S,O-acetals as novel "chiral aldehyde" equivalents

Palladium-catalyzed asymmetric allylic alkylations (AAA) to form "chiral aldehyde" equivalents were investigated. Alpha-acetoxysulfones were formed in high enantiomeric excess as single regioisomers in AAA reactions of allylic geminal dicarboxylates with sodium benzenesulfinate. The directing ability of this novel functional group was highlighted by a series of dihydroxylations, affording syn diols exclusively anti to the acetoxy sulfone as single diastereomers in excellent yields. This is the first example of an asymmetric dihydroxylation protocol that gives the equivalent of reaction with a simple enal. The synthetic value of this process was exemplified by subsequent transformations of the diols including the development of a one-pot dihydroxylation-deprotective acyl migration protocol to give differentially protected 1,2-diols.     

Study of 11B at high excitations with the 9Be(3He,p)11B and 9Be(α, d)11B reactions

The nucleus ¹¹B has been studied over the excitation energy range from 8.5 MeV to 21.5 MeV with the ⁹Be(³He, p)¹¹B / reaction at / E_{³He = 38 MeV}. The analogs of the parent states in ¹¹Be have been located at 12.56, 12.92, 14.40, 16.44, 17.69, 18.0, 19.15 and 21.27 MeV. A complementary measurement with the ⁹Be(α, d)¹¹B reaction at E_α = 48 MeV demonstrates that the 16.44, 17.69, 18.0 and 19.15 MeV resonances have rather pure isospin $\text{T}{}_{\mathrm{f}}\text{=}\text{3}\text{2}$. The 14.40 MeV state is a strongly isospin-mixed analog of the $\text{5}\text{2}{}^{\mathrm{+}}\text{1.78}\text{MeV}$ state in ¹¹Be. It is argued that spin S = 1 transfer is involved in the excitation of the 16.44 MeV state and its 3.887 MeV parent in ¹¹Be in a two-step stripping process. The $\text{T}{}_{\mathrm{f}}\text{=}\text{1}\text{2}$ states and the lowest three $\text{T}{}_{\mathrm{f}}\text{=}\text{3}\text{2}$ states are compared with the predictions of DWBA utilizing shell-model form factors. It is concluded that the $\text{T}{}_{\mathrm{f}}\text{=}\text{1}\text{2}$ strength is more strongly fragmented than is implied by the calculations of Teeters and Kurath.     

Coordinated Thematic Science in the Classroom: A View from Pilot Teachers

The purpose of this paper is threefold. First, we set out to describe a context for understanding events that fuel the need to reform secondary science education in Texas. Next, we present the results of a survey of the knowledge, beliefs, and attitudes of a group of central Texas science teachers related to implementing Coordinated Thematic Science (CTS) instruction, who were surveyed after field testing preliminary CTS instructional materials. Last, we argue that caution must be exercised in the design of inservice programs to prepare life science teachers in Texas to teach a coordinated thematic Science I course to rising Grade 7 students by the target date of Fall, 1994.     

Evidence forf 2 (1720) production in the reaction pomeron-pomeron→π+π−π+π−

Data are presented on pomeron-pomeron interactions which produce a central π⁺π^?π⁺π^? system in proton-proton collisions at √s=62 GeV at the CERN Intersecting Storage Rings. A spin-parity analysis of the π⁺π^?π⁺π^? system shows evidence for the production of the statef ₂ (1720) with decay to ρ⁰π⁺π^?. Since pomeron-pomeron interactions are expected to favor the production of gluonic bound states, observation of thef ₂ (1720) supports earlier interpretations of it as a glueball. In addition, enhancements near threshold give indication of the statef ₂ (1270) decaying to ρ⁰ρ⁰ and the statef ₀ (1400) decaying to ρ⁰π⁺π^?.     

Very slow in-plane flow with gradient echo imaging

It is well appreciated that gradient-echo imaging techniques with short recovery times are highly sensitive to flow. This article analyzes the effect of in-plane flow in gradient recalled acquisition in the steady state (GRASS). It is shown that there is loss of signal due to velocity-dependent dephasing effects at velo cities as slow as 0.2 mm per second. It is also shown that striations appear in GRASS images of flow phantoms. This effect, which has not been previously described, arises from a modulation of K-space in the phase-encoding direction during the transient approach to steady state. Although these bands can give the appearance of flow lines, they are completely artifactual and not readily interpretable. Thus, the appearance of in-plane fluid movement in clinical GRASS images is a complex combination of signal loss due to dephasing and artifactual banding. Therefore, the interpretation of flow in GRASS images should be attempted only with caution.     

Experimental tests of constitutive relations for polymers undergoing uniaxial shear flows

Summary Stress development at the onset of steady shear flow and stress relaxation from steady state were measured in a stiffened Weissenberg Rheogoniometer over wide ranges of shear rate for three polystyrene solutions. Time dependent shear stress and first normal stress differenceN ₁ were obtained from the torque and axial thrust. From extensive auxiliary tests we believe these data to be free of spurious effects associated with instrument compliance. The solutions have zero shear viscosities of 890, 3900 and 67 000 poise. Tests for consistency with strain rate constitutive models were made using thevan Es-Christensen relation and with relative strain models using theKearsley-Zapas relations. Substantial deviations were found in both cases. TheMarrucci model was also examined. As in theCarreau model B, the predicted start-up curves from theMarrucci model are in general qualitative accord with observations, but some systematic quantitative discrepancies remain.

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Zusammenfassung Der Spannungsaufbau beim Anfahren einer stationären Scherströmung und die Spannungsrelaxation nach dem Anhalten derselben werden in einem steifer gemachten Weissenberg-Rheogoniometer für drei Polystyrol-Lösungen über einem weiten Schergeschwindigkeitsbereich gemessen. Die zeitabhängige Schubspannung und die erste NormalspannungsdifferenzN ₁ werden aus dem Drehmoment und der Axialverschiebung bestimmt. Aus umfangreichen Nebenuntersuchungen kann man schließen, daß die Ergebnisse von Verfälschungen durch instrumentelle Effekte weitgehend frei sind. Die Lösungen haben Null-Viskositäten von 890, 3900 und 67000 Poise. Für eine Untersuchung der Verträglichkeit der Daten mit Stoffgesetzen vom strain rate-Typ wurde dievan Es-Christensen-Gleichung zugrundegelegt, für Stoffgesetze vom relative strain-Typ entsprechend dieKearsley-Zapas-Gleichung. In beiden Fällen wurden wesentliche Abweichungen gefunden. Ebenso wurde das Modell vonMarrucci geprüft. Ähnlich wie beimCarreau-Modell B sind die Voraussagen des Anlauf-Verhaltens durch dieses Modell durchgängig in qualitativer Übereinstimmung mit den Beobachtungen, aber einige systematische quantitative Unterschiede sind auch hier vorhanden.

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With 15 figures and 1 table     

Inclusive charged particle cross sections in full phase space from proton proton interactions at ISR energies

Measurements are presented of inclusive charged particle production in proton-proton collisions at √s=31, 44 and 62 GeV at the CERN ISR. The large acceptance of the Split Field Magnet detector allows a single experimental setup to cover almost the full longitudinal phase space up to a transverse momentum of 3 GeV/c.