SummaryNeuronal responses of sensory cortex are highly variable, and this variability is correlated across neurons. To assess how variability reflects factors shared across a neuronal population, we analyzed the activity of many simultaneously recorded neurons in visual cortex. We developed a simple model that comprises two sources of shared variability: a multiplicative gain, which uniformly scales each neuron’s sensory drive, and an additive offset, which affects different neurons to different degrees. This model captured the variability of spike counts and reproduced the dependence of pairwise correlations on neuronal tuning and stimulus orientation. The relative contributions of the additive and multiplicative fluctuations could vary over time and had marked impact on population coding. These observations indicate that shared variability of neuronal populations in sensory cortex can be largely explained by two factors that modulate the whole population.

We investigate the accuracy provided by different treatments of the exchange and correlation effects, in particular the London dispersion forces, on the properties of liquid water using ab initio molecular dynamics simulations with density functional theory. The lack of London dispersion forces in generalized gradient approximations (GGAs) is remedied by means of dispersion-corrected atom-centered potentials (DCACPs) or damped atom-pairwise dispersion corrections of the C6R(-6) form. We compare results from simulations using GGA density functionals (BLYP, PBE, and revPBE) with data from their van der Waals (vdW) corrected counterparts. As pointed out previously, all vdW-corrected BLYP simulations give rise to highly mobile water whose softened structure is closer to experimental data than the one predicted by the bare BLYP functional. Including vdW interactions in the PBE functional, on the other hand, has little influence on both structural and dynamical properties of water. Augmenting the revPBE functional with either damped atom-pairwise dispersion corrections or DCACP evokes opposite behaviors. The former further softens the already under-structured revPBE water, whereas the latter makes it more glassy. These results demonstrate the delicacy needed in describing weak interactions in molecular liquids.

We present ab initio molecular dynamics studies on liquid water using density functional theory in conjunction with either dispersion-corrected atom-centered potentials or empirical van der Waals corrections. Our results show that improving the description of van der Waals interactions in DFT-GGA leads to a softening of liquid water's structure with higher mobility. The results obtained with dispersion-corrected atom-centered potentials are especially encouraging. In particular, the radial distribution functions are in better agreement with experiment, and the self-diffusion coefficient increases by more than three-fold compared with the one predicted by the BLYP functional. This work demonstrates that van der Waals interactions are essential in fine-tuning both structural and dynamical properties of liquid water.

The ability to control the crystallization behaviour (including its absence) of particles, be they biomolecules such as globular proteins, inorganic colloids, nanoparticles, or metal atoms in an alloy, is of both fundamental and technological importance. Much can be learnt from the exquisite control that biological systems exert over the behaviour of proteins, where protein crystallization and aggregation are generally suppressed, but where in particular instances complex crystalline assemblies can be formed that have a functional purpose. We also explore the insights that can be obtained from computational modelling, focussing on the subtle interplay between the interparticle interactions, the preferred local order and the resulting crystallization kinetics. In particular, we highlight the role played by "frustration", where there is an incompatibility between the preferred local order and the global crystalline order, using examples from atomic glass formers and model anisotropic particles.

Parameters for analytical dispersion-corrected atom-centered potentials ͑DCACPs͒ are presented to improve the description of London dispersion forces within the generalized gradient approximation functionals BLYP, BP, and PBE. A library of DCACPs for hydrogen, carbon, nitrogen, oxygen, helium, neon, argon, and krypton was obtained by calibrating against high-level CCSD͑T͒ or configuration interaction references. The performance and transferability of DCACPs were tested on weakly bound complexes and provide excellent results throughout all investigated systems.

A variety of functional polymer chains prepared by RAFT were directly grafted onto 5, 10, and 20 nm gold nanoparticles (AuNPs). The polymer shell coating the AuNPs was densely packed because of the strong binding between the trithioester groups on the polymer chain-ends and gold. It was found that due to the densely packed nature of the shell the polymer chains were significantly stretched compared to their usual Gaussian coil conformation in water. This was even evident for polymer chains where ionic repulsion between neighboring chains should be significant. Therefore, with such high grafting densities the surface properties and size of the hybrid nanoparticles should be the only contributing factors in cellular uptake in epithelial Caco-2 cells. This study has provided valuable insight into the effects of charge and size of NPs for the application of NPs in the delivery of therapeutic agents across the intestine. Our results showed that the negatively charged AuNPs were taken up by the cells with greater efficiency than the neutral AuNPs, most probably due to binding with membrane proteins. The positively charged AuNPs as expected gave the greatest uptake efficiency. Interestingly, the uptake for PNIPAM-AuNPs (hydrophobic coating at 37 degrees C) increased from approximately 2% efficiency after a 30 min incubation to 8% after 2 h, and was much greater than the negative or neutral AuNPs. We believe that this was due to the interplay between the hydrophobic nature of the NPs and their increased size.

Special delivery: An effective group A streptococci vaccine is formed from a delivery device consisting of well‐defined dendritic structures with nanoscale dimensions (see picture). The structures are designed to display multiple copies of the minimal B‐cell epitopes, which were in the optimal conformation on the surface of the nanoparticles. The nanoparticles can be administered without the aid of an adjuvant.

Interaction energies and structural properties of van der Waals complexes of aliphatic hydrocarbons molecules and crystals of aromatic hydrocarbon compounds are studied using density functional theory augmented with dispersion corrected atom centered potentials (DCACPs). We compare the performance of two sets of DCACPs, (a) DCACP-MP2, a correction for carbon only, generated using MP2 reference data and a penalty functional that includes only equilibrium properties and (b) DCACP-CCSD(T), a set that has been calibrated against CCSD(T) reference data using a more elaborate penalty functional that explicitly takes into account some long-range properties and uses DCACP corrections for hydrogen and carbon atoms. The agreement between our results and high level ab initio or experimental data illustrates the transferability of the DCACP scheme for the gas and condensed phase as well as for different hybridization states of carbon. The typical error of binding energies for gas-phase dimers amounts to 0.3 kcal/mol. This work demonstrates that only one DCACP per element is sufficient to correct for weak interactions in a large variety of systems, irrespective of the hybridization state.