Apoptosis manifests in two major execution programs downstream of the death signal: the caspase pathway and organelle dysfunction. An important antiapoptosis factor, Bcl-2 protein, contributes in caspase pathway of ap...Apoptosis manifests in two major execution programs downstream of the death signal: the caspase pathway and organelle dysfunction. An important antiapoptosis factor, Bcl-2 protein, contributes in caspase pathway of apoptosis. Calcium, an important intracellular signal element in cells, is also observed to have changes during apoptosis, which maybe affected by Bcl-2 protein. We have previously reported that in Harringtonine (HT) induced apoptosis of HL-60 cells, there’s a change of intracellular calcium distribution, moving from cytoplast especially Golgi’s apparatus to nucleus and accumulating there with the highest concentration. We report here that caspase-3 becomes activated in HT-induced apoptosis of HL-60 cells, which can be inhibited by overexpression of Bcl-2 protein. No sign of apoptosis or intracellular calcium movement from Golgi’s apparatus to nucleus in HL-60 cells overexpressing Bcl-2 or treated with Ac-DEVD-CHO, a specific inhibitor of caspase-3. The results indicate that activated caspase-3 can promote the movement of intracellular calcium from Golgi’s apparatus to nucleus, and the process is inhibited by Ac-DEVD-CHO (inhibitor of caspase-3), and that Bcl-2 can inhibit the movement and accumulation of intracellular calcium in nucleus through its inhibition on caspase3. Calcium relocalization in apoptosis seems to be irreversible, which is different from the intracellular calcium changes caused by growth factor.展开更多
bmim]Cl/FeCl3 ionic liquids (where bmim = 1-butyl-3-methylimidazolium) were characterized by XPS (X-ray photoelectron spectroscopy), FT-IR (Fourier transform infrared spectroscopy), Raman and NMR (nuclear magnetic r...bmim]Cl/FeCl3 ionic liquids (where bmim = 1-butyl-3-methylimidazolium) were characterized by XPS (X-ray photoelectron spectroscopy), FT-IR (Fourier transform infrared spectroscopy), Raman and NMR (nuclear magnetic resonance) spectra. The results show that Fe2Cl7 and FeCl4 ions are the principal anions in acidic ionic liquids, - - whose concentrations change with the content of FeCl3 and an equilibrium exists between them. An isosbestic point existing in FT-IR spectra indicates that an interaction involving at least two species occurs and their concentrations vary with acidity. Chemical shifts of the hydrogen located in the cations of ionic liquids are sensitive to the composition of ionic liquids. The change in chemical shifts may be explained in terms of anion-cation interactions. The chemical shifts of 2-H are affected by metal halides, which shift downfield and the 2-H is more deshielded with the increase in metal halides.展开更多
The ages of organic matter of some dark-colored horizons and calcareous concretions in some Vertisols from tropical, subtropical and warm-temperate zones of China were studied using radiocarb on dating method. The rel...The ages of organic matter of some dark-colored horizons and calcareous concretions in some Vertisols from tropical, subtropical and warm-temperate zones of China were studied using radiocarb on dating method. The relationship between soil age and genesis of Vertisols was also expounded based on the study of their genetic charactens-tics and micromorphological features. The results show that although Vertisols have developed for a relatively long time, their weathering and soil forming process are weak and young with little horizonation. This is closely related to their special geochemical soil forming environment. Low-lying terrain, heavy texture, clay minerals dominated by montmorillonites and alternative drying- wetting climate give rise to the vertic features expressed in intense swelling-shrinking and cracking-closing in soils. As a result, the soil development and soil leaching process are resisted, and the climatic effect on the horizonation is impeded. Moreover, pedoturbation eliminates the horizonation in the upper part of soil profile, and postpones their evolution into zonal soils. So Vertisols show certain pedogenic inertia and stay at relatively young developmental stage. Therefore, Vertisols are intrazonal soils dominated by local soil forming factors such as the relief and parent materials.展开更多
A rapid and sensitive method for analyzing trace b-blockers in complex biological samples,which involved magnetic solid-phase extraction(MSPE)coupled with Fourier transform ion cyclotron resonance mass spectrometry(FT...A rapid and sensitive method for analyzing trace b-blockers in complex biological samples,which involved magnetic solid-phase extraction(MSPE)coupled with Fourier transform ion cyclotron resonance mass spectrometry(FTICR-MS),was developed.Novel nanosilver-functionalized magnetic nanoparticles with an interlayer of poly(3,4-dihydroxyphenylalanine)(polyDOPA@Ag-MNPs)were synthesized and used as MSPE adsorbents to extract trace b-blockers from biological samples.After extraction,the analytes loaded on the polyDOPA@Ag-MNPs were desorbed using an organic solvent and analyzed by FTICR-MS.The method was rapid and sensitive,with a total detection procedure of less than 10 min as well as limits of detection and quantification in the ranges of 3.5-6.8 pg/mL and 11.7-22.8 pg/mL,respectively.The accuracy of the method was also desirable,with recoveries ranging from 80.9%to 91.0%following the detection of analytes in human blood samples.All the experimental results demonstrated that the developed MSPE-FTICR-MS method was suitable for the rapid and sensitive analysis of trace b-blockers in complex biological samples.展开更多
Incomplete separation and recycling of nanoparticles are causing undesirable nanopollution and thus raising great concerns with regard to nanosafety.Since microorganisms are important regulator of physiological proces...Incomplete separation and recycling of nanoparticles are causing undesirable nanopollution and thus raising great concerns with regard to nanosafety.Since microorganisms are important regulator of physiological processes in many organisms,the interaction between nanopollution and microbial metabolomics and the resultant impact on the host’s health are important but unclear.To investigate how typical nanopollution perturbs microbial growth and metabolism,Escherichia coli(E.coli)in vitro was treated with six water-dispersible nanomaterials(nanoplastic,nanosilver,nano-TiO 2,nano-ZnO,semiconductor quantum dots(QDs),carbon dots(CDs))at human-/environment-relevant concentration levels.The nanomaterials exhibited type-specific toxic effects on E.coli growth.Global metabolite profiling was used to characterize metabolic disruption patterns in the model microorganism exposed to different nanopollutants.The percentage of significant metabolites(p<0.05,VIP>1)accounted for 6%–38%of the total 293 identified metabolites in each of the nanomaterial-contaminated bacterial groups.Metabolic results also exhibited significant differences between different nanopollutants and dose levels,revealing type-specific and untypical concentration-dependent metabolic responses.Key metabolites responsive to nanopollution exposures were mainly involved in amino acid and purine metabolisms,where 5,4,and 7 significant metabolic features were included in arginine and proline metabolism,phenylalanine metabolism,and purine metabolism,respectively.In conclusion,this study horizontally compared and demonstrated how typical nanopollution perturbs microbial growth and metabolomics in a type-specific manner,which broadens our understanding of the ecotoxicity of nanopollutants on microorganisms.展开更多
An atomic model of compound precipitation in alloys, which couples cellular automaton growth/dissociation of precipitates and randomwalk diffusion, has been developed and programmed for 2 dimensional computer simulati...An atomic model of compound precipitation in alloys, which couples cellular automaton growth/dissociation of precipitates and randomwalk diffusion, has been developed and programmed for 2 dimensional computer simulation. With boundary condition parameters and diffusion parameters variable, a series of simulation experiments were carried out for a qualitative study of nitride precipitation behavior in nitridation of alloy steels. Effects of nitrogen potential and alloy composition on kinetics and microstructure of the precipitation were addressed, and the so called "iso-activity aging" phenomenon was examined.展开更多
Finger-jointed lumber production has now become the most extensively used method for spliced lumbers jointing together endwise.The properties of finger-jointed lumber are affected by many different factors such as the...Finger-jointed lumber production has now become the most extensively used method for spliced lumbers jointing together endwise.The properties of finger-jointed lumber are affected by many different factors such as the end-pressure.The main mechanical properties to be tested for struc-tural use finger-jointed lumber include the modulus of elasticity in static bending and the bending strength.The most commonly used method for testing these properties at present is the experi-mental test.In this study,we used finite element method to investigate the end-pressure range,the modulus of elasticity in static bending and the bending strength for Pinus sylvistriv var.finger-jointed lumber under three different fitness ratios(0 mm,0.1 mm,0.3 mm).With finite element analysis(FEA)modelling results compared with the experimental test results,it is possible to find the relationship between these two kinds of results and use the FEA to predict the properties of finger-jointed lumber.The FEA applied in the end pressure tests showed a narrower range com-pared with the modelling results.It indicated that the FEA could be used in the prediction of the end pressure for finger-jointed lumber.The modelling results for modulus of elasticity(MOE)test and bending strength(MOR)test showed about 20%discrepancies compared with the experimen-tal results.Moreover,the MOE modelling results showed the same trend as experimental results under three different fitness levels while the MOR modelling results showed the different trend.It can be concluded that the FEA is a feasible way in analysing the properties of finger-jointed lumber if the errors could be eliminated properly.Some modifications should be made in order to realize the prediction of the properties of finger-jointed lumber more accurately.展开更多
The microcirculation blood volume in the hypothalamus-pituitary-ovary axis in adult female Wistar rats during each phase of the estrous cycle were measured by the techaique of radioactives biomicrosphere. The results ...The microcirculation blood volume in the hypothalamus-pituitary-ovary axis in adult female Wistar rats during each phase of the estrous cycle were measured by the techaique of radioactives biomicrosphere. The results arc as follows (unit:展开更多
In this paper, a novel prioritized Optical Burst Switching (OCBS) scheme for the next-generation optical Internet is proposed and investigated systematically through theoretical analysis and network simulation. Analys...In this paper, a novel prioritized Optical Burst Switching (OCBS) scheme for the next-generation optical Internet is proposed and investigated systematically through theoretical analysis and network simulation. Analysis shows that the proposed scheme is able to achieve modestly fine traffic differentiation in a simple and easy way. The simulation results agree with the theoretical analysis and they are useful in traffic engineering of optical burst switching networks.展开更多
Recently, attention has been focused on spatial query language which is used to query spatial databases. A design of spatial query language has been presented in this paper by extending the standard relational databas...Recently, attention has been focused on spatial query language which is used to query spatial databases. A design of spatial query language has been presented in this paper by extending the standard relational database query language SQL. It recognizes the significantly different requirements of spatial data handling and overcomes the inherent problems of the application of conventional database query languages. This design is based on an extended spatial data model, including the spatial data types and the spatial operators on them. The processing and optimization of spatial queries have also been discussed in this design. In the end, an implementation of this design is given in a spatial query subsystem.展开更多
＂I buy most of my cosmetics abroad usually buy a lot each time when I travel abroad. Sometimes, I askfriends to buy some for me.＂ So says Ms Wang, a 35-year-old Beijing resident. ＂I recently bought some L＇Oreal P...＂I buy most of my cosmetics abroad usually buy a lot each time when I travel abroad. Sometimes, I askfriends to buy some for me.＂ So says Ms Wang, a 35-year-old Beijing resident. ＂I recently bought some L＇Oreal Paris makeup and two bottles of Lancome products - one is a hydrating product and another is a whitening product - at tax-free stores during my trip to Phuket in Thailand during the Spring Festival holidays. The L＇Oreal Paris makeup was very cheap, and I saved almost all the 30% consumption tax.＂展开更多
China has dramatically enlarged the China （Shanghai） Pilot Free Trade Zone, to include the city＇scommercial and financial centre Lujiazui, as well as Jinqiao and Zhangjiang districts. The China （Guangdong） Pilot...China has dramatically enlarged the China （Shanghai） Pilot Free Trade Zone, to include the city＇scommercial and financial centre Lujiazui, as well as Jinqiao and Zhangjiang districts. The China （Guangdong） Pilot Free Trade Zone, which covers Nansha Hengqin, and Qianhai and Shekou of Shenzhen - a pioneering city in China＇s reform and opening-up, was formally established on April 27.展开更多
The problem of long transactions is a significant problem in spatial database. The checkout mechanism and multi version mechanism are two kind methods of solving the problem of long transactions. In this paper, we pre...The problem of long transactions is a significant problem in spatial database. The checkout mechanism and multi version mechanism are two kind methods of solving the problem of long transactions. In this paper, we present a Shallow Version Management mechanism to realize multi version mechanism in spatial database. And we introduced a increment storage and dynamic version views building method to improve efficiency of storing and consulting. We also illuminate how to resolve the problem of long transaction concurrency control in spatial database by using multi version mechanism. At the end of this paper, we introduce some required means to version management in spatial database, like converge, compress and delete.展开更多
Let π : Mn→Pn be an n-dimensional small cover over Pn and λ : F(Pn)→Z2n be its characteristic function. The author uses the symbol c(λ) to denote the cardinal number of the image Im(λ). If c(λ) = n + 1 or n + 2...Let π : Mn→Pn be an n-dimensional small cover over Pn and λ : F(Pn)→Z2n be its characteristic function. The author uses the symbol c(λ) to denote the cardinal number of the image Im(λ). If c(λ) = n + 1 or n + 2, then a necessary and sufficient condition on the existence of spin structure on Mnis given. As a byproduct, under some special conditions, the author uses the second Stiefel-Whitney class to detect when Pn is n-colorable or(n + 1)-colorable.展开更多
基金the National Natural Science Foundation of China(Grant No. 39730160).
文摘Apoptosis manifests in two major execution programs downstream of the death signal: the caspase pathway and organelle dysfunction. An important antiapoptosis factor, Bcl-2 protein, contributes in caspase pathway of apoptosis. Calcium, an important intracellular signal element in cells, is also observed to have changes during apoptosis, which maybe affected by Bcl-2 protein. We have previously reported that in Harringtonine (HT) induced apoptosis of HL-60 cells, there’s a change of intracellular calcium distribution, moving from cytoplast especially Golgi’s apparatus to nucleus and accumulating there with the highest concentration. We report here that caspase-3 becomes activated in HT-induced apoptosis of HL-60 cells, which can be inhibited by overexpression of Bcl-2 protein. No sign of apoptosis or intracellular calcium movement from Golgi’s apparatus to nucleus in HL-60 cells overexpressing Bcl-2 or treated with Ac-DEVD-CHO, a specific inhibitor of caspase-3. The results indicate that activated caspase-3 can promote the movement of intracellular calcium from Golgi’s apparatus to nucleus, and the process is inhibited by Ac-DEVD-CHO (inhibitor of caspase-3), and that Bcl-2 can inhibit the movement and accumulation of intracellular calcium in nucleus through its inhibition on caspase3. Calcium relocalization in apoptosis seems to be irreversible, which is different from the intracellular calcium changes caused by growth factor.
文摘bmim]Cl/FeCl3 ionic liquids (where bmim = 1-butyl-3-methylimidazolium) were characterized by XPS (X-ray photoelectron spectroscopy), FT-IR (Fourier transform infrared spectroscopy), Raman and NMR (nuclear magnetic resonance) spectra. The results show that Fe2Cl7 and FeCl4 ions are the principal anions in acidic ionic liquids, - - whose concentrations change with the content of FeCl3 and an equilibrium exists between them. An isosbestic point existing in FT-IR spectra indicates that an interaction involving at least two species occurs and their concentrations vary with acidity. Chemical shifts of the hydrogen located in the cations of ionic liquids are sensitive to the composition of ionic liquids. The change in chemical shifts may be explained in terms of anion-cation interactions. The chemical shifts of 2-H are affected by metal halides, which shift downfield and the 2-H is more deshielded with the increase in metal halides.
文摘The ages of organic matter of some dark-colored horizons and calcareous concretions in some Vertisols from tropical, subtropical and warm-temperate zones of China were studied using radiocarb on dating method. The relationship between soil age and genesis of Vertisols was also expounded based on the study of their genetic charactens-tics and micromorphological features. The results show that although Vertisols have developed for a relatively long time, their weathering and soil forming process are weak and young with little horizonation. This is closely related to their special geochemical soil forming environment. Low-lying terrain, heavy texture, clay minerals dominated by montmorillonites and alternative drying- wetting climate give rise to the vertic features expressed in intense swelling-shrinking and cracking-closing in soils. As a result, the soil development and soil leaching process are resisted, and the climatic effect on the horizonation is impeded. Moreover, pedoturbation eliminates the horizonation in the upper part of soil profile, and postpones their evolution into zonal soils. So Vertisols show certain pedogenic inertia and stay at relatively young developmental stage. Therefore, Vertisols are intrazonal soils dominated by local soil forming factors such as the relief and parent materials.
基金supported by the National Natural Science Foundation of China(Grant Nos.:21976168,22127810,and 22004113)Key Research and Development Program of Guangdong Province(Grant No.:2020B1111350002)+1 种基金Guangdong Basic and Applied Basic Research Foundation(Grant No.:2019A1515110420)GDAS0 Project of Science and Technology Development(Grant No.:2021GDASYL-20210103034).
文摘A rapid and sensitive method for analyzing trace b-blockers in complex biological samples,which involved magnetic solid-phase extraction(MSPE)coupled with Fourier transform ion cyclotron resonance mass spectrometry(FTICR-MS),was developed.Novel nanosilver-functionalized magnetic nanoparticles with an interlayer of poly(3,4-dihydroxyphenylalanine)(polyDOPA@Ag-MNPs)were synthesized and used as MSPE adsorbents to extract trace b-blockers from biological samples.After extraction,the analytes loaded on the polyDOPA@Ag-MNPs were desorbed using an organic solvent and analyzed by FTICR-MS.The method was rapid and sensitive,with a total detection procedure of less than 10 min as well as limits of detection and quantification in the ranges of 3.5-6.8 pg/mL and 11.7-22.8 pg/mL,respectively.The accuracy of the method was also desirable,with recoveries ranging from 80.9%to 91.0%following the detection of analytes in human blood samples.All the experimental results demonstrated that the developed MSPE-FTICR-MS method was suitable for the rapid and sensitive analysis of trace b-blockers in complex biological samples.
基金support from the projects of the National Natural Science Foundation of China(Nos.22006143,21806189)the Science and Technology Program of Guangzhou(China)(No.202102020601)+2 种基金the Natural Science Foundation of Guangdong Province(China)(No.2021A1515012336)the Guangdong Provincial Key R&D Programme(China)(No.2020B1111350002)the special project of Guangdong Enterprise Science and Technology Commissioner(China)(No.GDKTP2021011600).
文摘Incomplete separation and recycling of nanoparticles are causing undesirable nanopollution and thus raising great concerns with regard to nanosafety.Since microorganisms are important regulator of physiological processes in many organisms,the interaction between nanopollution and microbial metabolomics and the resultant impact on the host’s health are important but unclear.To investigate how typical nanopollution perturbs microbial growth and metabolism,Escherichia coli(E.coli)in vitro was treated with six water-dispersible nanomaterials(nanoplastic,nanosilver,nano-TiO 2,nano-ZnO,semiconductor quantum dots(QDs),carbon dots(CDs))at human-/environment-relevant concentration levels.The nanomaterials exhibited type-specific toxic effects on E.coli growth.Global metabolite profiling was used to characterize metabolic disruption patterns in the model microorganism exposed to different nanopollutants.The percentage of significant metabolites(p<0.05,VIP>1)accounted for 6%–38%of the total 293 identified metabolites in each of the nanomaterial-contaminated bacterial groups.Metabolic results also exhibited significant differences between different nanopollutants and dose levels,revealing type-specific and untypical concentration-dependent metabolic responses.Key metabolites responsive to nanopollution exposures were mainly involved in amino acid and purine metabolisms,where 5,4,and 7 significant metabolic features were included in arginine and proline metabolism,phenylalanine metabolism,and purine metabolism,respectively.In conclusion,this study horizontally compared and demonstrated how typical nanopollution perturbs microbial growth and metabolomics in a type-specific manner,which broadens our understanding of the ecotoxicity of nanopollutants on microorganisms.
基金We gratefully acknowledge the sponsorship of the present work by Natural Science Fundation of China under the project numbered
文摘An atomic model of compound precipitation in alloys, which couples cellular automaton growth/dissociation of precipitates and randomwalk diffusion, has been developed and programmed for 2 dimensional computer simulation. With boundary condition parameters and diffusion parameters variable, a series of simulation experiments were carried out for a qualitative study of nitride precipitation behavior in nitridation of alloy steels. Effects of nitrogen potential and alloy composition on kinetics and microstructure of the precipitation were addressed, and the so called "iso-activity aging" phenomenon was examined.
基金The work is supported by National Key Research&Development Program of China(No.2016YFD0600904)Integration and Demonstration of the Value-added&Efficiency-increased Technology across the Industry Chain for Bamboo。
文摘Finger-jointed lumber production has now become the most extensively used method for spliced lumbers jointing together endwise.The properties of finger-jointed lumber are affected by many different factors such as the end-pressure.The main mechanical properties to be tested for struc-tural use finger-jointed lumber include the modulus of elasticity in static bending and the bending strength.The most commonly used method for testing these properties at present is the experi-mental test.In this study,we used finite element method to investigate the end-pressure range,the modulus of elasticity in static bending and the bending strength for Pinus sylvistriv var.finger-jointed lumber under three different fitness ratios(0 mm,0.1 mm,0.3 mm).With finite element analysis(FEA)modelling results compared with the experimental test results,it is possible to find the relationship between these two kinds of results and use the FEA to predict the properties of finger-jointed lumber.The FEA applied in the end pressure tests showed a narrower range com-pared with the modelling results.It indicated that the FEA could be used in the prediction of the end pressure for finger-jointed lumber.The modelling results for modulus of elasticity(MOE)test and bending strength(MOR)test showed about 20%discrepancies compared with the experimen-tal results.Moreover,the MOE modelling results showed the same trend as experimental results under three different fitness levels while the MOR modelling results showed the different trend.It can be concluded that the FEA is a feasible way in analysing the properties of finger-jointed lumber if the errors could be eliminated properly.Some modifications should be made in order to realize the prediction of the properties of finger-jointed lumber more accurately.
文摘The microcirculation blood volume in the hypothalamus-pituitary-ovary axis in adult female Wistar rats during each phase of the estrous cycle were measured by the techaique of radioactives biomicrosphere. The results arc as follows (unit:
文摘In this paper, a novel prioritized Optical Burst Switching (OCBS) scheme for the next-generation optical Internet is proposed and investigated systematically through theoretical analysis and network simulation. Analysis shows that the proposed scheme is able to achieve modestly fine traffic differentiation in a simple and easy way. The simulation results agree with the theoretical analysis and they are useful in traffic engineering of optical burst switching networks.
基金This work is supported by the National High Technology Research and Development Program ofChina(2 0 0 2 AA135 2 30 ) and the Major Project of National Natural Science Foundation of Beijing(4 0 110 0 2 ) .
文摘Recently, attention has been focused on spatial query language which is used to query spatial databases. A design of spatial query language has been presented in this paper by extending the standard relational database query language SQL. It recognizes the significantly different requirements of spatial data handling and overcomes the inherent problems of the application of conventional database query languages. This design is based on an extended spatial data model, including the spatial data types and the spatial operators on them. The processing and optimization of spatial queries have also been discussed in this design. In the end, an implementation of this design is given in a spatial query subsystem.
文摘＂I buy most of my cosmetics abroad usually buy a lot each time when I travel abroad. Sometimes, I askfriends to buy some for me.＂ So says Ms Wang, a 35-year-old Beijing resident. ＂I recently bought some L＇Oreal Paris makeup and two bottles of Lancome products - one is a hydrating product and another is a whitening product - at tax-free stores during my trip to Phuket in Thailand during the Spring Festival holidays. The L＇Oreal Paris makeup was very cheap, and I saved almost all the 30% consumption tax.＂
文摘China has dramatically enlarged the China （Shanghai） Pilot Free Trade Zone, to include the city＇scommercial and financial centre Lujiazui, as well as Jinqiao and Zhangjiang districts. The China （Guangdong） Pilot Free Trade Zone, which covers Nansha Hengqin, and Qianhai and Shekou of Shenzhen - a pioneering city in China＇s reform and opening-up, was formally established on April 27.
基金This work is supported by the National High Technology Research and Development Program ofChina(2 0 0 2 AA135 2 30 ) and the Major Project of National Natural Science Foundation of Beijing(4 0 110 0 2 ) .
文摘The problem of long transactions is a significant problem in spatial database. The checkout mechanism and multi version mechanism are two kind methods of solving the problem of long transactions. In this paper, we present a Shallow Version Management mechanism to realize multi version mechanism in spatial database. And we introduced a increment storage and dynamic version views building method to improve efficiency of storing and consulting. We also illuminate how to resolve the problem of long transaction concurrency control in spatial database by using multi version mechanism. At the end of this paper, we introduce some required means to version management in spatial database, like converge, compress and delete.
文摘Let π : Mn→Pn be an n-dimensional small cover over Pn and λ : F(Pn)→Z2n be its characteristic function. The author uses the symbol c(λ) to denote the cardinal number of the image Im(λ). If c(λ) = n + 1 or n + 2, then a necessary and sufficient condition on the existence of spin structure on Mnis given. As a byproduct, under some special conditions, the author uses the second Stiefel-Whitney class to detect when Pn is n-colorable or(n + 1)-colorable.
