.Therefore,the two species described under Coilia(C.brachygnathus and C.nasus taihuensis) are treated as synonyms of C.nasus.

Cytochemical characterization of yolk granule acid phosphatase during early development of the oyster Crassostrea gigas(Thunberg)

In this study, a cytochemical method and transmission electron microscopy was used to examine acid phosphatase activities of yolk granules throughout the early developmental stages of the Pacific oyster Crassostrea gigas. This study aimed to investigate the dynamic change of yolk granule acid phosphatase, and the mechanisms underlying its involvement in yolk degradation during the early developmental stages of molluscs. Three types of yolk granules （YGI, YGⅡ, and YGⅢ） that differed in electron density and acid phosphatase reaction were identified in early cleavage, morula, blastula, gastrula, trochophore, and veliger stages. The morphological heterogeneities of the yolk granules were related to acid phosphatase activity and degrees of yolk degradation, indicating the association of acid phosphatase with yolk degradation in embryos and larvae of molluscs. Fusion of yolk granules was observed during embryogenesis and larval development of C. gigas. The fusion of YGI （free of acid phosphatase reaction） with YGII （rich in acid phosphatase reaction） could be the way by which yolk degradation is triggered.

Merit Figures for the Optical Design of CSP Plants

This work proposes some optical merit figures useful for solar concentration in the phase of optical design. The examined systems are CSP （concentrated solar power） plants with heliostats fields. In order to characterize them, it is suggested to use some optical merit figures, applicable to every CSP plant and synthetize its optical performance. The proposed merit figures have the aim of assessing mirrors field efficiency and receiver optical efficiency. In particular, they are identified using a new definition of the input flux on the mirrors field. The practical advantage of using the optical merit figures is illustrated by means of a simulation.

Designing the mechanical properties of peptide-based supramolecular hydrogels for biomedical applications

Hydrogels are a class of special materials that contain a large amount of water and behave like rubber.These materials have found broad applications in tissue engineering,cell culturing,regenerative medicine etc.Recently,the exploration of peptide-based supramolecular hydrogels has greatly expanded the repertoire of hydrogels suitable for biomedical applications.However,the mechanical properties of peptide-based hydrogels are intrinsically weak.Therefore,it is crucial to develop methods that can improve the mechanical stability of such peptide-based hydrogels.In this review,we explore the factors that determine or influence the mechanical stability of peptide-based hydrogels and summarize several key elements that may guide scientists to achieve mechanically improved hydrogels.In addition,we exemplified several methods that have been successfully developed to prepare hydrogels with enhanced mechanical stability.These mechanically strong peptide-based hydrogels may find broad applications as novel biomaterials.It is still challenging to engineer hydrogels in order to mimic the mechanical properties of biological tissues.More hydrogel materials with optimal mechanical properties suitable for various types of biological applications will be available in the near future.

Design of Off-statistics Axial-flow Fans by Means of Vortex Law Optimization

Off-statistics input data sets are common in axial-flow fans design and may easily result in some violation of the requirements of a good aerodynamic blade design.In order to circumvent this problem,in the present paper,a solution to the radial equilibrium equation is found which minimizes the outlet kinetic energy and fulfills the aerodynamic constraints,thus ensuring that the resulting blade has acceptable aerodynamic performance.The presented method is based on the optimization of a three-parameters vortex law and of the meridional channel size.The aerodynamic quantities to be employed as constraints are individuated and their suitable ranges of variation are proposed.The method is validated by means of a design with critical input data values and CFD analysis.Then,by means of systematic computations with different input data sets,some correlations and charts are obtained which are analogous to classic correlations based on statistical investigations on existing machines.Such new correlations help size a fan of given characteristics as well as study the feasibility of a given design.

Dynamics of populations with two sexes

A mathematical model is presented in order to describe the dynamics of polygamous populations, bearing in mind single individuals of both sexes and the development of reproductive groups. In this context, the description leads us to consider positive homogeneous dynamical systems, establishing conditions for the stationary state existence and its local stability. A fourth pre-reproductive stage was considered, i.e. males and females spend part of their lives before being in condition to reproduce, as a first step to consider more general models. Finally, we parametrized the proposed model using southern elephant seal data, to analyze the direct applicability to a real population.