237 research outputs found
Topological effects in ring polymers: A computer simulation study
Unconcatenated, unknotted polymer rings in the melt are subject to strong
interactions with neighboring chains due to the presence of topological
constraints. We study this by computer simulation using the bond-fluctuation
algorithm for chains with up to N=512 statistical segments at a volume fraction
\Phi=0.5 and show that rings in the melt are more compact than gaussian chains.
A careful finite size analysis of the average ring size R \propto N^{\nu}
yields an exponent \nu \approx 0.39 \pm 0.03 in agreement with a Flory-like
argument for the topologica interactions. We show (using the same algorithm)
that the dynamics of molten rings is similar to that of linear chains of the
same mass, confirming recent experimental findings. The diffusion constant
varies effectively as D_{N} \propto N^{-1.22(3) and is slightly higher than
that of corresponding linear chains. For the ring sizes considered (up to 256
statistical segments) we find only one characteristic time scale \tau_{ee}
\propto N^{2.0(2); this is shown by the collapse of several mean-square
displacements and correlation functions onto corresponding master curves.
Because of the shrunken state of the chain, this scaling is not compatible with
simple Rouse motion. It applies for all sizes of ring studied and no sign of a
crossover to any entangled regime is found.Comment: 20 Pages,11 eps figures, Late
Self-diffusion in binary blends of cyclic and linear polymers
A lattice model is used to estimate the self-diffusivity of entangled cyclic
and linear polymers in blends of varying compositions. To interpret simulation
results, we suggest a minimal model based on the physical idea that constraints
imposed on a cyclic polymer by infiltrating linear chains have to be released,
before it can diffuse beyond a radius of gyration. Both, the simulation, and
recently reported experimental data on entangled DNA solutions support the
simple model over a wide range of blend compositions, concentrations, and
molecular weights.Comment: 10 pages, 2 figure
Tailoring the flow of soft glasses by soft additives
We examine the vitrification and melting of asymmetric star polymers mixtures
by combining rheological measurements with mode coupling theory. We identify
two types of glassy states, a {\it single} glass, in which the small component
is fluid in the glassy matrix of the big one and a {\it double} glass, in which
both components are vitrified. Addition of small star polymers leads to melting
of {\it both} glasses and the melting curve has a non-monotonic dependence on
the star-star size ratio. The phenomenon opens new ways for externally steering
the rheological behavior of soft matter systems.Comment: 4 pages, 4 figures, accepted in Phys. Rev. Let
High-affinity recombinant phage antibodies to the pan-carcinoma marker epithelial glycoprotein-2 for tumour targeting.
The tumour-associated antigen epithelial glycoprotein-2 (EGP-2) is a promising target for detection and treatment of a variety of human carcinomas. Antibodies to this antigen have been successfully used in patients for imaging of small-cell lung cancer and for adjuvant treatment of minimal residual disease of colon cancer. We describe here the isolation and complete characterization of high-affinity single-chain variable fragments (scFv) to the EGP-2 antigen. First, the binding kinetics of four murine whole antibodies directed to EGP-2 (17-1A, 323/A3, MOC-31 and MOC-161) were determined using surface plasmon resonance (SPR). The MOC-31 antibody has the lowest apparent off-rate, followed by MOC-161 and 323/A3. The V-genes of the two MOC hybridomas were cloned as scFv in a phage display vector and antigen-binding phage were selected by panning on recombinant antigen. The scFvs compete with the original hybridoma antibodies for binding to antigen and specifically bind to human carcinomas in immunohistochemistry. MOC-31 scFv has an off-rate which is better than those of the bivalent 17-1A and 323/A3 whole antibodies, providing it with an essential characteristic for tumour retention in vivo. The availability of these high-affinity anti-EGP-2 antibody fragments and of their encoding V-genes creates a variety of possibilities for their future use as tumour-targeting vehicles
Минералогические исследования в пещерной системе Снежная-Меженного-Иллюзия (Западный Кавказ, Бзыбский хребет): предварительные результаты и направления дальнейших работ
В статье приводятся сведения о минеральном составе водных хемогенных и водных механических отложений в пещерной системе Снежная-Меженного-Иллюзия. В состав водных хемогенных отложений входят Mg- и Sr-содержащий кальцит, арагонит, гипс, гидромагнезит, целестин, стронцианит, доломит, гетит, рутил и циркон. Водные механические отложения сложены преимущественно доломитом, кварцем и кальцитом. В схожих по морфологии и микроклимату частях пещерной системы наблюдаются одинаковые вторичные минералы.У статті наводяться відомості про мінеральний склад водних хемогенних і водних механічних відкладень в печерній системі Сніжна-Меженого-Ілюзія. До складу водних хемогенних відкладень входять кальцит, який містить Mg і Sr, арагоніт, гіпс, гідромагнезіт, целестин, стронціаніт, доломіт, гетит, рутил і циркон. Водні механічні відкладення складені переважно доломітом, кварцом і кальцитом. У схожих за морфологєю та мікрокліматом частинах печерної системи спостерігаються однакові вторинні мінерали.The article presents the preliminary characteristic of the mineral composition of chemogenic formations and clastic deposits of Snezhnaya-Mezhennogo-Illusia cave system. Chemogenic formations are composed by Mg- and Sr-calcite, aragonite, gypsum and hydromagnesite, celestite, strontianite, dolomite, goethite, rutile and zircon. Clastic sediments are composed mainly by dolomite, quartz and calcite. Same secondary minerals are observed in those parts of the cave system that have similar morphology and microclimate
Polydisperse star polymer solutions
We analyze the effect of polydispersity in the arm number on the effective
interactions, structural correlations and the phase behavior of star polymers
in a good solvent. The effective interaction potential between two star
polymers with different arm numbers is derived using scaling theory. The
resulting expression is tested against monomer-resolved molecular dynamics
simulations. We find that the theoretical pair potential is in agreement with
the simulation data in a much wider polydispersity range than other proposed
potentials. We then use this pair potential as an input in a many-body theory
to investigate polydispersity effects on the structural correlations and the
phase diagram of dense star polymer solutions. In particular we find that a
polydispersity of 10%, which is typical in experimental samples, does not
significantly alter previous findings for the phase diagram of monodisperse
solutions.Comment: 14 pages, 7 figure
Anterior colporrhaphy does not induce bladder outlet obstruction
We aimed to evaluate if anterior colporrhaphy causes incomplete voiding due to bladder outlet obstruction. Women scheduled for anterior colporrhaphy were asked to undergo multichannel urodynamic investigation before surgery and the first postoperative day. Bladder outlet obstruction was assessed using the Blaivas-Groutz voiding nomogram. Maximum flow rate, detrusor pressure and residual volume were compared between pre- and postoperative measurements and between women with and without an abnormal post-void residual volume (PVR; volume exceeding 150 ml). Seventeen women participated. One woman who was unobstructed before surgery was obstructed after surgery. Overall, detrusor pressure and maximum flow rate before and after surgery did not differ. After surgery, six women had an abnormal PVR, one was unable to void, four were mildly obstructed and one moderately obstructed. Urodynamic investigation the first day after anterior colporrhaphy did not show that anterior colporrhaphy induces bladder outlet obstruction. The explanation for postoperative urinary retention can therefore also lie in non-anatomical causes such as postoperative pain and psychological factor
Enhancement of Polymeric Immunoglobulin Receptor Transcytosis by Biparatopic VHH
The polymeric immunoglobulin receptor (pIgR) ensures the transport of dimeric immunoglobulin A (dIgA) and pentameric immunoglobulin M (pIgM) across epithelia to the mucosal layer of for example the intestines and the lungs via transcytosis. Per day the human pIgR mediates the excretion of 2 to 5 grams of dIgA into the mucosa of luminal organs. This system could prove useful for therapies aiming at excretion of compounds into the mucosa. Here we investigated the use of the variable domain of camelid derived heavy chain only antibodies, also known as VHHs or Nanobodies®, targeting the human pIgR, as a transport system across epithelial cells. We show that VHHs directed against the human pIgR are able to bind the receptor with high affinity (∼1 nM) and that they compete with the natural ligand, dIgA. In a transcytosis assay both native and phage-bound VHH were only able to get across polarized MDCK cells that express the human pIgR gene in a basolateral to apical fashion. Indicating that the VHHs are able to translocate across epithelia and to take along large particles of cargo. Furthermore, by making multivalent VHHs we were able to enhance the transport of the compounds both in a MDCK-hpIgR and Caco-2 cell system, probably by inducing receptor clustering. These results show that VHHs can be used as a carrier system to exploit the human pIgR transcytotic system and that multivalent compounds are able to significantly enhance the transport across epithelial monolayers
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