title: Enzyme activity below the dynamical transition at 220 K

authors: Daniel, Roy M.

abstract: Enzyme activity requires the activation of anharmonic motions, such as jumps between potential energy wells. However, in general, the forms and time scales of the functionally important anharmonic dynamics coupled to motion along the reaction coordinate remain to be determined. In particular, the question arises whether the temperature-dependent dynamical transition from harmonic to anharmonic motion in proteins, which has been observed experimentally and using molecular dynamics simulation, involves the activation of motions required for enzyme function. Here we present parallel measurements of the activity and dynamics of a cryosolution of glutamate dehydrogenase as a function of temperature. The dynamical atomic fluctuations faster than ~100 ps were determined using neutron scattering. The results show that the enzyme remains active below the dynamical transition observed at ~220 K, i.e., at temperatures where no anharmonic motion is detected. Furthermore, the activity shows no significant deviation from Arrhenius behavior down to 190 K. The results indicate that the observed transition in the enzyme's dynamics is decoupled from the rate-limiting step along the reaction coordinate.

text: Enzyme activity below the dynamical transition at 220 K Enzyme activity requires the activation of anharmonic motions, such as jumps between potential energy wells. However, in general, the forms and time scales of the functionally important anharmonic dynamics coupled to motion along the reaction coordinate remain to be determined. In particular, the question arises whether the temperature-dependent dynamical transition from harmonic to anharmonic motion in proteins, which has been observed experimentally and using molecular dynamics simulation, involves the activation of motions required for enzyme function. Here we present parallel measurements of the activity and dynamics of a cryosolution of glutamate dehydrogenase as a function of temperature. The dynamical atomic fluctuations faster than ~100 ps were determined using neutron scattering. The results show that the enzyme remains active below the dynamical transition observed at ~220 K, i.e., at temperatures where no anharmonic motion is detected. Furthermore, the activity shows no significant deviation from Arrhenius behavior down to 190 K. The results indicate that the observed transition in the enzyme's dynamics is decoupled from the rate-limiting step along the reaction coordinate.

year: 1998-11

title: Evaluation of two Compton camera models for scintimammography

authors: Uche, Chibueze Zimuzo

subjects: Compton camera

abstract: We study the performance of a Si/LaBr3:Ce Compton camera model for scintimammography, and compare it with a Si/NaI(Tl) model of similar geometry. The GEANT4 simulation toolkit was used to study the behaviour of the cameras at 511 keV. Certain simulation steps, such as the modelling of radionuclide decay times, scintillation photon transport and interactions with photomultipliers, as well as detector dead time corrections were included to make the modelling of the cameras more realistic than previous studies. The Si/LaBr3:Ce Compton camera shows superior efficiency of 2.0×10⁻³ and resolution of 5.3 mm over the Si/NaI(Tl) Compton camera model which has the efficiency of 1.6×10⁻³ and resolution of 6.9 mm at a source-to-scatterer distance of interest, 2.5 cm. A similar result sequence is obtained for two breast tumours of 5 mm diameter embedded in the medial region of an average-size breast phantom of thickness 5 cm. Notably, the signal-to-noise ratios (SNR) obtained for the Si/LaBr3:Ce camera are 9.7 and 3.4 for tumour/background radiation uptakes of 10:1 and 6:1, whereas 6.8 and 2.4 were obtained for the Si/NaI(Tl) camera model for the same tumour/background radiation uptakes respectively. It is therefore envisioned that with lower cost, LaBr3:Ce could replace NaI(Tl) as the Compton camera absorber.

text: Evaluation of two Compton camera models for scintimammography We study the performance of a Si/LaBr3:Ce Compton camera model for scintimammography, and compare it with a Si/NaI(Tl) model of similar geometry. The GEANT4 simulation toolkit was used to study the behaviour of the cameras at 511 keV. Certain simulation steps, such as the modelling of radionuclide decay times, scintillation photon transport and interactions with photomultipliers, as well as detector dead time corrections were included to make the modelling of the cameras more realistic than previous studies. The Si/LaBr3:Ce Compton camera shows superior efficiency of 2.0×10⁻³ and resolution of 5.3 mm over the Si/NaI(Tl) Compton camera model which has the efficiency of 1.6×10⁻³ and resolution of 6.9 mm at a source-to-scatterer distance of interest, 2.5 cm. A similar result sequence is obtained for two breast tumours of 5 mm diameter embedded in the medial region of an average-size breast phantom of thickness 5 cm. Notably, the signal-to-noise ratios (SNR) obtained for the Si/LaBr3:Ce camera are 9.7 and 3.4 for tumour/background radiation uptakes of 10:1 and 6:1, whereas 6.8 and 2.4 were obtained for the Si/NaI(Tl) camera model for the same tumour/background radiation uptakes respectively. It is therefore envisioned that with lower cost, LaBr3:Ce could replace NaI(Tl) as the Compton camera absorber.

year: 2011

title: Governance and legitimacy: Indigenous development in Aotearoa

authors: Dodd, Materoa

subjects: Māori governance

abstract: Within the indigenous paradigm lies a paradox over what constitutes legitimate Māori authority: Iwi structures are legitimated and recognised by the state, and traditional forms (for example, Hapū and Māori women), have had their authority diminished. Iwi authorities are colonial constructs that diminish the rights of Hapū and Māori women. The manner in which such constructs have come about generally has not involved tribewide debate over important issues in which Hapū and Māori women have an interest. For their legitimacy, emergent self-governing structures will need to be grounded in principles that ensure legitimate representation of Māori people and not socially constructed hybrids of a colonial past. Structures need to recognise Hapū and Māori women in the formulation, anything less than this will trigger a legitimation crisis.

text: Governance and legitimacy: Indigenous development in Aotearoa Within the indigenous paradigm lies a paradox over what constitutes legitimate Māori authority: Iwi structures are legitimated and recognised by the state, and traditional forms (for example, Hapū and Māori women), have had their authority diminished. Iwi authorities are colonial constructs that diminish the rights of Hapū and Māori women. The manner in which such constructs have come about generally has not involved tribewide debate over important issues in which Hapū and Māori women have an interest. For their legitimacy, emergent self-governing structures will need to be grounded in principles that ensure legitimate representation of Māori people and not socially constructed hybrids of a colonial past. Structures need to recognise Hapū and Māori women in the formulation, anything less than this will trigger a legitimation crisis.

year: 2000-10