312 research outputs found
Proof Theory and Ordered Groups
Ordering theorems, characterizing when partial orders of a group extend to
total orders, are used to generate hypersequent calculi for varieties of
lattice-ordered groups (l-groups). These calculi are then used to provide new
proofs of theorems arising in the theory of ordered groups. More precisely: an
analytic calculus for abelian l-groups is generated using an ordering theorem
for abelian groups; a calculus is generated for l-groups and new decidability
proofs are obtained for the equational theory of this variety and extending
finite subsets of free groups to right orders; and a calculus for representable
l-groups is generated and a new proof is obtained that free groups are
orderable
On Deriving Nested Calculi for Intuitionistic Logics from Semantic Systems
This paper shows how to derive nested calculi from labelled calculi for propositional intuitionistic logic and first-order intuitionistic logic with constant domains, thus connecting the general results for labelled calculi with the more refined formalism of nested sequents. The extraction of nested calculi from labelled calculi obtains via considerations pertaining to the elimination of structural rules in labelled derivations. Each aspect of the extraction process is motivated and detailed, showing that each nested calculus inherits favorable proof-theoretic properties from its associated labelled calculus
Immediately restored full archâfixed prosthesis on implants placed in both healed and fresh extraction sockets after computerâplanned flapless guided surgery. A 3âyear followâup study
Background: The treatment of patients by the use of immediate implant placement in postâextractive site is a challenging procedure. / Purpose: A 3âyear clinical and radiological study of postâextractive implants placed using flapless guided surgery and immediately functioning. / Materials and Methods: Thirtyâtwo patients (23 females and 9 males), aged between 44 and 73 years (a mean age of 59.5) were treated with immediate full arch restorations and flapless implant surgery in fresh extraction and healed sites. A doubleâguide technique stent in conjunction with the NobelGuide system (Nobel Biocare AB, Göteborg, Sweden) was used. / Results: A total of 285 implants over 32 patients were assessed. The patients were clinically and radiologically followed for 3 years. One hundred and ninetyâfive implants were placed in the maxilla and 90 in the mandible. Eight patients received implants in both arches. One hundred and ninetyâseven implants were placed in extraction sites (137 maxilla, 60 mandible) and 88 in healed sites (58 maxilla and 30 mandible). The overall cumulative implant survival rate (CISR) was 97.54%. Two implants failed in maxillary healed sites (CISR 96.55%), three in maxillary extraction sites (CISR 97.81%), and two in mandibular extraction sites (CISR 96.66%). No implant failed in healed mandibular sites (CSR 100%). All fixed prostheses maintained stability and good functionality during the followâup, accounting for a cumulative prosthesis survival rate (CPSR) of 100%. The overall marginal bone level (MBL) was â0.52 mm (SD â0.18) after 6 months, â0.88 mm (SD â0.20) after 12 months, â1.05 mm (SD â0.21) after 24 months, and â1.32 mm (SD â0.41) after 36 months. / Conclusions: Computerâguided surgery using doubleâtemplate technique (DTT) shows a predictable outcome in the medium term, decreasing treatment timing and patient discomfort
Platelet activation and lipid peroxidation in patients with acute ischemic stroke
BACKGROUND AND PURPOSE: Both platelet activation and lipid peroxidation are potential sources of vasoactive eicosanoids that can be produced via the cyclooxygenase pathway, ie, thromboxane (TX) A2, or by free radical-catalyzed peroxidation of arachidonic acid, ie, isoprostanes. We investigated the biosynthesis of TXA2 and F2-isoprostanes, as reflected by the urinary excretion of 11-dehydro-TXB2 and 8-epi-prostaglandin (PG) F2 alpha respectively, in 62 consecutive patients (30 men, 32 women; mean age, 67 +/- 14 years) with acute ischemic stroke.
METHODS: At least two consecutive 6-hour urine samples were obtained during the first 72 hours after onset of symptoms. Urinary eicosanoids were measured by previously described radioimmunoassays.
RESULTS: Repeated periods of enhanced thromboxane biosynthesis were found in 52% of patients. Urinary 11-dehydro-TXB2 averaged 221 +/- 207 (mean +/- SD; n = 197; range, 13 to 967) pmol/mmol creatinine in 30 patients treated with cyclooxygenase inhibitors (mostly aspirin) at the time of study versus 392 +/- 392 (n = 186; range, 26 to 2533) in 32 untreated patients (P .05). The correlation between the two metabolites was moderate in both untreated patients (r = .41, P < .001) and patients with cyclooxygenase inhibitors (r = .31, P < .001). In a multiple regression analysis, increased thromboxane production was independently associated with severity of stroke on admission, atrial fibrillation, and treatment with cyclooxygenase-inhibiting drugs.
CONCLUSIONS: We conclude that during the first few days after an acute ischemic stroke (1) platelet activation occurs repeatedly in a cyclooxygenase-dependent fashion; (2) platelet activation is not associated with concurrent changes in isoprostane biosynthesis; (3) platelet activation is independently associated with stroke severity and atrial fibrillation; and (4) isoprostane biosynthesis is largely independent of platelet cyclooxygenase activity
From Display to Labelled Proofs for Tense Logics
We introduce an effective translation from proofs in the display calculus to proofs in the labelled calculus in the context of tense logics. We identify the labelled calculus proofs in the image of this translation as those built from labelled sequents whose underlying directed graph possesses certain properties. For the basic normal tense logic Kt, the image is shown to be the set of all proofs in the labelled calculus G3Kt
Automating Agential Reasoning: Proof-Calculi and Syntactic Decidability for STIT Logics
This work provides proof-search algorithms and automated counter-model extraction for a class of STIT logics. With this, we answer an open problem concerning syntactic decision procedures and cut-free calculi for STIT logics. A new class of cut-free complete labelled sequent calculi G3LdmL^m_n, for multi-agent STIT with at most n-many choices, is introduced. We refine the calculi G3LdmL^m_n through the use of propagation rules and demonstrate the admissibility of their structural rules, resulting in auxiliary calculi Ldm^m_nL. In the single-agent case, we show that the refined calculi Ldm^m_nL derive theorems within a restricted class of (forestlike) sequents, allowing us to provide proof-search algorithms that decide single-agent STIT logics. We prove that the proof-search algorithms are correct and terminate
Increased thromboxane biosynthesis is associated with poststroke dementia
BACKGROUND AND PURPOSE: It has been suggested that daily intake of aspirin
is associated with a reduction of cognitive decline, both in normal and in
demented subjects, but the mechanism is unclear. We have therefore studied
the relationship between thromboxane (TX) A(2) biosynthesis, as reflected
by the urinary excretion of 11-dehydro-TXB(2), and the presence of
dementia in patients after acute stroke. METHODS: Patients from the
Rotterdam Stroke Databank were screened for dementia between 3 and 9
months after stroke. Patients had a full neurological examination,
neuropsychological screening, and, if indicated, extensive
neuropsychological examination. Criteria used for the diagnosis of
dementia were from the Diagnostic and Statistical Manual of Mental
Disorders, Third Edition (Revised). Urine samples were taken at the time
of screening. Urinary 11-dehydro-TXB(2) was measured by means of a
previously validated radioimmunoassay. RESULTS: Dementia was diagnosed in
71 patients, and urine samples were available for 62. Median value (range)
of 11-dehydro-TXB(2) was 399 (89 to 2105) pmol/mmol creatinine for
demented patients versus 273 (80 to 1957) for 69 controls with stroke but
without dementia (P=0.013). No difference was found between 44 patients
with vascular dementia, 404 (89 to 2105) pmol/mmol creatinine, and 18
patients with Alzheimer's disease plus cerebrovascular disease, 399 (96 to
1467) pmol/mmol creatinine (P=0.68). In a stepwise logistic regression
analysis, in which possible confounders such as use of antiplatelet
medication, cardiovascular risk factors, and type of stroke were taken
into account, increased urinary excretion of 11-dehydro-TXB(2) remained
independently related to the presence of dementia (OR 1.12, 95% CI 1.03 to
1.22 per 100 pmol/mmol creatinine). The difference in metabolite excretion
rates between demented and nondemented patients was most prominent within
the subgroup of ischemic stroke patients who received aspirin (P<0.01).
CONCLUSIONS: Increased thromboxane biosynthesis in the chronic phase after
stroke is associated with the presence of but not the type of poststroke
dementia. It is particularly apparent in patients on aspirin, thereby
suggesting the involvement of extraplatelet sources of TXA(2) production
in this setting
Oxidative Stress and Platelet Activation in Homozygous Homocystinuria
Background
â
Severe hyperhomocysteinemia due to cystathionine ÎČ-synthase deficiency (CÎČSD) is associated with early atherothrombotic vascular disease. Homocysteine may exert its effects by promoting oxidative damage. In the present study, we investigated whether in vivo formation of 8-iso-prostaglandin (PG) F
2α
, a platelet-active product of arachidonic acid peroxidation, is enhanced in CÎČSD and whether it correlates with in vivo platelet activation, as reflected by thromboxane (TX) metabolite excretion.
Methods and Results
â
Urine and blood samples were obtained from patients with homozygous CÎČSD (n=13) and age-matched healthy subjects. Urinary 8-iso-PGF
2α
excretion was significantly higher in CÎČSD patients than in control subjects (640±384 versus 213±43 pg/mg creatinine;
P
=0.0015) and correlated with plasma homocysteine (Ï=0.398,
P
=0.0076). Similarly, urinary 11-dehydro-TXB
2
excretion was enhanced in CÎČSD (1166±415 versus 324±72 pg/mg creatinine;
P
=0.0015) and correlated with urinary 8-iso-PGF
2α
(Ï=0.362,
P
=0.0153). Vitamin E supplementation (600 mg/d for 2 weeks) was associated with a statistically significant increase in its plasma levels (from 16.6±4.6 to 40.4±8.7 Όmol/L,
P
=0.0002) and with reductions in 8-iso-PGF
2α
(from 790±159 to 559±111 pg/mg creatinine,
P
=0.018) and 11-dehydro-TXB
2
(from 1273±383 to 913±336 pg/mg creatinine,
P
=0.028). A statistically significant inverse correlation was found between urinary 8-iso-PGF
2α
and plasma vitamin E levels (Ï=â0.745,
P
=0.0135).
Conclusions
â
The results of the present study suggest that enhanced peroxidation of arachidonic acid to form bioactive F
2
-isoprostanes may represent an important mechanism linking hyperhomocysteinemia and platelet activation in CÎČSD patients. Moreover, they provide a rationale for dose-finding studies of vitamin E supplementation in this setting
Generic Modal Cut Elimination Applied to Conditional Logics
We develop a general criterion for cut elimination in sequent calculi for
propositional modal logics, which rests on absorption of cut, contraction,
weakening and inversion by the purely modal part of the rule system. Our
criterion applies also to a wide variety of logics outside the realm of normal
modal logic. We give extensive example instantiations of our framework to
various conditional logics. For these, we obtain fully internalised calculi
which are substantially simpler than those known in the literature, along with
leaner proofs of cut elimination and complexity. In one case, conditional logic
with modus ponens and conditional excluded middle, cut elimination and
complexity were explicitly stated as open in the literature
Towards a Proof Theory of G\"odel Modal Logics
Analytic proof calculi are introduced for box and diamond fragments of basic
modal fuzzy logics that combine the Kripke semantics of modal logic K with the
many-valued semantics of G\"odel logic. The calculi are used to establish
completeness and complexity results for these fragments
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