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Search Results: 1 - 10 of 297343 matches for " J. Yadavalli "
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A TWO-PRODUCT INVENTORY SYSTEM WITH PRODUCT INTERACTION
J. Yadavalli,C. Hargreaves
South African Journal of Industrial Engineering , 2012,
Abstract: ENGLISH ABSTRACT: In this paper, we study a two-component continuous review inventory system. We assume that demand occurs according to a Poisson process and that a demand can be satisfied only if both the components are available in the inventory. Back-orders are not permitted. We assume that the lead-time distribution of one product is arbitrary and the other is exponential. Identifying the underlying process as a semi-regeneration process we find the stationary distribution of the inventory level, the performance measures such as mean stationary rate of number of lost demands, the demands and the reorders made. A numerical example illustrates the results. AFRIKAANSE OPSOMMING: Die artikel ondersoek 'n tweekomponent- deurlopende oorsigvoorraadstelsel. Daar word aanvaar dat aanvraag 'n Poissonproses is en dat aanvraag slegs bevredig kan word indien beide die komponente in die voorraad beskikbaar is. Agterstallige bestellings word nie toegelaat nie. Daar word aanvaar dat die lewertydverdeling van die een produk arbitrêr en die ander eksponensie l is. Indien die onderliggende proses as 'n semigenerasieproses ge dentifiseer word, kan die stasionêre verspreiding van die voorraadvlak bepaal word. Maatstawwe van vertoning soos mediaan- stasionêre koers van die hoeveelheid verlore aanvraag, die aanvraag en herbestellings wat gedoen is word bepaal. 'n Numeriese voorbeeld illustreer die resultate.
CONTROL CHARTS FOR STATIONARY VECTOR ARMA PROCESSES
J. Yadavalli,S.J. Claasen,N. Singh
South African Journal of Industrial Engineering , 2012,
Abstract: ENGLISH ABSTRACT: In practice, there are many quality control situations where a product under consideration may have two or more interrelated quality characteristics and observations of each characteristic are serially correlated. One of the objectives of management is to investigate whether or not all these characteristics of the product simultaneously satisfy the required specifications. To the author's best knowledge, no concrete attempts have been made so far to construct the control charts for such situations, particularly when the data arise from vector autoregressive-moving average (VARMA) processes. It is this problem that has been addressed in this paper. A few methods are suggested for constructing the control charts. When assumptions about independence and normality break down, a bootstrap method, perhaps for the first time, is suggested to attack the problem. Some illustrative examples are discussed. AFRIKAANSE OPSOMMING: In die praktyk is daar vele kwaliteitbeheersituasies waar 'n betrokke produk een of twee onderling verbonde kenmerke kan hê en waarnemings van elke kenmerk serie gekorreleer is. Een van die doelwitte van bestuur is om te ondersoek of hierdie kenmerke van die produk gelyktydig aan die vereiste spesifikasies voldoen al dan nie. Na die outeur se beste wete, is daar tot dusver geen daadwerklike pogings aangewend om die beheergrafieke vir sodanige situasies op te stel nie, veral waar die data ontstaan uit vektor outoregressief bewegende gemiddelde (VARMA) prosesse. Hierdie probleem geniet in hierdie artikel aandag. 'n Aantal metodes vir die opstel van die beheergrafieke word voorgestel. Wanneer aannames oor selfstandigheid en normaliteit faal, word 'n skoenlusmetode voorgestel om die probleem die hoof te bied. 'n Aantal voorbeelde ter toeligting word bespreek.
MANAGING THE COLD CHAIN: A CASE STUDY AT A SOUTH AFRICAN ICE CREAM COMPANY
J. Grobler,V.S.S. Yadavalli
South African Journal of Industrial Engineering , 2012,
Abstract: ENGLISH ABSTRACT: This paper documents the results of a supply chain management (SCM) case study conducted at Centurion Ice Cream and Sweets CC, a producer of ice cream in the greater Gauteng area. The current SCM environment was first analyzed before the distribution function was identified as a prime candidate for further analysis. A Monte Carlo simulation was subsequently performed to investigate the effect of different distribution scenarios. The paper concludes with an investigation into information technology (IT) as the enabler for improved supply chain performance. AFRIKAANSE OPSOMMING: Hierdie artikel dokumenteer die resultate van ‘n voorsieningskanaalgevallestudie uitgevoer by Centurion Ice Cream and Sweets CC, ‘n roomysvervaardiger in die Gauteng-area. Die voorsieningskanaal is eers ontleed voordat die distribusiefunksie ge dentifiseer is as ‘n kandidaat vir verdere analise. ‘n Monte Carlo-simulasie uitgevoer om die effek van verskillende distribusiescenarios te ondersoek. Die artikel sluit af met ‘n ondersoek na inligtingstegnologie as katalisator vir verbeterde voorsieningskanaalprestasie.
ON GAVER’S PARALLEL SYSTEM
E.J. Vanderperre,V.S.S. Yadavalli,S.S. Makhanov
South African Journal of Industrial Engineering , 2012,
Abstract: ENGLISH ABSTRACT: Gaver’s parallel system (and its variants) has received considerable attention in the literature. The Laplace-transform (LT) of the survival function, corresponding to the underlying systems, has been derived by various (alternative) methods. Unfortunately, little-to-no attention has been paid to invert the corresponding transform. First, we present a general reliability analysis of Gaver’s basic parallel system (valid for an arbitrary repair time distribution). Then, we formulate some general hints to obtain the numerical inverse. Finally, we propose a tangible methodology to derive the exact inverse in some particular but important cases of non-rotational transforms. AFRIKAANSE OPSOMMING: Gaver se parallelsisteem (en variante daarvan) is reeds dikwels behandel in die literatuur. Die Laplacetransformasie van die oorlewingsfunksie van die onderliggende sisteme is reeds afgelei op verskillende uiteenlopende wyses. Ongelukkigerwys is min aandag gegee aan die ooreenstemmende inverse transformasie. Ten aanvang word 'n algemene betroubaarheidsontleding van Gaver se basiese parallelsisteem voorgehou (geldig vir 'n arbitrêre hersteltyd-verdeling). Dit word gevolg deur wenke vir bepaling van die numeriese inverse. Ten slotte word 'n tasbare metodologie vir die afleiding van die presiese inverse vir sekere belangrike nie-rotasionele transformasies voorgestel.
FLEXIBLE SOFTWARE RELIABILITY GROWTH MODELS
P.K. Kapur,A. Gupta,V.S.S. Yadavalli,S.J. Claasen
South African Journal of Industrial Engineering , 2012,
Abstract: ENGLISH ABSTRACT: Numerous Software Reliability Growth Models (SRGMs) have been discussed in the literature. These models are used to predict fault content and reliability of software. It has been observed that the relationship between testing time and the corresponding number of faults removed is either exponential or S-shaped, or a mix of the two. Another important class of SRGMs, known as flexible SRGMs, can depict both exponential and S-shaped growth curves. The paper introduces a new concept of power logistic learning function that proves to be very flexible, in the sense that it represents various curve types – exponential, Rayleigh, Weibull or simple logistic. The flexible nature of the power logistic function gives the flexible SRGM a higher degree of accuracy and wider applicability. AFRIKAANSE OPSOMMING: Verskeie voorbeelde van Betroubaarheidsgroeimodelle vir programmatuur word in die literatuur beskryf. Die modelle word gebruik vir die voorspelling van foutinhoud en programmatuurbetroubaarheid. Daar word waargeneem dat die verband tussen toetstyd en die resulterende foutverwydering eksponensiaal of S-vormig of ‘n kombinasie daarvan is. Aanpasbare modelle insluitende diskrete ekwivalente word ook behandel. Die publikasie ontleed vervolgens algemene plooibare maglogistieke leerkromme met wye toepasbaarheid wat slaan op eksponensi le, Rayleigh-, Weilbull- en logistieke funksies. Die plooibaarheid van die model waarborg akkuraatheid en wye toepasbaarheid met die verlangde gehalte van voorspelbaarheid.
A COMPLEX THREE-UNIT PARALLEL SYSTEM WITH PREPARATION TIME FOR REPAIR
Y.A. Mwanga,J.W. Joubert,V.S.S Yadavalli
South African Journal of Industrial Engineering , 2012,
Abstract: ENGLISH ABSTRACT: It is reasonable to expect that preparation time is needed to ready a repair facility before a repair can be carried out. A three-unit system with a `preparation time’ for the repair facility is studied in this paper. The steady-state availability of such a system is obtained. The asymptotic confidence limits of the steady state availability are obtained numerically. AFRIKAANSE OPSOMMING: Redelikerwys kan verwag word dat ‘n herstelproses voorafgegaan word deur ‘n voorbereidingsproses voordat herstel ‘n aanvang kan neem. ‘n Sisteem wat bestaan uit drie eenhede waar ‘n sodanige voorbereidingsproses voor herstelwerk moet plaasvind word ondersoek. Die gestadigde stelselbeskikbaarheid met asimptotiese vertrouegrense word numeries blootgestel.
BAYESIAN HIGHEST POSTERIOR DENSITY INTERVALS FOR THE AVAILABILITY OF A SYSTEM WITH A 'REST-PERIOD' FOR THE REPAIR FACILITY
V.S.S. Yadavalli,A. Bekker,P.J. Mostert,M. Botha
South African Journal of Industrial Engineering , 2012,
Abstract: ENGLISH ABSTRACT: In this paper Bayesian estimation for the steady state availability of a one-unit system with a rest-period for the repair facility is studied. The assumption is that the repair facility takes rest with probability p after each repair completion and the facility does not take the same with probability (l - p). The prior information is assumed to be vague and the Jeffreys' prior is used for the unknown parameters in the system. Gibbs sampling is used to derive the posterior distribution of the availability and subsequently the highest posterior density (HPD) intervals. A numerical example illustrates these results. AFRIKAANSE OPSOMMING: In .hierdie artikel word die Bayes-beraming van die ewewigstoestandsbeskikbaarheid van 'n steise1 wat afwisselend gebruik word, voorgestel. Daar word veronderstel dat die herstelfasiliteit na voltooiing van clke herstel Of 'n rustydperk binnegaan of nie. Die rustydperk sal geneem word met waarskynlikheid p en die waarskynlikheid dat daar nie 'n rustydperk genccm word nie, is (l - p). Jeffrey se a priori-verdeling word vir die onbekende parameters in die stelsel aanvaar. Gibbs-steekproefneming word gcbruik om die a posterioriverdeling van die beskikbaarheid en daarna die hoogste a posteriori-digtheidsintervalle (HPD) afte lei. 'n Numeriese voorbeeld illustreer hierdic resultate .
Berekening van a posteriori-verdeling in Bayes-analise: toepassing in ’n betroubaarheidstelsel wat afwisselend gebruik word
V. S.S. Yadavalli,P. J. Mostert,A. Bekker,M. Botha
Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie , 2002, DOI: 10.4102/satnt.v21i3.231
Abstract: Die Bayes-beraming van die stasionêre tempo van teleurstellings, D∞, vir twee modelle (met verskillende spesifikasies) van stelsels wat afwisselend gebruik word, word voorgestel. Daar word veronderstel dat die stogastiese veranderlikes van die stelsel onafhanklik eksponensiaal verdeel is. Jeffrey se a priori-verdeling word vir die onbekende parameters aanvaar. Die komplekse en nieliniêre definisie van D∞ beperk inferensie in albei modelle. Monte Carlo-simulasie word gebruik om die a posteriori-verdeling van D∞ en daarna die hoogste a posteriori-digtheidsintervalle (HPD) af te lei. ’n Numeriese voorbeeld waarin Bayes-beramers en die HPD-intervalle bereken word, illustreer hierdie resultate. Die frekwentistiese eienskappe van hierdie Bayes-prosedure word bepaal deur oordekkingsproporsies te bereken vir elk van hierdie HPD-intervalle vir vaste waardes van die parameters. Abstract Computation of posterior distribution in Bayesian analysis – application in an intermittently used reliability system Bayesian estimation is presented for the stationary rate of disappointments, D∞, for two models (with different specifications) of intermittently used systems. The random variables in the system are considered to be independently exponentially distributed. Jeffreys’ prior is assumed for the unknown parameters in the system. Inference about D∞ is being restrained in both models by the complex and non-linear definition of D∞. Monte Carlo simulation is used to derive the posterior distribution of D∞ and subsequently the highest posterior density (HPD) intervals. A numerical example where Bayes estimates and the HPD intervals are determined illustrates these results. This illustration is extended to determine the frequentistical properties of this Bayes procedure, by calculating covering proportions for each of these HPD intervals, assuming fixed values for the parameters.
Congenital melanocytic nevus of upper eyelid
Chauhan Dinesh,Guruprasad Yadavalli
Journal of Cutaneous and Aesthetic Surgery , 2011,
Abstract: Congenital nevi are present in approximately 2-3% of neonates. These lesions are present at birth. They are characterized by pigmented lesions with regular margins, smooth or lobular surfaces and occasionally have long coarse hair. The risk of melanoma development is proportional to the size, especially if it involves over 5% of the body surface, or is > 20 cm in adolescents (large/giant congenital nevus). The risk of malignant change ranges from 5-40%. We present a case of a congenital melanocytic nevus in a six-year-old female child which was surgically treated.
Reduction of Clostridium Difficile and vancomycin-resistant Enterococcus contamination of environmental surfaces after an intervention to improve cleaning methods
Brittany C Eckstein, Daniel A Adams, Elizabeth C Eckstein, Agam Rao, Ajay K Sethi, Gopala K Yadavalli, Curtis J Donskey
BMC Infectious Diseases , 2007, DOI: 10.1186/1471-2334-7-61
Abstract: During a 6-week period, we cultured commonly touched surfaces (i.e. bedrails, telephones, call buttons, door knobs, toilet seats, and bedside tables) in rooms of patients with CDAD and VRE colonization or infection before and after housekeeping cleaning, and again after disinfection with 10% bleach performed by the research staff. After the housekeeping staff received education and feedback, additional cultures were collected before and after housekeeping cleaning during a 10-week follow-up period.Of the 17 rooms of patients with VRE colonization or infection, 16 (94%) had one or more positive environmental cultures before cleaning versus 12 (71%) after housekeeping cleaning (p = 0.125), whereas none had positive cultures after bleach disinfection by the research staff (p < 0.001). Of the 9 rooms of patients with CDAD, 100% had positive cultures prior to cleaning versus 7 (78%) after housekeeping cleaning (p = 0.50), whereas only 1 (11%) had positive cultures after bleach disinfection by research staff (p = 0.031). After an educational intervention, rates of environmental contamination after housekeeping cleaning were significantly reduced.Our findings provide additional evidence that simple educational interventions directed at housekeeping staff can result in improved decontamination of environmental surfaces. Such interventions should include efforts to monitor cleaning and disinfection practices and provide feedback to the housekeeping staff.Patients colonized or infected with healthcare-associated pathogens often shed these organisms onto their skin and into the environment [1]. Although direct contact with patients is generally considered the major source for acquisition of pathogens on healthcare workers' hands and subsequent transmission to other patients, several recent studies suggest that contaminated environmental surfaces may also play an important role in pathogen transmission [2-10]. For example, we found that vancomycin-resistant enterococci (VRE) an
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