This study explores the current situation of inter-caste marriage in Eastern Nepal. It is based on a sample of 30 inter-caste couples collected in Sunsari District. It basically describes the extent and pattern of i...This study explores the current situation of inter-caste marriage in Eastern Nepal. It is based on a sample of 30 inter-caste couples collected in Sunsari District. It basically describes the extent and pattern of inter-caste marriage and responsible factors to be engaged in inter-caste marriage among diverse social groups. Inter-caste marriage is not only a matter of individual relation; it is also a matter of society and social transformation from traditional to modern. Love and affection, age factors, good moral character of the lower caste, modernization, migration, education, mass media, and identity based moments are taken major motivational factors for inter-caste marriage. Inter-caste couples are victimized from various factors of traditional society; they are facing different kinds of problems from their family, relatives, and society. Family problems, social problems, cultural problems, and psychological problems are the common for them.展开更多
To determine the extrusion force of pipe fabricated by continuous casting and extrusion (CASTEX) using an expansion combination die, the metallic expansion combination die was divided into diversion zone, expansion zo...To determine the extrusion force of pipe fabricated by continuous casting and extrusion (CASTEX) using an expansion combination die, the metallic expansion combination die was divided into diversion zone, expansion zone, flow dividing zone, welding chamber, and sizing zone, and the corresponding stress formulae in various zones were established using the slab method. The deformation zones of CASTEX groove were divided into liquid and semisolid zone, solid primary gripping zone, and solid gripping zone, and the formulae of pipe extrusion forces were established. Experiments were carried out on the self-designed CASTEX machine to obtain the aluminum pipe and measure its extrusion force using the expansion combination die. The experimental results of radial extrusion force for aluminum pipe are in good agreement with the calculated ones.展开更多
In honeybee （Apis mellifera） colonies, queens and workers are altemative forms of the adult female honeybee that develop from genetically identical zygotes but that depend on differential nourishment. Queens and wor...In honeybee （Apis mellifera） colonies, queens and workers are altemative forms of the adult female honeybee that develop from genetically identical zygotes but that depend on differential nourishment. Queens and workers display distinct morphologies, anatomies and behavior, better known as caste differentiation. Despite some basic insights, the exact mechanism responsible for this phenomenon, especially at the molecular level, remains unclear although some progress has been achieved. In this study, we examined mRNA levels of the TOR （target of rapamycin） and Dnmt3 （DNA methyltransferase 3） genes, closely related to caste differentiation in honeybees. We also investigated mRNA expression of the S6K （similar to RPS6-p70-protein kinase） gene linked closely to organismal growth and development in queen and worker larvae （1-day and 3-day old）. Last, we investigated the methylation status of these three genes in corresponding castes. We found no difference in mRNA expression for the three genes between 1st instar queen and worker larvae; however, 3rd instar queen larvae had a higher level of TOR mRNA than worker larvae. Methylation levels of all three genes were lower in queen larvae than worker larvae but the differences were not statistically significant. These findings provide basic data for broadening our understanding of caste differentiation in female honeybees.展开更多
The physical model of a ten-strand billet caster tundish was established to study the effects of various flow control devices on the melt flow. Before and after the optimization of the melt flow, the inclusion removal...The physical model of a ten-strand billet caster tundish was established to study the effects of various flow control devices on the melt flow. Before and after the optimization of the melt flow, the inclusion removal in the tundish was evaluated by plant trials. The physical modeling results show that when combined with a baffle, the turbulence inhibitor, instead of the impact pad, can significantly improve the melt flow. A turbulence inhibitor with a longer length of inner cavity and without an extending lip at the top of the sidewall seems to be efficient in the improvement of the melt flow. Various types and designs of baffles all influence the flow characteristics significantly. The "V" type baffles are better than the straight baffles for flow control. The "V" type baffle with four inclined holes at the sidewall away from the stopper rods is better in melt flow control than the one with one inclined hole at each sidewall. The combination of a well-designed turbulence inhibitor and an appropriate baffle shows high efficiency on improving the melt flow and an optimal proposal was presented. Plant trials indicate that, compared with the original tundish configuration in prototype, the inclusions reduce by 42% and the inclusion distribution of individual strands is more similar with the optimal one. The optimal tundish configuration effectively improves the melt flow in the ten-strand billet caster tundish.展开更多
Caste differentiation in social hymenopterans is an intriguing example of phenotypic plasticity. However, the co-ordination among gene regulatory factors to mediate caste differentiation remains inconclusive. In this ...Caste differentiation in social hymenopterans is an intriguing example of phenotypic plasticity. However, the co-ordination among gene regulatory factors to mediate caste differentiation remains inconclusive. In this study, we determined the role of gene regulation and related epigenetic processes in pre-imaginal caste differentiation in the primitively eusocial bumblebee Bombus terrestris. By combining RNA-Seq data from Illumina and Pac Bio and accurately quantifying methylation at whole-genomic base pair resolution, we found that queens, workers, and drones mainly differentiate in gene expression but not in alternative splicing and DNA methylation. Gynes are the most distinct with the lowest global level of whole-genomic methylation and with the largest number of caste-specific transcripts and alternative splicing events. By contrast, workers exhibit few uniquely expressed or alternatively spliced genes. Moreover, several genes involved in hormone and neurotransmitter metabolism are related to caste differentiation, whereas several neuropeptides are linked with sex differentiation. Despite little genome-wide association among differential gene expression, splicing, and differential DNA methylation, the overlapped gene ontology(GO) terms point to nutrition-related activity. Therefore, variations in gene regulation correlate with the behavioral differences among castes and highlight the specialization of toolkit genes in bumblebee gynes at the beginning of the adult stage.展开更多
Thomas Hardy(1840-1928)is a famous British Novelists.His excellent works have a far-reaching significance to the later gen erations.Treating his The Mayor of Casterbridge as a text,this paper is aimed to detect Hardy&...Thomas Hardy(1840-1928)is a famous British Novelists.His excellent works have a far-reaching significance to the later gen erations.Treating his The Mayor of Casterbridge as a text,this paper is aimed to detect Hardy's implied meanings of the symbols in a through textual analysis.This thesis is divided into three parts.The first part is the the symbol of the bridges.The second part deals with the symbol of the mel ody.Part three explores other symbols in The Mayor of Casterbridge.The symbols are all deliberately chosen in this book by the author to transmit his tragic view.Through the symbols of the bridges,the melody,the church,the tractor,the railway…,the author's tragic view is well presented.By the research of each of those three parts,the conclusion of Hardy's functions of the symbols can be drawn.展开更多
Caste differentiation in termites is one of the most conspicuous examples of facultative polyphenism in animals.It is clear that specific cuticular formation occurs in hard exocuticles during caste differentiation.How...Caste differentiation in termites is one of the most conspicuous examples of facultative polyphenism in animals.It is clear that specific cuticular formation occurs in hard exocuticles during caste differentiation.However,the developmental pattern of the soft endocuticle in the differentiation pathways of castes is unknown.To reveal whether the endocuticle is involved in caste differentiation,we compared the exocuticle and endocuticle thickness of individuals in 2 pathways(nymph line and worker line)of caste differentiation in the termite Reticulitermes aculabialis.The endocuticle protein genes were identified by transcriptome analysis and the expression patterns of these genes were confirmed in caste differentiation.We found that the endocuticle structure showed dynamic changes in 2 pathways,and the first difference in endocuticle structure occurred after larvae differentiation bifurcated into workers and nymphs.The thinning of the endocuticle was a significant event from nymphs developing into alates with the thickest exocuticle and thinnest endocuticle.The thickest endocuticle layers were found in the heads of the workers and the ultrastructure of the endocuticle in the heads was more complex than that in the thorax–abdomens.Six endocuticle protein genes were identified and annotated as endocuticle structural glycoproteins SgAbd-2,SgAbd-9,and Abd-5.The expression levels of endocuticle protein genes changed dramatically during caste development and the expression levels in neotenic reproductives(secondary reproductives)were significantly higher than those in alates(primary reproductives).These results reveal the roles of endocuticles in caste differentiation and adaptation to the environment.展开更多
The electromagnetic field and flow analysis model were developed to simulate the electromagnetic field and the flow pattern in a vertical curved continuous slab caster with the in-roll type strand electromagnetic stir...The electromagnetic field and flow analysis model were developed to simulate the electromagnetic field and the flow pattern in a vertical curved continuous slab caster with the in-roll type strand electromagnetic stirring. The transient electromagnetic field distribution and the induced electromagnetic force were numerically described. The effects of stirring current, stirring frequency, and different stirrer configurations on the electromagnetically driven flow field in the strand were investigated and the optimization of the stirring parameters was discussed by performing a relative comparison of numerical results. Results show that the in-roller type strand electromagnetic stirrer （S- EMS） pair generates the fluctuating magnetic fields, penetrating through the cast slab and periodically parallel shift- ing along the slab wide face w!th time evolution. The transient induced electromagnetic forces travels toward the magnetic flux shifting direction, Different stirring parameters （i. e. current and frequency） and stirrer configurations affect the stirring strength and the flow rbcirculation pattern in the strand, which are closely related to metallurgical performances of the stirrers. There is an optimum frequency to obtain the maximum stirring. The present model pro vides a relatively theoretical insight into the in-roll type strand electromagnetic stirring system for best operating.展开更多
The White Tiger is Aravind Adiga＇s first novel just like Son of the Native Soil which is Shadrach Ambanasom＇s first oeuvre. The two novels address two major social concerns （the caste system and tribal loyalty） th...The White Tiger is Aravind Adiga＇s first novel just like Son of the Native Soil which is Shadrach Ambanasom＇s first oeuvre. The two novels address two major social concerns （the caste system and tribal loyalty） that impair national cohesion in India and Cameroon respectively. Briefly speaking, the caste refers to the classification of peoples in India （and other South Asian countries） into in-marrying hereditary social classes of the privileged and the underprivileged while tribal loyalty refers to selfish attachment to a tribe or clan to the detriment of community or national feeling. The two concepts are related in the sense that the word ＂caste＂ derives from the Spanish or Portuguese ＂casta＂ meaning race, lineage, breed or clan. In both cases therefore, the issues of sectionalism, division, discrimination, selfishness, marginalization, and hegemony （amongst others） are at play--issues that impede the notion of nationhood. Read principally from the Marxist perspective of power dynamics and class struggle, the paper argues that Adiga and Ambanasom through skillful manipulation of symbols, time, characters and events, try to imagine the deconstruction of caste and ethnic loyalty in India and Cameroon respectively, which to the two authors, are only historically and socially erected edifices rather than natural order. For the two authors, although global forces may seem to play in favor of a more equitable human society, a necessarily violent revolution might be required to dismantle a blighted body politico-modus operandi that has operated in the people＇s psyche for a long time, as characters and events in the two novels reveal.展开更多
According to the theory of alternating magnetohydrodynamics and magnetic boundary renewal method,mathematical models were proposed for electromagnetic stirring in secondary cooling region( SEMS) of slab caster. The ma...According to the theory of alternating magnetohydrodynamics and magnetic boundary renewal method,mathematical models were proposed for electromagnetic stirring in secondary cooling region( SEMS) of slab caster. The magnetic fields and flow fields of melt were simulated with SEMS. It's shown that the electromagnetic forces with inward and sidelong components produced by travel magnetic field at the wide faces of slab make the melt whirling in horizontal section,and the convection of the melt is strengthened obviously there. In addition,magnetic flux density attenuates from the edge to the center of slab,and the profile of the melt velocity along slab thickness in the center of the horizontal section takes a two-opposite-peak configuration. Ultimately,the stirring intensity and features are determined by the electromagnetic parameters,coil arrangement and stirring types.展开更多
The 1：1 water model of a twin-roll strip caster was set up based on the Froude number and the Reynolds number similarity criteria. A new type metal delivery system was designed for the twin-roll strip caster. The lev...The 1：1 water model of a twin-roll strip caster was set up based on the Froude number and the Reynolds number similarity criteria. A new type metal delivery system was designed for the twin-roll strip caster. The level fluctuation and the fluid flow in the pool of the water model were measured using the level detector and the 3D-LDV （laser Doppler velocimetry） technology. It is shown that a wedged delivery system can produce the desirable level fluctuation and even fluid flow distribution in the pool Numerical simulations for the water model were performed. Comparisons between the numerical and physical simulation results show good agreement near the side dams.展开更多
In the thin slab continuous casting （TSCC） of steel, the issue of optimum fluid flow is very important due to higher casting speeds and has direct influence on the formation of solidified shells and the quality of f...In the thin slab continuous casting （TSCC） of steel, the issue of optimum fluid flow is very important due to higher casting speeds and has direct influence on the formation of solidified shells and the quality of final products. In the current work, a full-scale physical mod- eling of a thin slab easter on the basis of dimensionless Reynolds and Froude similarity criteria was constructed. The flow pattern in the funnel shaped mold with a new tetra-furcated submerged entry nozzle （SEN） was investigated. To determinate optimum operational parameters, some experiments were carried out under various casting conditions. The results show that the tetra-furcated design of the nozzle leads to a special flow pattern in the mold cavity with three-dimensional recirculating flow. It is also shown that the increase of casting speed and gas injection results in surface turbulence. On the other hand, using a higher depth of SEN decreases the vortex in the free surface of the caster. To avoid surface turbulent and related casting problems, it is recommended to use 30-cm and 40-cm SEN depth at the casting speeds of 3.5 and 4.5 m/min, respectively.展开更多
The SMART/ASTC dynamic soft reduction technology of VAI and its application on the 6-strand bloom continuous caster at Pangang, China are presented. The operation results show that soft reduction technology is effecti...The SMART/ASTC dynamic soft reduction technology of VAI and its application on the 6-strand bloom continuous caster at Pangang, China are presented. The operation results show that soft reduction technology is effective to improve the inner quality of continuously cast blooms. At Pangang, both the central porosity and the central segregation ratings are no more than 1.0, the central shrinkage cavity rating is no more than 0.5, and the central segregation index of carbon is no more than 1.05. Rails made from the blooms have excellent quality and are used for high-speed tracks.展开更多
An industrial trial was conducted on a billet casting machine at Atlas Steel, Canada, during which a mould was instrumented with 52 thermocouples. The measured data of ten heats were collected to determine mould wall...An industrial trial was conducted on a billet casting machine at Atlas Steel, Canada, during which a mould was instrumented with 52 thermocouples. The measured data of ten heats were collected to determine mould wall temperature profiles for different steel grades at different casting speeds. Based on these data, heat fluxes were calculated with inverse heat conduction model. Heat fluxes for different operating parameters were compared and analyzed.展开更多
A model experiment investigating entrapment of inclusions and bubbles on the solidified shell was performed using molten steel,and the conditions for inclusion and bubble entrapment and mechanism of entrapment were st...A model experiment investigating entrapment of inclusions and bubbles on the solidified shell was performed using molten steel,and the conditions for inclusion and bubble entrapment and mechanism of entrapment were studied. The results were applied to the flow behavior in the casting mold of a continuous caster.At the solid-liquid interface, entrapment of inclusions is greatly reduced by the existence of a low velocity flow,e.g.,0.05m/s.The above-mentioned interfacial flow velocity dependency of inclusion entrapment is considered to be largely influenced by changes in the thickness of the concentration boundary layer,which depend on the interfacial flow velocity.Specifically,bubbles and inclusions which enter the concentration boundary layer are drawn to the solid-liquid interface by a suction force which is several orders larger than the Saffman's force.In addition to the above-mentioned suction force,the so-called cleaning effect is determined by fluid-dynamic forces such as drag force,etc.which act on particles,and furthermore,by resident time of particles at the solid-liquid interface,which depends on the solidification rate.In a FC mold with a 2-stage electromagnetic brake,flotation of bubbles entrained in the jet flow from the nozzle is accelerated with the large DC magnetic field.This is attributed to the braking effect of the DC field on the nozzle jet and the upward flow by the buoyancy of the bubbles.As a result,the interfacial flow velocity can be normalized by increasing the strength of the magnetic field,and entrapment of large bubbles and inclusions can be reduced.展开更多
Thin slab casting is used widely in the world. The control of molten steel flow and solidification in the mold is difficult due to the high casting speed and complicated configuration of the mold. Numerical simulation...Thin slab casting is used widely in the world. The control of molten steel flow and solidification in the mold is difficult due to the high casting speed and complicated configuration of the mold. Numerical simulation was carried out to study the fluid flow and heat transfer in the funnel shaped mold. The influence of nozzle design, casting speed and nozzle submersion depth on the flow and temperature fields in the mold was investigated, and guidance for selecting configurations of submerged nozzle was obtained.展开更多
In order to reduce the rate of breakout of slab caster, improve the operating rate and ensure the stability of the caster, measures including the tundish casting auto-start, the mold level automatic control system opt...In order to reduce the rate of breakout of slab caster, improve the operating rate and ensure the stability of the caster, measures including the tundish casting auto-start, the mold level automatic control system optimization, the SEN one-button automatic quick-change technology, the mold breakout forecast system optimization, the mold oscillation parameters optimization, the mold taper measurement optimization and the mold powder management have been adopted by a steel plant of WISCO. As a result, the breakout rate of slab caster was significantly reduced to be zero level in the first 3 years, which is a new record for all steelmaking plant in China.展开更多
The microstructures of austenitic stainless steel strip were studied using color metallographic method and electron probe micro analysis （EPMA）. In the cast strips, there are three kinds of solidification structures...The microstructures of austenitic stainless steel strip were studied using color metallographic method and electron probe micro analysis （EPMA）. In the cast strips, there are three kinds of solidification structures： fine cel- lular dendrite in the surface layer, equiaxed grains in the center and fine dendrite between them. The solidification mode in the surface layer is the primary austenite AF mode because of extremely high cooling rate, with the retained ferrite located around the primary cellular austenite. In the fine dendrite zone, the solidification mode of molten stainless steel changes to FA mode and the residual ferrite with fish-bone morphology is located at the core of the dendrite. The retained ferrite of equiaxed grains in the center is located in the center of broken primary ferrite dendrite with vermicular morphology.展开更多
By optical inspection of macro-etched metallography and electron back-scattered diffraction （EBSD） mapping, this paper analyzed the microstructure of austenitic stainless steel strips produced with an equal-diameter...By optical inspection of macro-etched metallography and electron back-scattered diffraction （EBSD） mapping, this paper analyzed the microstructure of austenitic stainless steel strips produced with an equal-diameter twin-roll strip caster. The results indicate that the microstructure of the strips includes two columnar zones with highly compact dendrites and one equiaxed zone. The characteristics, such as grain size and growing direction of columnar grains and equiaxed grains, were investigated. An additional transitional area with many finer grains between the columnar zone and the equiaxed zone was found. As shown in EBSD analysis, small angle boundaries exist both in the columnar zone and the equiaxed zone, although they are especially more in the transitional area. Additionally, some 〈111〉 twin boundaries were found in the microstructure of the strips.展开更多
文摘This study explores the current situation of inter-caste marriage in Eastern Nepal. It is based on a sample of 30 inter-caste couples collected in Sunsari District. It basically describes the extent and pattern of inter-caste marriage and responsible factors to be engaged in inter-caste marriage among diverse social groups. Inter-caste marriage is not only a matter of individual relation; it is also a matter of society and social transformation from traditional to modern. Love and affection, age factors, good moral character of the lower caste, modernization, migration, education, mass media, and identity based moments are taken major motivational factors for inter-caste marriage. Inter-caste couples are victimized from various factors of traditional society; they are facing different kinds of problems from their family, relatives, and society. Family problems, social problems, cultural problems, and psychological problems are the common for them.
基金Projects(51334006,50274020)supported by the National Natural Science Foundation of China
文摘To determine the extrusion force of pipe fabricated by continuous casting and extrusion (CASTEX) using an expansion combination die, the metallic expansion combination die was divided into diversion zone, expansion zone, flow dividing zone, welding chamber, and sizing zone, and the corresponding stress formulae in various zones were established using the slab method. The deformation zones of CASTEX groove were divided into liquid and semisolid zone, solid primary gripping zone, and solid gripping zone, and the formulae of pipe extrusion forces were established. Experiments were carried out on the self-designed CASTEX machine to obtain the aluminum pipe and measure its extrusion force using the expansion combination die. The experimental results of radial extrusion force for aluminum pipe are in good agreement with the calculated ones.
基金supported by the Yunnan Government(2009CI119)Modern Agricultural Industry Technology System(Honeybee)(CARS-45-kxj14)
文摘In honeybee （Apis mellifera） colonies, queens and workers are altemative forms of the adult female honeybee that develop from genetically identical zygotes but that depend on differential nourishment. Queens and workers display distinct morphologies, anatomies and behavior, better known as caste differentiation. Despite some basic insights, the exact mechanism responsible for this phenomenon, especially at the molecular level, remains unclear although some progress has been achieved. In this study, we examined mRNA levels of the TOR （target of rapamycin） and Dnmt3 （DNA methyltransferase 3） genes, closely related to caste differentiation in honeybees. We also investigated mRNA expression of the S6K （similar to RPS6-p70-protein kinase） gene linked closely to organismal growth and development in queen and worker larvae （1-day and 3-day old）. Last, we investigated the methylation status of these three genes in corresponding castes. We found no difference in mRNA expression for the three genes between 1st instar queen and worker larvae; however, 3rd instar queen larvae had a higher level of TOR mRNA than worker larvae. Methylation levels of all three genes were lower in queen larvae than worker larvae but the differences were not statistically significant. These findings provide basic data for broadening our understanding of caste differentiation in female honeybees.
基金supported by the National Natural Science Foundation of China(No.51474059,No.51204042)the Program for Liaoning Excellent Talents in University(No.LJQ2014031)the Fundamental Research Funds for the Central Universities(No.N140205003)
文摘The physical model of a ten-strand billet caster tundish was established to study the effects of various flow control devices on the melt flow. Before and after the optimization of the melt flow, the inclusion removal in the tundish was evaluated by plant trials. The physical modeling results show that when combined with a baffle, the turbulence inhibitor, instead of the impact pad, can significantly improve the melt flow. A turbulence inhibitor with a longer length of inner cavity and without an extending lip at the top of the sidewall seems to be efficient in the improvement of the melt flow. Various types and designs of baffles all influence the flow characteristics significantly. The "V" type baffles are better than the straight baffles for flow control. The "V" type baffle with four inclined holes at the sidewall away from the stopper rods is better in melt flow control than the one with one inclined hole at each sidewall. The combination of a well-designed turbulence inhibitor and an appropriate baffle shows high efficiency on improving the melt flow and an optimal proposal was presented. Plant trials indicate that, compared with the original tundish configuration in prototype, the inclusions reduce by 42% and the inclusion distribution of individual strands is more similar with the optimal one. The optimal tundish configuration effectively improves the melt flow in the ten-strand billet caster tundish.
基金supported by the National Natural Science Foundation of China (31930012, 31920103004, and 31772531)the Science and Technology Service Network Initiative of the Chinese Academy of Sciences (KFJ-STS-ZDTP-073)+1 种基金the Joint NSFC-ISF Research Grant (3201101042)the State Key Laboratory of Integrated Management of Pest Insects and Rodents (Y852981203)。
文摘Caste differentiation in social hymenopterans is an intriguing example of phenotypic plasticity. However, the co-ordination among gene regulatory factors to mediate caste differentiation remains inconclusive. In this study, we determined the role of gene regulation and related epigenetic processes in pre-imaginal caste differentiation in the primitively eusocial bumblebee Bombus terrestris. By combining RNA-Seq data from Illumina and Pac Bio and accurately quantifying methylation at whole-genomic base pair resolution, we found that queens, workers, and drones mainly differentiate in gene expression but not in alternative splicing and DNA methylation. Gynes are the most distinct with the lowest global level of whole-genomic methylation and with the largest number of caste-specific transcripts and alternative splicing events. By contrast, workers exhibit few uniquely expressed or alternatively spliced genes. Moreover, several genes involved in hormone and neurotransmitter metabolism are related to caste differentiation, whereas several neuropeptides are linked with sex differentiation. Despite little genome-wide association among differential gene expression, splicing, and differential DNA methylation, the overlapped gene ontology(GO) terms point to nutrition-related activity. Therefore, variations in gene regulation correlate with the behavioral differences among castes and highlight the specialization of toolkit genes in bumblebee gynes at the beginning of the adult stage.
文摘Thomas Hardy(1840-1928)is a famous British Novelists.His excellent works have a far-reaching significance to the later gen erations.Treating his The Mayor of Casterbridge as a text,this paper is aimed to detect Hardy's implied meanings of the symbols in a through textual analysis.This thesis is divided into three parts.The first part is the the symbol of the bridges.The second part deals with the symbol of the mel ody.Part three explores other symbols in The Mayor of Casterbridge.The symbols are all deliberately chosen in this book by the author to transmit his tragic view.Through the symbols of the bridges,the melody,the church,the tractor,the railway…,the author's tragic view is well presented.By the research of each of those three parts,the conclusion of Hardy's functions of the symbols can be drawn.
基金supported by the National Natural Science Foundation of China[31870389].
文摘Caste differentiation in termites is one of the most conspicuous examples of facultative polyphenism in animals.It is clear that specific cuticular formation occurs in hard exocuticles during caste differentiation.However,the developmental pattern of the soft endocuticle in the differentiation pathways of castes is unknown.To reveal whether the endocuticle is involved in caste differentiation,we compared the exocuticle and endocuticle thickness of individuals in 2 pathways(nymph line and worker line)of caste differentiation in the termite Reticulitermes aculabialis.The endocuticle protein genes were identified by transcriptome analysis and the expression patterns of these genes were confirmed in caste differentiation.We found that the endocuticle structure showed dynamic changes in 2 pathways,and the first difference in endocuticle structure occurred after larvae differentiation bifurcated into workers and nymphs.The thinning of the endocuticle was a significant event from nymphs developing into alates with the thickest exocuticle and thinnest endocuticle.The thickest endocuticle layers were found in the heads of the workers and the ultrastructure of the endocuticle in the heads was more complex than that in the thorax–abdomens.Six endocuticle protein genes were identified and annotated as endocuticle structural glycoproteins SgAbd-2,SgAbd-9,and Abd-5.The expression levels of endocuticle protein genes changed dramatically during caste development and the expression levels in neotenic reproductives(secondary reproductives)were significantly higher than those in alates(primary reproductives).These results reveal the roles of endocuticles in caste differentiation and adaptation to the environment.
文摘The electromagnetic field and flow analysis model were developed to simulate the electromagnetic field and the flow pattern in a vertical curved continuous slab caster with the in-roll type strand electromagnetic stirring. The transient electromagnetic field distribution and the induced electromagnetic force were numerically described. The effects of stirring current, stirring frequency, and different stirrer configurations on the electromagnetically driven flow field in the strand were investigated and the optimization of the stirring parameters was discussed by performing a relative comparison of numerical results. Results show that the in-roller type strand electromagnetic stirrer （S- EMS） pair generates the fluctuating magnetic fields, penetrating through the cast slab and periodically parallel shift- ing along the slab wide face w!th time evolution. The transient induced electromagnetic forces travels toward the magnetic flux shifting direction, Different stirring parameters （i. e. current and frequency） and stirrer configurations affect the stirring strength and the flow rbcirculation pattern in the strand, which are closely related to metallurgical performances of the stirrers. There is an optimum frequency to obtain the maximum stirring. The present model pro vides a relatively theoretical insight into the in-roll type strand electromagnetic stirring system for best operating.
文摘The White Tiger is Aravind Adiga＇s first novel just like Son of the Native Soil which is Shadrach Ambanasom＇s first oeuvre. The two novels address two major social concerns （the caste system and tribal loyalty） that impair national cohesion in India and Cameroon respectively. Briefly speaking, the caste refers to the classification of peoples in India （and other South Asian countries） into in-marrying hereditary social classes of the privileged and the underprivileged while tribal loyalty refers to selfish attachment to a tribe or clan to the detriment of community or national feeling. The two concepts are related in the sense that the word ＂caste＂ derives from the Spanish or Portuguese ＂casta＂ meaning race, lineage, breed or clan. In both cases therefore, the issues of sectionalism, division, discrimination, selfishness, marginalization, and hegemony （amongst others） are at play--issues that impede the notion of nationhood. Read principally from the Marxist perspective of power dynamics and class struggle, the paper argues that Adiga and Ambanasom through skillful manipulation of symbols, time, characters and events, try to imagine the deconstruction of caste and ethnic loyalty in India and Cameroon respectively, which to the two authors, are only historically and socially erected edifices rather than natural order. For the two authors, although global forces may seem to play in favor of a more equitable human society, a necessarily violent revolution might be required to dismantle a blighted body politico-modus operandi that has operated in the people＇s psyche for a long time, as characters and events in the two novels reveal.
基金Item Sponsored by National Key Fundamental Research Development Project of China(G1998061510)National High Technology Research and Development Project of China(2001AA337040)
文摘According to the theory of alternating magnetohydrodynamics and magnetic boundary renewal method,mathematical models were proposed for electromagnetic stirring in secondary cooling region( SEMS) of slab caster. The magnetic fields and flow fields of melt were simulated with SEMS. It's shown that the electromagnetic forces with inward and sidelong components produced by travel magnetic field at the wide faces of slab make the melt whirling in horizontal section,and the convection of the melt is strengthened obviously there. In addition,magnetic flux density attenuates from the edge to the center of slab,and the profile of the melt velocity along slab thickness in the center of the horizontal section takes a two-opposite-peak configuration. Ultimately,the stirring intensity and features are determined by the electromagnetic parameters,coil arrangement and stirring types.
基金This work was financially supported by the National Natural Science Foundation of Inner Mongolia of China (No.200408020715).
文摘The 1：1 water model of a twin-roll strip caster was set up based on the Froude number and the Reynolds number similarity criteria. A new type metal delivery system was designed for the twin-roll strip caster. The level fluctuation and the fluid flow in the pool of the water model were measured using the level detector and the 3D-LDV （laser Doppler velocimetry） technology. It is shown that a wedged delivery system can produce the desirable level fluctuation and even fluid flow distribution in the pool Numerical simulations for the water model were performed. Comparisons between the numerical and physical simulation results show good agreement near the side dams.
文摘In the thin slab continuous casting （TSCC） of steel, the issue of optimum fluid flow is very important due to higher casting speeds and has direct influence on the formation of solidified shells and the quality of final products. In the current work, a full-scale physical mod- eling of a thin slab easter on the basis of dimensionless Reynolds and Froude similarity criteria was constructed. The flow pattern in the funnel shaped mold with a new tetra-furcated submerged entry nozzle （SEN） was investigated. To determinate optimum operational parameters, some experiments were carried out under various casting conditions. The results show that the tetra-furcated design of the nozzle leads to a special flow pattern in the mold cavity with three-dimensional recirculating flow. It is also shown that the increase of casting speed and gas injection results in surface turbulence. On the other hand, using a higher depth of SEN decreases the vortex in the free surface of the caster. To avoid surface turbulent and related casting problems, it is recommended to use 30-cm and 40-cm SEN depth at the casting speeds of 3.5 and 4.5 m/min, respectively.
文摘The SMART/ASTC dynamic soft reduction technology of VAI and its application on the 6-strand bloom continuous caster at Pangang, China are presented. The operation results show that soft reduction technology is effective to improve the inner quality of continuously cast blooms. At Pangang, both the central porosity and the central segregation ratings are no more than 1.0, the central shrinkage cavity rating is no more than 0.5, and the central segregation index of carbon is no more than 1.05. Rails made from the blooms have excellent quality and are used for high-speed tracks.
基金Item Sponsored by National Natural Science Foundation of China(59995440)
文摘An industrial trial was conducted on a billet casting machine at Atlas Steel, Canada, during which a mould was instrumented with 52 thermocouples. The measured data of ten heats were collected to determine mould wall temperature profiles for different steel grades at different casting speeds. Based on these data, heat fluxes were calculated with inverse heat conduction model. Heat fluxes for different operating parameters were compared and analyzed.
文摘A model experiment investigating entrapment of inclusions and bubbles on the solidified shell was performed using molten steel,and the conditions for inclusion and bubble entrapment and mechanism of entrapment were studied. The results were applied to the flow behavior in the casting mold of a continuous caster.At the solid-liquid interface, entrapment of inclusions is greatly reduced by the existence of a low velocity flow,e.g.,0.05m/s.The above-mentioned interfacial flow velocity dependency of inclusion entrapment is considered to be largely influenced by changes in the thickness of the concentration boundary layer,which depend on the interfacial flow velocity.Specifically,bubbles and inclusions which enter the concentration boundary layer are drawn to the solid-liquid interface by a suction force which is several orders larger than the Saffman's force.In addition to the above-mentioned suction force,the so-called cleaning effect is determined by fluid-dynamic forces such as drag force,etc.which act on particles,and furthermore,by resident time of particles at the solid-liquid interface,which depends on the solidification rate.In a FC mold with a 2-stage electromagnetic brake,flotation of bubbles entrained in the jet flow from the nozzle is accelerated with the large DC magnetic field.This is attributed to the braking effect of the DC field on the nozzle jet and the upward flow by the buoyancy of the bubbles.As a result,the interfacial flow velocity can be normalized by increasing the strength of the magnetic field,and entrapment of large bubbles and inclusions can be reduced.
文摘Thin slab casting is used widely in the world. The control of molten steel flow and solidification in the mold is difficult due to the high casting speed and complicated configuration of the mold. Numerical simulation was carried out to study the fluid flow and heat transfer in the funnel shaped mold. The influence of nozzle design, casting speed and nozzle submersion depth on the flow and temperature fields in the mold was investigated, and guidance for selecting configurations of submerged nozzle was obtained.
文摘In order to reduce the rate of breakout of slab caster, improve the operating rate and ensure the stability of the caster, measures including the tundish casting auto-start, the mold level automatic control system optimization, the SEN one-button automatic quick-change technology, the mold breakout forecast system optimization, the mold oscillation parameters optimization, the mold taper measurement optimization and the mold powder management have been adopted by a steel plant of WISCO. As a result, the breakout rate of slab caster was significantly reduced to be zero level in the first 3 years, which is a new record for all steelmaking plant in China.
基金Sponsored by National High Technology and Development Program of China (50434040)
文摘The microstructures of austenitic stainless steel strip were studied using color metallographic method and electron probe micro analysis （EPMA）. In the cast strips, there are three kinds of solidification structures： fine cel- lular dendrite in the surface layer, equiaxed grains in the center and fine dendrite between them. The solidification mode in the surface layer is the primary austenite AF mode because of extremely high cooling rate, with the retained ferrite located around the primary cellular austenite. In the fine dendrite zone, the solidification mode of molten stainless steel changes to FA mode and the residual ferrite with fish-bone morphology is located at the core of the dendrite. The retained ferrite of equiaxed grains in the center is located in the center of broken primary ferrite dendrite with vermicular morphology.
基金supported by the National Natural Science Foundation of China (No. 50434040)
文摘By optical inspection of macro-etched metallography and electron back-scattered diffraction （EBSD） mapping, this paper analyzed the microstructure of austenitic stainless steel strips produced with an equal-diameter twin-roll strip caster. The results indicate that the microstructure of the strips includes two columnar zones with highly compact dendrites and one equiaxed zone. The characteristics, such as grain size and growing direction of columnar grains and equiaxed grains, were investigated. An additional transitional area with many finer grains between the columnar zone and the equiaxed zone was found. As shown in EBSD analysis, small angle boundaries exist both in the columnar zone and the equiaxed zone, although they are especially more in the transitional area. Additionally, some 〈111〉 twin boundaries were found in the microstructure of the strips.
