Nirmala, Thampuran; Dr.Gopakumar, K(Cochin University of Science and Technology, January 1, 1987)
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Abstract:
The thesis is mainly concerned with the study of
the bacteriology of freezing of mackerel(Rastrelliger
kanaggrta)and prawn (Metgpggaeus ddbsoni)
The thesis in four sections describes the salient
features of the observations and inferences on the
bacteriology of freezing of fishes and prawns. This
includes the evaluation of methodology for the optimum
recovery of bacteria, bacteriology of the newly caught
fish and prawn, the effect of freezing temperatures on
the survival of selected species of isolates from fish
and prawn and the bacteriology of freezing, frozen
storage and thawing of prawn/fish emphasizing the effect
contributed by each.
Description:
School of marine Science, Cochin University of Science and Technology
Sreenivasan, C; Dr.Krishnamoorthy,A(Cochin University of Science and Technology, August 16, 2012)
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Abstract:
The objective of the study of \Queueing models with vacations and working
vacations" was two fold; to minimize the server idle time and improve the
e ciency of the service system. Keeping this in mind we considered queueing
models in di erent set up in this thesis.
Chapter 1 introduced the concepts and techniques used in the thesis and
also provided a summary of the work done. In chapter 2 we considered an
M=M=2 queueing model, where one of the two heterogeneous servers takes
multiple vacations. We studied the performance of the system with the help
of busy period analysis and computation of mean waiting time of a customer
in the stationary regime. Conditional stochastic decomposition of queue
length was derived. To improve the e ciency of this system we came up
with a modi ed model in chapter 3. In this model the vacationing server
attends the customers, during vacation at a slower service rate. Chapter
4 analyzed a working vacation queueing model in a more general set up.
The introduction of N policy makes this MAP=PH=1 model di erent from
all working vacation models available in the literature. A detailed analysis
of performance of the model was provided with the help of computation of
measures such as mean waiting time of a customer who gets service in normal
mode and vacation mode.
Description:
Department of Mathematics, Cochin University of Science and Technology
Sreenivasan, C; Dr.Krishnamoorthy,A(Cochin University of Science and Technology, June 16, 2012)
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Abstract:
The thesis entitled “Queueing Models with Vacations and Working Vacations" consists of seven chapters including the introductory chapter. In chapters 2 to 7 we analyze different queueing models highlighting the role played by vacations and working vacations. The duration of vacation is exponentially distributed in all these models and multiple vacation policy is followed.In chapter 2 we discuss an M/M/2 queueing system with heterogeneous servers, one of which is always available while the other goes on vacation in the absence of customers waiting for service. Conditional stochastic decomposition of queue length is derived. An illustrative example is provided to study the effect of the input parameters on the system performance measures. Chapter 3 considers a similar setup as chapter 2. The model is analyzed in essentially the same way as in chapter 2 and a numerical example is provided to bring out the qualitative nature of the model. The MAP is a tractable class of point process which is in general nonrenewal. In spite of its versatility it is highly tractable as well. Phase type distributions are ideally suited for applying matrix analytic methods. In all the remaining chapters we assume the arrival process to be MAP and service process to be phase type. In chapter 4 we consider a MAP/PH/1 queue with working vacations. At a departure epoch, the server finding the system empty, takes a vacation. A customer arriving during a vacation will be served but at a lower rate.Chapter 5 discusses a MAP/PH/1 retrial queueing system with working vacations.In chapter 6 the setup of the model is similar to that of chapter 5. The signicant dierence in this model is that there is a nite buer for arrivals.Chapter 7 considers an MMAP(2)/PH/1 queueing model with a nite retrial group
Description:
Department of
Mathematics, Cochin University of Science and Technology.
Jacob,K Daniel; Dr.Krishnamoorthy,A(Cochin University Of Science And Technology, 1985)
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Abstract:
In this thesis we study the effect of rest periods
in queueing systems without exhaustive service and inventory
systems with rest to the server. Most of the works in the
vacation models deal with exhaustive service. Recently
some results have appeared for the systems without exhaustive
service.
Description:
Department Of‘ Mathematics And Statistics,Cochin University Of Science And Technology
Varghese,Jacob; Dr.Krishnamoorthy,A; Dr.Narayanan Namboothiri, M N(Cochin University of Science and Technology, June 16, 2012)
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Abstract:
In this thesis we have introduced and studied the notion of self interruption of service by customers. Service interruption in queueing systems have been extensively discussed in literature (see, Krishnamoorthy, Pramod and Chakravarthy [38]) for the most recent survey. So far all work reported deal with cases in which service interruptions are generated by sources other than customers. However, there are situations where interruptions are due to the customers rather than the system. Such situations
are especially arise at doctors clinic, banks, reservation counter etc. Our attempt is to quantify a few of such problems. Systematically we have proceed from single server queue (in Chapter 2) to multi-server
queues (Chapter 3). In Chapte 4, we have studied a very general multiserver queueing model with service interruption and protection of service phases. We also introduced customer interruption in a retrial setup (in Chapter 5). All models (from Chapter 2 to Chapter 4) that were analyzed involve 'non-preemptive priority' for interrupted customers where as in the model discussed in Chapter 5 interruption of service by customers is not encouraged. So the interrupted customers cannot access the server as long as there are primary customers in the system. In Chapter 5 we have obtained an explicit expression for the stability condition of the system. In all models analyzed in this thesis, we have assumed that no more than one interruption is allowed for a customer while in service. Since the models are not analytically tractable, a large number of numerical illustrations were given in each chapter it illustrate the working of the systems.
We can extend the models discussed in this thesis to several directions. For example some of the models can be analyzed with both server induced and customer induced interruptions the results for which are not available till date. Another possible extension of work is to the case where there is
no bound on the number of interruptions a customer is permitted to have before service completion. More complex is the case where a customer is permitted to have a nite number (K ≥ 2) of We can extend the models discussed in this thesis to several directions.
Description:
Department of
Mathematics, Cochin University of Science and Technology.
Jaya, S; Dr. B Lakshmi(Cochin University of Science and Technology, August 3, 2015)
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Abstract:
In many situations probability models are more realistic than deterministic
models. Several phenomena occurring in physics are studied as random
phenomena changing with time and space. Stochastic processes originated
from the needs of physicists.Let X(t) be a random variable where t is a parameter assuming values
from the set T. Then the collection of random variables {X(t), t ∈ T} is
called a stochastic process. We denote the state of the process at time t
by X(t) and the collection of all possible values X(t) can assume, is called state space
Viswanath C Narayanan; Krishnamoorthy,A(Department of Mathematics, 2005)
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Abstract:
Application of Queueing theory in areas like Computer networking, ATM facilities, Telecommunications and to many other numerous situation made people study Queueing models extensively and it has become an ever expanding branch of applied probability. The thesis discusses Reliability of a ‘k-out-of-n system’ where the server also attends external customers when there are no failed components (main customers), under a retrial policy, which can be explained in detail. It explains the reliability of a ‘K-out-of-n-system’ where the server also attends external customers and studies a multi-server infinite capacity Queueing system where each customer arrives as ordinary but can generate into priority customer which waiting in the queue. The study gives details on a finite capacity multi-server queueing system with self-generation of priority customers and also on a single server infinite capacity retrial Queue where the customer in the orbit can generate into a priority customer and leaves the system if the server is already busy with a priority generated customer; else he is taken for service immediately. Arrival process is according to a MAP and service times follow MSP.
Nisha Nandakumar; Dr. Philip Kurian(Cochin University of Science and Technology, December 3, 2013)
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Abstract:
The Human race of our century is in gluttonous search for novel engineering
products which led to a skyrocketed progress in research and fabrication of filled
polymers. Recently, a big window has been opened up for speciality polymers
especially elastomers with promising properties. Among the many reasons why
rubbers are widely used in the process industries, three are considered as
important. Firstly, rubbers operate in a variety of environments and possess usable
ranges of deformity and durability and can be exploited through suitable and more
or less conventional equipment design principles. Secondly, rubber is an eminently
suitable construction material for protection against corrosion in the chemical plant
and equipment against various corrosive chemicals as, acids and alkalies and if
property tailored, can shield ionising radiations as X-rays and gamma rays in
medical industry, with minimum maintenance lower down time, negligible
corrosion and a preferred choice for aggressive corroding and ionising
environment. Thirdly, rubber can readily and hastily, and at a relatively lower cost,
be converted into serviceable products, having intricate shapes and dimensions. In a
century’s gap, large employment of flexible polymer materials in the different
segments of industry has stimulated the development of new materials with special
properties, which paved its way to the synthesis of various nanoscale materials. At
nano scale, one makes an entry into a world where multidisciplinary sciences meet
and utilises the previously unapproached infinitesimal length scale, having
dimension which measure upto one billionth of a meter, to create novel properties.
The nano fillers augment the elastomers properties in an astonishing fashion due to
their multifunctional nature and unprecedented properties have been exhibited by
these polymer-nanocomposites just to beat the shortcomings of traditional micro
composites. The current research aims to investigate the possibility of using
synthesised nano barium sulphate for fabricating elastomer-based nanocomposites
and thereby imparting several properties to the rubber. In this thesis, nano
materials, their synthesis, structure, properties and applications are studied. The
properties of barium sulphate like chemical resistance and radiopacity have been
utilized in the present study and is imparted to the elastomers by preparing
composites.
Nisha, Nandakumar; Dr. Philip, Kurian(Cochin University of Science And Technology, December 11, 2013)
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Abstract:
The Human race of our century is in gluttonous search for novel engineering
products which led to a skyrocketed progress in research and fabrication of filled
polymers. Recently, a big window has been opened up for speciality polymers
especially elastomers with promising properties. Among the many reasons why
rubbers are widely used in the process industries, three are considered as
important. Firstly, rubbers operate in a variety of environments and possess usable
ranges of deformity and durability and can be exploited through suitable and more
or less conventional equipment design principles. Secondly, rubber is an eminently
suitable construction material for protection against corrosion in the chemical plant
and equipment against various corrosive chemicals as, acids and alkalies and if
property tailored, can shield ionising radiations as X-rays and gamma rays in
medical industry, with minimum maintenance lower down time, negligible
corrosion and a preferred choice for aggressive corroding and ionising
environment. Thirdly, rubber can readily and hastily, and at a relatively lower cost,
be converted into serviceable products, having intricate shapes and dimensions. In a
century’s gap, large employment of flexible polymer materials in the different
segments of industry has stimulated the development of new materials with special
properties, which paved its way to the synthesis of various nanoscale materials. At
nano scale, one makes an entry into a world where multidisciplinary sciences meet
and utilises the previously unapproached infinitesimal length scale, having
dimension which measure upto one billionth of a meter, to create novel properties.
The nano fillers augment the elastomers properties in an astonishing fashion due to
their multifunctional nature and unprecedented properties have been exhibited by
these polymer-nanocomposites just to beat the shortcomings of traditional micro
composites. The current research aims to investigate the possibility of using
synthesised nano barium sulphate for fabricating elastomer-based nanocomposites
and thereby imparting several properties to the rubber. In this thesis, nano
materials, their synthesis, structure, properties and applications are studied. The
properties of barium sulphate like chemical resistance and radiopacity have been
utilized in the present study and is imparted to the elastomers by preparing
composites
Description:
Department of Polymer Science and Rubber Technology
Cochin University of Science and Technology
Nisha, V S; Rani, Joseph(Dept. of Polymer Science and Rubber Technology, May , 2006)
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Abstract:
The present work is to impart radiopacity in various natural polymers like chitosan, natural rubber and derivatives of chitosan and to characterize it. This thesis collated the radiopaque properties of these radiopaque polymers and various technological applications in the medical field. The applications of radiopaque polymers leads to an exploitation of radiopaque properties like X-ray visibility, optical density, effective atomic number, attenuation coefficient of biopolymers like chitosan, chitosan formate, chitosan acetate, carboxy methyl chitosan and natural rubber. The radiopaqe properties of these materials highly depend upon the size, shape, amount of radiopacifier and crystallinity of the radiopaque material. Radiopaque chitosan microspheres were prepared by cross linking with glutaraldehyde followed by the encapsulation of barium sulpahte. The effect of different emulsion systems on the morphology of chitosan microspheres were studied. The study concentrates radiopaque natural rubber for shielding applications. It reveals that to improve the particle size, morphology and crystalline phase of the zinc oxide particles, a novel method for the preparation of zinc oxide is adopted. A detailed radiopacity study was done in natural rubber containing 100phr precipitated zinc oxide prepared from different zinc salts. One of the significant findings of this investigation is that NR vulcanizates containing precipitated zinc oxide (from zinc acetate) shows higher attenuation coefficient. These interesting findings reveal the applications of these natural radiopaque systems in various fields like surgical tools, medical tubings, catheters, radiation shielding,etc.