Contactless gating,surface charging and illumination effects in a buried Al<Subscript>0.24</Subscript>Ga<Subscript>0.76</Subscript>As/GaAs quantum well structure

The conductivity of an Al_0.24Ga_0.76As/GaAs quantum well was studied as a function of the surface charge generated by electron bombardment of the sample in the absence of an externally applied surface electric field. Under a suitable rate of electron irradiation, it was possible to completely shut off the conductive channel, implying a surface density . Light illumination quenches the increase of the resistivity, apparently due to photoemission from the metastable surface states. Upon turning off the electron bombardment the surface charge on adsorbed layers of xenon and water at 8 K decays in room temperature darkness with a lifetime τ= 0.30 ±0.02 s. The average charging efficiency, is μ₀ ≃0.001. Surface charging is shown to be an effective method for contactless gating of field effect devices.     

Application of macroautoradiography and instantimage in radiopharmaceutical research

The evaluation of the pharmacokinetics of pure, beta radiopharmaceuticals is not possible with scintigraphy. Both whole-body autoradiography (WBAR) and Packard Instantimager, a device for rapid imaging, were used to study the whole body distribution of γ- and β-emitting radionuclides (^99mTc-MDP,^99mTc-sulfur colloid, or¹⁸⁸Re-HEDP), and results obtained from both methods were compared. The biodistribution of^99mTc-MDP and¹⁸⁸Re-HEDP were seen mainly in bones including skull, spine, and vertebrae of spine and cardiac and skeletal muscles. The^99mTc-sulfur colloid localized in liver, bone marrow, and spleen. The resolution of WBAR is superior than that of Packard Instantimager. However, the advantage of Packard Instantimager is that rapid imaging within few minutes is possible with it, while WBAR imaging requires several hours to days.     

An isobar model partial-wave analysis of three-body final states in π+p interactions from threshold to 1700 MeV c.m. energy

We present the results of an energy-independent partial-wave analysis of the reaction π⁺p→ππN at nine c.m. energies between 1400 and 1700 MeV. New bubble chamber data from the Cambridge-Imperial College-Westfield College Collaboration were fitted, together with earlier data from Oxford, using the isobar model in a maximum likehood fitting program. The isobars used were Δ(1236), N¹(1470) and ?(770) and allowance was made for an incoherent contribution from an I=2 s-wave phase shift produced by one-pion exchange in the t-channel. The results of this analysis are compared with the predictions of symmetry schemes. The ?₁N amplitudes of the S₃₁ and D₃₃ members of the {70, 1^?} multiplet are clearly observed and their signs unambiguously determined for the first time. Structure in the P₃₁ wave is discussed in relation to recent claims of a low mass resonance. Possible explanations of the complicated behaviour of the P₃₃ wave are discussed; its N¹(1470)π decay is observed for the first time.     

Development and Validation of the Mathematics Teachers' Beliefs About English Language Learners Survey (MTBELL)

Given the increasing number of English Language Learners (ELLs) in secondary mathematics classrooms, it is imperative that mathematics teacher educators develop measures for determining how and why secondary mathematics teachers (SMTs) understand and respond instructionally to these students. This paper reports on the initial development and validation of the Mathematics Teachers' Beliefs about English Language Learners survey, an instrument that measures SMTs beliefs, attitudes, knowledge base, and instructional practices in relation to meeting the academic and language needs of ELLs. Through piloting processes, the instrument was refined for a research study through which reliability and validity were established. The five constructs identified from exploratory factor analysis illustrate perceived opportunities and barriers in meeting ELLs' academic and language needs among SMTs. This article features a Research to Practice Companion Article . Please click on the supporting information link below to access.     

Use of personal computers for an integrated personnel dosimetry system

A dosimetric data processing system has been developed using inexpensive and simple small computers. Designed for limited dosimetry activities, this system can be operated by people with no special computer training, and is briefly described below.

     

Separation and determination of 4-(1,1,3,3-tetramethylbutyl)phenyl dihydrogenphosphate and di-[4-(1,1,3,3-tetramethylbutyl)phenyl] hydrogenphosphate by high-performance liquid chromatography

4-(1,1,3,3-Tetramethylbutyl)phenyl dihydrogenphosphate and di-[4-(1,1,3,3-tetramethylbutyl)phenyl] hydrogenphosphate (0.01–1 mg ml^-1) in aqueous phosphoric acid raffinates can be separated on a reversed-phase μ Bondapak C₁₈ column by gradient elution with methanol/water, and quantified at 267 nm. Raffinates are extracted with 4-methyl-2-pentanone; the two phosphates can then be determined with errors less than ±5%.     

Multiple periodic solutions for a nonlinear suspension bridge equation

We investigate nonlinear oscillations in a fourth-order partialdifferential equation which models a suspension bridge. Previouswork establishes multiple periodic solutions when a parameterexceeds a certain eigenvalue. In this paper, we use Leray-Schauderdegree theory to prove that if the parameter is increased further,beyond a second eigenvalue, then additional solutions are created.     

Analyse von Gemischen aus metallischem Nickel und Oxidhydraten des II- und h?herwertigen Nickels

Zusammenfassung Laugefeuchte Gemische aus metallischem Nickel und dessen Hydroxiden bzw. Oxidhydraten verschiedener Wertigkeitsstufen können in Proben von 50–200 mg bezüglich Zusammensetzung und effektiver Wertigkeit nach folgendem Schema analysiert werden:Reduktion der Probe mit alkalischer Arsenat(III)-Lösung, Umsatz des entstandenen Arsenats(V) mit KJ zu photometrisch bestimmbarem elementarem Jod, Extraktion der im Rückstand enthaltenen Nickelverbindungen mit verd. H₂SO₄, Auflösung des metallischen Nickels in H₂SO₄ + H₂O₂ und photometrische Bestimmung der Ni²⁺-Lösungen als ÄDTA-Komplex. Die effektive Wertigkeit der Nickelverbindungen kann auf ±0,02 Wertigkeitseinheiten genau ermittelt werden. Die Ergebnisse stimmen gut mit elektrochemisch erhaltenen Werten überein.Beachtet werden muß ein starker Phototropieeffekt der zu photometrierenden Jodlösung. Ein 380facher Überschuß an As(III) stört die As(V)-Bestimmung nicht.

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Analysis of mixtures of metallic nickel and oxide-hydrates of bivalent and higher-valency nickel

Mixtures consisting of metallic nickel and the hydroxides or oxide-hydrates in various valency stages moistened with alkali in samples of 50 to 200 mg can be analysed by the following scheme: Reduction of the sample with alkaline As(III) solution, reaction of As(V) with KI setting free elementary, photometrically determinable iodine, extraction of the Ni-compounds present in the residue with dilute H₂SO₄, dissolution of the metallic M in H₂SO₄ + H₂O₂, and photometric determination of the Ni²⁺ solutions as EDTA complex.In this manner the effective valency of the Ni-compounds can be determined within ± 0.02 valency units, The results agree well with those obtained electrochemically.The iodine solution from which the extinction has to be measured photometrically shows a strong phototropic effect.An excess of 380 parts of As(III) does not interfere with the As(V) determination.

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Auszugsweise vorgetragen auf der Hauptversammlung der Gesellschaft Deutscher Chemiker, 13. bis 18. September 1971 in Karlsruhe [6].

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Dem Vorstand der VARTA AGdanke ich für die freundliche Genehmigung zur Publikation. Besonderer Dank gebührt Fräulein H. Slomp, die alle Arbeiten durchgeführt und durch ihre Fähigkeit zu beobachten und zu kombinieren wesentlich zur Lösung des Problems beigetragen hat.