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Se EXAFS study of the elevated wurtzite to rock salt structural phase transition in CdSe nanocrystals

Description: High pressure Se EXAFS data has been obtained on 2.7 nm radius CdSe semiconductor nanocrystals. This system is observed to undergo a solid-solid phase transition at 6.5 GPa which is approximately twice the reported value for bulk CdSe. In combination with high pressure optical absorption experiments, EXAFS data can be used to identify the high-pressure phase structure as rock salt. EXAFS data can be fit with equations of state to yield pressure volume curves. Resultant values of bulk modulus and its derivative with respect to pressure are B{sub o} = 37 {plus_minus} 5 GPa and B{sub o}{prime} = 11 {plus_minus} 3. A thermodynamic model for the data is presented in which the internal energy in each phase is modified by a surface energy term. Differences in surface energy are used to explain the elevation in phase transition pressure. The model can be used to estimate a value for the surface energy in the rock salt phase; 1.9 {plus_minus} 0.3 N/m is obtained in comparison to 0.9 {plus_minus} 0. 1 N/m for the wurtzite phase.
Date: September 1, 1993
Creator: Tolbert, S. H. & Alivisatos, A. P.
Partner: UNT Libraries Government Documents Department

New QCD results from string theory

Description: We discuss new results in QCD obtained with string-based methods. These methods were originally derived from superstring theory and are significantly more efficient than conventional Feynman rules. This technology was a key ingredient in the first calculation of the one-loop five-gluon amplitude. We also present a conjecture for a particular one-loop helicity amplitude with an arbitrary number of external gluons.
Date: November 1, 1993
Creator: Bern, Z.; Dixon, L. & Kosower, D. A.
Partner: UNT Libraries Government Documents Department

SVX II a silicon vertex detector for run II of the tevatron

Description: A microstrip silicon detector SVX II has been proposed for the upgrade of the vertex detector of the CDF experiment to be installed for run II of the Tevatron in 1998. Three barrels of four layers of double sided detectors will cover the interaction region. The requirement of the silicon tracker and the specification of the sensors are discussed together with the proposed R&D to verify the performance of the prototypes detectors produced by Sintef, Micron and Hamamatsu.
Date: November 1, 1994
Creator: Bortoletto, D.
Partner: UNT Libraries Government Documents Department

A method of producing high quality oxide and related films on surfaces

Description: Aluminum oxide or aluminum nitride films were deposited on MBE grown GaAs(100) using a novel cryogenic-based reactive thin film deposition technique. The process involves the condensation of molecular oxygen, ammonia or other gases normally used for reactive thin film deposition on the substrate before the metal is deposited. The metal vapor is deposited into this layer and reacts with the molecular solid form the desired compound or a precursor than can be thermally decomposed to generate the desired compound. The films produced by this method are free of impurities and the low temperatures can be used to control the film and interfacial structure. The process can be easily integrated with existing MBE-systems and on going research using the same apparatus suggests than photon or electron irradiation could also be used to promote the reactions needed to give the intended material.
Date: December 31, 1991
Creator: Ruckman, M. W.; Strongin, M. & Gao, Yongli
Partner: UNT Libraries Government Documents Department

A method of producing high quality oxide and related films on surfaces

Description: Aluminum oxide or aluminum nitride films were deposited on MBE grown GaAs(100) using a novel cryogenic-based reactive thin film deposition technique. The process involves the condensation of molecular oxygen, ammonia or other gases normally used for reactive thin film deposition on the substrate before the metal is deposited. The metal vapor is deposited into this layer and reacts with the molecular solid form the desired compound or a precursor than can be thermally decomposed to generate the desired compound. The films produced by this method are free of impurities and the low temperatures can be used to control the film and interfacial structure. The process can be easily integrated with existing MBE-systems and on going research using the same apparatus suggests than photon or electron irradiation could also be used to promote the reactions needed to give the intended material.
Date: January 1, 1991
Creator: Ruckman, M.W.; Strongin, M. (Brookhaven National Lab., Upton, NY (United States)) & Gao, Yongli (Rochester Univ., NY (United States). Dept. of Physics and Astronomy)
Partner: UNT Libraries Government Documents Department

Recent progress in one-loop multi-parton calculations

Description: The authors describe techniques that simplify the calculation of one-loop QCD amplitudes with many external legs, which are needed for next-to-leading-order (NLO) corrections to multi-jet processes. The constraints imposed by perturbative unitarity, collinear singularities and a supersymmetry-inspired organization of helicity amplitudes are particularly useful. Certain sequences of one-loop helicity amplitudes may be obtained for an arbitrary number of external gluons using these techniques. They also report on progress in completing the set of one-loop helicity amplitudes required for NLO three-jet production at hadron colliders, namely the amplitudes with two external quarks and three gluons.
Date: September 1, 1994
Creator: Bern, Z.; Dixon, L.; Dunbar, D. C. & Kosower, D. A.
Partner: UNT Libraries Government Documents Department

Incommensurate magnetic order in UNi{sub 2}Al{sub 3}

Description: Elastic neutron scattering measurements performed on single crystal UNi{sub 2}Al{sub 3} show this heavy fermion superconductor to display long-range incommensurate (IC) magnetic order below T{sub N}=5.2K. The ordering wavevector is (1/2 {+-} {tau},0,1/2) with {tau}=0.110{+-}0.003, and the size of the maximum ordered moment is 0.24{+-}0.1{mu}{sub B}/U.
Date: December 31, 1993
Creator: Lussier, J. G.; Schroeder, A.; Gaulin, B. D.; Garrett, J. D.; Buyers, W. J. L.; Rebelsky, L. et al.
Partner: UNT Libraries Government Documents Department

A search for the top quark decaying to charged Higgs in p{bar p} collisions at {radical}s = 1.8 TeV

Description: We present results of a search for the top quark decaying to a charged. Higgs boson (H) in p{bar p} collisions at {radical}s = 1.8 TeV at the Fermilab Tevatron. Using 4.1 pb{sup {minus}1} of data collected during the 1988--1989 CDF run, we have searched for evidence of t{bar t} production assuming that t{r_arrow} Hb and H{r_arrow} {tau}{nu}{sub {tau}}. We find no evidence for this decay and are able to exclude regions in the (m{sub t}, m{sub H}) plane for different Br(H{r_arrow} {tau}{nu}{sub {tau}}). We also interpret these results for the two Higgs doublet(THD) model.
Date: August 1, 1993
Creator: Collaboration, CDF
Partner: UNT Libraries Government Documents Department

The CDF upgrade

Description: The Collider Detector at Fermilab (CDF) has been used to study proton-antiproton collisions at the Fermilab Tevatron since 1985. Over the years, the detector has evolved steadily to increase its physics capability and to keep pace with improvements to the Tevatron. Fermilab is currently building a new Main Injector accelerator which will lead to even larger luminosity values. This paper describes upgrades to CDF that will allow one to exploit the higher luminosity of the Main Injector.
Date: January 1, 1995
Creator: Newman-Holmes, C. & Collaboration, CDF
Partner: UNT Libraries Government Documents Department

Measurement of correlated b quark cross sections at CDF

Description: Using data collected during the 1992--93 collider run at Fermilab, CDF has made measurements of correlated b quark cross section where one b is detected from a muon from semileptonic decay and the second b is detected with secondary vertex techniques. We report on measurements of the cross section as a function of the momentum of the second b and as a function of the azimuthal separation of the two b quarks, for transverse momentum of the initial b quark greater than 15 GeV. Results are compared to QCD predictions.
Date: September 1, 1994
Creator: Gerdes, D. & Collaboration, CDF
Partner: UNT Libraries Government Documents Department

Test of structure functions using leptons with CDF

Description: The charge asymmetry as a function of lepton rapidity, A(yl), has been measured at {radical}s = 1.8 TeV for {vert_bar}yl{vert_bar} < 1.8, using the W decays to electrons and muons recorded by CDF during the 1992--1993 run of the Tevatron Collider. The luminosity used, approximately 20 pb{sup {minus}1}, and detector improvements have lead to a six fold increase in statistics making discrimination between sets of parton distributions possible. Our data favors the most recent parton distributions and demonstrates the value of collider data in the measurement of the proton`s structure. In addition, the Drell-Yan cross section has been measured using 4.13 pb{sup {minus}1} of dielectron and 2.77 pb{sup {minus}1} of dimuon data taken during the 1988--1989 run. These measurements probe the quark distributions to x < 0.01 at high Q{sup 2} where nonperturbative effects are minimal.
Date: November 1, 1993
Creator: Dickson, M. & Collaboration, CDF
Partner: UNT Libraries Government Documents Department