4,633 research outputs found
Studies in Dactylicapnos (Papaveraceae-Fumarioideae) part II. Revision of Dactylicapnos sect. Pogonosperma sect. nov., with D. arunachalensis sp. nov
No full textDactylicapnos sect. Pogonosperma Liden & M. K. Pathak sect. nov. is established and revised based on morphology, and found to include four species: D. gaoligongshanensis from west Yunnan, D. arunachalensis Liden & M. K. Pathak sp. nov., endemic to central Arunachal Pradesh, D. grandifoliolata (syn. D. ventii) and D. paucinervia (K. R. Stern) Liden & M. K. Pathak comb. nov., the two latter species widespread in the east Himalayas.</p
Magnetic ground states of Ce3TiSb5, Pr3TiSb5and Nd3TiSb5 determined by neutron powder diffraction and magnetic measurements
No full textThe R 3TiSb5 ternary compounds, with R a light rare earth (La to Sm) have been reported to crystallize with the anti-Hf5CuSn3-type hexagonal structure (Pearson's symbol hP18; space-group P63/mcm, N. 193). An early article that reported possible superconductivity in some of these intermetallic phases (namely those with R = La, Ce, and Nd) caught our attention. In this work, we have now refined the crystal structure of the R 3TiSb5 compounds with R = Ce, Pr and Nd by Rietveld methods using high-resolution neutron powder diffraction data. The magnetic ground states of these intermetallics have been investigated by low-temperature magnetization and high-intensity neutron diffraction. We find two different magnetic transitions corresponding to two related magnetic structures at T N1 = 4.8 K (k 1 = [0, 1/2, 1/8]) and T N2 = 3.4 K (k 2 = [0, 0, 1/8]), respectively for Ce3TiSb5. However, the magnetic ordering appears to occur following a peculiar hysteresis: the k 2-type magnetic structure develops only after the k 1-type phase fraction has first slowly ordered with time and the size of the ordered Ce3+ magnetic moment has become large enough to induce the second magnetic transition. At T = 1.5 K the maximum amplitude of the Ce moment in the coexisting phases amounts to μ Ce = 2.15 μ B. For Nd3TiSb5 an antiferromagnetic ordering below T N = 5.2 K into a relatively simpler commensurate magnetic structure with a magnetic moment of μ Nd = 2.14(3) μ B and magnetic propagation vector of k = [0, 0, 0], was determined. No evidence of superconductivity has been found in Nd3TiSb5. Finally, Pr3TiSb5 does not show any ordering down to 1.5 K in neutron diffraction while an antiferromagnetic ground state is detected in magnetization measurements. There is no sign of magnetic contribution from Ti atoms found in any of the studied compounds
Theory of collective motion in liquids
No full textThe approximation for the correlation function G(r,r',t) appearing in the theory of Hubbard and Beeby (1969) has been examined and found to be exact for short times. Further, it has been shown that the recent paper by Tewari and Tewari (1975) is erroneous and misleading, and that their results are greatly inferior to those obtained by Pathak and Bansal, (1973)
Fixed and coincidence points of hybrid mappings
No full textsummary:The purpose of this note is to provide a substantial improvement and appreciable generalizations of recent results of Beg and Azam; Pathak, Kang and Cho; Shiau, Tan and Wong; Singh and Mishra
Sleep apnea and cardiac arrhythmia: a timely wake-up call!
No full textRajeev K. Pathak, Rajiv Mahajan, Dennis H. Lau, Prashanthan Sander
Aggressive risk factor reduction study for atrial fibrillation and implications for the outcome of ablation: the ARREST-AF Cohort Study
No full textAbstract not availableRajeev K. Pathak, Melissa E. Middeldorp, Dennis H. Lau, Abhinav B. Mehta, Rajiv Mahajan, Darragh Twomey, Muayad Alasady, Lorraine Hanley, Nicholas A. Antic, R. Doug McEvoy, Jonathan M. Kalman, Walter P. Abhayaratna, Prashanthan Sander
Modelling the quantitative evaluation of soil nutrient supply, nutrient use efficiency, and fertilizer requirements of wheat in India
No full textWheat yields in many parts of India are stagnant. The main reason for this is conventional blanket fertilizer recommendation, lower fertilizer use efficiency, and imbalanced use of fertilizers. Estimation of fertilizer requirements based on quantitative approaches can assist in improving wheat yields and increasing nutrient use efficiency. We used the QUEFTS (QUantitative Evaluation of Fertility of Tropical Soils) model for estimation of nitrogen (N), phosphorus (P), and potassium (K) requirements and fertilizer recommendations for a target yield of wheat. The model considers the interactions of N, P, and K, and climate adjusted potential yield of the region. Published data from several field experiments dealing with N, P, and K conducted during the years 1970 to 1998 across wheat-growing environments of India, covering a wide range of soil and climatic conditions, were used to reflect the environmental variability. The relationships between indigenous N, P, and K supply and soil organic carbon, Olsen P, and ammonium acetate-extractable K, respectively, were established. The required N, P, and K accumulation in the plant for 1 tonne grain yield was 23.1, 3.5, and 28.5 kg, respectively, suggesting an average NPK ratio in the plant dry matter of about 6.6:1:8.1. The constants for minimum and maximum accumulation (kg grain kg-1) of N (27 and 60), P (162 and 390), and K (20 and 59) were derived as the standard model parameters in QUEFTS for fertilizer recommendation for irrigated wheat in the tropical and subtropical regions of India. Relationships of apparent recovery efficiencies of fertilizer N, P, and K with levels of their application were also determined. The observed yields of wheat with different amounts of these nutrients were in good agreement with the values predicted by the model, indicating that the model can be used for fertilizer recommendations
Formation, Stability and Magnetism of New Gd3TAl3Ge2 Quaternary Compounds (T = Mn, Cu)
No full textA study on the formation and stability of new quaternary compounds with the general chemical formula Gd3TAl3Ge2 (T = Mn, Cu) has been undertaken by experimental investigations (SEM-EDX, DTA and XRD) and density functional theory (DFT) calculations. These compounds crystallize in the hexagonal Y3NiAl3Ge2-type structure (hP9, P–62m, Z = 1) (an ordered, quaternary derivative of the ternary ZrNiAl or of the binary Fe2P prototypes), with lattice parameters values a = 7.0239(2) Å and c = 4.2580(1) Å for Gd3MnAl3Ge2 and a = 7.0434(1) Å and c = 4.2089(1) Å for Gd3CuAl3Ge2. DTA suggests a peritectic reaction for the formation of these compounds (at 1245 degrees C for Gd3CuAl3Ge2). The existence and stability of these phases has been explained on the basis of DFT calculations, and a comparison of ground state properties of the studied compounds with the earlier known Gd3CoAl3Ge2 phase is outlined. The negative formation energies in all three cases govern the stability of compounds from theory as well, predicting Gd3MnAl3Ge2 as the most stable phase with highest formation energy (–13.01 eV/f.u.). The total DOS are generic in nature and suggest the robust magnetism, with the Gd-f moments of approximately equal to 7 the Bohr magnetons. An antiparallel coupling among Gd-f and T-d states is observed for all compounds, as usually seen in rare earth (R) - transition metal (T) compounds. Preliminary magnetization measurements on Gd3MnAl3Ge2 show two ferromagnetic/ferrimagnetic (FM/FIM) like transitions at TC1 = 142 K and TC2 = 97 K, with another anomaly seen at approximately equal to15 K. Isothermal magnetization data show no hysteresis even at 5 K, and the magnetization does not saturate up to 50 kOe, further suggesting a possible FIM behavior.</p
Methods for Efficiently Computing the MoM Impedance Matrix for APEx Type Basis Functions
No full textAlternative methods for efficiently computing the elements of the impedance matrix arising in the method-of-moments (MoM) based asymptotic phasefront extraction (APEx) method are presented. In APEx, the number of unknowns can be drastically reduced by making use of the phasefront characteristics of the local currents at smooth parts of the scatterer obtained at a lower frequency. At the high frequency of interest, the scaled basis functions are in the form of linearly phased constant amplitude currents or traveling waves (TWs) defined on supports that are significantly larger than the ones for the conventional MoM. The standard way of computing the mutual coupling impedance between these TW basis/test functions requires a 4-fold numerical surface integration on the supports (or patches) that typically are a few wavelengths long over a single dimension. Specifically, three different methods are investigated to efficiently and accurately compute the mutual coupling impedance. The advantages and disadvantages as well as the range of applicability of each method are discussed. Accuracy and CPU time comparisons are provide
Catheter ablation of atrial fibrillation in patients with concomitant left ventricular impairment: a systematic review of efficacy and effect on ejection fraction
No full textAbstract not availableAnand N. Ganesan, Savvy Nandal, Jakob Lüker, Rajeev K. Pathak, Rajiv Mahajan, Darragh Twomey, Dennis H. Lau, Prashanthan Sander
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