摘要:

To present a paper in tribute to Hans Frauenfelder on the ocassion of his 65th birthday is a rare privilege. His work on iron protein reaction centers has changed our perception of protein dynamics and our view of the essential role of oxygen in biological systems. Most importantly, his continued efforts to increase the experimental precision and to develop new models have inspired a generation of multidisciplinary investigators and have thus enriched the chemistry and genetics of modern biology. I beg your indulgence for the following account of the gradual unravelling of an enzyme system in our labs, with strong participation from Physics and friends elsewhere, an account of peaks, valleys and a few crevasses encountered in a quest that is still in progress.

ISSN:0094-243X    

DOI:10.1063/1.37868

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The author describes the use of nuclear magnetic resonance to study simple molecules (CO, C2H2, C2H4) adsorbed on small particles composed of 6 of the Group VIII metals (Ru, Rh, Pd, Os, Ir, PtO. The data yield information about bonding of the molecules to the surface, the structure of the molecules, rupture of the C‐C bonds on heating, the observation of isolated C atoms on the metal surface, and measurement of diffusion rates of C atoms or CO molecules on the metal surface.

ISSN:0094-243X    

DOI:10.1063/1.37872

出版商:AIP    

年代:1988

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.37862

出版商:AIP    

年代:1988

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.37863

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Neutrinos continue to exhibit a number of unexplained features and unknown properties. Amongst these, the question of the neutrino restmass remains to be one of the most challenging problems of nowadays physics. Thus far, only upper limits on neutrino masses have resulted from direct measurements as well as from searches for neutrino oscillations. Neutrinos provide instant information on the solar fusion reactions. The reasons for the short‐age by a factor of three in the high energy portion of the solar neutrino flux observed in the Davis experiment are unknown at present. The ‘‘European Gallex Collaboration’’ will perform a solar neutrino experiment aiming at the low energy portion of the solar neutrino spectrum, which is directly related to the known solar luminosity. The new experiment due to the large distance involved will be highly sensitive to neutrino masses.

ISSN:0094-243X    

DOI:10.1063/1.37864

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The Darwinian concept of evolution through natural selection has been revised and put on a solid physical basis, in a form which applies to self‐replicable macromolecules. Two new concepts are introduced: sequence space and quasi‐species. Evolutionary change in the DNA‐ or RNA‐sequence of a gene can be mapped as a trajectory in a sequence space of dimension &ngr;, where &ngr; corresponds to the number of changeable positions in the genomic sequence. Emphasis, however, is shifted from the single surviving wildtype, a single point in the sequence space, to the complex structure of the mutant distribution that constitutes the quasi‐species. Selection is equivalent to an establishment of the quasi‐species in a localized region of sequence space, subject to threshold conditions for the error rate and sequence length. Arrival of a new mutant may violate the local threshold condition and thereby lead to a displacement of the quasi‐species into a different region of sequence space. This transformation is similar to a phase transition; the dynamical equations that describe the quase‐species have been shown to be analogous to those of the two‐dimensional Ising model of ferromagnetism. The occurrence of a selectively advantageous mutant is biased by the particulars of the quasi‐species distribution, whose mutants are populated according to their fitness relative to that of the wild‐type. Inasmuch as fitness regions are connected (like mountain ridges) the evolutionary trajectory is guided to regions of optimal fitness. Evolution experiments in test tubes confirm this modification of the simple chance and law nature of the Darwinian concept. The results of the theory can also be applied to the construction of a machine that provides optimal conditions for a rapid evolution of functionally active macromolecules.An introduction to the physics of molecular evolution by the author has appeared recently.1Detailed studies of the kinetics and mechanisms of replication of RNA, the most likely candidate for early evolution2,3, and of the implications on natural selection have been given in Refs. 4 and 5. The quasi‐species model has been constructed in Refs. 6 and 7 using the concept of sequence space. Subsequently various methods have been invented to elucidate this concept and to relate it to the theory of critical phenomena8−19. The instability of the quasi‐species at the error threshold is discussed in Ref. 10. Evolution experiments with RNA strands in test tubes are described in Refs. 21 and 22.

ISSN:0094-243X    

DOI:10.1063/1.37874

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The optical, electrical, magnetic and chemical properties of condensed phases are determined by the characteristics of the energy levels available to the outer electrons of the entities which make up the phase. Because of different spacial characteristics the energy levels associated with different orbitals are perturbed differently by compression. The consequences of this pressure tuning are very broad. Here we consider two categories: the characterization of states, excitations or processes, and the testing of theories concerning electronic phenomena. Three examples in each category are outlined.

ISSN:0094-243X    

DOI:10.1063/1.37865

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Unconventional superfluids and superconductors are fermion systems in which the phonon‐induced interaction between particles does not play an essential role, and in which the pairs of BCS theory may be found in higher angular momentum states. These are reviewed in the historical order in which their superfluidity was discovered: nuclei, neutron stars, liquid3He, and heavy electron metals. Some key experimental results on the copper oxide superconductors are reviewed, and the possibility that these are part of the heavy electron family, with a spin‐fluctuation‐induced interaction between quasi‐particles being responsible for their superconductivity, is examined.

ISSN:0094-243X    

DOI:10.1063/1.37866

出版商:AIP    

年代:1988

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.37875

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Theoretical and experimental studies of the problem of mirror symmetry breaking in Nature in the course of the origin of life are discussed.The interplay of three main factors—statistical fluctuations, advantage factor (AF) and racemizing processes is taken into account.The detailed analysis of existing data leads to the following scheme of main stages of the formation of life: 1. Prebiotic monomer formation, i.e., the formation and accumulation of various components of future biopolymers in racemic form (‘‘warm‘‘‐terrestrial, and ‘‘cold’’‐extraterrestrial scenarios are discussed). 2. Chiral purity formation, i.e., the cooperative bifurcation‐type chiral polarization of the prebiotic medium. The sign of such polarization at the Earth (D‐sugars andL‐amino acids) seems to be accidental rather than determined by the violation of parity in weak interactions. 3. Formation of oligomeric tracers of chiral specific activity, i.e., the formation of protobiological structures (apparently, starting with RNA) up to several hundreds monomer units by matrix polymerization in chirally pure media. 4. Self‐enzymatric block synthesis of biological macromolecules (RNA, DNA, proteins) and more complex systems.The possibilities of the destruction of the biosphere due to long‐term racemizing inpacts are also discussed.

ISSN:0094-243X    

DOI:10.1063/1.37867

出版商:AIP    

年代:1988

数据来源: AIP