California Institute of Technology

About: California Institute of Technology is a education organization based out in Pasadena, California, United States. It is known for research contribution in the topics: Galaxy & Population. The organization has 57649 authors who have published 146691 publications receiving 8620287 citations. The organization is also known as: Caltech & Cal Tech.

Exploring protein fitness landscapes by directed evolution

Abstract: Directed evolution circumvents our profound ignorance of how a protein's sequence encodes its function by using iterative rounds of random mutation and artificial selection to discover new and useful proteins. Proteins can be tuned to adapt to new functions or environments by simple adaptive walks involving small numbers of mutations. Directed evolution studies have shown how rapidly some proteins can evolve under strong selection pressures and, because the entire 'fossil record' of evolutionary intermediates is available for detailed study, they have provided new insight into the relationship between sequence and function. Directed evolution has also shown how mutations that are functionally neutral can set the stage for further adaptation.

The Cation-π Interaction

Abstract: The chemistry community now recognizes the cation−π interaction as a major force for molecular recognition, joining the hydrophobic effect, the hydrogen bond, and the ion pair in determining macromolecular structure and drug–receptor interactions. This Account provides the author’s perspective on the intellectual origins and fundamental nature of the cation−π interaction.Early studies on cyclophanes established that water-soluble, cationic molecules would forego aqueous solvation to enter a hydrophobic cavity if that cavity was lined with π systems. Important gas phase studies established the fundamental nature of the cation−π interaction. The strength of the cation−π interaction (Li+ binds to benzene with 38 kcal/mol of binding energy; NH4+ with 19 kcal/mol) distinguishes it from the weaker polar−π interactions observed in the benzene dimer or water–benzene complexes. In addition to the substantial intrinsic strength of the cation−π interaction in gas phase studies, the cation−π interaction remains energ...

The Advanced Composition Explorer

Abstract: The Advanced Composition Explorer was launched August 25, 1997 carrying six high-resolution spectrometers that measure the elemental, isotopic, and ionic charge-state composition of nuclei from H to Ni (1≤Z≤28) from solar wind energies (∼1 keV nucl−1) to galactic cosmic-ray energies (∼500 MeV nucl−1). Data from these instruments is being used to measure and compare the elemental and isotopic composition of the solar corona, the nearby interstellar medium, and the Galaxy, and to study particle acceleration processes that occur in a wide range of environments. ACE also carries three instruments that provide the heliospheric context for ion composition studies by monitoring the state of the interplanetary medium. From its orbit about the Sun-Earth libration point ∼1.5 million km sunward of Earth, ACE also provides real-time solar wind measurements to NOAA for use in forecasting space weather. This paper provides an introduction to the ACE mission, including overviews of the scientific goals and objectives, the instrument payload, and the spacecraft and ground systems.

Effect of Inhomogeneity on Cosmological Models.

Abstract: In the application of relativistic mechanics and relativistic thermodynamics to cosmology, it has been usual to consider homogeneous models of the universe, filled with an idealized fluid, which at any given time has the same properties throughout the whole of its spatial extent. This procedure has a certain heuristic justification on account of the greater mathematical simplicity of homogeneous as compared with non-homogeneous models, and has a measure of observational justification on account of the approximate uniformity in the large scale distribution of extra-galactic nebulae, which is found out to the some 108 light-years which the Mount Wilson 100-inch telescope has been able to penetrate. Nevertheless, it is evident that some preponderating tendency for inhomogeneities to disappear with time would have to be demonstrated, before such models could be used with confidence to obtain extrapolated conclusions as to the behavior of the universe in very distant regions or over exceedingly long periods of time.