Browsing by Author "Martinez, Cristian"

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    Overspinning naked singularities in AdS3 spacetime
    (2021) Briceno, Matias; Martinez, Cristian; Zanelli, Jorge
    The Banados-Teitelboim-Zanelli (BTZ) black hole belongs to a family of locally three-dimensional antide Sitter (AdS(3)) spacetimes labeled by their mass M and angular momentum J. The case Ml >= vertical bar J vertical bar, where l is the anti-de Sitter radius, provides the black hole. Extending the metric to other values of M and J leads to geometries with the same asymptotic behavior and global symmetries but containing a naked singularity at the origin. The case Ml <= -vertical bar J vertical bar corresponds to spinning conical singularities that are reasonably well understood. Here, we examine the remaining case, which is -vertical bar J vertical bar < Ml < vertical bar J vertical bar. These naked singularities are mathematically acceptable solutions describing classical spacetimes. They are obtained by identifications of the covering pseudosphere in R-2,R-2 and are free of closed timelike curves. Here, we study the causal structure and geodesics around these overspinning geometries. We present a review of the geodesics for the entire BTZ family. The geodesic equations are completely integrated, and the solutions are expressed in terms of elementary functions. Special attention is given to the determination of circular geodesics, where new results are found. According to the radial bounds, eight types of noncircular geodesics appear in the BTZ spacetimes. For the case of overspinning naked singularity, null, and spacelike geodesics can reach infinity passing by a point nearest to the singularity, others extend from the central singularity to infinity, and others still have a radial upper bound and terminate at the singularity. As expected for an anti-de Sitter spacetime, timelike geodesics cannot reach infinity; they either loop around the singularity or fall into it. The spatial projections of the geodesics (orbits) exhibit self-intersections, whose number is determined for null and spacelike geodesics, and it is found a special class of timelike geodesics whose spatial projections are closed.
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    SURVIVAL AND PERIOPERATIVE MORBIDITY OF TOTALLY LAPAROSCOPIC VERSUS OPEN GASTRECTOMY FOR EARLY GASTRIC CANCER: ANALYSIS FROM A SINGLE LATIN AMERICAN CENTRE
    (2019) Norero, Enrique; Vargas, Catalina; Achurra, Pablo; Ceroni, Marco; Mejia, Ricardo; Martinez, Cristian; Munoz, Rodrigo; Gonzalez, Paulina; Calvo, Alfonso; Diaz, Alfonso
    Background: Laparoscopic gastrectomy has numerous perioperative advantages, but the long-term survival of patients after this procedure has been less studied. Aim: To compare survival, oncologic and perioperative outcomes between completely laparoscopic vs. open gastrectomy for early gastric cancer. Methods: This study was retrospective, and our main outcomes were the overall and disease-specific 5-year survival, lymph node count and RO resection rate. Our secondary outcome was postoperative morbidity. Results: Were included 116 patients (59% men, age 68 years, comorbidities 73%, BMI 25) who underwent 50 laparoscopic gastrectomies and 66 open gastrectomies. The demographic characteristics, tumour location, type of surgery, extent of lymph node dissection and stage did not significantly differ between groups. The overall complication rate was similar in both groups (40% vs. 28%, p=ns), and complications graded at least Clavien 2 (36% vs. 18%, p=0.03), respiratory (9% vs. 0%, p=0.03) and wound-abdominal wall complications (12% vs. 0%, p= 0.009) were significantly lower after laparoscopic gastrectomy. The lymph node count (21 vs. 23 nodes; p=ns) and RO resection rate (100% vs. 96%; p=ns) did not significantly differ between groups. The 5-year overall survival (84% vs. 87%, p=0.31) and disease-specific survival (93% vs. 98%, p=020) did not significantly differ between the laparoscopic and open gastrectomy groups. Conclusion: The results of this study support similar oncologic outcome and long-term survival for patients with early gastric cancer after laparoscopic gastrectomy and open gastrectomy. In addition, the laparoscopic approach is associated with less severe morbidity and a lower occurrence of respiratory and wound-abdominal wall complications.