Integration of Dirac-Jacobi structures

We study precontact groupoids whose infinitesimal counterparts are Dirac-Jacobi structures. These geometric objects generalize contact groupoids. We also explain the relationship between precontact groupoids and homogeneous presymplectic groupoids. Finally, we present some examples of precontact groupoids.Comment: 10 pages. Brief changes in the introduction. References update

Phase-Control of Photoabsorption in Optically Dense Media

We present a self-consistent theory, as well as an illustrative application to a realistic system, of phase control of photoabsorption in an optically dense medium. We demonstrate that, when propagation effects are taken into consideration, the impact on phase control is significant. Independently of the value of the initial phase difference between the two fields, over a short scaled distance of propagation, the medium tends to settle the relative phase so that it cancels the atomic excitation. In addition, we find some rather unusual behavior for an optically thin layer.Comment: 5 pages, 3 figures, submitted to PR

Probing reaction channels via reinforcement learning

We propose a reinforcement learning based method to identify important configurations that connect reactant and product states along chemical reaction paths. By shooting multiple trajectories from these configurations, we can generate an ensemble of configurations that concentrate on the transition path ensemble. This configuration ensemble can be effectively employed in a neural network-based partial differential equation solver to obtain an approximation solution of a restricted Backward Kolmogorov equation, even when the dimension of the problem is very high. The resulting solution, known as the committor function, encodes mechanistic information for the reaction and can in turn be used to evaluate reaction rates

The association between patellar alignment on magnetic resonance imaging and radiographic manifestations of knee osteoarthritis

The aim of our study was to evaluate the association between patellar alignment by using magnetic resonance imaging images and radiographic manifestations of patello-femoral osteoarthritis (OA). Subjects were recruited to participate in a natural history study of symptomatic knee OA. We examined the relation of patellar alignment in the sagittal plane (patellar length ratio (PLR)) and the transverse plane (sulcus angle (SA), lateral patellar tilt angle (LPTA), and bisect offset (BO)) to radiographic features of patello-femoral OA, namely joint space narrowing and patellar osteophytes, using a proportional odds logistic regression model while adjusting for age, sex, and bone mass index (BMI). The study sample consisted of 126 males (average age 68.0 years, BMI 31.2) and 87 females (average age 64.7 years, BMI 31.6), 75% of whom had tibiofemoral OA (a Kellgren-Lawrence score of 2 or more). PLR showed a statistically significant association with joint space narrowing and osteophytosis in the lateral compartment. SA showed significant association with medial joint space narrowing and with lateral and medial patellar osteophytosis. LPTA and BO showed significant association with both radiographic indices of the lateral compartment. Clear linear trends were found in association between PLR, LPTA and BO, and with outcomes associated with lateral patello-femoral OA. SA, LPTA, and BO showed linear trends of association with medial joint space narrowing. Results of our study clearly suggest the association between indices of patellar alignment and such features of patello-femoral OA as osteophytosis and joint space narrowing. Additional studies will be required to establish the normal and abnormal ranges of patellar alignment indices and their longitudinal relation to patello-femoral OA

Bradykinin improves postischaemic recovery in the rat heart: role of high energy phosphates, nitric oxide, and prostacyclin

Objective: The aim was to define: (1) whether bradykinin administration during reperfusion improves postischaemic myocardial recovery; (2) whether high energy phosphate compounds are involved in the protective effects of bradykinin; and (3) whether bradykinin-induced release of prostacyclin and nitric oxide mediate the protective effects of bradykinin. Methods: In the Langendorff rat heart preparation, coronary flow, left ventricular developed pressure, and, using 31P magnetic resonance spectroscopy, the high energy phosphate compounds phosphocreatine and β-ATP were assessed during 15 min of global ischaemia and 30 min of reperfusion. Administration of 10−7 M bradykinin was started before ischaemia and maintained throughout the experiment (BK-pre). This was compared to 10−7 M bradykinin given exclusively with reperfusion (BK-post). Then 10−7 M bradykinin was given simultaneously with 10−4 M Nω-nitro-L-arginine-methyl ester (BK-LNAME) or 10−5 M indomethacin (BK-indo). Results: In comparison to control hearts, BK-pre exerted a significant protective effect on the postischaemic recovery of coronary flow [71(5)% v 43(4)%, P < 0.05], left ventricular pressure [81(8)% v 42(5)%, P < 0.05], phosphocreatine [105(4)% v 67(8)%, P < 0.05], and β-ATP [78(9)% v 48(7)%, P < 0.05]. With BK-post, recovery of coronary flow [71(4)% v 43(4)%, P < 0.05] and left ventricular pressure [78(4)% v 42(5)%, P < 0.05] significantly improved; however the recovery of phosphocreatine [70(4)% v 67(8)%, NS] and β-ATP [58(2)% v 48(7)%, NS] was not different from control. When bradykinin and L-NAME or indomethacin was given the beneficial effects of bradykinin on ischaemic hearts were abolished. Conclusions: (1) Bradykinin improved postischaemic myocardial recovery when given before ischaemia or starting exclusively with reperfusion; (2) this was only partially related to a protective action on the high energy phosphate compounds during ischaemia; (3) the beneficial effects of bradykinin on ischaemic hearts are dependent from an unrestrained action of prostacyclin and nitric oxid