Exhibit 24**POWER OF ATTORNEY**     Know all men by these presents, that the undersigned constitutes and appoints Frank J.Bramanti and Edward H. Ellis, Jr. and each of them, his true and lawful attorney-in-fact and agentwith full power of substitution and resubstitution, for him and in his name, place, and stead, inany and all capacities, to sign this Annual Report on Form 10-K and any and all amendments thereto,and to file same, with all exhibits thereto, and other documents in connection therewith, with theSecurities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each ofthem, full power and authority to do and perform each and every act and thing requisite andnecessary to be done in and about the premises, as fully to all intents and purposes as he might orcould do in person, hereby ratifying and confirming all that such attorneys-in-fact and agents orany of them, or their or his substitute or substitutes, may lawfully do or cause to be done byvirtue hereof.   February 25, 2008   /s/ Patrick B. Collins     Patrick B. Collins
 

 
**POWER OF ATTORNEY**     Know all men by these presents, that the undersigned constitutes and appoints Frank J.Bramanti and Edward H. Ellis, Jr. and each of them, his true and lawful attorney-in-fact and agentwith full power of substitution and resubstitution, for him and in his name, place, and stead, inany and all capacities, to sign this Annual Report on Form 10-K and any and all amendments thereto,and to file same, with all exhibits thereto, and other documents in connection therewith, with theSecurities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each ofthem, full power and authority to do and perform each and every act and thing requisite andnecessary to be done in and about the premises, as fully to all intents and purposes as he might orcould do in person, hereby ratifying and confirming all that such attorneys-in-fact and agents orany of them, or their or his substitute or substitutes, may lawfully do or cause to be done byvirtue hereof.   February 19, 2008   /s/ J. Robert Dickerson     J. Robert Dickerson
 

 
**POWER OF ATTORNEY**     Know all men by these presents, that the undersigned constitutes and appoints Frank J.Bramanti and Edward H. Ellis, Jr. and each of them, his true and lawful attorney-in-fact and agentwith full power of substitution and resubstitution, for him and in his name, place, and stead, inany and all capacities, to sign this Annual Report on Form 10-K and any and all amendments thereto,and to file same, with all exhibits thereto, and other documents in connection therewith, with theSecurities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each ofthem, full power and authority to do and perform each and every act and thing requisite andnecessary to be done in and about the premises, as fully to all intents and purposes as he might orcould do in person, hereby ratifying and confirming all that such attorneys-in-fact and agents orany of them, or their or his substitute or substitutes, may lawfully do or cause to be done byvirtue hereof.   February 25, 2008   /s/ Walter M. Duer     Walter M. Duer
 

 
**POWER OF ATTORNEY**     Know all men by these presents, that the undersigned constitutes and appoints Frank J.Bramanti and Edward H. Ellis, Jr. and each of them, his true and lawful attorney-in-fact and agentwith full power of substitution and resubstitution, for him and in his name, place, and stead, inany and all capacities, to sign this Annual Report on Form 10-K and any and all amendments thereto,and to file same, with all exhibits thereto, and other documents in connection therewith, with theSecurities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each ofthem, full power and authority to do and perform each and every act and thing requisite andnecessary to be done in and about the premises, as fully to all intents and purposes as he might orcould do in person, hereby ratifying and confirming all that such attorneys-in-fact and agents orany of them, or their or his substitute or substitutes, may lawfully do or cause to be done byvirtue hereof.   February 19, 2008   /s/ James C. Flagg, Ph.D.     James C. Flagg, Ph.D.
 

 
**POWER OF ATTORNEY**     Know all men by these presents, that the undersigned constitutes and appoints Frank J.Bramanti and Edward H. Ellis, Jr. and each of them, his true and lawful attorney-in-fact and agentwith full power of substitution and resubstitution, for him and in his name, place, and stead, inany and all capacities, to sign this Annual Report on Form 10-K and any and all amendments thereto,and to file same, with all exhibits thereto, and other documents in connection therewith, with theSecurities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each ofthem, full power and authority to do and perform each and every act and thing requisite andnecessary to be done in and about the premises, as fully to all intents and purposes as he might orcould do in person, hereby ratifying and confirming all that such attorneys-in-fact and agents orany of them, or their or his substitute or substitutes, may lawfully do or cause to be done byvirtue hereof.   February 22, 2008   /s/ Allan W. Fulkerson     Allan W. Fulkerson
 

 
**POWER OF ATTORNEY**     Know all men by these presents, that the undersigned constitutes and appoints Frank J.Bramanti and Edward H. Ellis, Jr. and each of them, his true and lawful attorney-in-fact and agentwith full power of substitution and resubstitution, for him and in his name, place, and stead, inany and all capacities, to sign this Annual Report on Form 10-K and any and all amendments thereto,and to file same, with all exhibits thereto, and other documents in connection therewith, with theSecurities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each ofthem, full power and authority to do and perform each and every act and thing requisite andnecessary to be done in and about the premises, as fully to all intents and purposes as he might orcould do in person, hereby ratifying and confirming all that such attorneys-in-fact and agents orany of them, or their or his substitute or substitutes, may lawfully do or cause to be done byvirtue hereof.   February 20, 2008   /s/ John N. Molbeck, Jr.     John N. Molbeck, Jr.
 

 
**POWER OF ATTORNEY**     Know all men by these presents, that the undersigned constitutes and appoints Frank J.Bramanti and Edward H. Ellis, Jr. and each of them, his true and lawful attorney-in-fact and agentwith full power of substitution and resubstitution, for him and in his name, place, and stead, inany and all capacities, to sign this Annual Report on Form 10-K and any and all amendments thereto,and to file same, with all exhibits thereto, and other documents in connection therewith, with theSecurities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each ofthem, full power and authority to do and perform each and every act and thing requisite andnecessary to be done in and about the premises, as fully to all intents and purposes as he might orcould do in person, hereby ratifying and confirming all that such attorneys-in-fact and agents orany of them, or their or his substitute or substitutes, may lawfully do or cause to be done byvirtue hereof.   February 20, 2008   /s/ James E. Oesterreicher     James E. Oesterreicher
 

 
**POWER OF ATTORNEY**     Know all men by these presents, that the undersigned constitutes and appoints Frank J.Bramanti and Edward H. Ellis, Jr. and each of them, his true and lawful attorney-in-fact and agentwith full power of substitution and resubstitution, for him and in his name, place, and stead, inany and all capacities, to sign this Annual Report on Form 10-K and any and all amendments thereto,and to file same, with all exhibits thereto, and other documents in connection therewith, with theSecurities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each ofthem, full power and authority to do and perform each and every act and thing requisite andnecessary to be done in and about the premises, as fully to all intents and purposes as he might orcould do in person, hereby ratifying and confirming all that such attorneys-in-fact and agents orany of them, or their or his substitute or substitutes, may lawfully do or cause to be done byvirtue hereof.   February 20, 2008   /s/ Michael A.F. Roberts     Michael A.F. Roberts
 

 
**POWER OF ATTORNEY**     Know all men by these presents, that the undersigned constitutes and appoints Frank J.Bramanti and Edward H. Ellis, Jr. and each of them, his true and lawful attorney-in-fact and agentwith full power of substitution and resubstitution, for him and in his name, place, and stead, inany and all capacities, to sign this Annual Report on Form 10-K and any and all amendments thereto,and to file same, with all exhibits thereto, and other documents in connection therewith, with theSecurities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each ofthem, full power and authority to do and perform each and every act and thing requisite andnecessary to be done in and about the premises, as fully to all intents and purposes as he might orcould do in person, hereby ratifying and confirming all that such attorneys-in-fact and agents orany of them, or their or his substitute or substitutes, may lawfully do or cause to be done byvirtue hereof.   February 22, 2008   /s/ Christopher J. B. Williams     Christopher J. B. Williams