We report an experimental study of the scattering of ultrasonic plane waves on a turbulent jet in air (Pr = 0.7). The jet is weakly heated so that the temperature fluctuations act as a passive scalar. In the backscattering geometry one measures the Fourier components of the temperature field T(q,t). The time averaged characteristics are analyzed in detail; in particular we observe a Kolmogorov -5/3 power law behavior for the passive scalar spectrum in the inertial range of scales. The study of the time fluctuations shows that the histograms of T(q,t) remain close to a Gaussian at all scales.
{"title":"Sound Scattering on a Turbulent, Weakly Heated Jet","authors":"A. Petrossian, J. Pinton","doi":"10.1051/JP2:1997152","DOIUrl":"https://doi.org/10.1051/JP2:1997152","url":null,"abstract":"We report an experimental study of the scattering of ultrasonic plane waves on a turbulent jet in air (Pr = 0.7). The jet is weakly heated so that the temperature fluctuations act as a passive scalar. In the backscattering geometry one measures the Fourier components of the temperature field T(q,t). The time averaged characteristics are analyzed in detail; in particular we observe a Kolmogorov -5/3 power law behavior for the passive scalar spectrum in the inertial range of scales. The study of the time fluctuations shows that the histograms of T(q,t) remain close to a Gaussian at all scales.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"43 1","pages":"801-812"},"PeriodicalIF":0.0,"publicationDate":"1997-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77414990","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We incorporate the effects of fluctuations in a density functional analysis of the freezing of a colloidal liquid in the presence of an external potential generated by interfering laser beams. A mean-field treatment, using a density functional theory, predicts that with the increase in the strength of the modulating potential, the freezing transition changes from a first order to a continuous one via a tricritical point for a suitable choice of the modulating wavevectors. We demonstrate here that the continuous nature of the freezing transition at large values of the external potential V-e survives the presence of fluctuations. We also show that fluctuations tend to stabilize the liquid phase in the large V-e regime.
{"title":"Effect of fluctuations on the freezing of a colloidal suspension in an external periodic potential","authors":"J. Chakrabarti, S. Sinha","doi":"10.1051/JP2:1997155","DOIUrl":"https://doi.org/10.1051/JP2:1997155","url":null,"abstract":"We incorporate the effects of fluctuations in a density functional analysis of the freezing of a colloidal liquid in the presence of an external potential generated by interfering laser beams. A mean-field treatment, using a density functional theory, predicts that with the increase in the strength of the modulating potential, the freezing transition changes from a first order to a continuous one via a tricritical point for a suitable choice of the modulating wavevectors. We demonstrate here that the continuous nature of the freezing transition at large values of the external potential V-e survives the presence of fluctuations. We also show that fluctuations tend to stabilize the liquid phase in the large V-e regime.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"14 1","pages":"729-741"},"PeriodicalIF":0.0,"publicationDate":"1997-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91371183","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Une nouvelle sequence de phase: phase a joints de grains suivie directement par des phases bleues sans phase cholesterique a recemment ete decouverte dans un compose chiral. Nous avons analyse ce compose en rayons X pour etudier l'ordre smectique a travers la sequence de phases. Le resultat principal que nous avons obtenu est la persistence de l'ordre smectique dans les phases bleues avec une longueur de correlation inferieure au pas TGB.
{"title":"Structural Measurements in Blue Phases with Smectic Ordering","authors":"B. Pansu, M. H. Li, H. Nguyen","doi":"10.1051/JP2:1997157","DOIUrl":"https://doi.org/10.1051/JP2:1997157","url":null,"abstract":"Une nouvelle sequence de phase: phase a joints de grains suivie directement par des phases bleues sans phase cholesterique a recemment ete decouverte dans un compose chiral. Nous avons analyse ce compose en rayons X pour etudier l'ordre smectique a travers la sequence de phases. Le resultat principal que nous avons obtenu est la persistence de l'ordre smectique dans les phases bleues avec une longueur de correlation inferieure au pas TGB.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"204 ","pages":"751-763"},"PeriodicalIF":0.0,"publicationDate":"1997-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91554199","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A systematic study of a Broida source producing atomic calcium in ground state 1 S and first metastable 1 D and 3 P states is presented. The relative concentration of the metastables, produced by a DC discharge, is monitored with carrier gas pressure, heating power and discharge current, and it is observed that low values of these parameters are favourable to 1 D formation. These results are interpreted in terms of relative values of cross section of energy pooling forming the first resonant state 1 P, and the ratio of these cross section is estimated to be σ( 3 P- 3 P)/σ( 1 D- 1 D) # 5 x 10 -4 . Some properties of the source are described, including auto-absorptions of transitions originating from the 3 P and collisional relaxation of reaction products of Ca with halogenated compounds. An example of utilization of the source for the study of metastable reactivity is presented.
{"title":"Study of a calcium afterglow in a Broida oven","authors":"F. Fethi, M. Bourgoin, F. Poblete, G. Taieb","doi":"10.1051/JP2:1997103","DOIUrl":"https://doi.org/10.1051/JP2:1997103","url":null,"abstract":"A systematic study of a Broida source producing atomic calcium in ground state 1 S and first metastable 1 D and 3 P states is presented. The relative concentration of the metastables, produced by a DC discharge, is monitored with carrier gas pressure, heating power and discharge current, and it is observed that low values of these parameters are favourable to 1 D formation. These results are interpreted in terms of relative values of cross section of energy pooling forming the first resonant state 1 P, and the ratio of these cross section is estimated to be σ( 3 P- 3 P)/σ( 1 D- 1 D) # 5 x 10 -4 . Some properties of the source are described, including auto-absorptions of transitions originating from the 3 P and collisional relaxation of reaction products of Ca with halogenated compounds. An example of utilization of the source for the study of metastable reactivity is presented.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"69 1","pages":"687-705"},"PeriodicalIF":0.0,"publicationDate":"1997-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83193764","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Patterns formed by inversion walls in nematic layers exposed to a rotating magnetic field were studied. Dilute solutions of a mesogenic side group polymethacrylate in a low molecular weight liquid crystal (5CB) were used in comparison with the pure solvent. As found in a previous work, in this system the intensity of backflow (fluid flow induced by director rotation) can be controlled by the polymer concentration due to a specific increase of shear viscosity coefficients. In the synchronous regime of director rotation no significant effects of backflow on the dynamics of the walls are observed. Dynamic solitons known from the synchronous regime were also found at asynchronous rotation, when soliton lattices are formed by continuous nucleation. Here comparison with theory for given values of the lattice period shows soliton currents significantly reduced by backflow. Two of the three additional pattern forming states exclusively found at asynchronous rotation were completely suppressed in solutions with sufficient polymer concentration. The third of these states is affected by backflow in the growth rate of its patterns. Numerical calculations were performed to explain behavior of the patterns in the asynchronous state. For pure 5CB a quantitative comparison with the experiment was possible.
{"title":"The Effect of Dissolved Side-Group Polymers on Pattern Dynamics in Nematic Liquid Crystals in a Rotating Magnetic Field","authors":"E. Pashkovsky, W. Stille, G. Strobl, D. Talebi","doi":"10.1051/JP2:1997154","DOIUrl":"https://doi.org/10.1051/JP2:1997154","url":null,"abstract":"Patterns formed by inversion walls in nematic layers exposed to a rotating magnetic field were studied. Dilute solutions of a mesogenic side group polymethacrylate in a low molecular weight liquid crystal (5CB) were used in comparison with the pure solvent. As found in a previous work, in this system the intensity of backflow (fluid flow induced by director rotation) can be controlled by the polymer concentration due to a specific increase of shear viscosity coefficients. In the synchronous regime of director rotation no significant effects of backflow on the dynamics of the walls are observed. Dynamic solitons known from the synchronous regime were also found at asynchronous rotation, when soliton lattices are formed by continuous nucleation. Here comparison with theory for given values of the lattice period shows soliton currents significantly reduced by backflow. Two of the three additional pattern forming states exclusively found at asynchronous rotation were completely suppressed in solutions with sufficient polymer concentration. The third of these states is affected by backflow in the growth rate of its patterns. Numerical calculations were performed to explain behavior of the patterns in the asynchronous state. For pure 5CB a quantitative comparison with the experiment was possible.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"34 1","pages":"707-727"},"PeriodicalIF":0.0,"publicationDate":"1997-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87151671","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
V. Reus, L. Belloni, T. Zemb, N. Lutterbach, H. Versmold
Des suspensions aqueuses de particules de bromopolystyrene ont ete caracterisees par diffusion de lumiere, diffusion de rayons X aux petits angles et par des mesures de pression osmotique. Nous avons ainsi etudie leur structure et les interactions interparticulaires en fonction de la fraction volumique a salinite constante de l'ordre de la micromole/1. Lorsque la cristallisation est lente, nous observons des cristaux parfaits cubiques centres par diffusion de lumiere pour des fractions volumiques comprises entre 0,04 et 0,7 % et cubiques faces centrees par diffusion de rayons X aux petits angles pour des fractions volumiques plus elevees (2-12 %). Apres cisaillement, des defauts apparaissent dans les cristaux ; ils sont caracterises par la disparition de certaines raies de Bragg en diffusion de lumiere pour des echantillons de fraction volumique comprise entre 0,1 et 0,3 % et par la presence d'un pre-pic observe par diffusion de rayons X aux petits angles avant le premier pic de Bragg, pour des echantillons plus concentres (2-12 %). Les pressions osmotiques ont ete mesurees par difference de pression hydrostatique entre la solution et le reservoir separes par une membrane hemipermeable. Les donnees experimentales sont bien reproduites par la theorie Poisson Boltzmann Reseau (PBR) qui montre que les interactions sont purement repulsives. Aucune force attractive faible de longue portee n'a ete detectee experimentalement. En calculant le deplacement moyen d'une particule a l'interieur de sa cage a l'aide du modele PBR excentre, nous avons verifie que le critere de Lindemann etait satisfait pour tous les cristaux observes. Cette etude a permis de determiner l'equation d'etat d'un cristal colloidal electrostatique. Les resultats sont equivalents a une mesure de force ultraprecise puisque les forces d'interaction mesurees entre particules sont de l'ordre de 10 -12 N pour des distances centre a centre de l'ordre de 4000 A.
{"title":"Equation of state and structure of electrostatic colloidal crystals: Osmotic pressure and scattering study","authors":"V. Reus, L. Belloni, T. Zemb, N. Lutterbach, H. Versmold","doi":"10.1051/JP2:1997142","DOIUrl":"https://doi.org/10.1051/JP2:1997142","url":null,"abstract":"Des suspensions aqueuses de particules de bromopolystyrene ont ete caracterisees par diffusion de lumiere, diffusion de rayons X aux petits angles et par des mesures de pression osmotique. Nous avons ainsi etudie leur structure et les interactions interparticulaires en fonction de la fraction volumique a salinite constante de l'ordre de la micromole/1. Lorsque la cristallisation est lente, nous observons des cristaux parfaits cubiques centres par diffusion de lumiere pour des fractions volumiques comprises entre 0,04 et 0,7 % et cubiques faces centrees par diffusion de rayons X aux petits angles pour des fractions volumiques plus elevees (2-12 %). Apres cisaillement, des defauts apparaissent dans les cristaux ; ils sont caracterises par la disparition de certaines raies de Bragg en diffusion de lumiere pour des echantillons de fraction volumique comprise entre 0,1 et 0,3 % et par la presence d'un pre-pic observe par diffusion de rayons X aux petits angles avant le premier pic de Bragg, pour des echantillons plus concentres (2-12 %). Les pressions osmotiques ont ete mesurees par difference de pression hydrostatique entre la solution et le reservoir separes par une membrane hemipermeable. Les donnees experimentales sont bien reproduites par la theorie Poisson Boltzmann Reseau (PBR) qui montre que les interactions sont purement repulsives. Aucune force attractive faible de longue portee n'a ete detectee experimentalement. En calculant le deplacement moyen d'une particule a l'interieur de sa cage a l'aide du modele PBR excentre, nous avons verifie que le critere de Lindemann etait satisfait pour tous les cristaux observes. Cette etude a permis de determiner l'equation d'etat d'un cristal colloidal electrostatique. Les resultats sont equivalents a une mesure de force ultraprecise puisque les forces d'interaction mesurees entre particules sont de l'ordre de 10 -12 N pour des distances centre a centre de l'ordre de 4000 A.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"2 1","pages":"603-626"},"PeriodicalIF":0.0,"publicationDate":"1997-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81983342","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
T. S. C. Singh, K. B. Choudhury, M. B. Singh, N. C. Deb, S. Mukherjee, P. Mazumdar
Total cross sections (TCS) and single differential cross sections (SDCS) have been computed for the single ionization of the ground state of helium by electron impact in a distorted wave formalism which takes into account the effects of the initial and final channel distortions. The present TCS and SDCS results are in fair agreement with the measured values and other theoretical predictions for the incident electron energy E i > 150 eV.
在考虑初始和最终通道畸变影响的畸变波形式下，计算了氦基态单次电离的总截面(TCS)和单微分截面(SDCS)。目前的TCS和SDCS结果与实测值和其他理论预测的入射电子能量E i > 150 eV基本一致。
{"title":"Total and Single Differential Cross Sections for the Electron Impact Ionization of the Ground State of Helium","authors":"T. S. C. Singh, K. B. Choudhury, M. B. Singh, N. C. Deb, S. Mukherjee, P. Mazumdar","doi":"10.1051/JP2:1997143","DOIUrl":"https://doi.org/10.1051/JP2:1997143","url":null,"abstract":"Total cross sections (TCS) and single differential cross sections (SDCS) have been computed for the single ionization of the ground state of helium by electron impact in a distorted wave formalism which takes into account the effects of the initial and final channel distortions. The present TCS and SDCS results are in fair agreement with the measured values and other theoretical predictions for the incident electron energy E i > 150 eV.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"1 1","pages":"519-522"},"PeriodicalIF":0.0,"publicationDate":"1997-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78834796","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
K. Zeldovich, E. Dormidontova, A. Khokhlov, T. Vilgis
The microphase separation transition in the weakly charged polyelectrolyte gels immersed in poor solvent and undergoing collapse transition is studied in the weak crystallization approximation. The chain connectivity in the gel is taken into account ma introducing "polar- ization" term first proposed by de Gennes. It is shown that in this case the gel can undergo multistage jump-like collapse where the intermediate states can have regular microstructures of different symmetry,. The availability of numerous metastable states in the collapse region may lead to the pronounced hysteresis effects. These results are compared with some of the recent experimental findings.
{"title":"Microphase separation transition for polyelectrolyte gels in poor solvents","authors":"K. Zeldovich, E. Dormidontova, A. Khokhlov, T. Vilgis","doi":"10.1051/JP2:1997147","DOIUrl":"https://doi.org/10.1051/JP2:1997147","url":null,"abstract":"The microphase separation transition in the weakly charged polyelectrolyte gels immersed in poor solvent and undergoing collapse transition is studied in the weak crystallization approximation. The chain connectivity in the gel is taken into account ma introducing \"polar- ization\" term first proposed by de Gennes. It is shown that in this case the gel can undergo multistage jump-like collapse where the intermediate states can have regular microstructures of different symmetry,. The availability of numerous metastable states in the collapse region may lead to the pronounced hysteresis effects. These results are compared with some of the recent experimental findings.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"1 1","pages":"627-635"},"PeriodicalIF":0.0,"publicationDate":"1997-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83120430","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Sergei Obvikhov, Dmitry Kobzev, D. Perchak, M. Rubinstein
We present a simple minimal model which allows numerical and analytical study of a glass transition. This is a model of rigid rods with fixed centers of rotation. The rods can rotate freely but cannot cross each other. The ratio L of the length of the rods to the distance between the centers of rotation is the only parameter of this model. With increasing L we observed a sharp crossover to practically infinite relaxation times in 2D arrays of rods. In 3D we found a real transition to a completely frozen random state at $L_{rm c}cong 4.5$.
{"title":"Topologically induced glass transition in freely rotating rods","authors":"Sergei Obvikhov, Dmitry Kobzev, D. Perchak, M. Rubinstein","doi":"10.1051/JP1:1997175","DOIUrl":"https://doi.org/10.1051/JP1:1997175","url":null,"abstract":"We present a simple minimal model which allows numerical and analytical study of a glass transition. This is a model of rigid rods with fixed centers of rotation. The rods can rotate freely but cannot cross each other. The ratio L of the length of the rods to the distance between the centers of rotation is the only parameter of this model. With increasing L we observed a sharp crossover to practically infinite relaxation times in 2D arrays of rods. In 3D we found a real transition to a completely frozen random state at $L_{rm c}cong 4.5$.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"29 1","pages":"563-568"},"PeriodicalIF":0.0,"publicationDate":"1997-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76180765","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A microscopic theory of the mixtures of polymer chains and colloidal particles immersed in a common solvent is developed on the basis of the RISM integral equation technique. The obtained general equations enable the calculation of the correlation functions and thermodynamic characteristics of the system at an arbitrary ratio of the components. The theory is used for a comprehensive study of interaction of small spherical particles with flexible polymer chains in the regimes of weak and strong adsorption of the macromolecules on the surface of the particles. The temperature and concentration regions characterized by different effect of the polymer on stability of the colloidal dispersion are determined. The corresponding temperature-concentration diagrams of state are constructed.
{"title":"Interaction of Colloidal Particles with Macromolecules: The RISM Integral Equation Theory","authors":"P. Khalatur, L. V. Zherenkova, A. Khokhlov","doi":"10.1051/JP2:1997145","DOIUrl":"https://doi.org/10.1051/JP2:1997145","url":null,"abstract":"A microscopic theory of the mixtures of polymer chains and colloidal particles immersed in a common solvent is developed on the basis of the RISM integral equation technique. The obtained general equations enable the calculation of the correlation functions and thermodynamic characteristics of the system at an arbitrary ratio of the components. The theory is used for a comprehensive study of interaction of small spherical particles with flexible polymer chains in the regimes of weak and strong adsorption of the macromolecules on the surface of the particles. The temperature and concentration regions characterized by different effect of the polymer on stability of the colloidal dispersion are determined. The corresponding temperature-concentration diagrams of state are constructed.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"43 1","pages":"543-582"},"PeriodicalIF":0.0,"publicationDate":"1997-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74124483","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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