Upstream Parameters Research Articles

Profiling of host cell proteins by two‐dimensional difference gel electrophoresis (2D‐DIGE): Implications for downstream process development

Host cell proteins (HCPs) constitute a major group of impurities for biologic drugs produced using cell culture technology. HCPs are required to be closely monitored and adequately removed in the downstream process. However, HCPs are a complex mixture of proteins with significantly diverse molecular and immunological properties. An overall understanding of the composition of HCPs and changes in their molecular properties upon changes in upstream and harvest process conditions can greatly facilitate downstream process design. This article describes the use of a comparative proteomic profiling method viz. two-dimensional difference gel electrophoresis (2D-DIGE) to examine HCP composition in the harvest stream of CHO cell culture. The effect of upstream process parameters such as cell culture media, bioreactor control strategy, feeding strategy, and cell culture duration/cell viability on HCP profile was examined using this technique. Among all the parameters studied, cell viability generated the most significant changes on the HCP profile. 2D-DIGE was also used to compare the HCP differences between monoclonal antibody producing and null cell cultures. The HCP species in production cell culture was found to be well represented in null cell culture, which confirms the suitability of using the null cell culture for immunoassay reagent generation. 2D-DIGE is complimentary to the commonly used HCP immunoassay. It provides a direct comparison of the changes in HCP composition under different conditions and can reveal properties (pI, MW) of individual species, whereas the immunoassay sensitively quantifies total HCP amount in a given sample.

Estimating stream metabolism from oxygen concentrations: Effect of spatial heterogeneity

Rivers are heterogeneous at various scales. River metabolism estimators based on oxygen time series provide average estimates of net oxygen production at the scale of a river reach. These estimators are derived for homogeneous river reaches. For this reason, they cannot be used to analyze how exactly they average over longitudinal variations in net production, reaeration, oxygen saturation concentration and flow velocity. We try to fill this gap by using a general analytical solution of the transport‐reaction equation to (1) demonstrate how downstream oxygen concentration is affected by upstream concentration and (possible) longitudinally varying values of net production, reaeration, oxygen saturation concentration and flow velocity within a reach, and (2) derive how the net production estimate depends on varying upstream river parameters. In addition, we derive a new net production estimator that extends previously suggested estimators. The equations derived in this paper provide a general framework for understanding the assumptions underlying net production estimators. They are used to derive recommendations on the use of single station or two stations measurement layouts to get accurate river metabolism estimates. The estimator is implemented in the freely available statistics and graphics software package R (www.r‐project.org). This makes it easily applicable to observed oxygen time series. Empirical evidence of the significance of heterogeneity in rivers is demonstrated by applying the estimator to four subsequent reaches of a river using oxygen measurements from the ends of all reaches.

Analytical solutions for anisotropic MHD shocks

A new method to analytically solve the anisotropic MHD system of equations describing shock transitions is presented. As this system is known to be under-determined (there is more unknown parameters than available equations) free parameters must be chosen. From observational contraints it appears that the magnetic amplitude jump is a good candidate as it is generally available more frequently and more precisely than other jump 5 variables. With this approach we obtain an explicit expression for the density compression ratio for arbitrary upstream parameters and shock geometry. Downstream anisotropy and pressure are also calculated. The results are tested against an other approach and compared with observations from the Earth’s bow shock and the solar wind termination shock.

Correlation properties of magnetosheath magnetic field fluctuations

The magnetosheath is characterized by a variety of low‐frequency fluctuations, but their features and sources are different. Taking advantage of multipoint magnetic field measurements of the Cluster spacecraft, we present a statistical study to reveal properties of waves. We compute cross‐correlation coefficients of magnetic field strengths as measured by pairs of the Cluster spacecraft and determine the correlation length of magnetosheath waves. We discuss the relationship between the correlation length and upstream parameters as well as its connection with the wave mode and frequency power spectrum. In the frequency interval of 0.001–0.125 Hz, we found that the correlation length of fluctuations increases (1) through intervals of high solar wind speeds, (2) with increasing interplanetary magnetic field (IMF) strength, (3) if the cross‐correlation between the IMF and magnetosheath magnetic field is higher, and (4) if the amplitude of fluctuations is larger.

Energy dissipation and ion heating at the heliospheric termination shock

The Los Alamos hybrid simulation code is used to examine heating and the partition of dissipation energy at the perpendicular heliospheric termination shock in the presence of pickup ions. The simulations are one‐dimensional in space but three‐dimensional in field and velocity components, and are carried out for a range of values of pickup ion relative density. Results from the simulations show that because the solar wind ions are relatively cold upstream, the temperature of these ions is raised by a relatively larger factor than the temperature of the pickup ions. An analytic model for energy partition is developed on the basis of the Rankine‐Hugoniot relations and a polytropic energy equation. The polytropic index γ used in the Rankine‐Hugoniot relations is varied to improve agreement between the model and the simulations concerning the fraction of downstream heating in the pickup ions as well as the compression ratio at the shock. When the pickup ion density is less than 20%, the polytropic index is about 5/3, whereas for pickup ion densities greater than 20%, the polytropic index tends toward 2.2, suggesting a fundamental change in the character of the shock, as seen in the simulations, when the pickup ion density is large. The model and the simulations both indicate for the upstream parameters chosen for Voyager 2 conditions that the pickup ion density is about 25% and the pickup ions gain the larger share (approximately 90%) of the downstream thermal pressure, consistent with Voyager 2 observations near the shock.

A new model of mass flow characteristics in electronic expansion valves considering metastability

This paper presents an experimental study on the mass flow characteristics of electronic expansion valves in a wide operating condition range. It was found that flow choking always occurs under common operating conditions in refrigeration systems. Based on metastability in EEVs, a new model predicting mass flow rate was proposed under flow choking conditions. Different from the conventional models using Bernoulli equation which employed downstream pressure at the EEV exit and a corrected mass flow coefficient, the present model considered metastable liquid flow caused by rapid depressurization, and employed single-phase incompressible flow coefficient and metastable pressure at the throat. An empirical correlation of the metastable pressure, based on the experimental data for R22 and its substitutes, R407C and R410A, was developed in a power law form of dimensionless parameters including upstream operating parameters and refrigerant thermophysical properties and throat area. The predictions of the present model were found to be in good agreement with the measured data, and approximately 95% of the measured data fall within a relative deviation of ±7.0%. The comparison with a prior model shows that, in terms of flashing mechanism application and predicting accuracy, the present model is better than the conventional model without considering metastability.

MAGNETIC RECONNECTION AT THE TERMINATION SHOCK OF A STRIPED PULSAR WIND

Most of the rotational luminosity of a pulsar is carried away by a relativistic magnetized wind in which the matter energy flux is negligible compared to the Poynting flux. However, observations indicate that most of the Poynting flux is eventually converted into ultrarelativistic particles. The mechanism responsible for this transformation remains poorly understood. Near the equatorial plane of an obliquely rotating pulsar magnetosphere, the magnetic field reverses polarity with the pulsar period, forming a wind with oppositely directed field lines, called a striped wind. We study the conditions required for magnetic energy release at the termination shock of the striped pulsar wind. Magnetic reconnection is considered via analytical methods and 1D relativistic PIC simulations. An analytical condition on the upstream parameters for partial and full magnetic reconnection is derived from the conservation laws of energy, momentum and particle number density across the relativistic shock. Furthermore, by using a 1D relativistic PIC code, we study in detail the reconnection process at the termination shock for different upstream Lorentz factors and magnetizations, and find good agreement with our analytical criterion. Thus, alternating magnetic fields annihilate easily at relativistic highly magnetized shocks. We apply our criterion for dissipation to deduce bounds on the pair multiplicity, κ, in the pulsar wind.

The rudiments of a theory of solar wind/magnetosphere coupling derived from first principles

A formula that expresses the dayside reconnection rate in terms of upstream solar wind parameters is derived and tested. The derivation is based on the hypothesis that dayside reconnection is governed by local plasma parameters and that whatever controls those parameters controls the reconnection rate. The starting point of the derivation is the Cassak‐Shay formula (from energy conservation principles), which expresses the dayside reconnection rate in terms of four parameters: the magnetic field strengths Bm and Bs in the magnetosphere and magnetosheath and the plasma mass densities ρm and ρs in the magnetosphere and magnetosheath. Using the Rankine‐Hugoniot relations at the bow shock and an analysis of the magnetosheath flow, three of these parameters are expressed in terms of upstream solar wind parameters. These three expressions are then used in the Cassak‐Shay formula to obtain the “solar wind control function.” The interpretation of the control function is that solar wind pressure largely sets the reconnection rate. The solar wind magnetic field enters into the control function because of a bow shock Mach number dependence. The onset of a “plasmasphere effect” occurs when ρm > MA0.87ρsolarwind, wherein the magnetosphere begins to exert control over solar wind/magnetosphere coupling. Using the OMNI2 data set and seven geomagnetic indices, the solar wind control function is tested on its ability to describe the variance in the geomagnetic indices. The control function is found to be successful, statistically as good as the best “solar wind driver function” in the literature. This picture opens a new pathway to understanding and calculating solar wind/magnetosphere coupling.

Structure of fast shocks in the presence of heat conduction

There are three types of magnetohydrodynamic (MHD) shocks: the fast shock, intermediate shock, and slow shock. The structure of slow shocks and intermediate shocks in the presence of heat conduction has been studied earlier [C. L. Tsai, R. H. Tsai, B. H. Wu, and L. C. Lee, Phys. Plasmas 9, 1185 (2002); C. L. Tsai, B. H. Wu, and L. C. Lee, Phys. Plasmas 12, 82501 (2005)]. Based on one-dimensional MHD numerical simulations with a heat conduction term, the evolution and structure of fast shocks are studied. The fast shock will form a foreshock in the presence of heat conduction. The foreshock is formed due to the heat flow from downstream to upstream and located in the immediate upstream of the main shock. In the steady state, the value of diffusion velocity Vd in the foreshock is found to nearly equal the upstream convection velocity in the fast shock frame. It is found that the density jump across the main shock in high Mach number case can be much larger than 4 in the early simulation time. However the density jump will gradually evolve to a value smaller than 4 at steady state. By using the modified Rankine-Hugoniot relations with heat flux, the density jump across the fast shock is examined for various upstream parameters. The results show that the calculated density jump with heat flux is very close to the simulation value and the density jump can far exceed the maximum value of 4 without heat conduction. The structure of foreshock and main shock is also studied under different plasma parameters, such as the heat conductivity K0, the ratio of upstream plasma pressure to magnetic pressure β1, Alfvén Mach number MA1, and the angle θ1 between shock normal and magnetic field. It is found that as the upstream shock parameters K0, β1, and MA1 increase or θ1 decreases, the width of foreshock Ld increases. The present results can be applied to fast shocks in the solar corona, solar wind, and magnetosphere, in which the heat conduction effects are important.

Hybrid modelling the Pioneer Venus Orbiter magnetic field observations

This study presents comparisons between the Pioneer Venus Orbiter (PVO) magnetometer (OMAG) observations and the HYB-Venus hybrid simulation code. The comparisons are made near periapsides of four PVO orbits using the full resolution PVO/OMAG data. Also, the statistics of the solar wind and interplanetary magnetic field (IMF) conditions at Venus are studied using the PVO interplanetary dataset. The statistics include the histograms and the probability density maps of the selected upstream parameters. The confidence intervals derived from the upstream statistics demonstrate the nominal simulation input parameter space. Moreover, the probability density maps give the dependencies between the upstream parameters. The comparisons between the simulation code and the data along the spacecraft trajectory show that the basic, large scale, trends seen in the magnetic field can be understood by the current simulation runs. The discrepancies between the simulation and the data were found to arise at low altitudes close to the planetary ionosphere in the region which cannot be resolved in detail by the grid size of the runs.

A solar wind driven model of geosynchronous plasma moments

We describe a tabular specification model of the density and temperature of ions and electrons at geosynchronous orbit as a function of magnetic local time and solar wind parameters. This model can be used to provide boundary conditions for numerical ring current models. Unlike previous specification models of geosynchronous plasma moments, this model is parameterized by upstream solar wind conditions. We find that solar wind parameters are a better predictor of geosynchronous ion density than magnetospheric indices, and as upstream parameters they are often more appropriate as model inputs since they causally precede the model outputs. Of the upstream parameters that were tested, the best predictors of geosynchronous conditions were the solar wind flow pressure and the magnitude and Z-component of the interplanetary magnetic field.

Magnetic reconnection at the termination shock in a striped pulsar wind

Context. Most of the rotational luminosity of a pulsar is carried away by a relativistic magnetised wind in which the matter energy flux is negligible compared to the Poynting flux. However, observations of the Crab nebula for instance clearly indicate that most of the Poynting flux is eventually converted into ultra-relativistic particles. The mechanism responsible for transformation of the electro-magnetic energy into the particle energy remains poorly understood. Near the equatorial plane of an obliquely rotating pulsar magnetosphere, the magnetic field reverses polarity with the pulsar period, forming a wind with oppositely directed field lines. This structure is called a striped wind; dissipation of alternating fields in the striped wind is the object of our study. Aims. The aim of this paper is to study the conditions required for magnetic energy release at the termination shock of the striped pulsar wind. Magnetic reconnection is considered via analytical methods and 1D relativistic PIC simulations. Methods. An analytical condition on the upstream parameters for partial and full magnetic reconnection is derived from the conservation laws of energy, momentum and particle number density across the relativistic shock. Furthermore, by using a 1D relativistic PIC code, we study in detail the reconnection process at the termination shock for different upstream Lorentz factors and magnetisations. Results. We found a very simple criterion for dissipation of alternating fields at the termination shock, depending on the upstream parameters of the flow, namely, the magnetisation σ , the Larmor radius r B and the wavelength l of the striped wind. The model depends also on a free parameter $\xi>1$, which is the ratio of the current sheet width to the particle Larmor radius. It is found that for $\sigma \gg l / \xi \, r_{\rm B}$, all the Poynting flux is converted into particle energy whereas for $\sigma \ll (l / \xi \, r_{\rm B} )^{2/3}$, no dissipation occurs. In the latter case, the shock can be accurately described by the ideal MHD shock conditions. Finally, 1D relativistic PIC simulations confirm this prediction and enable us to fix the free parameter ξ in the analytical model. Conclusions. Alternating magnetic fields annihilate easily at relativistic highly magnetised shocks. In plerions, our condition for full magnetic dissipation is satisfied at the termination shock so that the Poynting flux may be converted into ultra-relativistic particles not in the pulsar wind but just at the termination shock. The constraints are more severe for the intra-binary shocks in double pulsar systems. Available models explaining observations require low magnetisation in the downstream flow. The condition that the magnetic field dissipates at the intra-binary shock implies an upper limit on the pair multiplicity in the pulsar wind κ . We found $\kappa \lesssim {\rm few} \times 10^4$ for PSR 1259-63 and PSR 1957+20. In the double pulsar PSR 0737-3039, the radio emission from the pulsar B is modulated with the period of the pulsar A, which implies that the striped structure is not erased completely; this gives a lower limit for $\kappa \gtrsim 310$.

Experimental investigations on different modes of headcut migration/ Investigations expérimentales sur différents modes de migration de headcut

Flume experiments were conducted to characterize the headcut erosion process on low bed slope landforms such as floodplain. Two different series of experiments were performed to investigate the headcut erosion and migration phenomenon both in homogeneous and heterogeneous non-cohesive soil. The flume bed was prepared with homogeneous coarse sand of uniform diameter for the first series and a composite fill of coarse sand and fine particles of polyvinyl chloride for the second series. Adhesive spray was applied on the top surface, which resisted the surface erosion and ensured the development of headcut. The effects of hydraulic and geometric conditions on headcut migration rate were analyzed. When all the detached sediments resulting from the erosion process were transported easily far downstream as wash load, then the overland flow rate and the headcut height governed the plunge-pool erosion process and the headcut migration rate as well (second series of experiments). In contrast, when the detached sediment resulting from the erosion process was transported as bed-material load, then the migration rate was governed not only by the upstream parameters but also by the downstream bed morphology (first series of experiments). The experimental results of both series showed that the shape of the plunge-pool remained unchanged with time for a given flow discharge. For a given flow rate and initial headcut-height, variable migration rate was observed in the first series of experiments, whereas the second series of experiments showed a constant migration rate. Conceptual models were proposed to explain the details of headcut migration process for both cases. In addition to overland flow rate and headcut height, the sediment transport capacity as well as the bed slope downstream of headcut was found to be a significant parameter that controlled the migration rate when the detached sediment was transported as bed-material load. The plunge-pool scour-rate that is governed by the overland flow rate, headcut-height and the properties of bed material controlled the migration rate when the detached sediment was transported as wash load. The migration rates calculated using conceptual models reasonably agreed with the experimental data for both cases.

Small-scale deformation of the bow shock

The prediction of the bow shock location is a proof of our understanding of the processes governing the solar wind – magnetosphere interaction. However, the models describing the bow shock location as a function of upstream parameters are based on a statistical processing of bow shock crossings observed by a single spacecraft. Such crossings locate the bow shock in motion, i.e., in a non-equilibrium state and this fact can be a source of significant errors. We have carefully analyzed a long interval of simultaneous observations of the bow shock and magnetopause and another interval of bow shock observations at two well-separated points. Our results suggest that often a small-scale deformation of the bow shock front due to magnetosheath fluctuations is the most appropriate interpretation of observations. Since the low-frequency magnetosheath variations exhibit largest amplitudes, a simultaneous bow shock displacement over a distance of 10–15 R E can be observed. We suggest that bow shock models can be probably improved if the tilt angle would be implemented as a parameter influencing the bow shock location in high latitudes.

Solar wind interaction with lunar crustal magnetic anomalies

Using Lunar Prospector data, we review the magnetic field and electron signatures of solar wind interaction with lunar crustal magnetic sources. Magnetic field amplifications, too large to represent direct measurements of crustal fields, appear in the solar wind over strong crustal sources, with the chance of observing these amplifications depending on upstream solar wind parameters. We often observe increases in low-energy (≲100 eV) electron energy fluxes simultaneously with large magnetic field amplifications, consistent with an increase in plasma density across a shock surface. We also often observe low frequency wave activity in the magnetic field data (both broadband turbulence and monochromatic waves), often associated with electron energization, sometimes up to keV energies. Electron energization appears to be correlated more closely with wave activity than with magnetic amplifications. Detailed studies of the interaction region will be necessary in order to understand the physics of the Moon–solar wind interaction. At present, the Moon represents the only natural laboratory available to us to study solar wind interaction with small-scale crustal magnetic fields, though simulation results and theoretical work can also help us understand the physical processes at work.

Effect of mass spectrometric sampling interface on the fundamental parameters of an inductively coupled plasma as a function of its operating conditions: Part II. Central-gas flow rate and sampling depth

The fundamental parameters of an inductively coupled plasma (ICP) were measured by means of Thomson and Rayleigh scattering to study the changes induced by the presence of a mass spectrometer (MS) sampling cone. The electron number density ( n e), electron temperature ( T e), and gas-kinetic temperature ( T g) upstream from the mass spectrometer sampler were followed while the central-gas flow rate and MS interface sampling depth were varied. The gas-kinetic temperature was found to decline at greater central-gas flow rates, an effect that was elevated in the presence of the MS interface. As the MS interface was brought closer to the ICP load coil, decreases in upstream plasma T g ensued. Overall, changes in the upstream fundamental parameters caused by the presence of the MS interface were found to depend on operating conditions.

Glycosylation of therapeutic proteins in different production systems

Glycosylation plays an important role in a number of therapeutic proteins, including monoclonal antibodies. The enzymatic activity of a therapeutic protein is mainly determined by the protein structure, whereas the pharmacokinetics, pharmacodistribution, solubility, stability, enhancement of effector function and receptor binding are all influenced by the carbohydrate moiety. Hyperglycosylated proteins show increased serum half-life, are less sensitive to proteolysis and more heat-stable compared with the non-glycosylated forms. Molecular engineering of the TNK-tissue plasminogen activator molecule results in a more complex type of glycosylation and increases the half-life of the protein, which allows a single bolus injection at a lower dose for the treatment of acute myocardial infarction. Antibody-dependent cell cytotoxicity (ADCC) is determined partially by the specific N-glycosylation of the Fc domain of the monoclonal antibody. Specific glycoforms of monoclonal antibodies, which interact solely with the FcgammaRIIIa receptor of natural killer cells, result in superior ADCC compared with heterogeneous glycoforms that interact with different Fc receptors. This demonstrates that glycoengineering for directed glycosylation of therapeutic proteins can improve the therapeutic effect. While the amino acid sequence of the therapeutic protein is determined by the nucleotide sequence of the inserted gene, glycosylation depends on the glycosylating enzymes in the endoplasmatic reticulum and the Golgi apparatus of the eukaryotic host cell. In addition, the glycosylation of the therapeutic protein is affected by the culture medium used, the efficiency of protein expression and the physiological status of the host cell. For a given protein, changes in the type of host cell, composition of the culture media and fermentation conditions during process development will most likely result in changes in the site occupation and heterogeneity of glycosylation. This, of course, can influence the therapeutic profile. Therefore, the early selection of the host cell and selection of upstream parameters are key in the process development of a product.

Spatially resolved spectroscopy of detached recombining plasmas in the University of Manchester Linear System divertor simulator

The University of Manchester Linear System (ULS) [M. G. Rusbridge et al., Plasma Phys. Controlled Fusion 42, 588 (2000)] is an experiment in which a steady-state plasma stream is confined along a longitudinal magnetic field. The plasma passes through a tapered orifice into a separate gas target chamber (GTC) where it interacts with neutral gas at pressures of up to 15mTorr. The upstream plasma beam is 6–14mm in diameter with electron temperatures between 2and15eV, and densities in the range of 1017–1019m−3. The primary aim of this study is to investigate physical processes relevant to gas target divertors in tokamaks. Upstream parameters, in terms of electron temperature and density, can be varied in the ULS enabling the investigation of electron-ion recombination (EIR) or molecular-activated recombination (MAR) processes. Detached recombining plasmas have been studied in the GTC using an axially scanning spectroscopic system with a spatial resolution of less than 5mm. We have investigated two distinct plasma regimes having the same electron temperature upstream, but upstream densities that differ by an order of magnitude. Vibrationally excited molecules, which are a necessary prerequisite for MAR, have been detected in both these cases. In the higher density case, which ultimately detaches via EIR processes, these excited molecules are present upstream of the EIR region.

A coupling function for solar wind effect on geomagnetic activity

From a simple theoretical consideration, we obtained two coupling functions linking upstream solar wind parameters to geomagnetic activity. We took into account (1) a scaling factor related to polar cap expansion while increasing the reconnected magnetic flux in the dayside magnetosphere, and (2) a modified Akasofu function for the reconnected flux for combined IMF Bz and By components. One of these coupling functions may be written as Fα = aVswByz1/2 sinα (θ/2), where Vsw is the solar wind speed, Byz is the magnitude of the IMF vector in the Y‐Z plane, θ is the clock angle between the Z axis and IMF vector in the Y‐Z plane, a is a coefficient, and the exponent, α, is derived from the experimental data and equals approximately to 2. The Fα function is proportional to the square root of Byz, which makes it significantly different from the coupling functions proposed earlier. Nevertheless, the statistical data analysis supports this dependence. For testing the found coupling function, we used the solar wind and IMF data for four years. We computed 2‐D diagrams showing the correlation coefficients for the dependence of the polar cap PC geomagnetic activity index on different combinations of solar wind/IMF parameters. The obtained diagrams showed very good agreement with the theoretical coupling function. The correlation coefficient for the dependence of the PC index on the coupling function is about 0.8–0.85, which is significantly higher that that for other commonly used coupling functions for the same time intervals.

Plasma Morphology at Mars. Aspera-3 Observations

A total of about of 400 orbits during the first year of the ASPERA-3 operation onboard the Mars Express spacecraft were analyzed to obtain a statistical pattern of the main plasma domains in the Martian space environment. The environment is controlled by the direct interaction between the solar wind and the planetary exosphere/ionosphere which results in the formation of the magnetospheric cavity. Ionospheric plasma was traced by the characteristic “spectral lines” of photoelectrons that make it possible to detect an ionospheric component even far from the planet. Plasma of solar wind and planetary origin was distinguished by the ion mass spectrometry. Several different regions, namely, boundary layer/mantle, plasma sheet, region with ionospheric photoelectrons, ray-like structures near the wake boundary were identified. Upstream parameters like solar wind ram pressure and the direction of the interplanetary electric field were inferred as proxy from the Mars Global Surveyor magnetic field data at a reference point of the magnetic pile up region in the northern dayside hemisphere. It is shown that morphology and dynamics of the main plasma domains and their boundaries are governed by these factors as well as by local crustal magnetizations which add complexity and variability to the plasma and magnetic field environment.