Papers by Alejandro Perez
Weed Research, 2003
SummaryLolium multiflorum (Italian ryegrass) seeds suspected of being resistant to glyphosate wer... more SummaryLolium multiflorum (Italian ryegrass) seeds suspected of being resistant to glyphosate were collected from fruit orchards at two locations, San Bernardo (SB) and Olivar (OL), Chile, that had been treated an average of three times per year with the isopropylamine salt of ...
Acta Neurologica Scandinavica, 2009
A retrospective review is presented of neurologic complications in our first 143 consecutive adul... more A retrospective review is presented of neurologic complications in our first 143 consecutive adult patients (208 liver transplants in 143 adults and 18 children) undergoing liver transplantation. Nineteen (13.2%) of the 143 patients developed neurologic complications in the postoperative period. Immunosuppression was initiated intraoperatively with steroids with the addition of azathioprine on Day 1 and cyclosporine, adjusted by RIA to a level of 400-600 ng/ml, on Day 2 post-transplantation. Azathioprine is discontinued in the third month. Fourteen of the 19 patients (73.6%) presented with CNS complications characterized by: diffuse multifactorial encephalopathy (5 patients); leukoencephalopathy (2 patients) which required temporary (1 case) or permanent (1 case) discontinuation of cyclosporine A; hemorrhage (in 2 cases due to arterial hypertension and coagulopathy and another due to unknown causes); ischemic/anoxic injury secondary to cardiorespiratory arrest (2 patients) or arteriothrombosis (1 patient); and myelopathy (1 patient) due to vertebral compression (T10-T11) secondary to osteoporosis. The diagnostic studies most often employed were computed tomographic (CT) (85.7%) and electroencephalography (EEG) (42.8%). Five of 19 patients (26.3%) suffered peripheral nervous system (PNS) complications: 1 patient with reversible Claude-Bernard-Horner Syndrome caused by central venous catheterization during anesthesia: 2 patients with peroneal nerve palsy due to compression below the knees by operating room table supports; 1 patient with an irreversible lesion of the right recurrent laryngeal nerve secondary to prolonged intubation and central venous catheterization; and 1 patient with a reversible lesion of the left brachial plexus secondary to inadvertant hyperextension of the upper extremity on the O.R. table due to the need for dialysis and catheterization of the axillary vein for veno-venous bypass. Nine of fourteen (9/14, 64.2%) of patients with CNS lesion died. In five of the nine patients (55.5%) who died with CNS lesion, the neurologic lesions (CNS hemorrhage and anoxic-isquemic injury) were directly or indirectly responsable for death. Strict control of patient positioning in the operating room, arterial hypertension and coagulation disturbance in the immediate postoperative period and serum cyclosporine A levels would eliminate the majority of neurologic complications in patients undergoing liver transplantation.
Physical Review D, 2001
We present a spin foam formulation of Lorentzian quantum General Relativity. The theory is based ... more We present a spin foam formulation of Lorentzian quantum General Relativity. The theory is based on a simple generalization of an Euclidean model defined in terms of a field theory over a group. Its vertex amplitude turns out to be the one recently introduced by Barrett and Crane. As in the case of its Euclidean relatives, the model fully implements the desired sum over 2-complexes which encodes the local degrees of freedom of the theory.
Nuclear Physics B, 2001
We present a spin foam model in which the fundamental "bubble amplitudes" (the analog of the one-... more We present a spin foam model in which the fundamental "bubble amplitudes" (the analog of the one-loop corrections in quantum field theory) are finite as the cutoff is removed. The model is a natural variant of the field theoretical formulation of the Barrett-Crane model. As the last, the model is a quantum BF theory plus an implementation of the constraint that reduces BF theory to general relativity. We prove that the fundamental bubble amplitudes are finite by constructing an upper bound, using certain inequalities satisfied by the Wigner (3n)j-symbols, which we derive in the paper. Finally, we present arguments in support of the conjecture that the bubble diagrams of the model are finite at all orders.
Classical and Quantum Gravity, 2003
In this article we review the present status of the spin foam formulation of nonperturbative (bac... more In this article we review the present status of the spin foam formulation of nonperturbative (background independent) quantum gravity. The article is divided in two parts. In the first part we present a general introduction to the main ideas emphasizing their motivations from various perspectives. Riemannian 3-dimensional gravity is used as a simple example to illustrate conceptual issues and the main goals of the approach. The main features of the various existing models for 4-dimensional gravity are also presented here. We conclude with a discussion of important questions to be addressed in four dimensions (gauge invariance, discretization independence, etc.).
In the second part we concentrate on the definition of the Barrett-Crane model. We present the ma... more In the second part we concentrate on the definition of the Barrett-Crane model. We present the main results obtained in this framework from a critical perspective. Finally we review the combinatorial formulation of spin foam models based on the dual group field theory technology. We present the Barrett-Crane model in this framework and review the finiteness results obtained for both its Riemannian as well as its Lorentzian variants.
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Papers by Alejandro Perez