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TitleBiographical Memoirs
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Page 196

187W A L T E R D A V I D K N I G H T

of his immediate postwar research in a paper entitled “The
Knight Shift,” which appears in volume I of the Encyclope-
dia of Nuclear Magnetic Resonance, cited at the end of this
memoir. There one reads about the events that led to his
important discovery of the shift in nuclear magnetic reso-
nance frequencies that occurs in metals and provides a probe
of the local internal fields in materials without disturbing
the basic structure of the system under study. The research
for his Ph.D. thesis at Duke was carried out while Walter
was an assistant professor of physics at Trinity College,
Hartford, and while he was commuting to or “summering”
at the Nuclear Moments Laboratory at Brookhaven National
Laboratory, where his apparatus was put together. In practi-
cal matters of experimental technique he interacted closely
at Brookhaven with Bill Cohen and Bob Pound. In the theo-
retical interpretation of his results he interacted closely with
Norman Ramsey, Samuel Goudsmit, Conyers Herring, and
perhaps most importantly, with Charles Townes, whom Walter
sometimes described as his informal thesis supervisor.

EARLY RESEARCH AT BERKELEY

His successes in research brought him to the attention
of Berkeley physics professor Francis Jenkins, who had been
dispatched by other senior professors there to travel east-
ward and recruit new talent for the Physics Department,
where a new addition to LeConte Hall was nearing comple-
tion and where expansion of the department had been au-
thorized. One of Jenkins’s assignments had been to recruit
people who could establish a group in solid-state physics,
hitherto unrepresented as a field at Berkeley. His success in
this assignment can be gauged by the fact that he recruited
Erwin Hahn, Carson Jeffries, Arthur Kip, Charles Kittel, and
Walter Knight who eventually came to form the nucleus of
this group.

Page 197

188 B I O G R A P H I C A L M E M O I R S

Walter moved to Berkeley and began experimental work
there in the summer of 1950. Walter’s important discovery
in Brookhaven of the effect of the magnetism of conduc-
tion electrons in metals on the nucleus had opened up an
important subfield of research on nuclear magnetic reso-
nance. With this new way available to study properties of
electrons in conducting materials, Walter and his students
at Berkeley contributed a series of pioneering investigations
of many different types of conducting solids, including alloys,
semiconductors, and superconductors. As these experiments
evolved it was learned in more detail that the Knight shift
had to be distinguished more carefully from other competing
shifts. These were the chemical frequency shifts due to the
action of chemical bonds, and nuclear electric quadrupole
shifts occurring in non-cubic metals. Not only was the Knight
shift an important parameter but also the theory behind it
was closely connected with the parameter of nuclear spin-
lattice relaxation times measured in metals. Because of the
skin depth penetration limit of radio-frequency fields into
the interior of metals, Walter and his students were often
preoccupied in developing techniques to prepare metals in
the form of very small spheres, with as much uniformity in
diameter as possible.

Two very important research results came about. First,
in the course of looking for the shift properties in non-
cubic metals Walter and his students discovered the first
nuclear quadrupole resonance in a metal, namely, gallium.
They followed this discovery by seeing zero field quadru-
pole resonances in several other metals. Second, after the
BCS theory of superconductivity in metals was introduced
Walter exploited the Knight shift in such a way as to have it
play an important experimental role in probing the BCS
theory. The theory predicted that the Knight shift of the
superconducting electrons should be reduced (that is, the

Page 392

383J A C O B W O L F O W I T Z

With J. Kiefer. Stochastic estimation of the maximum of a regres-
sion function. Ann. Math. Stat. 23(3):462-66.

1953

With A. Dvoretzky and J. Kiefer. Sequential decision problems for
processes with continuous time parameter. Testing hypotheses.
Ann. Math. Stat. 24(2):254-64; 24(3):403-15.

With A. Dvoretzky and J. Kiefer. On the optimal character of the
(s, S) policy in inventory theory. Econometrica 21(4):586-96.

Estimation by the minimum distance method. Ann. Inst. Stat. Math.
5(1):9-23.

1955

With J. Kiefer. On the theory of queues with many servers. Trans.
Am. Math. Soc. 78(1):1-18.

1956

With J. Kiefer. Consistency of the maximum likelihood estimator in
the presence of infinitely many incidental parameters. Ann. Math.
Stat. 27(4):887-906.

1957

The minimum distance method. Ann. Math. Stat. 28(1):75-88.

1958

Information theory for mathematicians. Ann. Math. Stat. 29(2):351-56.

1959

With J. Kiefer. Optimum designs in regression problems. Ann. Math.
Stat. 30(2):271-94.

1960

Contributions to information theory. Proc. Natl. Acad. Sci. U. S. A.
46(4):557-61.

1967

With L. Weiss. Maximum probability estimators. Ann. Inst. Stat. Math.
19(2):193-206.

Page 393

384 B I O G R A P H I C A L M E M O I R S

1969

With L. Weiss. Asymptotically minimax tests of composite hypoth-
eses. Z. Wahrscheinlichkeitstheorie 14(2):161-68.

1974

With L. Weiss. Maximum Probability Estimators and Related Topics. New
York: Springer-Verlag.

1975

Signaling over a Gaussian channel with feedback and autoregressive
noise. J. Appl. Probab. 12(4):713-23.

1978

Coding Theorems of Information Theory. 3rd ed. New York: Springer
Verlag.

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