214 research outputs found
Lattice Knots in a Slab
In this paper the number and lengths of minimal length lattice knots confined
to slabs of width , is determined. Our data on minimal length verify the
results by Sharein et.al. (2011) for the similar problem, expect in a single
case, where an improvement is found. From our data we construct two models of
grafted knotted ring polymers squeezed between hard walls, or by an external
force. In each model, we determine the entropic forces arising when the lattice
polygon is squeezed by externally applied forces. The profile of forces and
compressibility of several knot types are presented and compared, and in
addition, the total work done on the lattice knots when it is squeezed to a
minimal state is determined
Minimal knotted polygons in cubic lattices
An implementation of BFACF-style algorithms on knotted polygons in the simple
cubic, face centered cubic and body centered cubic lattice is used to estimate
the statistics and writhe of minimal length knotted polygons in each of the
lattices. Data are collected and analysed on minimal length knotted polygons,
their entropy, and their lattice curvature and writhe
The perceptions of employment equity and black economic empowerment as predictors of union commitment.
The purpose of the study was to test whether the perceptions of employment equity (EE) and black economic empowerment (BEE) are related to union commitment and whether the perceptions about the mentor’s role significantly mediate this said relationship. The sampling frame for the study constituted 1200 employees of a division of a large public transport organisation and a convenience sample including all 1200 employees yielded 637 fully completed records (a 53% response rate). The results of the study indicate that the perceptions of EE and BEE are significantly related to union commitment, but that perceptions of the mentor’s role do not mediate this relationship. More detailed findings on the study are reported
Writing into design: An embedded writing course for architectural studies
Architects must be able to express their ideas clearly to communicate their designs; at the same time graduate professional degree programs demand advanced critical literacy and academic writing skills. Competence in this domain for high school graduates in South Africa often falls short of the expected proficiencies of first-year students at tertiary level. To address this gap, an embedded writing course was integrated into the first-year Design Studio and History of Architecture course. This intervention adopted the approaches provided by writing-intensive pedagogy, successfully improving students’ written expression, and their ability to engage with their architectural studies in deeper and more critical ways
Forcing Adsorption of a Tethered Polymer by Pulling
We present an analysis of a partially directed walk model of a polymer which
at one end is tethered to a sticky surface and at the other end is subjected to
a pulling force at fixed angle away from the point of tethering. Using the
kernel method, we derive the full generating function for this model in two and
three dimensions and obtain the respective phase diagrams.
We observe adsorbed and desorbed phases with a thermodynamic phase transition
in between. In the absence of a pulling force this model has a second-order
thermal desorption transition which merely gets shifted by the presence of a
lateral pulling force. On the other hand, if the pulling force contains a
non-zero vertical component this transition becomes first-order.
Strikingly, we find that if the angle between the pulling force and the
surface is beneath a critical value, a sufficiently strong force will induce
polymer adsorption, no matter how large the temperature of the system.
Our findings are similar in two and three dimensions, an additional feature
in three dimensions being the occurrence of a reentrance transition at constant
pulling force for small temperature, which has been observed previously for
this model in the presence of pure vertical pulling. Interestingly, the
reentrance phenomenon vanishes under certain pulling angles, with details
depending on how the three-dimensional polymer is modeled
Fresh look at randomly branched polymers
We develop a new, dynamical field theory of isotropic randomly branched
polymers, and we use this model in conjunction with the renormalization group
(RG) to study several prominent problems in the physics of these polymers. Our
model provides an alternative vantage point to understand the swollen phase via
dimensional reduction. We reveal a hidden Becchi-Rouet-Stora (BRS) symmetry of
the model that describes the collapse (-)transition to compact
polymer-conformations, and calculate the critical exponents to 2-loop order. It
turns out that the long-standing 1-loop results for these exponents are not
entirely correct. A runaway of the RG flow indicates that the so-called
-transition could be a fluctuation induced first order
transition.Comment: 4 page
Haemangiosarcoma of the os penis in a dog : the most common neoplasm of the canine penis
A castrated 9-year-old intact male boerboel cross-breed dog was presented with a month-long
history of stranguria. On physical examination, a mass was noted at the caudal extremity of
the os penis. Haematology, serum chemistry and urinalysis were all unremarkable. Abdominal
and urethral ultrasound demonstrated an enlarged bladder and a dilated urethra, which
was followed to the caudal extremity of the os penis. A hyperechoic, roughly spherical,
vascularised mass was noted at the caudal os penis, which resulted in obstruction of the penile
urethra. Radiographs demonstrated a soft tissue mass with osteolysis of the os penis. Cytology
suggested an osteosarcoma. Treatment included amputation of the penis and adjuvant
doxorubicin with carboplatin. Histopathology of the penis confirmed a haemangiosarcoma.
The patient survived for 20 months. This is only the second published case report describing
a penile haemangiosarcoma, and the first published report demonstrating the treatment and
outcome of a case of haemangiosarcoma of the os penis. Based on published and unpublished
reports, haemangiosarcoma appears to be the most common neoplasm of the canine penis.http://www.jsava.co.zaam201
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