Inner magnetospheric plasma interactions and coupling with the ionosphere

The inner magnetosphere occupies a vast volume in space containing a relatively low-density mixture of hot and cold plasmas: the ring current, plasmasphere and radiation belt. Energy is transferred from the ring current to the cold plasmas through Coulomb collisions and wave-particle interactions, producing temperature enhancements in the plasmasphere. The plasma waves generated in the plasmasphere cause pitch-angle and energy diffusion of the energetic particles. The magnetic disturbances generated from the ring current alter the drift paths of radiation belt particles, causing radiation belt flux dropout during magnetic storm main phases. The ionosphere is filled with dense and cold plasmas in a 1000-km-thick shell above the Earth\u27s surface at ～100km altitude. Despite the distinct differences in size, location and physical properties, the ionosphere and the inner magnetosphere are tightly connected to each other. The ionosphere is an important source of magnetospheric ions. Energy transported down from the inner magnetosphere to the ionosphere produces observable temperature enhancements and optical emissions in the ionosphere. The electric coupling between the ionosphere and magnetosphere explains features such as shielding field, non-linear response of the ring current to the plasma-sheet source, and the post-midnight enhancement of the storm-time ring current flux. Even though many signatures are well described from the perspective of magnetosphere-ionosphere coupling, there are still unanswered questions, for example, the precise roles of wave-particle interactions in ring current loss and plasmaspheric heating, the cause of rapid storm initial recovery, the source of O^+ enhancement at substorm expansion, and the causes of outer radiation belt enhancement during storm recovery. The unresolved questions can be answered through careful cross analysis of the observational data from the ongoing and future imaging and multi-point missions with simulation results of large-scale modeling

"Counting Your Customers": When will they buy next? An empirical validation of probabilistic customer base analysis models based on purchase timing

This research provides a new way to validate and compare buy-till-you-defect [BTYD] models. These models specify a customer’s transaction and defection processes in a non-contractual setting. They are typically used to identify active customers in a com- pany’s customer base and to predict the number of purchases. Surprisingly, the literature shows that models with quite different assumptions tend to have a similar predictive performance. We show that BTYD models can also be used to predict the timing of the next purchase. Such predictions are managerially relevant as they enable managers to choose appropriate promotion strategies to improve revenues. Moreover, the predictive performance on the purchase timing can be more informative on the relative quality of BTYD models. For each of the established models, we discuss the prediction of the purchase timing. Next, we compare these models across three datasets on the predictive performance on the purchase timing as well as purchase frequency. We show that while the Pareto/NBD and its Hierarchical Bayes extension [HB] models perform the best in predicting transaction frequency, the PDO and HB models predict transaction timing more accurately. Furthermore, we find that differences in a model’s predictive performance across datasets can be explained by the correlation between behavioral parameters and the proportion of customers without repeat purchases

The Need for Market Segmentation in Buy-Till-You-Defect Models

Buy-till-you-defect [BTYD] models are built for companies operating in a non- contractual setting to predict customers’ transaction frequency, amount and timing as well as customer lifetime. These models tend to perform well, although they often predict unrealistically long lifetimes for a substantial fraction of the customer base. This obvious lack of face validity limits the adoption of these models by practitioners. Moreover, it highlights a flaw in these models. Based on a simulation study and an empirical analysis of different datasets, we argue that such long lifetime predictions can result from the existence of multiple segments in the customer base. In most cases there are at least two segments: one consisting of customers who purchase the service or product only a few times and the other of those who are frequent purchasers. Customer heterogeneity modeling in the current BTYD models is insufficient to account for such segments, thereby producing unrealistic lifetime predictions. We present an extension over the current BTYD models to address the extreme lifetime prediction issue where we allow for segments within the customer base. More specifically, we consider a mixture of log-normals distribution to capture the heterogeneity across customers. Our model can be seen as a variant of the hierarchical Bayes [HB] Pareto/NBD model. In addition, the proposed model allows us to relate segment membership as well as within segment customer heterogeneity to selected customer characteristics. Our model, therefore, also increases the explanatory power of BTYD models to a great extent. We are now able to evaluate the impact of customers’ characteristics on the membership probabilities of different segments. This allows, for example, one to a-priori predict which customers are likely to become frequent purchasers. The proposed model is compared against the benchmark Pareto/NBD model (Schmittlein, Morrison, and Colombo 1987) and its HB extension (Abe 2009) on simulated datasets as well as on a real dataset from a large grocery e-retailer in a Western European country. Our BTYD model indeed provides a useful customer segmentation that allows managers to draw conclusions on how customers’ purchase and defection behavior are associated with their shopping characteristics such as basket size and the delivery fee paid

Dynamic Boundaries in Asymmetric Exclusion Processes

We investigate the dynamics of a one-dimensional asymmetric exclusion process with Langmuir kinetics and a fluctuating wall. At the left boundary, particles are injected onto the lattice; from there, the particles hop to the right. Along the lattice, particles can adsorb or desorb, and the right boundary is defined by a wall particle. The confining wall particle has intrinsic forward and backward hopping, a net leftward drift, and cannot desorb. Performing Monte Carlo simulations and using a moving-frame finite segment approach coupled to mean field theory, we find the parameter regimes in which the wall acquires a steady state position. In other regimes, the wall will either drift to the left and fall off the lattice at the injection site, or drift indefinitely to the right. Our results are discussed in the context of non-equilibrium phases of the system, fluctuating boundary layers, and particle densities in the lab frame versus the frame of the fluctuating wall.Comment: 13 page

Digital PCR on a SlipChip

This paper describes a SlipChip to perform digital PCR in a very simple and inexpensive format. The fluidic path for introducing the sample combined with the PCR mixture was formed using elongated wells in the two plates of the SlipChip designed to overlap during sample loading. This fluidic path was broken up by simple slipping of the two plates that removed the overlap among wells and brought each well in contact with a reservoir preloaded with oil to generate 1280 reaction compartments (2.6 nL each) simultaneously. After thermal cycling, end-point fluorescence intensity was used to detect the presence of nucleic acid. Digital PCR on the SlipChip was tested quantitatively by using Staphylococcus aureus genomic DNA. As the concentration of the template DNA in the reaction mixture was diluted, the fraction of positive wells decreased as expected from the statistical analysis. No cross-contamination was observed during the experiments. At the extremes of the dynamic range of digital PCR the standard confidence interval determined using a normal approximation of the binomial distribution is not satisfactory. Therefore, statistical analysis based on the score method was used to establish these confidence intervals. The SlipChip provides a simple strategy to count nucleic acids by using PCR. It may find applications in research applications such as single cell analysis, prenatal diagnostics, and point-of-care diagnostics. SlipChip would become valuable for diagnostics, including applications in resource-limited areas after integration with isothermal nucleic acid amplification technologies and visual readout

Magnetic Flux Circulation During Dawn-Dusk Oriented Interplanetary Magnetic Field

Magnetic flux circulation is a primary mode of energy transfer from the solar wind into the ionosphere and inner magnetosphere. For southward interplanetary magnetic field (IMF), magnetic flux circulation is described by the Dungey cycle (dayside merging, night side reconnection, and magnetospheric convection), and both the ionosphere and inner magnetosphere receive energy. For dawn-dusk oriented IMF, magnetic flux circulation is not well understood, and the inner magnetosphere does not receive energy. Several models have been suggested for possible reconnection patterns; the general pattern is: dayside merging; reconnection on the dayside or along the dawn/dusk regions; and, return flow on dayside only. These models are consistent with the lack of energy in the inner magnetosphere. We will present evidence that the Dungey cycle does not explain the energy transfer during dawn-dusk oriented IMF. We will also present evidence of how magnetic flux does circulate during dawn-dusk oriented IMF, specifically how the magnetic flux reconnects and circulates back

GPU-based Approaches for Multiobjective Local Search Algorithms. A Case Study: the Flowshop Scheduling Problem

International audienceMultiobjective local search algorithms are efficient methods to solve complex problems in science and industry. Even if these heuristics allow to significantly reduce the computational time of the solution search space exploration, this latter cost remains exorbitant when very large problem instances are to be solved. As a result, the use of GPU computing has been recently revealed as an efficient way to accelerate the search process. This paper presents a new methodology to design and implement efficiently GPU-based multiobjective local search algorithms. The experimental results show that the approach is promising especially for large problem instances

Exponential Distribution of Locomotion Activity in Cell Cultures

In vitro velocities of several cell types have been measured using computer controlled video microscopy, which allowed to record the cells' trajectories over several days. On the basis of our large data sets we show that the locomotion activity displays a universal exponential distribution. Thus, motion resulting from complex cellular processes can be well described by an unexpected, but very simple distribution function. A simple phenomenological model based on the interaction of various cellular processes and finite ATP production rate is proposed to explain these experimental results.Comment: 4 pages, 3 figure

Global Response to Local Ionospheric Mass Ejection

We revisit a reported "Ionospheric Mass Ejection" using prior event observations to guide a global simulation of local ionospheric outflows, global magnetospheric circulation, and plasma sheet pressurization, and comparing our results with the observed global response. Our simulation framework is based on test particle motions in the Lyon-Fedder-Mobarry (LFM) global circulation model electromagnetic fields. The inner magnetosphere is simulated with the Comprehensive Ring Current Model (CRCM) of Fok and Wolf, driven by the transpolar potential developed by the LFM magnetosphere, and includes an embedded plasmaspheric simulation. Global circulation is stimulated using the observed solar wind conditions for the period 24-25 Sept 1998. This period begins with the arrival of a Coronal Mass Ejection, initially with northward, but later with southward interplanetary magnetic field. Test particles are launched from the ionosphere with fluxes specified by local empirical relationships of outflow to electrodynamic and particle precipitation imposed by the MIlD simulation. Particles are tracked until they are lost from the system downstream or into the atmosphere, using the full equations of motion. Results are compared with the observed ring current and a simulation of polar and auroral wind outflows driven globally by solar wind dynamic pressure. We find good quantitative agreement with the observed ring current, and reasonable qualitative agreement with earlier simulation results, suggesting that the solar wind driven global simulation generates realistic energy dissipation in the ionosphere and that the Strangeway relations provide a realistic local outflow description

Simultaneous observations of the cusp with IMAGE Low Energy Neutral Atom Imager and SuperDARN radar

The Low Energy Neutral Atom (LENA) imager on the IMAGE spacecraft observed significant emission in the high-latitude magnetosheath direction during an extreme solar wind condition on April 11, 2001. The emission was modulated in such a manner that the sources shifted equatorward in the high-latitude sheath while sometimes undergoing brief poleward returns. This modulation and the IMF BZ tend to have correlative variations. During this interval of interest, SuperDARN was receiving strong backscattered signals from large potions of the dayside ionosphere. This observation indicates that the equatorward motion of the cusp latitude consists of rapid and slow phases. This kind of equatorward shift appears to correlate with the motion of the emission observed by LENA in the direction of the high-latitude sheath, which gives evidence for a means for monitoring the high-altitude cusp using IMAGE/LENA. It thus appears that the two remote sensing observations, i.e., IMAGE/LENA and SuperDARN radar would provide promising opportunities to understand the detailed dynamics of the polar cusp extending from the low-altitudes to the high-altitudes