Sreedevi, E P; Dr.Sankaran, P G(Cochin University Of Science And Technology, April 9, 2010)
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Abstract:
there has been much research
on analyzing various forms of competing risks data. Nevertheless, there are several
occasions in survival studies, where the existing models and methodologies are
inadequate for the analysis competing risks data. ldentifiabilty problem and various
types of and censoring induce more complications in the analysis of competing risks
data than in classical survival analysis. Parametric models are not adequate for the
analysis of competing risks data since the assumptions about the underlying lifetime
distributions may not hold well. Motivated by this, in the present study. we develop
some new inference procedures, which are completely distribution free for the
analysis of competing risks data.
Description:
Department of Statistics, Cochin University of Science and
Technology
Hareesh, G; Dr.Balakrishna, N(Cochin University of Science and Technology, August , 2010)
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Abstract:
The thesis has covered various aspects of modeling and analysis of finite mean time series
with symmetric stable distributed innovations. Time series analysis based on Box and
Jenkins methods are the most popular approaches where the models are linear and errors
are Gaussian. We highlighted the limitations of classical time series analysis tools and
explored some generalized tools and organized the approach parallel to the classical set up.
In the present thesis we mainly studied the estimation and prediction of signal plus noise
model. Here we assumed the signal and noise follow some models with symmetric stable
innovations.We start the thesis with some motivating examples and application areas of alpha stable
time series models. Classical time series analysis and corresponding theories based on finite
variance models are extensively discussed in second chapter. We also surveyed the existing
theories and methods correspond to infinite variance models in the same chapter.
We present a linear filtering method for computing the filter weights assigned to the observation
for estimating unobserved signal under general noisy environment in third chapter.
Here we consider both the signal and the noise as stationary processes with infinite variance
innovations. We derived semi infinite, double infinite and asymmetric signal extraction filters
based on minimum dispersion criteria. Finite length filters based on Kalman-Levy
filters are developed and identified the pattern of the filter weights. Simulation studies show that the proposed methods are competent enough in signal extraction for processes
with infinite variance.Parameter estimation of autoregressive signals observed in a symmetric stable noise
environment is discussed in fourth chapter. Here we used higher order Yule-Walker type
estimation using auto-covariation function and exemplify the methods by simulation and
application to Sea surface temperature data. We increased the number of Yule-Walker
equations and proposed a ordinary least square estimate to the autoregressive parameters.
Singularity problem of the auto-covariation matrix is addressed and derived a modified
version of the Generalized Yule-Walker method using singular value decomposition.In fifth chapter of the thesis we introduced partial covariation function as a tool for stable
time series analysis where covariance or partial covariance is ill defined. Asymptotic results
of the partial auto-covariation is studied and its application in model identification of stable
auto-regressive models are discussed. We generalize the Durbin-Levinson algorithm to
include infinite variance models in terms of partial auto-covariation function and introduce
a new information criteria for consistent order estimation of stable autoregressive model.In chapter six we explore the application of the techniques discussed in the previous
chapter in signal processing. Frequency estimation of sinusoidal signal observed in symmetric
stable noisy environment is discussed in this context. Here we introduced a parametric
spectrum analysis and frequency estimate using power transfer function. Estimate of the
power transfer function is obtained using the modified generalized Yule-Walker approach.
Another important problem in statistical signal processing is to identify the number of
sinusoidal components in an observed signal. We used a modified version of the proposed
information criteria for this purpose.
Description:
Department of Statistics,
Cochin University of Science and Technology
Anisha,P; Dr.Sankaran, P G(Cochin University of Science and Technology, May 4, 2012)
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Abstract:
This thesis Entitled “modelling and analysis of recurrent event data with multiple causes.Survival data is a term used for describing data that measures the time to occurrence of an event.In survival studies, the time to occurrence of an event is generally referred to as lifetime.Recurrent event data are commonly encountered in longitudinal studies when individuals are followed to observe the repeated occurrences of certain events. In many practical situations, individuals under study are exposed to the failure due to more than one causes and the eventual failure can be attributed to exactly one of these causes.The proposed model was useful in real life situations to study the effect of covariates on recurrences of certain events due to different causes.In Chapter 3, an additive hazards model for gap time distributions of recurrent event data with multiple causes was introduced. The parameter estimation and asymptotic properties were discussed .In Chapter 4, a shared frailty model for the analysis of bivariate competing risks data was presented and the estimation procedures for shared gamma frailty model, without covariates and with covariates, using EM algorithm were discussed.
In Chapter 6, two nonparametric estimators for bivariate survivor function of paired recurrent event data were developed. The asymptotic properties of the estimators were studied. The proposed estimators were applied to a real life data set. Simulation studies were carried out to find the efficiency of the proposed estimators.
Description:
Department of Statistics,
Cochin University of Science and Technology
Kesavan Nampoothiri,C; Balakrishna, N(Department of Statistics, Faculty of Science, 2001)
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Abstract:
The thesis deals with some of the non-linear Gaussian and non-Gaussian time models and mainly concentrated in studying the properties and application of a first order autoregressive process with Cauchy marginal distribution. In this thesis some of the non-linear Gaussian and non-Gaussian time series models and mainly concentrated in studying the properties and application of a order autoregressive process with Cauchy marginal distribution. Time series relating to prices, consumptions, money in circulation, bank deposits and bank clearing, sales and profit in a departmental store, national income and foreign exchange reserves, prices and dividend of shares in a stock exchange etc. are examples of economic and business time series. The thesis discuses the application of a threshold autoregressive(TAR) model, try to fit this model to a time series data. Another important non-linear model is the ARCH model, and the third model is the TARCH model. The main objective here is to identify an appropriate model to a given set of data. The data considered are the daily coconut oil prices for a period of three years. Since it is a price data the consecutive prices may not be independent and hence a time series based model is more appropriate. In this study the properties like ergodicity, mixing property and time reversibility and also
various estimation procedures used to estimate the unknown parameters of the process.
Susarla, Raghuram; Dr.Anil, Bhardwaj(Cochin University Of Science And Technology, July , 2013)
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Abstract:
Comets are the spectacular objects in the night sky since the dawn of mankind. Due to
their giant apparitions and enigmatic behavior, followed by coincidental calamities, they
were termed as notorious and called as `bad omens'. With a systematic study of these
objects modern scienti c community understood that these objects are part of our solar
system. Comets are believed to be remnant bodies of at the end of evolution of solar
system and possess the material of solar nebula. Hence, these are considered as most
pristine objects which can provide the information about the conditions of solar nebula.
These are small bodies of our solar system, with a typical size of about a kilometer
to a few tens of kilometers orbiting the Sun in highly elliptical orbits. The solid body
of a comet is nucleus which is a conglomerated mixture of water ice, dust and some
other gases. When the cometary nucleus advances towards the Sun in its orbit the ices
sublimates and produces the gaseous envelope around the nucleus which is called coma.
The gravity of cometary nucleus is very small and hence can not in
uence the motion
of gases in the cometary coma. Though the cometary nucleus is a few kilometers in size
they can produce a transient, extensive, and expanding atmosphere with size several
orders of magnitude larger in space. By ejecting gas and dust into space comets became
the most active members of the solar system. The solar radiation and the solar wind
in
uences the motion of dust and ions and produces dust and ion tails, respectively.
Comets have been observed in di erent spectral regions from rocket, ground and
space borne optical instruments. The observed emission intensities are used to quantify
the chemical abundances of di erent species in the comets. The study of various physical
and chemical processes that govern these emissions is essential before estimating chemical
abundances in the coma. Cameron band emission of CO molecule has been used to derive
CO2 abundance in the comets based on the assumption that photodissociation of CO2
mainly produces these emissions. Similarly, the atomic oxygen visible emissions have
been used to probe H2O in the cometary coma. The observed green ([OI] 5577 A) to
red-doublet emission ([OI] 6300 and 6364 A) ratio has been used to con rm H2O as the
parent species of these emissions. In this thesis a model is developed to understand the
photochemistry of these emissions and applied to several comets. The model calculated
emission intensities are compared with the observations done by space borne instruments
like International Ultraviolet Explorer (IUE) and Hubble Space Telescope (HST) and
also by various ground based telescopes.
Description:
Space Physics Laboratory
Vikram Sarabhai Space Centre
Indian Space Research Organisation
Thiruvananthapuram
Pravinkumar,P A; Dr.Nair, K G(Cochin University of Science and Technology, March 18, 1985)
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Abstract:
With the advent of satellite communication and radio astronomy, the need for large and efficient reflector antennas had triggered a widespread investigation in reflector feed design techniques. Major improvements sought are reduction in spill-over, cross polarization losses and the enhancement of aperture efficiency. The search for such a feed culminated in the corrugated horn. The main idea behind the present work is to use the H-plane sectoral horns fitted with,corrugated flanges as feeds of a paraboloid and see how the secondary pattern
of the reflector antenna varies with different parameters of the feed. An offset paraboloid is used as the secondary reflector in order to avoid the adverse effect of aperture ‘blocking by the feed horn structure on the secondary radiation pattern. The measurements were repeated for three
different H-plane sectoral horns with the same set of corrugated flanges at various X-band frequencies. The following parameters of the whole system are studied: (a) Beam shaping. (b) Gain. (c) Variation of VSWR and (d) Cross polarization
Description:
Department of Physics, Cochin University of Science and Technology
Seena, E B; Dr.Prathapachandra Kurup,M R(Cochin University of Science and Technology, August 16, 2006)
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Abstract:
The work embodied in the thesis is divided into eight chapters. Chapter I gives a
brief introduction about metal complexes of thiosemicarbazones, including their
structural and bonding properties. Chapter 2 deals with the synthesis and single crystal
X-ray diffraction studies of various thiosemicarbazones used up for the present
investigations and various characterization techniques. Chapter 3 deals with synthesis,
spectral and structural studies of Cu(U) complexes with ONS donor thiosemicarbazones.
Chapter 4 deals with synthesis and spectral studies of Ni(II) complexes \vith
2-hydroxyacetophenone N(4)-cyclohexyl thiosemicarbazone as the ligand. Chapter 5
includes synthesis and spectral studies of Mn(II) complexes. Chapter 6 deals with
synthesis, spectral and structural studies of Zn(II) complexes. Chapter 7 includes
synthesis and spectral studies of oxovanadium(IV) complexes. Chapter 8 deals with
synthesis, spectral and single crystal X-ray diffraction studies of dioxomolybdenum(VI)
complexes.
Description:
Department of Applied Chemistry, Cochin University of Science and
Technology
Renuka, T R; Paulose,C S(DEPARTMENT OF BIOTECHNOLOGY, June , 2003)
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Abstract:
The present work is an attempt to understand the role of acetylcholine
muscarinic M1 and M3 receptors during pancreatic regeneration and insulin
secretion. The work focuses on the changes in the muscarinic M1 and M3 receptors
in brain and pancreas during pancreatic regeneration. The effect of these receptor
subtypes on insulin secretion and pancreatic P-cell proliferation were studied in vitro
using rat primary pancreatic islet culture. Muscarinic Ml and M3 receptor kinetics
and gene expression studies during pancreatic regeneration and insulin secretion will
help to elucidate the role of acetylcholine functional regulation of pancreatic u-cell
proliferation and insulin secretion.The cholinergic system through muscarinic M1
and M3 receptors play an important role in the regulation of pancreatic (3-cell
proliferation and insulin secretion . Cholinergic activity as indicated by acetylcholine
esterase, a marker for cholinergic system, decreased in the brain regions -
hypothalamus, brain stem, corpus striatum, cerebral cortex and cerebellum during
pancreatic regeneration. Pancreatic muscarinic M1 and M3 receptor activity increased during proliferation indicating that both receptors are stimulatory to (3-cell division. Acetylcholine dose dependently increase EGF induced DNA synthesis in pancreatic islets in vitro, which is inhibited by muscarinic antagonist atropine confirming the role of muscarinic receptors. Muscarinic M1 and M3 receptor antagonists also block acetycholine induced DNA synthesis suggesting the importance of these receptors in regeneration. Acetylcholine also stimulated glucose induced insulin secretion in vitro which is inhibited by muscarinic M1 and M3 receptor antagonists. The muscarinic receptors activity and their functional balance in the brain and pancreas exert a profound influence in the insulin secretion and also regeneration of pancreas