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Biomedical subjects

M Graca

Publications and source records attributed to M Graca.

8 recordsLinked to original sources
PubMed2004

Relaxation processes in mixtures of liquid crystals and polymers near phase boundaries and during phase separation.

We present experimental studies of the relaxation of concentration fluctuations in a semidilute solution of polystyrene (PS) (30% by weight) in 4-cyano-4'-n-octyl-biphenyl (8CB) (70% by weight) using the photon correlation spectroscopy (PCS). In the homogeneous phase there are two modes of relaxation. The slow one (typical time scale is taus = 0.001 s) is due to the diffusion of polymer chains (of molecular mass 65,000) in the LC matrix (of molecular mass 290), while the fast one has the time scale of the order of tauf approximately 0.00001 s. The amplitude of the fast mode is much weaker than the one for the slow mode. Moreover it does not depend on the scattering wave vector, q. The value of the diffusion coefficient, Dc = 1/(tausq2) for the slow mode decreases with temperature according to the Arhenius law until we reach the coexistence curve. Its value close to the coexistence is Dc = 4 x 10(5) nm2/s and the activation energy in the homogeneous mixture is Ec=127 kJ/mol. If we gradually undercool the mixture below the coexistence into the metastable two-phase region without inducing the phase separation we find unexpectedly that Dc does not change with temperature even 4 degrees below the coexistence curve. The characteristic time of the fast mode does not depend on the scattering wave vector indicating that it is related to the transient gel structure. We have shown that it is possible to measure the short time relaxation of concentration fluctuations during the phase separation in the mixture. At low temperature close to the isotropic-nematic phase transition we have observed that the relaxation is well separated in time from the typical time of the domain growth. This relaxation mode is characterized by the large diffusion coefficient D = 2 x 10(8) nm2/s. The mode probably comes from the coupling between the orientational dynamics of liquid crystals and the transient gel structure of polymers.

Journal Article↗
PubMed2003

Polymer domain growth in ordered liquid crystalline matrices.

The growth of polymer domains in the isotropic, nematic, and smectic matrices is studied by the light scattering. In the smectic and isotropic matrices the growth is diffusive, and in the nematic matrix it is influenced by the elastic forces. The scaling is obeyed. A crossover to the wetting fast-mode hydrodynamic regime is also observed at long times. In order to perform these measurements we had to eliminate the multiple scattering of light.

Journal Article↗
PubMed2001

[Small intestine obstruction caused by primary malignant neoplasms].

The authors presented 4 cases of primary malignant neoplasm of the intestine caused by small intestine obstruction. These patients underwent emergency surgery. In all cases, a segmental resection of the intestine was performed. There were two cases of adenocarcinoma and two cases of carcinoid. Three patients were complementarily treated using chemotherapeutics. One of them died two years post operation. The last three patients survived 0.5-5 years post operation.

Adenocarcinoma↗
PubMed1999

[Primary malignant neoplasms of intestine].

The authors presented 6 cases of malignant neoplasms of intestine. Five of them were undergone emergency surgery, while one elective, due to complaints notified previously for a longer time. In all cases a segmental resection of intestine was done. Two patients were complementarily treated using chemiotherapeutics. Three patients survived 2-5 years after the operation. The last three patients are under the further follow up.

Adult↗
PubMed1999

[Gallstone ileus].

Since 1986 till 1996 in the Third Department of Surgery of the Collegium Medicum of the Jagiellonian University in Cracow, nine patients with biliary ileus were operated. Initial diagnosis, additional tests results, concomitant diseases, kinds of operative procedures and complications were analysed. Biliary ileus is still generally recognized during operation. Endoscopy, X-ray examination with contrast, ultrasound, and computed tomography are worth recommendation in preoperative diagnosis. Early decision about operative treatment and application of antibiotic prophylaxis may have an influence on improvement of treatment results.

Aged↗
PubMed1999

[Primary gastrointestinal lymphomas].

The paper presents clinical signs, diagnosis, treatment and therapeutic results in the group of patients with a primary gastrointestinal lymphomas. All of the patients had a surgical procedure: 5 of them were operated on according to a fixed plan and 3 had an emergency operation. 6 patients were subjected to chemotherapy and radiotherapy. The patients were analyzed along with the obtained therapeutic results.

Adult↗