Smooth Solutions to Portfolio Liquidation Problems under Price-Sensitive Market Impact

International audienceWe consider the stochastic control problem of a financial trader that needs to unwind a large asset portfolio within a short period of time. The trader can simultaneously submit active orders to a primary market and passive orders to a dark pool. Our framework is flexible enough to allow for price-dependent impact functions describing the trading costs in the primary market and price-dependent adverse selection costs associated with dark pool trading. We prove that the value function can be characterized in terms of the unique smooth solution to a PDE with singular terminal value, establish its explicit asymptotic behavior at the terminal time, and give the optimal trading strategy in feedback form

Chronicle of a death foretold: Plasmodium liver stage parasites decide on the fate of the host cell

Protozoan parasites of the genus Plasmodium are the causative agents of malaria. Despite more than 100years of research, the complex life cycle of the parasite still bears many surprises and it is safe to say that understanding the biology of the pathogen will keep scientists busy for many years to come. Malaria research has mainly concentrated on the pathological blood stage of Plasmodium parasites, leaving us with many questions concerning parasite development within the mosquito and during the exo-erythrocytic stage in the vertebrate host. After the discovery of the Plasmodium liver stage in the middle of the last century, it remained understudied for many years but the realization that it represents a promising target for vaccination approaches has brought it back into focus. The last decade saw many new and exciting discoveries concerning the exo-erythrocytic stage and in this review we will discuss the highlights of the latest developments in the field. During the last decade many surprising facts about exoerythrocytic development of Plasmodium parasites have been revealed and will be discusse

Stimulus Dependency of Object-Evoked Responses in Human Visual Cortex: An Inverse Problem for Category Specificity

Many studies have linked the processing of different object categories to specific event-related potentials (ERPs) such as the face-specific N170. Despite reports showing that object-related ERPs are influenced by visual stimulus features, there is consensus that these components primarily reflect categorical aspects of the stimuli. Here, we re-investigated this idea by systematically measuring the effects of visual feature manipulations on ERP responses elicited by both structure-from-motion (SFM)-defined and luminance-defined object stimuli. SFM objects elicited a novel component at 200–250 ms (N250) over parietal and posterior temporal sites. We found, however, that the N250 amplitude was unaffected by restructuring SFM stimuli into meaningless objects based on identical visual cues. This suggests that this N250 peak was not uniquely linked to categorical aspects of the objects, but is strongly determined by visual stimulus features. We provide strong support for this hypothesis by parametrically manipulating the depth range of both SFM- and luminance-defined object stimuli and showing that the N250 evoked by SFM stimuli as well as the well-known N170 to static faces were sensitive to this manipulation. Importantly, this effect could not be attributed to compromised object categorization in low depth stimuli, confirming a strong impact of visual stimulus features on object-related ERP signals. As ERP components linked with visual categorical object perception are likely determined by multiple stimulus features, this creates an interesting inverse problem when deriving specific perceptual processes from variations in ERP components

Cyanobacteria net community production in the Baltic Sea as inferred from profiling pCO(2) measurements

Organic matter production by cyanobacteria blooms is a major environmental concern for the Baltic Sea, as it promotes the spread of anoxic zones. Partial pressure of carbon dioxide (pCO(2)) measurements carried out on Ships of Opportunity (SOOP) since 2003 have proven to be a powerful tool to resolve the carbon dynamics of the blooms in space and time. However, SOOP measurements lack the possibility to directly constrain depth-integrated net community production (NCP) in moles of carbon per surface area due to their restriction to the sea surface. This study tackles the knowledge gap through (1) providing an NCP best guess for an individual cyanobacteria bloom based on repeated profiling measurements of pCO(2) and (2) establishing an algorithm to accurately reconstruct depth-integrated NCP from surface pCO(2) observations in combination with modelled temperature profiles.Goal (1) was achieved by deploying state-of-the-art sensor technology from a small-scale sailing vessel. The low-cost and flexible platform enabled observations covering an entire bloom event that occurred in July-August 2018 in the Eastern Gotland Sea. For the biogeochemical interpretation, recorded pCO(2) profiles were converted to C-T*, which is the dissolved inorganic carbon concentration normalised to alkalinity. We found that the investigated bloom event was dominated by Nodularia and had many biogeochemical characteristics in common with blooms in previous years. In particular, it lasted for about 3 weeks, caused a C-T* drawdown of 90 mu mol kg(-1), and was accompanied by a sea surface temperature increase of 10 degrees C. The novel finding of this study is the vertical extension of the C-T* drawdown up to the compensation depth located at around 12 m. Integration of the C-T* drawdown across this depth and correction for vertical fluxes leads to an NCP best guess of similar to 1:2 mol m(-2) over the productive period.Addressing goal (2), we combined modelled hydrographical profiles with surface pCO(2) observations recorded by SOOP Finnmaid within the study area. Introducing the temperature penetration depth (TPD) as a new parameter to integrate SOOP observations across depth, we achieve an NCP reconstruction that agrees to the best guess within 10 %, which is considerably better than the reconstruction based on a classical mixed-layer depth constraint.Applying the TPD approach to almost 2 decades of surface pCO(2) observations available for the Baltic Sea bears the potential to provide new insights into the control and long-term trends of cyanobacteria NCP. This understanding is key for an effective design and monitoring of conservation measures aiming at a Good Environmental Status of the Baltic Sea

Activation of a PAK-MEK signalling pathway in malaria parasite-infected erythrocytes

Merozoites of malaria parasites invade red blood cells (RBCs), where they multiply by schizogony, undergoing development through ring, trophozoite and schizont stages that are responsible for malaria pathogenesis. Here, we report that a protein kinase-mediated signalling pathway involving host RBC PAK1 and MEK1, which do not have orthologues in the Plasmodium kinome, is selectively stimulated in Plasmodium falciparum-infected (versus uninfected) RBCs, as determined by the use of phospho-specific antibodies directed against the activated forms of these enzymes. Pharmacological interference with host MEK and PAK function using highly specific allosteric inhibitors in their known cellular IC50 ranges results in parasite death. Furthermore, MEK inhibitors have parasiticidal effects in vitro on hepatocyte and erythrocyte stages of the rodent malaria parasite Plasmodium berghei, indicating conservation of this subversive strategy in malaria parasites. These findings have profound implications for the development of novel strategies for antimalarial chemotherapy

Improving the Longevity and Results of Mastopexy and Breast Reduction Procedures: Reconstructing an Internal Breast Support System with Biocompatible Mesh to Replace the Supporting Function of the Ligamentous Suspension

The original publication is available at http://www.springerlink.com/Publication of this article was funded by the Stellenbosch University Open Access Fund.The reasons for recurrent ptosis in mastopexy and breast reduction procedures are twofold. First, available surgical techniques do not reconstruct the normal breast anatomy responsible for maintaining breast shape. Second, in many instances the techniques rely on atrophied tissue to provide long-term support. The discovery in 1997 of the ligamentous suspension (the supporting system of the breast) gave rise to the concept that reconstruction of this anatomical structure was needed to ensure a sustained postoperative result. Applying the latest knowledge regarding the structural and vascular anatomy of the breast in the surgical technique and utilizing material other than atrophied breast tissue enabled us to prevent the recurrence of breast ptosis. Methods A surgical technique was developed to replace the supportive function of a failed ligamentous suspension in 112 patients with ptotic breasts. This was done by reconstructing an internal breast-supporting system (IBSS) with biocompatible mesh. Results Satisfactory breast shape, nipple projection, and upper breast fullness was obtained with this technique in mastopexy patients with moderate-sized ptotic breasts. In patients with larger breasts good results were obtained with a simultaneous breast reduction. The longest follow-up is 6 years 3 months. Conclusions With this technique recurrent breast ptosis can be prevented in mastopexy and breast reduction procedures. The results are such that it eliminates the need for silicone prostheses to obtain satisfactory upper-breast fullness. The surgical technique is especially indicated in patients with skin of poor quality or patients with high expectations.Stellenbosch University Open Access FundPublishers' Versio