Surface passivation of luminescent colloidal quantum dots with poly(dimethylaminoethyl methacrylate) through a ligand exchange process

Polydimethylaminoethyl methacrylate (PDMAEMA) was used as a multidentate ligand to modify the surface of CdSe/ZnS core-shell colloidal quantum dots in toluene with trioctylphosphine oxide (TOPO) as the surface ligand. Adsorption of PDMAEMA was accompanied by release of TOPO. The process is free of agglomeration, and the modified nanocrystals become soluble in methanol. The photoluminescence properties are well-preserved in either toluene or methanol.     

Mediation of ultrafast light-harvesting by a central dimer in phycoerythrin 545 studied by transient absorption and global analysis

We report ultrafast femtosecond transient absorption measurements of energy-transfer dynamics for the antenna protein phycoerythrin 545, PE545, isolated from a unicellular cryptophyte Rhodomonas CS24. The phycoerythrobilins are excited at both 485 and 530 nm, and the spectral response is probed between 400 and 700 nm. Room-temperature measurements are contrasted with measurements at 77 K. An evolution-associated difference spectra (EADS) analysis is combined with estimations of bilin spectral positions and energy-transfer rates to obtain a detailed kinetic model for PE545. It is found that sub pulse-width dynamics include relaxation between the exciton states of a chromophore dimer (beta 50/60) located in the core of the protein. Energy transfer from the lowest exciton state of the phycoerythrobilin (PEB) dimer to one of the periphery 15,16-dihydrobiliverdin (DBV) bilins is found to occur on a time scale of 250 fs at room temperature and 960 fs at 77 K. A host of energy-transfer dynamics involving the beta 158, beta 82, and alpha 19 bilins occur on a time scale of 2 ps at room temperature and 3 ps at 77 K. A final energy transfer occurs between the red-most DBV bilins with a time scale estimated to be approximately 30 ps. The role of the centrally located phycoerythrobilin dimer is seen as crucial-spectrally as it expands the cross-section of absorption of the protein; structurally as it sits in the middle of the protein acting as an intermediary trap; and kinetically, as the internal conversion and subsequent red-shift of the excitation is extremely fast.     

Endor of a dislocation center in a deformed silicon

We present the first ENDOR measurements on dislocations in silicon, which measurements directly show the extended nature of the electron wave function on the dislocation.     

Permeability anisotropy due to consolidation of compressible porous media

The characterisation of flow through porous media is important for all solid–liquid separation and fluid transport realms. The permeability of porous media can be anisotropic and furthermore, the extent of anisotropy can be increased as a result of an applied compressive force. However, the understanding of how anisotropy develops is incomplete. An overview of research on permeability anisotropy is given and an expression for predicting anisotropy as a function of void ratio is offered. The two underlying assumptions of the proposed model are: flow in different directions occurs within the same network of pores and deformation is primarily due to the compression of the particles in the direction of the applied force rather than due to particle rearrangement. The assumption of network connectivity allows permeability anisotropy to be described as a function of flow path tortuosity only. Results are presented for hydraulic anisotropy measured in lignite that has been upgraded by a compression dewatering method known as mechanical thermal expression. The lignite permeability is shown to be up to eight times greater in the direction perpendicular to compression, suggesting that the rate of dewatering could be significantly increased by choosing the drainage to also be perpendicular to the direction of the applied compressive force. It is illustrated that the proposed anisotropy model can be used to accurately predict the experimentally determined permeability anisotropy ratios for lignite, as well as for other materials including sand, clay and kaolin.     

Statistical analysis from a sound level meter

Increasingly, and particularly for motorway noise, sound level meters are being used to estimate $\text{L}{}_{\mathrm{<mtext>10</mtext>}}$, the noise level just exceeded for 10 per cent of the time, by noting the meter readings at regular intervals and manually analysing the array of data so obtained. In this paper we describe a simple attachment to a sound level meter, which is intended to ease the operator's task in making such measurements and to minimise operator bias. Comparisons are made between the results of sound level meter measurements of three types of noise and the results obtained using the more conventional technique which employs a level recorder and statistical analyser.It is concluded that, at least for motorway noise, the sound level meter technique gives values of $\text{L}{}_{\mathrm{<mtext>10</mtext>}}$ and of $\text{L}{}_{\mathrm{<mtext>90</mtext>}}$ within 1 dB(A) of the values obtained by the normal method. Furthermore, it is probable that the technique will be useful for the measurement of other types of noise in statistical terms, but further investigations of accuracy are required.