Mechanisms for the Oxonolysis of Ethene and Propene: Reliability of Quantum Chemical Predictions

Reactions of ozone with ethene and propene leading to primary ozonide (concerted and stepwise ozonolysis) or epoxide and singlet molecular oxygen (partial ozonolysis) are studied theoretically. The mechanism of concerted ozonolysis proceeds via a single transition structure which is a partial diradical. The transition structures and intermediates in the stepwise ozonolysis and partial ozonolysis mechanisms are singlet diradicals. Spin-restricted and unrestricted density functional methods are employed to calculate the structures of the closed-shell and diradical species. Although the partial diradicals exhibit moderate to pronounced instability in their RDFT and RHF solutions, RDFT is required to locate the transition structure for concerted ozonolysis. Spin projected fourth-order Møller–Plesset theory (PMP4) was used to correct the DFT energies. The calculated pre-exponential factors and activation energies for the concerted ozonolysis of ethene and propene are in good agreement with experimental values. However, the PMP4//DFT procedure incorrectly predicts the stepwise mechanism as the favored channel. UCCSD(T) predicts the concerted mechanism as the favored channel but significantly overestimates the activation energies. RCCSD(T) is found to be more accurate than UCCSD(T) for the calculation of the concerted mechanism but is not applicable to the diradical intermediates. The major difficulty in accurate prediction of the rate constant data for these reactions is the wide range of spin contamination for the reference UHF wave functions and UDFT solutions across the potential energy surface. The possibility of the partial ozonolysis mechanism being the source of epoxide observed in some experiments is discussed

Perfect countably infinite Steiner triple systems

We use a free construction to prove the existence of perfect Steiner triple systems on a countably infinite point set. We use a specific countably infinite family of partial Steiner triple systems to start the construction, thus yielding 2ℵ0 non-isomorphic perfect systems

Effect of Cao-Mgo-Re-Caf2 Synthetic Powder on Desulphurization of 12Cr20Ni38Mo5 Alloy

The desulphurization and the control of sulphides by treatment of CaO-MgO-RE-CaF2 synthetic powder in liquid alloy is used with success in ladle for many alloy prod-ucts. The results indicated that the synthetic powder ladle treatment is possible to reduce sulphur from 0.035% to 0.009%S by employing agents amounting l4kg/t liquid metal. The results also show that treated CaO-MgO-RE-CaF2 powder positively affect the globular type I morphology, small-smooth size and distribution of the remaining inclusions in the 12Cr20Ni38Mo5 alloy, The powder CaO- MgO-RE with increasing MgO shows better efficiency than powder with increasing CaO. Some calculated values have been compared with those reported in literature

Status of Supersymmetric Grand Unified Theories

We begin with a brief discussion of the building blocks of supersymmetric grand unified theories. We recall some of the compelling theoretical reasons for viewing supersymmetric grand unification as an attractive avenue for physics beyond the standard model. This is followed by a discussion of some of the circumstantial evidence for these ideas.Comment: 12 pages plain LaTeX to be run twice. Invited talk at the XII DAE Symposium on High Energy Physics, Guwahati, India, Dec. 26, 1996 - Jan. 1, 199

Geometry and braiding of Stokes data; Fission and wild character varieties

A family of new algebraic Poisson varieties will be constructed, generalising the complex character varieties of Riemann surfaces. Then the well-known (Poisson) mapping class group actions on the character varieties will be generalised.Comment: 61 pages, 5 figures (several improvements

NGC1052 - A study of the pc-scale twin jet

We present results of a VLBA multi-frequency study of the pc-scale twin jet in NGC1052. We observed this object at epoch 1998.99 with the VLBA at 5, 8.4, 22 and 43 GHz both in total and linearly polarized intensity. The spectral analysis confirms the necessity of a free-free absorbing medium, obscuring the innermost part of both jets. At 5 GHz we found a compact linearly polarized emission region at the base of the eastern jet with a degree of polarization of 1.5%. At higher frequencies there is no evidence for polarization in our data. A core shift analysis constrains the position of the central engine to ~0.03 pc. The shift rates of the apparent core position with frequency confirm the strong influence of free-free absorption in conjunction with steep pressure gradients at the bases of both jets.Comment: Proceedings of the conference "SRT: the impact of large antennas on Radio Astronomy and Space Science", Cagliari, Italy, 7-10 November 2001, in press; 6 pages, 5 figures, needs srt_style.st

Resolution of dilated cardiomyopathy in an adolescent with change of a failing highly active antiretroviral drug therapy

Background: Cardiovascular dysfunction is a recognized complication of HIV infection in children. Cardiac complications of HIV usually occur late in the course of the disease; they may be associated with drug therapy, and hence become more common as therapy and survival improve. Left ventricular (LV) dysfunction at baseline is a risk factor for death independent of the CD4 cell count, HIV viral load, and neurological disease.Clinical case: We present the case of a 15 year old girl with HIV who developed left ventricular dysfunction while non-compliant on highly active antiretroviral therapy (HAART). She presented with features of heart failure over a course of two months. Her laboratory evaluation was significant for leucopenia with a low CD4 count, high viral load, elevated ESR and CRP. The ECG showed a sinus tachycardia with diffuse ST-T segment changes and LVH with strain. Initial echo revealed dilated left heart chambers with poor LV systolic function and a small pericardial effusion with the development of an LV thrombus on follow up echo evaluation. She was started on heart failure medicines and had anticoagulation for the LV thrombus. She received adherence counseling and her HAART regimen was changed. Six months after presentation she became asymptomatic with higher CD4 counts and a normal LV size and function on echo.Conclusion: Immunological recovery following a switch of a failing or potentially cardiotoxic HAART in addition to improved HAART adherence may result in resolution of left ventricular dysfunction. Early and regular cardiology evaluation may improve outcomes in these patients.Key words: Dilated Cardiomyopathy, HAAR