The world's largest retail design firm, Callison, just got larger with the acquisition of Dallas-based retail architect RYA Design Consultancy. RYA specializes in U.S. and international department store and specialty retail brands, including Printemps, Palacio de Hierro, and Shinsegae. The new Callison RYA Studio will merge staff and clients into Callison's existing retail practice at its Dallas and New York offices.Shawmut Design and Construction, Boston, has promoted 16-year Shawmut veteran Brian Stys to the newly created position of VP of marketing and business development.Riverside, Calif.-based general contractor J.D. Diffenbaugh has named Jeff Dale president.Clayco, St. Louis, has appointed Scott Higgins director of government construction and design.The Orlando office of VOA Associates has named Daryl LeBlanc, AIA, and Thomas Matzke, CSI, LEED, AP, associate principals.Geoffrey Stryker, PE, has joined STV Inc. as a senior structural engineer and project manager in the firm's Transportation and Infrastructure Division. Stryker will be based out of STV's Harrisburg, Pa., office.Nashville, Tenn.-based Gresham, Smith and Partners has named eight staff members owners: Tim Arendt, Ken Baker, Roddy L. Boggus, Jody Braswell, Lori Lange, David Stewart, Jody Vance, and Mark Warriner.Chicago-based Environmental Systems Design has named David P. Callan, PE, LEED AP, senior VP chief technical director. Callan, a BD+C 40 Under 40 winner, specializes in the design of high-performance and sustainable building projects.