1,510 research outputs found
Confinement and soliton solutions in the SL(3) Toda model coupled to matter fields
We consider an integrable conformally invariant two dimensional model
associated to the affine Kac-Moody algebra SL(3). It possesses four scalar
fields and six Dirac spinors. The theory does not possesses a local Lagrangian
since the spinor equations of motion present interaction terms which are
bilinear in the spinors. There exists a submodel presenting an equivalence
between a U(1) vector current and a topological current, which leads to a
confinement of the spinors inside the solitons. We calculate the one-soliton
and two-soliton solutions using a procedure which is a hybrid of the dressing
and Hirota methods. The soliton masses and time delays due to the soliton
interactions are also calculated. We give a computer program to calculate the
soliton solutions.Comment: plain LaTeX, 37 page
Perforated peptic ulcer: main factors of morbidity and mortality.
World J Surg. 2003 Jul;27(7):782-7.
Perforated peptic ulcer: main factors of morbidity and mortality.
Noguiera C, Silva AS, Santos JN, Silva AG, Ferreira J, Matos E, Vilaça H.
Surgery Department, Surgery 1, Hospital Geral de Santo António, Instituto de Ciencias Biomédicas Abel Salazar, Largo do Prof. Abel Salazar, 4099-001 Oporto, Portugal.
Abstract
It is well stated in the literature that medical treatment for peptic ulcer is based on a combination of proton pump inhibitors (PPIs) and antibiotics to eradicate Helicobacter pylori. This treatment is associated with a high rate of immediate success and a low rate of recurrence at 12 months, although it is not effective in all patients. Peptic ulcer (PU) perforation is a serious problem that leads to high complication and mortality rates. Surgical treatment, with its various possibilities, constitutes the ideal treatment. Surgical intervention in these cases, however, can be directed to treating the perforation alone, or it can offer definitive treatment of the ulcer itself. With the hope of establishing why such complications and mortality were seen in the patients in our hospital population, we gathered the facts about PU perforations and the types of surgery performed. We studied 210 consecutive patients (150 men, 60 women) who had undergone surgery at our hospital because of perforation between January 1, 1990 and December 31, 2000. The patients' median age was 53.0 +/- 20.6 years (men 47.7 +/- 17.3 years; women 66.3 +/- 22.0 years). Altogether, 86 patients had significant associated illnesses, 62 were admitted more than 24 hours after the perforation, and 25 were admitted in shock. We performed resections in 10 patients; 88 patients were treated by suturing the perforation with or without a patch of epiploon; and 112 underwent a troncular vagotomy with drainage (VT + Dr). A total of 21 patients died (10%). Significant risk factors that led to complications were identified by statistical studies. They were a perforation that had been present more than 24 hours, the coexistence of significant associated illnesses, and resection surgery. The significant risk factors that led to death were the presence of shock at admission, the coexistence of significant illnesses, and resection surgery. There was no statistically significant difference concerning morbidity and mortality between simple closure of the perforation and definitive surgery (VT + Dr).
PMID: 14509505 [PubMed - indexed for MEDLINE
Early gastric cancer: ten years of experience
World J Surg. 2002 Mar;26(3):330-4. Epub 2001 Dec 21.
Early gastric cancer: ten years of experience.
Nogueira C, Silva AS, Santos JN, Silva AG, Ferreira J, Matos E, Vilaça H.
Surgery Department, Surgery 1, Hospital Geral de Santo António, Largo Prof. Abel Salazar, 4000 Oporto, Portugal. [email protected]
Abstract
Gastric cancer is a disease in which the main treatment is surgical extirpation. The modifications introduced in the surgical treatment over the last decades were accompanied by a clear increase of survival, which reaches global values of 61% at 5 years in Japan. One of the reasons that contribute to this improvement is early diagnosis of the lesions. In the period between January 1, 1990 and December 31, 1999 662 patients with gastric adenocarcinoma were treated in the Service of Surgery 1 of our hospital; 110 were refused surgical treatment. Of the resected patients, 91 (21.4%) were classified as early gastric cancer according to the definition of the Japanese Society of Digestive Endoscopy. There were 30 women and 61 men, with a median age of 60.2 +/- 15 years; 3 patients had a preoperative diagnosis of gastric ulcer; 2 others were operated without recent histology; and 1 patient was urgently resected for a bleeding ulcer. In all the remaining patients biopsy confirmed the presence of cancer (89%) or serious dysplasia (4.6%). The lesions had been distributed essentially in the medium 1/3 (48.3%) and distal 1/3 of the stomach. Subtotal gastrectomy was accomplished in 48 patients, total gastrectomy in 40, total desgastrogastrectomy in 3, and in 9 patients the surgery involved the spleen (8 patients) and the spleen and tail of the pancreas in 1 patient. Lymphadenectomy was not performed in 5 patients, lymph nodes by the first lymph node barrier were removed in 25 patients and by the second barrier in 61 patients (67%). Median tumor size was 26 +/- 1.8 mm. The lesion reached the mucosa in 46 patients and the mucosa and submucosa in 45. In 6 patients the removed lymph nodes were microscopically invaded (6.7%). Five patients died (5.7%). The median follow-up of the patients is 41 +/- 26 months; 7 patients died (8.1%) during this period; 4 died unequivocally of disease progression. The median survival of patients was 85% at 5 years and 80% at 10 years. In our series, survival was affected by the presence of invaded lymph nodes, not by the penetration in depth of the lesion or the size of the tumor.
PMID: 11865370 [PubMed - indexed for MEDLINE
Collapse of ringlike structures in 2DEGs under tilted magnetic fields
In the quantum Hall regime, the longitudinal resistivity plotted
as a density--magnetic-field () diagram displays ringlike structures
due to the crossings of two sets of spin split Landau levels from different
subbands [e.g., Zhang \textit{et al.}, Phys. Rev. Lett. \textbf{95}, 216801
(2005)]. For tilted magnetic fields, some of these ringlike structures "shrink"
as the tilt angle is increased and fully collapse at . Here we theoretically investigate the topology of these structures
via a non-interacting model for the 2DEG. We account for the inter Landau-level
coupling induced by the tilted magnetic field via perturbation theory. This
coupling results in anti-crossings of Landau levels with parallel spins. With
the new energy spectrum, we calculate the corresponding diagram of
the density of states (DOS) near the Fermi level. We argue that the DOS
displays the same topology as in the diagram. For the
ring with filling factor , we find that the anti-crossings make it
shrink for increasing tilt angles and collapse at a large enough angle. Using
effective parameters to fit the data, we find a collapsing
angle . Despite this factor-of-two discrepancy with
the experimental data, our model captures the essential mechanism underlying
the ring collapse.Comment: 3 pages, 2 figures; Proceedings of the PASPS V Conference Held in
August 2008 in Foz do Igua\c{c}u, Brazi
A New Cosmological Model of Quintessence and Dark Matter
We propose a new class of quintessence models in which late times
oscillations of a scalar field give rise to an effective equation of state
which can be negative and hence drive the observed acceleration of the
universe. Our ansatz provides a unified picture of quintessence and a new form
of dark matter we call "Frustrated Cold Dark Matter" (FCDM). FCDM inhibits
gravitational clustering on small scales and could provide a natural resolution
to the core density problem for disc galaxy halos. Since the quintessence field
rolls towards a small value, constraints on slow-roll quintessence models are
safely circumvented in our model.Comment: Revised. Important new results added in response to referees comment
Ambiguous Tests of General Relativity on Cosmological Scales
There are a number of approaches to testing General Relativity (GR) on linear
scales using parameterized frameworks for modifying cosmological perturbation
theory. It is sometimes assumed that the details of any given parameterization
are unimportant if one uses it as a diagnostic for deviations from GR. In this
brief report we argue that this is not necessarily so. First we show that
adopting alternative combinations of modifications to the field equations
significantly changes the constraints that one obtains. In addition, we show
that using a parameterization with insufficient freedom significantly tightens
the apparent theoretical constraints. Fundamentally we argue that it is almost
never appropriate to consider modifications to the perturbed Einstein equations
as being constraints on the effective gravitational constant, for example, in
the same sense that solar system constraints are. The only consistent
modifications are either those that grant near-total freedom, as in
decomposition methods, or ones which map directly to a particular part of
theory space
Cosmological Tracking Solutions
A substantial fraction of the energy density of the universe may consist of
quintessence in the form of a slowly-rolling scalar field. Since the energy
density of the scalar field generally decreases more slowly than the matter
energy density, it appears that the ratio of the two densities must be set to a
special, infinitesimal value in the early universe in order to have the two
densities nearly coincide today.
Recently, we introduced the notion of tracker fields to avoid this initial
conditions problem. In the paper, we address the following questions: What is
the general condition to have tracker fields? What is the relation between the
matter energy density and the equation-of-state of the universe imposed by
tracker solutions? And, can tracker solutions explain why quintessence is
becoming important today rather than during the early universe
Affine Toda model coupled to matter and the string tension in QCD
The affine Toda model coupled to matter (ATM) is shown to describe
various features, such as the spectrum and string tension, of the low-energy
effective Lagrangian of QCD (one flavor and colors). The
corresponding string tension is computed when the dynamical quarks are in the
{\sl fundamental} representation of SU(N) and in the {\sl adjoint}
representation of SU(2).Comment: LaTex, 10 pages. Revised version to appear in Phys. Rev.
The -essence scalar field in the context of Supernova Ia Observations
A -essence scalar field model having (non canonical) Lagrangian of the
form where
with constant is shown to be consistent with luminosity
distance-redshift data observed for type Ia Supernova. For constant ,
satisfies a scaling relation which is used to set up a differential
equation involving the Hubble parameter , the scale factor and the
-essence field . and are extracted from SNe Ia data and using
the differential equation the time dependence of the field is found to
be: . The constants
have been determined. The time dependence is similar to that of the
quintessence scalar field (having canonical kinetic energy) responsible for
homogeneous inflation. Furthermore, the scaling relation and the obtained time
dependence of the field is used to determine the -dependence of the
function .Comment: 8 pages, 5 figures, Late
- …