摘要:

An elementary discussion for physicists is given of the thermodynamic instability of proteins and DNA. The biochemical explanation is given of how these molecules are grown in the face of a large unfavorable free energy difference, as much as 0.2 MeV for DNA of106bonds. The role of ATP is described as the major fuel of the biological world.

ISSN:0002-9505    

DOI:10.1119/1.1986447

出版商:American Association of Physics Teachers    

年代:1972

数据来源: AIP

摘要:

The well-known application of the Lorentz transformation to the exactly relativistic Coulomb force in order to derive the force on a charge due to another in uniform motion is extended to arbitrary Lorentz-invariant one-body problems. It is shown that the result, in addition to being the force onm1from uniformly movingm2,is, to first order in coupling strength, the Lorentz-invariant force onm1whenm2is unconstrained and the two particles interact. Some attention is paid to Lagrangians for exactly relativistic one-body problems, and a new construction of Darwin-like1/c2corrections to nonrelativistic Lagrangians for a variety of interactions is presented. Among these is the EIH Lagrangian of general relativity, whence follows an interesting point concerning special relativistic gravitation.

ISSN:0002-9505    

DOI:10.1119/1.1986448

出版商:American Association of Physics Teachers    

年代:1972

数据来源: AIP

摘要:

An experiment is described for the undergraduate optics laboratory to verify the law of intensity in the Fesnel diffraction of a thin wire. A He-Ne gas laser is used as a light source and a CdS photocell as a detector to scan the diffraction pattern. The agreement with the theoretical pattern is remarkably good.

ISSN:0002-9505    

DOI:10.1119/1.1986449

出版商:American Association of Physics Teachers    

年代:1972

数据来源: AIP

摘要:

Relative to a clock at rest on the Earth's surface, the time recorded by an ideal clock after a circumnavigation of the Earth depends not only on the speed and altitude but also on the direction of the circumnavigation and on the rotational speed of the Earth. Such a clock may run either fast or slow, depending on the direction and ground speed for the circumnavigation. This directional dependence should be perceptible with commercial jet speeds and cesium beam clocks.

ISSN:0002-9505    

DOI:10.1119/1.1986450

出版商:American Association of Physics Teachers    

年代:1972

数据来源: AIP

摘要:

A relatively simple experiment is described for measuring the speed of light to three significant digits in an undergraduate research project. A laser beam modulated by a 21.3-MHz signal applied to a Pockels cell is used in an interferometer arrangement patterned after Palmer and Spratt's simplification of Anderson's precision method.

ISSN:0002-9505    

DOI:10.1119/1.1986451

出版商:American Association of Physics Teachers    

年代:1972

数据来源: AIP

摘要:

We show a pedagogically useful way of deriving both stationary and time-dependent perturbation theory from the field-theoretical Hartree-Fock approximation. The calculation clearly shows how the contributions of real and virtual processes differ.

ISSN:0002-9505    

DOI:10.1119/1.1986452

出版商:American Association of Physics Teachers    

年代:1972

数据来源: AIP

摘要:

Weinstock[Amer. J. Phys.38,1289 (1970)]has studied the problem of the propagation of a particular disturbance on a one-dimensional semi-infinite lattice of similar atoms, coupled by nearest-neighbor ideal springs; a solution to the same problem, in infinite lattice form, was given earlier in a book by Morse and Ingard [Theoretical Acoustics (McGraw-Hill, New York, 1968) p. 91]. The problem is essentially the following: Given a one-dimensional lattice that is stationary for all timest<0,what is the response of the lattice if one of the atoms (the end atom in the semi-infinite lattice case) is constrained to move with constant velocity for allt≥0?The method of response functions was developed by the author[J. Phys. Chem. Solids23,1269 (1962)]to solve related problems involving n-dimensional infinite and semi-infinite lattices; a summary of this method is presented for the special case of the one-dimensional lattices, and it is shown how it may be used to solve this problem in a slightly more general form.

ISSN:0002-9505    

DOI:10.1119/1.1986453

出版商:American Association of Physics Teachers    

年代:1972

数据来源: AIP

摘要:

Although it is well known that the exchange interaction is a basic property of Fermi systems, the available derivations of this interaction usually involve special assumptions that tend to obscure its origin. In this paper we present a more general derivation free from these assumptions. We show that this derivation leads directly to the diagrammatic representation of perturbation theory first used by Hugenholtz. The s-d exchange Hamiltonian of Kasuya is derived as a special case for systems with localized states.

ISSN:0002-9505    

DOI:10.1119/1.1986454

出版商:American Association of Physics Teachers    

年代:1972

数据来源: AIP

摘要:

A direct method is presented for the vector differential operations in orthogonal curvilinear coordinates. From the angular displacement vector of the diagonal of the parallelepiped formed by the orthogonal coordinate line elements the variation of the unit vectors are obtained. Then the vector differential operations are directly carried out. In this way, expressions for gradient, divergence, curl, and Laplacian in cylindrical, spherical, and elliptic coordinates are derived.

ISSN:0002-9505    

DOI:10.1119/1.1986455

出版商:American Association of Physics Teachers    

年代:1972

数据来源: AIP

摘要:

A pilot course is described that was designed to provide advanced undergraduate science students with an opportunity to explore the way in which several fields of science and technology interface with society at large. In addition, the course was designed to allow students to explore their interests and aptitudes for career work in the science-society interface area. Enthusiastic student response has led to plans to expand the course to a full year offering and suggests that similar courses would be well received by science students at other liberal arts colleges and universities in the country.

ISSN:0002-9505    

DOI:10.1119/1.1986456

出版商:American Association of Physics Teachers    

年代:1972

数据来源: AIP