Abstract:
A method of detecting particles during inspection is provided. The method includes establishing a security checkpoint including a detection system, wherein the detection system includes a chamber defining a passage and includes a plurality of jets. The method also includes passing an individual through the passage, enhancing a convection plume including particles from the individual by blowing air through at least one of the plurality of jets, and absorbing the particles in a preconcentrator including a filter encased in a frame having a high thermal conductivity. Moreover, the method includes evaporating the particles absorbed in the preconcentrator and using a detector to determine whether the particles are from at least one of an explosive material and a narcotic substance.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present application relates to and claims priority from Provisional Application Ser. No. 60/784,413, filed Mar. 21, 2006, titled “SYSTEMS AND METHODS FOR DETECTING PARTICLES”, the complete subject matter of which is hereby expressly incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Embodiments of this invention relate generally to systems and methods for detecting particles, and more particularly, to systems and methods for detecting nanogram levels of particles. 
         [0003]    Terrorism risks continue to exist at transportation facilities, government buildings and other high profile locations where there is a significant flow of pedestrian or vehicular traffic. As a result, most airports and many government buildings now include apparatus for detecting trace amounts of explosives. These devices typically operate on the principle that small amounts of the explosive materials will be transferred to the body, clothing and luggage of people who had handled the explosive. Generally, known trace portal systems use graded metal mesh for collecting samples. However, the graded metal mesh easily loses collection efficiency because it gets dirty and clogs easily. 
         [0004]    Some detectors employ small flexible fabric-like traps that can be wiped across a package or piece of luggage. The trap removes residue from the surface of the package or luggage. The trap then is placed in an apparatus, such as an ion trap mobility spectrometer, that tests the residue on the trap for trace amounts of explosive materials. A device of this type is disclosed in U.S. Pat. No. 5,491,337 and is marketed by the GE Ion Track, Inc. of Wilmington, Mass. These devices typically are employed in proximity to metal detectors at airports, and security personnel will perform screening on some of the passengers based on a random sampling or based on a determination that the passenger has met certain criteria for enhanced screening. 
         [0005]    The ion trap mobility spectrometer disclosed in U.S. Pat. No. 5,491,337 also can operate in a mode for detecting trace amounts of narcotics. Narcotics are illegal and insidious. Furthermore, it is known that many terrorists organizations fund their terrorism through the lucrative sale of narcotics. 
         [0006]    Only a fraction of airline passengers have their carry-on baggage checked for trace amounts of explosives or narcotics using fabric-like traps and the available ion trap mobility spectrometers or similar devices. Efforts to use such devices to check all carry-on bags for trace amounts of explosives or narcotics would impose greater time and cost penalties on the airline industry. Additionally, the above-described explosive detectors typically are used only on luggage and other parcels. An apparatus of this type would not identify plastic explosives worn by a passenger who had no carry-on luggage. These related approaches provide low sensitivity and low throughput. 
         [0007]    For the reasons stated above, and for other reasons discussed below, which will become apparent to those skilled in the art upon reading and understanding the present disclosure, there are needs unsolved by these related approaches to provide inspection devices having increased sensitivity to illegal substances carried by passengers, such as, but not limited to, narcotics and explosives, and devices having increased throughput. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0008]    The above mentioned shortcomings, disadvantages and problems are addressed herein, which will be understood by reading and studying the following disclosure. 
         [0009]    The embodiments described herein provide high sensitivity and high throughput. More specifically, the embodiments described herein provide a detector including a plurality of jets and a preconcentrator having a screen and a filter. The jets blow air on an individual to dislodge particles from the individual&#39;s clothes and skin, thus increasing a concentration of particles entrained in the individual&#39;s convention plume. The time required to evaporate particles from an individual&#39;s convection plume is decreased by increasing the effective area of the preconcentrator and surrounding the screen with a frame having high thermal conductivity. Thus, the embodiments described herein use a detector with high sensitivity and high throughput to quickly, accurately and efficiently identify illegal and insidious substances carried by passengers. 
         [0010]    In one aspect, a method of detecting particles during inspection is provided. The method includes establishing a security checkpoint including a detection system, wherein the detection system includes a chamber defining a passage and includes a plurality of jets. The method also includes passing an individual through the passage, enhancing a convection plume including particles from the individual by blowing air through at least one of the plurality of jets, and absorbing the particles in a preconcentrator including a filter encased in a frame having a high thermal conductivity. Moreover, the method includes evaporating the particles absorbed in the preconcentrator and using a detector to determine whether the particles are from at least one of an explosive material and a narcotic substance. 
         [0011]    In another aspect, a method of manufacturing a preconcentrator configured to decrease desorption time is provided. The method includes forming a frame having four sides that define an opening, positioning a filter over the opening in the frame, and bending each of the four sides of the frame about a corresponding side of the filter, wherein the frame has a high thermal conductivity. 
         [0012]    In yet another aspect, a system for detecting particles is provided. The system includes a chamber, a plurality of jets, a preconcentrator, a detector, and a controller. The chamber includes a passage and the controller is configured to determine whether an individual is positioned within the passage. The plurality of jets is positioned within the chamber and configured such that at least one of the plurality of jets blows air on an individual within the passage to enhance a convection plume including particles from the individual. The preconcentrator includes a filter encased within a thermally conductive plate, wherein the filter is configured to absorb the particles and wherein the detector is configured to determine whether the particles are at least one of an explosive material and a narcotic substance. 
         [0013]    In yet another aspect, an apparatus for detecting particles during inspection is provided. The apparatus includes a preconcentrator configured to decrease desorption time, wherein the preconcentrator comprises a filter encased by a thermally conductive frame. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a schematic diagram of an embodiment of a detection system. 
           [0015]      FIG. 2  is an isometric view of an embodiment of a preconcentrator of the detection system. 
           [0016]      FIG. 3  is another isometric view of the preconcentrator. 
           [0017]      FIG. 4  is yet another isometric view of the preconcentrator. 
           [0018]      FIG. 5  shows a top view of the preconcentrator. 
           [0019]      FIG. 6  shows a side view of the preconcentrator. 
           [0020]      FIG. 7  is a schematic of an embodiment of a screen of the preconcentrator. 
           [0021]      FIG. 8  is shows a top view of an embodiment of preconcentrator. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]      FIG. 1  is a schematic diagram of an embodiment of a detection system  10 . The detection system  10  includes a passage  14  extending through detection system  10 . The detection system  10  is installed at a security checkpoint and the passage  14  is dimensioned to conveniently accommodate a person who desires clearance at the security checkpoint. Detector  20  system  10  also includes a chamber  15 . 
         [0023]    A boundary layer of air adjacent to the person is heated by the person and generally is hotter than ambient air at farther distances from the person. Hot air is less dense than cooler air and rises relative to the more dense cooler air. As a result, a significant human convection plume of hot air rises in the boundary area adjacent to the person. The human convection plume generally achieves flow rates of 50-100 liters/second. This significant flow of the human convection plume tends to entrain a plurality of particles, such as particles of an explosive material or a narcotic substance, that are on the skin or clothing of the person passing through the passage  14 . Thus, the microscopic particles travel upwardly with the human convection plume. 
         [0024]    The detection system  10  includes a plurality of air jets  16  that direct short puffs of air towards the person in the passage  14 . The jets  16  are directed at an area of the person extending roughly from the feet to the head and help to dislodge the particles from the skin and clothing of the person to stimulate separation of the particles from the skin and clothing, and to increase a concentration of the particles entrained in the human convection plume. The detection system  10  further includes a compressed air supply  17  that is controlled to fire the jets  16  sequentially from bottom to top as explained in U.S. Pat. No. 6,708,572. However, other jet firing patterns can be used. 
         [0025]    The detection system  10  further includes a controller  18 , a preconcentrator  19  and a detector  20 . An example of detector  20  includes an ion trap mobility spectrometer as described in U.S. Pat. No. 5,491,337. Detection system  10  also includes an actuator  22 , such as an electric motor, and a desorber  24 . Controller  18 , actuator  22 , preconcentrator  19 , desorber  24 , and detector  20  are located within a chamber  15 . Alternatively, controller  18 , actuator  22 , preconcentrator  19 , desorber  24 , and detector  20  are located outside chamber  15 . As used herein, the term controller is not limited to just those integrated circuits referred to in the art as a controller, but broadly refers to computers, processors, microcontrollers, microcomputers, programmable logic controllers, application specific integrated circuits, and other programmable circuits, and these terms are used interchangeably herein. Actuator  22  is coupled to preconcentrator  19 . Preconcentrator  19  receives the human convection plume including the particles from the person. Preconcentrator  19  absorbs or attracts the particles received. Controller  18  determines, such as from a change of an electromagnetic field within passage  14 , whether the person is within passage  14 . Upon determining that the person is within passage  14 , controller  18  sends a controller output signal to drive actuator  22 . Actuator  22  receives the controller output signal and drives preconcentrator  19  to move preconcentrator  19  inside desorber  24 . Desorber  24 , via a plurality of heating elements, generates heat that is supplied to preconcentrator  19 . The particles absorbed by preconcentrator  19  are evaporated upon receiving the heat from desorber  24 . Detector  20  receives, via a tube  26 , the particles evaporated from desorber  24 . Detector  20  detects whether particles are of illegal substances, such as narcotics or explosive substances. When the person moves out of the passage  14 , controller  18  sends a signal to actuator  22  and actuator  22  retracts preconcentrator  19  from desorber  24 . Preconcentrator  19  is outside desorber  24  when retracted from desorber  24 . 
         [0026]      FIG. 2  is an isometric view of an embodiment of preconcentrator  19 . More specifically, preconcentrator  19  includes a metal frame  28  encasing metal mesh or screen  30 . Frame  28  is fabricated from a metal material, such as, but not limited to, aluminum, steel, and iron. Moreover, screen  30  is fabricated from a metal material, such as, but not limited to, aluminum, steel, and iron. Although the exemplary embodiment describes frame  28  as fabricated from a metal material, it should be appreciated that in other embodiments, frame  28  may be fabricated from any material of high thermal conductivity that enables detection system  10  to function as described herein. Frame  28  includes four sides  32 ,  34 ,  36 , and  38  and an opening  40  is formed between the sides  32 ,  34 ,  36 , and  38 . Side  32  is adjacent to side  34 , side  34  is adjacent to side  36 , side  36  is adjacent to side  38 , and side is  38  adjacent to side  32 . Opening  40  is adjacent to sides  32 ,  34 ,  36 , and  38 . Frame  28  has the same shape as that of screen  30 . In an alternative embodiment, frame  28  has more or less than four sides. As an example, frame  28  has three sides. As another example, frame  28  has five sides. In another alternative embodiment, screen  30  has more or less than four sides. As an example, screen  30  has three sides. As another example, screen  30  has six sides. In yet another alternative embodiment, frame  28  has another shape, such as square, triangular, hexagonal, or octagonal shape. In another alternative embodiment, screen  30  has another shape, such as square, triangular, hexagonal, or octagonal shape. 
         [0027]      FIG. 3  is an isometric view of an embodiment of preconcentrator  19 . Screen  30  is placed so that a side  42  of screen  30  is adjacent to side  32 , a side  44  of screen  30  is adjacent to side  34 , a side  46  of screen  30  is adjacent to side  36 , and a side  48  of screen  30  is adjacent to side  38 . Each side of frame  28  is bent to form a plurality of portions of frame  28 . For example, side  32  is bent to divide side  32  into portions  52  and  54 . As another example, side  34  is bent to divide side  34  into portions  56  and  58 . As yet another example, side  36  is bent to divide side  36  into portions  60  and  62 . As still another example, side  38  is bent to divide side  38  into portions  64  and  66 . 
         [0028]      FIG. 4  is an isometric view of an embodiment of preconcentrator  19 . Sides  32 ,  34 ,  36 , and  38  are bent to fit screen  30  within frame  28 . For example, side  32  is bent so that portion  52  is adjacent to a top face  70  of screen  30  and portion  56  is adjacent to a bottom face of screen  30 . As another example, side  34  is bent so that portion  56  is adjacent to top face  70  of screen  30  and portion  58  is adjacent to bottom face of screen  30 . As yet another example, side  36  is bent so that portion  60  is adjacent to top face  70  of screen  30  and portion  62  is adjacent to bottom face of screen  30 . As still another example, side  38  is bent so that portion  64  is adjacent to top face  70  of screen  30  and portion  66  is adjacent to bottom face of screen  30 .  FIG. 5  shows a top view of an embodiment of preconcentrator  19  and  FIG. 6  shows a side view of preconcentrator  19 . When screen  30  is fitted within frame  28  and preconcentrator  19  is placed within desorber  24 , the heat flows from desorber  24  to frame  28 . The heat from frame  28  flows to screen  30 . 
         [0029]      FIG. 7  is a schematic of an embodiment of screen  30 . Screen  30  includes a mesh formed from a plurality of conducting mediums, such as conducting mediums  82 ,  84 ,  86 ,  88 ,  90 , and  92 , that are made of a metal, such as aluminum, steel, or iron, that conducts heat. An example of a conducting medium includes a wire. Screen  30  includes a plurality of openings, such as openings  94 ,  96 , and  98 , formed between a plurality of conducting mediums of screen  30 . It should be appreciated that screen  30  may also be considered as a filter. For example, opening  98  is formed between conducting mediums  82 ,  84 ,  86 , and  88 . Examples of shapes of openings of screen  30  include square, rectangular, triangular, or hexagonal. When particles pass through screen  30 , the particles are attached or absorbed to a conducting medium of screen  30 . Each opening of screen  30  is designed so that one of the particles having a maximum dimension, such as a maximum length, from a plurality of dimensions of the one of the particles is attracted by a conducting medium surrounding the opening. As an example, a range of the maximum dimension includes a range from and including about 1 micron to about 100 microns. As another example, the maximum dimension is about 20 microns. Each conducting medium of screen  30  has the same thickness as another conducting medium of screen  30 . In an alternative embodiment, a conducting medium of screen  30  has a different thickness than at least one other conducting medium of screen  30 . An example of the thickness of a conducting medium includes a diameter of the conducting medium of screen  30 . 
         [0030]    It should be appreciated that although the exemplary embodiment describes screen  30  as fabricated from a mesh formed from a plurality of conducting mediums, in other embodiments, screen  30  may be fabricated from any material, such as a metal weave material, that enables detection system  10  to function as described herein. 
         [0031]      FIG. 8  is a top view of an embodiment of preconcentrator  19 . Screen  30  is sintered into a uniform, non-graded pore structure. A flow of the human convection plume towards any side of preconcentrator  19  generates the same result. When preconcentrator  19  is inserted into desorber  24 , the heat from desorber  24  flows from sides  32 ,  34 ,  36  and  38  to a center of preconcentrator  19 . Screen  30  can be installed in any direction, such as, a direction in which top face  70  faces up away from a ground on which detection system  10  is placed or a direction in which top face  70  faces towards the ground. Preconcentrator  19  is thin and lighter than a typical preconcentrator. Tables 1 and 2, provided below, show a plurality of characteristics of various embodiments of preconcentrator  19 . Although tables 1 and 2 describe characteristics of various embodiments of preconcentrator  19 , it should be appreciated that in other embodiments, preconcentrator  19  may have any characteristic that enables detection system  10  to function as described herein. 
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                 Avg. air 
                   
                   
                   
                   
                   
                   
               
               
                   
                   
                 Bubble 
                 Perm. at 
                   
                   
                   
                   
                   
                 Dirt 
               
               
                   
                 Abs. 
                 point 
                 200 Pa. 
                   
                   
                   
                   
                   
                 holding 
               
               
                   
                 filter 
                 press. 
                 (2) 
                   
                   
                   
                   
                   
                 Capacity 
               
               
                   
                 rating 
                 (1) 
                 [1/dm 2 / 
                 Perm. factor K 
                 H/K 
                 Thickness H 
                 Wt 
                 Porosity 
                 (3) 
               
               
                 Series 
                 [μm] 
                 [Pa] 
                 min] 
                 [m 2 ] 
                 [1/m] 
                 [mm] 
                 [g/m 2 ] 
                 [%] 
                 [mg/cm 2 ] 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 3AL3 
                 3 
                 12300 
                 9 
                 4.80E−13 
                 7.29E+08 
                 0.35 
                 975 
                 65 
                 6.40 
               
               
                 5AL3 
                 5 
                 7600 
                 34 
                 1.76E−12 
                 1.93E+08 
                 0.34 
                 600 
                 78 
                 5.47 
               
               
                 7AL3 
                 7 
                 5045 
                 57 
                 2.35E−12 
                 1.15E+08 
                 0.27 
                 600 
                 72 
                 6.47 
               
               
                 10AL3 
                 10 
                 3700 
                 100 
                 4.88E−12 
                 6.56E+07 
                 0.32 
                 600 
                 77 
                 7.56 
               
               
                 15AL3 
                 15 
                 2470 
                 175 
                 9.87E−12 
                 3.75E+07 
                 0.37 
                 600 
                 80 
                 7.92 
               
               
                 20AL3 
                 20 
                 1850 
                 255 
                 1.91E−11 
                 2.57E+07 
                 0.49 
                 750 
                 81 
                 12.44 
               
               
                 25AL3 
                 25 
                 1480 
                 320 
                 2.98E−11 
                 2.05E+07 
                 0.61 
                 1050 
                 79 
                 19.38 
               
               
                 30AL3 
                 30 
                 1235 
                 455 
                 4.37E−11 
                 1.44E+07 
                 0.63 
                 1050 
                 79 
                 23.07 
               
               
                 40AL3 
                 40 
                 925 
                 580 
                 5.84E−11 
                 1.13E+07 
                 0.66 
                 1200 
                 77 
                 25.96 
               
               
                 60AL3 
                 59 
                 630 
                 1000 
                 1.07E−10 
                 6.56E+06 
                 0.70 
                 750 
                 87 
                 33.97 
               
               
                 5CL3 
                 6 
                 6100 
                 35 
                 4.38E−12 
                 1.87E+08 
                 0.82 
                 975 
                 85 
                 11.67 
               
               
                 10CL3 
                 11 
                 3500 
                 95 
                 1.07E−11 
                 6.90E+07 
                 0.74 
                 900 
                 85 
                 17.13 
               
               
                 15CL3 
                 15 
                 2400 
                 200 
                 2.29E−11 
                 3.28E+07 
                 0.75 
                 900 
                 85 
                 18.95 
               
               
                 20CL3 
                 22 
                 1700 
                 325 
                 3.67E−11 
                 2.02E+07 
                 0.74 
                 900 
                 85 
                 29.10 
               
               
                 5CL4 
                 5 
                 7400 
                 27 
                 1.65E−12 
                 2.43E+08 
                 0.40 
                 900 
                 72 
                 6.80 
               
               
                 7CL4 
                 7 
                 5286 
                 45 
                 2.74E−12 
                 1.46E+08 
                 0.40 
                 900 
                 72 
                 9.50 
               
               
                 10CL4 
                 10 
                 3700 
                 71 
                 4.33E−12 
                 9.24E+07 
                 0.40 
                 900 
                 72 
                 9.50 
               
               
                 15CL4 
                 16 
                 2400 
                 150 
                 9.15E−12 
                 4.37E+07 
                 0.40 
                 900 
                 72 
                 11.90 
               
               
                 20CL4 
                 20 
                 1850 
                 200 
                 1.22E−11 
                 3.28E+07 
                 0.40 
                 900 
                 72 
                 12.00 
               
               
                 10FP3 
                 11 
                 3500 
                 90 
                 3.71E−12 
                 7.29E+07 
                 0.27 
                 600 
                 72 
                 3.50 
               
               
                 15FP3 
                 15 
                 2450 
                 135 
                 6.18E−12 
                 4.86E+07 
                 0.30 
                 600 
                 75 
                 7.50 
               
               
                 20FP3 
                 21 
                 1800 
                 200 
                 8.54E−12 
                 3.28E+07 
                 0.28 
                 675 
                 70 
                 6.00 
               
               
                 40FP3 
                 40 
                 925 
                 540 
                 2.39E−11 
                 1.21E+07 
                 0.28 
                 675 
                 71 
                 9.00 
               
               
                 5BL3 
                 5 
                 7000 
                 45 
                 1.17E−12 
                 1.46E+08 
                 0.17 
                 300 
                 78 
                 4.00 
               
               
                 10BL3 
                 10 
                 3700 
                 100 
                 2.59E−12 
                 6.56E+07 
                 0.17 
                 300 
                 78 
                 4.63 
               
               
                 15BL3 
                 15 
                 2470 
                 175 
                 4.54E−12 
                 3.75E+07 
                 0.17 
                 300 
                 78 
                 4.70 
               
               
                 20BL3 
                 20 
                 1850 
                 255 
                 6.61E−12 
                 2.57E+07 
                 0.17 
                 300 
                 78 
                 6.10 
               
               
                 40BL3 
                 40 
                 925 
                 580 
                 1.50E−11 
                 1.13E+07 
                 0.17 
                 300 
                 78 
                 14.60 
               
               
                 60BL3 
                 59 
                 650 
                 1100 
                 2.43E−11 
                 5.96E+06 
                 0.15 
                 300 
                 74 
                 21.50 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                   
                   
                 Permeability 
                 DOP 
                   
               
               
                   
                   
                   
                 At 200 Pa 
                 Efficiency [%] 
               
               
                   
                 Weight 
                   
                 (1) 
                 (2) 
               
             
          
           
               
                 Series 
                 (g/m 2 ) 
                 Porosity % 
                 (1/dm 2 /min) 
                 0.01 μm 
                 0.07 μm 
                 0.1 μm 
                 0.2 μm 
                 0.3 μm 
                 0.4 μm 
               
               
                   
               
             
          
           
               
                 3AL3 
                 975 
                 65 
                 9 
                 99.995 
                 97.656 
                 96.679 
                 96.805 
                 98.747 
                 99.484 
               
               
                 GA4 
                 600 
                 60 
                 4 
                 99.908 
                 98.417 
                 98.249 
                 99.379 
                 99.890 
                 99.960 
               
               
                 GA5 
                 900 
                 60 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 GA6 
                 1200 
                 60 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 GA7 
                 600 
                 85 
                 23 
                 99.974 
                 95.054 
                 92.503 
                 89.200 
                 93.864 
                 95.683 
               
               
                 GA8 
                 1200 
                 85 
                 11 
                 99.970 
                 99.929 
                 99.828 
                 99.695 
                 99.809 
                 99.938 
               
               
                 GA9 
                 2400 
                 85 
                 6 
                 100.000  
                 100.000  
                 99.999 
                 99.996 
                 99.999 
                 100.000  
               
               
                 GA10 
                 600 
                 85 
                 96 
                 99.939 
                 65.498 
                 59.296 
                 42.319 
                 57.351 
                 58.777 
               
               
                 GA11 
                 1200 
                 85 
                 85 
                 99.996 
                 94.161 
                 90.398 
                 81.438 
                 86.874 
                 89.044 
               
               
                 GA12 
                 2400 
                 85 
                 16 
                 99.994 
                 99.640 
                 99.111 
                 97.393 
                 98.311 
                 98.824 
               
               
                   
               
             
          
         
       
     
         [0032]    Technical effects of the herein described systems and method for detecting the particles include reducing a time taken by desorber  24  to evaporate the particles attracted to preconcentrator  19  by an amount ranging from and including one second to three seconds compared to a typical time taken by desorber  24  to evaporate the particles. Another technical effect includes increasing an effective area of preconcentrator  19  from which the particles evaporate from and including 1.5 times to twice an effective area of a typical preconcentrator from which the particles evaporate. Other technical effects include surrounding screen  30  with frame  28  to facilitate improved evaporation of the particles. 
         [0033]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the claims.