Papers by Wladyslaw J Kowalski
... Mike Sasges, Bill Carey, Tatiana Koutchma, Forrest Fencl, Russ Briggs, Josephine Lau, Carlos ... more ... Mike Sasges, Bill Carey, Tatiana Koutchma, Forrest Fencl, Russ Briggs, Josephine Lau, Carlos Gomes, Fahmi Yigit, Herbert Silderhuis, Joe Ritorto, Merrill Ritter, Brad Hollander, Scott Prahl, Karl Linden, William Balch, Atanu Sengupta, MD Lechner, Ketan Sharma, Donald Milton ...
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A mathematical model is presented to explain the ultraviolet susceptibility of viruses in terms o... more A mathematical model is presented to explain the ultraviolet susceptibility of viruses in terms of genomic sequences that have a high potential for photodimerization. The specific sequences with high dimerization potential include doublets of thymine (TT), thymine-cytosine (TC), cytosine (CC), and triplets composed of single purines combined with pyrimidine doublets. The complete genomes of 49 animal viruses and bacteriophages were evaluated using base-counting software to establish the frequencies of dimerizable doublets and triplets. The model also accounts for the effects of ultraviolet scattering. Constants defining the relative lethality of the four dimer types were determined via curve-fitting. A total 77 water-based UV rate constant data sets were used to represent 22 DNA viruses. A total of 70 data sets were used to represent 27 RNA viruses. Predictions are provided for dozens of viruses of importance to human health that have not previously been tested for UV susceptibility.
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P Art and Culture Magazine, 2004
A review of ancient Greek, Roman, and Egyptian Board Games.
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The Pennsylvania State University The Graduate School College of Engineering Design and Optimization of UVGI Air Disinfection Systems A Thesis in Architectural Engineering, 2001
Mathematical models of the response of populations of microorganisms exposed to ultraviolet
germi... more Mathematical models of the response of populations of microorganisms exposed to ultraviolet
germicidal irradiation (UVGI) are developed that include two-stage response curves and shoulder
effects. Models are used to develop a C++ computer program that is capable of predicting the
performance of UVGI air disinfection systems. The algorithms are based on models for 1) the
intensity field of UVGI lamps, 2) the intensity field due to UVGI reflective enclosures, and 3) the
kill rate of microorganisms to UVGI exposure as they pass through the modeled intensity field.
The validity of the UVGI lamp model is established by comparison with lamp photosensor data.
The validity of the overall predictive model is established by comparison of predictions with
laboratory bioassays for two species of airborne pathogens – Serratia marcescens and Bacillus
subtilis. First stage rate constants, second stage rate constants, and the defining shoulder
parameters are determined for Aspergillus niger and Rhizopus nigricans based on bioassay data,
and it is shown how predictions using only single stage rate constants can deviate significantly
from predictions using the complete survival curve. A dimensional analysis of UVGI systems
identifies nine dimensionless parameters responsible for determining the effectiveness of any
rectangular UVGI system. A factorial analysis of the dimensionless parameters based on data
output by the program identifies the most critical parameters and the inter-relationships that
determine UVGI system effectiveness. Response surfaces are generated using program output to
illustrate the inter-relationships of the dimensionless parameters. The optimum values of the
dimensionless parameters are summarized that result in optimized performance. Economic
optimization is demonstrated by a series of examples that calculate life cycle costs, and principles
of economic optimization are summarized. Conclusions are presented that will produce more
energy-efficient and effective designs and a proposed model for improved UVGI systems is
presented.
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HPAC Engineering, 2003
A review of the effectiveness of dilution ventilation,
filtration, and ultraviolet germicidal irr... more A review of the effectiveness of dilution ventilation,
filtration, and ultraviolet germicidal irradiation
in mitigating five biological-weapon agents
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IUVA News, 2009
The susceptibility of viruses to ultraviolet (UV) light has traditionally been defined in terms o... more The susceptibility of viruses to ultraviolet (UV) light has traditionally been defined in terms of the UV rate constant, also called a Z value, which is the slope of the survival curve on a logarithmic scale. The UV rate constant refers to either broad range UV in the UVB/UVC spectrum (200-320 nm) or, more commonly, to narrow-band UVC near the 253.7 nm wavelength. UV susceptibility can also be defined by the UV exposure dose (fluence) required for 90% inactivation (the D90 value), a more intuitive parameter that avoids the problem of defining shoulder effects and second stages in the survival curve. In this paper the UV rate constant is defined in terms of the D90 value to provide an absolute indicator of UV susceptibility in the first stage of decay, and these values are thereby interchangeable. The UV rate constant, in m 2 /J, applicable to the first stage of decay is defined as: (1) where S = survival, fractional D = UV exposure dose (fluence), J/m 2 The D90 value is then: (2) The subject of virus UV susceptibility has been extensively studied and the processes that occur at the molecular level have been quantified to an great degree, but the complexities of these processes and prior lack of fully sequenced genomes have heretofore precluded development of a complete quantitative model of virus inactivation. The actual theoretical basis for UV susceptibility has been elucidated in the works of Setlow and Carrier (1966), Smith and Hanawalt (1969), Becker and Wang (1989), and others. This paper applies the basic model of UV inactivation as detailed in these seminal works to viral genomes from the NCBI database (NCBI 2009) and statistically evaluates the correlation with known UV D90 values. With some enhancements of the basic model and adjustments to the parameters, a model is developed herein that provides predictions for both RNA and DNA viruses. This model also includes a new ultraviolet scattering model developed by the authors that contributes to the overall accuracy of the DNA model. Rate Constant Determinants Various intrinsic factors determine the sensitivity of a virus to UV exposure under any set of constant ambient conditions of temperature and humidity including physical size, molecular weight, DNA conformation, presence of chromophores, propensity for clumping, presence of repair enzymes or dark/light repair mechanisms, hydrophilic surface properties, relative index of refraction, specific spectrum of UV, G+C% content, and % of potential pyrimidine dimers. The physical size of a virus bears no clear direct relationship with UV susceptibility. UV-induced damage to DNA is independent of molecular weight (Scholes et al 1967). Virus nucleocapsids are too thin to allow any significant chromophore protection. The specific UV spectrum has a ABSTRACT A mathematical model is presented to explain the ultraviolet susceptibility of viruses in terms of genomic sequences that have a high potential for photodimerization. The specific sequences with high dimerization potential include doublets of thymine (TT), thymine-cytosine (TC), cytosine (CC), and triplets composed of single purines combined with pyrimidine doublets. The complete genomes of 49 animal viruses and bacteriophages were evaluated using base-counting software to establish the frequencies of dimerizable doublets and triplets. The model also accounts for the effects of ultraviolet scattering. Constants defining the relative lethality of the four dimer types were determined via curve-fitting. A total of 70 data sets were used to represent 27 RNA viruses. A total 77 water-based UV rate constant data sets were used to represent 22 DNA viruses. Predictions are provided for dozens of viruses of importance to human health that have not previously been tested for their UV susceptibility.
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IUVA News , 2008
Health Care facilities are subject to microbiological airborne
hazards that can cause infections ... more Health Care facilities are subject to microbiological airborne
hazards that can cause infections in both patients and
health care workers. Hospital-acquired, or nosocomial,
infections have been a persistent problem in hospitals and
they can have complex multifaceted etiologies. It is
possible that as much as a third or more of all nosocomial
infections may be the result of airborne transmission at
some point and, if so, air disinfection technologies may be
able to reduce the nosocomial infection rate.
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HPAC Engineering, 2007
The epidemiology and aerobiological
pathways of airborne nosocomial infections
and methods of air... more The epidemiology and aerobiological
pathways of airborne nosocomial infections
and methods of air and surface disinfection
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AIHA Journal, 2003
An enclosed flow-through system using airborne ozone for disinfection and which removes the ozone... more An enclosed flow-through system using airborne ozone for disinfection and which removes the ozone with a catalytic converter was tested with a strain of Escherichia coli. Petri dishes containing the microorganisms were inserted in a chamber and exposed for 10-480 min to ozone concentrations between 4 and 20 ppm. Death rates in excess of 99.99% were achieved. Survival data is fitted to a two-stage curve with a shoulder based on the multihit target model. Ozone was removed from the exhaust air to nondetectable levels using a metal oxide based catalyst. The possibility of using ozone as an airborne disinfectant for internal building surfaces and catalytically removing the ozone on exhaust is demonstrated to be feasible. A model for the decay of Bacillus cereus under ozone exposure is proposed as an example for predicting the sterilization of buildings contaminated with anthrax. The potential for disinfecting airstreams and removing ozone to create breathable air is also implied by the results of this experiment.
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IMCE Proceedings, 2002
Multizone network airflow analysis is used to analyze stack and mechanical system effects on the ... more Multizone network airflow analysis is used to analyze stack and mechanical system effects on the distribution of three representative biological agents in a prototype 40 story building. This approach relies on mass balances to compute airflow and contaminant transfer between the building zones. The analysis considers stack effects caused by cold outdoor temperatures, unintended positive and negative pressurization of the floor on which the release of the agent occurs, and three levels of contaminant removal using a combination filter/UVGI system. The results show that vertical shafts,
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Consulting Specifying Engineer, 2007
Much attention has been focused recently on pathogenic microorganisms and the threat these microo... more Much attention has been focused recently on pathogenic microorganisms and the threat these microorganisms are to communities. Especially problematic are microorganisms that have developed resistance to antibiotic treatment and that have begun to spread beyond the bounds of hospital walls. The most dangerous are those that may spread by the airborne route, which include methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant tuberculosis (XTB). Pathogens that develop pan-drug resistance (PDR) might be considered “superbugs” because they are virtually invulnerable to standard drug treatments. Once these microbes develop immunity to antibiotic treatment and cause outbreaks in hospital environments they may, and have on occasion, spread into local communities. How great an epidemic threat these microorganisms are to communities is a question worth examining in more detail.
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Engineered Systems, 2018
In the legal cannibis sector, unwanted microbes in the airstream can translate to big investments... more In the legal cannibis sector, unwanted microbes in the airstream can translate to big investments going up in smoke.
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This study investigated the ability of monochromatic ultraviolet (UV) light at 254 nm applied at ... more This study investigated the ability of monochromatic ultraviolet (UV) light at 254 nm applied at typical drinking water disinfection doses to damage the antibiotic-resistant genes mph(A), sul1, tet-A, and bla-Tem1 in water-borne bacteria. UV sensitivity rank was bla-TEM1 > tet-A > sul1 > mph(A), which is consistent with predictions of a previously presented genomic-based UV sensitivity model. It is the first time that predictions of the relative UV sensitivity of antibiotic resistance genes have been validated with experimental data and suggest that such modeling is useful for determining the UV sensitivity of other genes in waterborne microorganisms.
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IUVA Conference Proceedings, 2009
A mathematical model is presented for the ultraviolet susceptibility of microbes based on evaluat... more A mathematical model is presented for the ultraviolet susceptibility of microbes based on evaluation of complete genomes. The genomes of 49 animal viruses and bacteriophages, and 33 bacteria, were analyzed using base-counting software to establish the frequencies of potential dimers. A total of 71 data sets represented 27 ssRNA viruses, while 77 data sets represented 22 dsDNA viruses, and 64 data sets represented the bacteria. UV susceptibility (D 90) was correlated with the genomic model and produced R 2 values of 79%, 87%, and 70% for RNA viruses, DNA viruses and bacteria respectively. Predictions of UV susceptibility are provided for dozens of microbes important to human health.
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Journal of Architectural Engineering, 2003
This paper presents the results of research on the performance of air-cleaning and air-disinfecti... more This paper presents the results of research on the performance of air-cleaning and air-disinfection systems used for protecting buildings against intentional releases of biological agents. The air-cleaning technologies addressed include dilution ventilation, filtration, and ultraviolet germicidal irradiation. A 40-story commercial office building is modeled using typical occupancy levels and leakage rates for doors, walls, and floors. A steady-state single-zone model is used to predict steady-state conditions resulting from the use of various levels of air cleaning. A transient single-zone model is used to predict transient indoor concentrations from which inhaled doses and estimated casualties are predicted. A transient multizone model is used to evaluate contaminant dispersion and estimate potential casualties. Three design-basis attack scenarios are simulated using various biological weapon agents. Predicted casualties are estimated using an epidemiological model of the dose response curves for each of the agents. The effect of increasing levels of air cleaning is examined under the attack scenarios to evaluate their effectiveness. Results indicate that high levels of protection are possible for building occupants with moderate and affordable levels of air cleaning when filtration is combined with ultraviolet germicidal irradiation. Results also suggest that diminishing returns occur when increased levels of air cleaning are applied. It is hypothesized that the maximum useful size of any air-cleaning system is defined and limited by building physical characteristics alone.
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HPAC Engineering, 2000
L ethal to microorganisms, ultraviolet radiation in the range of 2250 to 3020 angstroms is used i... more L ethal to microorganisms, ultraviolet radiation in the range of 2250 to 3020 angstroms is used in a variety of disinfection applications , a process referred to as ultraviolet germicidal irradiation (UVGI). Since the first UVGI system was successfully implemented for disinfecting the municipal water system in Mar-seilles, France, 1 in 1909, the disinfec-tion of medical equipment using UVGI has been a common and reliable practice. But unlike water-and equipment-disinfection applications, the disinfec-tion of air streams using UVGI has a history of varying success and unpredictable performance. The first laboratory studies on UVGI of air in the 1920s showed such promise that the elimination of airborne disease seemed possible. In 1936, Hart used UVGI to sterilize air in a surgical operating room. 2 In 1937, the first application of UVGI for a school ventilation system dramatically reduced the incidence of measles, with subsequent applications enjoying similar success. 3 Experiments by Riley and O'Grady 4 resulted in the elimination of tuberculosis (TB) bacilli from hospital-ward exhaust air. A plethora of designs that were more imitative than engineered followed these early applications. The result was a mixture of successes and failures. This experience is reflected in various guidelines that decline to sanction the use of UVGI as a primary system. A 1954 study on the use of UVGI showed a failure to reduce disease in London schools. Although limited data are available to determine the causes of earlier design failures, the apparent cloning of UVGI systems without regard to operating conditions probably doomed many installations from the start. A review of current industry practices indicates that information on the design of UVGI systems lacks the detail necessary for engineers to ensure performance. This article addresses the factors that determine the design
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ASHRAE Transactions, 2000
This paper summarizes an improved methodology for predicting the rate of airstream disinfection f... more This paper summarizes an improved methodology for predicting the rate of airstream disinfection for UVGI systems that will enable effective designs and lower energy costs. This approach uses radiative view factors to define the three-dimensional intensity field for lamps and reflective surfaces inside enclosures. Lamp photosensor data for a variety of lamps are shown to agree more closely with the view factor model than with models using the Inverse Square Law. The intensity field due to reflectivity from internal surfaces is determined by assuming diffuse reflectivity. An analytical method is used to determine the inter-reflection component of intensity due to multiple internal reflections. The superposition of these components yields a three-dimensional intensity field matrix that can be used to calculate disinfection rates for any given microbial rate constant. Results from laboratory bioassays using S. marcescens in various duct configurations have corroborated model predictions within ±15% in most cases.
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HVAC&R Research, 2003
A dimensional analysis of an ultraviolet germicidal irradiation (UVGI) air disinfection system wi... more A dimensional analysis of an ultraviolet germicidal irradiation (UVGI) air disinfection system within a diffusely reflective enclosure is performed using the Buckingham pi theorem. The eight dimensionless parameters obtained include the duct aspect ratio, the lamp aspect ratio, the reflectivity, and terms that incorporate the UV dose, airflow, duct dimensions, and lamp location coordinates. Computer simulation of the dose absorbed by an airborne microbe is used to predict system performance for several thousand combinations of the dimensionless parameters. Statistical analysis of these results is performed to determine the significance of each of the dimensionless parameters and their interactions. Conclusions regarding performance are summarized. The most significant parameters that determine performance of diffusively reflective UVGI systems are shown to be the dose, the reflectivity, the duct geometry, the lamp aspect ratio, lamp location, and various combined functions of these parameters. Practical implications of this research may include the improvement or optimization of UVGI air disinfection systems for induct and recirculation unit applications, with a consequent improvement in energy efficiency.
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Quantitative Microbiology, 2000
A comprehensive treatment of the mathematical basis for modeling the disinfection process for air... more A comprehensive treatment of the mathematical basis for modeling the disinfection process for air using ultraviolet germicidal irradiation (UVGI). A complete mathematical description of the survival curve is developed that incorporates both a two stage inactivation curve and a shoulder. A methodology for the evaluation of the three-dimensional intensity fields around UV lamps and within reflective enclosures is summarized that will enable determination of the UV dose absorbed by aerosolized microbes. The results of past UVGI studies on airborne pathogens are tabulated. The airborne rate constant for Bacillus subtilis is confirmed based on results of an independent test. A re-evaluation of data from several previous studies demonstrates the application of the shoulder and two-stage models. The methods presented here will enable accurate interpretation of experimental results involving aerosolized microorganisms exposed to UVGI and associated relative humidity effects
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IOA IUVA World Congress Papers, 2011
Ultraviolet genomic modeling is a method for evaluating the ultraviolet sensitivity of microorgan... more Ultraviolet genomic modeling is a method for evaluating the ultraviolet sensitivity of microorganisms by reading and interpreting the complete microbial genome. Base counting software is used to identify short sequences of amino acids that have a high photodimerization potential. The specific sequences that can result in photodimers include thymine-thymine (TT), thymine-cytosine (TC or CT), cytosine-cytosine (CC), and purine-pyrimidine dimers that form under certain conditions. A mathematical algorithm is used to compute the relative UV sensitivity for each microbe. Correlation of the genomic model with known ultraviolet susceptibilities of over 160 microbes has resulted in a general model that can be used to predict the UV sensitivities of bacteria, RNA viruses and DNA viruses with predictive accuracies over 80% for bacteria and over 90% for viruses. Since current UV bioassays are estimated to have an error range of +/-30%, the genomic model may form a benchmark by which the accuracy of bioassay testing may be gauged. An extensive list of predicted UV sensitivities is presented for microbes that do not currently have published UV susceptibilities, including many nosocomial and zoonotic pathogens and bioweapon agents. Other applications of the model are discussed including the use of the genomic model to assess the survival of microbes in an airstream or water stream via PCR technology. Extension of the ultraviolet genomic model to UVA and UVB applications is feasible and the possibility of applying the model to human skin cancer research is discussed. Further extension of the genomic model to ionizing radiation and potential applications are discussed.
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Papers by Wladyslaw J Kowalski
germicidal irradiation (UVGI) are developed that include two-stage response curves and shoulder
effects. Models are used to develop a C++ computer program that is capable of predicting the
performance of UVGI air disinfection systems. The algorithms are based on models for 1) the
intensity field of UVGI lamps, 2) the intensity field due to UVGI reflective enclosures, and 3) the
kill rate of microorganisms to UVGI exposure as they pass through the modeled intensity field.
The validity of the UVGI lamp model is established by comparison with lamp photosensor data.
The validity of the overall predictive model is established by comparison of predictions with
laboratory bioassays for two species of airborne pathogens – Serratia marcescens and Bacillus
subtilis. First stage rate constants, second stage rate constants, and the defining shoulder
parameters are determined for Aspergillus niger and Rhizopus nigricans based on bioassay data,
and it is shown how predictions using only single stage rate constants can deviate significantly
from predictions using the complete survival curve. A dimensional analysis of UVGI systems
identifies nine dimensionless parameters responsible for determining the effectiveness of any
rectangular UVGI system. A factorial analysis of the dimensionless parameters based on data
output by the program identifies the most critical parameters and the inter-relationships that
determine UVGI system effectiveness. Response surfaces are generated using program output to
illustrate the inter-relationships of the dimensionless parameters. The optimum values of the
dimensionless parameters are summarized that result in optimized performance. Economic
optimization is demonstrated by a series of examples that calculate life cycle costs, and principles
of economic optimization are summarized. Conclusions are presented that will produce more
energy-efficient and effective designs and a proposed model for improved UVGI systems is
presented.
filtration, and ultraviolet germicidal irradiation
in mitigating five biological-weapon agents
hazards that can cause infections in both patients and
health care workers. Hospital-acquired, or nosocomial,
infections have been a persistent problem in hospitals and
they can have complex multifaceted etiologies. It is
possible that as much as a third or more of all nosocomial
infections may be the result of airborne transmission at
some point and, if so, air disinfection technologies may be
able to reduce the nosocomial infection rate.
pathways of airborne nosocomial infections
and methods of air and surface disinfection
germicidal irradiation (UVGI) are developed that include two-stage response curves and shoulder
effects. Models are used to develop a C++ computer program that is capable of predicting the
performance of UVGI air disinfection systems. The algorithms are based on models for 1) the
intensity field of UVGI lamps, 2) the intensity field due to UVGI reflective enclosures, and 3) the
kill rate of microorganisms to UVGI exposure as they pass through the modeled intensity field.
The validity of the UVGI lamp model is established by comparison with lamp photosensor data.
The validity of the overall predictive model is established by comparison of predictions with
laboratory bioassays for two species of airborne pathogens – Serratia marcescens and Bacillus
subtilis. First stage rate constants, second stage rate constants, and the defining shoulder
parameters are determined for Aspergillus niger and Rhizopus nigricans based on bioassay data,
and it is shown how predictions using only single stage rate constants can deviate significantly
from predictions using the complete survival curve. A dimensional analysis of UVGI systems
identifies nine dimensionless parameters responsible for determining the effectiveness of any
rectangular UVGI system. A factorial analysis of the dimensionless parameters based on data
output by the program identifies the most critical parameters and the inter-relationships that
determine UVGI system effectiveness. Response surfaces are generated using program output to
illustrate the inter-relationships of the dimensionless parameters. The optimum values of the
dimensionless parameters are summarized that result in optimized performance. Economic
optimization is demonstrated by a series of examples that calculate life cycle costs, and principles
of economic optimization are summarized. Conclusions are presented that will produce more
energy-efficient and effective designs and a proposed model for improved UVGI systems is
presented.
filtration, and ultraviolet germicidal irradiation
in mitigating five biological-weapon agents
hazards that can cause infections in both patients and
health care workers. Hospital-acquired, or nosocomial,
infections have been a persistent problem in hospitals and
they can have complex multifaceted etiologies. It is
possible that as much as a third or more of all nosocomial
infections may be the result of airborne transmission at
some point and, if so, air disinfection technologies may be
able to reduce the nosocomial infection rate.
pathways of airborne nosocomial infections
and methods of air and surface disinfection