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Search Results: 1 - 10 of 308 matches for " Sten Sarman "
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Local order variations in confined hard-sphere fluids
Kim Nyg?rd,Sten Sarman,Roland Kjellander
Physics , 2013, DOI: 10.1063/1.4825176
Abstract: Pair distributions of fluids confined between two surfaces at close distance are of fundamental importance for a variety of physical, chemical, and biological phenomena, such as interactions between macromolecules in solution, surface forces, and diffusion in narrow pores. However, in contrast to bulk fluids, properties of inhomogeneous fluids are seldom studied at the pair-distribution level. Motivated by recent experimental advances in determining anisotropic structure factors of confined fluids, we analyze theoretically the underlying anisotropic pair distributions of the archetypical hard-sphere fluid confined between two parallel hard surfaces using first-principles statistical mechanics of inhomogeneous fluids. For this purpose, we introduce an experimentally accessible ensemble-averaged local density correlation function and study its behavior as a function of confining slit width. Upon increasing the distance between the confining surfaces, we observe an alternating sequence of strongly anisotropic versus more isotropic local order. The latter is due to packing frustration of the spherical particles. This observation highlights the importance of studying inhomogeneous fluids at the pair-distribution level.
Packing frustration in dense confined fluids
Kim Nyg?rd,Sten Sarman,Roland Kjellander
Physics , 2014, DOI: 10.1063/1.4894137
Abstract: Packing frustration for confined fluids, i.e., the incompatibility between the preferred packing of the fluid particles and the packing constraints imposed by the confining surfaces, is studied for a dense hard-sphere fluid confined between planar hard surfaces at short separations. The detailed mechanism for the frustration is investigated via an analysis of the anisotropic pair distributions of the confined fluid, as obtained from integral equation theory for inhomogeneous fluids at pair correlation level within the anisotropic Percus-Yevick approximation. By examining the mean forces that arise from interparticle collisions around the periphery of each particle in the slit, we calculate the principal components of the mean force for the density profile - each component being the sum of collisional forces on a particle's hemisphere facing either surface. The variations of these components with the slit width give rise to rather intricate changes in the layer structure between the surfaces, but, as shown in this paper, the basis of these variations can be easily understood qualitatively and often also semi-quantitatively. It is found that the ordering of the fluid is in essence governed locally by the packing constraints at each single solid-fluid interface. A simple superposition of forces due to the presence of each surface gives surprisingly good estimates of the density profiles, but there remain nontrivial confinement effects that cannot be explained by superposition, most notably the magnitude of the excess adsorption of particles in the slit relative to bulk.
Formation of a Columnar Liquid Crystal in a Simple One-Component System of Particles
Alfredo Metere,Tomas Oppelstrup,Sten Sarman,Mikhail Dzugutov
Physics , 2014,
Abstract: We report a molecular dynamics simulation demonstrating that a columnar liquid crystal, commonly formed by disc-shaped molecules, can be formed by identical particles interacting via a spherically symmetric potential. Upon isochoric cooling from a low-density isotropic liquid state the simulated system performed a weak first order phase transition which produced a liquid crystal phase composed of parallel particle columns arranged in a hexagonal pattern in the plane perpendicular to the column axis. The particles within columns formed a liquid structure and demonstrated a significant intracolumn diffusion. Further cooling resulted in another first-order transition whereby the column structure became periodically ordered in three dimensions transforming the liquid-crystal phase into a crystal. This result is the first observation of a liquid crystal formation in a simple one-component system of particles. Its conceptual significance is in that it demonstrated that liquid crystals that have so far only been produced in systems of anisometric molecules, can also be formed by mesoscopic soft-matter and colloidal systems of spherical particles with appropriately tuned interatomic potential.
Non-Tuberculous Mycobacteria in TB-Endemic Countries: Are We Neglecting the Danger?
Krishnamoorthy Gopinath,Sarman Singh
PLOS Neglected Tropical Diseases , 2010, DOI: 10.1371/journal.pntd.0000615
Occult Hepatitis B Virus infection in ART-Naive HIV-Infected Patients seen at a Tertiary Care Centre in North India
Swati Gupta, Sarman Singh
BMC Infectious Diseases , 2010, DOI: 10.1186/1471-2334-10-53
Abstract: We estimated the burden of HBV infection in patients who were tested positive for HIV at a tertiary care centre in north India. We also attempted to determine the prevalence and clinical characteristics of occult HBV infection among these treatment-na?ve patients and compare their demographic features with other HIV patients. During a period of 6 years between January 2002 to December 2007, 837 HIV positive patients (631 males and 206 females (M: F :: 3.06:1) were tested for serological markers of HBV (HBsAg) and HCV (anti-HCV antibodies) infections in our laboratory. For comparison 1000 apparently healthy, HIV-negative organ donors were also included in the study. Data on demographics, sexual behaviour, medical history, laboratory tests including the serum ALT and CD4 count of these patients were recorded. A sub-group of 53 HBsAg negative samples from HIV positive patients were assessed for anti-HBs, anti-HBc total (IgG+IgM) and HBV-DNA using a highly sensitive qualitative PCR and analysed retrospectively.Overall, 7.28% of HIV positive patients showed presence of HBsAg as compared to 1.4% in the HIV negative control group. The prevalence of HBsAg was higher (8.55%) in males than females (3.39%). The study revealed that occult HBV infection with detectable HBV-DNA was prevalent in 24.5% of patients positive for anti-HBc antibodies; being 45.5% in HBsAg negative patients. Most importantly the occult infection was seen in 20.7% patients who were positive for anti-HBs antibodies. However, in none of the seronegative patient HBV-DNA was detected. Five of the nine HBV-DNA positive (55.6%) patients showed raised alanine aminotransferase levels and 66.7% had CD4+ T cell counts below 200 cells/cumm.High prevalence of HIV-HBV co-infection was found in our patients. A sizeable number of co-infected patients remain undiagnosed, if only conventional serological markers are used. Presence of anti-HBs antibodies was not a reliable surrogate marker to rule out occult HBV infection
Insect vectors of Leishmania: distribution, physiology and their control
Umakant Sharma,Sarman Singh
Journal of Vector Borne Diseases , 2008,
Abstract: Leishmaniasis is a deadly vector-borne disease that causes significant morbidity and mortality in Africa, Asia, Latin America and Mediterranean regions. The causative agent of leishmaniasis is transmitted from man to man by a tiny insect called sandfly. Approximately, 600 species of sandflies are known but only 10% of these act as disease vectors. Further, only 30 species of these are important from public health point. Fauna of Indian sub-zone is represented by 46 species, of these, 11 belong to Phlebotomine species and 35 to Sergentomyia species. Phlebotomus argentipes is the proven vector of kala-azar or visceral leishmaniasis in India. This review gives an insight into the insect vectors of human leishmaniasis, their geographical distribution, recent taxonomic classification, habitat, and different control measures including indoor residual spraying (IRS), insecticide-treated bednets (ITNs), environmental management, biological control, and emerging resistance to DDT. Role of satellite remote sensing for early prediction of the disease by identifying the sandflygenic conditions cannot be undermined. The article also underlines the importance of synthetic pheromones which can be used in near future for the control of these vectors.
Review of Microalgae Harvesting via Co-Pelletization with Filamentous Fungus
Sarman Oktovianus Gultom,Bo Hu
Energies , 2013, DOI: 10.3390/en6115921
Abstract: Cultivation of microalgae to utilize CO 2 and nutrients in the wastewater to generate biofuel products is a promising research objective. However, the process faces tremendous technical difficulties, especially the harvest of microalgae cells, an economically challenging step. Several researchers recently reported co-culturing of filamentous fungi with microalgae so that microalgae cells can be co-pelletized in order to facilitate the cell harvest. This algae pelletization via the filamentous fungi represents an innovative approach to address both the cost and sustainability issues in algae biofuel production and also has potential with direct commercial applications. This paper reviews the current research status in this area and some possible drawbacks of this method in order to provide some possible directions for the future research.
Mellan profession och akademi. Reflektioner kring arkitekturforskningens egenart
Sten Gromark
FORMakademisk , 2009,
Abstract: Sammanfattning Artikeln vill belysa fr gan om arkitekturforskningens egenart som forskningsdisciplin med h nsyn till dess kritiska betydelse f r arkitektyrkets professionella och akademiska framtid. Fr gan str cker sig l ngt utanf r den arkitektoniska eller konstn rliga v rldens begr nsningar och uppfordrar till att inom hela forskningssamh llet pr va radikalt nya begrepp om vetenskaplighet och kanske i synnerhet pr va gr nserna f r var skillnaden g r mellan strikt vetenskaplig sanning i en absolut mening och vad som r en professionsrelevant kunskap. Kan det vara s att den nya profil f r forskning i och om arkitektur som ser ut att v xa fram h ller p att bryta ny mark och ppna nya forskningsfronter ur metodologisk synvinkel inom ett vidare vetenskapssamh lle? Kan vi g ra en skillnad mellan forskning om arkitektur och den utforskande handling som ryms i den gestaltande akten som s dan, i en utforskande arkitektur? Framst llningen bygger p ett underlag av ett antal aktuella avhandlingar i det nordiska och europeiska sammanhanget d r f rfattaren varit indragen i olika roller som medlem av jury, som opponent eller handledare.
Tempus som tre uafh ngige tr k
Sten Vikner
Tidsskrift for Sprogforskning , 2003,
Abstract: Zum einen m chte ich dafür argumentieren, dass acht Tempusformen für die Analyse von Tempus in der Sprache relevant sind, besonders in Hinblick auf die temporalen Relationen, die von den Tempusformen ausgedrückt werden. Zum anderen will ich mit Ausgangspunkt in Reichenbach (1947) versuchen zu zeigen, dass es angemessen ist, für jede Tempusform nicht nur einen u erungszeitpunkt und einen Ereigniszeitpunkt anzunehmen, sondern darüber hinaus zwei verschiedene Referenzzeitpunkte. Erst diese Analyse erlaubt es, eine vollst ndige Korrespondenz zwischen morphologischen und semantischen Eigenschaften für jede Tempusform herzustellen.
NATO’s Enduring Challenge: Matching American Primacy and European Ambitions
Sten Rynning
UNISCI Discussion Papers , 2005,
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