Deposits on the bottom of lakes and seas is commonly meant when referring to sediments. Fluvial (see above) and aeolian (wind borne) deposits settling in rivers and on land also exist however. Sediments provide information about climate history. They may, for example, contain residues of plants or ash derived from volcanic eruptions. Study and calibration of such residues allow conclusions to be made on the prevailing climate and environmental conditions at the time in question.
SELEX (Systematic Evolution of Ligands by Exponential Enrichment) is an in vitro selective procedure for the production of aptamers. Analogous to natural evolution, the process proceeds via a cyclical process derived from selection and amplification routines, which are repeated so often until the nucleic acids exhibit the desired characteristics. Starting point for the selection of DNA aptamers is a oligonucleotide library of mainly chemically synthesized oligonucleotides encompassing a random region of around 30-80 nucleotides flanked by two constant primer regions. The oligonucleotide library is brought into contact with the target molecules and the non-bonded oligonucleotides removed in the next step. The bonded oligonucleotide target complexes are then separated again and the oligonucleotides previously bonded to the target amplified by means of PCR (Polymerase Chain Reaction). The relevant single stranded DNA is prepared from the double stranded PCR products and used as a starting point for the next SELEX round. Approx. 6-20 SELEX rounds are required for the enrichment of a selective aptamer pool. The individual aptamers produced from this pool by means of cloning can be sequenced in a follow-up procedure and subjected to a sequence analysis.
Semiarid climate zones are those where annual precipitation is usually less than annual evaporation. A semiarid climate exhibits an annual precipitation between 250 and 500 mm. Vegetation is only scant as a result of the prevailing dry conditions.
Stressors cover all internal and external stimulations that demand a reaction by the organism.
This process is applied in the mineral oil industry and chemistry with the purpose of driving off highly volatile water components such as ammonia or organic solvents. Decisive are properties of the substances due to be stripped such as the vapor pressure.
A Synthon is a molecular building unit. The reactive positions of a synthon are
indicated by the letters a for acceptor or d for donor.