Abstract:
A method and apparatus for determining the effect of various agents on the growth of biological material (biofilm), microbially-influenced corrosion and the deposition of organic and inorganic contaminants is disclosed. The method and apparatus allow for the modeling of the growth of biological contaminants and the deposition of organic and inorganic materials on industrial equipment surfaces, such as those used in the pulp and papermaking industry. The device consists of a tray which includes recessed areas for receiving coupons, as well as fluid inlets and fluid outlets for permitting the flow of liquid samples over the coupons. The design and configuration of the apparatus provides a great deal of versatility in testing various biocidal and other agents under select environmental conditions.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method and apparatus for studying and screening agents useful for regulating the growth of biological material and the deposition of organic and inorganic contaminants on coupons. More particularly, the present invention is directed to a method and apparatus for studying and screening biocidal agents useful in regulating the growth of bacteria on stainless steel coupons. 
     BACKGROUND OF RELATED TECHNOLOGY 
     Many industrial processes, such as pulp and paper making, utilize water and/or other liquid material in processing steps. Such process liquid typically provides an excellent supply of carbon and nutrients which promote bacterial growth. In paper mills, for instance, bacterial films (“biofilms”) undesirably and readily form on the steel surfaces of process equipment used during manufacture. Such biofilms typically are accompanied by protective exopolysaccharides (“slime”) and occur at the interface of these equipment surfaces and process water streams. Additionally, inorganic contaminants, such as calcium carbonate (“scale”) and organic contaminants often deposit on such surfaces. These organic contaminants are typically known as pitch (e.g., resins from wood) and stickies (e.g., glues, adhesives, tape, and wax particles). 
     The growth of biofilm and the deposition of these inorganic and organic contaminants can be detrimental to the efficiency of such equipment causing both reduced product quality, reduced operating efficiency, and general operational difficulties in the systems. Biofilm growth and organic and inorganic contaminant deposition on consistency regulators and other instrument probes can render these components useless, and such growth and deposition on screens can reduce throughput and upset operation of the system. Growth and deposition can occur not only on metal surfaces in the system, but also on plastic and synthetic surfaces such as machine wires, felts, foils, Uhle boxes and headbox components. The difficulties posed by these growths and deposits include direct interference with the efficiency of the contaminated surface, resulting in reduced production, as well as holes, dirt, and other sheet defects that reduce the quality and usefulness of the paper for operations that follow like coating, converting or printing. 
     Consequently, methods of preventing and removing the build-up of such growths and deposits on pulp and paper mill equipment surfaces are of great industrial importance. While paper machines can be shut down for cleaning, this is undesirable as it necessarily results in a loss of productivity and the product which results prior to such cleaning is of poor quality as it is partially contaminated from growths and deposits which break off and become incorporated into product sheets. Likewise, removing growths and deposits also necessarily results in the formation of poor quality product which is manufactured prior to such removal. Preventing biofilm growth and contaminant deposition is thus greatly preferred as it allows for consistently high quality product to be produced in an efficient manner. Particularly, the use of compositions comprising gelatin, such as those described in U.S. Pat. No. 5,536,363 to Nguyen, have been found to be well suited for regulating the deposition of organic and inorganic contaminants in pulp and papermaking systems. 
     The growth of slime on metal surfaces creates an environment which is conducive to corrosion. This microbially-influenced corrosion typically occurs at the interface between the slime and the metal surface. Also, fouling or plugging by slime readily occurs in pulp and paper mill systems. Typically, the slime becomes entrained in the paper produced and causes breakouts on the paper machines with consequent work stoppages and the loss of production time. It also causes unsightly blemishes in the final product, resulting in rejects and wasted output. These contamination problems have resulted in the extensive utilization of biocides in water used in pulp and paper mill systems. Agents which have enjoyed widespread use in such applications include chlorine, organo-mercurials, chlorinated phenols, organo-bromines, and various organo-sulfur compounds, all of which are generally useful as biocides but each of which is attended by a variety of impediments. 
     Known means of studying biological material typically involve the flow of an aqueous sample containing the biological material over a solid support, such as with a flow through cell assembly. Typically, a pressure means, such as an inert gas, and/or a vacuum means are used to cause the sample to contact the solid support. For example, U.S. Pat. No. 5,641,458 to Shockley, Jr. et al. discloses a flow through cell device for the non-invasive monitoring of bodily fluids. The device includes sensors which interact with a fluid sample through a semi-permeable membrane. Sensors attached to the membrane allow for photochemical reactions involving the fluid sample to be monitored optically. 
     U.S. Pat. No. 5,624,815 to Grant et al. discloses a method and apparatus for analyzing biological material by passing a liquid sample through a number of discrete wells which are adapted to retain the biological material. The liquid sample is drawn into the wells through a vacuum mechanism. Also, U.S. Pat. No. 5,792,430 to Hamper, U.S. Pat. No. 5,624,815 to Grant et al., U.S. Pat. No. 4,908,319 to Smyczek et al., and U.S. Pat. No. 4,753,775 to Ebersole et al., all disclose means for studying biological material in which a liquid sample is drawn over a solid support. 
     As conditions such as temperature, pH, and the presence of organic and inorganic materials can vary greatly among and within manufacturing processes, there is a continuing need to investigate materials useful for the prevention and removal of biofilms and organic and inorganic contaminants that form on process equipment functioning under these various conditions. Known experimental techniques, such as those described above, are not well suited for such investigations. While they are suited for the specific investigation of certain biological material, they do not allow for an efficient and thorough analysis of the effect of numerous and various chemicals and compositions on a variety of substrates under select conditions. 
     Additionally, it is known to monitor biofilm growth in water systems, such as through the apparatuses and methods described in U.S. Pat. No. 5,049,492 to Sauer et al. and U.S. Pat. No. 6,017,459 to Zeiher et al., to allow for the sampling of water during manufacturing processes. While these apparatuses and methods are important in determining, and consequently maintaining, the quality of the water stream, of greater importance is the discovery and development of compositions which will prevent and/or destroy the growth of biofilms and inorganic and organic contaminants in the water stream. Therefore, there exists a need for a model experimental system and a method involving such a system by which the efficient investigation of substances useful in regulating the growth of biological materials and the deposition of inorganic and organic contaminants on equipment surfaces such as those used in pulp and papermaking processes may be conducted. 
     SUMMARY OF THE INVENTION 
     In one aspect, the present invention provides a device for permitting fluid flow, such as whitewater or synthetic whitewater endemic to pulp and papermaking systems, over a coupon. The device includes a tray body (tray) which defines a coupon receiving chamber, a fluid inlet passageway in fluid communication with the coupon receiving chamber, and a fluid outlet passageway in fluid communication with the coupon receiving chamber. The tray body provides for fluid to enter the fluid inlet passageway, contact the coupon, and enter the fluid outlet passageway. 
     Preferably, the tray body is a substantially elongate member including first and second opposed side surfaces, first and second opposed major surfaces, with the coupon receiving chamber accessible through the first major surface. The tray body may include a plurality of coupon receiving chambers which are adapted to receive substantially elongate stainless steel coupons. 
     The coupon receiving chamber is in partial overlying registry with the fluid inlet passageway and the fluid outlet passageway and includes a coupon support surface and an upstanding perimetrical wall bounding the coupon support surface. The coupon support surface further defines a fluid inlet port in fluid communication with the fluid inlet passageway and further defines a fluid outlet port in fluid communication with the fluid outlet passageway. The tray body further defines a fluid inlet aperture which is opposite the fluid inlet port and which is in fluid communication with the fluid inlet passageway. 
     The tray body accommodates a fluid feed conduit for delivering a fluid through the fluid inlet aperture and further defines a fluid outlet aperture which is opposite the fluid outlet port and which is in fluid communication with the fluid outlet passageway. Further, the tray body accommodates a fluid discharge conduit for conducting fluid through the fluid outlet aperture. 
     In a preferred embodiment of the present invention, the coupon support surface is elongate and the fluid inlet and fluid outlet ports are defined at opposite ends of the coupon support surface. The present invention may also include a cover which is in removable sealing registry over the coupon receiving chamber. Additionally, the present invention may also include a gasket supported between the tray body and the cover for further sealing the coupon receiving chamber. 
     In a method aspect of the present invention, a method is provided for studying and screening agents useful for regulating the growth of biofilm and the deposition of organic and inorganic contaminants on a coupon surface which includes the steps of: (i) providing a device which regulates fluid flow over the coupon surface, wherein the device includes a tray body defining a coupon receiving chamber, a fluid inlet passageway in fluid communication with the coupon receiving chamber and a fluid outlet passageway in fluid communication with the coupon receiving chamber; (ii) placing the coupon in the coupon receiving chamber; and (iii) effecting a fluid flow over the coupon. The present invention may also include the step of determining the growth of biological material on the coupon, such as by subjecting the coupon to staining and microscopy. 
     The present invention may further include the step of directing the fluid flow through the fluid inlet passageway and directing the fluid flow to the fluid inlet passageway by a fluid feed conduit. Further, the present invention may include the step of directing the fluid flow across the coupon, through the fluid outlet passageway, and from the fluid outlet passageway through a fluid discharge conduit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top plan view of a biofilm growth tray of the present invention. 
     FIG. 2 is a top view of the present invention showing a tray defining a plurality of chambers and fluid inlet and fluid outlet ports. 
     FIG. 3 is a cross-sectional view of the tray of FIG. 1 taken along the line AA—AA. 
     FIG. 4 is an exploded perspective view of the tray of the present invention including a cover thereover. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is well suited for studying the growth of biological materials and the deposition of organic and inorganic contaminants on various substrates. Such biological materials include, for example, bacteria, fungi, yeast, algae, diatoms, protozoa, macroalgae, and the like. In the pulp and paper industry, process water provides an excellent supply of organic and inorganic materials which promote the growth of bacteria (biofilms) and protective exopolysaccharides (slime) which occur at the interface of machine surfaces (typically steel) and process water streams. Additionally, inorganic contaminants, such as calcium carbonate (“scale”) and organic contaminants often deposit on such surfaces. These organic contaminants are typically known as pitch (e.g., resins from wood) and stickies (e.g., glues, adhesives, tape, and wax particles). The present invention allows for compositions to be studied or screened which will serve to destroy or prevent the growth of such biofilms and slime and the deposition of such organic and inorganic contaminants. The present invention further may be used to monitor corrosion on such surfaces as well as the efficacy of corrosion-preventing agents. 
     Turning to FIGS. 1-4, a biofilm growth device of the present invention is shown. The device consists of a tray  100  defining one or more chambers  108  which are of an appropriate size to accommodate a material being investigated. Such material under investigation is typically referred to in the art as a coupon  109  and is of such composition, size, and shape as to model the surfaces of equipment used in industrial processes. Tray  100  is an elongate generally rectangular member having opposing first and second major planar surfaces  102  and  104 , opposing transverse side surfaces  106  and  106 ′, and opposing longitudinal side surfaces  107  and  107 ′. It will be recognized by one of skill in the art that the tray  100  may be manufactured of any suitable material such as plastic or metal and may be of any suitable shape and size. Desirably, the tray  100  is made of steel, in order to model equipment surfaces used in pulp and papermaking processes. 
     Each chamber  108  of tray  100  includes a recessed coupon support surface  110  for receiving a coupon  109  being investigated. Each chamber  108  is generally rectangular, is open at the top, and includes a perimetrical wall bounding the coupon support surface  110 . The perimetrical wall is defined by opposing transverse side surfaces  112  and  112 ′ and opposing longitudinal side surfaces  113  and  113 ′. Each chamber  108  further includes at least one fluid inlet port  114  and at least one fluid outlet port  114 ′ at each end thereof. Desirably, fluid inlet port  114  and fluid outlet port  114 ′ are defined by the coupon support surface  110  of each chamber  108 . It will be recognized by one of skill in the art that these chambers  108  can be of any suitable size and shape for purposes of the present invention. 
     As shown in FIGS. 1-4, chambers  108  are of such length to accommodate coupons  109  commonly used in research investigations. Further, it is desired that a plurality of chambers  108  of uniform shape and size be utilized in the present invention and that such chambers  108  are spaced apart from one another in a uniform manner. In such an arrangement, the present invention can be efficiently manufactured and easily adapted to simulate a variety of environmental conditions. Further, such an arrangement allows for a variety of biocidal and other agents to be screened simultaneously. 
     It is contemplated that the present invention may also be a tray defining a single chamber of any shape and size or may define multiple chambers of various shapes and sizes which are different than those shown in FIGS. 1-4. Such arrangements are contemplated as may be necessary to meet the unique demands of a particular screening procedure. 
     Turning again to FIGS. 1-4, fluid inlet ports  114  and fluid outlet ports  114 ′ are spaced apart such that the coupon  109  being investigated will rest therebetween. The fluid inlet port  114  and fluid outlet port  114 ′ are of such number, shape and size as to permit a desired flow of liquid over the surface of the coupon  109  being investigated. For example, as shown in FIGS. 1,  2 , and  4 , it has been found that when three fluid inlet ports  114  and three fluid outlet ports  114 ′ are used and are circular in shape, a desired flow of sample liquid, such as that which occurs during pulp and papermaking processes, is realized over the surface of the coupon  109  being investigated. As such, the present invention is capable of modeling the flow of liquid over equipment surfaces in a variety of industrial processes. As will be recognized by one of skill in the art, fluid inlet ports  114  and fluid outlet ports  114 ′ can exist in any number of configurations as necessary to achieve a desired flow of liquid over the coupon  109  being investigated and as to allow for the efficient manufacture thereof. 
     Each chamber  108  also has associated therewith at least on fluid inlet aperture  116  for supplying liquid samples to a chamber  108  and a fluid outlet aperture  116 ′ for removing the liquid sample after it has passed over the coupon  109  being investigated. As illustrated in FIG. 3, these apertures  116  and  116 ′ are in fluid communication with the coupon support surface  110  of each chamber  108 . Such fluid communication is defined by fluid inlet and fluid outlet passageways  118  and  118 ′, respectively, and fluid inlet and fluid outlet ports  114  and  114 ′, respectively. As will be recognized by one of skill in the art, fluid inlet aperture  116  and fluid outlet aperture  116 ′ may be present in many configurations. 
     In one desired aspect of the present invention, fluid inlet and fluid outlet apertures  116  and  116 ′, respectively, are bored into opposing longitudinal side surfaces  107  and  107 ′, respectively, of tray  100  and are adapted for receiving a fluid feed conduit  126  and a fluid discharge conduit  126 ′, respectively, as shown in FIGS. 1 and 3. For example, these apertures  116  and  116 ′ are desirably tapped for helical thread to provide a mating connector for receiving pipe thread. As shown in FIGS. 1 and 3, fluid inlet and fluid outlet nozzles  128  and  128 ′ are threaded into fluid inlet and fluid apertures  116  and  116 ′, respectively. Fluid feed and fluid discharge conduits  126  and  126 ′, which may be rubber tubing, are attached to fluid inlet and fluid outlet nozzles  128  and  128 ′, respectively. Further, fluid inlet and fluid outlet passageways  118  and  118 ′, respectively, are bored into tray  100  through opposing side surfaces  106  and  106 ′, respectively, as shown in FIGS. 1 and 3. 
     Tray  100  is desirably adapted for receiving a cover  124 , as shown in FIG. 4, which may be secured to tray  100  with screws at screw receiving recesses  120 . Cover  124  is of such size and shape to substantially enclose the open upper end of tray  100 . A rubber gasket  119 , shown in FIG. 3, may be provided between tray  100  when cover  124  is secured thereto by inserting such gasketing  119  into a recessed area  122  of tray  100 . Recessed area  122  is defined by first major surface  102  of tray  100  so as to receive the rubber gasketing  119  which has elongate holes therein which correspond to the size, shape, and position of chambers  108 , such that the coupon support surfaces  110  of chambers  108  are not covered by the gasketing  119 . As such, when a cover  124  manufactured of non-opaque material, such as clear plastic, is utilized, a researcher can observe the fluid flow over a coupon  109  seated in the coupon support surfaces  110  of chambers  108 . It will be recognized by one of skill in the art that the use of a cover  124  and/or gasketing  119  is not required in the present invention, but both are desirable as their combined use permits the efficient control of ambient conditions to which a coupon  109  being investigated is exposed. 
     As stated above, the present invention is suitable for use in investigating the growth of biofilm and the deposition of organic and inorganic contaminants on a coupon  109 . The present invention is further suitable for use in monitoring microbially-influenced corrosion of coupon  109  which results from such contamination as well as the efficacy of corrosion-preventing agents. This coupon  109  may be of any suitable material, such as metal or plastic, and may be of any suitable size and shape. Desirably, the coupon  109  will be of such size and shape to fit into the recessed coupon support surface  110  of chamber  108  such that a flow of water entering chamber  108  from fluid inlet port  114  will flow across the surface of the coupon  109  in a desired manner, such as at a rate which simulates the rate of flow over industrial machine surfaces. Examples of such coupons are described in U.S. Pat. No. 4,142,402 to Mattioli, et al. For example, in the paper and pulp industry, biofilm growth typically occurs on stainless steel machine parts. Consequently, stainless steel coupons would desirably be used to model the surfaces of such machines in order to investigate materials that may be useful for the prevention and/or destruction of such biofilm growth. 
     Additionally, the test conditions of the twelve chambers can be arranged in any grouping; for example, to test three different slime control agents plus a negative control with no agent added, four groups of three chambers can be used. Each group desirably draws bacteria and growth medium from a single reservoir. The design of the tray provides a great deal of versatility in experimental design. For example, slime control agents can be tested both for prevention of biofilm growth and for removal of established biofilms, simply by changing the time at which the agents are added to the fluid during the experiment. 
     EXAMPLE 
     In one desired aspect of the present invention, a stainless steel tray  100  defines twelve chambers  108 , as shown in FIGS. 1,  2  and  4 . Tray  100 , a clear plastic cover  124 , a gasket  119 , twelve stainless steel coupons  109  (approximately two and one half inches by one half inch), twenty four pieces of flexible rubber tubing, five pairs of forceps, and four carboy stopper assemblies were cleaned, autoclaved and allowed to dry overnight in a drying oven. The cleanings were done in a manner known in the art. For instance, the coupons  109  were cleaned with warm water and detergent and placed in a ten percent solution of bleach overnight. They were then rinsed with distilled water, cleaned with detergent, placed in a one percent acetone solution and sonicated for thirty minutes. 
     In accordance with the agents being investigated, various protocols were used as indicated below: 
     Pure Culture/Defined Mixtures of Laboratory Bacteria 
     Four nine-liter carboys that accept the stopper assemblies above were filled with two liters of a salts medium. Stir bars were then added to each carboy which were capped with foil, and the carboys were autoclaved. The carboys were removed from the autoclave such that the liquid cooled to room temperature prior to use. Two small flask cultures (25 ml each) were inoculated with the bacterial species tested and were incubated overnight. 
     The cultures of bacteria were then spun down at 3500 rpm for twenty minutes at 20° C. and resuspended in the salt mixture in each carboy to a final optical density of approximately 0.024. A copy of the spectrophotometer readings was then obtained. 
     Synthetic White Water Experimentation 
     Synthetic White Water was formulated as shown in Table 1: 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Enriched Synthetic White Water Concentrate Composition 
               
             
          
           
               
                 Component 
                 mg/L*dH 2 O (1X) 
                 mg/L dH 2 O (2X) 
                 Alternate formulation in mg/L 
               
               
                   
               
             
          
           
               
                 CaCl 2   
                 111 
                 222 
                 CaCl 2 .2(H 2 O) 147(1X), 294(2X) 
               
               
                 MgSO 4   
                 60 
                 120 
               
               
                 NaHCO 3   
                 168 
                 336 
               
               
                 K 2 HPO 4   
                 140 
                 280 
               
               
                 NH 4 Cl 
                 480 
                 960 
               
               
                 FeCl 3 .6(H 2 O) 
                 1.04 
                 2.08 
                 FeCl 3  anhyd. 0.62(1X), 1.24(2X) 
               
               
                 Na 2 EDTA 
                 1.48 
                 2.96 
                 Na 2 EDTA.2(H 2 O) 3.28(2X) 
               
               
                 Dextrose 
                 3000 
                 6000 
                 Starch 10(1X), 20(2X) 
               
               
                 Yeast extract 1   
                 1000 
                 2000 
               
               
                 HEPES 2  (pH 7) 
                 0.05 
                 0.10 
               
               
                 MES 3  (pH 5.5) 
                 9.76 
                 19.52 
               
               
                 Tricine (pH 8) 
                 8.96 
                 17.92 
               
               
                   
               
               
                 *All components are measured in mg/L expect HEPES, which is measured in M/L  
               
               
                   1 For example, Difco brand yeast extract, or Fisher Scientific brand yeast extract  
               
               
                   2 HEPES is 4-(2-hydroxyethyl)-1-piperazine ethanesulfonic acid  
               
               
                   3 MES is beta-morpholinoethansulfonaseure hydrate  
               
             
          
         
       
     
     The pH of the final composition was adjusted using either NaOH or HCl. 
     For experimentation using synthetic whitewater, the carboys were autoclaved empty (except for stir bars) and allowed to cool to room temperature. Eight liters of distilled water were autoclaved in large Erlenmeyer flasks capped with foil and allowed to cool overnight. Two large graduated cylinders, capped with foil, were also autoclaved and allowed to cool overnight. 100 ml of the 2×synthetic whitewater concentrate was then added to each carboy. This was then diluted with 1900 ml of sterile deionized water, measured using the autoclaved graduated cylinders. 
     Whitewater Experimentation 
     For experimentation using whitewater, the carboys were autoclaved empty (except for stir bars) and were allowed to cool to room temperature. The sterile carboys were filled with two liters of whitewater, as measured with a sterile graduated cylinder. The carboys were arranged next to the tray  100  and placed on stir plates where they were mixed. To this whitewater was added 1 g/L of yeast extract, as for example Difco brand yeast extract and Fisher Scientific brand yeast extract, which was allowed to mix overnight and covered with autoclaved aluminum foil. 
     For experimentation involving each of the above samples, once the above preparations were made, peristaltic pumps were assembled such that for all twelve chambers  108 , twelve pump heads sized for quarter-inch tubing, four motors, and four controllers were used. For each chamber  108 , quarter-inch tubing was attached to a fluid outlet nozzle  128 ′ associated with fluid outlet aperture  116 ′ on one end thereof and to a pump head on the other end thereof. The tray  100  was assembled by placing coupons  109  in each chamber  108  that was being investigated. Where machine surfaces involved in pulp and papermaking processes were under investigation, stainless steel coupons  109  were used. The cover  124  was then secured to tray  100  with five screws at screw receiving recesses  120  to form a tight seal between the tray  100 , cover  124 , and gasket member  119  which was positioned within a recessed area  122  of tray  100 . 
     The carboy and stoppers were then assembled. In experiments in which recirculated flow was desired, the tray fluid discharge conduit  126 ′ was then attached to the stoppers. The tray fluid feed conduit  126  was then attached to the stoppers, but not to the tray  100 . The stoppers were lifted and the above samples under investigation were added to the carboys. Additionally, 1 or 2 ml of the sample was collected and stored in a sterile container for plating and optical density readings. The stoppers were then fixed in place by wrapping Parafilm® around the stopper and the neck of the carboy. 
     The pumps were then primed by taking a sterile 5 or 10 ml pipette attached to a battery-powered pipettor and inserting them into the fluid feed conduit  126  that was not yet connected to the fluid inlet aperture  116 . The pipettor was then run so that fluid was drawn up through the fluid feed conduit  126  until it began to fill the pipette, at which time the tubing was clamped off two to three inches from the end and attached to a fluid inlet nozzlel  128  threaded into fluid inlet aperture  116 . This procedure was repeated for all fluid feed conduits  126 . 
     For each group of three chambers  108  whose pumps were on one controller, the clamps were removed from the fluid feed conduits  126 . The pumps were immediately started and maintained at approximately the same speed. Each chamber  108  in which a coupon  109  was being investigated was then monitored to ensure that the liquid sample flowed over each coupon  109  in a desired manner, and did not fill the chamber. Desirably, a thin layer of fluid covered the coupons  109 . Chambers  108  that filled up with liquid sample were drained. 
     After a designated period of time, each motor was shut off and the fluid feed conduit  126  was again clamped. The cover  124  was then removed from the tray  100 . The coupons  109  were removed and replaced with clean, sterile coupons for the next experiment, with both removal and replacement occurring through the use of sterile forceps. The used coupons  109  were set aside for analysis, including staining and microscopy. 
     The example set forth above serves to illustrate the present invention, but in no way is intended to limit the spirit and scope thereof, which is defined by the following claims.