Plasma flow in a curved magnetic field     

Lennart Lindberg 《Astrophysics and Space Science》1978,55(1):203-225

A beam of collisionless plasma is injected along a longitudinal magnetic field into a region of curved magnetic field. Two unpredicted phenomena are observed: The beam becomes deflected in the directionopposite to that in which the field is curved, and itcontracts to a flat slab in the plane of curvature of the magnetic field.The plasma is produced by a conical theta-pinch gun and studied by means of high speed photography, electric and magnetic probes, ion analyser, and spectroscopy.The plasma beam is collisionless and its behaviour is, in principle, understood on the basis of gyro-centre drift theory. A fraction of the transverse electric fieldE=–v×B, which is induced when the beam enters the curved magnetic field, is propagated upstream and causes the reverse deflection byE×B drift. The upstream propagation of the transverse electric field is due to electron currents.The circuit aspect on the plasma is important. The transverse polarization current in the region with the curved field connects to a loop of depolarization currents upstream. The loop has limited ability to carry current because of the collisionless character of the plasma; curlE is almost zero and electric field components arise parallel to the magnetic field. These play an essential role, producing runaway electrons, which have been detected. An increased electron temperature is observed when the plasma is shot into the curved field. Runaway electrons alone might propagate the electric field upstream in case the electron thermal velocity is insufficient.The phenomenon is of a general character and can be expected to occur in a very wide range of ensities. The lower density limit is set by the condition for self-polarization,nm _i / ₀ B ² 1 or, which is equivalent,c ²/v _A ² ;1, wherec is the velocity of light, andv _A the Alfvén velocity. The upper limit is presumably set by the requirement _{e e} 1.The phenomenon is likely to be of importance, for example, for the injection of plasma into magnetic bottles and in space and solar physics. The paper illustrates the complexity of plasma flow phenomena and the importance of close contact between experimental and theoretical work.Paper dedicated to Professor Hannes Alfvén on the occasion of his 70th birthday, 30 May, 1978  相似文献   

The distribution and relative toxic potential of organic chemicals in a PCB contaminated bay     

Sundberg H  Tjärnlund U  Kerman G  Blomberg M  Ishaq R  Grunder K  Hammar T  Broman D  Balk L 《Marine pollution bulletin》2005,50(2):195-207

For reliable monitoring of environmental improvement, the PCB contaminated bay Orserumsviken on Sweden's Baltic coast was investigated prior to remediation. We examined PCB congener patterns and the relative toxic potential of PCBs in extracts of three matrices: bottom sediment, settling particulate matter and the dissolved phase (obtained from semi-permeable membrane devices). Congener patterns were similar in all matrices. Three fractions were isolated from the extracts: (1) aliphatic and monocyclic aromatic compounds (MAC-fraction), (2) dicyclic aromatic compounds (DAC-fraction), including PCBs, and (3) polycyclic aromatic compounds (PAC-fraction), including PAHs. Total extracts and fractions were injected into newly fertilised rainbow trout eggs. At larval stage, hepatic EROD activities were quantified. Though high, the PCB contamination could explain only an estimated 1-5% of the total EROD induction. The order of EROD induction potential was: total extract > PAC-fraction > DAC-fraction > MAC-fraction in all matrices, suggesting that in Orserumsviken PACs made a larger contribution to the EROD induction potential than PCBs and other DACs.  相似文献   

Biotransformation enzyme activities and PCDD/PCDF levels in pike caught in a Swedish Lake     

Lars Frlin  Lennart Balk  Malin Celander  Sture Bergek  Maria Hjelt  Christoffer Rappe  Cynthia de Wit  Bo Jansson 《Marine environmental research》1992,34(1-4)

Recently, analysis of organochlorines in sediment and in pike from Lake Vänern, Sweden, showed a north-south gradient of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs). In the present study, good correlations were found between muscle 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) equivalents and liver ethoxyresorufin-O-deethylase (EROD) activities (and P4501A levels) in pike caught at three sampling sites along the north-south gradient in the lake. This comparison between tissue levels of PCDD/PCDF and EROD activity (and P4501A) may indicate that TCDD or structural analogs could be responsible for the observed induction of the pike P450 system. It must, however, be taken into account that the analysed contaminants often do not appear alone but are, rather, accompanied by a range of other substances which may be inducers or antagonists.  相似文献   

Migrations of the mackerel in the northern North Sea and in the Skagerak     

Lindquist  Armin; Hannerz  Lennart 《ICES Journal of Marine Science》1974,35(3):276-280

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A numerical study of the influence from pre‐existing cracks on granite rock fragmentation at percussive drilling          下载免费PDF全文

Mahdi Saadati  Pascal Forquin  Kenneth Weddfelt  Per‐Lennart Larsson  Francois Hild 《国际地质力学数值与分析法杂志》2015,39(5):558-570

The aim of this study is to investigate the effect of pre‐existing, or structural, cracks on dynamic fragmentation of granite. Because of the complex behavior of rock materials, a continuum approach is employed relying upon a plasticity model with yield surface locus as a quadratic function of the mean pressure in the principal stress space coupled with an anisotropic damage model. In particular, Bohus granite rock is investigated, and the material parameters are chosen based on previous experiments. The equation of motion is discretized using a finite element approach, and the explicit time integration method is employed. The pre‐existing cracks are introduced in the model by considering sets of elements with negligible tensile strength that leads to their immediate failure when loaded in tension even though they still carry compressive loads as crack closure occurs because of compressive stresses. Previously performed edge‐on impact tests are reconsidered here to validate the numerical model. Percussive drilling is simulated, and the influence of the presence of pre‐existing cracks is studied. The results from the analysis with different crack lengths and orientations are compared in terms of penetration stiffness and fracture pattern. It is shown that pre‐existing cracks in all investigated cases facilitate the drilling process. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Basic physiological biomarkers in adult female perch (Perca fluviatilis) in a chronically polluted gradient in the Stockholm recipient (Sweden)     

Linderoth M  Hansson T  Liewenborg B  Sundberg H  Noaksson E  Hanson M  Zebühr Y  Balk L 《Marine pollution bulletin》2006,53(8-9):437-450

By measuring a battery of basic physiological biomarkers and the concentration of SigmaDDT in adult female perch (Perca fluviatilis), an assumed aquatic pollution gradient was confirmed, with the city of Stockholm (Sweden) as a point source of anthropogenic substances. The investigation included an upstream gradient, westwards through Lake M?laren (46 km), and a downstream gradient, eastwards through the Stockholm archipelago (84 km). The results indicated a severe pollution situation in central Stockholm, with poor health status of the perch: retarded growth, increased frequency of sexually immature females, low gonadosomatic index, and disturbed visceral fat metabolism. SigmaDDT, measured as a pollution indicator, was 10-28 times higher than the background in perch from the Baltic Proper. Besides the main gradient other sources of pollution also influenced the response pattern of the measured biomarkers. In particular, there were strong indications of pollution coming from the Baltic Sea.  相似文献   

The Spectro Point Spread Function for GAIA     

Claus Fabricius  Lennart Lindegren 《Astrophysics and Space Science》2002,280(1-2):51-56

We discuss the point spread function for the Spectro instrument based on realistic effects of the time delayed integration, transverse image motion and pixelization, but assuming rather small wave front errors. Stars brighter than 10 mag, which will saturate the CCD, may be observed photometrically using the image wings, but the central wavelengths will be slightly shifted towards the red. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Metal (Al, Fe, Mn and Cu) distributions and origins of polycyclic aromatic hydrocarbons (PAHs) in the surface sediments of the Marmara Sea and the coast of Istanbul, Turkey     

Taşkın ÖS  Aksu A  Balkıs N 《Marine pollution bulletin》2011,62(11):2568-2570

In this study, total metal (Al, Fe, Mn and Cu) and PAHs analyses have been done in the surface sediments. Sediment samples have been collected from seven parts of the Marmara Sea and the coast of Istanbul during 2009. Total Al, Fe, Mn and Cu contents vary between 1.8% and 5.4%; 1.1% and 2.8%; 122 and 259 μg g⁻¹; 27 and 416 μg g⁻¹, respectively. EF and CF values of Fe and Mn are lower than 1.5 and 1, respectively, in all the stations. Total PAH contents range between 135 and 6009 ng g⁻¹ in the surface sediments. The origin of PAHs has been found pyrolitic according to the Phe/Ant ratio in the all stations. Contrastingly, at K0, MKC and MY1 Stations, PAH origins have been observed petrogenic according to the Flu/Pyr ratio.  相似文献   

A priori information and admissible complexity of the model of anomalous objects in the solution of inverse problems of gravity     

Balk  P. I. 《Izvestiya Physics of the Solid Earth》2013,49(2):165-176

Izvestiya, Physics of the Solid Earth - We study the problem of selecting an admissible complexity of the model of gravity sources, which largely governs the quality of the inverse problem solution...  相似文献   

Observational and predictive uncertainties for multiple variables in a spatially distributed hydrological model     

Lennart Benjamin Ehlers  Torben Obel Sonnenborg  Jens Christian Refsgaard 《水文研究》2019,33(5):833-848

In this study, uncertainty in model input data (precipitation) and parameters is propagated through a physically based, spatially distributed hydrological model based on the MIKE SHE code. Precipitation uncertainty is accounted for using an ensemble of daily rainfall fields that incorporate four different sources of uncertainty, whereas parameter uncertainty is considered using Latin hypercube sampling. Model predictive uncertainty is assessed for multiple simulated hydrological variables (discharge, groundwater head, evapotranspiration, and soil moisture). Utilizing an extensive set of observational data, effective observational uncertainties for each hydrological variable are assessed. Considering not only model predictive uncertainty but also effective observational uncertainty leads to a notable increase in the number of instances, for which model simulation and observations are in good agreement (e.g., 47% vs. 91% for discharge and 0% vs. 98% for soil moisture). Effective observational uncertainty is in several cases larger than model predictive uncertainty. We conclude that the use of precipitation uncertainty with a realistic spatio‐temporal correlation structure, analyses of multiple variables with different spatial support, and the consideration of observational uncertainty are crucial for adequately evaluating the performance of physically based, spatially distributed hydrological models.  相似文献