Geothermal Energy's Future
Iwould liketocommentontheBriefing of 22 November (p. 1113) concerningthe
outlook forgeothermalenergyinCalifornia. TheBriefing's somewhat gloomy outlook is duelargelytoaconfusion of thegeothermal
resourceestimates madeby the U.S.
Geolog-icalSurvey(USGS) in 1979 (contrarytothe assertionin theBriefing, the 1979 inventory is themost recentUSGS inventory) with the geothermal reserve estimates made by
Ebasco Services in 1991. By definition, re-serves represent only that fraction of the resource that can be exploited profitably with current technology. With an under-standing of this difference,one can seethat there isnoactual conflictbetweenthe 1979 USGSstudy and the 1991 Ebascoreport.
AlthoughproductionatTheGeysers has dropped significantly [to 1380 megawatts-electric(MWe) from the installedcapacity of 2000 MWe], much of this drop can be attributedtooveroptimismand overexploi-tation by the field developers. (The 1979 USGSstudyestimateda1610 MWe capac-ity for TheGeysers.) Withnew technologi-cal developments such as fluid injection, jointly researched by industry and govern-ment, it should be possible to recapture
someof the lostgenerating capacity. California's geology (and that in neigh-boringstates)stillpromisesanabundance of economical, environmentallyacceptable geo-thermal energy. Supportingstudies for the
NationalEnergy Strategy indicate that un-der reasonable assumptions approximately
11,000 MWefromhydrothermalresources can be on-line nationally by 2010, and 22,000 MWe by 2030. In addition, more advanced geothermal resources (hot dry rock,geopressured geothermalsystems,and
magma) can potentially play a significant role in satisfying America's long-term ener-gy needs. Geothermal energy truly has a brightfuture inhelpingtosatisfyAmerica's energyneeds.
JoHN E.MOCK GeothermalDivision,
Conservation and RenewableEnergy,
DepartmentofEnergy, Washington, DC 20585
Response: Contrary to the comment by Mock, we find no methodological
differ-ences between the 1979 inventory by the
U.S. Geological Survey (USGS) and the
1991 report by Ebasco Services, both of
which estimate California's geothermal
re-sources.AccordingtoPatrick Muffler ofthe
USGS, whosupervised the 1979 inventory, the terms "reserves" and "resources" were
inconsistently applied in the Ebasco report, butthemethods usedwerethe samein the
two studies. Muffler cannot vouch for the application of those methods in the "gloomy" Ebasco report, but finds it appropriate to directlycomparethetwostudies.-EDS.
Bellcore Basic Research
Contrarytotheimpression created by the ScienceScope item"Bellcore basic research-ersoutofwork" (10 Jan., p. 147),Bellcore is not "phasing out itsbasic research effort and closing downfacilities." We have made asmallreduction in the size ofoureffortin physical sciences and materials research and we are increasing our research in software and information technologies, but these changes aremodest and do notinvolvethe large-scale "retrenching" indicated in the ScienceScope piece. Onlyahandful of peo-ple were involved inourworkwith super-conductivity, notthe"20to25" mentioned in theScienceScope piece. That is the num-ber ofall the affected people in physical
sciences research. Several of our physical science researchers have been placed else-where in our research efforts, a few have chosentoretire, andtenhaveindicatedthey want to continue in their specific fields of research elsewhere.
The shifts we have made in our overall program,whilesignificanttotheindividuals involved,are smallandarethe normalones tobeexpected from timetotimeas techno-logical progress is made. It should not be necessary to state that Bellcore intends to continue being a leader in those areas of researchimportanttoour ownersandtothe telecommunicationsindustry, including ma-terialsanddeviceresearch.
GEORGE H. HEILME1ER
President, Bellore, 290 West Mt. PleasantAvenue, Livingston, NJ07039-0486
FullereneSuperconductivity and the Dynamic Jahn-Teller Effect
C. M.Varmaetal. (Reports, 15Nov.,p. 989) attribute superconductivity in the fullerenes to electron-phonon coupling of
Hg
vibrationalmodesofthecomponentC60 molecules induced by the dynamicJahn-Tellereffectofpartially occupied degenerate
tl(psr)
molecular orbitals.Superconductiv-1490
ity theorybased ondynamicJahn-Teller
vi-bronic coupling of degeneratemolecular
or-bitalswasappliedtoorganicsuperconductors
in 1983 (1), tohigh-transitiontemperature oxides in 1987(2), andtosuperconductive fullerenesin May 1991 (3). Indeed, dynamic Jahn-Teller couplingmayprovideaunifying quantum-chemical basis for high-transition temperature superconductivity in ceramics, organics, and fullerenes (4).
Experimental evidence for this mechanism infiullerene
C60
canbefound in the unusual electron-spin-resonance spectrum (5), which showstemperature-dependentline width and highly shiftedg value, well-established signa-tures of the dynamic Jahn-Teller effect (6). Raman spectra for superconductivefuller-enes show only the lowest frequency Hg vibrational mode (7), consistent with the dynamic Jahn-Teller scenario of (3). A re-cently reported carbon isotope shift expo-nentofa = 0.37 + 0.05 for the transition
temperatureofsuperconducting Rb3C60 (8) is close to the value predicted from the dynamic Jahn-Teller mechanism in (3).
KEITH H.JOHNSON
DepartmentofMaterialsScience,
MassachusettsInstitute of Technology, Cambridge, MA 02139 DENNIS P. CLOUGHERTY Departmentof Physics, University of California, SantaBarbara, CA 93108 MICHAEL E. McHENRY DepartmentofMaterialsScience, Carnegie-Mellon University, Pittsburgh, PA 15213 REFERENCES
1. K.H.Johnson and R. P. Messmer, Synth. Metals 5, 193(1983).
2. K. H.Johnsonetal., in Novel Superconductivity, S. A. Wolf and W. Z. Kresin, Eds. (Plenum, New
York, 1987),p.563.
3. K. H.Johnson,M. E.McHenry,D. P.Clougherty, PhysicaC183,319(1991).
4. K.H.Johnson,D. P.Clougherty,M. E.McHenry, in Electronic Structure andMechanismsforHigh-T,
Superconductivity,J. Ashkenazi and G.Vezzoli,Eds. (Plenum,NewYork, in press).
5. P. M. Alleman etal., J.Am.Chem.Soc. 113,2780
(1991).
6. I.B. Bersuker, TheJahn-TellerEffectand Vibronic Interactions in Modern Chemistry (Plenum, New
York, 1984), p. 103; __ and V.Z. Polinger, Vibronic Interactions in Molecules and Crystals
(Springer-Verlag,NewYork, 1989),p. 281. 7. S.J. Duclos et al., Science254,1625(1991). 8. A. P. Ramirez et al., Phys. Rev. Lett. 68, 1058
(1992).
Response: We are happy to note that
Johnson
et al. have alsothought
of the intramolecular vibrations in metallicfullerenes
as responsible for effectiveelec-tron-electronattraction in thefullerenes.We would liketopointoutthat thereare essen-tial differences between our results and theirs. (i)
Johnson
etal. considerthelemsintermsof "real-space pairing," where the partners ofa Cooper-pair reside on a
givenball. This requires Cooper-pair bind-ingenergylarger thantheelectronic
band-width.Superconductivity thenoccursby the
coherent hopping of this pair from ballto
ball. Our calculations show that even
though the interactions areintramolecular,
superconductivity is of the conventional BCSvariety. (ii) Johnsonetal. suggestthat low
frequency
vibrations with frequencies of approximately100cm`
areresponsible forthepairing. Ourcalculations show that the vibration modes with the dominant
cou-pling to electrons have frequencies over
1500
cm`.
Finally,wedonotbelieve that thephysics ofsuperconductivityinthe ftil-lerenes is relevant to the physics of high-temperaturesuperconductivityinthecopperoxide-based materials.
C. M. VARMA J. ZAANEN AT&TBell Laboratories,
600MountainAvenue,
MurrayHill, NJ 07974-0636
Physical Activity and Cancer
A reduction of risk of sex
hormone-sensitive cancers in women in association
with regular physical activity, as suggested inthereviewarticlebyBrian Hendersonet
al., "Toward theprimarypreventionof can-cer" (22 Nov., p. 1131), has already been
documented(1).Astudyofmorethan5000 Americanwomen college alumnae showed
thatformercollegeathleteshadsignificantly
lessbreastcancerandcancers ofthe repro-ductive system than their sedentary class-mates (1). More than 80% of the former
athletes begantheirregular,moderate phys-icalactivityinhigh schoolorearlier,which underscores the recommendation of Hen-derson et al. that this lifestyle be adopted early.
ROSE E. FRISCH
GRACE WYSHAK
Centerfor Population Studies,
Harvard SchoolofPublicHealth,
9BowStreet, Cambridge,MA 02138
TENLEY E. ALBRIGHT InstituteforClinicalApplications, Inc.,
126BrooklineAvenue,
Boston, MA02215
NILE L. ALBRIGHT
Advanced MedicalResearchFoundation,
333Longwood Avenue, Boston,MA 02115
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REFERENCES
1. R.E.Frischetal., Br. J.Cancer52,885(1985).
