Abstract:
Two complementary approaches to the science of IMS technology, IMS and differential IMS (DIMS), are combined into a single instrument to provide improvements in interference rejection without sacrificing detection sensitivity. The technology is applicable to, inter alia, the analysis of trace quantities of toxic or otherwise dangerous organic chemical materials. The approach improves both sensitivity and specificity (interference rejection) of field detection instrumentation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of priority to similarly titled U.S. Provisional Patent Application Ser. No. 61/871,927 filed Aug. 30, 2014, the contents of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE EMBODIMENTS 
     1. Field of the Embodiments 
     The embodiments are generally directed to chemical detectors and more particularly to an improved chemical detector which fuses previously independent approaches to ion mobility spectrometry (IMS) into a single detector. 
     2. Description of Related Art 
     Ion Mobility Spectrometry (IMS) has been the primary technology for chemical warfare agent detection for at least 30 years. Screening of airport passengers for explosives and illegal drugs has relied on IMS for about the same period. There are hundreds of thousands ion mobility spectrometers in use throughout the world. Instrumentation advantages in terms of small size and low electrical power requirements coupled with excellent sensitivity and spectrometric specificity make IMS an ideal technology for field detectors. As with any analytical chemistry technique, improved sensitivity and specificity without sacrificing size, weight, power and cost benefits are continually sought. The number one complaint by users of IMS instrumentation is that the systems are prone to interferences. As requirements for field detection of various and “non-traditional” substances increase, complaints of interferences are likely to increase. 
     Ion Mobility Spectrometry (IMS) is the study of the motion of gas-phase ions under influence of electric fields. Several methods for study on the ion motion are used throughout the IMS field. A combination or “fusion” of two of these methods is proposed—the IMS methods will be referred to here as “Linear” IMS or just IMS (the traditional term) and “Differential” IMS or DIMS. A detailed treatment of theory and practice of IMS can be found in the book “Ion Mobility Spectrometry—2 nd  Edition” by G. A. Eiceman and Z. Karpas, CRC Press Taylor &amp; Francis Group, Boca Raton (2005). The substance of this reference is considered to be known to those having skill in the present art and is incorporated herein by reference. 
     Currently, existing field detectors use either IMS or DIMS, but not both. For example, the LCD 3.3 (Light Weight Chemical Detector) from Smiths Detection uses IMS processing. While the JUNO detector developed by Chemring Detection Systems is exemplary of a previously proposed detector that uses DIMS processing for detection of CWA and low vapor pressure agents. 
     There is no literature record of IMS and DIMS sensor and data fusion where the two complementary technologies have been operated in parallel. There have been previous attempts to fuse IMS and DIMS technologies as described in E. Nazarov, et al.; “Miniature DMS-IMS Detector for Enhanced Resolving Power;” 16th International Conference on Ion Mobility Spectrometry, Mikkeli, Finland; July 2007 and in A. G. Anderson, et al; “DMS-IMS2, GC-DMS, DMS-MS: DMS hybrid devices combining orthogonal principles of separation for challenging applications;” Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing IX. Edited by A. W. Fountain, P. J Gardner; Proceedings of the SPIE, Volume 6954, pp. 69540H-69540H-12 (2008). The described approach used a DIMS device for rapid separation of target ions and introduction of separated ions into two IMS instruments. A DIMS device separates positive and negative ions simultaneously. Positively charged ions are directed into an IMS device which is appropriately biased and negative ions are directed into the other IMS device. While this design, theoretically, provides for enhanced separation of analyte ions—such is not necessarily the case. Referring to  FIG. 3  it can be seen that if the DIMS device selects small ions for analysis by the IMS systems, no resolution is gained since IMS cannot effectively separate small ions. For large ions there is little to no separation by the DIMS system, the IMS system is relied on to separate the ions. In both cases, sensitivity is sacrificed due to ion loses between the mobility spectrometers with insignificant improvements in resolution. 
     SUMMARY OF THE EMBODIMENTS 
     The present embodiments combine or “fuse” two complementary approaches to the science of IMS technology into a single instrument to provide improvements in interference rejection without sacrificing detection sensitivity. The two techniques are referred to as IMS and differential IMS (DIMS). The technology is applicable to, inter alia, the analysis of trace quantities of toxic or otherwise dangerous organic chemical materials. The approach described herein improves both sensitivity and specificity (interference rejection) of field detection instrumentation. 
     The embodiments combine the two techniques into a single instrument and combine the data outputs of the two technologies through the use of advanced signal processing techniques to take advantage of the complementary nature of the two approaches. The combination is such that each IMS technique processes an ingested sample independently, i.e., in parallel, and then the data is combined to give a single result with excellent sensitivity and interference rejection. 
     More particularly, in a first exemplary embodiment, a chemical agent detector includes: an ionization chamber including at least one ion source for generating positive and negative ions from a sample; a first ion mobility spectrometry cell integrated with the ionization chamber for receiving at least a first portion of the positive ions therefrom; a second ion mobility spectrometry cell integrated with the ionization chamber for receiving at least a first portion of the negative ions therefrom; a differential ion mobility spectrometry cell integrated with the ionization chamber for receiving at least a second portion of the positive ions and at least a second portion of the negative ions therefrom; and a processor for separately receiving first detection data from the first ion mobility spectrometry cell, second data from the second ion mobility spectrometry cell, and third data from the differential ion mobility spectrometry cell and processing the first, second and third detection data to determine presence of one or more chemical agents in the sample. 
     In a second exemplary embodiment, a process for parallel chemical agent detection includes: introducing a sample into an ionization chamber; ionizing the sample to create positive and negative ions; receiving at a first end of a first ion mobility spectrometry cell from the ionization chamber at least a portion of the positive ions; receiving at a first end of a second ion mobility spectrometry cell from the ionization chamber at least a portion of the negative ions; introducing a drift gas into a second end of each of the first and second ion mobility spectrometry cells, wherein the drift gas flows in an opposite direction from a flow of the portions of positive and negative ions in the first and second ion mobility spectrometry cells; receiving at a first end of a differential ion mobility spectrometry cell a second portion of each of the positive and negative ions from the ionization chamber and a first portion of the drift gas, wherein the first portion of the drift gas and the second portion of each of the positive and negative ions flow in the same direction within the differential ion mobility spectrometry cell; generating first and second chemical agent detection data at first and second detectors located at the second end of each of the first and second ion mobility spectrometry cells; generating third chemical agent detection data at a third detector associated with the differential ion mobility spectrometry cell; processing by a processing system the first, second and third chemical agent detection data determine presence of one or more chemical agents in the sample. 
     In a third exemplary embodiment, a hand-held chemical agent detector includes: an ionization chamber including at least one ion source for generating positive and negative ions from a sample, wherein the dimensions of the ionization chamber are less than 1 cm width, 2.5 cm length and 2.0 cm height; a first and second ion mobility spectrometry cells integrated with the ionization chamber for receiving at least a first portion of the positive and negative ions therefrom, wherein the dimensions of the first and second ion mobility spectrometry cells are less than 2.5 cm width, 2.0 cm length and 2.5 cm height; and a differential ion mobility spectrometry cell integrated with the ionization chamber for receiving at least a second portion of the positive ions and at least a second portion of the negative ions therefrom, wherein the dimensions of the differential ion mobility spectrometry cell are less than 1 cm width, 1.0 cm length and 3.0 cm height. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The Summary of the Embodiments, as well as the following Detailed Description, is best understood when read in conjunction with the following exemplary drawings: 
         FIG. 1  is a prior art schematic showing separation of ions in an IMS system; 
         FIG. 2  is a prior art schematic showing separation of ions in a DIMS system; 
         FIG. 3  illustrates that ion separation or spectral resolution of IMS and DIMS is dependent on the size of analyte ions; 
         FIG. 4  is a schematic showing a hybrid IMS-DIMS system in accordance with an embodiment herein; 
         FIGS. 5 a  and 5 b    are schematics showing a hybrid IMS-DIMS system having two IMS cells and scrubber configuration in accordance with an embodiment herein; 
         FIGS. 6 a  and 6 b    are schematics showing a more detailed schematic of  FIG. 5 a    with differing ionization sources; and 
         FIG. 7  is a schematic showing a hybrid IMSx2 mass spectrometer system in accordance with an embodiment herein; 
         FIGS. 8 a  and 8 b    are isometric views of an IMSx2 system in accordance with embodiments described herein; 
         FIGS. 9 a -9 f    provide views with exemplary dimensional information for key components of the IMSx2 system; 
         FIGS. 10 a  and 10 b    are isometric views of a first exemplary ionization chamber for use in the IMSx2 system described herein; and 
         FIGS. 11 a  and 11 b    are isometric views of a first exemplary ionization chamber for use in the IMSx2 system described herein. 
     
    
    
     DETAILED DESCRIPTION 
     With regard to IMS, the terminal velocity of an ion drifting under the influence of the electric field is proportional to the electric field strength;
 
 v   d   =KE   (1)
 
where v d  is the ion&#39;s terminal velocity, E is the electric field strength and the proportionality constant, K, is defined as ion mobility. IMS is the traditional term used for linear field dependence IMS—this terminology will continue here.
 
     Most ion mobility spectrometers are governed by Equation (1) which is an excellent approximation at relatively low electric field strengths, from zero to a few hundred volts per cm. At high electric field strengths upwards of a few kilovolts per cm, ion mobility cannot be represented as a constant value—ion mobility, K, takes the form
 
 K ( E/N )= K (0)[1+α( E/N )]  (2)
 
where K(0) is the ion mobility under zero (and low) field conditions and E/N is the electric field normalized for pressure—the coefficient α is used to describe the dependence of ion mobility on high electric fields. To differentiate field-dependent ion mobility spectrometry from the more traditional linear ion mobility spectrometry the term Differential Ion Mobility Spectrometry or DIMS is used to indicate that ion mobility is variable with electric field strength. It should be noted DIMS is sometimes referenced by other names including Field Asymmetric Ion Mobility Spectrometry (FAIMS) and Field Ion Spectrometry (FIS). DIMS is the term used herein.
 
     It is electric field dependence and the bases of operation that stimulated the idea for development of the embodiments described herein. IMS operates using DC electric fields and DIMS operates using a combination of RF and DC electric fields. Differences in separation of atmospheric pressure ions are significant. Although the techniques are not orthogonal in the strict sense, they are such that the fusion of ion mobility spectra will result in signal attributes that will enhance false alarm reduction and, in some cases, eliminate false alarms altogether. 
     Following  FIG. 1  from upper left to upper center down to lower center and finally to lower right the sequence of events is as follows: (1) “primary” ions are formed as a result of electric discharge or ionizing radiation, primary ions react with neutral species (target analytes) to form analyte ions and these ions drift into a reaction region where they are “trapped” by a grid that is electrically biased to prevent ions from passing through; (2) periodically the grid voltage is lowered for a short period (typically one to two hundred microseconds) which allows a packet of ions to enter the separation or drift region; (3) this packet of moves through the drift region under the influence of a constant electric field, E, where separation occurs according to the size of the ions and the charge on the ions—the smaller ions move faster than the larger ions; (4) as ions impact an ion collector a current is created in external circuitry and the variation of the ion current with “drift time” is an ion mobility spectrum—typically the spectrum drift time is 15-50 microseconds. This sequence is repeated as required by the application. 
     From left to right in  FIG. 2 : (1) analyte laden air flows through a source of ionization, usually radioactivity, producing primary ions; reactions between primary ions and neutral analyte molecules are identical with the reactions in IMS; (2) ions continue to flow between a set of closely spaced (&lt;1 mm) parallel plates or concentric cylinders; (3) as the ions flow between the plates they are subjected to an asymmetric RF field, the dispersion field, that varies at constant frequency, positively and negatively up to several kilovolts per cm wherein the high voltage part of the RF cycle is twice the amplitude and half the period of the low voltage part; (4) the RF field is superimposed on a DC voltage that is scanned over a few 10&#39;s of volts positively and negatively; (3,4) at a unique combination of RF dispersion voltage and DC compensation voltage an ionic species of a specific size and charge has a stable flight path through the plates, others impact walls and are neutralized—as the DC voltage is scanned other ions come into stability; (5) the stable ions are then directed into ion collectors that are biased to receive appropriately charged ions to create spectra, differential ion mobility spectra. The peak amplitude of the RF voltage is varied and another spectrum is obtained. 
     Experiment has shown that ion separation or spectral resolution of IMS and DIMS is dependent on the size of analyte ions.  FIG. 3  illustrates this point. The left hand side of  FIG. 3  indicates that as the size of an analyte ion increases, separation of IMS analyte ion peaks increases while DIMS exhibits the opposite relationship. The right hand side of  FIG. 3  is another representation of this characteristic—large ions tend to toward more overlap in DIMS, small ions tend to toward more overlap in IMS. Resolution can be adjusted through variation of electric fields, total drift voltage in IMS and RF voltage amplitude in DIMS. Reagent ion intensity, gate pulse width and repetition rate, length and spacing of DIMS electrodes, and other parameters affect sensitivity and resolution—some effects are in opposite directions. As in other analytical techniques, an improvement in resolution results in decreasing sensitivity. 
     The present embodiments utilize the two mobility spectrometry techniques described herein in parallel to take advantage of separation or resolution capabilities of both. Resolution of each of the techniques is maintained and there are no ion losses between the spectrometers. The detectors acting together as a “fused” sensor provide analytical chemical power for successful detection and identification of, for example, unknown bulk explosives (UBE) and homemade explosives (HME) in addition to detection of CW agents, TICs/TIMs, NTA, explosives and other dangerous materials. Sensitivity and response time are comparable. 
     Referring to exemplary configurations of the fused IMS and DIMS sensor technologies shown in  FIGS. 4 through 11 , in order to realize the full advantages of fusing the complementary aspects of the two technologies, the IMS and DIMS cells are such that a single ionization source and an ion-molecule reaction single reaction region is common to both. Exemplary DIMS cells which may be modified for use with the present embodiments are described in U.S. Pat. Nos. 8,146,404, 7,576,322 and 7,579,589. Taking advantage of common components allows for reduced footprint and implementation through a hand-held device. 
     In a first embodiment shown in  FIG. 4 , the detector  100  includes a single IMS cell  105  to switch between positive and negative ion modes and a single DIMS cell  110 . In the alternative embodiments of  FIGS. 5 through 8 , there are two IMS cells  205   a  and  205   b , one positive and one negative to a single DIMS  210  (the entire detector system  200  being referred to as IMSx2). The internal gas flow requirement of IMS and DIMS detector cells lends itself to the illustrated configurations. The IMS process requires that a drift gas flow in the opposite direction of the ion current while DIMS requires that this carrier gas flow is in the same direction as the ion current. In  FIG. 4 , the drift gas in the IMS becomes the carrier gas in the DIMS. A single ion source  115  will serve to initiate the necessary ion-molecule chemistry for both cells. A single gas scrubber  120  will suffice for both cells. 
     In  FIGS. 5 a  and 5 b   , the IMSx2 system  200  includes two IMS cells  205   a  and  205   b , one positive and one negative, and a single DIMS  210  as well as dual scrubbers  220   a ,  220   b . The IMSx2 system  200  is able to operate using a single ion source  215  for all three cells. Alternatively, a dual ion source configuration is also contemplated by one or more embodiments. Similarly,  FIGS. 6 a    and  7  also illustrate IMSx2 system  200  including two IMS cells  205   a  and  205   b , one positive and one negative, a single DIMS  210  and a single ion source  215 . In the ionization space  225  in the vicinity of the single ion source  215 , “primary” ions are formed as a result of electric discharge or ionizing radiation. The single ion source may be optimized in accordance with other system parameters and intended use for the system and may include, but is not limited to, corona discharge, atmospheric pressure photoionization (APPI), electrospray ionization (ESI), a radioactive source, laser-induced discharge and MALDI (matrix-assisted laser-desorption ionization). An analyte sample  230  is introduced to the system  200  through an inlet  235  and directed to ionization space  225 . The characteristics of the inlet  235  vary in accordance with the type of ion source as highlighted further below and in the figures. 
     Further to  FIGS. 6 a , 6 b    and  7 , the inlet  235  configuration may vary in accordance with the configuration of the ionization source  215 . That is, depending on the type of ionization source  215  that is utilized, the inlet  235  may be a membrane configuration  235   a  as shown in  FIG. 6 a    when the ion source  215  is a radiation ion source  215   a  or the inlet  235  may be a pulsed inlet  235   b  as shown in  FIG. 6 b    when the ion source  215  is a corona discharge source  215   b . The individual IMS cells  205   a  and  205   b  receive respective positive and negative ions from the ionization space  225  into drift chambers or tubes  240   a ,  240   b  (not shown) and detection occurs at detectors  245   a ,  245   b  located at the opposite ends of the drift tubes  240   a ,  240   b.    
     The configuration of the ion source  215  and ionization space  225  may be any configuration that allows for dual polarity ionization of the analyte sample. For example, the dual mode ion configuration described in U.S. Pat. No. 7,259,369 to Scott et al. or a variation thereof as contemplated by one skilled in the art may be utilized. U.S. Pat. No. 7,259,369 is incorporated herein by reference in its entirety. In a particular embodiment, the ion source  215  includes positive and negative DC corona ionization in ionization space  225 . Additional structural details and dimensions of the ionization space (or chamber)  225  are discussed further below and illustrated in various figures. 
     The drift chambers or tubes  240   a ,  240   b  of the individual IMS cells  205   a  and  205   b  are integrated with the ionization space  225  in any configuration which facilitates the detection of both positively and negatively charged ions produced from a common source. Exemplary configurations are described in, by way of example, U.S. Pat. No. 4,445,038 to Spangler et al., U.S. Pat. No. 5,543,331 to Puumalainen and U.S. Pat. No. 7,576,321 to Wu which are incorporated herein by reference in their entireties. Individual IMS cells such as those embodied in the Excellims HPIMS products are exemplary of the components and operational characteristics which are contemplated for use as the cells  205   a  and  205   b  of the present embodiments. For exemplary purposes, the drift current (EDC) through the drift tubes which are on the order of a few centimeters in length is measured to be approximately 200 V/cm. The RF voltage amplitude (E RF  max) in the DIMS component is in the approximate range of 0-20 kV/cm with an electrode spacing of ≦1 mm. 
       FIG. 7  illustrates yet another embodiment which is an IMSx2—Mass Spectrometry hybrid. DIMS, also known as FAIMS (Field Asymmetric Ion Mobility Spectrometry), interfaces  250  have been developed for mass spectrometers  255 . One example is the FAIMS Interface for the Thermo Scientific series of mass spectrometers and another is the ultraFAIMS MS interface offered by Owlstone Nanotech. It is anticipated that real time responses result from the IMSx2 system with “good” specificity and “great” sensitivity. Responses with “good” sensitivity and “great” specificity are derived from the IMSx2-MS system with longer response times. 
     Referring to  FIGS. 8 a  and 8 b   , an exemplary isometric view of an IMSx2 system configuration  200  in accordance with an embodiment is shown. As described above and shown in the view of  FIG. 8 a   , the system includes a high voltage source  260 , DIMS  210 , ionization chamber  225 , IMS sensor arrays  205   a ,  205   b , and flow control components  265 . In the second view shown in  FIG. 8 b   , the carbon drift gas scrubbers  220   a ,  220   b  are shown. Additionally,  FIG. 8 b    shows the system control panel, including on/off switch and, data port, the latter of which is critical to relaying sensor/detector data from the IMS cells and DIMS to the processing system  350 , which includes fusion software for fusing the received data and making chemical detection determinations based thereon. For exemplary purposes, the dimensions of the power and control portion of the system are shown in  FIG. 8 b    (the DIMS, IMS and ionization chamber component dimensions are discussed below and in later Figures). These dimensions 23.88 cm (L), 12.86 cm (W), and 8.56 cm (H) are exemplary and one skilled in the art recognizes variations in the dimensions in order to balance multiple factors including weight, footprint, mobility and results for the intended purpose and use. 
     The processing system  350  as illustrated is merely intended to be exemplary. One skilled in the art recognizes that there are numerous possible configurations and implementations for relaying data, i.e., the data port, and processing data. For example, the data port could be a wireless transmitter or a wireless transceiver wherein processing is completed remotely and results thereof are received back at the system and displayed to the user on a visual or audio display mounted on the system  200 . Alternatively, the system  200  could include the processing system  350  within its footprint using, e.g., microprocessing technology on-board. In combination with a visual, auditory or tactile display mounted on the system  200 , the system  200  is a stand-alone system and, as discussed below, may be constructed so as to be hand-held. 
       FIGS. 9 a  to 9 e    provide more detailed views of the configuration and integration of the IMS cells  205   a ,  205   b , DIMS  210  and ionization chamber  225  components indicated by the dotted box in  FIG. 8 a   . The exploded view in  FIG. 9 b    shows the DIMS  210  in relation to the ionization chamber  225  which, in this particular embodiment, includes the corona needle  270  and is formed of two halves,  225   a  and  225   b  as shown with inlet ports  235   a ,  235   b  (alternatively, a single inlet port is acceptable). Each half of the ionization chamber includes a gasket  275   a ,  275   b  and bracket  280   a ,  280   b  for attaching to a respective IMS sensor arrays  205   a ,  205   b . On the DIMS facing side of each half of the ionization chamber  225 , there is a partial DIMS outlet  285   b  (only one is shown) which form a full DIMS outlet (not shown) for engaging with the DIMS ion inlet  290 . Alternatively, the entirety of the DIMS outlet may be contained in a single half of the ionization chamber. 
       FIGS. 9 c  through 9 e    provide front, top and right side views with exemplary dimensional information. These dimensions, in centimeters, are provided for exemplary purposes and are not intended to limit the scope of the embodiments. One skilled in the art appreciates that variance in the dimensions are expected and would still be considered to be within the scope of the invention. 
     And  FIG. 9 f    provides an additional cutaway view showing two halves  225   a  and  225   b  of the ionization chamber with sample inlet ports  235   a ,  235   b , IMS outlets  300   a ,  300   b , IMS sensor arrays  205   a ,  205   b , DIMS outlet  285 , DIMS ion inlet  290  and pre-DIMS drift gas bleed-off outlets  305   a ,  305   b . The pre-DIMS drift gas bleed-off outlets are not a required feature. 
       FIGS. 10 a  and 10 b    provide comprehensive views of an ionization chamber  225  which, in this particular embodiment is formed of two halves,  225   a  and  225   b  and includes corona entry point  295 , sample inlet ports  235   a ,  235   b  (alternatively, a single inlet port may be used), DIMS outlet  285 , respective IMS outlets  300   a ,  300   b  and a pre-DIMS drift gas bleed-off outlet  305 . 
       FIGS. 11 a  and 11 b    provide comprehensive views of an alternative ionization chamber  225  which, in this particular embodiment is a single component with an added top plate  310  and includes corona entry point  295 , sample inlet port  235 , DIMS outlet  285 , respective IMS outlets  300   a ,  300   b  and an ion insulation shield  315 . 
     During operation, additional exemplary metrics for the detection process include rate of drift gas supply, rate of gas bleed-off and rate supplied to DIMS. In a non-limiting implementation, values were determined to be 1 L/min drift gas supply and exhaust and 290 cc/min to DIMS. One skilled in the art also recognizes that other operational characteristics of the individual components are controllable to achieve desired results, including flow rates, currents/voltages, sensor/detector temperatures and the like. 
     The fused detector described herein is able to detect chemicals in all states of matter in the air and on surfaces, including land, personnel, equipment and facilities. The varied capabilities included in a single detector using some common components allows for reduced size, weight and power requirements, resulting in a single device that may be used in the field. Additionally, the dual and parallel signal processing with back end discriminatory processing, results in better sensitivity, reduced interference and minimization of false alarms. Such fields including, but not limited to, combat, anti-terrorism, law enforcement and the like. Specific applications include, but are not limited to, site assessment for chemical hazards, site exploitation, decontamination screening and clearance, autonomous detection in near real-time whole moving (e.g., on soldier, police, ship, other vehicles), outdoor and indoor monitoring for chemical hazards. 
     In concluding the detailed description, it should be noted that it would be obvious to those skilled in the art that many variations and modifications can be made to the embodiments without substantially departing from the principles described herein. Also, such variations and modifications are intended to be included herein within the scope as set forth in the appended claims. 
     It should be emphasized that the above-described embodiments are merely possible examples of the implementations, merely set forth for a clear understanding of the principles of thereof. Any variations and modifications may be made to the above-described embodiments of without departing substantially from the spirit of the principles of the embodiments. All such modifications and variations are intended to be included herein within the scope of the disclosure. 
     The present invention has been described in sufficient detail with a certain degree of particularity. The utilities thereof are appreciated by those skilled in the art. It is understood to those skilled in the art that the present disclosure of embodiments has been made by way of examples only and that numerous changes in the arrangement and combination of parts may be resorted without departing from the spirit and scope thereof.