Determination of oxygen in silicon and carbide by activation with 27.2 meV alpha particles

The Si sample was polished on one side, and on the other side Ni was applied chemically and soldered with Pb to a water cooled Cu substrate. Optical quartz standard was fixed from the other side. Si carbide samples were soldered to a substrated with In. The prepared samples were irradiated in a cyclotron with a 27.2 MeV alpha particle beam. The layers were removed from the Si and Si carbide samples by grinding and the positron activity of F-18(t sub 1/2 110 min) was measured by using a gamma, gamma coincidence spectrometer with two NaI(TI) crystals. For analysis of Si carbide, the activity decay curve of the samples was recorded to find the contribution of the positron activity of Cu-65(t sub 1/2 12.9 hr) which formed from Ni impurity on irradiation

Creating traveling waves from standing waves from the gyrotropic paramagnetic properties of Fe3+^{3+} ions in a high-Q whispering gallery mode sapphire resonator

We report observations of the gyrotropic change in magnetic susceptibility of the Fe$^{3+}$ electron paramagnetic resonance at 12.037GHz (between spin states $|1/2>$ and $|3/2>$) in sapphire with respect to applied magnetic field. Measurements were made by observing the response of the high-Q Whispering Gallery doublet (WGH$_{\pm17,0,0}$) in a Hemex sapphire resonator cooled to 5 K. The doublets initially existed as standing waves at zero field and were transformed to traveling waves due to the gyrotropic response.Comment: Accepted for publication in Phys. Rev.

Prevalence of cardiac arrhythmias among patients undergoing chronic hemodialysis

Aim. To evaluate the prevalence of arrhythmias in patients undergoing chronic hemodialysis, to characterize the arrhythmia types in relation to the dialysis procedure and to determine their relationship with clinical findings and echocardiographic characteristics.Material and methods. The study involved 152 patients with kidney failure undergoing chronic hemodialysis. All patients underwent an assessment of dialysis parameters, collection of clinical data, and 48-hour Holter monitoring. In addition, 93 patients underwent an echocardiography with an assessment of left ventricular (LV) mass index, LV ejection fraction, left atrial (LA) volume index, E/e’, cardiac output and preload, which was defined as increased LV filling pressure (E/e’ >12) and LA enlargement (LA volume index >30 ml/m2).Results. Among the 152 examined patients, premature supraventricular and ventricular contractions (PVCs) were observed in almost all patients, while 41% had paroxysmal supraventricular tachycardia. Clinically significant arrhythmias included persistent atrial fibrillation (AF) in 8,6% of patients, paroxysmal AF in 3,9%, nonsustained ventricular tachycardia in 19,7%, bradycardia in 4,6%, second-degree atrioventricular block in 1,3% and third-degree atrioventricular block among 2,6%. PVCs were more common on dialysis days, while tachyarrhythmias were more common during dialysis and in the immediate post- dialysis period. Older age (odds ratio (OR) 10 years older, 1,53; 95% confidence interval (CI): 1,15-2,03; P=0,003), lower cardiac output (OR 1 L/min more, 0,66; 95% CI: 0,44-1,00; P=0,05) were independently associated with clinically relevant arrhythmias.Conclusion. In patients on chronic hemodialysis, older age, increased preload and lower cardiac output are independently associated with clinically relevant arrhythmias. In addition, a positive association between increased LV mass index and AF episodes has been demonstrated. Lower cardiac output had positive correlation with AF and ventricular arrhythmias

Multi-wavelength observations of afterglow of GRB 080319B and the modeling constraints

We present observations of the afterglow of GRB 080319B at optical, mm and radio frequencies from a few hours to 67 days after the burst. Present observations along with other published multi-wavelength data have been used to study the light-curves and spectral energy distributions of the burst afterglow. The nature of this brightest cosmic explosion has been explored based on the observed properties and it's comparison with the afterglow models. Our results show that the observed features of the afterglow fits equally good with the Inter Stellar Matter and the Stellar Wind density profiles of the circum-burst medium. In case of both density profiles, location of the maximum synchrotron frequency $\nu_m$ is below optical and the value of cooling break frequency $\nu_c$ is below $X-$rays, $\sim 10^{4}$s after the burst. Also, the derived value of the Lorentz factor at the time of naked eye brightness is $\sim 300$ with the corresponding blast wave size of $\sim 10^{18}$ cm. The numerical fit to the multi-wavelength afterglow data constraints the values of physical parameters and the emission mechanism of the burst.Comment: 8 Pages, 3 Figures, Accepted for publication to Astronomy and Astrophysics on 02/04/200

Computer modeling of rectangular-cylindrical trawl doors

Computer modeling of the rectangular-cylindrical trawl doors designed by P.P. Augulis (project 2490) is realized for calculation of their parameters to ensure stable functioning in the process of trawling. Correct choice of the warp point ensures stable functioning of the door for three ways of fastening: directly to the stringer or by means of horizontal strap or bail