High performance discharges near the operational limit in HT-7

International Nuclear Information System (INIS)

Li Jiangang; Wan Baonian; Luo Jiarong; Gao Xiang; Zhao Yanping; Kuang Guangli; Zhang Xiaodong; Yang Yu; Yi Bao; Bojiang Ding; Jikang Xie; Yuanxi Wan

2001-01-01

Efforts have been made on the HT-7 tokamak to extend the stable operation boundaries. Extensive RF boronization and siliconization have been used and a wider operational Hugill diagram has been obtained. The transit density reached 1.3 times the Greenwald density limit in ohmic discharges. A stationary high performance discharge with q a =2.1 has been obtained after siliconization. Confinement improvement was obtained as a result of the significant reduction of electron thermal diffusivity χ e in the outer region of the plasma. An improved confinement phase was also observed with LHCD in the density range of 70-120% of the Greenwald density limit. Off-axis LH wave power deposition was attributed to the weak hollow current density profile. Code simulations and measurements showed good agreement with the off-axis LH wave deposition. Supersonic molecular beam injection has been successfully used to achieve stable high density operation in the region of the Greenwald density limit. (author)

Correlation of the tokamak H-mode density limit with ballooning stability at the separatrix

Science.gov (United States)

Eich, T.; Goldston, R. J.; Kallenbach, A.; Sieglin, B.; Sun, H. J.; ASDEX Upgrade Team; Contributors, JET

2018-03-01

We show for JET and ASDEX Upgrade, based on Thomson-scattering measurements, a clear correlation of the density limit of the tokamak H-mode high-confinement regime with the approach to the ideal ballooning instability threshold at the periphery of the plasma. It is shown that the MHD ballooning parameter at the separatrix position α_sep increases about linearly with the separatrix density normalized to Greenwald density, n_e, sep/n_GW for a wide range of discharge parameters in both devices. The observed operational space is found to reach at maximum n_e, sep/n_GW≈ 0.4 -0.5 at values for α_sep≈ 2 -2.5, in the range of theoretical predictions for ballooning instability. This work supports the hypothesis that the H-mode density limit may be set by ballooning stability at the separatrix.

Physics of radiation-driven islands near the tokamak density limit

International Nuclear Information System (INIS)

Gates, D.A.; Delgado-Aparicio, L.; White, R.B.

2013-01-01

In previous work (Gates and Delgado-Aparicio 2012 Phys. Rev. Lett. 108 165004), the onset criterion for radiation-driven islands (Rebut et al 1985 Proc. 10th Int. Conf. on Plasma Physics and Controlled Nuclear Fusion Research 1984 (London, UK, 1984) vol 2 (Vienna: IAEA) p 197) in combination with a simple cylindrical model of tokamak current channel behaviour was shown to be consistent with the empirical scaling of the tokamak density limit (Greenwald et al 1988 Nucl. Fusion 28 2199). A number of the unexplained phenomena at the density limit are consistent with this novel physics mechanism. In this work, a more formal theoretical underpinning, consistent with cylindrical tearing mode theory, is developed for the onset criteria of these modes. The appropriate derivation of the radiation-driven addition to the modified Rutherford equation (MRE) is discussed. Additionally, the ordering of the terms in the MRE is examined in a regime near the density limit. It is hoped that, given the apparent success of this simple model in explaining the observed global scalings, it will lead to a more comprehensive analysis of the possibility that radiation-driven islands are the physics mechanism responsible for the density limit. In particular, with modern diagnostic capabilities detailed measurements of current densities, electron densities and impurity concentrations at rational surfaces should be possible, enabling verification of the concepts described above. (paper)

Effects of triangularity on confinement, density limit and profile stiffness of H-modes on ASDEX upgrade

International Nuclear Information System (INIS)

Stober, J.; Gruber, O.; Kallenbach, A.; Mertens, V.; Ryter, F.; Staebler, A.; Suttrop, W.; Treutterer, W.

2000-01-01

At ASDEX Upgrade the influence of triangularity on the H-mode performance has been studied intensively. It has been found that confinement increases with δ for a fixed line-averaged density. Though confinement decreases with increasing density for all analysed values of δ, H-factors (ITERH-98P) at the Greenwald density could be raised to 1 for the highest δ values achieved so far. The H-mode density limit could be increased by approx. 20%. There is a scatter of about 30% on the confinement data, which is anti-correlated to the average density in the scrape-off layer or the neutral fluxes outside the plasma. For nearly all discharges analysed so far, the temperature profiles are self-similar. This indication of profile stiffness could be verified by changing the heat-flux profile by changing the beam-voltage of the neutral-beam injection (NBI) at high density. At low density, first results indicate a deviation from this stiff behaviour. (author)

Non-axisymmetric equilibrium reconstruction and suppression of density limit disruptions in a current-carrying stellarator

Science.gov (United States)

Ma, Xinxing; Ennis, D. A.; Hanson, J. D.; Hartwell, G. J.; Knowlton, S. F.; Maurer, D. A.

2017-10-01

Non-axisymmetric equilibrium reconstructions have been routinely performed with the V3FIT code in the Compact Toroidal Hybrid (CTH), a stellarator/tokamak hybrid. In addition to 50 external magnetic measurements, 160 SXR emissivity measurements are incorporated into V3FIT to reconstruct the magnetic flux surface geometry and infer the current distribution within the plasma. Improved reconstructions of current and q profiles provide insight into understanding the physics of density limit disruptions observed in current-carrying discharges in CTH. It is confirmed that the final scenario of the density limit of CTH plasmas is consistent with classic observations in tokamaks: current profile shrinkage leads to growing MHD instabilities (tearing modes) followed by a loss of MHD equilibrium. It is also observed that the density limit at a given current linearly increases with increasing amounts of 3D shaping fields. Consequently, plasmas with densities up to two times the Greenwald limit are attained. Equilibrium reconstructions show that addition of 3D fields effectively moves resonance surfaces towards the edge of the plasma where the current profile gradient is less, providing a stabilizing effect. This work is supported by US Department of Energy Grant No. DE-FG02-00ER54610.

Density limit and cross-field edge transport scaling in Alcator C-Mod

International Nuclear Information System (INIS)

LaBombard, B.

2002-01-01

Experiments in Alcator C-Mod have uncovered a direct link between the character and scaling of edge transport and the empirical Greenwald density limit (n G ). In low to moderate density discharges, the scrape-off layer (SOL) exhibits a two-layer structure: a near SOL (∼5 mm zone) with steep density and temperature gradients and a far SOL with flatter profiles. In the far SOL, the transport fluxes exhibit large transport events ('bursts' which carry particles to main-chamber structures. In the near SOL, transport fluxes appear to be less 'bursty' particle diffusivities in this region is found to increase strongly with local plasma collisionality. As n/n G (or collisionality) is raised, cross-field heat convection begins to compete with parallel conduction to the divertor. At N/n G ∼0.5, T E at the separatrix is reduced. As n/n G approaches ∼1, regions inside the separatrix exhibit flatter profiles with 'bursty' transport behavior; cross-field heat convection to main-chamber structures becomes comparable to the radiated power. Thus as n/n G is increased, cross-field edge transport physics progressively changes, ultimately impacting the power balance of the discharge near N/n G ∼1. (author)

Chapter 7: High-Density H-Mode Operation in ASDEX Upgrade

International Nuclear Information System (INIS)

Stober, Joerg Karl; Lang, Peter Thomas; Mertens, Vitus

2003-01-01

Recent results are reported on the maximum achievable H-mode density and the behavior of pedestal density and central density peaking as this limit is approached. The maximum achievable H-mode density roughly scales as the Greenwald density, though a dependence on B t is clearly observed. In contrast to the stiff temperature profiles, the density profiles seem to allow more shape variation and especially with high-field-side pellet-injection, strongly peaked profiles with good confinement have been achieved. Also, spontaneous density peaking at high densities is observed in ASDEX Upgrade, which is related to the generally observed large time constants for the density profile equilibration. The equilibrated density profile shapes depend strongly on the heat-flux profile in the sense that central heating leads to significantly flatter profiles

A unified model of density limit in fusion plasmas

Science.gov (United States)

Zanca, P.; Sattin, F.; Escande, D. F.; Pucella, G.; Tudisco, O.

2017-05-01

In this work we identify by analytical and numerical means the conditions for the existence of a magnetic and thermal equilibrium of a cylindrical plasma, in the presence of Ohmic and/or additional power sources, heat conduction and radiation losses by light impurities. The boundary defining the solutions’ space having realistic temperature profile with small edge value takes mathematically the form of a density limit (DL). Compared to previous similar analyses the present work benefits from dealing with a more accurate set of equations. This refinement is elementary, but decisive, since it discloses a tenuous dependence of the DL on the thermal transport for configurations with an applied electric field. Thanks to this property, the DL scaling law is recovered almost identical for two largely different devices such as the ohmic tokamak and the reversed field pinch. In particular, they have in common a Greenwald scaling, linearly depending on the plasma current, quantitatively consistent with experimental results. In the tokamak case the DL dependence on any additional heating approximately follows a 0.5 power law, which is compatible with L-mode experiments. For a purely externally heated configuration, taken as a cylindrical approximation of the stellarator, the DL dependence on transport is found stronger. By adopting suitable transport models, DL takes on a Sudo-like form, in fair agreement with LHD experiments. Overall, the model provides a good zeroth-order quantitative description of the DL, applicable to widely different configurations.

High density operation on the HT-7 superconducting tokamak

International Nuclear Information System (INIS)

Xiang Gao

2000-01-01

The structure of the operation region has been studied in the HT-7 superconducting tokamak, and progress on the extension of the HT-7 ohmic discharge operation region is reported. A density corresponding to 1.2 times the Greenwald limit was achieved by RF boronization. The density limit appears to be connected to the impurity content and the edge parameters, so the best results are obtained with very clean plasmas and peaked electron density profiles. The peaking factors of electron density profiles for different current and line averaged densities were observed. The density behaviour and the fuelling efficiency for gas puffing (20-30%), pellet injection (70-80%) and molecular beam injection (40-50%) were studied. The core crash sawteeth and MHD behaviour, which were induced by an injected pellet, were observed and the events correlated with the change of current profile and reversed magnetic shear. The MARFE phenomena on HT-7 are summarized. The best correlation has been found between the total input ohmic power and the product of the edge line averaged density and Z eff . HT-7 could be easily operated in the high density region MARFE-free using RF boronization. (author)

ICRF power limitation relation to density limit in ASDEX

International Nuclear Information System (INIS)

Ryter, F.

1992-01-01

Launching high ICRF power into ASDEX plasmas required good antenna-plasma coupling. This could be achieved by sufficient electron density in front of the antennas i.e. small antenna-plasma distance (1-2 cm) and moderate to high line-averaged electron density compared to the density window in ASDEX. These are conditions eventually close to the density limit. ICRF heated discharges terminated by plasma disruptions caused by the RF pulse limited the maximum RF power which can be injected into the plasma. The disruptions occurring in these cases have clear phenomenological similarities with those observed in density limit discharges. We show in this paper that the ICRF-power limitation by plasma disruptions in ASDEX was due to reaching the density limit. (orig.)

ICRF power limitation relation to density limit in ASDEX

International Nuclear Information System (INIS)

Ryter, F.

1992-01-01

Launching high ICRF power into ASDEX plasmas required good antenna-plasma coupling. This could be achieved by sufficient electron density in front of the antennas i.e. small antenna-plasma distance (1-2 cm) and moderate to high line-averaged electron density compared to the density window in ASDEX. These are conditions eventually close to the density limit. ICRF heated discharges terminated by plasma disruptions caused by the RF pulse limited the maximum RF power which can be injected into the plasma. The disruptions occurring in these cases have clear phenomenological similarities with those observed in density limit discharges. We show in this paper that the ICRF-power limitation by plasma disruptions in ASDEX was due to reaching the density limit. (author) 3 refs., 3 figs

Long time-scale density peaking in JET

International Nuclear Information System (INIS)

Sartori, R.; Saibene, G.; Becoulet, M.

2002-01-01

This paper discusses how the proximity to the L-H threshold affects the confinement of ELMy H-modes at high density. The largest reduction in confinement at high density is observed at the transition from the Type I to the Type III ELMy regime. At medium plasma triangularity, δ≅0.3 (where δ is the average triangularity at the separatrix), JET experiments show that, by increasing the margin above the L-H threshold power and maintaining the edge temperature above the critical temperature for the transition to Type III ELMs, it is possible to avoid the degradation of the pedestal pressure with density, normally observed at lower power. As a result, the range of achievable densities (both in the core and in the pedestal) is increased. At high power above the L-H threshold power the core density was equal to the Greenwald limit with H97≅0.9. There is evidence that a mixed regime of Type I and Type II ELMs has been obtained at this intermediate triangularity, possibly as a result of this increase in density. At higher triangularity, δ≅0.5, the power required to achieve similar results is lower. (author)

Density limit in ASDEX discharges with peaked density profiles

International Nuclear Information System (INIS)

Staebler, A.; Niedermeyer, H.; Loch, R.; Mertens, V.; Mueller, E.R.; Soeldner, F.X.; Wagner, F.

1989-01-01

Results concerning the density limit in OH and NI-heated ASDEX discharges with the usually observed broad density profiles have been reported earlier: In ohmic discharges with high q a (q-cylindrical is used throughout this paper) the Murakami parameter (n e R/B t ) is a good scaling parameter. At the high densities edge cooling is observed causing the plasma to shrink until an m=2-instability terminates the discharge. When approaching q a =2 the density limit is no longer proportional to I p ; a minimum exists in n e,max (q a ) at q a ∼2.15. With NI-heating the density limit increases less than proportional to the heating power; the behaviour during the pre-disruptive phase is rather similar to the one of OH discharges. There are specific operating regimes on ASDEX leading to discharges with strongly peaked density profiles: the improved ohmic confinement regime, counter neutral injection, and multipellet injection. These regimes are characterized by enhanced energy and particle confinement. The operational limit in density for these discharges is, therefore, of great interest having furthermore in mind that high central densities are favourable in achieving high fusion yields. In addition, further insight into the mechanisms of the density limit observed in tokamaks may be obtained by comparing plasmas with rather different density profiles at their maximum attainable densities. 7 refs., 2 figs

Feedback controlled, reactor relevant, high-density, high-confinement scenarios at ASDEX Upgrade

Science.gov (United States)

Lang, P. T.; Blanken, T. C.; Dunne, M.; McDermott, R. M.; Wolfrum, E.; Bobkov, V.; Felici, F.; Fischer, R.; Janky, F.; Kallenbach, A.; Kardaun, O.; Kudlacek, O.; Mertens, V.; Mlynek, A.; Ploeckl, B.; Stober, J. K.; Treutterer, W.; Zohm, H.; ASDEX Upgrade Team

2018-03-01

One main programme topic at the ASDEX Upgrade all-metal-wall tokamak is development of a high-density regime with central densities at reactor grade level while retaining high-confinement properties. This required development of appropriate control techniques capable of coping with the pellet tool, a powerful means of fuelling but one which presented challenges to the control system for handling of related perturbations. Real-time density profile control was demonstrated, raising the core density well above the Greenwald density while retaining the edge density in order to avoid confinement losses. Recently, a new model-based approach was implemented that allows direct control of the central density. Investigations focussed first on the N-seeding scenario owing to its proven potential to yield confinement enhancements. Combining pellets and N seeding was found to improve the divertor buffering further and enhance the operational range accessible. For core densities up to about the Greenwald density, a clear improvement with respect to the non-seeding reference was achieved; however, at higher densities this benefit is reduced. This behaviour is attributed to recurrence of an outward shift of the edge density profile, resulting in a reduced peeling-ballooning stability. This is similar to the shift seen during strong gas puffing, which is required to prevent impurity influx in ASDEX Upgrade. First tests indicate that highly-shaped plasma configurations like the ITER base-line scenario, respond very well to pellet injection, showing efficient fuelling with no measurable impact on the edge density profile.

ITER Experts' meeting on density limits

International Nuclear Information System (INIS)

Borrass, K.; Igitkhanov, Y.L.; Uckan, N.A.

1989-12-01

The necessity of achieving a prescribed wall load or fusion power essentially determines the plasma pressure in a device like ITER. The range of operation densities and temperatures compatible with this condition is constrained by the problems of power exhaust and the disruptive density limit. The maximum allowable heat loads on the divertor plates and the maximum allowable sheath edge temperature practically impose a lower limit on the operating densities, whereas the disruptive density limit imposes an upper limit. For most of the density limit scalings proposed in the past an overlap of the two constraints or at best a very narrow accessible density range is predicted for ITER. Improved understanding of the underlying mechanisms is therefore a crucial issue in order to provide a more reliable basis for extrapolation to ITER and to identify possible ways of alleviating the problem

High density experiments with gas puffing and ECRH in T-10

International Nuclear Information System (INIS)

Esipchuk, Yu V; Kirneva, N A; Borschegovskij, A A; Chistyakov, V V; Denisov, V Ph; Dremin, M M; Gorbunov, E P; Grashin, S A; Kalupin, D V; Khimchenko, L N; Khramenkov, A V; Kirnev, G S; Krilov, S V; Krupin, V A; Myalton, T B; Pavlov, Yu D; Piterskij, V V; Ploskirev, G N; Poznyak, V I; Roy, I N; Shelukhin, D A; Skosyrev, Yu V; Trukhin, V M; Trukhina, E V; Vershkov, V A; Veschev, E A; Volkov, V V; Zhuravlev, V A

2003-01-01

High density experiments were carried out in T-10 with gas puffing and electron cyclotron resonance heating (with absorbed power value up to 1.4 MW) with oblique and perpendicular power launch. Densities exceeding the Greenwald limit (n Gw ) by up to a factor of 1.8 were achieved in a regime with a high value of the edge safety factor at the current flat-top, q(a)≅8.2. The decrease of q(a) to a value of 3 led to the reduction of the ratio ( n-bar e ) lim /n Gw to 1. Confinement degradation with density increase was not significant up to the density limit. However, the typical T-10 linear increase of energy confinement time with density saturates at n-bar e ≥0.6n Gw . This saturation is the result of the development of an additional transport in the electron heat channel. However, the saturated τ E values exceeded the ITER L-mode scaling predictions by up to a factor of 1.2 and were close to the value predicted by the ITER H-mode scaling. Effect of the strong gas puffing on the plasma confinement and experiments with neon seeding are also discussed in this paper

Density limits in Tokamaks

International Nuclear Information System (INIS)

Tendler, M.

1984-06-01

The energy loss from a tokamak plasma due to neutral hydrogen radiation and recycling is of great importance for the energy balance at the periphery. It is shown that the requirement for thermal equilibrium implies a constraint on the maximum attainable edge density. The relation to other density limits is discussed. The average plasma density is shown to be a strong function of the refuelling deposition profile. (author)

On thermodynamic limits of entropy densities

NARCIS (Netherlands)

Moriya, H; Van Enter, A

We give some sufficient conditions which guarantee that the entropy density in the thermodynamic limit is equal to the thermodynamic limit of the entropy densities of finite-volume (local) Gibbs states.

Edge operational space for high density/high confinement ELMY H-modes in JET

International Nuclear Information System (INIS)

Sartori, R.; Saibene, G.; Loarte, A.

2002-01-01

This paper discusses how the proximity to the L-H threshold affects the confinement of ELMy H-modes at high density. The largest reduction in confinement at high density is observed at the transition from the Type I to the Type III ELMy regime. At medium plasma triangularity, δ≅0.3 (where δ is the average triangularity at the separatrix), JET experiments show that by increasing the margin above the L-H threshold power and maintaining the edge temperature above the critical temperature for the transition to Type III ELMs, it is possible to avoid the degradation of the pedestal pressure with density, normally observed at lower power. As a result, the range of achievable densities (both in the core and in the pedestal) is increased. At high power above the L-H threshold power the core density was equal to the Greenwald limit with H97≅0.9. There is evidence that a mixed regime of Type I and Type II ELMs has been obtained at this intermediate triangularity, possibly as a result of this increase in density. At higher triangularity, δ≅0.5, the power required to achieve similar results is lower. (author)

Density limit in JT-60

International Nuclear Information System (INIS)

Kamada, Yutaka; Hosogane, Nobuyuki; Hirayama, Toshio; Tsunematsu, Toshihide

1990-05-01

This report studies mainly the density limit for a series of gas- and pellet-fuelled limiter discharges in JT-60. With the pellet injection into high-current/low-q (q(a)=2.3∼2.5) discharges, the Murakami factor reaches up to 10∼13 x 10 19 m -2 T -1 . The values are about factors of 1.5∼2.0 higher than those for usual gas-fuelled discharges. The pellet injected discharges have high central density, whereas the electron density in the outer region (a/2 abs and n e 2 (r=50 cm) x Z eff (r=50 cm). (author)

Scrape-off layer based modelling of the density limit in beryllated JET limiter discharges

International Nuclear Information System (INIS)

Borrass, K.; Campbell, D.J.; Clement, S.; Vlases, G.C.

1993-01-01

The paper gives a scrape-off layer based interpretation of the density limit in beryllated JET limiter discharges. In these discharges, JET edge parameters show a complicated time evolution as the density limit is approached and the limit is manifested as a non-disruptive density maximum which cannot be exceeded by enhanced gas puffing. The occurrence of Marfes, the manner of density control and details of recycling are essential elements of the interpretation. Scalings for the maximum density are given and compared with JET data. The relation to disruptive density limits, previously observed in JET carbon limiter discharges, and to density limits in divertor discharges is discussed. (author). 18 refs, 10 figs, 1 tab

High density regimes and beta limits in JET

International Nuclear Information System (INIS)

Smeulders, P.

1990-01-01

Results are first presented on the density limit in JET discharges with graphite (C), Be gettered graphite and Be limiters. There is a clear improvement in the case of Be limiters. The Be gettered phase showed no increase in the gas fueled density limit, except with Ion Cyclotron Resonance Heating (ICRH), but, the limit changed character. During MARFE-formation, any further increase in density was prevented, leading to a soft density limit. The soft density limit was a function of input power and impurity content with a week dependence on q. Helium and pellet fuelled discharges exceeded the gas-fuelled global density limits, but essentially had the same edge limit. In the second part, results are presented of high β operation in low-B Double-Null (DN) X-point configurations with Be-gettered carbon target plates. The Troyon limit was reached during H-mode discharges and toroidal β values of 5.5% were obtained. At high beta, the sawteeth were modified and characterised by very rapid heat-waves and fishbone-like pre- and post-cursors with strongly ballooning character. 17 refs., 5 figs

On radiative density limits in stellarators

International Nuclear Information System (INIS)

Wobig, H.

2001-01-01

Density limits in stellarators are caused mainly by enhanced impurity radiation leading to a collapse of the temperature. A simple model can be established, which computes the temperature in the plasma with a fixed heating profile and a temperature-dependent radiation profile. If the temperature-dependent radiation function has one or several extrema, multiple solutions of the transport equation exist and radiative collapse occurs when the high temperature branch merges with the unstable temperature branch. At this bifurcation point the temperature decreases to a stable low temperature solution. The bifurcation point is a function of the heating power and the plasma density. Thus a density limit can be defined as the point where bifurcation occurs. It is shown that bifurcation and sudden temperature collapse does not occur below a power threshold. Anomalous thermal conductivity and the details of the impurity radiation, which in the present model is assumed to be in corona equilibrium, determine the scaling of the density limit. A model of the anomalous transport is developed, which leads to Gyro-Bohm scaling of the confinement time. The density limit based on this transport model is close to experimental findings in Wendelstein 7-AS. (author)

On the density limit of Tokamaks

International Nuclear Information System (INIS)

Lehnert, B.

1982-12-01

Under the conditions of so far performed quasi-steady tokamak experiments near the density limit, the plasma pressure gradient in the outer layers of the plasma body becomes mainly determined by the plasma-neutral gas balance. An earlier analysis of ballooning instabilities driven by this gradient in regions of bad curvature has been extended to deduce an explicit stability criterion which determines the density limit. This criterion is closely related to the empirical Murakami limit. At relevant tokamak data, the deduced limit becomes proportional to J(sub)zR(sup)1/2 where J(sub)z is the average current density and R the major plasma radius. It is further found to be independent of the toroidal magnetic field strength and anomalous transport, as well as to be a slow function of the outer layer temperature and the mass number. The deduced stability criterion is consistent with so far performed experiments. Provided that the present analysis can be extrapolated to a wider range of parameter data and be combined with Alcator scaling, conditions near ignition appear to become realizable in small tokamaks by ohmic heating alone. These conditions can be satisfied at relevant magnetic field strengths and plasma currents, by imposing a high plasma current density. (author)

Density limit in FTU tokamak during Ohmic operation

International Nuclear Information System (INIS)

Frigione, D.; Pieroni, L.

1993-01-01

The understanding of the physical mechanisms that regulate the density limit in a Tokamak is very important in view of a future fusion reactor. On one hand density enters as a factor in the figure of merit needed to achieve a burning plasma, and on the other hand a high edge density is a prerequisite for avoiding excessive erosion of the first walls and to limit the impurity influx into the hot plasma core. Furthermore a reactor should work in a safe zone of the operation parameters in order to avoid disruptive instabilities. The density limit problem has been tackled since the 70's, but so far a unique physics picture has not still emerged. In the last few years, due to the availability of better diagnostics, especially for the plasma edge, the use of pellet injectors to fuel the plasma and the experience gained on many different Tokamak, a consensus has been reached on the edge density as the real parameter responsible for the density limit. There are still two main mechanisms invoked to explain this limit: one refers to the power balance between the heat conducted and/or convected across the plasma radius and the power lost by impurity line radiation at the edge. When the latter overcomes the former, shrinking of the current channel occurs, which leads to instabilities due to tearing modes (usually the m/n=2/1) and then to disruption. The other explanation, for now valid for divertor machines, is based on the particle and energy balance in the scrape off layer (SOL). The limit in the edge density is then associated with the thermal collapse of the divertor plasma. In this work we describe the experiments on the density limit in FTU with Ohmic heating, the reason why we also believe that the limit is on the edge density, and discuss its relation to a simple model based on the SOL power balance valid for a limiter Tokamak. (author) 7 refs., 4 figs

Plasma interactions with the outboard chamber wall in DIII-D

International Nuclear Information System (INIS)

Rudakov, D.L.; Boedo, J.A.; Yu, J.H.; Brooks, N.H.; Fenstermacher, M.E.; Groth, M.; Hollmann, E.M.; Lasnier, C.J.; McLean, A.G.; Moyer, R.A.; Stangeby, P.C.; Tynan, G.R.; Wampler, W.R.; Watkins, J.G.; West, W.P.; Wong, C.P.C.; Bastasz, R.J.; Buchenauer, D.; Whaley, J.

2009-01-01

Erosion of the main chamber plasma-facing components is of concern for ITER. Plasma interaction with the outboard chamber wall is studied in DIII-D using Langmuir probes and optical diagnostics. Fast camera data shows that edge localized modes (ELMs) feature helical filamentary structures propagating towards the outboard wall. Upon reaching the wall, filaments result in regions of local intense plasma-material interaction (PMI) where peak incident particle and heat fluxes are up to two orders of magnitude higher than those between ELMs. In low density/collisionality H-mode discharges, PMI at the outboard wall is almost entirely due to ELMs. A moderate change of the gap between the separatrix and the outer wall strongly affects PMI intensity at the wall. Material samples exposed near the outboard wall showed net carbon deposition in high-density discharges (near the Greenwald limit) and tendency towards net erosion in lower density discharges (∼0.45 of the Greenwald limit).

Density and impurity profile behaviours in HL-2A tokamak with different gas fuelling methods

International Nuclear Information System (INIS)

Zheng-Ying, Cui; Yan, Zhou; Wei, Li; Bei-Bin, Feng; Ping, Sun; Chun-Feng, Dong; Yi, Liu; Wen-Yu, Hong; Qing-Wei, Yang; Xuan-Tong, Ding; Xu-Ru, Duan

2009-01-01

The electron density profile peaking and the impurity accumulation in the HL-2A tokamak plasma are observed when three kinds of fuelling methods are separately used at different fuelling particle locations. The density profile becomes more peaked when the line-averaged electron density approaches the Greenwald density limit n G and, consequently, impurity accumulation is often observed. A linear increase regime in the density range n e G and a saturation regime in n e > 0.6n G are obtained. There is no significant difference in achieved density peaking factor f ne between the supersonic molecular beam injection (SMBI) and gas puffing into the plasma main chamber. However, the achieved f ne is relatively low, in particular, in the case of density below 0.7n G , when the working gas is puffed into the divertor chamber. A discharge with a density as high as 1.2n G , i.e. n e = 1.2n G , can be achieved by SMBI just after siliconization as a wall conditioning. The metallic impurities, such as iron and chromium, also increase remarkably when the impurity accumulation happens. The mechanism behind the density peaking and impurity accumulation is studied by investigating both the density peaking factor versus the effective collisionality and the radiation peaking versus density peaking. (fluids, plasmas and electric discharges)

Modelling of density limit phenomena in toroidal helical plasmas

International Nuclear Information System (INIS)

Itoh, Kimitaka; Itoh, Sanae-I.

2001-01-01

The physics of density limit phenomena in toroidal helical plasmas based on an analytic point model of toroidal plasmas is discussed. The combined mechanism of the transport and radiation loss of energy is analyzed, and the achievable density is derived. A scaling law of the density limit is discussed. The dependence of the critical density on the heating power, magnetic field, plasma size and safety factor in the case of L-mode energy confinement is explained. The dynamic evolution of the plasma energy and radiation loss is discussed. Assuming a simple model of density evolution, of a sudden loss of density if the temperature becomes lower than critical value, then a limit cycle oscillation is shown to occur. A condition that divides the limit cycle oscillation and the complete radiation collapse is discussed. This model seems to explain the density limit oscillation that has been observed on the Wendelstein 7-AS (W7-AS) stellarator. (author)

Modelling of density limit phenomena in toroidal helical plasmas

International Nuclear Information System (INIS)

Itoh, K.; Itoh, S.-I.

2000-03-01

The physics of density limit phenomena in toroidal helical plasmas based on an analytic point model of toroidal plasmas is discussed. The combined mechanism of the transport and radiation loss of energy is analyzed, and the achievable density is derived. A scaling law of the density limit is discussed. The dependence of the critical density on the heating power, magnetic field, plasma size and safety factor in the case of L-mode energy confinement is explained. The dynamic evolution of the plasma energy and radiation loss is discussed. Assuming a simple model of density evolution, of a sudden loss of density if the temperature becomes lower than critical value, then a limit cycle oscillation is shown to occur. A condition that divides the limit cycle oscillation and the complete radiation collapse is discussed. This model seems to explain the density limit oscillation that has been observed on the W7-AS stellarator. (author)

Density limit studies in the large helical device

International Nuclear Information System (INIS)

Peterson, B.J.; Miyazawa, J.; Nishimura, K.

2005-01-01

Steady state densities of up to 1.6 x 10 20 m -3 have been sustained using gas puff fuelling and NBI heating up to 11 MW in the Large Helical Device (LHD). The density limit in LHD is observed to be ∼ 1.6 times the Sudo limit. The density is ultimately limited by radiative collapse which is attributed to the onset of a radiative thermal instability of the light impurities in the edge region of the plasma based on several observations. First of all the onset of the radiative thermal instability is tied to a certain edge temperature threshold. Secondly, the onset of thermal instability occurs first in oxygen and then carbon as expected from their cooling rate temperature dependencies. Finally, radiation profiles show that as the temperature drops and the plasma collapses the radiating zone broadens and moves inward. In addition, comparison with the total radiated power behaviour indicates that Carbon is the dominant radiator. Two dimensional tomographic inversions of AXUVD array data and comparison of modelling with images of radiation brightness from imaging bolometers and indicate that the poloidal asymmetry which accompanies the radiative collapse is toroidally symmetric. Ain addition to the operational density limit where the discharge is terminated by radiative collapse, a confinement limit has been recognized in LHD. This confinement limit appears at lower density than the operational density limit, similar to the saturated ohmic confinement observed in tokamaks. To investigate the physics behind this degradation, the parameter dependence of the thermal diffusivity, χ, has been investigated. While the temperature dependence in ISS95 is as strong as the gyro-Bohm model of χ ∝ T e 1.5 , weaker T e dependence of χ ∝ T e 0.5 appears in the high-density regime. Such weak T e dependence results in the weak density dependence of the global energy confinement as τ E ∝ n e 13 -bar. (author)

The density limit in Tokamaks

International Nuclear Information System (INIS)

Alladio, F.

1985-01-01

A short summary of the present status of experimental observations, theoretical ideas and understanding of the density limit in tokamaks is presented. It is the result of the discussion that was held on this topic at the 4th European Tokamak Workshop in Copenhagen (December 4th to 6th, 1985). 610 refs

Improved confinement with ion cyclotron hydrogen minority heating on Tore Supra

International Nuclear Information System (INIS)

Hoang, G.T.; Monier-Garbet, P.; Aniel, T.; Bourdelle, C.; Eriksson, L.G.; Garbet, X.; Grisolia, C.; Platz, P.; Budny, R.V.

1999-02-01

Tore Supra experiments are presently devoted to study the high density and high radiation regimes with radio frequency heating. Recent results of ion cyclotron minority heating have been obtained with an improved L-mode confinement, close to ELMy H-mode, at relatively high density (up to 80% of Greenwald limit). Such a regime is very promising as possible scenario in a next step tokamak. (authors)

Magnetohydrodynamic simulations of density-limit disruptions in tokamaks

International Nuclear Information System (INIS)

Kleva, R.G.; Drake, J.F.; Denton, R.E.

1990-01-01

Magnetohydrodynamic simulations are presented which demonstrate that density limit disruptions can be triggered by edge radiation which destabilizes a q = 1 kink followed by a q = 2 tearing mode. A bubble of cold plasma is injected from the edge into the center by the q = 1 kink. The q = 2 mode then broadens the current profile and throws the hot plasma to the wall. The MHD simulations presented are the first to successfully reproduce several key features of density limit disruptions including (1) the rapid drop in the central temperature, (2) the rapid expansion of the current profile, (3) the m = 1 cold bubble which is seen to be injected from the edge into the center during density limit disruptions on JET, and (4) disruptions in sawtoothing discharges. (author)

Scalings of energy confinement and density limit in stellarator/heliotron

International Nuclear Information System (INIS)

Sudo, S.; Takeiri, Y.; Zushi, H.; Sano, F.; Itoh, K.; Kondo, K.; Iiyoshi, A.

1989-04-01

Empirical scaling of energy confinement observed experimentally in stellarator/heliotron (Heliotron E, Wendelstein 7A, L2, Heliotron DR) under the condition that plasmas are heated by ECH and/or NbI is proposed. Empirical scaling of density limit obtainable under the optimum condition is proposed. These scalings are compared with those of tokamaks. The energy confinement scaling has similar power dependence as 'L mode scaling' of tokamaks. The density limit scaling seems also to indicate the upper limit of achievable density in many tokamaks. Combining the energy confinement time and the density limit scaling a transport-limited beta value is also deduced. Thus, from the viewpoint of designing a machine, there should be some compromise in determing magnetic field strength on plasma axis, average minor radius and major radius, because their dependence on confinement time and transport-limited beta value is contradicting. (J.P.N.)

Study of density limit in JT-60 joule heated plasmas

Energy Technology Data Exchange (ETDEWEB)

Shirai, Hiroshi; Shimizu, Katsuhiro; Takizuka, Tomonori; Hirayama, Toshio; Azumi, Masafumi [Japan Atomic Energy Research Inst., Naka, Ibaraki (Japan). Naka Fusion Research Establishment

1995-11-01

Impurities which mingle in tokamak plasmas cause dominant radiation loss in the high density regime and the energy balance of plasma is lost. This gives rise to MHD instability and results in major disruption. Density limit in joule heated plasmas has been studied by using one dimensional transport code combined with MHD instability analysis code. When the diffusion of impurity is taken into account, the numerically obtained density limit diagram or Hugill diagram quantitatively agrees well with that obtained in the experiment. It is also clarified that the corona-equilibrium model overestimates the density limit. (author).

Fast wave current drive above the slow wave density limit

International Nuclear Information System (INIS)

McWilliams, R.; Sheehan, D.P.; Wolf, N.S.; Edrich, D.

1989-01-01

Fast wave and slow wave current drive near the mean gyrofrequency were compared in the Irvine Torus using distinct phased array antennae of similar principal wavelengths, frequencies, and input powers. The slow wave current drive density limit was measured for 50ω ci ≤ω≤500ω ci and found to agree with trends in tokamaks. Fast wave current drive was observed at densities up to the operating limit of the torus, demonstrably above the slow wave density limit

Density limit study on the W7-AS stellarator

International Nuclear Information System (INIS)

Grigull, P.; Giannone, L.; Stroth, U.

1998-01-01

Data from currentless NBI discharges in W7-AS strongly indicate that the maximum density for quasi-stationary operation is limited by detachment from limiters. The threshold density at the edge scales with P s 0.5 B 0.8 (with P s being the net power flow across the LCMS) which is consistent with an edge based analytic estimation presuming constant threshold downstream temperatures. (author)

Murakami density limit in tokamaks and reversed-field pinches

International Nuclear Information System (INIS)

Perkins, F.W.; Hulse, R.A.

1984-03-01

A theoretical upper limit for the density in an ohmically heated tokamak discharge follows from the requirement that the ohmic heating power deposited in the central current-carrying channel exceed the impurity radiative cooling in this critical region. A compact summary of our results gives this limit n/sub M/ for the central density as n/sub M/ = [Z/sub e//(Z/sub e/-1]/sup 1/2/n/sub eo/ (B/sub T//1T)(1m/R) where n/sub eo/ depends strongly on the impurity species and is remarkably independent of the central electron temperature T/sub e/(0). For T/sub e/(0) approx. 1 keV, we have n/sub eo/ = 1.5 x 10 14 cm -3 for beryllium, n/sub eo/ = 5 x 10 13 cm -3 for oxygen, n/sub eo/ = 1.0 x 10 13 cm -3 for iron, and n/sub eo/ = 0.5 x 10 13 cm -3 for tungsten. The results agree quantitatively with Murakami's original observations. A similar density limit, known as the I/N limit, exists for reversed-field pinch devices and this limit has also been evaluated for a variety of impurity species

H-mode and confinement studies in ASDEX Upgrade

International Nuclear Information System (INIS)

Suttrop, W.; Ryter, F.; Mertens, V.; Gruber, O.; Murmann, H.; Salzmann, H.; Schweinzer, J.

2001-01-01

H-mode operational boundaries and H-mode confinement are investigated on ASDEX Upgrade. The local edge parameter threshold for H-mode holds independent of divertor geometry and changes little with ion mass. The deviation of the H-mode power threshold at densities near the Greenwald limit can be understood as a consequence of a confinement deterioration, caused by 'stiff' temperature profiles and lack of core density gradients in gas puff fuelled discharges. Ion and electron temperature profiles can be described by a lower limit of gradient length L T =T/T'. (author)

Density limits imposed by the microstructure of magnetic recording media

International Nuclear Information System (INIS)

Richter, H.J.

2009-01-01

The fundamental limit of magnetic recording density on conventional media is set by the grain size. Once this grain size limit is reached, only a reduction of the grain size allows an increased SNR and thus an increased areal density. It is shown that, whilst maintaining thermal stability, scaling demands that the required anisotropy energy density K is proportional to the areal density, or the square of the areal density if the medium thickness reaches the critical thickness 4√(A/K) (A is the exchange stiffness of the material). Recording onto materials with such a high anisotropy requires some form of a write-assist. It is furthermore shown that the grain size limit cannot be obtained with intergranular exchange present, and six different requirements are listed that constitute ideal media. An alternative path for increasing areal density of magnetic recording is to use patterned media, where each bit contains only one grain. In this case, written-in errors dominate system performance and the maximum achievable areal density is estimated to be about 6 Tbit/in 2 . Patterned media need to exhibit narrow distributions of their physical and structural properties with standard deviations of the order of 5% or less

Prediction of density limit disruptions on the J-TEXT tokamak

International Nuclear Information System (INIS)

Wang, S Y; Chen, Z Y; Huang, D W; Tong, R H; Yan, W; Wei, Y N; Ma, T K; Zhang, M; Zhuang, G

2016-01-01

Disruption mitigation is essential for the next generation of tokamaks. The prediction of plasma disruption is the key to disruption mitigation. A neural network combining eight input signals has been developed to predict the density limit disruptions on the J-TEXT tokamak. An optimized training method has been proposed which has improved the prediction performance. The network obtained has been tested on 64 disruption shots and 205 non-disruption shots. A successful alarm rate of 82.8% with a false alarm rate of 12.3% can be achieved at 4.8 ms prior to the current spike of the disruption. It indicates that more physical parameters than the current physical scaling should be considered for predicting the density limit. It was also found that the critical density for disruption can be predicted several tens of milliseconds in advance in most cases. Furthermore, if the network is used for real-time density feedback control, more than 95% of the density limit disruptions can be avoided by setting a proper threshold. (paper)

Transport simulations of a density limit in radiation-dominated tokamak discharges: II

International Nuclear Information System (INIS)

Stotler, D.P.

1991-05-01

The procedures developed previously to simulate the radiatively induced tokamak density limit are used to examine in more detail the scaling of the density limit. It is found that the maximum allowable density increases with auxiliary power and decreases with impurity concentration. However, it is demonstrated that there is little dependence of the density limit on plasma elongation. These trends are consistent with experimental results. Our previous work used coronal equilibrium impurities; the primary result of that paper was that the maximum density increases with current when peaked profiles are assumed. Here, this behavior is shown to occur with a coronal nonequilibrium impurity as well. 26 refs., 4 figs

Determining the Limiting Current Density of Vanadium Redox Flow Batteries

Directory of Open Access Journals (Sweden)

Jen-Yu Chen

2014-09-01

Full Text Available All-vanadium redox flow batteries (VRFBs are used as energy storage systems for intermittent renewable power sources. The performance of VRFBs depends on materials of key components and operating conditions, such as current density, electrolyte flow rate and electrolyte composition. Mass transfer overpotential is affected by the electrolyte flow rate and electrolyte composition, which is related to the limiting current density. In order to investigate the effect of operating conditions on mass transport overpotential, this study established a relationship between the limiting current density and operating conditions. First, electrolyte solutions with different states of charge were prepared and used for a single cell to obtain discharging polarization curves under various operating conditions. The experimental results were then analyzed and are discussed in this paper. Finally, this paper proposes a limiting current density as a function of operating conditions. The result helps predict the effect of operating condition on the cell performance in a mathematical model.

Limits on the space density of gamma-ray burst sources

International Nuclear Information System (INIS)

Epstein, R.I.

1985-01-01

Gamma-ray burst spectra which extend to several MeV without significant steepening indicate that there is negligible degradation due to two-photon pair production. The inferred low rate of photon-photon reactions is used to give upper limits to the distances to the sources and to the intensity of the radiation from the sources. These limits are calculated under the assumptions that the bursters are neutron stars which emit uncollimated gamma rays. The principal results are that the space density of the gamma-ray burst sources exceeds approx.10 -6 pc -3 if the entire surface of the neutron star radiates and exceeds approx.10 -3 pc -3 if only a small cap or thin strip in the stellar surface radiates. In the former case the density of gamma-ray bursters is approx.1% of the inferred density of extinct pulsars, and in the latter case the mean mass density of burster sources is a few percent of the density of unidentified dark matter in the solar neighborhood. In both cases the X-ray intensity of the sources is far below the Rayleigh-Jeans limit, and the total flux is at most comparable to the Eddington limit. This implies that low-energy self-absorption near 10 keV is entirely negligible and that radiation-driven explosions are just barely possible

Neutral iron densities in front of a reference limiter in TEXTOR

International Nuclear Information System (INIS)

Schweer, B.; Bay, H.L.

1983-09-01

Preliminary measurements of the time and space resolved densities of neutral iron in front of a reference limiter in Textor have been performed using laser induced fluorescence. The limiter was made of stainless steel (SS 316) and formed as a half sphere, 10 cm in diameter. Neutral iron densities up to 5 x 10 9 atoms/cm 3 were found. The detection limit was below 10 7 atoms/cm 3 . (orig.)

Hybrid neural network for density limit disruption prediction and avoidance on J-TEXT tokamak

Science.gov (United States)

Zheng, W.; Hu, F. R.; Zhang, M.; Chen, Z. Y.; Zhao, X. Q.; Wang, X. L.; Shi, P.; Zhang, X. L.; Zhang, X. Q.; Zhou, Y. N.; Wei, Y. N.; Pan, Y.; J-TEXT team

2018-05-01

Increasing the plasma density is one of the key methods in achieving an efficient fusion reaction. High-density operation is one of the hot topics in tokamak plasmas. Density limit disruptions remain an important issue for safe operation. An effective density limit disruption prediction and avoidance system is the key to avoid density limit disruptions for long pulse steady state operations. An artificial neural network has been developed for the prediction of density limit disruptions on the J-TEXT tokamak. The neural network has been improved from a simple multi-layer design to a hybrid two-stage structure. The first stage is a custom network which uses time series diagnostics as inputs to predict plasma density, and the second stage is a three-layer feedforward neural network to predict the probability of density limit disruptions. It is found that hybrid neural network structure, combined with radiation profile information as an input can significantly improve the prediction performance, especially the average warning time ({{T}warn} ). In particular, the {{T}warn} is eight times better than that in previous work (Wang et al 2016 Plasma Phys. Control. Fusion 58 055014) (from 5 ms to 40 ms). The success rate for density limit disruptive shots is above 90%, while, the false alarm rate for other shots is below 10%. Based on the density limit disruption prediction system and the real-time density feedback control system, the on-line density limit disruption avoidance system has been implemented on the J-TEXT tokamak.

Impurity screening in high density plasmas in tokamaks with a limiter configuration

International Nuclear Information System (INIS)

Ferro, C.; Zanino, R.

1992-01-01

Impurity screening in high density plasmas in tokamaks with a limiter configuration is investigated by means of a simple semi-analytical model. An iterative scheme is devised, in order to determine self-consistently the values of scrape-off layer thickness, edge electron density and temperature, and main plasma contamination parameter Z eff , as a function of given average electron density and temperature in the main plasma and given input power. The model is applied to the poloidal limiter case of the Frascati Tokamak Upgrade, and results are compared with experimental data. A reasonable agreement between the trends is found, emphasizing the importance of a high edge plasma density for obtaining a clean main plasma in limiter tokamaks. (orig.)

Orbitally limited pair-density-wave phase of multilayer superconductors

Science.gov (United States)

Möckli, David; Yanase, Youichi; Sigrist, Manfred

2018-04-01

We investigate the magnetic field dependence of an ideal superconducting vortex lattice in the parity-mixed pair-density-wave phase of multilayer superconductors within a circular cell Ginzburg-Landau approach. In multilayer systems, due to local inversion symmetry breaking, a Rashba spin-orbit coupling is induced at the outer layers. This combined with a perpendicular paramagnetic (Pauli) limiting magnetic field stabilizes a staggered layer dependent pair-density-wave phase in the superconducting singlet channel. The high-field pair-density-wave phase is separated from the low-field BCS phase by a first-order phase transition. The motivating guiding question in this paper is: What is the minimal necessary Maki parameter αM for the appearance of the pair-density-wave phase of a superconducting trilayer system? To address this problem we generalize the circular cell method for the regular flux-line lattice of a type-II superconductor to include paramagnetic depairing effects. Then, we apply the model to the trilayer system, where each of the layers are characterized by Ginzburg-Landau parameter κ0 and a Maki parameter αM. We find that when the spin-orbit Rashba interaction compares to the superconducting condensation energy, the orbitally limited pair-density-wave phase stabilizes for Maki parameters αM>10 .

Limit cycle analysis of nuclear coupled density wave oscillations

International Nuclear Information System (INIS)

Ward, M.E.

1985-01-01

An investigation of limit cycle behavior for the nuclear-coupled density wave oscillation (NCDWO) in a boiling water reactor (BWR) was performed. A simplified nonlinear model of BWR core behavior was developed using a two-region flow channel representation, coupled with a form of the point-kinetics equation. This model has been used to investigate the behavior of large amplitude NCDWO's through conventional time-integration solutions and through application of a direct relaxation-oscillation limit cycle solution in phase space. The numerical solutions demonstrate the potential for severe global power and flow oscillations in a BWR core at off-normal conditions, such as might occur during Anticipated Transients without Scram. Because of the many simplifying assumptions used, it is felt that the results should not be interpreted as an absolute prediction of core behavior, but as an indication of the potential for large oscillations and a demonstration of the corresponding limit cycle mechanisms. The oscillations in channel density drive the core power variations, and are reinforced by heat flux variations due to the changing fuel temperature. A global temperature increase occurs as energy is accumulated in the fuel, and limits the magnitude of the oscillations because as the average channel density decreases, the amplitude and duration of positive void reactivity at a given oscillation amplitude is lessened

Radiation power profiles and density limit with a divertor in the W7-AS stellarator

International Nuclear Information System (INIS)

Giannone, L.; Burhenn, R.; McCormick, K.; Brakel, R.; Feng, Y.; Grigull, P.; Igitkhanov, Y.

2002-01-01

The addition of a divertor into the W7-AS stellarator has allowed access to a high density regime where the radiation profiles reach a steady state. In earlier limiter discharges, the plasma suffered a radiative collapse at high densities. In contrast to limiter experiments, where the impurity confinement time measured by Al laser blow-off increased with increasing line integrated density, in divertor discharges, above a density threshold, the impurity confinement time decreased with increasing line integrated density. The observation that the divertor plasma radiates mainly at the plasma edge rather than the plasma centre is a further indication that changes to the impurity transport coefficients at these high densities are the basis for the achievement of steady state discharges in the divertor configuration of W7-AS. The maximum line integrated density reached with a divertor is compared to that reached with a limiter. The previously derived scaling law for the density limit with a limiter shows that the achieved densities do not exceed those predicted when the higher deposited power is taken into account. In a divertor the radiated power is located at the plasma edge and increasing the density, cooling the plasma edge and radiating sufficient power to cause plasma detachment determines the density limit. (author)

47 CFR 25.208 - Power flux density limits.

Science.gov (United States)

2010-10-01

... 47 Telecommunication 2 2010-10-01 2010-10-01 false Power flux density limits. 25.208 Section 25.208 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON CARRIER SERVICES SATELLITE... emissions from all co-frequency space stations of a single non-geostationary-satellite orbit (NGSO) system...

High Confinement and High Density with Stationary Plasma Energy and Strong Edge Radiation Cooling in Textor-94

Science.gov (United States)

Messiaen, A. M.

1996-11-01

A new discharge regime has been observed on the pumped limiter tokamak TEXTOR-94 in the presence of strong radiation cooling and for different scenarii of additional hearing. The radiated power fraction (up to 90%) is feedback controlled by the amount of Ne seeded in the edge. This regime meets many of the necessary conditions for a future fusion reactor. Energy confinement increases with increasing densities (reminiscent of the Z-mode obtained at ISX-B) and as good as ELM-free H-mode confinement (enhancement factor verus ITERH93-P up to 1.2) is obtained at high densities (up to 1.2 times the Greenwald limit) with peaked density profiles showing a peaking factor of about 2 and central density values around 10^14cm-3. In experiments where the energy content of the discharges is kept constant with an energy feedback loop acting on the amount of ICRH power, stable and stationary discharges are obtained for intervals of more than 5s, i.e. 100 times the energy confinement time or about equal to the skin resistive time, even with the cylindrical q_α as low as 2.8 β-values up to the β-limits of TEXTOR-94 are achieved (i.e. β n ≈ 2 of and β p ≈ 1.5) and the figure of merit for ignition margin f_Hqa in these discharges can be as high as 0.7. No detrimental effects of the seeded impurity on the reactivity of the plasma are observed. He removal in these discharges has also been investigated. [1] Laboratoire de Physique des Plasmas-Laboratorium voor Plasmafysica, Association "EURATOM-Belgian State", Ecole Royale Militaire-Koninklijke Militaire School, Brussels, Belgium [2] Institut für Plasmaphysik, Forschungszentrum Jülich, GmbH, Association "EURATOM-KFA", Jülich, Germany [3] Fusion Energy Research Program, Mechanical Engineering Division, University of California at San Diego, La Jolla, USA [4] FOM Institüt voor Plasmafysica Rijnhuizen, Associatie "FOM-EURATOM", Nieuwegein, The Netherlands [*] Researcher at NFSR, Belgium itemize

Density as a factor limiting the workability of P/M materials

International Nuclear Information System (INIS)

Libura, W.; Zasadzinski, J.

1993-01-01

In this study a general scheme expressing the factors which affect a workability of powder materials is presented. It was found from laboratory experiments that workability of powder metal materials is limited by their density. Aluminium based materials with additions of Cu, Ni and Sn were used in the experiments. Workability determined in compression tests depends strongly on a sintered density, independently of the chemical composition of material. A linear dependence between workability and sintered density was found. The results are related to relatively high density values, taken from the range of 0.85-0.96 of theoretical density. (orig.)

Effect of neutral particles on density limits in tokamaks

International Nuclear Information System (INIS)

Abramov, V.A.; Morozov, D.Kh.; Bachmann, P.; Suender, D.

1993-01-01

The global stability and confinement of a tokamak plasma are significantly influenced by the boundary plasma parameters. The onset of density disruptions, which limit the maximum plasma density, is triggered by impurity radiation in the edge plasma and can be connected with the radiative thermal instability. At the density n c the total radiative power P rad is equal to the total input power P in into the plasma (S:=P rad /P in =1). Above n c (S>1) no steady state of the plasma column exists. Contrary to predictions made elsewhere, where neutral particle kinetics is not taken into consideration, experimental results show that disruptions can occur for S R as a function of the plasma temperature T, ξ N :=N/n and ξ i :=n i /n, where N, n i , n are the densities of hydrogen atoms, impurity ions and the plasma, respectively. We investigate the influence of the neutral particles on the critical densities and the stability of the system, taking into account ionization, charge exchange and impurity cooling. (author) 6 refs., 3 figs

An H minority heating regime in Tore Supra showing improved L mode confinement

International Nuclear Information System (INIS)

Hoang, G.T.; Monier-Garbet, P.; Aniel, T.

2000-01-01

Tore Supra experiments are at present devoted to the study of high density regimes with radiofrequency heating. Recently, an improved L mode confinement regime has been observed in plasmas heated by ion cyclotron hydrogen minority heating, at relatively high densities up to 80% of the Greenwald limit. The quality of energy confinement is as good as that of ELMy H mode. The main physical mechanism of this regime has not been clearly identified. However, some features very similar to those of previous improved confinement modes using neutral beam heating in other tokamaks have been observed. (author)

The effects of density dependent resource limitation on size of wild reindeer.

Science.gov (United States)

Skogland, Terje

1983-11-01

A density-dependent decrement in size for wild reindeer from 12 different Norwegian herds at 16 different densities was shown using lower jawbone-length as the criterion of size. This criterion was tested and found to adequately predict body size of both bucks and does. Lactation in does did not affect jaw length but significantly affected dressed weights.A decrement in the size of does as a result of gross density was found. This size decrement was further analysed in relation to the habitat densities in winter (R 2 =0.85) and in summer (R 2 =0.75) separately, in order to estimate the relative effects of each factor. For herds with adequate food in winter (no signs of overgrazing of lichens) density in relation to summer habitat and mires yielded the highest predictive power in a multiple regression. For herds with adequate summer pastures, densities per winter habitat and lichen volumes showed likewise a highly significant correlation. The inclusion of the lichen volume data in the regression increased its predictive power. The major effect of resource limitation was to delay the time of calving because a maternal carry-over effect allowed the calf a shorter period of growth to be completed during its first summer. Neonate size at birth was highly correlated with maternal size regardless of the mean calving date although the latter was significantly delayed for small-sized does in food resource-limited herds. Likewise the postnatal growth rate of all calves were not significantly different during 50 days postpartum regardless of maternal conditions in winter feeding. The summer growth rates of bucks ≧1 year did not vary significantly between herds. The age of maturity of food resource-limited does was delayed by one year and growth ceased after the initiation of reproduction. This shows that under conditions of limited resources the does with delayed births of calves allocated less energy to body growth simply because they had less time to replenish body

Limits on the transverse phase space density in the Fermilab Booster

International Nuclear Information System (INIS)

Ankenbrandt, C.; Holmes, S.D.

1987-09-01

Recent results on intensity and transverse density limitations in the Fermilab 8-GeV Booster are presented. The evidence suggests that the limits are set by incoherent space-charge effects at low energy. Data are interpreted in terms of the space-charge tune shift and possible means of improving performance further are discussed. 8 refs., 3 figs

How the climate limits the wood density of angiosperms

Science.gov (United States)

Choi, Jin Woo; Kim, Ho-Young

2017-11-01

Flowering trees have various types of wood structure to perform multiple functions under their environmental conditions. In addition to transporting water from the roots to the canopy and providing mechanical support, the structure should provide resistance to embolism to maintain soil-plant-atmosphere continuum. By investigating existing data of the resistivity to embolism and wood density of 165 angiosperm species, here we show that the climate can limit the intrinsic properties of trees. Trees living in the dry environments require a high wood density to slow down the pressure decrease as it loses water relatively fast by evaporation. However, building too much tissues will result in the decrease of hydraulic conductivity and moisture concentration around mesophyll cells. To rationalize the biologically observed lower bound of the wood density, we construct a mechanical model to predict the wood density as a function of the vulnerability to embolism and the time for the recovery. Also, we build an artificial system using hydrogel microchannels that can test the probability of embolism as a function of conduit distributions. Our theoretical prediction is shown to be consistent with the results obtained from the artificial system and the biological data.

Transition from Fowler-Nordheim field emission to space charge limited current density

International Nuclear Information System (INIS)

Feng, Y.; Verboncoeur, J. P.

2006-01-01

The Fowler-Nordheim law gives the current density extracted from a surface under strong fields, by treating the emission of electrons from a metal-vacuum interface in the presence of an electric field normal to the surface as a quantum mechanical tunneling process. Child's law predicts the maximum transmitted current density by considering the space charge effect. When the electric field becomes high enough, the emitted current density will be limited by Child's law. This work analyzes the transition of the transmitted current density from the Fowler-Nordheim law to Child's law space charge limit using a one-dimensional particle-in-cell code. Also studied is the response of the emission model to strong electric fields near the transition point. We find the transition without geometrical effort is smooth and much slower than reported previously [J. P. Barbour, W. W. Dolan, J. K. Trolan, E. E. Martin, and W. P. Dyke, Phys. Rev. 92, 45 (1953)]. We analyze the effects of geometric field enhancement and work function on the transition. Using our previous model for effective field enhancement [Y. Feng and J. P. Verboncoeur, Phys. Plasmas 12, 103301 (2005)], we find the geometric effect dominates, and enhancement β>10 can accelerate the approach to the space charge limit at practical electric field. A damped oscillation near the local plasma frequency is observed in the transient system response

Limitations in accurate electron density studies

International Nuclear Information System (INIS)

Wal, R. van der.

1982-01-01

Most of X-ray diffraction studies are devoted to the determination of three-dimensional crystal structures from the electron density distributions. In these cases the density distributions are described by the independent atom model (IAM model), which consists of a superposition of spherically averaged free atom densities, which are smeared by thermal vibrations. During the last few decades studies have been made into the deviations of the density distribution from the IAM model, which enables a study of the chemical binding between atoms. The total density can be described using pseudo-atom multipole models as a superposition of aspherical pseudo-atom densities. A fundamental problem is that the separation of this density into an IAM and a deformation part is not unique. This thesis considers the problem and besides deformation densities from X-ray diffraction also considers the corresponding deformation electric field and deformation potential. (C.F.)

Improvement of the density limit with an external helical field on JFT-2M tokamak

International Nuclear Information System (INIS)

Tamai, H.; Shoji, T.; Nagashima, K.; Miura, Y.; Yamauchi, T.; Ogawa, H.; Kawashima, H.; Matsuda, T.; Mori, M.; Ida, K.; Ohdachi, S.

1995-01-01

The density limit is increased by the application of an external helical field in the JFT-2M tokamak. The effect of the magnetic stochasticity due to the external field is investigated to study the mechanism of the improved density limit related to the edge plasma behaviour. The improvement is correlated with the retardation of the increase in the plasma inductance. At the improved density limit, local radiation loss is modified by the helical field, in which that from the vicinity of separatrix X-point is remarkably reduced, while that from outboard edge is slightly increased. The formation of a positive radial electric field at the plasma edge is also observed in the presence of the helical field. ((orig.))

Prediction of density limits in tokamaks: Theory, comparison with experiment, and application to the proposed Fusion Ignition Research Experiment

International Nuclear Information System (INIS)

Stacey, Weston M.

2002-01-01

A framework for the predictive calculation of density limits in future tokamaks is proposed. Theoretical models for different density limit phenomena are summarized, and the requirements for additional models are identified. These theoretical density limit models have been incorporated into a relatively simple, but phenomenologically comprehensive, integrated numerical calculation of the core, edge, and divertor plasmas and of the recycling neutrals, in order to obtain plasma parameters needed for the evaluation of the theoretical models. A comparison of these theoretical predictions with observed density limits in current experiments is summarized. A model for the calculation of edge pedestal parameters, which is needed in order to apply the density limit predictions to future tokamaks, is summarized. An application to predict the proximity to density limits and the edge pedestal parameters of the proposed Fusion Ignition Research Experiment is described

The control of plasma density profile in Tore Supra. Comparison of different fueling techniques

International Nuclear Information System (INIS)

Commaux, N.

2007-09-01

The behaviour of a reactor-class plasma when fuelled using the existing techniques (gas puffing, supersonic molecular beam injection and pellet injection) is still very difficult to foresee. The present work has been initiated on Tore Supra in order to extrapolate the consequences of the different fuelling systems on ITER. Two main topics have been studied: the comparison of the plasma behaviour when fuelled using the different techniques at high Greenwald density fractions and the study of the homogenization following a pellet injection (main fuelling technique for ITER burning plasmas). The experiments at high Greenwald density fractions performed on Tore Supra showed that the plasma behaviour is very dependent on the fuelling method. The plasma energy confinement is following the scaling laws determined at low density when fuelled using pellet injection. which is better than for gas puffing and SMBI. both inducing a significant confinement loss. This behaviour is nor related to a transport modification: the ratio between effective diffusion and convection is similar to the pellet case. The difference between these shots is related only to the position of the matter source (at the edge for gas and close to the center for pellets). The study concerning the homogenization phenomena following a pellet injection aims mainly to study the ∇B-drift effect that expels the mater deposited by a pellet toward the low field side. A new phenomenon. which appears to be particularly important for the ∇B-drift during low field side injections. was then discovered: the influence of magnetic surfaces with an integer-valued safety factor (q). When the mater drifting toward low field side crosses an integer q surface. it experiences an important braking effect which stops the drift motion. It implies that the pellet material is mainly deposited on the last integer q surface crossed by the pellet during its injection. This study allows also to determine that the �

Particle balance under global wall saturation in long-pulse discharges of JT-60U

International Nuclear Information System (INIS)

Nakano, T.; Asakura, N.; Takenaga, H.; Kubo, H.; Shimizu, K.; Kawashima, H.

2007-01-01

During 30s-ELMy H-mode discharges, the wall-pumping rate decreases with a decay constant of several seconds and then becomes constant. During the constant wall-pumping phase, in discharges with a density of 65% of the Greenwald density, the wall-pumping rate is negative, in other words, outgassing. It has been found that this outgassing rate correlates with an increase in the tile temperature around the outer strike point. In discharges with a density of 80% of the Greenwald density, the wall-pumping rate is positive. Unless a high net deposition rate (>60%) of hydrocarbon is assumed, the positive wall-pumping rate cannot be explained only by the co-deposition of deuterium with carbon even if the outgassing rate is assumed to be zero. The vessel deuterium inventory decreases by 1.1 x 10 24 on one experimental day with 17 long discharges. The main chamber wall is suggested as the deuterium source for the decrease of the inventory

Calculation of the effects of pumping, divertor configuration and fueling on density limit in a tokamak model problem

International Nuclear Information System (INIS)

Stacey, W. M.

2001-01-01

Several series of model problem calculations have been performed to investigate the predicted effect of pumping, divertor configuration and fueling on the maximum achievable density in diverted tokamaks. Density limitations due to thermal instabilities (confinement degradation and multifaceted axisymmetric radiation from the edge) and to divertor choking are considered. For gas fueling the maximum achievable density is relatively insensitive to pumping (on or off), to the divertor configuration (open or closed), or to the location of the gas injection, although the gas fueling rate required to achieve this maximum achievable density is quite sensitive to these choices. Thermal instabilities are predicted to limit the density at lower values than divertor choking. Higher-density limits are predicted for pellet injection than for gas fueling

Spatial distribution of limited resources and local density regulation in juvenile Atlantic salmon.

Science.gov (United States)

Finstad, Anders G; Einum, Sigurd; Ugedal, Ola; Forseth, Torbjørn

2009-01-01

1. Spatial heterogeneity of resources may influence competition among individuals and thus have a fundamental role in shaping population dynamics and carrying capacity. In the present study, we identify shelter opportunities as a limiting resource for juvenile Atlantic salmon (Salmo salar L.). Experimental and field studies are combined in order to demonstrate how the spatial distribution of shelters may influence population dynamics on both within and among population scales. 2. In closed experimental streams, fish performance scaled negatively with decreasing shelter availability and increasing densities. In contrast, the fish in open stream channels dispersed according to shelter availability and performance of fish remaining in the streams did not depend on initial density or shelters. 3. The field study confirmed that spatial variation in densities of 1-year-old juveniles was governed both by initial recruit density and shelter availability. Strength of density-dependent population regulation, measured as carrying capacity, increased with decreasing number of shelters. 4. Nine rivers were surveyed for spatial variation in shelter availability and increased shelter heterogeneity tended to decrease maximum observed population size (measured using catch statistics of adult salmon as a proxy). 5. Our studies highlight the importance of small-scale within-population spatial structure in population dynamics and demonstrate that not only the absolute amount of limiting resources but also their spatial arrangement can be an important factor influencing population carrying capacity.

Bolometer tomography at the density limit of the HDH mode in the W7-AS stellarator

International Nuclear Information System (INIS)

Giannone, L; Brakel, R; Burhenn, R; Ehmler, H; Feng, Y; Grigull, P; McCormick, K; Wagner, F; Baldzuhn, J; Igitkhanov, Y; Knauer, J; Nishimura, K; Pasch, E; Peterson, B J; Ramasubramanian, N; Rust, N; Weller, A; Werner, A

2003-01-01

The installation of divertor plates in the W7-AS stellarator has allowed attainment of a high energy confinement regime at high density, where the radiation profiles reached steady state. In this regime, the radial profile of the radiated power is hollow. Raising the density to the point where the radiated power approached the input power led to plasma detachment and a decrease in diamagnetic energy. This defines the density limit in a stellarator and a scaling law for this maximum density can be heuristically derived on the basis of power balance considerations. The installation of two bolometer cameras away from the divertor plates and three bolometer cameras in the vicinity of the divertor plates has provided insight into the features of high density operation of a divertor in a stellarator. In the main chamber, tomographic inversion at the density limit has shown that a poloidally asymmetric radiation profile developed as the density limit was approached. In the divertor, radiation in front of the divertor plates occurred while the plasma was attached and this radiation zone vanished at plasma detachment. Steady state discharges of up to 1.5 s have been achieved for neutral beam injection power of up to 2 MW. A precursor to a spontaneous transition out of the high confinement regime has been identified

A new limit on the rate-density of evaporating black holes

International Nuclear Information System (INIS)

1993-01-01

Data taken with the CYGNUS detector between 1989 and 1993 have been used to search for 1 second bursts of ultra-high energy (UHE) gamma rays from any point in the northern sky. There is no evidence for such bursts. Therefore the theory-dependent upper limit on the rate-density of evaporating black holes is 6.1 x 10 5 pc -3 yr -1 at the 99% C.L.. After renormalizing previous direct searches to the same theory, this limit is the most restrictive by more than 2 orders of magnitude

Density limit and cross-field edge transport scaling in Alcator C-Mod

International Nuclear Information System (INIS)

LaBombard, B.; Greenwald, M.; Hughes, J.W.; Lipschultz, B.; Mossessian, D.; Terry, J.L.; Boivin, R.L.; Carreras, B.A.; Pitcher, C.S.; Zweben, S.J.

2003-01-01

Recent experiments in Alcator C-Mod have uncovered a direct link between the character and scaling of cross-field particle transport in the edge plasma and the density limit, n G . As n-bar e /n G is increased from low values to values approaching ∼1, an ordered progression in the cross-field edge transport physics occurs: first benign cross-field heat convection, then cross-field heat convection impacting the scrape-off layer (SOL) power loss channels and reducing the separatrix electron temperature, and finally 'bursty' transport (normally associated with the far SOL) invading into closed flux surface regions and carrying a convective power loss that impacts the power balance of the discharge. These observations suggest that SOL transport and its scaling with plasma conditions plays a key role in setting the empirically observed density limit scaling law. (author)

Transport simulations of a density limit in radiation-dominated tokamak discharges: Profile effects

International Nuclear Information System (INIS)

Stotler, D.P.

1988-06-01

The density limit observed in tokamak experiments is thought to be due to a radiative collapse of the current channel. A transport code coupled with an MHD equilibrium routine is used to determine the detailed, self-consistent evolution of the plasma profiles in tokamak discharges with radiated power close to or equalling the input power. The present work is confined to ohmic discharges in steady state. It is found that the shape of the density profile can have a significant impact on the variation of the maximum electron density with plasma current. Analytic calculations confirm this result. 41 refs., 9 figs

Transport simulations of a density limit in radiation-dominated tokamak discharges: profile effects

International Nuclear Information System (INIS)

Stotler, D.P.

1988-01-01

The density limit observed in tokamak experiments is thought to be due to a radiative collapse of the current channel. A transport code coupled with a magnetohydrodynamic (MHD) equilibrium routine is used to determine the detailed, self-consistent evolution of the plasma profiles in tokamak discharges with radiated power close to or equaling the input power. The present work is confined to Ohmic discharges in steady state. It is found that the shape of the density profile can have a significant impact on the variation of the maximum electron density with plasma current. Analytic calculations confirm this result

Patient dose rate: An ultimate limit for spatial and density resolution of scanning systems

International Nuclear Information System (INIS)

Kowalski, G.; Wagner, W.

1979-01-01

In X-ray scanning systems, picture quality of the reconstructed slices is limited to a maximum spatial as well as density resolution by the applied radiation dose. Density resolution can be improved in proportion to the root of the patient dose, whereas a doubled spatial resolving power requires an eight times higher patient dose, assuming a fixed slice thickness. Only a careful trade-off between the applied patient dose, density resolution and spatial resolution yields a maximal diagnostic value for the physician. Specifications of a scanning system have to take into account these ultimate restrictions, so that picture quality really is limited by the patient's dose rather than by technical constraints. In addition a method is given by which the applied dose can be reduced by focusing the main intensity onto the region of interest, in case that region is known a priori. (orig.) [de

High-density limit of quantum chromodynamics

International Nuclear Information System (INIS)

Alvarez, E.

1983-01-01

By means of a formal expansion of the partition function presumably valid at large baryon densities, the propagator of the quarks is expressed in terms of the gluon propagator. This result is interpreted as implying that correlations between quarks and gluons are unimportant at high enough density, so that a kind of mean-field approximation gives a very accurate description of the physical system

Transition from order to chaos, and density limit, in magnetized plasmas.

Science.gov (United States)

Carati, A; Zuin, M; Maiocchi, A; Marino, M; Martines, E; Galgani, L

2012-09-01

It is known that a plasma in a magnetic field, conceived microscopically as a system of point charges, can exist in a magnetized state, and thus remain confined, inasmuch as it is in an ordered state of motion, with the charged particles performing gyrational motions transverse to the field. Here, we give an estimate of a threshold, beyond which transverse motions become chaotic, the electrons being unable to perform even one gyration, so that a breakdown should occur, with complete loss of confinement. The estimate is obtained by the methods of perturbation theory, taking as perturbing force acting on each electron that due to the so-called microfield, i.e., the electric field produced by all the other charges. We first obtain a general relation for the threshold, which involves the fluctuations of the microfield. Then, taking for such fluctuations, the formula given by Iglesias, Lebowitz, and MacGowan for the model of a one component plasma with neutralizing background, we obtain a definite formula for the threshold, which corresponds to a density limit increasing as the square of the imposed magnetic field. Such a theoretical density limit is found to fit pretty well the empirical data for collapses of fusion machines.

Breakdown of quasiparticle picture in the low-density limit of the 1D Hubbard model

International Nuclear Information System (INIS)

Qin Shaojin; Qian Tiezheng; Su Zhaobin

1995-03-01

Using the finite-size scaling of results obtained by exact diagonalization, we study the low-density limit of the one-dimensional Hubbard model. Calculating the quasiparticle weight, we demonstrate that for a given particle number N and system size L, there always exists a crossover point U c separating the Fermi-liquid (U c ) and non-Fermi-liquid (U > U c ) regimes (U is the Hubbard repulsion). We find that for a fixed N, U c is inversely proportional to L, keeping U c L/t constant (with t as the hopping integral), as L is large enough. It follows that in the low-density (in fact vanishing density) limit L → ∞, U c → 0, so the system is always in non-Fermi-liquid regime as long as U > 0. We show that our numerical results are consistent with the Bethe ansatz solution. (author). 11 refs, 3 figs

Latent Profiles of Macronutrient Density and their Association with Mobility Limitations in an Observational Longitudinal Study of Older U.S. Adults.

Science.gov (United States)

Bishop, N J; Zuniga, K E; Lucht, A L

2018-01-01

Our first objective was to estimate empirically-derived subgroups (latent profiles) of observed carbohydrate, protein, and fat intake density in a nationally representative sample of older U.S. adults. Our second objective was to determine whether membership in these groups was associated with levels of, and short term change in, physical mobility limitations. Measures of macronutrient density were taken from the 2013 Health Care and Nutrition Study, an off-year supplement to the Health and Retirement Study, which provided indicators of physical mobility limitations and sociodemographic and health-related covariates. 3,914 community-dwelling adults age 65 years and older. Percent of daily calories from carbohydrate, protein, and fat were calculated based on responses to a modified Harvard food frequency questionnaire. Latent profile analysis was used to describe unobserved heterogeneity in measures of carbohydrate, protein, and fat density. Mobility limitation counts were based on responses to 11 items indicating physical limitations. Poisson regression models with autoregressive controls were used to identify associations between macronutrient density profile membership and mobility limitations. Sociodemographic and health-related covariates were included in all Poisson regression models. Four latent subgroups of macronutrient density were identified: "High Carbohydrate", "Moderate with Fat", "Moderate", and "Low Carbohydrate/High Fat". Older adults with the lowest percentage of daily calories coming from carbohydrate and the greatest percentage coming from fat ("Low Carbohydrate/High Fat") were found to have greater reported mobility limitations in 2014 than those identified as having moderate macronutrient density, and more rapid two-year increases in mobility limitations than those identified as "Moderate with Fat" or "Moderate". Older adults identified as having the lowest carbohydrate and highest fat energy density were more likely to report a greater number

Induced critical current density limit of Ag sheathed Bi-2223 tape conductor

International Nuclear Information System (INIS)

Ogiwara, H.; Satou, M.; Yamada, Y.; Kitamura, T.; Hasegawa, T.

1994-01-01

The authors have already reported the best critical current density of 66,000 A/cm 2 with an Ag sheathed Bi-2223 tape conductor. The Brick-wall model is for explaining the current transport mechanism of this conductor. The model has its roots in the fact that the Bi-2223 tape core is a complicated stack of crystals which have a mica-flake structure. The orientation of the crystals which have a mica-flake structure. The orientation of the crystals seriously affects the current transport capability. Moreover, the contacts between the stacking crystals are very important. The transport current flows dividing into many branch paths. Under high magnetic field, the different paths experienced different electromagnetic forces. Differences between the electromagnetic forces on the different crystals can affect the contacts so as to increase resistivity and decrease overall critical current density of the tape. This effect can foretell the limit of the critical current density obtainable with these kinds of conductors

Spherically symmetric solutions, Newton's Law, and the infrared limit λ→1 in covariant Horava-Lifshitz gravity

International Nuclear Information System (INIS)

Alexandre, Jean; Pasipoularides, Pavlos

2011-01-01

In this note we examine whether spherically symmetric solutions in covariant Horava-Lifshitz gravity can reproduce Newton's Law in the IR limit λ→1. We adopt the position that the auxiliary field A is independent of the space-time metric [J. Alexandre and P. Pasipoularides, Phys. Rev. D 83, 084030 (2011).][J. Greenwald, V. H. Satheeshkumar, and A. Wang, J. Cosmol. Astropart. Phys. 12 (2010) 007.], and we assume, as in [A. M. da Silva, Classical Quantum Gravity 28, 055011 (2011).], that λ is a running coupling constant. We show that under these assumptions, spherically symmetric solutions fail to restore the standard Newtonian physics in the IR limit λ→1, unless λ does not run, and has the fixed value λ=1. Finally, we comment on the Horava and Melby-Thompson approach [P. Horava and C. M. Melby-Thompson, Phys. Rev. D 82, 064027 (2010).] in which A is assumed as a part of the space-time metric in the IR.

Energy density and rate limitations in structural composite supercapacitors

Science.gov (United States)

Snyder, J. F.; Gienger, E.; Wetzel, E. D.; Xu, K.

2012-06-01

The weight and volume of conventional energy storage technologies greatly limits their performance in mobile platforms. Traditional research efforts target improvements in energy density to reduce device size and mass. Enabling a device to perform additional functions, such as bearing mechanical load, is an alternative approach as long as the total mass efficiency exceeds that of the individual materials it replaces. Our research focuses on structural composites that function as batteries and supercapacitors. These multifunctional devices could be used to replace conventional structural components, such as vehicle frame elements, to provide significant system-level weight reductions and extend mission times. Our approach is to design structural properties directly into the electrolyte and electrode materials. Solid polymer electrolyte materials bind the system and transfer load to the fibers while conducting ions between the electrodes. Carbon fiber electrodes provide a route towards optimizing both energy storage and load-bearing capabilities, and may also obviate the need for a separate current collector. The components are being integrated using scalable, cost-effective composite processing techniques that are amenable to complex part shapes. Practical considerations of energy density and rate behavior are described here as they relate to materials used. Our results highlight the viability as well as the challenges of this multifunctional approach towards energy storage.

Radiation control in fusion plasmas by magnetic confinement

International Nuclear Information System (INIS)

Dachicourt, R.

2012-10-01

The present work addresses two important issues for the industrial use of fusion: plasma radiation control, as a part of the more general power handling issue, and high density tokamak operation. These two issues will be most critical in the demonstration reactor, called DEMO, intermediate step between ITER and a future commercial reactor. For DEMO, the need to radiate a large fraction of the power so as to limit the peak power load on the divertor will be a key constraint. High confinement will have to be combined with high radiated power fraction, and the required level of plasma purity. The main achievement of this thesis is to have shown experimental evidence of the existence of a stable plasma regime meeting the most critical requirements of a DEMO scenario: an electron density up to 40% above the Greenwald value, together with a fraction of radiated power close to 80%, with a good energy confinement and limited dilution. The plasma is additionally heated with ion cyclotron waves in a central electron heating scenario, featuring alpha particle heating. The original observations reported in this work bring highly valuable new pieces of information both to the physics of the tokamak edge layer and to the construction of an 'integrated operational scenario' required to successfully operate fusion devices. In the way for getting high density plasmas, the new observations involve the following topics. First, the formation of a poloidal asymmetry in the edge electron density profile, with a maximum density located close to toroidal pumped limiter. This asymmetry occurs inside the separatrix, with a constant plasma pressure on magnetic surfaces. Secondly, a correlative decrease of the electron temperature in the same edge region. Thirdly, the excellent coupling capabilities of the ICRH waves, up to a central line averaged electron density of 1.4 times the Greenwald density. Fourthly, a poloidally asymmetric edge radiation region, providing the dissipation of 80% of

Parametric dependence of density limits in the Tokamak Experiment for Technology Oriented Research (TEXTOR): Comparison of thermal instability theory with experiment

International Nuclear Information System (INIS)

Kelly, F.A.; Stacey, W.M.; Rapp, J.

2001-01-01

The observed dependence of the TEXTOR [Tokamak Experiment for Technology Oriented Research: E. Hintz, P. Bogen, H. A. Claassen et al., Contributions to High Temperature Plasma Physics, edited by K. H. Spatschek and J. Uhlenbusch (Akademie Verlag, Berlin, 1994), p. 373] density limit on global parameters (I, B, P, etc.) and wall conditioning is compared with the predicted density limit parametric scaling of thermal instability theory. It is necessary first to relate the edge parameters of the thermal instability theory to n(bar sign) and the other global parameters. The observed parametric dependence of the density limit in TEXTOR is generally consistent with the predicted density limit scaling of thermal instability theory. The observed wall conditioning dependence of the density limit can be reconciled with the theory in terms of the radiative emissivity temperature dependence of different impurities in the plasma edge. The thermal instability theory also provides an explanation of why symmetric detachment precedes radiative collapse for most low power shots, while a multifaceted asymmetric radiation from the edge MARFE precedes detachment for most high power shots

Evaluation of Yield and Yield Components of Black Cumin (Nigella sativa L. under different Plant Density and Limited Irrigation Condition

Directory of Open Access Journals (Sweden)

Sh Rezvan Beidokhti

2012-10-01

Full Text Available Research on crop response to deficit irrigation is important to reduce agriculture water use in areas where water is limited resource. Using drought resistant landraces with irrigation scheduling based on phenological stages in semi-arid and arid regions may provide an opportunity to optimize irrigation efficiency and water savings in these regions. In order to evaluate of yield and yield components of black cumin under different plant density and limited irrigation condition an experiment was conducted in Research Farm of Islamic Azad University of Damghan during growing season of 2007-2008. The experimental treatments were arranged in split plots based on a complete randomized block design with three replications. The limited irrigation (based on phenological stages treatments were included: cutting irrigation at blooming (folded flowers, cutting irrigation at flowering stage, cutting irrigation at seed formation and normal weekly irrigation (control were allocated to the main plots and different plant density: 100, 150, 200 and 250 plant per square meter (m2 were allocated to sub plots. The results showed that the effect of limited irrigation, plant density and their interaction on plant height, number of follicle, follicle weight, number of seed, 1000 seed weight, seed yield, biological yield and harvest index Black Cumin. The highest yield and yield components was obtained in normal irrigation (control and 200 plant density and the lowest yield were obtained when irrigation cut at the blooming stage and 250 plant density. There was a significant correlation between seed yield and number (r=0.90, 1000 seed weight (r=0.95 and biological yield (r=0.97. Optimum plant density of black cumin was decreased under limited irrigation treatments. Under normal (control and limited irrigation, optimum plant density was 200 and 150 plant per (m2 respectively.

Numerical studies of the g-hartree density functional in the Thomas-Fermi scaling limit

International Nuclear Information System (INIS)

Millack, T.; Weymans, G.

1986-02-01

Methods of finite temperature quantum field theory are used to construct the g-Hartree density functional for atoms. Low and high temperature expansions are discussed in detail. Numerical studies for atomic ground-state configurations are presented in the Thomas-Fermi-Scaling limit. (orig.)

Densities mixture unfolding for data obtained from detectors with finite resolution and limited acceptance

Energy Technology Data Exchange (ETDEWEB)

Gagunashvili, N.D., E-mail: nikolai@unak.is

2015-04-01

A procedure based on a Mixture Density Model for correcting experimental data for distortions due to finite resolution and limited detector acceptance is presented. Addressing the case that the solution is known to be non-negative, in the approach presented here, the true distribution is estimated by a weighted sum of probability density functions with positive weights and with the width of the densities acting as a regularization parameter responsible for the smoothness of the result. To obtain better smoothing in less populated regions, the width parameter is chosen inversely proportional to the square root of the estimated density. Furthermore, the non-negative garrote method is used to find the most economic representation of the solution. Cross-validation is employed to determine the optimal values of the resolution and garrote parameters. The proposed approach is directly applicable to multidimensional problems. Numerical examples in one and two dimensions are presented to illustrate the procedure.

Mechanical coupling limits the density and quality of self-organized carbon nanotube growth

Science.gov (United States)

Bedewy, Mostafa; Hart, A. John

2013-03-01

Aligned carbon nanotube (CNT) structures are promising for many applications; however, as-grown CNT "forests" synthesized by chemical vapor deposition (CVD) are typically low-density and mostly comprise tortuous defective CNTs. Here, we present evidence that the density and alignment of self-organized CNT growth is limited by mechanical coupling among CNTs in contact, in combination with their diameter-dependent growth rates. This study is enabled by comprehensive X-ray characterization of the spatially and temporally-varying internal morphology of CNT forests. Based on this data, we model the time evolution and diameter-dependent scaling of the ensuing mechanical forces on catalyst nanoparticles during CNT growth, which arise from the mismatch between the collective lengthening rate of the forest and the diameter-dependent growth rates of individual CNTs. In addition to enabling self-organization of CNTs into forests, time-varying forces between CNTs in contact dictate the hierarchical tortuous morphology of CNT forests, and may be sufficient to influence the structural quality of CNTs. These forces reach a maximum that is coincident with the maximum density observed in our growth process, and are proportional to CNT diameter. Therefore, we propose that improved manufacturing strategies for self-organized CNTs should consider both chemical and mechanical effects. This may be especially necessary to achieve high density CNT forests with low defect density, such as for improved thermal interfaces and high-permeability membranes.Aligned carbon nanotube (CNT) structures are promising for many applications; however, as-grown CNT "forests" synthesized by chemical vapor deposition (CVD) are typically low-density and mostly comprise tortuous defective CNTs. Here, we present evidence that the density and alignment of self-organized CNT growth is limited by mechanical coupling among CNTs in contact, in combination with their diameter-dependent growth rates. This study is

INTOR rescaling for non-intended plasma shape applying preliminary scalings for energy confinement and density limit

International Nuclear Information System (INIS)

Knobloch, A.F.

1986-11-01

On the basis of a simplified rescaling procedure with INTOR, as of Phase IIA Part 1, serving as reference case, alternative design points are discussed that take into account more recent findings on β-limits, density limits and possible extrapolations with respect to plasma elongation. Two tentative scalings for the energy confinement time as derived from ASDEX results and by Goldston are applied to find minimum size INTOR alternatives, which, of course, could be quite different for the two scalings. Large plasma elongation is needed for getting close to the original outlay for INTOR. The density limit according to some possible scalings requires some adjustment of the plasma temperature to above 10 keV. The neutron wall load, being the important parameter with respect to the INTOR test programme, can be practically kept at the reference level. For ASDEX confinement scaling this requires that an ignition margin of about 2 be adhered to. A sensitivity study on the impact of individual modifications in input assumptions of the order of 10% shows that only a limited range of such alternatives remains acceptable. (orig.)

Topology and transport in the edge region of RFX-mod helical regimes

International Nuclear Information System (INIS)

Scarin, P.; Vianello, N.; Agostini, M.; Spizzo, G.; Spolaore, M.; Zuin, M.; Cappello, S.; Carraro, L.; Cavazzana, R.; De Masi, G.; Martines, E.; Moresco, M.; Munaretto, S.; Puiatti, M. E.; Valisa, M.

2011-01-01

New edge diagnostics and detailed analysis of magnetic topology have significantly improved the comprehension of the processes developing at the boundary of a reversed-field pinch (RFP) plasma in RFX-mod (a = 0.46 m, R = 2 m). An upper critical density n C ∼ 0.4 n G (n G Greenwald density) is found to limit the operational space for the improved quasi-single helical (QSH) regime: magnetic topology reconstructions and diagnostic observations suggest that this limit is due to a helical plasma-wall interaction which determines toroidally and poloidally localized edge density accumulation and cooling. The experimental evidence is provided by a variety of diagnostics: the magnetic boundary as reconstructed from equilibrium codes reveals a helical deformation, which is well correlated with the modulation of edge pressure profile as reconstructed from the thermal helium beam diagnostic. Correlations with the helical deformation are also observed on the space- and time-resolved patterns of the floating potential measured at the wall, and with the edge plasma flow, obtained from different diagnostics. The relevance of these findings is that understanding the mechanisms that limit the operational space of QSH is decisive in achieving the goal of high-density stationary helical RFP equilibrium.

Trapped Fermions with Density Imbalance in the Bose-Einstein Condensate Limit

International Nuclear Information System (INIS)

Pieri, P.; Strinati, G.C.

2006-01-01

We analyze the effects of imbalancing the populations of two-component trapped fermions, in the Bose-Einstein condensate limit of the attractive interaction between different fermions. Starting from the gap equation with two fermionic chemical potentials, we derive a set of coupled equations that describe composite bosons and excess fermions. We include in these equations the processes leading to the correct dimer-dimer and dimer-fermion scattering lengths. The coupled equations are then solved in the Thomas-Fermi approximation to obtain the density profiles for composite bosons and excess fermions, which are relevant to the recent experiments with trapped fermionic atoms

Compatibility of advanced tokamak plasma with high density and high radiation loss operation in JT-60U

International Nuclear Information System (INIS)

Takenaga, H.; Asakura, N.; Kubo, H.; Higashijima, S.; Konoshima, S.; Nakano, T.; Oyama, N.; Ide, S.; Fujita, T.; Takizuka, T.; Kamada, Y.; Miura, Y.; Porter, G.D.; Rognlien, T.D.; Rensink, M.E.

2005-01-01

Compatibility of advanced tokamak plasmas with high density and high radiation loss has been investigated in both reversed shear (RS) plasmas and high β p H-mode plasmas with a weak positive shear on JT-60U. In the RS plasmas, the operation regime is extended to high density above the Greenwald density (n GW ) with high confinement (HH y2 >1) and high radiation loss fraction (f rad >0.9) by tailoring the internal transport barriers (ITBs). High confinement of HH y2 =1.2 is sustained even with 80% radiation from the main plasma enhanced by accumulated metal impurity. The divertor radiation is enhanced by Ne seeding and the ratio of the divertor radiation to the total radiation is increased from 20% without seeding to 40% with Ne seeding. In the high β p H-mode plasmas, high confinement (HH y2 =0.96) is maintained at high density (n-bar e /n GW =0.92) with high radiation loss fraction (f rad ∼1) by utilizing high-field-side pellets and Ar injections. The high n-bar e /n GW is obtained due to a formation of clear density ITB. Strong core-edge parameter linkage is observed, as well as without Ar injection. In this linkage, the pedestal β p , defined as β p ped =p ped /(B p 2 /2μ 0 ) where p ped is the plasma pressure at the pedestal top, is enhanced with the total β p . The radiation profile in the main plasma is peaked due to Ar accumulation inside the ITB and the measured central radiation is ascribed to Ar. The impurity transport analyses indicate that Ar accumulation by a factor of 2 more than the electron, as observed in the high β p H-mode plasma, is acceptable even with peaked density profile in a fusion reactor for impurity seeding. (author)

New upper limits on the local metagalactic ionizing radiation density

Science.gov (United States)

Vogel, Stuart N.; Weymann, Ray; Rauch, Michael; Hamilton, Tom

1995-01-01

We have obtained H-alpha observations with the Maryland-Caltech Fabry-Perot Spectrometer attached to the Cassegrain focus of the 1.5 m telescope at Palomer Observatory in order to set limits on the number of ionizing photons from the local metagalactic radiation field. We have observed the SW component of the Haynes-Giovanelli cloud H I 1225+01, an intergalactic cloud which should be optimum for measuring the metagalactic flux because it is nearly opaque to ionizing photons, it does not appear to be significantly shielded from the metagalactic radiation field, and the limits on embedded or nearby ionizing sources are unusually low. For the area of the cloud with an H I column density greater than 10(exp 19)/sq cm we set a 2 sigma limit of 1.1 x 10(exp -19) ergs/sq cm/s/sq arcsec (20 mR) for the surface brightness of diffuse H-alpha. This implies a 2 sigma upper limit on the incident one-sided ionizing flux of Phi(sub ex) is less than 3 x 10(exp 4)/sq cm/s. For a radiation field of the form J(sub nu) is approximately nu(exp -1.4), this yields a firm 2 sigma upper limit on the local metagalactic photoionization rate of Gamma is less than 2 x 10(exp -13)/s, and an upper limit for the radiation field J(sub nu) at the Lyman limit of J(sub nu0) is less than 8 x 10(exp -23) ergs/sq cm/Hz/sr. We discuss previous efforts to constrain the metagalactic ionizing flux using H-alpha surface brightness observations and also other methods, and conclude that our result places the firmest upper limit on this flux. We also observed the 7 min diameter region centered on 3C 273 in which H-alpha emission at a velocity of approximately 1700 km/s was initially reported by Williams and Schommer. In agreement with T. B. Williams (private communication) we find the initial detection was spurious. We obtain a 2 sigma upper limit of 1.8 x 10(exp -19) ergs/sq cm/s/sq arcsec (32 mR) for the mean surface brightness of diffuse H-alpha, about a factor of 6 below the published value.

Operations space diagram for ECRH and ECCD

DEFF Research Database (Denmark)

Bindslev, H.

2004-01-01

at the design phase. At the operations phase it may also prove useful in setting up experimental scenarios by showing operational possibilities, avoiding the need for survey type ray-tracing at the initial planning stages. The diagram may also serve the purpose of communicating operational possibilities to non......A Clemmov-Mullaly-Allis (CMA) type diagram, the ECW-CMA diagram, for representing the operational possibilities of electron cyclotron heating and current drive (ECRH/ECCD) systems for fusion plasmas is presented. In this diagram, with normalized density and normalized magnetic field coordinates......, the parameter range in which it is possible to achieve a given task (e.g. O-mode current drive for stabilizing a neoclassical tearing mode) appears as a region. With also the Greenwald density limit shown, this diagram condenses the information on operational possibilities, facilitating the overview required...

Augmented potential, energy densities, and virial relations in the weak- and strong-interaction limits of DFT

Science.gov (United States)

Vuckovic, Stefan; Levy, Mel; Gori-Giorgi, Paola

2017-12-01

The augmented potential introduced by Levy and Zahariev [Phys. Rev. Lett. 113, 113002 (2014)] is shifted with respect to the standard exchange-correlation potential of the Kohn-Sham density functional theory by a density-dependent constant that makes the total energy become equal to the sum of the occupied orbital energies. In this work, we analyze several features of this approach, focusing on the limit of infinite coupling strength and studying the shift and the corresponding energy density at different correlation regimes. We present and discuss coordinate scaling properties of the augmented potential, study its connection to the response potential, and use the shift to analyze the classical jellium and uniform gas models. We also study other definitions of the energy densities in relation to the functional construction by local interpolations along the adiabatic connection. Our findings indicate that the energy density that is defined in terms of the electrostatic potential of the exchange-correlation hole is particularly well suited for this purpose.

Limited Angle Torque Motors Having High Torque Density, Used in Accurate Drive Systems

Directory of Open Access Journals (Sweden)

R. Obreja

2011-01-01

Full Text Available A torque motor is a special electric motor that is able to develop the highest possible torque in a certain volume. A torque motor usually has a pancake configuration, and is directly jointed to a drive system (without a gear box. A limited angle torque motor is a torque motor that has no rotary electromagnetic field — in certain papers it is referred to as a linear electromagnet. The main intention of the authors for this paper is to present a means for analyzing and designing a limited angle torque motor only through the finite element method. Users nowadays require very high-performance limited angle torque motors with high density torque. It is therefore necessary to develop the highest possible torque in a relatively small volume. A way to design such motors is by using numerical methods based on the finite element method.

Laboratory experiments on the magnetic field and neutral density limits on CIV interaction

International Nuclear Information System (INIS)

Axnaes, I.; Brenning, N.

1990-03-01

Laboratory experiments are reported which determine the magnetic field and neutral density limit for Critical Ionization Velocity (CIV) interaction in the impact configuration. A combination of microwave interferometry and spectroscopy has been used to measure how the electron energy distribution varies with the neutral density and the magnetic field strength. The efficiency of the CIV process is evaluated in terms of the efficiency factor η of energy transfer to the electron. This efficiency is studied as function of the ratio V A /V 0 between the Alfven velocity and the plasma stream velocity and the ratio ν i /ω gi between the ionization frequency and the ion gyro frequency. With other parameters kept constant, V A /V 0 is proportional to the square root of the magnetic field, while ν i /ω gi is proportional to the neutral density. We have found that these two dimensionless parameters are coupled in such a fashion that a stronger magnetic field can compensate for a lower neutral density. For our strongest magnetic field, corresponding to V A /V 0 = 4, CIV interaction is found to occur for a comparatively low value ν i /ω gi ∼ 0.1. For V A /V 0 = 1, we found a clear absence of CIV interaction even for ν i /ω gi approaching unity. (authors)

Resource Limitation, Controphic Ostracod Density and Larval Mosquito Development.

Directory of Open Access Journals (Sweden)

Raylea Rowbottom

Full Text Available Aquatic environments can be restricted with the amount of available food resources especially with changes to both abiotic and biotic conditions. Mosquito larvae, in particular, are sensitive to changes in food resources. Resource limitation through inter-, and intra-specific competition among mosquitoes are known to affect both their development and survival. However, much less is understood about the effects of non-culicid controphic competitors (species that share the same trophic level. To address this knowledge gap, we investigated and compared mosquito larval development, survival and adult size in two experiments, one with different densities of non-culicid controphic conditions and the other with altered resource conditions. We used Aedes camptorhynchus, a salt marsh breeding mosquito and a prominent vector for Ross River virus in Australia. Aedes camptorhynchus usually has few competitors due to its halo-tolerance and distribution in salt marshes. However, sympatric ostracod micro-crustaceans often co-occur within these salt marshes and can be found in dense populations, with field evidence suggesting exploitative competition for resources. Our experiments demonstrate resource limiting conditions caused significant increases in mosquito developmental times, decreased adult survival and decreased adult size. Overall, non-culicid exploitation experiments showed little effect on larval development and survival, but similar effects on adult size. We suggest that the alterations of adult traits owing to non-culicid controphic competition has potential to extend to vector-borne disease transmission.

Disruptions in DIII-D

International Nuclear Information System (INIS)

Reiman, A.; Taylor, P.; Kellman, A.; LaHaye, R.

1996-01-01

We report on the results of a statistical analysis of the DIII-D disruption data base, and on an examination of a selected subset of the shots to determine the likely causes of disruptions. The statistical analysis focuses on the dependence of the disruption rate on key dimensionless parameters. We find that the disruption frequency is high at modest values of the parameters, and that it can be relatively low at operational limits. For example, the disruption frequency in an ITER relevant regime (β N /l i ∼ 2, 3 G > 0.6, where n G is the Greenwald limit) is approximately 23%. For this range of q, the disruption frequency rises only modestly to about 35% at the β limit, consistent with previous observations of a soft β limit for this q regime. For the range 6 95 G G < .9) in all q regimes we have studied. The location of the minimum moves to higher density with increasing q

Limiting density ratios in piston-driven compressions

International Nuclear Information System (INIS)

Lee, S.

1985-07-01

By using global energy and pressure balance applied to a shock model it is shown that for a piston-driven fast compression, the maximum compression ratio is not dependent on the absolute magnitude of the piston power, but rather on the power pulse shape. Specific cases are considered and a maximum density compression ratio of 27 is obtained for a square-pulse power compressing a spherical pellet with specific heat ratio of 5/3. Double pulsing enhances the density compression ratio to 1750 in the case of linearly rising compression pulses. Using this method further enhancement by multiple pulsing becomes obvious. (author)

The quiescent H-mode regime for high performance edge localized mode-stable operation in future burning plasmas

Energy Technology Data Exchange (ETDEWEB)

Garofalo, A. M., E-mail: garofalo@fusion.gat.com; Burrell, K. H.; Meneghini, O.; Osborne, T. H.; Paz-Soldan, C.; Smith, S. P.; Snyder, P. B.; Turnbull, A. D. [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Eldon, D.; Grierson, B. A.; Solomon, W. M. [Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543-0451 (United States); Hanson, J. M. [Columbia University, 2960 Broadway, New York, New York 10027-6900 (United States); Holland, C. [University of California San Diego, 9500 Gilman Dr., La Jolla, California 92093-0417 (United States); Huijsmans, G. T. A.; Liu, F.; Loarte, A. [ITER Organization, Route de Vinon sur Verdon, 13067 St Paul Lez Durance (France); Zeng, L. [University of California Los Angeles, P.O. Box 957099, Los Angeles, California 90095-7099 (United States)

2015-05-15

For the first time, DIII-D experiments have achieved stationary quiescent H-mode (QH-mode) operation for many energy confinement times at simultaneous ITER-relevant values of beta, confinement, and safety factor, in an ITER-like shape. QH-mode provides excellent energy confinement, even at very low plasma rotation, while operating without edge localized modes (ELMs) and with strong impurity transport via the benign edge harmonic oscillation (EHO). By tailoring the plasma shape to improve the edge stability, the QH-mode operating space has also been extended to densities exceeding 80% of the Greenwald limit, overcoming the long-standing low-density limit of QH-mode operation. In the theory, the density range over which the plasma encounters the kink-peeling boundary widens as the plasma cross-section shaping is increased, thus increasing the QH-mode density threshold. The DIII-D results are in excellent agreement with these predictions, and nonlinear magnetohydrodynamic analysis of reconstructed QH-mode equilibria shows unstable low n kink-peeling modes growing to a saturated level, consistent with the theoretical picture of the EHO. Furthermore, high density operation in the QH-mode regime has opened a path to a new, previously predicted region of parameter space, named “Super H-mode” because it is characterized by very high pedestals that can be more than a factor of two above the peeling-ballooning stability limit for similar ELMing H-mode discharges at the same density.

High beta tokamak operation in DIII-D limited at low density/collisionality by resistive tearing modes

International Nuclear Information System (INIS)

La Haye, R.J.; Lao, L.L.; Strait, E.J.; Taylor, T.S.

1997-01-01

The maximum operational high beta in single-null divertor (SND) long pulse tokamak discharges in the DIII-D tokamak with a cross-sectional shape similar to the proposed International Thermonuclear Experimental Reactor (ITER) device is found to be limited by the onset of resistive instabilities that have the characteristics of neoclassically destabilized tearing modes. There is a soft limit due to the onset of an m/n=3/2 rotating tearing mode that saturates at low amplitude and a hard limit at slightly higher beta due to the onset of an m/n=2/1 rotating tearing mode that grows, slows down and locks. By operating at higher density and thus collisionality, the practical beta limit due to resistive tearing modes approaches the ideal magnetohydrodynamic (MHD) limit. (author). 15 refs, 4 figs

The control of plasma density profile in Tore Supra. Comparison of different fueling techniques; Controle du profil de densite dans le plasma de Tore Supra. Comparaison de differentes methodes d'alimentation en particules

Energy Technology Data Exchange (ETDEWEB)

Commaux, N

2007-09-15

The behaviour of a reactor-class plasma when fuelled using the existing techniques (gas puffing, supersonic molecular beam injection and pellet injection) is still very difficult to foresee. The present work has been initiated on Tore Supra in order to extrapolate the consequences of the different fuelling systems on ITER. Two main topics have been studied: the comparison of the plasma behaviour when fuelled using the different techniques at high Greenwald density fractions and the study of the homogenization following a pellet injection (main fuelling technique for ITER burning plasmas). The experiments at high Greenwald density fractions performed on Tore Supra showed that the plasma behaviour is very dependent on the fuelling method. The plasma energy confinement is following the scaling laws determined at low density when fuelled using pellet injection. which is better than for gas puffing and SMBI. both inducing a significant confinement loss. This behaviour is nor related to a transport modification: the ratio between effective diffusion and convection is similar to the pellet case. The difference between these shots is related only to the position of the matter source (at the edge for gas and close to the center for pellets). The study concerning the homogenization phenomena following a pellet injection aims mainly to study the {nabla}B-drift effect that expels the mater deposited by a pellet toward the low field side. A new phenomenon. which appears to be particularly important for the {nabla}B-drift during low field side injections. was then discovered: the influence of magnetic surfaces with an integer-valued safety factor (q). When the mater drifting toward low field side crosses an integer q surface. it experiences an important braking effect which stops the drift motion. It implies that the pellet material is mainly deposited on the last integer q surface crossed by the pellet during its injection. This study allows also to determine that the {nabla

Growth limitation of Lemna minor due to high plant density

NARCIS (Netherlands)

Driever, S.M.; Nes, van E.H.; Roijackers, R.M.M.

2005-01-01

The effect of high population densities on the growth rate of Lemna minor (L.) was studied under laboratory conditions at 23°C in a medium with sufficient nutrients. At high population densities, we found a non-linear decreasing growth rate with increasing L. minor density. Above a L. minor biomass

Improved confinement mode induced by the MARFE on the HT-7 superconducting tokamak

International Nuclear Information System (INIS)

Gao, X.; Zhao, Y.P.; Luo, J.R.; Jie, Y.X.; Gong, X.Z.; Wan, B.N.; Li, J.G.; Yin, F.X.; Kuang, G.L.; Zhang, X.D.; Zhang, S.Y.; Qiu, N.; Liu, X.N.; Zhao, J.Y.; Yang, Y.; Bao, Y.; Lin, B.L.; Wu, Z.W.; Li, Y.D.; Xu, Y.H.; Yang, K.; Wang, G.X.; Ye, W.W.; Chen, L.; Shi, Y.J.; Song, M.; Zhang, X.M.; Qin, P.J.; Gu, X.M.; Cui, N.Z.; Fan, H.Y.; Liu, S.X.; Chen, Y.F.; Hu, L.Q.; Hu, J.S.; Xia, C.Y.; Ruan, H.L.; Tong, X.D.; Mao, J.S.; Xie, J.K.; Wan, Y.X.

1999-01-01

In the HT-7 superconducting tokamak, the onset of a multifaceted asymmetric radiation from the edge (MARFE) usually occurs in the early ohmic discharges of each experimental campaign before wall conditioning. The occurrence and location of a MARFE is identified by different diagnostic systems. An improved confinement mode plasma which was induced by the MARFE is observed, and the global particle confinement time increases 1.9 times. The relaxation time between the MARFE event trigger and the L-H transition is about 1.4 ms, the following L-H transition time is 1.9 ms, and the improved confinement mode phase is maintained for about 40 ms. The MARFE cools the plasma edge, and the electron density profile is observed to become more narrow and peaked. The occurrence of a MARFE is strongly correlated with Z eff but not with the density, and it always occurs at Z eff = 3-8 ohmic discharges. In the case of a good wall condition (Z eff = 1-2), the onset of MARFEs has not been observed before reaching the Greenwald density limit. (author)

Operations space diagram for ECRH and ECCD

International Nuclear Information System (INIS)

Bindslev, Henrik

2004-01-01

A Clemmov-Mullaly-Allis (CMA) type diagram, the ECW-CMA diagram, for representing the operational possibilities of electron cyclotron heating and current drive (ECRH/ECCD) systems for fusion plasmas is presented. In this diagram, with normalized density and normalized magnetic field coordinates, the parameter range in which it is possible to achieve a given task (e.g. O-mode current drive for stabilizing a neoclassical tearing mode) appears as a region. With also the Greenwald density limit shown, this diagram condenses the information on operational possibilities, facilitating the overview required at the design phase. At the operations phase it may also prove useful in setting up experimental scenarios by showing operational possibilities, avoiding the need for survey type ray-tracing at the initial planning stages. The diagram may also serve the purpose of communicating operational possibilities to non-experts. JET and ITER like plasmas are used, but the method is generic. (author)

Influence of an external gas puff on the RI-mode confinement properties in TEXTOR

International Nuclear Information System (INIS)

Kalupin, D.

2002-06-01

An actual subject of experimental and theoretical studies in present day fusion research is the development of an operational scenario combining simultaneously high confinement, with at least H-mode quality, and high densities, around or above the empirical Greenwald limit. Recently, this subject was studied in TEXTOR radiative improved (RI) mode discharges, in which the seeding of a small amount of impurities is helpful in a transition to the improved confinement stage. It was found that by the careful tailoring of external fuelling and optimisation of the wall conditions it is possible to maintain the H-mode or even higher quality confinement at densities much above Greenwald density limit. However, more intense fuelling, aimed to extend maximal achievable densities, led to the progressive confinement deterioration. The theory explains the transition to the RI-mode as a bifurcation into the stage where the transport governed by the ion temperature gradient (ITG) instability is significantly reduced due to a high density gradient and high value of the effective charge. The numerical studies of an influence of the gas puff intensity on confinement properties of plasma, done with the help of the 1-D transport code RITM, show that the same theory can be used for an explanation of the confinement rollover triggered by a strong gas puff. The code was modified in order to simulate the effect of the gas puff on the confinement properties. The anomalous transport coefficients in the plasma core include contributions from the ITG and dissipative trapped electron (DTE) instabilities. The transport at the plasma edge under RI-mode conditions might be described by the electrostatic turbulence caused by electric currents in the scrape-off layer of the limiter. The present computations show that this assumption for the edge transport does not allow the modeling of an effect of the gas puff intensity on the profiles evolution in agreement with experimental observations. The

The limiting current in a one-dimensional situation: Transition from a space charge limited to magnetically limited flow

International Nuclear Information System (INIS)

Kumar, Raghwendra; Biswas, Debabrata

2008-01-01

For a nonrelativistic electron beam propagating in a cylindrical drift tube, it is shown that the limiting current density does not saturate to the electrostatic one-dimensional (1D) estimate with increasing beam radius. Fully electromagnetic particle-in-cell (PIC) simulation studies show that beyond a critical aspect ratio, the limiting current density is lower than the 1D electrostatic prediction. The lowering in the limiting current density is found to be due to the transition from the space charge limited to magnetically limited flow. An adaptation of Alfven's single particle trajectory method is used to estimate the magnetically limited current as well as the critical radius beyond which the flow is magnetically limited in a drift tube. The predictions are found to be in close agreement with PIC simulations

New self-similar radiation-hydrodynamics solutions in the high-energy density, equilibrium diffusion limit

International Nuclear Information System (INIS)

Lane, Taylor K; McClarren, Ryan G

2013-01-01

This work presents semi-analytic solutions to a radiation-hydrodynamics problem of a radiation source driving an initially cold medium. Our solutions are in the equilibrium diffusion limit, include material motion and allow for radiation-dominated situations where the radiation energy is comparable to (or greater than) the material internal energy density. As such, this work is a generalization of the classical Marshak wave problem that assumes no material motion and that the radiation energy is negligible. Including radiation energy density in the model serves to slow down the wave propagation. The solutions provide insight into the impact of radiation energy and material motion, as well as present a novel verification test for radiation transport packages. As a verification test, the solution exercises the radiation–matter coupling terms and their v/c treatment without needing a hydrodynamics solve. An example comparison between the self-similar solution and a numerical code is given. Tables of the self-similar solutions are also provided. (paper)

End-anchored polymers in good solvents from the single chain limit to high anchoring densities.

Science.gov (United States)

Whitmore, Mark D; Grest, Gary S; Douglas, Jack F; Kent, Michael S; Suo, Tongchuan

2016-11-07

An increasing number of applications utilize grafted polymer layers to alter the interfacial properties of solid substrates, motivating refinement in our theoretical understanding of such layers. To assess existing theoretical models of them, we have investigated end-anchored polymer layers over a wide range of grafting densities, σ, ranging from a single chain to high anchoring density limits, chain lengths ranging over two orders of magnitude, for very good and marginally good solvent conditions. We compare Monte Carlo and molecular dynamics simulations, numerical self-consistent field calculations, and experimental measurements of the average layer thickness, h, with renormalization group theory, the Alexander-de Gennes mushroom theory, and the classical brush theory. Our simulations clearly indicate that appreciable inter-chain interactions exist at all simulated areal anchoring densities so that there is no mushroom regime in which the layer thickness is independent of σ. Moreover, we find that there is no high coverage regime in which h follows the predicted scaling, h ∼ Nσ 1/3 , for classical polymer brushes either. Given that no completely adequate analytic theory seems to exist that spans wide ranges of N and σ, we applied scaling arguments for h as a function of a suitably defined reduced anchoring density, defined in terms of the solution radius of gyration of the polymer chains and N. We find that such a scaling approach enables a smooth, unified description of h in very good solvents over the full range of anchoring density and chain lengths, although this type of data reduction does not apply to marginal solvent quality conditions.

Ablative Rayleigh-Taylor instability in the limit of an infinitely large density ratio

International Nuclear Information System (INIS)

Clavin, P.; Almarcha, Ch.

2005-01-01

The instability of ablation fronts strongly accelerated toward the dense medium under the conditions of inertial confinement fusion (ICF) is addressed in the limit of an infinitely large density ratio. The analysis serves to demonstrate that the flow is irrotational to first order, reducing the nonlinear analysis to solve a two-potential flows problem. Vorticity appears at the following orders in the perturbation analysis. This result simplifies greatly the analysis. The possibility for using boundary integral methods opens new perspectives in the nonlinear theory of the ablative Rayleigh-Taylor instability in ICF. A few examples are given at the end of the paper. (authors)

Operating parameters of a reactor for early demonstration of electric power generation and the expansion by realization of advanced tokamak plasma

International Nuclear Information System (INIS)

Okano, Kunihiko; Asaoka, Yoshiyuki; Hiwatari, Ryoji

2004-01-01

Beam driven stable equilibria for a conceptual reactor, Demo-CREST, which was designed for early demonstration of electric power generation, has been investigated. Considering current profiles driven by neutral beams, the attainable normalized beta β N with a stabilization wall is about 3.4 with a normal shear (NS). With reversed shear (RS), a higher β N is attainable. The stable equilibria up to 4.0 can be sustained by a couple of On- and Off-axis beams. In the range of 1.9 N N = 1.9 which is the base design point of Demo-CREST. In the case of RS operation with β N 4.0, the density ratio to the Greenwald limit can be maintain at about unity if high temperature operation with T e > 20 kV is allowable. (author)

Symmetry properties of the electron density and following from it limits on the KS-DFT applications

Science.gov (United States)

Kaplan, Ilya G.

2018-03-01

At present, the Density Functional Theory (DFT) approach elaborated by Kohn with co-authors more than 50 years ago became the most widely used method for study molecules and solids. Using modern computation facilities, it can be applied to systems with million atoms. In the atmosphere of such great popularity, it is particularly important to know the limits of the applicability of DFT methods. In this report, I will discuss two cases when the conventional DFT approaches, using only electron density ρ and its gradients, cannot be applied (I will not consider the Ψ-versions of DFT). The first case is quite evident. In the degenerated states, the electron density may not be defined, since electronic and nuclear motions cannot be separated, the vibronic interaction mixed them. The second case is related to the spin of the state. As it was rigorously proved by group theoretical methods at the theorem level, the electron density does not depend on the total spin S of the arbitrary N-electron state. It means that the Kohn-Sham equations have the same form for states with different S. The critical survey of elaborated DFT procedures, taking into account spin, shows that they modified only exchange functionals, the correlation functionals do not correspond to the spin of the state. The point is that the conception of spin cannot be defined in the framework of the electron density formalism, which corresponds to the one-particle reduced density matrix. This is the main reason of the problems arising in the study by DFT of magnetic properties of the transition metals. The possible way of resolving these problems can be found in the two-particle reduced density matrix formulation of DFT.

Fringing-field dielectrophoretic assembly of ultrahigh-density semiconducting nanotube arrays with a self-limited pitch

Science.gov (United States)

Cao, Qing; Han, Shu-Jen; Tulevski, George S.

2014-09-01

One key challenge of realizing practical high-performance electronic devices based on single-walled carbon nanotubes is to produce electronically pure nanotube arrays with both a minuscule and uniform inter-tube pitch for sufficient device-packing density and homogeneity. Here we develop a method in which the alternating voltage-fringing electric field formed between surface microelectrodes and the substrate is utilized to assemble semiconducting nanotubes into well-aligned, ultrahigh-density and submonolayered arrays, with a consistent pitch as small as 21±6 nm determined by a self-limiting mechanism, based on the unique field focusing and screening effects of the fringing field. Field-effect transistors based on such nanotube arrays exhibit record high device transconductance (>50 μS μm-1) and decent on current per nanotube (~1 μA per tube) together with high on/off ratios at a drain bias of -1 V.

Conceptual design of the SlimCS fusion DEMO reactor

International Nuclear Information System (INIS)

Tobita, Kenji; Nishio, Satoshi; Enoeda, Mikio; Nakamura, Hirofumi; Hayashi, Takumi; Asakura, Nobuyuki; Utoh, Hiroyasu; Tanigawa, Hiroyasu; Nishitani, Takeo; Isono, Takaaki; Sakurai, Shinji; Kurita, Genichi; Hayashi, Takao; Oyama, Naoyuki; Liu Changle; Hamamatsu, Kiyotaka; Inoue, Takashi; Ozeki, Takahisa; Sato, Masayasu; Suzuki, Satoshi; Kawashima, Hisato; Ezato, Koichiro; Tsuru, Daigo; Koizumi, Norikiyo; Sakamoto, Keiji; Ando, Masami; Sakamoto, Yoshiteru; Shibama, Yusuke; Suzuki, Takahiro; Takechi, Manabu; Takahashi, Koji; Hirose, Takanori; Sato, Satoru; Nozawa, Takashi; Tanigawa, Hisashi; Kakudate, Satoshi; Kawamura, Yoshinori; Yamanishi, Toshihiko; Hoshino, Tsuyoshi; Ochiai, Kentaro; Ide, Shunsuke; Aiba, Nobuyuki; Shimizu, Katsuhiro; Honda, Mitsuru; Nakamichi, Masaru; Nishi, Hiroshi; Seki, Yoji; Nakamura, Yukiharu; Tsuchiya, Kunihiko; Yoshida, Tohru; Song Yuntao

2010-08-01

This report describes the results of the conceptual design study of the SlimCS fusion DEMO reactor aiming at demonstrating fusion power production in a plant scale and allowing to assess the economic prospects of a fusion power plant. The design study has focused on a compact and low aspect ratio tokamak reactor concept with a reduced-sized central solenoid, which is novel compared with previous tokamak reactor concept such as SSTR (Steady State Tokamak Reactor). Owing to low aspect ratio, the reactor will be capable of having comparatively high beta limit and high elongation (which can elevate the Greenwald density limit), having potential for high power density. The reactor has the main parameters of a major radius of 5.5 m, aspect ratio of 2.6, elongation of 2.0, normalized beta of 4.3, fusion out put of 2.95 GW and average neutron wall load of 3 MW/m 2 . This report covers various aspects of design study including systematic design, physics design, torus configuration, blanket, superconducting magnet, maintenance and building, which were carried out increase the engineering feasibility of the concept. (author)

Divertor plasma physics experiments on the DIII-D tokamak

International Nuclear Information System (INIS)

Mahdavi, M.A.; Allen, S.L.; Evans, T.E.

1996-10-01

In this paper we present an overview of the results and conclusions of our most recent divertor physics and development work. Using an array of new divertor diagnostics we have measured the plasma parameters over the entire divertor volume and gained new insights into several divertor physics issues. We present direct experimental evidence for momentum loss along the field lines, large heat convection, and copious volume recombination during detachment. These observations are supported by improved UEDGE modeling incorporating impurity radiation. We have demonstrated divertor exhaust enrichment of neon and argon by action of a forced scrape off layer (SOL) flow and demonstrated divertor pumping as a substitute for conventional wall conditioning. We have observed a divertor radiation zone with a parallel extent that is an order of magnitude larger than that estimated from a 1-D conduction limited model of plasma at coronal equilibrium. Using density profile control by divertor pumping and pellet injection we have attained H-mode confinement at densities above the Greenwald limit. Erosion rates of several candidate ITER plasma facing materials are measured and compared with predictions of a numerical model

Ablative Rayleigh Taylor instability in the limit of an infinitely large density ratio

Science.gov (United States)

Clavin, Paul; Almarcha, Christophe

2005-05-01

The instability of ablation fronts strongly accelerated toward the dense medium under the conditions of inertial confinement fusion (ICF) is addressed in the limit of an infinitely large density ratio. The analysis serves to demonstrate that the flow is irrotational to first order, reducing the nonlinear analysis to solve a two-potential flows problem. Vorticity appears at the following orders in the perturbation analysis. This result simplifies greatly the analysis. The possibility for using boundary integral methods opens new perspectives in the nonlinear theory of the ablative RT instability in ICF. A few examples are given at the end of the Note. To cite this article: P. Clavin, C. Almarcha, C. R. Mecanique 333 (2005).

Density profiles and particle fluxes of heavy impurities in the limiter shadow region of a tokamak

International Nuclear Information System (INIS)

Claassen, H.A.; Repp, H.

1980-01-01

For the case of low impurity concentration, transport calculations have been performed for heavy impurities, in the scrape-off layer plasma of a tokamak with a poloidal ring limiter. The theory is based on the drift-kinetic equations for the various ionization states of the impurity ions taking due consideration of the convection and collision processes. The background plasma and the impurity sources from the torus wall and the limiter surface enter the theory as input parameters. The theory is developed for the first two orders of the drift approximation. Numerical results are given to zero order drift approximation for the radial profiles of density and particle fluxes parallel to the magnetic field. (orig.)

Milagro Limits and HAWC Sensitivity for the Rate-Density of Evaporating Primordial Black Holes

Science.gov (United States)

Abdo, A. A.; Abeysekara, A. U.; Alfaro, R.; Allen, B. T.; Alvarez, C.; Alvarez, J. D.; Arceo, R.; Arteaga-Velazquez, J. C.; Aune, T.; Ayala Solares, H. A.;

Coherent density fluctuation model as a local-scale limit to ATDHF

International Nuclear Information System (INIS)

Antonov, A.N.; Petkov, I.Zh.; Stoitsov, M.V.

1985-04-01

The local scale transformation method is used for the construction of an Adiabatic Time-Dependent Hartree-Fock approach in terms of the local density distribution. The coherent density fluctuation relations of the model result in a particular case when the ''flucton'' local density is connected with the plane wave determinant model function be means of the local-scale coordinate transformation. The collective potential energy expression is obtained and its relation to the nuclear matter energy saturation curve is revealed. (author)

Errors and limits in the determination of plasma electron density by measuring the absolute values of the emitted continuum radiation intensity

International Nuclear Information System (INIS)

Bilbao, L.; Bruzzone, H.; Grondona, D.

1994-01-01

The reliable determination of a plasma electron structure requires a good knowledge of the errors affecting the employed technique. A technique based on the measurements of the absolute light intensity emitted by travelling plasma structures in plasma focus devices has been used, but it can be easily modified to other geometries and even to stationary plasma structures with time-varying plasma densities. The purpose of this work is to discuss in some detail the errors and limits of this technique. Three separate errors are shown: the minimum size of the density structure that can be resolved, an overall error in the measurements themselves, and an uncertainty in the shape of the density profile. (author)

Use of Limiting Dilution Method for Isolation of Nucleus Pulposus Mesenchymal Stem/Progenitor Cells and Effects of Plating Density on Biological Characteristics and Plasticity

Directory of Open Access Journals (Sweden)

Linghan Lin

2017-01-01

Full Text Available Objectives. To evaluate the effects of the limiting dilution method and plating density in rat nucleus pulposus mesenchymal stem/progenitor cells (NPMSCs. Materials and Methods. Nucleus pulposus tissues were isolated from 12-week-old male Sprague-Dawley rats and NPMSCs were isolated using limiting dilution method. Cells were then classified into 3 groups according to plating density. Cell morphologies were observed, and colony-forming units, migration abilities, proliferative capacities, cell cycle percentages, multilineage differentiation capacities, stem cell biomarker expression levels, and immunophenotyping were also examined in each group. Results. Low density group (LD had higher morphological homogeneity, stronger colony-forming ability, higher cell proliferation capacity, and enhanced cell migration ability relative to the other two groups (p<0.05. Moreover, LD had more cells entering S phase, with fewer cells arrested in G0/G1 phase (p<0.05. While all three density groups showed a multilineage differentiation potential, LD showed a higher degree of observed and semiquantified lineage specific staining (p<0.05. Furthermore, LD displayed higher expression levels of stem cell biomarkers (Nanog, Oct4, and Sox2 and showed higher percentages of CD29+, CD44+, and CD90+ cells (p<0.05 following flow cytometry analysis. Conclusions. Limiting dilution method is suggested when isolating NPMSCs as a means of improving cell activity and plasticity.

Overview, Progress, and Plans for the Compact Toroidal Hybrid Experiment

Science.gov (United States)

Hartwell, G. J.; Allen, N. R.; Ennis, D. A.; Hanson, J. D.; Howell, E. C.; Johnson, C. A.; Knowlton, S. F.; Kring, J. D.; Ma, X.; Maurer, D. A.; Ross, K. G.; Schmitt, J. C.; Traverso, P. J.; Williamson, E. N.

2017-10-01

The Compact Toroidal Hybrid (CTH) is an l = 2 , m = 5 torsatron/tokamak hybrid (R0 = 0.75 m, ap 0.2 m, and | B | disruption studies. The main goals of the CTH experiment are to study disruptive behavior as a function of applied 3D magnetic shaping, and to test and advance the V3FIT reconstruction code and NIMROD modeling of CTH. The disruptive density limit is observed to exceed the Greenwald limit as the vacuum transform is increased with no observed threshold for avoidance. Low-q operations (1.1 routine, with disruptions ceasing if the vacuum transform is raised above 0.07. Sawteeth are observed in CTH and have a similar phenomenology to tokamak sawteeth despite employing a 3D confining field. Application of vacuum transform has been demonstrated to reduce and eliminate the vertical drift of elongated discharges. Internal SXR diagnostics, in conjunction with external magnetics, extend the range of reconstruction accuracy into the plasma core. This work is supported by U.S. Department of Energy Grant No. DE-FG02-00ER54610.

ALT-I pump limiter experiments

International Nuclear Information System (INIS)

Goebel, D.M.; Conn, R.W.; Campbell, G.A.

1987-09-01

Results from the ALT-I pump limiter experiments in TEXTOR are presented. ALT-I has demonstrated control of the plasma density in a high recycling tokamak by pumping up to 15% of the core efflux. The closed pump limiter designs with restricted entrance geometries to reduce the backflow of neutral gas to the plasma remove over 50% of the ion flux incident on the collection slot. Up to 80% of the entrance ion flux is removed when the edge electron temperature is less than 10 eV and plasma-neutral gas interactions are minimized inside the limiter. Results from a 3-D Monte Carlo neutral gas transport code agree closely with these experimental results. The compound curvature of the head is found to distribute the heat over the surface as predicted in the original designs. Impurity removal experiments demonstrate that significant helium exhaust can be achieved with a pump limiter. During ohmic heating in TEXTOR, the energy and particle confinement times are proportional to the line averaged core density. With ICRH auxiliary heating, tau/sub E/ follow L-mode scaling independent of particle removal by the pump limiter. Pump limiter operation does not directly modify the SOL plasma density and electron temperature, but controls the core plasma density by changing the global recycling at the boundary. The global particle confinement, the particle flux to the limiter, and the edge electron temperature follow the changes in the core density and auxiliary heating power. 25 refs

47 CFR 25.223 - Off-axis EIRP spectral density limits for feeder link earth stations in the 17/24 GHz BSS.

Science.gov (United States)

2010-10-01

... 47 Telecommunication 2 2010-10-01 2010-10-01 false Off-axis EIRP spectral density limits for feeder link earth stations in the 17/24 GHz BSS. 25.223 Section 25.223 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON CARRIER SERVICES SATELLITE COMMUNICATIONS Technical Standards § 25...

Observation of a High Performance Operating Regime with Small Edge-Localized Modes in the National Spherical Torus Experiment

International Nuclear Information System (INIS)

Maingi, R.; Tritz, K.; Fredrickson, E.D.; Menard, J.E.; Sabbagh, S.A.; Stutman, D.; Bell, M.G.; Bell, R.E.; Bush, C.E.; Gates, D.A.; Johnson, D.W.; Kaita, R.; Kaye, S.M.; Kugel, H.W.; LeBlanc, B.P.; Mueller, D.; Raman, R.; Roquemore, A.L.; Soukhanovskii, V.A.

2004-01-01

We report observation of a high performance scenario in the National Spherical Torus Experiment with very small edge-localized modes (ELMs). These ELMs have no measurable impact on stored energy and are consistent with high bootstrap current operation with line average density approaching Greenwald scaling. The ELM perturbation is observed to typically originate near the lower divertor region, as opposed to the outer midplane for ELMs described in the literature. If extrapolable, this scenario would provide an attractive operating regime for next step fusion experiments

Imaginary time density-density correlations for two-dimensional electron gases at high density

Energy Technology Data Exchange (ETDEWEB)

Motta, M.; Galli, D. E. [Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, 20133 Milano (Italy); Moroni, S. [IOM-CNR DEMOCRITOS National Simulation Center and SISSA, Via Bonomea 265, 34136 Trieste (Italy); Vitali, E. [Department of Physics, College of William and Mary, Williamsburg, Virginia 23187-8795 (United States)

2015-10-28

We evaluate imaginary time density-density correlation functions for two-dimensional homogeneous electron gases of up to 42 particles in the continuum using the phaseless auxiliary field quantum Monte Carlo method. We use periodic boundary conditions and up to 300 plane waves as basis set elements. We show that such methodology, once equipped with suitable numerical stabilization techniques necessary to deal with exponentials, products, and inversions of large matrices, gives access to the calculation of imaginary time correlation functions for medium-sized systems. We discuss the numerical stabilization techniques and the computational complexity of the methodology and we present the limitations related to the size of the systems on a quantitative basis. We perform the inverse Laplace transform of the obtained density-density correlation functions, assessing the ability of the phaseless auxiliary field quantum Monte Carlo method to evaluate dynamical properties of medium-sized homogeneous fermion systems.

Lying in wait: Limiting factors on a low-density ungulate population and the latent traits that can facilitate escape from them

Science.gov (United States)

Joly, Kyle; Craig, Tim; Cameron, Matthew D.; Gall, Adrian E.; Sorum, Mathew S.

2017-11-01

Predation, habitat, hunting, and environmental conditions have all been implicated as regulatory mechanisms in ungulate populations. The low-density equilibrium hypothesis predicts that in low-density populations, predators regulate their prey and that the population will not escape unless predation pressure is eased. We evaluated survival of adult and juvenile moose (Alces alces) in north-central Alaska to determine whether or not the population supported the hypothesis. We instrumented adult male and female moose with radiocollars and used aerial observations to track parturition and subsequent survival of juvenile moose. Generalized linear mixed-effects models were used to assess survival. Adult annual survival rates were high (∼89%), but may be negatively influenced by winter conditions. Migratory status did not affect moose survivorship or productivity. Approximately 60% of the calf crop died before 5 months of age. Productivity was significantly lower in the northern section of the study area where there is less high-quality habitat, suggesting that, even in this low-density population, nutrition could be a limiting factor. It appears that predation on young calves, winter weather, and nutritional constraints may be interacting to limit this population. Latent traits, such as overproduction of calves and migratory behavior, which do not currently enhance fitness, may persist within this population so that individuals with these traits can reap benefits when environmental conditions change.

CORRELATION BETWEEN GROUP LOCAL DENSITY AND GROUP LUMINOSITY

Energy Technology Data Exchange (ETDEWEB)

Deng Xinfa [School of Science, Nanchang University, Jiangxi 330031 (China); Yu Guisheng [Department of Natural Science, Nanchang Teachers College, Jiangxi 330103 (China)

2012-11-10

In this study, we investigate the correlation between group local number density and total luminosity of groups. In four volume-limited group catalogs, we can conclude that groups with high luminosity exist preferentially in high-density regions, while groups with low luminosity are located preferentially in low-density regions, and that in a volume-limited group sample with absolute magnitude limit M{sub r} = -18, the correlation between group local number density and total luminosity of groups is the weakest. These results basically are consistent with the environmental dependence of galaxy luminosity.

Locality of correlation in density functional theory

Energy Technology Data Exchange (ETDEWEB)

Burke, Kieron [Department of Chemistry, University of California, Irvine, California 92697 (United States); Cancio, Antonio [Department of Physics and Astronomy, Ball State University, Muncie, Indiana 47306 (United States); Gould, Tim [Qld Micro- and Nanotechnology Centre, Griffith University, Nathan, Qld 4111 (Australia); Pittalis, Stefano [CNR-Istituto di Nanoscienze, Via Campi 213A, I-41125 Modena (Italy)

2016-08-07

The Hohenberg-Kohn density functional was long ago shown to reduce to the Thomas-Fermi (TF) approximation in the non-relativistic semiclassical (or large-Z) limit for all matter, i.e., the kinetic energy becomes local. Exchange also becomes local in this limit. Numerical data on the correlation energy of atoms support the conjecture that this is also true for correlation, but much less relevant to atoms. We illustrate how expansions around a large particle number are equivalent to local density approximations and their strong relevance to density functional approximations. Analyzing highly accurate atomic correlation energies, we show that E{sub C} → −A{sub C} ZlnZ + B{sub C}Z as Z → ∞, where Z is the atomic number, A{sub C} is known, and we estimate B{sub C} to be about 37 mhartree. The local density approximation yields A{sub C} exactly, but a very incorrect value for B{sub C}, showing that the local approximation is less relevant for the correlation alone. This limit is a benchmark for the non-empirical construction of density functional approximations. We conjecture that, beyond atoms, the leading correction to the local density approximation in the large-Z limit generally takes this form, but with B{sub C} a functional of the TF density for the system. The implications for the construction of approximate density functionals are discussed.

An overview of the DIII-D program

International Nuclear Information System (INIS)

Luxon, J.L.

1996-10-01

The DIII-D program focuses on developing fusion physics in an integrated program of tokamak concept improvement. The intent is both to support the present ITER physics R and D and to develop more efficient concepts for the later phases of ITER and eventual power plants. Progress in this effort can be best summarized by recent results for a diverted deuterium discharge with negative central shear which reached a performance level of Q DT = 0.32. The ongoing development of the tools needed to carry out this program of understanding and optimization continues to be crucial to its success. Control of the plasma cross-sectional shape and the internal distributions of plasma current, density, and rotation has been essential to optimizing plasma performance. Advanced divertor concepts provide edge power and particle control for future devices such as ITER and provide techniques to help manage the edge power and particle flows for advanced tokamak concepts. New divertor diagnostics and improved modeling are developing excellent divertor understanding. Many of the plasma physics issues being posed by ITER are being addressed. Scrapeoff layer power flow is being characterized to provide an accurate basis for the design of reactor devices. Ongoing studies of the density limit focus on identifying ways in which ITER can achieve the required densities in excess of the Greenwald limit. Better understanding of disruptions is crucial to the design of future reactors

Energy density functionals from the strong-coupling limit applied to the anions of the He isoelectronic series

International Nuclear Information System (INIS)

Mirtschink, André; Gori-Giorgi, Paola; Umrigar, C. J.; Morgan, John D.

2014-01-01

Anions and radicals are important for many applications including environmental chemistry, semiconductors, and charge transfer, but are poorly described by the available approximate energy density functionals. Here we test an approximate exchange-correlation functional based on the exact strong-coupling limit of the Hohenberg-Kohn functional on the prototypical case of the He isoelectronic series with varying nuclear charge Z − and to capture in general the physics of loosely bound anions, with a tendency to strongly overbind that can be proven mathematically. We also include corrections based on the uniform electron gas which improve the results

Tokamak pump limiters

International Nuclear Information System (INIS)

Conn, R.W.

1984-05-01

Recent experiments with a scoop limiter without active internal pumping have been carried out in the PDX tokamak with up to 6MW of auxiliary neutral beam heating. Experiments have also been done with a rotating head pump limiter in the PLT tokamak in conjunction with RF plasma heating. Extensive experiments have been done in the ISX-B tokamak and first experiments have been completed with the ALT-I limiter in TEXTOR. The pump limiter modules in these latter two machines have internal getter pumping. Experiments in ISX-B are with ohmic and auxiliary neutral beam heating. The results in ISX-B and TEXTOR show that active density control and particle removal is achieved with pump limiters. In ISX-B, the boundary layer (or scape-off layer) plasma partially screens the core plasma from gas injection. In both ISX-B and TEXTOR, the pressure internal to the module scales linearly with plasma density but in ISX-B, with neutral beam injection, a nonlinear increase is observed at the highest densities studied. Plasma plugging is the suspected cause. Results from PDX suggest that a region may exist in which core plasma energy confinement improves using a pump limiter during neutral beam injection. Asymmetric radial profiles and an increased edge electron temperature are observed in discharges with improved confinement. The injection of small amounts of neon into ISX-B has more clearly shown an improved electron core energy confinement during neutral beam injection. While carried out with a regular limiter, this Z-mode of operation is ideal for use with pump limiters and should be a way to achieve energy confinement times similar to values for H-mode tokamak plasmas. The implication of all these results for the design of a reactor pump limiter is described

Tokamak pump limiters

International Nuclear Information System (INIS)

Conn, R.W.; California Univ., Los Angeles

1984-01-01

Recent experiments with a scoop limiter without active internal pumping have been carried out in the PDX tokamak with up to 6 MW of auxiliary neutral beam heating. Experiments have also been performed with a rotating head pump limiter in the PLT tokamak in conjunction with RF plasma heating. Extensive experiments have been done in the ISX-B tokamak and first experiments have been completed with the ALT-I limiter in TEXTOR. The pump limiter modules in these latter two machines have internal getter pumping. Experiments in ISX-B are with ohmic and auxiliary neutral beam heating. The results in ISX-B and TEXTOR show that active density control and particle removal is achieved with pump limiters. In ISX-B, the boundary layer (or scrape-off layer) plasma partially screens the core plasma from gas injection. In both ISX-B and TEXTOR, the pressure internal to the module scales linearly with plasma density but in ISX-B, with neutral beam injection, a nonlinear increase is observed at the highest densities studied. Plasma plugging is the suspected cause. Results from PDX suggest that a regime may exist in which core plasma energy confinement improves using a pump limiter during neutral beam injection. Asymmetric radial profiles and an increased edge electron temperature are observed in discharges with improved confinement. The injection of small amounts of neon into ISX-B has more clearly shown an improved electron core energy confinement during neutral beam injection. While carried out with a regular limiter, this 'Z-mode' of operation is ideal for use with pump limiters and should be a way to achieve energy confinement times similar to values for H-mode tokamak plasmas. The implication of all these results for the design of a reactor pump limiter is described. (orig.)

Physical design of JT-60 Super Upgrade

International Nuclear Information System (INIS)

Nagashima, K.; Kikuchi, M.; Kurita, G.; Ozeki, T.; Aoyagi, T.; Ushigusa, K.; Neyatani, Y.; Kubo, T.; Mori, K.; Nakagawa, S.; Kuriyama, M.; Nagami, M.

1997-01-01

The JT-60 Super Upgrade (JT-60SU) is an upgraded tokamak device of JT-60U for developing the steady-state reactor and advanced tokamak operation in the International Thermonuclear Experimental Reactor. The device is planned to utilize the JT-60 facilities fully and to minimize the needed modification. The major radius is 4.8 m and the maximum plasma current is 10 MA. Neutral beam injection with 750 keV beam energy is the primary heating method. The machine is capable of steady-state operation with high density up to 8.8 x 10 19 m -3 at 5 MA plasma current. The high operating density, over the Greenwald et al. limit, is critically important in order to achieve high bootstrap current fraction. Ballooning mode and low n ideal magnetohydrodynamic (MHD) mode including the bootstrap current were analyzed for steady-state operation. The current profile must be optimized to obtain a normalized beta up to 3. The plasma configuration with high triangularity was adopted in order to get good MHD stability and high energy confinement. A compact divertor was designed in order to get the large plasma space. (orig.)

Limits on fundamental limits to computation.

Science.gov (United States)

Markov, Igor L

2014-08-14

An indispensable part of our personal and working lives, computing has also become essential to industries and governments. Steady improvements in computer hardware have been supported by periodic doubling of transistor densities in integrated circuits over the past fifty years. Such Moore scaling now requires ever-increasing efforts, stimulating research in alternative hardware and stirring controversy. To help evaluate emerging technologies and increase our understanding of integrated-circuit scaling, here I review fundamental limits to computation in the areas of manufacturing, energy, physical space, design and verification effort, and algorithms. To outline what is achievable in principle and in practice, I recapitulate how some limits were circumvented, and compare loose and tight limits. Engineering difficulties encountered by emerging technologies may indicate yet unknown limits.

Density-density functionals and effective potentials in many-body electronic structure calculations

International Nuclear Information System (INIS)

Reboredo, Fernando A.; Kent, Paul R.

2008-01-01

We demonstrate the existence of different density-density functionals designed to retain selected properties of the many-body ground state in a non-interacting solution starting from the standard density functional theory ground state. We focus on diffusion quantum Monte Carlo applications that require trial wave functions with optimal Fermion nodes. The theory is extensible and can be used to understand current practices in several electronic structure methods within a generalized density functional framework. The theory justifies and stimulates the search of optimal empirical density functionals and effective potentials for accurate calculations of the properties of real materials, but also cautions on the limits of their applicability. The concepts are tested and validated with a near-analytic model.

Pump limiter studies in Tore Supra

International Nuclear Information System (INIS)

Chatelier, M.; Bonnel, P.; Bruneau, J.L.; Gil, C.; Grisolia, C.; Loarer, T.; Martin, G.; Pegourie, B.; Rodriguez, L.

1991-01-01

The aim of the Tore Supra pump limiter program is to study particle exhaust with a pump limiter system in long-pulse discharges with continuous pellet fueling and strong auxiliary heating. The pump limiter system consists of six vertical modules, located at the bottom of the machine, and one horizontal module at the outer midplane. The instrumentation of the limiter included pressure gauges, a residual gas analyser Langmuir probes, a spectrometer and water calorimeters. Initial results in low-density discharges, with the outboard limiter only, showed a modest effect on the plasma density, while large exhaust fluxes were measured in the pump limiter, without any external fueling

MHD stability, operational limits and disruptions

International Nuclear Information System (INIS)

1999-01-01

The present physics understandings of magnetohydrodynamic (MHD) stability of tokamak plasmas, the threshold conditions for onset of MHD instability, and the resulting operational limits on attainable plasma pressure (beta limit) and density (density limit), and the consequences of plasma disruption and disruption related effects are reviewed and assessed in the context of their application to a future DT burning reactor prototype tokamak experiment such as ITER. The principal considerations covered within the MHD stability and beta limit assessments are (i) magnetostatic equilibrium, ideal MHD stability and the resulting ideal MHD beta limit; (ii) sawtooth oscillations and the coupling of sawtooth activity to other types of MHD instability; (iii) neoclassical island resistive tearing modes and the corresponding limits on beta and energy confinement; (iv) wall stabilization of ideal MHD instabilities and resistive wall instabilities; (v) mode locking effects of non-axisymmetric error fields; (vi) edge localized MHD instabilities (ELMs, etc.); and (vii) MHD instabilities and beta/pressure gradient limits in plasmas with actively modified current and magnetic shear profiles. The principal considerations covered within the density limit assessments are (i) empirical density limits; (ii) edge power balance/radiative density limits in ohmic and L-mode plasmas; and (iii) edge parameter related density limits in H-mode plasmas. The principal considerations covered in the disruption assessments are (i) disruption causes, frequency and MHD instability onset; (ii) disruption thermal and current quench characteristics; (iii) vertical instabilities (VDEs), both before and after disruption, and plasma and in-vessel halo currents; (iv) after disruption runaway electron formation, confinement and loss; (v) fast plasma shutdown (rapid externally initiated dissipation of plasma thermal and magnetic energies); (vi) means for disruption avoidance and disruption effect mitigation; and

Characterization of the up-down asymmetry of density fluctuations induced by a lower modular limiter in Tore Supra

International Nuclear Information System (INIS)

Fenzi, C.; Devynck, P.; Garbet, X.; Antar, G.; Capes, H.; Laviron, C.; Truc, A.; Gervais, F.; Hennequin, P.; Quemeneur, A.

1999-01-01

In magnetic fusion devices, the effect of plasma facing components on plasma turbulence is a key issue for several reasons. Firstly, the edge turbulence controls the power deposition on plasma facing components. Secondly, the possible influence of the edge parameters on the core fluctuations is a central question, since the core turbulent transport is responsible for the confinement degradation. It is in practice difficult to determine whether the plasma core influences the edge, or the opposite. We show here that spatial edge asymmetries of density fluctuations, and particularly up-down asymmetries, provide a powerful tool to investigate this problem. In TORE SUPRA, previous scaling analyses with various plasma parameters have emphasized that a very clear effect on the asymmetry level appears when the plasma leans on the lower modular limiter located close to the measurement chord. We present here recent measurement results concerning that specific case. They tend to show that the limiter configuration has some effect on the core turbulence. (authors)

Development of high-current-density LAB6 thermionic emitters for a space-charge-limited electron gun

International Nuclear Information System (INIS)

Herniter, M.E.; Getty, W.D.

1987-01-01

An electron gun has been developed for investigation of high current density, space charge limited operation of a lenthanum hexaboride (LaB 6 ) thermionic cathode. The 2.8 cm 2 cathode disk is heated by electron bombardment from a tungsten filament. For LaB 6 cathode temperatures greater than 1600 0 C it has been found that evaporation from the LaB 6 causes an increase in the tungsten filament emission, leading to an instability in the bombardment heating system. This instability has been investigated and eliminated by using a graphite disk in place of the LaB 6 cathode or by shielding the filament from the LaB 6 cathode by placing the LaB 6 in a graphite cup and bombarding the cup. The graphite disk has been heated to 1755 0 C with 755 W of heating power, and the shielded LaB 6 cathode has been heated to 1695 0 C. This temperature range is required for emission current densities in the 30 Acm 2 range. It is believed that the evaporation of lanthanum lowers the tungsten work function. In electron-gun use, the LaB 6 cathode has been operated up to 6.7 Acm 2 at 36 kV. A 120 kV Marx generator has been built to allow operation up to 40 Acm 2

Limitations of threshold voltage engineering of AlGaN/GaN heterostructures by dielectric interface charge density and manipulation by oxygen plasma surface treatments

Science.gov (United States)

Lükens, G.; Yacoub, H.; Kalisch, H.; Vescan, A.

2016-05-01

The interface charge density between the gate dielectric and an AlGaN/GaN heterostructure has a significant impact on the absolute value and stability of the threshold voltage Vth of metal-insulator-semiconductor (MIS) heterostructure field effect transistor. It is shown that a dry-etching step (as typically necessary for normally off devices engineered by gate-recessing) before the Al2O3 gate dielectric deposition introduces a high positive interface charge density. Its origin is most likely donor-type trap states shifting Vth to large negative values, which is detrimental for normally off devices. We investigate the influence of oxygen plasma annealing techniques of the dry-etched AlGaN/GaN surface by capacitance-voltage measurements and demonstrate that the positive interface charge density can be effectively compensated. Furthermore, only a low Vth hysteresis is observable making this approach suitable for threshold voltage engineering. Analysis of the electrostatics in the investigated MIS structures reveals that the maximum Vth shift to positive voltages achievable is fundamentally limited by the onset of accumulation of holes at the dielectric/barrier interface. In the case of the Al2O3/Al0.26Ga0.74N/GaN material system, this maximum threshold voltage shift is limited to 2.3 V.

Tokamak advanced pump limiter experiments and analysis

International Nuclear Information System (INIS)

Conn, R.W.

1983-06-01

Experiments with pump limiter modules on several operating tokamaks establish such limiters as efficient collectors of particles and has demonstrated the importance of ballistic scattering as predicted theoretically. Plasma interaction with recycling neutral gas appears to become important as the plasma density increases and the effective ionization mean free path within the module decreases. In limiters with particle collection but without active internal pumping, the neutral gas pressure is found to vary nonlinearly with the edge plasma density at the highest densities studies. Both experiments and theory indicate that the energy spectrum of gas atoms in the pump ducting is non-thermal, consistent with the results of Monte Carlo neutral atom transport calculations. The distribution of plasma power over the front surface of such modules has been measured and appears to be consistent with the predictions of simple theory. Initial results from the latest experiment on the ISX-B tokamak with an actively pumped limiter module demonstrates that the core plasma density can be controlled with a pump limiter and that the scrape-off layer plasma can partially screen the core plasma from gas injection. The results from module pump limiter experiments and from the theory and design analysis of advanced pump limiters for reactors are used to suggest the major features of a definitive, axisymmetric, toroidal belt pump limiter experiment

Locating the rate-limiting step for the interaction of hydrogen with Mg(0001) using density-functional theory calculations and rate theory

DEFF Research Database (Denmark)

Vegge, Tejs

2004-01-01

The dissociation of molecular hydrogen on a Mgs0001d surface and the subsequent diffusion of atomic hydrogen into the magnesium substrate is investigated using Density Functional Theory (DFT) calculations and rate theory. The minimum energy path and corresponding transition states are located usi...... to be rate-limiting for the ab- and desorption of hydrogen, respectively. Zero-point energy contributions are found to be substantial for the diffusion of atomic hydrogen, but classical rates are still found to be within an order of magnitude at room temperature.......The dissociation of molecular hydrogen on a Mgs0001d surface and the subsequent diffusion of atomic hydrogen into the magnesium substrate is investigated using Density Functional Theory (DFT) calculations and rate theory. The minimum energy path and corresponding transition states are located using...

Accuracy limits for the determination of cortical width and density: the influence of object size and CT imaging parameters

International Nuclear Information System (INIS)

Prevrhal, S.; Engelke, K.; Kalender, W.A.

1999-01-01

In this study we analysed the accuracy of computed tomography (CT) measurements in assessing cortical bone. We determined the dependency of thickness and density measurements on the true width and density of the cortex and on the spatial resolution in the CT images using two optimized segmentation methods. As a secondary goal, we assessed the ability of CT to reflect small changes in cortical thickness. Two different bone-mimicking phantoms with varying cortical thickness were scanned with single-slice CT on a Somatom Plus 4 scanner. Images were reconstructed with both a standard and a high-resolution convolution kernel. Two special operator-independent segmentation methods were used to automatically detect the edges of the cortical shell. We measured cortical thickness and density and compared the phantom measurements with theoretical computations by simulating a cross-sectional shape of the cortical shell. Based on the simulations, we calculated CT's power to detect small changes in cortical thickness. Simulations and phantom measurements were in very good agreement. Cortical thickness could be measured with an error of less than 10% if the true thickness was larger than 0.9 (0.7) mm for the standard (high-resolution) kernel which is close to the full width at half maximum (FWHM) of the point spread functions for these kernels and our scanner. Density measurements yielded errors of less than 10% for true cortical thickness values above two to three times the FWHM corresponding to 2.5 (2) mm in our case. The simulations showed that a 10% change in cortical width would not be detected with satisfying probability in bones with a cortical shell thinner than 1.2 mm. An accurate determination of the cortical thickness is limited to bones with a thickness higher than the FWHM of the scanner's point spread function. Therefore, the use of a high-resolution reconstruction kernel is crucial. Cortical bone mineral density can only be measured accurately in bones two to three

Single-particle energies and density of states in density functional theory

Science.gov (United States)

van Aggelen, H.; Chan, G. K.-L.

2015-07-01

Time-dependent density functional theory (TD-DFT) is commonly used as the foundation to obtain neutral excited states and transition weights in DFT, but does not allow direct access to density of states and single-particle energies, i.e. ionisation energies and electron affinities. Here we show that by extending TD-DFT to a superfluid formulation, which involves operators that break particle-number symmetry, we can obtain the density of states and single-particle energies from the poles of an appropriate superfluid response function. The standard Kohn- Sham eigenvalues emerge as the adiabatic limit of the superfluid response under the assumption that the exchange- correlation functional has no dependence on the superfluid density. The Kohn- Sham eigenvalues can thus be interpreted as approximations to the ionisation energies and electron affinities. Beyond this approximation, the formalism provides an incentive for creating a new class of density functionals specifically targeted at accurate single-particle eigenvalues and bandgaps.

Effect of a superconducting coil as a fault current limiter on current density distribution in BSCCO tape after an over-current pulse

International Nuclear Information System (INIS)

Tallouli, M; Yamaguchi, S.; Shyshkin, O.

2017-01-01

The development of power transmission lines based on long-length high temperature superconducting (HTS) tapes is complicated and technically challenging task. A serious problem for transmission line operation could become HTS power cable damage due to over-current pulse conditions. To avoid the cable damage in any urgent case the superconducting coil technology, i.e. superconductor fault current limiter (SFCL) is required. Comprehensive understanding of the current density characteristics of HTS tapes in both cases, either after pure over-current pulse or after over-current pulse limited by SFCL, is needed to restart or to continue the operation of the power transmission line. Moreover, current density distribution along and across the HTS tape provides us with the sufficient information about the quality of the tape performance in different current feeding regimes. In present paper we examine BSCCO HTS tape under two current feeding regimes. The first one is 100A feeding preceded by 900A over-current pulse. In this case none of tape protection was used. The second scenario is similar to the fist one but SFCL is used to limit an over-current value. For both scenarios after the pulse is gone and the current feeding is set up at 100A we scan magnetic field above the tape by means of Hall probe sensor. Then the feeding is turned of and the magnetic field scanning is repeated. Using the inverse problem numerical solver we calculate the corresponding direct and permanent current density distributions during the feeding and after switch off. It is demonstrated that in the absence of SFCL the current distribution is highly peaked at the tape center. At the same time the current distribution in the experiment with SFCL is similar to that observed under normal current feeding condition. The current peaking in the first case is explained by the effect of an opposite electric field induced at the tape edges during the overcurrent pulse decay, and by degradation of

Pellet injection into ASDEX upgrade plasmas

International Nuclear Information System (INIS)

Lang, P.T.; Zohm, H.; Buechl, K.; Fuchs, J.C.; Gehre, O.; Gruber, O.; Lang, R.S.; Mertens, V.; Neuhauser, J.; Salzmann, H.

1996-04-01

This work comprises results obtained using the new centrifuge injection system for the two first years of pellet injection experiments at Asdex Upgrade until the end of the 1995 experimental campaign. The main aim of the pellet injection investigation is to develop scenarios allowing for a more flexible plasma density control means of injection of cryogenic solid hydrogen pellets. Efforts have been made to develop scenarios allowing more flexible plasma density control by injecting cryogenic solid hydrogen pellets. While the injection of pellets during ohmic discharges was found to be most efficient and also improves the plasma performance, increasing the auxiliary heating power causes a detoriation of the pellet fuelling efficiency. A further strong reduction of the pellet fuelling efficiency by an additional process was observed for the more reactor-relevant conditions of shallow particle deposition during H-mode phases. With injection during type I ELMy H-mode phases, each pellet was found to trigger the release of an ELM and therefore cause particle losses mainly from the edge region. In the type I ELMy H-mode, only sufficient pellet penetration allowed noticeable, persistent particle deposition in the plasma by the pellets. Applying adequate pellet injection conditions and favourable scenarios using combined pellet/gas puff refuelling, significant density ramp-up to densities exceeding the empirical Greenwald limit by up to a factor of two was achieved even for strongly heated H-mode plasmas. (orig.)

Low-temperature operating regime of the tokamak evacuating limiter

International Nuclear Information System (INIS)

Tokar', M.Z.

1987-01-01

The conditions for realizing the regime of strong recycling of a cold dense plasma of an evacuating limiter were determined based on a previously proposed model for describing the limiter layer of a tokamak. The scaling for the dependence of the gas pressure in the evacuation system on the average plasma density in the limiter layer was found, and agreed quantitatively with the results of measurements on the Alcator and ISX-B tokamaks. For the tokamak reactor of the INTOR scale the calculations show that the low-temperature operating regime of the evacuating limiter can be realized with a quite low pumping rate. It has the advantages of reduced erosion of the limiter and small fluxes of impurities into the working volume of the reactor. In addition, the relative concentration of the helium ash in the limiter layer does not exceed 2-3%, but the density of the main plasma is comparable to the proposed average density in the reactor. The concept of a stochastic limiter is of interest for lowering the plasma density in the limiter layer and lowering the thermal loads on the limiter

Studies of high-δ (baffled) and low-δ (open) pumped divertor operation on DIII-D

International Nuclear Information System (INIS)

Allen, S.L.; Fenstermacher, M.E.; Greenfield, C.M.

1998-08-01

The authors report new experimental results with the RDP-OB (Radiative Divertor Project-outer baffle) and cryopump in both upper single-null (USN) and double-null (DN) ELMing H-mode discharges. The baffled divertor reduced the core ionization (∼2--2.5x), in reasonable agreement with predictions from UEDGE/DEGAS modeling (∼3.75x). The upper cryopump achieved density control of n e /n gw ∼ 0.22 (line density/Greenwald density) with Z eff ∼ 2 in high-δ plasmas. The measured exhaust is comparable to the lower pump, except at lower core electron densities (n e 19 m -3 ). Efficient impurity exhaust was obtained with deuterium SOL flow. Preliminary experiments with DN operation has shown that the particle exhaust to the upper pump depends on the up/down magnetic balance. Preliminary experiments indicate that the DN exhaust is roughly 40--50% of the USN exhaust at n e ∼ 4 x 10 19 m -3

A new scaling for divertor detachment

Science.gov (United States)

Goldston, R. J.; Reinke, M. L.; Schwartz, J. A.

2017-05-01

The ITER design, and future reactor designs, depend on divertor ‘detachment,’ whether partial, pronounced or complete, to limit heat flux to plasma-facing components and to limit surface erosion due to sputtering. It would be valuable to have a measure of the difficulty of achieving detachment as a function of machine parameters, such as input power, magnetic field, major radius, etc. Frequently the parallel heat flux, estimated typically as proportional to P sep/R or P sep B/R, is used as a proxy for this difficulty. Here we argue that impurity cooling is dependent on the upstream density, which itself must be limited by a Greenwald-like scaling. Taking this into account self-consistently, we find the impurity fraction required for detachment scales dominantly as power divided by poloidal magnetic field. The absence of any explicit scaling with machine size is concerning, as P sep surely must increase greatly for an economic fusion system, while increases in the poloidal field strength are limited by coil technology and plasma physics. This result should be challenged by comparison with 2D divertor codes and with measurements on existing experiments. Nonetheless, it suggests that higher magnetic field, stronger shaping, double-null operation, ‘advanced’ divertor configurations, as well as alternate means to handle heat flux such as metallic liquid and/or vapor targets merit greater attention.

Experimental evidence for herbivore limitation of the treeline.

Science.gov (United States)

Speed, James D M; Austrheim, Gunnar; Hester, Alison J; Mysterud, Atle

2010-11-01

The treeline ecotone divides forest from open alpine or arctic vegetation states. Treelines are generally perceived to be temperature limited. The role of herbivores in limiting the treeline is more controversial, as experimental evidence from relevant large scales is lacking. Here we quantify the impact of different experimentally controlled herbivore densities on the recruitment and survival of birch Betula pubescens tortuosa along an altitudinal gradient in the mountains of southern Norway. After eight years of summer grazing in large-scale enclosures at densities of 0, 25, and 80 sheep/km2, birch recruited within the whole altitudinal range of ungrazed enclosures, but recruitment was rarer in enclosures with low-density sheep and was largely limited to within the treeline in enclosures with high-density sheep. In contrast, the distribution of saplings (birch older than the experiment) did not differ between grazing treatments, suggesting that grazing sheep primarily limit the establishment of new tree recruits rather than decrease the survival of existing individuals. This study provides direct experimental evidence that herbivores can limit the treeline below its potential at the landscape scale and even at low herbivore densities in this climatic zone. Land use changes should thus be considered in addition to climatic changes as potential drivers of ecotone shifts.

Efficiency and rumen responses in younger and older Holstein heifers limit-fed diets of differing energy density.

Science.gov (United States)

Zanton, G I; Heinrichs, A J

2016-04-01

The objective of this study was to evaluate the effects of limit feeding diets of different predicted energy density on the efficiency of utilization of feed and nitrogen and rumen responses in younger and older Holstein heifers. Eight rumen-cannulated Holstein heifers (4 heifers beginning at 257 ± 7 d, hereafter "young," and 4 heifers beginning at 610 ± 16 d, hereafter "old") were limit-fed high [HED; 2.64 Mcal/kg of dry matter (DM), 15.31% crude protein (CP)] or low (LED; 2.42 Mcal/kg of DM, 14.15% CP) energy density diets according to a 4-period, split-plot Latin square design with 28-d periods. Diets were limit-fed to provide isonitrogenous and isoenergetic intake on a rumen empty body weight (BW) basis at a level predicted to support approximately 800 g/d of average daily gain. During the last 7d of each period, rumen contents were subsampled over a 24-h period, rumen contents were completely evacuated, and total collection of feces and urine was made over 4d. Intakes of DM and water were greater for heifers fed LED, although, by design, calculated intake of metabolizable energy did not differ between age groups or diets when expressed relative to rumen empty BW. Rumen pH was lower, ammonia (NH3-N) concentration tended to be higher, and volatile fatty acids (VFA) concentration was not different for HED compared with LED and was unaffected by age group. Rumen content mass was greater for heifers fed LED and for old heifers, so when expressing rumen fermentation responses corrected for this difference in pool size, NH3-N pool size was not different between diets and total moles of VFA in the rumen were greater for heifers fed LED, whereas these pool sizes were greater for old heifers. Total-tract digestibility of potentially digestible neutral detergent fiber (NDF) was greater in heifers fed LED and for young heifers, whereas the fractional rate of ruminal passage and digestion of NDF were both greater in heifers fed LED. Digestibility of N was greater for

Limitation of critical current density by intermetallic formation in fine filament Nb-Ti superconductors

International Nuclear Information System (INIS)

Larbalestier, D.C.; Chengren, L.; Starch, W.; Lee, P.J.

1985-01-01

Two experiments have been performed to investigate the role that the intermetallic reaction between the copper matrix and the Nb-Ti filaments plays in limiting the critical current density (J/sub c/) of Nb 45.6 wt% Ti composites. The first experiment involved composites which were industrially extruded. It was found that as the number of heat treatments increased, the J/sub c/ declined, the resistive transition broadened and the filaments sausaged. The filament sausaging was initiated by intermetallic particles at the filament matrix interface. A series of many heat treatment procedures were then applied to composites fabricated in the authors own laboratories without extrusion. Very high J/sub c/ values were obtained at filament sizes of 20 μm. When the same heat treatment procedures were applied to 4 - 5 μm conductors, extensive sausaging and degraded J/sub c/ values resulted. This degradation was also found to be due to the formation of Cu-Nb-Ti intermetallic compounds. It is concluded that a reliable filament diffusion barrier technology is necessary to permit full flexibility in the heat treatment of 2 - 5 μ filament Nb-Ti composites

Limitation of critical current density by intermetallic formation in fine filament Nb-Ti superconductors

International Nuclear Information System (INIS)

Larbalestier, D.C.; Chengren, Li; Lee, P.J.; Starch, W.

1985-01-01

Two experiments have been performed to investigate the role that the intermetallic reaction between the copper matrix and the Nb-Ti filaments plays in limiting the critical current density (J /SUB c/ ) of Nb 46.5 wt% Ti composites. The first experiment involved composites which were industrially extruded. It was found that as the number of heat treatments increased, the J /SUB c/ declined, the resistive transition broadened and the filaments sausaged. The filament sausaging was initiated by intermetallic particles at the filament matrix interface. A series of many heat treatment procedures were then applied to composites fabricated in our own laboratories without extrusion. Very high J /SUB c/ values were obtained at filament sizes of 20 μm. When the same heat treatment procedures were applied to 4 - 5 μm conductors, extensive sausaging and degraded J /SUB c/ values resulted. This degradation was also found to be due to the formation of Cu-Nb-Ti intermetallic compounds. It is concluded that a reliable filament diffusion barrier technology is necessary to permit full flexibility in the heat treatment of 2 - 5 μm filament Nb-Ti composites

Competing Quantum Hall Phases in the Second Landau Level in Low Density Limit

Energy Technology Data Exchange (ETDEWEB)

Pan, Wei [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Serafin, A. [Univ. of Florida, Gainesville, FL (United States). National High Magnetic Field Lab. (MagLab); Xia, J. S. [Univ. of Florida, Gainesville, FL (United States). National High Magnetic Field Lab. (MagLab); Liang, Y. [Univ. of Florida, Gainesville, FL (United States). National High Magnetic Field Lab. (MagLab); Sullivan, N. S. [Univ. of Florida, Gainesville, FL (United States). National High Magnetic Field Lab. (MagLab); Baldwin, K. W. [Princeton Univ., NJ (United States); West, K. W. [Princeton Univ., NJ (United States); Pfeiffer, L. N. [Princeton Univ., NJ (United States); Tsui, D. C. [Princeton Univ., NJ (United States)

2015-01-01

Up to date, studies of the fractional quantum Hall effect (FQHE) states in the second Landau level have mainly been carried out in the high electron density regime, where the electron mobility is the highest. Only recently, with the advance of high quality low density MBE growth, experiments have been pushed to the low density regime [1], where the electron-electron interactions are strong and the Landau level mixing parameter, defined by κ = e²/εI_B/ℏω_e, is large. Here, l_B = (ℏe/B)^1/2 is the magnetic length and ω_c = eB/m the cyclotron frequency. All other parameters have their normal meanings. It has been shown that a large Landau level mixing effect strongly affects the electron physics in the second Landau level [2].

ITER-EDA physics design requirements and plasma performance assessments

International Nuclear Information System (INIS)

Uckan, N.A.; Galambos, J.; Wesley, J.; Boucher, D.; Perkins, F.; Post, D.; Putvinski, S.

1996-01-01

Physics design guidelines, plasma performance estimates, and sensitivity of performance to changes in physics assumptions are presented for the ITER-EDA Interim Design. The overall ITER device parameters have been derived from the performance goals using physics guidelines based on the physics R ampersand D results. The ITER-EDA design has a single-null divertor configuration (divertor at the bottom) with a nominal plasma current of 21 MA, magnetic field of 5.68 T, major and minor radius of 8.14 m and 2.8 m, and a plasma elongation (at the 95% flux surface) of ∼1.6 that produces a nominal fusion power of ∼1.5 GW for an ignited burn pulse length of ≥1000 s. The assessments have shown that ignition at 1.5 GW of fusion power can be sustained in ITER for 1000 s given present extrapolations of H-mode confinement (τ E = 0.85 x τ ITER93H ), helium exhaust (τ* He /τ E = 10), representative plasma impurities (n Be /n e = 2%), and beta limit [β N = β(%)/(I/aB) ≤ 2.5]. The provision of 100 MW of auxiliary power, necessary to access to H-mode during the approach to ignition, provides for the possibility of driven burn operations at Q = 15. This enables ITER to fulfill its mission of fusion power (∼ 1--1.5 GW) and fluence (∼1 MWa/m 2 ) goals if confinement, impurity levels, or operational (density, beta) limits prove to be less favorable than present projections. The power threshold for H-L transition, confinement uncertainties, and operational limits (Greenwald density limit and beta limit) are potential performance limiting issues. Improvement of the helium exhaust (τ* He /τ E ≤ 5) and potential operation in reverse-shear mode significantly improve ITER performance

Effect of pump limiter throat on pumping efficiency

International Nuclear Information System (INIS)

Ghendrih, P.; Grosman, A.; Samain, A.; Capes, H.; Morera, J.P.

1988-01-01

The necessary control of plasma edge density has led to the development of pump limiters to achieve this task. On Tore Supra, where a large part of the program is devoted to plasma edge studies, two types of such density control apparatus have been implemented, a set of pump limiters and the pumps associated to the ergodic divertor (magnetically assisted pump limiters). Generally two different kinds of pump limiters can be used, those with a throat which drives the plasma from the open edge plasma (SOL) to the neutralizer plate, and those without or with a very short throat. We are interested here in this aspect of the pump limiter concept, i.e. on the throat effect on neutral density build-up in the vicinity of the pumping plates (and hence on pumping efficieny). The underlying idea of this throat effect can be readily understood; indeed while the neutral capture in pump limiters without throats is only a ballistic effect, on expects the plasma to improve the efficiency of pump-limiters via plasma-neutral-sidewall interactions in the throat. This problem has been studied both numerically and analytically. The paper is divided as follows. In section 2, we describe the basic features of pump-limiters which are modelized by the numerical code Cezanne. Section 3 is devoted to the throat length effect considering in particular the neutral density profile in the throat and the neutral density buil-up as a function of the throat lenght. In section 4, we show that the plugging effect occurs for reasonnable values of throat lengths. An analytical value of the plugging length is discussed and compared to the values obtained numerically

On the origin of plasma density blobs

Energy Technology Data Exchange (ETDEWEB)

Krasheninnikov, S.I., E-mail: skrash@mae.ucsd.edu

2016-12-01

By keeping nonlinear Boltzmann factor in electron density dependence on electrostatic potential it is demonstrated that large plasma density blobs, often seen in experiment inside separatrix, can exist within the framework of drift wave dynamics. The estimates show that plasma density in a blob can be ∼3 times higher that average plasma density, but hardly exceeds this limit, which in a ball park is in agreement with experimental observations.

Metal-amplified Density Assays, (MADAs), including a Density-Linked Immunosorbent Assay (DeLISA).

Science.gov (United States)

Subramaniam, Anand Bala; Gonidec, Mathieu; Shapiro, Nathan D; Kresse, Kayleigh M; Whitesides, George M

2015-02-21

This paper reports the development of Metal-amplified Density Assays, or MADAs - a method of conducting quantitative or multiplexed assays, including immunoassays, by using Magnetic Levitation (MagLev) to measure metal-amplified changes in the density of beads labeled with biomolecules. The binding of target analytes (i.e. proteins, antibodies, antigens) to complementary ligands immobilized on the surface of the beads, followed by a chemical amplification of the binding in a form that results in a change in the density of the beads (achieved by using gold nanoparticle-labeled biomolecules, and electroless deposition of gold or silver), translates analyte binding events into changes in density measureable using MagLev. A minimal model based on diffusion-limited growth of hemispherical nuclei on a surface reproduces the dynamics of the assay. A MADA - when performed with antigens and antibodies - is called a Density-Linked Immunosorbent Assay, or DeLISA. Two immunoassays provided a proof of principle: a competitive quantification of the concentration of neomycin in whole milk, and a multiplexed detection of antibodies against Hepatitis C virus NS3 protein and syphilis T. pallidum p47 protein in serum. MADAs, including DeLISAs, require, besides the requisite biomolecules and amplification reagents, minimal specialized equipment (two permanent magnets, a ruler or a capillary with calibrated length markings) and no electrical power to obtain a quantitative readout of analyte concentration. With further development, the method may be useful in resource-limited or point-of-care settings.

Admissible Crosstalk Limits in a Two Colour Interferometers for Plasma Density Diagnostics. A Reduction Algorithm

International Nuclear Information System (INIS)

Sanchez, M.; Esteban, L.; Kornejew, P.; Hirsch, M.

2008-01-01

Mid Infrared (10,6 μm CO 2 laser lines) interferometers as a plasma density diagnostic must use two-colour systems with superposed interferometers beams at different wavelengths in order to cope with mechanical vibrations and drifts. They require a highly precise phase difference measurement where all sources of error must be reduced. One of these is the cross-talk between the signals which creates nonlinear spurious periodic mixing products. The reason may be either optical or electrical crosstalk both resulting in similar perturbations of the measurement. In the TJII interferometer a post-processing algorithm is used to reduce the crosstalk in the data. This post-processing procedure is not appropriate for very long pulses, as it is the case for in new tokamak (ITER) or stellarator (W7-X) projects. In both cases an on-line reduction process is required or--even better--the unwanted signal components must be reduced in the system itself CO 2 laser interferometers which as the second wavelength use the CO laser line (5,3 μm), may apply a single common detector sensitive to both wavelengths and separate the corresponding IF signals by appropriate bandpass filters. This reduces complexity of the optical arrangement and avoids a possible source of vibration induced phase noise as both signals share the same beam path. To avoid cross talk in this arrangement filtering must be appropriate. In this paper we present calculations to define the limits of crosstalk for a desired plasma density precision. A crosstalk reduction algorithm has been developed and is applied to experimental results from TJ-II pulses. Results from a single detector arrangement as under investigation for the CO 2 /CO laser interferometer developed for W7-X are presented

Matrix density alters zyxin phosphorylation, which limits peripheral process formation and extension in endothelial cells invading 3D collagen matrices.

Science.gov (United States)

Abbey, Colette A; Bayless, Kayla J

2014-09-01

integrate signals from multiple exogenous factors, including changes in matrix density, to accomplish successful sprouting responses. We show here for the first time that zyxin limited the formation and extension of fine peripheral processes used by ECs for matrix interrogation, providing a molecular explanation for altered EC responses to high and low density collagen matrices. Copyright © 2014 International Society of Matrix Biology. Published by Elsevier B.V. All rights reserved.

Immigration Rates during Population Density Reduction in a Coral Reef Fish

Science.gov (United States)

Turgeon, Katrine; Kramer, Donald L.

2016-01-01

Although the importance of density-dependent dispersal has been recognized in theory, few empirical studies have examined how immigration changes over a wide range of densities. In a replicated experiment using a novel approach allowing within-site comparison, we examined changes in immigration rate following the gradual removal of territorial damselfish from a limited area within a much larger patch of continuous habitat. In all sites, immigration occurred at intermediate densities but did not occur before the start of removals and only rarely as density approached zero. In the combined data and in 5 of 7 sites, the number of immigrants was a hump-shaped function of density. This is the first experimental evidence for hump-shaped, density-dependent immigration. This pattern may be more widespread than previously recognized because studies over more limited density ranges have identified positive density dependence at low densities and negative density dependence at high densities. Positive density dependence at low density can arise from limits to the number of potential immigrants and from behavioral preferences for settling near conspecifics. Negative density dependence at high density can arise from competition for resources, especially high quality territories. The potential for non-linear effects of local density on immigration needs to be recognized for robust predictions of conservation reserve function, harvest impacts, pest control, and the dynamics of fragmented populations. PMID:27271081

Anisotropic dynamic mass density for fluidsolid composites

KAUST Repository

Wu, Ying; Mei, Jun; Sheng, Ping

2012-01-01

By taking the low frequency limit of multiple-scattering theory, we obtain the dynamic effective mass density of fluidsolid composites with a two-dimensional rectangular lattice structure. The anisotropic mass density can be described by an angle

Anthropogenically-Mediated Density Dependence in a Declining Farmland Bird.

Directory of Open Access Journals (Sweden)

Jenny C Dunn

Full Text Available Land management intrinsically influences the distribution of animals and can consequently alter the potential for density-dependent processes to act within populations. For declining species, high densities of breeding territories are typically considered to represent productive populations. However, as density-dependent effects of food limitation or predator pressure may occur (especially when species are dependent upon separate nesting and foraging habitats, high territory density may limit per-capita productivity. Here, we use a declining but widespread European farmland bird, the yellowhammer Emberiza citrinella L., as a model system to test whether higher territory densities result in lower fledging success, parental provisioning rates or nestling growth rates compared to lower densities. Organic landscapes held higher territory densities, but nests on organic farms fledged fewer nestlings, translating to a 5 times higher rate of population shrinkage on organic farms compared to conventional. In addition, when parental provisioning behaviour was not restricted by predation risk (i.e., at times of low corvid activity, nestling provisioning rates were higher at lower territory densities, resulting in a much greater increase in nestling mass in low density areas, suggesting that food limitation occurred at high densities. These findings in turn suggest an ecological trap, whereby preferred nesting habitat does not provide sufficient food for rearing nestlings at high population density, creating a population sink. Habitat management for farmland birds should focus not simply on creating a high nesting density, but also on ensuring heterogeneous habitats to provide food resources in close proximity to nesting birds, even if this occurs through potentially restricting overall nest density but increasing population-level breeding success.

A mechanistic analysis of density dependence in algal population dynamics

Directory of Open Access Journals (Sweden)

Adrian eBorlestean

2015-04-01

Full Text Available Population density regulation is a fundamental principle in ecology, but the specific process underlying functional expression of density dependence remains to be fully elucidated. One view contends that patterns of density dependence are largely fixed across a species irrespective of environmental conditions, whereas another is that the strength and expression of density dependence are fundamentally variable depending on the nature of exogenous or endogenous constraints acting on the population. We conducted a study investigating the expression of density dependence in Chlamydomonas spp. grown under a gradient from low to high nutrient density. We predicted that the relationship between per capita growth rate (pgr and population density would vary from concave up to concave down as nutrient density became less limiting and populations experienced weaker density regulation. Contrary to prediction, we found that the relationship between pgr and density became increasingly concave-up as nutrient levels increased. We also found that variation in pgr increased, and pgr levels reached higher maxima in nutrient-limited environments. Most likely, these results are attributable to population growth suppression in environments with high intraspecific competition due to limited nutrient resources. Our results suggest that density regulation is strongly variable depending on exogenous and endogenous processes acting on the population, implying that expression of density dependence depends extensively on local conditions. Additional experimental work should reveal the mechanisms influencing how the expression of density dependence varies across populations through space and time.

β limit disruptions in the TFTR tokamak

International Nuclear Information System (INIS)

Fredrickson, E.D.; McGuire, K.; Janos, A.; Bell, M.; Budny, R.V.; Bush, C.E.; Manickam, J.; Mynick, H.; Nazikian, R.; Taylor, G.

1994-11-01

A disruptive β limit (β = plasma pressure/magnetic pressure) is observed in high performance plasmas in TFTR. The MHD character of these disruptions differs substantially from the disruptions in high density plasmas (density limit disruptions) on TFTR. The high β disruptions can occur with less than a milliseconds warning in the form of a fast growing precursor. The precursor appears to be an external kink or internal (m,n)=(1,1) kink strongly coupled through finite β effects and toroidal terms to higher m components. It does not have the open-quote cold bubble close-quote structure found in density limit disruptions. There is also no evidence for a change in the internal inductance, i.e., a major reconnection of the flux, at the time of the thermal quench

Passive fault current limiting device

Science.gov (United States)

Evans, Daniel J.; Cha, Yung S.

1999-01-01

A passive current limiting device and isolator is particularly adapted for use at high power levels for limiting excessive currents in a circuit in a fault condition such as an electrical short. The current limiting device comprises a magnetic core wound with two magnetically opposed, parallel connected coils of copper, a high temperature superconductor or other electrically conducting material, and a fault element connected in series with one of the coils. Under normal operating conditions, the magnetic flux density produced by the two coils cancel each other. Under a fault condition, the fault element is triggered to cause an imbalance in the magnetic flux density between the two coils which results in an increase in the impedance in the coils. While the fault element may be a separate current limiter, switch, fuse, bimetal strip or the like, it preferably is a superconductor current limiter conducting one-half of the current load compared to the same limiter wired to carry the total current of the circuit. The major voltage during a fault condition is in the coils wound on the common core in a preferred embodiment.

Magnetic fluctuations associated with density fluctuations in the tokamak edge

International Nuclear Information System (INIS)

Kim, Y.J.; Gentle, K.W.; Ritz, C.P.; Rhodes, T.L.; Bengtson, R.D.

1989-01-01

Electrostatic density and potential fluctuations occurring with high amplitude near the edge of a tokamak are correlated with components of the fluctuating magnetic field measured outside the limiter radius. It has been established that this turbulence is associated with fluctuations in current as well as density and potential. The correlation extends for substantial toroidal distances, but only if the probes are displaced approximately along field lines, consistent with the short coherence lengths poloidally but long coherence lengths parallel to the field which are characteristic for this turbulence. Furthermore, the correlation can be found only with density fluctuations measured inside the limiter radius; density fluctuations behind the limiter have no detectable magnetic concomitant for the toroidally spaced probes used here. (author). Letter-to-the-editor. 12 refs, 3 figs

The density of cement phases

International Nuclear Information System (INIS)

Balonis, M.; Glasser, F.P.

2009-01-01

The densities of principal crystalline phases occurring in Portland cement are critically assessed and tabulated, in some cases with addition of new data. A reliable and self-consistent density set for crystalline phases was obtained by calculating densities from crystallographic data and unit cell contents. Independent laboratory work was undertaken to synthesize major AFm and AFt cement phases, determine their unit cell parameters and compare the results with those recorded in the literature. Parameters were refined from powder diffraction patterns using CELREF 2 software. A density value is presented for each phase, showing literature sources, in some cases describing limitations on the data, and the weighting attached to numerical values where an averaging process was used for accepted data. A brief discussion is made of the consequences of the packing of water to density changes in AFm and AFt structures.

A note on asymptotic normality in the thermodynamic limit at low densities

DEFF Research Database (Denmark)

Jensen, J.L.

1991-01-01

We consider a continuous statistical mechanical system with a pair interaction in a region λ tending to infinity. For low densities asymptotic normality of the canonical statistic is proved, both in the grand canonical ensemble and in the canonical ensemble. The results are illustrated through...

Overview of recent results and future plans on the Compact Toroidal Hybrid experiment

Science.gov (United States)

Maurer, D. A.; Archmiller, M. C.; Cianciosa, M. R.; Ennis, D. A.; Hanson, J. D.; Hartwell, G. J.; Hebert, J. D.; Herfindal, J. L.; Knowlton, S. F.; Ma, X.; Massidda, S.; Pandya, M. D.; Roberds, N. A.; Traverso, P. J.

2015-11-01

Goals of the Compact Toroidal Hybrid (CTH) experiment are to: (1) investigate the dependence of plasma disruptive behavior on the level of applied 3D magnetic shaping, (2) test and advance 3D computational modeling tools in strongly shaped plasmas, and (3) study the implementation of a new island divertor. Progress towards these goals and other developments are summarized. The disruptive density limit is observed to exceed the Greenwald limit as the vacuum transform is increased, but a threshold for disruption avoidance is not observed. Low q operation is routine, with low q disruptions avoided when the vacuum transform is raised to the value of 0.07 or above. Application of vacuum transform has been demonstrated to reduce and eliminate the vertical drift of elongated discharges that would otherwise be vertically unstable. Current efforts at improved equilibrium reconstruction and diagnostic development will beoverviewed. NIMROD is used to model the current ramp phase of CTH and 3D shaped sawtooth behavior. An island divertor design has begun with connection length studies and initial EMC3-Eirene results to model energy deposition on divertor plates located in an edge 1/3 island. This work is supported by U.S. Department of Energy Grant No. DE- FG02-00ER54610.

Physics results from the National Spherical Torus Experiment

International Nuclear Information System (INIS)

Kaye, S.; Bell, M.

2000-01-01

The mission of the National Spherical Torus Experiment (NSTX) is to extend the understanding of toroidal physics to low aspect ratio (R/a ∼ 1.25) in low collisionality regimes. NSTX is designed to operate with up to 6 MW of High Harmonic Fast Wave (HHFW) heating and current drive, 5 MW of Neutral Beam Injection (NBI), and Co-Axial Helicity Injection (CHI) for non-inductive startup. Initial experiments focused on establishing conditions that will allow NSTX to achieve its aims of simultaneous high-β t and high-bootstrap current fraction, and to develop methods for non-inductive operation, which will be necessary for Spherical Torus power plants. Ohmic discharges with plasma currents up to 1 MA, stored energies up to 55 kJ, β t ∼ 10%, and a range of shapes and configurations were produced. Density limits in deuterium and helium reached 80% and 120% of the Greenwald limit respectively. Significant electron heating was observed with up to 2.3 MW of HHFW. Up to 270 kA of toroidal current for up to 200 msec was produced noninductively using CHI. Initial NBI experiments were carried out with up to two beam sources (3.2 MW). Plasmas with stored energies of up to 140 kJ and β t =21% were produced

Experiments in the HT-7 Superconducting Tokamak

International Nuclear Information System (INIS)

Wan Baonian

2002-01-01

The HT-7 tokamak experiment research has made important progress. The main efforts have dealt with quasi-steady-state operation, lower-hybrid (LH) current drive (LHCD), plasma heating with ion cyclotron range of frequencies (ICRF), ion Bernstein waves (IBWs), fueling with pellets and supersonic molecular beams, first-wall conditioning techniques, and plasma and wall interaction. Plasma parameters in the experiments were much improved; for example, n e = 6.5 x 10 19 m -3 , and a plasma pulse length of >10 s was achieved. ICRF boronization and conditioning resulted in Z eff close to unity. Steady-state full LH wave current drive has been achieved for >3 s. LHCD rampup and recharge have also been demonstrated. The best [eta] CD exp of 10 19 m -2 A/W is achieved. Quasi-steady-state H-mode-like plasmas with a density close to the Greenwald limit were obtained by LHCD, where energy confinement time was nearly five times longer than in the ohmic case. The synergy between the IBW, pellet, and LHCD was investigated. New doped graphite as limiter material and ferritic steel used to reduce the ripples have been developed. Research on the mechanism of microturbulence has been extensively carried out experimentally

The preliminary studies of HL-1 plasma with pump limiter

International Nuclear Information System (INIS)

Ran, L.B.; Li, G.D.; Sum, S.Q.

1991-01-01

Reduction of the impurity and control of the density are very important task in the present tokamak research. Some experiments showed that the pump limiter is effective to improve impurity and density control. A small-scale pump limiter has been installed on HL-1 tokamak in 1990 and the experiment has been carried out firstly with hydrogen ohmic discharge. In this paper we would present the improvements of the plasma properties as the pump limiter was main limiter and the movable limiter was auxiliary limiter. (author) 3 refs., 8 figs

Chiral dynamics and peripheral transverse densities

Energy Technology Data Exchange (ETDEWEB)

Granados, Carlos G. [Uppsala University (Sweden); Weiss, Christian [JLAB, Newport News, VA (United States)

2014-01-01

In the partonic (or light-front) description of relativistic systems the electromagnetic form factors are expressed in terms of frame-independent charge and magnetization densities in transverse space. This formulation allows one to identify the chiral components of nucleon structure as the peripheral densities at transverse distances b = O(M{sub {pi}}{sup -1}) and compute them in a parametrically controlled manner. A dispersion relation connects the large-distance behavior of the transverse charge and magnetization densities to the spectral functions of the Dirac and Pauli form factors near the two--pion threshold at timelike t = 4 M{ sub {pi}}{sup 2}, which can be computed in relativistic chiral effective field theory. Using the leading-order approximation we (a) derive the asymptotic behavior (Yukawa tail) of the isovector transverse densities in the "chiral" region b = O(M{sub {pi}}{sup -1}) and the "molecular" region b = O(M{sub N}{sup 2}/M{sub {pi}}{sup 3}); (b) perform the heavy-baryon expansion of the transverse densities; (c) explain the relative magnitude of the peripheral charge and magnetization densities in a simple mechanical picture; (d) include Delta isobar intermediate states and study the peripheral transverse densities in the large-N{ sub c} limit of QCD; (e) quantify the region of transverse distances where the chiral components of the densities are numerically dominant; (f) calculate the chiral divergences of the b{sup 2}-weighted moments of the isovector transverse densities (charge and anomalous magnetic radii) in the limit M{sub {pi}} -> 0 and determine their spatial support. Our approach provides a concise formulation of the spatial structure of the nucleon's chiral component and offers new insights into basic properties of the chiral expansion. It relates the information extracted from low-t elastic form factors to the generalized parton distributions probed in peripheral high-energy scattering processes.

Characterization of Nightside Mid-latitude Irregularities Observed with the Blackstone SuperDARN Radar

Science.gov (United States)

Ruohoniemi, J. M.; Ribeiro, A. J.; Baker, J. B.; Greenwald, R. A.; Newell, P. T.

2009-12-01

The new mid-latitude SuperDARN radars at Wallops Island and Blackstone observe strong coherent backscattering on an almost nightly basis from latitudes that appear to be subauroral. One study has demonstrated an excellent correlation with the occurrence of density and temperature gradients within the ionospheric projection of the plasmapause (Greenwald et al., Geophys. Res. Lett. [2006]). We have processed all the data collected with the Blackstone radar since its inception in February 2008 for a characterization of the occurrence and properties of ‘plasmapause’ scatter. We have determined the local time and Kp dependencies of the activity and the relation of the spatial distribution of the irregularities to magnetospheric boundaries and ionospheric density gradients. We establish that the irregularities are a feature of the quiet-time subauroral ionosphere and provide a valuable diagnostic of the electric fields in the inner magnetosphere.

Tolerance limits of X-ray image intensity

International Nuclear Information System (INIS)

Stargardt, A.; Juran, R.; Brandt, G.A.

1985-01-01

Evaluation of the tolerance limits of X-ray image density accepted by the radiologist shows that for different kinds of examinations, deviations of more than 50% from optimal density lead to images which cannot be used diagnostically. Within this range diagnostic accuracy shows a distinct maximum and diminishes to the limits by 20%. These figures are related to differences in the intensifying factor of screens, sensitivity of films, sensitometric parameters of film processing as well as the doses employed with automatic exposure control devices, measured in clinical conditions. Maximum permissible tolerance limits of the whole imaging system and of its constituents are discussed using the Gaussian law of error addition. (author)

Maximum time-dependent space-charge limited diode currents

Energy Technology Data Exchange (ETDEWEB)

Griswold, M. E. [Tri Alpha Energy, Inc., Rancho Santa Margarita, California 92688 (United States); Fisch, N. J. [Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States)

2016-01-15

Recent papers claim that a one dimensional (1D) diode with a time-varying voltage drop can transmit current densities that exceed the Child-Langmuir (CL) limit on average, apparently contradicting a previous conjecture that there is a hard limit on the average current density across any 1D diode, as t → ∞, that is equal to the CL limit. However, these claims rest on a different definition of the CL limit, namely, a comparison between the time-averaged diode current and the adiabatic average of the expression for the stationary CL limit. If the current were considered as a function of the maximum applied voltage, rather than the average applied voltage, then the original conjecture would not have been refuted.

Plasma probe characteristics in low density hydrogen pulsed plasmas

International Nuclear Information System (INIS)

Astakhov, D I; Lee, C J; Bijkerk, F; Goedheer, W J; Ivanov, V V; Krivtsun, V M; Zotovich, A I; Zyryanov, S M; Lopaev, D V

2015-01-01

Probe theories are only applicable in the regime where the probe’s perturbation of the plasma can be neglected. However, it is not always possible to know, a priori, that a particular probe theory can be successfully applied, especially in low density plasmas. This is especially difficult in the case of transient, low density plasmas. Here, we applied probe diagnostics in combination with a 2D particle-in-cell model, to an experiment with a pulsed low density hydrogen plasma. The calculations took into account the full chamber geometry, including the plasma probe as an electrode in the chamber. It was found that the simulations reproduce the time evolution of the probe IV characteristics with good accuracy. The disagreement between the simulated and probe measured plasma density is attributed to the limited applicability of probe theory to measurements of low density pulsed plasmas on a similarly short time scale as investigated here. Indeed, in the case studied here, probe measurements would lead to, either a large overestimate, or underestimate of the plasma density, depending on the chosen probe theory. In contrast, the simulations of the plasma evolution and the probe characteristics do not suffer from such strict applicability limits. These studies show that probe theory cannot be justified through probe measurements. However, limiting cases of probe theories can be used to estimate upper and lower bounds on plasma densities. These theories include and neglect orbital motion, respectively, with different collisional terms leading to intermediate estimates. (paper)

Progress of recent experimental research on the J-TEXT tokamak

Science.gov (United States)

Zhuang, G.; Gentle, K. W.; Chen, Z. Y.; Chen, Z. P.; Yang, Z. J.; Zheng, Wei; Hu, Q. M.; Chen, J.; Rao, B.; Zhong, W. L.; Zhao, K. J.; Gao, L.; Cheng, Z. F.; Zhang, X. Q.; Wang, L.; Jiang, Z. H.; Xu, T.; Zhang, M.; Wang, Z. J.; Ding, Y. H.; Yu, K. X.; Hu, X. W.; Pan, Y.; Huang, H.; the J-TEXT Team

2017-10-01

The progress of experimental research over the last two years on the J-TEXT tokamak is reviewed and reported in this paper, including: investigations of resonant magnetic perturbations (RMPs) on the J-TEXT operation region show that moderate amplitude of applied RMPs either increases the density limit from less than 0.7n G to 0.85n G (n G is the Greenwald density, {{n}\\text{G}}={{I}\\text{p}}/π {{a}2} ) or lowers edge safety factor q a from 2.15 to nearly 2.0; observations of influence of RMPs with a large m/n  =  3/1 dominant component (where m and n are the toroidal and poloidal mode numbers respectively) on electron density indicate electron density first increases (decreases) inside (around/outside) of the 3/1 rational surface, and it is increased globally later together with enhanced edge recycling; investigations of the effect of RMPs on the behavior of runaway electrons/current show that application of RMPs with m/n  =  2/1 dominant component during disruptions can reduce runaway production. Furthermore, its application before the disruption can reduce both the amplitude and the length of runaway current; experimental results in the high-density disruption plasmas confirm that local current shrinkage during a multifaceted asymmetric radiation from the edge can directly terminate the discharge; measurements by a multi-channel Doppler reflectometer show that the quasi-coherent modes in the electron diamagnetic direction occur in the J-TEXT ohmic confinement regime in a large plasma region (r/a ~ 0.3-0.8) with frequency of 30-140 kHz.

Traffic density determination and its applications using smartphone

Directory of Open Access Journals (Sweden)

Al-Sayed Ahmed Al-Sobky

2016-03-01

Full Text Available Smartphone is progressively becoming a dominant platform for many transportation applications. This paper introduces a new application for using smartphones to measure traffic density and speed. The proposed system consists of two smartphones and two cars, with observer to count vehicles between the two cars. This count is utilized with tracking data to give “measured” density and “measured” speed. The travel speed and manual traffic counts were used to derive “calculated” density. Measured density was validated against calculated one, and statistical t-test confirmed that the mean difference between two densities is not significant at 5% level. Calculated flow rates were also comparable to actual counts, with an average error of 8.2%. The proposed system was then applied to measure density on 6 of October Elevated Road in Egypt, and the level of service was determined accordingly on 15 road sections studied on this road. Furthermore, actual speed-density data were fitted using exponential model with R2 of 0.85. Advantages of proposed system qualify it for potential applications in developing countries where available resources limit installation of more costly systems. The application of proposed system is limited to daytime, uninterrupted flow conditions, and traffic streams with less percentage of heavy vehicles.

Strong Correlation in Kohn-Sham Density Functional Theory

NARCIS (Netherlands)

Malet, F.; Gori Giorgi, P.

2012-01-01

We use the exact strong-interaction limit of the Hohenberg-Kohn energy density functional to approximate the exchange-correlation energy of the restricted Kohn-Sham scheme. Our approximation corresponds to a highly nonlocal density functional whose functional derivative can be easily constructed,

correlation between maximum dry density and cohesion

African Journals Online (AJOL)

HOD

represents maximum dry density, signifies plastic limit and is liquid limit. Researchers [6, 7] estimate compaction parameters. Aside from the correlation existing between compaction parameters and other physical quantities there are some other correlations that have been investigated by other researchers. The well-known.

Factors limiting the domestic density of Triatoma infestans in north-west Argentina: a longitudinal study.

Science.gov (United States)

Cecere, M C; Gürtler, R E; Chuit, R; Cohen, J E

1998-01-01

Reported are the environmental and demographic risk factors associated with the domestic infestation and density of Triatoma infestans in three heavily infested rural villages in Santiago del Estero Province, Argentina. In a one-factor unadjusted analysis, the number of T. infestans captured per person-hour was associated significantly and negatively with the use of domestic insecticides by householders, type of thatch used in the roofs and the age of the house; and positively with the following: degree of cracking of the indoor walls and presence of hens nesting indoors. In one model, using multiple linear regression and a backward stepwise elimination procedure, most of the variation in the overall abundance of T. infestans was explained by insecticide use and the presence of hens nesting indoors; in another model using the same procedure it was explained by insecticide use, bug density in 1988 and previous spraying with deltamethrin in 1985. Variations in bug density per capture stratum (household goods, beds, walls and roof) were explained by the bug density in other strata and by one or two of the following risk factors: hens nesting indoors, type of roof, presence of cracks in the walls and number of people living in the house. Bug density might be locally controlled by the availability of refuges in the roofs and walls, by the presence of hens nesting indoors and by the use of domestic insecticides. Certain local materials, such as a grass known as simbol, could be successfully used in rural housing improvement programmes aimed at reducing the availability of refuges for insects in the roof.

Operational limits and disruptions in ITER

Energy Technology Data Exchange (ETDEWEB)

Tsunematsu, T; Mizoguchi, T; Yoshino, R [Japan Atomic Energy Research Inst., Tokyo (Japan); Borrass, K; Engelmann, F; Pacher, G; Pacher, H [Max-Planck-Institut fuer Plasmaphysik, Garching (Germany, F.R.). NET Design Team; Cohen, S; Post, D [Princeton Univ., NJ (USA). Plasma Physics Lab.; Hogan, J; Uckan, N A [Oak Ridge National Lab., TN (USA); Krasheninnikov, S; Mukhovatov, V; Parail, V

1990-12-15

Detailed knowledge of the operational limits for beta, q and the plasma density will be required for successful and flexible operation of ITER. In this paper, the present data base and guidelines on operational limits and disruptions in the ITER design are presented. 10 refs., 1 fig.

Effects of Density-Dependent Bag Constant and Strange Star Rotation

Institute of Scientific and Technical Information of China (English)

ZHOU Qiao-Er; GUO Hua

2003-01-01

With the emphasis on the effects of the density-dependent bag constant and the rotation of strange star the limiting mass of strange star is calculated. The obtained results show that the limiting mass and the corresponding radius of strange star increase as the rotation frequency increases, and tend to be lowered when the density-dependent bag constant is considered.

Electrode and limiter biasing experiments on the tokamak ISTTOK

International Nuclear Information System (INIS)

Silva, C.; Figueiredo, H.; Cabral, J.A.C.; Nedzelsky, I.; Varandas, C.A.F.

2003-01-01

In this contribution limiter and electrode biasing experiments are compared, in particular in what concerns their effects on the edge plasma parameters. For electrode AC bias a substantial increase (>50%) in the average plasma density is observed with positive voltage, without significant changes in the edge density, leading to steeper profiles. The ratio n e /Hα also increases significantly (>20%), indicating an improvement in gross particle confinement. The plasma potential profile is strongly modified as both the edge E r and its shear increase significantly. For positive limiter bias an increase in the average plasma density and the radiation losses is observed, resulting in almost no modification, or a slight, in particle confinement. Preliminary results of simultaneous electrode and limiter bias experiments show that the control of the plasma potential profile is very limited, since negative voltages do not modify the plasma parameters significantly. (author)

Modeling space-charge-limited currents in organic semiconductors: Extracting trap density and mobility

KAUST Repository

Dacuña, Javier

2011-11-28

We have developed and have applied a mobility edge model that takes drift and diffusion currents to characterize the space-charge-limited current in organic semiconductors into account. The numerical solution of the drift-diffusion equation allows the utilization of asymmetric contacts to describe the built-in potential within the device. The model has been applied to extract information of the distribution of traps from experimental current-voltage measurements of a rubrene single crystal from Krellner showing excellent agreement across several orders of magnitude in the current. Although the two contacts are made of the same metal, an energy offset of 580 meV between them, ascribed to differences in the deposition techniques (lamination vs evaporation) was essential to correctly interpret the shape of the current-voltage characteristics at low voltage. A band mobility of 0.13cm 2V-1s-1 for holes is estimated, which is consistent with transport along the long axis of the orthorhombic unit cell. The total density of traps deeper than 0.1 eV was 2.2×1016cm -3. The sensitivity analysis and error estimation in the obtained parameters show that it is not possible to accurately resolve the shape of the trap distribution for energies deeper than 0.3 eV or shallower than 0.1 eV above the valence-band edge. The total number of traps deeper than 0.3 eV, however, can be estimated. Contact asymmetry and the diffusion component of the current play an important role in the description of the device at low bias and are required to obtain reliable information about the distribution of deep traps. © 2011 American Physical Society.

Superconducting toroidal field coil current densities for the TFCX

International Nuclear Information System (INIS)

Kalsi, S.S.; Hooper, R.J.

1985-04-01

A major goal of the Tokamak Fusion Core Experiment (TFCX) study was to minimize the size of the device and achieve lowest cost. Two key factors influencing the size of the device employing superconducting magnets are toroidal field (TF) winding current density and its nuclear heat load withstand capability. Lower winding current density requires larger radial build of the winding pack. Likewise, lower allowable nuclear heating in the winding requires larger shield thickness between the plasma and coil. In order to achieve a low-cost device, it is essential to maximize the winding's current density and nuclear heating withhstand capability. To meet the above objective, the TFCX design specification adopted as goals a nominal winding current density of 3500 A/cm 2 with 10-T peak field at the winding and peak nuclear heat load limits of 1 MW/cm 3 for the nominal design and 50 MW/cm 3 for an advanced design. This study developed justification for these current density and nuclear heat load limits

Relating saturation capacity to charge density in strong cation exchangers.

Science.gov (United States)

Steinebach, Fabian; Coquebert de Neuville, Bertrand; Morbidelli, Massimo

2017-07-21

In this work the relation between physical and chemical resin characteristics and the total amount of adsorbed protein (saturation capacity) for ion-exchange resins is discussed. Eleven different packing materials with a sulfo-functionalization and one multimodal resin were analyzed in terms of their porosity, pore size distribution, ligand density and binding capacity. By specifying the ligand density and binding capacity by the total and accessible surface area, two different groups of resins were identified: Below a ligand density of approx. 2.5μmol/m 2 area the ligand density controls the saturation capacity, while above this limit the accessible surface area becomes the limiting factor. This results in a maximum protein uptake of around 2.5mg/m 2 of accessible surface area. The obtained results allow estimating the saturation capacity from independent resin characteristics like the saturation capacity mainly depends on "library data" such as the accessible and total surface area and the charge density. Hence these results give an insight into the fundamentals of protein adsorption and help to find suitable resins, thus limiting the experimental effort in early process development stages. Copyright © 2017 Elsevier B.V. All rights reserved.

Trivial constraints on orbital-free kinetic energy density functionals

Science.gov (United States)

Luo, Kai; Trickey, S. B.

2018-03-01

Approximate kinetic energy density functionals (KEDFs) are central to orbital-free density functional theory. Limitations on the spatial derivative dependencies of KEDFs have been claimed from differential virial theorems. We identify a central defect in the argument: the relationships are not true for an arbitrary density but hold only for the minimizing density and corresponding chemical potential. Contrary to the claims therefore, the relationships are not constraints and provide no independent information about the spatial derivative dependencies of approximate KEDFs. A simple argument also shows that validity for arbitrary v-representable densities is not restored by appeal to the density-potential bijection.

Microinstabilities in weak density gradient tokamak systems

International Nuclear Information System (INIS)

Tang, W.M.; Rewoldt, G.; Chen, L.

1986-04-01

A prominent characteristic of auxiliary-heated tokamak discharges which exhibit improved (''H-mode type'') confinement properties is that their density profiles tend to be much flatter over most of the plasma radius. Depsite this favorable trend, it is emphasized here that, even in the limit of zero density gradient, low-frequency microinstabilities can persist due to the nonzero temperature gradient

Study of plasma wall interactions in the long-pulse NB-heated discharges of JT-60U towards steady-state operation

International Nuclear Information System (INIS)

Takenaga, H.; Asakura, N.; Higashijima, S.; Nakano, T.; Kubo, H.; Konoshima, S.; Oyama, N.; Isayama, A.; Ide, S.; Fujita, T.; Miura, Y.

2005-01-01

Long time scale variation of plasma-wall interactions and its impact on particle balance, main plasma performance and particle behavior have been investigated in ELMy H-mode plasmas by extending the discharge pulse and the neutral beam heating pulse to 65 s and 30 s, respectively. The wall pumping rate starts to decrease in the latter phase by repeating the long-pulse discharges with 60% of Greenwald density sustained by gas-puffing. After several discharges, the wall inventory is saturated in the latter phase and, consequently, the density increases with neutral beam fuelling only. The edge pressure in the main plasma is reduced and ELMs are close to the type III regime under conditions of wall saturation. The intensities of C II emission near the X-point and CD band emission in the inner divertor start to increase before the wall saturates and continue to increase after the wall is saturated

Using eastern gamagrass to construct diets that limit intake and caloric density for dairy replacement heifers.

Science.gov (United States)

Coblentz, W K; Hoffman, P C; Esser, N M; Bertram, M G

2012-10-01

Previous research has shown that eastern gamagrass (EGG; Tripsacum dactyloides L.) will survive winter climatic conditions common throughout central Wisconsin, and will produce yields of dry matter (DM) ranging approximately from 7,000 to 10,000 kg/ha annually when managed with a 1-cut harvest system. The objective of this research was to determine whether the fibrous nature of this perennial warm-season grass could be effective in reducing the caloric density and DMI of corn silage/alfalfa haylage diets for replacement dairy heifers. A total of 120 Holstein dairy heifers were blocked by body weight (heavy, 424 ± 15.9 kg; medium, 369 ± 11.8 kg; light, 324 ± 22.4 kg), and then assigned to 15 individual pens containing 8heifers each. Eastern gamagrass forage was harvested, ensiled, and subsequently incorporated into blended corn silage/alfalfa haylage diets at rates of 0, 9.1, 18.3, or 27.4% of the total dietary DM (EGG0, EGG9, EGG18, and EGG27, respectively). These diets were offered during a 105-d evaluation period for ad libitum intake; however, the EGG0 diet also was offered on a limit-fed basis (LF), which was set at 85% of the voluntary intake of EGG0. Serial additions of EGG increased concentrations of neutral detergent fiber in blended diets from 39.6 (EGG0) to 48.7% (EGG27), and simultaneously reduced corresponding estimates of total digestible nutrients (TDN) from 68.2 to 61.3%, and net energy for gain from 1.07 to 0.83 Mcal/kg. Dry matter intakes for all diets offered ad libitum were greater than observed for LF (9.06 vs. 8.07 kg/d); however, DM intakes for diets containing EGG were reduced relative to EGG0 (9.40 vs. 8.94 kg/d). Similarly, intakes of TDN were greater for diets offered for ad libitum intake than for LF (5.84 vs. 5.50 kg/d); however, inclusion of EGG reduced TDN intakes relative to EGG0 (6.41 vs. 5.65 kg/d). This reduction was explained by both linear and quadratic effects of the inclusion rate of EGG in the diet. Over the 105-d trial

Disruption avoidance by means of electron cyclotron waves

International Nuclear Information System (INIS)

Esposito, B; Granucci, G; Nowak, S; Lazzaro, E; Maraschek, M; Giannone, L; Gude, A; Igochine, V; McDermott, R; Poli, E; Reich, M; Sommer, F; Stober, J; Suttrop, W; Treutterer, W; Zohm, H

2011-01-01

Disruptions are very challenging to ITER operation as they may cause damage to plasma facing components due to direct plasma heating, forces on structural components due to halo and eddy currents and the production of runaway electrons. Electron cyclotron (EC) waves have been demonstrated as a tool for disruption avoidance by a large set of recent experiments performed in ASDEX Upgrade and FTU using various disruption types, plasma operating scenarios and power deposition locations. The technique is based on the stabilization of magnetohydrodynamic (MHD) modes (mainly m/n = 2/1) through the localized injection of EC power on the resonant surface. This paper presents new results obtained in ASDEX Upgrade regarding stable operation above the Greenwald density achieved after avoidance of density limit disruptions by means of ECRH and suitable density feedback control (L-mode ohmic plasmas, I p = 0.6 MA, B t = 2.5 T) and NTM-driven disruptions at high-β limit delayed/avoided by means of both co-current drive (co-ECCD) and pure heating (ECRH) with power ≤1.7 MW (H-mode NBI-heated plasmas, P NBI ∼ 7.5 MW, I p = 1 MA, B t = 2.1 T, q 95 ∼ 3.6). The localized perpendicular injection of ECRH/ECCD onto a resonant surface leads to the delay and/or complete avoidance of disruptions. The experiments indicate the existence of a power threshold for mode stabilization to occur. An analysis of the MHD mode evolution using the generalized Rutherford equation coupled to the frequency and phase evolution equations shows that control of the modes is due to EC heating close to the resonant surface. The ECRH contribution (Δ' H term) is larger than the co-ECCD one in the initial and more important phase when the discharge is 'saved'. Future research and developments of the disruption avoidance technique are also discussed.

Electronic zero-point oscillations in the strong-interaction limit of density functional theory

NARCIS (Netherlands)

Gori Giorgi, P.; Vignale, G.; Seidl, M.

2009-01-01

The exchange-correlation energy in Kohn-Sham density functional theory can be expressed exactly in terms of the change in the expectation of the electron-electron repulsion operator when, in the many-electron Hamiltonian, this same operator is multiplied by a real parameter λ varying between 0

The use of infrared absorption to determine density of liquid hydrogen.

Science.gov (United States)

Unland, H. D.; Timmerhaus, K. D.; Kropschot, R. H.

1972-01-01

Experimental evaluation of the use of infrared absorption for determining the density of liquid hydrogen, and discussion of the feasibility of an airborne densitometer based on this concept. The results indicate that infrared absorption of liquid hydrogen is highly sensitive to the density of hydrogen, and, under the operating limitations of the equipment and experimental techniques used, the determined values proved to be repeatable to an accuracy of 2.7%. The desiderata and limitations of an in-flight density-determining device are outlined, and some of the feasibility problems are defined.

Overview on the progress of tokamak experimental research in China

International Nuclear Information System (INIS)

Xie Jikang . E-mail; Liu Yong; Wen Yizhi; Wang Long

2001-01-01

Tokamak experimental research in China has made important progress. The main efforts were related to quasi-steady-state operation, LHCD, plasma heating with ICRF, IBW, NBI and ECRH, fuelling with pellets and supersonic molecular beams, and first wall conditioning techniques. Plasma parameters in the experiments were much improved, for example n e =8x10 19 m -3 and a plasma pulse length of >10 s were achieved. ICRF boronization and conditioning resulted in Z eff close to unity. Steady state full LH wave current drive has been achieved for more than 3 s. LHCD ramp-up and recharge have also been demonstrated. The best η CD exp ∼0.5(1+0.085exp(4.8(B T -1.45)))n e I CD R p /P LH =10 19 m -2 A W -1 . Quasi-steady-state H-mode-like plasmas with a density close to the Greenwald limit were obtained by LHCD, where the energy confinement time was nearly five times longer than in the ohmic case. The synergy between IBW, pellet and LHCD was tested. Research on the mechanism of macroturbulence has been extensively carried out experimentally. AC tokamak operation has been successfully demonstrated. (author)

Relationships between the floral neighborhood and individual pollen limitation in two self-incompatible herbs.

Science.gov (United States)

Jakobsson, Anna; Lázaro, Amparo; Totland, Orjan

2009-07-01

Local flower density can affect pollen limitation and plant reproductive success through changes in pollinator visitation and availability of compatible pollen. Many studies have investigated the relationship between conspecific density and pollen limitation among populations, but less is known about within-population relationships and the effect of heterospecific flower density. In addition, few studies have explicitly assessed how the spatial scales at which flowers are monitored affect relationships. We investigated the effect of floral neighborhood on pollen limitation at four spatial scales in the self-incompatible herbs Armeria maritima spp. maritima and Ranunculus acris spp. acris. Moreover, we measured pollen deposition in Armeria and pollinator visits to Ranunculus. There was substantial variation in pollen limitation among Armeria individuals, and 25% of this variation was explained by the density of compatible and heterospecific flowers within a 3 m circle. Deposition of compatible pollen was affected by the density of compatible and incompatible inflorescences within a 0.5 m circle, and deposition of heterospecific pollen was affected by the density of heterospecific flowers within a 2 m circle. In Ranunculus, the number of pollinator visits was affected by both conspecific and heterospecific flower densities. This did not, however, result in effects of the floral neighborhood on pollen limitation, probably due to an absence of pollen limitation at the population level. Our study shows that considerable variation in pollen limitation may occur among individuals of a population, and that this variation is partly explained by floral neighborhood density. Such individual-based measures provide an important link between pollen limitation theory, which predicts ecological and evolutionary causes and consequences for individual plants, and studies of the effects of landscape fragmentation on plant species persistence. Our study also highlights the importance

Effect of lithium PFC coatings on NSTX density control

International Nuclear Information System (INIS)

Kugel, H.W.; Bell, M.G.; Bell, R.; Bush, C.; Gates, D.; Gray, T.; Kaita, R.; Leblanc, B.; Maingi, R.; Majeski, R.; Mansfield, D.; Mueller, D.; Paul, S.; Raman, R.; Roquemore, A.L.; Sabbagh, S.; Skinner, C.H.; Soukhanovskii, V.; Stevenson, T.; Zakharov, L.

2007-01-01

Lithium coatings on the graphite plasma facing components (PFCs) in NSTX are being investigated as a tool for density profile control and reducing the recycling of hydrogen isotopes. Repeated lithium pellet injection into Center Stack Limited and Lower Single Null ohmic helium discharges were used to coat graphite surfaces that had been pre-conditioned with ohmic helium discharges of the same shape to reduce their contribution to hydrogen isotope recycling. The following deuterium NBI reference discharges exhibited a reduction in density by a factor of about 3 for limited and 2 for diverted plasmas, respectively, and peaked density profiles. Recently, a lithium evaporator has been used to apply thin coatings on conditioned and unconditioned PFCs. Effects on the plasma density and the impurities were obtained by pre-conditioning the PFCs with ohmic helium discharges, and performing the first deuterium NBI discharge as soon as possible after applying the lithium coating

Limiting rotational period of neutron stars

Science.gov (United States)

Glendenning, Norman K.

1992-11-01

We seek an absolute limit on the rotational period for a neutron star as a function of its mass, based on the minimal constraints imposed by Einstein's theory of relativity, Le Chatelier's principle, causality, and a low-density equation of state, uncertainties in which can be evaluated as to their effect on the result. This establishes a limiting curve in the mass-period plane below which no pulsar that is a neutron star can lie. For example, the minimum possible Kepler period, which is an absolute limit on rotation below which mass shedding would occur, is 0.33 ms for a M=1.442Msolar neutron star (the mass of PSR1913+16). A still lower curve, based only on the structure of Einstein's equations, limits any star whatsoever to lie in the plane above it. Hypothetical stars such as strange stars, if the matter of which they are made is self-bound in bulk at a sufficiently large equilibrium energy density, can lie in the region above the general-relativistic forbidden region, and in the region forbidden to neutron stars.

Limiting rotational period of neutron stars

International Nuclear Information System (INIS)

Glendenning, N.K.

1992-01-01

We seek an absolute limit on the rotational period for a neutron star as a function of its mass, based on the minimal constraints imposed by Einstein's theory of relativity, Le Chatelier's principle, causality, and a low-density equation of state, uncertainties in which can be evaluated as to their effect on the result. This establishes a limiting curve in the mass-period plane below which no pulsar that is a neutron star can lie. For example, the minimum possible Kepler period, which is an absolute limit on rotation below which mass shedding would occur, is 0.33 ms for a M=1.442M circle-dot neutron star (the mass of PSR1913+16). A still lower curve, based only on the structure of Einstein's equations, limits any star whatsoever to lie in the plane above it. Hypothetical stars such as strange stars, if the matter of which they are made is self-bound in bulk at a sufficiently large equilibrium energy density, can lie in the region above the general-relativistic forbidden region, and in the region forbidden to neutron stars

Anisotropic mass density by two-dimensional acoustic metamaterials

Energy Technology Data Exchange (ETDEWEB)

Torrent, Daniel; Sanchez-Dehesa, Jose [Wave Phenomena Group, Department of Electronic Engineering, Polytechnic University of Valencia, C/Camino de Vera s/n, E-46022 Valencia (Spain)], E-mail: jsdehesa@upvnet.upv.es

2008-02-15

We show that specially designed two-dimensional arrangements of full elastic cylinders embedded in a nonviscous fluid or gas define (in the homogenization limit) a new class of acoustic metamaterials characterized by a dynamical effective mass density that is anisotropic. Here, analytic expressions for the dynamical mass density and the effective sound velocity tensors are derived in the long wavelength limit. Both show an explicit dependence on the lattice filling fraction, the elastic properties of cylinders relative to the background, their positions in the unit cell, and their multiple scattering interactions. Several examples of these metamaterials are reported and discussed.

Density profile evolution during dynamic processes in ASDEX Upgrade

International Nuclear Information System (INIS)

Nunes, I.; Santos, J.; Salzedas, F.; Manso, M.; Serra, F.; Conway, G.D.; Horton, L.D.; Neuhauser, J.; Suttrop, W.

2005-01-01

The current understanding of edge localized modes (ELMs) and the trigger of major disruptions is largely based on phenomenology. The need to better understand the processes underlying these phenomena requires high temporal and spatial resolution diagnostics. Fast diagnostics for the temperature measurements exist, such as the ECE radiometer but, for the plasma density, the existing diagnostics such as Lithium Beam and Thomson Scattering do not have the required high temporal resolution for a period long enough to characterize the entire ELM event. The microwave reflectometry system on ASDEX Upgrade has the capability to measure electron density profiles simultaneously at the low-field and high-field sides, in broadband swept ultrafast (35μs) operation with a spatial resolution of 5mm. In this paper we report on recent results on the effects of type I ELMs on density profiles and on the density pedestal width and ELM affected depth. During the ELM event, three phases are identified: precursor, collapse and recovery. The density pedestal width is found to be approximately constant for all the ELMy H-mode discharges analyzed here, except for high input power discharges, where an increase of the density pedestal width is observed. Major disruptions limit the range of parameters used in the operation of a tokamak, especially density limit disruptions, that limit the maximum usable density. Very abrupt increases of density are observed before the onset of the electron temperature profile erosion, supporting the hypothesis that this erosion is due to convection of the magnetic field. In ITER, during the long steady state flat-top phase of the discharges magnetic measurements may accumulate significant drifts. Plasma position and shape control using reflectometry is being assessed in ASDEX Upgrade for ITER like scenarios with successful results, where it is shown that position measurements from reflectometry compared to magnetic data satisfy the ITER requirements

The contribution of accreting black holes to the background radiation density

International Nuclear Information System (INIS)

Carr, B.J.

1979-01-01

Black holes could generate radiation as a result of accretion. The requirement that this radiation should not have a density exceeding the observed background density places an interesting limit on the number of black holes, depending on the wavelength at which the radiation is generated and the efficiency with which it is produced from accreted material. Consideration of the radiation produced in the present epoch already constrains the mass range in which black holes could have a significant cosmological density. For pregalactic black holes, which may have been accreting more rapidly in the past, the constraint could be even stronger. However, because pregalactic accretion will in general increase the matter temperature of the Universe, it is a self-limiting process. For this reason the pregalactic accretion limit is not as strong as one might naively expect and it is generally weaker than the present epoch limit. (author)

Restoring the consistency with the contact density theorem of a classical density functional theory of ions at a planar electrical double layer.

Science.gov (United States)

Gillespie, Dirk

2014-11-01

Classical density functional theory (DFT) of fluids is a fast and efficient theory to compute the structure of the electrical double layer in the primitive model of ions where ions are modeled as charged, hard spheres in a background dielectric. While the hard-core repulsive component of this ion-ion interaction can be accurately computed using well-established DFTs, the electrostatic component is less accurate. Moreover, many electrostatic functionals fail to satisfy a basic theorem, the contact density theorem, that relates the bulk pressure, surface charge, and ion densities at their distances of closest approach for ions in equilibrium at a smooth, hard, planar wall. One popular electrostatic functional that fails to satisfy the contact density theorem is a perturbation approach developed by Kierlik and Rosinberg [Phys. Rev. A 44, 5025 (1991)PLRAAN1050-294710.1103/PhysRevA.44.5025] and Rosenfeld [J. Chem. Phys. 98, 8126 (1993)JCPSA60021-960610.1063/1.464569], where the full free-energy functional is Taylor-expanded around a bulk (homogeneous) reference fluid. Here, it is shown that this functional fails to satisfy the contact density theorem because it also fails to satisfy the known low-density limit. When the functional is corrected to satisfy this limit, a corrected bulk pressure is derived and it is shown that with this pressure both the contact density theorem and the Gibbs adsorption theorem are satisfied.

A statistical study of high coronal densities from X-ray line-ratios of Mg XI

Science.gov (United States)

Linford, G. A.; Lemen, J. R.; Strong, K. T.

1991-01-01

An X-ray line-ratio density diagnostic was applied to 50 Mg XI spectra of flaring active regions on the sun recorded by the Flat Crystal Spectrometer on the SMM. The plasma density is derived from R, the flux ratio of the forbidden to intercombination lines of the He-like ion, Mg XI. The R ratio for Mg XI is only density sensitive when the electron density exceeds a critical value (about 10 to the 12th/cu cm), the low-density limit (LDL). This theoretical value of the low-density limit is uncertain as it depends on complex atomic theory. Reported coronal densities above 10 to the 12th/cu cm are uncommon. In this study, the distribution of R ratio values about the LDL is estimated and the empirical values are derived for the 1st and 2nd moments of this distribution from 50 Mg XI spectra. From these derived parameters, the percentage of observations is derived which indicated densities above this limit.

High density data storage principle, technology, and materials

CERN Document Server

Zhu, Daoben

2009-01-01

The explosive increase in information and the miniaturization of electronic devices demand new recording technologies and materials that combine high density, fast response, long retention time and rewriting capability. As predicted, the current silicon-based computer circuits are reaching their physical limits. Further miniaturization of the electronic components and increase in data storage density are vital for the next generation of IT equipment such as ultra high-speed mobile computing, communication devices and sophisticated sensors. This original book presents a comprehensive introduction to the significant research achievements on high-density data storage from the aspects of recording mechanisms, materials and fabrication technologies, which are promising for overcoming the physical limits of current data storage systems. The book serves as an useful guide for the development of optimized materials, technologies and device structures for future information storage, and will lead readers to the fascin...

Physiological response of soybean genotypes to plant density

NARCIS (Netherlands)

Gan, Y; Stulen, [No Value; van Keulen, H; Kuiper, PJC

2002-01-01

Response of soybean (Glycine max (L.) Merr.) to plant density has occupied a segment of agronomic research for most of the century. Genotype differences have been noted especially in response to planting date, lodging problems and water limitation. There is limited information on the physiological

Plasma edge physics in the TEXTOR tokamak with poloidal and toroidal limiters

International Nuclear Information System (INIS)

Samm, U.; Bogen, P.; Hartwig, H.; Hintz, E.; Hoethker, K.; Lie, Y.T.; Pospieszczyk, A.; Rusbueldt, D.; Schweer, B.; Yu, Y.J.

1989-01-01

Investigations of the plasma edge in TEXTOR are presented on the one hand by comparing results obtained with poloidal and toroidal limiters and on the other hand by discussing general problems of plasma edge physics which are independent of the limiter configuration. The characteristic properties of plasma flow to the different limiters are analyzed and show e.g. that the fraction of total ion flow to the limiter is much larger in the case of a toroidal limiter (80%). Density and heat flux profiles are presented which demonstrate that for both types of limiters a significant steepening of the scrape-off layer (SOL) occurs close to the limiter, leading to a small heat load e-folding length of 5-8 mm. The velocity distribution of recycled neutral hydrogen at a main limiter has been determined from the Doppler broadening of the H α line. The data clearly show that a large fraction of particles (30-50%) is reflected at the limiter surface having energies of about the sheath potential. Significant isotopic effects (H/D) concerning the plasma edge properties and the plasma core are presented and their relation to enhanced particle and energy transport in hydrogen compared to deuterium is discussed. A decrease of the cross field diffusion coefficient with increasing density can be deduced from density profile measurements in the SOL and a comparison with density fluctuations is given. The role of oxygen for impurity release is demonstrated. A new type of wall conditioning - boronization - is described, with two major improvements for quasi stationary conditions: reduction of oxygen and better density control. Best results with ICRH have been obtained under these conditions. (orig.)

Density-functional theory for internal magnetic fields

Science.gov (United States)

Tellgren, Erik I.

2018-01-01

A density-functional theory is developed based on the Maxwell-Schrödinger equation with an internal magnetic field in addition to the external electromagnetic potentials. The basic variables of this theory are the electron density and the total magnetic field, which can equivalently be represented as a physical current density. Hence, the theory can be regarded as a physical current density-functional theory and an alternative to the paramagnetic current density-functional theory due to Vignale and Rasolt. The energy functional has strong enough convexity properties to allow a formulation that generalizes Lieb's convex analysis formulation of standard density-functional theory. Several variational principles as well as a Hohenberg-Kohn-like mapping between potentials and ground-state densities follow from the underlying convex structure. Moreover, the energy functional can be regarded as the result of a standard approximation technique (Moreau-Yosida regularization) applied to the conventional Schrödinger ground-state energy, which imposes limits on the maximum curvature of the energy (with respect to the magnetic field) and enables construction of a (Fréchet) differentiable universal density functional.

Models for Experimental High Density Housing

Science.gov (United States)

Bradecki, Tomasz; Swoboda, Julia; Nowak, Katarzyna; Dziechciarz, Klaudia

2017-10-01

The article presents the effects of research on models of high density housing. The authors present urban projects for experimental high density housing estates. The design was based on research performed on 38 examples of similar housing in Poland that have been built after 2003. Some of the case studies show extreme density and that inspired the researchers to test individual virtual solutions that would answer the question: How far can we push the limits? The experimental housing projects show strengths and weaknesses of design driven only by such indexes as FAR (floor attenuation ratio - housing density) and DPH (dwellings per hectare). Although such projects are implemented, the authors believe that there are reasons for limits since high index values may be in contradiction to the optimum character of housing environment. Virtual models on virtual plots presented by the authors were oriented toward maximising the DPH index and DAI (dwellings area index) which is very often the main driver for developers. The authors also raise the question of sustainability of such solutions. The research was carried out in the URBAN model research group (Gliwice, Poland) that consists of academic researchers and architecture students. The models reflect architectural and urban regulations that are valid in Poland. Conclusions might be helpful for urban planners, urban designers, developers, architects and architecture students.

High power density yeast catalyzed microbial fuel cells

Science.gov (United States)

Ganguli, Rahul

Microbial fuel cells leverage whole cell biocatalysis to convert the energy stored in energy-rich renewable biomolecules such as sugar, directly to electrical energy at high efficiencies. Advantages of the process include ambient temperature operation, operation in natural streams such as wastewater without the need to clean electrodes, minimal balance-of-plant requirements compared to conventional fuel cells, and environmentally friendly operation. These make the technology very attractive as portable power sources and waste-to-energy converters. The principal problem facing the technology is the low power densities compared to other conventional portable power sources such as batteries and traditional fuel cells. In this work we examined the yeast catalyzed microbial fuel cell and developed methods to increase the power density from such fuel cells. A combination of cyclic voltammetry and optical absorption measurements were used to establish significant adsorption of electron mediators by the microbes. Mediator adsorption was demonstrated to be an important limitation in achieving high power densities in yeast-catalyzed microbial fuel cells. Specifically, the power densities are low for the length of time mediator adsorption continues to occur. Once the mediator adsorption stops, the power densities increase. Rotating disk chronoamperometry was used to extract reaction rate information, and a simple kinetic expression was developed for the current observed in the anodic half-cell. Since the rate expression showed that the current was directly related to microbe concentration close to the electrode, methods to increase cell mass attached to the anode was investigated. Electrically biased electrodes were demonstrated to develop biofilm-like layers of the Baker's yeast with a high concentration of cells directly connected to the electrode. The increased cell mass did increase the power density 2 times compared to a non biofilm fuel cell, but the power density

Prospects and Limits of Energy Storage in Batteries.

Science.gov (United States)

Abraham, K M

2015-03-05

Energy densities of Li ion batteries, limited by the capacities of cathode materials, must increase by a factor of 2 or more to give all-electric automobiles a 300 mile driving range on a single charge. Battery chemical couples with very low equivalent weights have to be sought to produce such batteries. Advanced Li ion batteries may not be able to meet this challenge in the near term. The state-of-the-art of Li ion batteries is discussed, and the challenges of developing ultrahigh energy density rechargeable batteries are identified. Examples of ultrahigh energy density battery chemical couples include Li/O2, Li/S, Li/metal halide, and Li/metal oxide systems. Future efforts are also expected to involve all-solid-state batteries with performance similar to their liquid electrolyte counterparts, biodegradable batteries to address environmental challenges, and low-cost long cycle-life batteries for large-scale energy storage. Ultimately, energy densities of electrochemical energy storage systems are limited by chemistry constraints.

Recent advances towards a lithium vapor box divertor

Directory of Open Access Journals (Sweden)

R.J. Goldston

2017-08-01

Full Text Available Fusion power plants are likely to require near complete detachment of the divertor plasma from the divertor target plates, in order to have both acceptable heat flux at the target to avoid prompt damage and also acceptable plasma temperature at the target surface, to minimize long-term erosion. However hydrogenic and impurity puffing experiments show that detached operation leads easily to x-point MARFEs, impure plasmas, degradation in confinement, and lower helium pressure at the exhaust. The concept of the Lithium Vapor Box Divertor is to use local evaporation and strong differential pumping through condensation to localize low-Z gas-phase material that absorbs the plasma heat flux and so achieve detachment while avoiding these difficulties. The vapor localization has been confirmed using preliminary Navier–Stokes calculations. We use ADAS calculations of εcool, the plasma energy lost per injected lithium atom, to estimate the lithium vapor pressure, and so temperature, required for detachment, taking into account power balance. We also develop a simple model of detachment to evaluate the required upstream density, based on further taking into account dynamic pressure balance. A remarkable general result is found, not just for lithium-vapor-induced detachment, that the upstream density divided by the Greenwald-limit density scales as nup/nGW ∝ (P5/8/B3/8 Tdet1/2/(εcool+γTdet, with no explicit size scaling. Tdet is the temperature just before strong pressure loss, assumed to be ∼ ½ of the ionization potential of the dominant recycling species, and γ is the sheath heat transmission factor.

Ultimate energy density of observable cold baryonic matter.

Science.gov (United States)

Lattimer, James M; Prakash, Madappa

2005-03-25

We demonstrate that the largest measured mass of a neutron star establishes an upper bound to the energy density of observable cold baryonic matter. An equation of state-independent expression satisfied by both normal neutron stars and self-bound quark matter stars is derived for the largest energy density of matter inside stars as a function of their masses. The largest observed mass sets the lowest upper limit to the density. Implications from existing and future neutron star mass measurements are discussed.

Effects of limiter biasing on the ATF torsatron

International Nuclear Information System (INIS)

Uckan, T.; Baylor, L.R.; Bell, J.D.; Bigelow, T.S.; England, A.C.; Harris, J.H.; Isler, R.C.; Jernigan, T.C.; Lyon, J.F.; Ma, C.H.; Mioduszewski, P.K.; Murakami, M.; Rasmussen, D.A.; Wilgen, J.B.; Aceto, S.C.; Zielinski, J.J.

1992-09-01

Positive limiter biasing on the currentless Advanced Toroidal Facility (ATF) torsatron produces a significant increase in the particle confinement with no improvement in the energy confinement. Experiments have been carried out in 1-T plasmas with ∼400 kill of electron cyclotron heating ECM. Two rail limiters located at the last closed flux surface (LCFS), one at the top and one at the bottom of the device, are biased at positive and negative potentials with respect to the vessel. When the limiters are positively biased at up to 300 V, the density increases sharply to the ECH cutoff value. At the same time, the H α radiation drops, indicating that the particle confinement improves. When the density is kept constant, the H α radiation is further reduced and there is almost no change in the plasma stored energy. Under these conditions, the density profile becomes peaked and the electric field becomes outward-pointing outside the LCFS and more negative inside the LCFS. In contrast, negative biasing yields some reduction of the density and stored energy at constant gas feed, and the plasma potential profile remains the same. Biasing has almost no effect on the intrinsic impurity levels in the plasma

Subalpine bumble bee foraging distances and densities in relation to flower availability.

Science.gov (United States)

Elliott, Susan E

2009-06-01

Bees feed almost exclusively on nectar and pollen from flowers. However, little is known about how food availability limits bee populations, especially in high elevation areas. Foraging distances and relationships between forager densities and resource availability can provide insights into the potential for food limitation in mobile consumer populations. For example, if floral resources are limited, bee consumers should fly farther to forage, and they should be more abundant in areas with more flowers. I estimated subalpine bumble bee foraging distances by calculating forager recapture probabilities at increasing distances from eight marking locations. I measured forager and flower densities over the flowering season in six half-hectare plots. Because subalpine bumble bees have little time to build their colonies, they may forage over short distances and forager density may not be constrained by flower density. However, late in the season, when floral resources dwindle, foraging distances may increase, and there may be stronger relationships between forager and flower densities. Throughout the flowering season, marked bees were primarily found within 100 m (and never >1,000 m) from their original marking location, suggesting that they typically did not fly far to forage. Although the density of early season foraging queens increased with early-season flower density, the density of mid- and late-season workers and males did not vary with flower density. Short foraging distances and no relationships between mid- and late-season forager and flower densities suggest that high elevation bumble bees may have ample floral resources for colony growth reproduction.

Analysis of density fluctuations in the Tore Supra tokamak. Up-down asymmetries and limiter effect on plasma turbulence; Etude des fluctuations de density dans les plasmas du tokamak Tore Supra. Asymetries haut-bas et effet du limiteur sur la turbulence

Energy Technology Data Exchange (ETDEWEB)

Fenzi, Ch

1999-10-29

In magnetic fusion devices, the optimisation of the power deposition profile on plasma facing components crucially depends on the heat diffusivity across the magnetic field fines, which is determined by the plasma edge turbulence. In this regard, spatial asymmetries of plasma edge turbulence are of great interest. In this work, we interest in up-down asymmetries of density fluctuations which are usually observed in Tore Supra, using a coherent light scattering experiment. It is shown that these asymmetries are correlated to the plasma edge geometrical configuration (plasma facing components, limiters). In fact, the plasma-limiter interaction induces locally in the plasma edge and the SOL (r/a > 0.9) an additional turbulence with short correlation length along the magnetic field fines, which spreads in the plasma core (0.9 {>=} r/a {>=} 0.5). The resultant up-down asymmetry weakly depends on density, increases with the edge safety factor, and inverts when the plasma current direction is reversed. Such up-down asymmetry observations bring strong impact on edge turbulence and transport models, which usually predict a ballooning of the turbulence in the high-field side but not an up-down asymmetry. A possible model is proposed here, based on the Kelvin Helmholtz instability. (author)

Hartree-Fock states in the thermodynamic limit

International Nuclear Information System (INIS)

Aguilera-Navarro, V.C.; Llano, M. de; Peltier, S.; Plastino, A.

1976-01-01

Two infinite families of two-parameter generalized Overhauser orbitals are introduced and shown to explicitly satisfy, for occupied states, the self-consistent Hartree-Fock equations in the thermodynamic limit. For an attractive delta interaction, they give lower Hartree-Fock energy than the usual plane-wave solutions, even for relatively weak coupling and/or low density. The limiting members (possessing an infinite number of harmonics) of both families appear to tend to a 'classical static lattice' state. The related density profiles and energy expressions are calculated as functions of the two new parameters. A direct-variation with respect to these parameters was done numerically and results are presented graphically. (Author) [pt

Density perturbations in a braneworld universe with dark radiation

International Nuclear Information System (INIS)

Gumjudpai, Burin; Maartens, Roy; Gordon, Christopher

2003-01-01

We investigate the effects on cosmological density perturbations of dark radiation in a Randall-Sundrum 2-type braneworld. Dark radiation in the background is limited by observational constraints to be a small fraction of the radiation energy density, but it has an interesting qualitative effect in the radiation era. On large scales, it serves to slightly suppress the radiation density perturbations at late times, while boosting the perturbations in dark radiation. In a kinetic (stiff) era, the suppression is much stronger, and drives the density perturbations to zero

Study of errors in absolute flux density measurements of Cassiopeia A

International Nuclear Information System (INIS)

Kanda, M.

1975-10-01

An error analysis for absolute flux density measurements of Cassiopeia A is discussed. The lower-bound quadrature-accumulation error for state-of-the-art measurements of the absolute flux density of Cas A around 7 GHz is estimated to be 1.71% for 3 sigma limits. The corresponding practicable error for the careful but not state-of-the-art measurement is estimated to be 4.46% for 3 sigma limits

Push it to the limit: Characterizing the convergence of common sequences of basis sets for intermolecular interactions as described by density functional theory

Energy Technology Data Exchange (ETDEWEB)

Witte, Jonathon [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Neaton, Jeffrey B. [Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Department of Physics, University of California, Berkeley, California 94720 (United States); Kavli Energy Nanosciences Institute at Berkeley, Berkeley, California 94720 (United States); Head-Gordon, Martin, E-mail: mhg@cchem.berkeley.edu [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

2016-05-21

With the aim of systematically characterizing the convergence of common families of basis sets such that general recommendations for basis sets can be made, we have tested a wide variety of basis sets against complete-basis binding energies across the S22 set of intermolecular interactions—noncovalent interactions of small and medium-sized molecules consisting of first- and second-row atoms—with three distinct density functional approximations: SPW92, a form of local-density approximation; B3LYP, a global hybrid generalized gradient approximation; and B97M-V, a meta-generalized gradient approximation with nonlocal correlation. We have found that it is remarkably difficult to reach the basis set limit; for the methods and systems examined, the most complete basis is Jensen’s pc-4. The Dunning correlation-consistent sequence of basis sets converges slowly relative to the Jensen sequence. The Karlsruhe basis sets are quite cost effective, particularly when a correction for basis set superposition error is applied: counterpoise-corrected def2-SVPD binding energies are better than corresponding energies computed in comparably sized Dunning and Jensen bases, and on par with uncorrected results in basis sets 3-4 times larger. These trends are exhibited regardless of the level of density functional approximation employed. A sense of the magnitude of the intrinsic incompleteness error of each basis set not only provides a foundation for guiding basis set choice in future studies but also facilitates quantitative comparison of existing studies on similar types of systems.

Density measurements of microsecond-conduction-time POS plasmas

International Nuclear Information System (INIS)

Hinshelwood, D.; Goodrich, P.J.; Weber, B.V.; Commisso, R.J.; Grossmann, J.M.; Kellogg, J.C.

1993-01-01

Measurements of the electron density in a coaxial microsecond conduction time plasma opening switch during switch operation are described. Current conduction is observed to cause a radial redistribution of the switch plasma. A local reduction in axial line density of more than an order of magnitude occurs by the time opening begins. This reduction, and the scaling of conduction current with plasma density, indicate that current conduction in this experiment is limited by hydrodynamic effects. It is hypothesized that the density reduction allows the switch to open by an erosion mechanism. Initial numerical modeling efforts have reproduced the principal observed results. A model that predicts accurately the conduction current is presented

Confinement properties of JET plasmas with different temperature and density profiles

International Nuclear Information System (INIS)

Watkins, M.L.; Balet, B.; Bhatnagar, V.P.

1989-01-01

The confinement properties of plasmas with substantially different temperature and density profiles have been analysed. The effects of fast particles and energy pedestals on the overall confinement of plasma energy in limiter (L-mode) and X-point (L- and H-modes) discharges heated by NBI or ICRF or both are determined. The importance of the bootstrap current when such energy pedestals are formed is noted. Using sets of consistent experimental data, including ion temperature profile measurements, the local transport properties are compared in the L- and H-phases of a single null X-point medium density NBI heated discharge, the ''enhanced'' confinement phase of a limiter high density pellet-fuelled and ICRF heated discharge, the hot-ion phase of a double null X-point low density NBI heated discharge and the hot-ion and H-phases of a double null X-point low density high temperature NBI heated discharge. (author)

Limitations on blanket performance

International Nuclear Information System (INIS)

Malang, S.

1999-01-01

The limitations on the performance of breeding blankets in a fusion power plant are evaluated. The breeding blankets will be key components of a plant and their limitations with regard to power density, thermal efficiency and lifetime could determine to a large degree the attractiveness of a power plant. The performance of two rather well known blanket concepts under development in the frame of the European Blanket Programme is assessed and their limitations are compared with more advanced (and more speculative) concepts. An important issue is the question of which material (structure, breeder, multiplier, coatings) will limit the performance and what improvement would be possible with a 'better' structural material. This evaluation is based on the premise that the performance of the power plant will be limited by the blankets (including first wall) and not by other components, e.g. divertors, or the plasma itself. However, the justness of this premise remains to be seen. It is shown that the different blanket concepts cover a large range of allowable power densities and achievable thermal efficiencies, and it is concluded that there is a high incentive to go for better performance in spite of possibly higher blanket cost. However, such high performance blankets are usually based on materials and technologies not yet developed and there is a rather high risk that the development could fail. Therefore, it is explained that a part of the development effort should be devoted to concepts where the materials and technologies are more or less in hand in order to ensure that blankets for a DEMO reactor can be developed and tested in a given time frame. (orig.)

Biased limiter experiments on text

International Nuclear Information System (INIS)

Phillips, P.E.; Wootton, A.J.; Rowan, W.L.; Ritz, C.P.; Rhodes, T.L.; Bengtson, R.D.; Hodge, W.L.; Durst, R.D.; McCool, S.C.; Richards, B.; Gentle, K.W.; Schoch, P.; Forster, J.C.; Hickok, R.L.; Evans, T.E.

1987-01-01

Experiments using an electrically biased limiter have been performed on the Texas Experimental Tokamak (TEXT). A small movable limiter is inserted past the main poloidal ring limiter (which is electrically connected to the vacuum vessel) and biased at V Lim with respect to it. The floating potential, plasma potential and shear layer position can be controlled. With vertical strokeV Lim vertical stroke ≥ 50 V the plasma density increases. For V Lim Lim > 0 the results obtained are inconclusive. Variation of V Lim changes the electrostatic turbulence which may explain the observed total flux changes. (orig.)

Power transport to the PDX scoop limiter

International Nuclear Information System (INIS)

Kugel, H.W.; Bol, K.; Budny, R.

1986-07-01

Power transport to the PDX graphite scoop limiter was measured during both ohmic- and neutral-beam-heated discharges by observing its front face temperatures using an infrared camera. Measurements were made as a function of plasma density, current, position, fueling mode, and heating power for both co- and counter-neutral beam injection. The measured thermal load on the scoop limiter was 25 to 50% of the total plasma heating power. The measured peak front face midplane temperature was 1500 0 C corresponding to a peak surface power density of 3 kW/cm 2 . This power density implies an effective parallel power flow of 54 kW/cm 2 in agreement with the radial power distribution extrapolated from TVTS and calorimetry measurements. Symmetric and asymmetric thermal loads were observed. The asymmetric heat loads were predominantly skewed toward the respective ion drift directions for both co- and counter-injected beams. The results of transport calculations are consistent with the direction and magnitude of the observed asymmetries

Experimental studies and modelling of high radiation and high density plasmas in the ASDEX upgrade tokamak

Energy Technology Data Exchange (ETDEWEB)

Casali, Livia

2015-11-24

Fusion plasmas contain impurities, either intrinsic originating from the wall, or injected willfully with the aim of reducing power loads on machine components by converting heat flux into radiation. The understanding and the prediction of the effects of these impurities and their radiation on plasma performances is crucial in order to retain good confinement. In addition, it is important to understand the impact of pellet injection on plasma performance since this technique allows higher core densities which are required to maximise the fusion power. This thesis contributes to these efforts through both experimental investigations and modelling. Experiments were conducted at ASDEX Upgrade which has a full-W wall. Impurity seeding was applied to H-modes by injecting nitrogen and also medium-Z impurities such as Kr and Ar to assess the impact of both edge and central radiation on confinement. A database of about 25 discharges has been collected and analysed. A wide range of plasma parameters was achieved up to ITER relevant values such as high Greenwald and high radiation fractions. Transport analyses taking into account the radiation distribution reveal that edge localised radiation losses do not significantly impact confinement as long as the H-mode pedestal is sustained. N seeding induces higher pedestal pressure which is propagated to the core via profile stiffness. Central radiation must be limited and controlled to avoid confinement degradation. This requires reliable control of the impurity concentration but also possibilities to act on the ELM frequency which must be kept high enough to avoid an irreversible impurity accumulation in the centre and the consequent radiation collapse. The key role of the f{sub ELM} is confirmed also by the analysis of N+He discharges. Non-coronal effects affect the radiation of low-Z impurities at the plasma edge. Due to the radial transport, the steep temperature gradients and the ELM flush out, a local equilibrium cannot be

Density-functional expansion methods: Grand challenges.

Science.gov (United States)

Giese, Timothy J; York, Darrin M

2012-03-01

We discuss the source of errors in semiempirical density functional expansion (VE) methods. In particular, we show that VE methods are capable of well-reproducing their standard Kohn-Sham density functional method counterparts, but suffer from large errors upon using one or more of these approximations: the limited size of the atomic orbital basis, the Slater monopole auxiliary basis description of the response density, and the one- and two-body treatment of the core-Hamiltonian matrix elements. In the process of discussing these approximations and highlighting their symptoms, we introduce a new model that supplements the second-order density-functional tight-binding model with a self-consistent charge-dependent chemical potential equalization correction; we review our recently reported method for generalizing the auxiliary basis description of the atomic orbital response density; and we decompose the first-order potential into a summation of additive atomic components and many-body corrections, and from this examination, we provide new insights and preliminary results that motivate and inspire new approximate treatments of the core-Hamiltonian.

Density control in ITER: an iterative learning control and robust control approach

Science.gov (United States)

Ravensbergen, T.; de Vries, P. C.; Felici, F.; Blanken, T. C.; Nouailletas, R.; Zabeo, L.

2018-01-01

Plasma density control for next generation tokamaks, such as ITER, is challenging because of multiple reasons. The response of the usual gas valve actuators in future, larger fusion devices, might be too slow for feedback control. Both pellet fuelling and the use of feedforward-based control may help to solve this problem. Also, tight density limits arise during ramp-up, due to operational limits related to divertor detachment and radiative collapses. As the number of shots available for controller tuning will be limited in ITER, in this paper, iterative learning control (ILC) is proposed to determine optimal feedforward actuator inputs based on tracking errors, obtained in previous shots. This control method can take the actuator and density limits into account and can deal with large actuator delays. However, a purely feedforward-based density control may not be sufficient due to the presence of disturbances and shot-to-shot differences. Therefore, robust control synthesis is used to construct a robustly stabilizing feedback controller. In simulations, it is shown that this combined controller strategy is able to achieve good tracking performance in the presence of shot-to-shot differences, tight constraints, and model mismatches.

Limitations on plasma acceleration due to synchrotron losses

International Nuclear Information System (INIS)

Barletta, W.A.; Lee, E.P.; Bonifacio, R.; De Salvo, L.

1999-01-01

In this letter we consider the effect of synchrotron radiation losses due to the betatron motion of the electron beam in its self-induced magnetic field in a plasma accelerator taking into account the charge neutralization factor. The most favorable case is where the plasma density is smaller than the beam density. The contrary regime is strongly disfavored by the synchrotron radiation loss for beams with characteristics for TeV energies. In both cases we find that upon increasing the plasma density the synchrotron losses kill the acceleration process, so that there are limitations on the maximum allowable plasma density

Precision Orbit Derived Atmospheric Density: Development and Performance

Science.gov (United States)

McLaughlin, C.; Hiatt, A.; Lechtenberg, T.; Fattig, E.; Mehta, P.

2012-09-01

Precision orbit ephemerides (POE) are used to estimate atmospheric density along the orbits of CHAMP (Challenging Minisatellite Payload) and GRACE (Gravity Recovery and Climate Experiment). The densities are calibrated against accelerometer derived densities and considering ballistic coefficient estimation results. The 14-hour density solutions are stitched together using a linear weighted blending technique to obtain continuous solutions over the entire mission life of CHAMP and through 2011 for GRACE. POE derived densities outperform the High Accuracy Satellite Drag Model (HASDM), Jacchia 71 model, and NRLMSISE-2000 model densities when comparing cross correlation and RMS with accelerometer derived densities. Drag is the largest error source for estimating and predicting orbits for low Earth orbit satellites. This is one of the major areas that should be addressed to improve overall space surveillance capabilities; in particular, catalog maintenance. Generally, density is the largest error source in satellite drag calculations and current empirical density models such as Jacchia 71 and NRLMSISE-2000 have significant errors. Dynamic calibration of the atmosphere (DCA) has provided measurable improvements to the empirical density models and accelerometer derived densities of extremely high precision are available for a few satellites. However, DCA generally relies on observations of limited accuracy and accelerometer derived densities are extremely limited in terms of measurement coverage at any given time. The goal of this research is to provide an additional data source using satellites that have precision orbits available using Global Positioning System measurements and/or satellite laser ranging. These measurements strike a balance between the global coverage provided by DCA and the precise measurements of accelerometers. The temporal resolution of the POE derived density estimates is around 20-30 minutes, which is significantly worse than that of accelerometer

Langmuir probe measurements in the TEXTOR tokamak during ALT-I pump limiter experiments

International Nuclear Information System (INIS)

Goebel, D.M.; Campbell, G.A.; Conn, R.W.; Leung, W.K.; Dippel, K.H.; Finken, K.H.; Thomas, G.J.; Pontau, A.E.

1986-04-01

Langmuir probes have been used to characterize the edge plasma of the TEXTOR tokamak and measure the parameters of the plasma incident on the ALT-I pump limiter during ohmic and ICRH heating. Probes mounted directly on the ALT limiter, and a scanning probe located 90 0 toroidally from the limiter, provide data for the evaluation of pump limiter performance and its effect on the edge plasma. The edge plasma is characterized by density and flux e-folding lengths of about 1.8cm when ALT is the main limiter. These scrape-off lengths do not vary significantly as ALT is moved between the normal 42-46cm minor radii, but increase to over 2.2cm when ALT is inserted to 40cm. The flux to probes at a fixed position in the limiter shadow varies by less than 25% for core density changes of a factor of five. This suggests that the global particle confinement time tau/sub p/, scales as the core density. Estimates from the probes indicate that tau/sub p/ is on the order of the energy confinement time, tau/sub E/. The edge electron temperature, T/sub e/, typically decreases by a factor of two when the core density is raised from 1 to 4 x 10 13 cm -3 . The T/sub e/ profile is essentially flat in the limiter shadow, with values of 10-25 eV depending on the core plasma density and ICRH power. ICRH heating increases the electron temperature and flux in proportion to the coupled power. With ALT as the primary limiter and no direct shadowing, the ion side receives 2 to 3 times the flux of the electron side during both ohmic and ICRH heating. The edge plasma is not directly modified by pump limiter operation, but changes with the core plasma density as particle removal lowers the recycling of neutrals in the boundary

Inference of core barrel motion from neutron noise spectral density. [PWR

Energy Technology Data Exchange (ETDEWEB)

Robinson, J.C.; Shahrokhi, F.; Kryter, R.C.

1977-03-15

A method was developed for inference of core barrel motion from the following statistical descriptors: cross-power spectral density, autopower spectral density, and amplitude probability density. To quantify the core barrel motion in a typical pressurized water reactor (PWR), a scale factor was calculated in both one- and two-dimensional geometries using forward, variational, and perturbation methods of discrete ordinates neutron transport. A procedure for selection of the proper frequency band limits for the statistical descriptors was developed. It was found that although perturbation theory is adequate for the calculation of the scale factor, two-dimensional geometric effects are important enough to rule out the use of a one-dimensional approximation for all but the crudest calculations. It was also found that contributions of gamma rays can be ignored and that the results are relatively insensitive to the cross-section set employed. The proper frequency band for the statistical descriptors is conveniently determined from the coherence and phase information from two ex-core power range neutron monitors positioned diametrically across the reactor vessel. Core barrel motion can then be quantified from the integral of the band-limited cross-power spectral density of two diametrically opposed ex-core monitors or, if the coherence between the pair is greater than or equal to 0.7, from a properly band-limited amplitude probability density function. Wide-band amplitude probability density functions were demonstrated to yield erroneous estimates for the magnitude of core barrel motion.

Does interference competition with wolves limit the distribution and abundance of coyotes?

Science.gov (United States)

Berger, Kim Murray; Gese, Eric M

2007-11-01

Interference competition with wolves Canis lupus is hypothesized to limit the distribution and abundance of coyotes Canis latrans, and the extirpation of wolves is often invoked to explain the expansion in coyote range throughout much of North America. We used spatial, seasonal and temporal heterogeneity in wolf distribution and abundance to test the hypothesis that interference competition with wolves limits the distribution and abundance of coyotes. From August 2001 to August 2004, we gathered data on cause-specific mortality and survival rates of coyotes captured at wolf-free and wolf-abundant sites in Grand Teton National Park (GTNP), Wyoming, USA, to determine whether mortality due to wolves is sufficient to reduce coyote densities. We examined whether spatial segregation limits the local distribution of coyotes by evaluating home-range overlap between resident coyotes and wolves, and by contrasting dispersal rates of transient coyotes captured in wolf-free and wolf-abundant areas. Finally, we analysed data on population densities of both species at three study areas across the Greater Yellowstone Ecosystem (GYE) to determine whether an inverse relationship exists between coyote and wolf densities. Although coyotes were the numerically dominant predator, across the GYE, densities varied spatially and temporally in accordance with wolf abundance. Mean coyote densities were 33% lower at wolf-abundant sites in GTNP, and densities declined 39% in Yellowstone National Park following wolf reintroduction. A strong negative relationship between coyote and wolf densities (beta = -3.988, P wolves limits coyote populations. Overall mortality of coyotes resulting from wolf predation was low, but wolves were responsible for 56% of transient coyote deaths (n = 5). In addition, dispersal rates of transient coyotes captured at wolf-abundant sites were 117% higher than for transients captured in wolf-free areas. Our results support the hypothesis that coyote abundance is

No need for external orthogonality in subsystem density-functional theory.

Science.gov (United States)

Unsleber, Jan P; Neugebauer, Johannes; Jacob, Christoph R

2016-08-03

Recent reports on the necessity of using externally orthogonal orbitals in subsystem density-functional theory (SDFT) [Annu. Rep. Comput. Chem., 8, 2012, 53; J. Phys. Chem. A, 118, 2014, 9182] are re-investigated. We show that in the basis-set limit, supermolecular Kohn-Sham-DFT (KS-DFT) densities can exactly be represented as a sum of subsystem densities, even if the subsystem orbitals are not externally orthogonal. This is illustrated using both an analytical example and in basis-set free numerical calculations for an atomic test case. We further show that even with finite basis sets, SDFT calculations using accurate reconstructed potentials can closely approach the supermolecular KS-DFT density, and that the deviations between SDFT and KS-DFT decrease as the basis-set limit is approached. Our results demonstrate that formally, there is no need to enforce external orthogonality in SDFT, even though this might be a useful strategy when developing projection-based DFT embedding schemes.

Development of internal transport barrier scenarios at ITER-relevant high triangularity in JET

International Nuclear Information System (INIS)

Rimini, F.G.; Becoulet, M.; Giovannozzi, E.; Lomas, P.J.; Tudisco, O.; Alper, B.; Crisanti, F.; Baar, M. de; Luna, E. de La; Vries, P. de; Ekedahl, A.; Hawkes, N.; Huysmans, G.; Litaudon, X.; Parail, V.; Saibene, G.; Tuccillo, A.A.; Zastrow, K.D.

2005-01-01

The development of scenarios characterized by H-mode confinement and internal transport barriers (ITBs) in high triangularity, δ ∼ 0.4-0.5, discharges is of particular interest for ITER advanced tokamak operation. Previous JET experiments have shown that high triangularity favours H-modes which are ELM-free or develop type I edge localized mode (ELM) activity, which inhibits long lasting ITBs. The recent experiments reported here concentrate on integrated optimization of edge and core conditions. The stability of the edge pedestal was controlled using gas injection, deuterium or light impurities, and plasma current ramps. Both methods yield more ITB-friendly edge pedestal conditions, varying from small type I to type III ELMs and, in extreme cases, resulting in L-mode. In parallel, the conditions for triggering and sustaining ITBs encompassing a large proportion of the plasma volume (outer ITBs) were optimized, as opposed to less performing ITBs located closer to the plasma centre (inner ITB). These plasmas have deeply reversed target current profiles with q min ∼ 3 and a narrow inner ITB, located typically at a small normalized radius ρ E , at q 95 = 7.5, H 89 β N ∼ 3.5-4 and ∼60% of the Greenwald density limit. In summary, a high triangularity scenario has been developed, which combines the desirable characteristics of controlled edge, long lasting wide ITBs and high performance at density higher than the low triangularity JET scenarios

Multidimensional flux-limited advection schemes

International Nuclear Information System (INIS)

Thuburn, J.

1996-01-01

A general method for building multidimensional shape preserving advection schemes using flux limiters is presented. The method works for advected passive scalars in either compressible or incompressible flow and on arbitrary grids. With a minor modification it can be applied to the equation for fluid density. Schemes using the simplest form of the flux limiter can cause distortion of the advected profile, particularly sideways spreading, depending on the orientation of the flow relative to the grid. This is partly because the simple limiter is too restrictive. However, some straightforward refinements lead to a shape-preserving scheme that gives satisfactory results, with negligible grid-flow angle-dependent distortion

Vihased dokumentalistid / Andris Feldmanis

Index Scriptorium Estoniae

Feldmanis, Andris, 1982-

2006-01-01

Berliini filmifestivalil näidatud sotsiaalkriitiline dokumentaal "Walmart : Iga hinna eest odavamalt" ("Walmart : The High Price of Low Cost") : režissöör Robert Greenwald : Ameerika Ühendriigid 2005

BPS limit of multi- D- and DF-strings in boundary string field theory

International Nuclear Information System (INIS)

Go, Gyungchoon; Ishida, Akira; Kim, Yoonbai

2007-01-01

A BPS limit is systematically derived for straight multi- D- and DF-strings from the D3D-bar3 system in the context of boundary superstring field theory. The BPS limit is obtained in the limit of thin D(F)-strings, where the Bogomolny equation supports singular static multi-D(F)-string solutions. For the BPS multi-string configurations with arbitrary separations, BPS sum rule is fulfilled under a Gaussian type tachyon potential and reproduces exactly the descent relation. For the DF-strings ((p,q)-strings), the distribution of fundamental string charge density coincides with its energy density and the Hamiltonian density takes the BPS formula of square-root form

On the energy confinement in the TM-G tokamak with high plasma density

International Nuclear Information System (INIS)

Stefanovskij, A.M.

1986-01-01

Energy confinement time τ E , when plasma density changing, has been measured at the TM-G-tokamak device with a graphite discharge chamber. The measurements have been carried out in three different discharge modes with a similar stability margin on the limiter (q L )=3) and with different values of the discharge current of a longitudinal field (I p =20, 40 and 60 kA, V T =0.8; 1.6 and 2.4 T). On the basis of experimental data analysis the conclusion is made that saturation of τ E (n e ) dependence at high plasma density occurs due to current channel compression and violation of a ''self-consistent'' profile of current density. Drift wave excitation at densities similar to the limiting Murakami density can also play an important role

Optimum extracted H- and D- current densities from gas-pressure-limited high-power hydrogen/deuterium tandem ion sources

International Nuclear Information System (INIS)

Hiskes, J.R.

1993-01-01

The tandem hydrogen/deuterium ion source is modelled for the purpose of identifying the maximum current densities that can be extracted subject to the gas-pressure constraints proposed for contemporary beam-line systems. Optimum useful extracted current densities are found to be in the range of approximately 7 to 10 mA cm -2 . The sensitivity of these current densities is examined subject to uncertainties in the underlying atomic/molecular rate processes; A principal uncertainty remains the quantification of the molecular vibrational distribution following H 3 + wall collisions

Evaluation of population density and distribution criteria in nuclear power plant siting

International Nuclear Information System (INIS)

Young, M.

1994-06-01

The NRC has proposed revisions to 10 CFR 100 which include the codification of nuclear reactor site population density limits to 500 people per square mile, at the siting stage, averaged over any radial distance out to 30 miles, and 1,000 people per square mile within the 40-year lifetime of a nuclear plant. This study examined whether there are less restrictive alternative population density and/or distribution criteria which would provide equivalent or better protection to human health in the unlikely event of a nuclear accident. This study did not attempt to directly address the issue of actual population density limits because there are no US risk standards established for the evaluation of population density limits. Calculations were performed using source terms for both a current generation light water reactor (LWR) and an advanced light water reactor (ALWR) design. The results of this study suggest that measures which address the distribution of the population density, including emergency response conditions, could result in lower average individual risks to the public than the proposed guidelines that require controlling average population density. Studies also indicate that an exclusion zone size, determined by emergency response conditions and reactor design (power level and safety features), would better serve to protect public health than a rigid standard applied to all sites

Power transport to the poloidal divertor experiment scoop limiter

International Nuclear Information System (INIS)

Kugel, H.W.; Budny, R.; Fonck, R.

1987-01-01

Power transport to the Poloidal Divertor Experiment graphite scoop limiter was measured during both ohmic- and neutral-beam-heated discharges by observing its front face temperatures using an infrared camera. Measurements were made as a function of a plasma density, current, position, fueling mode, and heating power for both co- and counter-neutral beam injection. The measured thermal load on the scoop limiter was 25 to 50%. of the total plasma heating power. The measured peak front face midplane temperature was 1500 0 C, corresponding to a peak surface power density of 3 kW/cm/sup 2/. This power density implies an effective parallel power flow of 54 kW/cm/sup 2/ in agreement with the radial power distribution extrapolated from television Thomson scattering and calorimetry measurements

Simulation of density measurements in plasma wakefields using photo acceleration

CERN Document Server

Kasim, Muhammad Firmansyah; Ceurvorst, Luke; Sadler, James; Burrows, Philip N; Trines, Raoul; Holloway, James; Wing, Matthew; Bingham, Robert; Norreys, Peter

2015-01-01

One obstacle in plasma accelerator development is the limitation of techniques to diagnose and measure plasma wakefield parameters. In this paper, we present a novel concept for the density measurement of a plasma wakefield using photon acceleration, supported by extensive particle in cell simulations of a laser pulse that copropagates with a wakefield. The technique can provide the perturbed electron density profile in the laser’s reference frame, averaged over the propagation length, to be accurate within 10%. We discuss the limitations that affect the measurement: small frequency changes, photon trapping, laser displacement, stimulated Raman scattering, and laser beam divergence. By considering these processes, one can determine the optimal parameters of the laser pulse and its propagation length. This new technique allows a characterization of the density perturbation within a plasma wakefield accelerator.

Bone Density and Dental External Apical Root Resorption

Science.gov (United States)

Iglesias-Linares, Alejandro; Morford, Lorri Ann

2016-01-01

When orthodontic patients desire shorter treatment times with aesthetic results and long-term stability, it is important for the orthodontist to understand the potential limitations and problems that may arise during standard and/or technology-assisted accelerated treatment. Bone density plays an important role in facilitating orthodontic tooth movement (OTM), such that reductions in bone density can significantly increase movement velocity. Lifestyle, genetic background, environmental factors and disease status all can influence a patients’ overall health and bone density. In some individuals, these factors may create specific conditions that influence systemic-wide bone metabolism. Both genetic variation and the onset of a bone-related disease can influence systemic bone density and local bone density, such as is observed in the mandible and maxilla. These types of localized density changes can affect the rate of OTM and may also influence the risk of unwanted outcomes, i.e., the occurrence of dental external apical root resorption (EARR). PMID:27766484

Dual effects of pedestrian density on emergency evacuation

Energy Technology Data Exchange (ETDEWEB)

Ma, Yi, E-mail: yima23-c@my.cityu.edu.hk [School of Transportation and Logistics, Southwest Jiaotong University, Chengdu (China); Department of Architecture and Civil Engineering, City University of Hong Kong, Kowloon (Hong Kong); Lee, Eric Wai Ming; Yuen, Richard Kwok Kit [Department of Architecture and Civil Engineering, City University of Hong Kong, Kowloon (Hong Kong)

2017-02-05

This paper investigates the effect of the pedestrian density in building on the evacuation dynamic with simulation method. In the simulations, both the visibility in building and the exit limit of building are taken into account. The simulation results show that the effect of the pedestrian density in building on the evacuation dynamics is dual. On the one hand, when the visibility in building is very large, the increased pedestrian density plays a negative effect. On the other hand, when the visibility in building is very small, the increased pedestrian density can play a positive effect. The simulation results also show that when both the exit width and visibility are very small, the varying of evacuation time with regard to the pedestrian density is non-monotonous and presents a U-shaped tendency. That is, in this case, too large or too small pedestrian density in building is disadvantageous to the evacuation process. Our findings provide a new insight about the effect of the pedestrian density in building on the evacuation dynamic. - Highlights: • Pedestrian density inside buildings has dual effects on evacuation. • Increased pedestrian density has a negative effect in cases of increased visibility. • Increased pedestrian density has a positive effect in cases of decreased visibility.

Dual effects of pedestrian density on emergency evacuation

International Nuclear Information System (INIS)

Ma, Yi; Lee, Eric Wai Ming; Yuen, Richard Kwok Kit

2017-01-01

This paper investigates the effect of the pedestrian density in building on the evacuation dynamic with simulation method. In the simulations, both the visibility in building and the exit limit of building are taken into account. The simulation results show that the effect of the pedestrian density in building on the evacuation dynamics is dual. On the one hand, when the visibility in building is very large, the increased pedestrian density plays a negative effect. On the other hand, when the visibility in building is very small, the increased pedestrian density can play a positive effect. The simulation results also show that when both the exit width and visibility are very small, the varying of evacuation time with regard to the pedestrian density is non-monotonous and presents a U-shaped tendency. That is, in this case, too large or too small pedestrian density in building is disadvantageous to the evacuation process. Our findings provide a new insight about the effect of the pedestrian density in building on the evacuation dynamic. - Highlights: • Pedestrian density inside buildings has dual effects on evacuation. • Increased pedestrian density has a negative effect in cases of increased visibility. • Increased pedestrian density has a positive effect in cases of decreased visibility.

Dual effects of pedestrian density on emergency evacuation

Science.gov (United States)

Ma, Yi; Lee, Eric Wai Ming; Yuen, Richard Kwok Kit

2017-02-01

This paper investigates the effect of the pedestrian density in building on the evacuation dynamic with simulation method. In the simulations, both the visibility in building and the exit limit of building are taken into account. The simulation results show that the effect of the pedestrian density in building on the evacuation dynamics is dual. On the one hand, when the visibility in building is very large, the increased pedestrian density plays a negative effect. On the other hand, when the visibility in building is very small, the increased pedestrian density can play a positive effect. The simulation results also show that when both the exit width and visibility are very small, the varying of evacuation time with regard to the pedestrian density is non-monotonous and presents a U-shaped tendency. That is, in this case, too large or too small pedestrian density in building is disadvantageous to the evacuation process. Our findings provide a new insight about the effect of the pedestrian density in building on the evacuation dynamic.

Sap flow measurements combining sap-flux density radial profiles with punctual sap-flux density measurements in oak trees (Quercus ilex and Quercus pyrenaica) - water-use implications in a water-limited savanna-

Science.gov (United States)

Reyes, J. Leonardo; Lubczynski1, Maciek W.

2010-05-01

Sap flow measurement is a key aspect for understanding how plants use water and their impacts on the ecosystems. A variety of sensors have been developed to measure sap flow, each one with its unique characteristics. When the aim of a research is to have accurate tree water use calculations, with high temporal and spatial resolution (i.e. scaled), a sensor with high accuracy, high measurement efficiency, low signal-to-noise ratio and low price is ideal, but such has not been developed yet. Granier's thermal dissipation probes (TDP) have been widely used in many studies and various environmental conditions because of its simplicity, reliability, efficiency and low cost. However, it has two major flaws when is used in semi-arid environments and broad-stem tree species: it is often affected by high natural thermal gradients (NTG), which distorts the measurements, and it cannot measure the radial variability of sap-flux density in trees with sapwood thicker than two centimeters. The new, multi point heat field deformation sensor (HFD) is theoretically not affected by NTG, and it can measure the radial variability of the sap flow at different depths. However, its high cost is a serious limitation when simultaneous measurements are required in several trees (e.g. catchment-scale studies). The underlying challenge is to develop a monitoring schema in which HFD and TDP are combined to satisfy the needs of measurement efficiency and accuracy in water accounting. To assess the level of agreement between TDP and HFD methods in quantifying sap flow rates and temporal patterns on Quercus ilex (Q.i ) and Quercus pyrenaica trees (Q.p.), three measurement schemas: standard TDP, TDP-NTG-corrected and HFD were compared in dry season at the semi-arid Sardon area, near Salamanca in Spain in the period from June to September 2009. To correct TDP measurements with regard to radial sap flow variability, a radial sap flux density correction factor was applied and tested by adjusting TDP

Beta limitation of matter-antimatter boundary layers

International Nuclear Information System (INIS)

Lehnert, B.

1987-08-01

A model has earlier been proposed for a boundary layer which separates a cloud of matter from one of antimatter in a magnetized ambiplasma. In this model steady pressure equilibrium ceases to exist when a certain beta limit is exceeded. The latter is defined as the ratio between the ambiplasma and magnetic field pressures which balance each other in the boundary layer. Thus, at an increasing density, the high-energy particles created by annihilation within the layer are 'pumped up' to a pressure which cannot be balanced by a given magnetic field. The boundary layer then 'disrupts'. The critical beta limit thus obtained falls within the observed parameter ranges of galaxies and other large cosmical objects. Provided that the considered matter-antimatter balance holds true, this limit is thus expected to impose certain existence conditions on matter-antimatter boundary layers. Such a limitation may apply to certain cosmical objects and cosmological models. The maximum time scale for the corresponding disruption development has been estimated to be in the range from about 10 -4 to 10 2 seconds for boundary layers at ambiplasma particle densities in the range from 10 4 to 10 -2 m -3 , respectively. (author)

Low-frequency oscillations at high density in JFT-2

International Nuclear Information System (INIS)

Maeno, Masaki; Katagiri, Masaki; Suzuki, Norio; Fujisawa, Noboru

1977-12-01

Low-frequency oscillations in a plasma were measured with magnetic probes and Si surface-barrier detectors, and behaviour of the high density plasmas was studied. The plasma current profile in the phase of decreasing density after the interruption of gas input is more peaked than during gas input. The introduction of hydrogen during a discharge results in a reduction of the impurities flux. The increase of density by fast gas input is limited with a negative voltage spike. Immediately before a negative voltage spike, oscillations of m=1,2 grow, leading to the spike. (auth.)

Experimental study on plasma parameters in the mushroom limiter shadow in the T-10 tokamak

International Nuclear Information System (INIS)

Alferov, A.A.; Vershkov, V.A.; Grashin, S.A.; Chankin, A.V.

1988-01-01

Plasma parameters in the shadow of mashroom limiter installed in the lower tokamak outlet are studied. Investigation into asymmetry of plasma fluxes to the ion and electrone limiter sides leads to a consumption concerning two meachanisms of its occurrance-toroidal plasma rotation and prevailing plasma departure to the wall through the external torus encirclement. Asymmetry of plasma drift potentials near the limiter observed during the experiment leads to current drift through the limiter close to Spitzer j s one. It is shown that with the increase of mean plasma density the plasma density in the limiter channels grows and its temperature is decreased so the charged particle losses for the limiter are weakly dependent on the mean density which is connected with plasma confinement degradation under the density reduction. A complete flux of charged particles to the limiter is comparable to their flux from plasma filament. Plasma flux into the channels is close to ambipolar one and the power fluxes to neutralization plates are of the order of 10 j s Te/e. Neutral gas pressure dependence in the volume under the limiter on the plasma fluxes to channels is nonlinear, the maximum pressure achieves 3x10 -2 T

Land use, forest density, soil mapping, erosion, drainage, salinity limitations

Science.gov (United States)

Yassoglou, N. J. (Principal Investigator)

1973-01-01

The author has identified the following significant results. The results of analyses show that it is possible to obtain information of practical significance as follows: (1) A quick and accurate estimate of the proper use of the valuable land can be made on the basis of temporal and spectral characteristics of the land features. (2) A rather accurate delineation of the major forest formations in the test areas was achieved on the basis of spatial and spectral characteristics of the studied areas. The forest stands were separated into two density classes; dense forest, and broken forest. On the basis of ERTS-1 data and the existing ground truth information a rather accurate mapping of the major vegetational forms of the mountain ranges can be made. (3) Major soil formations are mapable from ERTS-1 data: recent alluvial soils; soil on quarternary deposits; severely eroded soil and lithosol; and wet soils. (4) An estimation of cost benefits cannot be made accurately at this stage of the investigation. However, a rough estimate of the ratio of the cost for obtaining the same amount information from ERTS-1 data and from conventional operations would be approximately 1:6 to 1:10, in favor of the ERTS-1.

Simulation of density measurements in plasma wakefields using photon acceleration

Directory of Open Access Journals (Sweden)

Muhammad Firmansyah Kasim

2015-03-01

Full Text Available One obstacle in plasma accelerator development is the limitation of techniques to diagnose and measure plasma wakefield parameters. In this paper, we present a novel concept for the density measurement of a plasma wakefield using photon acceleration, supported by extensive particle in cell simulations of a laser pulse that copropagates with a wakefield. The technique can provide the perturbed electron density profile in the laser’s reference frame, averaged over the propagation length, to be accurate within 10%. We discuss the limitations that affect the measurement: small frequency changes, photon trapping, laser displacement, stimulated Raman scattering, and laser beam divergence. By considering these processes, one can determine the optimal parameters of the laser pulse and its propagation length. This new technique allows a characterization of the density perturbation within a plasma wakefield accelerator.

Plasma Photonic Devices for High Energy Density Science

International Nuclear Information System (INIS)

Kodama, R.

2005-01-01

High power laser technologies are opening a variety of attractive fields of science and technology using high energy density plasmas such as plasma physics, laboratory astrophysics, material science, nuclear science including medical applications and laser fusion. The critical issues in the applications are attributed to the control of intense light and enormous density of charged particles including efficient generation of the particles such as MeV electrons and protons with a current density of TA/cm2. Now these application possibilities are limited only by the laser technology. These applications have been limited in the control of the high power laser technologies and their optics. However, if we have another device consisted of the 4th material, i.e. plasma, we will obtain a higher energy density condition and explore the application possibilities, which could be called high energy plasma device. One of the most attractive devices has been demonstrated in the fast ignition scheme of the laser fusion, which is cone-guiding of ultra-intense laser light in to high density regions1. This is one of the applications of the plasma device to control the ultra-intense laser light. The other role of the devices consisted of transient plasmas is control of enormous energy-density particles in a fashion analogous to light control with a conventional optical device. A plasma fibre (5?m/1mm), as one example of the devices, has guided and deflected the high-density MeV electrons generated by ultra-intense laser light 2. The electrons have been well collimated with either a lens-like plasma device or a fibre-like plasma, resulting in isochoric heating and creation of ultra-high pressures such as Giga bar with an order of 100J. Plasmas would be uniquely a device to easily control the higher energy density particles like a conventional optical device as well as the ultra-intense laser light, which could be called plasma photonic device. (Author)

Entropy density of an adiabatic relativistic Bose-Einstein condensate star

Energy Technology Data Exchange (ETDEWEB)

Khaidir, Ahmad Firdaus; Kassim, Hasan Abu; Yusof, Norhasliza [Theoretical Physics Lab., Department of Physics, Faculty of Science Building, University of Malaya, 50603 Kuala Lumpur (Malaysia)

2015-04-24

Inspired by recent works, we investigate how the thermodynamics parameters (entropy, temperature, number density, energy density, etc) of Bose-Einstein Condensate star scale with the structure of the star. Below the critical temperature in which the condensation starts to occur, we study how the entropy behaves with varying temperature till it reaches its own stability against gravitational collapse and singularity. Compared to photon gases (pressure is described by radiation) where the chemical potential, μ is zero, entropy of photon gases obeys the Stefan-Boltzmann Law for a small values of T while forming a spiral structure for a large values of T due to general relativity. The entropy density of Bose-Einstein Condensate is obtained following the similar sequence but limited under critical temperature condition. We adopt the scalar field equation of state in Thomas-Fermi limit to study the characteristics of relativistic Bose-Einstein condensate under varying temperature and entropy. Finally, we obtain the entropy density proportional to (σT{sup 3}-3T) which obeys the Stefan-Boltzmann Law in ultra-relativistic condition.

Scrape-off profiles and effects of limiter pumping in Tore Supra

International Nuclear Information System (INIS)

Budny, R.

1986-11-01

A one dimensional plasma scrape-off model was used to simulate Tore Supra discharges which are limited by various combinations of the pumped and inner limiters. Scrape-off profiles of the electron density and temperature, ion temperature, and neutral density are given. For each case, various fractions of the ion flux to the neutralizers were assumed to be pumped. Modifications of the scrap-off profiles caused by pumping are predicted. Pumping efficiencies are calculated including the effects of flux amplification caused by recycling. The pumping efficiency is estimated to be 8% for low-power discharges formed on the outer pumped limiter, 7.5% for intermediate-power discharges formed on the seven-module pumped-limiter system, and 5% for full-power discharges formed on both the inner limiter and the pumped-limiter system. The maximum particle removal rate is estimated to be 150 Tl/s

Epidemiological reference ranges for low-density lipoprotein ...

African Journals Online (AJOL)

Although there is widespread acceptance that total cholesterol (TC) value reference ranges should be based on epidemiological rather than statistical considerations, the epidemiological action limits for Iow-density lipoprotein cholesterol (LDL-C) are still incomplete and only statistical reference ranges for apolipoprotein B ...

H-mode development in TEXT-U limiter plasmas

International Nuclear Information System (INIS)

Roberts, D.R.; Bravenec, R.V.; Bengtson, R.D.

1996-01-01

H-mode transitions in TEXT-U limiter plasmas have been observed at q a ∼ 3 and I p ∼ 250 kA (P OH ∼ 300 kW) with at least 300 kW of central electron-cyclotron heating (ECH). These are dithering transitions which are induced by sawtooth crashes and display the typical signatures of H-modes (D α drop, spontaneous density increase, evidence of a transport barrier). However, they show only a slight improvement over L-mode energy confinement. The vessel walls are boronized and conditioned prior to experiments to achieve low-impurity influx and particle recycling. Discharges which undergo transitions are fuelled almost entirely on residual recycling. Transitions are observed when limited on a toroidally localized top or bottom limiter and, more often, when the limiter surface is 'fresh', which is achieved by alternating between top and bottom limiters on successive shots. No strong dependence upon the distance from the low-field-side limiter has been found. Transitions are not yet observed when limited on the high-field-side wall tiles or in the case of TEXT-U diverted configurations. Preliminary measurements with the 2 MeV heavy-ion beam probe (HIBP) (in the core) and Langmuir probes (in the edge) indicate that the plasma potential drops outside the q = 1 radius while only small changes are observed in the density fluctuations level. (author)

Simulations of cold nuclear matter at sub-saturation densities

Energy Technology Data Exchange (ETDEWEB)

Giménez Molinelli, P.A., E-mail: pagm@df.uba.ar [Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and IFIBA, CONICET, Ciudad Universitaria, Buenos Aires 1428 (Argentina); Nichols, J.I. [Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and IFIBA, CONICET, Ciudad Universitaria, Buenos Aires 1428 (Argentina); López, J.A. [Department of Physics, University of Texas at El Paso, El Paso, TX 79968 (United States); Dorso, C.O. [Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and IFIBA, CONICET, Ciudad Universitaria, Buenos Aires 1428 (Argentina)

2014-03-01

Ideal nuclear matter is expected to undergo a first order phase transition at the thermodynamic limit. At such phase transitions the size of density fluctuations (bubbles or droplets) scale with the size of the system. This means that simulations of nuclear matter at sub-saturation densities will inexorably suffer from what is vaguely referred to as “finite size effects”. It is usually thought that these finite size effects can be diminished by imposing periodic boundary conditions and making the system large enough, but as we show in this work, that is actually not the case at sub-saturation densities. In this paper we analyze the equilibrium configurations of molecular dynamics simulations of a classical model for symmetric ideal (uncharged) nuclear matter at sub-saturation densities and low temperatures, where phase coexistence is expected at the thermodynamic limit. We show that the most stable configurations in this density range are almost completely determined by artificial aspects of the simulations (i.e. boundary conditions) and can be predicted analytically by surface minimization. This result is very general and is shown to hold true for several well known semi-classical models of nuclear interaction and even for a simple Lennard-Jones potential. Also, in the limit of very large systems, when “small size” effects can be neglected, those equilibrium configurations seem to be restricted to a few structures reminiscent to the “Pasta Phases” expected in Neutron Star matter, but arising from a completely different origin: In Neutron Star matter, the non-homogeneous structures arise from a competition between nuclear and Coulomb interactions while for ideal nuclear matter they emerge from finite (yet not “small”) size effects. The role of periodic boundary conditions and finite size effects in Neutron Star matter simulations are reexamined.

Propulsion Physics Under the Changing Density Field Model

Science.gov (United States)

Robertson, Glen A.

2011-01-01

To grow as a space faring race, future spaceflight systems will requires new propulsion physics. Specifically a propulsion physics model that does not require mass ejection without limiting the high thrust necessary to accelerate within or beyond our solar system and return within a normal work period or lifetime. In 2004 Khoury and Weltman produced a density dependent cosmology theory they called Chameleon Cosmology, as at its nature, it is hidden within known physics. This theory represents a scalar field within and about an object, even in the vacuum. Whereby, these scalar fields can be viewed as vacuum energy fields with definable densities that permeate all matter; having implications to dark matter/energy with universe acceleration properties; implying a new force mechanism for propulsion physics. Using Chameleon Cosmology, the author has developed a new propulsion physics model, called the Changing Density Field (CDF) Model. This model relates to density changes in these density fields, where the density field density changes are related to the acceleration of matter within an object. These density changes in turn change how an object couples to the surrounding density fields. Whereby, thrust is achieved by causing a differential in the coupling to these density fields about an object. Since the model indicates that the density of the density field in an object can be changed by internal mass acceleration, even without exhausting mass, the CDF model implies a new propellant-less propulsion physics model

MgB2-based superconductors for fault current limiters

Science.gov (United States)

Sokolovsky, V.; Prikhna, T.; Meerovich, V.; Eisterer, M.; Goldacker, W.; Kozyrev, A.; Weber, H. W.; Shapovalov, A.; Sverdun, V.; Moshchil, V.

2017-02-01

A promising solution of the fault current problem in power systems is the application of fast-operating nonlinear superconducting fault current limiters (SFCLs) with the capability of rapidly increasing their impedance, and thus limiting high fault currents. We report the results of experiments with models of inductive (transformer type) SFCLs based on the ring-shaped bulk MgB2 prepared under high quasihydrostatic pressure (2 GPa) and by hot pressing technique (30 MPa). It was shown that the SFCLs meet the main requirements to fault current limiters: they possess low impedance in the nominal regime of the protected circuit and can fast increase their impedance limiting both the transient and the steady-state fault currents. The study of quenching currents of MgB2 rings (SFCL activation current) and AC losses in the rings shows that the quenching current density and critical current density determined from AC losses can be 10-20 times less than the critical current determined from the magnetization experiments.

Secretory expression of functional barley limit dextrinase by Pichia pastoris using high cell-density fermentation

DEFF Research Database (Denmark)

Vester-Christensen, Malene Bech; Abou Hachem, Maher; Næsted, Henrik

2010-01-01

biosynthesis by trimming of intermediate branched alpha-glucan structures. Highly active barley LD is obtained by secretory expression during high cell-density fermentation of Pichia pastoris. The LD encoding gene fragment without signal peptide was subcloned in-frame with the Saccharomyces cerevisiae alpha...

FTU pump limiter

International Nuclear Information System (INIS)

Alessandrini, C.; Ciotti, M.; Mattei, A. De; Maddaluno, G.; Mazzitelli, G.

1989-01-01

The control of the refuelling and recycling of the plasma is crucial in providing enhanced performances in tokamaks and steady-state operation in future reactors. In this paper, we report details of the design and analysis for the pump limiter to be incorporated into the FTU tokamak. The FTU, presently under commissioning, is a compact high field (B=8T), medium high density, circular cross section machine with small accesses. The dimensions of the equatorial port (width 8 cm) would reduce the length of the entrance throat to a few centimeters, which is unacceptable for efficient particle trapping. We have, therefore, designed a rotating blade of the pump limiter head that, in the working position, extends in the toroidal direction inside the vacuum chamber. (author) 8 refs., 4 figs

Relativistic classical limit of quantum theory

International Nuclear Information System (INIS)

Shin, G.R.; Rafelski, J.

1993-01-01

We study the classical limit of the equal-time relativistic quantum transport theory. We discuss in qualitative terms the need to fold first the Wigner function with a coarse-graining function. Only then does the singularity at ℎ→0 seem to be manageable. In the limit ℎ→0, we obtain the relativistic Vlasov equations for the particle and the antiparticle sector of the Fock space. Similarly, we address the evolution equations of the spin and the magnetic-moment density

Computer modelling of superconductive fault current limiters

Energy Technology Data Exchange (ETDEWEB)

Weller, R.A.; Campbell, A.M.; Coombs, T.A.; Cardwell, D.A.; Storey, R.J. [Cambridge Univ. (United Kingdom). Interdisciplinary Research Centre in Superconductivity (IRC); Hancox, J. [Rolls Royce, Applied Science Division, Derby (United Kingdom)

1998-05-01

Investigations are being carried out on the use of superconductors for fault current limiting applications. A number of computer programs are being developed to predict the behavior of different `resistive` fault current limiter designs under a variety of fault conditions. The programs achieve solution by iterative methods based around real measured data rather than theoretical models in order to achieve accuracy at high current densities. (orig.) 5 refs.

Density Functional Methods for Shock Physics and High Energy Density Science

Science.gov (United States)

Desjarlais, Michael

2017-06-01

Molecular dynamics with density functional theory has emerged over the last two decades as a powerful and accurate framework for calculating thermodynamic and transport properties with broad application to dynamic compression, high energy density science, and warm dense matter. These calculations have been extensively validated against shock and ramp wave experiments, are a principal component of high-fidelity equation of state generation, and are having wide-ranging impacts on inertial confinement fusion, planetary science, and shock physics research. In addition to thermodynamic properties, phase boundaries, and the equation of state, one also has access to electrical conductivity, thermal conductivity, and lower energy optical properties. Importantly, all these properties are obtained within the same theoretical framework and are manifestly consistent. In this talk I will give a brief history and overview of molecular dynamics with density functional theory and its use in calculating a wide variety of thermodynamic and transport properties for materials ranging from ambient to extreme conditions and with comparisons to experimental data. I will also discuss some of the limitations and difficulties, as well as active research areas. Sandia is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Low-density moderation in the storage of PWR fuel assemblies

International Nuclear Information System (INIS)

Alcorn, F.M.

1987-01-01

The nuclear criticality safety of PWR fuel storage arrays requires that the potential of low-density moderation within the array be considered. The calculated criticality effect of low-density moderation in a typical PWR fuel assembly array is described in this paper. Calculated reactivity due to low-density moderation can vary significantly between physics codes that have been validated for well moderated systems. The availability of appropriate benchmark experiments for low-density moderation is quite limited; attempts to validate against the one set of suitable experiments at low density have been disappointing. Calculations indicate that a typical array may be unacceptable should the array be subjected to interstitial moderation equivalent to 5 % of full density water. Array parameters (such as spacing and size) will dramatically affect the calculated maximum K-eff at low-density moderation. Administrative and engineered control may be necessary to assure maintenance of safety at low-density moderation. Potential sources for low-density moderation are discussed; in general, accidentally achieving degrees of low-density moderation which might lead to a compromise of safety are not credible. (author)

City density and CO_2 efficiency

International Nuclear Information System (INIS)

Gudipudi, Ramana; Fluschnik, Till; Ros, Anselmo García Cantú; Walther, Carsten; Kropp, Jürgen P.

2016-01-01

Cities play a vital role in the global climate change mitigation agenda. City population density is one of the key factors that influence urban energy consumption and the subsequent GHG emissions. However, previous research on the relationship between population density and GHG emissions led to contradictory results due to urban/rural definition conundrum and the varying methodologies for estimating GHG emissions. This work addresses these ambiguities by employing the City Clustering Algorithm (CCA) and utilizing the gridded CO_2 emissions data. Our results, derived from the analysis of all inhabited areas in the US, show a sub-linear relationship between population density and the total emissions (i.e. the sum of on-road and building emissions) on a per capita basis. Accordingly, we find that doubling the population density would entail a reduction in the total CO_2 emissions in buildings and on-road sectors typically by at least 42%. Moreover, we find that population density exerts a higher influence on on-road emissions than buildings emissions. From an energy consumption point of view, our results suggest that on-going urban sprawl will lead to an increase in on-road energy consumption in cities and therefore stresses the importance of developing adequate local policy measures to limit urban sprawl. - Highlights: •We use gridded population, land use and CO_2 emissions data. •We attribute building and on-road sectoral emissions to populated settlements. •We apply CCA to identify unique city extents and population densities. •Doubling the population density increases CO_2 efficiency typically by 42%. •Population density has more influence on-road CO_2 efficiency than buildings sector.

Determine ISS Soyuz Orbital Module Ballistic Limits for Steel Projectiles Hypervelocity Impact Testing

Science.gov (United States)

Lyons, Frankel

2013-01-01

A new orbital debris environment model (ORDEM 3.0) defines the density distribution of the debris environment in terms of the fraction of debris that are low-density (plastic), medium-density (aluminum) or high-density (steel) particles. This hypervelocity impact (HVI) program focused on assessing ballistic limits (BLs) for steel projectiles impacting the enhanced Soyuz Orbital Module (OM) micrometeoroid and orbital debris (MMOD) shield configuration. The ballistic limit was defined as the projectile size on the threshold of failure of the OM pressure shell as a function of impact speeds and angle. The enhanced OM shield configuration was first introduced with Soyuz 30S (launched in May 2012) to improve the MMOD protection of Soyuz vehicles docked to the International Space Station (ISS). This test program provides HVI data on U.S. materials similar in composition and density to the Russian materials for the enhanced Soyuz OM shield configuration of the vehicle. Data from this test program was used to update ballistic limit equations used in Soyuz OM penetration risk assessments. The objective of this hypervelocity impact test program was to determine the ballistic limit particle size for 440C stainless steel spherical projectiles on the Soyuz OM shielding at several impact conditions (velocity and angle combinations). This test report was prepared by NASA-JSC/ HVIT, upon completion of tests.

Postfragmentation density function for bacterial aggregates in laminar flow.

Science.gov (United States)

Byrne, Erin; Dzul, Steve; Solomon, Michael; Younger, John; Bortz, David M

2011-04-01

The postfragmentation probability density of daughter flocs is one of the least well-understood aspects of modeling flocculation. We use three-dimensional positional data of Klebsiella pneumoniae bacterial flocs in suspension and the knowledge of hydrodynamic properties of a laminar flow field to construct a probability density function of floc volumes after a fragmentation event. We provide computational results which predict that the primary fragmentation mechanism for large flocs is erosion. The postfragmentation probability density function has a strong dependence on the size of the original floc and indicates that most fragmentation events result in clumps of one to three bacteria eroding from the original floc. We also provide numerical evidence that exhaustive fragmentation yields a limiting density inconsistent with the log-normal density predicted in the literature, most likely due to the heterogeneous nature of K. pneumoniae flocs. To support our conclusions, artificial flocs were generated and display similar postfragmentation density and exhaustive fragmentation. ©2011 American Physical Society

Transient habitats limit development time for periodical cicadas.

Science.gov (United States)

Karban, Richard

2014-01-01

Periodical cicadas (Magicicada spp.) mature in 13 or 17 years, the longest development times for any non-diapausing insects. Selection may favor prolonged development since nymphs experience little mortality and individuals taking 17 years have been shown to have greater fecundity than those taking 13 years. Why don't periodical cicadas take even longer to develop? Nymphs feed on root xylem fluid and move little. Ovipositing females prefer fast-growing trees at forest edges. I hypothesized that (1) adults emerging at edges would be heavier than those from forest interiors and (2) habitat changes could limit development time. I collected newly eclosed females that had neither fed as adults nor moved from their site of development. For M. septendecim, females from edges were 4.9% heavier than those from the interior. I assumed that emergence density indicated habitat quality and measured density at eight sites in 1979, 1996, and 2013. Over three generations, variation in densities was great; densities at two sites crashed, and at one site they exploded to 579/m2 Habitat transience may limit development time because only adults can reassess habitats and reposition offspring. In conclusion, cicadas are affected by habitat characteristics, habitats change over 17 years, and cicadas may emerge, mate, and redistribute their offspring to track habitat dynamics.

Observer variability of absolute and relative thrombus density measurements in patients with acute ischemic stroke

NARCIS (Netherlands)

E.M.M. Santos (Emilie M.); A.J. Yoo (Albert J.); L.F.M. Beenen (Ludo); O.A. Berkhemer (Olvert); M.D. Den Blanken (Mark D.); C. Wismans (Carrie); W.J. Niessen (Wiro); C.B. Majoie (Charles); H. Marquering (Henk)

2016-01-01

textabstractIntroduction: Thrombus density may be a predictor for acute ischemic stroke treatment success. However, only limited data on observer variability for thrombus density measurements exist. This study assesses the variability and bias of four common thrombus density measurement methods by

Effects of melt-temperature on limiting current density in Al electrodeposition and morphology of Al electrodeposits obtained from ambient temperature type molten salt; Joongata yoyuen kara no denki aluminium mekki no genkai denryu mitsudo oyobi denseki keitai ni oyobosu mekki ekion no eikyo

Energy Technology Data Exchange (ETDEWEB)

Shimizu, T.; Tatano, M.; Uchida, Y. [Nisshin Steel Co. Ltd., Tokyo (Japan)

1996-03-31

Some of more important electrolytic solutions for Al electrodeposition are organic solvents, high-temperature type molten salts and low-temperature type molten salts having a melting point of 30{degree}C or lower, such as ethylmethylimidazolium chloride (EMIC). This study uses a molten salt of AlCl3-EMIC as the low-temperature type solution for high-speed electrodeposition. Discussed herein are the effects of melt temperature on limiting current density in Al electrodeposition and Al electrodeposit morphology. Limiting current density increases as melt temperature increases at any AlCl3 concentration used in this study. The AlCl3 concentration that gives the maximum limiting current density shifts from 64 to 67mol% at a melt temperature of 120{degree}C. A dense, smooth Al electrodeposited film results at a melt temperature of 100{degree}C or lower, but the electrodeposited grains become coarser as melt temperature increases. Melt temperature can be increased to 140{degree}C to secure a smooth electrodeposited film, showing possibility of 2 times faster electrodeposition than the conventional one. 21 refs., 12 figs., 1 tab.

Using a Density-Management Diagram to Develop Thinning Schedules for Loblolly Pine Plantations

Science.gov (United States)

Thomas J. Dean; V. Clark Baldwin

1993-01-01

A method for developing thinning schedules using a density-management diagram is presented. A density-management diagram is a form of stocking chart based on patterns of natural stand development. The diagram allows rotation diameter and the upper and lower limits of growing stock to be easily transformed into before and after thinning densities. Site height lines on...

Density meter algorithm and system for estimating sampling/mixing uncertainty

International Nuclear Information System (INIS)

Shine, E.P.

1986-01-01

The Laboratories Department at the Savannah River Plant (SRP) has installed a six-place density meter with an automatic sampling device. This paper describes the statistical software developed to analyze the density of uranyl nitrate solutions using this automated system. The purpose of this software is twofold: to estimate the sampling/mixing and measurement uncertainties in the process and to provide a measurement control program for the density meter. Non-uniformities in density are analyzed both analytically and graphically. The mean density and its limit of error are estimated. Quality control standards are analyzed concurrently with process samples and used to control the density meter measurement error. The analyses are corrected for concentration due to evaporation of samples waiting to be analyzed. The results of this program have been successful in identifying sampling/mixing problems and controlling the quality of analyses

Density meter algorithm and system for estimating sampling/mixing uncertainty

International Nuclear Information System (INIS)

Shine, E.P.

1986-01-01

The Laboratories Department at the Savannah River Plant (SRP) has installed a six-place density meter with an automatic sampling device. This paper describes the statisical software developed to analyze the density of uranyl nitrate solutions using this automated system. The purpose of this software is twofold: to estimate the sampling/mixing and measurement uncertainties in the process and to provide a measurement control program for the density meter. Non-uniformities in density are analyzed both analytically and graphically. The mean density and its limit of error are estimated. Quality control standards are analyzed concurrently with process samples and used to control the density meter measurement error. The analyses are corrected for concentration due to evaporation of samples waiting to be analyzed. The results of this program have been successful in identifying sampling/mixing problems and controlling the quality of analyses

[Development of a software standardizing optical density with operation settings related to several limitations].

Science.gov (United States)

Tu, Xiao-Ming; Zhang, Zuo-Heng; Wan, Cheng; Zheng, Yu; Xu, Jin-Mei; Zhang, Yuan-Yuan; Luo, Jian-Ping; Wu, Hai-Wei

2012-12-01

To develop a software that can be used to standardize optical density to normalize the procedures and results of standardization in order to effectively solve several problems generated during standardization of in-direct ELISA results. The software was designed based on the I-STOD method with operation settings to solve the problems that one might encounter during the standardization. Matlab GUI was used as a tool for the development. The software was tested with the results of the detection of sera of persons from schistosomiasis japonica endemic areas. I-STOD V1.0 (WINDOWS XP/WIN 7, 0.5 GB) was successfully developed to standardize optical density. A serial of serum samples from schistosomiasis japonica endemic areas were used to examine the operational effects of I-STOD V1.0 software. The results indicated that the software successfully overcame several problems including reliability of standard curve, applicable scope of samples and determination of dilution for samples outside the scope, so that I-STOD was performed more conveniently and the results of standardization were more consistent. I-STOD V1.0 is a professional software based on I-STOD. It can be easily operated and can effectively standardize the testing results of in-direct ELISA.

Pauli potential from Heilmann-Lieb electron density obtained by summing hydrogenic closed-shell densities over the entire bound-state spectrum

International Nuclear Information System (INIS)

Bogar, Ferenc; Bartha, Ferenc; Bartha, Ferenc A.; March, Norman H.

2011-01-01

Independently, in the mid-1980s, several groups proposed to bosonize the density-functional theory (DFT) for fermions by writing a Schroedinger equation for the density amplitude ρ(r) 1/2 , with ρ(r) as the ground-state electron density, the central tool of DFT. The resulting differential equation has the DFT one-body potential V(r) modified by an additive term V P (r) where P denotes Pauli. To gain insight into the form of the Pauli potential V P (r), here, we invoke the known Coulombic density, ρ ∞ (r) say, calculated analytically by Heilmann and Lieb (HL), by summation over the entire hydrogenic bound-state spectrum. We show that V P∞ (r) has simple limits for both r tends to infinity and r approaching zero. In particular, at large r, V P∞ (r) precisely cancels the attractive Coulomb potential -Ze 2 /r, leaving V(r)+V P∞ (r) of O(r -2 ) as r tends to infinity. The HL density ρ ∞ (r) is finally used numerically to display V P∞ (r) for all r values.

Development of a Short-term Failure Assessment of High Density Polyethylene Pipe Welds - Application of the Limit Load Analysis -

Energy Technology Data Exchange (ETDEWEB)

Ryu, Ho-Wan; Han, Jae-Jun; Kim, Yun-Jae [Korea University, Seoul (Korea, Republic of); Kim, Jong-Sung [Sunchon National University, Suncheon (Korea, Republic of); Kim, Jeong-Hyeon; Jang, Chang-Heui [KAIST, Daejeon (Korea, Republic of)

2015-04-15

In the US, the number of cases of subterranean water contamination from tritium leaking through a damaged buried nuclear power plant pipe continues to increase, and the degradation of the buried metal piping is emerging as a major issue. A pipe blocked from corrosion and/or degradation can lead to loss of cooling capacity in safety-related piping resulting in critical issues related to the safety and integrity of nuclear power plant operation. The ASME Boiler and Pressure Vessel Codes Committee (BPVC) has recently approved Code Case N-755 that describes the requirements for the use of polyethylene (PE) pipe for the construction of Section III, Division 1 Class 3 buried piping systems for service water applications in nuclear power plants. This paper contains tensile and slow crack growth (SCG) test results for high-density polyethylene (HDPE) pipe welds under the environmental conditions of a nuclear power plant. Based on these tests, the fracture surface of the PENT specimen was analyzed, and the fracture mechanisms of each fracture area were determined. Finally, by using 3D finite element analysis, limit loads of HDPE related to premature failure were verified.

New X-ray bound on density of primordial black holes

Energy Technology Data Exchange (ETDEWEB)

Inoue, Yoshiyuki [Institute of Space and Astronautical Science JAXA, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan); Kusenko, Alexander, E-mail: yinoue@astro.isas.jaxa.jp, E-mail: kusenko@ucla.edu [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547 (United States)

2017-10-01

We set a new upper limit on the abundance of primordial black holes (PBH) based on existing X-ray data. PBH interactions with interstellar medium should result in significant fluxes of X-ray photons, which would contribute to the observed number density of compact X-ray objects in galaxies. The data constrain PBH number density in the mass range from a few M {sub ⊙} to 2× 10{sup 7} M {sub ⊙}. PBH density needed to account for the origin of black holes detected by LIGO is marginally allowed.

Realistic level densities in fragment emission at high excitation energies

International Nuclear Information System (INIS)

Mustafa, M.G.; Blann, M.; Ignatyuk, A.V.

1993-01-01

Heavy fragment emission from a 44 100 Ru compound nucleus at 400 and 800 MeV of excitation is analyzed to study the influence of level density models on final yields. An approach is used in which only quasibound shell-model levels are included in calculating level densities. We also test the traditional Fermi gas model for which there is no upper energy limit to the single particle levels. We compare the influence of these two level density models in evaporation calculations of primary fragment excitations, kinetic energies and yields, and on final product yields

Observer variability of absolute and relative thrombus density measurements in patients with acute ischemic stroke

NARCIS (Netherlands)

Santos, Emilie M. M.; Yoo, Albert J.; Beenen, Ludo F.; Berkhemer, Olvert A.; den Blanken, Mark D.; Wismans, Carrie; Niessen, Wiro J.; Majoie, Charles B.; Marquering, Henk A.; Fransen, Puck S. S.; Beumer, Debbie; van den Berg, Lucie A.; Lingsma, Hester F.; Schonewille, Wouter J.; Vos, Jan Albert; Nederkoorn, Paul J.; Wermer, Marieke J. H.; van Walderveen, Marianne A. A.; Staals, Julie; Hofmeijer, Jeannette; van Oostayen, Jacques A.; Lycklama à Nijeholt, Geert J.; Boiten, Jelis; Brouwer, Patrick A.; Emmer, Bart J.; de Bruijn, Sebastiaan F.; van Dijk, Lukas C.; Kappelle, L. Jaap; Lo, Rob H.; van Dijk, Ewoud J.; de Vries, Joost; de Kort, Paul L. M.; van den Berg, Jan S. P.; A A M van Hasselt, Boudewijn; Aerden, Leo A. M.; Dallinga, René J.; Visser, Marieke C.; Bot, Joseph C. J.; Vroomen, Patrick C.; Eshghi, Omid; Schreuder, Tobien H. C. M. L.; Heijboer, Roel J. J.; Keizer, Koos; Tielbeek, Alexander V.; Hertog, Heleen M. Den; Gerrits, Dick G.; van den Berg-Vos, Renske M.; Karas, Giorgos B.; Steyerberg, Ewout W.; Flach, H. Zwenneke; Sprengers, Marieke E. S.; Jenniskens, Sjoerd F. M.; van den Berg, René; Koudstaal, Peter J.; van Zwam, Wim H.; Roos, Yvo B. W. E. M.; van der Lugt, Aad; van Oostenbrugge, Robert J.; Dippel, Diederik W. J.

2016-01-01

Thrombus density may be a predictor for acute ischemic stroke treatment success. However, only limited data on observer variability for thrombus density measurements exist. This study assesses the variability and bias of four common thrombus density measurement methods by expert and non-expert

Observer variability of absolute and relative thrombus density measurements in patients with acute ischemic stroke

NARCIS (Netherlands)

Santos, E.M.; Yoo, A.J.; Beenen, L.F.; Berkhemer, O.A.; Blanken, M.D. den; Wismans, C.; Niessen, W.J.; Majoie, C.B.; Marquering, H.A.; Dijk, E.J. van; et al.,

2016-01-01

INTRODUCTION: Thrombus density may be a predictor for acute ischemic stroke treatment success. However, only limited data on observer variability for thrombus density measurements exist. This study assesses the variability and bias of four common thrombus density measurement methods by expert and

Level density of random matrices for decaying systems

International Nuclear Information System (INIS)

Haake, F.; Izrailev, F.; Saher, D.; Sommers, H.-J.

1991-01-01

Analytical and numerical results for the level density of a certain class of random non-Hermitian matrices H=H+iΓ are presented. The conservative part H belongs to the Gaussian orthogonal ensemble while the damping piece Γ is quadratic in Gaussian random numbers and may describe the decay of resonances through various channels. In the limit of a large matrix dimension the level density assumes a surprisingly simple dependence on the relative strength of the damping and the number of channels. 18 refs.; 4 figs

Isospectral Flows for the Inhomogeneous String Density Problem

Science.gov (United States)

Górski, Andrzej Z.; Szmigielski, Jacek

2018-02-01

We derive isospectral flows of the mass density in the string boundary value problem corresponding to general boundary conditions. In particular, we show that certain class of rational flows produces in a suitable limit all flows generated by polynomials in negative powers of the spectral parameter. We illustrate the theory with concrete examples of isospectral flows of discrete mass densities which we prove to be Hamiltonian and for which we provide explicit solutions of equations of motion in terms of Stieltjes continued fractions and Hankel determinants.

Quark-gluon plasma at finite baryons density and in limit of large Nc

International Nuclear Information System (INIS)

Azakov, S.I.

1987-01-01

Study of thermodynamics of ideal colourless quark-gluon (QG) gas in limit of large N C is carried out. Consideration of this limit much simplifies the problem on calculation of such system statsum. Unlike the papers where the properties of ideal colourless QG-gas were defined in approximation valid at large V volumes, in the given calculations the volume may be arbitrary. The ideal QG gas is considered in a final volume. Phase transition is shown to be absent in the problem more relativistic from the physical view point, when conservation of the baryon charge is taken into account

Determinants of stingless bee nest density in lowland dipterocarp forests of Sabah, Malaysia.

Science.gov (United States)

Eltz, Thomas; Brühl, Carsten A; van der Kaars, Sander; Linsenmair, Eduard K

2002-03-01

We measured the nest density of stingless bees (Apidae, Meliponini) in undisturbed and logged-over dipterocarp forests in Sabah, northern Borneo, and evaluated hypotheses on proximate factors leading to the observed variation: population control mediated by (1) nest predation, (2) limitation of nest trees, or (3) food limitation. Per-area nest density varied twentyfold across 14 forest sites and was significantly affected by locality, but not by the degree and history of disturbance. Nest density was generally high in sites located in the Sepilok Forest fragment (mean 8.4 nests/ha), bordering mangroves or plantations. In contrast, nest densities in continuous forests were all low (between 0 and 2.1 nests/ha, mean 0.5 nests/ha). Yearly nest mortality was low (13.5-15.0%) over 4 years of observation and did not vary between forest localities, thus limiting the potential of nest predation (1) in creating the observed variation in nest density. The presence of potential nest trees (2), though positively correlated with nest density, explained only a minute fraction of the observed variation. Nest density was best explained by differences in the pollen resources (3) available to the bees (quantified by analysis of pollen in bee garbage). Across five selected sites the amount of nonforest pollen (from mangrove or crop plants) included in diets of Trigona collina was positively correlated with T. collina nest density. External pollen sources are a likely supplement to bee diets at times when little flowering occurs inside the forest, thus increasing overall bee carrying capacity. Pollen limitation was also indicated by direct measurements of pollen import and foraging activity of T. collina in three selected sites: Pollen traps installed at nests in high-density Sepilok captured significantly more corbicular pollen than colonies in low-density Deramakot. At the same time, morning foraging activity was also greater in Sepilok, indicating a regulatory increase in foraging

High energy density capacitors fabricated by thin film technology

International Nuclear Information System (INIS)

Barbee, T W; Johnson, G W; Wagner, A V.

1999-01-01

Low energy density in conventional capacitors severely limits efforts to miniaturize power electronics and imposes design limitations on electronics in general. We have successfully applied physical vapor deposition technology to greatly increase capacitor energy density. The high dielectric breakdown strength we have achieved in alumina thin films allows high energy density to be achieved with this moderately low dielectric constant material. The small temperature dependence of the dielectric constant, and the high reliability, high resistivity, and low dielectric loss of Al 2 O 3 , make it even more appealing. We have constructed single dielectric layer thin film capacitors and shown that they can be stacked to form multilayered structures with no loss in yield for a given capacitance. Control of film growth morphology is critical for achieving the smooth, high quality interfaces between metal and dielectric necessary for device operation at high electric fields. Most importantly, high rate deposition with extremely low particle generation is essential for achieving high energy storage at a reasonable cost. This has been achieved by reactive magnetron sputtering in which the reaction to form the dielectric oxide has been confined to the deposition surface. By this technique we have achieved a yield of over 50% for 1 cm 2 devices with an energy density of 14 J per cubic centimeter of Al 2 O 3 dielectric material in 1.2 kV, 4 nF devices. By further reducing defect density and increasing the dielectric constant of the material, we will be able to increase capacitance and construct high energy density devices to meet the requirements of applications in power electronics

Tobacco Town: Computational Modeling of Policy Options to Reduce Tobacco Retailer Density.

Science.gov (United States)

Luke, Douglas A; Hammond, Ross A; Combs, Todd; Sorg, Amy; Kasman, Matt; Mack-Crane, Austen; Ribisl, Kurt M; Henriksen, Lisa

2017-05-01

To identify the behavioral mechanisms and effects of tobacco control policies designed to reduce tobacco retailer density. We developed the Tobacco Town agent-based simulation model to examine 4 types of retailer reduction policies: (1) random retailer reduction, (2) restriction by type of retailer, (3) limiting proximity of retailers to schools, and (4) limiting proximity of retailers to each other. The model examined the effects of these policies alone and in combination across 4 different types of towns, defined by 2 levels of population density (urban vs suburban) and 2 levels of income (higher vs lower). Model results indicated that reduction of retailer density has the potential to decrease accessibility of tobacco products by driving up search and purchase costs. Policy effects varied by town type: proximity policies worked better in dense, urban towns whereas retailer type and random retailer reduction worked better in less-dense, suburban settings. Comprehensive retailer density reduction policies have excellent potential to reduce the public health burden of tobacco use in communities.

Temperature- and density-dependent x-ray scattering in a low-Z plasma

International Nuclear Information System (INIS)

Brown, R.T.

1976-06-01

A computer program is described which calculates temperature- and density-dependent differential and total coherent and incoherent x-ray scattering cross sections for a low-Z scattering medium. Temperature and density are arbitrary within the limitations of the validity of local thermodynamic equilbrium, since ionic populations are calculated under this assumption. Scattering cross sections are calculated in the form factor approximation. The scattering medium may consist of any mixure of elements with Z less than or equal to 8, with this limitation imposed by the availability of atomic data

Heat removal in INTOR via a toroidal limiter

International Nuclear Information System (INIS)

Mioduszewski, P.

1981-01-01

In the present paper the potential of removing about 100 MW of thermal plasma power via a toroidal limiter in INTOR is studied. The heat flux distributions on various limiter configurations are calculated and the thermal response of a graphite tile limiter is estimated on the base of a one-dimensional heat conduction approach. The evaporation rates which have to be expected for the given energy flux densities and radiation cooled graphite tiles are evaluated. According to the present understanding it should be possible to remove 100 MW power from the INTOR plasma via a radiation cooled toroidal limiter. (author)

Spatial pattern corrections and sample sizes for forest density estimates of historical tree surveys

Science.gov (United States)

Brice B. Hanberry; Shawn Fraver; Hong S. He; Jian Yang; Dan C. Dey; Brian J. Palik

2011-01-01

The U.S. General Land Office land surveys document trees present during European settlement. However, use of these surveys for calculating historical forest density and other derived metrics is limited by uncertainty about the performance of plotless density estimators under a range of conditions. Therefore, we tested two plotless density estimators, developed by...

Limits on arcsecond-scale fluctuations in the cosmic microwave background

International Nuclear Information System (INIS)

Knoke, J.E.; Partridge, R.B.; Ratner, M.I.; Shapiro, I.I.

1984-01-01

We used the NRAO Very Large Array in its C configuration at a wavelength of 6 cm to set upper limits on the rms fluctuation of sky brightness on angular scales of 6''--18'' from sources too weak to be detected individually. At the highest resolution, we establish a limit of 8 μJy per beam area on the rms sky fluctuation. If this fluctuation level is the result of a Poisson distribution of unresolved sources, each of flux density S 0 Jy, then the number density of such sources per steradian must be less than 0.08 S 0 -2 sr -1 . For alternative models in which all sources are resolved, we derive less stringent limits. Our limits on the rms sky fluctuation also establish limits on the rms temperature fluctuation ΔT for simple models of fluctuations in the cosmic microwave background: (ΔT/2.7 K) -3 and (ΔT/2.7 K) -3 for Gaussian temperature fluctuations of angular scale 6'' and 18'', respectively

Experimental studies of the charge limit phenomenon in NEA GaAs photocathodes

International Nuclear Information System (INIS)

Tang, H.; Alley, R.K.; Aoyagi, H.; Clendenin, J.E.; Frisch, J.C.; Mulhollan, G.A.; Saez, P.J.; Schultz, D.C.; Turner, J.L.

1994-06-01

Negative electron affinity GaAs photocathodes have been in continuous use at SLAC for generating polarized electron beams since early 1992. If the quantum efficiency of a GaAs cathode is below a critical value, the maximum photoemitted charge with photons of energies close to the band gap in a 2-ns pulse is found to be limited by the intrinsic properties of the cathode instead of by the space charge limit. We have studied this novel charge limit phenomenon in a variety of GaAs photocathodes of different structures and doping densities. We find that the charge limit is strongly dependent on the cathode's quantum efficiency and the extraction electric field, and to a lesser degree on the excitation laser wavelength. In addition, we show that the temporal behavior of the charge limit depends critically on the doping density

Number density measurements on analytical discharge systems: application of ''hook'' spectroscopy

International Nuclear Information System (INIS)

Majidi, V.; Hsu, W.; Coleman, D.M.

1988-01-01

Various methods for determining atomic, ionic and electron number densities are reviewed. Time- and spatially-resolved number densities of sodium atoms in the post discharge environment of a high voltage spark are then quantitatively determined using the anomalous dispersion hook method. Number densities are calculated from hook separation near the Na D-lines. Lateral profiles are subsequently transformed to the radial domain using a derivative free Abel inversion process. Advantages, limitations, and practical ramification of the hook method are discussed. (author)

Density fluctuations and the structure of a nonuniform hard sphere fluid

OpenAIRE

Katsov, Kirill; Weeks, John D.

2000-01-01

We derive an exact equation for density changes induced by a general external field that corrects the hydrostatic approximation where the local value of the field is adsorbed into a modified chemical potential. Using linear response theory to relate density changes self-consistently in different regions of space, we arrive at an integral equation for a hard sphere fluid that is exact in the limit of a slowly varying field or at low density and reduces to the accurate Percus-Yevick equation fo...

Theoretical transport analysis of density limit with radial electric field in helical plasmas

International Nuclear Information System (INIS)

Toda, S.; Itoh, K.

2010-11-01

The confinement property in helical toroidal plasmas is clarified. The analysis is performed by use of the one-dimensional transport equations with the effect of the radiative loss and the radial profile of the electric field. The analytical results in the edge region show the steep gradient in the electron temperature, which indicates the transport barrier formation. Because of the rapid increase of the radiative loss at the low electron temperature, the anomalous heat diffusivity is reduced near the edge. Next, the efficiency of the heating power input in the presence of the radiative loss is studied. The scaling of the critical density in helical devices is also derived. (author)

Breakdown of the Siegert theorem and the many-body charge density operators

International Nuclear Information System (INIS)

Hyuga, H.; Ohtsubo, H.

1978-01-01

The exchange charge density operator is studied in the two-boson exchange model with consistent treatment of the exchange current and nuclear wave functions. A non-vanishing exchange charge density operator even in the static limit, which leads to the breakdown of the Siegert theorem, is found. (Auth.)

Modelling interactions of toxicants and density dependence in wildlife populations

Science.gov (United States)

Schipper, Aafke M.; Hendriks, Harrie W.M.; Kauffman, Matthew J.; Hendriks, A. Jan; Huijbregts, Mark A.J.

2013-01-01

1. A major challenge in the conservation of threatened and endangered species is to predict population decline and design appropriate recovery measures. However, anthropogenic impacts on wildlife populations are notoriously difficult to predict due to potentially nonlinear responses and interactions with natural ecological processes like density dependence. 2. Here, we incorporated both density dependence and anthropogenic stressors in a stage-based matrix population model and parameterized it for a density-dependent population of peregrine falcons Falco peregrinus exposed to two anthropogenic toxicants [dichlorodiphenyldichloroethylene (DDE) and polybrominated diphenyl ethers (PBDEs)]. Log-logistic exposure–response relationships were used to translate toxicant concentrations in peregrine falcon eggs to effects on fecundity. Density dependence was modelled as the probability of a nonbreeding bird acquiring a breeding territory as a function of the current number of breeders. 3. The equilibrium size of the population, as represented by the number of breeders, responded nonlinearly to increasing toxicant concentrations, showing a gradual decrease followed by a relatively steep decline. Initially, toxicant-induced reductions in population size were mitigated by an alleviation of the density limitation, that is, an increasing probability of territory acquisition. Once population density was no longer limiting, the toxicant impacts were no longer buffered by an increasing proportion of nonbreeders shifting to the breeding stage, resulting in a strong decrease in the equilibrium number of breeders. 4. Median critical exposure concentrations, that is, median toxicant concentrations in eggs corresponding with an equilibrium population size of zero, were 33 and 46 μg g−1 fresh weight for DDE and PBDEs, respectively. 5. Synthesis and applications. Our modelling results showed that particular life stages of a density-limited population may be relatively insensitive to

Electron density interferometry measurement in laser-matter interaction

International Nuclear Information System (INIS)

Popovics-Chenais, C.

1981-05-01

This work is concerned with the laser-interferometry measurement of the electronic density in the corona and the conduction zone external part. Particularly, it is aimed at showing up density gradients and at their space-time localization. The first chapter recalls the density profile influence on the absorption principal mechanisms and the laser energy transport. In chapter two, the numerical and analytical hydrodynamic models describing the density profile are analysed. The influence on the density profile of the ponderomotive force associated to high oscillating electric fields is studied, together with the limited thermal conduction and suprathermal electron population. The mechanism action, in our measurement conditions, is numerically simulated. Calculations are made with experimental parameters. The measurement interaction conditions, together with the diagnostic method by high resolution laser interferometry are detailed. The results are analysed with the help of numerical simulation which is the experiment modeling. An overview of the mechanisms shown up by interferometric measurements and their correlation with other diagnostics is the conclusion of this work [fr

Effective Ice Particle Densities for Cold Anvil Cirrus

Science.gov (United States)

Heymsfield, Andrew J.; Schmitt, Carl G.; Bansemer, Aaron; Baumgardner, Darrel; Weinstock, Elliot M.; Smith, Jessica

2002-01-01

This study derives effective ice particle densities from data collected from the NASA WB-57F aircraft near the tops of anvils during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers (CRYSTAL) Florida Area Cirrus Experiment (FACE) in southern Florida in July 2002. The effective density, defined as the ice particle mass divided by the volume of an equivalent diameter liquid sphere, is obtained for particle populations and single sizes containing mixed particle habits using measurements of condensed water content and particle size distributions. The mean effective densities for populations decrease with increasing slopes of the gamma size distributions fitted to the size distributions. The population-mean densities range from near 0.91 g/cu m to 0.15 g/cu m. Effective densities for single sizes obey a power-law with an exponent of about -0.55, somewhat less steep than found from earlier studies. Our interpretations apply to samples where particle sizes are generally below 200-300 microns in maximum dimension because of probe limitations.

Breast density in multiethnic women presenting for screening mammography.

Science.gov (United States)

Oppong, Bridget A; Dash, Chiranjeev; O'Neill, Suzanne; Li, Yinan; Makambi, Kepher; Pien, Edward; Makariou, Erini; Coleman, Tesha; Adams-Campbell, Lucile L

2018-05-01

Data on ethnic variations in breast density are limited and often not inclusive of underrepresented minorities. As breast density is associated with elevated breast cancer risk, investigating racial and ethnic difference may elucidate the observed differences in breast cancer risk among different populations. We reviewed breast density from initial screening of women from the Capital Breast Care Center and Georgetown University Hospital from 2010 to 2014. Patient demographics including race, age at screening, education, menopausal status, and body mass index were abstracted. We recorded the BI-RADS density categories: (1) "fatty," (2) "scattered fibroglandular densities," (3) "heterogeneously dense," and (4) "extremely dense." Multivariable unconditional logistic regression was used to identify predictors of breast density. Density categorization was recorded for 2146 women over the 5-year period, comprising Blacks (n = 940), Hispanics (n = 893), and Whites (n = 314). Analysis of subject characteristics by breast density showed that high category is observed in younger, Hispanic, nulliparous, premenopausal, and nonobese women (t-test or chi-square test, P-values density. Being Hispanic, premenopausal, and nonobese were predictive of high density on logistic regression. In this analysis of density distribution in a diverse sample, Hispanic women have the highest breast density, followed by Blacks and Whites. Unique in our findings is women who identify as Hispanic have the highest breast density and lower rates of obesity. Further investigation of the impact of obesity on breast density, especially in the understudied Hispanic group is needed. © 2017 Wiley Periodicals, Inc.

Characteristics of steady-state plasma flow in the tokamak limiter scrape-off layer

International Nuclear Information System (INIS)

Petrov, V.G.

1984-01-01

Steady state plasma flow in the scrape-off layer of a toroidal limiter is discussed. The force balance along the torus minor radius is taken into account, from which follows that the plasma pressure gradient is balanced by the ponderomotive force (1/c) j-vectorxB-vector, which arises in the presence of a current density component perpendicular to the magnetic field. The limiter has an important effect on the electric current flow in the scrape-off layer. It is shown that the electric potential and plasma density values differ from one side of the limiter to the other; this leads to plasma drift along the minor radius. The characteristic length of change in the plasma density is found to be of the order of the ion cyclotron radius calculated for a poloidal magnetic field. (author)

Tree density and permafrost thaw depth influence water limitations on stomatal conductance in Siberian Arctic boreal forests

Science.gov (United States)

Kropp, H.; Loranty, M. M.; Natali, S.; Kholodov, A. L.; Alexander, H. D.; Zimov, N.

2017-12-01

Boreal forests may experience increased water stress under global climate change as rising air temperatures increase evaporative demand and decrease soil moisture. Increases in plant water stress can decrease stomatal conductance, and ultimately, decrease primary productivity. A large portion of boreal forests are located in Siberia, and are dominated by deciduous needleleaf trees, Larix spp. We investigated the variability and drivers of canopy stomatal conductance in upland Larix stands with different stand density that arose from differing fire severity. Our measurements focus on an open canopy stand with low tree density and deep permafrost thaw depth, and a closed canopy stand with high tree density and shallow permafrost thaw depth. We measured canopy stomatal conductance, soil moisture, and micrometeorological variables. Our results demonstrate that canopy stomatal conductance was significantly lower in the closed canopy stand with a significantly higher sensitivity to increases in atmospheric evaporative demand. Canopy stomatal conductance in both stands was tightly coupled to precipitation that occurred over the previous week; however, the closed canopy stand showed a significantly greater sensitivity to increases in precipitation compared to the open canopy stand. Differences in access to deep versus shallow soil moisture and the physical characteristics of the soil profile likely contribute to differences in sensitivity to precipitation between the two stands. Our results indicate that Larix primary productivity may be highly sensitive to changes in evaporative demand and soil moisture that can result of global climate change. However, the effect of increasing air temperatures and changes in precipitation will differ significantly depending on stand density, thaw depth, and the hydraulic characteristics of the soil profile.

Breaking the current density threshold in spin-orbit-torque magnetic random access memory

Science.gov (United States)

Zhang, Yin; Yuan, H. Y.; Wang, X. S.; Wang, X. R.

2018-04-01

Spin-orbit-torque magnetic random access memory (SOT-MRAM) is a promising technology for the next generation of data storage devices. The main bottleneck of this technology is the high reversal current density threshold. This outstanding problem is now solved by a new strategy in which the magnitude of the driven current density is fixed while the current direction varies with time. The theoretical limit of minimal reversal current density is only a fraction (the Gilbert damping coefficient) of the threshold current density of the conventional strategy. The Euler-Lagrange equation for the fastest magnetization reversal path and the optimal current pulse is derived for an arbitrary magnetic cell and arbitrary spin-orbit torque. The theoretical limit of minimal reversal current density and current density for a GHz switching rate of the new reversal strategy for CoFeB/Ta SOT-MRAMs are, respectively, of the order of 105 A/cm 2 and 106 A/cm 2 far below 107 A/cm 2 and 108 A/cm 2 in the conventional strategy. Furthermore, no external magnetic field is needed for a deterministic reversal in the new strategy.

Effects of density imbalance on the BCS-BEC crossover in semiconductor electron-hole bilayers

International Nuclear Information System (INIS)

Pieri, P.; Strinati, G. C.; Neilson, D.

2007-01-01

We study the occurrence of excitonic superfluidity in electron-hole bilayers at zero temperature. We not only identify the crossover in the phase diagram from the BCS limit of overlapping pairs to the BEC limit of nonoverlapping tightly bound pairs but also, by varying the electron and hole densities independently, we can analyze a number of phases that occur mainly in the crossover region. With different electron and hole effective masses, the phase diagram is asymmetric with respect to excess electron or hole densities. We propose, as the criterion for the onset of superfluidity, the jump of the electron and hole chemical potentials when their densities cross

Density turbulence and disruption phenomena in TEXTOR

International Nuclear Information System (INIS)

Waidmann, G.; Kuang, G.; Jadoul, M.

1992-01-01

Disruptive processes are observed in tokamak plasmas not only at the operating limits (density limit or q-limit) but can be found under a variety of experimental conditions. Large forces are exerted then on vessel components and support structures. The sudden release of stored plasma energy presents a serious erosion problem for the first wall already in the next generation of large tokamak machines. Strong energy losses from the plasma and an influx of impurities are already present in minor plasma disruptions which do not immediately lead to a plasma current termination. The rapid loss of energy confinement was investigated within the framework of a systematic study on plasma disruption phenomena in TEXTOR. (author) 4 refs., 4 figs

Chemical reactions as $\\Gamma$-limit of diffusion

NARCIS (Netherlands)

Peletier, M.A.; Savaré, G.; Veneroni, M.

2012-01-01

We study the limit of high activation energy of a special Fokker–Planck equation known as the Kramers–Smoluchowski equation (KS). This equation governs the time evolution of the probability density of a particle performing a Brownian motion under the influence of a chemical potential

Anomalous evolution of Ar metastable density with electron density in high density Ar discharge

International Nuclear Information System (INIS)

Park, Min; Chang, Hong-Young; You, Shin-Jae; Kim, Jung-Hyung; Shin, Yong-Hyeon

2011-01-01

Recently, an anomalous evolution of argon metastable density with plasma discharge power (electron density) was reported [A. M. Daltrini, S. A. Moshkalev, T. J. Morgan, R. B. Piejak, and W. G. Graham, Appl. Phys. Lett. 92, 061504 (2008)]. Although the importance of the metastable atom and its density has been reported in a lot of literature, however, a basic physics behind the anomalous evolution of metastable density has not been clearly understood yet. In this study, we investigated a simple global model to elucidate the underlying physics of the anomalous evolution of argon metastable density with the electron density. On the basis of the proposed simple model, we reproduced the anomalous evolution of the metastable density and disclosed the detailed physics for the anomalous result. Drastic changes of dominant mechanisms for the population and depopulation processes of Ar metastable atoms with electron density, which take place even in relatively low electron density regime, is the clue to understand the result.

Development of internal transport barrier scenarios at ITER-relevant high triangularity in Jet

Energy Technology Data Exchange (ETDEWEB)

Rimini, F.G.; Becoulet, M.; Ekedahl, A.; Huysmans, G.; Joffrin, E.; Litaudon, X. [Association Euratom-CEA, Centre d' Etudes de Cadarache, 13 - Saint-Paul-lez-Durance (France). Dept. de Recherches sur la Fusion Controlee; Giovannozzi, E.; Tudisco, O.; Crisanti, F. [Association Euratol/ENEA/CNR sulla Fusione, Frascali, Rome (Italy); Lomas, P.J.; Alper, B.; Hawkes, N.; Parail, V.; Zastrow, K.D. [Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon (United Kingdom); Baar, M. de; Vries, P. de [Association Euratom-Fom, TEC Cluster, Nieuwegein (Netherlands); La Luna, E. de [Association Euratom-Ciemat, Madrid (Spain); Saibene, G. [EFDA CSU, Garching (Germany)

2004-07-01

The development of ITB s(Internal Transport Barrier) scenarios in high triangularity discharges is of particular interest for ITER advanced tokamak operation. Previous JET experiments have shown that high triangularity favours ELM (Edge Localized Mode)-Free or type I ELMs, which inhibit long lasting ITBs. The recent experiments reported here concentrate on integrated optimisation of edge and core conditions. Edge pedestal was controlled using gas injection, Deuterium or light impurities, and plasma current ramps. Both methods yield more ITB-friendly edge pedestal conditions, varying from small type I to type III ELMs and, in extreme cases, to L-mode edge. In parallel, the conditions for triggering and sustaining a wide ITB were optimised. This plasmas have deeply reversed target current profiles with g{sub min} 3. A narrow inner ITB, located in the reversed shear region, is routinely observed. Large radius ITBs are only triggered when the input power exceeds 20-22 MW, but they do not usually survive the transition into H-mode. The best results, in terms of sustained high performance, have been obtained with Neon injection: a wide ITB is triggered during the phase with L-mode edge and survives into H-mode for about 2 s at H{sub 89}{beta}{sub N} {approx} 3.5 and {approx} 60% of the Greenwald density limit. In summary, a high triangularity scenario has been developed, which combines the desirable I characteristics of controlled edge, long lasting wide ITBs and high performance at density higher than the low triangularity JET scenarios. (authors)

Modelling of mitigation of the power divertor loading for the EU DEMO through Ar injection

Science.gov (United States)

Subba, Fabio; Aho-Mantila, Leena; Coster, David; Maddaluno, Giorgio; Nallo, Giuseppe F.; Sieglin, Bernard; Wenninger, Ronald; Zanino, Roberto

2018-03-01

In this paper we present a computational study on the divertor heat load mitigation through impurity injection for the EU DEMO. The study is performed by means of the SOLPS5.1 code. The power crossing the separatrix is considered fixed and corresponding to H-mode operation, whereas the machine operating condition is defined by the outboard mid-plane upstream electron density and the impurity level. The selected impurity for this study is Ar, based on its high radiation efficiency at SOL characteristic temperatures. We consider a conventional vertical target geometry for the EU DEMO and monitor target conditions for different operational points, considering as acceptability criteria the target electron temperature (≤5 eV to provide sufficiently low W sputtering rate) and the peak heat flux (below 5-10 MW m-2 to guarantee safe steady-state cooling conditions). Our simulations suggest that, neglecting the radiated power deposition on the plate, it is possible to satisfy the desired constraints. However, this requires an upstream density of the order of at least 50% of the Greenwald limit and a sufficiently high argon fraction. Furthermore, if the radiated power deposition is taken into account, the peak heat flux on the outer plate could not be reduced below 15 MW m-2 in these simulations. As these simulations do not take into account neutron loading, they strongly indicate that the vertical target divertor solution with a radiative front distributed along the divertor leg has a very marginal operational space in an EU DEMO sized reactor.

Density functional theory for polymeric systems in 2D

International Nuclear Information System (INIS)

Słyk, Edyta; Bryk, Paweł; Roth, Roland

2016-01-01

We propose density functional theory for polymeric fluids in two dimensions. The approach is based on Wertheim’s first order thermodynamic perturbation theory (TPT) and closely follows density functional theory for polymers proposed by Yu and Wu (2002 J. Chem. Phys . 117 2368). As a simple application we evaluate the density profiles of tangent hard-disk polymers at hard walls. The theoretical predictions are compared against the results of the Monte Carlo simulations. We find that for short chain lengths the theoretical density profiles are in an excellent agreement with the Monte Carlo data. The agreement is less satisfactory for longer chains. The performance of the theory can be improved by recasting the approach using the self-consistent field theory formalism. When the self-avoiding chain statistics is used, the theory yields a marked improvement in the low density limit. Further improvements for long chains could be reached by going beyond the first order of TPT. (paper)

Cooking, industrial processing and caloric density of foods

NARCIS (Netherlands)

Pellegrini, Nicoletta; Fogliano, Vincenzo

2017-01-01

During human evolution, the development of a wide range of cooking processing techniques enabled humans to provide their social group with maximum benefits from limited food resources. Industrial processing and mass market distribution made available high food calorie density foods to the world

Hydrodynamic limit of a nongradient interacting particle process

International Nuclear Information System (INIS)

Wick, W.D.

1989-01-01

A simple example of a nongradient stochastic interacting particle system is analyzed. In this model, symmetric simple exclusion in one dimension in a periodic environment, the dynamical term in the Green-Kubo formula contributes to the bulk diffusion constant. The law of large numbers for the density field and the central limit theorem for the density fluctuation field are proven, and the Green-Kubo expression for the diffusion constant is computed exactly. The hydrodynamic equation for the model turns out to be linear

Nonlocal exchange and kinetic-energy density functionals for electronic systems

International Nuclear Information System (INIS)

Glossman, M.D.; Rubio, A.; Balbas, L.C.; Alonso, J.A.

1992-01-01

The nonlocal weighted density approximation (WDA) to the exchange and kinetic-energy functionals of many electron systems proposed several years ago by Alonso and Girifalco is used to compute, within the framework of density functional theory, the ground-state electronic density and total energy of noble gas atoms and of neutral jellium-like sodium clusters containing up to 500 atoms. These results are compared with analogous calculations using the well known Thomas-Fermi-Weizsacker-Dirac (TFWD) approximations for the kinetic (TFW) and exchange (D) energy density functionals. An outstanding improvement of the total and exchange energies, of the density at the nucleus and of the expectation values is obtained for atoms within the WDA scheme. For sodium clusters the authors notice a sizeable contribution of the nonlocal effects to the total energy and to the density profiles. In the limit of very large clusters these effects should affect the surface energy of the bulk metal

Examining the occupancy–density relationship for a low-density carnivore

Science.gov (United States)

Linden, Daniel W.; Fuller, Angela K.; Royle, J. Andrew; Hare, Matthew P.

2017-01-01

The challenges associated with monitoring low-density carnivores across large landscapes have limited the ability to implement and evaluate conservation and management strategies for such species. Non-invasive sampling techniques and advanced statistical approaches have alleviated some of these challenges and can even allow for spatially explicit estimates of density, one of the most valuable wildlife monitoring tools.For some species, individual identification comes at no cost when unique attributes (e.g. pelage patterns) can be discerned with remote cameras, while other species require viable genetic material and expensive laboratory processing for individual assignment. Prohibitive costs may still force monitoring efforts to use species distribution or occupancy as a surrogate for density, which may not be appropriate under many conditions.Here, we used a large-scale monitoring study of fisher Pekania pennanti to evaluate the effectiveness of occupancy as an approximation to density, particularly for informing harvest management decisions. We combined remote cameras with baited hair snares during 2013–2015 to sample across a 70 096-km2 region of western New York, USA. We fit occupancy and Royle–Nichols models to species detection–non-detection data collected by cameras, and spatial capture–recapture (SCR) models to individual encounter data obtained by genotyped hair samples. Variation in the state variables within 15-km2 grid cells was modelled as a function of landscape attributes known to influence fisher distribution.We found a close relationship between grid cell estimates of fisher state variables from the models using detection–non-detection data and those from the SCR model, likely due to informative spatial covariates across a large landscape extent and a grid cell resolution that worked well with the movement ecology of the species. Fisher occupancy and density were both positively associated with the proportion of coniferous

Lattice Yang-Mills theory at finite densities of heavy quarks

International Nuclear Information System (INIS)

Langfeld, Kurt; Shin, Gwansoo

2000-01-01

SU(N c ) Yang-Mills theory is investigated at finite densities of N f heavy quark flavors. The calculation of the (continuum) quark determinant in the large-mass limit is performed by analytic methods and results in an effective gluonic action. This action is then subject to a lattice representation of the gluon fields and computer simulations. The approach maintains the same number of quark degrees of freedom as in the continuum formulation and a physical heavy quark limit (to be contrasted with the quenched approximation N f →0). The proper scaling towards the continuum limit is manifest. We study the partition function for given values of the chemical potential as well as the partition function which is projected onto a definite baryon number. First numerical results for an SU(2) gauge theory are presented. We briefly discuss the breaking of the color-electric string at finite densities and shed light onto the origin of the overlap problem inherent in the Glasgow approach

Planck intermediate results - LII. Planet flux densities

DEFF Research Database (Denmark)

Akrami, Y.; Ashdown, M.; Aumont, J.

2017-01-01

Measurements of flux density are described for five planets, Mars, Jupiter, Saturn, Uranus, and Neptune, across the six Planck High Frequency Instrument frequency bands (100–857 GHz) and these are then compared with models and existing data. In our analysis, we have also included estimates...... of the brightness of Jupiter and Saturn at the three frequencies of the Planck Low Frequency Instrument (30, 44, and 70 GHz). The results provide constraints on the intrinsic brightness and the brightness time-variability of these planets. The majority of the planet flux density estimates are limited by systematic...... errors, but still yield better than 1% measurements in many cases. Applying data from Planck HFI, the Wilkinson Microwave Anisotropy Probe (WMAP), and the Atacama Cosmology Telescope (ACT) to a model that incorporates contributions from Saturn’s rings to the planet’s total flux density suggests a best...

Low temperature plasma near a tokamak reactor limiter

International Nuclear Information System (INIS)

Braams, B.J.; Singer, C.E.

1985-01-01

Analytic and two-dimensional computational solutions for the plasma parameters near a toroidally symmetric limiter are illustrated for the projected parameters of a Tokamak Fusion Core Experiment (TFCX). The temperature near the limiter plate is below 20 eV, except when the density 10 cm inside the limiter contact is 8 x 10 13 cm -3 or less and the thermal diffusivity in the edge region is 2 x 10 4 cm 2 /s or less. Extrapolation of recent experimental data suggests that neither of these conditions is likely to be met near ignition in TFCX, so a low plasma temperature near the limiter should be considered a likely possibility

Pedestrian Flow in the Mean Field Limit

KAUST Repository

Haji Ali, Abdul Lateef

2012-11-01

We study the mean-field limit of a particle-based system modeling the behavior of many indistinguishable pedestrians as their number increases. The base model is a modified version of Helbing\\'s social force model. In the mean-field limit, the time-dependent density of two-dimensional pedestrians satisfies a four-dimensional integro-differential Fokker-Planck equation. To approximate the solution of the Fokker-Planck equation we use a time-splitting approach and solve the diffusion part using a Crank-Nicholson method. The advection part is solved using a Lax-Wendroff-Leveque method or an upwind Backward Euler method depending on the advection speed. Moreover, we use multilevel Monte Carlo to estimate observables from the particle-based system. We discuss these numerical methods, and present numerical results showing the convergence of observables that were calculated using the particle-based model as the number of pedestrians increases to those calculated using the probability density function satisfying the Fokker-Planck equation.

Neighbourhood walkability, road density and socio-economic status in Sydney, Australia.

Science.gov (United States)

Cowie, Christine T; Ding, Ding; Rolfe, Margaret I; Mayne, Darren J; Jalaludin, Bin; Bauman, Adrian; Morgan, Geoffrey G

2016-04-27

Planning and transport agencies play a vital role in influencing the design of townscapes, travel modes and travel behaviors, which in turn impact on the walkability of neighbourhoods and residents' physical activity opportunities. Optimising neighbourhood walkability is desirable in built environments, however, the population health benefits of walkability may be offset by increased exposure to traffic related air pollution. This paper describes the spatial distribution of neighbourhood walkability and weighted road density, a marker for traffic related air pollution, in Sydney, Australia. As exposure to air pollution is related to socio-economic status in some cities, this paper also examines the spatial distribution of weighted road density and walkability by socio-economic status (SES). We calculated walkability, weighted road density (as a measure of traffic related air pollution) and SES, using predefined and validated measures, for 5858 Sydney neighbourhoods, representing 3.6 million population. We overlaid tertiles of walkability and weighted road density to define "sweet-spots" (high walkability-low weighted road density), and "sour- spots" (low walkability-high weighted road density) neighbourhoods. We also examined the distribution of walkability and weighted road density by SES quintiles. Walkability and weighted road density showed a clear east-west gradient across the region. Our study found that only 4 % of Sydney's population lived in sweet-spot" neighbourhoods with high walkability and low weighted road density (desirable), and these tended to be located closer to the city centre. A greater proportion of neighbourhoods had health limiting attributes of high weighted road density or low walkability (about 20 % each), and over 5 % of the population lived in "sour-spot" neighbourhoods with low walkability and high weighted road density (least desirable). These neighbourhoods were more distant from the city centre and scattered more widely. There were

Influence of primary-particle density in the morphology of agglomerates.

Science.gov (United States)

Camejo, M D; Espeso, D R; Bonilla, L L

2014-07-01

Agglomeration processes occur in many different realms of science, such as colloid and aerosol formation or formation of bacterial colonies. We study the influence of primary-particle density in agglomerate structures using diffusion-controlled Monte Carlo simulations with realistic space scales through different regimes (diffusion-limited aggregation and diffusion-limited colloid aggregation). The equivalence of Monte Carlo time steps to real time scales is given by Hirsch's hydrodynamical theory of Brownian motion. Agglomerate behavior at different time stages of the simulations suggests that three indices (the fractal exponent, the coordination number, and the eccentricity index) characterize agglomerate geometry. Using these indices, we have found that the initial density of primary particles greatly influences the final structure of the agglomerate, as observed in recent experimental works.

The energy density distribution of an ideal gas and Bernoulli’s equations

Science.gov (United States)

Santos, Leonardo S. F.

2018-05-01

This work discusses the energy density distribution in an ideal gas and the consequences of Bernoulli’s equation and the corresponding relation for compressible fluids. The aim of this work is to study how Bernoulli’s equation determines the energy flow in a fluid, although Bernoulli’s equation does not describe the energy density itself. The model from molecular dynamic considerations that describes an ideal gas at rest with uniform density is modified to explore the gas in motion with non-uniform density and gravitational effects. The difference between the component of the speed of a particle that is parallel to the gas speed and the gas speed itself is called ‘parallel random speed’. The pressure from the ‘parallel random speed’ is denominated as parallel pressure. The modified model predicts that the energy density is the sum of kinetic and potential gravitational energy densities plus two terms with static and parallel pressures. The application of Bernoulli’s equation and the corresponding relation for compressible fluids in the energy density expression has resulted in two new formulations. For incompressible and compressible gas, the energy density expressions are written as a function of stagnation, static and parallel pressures, without any dependence on kinetic or gravitational potential energy densities. These expressions of the energy density are the main contributions of this work. When the parallel pressure was uniform, the energy density distribution for incompressible approximation and compressible gas did not converge to zero for the limit of null static pressure. This result is rather unusual because the temperature tends to zero for null pressure. When the gas was considered incompressible and the parallel pressure was equal to static pressure, the energy density maintained this unusual behaviour with small pressures. If the parallel pressure was equal to static pressure, the energy density converged to zero for the limit of the

Critical density and disruptions in α-heated thermonuclear Tokamak discharges

International Nuclear Information System (INIS)

Cotsaftis, M.; Firestone, M.; Wang, P.K.C.

1985-02-01

The study of existence of a critical density limit has been extended to the case of thermonuclear α-particle heated regime. To proceed, a 0-D model including sources and sinks affecting the evolution of ion and electron temperatures and of electron and α-particle densities with auxiliary neutral injected power has been developed. It is mainly shown when considering a Tokamak machine adapted for thermonuclear performances that, like in previous case, there is a critical density above which no other equilibrium point than 0 does exist. Temperatures then drop down the 0 past this critical value, leading to disruption. Analytic expression for critical density is given in terme of auxiliary projected power Psup(N). For Psup(N)=0, critical density value is low, but it increases fast enough for small Psup(N) to give a large safety margin once Psup(N) is moderate, much below the power required for reaching thermonuclear regime. So it is only at shutdown power periods that critical density can be crossed. But in this case, the heat content of particles in the discharge can significantly contribute to smooth out the temperature drop off. This typically operates up to the point where, due to change in magnetic islands configuration resulting from profile modification due to energy release at critical density crossing, heat transport doubles. Then on a fast thermal diffusion time scale, temperature drops now to a new equilibrium value, which can be made above the limiting value for which position control system of the plasma cannot forbid the plasma current to drop off itself, which is the important phenomenon of disruption. So on top of controls previously discussed, it is possible to use the α-particles themselves as a new preventive control against disruptions, making this phenomenon less dangerous for thermonuclear regime operation

The topology of the Coulomb potential density. A comparison with the electron density, the virial energy density, and the Ehrenfest force density.

Science.gov (United States)

Ferreira, Lizé-Mari; Eaby, Alan; Dillen, Jan

2017-12-15

The topology of the Coulomb potential density has been studied within the context of the theory of Atoms in Molecules and has been compared with the topologies of the electron density, the virial energy density and the Ehrenfest force density. The Coulomb potential density is found to be mainly structurally homeomorphic with the electron density. The Coulomb potential density reproduces the non-nuclear attractor which is observed experimentally in the molecular graph of the electron density of a Mg dimer, thus, for the first time ever providing an alternative and energetic foundation for the existence of this critical point. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Bone mineral density among elderly patients with chronic ...

African Journals Online (AJOL)

Background: Osteoporosis is one of the major extra-pulmonary manifestations of chronic obstructive pulmonary disease (COPD), which limits the physical activity. The present study was undertaken to study the bone mineral density (BMD) and osteoporosis in the elderly COPD patients. Materials and Methods: This was a ...

Comparison of ITER performance predicted by semi-empirical and theory-based transport models

International Nuclear Information System (INIS)

Mukhovatov, V.; Shimomura, Y.; Polevoi, A.

2003-01-01

The values of Q=(fusion power)/(auxiliary heating power) predicted for ITER by three different methods, i.e., transport model based on empirical confinement scaling, dimensionless scaling technique, and theory-based transport models are compared. The energy confinement time given by the ITERH-98(y,2) scaling for an inductive scenario with plasma current of 15 MA and plasma density 15% below the Greenwald value is 3.6 s with one technical standard deviation of ±14%. These data are translated into a Q interval of [7-13] at the auxiliary heating power P aux = 40 MW and [7-28] at the minimum heating power satisfying a good confinement ELMy H-mode. Predictions of dimensionless scalings and theory-based transport models such as Weiland, MMM and IFS/PPPL overlap with the empirical scaling predictions within the margins of uncertainty. (author)

Stability of Sarma phases in density imbalanced electron-hole bilayer systems

International Nuclear Information System (INIS)

Subasi, A. L.; Tanatar, B.; Pieri, P.; Senatore, G.

2010-01-01

We study excitonic condensation in an electron-hole bilayer system with unequal layer densities at zero temperature. Using mean-field theory we solve the Bardeen-Cooper-Schrieffer (BCS) gap equations numerically and investigate the effects of intralayer interactions. The electron-hole system evolves from BCS in the weak coupling limit to Bose-Einstein condensation (BEC) in the strong coupling limit. We analyze the stability of the Sarma phase with k,-k pairing by calculating the superfluid mass density and also by checking the compressibility matrix. We find that with bare Coulomb interactions the superfluid density is always positive in the Sarma phase, due to a peculiar momentum structure of the gap function originating from the singular behavior of the Coulomb potential at zero momentum and the presence of a sharp Fermi surface. Introducing a simple model for screening, we find that the superfluid density becomes negative in some regions of the phase diagram, corresponding to an instability toward a Fulde-Ferrel-Larkin-Ovchinnikov-type superfluid phase. Thus, intralayer interaction and screening together can lead to a rich phase diagram in the BCS-BEC crossover regime in electron-hole bilayer systems.

Unification of field theory and maximum entropy methods for learning probability densities

Science.gov (United States)

Kinney, Justin B.

2015-09-01

The need to estimate smooth probability distributions (a.k.a. probability densities) from finite sampled data is ubiquitous in science. Many approaches to this problem have been described, but none is yet regarded as providing a definitive solution. Maximum entropy estimation and Bayesian field theory are two such approaches. Both have origins in statistical physics, but the relationship between them has remained unclear. Here I unify these two methods by showing that every maximum entropy density estimate can be recovered in the infinite smoothness limit of an appropriate Bayesian field theory. I also show that Bayesian field theory estimation can be performed without imposing any boundary conditions on candidate densities, and that the infinite smoothness limit of these theories recovers the most common types of maximum entropy estimates. Bayesian field theory thus provides a natural test of the maximum entropy null hypothesis and, furthermore, returns an alternative (lower entropy) density estimate when the maximum entropy hypothesis is falsified. The computations necessary for this approach can be performed rapidly for one-dimensional data, and software for doing this is provided.

Unification of field theory and maximum entropy methods for learning probability densities.

Science.gov (United States)

Kinney, Justin B

2015-09-01

The need to estimate smooth probability distributions (a.k.a. probability densities) from finite sampled data is ubiquitous in science. Many approaches to this problem have been described, but none is yet regarded as providing a definitive solution. Maximum entropy estimation and Bayesian field theory are two such approaches. Both have origins in statistical physics, but the relationship between them has remained unclear. Here I unify these two methods by showing that every maximum entropy density estimate can be recovered in the infinite smoothness limit of an appropriate Bayesian field theory. I also show that Bayesian field theory estimation can be performed without imposing any boundary conditions on candidate densities, and that the infinite smoothness limit of these theories recovers the most common types of maximum entropy estimates. Bayesian field theory thus provides a natural test of the maximum entropy null hypothesis and, furthermore, returns an alternative (lower entropy) density estimate when the maximum entropy hypothesis is falsified. The computations necessary for this approach can be performed rapidly for one-dimensional data, and software for doing this is provided.

Limitations of retarded (bisulfite) x-ray film processing

International Nuclear Information System (INIS)

Stoering, J.P.; Dittmore, C.

1979-01-01

We demonstrate the limitations of using retarded (bisulfite) developer to abate film sensitivity of x-ray films that have been exposed to intense radiation. We compared the measured densities of a large number of Kodak Type-M x-ray film samples exposed to a known fluence of monochromatic x-rays. These film samples were processed in three separate batches of bisulfite developer mixed in the same proportions. We concluded that reproducible film-density information cannot be obtained using different batches of (bisulfite) developer solutions

Semi-classical limit of relativistic quantum mechanics

Indian Academy of Sciences (India)

It is shown that the semi-classical limit of solutions to the Klein–Gordon equation gives the particle probability density that is in direct proportion to the inverse of the particle velocity. It is also shown that in the case of the Dirac equation a different result is obtained.

47 CFR 27.55 - Power strength limits.

Science.gov (United States)

2010-10-01

... following bands, the predicted or measured median field strength at any location on the geographical border... predicted or measured median field strength at any location on the geographical border of a licensee's... antenna mounting structure. (c) Power flux density limit for stations operating in the 746-757 MHz, 758...

High follicle density does not decrease sweat gland density in Huacaya alpacas.

Science.gov (United States)

Moore, K E; Maloney, S K; Blache, D

2015-01-01

When exposed to high ambient temperatures, mammals lose heat evaporatively by either sweating from glands in the skin or by respiratory panting. Like other camelids, alpacas are thought to evaporate more water by sweating than panting, despite a thick fleece, unlike sheep which mostly pant in response to heat stress. Alpacas were brought to Australia to develop an alternative fibre industry to sheep wool. In Australia, alpacas can be exposed to ambient temperatures higher than in their native South America. As a young industry there is a great deal of variation in the quality and quantity of the fleece produced in the national flock. There is selection pressure towards animals with finer and denser fleeces. Because the fibre from secondary follicles is finer than that from primary follicles, selecting for finer fibres might alter the ratio of primary and secondary follicles. In turn the selection might alter sweat gland density because the sweat glands are associated with the primary follicle. Skin biopsy and fibre samples were obtained from the mid-section of 33 Huacaya alpacas and the skin sections were processed into horizontal sections at the sebaceous gland level. Total, primary, and secondary follicles and the number of sweat gland ducts were quantified. Fibre samples from each alpaca were further analysed for mean fibre diameter. The finer-fibred animals had a higher total follicle density (Palpacas with high follicle density should not be limited for potential sweating ability. Copyright © 2014 Elsevier Ltd. All rights reserved.

Effects of Social Desirability Bias on Self-Report and Non Self-Report Assessments During Smoking Cessation

Science.gov (United States)

2010-09-30

State-Trait-Anxiety-Inventory (STAI; Spielberger , Gorsuch, & Lushene, 1970), an Anxiety Implicit Association Test (IAT; Greenwald et al., 1998), and...links to underlying memory systems. Personality and Social Psychology Review, 4, 108-131. Spielberger , C. D., Gorsuch, R. L., & Lushene, R. E. (1970

Scattering of ECRF waves by edge density fluctuations and blobs

Directory of Open Access Journals (Sweden)

Ram Abhay K.

2015-01-01

Full Text Available The scattering of electron cyclotron waves by density blobs embedded in the edge region of a fusion plasma is studied using a full-wave model. The full-wave theory is a generalization of the usual approach of geometric optics ray scattering by blobs. While the latter allows for only refraction of waves, the former, more general formulation, includes refraction, reflection, and diffraction of waves. Furthermore, the geometric optics, ray tracing, model is limited to blob densities that are slightly different from the background plasma density. Observations in tokamak experiments show that the fluctuating density differs from the background plasma density by 20% or more. Thus, the geometric optics model is not a physically realistic model of scattering of electron cyclotron waves by plasma blobs. The differences between the ray tracing approach and the full-wave approach to scattering are illustrated in this paper.

Resolution in QCM sensors for the viscosity and density of liquids: application to lead acid batteries.

Science.gov (United States)

Cao-Paz, Ana María; Rodríguez-Pardo, Loreto; Fariña, José; Marcos-Acevedo, Jorge

2012-01-01

In battery applications, particularly in automobiles, submarines and remote communications, the state of charge (SoC) is needed in order to manage batteries efficiently. The most widely used physical parameter for this is electrolyte density. However, there is greater dependency between electrolyte viscosity and SoC than that seen for density and SoC. This paper presents a Quartz Crystal Microbalance (QCM) sensor for electrolyte density-viscosity product measurements in lead acid batteries. The sensor is calibrated in H(2)SO(4) solutions in the battery electrolyte range to obtain sensitivity, noise and resolution. Also, real-time tests of charge and discharge are conducted placing the quartz crystal inside the battery. At the same time, the present theoretical "resolution limit" to measure the square root of the density-viscosity product [Formula: see text] of a liquid medium or best resolution achievable with a QCM oscillator is determined. Findings show that the resolution limit only depends on the characteristics of the liquid to be studied and not on frequency. The QCM resolution limit for [Formula: see text] measurements worsens when the density-viscosity product of the liquid is increased, but it cannot be improved by elevating the work frequency.

Economic dynamics with financial fragility and mean-field interaction: A model

Science.gov (United States)

Di Guilmi, C.; Gallegati, M.; Landini, S.

2008-06-01

Following Aoki’s statistical mechanics methodology [Masanao Aoki, New Approaches to Macroeconomic Modeling, Cambridge University Press, 1996; Masanao Aoki, Modeling Aggregate Behaviour and Fluctuations in Economics, Cambridge University Press, 2002; Masanao Aoki, and Hiroshi Yoshikawa, Reconstructing Macroeconomics, Cambridge University Press, 2006], we provide some insights into the well-known works of [Bruce Greenwald, Joseph Stiglitz, Macroeconomic models with equity and credit rationing, in: R. Hubbard (Ed.), Information, Capital Markets and Investment, Chicago University Press, Chicago, 1990; Bruce Greenwald, Joseph Stiglitz, Financial markets imperfections and business cycles, Quarterly journal of Economics (1993)]. Specifically, we reach analytically a closed form solution of their models overcoming the aggregation problem. The key idea is to represent the economy as an evolving complex system, composed by heterogeneous interacting agents, that can be partitioned into a space of macroscopic states. This meso level of aggregation permits to adopt mean-field interaction modeling and master equation techniques.

Particle exhaust studies in Tore Supra with a pump limiter

International Nuclear Information System (INIS)

Klepper, C.C.; Haste, G.R.; Horton, L.D.; Mioduszewski, P.K.; Uckan, T.; Bonnel, P.; Bruneau, J.L.; Chatelier, M.; Gil, C.; Grisolia, C.; Loarer, T.; Martin, G.; Pegourie, B.; Rodriguez, L.; Watkins, J.G.

1990-01-01

The aim of the Tore Supra pump limiter program is to study particle exhaust with a pump limiter system in long-pulse discharges with continuous pellet fueling and strong auxiliary heating. The pump limiter system consists of six vertical modules, located at the bottom of the machine, and one horizontal module at the outer midplane. The results presented here were obtained with the horizontal module only. This module was equipped with two titanium pumps with a total pumping speed of 100000 L/s. The instrumentation of the limiter included pressure gauges, a residual gas analyzer, Langmuir probes, a spectrometer viewing the neutralizer plate for H α and impurity measurements, and water calorimeters. All diagnostics have been commissioned and are operational. Initial results were obtained in low-density discharges, with no gas puffing during the shot. While only a modest effect on the plasma density was observed, large exhaust fluxes were measured in the pump limiter. The most likely source of this gas was outgassing of the graphite walls. Straightforward particle balance between the plasma efflux and the pump limiter exhaust, as applied in previous pump limiter experiments, did not apply. The core plasma and the edge plasma seemed to be largely decoupled and a multi-layer model is being developed to explain the experimental results. (orig.)

Anisotropic dynamic mass density for fluidsolid composites

KAUST Repository

Wu, Ying

2012-10-01

By taking the low frequency limit of multiple-scattering theory, we obtain the dynamic effective mass density of fluidsolid composites with a two-dimensional rectangular lattice structure. The anisotropic mass density can be described by an angle-dependent dipole solution, to the leading-order of solid concentration. The angular dependence vanishes for the square lattice, but at high solid concentrations there is a structure-dependent factor that contributes to the leading-order solution. In all cases, Woods formula is found to be accurately valid for the effective bulk modulus, independent of the structures. Numerical evaluations from the solutions are shown to be in excellent agreement with finite-element simulations. © 2012 Elsevier B.V.

The dependence of stellar properties on initial cloud density

Science.gov (United States)

Jones, Michael O.; Bate, Matthew R.

2018-05-01

We investigate the dependence of stellar properties on the initial mean density of the molecular cloud in which stellar clusters form using radiation hydrodynamical simulations that resolve the opacity limit for fragmentation. We have simulated the formation of three star clusters from the gravitational collapse of molecular clouds whose densities vary by a factor of a hundred. As with previous calculations including radiative feedback, we find that the dependence of the characteristic stellar mass, Mc, on the initial mean density of the cloud, ρ, is weaker than the dependence of the thermal Jeans mass. However, unlike previous calculations, which found no statistically significant variation in the median mass with density, we find a weak dependence approximately of the form Mc∝ρ-1/5. The distributions of properties of multiple systems do not vary significantly between the calculations. We compare our results to the result of observational surveys of star-forming regions, and suggest that the similarities between the properties of our lowest density calculation and the nearby Taurus-Auriga region indicate that the apparent excess of solar-type stars observed may be due to the region's low density.

Spinning solutions in general relativity with infinite central density

Science.gov (United States)

Flammer, P. D.

2018-05-01

This paper presents general relativistic numerical simulations of uniformly rotating polytropes. Equations are developed using MSQI coordinates, but taking a logarithm of the radial coordinate. The result is relatively simple elliptical differential equations. Due to the logarithmic scale, we can resolve solutions with near-singular mass distributions near their center, while the solution domain extends many orders of magnitude larger than the radius of the distribution (to connect with flat space-time). Rotating solutions are found with very high central energy densities for a range of adiabatic exponents. Analytically, assuming the pressure is proportional to the energy density (which is true for polytropes in the limit of large energy density), we determine the small radius behavior of the metric potentials and energy density. This small radius behavior agrees well with the small radius behavior of large central density numerical results, lending confidence to our numerical approach. We compare results with rotating solutions available in the literature, which show good agreement. We study the stability of spherical solutions: instability sets in at the first maximum in mass versus central energy density; this is also consistent with results in the literature, and further lends confidence to the numerical approach.

Modeling space-charge-limited currents in organic semiconductors: Extracting trap density and mobility

KAUST Repository

Dacuñ a, Javier; Salleo, Alberto

2011-01-01

We have developed and have applied a mobility edge model that takes drift and diffusion currents to characterize the space-charge-limited current in organic semiconductors into account. The numerical solution of the drift-diffusion equation allows

Gamma densitometer for measuring Pu density in fuel tubes

International Nuclear Information System (INIS)

Winn, W.G.

1982-01-01

A fuel-gamma-densitometer (FGD) has been developed to examine nondestructively the uniformity of plutonium in aluminum-clad fuel tubes at the Savannah River Plant (SRP). The monitoring technique is γ-ray spectroscopy with a lead-collimated Ge(Li) detector. Plutonium density is correlated with the measured intensity of the 208 keV γ-ray from 237 U (7d) of the 241 Pu (15y) decay chain. The FGD measures the plutonium density within 0.125- or 0.25-inch-diameter areas of the 0.133- to 0.183-inch-thick tube walls. Each measurement yields a density ratio that relates the plutonium density of the measured area to the plutonium density in normal regions of the tube. The technique was used to appraise a series of fuel tubes to be irradated in an SRP reactor. High-density plutonium areas were initially identified by x-ray methods and then examined quantitatively with the FGD. The FGD reliably tested fuel tubes and yielded density ratios over a range of 0.0 to 2.5. FGD measurements examined (1) nonuniform plutonium densities or hot spots, (2) uniform high-density patches, and (3) plutonium density distribution in thin cladding regions. Measurements for tubes with known plutonium density agreed with predictions to within 2%. Attenuation measurements of the 208-keV γ-ray passage through the tube walls agreed to within 2 to 3% of calculated predictions. Collimator leakage measurements agreed with model calculations that predicted less than a 1.5% effect on plutonium density ratios. Finally, FGD measurements correlated well with x-ray transmission and fluoroscopic measurements. The data analysis for density ratios involved a small correction of about 10% for γ-shielding within the fuel tube. For hot spot examinations, limited information for this correction dictated a density ratio uncertainty of 3 to 5%

Limits of detection and decision. Part 4

International Nuclear Information System (INIS)

Voigtman, E.

2008-01-01

Probability density functions (PDFs) have been derived for a number of commonly used limit of detection definitions, including several variants of the Relative Standard Deviation of the Background-Background Equivalent Concentration (RSDB-BEC) method, for a simple linear chemical measurement system (CMS) having homoscedastic, Gaussian measurement noise and using ordinary least squares (OLS) processing. All of these detection limit definitions serve as both decision and detection limits, thereby implicitly resulting in 50% rates of Type 2 errors. It has been demonstrated that these are closely related to Currie decision limits, if the coverage factor, k, is properly defined, and that all of the PDFs are scaled reciprocals of noncentral t variates. All of the detection limits have well-defined upper and lower limits, thereby resulting in finite moments and confidence limits, and the problem of estimating the noncentrality parameter has been addressed. As in Parts 1-3, extensive Monte Carlo simulations were performed and all the simulation results were found to be in excellent agreement with the derived theoretical expressions. Specific recommendations for harmonization of detection limit methodology have also been made

The shapes of column density PDFs. The importance of the last closed contour

Science.gov (United States)

Alves, João; Lombardi, Marco; Lada, Charles J.

2017-10-01

The probability distribution function of column density (PDF) has become the tool of choice for cloud structure analysis and star formation studies. Its simplicity is attractive, and the PDF could offer access to cloud physical parameters otherwise difficult to measure, but there has been some confusion in the literature on the definition of its completeness limit and shape at the low column density end. In this letter we use the natural definition of the completeness limit of a column density PDF, the last closed column density contour inside a surveyed region, and apply it to a set of large-scale maps of nearby molecular clouds. We conclude that there is no observational evidence for log-normal PDFs in these objects. We find that all studied molecular clouds have PDFs well described by power laws, including the diffuse cloud Polaris. Our results call for a new physical interpretation of the shape of the column density PDFs. We find that the slope of a cloud PDF is invariant to distance but not to the spatial arrangement of cloud material, and as such it is still a useful tool for investigating cloud structure.

Plasma motion in the scrape-off layer of a nonequipotential tokamak limiter

International Nuclear Information System (INIS)

Fidel'man, G.N.

1987-01-01

A theory is derived for the laminar convection of the plasma in the scrape-off layer of a poloidal limiter with a distributed potential. The plasma potential and density distributions are derived for the cases of poloidal and slightly nonuniform radial distributions of the potential on the limiter. The stability of these solutions against flute perturbations is analyzed. Criteria for the control of the density profile are derived in the models of laminar and turbulent scrape-off layers. The energy expended in sustaining the limiter potential distribution is studied. If a suitable potential distribution is selected, it is possible to obtain ∼10% of the total convective heat flux from the plasma column in the form of purely electrical energy

Low Bone Density

Science.gov (United States)

... Density Exam/Testing › Low Bone Density Low Bone Density Low bone density is when your bone density ... people with normal bone density. Detecting Low Bone Density A bone density test will determine whether you ...

Human Low Density Lipoprotein as a Vehicle of Atherosclerosis ...

African Journals Online (AJOL)

Low-density lipoproteins have been sufficiently established as an important precursor of atherosclerosis. The actual mechanism is still unclear, and the current technique of using radioisotopes has clinical limitation. However, the current study techniques or methods excellently elucidate the functional aspects of ...

Bounded Densities and Their Derivatives

DEFF Research Database (Denmark)

Kozine, Igor; Krymsky, V.

2009-01-01

This paper describes how one can compute interval-valued statistical measures given limited information about the underlying distribution. The particular focus is on a bounded derivative of a probability density function and its combination with other available statistical evidence for computing ...... quantities of interest. To be able to utilise the evidence about the derivative it is suggested to adapt the ‘conventional’ problem statement to variational calculus and the way to do so is demonstrated. A number of examples are given throughout the paper....

Tests of Multiplicative Models in Psychology: A Case Study Using the Unified Theory of Implicit Attitudes, Stereotypes, Self-Esteem, and Self-Concept

Science.gov (United States)

Blanton, Hart; Jaccard, James

2006-01-01

Theories that posit multiplicative relationships between variables are common in psychology. A. G. Greenwald et al. recently presented a theory that explicated relationships between group identification, group attitudes, and self-esteem. Their theory posits a multiplicative relationship between concepts when predicting a criterion variable.…

Implicit and explicit alcohol-related cognitions in heavy and light drinkers

NARCIS (Netherlands)

Wiers, RW; van Woerden, N; Smulders, FTY; de Jong, Peter

2002-01-01

Implicit and explicit alcohol-related cognitions were measured in 2 dimensions: positive-negative (valence) and arousal-sedation, with 2 versions of the Implicit Association Test (IAT; A. G. Greenwald, D. E. McGhee, & J. L. Schwartz) and related explicit measures. Heavy drinkers (h 24) strongly

Density determination of nail polishes and paint chips using magnetic levitation

Science.gov (United States)

Huang, Peggy P.

Trace evidence is often small, easily overlooked, and difficult to analyze. This study describes a nondestructive method to separate and accurately determine the density of trace evidence samples, specifically nail polish and paint chip using magnetic levitation (MagLev). By determining the levitation height of each sample in the MagLev device, the density of the sample is back extrapolated using a standard density bead linear regression line. The results show that MagLev distinguishes among eight clear nail polishes, including samples from the same manufacturer; separates select colored nail polishes from the same manufacturer; can determine the density range of household paint chips; and shows limited levitation for unknown paint chips. MagLev provides a simple, affordable, and nondestructive means of determining density. The addition of co-solutes to the paramagnetic solution to expand the density range may result in greater discriminatory power and separation and lead to further applications of this technique.

Diet quality limits summer growth of field vole populations.

Directory of Open Access Journals (Sweden)

Kristian M Forbes

Full Text Available Marked variation occurs in both seasonal and multiannual population density peaks of northern European small mammal species, including voles. The availability of dietary proteins is a key factor limiting the population growth of herbivore species. The objective of this study is to investigate the degree to which protein availability influences the growth of increasing vole populations. We hypothesise that the summer growth of folivorous vole populations is positively associated with dietary protein availability. A field experiment was conducted over a summer reproductive period in 18 vegetated enclosures. Populations of field voles (Microtus agrestis were randomised amongst three treatment groups: 1 food supplementation with ad libitum high protein (30% dry weight pellets, 2 food supplementation with ad libitum low protein (1% dry weight; both supplemented foods had equivalent energy content pellets, and 3 control (no food supplementation, n = 6 per treatment. Vole density, survival, demographic attributes and condition indicators were monitored with live-trapping and blood sampling. Highest final vole densities were attained in populations that received high protein supplementation and lowest in low protein populations. Control populations displayed intermediate densities. The survival rate of voles was similar in all treatment groups. The proportion of females, and of those that were pregnant or lactating, was highest in the high protein supplemented populations. This suggests that variation in reproductive, rather than survival rates of voles, accounted for density differences between the treatment groups. We found no clear association between population demography and individual physiological condition. Our results demonstrate that dietary protein availability limits vole population growth during the summer growing season. This suggests that the nutritional quality of forage may be an underestimated source of interannual variation in the

Density-dependent vulnerability of forest ecosystems to drought

Science.gov (United States)

Alessandra Bottero; Anthony W. D' Amato; Brian J. Palik; John B. Bradford; Shawn Fraver; Mike A. Battaglia; Lance A. Asherin; Harald Bugmann

2017-01-01

Climate models predict increasing drought intensity and frequency for many regions, which may have negative consequences for tree recruitment, growth and mortality, as well as forest ecosystem services. Furthermore, practical strategies for minimizing vulnerability to drought are limited. Tree population density, a metric of tree abundance in a given area, is a primary...

Waves and solitons in the continuum limit of the Calogero-Sutherland model

CERN Document Server

Polychronakos, A P

1995-01-01

We examine a collection of classical particles interacting with inverse-square two-body potentials in the thermodynamic limit of finite particle density. We find explicit large-amplitude density waves and soliton solutions for the motion of the system. Waves can be constructed as coherent states of either solitons or phonons (small-amplitude waves). Therefore, either solitons or phonons can be considered as the fundamental excitations. The generic wave is shown to correspond to a two-band state in the quantum description of the system, while the limiting cases of solitons and phonons correspond to particle and hole excitations.

Diffusion limited reactions in crystalline solids

International Nuclear Information System (INIS)

Fastenau, R.

1982-01-01

Diffusion limited reactions in crystal lattices are studied with diffusion and random walk theory. First the random walk on a crystal lattice is studied. These results are used in a formal study of diffusion limited reactions in which the following simplified traps are discussed: planes, cylinders, spheres, disks and rings. The traps are either present at the start of the process (annealing) or fed into the crystal at a constant rate (continuous production). For the study of trapping processes occurring in real crystals it was necessary to investigate the interaction of the reacting species on the atomic level. Using lattice relaxation calculations, several reactions were studied. These calculations result in a model for the potential energy of the crystal versus the separation of the reaction partners. This model is used in Monte Carlo simulations of the trapping process, which are made at a high trap density, since the extrapolation to the low density regime can be made using the formal part of this work. The following reactions were studied: the trapping of interstitial helium atoms by vacancies, self interstitial vacancy recombination, the trapping of vacancies by immobile, helium filled, vacancies and the capture of self interstitials and vacancies by dislocations. A part of these results is used in two models for the low temperature nucleation and growth of bubbles due to helium bombardment. The models described give the right bubble density versus helium dose, but differ widely in the fraction of helium present in the bubbles found. A mechanism of blistering based on a percolation effect is also discussed. (Auth.)

Density Fluctuations of Hard-Sphere Fluids in Narrow Confinement

Directory of Open Access Journals (Sweden)

Kim Nygård

2016-02-01

Full Text Available Spatial confinement induces microscopic ordering of fluids, which in turn alters many of their dynamic and thermodynamic properties. However, the isothermal compressibility has hitherto been largely overlooked in the literature, despite its obvious connection to the underlying microscopic structure and density fluctuations in confined geometries. Here, we address this issue by probing density profiles and structure factors of hard-sphere fluids in various narrow slits, using x-ray scattering from colloid-filled nanofluidic containers and integral-equation-based statistical mechanics at the level of pair distributions for inhomogeneous fluids. Most importantly, we demonstrate that density fluctuations and isothermal compressibilities in confined fluids can be obtained experimentally from the long-wavelength limit of the structure factor, providing a formally exact and experimentally accessible connection between microscopic structure and macroscopic, thermodynamic properties. Our approach will thus, for example, allow direct experimental verification of theoretically predicted enhanced density fluctuations in liquids near solvophobic interfaces.

High volumetric power density, non-enzymatic, glucose fuel cells.

Science.gov (United States)

Oncescu, Vlad; Erickson, David

2013-01-01

The development of new implantable medical devices has been limited in the past by slow advances in lithium battery technology. Non-enzymatic glucose fuel cells are promising replacement candidates for lithium batteries because of good long-term stability and adequate power density. The devices developed to date however use an "oxygen depletion design" whereby the electrodes are stacked on top of each other leading to low volumetric power density and complicated fabrication protocols. Here we have developed a novel single-layer fuel cell with good performance (2 μW cm⁻²) and stability that can be integrated directly as a coating layer on large implantable devices, or stacked to obtain a high volumetric power density (over 16 μW cm⁻³). This represents the first demonstration of a low volume non-enzymatic fuel cell stack with high power density, greatly increasing the range of applications for non-enzymatic glucose fuel cells.

The local dark matter phase-space density and impact on WIMP direct detection

International Nuclear Information System (INIS)

Catena, Riccardo; Ullio, Piero

2012-01-01

We present a new determination of the local dark matter phase-space density. This result is obtained implementing, in the limit of isotropic velocity distribution and spherical symmetry, Eddington's inversion formula, which links univocally the dark matter distribution function to the density profile, and applying, within a Bayesian framework, a Markov Chain Monte Carlo algorithm to sample mass models for the Milky Way against a broad and variegated sample of dynamical constraints. We consider three possible choices for the dark matter density profile, namely the Einasto, NFW and Burkert profiles, finding that the velocity dispersion, which characterizes the width in the distribution, tends to be larger for the Burkert case, while the escape velocity depends very weakly on the profile, with the mean value we obtain being in very good agreement with estimates from stellar kinematics. The derived dark matter phase-space densities differ significantly — most dramatically in the high velocity tails — from the model usually taken as a reference in dark matter detection studies, a Maxwell-Boltzmann distribution with velocity dispersion fixed in terms of the local circular velocity and with a sharp truncation at a given value of the escape velocity. We discuss the impact of astrophysical uncertainties on dark matter scattering rates and direct detection exclusion limits, considering a few sample cases and showing that the most sensitive ones are those for light dark matter particles and for particles scattering inelastically. As a general trend, regardless of the assumed profile, when adopting a self-consistent phase-space density, we find that rates are larger, and hence exclusion limits stronger, than with the standard Maxwell-Boltzmann approximation. Tools for applying our result on the local dark matter phase-space density to other dark matter candidates or experimental setups are provided

High Power Density Power Electronic Converters for Large Wind Turbines

DEFF Research Database (Denmark)

Senturk, Osman Selcuk

. For these VSCs, high power density is required due to limited turbine nacelle space. Also, high reliability is required since maintenance cost of these remotely located wind turbines is quite high and these turbines operate under harsh operating conditions. In order to select a high power density and reliability......In large wind turbines (in MW and multi-MW ranges), which are extensively utilized in wind power plants, full-scale medium voltage (MV) multi-level (ML) voltage source converters (VSCs) are being more preferably employed nowadays for interfacing these wind turbines with electricity grids...... VSC solution for wind turbines, first, the VSC topology and the switch technology to be employed should be specified such that the highest possible power density and reliability are to be attained. Then, this qualitative approach should be complemented with the power density and reliability...

Improvement of density control by feedback on Langmuir probe signals in Tore Supra

International Nuclear Information System (INIS)

Gunn, J.; Bucalossi, J.; Costanzo, L.; Grisolia, C.; Ghendrih, Ph.; Grosman, A.; Loarer, T.; Martin, G.; Monier-Garbet, P.; Moulin, D.; Pascal, J.Y.; Saint-Laurent, F.

1999-12-01

Real time control of deuterium or helium gas injection by feedback on Langmuir probe signals is implemented in Tore Supra ergodic divertor discharges. The feedback schemes are based on the robust experimental observation that the density limit coincides with edge temperature T e ∼ 10 eV. Three control algorithms are used: (1) proportional feedback on the central line-averaged density with real-time attenuation of the system gain and security cut-off of the gas injection if the edge temperature becomes too low; (2) proportional feedback on the central line-averaged density with security cut-off controlled by the degree of detachment (DoD); (3) proportional feedback on edge temperature with security cut-off on the DoD. The DoD is defined for deuterium discharges, but not for helium since those do not detach. All three feedback modes permit operation close to the density limit and have been successfully applied for plasma currents 0.4 p p =1.4 MA with up to 4 MW of ICRH power. (author)

Economic values of growth and feed efficiency for fish farming in recirculating aquaculture system with density and nitrogen output limitations: a case study with African catfish (Clarias gariepinus).

Science.gov (United States)

Besson, M; Komen, H; Aubin, J; de Boer, I J M; Poelman, M; Quillet, E; Vancoillie, C; Vandeputte, M; van Arendonk, J A M

2014-12-01

In fish farming, economic values (EV) of breeding goal traits are lacking, even though they are key parameters when defining selection objectives. The aim of this study was to develop a bioeconomic model to estimate EV of 2 traits representing production performances in fish farming: the thermal growth coefficient (TGC) and the feed conversion ratio (FCR). This approach was applied to a farm producing African catfish (Clarias gariepinus) in a recirculating aquaculture system (RAS). In the RAS, 2 factors could limit production level: the nitrogen treatment capacity of the biofilter or the fish density in rearing tanks at harvest. Profit calculation includes revenue from fish sales, cost of juveniles, cost of feed, cost of waste water treatment, and fixed costs. In the reference scenario, profit was modeled to zero. EV were calculated as the difference in profit per kilogram of fish between the current population mean for both traits (µt) and the next generation of selective breeding (µt+Δt) for either TGC or FCR. EV of TGC and FCR were calculated for three generations of hypothetical selection on either TGC or FCR (respectively 6.8% and 7.6% improvement per generation). The results show that changes in TGC and FCR can affect both the number of fish that can be stocked (number of batches per year and number of fish per batch) and the factor limiting production. The EV of TGC and FCR vary and depend on the limiting factors. When dissolved NH3-N is the limiting factor for both µt and µt+Δt, increasing TGC decreases the number of fish that can be stocked but increases the number of batches that can be grown. As a result, profit remains constant and EVTGC is zero. Increasing FCR, however, increases the number of fish stocked and the ratio of fish produced per kilogram of feed consumed ("economic efficiency"). The EVFCR is 0.14 €/kg of fish, and profit per kilogram of fish increases by about 10%. When density is the limiting factor for both µt and µt+Δt, the

Particle removal with pump limiters in ISX-B

International Nuclear Information System (INIS)

Mioduszewski, P.; Emerson, L.C.; Simpkins, J.E.

1983-01-01

First pump limiter experiments were performed on ISX-B. Two pump limiter modules were installed in the top and bottom of one toroidal sector of the tokamak. The modules consist of inertia cooled, TiC coated graphite heads and Zr-Al getter pumps each with a pumping speed of 1000 to 2000 l/s. The objective of the initial experiments was the demonstration of plasma particle control with pump limiters. The first set of experiments were performed in ohmic discharges (OH) in which the effect of the pump limiters on the plasma density was clearly demonstrated. In discharges characterized by: I/sub p/ = 110 kA, B/sub T/ = 15 kG, anti n/sub e/ = 1 - 5 x 10 13 cm -3 and t = 0.3 s the pressure rise in the pump limiters was typically 2 mTorr with the pumps off and 0.7 mTorr after activating the pumps. When the pumps were activated, the line-average plasma density decreased by up to a factor 2 at identical gas flow rates. The second set of measurements were performed in neutral beam heated discharges (NBI) with injected powers between 0.6 MW and 1.0 MW. Due to a cooling problem on one of the Zr-Al pumps the NBI experiments were carried out with one limiter only. The maximum pressure observed in NBI-discharges was 5 mTorr without activating the pumps, i.e., approximately twice as high as in OH-discharges. The exhaust efficiency, which is defined as the removed particle flux over the total particle flux in the scrape-off layer is estimated to be 5%

Graphene Coatings: Probing the Limits of the One Atom Thick Protection Layer

DEFF Research Database (Denmark)

Nilsson, Louis; Andersen, Mie; Balog, Richard

2012-01-01

The limitations of graphene as an effective corrosion-inhibiting coating on metal surfaces, here exemplified by the hex-reconstructed Pt(100) surface, are probed by scanning tunneling microscopy measurements and density functional theory calculations. While exposure of small molecules directly onto...... against CO is observed at CO pressures below 106 mbar. However, at higher pressures CO is observed to intercalate under the graphene coating layer, thus lifting the reconstruction. The limitations of the coating effect are further tested by exposure to hot atomic hydrogen. While the coating can withstand...... these extreme conditions for a limited amount of time, after substantial exposure, the Pt(100) reconstruction is lifted. Annealing experiments and density functional theory calculations demonstrate that the basal plane of the graphene stays intact and point to a graphene-mediated mechanism for the H...

Confinement margins for ignition and driven operation in Iter Eda ID

International Nuclear Information System (INIS)

Johner, J.

1995-09-01

Preliminary calculations for ITER EDA ID have been performed using the 1/2D thermal equilibrium code HELIOS. It is found that: - The maximum ignition margin for ITER ID (29%) is 6% less than for ITER OD (35%) and 5% less than for ITER CDA (34%). - Decreasing the ration τ * He /τ E from the nominal value 10 to a value of 5 gives a 12% gain in the maximum ignition margin. Increasing the ration from 10 to 15 causes a 22% loss in the margin. Furthermore, ignited equilibria non longer exist for τ * He /τ E ≥ 17.6. - Operation in driven mode with 50 MW of external power increases the confinement capability by 13%. With 100 MW, the improvement is 24%. - Lowering the fusion power from 1500 to 1000 MW slightly improves the maximum ignition margin (+5%) and allows operation below the Greenwald density limit. - A 10% reduction of the toroidal magnetic field with a correlative diminution of the plasma current for constant safety factor operation, causes a dramatic reduction (-18%) of the maximum ignition margin. - A fraction of neon of 0.68% would completely suppress the ignition margin. Furthermore, ignited equilibria, with the nominal fusion power and τ * He /τ E , no longer exist when the neon fraction exceeds 0.75%. (Author). 2 refs., 10 figs

Separate density and viscosity measurements of unknown liquid using quartz crystal microbalance

Directory of Open Access Journals (Sweden)

Feng Tan

2016-09-01

Full Text Available Aqueous liquids have a wide range of applications in many fields. Basic physical properties like the density and the viscosity have great impacts on the functionalities of a given ionic liquid. For the millions kinds of existing liquids, only a few have been systematically measured with the density and the viscosity using traditional methods. However, these methods are limited to measure the density and the viscosity of an ionic liquid simultaneously especially in processing micro sample volumes. To meet this challenge, we present a new theoretical model and a novel method to separate density and viscosity measurements with single quartz crystal microbalance (QCM in this work. The agreement of experimental results and theocratical calculations shows that the QCM is capable to measure the density and the viscosity of ionic liquids.

Recent experimental results on level densities for compound reaction calculations

International Nuclear Information System (INIS)

Voinov, A.V.

2012-01-01

There is a problem related to the choice of the level density input for Hauser-Feshbach model calculations. Modern computer codes have several options to choose from but it is not clear which of them has to be used in some particular cases. Availability of many options helps to describe existing experimental data but it creates problems when it comes to predictions. Traditionally, different level density systematics are based on experimental data from neutron resonance spacing which are available for a limited spin interval and one parity only. On the other hand reaction cross section calculations use the total level density. This can create large uncertainties when converting the neutron resonance spacing to the total level density that results in sizable uncertainties in cross section calculations. It is clear now that total level densities need to be studied experimentally in a systematic manner. Such information can be obtained only from spectra of compound nuclear reactions. The question is does level densities obtained from compound nuclear reactions keep the same regularities as level densities obtained from neutron resonances- Are they consistent- We measured level densities of 59-64 Ni isotopes from proton evaporation spectra of 6,7 Li induced reactions. Experimental data are presented. Conclusions of how level density depends on the neutron number and on the degree of proximity to the closed shell ( 56 Ni) are drawn. The level density parameters have been compared with parameters obtained from the analysis of neutron resonances and from model predictions

Breast density estimation from high spectral and spatial resolution MRI

Science.gov (United States)

Li, Hui; Weiss, William A.; Medved, Milica; Abe, Hiroyuki; Newstead, Gillian M.; Karczmar, Gregory S.; Giger, Maryellen L.

2016-01-01

Abstract. A three-dimensional breast density estimation method is presented for high spectral and spatial resolution (HiSS) MR imaging. Twenty-two patients were recruited (under an Institutional Review Board--approved Health Insurance Portability and Accountability Act-compliant protocol) for high-risk breast cancer screening. Each patient received standard-of-care clinical digital x-ray mammograms and MR scans, as well as HiSS scans. The algorithm for breast density estimation includes breast mask generating, breast skin removal, and breast percentage density calculation. The inter- and intra-user variabilities of the HiSS-based density estimation were determined using correlation analysis and limits of agreement. Correlation analysis was also performed between the HiSS-based density estimation and radiologists’ breast imaging-reporting and data system (BI-RADS) density ratings. A correlation coefficient of 0.91 (pdensity estimations. An interclass correlation coefficient of 0.99 (pdensity estimations. A moderate correlation coefficient of 0.55 (p=0.0076) was observed between HiSS-based breast density estimations and radiologists’ BI-RADS. In summary, an objective density estimation method using HiSS spectral data from breast MRI was developed. The high reproducibility with low inter- and low intra-user variabilities shown in this preliminary study suggest that such a HiSS-based density metric may be potentially beneficial in programs requiring breast density such as in breast cancer risk assessment and monitoring effects of therapy. PMID:28042590

Plugging regime in the pump limiter throat

International Nuclear Information System (INIS)

Ghendrih, P.; Grosman, A.; Samain, A.; Capes, H.; Morera, J.P.

1988-08-01

The plugging regime -with no outstreaming neutral flux- is studied for a closed configuration pump limiter (throat). We derive the plugging length and the neutral density build-up at the neutralizer plate. The analytical expressions are supported by numerical evidence. We find an improved efficiency related to the throat effect mainly due to neutral-sidewall interactions

Double-layer capacitors with a higher energy density; Doppelschichtkondensatoren mit hoeherem Energieinhalt

Energy Technology Data Exchange (ETDEWEB)

Presser, Volker [Leibniz-Institut fuer Neue Materialien (INM) gGmbH, Saarbruecken (Germany). Juniorforschungs-Gruppe Energie-Materialien; Universitaet des Saarlandes, Saarbruecken (Germany)

2013-05-15

Electrical double-layer capacitors, also known as supercapacitors (SC) are devices for electrical energy storage used for fast acceleration of hybrid cars or for the energy recovery during breaking operations. In contrast, lithium-ion batteries (LIB) are used as energy storage devices to provide an extended travel distance for plug-in hybrid cars and electric vehicles. Current research aims to overcome the major limitations of both technologies (SC: low energy density/LIB: slow recharge and limited service life) and hybrid cells are considered a promising solution. The goal is to improve the performance and energy density of storage devices which can be achieved, as shown by the Leibniz-Institute for New Materials (INM), with the use of nanotechnology. (orig.)

Den skrøbelige sandhed

DEFF Research Database (Denmark)

Pedersen, Peter Ole

2010-01-01

Artiklen retter fokus mod de seneste års udvikling af den aktivistiske dokumentarfilm. Med analytiske punktnedslag hos instruktørerne Michael Moore, Morgan Spurlock, Dylan Avery, Robert Greenwald og Mauro Andrizzi undersøges de forbindelser der eksisterer mellem udtrykket i de populære spillefilm...

Threat Based Risk Assessment for Enterprise Networks

Science.gov (United States)

2016-02-15

devastating insider attacks, Edward Snowden exfiltrated 1.7 million documents from the National Security Agency [1]. That same year, the security company...Weller-Fahy, and Tamara Yu. References 1. G. Greenwald, No Place to Hide: Edward Snowden , the NSA, and the U.S. Surveillance State. London: Hamish

What's in a name: Implicit self-esteem and the automatic self

NARCIS (Netherlands)

Koole, S.L.; Dijksterhuis, A.; van Knippenberg, A.

2001-01-01

This article explores the links between implicit self-esteem and the automatic self (D. L. Paulhus, 1993). Across 4 studies, name letter evaluations were positively biased, confirming that implicit self-esteem is generally positive (A. G. Greenwald & M. R. Banaji, 1995). Study 1 found that this name

76 FR 62259 - Endangered and Threatened Wildlife and Plants; Partial 90-Day Finding on a Petition To List 404...

Science.gov (United States)

2011-10-06

... electronic mail, a petition from the Center for Biological Diversity (CBD), Alabama Rivers Alliance, Clinch... electronic mail to Noah Greenwald at CBD, we acknowledged receipt of the Petition. On May 10, 2010, we... the petition. Crystal Darter (Crystallaria asprella) The crystal darter is a slender, cigar-shaped...

Space-charge-limit instabilities in electron beams

International Nuclear Information System (INIS)

Coutsias, E.A.; Sullivan, D.J.

1983-01-01

The method of characteristics and multiple-scaling perturbation techniques are used to study the space-charge instability of electron beams. It is found that the stable oscillating state (virtual cathode) created when the space-charge limit is exceeded is similar to a collisionless shock wave. The oscillatory solution originates at the bifurcation point of two unstable steady states. Complementary behavior (virtual anode) results when an ion beam exceeds its space-charge limit. The virtual cathode can also exist in the presence of a neutralizing heavy-ion background. The Pierce instability, where the electron and ion charge densities are equal, is a special case of this broader class. Estimates of the nonlinear growth rate of the instability at the space-charge limit are given

Fast clustering using adaptive density peak detection.

Science.gov (United States)

Wang, Xiao-Feng; Xu, Yifan

2017-12-01

Common limitations of clustering methods include the slow algorithm convergence, the instability of the pre-specification on a number of intrinsic parameters, and the lack of robustness to outliers. A recent clustering approach proposed a fast search algorithm of cluster centers based on their local densities. However, the selection of the key intrinsic parameters in the algorithm was not systematically investigated. It is relatively difficult to estimate the "optimal" parameters since the original definition of the local density in the algorithm is based on a truncated counting measure. In this paper, we propose a clustering procedure with adaptive density peak detection, where the local density is estimated through the nonparametric multivariate kernel estimation. The model parameter is then able to be calculated from the equations with statistical theoretical justification. We also develop an automatic cluster centroid selection method through maximizing an average silhouette index. The advantage and flexibility of the proposed method are demonstrated through simulation studies and the analysis of a few benchmark gene expression data sets. The method only needs to perform in one single step without any iteration and thus is fast and has a great potential to apply on big data analysis. A user-friendly R package ADPclust is developed for public use.

The spectrum of density perturbations in an expanding universe

Science.gov (United States)

Silk, J.

1974-01-01

The basic dynamic equations that govern the evolution of perturbations in a Friedmann-Lemaitre universe are derived. General solutions describing the evolution of adiabatic perturbations in the density of matter are obtained, and the choice of the appropriate initial conditions is examined. The various perturbation modes are compared, and the effects of decoupling on the perturbation spectrum are studied. The scheme used to follow the evolution of density perturbations through decoupling is based on an extension of the Eddington approximation to the radiative transfer equation, and is strictly valid in both optically thick and thin limits.

Microwave background anisotropies and the primordial spectrum of cosmological density fluctuations

International Nuclear Information System (INIS)

Suto, Yasushi; Gouda, Naoteru; Sugiyama, Naoshi

1990-01-01

Microwave background anisotropies in various cosmological scenarios are studied. In particular, the extent to which nonscale-invariant spectra of the primordial density fluctuations are consistent with the observational upper limits is examined. The resultant constraints are summarized as contours on (n, Omega)-plane, where n is the power-law index of the primordial spectrum of density fuctuations and Omega is the cosmological density parameter. They are compared also with the constraints from the cosmic Mach number test, recently proposed by Ostriker and Suto (1990). The parameter regions which pass both tests are not consistent with the theoretical prejudice inspired by the inflationary model. 44 refs

Pump limiter experiment in the TFR tokamak

International Nuclear Information System (INIS)

Anon.

1987-01-01

Pump limiter experiments are carried out in the TFR Tokamak. The first TFR pump limiter is located in the outer part of the torus, its double-throat head is made of graphite tiles, the neutralizer plates are made of stainless steel, and it is pumped by a 3500 l s -1 titanium sublimation pump. The first attempts showed that the exhaust efficiency ε of this pump limiter was low (1.5% of the total plasma particle efflux). To improve on these results, a new limiter head with a single longer throat has been built. The particles were better trapped and the pumping achieved an important decrease of the recycling coefficient. Geometric features and also the highly non linear regime of pressure in the pump limiter as a function of the density at the entrance slot could explain the increase by a factor 3.5 of the exhaust efficiency (ε = 5%). Ion temperatures of the order of a few eV have been deduced from Doppler broadening measurements at the neutralizer plate of the pump limiter. (orig.)

Experiments to test an intra-island scoop limiter on TEXT

International Nuclear Information System (INIS)

Evans, T.E.; DeGrassie, J.S.; Jackson, G.L.; Ohyabu, N.; Wootton, A.J.; Gentle, K.W.; Hodge, W.L.; McCool, S.C.; Phillips, P.E.; Rhodes, T.L.; Richards, B.; Ritz, C.P.; Rowan, W.L.

1987-01-01

An instrumented scoop limiter probe is being operated on TEXT to test the concept of limiter cooling and improved particle removal efficiencies using an externally-applied resonant magnetic field perturbation (the resonant helical divertor concept). Cooling of the limiter face has been demonstrated for limiter positions ranging from r L = 29.0 cm inward to r L = 25.5 cm (the TEXT primary poloidal hoop limiter radius r a = 27.0 cm). Pressure rises in the limiter throat of approximately 40% are observed under optimized conditions. Interchangable limiter heads with thicknesses of 1.0 cm and 0.3 cm have been used to examine particle ducting into the scoop aperture. Experimental results are discussed along with observations of the limiter floating potential, H α recycling emissions, pressure measurements, and edge density and temperature measurements. (orig.)

Low larval densities in northern populations reinforce range expansion by a Mediterranean damselfly

DEFF Research Database (Denmark)

Therry, Lieven; Swaegers, Janne; Dinh, Khuong Van

2016-01-01

indicated higher food availability at low conspecific densities. Interestingly, the initial density treatment had stronger effect than densities experienced at the time of quantification on survival during the pre-freezing winter period and body condition estimates at the end of the experiment, indicating...... also delayed effects of the initial density treatment. Survival throughout a freezing period indicated extreme winter conditions are not likely a limiting factor in the range expansion of this Mediterranean species. 4. The increased survival and individual growth rates (through causing shifts......1. Contemporary climate change triggers a poleward range shift in many species. A growing number of studies document evolutionary changes in traits accelerating range expansion (such as growth rate and dispersal-related traits). In contrast, the direct impact of decreasing conspecific densities...

Limit cycles in quantum systems

Energy Technology Data Exchange (ETDEWEB)

Niemann, Patrick

2015-04-27

In this thesis we investigate Limit Cycles in Quantum Systems. Limit cycles are a renormalization group (RG) topology. When degrees of freedom are integrated out, the coupling constants flow periodically in a closed curve. The presence of limit cycles is restricted by the necessary condition of discrete scale invariance. A signature of discrete scale invariance and limit cycles is log-periodic behavior. The first part of this thesis is concerned with the study of limit cycles with the similarity renormalization group (SRG). Limit cycles are mainly investigated within conventional renormalization group frameworks, where degrees of freedom, which are larger than a given cutoff, are integrated out. In contrast, in the SRG potentials are unitarily transformed and thereby obtain a band-diagonal structure. The width of the band structure can be regarded as an effective cutoff. We investigate the appearance of limit cycles in the SRG evolution. Our aim is to extract signatures as well as the scaling factor of the limit cycle. We consider the 1/R{sup 2}-potential in a two-body system and a three-body system with large scattering lengths. Both systems display a limit cycle. Besides the frequently used kinetic energy generator we apply the exponential and the inverse generator. In the second part of this thesis, Limit Cycles at Finite Density, we examine the pole structure of the scattering amplitude for distinguishable fermions at zero temperature in the medium. Unequal masses and a filled Fermi sphere for each fermion species are considered. We focus on negative scattering lengths and the unitary limit. The properties of the three-body spectrum in the medium and implications for the phase structure of ultracold Fermi gases are discussed.

Application of interferometry and Faraday rotation techniques for density measurements on ITER

International Nuclear Information System (INIS)

Snider, R.T.; Carlstrom, T.N.; Ma, C.H.; Peebles, W.A.

1995-01-01

There is a need for real time, reliable density measurement for density control, compatible with the restricted access and radiation environment on ITER. Line average density measurements using microwave or laser interferometry techniques have proven to be robust and reliable for density control on contemporary tokamaks. In ITER, the large path length, high density and density gradients, limit the wavelength of a probing beam to shorter then about 50 microm due to refraction effects. In this paper the authors consider the design of short wavelength vibration compensated interferometers and Faraday rotation techniques for density measurements on ITER. These techniques allow operation of the diagnostics without a prohibitively large vibration isolated structure and permits the optics to be mounted directly on the radial port plugs on ITER. A beam path designed for 10.6 microm (CO2 laser) with a tangential path through the plasma allows both an interferometer and a Faraday rotation measurement of the line average density with good density resolution while avoiding refraction problems. Plasma effects on the probing beams and design tradeoffs will be discussed along with radiation and long pulse issues. A proposed layout of the diagnostic for ITER will be present

CO2 laser interferometer for temporally and spatially resolved electron density measurements

Science.gov (United States)

Brannon, P. J.; Gerber, R. A.; Gerardo, J. B.

1982-09-01

A 10.6-μm Mach-Zehnder interferometer has been constructed to make temporally and spatially resolved measurements of electron densities in plasmas. The device uses a pyroelectric vidicon camera and video memory to record and display the two-dimensional fringe pattern and a Pockels cell to limit the pulse width of the 10.6-μm radiation. A temporal resolution of 14 ns has been demonstrated. The relative sensitivity of the device for electron density measurements is 2×1015 cm-2 (the line integral of the line-of-sight length and electron density), which corresponds to 0.1 fringe shift.

CO2 laser interferometer for temporally and spatially resolved electron density measurements

International Nuclear Information System (INIS)

Brannon, P.J.; Gerber, R.A.; Gerardo, J.B.

1982-01-01

A 10.6-μm Mach--Zehnder interferometer has been constructed to make temporally and spatially resolved measurements of electron densities in plasmas. The device uses a pyroelectric vidicon camera and video memory to record and display the two-dimensional fringe pattern and a Pockels cell to limit the pulse width of the 10.6-μm radiation. A temporal resolution of 14 ns has been demonstrated. The relative sensitivity of the device for electron density measurements is 2 x 10 15 cm -2 (the line integral of the line-of-sight length and electron density), which corresponds to 0.1 fringe shift

Effects of an RF limiter on TEXTOR's edge plasmas

International Nuclear Information System (INIS)

Boedo, J.A.; Sakawa, Y.; Gray, D.S.; Mank, G.; Noda, N.

1997-01-01

Studies directed towards the reduction of particle and heat fluxes to plasma facing components by the application of ponderomotive forces generated by radio frequency (RF) are being conducted in TEXTOR. A modified poloidal limiter is used as an antenna with up to 3 kW of RF power; the data obtained show that the plasma is repelled by the RF ponderomotive potential. The density is reduced by a factor of 2-4 and the radial decay length is substantially altered. The density near the limiter decays exponentially with RF power. The electron temperature profile changes, with the decay length becoming longer (almost flat) during the RF. The temperature in the scrape off layer (SOL) increases and its increase is roughly proportional to the RF power until it saturates, suggesting that the heating efficiency drops with power, and that improved performance is to be expected at higher powers. (orig.)

First pump limiter experiments in Tore Supra

International Nuclear Information System (INIS)

Chatelier, M.; Bruneau, J.L.; Chappuis, P.; Gil, C.; Guilhem, D.; Lipa, M.; Rodriguez, L.; Vallet, J.C.; Van Houtte, D.; Watkins, J.G.

1989-01-01

The thermal load and the particle pumping effects on the outboard pump limiters (OPL), in Tore Supra are analyzed. The investigations are performed for the plasma either in contact with the OPL/ONPL (outboard non pumped limiters) alone or with the OPL and the vertical limiters together. Calorimetric measurements provide estimates of the time-integrated balance of the energy flow at the plasma edge. Radiated and charge exchange energy losses are deduced from the inner vessel calorimetry (R=242cm, a=94cm). Conductive/convective losses on the OPL and vertical (top and bottom) limiters are independently measured, as well as the integrated energy flow on the ergodic divertors. The calorimetric results, the bolometric measurements of the radiated power and the Ohmic power estimates, are indicated. The central line density from interferometric measurement for the two successive shots, with the ONPL and with the OPL, are given

Lung density

DEFF Research Database (Denmark)

Garnett, E S; Webber, C E; Coates, G

1977-01-01

The density of a defined volume of the human lung can be measured in vivo by a new noninvasive technique. A beam of gamma-rays is directed at the lung and, by measuring the scattered gamma-rays, lung density is calculated. The density in the lower lobe of the right lung in normal man during quiet...... breathing in the sitting position ranged from 0.25 to 0.37 g.cm-3. Subnormal values were found in patients with emphsema. In patients with pulmonary congestion and edema, lung density values ranged from 0.33 to 0.93 g.cm-3. The lung density measurement correlated well with the findings in chest radiographs...... but the lung density values were more sensitive indices. This was particularly evident in serial observations of individual patients....

A Survey of Metal Lines at High Redshift. II. SDSS Absorption Line Studies—O VI Line Density, Space Density, and Gas Metallicity at z abs ~ 3.0

Science.gov (United States)

Frank, S.; Mathur, S.; Pieri, M.; York, D. G.

2010-09-01

We have analyzed a large data set of O VI absorber candidates found in the spectra of 3702 Sloan Digital Sky Survey (SDSS) quasars, focusing on a subsample of 387 active galactic nuclei sight lines with an average S/N >=5.0, allowing for the detection of absorbers above a rest-frame equivalent width limit of W r >= 0.19 Å for the O VI 1032 Å component. Accounting for random interlopers mimicking an O VI doublet, we derive for the first time a secure lower limit for the redshift number density ΔN/Δz for redshifts z abs >= 2.8. With extensive Monte Carlo simulations, we quantify the losses of absorbers due to blending with the ubiquitous Lyα forest lines and estimate the success rate of retrieving each individual candidate as a function of its redshift, the emission redshift of the quasar, the strength of the absorber, and the measured signal-to-noise ratio (S/N) of the spectrum by modeling typical Lyman forest spectra. These correction factors allow us to derive the "incompleteness and S/N-corrected" redshift number densities of O VI absorbers: ΔN O VI,c /Δzc (2.8 secure lower limit for the contribution of O VI to the closure mass density at the redshifts probed here: ΩO VI (2.8 = 1.9 × 10-8 h -1. We show that the strong lines we probe account for over 65% of the mass in the O VI absorbers; the weak absorbers, while dominant in line number density, do not contribute significantly to the mass density. Making a conservative assumption about the ionization fraction, {O VI}/{O}, and adopting the Anders & Grevesse solar abundance values, we derive the mean metallicity of the gas probed in our search: ζ(2.8 = 3.6 × 10-4 h, in good agreement with other studies. These results demonstrate that large spectroscopic data sets such as SDSS can play an important role in QSO absorption line studies, in spite of the relatively low resolution.

Limiter H-mode experiments on TFTR

Energy Technology Data Exchange (ETDEWEB)

Bush, C [Oak Ridge National Lab., TN (USA); Bretz, N L; Fredrickson, E D; McGuire, K M; Nazikian, R; Park, H K; Schivell, J; Taylor, G; Bitter, B; Budny, R; Cohen, S A; Kilpatrick, S J; LeBlanc, B; Manos, D M; Meade, D; Paul, S F; Scott, S D; Stratton, B C; Synakowski, E J; Towner, H H; Weiland, R M; Arunasalam, V; Bateman, G; Bell, M G; Bell, R; Boivin, R; Cavallo, A; Cheng, C Z; Chu, T K; Cowl,

1990-12-15

Limiter H-modes with centrally peaked density profiles have been obtained in TFTR using a highly conditioned graphite limiter. The transition to these centrally peaked H-modes takes place from the supershot to the H-mode rather than the usual L- to H-mode transition observed on other tokamaks. Bi-directional beam heating is required to induce the transition. Density peaking factors, n{sub e}(0)/{l angle}n{sub e}{r angle}, >2.3 are obtained and at the same time the H-mode characteristics are similar to those of limiter H-modes on other tokamaks and the global confinement, {tau}{sub E}, can be >2.5 times L-mode scaling. The TRANSP analysis shows that transport in these H-modes is similar to that of supershots within the inner 60 cm of the plasma, but the stored electron energy (calculated using measured values of T{sub e} and n{sub e}) is higher for the H-mode at the plasma edge. Microwave scattering near the edge shows broad spectra at k = 5.5 cm{sup {minus}1} which begin at the drop in D{sub {alpha}} radiation and are strongly shifted in the electron diamagnetic drift direction. At the same time beam emission spectroscopy shows a coherent mode near the boundary with m = 15--20 at 20--30 kHz which is propagating in the ion direction. During an ELM event these apparent rotations cease and Mirnov fluctuations in the 50--500 kHz increase in intensity.

On Soft Limits of Large-Scale Structure Correlation Functions

OpenAIRE

Ben-Dayan, Ido; Konstandin, Thomas; Porto, Rafael A.; Sagunski, Laura

2014-01-01

We study soft limits of correlation functions for the density and velocity fields in the theory of structure formation. First, we re-derive the (resummed) consistency conditions at unequal times using the eikonal approximation. These are solely based on symmetry arguments and are therefore universal. Then, we explore the existence of equal-time relations in the soft limit which, on the other hand, depend on the interplay between soft and hard modes. We scrutinize two approaches in the literat...

Chain length dependence of the critical density of organic homologous series

DEFF Research Database (Denmark)

Kontogeorgis, Georgios M.; Fredenslund, Aage; Tassios, Dimitrios P.

1995-01-01

Whether the critical density of organic compounds belonging to a certain homologous series increases or decreases with (increasing) molecular weight has been a challenging question over the years. Two sets of experimental data have recently appeared in the literature for the critical density of n......-alkanes: Steele's data (up to n-decane) suggest that critical density increases with carbon number and reaches a limiting value. On the other hand, the data of Teja et al., 1990 which cover a broader range of n-alkanes (up to n-octadecane), reveal a decreasing trend of the critical density after a maximum at n......-heptane. Teja et al. have also presented critical density measurements for 1-alkenes (up to 1-decene) and 1-alkanols (up to 1-undecanol). These data follow the same decreasing trend with the molecular weight as n-alkanes. This trend is not in agreement with the predictions of most group-contribution methods...

Brave new world of unconventional density waves

International Nuclear Information System (INIS)

Maki, K.; Dora, B.; Korin-Hamzic, B.; Basletic, M.; Virosztek, A.; Kartsovnik, M.V.

2003-10-01

Recently many people have discussed unconventional density wave (i.e. UCDW and USDW). Unlike in conventional density waves, the quasiparticle excitations in these systems are gapless. The appearance of these systems suggests paradigm shift from quasi 1D system to quasi 2D and 3D systems. Here we limit ourselves to the angular dependent magnetoresistance (ADMR) observed in the low temperature phase (LTP) of α-(BEDT-TTF) 2 KHg(SCN) 4 . Here we show that UCDW describes successfully many features of ADMR as manifestation of the Landau quantization of the quasiparticle spectrum in magnetic field. Indeed ADMR will provide a unique window to access UDW like the AF phase in URu 2 Si 2 , the pseudogap phase in high T c cuprates and the glassy phase in organic superconductor k-(ET) 2 salts. (author)

Space-charge-limited currents for cathodes with electric field enhanced geometry

Energy Technology Data Exchange (ETDEWEB)

Lai, Dingguo, E-mail: laidingguo@nint.ac.cn; Qiu, Mengtong; Xu, Qifu [State Key Laboratory of Intense Pulsed Radiation Simulation and Effect, Northwest Institute of Nuclear Technology, Xi' an 701124 (China); Huang, Zhongliang [Department of Engineering Physics, Tsinghua University, Beijing 100084 (China)

2016-08-15

This paper presents the approximate analytic solutions of current density for annulus and circle cathodes. The current densities of annulus and circle cathodes are derived approximately from first principles, which are in agreement with simulation results. The large scaling laws can predict current densities of high current vacuum diodes including annulus and circle cathodes in practical applications. In order to discuss the relationship between current density and electric field on cathode surface, the existing analytical solutions of currents for concentric cylinder and sphere diodes are fitted from existing solutions relating with electric field enhancement factors. It is found that the space-charge-limited current density for the cathode with electric-field enhanced geometry can be written in a general form of J = g(β{sub E}){sup 2}J{sub 0}, where J{sub 0} is the classical (1D) Child-Langmuir current density, β{sub E} is the electric field enhancement factor, and g is the geometrical correction factor depending on the cathode geometry.

Field device to measure viscosity, density, and other slurry properties in drilled shafts : final report.

Science.gov (United States)

2016-04-01

Proper performance of mineral slurries used to stabilize drilled shaft excavations is maintained by assuring the : density, viscosity, pH, and sand content stay within state specified limits. These limits have been set either by : past experience, re...

The effect of a single blade limiter on energetic neutral beam particles in Doublet III

International Nuclear Information System (INIS)

Petrie, T.W.; Armentrout, C.; Burrell, K.H.; Hino, T.; Kahn, C.; Kim, J.; Lohr, J.; Rottler, L.; Schissel, D.; St John, H.

1984-01-01

Energetic beam ion collisions with the main limiter can be a significant power loss process under certain operating conditions in Doublet III. Futhermore, these collisions may cause measurable damage to the limiter itself. Under low current and low toroidal field conditions (e.g., Isub(p) = 290 kA and Bsub(T) = 6.3 kG), 20-38% of the inferred absorbed beam power may be deposited directly on the ion drift side of the limiter by the beam ions. However, for higher plasma current and toroidal fields (e.g., Isub(p) = 480 kA and Bsub(t) = 15 kG), the fraction of inferred absorbed beam power deposited on the limiter is reduced to < 10%. Monte Carlo code simulations show that this loss of beam power is primarily a result of the large poloidal and toroidal gyro-orbits of the energetic beam ions. Other factors which may enhance beam ion losses to the limiter are (1) large separation distances between the primary limiter and the (outboard) vacuum vessel wall, and (2) plasma density buildup near the plasma edge during high gas puff operation. In addition, our data suggests enhanced plasma density and recycling near the limiter. This localized density can cause appreciable premature ionizations of the incoming beam neutrals and thus reduce the effective plasma heating of the beamline which is immediately upcurrent of the limiter. The prematurely-ionized beam particles from this adjacent beamline are responsible for much of the damage to the ion drift side of the limiter. We have found that under certain operating conditions (1) the direct beam heating of the limiter is 50% greater and (2) the stored plasma energy is 10% less when the beamline immediately upcurrent of the limiter heats the plasma. Thus, the relative positions of the limiters to the beamlines are important in designing future tokamaks. (orig.)

An intermittency route to global instability in low-density jets

Science.gov (United States)

Murugesan, Meenatchidevi; Zhu, Yuanhang; Li, Larry K. B.

2017-11-01

Above a critical Reynolds number (Re), a low-density jet can become globally unstable, transitioning from a steady state (i.e. a fixed point) to a self-excited oscillatory state (i.e. a limit cycle) via a Hopf bifurcation. In this experimental study, we show that this transition can sometimes involve intermittency. When Re is just slightly above the critical point, intermittent bursts of high-amplitude periodic oscillations emerge amidst a background of low-amplitude aperiodic fluctuations. As Re increases further, these intermittent bursts persist longer in time until they dominate the overall dynamics, causing the jet to transition fully to a periodic limit cycle. We identify this as Type-II Pomeau-Manneville intermittency by quantifying the statistical distribution of the duration of the aperiodic fluctuations at the onset of intermittency. This study shows that the transition to global instability in low-density jets is not always abrupt but can involve an intermediate state with characteristics of both the initial fixed point and the final limit cycle. This work was supported by the Research Grants Council of Hong Kong (Project No. 16235716 and 26202815).

Symmetrized partial-wave method for density-functional cluster calculations

International Nuclear Information System (INIS)

Averill, F.W.; Painter, G.S.

1994-01-01

The computational advantage and accuracy of the Harris method is linked to the simplicity and adequacy of the reference-density model. In an earlier paper, we investigated one way the Harris functional could be extended to systems outside the limits of weakly interacting atoms by making the charge density of the interacting atoms self-consistent within the constraints of overlapping spherical atomic densities. In the present study, a method is presented for augmenting the interacting atom charge densities with symmetrized partial-wave expansions on each atomic site. The added variational freedom of the partial waves leads to a scheme capable of giving exact results within a given exchange-correlation approximation while maintaining many of the desirable convergence and stability properties of the original Harris method. Incorporation of the symmetry of the cluster in the partial-wave construction further reduces the level of computational effort. This partial-wave cluster method is illustrated by its application to the dimer C 2 , the hypothetical atomic cluster Fe 6 Al 8 , and the benzene molecule

Glaucoma Diagnostic Ability of the Optical Coherence Tomography Angiography Vessel Density Parameters.

Science.gov (United States)

Chung, Jae Keun; Hwang, Young Hoon; Wi, Jae Min; Kim, Mijin; Jung, Jong Jin

2017-11-01

To investigate the glaucoma diagnostic abilities of vessel density parameters as determined by optical coherence tomography (OCT) angiography in different stages of glaucoma. A total of 113 healthy eyes and 140 glaucomatous eyes were enrolled. Diagnostic abilities of the OCT vessel density parameters in the optic nerve head (ONH), peripapillary, and macular regions were evaluated by calculating the area under the receiver operation characteristic curves (AUCs). AUCs of the peripapillary vessel density parameters and circumpapillary retinal nerve fiber layer (RNFL) thickness were compared. OCT angiography vessel densities in the ONH, peripapillary, and macular regions in the glaucomatous eyes were significantly lower than those in the healthy eyes (P glaucoma detection. The peripapillary vessel density parameters showed similar AUCs with the corresponding sectoral RNFL thickness (P > 0.05). However, in the early stage of glaucoma, the AUCs of the inferotemporal and temporal peripapillary vessel densities were significantly lower than that of the RNFL thickness (P glaucoma diagnostic ability with circumpapillary RNFL thickness, in the early stage, the vessel density parameters showed limited clinical value.

On soft limits of large-scale structure correlation functions

International Nuclear Information System (INIS)

Ben-Dayan, Ido; Konstandin, Thomas; Porto, Rafael A.; Sagunski, Laura

2014-11-01

We study soft limits of correlation functions for the density and velocity fields in the theory of structure formation. First, we rederive the (resummed) consistency conditions at unequal times using the eikonal approximation. These are solely based on symmetry arguments and are therefore universal. Then, we explore the existence of equal-time relations in the soft limit which, on the other hand, depend on the interplay between soft and hard modes. We scrutinize two approaches in the literature: The time-flow formalism, and a background method where the soft mode is absorbed into a locally curved cosmology. The latter has been recently used to set up (angular averaged) 'equal-time consistency relations'. We explicitly demonstrate that the time-flow relations and 'equal-time consistency conditions' are only fulfilled at the linear level, and fail at next-to-leading order for an Einstein de-Sitter universe. While applied to the velocities both proposals break down beyond leading order, we find that the 'equal-time consistency conditions' quantitatively approximates the perturbative results for the density contrast. Thus, we generalize the background method to properly incorporate the effect of curvature in the density and velocity fluctuations on short scales, and discuss the reasons behind this discrepancy. We conclude with a few comments on practical implementations and future directions.