Abstract:
Singular sealed apparatus and method suitable for confirming pressure measurements in a rebreather prior to use of the rebreather. The singular sealed apparatus may have a canister lid, gas sensors and a processor, all from a rebreather, as well as a pressure sensor, an input device, a processor, an indicator and a pod with a pressure measurement outlet, a gas supply inlet, a relief valve and a gas exit valve. Alternatively, the singular sealed apparatus may have a gas sensor from a rebreather and an analyzer, a pressure sensor, an input device, a processor, an indicator, a lid and a pod with a pressure measurement outlet, a gas supply inlet, a relief valve and a gas exit valve. 
     The inventive method is characterized by assembling the singular sealed apparatus, inputting a concentration of a gas present in a gas mixture, admitting the gas mixture into the singular sealed apparatus, expelling ambient gas present in the singular sealed apparatus, measuring absolute pressure of the gas mixture, calculating partial pressure of the gas, indicating the calculated partial pressure of the gas, measuring partial pressure of the gas, indicating the measured partial pressure of the gas and comparing the calculated partial pressure of the gas to the measured partial pressure of the gas.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of Provisional Application No. 61/196,982 filed Oct. 21, 2008, which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to enhancing safety in the use of breathing systems.  2 . Background Discussion 
         [0004]    Conventional breathing systems, such as systems used for underwater diving situations, mining, firefighting or outer space, typically provide a gas supply system to a user who is underwater, or in another oxygen-depleted or toxic gas environment. These systems are typically portable and are adapted to provide sustained usable air for breathing for an estimated period of time. 
         [0005]    Examples include AQUA-LUNG® or SCUBA (Self Contained Underwater Breathing Apparatus), which is used by free divers and, in similar fashion, by fire fighters in many hazardous situations. Typically, a SCUBA-type apparatus employs a relatively large tank containing a compressed gas mixture and a mouthpiece or face mask connected to the tank through a flow regulator. The gas mixture commonly consists of two or more constituent gases, such as oxygen and one or more inert gases such as nitrogen. A user inhales from the tank and exhales into the ambient atmosphere. 
         [0006]    Another type of apparatus, a rebreathing apparatus, has been developed to recycle gases exhaled by a user to remove carbon dioxide therefrom with a “scrubber” and then recycle the unmetabolized oxygen. Oxygen or an oxygen-enriched gas mixture is injected into the “scrubbed” gas from a supply source to maintain the partial pressure of oxygen in the gas mixture at a desired level, and then the gas mixture is passed back to the user for rebreathing. Rebreathers can therefore extend the amount of time the breathing device can be used by lowering the rate of consumption of the gas mixture. 
         [0007]    Pure oxygen is often utilized in rebreathers, introducing the problem of hyperoxia, which is excess oxygen in body tissues caused by breathing oxygen at elevated partial pressures or oxygen-rich gases at normal atmospheric pressure for a prolonged period of time. Hyperoxia can cause cell damage in the central nervous system and the lungs of a user. 
         [0008]    Early rebreather systems were relegated to use by professionals in unsafe environmental conditions, such as diving or firefighting, due to the complexity and costs of the systems as well as the extensive training required for the use of these systems. These systems exhibited an undesirable level of control over partial pressure of oxygen (PP oxygen ) in the gas mixture present in the rebreather system, potentially resulting in a user experiencing hyperoxia or hypoxia, which is oxygen deprivation capable of causing loss of consciousness, seizures, coma, priapism or death. An increase or decrease in PP oxygen  in a rebreather can result in a hyperoxic or hypoxic gas detrimental to the rebreather user. 
         [0009]    Because of the dangers posed by hyperoxia and hypoxia, it is essential for the diver to monitor and have accurate data for PP oxygen  for the duration of a dive. Currently-available rebreather systems incorporate sensors, processors and indicators to detect, measure, control and display PP oxygen  continuously during a dive. However, the sensors used in these systems, while improved over early rebreather systems, are still prone to malfunctions, rendering the systems less reliable than desired for maintaining target oxygen levels. Often, the problem of malfunctioning sensors is not resolved even by incorporating redundant sensors in the rebreather and utilizing a protocol implemented by the processor to identify whether one or more of the sensors is not operating correctly. 
         [0010]    Methods and protocols known in the art are directed to monitoring oxygen levels during a dive. For the foregoing reasons, there is a need for an apparatus and method that may be used by a diver prior to undertaking a dive in order to confirm proper functioning of the rebreather sensors and processor. 
       SUMMARY 
       [0011]    Using a singular sealed apparatus and method of the present invention, it is advantageous to perform a pre-dive safety check of the sensors and processor in a rebreather by measuring the partial pressure of oxygen or another selected gas in a gas mixture of known composition using at least one rebreather sensor, while at the same time independently measuring absolute gas pressure, which is the total pressure of the gas mixture in the singular sealed apparatus, and calculating the partial pressure of the selected as a product of absolute gas pressure and the concentration of the gas in the gas mixture. In other words, PP gas =(absolute gas pressure)×(% gas concentration), where % gas concentration in the gas mixture is known and absolute gas pressure and PP gas  are expressed in any suitable units. 
         [0012]    This pre-dive safety check provides the advantage of determining PP oxygen  independent of the rebreather sensor, eliminating a potential source of error. The PP oxygen  value calculated using the singular sealed apparatus and method of the present invention may be compared with the PP oxygen  value measured by the rebreather sensor and processor. A difference between the calculated PP oxygen  value and the measured PP oxygen  value indicates that the rebreather sensor or the rebreather processor is not operating properly and must be serviced or replaced before use during a dive. 
         [0013]    Accordingly, an object of this invention is a singular sealed apparatus suitable for comparing gas pressure measurements in a rebreather. The singular sealed apparatus comprises a rebreather canister lid, a rebreather processor, a rebreather sensor, a rebreather indicator, a rebreather hole formed in the rebreather canister lid, a pod, a relief valve, a gas supply inlet, a pressure measurement outlet, a gas exit valve, a plug, a pressure sensor, a processor, an indicator and an input device. In some embodiments, the apparatus further comprises an interface that comprises the pressure sensor, processor, indicator and input device. 
         [0014]    The rebreather processor is adapted to receive measurement signals corresponding to partial pressure of a gas in a gas mixture present in the apparatus and to transmit measurement data for concentration or partial pressure of the gas. 
         [0015]    The rebreather sensor is attached to a surface of the rebreather canister lid that is exposed to the gas mixture present in the apparatus. The rebreather sensor has a connection with the rebreather processor for transmitting signals and is adapted to produce measurement signals corresponding to concentration or partial pressure of the gas in the gas mixture present in the apparatus and to transmit the measurement signals to the rebreather processor. 
         [0016]    The rebreather indicator has a connection with the rebreather processor for receiving measurement data and is adapted to receive and indicate measurement data for concentration or partial pressure of the gas in the gas mixture present in the apparatus. 
         [0017]    The rebreather hole is formed in the rebreather canister lid. In some embodiments, the rebreather hole is adapted to removably receive a hose. 
         [0018]    The pod is adapted to be removably attached to the rebreather canister lid. 
         [0019]    In some embodiments, the apparatus further comprises a fastener adapted to removably secure the pod to the rebreather canister lid. 
         [0020]    The relief valve, gas supply inlet, gas pressure regulator, pressure measurement outlet and gas exit valve are integrated into the pod. The relief valve limits absolute gas pressure in the apparatus. 
         [0021]    The plug is adapted to removably fill the rebreather hole. 
         [0022]    In some embodiments, the pressure sensor is adapted to be removably connected to the pressure measurement outlet. 
         [0023]    In some embodiments, the interface is adapted to be removably connected to the pressure measurement outlet. In some embodiments, the interface comprises a pressure sensor adapted to measure absolute gas pressure in the apparatus and transmit absolute pressure measurement signals. 
         [0024]    In some embodiments, the interface further comprises an input device adapted to permit a user to input a concentration of a gas in a gas mixture present in the apparatus and to transmit data corresponding to the concentration of the gas in the gas mixture. 
         [0025]    In some embodiments, the interface further comprises a processor adapted to receive absolute pressure measurement signals from the pressure sensor, receive data for concentration of the gas present in the apparatus from the input device, calculate partial pressure of a gas in a gas mixture present in the apparatus as a product of absolute gas pressure and the concentration of the gas in the gas mixture, and transmit data corresponding to absolute gas pressure and partial pressure of the gas in the gas mixture. 
         [0026]    In some embodiments, the interface further comprises an indicator adapted to receive data from the processor and indicate absolute gas pressure and partial pressure of the gas in the gas mixture. 
         [0027]    In some embodiments, the pressure sensor, input device, processor and indicator have connections adapted for transmitting and receiving data and signals. 
         [0028]    Another object of this invention is a method suitable for comparing gas pressure measurements in a singular sealed apparatus. The method comprises removably attaching the rebreather canister lid to the pod; removably filling the rebreather hole with the plug; opening the gas exit valve; inputting a concentration of a gas using the input device; admitting a gas mixture comprising the gas into the gas supply inlet; closing the gas exit valve; measuring absolute pressure of the gas mixture using the pressure sensor; calculating partial pressure of the gas using the processor; indicating partial pressure of the gas using the indicator; measuring partial pressure of the gas using the rebreather sensor and rebreather processor; indicating partial pressure of the gas using the rebreather indicator; and comparing partial pressure of the gas as indicated by the rebreather indicator to partial pressure of the gas as indicated by the indicator. One of ordinary skill in the art will recognize that the initial addition of the gas mixture will expel the ambient atmosphere present in the singular sealed apparatus, and the gas exit valve may be closed once the singular sealed apparatus contains only the gas mixture. 
         [0029]    In some embodiments, the method further comprises removably attaching the pressure sensor to the pressure measurement outlet; 
         [0030]    In some embodiments, the method further comprises removably attaching the interface to the pressure measurement outlet. 
         [0031]    Although very narrow claims are presented herein, it should be recognized that the scope of this invention is much broader than presented by the claim. It is intended that broader claims will be submitted in an application that claims the benefit of priority from this application. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims and accompanying drawings where: 
           [0033]      FIG. 1  shows a front perspective view of an apparatus embodying features of the present invention; 
           [0034]      FIG. 2  shows a sectional view of an apparatus embodying features of the present invention; 
           [0035]      FIG. 3  shows a perspective view of an apparatus embodying features of the present invention; 
           [0036]      FIG. 4  shows a flowchart of a method embodying features of the present invention; 
           [0037]      FIG. 5  shows a front perspective view of an apparatus embodying features of the present invention; 
           [0038]      FIG. 6  shows a sectional view of an apparatus embodying features of the present invention; and 
           [0039]      FIG. 7  shows a sectional view of an apparatus embodying features of the present invention. 
       
    
    
     DESCRIPTION 
       [0040]    A rebreather comprises a rebreather scrubber canister, which comprises a rebreather canister lid  100  and a rebreather canister body. A rebreather further comprises at least one rebreather sensor  102 , a rebreather processor  104  for receiving signals from the rebreather sensor  102  and for transmitting data, including absolute gas pressure of a gas mixture present in the rebreather and partial pressure of a selected gas in the gas mixture, and a rebreather indicator  108  for receiving and displaying data from the rebreather processor. Many commercially-available rebreathers incorporate as many as three rebreather sensors  102 . In common dive practice, the rebreather sensor  102 , rebreather processor  104  and rebreather indicator  108  are used by a diver to measure, control and indicate PP oxygen  continuously during a dive. 
         [0041]    In some embodiments, the gas mixture comprises a single gas. In some embodiments, the selected gas is oxygen. 
         [0042]    The rebreather sensor  102  is customarily attached to the rebreather canister lid  100 , and connections  103  are provided between the rebreather sensor  102  and rebreather processor  104  and between the rebreather processor  104  and rebreather indicator  108  for transmitting and receiving data and signals. The rebreather sensor  102  is attached to a surface of the rebreather canister lid  100  that is exposed to the gas mixture present in the rebreather. 
         [0043]    One or more rebreather holes  106  typically are present in the rebreather canister lid  100 . In some embodiments, the rebreather holes  106  have shapes and configurations adapted to removably receive one or more hoses through which gases move into or out of the rebreather scrubber canister. 
         [0044]    In some embodiments, the rebreather processor  104  applies a selection protocol to the signals from the rebreather sensor  102 . 
         [0045]    As shown in  FIGS. 1 and 2 , the present invention provides a pod  200 . In some embodiments, the pod  200  is cylindrical with an annular cross-section, closed on one end and open on the opposite end. In some embodiments, the pod  200  incorporates an o-ring or other seal around the periphery of the open end. In some embodiments, the pod  200  is constructed from any plastic, metal or other material providing suitable rigidity and impermeability to gases at pressures of approximately  30  pounds per square inch, or psi. In some embodiments, the pod  200  is constructed from aluminum alloy. 
         [0046]    In some embodiments, the pod  200  is adapted to be removably attached to the rebreather canister lid  100 , such that different embodiments or models of the pod  200  may be distinctly adapted to mate with different rebreather canister lid  100  of various commercially-available rebreathers having different shapes and configurations. In some embodiments, the singular sealed apparatus includes a fastener adapted to removably secure the pod  200  to the rebreather canister lid  100 . 
         [0047]    In some embodiments, a relief valve  202  is integrated into the pod  200  to limit absolute gas pressure in the singular sealed apparatus apparatus and thereby protect structural integrity of the singular sealed apparatus and the rebreather sensor  102 . The relief valve  202  operates by allowing gas present in the singular sealed apparatus to escape when the absolute gas pressure in the singular sealed apparatus exceeds a preset level. The absolute gas pressure in the singular sealed apparatus preferably is kept at  30  psi or less. Suitable relief valves are commercially-available from, for example, Swagelok®. 
         [0048]    In some embodiments, a gas supply inlet  204  is integrated into the pod  200  to permit addition of a gas mixture into the singular sealed apparatus, usually from a pressurized tank. In some embodiments, a gas pressure regulator is integrated into the gas supply inlet  204 . Gas mixtures are commonly supplied from tanks pressurized to 140 psi, which, in some embodiments, exceeds the operating limit of the singular sealed apparatus. The gas pressure regulator reduces the pressure of the gas mixture at the gas supply inlet  204  to 30 psi, which is within the operating limit of the apparatus. Suitable gas pressure regulators are commercially-available from, for example, Victor® Manufacturing. 
         [0049]    In some embodiments, a pressure measurement outlet  206  is integrated into the pod  200 . The pressure measurement outlet  206  is adapted to permit sampling of the gas present in the singular sealed apparatus to measure absolute gas pressure. 
         [0050]    In some embodiments, a gas exit valve  207  is integrated into the pod  200 . The gas exit valve  207  is adapted to permit expulsion of gas present in the singular sealed apparatus and to be opened or closed, such as a needle valve. The gas exit valve  207  may include a one-way check valve to permit only outflow of gas from the singular sealed apparatus. 
         [0051]    In some embodiments, the present invention comprises a pressure sensor, a processor, an input device and an indicator. In some embodiments, the pressure sensor is adapted to measure absolute gas pressure in the singular sealed apparatus and transmit absolute gas pressure measurement signals. 
         [0052]    In some embodiments, the input device is adapted to permit a user to input a known concentration of a gas present in the singular sealed apparatus and to transmit data for concentration of the gas present in the singular sealed apparatus. 
         [0053]    In some embodiments, the processor is a general purpose computer adapted to receive absolute gas pressure measurement signals from the pressure sensor, receive data corresponding to the concentration of a gas in a gas mixture present in the singular sealed apparatus from the input device, calculate the partial pressure of the gas in the gas mixture present in the singular sealed apparatus and transmit data corresponding to absolute gas pressure and partial pressure of the gas in the gas mixture to the indicator. 
         [0054]    In some embodiments, the indicator is adapted to receive data from the processor and indicate absolute gas pressure and the partial pressure of the gas in the gas mixture present in the singular sealed apparatus. In some embodiments, the indicator may incorporate a liquid crystal display screen or other suitable visual indicating mechanism to display data. 
         [0055]    In some embodiments, the pressure sensor, input device, processor and indicator have connections adapted for transmitting and receiving data and signals. 
         [0056]    In some embodiments, the present invention comprises an interface  208 . In some embodiments, the interface  208  comprises the pressure sensor, input device, processor and indicator. 
         [0057]    As shown in  FIGS. 3 ,  6  and  7 , in some embodiments, the interface  208  comprises a solid housing  210 , a stem  211  and a gas inlet valve  212 . In some embodiments, the interface  208  is adapted to be removably connected to the pressure measurement outlet  206 . In some embodiments, the interface  208  may be connected directly to the pressure measurement outlet  206 , for example, by a threaded or quick-release connection mounted on the stem  211 . In some embodiments, the interface  208  may be connected to the pressure measurement outlet  206  using hose or pipe suitable for containment of pressurized gas present in the singular sealed apparatus. In some embodiments, the input device is a keypad  214  adapted to permit entry of numerical data. In some embodiments, the indicator is a display  216  adapted to show numerical data. 
         [0058]    In some embodiments, the present invention further provides one or more plugs having shapes and configurations suitable for filling and hermetically sealing the rebreather holes  106  found in the rebreather canister lid. 
         [0059]    In some embodiments, the interface  208  comprises a power source  213  and a pressure transducer assembly  215 , which may further comprise an electrical connector  217 . In some embodiments, the interface  208  comprises a microprocessor mounted behind the display  216  and adjacent to the power source  213  and connections between the microprocessor, the electrical connector  217 , the display  216  and the keypad  214  adapted for transmitting and receiving data and signals. 
         [0060]    In some embodiments, the gas inlet valve  212  is adapted to receive a gas mixture flowing from the pressure measurement outlet  206 . In some embodiments, the pressure transducer assembly  215  is adapted to measure the absolute pressure of the gas mixture flowing from the pressure measurement outlet  206  into the gas inlet valve  212  and to convert pressure measurements into electrical signals, and the electrical connector  217  is adapted to transmit the electrical signals to the microprocessor. In some embodiments, the microprocessor is adapted to receive electrical signals from the electrical connector  217 , determine the absolute pressure of the gas mixture flowing from the pressure measurement outlet  206  into the gas inlet valve  212 , receive input signals from the keypad  214  identifying the concentration of a selected gas in the gas mixture flowing from the pressure measurement outlet  206  into the gas inlet valve  212 , calculate the partial pressure of the selected gas in the gas mixture flowing from the pressure measurement outlet  206  into the gas inlet valve  212  and transmit data to the display  216  corresponding to the absolute pressure of the gas mixture flowing from the pressure measurement outlet  206  into the gas inlet valve  212  and the partial pressure of the selected gas in the gas mixture. 
         [0061]    A singular sealed apparatus of the present invention may be assembled by attaching the open end of the pod  200  to the rebreather canister lid  100 , attaching the pressure sensor or the interface  208  to the pressure measurement outlet  206 , filling any rebreather holes  106  present in the rebreather canister lid  100  with the plugs and attaching a gas supply, typically a pressurized tank, to the gas supply inlet  204  to admit a gas mixture into the singular sealed apparatus. One of ordinary skill in the art will recognize that the singular sealed apparatus thus assembled provides a closed system that is hermetically sealed. 
         [0062]    In accordance with a method provided by the present invention, as shown in  FIG. 4 , the user can assemble the singular sealed apparatus as described above, open the gas exit valve, input the gas concentration and admit the gas mixture from the gas supply into the singular sealed apparatus. 
         [0063]    The initial addition of the gas mixture will expel the ambient atmosphere present in the singular sealed apparatus, and the gas exit valve may be closed once the singular sealed apparatus contains only the gas mixture. 
         [0064]    Because the singular sealed apparatus is closed and hermetically sealed, absolute gas pressure in the singular sealed apparatus will reach steady-state. 
         [0065]    After the gas mixture is admitted into the singular sealed apparatus, the pressure sensor measures absolute gas pressure in the singular sealed apparatus and transmits pressure measurement signals to the processor. The processor receives the absolute gas pressure measurement signals from the pressure sensor and the concentration of a selected gas in the gas mixture from the input device and then calculates the partial pressure of the selected gas in the gas mixture as a product of absolute gas pressure and the concentration of the selected gas in the gas mixture, or PP gas =(absolute gas pressure)×(% gas concentration). The processor transmits the calculated value of the partial pressure of the gas to the indicator, and the indicator can display the absolute gas pressure and the calculated value of the partial pressure of the selected gas. 
         [0066]    After the gas mixture is admitted into the singular sealed apparatus, the rebreather sensor  102  measures the partial pressure of the gas and transmits the measurement data to the rebreather processor  104 , which transmits the measured value of the partial pressure of the gas to the rebreather indicator  108 . 
         [0067]    One of ordinary skill in the art will understand that the measured and calculated partial pressure values can be determined in any order or simultaneously. 
         [0068]    The user can compare the calculated partial pressure value shown on the indicator with the measured partial pressure value shown on the rebreather indicator  108 . The calculated partial pressure value is independent of sensor related effects and can serve as the standard for comparison. Accordingly, a discrepancy between the calculated partial pressure value and the measured partial pressure value would indicate that the rebreather sensor  102  or the rebreather processor  104  is not operating correctly. 
         [0069]    The singular sealed apparatus of the present invention may be modified to further comprise an analyzer  105  adapted to measure and indicate partial pressure values of the selected gas received from a rebreather sensor  102 , wherein the analyzer may comprise any suitable microprocessor adapted to receive data and signals corresponding to measurements of the partial pressure of a gas and an indicator adapted to display numerical data corresponding to measurements of the partial pressure of a gas. The rebreather sensor  102  can be connected to transmit signals and data to both the analyzer  105  and the rebreather processor  104 . When a user assembles this embodiment of the singular sealed apparatus and admits a gas mixture from a gas supply, the interface  208  will indicate a calculated partial pressure value for the selected gas and the analyzer  105  and the rebreather indicator  108  will indicate measured partial pressure values for the selected gas. 
         [0070]    This embodiment provides the further advantage of identifying whether either the rebreather sensor  102  or the rebreather processor  104  is not operating properly. If the measured partial pressure value indicated by the rebreather indicator  108  is different from the calculated partial pressure value and the measured partial pressure value indicated by the analyzer  105 , then the rebreather processor  104  is not operating properly. If both measured partial pressure values indicated by the analyzer  105  and the rebreather indicator  108  are different from the calculated partial pressure value, then the rebreather sensor  102  is not operating properly. 
         [0071]    Another embodiment of the present invention is a singular sealed apparatus as shown in  FIG. 5 . The apparatus comprises a pod  200  and a lid  218  adapted to be removably attached to the pod  200 . In some embodiments, the singular sealed apparatus comprises a relief valve  202 , a gas supply inlet  204 , a pressure measurement outlet  206  and a gas exit valve  207  integrated into the pod  200  and/or the lid  218 . In some embodiments, the singular sealed apparatus comprises a rebreather sensor  102  disposed inside of the singular sealed apparatus and an analyzer  105  disposed outside of the singular sealed apparatus that is adapted to measure and indicate values of the partial pressure of a gas from a rebreather sensor  102 , with connections  103  between the rebreather sensor  102  and the analyzer  105  for transmitting and receiving data and signals. In some embodiments, the rebreather sensor  102  and the analyzer  105  may be connected through either the pod  200  or lid  218 . In some embodiments, the singular sealed apparatus further comprises an interface  208  comprising a pressure sensor, input device, processor and indicator. In some embodiments, the analyzer  105  may incorporate a liquid crystal display screen or other suitable visual indicating mechanism to display data. 
         [0072]    A user may assemble the embodiment of the present invention shown in  FIG. 5  by disconnecting the rebreather sensor  102  from a rebreather apparatus and connecting the rebreather sensor  102  to the analyzer  105  through the lid  218 . In other embodiments, the rebreather sensor  102  and analyzer  105  may be connected through the pod  200 . The user may then attach the lid  218  to the pod  200  and attach the interface  208  to the singular sealed apparatus. The user may then open the gas exit valve  207 , input a known gas concentration, admit a gas mixture from a gas supply into the singular sealed apparatus and close the gas exit valve  207  when the ambient atmosphere present in the singular sealed apparatus has been expelled by the addition of the gas mixture. The user can then compare the calculated gas partial pressure value displayed by the interface  208  with the measured gas partial pressure value displayed by the analyzer  105 . 
         [0073]    The previously described embodiments of the present invention have many advantages, including enabling a diver to verify the accuracy of gas partial pressure measurements made by the rebreather sensor  102  and thereby to confirm the operability status of the rebreather sensor  102  and rebreather processor  104  prior to using such equipment during a dive. The invention does not require that all advantageous features be incorporated into, or all advantages provided by, every embodiment of the invention. 
         [0074]    Although the present invention has been described in considerable detail with reference to certain embodiments thereof, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained therein. 
         [0075]    Insofar as the description above and the accompanying drawing disclose any additional subject matter that is not within the scope of the single claim below, the inventions are not dedicated to the public and the right to file one or more applications to claim such additional inventions is reserved.