Question: At which laboratory was Carsten Olsen employed as an assistant to the Danish chemist who introduced the concept of pH?

full_context: Document 1: Haldor Topsøe (1842–1935): Haldor Frederik Axel Topsøe (29 April 1842 in Skælskør, Slagelse Municipality, Denmark – 31 December 1935 in Frederiksberg, Denmark) was a Danish chemist and crystallographer. He is grandfather of the engineer Haldor Topsøe (1913–2013) who has got his name from his grandfather, and great-grandfather of the mathematician Flemming Topsøe (born 25 August 1938) and the engineer Henrik Topsøe (born 10 August 1944).
Document 2: S. P. L. Sørensen: Søren Peder Lauritz Sørensen (9 January 1868 – 12 February 1939) was a Danish chemist, famous for the introduction of the concept of pH, a scale for measuring acidity and alkalinity. He was born in Havrebjerg, Denmark.
Document 3: Peter Debye: Peter Joseph William Debye {'1': ", '2': ", '3': 'ForMemRS', '4': "} ( ; ] ; March 24, 1884 – November 2, 1966) was a Dutch-American physicist and physical chemist, and Nobel laureate in Chemistry.
Document 4: Carl Hansen &amp; Søn: Carl Hansen & Søn is a Danish furniture company. It is the company behind many of the classical furniture designs of Hans J. Wegner, one of the leading figures of the Danish modern movement.
Document 5: Holger F. Struer: Holger F. Struer was a Danish chemist and founder of "H. Struers Chemiske Laboratorium" (In Danish: "Struers Kemiske Laboratorium") in 1875 at Skindergade 38, the centre of Copenhagen. Struers introduced in 1943 Micropol, a new principle for electrolytic polishing which made the preparation process within metallography more controlled in order to achieve better preparation results.
Document 6: Nils Ohlsen: Nils Ohlsen (born 1967 in Oldenburg, Germany), has worked as the director of old masters and modern art at the National Museum of Art, Architecture and Design in Oslo since 2010. Before that he worked as curator at the Kunsthalle Emden, from 2006 as scientific director. He studied art history, classical archaeology and prehistory, as well as multimedia design, in Berlin and Stockholm, also working as an archaeologist in 1996/97. In 1993 he obtained a "magister artium" degree at the Freie Universität Berlin with a thesis on Max Beckmann, before completing his PhD in 1997 at the same university with a dissertation on Scandinavian interior painting in the late 19th and early 20th centuries.
Document 7: List of Danish Nobel laureates: This is a list of Danish Nobel laureates. Since the Nobel Prize was established per the will of Swedish inventor Alfred Nobel in 1895, 12 of the prize winners have been from Denmark. The first Danish Nobel laureate was Niels Ryberg Finsen, who won a Nobel Prize for medicine in 1903 for his work in using light therapy to treat diseases. The most recent Danish Nobel Prize winner was Jens Skou who won the prize in chemistry for his discovery over the enzyme, Na+/K+-ATPase in 1997. To date, of the 13 Nobel Prizes won by Danish people, 5 have been for medicine, 3 have been for physics, 3 have been for literature, 1 has been for chemistry and one has been for peace.
Document 8: Charles J. Pedersen: Charles John Pedersen (October 3, 1904 – October 26, 1989) was an American organic chemist best known for describing methods of synthesizing crown ethers. He shared the Nobel Prize in Chemistry in 1987 with Donald J. Cram and Jean-Marie Lehn. His Japanese first name was Yoshio (良男 ) . He is the only Nobel Prize laureate born in Korea other than Peace Prize laureate Kim Dae-jung.
Document 9: Carl Stumpf: Carl Stumpf (] ; 21 April 1848 – 25 December 1936) was a German philosopher and psychologist. He studied with Franz Brentano at the University of Würzburg before receiving his doctorate at the University of Göttingen in 1868. He also tutored the modernist literature writer Robert Musil at the University of Berlin, and worked with Hermann Lotze, who is famous for his work in perception, at Göttingen. Stumpf is known for his work on the "psychology of tones". He had an important influence on his students Wolfgang Köhler and Kurt Koffka who were instrumental in the founding of "Gestalt" psychology as well as Kurt Lewin, who was also a part of the Gestalt group and was key in the establishment of experimental social psychology in America. Stumpf is considered one of the pioneers of comparative musicology and ethnomusicology, as documented in his study of the origins of human musical cognition "The Origins of Music" (1911). He held positions in the philosophy departments at the Universities of Göttingen, Würzburg, Prague, Munich and Halle, before obtaining a professorship at the University of Berlin.
Document 10: Carsten Olsen: Carsten Erik Olsen (March 1, 1891 – August 19, 1974) was a Danish plant ecologist and plant physiologist, who pioneered the study of plant nutrition in soils of different pH. He was born in Copenhagen and began studies of botany at the University of Copenhagen in 1910, at first with professor Eugenius Warming, then with professor Christen Raunkiær. His doctoral dissertation (1921) was on the influence of soil pH on the natural distribution of plants. He was then employed by the Carlsberg Laboratory as an assistant to the chemist S. P. L. Sørensen, later in his own lab. There, he worked on plant uptake of ions, especially iron, nitrogen fixation and calcicolous plants.
Document 11: Peder Syv: Peder Pedersen Syv (also spelled Siuf) or in Latin Petrus Petri Septimius (February 22, 1631 – February 17, 1702) was a Danish philologist, folklorist and priest, known for his collections of Danish proverbs and folksongs, and his contributions to the development of Danish as a written language.
Document 12: Carsten Thomassen: Carsten Thomassen (born August 22, 1948 in Grindsted) is a Danish mathematician. He has been a Professor of Mathematics at the Technical University of Denmark since 1981, and since 1990 a member of the Royal Danish Academy of Sciences and Letters. His research concerns discrete mathematics and more specifically graph theory.
Document 13: Ericaceous bed: An Ericaceous bed is a bed (or garden) with acidic and often nutrient-poor soil such as Ericaceous compost and different types of peat. The pH of the soil is typically between 4.5 and 6. The purpose is typically to grow a number of garden plants which require (or thrives best in) acidic soil. Such plants commonly include heathers (Erica, Calluna and more) and Rhododendrons. Another group of plants common in ericaceous beds are those belonging to the boreal coniferous forest, e.g. Vacciniums. A number of orchids also grow well in nutrient-poor soil.
Document 14: Johan Kjeldahl: Johan Gustav Christoffer Thorsager Kjeldahl (] 16 August 1849 – 18 July 1900), was a Danish chemist who developed a method for determining the amount of nitrogen in certain organic compounds using a laboratory technique which was named the Kjeldahl method after him.
Document 15: Jørgen Buhl Rasmussen: Jørgen Buhl Rasmussen (born 18 August 1955) is the Danish Chief Executive of the Danish multi-national brewing company Carlsberg Group (Carlsberg A/S), based in Copenhagen (native "København") in Denmark. Carlsberg is the name of a district of Copenhagen. The main shareholder of Carlsberg is the Carlsberg Foundation.
ground_truth: Carlsberg Laboratory