US2311487A - Ultra violet lamp - Google Patents

Description

Feb. 16, 1943. J. w. MARDEN ET AL ULTRA VIOLET LAMP Filed Nov. 19, 1951 INVENTORS J'M MHRDEN MGz/V/ H W 'z/ RNE Y ATTO Patented Feb. 16, 1943 2,311,487 ULTRA vrone'r LAMP John Wesley Mal-den an In, East Orange,

signments, to Wasting facturlng Company 1! Madison G. Nicholson,

., assixnor, by mesne ashouse Electric and Main- East Pittsburgh, Pa... a corporation of Pennsylvania Application November 19, 1931, Serial No. 576,022

, active electrodes, support leads and filaments of 26 Claims.

This invention relates to electric lamps and is more particularly directed to lamps of this character adapted to be employed for the production of rays, and especially a spectrum relatively rich in ultra violet rays. Gaseous conduct-ion lamps of the negative glow type yield ultra violet rays and are generally termed glow lamps and it is with this particular class of lamps that the invention is specifically concerned and will hereinafter be particularly described.

These lamps generally comprise an exhausted bulbous or cylindrical gas tight enclosing en' velope having a small proportion of mercury therein and if desired also a small quantity of a monatomic gas such as helium, neon, argon or the like. The envelope commonly has a reentrant stem with a press in which are sealed a pair of lead-in wires and supporting wires, the latter extending into said envelope and having upper free ends in spaced relation therein.

Electrically secured to said free ends and supported thereby is a pair of spaced parallel heater elements extending in a direction approximately parallel to the longitudinal axis of the bulb and being located in or closely adjacent the virtual longitudinal center plane of the envelope. Each of said heater elements is surrounded by a thermionically active cylindrical cathode whose inner surface is spaced from the heater element.

In the course of our experimentations with lamps of this character, we have found that the quantity of ultra violet radiations produced thereby is generally dependent on the magnitude of the current, and that the life and elliciency of these lamps is dependent on the magnitude of the current and its relation to the sizes of the electrodes, internal supporting leads and the heater elements. That is to say, for example. a glow lamp characterized by 40-60 mils nickel internal support leads, 75 turns of 125 turns per inch of a 21 milligram wire wound on a 21 mil mandrel as heater filaments and thermionically active electrodes 14.5 mm. long and 122 mils outside diameter may be efiiciently operated at about 20 volts and 1.25 amperes for a comparatively long period of time. 4

If, however, a lamp of the same construction and size were operated at about the same voltage and about 2.5 amperes, its life would be considerably decreased. These consequences are due mainly to overheating of the internal structure of the lamp and loss of electron emission because of the excessive bombardment of this internal structure by the electrons and positive 10115.

In order that we may be enabled to produce large quantities of ultra violet radiations by employing a single lamp at a comparatively high amperes, we may provide said lamp with an internal structure characterized by thermionically comparatively large sizes so that the life of the lamp shall be of a practical value. Such a lamp because 01' the large envelope necessary to accommodate its large internal structure, is not amenable to the degree of compactness and to other advantages characterizing the present invention.

One other disadvantage incident to the employment of large electrodes is that it is difficult to maintain the proper amount of electron emission therefrom. It is often found that when electrodes of a size sufficiently large to withstand bombardment are employed with a coating of the best available thermionically active material, that the number of electrons emitted therefrom is greater than that desired for a given voltage drop between the electrodes.

Other difliculties include especially that of excessive bombardment which may cause sputtering of the support leads and/or vaporization of the thermionically active material on the electrodes. The latter is generally incidental to the operation of a compact 1.25 ampere lamp, heretofore described, when said lamp is operated at 2.5 amperes. To obviate these disadvantages we have provided the present invention. Besides having these bility of the negative glow produced in a lamp embodying our invention is materially enhanced.

The invention in its specific aspect briefly stated comprises a gas-tight exhausted envelope containing therein a small proportion of mercury and, if desired, also a small proportion of a monatomic gas such as helium, neon or argon. Within said envelope are mounted heating coils, each surrounded by and spaced from a thermionically active electrode having shielding means associated therewith.

An object of the invention is to provide a lamp of the gaseous conduction negative glow type.

which is simple, compact, and adapted to operate eificiently at comparatively high amperages for a relatively long period of time.

Another object of the invention is to provide a relatively compact lamp adapted to produce a negative glow rich in ultra violet radiations and characterized by relatively high dii'rusibility.

A further object of the invention is to provide a lamp of the negative glow gaseous conduction type whose efiiciency is relatively high and which is adapted to operate for a comparatively long period of time under predetermined conditions.

Other objects and advantages of the invention will be apparent from the following description and drawing wherein,

Figure 1 represents a horizontal sectional view, with some parts shown in plan, of an embodiment of our invention;

Figure 2 represents a developed elevational important properties the diffusiview of the envelope-contained parts of the embodiment shown in Figure 1, with the envelope omitted, some of the parts being shown in section and others diagrammatically;

Figure 3 represents a side elevation, with some of the parts in section, of another embodiment of our invention; I

Figure 4 is a section taken on line IV-IV of Figure 3;

Figure 5 represents the vital internal structure with the electrical connections of the embodiment illustrated in Figure 3;

Figure 6 is a cross sectional view, similar to Figure 4, of a modification of the internal structure shown in Figure 3;

Figure 'l' is a view, similar to Fig. 3, of still another embodiment of our invention.

In order that a compact glow lamp heretofore employed, as for example, a 1.25 ampere glow lamp may be operated on a higher current, as for example 2.5 amperes, without any decrease in its efficiency or minimizing of its life, there is provided the structure shown in Figure 1 as an illustrative embodiment of our invention. As will be hereinafter apparent, these results are possible, without increasing the size of any one electrode and without increasing the size of the enclosing envelope, because we utilize the space on either side of the virtual plane embodying the two parallel electrodes of the 1.25 ampere lamp.

As shown in Figures 1 and 2, an embodiment of our invention comprises a gas-tight exhausted envelope consisting of a bulb ill and a reentrant stem ll having a press i2. The bulb It may be of any suitable material, such as quartz or the like, which is permeable to the ultra violet radiations produced therein. The stem II is provided with an upstanding wire, pedestal l3 and with the customary exhaust tube (not shown) and in the envelope is disposed a small quantity of mercury to provide mercury vapor for the efficient operation of the lamp. If desired, there may be also contained therein a small proportion of a monatomic gas such as helium, neon, argon, or the like.

Sealed into the press 12 are a plurality of leadin wires 15 and I6 and supporting wires l1 and i8 which are electrically connected to the respective lead-in wires 15 and I6. These support wires i1 and I8 may be composed of nickel and extend r upwardly and outwardly from the press f2.

Adjacent the free ends of the respective support wires l1 and iii are electrically secured, as

by means of welding, rigid guides or support leads i9 and on the upper ends of whichare weldedly secured coiled heater filaments 2i and 22 respec-j tively. These filaments 2i .,2 2--ar.e of materially lesser orosssectional area than the respectiveguides'or supports l9 and 20 and are respectively weldedly secured to a pair ofupper guides or support leads 23 and 2|. Telescoping with the filaments 2i and 22 are electrodes 25 and 26 respectively, .each consisting of a cylindrical metallic base such as nickel, having an outer coating of a thermionically active material, such as an alkali or alkaline earth, as for example barium oxide.

The lower ends of these electrodes 25 and 26 have respectively welded thereto conducting wires 25' and 26' which are also welded to the support wires i1 and I3 respectively. These electrodes are spaced about 180 degrees apart and are approximately located in an axial plane of the bulb l0.

With the type of glow lamp heretofore emplayed there is a connecting wire secured to the ends of the upper supports or leads 23 and 24 in order to complete the circuit. In our invention, however, we depart from the prior/art by utilizing the space on each side of the virtual longitudinal plane of these electrodes by providing an electrode structure in each of said heretofore unused spaces.

As shown in Figures 1 and 2, our invention may be carried out by welding a cross arm 21 of nickel wire to the lower portion of the vertical support l3. Upstanding rigid supports or guide leads 23 and 29 are secured, as by electric welding, to the respective ends of the cross arm 21. At the upper ends of the respective leads 23 and 23 are weldedly secured coiled filaments or heater elements 3!! and 3!, similar in all respects to the filaments 2| and 22, and at the upper ends of these filaments 30 and 31 are weldedly secured upper ridge guides or support leads 32 and 23. Telescoping with the filaments 30 and 3|, mounted in the same general manner and of the same general composition as electrodes 25 and 26, are electrodes 34 and 35.

The filaments 2i, 33, 3| and '22 are connected in series by means of the support 21 and nickel wires 36 and 31, the latter being welded to the pairs of upper rigid guides or support leads 23,

32 and 24, 33 respectively. The electrodes 25 and are connected in parallel, andtherefore are at the same potential in operation, by means of connector 38, and electrodes 23 and 34 are connected in parallel, and are at the same potential in operation, by means of connector 39.

In order that our novel lamp shall be amenable to efllcient operation and comparatively long life, the electrodes 25, 26, ll and 35 are so arranged within the bulb 10 that they all are substantially parallel to and approximately equi-spaced from the longitudinal axis of the lamp, and disposed on approximately the same virtual circumference about ninety degrees apart.

We have found that with a lamp of this general construction larger quantities of ultra violet rays may be produced because it permits the employment of higher amperage-without any material decrease in lifeor efficiency which wasnot possible with the same size lamps heretofore employed. Besides this our novel lamp has the further salient advantage that the amount of ultra violet radiations produced therewith at a certain amperage value is greater than that produced in any othersingle or plurality of two electrode lamps operating at the same amperage. That is'to say, the quantity of ultra violet radiations [produced by an ordinary two electrode 2.5 ampere, large size glow lamp or by two relatively compact smallsize 1.25 ampere glow lamps is less than that produced by our novel 4 electrode glowlamp whose size may be that of the 1.25

ampere lamp and whose electrodes and filaments are of the same size as those of the 1.25 ampere lamp. Further advantages of this particular structure are that the amperage may be materially increased above 2.5 without impairing the efliciency or decreasing the life of the lamp and, moreover, the diffusibility of the ultra violet rays is considerably enhanced. Although we have compared our novel glow lamp of a size corresponding to that of a 1.25 ampere glow lamp. we do not mean to be limited thereby but have merely used this particular size as an illustration for the sake of clearness of comparison.

In order that we may further enhance the diiiusibility of the radiations produced in our novel lamp heretofore described, we provide its internal structure with one or more shields or grids which also serves to increase the efliciency and life of the device and permits the emplo ment of still higher amperages without decreasing the normal life of the lamp.

For these purposes we provide one or preferably two shields or grids 40 and 4| asshown in Figures 1 and 2. Each of these shields or grids may be in the form of a nickel wire mesh screen or a perforated-plate of nickel or the like, characterized by an outwardly flared V shape and of a with materially greater than the length of the e :trodes. The shield or grid 40 is mounted be ween the electrodes 34 and and the shield or grid 4| is mounted between the electrodes and 26 with the apices of the screens or grids opposite each other and the flared portions thereof being in approximately parallel relation with and spaced from each other. The grid is maintained at the same potential as the electrodes 25 and 35 and the grid 41 is maintained at the same potential as the electrodes 26 and 34. For this purpose we provide rigid nickel supporting wires 42 electrically secured, as by welding, to one arm of the grid 40 and to the lead l1, and a rigid supporting wire 43 electrically secured as by welding to one arm of the grid 4i and the lead l8.

The structure is braced at its upper ends by means of an elongated glass bead 44 firmly sealed to the pedestal l3, and carrying a plurality of wires 45 and 46 which are welded to the cross arms 36 and 3] respectively.

The cross arms glass beads to which are secured wires 41 and 48, welded to the arms of the grids 40 and 4! respectively. These wires are mere supporting means and the glass beads serve as bracing means and insulating media between them and the cross arms.

Instead of using a four cathode structure as shown in Figures 1 and 2. one other aspect of our invention is the embodiment shown in Figures 3, 4 and 5. As illustrated, we may employ but two electrodes in the lamp which comprises an exhausted envelope 56, of the type heretofore described, and contains a small proportion of mercury and, if desired, a small quantity of a monatomic gas such as neon, argon or the like. Extending upwardly and outwardly from the press and sealed thereto are a plurality of nickel supporting wires 5 and These wires are electrically secured to lead-in wires 53 and 5 3- respectively, and have rigid guide or support wires 56 and 57 electrically secured thereto adjacent the rree ends thereof as by means of welding. To the upper end of these guides or sup-- ports 56 and 57 are electrically secured, as by means of Welding, coiled heater filaments and to the upper ends of which are electrically secured upper rigid guides or supports and M, which are in turn welded to a common cross wire {52.

The cathode assembly illustrated is or the type heretofore described and consists of sleeves 63 and 65 respectively surrounding and spaced from the filaments 58 and 59. Each of these electrodes comprises a cylindrical sleeve consisting of nickel base having a coating of a thermionically active material thereon and is secured to its respective guide or support in the manner heretofore described.

Adjacent the support leads 6G and Si is an elongated glass bead 65 having metallic spurs 36 and 31 carry a plurality of 3 86 and 61 integrally united therewith and secured to the cross a 62,

In order that a construction of this character may be operated at relatively high amperages to produce relatively large quantities of highly diffused ultra violet radiations without the necessity of materially increasing the size of the lamp, we provide according to our invention a shield or grid, or preferably a plurality of shields or grids 88 and 69, hereinafter described, surrounding the electrodes 63 and 64 and spaced from the outer surface thereof. Each of these shields or grids 68 and 69 may be in the form of a. 20 mesh nickel wire screen whose diameter is materially greater than that of the electrodes 83 and 64, and are kept at the same potential as the respective electrodes by means 01' electrical connector 10 welded to the lower portion of the grid 68 and to the support lead 5|, and electrical connector H welded to the lower portion of the grid 69 and to the support lead 52. The shields or grids are braced at their upper ends by means of U wires I2 and 13 welded to therespective pairs of elements 63, 60 and 64, 69 and by means of wires 14 and 15 integral with the bead 65 and welded to the respective shields or grids 88 and 69.

In order to further improve this lamp, we provide a longitudinally extending plate or mesh nickel shield 16 located between and equi-distantly spaced from the electrodes and shielding one electrode from the other.

Unlike the grids 68 and 69 the shield 16 is not connected to either of the leads Si or 52, but is carried by the insulator 65 and another insulator 'ii secured to the supports 5| and 52. This shield is of a width greater than the diameter of the grids 68 and 6t and its longitudinal edges are located beyond the periphery of each of these grids.

As an alternative shield or grid structure, we may employ a plurality of parallel nickel rods Bil circumferentially spaced around each electrode as shown in Figure 6.

Still another embodiment of our invention is shown in Figure 7. As illustrated there is protype heretofore described, 95. This shield 98 may he nickel screen carried by a supporting wire 96 which may have one end sealed to the press of the envelope and its other end welded to the cross arm connecting the two filaments. The shield per so may be of a width which is about four to eight times the diameter of the electrodes and may be composed of nickel or the like in the form of a plate, mesh or spaced rod struc ture. Like the shield 16 of the embodiment shown in Figure 3, this shield Si? is in a broad c side position between the electrodes and serves to spread out the discharge and reduces Quantity of ions going directly from one electrode to another. These considerations are of importance in the operation of lamps of this character because of the diffusibility of the radiation produced, the eiiiciency and the life of the lamp which are increased by means of the construction heretofore described.

Although we have shown and described several may be made without departing from the spirit and scope of the invention as defined by the appended claims.

We claim:

1. A negative glow lamp of the gaseous-conduction type comprising an enclosing envelope having four electrodes therein, two of said electrodes being in parallel electrical relationship with each other and the other two of said electrodes also being in parallel electrical relationship with each other, saidfour electrodes spaced from each other and approximately located on a common virtual circumference.

2. A negative glow lamp of the gaseous conduction type comprising an enclosing envelope having four electrodes therein, two of said electrodes being in parallel electrical relationship with each other and the other two of said electrodes also being in parallel electrical relationship with each other, said electrodes spaced about 90 apart and located adjacent a common virtual circumference.

3. A negative glow lamp of the gaseousconduction type comprising an enclosing envelope having four electrodes therein, two of said electrodes being in parallel electrical relationship with each other and the other two of said electrodes also being in parallel electrical relationship with each other, each of said electrodes being generally parallel to the longitudinal axis of the envelope and located adjacent a common virtual circumference, each of said electrodes being spaced about 90 apart.

4. A negative glow lamp of the gaseous conduction type comprising an enclosing envelope, a plurality of closely spaced thermionically active electrodes therein, a grid located between said electrodes and disposed closerto one than the other, and means directly connecting said grid to the closer electrode so that they always operate at the same potential.

5.-A negative glow lamp of the gaseous conduction type comprising an enclosing envelope, a plurality of thermionically active electrodes therein, a woven wire grid located between said electrodes, said grid being directly connected, and closer, to one of said electrodes than the other, so that it is always at the same operating potential as said connected electrode.

6. A negative glow lamp of the gaseous conduction type comprising an enclosing envelope, a plurality of closely spaced electrodes therein and a plurality of grids located adjacentto said electrodes, one of said grids being directly connected to one of said electrodes so as to always have the same operating potential, and the other grid being directly connected to the other electrode so as to always have the same operating potential.

7. A negative glow lamp of the gaseous conduction type comprising an enclosing envelope, a plurality of closely spaced thermionically active electrodes therein and a grid surrounding and spaced from one of said electrodes, said grid being directly connected to said electrode so as to always have the same operating potential.

8. A negative glow lamp of the gaseous conduction type comprising an enclosing envelope,'

a plurality of closely spaced electrodes therein, a grid surrounding and spaced from each of said electrodes, each of said grids being directly connected to the electrode surrounded thereby so as to always have the same operating potential.

9. A negative glow lamp of the gaseous conduction type comprising an enclosing envelope having four electrodes therein, two of said electrodes being in parallel electrical relationship with each other and the other two of said electrodes also being in parallel electrical relationship with each other and a grid located between two of said electrodes.

i0. A negative glow lamp of the gaseous conduction type comprising an enclosing envelope having four electrodestherein, two of said electrodes being in parallel electrical relationship with each other and the other two of said electrodes also being in parallel electrical relationship with each other and a grid located between two of said electrodes, said grid being in parallel electrical relationship with one of said electrodes.

11. A negative glow lamp of the gaseous conduction type comprising an enclosing envelope having four electrodes therein, two of said electrodes being in parallel electrical relationship with each other and the other two of said electrodes also being in parallel electrical relationship with each other, said four electrodes spaced from each other and approximately located on a common virtual circumference and a grid located between two of said electrodes.

12. A negative glow lamp of the gaseous conduction type comprising an enclosing envelope having four electrodes therein, two of said electrodes being in parallel electrical relationship with each other and the other two of said electrodes also being in parallel electrical relationship with each other, a plurality of grids located between said electrodes, one of said grids being in parallel electrical'relationship with one of said electrodes and the other of said grids being in parallel relationship with another one of said electrodes.

13. A negative glow lamp of the gaseous conduction type comprising an enclosing envelope having four electrodes therein, two of said electrodes being in parallel electrical relationship with each other and the other two of said electrodes also being in parallel electrical relationship with each other, each of said electrodes including a thermionically active material and a heater element for rendering said material electron emissive, all oi! said heater elements being in electrical series relationship with each other.

14. An ultra violet lamp comprising an enclosing envelope, an ionizable medium therein, said envelope having a press, a plurality of electrodes supported by said press each of said electrodes including a heating element and a thermionically active material, the heating elements of said electrodes being in electrical series relationship and a grid located in the space between said electrodes and directly connected to the active material of one electrode so as .to always operate at the potential thereof.

15. An ultra violet lamp comprising an enclosing envelope, an ionizable medium therein, a plurality of spaced thermionically active electrodes, a grid located in the space between said electrodes, said envelope having a press, said electrodes being supported by said press, each of said electrodes including a heater element and a hollow body having a thermionically active surface, said heater element being located in said hollow body for heating the same, said heater elements being connected in electrical series relationship, said grid being directly connected to one hollow body so as to always operate at the potential thereof.

16. An ultra violet lamp comprising an envelope, an ionizable medium therein, a plurality of thermionic electrodes and a grid also located therein, said electrodes being spaced from each .electrical series relationship,

other, said grid being located in the space between said electrodes, each of said electrodes including a hollow body having a thermionically active surface and a heater element, said heater elements being connected in electrical series relationship, said grid being directly connected to one of said hollow bodies so as to always operate at the potential thereof.

17. An ultra violet lamp comprising an enclosing envelope, an ionizable medium, a plurality of electrodes and a grid located therein, said electrodes being spaced from each other and supported by a press, each of said electrodes ineluding a heater element and a thermionically active material, a grid located in the space between said electrodes said grid being directly connected to the thermionically active material on one of said electrodes so as to always operate at the potential thereof.

18. An ultra violet lamp comprising an envelope, an ionizable medium, four thermionically active spaced electrodes and a grid located therein, each of said electrodes including a heater element and a thermionically active material, two of said electrodes being in electrical parallel relationship, said heater elements being in electrical series relationship, said grid being directly connected to one of said electrodes so as to always operate at the potential thereof.

19. An ultra-violet lamp comprising an envelope, an ionizable medium therein, a plurality of thermionic electrodes and a grid also located therein, said electrodes being spaced from each other and supported by a press, said grid being located in the space between said electrodes, each of said electrodes including a hollow body having a thermionically active surface and a heater element, said heater elements being connected in said grid also being supported by said press and directly connected to one of said hollow bodies so as to always operate at the potential thereof.

20. An ultra-violet lamp comprising an enclosing envelope, an ionizable medium, a plurality of electrodes and a grid located therein, said electrodes being spaced from each other and supported by a press, each of said electrodes including a heater element and a thermionically active material, a grid located in the space between said electrodes said grid being directly connected to the thermionically active material of one of said electrodes so as to always operate at the potential thereof.

21. A gaseous conduction lamp comprising an enclosingenvelope, an ionizable medium therein, said envelope having a press, a plurality of electrodes supported by said press each of said electrodes including a heating element and a thermionically active material, the heating elements of said electrodes being in electrical series relationship, and a grid located in the space between said electrodes and directly connected to the thermionically active material of one of said electrodes so as to always operate at the potential thereof.

22. A gaseous conduction lamp comprising an envelope, an ionizable medium therein, a plurality of thermionic electrodes and a grid also located therein, said electrodes being spaced from each other and supported by a press, said grid being located in the space between said electrodes, each of said electrodes including a hollow body having a thermionically active surface and a heater element, said heater elements being grid also being supported by said press and directly connected to one of said hollow bodies so as to always operate at the potential thereof.

23. A gaseous conduction lamp comprising an enclosing envelope, an ionizable medium therein, said envelope having a press, a plurality of electrodes supported by said press each of said electrodes including a heating element and a thermionically active material, the heating elements of said electrodes being in electrical series relationship, and a plurality of apertured electrically conducting cylindrical grid elements completely surrounding said electrodes respectively and each directly connected to the thermion-cally active material of the surrounded electrode so as to always operate at the potential thereof.

24. A gaseous conduction lamp comprising an envelope, an ionizable medium therein, a pluconnected in electrical series relationship, said rality of thermionic electrodes and a grid also located therein, said grid being formed as an apertured electrically conducting cylindrical element and completely surrounding at least one of said electrodes, said electrodes being spaced from each other and supported by a press, said grid being located in the space between said electrodes, each of said electrodes including a hollow body having a thermionically active surface and a heater element, said heater elements being connected in electrical series relationship, said grid also being supported by said press and directly connected to one of said thermlonically active surfaces so as to always operate at the potential thereof.

25. A discharge lamp comprising a vitreous envelope containing gas at a relatively low pressure admixed with mercury vapor, a plurality of electrodes in said envelope, each electrode comprising a hollow tubular member having a surface adapted to emit electrons when heated, a lead from each tubular member directly to the exterior of the envelope whereby the potential of the energizing power is applied between said tubular members when the lamp is operated. means connected in series across said leads and comprising incandescible filaments disposed interiorly of said tubular members for heating them to electron-emitting temperature, and a grid associated with one of said tubular members and directly connected thereto so as to operate at the potential thereof and protect its electron-emitting surface from bombardment during operation of said lamp.

26. A discharge lamp comprising a vitreous envelope, a plurality of electrodes therein, each electrode comprising a hollow tubular member having a surface adapted to emit electrons when heated, a lead from each tubular member directly to the exterior of the envelope whereby the potential of the energizing power is applied between said tubular members when the lamp is operated, means connected in series across said leads and comprising incandescible filaments disposed interiorly of said tubular. members for heating them to electron-emitting temperatures, a grid associated with each of said tubular members to protect its electron-emitting surface from bombardment during operation of the lamp, and a shield disposed broadside between said grids to spread out the discharge and reduce the quantity of ions going directly from one electrode to another.

JOHN WESLEY MARDEN. MADISON G. NICHOLSON. Ja-

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