294 research outputs found
Reagent for Introducing Base-Stabilized Phosphorus Atoms into Organic and Inorganic Compounds
No full textCompeting risks in the step-stress model with lagged effects
No full textThis item is available only to currently enrolled UTSA students, faculty or staff. To download, navigate to Log In in the top right-hand corner of this screen, then select Log in with my UTSA ID.In reliability and survival analysis, accelerated tests are often used to reduce the duration of the test. In this dissertation, we consider the class of step-stress tests where items are subject to an initial stress level which is subsequently increased at pre-determined times during the exposure. The stress factor may represent temperature, drug dosage, or voltage. The most common model used for step-stress tests is Nelson's Cumulative Exposure Model, originally proposed by Sedyakin. A significant drawback of the model is that the underlying hazard function is discontinuous at points where the stress is changed. The Cumulative Risk Model discussed by Kannan, Kundu, and Balakrishnan addressed this issue by incorporating a lag period in the model, resulting in a continuous hazard function.
In many applications, there are several competing causes of failure. We generalize the stepstress model of Kannan et al. to include two competing causes. The first model assumes constant hazards at both the initial and elevated stress levels. The second model assumes a monotone hazard function for the two stress levels based on the Weibull distribution. In the lag period, we assume the hazard is linearly increasing. We obtain the maximum likelihood estimators of the unknown parameters and construct the observed Fisher information matrices.
To evaluate the performance of the estimators, a Monte Carlo simulation study is performed for different sample sizes and parameter values. The bias and mean squared error of the estimators are computed as well as confidence intervals and coverage probabilities using large sample theory and bootstrap methods.Management Science and Statistic
Catecholase activity of Mannich-based dinuclear CuII complexes with theoretical modeling: New insight into the solvent role in the catalytic cycle
No full textFour new dinuclear CuII complexes were synthesised from two Mannich-base ligands namely 2,6-bis[bis(2-methoxyethyl)aminomethyl]-4-chlorophenol (HL1) and 2-[bis(2-methoxyethyl)aminomethyl]-4-chlorophenol
(HL2): [Cu2(L1)(OH)](ClO4)2CH3OH (1), [Cu2(L2)2](ClO4)2H2O (2), [Cu2(L2)2(NO3)2] (3) and [Cu2(L2)2(OAc)2] H2O (4) and well characterised. X-ray diffraction analysis of the complexes reveals a Cu Cu distance of 2.9183(13), 2.9604(6), 3.0278(4) and 3.0569(11) Å, respectively. In 1 the metal coordination geometry is intermediate between trigonal bipyramidal (TBP) and square pyramidal (SP) (t = 0.488), in 2 the geometry is
TBP (0.828 and 0.639) and in 3 and 4 is SP (t = 0.188 and 0.083, respectively). Spectrophotometric investigations to evaluate the catecholase activity of complexes against 3,5-di-tert-butylcatechol (3,5-DTBC) and tetrachlorocatechol (TCC) in three different solvents (acetonitrile, methanol and DMSO) under completely aerobic conditions reveal that complexes 1–4 are able to oxidise 3,5-DTBC in all the solvents, while TCC can be oxidised only in acetonitrile (kcat = 0.0002–0.02 s1). Intensive DFT calculations prove an ionic pathway for 1–3 while a unique neutral catalytic cycle for 4
On Type-II Progressively Hybrid Censoring
Get PDFThe progressive Type-II censoring scheme has become quite popular. A drawback of a progressive censoring scheme is that the length of the experiment can be very large if the items are highly reliable. Recently, Kundu and Joarder (2006) introduced the Type-II progressively hybrid censored scheme and analyzed the data assuming that the lifetimes of the items are exponentially distributed. This article presents the analysis of Type-II progressively hybrid censored data when the lifetime distributions of the items follow Weibull distributions. Maximum likelihood estimators and approximate maximum likelihood estimators are developed for estimating the unknown parameters. Asymptotic confidence intervals based on maximum likelihood estimators and approximate maximum likelihood estimators are proposed. Different methods are compared using Monte Carlo simulations and one real data set is analyzed
Efficient algorithm for estimating the parameters of a chirp signal
No full textAbstractChirp signals play an important role in the statistical signal processing. Recently Kundu and Nandi (2008) [8] derived the asymptotic properties of the least squares estimators of the unknown parameters of the chirp signals model in the presence of stationary noise. Unfortunately they did not discuss any estimation procedures. In this article we propose a computationally efficient algorithm for estimating different parameters of a chirp signal in presence of stationary noise. From proper initial guesses, the proposed algorithm produces efficient estimators in a fixed number of iterations. We also suggest how to obtain the proper initial guesses. The proposed estimators are consistent and asymptotically equivalent to least squares estimators of the corresponding parameters. We perform some simulation experiments to see the effectiveness of the proposed method, and it is observed that the proposed estimators perform very well. For illustrative purposes, we have performed the data analysis of a simulated data set. Finally, we propose some generalization in the conclusions
An unprecedented 1,4-diphospha-2,3-disila butadiene (–PSi–SiP–) derivative and a 1,3-diphospha-2-silaallyl anion, each stabilized by the amidinate ligand
No full textThe synthesis of a 1,4-bisphosphino-2,3-disila butadiene and a 1,3-diphospha-2-silaallyl anion has been reported.The first acyclic 4π-electron –PSi–SiP– motif with two four coordinate silicon substituents supported by the amidinate ligand and two coordinate phosphorus has been synthesized from the reaction of heteroleptic chlorosilylene LSiCl (1), TripPCl 2 (Trip = 2,4,6- i Pr 3 C 6 H 2 ) and KC 8 in a 1 : 1 : 3 ratio. The same reaction in a 1 : 2 : 6 ratio in the presence of one equivalent of 18-crown-6 ether affords the 1,3-diphospha-2-silaallyl anion
Synthesis and characterization of Lewis base stabilized mono- and di-organo aluminum radicals
No full textSynthesis, structure, EPR and theoretical calculations of cyclic (alkyl)(amino)carbene stabilized mononuclear neutral radicals of aluminum containing mono- and di-organo groups.</p
Silanylidene and Germanylidene Anions: Valence‐Isoelectronic Species to the Well‐Studied Phosphinidene
No full textAbstract The reduction of TipMCl 3 (Tip=2,4,6‐triisopropylphenyl) (M=Si, Ge) with KC 8 in the presence of cyclic alkyl(amino) carbene (cAAC) afforded the acyclic silanylidene and germanylidene anions in the form of potassium salt [K(cAAC)MTip] 2 (M=Si ( 1 ); Ge ( 2 )). The silanylidene and germanylidene anions are valence‐isoelectronic to the well‐studied phosphinidene and are a new class of acyclic anions of Group 14. Compounds 1 and 2 were isolated and well characterized by NMR and single‐crystal X‐ray structure analysis. Furthermore, the structure and bonding of compounds 1 and 2 was investigated by computational methods
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