2,956 research outputs found
On the location of the surface-attached globule phase in collapsing polymers
We investigate the existence and location of the surface phase known as the
"Surface-Attached Globule" (SAG) conjectured previously to exist in lattice
models of three-dimensional polymers when they are attached to a wall that has
a short range potential. The bulk phase, where the attractive intra-polymer
interactions are strong enough to cause a collapse of the polymer into a
liquid-like globule and the wall either has weak attractive or repulsive
interactions, is usually denoted Desorbed-Collapsed or DC. Recently this DC
phase was conjectured to harbour two surface phases separated by a boundary
where the bulk free energy is analytic while the surface free energy is
singular. The surface phase for more attractive values of the wall interaction
is the SAG phase. We discuss more fully the properties of this proposed surface
phase and provide Monte Carlo evidence for self-avoiding walks up to length 256
that this surface phase most likely does exist. Importantly, we discuss
alternatives for the surface phase boundary. In particular, we conclude that
this boundary may lie along the zero wall interaction line and the bulk phase
boundaries rather than any new phase boundary curve.Comment: slightly extended versio
The competition of hydrogen-like and isotropic interactions on polymer collapse
We investigate a lattice model of polymers where the nearest-neighbour
monomer-monomer interaction strengths differ according to whether the local
configurations have so-called ``hydrogen-like'' formations or not. If the
interaction strengths are all the same then the classical -point
collapse transition occurs on lowering the temperature, and the polymer enters
the isotropic liquid-drop phase known as the collapsed globule. On the other
hand, strongly favouring the hydrogen-like interactions give rise to an
anisotropic folded (solid-like) phase on lowering the temperature. We use Monte
Carlo simulations up to a length of 256 to map out the phase diagram in the
plane of parameters and determine the order of the associated phase
transitions. We discuss the connections to semi-flexible polymers and other
polymer models. Importantly, we demonstrate that for a range of energy
parameters two phase transitions occur on lowering the temperature, the second
being a transition from the globule state to the crystal state. We argue from
our data that this globule-to-crystal transition is continuous in two
dimensions in accord with field-theory arguments concerning Hamiltonian walks,
but is first order in three dimensions
Layering transitions for adsorbing polymers in poor solvents
An infinite hierarchy of layering transitions exists for model polymers in
solution under poor solvent or low temperatures and near an attractive surface.
A flat histogram stochastic growth algorithm known as FlatPERM has been used on
a self- and surface interacting self-avoiding walk model for lengths up to 256.
The associated phases exist as stable equilibria for large though not infinite
length polymers and break the conjectured Surface Attached Globule phase into a
series of phases where a polymer exists in specified layer close to a surface.
We provide a scaling theory for these phases and the first-order transitions
between them.Comment: 4 pages, 4 figure
Stretching of a chain polymer adsorbed at a surface
In this paper we present simulations of a surface-adsorbed polymer subject to
an elongation force. The polymer is modelled by a self-avoiding walk on a
regular lattice. It is confined to a half-space by an adsorbing surface with
attractions for every vertex of the walk visiting the surface, and the last
vertex is pulled perpendicular to the surface by a force. Using the recently
proposed flatPERM algorithm, we calculate the phase diagram for a vast range of
temperatures and forces. The strength of this algorithm is that it computes the
complete density of states from one single simulation. We simulate systems of
sizes up to 256 steps.Comment: 13 pages, 7 figure
Charakterystyka roznych form zajec wychowania fizycznego w centrum kultury fizycznej umcs w Lublinie
Szkoła wyższa jest niezależną jednostką, określającą program nauczania i zakres realizowanych zadań edukacyjnych. Decyduje także o rozwoju kultury fizycznej na uczelni, a do jej zadań należy stworzenie odpowiednich warunków. Aktualnie system szkolnictwa wyższego potwierdza konieczność podejmowania działań mających na celu ustawiczne podnoszenie jakości kształcenia. Wychodząc z takiego założenia Centrum Kultury Fizycznej wychodzi naprzeciw oczekiwań studentów i dokonuje zmian w organizacji zajęć wychowania fizycznego w Uniwersytecie Marii Curie Skłodowskiej w Lublinie przygotowując ofertę zajęć dydaktycznych
Pulling absorbing and collapsing polymers from a surface
A self-interacting polymer with one end attached to a sticky surface has been
studied by means of a flat-histogram stochastic growth algorithm known as
FlatPERM. We examined the four-dimensional parameter space of the number of
monomers up to 91, self-attraction, surface attraction and force applied to an
end of the polymer. Using this powerful algorithm the \emph{complete} parameter
space of interactions and force has been considered. Recently it has been
conjectured that a hierarchy of states appears at low temperature/poor solvent
conditions where a polymer exists in a finite number of layers close to a
surface. We find re-entrant behaviour from a stretched phase into these
layering phases when an appropriate force is applied to the polymer. We also
find that, contrary to what may be expected, the polymer desorbs from the
surface when a sufficiently strong critical force is applied and does
\emph{not} transcend through either a series of de-layering transitions or
monomer-by-monomer transitions.Comment: 4 pages, 4 figure
Aktywnosc fizyczna, a poziom wskaznikow somatycznych studentow umcs w Lublinie
Systematyczna aktywność fizyczna wpływa korzystnie na
organizm i pomaga w uzyskiwaniu wartości potęgujących zdrowie.
Wśród potencjalnych wartości wymieniane są np. wzrost
wydolności fizycznej organizmu, wystąpienie objawów wagotonii
takich jak zwolnienie spoczynkowej częstości skurczów serca, czy
oszczędnej pracy układu oddechowego, utrzymanie pożądanych
stężeń hemoglobiny we krwi, obniżanie nadmiernej masy ciała i
zawartości podskórnej tkanki tłuszczowej, a także siły mięśni
stabilizujących kręgosłup [Bouchard i wsp., 2007]
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