Effective viscosity of non-gravitactic Chlamydomonas Reinhardtii microswimmer suspensions

Active microswimmers are known to affect the macroscopic viscosity of suspensions in a more complex manner than passive particles. For puller-like microswimmers an increase in the viscosity has been observed. It has been suggested that the persistence of the orientation of the microswimmers hinders the rotation that is normally caused by the vorticity. It was previously shown that some sorts of algaes are bottom-heavy swimmers, i.e. their centre of mass is not located in the centre of the body. In this way, the algae affects the vorticity of the flow when it is perpendicular oriented to the axis of gravity. This orientation of gravity to vorticity is given in a rheometer that is equipped with a cone-plate geometry. Here we present measurements of the viscosity both in a cone-plate and a Taylor-Couette cell. The two set-ups yielded the same increase in viscosity although the axis of gravitation in the Taylor-Couette cell is parallel to the direction of vorticity. In a complementary experiment we tested the orientation of the direction of swimming through microscopic observation of single \textit{Chlamydomonas reinhardtii} and could not identify a preferred orientation, i. e. our specific strain of \textit{Chlamydomonas reinhardtii} are not bottom-heavy swimmers. We thus conclude that bottom heaviness is not a prerequisite for the increase of viscosity and that the effect of gravity on the rheology of our strain of \textit{Chlamydomonas reinhardtii} is negligible. This finding reopens the question of whether origin of persistence in the orientation of cells is actually responsible for the increased viscosity of the suspension

An original stepwise multilevel logistic regression analysis of discriminatory accuracy:The case of neighbourhoods and health

Background and Aim Many multilevel logistic regression analyses of "neighbourhood and health" focus on interpreting measures of associations (e.g., odds ratio, OR). In contrast, multilevel analysis of variance is rarely considered. We propose an original stepwise analytical approach that distinguishes between "specific" (measures of association) and "general" (measures of variance) contextual effects. Performing two empirical examples we illustrate the methodology, interpret the results and discuss the implications of this kind of analysis in public health. Methods We analyse 43,291 individuals residing in 218 neighbourhoods in the city of Malm, Sweden in 2006. We study two individual outcomes (psychotropic drug use and choice of private vs. public general practitioner, GP) for which the relative importance of neighbourhood as a source of individual variation differs substantially. In Step 1 of the analysis, we evaluate the OR and the area under the receiver operating characteristic (AUC) curve for individual-level covariates (i.e., age, sex and individual low income). In Step 2, we assess general contextual effects using the AUC. Finally, in Step 3 the OR for a specific neighbourhood characteristic (i.e., neighbourhood income) is interpreted jointly with the proportional change in variance (i.e., PCV) and the proportion of ORs in the opposite direction (POOR) statistics. Results For both outcomes, information on individual characteristics (Step 1) provide a low discriminatory accuracy (AUC = 0.616 for psychotropic drugs; = 0.600 for choosing a private GP). Accounting for neighbourhood of residence (Step 2) only improved the AUC for choosing a private GP (+0.295 units). High neighbourhood income (Step 3) was strongly associated to choosing a private GP (OR = 3.50) but the PCV was only 11% and the POOR 33%. Conclusion Applying an innovative stepwise multilevel analysis, we observed that, in Malmo, the neighbourhood context per se had a negligible influence on individual use of psychotropic drugs, but appears to strongly condition individual choice of a private GP. However, the latter was only modestly explained by the socioeconomic circumstances of the neighbourhoods. Our analyses are based on real data and provide useful information for understanding neighbourhood level influences in general and on individual use of psychotropic drugs and choice of GP in particular. However, our primary aim is to illustrate how to perform and interpret a multilevel analysis of individual heterogeneity in social epidemiology and public health. Our study shows that neighbourhood "effects" are not properly quantified by reporting differences between neighbourhood averages but rather by measuring the share of the individual heterogeneity that exists at the neighbourhood level

On the Epidemiology of Soft Tissue Sarcoma and Risk of Cancer following Knee prosthesis surgery. Important factors and methodological notes

Den aktuella avhandlingen härrör ur forskningsinsatser inom klinikerna för onkologi och ortopedi vid Universitetssjukhuset i Lund, och behandlar vad som ursprungligen verkade vara två skilda ämnen.Ena ämnet behandlar epidemiologin för mjukdelssarkom hos vuxna (MDS), en grupp av ofta dödliga sjukdomar av okänd orsak, som behandlas av både onkologer och ortopeder. Här har den historiska oförmågan att kartlägga etiologin för dessa tumörer resulterat i en brist på förebyggande åtgärder med en betydande förlust av levnadsår som följd. I det här avhandlingsarbetet studerar vi faktorer förknippade med kroppskonstitution, reproduktiva händelser, ärftlighet och vävnadstrauma.Det andra ämnet behandlar risken för cancer efter knäproteskirurgi, en oro bland ortopedforskare och en viktig folkhälsofråga, då antalet proteser stadigt ökar, inte minst hos yngre patienter.Dessa två ämnen har visat sig vara relaterade då mjukdelstumörer har identifierats i anslutning till protesimplantat, vilket fört med sig att kunskap kring riskfaktorer för MDS potentiellt skulle kunna ge ledtrådar om carcinogena effekter hos protesimplantat och dess associerade faktorer, så som underliggande sjukdom och behandling.I studien av båda ämnena, arbetar vi med några av världens största och mest detaljerade studiepopulationer. En är en populationsbaserad fall-kontrollstudie med alla fall av MDS från södra sjukvårdsregionen mellan åren 1998 och 2009, vilket inkluderar nästan 1000 fall. En annan är Svenska Knäprotesregistret, världens äldsta register i sitt slag, som inkluderar alla opererade patienter från 1975 till nutid.Vi fann att 57% av MDS-fallen, och 74% av de MDS-fall som uppstod i extremiteter, i vår studiekohort kunde tillskrivas faktorer relaterade till kroppskonstitution och reproduktiva händelser, ärftlighet och vävnadstrauma. Vi finner också ett överskott av MDS-tumörer i knäproteskohorten, tillsammans med ett lågt, men statistiskt signifikant, överskott av mer vanliga cancerformer. Dessa inkluderade prostata cancer, malignt melanom och hematologiska maligniteter. Med tanke på förekomsten av MDS, drar vi slutsatsen att vävnadstrauma kan vara en bidragande faktor i till den ökade cancerrisken.Även om dessa ämnen i sig är viktiga, presenterar de också en rad intressanta utmaningar när det gäller epidemiologisk och statistisk metodik. Till exempel utgör studiet av MDS, som en heterogen grupp av sällsynta tumörsjukdomar med potentiellt skilda etiologier, problem i termer av subgruppsanalyser samt justering för multipla störfaktorer i små studier. Den sällsynta sjukdomen leder också till svårigheter att utreda effekten av ärftlighet, då etablerade analysmetoder för detta inte på ett enkelt sätt går att förena med den etablerade studiedesign som ofta används i dessa fall. Studien av proteskirurgirelaterad cancer inkluderar utmaningar i att skilja mellan kausala effekter och den bias som uppstår när sjukhuspatienter undersöks på grund av sin sjukdom och cancerdiagnoser uppkommer som ett bifynd

Bacterial colonization and resistance patterns in 133 patients undergoing a primary hip- or knee replacement in Southern Sweden.

Background and purpose Prosthetic joint infections can be caused by bacteria derived from the patient's skin. The aim of the study was: (1) to determine which bacteria colonize the nose and groin in patients planned for primary hip or knee arthroplasty, (2) to determine the antimicrobial resistance patterns, and (3) to monitor changes in bacterial colonization and resistance patterns connected to surgery. Patients and methods 2 weeks before scheduled primary hip or knee arthroplasty, culture samples were taken from the anterior nares and from the groin of 133 consecutive patients. At surgery, cloxacillin was given prophylactically and cement with gentamicin was used. 2 weeks after surgery, another set of samples were taken from 120 of these patients. Bacterial findings and resistance patterns were analyzed. Results Preoperatively, 95% of the patients had coagulase-negative staphylococci (CNS) in the groin and 77% in the nose. The proportion of patients with a methicillin-resistant CNS in the groin increased from 20% preoperatively to 50% postoperatively (p < 0.001), and the proportion of patients with a gentamicin-resistant CNS in the groin increased from 5% to 45% (p < 0.001). 28% of the patients had Staphylococcus aureus in the nose preoperatively, and 7% in the groin. Methicillin-resistant Staphylococcus aureus (MRSA) was found in the nose of 1 patient. Interpretation In southern Sweden, beta-lactams were effective against 99% of the Staphylococcus aureus strains and 80% of the CNS strains colonizing the patients undergoing primary hip or knee arthroplasty. Gentamicin protects against most CNS strains in cemented primary joint replacements

Who Should Do NOTES? Initial Endoscopic Performance of Laparoscopic Surgeons Compared to Gastroenterologists and Untrained Individuals

Introduction: Natural orifice transluminal endoscopic surgery (NOTES) is a multidisciplinary surgical technique. If conventional endoscopic instrumentation can be easily mastered, surgeons with laparoscopic experience could head NOTES interventions. Materials and Methods: Thirty individuals were tested for endoscopic dexterity. Group 1 included seven gastroenterologists, group 2 included 12 laparoscopically experienced surgeons lacking endoscopic experience, and group 3 included 11 interns who had no hands-on endoscopic or surgical experience. Each individual repeated an easy (T1), medium (T2), and difficult (T3) task ten times with endoscopic equipment on a NOTES skills-box. Results: Group 3 had significantly poorer performances for all three tasks compared to the other groups. No significant differences were seen between groups 1 and 2 for T1 and T2. The initial T3 performance of group 1 was better than that of group 2, but their performance after repetition was not statistically different. Groups 2 and 3 improved significantly with repetition, and group 2 eventually performed as well as group 1. Conclusions: The data indicate that laparoscopic surgeons quickly learned to handle the endoscopic equipment. This suggests that a lack of endoscopic experience does not handicap laparoscopic surgeons when performing endoscopic tasks. Based on their knowledge of anatomy and the complication management acquired during surgical education, surgeons are well equipped to take the lead in interdisciplinary NOTES collaboration

Kaon and D meson masses with Nf = 2+1+1 twisted mass lattice QCD

We discuss the computation of the kaon and D meson masses in the Nf = 2+1+1 twisted mass lattice QCD setup, where explicit heavy flavor and parity breaking occurs at finite lattice spacing. We present three methods suitable in this context and verify their consistency

In Vitro Red Blood Cell Segregation in Sickle Cell Anemia

Red blood cells in sickle cell anemia (sRBC) are more heterogeneous in their physical properties than healthy red blood cells, spanning adhesiveness, rigidity, density, size, and shape. sRBC with increased adhesiveness to the vascular wall would trigger vaso-occlusive like complications, a hallmark of sickle cell anemia. We investigated whether segregation occurs among sRBC flowing in micron-sized channels and tested the impact of aggregation on segregation. Two populations of sRBC of different densities were separated, labeled, and mixed again. The mixed suspension was flowed within glass capillary tubes at different pressure-drops, hematocrit, and suspending media that promoted or not cell aggregation. Observations were made at a fixed channel position. The mean flow velocity was obtained by using the cells as tracking particles, and the cell depleted layer (CDL) by measuring the distance from the cell core border to the channel wall. The labeled sRBC were identified by stopping the flow and scanning the cells within the channel section. The tube hematocrit was estimated from the number of fluorescence cells identified in the field of view. In non-aggregating media, our results showed a heterogeneous distribution of sRBC according to their density: low-density sRBC population remained closer to the center of the channel, while the densest cells segregated towards the walls. There was no impact of the mean flow velocity and little impact of hematocrit. This segregation heterogeneity could influence the ability of sRBC to adhere to the vascular wall and slow down blood flow. However, promoting aggregation inhibited segregation while CDL thickness was enhanced by aggregation, highlighting a potential protective role against vaso-occlusion in patients with sickle cell anemia

Metal-on-metal joint bearings and hematopoetic malignancy.

To access publisher's full text version of this article. Please click on the hyperlink in Additional Links field.This is a review of the hip arthroplasty era. We concentrate on new metal bearings, surface replacements, and the lessons not learned, and we highlight recent reports on malignancies and joint implants. A low incidence of blood malignancies has been found in bone marrow taken at prosthetic surgery. The incidence is increased after replacement with knee implants that release very low systemic levels of metal ions. A carcinogenic effect of the high levels of metal ions released by large metal-on-metal implants cannot be excluded. Ongoing Swedish implant registry studies going back to 1975 can serve as a basis for evaluation of this risk.Swedish Association of Local Authorities and Regions Faculty of Medicine, Lund University Stiftelsen for Bistand at Rorelsehindrade i Skane Region Skan